Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine

Effects of different selenium sources and levels on the physiological state, selenoprotein expression, and production and preservation of selenium-enriched eggs in laying hens

Selenium (i.e., Se) is a trace element that is vital in poultry nutrition, and optimal forms and levels of Se are critical for poultry productivity and health. This study aimed to compare the effects of sodium selenite (SS), yeast selenium (SY), and methionine selenium (SM) at selenium levels of 0.15 mg/kg and 0.30 mg/kg on production performance, egg quality, egg selenium content, antioxidant capacity, immunity and selenoprotein expression in laying hens. The trial was conducted in a 3 × 2 factorial arrangement, and a total of 576 forty-three-wk-old Hyland Brown laying hens were randomly assigned into 6 treatment groups, with diets supplemented with 0.15 mg Se/kg and 0.3 mg Se/kg of SS, SY and SM for 8 wk, respectively. Results revealed that SM increased the laying rate compared to SS and SY (P < 0.05), whereas different selenium levels had no effect. Organic selenium improved egg quality, preservation performance, and selenium deposition compared to SS (P < 0.05), while SY and SM had different preferences for Se deposition in the yolk and albumen. Also, organic selenium enhanced the antioxidant capacity and immune functions of laying hens at 0.15 mg Se/kg, whereas no obvious improvement was observed at 0.30 mg Se/kg. Moreover, SY and SM increased the mRNA expression of most selenoproteins compared to SS (P < 0.05), with SM exhibiting a more pronounced effect. Correlation analysis revealed a strong positive association between glutathione peroxidase 2 (GPx2), thioredoxin reductases (TrxRs), selenoprotein K (SelK), selenoprotein S (SelS), and antioxidant and immune properties. In conclusion, the use of low-dose organic selenium is recommended as a more effective alternative to inorganic selenium, and a dosage of 0.15 mg Se/kg from SM is recommended based on the trail conditions.

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H₂O₂-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H₂O₂ as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H₂O₂ and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

A review on selenium-enriched proteins: preparation, purification, identification, bioavailability, bioactivities and application

Selenium (Se) deficiency can cause many diseases and thereby affect human health. Traditional inorganic Se supplements have disadvantages of toxicity and low bioavailability. Se-Enriched proteins exhibit good bio-accessibility and high biological activities. This review provides a comprehensive overview of the preparation, purification, identification, bioavailability, bioactivities and application of Se-enriched proteins. The method of extracting Se-enriched proteins from animals, microorganisms and plants mainly includes solvent extraction (water, salt, ethanol and alkali solution extraction) and novel extraction technologies (ultrasound-assisted and pulsed electric field assisted extraction). Se-Enriched proteins and their hydrolysates exhibit good bioactivities, mainly including antioxidant activity, immune regulation, neuroprotective activity, and inhibition of hyperglycemic activity, among others. Future research should focus on the relationship between Se-enriched protein metabolism and the selenium regulatory protein metabolic pathway by using multi-omics technology. In addition, it is necessary to comprehensively study the structure-activity relationship of Se-enriched proteins/hydrolysates from different sources, to further clarify their bioactive mechanism and to verify their health benefits in vivo.

Organic Selenium Increased Gilts Antioxidant Capacity, Immune Function, and Changed Intestinal Microbiota

Selenium is an indispensable essential micronutrient for humans and animals, and it can affect biological functions by combining into selenoproteins. The purpose of this study was to investigate the effects of 2-hydroxy-4-methylselenobutanoic acid (HMSeBA) on the antioxidant performance, immune function, and intestinal microbiota composition of gilts. From weaning to the 19th day after the second estrus, 36 gilts (Duroc × Landrace × Yorkshire) were assigned to three treatments: control group, sodium selenite group (0.3 mg Se/kg Na₂SeO₃), and HMSeBA group (0.3 mg Se/kg HMSeBA). Dietary supplementation with HMSeBA improved the gilts tissue selenium content (except in the thymus) and selenoprotein P (SelP1) concentration when compared to the Na₂SeO₃ or control group. Compared with the control group, the antioxidant enzyme activity in the tissues from gilts in the HMSeBA group was increased, and the concentration of malondialdehyde in the colon had a decreasing trend (p = 0.07). Gilts in the HMSeBA supplemented group had upregulated gene expression of GPX2, GPX4, and SelX in spleen tissue, TrxR1 in thymus; GPX1 and SelX in duodenum, GPX3 and SEPHS2 in jejunum, and GPX1 in the ileum tissues (p < 0.05). In addition, compared with the control group, the expression of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) in the liver, spleen, thymus, duodenum, ileum, and jejunum of gilts in the HMSeBA group were downregulated (p < 0.05), while the expression of interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) in the liver, thymus, jejunum, and ileum were upregulated (p < 0.05). Compared with the control group and the Na₂SeO₃ group, HMSeBA had increased concentration of serum cytokines interleukin-2 (IL-2) and immunoglobulin G (IgG; p < 0.05), increased concentration of intestinal immunoglobulin A (sIgA; p < 0.05), and decreased concentration of serum IL-6 (p < 0.05). Dietary supplementation with HMSeBA also increased the abundance of intestinal bacteria (Ruminococcaceae and Phascolarctobacterium; p < 0.05) and selectively inhibited the abundance of some bacteria (Parabacteroides and Prevotellaceae; p < 0.05). In short, HMSeBA improves the antioxidant performance and immune function of gilts, and changed the structure of the intestinal microflora. And this study provided data support for the application of HMSeBA in gilt and even pig production.

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

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

Food Chemistry of Selenium and Controversial Roles of Selenium in Affecting Blood Cholesterol Concentrations

Hypercholesterolemia, one of the major risk factors of cardiovascular diseases, is a worldwide public health problem. Nutraceuticals and phytochemicals are attracting attention as a result of their cholesterol-lowering ability and minimal side effects. Among them, selenium (Se) is on the list. The amount of Se in foods varies by region. Se-enriched fertilizers and feeds can raise the Se content in plants and animals, while some processing methods decrease food Se content. This review summarizes recent studies on (1) the content distribution of Se in foods and factors influencing Se-enriched foods, (2) the bioavailability and metabolism of Se, and (3) the role of Se in affecting blood cholesterol and cholesterol metabolism. Although the hypocholesterolemic effect of Se is equivocal, its cholesterol-lowering activity may be more remarkable when the Se supplementation is 200 μg/day or the baseline blood total cholesterol is above 200 mg/dL in humans with low Se status.

Advances in Research on the Toxicological Effects of Selenium

Selenium is a trace element necessary for the growth of organisms. Moreover, selenium supplementation can improve the immunity and fertility of the body, as well as its ability to resist oxidation, tumors, heavy metals, and pathogenic microorganisms. However, owing to the duality of selenium, excessive selenium supplementation can cause certain toxic effects on the growth and development of the body and may even result in death in severe cases. At present, increasing attention is being paid to the development and utilization of selenium as a micronutrient, but its potential toxicity tends to be neglected. This study systematically reviews recent research on the toxicological effects of selenium, aiming to provide theoretical references for selenium toxicology-related research and theoretical support for the development of selenium-containing drugs, selenium-enriched dietary supplements, and selenium-enriched foods.

The rationale for selenium supplementation in inflammatory bowel disease: A mechanism-based point of view

Management of inflammatory bowel disease (IBD) has always been a challenge for physicians. Current treatment protocols may cause numerous adverse effects. Selenium is known for its putative antiinflammatory properties. Selenium is needed for the biosynthesis of enzymatically active selenoproteins, which contribute to antioxidative defense, and effective function of immune systems. Several studies have shown that patients with IBD have a lower selenium level compared to healthy subjects. Hence, experimental studies mimicking ulcerative colitis and Crohn's disease investigated the effect of selenium supplementation on IBD. Previous studies indicated the following: 1) Selenoproteins can curb the inflammatory response and attenuate oxidative stress. This antiinflammatory property caused remission in animal models of colitis. 2) Selenium supports protective gut microbiota, which indirectly improves management of IBD. 3) Selenium may block some of the predominant tumorigenesis pathways proposed in colitis-associated colorectal cancer. 4) Selenium supplementation showed promising results in preliminary clinical studies, particularly in patients with selenium deficiency. While selenium supplementation seems to be beneficial for IBD, clinical studies have remained too preliminary in this regard. Randomized clinical trials are needed to measure the short-term and long-term effects of selenium on both active and quiescent IBD, particularly in patients with IBD who have documented selenium deficiency.

Selenium-Containing Proteins/Peptides from Plants: A Review on the Structures and Functions

Selenium is an essential microelement required for biological processes. Traditional selenium supplements (selenite and selenomethionine mainly) remain concerns due to toxicity and bioavailability. In recent decades, biofortification strategies have been applied to produce selenium-enriched edible plants to address the challenges of superior nutritional quality requirements. Plant-derived selenium-containing proteins/peptides offer potential health benefits beyond the basic nutritional requirements of Se. Highly nucleophilic seleno-amino acids, special peptide sequences, and favorable bioavailability contribute to the biological activities of selenium-containing proteins/peptides, such as antioxidant, antihypertensive, anti-inflammatory, and immunomodulatory effects. However, their applications on a commercial scale are insufficient owing to the complexity of purification and identification techniques and the sparse information on bioavailability and metabolism. In this review, selenium status, structural features, bioactivities, structure-activity relationships, and bioavailability, as well as the mechanisms underlying the bioactivities and metabolism of plant-derived selenium-containing proteins/peptides, are summarized and discussed for their nutraceutical use.

Evaluating Mineral Status in Ruminant Livestock

Determining mineral status of production animals is important when developing an optimum health program. Nutrition is the largest expense in food animal production and has the greatest impact on health and productivity of the animals. Knowing the bioavailability of minerals in the diet is difficult. Evaluating fluid or tissues from animals is the optimum method to determine bioavailability. Evaluating the diet provides some information. Serum/blood or liver from the animal needs to be analyzed to determine bioavailability of vitamin and minerals in the diet. This article reviews how to sample and the function of these minerals in cattle.

Selenium-rich maize modulates the expression of prostaglandin genes in lipopolysaccharide-stimulated RAW264.7 macrophages

Cell signaling is necessary for the organs to co-ordinate with the whole body and it includes response to external stimuli, inflammation, hormonal secretions and other various metabolic functions. In the present study, we have focused on the inflammatory signals modulated by the reactive oxygen and nitrogen species (RONS). Under homeostatic conditions, these species turn on the COX-1-dependent arachidonic acid (AA) pathway towards the release of anti-inflammatory enzymes. However, the excess release of these ions induces negative effects in the form of inflammation by turning on the COX-2-dependent AA pathway to release pro-inflammatory enzymes. In the present study, we observed the shunting of the COX-2-dependent AA pathway towards the release of anti-inflammatory enzymes with the supplementation of organic dietary selenium in the form of seleniferous maize extracts. We observed that 500 nM selenium concentration in Se-maize extracts downregulated the COX-2 and mPGES-1 expressions by 3.8- and 3.2-fold and upregulated the GPx-1 and H-PGDS expressions by 5.0- and 5.4-fold, respectively. To facilitate more availability of Se from the dietary matrices, Se-maize extracts were incubated with rMETase. It was observed that the enzyme-treated cells increased the downregulation of COX-2 and mPGES-1 expressions by 24.8- and 21.0-fold and the upregulation of GPx-1 and H-PGDS expressions by 13.2- and 16.5-fold, respectively.

From Selenium Absorption to Selenoprotein Degradation

Selenium is an essential dietary micronutrient. Ingested selenium is absorbed by the intestines and transported to the liver where it is mostly metabolized to selenocysteine (Sec). Sec is then incorporated into selenoproteins, including selenoprotein P (SELENOP), which is secreted into plasma and serves as a source of selenium to other tissues of the body. Herein, we provide an overview of the biology of selenium from its absorption and distribution to selenoprotein uptake and degradation, with a particular focus on the latter. Molecular mechanisms of selenoprotein degradation include the lysosome-mediated pathway for SELENOP and endoplasmic reticulum-mediated degradation of selenoproteins via ubiquitin-activated proteasomal pathways. Ubiquitin-activated pathways targeting full-length selenoproteins include the peroxisome proliferator-activated receptor gamma-dependent pathway and substrate-dependent ubiquitination. An alternate mechanism is utilized for truncated selenoproteins, in which cullin-RING E3 ubiquitin ligase 2 targets the defective proteins for ubiquitin-proteasomal degradation. Selenoproteins, particularly SELENOP, may have their Sec residues reutilized for new selenoprotein synthesis via Sec decomposition. This review will explore these aspects in selenium biology, providing insights to knowledge gaps that remain to be uncovered.

Bioavailability Assessment of Copper, Iron, Manganese, Molybdenum, Selenium, and Zinc from Selenium-Enriched Lettuce

Cu, Fe, Mn, Mo, Selenium (Se), and Zn bioavailability from selenate- and selenite-enriched lettuce plants was studied by in vitro gastrointestinal digestion followed by an assay with Caco-2 cells. The plants were cultivated in the absence and presence of two concentrations (25 and 40 µmol/L of Se). After 28 days of cultivation, the plants were harvested, dried, and evaluated regarding the total concentration, bioaccessibility, and bioavailability of the analytes. The results showed that biofortification with selenate leads to higher Se absorption by the plant than biofortification with selenite. For the other nutrients, Mo showed high accumulation in the plants of selenate assays, and the presence of any Se species led to a reduction of the plant uptake of Cu and Fe. The accumulation of Zn and Mn was not strongly influenced by the presence of any Se species. The bioaccessibility values were approximately 71%, 10%, 52%, 84%, 71%, and 86% for Cu, Fe, Mn, Mo, Se, and Zn, respectively, and the contribution of the biofortified lettuce to the ingestion of these minerals is very small (except for Se and Mo). Due to the low concentrations of elements from digested plants, it was not possible to estimate the bioavailability for some elements, and for Mo and Zn, the values are below 6.9% and 3.4% of the total concentration, respectively. For Se, the bioavailability was greater for selenite-enriched than selenate-enriched plants (22% and 6.0%, respectively), because selenite is biotransformed by the plant to organic forms that are better assimilated by the cells.

Effects of different selenium sources and levels on antioxidant status in broiler breeders

OBJECTIVE

This study was conducted with the objectives to examine the impacts of inorganic selenium (Se) and different types and levels of organic selenium on the serum and tissues Se status and antioxidant capacity in broiler breeders.

METHODS

Five hundred and forty 48-wk-old Lingnan Yellow broiler breeders were randomly assigned to 6 dietary treatments, provided same basal diet (0.04 mg/kg of Se) with 0.15 mg/kg, or 0.30 mg/kg of Se from sodium selenite (SS) or from selenium-enriched yeast (SY) or from selenomethionine (SM). The broiler breeders were slaughtered after an 8-wk experiment.

RESULTS

The results showed that SM was better than SY and SS, 0.30 mg/kg level was better than 0.15 mg/kg level in Se deposition (p<0.05) in serum, liver, kidney, pancreas and muscle; in antioxidant status, organic selenium had better effects than SS in broiler breeders (p<0.05), but SM and SY had a similar result, and 0.15 mg/kg level was better than 0.30 mg/kg (p<0.05).

CONCLUSION

The results demonstrated the evident advantage of supplementation of broiler breeders with 0.15 mg/kg SM, which improved tissue Se concentrations and antioxidant status, and can be considered as the best selenium source.

Selenium-Dependent Antioxidant Enzymes: Actions and Properties of Selenoproteins

Unlike other essential trace elements that interact with proteins in the form of cofactors, selenium (Se) becomes co-translationally incorporated into the polypeptide chain as part of 21st naturally occurring amino acid, selenocysteine (Sec), encoded by the UGA codon. Any protein that includes Sec in its polypeptide chain is defined as selenoprotein. Members of the selenoproteins family exert various functions and their synthesis depends on specific cofactors and on dietary Se. The Se intake in productive animals such as chickens affect nutrient utilization, production performances, antioxidative status and responses of the immune system. Although several functions of selenoproteins are unknown, many disorders are related to alterations in selenoprotein expression or activity. Selenium insufficiency and polymorphisms or mutations in selenoproteins' genes and synthesis cofactors are involved in the pathophysiology of many diseases, including cardiovascular disorders, immune dysfunctions, cancer, muscle and bone disorders, endocrine functions and neurological disorders. Finally, heavy metal poisoning decreases mRNA levels of selenoproteins and increases mRNA levels of inflammatory factors, underlying the antagonistic effect of Se. This review is an update on Se dependent antioxidant enzymes, presenting the current state of the art and is focusing on results obtained mainly in chicken.

Selenium status of children in Kashin-Beck disease endemic areas in Shaanxi, China: assessment with mercury

The causes of Kashin-Beck disease (KBD) in children are multifactorial, and particular consideration has been given to childhood selenium (Se) deficiency. In this study, dietary intake of Se and mercury (Hg) was determined at KBD areas to investigate the Se status and risks. Therefore, total Hg and Se levels were investigated in scalp hair samples and in daily intake food samples of 150 schoolchildren in Yongshou County of Shaanxi, China. The results showed that the average concentration of Se in children's hair has risen to 302 ng g^-1 and significantly increased compared to the data reported decades ago. Children at KBD endemic areas likely have improved Se status due to the Se supplementation in food at recent decades. However, all the children in the study areas still showed lower Se status compared to those in other non-KBD areas of China. The probable daily intake of Se in the study areas was still lower after stopping Se supplementation in food at KBD areas, which is 17.96 μg day^-1. Food produced locally cannot satisfy the lowest demand for Se nutrition for local residents. If the interactions of Se-Hg detoxification are considered, Hg intake from food exacerbates Se deficiency at the KBD areas.

Comparative oral dose toxicokinetics of sodium selenite and selenomethionine

Selenium (Se) poisoning by different forms of Se occurs in the United States. However, the toxicokinetics of different selenocompounds after oral ingestion is not well documented. In this study the toxicokinetics of Se absorption, distribution and elimination were determined in serum and whole blood of lambs that were orally dosed with increasing doses of Se as sodium selenite (inorganic Se) or selenomethionine (SeMet, organic Se). Thirty-two lambs were randomly assigned to eight treatment groups, with four animals per group. Se was administered at 1, 2 or 3 mg kg^-1 body weight, as either sodium selenite or SeMet with proper control groups. Blood and serum were collected at predetermined time points for 7 days post-dosing. Resulting Se concentrations in both serum and whole blood from SeMet treatment groups were significantly greater than those given equimolar doses of Se as sodium selenite. Se concentrations in serum and whole blood of lambs dosed with SeMet peaked at significantly greater concentrations when compared with lambs dosed with equimolar doses of sodium selenite. Based on the serum and whole blood kinetics, the rate of Se absorption was greater for SeMet than for sodium selenite although rates of absorption for both Se forms decreased with increasing dose. The rates of Se elimination increased with dose. These results demonstrate that SeMet has a greater absorption rate and a similar retention time resulting in a greater area under the curve and thus bioavailability than sodium selenite, which must be considered in both overdose and nutritional exposures. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Meat composition and quality of young growing Belgian Blue bulls offered a fattening diet with selenium enriched cereals

Mehdi, Y., Clinquart, A., Hornick, J.-L., Cabaraux, J.-F., Istasse, L. and Dufrasne, I. 2015. Meat composition and quality of young growing Belgian Blue bulls offered a fattening diet with selenium enriched cereals. Can. J. Anim. Sci. 95: 465–473. The objective of this study was to evaluate the effects of selenium (Se) enrichment of cereals on the performance of Belgian Blue bulls, meat quality and chemical composition. Twenty-three bulls were used in the present study. Twelve bulls were offered a control diet containing Se at a basal concentration of 58 µg kg−1 of dry matter (DM) and the other 11 bulls were given a diet containing 173 µg kg−1 DM of Se by means of Se-enriched spelt and barley. The Se enrichment of the diet did not affect the growth performance, the slaughter data or meat quality (P > 0.05). There were no effects of Se on tenderness, oxidative rancidity and water losses. However, there were some effects of Se enrichment on the meat chemical composition. The ether extract was decreased from 2.1 to 1.7% DM (P<0.05). There was also significant Se enrichment (P<0.001) in the longissimus thoracis muscle (177 vs. 477 ng g−1 DM) and organs: liver (474 vs. 1126 ng g−1 DM) and kidney (4956 vs. 5655 ng g−1 DM), Under such conditions, the human consumption of a piece of such meat or liver can provide a large part of the recommended daily Se intake, estimated between 30 and 57%.

Comparative oral dose toxicokinetics of selenium compounds commonly found in selenium accumulator plants

Consumption of Se accumulator plants by livestock can result in Se intoxication. Recent research indicates that the Se forms most common in Se accumulator plants are selenate and Se-methylselenocysteine (MeSeCys). In this study the absorption, distribution, and elimination kinetics of Se in serum and whole blood of lambs dosed with a single oral dose of (1, 2, 3, or 4 mg Se/kg BW) of sodium selenate or MeSeCys were determined. The Se concentrations in serum and whole blood for both chemical forms of Se followed simple dose-dependent relationships. Se-methylselenocysteine was absorbed more quickly and to a greater extent in whole blood than sodium selenate, as observed by a greater peak Se concentration (Cmax; P < 0.0001), and faster time to peak concentration (Tmax; P < 0.0001) and rate of absorption (P < 0.0001). The rate of absorption and Tmax were also faster (P < 0.0001) in serum of lambs dosed with MeSeCys compared with those dosed sodium selenate at equimolar doses; however, Cmax in serum was greater (P < 0.0001) in lambs dosed with sodium selenate compared with those dosed MeSeCys at equimolar doses. The MeSeCys was absorbed 4 to 5 times faster into serum and 9 to 14 times faster into whole blood at equimolar Se doses. There were dose-dependent increases in the area under the curve (AUC) for Se in serum and whole blood of lambs dosed with both sodium selenate and MeSeCys. In whole blood the MeSeCys was approximately twice as bioavailable as sodium selenate at equimolar doses as observed by the AUC, whereas in serum there were no differences (P > 0.05) in AUC at the same doses. At 168 h postdosing the Se concentration in whole blood remained much greater (P < 0.0001) in lambs dosed with MeSeCys as compared with lambs dosed with sodium selenate; however, the serum Se concentrations were not different between treatments at the same time point. The results presented in this study demonstrate that there are differences between the kinetics of different selenocompounds when orally dosed to sheep. Therefore, in cases of acute selenosis, it is important to understand the chemical form to which an intoxicated animal was exposed when determining the importance and meaning of Se concentration in serum or whole blood obtained at various times postexposure.

Selenium in the environment, metabolism and involvement in body functions

Selenium (Se³⁴₇₉) is a metalloid which is close to sulfur (S) in terms of properties. The Se concentration in soil varies with type, texture and organic matter content of the soil and with rainfall. Its assimilation by plants is influenced by the physico-chemical properties of the soil (redox status, pH and microbial activity). The presence of Se in the atmosphere is linked to natural and anthropogenic activities. Selenoproteins, in which selenium is present as selenocysteine, present an important role in many body functions, such as antioxidant defense and the formation of thyroid hormones. Some selenoprotein metabolites play a role in cancer prevention. In the immune system, selenium stimulates antibody formation and activity of helper T cells, cytotoxic T cells and Natural Killer (NK) cells. The mechanisms of intestinal absorption of selenium differ depending on the chemical form of the element. Selenium is mainly absorbed in the duodenum and caecum by active transport through a sodium pump. The recommended daily intake of selenium varies from 60 μg/day for women, to 70 μg/day for men. In growing ruminants the requirements are estimated at 100 μg/kg dry matter and 200 μg/Kg for pregnant or lactating females. A deficiency can cause reproductive disorders in humans and animals.

Effects of selenium source and level on growth performance, tissue selenium concentrations, antioxidation, and immune functions of heat-stressed broilers

An experiment is conducted to investigate the effects of selenium (Se) source and level on growth performance, tissue Se concentrations, antioxidation, and immune functions of heat-stressed broilers from 22 to 42 days of age. A total of 210 22-day-old Arbor Acres commercial male chicks were assigned by body weight to one of seven treatments with six replicates of five birds each in a completely randomized design involving a 3 × 2 factorial arrangement plus one Se-unsupplemented basal diet control (containing 0.027 mg of Se/kg). The three Se sources were sodium selenite (Na₂SeO₃), Se yeast, and AMMS Se (Se protein), and the two supplemental Se levels were 0.15 or 0.30 mg Se/kg. All birds were reared under heat-stressed condition (33 ± 1 °C during 0900-1700 hours and 27 ± 1 °C during 1900-0700 hours with a relative humidity of 60-80 %). The results showed that heat-stressed chicks fed Se-supplemented diets had higher (P < 0.10) average daily feed intake, Se concentrations in liver and breast muscle, liver glutathione peroxidase (GSH-Px) activity, serum antibody titers against H5N1(Re-4 strain), H5N1(Re-5 strain) and lower (P < 0.01) mortality compared with the control. Chicks fed the diets supplemented with 0.30 mg/kg of Se had higher (P < 0.05) Se concentrations in liver and breast muscle, liver GSH-Px activity, and serum antibody titer against H5N1 (Re-4 strain) than those fed the diets supplemented with 0.15 mg/kg of Se. Broilers fed the diets supplemented with Se yeast had higher (P < 0.001) Se concentrations in liver and breast muscle than those fed the diets supplemented with Na₂SeO₃ or AMMS Se. However, broilers fed the diets supplemented with AMMS Se had higher (P < 0.05) serum antibody titers against H5N1 (Re-4 strain) and H5N1 (Re-5 strain) than those fed the diets supplemented with Na₂SeO₃. These results indicated that Se yeast was more effective than Na₂SeO₃ or AMMS Se in increasing tissue Se retention; however, AMMS Se was more effective than Na₂SeO₃ or Se yeast in improving immune functions of heat-stressed broilers.

An in vitro investigation of species-dependent intestinal transport of selenium and the impact of this process on selenium bioavailability

A range of Se species has been shown to occur in a variety of different foodstuffs. Depending on its speciation, Se is more or less bioavailable to human subjects. In the present study, the role of speciation as a determinant of Se bioavailability was addressed with an investigation of species-specific mechanisms of transport at the intestinal level. The present work focused on four distinct Se compounds (selenate (Se(VI)), selenite (Se(IV)), selenomethionine (SeMet) and methylselenocysteine (MeSeCys)), whose intestinal transport was mimicked through an in vitro bicameral model of enterocyte-like differentiated Caco-2 cells. Efficiency of Se absorption was shown to be species dependent (SeMet>MeSeCys>Se(VI)>Se(IV)). In the case of SeMet, MeSeCys and Se(VI), the highly polarised passage from the apical to basolateral pole indicated that a substantial fraction of transport was transcellular, whilst results for Se(IV) indicated paracellular diffusion. Passage of the organic Se species (SeMet and MeSeCys) became saturated after 3 h, but no such effect was observed for the inorganic species. In addition, SeMet and MeSeCys transport was significantly inhibited by their respective S analogues methionine and methylcysteine, which suggests a common transport system for both kinds of compounds.

Effects of selenium sources and levels on reproductive performance and selenium retention in broiler breeder, egg, developing embryo, and 1-day-old chick

An 8-week experiment was conducted using 540 48-week-old Lingnan Yellow broiler breeders to evaluate the effect of the sources and levels of selenium (Se) on reproduction and Se retention. After receiving basal diet for 8 weeks, breeders were randomly assigned to six dietary treatments and fed corn-soy-based diets supplemented with 0.15 or 0.30 mg/kg of Se from sodium selenite (SS) or from Se-enriched yeast (SY) or from selenomethionine (SM). The Se concentration of basal diet was 0.04 mg/kg of Se. With the increase of dietary Se level, hatchability decreased (P < 0.05), but the Se concentrations were elevated in liver, kidney, pancreas, and breast muscle of breeders, yolk and albumen, liver and breast muscle of developing embryos, and tissues (liver, kidney, pancreas, and breast muscle) of 1-day-old chicks (P < 0.01). Irrespective of the Se level, the Se concentrations in liver, kidney, pancreas, and breast muscle were greater (P < 0.01) in breeders fed SY or SM compared with breeders fed SS, and kidney from breeders fed SM had greater Se concentration than that from breeders fed SY (P < 0.01). Yolk and albumen from SM treatments also had the greatest Se concentrations (P < 0.01). The embryonic liver and breast muscle from SM treatments had higher (P < 0.01) Se concentrations than those of SS treatments. The Se concentrations in liver, kidney, and breast muscle of 1-day-old chicks were greater (P < 0.01) in SY or SM treatments compared with SS treatments, and there was a more significant increase in Se concentrations in kidney and breast muscle of 1-day-old chicks from SM treatments than those from SY treatments (P < 0.01). The results suggest that the Se retention efficiency of SM is higher than that of SY, which, in turn, is higher than that of SS for broiler breeders and their offspring.

Effect of different selemethionine forms and levels on performance of breeder hens and se distribution of tissue and egg inclusion

A 2×2 factorial arrangement of treatments in randomized design was conducted to investigate the effect of different selenomethionine (SM) sources and levels on the productive performance of breeder hens and the Se distribution in the inclusion of eggs and serum and tissues of breeder hens and its offspring. A total of 480 Ling-Nan-Huang breeder hens, 48 weeks of age, were allocated to four treatments, each of which included three replicates of 40 hens. Pretreatment period was 2 weeks, and the experiment lasted 8 weeks. Two SM forms of DL-SM and L-SM were supplemented at 0.15 or 0.30 mg Se/kg into the basal diet. Results showed that the Se level of 0.15 mg/kg supplemented in the diet, compared to 0.30 mg/kg, significantly elevated the percentage of egg production (p<0.05), hatchability (p<0.01), and birthrate (p<0.01), whereas the Se level of 0.30 mg/kg led to a higher Se content in egg contents, serum, and all tissues (p<0.01). In addition, the form of DL-SM showed a significant increase in Se content of egg inclusion (p<0.01), serum (p<0.01), and all tissues (p<0.01, except breeder hens' pancreas and its offspring's liver and breast muscle). The birthrate and yolk Se content were markedly influenced by the interaction between Se source and Se level (p<0.01). The above results suggested that DL-SM, compared to L-SM, had a similar equal effect on the performance of breeder hens, but DL-SM was superior to L-SM with respect to selenium distribution in egg inclusion, serum, and tissues.

Effects of selenomethionine in irradiated human thyroid epithelial cells and tumorigenicity studies

The objectives of the present study were to characterize γ-ray, 1 GeV/n proton, and 1 GeV/n iron ion radiation-induced adverse biological effects in terms of toxicity and transformation of HTori-3 human thyroid epithelial cells; to evaluate the ability of L-selenomethionine (SeM) to protect against radiation-induced transformation when present at different times during the assay period; and to evaluate the tumorigenicity of HTori-3 cells derived from anchorage-independent colonies following iron ion radiation exposure. Cell survival was determined by a clonogenic assay, transformation was measured by a soft agar colony formation assay, and the tumorigenic potential of the cells was determined by injecting them subcutaneously into athymic nude mice and monitoring tumor formation. The results demonstrate that exposure of HTori-3 cells to γ-ray, proton, or iron ion radiation resulted in decreased clonogenic survival, which persisted for weeks after the radiation exposure. Treatment with SeM initiated up to 7 days after the radiation exposure conferred significant protection against radiation-induced anchorage-independent growth. HTori-3 cells derived from all evaluated anchorage-independent colonies formed tumors when injected into athymic nude mice, indicating that these cells are tumorigenic and that anchorage-independent colony growth is a reliable surrogate endpoint biomarker for the radiation-induced malignant transformation of HTori-3 cells.

Effect of different selenium sources on productive performance, serum and milk Se concentrations, and antioxidant status of sows

The experiment was conducted to study the effects of different selenium (Se) sources on productive performance, serum and milk Se concentrations, and antioxidant status of sows. A total of 12 sows (Landrace×Yorkshire) with same pregnancy were randomly divided into two groups; each group was replicated six times. These two groups received the same basal gestation and lactation diets containing 0.042 mg Se/kg, supplemented with 0.3 mg Se/kg sodium selenite or selenomethionine (i.e., seneno-DL: -methylseleno), respectively. The feeding trial lasted for 60 days, with 32 and 28 days for gestation and lactation period, respectively. Compared with sodium selenite, maternal selenomethionine intake significantly increased (P < 0.05) the weaning litter weight and average weight of piglet. The Se concentration in the serum, colostrum, and milk of sows were significantly higher (p < 0.05) in the selenomethionine-treated group. The antioxidant status was greatly improved in sows of selenomethionine-treated group and was illuminated by the increased total antioxidant capability (T-AOC; P < 0.05) and decreased malondialdehyde (MDA; P < 0.01) level in the serum of sows, increased T-AOC (P < 0.05), glutathione (GSH) peroxidase (P < 0.05), superoxide dismutase (P < 0.05) and GSH (P < 0.05), and MDA (P < 0.05) level in the colostrum and milk of sows. These results suggested that maternal selenomethionine intake improved Se concentration and antioxidant status of sows, thus maintain maternal health and increase productive performance after Se was transferred to its offspring.

Selenomethionine: an effective selenium source for sow to improve Se distribution, antioxidant status, and growth performance of pig offspring

The present study was to investigate the efficiency of maternal selenomethionine intake on growth performance, Se distribution, and antioxidant status of pig offspring by comparing with sodium selenite. A total of 12 sows (Landrace × Yorkshire) with same pregnancy were randomly divided into two groups; each group was replicated six times. These two groups received the same basal gestation and lactation diets containing 0.04 mg Se/kg, supplemented with 0.3 mg Se/kg sodium selenite and selenomethionine (i.e., seneno-DL: -methylseleno), respectively. The feeding trial lasted for 60 days, with 32 and 28 days for gestation and lactation period, respectively. Compared with sodium selenite, maternal selenomethionine intake significantly (p < 0.05) increased the daily weight gain of piglet from birth to weaning. The Se concentration in the colostrum and milk and tissue Se content of piglets were significantly higher (p < 0.05) in the selenomethionine-treated group. The antioxidant status was greatly improved in piglets of selenomethionine-treated group and was illuminated by the increased total antioxidant capability, glutathione peroxidase, superoxide dismutase, and glutathione, and decreased the malondialdehyde level in the organs of piglets. The increased (p < 0.05) triiodothyronine (T(3)) and decreased (p < 0.05) thyroxine (T(4)) concentration indicated the improved protein synthesis and energy production in the selenomethionine-treated group. The increased (p < 0.05) pancreatic digestive enzymes of protease, amylase, and lipase activities indicated that maternal selenomethionine intake may have a positive effect on the degradation and absorption of nutrients in its piglets. In summary, we concluded that maternal selenomethionine intake increased Se deposition, antioxidant status, and nutrient use efficiency, thus providing an effective way to improve the growth performance of piglets from birth to weaning.

Comparative toxicosis of sodium selenite and selenomethionine in lambs

Excess consumption of selenium (Se) accumulator plants can result in selenium intoxication. The objective of the study reported here was to compare the acute toxicosis caused by organic selenium (selenomethionine) found in plants with that caused by the supplemental, inorganic form of selenium (sodium selenite). Lambs were orally administered a single dose of selenium as either sodium selenite or selenomethionine and were monitored for 7 days, after which they were euthanized and necropsied. Twelve randomly assigned treatment groups consisted of animals given 0, 1, 2, 3, or 4 mg of Se/kg of body weight as sodium selenite, or 0, 1, 2, 3, 4, 6, or 8 mg of Se/kg as selenomethionine. Sodium selenite at dosages of 2, 3, and 4 mg/kg, as well as selenomethionine at dosages of 4, 6, and 8 mg/kg resulted in tachypnea and/or respiratory distress following minimal exercise. Severity and time to recovery varied, and were dose dependent. Major histopathologic findings in animals of the high-dose groups included multifocal myocardial necrosis and pulmonary alveolar vasculitis with pulmonary edema and hemorrhage. Analysis of liver, kidney cortex, heart, blood, and serum revealed linear, dose-dependent increases in selenium concentration. However, tissue selenium concentration in selenomethionine-treated lambs were significantly greater than that in lambs treated with equivalent doses of sodium selenite. To estimate the oxidative effects of these selenium compounds in vivo, liver vitamin E concentration also was measured. Sodium selenite, but not selenomethionine administration resulted in decreased liver vitamin E concentration. Results of this study indicate that the chemical form of the ingested Se must be known to adequately interpret tissue, blood, and serum Se concentrations.

Selenium, the thyroid, and the endocrine system

Recent identification of new selenocysteine-containing proteins has revealed relationships between the two trace elements selenium (Se) and iodine and the hormone network. Several selenoproteins participate in the protection of thyrocytes from damage by H(2)O(2) produced for thyroid hormone biosynthesis. Iodothyronine deiodinases are selenoproteins contributing to systemic or local thyroid hormone homeostasis. The Se content in endocrine tissues (thyroid, adrenals, pituitary, testes, ovary) is higher than in many other organs. Nutritional Se depletion results in retention, whereas Se repletion is followed by a rapid accumulation of Se in endocrine tissues, reproductive organs, and the brain. Selenoproteins such as thioredoxin reductases constitute the link between the Se metabolism and the regulation of transcription by redox sensitive ligand-modulated nuclear hormone receptors. Hormones and growth factors regulate the expression of selenoproteins and, conversely, Se supply modulates hormone actions. Selenoproteins are involved in bone metabolism as well as functions of the endocrine pancreas and adrenal glands. Furthermore, spermatogenesis depends on adequate Se supply, whereas Se excess may impair ovarian function. Comparative analysis of the genomes of several life forms reveals that higher mammals contain a limited number of identical genes encoding newly detected selenocysteine-containing proteins.

Influence of Dietary Habits on Serum Selenium Concentration

BACKGROUND

A serum selenium concentration of 70 microg/l is considered to be sufficient for glutathione peroxidase (GSHPx) activity, a selenium-dependent enzyme reflecting the body selenium status. The purpose of the study was to assess which foods or food groups best affect serum selenium in subjects with selenium concentrations below or above 70 microg/l.

METHODS

A food frequency questionnaire was employed to describe the dietary habits of 129 subjects. Serum selenium concentrations were determined using the electrothermal absorption spectrometry (ETAAS) technique following serum dilution.

RESULTS

Multiple regression analysis revealed that consumption of ham, honey and tea was positively associated with the selenium concentration in the sera of selenium-inadequate subjects. In selenium-inadequate subjects, alcohol consumption may be responsible for selenium losses. Unlike the selenium-inadequate subjects, the selenium concentrations in the sera of the selenium-adequate subjects were positively correlated with the frequencies of wholegrain bread consumption and processed fruit consumption. In all the groups tested, the serum selenium concentration was not affected by cigarette smoking.

CONCLUSIONS

The serum selenium concentration is influenced by dietary habits, but not by cigarette smoking. Frequent consumption of ham, tea and honey may be effective to improve the selenium concentration in the sera of selenium-inadequate subjects.

Effect of dietary organic versus inorganic selenium in laying hens on the productivity, selenium distribution in egg and selenium content in blood, liver and kidney

We investigated the effect of organic versus inorganic dietary selenium in laying hens on the productivity, selenium distribution in egg and selenium content in blood, liver and kidney. Sixty Leghorn laying hens were fed a basic diet containing 0.23mg Se/kg DM (dry matter) for 2 weeks and then were allocated randomly into three groups. Thereafter, the hens were given the same basic diet without supplementation, or with 0.51 mg Se/kg DM as sodium selenite (SS) or Se-malt (SM). During the experiment, egg rate and dietary intake were recorded, blood was sampled on days 10 and 20, and six eggs were sampled on days 8, 16 and 24 from each treatment group for Se content determination. At the end of the experiment, 10 hens from each treatment were slaughtered, and liver and kidney were sampled for the determination of Se content. The result showed that with the increase of dietary Se level, the Se content in egg, blood, liver and kidney was elevated (P < 0.05), but the hens' productivity was not affected. SS increased liver Se content more than SM (P < 0.05), while the Se content both in blood and kidney did not differ significantly between the SS and SM treatments. Se from SM and SS mainly deposited in the egg yolk. This suggests that the metabolic route of Se from SM is similar to that of Se from SS in laying hens.

The antioxidant role of selenium and seleno-compounds

Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.

The nutritional significance, metabolism and toxicology of selenomethionine

SeMet is a naturally occurring toxic amino acid but at the same time represents the major nutritional source of selenium for higher animals and humans. The ability of SeMet to be incorporated into the body proteins in place of Met furthermore provides a means of reversible Se storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet. Since higher animals cannot synthesize SeMet, yet from it all needed forms of Se are produced, SeMet meets the criteria of an essential amino acid. Accordingly, SeMet, or enriched food sources thereof, are appropriate forms of Se for human nutritional Se supplementation. However, while SeMet or Se yeast are already widely used in over-the-counter nutritional supplements, infant formulas and parenteral feeding mixtures still contain Se in the form of sodium selenate or sodium selenite, even though these are not the normal nutritional forms of Se. In animal nutrition, these inorganic selenium salts are increasingly replaced by food sources of SeMet such as Se yeast. Synthetic SeMet could also be employed as a feed additive, but its regulatory status is as yet undetermined. The optimal nutritional levels of SeMet for different animal species still need to be determined. The expectation is that lower additions to feedstock of equivalent levels of SeMet will suffice to achieve adequacy than currently approved maximum levels of Se in the form of inorganic Se salts.

Selenomethionine: a review of its nutritional significance, metabolism and toxicity

Although the need for selenium in human and animal nutrition is well recognized, the question concerning the proper form of selenium for supplemental use is still being debated. Ideally, selenium should be supplemented in the form in which it occurs naturally in foods. Because the L-isomer of selenomethionine (Se-met) is a major natural food-form of selenium, synthetic L-Se-met or enriched food sources thereof such as selenium yeast are appropriate supplemental forms of Se for humans; for animals, DL-Se-met is acceptable. Ingested Se-met is either metabolized directly to reactive forms of selenium or stored in place of methionine in body proteins. Se-met metabolism is closely linked to protein turnover. At constant intakes in the nutritional range, tissue Se levels increase until a steady state is established, preventing the build-up to toxic levels.

Toxicity, metabolism and absorption of selenite by isolated rat hepatocytes

The uptake of various levels of selenite by isolated rat hepatocytes was investigated. The LD50 value of selenite was about 500 microM. The activity of lactic dehydrogenase in the medium was correlated with cell viability as determined by trypan blue exclusion. After incubation of selenite with hepatocytes, protein-bound Se was the predominant form (80-90% of the cellular Se) present. Subcellular fractionation indicated that most of the radioactivity was present in the cytosol when hepatocytes were incubated with 75Se-selenite. The uptake of 75Se by isolated rat hepatocytes was linear with selenite concentration up to the highest amount tested, 200 microM. Sulfite inhibited the uptake of selenite by hepatocytes.