Selenium antioxidant activities

It has been reported that substitution of selenium by tellurium in a series of diarylchalcogenides results in a pronounced increase of antioxidant activity. Therefore the development of new and potent antioxidants is an important goal. Diaryl tellurides exhibit potent glutathione-peroxidase-like activity. 

Another class of compounds, dihydrotellurophenes, exhibits antioxidant activity together with the oxygen, sulphur and selenium analogues. ... 

Selenium has long been known to enhance the antioxidant activity of vitamin E. Recent work suggests that vitamin E acts as a radical scavenger, preventing... 

Selenium is an amphoteric element whose chemistry and biochemistry has mnch in common with snlfur. The essentiality of selenium in experimental animals was demonstrated in 1957. It was necessary that the animals be vitamin E deficient to manifest selenium deficiency. Selenium manifests antioxidant activity by its incorporation into selenocysteine and its subseqnent participation at the... 

Factor 3/selenium are without any influence whatsoever on the breakdown of oxygen consumption. These differences between the effects of vitamin E and those of Factor 3/selenium show once more that these two agents do not substitute for each other, as pointed out previously (Schwarz, 1961b, 1962). It is also evident from this discrepancy that the principal mode of action of tocopherol cannot be dismissed in terms of antioxidant activity. More intricate metabolic relationships must play a part. 

Because a number of vitamin E deficiency syndromes are responsive to dietary selenium, the possibility of selenium functioning as a lipid antioxidant has been examined. Some very powerful selenium antioxidants are known (Woodbridge, 1959). In the vitamin E-deficient chick, dietary selenite inhibited in vivo and in vitro lipid peroxidation (Zalkin et al., 1960). Further, antioxygenic activity was found for various selenium compounds in simple lipid peroxidation reactions selenoamino acids were weak antioxidants. On the basis of this evidence and the known incorporation of selenium into tissue proteins, Zalkin et al. (1960) suggested that the antioxidants formed in the chick may be selenoamino acids and selenoproteins. Bieri (1961) and Bieri et al. (1961) have reported extensive evidence for inhibition of in vitro lipid peroxidation of liver, kidney, and heart tissue from selenium fed chickens. They also suggested that the lipid antioxidant may be a selenoprotein. Olcott et al. (1961) showed that selenomethionine is a stronger lipid antioxidant than methionine and that selenomethionine decomposes lipid peroxides. 

A variety of other metals and their complexes have been studied for radioprotective activity. Among these are copper glycinate, strontium chloride, ZnNa -diethylenetriaminepentaacetate (ZnDTPA), and selenium, which has been studied because of its relationship to endogenous antioxidant mechanisms, especiaHy GSH peroxidase and vitamin E. 

Rubber. The mbber industry consumes finely ground metallic selenium and Selenac (selenium diethyl dithiocarbamate, R. T. Vanderbilt). Both are used with natural mbber and styrene—butadiene mbber (SBR) to increase the rate of vulcanization and improve the aging and mechanical properties of sulfudess and low sulfur stocks. Selenac is also used as an accelerator in butyl mbber and as an activator for other types of accelerators, eg, thiazoles (see Rubber chemicals). Selenium compounds are useflil as antioxidants (qv), uv stabilizers, (qv), bonding agents, carbon black activators, and polymerization additives. Selenac improves the adhesion of polyester fibers to mbber. 

Situnayake et al., 1991). No correlation between disease activity and serum vitamin E concentrations was found, but it was su ested that such patients might suffer a reduced antioxidant capacity. However, it is conceivable that a decreased serum antioxidant status is a primary event in the evolution of RA. Recent studies (Heliovaara etal., 1994) have demonstrated that lowered levels of vitamin E, /3-carotene and selenium (required for glutathione peroxidase) together may be a risk fector for subsequent development of RA. 

All selenium-containing proteins and enzymes in animals, microorganisms and plants incorporate selenocysteine non-specifically105 or as part of Se-dependent antioxidant enzymes such as glutathione peroxidase, (EC 1.11.1.9) which has a Se-cysteine residue in its active site.116 120 An active form of Se, selenophosphate, is produced by selenophosphate synthetase in several bacteria. This active form is required for the production of Secys-tRNA, a precursor for Se-cysteine.121 In a similar vein, a Se-containing modified-tRNA nucleoside, 5-methylaminomethyl-2-selenouridine, encodes a selenouridine synthase which replaces sulfur in tRNA with selenium.122... 

Mammalian thioredoxin reductases are a family of selenium-containing pyridine nucleotide-disulfide oxidoreductases. These enzymes catalyze NADPH-dependent reduction of the redox protein thioredoxin (Trx), which contains a redox-active disulfide and dithiol group and by itself may function as an efficient cytosolic antioxidant [77]. One of the functions of Trx/ thioredoxin reductase system is the NADPH-catalyzed reduction of protein disulfide [78] ... 

The possible involvement of free radicals in the development of hypertension has been suspected for a long time. In 1988, Salonen et al. [73] demonstrated the marked elevation of blood pressure for persons with the lowest levels of plasma ascorbic acid and serum selenium concentrations. In subsequent studies these authors confirmed their first observations and showed that the supplementation with antioxidant combination of ascorbic acid, selenium, vitamin E, and carotene resulted in a significant decrease in diastonic blood pressure [74] and enhanced the resistance of atherogenic lipoproteins in human plasma to oxidative stress [75]. Kristal et al. [76] demonstrated that hypertention is accompanied by priming of PMNs although the enhancement of superoxide release was not correlated with the levels of blood pressure. Russo et al. [77] showed that essential hypertension patients are characterized by higher MDA levels and decreased SOD activities. 

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