We investigated the ability of hepatic cytosolic samples from human, rat, rabbit and pig to metabolize an important industrial pollutant and a potent carcinogen for rodents, 2-nitroanisole (1-methoxy-2-nitrobenzene). A comparison between experimental animals and the human enzymatic system is essential for the extrapolation of animal carcinogenicity data to humans to assess a health risk to humans. Two major metabolites produced from 2-nitroanisole by cytosols of all species wereN-(2-methoxyphenyl)hydroxylamine and 2-methoxyaniline. An additional minor product of 2-nitroanisole metabolism has not yet been characterized. Both the identified metabolites are generated from 2-nitroanisole by reduction of the nitro group. To define the role of cytosolic reductases in the reduction of 2-nitroanisole, we investigated the modulation of 2-nitroanisole reduction by cofactors of the cytosolic reductases, DT-diaphorase and xanthine oxidase. The role of the human enzymes in 2-nitroanisole reduction was also investigated by correlating the xanthine oxidase-linked catalytic activities in each human cytosolic sample with the concentration of the 2-nitroanisole reduction product, 2-methoxyaniline, formed by the action of the same cytosol. On the basis of these analyses, most of hepatic cytosolic reduction of 2-nitroanisole was attributed to xanthine oxidase, but participation of DT-diaphorase in the reduction of this carcinogen in hepatic cytosols of rabbit and pigs cannot be excluded. Using the purified xanthine oxidase, its participation in 2-nitroanisole reduction was confirmed. The data clearly demonstrate the predominant role of xanthine oxidase in 2-nitroanisole reduction in human and rat hepatic cytosols and suggest a carcinogenic potency of this rodent carcinogen for humans.
我们研究了来自人类、大鼠、兔子和猪的肝细胞溶胞样本代谢一种重要的工业污染物和对啮齿动物具有强烈致癌作用的2-硝基苯甲醚(1-甲氧基-2-硝基苯)。实验动物与人类酶系统之间的比较对于将动物致癌数据推广到人类以评估对人类的健康风险至关重要。所有物种的细胞溶胞体产生的2-硝基苯甲醚的两种主要代谢物是N-(2-甲氧基苯基)羟胺和2-甲氧基苯胺。2-硝基苯甲醚代谢的另一个次要产物尚未被表征。已确定的代谢物都是通过还原硝基团从2-硝基苯甲醚产生的。为了定义细胞溶胞还原酶在2-硝基苯甲醚还原中的作用,我们研究了细胞溶胞还原酶辅因子DT-二氧还酶和黄嘌呤氧化酶对2-硝基苯甲醚还原的调节。通过将每个人类细胞溶胞样本中黄嘌呤氧化酶相关的催化活性与相同细胞溶胞作用形成的2-甲氧基苯胺的浓度相关联,还研究了人类酶在2-硝基苯甲醚还原中的作用。根据这些分析,2-硝基苯甲醚的大部分肝细胞溶胞还原被归因于黄嘌呤氧化酶,但不能排除DT-二氧还酶在兔子和猪的肝细胞溶胞中对这种致癌物质还原的参与。使用纯化的黄嘌呤氧化酶,已确认其在2-硝基苯甲醚还原中的参与。数据清楚地表明了黄嘌呤氧化酶在人类和大鼠肝细胞溶胞中2-硝基苯甲醚还原中的主导作用,并暗示了这种啮齿动物致癌物质对人类的致癌潜力。