标题：Identification of Enzymes Responsible for the N-Oxidation of Darexaban Glucuronide, the Pharmacologically Active Metabolite of Darexaban, and the Glucuronidation of Darexaban N-Oxides in Human Liver Microsomes
摘要：Darexaban maleate is a novel oral direct factor Xa inhibitor. Darexaban glucuronide (YM-222714) was the major component in plasma after oral administration of darexaban to humans and is the pharmacologically active metabolite. Additionally, YM-222714 N -oxides were detected as minor metabolites in human plasma and urine. It is possible that YM-222714 N -oxides are formed by the N -oxidation of YM-222714 and/or the glucuronidation of darexaban N -oxides (YM-542845) in vivo . The former reaction is the pharmacological inactivation process. In this study, we identified the human enzymes responsible for YM-222714 N -oxidation and the uridine 5′-diphosphate (UDP)-glucuronosyltransferase (UGT) isoforms involved in YM-542845 glucuronidation in vitro . YM-222714 N -oxidation activity was detected in human liver microsomes (HLM), but not in human intestinal microsomes. In HLM, YM-222714 N -oxidation activities were significantly correlated with flavin-containing monooxygenase (FMO) marker enzyme activities ( p <0.001) and inhibited by methimazole, a typical inhibitor of FMOs. Recombinant human FMO3 and FMO1 were capable of efficiently catalyzing YM-222714 N -oxidation, but not FMO5 or any recombinant human cytochrome P450 (CYP) isoforms. Considering the mRNA expression levels of FMO isoforms in human liver, these results strongly suggest that YM-222714 N -oxidation in HLM is mainly catalyzed by FMO3. In HLM, YM-542845 glucuronidation was strongly inhibited by typical substrates for UGT1A8, UGT1A9, and UGT1A10. Recombinant human UGT1A7, UGT1A8, UGT1A9, and UGT1A10 were capable of catalyzing YM-542845 glucuronidation, and UGT1A9 exhibited the highest intrinsic clearance. Considered together with the expression levels of UGT isoforms in human liver, these results strongly suggest that YM-542845 glucuronidation in HLM is mainly catalyzed by UGT1A9.
关键词：darexaban;N-oxidation;flavin-containing monooxygenase 3;glucuronidation;uridine 5′-diphosphate-glucuronosyltransferase 1A9;pharmacologically active metabolite
