Showing papers on "Selenium published in 1996"

Selenium metabolism and bioavailability.

Abstract: Selenium (Se) is at once an essential and toxic nutrient that occurs in both inorganic and organic forms. The biological functions of Se are mediated through at least 13 selenoproteins that contain Se as selenocysteine (Se-cyst). The endogenous synthesis of this amino acid from inorganic Se (selenide Se-2) and serine is encoded by a stop codon UGA in mRNA and involves a unique tRNA. Selenium can also substitute for sulfur in methionine to form an analog, selenomethionine (Se-meth), which is the main form of Se found in food. Animals cannot synthesize Se-meth or distinguish it from methionine and as a result it is nonspecifically incorporated into a wide range of Se-containing proteins. The metabolic fate of Se varies according to the form ingested and the overall Se status of an individual. This paper reviews the bioavailability, including absorption, transport, metabolism, storage, and excretion, of the different forms of exogenous and endogenous Se.

Bioavailability of Minerals and Trace Elements

Abstract: In this review a brief summary will be given of the food sources, absorptive mechanism and subsequent metabolism of the nine mineral and trace element identified as being nutritionally important (calcium, chromium, cuivre, iodine, iron, magnesium, manganese, selenium, zinc)

Selenoprotein P Concentration in Plasma is an Index of Selenium Status in Selenium-Deficient and Selenium-Supplemented Chinese Subjects

Abstract: Selenoprotein P, a selenium-rich plasma protein, is an index of selenium status in rats. Antibodies against human selenoprotein P were raised to study the protein and to develop a radioimmunoassay for it. A single collection of plasma from a healthy person in the United States contained 1.84 mumol selenium/L and was defined as containing 1 Unit (U) selenoprotein P/L. Removal of selenoprotein P from the reference plasma by an antibody column indicated that 0.81 mumol selenium/L, or 44% of the plasma selenium, was present as selenoprotein P. Work by others had determined that glutathione peroxidase accounted for 12% of plasma selenium. Stored plasma samples from selenium-deficient (Dechang County) and selenium-supplemented (Mianning County) populations in China were assayed for selenoprotein P. Boys aged 8-12 y had selenoprotein P concentrations of 0.10 +/- 0.04 U/L (n = 22) in Dechang and 0.39 +/- 0.17 U/L (n = 17) in Mianning. Supplementation with 100 micrograms selenium as selenate per day for 14 d raised those levels to 0.51 +/- 0.13 U/L in Dechang and to 0.76 +/- 0.27 U/L in Mianning. Similar results were obtained in men, and plasma selenium concentrations correlated with selenoprotein P concentrations. A study comparing indices of selenium status was conducted in the two counties. Selenoprotein P concentration in Dechang subjects (n = 79) was 36% of that in Mianning subjects (n = 117). For plasma glutathione peroxidase activity the value was 54%; for plasma selenium, 47%; and for whole blood selenium, 64%. We conclude that selenoprotein P is the major selenoprotein in human plasma and that its concentration is an index of selenium nutritional status that appears to be as sensitive as other indices in common use.

On the Mechanism of Selenium Tolerance in Selenium-Accumulating Plants

Abstract: Selected members of the genus Astragulus (Fabaceae) are known for their ability to accumulate high levels of selenium, mainly in the form of Se-methyl-selenocysteine. With the aid of cell cultures we have investigated the molecular basis for selenium tolerance of these plants. It is shown that cultured cells from a selenium-accumulating Astragalus species synthesize Se-methyl-selenocysteine in contrast to those of a non-accumulating species and do not unspecifically incorporate selenium into proteins. The purification and biochemical characterization of a selenocysteine methyltransferase from cultured Astragalus bisculatus cells is described, which does not accept cysteine as a substrate. We propose that this enzyme plays a crucial role in conferring selenium tolerance.

Use of selenium concentration in whole blood, serum, toenails, or urine as a surrogate measure of selenium intake.

Abstract: We examined the validity of using the selenium level in a single biological specimen as a surrogate measure of usual intake. We used data from 77 free-living adults from South Dakota and Wyoming. Subjects provided multiple 1-day duplicate-plate food composites, repeated specimens of blood and toenails, and 24-hour urine collections. We developed a statistical calibration method that incorporated measurement error correction to analyze the data. The Pearson correlation coefficients between selenium intake and a single selenium status measure, after deattenuation to adjust for the effect of within-person variation in intake, were: 0.78 for whole blood, 0.74 for serum, 0.67 for toenails, and 0.86 for urine. We present formulas to estimate the intake of individuals, based on selenium levels in a single specimen of blood, toenails, or urine. In these data, the concentration of selenium in a single specimen of whole blood, serum, or toenails served reasonably well as a measure for ranking subjects according to long-term selenium intake but provided only a rough estimate of intake for each subject.

Selenium as a risk factor for cardiovascular diseases.

Abstract: Selenium is a powerful antioxidant regulating the activity of the glutathione peroxidase enzymes, which catalyse the detoxification of hydrogen peroxide and organic hydroperoxides. Selenium deficiency has been implicated in the aetiopathogeny of Keshan disease, an endemic cardiomyopathy observed in China, and in other cases of congestive cardiomyopathy in subjects on artificial nutrition. However, the evidence from case-control and prospective studies for an association between low selenium status and cardiovascular diseases remains controversial. Mechanisms whereby selenium protects against such diseases include increased resistance of low-density lipoproteins against oxidative modification, modulation of prostaglandin synthesis and platelet aggregation, and protection against toxic heavy metals. The therapeutic benefit of selenium administration in the prevention and treatment of cardiovascular diseases still remains insufficiently documented.

Intracellular storage of mercury and selenium in different marine vertebrates

Abstract: Intracellular storage and levels of mercury and selenium were studied in the livers of top marine predators belong~ng to different vertebrate taxa. Total mercury levels showed very important interspecific variations, ranging from 2.6 pg g.' In tuna and swordfish to several thousand pg g-' (dry weight) in bottle-nosed and Risso's dolphins. However, methylmercury was less variable, ranging from 1 to 174 pg g.' (dry weight). The ratio between Hg and Se levels was close to equimolarity in marine mammals and cormorants, but a large excess of selenium in relation to mercury was observed in fish. Electron microscopy and x-ray microanalysis revealed mineral granules consisting of clustered crystalline particles in toothed cetaceans, sea llons and cormorants but not in tuna and swordfish. Granules containing mercury and selenium were malnly located in the cytoplasm of macrophages. These results suggest that the blosynthesis of mineral granules containing mercury and selenium in top marine predators is a common feature among these animals and that the existence of elimination pathways for the excretion of organic mercury might Influence the amount of mercury and selenium stored a s mineral granules in a particular species.

Selenium Fractionation and Speciation in a Wetland System

Abstract: Selenium fractionation and speciation in Benton Lake National Wildlife Refuge (Montana), a wetland system containing moderate levels of selenium, were studied to determine the biogeochemical processes of selenium in wetlands. Results showed that selenate was a major selenium species of dissolved selenium in drainage water. It decreased substantially through the pond system as the relative percentages of organic selenium and selenite increased. Elemental selenium and selenium associated with organic materials were the major fractions in sediments, accounting for a mean of 46% and 33% of total selenium, respectively. Concentrations of soluble selenium and adsorbed selenium were relatively low, respectively accounting for a mean of 5% and 13%. Within the soluble and adsorbed fraction of selenium in sediment, selenate and organic selenium were the major selenium species. Selenium associated with oxides was very low (less than 4%). In this wetland environment, microbial reduction of selenate to elemental selen...

Pilot-scale selenium bioremediation of San Joaquin drainage water with Thauera selenatis

Abstract: This report describes a simple method for the bioremediation of selenium from agricultural drainage water. A medium-packed pilot-scale biological reactor system, inoculated with the selenate-respiring bacterium Thauera selenatis, was constructed at the Panoche Water District, San Joaquin Valley, Calif. The reactor was used to treat drainage water (7.6 liters/min) containing both selenium and nitrate. Acetate (5 mM) was the carbon source-electron donor reactor feed. Selenium oxyanion concentrations (selenate plus selenite) in the drainage water were reduced by 98%, to an average of 12 (plusmn) 9 (mu)g/liter. Frequently (47% of the sampling days), reactor effluent concentrations of less than 5 (mu)g/liter were achieved. Denitrification was also observed in this system; nitrate and nitrite concentrations in the drainage water were reduced to 0.1 and 0.01 mM, respectively (98% reduction). Analysis of the reactor effluent showed that 91 to 96% of the total selenium recovered was elemental selenium; 97.9% of this elemental selenium could be removed with Nalmet 8072, a new, commercially available precipitant-coagulant. Widespread use of this system (in the Grasslands Water District) could reduce the amount of selenium deposited in the San Joaquin River from 7,000 to 140 lb (ca. 3,000 to 60 kg)/year.

Selenium and fertility in animals and man--a review.

Abstract: To evaluate the information on selenium with relation to fertility in animals and man the available literature was reviewed. Selenium is incorporated in the sperm mitochondria capsule and may thus affect the behavior and function of the spermazoon. Se seems to be essential for normal spermatozoa development in both experimental animals and in livestock and probably also in humans. Regarding selenium and female fertility only sparse information exists. In experimental animals a low selenium level affects fertility in males, but little attention has been devoted to female reproductive performance, and the data are insufficient for conclusion. In livestock numerous investigations have been performed and the effects of selenium supplementation often in combination with other antioxidants have been evaluated, but no valid conclusion can be drawn. In general adequate nutritional supply will secure optimal reproduction in both males and females, while additional supplementation seems to have a negative effect. In humans contradictive information is found. Both low and high sperm selenium concentrations are reported to have a negative influence on the number of spermatozoa and on the motility. The optimal sperm selenium concentration waits to be defined. Some evidence indicates that a metabolic defect in a selenium incorporation into sperm cells may be associated with human infertility. No human data relating selenium to female infertility were found.

Selenium-mediated inhibition of transcription factor NF-kappa B and HIV-1 LTR promoter activity.

Abstract: The eukaryotic transcription factor NF-κB is involved in the inducible expression of various inflammatory genes as well as in HIV-1 replication. Activation of NF-κB is induced by prooxidants and several stimuli eliciting oxidative stress, such as cytokines, lipopolysaccharide, UV irradiation and other mediators. Various antioxidants inhibit NF-κB activation in response to these stimuli. In this study, we have investigated the effects of selenium, an integral component of glutathione peroxidase (GPX), on NF-κB activation. In selenium-deprived Jurkat and ESb-L T lymphocytes, supplementation of selenium led to a substantial increase of GPX activity. Analysis of DNA binding revealed that NF-κB activation in response to TNF was significantly inhibited under these conditions. Likewise, reporter gene assays using luciferase constructs driven by the HIV-1 long terminal repeat showed a dose-dependent inhibition of NF-κB controlled gene expression by selenium. The effects of selenium were specific for NF-κB, since the activity of the transcription factor AP-1 was not suppressed. These data suggest that selenium supplementation may be used to modulate the expression of NF-κB target genes and HIV-1.

Metabolism of subtoxic levels of selenium in animals and humans

Abstract: Since high levels of selenium are used as cancer chemopreventive agents in animals and humans, a better understanding of the metabolism of subtoxic levels is desirable. Absorption from rat small intestine using in situ double perfusion, ligated intestinal segments, and brush border membrane vesicles (BBMV) was used to study selenium absorption. A level of 1.2 mM intraluminal selenite was required to inhibit 50 percent of the transepithelial transport of 3-0-methylglucose, indicating a high tolerance of the intestinal tract to selenium. The relative efficiency patterns for uptake of different selenocompounds during in vitro perfusion and in vivo ligated segments were identical with selenomethionine (SeMet) > selenate > selenite. In contrast, selenite was taken up most rapidly by BBMV, followed by SeMet and selenate in decreasing order. Ligated segments, double perfusion experiments, and uptake by BBMV indicated that selenium as selenodiglutathione or selenodicysteine was taken up faster than when present as selenite. Selenate and SeMet appeared in the vascular effluent largely unchanged, but selenite was metabolized extensively during absorption. Most of the selenium in plasma from subjects living in a high selenium area of China was associated with albumin, which is likely a result of high dietary intake of SeMet. Cracked fingernails and extensive hair loss were the symptoms of selenium toxicity in these individuals. Low adverse effect level of dietary (mean LOAEL) selenium was calculated to be about 1540 +/- 653 micrograms per day (or 28 micrograms/kg body weight) and the maximum safe dietary (mean NOAEL) selenium was calculated to be 819 +/- 126 micrograms per day (or 15 micrograms/kg body weight).

Antimicrobial composition composed of controlled release glasses

Abstract: There is provided an antimicrobial composition for combatting infections. The material is a controlled release glass having two or more agents selected from the group consisting of metals, selenium and boron. Preferably the agents are selected from the group consisting of copper, silver, magnesium, zinc, cerium, manganese bismuth, selenium and boron. The combinations of copper and silver and of copper and zinc are particularly preferred and exhibit synergistic activity. The antimicrobial composition is effective against infections due to Proteus spp.

Investigation of selenium speciation in in vitro gastrointestinal extracts of cooked cod by high-performance liquid chromatography–inductively coupled plasma mass spectrometry and electrospray mass spectrometry

Abstract: As part of an ongoing study of Se bioavailability from the human diet, Se was determined in cooked cod and in enzyme extracts of cooked cod. Total Se was measured by direct nebulization ICP-MS and standard additions, following digestion with HNO3 in stainless steel pressure decomposition vessels. The concentration of Se in the cod was 1.52 mg kg–1 with an LOD of 0.008 mg kg–1. An in vitro gastrointestinal enzymolysis procedure was used to extract Se species from the cooked cod. HPLC, using an anion-exchange column, was used to separate Se standards (selenomethionine, selenocystine, sodium selenite and sodium selenate) and the species soluble in the gastrointestinal extract (pH 6.8). The 82Se signal was used to quantify the individual Se species. In the extracts of cooked cod, approximately 12% of total Se was thought to be selenite whilst the remaining Se eluted at a retention time different to that of any of the Se standards measured. However, as the retention time was close to that of selenomethionine, it was suggested that the Se-containing species was organic rather than inorganic. A similar peak was also found in the enzyme blanks. In order to gain further information as to the identity of the unknown species, the samples and standards were subjected to electrospray-MS (ES-MS) in both positive and negative ionization modes. Although the four standards were amenable to analysis by ES-MS, more work is required to improve the sensitivity of the system. This will involve modifying the chromatography for both ICP-MS and ES-MS.

Selenium capture using sorbent powders: Mechanism of sorption by hydrated lime

Abstract: This study investigates the potential of mineral sorbents to capture selenium which is sufficiently volatile to occur in the flue gas in vapor state. The sorption studies are conducted in a high-temperature reactor using SeO{sub 2} as the source of selenium. In both high (800-1000{degree}C) and medium-temperature (400-700{degree}C) range, hydrated lime exhibits superior selenium sorption capability compared to other sorbent powders. The results show that the mechanism of capture by CA(OH){sub 2} is not a simple physical adsorption process but seems to involve a chemical reaction between CaO and SeO{sub 2}. The medium temperature range of 400-600{degree}C is favorable for the reaction to occur and leads to high selenium sorption. At higher temperatures, thermodynamic equilibrium aids dissociation of the reaction product, and the amount of metal capture reduces drastically with increasing temperature. XRD studies further confirm that calcium selenite is the dominant reaction product. 15 refs., 7 figs., 1 tab.

Influence of zinc and selenium deficiency on parameters relating to thyroid hormone metabolism.

Abstract: 48 weaned male Sprague-Dawley rats with an initial average body weight of 41 g were divided into 4 groups of 12 animals (zinc-deficient; zinc-adequate, pair-fed with zinc-deficient group; selenium-deficient; selenium-adequate) for 40 days. All groups were fed a semisynthetic diet with casein being the source of protein. In the selenium-deficient diet, there was a selenium concentration of 0.038 mg/kg. The other diets were supplemented with Na-selenite in order to adjust the selenium concentration to 0.3 mg/kg. In the zinc-deficient diet, there was a zinc concentration of 4.1 mg/kg. The zinc concentrations in the other diets were adjusted to 45 mg/kg by the addition of zinc-sulfate heptahydrate. Zinc-deficient rats were characterized by a markedly reduced alkaline phosphatase activity in their serum, whilst selenium-deficient rats showed a markedly reduced glutathione peroxidase in serum proving their respective zinc-deficient and selenium-deficient states. Zinc deficiency decreased concentrations of triiodothyronine (T3) and free thyroxine (fT4) in serum by approximately 30% when compared with zinc-adequate controls. The concentration of thyroxine (T4) in serum was not affected by zinc deficiency. Selenium-deficient animals had lower concentrations of T3 and T4 than selenium-adequate animals. The concentration of fT4 in serum was not affected by selenium deficiency. The activity of hepatic type I 5'deiodinase was decreased by 67% by zinc deficiency and by 47% by selenium deficiency compared to adequate controls. The study data show that both zinc and selenium deficiency affect the metabolism of thyroid hormones.

Selenite and Selenate Inhibit Human Lymphocyte Growth via Different Mechanisms

Abstract: Selenium compounds like selenite and selenate have strong inhibitory effects, particularly on mammalian tumor cell growth by unknown mechanisms We found that the addition of sodium selenite and sodium selenate inhibited the growth of human 3B6 and BL41 lymphocytes Selenite was more potent because 10 microM selenite produced a growth inhibitory effect similar to that of 250 microM selenate The mechanism of action of selenite and selenate appears to be different 3B6 and BL41 cells treated with selenite accumulated in the S-phase; however, selenate caused an accumulation of cells in G2 Selenite-mediated growth inhibition was irreversible, although the effects of selenate could be reversed Selenite, in contrast to selenate, is efficiently reduced by the thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH) At concentrations required to observe a similar effect on cell growth, the activity of thioredoxin reductase, recently shown to be a selenoprotein, increased in selenite-treated cells and decreased in selenate-treated cells Ribonucleotide reductase activity was inhibited in an in vitro assay by selenite and selenodiglutathione but not by selenate These results show that selenite and selenate use different mechanisms to inhibit cell growth

Speciation of inorganic selenium and selenoaminoacids by on-line reversed-phase high-performance liquid chromatography–focused microwave digestion–hydride generation-atomic detection

Abstract: A high-performance liquid chromatographic–microwave digestion–hydride generation system coupled on-line with three atomic detectors (atomic absorption, inductively coupled plasma atomic emission and inductively coupled plasma mass spectrometry) has been developed and investigated for selenium species separation and determination. Total inorganic selenium, selenomethionine and selenoethionine are separated by reversed-phase chromatography prior to on-line microwave digestion of selenocompounds with a KBrO3–HBr mixture to form continuously SeIV, which is finally transformed into H2Se, also in a continuous manner, with a merging flow of sodium borohydride. Detection limits obtained for each Se species in water and urine using the three atomic detectors have been worked out and compared (i.e., for SeIV DLs were 6.8 µg l–1 by AAS, 30 µg l–1 by ICP-AES and 0.16 µg l–1 by ICP-MS).The integrated flow system, HPLC–MW digestion–HG-atomic detection, proposed here allows, in a single injection, reliable speciation in urine of the selenoaminoacids tested versus total inorganic selenium. Further speciation of the overlapped inorganic SeIV and SeVI peaks is accomplished by a second injection of the urine sample to determine only SeIV by avoiding microwave heating. Results on Se speciation in human urine have shown that more speciation information of the actual species, perhaps unknown, present in real samples could be gathered by resorting to the use of two, or more, atomic detectors coupled to the same separation scheme.

Speciation of organic selenium compounds by high-performance liquid chromatography–inductively coupled plasma mass spectrometry in natural samples

Abstract: The importance of selenium in the environment and in biological systems is now well recognized. Its biochemical functions, e.g., its anti-oxidant role and therefore cell protecting function, as an essential constituent of the enzyme glutathione peroxidase, has provoked a growing interest in the determination of this element. Selenoamino acids are essential for the understanding of the biogeochemical cycle of Se and TMSe+ is a known urinary metabolite present at high levels when Se is taken in excess. In this work we present a hyphenated technique (HPLC–ICP-MS) available for the separation of the organic Se compounds (selenocystine, selenomethionine and trimethylselenonium ion). The choice of column and solvents has been a critical parameter. Good repeatability and excellent detection limits (less than 1 µg l–1 for each species) have been reached for standard solutions and the application to some natural samples (enriched yeast, human serum and urine) has shown quite promising results.

The influence of pH and media composition on the uptake of inorganic selenium by Chlamydomonas reinhardtii

Abstract: The uptake of inorganic selenium species, selenate and selenite, by the green alga Chlamydomonas reinhardtii Dang was examined as a function of pH over the range 5 to 9 and in media with varying concentrations of major ions and nutrients using {sup 75}Se as a radiotracer. Little difference was noted in the uptake of selenate as a function of pH, with the maximum uptake occurring at pH 8; however, selenite uptake increased substantially at the lower pH values. Selenate uptake was significantly decreased by higher sulfate concentrations and increased significantly by calcium, magnesium, and ammonium. Selenite uptake was significantly increased when the phosphate concentrations in the media were reduced. The results of these experiments demonstrate that varying water chemistry may significantly affect the uptake of inorganic selenium by phytoplankton and the subsequent transfer of the selenium to higher trophic levels.

Identification of selenium species in selenium-enriched garlic, onion and broccoli using high-performance ion chromatography with inductively coupled plasma mass spectrometry detection

Abstract: Six standard selenium species including selenocystine, methyl selenocysteine, selenite, selenomethionine, allyl selenocysteine and selenate have been separated by high-performance ion chromatography on a Hamilton PRPX-100 column and detected by ICP-MS. Selenium enriched vegetables were analysed. Five selenium species and several unknown peaks were detected.

Heavy metals in laughing gulls: Gender, age and tissue differences

Abstract: The authors examined concentrations of lead, cadmium, mercury, manganese, selenium, and chromium in feathers, liver, kidney, heart, and muscle of known-aged laughing gulls (Larus atricilla) that hatched in Barnegat Bay, New Jersey and were collected at John F. Kennedy International Airport, New York 1 to 7 years later. Concentrations differed significantly among tissues, and tissue entered all the regression models explaining the greatest variation in metal levels. Age of bird contributed significantly to the models for lead, cadmium, selenium, and chromium. Although there were significant gender differences in all body measurements except wing length, there were few differences in metal levels. Males had significantly higher lead levels in feathers, and females had significantly higher selenium levels in heart and muscle tissue. For lead, 3-year olds had the highest levels in the heart, liver, and kidney, and levels were lower thereafter. Mercury levels in feathers and heart decreased significantly with age. Cadmium levels increased significantly with age for feathers, heart, liver, and muscle, although there was a slight decrease in the 7-year olds. Selenium levels decreased significantly with age for all tissues. Chromium levels increased with age for liver and heart.

Bioavailability of selenium accumulated by selenite-reducing bacteria.

Abstract: The bioavailability of selenium (Se) was determined in bacterial strains that reduce selenite to red elemental Se (SeO). A laboratory strain of Bacillus subtilis and a bacterial rod isolated from soil in the vicinity of the Kesterson Reservoir, San Joaquin Valley, CA, (Microbacterium arborescens) were cultured in the presence of 1 mM sodium selenite (Na2SeO3). After harvest, the washed, lyophilized B. Subtilis and M. arborescens samples contained 2.62 and 4.23% total Se, respectively, which was shown to consist, within error, entirely of SeO. These preparations were fed to chicks as supplements to a low-Se, vitamin E-free diet. Three experiments showed that the Se in both bacteria had bioavailabilities of approx 2% that of selenite. A fourth experiment revealed that gray SeO had a bioavailability of 2% of selenite, but that the bioavailability of red SeO depended on the way it was prepared (by reduction of selenite). When glutathione was the reductant, bioavailability resembled that of gray SeO and bacterial Se; when ascorbate was the reductant, bioavailability was twice that level (3-4%). These findings suggest that aerobic bacteria such as B. subtilis and M. arborescens may be useful for the bioremediation of Se-contaminated sites, i.e., by converting selenite to a form of Se with very low bioavailability.

Chiral Diselenides in the Total Synthesis of (+)-Samin

Abstract: Chiral selenium compounds are applied to stoichiometric as well as to catalytic reactions in the synthesis of substituted tetrahydrofuran derivatives: The selenium compound 1 was used in catalytic amounts for a rapid access to chiral diselenide 3. The efficient stereoselective addition to alkene 5 yields product 8 with a selenium functionality as a precursor for an intramolecular radical cyclization. In this way a short total synthesis of (+)-samin (11), a naturally occurring furofuran lignan, was achieved.