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Journal ArticleDOI

Effect of dietary methionine on utilization of tissue selenium from dietary selenomethionine for glutathione peroxidase in the rat.

01 Mar 1988-Journal of Nutrition (American Society for Nutrition)-Vol. 118, Iss: 3, pp 367-374
TL;DR: The results indicate that the dietary methionine level can modulate the availability of Se from dietary [ Se]Met and from stored tissue [Se]Met; the inability of stored Se to provide Se for GSH-Px synthesis over a prolonged period of time suggests that [Se?]Met may not be an optimum form for Se supplementation.
Abstract: To study the effect of dietary methionine on the bioavailability of Se from selenomethionine ([Se]Met), weanling rats were first loaded with Se by feeding 05 mg Se as [Se]Met per kg diet of a low methionine (017% by analysis) torula yeast-based diet for 21 d, and then were fed an Se-deficient diet (less than 002 mg Se/kg) supplemented with 0, 04 or 09% methionine for 28 d Plasma, liver and muscle Se increased 26-, 25- and 22-fold, respectively, during [Se]Met supplementation, and then the tissue Se declined exponentially during the Se-deficient diet period Plasma, liver and muscle glutathione peroxidase (GSH-Px) activities decreased 43-50% during the [Se]Met supplementation period in spite of the increase in tissue Se When these [Se]Met-loaded rats were fed the Se-deficient diet and supplemented with methionine, tissue GSH-Px activities increased significantly within 3 to 7 d, but then decreased for the remainder of the experiment Calculation of the percentage of tissue Se present as Se in GSH-Px indicated that substantial Se from dietary [Se]Met was stored in tissues in a form different from GSH-Px when a low methionine diet was fed These results indicate that the dietary methionine level can modulate the availability of Se from dietary [Se]Met and from stored tissue [Se]Met; the inability of stored [Se]Met to provide Se for GSH-Px synthesis over a prolonged period of time suggests that [Se]Met may not be an optimum form for Se supplementation
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Journal ArticleDOI
TL;DR: Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the best choice for reduction of colon tumours because several mechanisms have been proposed on the mechanism whereby Se reduces tumours.
Abstract: Selenomethionine (Semet) is the major seleno-compound in cereal grains and enriched yeast whereas Se-methylselenocysteine (SeMCYS) is the major seleno-compound in Se-accumulator plants and some plants of economic importance such as garlic and broccoli exposed to excess Se. Animals can metabolize both Semet and SeMCYS. Epidemiological studies have indicated an inverse relationship between Se intake and the incidence of certain cancers. Blood or plasma levels of Se are usually lower in patients with cancer than those without this disorder, but inconsistent results have been found with toenail-Se values and the incidence of cancer. There have been eight trials with human subjects conducted on the influence of Se on cancer incidence or biomarkers, and except for one, all have shown a positive benefit of Se on cancer reduction or biomarkers of this disorder. This is consistent with about 100 small-animal studies where Se has been shown to reduce the incidence of tumours in most of these trials. Se-enriched yeast is the major form of Se used in trials with human subjects. In the mammary-tumour model, SeMCYS has been shown to be the most effective seleno-compound identified so far in reduction of tumours. Several mechanisms have been proposed on the mechanism whereby Se reduces tumours. Even though SeMCYS was shown to be the most effective seleno-compound in the reduction of mammary tumours, it may not be the most effective seleno-compound for reduction of colon tumours.

578 citations


Cites background from "Effect of dietary methionine on uti..."

  • ...It is not known whether this stored Se can serve as a reserved pool of this element, but the evidence indicates that it is metabolically active (Waschulewski & Sunde, 1988)....

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Journal ArticleDOI
TL;DR: There are several selenocompounds in tissues of plants and animals, and selenocysteine, the predominant selenoamino acid in tissues when inorganic selenium is given to animals, is one of them.
Abstract: There are several selenocompounds in tissues of plants and animals. Selenate is the major inorganic selenocompound found in both animal and plant tissues. Selenocysteine is the predominant selenoamino acid in tissues when inorganic selenium is given to animals. Selenomethionine is the major selenocompound found initially in animals given this selenoamino acid, but is converted with time afterwards to selenocysteine. Selenomethionine is the major selenocompound in cereal grains, grassland legumes and soybeans. Selenomethionine can also be the major selenocompound in selenium enriched yeast, but the amount can vary markedly depending upon the growth conditions. Se-methylselenocysteine is the major selenocompound in selenium enriched plants such as garlic, onions, broccoli florets and sprouts, and wild leeks.

470 citations


Cites background from "Effect of dietary methionine on uti..."

  • ...It is not known whether this stored selenium can serve as a reserved pool of selenium, but the evidence indicates that it is metabolically active [70]....

    [...]

Journal ArticleDOI
TL;DR: It is demonstrated that herb teas, as well as black tea, coffee and coca can be potent inhibitors of Fe absorption, and this property should be considered when giving dietary advice in relation to Fe nutrition.
Abstract: The effects of different polyphenol-containing beverages on Fe absorption from a bread meal were estimated in adult human subjects from the erythrocyte incorporation of radio-Fe. The test beverages contained different polyphenol structures and were rich in either phenolic acids (chlorogenic acid in coffee), monomeric flavonoids (herb teas, camomile (Matricaria recutita L.), vervain (Verbena officinalis L.), lime flower (Tilia cordata Mill.), pennyroyal (Mentha pulegium L.) and peppermint (Mentha piperita L.), or complex polyphenol polymerization products (black tea and cocoa). All beverages were potent inhibitors of Fe absorption and reduced absorption in a dose-dependent fashion depending on the content of total polyphenols. Compared with a water control meal, beverages containing 20-50 mg total polyphenols/serving reduced Fe absorption from the bread meal by 50-70%, whereas beverages containing 100-400 mg total polyphenols/serving reduced Fe absorption by 60-90%. Inhibition by black tea was 79-94%, peppermint tea 84%, pennyroyal 73%, cocoa 71%, vervain 59%, lime flower 52% and camomile 47%. At an identical concentration of total polyphenols, black tea was more inhibitory than cocoa, and more inhibitory than herb teas camomile, vervain, lime flower and pennyroyal, but was of equal inhibition to peppermint tea. Adding milk to coffee and tea had little or no influence on their inhibitory nature. Our findings demonstrate that herb teas, as well as black tea, coffee and coca can be potent inhibitors of Fe absorption. This property should be considered when giving dietary advice in relation to Fe nutrition.

426 citations

Journal ArticleDOI
TL;DR: The regulated whole-body pool of selenium is shifted to needy cells and then to vital selenoproteins in them to supply seenium where it is needed, creating a whole- body seleniprotein hierarchy.
Abstract: Selenium is regulated in the body to maintain vital selenoproteins and to avoid toxicity. When selenium is limiting, cells utilize it to synthesize the selenoproteins most important to them, creating a selenoprotein hierarchy in the cell. The liver is the central organ for selenium regulation and produces excretory selenium forms to regulate whole-body selenium. It responds to selenium deficiency by curtailing excretion and secreting selenoprotein P (Sepp1) into the plasma at the expense of its intracellular selenoproteins. Plasma Sepp1 is distributed to tissues in relation to their expression of the Sepp1 receptor apolipoprotein E receptor-2, creating a tissue selenium hierarchy. N-terminal Sepp1 forms are taken up in the renal proximal tubule by another receptor, megalin. Thus, the regulated whole-body pool of selenium is shifted to needy cells and then to vital selenoproteins in them to supply selenium where it is needed, creating a whole-body selenoprotein hierarchy.

380 citations

Journal ArticleDOI
TL;DR: Selenocysteine-containing enzymes that have been identified in mammals include the glutathione peroxidase family, one or more iodothyronine deiodinases and two thioredixin reductases, which are less sensitive to dietary selenium fluctuation than the corresponding selenoprotein levels in other tissues.
Abstract: Selenocysteine-containing enzymes that have been identified in mammals include the glutathione peroxidase family (GPX1, GPX2, GPX3, and GPX4), one or more iodothyronine deiodinases and two thioredixin reductases. Selenoprotein P, a glycoprotein that contains 10 selenocysteine residues per 43 kDa polypeptide and selenoprotein W, a 10 kDa muscle protein, are unidentified as to function. Levels of all of these selenocysteine-containing proteins in various tissues are affected to different extents by selenium availability. Increased amounts of selenoproteins observed in response to selenium supplementation were shown in several studies to correlate with increases in the corresponding mRNA levels. In general, selenoprotein levels in brain are less sensitive to dietary selenium fluctuation than the corresponding selenoprotein levels in other tissues.

352 citations