Oxidation States Of Selenium Research Articles

Efficacy of two different forms of selenium towards reduction of arsenic toxicity and accumulation in Cicer arietinum L.

Arsenic migration from soil to crop plants and subsequently human consumption of contaminated foodstuffs is a serious threat for society. In the present study, two oxidation states of selenium [Se(0) and Se(VI)] were used to check their efficacy towards amelioration of arsenic toxicity in chickpeas (Cicer arietinum L.). Three different concentrations (1, 5, and 10 mg/L) of both oxidation states of selenium were applied separately and in combination against a fixed dose (10 mg/L) of arsenic [(As(V)] treatment on chickpea seedlings. Further, seed germination and seedling growth attributes, oxidative stress, and antioxidant defense under different treatments were analyzed. The changes in anatomical structures and arsenic accumulation in different parts of seedlings were also studied. Results revealed that increased generation of oxidative stress affected physiobiochemical parameters of seedlings and diminished plant growth and deformation in vascular bundles under arsenic stress. However, the combined application of Se with As showed overall improvement in seedling growth, reduced oxidative stress, and organized vascular bundles of chickpea seedlings as compared to arsenic stress alone. The arsenic uptake and accumulation in chickpea seedlings were also reduced upon supplementation of Se. The highest reduction of arsenic accumulation by 42 and 56 % in roots, while 47 and 58 % in shoots were recorded by the application of 10 mg/L of Se(0) and Se (VI) under As stress, respectively. Overall, Se(VI) showed much better performance towards the minimization of arsenic-induced phytotoxicity and arsenic accumulation as compared to Se(0). Therefore, this study explored the efficacy of different forms of selenium towards the mitigation of arsenic toxicity in plants.

Adsorption and diffusion of selenite on Boda Claystone Formation

This study provides adsorption and diffusion data of selenite on Boda Claystone Formation (BCF) which is a potential host rock of a deep geological disposal of high-level radioactive waste. The experiments were performed on two diverse core samples: one albitic claystone sample characteristic for the entire BCF and one pyrite containing sample sparsely occurring in BCF. The experiments were carried out under atmospheric conditions. Batch experiments were carried out to study the kinetics of adsorption at a high initial concentration (1.2 × 10−3 M), the adsorption isotherms and reversibility were investigated in the 10−10–10−3 M concentration range. Adsorption onto petrographic thin sections was done to study the elemental distribution on the microscale and the oxidation state of selenium. The maximum of the distribution coefficient was found as Kd ≈ 200 L/kg and a decrease was experienced around 10−6–10−7 M equilibrium concentration, which showed similarities to other argillaceous rocks. Isotopic exchange experiments revealed reversibility of selenite adsorption. Diffusion was studied with through-diffusion and in-diffusion experiments. Using X-ray fluorescence, despite a low initial concentration of 2.3 × 10−5 M in the in-diffusion experiment, a meaningful diffusion profile of selenium could be obtained, from which the selenite apparent diffusion coefficient Dappselenite = (1.5–4.3) × 10−14 m2/s and the selenite rock capacity factor αselenite = 1.4–2.2 were determined. As selenium species are redox sensitive the oxidation state of adsorbed species was studied with X-ray absorption near edge structure spectroscopy on SeK edge. Adsorbed selenium remained in +IV oxidation state, however reduction was experienced on the pyritic sample.

Synthesis and characterization of 0D and 1D selenium nanostructures by green chemistry and evaluation of the radioprotective, radiosensitizing and antioxidant properties following exposure to ionizing radiation in vitro

We describe green routes to synthesize selenium nanostructures employing sodium selenite and green tea extract with mild heating (70 °C with stationary incubation) denoted Se-GT, and Na2SeO3 plus bovine serum albumin (BSA) and autoclaving (127 °C, 15 min) as Se-BSA. Nanostructure's characterizations used different analytical techniques and nanostructures' antioxidant capacity was determined by three methodologies. The effect of nanostructure concentration (1–20 mg/mL) on cell viability after 24h was assessed. At 20 mg/mL, no alterations in cell viability in liquid or on solid medium were observed. Preincubating cells with Se-GT or Se-BSA (5 mg/mL each) and subsequent exposition to 400 Gy of 60Cobalt radiation demonstrated that Se-GT affords radioprotection due to the presence of selenium in the elemental form (Se0) and radiosensitizing action because of the two different oxidation states of selenium (Se0 and Se+4) in Se-BSA. The effects were discussed, considering the differential redox behavior of selenium in cancer cells.

Design Principle of Monoclinic NiCo2Se4 and Co3Se4 Nanoparticles with Opposing Intrinsic and Geometric Electrocatalytic Activity toward the OER.

Despite predictions of high electrocatalytic OER activity by selenide-rich phases, such as NiCo2Se4 and Co3Se4, their synthesis through a wet-chemical route remains a challenge because of the high sensitivity of the various oxidation states of selenium to the reaction conditions. In this work, we have determined the contribution of individual reactants behind the maintenance of conducive solvothermal reaction conditions to produce phase-pure NiCo2Se4 and Co3Se4 from elemental selenium. The maintenance of reductive conditions throughout the reaction was found to be crucial for their synthesis, as a decrease in the reductive conditions over time was found to produce nickel/cobalt selenites as the primary product. Further, the reluctance of Ni(II) to oxidize into Ni(III) in comparison to the proneness of Co(II) to Co(III) oxidation was found to have a profound effect on the final product composition, as a deficiency of ions in the III oxidation state under nickel-rich reaction conditions hindered the formation of a monoclinic "Co3Se4-type" phase. Despite its lower intrinsic OER activity, Co3Se4 was found to show geometric performance on a par with NiCo2Se4 by virtue of its higher textural and microstructural properties.

Selenium-Containing Polysaccharides—Structural Diversity, Biosynthesis, Chemical Modifications and Biological Activity

Selenosugars are a group of sugar derivatives of great structural diversity (e.g., molar masses, selenium oxidation state, and selenium binding), obtained as a result of biosynthesis, chemical modification of natural compounds, or chemical synthesis. Seleno-monosaccharides and disaccharides are known to be non-toxic products of the natural metabolism of selenium compounds in mammals. In the case of the selenium-containing polysaccharides of natural origin, their formation is also postulated as a form of detoxification of excess selenium in microorganisms, mushroom, and plants. The valency of selenium in selenium-containing polysaccharides can be: 0 (encapsulated nano-selenium), IV (selenites of polysaccharides), or II (selenoglycosides or selenium built into the sugar ring to replace oxygen). The great interest in Se-polysaccharides results from the expected synergy between selenium and polysaccharides. Several plant- and mushroom-derived polysaccharides are potent macromolecules with antitumor, immunomodulatory, antioxidant, and other biological properties. Selenium, a trace element of fundamental importance to human health, has been shown to possess several analogous functions. The mechanism by which selenium exerts anticancer and immunomodulatory activity differs from that of polysaccharide fractions, but a similar pharmacological effect suggests a possible synergy of these two agents. Various functions of Se-polysaccharides have been explored, including antitumor, immune-enhancement, antioxidant, antidiabetic, anti-inflammatory, hepatoprotective, and neuroprotective activities. Due to being non-toxic or much less toxic than inorganic selenium compounds, Se-polysaccharides are potential dietary supplements that could be used, e.g., in chemoprevention.

Na2SeO3: A Na-Ion Battery Positive Electrode Material with High Capacity

Recent experimental and theoretical studies on the family of Li-rich layered materials show that they can deliver much higher capacities than traditional Li-transitional metal oxides. This also leads to great interests in Na-rich layered oxides as alternative positive electrode materials for sodium-ion batteries for large-scale energy storage. Herein, we report a Na-rich material, Na2SeO3 with an unconventional layered structure as a positive electrode material in NIBs for the first time. This material can deliver a discharge capacity of 232 mAh g−1 after activation, one of the highest capacities from sodium-based positive electrode materials. X-ray photoelectron spectroscopy indicates the oxidation state of selenium remains unchanged during the charge process. Theoretical simulation shows that after removal of Na, spin is situated around oxygen atoms near the Na vacancy, and the projected density of state of oxygen electron is close to the Fermi level. These suggest the involvement of oxygen during charge-discharge. This work will propel new searches of high-capacity sodium-based positive electrode materials.

Unexpected Behavior of Np in Oxo-selenate/Oxo-selenite Systems.

A study of neptunium (Np) chemistry in the complex oxo-selenium system has been performed. Hereby, two sets of precipitation experiments were conducted, investigating the influence of the initial oxidation state of selenium using SeIVO2 and H2SeVIO4 with NpV in alkali nitrate solution, keeping the ratio of Np/Se constant. Surprising results were observed. Five novel neptunium and selenium bearing compounds have been obtained by slow evaporation from aqueous solution. The novel NpIV phase K4-x[Np(SeO3)4-x(HSeO3)x]·(H2O)1.5 (1) crystallizes in green-colored, plate-shaped crystals and was obtained by adding SeO2 and ANO3 to a NpV stock solution. Single-crystal X-ray diffraction reveals one-dimensional chain structures composed of square antiprismatic NpO8 polyhedra linked via four trigonal pyramidal SeO3 and HSeO3 units. Raman spectral analysis supports the presence of both selenite and hydroselenite due to the presence of corresponding modes within the spectra. The addition of selenic acid to a NpV stock solution resulted in the precipitation of elongated rose prisms of K2[(NpO2)2(SeO4)3(H2O)2]·(H2O)1.5 (2), Rb2[(NpO2)2(SeO4)3(H2O)2]·(H2O)2 (3) and K9[(NpO2)9(SeO4)13.5(H2O)6]·(H2O)12 (4) as well as light red plates of Cs2[(NpO2)2(SeO4)3] (5). To our knowledge, this is the first report of NpVI selenates. All four structures show two-dimensional layered structures with alkali cations acting as charge balancing counter cations. Hereby the layers of compounds 2 and 3 are found to be orientational geometric isomers. Distinctly different phenomena are made responsible for the phase formation within these systems. The kinetically driven process of NpV disproportionation led to the formation of the NpIV selenites in the SeIV-based system, whereas the oxidation of NpV by reduction of nitrate in acidic conditions is responsible for the formation of the NpVI selenates in the SeVI system. The influence of air oxygen is also discussed for the latter reaction.

Electrocatalytic Reduction of Selenate on Gold Electrodes Alongside Copper Deposition

Reduction of aqueous selenate (SeO4 2-) to lower oxidation states of selenium is regarded as a very difficult reaction and thus far, only very few methods have yielded positive results [1-6]. One such previous study asserts that gold electrodes can catalyze reduction of commercial selenate at potentials below 0.6 V vs SHE [1], forming an elemental selenium deposit that can be anodically stripped above 0.9 V vs SHE, (see peaks A and B, black curve in Fig. 1 recorded in 1 mM Na2SeO4 in 0.1 M HClO4). However, commercially supplied selenate usually contains some selenite (SeO3 2-), a far more electroactive selenium oxyanion believed to yield elemental selenium and/or selenides as the product(s) of reduction. In fact, as shown by experiments performed in our laboratories, such voltammetric features vanished upon removal of selenite from the selenate solutions by adsorption on TiO2(see red curve in Fig. 1). This contribution will present strong evidence that the reduction of selenate under the same conditions can proceed on a layer of underpotentially deposited copper on Au, yielding a corresponding layer of CuxSe. To be discussed are various aspects of the formation mechanism of this CuxSe using potentiostatic deposition and linear sweep stripping voltammetry (LSSV) experiments. During LSSV experiments, Cu can be anodically stripped, leaving behind a layer of adsorbed elemental Se (peak C, Fig. 2). At higher potentials, this layer is oxidized to selenite (peak B, Fig. 2) [7-9]. Repetitive formation and oxidation of the CuxSe product on gold electrodes via an AC deposition / stripping waveform may allow for continuous turnover of selenate into selenite.

Electrocatalytic Reduction of Selenate on Gold Electrodes in the Presence of Copper (II)

Reduction of aqueous selenate (SeO4 2-) to lower oxidation states of selenium is typically a very slow reaction, but important to the detection and removal of soluble selenium from wastewater. Electrocatalytic reduction of selenate has not been exhaustively explored; only a few electrocatalytic methods for reducing selenate have been reported to date [1-6]. Commercially available selenate is often contaminated with selenite (SeO3 2-), a species that can be readily reduced to yield elemental selenium or selenides. No selenate reduction studies to date acknowledge the presence of this impurity. Furthermore, not all these studies unambiguously show that selenate itself is reduced, as opposed to these traces of selenite. Previous literature claims that gold electrodes are capable of reducing selenate at electrode potentials below 0.6 V vs SHE [1], forming a selenium deposit that strips anodically above 0.9 V vs SHE. Cyclic voltammetry experiments in this work reproduced the reported redox features, shown in Fig. 1 as peak A and B, respectively. However, when selenite was removed from selenate solutions with a titania adsorbent, no redox activity is seen on gold electrodes. It can be concluded that the previous report [1] was in fact measuring currents associated with trace selenite reduction. Selenate undergoes specific adsorption on gold and no other reaction. Peak C in Fig. 1 can be attributed to specific adsorption of selenate. Figure 1: Cyclic voltammetry at 0.2 V/s on Au wire electrode with 1mM of selenate in 0.1 M HClO4. Two purities of selenate were used. The first was selenate decahydrate purchased from Alfa Aesar at a purity of 99.9%, used as received. The other sample of selenate was the same, but was exposed to a titania adsorbent in order to remove traces of selenite. A cyclic voltammogram is also shown after selenite addition. We have found that the chemical inertness of selenate can be overcome by addition of copper (II) salts. Copper (II) can be reduced to an adlayer of underpotential deposited copper on gold electrodes between 0.64 and 0.24 V SHE. Once formed, we have found that this adlayer induces slow reduction of selenate, yielding a thin copper selenide film. The mechanism for CuxSe formation was investigated using potentiostatic deposition, followed by linear sweep stripping voltammetry. This technique allows determination of Cu and Se stripping charges separately, observed in Fig. 2 as peak D and E, respectively. At lower electrode potentials (< 0.24 V vs SHE), where copper (II) is reduced to bulk copper metal, selenate both accelerates Cu deposition and is reduced. Selenium co-deposits with bulk copper formed in selenate / copper (II) solutions. In this regime, selenate reduction is much faster than reduction by UPD copper. Figure 2: Linear sweep stripping voltammograms at 0.1 V/s after potential holds at 0.325 V on a Au electrode. Solution was 0.1 M HClO4 with 5 mM Cu(ClO4)2 and 1 mM Na2SeO4(titania purified). Potential hold duration for each curve is indicated in the legend.

化学形態の異なるセレン化合物の XAFS スペクトルによる酸化状態推定法

X-ray absorption fine structure （XAFS） spectroscopy is one of the effective analytical methods to determine the chemical form of trace elements in the complex powder mixtures such as soil, coal ash, sludge, and so on. XAFS spectra with different oxidation state of selenium （Se） compounds were collected in order to estimate the chemical form such as an oxidation state and a mixing ratio from the near edge XAFS spectra of Se. X-ray absorption energy and shape of the near edge spectra were sensitively varied in the range from 12,656 to 12,667eV with increasing the oxidation number of Se. It was found that the chemical form of Se contained in coal ash was able to estimate by using a linear fitting analysis with the collected XAFS spectra of this study.

Biological and chemical investigation of Allium cepa L. response to selenium inorganic compounds

The aim of this study was to evaluate the biological and chemical response of Allium cepa L. exposed to inorganic selenium compounds. Besides the investigation of the total content of selenium as well as its chemical speciation, the Allium test was used to evaluate the growth of onion roots and mitotic activity in the roots’ meristem. The total content of selenium was determined by inductively coupled plasma mass spectrometry (ICP MS). High-performance liquid chromatography (HPLC), coupled to ICP MS, was used for the selenium chemical speciation. Results indicated that A. cepa plants are able to biotransform inorganic selenium compounds into their organic derivatives, e.g., Se-methylselenocysteine from the Se(IV) inorganic precursor. Although the differences in the biotransformation of selenium are due mainly to the oxidation state of selenium, the experiment has also shown a fine effect of counter ions (H+, Na+, NH4 +) on the response of plants and on the specific metabolism of selenium. Figureᅟ

Hg(0) Removal Using Se(0)-doped Montmorillonite from Selenite(IV)

Potassium methylselenite (KSeO2(OCH3)) was reduced to elemental selenium, Se(0), and then doped onto montmorillonite K 10 (MK10) clay to examine the interaction between elemental mercury (Hg(0)) vapor and Se(0) in an effort to understand the possible heterogeneous reaction of Hg(0) vapor and Se(0) solid. The clay was used as a cost-effective support material for uniform dispersion of Se(0). The Se(0)-doped MK10 showed an excellent reaction performance with Hg(0) under an inert nitrogen gas at 70 and 140 oC in our lab-scale fixed-bed system. However, the precursor, KSeO2(OCH3)-doped MK10 showed a negligible reaction performance with Hg(0), suggesting that the oxidation state of selenium plays a key role in the reaction of Hg(0) vapor and selenium compounds.

Speciation and oxidation reaction analysis of selenium in aqueous solution using X-ray absorption spectroscopy for management of trace element in FGD liquor

Batch and in situ X-ray absorption spectroscopy (XAS) analysis were applied to the identification of selenium in aqueous solution containing selenite (Se(IV)O32-) and selenate (Se(VI)O42-) ranging from 10 to 1000mg-Se/L, respectively. Se K-edge XANES spectra were detected by means of a multi-channel silicon drift detector (SDD). Furthermore, the oxidation state of selenium was identified by measuring the energy of X-ray absorption, and the local structure around selenium atom was determined by analyzing the EXAFS. The Se K-edge XANES spectrum of selenite was gradually shifted to that of selenate in the presence of peroxodisulfate ion (S2O82-) which was the dominant oxidizing agent in wet flue gas desulfurization (FGD) liquor and had a subsequent effect on the selenium oxidation in the liquid phase. Concentrations of selenite and selenate calculated by linear fitting analysis of the XANES spectra were in good agreement with the results of quantitative analysis for selenite and selenate by ICP-AES.

Sorption of selenite onto chlorite considering mineral dissolution

In this study we investigated the sorption of selenite (SeO3 2−) onto chlorite as a function of Se(IV) concentration, pH, and ionic strength. The sorption isotherm of Se(IV) onto chlorite was successfully presented by both the Langmuir isotherm and Tempkin equation although the Langmuir isotherm is somewhat better than the Tempkin equation. The sorption of Se(IV) onto chlorite was maintained to be constant at an acidic pH region, while the sorption decreased with an increasing pH at neutral and alkaline pH regions. However, the Se(IV) sorption onto chlorite was independent of the ionic strength of NaClO4 solution. The amount of Se(IV) sorbed onto chlorite was significantly low compared to those of iron oxides such as apatite, goethite, hematite, and magnetite because of the lower content of Fe. We also investigated the effect of Fe(II) ions dissolved from chlorite on the Se(IV) sorption as a function of contact time. The chemical oxidation states of selenium sorbed onto chlorite surface were identified using X-ray absorption near edge structure (XANES) at the Pohang synchrotron light source. The amount of Fe(II) dissolved was increased by the contact time of 28 days but decreased after 28–56 days although the amount of dissolved Fe(II) ions was significantly small. This decrease of the dissolved Fe(II) may be due to the formation of Fe-oxyhydroxides such as ferrihydrite. The results of XANES measurements also showed that the Se(IV) sorbed onto chlorite was not reduced into Se(0) or Se(-II) even in the presence of Fe(II) ions in the solution because of the low Fe content of the chlorite although the mechanism was not clearly understood.

Chemical Speciation and Bioavailability of Selenium in the Rhizosphere of Symphyotrichum eatonii from Reclaimed Mine Soils

Knowledge of rhizosphere influences on Se speciation and bioavailability is required to predict Se bioavailability to plants. In the present study, plant-availability of Se to aster (Symphyotrichum eatonii (A. Gray) G.L. Nesom) was compared in rhizosphere soils and nonrhizosphere (bulk) soils collected from a reclaimed mine site in southeastern Idaho, U.S. X-ray spectroscopy was used to characterize the oxidation state and elemental distribution of Se in aster roots, rhizosphere soils, and bulk soils. Percent extractable Se in aster rhizosphere soil was greater than extractable Se in corresponding bulk soils in all samples (n = 4, p = 0.042, 0.051, and 0.052 for three extractions). Selenium oxidation state mapping of 28 regions within the samples and X-ray absorption near edge structure (XANES) spectra from 26 points within the samples indicated that the rhizosphere and bulk soil Se species was predominantly reduced Se(-II,0), while in the aster roots, high concentrations of Se(VI) were present. Results show that within the rhizosphere, enhanced Se bioavailability is occurring via oxidation of reduced soil Se to more soluble Se(VI) species.

Transforming Orthopedic Biomaterials Into Bone Cancer Inhibiting Implants: The Role of Selenium Nanoclusters

ABSTRACTCurrent orthopedic implants have numerous problems that include poor osseointegration, stress shielding and wear debris-associated bone cell death. In addition, numerous patients receive orthopedic implants as a result of bone cancer resection, yet none of the current orthopedic materials are designed to prevent either the occurrence or reoccurrence of cancer. The objective of this study was to transform a traditional orthopedic material into an implant that can both restore bone and prevent bone cancer growth at the implant-tissue interface. Elemental selenium was chosen as the biologically active agent in this material because of its known chemopreventive and chemotherapeutic properties. It was found that when selenite salts were reduced by glutathione in the presence of an immersed substrate (titanium (Ti), stainless steel (SS) or ultra high molecular weigh polyethylene (UHMWPE)), elemental selenium nucleated and grew into adherent, hemispherical nanoclusters. For each type of substrate (Ti, SS and UHMWPE), three types of surfaces with different selenium surface densities were fabricated. The zero oxidation state of selenium was confirmed on Ti substrates by XPS profiles. Compared to uncoated Ti and SS substrates, the high-density selenium-coated surfaces inhibited cancerous bone cell functions while promoting healthy bone cell functions. Very little selenium was also found to release (about 250ppb) into the cell culture media after 3 days of immersion. These findings showed for the first time the potential of using selenium nanoclusters as a coating to transform a traditional orthopedic material into a bone cancer inhibiting implant.

Effect of selenium oxidation state on cadmium translocation in chamomile plants

AbstractSyntheses and spectral characteristics of cadmium(II) compounds (CdSeO4, CdSeO3, and Cd(NCSe)2(nia)2) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)2(nia)2, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)2(nia)2 on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 µmol dm−3) Cd(NCS)2(nia)2 affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 µmol dm−3 and 60 µmol dm−3 significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF) and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values determined for Cd accumulation in shoots were obtained with CdSeO4. Substitution of S with Se in the Cd(NCX)2(nia)2 (X = Se or S) caused an increase of Cd translocation into the shoots.

Selenium, an Ambivalent Factor in Diabetes? Established Facts, Recent Findings and Perspectives

It is widely known that selenium develops its biological activity via an active selenocysteine residue in the catalytically active centre of functional selenoproteins. By its function in glutathione peroxidases and thioredoxin reductases selenium contributes to a remarkable extent to the maintenance of the cellular antioxidative balance when taken up at the recommended dietary level (animals: 0.1 - 0.3 μg/kg diet, humans: 50 - 150 µg Se daily). In recent years an interesting physiological aspect has been found for selenate (selenium oxidation state +VI). High doses of selenate displayed antidiabetic properties when applied to diabetic animals or added to the media of tissue cultures. Thus selenate treatment could be shown to normalise hyperglycaemia as well as changed activities of glycolytic and gluconeogenic marker enzymes. Mechanistically an increased phosphorylation of single proteins of the insulin signalling cascade could be attributed to the insulinomimetic action of selenate. The examination of the antidiabetic features of selenate in type II diabetic animals revealed that the increase in phosphorylation is presumably based on the inhibition of protein tyrosine phosphatases, which act as negative regulators of insulin signalling. In contrast to the antidiabetic features of high selenate doses, selenite administration to diabetic animals showed no effect on diabetes. In a recent study it could even be demonstrated that the overexpression of glutathione peroxidase 1 (the best characterized selenoprotein) in healthy mice led to an increase in insulin resistance and obesity. These results could partially be confirmed by the data of our most recent investigation in which a high expression and activity of glutathione peroxidase, obtained by feeding selenium at the nutritionally recommended level and at a moderately supranutritive level corresponded to an up-regulated expression of proteins whose expression is increased in insulin resistant type 2 diabetes. From studies on the role of selenium in diabetes carried out so far it can be concluded that selenium plays an ambivalent role with regard to diabetes depending on the compound and on the applied concentration. Thus only high doses of selenate evolve antidiabetic properties. Investigations into an even negative influence of moderate supranutritive doses of selenium on diabetes and the molecular events linked to this are necessary. The review summarizes the information currently available on the ambivalent role of selenium in diabetes which seems to depend on the chemical form and the applied concentration. Established facts, recent findings of our own studies using microarray analysis and RT-PCR and perspectives of the role of selenium in diabetes are presented and discussed against the background of selenium metabolism. Keywords: Selenium, selenate, selenite, antidiabetic effects and insulin resistance

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 LD 50 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 (PPARγ), 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 PPARγ, 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.

Novel chemiluminescence-inducing cocktails, part I: The role in light emission of combinations of luminal with SIN-1, selenite, albumin, glucose oxidase and Co2+

It is known that many agents influence the capacity of cells to produce reactive oxygen species. However, assaying these agents, both those that stimulate and those that inhibit reactive oxygen production, can be complicated and time consuming. Here, a method is described in which two different cocktails are employed to stimulate luminol-dependent chemiluminescence (LDCL). These cocktails are comprised of luminol, with either sodium selenite [IV] (SEL) or tellurite [IV] (TEL) (where IV and VI refer to the 4+ or 6+ oxidation state of selenium or tellurium salts, respectively), morpholinosidonimine (SIN-1), serum albumin and Co(2+), called the SIN-1a (with selenite) and SIN1b (with tellurite) cocktails, respectively; or luminol with glucose oxidase (GO), sodium selenite [IV] and Co(2+), called the GO cocktail. The cocktails functioned best in Hank's balanced salt solution (HBSS) containing 1% glucose at pH 7.4, incubated at approximately 22 degrees C. Within 30-60 s there was a burst of luminescence, which lasted for 7-10 min. In 100% ethanol, the SIN-1 cocktails also generated LDCL to 70% of that produced in HBSS. Neither selenite [VI], seleno-cystine, seleno-methionine, nor the selenium-containing drug, ebselen, could replace SEL. Moreover, the effects of the NO-donor, SIN-1, could not be replicated by the oxyradical generators, xanthine-xanthine oxidase or hypochlorous acid. Only low levels of luminescence were generated by combinations of the peroxyl radical generator, 2,2'-azobis-2-amidinopropane dihydrochloride (AAPH) with either SEL or TEL. It is suggested that light emission induced by the SIN1 cocktail results from the oxidation of SEL [IV] to the [VI] state, possibly due to the generation of mixtures of superoxide, peroxide, peroxynitrite and also of unidentified oxidant species, catalyzed by CoCo(2+). However, the involvement of hydroxyl radicals in LDCL could not be confirmed by use of either dimethyl thiourea or by electron spin resonance (ESR). LDCL induced by the two cocktails is strongly reduced by phosphates, EDTA, deferoxamine, CuCo(2+), MnCo(2+), as well as by the "classical" antioxidants superoxide dismutase (SOD), ascorbate, vitamin E, uric acid or thiols. It is suggested that these chemiluminescence cocktail systems can be used to determine the total anti-oxidant capacities of biological fluids and commercially available anti-oxidants.