Metabolism of aflatoxin B₁ by rat hepatic microsomes induced by polyhalogenated biphenyl congeners

The metabolism of aflatoxin B₁ to aflatoxins M₁ and Q₁ by rat liver microsomes from animals pretreated with polychlorinated or polybrominated biphenyl congeners depended on the structure of the halogenated biphenyl inducers. Microsomes from rats treated with phenobarbital (PB) or halogenated biphenyls that exhibit PB-type activity preferentially enhanced the conversion of aflatoxin B₁ to aflatoxin Q₁. In contrast, microsomes from rats treated with 3-methylcholanthrene (MC) or halogenated biphenyls that exhibit MC-type induction activity increased the metabolism of aflatoxin B₁ to aflatoxin M₁. The coadministration of PB and MC produced microsomes that exhibited both types of induction activity (mixed type) in catalyzing the oxidative metabolism of diverse xenobiotic agents. However, PB-plus-MC-induced hepatic microsomes from immature male Wistar rats preferentially increased the metabolism of aflatoxin B₁ to aflatoxin M₁ but did not enhance the conversion of aflatoxin B₁ to aflatoxin Q₁. Comparable results were observed with microsomes from rats pretreated with halogenated biphenyls classified as mixed-type inducers; moreover, in some cases there was a significant decrease in the conversion of aflatoxin B₁ to aflatoxin Q₁ (compared with that of controls treated with corn oil).