Characterization of xenobiotic-metabolizing cytochrome P450 (CYP) forms inringed and grey seals from the Baltic Sea and reference sites

Earlier studies have shown that members of the cytochrome P4501 (CYP1) enzy me family are constitutively expressed, and are elevated in the livers of r inged seals (Phoca hispida) and grey seals (Halichoerus grypus) living in t he heavily polluted Baltic Sea. In this study, we compared the expression p rofiles of several additional CYP enzymes in the liver and extrahepatic tis sues of Baltic ringed and grey seals with the corresponding CYP expression in seals from relatively unpolluted waters. We used marker enzyme activity levels, diagnostic inhibitors and immunoblot analysis to assess members of the CYP2A, CYP2B, CYP2C, CYP2D, CYP2E and CYP3A sub-families. Coumarin 7-hy droxylation (COH), a marker of CYP2A activity, was high in the liver and th e lungs of all the studied seal populations. The presence of a putative CYP 2A form in these seals was further supported by the strong inhibition of CO H activity by a chemical inhibitor and by an anti-CYP2A5 antibody. However, antibodies to human and rodent CYP2B, CYP2C and CYP2E forms did not recogn ize any proteins in these seal species. Dextromethorphan O-demethylation (m arker for CYP2D activity) and chlorzoxazone 6-hydroxylation (marker for CYP 2E activity) were measurable in the livers of all the seals we studied. Bot h activities were elevated in the Baltic seal populations, showed a strong positive correlation with CYP1A activity and were at least partly inhibited by a typical CYP1A inhibitor, alpha -naphthoflavone. Further studies are n eeded to determine the presence and characteristics of CYP2D and CYP2E enzy mes in ringed and grey seals. Testosterone 6 beta -hydroxylation, a CYP3A m arket, showed a relatively high level of activity in the livers of both sea l species and was potently inhibited by ketoconazole, a CYP3A-selective inh ibitor. The putative CYP3A activity showed an opposing geographical trend t o that of CYP2D and CYP2E, since it was elevated in the control area. CYP3A protein levels, revealed by immunoblotting, showed a positive correlation with testosterone 6 beta -hydroxylation. We conclude tentatively that CYP2A - and CYP3A-like enzymes are expressed in ringed and grey seals, but that C YP2B- and CYP2C-like ones are not. Further information on the individual co ntaminant profile is needed before any conclusions can be drawn on a possib le connection between the varying CYP expressions and the contaminant load. (C) 2001 Elsevier Science Inc. All rights reserved.