Hepatocarcinogens induce gene mutations in rats in fibroblast-like cells from a subcutaneous granulation tissue

Gene-mutations at the 6-thioguanine locus, in fibroblast like-cells rapidly proliferating on the inside of rat subcutaneous air pouches were analysed (Granuloma Pouch Assay). Target cells were exposed directly by injection into the air pouch, or systemically by oral or intraperitoneal administration to three hepatocarcinogens aflatoxin B1, 2-acetylaminofluorene (2-AAF) and vinylchloride. In addition ethylnitrosourea (ENU) was used as a positive control, and 2-aminofluorene to characterize the pharmacokinetic behaviour of 2-AAF. When administered directly, all chemicals except 2-AAF induced a dose-dependent increase in gene-mutation frequencies. However, 2-AAF was mutagenic after oral administration. The highest inducible mutation frequencies found with the hepatocarcinogens were 8 to 10 times the spontaneous mutation frequency, but only approximately 10% of that found with the control mutagen ENU. The known enzymic activation capacity of the granulation tissue, and the mutagenic activity of other chemicals in this system already reported, suggest that after direct exposure, the prostaglandin H synthetase pathway or lipoxygenases are involved in the activation of the hepatotoxins to gene mutation inducing species in vivo. 2-AAF seems to be converted via stable intermediates to the ultimate mutagenic species in the extra-hepatic target tissues.