Silvers K J, Couch L H, Rorke E A, Howard P C
Department of Environmental Health Sciences, School of Medicine, Case Western Reserve University, Cleveland, OH 44106-4940, U.S.A.
Biochem Pharmacol. 1997 Oct 15;54(8):927-36. doi: 10.1016/s0006-2952(97)00268-2.
1-Nitropyrene is an environmental contaminant that is mutagenic in many prokaryotic and eukaryotic systems, including the hypoxanthine-guanosine phosphoribosyl transferase (HGPRT) locus in the human hepatoma cell line HepG2. Metabolism and DNA adduct formation of [3H]1-nitropyrene in the HepG2 were quantified to understand the role of nitroreduction and/or cytochrome P450-mediated C-oxidation of 1-nitropyrene in DNA adduct formation and mutagenicity. In uninduced HepG2 cells, 10 microM [3H]1-nitropyrene was metabolized principally by nitroreduction to 1-aminopyrene (516 pmol/24 hr/10(6) cells), and by cytochrome P450-mediated C-oxidation to K-region trans-dihydrodiols (37 pmol/24 hr/10(6) cells), 1-nitropyren-3-ol (51 pmol/24 hr/10(6) cells), and 1-nitropyren-6-ol and 1-nitropyren-8-ol (77 pmol/24 hr/10(6) cells). Pretreatment of the HepG2 cells for 24 hr with 5 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a complete change in the metabolism of [3H]1-nitropyrene, with 1-nitropyren-6-ol and 1-nitropyren-8-ol formation (449 pmol/24 hr/10(6) cells) being 80-fold greater than 1-aminopyrene formation (6 pmol/24 hr/10(6) cells). This increase in C-oxidation of 1-nitropyrene was consistent with increased levels of cytochrome P450 1A. The only DNA adduct detected using the 32P-postlabeling assay in the HepG2 cells administered 1-nitropyrene was N-(2'-deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP). Induction of C-oxidative metabolism through TCDD treatment resulted in a concomitant decrease in dG-C8-AP formation. DNA adducts for oxidized 1-nitropyrene metabolites were not detected in the TCDD-treated HepG2 cells administered 1-nitropyrene, which indicates that cytochrome P450-mediated C-oxidative pathways are detoxification pathways in HepG2 cells.
1-硝基芘是一种环境污染物，在许多原核和真核系统中具有致突变性，包括人肝癌细胞系HepG2中的次黄嘌呤-鸟嘌呤磷酸核糖转移酶（HGPRT）位点。对HepG2细胞中[3H]1-硝基芘的代谢和DNA加合物形成进行定量，以了解1-硝基芘的硝基还原和/或细胞色素P450介导的C-氧化在DNA加合物形成和致突变性中的作用。在未诱导的HepG2细胞中，10微摩尔[3H]1-硝基芘主要通过硝基还原代谢为1-氨基芘（516皮摩尔/24小时/10^6个细胞），并通过细胞色素P450介导的C-氧化代谢为K-区域反式二氢二醇（37皮摩尔/24小时/10^6个细胞）、1-硝基芘-3-醇（51皮摩尔/24小时/10^6个细胞）以及1-硝基芘-6-醇和1-硝基芘-8-醇（77皮摩尔/24小时/10^6个细胞）。用5纳摩尔2,3,7,8-四氯二苯并对二恶英（TCDD）对HepG2细胞预处理24小时，导致[3H]1-硝基芘的代谢发生完全改变，1-硝基芘-6-醇和1-硝基芘-8-醇的形成（449皮摩尔/24小时/10^6个细胞）比1-氨基芘的形成（6皮摩尔/24小时/10^6个细胞）高80倍。1-硝基芘C-氧化的这种增加与细胞色素P450 1A水平的升高一致。在给予1-硝基芘的HepG2细胞中，使用32P后标记分析法检测到的唯一DNA加合物是N-（2'-脱氧鸟苷-8-基）-1-氨基芘（dG-C8-AP）。通过TCDD处理诱导C-氧化代谢导致dG-C8-AP形成相应减少。在给予1-硝基芘的经TCDD处理的HepG2细胞中未检测到氧化的1-硝基芘代谢物的DNA加合物，这表明细胞色素P450介导的C-氧化途径是HepG2细胞中的解毒途径。
