Existence of no hepatocarcinogenic effect levels of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline with or without coadministration with ethanol.

There is increasing evidence of the existence of no effect levels for genotoxic carcinogens. However, only limited information is available regarding dose-response curves for combination effects of multiple carcinogens at low dose. In the present study, 280 male F344 rats were divided into 14 groups to determine the effects of co-administration of various doses of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 10% ethanol on the development of glutathione S-transferase placental form (GST-P)-positive foci in the liver. The results provided concrete evidence for the existence of no effect levels for hepatocarcinogenicity of MeIQx either in presence or absence of ethanol and, therefore, for a practical threshold for this genotoxic carcinogen.