Selenium speciation in rat colon tissues

A study of selenium (Se) speciation in rat colon tissues is presented. Four different procedures for the extraction of Se compounds were evaluated in terms of recovery and species preservation. Total Se in tissue and extracts was determined by ICP-MS and isotope dilution analysis. The selected and optimized protocol allowed an extraction of 43% of Se, while continuously bubbling nitrogen in the solution during the procedure was mandatory to prevent the oxidative degradation of selenoproteins. Speciation analysis was then performed on the extracts using size exclusion- and anion exchange-HPLC for species separation. A number of Se compounds were detected in rat colon extracts, and individually quantified by coupling HPLC-ICP-MS and species-unspecific on-line (post-column) isotope dilution analysis. Among the isolated selenospecies, the two major proteins glutathione peroxidase type 2 and thioredoxin reductase type 1 have been potentially identified by their molecular weight using MALDI-TOF-MS.