Selenium‐containing amino acids as direct and indirect antioxidants

Selenium is a trace element essential for normal physiological processes. Organic selenium‐containing amino acids, such as selenocysteine (Sec) / selenocystine and selenomethionine (SeMet, the major dietary form), can provide antioxidant benefits by acting both as direct antioxidants as well as a so...

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Bibliographic Details
Published in:IUBMB life 2012-11, Vol.64 (11), p.863-871
Main Authors: Rahmanto, Aldwin Suryo, Davies, Michael J.
Format: Article
Language:English
Subjects:
Amino Acids - pharmacology
Animals
antioxidants
Antioxidants - pharmacology
glutathione peroxidase
Humans
oxidants
Oxidation-Reduction
radicals
selenium
Selenium - pharmacology
selenocysteine
selenomethionine
thioredoxin reductase
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Summary:Selenium is a trace element essential for normal physiological processes. Organic selenium‐containing amino acids, such as selenocysteine (Sec) / selenocystine and selenomethionine (SeMet, the major dietary form), can provide antioxidant benefits by acting both as direct antioxidants as well as a source of selenium for synthesis of selenium‐dependent antioxidant and repair proteins (e.g., glutathione peroxidases, thioredoxin reductases, methionine sulfoxide reductases). The direct antioxidant actions of these amino acids arise from the nucleophilic properties of the ionized selenol (RSe−, which predominates over the neutral form at physiological pH values) and the ease of oxidation of Sec and SeMet. This results in higher rate constants for reaction with multiple oxidants, than for the corresponding thiols/thioethers. Furthermore, the resulting oxidation products are more readily and rapidly reversed by both enzyme and nonenzymatic reactions. The antioxidant effects of these seleno species can therefore be catalytic. Seleno amino acids may also chelate redox‐active metal ions. The presence of Sec in the catalytic site of selenium‐dependent antioxidant enzymes enhances the kinetic properties and broadens the catalytic activity of antioxidant enzymes against biological oxidants when compared with sulfur‐containing species. However, while normal physiological selenium levels afford protection, when compared with deficiency, excessive selenium may induce damage and adverse effects, with this being manifest, for example, as an increased incidence of type 2 diabetes. Further studies examining the availability of redox‐active selenium species and their mechanisms and kinetics of action are therefore of critical importance in the potential development of seleno species as a therapeutic strategy. © 2012 IUBMB. IUBMB Life, 64(11): 863–871, 2012
ISSN:1521-6543
1521-6551
DOI:10.1002/iub.1084