Endocrine effects in polar cod (Boregadus saida) liver tissue after exposure to crude oil and 17β-estradiol

Summary

The polar cod is found further north than any other fish species and is a key species in the arctic ecosystem. From a toxicological standpoint, little is known about pollutants effects in polar cod. In the present study, we have investigated the endocrine disrupting effects after exposure to an estrogen and crude oil. Polar cod from the Svalbard region were intraperitoneally exposed with a single injection of 17β-estradiol (E2). Additional fish were exposed to environmentally relevant concentrations of water-soluble fraction (WSF) of crude oil and an oil-contaminated diet. Fish (n=5-6) were sacrificed after 2-4 weeks exposure and after a 2-week recovery period. Hepatic expression of the biomarkers, vitellogenin (Vtg), Zona radiata proteins (Zrp) and CYP1A were determined at the transcriptional (mRNA) level by quantitative PCR and at the protein level by capture ELISAs. Our results show that fish exposure to E2 produced an increase in Vtg mRNA and protein expression, paralleled by a reduction in CYP1A mRNA, but not protein level. Interestingly, Zrp mRNA and protein expression did not parallel Vtg expression after E2 exposure. Exposure of polar cod to WSFs and oil produced an apparent dose-dependent increase in CYP1A mRNA and protein expression, but did not produce a clear response in Vtg expression, possibly due to co-exposure of putative estrogens and antiestrogens present in oil. In conclusion, our study has provided novel insight into a selection of biomarker responses in a keystone species in the arctic ecosystem.