Insights for Setting of Nutrient Requirements, Gleaned by Comparison of Selenium Status Biomarkers in Turkeys and Chickens versus Rats, Mice, and Lambs

Use of laser-ablation inductively-coupled plasma mass spectrometry for analysis of selenosugars bound to proteins

We previously used high pressure liquid chromatography coupled with Se-specific inductively coupled plasma mass spectrometry and molecule specific (ESI Orbitrap MS/MS) detection to study the increase in liver Se in turkeys and rats supplemented as selenite in high-Se (5 µg Se/g diet) and adequate-Se diets. We found that far more Se is present as selenosugar (seleno-N-acetyl galactosamine) than is present as selenocysteine (Sec) in true selenoproteins. In high-Se liver, the increase in liver Se was due to low molecular weight selenometabolites such as glutathione-, cysteine-, and methyl-conjugates of the selenosugar, but also as high molecular weight species as selenosugars decorating general proteins via mixed Se-S bonds. To demonstrate selenosugar binding to proteins, aqueous liver extracts from animals fed Se-adequate and high-Se were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Native-PAGE with and without pretreatment with β-mercaptoethanol (βME). The separated proteins were then electrophoretically transferred to membranes, and the membranes subsequently were subjected to laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) analysis of 78Se profiles. Without βME treatment, Se was widely distributed across the molecular weight profile for both SDS-PAGE and Native-PAGE, whereas βME pretreatment dramatically reduced Se binding, reducing the profile to true Sec-selenoproteins. This reduction was ∼50% for both high-Se rat and turkey extracts. The increased Se in non-βME treated samples was distributed across the full profile. The use of LA-ICP-MS indicates that selenosugar residues are bound to protein subunits of multiple sizes, and that targeted attachment of selenosugars to a single or limited number of protein subunits does not occur.

Optimizing selenium-enriched yeast supplementation in laying hens: Enhancing egg quality, selenium concentration in eggs, antioxidant defense, and liver health

This study evaluated the effects of selenium-enriched yeast (SY) supplementation at various levels on health and production parameters in laying hens, including egg production, egg quality, selenium (Se) concentrations in eggs, liver health, serum biochemical markers, antioxidant function, and immune responses. A total of 360 Hy-Line Brown hens (28 weeks old) were randomly assigned to four dietary groups with six replicates of 15 birds each, monitored over a 12-week feeding trial after a two-week acclimatization period. The dietary groups included a control (basal diet without selenium) and three SY-supplemented groups with Se levels of 0.3 mg/kg (SY03), 1.5 mg/kg (SY15), and 6.0 mg/kg (SY60). The results showed no significant effects of dietary SY on laying performance or feed efficiency (P > 0.05). However, the SY15 group showed significant improvements in egg quality, particularly in albumen height, Haugh Unit and yolk color (P < 0.05). Selenium concentrations in eggs, albumen, and yolk increased dose-dependently, with significant differences in the SY-supplemented groups (P < 0.001). Increased activities of liver enzymes including alanine transaminase, alkaline phosphatase, and aspartate transaminase, alongside elevated levels of uric acid were notable in the SY60 group (P < 0.05). In addition, histological analysis revealed significant hepatocyte degeneration and a higher liver organ index (P < 0.05), in the SY60 group. All of which suggests potential liver toxicity at higher selenium levels. Antioxidant capacity of the birds were significantly enhanced due to dietary supplementation of SY as indicated by increased serum levels of total antioxidant capacity, and activities of catalase, glutathione peroxidase, and superoxide dismutase (P < 0.05). Analysis of hepatic genes expression revealed that SY15 supplementation significantly upregulated key antioxidant-related genes (Nrf2, HO-1, CAT, and NQO1) and downregulated Keap1 expression (P < 0.05), suggesting strong activation of the antioxidant defense system. In conclusion, SY supplementation at 1.5 mg/kg improved egg quality, increased Se concentrations in eggs, and enhanced antioxidant capacity without affecting laying performance or liver health. This makes it a balanced approach to improving egg quality and poultry health. However, higher supplementation levels (6.0 mg/kg) resulted in liver damage, underscoring the importance of careful dosage consideration.

Possible Metabolic Remodeling based on de novo Biosynthesis of L-serine in Se-Subtoxic or -Deficient Mammals

Current research studies point to an increased risk of diabetes with selenium (Se) intake beyond the physiological requirement used to prevent cancers. The existing hypothesis of "selenoprotein overexpression leads to intracellular redox imbalance" cannot clearly explain the U-shaped dose-effect relationship between Se intake and the risk of diabetes. In this review, it is speculated that metabolic remodeling based on the de novo biosynthesis of L-serine may occur in mammals at supranutritional or subtoxic levels of Se. It is also speculated that a large amount of L-serine is consumed by the body during insufficient Se intake, thus resulting in similar metabolic reprogramming. The increase in atypical ceramide and its derivatives due to the lack of L-serine may also play a role in the development of diabetes.

PRDX6 dictates ferroptosis sensitivity by directing cellular selenium utilization

Selenium-dependent glutathione peroxidase 4 (GPX4) is the guardian of ferroptosis, preventing unrestrained (phospho)lipid peroxidation by reducing phospholipid hydroperoxides (PLOOH). However, the contribution of other phospholipid peroxidases in ferroptosis protection remains unclear. We show that cells lacking GPX4 still exhibit substantial PLOOH-reducing capacity, suggesting a contribution of alternative PLOOH peroxidases. By scrutinizing potential candidates, we found that although overexpression of peroxiredoxin 6 (PRDX6), a thiol-specific antioxidant enzyme with reported PLOOH-reducing activity, failed to prevent ferroptosis, its genetic loss sensitizes cancer cells to ferroptosis. Mechanistically, we uncover that PRDX6, beyond its known peroxidase activity, acts as a selenium-acceptor protein, facilitating intracellular selenium utilization and efficient selenium incorporation into selenoproteins, including GPX4. Its physiological significance was demonstrated by reduced GPX4 expression in Prdx6-deficient mouse brains and increased sensitivity to ferroptosis in PRDX6-deficient tumor xenografts in mice. Our study highlights PRDX6 as a critical player in directing cellular selenium utilization and dictating ferroptosis sensitivity.

Effects of supplementation of different selenium sources on lipid profile, selenium, and vitamin E concentration of yolk

Egg preference as a source of protein also provides beneficial fatty acids, vital for human consumption. However, rich in lipid products are prone to oxidative damage. The study aims to determine the effect of supplementing biogenic selenium (Se) from Stenotrophomonas maltophilia, ADS18 (ADS18) in laying hens' diet on yolk lipid oxidation status (MDA), beta-carotene (β-carotene) content, cholesterol, fatty acids, Se, and vitamin E (VE) level. A total of one hundred and twenty (120) laying hens of Lohmann Brown strains aged 50 weeks, weighing 1500 to 2000 g were reared individually in A-shape two-tier stainless-steel cages sized 30 cm x 50 cm x 40 cm (width, depth height). The hens were randomly allotted into four treatments with six replications in a complete randomised design for the period of 12 weeks. The basal diet contains 100 mg/kg VE. Treatment diets consist of basal diet as control, SS containing 0.3 mg/kg sodium selenite, Se-yeast containing 0.3 mg/kg selenised yeast, and VADS18 containing 0.3 mg/kg of ADS18. Forty-eight eggs were collected and freeze-dried biweekly for analysis. The results of the present study showed that hens supplemented ADS18 had significantly (P < 0.05) lower MDA and cholesterol levels while their egg yolks had higher levels of Se and mono-unsaturated fatty acids (MUFA). The control group had significantly (P < 0.05) higher saturated fatty acid (SFA) contents than the VE and dietary Se-supplemented groups, while the ADS18 group had the lowest SFA contents. Conversely, in comparison to the inorganic and control groups, the VE content of the egg yolk was significantly (P < 0.05) higher in organic Se-supplemented (Se-yeast and VADS18) groups. Hens with SS supplementation had significantly (P < 0.05) higher egg yolk β-carotene content. When compared to other treatment groups, the control group had higher (P < 0.05) polyunsaturated fatty acids (PUFA) content. The ADS18 is therefore deemed comparable to other Se sources. To prevent Se toxicity, however, a better understanding of the levels of ADS18 incorporation in poultry diets is required.

Selenomethionine supplementation and expression of selenosugars, selenocysteine, and other selenometabolites in rat liver

Selenomethionine (SeMet) as a methionine analog can be incorporated into protein. In turkeys, we recently found that selenium (Se) as selenite is not metabolized to SeMet but rather to selenosugars (seleno-N-acetyl galactosamine) bound to protein as well as to selenocysteine (Sec) in selenoproteins. To characterize the metabolism of SeMet, we fed rats graded levels of SeMet from 0 to 5 µg Se/g in a Se-deficient diet for 4 wk, and investigated the fate and accumulation of liver Se using high pressure liquid chromatography (HPLC) coupled with Se-specific inductively coupled plasma mass spectrometry (ICP-MS) and molecule specific (Orbitrap MS/MS) detection. Up to 0.24 µg Se/g (Se requirement for maximal glutathione peroxidase activity), Sec accounted for ∼40% of total liver Se whereas SeMet only accounted for 3-11%. Analysis of water-soluble extracts found negligible low molecular weight (LMW) Se species in rats fed 0 and 0.08 µg Se/g, including no SeMet. At 0.24 µg Se/g and above, SeMet accounted for only 10% of LMW Se species, whereas methyl- and glutathionyl-selenosugars accounted for 70% of LMW Se species. Above the Se requirement, SeMet was ∼30% of the proteinaceous amino acids, whereas Sec levels fell to 5% in rats fed 5 µg Se/g as SeMet. Last, considerably less inorganic Se was bound to liver protein with high SeMet as compared to selenite in a parallel study. SeMet is efficiently metabolized and mixes with the common Se metabolite pool, where Se is preferentially incorporated into Sec and Sec-selenoproteins until selenoproteins plateau; with high SeMet intake, Se is increasingly accumulated as LMW selenosugars and as selenosugar-decorated proteins.

Effect of graded levels of selenium supplementation as selenite on expression of selenosugars, selenocysteine, and other selenometabolites in rat liver

Using high pressure liquid chromatography (HPLC) coupled with selenium-specific inductively coupled plasma mass spectrometry (ICP-MS) and molecule specific (Orbitrap MS/MS) detection, we previously found that far more selenium (Se) is present as selenosugar (seleno-N-acetyl galactosamine) in Se-adequate turkey liver than is present as selenocysteine (Sec) in true selenoproteins, and that selenosugars account for half of the Se in high-Se turkey liver. To expand these observations to mammals, we studied Se metabolism in rats fed graded levels of selenite from 0 to 5 μg Se/g for 4 wk. In Se-adequate (0.24 μg Se/g) rats, 43% of liver Se was present as Sec, 32% was present as selenosugars, and 22% as inorganic Se bound to protein. In liver of rats fed 5 μg Se/g as selenite, the quantity of Sec remained at the Se-adequate plateau (11% of total Se), 22% was present as low molecular weight (LMW) selenosugars with substantial additional selenosugars linked to protein, but 64% was present as inorganic Se bound to protein. No selenomethionine was found at any level of selenite supplementation. Below the Se requirement, Se is preferentially incorporated into Sec-selenoproteins. Above the dietary Se requirement, selenosugars become by far the major LMW water soluble Se species in liver, and levels of selenosugar-decorated proteins are far higher than Sec-selenoproteins, making these selenosugar-decorated proteins the major Se-containing protein species in liver with high Se supplementation. This accumulation of selenosugars linked to cysteines on proteins or the build-up of inorganic Se bound to protein may underlie Se toxicity at the molecular level.

Selenium deficiency-induced multiple tissue damage with dysregulation of immune and redox homeostasis in broiler chicks under heat stress

Broiler chicks are fast-growing and susceptible to dietary selenium (Se) deficiency. This study sought to reveal the underlying mechanisms of how Se deficiency induces key organ dysfunctions in broilers. Day-old male chicks (n=6 cages/diet, 6 chicks/cage) were fed with a Se-deficient diet (Se-Def, 0.047 mg Se/kg) or the Se-Def+0.3 mg Se/kg (Control, 0.345 mg Se/kg) for 6 weeks. The serum, liver, pancreas, spleen, heart, and pectoral muscle of the broilers were collected at week 6 to assay for Se concentration, histopathology, serum metabolome, and tissue transcriptome. Compared with the Control group, Se deficiency induced growth retardation and histopathological lesions and reduced Se concentration in the five organs. Integrated transcriptomics and metabolomics analysis revealed that dysregulation of immune and redox homeostasis related biological processes and pathways contributed to Se deficiency-induced multiple tissue damage in the broilers. Meanwhile, four metabolites in the serum, daidzein, epinephrine, L-aspartic acid and 5-hydroxyindoleacetic acid, interacted with differentially expressed genes with antioxidative effects and immunity among all the five organs, which contributed to the metabolic diseases induced by Se deficiency. Overall, this study systematically elucidated the underlying molecular mechanisms in the pathogenesis of Se deficiency-related diseases, which provides a better understanding of the significance of Se-mediated heath in animals.

Gpx4, Selenov, and Txnrd3 Are Three Most Testis-Abundant Selenogenes Resistant to Dietary Selenium Concentrations and Actively Expressed During Reproductive Ages in Rats

Almost all selenogenes are expressed in the testis, and those have the highest and constant expressions will be the primary candidates for functional analysis of selenium (Se) in male reproduction. This study aimed to profile the mRNA expressions of the testis-abundant selenogenes of rat models in responses to growth and dietary Se concentrations. Forty-eight weaning SD male rats were fed Se deficient basal diet (BD) for 5 weeks and then randomly grouped (n = 12/group) for being fed BD or BD plus 0.25, 3, or 5 mg Se/kg for 4 more weeks before sacrifice. Abundances of selenogenomic mRNAs in the liver and testis were determined with relative qPCR and those of the testis-abundant selenogenes in 13 kinds of tissues were assayed with a molecular beacon-based qPCR. Spatiotemporal expressions of rat selenogenome were also analyzed with the RNA-Seq transcriptomic data published by NCBI. mRNA abundances of glutathione peroxidase 4 (Gpx4), nuclear Gpx4 (nGpx4), selenoprotein V (Selenov), and thioredoxin reductase 3 (Txnrd3) in the testis were significantly higher than that in any other tissues (P < 0.05). Moreover, testicular mRNA abundances of Gpx4, Selenov, and Txnrd3 were not affected by levels of dietary Se supplementation (P > 0.05), and much higher at 6-21 weeks old than at 2 and 104 weeks old (P < 0.05). The result showed that Gpx4, Selenov, and Txnrd3 were most highly expressed in the testis of rats especially at reproductive ages and resistant to the impact of dietary Se levels, which suggested their specific importance in male reproduction.

Selenium Deficiency Dysregulates One-Carbon Metabolism in Nutritional Muscular Dystrophy of Chicks

BACKGROUND

Nutritional muscular dystrophy (NMD) in animals is induced by dietary selenium (Se) deficiency.

OBJECTIVES

This study was conducted to explore the underlying mechanism of Se deficiency-induced NMD in broilers.

METHODS

One-day-old male Cobb broilers (n = 6 cages/diet, 6 birds/cage) were fed a Se-deficient diet (Se-Def, 47 μg Se/kg) or the Se-Def supplemented with 0.3 mg Se/kg (control) for 6 wk. Thigh muscles of broilers were collected at week 6 for measuring Se concentration, histopathology, and transcriptome and metabolome assays. The transcriptome and metabolome data were analyzed with bioinformatics tools and other data were analyzed with Student's t tests.

RESULTS

Compared with the control, Se-Def induced NMD in broilers, including reduced (P < 0.05) final body weight (30.7%) and thigh muscle size, reduced number and cross-sectional area of fibers, and loose organization of muscle fibers. Compared with the control, Se-Def decreased (P < 0.05) the Se concentration in the thigh muscle by 52.4%. It also downregulated (P < 0.05) GPX1, SELENOW, TXNRD1-3, DIO1, SELENOF, H, I, K, M, and U by 23.4-80.3% in the thigh muscle compared with the control. Multi-omics analyses indicated that the levels of 320 transcripts and 33 metabolites were significantly altered (P < 0.05) in response to dietary Se deficiency. Integrated transcriptomics and metabolomics analysis revealed that one-carbon metabolism, including the folate and methionine cycle, was primarily dysregulated by Se deficiency in the thigh muscles of broilers.

CONCLUSIONS

Dietary Se deficiency induced NMD in broiler chicks, potentially with the dysregulation of one-carbon metabolism. These findings may provide novel treatment strategies for muscle disease.

Long-Term Excessive Selenium Supplementation Affects Gene Expression in Esophageal Tissue of Rats

Esophageal cancer is one of the leading causes of cancer death and the seventh most prevalent cancer worldwide. Considering the positive association of high selenium with the prevalence of esophageal cancer, we have investigated the effect of high doses of selenium on gene expression in the normal esophageal tissue of rats. Twenty male rats were randomly divided into four groups: control group, group 2 mg Se/L, 10 mg Se/L, and 20 mg Se/L rats fed with a basal basic diet and 2, 10, and 20 mg Se/L as sodium selenite in drinking water, respectively, for 20 weeks. Serum malondialdehyde and glutathione peroxidase activity were measured. Moreover, the expression and concentration of the cyclin D1, cyclin E, KRAS, p53, NF-kB, TGF-β, and MGMT in the esophageal tissue were analyzed and compared between the four groups. In normal esophageal tissue, selenium supplementations (2, 10, and 20 mg Se/L) increased the mRNA levels of cyclin D1, P53, KRAS, NF-κB p65, and MGMT and decreased the mRNA level of TGFß1. The concentrations of cyclin D1 and MGMT were also significantly increased by selenium supplementations. Selenium supplementations had no significant effect on serum MDA but significantly increased GPX activity. The present study suggests that selenium supplementation (2, 10, and 20 mg Se/L) affects gene expression related to inflammation, Cell proliferation, and apoptosis in the normal esophageal tissue. However, there were no observed abnormalities other than reduced growth with supplementation of 20 mg/L as Na2SeO3 in rats.

Dietary Selenium Across Species

This review traces the discoveries that led to the recognition of selenium (Se) as an essential nutrient and discusses Se-responsive diseases in animals and humans in the context of current understanding of the molecular mechanisms of their pathogeneses. The article includes a comprehensive analysis of dietary sources, nutritional utilization, metabolic functions, and dietary requirements of Se across various species. We also compare the function and regulation of selenogenomes and selenoproteomes among rodents, food animals, and humans. The review addresses the metabolic impacts of high dietary Se intakes in different species and recent revelations of Se-metabolites, means of increasing Se status, and the recycling of Se in food systems and ecosystems. Finally, research needs are identified for supporting basic science and practical applications of dietary Se in food, nutrition, and health across species. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The health benefits of selenium in food animals: a review

Selenium is an essential trace mineral important for the maintenance of homeostasis in animals and humans. It evinces a strong antioxidant, anti-inflammatory and potential antimicrobial capacity. Selenium biological function is primarily achieved by its presence in selenoproteins as a form of selenocysteine. Selenium deficiency may result in an array of health disorders, affecting many organs and systems; to prevent this, dietary supplementation, mainly in the forms of organic (i.e., selenomethionine and selenocysteine) inorganic (i.e., selenate and selenite) sources is used. In pigs as well as other food animals, dietary selenium supplementation has been used for improving growth performance, immune function, and meat quality. A substantial body of knowledge demonstrates that dietary selenium supplementation is positively associated with overall animal health especially due to its immunomodulatory activity and protection from oxidative damage. Selenium also possesses potential antiviral activity and this is achieved by protecting immune cells against oxidative damage and decreasing viral replication. In this review we endeavor to combine established and novel knowledge on the beneficial effects of dietary selenium supplementation, its antioxidant and immunomodulatory actions, and the putative antimicrobial effect thereof. Furthermore, our review demonstrates the gaps in knowledge pertaining to the use of selenium as an antiviral, underscoring the need for further in vivo and in vitro studies, particularly in pigs.

Obesity Hinders the Protective Effect of Selenite Supplementation on Insulin Signaling

The intake of high-fat diets (HFDs) containing large amounts of saturated long-chain fatty acids leads to obesity, oxidative stress, inflammation, and insulin resistance. The trace element selenium, as a crucial part of antioxidative selenoproteins, can protect against the development of diet-induced insulin resistance in white adipose tissue (WAT) by increasing glutathione peroxidase 3 (GPx3) and insulin receptor (IR) expression. Whether selenite (Se) can attenuate insulin resistance in established lipotoxic and obese conditions is unclear. We confirm that GPX3 mRNA expression in adipose tissue correlates with BMI in humans. Cultivating 3T3-L1 pre-adipocytes in palmitate-containing medium followed by Se treatment attenuates insulin resistance with enhanced GPx3 and IR expression and adipocyte differentiation. However, feeding obese mice a selenium-enriched high-fat diet (SRHFD) only resulted in a modest increase in overall selenoprotein gene expression in WAT in mice with unaltered body weight development, glucose tolerance, and insulin resistance. While Se supplementation improved adipocyte morphology, it did not alter WAT insulin sensitivity. However, mice fed a SRHFD exhibited increased insulin content in the pancreas. Overall, while selenite protects against palmitate-induced insulin resistance in vitro, obesity impedes the effect of selenite on insulin action and adipose tissue metabolism in vivo.

Determination of optimal dietary selenium levels by full expression of selenoproteins in various tissues of broilers from 22 to 42 d of age

The current NRC dietary selenium (Se) requirement (0.15 mg/kg) of broilers from 22 to 42 d of age is primarily based on a previous study reported in 1986, which might not be applicable to modern classes of rapidly growing broilers. The present experiment was conducted to determine the optimal dietary Se level for meeting metabolic and functional Se requirements of broilers fed a corn-soybean meal diet from 22 to 42 d of age. A total of 336 Arbor Acres male broilers at 22 d old were randomly assigned to 1 of 6 treatments with 7 replicates and fed a basal corn-soybean meal diet (control, containing 0.014 mg Se/kg) and the basal diet supplemented with 0.10, 0.20, 0.30, 0.40, or 0.50 mg Se/kg from Na₂SeO₃ for 21 d. The results showed that the Se concentrations in plasma, liver, kidney, pancreas, breast and thigh muscles, the activity of glutathione peroxidase (GPX) in plasma, liver and kidney, the mRNA expression levels of Gpx4, selenoprotein (Seleno) h and Selenou in liver, Selenop and Selenoh in kidney, and the protein expression levels of GPX4 in the liver and kidney of broilers were affected (P < 0.05) by supplemental Se level, and increased quadratically (P < 0.05) with the increase of supplemental Se level. The estimates of optimal dietary Se levels were 0.10 to 0.49 mg/kg based on the fitted broken-line or asymptotic models (P < 0.0001) of the above Se concentration indices, and 0.08 to 0.37 mg/kg based on the fitted broken-line, quadratic or asymptotic models (P < 0.007) of the above selenoprotein expression indices. These results indicate that the optimal dietary Se levels would be 0.49 mg/kg to support the maximum Se concentrations and 0.37 mg/kg to support the full expression of selenoproteins in plasma and various tissues of broilers fed a corn-soybean meal diet from 22 to 42 d of age.

Effects of bacterial organic selenium, selenium yeast and sodium selenite on antioxidant enzymes activity, serum biochemical parameters, and selenium concentration in Lohman brown-classic hens

This study compares the effects of sodium selenite, selenium yeast, and enriched bacterial organic selenium protein on antioxidant enzyme activity, serum biochemical profiles, and egg yolk, serum, and tissue selenium concentration in laying hens. In a 112-d experiment, 144 Lohman Brown Classic hens, 23-wks old were divided into four equal groups, each has six replicates. They were assigned to 4 treatments: 1) a basal diet (Con), 2) Con plus 0.3 mg/kg feed sodium selenite (SS); 3) Con plus 0.3 mg/kg feed Se-yeast (SY): 4) Con plus 0.3 mg/kg feed bacterial enriched organic Se protein (ADS18) from Stenotrophomonas maltophilia bacteria. On d 116, hens were euthanized (slaughtered) to obtain blood (serum), liver organ, and breast tissue to measure antioxidant enzyme activity, biochemical profiles, and selenium concentration. The results show that antioxidant enzyme activity of hens was increased when fed bacterial organic Se (ADS18), resulting in a significant (P < 0.05) increase in serum GSH-Px, SOD, and CAT activity compared to other treatment groups. However, ADS18 and SY supplementation increase (P < 0.05) hepatic TAC, GSH-Px, and CAT activity, unlike the SS and Con group. Similarly, dietary Se treatment reduced total cholesterol and serum triglycerides concentrations significantly (P < 0.05) compared to the Con group. At 16 and 18 weeks, selenium concentration in hen egg yolks supplemented with dietary Se was higher (P < 0.05) than in Con, with similar patterns in breast tissue and serum. Supplementation with bacterial organic Se (ADS18) improved antioxidant enzyme activity, decreased total serum cholesterol and serum lipids, and increased Se deposition in egg yolk, tissue, and serum. Hence, organic Se may be considered a viable source of Se in laying hens.

Determination of optimal dietary selenium levels by full expression of selenoproteins in various tissues of broilers from 1 to 21 d of age

The current NRC dietary selenium (Se) requirement (0.15 mg/kg) of broilers is primarily based on growth performance data reported in 1986. Our study aimed to determine optimal dietary Se levels of broilers fed a practical corn-soybean meal diet for the full expression of selenoproteins in various tissues. A total of 384 one-d-old male broilers (n = 8 replicates/diet) were fed a basal corn-soybean meal diet or the basal diet supplemented with 0.1, 0.2, 0.3, 0.4 or 0.5 mg Se/kg in the form of Na₂SeO₃ for 21 d. Regression analysis was conducted to evaluate the optimal dietary Se levels using broken-line, quadratic or asymptotic models. The activity of glutathione peroxidase (GPX) in the plasma, liver, kidney and pancreas, iodothyronine deiodinase (DIO) in the plasma, liver and pancreas, and thioredoxin reductase (Txnrd) in the liver and pancreas, the mRNA levels of Gpx1, Gpx4, Dio1, selenoprotein (Seleno) h, Selenop and Selenou in the liver, Gpx4, Dio1, Txnrd1, Txnrd2, Selenoh, Selenop and Selenou in the kidney, and Gpx1, Gpx4, Selenoh and Selenou in the pancreas, and the protein levels of GPX4 in the liver and kidney of broilers were influenced (P < 0.05) by added Se levels, and increased quadratically (P < 0.05) with the increase of added Se levels. The estimates of optimal dietary Se levels were 0.07 to 0.36 mg/kg based on the fitted broken-line, quadratic or asymptotic models (P < 0.001) of the aforementioned selenoprotein expression in the plasma, liver and kidney, and 0.09 to 0.46 mg/kg based on the fitted broken-line models (P < 0.001) of the aforementioned selenoprotein expression in the pancreas. The results indicate that the optimal dietary Se levels would be 0.36 mg/kg to support the full expression of selenoproteins in the plasma, liver and kidney, and 0.46 mg/kg to support the full expression of selenoproteins in the pancreas of broilers fed a practical corn-soybean meal diet from 1 to 21 d of age.

Antitumor Effects of Selenium

Functions of selenium are diverse as antioxidant, anti-inflammation, increased immunity, reduced cancer incidence, blocking tumor invasion and metastasis, and further clinical application as treatment with radiation and chemotherapy. These functions of selenium are mostly related to oxidation and reduction mechanisms of selenium metabolites. Hydrogen selenide from selenite, and methylselenol (MSeH) from Se-methylselenocyteine (MSeC) and methylseleninicacid (MSeA) are the most reactive metabolites produced reactive oxygen species (ROS); furthermore, these metabolites may involve in oxidizing sulfhydryl groups, including glutathione. Selenite also reacted with glutathione and produces hydrogen selenide via selenodiglutathione (SeDG), which induces cytotoxicity as cell apoptosis, ROS production, DNA damage, and adenosine-methionine methylation in the cellular nucleus. However, a more pronounced effect was shown in the subsequent treatment of sodium selenite with chemotherapy and radiation therapy. High doses of sodium selenite were effective to increase radiation therapy and chemotherapy, and further to reduce radiation side effects and drug resistance. In our study, advanced cancer patients can tolerate until 5000 μg of sodium selenite in combination with radiation and chemotherapy since the half-life of sodium selenite may be relatively short, and, further, selenium may accumulates more in cancer cells than that of normal cells, which may be toxic to the cancer cells. Further clinical studies of high amount sodium selenite are required to treat advanced cancer patients.

Selenoproteins Protect Against Avian Liver Necrosis by Metabolizing Peroxides and Regulating Receptor Interacting Serine Threonine Kinase 1/Receptor Interacting Serine Threonine Kinase 3/Mixed Lineage Kinase Domain-Like and Mitogen-Activated Protein Kinase Signaling

Liver necroptosis of chicks is induced by selenium (Se)/vitamin E (VE) deficiencies and may be associated with oxidative cell damage. To reveal the underlying mechanisms of liver necrosis, a pool of the corn-soy basal diet (10 μg Se/kg; no VE added), a basal diet plus all-rac-α-tocopheryl acetate (50 mg/kg), Se (sodium selenite at 0.3 mg/kg), or both of these nutrients were provided to day-old broiler chicks (n = 40/group) for 6 weeks. High incidences of liver necrosis (30%) of chicks were induced by -SE-VE, starting at day 16. The Se concentration in liver and glutathione peroxidase (GPX) activity were decreased (P < 0.05) by dietary Se deficiency. Meanwhile, Se deficiency elevated malondialdehyde content and decreased superoxide dismutase (SOD) activity in the liver at weeks 2 and 4. Chicks fed with the two Se-deficient diets showed lower (P < 0.05) hepatic mRNA expression of Gpx1, Gpx3, Gpx4, Selenof, Selenoh, Selenok, Selenom, Selenon, Selenoo, Selenop, Selenot, Selenou, Selenow, and Dio1 than those fed with the two Se-supplemented diets. Dietary Se deficiency had elevated (P < 0.05) the expression of SELENOP, but decreased the downregulation (P < 0.05) of GPX1, GPX4, SELENON, and SELENOW in the liver of chicks at two time points. Meanwhile, dietary Se deficiency upregulated (P < 0.05) the abundance of hepatic proteins of p38 mitogen-activated protein kinase, phospho-p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, phospho-c-Jun N-terminal kinase, extracellular signal-regulated kinase, phospho-mitogen-activated protein kinase, receptor-interacting serine-threonine kinase 1 (RIPK1), receptor-interacting serine-threonine kinase 3 (RIPK3), and mixed lineage kinase domain-like (MLKL) at two time points. In conclusion, our data confirmed the differential regulation of dietary Se deficiency on several key selenoproteins, the RIPK1/RIPK3/MLKL, and mitogen-activated protein kinase signaling pathway in chicks and identified new molecular clues for understanding the etiology of nutritional liver necrosis.

Differential protein expression due to Se deficiency and Se toxicity in rat liver

There is a U-shaped dose-response between selenium (Se) status and health outcomes, but underlying metabolic processes are unclear. This study aims to identify candidate proteins in liver regulated by dietary Se, ranging from deficiency to toxic. Male rats (n=4) were fed graded Se concentrations as selenite for 28 days. Bulk Se analysis was performed by ICP-MS on both soluble and insoluble fractions. Soluble fraction samples were chromatographically separated for identification of selenocompounds by SEC-ICP-MS and protein quantification by LC-MS/MS. Bioinformatics analysis compared low-Se (0 and 0.08 µg Se g^-1) and high-Se (0.8, 2 and 5 µg Se g^-1) with adequate-Se (0.24 µg Se g^-1) diets. Major breakpoints for Se were seen at 0.8 and 2 µg Se g^-1 in the insoluble and soluble fractions, respectively. Glutathione peroxidase 1 protein abundance reached a plateau at ≥0.08 µg Se g^-1diet; Se bound to selenium binding protein 2 was observed with 2 and 5 µg Se g^-1 Se. The extreme diets presented the highest number of differentially expressed (P value <0.05, FC ≥1.2) proteins in comparison to the adequate-Se diet (0 µg Se g^-1: 45 proteins; 5 µg Se g^-1: 59 proteins); 13 proteins were commonly affected in 0 and 5 µg Se g^-1 treatments. Network analysis revealed that the metabolism of glutathione, xenobiotics and amino acids were enriched in both 0 and 5 µg Se g^-1 diets, indicating a U-shape effect of Se. This similarity is likely due to down-stream effects of lack of essential selenoproteins in Se deficiency and due to toxic effects of Se that exceeds the capacity to cope with excess Se.

Metabolism of Tracer 75Se Selenium From Inorganic and Organic Selenocompounds Into Selenoproteins in Rats, and the Missing 75Se Metabolites

We now know much about selenium (Se) incorporation into selenoproteins, and there is considerable interest in the optimum form of Se for supplementation and prevention of cancer. To study the flux of ⁷⁵Se into selenoprotein, rats were fed 0 to 5 μg Se/g diet as selenite for 50-80 d and injected iv with 50 μCi of ⁷⁵Se-labeled selenite, selenate, selenodiglutathione, selenomethionine, or selenobetaine at tracer levels (~0.5 μg Se). The rats were killed at various times and ⁷⁵Se incorporation into selenoproteins was assessed by SDS/PAGE. These studies found that there is very rapid Se metabolism from this diverse set of selenocompounds to the common intermediate used for synthesis and incorporation of ⁷⁵Se into the major selenoproteins in a variety of tissues. No selenocompound was uniquely or preferentially metabolized to provide Se for selenoprotein incorporation. Examination of the SDS/PAGE selenoprotein profiles, however, reveals that synthesis of selenoproteins is only part of the full Se metabolism story. The ⁷⁵Se missing from the selenoprotein profiles, especially at early timepoints, is likely to be both low-MW and high-MW selenosugars and related precursors, as we recently found in livers of turkeys fed Se-adequate and high-Se diets. Differential metabolism of different selenocompounds into different selenosugar species may occur; these species may be involved in prevention of cancer or other diseases linked to Se status and may be associated with Se toxicity. Additional studies using HPLC-mass spectroscopy will likely be needed to fully flesh out the complete metabolism of selenium.

Identification and determination of selenocysteine, selenosugar, and other selenometabolites in turkey liver

Liver and other tissues accumulate selenium (Se) when animals are supplemented with high dietary Se as inorganic Se. To further study selenometabolites in Se-deficient, Se-adequate, and high-Se liver, turkey poults were fed 0, 0.4, and 5 μg Se g-1 diet as Na2SeO3 (Se(iv)) in a Se-deficient (0.005 μg Se g-1) diet for 28 days, and the effects of Se status determined using HPLC-ICP-MS and HPLC-ESI-MS/MS. No selenomethionine (SeMet) was detected in liver in turkeys fed either this true Se-deficient diet or supplemented with inorganic Se, showing that turkeys cannot synthesize SeMet de novo from inorganic Se. Selenocysteine (Sec) was also below the level of detection in Se-deficient liver, as expected in animals with negligible selenoprotein levels. Sec content in high Se liver only doubled as compared to Se-adequate liver, indicating that the 6-fold increase in liver Se was not due to increases in selenoproteins. What increased dramatically in high Se liver were low molecular weight (MW) selenometabolites: glutathione-, cysteine- and methyl-conjugates of the selenosugar, seleno-N-acetyl galactosamine (SeGalNac). Substantial Se in Se-adequate liver was present as selenosugars decorating general proteins via mixed-disulfide bonds. In high-Se liver, these "selenosugar-decorated" proteins comprised ∼50% of the Se in the water-soluble fraction, in addition to low MW selenometabolites. In summary, more Se is present as the selenosugar moiety in Se-adequate liver, mostly decorating general proteins, than is present as Sec in selenoproteins. With high Se supplementation, increased selenosugar formation occurs, further increasing selenosugar-decorated proteins, but also increasing selenosugar linked to low MW thiols.

Selenium Status Affects Hypertrophic Growth of Skeletal Muscle in Growing Zebrafish by Mediating Protein Turnover

BACKGROUND

Selenium (Se) status is closely related to skeletal muscle physiological status. However, its influence on skeletal muscle growth has not been well studied.

OBJECTIVES

This study aimed to analyze the impacts of overall Se status (deficient, adequate, and high) on skeletal muscle growth using a growing zebrafish model.

METHODS

Zebrafish (1.5-mo-old) were fed graded levels of Se (deficient: 0.10 mg Se/kg; marginally deficient: 0.22 mg Se/kg; adequate: 0.34 mg Se/kg; high: 0.44, 0.57, and 0.69 mg Se/kg) as Se-enriched yeast for 30 d. Zebrafish growth, and Se accumulation, selenoenzyme activity, selenotranscriptome profiles, and oxidative status in the whole body, and selenotranscriptome profiles, histological characteristics, biochemicals, and gene and protein expression profiles related to muscle growth in the skeletal muscle were analyzed by model fitting and/or 1-factor ANOVA.

RESULTS

Se status biomarkers within the whole body and skeletal muscle indicated that 0.34 mg Se/kg was adequate for growing zebrafish. For biomarkers related to skeletal muscle growth, compared with 0.34 mg Se/kg, 0.10 mg Se/kg decreased the white muscle cross-sectional area (WMCSA) and the mean diameter of white muscle fibers (MDWMF) by 14.4%-15.1%, inhibited protein kinase B-target of rapamycin complex 1 signaling by 63.7%-68.5%, and stimulated the autophagy-lysosome pathway by 1.07 times and the ubiquitin-proteasome pathway (UPP) by 96.0% (P < 0.05), whereas 0.22 mg Se/kg only decreased the WMCSA by 7.8% (P < 0.05); furthermore, 0.44 mg Se/kg had no clear effects on skeletal muscle biomarkers, whereas 0.57-0.69 mg Se/kg decreased the WMCSA and MDWMF by 6.3%-25.9% and 5.1%-21.3%, respectively, and stimulated the UPP by 2.23 times (P < 0.05).

CONCLUSIONS

A level of 0.34 mg Se/kg is adequate for the growth of zebrafish skeletal muscle, whereas ≤0.10 and ≥0.57 mg Se/kg are too low or too high, respectively, for maintaining efficient protein accretion and normal hypertrophic growth.

Effect of Selenium Sources on Laying Performance, Egg Quality Characteristics, Intestinal Morphology, Microbial Population and Digesta Volatile Fatty Acids in Laying Hens

The use of toxic and less bioavailable inorganic selenium can now be supplemented with an alternative organic source from bacterial species in nutrition for human and animal benefit. This study investigated the effects of selenium sources on laying performance, egg quality characteristics, intestinal morphology, caecum microbial population, and digesta volatile fatty acids in laying hens. One hundred and forty-four Lohman Brown Classic laying hens, at 23 weeks of age, were divided into four experimental groups (36 hens in each), differing in form of Se supplementation: no Se supplementation (Con), 0.3 mg/kg of inorganic Se in the form of sodium selenite (Na2SeO3), 0.3 mg/kg of organic Se from selenium yeast (Se-Yeast), and 0.3 mg/kg of organic Se from Stenotrophomonas maltophilia (bacterial organic Se, ADS18). The results showed that different dietary Se sources significantly affected laying rate, average egg weight, daily egg mass, feed conversion ratio (FCR), and live bodyweight (LBW) (p < 0.05). However, average daily feed intake and shell-less and broken eggs were unaffected (p > 0.05) among the treatment groups. The findings revealed that selenium sources had no (p > 0.05) effect on egg quality (external and internal) parameters. However, eggshell breaking strength and Haugh unit were significantly (p < 0.05) improved with organic (ADS18 or Se-yeast) Se-fed hens compared to the control group. In addition, egg yolk and breast tissue Se concentrations were higher (p < 0.05) in the dietary Se supplemented group compared to the control. Intestinal histomorphology revealed that hens fed ADS18 or Se-Yeast groups had significantly (p < 0.05) higher villi height in the duodenum and jejunum compared to those fed Na2SeO3 or a basal diet. However, when compared to organic Se fed (ADS18 or Se-Yeast) hens, the ileum villus height was higher (p < 0.05) in the basal diet group; with the lowest in the SS among the treatment groups. A significant increase (p < 0.05) of Lactobacilli spp. and Bifidobacteria spp., and a decrease of Escherichia coli and Salmonella spp. population were observed in the organic (ADS18 or Se-yeast) compared to inorganic supplemented and control hens. The individual digesta volatile fatty acid (VFA) was significantly different, but with no total VFA differences. Thus, bacterial selenoprotein or Se-yeast improved the performance index, egg quality characteristics, egg yolk and tissue Se contents, and intestinal villus height in laying hens. Moreover, caecum beneficial microbes increased with a decrease in the harmful microbe population and affected individual cecal volatile fatty acids without affecting the total VFA of the laying hens digesta.

Nanoselenium and Selenium Yeast Have Minimal Differences on Egg Production and Se Deposition in Laying Hens

The objective of this study was to compare the effects of nanoselenium (NS) and selenium yeast (SY) on the performance, egg selenium (Se) concentration, and anti-oxidative capacity of hens. A total of 216 Brown Hy-line hens (29-week old) were randomly allocated into three treatments (6 replicate/treatment, 12 hens/replicate). The pre-trial period lasted 7 days, and the experimental period lasted 35 days. Dietary treatments included corn-soybean meal basal diet (containing 0.16 μg Se/g, as control group), and basal diet supplemented with 0.3 mg Se/kg diet (Se was from NS or SY), called as SY group or NS group, respectively. At the end of the experiment, one hen per replicate from each treatment was slaughtered. Liver, spleen, and kidney tissues were sampled for the determination of Se concentrations. The results showed that NS or SY supplement significantly improved feed conversion ratio (P < 0.05), soft broken egg rate (P < 0.05), and the serum T-AOC value (P < 0.05) when compared with control group. Remarkably, the deposition of Se increased significantly (P < 0.05) and equivalently in egg, liver, and kidney of hens supplemented with both NS and SY. Interestingly, SY supplement also enhanced the serum CAT and SOD activities (P < 0.05), NS but not SY significantly reduced serum MDA (P < 0.05), whereas RT-PCR results did not show significant differences in the mRNA levels of antioxidant genes among three groups (P > 0.05). Taken together, dietary supplemented with SY or NS improved the Se deposition in eggs, liver and kidney of laying hens, increased antioxidant activity, and NS supplement had greater Se deposition in the kidney tissue than SY supplement. SY or NS supplement could be considered to be applied for Se-enriched egg production.

Gene Set Enrichment Analysis of Selenium-Deficient and High-Selenium Rat Liver Transcript Expression and Comparison With Turkey Liver Expression

BACKGROUND

Better biomarkers of selenium (Se) status and a better understanding of toxic Se biochemistry are needed to set safe dietary upper limits. In previous studies, differential expression (DE) of individual liver transcripts in rats and turkeys failed to identify a single transcript that was consistently and significantly (q < 0.05) altered by high Se.

OBJECTIVES

To evaluate the effect of Se status on rat liver transcript expression data at the level of gene sets, and to compare transcript expression in rats with that in turkeys to identify common regulated transcripts.

METHODS

Gene set enrichment analysis (GSEA) was conducted on liver from weanling rats fed an Se-deficient basal diet (0.005 μg Se/g) supplemented with 0, 0.24 (Se-adequate), 2, or 5 μg Se/g diet as selenite for 28 d. In addition, transcript expression was compared with liver expression in turkeys fed 0, 0.4, 2, or 5 μg Se/g diet as selenite.

RESULTS

Se deficiency significantly downregulated the rat selenoprotein gene set but also upregulated gene sets for a variety of pathways, processes, and disease states. GSEA of 2 compared with 0.24 μg Se/g found no significantly up- or downregulated gene sets, showing that 2 μg Se/g is not particularly toxic to the rat. GSEA analysis of 5 compared with 0.24 μg Se/g transcripts, however, found 27 significantly upregulated gene sets for a wide variety of conditions. Cross-species GSEA comparison of transcript expression, however, identified no common gene sets significantly and consistently regulated by high Se in rats and turkeys. In addition, comparison of individual marginally significant (unadjusted P < 0.05) DE transcripts between rats and turkeys also failed to find common transcripts.

CONCLUSIONS

The dramatic increase in significant liver transcript DE and GSEA gene sets in rats fed 5 compared with 2 μg Se/g clearly appears to be a biomarker for Se toxicity, albeit not Se-specific. These analyses, however, failed to identify specific transcripts or pathways, biological states, or processes that were directly linked with high Se status, strongly indicating that adaptation to high Se lies outside transcriptional regulation.

Dietary Selenium Requirement for the Prevention of Glucose Intolerance and Insulin Resistance in Middle-Aged Mice

BACKGROUND

Although dietary selenium (Se) deficiency or excess induces type 2 diabetes-like symptoms in mice, suboptimal body Se status usually causes no symptoms but may promote age-related decline in overall health.

OBJECTIVES

We sought to determine the dietary Se requirement for protection against type 2 diabetes-like symptoms in mice.

METHODS

Thirty mature (aged 4 mo) male C57BL/6J mice were fed a Se-deficient torula yeast AIN-93M diet supplemented with Na2SeO4 in graded concentrations totaling 0.01 (basal), 0.04, 0.07, 0.10, and 0.13 (control) mg Se/kg for 4 mo (n = 6) until they were middle-aged (8 mo). Droplets of whole blood were used to determine glucose tolerance and insulin sensitivity in the mice from ages 5 to 8 mo. Postmortem serum, liver, and skeletal muscle were collected to assay for selenoprotein expression and markers of glucose metabolism. Data were analyzed by 1-way ANCOVA with or without random effects for time-repeated measurements using live mice or postmortem samples, respectively.

RESULTS

Compared with control, the consumption of basal diet increased (P < 0.05) fasting serum insulin (95% CI: 52%, 182%) and leptin (95% CI: 103%, 118%) concentrations in middle-aged mice. Dietary Se insufficiency decreased (P < 0.05) 1) glucose tolerance (13-79%) and insulin sensitivity (15-65%) at ≤0.10 mg Se/kg; 2) baseline thymoma viral proto-oncogene phosphorylation on S473 (27-54%) and T308 (22-46%) at ≤0.10 and ≤0.07 mg Se/kg, respectively, in the muscle but not the liver; and 3) serum glutathione peroxidase 3 (51-83%), liver and muscle glutathione peroxidase 1 (32-84%), serum and liver selenoprotein P (28-42%), and liver and muscle selenoprotein H (39-48%) and selenoprotein W (16-73%) protein concentrations at ≤0.04, ≤0.10, ≤0.07, and ≤0.10 mg Se/kg, respectively.

CONCLUSIONS

Mice fed diets containing ≤0.10 mg Se/kg display impaired glucose tolerance and insulin sensitivity, suggesting increased susceptibility to type 2 diabetes by suboptimal Se status at levels ≤23% of nutritional needs.

Short Communication: Effects of Dietary Selenium Supplementation on Selenium Deposition and Antioxidant Status in Postpartum Mice

This study aimed to investigate the effects of dietary selenium during pregnancy on the selenium deposition and antioxidant enzymes in postpartum mouse serum, liver, and mammary gland. Eighty BALB/c pregnant mice were randomly divided into four groups: CG (Se-deficient basal diet, n = 20), LG (0.05 mg/kg Se-supplemented diet, n = 20), MG (0.1 mg/kg Se-supplemented diet, n = 20), and HG (0.2 mg/kg Se-supplemented diet, n = 20). Four days after parturition, all mice were euthanized. The selenium deposition and antioxidants enzymes in serum, liver, and mammary gland were detected. Results show that with increasing selenium supplementation, the selenium deposition and activation of T-AOC, T-SOD, and GSH-Px increased, meanwhile the concentration of MDA decreased in serum, liver, and mammary gland. Therefore, this study suggested selenium was mainly deposited in the liver, and dietary selenium during pregnancy might improve the antioxidant status in postpartum animals.

Dietary Marginal and Excess Selenium Increased Triglycerides Deposition, Induced Endoplasmic Reticulum Stress and Differentially Influenced Selenoproteins Expression in the Anterior and Middle Intestines of Yellow Catfish Pelteobagrus fulvidraco

Selenium (Se) is an essential micro-mineral and plays important roles in antioxidant responses, and also influences lipid metabolism and selenoprotein expression in vertebrates, but the effects and mechanism remain unknown. The study was undertaken to decipher the insights into dietary Se influencing lipid metabolism and selenoprotein expression in the anterior and middle intestine (AI and MI) of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (weight: 8.27 ± 0.03 g) were fed a 0.03- (M-Se), 0.25- (A-Se), or 6.39- (E-Se) mg Se/kg diet for 12 wk. AI and MI were analyzed for triglycerides (TGs) and Se concentrations, histochemistry and immunofluorescence, enzyme activities, and gene and protein levelsassociated with antioxidant responses, lipid metabolism, endoplasmic reticulum (ER) stress, and selenoproteome. Compared to the A-Se group, M-Se and E-Se diets significantly decreased weight gain (WG) and increased TGs concentration in the AI and MI. In the AI, compared with A-Se group, M-Se and E-Se diets significantly increased activities of fatty acid synthase, expression of lipogenic genes, and suppressed lipolysis. In the MI, compared to the A-Se group, M-Se and E-Se diets significantly increased activities of lipogenesis and expression of lipogenic genes. Compared with A-Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the AI and MI, and M-Se diet did not significantly reduce GPX activities in the AI and MI. Compared with the A- Se group, E-Se diet significantly increased glutathione peroxidase (GPX) activities in the plasma and liver, and M-Se diet significantly reduced GPX activities in the plasma and liver. Compared with the A-Se group, M-Se and E-Se groups also increased glucose-regulated protein 78 (GRP78, ER stress marker) protein expression of the intestine. Dietary Se supplementation also differentially influenced the expression of the 28 selenoproteins in the AI and MI, many of which possessed antioxidant characteristics. Compared with the A-Se group, the M-Se group significantly decreased mRNA levels of txnrd2 and txnrd3, but made no difference on mRNA levels of these seven GPX proteins in the MI. Moreover, we characterized sterol regulatory element binding protein 1c (SREBP1c) binding sites of three ER-resident proteins (selenom, selenon, and selenos) promoters, and found that Se positively controlled selenom, selenon, and selenos expression via SREBP1c binding to the selenom, selenon, and selenos promoter. Thus, dietary marginal and excess Se increased TGs deposition of yellow catfish P. fulvidraco, which might be mediated by ER-resident selenoproteins expression and ER stress.

Analysis of Bioavailability and Induction of Glutathione Peroxidase by Dietary Nanoelemental, Organic and Inorganic Selenium

Dietary organic selenium (Se) is commonly utilized to increase formation of selenoproteins, including the major antioxidant protein, glutathione peroxidase (GPx). Inorganic Se salts, such as sodium selenite, are also incorporated into selenoproteins, and there is evidence that nanoelemental Se added to the diet may also be effective. We conducted two trials, the first investigated inorganic Se (selenite), organic Se (L-selenomethionine) and nanoelemental Se, in conventional mice. Their bioavailability and effectiveness to increase GPx activity were examined. The second trial focused on determining the mechanism by which dietary Se is incorporated into tissue, utilising both conventional and germ-free (GF) mice. Mice were fed a diet with minimal Se, 0.018 parts per million (ppm), and diets with Se supplementation, to achieve 0.07, 0.15, 0.3 and 1.7 ppm Se, for 5 weeks (first trial). Mass spectrometry, Western blotting and enzymatic assays were used to investigate bioavailability, protein levels and GPx activity in fresh frozen tissue (liver, ileum, plasma, muscle and feces) from the Se fed animals. Inorganic, organic and nanoelemental Se were all effectively incorporated into tissues. The high Se diet (1.7 ppm) resulted in the highest Se levels in all tissues and plasma, independent of the Se source. Interestingly, despite being ~11 to ~25 times less concentrated than the high Se, the lower Se diets (0.07; 0.15) resulted in comparably high Se levels in liver, ileum and plasma for all Se sources. GPx protein levels and enzyme activity were significantly increased by each diet, relative to control. We hypothesised that bacteria may be a vector for the conversion of nanoelemental Se, perhaps in exchange for S in sulphate metabolising bacteria. We therefore investigated Se incorporation from low sulphate diets and in GF mice. All forms of selenium were bioavailable and similarly significantly increased the antioxidant capability of GPx in the intestine and liver of GF mice and mice with sulphate free diets. Se from nanoelemental Se resulted in similar tissue levels to inorganic and organic sources in germ free mice. Thus, endogenous mechanisms, not dependent on bacteria, reduce nanoelemental Se to the metabolite selenide that is then converted to selenophosphate, synthesised to selenocysteine, and incorporated into selenoproteins. In particular, the similar efficacy of nanoelemental Se in comparison to organic Se in both trials is important in the view of the currently limited cheap sources of Se.

Se Status Prediction by Food Intake as Compared to Circulating Biomarkers in a West Algerian Population

Algeria is the largest country in Africa, located close to the Mediterranean coastal area, where nutrients consumption varies widely. Local data on selenium composition of foods are not available. We postulated a close correlation between selenium status predictions from food consumption analysis with a quantitative analysis of circulating biomarkers of selenium status. Population characteristics were recorded from 158 participants and dietary selenium intake was calculated by 24-h recall. The average total plasma selenium was 92.4 ± 18.5 µg/L and the mean of selenium intake was 62.7 µg/day. The selenoprotein P concentration was 5.5 ± 2.0 mg/L and glutathione peroxidase 3 activity was 247.3 ± 41.5 U/L. A direct comparison of the dietary-derived selenium status to the circulating selenium biomarkers showed no significant interrelation. Based on absolute intakes of meat, potato and eggs, a model was deduced that outperforms the intake composition-based prediction from all food components significantly (DeLong’s test, p = 0.029), yielding an area under the curve of 82%. Selenium status prediction from food intake remains a challenge. Imprecision of survey method or information on nutrient composition makes extrapolating selenium intake from food data providing incorrect insights into the nutritional status of a given population, and laboratory analyses are needed for reliable information.

The hepatic transcriptome of the turkey poult (Meleagris gallopavo) is minimally altered by high inorganic dietary selenium

There is interest in supplementing animals and humans with selenium (Se) above Se-adequate levels, but the only good biomarker for toxicity is tissue Se. We targeted liver because turkeys fed 5 μg Se/g have hepatic Se concentrations 6-fold above Se-adequate (0.4 μg Se/g) levels without effects on growth or health. Our objectives were (i) to identify transcript biomarkers for high Se status, which in turn would (ii) suggest proteins and pathways used by animals to adapt to high Se. Turkey poults were fed 0, 0.025, 0.4, 0.75 and 1.0 μg Se/g diet in experiment 1, and fed 0.4, 2.0 and 5.0 μg Se/g in experiment 2, as selenite, and the full liver transcriptome determined by RNA-Seq. The major effect of Se-deficiency was to down-regulate expression of a subset of selenoprotein transcripts, with little significant effect on general transcript expression. In response to high Se intake (2 and 5 μg Se/g) relative to Se-adequate turkeys, there were only a limited number of significant differentially expressed transcripts, all with only relatively small fold-changes. No transcript showed a consistent pattern of altered expression in response to high Se intakes across the 1, 2 and 5 μg Se/g treatments, and there were no associated metabolic pathways and biological functions that were significant and consistently found with high Se supplementation. Gene set enrichment analysis also found no gene sets that were consistently altered by high-Se and supernutritional-Se. A comparison of differentially expressed transcript sets with high Se transcript sets identified in mice provided high Se (~3 μg Se/g) also failed to identify common differentially expressed transcript sets between these two species. Collectively, this study indicates that turkeys do not alter gene expression in the liver as a homeostatic mechanism to adapt to high Se.

Stimulatory effects of nano-selenium and conjugated linoleic acid ‎ on antioxidant activity, trace minerals, and gene expression response of growing male Moghani lambs

Sheep keepers need suitable strategies to improve animal immunity and the quality of their products. This study was aimed to evaluate the effect of nano-selenium (nano-Se) and conjugated linoleic acid (CLA) on an antioxidant statue, trace minerals, and mRNA expression of glutathione peroxidase 1 (GPX1) and selenoprotein W1 (SEPW1) genes in the liver and peroxisome proliferator-activated receptor-gamma (PPARγ) and stearoyl COA desaturase 1 (SCD1) genes in fat- tail of male Moghani lambs. Thirty male Moghani lambs, three months old and average weight 30.00 ± 0.25 kg, were assigned to a completely randomized design in a 2×3 factorial arrangement with dietary supplementation of nano-Se (0, 1.00 and 2.00 mg kg^-1 dry matter) and CLA (0.00 and 15.00 g kg^-1 dry matter). The lambs were slaughtered at the end of the experiment, on day 90 of the experiment. Results showed that dietary inclusion of nano-Se significantly improved antioxidant enzymes glutathione peroxidase and superoxide dismutase in blood, however, did not show any differences in trace mineral treatments. The analysis of qPCR showed that nano-Se inclusion at the highest level (2.00 g kg^-1 dry matter) enhanced gene expression of GPX1 (0.64 vs 0.34) and SEPW1 (0.72 vs 0.35) in the liver. Dietary inclusion of CLA increased the expression of PPARγ (0.63 vs 0.38) and decreased SCD1 (0.63 vs 0.33) genes in fat- tail. It could be concluded that selenium inclusion in the growing lamb's diet could improve antioxidant status, however, no synergistic interaction was observed along with CLA on the mentioned parameters.

High- and low- selenium diets affect endocrine energy balance during early programming

High- and low- Se diets received by dams during gestation and lactation are related to insulin resistance in their pups. High-Se diet leads to an increase in serum insulin levels, which does not function properly, and an anabolic process. Low-Se diet is related to very low insulin values and an extreme catabolic energy imbalance. Selenoproteins have been implicated directly in the general endocrine regulation of appetite and energy homeostasis. To obtain information concerning how Se intake by dams is involved in regulating endocrine energy balance in progeny, three experimental groups of dam rats were used: control (Se: 0.1 ppm), Se-supplemented (Se: 0.5 ppm) and Se-deficient (Se: 0.01 ppm). At the end of lactation (21d old), the pups' appetite profile, Se levels, peptides from gastrointestinal tract (including pancreas), leptin, thyroid hormones, skeletal growth markers and cytokines in serum were measured. Low-Se diet leads to severe growth retardation, underdeveloped glands, a non-functional pancreas, non-operative high serum leptin levels and low GIT-anorexigenic signals. High-Se diet leads to non-operative high insulin secretion, obesity, inflammation and low leptin levels. These results point to Se as an important marker and a possible dietary supplementation treatment for gestating and lactating mothers in order to avoid metabolic disorders such as gestational diabetes or intrauterine growth retardation which could affect their progeny's future health in adulthood.

Impact of Glutathione Peroxidase-1 (Gpx1) Genotype on Selenoenzyme and Transcript Expression When Repleting Selenium-Deficient Mice

Glutathione peroxidase (Gpx1) is the major selenoprotein in most tissues in animals. Knockout (KO) of Gpx1 decreases Gpx1 activity to near zero and substantially reduces liver selenium (Se) levels, but has no overt effects in otherwise healthy mice. To investigate the impact of deletion of Gpx1 on Se metabolism, Se flux, and apparent Se requirements, KO, Gpx1 heterozygous (Het), and Gpx1 wild-type (WT) mice were fed Se-deficient diet for 17 weeks, then repleted with graded levels of Se (0-0.3 μg Se/g as Na₂SeO₃) for 7 days, and selenoprotein activities and transcripts were determined in blood, liver, and kidney. Se deficiency decreased the activities of plasma Gpx3, liver Gpx1, liver Txnrd, and liver Gpx4 to 3, 0.3, 11, and 50% of WT Se-adequate levels, respectively, but the Gpx1 genotype had no effect on growth or changes in activity or expression of selenoproteins other than Gpx1. Se repletion increased selenoprotein transcripts to Se-adequate levels after 7 days; Se response curves and apparent Se requirements for selenoprotein transcripts were similar to those observed in studies starting with Se-adequate mice. With short-term Se repletion, selenoenzyme activities resulted in three Se response curve patterns: (1) liver and kidney Gpx1, Gpx4, and Txnrd activities were sigmoidal or hyperbolic with breakpoints (0.08-0.19 μg Se/g) that were double those observed in studies starting with Se-adequate mice; (2) red blood cell Gpx1 activity was not significantly changed; and (3) plasma Gpx3 activity only increased substantially with 0.3 μg Se/g. Plasma Gpx3 is secreted from kidney. In this short-term study, kidney Gpx3 mRNA reached plateau levels at 0.1 μg Se/g, and other kidney selenoenzyme activities reached plateau levels at ≤ 0.2 μg Se/g, so sufficient Se should have been present in kidney. Thus, the delayed increase in plasma Gpx3 activity suggests that newly synthesized and secreted kidney Gpx3 is preferentially retained in kidney or rapidly cleared by binding to basement membranes in kidney or in other tissues. This repletion study shows that loss of capacity to incorporate Se into Gpx1 in Gpx1 KO mice does not dramatically alter expression of other Se biomarkers, nor the short-term flux of Se from intestine to liver to kidney.

Regulation and function of avian selenogenome

BACKGROUND

Selenium (Se) is an essential micronutrient required by avian species. Dietary Se/vitamin E deficiency induces three classical diseases in chicks: exudative diathesis, nutritional pancreatic atrophy, and nutritional muscular dystrophy.

SCOPE OF REVIEW

This review is to summarize and analyze the evolution, regulation, and function of avian selenogenome and selenoproteome and their relationship with the three classical Se/vitamin E deficiency diseases.

MAJOR CONCLUSIONS

There are 24 selenoproteins confirmed in chicks, with two avian-specific members (SELENOU and SELENOP2) and two missing mammalian members (GPX6 and SELENOV). There are two forms of SELENOP containing 1 or 13 selenocysteine residues. In addition, a Gallus gallus gene was conjectured to be the counterpart of the human SEPHS2. Expression of selenoprotein genes in the liver, pancreas, and muscle of chicks seemed to be highly responsive to dietary Se changes. Pathogeneses of the Se/vitamin E deficient diseases in the chicks were likely produced by missing functions of selected selenoproteins in regulating cellular and tissue redox balance and inhibiting oxidative/reductive stress-induced cell death.

GENERAL SIGNIFICANCE

Gene knockout models, similar to those of rodents, will help characterize the precise functions of avian selenoproteins and their comparisons with those of mammalian species.

Selenium requirements based on muscle and kidney selenoprotein enzyme activity and transcript expression in the turkey poult (Meleagris gallopavo)

The current NRC selenium (Se) requirement for turkeys is 0.2 μg Se/g diet. We previously fed turkey poults a Se-deficient diet (0.005 μg Se/g) supplemented with 10 graded levels of Se (0, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1.0 μg Se/g as Na2SeO3, 5/treatment) for 4 wk, and found that the minimum dietary Se requirement was 0.3 μg Se/g based on selenoprotein enzyme activity in blood, liver, gizzard and pancreas. Because the turkey is primarily a production animal, we expanded this analysis to kidney, heart, breast and thigh. Se concentrations in Se-deficient poults were 5.0, 9.8, 33, and 15% of levels in poults fed 0.4 μg Se/g in liver, kidney, thigh and breast, respectively. Increasing Se supplementation resulted in hyperbolic response curves for all tissues; breakpoint analysis indicated minimum Se requirements of 0.34-0.36 μg Se/g based on tissue Se levels in liver, kidney and thigh. Similarly, GPX1 activity in muscle tissues and kidney responded hyperbolically to increasing dietary Se, reaching well-defined plateaus with breakpoints at 0.30-0.36 μg Se/g. Minimum Se requirements based on GPX4 activity were 0.30-0.32 μg Se/g for breast and thigh. Selenoprotein transcript expression decreased significantly in Se deficiency for only 2, 3, 5, and 6 mRNA in breast, thigh, heart, and kidney, respectively, out of 24 known avian selenoproteins. Se response curves for regulated selenoprotein transcripts were hyperbolic, and reached well-defined plateaus with breakpoints in a narrow range of 0.08-0.19 μg Se/g. No selenoprotein transcript was altered by supernutritional Se. In summary, these results clearly indicate that the NRC dietary Se requirement should be raised to 0.4 μg Se/g, at least for poults, to meet the nutritional needs of the young turkey. The Se response curve plateaus further show that limits for turkey supplementation with selenite could safely be raised to 0.5 μg Se/g diet.

Analyses of Selenotranscriptomes and Selenium Concentrations in Response to Dietary Selenium Deficiency and Age Reveal Common and Distinct Patterns by Tissue and Sex in Telomere-Dysfunctional Mice

Background: The hierarchies of tissue selenium distribution and selenotranscriptomes are thought to critically affect healthspan and longevity.Objective: We determined selenium status and selenotranscriptomes in response to long-term dietary selenium deficiency and age in tissues of male and female mice.Methods: Weanling telomerase RNA component knockout C57BL/6 mice were fed a selenium-deficient (0.03 mg Se/kg) Torula yeast-based AIN-93G diet or a diet supplemented with sodium selenate (0.15 mg Se/kg) until age 18 or 24 mo. Plasma, hearts, kidneys, livers, and testes were collected to assay for selenotranscriptomes, selected selenoproteins, and tissue selenium concentrations. Data were analyzed with the use of 2-factor ANOVA (diet × age) in both sexes.Results: Dietary selenium deficiency decreased (P ≤ 0.05) selenium concentrations (65-72%) and glutathione peroxidase (GPX) 3 (82-94%) and selenoprotein P (SELENOP) (17-41%) levels in the plasma of both sexes of mice and mRNA levels (9-68%) of 4, 4, and 12 selenoproteins in the heart, kidney, and liver of males, respectively, and 5, 16, and 14 selenoproteins, respectively, in females. Age increased selenium concentrations and SELENOP levels (27% and 30%, respectively; P ≤ 0.05) in the plasma of males only but decreased (12-46%; P < 0.05) mRNA levels of 1, 5, and 13 selenoproteins in the heart, kidney, and liver of males, respectively, and 6, 5, and 0 selenoproteins, respectively, in females. Among these mRNAs, selenoprotein H (Selenoh), selenoprotein M (Selenom), selenoprotein W (Selenow), methionine-R-sulfoxide reductase 1 (MsrB1), Gpx1, Gpx3, thioredoxin reductase 1 (Txnrd1), Txnrd2, selenoprotein S (Selenos), selenoprotein F (Selenof), and selenoprotein O (Selenoo) responded in parallel to dietary selenium deficiency and age in ≥1 tissue or sex, or both. Dietary selenium deficiency upregulated (40-160%; P ≤ 0.05) iodothyronine deiodinase 2 (Dio2) and selenoprotein N (Selenon) in the kidneys of males. Age upregulated (11-44%; P < 0.05) Selenon in the kidneys of males, selenoprotein K (Selenok) and selenoprotein I (Selenoi) in the kidneys of females, and Selenof and Selenok in the testes.Conclusions: These results illustrate tissue-specific sexual dimorphisms of selenium status and selenotranscriptomes because of dietary selenium deficiency and age.

The effect of dietary bacterial organic selenium on growth performance, antioxidant capacity, and Selenoproteins gene expression in broiler chickens

Background

Selenium (Se) is an essential trace mineral in broilers, which has several important roles in biological processes. Organic forms of Se are more efficient than inorganic forms and can be produced biologically via Se microbial reduction. Hence, the possibility of using Se-enriched bacteria as feed supplement may provide an interesting source of organic Se, and benefit broiler antioxidant system and other biological processes. The objective of this study was to examine the impacts of inorganic Se and different bacterial organic Se sources on the performance, serum and tissues Se status, antioxidant capacity, and liver mRNA expression of selenoproteins in broilers.

Results

Results indicated that different Se sources did not significantly (P ≤ 0.05) affect broiler growth performance. However, bacterial organic Se of T5 (basal diet +0.3 mg /kg feed ADS18 Se), T4 (basal diet +0.3 mg /kg feed ADS2 Se), and T3 (basal diet +0.3 mg /kg feed ADS1 Se) exhibited significantly (P ≤ 0.05) highest Se concentration in serum, liver, and kidney respectively. Dietary inorganic Se and bacterial organic Se were observed to significantly affect broiler serum ALT, AST, LDH activities and serum creatinine level. ADS18 supplemented Se of (Stenotrophomonas maltophilia) bacterial strain showed the highest GSH-Px activity with the lowest MDA content in serum, and the highest GSH-Px and catalase activity in the kidney, while bacterial Se of ADS2 (Klebsiella pneumoniae) resulted in a higher level of GSH-Px1 and catalase in liver. Moreover, our study showed that in comparison with sodium selenite, only ADS18 bacterial Se showed a significantly higher mRNA level in GSH-Px1, GSH-Px4, DIO1, and TXNDR1, while both ADS18 and ADS2 showed high level of mRNA of DIO2 compared to sodium selenite.

Conclusions

The supplementation of bacterial organic Se in broiler chicken, improved tissue Se deposition, antioxidant status, and selenoproteins gene expression, and can be considered as an effective alternative source of Se in broiler chickens.

Minimum Selenium Requirements Increase When Repleting Second-Generation Selenium-Deficient Rats but Are Not Further Altered by Vitamin E Deficiency

Second-generation selenium-deficient weanling rats fed graded levels of dietary Se were used (a) to study the impact of initial Se deficiency on dietary Se requirements; (b) to determine if further decreases in selenoperoxidase expression, especially glutathione peroxidase 4 (Gpx4), affect growth or gross disease; and (c) to examine the impact of vitamin E deficiency on biochemical and molecular biomarkers of Se status. Rats were fed a vitamin E-deficient and Se-deficient crystalline amino acid diet (3 ng Se/g diet) or that diet supplemented with 100 μg/g all-rac-α-tocopheryl acetate and/or 0, 0.02, 0.05, 0.075, 0.1, or 0.2 μg Se/g diet as Na₂SeO₃ for 28 days. Se-supplemented rats grew 6.91 g/day as compared to 2.17 and 3.87 g/day for vitamin E-deficient/Se-deficient and vitamin E-supplemented/Se-deficient groups, respectively. In Se-deficient rats, liver Se, plasma Gpx3, red blood cell Gpx1, liver Gpx1 and Gpx4 activities, and liver Gpx1 mRNA levels decreased to <1, <1, 21, 1.6, 49, and 11 %, respectively, of levels in rats fed 0.2 μg Se/g diet. For all biomarkers, ANOVA indicated significant effects of dietary Se, but no significant effects of vitamin E or vitamin E × Se interaction, showing that vitamin E deficiency, even in severely Se-deficient rat pups, does not result in compensatory changes in these biochemical and molecular biomarkers of selenoprotein expression. Se requirements determined in this study, however, were >50 % higher than in previous studies that started with Se-adequate rats, demonstrating that dietary Se requirements determined using initially Se-deficient animals can result in overestimation of Se requirements.