Selenium-containing proteins in mammals and other forms of life

Hg and Se in Muscle and Liver of Blue Shark (Prionace glauca) from the Entrance of the Gulf of California: An Insight to the Potential Risk to Human Health

The blue shark (Prionace glauca) is the most commonly caught species of Elasmobranchii at the entrance to the Gulf of California. Although fins are the primary target commodity, the entire organism is consumed. This study examined the concentration of Hg and Se in muscle and liver to understand the antagonistic process that occurs between these two elements within the organism. Twenty-two individuals were captured at the Gulf of California inlet between September 2019 and March 2021. Hg was measured by cold vapor atomic absorption, and Se by atomic absorption spectrophotometry in a graphite furnace. All individuals studied showed higher concentrations (µg g-1 wet weight) of Hg (0.69) and Se (2.49) in liver than in muscle (Hg 0.63 and Se 0.08). Although the mean Hg values were below the maximum allowable limits (Hg 1.0 µg g-1 wet weight), the molar ratio (< 1.0) and the negative health benefit value of selenium (HBVSe) in muscle show that additional caution should be taken when consuming this species. We recommend a more thorough study of the antagonistic interaction between Hg and Se to accurately assess the health risk for consumers of blue shark.

Selenocompounds and Sepsis-Redox Bypass Hypothesis: Part B-Selenocompounds in the Management of Early Sepsis

Significance: Endothelial barrier damage, which is in part caused by excess production of reactive oxygen, halogen and nitrogen species (ROHNS), especially peroxynitrite (ONOO^-), is a major event in early sepsis and, with leukocyte hyperactivation, part of the generalized dysregulated immune response to infection, which may even become a complex maladaptive state. Selenoenzymes have major antioxidant functions. Their synthesis is related to the need to limit deleterious oxidant redox cycling by small selenocompounds, which may be of therapeutic cytotoxic interest. Plasma selenoprotein-P is crucial for selenium transport from the liver to the tissues and for antioxidant endothelial protection, especially against ONOO^-. Above micromolar concentrations, sodium selenite (Na₂SeO₃) becomes cytotoxic, with a lower cytotoxicity threshold in activated cells, which has led to cancer research. Recent Advances: Plasma selenium (<2% of total body selenium) is mainly contained in selenoprotein-P, and concentrations decrease rapidly in the early phase of sepsis, because of increased selenoprotein-P binding and downregulation of hepatic synthesis and excretion. At low concentrations, Na₂SeO₃ acts as a selenium donor, favoring selenoprotein-P synthesis in physiology, but probably not in the acute phase of sepsis. Critical Issues: The cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes, especially the most immature forms that liberate ROHNS, may be beneficial, but they may also be harmful for activated endothelial cells. Endothelial protection against ROHNS by selenoprotein-P may reduce Na₂SeO₃ toxicity, which is increased in sepsis. Future Direction: The combination of selenoprotein-P for endothelial protection and the cytotoxic effects of Na₂SeO₃ against hyperactivated leukocytes may be a promising intervention for early sepsis. Antioxid. Redox Signal. 37, 998-1029.

Selenocompounds and Sepsis: Redox Bypass Hypothesis for Early Diagnosis and Treatment: Part A-Early Acute Phase of Sepsis: An Extraordinary Redox Situation (Leukocyte/Endothelium Interaction Leading to Endothelial Damage)

Significance: Sepsis is a health disaster. In sepsis, an initial, beneficial local immune response against infection evolves rapidly into a generalized, dysregulated response or a state of chaos, leading to multiple organ failure. Use of life-sustaining supportive therapies creates an unnatural condition, enabling the complex cascades of the sepsis response to develop in patients who would otherwise die. Multiple attempts to control sepsis at an early stage have been unsuccessful. Recent Advances: Major events in early sepsis include activation and binding of leukocytes and endothelial cells in the microcirculation, damage of the endothelial surface layer (ESL), and a decrease in the plasma concentration of the antioxidant enzyme, selenoprotein-P. These events induce an increase in intracellular redox potential and lymphocyte apoptosis, whereas apoptosis is delayed in monocytes and neutrophils. They also induce endothelial mitochondrial and cell damage. Critical Issues: Neutrophil production increases dramatically, and aggressive immature forms are released. Leukocyte cross talk with other leukocytes and with damaged endothelial cells amplifies the inflammatory response. The release of large quantities of reactive oxygen, halogen, and nitrogen species as a result of the leukocyte respiratory burst, endothelial mitochondrial damage, and ischemia/reperfusion processes, along with the marked decrease in selenoprotein-P concentrations, leads to peroxynitrite damage of the ESL, reducing flow and damaging the endothelial barrier. Future Directions: Endothelial barrier damage by activated leukocytes is a time-sensitive event in sepsis, occurring within hours and representing the first step toward organ failure and death. Reducing or stopping this event is necessary before irreversible damage occurs.

Selenium in sediment and food webs of the Tapajós River basin (Brazilian Amazon) and its relation to mercury

BACKGROUND

We investigated Se levels along the Tapajós River basin - which is an important tributary of the Amazon River - and the possible antagonistic effect of Se in Hg availability. This is the first study to investigate Se transfer from abiotic to biotic compartments and along the food chain in aquatic ecosystems of the Amazon basin.

METHODS

Se concentrations were measured in superficial sediment (n = 29), plankton (n = 28) and fishes (n = 121) along two stretches of the Tapajós River basin (Tap_up/mi and Tap_low), comprising approximately 500 km with different hydrological characteristics.

RESULTS

Se concentrations in sediment were significantly higher in the Tap_low (345-664 μg kg^-1) than in the Tap_up/mi (60-424 μg kg^-1). The seasonal flooding of the Amazon River probably helps to carry selenium-rich sediment to the Tapajós mouth (Tap_low stretch). We suggest that Se in sediment could decrease the bioavailability of Hg resulting in lower MeHg concentrations in fish, as observed in the Tap_low (45-934 μg kg^-1). Sediment and plankton were positively correlated in relation to their Se concentrations (r = 0.62; p = 0.001) suggesting that sediment can possibly be the main source of Se to plankton. Our data indicate Se uptake by primary consumers, as noted in phytoplankton levels. The decrease of Se concentrations along the food chain was also noteworthy.

CONCLUSION

This work elucidates some aspects of Se biogeochemistry in the Amazon basin and shows its importance regarding Hg cycles in aquatic ecosystems.

Cytosolic Distribution of Metals (Cd, Cu) and Metalloids (As, Se) in Livers and Gonads of Field-Collected Fish Exposed to an Environmental Contamination Gradient: An SEC-ICP-MS Analysis

The distribution of As, Cd, Cu and Se among biomolecules of different molecular weight (MW) in the heat-treated cytosolic fraction of livers and gonads of white suckers (WS; Catostomus commersonii) collected in a reference lake and in a lake subject to multi-metal contamination was investigated. Distribution profiles were obtained by separation of the heat-stable protein and peptide (HSP) fractions using size-exclusion high performance-liquid chromatography, coupled online to an inductively coupled plasma mass spectrometer, to quantify the associated metals. Metal-handling strategies did not vary between the reference and exposed fish, with the exception of As. Cadmium and Cu appeared associated with the heat-stable peptides metallothioneins (MTs), indicating their reasonable detoxification and regulation in WS. In contrast, Se and As were not bound to MTs, but rather, to biomolecules of lower MW (<2 kDa). Arsenic was found associated with the same biomolecules in fish from both lakes, but their proportions changed between reference and exposed fish. For future work, the identification of the Se and As binding biomolecules would be of great interest to determine if these metalloids are detoxified or if, conversely, the biomolecules are metal-sensitive and their binding to Se or As represents a threat for the health of these fish.

Electrophilic trifluoromethylselenolation of terminal alkynes with Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate

Herein the nucleophilic addition of Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate, a stable and easy-to-handle reagent, to alkynes is described. This reaction provides trifluoromethylselenylated vinyl sulfones with good results and the method was extended also to higher fluorinated homologs. The obtained compounds are valuable building blocks for further syntheses of fluoroalkylselenolated molecules.

Biosynthesis of selenium-nanoparticles and -nanorods as a product of selenite bioconversion by the aerobic bacterium Rhodococcus aetherivorans BCP1

The wide anthropogenic use of selenium compounds represents the major source of selenium pollution worldwide, causing environmental issues and health concerns. Microbe-based strategies for metal removal/recovery have received increasing interest thanks to the association of the microbial ability to detoxify toxic metal/metalloid polluted environments with the production of nanomaterials. This study investigates the tolerance and the bioconversion of selenite (SeO₃^2-) by the aerobically grown Actinomycete Rhodococcus aetherivorans BCP1 in association with its ability to produce selenium nanoparticles and nanorods (SeNPs and SeNRs). The BCP1 strain showed high tolerance towards SeO₃^2- with a Minimal Inhibitory Concentration (MIC) of 500mM. The bioconversion of SeO₃^2- was evaluated considering two different physiological states of the BCP1 strain, i.e. unconditioned and/or conditioned cells, which correspond to cells exposed for the first time or after re-inoculation in fresh medium to either 0.5 or 2mM of Na₂SeO₃, respectively. SeO₃^2- bioconversion was higher for conditioned grown cells compared to the unconditioned ones. Selenium nanostructures appeared polydisperse and not aggregated, as detected by electron microscopy, being embedded in an organic coating likely responsible for their stability, as suggested by the physical-chemical characterization. The production of smaller and/or larger SeNPs was influenced by the initial concentration of provided precursor, which resulted in the growth of longer and/or shorter SeNRs, respectively. The strong ability to tolerate high SeO₃^2- concentrations coupled with SeNP and SeNR biosynthesis highlights promising new applications of Rhodococcus aetherivorans BCP1 as cell factory to produce stable Se-nanostructures, whose suitability might be exploited for biotechnology purposes.

Electrophilic Trifluoromethylselenolation of Boronic Acids

Trifluoromethylselenylated compounds are emergent compounds with interesting physicochemical properties that still suffer from a lack of efficient synthetic methods. We recently developed an efficient one-pot strategy to generate in situ CF₃SeCl and use it in various reactions. Herein, we continue our study of the reactivity scope of this preformed reagent. Cross-coupling reactions with aromatic and heteroaromatic boronic acids have been investigated. The expected products have been obtained, using a stoichiometric amount of copper, with moderate yields.

Overexpression of Selenoprotein SelK in BGC-823 Cells Inhibits Cell Adhesion and Migration

Effects of human selenoprotein SelK on the adhesion and migration ability of human gastric cancer BGC-823 cells using Matrigel adhesion and transwell migration assays, respectively, were investigated in this study. The Matrigel adhesion ability of BGC-823 cells that overexpressed SelK declined extremely significantly (p < 0.01) compared with that of the cells not expressing the protein. The migration ability of BGC-823 cells that overexpressed SelK also declined extremely significantly (p < 0.01). On the other hand, the Matrigel adhesion ability and migration ability of the cells that overexpressed C-terminally truncated SelK did not decline significantly. The Matrigel adhesion ability and migration ability of human embryonic kidney HEK-293 cells that overexpressed SelK did not show significant change (p > 0.05) with the cells that overexpressed the C-terminally truncated protein. In addition to the effect on Matrigel adhesion and migration, the overexpression of SelK also caused a loss in cell viability (as measured by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MTT) colorimetric assay) and induced apoptosis as shown by confocal microscopy and flow cytometry. The cytosolic free Ca2+ level of these cells was significantly increased as detected by flow cytometry. But the overexpression of SelK in HEK-293 cells caused neither significant loss in cell viability nor apoptosis induction. Only the elevation of cytosolic free Ca2+ level in these cells was significant. Taken together, the results suggest that the overexpression of SelK can inhibit human cancer cell Matrigel adhesion and migration and cause both the loss in cell viability and induction of apoptosis. The release of intracellular Ca2+ from the endoplasmic reticulum might be a mechanism whereby the protein exerted its impact. Furthermore, only the full-length protein, but not C-terminally truncated form, was capable of producing such impact. The embryonic cells were not influenced by the elevation of free Ca2+ level in cytosol, probably due to their much greater tolerance to the variation.

Antioxidant strategies in respiratory medicine

Pulmonary oxidant stress plays an important pathogenetic role in disease conditions including acute lung injury/adult respiratory distress syndrome (ALI/ARDS), hyperoxia, ischemia-reperfusion, sepsis, radiation injury, lung transplantation, COPD, and inflammation. Reactive oxygen species (ROS), released from activated macrophages and leukocytes or formed in the pulmonary epithelial and endothelial cells, damage the lungs and initiate cascades of pro-inflammatory reactions propagating pulmonary and systemic stress. Diverse molecules including small organic compounds (e.g. gluthatione, tocopherol (vitamin E), flavonoids) serve as natural antioxidants that reduce oxidized cellular components, decompose ROS and detoxify toxic oxidation products. Antioxidant enzymes can either facilitate these antioxidant reactions (e.g. peroxidases using glutathione as a reducing agent) or directly decompose ROS (e.g. superoxide dismutases [SOD] and catalase). Many antioxidant agents are being tested for treatment of pulmonary oxidant stress. The administration of small antioxidants via the oral, intratracheal and vascular routes for the treatment of short- and long-term oxidant stress showed rather modest protective effects in animal and human studies. Intratracheal and intravascular administration of antioxidant enzymes are being currently tested for the treatment of acute oxidant stress. For example, intratracheal administration of recombinant human SOD is protective in premature infants exposed to hyperoxia. However, animal and human studies show that more effective delivery of drugs to cells experiencing oxidant stress is needed to improve protection. Diverse delivery systems for antioxidants including liposomes, chemical modifications (e.g. attachment of masking pegylated [PEG]-groups) and coupling to affinity carriers (e.g. antibodies against cellular adhesion molecules) are being employed and currently tested, mostly in animal and, to a limited extent, in humans, for the treatment of oxidant stress. Further studies are needed, however, in order to develop and establish effective applications of pulmonary antioxidant interventions useful in clinical practice. Although beyond the scope of this review, antioxidant gene therapies may eventually provide a strategy for the management of subacute and chronic pulmonary oxidant stress.

Comparative study of DL-selenomethionine vs sodium selenite and seleno-yeast on antioxidant activity and selenium status in laying hens

The aim of this study was to compare the effect of DL-selenomethionine (SM) with 2 routinely used Se sources, sodium selenite (SS) and seleno-yeast (SY), on relative bioavailability based on antioxidant activity and tissue Se content. Six hundred thirty 131-day-old brown laying hens were randomly assigned to 7 treatments for 168 d (24 wks) with 6 replicates of 15 hens per replicate. The SS and SY animals were supplemented a cornmeal and soybean diet that supplied a total Se 0.3 mg/kg whereas SM was added at 4 different levels to the total Se at 0.1, 0.3, 0.5 and 0.7 mg/kg. All hens fed the Se-supplemented diet showed higher glutathione peroxidase (GSH-Px) activity (P < 0.01), higher superoxide dismutase (SOD) activity (P < 0.05), lower malondialdehyde (MDA) content (P < 0.05) in plasma, and greater Se contents in egg yolks, albumen, leg muscle, breast muscle, liver, and plasma compared with those fed the control diet (P < 0.01). The organic sources (SY and SM) exhibited a greater ability to increase the GSH-Px activity (P < 0.01) and Se content in albumen (P < 0.01), leg, and breast muscles (P = 0.0099 and P = 0.0014, respectively) than the SS that was added at 0.3 mg Se/kg. The higher SM added levels increased the GSH-Px activity until the dose of 0.5mg Se/kg (P < 0.01).The greater Se concentrations in albumen, muscle and liver appeared in the higher SM-added level, as well as above the dose of 0.1 mg Se/kg (P < 0.01). In addition, hens fed the diet with SM accumulated more Se in albumen, leg, and breast muscle than those fed diets with SY (P < 0.05). These results confirmed the higher ability of organic Se sources to increase the antioxidant activity and Se deposition in egg albumen, leg, and breast muscles compared with SS, and demonstrated a significantly better efficiency of SM compared with SY for albumen and muscle Se enrichment.

Potential Role of Selenoenzymes and Antioxidant Metabolism in relation to Autism Etiology and Pathology

Autism and autism spectrum disorders (ASDs) are behaviorally defined, but the biochemical pathogenesis of the underlying disease process remains uncharacterized. Studies indicate that antioxidant status is diminished in autistic subjects, suggesting its pathology is associated with augmented production of oxidative species and/or compromised antioxidant metabolism. This suggests ASD may result from defects in the metabolism of cellular antioxidants which maintain intracellular redox status by quenching reactive oxygen species (ROS). Selenium-dependent enzymes (selenoenzymes) are important in maintaining intercellular reducing conditions, particularly in the brain. Selenoenzymes are a family of ~25 genetically unique proteins, several of which have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain's high rate of oxygen consumption is accompanied by high ROS production, selenoenzyme activities are particularly important in this tissue. Because selenoenzymes can be irreversibly inhibited by many electrophiles, exposure to these organic and inorganic agents can diminish selenoenzyme-dependent antioxidant functions. This can impair brain development, particularly via the adverse influence of oxidative stress on epigenetic regulation. Here we review the physiological roles of selenoproteins in relation to potential biochemical mechanisms of ASD etiology and pathology.

New insights into traditional health risk assessments of mercury exposure: implications of selenium

There is increasing evidence that selenium (Se) has a significant effect on mercury (Hg) toxicology; however, Hg exposure risk assessments usually consider only the amount of Hg present in the environment or in food. On the basis of the present understanding of mechanisms of interaction between Se and Hg, the physiology/toxicology of Se, and the toxicology of Hg, we propose a new criterion for Se/Hg exposure assessment. This criterion, which is based on Se-Hg interactions, considers not only the toxicological consequences of Hg exposure but also the benefits and/or adverse effects of Se intake, especially the adverse effects related to a Se deficiency/excess. According to an illustrative assessment based on the new criterion and nine existing criteria, large knowledge gaps in the traditional assessments of exposure to Hg and/or Se were found, including those that assessed the interactions between Hg and Se. These results suggest that future assessments of Hg exposure (or Se intake) should include both Se and Hg.

Dramatic substituent effects on the mechanisms of nucleophilic attack on Se-S bridges

The reactions of XSeSX, XSeSY, and YSeSX (X, Y = CH3, NH2, OH, F) with F(-) and CN(-) nucleophiles have been investigated by means of B3PW91/6-311+G(2df,p) and G4 calculations. In systems where the two substituents are not identical (XSeSY), the more stable of the two possible isomers corresponds to those in which the most electronegative substituent is attached to Se. Nucleophilic attack takes place at Se, independent of the nature of the nucleophile, with the only exception being XSeSF (X = CH3 , NH2 , OH), in which case the attack occurs at S. In agreement with recent results for disulfide and diselenide linkages, the mechanisms leading to Se-S bond cleavage are not always the more favorable ones because for highly electronegative substituents the most favorable process is fission of the chalcogen-substituent bond. These dissimilarities in the observed reactivity pattern as a function of the electronegativity of the substituents are due to the fact that the σ-type Se-S antibonding orbital, which for low-electronegative substituents is the lowest unnoccupied molecular orbital (LUMO), becomes strongly destabilized when the electronegativity of the substituent increases, and is replaced by an antibonding π-type Se-X (or S-X) orbital. In contrast, however, with what has been found for disulfide and diselenide derivatives, the observed reactivity does not change with the nature of the nucleophile. The activation strain model provides interesting insight into these processes, showing that in most cases the activation barriers are the consequence of subtle differences in the strain or in the interaction energies.

A metallomics approach discovers selenium-containing proteins in selenium-enriched soybean

Our previous study found that high-molecular-weight selenium (Se) species make up 82% of the total Se in the bean of Se-enriched soybean plants (Chan et al. 2010, Metallomics, 2(2): p. 147-153). The Se species have been commonly seen in other plants in addition to soybean, but their identities remain unresolved. The present study employs a multi-technique metallomics approach to characterize the proteins containing Se in the beans of Se-enriched soybean plants. Two main categories of proteins, maturation proteins and protease inhibitors, were found in Se-containing high-performance liquid chromatography (HPLC) fractions. The proteins were screened by two-dimensional HPLC-inductively coupled plasma mass spectrometry, size-exclusion chromatography, and anion-exchange chromatography, and the Se-containing fractions were then identified by peptide mapping using HPLC-Chip-electrospray ion trap mass spectrometry. Based on the belief that Se goes into proteins through non-specific incorporation, a new method was designed and applied for the Se-containing peptide identification. The Se-containing peptide KSDQSSSYDDDEYSKPCCDLCMCTRS, part of the sequence of protein Bowman-Birk proteinase isoinhibitor (Glycine max), was found in one of the Se-containing fractions. The nutritional value of the Se-containing proteins in Se-enriched soybeans will be an interesting topic for the future studies.

Reproductive function of Selenoprotein M in Chinese mitten crabs (Eriocheir sinesis)

Selenoproteins are present in all major forms of life, including eukaryotes, bacteria and archaea. In eukaryotic animals, selenoproteins often function as antioxidants, but rare or absent in other phyla, such as plants and fungi (except for the green alga Chlamydomonas). Selenoprotein M (SelM) is a selenocysteine containing protein with redox activity, which is involved in the antioxidant response. However, information remains limited about SelM physiology and function in marine invertebrates, particularly in crustaceans. Hence, we investigated the reproductive functionality of SelM in the Chinese mitten crab (Eriocheir sinensis), which is a commercially important yet disease vulnerable aquaculture species. The full-length SelM cDNA (928bp) strand was cloned by using PCR, based on an initial expressed sequence tag (EST) that was isolated from a hepatopancreatic cDNA library. The SelM cDNA contained a 390bp open reading frame (ORF) that encoded a putative 129 amino acid (aa) protein. SelM mRNA expression in E. sinensis was (a) tissue-specific, with the highest expression observed in the hepatopancreas, testis, ovaries and intestines. Based on this information, we then detected the different stages of tissue expression for SelM in the testis, ovary, and male crab hepatopancreas and hemolymph, and the enzyme activity of SelM in the testis. Overall, SelM was isolated successfully from the Chinese mitten crab, and its involvement in the regulation of reproduction during the period of rapid development in E. sinensis was confirmed.

The properties, functions, and use of selenium compounds in living organisms

Selenium occurs in the environment in inorganic and organic compounds. For many years it was regarded as a toxic element, causing numerous illnesses and diseases. But research in the past 50 years has revealed a "bright side" to this element, especially as a component of selenoproteins, selenium makes a significant contribution to the health of humans and animals. The selenium content in an organism depends on its concentration and bioavailability in the soil, and the differences between its deficiency, appropriate intake, and excess are very slight. This article gathers information from the literature on: • the consequences of a deficiency and an excess of selenium in the body, as well as the health-promoting mechanisms of selenium, including the functions of selenoproteins • the uptake and transformation of selenium compounds by plants, because of the fact that selenium is better assimilated from plant food and also the classification of plants with respect to their ability to take up selenium from the soil and to accumulate it.

Selenium speciation profiles in selenite-enriched soybean (Glycine Max) by HPLC-ICPMS and ESI-ITMS

Soybean (Glycine Max) plants were grown in soil supplemented with sodium selenite. A comprehensive selenium profile, including total selenium concentration, distribution of high molecular weight selenium and characterization of low molecular weight selenium compounds, is reported for each plant compartment: bean, pod, leaf and root of the Se-enriched soybean plants. Two chromatographic techniques, coupled with inductively coupled plasma mass spectrometry (ICPMS) for specific selenium detection, were employed in this work to analyze extract solutions from the plant compartments. Size-exclusion chromatography revealed that the bean compartment, well-known for its strong ability to make proteins, produced high amounts (82% of total Se) of high molecular weight selenospecies, which may offer additional nutritional value and suggest high potential for studying proteins containing selenium in plants. The pod, leaf and root compartments primarily accumulate low molecular weight selenium species. For each compartment, low molecular weight selenium species (lower than 5 kDa) were characterized by ion-pairing reversed phase HPLC-ICPMS and confirmed by electrospray ionization ion trap mass spectrometry (ESI-ITMS). Selenomethionine and selenocystine are the predominant low molecular weight selenium compounds found in the bean, while inorganic selenium was the major species detected in other plant compartments.

Selenium prevents cognitive decline and oxidative damage in rat model of streptozotocin-induced experimental dementia of Alzheimer's type

Selenium (Se), a nutritionally essential trace element with known antioxidant potential, protects the brain from oxidative damage in various models of neurodegeneration. Intracerebroventricular-streptozotocin (ICV-STZ) in rats causes impairment of brain glucose and energy metabolism along with oxidative damage and cholinergic dysfunction, and provides a relevant model for sporadic dementia of Alzheimer's type (SDAT). The present study demonstrates the therapeutic efficacy of Se on cognitive deficits and oxidative damage in ICV-STZ in rats. Male Wistar rats were pre-treated with sodium selenite, a salt of Se (0.1 mg/kg; body weight) for 7 days and then were injected bilaterally with ICV-STZ (3 mg/kg), while sham rats received the same volume of vehicle. After two ICV-STZ infusions, rats were tested for memory deficits in passive avoidance and Morris water maze (MWM) tests and then were sacrificed for biochemical and histopathological assays. ICV-STZ-infused rats showed significant loss in learning and memory ability, which were significantly improved by Se supplementation. A significant increase in thio-barbituric acid reactive species (TBARS), protein carbonyl (PC) and a significant decrease in reduced glutathione (GSH), antioxidant enzymes (glutathione peroxidase [GPx] and glutathione reductase [GR]) and adenosine triphosphate (ATP) in the hippocampus and cerebral cortex and choline acetyltransferase (ChAT) in hippocampus were observed in ICV-STZ rats. Se supplementation significantly ameliorated all alterations induced by ICV-STZ in rats. Our study reveals that Se, as a powerful antioxidant, prevents cognitive deficits, oxidative damage and morphological changes in the ICV-STZ rats. Thus, it may have a therapeutic value for the treatment of SDAT.

Importance of molar ratios in selenium-dependent protection against methylmercury toxicity

The influence of dietary selenium (Se) on mercury (Hg) toxicity was studied in weanling male Long Evans rats. Rats were fed AIN-93G-based low-Se torula yeast diets or diets augmented with sodium selenite to attain adequate- or rich-Se levels (0.1, 1.0 or 15 micromol/kg, respectively) These diets were prepared with no added methylmercury (MeHg) or with moderate- or high-MeHg (0.2, 10 or 60 micromol/kg, respectively). Health and weights were monitored weekly. By the end of the 9-week study, MeHg toxicity had impaired growth of rats fed high-MeHg, low-Se diets by approximately 24% (p < 0.05) compared to the controls. Growth of rats fed high-MeHg, adequate-Se diets was impaired by approximately 8% (p < 0.05) relative to their control group, but rats fed high-MeHg, rich-Se diets did not show any growth impairment. Low-MeHg exposure did not affect rat growth at any dietary Se level. Concentrations of Hg in hair and blood reflected dietary MeHg exposure, but Hg toxicity was more directly related to the Hg to Se ratios. Results support the hypothesis that Hg-dependent sequestration of Se is a primary mechanism of Hg toxicity. Therefore, Hg to Se molar ratios provide a more reliable and comprehensive criteria for evaluating risks associated with MeHg exposure.

The role of selenite on microglial migration

Oxidative brain damage, such as excitotoxicity and stroke, leads to primary neuronal destruction. The primary damage is further potentiated by macrophages and microglial cells, which are attracted and invade into the zone of damage resulting in secondary neuronal death. Since the essential trace element selenium has anti-inflammatory properties, we analyzed the effects of selenium on these inflammatory cells. Here, we show that the essential trace element selenium abrogates the stress-induced migration of microglial cells. Thus, the antimigratory effects of selenium may attenuate the secondary cell death cascade by preventing microglial invasion.

Extraction and determination of elemental selenium in sediments—A comparative study

This paper proposes a new technique to extract elemental Se from soil and sediment samples. In this study, we have identified that the purchased red elemental selenium standard (PF-Se) was impure and rather consisted of a mixture of CS2 soluble amorphous elemental Se (ca. 10%, w/w), water soluble oxidized Se (ca. 15-17%, w/w) and, CS2 insoluble red monoclinic elemental Se. In more recent studies, a slow oxidation and a mineral phase transition of this sample was also observed. The solubility of the amorphous elemental Se in CS2 was at least 0.64 mg L(-1). The black elemental Se purchased from Sigma-Aldrich had a much lower solubility in CS2 (7.2 microg mL(-1)) compared to that given in the literature. Any selenium compounds with electrical charge and polar nature is insoluble in CS2. In a sodium sulphite solution, PF-Se was completely dissolved thus giving a clear indication of the lack of selectivity in that extraction system. Other comparative studies also demonstrated that over extraction did occur with the Na2SO3 method. Compared to Na2SO3, CS2 extraction of elemental Se is not only much simpler, straightforward and with higher analytical precision, but also much more selective and accurate. With HG-AFS, the detection limit can reach as low as 1.0 ng g(-1) in sediment sample owing to a low reagent blank of CS2 solvent.

Selenium Supplementation Restores the Antioxidative Capacity and Prevents Cell Damage in Bone Marrow Stromal Cells In Vitro

Bone marrow stromal cells (BMSCs) and other cell populations derived from mesenchymal precursors are developed for cell-based therapeutic strategies and undergo cellular stress during ex vivo procedures. Reactive oxygen species (ROS) of cellular and environmental origin are involved in redox signaling, cumulative cell damage, senescence, and tumor development. Selenium-dependent (glutathione peroxidases [GPxs] and thioredoxin reductases [TrxRs]) and selenium-independent (superoxide dismutases [SODs] and catalase [CAT]) enzyme systems regulate cellular ROS steady state levels. SODs process superoxide anion to hydrogen peroxide, which is subsequently neutralized by GPx and CAT; TrxR neutralizes other ROS, such as peroxinitrite. Primary BMSCs and telomerase-immortalized human mesenchymal stem cells (hMSC-TERT) express GPx1-3, TrxR1, TrxR2, SOD1, SOD2, and CAT. We show here that in standard cell cultures (5%-10% fetal calf serum, 5-10 nM selenite), the activity of antioxidative selenoenzymes is impaired in hMSC-TERT and BMSCs. Under these conditions, the superoxide anion processing enzyme SOD1 is not sufficiently stimulated by an ROS load. Resulting oxidative stress favors generation of micronuclei in BMSCs. Supplementation of selenite (100 nM) restores basal GPx and TrxR activity, rescues basal and ROS-stimulated SOD1 mRNA expression and activity, and reduces ROS accumulation in hMSC-TERT and micronuclei generation in BMSCs. In conclusion, BMSCs in routine cell culture have low antioxidative capacity and are subjected to oxidative stress, as indicated by the generation of micronuclei. Selenite supplementation of BMSC cultures appears to be an important countermeasure to restore their antioxidative capacity and to reduce cell damage in the context of tissue engineering and transplantation procedures.

Involvement of selenoprotein P in protection of human astrocytes from oxidative damage

Selenoprotein P (SeP) is a highly glycosylated, selenium-rich plasma protein. Aside from its role as selenium carrier protein, an antioxidative function of SeP has been suggested. Astrocytes, which detoxify reactive oxygen species in the brain, were described as potential target cells of SeP. We investigated the expression of SeP in human astrocytes and its involvement in the protection of these cells against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage. We show that primary human astrocytes and the human astrocytoma cell line MOG-G-CCM express SeP as an unglycosylated protein, which is not secreted. SeP expression in astrocytes is constitutive. Preincubation of astrocytes with hepatocyte-derived SeP mimicks the protective effect of low-molecular-weight selenocompounds such as sodium selenite or selenomethionine against oxidative damage, shielding astrocytes from t-BHP-induced cytotoxicity. Selenium supplementation of astrocytes counteracts oxidative stress via an increase in expression and activity of the selenoenzyme cytosolic glutathione peroxidase (cGPx). Furthermore, specific downregulation of SeP expression by small interfering RNA decreases cell viability of human astrocytes and makes them more susceptible to t-BHP-induced cytotoxicity. Our results implicate an antioxidant activity of constitutively expressed SeP in selenium-deficient astrocytes, while during adequate selenium supply the enhanced protection against oxidative stress is exerted by cGPx.

One pot synthesis of selenocysteine containing peptoid libraries by Ugi multicomponent reactions in water

Selenocysteine containing peptoids and peptide-peptoid conjugates were synthesized by combinatorial Ugi-MCRs (multicomponent reactions) in water: for the first time, an acetal (selenoacetal 2a) was used in Ugi-MCR to furnish selenocysteine peptoids in one step as model compounds for selenocysteine peptides and proteins.

Selenocysteine tRNA-specific elongation factor SelB is a structural chimaera of elongation and initiation factors

In all three kingdoms of life, SelB is a specialized translation elongation factor responsible for the cotranslational incorporation of selenocysteine into proteins by recoding of a UGA stop codon in the presence of a downstream mRNA hairpin loop. Here, we present the X-ray structures of SelB from the archaeon Methanococcus maripaludis in the apo-, GDP- and GppNHp-bound form and use mutational analysis to investigate the role of individual amino acids in its aminoacyl-binding pocket. All three SelB structures reveal an EF-Tu:GTP-like domain arrangement. Upon binding of the GTP analogue GppNHp, a conformational change of the Switch 2 region in the GTPase domain leads to the exposure of SelB residues involved in clamping the 5' phosphate of the tRNA. A conserved extended loop in domain III of SelB may be responsible for specific interactions with tRNA(Sec) and act as a ruler for measuring the extra long acceptor arm. Domain IV of SelB adopts a beta barrel fold and is flexibly tethered to domain III. The overall domain arrangement of SelB resembles a 'chalice' observed so far only for initiation factor IF2/eIF5B. In our model of SelB bound to the ribosome, domain IV points towards the 3' mRNA entrance cleft ready to interact with the downstream secondary structure element.

Selenium and brain function: a poorly recognized liaison

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

Selenium deficiency increases susceptibility to glutamate-induced excitotoxicity

Excitotoxic brain lesions, such as stroke and epilepsy, lead to increasing destruction of neurons hours after the insult. The deadly cascade of events involves detrimental actions by free radicals and the activation of proapoptotic transcription factors, which finally result in neuronal destruction. Here, we provide direct evidence that the nutritionally essential trace element selenium has a pivotal role in neuronal susceptibility to excitotoxic lesions. First, we observed in neuronal cell cultures that addition of selenium in the form of selenite within the physiological range protects against excitotoxic insults and even attenuates primary damage. The neuroprotective effect of selenium is not directly mediated via antioxidative effects of selenite but requires de novo protein synthesis. Gel shift analysis demonstrates that this effect is connected to the inhibition of glutamate-induced NF-kappaB and AP-1 activation. Furthermore, we provide evidence that selenium deficiency in vivo results in a massive increase in susceptibility to kainate-induced seizures and cell loss. These findings indicate the importance of selenium for prevention and therapy of excitotoxic brain damage.