Genotoxic potential of xenobiotic growth promoters and their metabolites

This paper reviews data reported in the literature as well as recent and un published studies from our laboratory on the metabolism and genotoxicity of the xenobiotic growth promoters 17 beta -trenbolone, melengestrol acetate and zeranol. In our metabolic study, the oxidative in vitro metabolites gen erated by hepatic microsomes from rats, bovine and humans were analyzed by HPLC and GC/MS. 17 beta -Trenbolone gave rise to at least 13 monohydroxylat ed products, whereas 12 mono- and dihydroxylated metabolites were obtained with melengestrol acetate and at least 5 with zeranol. The genotoxic potent ial of the parent compounds was studied using the following endpoints: indu ction of HPRT mutations in cultured V79 cells and of lacI mutations in E. c oli; induction of micronuclei in V79 cells; and formation of DNA adducts in cultured primary rat hepatocytes. Negative results were obtained in most o f these assay systems. Only the micronucleus induction was marginally posit ive with 17 beta -trenbolone and zeranol at near-cytotoxic concentrations. Commercial melengestrol acetate was found to contain an impurity causing ap optosis in V79 cells. The genotoxic potential of the numerous oxidative met abolites of the xenobiotic growth promoters remains to be studied.