Dietary selenium modulates activation and differentiation of CD4+ T cells in mice through a mechanism involving cellular free thiols

A Mechanistic Link Between Selenium and Coronavirus Disease 2019 (COVID-19)

PURPOSE OF REVIEW

Coronavirus disease 2019 (COVID-19) is a rapidly emerging disease caused by a highly contagious virus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and this disease has affected millions of people across the world and led to hundreds of thousands of deaths worldwide. Nutrition is a key factor related to this disease, and nutritional status may determine the risk and outcomes of SARS-CoV-2 infection. Selenium is one of the major trace elements required for redox functions and has significant roles in viral infections. The purpose of this review was to examine the current evidence on the role of selenium in COVID-19. We reviewed studies on selenium and COVID-19, and other relevant studies to understand how selenium status can modify the risk of SARS-CoV-2 infection, and how selenium status might affect a person post-infection.

RECENT FINDINGS

We found that oxidative stress is a characteristic feature of COVID-19 disease, which is linked with the immunopathological disorder observed in individuals with severe COVID-19. Selenium plays a key role in strengthening immunity, reducing oxidative stress, preventing viral infections and supporting critical illness. Moreover, selenium deficiency is related to oxidative stress and hyperinflammation seen in critical illness, and selenium deficiency is found to be associated with the severity of COVID-19 disease. Selenium supplementation at an appropriate dose may act as supportive therapy in COVID-19. Future studies in large cohorts of COVID-19 are warranted to verify the benefits of selenium supplementation for reducing risk and severity of COVID-19.

The Influence of Nutritional Factors on Immunological Outcomes

Through food intake, humans obtain a variety of nutrients that are essential for growth, cellular function, tissue development, energy, and immune defense. A special interaction between nutrients and gut-associated lymphoid tissue occurs in the intestinal tract. Enterocytes of the intestinal barrier act as sensors for antigens from nutrients and the intestinal microbiota, which they deliver to the underlying immune system of the lamina propria, triggering an immune response. Studies investigating the mechanism of influence of nutrition on immunological outcomes have highlighted an important role of macronutrients (proteins, carbohydrates, fatty acids) and micronutrients (vitamins, minerals, phytochemicals, antioxidants, probiotics) in modulating immune homeostasis. Nutrients exert their role in innate immunity and inflammation by regulating the expression of TLRs, pro- and anti-inflammatory cytokines, thus interfering with immune cell crosstalk and signaling. Chemical substrates derived from nutrient metabolism may act as cofactors or blockers of enzymatic activity, influencing molecular pathways and chemical reactions associated with microbial killing, inflammation, and oxidative stress. Immune cell function appears to be influenced by certain nutrients that form parts of the cell membrane structure and are involved in energy production and prevention of cytotoxicity. Nutrients also contribute to the initiation and regulation of adaptive immune responses by modulating B and T lymphocyte differentiation, proliferation and activation, and antibody production. The purpose of this review is to present the available data from the field of nutritional immunology to elucidate the complex and dynamic relationship between nutrients and the immune system, the delineation of which will lead to optimized nutritional regimens for disease prevention and patient care.

Intestinal Anti-Inflammatory Effects of Selenized Ulva pertusa Polysaccharides in a Dextran Sulfate Sodium-Induced Inflammatory Bowel Disease Model

The purpose of this study was to examine the alleviative effects of selenized polysaccharides from Ulva pertusa (ulvan-Se) on inflammatory bowel disease (IBD) in mice. The dextran sulfate sodium (DSS)-induced IBD mouse model was used to explore the protective effects of ulvan-Se on the intestinal mechanical and immune barrier. At doses less than 1208 mg/kg·bw ulvan-Se showed no significant damage to Institute of Cancer Research (ICR) mice in an acute toxicity test. The results showed that DSS destroyed the mechanical barrier, which includes epithelial cells, while ulvan-Se promoted mRNA expression of tight junction proteins (zonula occludens protein 1, occludin, and claudin-1) and inhibited the infiltration of white blood cells into the intestines. At 100 mg/kg·bw, ulvan-Se enhanced the antioxidant capacity of mice more effectively than the 50 mg/kg·bw ulvan-Se. Furthermore, ulvan-Se improved the intestinal immune barrier by increasing immunoglobulin A and immunoglobulin M, while regulating the levels of interleukin (IL)-1β, interferon-γ, and IL-4. Oral administration of ulvan-Se also suppressed tumor necrosis factor-α, IL-1β, IL-6, and cyclooxygenase-2 mRNA expression mediated by the nuclear factor kappa B pathway. Taken together, our findings reveal that ulvan-Se could be used as a potential alternative supplement for reducing intestinal inflammation in IBD.

Selenium as a Bioactive Micronutrient in the Human Diet and Its Cancer Chemopreventive Activity

This review answers the question of why selenium is such an important trace element in the human diet. Daily dietary intake of selenium and its content in various food products is discussed in this paper, as well as the effects of its deficiency and excess in the body. Moreover, the biological activity of selenium, which it performs mainly through selenoproteins, is discussed. These specific proteins are responsible for thyroid hormone management, fertility, the aging process, and immunity, but their key role is to maintain a redox balance in cells. Furthermore, taking into account world news and the current SARS-CoV-2 virus pandemic, the impact of selenium on the course of COVID-19 is also discussed. Another worldwide problem is the number of new cancer cases and cancer-related mortality. Thus, the last part of the article discusses the impact of selenium on cancer risk based on clinical trials (including NPC and SELECT), systematic reviews, and meta-analyses. Additionally, this review discusses the possible mechanisms of selenium action that prevent cancer development.

Effect of Selenium and Peroxynitrite on Immune Function of Immature Dendritic Cells in Humans

Background

Selenium and peroxynitrite are known to support the growth and activity of immune cells, including T cells, B cells and macrophages. However, the role of these factors in the immune function of human immature dendritic cells (imDCs) is not clear.

Material/Methods

Monocytes from a mixture of blood samples were isolated using Ficoll density gradient centrifugation and purified with immunomagnetic beads before being induced into imDCs. Cells then either received no treatment (control group), or treatment with sodium selenite (Na₂SeO₃, Se), 3-morpholinosydnonimine (SIN1, which decomposes into peroxynitrite), or Se+SIN1. Cell viability, migration, and antiphagocytic abilities, oxidative stress, and protein expression of extracellular signal-regulated kinases (ERK) and MMP2 were assessed using a CCK8 assay, cell counter and flow cytometry, microplate spectrophotometer, and Western blot analysis, respectively.

Results

Viability of imDCs was unaffected by 0.1 μmol/L of Na₂SeO₃, although 1 mmol/L of SIN1 decreased it significantly (P<0.05). Chemotactic migration and antiphagocytic abilities were inhibited and enhanced, respectively, by treatment with Na₂SeO₃ and SIN1 (P<0.05). Activities of superoxide dismutase and glutathione peroxidase were increased by Na₂SeO₃ and Se+SIN1 (P<0.001). Glutathione content decreased with exposure to Na₂SeO₃ and SIN1 (P<0.05), but increased after treatment with Se+SIN1 (P<0.05). Levels of reactive oxygen species only increased with SIN1 treatment (P<0.05). Treatment with Na₂SeO₃, SIN1 and Se+SIN1 increased ERK phosphorylation and decreased MMP2 protein expression (P<0.05).

Conclusions

Selenium and peroxynitrite can influence immune function in imDCs by regulating levels of reactive oxygen species or glutathione to activate ERK and promote antigen phagocytosis, as well as by decreasing MMP2 expression to inhibit chemotactic migration.

Research progress on separation of selenoproteins/Se-enriched peptides and their physiological activities

Selenium (Se) is an essential nutrient associated with several physiological processes in humans and has raised interest because of its antioxidant and immune properties. Se deficiency is related to a variety of diseases and dysfunctions in humans. Due to its higher bioavailability and lower toxicity, organic Se is more recommendable than inorganic Se in the frame of a balanced diet. Se is present in 25 identified selenoproteins that commonly occur in human organisms. As part of selenocysteine (SeC), Se becomes co-translationally incorporated into the polypeptide chain and involved in the regulation of oxidative stress, redox mechanisms, and other crucial cellular processes responsible for innate and adaptive immune responses. This review presents the current information regarding the presence of selenoproteins in the human body, and the separation of selenoproteins and selenopeptides from various plants and their physiological roles in the immune and oxidation systems of humans. In general, the application of selenoproteins and Se-enriched peptides are practically important for the clinical arena, whereby it can be used for exploring new healthy foods.

Redox Regulation of Tolerogenic Dendritic Cells and Regulatory T Cells in the Pathogenesis and Therapy of Autoimmunity

Significance: Autoimmune diseases are progressively affecting westernized societies, as the proportion of individuals suffering from autoimmunity is steadily increasing over the past decades. Understanding the role of reactive oxygen species (ROS) in modulation of the immune response in the pathogenesis of autoimmune disorders is of utmost importance. The focus of this review is the regulation of ROS production within tolerogenic dendritic cells (tolDCs) and regulatory T (Treg) cells that have the essential role in the prevention of autoimmune diseases and significant potency in their therapy. Recent Advances: It is now clear that ROS are extremely important for the proper function of both DC and T cells. Antigen processing/presentation and the ability of DC to activate T cells depend upon the ROS availability. Treg differentiation, suppressive function, and stability are profoundly influenced by ROS presence. Critical Issues: Although a plethora of results on the relation between ROS and immune cells exist, it remains unclear whether ROS modulation is a productive way for skewing T cells and DCs toward a tolerogenic phenotype. Also, the possibility of ROS modulation for enhancement of regulatory properties of DC and Treg during their preparation for use in cellular therapy has to be clarified. Future Directions: Studies of DC and T cell redox regulation should allow for the improvement of the therapy of autoimmune diseases. This could be achieved through the direct therapeutic application of ROS modulators in autoimmunity, or indirectly through ROS-dependent enhancement of tolDC and Treg preparation for cell-based immunotherapy. Antioxid. Redox Signal. 34, 364-382.

Impact of Dietary Selenium on Modulation of Expression of Several Non-Selenoprotein Genes Related to Key Ovarian Functions, Female Fertility, and Proteostasis: a Transcriptome-Based Analysis of the Aging Mice Ovaries

Female reproductive (ovarian) aging is characterized by a marked decline in quantity and quality of follicles and oocytes, as well as alterations in the surrounding ovarian stroma. In our previous report, we have shown that dietary selenium (Se) insufficiency and supplementation differentially impacted the reproductive efficiency in aging mice; however, the precise understanding of such modulation is still incomplete. In the present study, we sought to determine the impact of low (mildly low level) and moderately high (medium level) Se diets on expression profile of non-selenoprotein genes in the ovaries of aging mice. For this purpose, the aged mice were divided in two groups and fed either a low Se (Se-L; 0.08 mg Se/kg) diet or a moderately high Se (Se-M; 0.33 mg Se/kg) diet. RNA-seq analysis revealed that a total of 168 genes were differentially expressed between the two groups. From these, 72 and 96 differentially expressed genes (DEGs) were found to be upregulated and downregulated, respectively. Gene Ontology (GO) and pathways enrichment (KEGG) analyses revealed that these DEGs were enriched in several key GO terms and biological pathways including PI3K-Akt signaling pathway, steroid hormone biosynthesis, signaling pathways regulating pluripotency of stem cells, Hippo signaling pathway, ovarian steroidogenesis, and Wnt signaling pathway. Further filtering of RNA-seq data revealed that several DEGs such as Star, Hsd3b6, Scd1, Bmp7, Aqp8, Gas1, Fzd1, and Wwc1 were implicated in key ovarian- and fertility-related functions. In addition, some of the DEGs were related to ER homeostasis and/or proteostasis. These results highlight that dietary low and moderately high (medium level) Se diets, in addition to modulation of selenoproteins, can also have an impact on expression of several non-selenoprotein genes in the ovaries of aging mice. To sum up, these findings add more value to our understanding of Se modulation of ovarian functions and female fertility and will pave a way for the focused mechanistic and functional studies in this domain.

Upregulated ethanolamine phospholipid synthesis via selenoprotein I is required for effective metabolic reprogramming during T cell activation

OBJECTIVE

T cell activation triggers metabolic reprogramming to meet increased demands for energy and metabolites required for cellular proliferation. Ethanolamine phospholipid synthesis has emerged as a regulator of metabolic shifts in stem cells and cancer cells, which led us to investigate its potential role during T cell activation.

METHODS

As selenoprotein I (SELENOI) is an enzyme participating in two metabolic pathways for the synthesis of phosphatidylethanolamine (PE) and plasmenyl PE, we generated SELENOI-deficient mouse models to determine loss-of-function effects on metabolic reprogramming during T cell activation. Ex vivo and in vivo assays were carried out along with metabolomic, transcriptomic, and protein analyses to determine the role of SELENOI and the ethanolamine phospholipids synthesized by this enzyme in cell signaling and metabolic pathways that promote T cell activation and proliferation.

RESULTS

SELENOI knockout (KO) in mouse T cells led to reduced de novo synthesis of PE and plasmenyl PE during activation and impaired proliferation. SELENOI KO did not affect T cell receptor signaling, but reduced activation of the metabolic sensor AMPK. AMPK was inhibited by high [ATP], consistent with results showing SELENOI KO causing ATP accumulation, along with disrupted metabolic pathways and reduced glycosylphosphatidylinositol (GPI) anchor synthesis/attachment CONCLUSIONS: T cell activation upregulates SELENOI-dependent PE and plasmenyl PE synthesis as a key component of metabolic reprogramming and proliferation.

Selenoproteins as regulators of T cell proliferation, differentiation, and metabolism

Selenium (Se) is an essential micronutrient that plays a key role in regulating the immune system. T cells are of particular interest due to their important role in promoting adaptive immunity against pathogens and cancer as well as regulating tolerance, all of which are influenced by dietary Se levels. The biological effects of Se are mainly exerted through the actions of the proteins into which it is inserted, i.e. selenoproteins. Thus, the roles that selenoproteins play in regulating T cell biology and molecular mechanisms involved have emerged as important areas of research for understanding how selenium affects immunity. Members of this diverse family of proteins exhibit a wide variety of functions within T cells that include regulating calcium flux induced by T cell receptor (TCR) engagement, shaping the redox tone of T cells before, during, and after activation, and linking TCR-induced activation to metabolic reprogramming required for T cell proliferation and differentiation. This review summarizes recent insights into the roles that selenoproteins play in these processes and their implications in understanding how Se may influence immunity.

Mini-Review on the Roles of Vitamin C, Vitamin D, and Selenium in the Immune System against COVID-19

Low levels of micronutrients have been associated with adverse clinical outcomes during viral infections. Therefore, to maximize the nutritional defense against infections, a daily allowance of vitamins and trace elements for malnourished patients at risk of or diagnosed with coronavirus disease 2019 (COVID-19) may be beneficial. Recent studies on COVID-19 patients have shown that vitamin D and selenium deficiencies are evident in patients with acute respiratory tract infections. Vitamin D improves the physical barrier against viruses and stimulates the production of antimicrobial peptides. It may prevent cytokine storms by decreasing the production of inflammatory cytokines. Selenium enhances the function of cytotoxic effector cells. Furthermore, selenium is important for maintaining T cell maturation and functions, as well as for T cell-dependent antibody production. Vitamin C is considered an antiviral agent as it increases immunity. Administration of vitamin C increased the survival rate of COVID-19 patients by attenuating excessive activation of the immune response. Vitamin C increases antiviral cytokines and free radical formation, decreasing viral yield. It also attenuates excessive inflammatory responses and hyperactivation of immune cells. In this mini-review, the roles of vitamin C, vitamin D, and selenium in the immune system are discussed in relation to COVID-19.

Clinical Impact Potential of Supplemental Nutrients as Adjuncts of Therapy in High-Risk COVID-19 for Obese Patients

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease (COVID-19) in China at the end of 2019 caused a major global pandemic and continues to be an unresolved global health crisis. The supportive care interventions for reducing the severity of symptoms along with participation in clinical trials of investigational treatments are the mainstay of COVID-19 management because there is no effective standard therapy for COVID-19. The comorbidity of COVID-19 rises in obese patients. Micronutrients may boost the host immunity against viral infections, including COVID-19. In this review, we discuss the clinical impact potential of supplemental nutrients as adjuncts of therapy in high-risk COVID-19 for obese patients.

Selenium and selenoproteins in viral infection with potential relevance to COVID-19

Selenium is a trace element essential to human health largely because of its incorporation into selenoproteins that have a wide range of protective functions. Selenium has an ongoing history of reducing the incidence and severity of various viral infections; for example, a German study found selenium status to be significantly higher in serum samples from surviving than non-surviving COVID-19 patients. Furthermore, a significant, positive, linear association was found between the cure rate of Chinese patients with COVID-19 and regional selenium status. Moreover, the cure rate continued to rise beyond the selenium intake required to optimise selenoproteins, suggesting that selenoproteins are probably not the whole story. Nonetheless, the significantly reduced expression of a number of selenoproteins, including those involved in controlling ER stress, along with increased expression of IL-6 in SARS-CoV-2 infected cells in culture suggests a potential link between reduced selenoprotein expression and COVID-19-associated inflammation. In this comprehensive review, we describe the history of selenium in viral infections and then go on to assess the potential benefits of adequate and even supra-nutritional selenium status. We discuss the indispensable function of the selenoproteins in coordinating a successful immune response and follow by reviewing cytokine excess, a key mediator of morbidity and mortality in COVID-19, and its relationship to selenium status. We comment on the fact that the synthetic redox-active selenium compound, ebselen, has been found experimentally to be a strong inhibitor of the main SARS-CoV-2 protease that enables viral maturation within the host. That finding suggests that redox-active selenium species formed at high selenium intake might hypothetically inhibit SARS-CoV-2 proteases. We consider the tactics that SARS-CoV-2 could employ to evade an adequate host response by interfering with the human selenoprotein system. Recognition of the myriad mechanisms by which selenium might potentially benefit COVID-19 patients provides a rationale for randomised, controlled trials of selenium supplementation in SARS-CoV-2 infection.

Dietary selenium deficiency and supplementation differentially modulate the expression of two ER-resident selenoproteins (selenoprotein K and selenoprotein M) in the ovaries of aged mice: Preliminary data

In the present report, we determined the impact of dietary selenium (Se) deficiency and supplementation on the expression of two ER-resident selenoproteins i.e., Selenok and Selenom in the ovaries of aging mice. The mRNA expression of Selenok and Selenom (RT-qPCR) was significantly higher in the ovaries of mice fed diets supplemented with inorganic (ISe-S: 0.33 mg Se/kg) and organic (OSe-S: 0.33 mg Se/kg) Se compared to those fed a Se-deficient (Se-D: 0.08 mg Se/kg) diet and both Se-adequate (ISe-A: 0.15 mg Se/kg and OSe-A: 0.15 mg Se/kg) diets. Similarly, the protein signals of SELENOK (immunofluorescence assay) were also significantly higher in the Se-supplemented groups compared to those fed Se-D and Se-adequate (ISe-A and OSe-A) diets. Meanwhile, the rate of in vitro-produced blastocysts developing from MII oocytes was also evaluated and it was revealed that this rate was significantly higher in the Se-supplemented mice compared to those fed a Se-D diet. Altogether, the dietary Se supplementation increased the expression of Selenok (also its protein expression) and Selenom in the ovaries of aging mice, potentially contributing to an improved developmental potential of in vitro-matured M II oocytes.

The Essential Role of Selenoproteins in the Resolution of Citrobacter rodentium-Induced Intestinal Inflammation

Enteropathogenic Escherichia coli (EPEC) leads to adverse colonic inflammation associated with poor resolution of inflammation and loss of epithelial integrity. Micronutrient trace element selenium (Se) is incorporated into selenoproteins as the 21st amino acid, selenocysteine (Sec). Previous studies have shown that such an incorporation of Sec into the selenoproteome is key for the anti-inflammatory functions of Se in macrophages and other immune cells. An intriguing mechanism underlying the anti-inflammatory and pro-resolving effects of Se stems from the ability of selenoproteins to skew arachidonic acid metabolism from pro-inflammatory mediators, prostaglandin E₂ (PGE₂) toward anti-inflammatory mediators derived from PGD₂, such as 15-deoxy-Δ^{12, 14}- prostaglandin J₂ (15d-PGJ₂), via eicosanoid class switching of bioactive lipids. The impact of Se and such an eicosanoid-class switching mechanism was tested in an enteric infection model of gut inflammation by C. rodentium, a murine equivalent of EPEC. C57BL/6 mice deficient in Se (Se-D) experienced higher mortality when compared to those on Se adequate (0.08 ppm Se) and Se supplemented (0.4 ppm Se) diets following infection. Decreased survival was associated with decreased group 3 innate lymphoid cells (ILC3s) and T helper 17 (Th17) cells in colonic lamina propria of Se-D mice along with deceased expression of epithelial barrier protein Zo-1. Inhibition of metabolic inactivation of PGE₂ by 15-prostaglandin dehydrogenase blocked the Se-dependent increase in ILC3 and Th17 cells in addition to reducing epithelial barrier integrity, as seen by increased systemic levels of FITC-dextran following oral administration; while 15d-PGJ₂ administration in Se-D mice alleviated the effects by increasing ILC3 and Th17 cells. Mice lacking selenoproteins in monocyte/macrophages via the conditional deletion of the tRNA^[Sec] showed increased mortality post infection. Our studies indicate a crucial role for dietary Se in the protection against inflammation following enteric infection via immune mechanisms involving epithelial barrier integrity.

Aging affects sex- and organ-specific trace element profiles in mice

A decline of immune responses and dynamic modulation of the redox status are observed during aging and are influenced by trace elements such as copper, iodine, iron, manganese, selenium, and zinc. So far, analytical studies have focused mainly on single trace elements. Therefore, we aimed to characterize age-specific profiles of several trace elements simultaneously in serum and organs of adult and old mice. This allows for correlating multiple trace element levels and to identify potential patterns of age-dependent alterations. In serum, copper and iodine concentrations were increased and zinc concentration was decreased in old as compared to adult mice. In parallel, decreased copper and elevated iron concentrations were observed in liver. The age-related reduction of hepatic copper levels was associated with reduced expression of copper transporters, whereas the increased hepatic iron concentrations correlated positively with proinflammatory mediators and Nrf2-induced ferritin H levels. Interestingly, the age-dependent inverse regulation of copper and iron was unique for the liver and not observed in any other organ. The physiological importance of alterations in the iron/copper ratio for liver function and the aging process needs to be addressed in further studies.

Selenium Deficiency in Lymphedema and Lipedema-A Retrospective Cross-Sectional Study from a Specialized Clinic

Background: Selenium is a trace element, which is utilized by the human body in selenoproteins. Their main function is to reduce oxidative stress, which plays an important role in lymphedema and lipedema. In addition, selenium deficiency is associated with an impaired immune function. The aim of this study was to determine the prevalence of selenium deficiency in these conditions, and if it is associated with disease severity and an associated medical condition such as obesity. Methods: This cross-sectional study is an anonymized, retrospective analysis of clinical data that was routinely recorded in a clinic specialized in lymphology. The data was comprised from 791 patients during 2012–2019, in which the selenium status was determined as part of their treatment. Results: Selenium deficiency proved common in patients with lymphedema, lipedema, and lipo-lymphedema affecting 47.5% of the study population. Selenium levels were significantly lower in patients with obesity-related lymphedema compared to patients with cancer-related lymphedema (96.6 ± 18.0 μg/L vs. 105.1 ± 20.2 μg/L; p < 0.0001). Obesity was a risk factor for selenium deficiency in lymphedema (OR 2.19; 95% CI 1.49 to 3.21), but not in lipedema. Conclusions: In countries with low selenium supply, selenium deficiency is common, especially in lymphedema patients. Therefore, it would be sensible to check the selenium status in lymphedema patients, especially those with obesity, as the infection risk of lymphedema is already increased.

Potential Role of Trace Elements (Al, Cu, Zn, and Se) in Multiple Sclerosis Physiopathology

Multiple sclerosis (MS) is an unpredictable disease of the central nervous system. The cause of MS is not known completely, and pathology is specified by involved demyelinated areas in the white and gray matter of the brain and spinal cord. Inflammation and peripheral tolerance breakdown due to Treg cell defects and/or effector cell resistance are present at all stages of the disease. Several invading peripheral immune cells are included in the process of the disease such as macrophages, CD8+ T cells, CD4+ T cells, B cells, and plasma cells. Trace elements are known as elements found in soil, plants, and living organisms in small quantities. Some of them (e.g., Al, Cu, Zn, Mn, and Se) are essential for the body's functions like catalysts in enzyme systems, energy metabolism, etc. Al toxicity and Cu, Zn, and Se toxicity and deficiency can affect the immune system and following neuron inflammation and degeneration. These processes may result in MS pathology. Of course, factors such as lifestyle, environment, and industrialization can affect levels of trace elements in the human body.

Selenium and hydrogen selenide: essential micronutrient and the fourth gasotransmitter?

Selenium (Se) is an essential micronutrient required by organisms of diverse lineage. Dietary Se is converted to hydrogen selenide either enzymatically or by endogenous antioxidant proteins. This convergent biochemical step crucially underlies the subsequent biological activity of Se and argues for inclusion of hydrogen selenide as the fourth endogenous gasotransmitter alongside nitric oxide, carbon monoxide and hydrogen sulfide.Endogenously generated hydrogen selenide is incorporated into numerous 'selenoprotein' oxidoreductase enzymes, essential for maintaining redox-status homeostasis in health and disease. Direct effects of endogenous hydrogen selenide on cellular and molecular targets are currently unknown. Given exogenously, hydrogen selenide acts as a modulator of metabolism via transient inhibition of mitochondrial cytochrome C oxidase. Here we provide an overview of Se biology, its impact on several physiological systems (immune, endocrine, cardiovascular and metabolic) and its utility as a supplement in acute and critical illness states. We further explore the evidence base supporting its role as the fourth gasotransmitter and propose a strategic case towards generation of novel selenomimetic therapeutics.

Selenium and selenoproteins in prostanoid metabolism and immunity

Selenium (Se) is an essential trace element that functions in the form of the 21st amino acid, selenocysteine (Sec) in a defined set of proteins. Se deficiency is associated with pathological conditions in humans and animals, where incorporation of Sec into selenoproteins is reduced along with their expression and catalytic activity. Supplementation of Se-deficient population with Se has shown health benefits suggesting the importance of Se in physiology. An interesting paradigm to explain, in part, the health benefits of Se stems from the observations that selenoprotein-dependent modulation of inflammation and efficient resolution of inflammation relies on mechanisms involving a group of bioactive lipid mediators, prostanoids, which orchestrate a concerted action toward maintenance and restoration of homeostatic immune responses. Such an effect involves the interaction of various immune cells with these lipid mediators where cellular redox gatekeeper functions of selenoproteins further aid in not only dampening inflammation, but also initiating an effective and active resolution process. Here we have summarized the current literature on the multifaceted roles of Se/selenoproteins in the regulation of these bioactive lipid mediators and their immunomodulatory effects.

Effect of selenium supplementation on glycemic indices: a meta-analysis of randomized controlled trials

PURPOSE

The association between selenium supplementation and glycemic indices seems to be a controversial issue. This systematic review and meta-analysis was conducted to evaluate the effect of selenium supplementation on glycemic indices.

METHODS

We systematically searched PubMed/MEDLINE, ISI/WOS, and Scopus (from their commencements up to Jan 2016) for relevant studies examining the association between intake of selenium and glycemic indices. The data were extracted from relevant qualified studies and estimated using the random-effect or pooled model and standardized mean difference (SMD) with 95% confidence interval (CI).

RESULTS

Twelve articles published between 2004 and 2016 were included. In all the studies, the participants were randomly assigned to an intervention group (n = 757) or a control group(n = 684). All the studies were double blind, placebo controlled trials. Selenium supplementation resulted in a significant decrease in homeostasis model of assessment-estimated β-cell function (HOMA-B) (SMD: -0.63; 95%CI: -0.89 to -0.38) and a significant increase in quantitative insulin sensitivity check index (QUICKI) (SMD: by 0.74; 95%CI: 0.49 to 0.1) as compared with the controls. There were no statistically significant improvements in glycemic indices, such as fasting plasma glucose (FPG), insulin, homeostasis model of assessment-estimated insulin resistance (HOMA-IR), Hemoglobin A1c (HbA1c) and adiponectin.

CONCLUSION

This meta-analysis indicated that selenium supplementation significantly decreased HOMA-B and increased QUICKI score. There was no statistically significant improvement in FPG, insulin, HOMA-IR, HbA1c and adiponectin indices following selenium supplementation.

Selenium Treatment Enhanced Clearance of Salmonella in Chicken Macrophages (HD11)

As an important micronutrient, selenium (Se) plays many essential roles in immune response and protection against pathogens in humans and animals, but underlying mechanisms of Se-based control of salmonella growth within macrophages remain poorly elucidated. In this study, using RNA-seq analyses, we demonstrate that Se treatment (at an appropriate concentration) can modulate the global transcriptome of chicken macrophages HD11. The bioinformatic analyses (KEGG pathway analysis) revealed that the differentially expressed genes (DEGs) were mainly enriched in retinol and glutathione metabolism, revealing that Se may be associated with retinol and glutathione metabolism. Meanwhile, Se treatment increased the number of salmonella invading the HD11 cells, but reduced the number of salmonella within HD11 cells, suggesting that enhanced clearance of salmonella within HD11 cells was potentially modulated by Se treatment. Furthermore, RNA-seq analyses also revealed that nine genes including SIVA1, FAS, and HMOX1 were differentially expressed in HD11 cells infected with salmonella following Se treatment, and GO enrichment analysis showed that these DEGs were mainly enriched in an extrinsic apoptotic signaling pathway. In summary, these results indicate that Se treatment may not only affect retinol and glutathione metabolism in macrophages, but could also inhibit salmonella-induced macrophage apoptosis via an extrinsic apoptotic signaling pathway involving SIVA1.

Selenium, Selenoproteins and Viral Infection

Reactive oxygen species (ROS) are frequently produced during viral infections. Generation of these ROS can be both beneficial and detrimental for many cellular functions. When overwhelming the antioxidant defense system, the excess of ROS induces oxidative stress. Viral infections lead to diseases characterized by a broad spectrum of clinical symptoms, with oxidative stress being one of their hallmarks. In many cases, ROS can, in turn, enhance viral replication leading to an amplification loop. Another important parameter for viral replication and pathogenicity is the nutritional status of the host. Viral infection simultaneously increases the demand for micronutrients and causes their loss, which leads to a deficiency that can be compensated by micronutrient supplementation. Among the nutrients implicated in viral infection, selenium (Se) has an important role in antioxidant defense, redox signaling and redox homeostasis. Most of biological activities of selenium is performed through its incorporation as a rare amino acid selenocysteine in the essential family of selenoproteins. Selenium deficiency, which is the main regulator of selenoprotein expression, has been associated with the pathogenicity of several viruses. In addition, several selenoprotein members, including glutathione peroxidases (GPX), thioredoxin reductases (TXNRD) seemed important in different models of viral replication. Finally, the formal identification of viral selenoproteins in the genome of molluscum contagiosum and fowlpox viruses demonstrated the importance of selenoproteins in viral cycle.

Impact of Micronutrients on the Immune Response of Animals

Vitamins and minerals (micronutrients) play an important role in regulating and shaping an immune response. Deficiencies generally result in inadequate or dysregulated cellular activity and cytokine expression, thereby affecting the immune response. Decreased levels of natural killer, granulocyte, and phagocytic cell activity and T and B cell proliferation and trafficking are associated with inadequate levels of micronutrients, as well as increased susceptibility to various adverse health conditions, including inflammatory disorders, infection, and altered vaccine efficacy. In addition, most studies of micronutrient modulation of immune responses have been done in rodents and humans, thus limiting application to the health and well-being of livestock and companion animals. This exploratory review elucidates the role of vitamins and minerals on immune function and inflammatory responses in animals (pigs, dogs, cats, horses, goats, sheep, and cattle), with reference to rodents and humans.

Role of Zinc and Selenium in Oxidative Stress and Immunosenescence: Implications for Healthy Aging and Longevity

Aging is a complex process that includes gradual and spontaneous biochemical and physiological changes which contributes to a decline in performance and increased susceptibility to diseases. Zn and Se are essential trace elements that play a pivotal role in immune functions and antioxidant defense and, consequently, are claimed to play also a role in successful aging trajectories. Consistently with their nature of essential trace elements, a plethora of data obtained “in vitro” and “in vivo” (in humans and animal models) support the relevance of Zn and Se for both the innate and adoptive immune response. Moreover, Zn and Se are strictly involved in the synthesis and regulation of activity of proteins and enzymes, e.g., metallothioneins (MT) and glutathione peroxidase (GPX), that are necessary for our endogenous antioxidant response. This is clearly important to protect our cells from oxidative damage and to slow the decline of our immune system with aging. Age-related changes affecting tissue levels of Zn and Se may indicate that the risk of Zn and Se deficiency increases with aging. However, it is still unclear which of these changes can be the consequence of a “real deficiency” and which can be part of our physiological compensatory response to the accumulating damage occurring in aging. Furthermore, the upregulation of antioxidant proteins (Zn and Se dependent) may be a manifestation of self-induced oxidative stress. By the way, Zn and Se dependent proteins are modulated not only by nutritional status, but also by well-known hallmarks of aging that play antagonistic functions, such as the deregulated nutrient sensing pathways and cellular senescence. Thus, it is not an easy task to conduct Zn or Se supplementation in elderly and it is emerging consistent that these kind of supplementation requires an individualized approach. Anyway, there is consistent support that supplementation with Zn using doses around 10 mg/day is generally safe in elderly and may even improve part of immune performances in those subjects with a baseline deficiency. Regarding Se supplementation, it may induce both beneficial and detrimental effects on cellular immunity depending on the form of Se, supplemental dose, and delivery matrix. The nutritional association of supplements based on “Zn plus Se” is hypothesized to provide additional benefits, but this will likely need a more complex individualized approach. The improvement of our knowledge around screening and detection of Zn and Se deficiency in aging could lead to substantial benefits in terms of efficacy of nutritional supplements aimed at ameliorate performance and health in aging.

The hydroxy-analogue of selenomethionine alleviated lipopolysaccharide-induced inflammatory responses is associated with recover expression of several selenoprotein encoding genes in the spleens of Kunming mice

This study aimed to determine whether hydroxy-analogue of selenomethionine (HMSeBA) supplementation could alleviate LPS-induced immunological stress in mice. A total of 90 Kunming mice were randomly assigned into 5 groups. The CON-LPS and CON+LPS groups were fed basal diet (BD), the others were fed BD with different levels of HMSeBA (0.15, 0.30 and 0.45 mg Se per kg) for 4 weeks. Mice were injected with LPS (3 mg per kg BW) or the corresponding physiological saline at 14 d and 28 d. Plasma and spleens were collected at 28 d. The results showed that: (1) LPS injection decreased ADG of mice at the 3^rd week, and increased the concentration of IL-6 and TNF-α in plasma and the spleen index; (2) LPS injection induced immunological stress, up-regulated 8 inflammation-related genes and 3 selenoprotein encoding genes, and down-regulated 16 selenoprotein encoding genes in spleens; (3) compared with the CON+LPS group, HMSeBA supplementation increased ADG of mice at 3 weeks and GSH-Px activity in plasma and spleens, decreased spleen index and plasma IL-6 and TNF-α levels, down-regulated mRNA levels of COX-2, ICAM-1, TNF-α, IL-6, and MCP-1, and up-regulated IL-10 and iNOS in spleens. 0.30 mg Se per kg of HMSeBA exhibited the optimal protective effect; (4) HMSeBA supplementation modestly recovered the expression of 8 selenoprotein encoding genes in the spleens of the stressed mice. The results indicated that HMSeBA supplementation alleviated LPS-induced immunological stress accompanied up-regulation of a subset of selenoprotein encoding genes in spleens of mice.

This study aimed to determine whether hydroxy-analogue of selenomethionine (HMSeBA) supplementation could alleviate LPS-induced immunological stress in mice.

The Role of the Status of Selected Micronutrients in Shaping the Immune Function

OBJECTIVE

This narrative review gives an overview on the essential role of adequate nutrition to an optimally functioning immune defence. Micronutrients act as regulators of the immune response, with the focus of this review on the immunomodulatory effects of the trace elements iron, zinc and selenium, and the vitamins A, D, E, C, B6 and B12 and folic acid.

RESULTS

Iron deficiency especially impairs the Th1 cell-borne cellular immunity. T lymphocytes are also most affected by a deficiency of zinc, needed for their maturation and the balance between the different T cell subpopulations and acting as a redox signal in the regulation of many enzymes. Selenium is also involved in redox reactions as the glutathione peroxidases and other redox enzymes are selenoproteins. Selenium status has shown special effects on cellular immunity and resistance to viral infections. Vitamin A in the form of retinoic acid induces a humoral Th2 cell response via antigen-presenting cells and is involved in maintaining intestinal immune defence and tolerance through its nuclear receptor RAR and via kinase signalling cascades. Immune tolerance is particularly promoted by vitamin D acting through dendritic cells to stimulate the differentiation of regulatory T cells. Vitamin E has antiinflammatory effects and stimulates naïve T cells especially in the elderly. Besides its antioxidative properties, vitamin C has effects on cell signalling and epigenetic regulation. The B vitamins are required for cytotoxic cellular immunity and modulate T cell responses.

CONCLUSION

A diverse diet and regular exposure to sunlight are the best sources for a balanced nutrient supply to maintain an optimal immune defence.

Relationship between selenoprotein P and selenocysteine lyase: Insights into selenium metabolism

Selenoprotein P (SelenoP) functions as a plasma transporter of selenium (Se) from liver to other tissues via incorporation into multiple selenocysteine (Sec) residues. Selenocysteine lyase (Scly) is an intracellular enzyme that decomposes Sec into selenide, providing Se for the synthesis of new selenoproteins. Both SelenoP and Scly are mostly produced by the liver. Previous studies demonstrated that male mice lacking SelenoP (SelenoP KO) or Scly (Scly KO) had increased or decreased total hepatic Se, respectively. While SelenoP regulation by Se is well-studied, Scly regulation by Se has not been reported. We hypothesize that Scly is negatively regulated by Se levels, and that absence of SelenoP jeopardizes Scly-dependent Se recycling. Using in vitro and in vivo models, we unveiled a tissue-specific Se regulation of Scly gene expression. We also determined that SelenoP, a considered source of intracellular Se, affects Scly expression and activity in vitro but not in vivo, as in the absence of SelenoP, Scly levels and activity remain normal. We also showed that absence of SelenoP does not increase levels of transsulfuration pathway enzymes, which would result in available selenocompounds being decomposed by the actions of cystathionine γ-lyase (CGL or CTH) and cystathionine β-synthase (CBS). Instead, it affects levels of thioredoxin reductase 1 (Txnrd1), an enzyme that can reduce selenite to selenide to be used in selenoprotein production. This study evaluates a potential interplay between SelenoP and Scly, providing further insights into the regulation of selenium metabolism.

Selenium, Selenoproteins, and Immunity

Selenium is an essential micronutrient that plays a crucial role in development and a wide variety of physiological processes including effect immune responses. The immune system relies on adequate dietary selenium intake and this nutrient exerts its biological effects mostly through its incorporation into selenoproteins. The selenoproteome contains 25 members in humans that exhibit a wide variety of functions. The development of high-throughput omic approaches and novel bioinformatics tools has led to new insights regarding the effects of selenium and selenoproteins in human immuno-biology. Equally important are the innovative experimental systems that have emerged to interrogate molecular mechanisms underlying those effects. This review presents a summary of the current understanding of the role of selenium and selenoproteins in regulating immune cell functions and how dysregulation of these processes may lead to inflammation or immune-related diseases.

Developmental selenium exposure and health risk in daily foodstuffs: A systematic review and meta-analysis

Selenium (Se) is a trace mineral and an essential nutrient of vital importance to human health in trace amounts. It acts as an antioxidant in both humans and animals, immunomodulator and also involved in the control of specific endocrine pathways. The aim of this work is to provide a brief knowledge on selenium content in daily used various foodstuffs, nutritional requirement and its various health consequences. In general, fruits and vegetables contain low content of selenium, with some exceptions. Selenium level in meat, eggs, poultry and seafood is usually high. For most countries, cereals, legumes, and derivatives are the major donors to the dietary selenium intake. Low level of selenium has been related with higher mortality risk, dysfunction of an immune system, and mental failure. Selenium supplementation or higher selenium content has antiviral outcomes and is necessary for effective reproduction of male and female, also decreases the threat of chronic disease (autoimmune thyroid). Generally, some advantages of higher content of selenium have been shown in various potential studies regarding lung, colorectal, prostate and bladder cancers risk, nevertheless results depicted from different trials have been diverse, which perhaps indicates the evidence that supplementation will merely grant advantage if the intakes of a nutrient is deficient. In conclusion, the over-all people should be advised against the usage of Se supplements for prevention of cardiovascular, hepatopathies, or cancer diseases, as advantages of Se supplements are still ambiguous, and their haphazard usage could result in an increased Se toxicity risk. The associations among Se intake/status and health, or disease risk, are complicated and need exposition to notify medical practice, to improve dietary recommendations, and to develop adequate communal health guidelines.

Association of expression of selenoprotein P in mRNA and protein levels with metabolic syndrome in subjects with cardiovascular disease: Results of the Selenegene study

BACKGROUND

Selenoprotein P (SeP) is involved in transporting selenium from the liver to target tissues. Because SeP confers protection against disease by reducing chronic oxidative stress, the present study aimed to assess the level of SeP in the serum of patients with metabolic syndrome (MetS) with a history of cardiovascular disease (CVD).

METHODS

A cross-sectional study was conducted in 63 and 71 subjects with and without MetS in the presence of documented CVD. All demographic, anthropometric and cardiometabolic variables (lipids, blood glucose, blood pressure) were assessed. Lifestyle-related factors and personal history and familial CVD risk factors were recorded. The expression of SELP in mRNA and protein levels in the serum was measured, and MetS was determined using ATPIII criteria. Binary logistic regression analysis demonstrated MetS and SeP to be dependent and independent variables, respectively.

RESULTS

Mean of systolic and diastolic blood pressure, triglyceride, high-density lipoprotein-cholesterol, fasting blood sugar, body mass index and waist circumference were higher among subjects with MetS (p = 0.05). The mean of selenium was higher among subjects with MetS, whereas the mean of SeP was lower among subjects with MetS (p < 0.001). In the unadjusted model, the SeP had decreased odds for MetS [odds ratio (OR) = 0.995; 95% confidence interval (CI) = 0.989-1.00] (p < 0.04). Furthermore, the association between MetS and SeP levels remained marginally significant even after adjusting for potential confounders such as age, gender, family history, smoking status and nutrition. SeP and waist circumference show a significant relationship (OR =0.995; 95% CI = 0.990-1.00) (p < 0.033).

CONCLUSIONS

We have demonstrated a significant decrease in circulating SeP levels according to MetS status in patients with documented cardiovascular disease.

Selenium deficiency induces duodenal villi cell apoptosis via an oxidative stress-induced mitochondrial apoptosis pathway and an inflammatory signaling-induced death receptor pathway

Selenium is an important nutritional trace element possessing antioxidant and anti-apoptotic properties in intestinal.

Impact of Childhood Malnutrition on Host Defense and Infection

The global impact of childhood malnutrition is staggering. The synergism between malnutrition and infection contributes substantially to childhood morbidity and mortality. Anthropometric indicators of malnutrition are associated with the increased risk and severity of infections caused by many pathogens, including viruses, bacteria, protozoa, and helminths. Since childhood malnutrition commonly involves the inadequate intake of protein and calories, with superimposed micronutrient deficiencies, the causal factors involved in impaired host defense are usually not defined. This review focuses on literature related to impaired host defense and the risk of infection in primary childhood malnutrition. Particular attention is given to longitudinal and prospective cohort human studies and studies of experimental animal models that address causal, mechanistic relationships between malnutrition and host defense. Protein and micronutrient deficiencies impact the hematopoietic and lymphoid organs and compromise both innate and adaptive immune functions. Malnutrition-related changes in intestinal microbiota contribute to growth faltering and dysregulated inflammation and immune function. Although substantial progress has been made in understanding the malnutrition-infection synergism, critical gaps in our understanding remain. We highlight the need for mechanistic studies that can lead to targeted interventions to improve host defense and reduce the morbidity and mortality of infectious diseases in this vulnerable population.

Selenium Pretreatment for Mitigation of Ischemia/Reperfusion Injury in Cardiovascular Surgery: Influence on Acute Organ Damage and Inflammatory Response

Ischemia/reperfusion injury (IRI) contributes to morbidity and mortality after cardiovascular surgery requiring cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA). Multi-organ damage is associated with substantial decreases of blood selenium (Se) levels in patients undergoing cardiac surgery with CPB. We compared the influence of a dietary surplus of Se and pretreatment with ebselen, a mimic of the selenoenzyme glutathione peroxidase, on IRI-induced tissue damage and inflammation. Male Wistar rats were fed either a Se-adequate diet containing 0.3 ppm Se or supplemented with 1 ppm Se (as sodium selenite) for 5 weeks. Two other groups of Se-adequate rats received intraperitoneal injection of ebselen (30 mg/kg) or DMSO (solvent control) before surgery. The animals were connected to a heart-lung-machine and underwent 45 min of global ischemia during circulatory arrest at 16 °C, followed by re-warming and reperfusion. Selenite and ebselen suppressed IRI-induced leukocytosis and the increase in plasma levels of tissue damage markers (AST, ALT, LDH, troponin) during surgery but did not prevent the induction of proinflammatory cytokines (IL-6, TNF-α). Both Se compounds affected phosphorylation and expression of proteins related to stress response and inflammation: Ebselen increased phosphorylation of STAT3 transcription factor in the heart and decreased phosphorylation of ERK1/2 MAP kinases in the lungs. Selenite decreased ERK1/2 phosphorylation and HSP-70 expression in the heart. Pretreatment with selenite or ebselen protected against acute IRI-induced tissue damage during CPB and DHCA. Potential implications of their different actions with regard to molecular stress markers on the recovery after surgery represent promising targets for further investigation.

Selenium nanoparticles decorated with Ulva lactuca polysaccharide potentially attenuate colitis by inhibiting NF-κB mediated hyper inflammation

Background

Selenium (Se) is an essential micronutrient trace element and an established nutritional antioxidant. Low Se status exacerbates inflammatory bowel diseases progression, which involves hyper inflammation in the digestive tract. Se nanoparticles (SeNPs) exhibit anti-inflammatory activity accompanied by low toxicity, especially when decorated with natural biological compounds. Herein, we explored the beneficial effects of SeNPs decorated with Ulva lactuca polysaccharide (ULP) in mice subjected to the acute colitis model.

Results

We constructed SeNPs coated with ULP (ULP-SeNPs) in average diameter ~130 nm and demonstrated their stability and homogeneity. Supplementation with ULP-SeNPs (0.8 ppm Se) resulted in a significant protective effect on DSS-induced acute colitis in mice including mitigation of body weight loss, and colonic inflammatory damage. ULP-SeNPs ameliorated macrophage infiltration as evidenced by decreased CD68 levels in colon tissue sections. The anti-inflammatory effects of ULP-SeNPs were found to involve modulation of cytokines including IL-6 and TNF-α. Mechanistically, ULP-SeNPs inhibited the activation of macrophages by suppressing the nuclear translocation of NF-κB, which drives the transcription of these pro-inflammatory cytokines.

Conclusions

ULP-SeNPs supplementation may offer therapeutic potential for reducing the symptoms of acute colitis through its anti-inflammatory actions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-017-0252-y) contains supplementary material, which is available to authorized users.

Is immunosenescence influenced by our lifetime "dose" of exercise?

The age-associated decline in immune function, referred to as immunosenescence, is well characterised within the adaptive immune system, and in particular, among T cells. Hallmarks of immunosenescence measured in the T cell pool, include low numbers and proportions of naïve cells, high numbers and proportions of late-stage differentiated effector memory cells, poor proliferative responses to mitogens, and a CD4:CD8 ratio <1.0. These changes are largely driven by infection with Cytomegalovirus, which has been directly linked with increased inflammatory activity, poor responses to vaccination, frailty, accelerated cognitive decline, and early mortality. It has been suggested however, that exercise might exert an anti-immunosenescence effect, perhaps delaying the onset of immunological ageing or even rejuvenating aged immune profiles. This theory has been developed on the basis of evidence that exercise is a powerful stimulus of immune function. For example, in vivo antibody responses to novel antigens can be improved with just minutes of exercise undertaken at the time of vaccination. Further, lymphocyte immune-surveillance, whereby cells search tissues for antigens derived from viruses, bacteria, or malignant transformation, is thought to be facilitated by the transient lymphocytosis and subsequent lymphocytopenia induced by exercise bouts. Moreover, some forms of exercise are anti-inflammatory, and if repeated regularly over the lifespan, there is a lower morbidity and mortality from diseases with an immunological and inflammatory aetiology. The aim of this article is to discuss recent theories for how exercise might influence T cell immunosenescence, exploring themes in the context of hotly debated issues in immunology.

Role of SEP15 Gene Polymorphisms in the Time of Progression to AIDS

AIMS

HIV infection is a chronic disease that requires intensive treatment in its later phases, including dietary supplementation. Several studies have suggested clinical improvements in patients with high levels of selenium, linking these levels with a longer progression to AIDS. The objective of this study was to verify the association of two polymorphisms in the SEP15 gene, which encodes a selenoprotein that is responsible for the transport of selenium in cells, with the time of progression to AIDS in HIV-1-infected patients.

METHODS

Blood samples were obtained from 139 HIV-1-positive individuals after they provided informed consent. DNA was isolated and genotyped using real-time polymerase chain reaction for the presence of SEP15 single nucleotide polymorphisms (rs5859 and rs561104). Questionnaires on sociodemographic features and behavior were answered, and the time of progression to AIDS was estimated based on a medical chart analysis.

RESULTS

The allelic and genotypic frequencies did not differ between rapid and nonrapid progressors; however, the presence of the AA genotype of the rs5859 polymorphism was associated with a shorter time of progression to AIDS compared with GG homozygotes (hazard ratio = 3.62, 95% CI = 1.55-8.43, p = 0.003).

CONCLUSION

These findings show the importance of genetic analysis of the SEP15 gene in individual patients with regard to predicting time of progression to AIDS.

Selenium Alleviates Aflatoxin B₁-Induced Immune Toxicity through Improving Glutathione Peroxidase 1 and Selenoprotein S Expression in Primary Porcine Splenocytes

Selenium (Se) is generally known as an essential micronutrient and antioxidant for humans and animals. Aflatoxin B1 (AFB1) is a frequent contaminant of food and feed, causing immune toxicity and hepatotoxicity. Little has been done about the mechanisms of how Se protects against AFB1-induced immune toxicity. The aim of this present study is to investigate the protective effects of Se against AFB1 and the underlying mechanisms. The primary splenocytes isolated from healthy pigs were stimulated by anti-pig-CD3 monoclonal antibodies and treated by various concentrations of different Se forms and AFB1. The results showed that Se supplementation alleviated the immune toxicity of AFB1 in a dose-dependent manner, as demonstrated by increasing T-cell proliferation and interleukin-2 production. Addition of buthionine sulfoximine abrogated the protective effects of SeMet against AFB1. SeMet enhanced mRNA and protein expression of glutathione peroxidase 1 (GPx1), selenoprotein S (SelS), and thioredoxin reductase 1 without and with AFB1 treatments. Furthermore, knockdown of GPx1 and SelS by GPx1-specific siRNA and SelS-specific siRNA diminished the protective effects of SeMet against AFB1-induced immune toxicity. It is concluded that SeMet diminishes AFB1-induced immune toxicity through increasing antioxidant ability and improving GPx1 and SelS expression in splenocytes. This study suggests that organic selenium may become a promising supplementation to protect humans and animals against the decline in immunity caused by AFB1.

Impact of selenium supplementation on fish antiviral responses: a whole transcriptomic analysis in rainbow trout (Oncorhynchus mykiss) fed supranutritional levels of Sel-Plex®

Background

Selenium (Se) is required for the synthesis of proteins (selenoproteins) with essential biological functions. Selenoproteins have a crucial role in the maintenance of cellular redox homeostasis in nearly all tissues, and are also involved in thyroid hormone metabolism, inflammation and immunity. Several immune processes rely on Se status and can be compromised if this element is present below the required level. Previous work has supported the notion that when Se is delivered at levels above those deemed to be the minimal required but below toxic concentrations it can have a boosting effect on the organism’s immune response. Based on this concept Se-enriched supplements may represent a valuable resource for functional feeds in animal farming, including aquaculture.

Results

In this study we tested the effects of Se supplemented as Sel-Plex during an immune challenge induced by polyinosinic:polycytidylic acid (poly(I:C)), a pathogen-associated molecular pattern (PAMP) that mimics viral infection. Trout were fed two diets enriched with 1 or 4 mg Se Kg⁻¹ of feed (dry weight) by Sel-Plex addition and a commercial formulation as control. The whole trout transcriptomic response was investigated by microarray and gene ontology analysis, the latter carried out to highlight the biological processes that were influenced by Sel-Plex supplementation in the head kidney (HK) and liver, the main immune and metabolic organs in fish. Overall, Sel-Plex enrichement up to 4 mg Se Kg⁻¹ induced an important response in the trout HK, eliciting an up-regulation of several genes involved in pathways connected with hematopoiesis and immunity. In contrast, a more constrained response was seen in the liver, with lipid metabolism being the main pathway altered by Se supplementation. Upon stimulation with poly(I:C), supplementation of 4 mg Se Kg⁻¹ increased the expression of principal mediators of the antiviral defences, especially IFN-γ, and down-stream molecules involved in the cell-mediated immune response.

Conclusions

Supplementation of diets with 4 mg Se Kg⁻¹ using Sel-Plex remarkably improved the fish response to viral PAMP stimulation. Sel-Plex, being a highly bioavailable supplement of organic Se, might represent a suitable option for supplementation of fish feeds, to achieve the final aim of improving fish fitness and resistance against immune challenges.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2418-7) contains supplementary material, which is available to authorized users.

Redox homeostasis, T cells and kidney diseases: three faces in the dark

The redox equilibrium is crucial for the maintenance of immune homeostasis. Here, we summarize recent data showing that oxidation regulates T-cell functions and that alterations of the redox equilibrium may play an important role in the pathogenesis of inflammatory conditions affecting the kidneys. We further discuss potential links between oxidation, T cells and renal diseases such as systemic lupus erythematosus, renal ischaemia/reperfusion injury, end-stage renal disease and hypertension. The basic understanding of oxidation as a means by which diseases are directly affected results in unexpected pathophysiological similarities. Finally, we describe potential therapeutic options targeting redox systems for the treatment of nephropathies affecting humans.

Diet-induced obesity in the selenocysteine lyase knockout mouse

AIMS

Selenocysteine lyase (Scly) mediates selenocysteine decomposition. It was previously demonstrated that, upon adequate caloric intake (12% kcal fat) and selenium deficiency, disruption of Scly in mice leads to development of metabolic syndrome. In this study, we investigate the effect of a high-fat (45% kcal) selenium-adequate diet in Scly knockout (KO) mice on development of metabolic syndrome. Involvement of selenoproteins in energy metabolism after Scly disruption was also examined in vitro in the murine hepatoma cell line, Hepa1-6, following palmitate treatment.

RESULTS

Scly KO mice were more susceptible to diet-induced obesity than their wild-type counterparts after feeding a high-fat selenium-adequate diet. Scly KO mice had aggravated hyperinsulinemia, hypercholesterolemia, glucose, and insulin intolerance, but unchanged inflammatory cytokines and expression of most selenoproteins, except increased serum selenoprotein P (Sepp1). Scly KO mice also exhibited enhanced hepatic levels of pyruvate and enzymes involved in the regulation of pyruvate cycling, such as pyruvate carboxylase (Pcx) and pyruvate dehydrogenase (Pdh). However, in vitro silencing of Scly in Hepa1-6 cells led to diminished Sepp1 expression, and concomitant palmitate treatment decreased Pdh expression.

INNOVATION

The role of selenium in lipid metabolism is recognized, but specific selenium-dependent mechanisms leading to obesity are unclear. This study uncovers that Scly has a remarkable effect on obesity and metabolic syndrome development triggered by high-fat exposure, independent of the expression of most selenoproteins.

CONCLUSION

Diet-induced obesity in Scly KO mice is aggravated, with effects on pyruvate levels and consequent activation of energy metabolism independent of selenoprotein levels.

Increased selenoprotein P in choroid plexus and cerebrospinal fluid in Alzheimer's disease brain

Subjects with Alzheimer's disease (AD) have elevated brain levels of the selenium transporter selenoprotein P (Sepp1). We investigated if this elevation results from increased release of Sepp1 from the choroid plexus (CP). Sepp1 is significantly increased in CP from AD brains in comparison to non-AD brains. Sepp1 localizes to the trans-Golgi network within CP epithelia, where it is processed for secretion. The cerebrospinal fluid from AD subjects also contains increased levels Sepp1 in comparison to non-AD subjects. These findings suggest that AD pathology induces increased levels of Sepp1 within CP epithelia for release into the cerebrospinal fluid to ultimately increase brain selenium.

The Role of Iodine and Selenium in Autoimmune Thyroiditis

Iodine and selenium (Se) are both essential elements to thyroid hormone economy, while they represent key players in the development of autoimmune thyroiditis.Chronic high iodine intake has been associated in various studies with increased frequency of autoimmune thyroiditis. In susceptible individuals, iodine excess increases intra-thyroid infiltrating Th17 cells and inhibits T regulatory (TREG) cells development, while it triggers an abnormal expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in thyrocytes, thus inducing apoptosis and parenchymal destruction. As was shown in a mouse model, high iodine supply leads to changes in the immunogenicity of the thyroglobulin molecule, upregulation of vascular intercellular adhesion molecule-1 (ICAM-1), and reactive oxygen species (ROS) generation in the thyrocytes. Serum Se levels were found decreased in Hashimoto thyroiditis and especially in Graves' disease as well as in thyroid-associated ophthalmopathy patients, the levels being related to the pathogenesis and outcome. Selenium is strongly involved, via the variable selenoproteins, in antioxidant, redox, and anti-inflammatory processes. Selenium enhances CD4+/CD25 FOXP3 and T regulatory cells activity while suppressing cytokine secretion, thus preventing apoptosis of the follicular cells and providing protection from thyroiditis. Selenium supplementation may be useful in autoimmune thyroid diseases, though, while usually well-tolerated, it should not be universally recommended, and it is also likely to be helpful for those with low Se status and autoimmunity. Broadly speaking, the achievement and maintenance of "selenostasis" as well as adequate urinary iodine excretion are mandatory to control disease, while, putatively, they may additionally be critical to preventing disease.

Dietary Selenium Levels Affect Selenoprotein Expression and Support the Interferon-γ and IL-6 Immune Response Pathways in Mice

Selenium is an essential element that is required to support a number of cellular functions and biochemical pathways. The objective of this study was to examine the effects of reduced dietary selenium levels on gene expression to assess changes in expression of non-selenoprotein genes that may contribute to the physiological consequences of selenium deficiency. Mice were fed diets that were either deficient in selenium or supplemented with selenium in the form of sodium selenite for six weeks. Differences in liver mRNA expression and translation were measured using a combination of ribosome profiling, RNA-Seq, microarrays, and qPCR. Expression levels and translation of mRNAs encoding stress-related selenoproteins were shown to be up-regulated by increased selenium status, as were genes involved in inflammation and response to interferon-γ. Changes in serum cytokine levels were measured which confirmed that interferon-γ, as well as IL-6, were increased in selenium adequate mice. Finally, microarray and qPCR analysis of lung tissue demonstrated that the selenium effects on immune function are not limited to liver. These data are consistent with previous reports indicating that adequate selenium levels can support beneficial immune responses, and further identify the IL-6 and interferon-γ pathways as being responsive to dietary selenium intake.

A Prospective Investigation of Graves' Disease and Selenium: Thyroid Hormones, Auto-Antibodies and Self-Rated Symptoms

BACKGROUND

In Graves' thyrotoxicosis tachycardia, weight loss and mental symptoms are common. Recovery takes time and varies between patients. Treatment with methimazole reduces thyroid hormone levels. According to previous research, this reduction has been faster if selenium (Se) is added.

OBJECTIVE

The objective was to investigate whether supplementing the pharmacologic treatment with Se could change the immune mechanisms, hormone levels and/or depression and anxiety.

METHODS

We prospectively investigated 38 patients with initially untreated thyrotoxicosis by measuring the thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), thyroid receptor antibodies and thyroid peroxidase auto-antibodies before medication and at 6, 18 and 36 weeks after commencing treatment with methimazole and levo-thyroxine, with a randomized blinded oral administration of 200 µg Se/day or placebo. The selenoprotein P concentration was determined in plasma at inclusion and after 36 weeks. The patients were also assessed with questionnaires about depression, anxiety and self-rated symptoms before medication was started and after 36 weeks.

RESULTS

FT4 decreased more in the Se group at 18 weeks (14 vs. 17 pmol/l compared to the placebo group, p = 0.01) and also at 36 weeks (15 vs. 18 pmol/l, p = 0.01). The TSH increased more in the Se group at 18 weeks (0.05 vs. 0.02 mIU/l, p = 0.04). The depression and anxiety scores were similar in both groups. In the Se group, the depression rates correlated negatively with FT3 and positively with TSH. This was not seen in the placebo group.

CONCLUSIONS

Se supplementation can enhance biochemical restoration of hyperthyroidism, but whether this could shorten clinical symptoms of thyrotoxicosis and reduce mental symptoms must be investigated further.

Selenium and exposure to fibrogenic mineral dust: a mini-review

Individuals exposed to fibrogenic mineral dust may exhibit an impaired antioxidant system and produce high levels of reactive oxygen and nitrogen species through immune cells, contributing to the perturbation of immune cell function, inflammation, fibrosis and lung cancer. The lung diseases which are caused by inhalation of fibrogenic mineral dust, known as pneumoconioses, develop progressively and irreversibly over decades. At the moment there is no known cure. The trace element selenium has potent antioxidant and anti-inflammatory properties mediated mainly through selenoproteins. Research has demonstrated that selenium has the ability to protect against cardiovascular diseases; to kill cancer cells in vitro and reduce cancer incidence; and to immunomodulate various cellular signaling pathways. For these reasons, selenium has been proposed as a promising therapeutic agent in oxidative stress associated pathology that in theory would be beneficial for the prevention or treatment of pneumoconioses such as silicosis, asbestosis, and coal worker's pneumoconiosis. However, studies regarding selenium and occupational lung diseases are rare. The purpose of this study is to conduct a mini-review regarding the relationship between selenium and exposure to fibrogenic mineral dust with emphasis on epidemiological studies. We carried out a systematic literature search of English published studies on selenium and exposure to fibrogenic mineral dust. We found four epidemiological studies. Reviewed studies show that selenium is lower in individuals exposed to fibrogenic mineral dust. However, three out of the four reviewed studies could not confirm cause-and-effect relationships between low selenium status and exposure to fibrogenic mineral dust. This mini-review underscores the need for large follow-up and mechanistic studies for selenium to further elucidate its therapeutic effects.