Department of Pharmacology and Toxicology, University of Utah, 30 S 2000 E, Room 201, Salt Lake City, Utah 84112, USA.
Chem Res Toxicol. 2010 Mar 15;23(3):696-704. doi: 10.1021/tx9004506.
3-Methylindole (3MI) is a highly selective pneumotoxicant that is present in abundant amounts (as high as 1.4 mug/cigarette) in cigarette smoke. Several human cytochrome P450 enzymes that are expressed in lung, such as CYP1A1, CYP2F1, CYP2A13, and CYP4B1, catalyze the dehydrogenation of 3MI to the reactive intermediate 3-methyleneindolenine, which alkylates DNA and induces cell death through apoptosis. In addition, 3MI potently damages DNA at low concentrations (observable at 0.1 muM). However, it seemed possible that 3MI could induce the levels of P450 enzymes, so transcription and translation of 1A1 and 2F1 genes were measured in primary normal human bronchial epithelial cells. In this study, 3MI-induced DNA damage at the 10 muM concentration was ameliorated when P450 turnover was inactivated with the cytochrome P450 suicide substrate inhibitor 1-aminobenzotriazole. Thus, the observed DNA damage was cytochrome P450-dependent. Quantitative real-time polymerase chain reaction analysis revealed both concentration- and time-dependent increases in CYP1A1 and CYP2F1 transcription by the same 3MI concentrations that damaged DNA. Aryl hydrocarbon receptor (AhR) activation lead to CYP1A1 induction. Treatment with 3MI in combination with the AhR antagonist alpha-naphthoflavone prevented 3MI-mediated CYP1A1 induction, indicating that the induction was AhR-dependent. Conversely, CYP2F1 induction did not appear to require activation of AhR. These intriguing findings show that not only is induction of 1A1 and 2F1 caused by 3MI metabolites, rather than 3MI itself, but transcriptional activation of these pulmonary genes occurs through disparate mechanisms. Thus, the induction process, and subsequent increased bioactivation of 3MI to toxic intermediates, is a facile process that might enhance the acute toxicity and/or mutagenicity of this chemical.
3-甲基吲哚（3MI）是一种高度选择性的肺毒剂，在香烟烟雾中含量丰富（高达 1.4 微克/支）。几种在肺部表达的人细胞色素 P450 酶，如 CYP1A1、CYP2F1、CYP2A13 和 CYP4B1，催化 3MI 的脱氢反应生成活性中间产物 3-亚甲基吲哚啉，它通过细胞凋亡使 DNA 烷基化并诱导细胞死亡。此外，3MI 在低浓度（在 0.1 μM 时可观察到）下强烈破坏 DNA。然而，3MI 似乎可以诱导 P450 酶的水平，因此在原代正常人支气管上皮细胞中测量了 1A1 和 2F1 基因的转录和翻译。在这项研究中，用细胞色素 P450 自杀底物抑制剂 1-氨基苯并三唑使 P450 周转失活，可减轻 3MI 在 10 μM 浓度下诱导的 DNA 损伤。因此，观察到的 DNA 损伤依赖于细胞色素 P450。定量实时聚合酶链反应分析显示，在相同的 3MI 浓度下，CYP1A1 和 CYP2F1 的转录均呈浓度和时间依赖性增加，这些浓度会破坏 DNA。芳烃受体（AhR）的激活导致 CYP1A1 的诱导。用 AhR 拮抗剂α-萘黄酮与 3MI 联合处理可防止 3MI 介导的 CYP1A1 诱导，表明诱导依赖于 AhR。相反，CYP2F1 的诱导似乎不需要 AhR 的激活。这些有趣的发现表明，不仅 3MI 代谢物而不是 3MI 本身引起 1A1 和 2F1 的诱导，而且这些肺基因的转录激活是通过不同的机制发生的。因此，诱导过程以及随后 3MI 向有毒中间体的生物活化增加，是一个容易发生的过程，可能会增强这种化学物质的急性毒性和/或致突变性。
