Addition Of Sodium Selenite Research Articles

Selenium enrichment, fruit quality and yield of winter jujube as affected by addition of sodium selenite

Winter jujube (Zizyphus jujuba Mill.) is a kind of high quality, fresh jujube fruit originated from China. Selenium (Se) affects the chemical composition and antioxidative properties in plants. At appropriate concentrations, Se acts as an antioxidant or activates mechanisms that can alleviate oxidative stress in the chloroplast, and enhances plant growth. Although the addition of Se is known to increase Se uptake in crops, it is unclear whether exogenous Se affects nutritional and functional components in winter jujube. Winter jujube trees were sprayed with selenium (as sodium selenite) at five concentrations (0, 25, 50, 100, or 200mg/L of Se) three times at the fruitlet stage between July and August. The Se content, ratio of organic Se to total Se in leaves and fruits, fruit quality, and yield were measured. At Se concentrations of 50mg/L or higher, total Se content increased rapidly whereas the ratio increased initially and decreased later. Different Se concentrations affected the quality of fruits differently: at 50mg/L, compared to their values in the unsprayed control trees, vitamin C content was greater by 20.94%; soluble sugars, 29.48%; total flavonoids, 43.48%; and the sugar: acid ratio, 41.81%. Along with the increase of Se addition, average fruit weight and yield of winter jujube presented a trend of increasing up to 50mgL−1 and decreasing thereafter. Thus, the foliar spray of sodium selenite at Se concentration of 50mg/L is recommended during the fruitlet stage of Zhanhua winter jujube.

Selenium in Cattle: A Review.

This review article examines the role of selenium (Se) and the effects of Se supplementation especially in the bovine species. Selenium is an important trace element in cattle. Some of its roles include the participation in the antioxidant defense the cattle farms. The nutritional requirements of Se in cattle are estimated at 100 μg/kg DM (dry matter) for beef cattle and at 300 μg/kg DM for dairy cows. The rations high in fermentable carbohydrates, nitrates, sulfates, calcium or hydrogen cyanide negatively influence the organism’s use of the selenium contained in the diet. The Se supplementation may reduce the incidence of metritis and ovarian cysts during the postpartum period. The increase in fertility when adding Se is attributed to the reduction of the embryonic death during the first month of gestation. A use of organic Se in feed would provide a better transfer of Se in calves relative to mineral Se supplementation. The addition of Se yeasts in the foodstuffs of cows significantly increases the Se content and the percentage of polyunsaturated fatty acids (PUFA) in milk compared to the addition of sodium selenite. The enzyme 5-iodothyronine deiodinase is a seleno-dependent selenoprotein. It is one of the last proteins to be affected in the event of Se deficiency. This delay in response could explain the fact that several studies did not show the effect of Se supplementation on growth and weight gain of calves. Enrichment of Se in the diet did not significantly affect the slaughter weight and carcass yield of bulls. The impact and results of Se supplementation in cattle depend on physiological stage, Se status of animals, type and content of Se and types of Se administration. Further studies in Se supplementation should investigate the speciation of Se in food and yeasts, as well as understanding their metabolism and absorption. This constitute a path to exploit in order to explain certain different effects of Se.

Selenoprotein P Inhibits Radiation-Induced Late Reactive Oxygen Species Accumulation and Normal Cell Injury

Radiation is a common mode of cancer therapy whose outcome is often limited because of normal tissue toxicity. We have shown previously that the accumulation of radiation-induced late reactive oxygen species (ROS) precedes cell death, suggesting that metabolic oxidative stress could regulate cellular radiation response. The purpose of this study was to investigate whether selenoprotein P (SEPP1), a major supplier of selenium to tissues and an antioxidant, regulates late ROS accumulation and toxicity in irradiated normal human fibroblasts (NHFs). Flow cytometry analysis of cell viability, cell cycle phase distribution, and dihydroethidium oxidation, along with clonogenic assays, were used to measure oxidative stress and toxicity. Human antioxidant mechanisms array and quantitative real-time polymerase chain reaction assays were used to measure gene expression during late ROS accumulation in irradiated NHFs. Sodium selenite addition and SEPP1 overexpression were used to determine the causality of SEPP1 regulating late ROS accumulation and toxicity in irradiated NHFs. Irradiated NHFs showed late ROS accumulation (4.5-fold increase from control; P<.05) that occurs after activation of the cell cycle checkpoint pathways and precedes cell death. The mRNA levels of CuZn- and Mn-superoxide dismutase, catalase, peroxiredoxin 3, and thioredoxin reductase 1 increased approximately 2- to 3-fold, whereas mRNA levels of cold shock domain containing E1 and SEPP1 increased more than 6-fold (P<.05). The addition of sodium selenite before the radiation treatment suppressed toxicity (45%; P<.05). SEPP1 overexpression suppressed radiation-induced late ROS accumulation (35%; P<.05) and protected NHFs from radiation-induced toxicity (58%; P<.05). SEPP1 mitigates radiation-induced late ROS accumulation and normal cell injury.

Effect of sodium selenite addition and sponge dough fermentation on selenomethionine generation during production of yeast-leavened breads

The effect of sodium selenite addition and fermentation times on production of selenomethionine (SeM) during sponge bread production was evaluated. Doughs were supplemented with sodium selenite (Na2SeO3) and fermented with yeast, avoiding addition of sulfur salts. The effect of Na2SeO3 on yeast activity was evaluated using a pressurometer. Results showed that there were not statistical differences (p < 0.05) in CO2 production and dough pH at all the sodium selenite concentrations tested. HPLC-fluorescence data showed that SeM production was higher with the increase of fermentation times, while less significant effects were observed due to changes in Na2SeO3 concentration. Two slices of Se-enriched bread can provide about 200 μg SeM, the dose recommended to prevent cancer and oxidative stress. The physical features (water absorption, bread weight, bread volume, color, density, oven spring, etc.) and organoleptic evaluations for the enriched loaves were evaluated. In all these parameters, the experimental enriched breads had practically identical attributes compared to the control. The breads rich in SeM have potential to be used as functional foods because this amino acid is synthesized into higher quantities of glutathione peroxidase, an enzyme considered as one of the most protective mechanisms against oxidative stress and preventive of cancer and chronic diseases.

Influence of inorganic and organic selenium on number of living mycelial cells and their ultrastructure in culture ofHericium erinaceum(Bull.: Fr. Pers.)

Mycelium of the white-rot fungus (Hericium erinaceum (Bull.: Fr. Pers.) produces polysaccharides showing anticancer and immunostimulating activity. In our previous works, we have shown that organic selenitetriglycerides (Selol) contribute to the increase of biosynthesis of exopolysaccharides (EPS) having antioxidative properties and containing large amounts of selenium. The present work is a study of influence of inorganic and organic form of selenium on viability of H. erinaceum mycelium and on ultrastructural changes taking place during its development in submerged culture. The mycelium was grown on media containing sodium selenite (Na2SeO3), a mixture of Na2SeO3 + Selol2% and on control medium (no selenium added). It was shown that mycelium cultured for 3 days in control conditions on standard media contained almost 100% of living cells, with over 80% after 24 days. Treatment with 100 ppm of Na2SeO3 lowered the number of viable cells to 11.8% and 9.1% after 3 and 24 days, respectively. The addition of 2% Selol caused the amounts of living cells to remain at ca 90%. Apparently, Selol helped the cells to cope with the toxic activity of inorganic selenium ions. The addition of sodium selenite induced degradative changes in cell organelles. Such changes were not observed in the case of Na2SeO3 + Selol mixture, in which case cells contained numerous ribosomes and small lipid bodies.

Selenium-enriched Candida utilis: Efficient preparation with l-methionine and antioxidant capacity in rats

Selenium-enriched Candida utilis has attracted much attention due to its expanding application in food and feed additives. The objective of this study was to efficiently prepare selenium-enriched C. utilis and to investigate the effects of the prepared yeast on antioxidant capacity in rats. A batch culture of selenium-enriched C. utilis was first carried out, and the addition of sodium selenite (Na2SeO3) after all glucose had been consumed was found to favor higher intracellular glutathione and organic selenium content. Moreover, l-methionine boosted yeast cell growth and glutathione biosynthesis, and prevented glutathione from leaking to the extracellular space that can be caused by Na2SeO3. We therefore developed a two-stage culture strategy involving supplementation with l-methionine and Na2SeO3 at separate culture phases to improve the performance of selenized C. utilis. Using this two-stage culture strategy, intracellular glutathione content reached 18.6mg/g and 15.5mg/g, respectively, in batch and fed-batch systems, and organic selenium content reached 905.2μg/g and 984.7μg/g, respectively. The effects of selenium-enriched C. utilis on the activities of antioxidant related enzymes in rats were investigated, and the prepared selenium-enriched C. utilis was shown to be an optimal dietary supplement for enhancing antioxidant capacity in rats.

Selenite biotransformation during brewing. Evaluation by HPLC–ICP-MS

Yeast (Saccharomyces cerevisiae) and lactic bacteria have shown their ability to accumulate and transform inorganic selenium into organo Se compounds. The objective of this work was to evaluate selenium biotransformation during brewing by using S. cerevisiae and Saccharomyces uvarum for Ale and Lager fermentation, respectively. Se-enriched beer was produced by the addition of sodium selenite (0, 0.2, 1.0, 2.0, 10.0, 20.0μgSemL−1, respectively) to the fermentation media composed of yeast, malt extract and water. The alcoholic fermentation process was not affected by the presence of selenium regardless of the type of Saccharomyces being used. The percentage of selenium incorporated into beer, added between 1.0 and 10μgmL−1 was 55–60% of the selenium initially present. Se-compounds in post-fermentation (beer and yeast) products were investigated by using an analytical methodology based on HPLC–ICP-MS. For this purpose, several sample treatments, including ultrasonic-assisted enzymatic hydrolysis, in conjunction with different separation mechanisms like dialysis and anion exchange HPLC chromatography were applied for unambiguously identifying Se-species that produce during brewing. Selenomethionine was the main selenium compound identified in beer and yeast, being this species in the only case of the former not associated to peptides or proteins.

Optimization of Selenium-Enriched Mycelium of Lentinula edodes (Berk.) Pegler as a Food Supplement

Our goal was to optimize the growth conditions of submerged mycelial cultures of Lentinula edodes (Shiitake mushroom) in order to obtain a new dietary supplement enriched in selenium We designed a process technology in which mycelial cultures were cultivated in media composed of beet molasses, 10%; liquid stillage, 5%; corn steep liquor, 0.15%; and KH2PO4, 0.3%, enriched with selenium in concentrations ranging from 0 to 100 μg/mL by the addition of sodium selenite of selenic acid. Se concentrations in mycelial dry mass rose from 0.001 mg/g (mycelia cultivated in media containing no selenium) to 50 mg/g (mycelia cultivated in medium containing 100 μg Se/mL). The highest mycelial specific growth rate (0.46/day) was recorded when the concentration of selenium in the medium was lower than 20 μg/mL. In vitro, estimated Se bioavailabilities from selenized mycelium strongly depended on its preparation in a proper manner and were 60% and 82% for dried mycelium and mycelial lyophilizate, respectively. Our results suggest that these optimized culture conditions could be applied to obtain a new Se-enriched dietary supplement.

INFLUENCE OF PULSED ELECTRIC FIELD ON SELENOCYSTEINE CONTENT INSACCHAROMYCES CEREVISIAE

ABSTRACT Culture of Saccharomyces cerevisiae with sodium selenite addition in medium was treated by pulsed electric fields (PEFs). Amino acids from yeast hydrolysates were separated by means of ion-exchange chromatography on amino acid analyzer according to previously established procedure. Selenocysteine was determined in a form of complex with ninhydrin, applying photometric technique. PEF treatment of S. cerevisiae cells resulted in about threefold content increase of selenium bonded within selenocysteine. PRACTICAL APPLICATIONS Se yeast is an attractive source of Se because of its low cost and its ability to act as a precursor for selenoprotein synthesis. Se yeast can be consumed as such and as a nutritional supplement. Another possibility is to use selenized yeast instead of conventional yeast for baking bread. Bread is generally low in Se, and hence the use of selenized yeast for this purpose could result in higher Se intakes because bread is a common product consumed by many individuals (Dumont et al. 2006). The presented way to enrich the baking yeast in selenium, namely selenomethionine, may be successfully applied in yeast production, because the studied method is a relatively simple, nontoxic and cheap technique for introducing macrocompounds into the yeast cells. Such enriched selenium yeast may be a valuable and safe source of selenium at diet supplementation.

Glial-Derived Neurotrophic Factor Modulates Enteric Neuronal Survival and Proliferation Through Neuropeptide Y

Glial-derived neurotrophic factor (GDNF) promotes the survival and proliferation of enteric neurons. Neuropeptide Y (NPY) is an important peptide regulating gastrointestinal motility. The role of NPY on the survival and proliferation of enteric neurons is not known. We examined the effects of GDNF on the expression and release of NPY from enteric neurons and the role of NPY in promoting enteric neuronal proliferation and survival. Studies were performed in primary enteric neuronal cultures and NPY knockout mice (NPY(-/-)). GDNF-induced expression of NPY was assessed by reverse-transcription polymerase chain reaction (RT-PCR), immunocytochemistry, and enzyme-linked immunosorbent assay. Using NPY-siRNA and NPY-Y1 receptor antagonist, we examined the role of NPY in mediating the survival and proliferation effects of GDNF. Gastrointestinal motility was assessed by measuring gastric emptying, intestinal transit, and isometric muscle recording from intestinal muscle strips. GDNF induced a significant increase in NPY messenger RNA and protein expression in primary enteric neurons and the release of NPY into the culture medium. NPY (1 mumol/L) significantly increased proliferation of neurons and reduced apoptosis. In the presence of NPY-siRNA and NPY-Y1 receptor antagonist or in enteric neurons cultured from NPY(-/-) mice, GDNF-mediated neuronal proliferation and survival was reduced. NPY increased the phosphorylation of Akt, a downstream target of the PI-3-kinase pathway. In NPY(-/-) mice, there were significantly fewer nNOS-containing enteric neurons compared with wild-type (WT) mice. NPY(-/-) mice had accelerated gastric emptying and delayed intestinal transit compared with WT mice. We demonstrate that NPY acts as an autocrine neurotrophic factor for enteric neurons.

Effect of Sodium Selenite-Enriched Reperfusion Solutions on Rat Cardiac Ischemia Reperfusion Injury

Cardiac surgery often generates oxidative stress leading to ischemia reperfusion injury (I-R). Antioxidants have been shown to prevent this injury and have been added to cardioplegic solutions to assist in recovery. In this study, we tested the effectiveness of sodium selenite in protecting against ischemia reperfusion injury and investigated the mechanisms behind this protection. Hearts from male Wistar rats were subjected to ischemia reperfusion using the Langendorf model. Krebs-Henseleit perfusion solutions were supplemented with 0, 0.1, 0.5, 1.0, and 10 microM sodium selenite. Hearts were perfused for 30 min and then subjected to 22.5 min of global ischemia followed by 45 min reperfusion. Heart rate, ischemic contracture, end diastolic pressure, and developed ventricular pressure were monitored. At the completion of the experiment, hearts were homogenized and tissue extracts were assayed for glutathione peroxidase (GSH-Px) and thioredoxin reductase (Thx-Red) activity. Sodium selenite, at a concentration of 0.5 microM, demonstrated a protective effect on the recovery of cardiac function following I-R, as evidenced by a lower end diastolic pressure and enhanced recovery of rate pressure product. There was no beneficial effect observed in hearts perfused with 0.1 microM sodium selenite-supplemented buffer, whereas poorer functional recovery was observed in hearts perfused with 10 microM sodium selenite-supplemented buffer. The beneficial effect of sodium selenite was not mediated through increased activity of GSH-Px or Thx-Red. This study demonstrates that the addition of sodium selenite to reperfusion solutions, at an optimal concentration of 0.5 microM, assists in cardiac recovery following ischemia reperfusion.

Effect of Animal Feed Enriched with Se and Clays on Hg Bioaccumulation in Chickens: In Vivo Experimental Study

An in vivo experiment was conducted to evaluate the effects of sodium selenite, sepiolite, and bentonite on inorganic mercury (Hg) and methylmercury (MeHg) bioaccumulation. For this purpose 160 chickens were fed under different controlled conditions. Chickens were exposed to Hg(II) and MeHg added to feed with or without selenium or clays supplementation. No significant differences were observed in the voluntary intake and feed/gain conversion rates. The target organs of Hg(II) and MeHg in chickens were the liver and kidney, respectively, but the greatest body store was the muscle in both cases. A higher bioaccumulation for MeHg than for Hg(II) was observed. The results showed that addition of sodium selenite, sepiolite, or bentonite induced a decrease of up to 60-100% in the inorganic mercury bioabsorption. Bentonite addition to a MeHg-containing diet also caused a decrease in organic mercury bioaccumulation (29-67%). On the other hand, inorganic selenium and sepiolite did not decrease MeHg accumulation.

Effect of increased dietary selenium intake on blood and cardiac selenium status during aging in rats

Oral selenium supplementation has been described as cardioprotective against pathophysiological situations involving oxidative stress in young adults rats. However no data are available concerning the effects of selenium supplementation on selenium status and glutathione peroxidase (GPX) activity in senescent rats. In the present study young adult and senescent rats were fed a diet containing selenium either 0.05 mg/kg (control) or 1.5 mg/kg (selenium) for 10 weeks. Selenium content in both diets was adjusted by sodium selenite addition. At the end of the supplementation period although plasma selenium level was lower in the two groups of aged rats than in the corresponding adults (p < 0.05), cardiac GPX activity, measured in both cytosolic and mitochondrial extracts appeared to be similarly increased in both categories of age. These data are the first to indicate that oral Se-supplementation is able to increase the plasma selenium concentration and cardiac GPX activity in senescent rats as well as in young adults.

Selenium from Selenium-Rich Spirulina Is Less Bioavailable than Selenium from Sodium Selenite and Selenomethionine in Selenium-Deficient Rats

The bioavailabilty of selenium (Se) from selenium-rich Spirulina (SeSp) was assessed in Se-deficient rats by measuring tissue Se accumulation and glutathione peroxidase (GSH-Px) activity. For 42 d, rats were subjected to dietary Se depletion by consumption of a Torula yeast (TY)-based diet with no Se; controls were fed the same diet supplemented with 75 microg Se/kg diet as sodium selenite. Se-deficient rats were then repleted with Se (75 microg/kg) by the addition of sodium selenite, selenomethionine (SeMet) or SeSp to the TY basal diet. Selenium speciation in SeSp emphasized the quasi-absence of selenite (2% of total Se); organic Se comprised SeMet (approximately 18%), with the majority present in the form of two selenoproteins (20-30 kDa and 80 kDa). Gross absorption of Se from SeSp was significantly lower than from free SeMet and sodium selenite. SeMet was less effective than sodium selenite in restoring Se concentration in the liver but not in kidney. SeSp was always much less effective. Similarly, Se from SeSp was less effective than the other forms of Se in restoring GSH-Px activity, except in plasma and red blood cells where no differences were noted among the three sources. This was confirmed by measuring the bioavailability of Se by slope-ratio analysis using selenite as the reference form of Se. Although Se from SeSp did not replenish Se concentration and GSH-Px activity in most tissues to the same degree as the other forms of Se, we conclude that it is biologically useful and differently metabolized due to its chemical form.

A Combined Scanning Tunneling Microscopy and Electrochemical Study of Copper Electrodeposition from a Cyanide Solution on a Zinc Alloy

The electrodeposition of Cu on zinc alloy diecast from a cyanide bath was studied using electrochemical techniques and scanning tunneling microscopy (STM) imaging. As the current density (j) is changed from 1 to , the root mean square roughness of the deposit (ξ) first increases, reaching a maximum value at , and then decreases. This behavior is explained by the strong interference of the hydrogen evolution reaction at the highest current densities. The dynamic scaling theory applied to the STM images for the advanced stages of Cu electrodeposition obtained at leads to a roughness exponent α = 0.80 and growth exponent β > 0.5 consistent with an unstable interface evolution. The addition of sodium selenite promotes a leveling effect by hindering the growth of instabilities, leading to an interface evolution consistent with the predictions of the Edwards‐Wilkinson growth model. © 2000 The Electrochemical Society. All rights reserved.

The efficiency of Escherichia coli selenocysteine insertion is influenced by the immediate downstream nucleotide.

Selenocysteine (Sec) incorporation requires the TGA opal codon and a downstream Sec insertion sequence (SECIS), which can be partially randomized and cloned into M13 pIII fusion constructs for phage display. This combinatorial approach provides a convenient non-radioactive assay that couples phage production to opal suppression. Two SECIS libraries were prepared, with the immediate downstream nucleotide either randomized (TGAN) or fixed as thymidine (TGAT). The TGAN library resulted in a majority of clones with a downstream purine and selenium-independent phage production, implicating the endo-genous tryptophan-inserting opal suppression pathway. Although the addition of sodium selenite to the growth medium did not affect phage production, it did increase the level of Sec insertion, as shown by the chemical reactivity of the resulting phage. The TGAT phage library yielded clones with strictly selenium-dependent phage production and reactivity consistent with the presence of Sec. These clones were prone to spontaneous mutation upon further propagation, however, resulting in loss of the selenium-dependent phenotype. We conclude that the immediate downstream nucleotide determines whether the endogenous opal suppression pathway competes with co-translational Sec insertion.

Production of organically bound selenium yeast by continuous fermentation.

This paper describes a protocol for incorporation of sodium selenite or sodium selenate into Saccharomyces cerevisiae biomass by continuous fermentation in a medium with minimal sulfur and methionine concentrations. Selenium incorporation was followed by atomic absorption analysis and methylene blue reduction time (MBRT). Continuous fermentation at 0.2 h(-1) dilution rate and sodium selenite addition gradient up to 0.69 g/L of Na(2)SeO(3) yielded 1. 89 g/L of biomass with 1904 microg of selenium/g of dry biomass. However, MBRT was 0.1 min, which indicated that the majority of selenium was in the inorganic form. On the other hand, continuous fermentation at 0.2 h(-1) dilution rate and sodium selenate gradient up to 0.28 g/L of Na(2)SeO(4) yielded 0.76 g/L of dry biomass with 687 microg of selenium/g of dry biomass, and MBRT was 26 min, which indicated a high concentration of organically bound selenium. Overall, the results indicate a Se/S ratio of 3.9:1 and a dry biomass/Se ratio of 5.5:1 as optimal for continuous production of organically bound selenium.

The inhibition of radiation-induced mutagenesis by the combined effects of selenium and the aminothiol WR-1065

In order to evaluate the anti-mutagenic effects of the potential chemoprotective compounds selenium and ( S)-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-1065), CHO AA8 cells were exposed to both compounds either individually or in combination prior to irradiation. Mutation frequency following exposure to 8 Gy was evaluated by quantitation of the mutations detected at the hprt locus of these cells. Protection against radiation-induced mutation was observed for both 30 nM sodium selenite or 4 mM WR-1065. In addition, the protection against mutation induction provided by the combination of these agents appeared additive. In contrast, sodium selenite did not provide protection against radiation toxicity when provided either alone or in conjunction with WR-1065. In order to evaluate the possible mechanisms of the anti-mutagenic effects observed in these cells, glutathione peroxidase (GPx) activity was evaluated following exposure to the chemopreventative compounds. The addition of sodium selenite to the culture media resulted in a 5-fold increase in GPx activity, which was unaltered by the presence of the WR-1065. Northern analysis of RNA derived from these cells indicated that selenium supplementation resulted in a marginal increase in the mRNA for the cytosolic GPx (GSHPx-1) which was insufficient to account for the stimulation of GPx activity observed in cellular extracts. These results suggest that selenium and WR-1065 offer protection via independent mechanisms and that GPx stimulation remains a possible mechanism of the anti-mutagenic effect of selenium.

Effect of selenium depletion on thyroidal type-I iodothyronine deiodinase activity in isolated human thyrocytes and rat thyroid and liver.

The effects of dietary selenium deficiency on hepatic and thyroidal type I iodothyronine deiodinase (ID-I) and selenium-dependent glutathione peroxidase (GPx) activities have been studied in weanling rats. In selenium-deficient animals hepatic ID-I activity was reduced to 11% of the activity found in the selenium-replete groups, whilst thyroidal ID-I activity increased by 42%. Hepatic and thyroidal GPx activities were also reduced by selenium deficiency to approximately 0.6 and 70%, respectively, of the values found in the selenium-replete animals. We have also studied the effects of thyrotropin (TSH), and selenium supply on the activity of IDI and GPx in human thyrocytes grown in primary culture. When thyrocytes were grown in selenium-deficient (< 1 nmol l-1 Se) medium in the absence of TSH, addition of sodium selenite up to 1000 nmol l-1 had little or no effect on ID-I activity. In the absence of added selenite, TSH addition produced a significant increase in ID-I activity and this stimulation was increased further when selenite was added at concentrations of 50-1000 nmol l-1 with an optimal effect on ID-I activity being observed at a 500 nmol l-1. Selenium content and GPx activity in human thyrocytes grown in selenium-free media (selenium content < 1 nmol l-1) were not significantly lower than the corresponding measurements made in cells grown in media containing selenium at a concentration of 5.4 nmol l-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium selenite as modulator of red cell shape

Addition of sodium selenite to human red cells, under ATP deplete conditions, induces a rapid oxidation of both glutathione and protein sulphydryl groups. Selenite also inhibits the discocyte-echinocyte shape transformation and stops the process before completion. Parallel to the effect on shape, selenite reduces the dephosphorylation of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate. Therefore our results support a shape change mechanism based on the metabolism of phosphoinositides and compatible with the bilayer-couple hypothesis.