Development and validation of gene and protein biomarker responses for endocrine disruption in the polar cod

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, very little is known about pollutants effects, including endocrine disruptors, in polar cod. In this study, we have investigated biomarkers for endocrine disruption. Polar cod from the Svalbard region were exposed intraperitoneally with a single injection of 17-β estradiol (E2) (5mg E2/kg fish). Additional fish were exposed to water-soluble fraction (WSF) of crude oil through a rock column system (3, 6 and 12 g crude oil/kg of gravels) or they were fed once a week with a oil contaminated diet (500 or 2000 mg of crude oil/kg amphipod). Fish (n=5-6) were sampled after 0, 2, and 4 weeks of exposure, followed by a 2-week recovery period. Effects on the RNA level was determined using quantitative real-time PCR, and analysis on the protein level is currenly being performed using capture ELISAs. The results show that fish exposure to E2 produced an increase in vitellogenin (Vtg) mRNA expression that parallelled reduction in CYP1A mRNA. Zona radiata protein (Zrp) mRNA expression did not parallel Vtg pattern after E2 exposure, possibly because of low responsiveness of zrp to estrogens in the polar cod or because of an experimental artifact (low cross-hybridisation). Exposure of the polar cod to the WSF fraction of crude oil and dietary oil components did not produce a clear response in Vtg expression, neither with times nor doses, possibly due to the potential co-exposure of environmental estrogens and antiestrogens present in crude oil and WSFs. In conclusion, polar cod seems to respond in a similar way as other fish species to estrogen, crude oil and WSF exposure, although the lack of Zrp induction warrant further studies.