Dennison Jennifer B, Mohutsky Michael A, Barbuch Robert J, Wrighton Steven A, Hall Stephen D
Division of Clinical Pharmacology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
J Pharmacol Exp Ther. 2008 Oct;327(1):248-57. doi: 10.1124/jpet.108.139998. Epub 2008 Jul 23.
Vincristine is metabolized to one primary metabolite, M1, by cDNA-expressed CYP3A4 and CYP3A5 and by CYP3A enzymes in human liver microsomes. For both systems, CYP3A5 is predicted to mediate approximately 80% of the CYP3A metabolism for individuals with high CYP3A5 expression (at least one CYP3A5()1 allele). In the current study, the role of CYP3A5 was quantified in the metabolism of vincristine with human cryopreserved hepatocytes. The hepatocytes were genotyped for common CYP3A5 allelic variants (CYP3A5()3, CYP3A5()6, and CYP3A5()7) to predict CYP3A5 expression. For each hepatocyte preparation, the rates of vincristine depletion and metabolite formation were quantified. Whereas human hepatocytes with predicted low CYP3A5 expression did not detectably metabolize vincristine, human hepatocytes with predicted high CYP3A5 expression metabolized vincristine to one primary metabolite, M1. In paired experiments using cryopreserved hepatocytes from the same donor, vincristine was incubated with intact cells and cell lysates supplemented with NADPH. The rates of M1 formation were 4 to 69-fold higher for the cell lysates compared with the intact cells. For one representative donor, the intact cells had a 3-fold higher K(m) value and a 3-fold lower V(max) value for M1 formation compared with the cell lysates. Thus, the rate of M1 formation in the hepatocytes may be influenced by the rate of vincristine translocation across the plasma membrane. We conclude that genetically determined CYP3A5 expression in human cryopreserved hepatocytes plays a major role in vincristine metabolism.
长春新碱在人肝微粒体中可被cDNA表达的CYP3A4和CYP3A5以及CYP3A酶代谢为一种主要代谢产物M1。对于这两种系统，预计CYP3A5可介导CYP3A代谢的约80%，适用于CYP3A5高表达个体（至少有一个CYP3A5()1等位基因）。在本研究中，利用人冷冻保存的肝细胞对CYP3A5在长春新碱代谢中的作用进行了定量分析。对肝细胞进行常见CYP3A5等位基因变异（CYP3A5()3、CYP3A5()6和CYP3A5()7）的基因分型，以预测CYP3A5的表达。对于每种肝细胞制剂，对长春新碱的消耗速率和代谢产物形成速率进行了定量分析。预计CYP3A5低表达的人肝细胞未检测到长春新碱的代谢，而预计CYP3A5高表达的人肝细胞将长春新碱代谢为一种主要代谢产物M1。在使用来自同一供体的冷冻保存肝细胞的配对实验中，将长春新碱与完整细胞和补充了NADPH的细胞裂解物一起孵育。与完整细胞相比，细胞裂解物中M1的形成速率高4至69倍。对于一位代表性供体，完整细胞形成M1的Km值高3倍，Vmax值低3倍。因此，肝细胞中M1的形成速率可能受长春新碱跨质膜转运速率的影响。我们得出结论，人冷冻保存肝细胞中由基因决定的CYP3A5表达在长春新碱代谢中起主要作用。
