Nunoya K, Yokoi Y, Kimura K, Kodama T, Funayama M, Inoue K, Nagashima K, Funae Y, Shimada N, Green C, Kamataki T
Division of Drug Metabolism, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
J Pharmacol Exp Ther. 1996 May;277(2):768-74.
(+)-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.
（+）-顺式-3,5-二甲基-2-（3-吡啶基）噻唑烷-4-酮盐酸盐（SM-12502）被人肝微粒体氧化，生成唯一的代谢产物S-氧化物。间接证据表明，S-氧化反应由细胞色素P450（CYP）催化。伊迪-霍夫斯泰因图呈现双相模式，表明人肝微粒体中的S-氧化反应至少涉及两种酶。高亲和力S-氧化酶的动力学参数显示，Km和Vmax值分别为20.9±4.4微摩尔和0.111±0.051纳摩尔/分钟/毫克微粒体蛋白。香豆素和抗CYP2A抗体可抑制S-氧化酶活性。在人肝微粒体20个样本的CYP形式含量中，CYP2A6的含量与用50微摩尔SM-12502测得的S-氧化酶活性相关（r = 0.808，P < 0.0005）。观察到SM-12502 S-氧化酶活性与香豆素7-羟化酶活性之间存在密切相关性（r = 0.908，P < 0.0001）。表达CYP2A6的基因工程人B淋巴母细胞的微粒体可有效地将SM-12502代谢为S-氧化物。结果表明，CYP2A6同工酶是负责在人肝微粒体中对SM-12502进行S-氧化的主要CYP形式。因此，SM-12502将成为进一步研究分析CYP2A6人类基因多态性的有用工具。
