ORIGINAL ARTICLE Permeability studies of Kavalactones using a Caco-2 cell monolayer model A. Matthias* PhD, J. T. Blanchfield PhD, K. G. Penman* PhD, K. M. Bone* à BSc (Hons) Dip Phyt , I. Toth § PhD DSc and R. P. Lehmann* PhD *MediHerb Research Laboratories, Brisbane, Queensland, Australia,  School of Molecular and Microbial Sciences, The University of Queensland, Brisbane, Queensland, Australia, àSchool of Health, University of New England, Armidale, Australia and §School of Pharmacy, The University of Queensland, Brisbane, Queensland, Australia SUMMARY Objective: To examine the bioavailability of kavalactones in vitro and the possible differences in their bioavailability because of variations in either chemical structure or the method of extraction used. Research design and methods: Caco-2 cell mono- layers were used to determine the potential bioavailability of kavalactones. Kavalactones were added to the apical layer and basolateral samples were taken over 150 min to examine the concentration diffusing across the cell monolayer. Kavalactone concentrations in these samples were determined by high pressure liquid chromatography. Results: Kavalactones were found to be poten- tially bioavailable as they all readily crossed the Caco-2 monolayers with apparent permeabilities (P app ) increasing from 42 · 10 )6 cm/s and most exhibiting more than 70% crossing within 90 min. Not all differences in their bioavailability can be related to kavalactone structural differences as it appears that bioavailability may also be affected by co-extracted compounds. For example, the P app for kawain from ethanol extracts was higher than the values obtained for the same compound from water extracts or for the kavalactone alone. Conclusions: While the extraction method used (ethanol or water) influences the total (but not the relative) concentrations of kavalactones, it does not markedly affect their bioavailability. Hence, any differences between an ethanolic or an aqueous extract in terms of the propensity of kava to cause liver damage is not because of differing kavalactone bioavailabilities. Keywords: bioavailability, Caco-2 monolayers, kava, kavalactone, Piper methysticum INTRODUCTION Kava is a traditional beverage and psychotropic drug used by South Pacific Islanders for both ceremonial and medical purposes. It is derived from the rootstock of a sterile cultivated species of Piper methysticum and contains natural products from a number of phytochemical groups including kavalactones and chalcones (flavokavains) as well as small amounts of essential oil. Traditionally, potent beverages are prepared by chewing or pounding the root to produce a cloudy, milky mash which is then consumed orally. The major physiological action in humans is that of a mild centrally acting relaxant (1, 2), with a numbing of the mucous membranes of the mouth and tongue noted when the beverage is consumed. In Europe, it was popularly consumed as a treatment for anxiety as clinical observations have revealed increased calmness, a reduction of tension, irritability and anxiety as well as improvements in concentration and efficiency in intellectual and practical work in patients consuming kava extracts (3). In a review of six kava clinical trials (n = 345 subjects), meta-ana- lysis revealed significant (P = 0Æ01) reductions in anxiety, using the Hamilton anxiety scale, with kava as compared with placebo (4). Received 06 July 2006, Accepted 2 January 2007 Correspondence: Assoc. Prof. R. P. Lehmann, MediHerb Research Laboratories, 3/85 Brandl Street, Eight Mile Plains, Brisbane, Queensland 4113, Australia. Tel.: +61 7 3423 6521; fax: +61 7 3423 6599; e-mail: reg@mediherb.com.au Journal of Clinical Pharmacy and Therapeutics (2007) 32, 233–239 Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Publishing Ltd 233