Basal and Pollutant-induced Expression of CYP1A, 1B and 1C isoforms in Fish Implications for Biomonitoring

Abstract: Aquatic wildlife are exposed to contaminants in their natural habitats, and toxic pollutants may induce toxicity in sensitive target tissues and cells. There is therefore a need to establish biomarkers to determine exposure to certain classes of contaminants and the subsequent biological responses. In the present work the whole suite of cytochrome P450 1 (CYP1) genes expressed in fish were examined with regard to their inducibility and potential use as biomarkers. Complementary DNA of the CYP1A, 1B and 1C transcripts in rainbow trout and three-spined stickleback were cloned and characterized by quantitative mRNA expression analysis. All CYP1 transcripts could be induced by two selected aryl hydrocarbon receptor (AhR) agoinsts (indigo and PCB 126) in both species, suggesting that all genes were regulated by the AhR. CYP1 mRNA expression profiles induced by PCB 126 and indigo varied over time showing that PCB 126 gave rise to a high and persistent induction in gills and liver while induction by indigo was transient in both organs. The uptake and kinetics of 14C-indigo was studied by autoradiography in rainbow trout. A rapid uptake of 14C-indigo from the water and a subsequent elimination in bile and intestinal contents was observed, explaining the transient CYP1 induction. A high accumulation of 14C-indigo in the gills was completely blocked the CYP1 inhibitor ellipticine, suggesting a CYP1-dependent uptake. High dilutions of a sewage treatment plant effluent containing a complex mixture of pharmaceuticals were investigated. The same water sample both induced CYP1A mRNA expression and inhibited catalytic activity of CYP1A. A field study revealed different induction signatures of the CYP1 genes examined at various locations in Uppsala water environments. As concluded by the temporal and spatial responses obtained, the results of this work suggest that the CYP1 gene panel could be used for biomonitoring of environmental contaminants acting on the CYP system. Further field studies will be required to evaluate this possibility.