Inhibition of CYP2C9 by natural products: insight into the potential risk of herb-drug interactions

Due to the rapidly increasing global interest in the use of herbs, phytomedicines and other natural products as medical or complementary remedies, concerns about the clinical medication safety have drawn much attention worldwide. Particularly, many natural ingredients exhibit inhibitory effects on cytochrome P450 (CYP) enzymes, which are the most important Phase I metabolism enzymes in liver. CYP2C9 is one of the most abundant CYP enzymes and responsible for the metabolism of over 15% clinical drugs, including oral sulfonylurea hypoglycemics, nonsteroidal anti-inflammatory agents, selective cyclooxygenase-2 inhibitors, antiepileptics, angiotensin II receptor inhibitors and anticoagulants. Diclofenac (4'-hydroxylase) and tolbutamide (methylhydroxylation) are widely used as probe substrates for CYP2C9. To date, numerous natural products have been reported to have the capabilities of inhibiting the catalytic activity of CYP2C9 and further influencing the pharmacokinetic and pharmacodynamic behaviors of drugs that are mainly metabolized by CYP2C9, leading to potential herb-drug interactions. Moreover, some fatal adverse interactions may occur for drugs with a narrow therapeutic window when they are coadministered with a CYP2C9 inhibitor, especially irreversible inactivators. For the purpose of better understanding the interactions of natural products with CYP2C9, we comprehensively reviewed the characteristics of CYP2C9, the natural ingredients that inhibit CYP2C9, the related research approaches and strategies, the types of inhibition and the underlying mechanisms.