Species, sex and inter-individual differences in DNA repair induced by nine sex steroids in primary cultures of rat and human hepatocytes

Sex steroids, due to the generally negative responses observed in routinely employed standard genotoxicity assays, are considered epigenetic carcinogens. Some doubts on this conviction are raised by the results of recent studies providing evidence that cyproterone acetate and two structural analogues, chlormadinone acetate and megestrol acetate, are genotoxic in female rats but only for the liver, and in primary human hepatocytes from donors of both genders. The experimental evidence suggests that the metabolic activation of these molecules to reactive species and the consequent formation of DNA adducts occur only in the intact hepatocyte. Since the possibility that other sex steroids cause a liver-specific genotoxic effect cannot be ruled out a priori, we investigated nine drugs of this family for their ability to induce DNA repair synthesis in primary cultures of rat and human hepatocytes. Each steroid was tested in cultures from at least two male and two female donors of each species. Hepatocytes were exposed for 20 h to sub-toxic concentrations ranging from I to 50 muM, and DNA repair induction was measured by quantitative autoradiography. In primary rat hepatocytes, induction of DNA repair indicative of a frankly positive response was detected in cultures from: 2/2 males and 3/3 females with drospirenone, 2/2 males and 1/2 females with ethinylestradiol, 1/2 males and 1/2 females with oxymetholone, 1/2 males with norethisterone, 1/4 females with progesterone, and 1/4 males with methyltestosterone. Consistent negative responses were obtained with testosterone and stanozolol. A few inconclusive responses were observed in rat hepatocytes exposed to progesterone, medroxyprogesterone, norethisterone, methyltestosterone and oxymetholone. In contrast, under the same experimental conditions the nine sex steroids provided frankly negative responses in the large majority of cultures of primary hepatocytes from both male and female human donors; the only exceptions being the inconclusive responses obtained in cultures from two of the donors exposed to norethisterone and to ethinylestradiol, and from one of the donors exposed to testosterone, methyltestosterone, and stanozolol. These results and previous findings concerning cyproterone and its structural analogues suggest that sex steroids differ for their ability to induce DNA repair, and that their genotoxicity may be: (i) different in rat and human hepatocytes, (ii) dependent on the sex of the donor, and (iii) affected by inter-individual variability. (C) 2003 Elsevier Science B.V. All rights reserved.