In vivo effect of dietary factors on the molecular action of aflatoxin B1: role of riboflavin on the catalytic activity of liver fractions.

Weanling rats were kept on a synthetic riboflavin-free diet for 4 weeks, and subsequently on the same diet but supplemented with riboflavin for 2 weeks. The ability of liver microsomes to catalyze reactions of aflatoxin B1 (AFB1) leading to its activation and DNA adduct formation was measured after each period of experimental feeding. A decrease in both activities was evident during riboflavin deficiency, and this could be restored after normal supply of the vitamin. The decrease was attributed to a fall in the endogenous flavin content, specifically the coenzyme flavin adenine dinucleotide which forms an integral part of the microsomal monooxygenase that catalyzes the activation reactions. The vitamin and its coenzymes, however, inhibit the microsomal enzyme activity when added in excess in the in vitro system. It is envisaged that riboflavin may play a role in regulating the carcinogenic activity of AFB.