Kavalactone profiling of Piper methysticum root and rhizome extracts and the modulation of CYP450 activity in vitro.

Kava (Piper methysticum Forst) has historically been consumed throughout the Pacific Islands, where traditional water-based preparations have exhibited a favorable safety record for centuries. In the late 20th century, kava gained global popularity as a medicinal product used for anxiolytic purposes, leading to rapid expansion of both use and production, primarily in Europe and the United States. A small number of rare but serious liver injury cases followed, raising concerns about kava's global safety profile. Despite 25 years of investigation, a causal link between kava and liver injury remains undefined. A validated UHPLC-UV method confirmed distinct profiles for aqueous and ethanol extracts derived from the same biomass, highlighting enriched levels of methysticin and yangonin in ethanol extracted kava, while dihydrokavain alone constituted over 67% of the kavalactone (KL) content of the water extracted kava. Cytotoxicity assays in human hepatocytes demonstrated no toxicity for either extract, however, flavokavain B exhibited distinct cytotoxicity. Investigations into cytochrome P450 enzyme modulation indicated significant inhibition on CYP3A4 and CYP1A2 by both extracts and specific KLs, notably dihydromethysticin and methysticin, while an unexpected increase in CYP2D6 assay response was observed with higher concentrations of yangonin and both extracts in a fluorescence-based baculosome system. Interestingly, neither the individual KLs, the individual flavokavains, nor a reconstituted sample mimicking the KL fraction of the ethanol extract inhibited CYP3A4 activity, suggesting that other phytochemicals present in kava extracts may contribute to CYP modulation. These findings underscore the complexity of kava's toxicological interactions, suggesting that hepatotoxic risks might be linked to specific extraction methods and chemotypes. However, the ongoing widespread use of both water and organic solvent extracted kava with minimal reports of hepatotoxicity supports the need for translational studies to clarify whether the observed CYP modulation and cytotoxicity are clinically meaningful.