CYP3A5 Contributes Significantly to CYP3A-mediated Drug Oxidations in Liver Microsomes from Japanese Subjects

• Published in: DRUG METABOLISM AND PHARMACOKINETICS Vol. 19; no. 2; pp. 120 - 129
• Main Authors: Yamaori, Satoshi, Yamazaki, Hiroshi, Iwano, Shunsuke, Kiyotani, Kazuma, Matsumura, Keiko, Honda, Goro, Nakagawa, Kazuko, Ishizaki, Takashi, Kamataki, Tetsuya
• Format: Journal Article
• Language: English; Japanese
• Published: England Elsevier Ltd 2004; Japanese Society for the Study of Xenobiotics
• Subjects: Calcium Channel Blockers - metabolism; CYP3A5; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Dealkylation; diltiazem; Diltiazem - metabolism; DNA - genetics; DNA Primers; Escherichia coli - metabolism; GABA Modulators - metabolism; Genotype; Humans; Hydroxylation; In Vitro Techniques; Japan; Kinetics; liver; Microsomes, Liver - enzymology; midazolam; Midazolam - metabolism; NADPH-Ferrihemoprotein Reductase - genetics; NADPH-Ferrihemoprotein Reductase - metabolism; Oxidation-Reduction; Pharmaceutical Preparations - metabolism; polymorphism; Reverse Transcriptase Polymerase Chain Reaction; testosterone; Testosterone - metabolism; diltiazem; polymorphism; testosterone; liver; midazolam; CYP3A5
• ISSN: 1347-4367; 1880-0920
• DOI: 10.2133/dmpk.19.120

The purpose of this study was to evaluate a contribution of polymorphic cytochrome P450 (CYP) 3A5 to the oxidation of diltiazem, midazolam and testosterone by liver microsomes from Japanese subjects. Twenty-seven liver samples were classified into three groups according to the CYP3A5 genotypes; CYP3A5*1/*1 (n 3), *1/*3 (n = 12) and *3/*3 (n = 12). The results of genotyping and immunochemical quantitation of CYP3A5 protein showed a good accordance between the CYP3A5 genotype and CYP3A5 content but not CYP3A4 content in liver microsomes. The expression levels of hepatic CYP3A5 protein ranged from 20 to 60z of the sum of CYP3A4 and CYP3A5 contents in subjects with at least one wild type allele (*1). The CYP3A5 contents correlated well with liver microsomal activities of diltiazem N-demethylation, midazolam 1′- and 4-hydroxylations and testosterone 6β-hydroxylation among subjects carrying at least one *1 allele. In addition, the correlation coefficients of CYP3A5 contents with the rates of diltiazem N-demethylation, midazolam 1′-hydroxylation and testosterone 6β-hydroxylation were higher than those of CYP3A4, although the value of CYP3A5 with the midazolam 4-hydroxylation rate was similar to that of CYP3A4. Kinetic analyses revealed a biphasic diltiazem N-demethylation in liver microsomes from subjects carrying the *1 allele. The apparent Vmax/Km values for recombinant CYP3A5 indicated the greater contributions to diltiazem N-demethylation and midazolam 1′-hydroxylation as compared with CYP3A4. These results suggest that polymorphic CYP3A5 contributes markedly to the drug oxidations, particularly diltiazem N-demethylation, midazolam 1′-hydroxylation and testosterone 6β-hydroxylation by liver microsomes from Japanese subjects.