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

Abstract The rate of microsomal metabolism of aflatoxin B 1 (AFB 1 ) 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 B 1 epoxidation (assessed by Tris-AFB 1 -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 B 1 metabolism. In the rat the corresponding inductions were 1.7 and 1.3, respectively. The aflatoxin B 1 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 B 1 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 B 1 .