Immunoregulation of natural and lymphokine-activated killer cells by selenium

Relationship between selenium status, selenoproteins and COVID-19 and other inflammatory diseases: A critical review

The antioxidant effects of selenium as a component of selenoproteins has been thought to modulate host immunity and viral pathogenesis. Accordingly, the association of low dietary selenium status with inflammatory and immunodeficiency has been reported in the literature; however, the causal role of selenium deficiency in chronic inflammatory diseases and viral infection is still undefined. The COVID-19, characterized by acute respiratory syndrome and caused by the novel coronavirus 2, SARS-CoV-2, has infected millions of individuals worldwide since late 2019. The severity and mortality from COVID-19 have been associated with several factor, including age, sex and selenium deficiency. However, available data on selenium status and COVID-19 are limited, and a possible causative role for selenium deficiency in COVID-19 severity has yet to be fully addressed. In this context, we review the relationship between selenium, selenoproteins, COVID-19, immune and inflammatory responses, viral infection, and aging. Regardless of the role of selenium in immune and inflammatory responses, we emphasize that selenium supplementation should be indicated after a selenium deficiency be detected, particularly, in view of the critical role played by selenoproteins in human health. In addition, the levels of selenium should be monitored after the start of supplementation and discontinued as soon as normal levels are reached. Periodic assessment of selenium levels after supplementation is a critical issue to avoid over production of toxic metabolites of selenide because under normal conditions, selenoproteins attain saturated expression levels that limits their potential deleterious metabolic effects.

Preliminary study on Se-enriched Lentinula edodes mycelium as a proposal of new feed additive in selenium deficiency

The presence of selenium in European soil is low and this causes its deficiency in livestock and, in consequence, in humans. This study aimed to obtain Lentinula (L.) edodes mycelium with the maximum content of selenium. This species was used for experiment based on its documented medicinal properties. Calves were fed with selenium-enriched L. edodes mycelium, and serum selenium concentration, average daily weight gains and selected immune parameters were estimated. The selenium-enriched mushroom was found to be safe based on cytotoxicity tests (MTT and LDH tests) and for this reason it was used for further experiments. The mean quantity of selenium in the serum of calves fed with selenium-enriched L. edodes mycelium was significantly higher than that of control calves. Additionally, the calves fed with selenium-enriched L. edodes mycelium had higher body weight gains than those of control calves. White blood cell counts and subpopulations of lymphocytes in the experimental and control calves were within the reference range. The administration of L. edodes enriched with selenium had a beneficial effect on state of health of the calves.

Selenium in Cattle: A Review

This review article examines the role of selenium (Se) and the effects of Se supplementation especially in the bovine species. Selenium is an important trace element in cattle. Some of its roles include the participation in the antioxidant defense the cattle farms. The nutritional requirements of Se in cattle are estimated at 100 μg/kg DM (dry matter) for beef cattle and at 300 μg/kg DM for dairy cows. The rations high in fermentable carbohydrates, nitrates, sulfates, calcium or hydrogen cyanide negatively influence the organism's use of the selenium contained in the diet. The Se supplementation may reduce the incidence of metritis and ovarian cysts during the postpartum period. The increase in fertility when adding Se is attributed to the reduction of the embryonic death during the first month of gestation. A use of organic Se in feed would provide a better transfer of Se in calves relative to mineral Se supplementation. The addition of Se yeasts in the foodstuffs of cows significantly increases the Se content and the percentage of polyunsaturated fatty acids (PUFA) in milk compared to the addition of sodium selenite. The enzyme 5-iodothyronine deiodinase is a seleno-dependent selenoprotein. It is one of the last proteins to be affected in the event of Se deficiency. This delay in response could explain the fact that several studies did not show the effect of Se supplementation on growth and weight gain of calves. Enrichment of Se in the diet did not significantly affect the slaughter weight and carcass yield of bulls. The impact and results of Se supplementation in cattle depend on physiological stage, Se status of animals, type and content of Se and types of Se administration. Further studies in Se supplementation should investigate the speciation of Se in food and yeasts, as well as understanding their metabolism and absorption. This constitute a path to exploit in order to explain certain different effects of Se.

Dietary selenium supplementation and whole blood gene expression in healthy North American men

Selenium (Se) is a trace nutrient required in microgram amounts, with a recommended dietary allowance of 55 μg/day in humans. The nutritional functions of Se are performed by a group of 25 selenoproteins containing the unusual amino acid selenocysteine at their active sites. The selenoproteins with known activities are oxidation-reduction enzymes with roles in antioxidant protection, redox homeostasis and signaling, and thyroid hormone metabolism. Both deficiencies and excesses of Se are associated with impaired innate and adaptive immune responses. We supplemented 16 healthy men for 1 year with 300 μg Se/day as high-Se yeast or placebo yeast and measured whole blood gene expression with DNA microarrays before and after supplementation. Protein phosphorylation was the main biological process in common among the Se-responsive genes, which included a prominent cluster of protein kinases, suggesting that protein phosphorylation in leukocytes is sensitive to Se supplementation. We found highly ranked clusters of genes associated with RNA processing and protein transport, suggesting that dietary Se may regulate protein expression in leukocytes at both the posttranscriptional and posttranslational levels. The main functional pathway affected by Se supplementation was FAS apoptosis signaling, and expression of genes associated with T cell and natural killer cell cytotoxicity was increased. At the same time, the numbers of circulating natural killer and T cells expressing activation markers decreased. These changes are consistent with an anti-inflammatory effect of Se supplementation exerted through regulation of protein phosphorylation.

The need for a reassessment of the safe upper limit of selenium in drinking water

Results of recent epidemiologic studies suggest the need to reassess the safe upper limit in drinking water of selenium, a metalloid with both toxicological and nutritional properties. Observational and experimental human studies on health effects of organic selenium compounds consumed through diet or supplements, and of inorganic selenium consumed through drinking water, have shown that human toxicity may occur at much lower levels than previously surmised. Evidence indicates that the chemical form of selenium strongly influences its toxicity, and that its biological activity may differ in different species, emphasizing the importance of the few human studies on health effects of the specific selenium compounds found in drinking water. Epidemiologic studies that investigated the effects of selenate, an inorganic selenium species commonly found in drinking water, together with evidence of toxicity of inorganic selenium at low levels in from in vitro and animal studies, indicate that health risks may occur at exposures below the current European Union and World Health Organization upper limit and guideline of 10 and 40 μg/l, respectively, and suggest reduction to 1 μg/l in order to adequately protect human health. Although few drinking waters are currently known to have selenium concentrations exceeding this level, the public health importance of this issue should not be overlooked, and further epidemiologic research is critically needed in this area.

Phenotypic and functional considerations in the evaluation of immunity in nutritionally compromised hosts

It is well established that proper nutrition is critical to the development of an effective immune system and to enhance the natural immunosurveillance and its effector mechanisms. This enhancement could be mediated either by increasing the frequency and absolute numbers of effector cells or by up-regulation of the cellular mechanisms by which these effector cells carry out their functions. Even in the Western world, large sectors of society often remain undernourished and show suboptimal immune responses, but the relationship between nutrition and immunity is best seen in developing and underdeveloped countries. Although there are many large-scale field studies that investigate the issue of nutrition and immunity, there are relatively few data that go beyond descriptive measurements and directly address how well the immune system functions. This review summarizes interactions between nutrition and immunity and focuses on practical aspects for evaluation of the immune function in the field.

Chemopreventive agents: selenium

The element selenium (Se) was recognized only 40 years ago as being essential in the nutrition of animals and humans. It is recognized as being an essential component of a number of enzymes, in which it is present as the amino acid selenocysteine. Se compounds have also been found to inhibit tumorigenesis in a variety of animal models, and recent studies indicate that supplemental Se in human diets may reduce cancer risk. The antitumorigenic activities have been associated with Se intakes that correct nutritionally deficient status in animals, as well as higher intakes that are substantially greater than those associated with maximal expression of the selenocysteine-containing enzymes. Therefore, it is proposed that while some cancer protection, particularly that involving antioxidant protection, involves selenoenzymes, specific Se metabolites, which are produced in significant amounts at relatively high Se intakes, also discharge antitumorigenic functions. According to this two-stage model of the roles of Se in cancer prevention, individuals with nutritionally adequate Se intakes may benefit from Se supplementation. Evidence for chemoprevention by Se and for the apparent mechanisms underlying these effects is reviewed to the end of facilitating the development of the potential of Se compounds as cancer chemopreventive agents.

Translactational exposure of F1 mouse pups to selenium

In an investigation of the modulation of certain neonatal xenobiotic-metabolizing enzymes in liver of mouse pups postnatally exposed to selenium through the transmammary route, sodium selenite was administered in drinking water to lactating dams at the dose levels of 1 or 5 ppm from day 1 of lactation and continued daily for 14 or 21 days. The higher dose of selenium was found to increase the hepatic acid-soluble sulfhydryl content significantly after 21 days of treatment in dams, their pups (P < 0.01) and in the 14-day-old male pups (P < 0.05). Cytochrome b5 content decreased in the livers of dams that received 5 ppm selenium (P < 0.01) and in the F1 pups (P < 0.01) translactationally exposed to selenium for 14 days. Cytochrome P-450 content decreased in dams and pups exposed to 5 ppm selenium for 14 days and either dose for 21 days (P < 0.01). Hepatic glutathione S-transferase decreased in the dam that had received 5 ppm selenium for 14 days (P < 0.05) and in the 14-day-old pups (P < 0.01). Glutathione reductase and glutathione peroxidase activities decreased in both dams and pups (P < 0.01). The overall suppression of neonatal hepatic detoxification enzymes demonstrates that selenium may have far-reaching consequences on neonatal growth, development and drug pharmacokinetics.

Apparent partial remission of breast cancer in 'high risk' patients supplemented with nutritional antioxidants, essential fatty acids and coenzyme Q10

Thirty-two typical patients with breast cancer, aged 32-81 years and classified 'high risk' because of tumor spread to the lymph nodes in the axilla, were studied for 18 months following an Adjuvant Nutritional Intervention in Cancer protocol (ANICA protocol). The nutritional protocol was added to the surgical and therapeutic treatment of breast cancer, as required by regulations in Denmark. The added treatment was a combination of nutritional antioxidants (Vitamin C: 2850 mg, Vitamin E: 2500 iu, beta-carotene 32.5 iu, selenium 387 micrograms plus secondary vitamins and minerals), essential fatty acids (1.2 g gamma linolenic acid and 3.5 g n-3 fatty acids) and Coenzyme Q10 (90 mg per day). The ANICA protocol is based on the concept of testing the synergistic effect of those categories of nutritional supplements, including vitamin Q10, previously having shown deficiency and/or therapeutic value as single elements in diverse forms of cancer, as cancer may be synergistically related to diverse biochemical dysfunctions and vitamin deficiencies. Biochemical markers, clinical condition, tumor spread, quality of life parameters and survival were followed during the trial. Compliance was excellent. The main observations were: (1) none of the patients died during the study period. (the expected number was four.) (2) none of the patients showed signs of further distant metastases. (3) quality of life was improved (no weight loss, reduced use of pain killers). (4) six patients showed apparent partial remission.

Effects of diheptyldiselenide (DDS) on human tumor cell lines and on peripheral blood mononuclear cells

In vitro effects of graded concentrations of diheptyldiselenide (DDS) on human tumor cell proliferation, and on the proliferative responses and immunological functions of peripheral blood mononuclear cells (MNC) were investigated. The agent significantly decreased tumor cell proliferation in a dose and time dependent manner. Proliferative responses of MNC to phytohemagglutinin (PHA) and interleukin-2 (IL-2) were also significantly depressed when MNCs were exposed to DDS (250 microM for 18 h) led to a significant increase in NK activity only in MNC samples showing very limited baseline NK function. On the other hand, generation of LAK cells was significantly inhibited by DDS. However, when the agent was added to the effector and target cell mixture during the 4 h 51Cr release cytotoxicity assay, no influence was found on NK and LAK-mediated target cell lysis. These studies show that high concentrations of DDS inhibit tumor cell proliferation and could also impair certain proliferative-dependent immune functions, without directly affecting cell-mediated cytolytic activity of effector cells.

Human immune toxicity

This review examines xenobiotic toxicity to the immune system, stressing in particular those aspects of most relevance to humans. Immunotoxicity is examined especially from three points of view: by what immunological component is affected, by classes of foreign agents that adversely affect the human immune system and by critical evaluation of human case reports and epidemics. Mechanisms by which xenobiotics interrupt cytokine networks are emphasized. The concept that microbial agents, both environmental as well as infectious, may act as immunotoxicants, either alone or in synergism with conventional agents is introduced. Instances of human immunotoxicology are critically evaluated in terms of clinical relevance, i.e. whether increased susceptibility to opportunistic infections or tumor emergence takes place in the affected individuals.