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Kava Research

Kava Research

Kava Research Part 2

General Kava FAQ

General Kava FAQ - Pt. 2

Cultivars, Grinds & Kavalactones

Is Kava Safe?

Kava Terms and Videos

Therapeutic Uses, Effects, Addiction

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Caffeine And Kava

Overview Studies

Volgin A, Yang L, Amstislavskaya T, Demin K, Wang D, Yan D, Wang J, Wang M, Alpyshov E, Hu G, Serikuly N, Shevyrin V, Wappler-Guzzetta E, de Abreu M, Kalueff A. DARK Classics in Chemical Neuroscience: Kava. ACS Chem Neurosci. 2020 Jan 21. doi: 10.1021/acschemneuro.9b00587. Epub ahead of print. PMID: 31904216.

Abstract:
Kava (kava kava, Piper methysticum) is a common drug-containing plant in the Pacific islands. Kavalactones, its psychoactive compounds, exert potent central nervous system (CNS) action clinically and in animal models. However, the exact pharmacological profiles and mechanisms of action of kava on the brain and behavior remain poorly understood. Here, we discuss clinical and experimental data on kava psychopharmacology and summarize chemistry and synthesis of kavalactones. We also review its societal impact, drug use and abuse potential, and future perspectives on translational kava research.
(https://doi.org/10.1021/acschemneuro.9b00587)

Open Access Document
Food,, Nations, A. O. o. t. U. & Organization, W. H. Kava: a review of the safety of traditional and recreational beverage consumption. World Health Organization , 1-47 (2016).

Abstract:
Kava beverage has a long history of consumption in the South Pacific and has an important role in traditional community ceremonies. In recent times, it has become more widely consumed as a recreational beverage in both the South Pacific islander community as well as in the wider international community. Within these communities, kava is considered to be a safe and enjoyable beverage, based on a long tradition of use and little evidence of harm. This review has examined existing data relevant to the safety of kava beverage and identified any gaps in the available data, as well as steps that are needed to ensure the safe use of kava beverage. Consideration has been given to the method of preparation of kava beverage, the toxicity of its chemical components, the levels of consumption and the adverse health effects observed in consumers. Consideration has also been given to the relevance of the cases of hepatotoxicity that have been associated with consumption of kava medicinal products in non–Pacific island countries.
(http://www.fao.org/publications/card/en/c/1b72914b-8ac8-428f-8fc9-40f1fb4e6f3a/)

Sarris, J., Laporte, E. & Schweitzer, I. Kava: A comprehensive review of efficacy, safety, and psychopharmacology. Australian and New Zealand Journal of Psychiatry 45, 27-35 (2011).

Abstract:
Overview: Kava (Piper methysticum) is a South Pacific psychotropic plant medicine that has anxiolytic activity. This effect is achieved from modulation of GABA activity via alteration of lipid membrane structure and sodium channel function, monoamine oxidase B inhibition, and noradrenaline and dopamine re-uptake inhibition. Kava is available over the counter in jurisdictions such as the USA, Australia and New Zealand. Due to this, a review of efficacy, safety and clinical recommendations is advised.

Objective: To conduct a comprehensive review of kava, in respect to efficacy, psychopharmacology, and safety, and to provide clinical recommendations for use in psychiatry to treat generalized anxiety disorder (GAD).

Methods: A review was conducted using the electronic databases MEDLINE, CINAHL, PsycINFO and the Cochrane Library during mid 2010 of search terms relating to kava and GAD. A subsequent forward search was conducted of key papers using Web of Science cited reference search.

Results: The current weight of evidence supports the use of kava in treatment of anxiety with a significant result occurring in four out of six studies reviewed (mean Cohen's d = 1.1). Safety issues should however be considered. Use of traditional water soluble extracts of the rhizome (root) of appropriate kava cultivars is advised, in addition to avoidance of use with alcohol and caution with other psychotropic medications. Avoidance of high doses if driving or operating heavy machinery should be mandatory. For regular users routine liver function tests are advised.

Conclusions: While current evidence supports kava for generalized anxiety, more studies are required to assess comparative efficacy and safety (on the liver, cognition, driving, and sexual effects) versus established pharmaceutical comparators.
(https://doi.org/10.3109/00048674.2010.522554)

Musselmann, B., & Cappellaro, C. (2015). Kava Kava. Zeitschrift Für Komplementärmedizin, 07(03), 44–45.
(https://doi.org/10.1055/s-0035-1554957)

Singh, Y. N., Kava: an overview. Journal of Ethnophurmacology 37, 13-45 (1992).

Abstract:
Since the first significant contact with Europeans in the 18th century, the Oceanic plant, Piper methysticum Forst. (Piperaceae) and the beverage prepared from it, both of which are called kava, have become familiar to much of the outside world through both the written and visual media. The ceremonial preparation and consumption of the beverage are probably its most conspicuous and spectacular features. Kava continues to occupy a central place in everyday life in the islands concerned, although its role has been somewhat diminished by time and outside influences. Despite the large body of literature on kava — about 800 entries are listed in a recent bibliography by Singh (1986) — there has been no comprehensive review on the subject. Earlier contributions by Keller and Klohs (1963) and Shulgin (1973) were selective in treatment and dealt primarily with chemical and pharmacological aspects. The monograph by Steinmetz (1960) remains a standard reference but understandably some of the information in it has become dated. The attention of the reader is also drawn to two excellent additions to the recent kava literature, by Lebot and Cabalion (1988) and Brunton (1989), which are, although somewhat restricted in focus, are very significant contributions to the subject. The present review paper provides an updated and a multidisciplinary overview of the subject. It was prepared on the basis of the author's personal experience — he is a native of Fiji and lived in that country for about 30 years as well as the relevant literature listed in the Singh (1986) bibliography and some more recent publications.
(https://doi.org/10.1016/0378-8741(92)90003-a)

Open Access Document
Barnes, J., Anderson, L. A. & Phillipson, D. J. Kava - Herbal Medicine - Overview. Herbal Medicines - Third Edition , 389-402 (2007).

Description:
This third edition of Herbal Medicines: A guide for healthcare professionals comes a little over ten years after publication of the first edition, and reflects continuing public, professional, research, commercial and other interests in medicinal plants. At the same time, there have been ongoing concerns surrounding the quality, safety and efficacy of herbal medicinal products, and heightened awareness of the need to protect the public against poor-quality and unsafe products. Pharmacists, doctors, nurses, herbal-medicine practitioners and other healthcare providers should be knowledgeable about these issues and should be able to advise patients and the public on the safe, effective and appropriate use of herbal preparations; this book aims to provide pharmacists and other healthcare professionals with summarized, yet sufficiently detailed, scientific information to enable them to do so.
(https://naturalingredient.org/wp/wp...nneBarnesJ.DavidPhillipsonLindaA.Anderson.pdf)

Open Access Article
Davis, R. I. & Brown, J. F. Kava (Piper methysticum) in the South Pacific: its importance, methods of cultivation, cultivars, diseases and pests , (1999).

Description:
This report discusses kava myths and ceremonies, the relative importance of kava as a cash crop, the kava plant and its cultivation, and the diseases and pests commonly found in kava gardens. It also describes the main kava cultivars grown in Fiji, Tonga, Vanuatu and Samoa, reports the results of field trials on the effects of shading on kava growth and yield, and compares the growth patterns and yields of 10 different kava cultivars in Vanuatu
(http://dx.doi.org/10.22004/ag.econ.113917)

Open Access Article
Bian, T., Corral, P., Wang, Y., Botello, J., Kingston, R., Daniels, T., Salloum, R. G., Johnston, E., Huo, Z., Lu, J. & Liu, A. C. Kava as a Clinical Nutrient : Promises and Challenges. Nutrients 12, 3044-undefined (2020).

Abstract:
Kava beverages are typically prepared from the root of Piper methysticum. They have been consumed among Pacific Islanders for centuries. Kava extract preparations were once used as herbal drugs to treat anxiety in Europe. Kava is also marketed as a dietary supplement in the U.S. and is gaining popularity as a recreational drink in Western countries. Recent studies suggest that kava and its key phytochemicals have anti-inflammatory and anticancer effects, in addition to the well-documented neurological benefits. While its beneficial effects are widely recognized, rare hepatotoxicity had been associated with use of certain kava preparations, but there are no validations nor consistent mechanisms. Major challenges lie in the diversity of kava products and the lack of standardization, which has produced an unmet need for quality initiatives. This review aims to provide the scientific community and consumers, as well as regulatory agencies, with a broad overview on kava use and its related research. We first provide a historical background for its different uses and then discuss the current state of the research, including its chemical composition, possible mechanisms of action, and its therapeutic potential in treating inflammatory and neurological conditions, as well as cancer. We then discuss the challenges associated with kava use and research, focusing on the need for the detailed characterization of kava components and associated risks such as its reported hepatotoxicity. Lastly, given its growing popularity in clinical and recreational use, we emphasize the urgent need for quality control and quality assurance of kava products, pharmacokinetics, absorption, distribution, metabolism, excretion, and foundational pharmacology. These are essential in order to inform research into the molecular targets, cellular mechanisms, and creative use of early stage human clinical trials for designer kava modalities to inform and guide the design and execution of future randomized placebo controlled trials to maximize kava’s clinical efficacy and to minimize its risks.
(https://doi.org/10.3390/nu12103044)

Saroya A.S., Singh J. (2018) Piper methysticum G.Forst: A Potent Antianxiety Agent. In: Pharmacotherapeutic Potential of Natural Products in Neurological Disorders. Springer, Singapore.

(https://doi.org/10.1007/978-981-13-0289-3_7)

Liver Toxicology

Teschke R. Kava hepatotoxicity--a clinical review. Ann Hepatol. 2010 Jul-Sep;9(3):251-65. PMID: 20720265.

Abstract:
This review critically analyzes the clinical data of patients with suspected kava hepatotoxicity and suggests recommendations for minimizing risk. Kava is a plant (Piper methysticum) of the pepper family Piperaceae, and its rhizome is used for traditional aqueous extracts in the South Pacific Islands and for commercial ethanolic and acetonic medicinal products as anxiolytic herbs in Western countries. A regulatory ban for ethanolic and acetonic kava extracts was issued in 2002 for Germany on the basis of reports connecting liver disease with the use of kava, but the regulatory causality assessment was a matter of international discussions. Based on one positive reexposure test with the kava drug, it was indeed confirmed that kava is potentially hepatotoxic. In subsequent studies using a structured, quantitative and hepatotoxicity specific causality assessment method in 14 patients with liver disease described worldwide, causality for kava +/- comedicated drugs and dietary supplements including herbal ones was highly probable (n = 1), probable (n = 4) or possible (n = 9) regarding aqueous extracts (n = 3), ethanolic extracts (n = 5), acetonic extracts (n = 4), and mixtures containing kava (n = 2). Risk factors included overdose, prolonged treatment, and comedication with synthetic drugs and dietary supplements comprizing herbal ones in most of the 14 patients. Hepatotoxicity occurred independently of the used solvent, suggesting poor kava raw material quality as additional causative factor. In conclusion, in a few individuals kava may be hepatotoxic due to overdose, prolonged treatment, comedication, and probably triggered by an unacceptable quality of the kava raw material; standardization is now required, minimizing thereby hepatotoxic risks.
(https://pubmed.ncbi.nlm.nih.gov/20720265/)

Open Access Article
Danan G, Teschke R. RUCAM in Drug and Herb Induced Liver Injury: The Update. Int J Mol Sci. 2015 Dec 24;17(1):14. doi: 10.3390/ijms17010014. PMID: 26712744; PMCID: PMC4730261.

Abstract:
RUCAM (Roussel Uclaf Causality Assessment Method) or its previous synonym CIOMS (Council for International Organizations of Medical Sciences) is a well established tool in common use to quantitatively assess causality in cases of suspected drug induced liver injury (DILI) and herb induced liver injury (HILI). Historical background and the original work confirm the use of RUCAM as single term for future cases, dismissing now the term CIOMS for reasons of simplicity and clarity. RUCAM represents a structured, standardized, validated, and hepatotoxicity specific diagnostic approach that attributes scores to individual key items, providing final quantitative gradings of causality for each suspect drug/herb in a case report. Experts from Europe and the United States had previously established in consensus meetings the first criteria of RUCAM to meet the requirements of clinicians and practitioners in care for their patients with suspected DILI and HILI. RUCAM was completed by additional criteria and validated, assisting to establish the timely diagnosis with a high degree of certainty. In many countries and for more than two decades, physicians, regulatory agencies, case report authors, and pharmaceutical companies successfully applied RUCAM for suspected DILI and HILI. Their practical experience, emerging new data on DILI and HILI characteristics, and few ambiguous questions in domains such alcohol use and exclusions of non-drug causes led to the present update of RUCAM. The aim was to reduce interobserver and intraobserver variability, to provide accurately defined, objective core elements, and to simplify the handling of the items. We now present the update of the well accepted original RUCAM scale and recommend its use for clinical, regulatory, publication, and expert purposes to validly establish causality in cases of suspected DILI and HILI, facilitating a straightforward application and an internationally harmonized approach of causality assessment as a common basic tool.
(https://doi.org/10.3390/ijms17010014)

Kuchta K, Schmidt M, Nahrstedt A. German Kava Ban Lifted by Court: The Alleged Hepatotoxicity of Kava (Piper methysticum) as a Case of Ill-Defined Herbal Drug Identity, Lacking Quality Control, and Misguided Regulatory Politics. Planta Med. 2015 Dec;81(18):1647-53. doi: 10.1055/s-0035-1558295. Epub 2015 Dec 22. PMID: 26695707.

Abstract:
Kava, the rhizome and roots of Piper methysticum, are one of the most important social pillars of Melanesian societies. They have been used for more than 1000 years in social gatherings for the preparation of beverages with relaxing effects. During the colonial period, extract preparations found their way into Western medicinal systems, with experience especially concerning the treatment of situational anxiety dating back more than 100 years. It therefore came as a surprise when the safety of kava was suddenly questioned based on the observation of a series of case reports of liver toxicity in 1999 and 2000. These case reports ultimately led to a ban of kava products in Europe – a ban that has been contested because of the poor evidence of risks related to kava. Only recently, two German administrative courts decided that the decision of the regulatory authority to ban kava as a measure to ensure consumer safety was inappropriate and even associated with an increased risk due to the higher risk inherent to the therapeutic alternatives. This ruling can be considered as final for at least the German market, as no further appeal has been pursued by the regulatory authorities. However, in order to prevent further misunderstandings, especially in other markets, the current situation calls for a comprehensive presentation of the cardinal facts and misconceptions concerning kava and related drug quality issues.
(https://doi.org/10.1055/s-0035-1558295)

Open Access Article
LiverTox: Clinical and Research Information on Drug- Induced Liver Injury [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012-. Kava Kava.

Background:
Kava kava is an herbal derived from roots of the plant Piper methysticum (“intoxicating Pepper” plant), a member of the pepper family found in the Western and South Pacific. More commonly referred to simply as “kava” (bitter), it has been used for centuries as a recreational and ceremonial drink in Oceania (Polynesia, Micronesia and Macronesia). It is prepared from the roots of the plant which are ground into a fine pulp to which water is added. The active ingredients are kavapyrones (kavalactones), which have effects similar to alcohol, such as relaxation, talkativeness, and euphoria, while reportedly maintaining mental clarity. For these reasons, kava has been proposed to be anxiolytic and used in patients with anxiety disorders and as treatment for insomnia, premenstrual syndrome and stress. Kava appears to have an abuse potential, but it is rare with conventional doses. Recently, concerns have arisen regarding the safety of kava products, in particular due to reports of liver injury. For this reason, the use of kava has been banned or restricted in many countries of the world such as Germany, Switzerland, France, Canada, and Great Britain. However, several groups have disputed the evidence for hepatotoxicity, suggesting that responsibility for liver injury lies with adulterants or concomitant drugs or herbals. Furthermore, the literature on liver injury from kava has included several incomplete or overlapping reports, and causality was rarely well shown. Nevertheless, there are a small number of cases of severe hepatic injury arising during therapy that are convincing. Kava in many formulations remains available from nutrition stores and the Internet.
(https://www.ncbi.nlm.nih.gov/books/n/livertox/KavaKava/)

Fu, D., & Ramzan, I. (2015). Use of kava as a phytotherapeutic agent and kava‐related hepatotoxicity.

Summary:
Kava has been widely used as a herbal medicine for alternative treatment of anxiety and insomnia. In Europe, kava has been used for the treatment of anxiety and nervous disorders such as stress and restlessness, and in the United States kava is used as a natural alternative to anti‐anxiety drugs and sleeping remedies. The most important medical application of kava is associated with its anti‐psychotic effects. This chapter discusses the detailed mechanisms of kava‐mediated hepatotoxicity, including (i) inhibition of cytochrome P450 enzyme activities that are important for drug metabolism; (ii) decreasing liver glutathione content that is linked to drug detoxification; (iii) inhibition of cyclooxygenase enzyme activity; (iv) induction of inflammatory responses; (v) inhibition of hepatic transporter function, which results in accumulation of drugs, toxins, and bile acids; and (vi) direct mitochondrial damage that plays a central role in drug‐induced liver injury.
(https://doi.org/10.1002/9781119006039.ch13)

Teschke, R., Qiu, S. X., & Lebot, V. (2011). Herbal hepatotoxicity by kava: Update on pipermethystine, flavokavain B, and mould hepatotoxins as primarily assumed culprits. In Digestive and Liver Disease (Vol. 43, Issue 9, pp. 676–681).

Abstract:
Herbal hepatotoxicity by the anxiolytic kava (Piper methysticum Forst. f.) emerged unexpectedly and was observed in a few patients worldwide. Liver injury occurred after the use of traditional aqueous kava extracts in the South Pacific region and of acetonic and ethanolic extracts in Western countries in rare cases, suggesting that the solvents used play no major causative role. In this review, we discuss actual pathogenetic issues of kava hepatotoxicity with special focus on developments regarding pipermethystine, flavokavain B, and mould hepatotoxins as possible culprits. There is abundant data of in vitro cytotoxicity including apoptosis by pipermethystine and flavokavain B added to the incubation media, yet evidence is lacking of in vivo hepatotoxicity in experimental animals under conditions similar to human kava use. Furthermore, in commercial Western kava extracts, pipermethystine was not detectable and flavokavain B was present as a natural compound in amounts much too low to cause experimental liver injury. There is concern, however, that due to high temperature and humidity in the South Pacific area, kava raw material might have been contaminated by mould hepatotoxins such as aflatoxins after harvest and during storage. Whether kava hepatotoxicity may be due to aflatoxicosis or other mould hepatotoxins, requires further studies.
(https://doi.org/10.1016/j.dld.2011.01.018)

Open Access Document
Ramzan, I., Rowe, A., & Zhang, L. Y. (2011). Toxicokinetics of kava. In Advances in Pharmacological Sciences (Vol. 2011).

Abstract:
Kava is traditionally consumed by South Pacific islanders as a drink and became popular in Western society as a supplement for anxiety and insomnia. Kava extracts are generally well tolerated, but reports of hepatotoxicity necessitated an international reappraisal of its safety. Hepatotoxicity can occur as an acute, severe form or a chronic, mild form. Inflammation appears to be involved in both forms and may result from activation of liver macrophages (Kupffer cells), either directly or via kava metabolites. Pharmacogenomics may influence the severity of this inflammatory response.
(https://doi.org/10.1155/2011/326724)

Whitton, A. P., Response to Schmidt "Are Kavalactones the Hepatotoxic Principle of Kava Extracts? The Pitfalls of the Glutathione Theory. The Journal of Alternative and Complementary Medicine 9, 187-188 (2003).

Description:
Letter to the editor Dr. Schmidt regarding his paper about kavalactones being hepatoxic.
(https://doi.org/10.1089/10755530360623293)

Open Access Article
Narayanapillai, S. C., Leitzman, P., O'Sullivan, M. G. & Xing, C. Flavokawains A and B in kava, not dihydromethysticin, potentiate acetaminophen-induced hepatotoxicity in C57BL/6 mice. Chem. Res. Toxicol. 27, 1871-1876 (2014).

Abstract:
Anxiolytic kava products have been associated with rare but severe hepatotoxicity in humans. This adverse potential has never been captured in animal models, and the responsible compound(s) remains to be determined. The lack of such knowledge greatly hinders the preparation of a safer kava product and limits its beneficial applications. In this study we evaluated the toxicity of kava as a single entity or in combination with acetaminophen (APAP) in C57BL/6 mice. Kava alone revealed no adverse effects for long-term usage even at a dose of 500 mg/kg bodyweight. On the contrary a three-day kava pretreatment potentiated APAP-induced hepatotoxicity, resulted in an increase in serum ALT and AST, and increased severity of liver lesions. Chalcone-based flavokawains A (FKA) and B (FKB) in kava recapitulated its hepatotoxic synergism with APAP while dihydromethysticin (DHM, a representative kavalactone and a potential lung cancer chemopreventive agent) had no such effect. These results, for the first time, demonstrate the hepatotoxic risk of kava and its chalcone-based FKA and FKB in vivo and suggest that herb-drug interaction may account for the rare hepatotoxicity associated with anxiolytic kava usage in humans.
(https://pubmed.ncbi.nlm.nih.gov/25185080/)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25185080/)

Open Access Article
Martin, A. C., Johnston, E., Xing, C. & Hegeman, A. D. Measuring the chemical and cytotoxic variability of commercially available kava (Piper methysticum G. Forster). PLoS One 9, (2014).

Abstract:
Formerly used world-wide as a popular botanical medicine to reduce anxiety, reports of hepatotoxicity linked to consuming kava extracts in the late 1990s have resulted in global restrictions on kava use and have hindered kava-related research. Despite its presence on the United States Food and Drug Administration consumer advisory list for the past decade, export data from kava producing countries implies that US kava imports, which are not publicly reported, are both increasing and of a fairly high volume. We have measured the variability in extract chemical composition and cytotoxicity towards human lung adenocarcinoma A549 cancer cells of 25 commercially available kava products. Results reveal a high level of variation in chemical content and cytotoxicity of currently available kava products. As public interest and use of kava products continues to increase in the United States, efforts to characterize products and expedite research of this potentially useful botanical medicine are necessary.
(https://pubmed.ncbi.nlm.nih.gov/25365244/)
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4218769/)

Open Access Article
Christl, S. U., Seifert, A. & Seeler, D. Toxic hepatitis after consumption of traditional kava preparation. Journal of Travel Medicine 16, 55-56 (2009).

Description:
A 42‐year‐old previously healthy white male presented with weakness, loss of appetite, and jaundice. He did not report specific organ symptoms, and there was no history of liver disease. He admitted alcohol consumption of not more than one drink daily but denied medication or drug use. He also had no contact with hazardous substances at work. Three weeks before, he had returned from a 20‐day honeymoon that he and his wife spent on the Samoan islands.
(https://doi.org/10.1111/j.1708-8305.2008.00259.x)
(https://academic.oup.com/jtm/article/16/1/55/1803384)

Teschke, R., Schwarzenboeck, A. & Hennermann, K. H. Kava hepatotoxicity: A clinical survey and critical analysis of 26 suspected cases. European Journal of Gastroenterology and Hepatology 20, 1182-1193 (2008).

Abstract:
Background/Aims
Hepatotoxicity has been previously suspected by national regulatory agencies in 26 patients in causal relationship with the treatment by kava extracts commonly used as herbal anxiolytic drugs.

Methods
A quantitative causality assessment was undertaken using the system of the Council for International Organizations of Medical Sciences, scale of objective probability scoring.

Results
Causality was unassessable, unrelated, or excluded in 16 patients owing to lack of temporal association and causes independent of kava or comedicated drugs. Low Council for International Organizations of Medical Sciences scores additionally resulted in excluded or unlikely causality assessments (n=2), leaving a total of eight patients with various degrees of causality for kava ± comedicated drugs. Only one out of these eight patients adhered to the regulatory recommendations regarding both daily dose (≤120 mg kavapyrones) and duration of therapy (≤3 months) and experienced toxic liver injury with a probable causality for kava. In six cases with kava overdose and/or increased duration of kava treatment causality for kava was possible (n=3) and for kava together with the comedicated drug(s) possible (n=2) or probable (n=1).

Conclusion
Kava taken as recommended is associated with rare hepatotoxicity, whereas overdose, prolonged treatment, and comedication may carry an increased risk.
(https://doi.org/10.1097/meg.0b013e3283036768)

Stickel, F., Baumüller, H. M., Seitz, K., Vasilakis, D., Seitz, G., Seitz, H. K., & Schuppan, D. (2003). Hepatitis induced by Kava (Piper methysticum rhizoma). Journal of Hepatology, 39(1), 62–67.

Abstract:
Background/Aims: Botanical drugs are widely used and often contain highly active compounds. Kava root (Piper methysticum rhizoma), used frequently in Europe as a remedy against anxiety, contains kavapyrones with sedative effects. Seven case reports suggested the development of hepatitis after the intake of Kava.

Methods: We analyzed 29 novel cases of hepatitis along with Kava ingestion which occurred between 1990 and 2002 in addition to the seven already published case reports using a clinical diagnostic scale established for adverse hepatic drug reactions.

Results: Hepatic necrosis or cholestatic hepatitis were noticed with both alcoholic and acetonic Kava extracts. The majority of the 29 patients and the additional seven published reports were women (27 females, nine males). Both the cumulative dose and the latency to when the hepatotoxic reaction emerged were highly variable. Nine patients developed fulminant liver failure, of which eight patients underwent liver transplantation. Three patients died, two following unsuccessful liver transplantation and one without. In all other patients, a complete recovery was noticed after the withdrawal of Kava. Pathophysiologically, both immunoallergic and idiosyncratic factors may be responsible.

Conclusions: The present report emphasizes the potentially severe hepatotoxicity of Kava which has recently led to the retraction of Kava-containing drugs by the pharmacovigilance authorities in Germany.
(https://doi.org/10.1016/S0168-8278(03)00175-2)

Lüde, S., Török, M., Dieterle, S., Jäggi, R., Büter, K. B., & Krähenbühl, S. (2008). Hepatocellular toxicity of kava leaf and root extracts. Phytomedicine, 15(1–2), 120–131.

Abstract:
Kava extracts are used widely for different purposes and were thought to be safe. Recently, several cases of hepatotoxicity have been published. To explore possible mechanisms of kava hepatotoxicity, we prepared and analyzed three different kava extracts (a methanolic and an acetonic root and a methanolic leaf extract), and investigated their toxicity on HepG2 cells and isolated rat liver mitochondria. All three extracts showed cytotoxicity starting at a concentration of 50 μg/ml (lactate dehydrogenase leakage) or 1 μg/ml (MTT test). The mitochondrial membrane potential was decreased (root extracts starting at 50 μg/ml) and the respiratory chain inhibited and uncoupled (root extracts) or only uncoupled (leaf extract) at 150 μg/ml, and mitochondrial β-oxidation was inhibited by all extracts starting at 100 μg/ml. The ratio oxidized to reduced glutathione was increased in HepG2 cells, whereas the cellular ATP content was maintained. Induction of apoptosis was demonstrated by all extracts at a concentration of 150 μg/ml. These results indicate that the kava extracts are toxic to mitochondria, leading to inhibition of the respiratory chain, increased ROS production, a decrease in the mitochondrial membrane potential and eventually to apoptosis of exposed cells. In predisposed patients, mitochondrial toxicity of kava extract may explain hepatic adverse reactions of this drug.
(https://doi.org/10.1016/j.phymed.2007.11.003)

Open Access Article
Teschke, R., Sarris, J., Glass, X. & Schulze, J. Kava, the anxiolytic herb: Back to basics to prevent liver injury?. British Journal of Clinical Pharmacology 71, 445-448 (2011).

Abstract:
The use of the anxiolytic herb kava has caused toxic liver injury in Western countries and economic problems in South Pacific Islands due to tthe regulatory ban on kava. This analysis shows poor quality of kava raw material as a cause for its toxicity and suggests preventative measures by going back to the traditional use of kava for the sake of the patients and the South Pacific economy.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3045554/)

Jhoo, J. W., Freeman, J. P., Heinze, T. M., Moody, J. D., Schnackenberg, L. K., Beger, R. D., Dragull, K., Tang, C. S. & Ang, C. Y. In vitro cytotoxicity of nonpolar constituents from different parts of kava plant (Piper methysticum). J. Agric. Food Chem. 54, 3157-3162 (2006).

Abstract:
Kava (Piper methysticum), a perennial shrub native to the South Pacific islands, has been used to relieve anxiety. Recently, several cases of severe hepatotoxicity have been reported from the consumption of dietary supplements containing kava. It is unclear whether the kava constituents, kavalactones, are responsible for the associated hepatotoxicity. To investigate the key components responsible for the liver toxicity, bioassay-guided fractionation was carried out in this study. Kava roots, leaves, and stem peelings were extracted with methanol, and the resulting residues were subjected to partition with a different polarity of solvents (hexane, ethyl acetate, n-butanol, and water) for evaluation of their cytotoxicity on HepG2 cells based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and lactate dehydrogenase and aspartate aminotransferase enzyme leakage assays. Organic solvent fractions displayed a much stronger cytotoxicity than water fractions for all parts of kava. The hexane fraction of the root exhibited stronger cytotoxic effects than fractions of root extracted with other solvents or extracts from the other parts of kava. Further investigations using bioassay-directed isolation and analysis of the hexane fraction indicated that the compound responsible for the cytotoxicity was flavokavain B. The identity of the compound was confirmed by 1H and 13 C NMR and MS techniques.
(https://doi.org/10.1021/jf051853j)

Moulds, R. F. & Malani, J. Kava: Herbal panacea or liver poison?. Medical Journal of Australia 178, 451-453 (2003).

Abstract:
  • Following reports of liver toxicity, including liver failure, associated with extracts from the Pacific islands plant kava (Piper methysticum), these have been banned from sale as a herbal anxiolytic in many Western countries, to the detriment of Pacific island economies.
  • Pacific Islanders have used kava extensively for centuries, without recognised liver toxicity. However, the population is small, and there has been no systematic evaluation of possible liver damage.
  • For both economic and public health reasons, it is important to determine if kava is inherently hepatotoxic, and what the mechanisms of toxicity are.
  • Such research could lead to safer kava extracts for sale in Western countries, or identification of a subpopulation who should not consume kava.
(https://doi.org/10.5694/j.1326-5377.2003.tb05289.x)

Open Access Article
Behl, M., Nyska, A., Chhabra, R. S., Travlos, G. S., Fomby, L. M., Sparrow, B. R., Hejtmancik, M. R. & Chan, P. C. Liver toxicity and carcinogenicity in F344/N rats and B6C3F1 mice exposed to Kava Kava. Food Chem. Toxicol. 49, 2820-2829 (2011).

Abstract:
Kava Kava is an herbal supplement used as an alternative to antianxiety drugs. Although some reports suggest an association of Kava Kava with hepatotoxicity , it continues to be used in the United States due to lack of toxicity characterization. In these studies F344/N rats and B6C3F1 mice were administered Kava Kava extract orally by gavage in corn oil for two weeks, thirteen weeks or two years. Results from prechronic studies administered Kava Kava at 0.125- to 2g/kg body weight revealed dose-related increases in liver weights and incidences of hepatocellular hypertrophy. In the chronic studies, there were dose-related increases in the incidences of hepatocellular hypertrophy in rats and mice administered Kava Kava for up to 1 g/kg body weight. This was accompanied by significant increases in incidences of centrilobular fatty change. There was no treatment- related increase in carcinogenic activity in the livers of male or female rats in the chronic studies. Male mice showed a significant dose-related increase in the incidence of hepatoblastomas. In female mice, there was a significant increase in the combined incidence of hepatocellular adenoma and carcinoma in the low and mid dose groups but not in the high dose group. These findings were accompanied by several nonneoplastic hepatic lesions.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3190036/)

Tugcu, G., Kırmızıbekmez, H. & Aydın, A. The integrated use of in silico methods for the hepatotoxicity potential of Piper methysticum. Food Chem. Toxicol. 145, (2020).

Abstract:
Herbal products as supplements and therapeutic intervention have been used for centuries. However, their toxicities are not completely evaluated and the mechanisms are not clearly understood. Dried rhizome of the plant kava (Piper methysticum) is used for its anxiolytic, and sedative effects. The drug is also known for its hepatotoxicity potential. Major constituents of the plant were identified as kavalactones, alkaloids and chalcones in previous studies. Kava hepatotoxicity mechanism and the constituent that causes the toxicity have been debated for decades. In this paper, we illustrated the use of computational tools for the hepatotoxicity of kava constituents. The proposed mechanisms and major constituents that are most probably responsible for the toxicity have been scrutinized. According to the experimental and prediction results, the kava constituents play a substantial role in hepatotoxicity by some means or other via glutathione depletion, CYP inhibition, reactive metabolite formation, mitochondrial toxicity and cyclooxygenase activity. Some of the constituents, which have not been tested yet, were predicted to involve mitochondrial membrane potential, caspase-3 stimulation, and AhR activity. Since Nrf2 activation could be favorable for prevention of hepatotoxicity, we also suggest that these compounds should undergo testing given that they were predicted not to be activating Nrf2. Among the major constituents, alkaloids appear to be the least studied and the least toxic group in general. The outcomes of the study could help to appreciate the mechanisms and to prioritize the kava constituents for further testing.
(https://doi.org/10.1016/j.fct.2020.111663)

Open Access Article
Gow, P. J., Connelly, N. J., Hill, R. L., Crowley, P. & Angus, P. W. Fatal fulminant hepatic failure induced by a natural therapy containing kava. Medical Journal of Australia 178, 442-443 (2003).

Abstract:
We describe a case of acute liver failure and death associated with the use of a preparation containing the "natural" anxiolytic kava (Piper methysticum) and passionflower (Passiflora incarnata). The patient died after a report by the Therapeutic Goods Administration (TGA) warning of the potential for hepatotoxicity associated with the use of kava-containing products. The general public and alternative medicine practitioners need to be aware of the potential for non-prescription drugs to cause serious hepatic reactions.
(https://www.mja.com.au/journal/2003...ilure-induced-natural-therapy-containing-kava)

Open Access Document
Coulter, D., Tamayo, C., Sotheeswaran, S. & Ulbricht, C. Assessment of the risk of hepatotoxicity with kava products. WHO Library Cataloguing-in-Publication Data , 1-82 (2007).

Summary:
General overview
There has been international concern over the association of kava products and serious hepatotoxicity. Regulatory action banning these products in Europe has been controversial.
The objective of this report is to investigate the possibility of hepatotoxicity with kava.
This report is written in four major sections:
I Description of kava
IIA Safety information -literature review
liB Safety information -analysis of case reports
III Regulatory issues
IV Conclusions and recommendations
The first 3 sections are written as stand-alone documents with their own references. In addition there is:
• A summary of findings
• A summary of recommendations
• A bibliography
(https://apps.who.int/iris/handle/10665/43630)

Teschke, R., Sarris, J. & Lebot, V. Contaminant hepatotoxins as culprits for kava hepatotoxicity - Fact or fiction?. Phytotherapy Research 27, 472-474 (2013).

Abstract:
The culprit of kava hepatotoxicity will continue to remain a mystery in humans, if the underlying reaction is of idiosyncratic, unpredictable, and dose‐independent nature due potentially to some metabolic aberration in a few individuals emerging from kava use. In addition, kava hepatotoxicity is presently not reproducible experimentally in preclinical models, as demonstrated by studies showing whole kava extracts are not hepatotoxic. This led us to propose our ‘working hypothesis’ that contaminant hepatotoxins including moulds might have caused rare kava hepatotoxicity in humans. Further studies are now warranted to proof or disproof our working hypothesis, because kava hepatotoxicity possibly based on contaminant hepatotoxins could be a preventable disease. In the meantime, however, for minimizing toxicity risk in kava users, a pragmatic approach should focus on the medicinal use of an aqueous extract derived from peeled rhizomes and roots of a non‐mouldy noble kava cultivar, limited to maximum 250‐mg kavalactones daily for acute or intermittent use.
(https://doi.org/10.1002/ptr.4729)

Teschke, R., Sarris, J. & Lebot, V. Kava hepatotoxicity solution: A six-point plan for new kava standardization. Phytomedicine 18, 96-103 (2011).

Abstract:
Kava-induced liver injury has been demonstrated in a few patients worldwide and appears to be caused by inappropriate quality of the kava raw material. When cases of liver disease in connection with the use of kava emerged, this was an unexpected and challenging event considering the long tradition of safe kava use. In order to prevent kava hepatotoxicity in future, a set of quality specifications as standard is essential for the preparation not only of kava drugs and kava dietary supplements in the Western world but also for traditional kava drinks in the South Pacific Islands.

For all these purposes a uniform approach is required, using water based extracts from the peeled rhizomes and roots of a noble cultivar such as Borogu with at least 5 years of age at the time of harvest. Cultivated in Vanuatu for centuries, noble varieties (as defined in the Vanuatu Kava Act of December 2002) are well tolerated traditional cultivars with a good safety record. At present, Vanuatu kava legislation is inadequately enforced to meet quality issues for kava, and further efforts are required in Vanuatu, in addition to similar legislation in other kava producing South Pacific Islands. Future regulatory and commercial strategies should focus not only on the standardization of kava drugs, kava dietary supplements, and traditional kava extracts, but also on thorough surveillance during the manufacturing process to improve kava quality for safe human use. The efficacy of kava extracts to treat patients with anxiety disorders is well supported, but further clinical trials with aqueous kava extracts are necessary.

We thereby propose a six-point kava solution plan: (1) use of a noble kava cultivar such as Borogu, at least 5 years old at time of harvest, (2) use of peeled and dried rhizomes and roots, (3) aqueous extraction, (4) dosage recommendation of ≤250 mg kavalactones per day (for medicinal use), (5) systematic rigorous future research, and (6) a Pan Pacific quality control system enforced by strict policing.

In conclusion, at different levels of responsibility, new mandatory approaches are now required to implement quality specification for international acceptance of kava as a safe and effective anxiolytic herb.
(https://doi.org/10.1016/j.phymed.2010.10.002)

Open Access Article
Fu, P. P., Xia, Q., Guo, L., Yu, H. & Chan, P. C. Toxicity of kava kava. Journal of Environmental Science and Health - Part C Environmental Carcinogenesis and Ecotoxicology Reviews 26, 89-112 (2008).

Abstract:
Kava is a traditional beverage of various Pacific Basin countries. Kava has been introduced into the mainstream U.S. market principally as an anti-anxiety preparation. The effects of the long-term consumption of kava have not been documented adequately. Preliminary studies suggest possible serious organ system effects. The potential carcinogenicity of kava and its principal constituents are unknown. As such, kava extract was nominated for the chronic tumorigenicity bioassay conducted by the National Toxicology Program (NTP). At present toxicological evaluation of kava extract is being conducted by the NTP. The present review focuses on the recent findings on kava toxicity and the mechanisms by which kava induces hepatotoxicity.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5868963)

Russmann, S., Barguil, Y., Cabalion, P., Kritsanida, M., Duhet, D. & Lauterburg, B. H. Hepatic injury due to traditional aqueous extracts of kava root in New Caledonia. European Journal of Gastroenterology & Hepatology , 1033-1036 (2003).

Abstract:
Traditional aqueous kava extracts were the most probable cause of hepatitis in two patients presenting with markedly elevated transaminases and hyperbilirubinaemia. A consequent survey of 27 heavy kava drinkers in New Caledonia showed elevated gamma glutamyl transferase in 23/27 and minimally elevated transaminases in 8/27. We conclude that not only commercially available, but also traditionally prepared kava extracts may rarely cause liver injury. The increased activity of gamma glutamyl transferase in heavy kava consumers in the presence of normal or minimally elevated transaminases is probably not a sign of liver injury, but rather reflects an induction of CYP450 enzymes.
(https://doi.org/10.1097/00042737-200309000-00015)

Becker, M. W., Lourençone, E. M. S., De Mello, A. F., Branco, A., Filho, E. M. R., Blatt, C. R., Mallmann, C. A., Schneider, M., Caregnato, R. C. A., & Blatt, C. R. (2019). Liver transplantation and the use of KAVA: Case report. Phytomedicine, 56, 21–26.

Abstract:
Background
Self-medication and the belief that herbal products are free of health risks are common in Brazil. The kava (Piper methysticum), known for its anxiolytic action, has a widespread popular use. Hepatotoxicity of kava is reported, including cases of liver transplantation and death. The kava had its use prohibited or restricted in countries like Germany, France, among others. Toxicity may be related to overdosage; however, factors such as botanical characteristics of the plant, the harvesting, storage, and production process may be associated with the development of hepatotoxic substances, such as triggering idiosyncratic reactions.

Hypothesis
In this case, there is a suspicion that the toxicide is intrinsic to the drug; however, the possibility of adulterants and contaminants must be ruled out.

Study design
This study reports the case of a patient who, after using the herbal kava for 52 days, evolved into acute liver failure and liver transplantation.

Methods
The data were collected directly with the patient and compared with their clinical records. Causality was determined through the RUCAM algorithm. In addition, a phytochemical analysis of the drug used was performed.

Results
According to the patient's report, there is no evidence of overdosage. Results from RUCAM algorithm infer causality between liver damage and the use of kava. The analysis chemical constituents did not find any possible contaminants and major changes in the active compounds. Seven months after transplantation, the patient is well and continues to be followed up by a medical team.

Conclusion
Our investigation indicates that there was kava-induced hepatotoxicity at standard dosages. In Brazil, self-medication by herbal medicines is frequent and many patients and health professionals do not know the risks associated with their use. Diagnosing and notifying cases in which plants and herbal medicine induce liver damage is of paramount importance to increase the knowledge about DILI and to prevent or treat similar cases quickly.
(https://doi.org/10.1016/j.phymed.2018.08.011)

Olsen, L. R., Grillo, M. P. & Skonberg, C. Constituents in Kava extracts potentially involved in hepatotoxicity: A review. Chem. Res. Toxicol. 24, 992-1002 (2011).

Abstract:
Aqueous kava root preparations have been consumed in the South Pacific as an apparently safe ceremonial and cultural drink for centuries. However, several reports of hepatotoxicity have been linked to the consumption of kava extracts in Western countries, where mainly ethanolic or acetonic extracts are used. The mechanism of toxicity has not been established, although several theories have been put forward. The composition of the major constituents, the kava lactones, varies according to preparation method and species of kava plant, and thus, the toxicity of the individual lactones has been tested in order to establish whether a single lactone or a certain composition of lactones may be responsible for the increased prevalence of kava-induced hepatotoxicity in Western countries. However, no such conclusion has been made on the basis of current data. Inhibition or induction of the major metabolizing enzymes, which might result in drug interactions, has also gained attention, but ambiguous results have been reported. On the basis of the chemical structures of kava constituents, the formation of reactive metabolites has also been suggested as an explanation of toxicity. Furthermore, skin rash is a side effect in kava consumers, which may be indicative of the formation of reactive metabolites and covalent binding to skin proteins leading to immune-mediated responses. Reactive metabolites of kava lactones have been identified in vitro as glutathione (GSH) conjugates and in vivo as mercapturates excreted in urine. Addition of GSH to kava extracts has been shown to reduce cytotoxicity in vitro, which suggests the presence of inherently reactive constituents. Only a few studies have investigated the toxicity of the minor constituents present in kava extract, such as pipermethystine and the flavokavains, where some have been shown to display higher in vitro cytotoxicity than the lactones. To date, there remains no indisputable reason for the increased prevalence of kava-induced hepatotoxicity in Western countries.
(https://doi.org/10.1021/tx100412m)

Sorrentino, L., Capasso, A. & Schmidt, M. Safety of ethanolic kava extract: Results of a study of chronic toxicity in rats. Phytomedicine 13, 542-549 (2006).

Abstract:
Backgrounds
Recently, potential liver toxicity was discussed with the intake of kava extract preparations (Piper methysticum) as anxiolytic drugs. The aim of this study was to test chronic toxicity in rats by oral application of an ethanolic kava full extract.

Methods
Wistar rats of both sexes were fed 7.3 or 73 mg/kg body weight of ethanolic kava extract for 3 and 6 months. The animals were examined for changes in body weight, hematological and liver parameters, and macroscopical and microscopical histological changes in the major organs.

Results
No signs of toxicity could be found.

Conclusions
The results are in accordance with the medical experience regarding the use of kava preparations and the long tradition of kava drinking in the South Pacific island states. Specifically, the results do not back the suspicion of potential liver toxicity.
(https://doi.org/10.1016/j.phymed.2006.01.006)

Ulbricht, C., Basch, E., Boon, H., Ernst, E., Hammerness, P., Sollars, D., Tsourounis, C., Woods, J. & Bent, S. Safety review of kava (Piper methysticum) by the Natural Standard Research Collaboration. Expert Opinion on Drug Safety 4, 779-794 (2005).

Abstract:
This systematic review discusses the proposed uses, dosing parameters, adverse effects, toxicology, interactions and mechanism of action of kava. The widespread concern regarding the potential hepatotoxicity of kava is discussed. A recommendation is made to consolidate and analyse available reports and to continue postmarket surveillance in an international repository to prevent duplicates and promote collection of thorough details at the time of each report so that any association with kava is clearly defined.
(https://doi.org/10.1517/14740338.4.4.779)

Kong, Y., Gao, X., Wang, C., Ning, C., Liu, K., Liu, Z., Sun, H., Ma, X., Sun, P. & Meng, Q. Protective effects of yangonin from an edible botanical Kava against lithocholic acid-induced cholestasis and hepatotoxicity. Eur. J. Pharmacol. 824, 64-71 (2018).

Abstract:
Accumulation of toxic bile acids in liver could cause cholestasis and liver injury. The purpose of the current study is to evaluate the hepatoprotective effect of yangonin, a product isolated from an edible botanical Kava against lithocholic acid (LCA)-induced cholestasis, and further to elucidate the involvement of farnesoid X receptor (FXR) in the anticholestatic effect using in vivo and in vitro experiments. The cholestatic liver injury model was established by intraperitoneal injections of LCA in C57BL/6 mice. Serum biomarkers and H&E staining were used to identify the amelioration of cholestasis after yangonin treatment. Mice hepatocytes culture, gene silencing experiment, real-time PCR and Western blot assay were used to elucidate the mechanisms underlying yangonin hepatoprotection. The results indicated that yangonin promoted bile acid efflux and reduced hepatic uptake via an induction in FXR-target genes Bsep, Mrp2 expression and an inhibition in Ntcp, all of which are responsible for bile acid transport. Furthermore, yangonin reduced bile acid synthesis through repressing FXR-target genes Cyp7a1 and Cyp8b1, and increased bile acid metabolism through an induction in gene expression of Sult2a1, which are involved in bile acid synthesis and metabolism. In addition, yangonin suppressed liver inflammation through repressing inflammation-related gene NF-κB, TNF-α and IL-1β. In vitro evidences showed that the changes in transporters and enzymes induced by yangonin were abrogated when FXR was silenced. In conclusions, yangonin produces protective effect against LCA-induced hepatotoxity and cholestasis due to FXR-mediated regulation. Yangonin may be an effective approach for the prevention against cholestatic liver diseases.
(https://doi.org/10.1016/j.ejphar.2018.02.002)

Open Access Article
Zhou, P., Gross, S., Liu, J.-H., Yu, B.-Y., Feng, L.-L., Nolta, J., Sharma, V., Piwnica-Worms, D., & Qiu, S. X. (2010). Flavokawain B, the hepatotoxic constituent from kava root, induces GSH-sensitive oxidative stress through modulation of IKK/NF-κB and MAPK signaling pathways. The FASEB Journal, 24(12), 4722–4732.

Abstract:
Kava (Piper methysticum Foster, Piperaceae) organic solvent-extract has been used to treat mild to moderate anxiety, insomnia, and muscle fatigue in Western countries, leading to its emergence as one of the 10 best-selling herbal preparations. However, several reports of severe hepatotoxicity in kava consumers led the U.S. Food and Drug Administration and authorities in Europe to restrict sales of kava-containing products. Herein we demonstrate that flavokawain B (FKB), a chalcone from kava root, is a potent hepatocellular toxin, inducing cell death in HepG2 (LD50=15.3±0.2 μM) and L-02 (LD50=32 μM) cells. Hepatocellular toxicity of FKB is mediated by induction of oxidative stress, depletion of reduced glutathione (GSH), inhibition of IKK activity leading to NF-κB transcriptional blockade, and constitutive TNF-α-independent activation of mitogen-activated protein kinase (MAPK) signaling pathways, namely, ERK, p38, and JNK. We further demonstrate by noninvasive bioluminescence imaging that oral consumption of FKB leads to inhibition of hepatic NF-κB transcriptional activity in vivo and severe liver damage. Surprisingly, replenishment with exogenous GSH normalizes both TNF-α-dependent NF-κB as well as MAPK signaling and rescues hepatocytes from FKB-induced death. Our data identify FKB as a potent GSH-sensitive hepatotoxin, levels of which should be specifically monitored and controlled in kava-containing herb products.—Zhou, P., Gross, S., Liu, J.-H., Yu, B.-Y., Feng, L.-L., Nolta, J., Sharma, V., Piwnica-Worms, D., Qiu, S. X. Flavokawain B, the hepatotoxic constituent from kava root, induces GSH-sensitive oxidative stress through modulation of IKK/NF-κB and MAPK signaling pathways.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2992378/)

Open Access Article
Chou, T. W., Feng, J. H., Huang, C. C., Cheng, Y. W., Chien, S. C., Wang, S. Y. & Shyur, L. F. A Plant Kavalactone Desmethoxyyangonin Prevents Inflammation and Fulminant Hepatitis in Mice. PLoS One 8, (2013).

Abstract:
Alpinia pricei Hayata is a Formosan plant which has been popularly used as nutraceutical or folk medicine for inflammation and various disorders. An active compound of the plant rhizomes, desmethoxyyangonin (DMY), was identified in this study for its novel effect against endotoxin lipopolysaccharide (LPS)-stimulated inflammation in murine macrophages and LPS/D-galactosamine (LPS/D-GalN)-induced fulminant hepatitis in mice. DMY was observed to significantly inhibit proliferation and activation of T cells ex vivo and the activity of several pro-inflammatory mediators in vitro. DMY also protected LPS/D-GalN−induced acute hepatic damages in mice through inhibiting aminotransferases activities and infiltrations of inflammatory macrophages, neutrophils and pathogenic T cells into the liver tissues. In addition, pretreatment with DMY significantly improved the survival rate of LPS/D-GalN−treated mice to 90% (9/10), compared to LPS/D-GalN−treated group (40%, 4/10). UPLC/MS platform-based comparative metabolomics approach was used to explore the serum metabolic profile in fulminant hepatic failure (FHF) mice with or without the DMY pretreatment. The results showed that LPS/D-GalN−induced hepatic damage is likely through perturbing amino acid metabolism, which leads to decreased pyruvate formation via catalysis of aminotransferases, and DMY treatment can prevent to a certain degree of these alterations in metabolic network in mouse caused by LPS/D-GalN. Mechanistic investigation demonstrated that DMY protects LPS or LPS/D-GalN−induced damages in cell or liver tissues mainly through de-regulating IKK/NFκB and Jak2/STAT3 signaling pathways. This report provides evidence-based knowledge to support the rationale for the use of A. pricei root extract in anti-inflammation and also its new function as hepatoprotetive agent against fulminant hepatitis.
(https://doi.org/10.1371/journal.pone.0077626)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/24143247/)

Open Access Article
Abu, N., Mohamed, N. E., Tangarajoo, N., Yeap, S. K., Nadeem Akhtar, M., Abdullah, M. P., Omar, A. R. & Alitheen, N. B. In vitro toxicity and in vivo immunomodulatory effects of flavokawain a and flavokawain B in balb/C mice. Natural Product Communications 10, 1199-1202 (2015).

Abstract:
Flavokawains are chalcones that can be found in the root extracts of the kava-kava (Piper methysticum) plant. Flavokawain A and flavokawain B are known to possess potential anti-inflammation and anti-cancer activities. Nevertheless, the effects of both these compounds on the normal function of the host have not been studied. There is a need to find agents that can enhance the functionality of the immune system without disturbing the homeostatic balance. This study aimed to determine the toxicity and immunomodulatory effects of flavokawain A and flavokawain B on Balb/c mice. Several assays were conducted, the MTT viability assay, cytokine detection (IL-2 and TNF-), immunophenotyping of important immune markers, serum biochemical analysis and detection of nitric oxide levels. Based on our results, flavokawain A and B did not cause mortality and all mice were observed normal after the treatment period. Both
flavokawains stimulated splenocyte proliferation, the secretion of IL-2 and TNF-α and raised the population of T cell subsets without significantly altering the level of several serum biochemical parameters. Overall, flavokawain A and B could serve as potential immune-modulator drugs without causing any toxicity, however further in vivo evidence is needed.
(https://journals.sagepub.com/doi/pdf/10.1177/1934578X1501000716)

Open Access Article
JK, T., Flavokawains A and B from kava (Piper methysticum) activate heat shock and antioxidant responses and protect against hydrogen peroxide-induced cell death in HepG2 hepatocytes. Physiol. Behav. 176, 139-148 (2017).

Abstract:
Context
Flavokawains are secondary metabolites from the kava plant (Piper methysticum Forst. f., Piperaceae) that have anticancer properties and demonstrated oral efficacy in murine cancer models. However, flavokawains also have suspected roles in rare cases of kava-induced hepatotoxicity.

Objective
To compare the toxicity flavokawains A and B (FKA, FKB) and monitor the resulting transcriptional responses and cellular adaptation in the human hepatocyte cell line, HepG2.

Materials and methods
HepG2 were treated with 2–100 μM FKA or FKB for 24–48 h. Cellular viability was measured with calcein-AM and changes in signaling and gene expression were monitored by luciferase reporter assay, real-time PCR and Western blot of both total and nuclear protein extracts. To test for subsequent resistance to oxidative stress, cells were pre-treated with 50 μM FKA, 10 μM FKB or 10 μM sulforaphane (SFN) for 24 h, followed by 0.4–2.8 mM H2O2 for 48 h, and then viability was assessed.

Results
FKA (≤ 100 μM) was not toxic to HepG2, whereas FKB caused significant cell death (IC50 = 23.2 ± 0.8 μM). Both flavokawains activated Nrf2, increasing HMOX1 and GCLC expression and enhancing total glutathione levels over 2-fold (p < 0.05). FKA and FKB also activated HSF1, increasing HSPA1A and DNAJA4 expression. Also, flavokawain pretreatment mitigated cell death after a subsequent challenge with H2O2, with FKA being more effective than FKB, and similar to SFN.

Conclusions
Flavokawains promote an adaptive cellular response that protect hepatocytes against oxidative stress. We propose that FKA has potential as a chemopreventative or chemotherapeutic agent.
(https://doi.org/10.3109/13880209.2015.1107104)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/26789234/)

Dragull, K., Yoshida, W. Y. & Tang, C. S. Piperidine alkaloids from piper methysticum. Phytochemistry 63, 193-198 (2003).

Abstract:
Pipermethystine (1), 3α,4α-epoxy-5β-pipermethystine (2) and awaine (3) were isolated from the aerial parts of kava (Piper methysticum G. Forster, Piperaceae) and identified by HRMS and NMR spectroscopic analysis. 1 was concentrated in the stem peelings and leaves. 2 and 3 are new alkaloids with 2 found only in cv. Isa among the 11 cultivars examined, and 3 occurred primarily in young leaves of all cultivars. The stem peelings have been used in recent years as a source of kavalactones in kava dietary supplement industry. Quantitative aspects of these piperidine alkaloids in P. methysticum and their potential activities on human physiology are discussed.

The concentrations of pipermethystine (1), and the new alkaloids 3α,4α-epoxy-5β-pipermethystine (2) and awaine (3) in kava are cultivar and plant part dependent.
(https://doi.org/10.1016/s0031-9422(03)00111-0)

Teschke, R., Qiu, S. X., Xuan, T. D. & Lebot, V. Kava and Kava hepatotoxicity: Requirements for novel experimental, ethnobotanical and clinical studies based on a review of the evidence. Phytotherapy Research 25, 1263-1274 (2011).

Abstract:
Kava hepatotoxicity is a well described disease entity, yet there is uncertainty as to the culprit(s). In particular, there is so far no clear evidence for a causative role of kavalactones and non‐kavalactone constituents, such as pipermethystine and flavokavain B, identified from kava. Therefore, novel enzymatic, analytical, toxicological, ethnobotanical and clinical studies are now required. Studies should focus on the identification of further potential hepatotoxic constituents, considering in particular possible adulterants and impurities with special reference to ochratoxin A and aflatoxins (AFs) producing Aspergillus varieties, which should be urgently assessed and published. At present, Aspergillus and other fungus species producing hepatotoxic mycotoxins have not yet been examined thoroughly as possible contaminants of some kava raw materials. Its occurence may be facilitated by high humidity, poor methods for drying procedures and insufficient storage facilities during the time after harvest. Various experimental studies are recommended using aqueous, acetonic and ethanolic kava extracts derived from different plant parts, such as peeled rhizomes and peeled roots including their peelings, and considering both noble and non‐noble kava cultivars. In addition, ethnobotanical studies associated with local expertise and surveillance are required to achieve a good quality of kava as the raw material. In clinical trials of patients with anxiety disorders seeking herbal anxiolytic treatment with kava extracts, long‐term safety and efficacy should be tested using traditional aqueous extracts obtained from peeled rhizomes and peeled roots of a noble kava cultivar, such as Borogu, to evaluate the risk: benefit ratio. Concomitantly, more research should be conducted on the bioavailability of kavalactones and non‐kavalactones derived from aqueous kava extracts. To be on the side of caution and to ensure lack of liver injury, kava consuming inhabitants of the kava producing or importing South Pacific islands should undergo assessment of their liver function values and serum aflatoxin levels. The primary aim is to achieve a good quality of kava raw material, without the risk of adulterants and impurities including ochratoxin A and AFs, which represent the sum of aflatoxin B1, B2, G1 and G2. Although it is known that kava may naturally be contaminated with AFs, there is at present no evidence that kava hepatotoxicity might be due to aflatoxicosis. However, appropriate studies have yet to be done and should be extended to other mould hepatotoxins, with the aim of publishing the obtained results. It is hoped that with the proposed qualifying measures, the safety of individuals consuming kava will substantially be improved.
(https://doi.org/10.1002/ptr.3464)

Open Acces Article
Petersen, G. E., Tang, Y. & Fields, C. Chemical and in vitro toxicity analysis of a supercritical fluid extract of Kava kava (Piper methysticum). Journal of Ethnopharmacology 235, 301-308 (2019).

Abstract:
Ethnopharmacological relevance
Kava and kava extracts have shown great potential as a way to minimize anxiety-associated symptoms and to help alleviate pain. Hepatoxicity has been associated with the consumption of kava products. The chemical compounds, kavalactones (KL) and flavokavains (FK) have been implicated in kava’s psychotropic and possible hepatotoxic properties.

Aim of the study
To investigate the kavalactone and flavokavain content and in vitro toxicity of KAVOA™, a supercritical carbon dioxide extraction (SFE) of kava.

Materials and methods
Kavalactone and flavokavain content of SFE kava and noble kava root were determined following extraction in acetone, cell culture media, and water using ultra high-performance liquid chromatography (UHPLC). Using water extractions of the kava products, the cell viability and toxicity on the human hepatocellular carcinoma cell line (HepG2) were determined using luminescent and fluorescent assays, respectively. The half maximal inhibitory concentration (IC50) of the SFE kava and noble kava root, extracted in cell culture media, were determined utilizing a luminescent cell viability assay.

Results
Quantification of the KAVOA™, a SFE extract of kava and kava root showed similar profiles of kavalactone and flavokavain content. Water extracted SFE and root kava did not show a negative impact on cell viability and toxicity when compared to the vehicle control treated cells. IC50 values were determined for the SFE kava and kava root extracted in cell culture media in respect to cell viability, 78.63 and 47.65 µg/mL, respectively.

Conclusions
KAVOA™, a supercritical carbon dioxide extract of kava displays a similar kavalactone profile to a noble variety of kava. In relation to total kavalactone content, KAVOA™ also has a lower content of the cytotoxic compound FKB. Aqueous extractions of KAVOA™ and noble kava root had no significant negative impact on cell viability and toxicity on HepG2 cells when compared to vehicle controlled treated cells. Results indicate KAVOA™ demonstrates a similar in vitro safety profile to that of noble kava root when experiments are normalized to kavalactone content.
(https://doi.org/10.1016/j.jep.2019.01.032)
(https://linkinghub.elsevier.com/retrieve/pii/S0378-8741(18)34053-4)

Baker, J. D., Tradition and toxicity: Evidential cultures in the kava safety debate. Social Studies of Science 41, 361-384 (2011).

Abstract:
This paper examines the debate about the safety of kava (Piper methysticum Forst. f., Piperaceae ), a plant native to Oceania, where it has a long history of traditional use. Kava became popular as an anti-anxiety treatment in Western countries in the late 1990s, but it was subsequently banned in many places due to adverse reports of liver toxicity. This paper focuses on the responses to the bans by scientists involved in kava research, contrasting their evidential culture with that employed by clinicians and regulatory officials. Cultural constructions and social negotiations of risk are shown to be context-specific, and are shaped by professional, disciplinary, and organizational factors, among others. Though the science of hepatotoxicity is uncertain enough to allow for multiple interpretations of the same data, the biomedical/clinical narrative about kava remains dominant. This case study explores the influence of these cultural, social, and political factors on the production of scientific knowledge and the assessment of benefit/risk posed by comestibles.
(https://doi.org/10.1177/0306312710395341)

Teschke R, Gaus W, Loew D. Kava extracts: safety and risks including rare hepatotoxicity. Phytomedicine. 2003;10(5):440-6. doi: 10.1078/0944-7113-00314. PMID: 12834011. .

Summary:
Kava is a perennial shrub native to some islands of the South Pacific and has been cultivated for centuries to prepare a psychoactive beverage from its rhizoma by means of extraction. Subsequently, kava extracts are commonly used as herbal anxiolytic drugs also in many other countries all over the world including European ones and the USA. Toxicological and clinical studies have shown that kava extracts are virtually devoid of toxic effects with the exception of rare hepatotoxic side effects reported in few patients. When assessed primarily by the British regulatory authority MCA but also by us, a critical analysis of the suspected cases (n = 19) in Germany reveals that only in 1 single patient a very probable causal relationship could be established between kava treatment and the development of toxic liver disease due to a positive result of an unscheduled reexposure test, whereas in another patient there might be a possible association. Out of the remaining 17 cases 12 patients were not yet assessable due to insufficient data and in 5 other cases a causal relationship was unlikely or could be excluded. The German regulatory authority might therefore well be advised to provide now additional information for those 12 patients with so far unsatisfactory data, facilitating a more appropriate assessment of causality. Nevertheless, in the meantime physicians and patients should continue to keep an eye on possible hepatotoxic side effects in the course of kava treatment, to stop the treatment alredy at first suspicion and to start with a careful diagnostic work up ruling out all other causes.
(https://doi.org/10.1078/0944-7113-00314)

Open Access Article
Lim, S. T., Dragull, K., Tang, C. S., Bittenbender, H. C., Efird, J. T. & Nerurkar, P. V. Effects of kava alkaloid, pipermethystine, and kavalactones on oxidative stress and cytochrome P450 in F-344 rats. Toxicol. Sci. 97, 214-221 (2007).

Abstract:
Kava-containing products remain popular in the United States and continue to be sold in health food stores and ethnic markets regardless of the fact that it was banned in Western countries such as Germany, France, Switzerland, Australia, and Canada, following reports of alleged hepatotoxicity. It is therefore critical to establish efficacy and verify adverse effects and/or herb-drug interactions for kava-kava (Piper methysticum). We have previously demonstrated that kava alkaloid, pipermethystine (PM), abundant in leaves and stem peelings, induces mitochondrial toxicity in human hepatoma cells, HepG2, as compared with the bioactive components, kavalactones (KL), abundant in the rhizome. The current study compared short-term toxic effects of PM in Fischer-344 (F-344) rats to acetone-water extracts of kava rhizome (KRE). Treatment of F-344 rats with PM (10 mg/kg) and KRE (100 mg/kg) for 2 weeks failed to elicit any significant changes in liver function tests or cause severe hepatic toxicity as measured by lipid peroxidation and apoptosis markers such as malondialdehyde, Bax, and Bcl-2. However, PM-treated rats demonstrated a significant increase in hepatic glutathione, cytosolic superoxide dismutase (Cu/ZnSOD), tumor necrosis factor α mRNA expression, and cytochrome P450 (CYP) 2E1 and 1A2, suggesting adaptation to oxidative stress and possible drug-drug interactions.
(https://doi.org/10.1093/toxsci/kfm035)

Teschke, R., Fuchs, J., Bahre, R., Genthner, A. & Wolff, A. Kava hepatotoxicity: Comparative study of two structured quantitative methods for causality assessment. Journal of Clinical Pharmacy and Therapeutics 35, 545-563 (2010).

Summary:
Background and objective: Ingestion of the medicinal herb kava has been associated with hepatotoxicity. We aimed to compare two different quantitative methods of causality assessment of patients with assumed hepatotoxicity by the herb.

Methods: We assessed causality in 26 patients from Germany and Switzerland, using two structured quantitative analytical methods: the system of Maria and Victorino (MV) and that of the Council for International Organizations of Medical Sciences (CIOMS). In all 26 patients, regulatory ad hoc evaluation had suggested a causal relationship between liver disease and kava use.

Results and discussion: Assessment with the MV scale resulted in no or low graded causality for kava in the 26 patients with liver disease. Causality was probable (n = 1), possible (n = 2), unlikely (n = 7), and excluded (n = 16). Causality for kava was more evident with the CIOMS scale: highly probable (n = 1), probable (n = 2), possible (n = 6), unlikely (n = 2) and excluded (n = 15). However, the results of both quantitative causality assessments are not supportive for most of the regulatory ad hoc causality assessments of the 26 patients.

Conclusion: Grades of causality for suspected hepatotoxicity by kava were much lower when evaluated by structured quantitative causality assessment scales than by regulatory ad hoc judgements. The quantitative CIOMS scale is the preferable tool for causality assessment of spontaneous reports of hepatotoxcity involving kava.
(https://doi.org/10.1111/j.1365-2710.2009.01131.x)

DiSilvestro, R. A., Zhang, W. & DiSilvestro, D. J. Kava feeding in rats does not cause liver injury nor enhance galactosamine-induced hepatitis. Food Chem. Toxicol. 45, 1293-1300 (2007).

Abstract:
Kava, like a number of herbals, has been associated with causing liver damage based on limited evidence. In contrast, the present study found that in rats, 3 mo feedings of two types of kava extracts (an acetone extract and an ethanol extract of the Samoan kava cultivar Ava Laau) at three different doses (31.25, 62.5 and 133 mg/kg diet) produced no liver injury based on serum markers of liver damage (sorbitol dehydrogenase activities, bile acid concentrations, and β-glucuronidase activities) and serum lipid peroxide readings. In fact, for some measurements and some kava doses, the injury marker readings were below control values. Moreover, for these same parameters, kava feeding did not enhance the effects of the hepatotoxin galacatosamine (500 mg/kg ip); some kava doses even showed modest protection against liver injury. Liver histology analysis showed no signs of kava causing or enhancing liver injury. Thus, this study does not support the concept that kava produces or aggravates liver injury.
(https://doi.org/10.1016/j.fct.2007.01.015)

Bilia, A. R., Gallori, S. & Vincieri, F. F. Kava-kava and anxiety: Growing knowledge about the efficacy and safety. Life Sci. 70, 2581-2597 (2002).

Abstract:
Kava-kava (Piper methysticum G. Forster) has been used in social and ceremonial life in the Pacific islands from ancient times for the soporific and narcotic effects. Today several extracts standardized in the biologically active constituents kavalactones are marketed both as herbal medicinal products for anxiety disorders and as dietary supplements to improve stress disorders, nervous tension and restlessness.

Unlike other substances used for these purposes, kava-kava has been shown to have minimal negative effects, and possibly positive effects, on reaction time and cognitive processing. Furthermore, it decreases anxiety without the loss of mental acuity. Although kava-kava has been found to be very effective, well tolerated, and non-addictive at therapeutic dosages, potential side effects can occur when very high doses are taken for extended periods. In addition, in the last two years unexpected high liver toxicity has been reported in two patients. Until now no studies support the liver toxicity of kavalactones and it is unknown which compound could have provoked the liver disease. On the other hand, it should be possible that unknown or unexpected constituents are the responsible or contributed to the liver toxicity.
(https://doi.org/10.1016/s0024-3205(02)01555-2)

Ernst E. A re-evaluation of kava (Piper methysticum). Br J Clin Pharmacol. 2007 Oct;64(4):415-7. doi: 10.1111/j.1365-2125.2007.02932.x. Epub 2007 Jun 6. PMID: 17555466; PMCID: PMC2048557.

Description:
About 70 case reports had suggested hepatotoxicity. This article summarizes the research since the ban. Several theories have emerged to explain possible mechanisms of toxicity. Yet uncertainty as to whether or not kava is hepatotoxic prevails. Some experts therefore believe that the prohibition was not justified. The evidence, however, continues to implicate kava, and the ban was recently upheld by the UK licensing authority
(https://doi.org/10.1111/j.1365-2125.2007.02932.x)

Dong, R., Yang, X., Wang, C., Liu, K., Liu, Z., Ma, X., Sun, H., Huo, X., Fu, T., & Meng, Q. (2019). Yangonin protects against non-alcoholic fatty liver disease through farnesoid X receptor. Phytomedicine, 53, 134–142.

Abstract:
Backgroud: Non-alcoholic fatty liver disease (NAFLD) is currently evolving as the most common liver disease worldwide. Dyslipidemia, pathoglycemia and insulin resistance are the major risk factors for the development of NAFLD. To date, no effective drug therapies for this condition have been approved.

Purpose: The present study was to investigate the protective effects of yangonin, a kavalactone isolated from Kava, against NAFLD and further elucidate the mechanisms in vivo and in vitro.

Study design:A high-fat diet (HFD) induced mouse NAFLD model was used with or without yangonin treatment.

Methods: The body weight, relative liver weight and serum biochemical indicators were measured. H&E and Oil Red O staining were used to identify the amelioration of the liver histopathological changes. Serum and hepatic triglyceride, free fatty acids and total cholesterol were analyzed. siRNA, quantitative real-time PCR and Western blot assay were used to clarify the mechanisms underlying yangonin protection.

Results: Yangonin had obvious protective effects against NAFLD via farnesoid X receptor (FXR) activation. Through FXR activation, yangonin attenuated lipid accumulation in the liver via inhibition of hepatic lipogenesis-related protein including sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthetase (FAS), acetyl-CoA carboxylase 1 (ACC1) and stearoyl-CoA desaturase 1 (SCD1). Besides, yangonin promoted lipid metabolism through an induction in genes required for lipoprotein lipolysis and fatty acid β-oxidation. Furthermore, yangonin modulated blood glucose homeostasis through regulation of gluconeogenesis-related gene phosphoenol pyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), and glycogen synthesis-related gene glycogen synthase kinase 3β (GSK3β) and pyruvate dehydrogenase (PDase). Also, yangonin increased insulin sensitivity through upregulating phosphorylation of insulin responsive substrate 1, 2 (IRS-1 and IRS-2). Then, in vivo and in vitro evidence further demonstrated the involvement of FXR activation in yangonin hepatoprotection.

Conclusions: Yangonin protects against NAFLD due to its activation of FXR signaling to inhibit hepatic lipogenesis and gluconeogenesis, and to promote lipid metabolism and glycogen synthesis, as well as insulin sensitivity.
https://doi.org/10.1016/j.phymed.2018.09.006

Open Access Article
Teschke, R. (2010). Kava hepatotoxicity: Pathogenetic aspects and prospective considerations. Liver International, 30(9), 1270–1279.

Abstract:
Kava hepatotoxicity is a well-defined herb-induced liver injury, caused by the use of commercial anxyolytic ethanolic and acetonic kava extracts, and of traditional recreational aqueous kava extracts. The aim of this review is to elucidate possible pathogenetic factors for the development of kava-induced liver injury, considering also confounding variables. In patients with liver disease in a causal relation to kava ± comedication, confounding factors include non-adherence to therapy recommendations and comedication consisting of synthetic and herbal drugs and dietary supplements including herbal ones and herbs-kava mixtures. Various possible pathogenetic factors have to be discussed and comprise metabolic interactions with exogenous compounds at the hepatic microsomal cytochrome P450 level; genetic enzyme deficiencies; toxic constituents and metabolites derived from the kava extract including impurities and adulterations; cyclooxygenase inhibition; P-glycoprotein alterations; hepatic glutathione depletion; solvents and solubilizers of the extracts; and kava raw material of poor quality. In particular, inappropriate kava plant parts and unsuitable kava cultivars may have been used sometimes for manufacturing the kava extracts instead of the rhizome of a noble cultivar of the kava plant (Piper methysticum G. Forster). In conclusion, kava hepatotoxicity occurred independently of the extraction medium used for the kava extracts and may primarily be attributed to daily overdose, prolonged treatment and to a few kava extract batches of poor quality; by improving kava quality and adherence to therapy recommendation under avoidance of comedication, liver injury by kava should be a preventable disease, at least to a major extent. © 2010 John Wiley & Sons A/S.
(https://doi.org/10.1111/j.1478-3231.2010.02308.x)

Adverse Events

White CM. The Pharmacology, Pharmacokinetics, Efficacy, and Adverse Events Associated With Kava. J Clin Pharmacol. 2018 Nov;58(11):1396-1405. doi: 10.1002/jcph.1263. Epub 2018 May 23. PMID: 29791008.

Abstract:
Kava is a plant with numerous kavapyrones that can induce pharmacologic effects and drug interactions through the cytochrome P450 and P‐glycoprotein systems. Kava is used recreationally and for the treatment of anxiety. Clinical trials verify anxiolytic effects in excess of placebo, but the effects are not seen immediately and the optimal dose and dosing schedule needs to be determined. Clinical trials usually lasting for 4 weeks found generally good tolerability and safety; however, dermatologic, hepatologic, and cognitive adverse effects may occur. Some of these adverse effects are known to occur from the kavapyrones themselves, while others can be caused or exacerbated by use of substandard kava products. There is tremendous variability in the constitution of a kava product based on the parts of the plant that are being extracted and the extraction method. The most commonly studied extract for the treatment of anxiety is the acetone extract.
(https://doi.org/10.1002/jcph.1263)

Rychetnik L, Madronio CM. The health and social effects of drinking water-based infusions of kava: a review of the evidence. Drug Alcohol Rev. 2011 Jan;30(1):74-83. doi: 10.1111/j.1465-3362.2010.00184.x. PMID: 21219501.

Abstract:
Issues. To review the evidence on the health and social effects of drinking kava; a water‐based infusion of the roots of the kava plant.

Approach. Included all empirical studies of the effects of kava published 1987–2008 reporting health and social outcomes. Evidence appraised on study design (level of evidence) and standard epidemiological criteria for causality.

Key Findings. Causality indicated: scaly skin rash, weight loss, raised Gamma Glutamyl Transpeptidase liver enzyme levels, nausea, loss of appetite or indigestion; Association indicated but causality unclear: red sore eyes, impotence or loss of sexual drive, self‐reported poor health, raised cholesterol, and loss of time and money, low motivation and ‘slow/lazy’ days following use, reduced alcohol consumption and related violence; Association hypothesised: fits or seizures, Melioidosis, Ischaemic Heart Disease, protective effects for cancer; No association indicated: cognitive performance; No association suggested: cognitive impairment, liver toxicity or permanent liver damage, other pneumonia; No association hypothesised: hallucinations.

Implications. The health and social implications of chronic kava drinking can be significant for individuals and communities, although most effects of even heavy consumption appear to be reversible when consumption is stopped.

Conclusion. An Australia‐wide ban on commercial importation of kava has been in place since mid‐2007, but there is no published literature to date on the impact of the ban.
(https://doi.org/10.1111/j.1465-3362.2010.00184.x)

Aporosa, S. & Tomlinson, M. Kava hangover and gold-standard science. Anthropologica 56, 163-175 (2014).

Abstract:
Kava, a beverage drunk in much of the South Pacific, is both celebrated and controversial. It is often considered an emblem of traditional indigenous practice but also criticized for its physical effects on heavy drinkers. This article reports the results of a study wherein tests were administered to schoolteachers in Fiji to measure effects of the previous night's drinking. The tests revealed that kava intoxication seems to affect processing speed but not working memory. The authors caution that the results must be balanced by acknowledgement of kava's role in bringing communities together in support of institutions such as schools.
(https://www.jstor.org/stable/24469648)

Berry, J., Gilbert, A. & Grodnitzky, J. Cases of Kava Impairment in Iowa Drivers. Journal of Forensic Sciences 64, 1943-1949 (2019).

Abstract:
Kava is an Oceanic plant in which the root is consumed as a beverage and is becoming increasingly popular. The effects of kava consumption may include sedation, euphoria, and impairment of motor coordination. This article demonstrates kava impairment through four cases of self‐reported kava use supported with Drug Recognition Expert (DRE) evaluations of each subject. Subject's urines screened negative for common drugs of abuse by immunoassay analysis. Urine from cases 3 and 4 were analyzed by liquid chromatography–tandem mass spectrometry, and gas chromatography–mass spectrometry, which yielded the presence of kavalactones. Subjects exhibited poor driving behavior and signs of intoxication. Indicators of impairment from multiple drug categories, central nervous system (CNS) depressants, CNS stimulants, and cannabis were observed, which may be consistent with the presence of multiple kavalactones and their diverse array of mechanisms of action. The consumption of kava can hinder one's ability to operate a vehicle safely.
(https://doi.org/10.1111/1556-4029.14130)

Ketola, R. A., Viinamaki, J., Rasanen, I., Pelander, A. & Goebeler, S. Fatal kavalactone intoxication by suicidal intravenous injection. Forensic Science International 249, e7-e11 (2015).

Abstract:
Kavalactones are a group of compounds found in kava, a beverage or extract prepared from the rhizome of the kava plant (Piper methysticum). Traditionally kava extracts have been used for their anxiolytic and sedative properties. Sales of kava extracts were severely restricted or prohibited in European countries in 2002 following several cases of serious hepatotoxicity. Here we report a case where high concentrations of kavalactones and ethanol were detected in post mortem femoral blood. An injection needle with a 10-mL syringe containing 7.5 mL of slightly yellowish liquid was found next to the victim, and there were numerous needle prints on both lower arms following the venous tracks. No evidence of other cause of death was found in the medico-legal investigation. The case was therefore classified as suicide using an injection of kavalactones intravenously together with alcohol poisoning.
(https://doi.org/10.1016/j.forsciint.2015.01.032)

Huynh, J. C., Asgari, M. M. & Moore, M. M. Sebotropic eruption associated with use of oral kava kava supplement. Clinical and Experimental Dermatology 39, 816-818 (2014).

Summary:
Supplement use is prevalent, and its use is increasing among older adults. Dermatologists need to be aware of the adverse cutaneous effects that can result from herbal supplement use. A 55‐year‐old man presented with an eruption in a sebotropic distribution after consuming kava kava for 3 weeks, which resolved after discontinuation of the supplement. This case highlights the need for clinicians to consider kava kava in the differential of sebotropic eruptions. The biology, mechanism of action, and potential systemic and cutaneous effects of kava kava are reviewed.
(https://doi.org/10.1111/ced.12439)

Yang, X. & Salminen, W. F. Kava extract, an herbal alternative for anxiety relief, potentiates acetaminophen-induced cytotoxicity in rat hepatic cells. Phytomedicine 18, 592-600 (2011).

Abstract:
The widely used over-the-counter analgesic acetaminophen (APAP) is the leading cause of acute liver failure in the United States and due to this high incidence, a recent FDA Advisory Board recommended lowering the maximum dose of APAP. Kava herbal dietary supplements have been implicated in several human liver failure cases leading to the ban of kava-containing products in several Western countries. In the US, the FDA has issued warnings about the potential adverse effects of kava, but kava dietary supplements are still available to consumers. In this study, we tested the potential of kava extract to potentiate APAP-induced hepatocyte cytotoxicity. In rat primary hepatocytes, co-treatment with kava and APAP caused 100% loss of cell viability, while the treatment of kava or APAP alone caused ∼50% and ∼30% loss of cell viability, respectively. APAP-induced glutathione (GSH) depletion was also potentiated by kava. Co-exposure to kava decreased cellular ATP concentrations, increased the formation of reactive oxygen species, and caused mitochondrial damage as indicated by a decrease in mitochondrial membrane potential. In addition, similar findings were obtained from a cultured rat liver cell line, clone-9. These observations indicate that kava potentiates APAP-induced cytotoxicity by increasing the magnitude of GSH depletion, resulting in oxidative stress and mitochondrial dysfunction, ultimately leading to cell death. These results highlight the potential for drug–dietary supplement interactions even with widely used over-the-counter drugs.
(https://doi.org/10.1016/j.phymed.2011.02.006)

Cairney, S., Maruff, P., Clough, A. R., Collie, A., Currie, J. & Currie, B. J. Saccade and cognitive impairment associated with kava intoxication. Human Psychopharmacology 18, 525-533 (2003).

Abstract:
Kava is an extract from the Piper methysticum Forst. f. plant that has social and spiritual importance in Pacific islands societies. Herbal remedies that contain kava are used for the psychiatric treatment of anxiety and insomnia. Laboratory studies have found only subtle, if any, changes on cognitive or motor functions from the acute effects of consuming small clinical doses of kava products. Intoxication from recreational doses of kava has not been studied. The performance of individuals intoxicated from drinking kava (n=11) was compared with a control group (n=17) using saccade and cognitive tests. On average, intoxicated individuals had consumed 205 g of kava powder each (approximately 150 times clinical doses) in a group session that went for 14.4 h and ended 8 h prior to testing. Intoxicated kava drinkers showed ataxia, tremors, sedation, blepharospasm and elevated liver enzymes (GGT and ALP), together with saccadic dysmetria, saccadic slowing and reduced accuracy performing a visual search task that only became evident as the task complexity increased. Kava intoxication is characterized by specific abnormalities of movement coordination and visual attention but normal performance of complex cognitive functions. Saccade abnormalities suggest disruption of cerebellar and GABAergic functions.
(https://doi.org/10.1002/hup.532)

Garner, L. F. & Klinger, J. D. SOME VISUAL EFFECTS CAUSED BY THE BEVERAGE KAVA. Journal of Ethnopharmacology 13, 307-311 (1985).

Abstract:
Kava is a drink produced from the plant Piper methysticum and used as a social and ceremonial beverage on many South Pacific islands. Visual functions were measured in one subject following the taking of this drink. A reduced near point of accommodation and convergence, an increase in pupil diameter and disturbance to the oculomotor balance were noted. No changes were recorded in visual or stereoacuity or in ocular refractive error.
(https://doi.org/10.1016/0378-8741(85)90076-5)

Barguil, Y., Choblet, E., Warter, S. & Nour, M. Kava ichthyosis: A nitric oxide synthase inhibition?. Annales de Toxicologie Analytique 25, 165-168 (2013).

Abstract:
Purpose: Kava is a traditional Pacific beverage made from the root of Piper methysticum. It is mainly used for its sedative properties due to lipophilic lactones called kavalactones. Various preparations or medications made from this plant can be purchased via the internet. Kava action mechanisms include cell membrane stabilisation, inhibition of intracellular Ca2+ increase and enzyme inactivation. Chronic or heavy kava consumption results in the skin taking on a scaly aspect. Biologically, an isolated increase in serum gamma-glutamyltransferase is apparent. Cases of sudden death after heavy kava sessions have occurred in Australia, and nine cases in New Caledonia were reported by our forensic laboratory during the 2000−mid-2013 period. No clear explanation has been given. We describe the possible action mechanism.
Methods: We monitored 116 heavy kava drinkers. A multiple-probe drug cocktail was used on six other volunteers, all heavy and chronic kava drinkers, before and after kava abstinence to carry out CYP450 phenotyping.
Results: The heavy chronic drinkers showed an isolated increase in GGT without any biological or clinical abnormality other than scaly skin. With the multiple-probe drug cocktail an inhibition of the CYP1A2 isoenzyme was demonstrated. In kava dermopathy a lack of epithelial nitric oxide production leading to an increased S-nitroso-glutathione degradation by the epithelial gamma-glutamyltransferase should be considered.
Conclusions: As there are close structural and functional similarities between nitric oxide synthase (NOS) and CYP1A2, and as we have formerly demonstrated that kava inhibits CYP1A2, an inhibition of NOS in chronic kava drinkers must be studied to see if ichthyosis can be explained, and if high blood GGT level is a reflection of epithelial cell GGT activity. Furthermore, a decrease in NO bioavailability can cause myocardial and vascular dysfunctions and hypercoagulability, leading to acute coronary syndrome or ischemic stroke. This mechanism should be explored in cases of “post-kava session sudden death”.
(https://doi.org/10.1051/ata/2014001)

Open Access Article
Hannam, S., Murray, M., Pharm, B., Romani, L., Tuicakau, M., Whitfeld, M. J. & {Sarah Hannam}, C. Kava dermopathy in Fiji: an acquired ichthyosis?. Tropical Medicine Rounds , (2014).

Abstract:
Kava dermopathy is a common cutaneous effect of regular or heavy use of Kava, a psychoactive beverage consumed widely throughout the Pacific. In Fiji in 2012, over 1000 study participants underwent full skin examination, and kava dermopathy was a common cutaneous finding. The clinical manifestations of kava dermopathy share similarities with the spectrum of autosomal recessive congenital ichthyoses, predominantly lamellar ichthyosis. The pathogenesis of Kava dermopathy may be associated with a functional defect in one or more cytochrome P450 enzymes implicated in epidermal integrity, thus mimicking the genetic defect as seen in lamellar ichthyosis type 3.
(https://doi.org/10.1111/ijd.12546)

Clough, A. R., Cairney, S., Maruff, P., Burns, C. B., & Currie, B. J. (2001). Possible toxicity and withdrawal seizures in Aboriginal kava drinkers in Arnhem Land, (Australia). South Pacific Journal of Psychology, 13, 26–33.

Abstract:
Background: In the 1990s, heavy kava use in Aboriginal communities was linked to reports of unusual neurological events which were often described as ‘fits’ or ‘seizures’. Kava use has also been associated with extra-pyramidal movements. We now raise the possibility that kava toxicity and kava withdrawal may be associated with grand mal seizures. This paper describes some of ’these “seizure” episodes’ in kava drinkers. Nine communities and associated homelands in the eastern Arnhem Land (Miwatj) region (Northern Territory, NT) including 7001 Aboriginal people of whom 4217 were over 15 years. Twenty-one kava users experienced 32 “seizure” episodes for which the date of occurrence and other data was recorded in notes in community health clinic files dating from the 1980s up to 1999 in a sample of the Miwatj population. Kava, alcohol, tobacco, cannabis use and petrol sniffing, year in which “seizure” occurred, notes of kava toxicity or withdrawal. Kava toxicity effects were suspected in 15 and withdrawal effects in six of 32 “seizure” episodes. In seven episodes impaired consciousness and abnormal movements were adequately documented to suggest grand mal seizures. The maximum number of “seizures” experienced was three and three individuals experienced this number between 1990 and 1999. One was a heavy kava user. Six other individuals experienced two “seizures” each and five of these were heavy users. Sixteen individuals experienced 19 “seizures” during 1994-1997 when kava supply may have reached its peak. Fifteen of the 21 individuals experiencing “seizures” were heavy users described locally as dja[aw'marama. The clinical data and the coincidence of peak supply with records of “seizures” suggest kava toxicity and withdrawal seizures may both occur with heavy kava use. Further systematic analysis is warranted to confirm this and to assess kava's effects with respect to possible confounders such as alcohol.
(https://doi.org/10.1017/s025754340000033x)

Health Effects

Sarris J. Herbal medicines in the treatment of psychiatric disorders: 10-year updated review. Phytother Res. 2018 Jul;32(7):1147-1162. doi: 10.1002/ptr.6055. Epub 2018 Mar 25. PMID: 29575228.

Abstract:
This paper provides a 10‐year update of the 2007 systematic review of herbal medicines studied in a broad range of psychiatric disorders, including depression, anxiety, obsessive–compulsive, seasonal affective, bipolar, psychotic, phobic, somatoform, and attention‐deficit hyperactivity disorders. Ovid Medline, PubMed, and the Cochrane Library were searched for herbal medicines with both pharmacological and clinical evidence of psychotropic activity. This updated review now covers clinical trial evidence for 24 herbal medicines in 11 psychiatric disorders. High‐quality evidence was found to exist for the use of Piper methysticum (Kava), Passiflora spp. (passionflower) and Galphimia glauca (galphimia) for anxiety disorders; and Hypericum perforatum (St John's wort) and Crocus sativus (saffron) for major depressive disorder. Other encouraging herbal medicines with preliminary evidence include Curcuma longa (turmeric) in depression, Withania somnifera (ashwagandha) in affective disorders, and Ginkgo biloba (ginkgo) as an adjunctive treatment in Schizophrenia. Although depression and anxiety are commonly researched, many other mental disorders still require further prospective investigation. Although the previous review suggested increasing the adjunctive study of select herbal medicines with pharmaceuticals, this was still only found to sparingly occur in research designs. Aside from this, future focus should involve the incorporation of more biomarker analysis, in particular pharmacogenomics, to determine genetic factors moderating response to herbal medicines.
(https://doi.org/10.1002/ptr.6055)

Clough AR, Jacups SP, Wang Z, Burns CB, Bailie RS, Cairney SJ, Collie A, Guyula T, McDonald SP, Currie BJ. Health effects of kava use in an eastern Arnhem Land Aboriginal community. Intern Med J. 2003 Aug;33(8):336-40. doi: 10.1046/j.1444-0903.2003.00405.x. PMID: 12895162.

Abstract:
Background:  Heavy kava use in Aboriginal communities has been linked to various health effects, including anecdotes of sudden cardiac deaths.

Aims:  To examine associations between kava use and potential health effects.

Methods:  A cross‐sectional study was carried out within a kava‐using east Arnhem Land Aboriginal community in tropical northern Australia. One‐hundred‐and‐one adults who were current, recent or non‐users of kava were enrolled in March 2000. Main outcome measures were physical, anthropometric, biochemical, haematological, immunological and neurocognitive assessments.

Results:  Kava users more frequently showed a characteristic dermopathy (P < 0.001). They had increased levels of γ‐glutamyl transferase and alkaline phosphatase (P < 0.001). Lymphocyte counts were significantly lower in kava users (P < 0.001). Fibrinogen, plasminogen activator inhibitor‐1 and neurocognitive tests were not different between kava use categories. IgE and IgG antibodies were elevated across the whole group, as were C‐reactive protein and homocysteine.

Conclusions:  Kava use was associated with dermopathy, liver function abnormalities and decreased lymphocytes. If kava continues to be used by Aboriginal populations, monitoring should focus on the health consequences of these findings, including a possible increase in serious infections. The interaction between kava, alcohol and other substances requires further study. Although markers of cardiovascular risk are increased across the population, these were not higher in kava users, and this increase may be linked to the large infectious pathogen burden reflective of the socioeconomic disadvantage seen in many remote Aboriginal communities.
(https://doi.org/10.1046/j.1444-0903.2003.00405.x)

Open Access Document
Food Standards Australia New Zealand. (2004). KAVA A Human Health Risk Assessment.

Summary:
Kava is an intoxicating non-alcoholic water-based beverage prepared from the root of the plant Piper methysticum. Kava has a long history of use as a beverage in social ceremonies, particularly by South Pacific communities. Kava was also introduced into Australian Aboriginal communities, predominantly in Arnhem Land in the 1980s as an alternative to alcohol. The kava plant (Piper methysticum) is a member of the pepper family. The term ‘kava’ is primarily used to refer to the kava plant and the drink prepared from the fresh or dried roots of that plant. The term ‘kava’, however, is also used to refer to other preparations such as powdered kava made up as the traditional drink and for use in medicinal products, and acetone or ethanol extracts of the plant for use in medicinal products.
(http://www.foodstandards.gov.au)
(https://www.foodstandards.gov.au/publications/documents/30_Kava1.pdf)

De Leo, V., La Marca, A., Morgante, G., Lanzetta, D., Florio, P., & Petraglia, F. (2001). Evaluation of combining kava extract with hormone replacement therapy in the treatment of postmenopausal anxiety. In Maturitas (Vol. 39).

Abstract:
Objective: to evaluate the efficacy of combining kava extract with hormone replacement therapy in the treatment of menopausal anxiety.
Materials and methods: HAMA score was evaluated before and after therapy in four groups of women in menopause (duration of menopause ranged from 1 to 12 years). The groups were treated with hormone replacement therapy (with and without progestogens) and kava extract or placebo for 6 months.
Results: A significant reduction in HAMA score was observed in all four groups of women. The reduction was more significant in groups taking kava extract than in groups on hormones only.
Discussion: The combined use of hormone replacement therapy and kava extract seems to be effective against menopausal anxiety. Kava extract accelerates resolution of psychological symptoms while hormone therapy safeguards against osteoporosis and cardiovascular disease.
(https://doi.org/10.1016/s0378-5122(01)00197-9)

Schmidt, N., & Ferger, B. (2001). Neuroprotective Effects of ()-Kavain in the MPTP Mouse Model of Parkinson’s Disease.

Abstract:
This is the first study to investigate the potential protective effects of the lipophilic kavapyrone (±)‐kavain in the experimental MPTP (1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine) model of Parkinson's disease (PD). Male C57BL/6 mice were treated with (±)‐kavain (50, 100, or 200 mg/kg i.p.) or vehicle 60 min before and 60 min after a single administration of MPTP (30 mg/kg s.c.) or saline, respectively. Mice were sacrificed after 7 days and the neostriatum was analyzed for dopamine and its metabolites using HPLC with electrochemical detection. Furthermore, nigral sections were processed for tyrosine hydroxylase (TH) immunocytochemistry. To determine the effects of (±)‐kavain (200 mg/kg) on MPTP metabolism, HPLC analysis of striatal MPP+ (1‐methyl‐4‐phenylpyridinium) levels was performed. MPTP treatment alone led to a significant depletion of striatal dopamine levels to 12.61% of saline controls. The lower dosages of (±)‐kavain (50 and 100 mg/kg) showed only a nonsignificant attenuation of MPTP‐induced dopamine depletion, but a high dosage of (±)‐kavain (200 mg/kg) significantly antagonized the dopamine depletion to 58.93% of saline control values. Remarkably, the MPTP‐induced decrease of TH‐immunoreactivity as well as the loss of nigral neurons was completely prevented by (±)‐kavain (200 mg/kg). Striatal MPP+ levels were not altered by (±)‐kavain treatment. In conclusion, we found that MPTP metabolism was not influenced by (±)‐kavain and postulate the antiglutamatergic effects of (±)‐kavain for its protective effects against MPTP toxicity. (±)‐Kavain may be a novel candidate for further preclinical studies in animal models of PD and other disorders with glutamatergic overactivity.
(https://doi.org/10.1002/1098-2396(200104)40:1<47::AID-SYN1025>3.0.CO;2-S)

Tanaka, A., Hamada, N., Fujita, Y., Itoh, T., Nozawa, Y., Iinuma, M. & Ito, M. A novel kavalactone derivative protects against H2O2-induced PC12 cell death via Nrf2/ARE activation. Bioorganic and Medicinal Chemistry 18, 3133-3139 (2010).

Abstract:
Oxidative stress is involved in the pathogenesis of neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases. Natural kavalactones isolated from Piper methysticum (Piperaceae) are capable of activating the Nrf2/ARE (antioxidant response element) pathway and thus enhancing the expression of phase II antioxidant enzymes such as heme oxygenase-1 (HO-1). In an attempt to identify kavalactone derivatives that are more potent in Nrf2/ARE activation than natural compounds, we synthesized a series of chemically-modified kavalactones and studied their effects on the ARE enhancer activity in rat pheochromocytoma PC12 cells. Among 81 compounds tested, a kavalactone derivative, 2′,6′-dichloro-5-methoxymethyl-5,6-dehydrokawain [(E)-6-(2′,6′-dichlorostyryl)-4-methoxy-5-(methoxymethyl)-2H-pyran-2-one] (1), exhibited the strongest ARE enhancer activity. The ARE activation and HO-1 protein induction by the compound 1 were higher than those by natural kavalactones. The compound did not affect cell viability and induced expression of various phase II enzymes. Nuclear translocation of Nrf2 after treatment with 1 was preceded by phosphorylation of ERK1/2 and p38. The compound transiently increased intracellular ROS levels. Finally, pretreatment with the compound ameliorated H2O2-induced cell death, which was associated with increased expression of HO-1. These results suggest that the compound 1 protects against oxidative stress-induced neuronal cell death via a preconditioning effect on the Nrf2/ARE activation.
(https://doi.org/10.1016/j.bmc.2010.03.034)

Boerner, J. R. & Klement, S. Attenuation of neuroleptic-induced extrapyramidal side effects. Wiener medizinische Wochenschrift 154, 508-510 (2004).

Abstract:
We studied at 42 patients (17 female, 25 male) with different psychiatric diagnoses, who were pretreated by neuroleptics, the efficacy and tolerability of the Kava special extract WS 1490 on extrapyramidal side effects. In both patient and physician questionnaires as well as in the physician's global ratings, significant improvements were found for all extrapyramidal signs and symptoms recorded. The concomitant intake of WS 1490 was well tolerated by the patients. The findings of this observational study suggest that extrapyramidal side effects of neuroleptic drugs may be attenuated by Kava special extract WS 1490.
(https://pubmed.ncbi.nlm.nih.gov/15638068/)

Cairney, S., Maruff, P. & Clough, A. R. The neurobehavioural effects of kava. , (2002).

Abstract:
Objective: This review considers the context in which kava is used, together with its underlying psychopharmacological mechanisms, to investigate the neurobehavioural effects associated with kava use.

Method: We conducted a systematic search using the computerized databases MEDLINE, OVID and PsychLIT for all articles containing any of the following words: kava, kavain, kawa and Piper methysticum. In the opinion of the authors, all articles from this collection containing data that could inform the neurological and cognitive sequelae of kava use were included for the purpose of this review.

Results: The use of kava occurs among indigenous populations in the South Pacific and in northern Australia, while also being used throughout the western world as a herbal medicine. Animal studies show that kava lactones alter neuronal excitation through direct interactions with voltage-dependent ion channels, giving rise to kava's muscle relaxant, anaesthetic, anxiolytic and anticonvulsive properties. Several isolated cases of psychotic and severe dystonic reactions following kava use suggest that kava also has psychoactive properties, yet there is no conclusive evidence that kava interferes with normal cognitive processes.

Conclusions: Kava is effective in the treatment of tension and anxiety. There may be risk-factors for severe motor and psychiatric responses to kava use, although these are not well-understood. Given the increasingly widespread use of kava, further investigation is necessary to gain an understanding of its immediate neuropsychiatric effects and long-term cognitive effects.
(https://pubmed.ncbi.nlm.nih.gov/12225450)

Martin, H., McCallum, M., Stofer, D. W. & Eichinger, M. R. Kavain attenuates vascular contractility through inhibition of calcium channels. Planta Med 68, 784-789 (2002).

Abstract:
Kavain is a biologically active compound from the Oceanic plant Piper methysticum (kava). Traditional medicinal uses of the kava root are many. Kava is increasingly being utilized by Western societies for its anxiolytic effects. Recent reports indicate that kavain blocks ion channels in neural tissue, relaxes precontracted ileum, and relaxes precontracted airway. Thus, we investigated the potential ability of this plant-derived compound to alter vascular smooth muscle function. Thoracic aortae were isolated from Sprague-Dawley rat and cut into 4 mm rings. Rings were placed in tissue baths and suspended from force-displacement transducers for the measurement of isometric tension. In a dose-dependent manner, kavain (10(-6) M to 10(-3) M) was found to relax aortic rings precontracted with phenylephrine (PE). This response was not dependent on functional endothelium. In addition, kavain pretreatment (3 x 10(-5) M or 3 x 10(-4) M) attenuated vascular smooth muscle contraction evoked by PE. However, kavain failed to attenuate PE-mediated contraction in calcium (Ca(++))-free buffer, indicating that intracellular signaling processes were likely not affected. Also, kavain did attenuate the contraction elicited by administration of Ca(++) to depolarized tissue. Interestingly, in rings pre-treated with the selective L-type Ca(++) channel blocker nifedipine, kavain-mediated relaxation was inhibited. Lastly, in rings selectively contracted with an L-type calcium channel activator, kavain elicited dose-dependent (and ultimately complete) relaxation. These data strongly suggest that kavain impairs vascular smooth muscle contraction, likely through inhibition of Ca(++) channels.
(https://pubmed.ncbi.nlm.nih.gov/12357387/)

Klohs, W., Keller, F., Williar, R. E., Toekes, M. I. & Cronheim, G. E. A Chemical and Pharmacological Investigation of Piper Methysticum Forst. J. Med. Chem. 1, 95-103 (1959).
(https://pubs.acs.org/doi/abs/10.1021/jm50002a007/)

Norton, S. A., Kava dermopathy. Journal of the American Academy of Dermatology 31, 89-97 (1994).

Abstract:
Kava is a psychoactive beverage used ceremonially for thousands of years by Pacific Islanders. Kava is made from the root of the pepper plant, Piper methysticum, found in Polynesia, Melanesia, and Micronesia. The beverage is a nonfermented depressant with complex neuropharmacologic properties that causes a tranquil state of intoxication. Kava also affects the skin, causing a peculiar scaly eruption. The cutaneous effects were first reported by members of Captain James Cook's Pacific expeditions, but they have never been described in dermatologic literature. Heavy kava drinkers acquire a reversible ichthyosiform eruption, kava dermopathy. The cause is unknown but may relate to interference with cholesterol metabolism. Today kava is used across the Pacific in both traditional ceremonies and informal social events. In Western nations, kava is sold as a relaxant by health food stores. This article explores the history of kava dermopathy from Cook's early reports to its presence today.
(https://pubmed.ncbi.nlm.nih.gov/8021378/)

'Apo', A. S., Is Kava Alcohol?: The Myths and the Facts. Pacific Health Dialog 17, 157-164 (2011).

Abstract:
This paper addresses the misconception that kava is an alcoholic substance. After a brief introduction as to what prompted the writing of this, I follow by discussing kava's cultural importance to Pacific peoples, and then compare kava 'intoxication' with alcohol intoxication. The paper concludes with a discussion of the historical influences that have promoted some of the misconceptions surrounding kava. Ultimately the paper demonstrates that kava and alcohol are entirely different kinds of beverages with different effects, and that lingering misconceptions can be seen as a 'colonial hangover'.
(https://pubmed.ncbi.nlm.nih.gov/23008981/)

Open Access Article
McDonald, D. & Jowitt, A. Kava in the Pacific Islands: A contemporary drug of abuse?. Drug and Alcohol Review 19, 217-227 (2000).

Summary:
Kava is both the common name of a plant (Piper methysticum , —the intoxicating pepper˜) and of a beverage derived from the stumps and roots of the plant. Kava has immense traditional significance to many of the peoples of the Pacific Islands. Melanesia is widely considered to be the home of kava and strongholds of kava drinking include Vanuatu and Fiji. All major Polynesian groups, except for the New Zealand Maori who lived in too cold a climate to grow the plant successfully, ritually consume kava. Two Micronesian Islands, Pohnpei and Kosrae, also include kava drinking in their custom [1]. This traditional use of kava is ritualized, and employed for purposes such as strengthening kinship ties and communicating with spirits.

(http://repository.usp.ac.fj/8048/1/Kava_in_the_Pacific_Islands__A_Contemporary_Drug_of_Abuse.pdf)

Whitton, P. A., Lau, A., Salisbury, A., Whitehouse, J. & Evans, C. S. Kava lactones and the kava-kava controversy. Phytochemistry 64, 673-679 (2003).

Abstract:
Kava-kava is a traditional beverage of the South Pacific islanders and has had centuries of use without major side effects. Standardised extracts of kava-kava produced in Europe have led to many serious health problems and even to death. The extraction process (aqueous vs. acetone in the two types of preparations) is responsible for the difference in toxicity as extraction of glutathione in addition to the kava lactones is important to provide protection against hepatotoxicity. The Michael reaction between glutathione and kava lactones, resulting in opening of the lactone ring, reduces the side effects of the kava kava extracts. This protective activity was demonstrated using Acanthamoebae castellanii in which 100% cell death occurred with 100 mg ml(-1) kava lactones alone, and 40% cell death with a mixture of 100 mg ml (-1)glutathione and 100 mg ml (-1) kava lactones. A comparison of kava lactone toxicity with other pharmaceutical products is discussed and recommendations made for safe usage of kava-kava products
(https://pubmed.ncbi.nlm.nih.gov/13679089/)

Côté, C. S., Kor, C., Cohen, J., & Auclair, K. (2004). Composition and biological activity of traditional and commercial kava extracts. Biochemical and Biophysical Research Communications, 322(1), 147–152.

Abstract:
For centuries the South Pacific islanders have consumed kava (Piper methysticum) as a ceremonial intoxicating beverage. More recently, caplets of kava extracts have been commercialized for their anxiolytic and antidepressant activities. Several cases of hepatotoxicity have been reported following consumption of the commercial preparation whereas no serious health effects had been documented for the traditional beverage. A detailed comparison of commercial kava extracts (prepared in acetone, ethanol or methanol) and traditional kava (aqueous) reveals significant differences in the ratio of the major kavalactones. To show that these variations could lead to differences in biological activity, the extracts were compared for their inhibition of the major drug metabolizing P450 enzymes. In all cases (CYP3A4, CYP1A2, CYP2C9, and CYP2C19), the inhibition was more pronounced for the commercial preparation. Our results suggest that the variations in health effects reported for the kava extracts may result from the different preparation protocols used.
(https://doi.org/10.1016/j.bbrc.2004.07.093)

Clough, A., Enough! or too much. What is 'excessive' kava use in Arnhem Land?. Drug and Alcohol Review 22, 43-51 (2003).

Abstract:
The objective of the study was to describe parameters for use in monitoring health, social and economic effects of kava use in Arnhem Land Aboriginal communities in the Northern Territory (NT). Kava has been used mainly in eight communities (population > 200), and in smaller associated homeland areas since 1982 with a total population of approximately 6800, using cross‐sectional description and comparison using data from three kava‐using communities. Interview data combined with health worker assessments were compiled using: (1) a sample (n = 136) aged 16–34 years in one community in 2001–02; (2) a sample (n = 101) aged 16 years and over in 2000 where physical assessments and biochemical and haematological data were also collected; (3) participant‐observation in one community (133 people aged 18 years and over) during 1989–91. Kava, supplied illegally, was still being used in Arnhem Land in 2001–02. In 2000 dermopathy characteristic of heavy use, abnormally low body mass index (BMI), low blood lymphocytes and abnormally high γ‐glutamyl transferase (GGT) occurred more frequently with increased kava use. These acute effects emerge at average consumption levels of from 310–440 g/week of kava powder. When kava users in one community began to consume it at an average of 240–425 g/week from mid‐1990, 19% of available cash resources were spent on kava with 11% of cash resources leaving the local community economy. The proportion of men drinking kava reached 70% and women 62% from mid‐1990, with 20% of the population spending unprecedented amounts of time (14 + hours/week) in activities where kava was consumed. These parameters may be useful to monitor kava's adverse health, social and economic effects. Their association with increased kava use suggests that approaches to minimizing harm from its abuse may begin fruitfully with controlling supply.
(https://doi.org/10.1080/0959523021000059820)

Groth-Marnat, G., Leslie, S. & Renneker, M. TOBACCO CONTROL IN A TRADITIONAL FIJIAN VILLAGE: INDIGENOUS METHODS OF SMOKING CESSATION AND RELAPSE PREVENTION. Soc. Sci. Med 43, 473-477 (1996).

Abstract:
This case study outlines the unique process by which a village in Fiji (N = 238) developed and implemented an extremely successful community-based smoking cessation program. Both Western smoking cessation methods and native traditional rituals were used. Specific strategies included a group pledge, village rapid inhalation ceremony, social contracting through notices and media, and a tabu formalized through a kava ceremony. Whereas the more conventional, external, health professional oriented approaches were largely unsuccessful, longer term collaborative and village empowerment methods proved most successful. Eventually all persons in the village who smoked were able to give up smoking, with specific exceptions (elders, visitors, etc.) and became nationally known as the village that gave up smoking. Follow up evaluation at 9 and 21 months indicated sustained success. Cases of relapse are described involving supernatural consequences remedied by group and ceremonial methods. The socio-cultural context and larger relationship issues are discussed in order to more fully understand the effectiveness of the program.
(https://doi.org/10.1016/0277-9536(95)00425-4)

Uebelhock, R., Fronke, L. & Schewe, H.-1. Inhibition of Platelet MAO-6 by Kava Pyrone-Enriched Extract from Piper Methysticum Forster (Kava-Kava). Pharmacopsychiatry 31, 187-192 (1998).

Abstract:
Kava-kava, a psychoactive beverage, induces relaxation, improves social interaction, promotes sleep and plays an important role in the sociocultural life in the islands of the South Pacific. On the other hand, standardized extracts of kava-kava roots are used for the therapy of anxiety, tension and restlessness. Kava pyrones, the major constituents of kava kava, are generally considered to be responsible for the pharmacological activity in humans and animals. To obtain more information on the mechanisms by which kava-kava exerts psychotropic properties we investigated the in vitro effects of kava-kava extract and pure synthetic kava pyrones on human platelet MAO-B, in comparison to amitriptyline, imipramine and brofaromine. Kava-kava extract was found to be a reversible inhibitor of MAO-B in intact platelets (IC50 24 μM) and disrupted platelet homogenates (IC50 1.2 μM). Structural differences of kava pyrones resulted in a different potency of MAO-B inhibition. The order of potency was desmethoxyyangonin > (±)-methysticin > yangonin > (±)-dihydromethysticin > (+)- dihydrokavain > (±)-kavain. The two most potent kava pyrones, desmethoxyyangonin and (±)-methysticin displayed a competetive inhibition pattern with mean Ki 0.28 μM and 1.14 ?M respectively. The inhibition of MAO-B by kava pyrone-enriched extracts might be an important mechanism for their psychotropic activity.
(https://doi.org/10.1055/s-2007-979325)

Open Access Article
Gurley, B. J., Swain, A., Hubbard, M. A., Williams, D. K., Barone, G., Hartsfield, F., Tong, Y., Carrier, D. J., Cheboyina, S. & Battu, S. K. Clinical assessment of CYP2D6-mediated herb-drug interactions in humans: Effects of milk thistle, black cohosh, goldenseal, kava kava, St. John's wort, and Echinacea. Molecular Nutrition and Food Research 52, 755-763 (2008).

Abstract:
Cytochrome P450 2D6 (CYP2D6), an important CYP isoform with regard to drug-drug interactions, accounts for the metabolism of ∼30% of all medications. To date, few studies have assessed the effects of botanical supplementation on human CYP2D6 activity in vivo. Six botanical extracts were evaluated in three separate studies (2 extracts per study), each incorporating 18 healthy volunteers (9 females). Subjects were randomized to receive a standardized botanical extract for 14 days on separate occasions. A 30-day washout period was interposed between each supplementation phase. In study 1, subjects received milk thistle (Silybum marianum) and black cohosh (Cimicifuga racemosa). In study 2, kava kava (Piper methysticum), and goldenseal (Hydrastis canadensis) extracts were administered, and in study 3 subjects received St. John's wort (Hypericum perforatum) and Echinacea (Echinacea purpurea). The CYP2D6 substrate, debrisoquine (5 mg), was administered before and at the end of supplementation. Pre- and post-supplementation phenotypic trait measurements were determined for CYP2D6 using 8-hour debrisoquine urinary recovery ratios (DURR). Comparisons of pre- and post-supplementation DURR revealed significant inhibition (∼50%) of CYP2D6 activity for goldenseal, but not for the other extracts. Accordingly, adverse herb-drug interactions may result with concomitant ingestion of goldenseal supplements and drugs that are CYP2D6 substrates.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2562884/)

Hegazy, N. H., Breitinger, H. G. & Breitinger, U. Kavalactones from Kava (Piper methysticum) root extract as modulators of recombinant human glycine receptors. Biol. Chem. 400, 1205-1215 (2019).

Abstract:
Pacific Ocean cultures to prepare a drink with sedative, anesthetic and euphoric properties. One of the main active ingredients of the extract are kava lactones. Here, kava root CO2 extract and three kavalactones, DL-kavain, dihydrokavain and yangonin (isolated from whole extract by column chromatography) were tested for their inhibitory action on recombinant homomeric human α1 glycine receptors expressed in HEK293 cells. Kava CO2 root extract, as well as the individual components DL-kavain, dihydrokavain and yangonin inhibited glycine receptor activity in a dose-dependent manner. DL-kavain was the most potent inhibitor (IC50= 0.077 ± 0.002 mm), followed by yangonin (IC50= 0.31 ± 0.04 mm) and dihydrokavain (IC50= 3.23 ± 0.10 mm) which were 4- and 40-fold less active than DL-kavain, respectively. Application of kava root extract did not reduce maximum currents, but increased EC50 of glycine. Simultaneous application of kava extract and strychnine showed additive inhibition, suggesting that binding of kavalactones and strychnine on the receptor is mutually exclusive. Overall, kavalactones exert a moderate inhibitory effect on the human α1 glycine receptor with DL-kavain being the most potent constituent
(https://doi.org/10.1515/hsz-2019-0112)

Wang, D., Yang, L. E., Wang, J., Hu, G., Liu, Z. Y., Yan, D., Serikuly, N., Alpyshov, E. T., Demin, K. A., Galstyan, D. S., Strekalova, T., de Abreu, M. S., Amstislavskaya, T. G. & Kalueff, A. V. Behavioral and physiological effects of acute and chronic kava exposure in adult zebrafish. Neurotoxicol. Teratol. 79, 106881 (2020).

Abstract:
Kava kava (Piper methysticum) is a medicinal plant containing kavalactones that exert potent sedative, analgesic and anti-stress action. However, their pharmacological effects and molecular targets remain poorly understood. The zebrafish (Danio rerio) has recently emerged as a powerful new model organism for neuroscience research and drug discovery. Here, we evaluate the effects of acute and chronic exposure to kava and kavalactones on adult zebrafish anxiety, aggression and sociality, as well as on their neurochemical, neuroendocrine and genomic responses. Supporting evolutionarily conserved molecular targets, acute kava and kavalactones evoked dose-dependent behavioral inhibition, upregulated brain expression of early protooncogenes c-fos and c-jun, elevated brain monoamines and lowered whole-body cortisol. Chronic 7-day kava exposure evoked similar behavioral effects, did not alter cortisol levels, and failed to evoke withdrawal-like states upon discontinuation. However, chronic kava upregulated several microglial (iNOS, Egr-2, CD11b), astrocytal (C3, C4B, S100a), epigenetic (ncoa-1) and pro-inflammatory (IL-1β, IL-6, TNFa) biomarker genes, downregulated CD206 and IL-4, and did not affect major apoptotic genes in the brain. Collectively, this study supports robust, evolutionarily conserved behavioral and physiological effects of kava and kavalactones in zebrafish, implicates brain monoamines in their acute effects, and provides novel important insights into potential role of neuroglial and epigenetic mechanisms in long-term kava use.
(https://doi.org/10.1016/j.ntt.2020.106881)

Murray, M., Toxicological actions of plant-derived and anthropogenic methylenedioxyphenyl-substituted chemicals in mammals and insects. Journal of Toxicology and Environmental Health - Part B: Critical Reviews 15, 365-395 (2012).

Abstract:
The methylenedioxyphenyl (MDP) substituent is a structural feature present in many plant chemicals that deter foraging by predatory insects and herbivores. With increasing use of herbal extracts in alternative medicine, human exposure to MDP-derived plant chemicals may also be significant. Early studies found that most MDP agents themselves possess relatively low intrinsic toxicity, but strongly influence the actions of other xenobiotics in mammals and insects by modulating cytochrome P-450 (CYP)-dependent biotransformation. Thus, after exposure to MDP chemicals an initial phase of CYP inhibition is followed by a sustained phase of CYP induction. In insects CYP inhibition by MDP agents underlies their use as pesticide synergists, but analogous inhibition of mammalian CYP impairs the clearance of drugs and foreign compounds. Conversely, induction of mammalian CYP by MDP agents increases xenobiotic oxidation capacity. Exposure of insects to MDP-containing synergists in the environment, in the absence of coadministered pesticides, may also enhance xenobiotic detoxication. Finally, although most MDP agents are well tolerated, several, typified by safrole, aristolochic acid, and MDP-kavalactones, are associated with significant toxicities, including the risk of hepatotoxicity or tumorigenesis. Thus, the presence of MDP-substituted chemicals in the environment may produce a range of direct and indirect toxicities in target and nontarget species.
(https://doi.org/10.1080/10937404.2012.705105)

Lin, C. T., Kumar, K. J. S., Tseng, Y. H., Wang, Z. J., Pan, M. Y., Xiao, J. H., Chien, S. C. & Wang, S. Y. Anti-inflammatory activity of flavokawain B from Alpinia pricei hayata. J. Agric. Food Chem. 57, 6060-6065 (2009).

Abstract:
Alpinia pricei (Zingiberaceae) is a spicy herb indigenous to Taiwan. A potent anti-inflammatory compound, flavokawain B (FKB), was obtained from A. pricei. FKB significantly inhibited production of NO and PGE2 in LPS-induced RAW 264.7 cells. Moreover, it also notably decreased the secretion of TNF-α. Expression of iNOS and COX-2 proteins was also inhibited by FKB in a dose-dependent manner. FKB blocked the nuclear translocation of NF-κB induced by LPS, which was associated with prevention IκB degradation, and subsequently decreased NF-κB protein levels in the nucleus. Similar anti-inflammatory activities of FKB were observed in an animal assay. NO concentrations in mouse serum rose dramatically from 3.2 to 28.8 μM after mice were challenged with LPS; however, preadministration of 200 mg/kg FKB reduced the NO concentration to 3.8 μM after challenge with LPS. Moreover, FKB strongly suppressed LPS-induced iNOS, COX-2, and NF-κB proteins expression in mouse liver.
(https://doi.org/10.1021/jf900517d)

Zou, L., Harkey, M. R. & Henderson, G. L. Effects of herbal components on cDNA-expressed cytochrome P450 enzyme catalytic activity. Life Sci. 71, 1579-1589 (2002).

Abstract:
We evaluated the effects of 25 purified components of commonly used herbal products on the catalytic activity of cDNA-expressed cytochrome P450 isoforms in in vitro experiments. Increasing concentrations of the compounds were incubated with a panel of recombinant human CYP isoforms (CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) and their effects on the conversion of specific surrogate substrates measured fluorometrically in a 96-well plate format. For each test substance, the IC50 (the concentration required to inhibit metabolism of surrogate substrates by 50%) was estimated and compared with IC50's for the positive control inhibitory drugs furafylline, sulfaphenazole, tranylcypromine, quinidine, and ketoconazole. Constituents of Ginkgo biloba (ginkgolic acids I and II), kava (desmethoxyyangonin, dihydromethysticin, and methysticin), garlic (allicin), evening primrose oil (cis-linoleic acid), and St. John's wort (hyperforin and quercetin) significantly inhibited one or more of the cDNA human P450 isoforms at concentrations of less than 10 uM. Some of the test compounds (components of Ginkgo biloba, kava, and St. John's wort) were more potent inhibitors of the isoforms 1A2, 2C19, and 2C19 than the positive controls used in each assay (furafylline, sulfaphenazole, and tranylcypromine, respectively), which are known to produce clinically significant drug interactions. The enzyme most sensitive to the inhibitory of effects of these compounds was CYP2C19, while the isoform least effected was CYP2D6. These data suggest that herbal products containing evening primrose oil, Ginkgo biloba, kava, and St. John's Wort could potentially inhibit the metabolism of co-administered medications whose primary route of elimination is via cytochrome P450.
(https://doi.org/10.1016/s0024-3205(02)01913-6)

Open Access Article
Cairney, S., Clough, A. R., Maruff, P., Collie, A., Currie, B. J. & Currie, J. Saccade and cognitive function in chronic kava users. Neuropsychopharmacology 28, 389-396 (2003).

Abstract:
Kava is an extract from the Piper methysticum Forst. f. plant that has been consumed in the Pacific islands for millennia and more recently, among indigenous populations, in northern Australia and throughout the Western world as an herbal medicine. Through alterations on neuronal excitation, kava induces muscle relaxation, anasthesia, and has anxiolytic properties. There have been several isolated reports of psychotic syndromes, severe choreoathetosis and possible seizures following kava use. However, there is no conclusive evidence that kava interferes with normal cognitive processes. We tested a group of current, ex, and nonkava users among an indigenous population in northern Australia, using saccade and cognitive tests that have proven cross-cultural validity and are sensitive to subtle disruptions of the brain arising from substance abuse or neuropsychiatric illness. Despite collecting data from among the heaviest reported kava drinkers in the world, we found no impairment in cognitive or saccade function in individuals who were currently heavy kava users (and had been for up to 18 years), nor was there any impairment in individuals who had been heavy kava users in the past but had abstained for longer than 6 months. Current and ex-kava users showed a higher rate of kava dermopathy, lower body mass index, lowered blood lymphocytes and, in addition, current kava users showed elevated liver enzymes. While there has recently been increasing concern about potentially fatal liver damage attributed to kava use, we have found no evidence of brain dysfunction in heavy and long-term kava users.
(https://doi.org/10.1038/sj.npp.1300052)

Gleitz1', J., Beiie1, A., Wiikens1, P., Amen1, A. & Peterst, T. Antithrombotic Action of the Kava Pyrone (+)-Kavain Prepared from Piper methysticum on Human Platelets. , (1997).

Abstract:
(+)-Kavain, a 4-methoxy-α-pyrone prepared from Piper methysticum Forst. (Piperaceae), was investigated regarding its assumed antithrombotic action on human platelets which was deduced from its ability to suppress arachidonic acid (AA)-induced aggregation, exocytosis of ATP, and inhibition of cyclooxygenase (COX) and thromboxane synthase (TXS) activity, the latter two effects being estimated from the generation of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2), respectively. Exogenously applied AA (100 µmol/l) provoked a 90% aggregation of platelets, the release of 14pmol ATP, and the formation of either 220 pg TXA2 or 43 pg PGE2, each parameter being related to 106 platelets. An application of (+)-kavain 5 min before AA, dose-dependently diminished aggregation, ATP-release, and the synthesis of TXA2 and PGE2 with IC50 values of 78, 115, 71, and 86 µmol/l, respectively. The similarity of the IC50 values suggest an inhibition of COX by (+)-kavain as primary target, thus suppressing the generation of TXA2 which induces aggregation of platelets and exocytosis of ATP by its binding on TXA2-receptors.
(https://doi.org/10.1055/s-2006-957597)

Aporosa, A. S., Atkins, M. & Brunton, R. Kava drinking in traditional settings: Towards understanding effects on cognitive function. Human Psychopharmacology 35, 1-11 (2020).

Abstract:
Background
Kava drinking is a tradition among Pacific Island people, although growing in popularity with other ethnicities. However, drinking substantial quantities of kava has raised concerns regarding physical manifestations of slow response and lack of precision in bodily control. These impairments can have significant consequences when after consuming large volumes of kava an individual makes a choice to drive.

Aims
The objective of this study was to measure selected cognitive functions following high traditionally consumed kava volumes (greater than 2,000 mg of kavalactones) aimed at identifying potential risks for kava drink‐drivers.

Methods
The reaction and divided attention of 20 control participants was assessed against 20 active kava‐drinking participants during and following a 6‐hr kava session in a “naturalised” setting. Assessment measures were drawn from Vienna Test System—Traffic's test battery.

Results/Outcomes
Results showed no statistical significant difference between control and active participants at any measurement point over a 6‐hr testing period regardless that the movements and speech of the active participants were observed to slow as the test session and kava consumption progressed.

Conclusion
Inconsistencies between test results and observations during testing and by road policing officers demonstrate an urgent need for more research in this field.
(https://doi.org/10.1002/hup.2725)

Open Access Article
Li, Y., Mei, H., Wu, Q., Zhang, S., Fang, J. L., Shi, L. & Guo, L. Methysticin and 7,8-dihydromethysticin are two major kavalactones in kava extract to induce CYP1A1. Toxicol. Sci. 124, 388-399 (2011).

Abstract:
Kava is a plant traditionally used for making beverages in Pacific Basin countries and has been used for the treatment of nervous disorders in the United States. The pharmacological activity of kava is achieved through kavalactones in kava extract, which include kawain, 7,8-dihydrokawain, yangonin, 5,6-dehydrokawain, methysticin, and 7,8-dihydromethysticin. Recent studies have shown that kava extract induces hepatic CYP1A1 enzyme; however, the mechanisms of CYP1A1 induction have not been elucidated, and the kavalactones responsible for CYP1A1 induction have not yet been identified. Using a combination of biochemical assays and molecular docking tools, we determined the functions of kava extract and kavalactones and delineated the underlying mechanisms involved in CYP1A1 induction. The results showed that kava extract displayed a concentration-dependent effect on CYP1A1 induction. Among the six major kavalactones, methysticin triggered the most profound inducing effect on CYP1A1 followed by 7,8-dihydromethysticin. The other four kavalactones (yangonin, 5,6-dehydrokawain, kawain, and 7,8-dihydrokawain) did not show significant effects on CYP1A1. Consistent with the experimental results, in silico molecular docking studies based on the aryl hydrocarbon receptor (AhR)-ligand binding domain homology model also revealed favorable binding to AhR for methysticin and 7,8-dihydromethysticin compared with the remaining kavalactones. Additionally, results from a luciferase gene reporter assay suggested that kava extract, methysticin, and 7,8-dihydromethysticin were able to activate the AhR signaling pathway. Moreover, kava extract-, methysticin-, and 7,8-dihydromethysticin-mediated CYP1A1 induction was blocked by an AhR antagonist and abolished in AhR-deficient cells. These findings suggest that kava extract induces the expression of CYP1A1 via an AhR-dependent mechanism and that methysticin and 7,8-dihydromethysticin contribute to CYP1A1 induction. The induction of CYP1A1 indicates a potential interaction between kava or kavalactones and CYP1A1-mediated chemical carcinogenesis.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5736320/)

Weiss, J., Sauer, A., Frank, A. & Unger, M. Extracts and kavalactones of Piper methysticum G. Forst (kava-kava) inhibit P-glycoprotein in vitro. Drug Metabolism and Disposition 33, 1580-1583 (2005).

Abstract:
Root extracts from kava-kava (Piper methysticum G. Forst) are clinically used for the treatment of anxiety and restlessness. Due to reported cases of liver toxicity, kava-kava extracts were withdrawn from the market in several countries in 2002. Because the efflux transporter P-glycoprotein (P-gp) is involved in the absorption, distribution, and excretion of many drugs and often participates in drug-drug interactions, we studied the effect of a crude kava extract and the main kavalactones kavain, dihydrokavain, methysticin, dihydromethysticin, yangonin, and desmethoxyyangonin on the P-gp-mediated efflux of calcein-acetoxymethylester in the P-gp-overexpressing cell line P388/dx and the corresponding cell line P388. The crude extract and the kavalactones showed a moderate to potent inhibitory activity with f2 (concentration needed to double baseline fluorescence) values of 170 μg/ml and 17 to 90 μM, respectively. The f2 value of yangonin could not be determined due to its higher lipophilicity. In conclusion, our results for the first time demonstrate P-gp-inhibitory activity of kava-kava and its components in vitro.
(https://doi.org/10.1124/dmd.105.005892)

Ma, Y., Sachdeva, K., Liu, J., Ford, M., Yang, D., Khan, I. A., Chichester, C. O. & Yan, B. Desmethoxyyangonin and dihydromethysticin are two major pharmacologigal kavalactones with marked activity on the induction of CYP3A23. Drug Metabolism and Disposition 32, 1317-1324 (2004).

Abstract:
Kava kava (Piper methysticum), an herbal remedy, is widely used for the treatment of mild to moderate cases of anxiety. The therapeutic activity is presumably achieved through multiple constituents called kavalactones. Recently, kava extracts were shown to induce CYP3A4 and activate human pregnane X receptor (PXR). This study was undertaken to test the ability of purified kavalactones to induce CYP3A23 and activate PXR. Rat hepatocytes were treated with desmethoxyyangonin, dihydrokawain, dihydromethysticin, kawain, methysticin, or yangonin, and the expression of CYP3A23 was monitored. Among the kavalactones, only desmethoxyyangonin and dihydromethysticin markedly induced the expression of CYP3A23 (∼7-fold). A similar magnitude of induction was detected with combined six kavalactones at a noninductive concentration when individually used. The induced expression, however, was markedly reduced or completely abolished if dihydromethysticin, desmethoxyyangonin, or both were excluded from the mixtures. Interestingly, regardless of whether dihydromethysticin or desmethoxyyangonin was used alone or together with other kavalactones, similar amounts of total kavalactones were needed to produce comparable induction, suggesting that the inductive activity of dihydromethysticin and desmethoxyyangonin is additively/synergistically enhanced by other kavalactones. In addition, treatment with dihydromethysticin, desmethoxyyangonin, or pregnenolone 16α-carbonitrile (PCN) markedly increased the levels of CYP3A23 mRNA, and inhibition of mRNA synthesis abolished the induction. In contrast to PCN, dihydromethysticin and desmethoxyyangonin only slightly activated rat or human PXR. These findings suggest that the induction of CYP3A23 by dihydromethysticin and desmethoxyyangonin involves transcription activation, probably through a PXR-independent or PXR-involved indirect mechanism.
(https://doi.org/10.1124/dmd.104.000786)

Martin HB, McCallum M, Stofer WD, Eichinger MR. Kavain attenuates vascular contractility through inhibition of calcium channels. Planta Med. 2002 Sep;68(9):784-9. doi: 10.1055/s-2002-34443. PMID: 12357387.

Abstract:
Kavain is a biologically active compound from the Oceanic plant Piper methysticum (kava). Traditional medicinal uses of the kava root are many. Kava is increasingly being utilized by Western societies for its anxiolytic effects. Recent reports indicate that kavain blocks ion channels in neural tissue, relaxes precontracted ileum, and relaxes precontracted airway. Thus, we investigated the potential ability of this plant-derived compound to alter vascular smooth muscle function. Thoracic aortae were isolated from Sprague-Dawley rat and cut into 4 mm rings. Rings were placed in tissue baths and suspended from force-displacement transducers for the measurement of isometric tension. In a dose-dependent manner, kavain (10-6 M to 10-3 M) was found to relax aortic rings precontracted with phenylephrine (PE). This response was not dependent on functional endothelium. In addition, kavain pretreatment (3 × 10-5 M or 3 × 10-4 M) attenuated vascular smooth muscle contraction evoked by PE. However, kavain failed to attenuate PE-mediated contraction in calcium (Ca++)-free buffer, indicating that intracellular signaling processes were likely not affected. Also, kavain did attenuate the contraction elicited by administration of Ca++ to depolarized tissue. Interestingly, in rings pre-treated with the selective L-type Ca++ channel blocker nifedipine, kavain-mediated relaxation was inhibited. Lastly, in rings selectively contracted with an L-type calcium channel activator, kavain elicited dose-dependent (and ultimately complete) relaxation. These data strongly suggest that kavain impairs vascular smooth muscle contraction, likely through inhibition of Ca++ channels.
(https://doi.org/10.1055/s-2002-34443)

Upadhyay, A., Tuenter, E., Ahmad, R., Amin, A., Exarchou, V., Apers, S., Hermans, N. & Pieters, L. Kavalactones, A novel class of protein glycation and lipid peroxidation inhibitors. Planta Med. 80, 1001-1008 (2014).

Abstract:
Both advanced glycation endproducts and advanced lipoxidation endproducts are implicated in many age-related chronic diseases and in protein ageing. In this study, kawain, methysticin, and dihydromethysticin, all belonging to the group of kavalactones, were identified as advanced glycation endproduct inhibitors. With IC50 values of 43.5 ± 1.2 µM and 45.0 ± 1.3 µM for kawain and methysticin, respectively, the compounds inhibited the in vitro protein glycation significantly better than aminoguanidine (IC50 = 231.0 ± 11.5 µM; p = 0.01), an established reference compound. Kawain and methysticin also inhibited the formation of dicarbonyl compounds, which are intermediates in the process of advanced glycation endproduct formation. Similarly, kawain and aminoguanidine prevented the formation of thiobarbituric reactive substances in both low-density lipoprotein and linoleic acid oxidation. Moreover, kawain and aminoguanidine prevented advanced glycation endproduct formation by chelating Fe3+ and Cu2+ two to three times better than aminoguanidine. Furthermore, kawain increased the mean life span of Caenorhabditis elegans exposed to high glucose. With glycation inhibiting, lipid peroxidation inhibiting, metal chelating properties, and life span extending ability, kavalactones show a high potential as advanced glycation endproducts and advanced lipoxidation endproduct inhibitors.
(https://doi.org/10.1055/s-0034-1382949)

Open Access Document
Jaleel, G. A. A., Saleh, D. O. & El-Awdan, S. A. Antihyperglycaemic effect of kava kava (piper methysticum) in streptozotocin-induced diabetic rats. Scholars Research Library , (2013).

Abstract:
The present study aimed to investigate the possible effects of kava kava (KK) (Piper methysticum) on the hyperglycaemia induced in rats by streptozotocin (STZ; 55 mg/kg; i.p.). Blood samples, were used to determine serum levels of glucose, insulin, total cholesterol (TC) and triglycerides (TG). Some relevant markers for oxidative stress viz., serum lipid peroxides level (measured as malondialdehyde; MDA) and total antioxidant capacity as well as serum nitric oxide (NO) level measured as nitrate/nitrite were determined. Hyperglycaemic animals received orally KK (200 mg/kg) or (500 mg/kg) on daily basis for 28 consecutive days and their effects were determined 24 h after the administration of the last dose. In addition to another group received gliclazide (5 mg/kg; p.o.) as a reference drug. Results of the present study revealed that STZ-induced hyperglycaemia is associated with decreased serum insulin level with increased level of TC and TG. Hyperglycaemia was also associated increased level of plasma MDA together with decreased total antioxidant capacity and level of plasma NO. KK was able to improve the hyperglycaemia in STZ injected rats with an increase in the serum insulin level and a decrease in the level of TG. The higher dose of KK showed a restoration of the increased serum level of TC and MDA and of the suppressed insulin and total antioxidant capacity as well as the decreased plasma level of NO. From our results it can be conclude that KK has an antihyperglycaemic effect and has the ability to attenuate some of its associated abnormalities.
(https://www.scholarsresearchlibrary...cum-in-streptozotocininduceddiabetic-rats.pdf)

Open Access Article
Fragoulis, A., Siegl, S., Fendt, M., Jansen, S., Soppa, U., Brandenburg, L. O., Pufe, T., Weis, J. & Wruck, C. J. Oral administration of methysticin improves cognitive deficits in a mouse model of Alzheimer's disease. Redox Biol. 12, 843-853 (2017).

Introduction:
There is increasing evidence for the involvement of chronic inflammation and oxidative stress in the pathogenesis of Alzheimer's disease (AD). Nuclear factor erythroid 2-related factor 2 (Nrf2) is an anti-inflammatory transcription factor that regulates the oxidative stress defense. Our previous experiments demonstrated that kavalactones protect neuronal cells against Amyloid β (Aβ)-induced oxidative stress in vitro by Nrf2 pathway activation. Here, we tested an in vivo kavalactone treatment in a mouse model of AD.
(https://doi.org/10.1016/j.redox.2017.04.024)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/28448946/)

Open Access Article
Wainiqolo, I., Kool, B., Nosa, V. & Ameratunga, S. Is driving under the influence of kava associated with motor vehicle crashes? A systematic review of the epidemiological literature. Australian and New Zealand Journal of Public Health 39, 495-499 (2015).

Abstract:
A systematic method was used to review the existing epidemiologic literature and determine the state of the scientific evidence for potential adverse health outcomes in populations living near oil and natural gas (ONG) operations in the United States. The review utilized adapted systematic review frameworks from the medical and environmental health fields, such as Grading of Recommendations, Assessment, Development and Evaluations (GRADE), the Navigation Guide, and guidance from the National Toxicology Program’s Office of Health Assessment and Translation (OHAT). The review included 20 epidemiologic studies, with 32 different health outcomes. Studies of populations living near ONG operations provide limited evidence (modest scientific findings that support the outcome, but with significant limitations) of harmful health effects including asthma exacerbations and various self-reported symptoms. Study quality has improved over time and the highest rated studies within this assessment have primarily focused on birth outcomes. Additional high-quality studies are needed to confirm or dispute these correlations.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6616936/)

Open Access Article
Shimoda, L. M., Park, C., Stokes, A. J., Gomes, H. H. & Turner, H. Pacific Island 'Awa (Kava) extracts, but not isolated kavalactones, promote proinflammatory responses in model mast cells. Phytotherapy Research 26, 1934-1941 (2012).

Abstract:
Kava (‘Awa) is a traditional water-based beverage in Pacific island communities, prepared from the ground root and stems of Piper methysticum. Kava use is associated with an ichthyotic dermatitis and delayed type hypersensitivity reactions. In the current study we collated preparative methodologies from cultural practitioners and recreational kava users in various Pacific communities. We standardized culturally-informed aqueous extraction methods and prepared extracts that were subjected to basic physicochemical analysis. Mast cells exposed to these extracts displayed robust intracellular free calcium responses, and concomitant release of pro-inflammatory mediators. In contrast, mast cells were refractory to single or combinatorial stimulation with kavalactones including methysticin, dihydromethysticin and kavain. Moreover, we reproduced a traditional modification of the kava preparation methodology, pre-mixing with the mucilage of Hibiscus taliaceus, and observed its potentiating effect on the activity of aqueous extracts in mast cells. Taken together, these data indicate that water extractable active ingredients may play a role in the physiological and pathophysiological effects of kava, and suggests that mast cell activation may be a mechanistic component of kava-related skin inflammations.
(https://doi.org/10.1002/ptr.4652)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/22473598/)

L. Zou, G. L. Henderson, M. R. Harkey, Y. Sakai, & A. Li2. (2004). Effects of Kava (Kava-kava, ‘Awa, Yaqona, Piper methysticum) on c-DNA-expressed cytochrome P450 enzymes and human cryopreserved hepatocytes. Phytomedicine, 11(4), 285–294.

Access:
The effects of the herbal product kava (Kava kava, 'Awa, Yaqona, Piper methysticum) on human P450 isoforms were studied in vitro using both cDNA-expressed human enzymes and cryopreserved human hepatocytes. Increasing concentrations of an ethanolic extract of dried kava root and three purified kava lactones (methysticin, desmethoxyyangonin, and yangonin) were tested for their ability to inhibit the catalytic activity of a panel of P450 isoforms (1A2, 2A6, 2C9, C2C19, 2D6, 2E1, and 3A4) present as c-DNA expressed-enzymes and in previously cryopreserved human hepatocytes. In addition, the test compounds' effect on hepatocyte viability was evaluated by measuring cellular ATP content. In both models, the kava extract and the three kava lactones were found to be potent inhibitors of CYPs 1A2, 2C9, 2C19, 2E1, and 3A4 with IC50 values of approximately 10 μM. The test compounds were also moderately cytotoxic to human hepatocytes (EC50 values of approximately 50 μM). Methysticin was the most potent enzyme inhibitor as well as the most cytotoxic, followed by (in order of potency:) the kava root extract, desmethoxyyangonin, and yangonin. Our results suggest that the drug interaction and hepatotoxic potential of kava should be further investigated.
(https://doi.org/10.1078/0944711041495263)

Shinomiya, K., Inoue, T., Utsu, Y., Tokunaga, S., Masuoka, T., Ohmori, A., &amp; Kamei, C. (2005). Effects of kava-kava extract on the sleep–wake cycle in sleep-disturbed rats. Psychopharmacology, 180(3), 564-569.

Abstract:
Rationale: Kava-kava extract may be useful as an herbal medicine for treatment of insomnia and anxiety.

Objectives: The present study was undertaken to investigate the effects of kava-kava extract on the sleep-wake cycle in comparison with that of flunitrazepam using sleep-disturbed rats.

Methods: Electrodes for measurement of electroencephalogram (EEG) and electromyogram (EMG) were implanted into the frontal cortex and the dorsal neck muscle of rats. EEG and EMG were recorded with an electroencephalogram. SleepSign ver.2.0 was used for EEG and EMG analysis. Total times of wakefulness, non-rapid eye movement (non-REM) and REM sleep were measured from 09:00 to 15:00.

Results: A significant shortening of the sleep latency in sleep-disturbed rats was observed following the administration of kava-kava extract at a dose of 300 mg/kg, while no effects were observed on the total waking and non-REM sleep time. On the other hand, flunitrazepam showed a significant shortening in sleep latency, decrease in total waking time and increase in total non-REM sleep time. Although the effects of flunitrazepam were antagonized by the benzodiazepine receptor antagonist flumazenil, the effect of kava-kava extract was not antagonized by flumazenil. Kava-kava extract showed a significant increase in delta activity during non-REM sleep in sleep-disturbed rats, whereas a significant decrease in delta power during non-REM sleep was observed with flunitrazepam. Flumazenil caused no significant effect on the changes in delta activity induced by both kava-kava extract and flunitrazepam.

Conclusions: Kava-kava extract is an herbal medicine having not only hypnotic effects, but also sleep quality-enhancement effects.
(https://doi.org/10.1007/s00213-005-2196-4)

Combination with other plants/drugs

Foo H, Lemon J. Acute effects of kava, alone or in combination with alcohol, on subjective measures of impairment and intoxication and on cognitive performance. Drug Alcohol Rev. 1997 Jun;16(2):147-55. doi: 10.1080/09595239700186441. PMID: 16203421.

Abstract:
Kava (Piper methysticum) and alcohol were administered either separately or in combination to human subjects. Self‐reports of their levels of impairment and intoxication were collected, and performance skills on a number of cognitive and visuomotor tests were determined, before and three times after consumption of the experimental drink. Kava alone had no effect on reported condition. In contrast, alcohol produced marked changes in each of the five subjective measures, all of which were in the direction of lowered ability. The combination of these two substances produced even larger negative changes on these measures. In the cognitive tests, kava produced a decrement in performance on Digit Symbol Coding. Alcohol produced a significant decrease in performance on a divided attention test, which was almost entirely on the peripheral, discontinuous component of the test. The combination of kava and alcohol produced an even greater decrease in performance on this test, and in the same component. The present findings suggest that kava alone has little effect on reported condition and cognitive performance, but appears to potentiate both perceived and measured impairment when combined with alcohol.
(https://doi.org/10.1080/09595239700186441)

Singh YN. Potential for interaction of kava and St. John's wort with drugs. J Ethnopharmacol. 2005 Aug 22;100(1-2):108-13. doi: 10.1016/j.jep.2005.05.014. PMID: 16005588.

Abstract:
The present interest and widespread use of herbal remedies has created the possibility of interaction between them and pharmaceutical drugs if they are used simultaneously. Before the recent reports of apparent hepatotoxicity associated with its use, kava (Piper methysticum Forst. F.), was one of the top 10 selling herbal remedies in Europe and North America. This adverse effect was not previously encountered with the traditional beverage which was prepared as a water infusion in contrast to the commercial products which are extracted with organic solvents. Kavalactones, the active principles in kava, are potent inhibitors of several of the CYP 450 enzymes, suggesting a high potential for causing pharmacokinetic interactions with drugs and other herbs which are metabolized by the same CYP 450 enzymes. Furthermore, some kavalactones have been shown to possess pharmacological effects, such as blockade of GABA receptors and sodium and calcium ion channels, which may lead to pharmacodynamic interactions with other substances which possess similar pharmacological proprieties. St. John's wort (Hypericum perforatum L.), used extensively for the treatment of mild to moderate clinical depression, has long been considered safer than the conventional pharmaceutical agents. However, its ability, through its active constituents hypericin, pseudohypericin and hyperforin, to induce intestinal P-glycoprotein/MRD1 and both intestinal and hepatic CYP3A4 enzyme, could markedly reduce the distribution and disposition of their co-substrates. In addition, St. John's wort is a potent uptake inhibitor of the neurotransmitters serotonin, norepinephrine and dopamine all of which have a role in mood control. Consequently, the very real potential for a pharmacodynamic interaction between the herb and pharmaceutical drugs which share this mechanism of action and, like St. John's wort, are used for mood elevation. However, presently there is very little evidence to substantiate actual pharmacokinetic and/or pharmacodynamic interaction between drugs and kava or St. John's wort. This review provides a brief overview of the existing data on interactions of kava and St. John's wort with pharmaceutical agents and as a result reveals the urgent need for detailed investigations to identify clinically significant interactions for these herbal remedies that have the potential to cause adverse effects.
(https://doi.org/10.1016/j.jep.2005.05.014)

Anke, J., & Ramzan, I. (2004). Pharmacokinetic and pharmacodynamic drug interactions with Kava (Piper methysticum Forst. f.). In Journal of Ethnopharmacology (Vol. 93, Issues 2–3, pp. 153–160).

Abstract:
Kava kava, a beverage or extract prepared from the rhizome of the kava plant (Piper methysticum Forst. f.), was used for many centuries as a traditional beverage in the Pacific Islands. During the past few decades, kava has also gained popularity in Western countries as well, due to its anxiolytic and sedative properties. However, in recent years, kava has been implicated in several liver failure cases which led to its ban in many countries and this has prompted wide discussion on its relative benefits and risks as a social beverage and a herbal remedy. Recently, it has been shown that several kavalactones, the assumed active principles of kava extracts, are potent inhibitors of several enzymes of the CYP 450 system (CYP1A2, 2C9, 2C19, 2D6, 3A4 and 4A9/11). This indicates that kava has a high potential for causing pharmacokinetic drug interactions with other herbal products or drugs, which are metabolised by the CYP 450 enzymes. In addition, several pharmacodynamic interactions have been postulated and indeed observed. Nevertheless, evidence of true pharmacokinetic and/or pharmacodynamic interactions remains unsubstantiated, and only few investigations of the potential of kava preparations to interact with specific drugs have been carried out. This review provides a critical overview of the existing data on interactions of kava with other drugs and concludes that there is an urgent need for further in vitro and in vivo investigations to fully understand clinically significant interactions with kava that have the potential to cause adverse effects or toxicity in kava users.
(https://doi.org/10.1016/j.jep.2004.04.009)

Amdidouche-Hussain, D. & Levesque, J. Selection of kavalactones by complexation of kava extract with cyclodextrins. Drug Dev. Ind. Pharm. 23, 1223-1226 (1997).

Abstract:
Kavalactones, active ingredients extracted from Piper methysticum Forst. Piperaceae, have many therapeutic properties including relaxing, anaesthetic, analgesic, and antifungic properties. Kavalactones are insoluble in aqueous vehicles. These active ingredients are inclused in cyclodextrins to improve their water solubility and to realize a galenic form.

Gamma cyclodextrin (γ-CD) and beta cyclodextrin (β-CD) were used. The amounts of kavalactones inclused in cyclodextrins have been measured by HPLC with UV spectrophotometric detection.

The results showed that besides increasing the water solubility of kavalactones, the complexation leads to a selection of the most active compounds that are preferentially included.
(https://doi.org/10.3109/03639049709146161)

Open Access Article
Tawfiq, R. A., Nassar, N. N., El-Eraky, W. I. & El-Denshary, E. S. Enhanced efficacy and reduced side effects of diazepam by kava combination. Journal of Advanced Research 5, 587-594 (2014).

Abstract:
The long term use of antiepileptic drugs possesses many unwanted effects; thus, new safe combinations are urgently mandated. Hence, the present study aimed to investigate the anticonvulsant effect of kava alone or in combination with a synthetic anticonvulsant drug, diazepam (DZ). To this end, female Wistar rats were divided into two subsets, each comprising 6 groups as follows: group (i) received 1% Tween 80 p.o. and served as control, while groups (ii) and (iii) received kava at two dose levels (100 and 200 mg/kg, p.o.). The remaining three groups received (iv) DZ alone (10 mg/kg p.o.) or kava in combination with DZ (v) (5 mg/kg, p.o.) or (vi) (10 mg/kg, p.o.). Results of the present study revealed that kava increased the maximal electroshock seizure threshold (MEST) and enhanced the anticonvulsant effect of diazepam following both acute and chronic treatment. Moreover, neither kava nor its combination with DZ impaired motor co-ordination either acutely or chronically. Furthermore, kava ameliorated both the reduction in locomotor activity as well as changes in liver function tests induced by chronic administration of DZ. Moreover, no elevation was shown in the creatinine concentration vs. control group following chronic administration of kava or DZ either alone or in combination with kava. In conclusion, the present study suggests the possibility of combining a low dose DZ with kava to reduce harmful effects and might be recommended for clinical use in patients chronically treated with this synthetic anticonvulsant drug.
(https://doi.org/10.1016/j.jare.2013.08.002)

Anke, J., Fu, S. & Ramzan, I. Kavalactones fail to inhibit alcohol dehydrogenase in vitro. Phytomedicine 13, 192-195 (2006).

Abstract:
In recent years, Kava kava (Piper methysticum, Forst. f., Piperaceae), a folkloric beverage and popular herbal remedy, has been implicated in a number of liver failure cases. Many hypotheses as to the mechanism of its hepatotoxicity, for example interactions with other co-ingested medication, have been postulated. This present study investigated whether pharmacokinetic interactions between kava constituents and alcohol via alcohol dehydrogenase (ADH) inhibition by individual kavalactones might explain its claimed hepatotoxic effects. Four kavalactones, (±)-kavain, methysticin, yangonin and desmethoxyyangonin, fail to inhibit ADH in vitro at 1, 10 or 100 μM concentrations.
(https://doi.org/10.1016/j.phymed.2004.07.005)

Heinze HJ, Münthe TF, Steitz J, Matzke M. Pharmacopsychological effects of oxazepam and kava-extract in a visual search paradigm assessed with event-related potentials. Pharmacopsychiatry. 1994 Nov;27(6):224-30. doi: 10.1055/s-2007-1014309. PMID: 7870743.

Abstract:
The effects of oxazepam and a standardized extract of kava-roots (WS1490, W. Schwabe, Karlsruhe) on reaction time and event-related potentials (ERPs) were investigated in a visual search paradigm using a double-blind design in young, healthy males. Significant effects of oxazepam were obtained in a number of psychometric tests as well as search time and quality. Several ERP components of different latency, topography and functional significance were affected by the medications. Oxazepam led to a reduction of the amplitude of the parietal N1, frontal N2, posterior contralateral N2, and occipital P3 components. WS 1490 was associated with a greater posterior N1, posterior contralateral N2, and occipital P3. The effects are discussed in the light of the functional properties of the components and provide clues as to the psychological site of action of the drugs.
(https://doi.org/10.1055/s-2007-1014309)

Brain Science Involving Kavalactones

Waldeni, J., VON WEGERERl, J., Winterz, U., BERGERl, M., & Grunze, H. (1997). Effects of kawain and dihydromethysticin on field potential changes in the hippocampus. In Elsevler Science Inc. Neuro-Psychopharmacol. & Biol. Psychiat (Vol. 21).

Abstract:

1. The kava-pyrones kawain and dihydromethysticin are constituents of Piper methysticum which exert anticonvulsant, analgesic and anxiolytic properties.

2. In the present study the effect of these kava-pyrones were tested on field potential changes (fp) induced by omission of the extracellular Mg2+, recorded from the area CA1 and CA3 of the hippocampal slice preparation of guinea pigs. These fp are generated by an activation of NMDA receptors and voltage dependent calcium channels.

3. Kawain and dihydromethysticin reduced reversibly the frequency of occurrence of fp in a concentration range from 5 to 40 μmol/1 and 10 to 40 μmol/1, respectively.

4. Reduction of the fp frequency after addition of subthreshold concentrations of 5 μmol/1 kawain and 10 μmol/1 dihydromethysticin indicated additive actions of both drugs.

5. Since the serotonin-1A agonist ipsapirone also exerts anxiolytic effects, subthreshold concentrations of kawain or dihydromethysticin were combined with a subthreshold concentration of ipsapirone in another set of experiments. Combining kawain and ipsapirone or dihydromethysticin and ipsapirone caused a reduction of the rate of fp to 0.76 and 0.81 of the baseline value, respectively.

6. The findings suggest that (i) single constituents of Piper methysticum may have additive actions, (ii) that the two components kawain and dihydromethysticin may enhance the effects of the anxiolytic serotonin-1A agonist ipsapirone and (iii) that activation of NMDA receptors and/or voltage dependent calcium channels may be involved in the elementary mechanism of action of some kava-pyrones.
(https://doi.org/10.1016/s0278-5846(97)00042-0)

Yuan CS, Dey L, Wang A, Mehendale S, Xie JT, Aung HH, Ang-Lee MK. Kavalactones and dihydrokavain modulate GABAergic activity in a rat gastric-brainstem preparation. Planta Med. 2002 Dec;68(12):1092-6. doi: 10.1055/s-2002-36338. PMID: 12494336.

Abstract:
Using an in vitro neonatal rat gastric-brainstem preparation, the activity of majority neurons recorded in the nucleus tractus solitarius (NTS) of the brainstem were significantly inhibited by GABA A receptor agonist, muscimol (30 microM), and this inhibition was reversed by selective GABA A receptor antagonist, bicuculline (10 microM). Application of kavalactones (300 microg/ml) and dihydrokavain (300 microM) into the brainstem compartment of the preparation also significantly reduced the discharge rate of these NTS neurons (39 % and 32 %, respectively, compared to the control level), and this reduction was partially reversed by bicuculline (10 microM). Kavalactones or dihydrokavain induced inhibitory effects were not reduced after co-application of saclofen (10 microM; a selective GABA B receptor antagonist) or naloxone (100 nM; an opioid receptor antagonist). Pretreatment with kavalactones (300 microg/ml) or dihydrokavain (300 microM) significantly decreased the NTS inhibitory effects induced by muscimol (30 microM), approximately from 51 % to 36 %. Our results demonstrated modulation of brainstem GABAergic mechanism by kavalactones and dihydrokavain, and suggested that these compounds may play an important role in regulation of GABAergic neurotransmission.
(https://pubmed.ncbi.nlm.nih.gov/12494336/)

Long, D. D., Urs, S., Karin Berger Bueter, Bernd Bueter, Kenneth Lundstrom, & Willi Schaffner. (2001). Interaction of Various Piper methysticum Cultivars with CNS Receptors in vitro. Planta Med, 67(4), 306–311.

Abstract:
Methanolic leaf and root extracts of the Hawaiian kava (Piper methysticum Forst.) cultivars, Mahakea, Nene, Purple Moi and PNG, were tested on binding affinities to CNS receptors including GABAA (GABA and benzodiazepine binding site), dopamine D2, opioid (μ and δ), serotonin (5-HT6 and 5-HT7) and histamine (H1 and H2). HPLC analysis was carried out in order to determine the amount of the main kavalactones kavain, 7,8-dihydrokavain, methysticin, 7,8-dihydromethysticin, yangonin and 5,6-demethoxyyangonin. The most potent binding inhibition was observed for leaf extracts to GABAA receptors (GABA binding site) with IC50 values of approximately 3 μg/ml, whereas root extracts were less active with IC50 values ranging from 5 μg/ml (Nene) to 87 μg/ml (Mahakea). Since the leaf extracts generally contained lower amounts of the kavalactones than the root extracts, there might exist additional substances responsible for these activities. Leaf extracts also inhibited binding to dopamine D2, opioid (μ and δ) and histamine (H1 and H2) receptors more potently than the corresponding root extracts with IC50 values ranging from 1 to 100 μg/ml vs. ≥ 100 μg/l, respectively. Significant differences in the potential of binding inhibition were also observed between cultivars. Binding to serotonin (5-HT6 and 5-HT7) and benzodiazepine receptors was only weakly inhibited by both root and leaf extracts of all four cultivars. In conclusion, our investigation indicates that the GABAA, dopamine D2, opioid (μ and δ) and histamine (H1 and H2) receptors might be involved in the pharmacological action of kava extracts. Since the cultivars contained similar amounts of kavalactones, while their pharmacological activities differed markedly, other constituents may play a role in the observed activities. Additionally, leaves generally exhibited more potent binding inhibition than roots, therefore leaf of P. methysticum might be an interesting subject for further pharmacological studies.
https://doi.org/10.1055/s-2001-14334

Schmitz, D., Zhang, C., Chatterjee, S., Heinemaun, U., Chatterjee Abteilung Pharmakologie Fa Schwabe, S. W. & Heinemann, U. Effects of methysticin on three different models of seizure like events studied in rat hippocampal and entorhinal cortex slices. Naunyn-Schmiedeberg's Arch Pharmacol 351, 348-355 (1995).

Abstract:
Methysticin is one of the constituents of Piper methysticum which possesses anticonvulsant and neuroprotective properties. Its effects on different in vitro seizure models were tested using extracellular recordings in rat temporal cortex slices containing the hippocampus and the entorhinal cortex. Elevating [K+]o0 induced seizure-like events with tonic and clonic electrographic phases in area CA1. Lowering [Ca2+]0 caused recurrent seizure like episodes with large negative field potential shifts. Lowering Mg2+ induced short recurrent discharges in area CA3 and CA1 while ictaform events lasting for many seconds were induced in the subiculum, entorhinal and temporal neocortex. In the hippocampus the activity stayed stable over a number of hours. In contrast, the ictaform events in the subiculum, entorhinal and temporal cortex changed their characteristics after one to two hours to late recurrent discharges. In a concentration-range from 10 to 100 μM methysticin reversibly blocked all these types of epileptiform activity. Decreases in [Ca2+]0 and associated slow field potentials evoked by repetitive stimulation of the stratum radiatum or the alveus remained almost unaffected by methysticin. A paired pulse stimulus paradigm used to test for effects of methysticin on synaptically evoked transient field potentials in normal medium revealed interference with mechanisms involved in frequency potentiation. While responses to alvear stimulation were largely unaffected, the responses to a paired pulse stimulus to stratum radiatum were depressed over the whole range of tested stimulus intervals. The findings suggest that methysticin has effects on different patterns of epileptiform activity possibly by interfering with processes responsible for frequency potentiation.
(https://pubmed.ncbi.nlm.nih.gov/7630425/)

Mathews, J. M., Etheridge, A. S., Valentine, J. L., Black, S. R., Coleman, D. P., Patel, P., So, J. & Burka, L. T. Pharmacokinetics and disposition of the kavalactone kawain: Interaction with kava extract and kavalactones in vivo and in vitro. Drug Metabolism and Disposition 33, 1555-1563 (2005).

Abstract:
Reported adverse drug interactions with the popular herb kava have spurred investigation of the mechanisms by which kava could mediate these effects. In vivo and in vitro experiments were conducted to examine the effects of kava extract and individual kavalactones on cytochrome P450 (P450) and P-glycoprotein activity. The oral pharmacokinetics of the kavalactone, kawain (100 mg/kg), were determined in rats with and without coadministration of kava extract (256 mg/kg) to study the effect of the extract on drug disposition. Kawain was well absorbed, with >90% of the dose eliminated within 72 h, chiefly in urine. Compared with kawain alone, coadministration with kava extract caused a tripling of kawain AUC0–8 h and a doubling of Cmax. However, a 7-day pretreatment with kava extract (256 mg /kg/day) had no effect on the pharmacokinetics of kawain administered on day 8. The 7-day pretreatment with kava extract only modestly induced hepatic P450 activities. The human hepatic microsomal P450s most strongly inhibited by kava extract (CYP2C9, CYP2C19, CYP2D6, CYP3A4) were inhibited to the same degree by a “composite” kava formulation composed of the six major kavalactones contained in the extract. Ki values for the inhibition of CYP2C9 and CYP2C19 activities by methysticin, dihydromethysticin, and desmethoxyyangonin ranged from 5 to 10 μM. Kava extract and kavalactones (≤9 μM) modestly stimulated P-glycoprotein ATPase activities. Taken together, the data indicate that kava can cause adverse drug reactions via inhibition of drug metabolism.
(https://doi.org/10.1124/dmd.105.004317)

Krum, B. N., Molz de Freitas, C., Chiapinotto Ceretta, A. P., Barbosa, C. P., de Moraes Reis, E., Scussel, R., da Silva Córneo, E., Machado-de-Ávila, R. A., Boligon, A. A., & Fachinetto, R. (2020). Kava decreases the stereotyped behavior induced by amphetamine in mice. Journal of Ethnopharmacology, 265(July 2020).

Abstract:
Ethnopharmacological relevance
Kava extract (Piper methysticum) is a phytotherapic mainly used for the treatment of anxiety. Although the reported effects of Kava drinking improving psychotic symptoms of patients when it was introduced to relieve anxiety in aboriginal communities, its effects on models of psychosis-like symptoms are not investigated.

Aim of the study
To investigate the effects of Kava extract on behavioral changes induced by amphetamine (AMPH) and its possible relation with alterations in monoamine oxidase (MAO) activity.

Materials and methods
Mice received vehicle or Kava extract by gavage and, 2 h after vehicle or AMPH intraperitoneally. Twenty-five minutes after AMPH administration, behavioral (elevated plus maze, open field, stereotyped behavior, social interaction and Y maze) and biochemical tests (MAO-A and MAO-B activity in cortex, hippocampus and striatum) were sequentially evaluated.

Results
Kava extract exhibited anxiolytic effects in plus maze test, increased the locomotor activity of mice in open field test and decreased MAO-A (in cortex) and MAO-B (in hippocampus) activity of mice. Kava extract prevented the effects of AMPH on stereotyped behavior and, the association between Kava/AMPH increased the number of entries into arms in Y maze test as well as MAO-B activity in striatum. However, Kava extract did not prevent hyperlocomotion induced by AMPH in open field test. The social interaction was not modified by Kava extract and/or AMPH.

Conclusion
The results showed that Kava extract decreased the stereotyped behavior induced by AMPH at the same dose that promotes anxiolytic effects, which could be useful to minimize the psychotic symptoms in patients.
(https://doi.org/10.1016/j.jep.2020.113293)

Boonen1, G., Ferger2, B., Kuschinsky2, K., & Häberleinl, H. (1998). In vivo Effects of the Kavapyrones (+)- dihydromethysticin and (±)-Kavain on Dopamine, 3,4-Dihydroxyphenylacetic Acid, Serotonin and 5-Hydroxyindoleacetic Acid Levels in Striatal and Cortical Brain Regions. 4.Watkins, L. L., Connor, K. M. & Davidson, J. R. Effect of kava extract on vagal cardiac control in generalized anxiety disorder: Preliminary findings. Journal of Psychopharmacology 15, 283-286 (2001).

Abstract:
The in vivo effect of a single oral dose of 100 mg (+)-dihydromethysticin/kg body weight on striatal and cortical tissue concentrations of dopamine, serotonin, 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid, as well as the dopamine and serotonin turnover, was tested in rats. Additionally, other rats were fed with a (+/-)-kavain containing food over a period of 78 days in order to calculate the influence of a chronic treatment with kavapyrones on the neurotransmitters. The results of the present in vivo study clearly demonstrate that neither (+)-dihydromethysticin in a high single dose, nor (+/-)-kavain chronically administered, altered the dopaminergic or serotonergic tissue levels in rats significantly.
(https://pubmed.ncbi.nlm.nih.gov/9741294/)

Davies, L. P., Drew, C. A., Duftield, P., {R Johnston}, G. A. & Jamieson, D. D. Kava Pyrones and Resin: Studies on GABAA, GABAB and Benzodiazepine Binding Sites in Rodent Brain. Pharmacology & Toxicology 71, 120-126 (1992).

Abstract:
Kava, an intoxicating beverage prepared from the pepper plant Piper methysticum, is widely consumed by the indigenous peoples in the islands of the South Pacific. As the first of a series of studies on the neuropharmacological interactions of kava with CNS receptors we tested purified pyrones and kava resin for activity on GABA and benzodiazepine binding sites in rat and mouse brain membranes. Only weak activity was observed on GABAA binding sites in washed synaptosomal membranes prepared from rat brain and this was abolished by extraction of the membranes with Triton X‐100, suggesting that lipid soluble components were involved. No effects were observed on GABAa binding sites in rat brain membranes in vitro. Kava resin and pyrones exerted some weak effects on benzodiazepine binding in vitro but this did not correlate with pharmacological activity. In addition, in ex vivo studies, no effects were observed on [3H]diazepam binding to brain membranes prepared from mice in which selected kava constituents were injected intraperitoneally, whereas similarly administered diazepam (5 mg/kg) inhibited [3H]diazepam binding by >95%. Similar lack of activity was observed in in vivo binding studies; injection of kava resin failed to influence the CNS binding of the benzodiazepine‐receptor ligand [3H]Ro15‐1788 injected into mice prior to sacrifice. The pharmacological activities of kava resin and pyrones do not appear to be explained by any significant interaction with GABA or benzodiazepine binding sites.
(https://doi.org/10.1111/j.1600-0773.1992.tb00530.x)

Yuan Chun-Su, Dey, L., Wang, A., Mehendale, S., Xie Jing, Aung Han, & Ang-Lee Michael. (2002). Kavalactones and Dihdrokavain Modulate GABAergic Activity in Rat Gastric-Brainstem Preparation. Planta Medica, 1092–1096.

Abstract:
Using an in vitro neonatal rat gastric-brainstem preparation, the activity of majority neurons recorded in the nucleus tractus solitarius (NTS) of the brainstem were significantly inhibited by GABA A receptor agonist, muscimol (30 microM), and this inhibition was reversed by selective GABA A receptor antagonist, bicuculline (10 microM). Application of kavalactones (300 microg/ml) and dihydrokavain (300 microM) into the brainstem compartment of the preparation also significantly reduced the discharge rate of these NTS neurons (39 % and 32 %, respectively, compared to the control level), and this reduction was partially reversed by bicuculline (10 microM). Kavalactones or dihydrokavain induced inhibitory effects were not reduced after co-application of saclofen (10 microM; a selective GABA B receptor antagonist) or naloxone (100 nM; an opioid receptor antagonist). Pretreatment with kavalactones (300 microg/ml) or dihydrokavain (300 microM) significantly decreased the NTS inhibitory effects induced by muscimol (30 microM), approximately from 51 % to 36 %. Our results demonstrated modulation of brainstem GABAergic mechanism by kavalactones and dihydrokavain, and suggested that these compounds may play an important role in regulation of GABAergic neurotransmission.
(https://pubmed.ncbi.nlm.nih.gov/12494336/)

Sällström Baum, S., Hill, R., & Rommelspacher, H. (1998). Effect of kava extract and individual kavapyrones on neurotransmitter levels in the nucleus accumbens of rats. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 22(7), 1105–1120.

Abstract:

1. Kavapyrones have well-known psychotropic properties. The most common actions of the extract are relaxation and euphoria, depending on the circumstances of ingestion, whereas higher doses cause sleepiness and skeletal muscle relaxation. Several other actions have been reported such as anticonvulsant properties, neuroprotection and analgesia. No interactions with neuroreceptors have yet been found that would explain the multiple actions.

2. To reveal neuronal functions affected by the kavapyrones the authors studied their actions on the mesolimbic reward system using in vivo microdialysis.

3. A small dose of kava extract (20 mg/kg body weight i.p.) caused changes in rat behaviour and concentrations of dopamine in the nucleus accumbens. Higher doses (120 mg/kg i.p.) increased the levels of dopamine. With respect to the individual compounds, D,L-kawain induced in low doses a decrease in dopamine levels and in higher amounts either an increase or no change In dopamine concentrations. Yangonin resulted in a decrease of dopamine levels to below the detection limit and desmethoxyyangonin in an increase of dopamine levels. Dihydrokawain, methysticin and dihydromethysticin did not produce any significant changes of dopamine levels. D,L-kawain caused a decrease in 5-HT concentrations. Some of the other kavapyrones affected 5-HT levels as well.

4. The results suggest that the relaxing and slightly euphoric actions may be caused by the activation of the mesolimbic dopaminergic neurones. Changes of the activity of 5-HT neurones could explain the sleep-inducing action.
(https://doi.org/10.1016/S0278-5846(98)00062-1)

Tang, X. & Amar, S. Kavain Involvement in LPS-Induced Signaling Pathways. J. Cell. Biochem. , 2272-2280 (2016).

Abstract:
Kavain, a compound extracted from the Kava plant, Piper methysticum, is found to be involved in TNF‐α expression in human and mouse cells via regulation of transcriptional factors such as NF‐kB and LITAF. LITAF is known to activate the transcription of more than 20 cytokines that are involved in a variety of cellular processes and is associated with many inflammatory diseases, including angiogenesis, cancer, arthritis, and more. The modulation of LITAF is expected to positively affect cytokine‐mediated diseases. Thus, intensive efforts have been deployed in search of LITAF inhibitors. In this work, we found that, in vitro, Kavain reduced LPS‐ induced TNF‐α secretion in mouse macrophages, mouse bone marrow macrophages (BMM), and human peripheral blood mononuclear cells (HPBMC). We also found that Kavain treatment in RAW264.7 cells deactivated MyD88 and Akt, inhibited LITAF, and reduced the production of TNF‐α, IL‐27, and MIG in response to LPS. Similarly, it had a significant in vivo anti‐inflammatory effect on wild‐type (WT) mice that developed Collagen Antibody Induced Arthritis (CAIA). Overall, MyD88 was found to be an important mediator of the LPS‐induced inflammatory response that can be distinguished from the NF‐κB pathway. We also found that MyD88 is involved in the pathway linking LPS/LITAF to TNF‐α. Therefore, given that Kavain modulates LPS‐induced signaling pathways leading to cytokine expression, therapeutic interventions involving Kavain in inflammatory diseases are warranted.
(https://doi.org/10.1002/jcb.25525)

Prinsloo, D., Van Dyk, S., Petzer, A. & Petzer, J. P. Monoamine Oxidase Inhibition by Kavalactones from Kava (Piper Methysticum). Planta Med. 85, 1136-1142 (2019).

Abstract:
Monoamine oxidases (MAOs) are key metabolic enzymes for neurotransmitter and dietary amines and are targets for the treatment of neuropsychiatric and neurodegenerative disorders. This study examined the MAO inhibition potential of kavain and other kavalactones from the roots of kava (Piper methysticum), a plant that has been used for its anxiolytic properties. (±)-Kavain was found to be a good potency in vitro inhibitor of human MAO-B with an IC50 of 5.34 µM. (±)-Kavain is a weaker MAO-A inhibitor with an IC50 of 19.0 µM. Under the same experimental conditions, the reference MAO inhibitor, curcumin, displays IC50 values of 5.01 µM and 2.55 µM for the inhibition of MAO-A and MAO-B, respectively. It was further established that (±)-kavain interacts reversibly and competitively with MAO-A and MAO-B with enzyme-inhibitor dissociation constants (Ki) of 7.72 and 5.10 µM, respectively. Curcumin in turn, displays a Ki value of 3.08 µM for the inhibition of MAO-A. Based on these findings, other kavalactones (dihydrokavain, methysticin, dihydromethysticin, yangonin, and desmethoxyyangonin) were also evaluated as MAO inhibitors in this study. Yangonin proved to be the most potent MAO inhibitor with IC50 values of 1.29 and 0.085 µM for MAO-A and MAO-B, respectively. It may be concluded that some of the central effects (e.g., anxiolytic) of kava may be mediated by MAO inhibition.
(https://doi.org/10.1055/a-1008-9491)

Magura, E. I., Kopanitsa, ‡. M. V., Gleitz, J., Peters, T. & Krishtal, O. A. Kava extract ingredients, (+)-methysticin and (±)-kavain inhibit voltage-operated Na+-channels in rat CA1 hippocampal neurons. Neuroscience 81, 345-351 (1997).

Abstract:
The action of synthetic kava pyrones, (+)-methysticin and (±)-kavain, on voltage-operated Na+-channels was studied in whole-cell patch-clamped CA1 hippocampal neurons. In doses of 1–400 μM, both compounds exerted a rapid and reversible inhibition of the peak amplitude of Na+-currents. Shifting holding membrane potential (Vhold) to more positive values enhanced their blocking effect. The drugs studied did not demonstrate use-dependent properties at 10 Hz stimulation but shifted h∞ curve toward more negative potentials, accelerated time course of inactivation and slowed down the recovery from inactivation.

Voltage-dependence of Na+-channel inhibition can be explained by interaction of (+)-methysticin and (±)-kavain with resting closed and inactivated states of Na+-channel.
(https://doi.org/10.1016/s0306-4522(97)00177-2)

Wruck, C. J., Götz, M. E., Herdegen, T., Varoga, D., Brandenburg, L. O., & Pufe, T. (2008). Kavalactones protect neural cells against amyloid β peptide-induced neurotoxicity via extracellular signal-regulated kinase 1/2-dependent nuclear factor erythroid 2-related factor 2 activation. Molecular Pharmacology, 73(6), 1785–1795.

Abstract:
One hallmark of Alzheimer's disease is the accumulation of amyloid β-peptide (AP), which can initiate a cascade of oxidative events that may result in neuronal death. Because nuclear factor erythroid 2-related factor 2 (Nrf2) is the major regulator for a battery of genes encoding detoxifying and antioxidative enzymes via binding to the antioxidant response element (ARE), it is of great interest to find nontoxic activators of Nrf2 rendering neuronal cells more resistant to AP toxicity. Using ARE-luciferase assay and Western blot, we provide evidence that the kavalactones methysticin, kavain, and yangonin activate Nrf2 time- and dose-dependently in neural PC-12 and astroglial C6 cells and thereby up-regulate cytoprotective genes. Viability and cytotoxicity assays demonstrate that Nrf2 activation is able to protect neural cells from amyloid β-(1-42) induced neurotoxicity. Down-regulation of Nrf2 by small hairpin RNA as well as extracellular signal-regulated kinase 1/2 inhibition abolishes cytoprotection. We further give evidence that kavalactone-mediated Nrf2 activation is not dependent on oxidative stress production. Our results demonstrate that kavalactones attenuate amyloid β-peptide toxicity by inducing protective gene expression mediated by Nrf2 activation in vitro. These findings indicate that the use of purified kavalactones might be considered as an adjunct therapeutic strategy to combat neural demise in Alzheimer disease and other oxidative stress-related diseases.
(https://doi.org/10.1124/mol.107.042499)

Tarbah, F., Mahler, H., Kardel, B., Weinmann, W., Hafner, D. & Daldrup, T. Kinetics of kavain and its metabolites after oral application. J. Chromatogr. B: Anal. Technol. Biomed. Life Sci. 789, 115-130 (2003).

Abstract:
Kavain metabolism in humans was the target of this current investigation. In the present study a high-performance liquid chromatographic (HPLC–DAD) assay method for the simultaneous determination of kavain and its main metabolites (p-hydroxykavain, p-hydroxy-5,6-dehydrokavain and p-hydroxy-7,8-dihydrokavain) in serum and urine was developed and validated. The metabolites were mainly excreted in the form of their conjugates. All kavain metabolites were detectable in serum and urine, except for p-hydroxy-7,8-dihydrokavain, which was found in urine only. Confirmation of the results and identification of the metabolites were performed by LC–MS or LC–MS–MS. Kinetics of kavain and its metabolites in serum were investigated after administration of a single oral dose (800 mg kavain). Within 1 and 4 h after uptake, the serum concentrations ranged between 40 and 10 ng/ml for kavain, 300 and 125 ng/ml for p-hydroxykavain, 90 and 40 ng/ml for o-desmethyl-hydroxy-5,6-dehydrokavain, and 50 and 30 ng/ml for 5,6-dehydrokavain.
(https://doi.org/10.1016/s1570-0232(03)00046-1)

Backhauß, C., & Krieglstein, J. (1992). Extract of kava (Piper methysticum) and its methysticin constituents protect brain tissue against ischemic damage in rodents. European Journal of Pharmacology, 215(2–3), 265–269.

Abstract:
The purpose of the present study was to test whether kava extract and its constituents kawain, dihydrokawain, methysticin, dihydromethysticin and yangonin provide protection against ischemic brain damage. To this end, we used a model of focal cerebral ischemia in mice and rats. Ischemia was induced by microbipolar coagulation of the left middle cerebral artery (MCA). To quantify the size of the lesion in mice, the area of the infarct on the brain surface was assessed planimetrically 48 h after MCA occlusion by transcardial perfusion of carbon black. In the rat model infarct volume was determined 48 h after MCA occlusion by planimetric analysis and subsequent integration of the infarct areas on serial coronal slices. Compounds were administered i.p., except the kava extract, which was administered orally. The effects of the kava extract and its constituents were compared with those produced by the typical anticonvulsant, memantine. The kava extract, methysticin and dihydromethysticin produced effects similar to those of the reference substance memantine. The kava extract (150 mg/kg, 1 h before ischemia) diminished the infarct area (P<0.05) in mouse brains and the infarct volume (P<0.05) in rat brains. Methysticin, dihydromethysticin (both 10 and 30 mg/kg, 15 min before ischemia) and memantine (20 mg/kg, 30 min before ischemia) significantly reduced the infarct area in mouse brains. All other compounds failed to produce a beneficial effect on the infarct area in mouse brains. In conclusion, the kava extract exhibited neuroprotective activity, which was probably mediated by its constituents methysticin and dihydromethysticin.
(https://doi.org/10.1016/0014-2999(92)90037-5)

Boonen G, Häberlein H. Influence of genuine kavapyrone enantiomers on the GABA-A binding site. Planta Med. 1998 Aug;64(6):504-6. doi: 10.1055/s-2006-957502. PMID: 9776662.

Abstract:
The influence of kavapyrones from Piper methysticum Forst. on the GABAA receptor was demonstrated using radioreceptor assays. Both the dienolide yangonin and the genuine enolide enantiomers (+)-kavain, (+)-dihydrokavain, (+)-methysticin, and (+)-dihydromethysticin enhanced the specific binding of [3 H]bicuculline methochloride ([3 H]BMC). The kavapyrones have been investigated at assay concentrations between 100 µM and 10 nM. (+)-Kavain, (+)-methysticin and (+)-dihydromethysticin showed maximal enhancements of 18% to 28% at a concentration of 0.1 µM, whereas a 100-fold concentration of (+)-dihydrokavain revealed a similar modulatory activity of 22%. In the presence of 1 µM yangonin an increase of about 21% of the specific [3 H]BMC binding was observed. Desmethoxy-yangonin did not alter the binding behavior of the GABAA-receptor. A structure comparison of desmethoxyyangonin and yangonin indicated that the aromatic methoxy group was of particular importance for the modulatory activity. In contrast, the substitution pattern of the aromatic ring did not influence the modulatory activity of the enolides in a decisive manner. A structure comparison of desmethoxyyangonin and (+)-kavain revealed that an angular lactone ring was an important structure requirement. Both the enolides and the dienolides did not inhibit the specific binding of [3 H]flunitrazepam. Thus, the influence on the GABAA receptor was not based upon an interaction of these kavapyrones with the benzodiazepine receptor.
(https://doi.org/10.1055/s-2006-957502)

Open Access Article
Chua, H. C., Christensen, E. T., Hoestgaard-Jensen, K., Hartiadi, L. Y., Ramzan, I., Jensen, A. A., Absalom, N. L. & Chebib, M. Kavain, the major constituent of the anxiolytic kava extract, potentiates gabaa receptors: Functional characteristics and molecular mechanism. PLoS One 11, 1-17 (2016).

Abstract:
Extracts of the pepper plant kava (Piper methysticum) are effective in alleviating anxiety in clinical trials. Despite the long-standing therapeutic interest in kava, the molecular target(s) of the pharmacologically active constituents, kavalactones have not been established. γ-Aminobutyric acid type A receptors (GABAARs) are assumed to be the in vivo molecular target of kavalactones based on data from binding assays, but evidence in support of a direct interaction between kavalactones and GABAARs is scarce and equivocal. In this study, we characterised the functional properties of the major anxiolytic kavalactone, kavain at human recombinant α1β2, β2γ2L, αxβ2γ2L (x = 1, 2, 3 and 5), α1βxγ2L (x = 1, 2 and 3) and α4β2δ GABAARs expressed in Xenopus oocytes using the two-electrode voltage clamp technique. We found that kavain positively modulated all receptors regardless of the subunit composition, but the degree of enhancement was greater at α4β2δ than at α1β2γ2L GABAARs. The modulatory effect of kavain was unaffected by flumazenil, indicating that kavain did not enhance GABAARs via the classical benzodiazepine binding site. The β3N265M point mutation which has been previously shown to profoundly decrease anaesthetic sensitivity, also diminished kavain-mediated potentiation. To our knowledge, this study is the first report of the functional characteristics of a single kavalactone at distinct GABAAR subtypes, and presents the first experimental evidence in support of a direct interaction between a kavalactone and GABAARs.
(https://doi.org/10.1371/journal.pone.0157700)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/27332705/)

Ligresti, A., Villano, R., Allarà, M., Ujváry, I., & Di Marzo, V. (2012). Kavalactones and the endocannabinoid system: The plant-derived yangonin is a novel CB 1 receptor ligand. Pharmacological Research, 66(2), 163–169.

Abstract:
To investigate the possible interactions between kavalactone-based molecules and proteins of the endocannabinoid system and provide novel and synthetically accessible structural scaffolds for the design of cannabinoid receptor ligands sharing pharmacological properties with kavapyrones, a preliminary SAR analysis was performed on five commercially available natural kavalactones and nine kavalactone-analogues properly synthesized. These compounds were investigated for assessing their cannabinoid receptor binding affinity and capability of inhibiting the activity of the two major metabolic enzymes of the endocannabinoid system, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Among the molecules tested, only yangonin exhibited affinity for the human recombinant CB1 receptor with a Ki = 0.72 μM and selectivity vs. the CB2 receptor (Ki > 10 μM). None of the compounds exhibited strong inhibitory effects on the two enzymes analyzed. The CB1 receptor affinity of yangonin suggests that the endocannabinoid system might contribute to the complex human psychopharmacology of the traditional kava drink and the anxiolytic preparations obtained from the kava plant.
(https://doi.org/10.1016/j.phrs.2012.04.003)

Keledjian, J., Duffield~, P. H., Jamieson, D. D., Lidcards, R. 0, & Duffields, A. M. (1988). Uptake into Mouse Brain of Four Compounds Present in the Psychoactive Beverage Kava. Journal of Pharmaceutical Sciences, 77(12), 1003–1006.

Abstract:
A technique using gas chromatography–mass spectrometry and deuterated internal standards is described for the quantitation in brain tissue of four constituents of the intoxicating beverage kava. Dihydrokawain, kawain, desmethoxyyangonin, and yangonin were administered ip to mice at a dosage of 100 mg/kg. At specific time intervals (5, 15, 30, and 45 min), the mice were sacrificed and the brain concentrations of these four compounds determined. After 5 min, dihydrokawain and kawain attained maximum concentrations of 64.7 ± 13.1 and 29.3 ± 0.8 ng/mg wet brain tissue, respectively, and were rapidly eliminated. In contrast, desmethoxyyangonin and yangonin had poorly defined maxima corresponding to concentrations of 10.4 ± 1.5 and 1.2 ± 0.3 ng/mg wet brain tissue, respectively, and these compounds were more slowly eliminated from brain tissue. When crude kava resin was administered ip at a dosage of 120 mg/kg, the concentration in brain of kawain and yangonin markedly increased (2 and 20 times, respectively) relative to the values measured from their individual injection. In contrast, dihydrokawain and desmethoxyyangonin, after the administration of crude resin, remained at the percentage incorporation into brain tissue established for their individual ip injection.
(https://doi.org/10.1002/jps.2600771203).

Anxiety Focused Studies

Connor, K., Davidson, J., & Connor, K. M. (2002). A placebo-controlled study of Kava kava in generalized anxiety disorder.

Abstract:
We assessed the efficacy and safety of a botanical anxiolytic, Kava kava (Piper methysticum), in treating generalized anxiety disorder (GAD). Thirty-seven adults with DSM-IV GAD were randomly assigned to 4 weeks of double-blind treatment with kava or a matching placebo. Weekly efficacy assessments [Hamilton Anxiety Scale, Hospital Anxiety and Depression Scale (HADS), Self Assessment of Resilience and Anxiety (SARA)] and safety evaluations were conducted. Improvement was observed with both treatments but no differences were found in the principal analysis. Post-hoc analyses revealed significant differences based on baseline anxiety severity, whereby kava was superior on the SARA in low anxiety and placebo was superior on the HADS and SARA in high anxiety. Both treatments were well tolerated. Although kava was not superior to placebo, it would be premature to rule it out as efficacious in GAD.
(https://doi.org/10.1097/00004850-200207000-00005)

Kuchta, K., Hladikova, M., Thomsen, M., Nahrstedt, A. & Schmidt, M. Kava (Piper methysticum) Extract for the Treatment of Nervous Anxiety, Tension and Restlessness. Drug Res (Stuttg) 71, 83-93 (2021).

Abstract:
Aim: Prior to the kava ban of 2002, the indication for kava (Piper methysticum) extracts defined by the German Commission E was "nervous anxiety, tension and restlessness". In 2000, an observational trial was started in Germany with the aim of defining symptoms of these indications best treated with kava extract. The trial was interrupted and archived "unevaluated" in 2001 due to the upcoming safety debate on kava. The data from this study has now been analyzed in order to identify symptoms best treated with kava.

Methods: Documentation was available from 156 patients. Twelve typical symptoms of nervous anxiety, tension and restlessness were assessed on a five-item rating scale, together with the therapeutic context, the perceived time of onset of effects and the safety of application.

Results: The median duration of treatment was 28 days. All individual symptoms showed significant and clinically relevant improvements. The most effective results were seen for nervous tension and restlessness, with better effects in patients with acute versus chronic complaints. The safety of the treatment was found to be excellent, which included the assessment of laboratory data.

Conclusions: Overall, the study confirms the effective and safe short-term use of kava in the Commission E-defined indication of "nervous anxiety, tension and restlessness", especially in other than chronic cases. The clinical use of kava might be translated into context-related phobias according to ICD-10 F40, or to nervous tension (ICD10 R45.0) or restlessness and excitation (ICD-10 R45.1).
(https://pubmed.ncbi.nlm.nih.gov/33207379/)

Boerner, R. J., Kava kava in the treatment of generalized anxiety disorder, simple phobia and specific social phobia. Phytotherapy Research 15, 646-647 (2001).

Abstract:
A 37‐year‐old female outpatient with generalized anxiety disorder, a simple phobia and a specific social phobia was treated with phytotherapy (Kava kava). Within 4 weeks, symptoms had improved by 75% and by 6 months an almost total remission of symptoms was observed. The herbal medicine was well tolerated. Kava has considerable potential value in the treatment of anxiety disorders.
(https://doi.org/10.1002/ptr.1006)

Open Access Article
Luxminarayan, L., Neha, S., Amit, V. & Khinchi, M. A Research Article on Antistress Activity of Herbal Extract Oil of Piper Methysticum on Wistar Albino. Asian Journal of Pharmaceutical Research and Development. Asian Journal of Pharmaceutical Research and Development 5, 1-8 (2017).

Abstract:
The research was carried out to determine the antistress activity of piper methysticum and the animal model used was wistar albino due to it’s worldwide acceptability in researches related to psychology .kava (piper methysticum) root extract was used for abundance of kavlactones hence for the sake of study different percentage of suspensions like 4%, 6%, 8%, 12%, 18%, 30% were prepared and diazepam was selected as standard drug.oecd guideline 423 was followed during acute toxicity studies.no symptoms of acute toxicity was seen during 14 days observational period when given a dose of 2000 mg/kg so on this basis two dose level of 200mg/kg and 400 kg were selected for antistress activity.test model selected for antistress activity were forced swim test, tail suspension test and anoxia stress tolerance test.for respective tests a sharp decline in duration of immobility and increase in anoxia stress tolerance was seen.hence we can conclude that piper methysticum can play a significant role in the field of treating stress after futhur extensive clinical research.
(https://ajprd.com/index.php/journal/article/view/892)

Lehrl, S., Clinical efficacy of kava extract WS1490 in sleep disturbances associated with anxiety disorders: Results of a multicenter, randomized, placebo-controlled, double-blind clinical trial. Journal of Affective Disorders 78, 101-110 (2004).

Abstract:
Background: The aim of the present trial was to investigate the efficacy and safety of kava special extract WS® 1490 in patients with sleep disturbances associated with anxiety, tension and restlessness states of non-psychotic origin.

Methods: In a multicenter, randomized, double-blind clinical study, 61 patients received daily doses of 200 mg WS® 1490 or placebo over a period of 4 weeks. Efficacy was measured by the sleep questionnaire SF-B, the Hamilton Anxiety Scale (HAMA), the Bf-S self-rating scale of well-being and the Clinical Global Impressions (CGI) scale.

Results: The confirmatory analysis of the two primary efficacy variables, the differences of sleep questionnaire SF-B sub-scores ‘Quality of sleep’ and ‘Recuperative effect after sleep’ after 4 weeks of double-blind treatment compared to baseline, demonstrated statistically significant group differences in favor of kava extract WS® 1490 (P=0.007 and P=0.018, respectively). Superior effects of kava extract were also present in the HAMA psychic anxiety sub-score (P=0.002). More pronounced effects with respect to the self-rating of well-being and the global clinical evaluation also indicated superior therapeutic efficacy of kava extract. Safety and tolerability were good, with no drug-related adverse events or changes in clinical or laboratory parameters.

Conclusions: We conclude that sleep disturbances associated with non-psychotic anxiety disorders can be effectively and safely treated with kava extract WS® 1490.
(https://pubmed.ncbi.nlm.nih.gov/14706720/)

Open Access Article
Chaurasiya, N. D., León, F., Ding, Y., Gómez-Betancur, I., Benjumea, D., Walker, L. A., Cutler, S. J., & Tekwani, B. L. (2017). Interactions of Desmethoxyyangonin, a Secondary Metabolite from Renealmia alpinia, with Human Monoamine Oxidase-A and Oxidase-B. Evidence-Based Complementary and Alternative Medicine, 2017.

Abstract:
Renealmia alpinia (Zingiberaceae), a medicinal plant of tropical rainforests, is used to treat snakebites and other injuries and also as a febrifuge, analgesic, antiemetic, antiulcer, and anticonvulsant. The dichloromethane extract of R. alpinia leaves showed potent inhibition of human monoamine oxidases- (MAOs-) A and B. Phytochemical studies yielded six known compounds, including pinostrobin
1, 4′-methyl ether sakuranetin
2, sakuranetin
3, pinostrobin chalcone
4, yashabushidiol A
5, and desmethoxyyangonin
6. Compound 6 displayed about 30-fold higher affinity for MAO-B than MAO-A, with Ki values of 31 and 922 nM, respectively. Kinetic analysis of inhibition and equilibrium-dialysis dissociation assay of the enzyme-inhibitor complex showed reversible binding of desmethoxyyangonin 6 with MAO-A and MAO-B. The binding interactions of compound 6 in the active site of the MAO-A and MAO-B isoenzymes, investigated through molecular modeling algorithms, confirmed preferential binding of desmethoxyyangonin 6 with MAO-B compared to MAO-A. Selective reversible inhibitors of MAO-B, like desmethoxyyangonin 6, may have important therapeutic significance for the treatment of neurodegenerative disorders, such as Parkinson’s disease and Alzheimer’s disease.
(https://doi.org/10.1155/2017/4018724)

Sharma, A., Anchariya, R. & Dubey, C. Asian Journal of Pharmaceutical Research and Development A Review on Anti-Stress Activity of Piper Methysticum. 8, 130-136 (2020).

Abstract:
On the basis of study conducted on the plant Piper methysticum G. (Forst), Piperaceae, it was found that Kava has storage of active constituents present in its roots and rhizomes. Traditionally its root part is used to relax body and mind and promote restful sleep, therefore it is necessary to explore its importance as excellent nervine herb. Literature survey revealed that kavalactones are responsible for biological activity which include local anaesthetic, antispasmodic, Musculo-relaxant, antimycotic, sedative, anticonvulsive, analgesic, antianxiety and neuroprotective effects etc. which proves it has potent psychoactive ability but, the claim of therapeutic efficacy of the plant as an anti-stress or adaptogen yet has not been scientifically scrutinized. However, synthetic drugs are widely prescribed to reduce stress and stress induced symptoms but their soporific effect, risk of dependence and withdrawal effects limits their long-term use. Based on clinical studies Kava shows its efficacy within one week at moderate dose. Evidently, the herbal formulations claimed to enhance physical endurance; mental functions and non-specific resistance to withstand stress without altering the physiological functions of the body hence, it is essential to study its safety and efficacy for its therapeutic use.
(https://ajprd.com/index.php/journal/article/view/688)

H.-P. Volz, M. K., Kava-kava Extract WS 1490 versus Placebo in Anxiety Disorders-A Randomized Placebo-controlled 25-week Outpatient Trial. Pharmacopsychiatry 30, 1-5 (1997).

Abstract:
101 outpatients suffering from anxiety of non-psychotic origin (DSM-III-R criteria: agoraphobia, specific phobia, generalized anxiety disorder, and adjustment disorder with anxiety) were included in a 25-week multicenter randomized placebo-controlled double-blind trial with WS 1490, a special extract of kava-kava. In the main outcome criterion, the Hamilton Anxiety Scale (HAMA), there was a significant superiority of the test drug starting from week 8 on. WS 1490 was also found to be superior with respect to the secondary outcome variables. HAMA subscores somatic and psychic anxiety, Clinical Global Impression, Self-Report Symptom Inventory - 90 Items revised, and Adjective Mood Scale. Adverse events were rare and distributed evenly in both groups. These results support WS 1490 as a treatment alternative to tricyclic antidepressants and benzodiazepines in anxiety disorders, with proven long-term efficacy and none of the tolerance problems associated with tricyclics and benzodiazepines.
(https://doi.org/10.1055/s-2007-979474)

Singh, Y. N. & Singh, N. N. Therapeutic potential of kava in the treatment of anxiety disorders. CNS Drugs 16, 731-743 (2002).

Abstract:
Anxiety disorders are among the most common psychiatric disorders that affect all age groups of the general population. Currently, the preferred treatment is with pharmacological drugs that have antidepressant or anti-anxiety properties. However, these agents have numerous and often serious adverse effects, including sedation, impaired cognition, ataxia, aggression, sexual dysfunction, tolerance and dependence. Withdrawal reactions on termination after long-term administration are also a major limiting factor in the use of these agents. Herbal remedies, including kava (Piper methysticum), have been shown to be effective as alternative treatments, at least in mild to moderate cases of anxiety. Kava is a social and ceremonial herb from the South Pacific. It is available in the west as an over-the-counter preparation. Its biological effects, due to a mixture of compounds called kavalactones, are reported to include sedative, anxiolytic, antistress, analgesic, local anaesthetic, anticonvulsant and neuroprotective properties. The pharmacological properties of kava are postulated to include blockade of voltage-gated sodium ion channels, enhanced ligand binding to gamma-aminobutyric acid (GABA) type A receptors, diminished excitatory neurotransmitter release due to calcium ion channel blockade, reduced neuronal reuptake of noradrenaline (norepinephrine), reversible inhibition of monoamine oxidase B and suppression of the synthesis of the eicosanoid thromboxane A(2), which antagonises GABA(A) receptor function. Clinical studies have shown that kava and kavalactones are effective in the treatment of anxiety at subclinical and clinical levels, anxiety associated with menopause and anxiety due to various medical conditions. Until recently, the adverse effects attributed to kava use were considered mild or negligible, except for the occurrence of a skin lesion. This disorder, called kava dermopathy, occurs only with prolonged use of large amounts of kava and is reversible on reduced intake or cessation. Rare cases of interactions have occurred with pharmaceutical drugs that share one or more mechanisms of action with the kavalactones. In the past few years, about 35 cases of severe liver toxicity associated with kava intake have been reported in Europe and the US. However, a direct causal relationship with kava use has been difficult to establish in the majority of the cases, and there is insufficient evidence to implicate kava as the responsible agent. Nevertheless, until further research clarifies any causality, kava should be used with caution.
(https://pubmed.ncbi.nlm.nih.gov/12383029/)

Kuchta, K., de Nicola, P. & Schmidt, M. Randomized, dose-controlled double-blind trial: Efficacy of an ethanolic kava ( Piper methysticum rhizome) extract for the treatment of anxiety in elderly patients. Traditional & Kampo Medicine 5, 3-10 (2018).

Abstract:
Aim
Kava, an aqueous drink from the roots and peeled rootstock of the plant Piper methysticum G.Forst., is renowned in Melanesia, Polynesia and Micronesia for its relaxant effect. Modern extract preparations with defined contents of kavalactones – the major active constituents – are well established as herbal medicinal products on the European market. The aim of this trial was to present data on the clinical efficacy of an ethanolic kava extract.

Methods
In the present double‐blind clinical trial, the differences in clinical outcome between a low dose of ethanolic kava extract (equivalent to 20 mg kavalactones daily) and a respective high dose (equivalent to 200 mg kavalactones daily) were investigated. Patients with anxiety disorders were randomized into the two groups, resulting in 33 patients in the high‐dose group and 36 patients in the low‐dose group. The study duration was 4 weeks; the primary parameter was the Hamilton anxiety (HAMA) score. Global efficacy was rated by the physician at the end of the study. Safety of application was based on the documentation of adverse events.

Results
The high‐dose group was statistically significantly superior to the low‐dose group on HAMA total score and its subscores for psychological and physical manifestations of anxiety (P < 0.001), with a total improvement of −41.5% versus −13.6% relative to baseline HAMA total score on day 28. No adverse events occurred.

Conclusion
Kava preparations have a dose‐dependent anxiolytic effect.
(https://doi.org/10.1002/tkm2.1079)

Scherer, J., Kava-kava extract in anxiety disorders: An outpatient observational study. Advances in Therapy 15, 261-269 (1998).

Abstract:
Fifty-two outpatients suffering from anxiety of nonpsychotic origin were included in an observational study of a kava-kava preparation. Drug efficacy was evident on measures of a global improvement scale, with 42 patients (80.8%) rating treatment as "very good" or "good". Adverse events were rare. These results support kava-kava extract as an effective and safe alternative to antidepressants and tranquilizers in anxiety disorder without the tolerance problems associated with benzodiazepines.
(https://pubmed.ncbi.nlm.nih.gov/10186945/)

Sarris, J., Stough, C., Bousman, C. A., Wahid, Z. T., Murray, G., Teschke, R., Savage, K. M., Dowell, A., Ng, C. & Schweitzer, I. Kava in the treatment of generalized anxiety disorder: A double-blind, randomized, placebo-controlled study. Journal of Clinical Psychopharmacology 33, 643-648 (2013).

Abstract:
Kava (Piper methysticum) is a plant-based medicine, which has been previously shown to reduce anxiety. To date, however, no placebo-controlled trial assessing kava in the treatment of generalized anxiety disorder (GAD) has been completed. A total of 75 participants with GAD and no comorbid mood disorder were enrolled in a 6-week double-blind trial of an aqueous extract of kava (120/240 mg of kavalactones per day depending on response) versus placebo. γ-Aminobutyric acid (GABA) and noradrenaline transporter polymorphisms were also analyzed as potential pharmacogenetic markers of response. Reduction in anxiety was measured using the Hamilton Anxiety Rating Scale (HAMA) as the primary outcome. Intention-to-treat analysis was performed on 58 participants who met inclusion criteria after an initial 1 week placebo run-in phase. Results revealed a significant reduction in anxiety for the kava group compared with the placebo group with a moderate effect size (P = 0.046, Cohen d = 0.62). Among participants with moderate to severe Diagnostic and Statistical Manual of Mental Disorders–diagnosed GAD, this effect was larger (P = 0.02; d = 0.82). At conclusion of the controlled phase, 26% of the kava group were classified as remitted (HAMA ≤ 7) compared with 6% of the placebo group (P = 0.04). Within the kava group, GABA transporter polymorphisms rs2601126 (P = 0.021) and rs2697153 (P = 0.046) were associated with HAMA reduction. Kava was well tolerated, and aside from more headaches reported in the kava group (P = 0.05), no other significant differences between groups occurred for any other adverse effects, nor for liver function tests. Standardized kava may be a moderately effective short-term option for the treatment of GAD. Furthermore, specific GABA transporter polymorphisms appear to potentially modify anxiolytic response to kava.
(https://doi.org/10.1097/jcp.0b013e318291be67)

Connor, K. M., Payne, V. & Davidson, J. R. Kava in generalized anxiety disorder: Three placebo-controlled trials. International Clinical Psychopharmacology 21, 249-253 (2006).

Abstract:
In this study, we evaluated the efficacy and safety of kava kava (Piper methysticum) in generalized anxiety disorder. Data were analyzed from three randomized, double-blind, placebo-controlled trials of kava, including one study with an active comparator (venlafaxine), in adult outpatients with DSM-IV generalized anxiety disorder. The pooled sample (n=64) included the following number of participants: kava, n=28; placebo, n=30; and venlafaxine, n=6. Given the comparability of the study designs, the data comparing kava and placebo were then pooled for further efficacy and safety analyses. No significant differences were observed between the treatment groups in any of the trials. In the pooled analyses, no effects were found for kava, while a significant effect in favor of placebo was observed in participants with higher anxiety at baseline. No evidence of hepatotoxicity was found with kava, and all of the treatments were well tolerated. Findings from these three controlled trials do not support the use of kava in DSM-IV generalized anxiety disorder.
(https://doi.org/10.1097/00004850-200609000-00001)

Boerner, R. J., Sommer, H., Berger, W., Kuhn, U., Schmidt, U. & Mannel, M. Kava-Kava extract LI 150 is as effective as Opipramoland Buspirone in Generalised Anxiety Disorder –An 8-week randomized, double-blind multi-centre clinicaltrial in 129 out-patients. , (2003).

Abstract:
Objective: An 8-week randomized, reference-controlled, double-blind, multi-centre clinical trial investigated Kava-Kava LI 150 in Generalized Anxiety Disorder (GAD; ICD-10: F41.1).

Method: 129 out-patients received either 400 mg Kava LI 150, 10 mg Buspirone or 100mg Opipramol daily for 8 weeks. At week 9, subjects were seen to check for symptoms of withdrawal or relapse. Primary outcome measures comprised the HAMA scale and the proportion of responders at week 8. Secondary measures were the Boerner Anxiety Scale (BOEAS), SAS, CGI, a self-rating scale for well-being (Bf-S), a sleep questionnaire (SF-B), a quality-of-life questionnaire (AL) and global judgements by investigator and patients.

Results: In 127 patients (ITT) no significant differences could be observed regarding all efficacy and safety measures. About 75% of patients were classified as responders (50% reduction of HAMA score) in each treatment group, about 60% achieved full remission.

Conclusion: Kava-Kava LI150 is well tolerated and as effective as Buspirone and Opipramol in the acute treatment of out-patients suffering from GAD.
(https://doi.org/10.1078/1433-187x-00309)

Sarris, J., Byrne, G. J., Bousman, C. A., Cribb, L., Savage, K. M., Holmes, O., Murphy, J., Macdonald, P., Short, A., Nazareth, S., Jennings, E., Thomas, S. R., Ogden, E., Chamoli, S., Scholey, A. & Stough, C. Kava for generalised anxiety disorder: A 16-week double-blind, randomised, placebo-controlled study. Australian and New Zealand Journal of Psychiatry 54, 288-297 (2020).

Abstract:
Objective:
Previous randomised, double-blind, placebo-controlled studies have shown that Kava (a South Pacific medicinal plant) reduced anxiety during short-term administration. The objective of this randomised, double-blind, placebo-controlled study was to perform a larger, longer-term trial assessing the efficacy and safety of Kava in the treatment of generalised anxiety disorder and to determine whether gamma-aminobutyric acid transporter (SLC6A1) single-nucleotide polymorphisms were moderators of response.

Methods:
The trial was a phase III, multi-site, two-arm, 16-week, randomised, double-blind, placebo-controlled study investigating an aqueous extract of dried Kava root administered twice per day in tablet form (standardised to 120 mg of kavalactones twice/day) in 171 currently non-medicated anxious participants with diagnosed generalised anxiety disorder. The trial took place in Australia.

Results:
An analysis of 171 participants revealed a non-significant difference in anxiety reduction between the Kava and placebo groups (a relative reduction favouring placebo of 1.37 points; p = 0.25). At the conclusion of the controlled phase, 17.4% of the Kava group were classified as remitted (Hamilton Anxiety Rating Scale score < 7) compared to 23.8% of the placebo group (p = 0.46). No SLC6A1 polymorphisms were associated with treatment response, while carriers of the rs2601126 T allele preferentially respond to placebo (p = 0.006). Kava was well tolerated aside from poorer memory (Kava = 36 vs placebo = 23; p = 0.044) and tremor/shakiness (Kava = 36 vs placebo = 23; p = 0.024) occurring more frequently in the Kava group. Liver function test abnormalities were significantly more frequent in the Kava group, although no participant met criteria for herb-induced hepatic injury.

Conclusion:
While research has generally supported Kava in non-clinical populations (potentially for more ‘situational’ anxiety as a short-term anxiolytic), this particular extract was not effective for diagnosed generalised anxiety disorder.
(https://doi.org/10.1177/0004867419891246)

Sarris, J., Kavanagh, D. J., Byrne, G., Bone, K. M., Adams, J. & Deed, G. The Kava Anxiety Depression Spectrum Study (KADSS): A randomized, placebo-controlled crossover trial using an aqueous extract of Piper methysticum. Psychopharmacology 205, 399-407 (2009).

Abstract:
Rationale
Piper methysticum (Kava) has been withdrawn in European, British, and Canadian markets due to concerns over hepatotoxic reactions. The WHO recently recommended research into “aqueous” extracts of Kava.

Objective
The objective of this study was to conduct the first documented human clinical trial assessing the anxiolytic and antidepressant efficacy of an aqueous extract of Kava.

Design and participants
The Kava Anxiety Depression Spectrum Study was a 3-week placebo-controlled, double-blind crossover trial that recruited 60 adult participants with 1 month or more of elevated generalized anxiety. Five Kava tablets per day were prescribed containing 250 mg of kavalactones/day.

Results
The aqueous extract of Kava reduced participants' Hamilton Anxiety Scale score in the first controlled phase by −9.9 (CI = 7.1, 12.7) vs. −0.8 (CI = −2.7, 4.3) for placebo and in the second controlled phase by −10.3 (CI = 5.8, 14.7) vs. +3.3 (CI = −6.8, 0.2). The pooled effect of Kava vs. placebo across phases was highly significant (p < 0.0001), with a substantial effect size (d = 2.24, η2p=0.428). Pooled analyses also revealed highly significant relative reductions in Beck Anxiety Inventory and Montgomery–Asberg Depression Rating Scale scores. The aqueous extract was found to be safe, with no serious adverse effects and no clinical hepatotoxicity.

Conclusions
The aqueous Kava preparation produced significant anxiolytic and antidepressant activity and raised no safety concerns at the dose and duration studied. Kava appears equally effective in cases where anxiety is accompanied by depression. This should encourage further study and consideration of globally reintroducing aqueous rootstock extracts of Kava for the management of anxiety.
(https://doi.org/10.1007/s00213-009-1549-9)

Thomsen, M. & Schmidt, M. Health policy versus kava (Piper methysticum): Anxiolytic efficacy may be instrumental in restoring the reputation of a major South Pacific crop. Journal of Ethnopharmacology , 113582 (2020).

Abstract:
Abstract
Ethnopharmacological relevance
Kava (Piper methysticum G. Forst. f.) is by far the most important plant used in the islands of Melanesia, Polynesia and Micronesia for its relaxing effects. Kava drinking is a pillar of South Pacific societies and is also the foundation of their economies. Preparations of kava extract as herbal medicinal drugs were banned in Germany in 2002 and again in 2019, with dramatic consequences for the South Pacific economies. In 2002, the major regulatory argument for the ban of kava was safety issues. In 2019, the assessment report of the European Medicines Agency's Herbal Medicinal Product Committee (HMPC) justified a negative benefit-to-risk ratio by a supposed lack of efficacy of ethanolic extracts for an indication of which kava extract preparations never had an approval. In this HMPC report the efficacy in the approved indications ‘nervous anxiety, tension and restlessness’ was attributed to the extract branded as ‘WS 1490’, which was assumed to have been prepared with acetone as an extraction solvent. In addition to this change of indication and the attribution of efficacy to acetone kava extract alone, the German health authorities and the HMPC still refuse to discuss quality issues as a likely factor impacting drug safety. The first case reports of liver toxicity were observed with an acetone extract in a timely relationship with the introduction of ‘two-day kava’ instead of ‘noble kava’ as used in ethanolic kava extracts.

Aim of the study
The correlation between clinical benefits and the type of extract preparation was examined.

Methods
In order to identify the types of kava material and extracts used in clinical trials, the respective publications were compared with regulatory databases and protocols of a German regulatory advisory board.

Results and conclusions
The comparison reveals inconsistencies in the regulatory decisions. In all studies with WS 1490, the evidence points to the use of an ethanolic extract. The efficacy of kava extract for the approved indication was clearly demonstrated. The HMPC report and the recent renewed German regulatory ban of kava therefore require major revision, which should include the impact of the use of “two-day kava” on drug safety. Such a revision could contribute to restoring the reputation of “noble kava” on the international markets.
(https://doi.org/10.1016/j.jep.2020.113582)

Gastpar M, Klimm HD. Treatment of anxiety, tension and restlessness states with Kava special extract WS 1490 in general practice: a randomized placebo-controlled double-blind multicenter trial. Phytomedicine. 2003 Nov;10(8):631-9. doi: 10.1078/0944-7113-00369. PMID: 14692723.

Summary:
The efficacy and tolerability of 150 mg/d Kava special extract WS® 1490 were investigated in a randomized, placebo-controlled, double-blind multicenter study in patients suffering from neurotic anxiety (DSM-III-R diagnoses 300.02, 300.22, 300.23, 300.29, or 309.24). 141 adult, male and female out-patients received 3 × 1 capsule of 50 mg/d WS® 1490 or placebo for four weeks, followed by two weeks of observation without study-specific treatment.

During randomized treatment the total score of the Anxiety Status Inventory (ASI) observer rating scale showed more pronounced decreases in the WS® 1490 group than in the placebo group. Although a treatment group comparison of the post-treatment ASI scores was not significant (p > 0.05), an exploratory analysis of variance across the differences between treatment end and baseline, with center as a second factor, showed superiority of the herbal extract over placebo (p < 0.01, two-sided). 73% of the patients treated with WS® 1490 exhibited ASI score decreases >5 points versus baseline, compared to 56% for placebo. Significant advantages for WS® 1490 were also evident in a structured well-being self-rating scale (Bf-S) and the Clinical Global Impressions (CGI), while the Erlangen Anxiety, Tension and Aggression Scale (EAAS) and the Brief Test of Personality Structure (KEPS) showed only minor treatment group differences.

Although the results show consistent advantages for WS® 1490 over placebo in several psychiatric scales and indicate significant improvements in the patients' general well-being, the differences versus placebo were not as large as in previous trials which employed 300 mg/d of the same extract.

WS® 1490 was well tolerated, with no influence on liver function tests and only one trivial adverse event (tiredness) attributable to the study drug.
(https://doi.org/10.1078/0944-7113-00369)

Kava (Piper methysticum) Extract for the Treatment of Nervous Anxiety, Tension and Restlessness. Drug Res , (2020).

Abstract:
Aim Prior to the kava ban of 2002, the indication for kava (Piper methysticum) extracts defined by the German Commission E was “nervous anxiety, tension and restlessness”. In 2000, an observational trial was started in Germany with the aim of defining symptoms of these indications best treated with kava extract. The trial was interrupted and archived “unevaluated” in 2001 due to the upcoming safety debate on kava. The data from this study has now been analyzed in order to identify symptoms best treated with kava.

Methods Documentation was available from 156 patients. Twelve typical symptoms of nervous anxiety, tension and restlessness were assessed on a five-item rating scale, together with the therapeutic context, the perceived time of onset of effects and the safety of application.

Results The median duration of treatment was 28 days. All individual symptoms showed significant and clinically relevant improvements. The most effective results were seen for nervous tension and restlessness, with better effects in patients with acute versus chronic complaints. The safety of the treatment was found to be excellent, which included the assessment of laboratory data.

Conclusions Overall, the study confirms the effective and safe short-term use of kava in the Commission E-defined indication of “nervous anxiety, tension and restlessness”, especially in other than chronic cases. The clinical use of kava might be translated into context-related phobias according to ICD-10 F40, or to nervous tension (ICD10 R45.0) or restlessness and excitation (ICD-10 R45.1).
(https://doi.org/10.1055/a-1268-7135)

Open Access Article
Rivers, Z., Kava as a Pharmacotherapy of Anxiety Disorders: Promises and Concerns. Medicinal Chemistry 6, 81-87 (2016).

Abstract:
Current standard pharmacotherapies for anxiety management come with a host of side-effects that may deter the patients from utilizing them. Kava, a traditional beverage from the South Pacific region, has been used as a natural medicine for centuries and has been hypothesized to contain anxiolytic properties. There are a few well-designed, randomly controlled trials that have evaluated the effectiveness of kava or its constituents against anxiety disorders. They have generally shown kava to be effective in managing the disease. However, there has been a serious concern about the hepatotoxic risk of kava, which greatly limits its anxiolytic development and application. This review attempts to summarize the recent anxiolytic trials using kava, the associated hepatotoxicity risks, the potential responsible chemicals for these two activities, and the mechanisms of action. Overall, kava has a great potential to be developed as a natural anxiolytic agent through a systematic approach, but the present form should be used with caution. (https://www.researchgate.net/deref/http://dx.doi.org/10.4172/2161-0444.1000329)

Open Access Article
Atezaz Saeed, S., Bloch, R. M. & Antonacci, D. J. Herbal and Dietary Supplements for Treatment of Anxiety Disorders. Complementary and Alternative Medicine , (2007).

Abstract:
Use of complementary and alternative medicine has increased over the past decade. A variety of studies have suggested that this use is greater in persons with symptoms or diagnoses of anxiety and depression. Data support the effectiveness of some popular herbal remedies and dietary supplements; in some of these products, particularly kava, the potential for benefit seems greater than that for harm with short-term use in patients with mild to moderate anxiety. Inositol has been found to have modest effects in patients with panic disorder or obsessive-compulsive disorder. Physicians should not encourage the use of St. John's wort, valerian, Sympathyl, or passionflower for the treatment of anxiety based on small or inconsistent effects in small studies. Although the evidence varies depending on the supplement and the anxiety disorder, physicians can collaborate with patients in developing dietary supplement strategies that minimize risks and maximize benefits.
(https://www.aafp.org/afp/2007/0815/p549.html)

Geier, F. P. & Konstantinowicz, T. Kava Treatment in Patients with Anxiety. Phytotherapy Research 18, 297-300 (2004).

Abstract:
In several clinical trials, mainly conducted with a dose of 300 mg kava extract per day, kava has been employed successfully for the treatment of anxiety disorders.

The goal of the placebo‐controlled double‐blind outpatient trial was to obtain more information on the dosage range and efficacy of a kava special extract WS 1490 in patients with non‐psychotic anxiety. 50 patients were treated with a daily dose of 3 × 50 mg WS 1490 during a 4‐week treatment period followed by a 2‐week safety observation phase.

In the active treatment group, the total score of the Hamilton anxiety scale (primary efficacy variable), showed a therapeutically relevant reduction in anxiety versus placebo (more than 4 points). In the secondary variables studied, HAMA ‘somatic and psychic anxiety’ subscales, the Erlangen anxiety, tension and aggression scale (EAAS), the brief personality structure scale (KEPS), the adjective checklist (EWL 60‐S) and clinical global impressions scale (CGI), a trend in favour of the active treatment was detectable. WS 1490 was well tolerated and showed a safety profile with no drug‐related adverse events or post‐study withdrawal symptoms.

It can be concluded that the applied 150 mg WS 1490 per day is an effective and safe treatment of non‐psychotic anxiety syndromes in the described population.
(https://doi.org/10.1002/ptr.1422)

Open Access Article
Pittler, M. H. & Ernst, E. Kava extract versus placebo for treating anxiety. Cochrane Database of Systematic Reviews , (2003).

Abstract:
Background
Constraints on resources and time often render treatments for anxiety such as psychological interventions impracticable. While synthetic anxiolytic drugs are effective, they are often burdened with adverse events. Other options which are effective and safe are of considerable interest and a welcome addition to the therapeutic repertoire.

Objectives
To assess the effectiveness and safety as reported in rigorous clinical trials of kava extract compared with placebo for treating anxiety.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6999799/)

Malsch, U. & Kieser, M. Efficacy of kava-kava in the treatment of non-psychotic anxiety, following pretreatment with benzodiazepines. Psychopharmacology 157, 277-283 (2001).

Abstract:
A 5-week randomized, placebo-controlled, double-blind study was carried out to investigate the efficacy of kava-kava special extract WS®1490 in non-psychotic nervous anxiety, tension and restlessness states. During the first treatment week, the study dose drug was increased from 50 mg to 300 mg per day and pretreatment with benzodiazepines was tapered off over 2 weeks. These dosage adjustments were followed by 3 weeks of monotherapy with WS®1490 or placebo. Outcome measures were the differences between baseline and end of treatment on the Hamilton Anxiety Scale (HAMA) and on a subjective well-being scale (Bf-S), as well as the benzodiazepine withdrawal symptoms. Changes in the Erlanger Anxiety, Tension and Aggression Scale (EAAS) and Clinical Global Impressions (CGI) were analyzed as secondary measures. Treatment safety was checked by interviews, adverse event reports and laboratory investigations. Forty patients (2×20) were included into the study. WS®1490 was superior to placebo regarding the HAMA (P=0.01) and Bf-S (P=0.002) total scores and all secondary efficacy measures. The tolerance of WS®1490 was not inferior to placebo. The study confirms the anxiolytic efficacy and good tolerance of WS®1490 and shows that a further symptom reduction is possible after a change-over from benzodiazepine treatment.
(https://doi.org/10.1007/s002130100792)

Smith, K. & Leiras, C. The effectiveness and safety of Kava Kava for treating anxiety symptoms: A systematic review and analysis of randomized clinical trials. Complementary Therapies in Clinical Practice 33, 107-117 (2018).

Abstract:
Background
To determine if Kava Kava is an effective treatment for combating symptoms of anxiety despite warnings of hepatotoxicity from the Centers for Disease Control and Prevention (CDC).

Methods
Databases PubMed, CINAHL, and PsycINFO were utilized to obtain clinical trials on Kava Kava and its effects on anxiety. A total of 11 articles met inclusion/exclusion criteria: 2 for Kava Kava vs. another anti-anxiety medication, 2 detailing additional adverse events, and 7 for Kava Kava vs. placebo. Mantel-Haenszel fixed–effects model was used to analyze the data, with responder rates being pooled to compute weighted risk ratios.

Results
Kava Kava was shown to be more effective than placebo in 3 of the 7 trials. A final risk ratio of 1.50 (95% CI: 1.12, 2.01) from responder rates was calculated in favor of the intervention from 5 clinical trials (n = 330). Adverse events were shown to be the same as placebo (P = 0.574), and laboratory values analyzing hepatotoxicity were no different when compared to baseline except in two studies.

Conclusions
Kava Kava appears to be a short-term treatment for anxiety, but not a replacement for prolonged anti-anxiety use. Although not witnessed in this review, liver toxicity is especially possible if taken longer than 8 weeks.
(https://doi.org/10.1016/j.ctcp.2018.09.003)

Sarris, J., Stough, C., Teschke, R., Wahid, Z. T., Bousman, C. A., Murray, G., Savage, K. M., Mouatt, P., Ng, C. & Schweitzer, I. Kava for the treatment of generalized anxiety disorder RCT: Analysis of adverse reactions, liver function, addiction, and sexual effects. Phytotherapy Research 27, 1723-1728 (2013).

Abstract:
Presently, little is known about a number issues concerning kava (Piper methysticum), including (i) whether kava has any withdrawal or addictive effects; (ii) if genetic polymorphisms of the cytochrome (CYP) P450 2D6 liver enzyme moderates any potential adverse effects; and (iii) if medicinal application of kava has any negative or beneficial effect on sexual function and experience. The study design was a 6‐week, double‐blind, randomized controlled trial (n = 75) involving chronic administration of kava (one tablet of kava twice per day; 120 mg of kavalactones per day, titrated in non‐response to two tablets of kava twice per day; 240 mg of kavalactones) or placebo for participants with generalized anxiety disorder. Results showed no significant differences across groups for liver function tests, nor were there any significant adverse reactions that could be attributed to kava. No differences in withdrawal or addiction were found between groups. Interesting, kava significantly increased female's sexual drive compared to placebo (p = 0.040) on a sub‐domain of the Arizona Sexual Experience Scale (ASEX), with no negative effects seen in males. Further, it was found that there was a highly significant correlation between ASEX reduction (improved sexual function and performance) and anxiety reduction in the whole sample.
(https://doi.org/10.1002/ptr.4916)

Open Access Article
Noor, N. A.. “Anxiolytic action and safety of Kava: Effect on rat brain acetylcholinesterase activity and some serum biochemical parameters.” African Journal of Pharmacy and Pharmacology 4 (2010): 823-828.

Abstract:
Kava is a herbal anxiolytic drug. The present study investigates the response of central cholinergic neurotransmission to kava treatment by measuring acetylcholinesterase (AChE) activity in cortex, hippocampus and striatum of adult male rats. The present study demonstrates also the effect of chronic use of kava on some liver and kidney function parameters in the sera of rats. Kava administration (75 mg/kg) induced an increase in AChE activity in the striatum after 1 week. However, significant decreases in the enzyme activity were obtained after 4 weeks of treatment in the three brain areas examined. No significant changes were observed in the enzyme activity on stopping kava administration. Kava administration for 4 weeks resulted in significant decreases in serum aspartate transaminase (AST) and alanine transaminase (ALT) activities and creatinine level, while alkaline phosphatase activity and albumin level did not show any significant changes. However, total protein and urea levels were increased significantly. In conclusion, the cholinergic system in the cortex, hippocampus and striatum may play a vital role in the anxiolytic action of kava. The present study showed no adverse effects of kava on liver and kidney function parameters.
(https://www.researchgate.net/publication/228678736)

Feltenstein, M. W., Lambdin, L. C., Ganzera, M., Dharmaratne, H. R. W., Nanayakkara, N. P., Khan, I. A. & Sufka, K. J. Anxiolytic properties of Piper methysticum extract samples and fractions in the chick social-separation-stress procedure. Phytotherapy Research 17, 210-216 (2003).

Abstract:
Piper methysticum extract (Kava kava) possesses anxiolytic properties. However, it is unknown whether these effects are best predicted by total kavalactone content or by one or more of its primary kavalactone constituents. Using the chick social separation‐stress procedure as an anxiolytic bioassay, P. methysticum samples containing 12.8–100.0% total kavalactones (Exp. 1) and fractions containing 1–6 kavalactones of varying concentrations (0.1–67.5%; Exps. 2–3) were screened for activity and compared against a 5.0 mg/kg dose of chlordiazepoxide (CDP; Exp. 3). Eight‐day‐old chicks received IP injections of either vehicle or test compounds 30 min before being placed in the presence of two conspecifics or in isolation for a 3 min observation period. Dependent measures were ventral recumbency latency (sedation), distress vocalizations, and a measure of stress‐induced analgesia (in Exps. 1 and 2 only). P. methysticum extract samples attenuated distress vocalizations in a concentration‐dependent manner. The P. methysticum fraction that contained the highest concentration of dihydrokavain attenuated distress vocalizations in a manner equivalent to that of CDP. The extract samples and fractions that possessed anxiolytic properties did not possess the sedative properties found in CDP. Collectively, these findings suggest that dihydrokavain may be necessary and sufficient in mediating the anxiolytic properties of P. methysticum extract.
(https://doi.org/10.1002/ptr.1107)

Ooi, S. L., Henderson, P. & Pak, S. C. Kava for generalized anxiety disorder: A review of current evidence. Journal of Alternative and Complementary Medicine 24, 770-780 (2018).

Abstract:
Background: Generalized anxiety disorder (GAD) is a chronic and debilitating condition characterized by persistent and overpowering anxiety. Treatment of GAD with antidepressants and benzodiazepines is only moderately effective and not free from side effects. Kava (Piper methysticum) has been explored as a potential phytotherapeutic option for GAD.

Objectives: To perform a systematic review and meta-analysis of the available evidence on Kava as a treatment for GAD.

Methods: Systematic search of English-language publications from major databases for clinical trials reporting the effects of Kava for the treatment of GAD.

Results: Twelve articles were included in this review. Evidence supporting Kava as an effective treatment for GAD was found in two placebo-controlled trials and a reference-controlled trial. One negative trial demonstrated that Kava was not more effective than placebo. Meta-analyses of the results of three placebo-controlled trials (n = 130) favored Kava for GAD treatment with effect sizes between 0.59 and 0.99 (standard mean difference) without reaching statistical significance. Kava is an appealing treatment option to GAD patients who are more attune to natural remedies or lifestyle approaches to reduce stress. Positive patient experiences and improvement of vagal cardiac control due to Kava treatment were also reported in the literature. Kava is safe and well tolerated for short-term (4–8 weeks) therapeutic use at a dosage of 120–280 mg per day of Kavalactones, regardless of dosage schedule.

Conclusions: Current evidence, although promising, is insufficient to confirm the effect of Kava for GAD treatment beyond placebo. New evidence is expected from a large, multisite ongoing trial.
(https://doi.org/10.1089/acm.2018.0001)

Solvent Focused Studies

Kubatova, A., Miller, D. J., & Hawthorne, S. B. (2001). Comparison of subcritical water and organic solvents for extracting kava lactones from kava root. In Journal of Chromatography A.

Abstract:
Subcritical water extraction of lactones from a kava (Piper methysticum) root was compared to a Soxhlet extraction with water, to boiling in water, and to a sonication in acetone. For ground kava (250–500 μm), 2 h of subcritical water extraction were required for a complete extraction at 100°C, while at 175°C, 20 min were sufficient. For a complete extraction of the unground (shredded) kava, the time of extraction was extended to 40 min at 175°C. Boiling for 2 h and extraction with Soxhlet apparatus for 6 h, both of which employed water at atmospheric pressure, produced yields 40–60% lower than those obtained with subcritical water. With unground kava, 40 min of subcritical water extraction yielded essentially the same recoveries of lactones as 18 h of sonication with acetone, methylene chloride, or methanol.
(https://doi.org/10.1016/s0021-9673(01)00979-7)

Lopez-Avila, V., & Benedicto, J. (1997). Supercritical Fluid Extraction of Kava Lactones from Piper methysticum (Kava) Herb.

Abstract:
Supercritical fluid extraction of kava lactones from Piper methysticum Forst. herb is described here. The extraction was performed with supercritical carbon dioxide alone and supercritical carbon dioxide modified with 15% ethanol, and the extracts were analyzed by gas chromatography/mass spectrometry. Seven lactones including: 7,8‐dihydrokavain; kavain; 5,6‐dehydrokavain; 5, 6, 7, 8‐tetrahydroyangonin; dihydromethysticin; yangonin; and methysticin were the major constituents in the SFE extract.
(https://doi.org/10.1002/jhrc.1240201007)

Open Access Article
Wang, J., Qu, W., Bittenbender, H. C. & Li, Q. X. Kavalactone content and chemotype of kava beverages prepared from roots and rhizomes of Isa and Mahakea varieties and extraction efficiency of kavalactones using different solvents. Journal of Food Science and Technology 52, 1164-1169 (2013).

Abstract:
The South Pacific islanders have consumed kava beverage for thousands of years. The quality of kava and kava beverage is evaluated through determination of the content of six major kavalactones including methysticin, dihydromethysticin, kavain, dihydrokavain, yangonin and desmethoxyyangonin. In this study, we determined contents of kavalactones in and chemotype of kava beverages prepared from roots and rhizomes of Isa and Mahakea varieties and extraction efficiency of five different solvents including hexane, acetone, methanol, ethanol and ethyl acetate. The six major kavalactones were detected in all kava beverages with these five solvents. Different solvents had different extraction efficiencies for kavalactones from the lyophilized kava preparations. The contents of kavalactones in the extracts with acetone, ethanol, and methanol did not differ significantly. Ethanol had the highest extraction efficiency for the six major kavalactones whereas hexane gave the lowest extraction efficiency.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4325077/)

O'hara, M. J., Kinnard, W. J. & Buckley, J. P. Preliminary Characterization of Aqueous Extracts of P+er methysticzm (Kava, Kawa Kawa). J. Pharm. Sci. 54, 1021-1025 (1965).

Abstract:
An extract of Piper methysticum Forst. prepared by steam distillation was separated by means of differential solubility into two fractions, F1 and F2. These fractions had different physical and chemical characteristics, and known α-pyrones were identified only in subfraction F2. Both fractions decreased spontaneous motor activity in doses which did not alter forced motor activity of mice. Fraction F2, dihydromethysticin, desmethoxy-yangonin, and kawain exhibited potent antiserotonin activity on the isolated rat uterus, whereas F1 appeared to be devoid of antiserotonin activity. F1, F2, and dihydromethysticin did not alter serotonin brain levels in mice.
(https://doi.org/10.1002/jps.2600540715)

Ashraf-Khorassani, M., Taylor, /. L. T. & Martin, M. /. Supercritical Fluid Extraction of Kava Lactones from Kava Root and Their Separation Via Supercritical Fluid Chromatography. Chromatographia 50, 287-292 (1999).

Abstract:
Supercritical fluid extraction of kava lactones from Piper methysticum Forst. herb is described here. The extraction was performed with supercritical carbon dioxide alone and supercritical carbon dioxide modified with 15% ethanol, and the extracts were analyzed by gas chromatography/mass spectrometry. Seven lactones including: 7,8‐dihydrokavain; kavain; 5,6‐dehydrokavain; 5, 6, 7, 8‐tetrahydroyangonin; dihydromethysticin; yangonin; and methysticin were the major constituents in the SFE extract.
(https://doi.org/10.1002/jhrc.1240201007)

Xuan, T. D., Fukuta, M., Wei, A. C., Elzaawely, A. A., Khanh, T. D. & Tawata, S. Efficacy of extracting solvents to chemical components of kava (Piper methysticum) roots. Journal of Natural Medicines 62, 188-194 (2008).

Abstract:
The chemical composition of kava (Piper methysticum) lactones and various phytochemicals obtained following the sonication of ground kava roots extracted in the solvents hexane, chloroform, acetone, ethanol, methanol and water, respectively, was analyzed. Eighteen kava lactones, cinnamic acid bornyl ester and 5,7-dimethoxy-flavanone, known to be present in kava roots, were identified, and seven compounds, including 2,5,8-trimethyl-1-naphthol, 5-methyl-1-phenylhexen-3-yn-5-ol, 8,11-octadecadienoic acid-methyl ester, 5,7-(OH)2-4′-one-6,8-dimethylflavanone, pinostrobin chalcone and 7-dimethoxyflavanone-5-hydroxy-4′, were identified for the first time. Glutathione (26.3 mg/g) was found in the water extract. Dihydro-5,6-dehydrokavain (DDK) was present at a higher level than methysticin and desmethoxyyagonin, indicating that DDK is also a major constituent of kava roots. Acetone was the most effective solvent in terms of maximum yield and types of kava lactones isolated, followed by water and chloroform, whereas hexane, methanol, and ethanol were less effective as solvents. Total phenolic and antioxidant activity varied among the extracting solvents, with acetone and chloroform producing the highest effects, followed by water, while methanol, ethanol and hexane were less effective.
(https://doi.org/10.1007/s11418-007-0203-2)

Loew, D. & Franz, G. Quality aspects of traditional and industrial Kava-extracts. Phytomedicine 10, 610-612 (2003).

Summary:
An aqueous decoction of Piper methysticum has been used since centuries of Pacific Island at social religious-ceremonial and social events without hepatotoxic side effects in contrast to the speculation on industrial Kava preparations. It was assumed that the traditional non-alcoholic drink contains a spectrum of other constituents compared to the acetonic and ethanolic extracts. The TLC-analysis demonstrates, however, that under qualitative aspects there is no difference between aqueous and acetonic and ethanolic extracts respectively.
(https://doi.org/10.1078/094471103322331638)

Anti-Cancer Studies

Tabudravu, J. N., & Jaspars, M. (2005). Anticancer activities of constituents of kava (Piper methysticum).

Abstract:
Crude extracts of kava (Piper methysticum G. Forster, Piperaceae) showed good activity against ovarian tumor and leukemia cancer cell lines. Bioassay-guided isolation resulted in the isolation of six known kava lactones and two flavokavains. The structure of the compounds were elucidated by spectroscopic techniques and by comparison with data in the literature.
(https://www.publish.csiro.au/sp/SP05005)

Open Access Article
Abu, N., Mohamed, N. E., Yeap, S. K., Lim, K. L., Akhtar, M. N., Zulfadli, A. J., Kee, B. B., Abdullah, M. P., Omar, A. R. & Alitheen, N. B. In vivo antitumor and antimetastatic effects of flavokawain B in 4T1 breast cancer cell-challenged mice. Drug Design, Development and Therapy 9, 1401-1417 (2015).

Abstract:
Flavokawain B (FKB) is a naturally occurring chalcone that can be isolated through the root extracts of the kava-kava plant (Piper methysticum). It can also be synthesized chemically to increase the yield. This compound is a promising candidate as a biological agent, as it is reported to be involved in a wide range of biological activities. Furthermore, FKB was reported to have antitumorigenic effects in several cancer cell lines in vitro. However, the in vivo antitumor effects of FKB have not been reported on yet. Breast cancer is one of the major causes of cancer-related deaths in the world today. Any potential treatment should not only impede the growth of the tumor, but also modulate the immune system efficiently and inhibit the formation of secondary tumors. As presented in our study, FKB induced apoptosis in 4T1 tumors in vivo, as evidenced by the terminal deoxynucleotidyl transferase dUTP nick end labeling and hematoxylin and eosin staining of the tumor. FKB also regulated the immune system by increasing both helper and cytolytic T-cell and natural killer cell populations. In addition, FKB also enhanced the levels of interleukin 2 and interferon gamma but suppressed interleukin 1B. Apart from that, FKB was also found to inhibit metastasis, as evaluated by clonogenic assay, bone marrow smearing assay, real-time polymerase chain reaction, Western blot, and proteome profiler analysis. All in all, FKB may serve as a promising anticancer agent, especially in treating breast cancer.
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4358690/)

Open Access Article
Puppala, M., Narayanapillai, S. C., Leitzman, P., Sun, H., Upadhyaya, P., O'Sullivan, M. G., Hecht, S. S. & Xing, C. Pilot in Vivo Structure-Activity Relationship of Dihydromethysticin in Blocking 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced O6-Methylguanine and Lung Tumor in A/J Mice. J. Med. Chem. 60, 7935-7940 (2017).

Abstract:
(+)-Dihydromethysticin was recently identified as a promising lung cancer chemopreventive agent while (+)-dihydrokavain was completely ineffective. A pilot in vivo structure-activity relationship (SAR) was explored, evaluating the efficacy of its analogs in blocking 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced short-term O6-methylguanine and long-term adenoma formation in the lung tissues in A/J mice. Both results revealed cohesive SARs, demonstrating that the methylenedioxy functional group in DHM is essential while the lactone functional group tolerates modifications.
(https://doi.org/10.1021/acs.jmedchem.7b00921)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/28806079/)

Open Access Article
Tang, Y., Li, X., Liu, Z., Simoneau, A. R., Xie, J. & Zi, X. Flavokawain B, a kava chalcone, induces apoptosis via up-regulation of death-receptor 5 and Bim expression in androgen receptor negative, hormonal refractory prostate cancer cell lines and reduces tumor growth. Int. J. Cancer 127, 1758-1768 (2010).

Abstract:
Limited success has been achieved in extending the survival of patients with metastatic and hormone-refractory prostate cancer (HRPC). There is a strong need for novel agents in the treatment and prevention of HRPC. We have shown that flavokawain B (FKB), a kava chalcone, is about 4 to 12 fold more effective in reducing the cell viabilities of androgen receptor (AR)-negative, HRPC cell lines DU145 and PC-3 than AR–positive, hormone-sensitive prostate cancer cell lines LAPC4 and LNCaP, with minimal effect on normal prostatic epithelial and stromal cells. FKB induces apoptosis with an associated increased expression of proapoptotic proteins: death receptor-5, Bim and Puma, and a decreased expression of inhibitors of apoptosis protein: XIAP and survivin. Among them, Bim expression was significantly induced by FKB as early as four hours of the treatment. Knockdown of Bim expression by short-hairpin RNAs attenuates the inhibitory effect on anchorage-dependent and-independent growth and caspase cleavages induced by FKB. These findings suggesting the effect of FKB, at least in part, requires Bim expression. In addition, FKB synergize with TRAIL for markedly enhanced induction of apoptosis. Furthermore, FKB treatment of mice bearing DU145 xenograft tumors results in tumor growth inhibition and increases Bim expression in tumor tissues. Together, these results suggest robust mechanisms for FKB induction of apoptosis preferentially for HRPC and the potential usefulness of FKB for prevention and treatment of HRPC in an adjuvant setting.
(https://doi.org/10.1002/ijc.25210)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/20112340/)

Open Access Article
Zi, X. & Simoneau, A. R. Flavokawain A, a novel chalcone from kava extract, induces apoptosis in bladder cancer cells by involvement of Bax protein-dependent and mitochondria-dependent apoptotic pathway and tumor growth in mice. Cancer Res. 65, 3479-3486 (2005).

Abstract:
Consumption of the traditional kava preparation was reported to correlate with low and uncustomary gender ratios (more cancer in women than men) of cancer incidences in three kava-drinking countries: Fiji, Vanuatu, and Western Samoa. We have identified flavokawain A, B, and C but not the major kavalactone, kawain, in kava extracts as causing strong antiproliferative and apoptotic effect in human bladder cancer cells. Flavokawain A results in a significant loss of mitochondrial membrane potential and release of cytochrome c into the cytosol in an invasive bladder cancer cell line T24. These effects of flavokawain A are accompanied by a time-dependent decrease in Bcl-xL, a decrease in the association of Bcl-xL to Bax, and an increase in the active form of Bax protein. Using the primary mouse embryo fibroblasts Bax knockout and wild-type cells as well as a Bax inhibitor peptide derived from the Bax-binding domain of Ku70, we showed that Bax protein was, at least in part, required for the apoptotic effect of flavokawain A. In addition, flavokawain A down-regulates the expression of X-linked inhibitor of apoptosis and survivin. Because both X-linked inhibitor of apoptosis and survivin are main factors for apoptosis resistance and are overexpressed in bladder tumors, our data suggest that flavokawain A may have a dual efficacy in induction of apoptosis preferentially in bladder tumors. Finally, the anticarcinogenic effect of flavokawain A was evident in its inhibitory growth of bladder tumor cells in a nude mice model (57% of inhibition) and in soft agar.
(https://doi.org/10.1158/0008-5472.can-04-3803)
(https://cancerres.aacrjournals.org/content/65/8/3479.long)

Open Access Article
Wang, Y., Narayanapillai, S. C., Tessier, K. M., Strayer, L. G., Upadhyaya, P., Hu, Q., Kingston, R., Salloum, R. G., Lu, J., Hecht, S. S., Hatsukami, D. K., Fujioka, N. & Xing, C. The Impact of One-week Dietary Supplementation with Kava on Biomarkers of Tobacco Use and Nitrosamine-based Carcinogenesis Risk among Active Smokers. Cancer prevention research (Philadelphia, Pa.) 13, 483-492 (2020).

Abstract:
Tobacco smoking is the primary risk factor for lung cancer, driven by the addictive nature of nicotine and the indisputable carcinogenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) as well as other compounds. The integration of lung cancer chemoprevention with smoking cessation is one potential approach to reduce this risk and mitigate lung cancer mortality. Experimental data from our group suggest that kava, commonly consumed in the South Pacific Islands as a beverage to promote relaxation, may reduce lung cancer risk by enhancing NNK detoxification and reducing NNK-derived DNA damage. Building upon these observations, we conducted a pilot clinical trial to evaluate the effects of a 7-day course of kava on NNK metabolism in active smokers. The primary objective was to compare urinary total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL plus its glucuronides, major metabolites of NNK) before and after kava administration as an indicator of NNK detoxification. Secondary objectives included determining kava’s safety, its effects on DNA damage, tobacco use, and cortisol (a biomarker of stress). Kava increased urinary excretion of total NNAL and reduced urinary 3-methyladenine (3-mA) in participants, suggestive of its ability to reduce the carcinogenicity of NNK. Kava also reduced urinary total nicotine equivalents (TNE), indicative of its potential to facilitate tobacco cessation. Plasma cortisol and urinary total cortisol equivalents (TCE) were reduced upon kava use, which may contribute to reductions in tobacco use. These results demonstrate the potential of kava intake to reduce lung cancer risk among smokers.
(https://doi.org/10.1158/1940-6207.capr-19-0501)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/32102948/)

Triolet, J., Shaik, A. A., Gallaher, D. D., Osullivan, M. G. & Xing, C. Reduction in colon cancer risk by consumption of kava or kava fractions in carcinogen-treated rats. Nutrition and Cancer 64, 838-846 (2012).

Abstract:
Epidemiological studies suggest that kava reduces colon cancer risk. However, no experimental studies of the chemopreventive properties of kava toward colon cancer have been reported. Further, there are concerns regarding hepatotoxicity of kava. The goal of this study was to determine whether kava consumption reduces markers of colon cancer in an animal model and to study the safety of kava. An ethanolic extract and polar and nonpolar fractions of the kava extract were fed to rats for 12 days prior to, during, and after administration of dimethylhydrazine, a colon-specific carcinogen. After 14 wk, rats fed the nonpolar extract had a significant reduction in precancerous lesions [aberrant crypt (AC) foci (ACF)] as well as large (≥4 AC/ACF) sialomucin-only expressing foci, an indicator of greater tumorigenic potential, compared to the control group. Groups fed the ethanolic extract and polar kava fraction trended toward reductions in ACF and large sialomucin-only expressing foci. The combined kava groups had significantly fewer total AC, ACF, large ACF, and large sialomucin-only expressing foci compared to the control group. Histological examination found no hepatic lesions in animals consuming the kava diets, suggesting that kava is safe to consume. Our results support that kava may reduce colon cancer risk.
(https://doi.org/10.1080/01635581.2012.689917)

Botello, J. F., Corral, P., Bian, T. & Xing, C. Kava and its kavalactones inhibit norepinephrine-induced intracellular calcium influx in lung cancer cells. Planta Med. 86, 26-31 (2020).

Abstract:
Kava, the extract of the roots of Piper methysticum, has been traditionally consumed in the South Pacific islands for its natural relaxing property. Epidemiological data suggests that kava consumption may reduce human cancer risk, and in vitro and in vivo models suggest chemopreventive potential against carcinogen-induced tumorigenesis. Therefore, knowledge about its molecular mechanisms and responsible ingredient(s) for these beneficial properties will better guide kavaʼs use for the management of these disorders. Psychological stress typically results in increased production of stress hormones, such as norepinephrine (NE), which activate adrenergic receptors (ARs). Psychological stress has also been associated with increased cancer incidence and poor clinical outcomes in cancer patients. Mechanistically, binding of NE to ARs induces intracellular calcium influx, which activates downstream signaling pathways involved in both stress and cancer development. In this study, we characterized the effect of kava and its components, 3 fractions and 6 major kavalactones, on NE-induced intracellular calcium influx in H1299, a human non-small cell lung carcinoma cell line. Results show that kava extract effectively inhibits NE-mediated intracellular calcium influx in H1299 cells, potentially through antagonizing β-AR signaling. This inhibitory activity is recapitulated by the major kavalactones in kava. Among the 6 major kavalactones, DHK demonstrated the best potency. Taken together, our study suggests a novel mechanism through which kava and its ingredients potentially offer the anxiolytic and cancer-preventive activity.
(https://doi.org/10.1055/a-1035-5183)

Celentano, A., Tran, A., Testa, C., Thayanantha, K., Tan-Orders, W., Tan, S., Syamal, M., McCullough, M. J. & Yap, T. The protective effects of Kava (Piper Methysticum) constituents in cancers: A systematic review. Journal of Oral Pathology and Medicine 48, 510-529 (2019).

Abstract:
Background
Kava is a beverage made from the ground roots of the plant Piper Methysticum and has long‐held a significant place within Pacific island communities. Active compounds were extracted from kava, and secondary metabolites include kavalactones, chalcones, cinnamic acid derivatives and flavanones. It is thought that components of kava may exert an antiproliferative effect through cell cycle arrest and promotion of apoptosis.

Methods
We conducted a systematic review to summarize available evidence of the anticancer effects of kava components and investigate their potential use for oral squamous cell carcinoma (OSCC) treatment. Eligible studies were identified through a comprehensive search of OVID EMBASE, OVID MEDLINE and Web of Science, as at April 2018.

Results
Of 39 papers that met the inclusion criteria, 32 included in vitro models and 13 included animal studies. A total of 26 different cancers were assessed with 32 studies solely assessing epithelial cancers, 6 mesenchymal cancers and 1 study including both. There was only one report assessing an OSCC cell line. Antiproliferative properties were demonstrated in 32 out of 39 papers. The most researched constituent of kava was flavokavain B followed by flavokavain A. Both were associated with increased expression of pro‐apoptotic proteins and decreased expression of anti‐apoptotic proteins. Further, they were associated with a dose‐dependent reduction of angiogenesis.

Conclusion
There was heterogeneity of study models and methods of investigation across the studies identified. Components of kava appear to present an area of interest with chemotherapeutic potential in cancer prevention and treatment, particularly for epithelial neoplasms. To date, there is a paucity of literature of the utility of kava components in the prevention and treatment of oral squamous cell carcinoma.
(https://doi.org/10.1111/jop.12900)

Shaik, A. A., Hermanson, D. L., & Xing, C. (2009). Identification of methysticin as a potent and non-toxic NF-κB inhibitor from kava, potentially responsible for kava’s chemopreventive activity. Bioorganic and Medicinal Chemistry Letters, 19, 5732–5736.

Abstract:
Nuclear factor-κB (NF-κB) is a transcription factor that plays an essential role in cancer development. The results of our recent chemopreventive study demonstrate that kava, a beverage in the South Pacific Islands, suppresses NF-κB activation in lung adenoma tissues, potentially a mechanism responsible for kava’s chemopreventive activity. Methysticin is identified as a potent NF-κB inhibitor in kava with minimum toxicity. Other kava constituents, including four kavalactones of similar structures to methysticin, demonstrate minimum activities in inhibiting NF-κB.
(https://doi.org/10.1016/j.bmcl.2009.08.003)

Open Access Article
Johnson, T. E., Kassie, F., O'Sullivan, M. G., Negia, M., Hanson, T. E., Upadhyaya, P., Ruvolo, P. P., Hecht, S. S. & Xing, C. Chemopreventive effect of kava on 4-(methylnitrosamino)-1-(3-pyridyl)-1- butanone plus benzo[a]pyrene-induced lung tumorigenesis in A/J mice. Cancer Prevention Research 1, 430-438 (2008).

Abstract:
Lung cancer is the leading cause of cancer death, and chemoprevention is a potential strategy to help control this disease. Epidemiologic survey indicates that kava may be chemopreventive for lung cancer, but there is a concern about its potential hepatotoxicity. In this study, we evaluated whether oral kava could prevent 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) plus benzo[a]pyrene (B[a]P)–induced lung tumorigenesis in A/J mice. We also studied the effect of kava to liver. At a dose of 10 mg/g diet, 30-week kava treatment (8 weeks concurrent with NNK and B[a]P treatment followed by 22 weeks post-carcinogen treatment) effectively reduced lung tumor multiplicity by 56%. Kava also reduced lung tumor multiplicity by 47% when administered concurrently with NNK and B[a]P for 8 weeks. Perhaps most importantly, kava reduced lung tumor multiplicity by 49% when administered after the final NNK and B[a]P treatment. These results show for the first time the chemopreventive potential of kava against lung tumorigenesis. Mechanistically, kava inhibited proliferation and enhanced apoptosis in lung tumors, as shown by a reduction in proliferating cell nuclear antigen (PCNA), an increase in caspase-3, and cleavage of poly(ADP-ribose) polymerase (PARP). Kava treatment also inhibited the activation of nuclear factor κBNF-κB, a potential upstream mechanism of kava chemoprevention. Although not rigorously evaluated in this study, our preliminary data were not suggestive of hepatotoxicity. Based on these results, further studies are warranted to explore the chemopreventive potential and safety of kava.
(https://doi.org/10.1158/1940-6207.capr-08-0027)

Johnson, T. E., Hermanson, D., Wang, L., Kassie, F., Upadhyaya, P., O'Sullivan, M. G., Hecht, S. S., Lu, J. & Xing, C. Lung tumorigenesis suppressing effects of a commercial kava extract and its selected compounds in A/J mice. American Journal of Chinese Medicine 39, 727-742 (2011).

Abstract:
Lung cancer is the most deadly malignancy in the US. Chemoprevention is potentially a complementary approach to smoking cessation for lung cancer control. Recently, we reported that a commercially available form of kava extract significantly inhibits 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and benzo(a)pyrene (BaP)-induced lung tumorigenesis in A/J mice at a dose of 10 mg per gram diet. In the present study, we examined the dose-dependent lung tumor inhibitory activities of kava and investigated potential active constituent(s). Mice treated with carcinogen alone contained 12.1±5.8 lung adenomas per mouse 22 weeks after final carcinogen administration. Mice that were fed diets containing kava at dosages of 1.25, 2.5, 5, and 10 mg/g of diet had 8.4±3.5, 6.6±3.5, 4.3±2.4, and 3.8±2.3 lung adenomas per mouse, respectively. This corresponds to a reduction of 31%, 46%, 65% and 69% in tumor multiplicity, which were all statistically significant (p < 0.05). Analyses of lung adenoma tissues derived from kava-treated animals revealed that kava significantly inhibited adenoma cell proliferation while it had no detectable effect on cell death, indicating that kava primarily suppressed lung tumorigenesis in A/J mice via inhibition of cell proliferation. Flavokawains A, B, and C, three chalcone-based components from kava, demonstrated greatly reduced chemopreventive efficacies even at concentrations much higher than their natural abundance, suggesting that they alone were unlikely to be responsible for kava's chemopreventive activity. Kava at all dosages and treatment regimens did not induce detectable adverse effects, particularly with respect to liver. Specifically, kava treatment showed no effect on liver integrity indicator enzymes or liver weight, indicating that kava may be potentially safe for long-term chemopreventive application.
(https://doi.org/10.1142/s0192415x11009202)

Open Access Article
Tang, S. N., Zhang, J., Jiang, P., Datta, P., Leitzman, P., O’Sullivan, M. G., Jiang, C., Xing, C., & Lü, J. (2016). Gene expression signatures associated with suppression of TRAMP prostate carcinogenesis by a kavalactone-rich Kava fraction. Molecular Carcinogenesis, 55(12), 2291–2303.

Abstract:
Kava (Piper methysticum Forster) extract and its major kavalactones have been shown to block chemically induced lung tumor initiation in mouse models. Here we evaluated the chemopreventive effect of a kavalactone-rich Kava fraction B (KFB), free of flavokavains, on carcinogenesis in a transgenic adenocarcinoma of mouse prostate (TRAMP) model and characterized the prostate gene expression signatures. Male C57BL/6 TRAMP mice were fed AIN93M diet with or without 0.4% KFB from 8 wk of age. Mice were euthanized at 16 or 28 wk. The growth of the dorsolateral prostate (DLP) lobes in KFB-treated TRAMP mice was inhibited by 66% and 58% at the respective endpoint. Anterior and ventral prostate lobes in KFB-treated TRAMP mice were suppressed by 40% and 49% at 28 wk, respectively. KFB consumption decreased cell proliferation biomarker Ki-67 and epithelial lesion severity in TRAMP DLP, without detectable apoptosis enhancement. Real time qRT-PCR detection of mRNA from DLP at 28 wk showed decreased expression of cell cycle regulatory genes congruent with Ki-67 suppression. Microarray profiling of DLP mRNA indicated that “oncogene-like” genes related to angiogenesis and cell proliferation were suppressed by KFB but tumor suppressor, immunity, muscle/neuro, and metabolism-related genes were upregulated by KFB in both TRAMP and WT DLP. TRAMP mice fed KFB diet developed lower incidence of neuroendocrine carcinomas (NECa) (2 out of 14 mice) than those fed the basal diet (8 out of 14 mice, χ2 = 5.6, P < 0.025). KFB may, therefore, inhibit not only TRAMP DLP epithelial lesions involving multiple molecular pathways, but also NECa.
(https://doi.org/10.1002/mc.22469)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/26840761/)

Open Access Document
Steiner, G. G., The Correlation between Cancer Incidence and Kava Consumption. Hawaii Med J 59, 420-422 (2000).

Abstract:
Background. A number of countries in the South Pacific have very low cancer incidence. In spite of a high percentage of the population habituated to tobacco, the cancer incidence in countries such as Vanuatu and Fiji experience age-standardized cancer incidence in the 70’s. A number of studies have noted the low cancer incidence in these countries and have postulated that a dietary chemopreventive agent might be responsible. Methods. The cancer incidence studies for the Pacific Islands were completed in the 1980’s. During this time period accurate records allow for a calculation of local kava consumption. This study compares the cancer incidence for a number of Pacific Island Nations with local kava consumption. Results/Conclusions. The data indicates that the more kava consumed by a population the lower the cancer incidence for that population. The data suggests there is a close inverse relationship between cancer incidence and kava consumption.
(https://core.ac.uk/download/pdf/77123272.pdf)

Open Access Article
Li, X., Liu, Z., Xu, X., Blair, C. A., Sun, Z., Xie, J., Lilly, M. B. & Zi, X. Kava components down-regulate expression of AR and AR splice variants and reduce growth in patient-derived prostate cancer xenografts in mice. PLoS One 7, (2012).

Abstract:
Men living in Fiji and drinking kava have low incidence of prostate cancer (PCa). However, the PCa incidence among Fijian men who had migrated to Australia, increased by 5.1-fold. We therefore examined the potential effects of kava root extracts and its active components (kavalactones and flavokawains) on PCa growth and androgen receptor (AR) expression. PCa cell lines (LNCaP, LAPC-4, 22Rv1, C4-2B, DU145 and PC-3) with different AR expression, and a transformed prostate myofibroblast cell line (WPMY-1), were treated with a commercial kava extract, kavalactones (kawain, 5′6′-dehydrokawain, yangonin, methysticin) and flavokawain B. Expression of AR and its target genes (PSA and TMPRSS2) was examined. Two novel patient-derived PCa xenograft models from high grade PCa specimens were established by implanting the specimens into nude mice and passing tumor pieces through subcutaneous injection in nude mice, and then treated with kava extract and flavokawain B to examine their effects on tumor growth, AR expression and serum PSA levels. The kava extract and flavokawain B effectively down-regulated the expression of both the full-length AR and AR splice variants. The kava extract and kavalactones accelerated AR protein degradation, while flavokawain B inhibited AR mRNA transcription via decreasing Sp1 expression and the binding of Sp1 to the AR promoter. The kava root extract and flavokawain B reduce tumor growth, AR expression in tumor tissues and levels of serum PSA in the patient-derived PCa xenograft models. These results suggest a potential usefulness of a safe kava product or its active components for prevention and treatment of advanced PCa by targeting AR.
(https://doi.org/10.1371/journal.pone.0031213)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/22347450/)

Open Access Article
Li, X., Yokoyama, N. N., Zhang, S., Ding, L., min Liu, H., Lilly, M. B., Mercola, D. & Zi, X. Flavokawain A induces deNEDDylation and Skp2 degradation leading to inhibition of tumorigenesis and cancer progression in the TRAMP transgenic mouse model. Oncotarget 6, 41809-41824 (2015).

Abstract:
S phase kinase-associated protein 2 (Skp2) has been shown to be required for spontaneous tumor development that occurs in the retinoblastoma protein (pRb) deficient mice. Here we have demonstrated that flavokawain A (FKA), a novel chalcone from the kava plant, selectively inhibited the growth of pRb deficient cell lines and resulted in a proteasome-dependent and ubiquitination-mediated Skp2 degradation. Degradation of Skp2 by FKA was found to be involved in a functional Cullin1, but independent of Cdh1 expression. Further studies have demonstrated that FKA docked into the ATP binding pocket of the precursor cell-expressed developmentally down-regulated 8 (NEDD8)-activating enzyme (NAE) complex, inhibited NEDD8 conjugations to both Cullin1 and Ubc12 in PC3 cells and Ubc12 NEDDylation in an in vitro assay. Finally, dietary feeding of the autochthonous transgenic adenocarcinoma of the mouse prostate (TRAMP) mice with FKA inhibited the formation of high-grade prostatic intra-epithelial neoplasia lesions (HG-PIN) and prostate adenocarcinomas, reduced the tumor burden and completely abolished distant organ metastasis. Immunohistochemistry studies revealed that dietary FKA feeding resulted in marked anti-proliferative and apoptotic effects via down-regulation of Skp2 and NEDD8 and up-regulation of p27/Kip1 in the prostate of TRAMP mice. Our findings therefore provide evidence that FKA is a promising NEDDylation inhibitor for targeting Skp2 degradation in prostate cancer prevention and treatment.
(https://doi.org/10.18632/oncotarget.6166)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/26497688/)

Open Access Article
Liu, Z., Xu, X., Li, X., Liu, S., Simoneau, A. R., He, F., Wu, X. R. & Zi, X. KAVA chalcone, flavokawain A, inhibits urothelial tumorigenesis in the UPII-SV40T transgenic mouse model. Cancer Prevention Research 6, 1365-1375 (2013).

Abstract:
Flavokawain A (FKA) is the predominant chalcone identified from the kava plant. We have previously demonstrated that FKA preferentially inhibits the growth of p53 defective bladder cancer cell lines. Here we examined whether FKA could inhibit bladder cancer development and progression in vivo in the UPII-SV40T transgenic model that resembles human urothelial cell carcinoma (UCC) with defects in the p53 and the retinoblastoma (RB) protein pathways. Genotyped UPII-SV40T mice were fed orally with vehicle control (AIN-93M) or FKA (6 g/kg food; 0.6%) for 318 days starting at 28 days of age. More than 64% of the male mice fed with FKA-containing food survived beyond 318 days of age, whereas only about 38% of the male mice fed with vehicle control food survived to that age (p= 0.0383). The mean bladder weights of surviving male transgenic mice with the control diet versus the FKA diet were 234.6 ± 72.5 versus 96.1±69.4 mg (P=0.0002). FKA was excreted primarily through the urinary tract and concentrated in the urine up to 8.4 μmol/L, averaging about 38 times (males) and 15 times (females) more concentrated than in the plasma (P=0.0001). FKA treatment inhibited the occurrence of high-grade papillary UCC, a precursor to invasive urothelial cancer, by 42.1%. A decreased expression of Ki67, survivin and XIAP and increased expression of p27 and DR5 and number of TUNEL-positive apoptotic cells were observed in the urothelial tissue of FKA-fed mice. These results suggest a potential of FKA in preventing the recurrence and progression of non-muscle invasive UCC.
(https://doi.org/10.1158/1940-6207.capr-13-0219)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/24121102/)

Open Access Article
Tang, Y., Simoneau, A. R., Xie, J., Shahandeh, B. & Zi, X. Effects of the kava chalcone flavokawain A differ in bladder cancer cells with wild-type versus mutant p53. Cancer Prevention Research 1, 439-451 (2008).

Abstract:
Flavokawain A is the predominant chalcone from kava extract. We have assessed the mechanisms of flavokawain A's action on cell cycle regulation. In a p53 wild-type, low-grade, and papillary bladder cancer cell line (RT4), flavokawain A increased p21/WAF1 and p27/KIP1, which resulted in a decrease in cyclin-dependent kinase-2 (CDK2) kinase activity and subsequent G1 arrest. The increase of p21/WAF1 protein corresponded to an increased mRNA level, whereas p27/KIP1 accumulation was associated with the down-regulation of SKP2 and then increased the stability of the p27/KIP1 protein. The accumulation of p21/WAF1 and p27/KIP1 was independent of cell cycle position and thus not a result of the cell cycle arrest. In contrast, flavokawain A induced a G2-M arrest in six p53 mutant-type, high-grade bladder cancer cell lines (T24, UMUC3, TCCSUP, 5637, HT1376, and HT1197). Flavokawain A significantly reduced the expression of CDK1-inhibitory kinases, Myt1 and Wee1, and caused cyclin B1 protein accumulation leading to CDK1 activation in T24 cells. Suppression of p53 expression by small interfering RNA in RT4 cells restored Cdc25C expression and down-regulated p21/WAF1 expression, which allowed Cdc25C and CDK1 activation and then led to a G2-M arrest and an enhanced growth-inhibitory effect by flavokawain A. Consistently, flavokawain A also caused a pronounced CDK1 activation and G2-M arrest in p53 knockout but not in p53 wild-type HCT116 cells. This selectivity of flavokawain A for inducing a G2-M arrest in p53-defective cells deserves further investigation as a new mechanism for the prevention and treatment of bladder cancer.
(https://doi.org/10.1158/1940-6207.capr-08-0165)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/19138991/)

Pollastri, M. P., Whitty, A., Merrill, J. C., Tang, X., Ashton, T. D., & Amar, S. (2009). Identification and characterization of kava-derived compounds mediating TNF-α suppression. Chemical Biology and Drug Design, 74(2), 121–128.

Abstract:
There is a substantial unmet need for new classes of drugs that block TNF‐α‐mediated inflammation, and particularly for small molecule agents that can be taken orally. We have screened a library of natural products against an assay measuring TNF‐α secretion in lipopolysaccharide‐stimulated THP‐1 cells, seeking compounds capable of interfering with the TNF‐α‐inducing transcription factor lipopolysaccharide‐induced TNF‐α factor. Among the active compounds were several produced by the kava plant (Piper mysticum), extracts of which have previously been linked to a range of therapeutic effects. When tested in vivo, a representative of these compounds, kavain, was found to render mice immune to lethal doses of lipopolysaccharide. Kavain displays promising pharmaceutical properties, including good solubility and high cell permeability, but pharmacokinetic experiments in mice showed relatively rapid clearance. A small set of kavain analogs was synthesized, resulting in compounds of similar or greater potency in vitro compared with kavain. Interestingly, a ring‐opened analog of kavain inhibited TNF‐α secretion in the cell‐based assay and suppressed lipopolysaccharide‐induced TNF‐α factor expression in the same cells, whereas the other compounds inhibited TNF‐α secretion without affecting lipopolysaccharide‐induced TNF‐α factor levels, indicating a potential divergence in mechanism of action.
(https://doi.org/10.1111/j.1747-0285.2009.00838.x)

Li, J., Zheng, L., Yan, M., Wu, J., Liu, Y., Tian, X., Jiang, W., Zhang, L. & Wang, R. Activity and mechanism of flavokawain A in inhibiting P-glycoprotein expression in paclitaxel resistance of lung cancer. Oncology Letters 19, 379-387 (2020).

Abstract:
Lung cancer is one of the most common cancers, which is the leading cause of cancer-related death among various cancers worldwide. Flavokawain A (FKA), a chalcone found in the kava plant, exerts potent anticancer activity. However, the activity and mechanisms of FKA in inhibiting the viability of paclitaxel (PTX)-resistant lung cancer A549 (A549/T) have not been investigated. In the present study, the effect of FKA on the viability of A549/T and hepatotoxicity in normal liver epithelial cells was detected by Cell Counting Kit-8 assay. Flow cytometry, western blot analysis and Annexin V-FITC/PI apoptosis detection kit were used to assess cell apoptosis. The effect of FKA on permeability-glycoprotein (P-gp) expression was measured by reverse transcription-PCR and western blot analysis. The results indicated that FKA dose-dependently inhibited cell proliferation and induced cell apoptosis in PTX-resistant A549/T cells, with an IC50 value of ~21 µM, while the IC50 value of A549/T cells to PTX was 34.64 µM. FKA had no hepatic toxicity in liver epithelial cells. P-gp, which contributes to the chemoresistant phenotype, was not expressed in A549 cells but was remarkably enhanced in A549/T cells. FKA (30 µM) decreased P-gp protein expression at 24 h by 3-fold. Furthermore, FKA downregulated P-gp expression by blocking the PI3K/Akt pathway. These findings suggest FKA as a potential candidate for the treatment of PTX-resistant lung cancer.
(https://dx.doi.org/10.3892/ol.2019.11069)
(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6923923/)

Open Access Article
Narayanapillai, S. C., Balbo, S., Leitzman, P., Grill, A. E., Upadhyaya, P., Shaik, A. A., Zhou, B., {Gerard O'Sullivan}, M., Peterson, L. A., Lu, J., Hecht, S. S. & Xing, C. Dihydromethysticin from kava blocks tobacco carcinogen 4-(methylnitrosamino)-1- (3-pyridyl)-1-butanone-induced lung tumorigenesis and differentially reduces DNA damage in A/J mice. Carcinogenesis 35, 2365-2372 (2014).

Abstract:
We have previously shown that kava and its flavokavain-free Fraction B completely blocked 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in A/J mice with a preferential reduction in NNK-induced O 6-methylguanine (O 6-mG). In this study, we first identified natural (+)-dihydromethysticin (DHM) as a lead compound through evaluating the in vivo efficacy of five major compounds in Fraction B on reducing O 6-mG in lung tissues. (+)-DHM demonstrated outstanding chemopreventive activity against NNK-induced lung tumorigenesis in A/J mice with 97% reduction of adenoma multiplicity at a dose of 0.05mg/g of diet (50 ppm). Synthetic (±)-DHM was equally effective as the natural (+)-DHM in these bioassays while a structurally similar analog, (+)-dihydrokavain (DHK), was completely inactive, revealing a sharp in vivo structure–activity relationship. Analyses of an expanded panel of NNK-induced DNA adducts revealed that DHM reduced a subset of DNA adducts in lung tissues derived from 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, the active metabolite of NNK). Preliminary 17-week safety studies of DHM in A/J mice at a dose of 0.5mg/g of diet (at least 10× its minimum effective dose) revealed no adverse effects, suggesting that DHM is likely free of kava’s hepatotoxic risk. These results demonstrate the outstanding efficacy and promising safety margin of DHM in preventing NNK-induced lung tumorigenesis in A/J mice, with a unique mechanism of action and high target specificity.
(https://doi.org/10.1093/carcin/bgu149)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25053626/)

Open Access Article
Zhang, Y., Zvi, Y. S., Batko, B., Zaphiros, N., O'Donnell, E. F., Wang, J., Sato, K., Yang, R., Geller, D. S., Koirala, P., Zhang, W., Du, X., Piperdi, S., Liu, Y., Zheng, D., Roth, M., Gill, J., Zhang, J., Ren, T., Gorlick, R., Zi, X. & Hoang, B. H. Down-regulation of Skp2 expression inhibits invasion and lung metastasis in osteosarcoma. Sci. Rep. 8, 1-13 (2018).

Abstract:
Osteosarcoma (OS), the most common primary cancer of bone, exhibits a high propensity for local invasion and distant metastasis. This study sought to elucidate the role of S phase kinase-associated protein (Skp2) in osteosarcoma invasion and metastasis and to explore flavokawain A (FKA), a natural chalcone from kava extract, as a potential Skp2 targeting agent for preventing osteosarcoma progression. Skp2 was found to be overexpressed in multiple osteosarcoma cell lines, including 5 standard and 8 primary patient-derived cell lines. Patients whose tumors expressed high levels of Skp2 sustained a significantly worse metastasis-free (p = 0.0095) and overall survival (p = 0.0013) than those with low Skp2. Skp2 knockdown markedly reduced in vitro cellular invasion and in vivo lung metastasis in an orthotopic mouse model of osteosarcoma. Similar to Skp2 knockdown, treatment with FKA also reduced Skp2 expression in osteosarcoma cell lines and blocked the invasion of osteosarcoma cells in vitro and lung metastasis in vivo. Together, our findings suggest that Skp2 is a promising therapeutic target in osteosarcoma, and that FKA may be an effective Skp2-targeted therapy to reduce osteosarcoma metastasis.
(https://doi.org/10.1038/s41598-018-32428-9)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/30250282/)

Open Access Article
Abu, N., Akhtar, M. N., Yeap, S. K., Lim, K. L., Ho, W. Y., Zulfadli, A. J., Omar, A. R., Sulaiman, M. R., Abdullah, M. P. & Alitheen, N. B. Flavokawain a induces apoptosis in MCF-7 and MDA-MB231 and inhibits the metastatic process in vitro. PLoS One 9, 1-12 (2014).

Abstract:
Introduction
The kava-kava plant (Piper methsyticum) is traditionally known as the pacific elixir by the pacific islanders for its role in a wide range of biological activities. The extract of the roots of this plant contains a variety of interesting molecules including Flavokawain A and this molecule is known to have anti-cancer properties. Breast cancer is still one of the leading diagnosed cancers in women today. The metastatic process is also very pertinent in the progression of tumorigenesis.

Methods
MCF-7 and MDA-MB231 cells were treated with several concentrations of FKA. The apoptotic analysis was done through the MTT assay, BrdU assay, Annexin V analysis, cell cycle analysis, JC-1 mitochondrial dye, AO/PI dual staining, caspase 8/9 fluorometric assay, quantitative real time PCR and western blot. For the metastatic assays, the in vitro scratch assay, trans-well migration/invasion assay, HUVEC tube formation assay, ex vivo rat aortic ring assay, quantitative real time PCR and western blot were employed.

Results
We have investigated the effects of FKA on the apoptotic and metastatic process in two breast cancer cell lines. FKA induces apoptosis in both MCF-7 and MDA-MB231 in a dose dependent manner through the intrinsic mitochondrial pathway. Additionally, FKA selectively induces a G2/M arrest in the cell cycle machinery of MDA-MB231 and G1 arrest in MCF-7. This suggests that FKA's anti-cancer activity is dependent on the p53 status. Moreover, FKA also halted the migration and invasion process in MDA-MB231. The similar effects can be seen in the inhibition of the angiogenesis process as well.

Conclusions
FKA managed to induce apoptosis and inhibit the metastatic process in two breast cancer cell lines, in vitro. Overall, FKA may serve as a promising candidate in the search of a new anti-cancer drug especially in halting the metastatic process but further in vivo evidence is needed.
(https://doi.org/10.1371/journal.pone.0105244)
(https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25286005/)
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