Toxicity of Selenium Compounds and Nano‐Selenium Particles

Selenium is a necessary dietary constituent of at least 25 human selenoproteins and enzymes all containing selenocysteine. In excessive amounts, all selenium compounds become toxic in a dose-dependent fashion to cells in vitro and to the primary target tissue of chronic selenium toxicity, the liver. Elemental selenium of zero valence state has long been considered to be biologically inert. With bovine serum albumin or other dispersant agents such as polysaccharide, biologically active nano-selenium particles (Nano-Se) are formed from sodium selenite and glutathione. Different from the biologically inert black elemental selenium with coarse size, red Nano-Se manifests toxicity which conforms to the concern of nanotoxicity. However, compared with selenium compounds such as sodium selenite, selenomethionine and Se-methylselenocysteine, Nano-Se is not compromised in increasing the activities of selenoenzymes including glutathione peroxidase and thioredoxin reductase at nutritional levels and phase 2 detoxification enzymes such as glutathione S-transferase at supranutritional levels, but exhibits much lower toxicities. Nano-Se is thus a potential selenium source with a prominent characteristic of lower toxicity for supplementation. Keywords: toxicity; selenite; selenomethionine; Se-methylselenocysteine; nano-selenium particles