A correlation of the rate of N-hydroxylation of aminoazo dyes with their carcinogenic activity in the rat

Abstract
The rate of formation of N-hydroxy-N-methyl-4-aminoazobenzene (N-OH-MAB) derivatives from N,N-dimethyl-4-aminoazobenzene (DAB) derivatives and from N-methyl-4-aminoazobenzne (MAB) derivatives was measured by the ESR spectroscopy, and the rate of N-demethylation of DAB derivatives was measured by HPLC [high pressure liquid chromatography]. The rate of formation of N-OH-MAB derivatives from DAB derivatives showed a strong correlation with their carcinogenic activity. This reaction occurs in 2-steps, i.e., N-demethylation followed by N-hydroxylation. The rate of N-demethylation of DAB derivatives was not correlated with their carcinogenic activity. On the other hand, the rate of N-hydroxylation of MAB derivatives was well correlated with the carcinogenic activity of corresponding DAB derivatives. The carcinogenic activity of DAB derivatives in the rat was dependent upon the enzyme concerned with N-hydroxylation. The positive carcinogenicity is limited to those derivatives with a rate of N-hydroxylation above the threshold value.