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- Title
The Role of Selenium in Thyroid Autoimmunity and Cancer.
- Authors
Leonidas H. Duntas
- Abstract
The essential micronutrient selenium (Se) occurs in the form of the amino acid selenocysteine in selenoproteinswhich exert various effects, while maintaining the cell reduction-oxidation balance. The discovery that all threedeiodinases that convert thyroxine (T4) into triiodothyronine (T3) contain selenocysteine illustrates how the productionof the active thyroid hormone is dependent on Se status. The selenoenzyme families of glutathione peroxidases(GPx) and thioredoxin reductases (TRx) possess powerful antioxidant properties and form a complexdefense system that protects thyrocytes from oxidative damage. Se supplementation in patients with autoimmunethyroiditis seems to modify the immune response, probably by enhancing plasma GPx activity and decreasingexcess levels of hydrogen peroxide. However, the enhancement of immunocompetence may also bethe result of the synergistic action of various selenoproteins and not exclusively of GPx. There is evidence supportingconsiderable oxidative stress in Graves'' disease where Se supplementation, because of its free radicalscavenging properties, may increase the enzymatic antioxidant activity. TRx has been found significantly elevatedin GD revealing its involvement in the pathogenesis of this condition and representing a potential futuretarget for therapeutical intervention. Low Se serum levels have also been associated with increased risk of thyroidcancer and may play a role in carcinogenesis. It is noteworthy, that the Food and Drug Administrationhas recently determined that there is sufficient evidence to warrant a qualified health claim for Se and cancer.Furthermore, the recent discovery that defects in the SECIS-binding protein 2 (SBP2), which is an indispensableprotein for the incorporation of Se into the selenoproteins, result in thyroid dysfunction, together with therecognition of the many roles of selenoprotein P in Se distribution and storage in the human body, reveal notonly the indispensability of Se and the selenoproteins as essential factors in thyroid metabolism and pathogenesis,but open up new prospects for enhanced treatment.
- Subjects
SELENIUM; AMINO acids; THYROXINE; TRIIODOTHYRONINE
- Publication
Thyroid, 2006, Vol 16, Issue 5, p455
- ISSN
1050-7256
- Publication type
Article