Differential serum protein binding of benzidine- and benzidine-congener based dyes and their derivatives.

Environmental dyes and their derivatives, some of which are genotoxic, must be transported within the body to the tissues which they affect. One mechanism for this can be observed directly by crossed immunoelectrophoresis (X-IEP). Binding of these chemicals to certain serum proteins changes electrophoretic and immunoprecipitation morphology in X-IEP patterns. This is demonstrated here for four azo dyes derived from benzidine, 3,3'-dimethylbenzidine, and 3,3'-dimethoxybenzidine, and their parent aromatic amines. Direct Red 2 (a 3,3'-dimethylbenzidine-based dye), Direct Blue 15 (a 3,3'-dimethoxybenzidine-based dye), Direct Black 38 (a benzidine-based dye), and Evans Blue (a 3,3'-dimethylbenzidine-based dye) all bound to albumin, alpha 1-lipoprotein, beta-lipoprotein, and hemopexin. Direct Red 2 only slightly affected the mobilities of these proteins. Direct Blue 15 bound also to prealbumin and alpha 1-antichymotrypsin, and degraded C3 globulin. Direct Black 38 and Evans Blue bound to numerous additional proteins. Evans Blue bound variably to proteins of sera from different individuals, suggesting that there are individual differences in serum protein binding capabilities for these chemicals. Of the three derivatives of the benzidine dyes, only 3,3'-dimethylbenzidine caused changes in X-IEP patterns, indicating its binding to the serum proteins. This chemical differentially affected sub-populations of alpha 1-lipoprotein, either by altering its electrophoretic mobility or inhibiting its recognition by antibodies. Autoradiographic analyses demonstrated the binding of benzidine and 3,3'-dimethylbenzidine to both alpha 1- and beta-lipoproteins.