In vivo genotoxicity and DNA adduct levels in the liver of rats treated with safrole

The induction of chromosome aberrations, sister chromatid exchanges (SCEs),and the formation of DNA adducts was studied in hepatocytes of F344 ratsexposed in vivo to safrole. Hepatocytes were isolated 24 h after a singledose of safrole or five repeated doses (once a day) by gastric intubationand allowed to proliferate in Williams' medium E supplemented withepidermal growth factor. Cells were fixed after 48 h in culture.Safrole-DNA adducts were detected by a nuclease P1-enhanced32P-post-labeling assay in isolated hepatocytes from the rats. While asingle dose was not sufficient to induce detectable levels of chromosomeaberrations at the time of assay, five repeated doses induced these changeswith a maximum frequency of 13.4%, compared with the control value of 1.8%.Both a single dose and five repeated doses induced significant SCEs, to amaximum frequency of 0.81 SCEs per chromosome, while the control value was0.59 SCEs per chromosome. Two major and two minor DNA adducts were detectedafter treatment with either a single dose or five repeated doses. Themaximum amount of total DNA adducts was 89.8 DNA adducts/10(7) nucleotides.These results show that safrole is a genotoxic carcinogen in the rat liverin vivo and suggest that the cytogenetic effects of this compound mayresult from covalent DNA modification in the rat liver. This in vivocytogenetic assay should provide a useful means of evaluation of thegenotoxicity of hepatocarcinogens.