Comparative metabolism of benzo(a)pyrene, chrysene and phenanthrene by brown bullhead liver microsomes

The metabolism of benzo(a)pyrene (BaP), chrysene and phenanthrene by liver microsomes of brown bullhead (Ictalurus nebulosus) was investigated. Among the three PAHs, BaP was metabolized at the highest rate, chrysene at an intermediate rate and phenanthrene at the lowest rate. The liver microsomes from the control fish metabolized all three PAHs to their corresponding K-region dihydrodiols to a small extent. A greater proportion of diols with a bay-region double bond (proximate carcinogenic metabolites) than of bay-region diols was formed from the three PAHs, but the proportion of diols with a bay-region double bond varied with the hydrocarbon. Metabolically-formed BaP-7,8-diol, chrysene-1,2-diol and phenithrene 1,2-diol consisted predominantly of the R,R enantiomer. The data show that brown bullhead liver microsomes metabolize the three PAHs, which vary in molecular size and shape, with essentially similar regio- and stereoselectivity.