Frantz C N, Malling H V
Cancer Res. 1975 Sep;35(9):2307-14.
For exploration of the factors affecting dimethylnitrosamine (DMN) mutagenicity, for gathering of information on the metabolism of DMN, a frequently used and relatively well-understood carcinogen, and for explanation of metabolic variations in DMN carcinogenicity, parallel in vitro assays of the microsomal activation of DMN to a mutagen and of DMN demethylation were performed. Salmonella typhimurium G46 reversions to histidine independence increase linearly with time of incubation for 30 min. At low concentrations of microsomal protein, increases in protein yield a more than proportional increase in mutations. Increasing DMN concentration saturates the enzyme, yielding less demethylation and fewer mutations proportionately. Mutagenesis is completely inhibited by 1 mM 2-diethyl-aminoethyl-2,2-diphenylvalerate. When both DMN and microsomal protein are varied at high concentrations, there is a simple linear relationship between mutagenicity and DMN demethylase activity. Thus DMN demethylase activity may be the primary controlling factor in the metabolism of DMN to a mutagen, and probably to a carcinogen; other simultaneous pathways of DMN metabolism proportional to demethylation have not been ruled out. Induction with both phenobarbital and 3-methylcholanthrene (3-MC) increased rat and mouse liver DMN demethylase activity. Mouse liver microsomes from the C57BL/6 strain demethylate DMN at a markedly lower rate than do microsomes from the C3H strain, but after 3-MC induction the relationship is reversed. Strain differences in activation of DMN were not found in the activation of diethylnitrosamine to a mutagen. Hepatic dealkylation of DMN and diethylnitrosamine to active mutagenic metabolites is increased in both rats and mice by both 3-MC and phenobarbital induction, which is in contrast to the findings of others that 3-MC and phenobarbital induction, which is in contrast to the findings of others that 3-MC decreases the incidence of DMN-induced hepatic tumors in rats, and phenobarbital decreases the incidence of diethylnitrosamine-induced hepatic tumors in mice.
为了探究影响二甲基亚硝胺（DMN）致突变性的因素，收集关于DMN代谢的信息（DMN是一种常用且相对了解的致癌物），并解释DMN致癌性的代谢差异，我们进行了平行的体外实验，检测DMN微粒体激活成诱变剂以及DMN去甲基化的情况。鼠伤寒沙门氏菌G46回复为不依赖组氨酸的菌株，其回复率在30分钟的孵育时间内随时间呈线性增加。在低浓度的微粒体蛋白条件下，蛋白产量的增加会使突变增加的比例超过预期。DMN浓度的增加会使酶饱和，导致去甲基化减少，相应地突变也减少。1 mM的2 - 二乙氨基乙基 - 2,2 - 二苯基戊酸可完全抑制诱变作用。当高浓度下同时改变DMN和微粒体蛋白时，致突变性与DMN去甲基酶活性之间存在简单的线性关系。因此，DMN去甲基酶活性可能是DMN代谢为诱变剂，可能也是致癌物过程中的主要控制因素；与去甲基化成比例的其他同时发生的DMN代谢途径尚未被排除。苯巴比妥和3 - 甲基胆蒽（3 - MC）诱导均增加了大鼠和小鼠肝脏的DMN去甲基酶活性。C57BL/6品系小鼠肝脏微粒体使DMN去甲基的速率明显低于C3H品系的微粒体，但经3 - MC诱导后这种关系发生了逆转。在将二乙基亚硝胺激活成诱变剂的过程中未发现DMN激活存在品系差异。3 - MC和苯巴比妥诱导均增加了大鼠和小鼠肝脏中DMN和二乙基亚硝胺脱烷基生成活性诱变代谢物的过程，这与其他人的研究结果相反，其他人发现3 - MC会降低大鼠中DMN诱导的肝肿瘤发生率，苯巴比妥会降低小鼠中二乙基亚硝胺诱导的肝肿瘤发生率。
