Metabolic activation and bacterial mutagenicity of aflatoxin B1 in two different test systems

The metabolism of aflatoxin B1 (AFB1) by liver post-mitochondrial supernatant fraction from phenobarbitone treated male albino rats in liquid suspension and soft-agar plate incorporation bacterial mutation assay systems has been studied. The AFB1 concentration used was in the range of those added to bacterial mutagenicity tests with this mycotoxin. Three oxidative metabolites of AFB1 viz the Tris derivative of AFB1 8,9-diol (derived from the 8,9-epoxide), aflatoxin Q1 (AFQ1) and M1 (AFM1) were observed. The metabolite profile and time course of formation were qualitatively similar in both assay systems. The rate and overall formation of metabolites in the soft-agar system was approximately one half that in the liquid suspension system which was reflected in decreased AFB1 induced bacterial mutation in the former system. The AFB1 metabolite profile in these in vitro systems did not mirror completely the reported in vivo profile seen in the rat, as aflatoxin P1 (AFP1) and a glutathione conjugate were not detected. No evidence was found for a prolongation of metabolism in the soft-agar system.