Mechanism-Based Inactivation of CYP2C19 by Anwuligan Resulting in Changes in Pharmacokinetic Properties of Amitriptyline

The worldwide consumption of traditional herbal preparations has risen markedly in recent years, raising increasing toxicological concern regarding drug-drug interactions. A major mechanistic basis for these interactions is the ability of specific phytochemicals to inhibit cytochrome P450 enzymes, thereby altering xenobiotic metabolism at the molecular and enzymatic levels. Anwuligan (ANL), a bioactive compound isolated from nutmeg and Schisandra chinensis, has attracted considerable pharmacological interest, yet its inhibitory potential toward P450 enzymes remains poorly defined. In this study, we systematically investigated the effects of ANL on CYP2C19 and evaluated its pharmacokinetic interaction with amitriptyline. Enzyme kinetics revealed that ANL is a mechanism-based inhibitor of CYP2C19, and NAC trapping assays indicated that an o-quinone intermediate generated during its metabolism is the key species responsible for irreversible enzyme inactivation. In vivo pharmacokinetic studies in rats showed that ANL pretreatment increased amitriptyline exposure, with Cmax and AUC0-∞ increased by 1.4-fold and ∼30%, respectively, and CLz/F reduced by 24%. In contrast, nortriptyline exposure decreased, with reductions in Cmax (39%) and AUC (29-34%). These results demonstrate CYP2C19 inhibition by ANL and its potential to cause clinically relevant drug-drug interactions.