Immunohistochemical Localization of CYP1A-Like and CYP3A-like Isozymes in Hepatic and Extrahepatic Tissues of Atlantic Cod (Gadus morhua L), a Marine Fish

Abstract

The cellular localization of inducible CYP1A and constitutive CYP3A-like forms in different organ systems of Atlantic cod (Gadus morhua) was determined in control fish and fish exposed to β-naphthoflavone (BNF). Paraffin-embedded sections were stained with polyclonal rabbit anti-cod P450 1A IgG or rabbit anti-rainbow trout P450con (a putative CYP3A form which cross-reacts with purified cod P450b) serum by the avidin-biotin peroxidase complex method. Following BNF-exposure of cod, CYP1A induction was immunohistochemically demonstrated in hepatocytes and endothelial cells of liver, the endocardium and vascular endothelium in the atrium and ventricle, and epithelial cells of the proximal tubular segment, endothelial cells, and interrenal cells in kidney. The vascular endothelium was the main site of induction of CYP1A in gills, spleen, gut, pyloric caecae, and gonads. The CYP3A-like isozyme P450b was mainly localized to hepatocytes, renal tubular epithelium, and epithelial cells of the mucosa in the intestine. Furthermore, the distribution of P450b was not affected by BNF exposure. The localization of P450b bears interesting similarities to the localization of CYP3A in mammals supporting the CYP3A-like identity of cod P450b. Simultaneous localization of inducible CYP1A and a constitutively expressed CYP isoenzyme has not previously been reported in fish. This is also the first presentation of cellular distribution of a CYP3-like isozyme in fish. Staining of CYP1A in endothelial cells supports previous observations that endothelium is a major site of CYP1A induction following xenobiotic exposure in fish. The observation of CYP1A induction in interrenal cells has important implications for possible endocrine effects of xenobiotic exposure.