A product of incomplete combustion of diesel fuel, 3-nitrobenzanthrone (3-NBA), has been classified as a cancer-causing substance. It first gained attention as a potential urinary bladder carcinogen due to the presence of its metabolite in urine and formation of DNA adducts. The aim of the present study was to characterize the dose–response relationship of 3-NBA in human urothelial cancer cell line (RT4) exposed to concentrations ranging from 0.0003 μM (environmentally relevant) to 80 μM by utilizing toxicological and metabolomic approaches. We observed that the RT4 cells were capable of bioactivation of 3-NBA within 30 min of exposure. Activity measurements of various enzymes involved in the conversion of 3-NBA in RT4 cells demonstrated NAD(P)H:quinone oxidoreductase (NQO1) as the main contributor for its bioactivation. Moreover, cytotoxicity assessment exhibited an initiation of adaptive mechanisms at low dosages, which diminished at higher doses, indicating that the capacity of these mechanisms no longer suffices, resulting in increased levels of intracellular reactive oxygen species, reduced proliferation, and hyperpolarisation of the mitochondrial membrane. To characterize the underlying mechanisms of this cellular response, the metabolism of 3-NBA and metabolomic changes in the cells were analyzed. The metabolomic analysis of the cells (0.0003, 0.01, 0.08, 10, and 80 μM 3-NBA) showed elevated levels of various antioxidants at low concentrations of 3-NBA. However, at higher exposure concentrations, it appeared that the cells reprogrammed their metabolism to maintain the cell homeostasis via activation of pentose phosphate pathway (PPP).

中文翻译：

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人尿道癌细胞中对3-硝基苯并蒽醌暴露的剂量依赖性反应

柴油不完全燃烧的产物3-硝基苯并蒽醌（3-NBA）被归类为致癌物质。由于其代谢产物在尿液中存在和DNA加合物的形成，它首先作为一种潜在的膀胱致癌物受到关注。本研究的目的是通过毒理学和代谢组学方法，表征暴露于浓度为0.0003μM（与环境相关）至80μM的人类尿路上皮癌细胞系（RT4）中3-NBA的剂量反应关系。我们观察到RT4细胞能够在暴露后30分钟内生物激活3-NBA。在RT4细胞中参与3-NBA转化的各种酶的活性测量表明NAD（P）H：醌氧化还原酶（NQO1）是其生物激活的主要贡献者。而且，细胞毒性评估显示了低剂量时适应性机制的启动，而高剂量时则减弱了，这表明这些机制的能力不再足够，导致细胞内活性氧水平升高，线粒体膜增殖和超极化。为了表征这种细胞应答的潜在机制，分析了3-NBA的代谢和细胞中的代谢组学变化。细胞的代谢组学分析（0.0003、0.01、0.08、10和80μM3-NBA）显示，在低浓度的3-NBA中各种抗氧化剂的含量升高。然而，在较高的暴露浓度下，细胞似乎通过活化戊糖磷酸途径（PPP）重新编程其代谢以维持细胞稳态。