Genotoxicity testing of potassium canrenoate in cultured rat and human cells

Potassium canrenoate (PC), a competitive aldosterone antagonist used as a diuretic and in the treatment of hypertension, was examined for its capacity to produce genotoxic effects in cultured rat and human cells. At subtoxic concentrations (10-90 microM) PC was found to induce a dose-dependent degree of DNA fragmentation, as detected by the Comet assay, and of DNA repair synthesis, as measured by quantitative autoradiography, in primary cultures of hepatocytes from rat and human donors of both genders. In rat hepatocytes both DNA fragmentation and DNA repair were more marked after 3 h than after 20 h exposure and in cultures from females than from males. In human hepatocytes from one male and two female donors, PC caused a similar effect in terms of DNA fragmentation, whereas DNA repair was detected in cultures from only two of the same three donors and was less marked than in rat hepatocytes. A modest but statistically significant increase in micronucleated cells was present in primary cultures of replicating rat hepatocytes exposed to 10 or 30 microM PC for 48 h, the response being, in this case also, more evident in females than in males. In contrast, PC did not induce micronucleus formation in human hepatocytes from two female donors. Any evidence of DNA fragmentation and micronucleus formation was absent in cultured human lymphocytes. Taken as a whole these findings support the hypothesis that hepatocytes activate PC to DNA-damaging reactive species. PC induced the observed genotoxic effects at concentrations close to those produced in humans by the administration of therapeutic doses, but these effects were as a whole more marked in rat than in human hepatocytes. Since PC shares the 17-hydroxy-3-oxopregna-4,6-diene structure with cyproterone acetate, chlormadinone acetate and megestrol acetate, previously found to be genotoxic to both rat and human hepatocytes, the potential carcinogenic hazard of this type of steroids cannot be neglected.