Metabolic activation of the genotoxic environmental contaminants 2- and 3-nitrofluoranthene in variants of <i>Salmonella typhimurium</i> TA98
作者:L. M. Ball、L. M. Stocking、M. J. Kohan、S. H. Warren、J. Lewtas
DOI:10.1093/mutage/10.6.497
日期:——
The mutagenic environmental pollutants 2-nitrofluoran-thene (2-NFA) and 3-nitrofluoranthene (3-NFA), labelled with 3H and 14C respectively, were incubated with Salmonella typhimurium strain TA98, its nitroreductase-deficient variant TA98NR and its 0-acetytransferase-deficient variant TA98/1,8-DNP6, to investigate the activity of these metabolic pathways under conditions approximating those of the Ames assay, hence their contribution to mutagenic potency. 2-Aminofluoranthene (2-AFA) was the major metabolite of 2-NFA (4 μM) in all three TA98 variants, isolated by reverse-phase HPLC and identified by UV-vis and NMR spectroscopy and mass spectrometry. 2-AFA was formed more slowly in TA98NR (65 pmol/h/ml resting phase bacterial broth, 1 to 2×109 bacteria/ml) than in TA98 (295 pmol/h/ml) or TA98/1,8-DNP6 (82 pmol/h/ml). 2-Acetamidofluoranthene (2-AAFA) was also identified in incubations with TA98 (80 pmol/h/ml), TA98NR (21 pmol/ h/ml), and TA98/1,8-DNP6 (8 pmol/h/ml). 3-Aminofluoran-thene (3-AFA, confirmed by UV-vis and NMR spectroscopy and mass spectrometry) was formed by all three variants from 3-NFA (4 µM): TA98, 1.76 nmol/h/ml; TA98NR, 0.55 nmol/h/ml; TA98/1,8-DNP6, 2.93 nmol/h/ml. 3-Acetamidofluoranthene (3-AAFA) was not detected in any of the variants. 3-AFA and 3-AAFA were less mutagenic than 3-NFA, and required S9 for activation. Mutagenicity of 3-NFA relative to initial nitroreduction rate was similar in TA98 and in TA98NR, but almost 10-fold lower in TA98/ 1,8-DNP6; hence 0-acetylation considerably enhances the mutagenicity of reduction products of 3-NFA. Mutagenicity of 2-NFA relative to initial nitroreduction rate was similar in TA98 and in TA98/1,8-DNP6; the bacterial genotoxicity of 2-NFA is therefore largely independent of O-acetyltrans-ferase activity. Ratios of mutagenicity to nitroreduction rate were similar in TA98 for 2-NFA and 3-NFA; differences in the potency of these isomers arise primarily from their respective suitabilities as substrates for nitroreductase enzymes.
分别用 3H 和 14C 标记的致突变环境污染物 2-硝基荧蒽(2-NFA)和 3-硝基荧蒽(3-NFA)与鼠伤寒沙门氏菌菌株 TA98、和 0-乙酰转移酶缺陷变种 TA98/1,8-DNP6,以研究这些代谢途径在近似艾姆斯试验条件下的活性,以及它们对诱变效力的贡献。2-氨基荧蒽(2-AFA)是 2-NFA(4 μM)在所有三个 TA98 变异株中的主要代谢产物,通过反相高效液相色谱法分离出来,并通过紫外-可见光光谱、核磁共振光谱和质谱法进行鉴定。与 TA98(295 pmol/h/ml)或 TA98/1,8-DNP6 (82 pmol/h/ml)相比,2-AFA 在 TA98NR(65 pmol/h/ml 静止期细菌肉汤,1 至 2×109 个细菌/ml)中的形成速度更慢。在与 TA98(80 pmol/h/ml)、TA98NR(21 pmol/h/ml)和 TA98/1,8-DNP6(8 pmol/h/ml)的培养液中也发现了 2-乙酰胺基荧蒽(2-AAFA)。所有三种变体都从 3-NFA(4 µM)中生成了 3-氨基荧蒽(3-AFA,经紫外-可见光光谱、核磁共振光谱和质谱分析证实):TA98,1.76 nmol/h/ml;TA98NR,0.55 nmol/h/ml;TA98/1,8-DNP6,2.93 nmol/h/ml。在所有变体中均未检测到 3-乙酰胺基荧蒽(3-AAFA)。3-AFA 和 3-AAFA 的致突变性低于 3-NFA,并且需要 S9 才能激活。在 TA98 和 TA98NR 中,3-NFA 相对于初始硝基还原率的致突变性相似,但在 TA98/ 1,8-DNP6 中则低近 10 倍;因此,0-乙酰化大大增强了 3-NFA 还原产物的致突变性。2-NFA 的诱变性与初始硝基还原率在 TA98 和 TA98/1,8-DNP6 中相似;因此,2-NFA 的细菌遗传毒性在很大程度上与 O-乙酰反式酶活性无关。在 TA98 中,2-NFA 和 3-NFA 的诱变性与硝基还原率的比率相似;这些异构体的效力差异主要源于它们各自作为硝基还原酶底物的适宜性。