Showing papers on "Selenium published in 2002"
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
TL;DR: The biochemistry of selenium-containing natural products, including selenoproteins, is reviewed up to May 2002 and contains 393 references on key discoveries and recent progress.
391 citations
TL;DR: Important principles of selenium cycling and toxicity were documented in the Belews Lake studies, and information useful for protecting aquatic ecosystems as newSelenium issues emerge are provided.
355 citations
TL;DR: Since most estimates of selenium intake in the United States are 80 micrograms per day or greater, routine seenium supplementation is not recommended in theUnited States.
Abstract: Selenium is an essential constituent of a number of enzymes, some of which have antioxidant functions. Deficiency of the element in animals makes them susceptible to injury by certain types of oxidative stress. At least 1 human disease occurs only in selenium-deficient individuals. Therefore, it seems prudent to avoid selenium deficiency. The plasma (or serum) selenium concentration is often used to assess selenium nutritional status. A plasma selenium concentration of 8 micrograms/dL or greater in a healthy subject indicates that plasma selenoproteins are optimized and the subject is selenium replete. The Third National Health and Nutrition Examination Survey determined plasma selenium in 17,630 subjects in the United States. Its results indicate that more than 99% of the subjects studied were selenium replete. The Institute of Medicine has set the Recommended Dietary Allowance for selenium at 55 micrograms per day for adults. Since most estimates of selenium intake in the United States are 80 micrograms per day or greater, routine selenium supplementation is not recommended in the United States.
296 citations
266 citations
TL;DR: Urinary monomethylated (selenosugar) and trimethylated selenium can be used as specific indices that increase within the required to low-toxic range and with a distinct toxic dose, respectively.
Abstract: Essential micronutrient selenium is excreted into the urine and/or expired after being transformed to methylated metabolites. Monomethylated selenium is excreted into the urine in response to a supply within the required to low-toxic range, whereas tri- and dimethylated selenium increase with excessive supply at a toxic dose. Here we show that the major urinary selenium metabolite within the required to low-toxic range is a selenosugar. The structure of 1β-methylseleno-N-acetyl-d-galactosamine was deduced from the spectroscopic data and confirmed by chemical synthesis. This metabolite was also detected in the liver, and an additional metabolite increased with inhibition of methylation. The latter metabolite was again a selenosugar conjugated with glutathione instead of a methyl group and was assumed to be a precursor for methylation to the former metabolite. A metabolic pathway for the urinary excretion of selenium, i.e., from the glutathione-S-conjugated selenosugar to the methylated one, was proposed. Urinary monomethylated (selenosugar) and trimethylated selenium can be used as specific indices that increase within the required to low-toxic range and with a distinct toxic dose, respectively.
260 citations
TL;DR: There is no suggestion from the literature that the levels of L-selenomethionine that would be expected to accumulate in eggs in the absence of environmental concentration of selenium pose harm to the developing embryo, but for several species of aquatic birds, levels of Se as selenomethions in the egg above 3 ppm on a wet weight basis result in reduced hatchability and deformed embryos.
238 citations
TL;DR: Selenium has a special place among the feed-derived natural antioxidants, being an integral part of selenoproteins participating in the regulation of various physiological processes in the body as discussed by the authors.
Abstract: Selenium (Se) has a special place among the feed-derived natural antioxidants, being an integral part of selenoproteins participating in the regulation of various physiological processes in the bod...
216 citations
TL;DR: Because rice is a staple food in China, selenium-enriched rice obtained by bioenrichment of selenIUM to increase the Se content of rice could be a good seenium source for the population in selenum-deficient regions.
Abstract: A method of hydride generation atomic fluorescence spectrometry was applied to the determination of the selenium concentration of regular polished rice in China and selenium-enriched polished rice obtained by foliar application of selenium-enriched fertilizer in the forms of selenite and selenate. The average selenium content of regular rice was 0.025 +/- 0.011 microg g(-)(1). On the basis of a daily dietary rice intake of 300-500 g suggested by the China Nutrition Society, the total selenium intake from regular rice was calculated to be 7.5-12.5 microg per person per day for an adult. The selenium contents of rice were significantly increased to 0.471-0.640 microg g(-)(1) by foliar application of selenium-enriched fertilizer at rate of 20 g of Se ha(-)(1) in the forms of sodium selenite and sodium selenate. The selenium content of rice by application of a fertilizer of selenate was 35.9% higher than that by a fertilizer of selenite, which showed that Se-enriched fertilizer in selenate exhibited greater efficiency in increasing Se content in rice products. The Se-enriched rice products can increase daily Se intake on average by 100-200 microg of Se per day by the consumption of 400 g of rice products if the Se level of rice products is controlled at 0.3-0.5 microg of Se g(-)(1). Because rice is a staple food in China, selenium-enriched rice obtained by bioenrichment of selenium to increase the Se content of rice could be a good selenium source for the population in selenium-deficient regions.
204 citations
TL;DR: Close contacts between sulfur, selenium, and tellurium centers are used to construct nanotubes in the solid state which are able to host other molecules.
Abstract: Close contacts between sulfur, selenium, and tellurium centers are used to construct nanotubes in the solid state which are able to host other molecules.
202 citations
TL;DR: In this article, the characteristics of selenium in various solvents under solvothermal conditions were investigated in detail and the different dissolution behavior was investigated and a brown homogeneous solution was obtained in ethylenediamine.
Abstract: The characteristics of selenium in various solvents under solvothermal conditions were investigated in detail and the different dissolution behavior of selenium in the solvents identified. A brown homogeneous solution was obtained in ethylenediamine. This solution is metastable and is a suitable selenium feedstock for the preparation of selenides at room temperature. A nucleophilic mechanism is proposed for the formation of metal selenides. Millimeter-scale selenium crystals were obtained in the other solvents, i.e. ethanol, pyridine, benzene, toluene, and carbon tetrachloride (CCl4). XRD and ED patterns indicate that the crystals grew in orientation. SEM images show that these crystals have a tubular hexagonal prism morphology with tubular sizes of ca. 1–1.5 mm in length, 15 µm in diameter and 5 µm in thickness. We also prepared micro-tubular tellurium crystals in ethylenediamine. The growth mechanism of the tubular crystals
is discussed.
TL;DR: In this paper, the authors developed a method for the pre-treatment and determination of antimony, arsenic, cadmium, chromium, lead, mercury and selenium in human hair by inductively coupled plasma mass spectrometry (ICP-MS).
01 Oct 2002-Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment
TL;DR: The chemical species-specific metabolic pathway for Se was explained by the metabolic regulation through selenide as the assumed common intermediate for the inorganic and organic Se sources and as the checkpoint metabolite between utilization for the selenoprotein synthesis and methylation for the excretion of Se.
Abstract: Selenium (Se) is an ultramicro essential nutrient and both inorganic (selenite and selenate) and organic (selenocysteine and selenomethionine) forms of Se can be used as nutritional sources. Metabolic pathways for Se in the body were studied for selenite and selenate, with the use of enriched 82Se, by speciation with separation by gel filtration HPLC and detection by element-specific mass spectrometry with ionization with inductively coupled argon plasma (HPLC-ICP MS). The concentrations of 82Se in organs and body fluids and the distributions of their constituents depending on the dose and time after the intravenous administration of 82Se-selenite and -selenate to rats were determined. Selenite was taken up by red blood cells within several minutes, reduced to selenide by glutathione, and then transported to the plasma, bound selectively to albumin and transferred to the liver. Contrary to selenite, intact selenate was either taken up directly by the liver or excreted into the urine. The 82Se of selenite origin and that of selenate origin were detected in the forms of the two Se peak materials in the liver, A and B. The former one was methylated to the latter in vivo and in vitro. The latter one was identical with the major urinary metabolite and it was identified as Se-methyl-N-acetyl-selenohexosamine (selenosugar). The chemical species-specific metabolic pathway for Se was explained by the metabolic regulation through selenide as the assumed common intermediate for the inorganic and organic Se sources and as the checkpoint metabolite between utilization for the selenoprotein synthesis and methylation for the excretion of Se.
TL;DR: The reduction of Se in the liver and plasma during APR may be associated with the increased CRP synthesis in the Liver by inducing acute phase response (APR) in rats by injection of lipopolysaccharide.
TL;DR: The occurrence of multiple mechanisms involving different enzymes for arsenic and selenium transformation indicates several different evolutionary pathways and underscores the environmental significance and selective impact in microbial evolution of these two elements.
Abstract: Microbial activity is responsible for the transformation of at least one third of the elements in the periodic table. These transformations are the result of assimilatory, dissimilatory, or detoxification processes and form the cornerstones of many biogeochemical cycles. Arsenic and selenium are two elements whose roles in microbial ecology have only recently been recognized. Known as "essential toxins", they are required in trace amounts for growth and metabolism but are toxic at elevated concentrations. Arsenic is used as an osmolite in some marine organisms while selenium is required as selenocysteine (i.e. the twenty-first amino acid) or as a ligand to metal in some enzymes (e.g. FeNiSe hydrogenase). Arsenic resistance involves a small-molecular-weight arsenate reductase (ArsC). The use of arsenic and selenium oxyanions for energy is widespread in prokaryotes with representative organisms from the Crenarchaeota, thermophilic bacteria, low and high G+C gram-positive bacteria, and Proteobacteria. Recent studies have shown that both elements are actively cycled and play a significant role in carbon mineralization in certain environments. The occurrence of multiple mechanisms involving different enzymes for arsenic and selenium transformation indicates several different evolutionary pathways (e.g. convergence and lateral gene transfer) and underscores the environmental significance and selective impact in microbial evolution of these two elements.
TL;DR: The selenium concentration of representative bread-making wheat (Triticum aestivum L) samples was measured in national grain surveys collected in 1982, 1992 and 1998 from major wheat-growing regions around the UK.
Abstract: The selenium concentration of representative bread-making wheat (Triticum aestivum L) samples was measured in national grain surveys collected in 1982 (n (number of samples) = 180), 1992 (n = 187) and 1998 (n = 85) from major wheat-growing regions around the UK. The means and distributions of selenium concentrations over the three years were similar, with mean grain concentrations of 0.025, 0.033 and 0.025 mg kg−1 dry weight respectively and inter-quartile ranges varying from 0.015 mg kg−1 in 1982 to 0.019 mg kg−1 in 1992 samples. No long-term changes in the distribution of wheat selenium concentrations were found over the 17 year period. Geographical mapping of the concentrations identified an area of eastern England as having high grain concentrations compared with other UK regions. There were no significant correlations between grain selenium and grain sulphur concentrations for the national survey samples. However, at an individual field experimental site, increasing the rate of sulphur addition was found to decrease grain selenium concentration significantly. The daily UK dietary contribution of selenium from wheat-based products was estimated and the daily intake was calculated to be 6.4 µg selenium, around one-tenth of the UK recommended intake values for men and women.
© 2002 Society of Chemical Industry
TL;DR: Although there is evidence that supplementation with anti-oxidant vitamins shown some promise with Alzheimer's patients, and in preventing the development of tardive dyskinesia in schizophrenics taking neuroleptics, a role for selenium has been little considered.
Abstract: Selenium is an essential trace element although the level of selenium in food items reflects the soil in which they were grown and thus varies markedly between different parts of the world. The metabolism of selenium by the brain differs from other organs in that at times of deficiency the brain retains selenium to a greater extent. The preferential retention of selenium in the brain suggests that it plays important functions. To date mood is the clearest example of an aspect of psychological functioning that is modified by selenium intake. Five studies have reported that a low selenium intake was associated with poorer mood. The underlying mechanism is unclear although a response to supplementation was found with doses greater than those needed to produce maximal activity of the selenoprotein glutathione peroxidase. Although the functions of many selenoproteins are unknown some play important roles in anti-oxidant mechanisms. As there are suggestions that oxidative injury plays a role in normal aging, schizophrenia, Parkinson's and Alzheimer's disease, the possible role of selenium is considered. Although there is evidence that supplementation with anti-oxidant vitamins shown some promise with Alzheimer's patients, and in preventing the development of tardive dyskinesia in schizophrenics taking neuroleptics, a role for selenium has been little considered.
TL;DR: Various sample preparation approaches are examined with the goal of species preservation and subsequent selenium speciation; of these approaches, an enzymatic treatment with Proteinase K proved most effective.
Abstract: Brazil nuts have been classified as the foodstuffs that contain the highest level of unadulterated selenium, an essential trace element that appears to prevent cancer. To date, characterization of the selenium species in brazil nuts has not yet been investigated. In this work, various sample preparation approaches, including microwave extractions and enzymatic treatments, are examined with the goal of species preservation and subsequent selenium speciation; of these approaches, an enzymatic treatment with Proteinase K proved most effective. High-performance liquid chromatography (HPLC) separation strategies and inductively coupled plasma mass spectrometry (ICP-MS) detection schemes will also be presented. Extracts are evaluated against available standards for the commercially obtainable seleno-amino acids, selenomethionine (SeMet), selenoethionine (SeEt), and selenocystine (SeCys); selenomethionine was demonstrated to be the most abundant of these seleno-amino acids. Further characterization of unidentified selenium-containing peaks is attempted by the employment of several procedures, including electrospray-mass spectrometry (ES-MS). A peptide structure was identified; however, this was considered a tentative proposal due to the large background produced by the extremely complicated brazil nut matrix.
TL;DR: The interaction between inorganic mercury and sodium selenite, the most extensively studied, as well as the interaction between methylmercury (MeHg) and selenium, the interaction perhaps most significant for non-occupational human populations, will be discussed.
Abstract: The interaction between mercury and selenium may involve a variety of toxicologically and biochemically distinct processes. In this paper, the interaction between inorganic mercury and sodium selenite, the interaction most extensively studied, as well as the interaction between methylmercury (MeHg) and selenium, the interaction perhaps most significant for non-occupational human populations, will be discussed. It has been shown that the former interaction can be understood as a modification of the kinetic behavior of inorganic mercury by selenite, but this interaction may occur only under very limited conditions. On the other hand, the mechanism of the latter interaction is largely unknown, and kinetic modification appears to play only a minor role. An interaction between MeHg and selenoproteins or a possible interaction between the inorganic mercury, resulting from the demethylation of MeHg, and the selenium may be important. Compared to the experimental findings, little evidence of the toxicological modification of MeHg by selenium was obtained in epidemiological studies.
TL;DR: The essential nature of selenium as well as its toxicity depend on the concentration and the chemical forms in which this element is present in a given sample as mentioned in this paper, which is a summary of recent research on the determination of SE in environmental samples such as water, air, soil and plants.
Abstract: The essential nature of selenium as well as its toxicity depend on the concentration and the chemical forms in which this element is present in a given sample. Dissolved inorganic selenium can be found in natural water and soil as selenides, selenite and selenate. Organoselenium compounds present in air, soil and plants are volatile methylselenides, trimethylselenonium ion and several selenoamino acids. This review is a summary of recent research on the determination of selenium species in environmental samples such as water, air, soil and plants. Stability of selenium species in solutions and their storage is also discussed. In the metabolic pathway in the body selenide could act as the common intermediate for inorganic and organic Se sources as well as the checkpoint between further utilisation and excretion of selenium.
TL;DR: In this initial study, the possible identification (by ES-MS) of a small chromatographic peak containing a Se-S bridged seleno amino acid with a structure similar to cystine is suggested.
Abstract: Various Brassica species accumulate Se into the thousands of ppm. This suggests some of them as candidates for Se phytoremediation. Brassica juncea (Indian mustard) was used to accumulate selenium by growing with sodium selenite as the selenium source under hydroponic conditions resulting in Se accumulation of up to hundreds of ppm in various parts of the plant. To date, few selenium speciation studies have been done in plants, with most studies reporting total selenium concentration in various parts of the plant. Se species extraction was evaluated by several digestion/extraction procedures, including the use of HCl, Tris-HCl buffer, and enzymatic hydrolysis (using proteinase K and protease XIV). The best extraction was obtained with proteinase K (extracting ∼75% of the total Se present in the plant). Some of the species produced by the plant, such as selenomethionine, can be identified at ppb levels by RP-HPLC−ICPMS, since standards are readily available. Others needed to be further characterized by ES-...
TL;DR: This work has developed a route for the synthesis of 2'-selenium uridine analogues and oligonucleotides containing selenium labels, and demonstrated for the first time a new strategy to covalently derivatize nucleotides with seenium for phase and structure determination in X-ray crystallography.
Abstract: We have developed a route for the synthesis of 2'-selenium uridine analogues and oligonucleotides containing selenium labels, and have demonstrated for the first time a new strategy to covalently derivatize nucleotides with selenium for phase and structure determination in X-ray crystallography.
TL;DR: Results obtained for Brazil nuts by size-exclusion chromatography with on-line ICP–MS detection, in the absence and in the presence of β-mercaptoethanol, showed that approximately 12% of total selenium was weakly bound to proteins.
Abstract: In addition to determination of total selenium in nuts, the element distribution among different fractions (lipid extract, low molecular weight, and protein fractions), and speciation analysis were studied. Improved precision for total selenium determination was observed after elimination of lipids. Because selenium was not detected in any of the lipid extracts obtained from the different types of nuts (ICP–MS), in each determination and/or speciation procedure used in this work lipids were extracted (chloroform–methanol, 2:1) and discarded before analysis. In agreement with previously reported data, high selenium levels were found in Brazil nuts (those purchased without shells contained approximately a quarter the content than those purchased with shells) and significantly lower levels in walnuts, cashews, and pecans nuts. Low-molecular-weight compounds were extracted with perchloric acid (0.4 mol L–1) to furnish a fraction containing 3 to 15% of the total selenium in different types of nuts. The proteins were isolated from nut samples by dissolution in 0.1 mol L–1 sodium hydroxide and subsequent precipitation with acetone. They were then dissolved in phosphate buffer pH 7.5. Analysis of protein fractions focused on selenium in two possible states – weakly and firmly bound to proteins. Results obtained for Brazil nuts by size-exclusion chromatography with on-line ICP–MS detection, in the absence and in the presence of β-mercaptoethanol, showed that approximately 12% of total selenium was weakly bound to proteins. To obtain information about firmly bound selenium, the protein extracts were hydrolyzed enzymatically with proteinase K. Speciation was performed by means of ion-pairing HPLC–ICP–MS. The primary species found in all types of nuts was Se-methionine (19–25% of total selenium for different types of nuts).
TL;DR: Results suggest that aza-dC treatment may protect selenium-deficient rats against carcinogen-induced aberrant crypt formation.
Abstract: Several observations implicate a role for altered DNA methylation in cancer pathogenesis. The global level of DNA methylation is generally lower; however, DNA methyltransferase (Dnmt1) activity is usually higher in tumor cells than in normal cells. The purpose of this study was to investigate whether the Dnmt1 inhibitor, 5-aza-2'-deoxycytidine (aza-dC) would alter the effect of dietary selenium on the formation of aberrant crypts. Weanling rats (n = 60) were fed three concentrations of selenium (deficient, 0.1 and 2.0 mg/kg diet) in a Torula yeast-based diet. Half of the rats were injected weekly with aza-dC (1 mg/kg, subcutaneously) and half were injected with the vehicle control (PBS). After 3.5 wk of consuming the experimental diets, the rats were given two injections of dimethylhydrazine (DMH; 25 mg/kg, intraperitoneally). Rats fed the selenium-deficient diet and injected with PBS had significantly (P < 0.006) more aberrant crypts than rats fed 0.1 or 2.0 mg selenium/kg diet (244 +/- 21 vs. 165 +/- 9 and 132 +/- 14, respectively). In contrast, when rats were injected with aza-dC, there was a significant (P < 0.0001) reduction in aberrant crypt formation and dietary selenium had no effect (62 +/- 8 vs. 77 +/- 13 vs. 54 +/- 8, in rats fed 0, 0.1 and 2.0 mg selenium/kg diet, respectively). HT-29 cells cultured in the absence of selenium had significantly hypomethylated DNA but significantly more Dnmt1 protein expression than cells cultured in the presence of 1 or 2 micromol/L selenium. These results suggest that aza-dC treatment may protect selenium-deficient rats against carcinogen-induced aberrant crypt formation.
Patent•
31 Jan 2002
TL;DR: In this article, a patterned mass comprising elemental silver over a substrate is formed over the substrate and a germanium selenide comprising material is provided in electrical connection with another portion of the patterning mass comprising silver.
Abstract: A method of forming a non-volatile resistance variable device includes forming a patterned mass comprising elemental silver over a substrate. A layer comprising elemental selenium is formed over the substrate and including the patterned mass comprising elemental silver. The substrate is exposed to conditions effective to react only some of the elemental selenium with the elemental silver to form the patterned mass to comprise silver selenide. Unreacted elemental selenium is removed from the substrate. A first conductive electrode is provided in electrical connection with one portion of the patterned mass comprising silver selenide. A germanium selenide comprising material is provided in electrical connection with another portion of the patterned mass comprising silver selenide. A second conductive electrode is provided in electrical connection with the germanium selenide comprising material.
TL;DR: A novel role for selenium at 0.25 micromol/L in up-regulation of the expression of numerous cell cycle-related genes and total cellular phosphorylated proteins in HL-60 cells in serum-free culture media is suggested.
Abstract: The essential role of selenium (Se) in nutrition is well established. The elucidation of the mechanisms by which selenium regulates the cell cycle can lead to a better understanding of the nature of selenium's essentiality and its role in disease prevention. In this study, the effects of selenium deficiency or adequacy (0.25 micromol/L selenite or selenomethionine) on HL-60 cell cycle progression were examined in serum-free media. Selenium was critical for promotion of HL-60 cell growth. Cell-cycle analysis revealed that selenium deficiency caused a decrease in G1 phase cells that corresponded to an increase in G2 and sub-G1 phase cells. Gene array analysis suggested that c-Myc, cyclin C, proliferating cell nuclear antigen, cyclin-dependent kinase (cdk)1, cdk2, cdk4, cyclin B and cyclin D2 mRNA levels were lower in selenium-deficient cells than in the cells supplemented with 0.25 micromol/L selenomethionine. The decrease in the c-Myc mRNA level in selenium-deficient cells was confirmed by reverse transcription-polymerase chain reaction analysis. Furthermore, the phosphorylation state of total cellular protein was higher (57%) in selenium-supplemented cells than in selenium-deficient cells. Collectively, these results suggest a novel role for selenium at 0.25 micromol/L in up-regulation of the expression of numerous cell cycle-related genes and total cellular phosphorylated proteins in HL-60 cells in serum-free culture media. This leads to the promotion of cell cycle progression, particularly G2/M transition and/or the reduction of apoptosis, primarily in G1 cells. These observations may have additional implications for understanding the nature of selenium's essentiality.
TL;DR: The results of this study support the use of selenium agents in colon cancer chemoprevention trials and suggest that Se-Met-induced cell growth inhibition may be, in part, mediated by COX-2 dependent mechanisms.
Abstract: Currently, selenium (in the form of high selenium containing yeast or selenomethionine) is being evaluated for anticancer effects against both human colon polyp recurrence and human prostate cancer, respectively. Chemical speciation analysis of the high selenium containing yeast indicates that selenomethionine (SeMet) is a major constituent of selenized yeast. We tested the hypothesis that SeMet might affect colon cancer cell growth by mechanisms involving cyclooxygenases (COX). The growth of all four-colon cancer cell lines tested was inhibited by selenomethionine. Furthermore, selenomethionine decreased COX-2 protein and PGE2 levels in HCA-7 cells. Selenomethionine suppressed COX-2 RNA levels in HCA-7 cells which could account for decreased COX-2 protein levels. Finally, the addition of PGE2 protected cells from the antiproliferative effects of selenomethionine in a concentration dependent manner. Selenomethionine might regulate COX-2 at the transcriptional level. These data suggests that Se-Met-induced cell growth inhibition may be, in part, mediated by COX-2 dependent mechanisms. The results of this study support the use of selenium agents in colon cancer chemoprevention trials.
TL;DR: Serious nutritional changes are significantly higher in older children than in infants under 1 year of age, and the application of age-adjusted reference values may provide more specific criteria for selenium supplementation.
Abstract: Background: Children are at particular risk for selenium deficiency, which has potentially serious medical implications. Reliable age-specific reference values for serum selenium concentrations in children are sparse, but are essential for the identification of selenium deficiency and decisions regarding selenium supplementation.
Methods: Using electrothermal atomic absorption spectrometry, we analyzed serum selenium concentrations from 1010 apparently healthy children (age range, 1 day to 18 years) and from 60 patients on a protein-restricted diet because of inborn errors of metabolism. Reference intervals were defined according to recommended guidelines.
Results: Medians for serum selenium concentrations showed a statistically significant age dependency: a decrease from the age <1 month (0.64 μmol/L) to 4 months (0.44 μmol/L); an increase to 0.62 μmol/L in the 4–12 months age group; constant values in children between 1 and 5 years of age (0.90 μmol/L); and an additional slight increase to reach a plateau between 5 and 18 years (0.99 μmol/L). Of 43 children older than 1 year and on a protein-restricted diet, 87% showed serum selenium concentrations below the 2.5 percentile.
Conclusions: Because of nutritional changes, serum selenium concentrations are significantly higher in older children than in infants under 1 year of age. The application of age-adjusted reference values may provide more specific criteria for selenium supplementation. Long-term protein restriction in children is reflected by a failure to achieve higher serum selenium concentrations with increasing age.
01 Jan 2002
TL;DR: Tellurite- and selenite-reducing strains were isolated in high numbers from ocean water near hydrothermal vents, bacterial films, and sulfide-rich rocks, and found to be salt tolerant, pH tolerant, and thermotolerant.
Abstract: Deep-ocean hydrothermal-vent environments are rich in heavy metals and metalloids and present excellent sites for the isolation of metal-resistant microorganisms. Both metalloid-oxide-resistant and metalloid-oxidereducing bacteria were found. Tellurite- and selenite-reducing strains were isolated in high numbers from ocean water near hydrothermal vents, bacterial films, and sulfide-rich rocks. Growth of these isolates in media containing K2TeO3 or Na2SeO3 resulted in the accumulation of metallic tellurium or selenium. The MIC of K2TeO3 ranged from 1,500 to greater than 2,500 g/ml, and the MIC of Na2SeO3 ranged from 6,000 to greater than 7,000 g/ml for 10 strains. Phylogenetic analysis of 4 of these 10 strains revealed that they form a branch closely related to members of the genus Pseudoalteromonas, within the -3 subclass of the Proteobacteria. All 10 strains were found to be salt tolerant, pH tolerant, and thermotolerant. The metalloid resistance and morphological, physiological, and phylogenetic characteristics of newly isolated strains are described. Selenium (Se), a naturally occurring element, is essential for biological systems at low concentrations and toxic at higher levels. Under aerobic conditions Se is present in several redox forms, including the elemental form Se; however, it exists predominantly in the high-valence toxic and soluble forms selenate (Se VI O4 2 ) and selenite (Se IV O3 2 ) (4). The roles of
TL;DR: Analysis of the proteomic response of Escherichia coli cells to selenate and selenite treatment under aerobic conditions indicates that superoxide dismutase activity is essential for the cellular defense against selenium salts, suggesting thatsuperoxide production is a major mechanism of seenium toxicity under aerobic Conditions.
Abstract: Selenium can provoke contrasting effects on living organisms. It is an essential trace element, and low concentrations have beneficial effects, such as the reduction of the incidence of cancer. However, higher concentrations of selenium salts can be toxic and mutagenic. The bases for both toxicity and protection are not clearly understood. To provide insights into these mechanisms, we analyzed the proteomic response of Escherichia coli cells to selenate and selenite treatment under aerobic conditions. We identified 23 proteins induced by both oxides and ca. 20 proteins specifically induced by each oxide. A striking result was the selenite induction of 8 enzymes with antioxidant properties, particularly the manganese and iron superoxide dismutases (SodA and SodB). The selenium inductions of sodA and sodB were controlled by the transcriptional regulators SoxRS and Fur, respectively. Strains with decreased superoxide dismutase activities were severely impaired in selenium oxide tolerance. Pretreatment with a sublethal selenite concentration triggered an adaptive response dependent upon SoxRS, conferring increased selenite tolerance. Altogether, our data indicate that superoxide dismutase activity is essential for the cellular defense against selenium salts, suggesting that superoxide production is a major mechanism of selenium toxicity under aerobic conditions.