In vitro mutagenicity studies on cyproterone acetate using female rat hepatocytes for metabolic activation and as indicator cells

The synthetic sex steroid cyproterone acetate (CPA) was shown to induce DNA repair in primary hepatocytes from female rats, confirming previous reports about a sex-specific genotoxic potential of CPA in female rat liver. CPA did not induce gene mutations or chromosomal aberrations in V79 Chinese hamster cells co-cultivated with hepatocytes from female rats as the metabolizing system. Hepatocytes from the same rats under identical exposure conditions as in the positive unscheduled DNA synthesis (UDS) test were used in these experiments. The maximum concentrations tested in the mutagenicity assays were 30-100 times higher compared with the lowest observed effect concentration of 3x10 -6 mol/l in the DNA repair test. The requirement for cell-cell transfer of the putative genotoxic metabolites in the co-culture experiments may be the reason for the discrepancy between positive UDS effects and negative mutagenicity and clastogenicity results. To further investigate if CPA can induce chromosomal mutations within the same cells that provide metabolic activation an in vitro micronucleus assay with proliferating female rat hepatocytes was performed. The results gave some indications of a micronucleus-inducing potential of CPA. However, under the conditions of the micronucleus assay CPA was also shown to increase the proliferative activity of hepatocytes. Since micronucleus formation is also dependent on mitotic activity, it cannot be determined whether the increase in micronucleus formation after CPA exposure indicates a clastogenic potential or whether it is just a consequence of the mitogenic potential of CPA. Although CPA or its metabolites obviously have a DNA damaging potential and stimulate considerable DNA excision repair, our findings do not establish a clear mutagenic potential.