Selenium status and type 2 diabetes risk.

Optimal selenium (Se) status is necessary for overall health. That status can be affected by food intake pattern, age, sex, and health status. At nutritional levels of intake, Se functions metabolically as an essential constituent of some two dozen selenoproteins, most, if not all, of which have redox functions. Insufficient dietary intake of Se reduces, to varying degrees, the expression of these selenoproteins. Recent clinical and animal studies have indicated that both insufficient and excessive Se intakes may increase risk of type 2 diabetes mellitus (T2D), perhaps by way of selenoprotein actions. In this review, we discuss the current evidence linking Se status and T2D risk, and the roles of 14 selenoproteins and other proteins involved in selenoprotein biosynthesis. Understanding such results can inform the setting of safe and adequate Se intakes.

Identification of Selenoprotein H Isoforms and Impact of Selenoprotein H Overexpression on Protein But Not mRNA Levels of 2 Other Selenoproteins in 293T Cells.

BACKGROUND: Selenoprotein H (SELONOH), a member of the thioredoxin-like family proteins, is prioritized to degradation in selenium (Se) insufficiency. Recent studies implicate protective roles of SELENOH in oxidative stress, cellular senescence, and intestinal tumorigenesis. Although the nonselenoprotein H0YE28 is suggested as shortened SELENOH according to genomic and proteomic data repositories, this variant has not been verified biochemically. OBJECTIVES: We sought to identify SELENOH isoforms and explore the impact of Se flux on selenoprotein expression in SELENOH-overexpressing cells. METHODS: A vector expressing a FLAG (the DYKDDDDK sequence) tag on the N-terminal end of wild-type SELENOH was constructed and transiently transfected into 293T cells incubated with graded concentrations of Na2SeO3 (0-200 nM). Cells were subjected to immunoprecipitation, LC-MS/MS protein analysis, immunoblotting, qRT-PCR, and senescence assays. Data were analyzed by 1-way or 2-way ANOVA. RESULTS: Results of anti-FLAG immunoblotting showed that FLAG-SELENOH transfection increased (3.7-fold; P < 0.05) protein levels of the long, but not the short, SELENOH variants in the presence of Na2SeO3 (100 nM). By contrast, SELENOH mRNA levels were increased by 53-fold upon FLAG-SELENOH transfection but were comparable with or without supplemental Se (100 nM). LC-MS/MS analyses of anti-FLAG immunoprecipitates designated both anti-FLAG bands as SELENOH and co-identified three 60S ribosomal and 9 other proteins. Overexpression of FLAG-SELENOH 1) reduced glutathione peroxidase 1 and thioredoxin reductase 1 expression at the protein rather than the mRNA level in the absence but not presence of supplemental Se (100 nM; P < 0.05); 2) increased mRNA levels of 3 heat shock proteins (HSP27, HSP70-1A, and HSP70-1B; P < 0.05); and 3) reduced senescence induced by H2O2 (20 µM, 4 hours; P < 0.05). CONCLUSIONS: These cellular studies demonstrate a Se-independent, shortened SELENOH variant and suggest competition of overexpressed FLAG-SELENOH with 2 other selenoproteins for the expression at the protein but not the mRNA level in Se insufficiency.

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.

Prioritized brain selenium retention and selenoprotein expression: Nutritional insights into Parkinson's disease.

Selenium (Se), an essential trace mineral, confers its physiological functions mainly through selenoproteins, most of which are oxidoreductases. Results from animal, epidemiological, and human genetic studies link Parkinson's disease to Se and certain selenoproteins. Parkinson's disease is characterized by multiple motor and non-motor symptoms that are difficult to diagnose at early stages of the pathogenesis. While irreversible, degenerative and age-related, the onset of Parkinson's disease may be delayed through proper dietary and environmental controls. One particular attribute of Se biology is that brain has the highest priority to receive and retain this nutrient even in Se deficiency. Thus, brain Se deficiency is rare; however, a strong body of recent evidence implicates selenoprotein dysfunction in Parkinson's disease. Direct and indirect evidence from mouse models implicate selenoprotein T, glutathione peroxidase 1, selenoprotein P and glutathione peroxidase 4 in counteracting Parkinson's disease through Se transportation to the brain and reduced oxidative stress. It is of future interest to further characterize the full selenoproteomes in various types of brain cells and elucidate the mechanism of their actions in Parkinson's disease.

The Thioredoxin-Like Family of Selenoproteins: Implications in Aging and Age-Related Degeneration.

The thioredoxin-like (Rdx) family proteins contain four selenoproteins (selenoprotein H, SELENOH; selenoprotein T, SELENOT; selenoprotein V, SELENOV; selenoprotein W, SELENOW) and a nonselenoprotein Rdx12. They share a CxxU or a CxxC (C, cysteine; x, any amino acid; U, selenocysteine) motif and a stretch of eGxFEI(V) sequence. From the evolutionary perspective, SELENOW and SELENOV are clustered together and SELENOH and SELENOT are in another branch. Selenoproteins in the Rdx family exhibit tissue- and organelle-specific distribution and are differentially influenced in response to selenium deficiency. While SELENOH is nucleus-exclusive, SELENOT resides mainly in endoplasmic reticulum and SELENOW in cytosol. SELENOV is expressed essentially only in the testes with unknown cellular localization. SELENOH and SELENOW are more sensitive than SELENOT and SELENOV to selenium deficiency. While physiological functions of the Rdx family of selenoproteins are not fully understand, results from animal models demonstrated that (1) brain-specific SELENOT knockout mice are susceptible to 1-methyl-4-phenylpyridinium-induced Parkinson's disease in association with redox imbalance and (2) adult zebrafishes with heterozygous SELENOH knockout are prone to dimethylbenzanthracene-induced tumorigenesis together with increased DNA damage and oxidative stress. Further animal and human studies are needed to fully understand physiological roles of the Rdx family of selenoproteins in redox regulation, genome maintenance, aging, and age-related degeneration.

Beneficial and paradoxical roles of selenium at nutritional levels of intake in healthspan and longevity.

Accumulation of genome and macromolecule damage is a hallmark of aging, age-associated degeneration, and genome instability syndromes. Although processes of aging are irreversible, they can be modulated by genome maintenance pathways and environmental factors such as diet. Selenium (Se) confers its physiological functions mainly through selenoproteins, but Se compounds and other proteins that incorporate Se nonspecifically also impact optimal health. Bruce Ames proposed that the aging process could be mitigated by a subset of low-hierarchy selenoproteins whose levels are preferentially reduced in response to Se deficiency. Consistent with this notion, results from two selenotranscriptomic studies collectively implicate three low-hierarchy selenoproteins in age or senescence. Experimental evidence generally supports beneficial roles of selenoproteins in the protection against damage accumulation and redox imbalance, but some selenoproteins have also been reported to unexpectedly display harmful functions under sporadic conditions. While longevity and healthspan are usually thought to be projected in parallel, emerging evidence suggests a trade-off between longevity promotion and healthspan deterioration with damage accumulation. We propose that longevity promotion under conditions of Se deficiency may be attributed to 1) stress-response hormesis, an advantageous event of resistance to toxic chemicals at low doses; 2) reduced expression of selenoproteins with paradoxical functions to a lesser extent. In particular, selenoprotein H is an evolutionally conserved nuclear selenoprotein postulated to confer Se functions in redox regulation, genome maintenance, and senescence. This review highlights the need to pinpoint roles of specific selenoproteins and Se compounds in healthspan and lifespan for a better understanding of Se contribution at nutritional levels of intake to healthy aging.

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.

Opposing impacts on healthspan and longevity by limiting dietary selenium in telomere dysfunctional mice.

Selenium (Se) is a trace metalloid essential for life, but its nutritional and physiological roles during the aging process remain elusive. While telomere attrition contributes to replicative senescence mainly through persistent DNA damage response, such an aging process is mitigated in mice with inherently long telomeres. Here, weanling third generation telomerase RNA component knockout mice carrying short telomeres were fed a Se-deficient basal diet or the diet supplemented with 0.15 ppm Se as sodium selenate to be nutritionally sufficient throughout their life. Dietary Se deprivation delayed wound healing and accelerated incidence of osteoporosis, gray hair, alopecia, and cataract, but surprisingly promoted longevity. Plasma microRNA profiling revealed a circulating signature of Se deprivation, and subsequent ontological analyses predicted dominant changes in metabolism. Consistent with this observation, dietary Se deprivation accelerated age-dependent declines in glucose tolerance, insulin sensitivity, and glucose-stimulated insulin production in the mice. Moreover, DNA damage and senescence responses were enhanced and Pdx1 and MafA mRNA expression were reduced in pancreas of the Se-deficient mice. Altogether, these results suggest a novel model of aging with conceptual advances, whereby Se at low levels may be considered a hormetic chemical and decouple healthspan and longevity.

Loss of Selenium-Binding Protein 1 Decreases Sensitivity to Clastogens and Intracellular Selenium Content in HeLa Cells.

Selenium-binding protein 1 (SBP1) is not a selenoprotein but structurally binds selenium. Loss of SBP1 during carcinogenesis usually predicts poor prognosis. Because genome instability is a hallmark of cancer, we hypothesize that SBP1 sequesters cellular selenium and sensitizes cancer cells to DNA-damaging agents. To test this hypothesis, we knocked down SBP1 expression in HeLa cervical cancer cells by employing a short hairpin RNA (shRNA) approach. Reduced sensitivity to hydrogen peroxide, paraquat and camptothecin, reactive oxygen species content, and intracellular retention of selenium after selenomethionine treatment were observed in SBP1 shRNA HeLa cells. Results from Western analyses showed that treatment of HeLa cells with selenomethionine resulted in increased SBP1 protein expression in a dose-dependent manner. Knockdown of SBP1 rendered HeLa cells increased expression of glutathione peroxidase-1 but not glutathione peroxidase-4 protein levels and accelerated migration from a wound. Altogether, SBP1 retains supplemental selenium and sensitizes HeLa cancer cells to clastogens, suggesting a new cancer treatment strategy by sequestering selenium through SBP1.

Selenium supranutrition: are the potential benefits of chemoprevention outweighed by the promotion of diabetes and insulin resistance?

Selenium was considered a toxin until 1957, when this mineral was shown to be essential in the prevention of necrotic liver damage in rats. The hypothesis of selenium chemoprevention is principally formulated by the observations that cancer incidence is inversely associated with selenium status. However, recent clinical and epidemiological studies demonstrate a role for some selenoproteins in exacerbating or promoting other disease states, specifically type 2 diabetes, although other data support a role of selenium in stimulating insulin sensitivity. Therefore, it is clear that our understanding in the role of selenium in glucose metabolism and chemoprevention is inadequate and incomplete. Research exploring the role of selenium in individual healthcare is of upmost importance and possibly will help explain how selenium is a double-edged sword in the pathologies of chronic diseases.

The catalytic subunit of DNA-dependent protein kinase is downstream of ATM and feeds forward oxidative stress in the selenium-induced senescence response.

Selenium induces a senescence response in cells through induction of ataxia-telangiectasia mutated (ATM) and reactive oxygen species (ROS). Although a role of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in DNA double-strand break repair is established, it is unclear how these proteins function in response to selenium-induced oxidative stress and senescence induction. In this study, we demonstrated that pretreating normal human diploid fibroblasts with DNA-PK kinase inhibitor NU 7026 suppressed selenium-induced senescence response. Selenium treatment induced phosphorylation of DNA-PKcs on Thr-2647 and Ser-2056, the extent of which was decreased in the presence of ATM kinase inhibitor KU 55933 or the antioxidants N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl. In contrast, the selenium-induced phosphorylation of ATM on Ser-1981 was not affected by NU 7026. Cells deficient in DNA-PKcs or pretreated with NU 7026 or N-acetylcysteine were defective in selenite-induced ROS formation. Taken together, these results indicate a distinct role of DNA-PKcs, in which this kinase can respond to and feed forward selenium-induced ROS formation and is placed downstream of ATM in the resultant senescence response.

Effect of dietary selenium and cancer cell xenograft on peripheral T and B lymphocytes in adult nude mice.

Selenium (Se) is known to regulate tumorigenesis and immunity at the nutritional and supranutritional levels. Because the immune system provides critical defenses against cancer and the athymic, immune-deficient NU/J nude mice are known to gradually develop CD8(+) and CD4(+) T cells, we investigated whether B and T cell maturation could be modulated by dietary Se and by tumorigenesis in nude mice. Fifteen homozygous nude mice were fed a Se-deficient, Torula yeast basal diet alone (Se-) or supplemented with 0.15 (Se+) or 1.0 (Se++) mg Se/kg (as Na(2)SeO(4)) for 6 months, followed by a 7-week time course of PC-3 prostate cancer cell xenograft (2 × 10(6) cells/site, 2 sites/mouse). Here, we show that peripheral B cell levels decreased in nude mice fed the Se - or Se++ diet and the CD4(+) T cell levels increased in mice fed the Se++ diet. During the PC-3 cell tumorigenesis, dietary Se status did not affect peripheral CD4(+) or CD8(+) T cells in nude mice whereas mice fed with the Se++ diet appeared to exhibit greater peripheral CD25(+)CD4(+) T cells on day 9. Dietary Se status did not affect spleen weight in nude mice 7 weeks after the xenograft. Spleen weight was associated with frequency of peripheral CD4(+), but not CD8(+) T cells. Taken together, dietary Se at the nutritional and supranutritional levels regulates peripheral B and T cells in adult nude mice before and after xenograft with PC-3 prostate cancer cells.

Nutritional and supranutritional levels of selenate differentially suppress prostate tumor growth in adult but not young nude mice.

The inhibitory effect of oral methylseleninic acid or methylselenocysteine administration on cancer cell xenograft development in nude mice is well characterized; however, less is known about the efficacy of selenate and age on selenium chemoprevention. In this study, we tested whether selenate and duration on diets would regulate prostate cancer xenograft in nude mice. Thirty-nine homozygous NU/J nude mice were fed a selenium-deficient, Torula yeast basal diet alone (Se-) or supplemented with 0.15 (Se) or 1.0 (Se+) mg selenium/kg (as Na2SeO4) for 6 months in Experiment 1 and for 4 weeks in Experiment 2, followed by a 47-day PC-3 prostate cancer cell xenograft on the designated diet. In Experiment 1, the Se- diet enhanced the initial tumor development on days 11-17, whereas the Se+ diet suppressed tumor growth on days 35-47 in adult nude mice. Tumors grown in Se- mice were loosely packed and showed increased necrosis and inflammation as compared to those in Se and Se+ mice. In Experiment 2, dietary selenium did not affect tumor development or histopathology throughout the time course. In both experiments, postmortem plasma selenium concentrations in Se and Se+ mice were comparable and were twofold greater than those in Se- mice. Taken together, dietary selenate at nutritional and supranutritional levels differentially inhibit tumor development in adult, but not young, nude mice engrafted with PC-3 prostate cancer cells.

Role for p53 in selenium-induced senescence.

The tumor suppressor p53 and the ataxia-telangiectasia mutated (ATM) kinase play important roles in the senescence response to oncogene activation and DNA damage. It was previously shown that selenium-containing compounds can activate an ATM-dependent senescence response in MRC-5 normal fibroblasts. Here, the shRNA knockdown approach and other DNA damage assays are employed to test the hypothesis that p53 plays a role in selenium-induced senescence. In MRC-5 cells treated with methylseleninic acid (MSeA, 0-10 µM), depletion of p53 hampers senescence-associated expression of ß-galactosidase, disrupts the otherwise S and G2/M cell cycle arrest, desensitizes such cells to MSeA treatment, and increases genome instability. Pretreatment with KU55933, an ATM kinase inhibitor, or NU7026, an inhibitor of DNA-dependent protein kinase, desensitizes MSeA cytotoxicity in scrambled but not p53 shRNA MRC-5 cells. These results suggest that p53 is critical for senescence induction in the response of MRC-5 noncancerous cells to selenium compounds.

Dietary selenomethionine increases exon-specific DNA methylation of the p53 gene in rat liver and colon mucosa.

The regulation of site-specific DNA methylation of tumor suppressor genes has been considered as a leading mechanism by which certain nutrients exert their anticancer property. This study was to investigate whether selenium (Se) affects the methylation of globe genomic DNA and the exon-specific p53 gene. Three groups of rats (n = 6-7/group) were fed the AIN-93G basal diet supplemented with 0 [Se deficient (D)], 0.15 [Se adequate (A)], or 4 mg [Se supranutritional (S)] (Se as l-selenomethionine)/kg diet for 104 d, respectively. Rats fed the A or S diet had greater plasma and liver glutathione peroxidase activity, liver thioredoxin reductase activity, and plasma homocysteine concentration than those fed the D diet. However, compared with the A diet, rats fed the S diet did not further increase these Se-dependent enzyme activities or homocysteine concentration. In contrast, Se concentrations in kidney, liver, gastrocnemius muscle, and plasma were increased in a Se-dose-dependent manner. Interestingly, rats fed the S diet had significantly less global liver genomic DNA methylation than those fed the D diet. However, the S diet significantly increased the methylation of the p53 gene (exons 5-8) but not the ß-actin gene (exons 2-3) DNA in liver and colon mucosa compared with those fed the D diet. Taken together, long-term Se consumption not only affects selenoprotein enzyme activities, homocysteine, tissue Se concentrations, and global genomic DNA methylation but also increases exon-specific DNA methylation of the p53 gene in a Se-dose-dependent manner in rat liver and colon mucosa.

Encapsulation of selenium in chitosan nanoparticles improves selenium availability and protects cells from selenium-induced DNA damage response.

Selenium, an essential mineral, plays important roles in optimizing human health. Chitosan (CS) is an effective, naturally oriented material for synthesizing nanoparticles with preferable properties such as biocompatibility, biodegradation and resistance to certain enzymes. We have recently shown that cellular exposure to selenium compounds activates ataxia-telangiectasia mutated (ATM)-dependent DNA damage responses, a tumorigenesis barrier. To test whether nanoencapsulation of selenium modulates the cellular response to selenium compounds, the HCT 116 cancerous and the MRC-5 normal cells were treated with Na(2)SeO(3) and methylseleninic acid (MSeA) encapsulated in CS/polyphosphate nanoparticles. Analyses of cellular selenium levels demonstrate that (1) the nanoencapsulation enhances selenium levels in cells after exposure to Na(2)SeO(3) and MSeA (1-10 µM); (2) cells retained more selenium when treated with Na(2)SeO(3) than with MSeA; (3) selenium levels are greater in HCT 116 than in MRC-5 cells after Na(2)SeO(3), but not MSeA, exposure. Survival analysis shows that CS encapsulation desensitizes HCT 116 and MRC-5 cells to Na(2)SeO(3) or MSeA exposure. Immunofluorescent analysis demonstrates that CS encapsulation attenuates the selenium-induced ATM phosphorylation on Ser-1981, and the extent is greater in HCT 116 than in MRC-5 cells. Our results reveal features of selenium nanoencapsulation in CS, including increased selenium retention in cells and decreased cellular sensitivity and DNA damage response to selenium exposure.

Chemical form of selenium affects its uptake, transport, and glutathione peroxidase activity in the human intestinal Caco-2 cell model.

Determining the effect of selenium (Se) chemical form on uptake, transport, and glutathione peroxidase activity in human intestinal cells is critical to assess Se bioavailability at nutritional doses. In this study, we found that two sources of L-selenomethionine (SeMet) and Se-enriched yeast each increased intracellular Se content more effectively than selenite or methylselenocysteine (SeMSC) in the human intestinal Caco-2 cell model. Interestingly, SeMSC, SeMet, and digested Se-enriched yeast were transported at comparable efficacy from the apical to basolateral sides, each being about 3-fold that of selenite. In addition, these forms of Se, whether before or after traversing from apical side to basolateral side, did not change the potential to support glutathione peroxidase (GPx) activity. Although selenoprotein P has been postulated to be a key Se transport protein, its intracellular expression did not differ when selenite, SeMSC, SeMet, or digested Se-enriched yeast was added to serum-contained media. Taken together, our data show, for the first time, that the chemical form of Se at nutritional doses can affect the absorptive (apical to basolateral side) efficacy and retention of Se by intestinal cells; but that, these effects are not directly correlated to the potential to support GPx activity.