Biological effects of a nano red elemental selenium.

A novel selenium form, nano red elemental selenium (Nano-Se) was prepared by adding bovine serum albumin to the redox system of selenite and glutathione. Nano-Se has a 7-fold lower acute toxicity than sodium selenite in mice (LD(50) 113 and 15 mg Se/kg body weight respectively). In Se-deficient rat, both Nano-Se and selenite can increase tissue selenium and GPx activity. The biological activities of Nano-Se and selenite were compared in terms of cell proliferation, enzyme induction and protection against free racial-mediated damage in human hepatoma HepG2 cells. Nano-Se and selenite are similarly cell growth inhibited and stimulated synthesis of glutathione peroxidase (GPx), phospholipid hydroperoxide glutathione peroxidase (PHGPx) and thioredoxin reductase (TR). When HepG2 cells were co-treated with selenium and glutathione, Nano-Se showed less pro-oxidative effects than selenite, as measured by cell growth. These results demonstrate that Nano-Se has a similar bioavailability in the rat and antioxidant effects on cells.     

Effect of sodium selenite on RNA synthesis in loach embryos

The effects of sodium selenite on the ribonucleic acid synthesis in normal diploid embryos and isolated nuclei of the loach Misgurnus fossilis were studied. The relative rate of synthesis was determined from incorporation of [3H]uridine into the total RNA, taking into consideration the incorporation of the label into the total acid-soluble fraction and into phosphorylated derivatives of uridine. It was shown that sodium selenite inhibits the RNA synthesis in loach embryos at the gastrula stage. It was also found that sodium selenite exerts an inhibiting effect on the activity of form I of DNA-dependent RNA-polymerase in isolated loach nuclei without affecting the activity of the enzyme form II.     

Effect of selenium on the enzymatic transformation of retinal and vitamin A assimilation

The effect of sodium selenite on the enzymatic oxidation of retinal in vitro and vitamin A accumulation in the rat liver was examined. Selenium as sodium selenite at concentrations of 0.5--2.5 microgram/ml inhibited significantly (40--45%) the enzymatic irreversible oxidation of retinal. Dietary supplements of sodium selenite at a dose of 50--250 microgram/kg body weight caused an almost two-fold increase of the vitamin A content in the rat liver as compared with the controls that were given no selenium.     

Structural alterations of peripheral nerve monogalactosylceramides during development and Wallerian degeneration

Reaction products of selenite with thiols were tested for an inhibitory effect on amino acid incorporation in a cell-free system derived from rat liver and on protein synthesis in intact P815 and L1210 cells. In the cell-free system maximum inhibition, up to 96%, was reached at about 10 microM selenium. In intact cells inhibitory effect varied depending on which reaction product or cell line was used. Maximum inhibition was obtained after 30 min of incubation with selenium concentrations ranging from 0.25 microM to over 7 microM. Selenite itself also inhibited protein synthesis of L1210 cells, but only after 90 min of incubation and starting at selenium concentrations of 2 microM. Inhibition of protein synthesis in intact cells was followed by cell death. Pre-incubation of the reaction products of a monothiol (2-propanethiol) and of a vicinal dithiol (2,3-dimercapto-1-propanol) in culture medium showed a rapid decrease of the inhibitory capability of the product from the monothiol, but not of the product from the dithiol. The results indicate that selenite and a thiol react to form products which have differential toxic effects to cells in vitro.     

Effect of cell density on the inhibition of tumor cell attachment and nucleic acid synthesis by selenite

The effect of cell density on the sensitivity of tumor celles to selenite has been examined. The inhibitory effect of selenite on cellular DNA and RNA synthesis was significantly greater in higher density cultures of HeLa cells and A2780 ovarian tumor cells. High-density cells were also more sensitive to the inhibitory effect of selenite on cell attachment. This difference could not be accounted for by a higher intracellular level of glutathione, since there was no significant difference between the cells at high or low density. The high-density cells were found to take up more selenium per cell during the exposure period; the resulting higher level of intracellular Se could explain their greater sensitivity to selenite. This hypothesis is supported by the observation that DNA synthesis in nuclei isolated from high-density cells did not exhibit higher sensitivity to inhibition by selenite than synthesis in nuclei isolated from low-density cells.     

Selenium antagonizes the induction of human heme oxygenase by arsenite and cadmium ions.

Effects of selenium compounds on the induction of heme oxygenase in human cells exposed to sodium arsenite or cadmium chloride have been investigated by an immunoblotting technique. Exposure of HeLa cells to arsenite or cadmium ions caused a marked increase in the synthesis of heme oxygenase, and the presence of sodium selenite suppressed the induction. DL-Selenocystine was an effective suppressor, and sodium selenate was less effective. DL-Selenomethionine had no effect. Northern blot analysis showed that selenite abolished the induction of heme oxygenase mRNA in the cells exposed to arsenite or cadmium ions. These results indicated that selenium antagonizes the induction of heme oxygenase by heavy metals ions.     

Effect of fertilization on selenium content of tea and the nutritional function of Se-enriched tea in rats

The present study examined the effect of fertilization with sodium selenite on the selenium content of tea and the nutritional function of Se-enriched tea. Selenium content of tea leaves was increased up to 0.36 g g^–1 by the application of sodium selenite to soil at 0.5 and 1.0 kg Se ha^–1. Application by a Se-enriched organic manure at a rate of 0.5 kg Se ha^–1 provided a higher biological availability of selenium for plant uptake compared with a similar amount of sodium selenite. Foliar spray of sodium selenite at 50–100 g Se ha^–1 increased the selenium content to 0.32–1.45 g g^–1 in tea leaves sampled at the 8–26 days after spraying. Selenium content in the blood and liver, glutathione peroxidase activity in blood of rats were significantly enhanced by feeding of an extracted solution of Se-enriched tea leaves and sodium selenite. Glutathione peroxidase activity in liver of rats fed with Se-enriched tea was higher than that fed with sodium selenite, indicating that the selenium in Se-enriched tea leaves is a more effective Se source than sodium selenite. Increasing the Se level in food products through the application of a selenium fertilizer is a safe, effective and feasible means of increasing the selenium intake of human and animals in low selenium areas of China.     

Selenium suppresses oxidative-stress-enhanced vascular smooth muscle cell calcification by inhibiting the activation of the PI3K/AKT and ERK signaling pathways and endoplasmic reticulum stress

Vascular calcification is a prominent feature of many diseases, including atherosclerosis, and it has emerged as a powerful predictor of cardiovascular morbidity and mortality. A number of studies have examined the association between selenium and risk of cardiovascular diseases, but little is known about the role of selenium in vascular calcification. To determine the role of selenium in regulating vascular calcification, we assessed the effect of sodium selenite on oxidative-stress-enhanced vascular smooth muscle cell (VSMC) calcification and the underlying mechanism. Oxidative stress induced by xanthine/xanthine oxidase increased apoptosis, as determined by Hoechst 33342 staining and annexin V/propidium iodide staining, and it enhanced osteoblastic differentiation and calcification of VSMCs, on the basis of alkaline phosphatase activity, the expression of Runx2 and type I collagen, and calcium deposition. These effects of oxidative stress were significantly inhibited by selenite. The following processes may explain the inhibitory effects of selenite: (1) selenite significantly suppressed oxidative stress, as evidenced by the decrease of the oxidative status of the cell and lipid peroxidation levels, as well as by the increase of the total protein thiol content and the activity of the antioxidant selenoenzyme glutathione peroxidase; (2) selenite significantly attenuated oxidative-stress-induced activation of the phosphatidylinositol 3-kinase/AKT and extracellular-signal-regulated kinase signaling pathways, resulting in decreased osteoblastic differentiation of VSMCs; (3) selenite significantly inhibited oxidative-stress-activated endoplasmic reticulum stress, thereby leading to decreased apoptosis. Our results suggest a potential role of selenium in the prevention of vascular calcification, which may provide more mechanistic insights into the relationship between selenium and cardiovascular diseases.     

Selenium homeostasis and induction of thioredoxin reductase during long term selenite supplementation in the rat

Selenium is a candidate treatment for liver tumour prevention in chronic liver disease. In this study, we have studied selenium uptake, distribution and accumulation in rats provided with water containing tumour-preventive doses of sodium selenite for 10 weeks. Male Fischer 344 rats were given drinking water containing 1 μg/mL or 5 μg/mL sodium selenite. Selenium levels were monitored in serum and liver tissue over the 10-week period, and the kinetics of induction of the redox-active cytosolic selenoenzyme thioredoxin reductase were followed. Selenite exposure via drinking water caused a dose-dependent increase in blood and liver selenium levels, with plateaus at 6 and 8 weeks, respectively. These plateaus were reached at the same level of selenium regardless of dose, and no further accumulation was observed. A selenium-dependent increase in the activity of TrxR1 in parallel with the increase in liver selenium levels was also seen, and the induction of TrxR1 mRNA was seen only during the first three days of treatment, when the levels of selenium in the liver were increasing. Sodium selenite at 1 and 5 μg/mL did not affect body weight or relative liver mass. We concluded that long-term treatment with selenite did not cause accumulation of selenium and that the activity of TrxR1 in the liver rose with the selenium levels. We therefore suggest that sodium selenite at doses up to 5 μg/mL could be used for long-term tumour prevention.     

Influence of selenium on the growth of N-nitrosomethylurea-induced mammary tumor cells in culture

Selenium is an essential dietary trace element which has anticancer properties. Among its effects in rats, selenium has been shown to inhibit the development of carcinogen-induced mammary tumors by interfering with the postinitiation, promotion phase of carcinogenesis. We studied the effects of selenium on the growth of rat mammary tumor cells in primary culture. Our objective was to determine whether selenium had any direct influence on cell growth which might explain its influence on tumor development. Rat mammary tumors were induced by N-nitrosomethylurea. Tumor epithelium was prepared by collagenase dispersion and the cells were separated by Ficoll gradient centrifugation. The tumor epithelium was grown in primary culture using a defined serum-free medium. The addition of low concentrations of sodium selenite, less than 1.0 micrograms/ml, stimulated tumor cell proliferation. Protein synthesis and the production of type IV collagen increased within the first hour of exposure, prior to any measurable increase in DNA synthesis. Concentrations of selenite greater than 1.0 micrograms/ml inhibited cell proliferation, the synthesis of protein, and the replication of DNA in a dose-related manner. These studies demonstrated that selenium has the potential to influence the postinitiation phase of rat mammary tumorigenesis by directly altering the growth of tumor cells, possibly through the regulation of protein synthesis.     

Influence of sodium selenite and selenomethionine on DNA/RNA synthesis and BaP binding to spleen lymphocytes in culture

In the present study, an attempt was made to provide some information regarding the effects of organic and inorganic selenium compounds on DNA/RNA synthesis and benzo(a)pyrene uptake in cultured lymphocytes from mice spleen. It was clear from the results that there was a significant inhibition of DNA/RNA synthesis with increasing concentration of either form of selenium from 0.1ΜM to 1 mM in culture medium. However, when used at the same level as selenite with respect to selenium content, selenomethionine exerted more DNA/RNA synthesis inhibitory effect than selenite. Benzo(a)pyrene uptake by proliferating lymphocytes was also significantly reduced with increasing selenium concentration (0.1 ΜM to 1 mM). However, both forms of selenium at the same selenium concentration showed almost the same inhibitory effect on the cellular uptake of benzo(a)pyrene, which indicated that some factor(s) other than the DNA synthesis are also involved in the interaction between benzo(a)pyrene and cells. Involvement of the changes in the carcinogen metabolism and glutathione level has been discussed. Present studies show that organic selenium as a source of selenium is a more potent chemopreventive compared to the inorganic one. This information may have a useful therapeutic potential.     

The chemical form of selenium affects insulinomimetic properties of the trace element: investigations in type II diabetic dbdb mice

The objective of the present study was to investigate the effects of oral selenate application in comparison to selenium deficiency and selenite treatment on the development of the diabetic status (glucose tolerance, insulin resistance and activities of glycolytic and gluconeogenic marker enzymes) in dbdb mice, representing a type II diabetic animal model. Therefore 21 adult male dbdb mice were assigned to 3 experimental groups of 7 animals each and put on a selenium deficient diet (< 0.03 mg/kg diet) based on torula yeast. Group 0Se was kept on selenium deficiency for 10 weeks while the mice of the groups SeIV and SeVI were supplemented daily with 15% of their individual LD(50) of sodium selenite or sodium selenate in addition to the diet. After 10 weeks a distinct melioration of the diabetic status indicated by a corrected glucose tolerance and a lowered insulin resistance was measured in selenate treated mice (group SeVI) in comparison to their selenium deficient and selenite treated companions and to their initial status. Activities of the glycolytic marker enzymes hexokinase, phosphofructokinase and pyruvate kinase were increased 1.7 to 3-fold in liver and/or adipose tissue by selenate treatment as compared to mice on selenium deficiency and mice with selenite administration. In contrast selenate treatment (SeVI) repressed the activity of liver pyruvate carboxylase the first enzyme in gluconeogenesis by about 33% in comparison to the selenium deficient (0Se) and selenite treated mice (SeIV). However the current study revealed an insulinomimetic role for selenate (selenium VI) also in type II diabetic animals due to a melioration of insulin resistance. In contrast selenium deficiency and especially selenite (selenium IV) impaired the diabetic status of dbdb mice, demonstrating the need for investigations on the insulinomimetic action of selenium due to the metabolism of different selenium compounds.     

Selenium and Glutathione Peroxidase Levels in Lambs Receiving Feed Supplemented with Sodium Selenite or Selenomethionine

Twenty-one 6 months old female lambs were divided into 7 groups and fed a basal diet containing 0.13 mg Se/kg. The basal diet was further supplemented with 0, 0.1, 0.5 or 1.0 mg Se/kg either as sodium selenite or as selenomethionine, and was fed for 10 weeks. Both feed additives produced an increase in the selenium concentration in the tissues analysed. Significant correlations were found between the concentrations of selenomethionine or sodium selenite added to the feed and the subsequent tissue levels. However, the selenium levels seemed to plateau at approximately 0.5 mg Se/kg of supplemented sodium selenite. The total glutathione peroxidase (GSH-Px) activity of the tissues increased when the selenium supplementation increased from 0 to 0.1 mg/kg for both selenium compounds. With further increase in selenium supplementation the GSH-Px activity in the tissues plateaued except in the blood where the activity continued to rise with increasing selenomethionine supplementation. The selenium dependent GSH-Px activity in the liver rose with increasing selenomethionine supplementation, but approached a plateau when 0.1 mg Se/kg as sodium selenite was added to the feed. The selenium concentration in whole blood responded more rapidly to the selenium supplementation than did GSH-Px activity. The experiment indicates that the optimal selenium concentration in the feed is considerably higher than 0.1 mg Se/kg, and that selenium levels of 1.0 mg/kg in the feed do not result in any risk for the animals or the consumers of the products.     

Full replacement of 2-mercaptoethanol by cysteine plus selenium compounds in augmenting DNA synthesis of mitogen-stimulated mouse spleen lymphocytes

Mouse spleen lymphocytes require 2-mercaptoethanol for maximal mitogenic activation in vitro. Previous studies indicate that the lymphocytes are defective in the cystine transport activity and that they require 2-mercaptoethanol to utilize cystine. 2-Mercaptoethanol catalytically carries cysteine moiety into the cells in a mixed disulfide form. Because cysteine is easily oxidized to cysteine in the culture medium, it has been not easy to precisely examine the effect of near-physiological concentrations of cysteine on the activation of lymphocytes. By controlling the cysteine content in the medium, we have reviewed the effect of cysteine to see if cysteine replaces 2-mercaptoethanol in enhancing the DNA synthesis of lipopolysaccharide-stimulated lymphocytes. It was found that cysteine was less effective than 2-mercaptoethanol, and that cysteine fully replaced 2-mercaptoethanol when a selenium compound was supplemented. The effects of cysteine and selenium compounds were apparently independent and additive. Among the selenium compounds examined, sodium selenite and L-selenocystine were much more effective in stimulating DNA synthesis than sodium selenate and L-selenomethionine.     

Protein synthesis is not required for the inhibitory effect of selenite on cell colony formation and RNA synthesis

Selenite has been shown to undergo intracellular metabolism that results in its conversion to other low molecular weight Secontaining species and also to its incorporation into a selenocysteine residue in selenoprotein. In order to investigate whether the incorporation into protein is required for the cytotoxic effects of selenite, we have examined whether inhibition of protein synthesis prevents the inhibitory effect of selenite on the ability of cells to form colonies or to synthesize RNA. We have found that treatment of HeLa cells with cycloheximide inhibited protein synthesis by >90% but had no effect on the inhibitory effect of selenite on cell colony formation or RNA synthesis. Since protein synthesis is not necessary for these cytotoxic effects of selenite they are unlikely to result from an increase in the synthesis of selenoproteins.     

Intracellular glutathione is a cofactor in methylseleninic acid-induced apoptotic cell death of human hepatoma HEPG(2) cells

Selenium is a widely studied dietary anticancer agent. Among various selenium compounds, the methylated forms appear to be particularly effective in cancer prevention. Intracellular glutathione (GSH) is known to be involved in the metabolism of many methylated forms of selenium. In this study, we investigated the role of intracellular GSH in methylseleninic acid (MSeA)-induced apoptosis in human hepatoma (HepG(2)) cells. MSeA was shown to deplete intracellular GSH rapidly, preceding the typical apoptotic changes such as DNA fragmentation as measured by the TUNEL assay. When the intracellular GSH concentration was enhanced using N-acetylcysteiene (NAC) (a GSH synthesis precursor) and decreased using buthionine sufoxamine (BSO) (a GSH synthesis inhibitor), NAC markedly augmented MSeA-induced apoptosis, while BSO significantly inhibited MSeA-induced apoptosis. Different from the effect of sodium selenite, there was no measurable superoxide radical level in MSeA-treated cells. These observations suggest that intracellular GSH mainly acts as a cofactor to facilitate MSeA-induced apoptosis, while its antioxidant function becomes largely irrelevant. It is thus postulated that some cancer cells, such as liver cancer cells with higher level of intracellular GSH, would be more susceptible to MSeA cytotoxicity.     

Effect of selenium compounds and thiols on human mammary tumor cells

The effect on cell viability and growth rate of sodium selenite, selenocystine, sodium selenate, and selenomethionine at selenium concentrations of 6.25 and 12.5 uM was studied in vitro on cells of the human mammary tumor cell line HTB123/DU4475. Selenite and selenocystine affected both cell viability and growth rate of the tumor cells at these selenium concentrations. Selenite and selenocystine decreased intracellular glutathione concentrations, but did not affect tumor cell glutathione peroxidase activity. After six days of exposure to either selenate or selenomethionine, the viability of tumor cells remained stable, but cell growth, as measured by numbers of cells, was retarded. Neither selenate nor selenomethionine produced changes in concentrations of intracellular glutathione. The toxic effect of selenite on tumor cells was enhanced by addition of 0.25 mM glutathione to the growth medium. Preincubation of the tumor cells with 62.5 uM buthionine sulfoximine decreased cellular glutathione to 15% of controls at 24 h and enhanced the toxicity of selenite toward the tumor cells. Glutathione, 2-mercaptoethanol, and L-cysteine were all toxic to the tumor cells in a dose-dependent manner.     

Redox regulation of cytosolic glycerol-3-phosphate dehydrogenase: Cys(102) is the target of the redox control and essential for the catalytic activity

Cytosolic glycerol-3-phosphate dehydrogenase (cG3PDH) occupies the branch point between the glycolytic pathway and triglyceride biosynthesis. However, the regulatory mechanism of the cG3PDH activity has remained obscure. Here we report that cG3PDH is efficiently inhibited by modification of the thiol group through a redox mechanism. In this study, we found that sodium selenite and nitric oxide (NO) donors such as S-nitroso-N-acetylpenicillamine and 3-morpholinosydnonimine inhibited cG3PDH activity, and that similar effects could be achieved with selenium metabolites such as selenocysteine and selenomethionine. Furthermore, we found that reducing agents, such as dithiothreitol and beta-mercaptoethanol, restored the cG3PDH activity suppressed by selenite and NO both in vitro and in cultured cells. Buthionine sulfoximine depleted levels of both reduced glutathione and the oxidized form but had no effect on the suppression of cG3PDH activity by selenite in cultured cells. Moreover, thiol-reactive agents, such as N-ethylmaleimide and o-iodosobenzoic acid, blocked the enzyme activity of cG3PDH through the modification of redox-sensitive cysteine residues in cG3PDH. The inhibitor of NO synthase, L-N(G)-nitro-arginine, restored the cG3PDH activity inhibited by NO in cultured cells, whereas the inhibitor of guanylyl cyclase, 1H-[1,2,4] oxadiazole[4,3-alpha] quinoxalin-1-one (ODQ), has no effect. NO directly inhibits cG3PDH activity not via a cGMP-dependent mechanism. Finally, using site-directed mutagenesis, we found that Cys(102) of cG3PDH was sensitive to both selenite and NO. From the results, we suggest that cG3PDH is a target of cellular redox regulation.     

Effects of selenium on RNA synthesis and content in rat pancreas.

In order to investigate the effect of selenium supplementation on RNA in the rat pancreas, the rate of in vitro incorporation of [3H]uridine into RNA by pancreas slices derived from two groups of rats fed either a low-selenium diet or a diet supplemented with 0.25 mg/kg selenium as selenite was examined. The RNA and lipid peroxide contents and glutathione peroxidase activity in homogenates from the pancreas were also determined. After feeding for 12-14 weeks, the rates of [3H]uridine incorporation were significantly higher in the pancreatic tissue from the selenium-supplemented diet group. Concomitantly, an increase in glutathione peroxidase activities and RNA content, and a reduction of lipid peroxides, were also found in the pancreatic tissue of the selenium-supplemented group. The results suggest that selenium supplementation at a level of 0.25 mg/kg selenium could promote RNA synthesis with an increase in glutathione peroxidase activity and a decrease of lipid peroxides.