Brennan R J, Schiestl R H
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, MA 02115, USA.
Mutagenesis. 1997 Jul;12(4):215-20. doi: 10.1093/mutage/12.4.215.
The carcinogen aniline is negative in the Ames Salmonella mutagenicity assay. Aniline does, however, induce intrachromosomal recombination between repeated sequences in Saccharomyces cerevisiae, resulting in deletion (DEL) of intervening sequences. We have investigated whether the generation of oxidative free radical species by aniline and/ or its metabolites may be responsible for its recombinagenic activity in yeast. The toxicity and recombinagenicity of aniline in yeast were greatly reduced in the presence of the free radical scavenger N-acetyl cysteine. Aniline cytotoxicity was many-fold increased in strains of S.cerevisiae lacking the antioxidant enzyme superoxide dismutase. Aniline also induced oxidation of the intracellular free radical-sensitive reporter compound 2,4-dichlorofluorescin diacetate to its fluorescent derivative 2,4-dichlorofluorescein in vivo in S.cerevisiae. The aniline metabolites 4-aminophenol and 2-aminophenol were significantly more potent inducers of DEL recombination in yeast than aniline. In contrast, the secondary metabolite 4-acetamidophenol (acetaminophen) was non-toxic and non-recombinagenic in yeast. 4-Aminophenol and 2-aminophenol were also significantly more toxic than aniline in a superoxide dismutase deficient yeast strain. 4-aminophenol was a significantly more potent oxidizer of 2,4-dichlorofluorescin diacetate than aniline. The Escherichia coli soxS promoter, which is induced in the presence of redox cycling agents like paraquat, was induced weakly by aniline at toxic doses. The soxS promoter was strongly induced by 4-aminophenol and 2-aminophenol. The results indicate a role for oxidative stress, mediated by generation of superoxide radical, in the toxicity and recombinagenicity of aniline. The increased activity of 4-aminophenol and 2-aminophenol suggests that ring hydroxylation may be an important activating step in this process.
致癌物苯胺在艾姆斯沙门氏菌致突变性试验中呈阴性。然而，苯胺确实能诱导酿酒酵母中重复序列之间的染色体内重组，导致中间序列缺失（DEL）。我们研究了苯胺及其代谢产物产生的氧化自由基是否可能是其在酵母中的重组活性的原因。在自由基清除剂N - 乙酰半胱氨酸存在下，苯胺在酵母中的毒性和重组活性大大降低。在缺乏抗氧化酶超氧化物歧化酶的酿酒酵母菌株中，苯胺的细胞毒性增加了许多倍。苯胺还在酿酒酵母体内将细胞内对自由基敏感的报告化合物2,4 - 二氯荧光素二乙酸酯氧化为其荧光衍生物2,4 - 二氯荧光素。苯胺代谢产物4 - 氨基酚和2 - 氨基酚在酵母中诱导DEL重组的能力明显比苯胺更强。相比之下，二级代谢产物4 - 乙酰氨基酚（对乙酰氨基酚）在酵母中无毒且无重组活性。在超氧化物歧化酶缺陷的酵母菌株中，4 - 氨基酚和2 - 氨基酚的毒性也明显比苯胺更大。4 - 氨基酚氧化2,4 - 二氯荧光素二乙酸酯的能力明显比苯胺更强。大肠杆菌soxS启动子在百草枯等氧化还原循环剂存在时会被诱导，在有毒剂量的苯胺作用下诱导较弱。4 - 氨基酚和2 - 氨基酚能强烈诱导soxS启动子。结果表明，由超氧自由基产生介导的氧化应激在苯胺的毒性和重组活性中起作用。4 - 氨基酚和2 - 氨基酚活性的增加表明环羟基化可能是这一过程中的一个重要激活步骤。
