QUANTITATION OF CYP1A EXPRESSION IN 2 FLATFISH SPECIES SHOWING DIFFERENT PREVALENCES OF CONTAMINANT-INDUCED HEPATIC-DISEASE

English sole (Pleuronectes vetulus) and starry flounder (Platichthys s tellatus) are two sympatric flatfish species which show markedly diffe rent responses to chemical contaminant exposure. Whereas English sole develop hepatic neoplasms, the prevalences of which are strongly linke d to exposure to polycyclic aromatic hydrocarbons (PAHs), evidence of neoplasia is virtually nonexistent in starry flounder, even those resi ding in areas with very high levels of PAH in the sediments. Because P AHs are activated to genotoxic forms by the action of cytochrome P450 1A (CYP1A) in teleosts, we are examining the hypothesis that variation in the hepatic expression of this major inducible cytochrome P450 iso zyme may contribute to the differential contaminant response. These tw o species were captured in the Duwamish Waterway, a contaminated area of Puget Sound, Washington. Catalytic activity of CYP1A [determined as aryl hydrocarbon hydroxylase (AHH) activity] was measured in the live r to quantitatively assess the relative induction of CYP1A in these tw o species, and AHH activity was significantly higher in English sole t han in starry flounder (p = 0.015). Cellular expression of CYP1A was d etermined by immunohistochemical localization of tissues, using an avi din-biotin peroxidase complex method with polyclonal rabbit anti-cod C YP1A. The results showed a markedly reduced expression of CYP1A in hep atocytes of starry flounder, which is consistent with the apparent res istance of this species to the development of hepatocellular neoplasia . This reduced expression of CYP1A in hepatocytes of contaminant-expos ed fish was previously seen in oyster toadfish from the Elizabeth Rive r, Virginia, and this species is also apparently resistant to hepatoce llular neoplasia. (C) 1998 Elsevier Science Ltd. All rights reserved.