Induction of Cytochrome P4501A in the Intertidal Fish Anoplarchus purpurescens by Prudhoe Bay Crude Oil and Environmental Induction in Fish from Prince William Sound

Abstract

Cytochrome P4501A (CYP1A) induction is a sensitive and specific adaptive response in fish exposed to xenobiotics including petroleum hydrocarbons. CYP1A expression was examined in the intertidal fish Anoplarchus purpurescens collected from or caged at reference sites and sites oiled by the Exxon Valdez spill in Prince William Sound. Immunoblotting of hepatic microsomes showed that the content of CYP1A in fish at oiled sites was up to 6-fold greater than that in reference site fish. Fish injected with the CYP1A inducer β-naphthoflavone showed a 70-fold induction of CYP1A, to levels six times the highest level seen in the field. To model the field exposure, fish were maintained over oiled sediments and/or fed amphipods collected from an oiled site. Hepatic microsomal CYP1A was induced 49-fold in fish exposed to oiled sediments but rapidly returned to control levels after fish were removed from oil exposure. Immunohistochemistry showed CYP1A induction in multiple organs. CYP1A staining in hepatic and some extrahepatic cells was highly correlated (r 2 ≥ 0.95) with the hepatic CYP1A content detected by immunoblot. Oiled food induced CYP1A most strongly in intestinal mucosal epithelial and endothelial cells. Relatively low levels of CYP1A were observed in liver, gill, and gonad of fish exposed to oil through the diet, consistent with the metabolism of dietary hydrocarbons by intestinal CYP1A. Exposure to oiled sediment alone strongly induced CYP1A in endothelial cells in all organs examined. Thus, oil present in Prince William Sound sediments more than 1 year after the spill was able to induce CYP1A in intertidal fish. The caging and laboratory experiments indicate that the induction of CYP1A observed in field specimens of A. purpurescens from oiled sites was due primarily to persistent spill-derived hydrocarbons.