Plenary Lectures L4.1 Accumulation and biotransformation of Se in African catfish (Glarias gariepinus) fed with Se enriched garlic: the role of several analytical approaches using MS as detector

Selenium is an essential element known to take part in human antioxidative defense and to protect against cardiovascular diseases and cancer. Consequently, supplementation of the diet with this element is necessary in order to achieve the protective effect. Several allium plants, radish etc have demonstrated the ability to preconcentrate and biotransform inorganic selenium into selenoaminoacids. Taking into account that fish, meat and vegetables are the main sources of selenium for humans, the capability of african catfish to biopreconcentrate and biotransform selenium when fed with Se-enriched garlic has been evaluated. Selenomethyl-selenocysteine and γ-Gluthamyl-selenomethyl-selenocysteine, reported as the most effective chemopreventive selenoamino acids, were the main species in the garlic enriched dietary source. However, selenomethionine was the main species in the fish fillet, suggesting the transformation of these species during the fish metabolism. Enzymatic hydrolysis of the fish fillet was performed under two different conditions: ultrasound probe sonication and incubation in a water bath at controlled temperature. The extracts were analysed by HPLC-ICP-MS by using different chromatographic columns based on size exclusion, anion exchange and reversed phase. The speciation analysis revealed the presence not only of Selenomethionine but also of several unknown Se compounds that could not be identified by comparison with the retention time of the available Se-standards. It is well knon that Selenomethionine can replace methionine and be easily incorporated into proteins. In order to identify proteins containing Se, the soluble proteins were extracted and analysed by size exclusion chromatography-ICP-MS. Fractions containing selenium were collected and after separation by SDSPAGE analysed by Laser ablation-ICP-MS. Eight proteins contain selenium were identified. Furhter identification of these proteins and unknown species in the enzymatic extracts requires the application of ESI-MS. The results obtained will be discussed. L4.2