title: Estimation of the Contribution of CYP2C8 and CYP3A4 in Repaglinide Metabolism by Human Liver Microsomes Under Various Buffer Conditions.
abstract: We have previously reported that the microsomal activities of CYP2C8 and CYP3A4 largely depend on the buffer condition used in in vitro metabolic studies, with different patterns observed between the 2 isozymes. In the present study, therefore, the possibility of buffer condition dependence of the fraction metabolized by CYP2C8 (fm2C8) for repaglinide, a dual substrate of CYP2C8 and CYP3A4, was estimated using human liver microsomes under various buffer conditions. Montelukast and ketoconazole showed a potent and concentration-dependent inhibition of CYP2C8-mediated paclitaxel 6α-hydroxylation and CYP3A4-mediated triazolam α-hydroxylation, respectively, without dependence on the buffer condition. Repaglinide depletion was inhibited by both inhibitors, but the degree of inhibition depended on buffer conditions. Based on these results, the contribution of CYP2C8 in repaglinide metabolism was estimated to be larger than that of CYP3A4 under each buffer condition, and the fm2C8 value of 0.760, estimated in 50 mM phosphate buffer, was the closest to the value (0.801) estimated in our previous modeling analysis based on its concentration increase in a clinical drug interaction study. Researchers should be aware of the possibility of buffer condition affecting the estimated contribution of enzyme(s) in drug metabolism processes involving multiple enzymes.
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kudo
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Goda
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yokosuka
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Tanaka
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan.
authors.forename: Seina
authors.initials: S
authors.lastname: Komatsu
authors.affiliation: Research Institute of Pharmaceutical Sciences, Musashino University, 1-1-20 Shinmachi, Nishitokyo-shi, Tokyo 202-8585, Japan. Electronic address: k-ito@musashino-u.ac.jp.
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Ito
mesh_terms: D000085:Acetates / Q000494:pharmacology; D002021:Buffers; D002219:Carbamates / Q000378:metabolism*; D003521:Cyclopropanes; D065727:Cytochrome P-450 CYP2C8 / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D065693:Cytochrome P-450 Enzyme Inducers / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors / Q000494:pharmacology; D004347:Drug Interactions; D006801:Humans; D007004:Hypoglycemic Agents / Q000378:metabolism*; D007654:Ketoconazole / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010880:Piperidines / Q000378:metabolism*; D011804:Quinolines / Q000494:pharmacology; D013440:Sulfides
chemical_list: D000085:Acetates; D002021:Buffers; D002219:Carbamates; D003521:Cyclopropanes; D065693:Cytochrome P-450 Enzyme Inducers; D065607:Cytochrome P-450 Enzyme Inhibitors; D007004:Hypoglycemic Agents; D010880:Piperidines; D011804:Quinolines; D013440:Sulfides; C072379:repaglinide; D065727:Cytochrome P-450 CYP2C8; D051544:Cytochrome P-450 CYP3A; C093875:montelukast; D007654:Ketoconazole
keywords: cytochrome P450; drug interactions; hepatic metabolism; inhibition; in vitro/in vivo correlations (IVIVC); metabolic clearance; microsomes