Is hepatic cytochrome P4501A1 expression predictive of hepatic burdens of dioxins, furans, and PCBs in Atlantic tomcod from the Hudson River estuary?

Hepatic cytochrome P4501A1 (CYP1A1) expression in fishes is frequently used to evaluate bioavailable aromatic hydrocarbon contamination of aquatic eco systems. In controlled laboratory experiments, CYP1A1 expression in naive f ishes is usually dose-responsive to aromatic hydrocarbons and in field stud ies levels of gene expression in natural populations often correspond with known levels of sediment-borne contaminants. We quantified CYP1A1 mRNA leve ls in juvenile Atlantic tomcod Microgadus tomcod from 42 sites in the Hudso n River estuary to evaluate the correspondence between hepatic CYP1A1 expre ssion and hepatic concentrations of persistent halogenated aromatic hydroca rbons and to determine the utility of CYP1A1 expression as a biomarker in e valuating the microgeographic distribution of bioavailable contaminants wit hin a large aquatic ecosystem. We found significant spatial heterogeneity i n CYP1A1 mRNA levels among collection sites with levels of gene expression differing in some cases by 23-34 folds. CYP1A1 mRNA expression was highest in tomcod from the Newark Bay complex and lowest in tomcod from the most up river collection sites in the main stem of the Hudson River. Although level s of PCDDs, PCDFs, and PCBs expressed as TCDD TEQs and CYP1A1 mRNA were hig hest in tomcod from the Newark Bay complex, there was no relationship betwe en hepatic halogenated aromatic hydrocarbon levels and hepatic CYP1A1 mRNA in tomcod from sites in the main stem of the Hudson River. These results su ggest that levels of CYP1A1 expression in fish from sites highly polluted w ith mixtures of halogenated aromatic hydrocarbons and other xenobiotics may not always be reflective of levels of bioavailable aromatic hydrocarbon co ntaminants. Based on these results and earlier controlled laboratory experi ments, we hypothesize that elevated levels of CYP1A1 expression in tomcod f rom the Hudson River may be due primarily to PAHs or other contaminants not measured in this study. (C) 2001 Elsevier Science B.V. All rights reserved .