Transfer RNA methylase activity and capacity during aflatoxin B1-induced hepatocellular carcinogenesis.

Transfer RNA methylase (tRNA methylase) activity and capacity were monitored in whole-rat-liver preparations during the induction of hepatocellular carcinomas by an 8-week aflatoxin B1 dosing regimen that produced minimal toxic effects. Significant phases of elevated tRNA methylase capacity occurred at 6 to 9 weeks (20%) and 24 to 29 weeks (40%). No significant change in tRNA methylase activity was noted over the course of the 55-week experiment. Higher aflatoxin B1 doses, producing acute toxic liver damage, resulted in elevated tRNA methylase activity (50%) and capacity (30%) at least as early as 1 week after dosing. Experiments with individual nodular lesions excised from livers of rats continuously fed a diet containing 2 ppm aflatoxin B1 demonstrated similarly elevated tRNA methylase activities and capacities in hyperplastic (preneoplastic)nodules, with and without histological evidence of carcinoma.