Dietary selenium increases selenoprotein W levels in rat tissues

Impaired Upper Airway Muscle Function with Excessive or Deficient Dietary Intake of Selenium in Rats

Obstructive sleep apnoea (OSA) involves impaired upper airway muscle function and is linked to several pathologies including systemic hypertension, daytime somnolence and cognitive decline. Selenium is an essential micronutrient that exerts many of its effects through selenoproteins. Evidence indicates that either deficient or excessive dietary selenium intake can result in impaired muscle function, termed nutritional myopathy. To investigate the effects of selenium on an upper airway muscle, the sternohyoid, rats were fed on diets containing deficient, normal (0.5 ppm sodium selenite) or excessive (5 ppm selenite) selenium for a period of two weeks. Sternohyoid contractile function was assessed ex vivo. Serum selenium levels and activity of the glutathione antioxidant system were determined by biochemical assays. The abundance of three key muscle selenoproteins (selenoproteins -N, -S and -W (SELENON, SELENOS and SELENOW)) in sternohyoid muscle were quantified by immunoblotting. Levels of these selenoproteins were also compared between rats exposed to chronic intermittent hypoxia, a model of OSA, and sham treated animals. Although having no detectable effect on selected organ masses and whole-body weight, either selenium-deficient or -excessive diets severely impaired sternohyoid contractile function. These changes did not involve altered fibre size distribution. These dietary interventions resulted in corresponding changes in serum selenium concentrations but did not alter the activity of glutathione-dependent antioxidant systems in sternohyoid muscle. Excess dietary selenium increased the abundance of SELENOW protein in sternohyoid muscles but had no effect on SELENON or SELENOS. In contrast, chronic intermittent hypoxia increased SELENON, decreased SELENOW and had no significant effect on SELENOS in sternohyoid muscle. These findings indicate that two-week exposure to selenium-deficient or -excessive diets drastically impaired upper airway muscle function. In the sternohyoid, SELENON, SELENOS and SELENOW proteins show distinct alterations in level following exposure to different dietary selenium intakes, or to chronic intermittent hypoxia. Understanding how alterations in Se and selenoproteins impact sternohyoid muscle function has the potential to be translated into new therapies for prevention or treatment of OSA.

Selenoprotein W modulates tau homeostasis in an Alzheimer's disease mouse model

Lower selenium levels are observed in Alzheimer's disease (AD) brains, while supplementation shows multiple benefits. Selenoprotein W (SELENOW) is sensitive to selenium changes and binds to tau, reducing tau accumulation. However, whether restoration of SELENOW has any protective effect in AD models and its underlying mechanism remain unknown. Here, we confirm the association between SELENOW downregulation and tau pathology, revealing SELENOW's role in promoting tau degradation through the ubiquitin‒proteasome system. SELENOW competes with Hsp70 to interact with tau, promoting its ubiquitination and inhibiting tau acetylation at K281. SELENOW deficiency leads to synaptic defects, tau dysregulation and impaired long-term potentiation, resulting in memory deficits in mice. Conversely, SELENOW overexpression in the triple transgenic AD mice ameliorates memory impairment and tau-related pathologies, featuring decreased 4-repeat tau isoform, phosphorylation at Ser396 and Ser404, neurofibrillary tangles and neuroinflammation. Thus, SELENOW contributes to the regulation of tau homeostasis and synaptic maintenance, implicating its potential role in AD.

Deciphering the role of metal and non-metals in the treatment of epilepsy

Metals and non-metals have known to play a significant role in various physiological roles in the body including the central nervous system (CNS). The alterations in their concentration in the CNS leads to abnormalities in the normal functions which may lead to various neurological conditions including epilepsy. Manganese is a cofactor required for antioxidant enzymes such as Superoxide dismutase, Glutamine synthetase, etc. The accumulation of iron leads to formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which have the potential to cause ferroptosis, one of the reasons for epileptogenesis. Zinc has biphasic response, both neurotoxic and neuroprotective, based on concentration levels in the CNS. Selenium is a main element for selenoproteins which is responsible for the regulation of oxidative state and antioxidant defence mechanism. The reduction in the phosphorous levels in the CNS is widely observed after generalised tonic clonic seizures (GTC), which can be a potential diagnostic biomarker. Copper acts in the CNS in an identical manner, i.e., by blocking both AMPA mediated and GABA mediated neuronal transmission. Magnesium blocks calcium channels in the NMDA receptor and prevents glutamatergic transmission, thus inhibiting excitotoxicity. Lithium acts as a proconvulsive agent and is used in combination with pilocarpine to induce seizures. The identified potential of metals and non-metals in epilepsy can be utilised in order to devise new adjuvant therapies for the management of epilepsy. The article summaries in depth the role of metals and non-metals in the treatment of epilepsy supported with special paragraph on author perspective on to the topic. Furthermore, an update of preclinical and clinical evidences are discussed in the review to give evidence on metal and non-metal based therapies in epilepsy.

Comparative Proteomic Analysis Reveals the Effect of Selenoprotein W Deficiency on Oligodendrogenesis in Fear Memory

The essential trace element selenium plays an important role in maintaining brain function. Selenoprotein W (SELENOW), the smallest selenoprotein that has been identified in mammals, is sensitive to selenium levels and abundantly expressed in the brain. However, its biological role in the brain remains to be clarified. Here, we studied the morphological and functional changes in the brain caused by SELENOW deficiency using its gene knockout (KO) mouse models. Histomorphological alterations of the amygdala and hippocampus, specifically in the female SELENOW KO mice, were observed, ultimately resulting in less anxiety-like behavior and impaired contextual fear memory. Fear conditioning (FC) provokes rapidly intricate responses involving neuroplasticity and oligodendrogenesis. During this process, the females generally show stronger contextual FC than males. To characterize the effect of SELENOW deletion on FC, specifically in the female mice, a Tandem mass tag (TMT)-based comparative proteomic approach was applied. Notably, compared to the wildtype (WT) no shock (NS) mice, the female SELENOW KO NS mice shared lots of common differentially expressed proteins (DEPs) with the WT FC mice in the hippocampus, enriched in the biological process of ensheathment and oligodendrocyte differentiation. Immunostaining and Western blotting analyses further confirmed the proteomic results. Our work may provide a holistic perspective of gender-specific SELENOW function in the brain and highlighted its role in oligodendrogenesis during fear memory.

A Comprehensive Review on Selenium and Its Effects on Human Health and Distribution in Middle Eastern Countries

Selenium (Se) is an important microelement with numerous positive effects on human health and diseases. It is important to specify that the status and consumption of Se are for a specific community as the levels of Se are extremely unpredictable between different populations and regions. Our existing paper was based on the impacts of Se on human health and disease along with data on the Se levels in Middle Eastern countries. Overall, the findings of this comprehensive review show that the consumption and levels of Se are inadequate in Middle Eastern nations. Such findings, together with the growing awareness of the importance of Se to general health, require further work primarily on creating an acceptable range of blood Se concentration or other measures to determine optimal Se consumption and, consequently, to guarantee adequate Se supplementation in populations at high risk of low Se intake.

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.

Selenoprotein W as a molecular target of d-amino acid oxidase is regulated by d-amino acid in chicken neurons

Selenoprotein W (SelW), an important member of the avian selenoprotein family, can combine with d-amino acid oxidase (DAAO). Selenium (Se) can inhibit the toxicity of d-serine and maybe has a detoxifying ability by increasing the expression of SelW and decreasing the activity of DAAO.

Protective effects of antioxidants on acrylonitrile-induced oxidative stress in female F344 rats

The induction of oxidative stress and damage appears to be involved in acrylonitrile induction of brain astrocytomas in rat. The present study examined the effects of dietary antioxidant supplementation on acrylonitrile-induced oxidative stress and oxidative damage in rats in vivo. To assess the effects of antioxidants on biomarkers of acrylonitrile-induced oxidative stress, female F344 rats were provided with diets containing vitamin E (0.05%), green tea polyphenols (GTP, 0.4%), N-acetyl cysteine (NAC, 0.3%), sodium selenite (0.1mg/kg), and taurine (10g/kg) for 7 days, and then co-administered with 0 and 100 ppm acrylonitrile in drinking water for 28 days. Significant increase in oxidative DNA damage in brain, evidenced by elevated 8OHdG levels, was seen in acrylonitrile-exposed rats. Supplementation with vitamin E, GTP, and NAC reduced acrylonitrile-induced oxidative DNA damage in brain while no protective effects were seen with the selenium or taurine supplementation. Acrylonitrile increased oxidative DNA damage, measured by the fpg-modified alkaline Comet assay in rat WBCs, which was reduced by supplementation of Vitamin E, GTP, NAC, selenium, and taurine. In addition to stimulation of oxidative DNA damage, acrylonitrile triggered induction of pro-inflammatory cytokines Tnfα, Il-1β, and Ccl2, and the growth stimulatory cyclin D1 and cyclin D2 genes, which were effectively down-regulated with antioxidant treatment. Antioxidant treatment also was able to stimulate the pro-apoptotic genes Bad, Bax, and FasL and DNA repair genes Xrcc6 and Gadd45α. The results of this study support the involvement of oxidative stress in the development of acrylonitrile-induced astrocytomas and suggest that antioxidants block acrylonitrile-mediated damage through mechanisms that may involve in the suppression of inflammatory responses, inhibition of cell proliferation and stimulation of apoptosis. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1808-1818, 2016.

The role of selenoprotein W in inflammatory injury in chicken immune tissues and cultured splenic lymphocyte

Selenoprotein W (SelW) is mainly understood in terms of its antioxidant effects in the cellular defense system. Inflammation is an important indicator of animal tissue injury, and the inflammatory cells may trigger a sophisticated and well-orchestrated inflammatory cascade, resulting in exaggerated oxidative stress. To investigate the role of SelW in inflammatory injury in chicken immune tissues and cultured splenic lymphocyte, in this report, the effects of selenium (Se) on mRNA expressions of SelW and inflammatory factors (iNOS, COX-2, NF-κB, PTGEs, and TNF-α) in the chicken immune organs (spleen, thymus and bursa of Fabricius) and cultured splenic lymphocyte treated with sodium selenite and H2O2, or knocked down SelW with small interfering RNAs (siRNAs) were examined. The results showed that Se-deficient diets effectively decreased the mRNA expression of SelW (P < 0.05), and induced a significantly up-regulation of COX-2, iNOS, NF-κB, PTGEs and TNF-α mRNA levels (P < 0.05). The histopathological analysis showed that immune tissues were obviously injured in the low-Se groups. In vitro, H2O2 induced a significantly up-regulation of the mRNA levels of inflammation-related genes (iNOS, COX-2, NF-κB, PTGEs, and TNF-α) in cultured splenic lymphocyte (P < 0.05). When lymphocytes were pretreated with Se before treated with H2O2, the inflammation-related genes were significantly decreased (P < 0.05). Silencing of SelW significantly up-regulated the inflammation-related genes (iNOS, COX-2, NF-κB, PTGEs, and TNF-α) in cultured splenic lymphocyte (P < 0.05). The results suggested that the expression levels of inflammatory factors (iNOS, COX-2, NF-κB, PTGEs, and TNF-α) and SelW can be influenced by Se in birds. SelW commonly played an important role in the protection of immune organs of birds from inflammatory injury by the regulations of inflammation-related genes.

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.

Effects of different selenium levels on gene expression of a subset of selenoproteins and antioxidative capacity in mice

This study aimed to evaluate how excess selenium induces oxidative stress by determining antioxidant enzyme activity and changes in expression of selected selenoproteins in mice. BALB/c mice (n = 20 per group) were fed a diet containing 0.045 (Se-marginal), 0.1 (Se-adequate), 0.4 (Se-supernutrition), or 0.8 (Se-excess) mg Se/kg. Gene expression was quantified in RNA samples extracted from the liver, kidney, and testis by real-time quantitative reverse transcription-polymerase chain reaction. We found that glutathione peroxidase (GPx) and catalase activities decreased in livers of mice fed the marginal or excess dose of Se as compared to those in the Se-adequate group. Additionally, superoxide dismutase and glutathione reductase activities were significantly reduced only in mice fed the excess Se diet, compared to animals on the adequate Se diet. Se-supernutrition had no effect on hepatic mRNA levels of GPx isoforms 1 and 4 (GPx1 and GPx4), down-regulated GPx isoform 3 (GPx3), and upregulated selenoprotein W (SelW) mRNA expression. The excess Se diet led to decreased hepatic mRNA levels of GPx1, GPx3 and GPx4 but no change in testicular mRNA levels of GPx1, GPx3 or SelW. Dietary Se had no effect on testicular mRNA levels of GPx4. Thus, our results suggest that Se exposure can reduce hepatic antioxidant capacity and cause liver dysfunction. Dietary Se was found to differentially regulate mRNA levels of the GPx family or SelW, depending on exposure. Therefore, these genes may play a role in the toxicity associated with Se.

Impact of dietary selenium intake on cardiac health: experimental approaches and human studies

Selenium, a dietary trace mineral, essential for humans and animals, exerts its effects mainly through its incorporation into selenoproteins. Adequate selenium intake is needed to maximize the activity of selenoproteins, among which glutathione peroxidases have been shown to play a major role in cellular defense against oxidative stress initiated by excess reactive oxygen species. In humans, a low selenium status has been linked to increased risk of various diseases, including heart disease. The main objective of this review is to present current knowledge on the role of selenium in cardiac health. Experimental studies have shown that selenium may exert protective effects on cardiac tissue in animal models involving oxidative stress. Because of the narrow safety margin of this mineral, most interventional studies in humans have reported inconsistent findings. Major determinants of selenium status in humans are not well understood and several nondietary factors might be associated with reduced selenium status. In this review, we discuss recent studies regarding the role of selenoproteins in the cardiovascular system, the effect of dietary intake on selenium status, the impact of selenium status on cardiac health, and the cellular mechanisms that can be involved in the physiological and toxic effects of selenium.

Effects of chicken selenoprotein W on H2O2-induced apoptosis in CHO-K1 cells

Selenoprotein W (SelW) is expressed in various tissues of many animals and acts as an oxidoreductase in mammals. However, little is known about the role of the SelW in birds. To investigate the role of the chicken SelW on H(2)O(2)-induced apoptosis in CHO-K1 cells, overexpression of a chicken SelW cell lines (CHO-K1/SelW) were constructed. Using acridine orange/ethidium bromide (AO/EB) double staining and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assays, as well as WST-1 cell viability assay, we monitored the extent of the H(2)O(2)-induced apoptosis and detected the abundance of the caspase-3, caspase-8, and fas mRNA by real-time quantitative reverse transcription PCR (qPCR). We here found that overexpression of SelW cells, compared with the wild-type cells, resulted in a markedly decrease in sensitivity to H(2)O(2)-induced oxidative stress and had a lower apoptotic cell death in AO/EB and TUNEL assays. Cell viability revealed that overexpression of SelW cells had higher cell viability than wild-type cells. qPCR results found that overexpression of SelW cells had a lower levels of caspase-3, caspase-8, and fas mRNA than wild-type cells. Taken together, our findings suggested that SelW could reduce the oxidative damage induced by H(2)O(2) and had an important protective function in against oxidative damage.

Selenium regulates gene expression of selenoprotein W in chicken gastrointestinal tract

Selenoprotein W (SelW) is an existing form of selenium (Se). Se influences the levels of SelW in mammals. However, little is known about the pattern of SelW expression in the gastrointestinal tract tissue of bird. The present paper describes the effects of different dietary levels of Se on the SelW mRNA expression in the gastrointestinal tract tissue of chicken. The expression levels of SelW mRNA and the Se contents in the gastrointestinal tract tissues (glandular stomach, gizzard, duodenum, small intestine, and rectum) were determined on days 15, 25, 35, 45, and 55, respectively. The results showed that the Se contents and the SelW mRNA expression were significantly higher (p < 0.05) in the high-Se group, and the Se contents and SelW mRNA expression in the low-Se group were significantly lower (p < 0.05) than in the controls. The Se contents were the highest in the duodenum and the lowest in the rectum, while the SelW mRNA expression was the highest in the gizzard and the lowest in the rectum. In addition, the SelW mRNA levels in the gastrointestinal tract tissue were found to increase in a time-dependent manner with increasing feeding time. Furthermore, the expression of the SelW mRNA in the gastrointestinal tract tissues of chickens was found to correlate with the dietary Se concentrations, but not with the tissue Se contents.

Selenium regulates gene expression of selenoprotein W in chicken skeletal muscle system

Selenoprotein W (SelW) is abundantly expressed in skeletal muscles of mammals and necessary for the metabolism of skeletal muscles. However, its expression pattern in skeletal muscle system of birds is still uncovered. Herein, to investigate the distribution of SelW mRNA in chicken skeletal muscle system and its response to different selenium (Se) status, 1-day-old chickens were exposed to various concentrations of Se as sodium selenite in the feed for 35 days. In addition, myoblasts were treated with different concentrations of Se in the medium for 72 h. Then the levels of SelW mRNA in skeletal muscles (wing muscle, pectoral muscle, thigh muscle) and myoblasts were determined on days 1, 15, 25, and 35 and at 0, 24, 48, and 72 h, respectively. The results showed that SelW was detected in all these muscle components and it increased both along with the growth of organism and the differentiation process of myoblasts. The thigh muscle is more responsive to Se intake than the other two skeletal muscle tissues while the optimal Se supplementation for SelW mRNA expression in chicken myoblasts was 10(-7) M. In summary, Se plays important roles in the development of chicken skeletal muscles. To effect optimal SelW gene expression, Se must be provided in the diet and the media in adequate amounts and neither at excessive nor deficient levels.

Dietary selenium affects selenoprotein W gene expression in the liver of chicken

As selenium in the form of "Selenoprotein W (SelW)" is essential for the maintenance of normal liver function, the expression of SelW liver depends on the level of selenium supplied with the diet. Whereas this is well known to be the case in mammals, relatively little is known about the effect of dietary Se on the expression SelW in the livers of avian species. To investigate the effects of dietary Se levels on the SelW mRNA expression in the liver of bird, 1-day-old male chickens were fed either a commercial diet or a Se-supplemented diet containing 1.0, 2.0, 3.0, and 5.0 mg/kg sodium selenite (Na(2)SeO(3)) for 90 days. The livers were collected and examined for Se content and mRNA levels of SelW, Selenophosphate synthetase-1, and selenocysteine-synthase (SecS). The data indicate that, within a certain range, a Se-supplemented diet can increase the expression of SelW and the mRNA levels of SecS, and also, that the transcription of SelW is very sensitive to dietary Se.

Effects of dietary selenium on selenoprotein W gene expression in the chicken immune organs

Selenoprotein W (SelW) is expressed in the immune systems of mammals. However, its pattern of expression in the immune organs of birds is still unclear. To investigate the distribution of SelW and effects of dietary Se levels on the SelW mRNA expression in the immune organs of birds, 1-day-old male chickens were fed either a commercial diet or an Se-supplemented diet containing 0.601, 1.058, 1.514, or 2.427 mg Se per kilogram, and 1.0, 2.0, 3.0 or 5.0 mg sodium selenite per kilogram for 90 days. The immune organs (spleen, thymus, and bursa of Fabricius) were collected and examined for Se content and SelW mRNA levels. The mRNA expression of SelW was detected in all the tissues. Although Se content was the highest in the spleen, the remarkable stability of the SelW mRNA level was observed in this organ during different times of dietary Se supplementation. Se-supplemented diet can make the SelW expression levels higher within a certain range in thymus and bursa of Fabricius. The present study demonstrates that SelW is widely expressed in immune organs of birds and that Se-supplementation of the feed increases SelW expression in the thymus and the bursa of Fabricius.

Dietary selenium influences pancreatic tissue levels of selenoprotein W in chickens

Selenium (Se) influences the levels of selenoprotein W (SelW) in mammals. However, little is known about the pattern of SelW expression in the pancreatic tissue of birds. To investigate the effects of dietary Se levels on the expression of SelW mRNA in the pancreatic tissue of birds, one-day-old chickens were randomly allocated to three groups. The L group was fed a basal diet deficient in Se (containing 0.033mg/kg Se); the M and H groups were fed Se-supplemented diets with either 0.15 or 1.5mg/kg Se, respectively (as sodium selenite) for 55days. The pancreatic tissue was collected and examined for Se content and mRNA levels of SelW at 15, 25, 35, 45 and 55days old. In the H group, a significant increase (P<0.05) in mRNA levels of SelW was observed. When the chickens were fed a Se-deficient basal diet, the abundance of SelW mRNA significantly decreased (P<0.05) during the sampling period. In this study, two enzymes were also examined, namely, selenocysteine-tRNA([Ser]Sec) synthase (SecS) and selenophosphate synthetase 1 (SPS1). The mRNA levels of two factors were slightly enhanced in the Se-supplemented groups, and a Se-deficient diet down regulated the mRNA expression of SecS. These data indicate that SelW is expressed in the pancreatic tissue of birds and that the transcription of the SelW gene is very sensitive to dietary Se. Se also has an effect on the mRNA levels of SecS, but has a little effect on SPS1 in this study.

Selenium regulation of the selenoprotein and nonselenoprotein transcriptomes in rodents

This review discusses progress in understanding the hierarchy of selenoprotein expression at the transcriptome level from selenium (Se) deficiency to Se toxicity. Microarray studies of the full selenoproteome have found that 5 of 24 rodent selenoprotein mRNA decrease to <40% of Se adequate levels in Se deficient liver but that the majority of selenoprotein mRNA are not regulated by Se deficiency. These differences match with the hierarchy of selenoprotein expression, helping to explain these differences and also showing that selenoprotein transcripts can be used as molecular biomarkers for assessing Se status. The similarity of the response curves for regulated selenoproteins suggests one underlying mechanism is responsible for the downregulation of selenoprotein mRNA in Se deficiency, but the heterogeneity of the UGA position in regulated and nonregulated selenoprotein transcripts now indicates that current nonsense mediated decay models cannot explain which transcripts are susceptible to mRNA decay. Microarray studies on the full liver transcriptome in rats found only <10 transcripts/treatment were significantly down- or upregulated by Se deficiency or by supernutritional Se up to 2.0 μg Se/g diet (20× requirement), suggesting that cancer prevention associated with supernutritional Se may not be mediated by transcriptional changes. Toxic dietary Se at 50× requirement (5 μg Se/g diet), however, significantly altered ∼4% of the transcriptome, suggesting number of transcriptional changes itself as a biomarker of Se toxicity. Finally, panels of Se regulated selenoprotein plus nonselenoprotein transcripts predict Se status from deficient to toxic better than conventional biomarkers, illustrating potential roles for molecular biomarkers in nutrition.

Phospholipid hydroperoxide glutathione peroxidase (Gpx4) is highly regulated in male turkey poults and can be used to determine dietary selenium requirements

The dietary selenium recommendation for turkeys of 0.2 microg Se/g is higher than for many other species. Liver glutathione peroxidase-1 (Gpx1) activity levels determined using hydrogen peroxide (H(2)O(2)) in previous studies suggest that 0.2 microg Se/g may still be too low and that some of this Gpx1 activity might be due to phospholipid hydroperoxide Gpx (Gpx4). Thus we separated Gpx1 from Gpx4 by chromatography, demonstrated that 47% of the H(2)O(2) activity in Se-adequate turkey liver was due to Gpx4, and determined a factor for calculation of each activity. Day-old male poults were fed an Se-deficient torula diet (0.007 microg Se/g) supplemented with graded levels of Se (0-0.5 microg Se/g) for 27 days. Final body weights indicated a minimum Se requirement for growth of 0.05 microg Se/g. The liver had the highest Gpx4 activity in Se-adequate poults, and Gpx4 activity in Se-deficient liver decreased to 5% of Se-adequate levels, with an Se requirement of 0.29 microg Se/g. Liver Gpx1, gizzard Gpx1 and gizzard Gpx4 activities also had Se requirements of 0.28-0.30 microg Se/g, collectively yielding an Se requirement of 0.3 microg Se/g, which is three times higher than the requirements found in comparable rodent studies. We also sequenced partial cDNA clones for turkey Gpx1 (GQ502186) and Gpx4 (GQ502187), and found >60% identity with rodents and humans and >90% identity with chickens. Ribonuclease protection analysis showed that Gpx4 mRNA levels decrease substantially in Se-deficient turkey liver, unlike in rodents. These underlying differences in selenoprotein molecular biology may explain the elevated dietary Se requirements of turkeys.

Four selenoproteins, protein biosynthesis, and Wnt signalling are particularly sensitive to limited selenium intake in mouse colon

Selenium is an essential micronutrient. Its recommended daily allowance is not attained by a significant proportion of the population in many countries and its intake has been suggested to affect colorectal carcinogenesis. Therefore, microarrays were used to determine how both selenoprotein and global gene expression patterns in the mouse colon were affected by marginal selenium deficiency comparable to variations in human dietary intakes. Two groups of 12 mice each were fed a selenium-deficient (0.086 mg Se/kg) or a selenium-adequate (0.15 mg Se/kg) diet. After 6 wk, plasma selenium level, liver, and colon glutathione peroxidase (GPx) activity in the deficient group was 12, 34, and 50%, respectively, of that of the adequate group. Differential gene expression was analysed with mouse 44K whole genome microarrays. Pathway analysis by GenMAPP identified the protein biosynthesis pathway as most significantly affected, followed by inflammation, Delta-Notch and Wnt pathways. Selected gene expression changes were confirmed by quantitative real-time PCR. GPx1 and the selenoproteins W, H, and M, responded significantly to selenium intake making them candidates as biomarkers for selenium status. Thus, feeding a marginal selenium-deficient diet resulted in distinct changes in global gene expression in the mouse colon. Modulation of cancer-related pathways may contribute to the higher susceptibility to colon carcinogenesis in low selenium status.

Blood glutathione peroxidase-1 mRNA levels can be used as molecular biomarkers to determine dietary selenium requirements in rats

Transcript (mRNA) levels are increasingly being used in medicine as molecular biomarkers for disease and disease risk, including use of whole blood as a target tissue for analysis. Development of blood molecular biomarkers for nutritional status, too, has potential application that parallels opportunities in medicine, including providing solid data for individualized nutrition. We previously reported that blood glutathione peroxidase-1 (Gpx1) mRNA was expressed at levels comparable to major tissues in rats and humans. To determine the efficacy of using blood Gpx1 mRNA to assess selenium (Se) status and requirements, we fed graded levels of Se (0-0.3 microg Se/g as selenite) to weanling male rats. Se status was determined by liver Se concentration and selenoenzyme activity, and selenoprotein mRNA abundance in liver and blood was determined by ribonuclease protection analysis. Liver Se and plasma glutathione peroxidase-3 and liver Gpx1 activities indicated that minimal Se requirements were at 0.08 microg Se/g diet. When total RNA was isolated from whole blood, Gpx1 mRNA in Se-deficient rats decreased to 10% of levels in Se-adequate (0.2 microg Se/g diet) rats. With Se supplementation, blood Gpx1 mRNA levels increased sigmoidally to a plateau with a minimum Se requirement of 0.08 microg Se/g diet, whereas glutathione peroxidase-4 mRNA levels were unaffected. Similarly, Gpx1 mRNA in RNA isolated from fractionated red blood cells decreased in Se-deficient rats to 23% of Se-adequate levels, with a minimum Se requirement of 0.09 microg Se/g diet. Additional studies showed that the preponderance of whole blood Gpx1 mRNA arises from erythroid cells, most likely reticulocytes and young erythrocytes. In summary, whole blood selenoprotein mRNA levels can be used as molecular biomarkers for assessing Se requirements, illustrating that whole blood has potential as a target tissue in development of molecular biomarkers for use in nutrition as well as in medicine.

Methods of assessment of selenium status in humans: a systematic review

BACKGROUND

To understand the effect of selenium intake on health, it is important to identify sensitive and population-specific biomarkers of selenium status.

OBJECTIVE

The objective of this systematic review was to assess the usefulness of biomarkers of selenium status in humans.

DESIGN

The methods included a structured search strategy on Ovid MEDLINE, EMBASE (Ovid), and Cochrane databases; formal inclusion and exclusion criteria; data extraction into an Access database; validity assessment; and meta-analysis.

RESULTS

The data from 18 selenium supplementation studies (of which 9 were randomized controlled trials and 1 was considered to be at low risk of bias) indicate that plasma, erythrocyte, and whole-blood selenium, plasma selenoprotein P, and plasma, platelet, and whole-blood glutathione peroxidase activity respond to changes in selenium intake. Although there is a substantial body of data for plasma selenium, more large, high-quality, randomized controlled trials are needed for this biomarker, as well as for the other biomarkers, to explore the reasons for heterogeneity in response to selenium supplementation. There was insufficient evidence to assess the usefulness of other potential biomarkers of selenium status, including urinary selenium, plasma triiodothyroxine:thyroxine ratio, plasma thyroxine, plasma total homocysteine, hair and toenail selenium, erythrocyte, and muscle glutathione peroxidase activity.

CONCLUSIONS

For all potentially useful biomarkers, more information is needed to evaluate their strengths and limitations in different population groups, including the effects of varying intakes, the duration of intervention, baseline selenium status, and possible confounding effects of genotype.

Antioxidative role of selenoprotein W in oxidant-induced mouse embryonic neuronal cell death

It has been reported that selenoprotein W (SelW) mRNA is highly expressed in the developing central nerve system of rats, and its expression is maintained until the early postnatal stage. We here found that SelW protein significantly increased in mouse brains of postnatal day 8 and 20 relative to embryonic day 15. This was accompanied by increased expression of SOD1 and SOD2. When the expression of SelW in primary cultured cells derived from embryonic cerebral cortex was knocked down with small interfering RNAs (siRNAs), SelW siRNA-transfected neuronal cells were more sensitive to the oxidative stress induced by treatment of H2O2 than control cells. TUNEL assays revealed that H2O2-induced apoptotic cell death occurred at a higher frequency in the siRNA-transfected cells than in the control cells. Taken together, our findings suggest that SelW plays an important role in protection of neurons from oxidative stress during neuronal development.

Transcript analysis of the selenoproteome indicates that dietary selenium requirements of rats based on selenium-regulated selenoprotein mRNA levels are uniformly less than those based on glutathione peroxidase activity

Dietary selenium (Se) requirements in rats have been based largely upon glutathione peroxidase-1 (Gpx1) enzyme activity and Gpx1 mRNA levels can also be used to determine Se requirements. The identification of the complete selenoprotein proteome suggests that we might identify additional useful molecular biomarkers for assessment of Se status. To characterize Se regulation of the entire rat selenoproteome, weanling male rats were fed a Se-deficient diet (<0.01 microg Se/g) supplemented with graded levels of Se (0-0.8 microg/g diet) for 28 d, Se status was determined by tissue Se concentration and selenoenzyme activity, and selenoprotein mRNA abundance in liver, kidney, and muscle was determined by quantitative real-time-PCR. Tissue Se and selenoenzyme biomarkers indicated that minimal Se requirements were <or=0.1 microg Se/g diet for most biomarkers. Liver Gpx1 mRNA also decreased to <10% of Se-adequate levels, with a minimum Se requirement at 0.07 microg/g diet. Five selenoprotein mRNA in liver, 4 in kidney, and 2 in muscle decreased to <41% of Se-adequate levels, all with minimum Se requirements at <or=0.07 microg/g diet; the majority of selenoprotein mRNA in each tissue were not significantly regulated by Se status, and 1 selenoprotein, selenophosphate synthetase-2, was upregulated in Se-deficient kidney. Plateau breakpoints for all regulated selenoprotein mRNA were very similar, suggesting that 1 underlying mechanism is in play in Se regulation of selenoprotein mRNA. Lastly, we did not find any selenoprotein mRNA that could be used as biomarkers for super-nutritional/anticarcinogenic levels (up to 0.8 microg Se/g diet) of Se.

Dietary diphenyl diselenide reduces the STZ-induced toxicity

Oxidative stress is implicated in the pathogenesis of diabetes mellitus. Selenium supplementation has some benefits in experimental models of diabetes mellitus. This study evaluated whether dietary diphenyl diselenide, a simple synthetic organoselenium compound with antioxidant properties, reduces the streptozotocin (STZ)-induced toxicity. STZ-induced diabetic rats were fed with either standard and diphenyl diselenide (10 ppm) supplemented diets. In experimental trials, dietary diphenyl diselenide significantly decreased mortality rate (p<0.05) induced by STZ treatment. No correlation between this effect and glycemic levels were found. Diphenyl diselenide intake also promoted an increase in vitamin C, -SH levels (liver, kidney and blood) and in catalase (liver and kidney) activity, which were decreased in STZ-treated rats. In enzyme assays, diphenyl diselenide supplementation caused a significant improvement in platelets NTPDase and 5'-nucleotidase activities in STZ-induced diabetic rats when compared to the control and diabetic groups (p<0.05). Nevertheless, this supplementation did not modify the inhibition induced by STZ in delta-ALA-D activity. Our findings suggest that diphenyl diselenide compound showed beneficial effects against the development of diabetes by exhibiting antioxidant properties.

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.

High dietary intake of sodium selenite induces oxidative DNA damage in rat liver

One mechanism for the cancer-chemopreventive effects of high selenium (Se) intake is hypothesized to be antioxidant protection of DNA. In this work we examine DNA oxidation in whole animals as a function of dietary Se intake and carcinogen administration. Weanling male Sprague-Dawley rats were fed a basal, Torula yeast-based, Se-deficient diet supplemented with 0, 0.15, or 2.0 ppm Se as sodium selenite for 10 wk. They were then injected with 0, 0.1, or 10 mg /kg body weight of the pro-oxidant carcinogen N-nitrosodiethylamine. High levels of carcinogen and high levels of selenite intake each increased concentration of 8-hydroxy-2'-deoxyguanosine in liver DNA. Se-dependent glutathione peroxidase I gene expression and enzyme activity were dramatically reduced by dietary Se deficiency but were unaffected by carcinogen administration. There were no significant main or interactive effects of Se or carcinogen on activity or gene expression of the DNA repair enzyme 8-oxoguanine glycosylase I. These results do not support the hypothesis that high Se intake may be cancer-preventive by inhibiting oxidative DNA damage. Rather than inhibiting oxidative DNA damage, these findings suggest that high dietary intake of inorganic Se may promote in vivo DNA oxidation.

Identification of putative transcription factor binding sites in rodent selenoprotein W promoter

To understand transcriptional regulation of the selenoprotein W (SeW) gene, we used in vitro binding assays to identify transcription factors that may be involved in the transcriptional regulation of the SeW gene. Using protein from rat C6 (glial) cell nuclear extracts, oligonucleotides containing putative regulatory elements in the SeW promoter and antibodies, we observed that specificity protein 1(Sp1) transcription factor binds to the Sp1 consensus sequence in the SeW promoter as well as to the metal response element (MRE). Although competition analysis showed specific binding at the TFII-1 site, super-shift analysis using anti-TFII-1 antibody did not yield any super-shifted band. Therefore, the SeW gene may be a target for Sp1 whose binding to various regulatory sequences of the SeW promoter may activate or repress the transcription of SeW. The MRE, GRE, AP-1 and LF-A1 sites were also tested but no evidence was obtained for specific binding as indicated by lack of competition with unlabeled probes.

Gene structure and tissue expression of human selenoprotein W, SEPW1, and identification of a retroprocessed pseudogene, SEPW1P

We have determined that the human SEPW1 (selenoprotein W) gene maps to chromosome 19q13.3, spans approximately 6.3 kb and comprises six exons, in contrast to the previously published five exons. The gene lacks canonical TATA and CAAT boxes, but has numerous Sp1 consensus binding sites upstream of multiple transcription start sites. SEPW1 is expressed in all of the 22 tissues assayed, and shows highest expression in skeletal muscle and heart. Additionally, we have also identified a retroprocessed SEPW1 pseudogene, SEPW1P, which maps to chromosome 1p34-35.

Effect of copper, zinc and cadmium on the promoter of selenoprotein W in glial and myoblast cells

Rat selenoprotein W (SeW) promoter activity was investigated using different concentrations of cadmium, copper, and zinc. Two fragments (404 and 1265 bp) of the SeW promoter, containing a single metal response element (MRE), were ligated into the multiple cloning site of a pGL3-Basic reporter plasmid. The constructs were transfected into cultured C6 (rat glial) and L8 (myoblast) cells and promoter activity measured by means of luciferase reporter gene fused to the SeW promoter fragments in the reporter plasmid. With post-transfection exposure of these cell lines to these metals, copper and zinc, but not cadmium, significantly increased promoter activity of the unmutated 1265 bp (not 404 bp) construct (p<0.05) only in the C6 cells. Mutation of the MRE sequence abolished promoter response to metal exposure but did not eliminate promoter activity. The results suggest that SeW expression in glial cells can be increased on exposure to copper and zinc and that this response is dependent on the MRE sequence present in the SeW promoter.

Host selenium deficiency increases the severity of chronic inflammatory myopathy in Trypanosoma cruzi-inoculated mice

Weanling C3H/HeN mice were fed either a torula yeast-based diet deficient in selenium (Se) or the same diet supplemented with 0.2 ppm Se as sodium selenite. After 4 wk of feeding, the mice were inoculated intraperitoneally with the CA-I strain (clone K98) of Trypanosoma cruzi (TC). Before inoculation, mean serum Se levels were 430 versus 61 ng/ml in adequate and deficient mice, respectively. During the ascending phase of parasitemia, the Se-deficient mice exhibited significantly higher levels of parasites at 22-34 days postinfection (PI). However, no difference was found in the subsequent descending phase. As judged by visual examination at 2-mo-PI, some Se-deficient infected mice presented clinical signs of motor dysfunction. At 3-mo-PI, the end of the observation period, this chronic disease developed into a hind limb flaccid paralysis affecting 5 of 8 infected deficient mice. No signs of paralysis were seen in noninfected mice fed either diet or in infected mice fed the Se-adequate diet. At the histological level, both Se-adequate and Se-deficient infected mice showed mild myocarditis and moderate to severe myositis, with increasing intensity from 1- to 3-mo-PI in both groups. However, the severity of myositis was always more intense in the Se-deficient mice so that prominent areas of skeletal muscle replaced by fibrotic tissue were frequently observed. Thus, it can be concluded that Se deficiency in the murine host increases the severity of TC-induced myositis.

Selenoprotein W is a glutathione-dependent antioxidant in vivo

The function of selenoprotein W (Se-W) was investigated by cloning the corresponding cDNA from mouse brain and expressing it in CHO cells and H1299 human lung cancer cells. Overexpression of Se-W markedly reduced the sensitivity of both cell lines to H2O2 cytotoxicity. The intracellular peroxide concentration of the transfected cells was lower than that of the parental cells in the absence or presence of extracellular H2O2. The resistance to oxidative stress conferred by Se-W was dependent on glutathione. Expression of Se-W mutants in which selenocysteine-13 or cysteine-37 was replaced by serine did not confer resistance to H2O2, implicating these residues in the antioxidant activity of Se-W in vivo.

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.

Alterations of serum selenium concentrations in the acute phase of pathological conditions

BACKGROUND

Selenium (Se), an essential trace element, is known to be a cofactor of antioxidative selenoenzymes such as glutathione peroxidase and thioredoxin reductase.

METHODS

We assessed the pathophysiological significance of selenium (Se) by comparing the concentrations of serum Se and C-reactive protein (CRP) in healthy subjects (141; M=71, F=70) vs. patients with various pathological conditions.

RESULTS

In normal males in their 40s, peak serum Se concentrations were observed (2.03+/-0.30 microg/g of serum protein, 128%, P<0.001) vs. males in their 20s (1.59+/-0.20), whereas a peak was observed in females in their 30s (1.87+/-0.31, 119%, P<0.025) vs. those in their 20s (1.57+/-0.22). The serum Se concentrations in the high CRP value group (n=40, 1.07+/-0.29 microg/g, 64.1%), the rheumatoid arthritis (RA) test positive group (n=24, 1.37+/-0.29, 82.0%), the lung cancer group (n=16, 1.38+/-0.30, 82.6%), and the adult T-cell leukemia (ATL) group (n=22, 1.26+/-0.35, 75.4%) were significantly lower (P<0.001) than those in the healthy subjects (1.67+/-0.29 microg/g). This finding was confirmed by inducing acute phase response (APR) in rats by injection of lipopolysaccharide (LPS), which produced a significant decrease of Se in plasma and liver (69.5% and 81.6% vs. untreated rats, P<0.05). In contrast, the Se content in muscle, kidney, lung, spleen, heart, and thymus showed increases of <10%. Se mobilized from liver after LPS-challenge appeared to be translocated to muscle, and Se concentrations recovered by 80 h after APR to the control concentrations in parallel with the subsidence of APR.

CONCLUSIONS

The reduction of Se in the liver and plasma during APR may be associated with the increased CRP synthesis in the liver.

Selenium, selenoproteins and human health: a review

Selenium is of fundamental importance to human health. It is an essential component of several major metabolic pathways, including thyroid hormone metabolism, antioxidant defence systems, and immune function. The decline in blood selenium concentration in the UK and other European Union countries has therefore several potential public health implications, particularly in relation to the chronic disease prevalence of the Western world such as cancer and cardiovascular disease. Ten years have elapsed since recommended dietary intakes of selenium were introduced on the basis of blood glutathione peroxidase activity. Since then 30 new selenoproteins have been identified, of which 15 have been purified to allow characterisation of their biological function. The long term health implications in relation to declining selenium intakes have not yet been thoroughly examined, yet the implicit importance of selenium to human health is recognised universally. Selenium is incorporated as selenocysteine at the active site of a wide range of selenoproteins. The four glutathione peroxidase enzymes (classical GPx1, gastrointestinal GPx2, plasma GPx3, phospholipid hydroperoxide GPx4)) which represent a major class of functionally important selenoproteins, were the first to be characterised. Thioredoxin reductase (TR) is a recently identified seleno-cysteine containing enzyme which catalyzes the NADPH dependent reduction of thioredoxin and therefore plays a regulatory role in its metabolic activity. Approximately 60% of Se in plasma is incorporated in selenoprotein P which contains 10 Se atoms per molecule as selenocysteine, and may serve as a transport protein for Se. However, selenoprotein-P is also expressed in many tissues which suggests that although it may facilitate whole body Se distribution, this may not be its sole function. A second major class of selenoproteins are the iodothyronine deiodinase enzymes which catalyse the 5'5-mono-deiodination of the prohormone thyroxine (T4) to the active thyroid hormone 3,3'5-triiodothyronine (T3). Sperm capsule selenoprotein is localised in the mid-peice portion of spermatozoa where it stabilises the integrity of the sperm flagella. Se intake effects tissue concentrations of selenoprotein W which is reported to be necessary for muscle metabolism. It is of great concern that the health implications of the decline in Se status in the UK over the past two decades have not been systematically investigated. It is well recognised that dietary selenium is important for a healthy immune response. There is also evidence that Se has a protective effect against some forms of cancer; that it may enhance male fertility; decrease cardiovascular disease mortality, and regulate the inflammatory mediators in asthma. The potential influence of Se on these chronic diseases within the European population are important considerations when assessing Se requirement.

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

Previous studies in selenium (Se)-depleted sheep and rats showed that selenoprotein W (SeW) levels decreased in all tissues except brain. To further investigate this depletion in different parts of the brain, second generation Se-depleted rats were used. Dams consumed a Se-deficient basal diet during gestation and lactation, and deficient rats were obtained by continuation on the same diet. Control rats were fed a diet with 0.1-mg Se/kg diet after weaning. Glutathione peroxidase (GPX) activities were measured for comparative purposes to SeW levels. GPX activity in muscle, skin, spleen, and testis increased about 4-fold with Se repletion and reached a plateau after 6 or 10 weeks, but GPX activity decreased to almost one tenth of the original activity with continuous Se depletion. In contrast, GPX activities increased, rather than declined, in various brain regions (cortex, cerebellum, and thalamus) with time of feeding the deficient diet. An experiment with first generation rats, however, indicated that GPX activity was significantly lower in these three brain regions from rats fed the deficient diet as compared to rats fed the supplemented diet. SeW levels in skin, spleen, muscle, and testis were undetectable in weanling rats, but became detectable after 6 weeks of Se repletion. In contrast, the expression of SeW in cortex, cerebellum, and thalamus was not significantly affected by Se depletion, but increased SeW levels occurred only in thalamus with Se supplementation. The results with GPX using first and second generation rats suggest that there are "mobile" and "immobile" GPX fractions in the brain.

New approaches to assess selenium status and requirement

Selenium is one of the essential nutrients that may have beneficial effects on health at dietary intakes higher than the established Recommended Dietary Allowances in the United States. Dietary recommendations for this element have been the subject of much controversy, illustrating the difficulties involved in the definition of requirements based on the interpretation of biochemical markers. This review will show how concepts may differ and even change as a consequence of the evolution of the knowledge concerning classical parameters (e.g., identification of isoforms of the classical selenium-dependent enzyme glutathione peroxidase) or following the discovery of new biologic markers for selenium such as iodothyronine desiodinase, thioredoxin reductase, or the selenoproteins P and W.