Chapter Five - Selenoprotein W as Biomarker for the Efficacy of Selenium Compounds to Act as Source for Selenoprotein Biosynthesis

Abstract

Selenium is an essential trace element and, like all elements, present in many different compounds with unequivocal functions. This fact is only sporadically mentioned when recommended intake or supplementation is indicated just as "selenium." In mammals, selenium is an integral part of selenoproteins as selenocysteine. Selenocysteine is formed from serine at the respective tRNA((ser)sec), a reaction that requires selenophosphate formed from selenide and ATP. Thus, only compounds that can be metabolized into selenide can serve as sources for selenoprotein biosynthesis. We therefore tested the ability of selenium compounds such as sodium selenite, methylseleninic acid (MeSeA), Se-methyl selenocysteine, and selenomethionine to increase the activity, protein, or mRNA levels of commonly used biomarkers of the selenium status, glutathione peroxidase-1 (GPx1) and thioredoxin reductase, and of putatively new biomarkers, selenoprotein W1 (SepW1), selenoprotein H, and selenoprotein 15 in three different cell lines. Selenite and MeSeA were most efficient in increasing all markers tested, whereas the other compounds had only marginal effects. Effects were higher in the noncancerous young adult mouse colon cells than in the cancer cell lines HepG2 and HT-29. At the protein level, SepW1 responded as well as GPx1 and at the mRNA level, even better. Thus, the outcome of selenium treatment strongly depends on the chemical form, the cell type, and the biomarker used for testing efficacy.