Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada (C.L., D.S.R.); and Laboratory of Molecular Toxicology, Wadsworth Center, New York State Department of Health, and School of Public Health, State University of New York at Albany, Albany, New York (X.D.).
Drug Metab Dispos. 2013 Oct;41(10):1782-6. doi: 10.1124/dmd.113.052993. Epub 2013 Jul 11.
The aryl hydrocarbon receptor (AHR)-dependent induction of cytochromes P450 (P450) such as CYP1A1 by 3-methylcholanthrene (MC) and related polycyclic aromatic hydrocarbons is well characterized. We reported previously that MC treatment triggers a pronounced downregulation, particularly at the protein level, of mouse hepatic Cyp3a11, a counterpart of the key human drug-metabolizing enzyme CYP3A4. To determine whether this effect of MC requires hepatic microsomal P450 activity, we studied liver Cpr-null (LCN) mice with hepatocyte-specific conditional deletion of the NADPH-cytochrome P450 oxidoreductase gene. In vehicle-treated animals, basal levels of CYP3A11 mRNA and CYP3A protein immunoreactivity were elevated by approximately 9-fold in LCN mice compared with wild-type (WT) mice, whereas CYP3A catalytic activity was profoundly compromised in LCN mice. MC treatment caused suppression of CYP3A11 mRNA, CYP3A protein immunoreactivity, and CYP3A catalytic activity in WT mice, and the MC effects at the mRNA and protein levels were maintained in LCN mice. Flavin-containing monooxygenase-3 (Fmo3) induction by MC was suggested previously to occur via an AHR-dependent mechanism requiring conversion of the parent compound to DNA-damaging reactive metabolites; however, hepatic FMO3 mRNA levels were dramatically increased by MC in both WT and LCN mice. MC did not function as a mechanism-based inactivator of CYP3A enzymes in hepatic microsomes prepared from untreated WT mice, under conditions in which 1-aminobenzotriazole caused marked NADPH-dependent loss of total P450 content and CYP3A catalytic activity. These results indicate that MC downregulates mouse hepatic CYP3A protein via a pretranslational mechanism that does not require hepatic microsomal P450-dependent activity.
芳基烃受体 (AHR) 依赖性诱导细胞色素 P450 (P450)，如 3-甲基胆蒽 (MC) 和相关多环芳烃诱导的 CYP1A1，已有很好的描述。我们之前报道过，MC 处理会触发小鼠肝 CYP3A11 的明显下调，特别是在蛋白质水平上，CYP3A11 是关键的人类药物代谢酶 CYP3A4 的对应物。为了确定 MC 的这种作用是否需要肝微粒体 P450 活性，我们研究了肝细胞特异性条件性缺失 NADPH-细胞色素 P450 氧化还原酶基因的 Cpr 基因敲除 (LCN) 小鼠。在载体处理的动物中，与野生型 (WT) 小鼠相比，LCN 小鼠的 CYP3A11 mRNA 和 CYP3A 蛋白免疫反应性的基础水平升高了约 9 倍，而 CYP3A 催化活性在 LCN 小鼠中严重受损。MC 处理导致 WT 小鼠 CYP3A11 mRNA、CYP3A 蛋白免疫反应性和 CYP3A 催化活性的抑制，而在 LCN 小鼠中，MC 的作用在 mRNA 和蛋白水平上得以维持。先前提出，MC 诱导黄素单加氧酶-3 (Fmo3) 的发生是通过一种需要将母体化合物转化为具有 DNA 损伤的反应性代谢物的 AHR 依赖性机制；然而，在 WT 和 LCN 小鼠中，MC 都显著增加了肝 FMO3 mRNA 水平。在未处理的 WT 小鼠肝微粒体中，MC 不能作为 CYP3A 酶的机制基础失活剂起作用，在这些条件下，1-氨基苯并三唑导致 NADPH 依赖性的总 P450 含量和 CYP3A 催化活性的显著丧失。这些结果表明，MC 通过一种不依赖于肝微粒体 P450 依赖性活性的翻译前机制下调小鼠肝 CYP3A 蛋白。
