Dietary Lipotropes, Hepatic Microsomal Mixed-Function Oxidase Activities, and in Vivo Covalent Binding of Aflatoxin B₁ in Rats¹

Weanling male Sprague-Dawley rats were fed either a nutritionally complete synthetic diet (Diet 1) or a diet marginally deficient in choline and methionine, and lacking folacin (lipotrope deficient, Diet 2) to determine the role of hepatic mixed-function oxidase metabolism of aflatoxin B₁ (AFB₁) in the Diet 2-induced enhancement of AFB₁ hepatocarcinogenesis previously reported. Hepatic microsomal mixed-function oxidase activities, as assayed by ethylmorphine N-demethylation, ethoxycoumarin O-dealkylation, cytochrome c reduction, AFB₁ metabolism, and cytochrome P-450 content, were all depressed by Diet 2. Furthermore, the proportion of an i.p. dose of AFB₁ (1 mg/kg) that became covalently bonded to DNA and RNA was similarly reduced when measured 6 hr after administration. The formation of AFB₁-protein adducts was not influenced by dietary treatment. The depression of DNA and RNA adduct formation in the Diet 2 animals was probably related to the lower mixed-function oxidase activities and not to an alteration of glutathione levels, which remained unchanged by dietary treatment. These results suggest that the marginally lipotrope-deficient diet does not enhance tumor formation through an increased microsomal activation of AFB₁. Alternative hypotheses without data are suggested.