Aukerman S L, Brundrett R B, Hartman P E
Environ Mutagen. 1984;6(6):835-49. doi: 10.1002/em.2860060610.
Nitrosamides and nitrosocarbamates exhibit relatively high mutagenic activity in Salmonella when compared with nitrosoureas. This high activity can be accounted for by activation of nitrosamides and nitrosocarbamates by cellular thiols, predominantly reduced glutathione, that are present intracellularly at concentrations in the millimolar range. In striking contrast to the in vitro mutagenicity tests, a number of studies have indicated that nitrosamides and nitrosocarbamates are less potent than nitrosoureas when tested in vivo in model systems such as the mouse. We extend here previous studies [Aukerman et al, 1983] that demonstrate striking chemical decomposition and inactivation of mutagenic activity of nitrosamides and nitrosocarbamates during exposure to murine blood plasma. Plasma glutathione concentrations are inadequate to account for the rapid inactivations noted. Furthermore, the predominant inactivating species is heat-sensitive, nondialyzable, and is greater than 25,000 daltons in size as judged by ultrafiltration experiments. Serum albumin has some inactivating capacity at the concentration found in undiluted plasma and could account for the very low but significant inactivating capacity of human plasma. On the other hand, serum albumin lacks the potency necessary to account for the extremely high levels of inactivating activity observed in rodent and rabbit plasma. Elsewhere we present evidence that carboxylesterase activity is the predominant inactivating species in mouse plasma [Aukerman et al, 1983; Aukerman, 1983; Brundrett and Aukerman, 1984]. Mouse liver, large intestine, kidney, and stomach have more activity per milligram protein under the assay conditions used than plasma itself. Rat liver S9 is also active at enhancing the decomposition of nitrosamides and nitrosocarbamates; most of this inactivating capacity resides in the microsomal fraction. The relatively rapid detoxification of these N-nitroso compounds by plasma and other tissues of rodents has important implications regarding the utility of rodents in assessment of tumorigenicity and/or antitumor activity of these classes of drugs in other animal species. Tests with Salmonella may be of use in estimating relative levels of protection that vary widely among mammalian species.
与亚硝基脲相比，亚硝基酰胺和亚硝基氨基甲酸酯在沙门氏菌中表现出相对较高的诱变活性。这种高活性可以通过细胞内硫醇（主要是还原型谷胱甘肽）对亚硝基酰胺和亚硝基氨基甲酸酯的激活来解释，还原型谷胱甘肽在细胞内的浓度处于毫摩尔范围内。与体外诱变试验形成鲜明对比的是，许多研究表明，在小鼠等模型系统中进行体内试验时，亚硝基酰胺和亚硝基氨基甲酸酯的效力低于亚硝基脲。我们在此扩展了先前的研究 [奥克曼等人，1983年]，这些研究表明，亚硝基酰胺和亚硝基氨基甲酸酯在暴露于小鼠血浆期间会发生显著的化学分解并使其诱变活性失活。血浆中谷胱甘肽的浓度不足以解释所观察到的快速失活现象。此外，主要的失活物质对热敏感、不可透析，通过超滤实验判断其大小大于25,000道尔顿。血清白蛋白在未稀释血浆中的浓度下具有一定的失活能力，这可以解释人血浆非常低但显著的失活能力。另一方面，血清白蛋白缺乏解释在啮齿动物和兔血浆中观察到的极高失活活性水平所需的效力。我们在其他地方提供了证据，表明羧酸酯酶活性是小鼠血浆中的主要失活物质 [奥克曼等人，1983年；奥克曼，1983年；布伦德里特和奥克曼，1984年]。在所使用的测定条件下，小鼠肝脏、大肠、肾脏和胃每毫克蛋白质的活性比血浆本身更高。大鼠肝脏S9在增强亚硝基酰胺和亚硝基氨基甲酸酯的分解方面也具有活性；这种失活能力大部分存在于微粒体部分。这些N-亚硝基化合物在啮齿动物的血浆和其他组织中相对快速的解毒作用对于在评估这些类药物在其他动物物种中的致瘤性和/或抗肿瘤活性时使用啮齿动物具有重要意义。用沙门氏菌进行的试验可能有助于估计在不同哺乳动物物种中差异很大的相对保护水平。
