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.