Biological selenium species and selenium speciation in biological samples
Résumé
The chapter summarizes the state-of-the-art of the analytical methodology for the speciation of selenium (Se) in biological samples relevant to human health (body fluids, cell cultures, tissues, food supplements). Selenoproteins with genetically encoded selenocysteine, Se-containing proteins with Met substituted by selenomethionine, and Se-containing metabolites are discussed. Whereas gel electrophoresis followed by radiography of 75 Se is the benchmark for selenoprotein and Se-containing protein detection, the recent advances in laser ablation-ICP MS allow the scanning of the gels for stable Se isotopes, increasing the number of biological systems to be investigated and enhancing the depth of the studies. The democratization of proteomics approaches opens the way to the high throughput identification of selenoproteins, although several bottlenecks, such as loss of Sec during sample preparation, identification on the basis of the part of the proteins without Se, and insufficient sensitivity, are still demanding considerable improvements of analytical methodology. In the field of metabolomics, the combined use of multidimensional HPLC with the combined Se-specific ICP MS detection and Orbitrap MS n detection, seems to be an ultimate tool for the comprehensive quantitative and qualitative Se speciation analysis.