In vitro inhibition of human cytochrome P450 by cudratricusxanthone A

Cudratricusxanthone A (CTXA) isolated from the roots of Cudrania tricuspidata Bureau (Moraceae) has several biological activities, including hepatoprotective, neuroprotective, anti-inflammatory, monoamine oxidase inhibitory, and antithrombotic activities. In this study, we investigated the potential herb-drug interaction of CTXA and nine cytochrome P450 (CYP) isoforms in pooled human liver microsomes (HLMs) using a cocktail probe assay. CTXA reversibly inhibited the CYP1A2-catalyzed phenacetin O-deethylation, CYP2C8-catalyzed paclitaxel 6-hydroxylation, and CYP2C9-catalyzed diclofenac 4′-hydroxylation with half-maximal inhibitory concentration (IC50) values of 3.9, 4.7, and 2.9 µM, respectively. The IC50 values did not change under different preincubation conditions. CTXA showed marked dose-dependent, but not time-dependent, inhibition of CYP1A2 and 2C9 activities in HLMs. Dixon plots showed typical competitive inhibition of CYP1A2 and CYP2C9 with Ki values of 1.3 and 1.5 µM, respectively. Further, CTXA inhibited CYP2C8 in a non-competitive manner with a Ki value of 2.2 µM. Our results showed that CTXA reversibly inhibits CYP1A2, 2C8, and 2C9.