Effect of selenium compounds on selenium content, growth and 35S-cystine metabolism of skin fibroblasts from normal and cystinotic individuals.

Kidney samples from children with the inborn metabolic disease cystinosis contain 4 times more selenium (Se) than do kidney samples from normal individuals (p = 0.1). However, when cultured skin fibroblasts from cystinotic patients and normal control individuals are incubated in Se-D,L-methionine, Se-D,L-cystine, Se-cystamine X HCl, Se-urea, selenite or in medium without added selenium, only the cystinotic fibroblasts grown in Se-urea or selenite (SeO3=) contain more selenium than do the corresponding normal cells (p less than 0.05). In both types of cultured fibroblasts, the order of descending toxicity per ppm selenium is: Se-urea greater than Se-cystamine greater than Se-cystine greater than or equal to SeO3= much greater than Se-methionine. High (apparently toxic) concentrations of Se-urea and Se-cystamine lower the elevated intracellular free (nonprotein) cystine content of cystinotic fibroblasts to less than 60% of control values; at lower concentrations, these compounds raise the cystine content of these cells to over 140% of control values. Appropriate concentrations of SeO3=, Se-cystine and Se-methionine also elevate the free cystine content of the cystinotic cells. During a 75 minute incubation in 35S-cystine, the incorporation of 35S into the acid precipitable (protein) fraction of both cell types is significantly inhibited by Se-cystamine (approximately 55% control; p less than 0.05). The incorporation of 35S-cystine into glutathione is inhibited by Se-cystine (approximately 40% control) in both fibroblast types (p less than 0.05). In cystinotic cells, Se-cystamine significantly reduces incorporation of 35S-cystine into the cystine pool (40% control) as does SeO3= (67% control; p less than 0.05). Protein and glutathione synthesis in cystinotic fibroblasts are more strongly inhibited by Se-cystine and SeO3=, respectively, than in normal fibroblasts (p less than 0.05). These studies demonstrate that selenium compounds exhibit a different sequence of toxicity in fibroblasts than in the intact animal and that some previously unreported metabolic effects (i.e. inhibition of glutathione synthesis) may contribute to their toxicity.     

Selenium speciation in human milk with special respect to quality control

Selenium-(SE) organo compounds of pooled human milk (7th-14th d after delivery) were separated by centrifugation and subsequent size-exclusion chromatography (SEC) as described in ref. (1). The SEC fractions were used for Se determinations by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) in parallel to identification procedures of the organic ligands by two different capillary zone electrophoresis (CZE) methods. Further, the combination of isotachophoresis-(ITP) CZE with ETV-ICP-MS was used for final identifications. Mass balances were carried out at each analytical step for quality assurance. Reinjection experiments were performed to check the stability of Se-organo compounds during the analytical procedure. These quality-control experiments showed that no species transformations took place during the analytical procedure, and the Se species were native in human milk. The identification and quantification of organic ligands were clear and resulted in values of 2 (±0.2) mg/L GSH/GSeH, 2 (±0.22) mg/L cystamine/Se-cystamine, 4 (±0.4) mg/L cystine/ Se-cystine, and 1 (±0.18) mg/L methionine/Se-methionine. Unfortunately, a differentiation between sulfur (S) and Se analogs was not possible with the applied CE methods. The Se values per organic ligand were determined as 2.5 (±0.23) mg/L associated with GSH (as GSeH), 3.1 (±0.31) mg/L associated with cystamine (as Se-cystamine), 5.2 (±0.4) mg/L associated with cystine (as Se-cystine), and 1 (±0.1) mg/L associated with methionine (as Se-methionine).     

富硒大蒜含硒蛋白的分离、鉴定和生物活性研究

本文报道了富硒大蒜含硒蛋白的分离、鉴定和生物活性研究。富硒大蒜水溶性蛋白多为酸性蛋白。通过Sephadex G—200柱层析和聚丙烯酰胺梯度凝胶电泳分离出两种分子量约为30,000和33,000的酸性含硒蛋白。大蒜含硒蛋白和亚硒酸钠一样,具有提高含硒谷胱甘肽过氧化物酶(SeGSHpx)活性,促进软骨细胞生长的生理效应。实验结果提示,富硒大蒜有可能成为良好的补硒来源。     

Fish arsenic may influence human blood arsenic,selenium, and T4:T3 ratio

The effects of an arsenic-rich fish diet and selenium (Se) supplementation on blood arsenic (As), Se, and thyroid hormones were studied in 32 women divided into four equal groups. Groups 1 and 4 received 400 μg Se-methionine daily, group 2 received 400 μg selenite daily, and group 3 received placebo tablets for 15 wk. In addition, groups 1–3 increased their fish intake, eating at least three fish dinners weekly. Mean blood Se concentrations (initially 1.68 ± 0.24 μmol/L) increased twofold in the Se-methionine groups (p < 0.0001) and by 32% in the selenite group (p < 0.01). Group means of blood As concentrations increased by 63% (p < 0.01), 50% (p < 0.01), 106% (p < 0.01), and 29% (p < 0.05) in the four groups, respectively. Analyzed As intake from duplicate portions of consumed fish correlated with final blood As concentrations (r=0.85, p < 0.001, n=32). In the group not receiving Se, there was a positive correlation between final blood As concentrations and plasma T4 : T3 ratio (r=0.80, p < 0.02, n=8). Initially, blood As concentrations correlated negatively with both T3 and T4 in plasma, but this correlation disappeared upon Se supplementation. The results demonstrate that increased intake of fish may influence blood As concentrations and that circulating thyroid hormones may be influenced by Se-As interactions.     

Uptake of selenotrisulfides of glutathione and cysteine by brush border membranes from rat intestines.

The uptake of selenodiglutathione and selenodicysteine was compared to that of selenite by brush border membrane vesicles (BBMV) prepared from rat intestinal tracts. It was found that it is critical to maintain a pH of 6.0 or below to prevent the spontaneous breakdown of these compounds. When conducted at pH 6.0, the uptake of selenodiglutathione and selenodicysteine was more than ten times faster than for selenite selenium. Ligated intestinal loop studies were conducted to determine if similar results would be obtained in vivo. In comparison to selenite, selenium absorption was enhanced 68% and the transfer to the body increased 2.4-fold when selenium as selenodiglutathione was placed in the ileum. The absorption of selenium as selenodicysteine was increased by 57% and the transfer doubled in comparison to selenite when placed in the ileum. Thus, the stimulated absorption of selenite by glutathione or cysteine appears to be through the formation of complexes with these compounds.     

Investigation of the selenium metabolism in cancer cell lines

The aim of this work was to compare different selenium species for their ability to induce cell death in different cancer cell lines, while investigating the underlying chemistry by speciation analysis. A prostate cancer cell line (PC-3), a colon cancer cell line (HT-29) and a leukaemia cell line (Jurkat E6-1) were incubated with five selenium compounds representing inorganic as well as organic Se compounds in different oxidation states. Selenomethionine (SeMet), Se-methylselenocysteine (MeSeCys), methylseleninic acid (MeSeA), selenite and selenate in the concentration range 5-100 μM were incubated with cells for 24 h and the induction of cell death was measured using flow cytometry. The amounts of total selenium in cell medium, cell lysate and the insoluble fractions was determined by ICP-MS. Speciation analysis of cellular fractions was performed by reversed phase, anion exchange and size exclusion chromatography and ICP-MS detection. The selenium compounds exhibited large differences in their ability to induce cell death in the three cell lines and the susceptibilities of the cell lines were different. Full recovery of selenium in the cellular fractions was observed for all Se compounds except MeSeA. Speciation analysis showed that MeSeA was completely transformed during the incubations, while metabolic conversion of the other Se compounds was limited. Production of volatile dimethyl diselenide was observed for MeSeA and MeSeCys. MeSeA, MeSeCys and selenite showed noticeable protein binding. Correlations between cell death induction and the Se compounds transformations could not be demonstrated.     

Chemopreventive activity of selenocysteine prodrugs against tobacco‐derived nitrosamine (NNK) induced lung tumors in the A/J mouse

Prodrugs of L ‐selenocysteine have potential utility in cancer chemoprevention. This study reports the efficacy of three selenazolidine‐4(R)‐carboxylic acids, (2‐unsubstituted, 2‐oxo, and 2‐methyl derivatives; SCA, OSCA, and MSCA, respectively) against tobacco‐related lung tumorigenesis in a mouse model. Seven days after initiation of an AIN‐76A diet supplemented with sodium selenite (5 ppm Se), L ‐selenomethionine (3.75 ppm Se), Se‐methyl‐L ‐selenocysteine (3 ppm Se), L ‐selenocystine (15 ppm Se), SCA (15 ppm Se), OSCA (15 ppm Se), or MSCA (15 ppm Se), mice received 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK; 10 μmol, i.p.). After an additional 16 weeks on the diets, two compounds, OSCA and selenocystine, significantly reduced lung adenoma multiplicity from 7.2 tumors per mouse in the NNK group to 4.5 and 4.6 tumors per mouse, respectively. Neither selenium concentration nor glutathione peroxidase activity in either RBCs or liver served as surrogate indicators of tumor reduction. Hepatic selenium levels were significantly elevated by all selenium‐containing compounds except Se‐methyl‐L ‐selenocysteine and SCA; RBC selenium levels by all except sodium selenite and MSCA. With the exception of L ‐selenomethionine, RBC glutathione peroxidase activity was increased along with the elevated selenium levels. Hepatic glutathione peroxidase activity was elevated by all Se‐compounds except SCA. The two compounds showing significant tumor reduction (OSCA and selenocystine) were the only two compounds that showed ubiquity of changes, elevating both selenium levels and GPx activity in both liver and RBC. © 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 19:396‐405, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20105     

Chemopreventive activity of selenocysteine prodrugs against tobacco-derived nitrosamine (NNK) induced lung tumors in the A/J mouse

Prodrugs of L-selenocysteine have potential utility in cancer chemoprevention. This study reports the efficacy of three selenazolidine-4(R)-carboxylic acids, (2-unsubstituted, 2-oxo, and 2-methyl derivatives; SCA, OSCA, and MSCA, respectively) against tobacco-related lung tumorigenesis in a mouse model. Seven days after initiation of an AIN-76A diet supplemented with sodium selenite (5 ppm Se), L-selenomethionine (3.75 ppm Se), Se-methyl-L-selenocysteine (3 ppm Se), L-selenocystine (15 ppm Se), SCA (15 ppm Se), OSCA (15 ppm Se), or MSCA (15 ppm Se), mice received 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; 10 micromol, i.p.). After an additional 16 weeks on the diets, two compounds, OSCA and selenocystine, significantly reduced lung adenoma multiplicity from 7.2 tumors per mouse in the NNK group to 4.5 and 4.6 tumors per mouse, respectively. Neither selenium concentration nor glutathione peroxidase activity in either RBCs or liver served as surrogate indicators of tumor reduction. Hepatic selenium levels were significantly elevated by all selenium-containing compounds except Se-methyl-L-selenocysteine and SCA; RBC selenium levels by all except sodium selenite and MSCA. With the exception of L-selenomethionine, RBC glutathione peroxidase activity was increased along with the elevated selenium levels. Hepatic glutathione peroxidase activity was elevated by all Se-compounds except SCA. The two compounds showing significant tumor reduction (OSCA and selenocystine) were the only two compounds that showed ubiquity of changes, elevating both selenium levels and GPx activity in both liver and RBC.     

Investigation of the form of selenium in the hydrogenase from chemolithotrophically cultured Bradyrhizobium japonicum

It has been established that the hydrogenase from autotrophically cultured Bradyrhizobium japonicum contains selenium as a bound constituent. About 80% of the enzyme selenium remains bound during precipitation with 5% trichloroacetic acid (TCA). However, 85% of the selenium bound to the enzyme is released by a combined treatment of urea, heat and TCA. Neither selenomethionine nor selenocysteine could be detected on analysis of anaerobically hydrolyzed enzyme. These results are consistent with the report showing that the structural genes for this enzyme do not contain a TGA codon (Sayavedra-Soto et al. 1988) which has been reported to code for selenocysteine incorporation into several proteins (Chambers et al. 1986; Zinoni et al. 1986; Stadtman 1987). We have demonstrated that ⁷⁵Se from the labeled hydrolyzed enzyme forms the derivative' selenodicysteine. The form of selenium resulting in the synthesis of this derivative apparently is SeO _inf3 ^sup= or a compound such as Se⁼ which is easily oxidized to SeO _inf3 ^sup= . In a separate approach it was established that 12–16% of the total ⁷⁵Se in the native enzyme reacted with 2,3-diaminonaphthalene indicating that this fraction was present as SeO _inf3 ^sup= . The remaining ⁷⁵Se was bound to the enzyme protein. From this research, we concluded that Se in Bradyrhizobium japonicum hydrogenase is present in a labile bound form. In this respect, this enzyme is similar to xanthine dehydrogenase and nicotinic acid hydroxylase, both of which contain labile Se constituents that have not been defined.Technical paper no. 8980 from the Oregon Agricultural Experiment Station     

Stimulation of mucosal uptake of selenium from selenite byl-cysteine in sheep small intestine

The influence of cysteine (Cys) on mucosal uptake of 75Se-labeled selenite in sheep midjejunum was investigated using a short-term uptake technique. L-Cys (concn.: 1.0 mmol/L) significantly stimulated uptake of Se from selenite (concn.: 10 mumols/L). The stimulatory effect of L-Cys on mucosal uptake of Se from selenite was Na(+)- and pH-dependent. In the absence of Na+, or at an acidic pH (5.0), the stimulatory effect of L-Cys was abolished. L-alanine and L-lysine, but not L-glutamic acid inhibited uptake of Se from selenite in the presence of L-Cys. Preincubation of mucosal preparations with 10 mmol/L L-Cys produced enhanced mucosal uptake of Se from selenite. It is concluded from these results that L-Cys stimulates absorption of Se from selenite probably by generation of selenodicysteine and maybe cysteine selenopersulfide that are subsequently transported across the intestinal brush border membrane by Na(+)-dependent amino acid carriers. Furthermore, intracellular generation of selenodicysteine might contribute to the uptake of Se from selenite by maintaining the concentration gradient for diffusive uptake of selenite.     

Compendium of the antidiabetic effects of supranutritional selenate doses. In vivo and in vitro investigations with type II diabetic db/db mice

In recent years, a number of investigations on the antidiabetic effects of supranutritional selenate doses have been carried out. Selenate (selenium oxidation state +VI) was shown to possess regulatory effects on glycolysis, gluconeogenesis and fatty acid metabolism, metabolic pathways which are disturbed in diabetic disorders. An enhanced phosphorylation of single components of the insulin signalling pathway could be shown to be one molecular mechanism responsible for the insulinomimetic properties of selenate. In type II diabetic animals, a reduction of insulin resistance could be shown as an outcome of selenate treatment. The present study with db/db mice was performed to investigate the antidiabetic mechanisms of selenate in type II diabetic animals. Twenty-one young adult female db/db mice were randomly assigned to three experimental groups (selenium deficient=0Se, selenite-treated group=SeIV and selenate-treated group=SeVI) with seven animals each. Mice of all groups were fed a selenium-deficient diet for 8 weeks. The animals of the groups SeIV and SeVI were supplemented with increasing amounts of sodium selenite or sodium selenate up to 35% of the LD50 in week 8 in addition to the diet by tube feeding. Selenate treatment reduced insulin resistance significantly and reduced the activity of liver cytosolic protein tyrosine phosphatases (PTPs) as negative regulators of insulin signalling by about 50%. In an in vitro inhibition test selenate (oxidation state +VI) per se did not inhibit PTP activity. In this test, however, selenium compounds of the oxidation state +IV were found to be the actual inhibitors of PTP activity. Selenate administration in vivo further led to characteristic changes in the selenium-dependent redox system, which could be mimicked in an in vitro assay and provided further evidence for the intermediary formation of SeIV metabolites. The expression of peroxisome proliferator-activated receptor gamma (PPARgamma), another important factor in the context of insulin resistance and lipid metabolism, was significantly increased by selenate application. In particular, liver gluconeogenesis and lipid metabolism were influenced strongly by selenate treatment. In conclusion, our results showed that supranutritional selenate doses influenced two important mechanisms involved in insulin-resistant diabetes, namely, PTPs and PPARgamma, which, in turn, can be assumed as being responsible for the changes in intermediary metabolism, e.g., gluconeogenesis and lipid metabolism. The initiation of these mechanisms thereby seems to be coupled to the intermediary formation of the selenium oxidation state +IV (selenite state) from selenate.     

The Molecular Mechanisms of Protective Role of Se on the G<Subscript>2</Subscript>/M Phase Arrest of Jejunum Caused by AFB<Subscript>1</Subscript>

Aflatoxin B₁ (AFB₁) is the most toxic among the mycotoxins and causes detrimental health effects on human and animals. Selenium (Se) plays an important role in chemopreventive, antioxidant, anticarcinogen, and detoxification and involved in cell cycle regulation. The aim of this study was to explore the molecular mechanisms of selenium involved in inhibition of G₂/M cell cycle arrest of broiler’s jejunum. A total of 240 one-day-old healthy Cobb broilers were randomly divided into four groups and fed with basal diet (control group), 0.6 mg/kg AFB₁ (AFB₁ group), 0.4 mg/kg Se (+Se group), and 0.6 mg/kg AFB₁ + 0.4 mg/kg Se (AFB₁ + Se group) for 21 days, respectively. The histological observation and morphological analysis revealed that 0.4 mg/kg Se prevented the AFB₁-associated lesions of jejunum including the shedding of the apical region of villi, the decreased villus height, and villus height/crypt ratio. The cell cycle analysis by flow cytometry showed that 0.4 mg/kg Se ameliorated the AFB₁-induced G₂/M phase arrest in jejunal cells. Moreover, the expressions of ATM, Chk2, p53, Mdm2, p21, PCNA, Cdc25, cyclin B, and Cdc2 analyzed by immunohistochemistry and qRT-PCR demonstrated that 0.4 mg/kg Se restored these parameters to be close to those in the control group. In conclusion, Se promoted cell cycle recovery from the AFB₁-induced G₂/M phase arrest by the molecular regulation of ATM pathway in the jejunum of broilers. The outcomes from the present study may lead to a better understanding of the nature of selenium’s essentiality and its protective roles against AFB₁.     

The effect of vitamin E on the oxidation state of selenium in rat liver

1. (75)Se as Na(2) (75)SeO(3) was administered orally to rats under different nutritional conditions. 2. The selenium found in the liver subcellular organelle fractions was present in at least three oxidation states: acid-volatile selenium, assumed to be selenide, zinc-hydrochloric acid-reducible selenium, assumed to be selenite, and higher oxidation states of selenium and organic derivatives, called selenate for convenience. 3. The proportion of the total selenium present as selenide present as selenide is susceptible to oxidation in vitro, which can be prevented by the addition of antioxidants in vitro. 4. The proportion of selenide is also directly related to the vitamin E status of the rats, and treatment of vitamin E-deficient rats with vitamin E results in an increase in the proportion of selenide. 5. Freezing the liver in situ before preparation of the organelle fractions did not alter the susceptibility of the selenide proportion to dietary vitamin E, indicating that the observed effects occur in vivo and not as a result of oxidation post mortem. 6. Intravenous administration of Na(2) (75)SeO(3), to rats whose alimentary tract was partially sterilized by neomycin treatment, gave a similar result to that in paragraph 4, indicating that the reduction of selenite to selenide probably occurs in vivo, and that intestinal micro-organisms are not responsible. 7. Treatment of vitamin E-deficient rats with silver produced a fall in the total (75)Se content of the liver, an effect only partially reversed by vitamin E administration. The proportion of the total selenium present as selenide was also lowered by the treatments with silver, and vitamin E significantly reversed this trend in most cases. 8. These results are consistent with the hypothesis that the active form of Se may be selenide and that the selenide may form part of the active centre of an uncharacterized class of catalytically active non-haem-iron proteins that are protected from oxidation in vivo by vitamin E.     

Effect of acute selenium restriction on whole body endogenous selenium and the selenite-exchangeable metabolic pool in the adult rat

The time course of changes in whole body endogenous selenium (Se(end)) was investigated during a short-term (7-day) selenium restriction study in the adult rat. The method of continuous feeding with a stable isotope of selenium was used to permit normal intake of selenium while distinguishing between the dietary and endogenous components of body selenium. Additionally, the effect of short-term selenium restriction on the time course of the selenite-exchangeable metabolic pool (Se-EMP) was investigated. Two groups of adult male rats were intubated with the in vivo stable isotope (74)SeO(3)(2-), then fed a Torula yeast diet (selenium <0.02 microg/g) and either deionized water (-Se group) or deionized water containing selenium as (76)SeO(3)(2-) (0.1 microg selenium/ml) (+Se group). Three animals from each group were killed at 24-hour intervals. Whole body Se(end) and the estimated size of Se-EMP (W(Se-EMP)) were determined using hydride generation-inductively coupled plasma mass spectrometry for isotopic measurements. Whole body Se(end) decreased linearly in the +Se group (Se degrees (end): 54.4 microg; Se(end) at 3 days: 49.3 +/- 2.1; Se(end) at 7 days: 45.2 +/- 2.2). The decrease was exponential for the -Se group (Se degrees (end): 54.4 microg; Se(end) at 3 days: 42.9 +/- 0.3; Se(end) at 7 days: 42.2 +/- 0.7). The value of W(Se-EMP,pl) (microg) was 19.8 +/- 0.6 at 1 day and 19.7 +/- 1.0 at 7 days for the +Se group. The corresponding values for the -Se group were 15.7 +/- 1.5 and 18.8 +/- 0.4. All respective values of W(Se-EMP,pl) for the -Se group were significantly smaller than for the +Se group (P < 0.05), with the exception of values at days 6 and 7. The value of W(Se-EMP,urine) (microg) was 2.1 +/- 0.2 at 1 day, increasing rapidly to 23.5 +/- 1.5 at 7 days for the +Se group. The corresponding values for the -Se group were 3.0 and 23.1.     

Chemical forms of selenium present in rat and ram spermatozoa

In vivo and in vitro studies were conducted to investigate the chemical forms by ion-exchange chromatography of selenium (Se) present in rat and ovine spermatozoa. After injection with ⁷⁵Se-selenite, the form of ⁷⁵Se in rat sperm was selenocysteine, but selenocysteine and selenomethionine (SeMet) were present in ovine sperm. Presumably, synthesis of SeMet by rumen microbes are responsible for its presence in ovine sperm. In vitro incubation of ram sperm with selenocysteine or SeMet produced no changes, but incubation with selenite produced a compound that eluted one fraction before SeMet from the ion-exchange column. After treatment of this fraction with mercaptoethanol, it eluted in a later fraction upon rechromatography, suggesting it to be selenodicysteine. This compound is apparently formed because of high levels of cysteine in semen. Cysteine, reduced glutathione, and oxidized glutathione were also found in semen. The significance of the results is discussed.     

Selenium increases hydrogenase expression in autotrophically cultured Bradyrhizobium japonicum and is a constituent of the purified enzyme.

We have investigated the effect of added selenite on autotrophic growth and the time course of hydrogen oxidation derepression in Bradyrhizobium japonicum 122DES cultured in a medium purified to remove selenium compounds. In addition, hydrogenase was purified to near homogeneity and examined for the specific incorporation of Se into the enzyme. The addition of Se at 0.1 microM significantly increased total cell protein and hydrogenase specific activity of harvested cells. Also, the addition of SeO3(2-) enhanced the time course of hydrogenase derepression by 133%, whereas VO3, AsO2(2-), SO2(2-), and TeO3(2-) failed to substantially affect hydrogenase derepression. During the final chromatographic purification of hydrogenase, a striking coincidence in peaks of protein content, Se radioactivity, and hydrogenase activity of fractions was obtained. The total Se content expressed per milligram of protein increased manyfold during the purification procedure. The mean Se content of the purified hydrogenase was 0.56 +/- 0.13 mol of Se per mol of enzyme. These results indicate that Se is an important element in the H2 metabolism of B. japonicum and that hydrogenase from B. japonicum is a seleno protein.     

Effects of Dietary Form of Selenium on Its Distribution in Eggs

The objective of this experiment was to investigate the selenium distribution in eggs from hens fed diets supplemented with Se from sodium selenite (SS) or selenium-enriched yeast (SY). One-day-old female chickens of Hy-Line Brown breed were randomly divided into four groups according to dietary treatments and, for the subsequent 9?months, were fed diets which differed only in the form or amount of Se supplemented. During the whole experiment, group 1 (control) was fed basal diet (BD) with only background Se level of 0.13?mg/kg dry matter (DM). Diets for groups 2 and 3 consisted of BD supplemented with an Se dose of 0.4?mg/kg DM either in the form of SS or SY, respectively. Group 4 was fed BD supplemented with 0.9?mg Se/kg DM from SY. After 9?months of dietary treatments, the Se levels in egg yolk and albumen from hens fed unsupplemented diet were almost identical whereas eggs from hens given diet supplemented with SS showed significantly higher Se deposition in yolk than in albumen (P?相似文献   

Oxidation of glutathione and superoxide generation by inorganic and organic selenium compounds

The carcinostatic activities of selenium (Se) compounds have been shown to be composition and concentration dependent. Several studies have indicated that the ratios between glutathione (GSH) and Se may play an important role in Se catalysis and toxicity. The present study examined the catalytic effect of three selenium compounds on GSH oxidation using lucigenin-dependent chemiluminescence (CL) as an indirect measure of superoxide generation. Various GSH:Se ratios were assayed for the glutathione oxidase activity of selenite, selenocystamine and diselenodipropionic acid. CL emitted from the reaction of selenite with GSH increased more rapidly and was greater than those from the diselenides, but the diselenide CL reactions were sustainable. Both selenite- and diselenide-induced CL were markedly suppressed by superoxide dismutase (SOD). Iodoacetic acid (IAc) effectively inhibited CL generated from selenite-, selenocystamine- and diselenodipropionic acid-catalyzed GSH oxidation. These results suggest that GSH oxidation catalyzed by selenite, and the diselenides selenocystamine and diselenodipropionic acid, generated the superoxide radical in which the CL was inhibited by SOD. Furthermore, CL inhibition by IAc suggests that the catalytic species producing superoxide were the GSSe(-) or RSe(-) anion. This redox chemistry may be responsible for selenite and organoselenium toxicity and apoptosis, making possible the design and synthesis of organoselenium-containing pharmaceuticals.     

Selenium determination in human plasma lipoprotein fractions by mass spectrometry analysis

Previous observations have suggested that lipoproteins may be involved in the transport of selenium in humans. To further investigate this question, selenium was measured in lipoprotein fractions isolated from plasma of healthy adults. A gas chromatographic-mass spectrometric method using the isotopic dilution technique was developed to ensure a reliable measurement of low amounts of selenium. About 3% of total plasma selenium was bound to lipoproteins, mainly to the LDL fraction. After solvent fractionation of LDL and HDL, the major part of the selenium was recovered in the protein extract, suggesting that it may be incorporated in apolipoproteins. The exact form of Se is not yet clearly established. Considering the different Se compounds found in proteins, it is postulated to be selenomethionine, and/or participating in a selenium-sulphur bond. This could explain why the amount of selenium bound to apolipoprotein B in LDL was about twice that which could be expected from a random substitution of selenomethionine for methionine.     

Interaction of glutathione and sodium selenite in vitro investigated by electrospray ionization tandem mass spectrometry

Selenite has been found to be an active catalyst for the oxidation of sulphhydryl compounds, such as glutathione (GSH). Considering the biological importance of GSH oxidation and the implication of sulphhydryl compounds in selenium poisoning and other biological activities, more information on selenite oxidation of GSH in enzyme-free conditions is desirable. Herein, we describe glutathione and sodium selenite simply mixed in aqueous solutions. The interaction products and transient intermediate are identified and characterized using electrospray ionization (ESI) tandem mass spectrometry. In the first step, GSH directly reacts to form diglutathione (GSSG) and unstable selenodiglutathione (GS-Se-SG). Then selenodiglutathione further reacted with remaining GSH to form diglutathione and elemental selenium, Se(0). As the amount of GSSG significantly increased or acidity of the solution increased, the redox potential of glutathione [E(0')(GSSG/2GSH) approximately -250 mV (NHE)] significantly shifted to the positive direction. This makes the GSSG react with elemental selenium formed in the solution, which can be demonstrated by another unstable intermediate ion identified at m/z 418 by mass spectrometry with the elemental composition of [GSS-Se](-). The reaction mechanism between GSH and sodium selenite has been proposed according to the ESI-MS, NMR and UV-vis spectrometric measurements.