Detection of in vitro genotoxicity of pro-mutagens using the comet assay under human and rat liver S9 fractions

The metabolic activating ability of human liver S human lung S HLuSP E and rat liver S were compared One of the human liver S HLSP E was prepared from a pool from donors and the other HLS E from a liver sample that had high levels of P activities Rat liver S was prepared from male Sprague ndash Dawley rats either untreated RLSP E or pretreated with phenobarbital benzoflavone RL PB BF Human lymphoma WTK cells were treated with pro mutagens that required cytochrome P or NADPH P reductase for metabolic activation and their genotoxicity was determined by the comet assay HLS E and RL PB BF had a higher P enzyme activity and activated a greater variety of pro mutagens than others The results of the human liver S and RL PB BF were discrepant for only out of pro mutagens phenacetin was positive with human liver S but not with RL PB BF and benz a anthrathene was positive with RL PB BF but not with human liver S Both RL PB BF and human liver S activated pyrene IQ MeIQ nitropyrene and N nitrosopiperidine while RLSP E did not In spite of the existence of species differences in CYP isoforms and differences of CYP activity therefore there were no appreciable qualitative differences in pro mutagen activating ability of the human liver S and RL PB BF suggesting the possibility that the genotoxicity of some pro mutagens that are genotoxic with human liver S are missed by the use of liver S from rats that were not pretreated to induce CYP Therefore conventionally used CYP induced rat liver S fraction is useful for the evaluation of the genotoxic risk for humans in spite of the species difference in CYP isoforms nbsp