Characterization of Human Cytochrome P450s Involved in the Bioactivation of Clozapine
Characterization of Human Cytochrome P450s Involved in the Bioactivation of Clozapine
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DOI：
10.1124/dmd.112.050484
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发表时间：
2013-03-01
影响因子：
3.9
通讯作者：
Commandeur, Jan N. M.
中科院分区：
文献类型：
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作者：
Dragovic, Sanja;Gunness, Patrina;Commandeur, Jan N. M.
已知氯氮平在一小部分患者中会引起肝毒性。肝细胞色素P450（P450）的氧化生物活化活性中间体已被提出作为一个可能的机制。然而，与它们在N-去甲基氯氮平和氯氮平N-氧化物形成中的作用相反，个别P450参与活性中间体的生物活化的特征要少得多。本研究的结果表明，14个重组人P450中的7个能够将氯氮平生物活化为谷胱甘肽反应性氮离子。CYP 3A 4和CYP 2D 6的比活性最高。这些P450的酶动力学表征显示生物活化的固有清除率相当，这意味着与CYP 2D 6相比，CYP 3A 4由于其更高的肝脏表达而更重要。使用合并的人肝微粒体的抑制实验证实了CYP 3A 4在氯氮平的肝生物活化中的主要作用。通过研究氯氮平在100个不同个体的人肝微粒体中的生物活化，观察到生物活化活性的8倍变异性。在两个人的生物活化活性超过N-脱甲基和N-氧化活性。奎尼丁没有表现出显着的抑制任何这些肝脏组分的生物活性，表明CYP 2D 6多态性不是一个重要的因素，在确定氯氮平肝毒性的敏感性。因此，CYP 3A 4水平的个体间差异和药物间相互作用可能是决定肝组织暴露于活性氯氮平代谢物的因素。
Clozapine is known to cause hepatotoxicity in a small percentage of patients. Oxidative bioactivation to reactive intermediates by hepatic cytochrome P450s (P450s) has be proposed as a possible mechanism. However, in contrast to their role in formation of N-desmethylclozapine and clozapine N-oxide, the involvement of individual P450s in the bioactivation to reactive intermediates is much less well characterized. The results of the present study show that 7 of 14 recombinant human P450s were able to bioactivate clozapine to a glutathione-reactive nitrenium ion. CYP3A4 and CYP2D6 showed the highest specific activity. Enzyme kinetical characterization of these P450s showed comparable intrinsic clearance of bioactivation, implicating that CYP3A4 would be more important because of its higher hepatic expression, compared with CYP2D6. Inhibition experiments using pooled human liver microsomes confirmed the major role of CYP3A4 in hepatic bioactivation of clozapine. By studying bioactivation of clozapine in human liver microsomes from 100 different individuals, an 8-fold variability in bioactivation activity was observed. In two individuals bioactivation activity exceeded N-demethylation and N-oxidation activity. Quinidine did not show significant inhibition of bioactivation in any of these liver fractions, suggesting that CYP2D6 polymorphism is not an important factor in determining susceptibility to hepatotoxicity of clozapine. Therefore, interindividual differences and drug-drug interactions at the level of CYP3A4 might be factors determining exposure of hepatic tissue to reactive clozapine metabolites.