Characterization of human cytochromes P450 involved in theophylline 8-hydroxylation.
Characterization of human cytochromes P450 involved in theophylline 8-hydroxylation.
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DOI：
10.1016/0006-2952(95)00120-o
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发表时间：
1995-07
影响因子：
5.8
通讯作者：
Z. Zhang;L. Kaminsky
中科院分区：
文献类型：
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作者：
Z. Zhang;L. Kaminsky
进行研究以确定哪些人P450酶催化茶碱代谢为1，3-二甲基尿酸（1，3-DU），以促进茶碱药物-药物相互作用的预测，并开发人P4501 A2的非侵入性测试。来自用P4501 A1、1A 2、2A 6、2B 6、2C 9、2D 6、2 E1或3A 4的人P450 cDNA单独转染的人细胞系的微粒体用于证明仅P4501 A2表现出高亲和力和低容量的茶碱代谢为1，3-DU的催化活性（Km= 0.6 mM，Vmax= 37.8，pmol/min/mg），而P4502 D 6、2 E1和3A 4（m分别为14.4、19.9和25.1 mM，Vmax分别为219.8、646.4和20.8 pmol/min/mg）表现出低亲和力和可变容量的活性。在一系列的10个人肝微粒体制剂中，在5和40 mM茶碱浓度下，茶碱8-羟基化为1，3-DU的速率与其他P450形式特异性活性的相关性表明，在低浓度下，代谢主要由P4501 A2催化，而在高底物浓度下，P4502 E1主要负责催化。单独表达的P450和肝微粒体制备物的结果是一致的，表明前者的系统提供了对异质表达的肝脏P450功能的定性准确反映。在体内达到的茶碱药理学浓度下，其代谢必须主要由P4501 A2催化。
Studies were undertaken to determine which human P450 enzymes catalyze the metabolism of theophylline to 1,3-dimethyluric acid (1,3-DU), to facilitate predictions of theophylline drug-drug interactions, and to develop a noninvasive test for human P4501A2. Microsomes from a human cell line transfected individually with human P450 cDNAs for P4501A1, 1A2, 2A6, 2B6, 2C9, 2D6, 2E1, or 3A4 were used to demonstrate that only P4501A2 exhibited catalytic activity for theophylline metabolism to 1,3-DU with high affinity and low capacity (Km= 0.6 mM, Vmax= 37.8, pmol/min/mg), while P4502D6, 2E1, and 3A4 (m= 14.4, 19.9, and 25.1 mM, respectively, andmax= 219.8, 646.4, and 20.8 pmol/min/mg, respectively) exhibited activities with low affinity and variable capacities. Correlations of rates of theophylline 8-hydroxylation to 1,3-DU with other P450 form-specific activities, in a series of ten human liver microsomal preparations, at 5 and 40 mM theophylline concentrations, revealed that at low concentrations the metabolism was catalyzed primarily by P4501A2, while at high substrate concentrations P4502E1 was primarily responsible for catalysis. The results with individually expressed P450s and hepatic microsomal preparations were consistent, indicating that the former system provides a qualitatively accurate reflection of the function of the heterogeneously expressed liver P450s. At pharmacologic theophylline concentrations achieved in vivo, its metabolism must thus be catalyzed primarily by P4501A2.