APPARENT INDUCTION OF A CYTOCHROME-P450 WITH IMMUNOCHEMICAL SIMILARITIES TO CYP1A IN DIGESTIVE GLAND OF THE COMMON MUSSEL (MYTILUS-GALLOPROVINCIALIS L) WITH EXPOSURE TO 2,2',3,4,4',5'-HEXACHLOROBIPHENYL AND AROCHLOR-1254

The induction of a cytochrome P450 with immunochemical similarities to CYP1A, and accompanying changes in microsomal NADPH-dependent benzo[a ]pyrene (BaP) metabolism, were examined in digestive gland of the comm on mussel (Mytilus galloprovincialis L.) with exposure to 20 ppb water -borne polychlorobiphenyl (PCB) mixture (Arochlor 1254) for 4 or 10 da ys, or 4 days after a single injection into the mantle cavity of the m ixed-type inducer PCB congener 2,2',3,4,4',5'-hexachlorobiphenyl (CB-1 38; 2.5 mu g g(-1) wet weight). Whole animal tissue levels of PCB foll owing water-column exposure or injection were similar to those for mus sel species from polluted field sites, viz. 0.8 to 1.9 mu g g(-1) wet weight. Levels of microsomal CYP1A-immunopositive protein increased 59 % (CB-138) and 72% (Arochlor 1254; 10 days exposure) as determined by Western blot analysis using polyclonal antibodies to hepatic CYP1A of perch (Perca fluviatilis). No changes were seen in levels of digestive gland CYP1A-like mRNA 4 days after injection of CB-138 as determined by Northern analysis using cDNA to hepatic CYP1A1 of rainbow trout (On corhynchus mykiss). The increases in levels of CYP1A-immunopositive pr otein were accompanied by a shift in microsomal NADPH-dependent BaP me tabolism towards phenol and diol and away from dione production, the f ormer increasing from 32 to 85% of total free metabolites. The marked decrease in dione production (which is the major BaP metabolite formed in control microsomes) resulted in no increase in total microsomal Ba P metabolism with exposure to PCBs. The Type I ligand alpha-naphthofla vone markedly inhibited microsomal phenol but had no affect on dione p roduction, whereas the Type II ligand clotrimazole markedly inhibited dione, but had much less effect on phenol production. The overall resu lts are interpreted in terms of the existence of an inducible CYP1A-li ke enzyme catalysing predominantly 2-electron monooxygenation leading to epoxide (and hence phenol and diol) formation, and a constitutive n on-inducible cytochrome P450 catalysing predominantly 1-electron oxida tion leading to dione formation. Both Arochlor 1254 or CB-138 produced cellular damage in the digestive gland in the form of decreased epith elial digestive cell height and decreased lysosomal membrane stability . (C) 1997 Elsevier Science B.V.