Glutathione peroxidase activity and selenoprotein W levels in different brain regions of selenium-depleted rats(1)

MicroRNA-294 Regulates Apoptosis of the Porcine Cerebellum Caused by Selenium Deficiency via Targeting iNOS

Deficiency of the essential trace element selenium (Se) can lead to cell apoptosis, and various microRNAs (miRNAs) are known to participate in the regulation of apoptosis by regulating their target genes. In this study, we explore the effect of Se deficiency on porcine cerebellar cell apoptosis and the role of miRNA in this process. After constructing a low-Se pig model, we observed the porcine cerebellum through an electron microscope and observed obvious characteristics of apoptosis. Moreover, it was found that the expression of miR-294 in Se-deficient pigs was significantly lower than that in the control group. Through bioinformatics, qRT-PCR, western blot analysis, and other experimental techniques, we further confirmed that inducible nitric oxide synthase (iNOS) is one of the target genes of miR-294. Our experimental results show that Se deficiency can reduce the expression of miR-294 and increase both the expression of iNOS and the nitric oxide (NO) content (P < 0.01). The expression of heat shock proteins (HSPs, such as HSP70, HSP90, HSP60, HSP40, and HSP27) and mitochondrial pathway-related indicators, such as Bcl2-associated X protein (Bax), cytochrome C (Cyt-C), and cysteinyl aspartate-specific proteinases (caspase 3, caspase 7, and caspase 8), was upregulated (P < 0.05), and the expression of B cell lymphoma-2 (Bcl-2) was downregulated (P < 0.05). In summary, we believe that Se deficiency can lead to abnormal expression of miR-294 and HSPs; moreover, the mitochondrial apoptosis pathway is activated, which significantly enhances apoptosis of cerebellar cells in Se-deficient pigs. These results enrich the biological effects of Se deficiency.

Juvenile Selenium Deficiency Impairs Cognition, Sensorimotor Gating, and Energy Homeostasis in Mice

Selenium (Se) is an essential micronutrient of critical importance to mammalian life. Its biological effects are primarily mediated via co-translational incorporation into selenoproteins, as the unique amino acid, selenocysteine. These proteins play fundamental roles in redox signaling and includes the glutathione peroxidases and thioredoxin reductases. Environmental distribution of Se varies considerably worldwide, with concomitant effects on Se status in humans and animals. Dietary Se intake within a narrow range optimizes the activity of Se-dependent antioxidant enzymes, whereas both Se-deficiency and Se-excess can adversely impact health. Se-deficiency affects a significant proportion of the world's population, with hypothyroidism, cardiomyopathy, reduced immunity, and impaired cognition being common symptoms. Although relatively less prevalent, Se-excess can also have detrimental consequences and has been implicated in promoting both metabolic and neurodegenerative disease in humans. Herein, we sought to comprehensively assess the developmental effects of both Se-deficiency and Se-excess on a battery of neurobehavioral and metabolic tests in mice. Se-deficiency elicited deficits in cognition, altered sensorimotor gating, and increased adiposity, while Se-excess was surprisingly beneficial.

Roles of Selenoproteins in Brain Function and the Potential Mechanism of Selenium in Alzheimer's Disease

Selenium (Se) and its compounds have been reported to have great potential in the prevention and treatment of Alzheimer's disease (AD). However, little is known about the functional mechanism of Se in these processes, limiting its further clinical application. Se exerts its biological functions mainly through selenoproteins, which play vital roles in maintaining optimal brain function. Therefore, selenoproteins, especially brain function-associated selenoproteins, may be involved in the pathogenesis of AD. Here, we analyze the expression and distribution of 25 selenoproteins in the brain and summarize the relationships between selenoproteins and brain function by reviewing recent literature and information contained in relevant databases to identify selenoproteins (GPX4, SELENOP, SELENOK, SELENOT, GPX1, SELENOM, SELENOS, and SELENOW) that are highly expressed specifically in AD-related brain regions and closely associated with brain function. Finally, the potential functions of these selenoproteins in AD are discussed, for example, the function of GPX4 in ferroptosis and the effects of the endoplasmic reticulum (ER)-resident protein SELENOK on Ca²⁺ homeostasis and receptor-mediated synaptic functions. This review discusses selenoproteins that are closely associated with brain function and the relevant pathways of their involvement in AD pathology to provide new directions for research on the mechanism of Se in AD.

Identification of FAM96B as a novel selenoprotein W binding partner in the brain

Selenoprotien W (SelW) plays a key role in brain development, although the exact biological function and mechanisms remain unclear. We performed a yeast two-hybrid screen on a human fetal brain cDNA library and identified FAM96B as a novel binding partner of SelW. FRET analyses confirmed the interaction between SelW' and FAM96B. The mutated SelW' construct was cloned and overexpressed in E. coli, and a pull-down assay verified a direct interaction between SelW' and FAM96B. Finally, Co-Immunoprecipitation on murine brain tissue proteins demonstrated an endogenous interaction between the two proteins in the brain. Taken together, our findings prove a direct interaction between SelW and FAM96B, which may provide new insights into the role of SelW in brain development and neurodegenerative diseases.

Effects of soft electrophiles on selenium physiology

This review examines the effects of neurotoxic electrophiles on selenium (Se) metabolism. Selenium-dependent enzymes depend on the unique and elite functions of selenocysteine (Sec), the 21st proteinogenic amino acid, to perform their biochemical roles. Humans possess 25 selenoprotein genes, ~ half of which are enzymes (selenoenzymes) required for preventing, controlling, or reversing oxidative damage, while others participate in regulating calcium metabolism, thyroid hormone status, protein folding, cytoskeletal structure, Sec synthesis and Se transport. While selenoproteins are expressed in tissue dependent distributions and levels in all cells of all vertebrates, they are particularly important in brain development, health, and functions. As the most potent intracellular nucleophile, Sec is subject to binding by mercury (Hg) and other electron poor soft neurotoxic electrophiles. Epidemiological and environmental studies of the effects of exposures to methyl-Hg (CH₃Hg⁺), elemental Hg (Hg°), and/or other metallic/organic neurotoxic soft electrophiles need to consider the concomitant effects of all members of this class of toxicants in relation to the Se status of their study populations. The contributions of individual electrophiles' discrete and cooperative rates of Se sequestration need to be evaluated in relation to tissue Se reserves of the exposed populations to identify sensitive subgroups which may be at accentuated risk due to poor Se status. Additional study is required to examine possibilities of inherited, acquired, or degenerative neurological disorders of Se homeostasis that may influence vulnerability to soft electrophile exposures. Investigations of soft electrophile toxicity will be enhanced by considering the concomitant effects of combined exposures on tissue Se-availability in relation to pathological consequences during fetal development or in relation to etiologies of neurological disorders and neurodegenerative diseases. Since selenoenzymes are molecular "targets" of soft electrophiles, concomitant evaluation of aggregate exposures to these toxicants in relation to dietary Se intakes will assist regulatory agencies in their goals of improving and protecting public health.

Effects of Selol 5% supplementation on tissue antioxidant enzyme levels and peroxidation marker in healthy mice

BACKGROUND

Selenium (Se) is an essential micronutrient for animals and humans used in the prevention or treatment of cancer. Selol is a mixture of selenitetriglycerides, containing Se(IV). It does not exhibit mutagenic activity and is less toxic than inorganic sodium selenite containing Se(IV). The antioxidant properties of the Selol were demonstrated using the blood of healthy animals. The aim of the study was to evaluate Selol as a Se supplement by determining the effect of its administration on the Se level and the antioxidant status in the tissues.

METHODS

We examined the effect of long-term (28-day) Selol 5% supplementation on the activity of antioxidant enzymes, including the main selenoenzymes in healthy mice organs, such as liver, brain, lungs, and testis. Enzyme activities of the tissue homogenates and the concentration of malondialdehyde (MDA) as a biomarker of oxidative stress were measured using spectrophotometric methods. The selenium concentrations in the tissues were determined by inductively coupled plasma mass spectrometer (ICP-MS) as well.

RESULTS

A significant increase in glutathione peroxidase, thioredoxin reductase, and glutathione S-transferase activity as well as the MDA concentration was observed in most of the studied tissues during the Selol 5% supplementation.

CONCLUSIONS

Long-term supplementation with the new Se(IV) compound - Selol 5% significantly affects the activity of antioxidant enzymes and the redox state in healthy mice organs. In the healthy population Selol 5% seems to be a promising new antioxidant compound.

Sodium selenite ameliorates both intestinal and extra-intestinal changes in acetic acid-induced colitis in rats

Selenium and its derivatives including sodium selenite (sod sel) belong to the group of essential trace elements needed for proper health and nutrition. They are fairly safe and possess antioxidant and anti-inflammatory properties. The aim of present investigation was to elucidate the effect of sod sel on experimental colitis model in rats. Colitis was induced by intrarectal instillation of 4% (v/v) acetic acid. Two hours later, sod sel was given to rats on a daily basis for 15 consecutive days. Clinical symptoms, colon mass index, spleen weight inflammatory markers, hematological, biochemical, macroscopic, and histological changes were determined. Sod sel markedly ameliorated colitis as evidenced by a significant decrease in macroscopic and microscopic score, disease activity index, colon mass index, and spleen weight. Treatment with sod sel attenuated oxidative stress in the colon by normalizing the colonic content of nitric oxide, malondialdehyde, and reduced glutathione, as well as the activities of catalase, superoxide dismutase, and junctional adhesion molecule (JAM-a). In addition, it significantly reduced colonic myeloperoxidase content, the intercellular adhesion molecule (ICAM-1), and the proinflammatory cytokines; TNF-α, IL-1β. Moreover, sod sel normalized hematological parameters, serum transaminases, and kidney and liver function enzymes. The current study indicates that sod sel was effective in ameliorating the intestinal and extra-intestinal manifestation in acetic acid-induced colitis through its antioxidant, anti-inflammatory, and immunomodulatory effects.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

Selenotranscriptomic Analyses Identify Signature Selenoproteins in Brain Regions in a Mouse Model of Parkinson's Disease

Genes of selenoproteome have been increasingly implicated in various aspects of neurobiology and neurological disorders, but remain largely elusive in Parkinson’s disease (PD). In this study, we investigated the selenotranscriptome (24 selenoproteins in total) in five brain regions (cerebellum, substantia nigra, cortex, pons and hippocampus) by real time qPCR in a two-phase manner using a mouse model of chronic PD. A wide range of changes in selenotranscriptome was observed in a manner depending on selenoproteins and brain regions. While Selv mRNA was not detectable and Dio1& 3 mRNA levels were not affected, 1, 11 and 9 selenoproteins displayed patterns of increase only, decrease only, and mixed response, respectively, in these brain regions of PD mice. In particular, the mRNA expression of Gpx1-4 showed only a decreased trend in the PD mouse brains. In substantia nigra, levels of 17 selenoprotein mRNAs were significantly decreased whereas no selenoprotein was up-regulated in the PD mice. In contrast, the majority of selenotranscriptome did not change and a few selenoprotein mRNAs that respond displayed a mixed pattern of up- and down-regulation in cerebellum, cortex, hippocampus, and/or pons of the PD mice. Gpx4, Sep15, Selm, Sepw1, and Sepp1 mRNAs were most abundant across all these five brain regions. Our results showed differential responses of selenoproteins in various brain regions of the PD mouse model, providing critical selenotranscriptomic profiling for future functional investigation of individual selenoprotein in PD etiology.

Molecular cloning and sequence analysis of selenoprotein W gene and its mRNA expression patterns in response to metabolic status and cadmium exposure in goldfish, Carassius auratus

Selenoprotein W (SelW) is a low molecular weight and selenocysteine containing protein with redox activity involved in the antioxidant response. In the present study, the full-length cDNA of goldfish (Carassius auratus) selenoprotein W (gfSelW) was successfully cloned from the liver tissue by rapid amplification of cDNA ends technique. The obtained gfSelW cDNA was 730 bp long with a 79 bp 5'-untranslated region (UTR), a 390 bp 3'-UTR containing the consensus polyadenylation signal AATAAA and a 261 bp open reading frame coding a protein of 86 amino acid residues. gfSelW mRNA was observed in all regions of brain and peripheral tissues by semi-quantitative RT-PCR, and the most abundant was detected in testis. After fasting for 1 week, gfSelW mRNA expression levels were significantly decreased compared to the fed group in hypothalamus and liver. After refeeding for 7 days, gfSelW mRNA expression levels were increased back. Furthermore, the mRNA expressions of gfSelW in hypothalamus and liver were varied in periprandial changes and significantly up-regulated after meal 2 h and 4 h, respectively. With cadmium exposure for 24 h, gfSelW mRNA expression levels in gill and leucocytes were significantly decreased at different cadmium concentrations changing from 0.5 ppm to 10 ppm. However, the gfSelW mRNA expression level was sharply increased in liver, relatively to the control about 4.98-fold at 0.5 ppm. The results in this study provide molecular characterization of SelW in goldfish and imply that SelW mRNA expression may be associated with metabolic status and oxidative stress and regulated by metabolic factors and cadmium in fish.

Selenium-enriched foods are more effective at increasing glutathione peroxidase (GPx) activity compared with selenomethionine: a meta-analysis

Selenium may play a beneficial role in multi-factorial illnesses with genetic and environmental linkages via epigenetic regulation in part via glutathione peroxidase (GPx) activity. A meta-analysis was undertaken to quantify the effects of dietary selenium supplementation on the activity of overall GPx activity in different tissues and animal species and to compare the effectiveness of different forms of dietary selenium. GPx activity response was affected by both the dose and form of selenium (p < 0.001). There were differences between tissues on the effects of selenium supplementation on GPx activity (p < 0.001); however, there was no evidence in the data of differences between animal species (p = 0.95). The interactions between dose and tissue, animal species and form were significant (p < 0.001). Tissues particularly sensitive to changes in selenium supply include red blood cells, kidney and muscle. The meta-analysis identified that for animal species selenium-enriched foods were more effective than selenomethionine at increasing GPx activity.

Selenoprotein W expression and regulation in mouse brain and neurons

Background Selenoprotein W (Sepw1) is a selenium-containing protein that is abundant in brain and muscle of vertebrate animals. Muscular expression of Sepw1 is reduced by dietary selenium (Se) deficiency in mammals, whereas brain expression is maintained. However, expression of Sepw1 depends on the Se transporter selenoprotein P (Sepp1). Methods We assessed the regional and cellular expression of Sepw1 in the mouse brain and neuronal cultures. Results We found that Sepw1 is widespread in neurons and neuropil of mouse brain and appears in both the soma and processes of neurons in culture. Pyramidal neurons of cortex and hippocampus express high levels of Sepw1. It is also abundant in Purkinje neurons and their dendritic arbors in the cerebellum. Analysis of synaptosome fractions prepared from mice brains indicated that Sepw1 is present at synapses, as were several proteins involved in selenoprotein synthesis. Synaptic expression of Sepw1 expression is reduced in mice lacking Sepp1 compared with control mice, although selenoprotein synthesis factors were similarly expressed in both genotypes. Lastly, Sepw1 mRNA coimmunoprecipitates with Staufen 2 protein in a human neuronal cell line. Conclusions Our results suggest that Sepw1 may be locally synthesized in distal compartments of neurons including synapses.

Protective and antioxidant role of selenium on arsenic trioxide-induced oxidative stress and genotoxicity in the fish hepatoma cell line PLHC-1

In vitro models are useful tools for rapid screening for toxicity, elucidation of mechanisms of toxicity, and understanding complex interactions among environmental toxicants. These evaluations may provide useful information for ecological evaluations if the relationship between in vitro and in vivo effects is established. The present study was undertaken to evaluate the protective effect of selenium on arsenic trioxide (As(2) O(3) )-induced cytotoxicity, DNA damage, and apoptosis. N-acetylcysteine (NAC), a free radical scavenger, was used to determine the involvement of reactive oxygen species (ROS) in As(2) O(3) -induced DNA damage and apoptosis. Poeciliopsis lucida hepatocellular carcinoma line 1 (PLHC-1) cells were pretreated with selenium (1, 5, and 10 µM) and NAC (50 and 100 µM) for 2 h. After pretreatment, cells were exposed to 100 µM of As(2) O(3) for 10-, 20-, and 40-h intervals. The As(2) O(3) exposure promoted extensive DNA damage and apoptosis compared to control, while selenium- and NAC-pretreated cells improved cell survival rate against As(2) O(3) -induced cell death. Improved survival likely resulted from increasing glutathione peroxidase activity and reduction of ROS formation, reduction of mitochondrial membrane potential damage, DNA damage, and caspase-3 activity. During As(2) O(3) exposure, selenium played the same role as NAC. The authors conclude that As(2) O(3) -induced DNA damage and apoptosis are mediated by oxidative stress and selenium and that, although toxic at higher concentrations, selenium provides significant protection against As(2) O(3) effects in PLHC-1 cells.

Priority in selenium homeostasis involves regulation of SepSecS transcription in the chicken brain

O-phosphoseryl-tRNA:selenocysteinyl-tRNA synthase (SepSecS) is critical for the biosynthesis and transformation of selenocysteine (Sec) and plays an important role in the biological function of Se through the regulation of selenoprotein synthesis. Selenium (Se) and Selenoprotein play a pivotal role in brain function. However, how intake of the micronutrient Se affects gene expression and how genetic factors influence Se metabolism in the brain is unknown. To investigate the regulation of SepSecS transcription induced by Se in the chicken brain, we determined the Se content of brain tissue, SepSecS gene expression levels and mRNA stability in the chicken brain and primary cultured chicken embryos neurons receiving Se supplements. These results showed that Se content in the brain remains remarkably stable during Se supplementation. A significant increase in SepSecS mRNA levels was observed in all of the brain tissues of chickens fed diets containing 1-5 mg/kg sodium selenite. Most strikingly, significant changes in SepSecS mRNA levels were not observed in neurons treated with Se. However, Se altered the SepSecS mRNA half-life in cells. These data suggest that Se could regulate SepSecS mRNA stability in the avian brain and that SepSecS plays an important role in Se homeostasis regulation.

Selenium health benefit values as seafood safety criteria

Selenium (Se) is absolutely required for activity of 25-30 genetically unique enzymes (selenoenzymes). All forms of life that have nervous systems possess selenoenzymes to protect their brains from oxidative damage. Homeostatic mechanisms normally maintain optimal selenoenzyme activities in brain tissues, but high methylmercury (MeHg) exposures sequester Se and irreversibly inhibit selenoenzyme activities. However, nutritionally relevant amounts of Se can replace the Se sequestered by MeHg and maintain normal selenoenzyme activities, thus preventing oxidative brain damage and other adverse consequences of MeHg toxicity. Findings of studies that seem contradictory from MeHg exposure perspectives are entirely consistent from MeHg:Se molar ratio perspectives. Studies that have reported dose-dependent consequences of maternal MeHg exposures on child development uniformly involved seafoods that contained much more Hg than Se. Meanwhile more typical varieties of ocean fish contain much more Se than Hg. This may explain why maternal MeHg exposure from eating ocean fish is associated with major IQ benefits in children instead of harm. Therefore, instead of being avoided, ocean fish consumption should be encouraged during pregnancy. However, the safety of freshwater fish consumption is less certain. In freshwater fish, MeHg bioaccumulation and toxicity are both inversely related to Se bioavailability. Their Se can be far lower than their MeHg contents, potentially making them more dangerous than pilot whale meats. Therefore, to provide accurate and appropriate regulatory advice regarding maternal consumption of seafoods and freshwater fish, Hg:Se molar ratios need to be incorporated in food safety criteria.

Thyroid hormones and methylmercury toxicity

Thyroid hormones are essential for cellular metabolism, growth, and development. In particular, an adequate supply of thyroid hormones is critical for fetal neurodevelopment. Thyroid hormone tissue activation and inactivation in brain, liver, and other tissues is controlled by the deiodinases through the removal of iodine atoms. Selenium, an essential element critical for deiodinase activity, is sensitive to mercury and, therefore, when its availability is reduced, brain development might be altered. This review addresses the possibility that high exposures to the organometal, methylmercury (MeHg), may perturb neurodevelopmental processes by selectively affecting thyroid hormone homeostasis and function.

Protective effects of selenium on mercury-induced DNA damage in mussel haemocytes

Little is known of the antioxidant role of selenium (Se) in aquatic invertebrates. We investigated the effects of Se on mercury-induced DNA damage in haemocytes from Mytilus edulis using alkaline single cell gel electrophoresis, that is, the Comet assay. The basal percentage tail DNA value for mussel haemocytes was 9.8+/-0.2% (mean+/-S.E.M., n=70). Exposing mussels to Hg(2+) (nominal concentration 20 microgL(-1)) for three days led to an increase in tail DNA to 61.1+/-1.8% (n=10). With added Se (as selenite, nominal concentration 4 microgL(-1)), Hg-induced DNA damage was reduced to 39.5+/-3.1% (n=10). Se pre-exposure also provided some protection against Hg-induced DNA damage (% tail DNA=51.0+/-2.9%, n=10). Basal glutathione peroxidase (GPx) activity in cell-free haemolymph was 93.7+/-3.5 nmol min(-1)mg(-1) (mean+/-S.E.M., n=70). Increases in GPx activity were seen when Se was added during and/or after exposure to Hg. For example, a 3-4-fold increase was seen after three days exposure to Hg in the presence of added Se. Interestingly GPx activity doubled after three days in the presence of added Se alone, but was unchanged after exposure to HgCl(2) alone. These results suggest that the availability of Se in the natural environment could affect the antioxidant status of mussels, and consequently could affect levels of DNA damage.

Selenium and the control of thyroid hormone metabolism

Thyroid hormone synthesis, metabolism and action require adequate availability of the essential trace elements iodine and selenium, which affect homeostasis of thyroid hormone-dependent metabolic pathways. The three selenocysteine-containing iodothyronine deiodinases constitute a novel gene family. Selenium is retained and deiodinase expression is maintained at almost normal levels in the thyroid gland, the brain and several other endocrine tissues during selenium deficiency, thus guaranteeing adequate local and systemic levels of the active thyroid hormone T(3). Due to their low tissue concentrations and their mRNA SECIS elements deiodinases rank high in the cellular and tissue-specific hierarchy of selenium distribution among various selenoproteins. While systemic selenium status and expression of abundant selenoproteins (glutathione peroxidase or selenoprotein P) is already impaired in patients with cancer, disturbed gastrointestinal resorption, unbalanced nutrition or patients requiring intensive care treatment, selenium-dependent deiodinase function might still be adequate. However, disease-associated alterations in proinflammatory cytokines, growth factors, hormones and pharmaceuticals modulate deiodinase isoenzyme expression independent from altered selenium status and might thus pretend causal relationships between systemic selenium status and altered thyroid hormone metabolism. Limited or inadequate supply of both trace elements, iodine and selenium, leads to complex rearrangements of thyroid hormone metabolism enabling adaptation to unfavorable conditions.

Selenoprotein W as molecular target of methylmercury in human neuronal cells is down-regulated by GSH depletion

Methylmercury (MeHg) is well known as a neurotoxic chemical. However, little is mentioned about its neurotoxic mechanism or molecular target in human neuronal cells in particular. We show in this study that exposure of human neuronal cell line, SH-SY5Y, to MeHg dose- and time-dependently impairs viability and mRNA expression of selenoprotein W (SeW) with a significant difference, unlike other selenoenzymes such as, SeP, GPX4, 5DI, and 5'DI. Using real-time RT PCR, the influence of selenium (Se) and glutathione (GSH) on SeW expression was also investigated. While Se depletion caused a weakly reduced SeW mRNA levels, additional Se caused an increase of SeW mRNA levels. Although 2 mM GSH had induced a weak shift on SeW level, the expression of SeW mRNA was down-regulated in SH-SY5Y cells treated with 25 microM BSO, an inhibitor of GSH synthesis. To understand the relationship between a decrease of SeW expression and intracellular GSH and ROS, we measured the concentration of intracellular GSH and ROS in cells treated to 1.4 microM MeHg using fluorescence based assays. A positive correlation was found between SeW mRNA level and intracellular GSH but no significant correlation was observed between intracellular ROS and SeW mRNA level or intracellular GSH contents. Therefore, we suggest that SeW is the novel molecular target of MeHg in human neuronal cells and down-regulation of this selenoenzyme by MeHg is dependent not on generation of ROS but on depletion of GSH.

Selective production of rat mutant selenoprotein W with and without bound glutathione

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and electrospray ionization mass spectrometry (ESI MS) analysis of a 6x His-tagged recombinant form of rat mutant selenoprotein W (RMSW) reveals that aerobic growth conditions primarily produce a form of RMSW without bound glutathione (10,305 Da) whereas anaerobic conditions produce a glutathione-bound (305 Da) form (10,610 Da). Purification of RMSW was achieved with a procedure employing acetone precipitation and DEAE-cellulose chromatography, in addition to Ni-NTA agarose chromatography. Additional steps, including polyvalent metal ion binding (PMIB) resin chromatography and CM-cellulose chromatography, were necessary after elution from the Ni-NTA agarose column, in order to maintain solubility of the purified protein.

Trends in selenium biochemistry

The biochemistry of selenium-containing natural products, including selenoproteins, is reviewed up to May 2002. Particular emphasis is placed on the assimilation of selenium from inorganic and organic selenium sources for selenoprotein synthesis, the catalytic role of selenium in enzymes, and medical implications of an unbalanced selenium supply. The review contains 393 references on key discoveries and recent progress.

Selenium and the brain: a review

Similar to other tissues selenium from selenomethionine is deposited in the brain at higher concentrations than selenium in other forms. Vitamin E has a greater effect than selenium in reducing lipid peroxidation in various brain regions. Selenium does not have as great effect on glutathione peroxidase (GPX) activity in the brain as in most other organs. Prolonged selenium and iodine deficiencies will compromise thyroid hormone homeostatus in the brain and this is due to changes in deiodinases activities and lipid peroxidation. Even though selenium deficiency results in reduced GPX activity and selenium content in the brain, there is no reduction in thioredoxin reductase activity or selenoprotein W levels. Selenoprotein P is taken up in greater amounts by the brain but not by other organs in selenium deficient animals, suggesting a critical function of this selenoprotein in this organ. Selenium will influence compounds with hormonal activity (and neurotransmitters) in the brain, and this is postulated to be the reason selenium affects moods in humans and behavior in animals. Even though selenium counteracts the neurotoxicity of mercury, cadmium, lead and vanadium, it causes them to accumulate in the brain, presumably in a nontoxic complex.