Selenium

Abstract

Selenium is an essential trace element that is incorporated into proteins in the form of the 21st amino acid, selenocysteine (Sec),³ via the specific transfer RNA^[Sec]. Bioinformatics studies led to the identification of a total of 25 selenoprotein genes ( 1). Selenoproteins such as glutathione peroxidases (GPXs) 1–4 efficiently metabolize cellular peroxides and function as an antioxidant defense mechanism that protects against reactive oxygen/nitrogen species. Thioredoxin reductases (TRs) 1–3 are oxidoreductases that regulate the redox status of proteins such as thioredoxin as well as small molecules such as lipoic acid, tetrathionate, and others. Deiodinases 1–3 cleave iodine-carbon bonds in the metabolism of thyroid hormones, leading to the monodeiodination of prohormone thyroxine (T4) to the active form triiodothyronine (T3). A progressive decrease of the T3/T4 ratio (because of increased T4 concentrations) and of erythrocyte GPX activity has been observed with advancing age that negatively correlates with increases in reactive oxygen species. Human selenoprotein P (SEPP1) contains 10 Sec residues and functions mainly to deliver selenium to other body organs after its synthesis in the liver. SEPP1 and GPX3, which are present in the plasma, are often used as biomarkers for assessing body selenium status.