title: (+)-cis-3,5-dimethyl-2-(3-pyridyl) thiazolidin-4-one hydrochloride (SM-12502) as a novel substrate for cytochrome P450 2A6 in human liver microsomes.
abstract: (+)-cis-3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one hydrochloride (SM-12502) was oxidized by human liver microsomes to produce the S-oxide as a sole metabolite. Indirect evidence suggested that the S-oxidation was catalyzed by cytochrome P450 (CYP). Eadie-Hofstee plots showed biphasic pattern, suggesting that at least two enzymes were involved in the S-oxidation in human liver microsomes. Kinetic parameters of the S-oxidase with high-affinity showed Km and Vmax values of 20.9 +/- 4.4 microM and 0.111 +/- 0.051 nmol/min/mg microsomal protein, respectively. The S-oxidase activity was inhibited by coumarin and anti-CYP2A antibody. Among the contents of forms of CYP 20 samples of human liver microsomes, the content of CYP2A6 correlated with S-oxidase activity measured with 50 microM SM-12502 (r = .808, P < .0005). A close correlation (r = .908, P < .0001) was observed between activities of SM-12502 S-oxidase and coumarin 7-hydroxylase. Microsomes from genetically engineered human B-lymphoblastoid cells expressing CYP2A6 metabolized SM-12502 to the S-oxide efficiently. The results indicate that CYP2A6 isozyme is a major form of CYP responsible for the S-oxidation of SM-12502 in human liver microsomes. Thus, SM-12502 will be a useful tool in further research to analyze a human genetic polymorphism of CYP2A6.
authors.affiliation: Division of Drug Metabolism, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Nunoya
authors.forename: Y
authors.initials: Y
authors.lastname: Yokoi
authors.forename: K
authors.initials: K
authors.lastname: Kimura
authors.forename: T
authors.initials: T
authors.lastname: Kodama
authors.forename: M
authors.initials: M
authors.lastname: Funayama
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.forename: K
authors.initials: K
authors.lastname: Nagashima
authors.forename: Y
authors.initials: Y
authors.lastname: Funae
authors.forename: N
authors.initials: N
authors.lastname: Shimada
authors.forename: C
authors.initials: C
authors.lastname: Green
authors.forename: T
authors.initials: T
authors.lastname: Kamataki
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D006801:Humans; D007527:Isoenzymes / Q000032:analysis; D008862:Microsomes, Liver / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000502:physiology*; D010084:Oxidation-Reduction; D051381:Rats; D013844:Thiazoles / Q000378:metabolism*; D053778:Thiazolidines
chemical_list: D007527:Isoenzymes; D013844:Thiazoles; D053778:Thiazolidines; C065776:3,5-dimethyl-2-(3-pyridyl)thiazolidin-4-one; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6