Comparative metabolism of dibenzo[a,l]pyrene by liver microsomes from rainbow trout and rats

In order to assess the differences in the ability of fish and rat liver to metabolize carcinogenic polycyclic aromatic hydrocarbons (PAHs), we have in vestigated the metabolism of dibenzo[a,l]pyrene (DB[a,l]P), a highly potent carcinogenic PAH, by liver microsomes from 3-methylcholanthrene-treated Sh asta rainbow trout (Oncorhynchus mykiss) and rats. Rat liver microsomes met abolized DB[a,l]P at a slightly higher rats (1.3-fold) than trout liver mic rosomes. Compared to benzo[a]pyrene (B[a]P), DB[a.l]P was metabolized at a significantly lower rate by both rat and trout liver microsomes. Although t he microsomes from the two species metabolized DB[a.l]P to qualitatively si milar metabolites, they showed significant differences in the profile of th e metabolites formed. The proportion of DB[a,l]P-11,12-diol, the proximate carcinogen of DB[a,l]P, formed by trout microsomes was over two-fold greate r (32.6%:) than the corresponding value for rat microsomes (15.6%). Unlike rat microsomes, trout microsomes metabolized DB[a,l]P to its K-region diol (8.9-diol) to a small extent (26.1 vs 3.6%). As previously noted with B[a]P , trout liver, compared to rat liver, appears to be more efficient in formi ng the proximate carcinogenic metabolite of DB[a.l]P but less efficient in producing its K-region diol, a non-carcinogenic metabolite. (C) 1999 Elsevi er Science B.V. All rights reserved.