Metabolism by cytochrome P4503A (CYP3A) is the most prevalent clearance pathway for drugs. Designation of metabolism by CYP3A commonly refers to the potential contribution by one or both of two enzymes, CYP3A4 and CYP3A5. The metabolic turnover of 32 drugs known to be largely metabolized by CYP3A was examined in human liver microsomes (HLMs) from CYP3A5 expressers (\*1/\*1 genotype) and nonexpressers (\*3/\*3 genotype) in the presence and absence of ketoconazole and CYP3cide (a selective CYP3A4 inactivator) to calculate the contribution of CYP3A5 to metabolism. Drugs with the highest contribution of CYP3A5 included atazanavir, vincristine, midazolam, vardenafil, otenabant, verapamil, and tacrolimus, whereas 17 of the 32 tested showed negligible CYP3A5 contribution. For specific reactions in HLMs from \*1/\*1 donors, CYP3A5 contributes 55% and 44% to midazolam 1′- and 4-hydroxylation, 16% to testosterone 6 β -hydroxylation, 56% and 19% to alprazolam 1′- and 4-hydroxylation, 10% to tamoxifen N-demethylation, and 58% to atazanavir p -hydroxylation. Comparison of the in vitro observations to clinical pharmacokinetic data showed only a weak relationship between estimated contribution by CYP3A5 and impact of CYP3A5 genotype on oral clearance, in large part because of the scatter in clinical data and the low numbers of study subjects used in CYP3A5 pharmacogenetics studies. These data should be useful in guiding which drugs should be evaluated for differences in pharmacokinetics and metabolism between subjects expressing CYP3A5 and those who do not express this enzyme.
由细胞色素P4503A(CYP3A)介导的新陈代谢是药物清除的最主要途径。对CYP3A的新陈代谢的称谓通常指的是两种酶CYP3A4和CYP3A5的一个或两个的潜在贡献。研究了32种主要通过CYP3A代谢的药物在来自CYP3A5表达者(\*1/\*1
基因型)和非表达者(\*3/\*3
基因型)人肝微粒体(HLMs)中的代谢转换,并在存在和不存在
酮康唑及CYP3cide(选择性CYP3A4失活剂)的情况下计算CYP3A5对代谢的贡献。CYP3A5贡献最高的药物包括
阿扎那韦、
长春新碱、
美克洛嗪、
伐地那非、奥特那班、
维拉帕米和
他克莫司,而32种被测试的药物中有17种显示出CYP3A5的贡献微不足道。在\*1/\*1供体的HLMs中特定反应中,CYP3A5分别对
美克洛嗪的1'-和
4-羟基化贡献55%和44%,对
睾酮的6β-羟基化贡献16%,对
阿普唑仑的1'-和
4-羟基化贡献56%和19%,对
他莫昔芬的N-去甲基化贡献10%,以及对
阿扎那韦的p-羟基化贡献58%。将体外观察结果与临床药代动力学数据进行比较,发现CYP3A5的估计贡献与CYP3A5
基因型对口服清除的影响之间只有微弱的关系,这在很大程度上是由于临床数据的分散性以及在CYP3A5药物
基因组学研究中使用的研究对象数量较少。这些数据应有助于指导哪些药物应该评估表达CYP3A5的个体与不表达该酶的个体在药代动力学和代谢方面的差异。