title: Roles of two allelic variants (Arg144Cys and Ile359Leu) of cytochrome P4502C9 in the oxidation of tolbutamide and warfarin by human liver microsomes.
abstract: 1. Tolbutamide methyl hydroxylation and racemic warfarin 7-hydroxylation activities were determined in liver microsomes of 39 Japanese and 45 Caucasians genotyped for the cytochrome P450 (P450 or CYP) 2C9 gene into three groups, namely the wild-type (Arg144.Ile359), and two heterozygous Cys allele (Cys144.Ile359) and Leu allele (Arg144.Leu359) variants. 2. Good correlations were found between tolbutamide methyl hydroxylation and racemic warfarin 7-hydroxylation activities in liver microsomes of Japanese and Caucasians. Humans with the Cys allele CYP2C9 variant, which was detected in 22% of Caucasians, were found to have similar catalytic rates to those of the wild-type in the oxidations of tolbutamide and racemic warfarin, whereas humans with the Leu allele, which was detected in 8% Japanese and 7% Caucasian samples, had lower catalytic rates than those of other two groups. 3. The rates of 6- and 7-hydroxylation of racemic warfarin were correlated well with those of S-warfarin, but not R-warfarin, in human liver microsomes. 4. Both human liver microsomes and recombinant CYP2C9 catalysed 7-hydroxylation of S-warfarin more extensively than those of R-warfarin. K(m)'s for the 7-hydroxylation of S-warfarin were not very different in liver microsomes of humans with these three genotypes. Anti-CYP2C9 antibodies and sulphaphenazole inhibited the 6- and 7-hydroxylation of S-warfarin, but not R-warfarin, by > 90% and the methyl hydroxylation of tolbutamide by about 50%. 5. These results suggest that humans with Leu allele of CYP2C9 have lower Vmax's for S-warfarin 7-hydroxylation and tolbutamide methyl hydroxylation than those with wild-type and Cys allele CYP2C9, although the K(m)'s are not very different in liver microsomes of these three groups of humans. R-warfarin hydroxylation may be catalysed by P450 enzymes other than CYP2C9 in man.
authors.affiliation: Osaka Prefectural Institute of Public Health, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Yamazaki
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.forename: T
authors.initials: T
authors.lastname: Shimada
mesh_terms: D000483:Alleles; D001189:Aryl Hydrocarbon Hydroxylases; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004791:Enzyme Inhibitors; D005838:Genotype; D006801:Humans; D006900:Hydroxylation; D007564:Japan / Q000208:ethnology; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology*; D011110:Polymorphism, Genetic / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D013237:Stereoisomerism; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000235:genetics*; D013426:Sulfaphenazole / Q000494:pharmacology; D014044:Tolbutamide / Q000378:metabolism*; D014859:Warfarin / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D013426:Sulfaphenazole; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System; D014044:Tolbutamide; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; D039181:Steroid 16-alpha-Hydroxylase