The in vitro metabolism of aflatoxin B1 catalyzed by hepatic microsomes isolated from control or 3-methylcholanthrene-stimulated rats and quail.

The rate of microsomal metabolism of aflatoxin B1 (AFB1) by the male quail hepatic microsomal polysubstrate monooxygenase P-450 in vitro was eight times greater than that catalyzed by male rat cytochrome. In the quail almost all the metabolism proceeded via 8,9-aflatoxin B1 epoxidation (assessed by Tris-AFB1-8,9-dihydrodiol formation), whereas in the rat only 36% of soluble metabolites were by this pathway. Pretreatment with 3-methylcholanthrene in the quail resulted in a 9-fold induction of cytochrome P-450 per unit liver weight, but only a 1.7-fold increase in the rate of aflatoxin B1 metabolism. In the rat the corresponding inductions were 1.7 and 1.3, respectively. The aflatoxin B1 metabolism catalyzed by control and 3-methylcholanthrene-stimulated quail microsomes differed qualitatively from that observed with the corresponding fractions from the rat. It was concluded that not only do the basal aflatoxin B1 microsomal metabolism of rat and quail differ, but also that 3-methylcholanthrene induces cytochromes with very different properties in the two species. Assays of ethoxyresorufin O-deethylase activities and polyacrylamide gel electrophoresis analyses further demonstrated these differences between the species. These studies provide further insight into the metabolic differences underlying individual species sensitivities to aflatoxin B1.