Bioavailability Of Selenium Research Articles

Platelet Glutathione Peroxidase Activity as an Index of Selenium Status in Rats

Glutathione peroxidase activity in platelets increased stepwise in selenium-depleted rats that were repleted with graded levels of dietary sodium selenite. In a 3-phase depletion/repletion/depletion feeding study, glutathione peroxidase activity was similar in platelets and liver, which apparently contains the largest labile pool of selenium in the body. The activity of glutathione S-transferase (selenium-independent glutathione peroxidase) in platelets was low and was not affected by selenium deficiency, even though hepatic transferase was markedly elevated in selenium-deficient rats. Vitamin E deficiency did not affect activities of glutathione peroxidase or glutathione S-transferase in platelets or liver. Determination of glutathione peroxidase activity in platelets apparently is a promising technique for assessing selenium status and, possibly, for measuring selenium bioavailability.

Selenium bioavailability with reference to human nutrition

Various aspects of selenium metabolism and nutrition in relation to the question of selenium bioavailability in foods and the diet of man are reviewed. Few published studies exist on selenium metabolism in human subjects, particularly those representative of healthy individuals in the United States. Animal studies reveal that various factors, including the source and chemical form of selenium in foods and feeds, influence selenium bioavailability. However, the quantitative significance of animal assay data for human nutrition is not known. The limited number of published studies in man suggest that the metabolic fate and physiological function of dietary selenite may differ from that of selenomethionine or of food selenium. However, much additional research will be required to establish an adequate picture of the significance of dietary selenium bioavailability in human nutrition and health. Based on initial human experiments carried out at the Massachusetts Institute of Technology, use of stable isotopes of selenium offers promising opportunities for closing the gap of knowledge that now exists concerning the role and significance of factors that determine how the selenium present in foods is used to meet the physiological requirements of the consumer.

Nutritional Availability to Rats of Selenium in Tuna, Beef Kidney, and Wheat

Weanling male rats were fed a selenium (Se)-deficient 40% Torula yeast diet for 4 weeks and were then continued on depletion for another 4 weeks or were repleted with 0.1, 0.2, or 0.3 ppm Se as sodium selenite or 0.2 ppm Se as tuna, beef kidney, or high-Se wheat. There were no significant differences in young red blood cell Se, unfractionated red blood cell Se, or liver Se levels in groups fed diets containing 0.2 ppm Se. Glutathione peroxidase (GSH-Px) activity in young red blood cells was lower in the three groups fed food Se than in the group fed selenite (0.2 ppm Se). Young red blood cell GSH-Px was significantly lower in rats fed tuna than in rats fed wheat. Unfractionated red blood cell GSH-Px was lower in rats fed tuna than in rats fed selenite, but did not differ significantly among groups fed food Se sources. Liver GSH-Px was significantly lower in rats fed tuna than in rats fed kidney, wheat, or selenite. Availability of Se was only 54–58% as great from tuna as from selenite for induction of GSH-Px in liver and in red blood cell populations. Therefore, low availability of Se from fish may have to be considered when assessing Se status of human beings from dietary intake.Selenium selenium bioavailability glutathione peroxidase tuna mercury

Feasibility of Intrinsic Labeling of Poultry Meat with Stable Isotope of Selenium (74Se) for Use in Human Metabolic Studies

Sixteen day-old cockerel broiler-type chickens were placed on a simplified, corn-soybean meal broiler starter ration. Each chick was gavaged on 12 separate days over a growth period of 42 days with solutions of Na2SeO3 (control group) or Na74SeO3 (test group). The animals were killed on the 43rd day and the concentrations of the stable isotopes 74Se and 76Se were determined in meat, skin and liver samples using the method of radiochemical neutron activation analysis. We found that significant enrichment of 74Se occurred in the tissues of test animals as compared with the controls and that the degree of enrichment achieved was sufficient to allow use of these chickens in human feeding experiments designed to investigate bioavailability of dietary selenium employing the method of stable isotopes and fecal monitoring.intrinsic labeling selenium poultry meat

Organ clearance of 75SeO 32− and 203HgCl 2 administered separately and simultaneously to mice

A study on organ clearance of mercury ( 203HgCl 2) and selenium ( 75SeO 3 2−) given separately or simultaneously in single doses by intraperitoneal injections to mice has been performed. The simultaneous administrations are handled in molar ratios (Hg/Se) less, than equal to or greater than one. Liver, kidneys, spleen and blood contain most of the mercury and selenium, administered, while heart, lungs, skin, muscle and brain only contain small amounts. Both elements are retained to a higher degree in especially kidneys, liver, spleen and blood when co-administered than when administered alone. In kidneys, clearance rate of selenium is found to be independent of mercury administration, with an effective halflife 11.2–13.5 days in accordance with the whole elimination. The clearance of mercury is, however, strongly dependent on coadministered selenium. At low molar ration (Hg/Se ⩽ 1) of administered doses clearance rate is identical to that of selenium, compared to an effective halflife when administered alone. In liver the effective halflife of selenium when administered alone or coadministered with mercury (Hg/Se ratio < 1) is found identical to that of kidneys: 11.2–12.5 days. At increasing molar ratios retention of selenium increases and clearance rate decreases. A marked decrease in mercury clearance from liver is induced by simultaneously administered selenium. The effective halflife becoming extremely administered selenium. The effective halflife becoming extremely long and under certain conditions even an accumulation is found to take place. Concordant relations are found for liver and spleen. Selenium in blood is only affected to a minor degree by mercury. Clearance rate for mercury is decreased by selenium. At a molar ratio between doses (Hg/Se) ⩾ 1 clearance rate is approximately identical to that of selenium. It is indicated that selenium metabolism is quantitatively rather than qualitatively influenced by mercury as mercury administration provokes a higher retention of a given dose of selenium while clearance rate in kidneys and blood is only influenced by high molar ratios (Hg/Se). Contrary to selenium, mercury metabolism is altered both qualitatively and quantitatively as retention as well as clearance rate are influenced by selenium in all organs and in all molar ratios given in kidneys and blood. It is assumed that at least 2 mechanisms exist in the metabolic pathways of mercury: (1) binding to metallothionein; and (2) binding to selenium containing metabolic compounds. As selenium induced an increase in mercury retention it is questioned whether selenium is beneficial in case of chroniic exposure to inorganic mercury. It also implies the question of bioavailability of selenium in animal food items.

Mercury Metabolism in Japanese Quail II: The Effects of Dietary Mercury and Selenium on Blood and Liver Glutathione Peroxidase Activity and Selenium Concentration

Adult Japanese quail were fed isolated soybean protein diets to which methylmercuric chloride (CH3 HgCl) or mercuric chloride (HgCl2) were added with or without supplemental selenium for seven days. Samples of blood and liver were analyzed for total selenium via atomic absorption spectrophotometry and for glutathione peroxidase (GSH-Px) activity by spectrophotometry assay. The addition of 285 ppm mercury as HgCl2 caused a significant depression in weight gain and feed consumption. Selenium administration alleviated the depression in weight gain and feed consumption. Selenium administration alleviated the depression in most cases. No other overt signs of toxicity were observed.Selenium addition increased the selenium concentration of the liver and to a lesser extent of the blood. CH3 HgCl addition resulted in increased selenium concentration in the blood of the selenium-supplemented group. Liver selenium was unaffected by the mercury addition.Selenium administration increased blood GSH-Px activity, but not liver GSH-Px activity. HgCl2 decreased blood GSH-Px activity in the selenium-supplemented group; CH3 HgCl had no effect. Since CH3 HgCl increased blood selenium and there was no concurrent increase in blood GSH-Px activity, it appears that the redistributed selenium is not available to be incorporated into GSH-Px. Therefore, mercury may be decreasing selenium bioavailability by some as yet unknown mechanism.

Antioxidants and cancer. Part VI. Selenium and age-adjusted human cancer mortality.

The possible epidemiologic relationship between selenium occurrence and cancer mortality was studied in cities and states located in areas with different levels of selenium bioavailability. Statistically significant differences were found in age-specific cancer death rates among states with high, medium, and low selenium levels. The death rates for specific types of cancer showed a larger difference in males than in females in the states with high selenium levels. The greater difference between males and females may be related to sex difference or to the fact that males are heavier smokers and are aslo more likely to be exposed to industrial pollution. In the states with high selenium levels, there was significantly lower mortality in both males and females from several types of cancer, particularly the environmental problem indicators, such as gastrointestinal and urogenital types of cancer.