Binding of metabolites of dietary 4-dimethyl-aminoazobenzene and 2-methyl-4-dimethylamino-azobenzene to rat liver DNA and protein of subcellular fractions.

The binding of metabolites of two related azo dyes of different carcinogenic potency, the carcinogenic 4-dimethylaminoazobenzene (DAB) and the weakly carcinogenic 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB), to rat liver DNA and to subcellular fraction protein was studied following chronic oral administration for 1 to 3 weeks. Different techniques for measuring the amount of DAB metabolites bound to protein were first compared, then the whole study was performed with labelled DAB and 2-Me-DAB (aniline ring-14C) of moderate specific activity. DAB metabolites were bound to liver DNA to a higher extent than those of 2-Me-DAB. In contrast, the binding of 2-Me-DAB metabolites was equal to or higher than that of DAB metabolites to protein. The amount of protein-bound metabolites was studied on the nucleo-mito-chondrial fraction, microsomes, supernatant, nuclei, chromatin, nucleoplasm, nucleolar fraction and nuclear membrane. Following the administration of both dye diets, the supernatant protein bound the highest level of metabolites. The time-course of binding of DAB metabolites to DNA and protein was different from that of 2-Me-DAB metabolites. These results show the possible involvement of carcinogen-DNA binding in the mechanism of carcinogenesis. Liaison des Metabolites du 4-Dimethylaminoazobenzene et du 2-Methyl-4-Dimethylaminoazobenzene au DNA et Aux Proteines des Fractions Subcellulaires de Foie de Rat La liaison des metabolites de deux composes azoiques voisins, de pouvoir cancerogene different, le 4-dimethylaminoazobenzene (DAB) cancerogene, et le 2-methyl-4-dimethylaminoazobenzene (2-Me-DAB) faiblement cancerogene, au DNA et aux proteines des fractions subcellulaires de foie de rat apres administration chronique dans le regime a ete etudiee pendant une periode de 1 a 3 semaines. Apres avoir compare differentes techniques de mesure des metabolites du DAB lies aux proteines, nous avons utilise pour l'experimentation les composes azoiques marques au 14C dans le cycle aniline, de faible activite specifique. La fixation au DNA des metabolites du DAB est tres superieure a celle des metabolites du 2-Me-DAB, alors que la fixation des metabolites du 2-Me-DAB aux proteines est egale ou superieure a celle du DAB. Nous avons en outre mesure les quantites de metabolites des 2 composes azoiques lies aux proteines des fractions suivantes: fraction nucleomitochondriale, microsomes, surnageant cytoplasmique, noyau, chromatine, nucleoplasme, fraction nucleolaire et membrane nucleaire. Les proteines du surnageant ont le plus haut niveau de metabolites lies, quel que soit le compose azoique administre dans le regime. La cinetique de fixation des metabolites du DAB et du 2-Me-DAB au DNA et aux proteines est differente. Les resultats mettent en evidence l'importance possible de la liaison des cancerogenes au DNA dans le mecanisme de la cancerogenese.