Use of rat and human liver slices for the detection of steroid hormone-induced DNA-adducts in vitro by means of the (32)P-postlabeling technique

Precision cut liver slices from humans and rats were used to investigate the covalent binding of xenobiotics to the DNA by means of the (32)P-postlabeling technique. Human liver slices were incubated with the structurally related steroid hormones chlormadinone acetate (5 mu g/ml), cyproterone acetate (0.01-5 mu g/ml), megestrol acetate (5 mu g/ml), and the positive control 2-aminofluorene (0.01-5 mu g/ml), which is known for its marked ability to form DNA-adducts in vivo. Rat liver slices were incubated with cyproterone acetate in concentrations of 0.1, 1, and 5 mu g/ml. The functional viability and metabolic activity of the slices were shown to be sufficiently maintained during the incubation time by measurement of the intracellular K(+)-content and the metabolic turnover of the model substrate 7-ethoxycoumarin, respectively. All three test substances and the control induced DNA-adducts in human liver slices, however, with a different adduct pattern. While the total DNA-adduct levels obtained with cyproterone acetate and megestrol acetate were in the same order of magnitude (on average 1000 DNA-adducts/10(9) nucleotides after incubation with 5 mu g /ml), the relative adduct labeling calculated for chlormadinone acetate was about 400. Following in vitro incubation of rat liver slices with cyproterone acetate, the relative adduct labeling values increased proportionally with increasing concentrations and added linearily to in vivo generated DNA-adducts. At the level of liver slices, different DNA-adduct patterns were induced by cyproterone acetate in rat and man. In contrast to the finding of others, using rat hepatocytes, the relative adduct labeling values of cyproterone acetate and megestrol acetate were in the same order of magnitude after incubation with human liver slices. The present study indicates that liver slices are a useful tool to investigate the in vitro DNA-adduct inducing potential of xenobiotics.