Potential Alterations of the Bile Acid Synthesis and Hepatic Detoxifying Mechanisms in European sea bass (Dicentrachus labrax) after in vivo Exposure to a Xenoestrogen Mixture

Supervisors: Maren Ortiz-Zarragoitia, Eider Bilbao (UPV/EHU)
This project was aimed to shed light on an unexpected outcome of an in vivo experiment. Juveniles of European sea bass (Dicentrarchus labrax) exposed to a mixture of xenoestrogens (bisphenol A, 4-tert-octylphenol, diethylstilbestrol and 17beta-estradiol), showed a gradual change of bile colour (from green to white) over the exposure time. After the recovery period, the bile colour reversed to its normal, physiological, green colour. In addition, plasma clotting was common in exposed fish and chemical tissue distribution changed from high levels in the bile at the first days to high concentrations of BPA in liver and blood during the last days of exposure period and recovery time. Thus, it was hypothesised, that the mixture of xenoestrogens altered bile acid synthesis and liver detoxification pathways. To provide a deeper insight into these processes, genes involved in bile acid synthesis, such as cyp7a1, fxr, lxr and hmg-CoA reductase were amplified and sequenced for qPCRs analysis. Likewise, genes involved in detoxification such as cyp1a, cyp3a, udp and abcb11 were investigated as well as vtg, a marker of xenoestrogenicity. Liver samples were processed at day 3 and 7 of exposure and at day 7 of recovering (day 17 of the experiment). Liver somatic index significantly decreased after 10 days of exposure. After 3 days of exposure cyp7a1, fxr, lxr, cyp1a and udp were down-regulated, whereas hmg-Coar, cyp3a and abcb11 were not altered. Then all these gene as well as cyp3a and udp were upregulated after 7 days of exposure. No changes were registered in vtg levels. At the end of the recovery period all assessed genes were significantly down-regulated compared to the transcription levels at day 7. Overall, it was considered that the exposure to xenoestrogens may have induced a severe impact in normal liver metabolism impairing bile acid synthesis, detoxification mechanisms and xenoestrogenic response.