Speaker
Description
[Background]
Xanthoxylin (2′-hydroxy-4′,6′-dimethoxyacetophenone) is a natural compound found in traditional medicinal plants such as Zanthoxylum species, which have been used for pain relief and inflammatory conditions. While several biological activities have been reported in vitro, the metabolic fate of xanthoxylin in humans remains completely unknown. Understanding its metabolism by human cytochrome P450 (P450 or CYP) enzymes is a prerequisite for assessing potential herb-drug interactions and guiding safe clinical use.
[Methods]
Xanthoxylin metabolism was investigated using pooled human liver microsomes (HLMs) and recombinant human P450 enzymes, including CYP2C9, CYP2C19, CYP2D6, and CYP3A4. Metabolites produced by HLMs were separated and structurally characterized by high-performance liquid chromatography (HPLC), gas chromatography–mass spectrometry (GC–MS), and nuclear magnetic resonance (NMR) spectroscopy. The contributions of individual P450 isoforms were evaluated using isoform-selective chemical inhibitors and immunoinhibition with anti-P450 antibodies. The inhibitory effects of xanthoxylin on CYP-mediated drug metabolism were further assessed using representative probe substrate assays.
[Results]
Three major metabolites and one minor metabolite of xanthoxylin were identified. Structural analysis revealed that the metabolites were formed through O-demethylation and aromatic hydroxylation reactions. Reaction phenotyping demonstrated that CYP3A4 and CYP2C19 were the primary enzymes responsible for xanthoxylin oxidation in HLMs. CYP2C19 predominantly catalyzed O-demethylation leading to formation of the major metabolite M1, whereas CYP3A4 mainly mediated aromatic hydroxylation producing M2 and M3. CYP2C9 and CYP2D6 contributed to a lesser extent.
[Conclusions]
This study identified three major metabolites of xanthoxylin and demonstrated that CYP3A4 and CYP2C19 are the primary enzymes responsible for its hepatic metabolism, with CYP2C9 and CYP2D6 contributing to a lesser extent. The observed inhibitory effects of xanthoxylin on these P450 enzymes suggest the potential for herb–drug interactions, particularly with drugs metabolized by CYP2C19 and CYP3A4. These findings provide important information for the safe use of xanthoxylin-containing herbal products and highlight the need for further pharmacokinetic and clinical interaction studies.
