Reduced nicotinamide adenine dinucleotide phosphate-dependent formation of 2,3-dihydro-2,3-dihydroxyaflatoxin B1 from aflatoxin B1 by hepatic microsomes.

2,3-Dihydro-2,3-dihydroxyaflatoxin B1 (dihydrodiol) was formed as a major metabolite in the incubation of aflatoxin B1 with rat and hamster liver microsomes. The yield of the dihydrodiol was maximal at pH 6.5, was reduced nicotinmide adenine dinucleotide phosphate- and cytochrome P-450-dependent, and was increased 2- to 4-fold by pretreatment of the animals with phenobarbital; pretreatment with 3-methylcholanthrene did not alter the activity of rat hepatic microsomes. Inhibitors of epoxide hydrase did not lower the yield of the dihydrodiol in these systems. Negligible yields of the dihydrodiol were formed from aflatoxin B1 and rat liver microsomes in the presence of DNA. Little or no formation of the dihydrodiol was noted with microsomes from rat intestinal mucosa, kidney, or lung. These results further support the formation of aflatoxin B1 2,3-oxide as a major electrophilic metabolite of aflatoxin B1 in rat and hamster liver microsomal systems, since this highly reactive epoxide would be expected to hydrolyze readily to form the dihydrodiol.