Assessing the potential toxic effect of selenium on the toxic effects of methylmercury using a battery of biomarkers on juvenile Euopean seabass (D. labrax)

Supervisor: Iciar Martinez, Urtzi Izagirre (PIE-UPV/EHU)
Methylmercury (MeHg) is recognised as one of the most abundant forms of organic mercury. It is of concern in the marine environment from a toxicology perspective due to its ability to bioaccumulate in organisms and biomagnify through the food chain. Previous outbreaks of severe mercury poisoning have shown MeHg’s capability to impair neurological functions in humans. It is particularly worrisome as it can pass from pregnant mothers into the foetus via the placenta and have a significant impact on the development in young children. Long lived predator fish species high in the trophic chain are considered a potential source of MeHg contamination due the ability of MeHg to accumulate in the tissues, but are also rich sources of selenium. Fish feeds for aquaculture are usually supplemented with vitamins and minerals, including sodium selenite (of which concentrations vary with feed source and type of processing). Selenium is a trace element, essential as a component of numerous metabolites and proteins including anti-oxidant enzymes that has been shown to aid in eliminating MeHg in in vivo experiments. Some fish species are rich sources of selenium. Fish are therefore interesting models to study the accumulation of MeHg in different tissues, and of particular interest is their edible tissue, i.e. the muscle. This study aims to identify, in a fast and cost-effective manner, changes in the protein pattern of European seabass (Dicentrarchus labrax) muscle after 2-weeks exposure to MeHg (4μg/L), and the effect that 1 week pre-treatment of sodium selenite (10μg/L) may exert on the MeHg-induced changes. The results presented in this work correspond to the SDS – PAGE and immunoblot analysis of skeletal muscle proteins extracted with Laemmli buffer. Immunoblots were run to examine the effect of the treatment on myofibrilar proteins (using antibodies anti – myosin heavy chain (MHC), anti – actin and anti – α-actinin) on protein oxidation (detecting carbonyl groups with anti – DNP antibodies) and on protein ubiquitination. The results showed small but noticeable changes in the protein pattern between the control and the MeHg treated seabass by SDS – PAGE. Further analyses are required for the groups exposed to sodium selenite. Only very subtle differences were detected in the anti – DNP and anti – ubiquitin reactivity of MeHg-treated muscle. It can therefore be concluded that MeHg contaminated water seems to affect, to a small extent, the skeletal muscle protein pattern. The identified protein bands will be submitted to further analyses (e.g. mass spectrometry analysis) to identify them and progress in evaluating their potential use as markers of MeHg- contamination and of the potential protective effect of Se – pre-treatment.