Selenium As Anti Oxidant
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ITHACA, N.Y. — A study by researchers at Cornell University suggests that higher-than-normal amounts of a selenium-containing enzyme could promote type 2 diabetes. The researchers found that mice with elevated levels of the antioxidant enzyme develop the precursors of diabetes at much higher rates than did control mice. 5
Selenium, a common dietary supplement, is an antioxidant, materials that help mop up harmful free radicals, molecules that can damage cell membranes and genetic material and contribute to the development of cancer and heart disease. Many of the benefits of selenium are related to its role in the production of glutathione peroxidase (GP), an antioxidant enzyme that helps detoxify the body. 28
Selenium is an essential nutrient of fundamental importance for human biology, witch has an anti-oxidant function as a component of selenoproteins with enzymatic function, besides their role in cancer and immune response (Rayman, 2000). Furthermore, selenium supplement is being adopted in animal nutrition, especially in dairy cows, as a resistance factor for clinical mastitis (Smith et al., 1983; Paschoal et al., 2003). 8
ITHACA, N.Y. — A study by researchers at Cornell University suggests that higher-than-normal amounts of a selenium-containing enzyme could promote type 2 diabetes. The researchers found that mice with elevated levels of the antioxidant enzyme develop the precursors of diabetes at much higher rates than did control mice. 5
Selenium, a common dietary supplement, is an antioxidant, materials that help mop up harmful free radicals, molecules that can damage cell membranes and genetic material and contribute to the development of cancer and heart disease. Many of the benefits of selenium are related to its role in the production of glutathione peroxidase (GP), an antioxidant enzyme that helps detoxify the body. 28
Selenium is an essential nutrient of fundamental importance for human biology, witch has an anti-oxidant function as a component of selenoproteins with enzymatic function, besides their role in cancer and immune response (Rayman, 2000). Furthermore, selenium supplement is being adopted in animal nutrition, especially in dairy cows, as a resistance factor for clinical mastitis (Smith et al., 1983; Paschoal et al., 2003). 8
The current evidence does not support the use of antioxidant supplements in the general population or in patients with certain diseases. The combined evidence suggests that additional research on antioxidant supplements is needed. The evidence on vitamin C and selenium was not conclusive. Future trials could focus on vitamin C and selenium and should assess both potential beneficial and harmful effects. Conduct of additional primary and secondary prevention trials on vitamin A, beta-carotene, and vitamin E seems questionable, at least in the dosage range examined. 26
Low antioxidant intake and status have been shown to be associated with an elevated risk for various diseases. Data on the status of antioxidant vitamins, selenium and coenzyme Q10 of younger female seniors are scarce. The aim of this study was to assess the status of these antioxidants, as well as influencing factors such as dietary intake, anthropometric data and educational level in female seniors (60–70 years) in Germany. 13
In 1973, when selenium was discovered to be a constituent of the enzyme glutathione peroxidase (hence the enzyme’s abbreviation, SeGPx), it became a little clearer why many conditions that are helped by selenium occur only when both selenium and vitamin E are deficient. Both molecules have an antioxidant function. SeGPx prevents free radical formation by breaking peroxide into harmless water; without that pathway, peroxide can be converted to an initiator of free radical formation, which can lead to the undesirable peroxidation of lipids and other molecules. Normally, fat-soluble vitamin E quenches free radicals. If vitamin E–or possibly some other as yet undetermined antioxidant–is not there to do the quenching, and the population of free radicals enlarges because of insufficient SeGPx to break down peroxide, molecular mayhem ensues. 15
In 1973, when selenium was discovered to be a constituent of the enzyme glutathione peroxidase (hence the enzyme’s abbreviation, SeGPx), it became a little clearer why many conditions that are helped by selenium occur only when both selenium and vitamin E are deficient. Both molecules have an antioxidant function. SeGPx prevents free radical formation by breaking peroxide into harmless water; without that pathway, peroxide can be converted to an initiator of free radical formation, which can lead to the undesirable peroxidation of lipids and other molecules. Normally, fat-soluble vitamin E quenches free radicals. If vitamin E—or possibly some other as yet undetermined antioxidant—is not there to do the quenching, and the population of free radicals enlarges because of insufficient SeGPx to break down peroxide, molecular mayhem ensues. 22
Results showed no association between selenium supplementation on any of the endpoints studied: coronary heart disease, stroke or deaths from cardiovascular disease, Stranges said. There also was no difference in the endpoints based on the level of selenium at baseline. In addition, the lack of significant association with CVD endpoints was confirmed even in the 246 participants who had CVD at baseline. 4
The glutathione and thioredoxin antioxidant systems function to regenerate other antioxidants while themselves providing the primary antioxidant defense in the water phase of the body. Glutathione peroxidase and thioredoxin reductase are two natural antioxidant enzymes that contain selenium and depend upon selenium activity for their antioxidant functionality. Both the glutathione and thioredoxin systems enhance their own antioxidant activity by inducing the production of other natural antioxidant enzymes[TOXICOLOGICAL SCIENCES; Hansen,JM; 82(1):308-317 (2004)], including superoxide dismutase[AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY; Das,KC; 17(6):713-726 (1997)]. Both selenite and selenomethionine supplementation have been shown to significantly reduce oxidative DNA damage (8−OHdG formation) due to ultraviolet radiation[BRITISH JOURNAL OF DERMATOLOGY; Rafferty,TS; 148:1001-1009 (2003)]. 1
Selenium’s exact biochemical role in all situations in which it appears to have an effect is not known. One area of interest is selenium’s protective role against cancer. Selenium intervention studies conducted in China show selenium supplementation programs are associated with significant drops in liver and esophageal cancer rates. Frank selenium deficiency doesn’t occur in the United States because Americans’ food sources and varied diet provide enough selenium to prevent deficiencies–even in low-selenium areas of the country. 15
What is unanswered by this current study is whether a higher level of selenium in the diet or through supplementation will cause an unhealthily high level of glutathione peroxidase (GP) activity. In this experiment the scientists made the mice produce more GP. Just taking more selenium may not up GP activity to a level that will be unhealthy since the supply of GP will become a rate-limiting factor once all GP enzymes have selenium in their active centers. Still, the fact that excessive antioxidant activity can contribute to type II diabetes is important news. 44
Selenium has so many anti-cancer actions that it is difficult to establish which ones are predominant. Selenium affects oxidative stress, DNA methylation, DNA repair, inflammation, apoptosis, cell proliferation, carcinogen metabolism, hormone production, angiogenesis and immune function[JNCI, JOURNAL OF THE NATIONAL CANCER INSTITUTE; Taylor,PR; 96(6):645-647 (2004)]. 1
Another meta-analysis cited (Bjelakovic) reported that antioxidant vitamins may increase death rates. But the authors did not determine a dose-dependent or cause-and-effect relationship between antioxidants and deaths (from all causes) of study participants. The researchers pooled 68 published trials, excluding 405 published studies with no deaths reported. Too wide a range of potencies (Vitamin A 1333 IU - 200,000 IU, vitamin E 10 IU to 1000 IU), and durations (28 days to 12 years) were lumped together. 8
Selenium’s exact biochemical role in all situations in which it appears to have an effect is not known. One area of interest is selenium’s protective role against cancer. Selenium intervention studies conducted in China show selenium supplementation programs are associated with significant drops in liver and esophageal cancer rates. 22
Selenium compounds have been shown to block DNA transcription factors that would otherwise worsen the inflammatory response[FREE RADICAL BIOLOGY & MEDICINE; Jozsef,L; 35(9):1018-1027 (2003) and JOURNAL OF BIOLOGICAL CHEMISTRY; Yoon,SO; 276(23):20085-20092 (2001)]. Glutathione peroxidase and possibly other selenoproteins directly reduce peroxynitrite to nitrite[JOURNAL OF BIOLOGICAL CHEMISTRY; Sies,H; 272(44):27812-27817 (1997)]. Selenomethionine was shown to be more effective than selenocysteine, whereas sodium selenite had no effect[BIOCHEMICAL JOURNAL; Briviba,K; 319(Pt1):13-15 (1996)]. 1
References
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