Center for Drug Safety and Evaluation Research, State Key Laboratory of New Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Haike Road 501, Shanghai, China.
Arch Toxicol. 2012 Nov;86(11):1753-61. doi: 10.1007/s00204-012-0891-6. Epub 2012 Jun 19.
The cytochrome P450 (P450 or CYP) is involved in both detoxification and metabolic activation of many carcinogens. In order to identify the role of hepatic P450 in the mutagenesis of genotoxic carcinogens, we generated a novel hepatic P450 reductase null (HRN) gpt delta mouse model, which lacks functional hepatic P450 on a gpt delta mouse background. In this study, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was used to treat HRN gpt delta mice and control littermates. Gene mutations in the liver and lungs were detected, and mutation spectra were analyzed. Pharmacokinetic analyses were performed, and tissue levels of NNK and metabolite were determined. NNK-induced mutant frequencies (MFs) were equivalent to spontaneous MFs in the liver, but increased more than 3 times in the lungs of HRN gpt delta mice compared to control mice. NNK-induced mutation spectra showed no difference between HRN gpt delta mice and control littermates. Toxicokinetic studies revealed reduced clearance of NNK with elevated tissue concentrations in HRN gpt delta mice. To our knowledge, these are the first data demonstrating that NNK cannot induce mutagenesis in the liver without P450 metabolic activation, but can induce mutagenesis in lungs by a hepatic P450-independent mechanism. Moreover, our data show that hepatic P450 plays a major role in the systemic clearance of NNK, thereby protecting the lungs against NNK-induced mutagenesis. Our model will be useful in establishing the role of hepatic versus extrahepatic P450-mediated mutagenesis, and the relative contributions of P450 compared to other biotransformation enzymes in the genotoxic carcinogens' activation.
细胞色素 P450（P450 或 CYP）参与许多致癌物的解毒和代谢激活。为了确定肝 P450 在遗传毒性致癌物致突变中的作用，我们生成了一种新型的肝 P450 还原酶缺失（HRN）gpt delta 小鼠模型，该模型在 gpt delta 小鼠背景下缺乏功能性肝 P450。在这项研究中，我们使用 4-（甲基亚硝氨基）-1-（3-吡啶基）-1-丁酮（NNK）处理 HRN gpt delta 小鼠和对照同窝仔鼠。检测了肝和肺中的基因突变，并分析了突变谱。进行了药代动力学分析，并测定了 NNK 和代谢物的组织水平。NNK 诱导的突变频率（MF）与肝中的自发 MF 相当，但与对照小鼠相比，HRN gpt delta 小鼠的肺中增加了 3 倍以上。NNK 诱导的突变谱在 HRN gpt delta 小鼠和对照同窝仔鼠之间没有差异。毒代动力学研究表明，HRN gpt delta 小鼠中 NNK 的清除率降低，组织浓度升高。据我们所知，这些是首次数据表明，NNK 没有 P450 代谢激活就不能在肝脏中诱导突变，但可以通过肝 P450 非依赖性机制在肺部诱导突变。此外，我们的数据表明，肝 P450 在 NNK 的全身清除中起主要作用，从而保护肺部免受 NNK 诱导的突变。我们的模型将有助于确定肝 P450 与肝外 P450 介导的突变的作用，以及 P450 与其他生物转化酶在遗传毒性致癌物激活中的相对贡献。
