Hydroxylation of warfarin by human cDNA-expressed cytochrome P-450: a role for P-4502C9 in the etiology of (S)-warfarin-drug interactions

Abstract

Previous kinetic studies have identified a high-affinity (S)-warfarin 7-hydroxylase present in human liver microsomes which appears to be responsible for the termination of warfarin's biological activity. Inhibition of the formation of (S)-7-hydroxywarfarin, the inactive, major metabolite of racemic warfarin in humans, is known to be the cause of several of the drug interactions experienced clinically upon coadministration of warfarin with other therapeutic agents. In order to identify the specific form(s) of human liver cytochrome P-450 involved in this particular toxicity, we have determined the metabolic profiles of 11 human cytochrome P-450 forms expressed in HepG2 cells toward both (R)- and (S)-warfarin. Of the 11 forms examined only 2C9 displayed the regioselectivity and stereoselectivity appropriate for the high-affinity human liver microsomal (S)-7-hydroxylase. We further compared Michaelis-Menten and sulfaphenazole inhibition constants for (S)-warfarin 7-hydroxylation catalyzed by cDNA-expressed 2C9 and by human liver microsomes. Similar kinetic constants were obtained for each enzyme source. It is concluded that 2C9 is likely to be a principal form of human liver P-450 which modulates the in vivo anticoagulant activity of the drug. It is further concluded that those drug interactions with warfarin that arise as a result of decreased clearance of the biologically more potent S-enantiomer may have as their common basis the inhibition of P-450 2C9.

Pharmacogenomics and personalized medicine: a review focused on their application in the Chinese population

“…The search for genetic determinants influencing warfarin response began in the 1990s. The first target genetic factor was the warfarin-metabolizing enzyme cytochrome P450 2C9 (CYP2C9) [60] . The most common variants in Caucasians are CYP2C9*2 (rs1799853), which has an Arg144Cys substitution, and CYP2C9*3 (rs1057920), which has an Ile359Thr substitution [61,62] .…”

The Importance of Drug Interactions in Epilepsy Therapy

“…Warfarin is an anticoagulant that is therapeutically similar to dicoumarol. Its metabolism is primarily via CYP2C9, although CYP3A4 and CYP1A2 also are involved (105). Enzyme-inducing AEDs, such as PB, PHT, and CBZ can reduce the anticoagulant effects of both drugs by increasing their metabolism, possibly via an induction of CYP2C9 (106,107).…”

Common VKORC1 and GGCX polymorphisms associated with warfarin dose

“…15 Warfarin is administered as a racemate that consists of R-and S-enantiomers, the S-form being three to five times more active than the R form. 16,17 S-warfarin is metabolised by the cytochrome P450 enzyme CYP2C9, 18 and genetic variability in CYP2C9 partly explains the large differences in the required warfarin dose. 15 Two variants that encode enzymes with single amino-acid substitutions, CYP2C9*2 and CYP2C9*3, are associated with a significant decrease in warfarin dose requirement, especially among Europeans.…”