Glucuronidation of Warfarin Metabolites by Human Recombinant UDP-Glucnronosyltransferases (UGTs).

Warfarin is an anticoagulant used for the prevention of thrombosis and embolism. Hydroxylation of warfarin via CYP450s is well documented; however, its biotransformation by UGTs has not been investigated. The activities of 8 human recombinant UGTs, towards warfarin and its hydroxylated metabolites have been assessed with R-warfarin and racemic warfarin, 4′-OH-, 6-OH-, 7-OH-, and 10-OH-warfarin. HPLC-UV-Vis assays and HPLC-MS/MS product confirmations established that UGT1A10, -1A1, -1A3, and -1A8 (highest to lowest activity) conjugated 7-OH-warfarin. Kinetic assays measured K_m and V_max values for 7-OH-warfarin glucuronidation at 165.5 ± 42.7 µM and 1.14 ± 0.1 nmol/mg protein/min, respectively by UGT1A10. 6-OH-warfarin is glucuronidated by 1A1 and 1A10, and 4′-OH-warfarin is glucuronidated by 1A10, but at low levels. Warfarin, 10-OH-warfarin, or R-warfarin were not glucuronidated. This is the first demonstration that major CYP450 metabolites of warfarin are glucuronidated by human recombinant UGTs, with UGT1A10 being the major isoform involved in human phase II biotransformation. [ABSTRACT FROM AUTHOR]