Comparative metabolism of benzo[a]pyrene by liver microscomes from brown bullhead and carp

We examined the metabolism of the carcinogen benzo[a]pyrene [BP] by hepatic microsomes from untreated brown bullhead (Ictalurus nebulosus) and mirror garp (Cyprinus carpio), two bottom-dwelling fish species. The rate of metabolism of BP by carp liver microsomes (455.1 ± 141.5 pmol/min per mg protein) was considerably higher than that obtained with bullhead liver microsomes (38.1 ± 12.3 pmol/min per mg protein). The major BP metabolites formed by liver microsomes from both species were qualitatively similar and included BP-7,8-diol, BP-9,10-diol, 3-hydroxy-BP, 9-hydroxy-BP, BP-1,6-quinone, BP-3,6-quinone, and BP-6,12-quinone. However, the patterns of BP metabolites generated by the liver microsomes of the two species were considerably different from each other. The carp liver microscomes converted a much greater proportion of BP to benzo-ring dihydrodiols than did the bullhead liver microsomes. Compared to carp liver microsomes, bullhead liver microsomes formed a considerably higher percentage of BP-pheols and BP-quinones as a fraction of the total metabolites. The predominant enantiomer of BP-7,8-diol formed by liver microsomes of both species had an (-)R,R absolute stereochemistry, suggesting a similar stereoselectively in the metabolism of BP to BP-7,8-diol by both carp and bullhead liver microsomes.