Effects of dietary fat on hepatic mixed-function oxidases and hepatocellular carcinoma induced by aflatoxin B1 in rats.

Some groups of male Sprague-Dawley rats were fed a diet containing either 28% beef fat and 2% corn oil or 30% corn oil (high fat), and others were fed either 13% beef fat and 2% corn oil or 15% corn oil (moderate fat), for varying periods of time, with or without exposure to aflatoxin B, (AFBi). Assays for hepatic microsomal oxidases [p-nitroanisole demethylase and benzo(a)pyrene hydroxylase] were performed on liver samples to determine the activity associated with the two types of fat at different dietary concentrations. Beef fat increased liver fat concentrations and resulted in a higher mortality rate from a dose of AFBi at which 50% of animals died, compared to corn oil-fed groups. In an additional study, the resting levels of microsomal enzyme activity increased sequentially in all groups over a 3-week period after animals were placed on the respec tive diets. Corn oil diets permitted the greatest increase (induc tion) in activity of both enzymes at weekly intervals for 3 weeks. In another experiment, in which rats from all dietary groups were exposed to AFBi, corn oil permitted a significantly higher induction of enzyme activity by AFB,. In a 14-month study of rats fed the high corn oil diet, those exposed to the diet during and after AFBi treatment developed significantly more liver tumors than those consuming the diet only after administration of a carcinogenic dose of AFB,. In animals fed beef fat, tumor incidence was depressed compared to those fed corn oil, but no differences were observed between groups fed beef fat throughout exposure to AFB, and afterward and those fed beef fat only after AFB, exposure. These observations suggest that corn oil may act as a promoter through microsomal enzyme induction and AFB, activation.