Selenoenzyme Activities Research Articles

290 - Optimization of selenium in cell culture media to maximize selenoenzyme activity

Selenium plays an essential role in redox biology and redox toxicology. It is found at the active site of redox enzymes such as, glutathione peroxidases (GPx) and thioredoxin reductases (TrxR). Cell culture media is typically deficient in selenium; this deficiency could limit seleno-enzyme expression and activity, compromising the translation of data from in vitro experiments to in vivo settings. The level of selenium in cell culture media should always be a consideration. However, any supplementation must be within a range to overcome deficiency and yet not induce toxicity. The optimal level of supplementation has not been well characterized. To determine optimal levels of Se-supplementation of cell culture media we introduced varying levels of sodium selenite (Na2SeO3) or seleno-L-methionine (SLM). We established, that the window to avoid potential toxicity can be widened by using SLM instead of selenite. We assessed the expression and activity of GPx1 and GPx4 to determine the level of optimal selenium supplementation for a variety of cells. Supplementing cell culture media containing 10% FBS with 100 – 300 nM SLM, we were able to maximize GPx1 and GPx4 enzyme expression and activity. Interestingly, data from a clinical trial at The University of Iowa indicates that supplementing Se in humans does not increase GPx1 activity in blood. Subjects received ~30x the RDA (55 mg d-1) of Se as SLM daily for more than 7 mo. The level of total Se in blood increased about 50-fold. However, the activity of GPx1 in blood remained constant. Our cell culture data show the importance of supplementing cell culture media with Se to insure full activity of these enzymes. This simple maneuver will increase the rigor and reproducibility of cell culture experiments and may lead to better translation of data addressing basic redox biology.

Selenium nanoparticles are more efficient than sodium selenite in producing reactive oxygen species and hyper-accumulation of selenium nanoparticles in cancer cells generates potent therapeutic effects

We have previously demonstrated that selenium nanoparticles (SeNPs) administered via oral route possess similar capacities of increasing selenoenzyme activities as the extensively examined sodium selenite, selenomethionine and methylselenocysteine, and yet display the lowest toxicity among these selenium compounds in mouse models. However, the low toxicity of SeNPs found in mammalian systems would lead to the interpretation that the punctate distribution of elemental selenium found in cultured cancer cells subjected to selenite treatment that triggers marked cytotoxicity represents a detoxifying mechanism. The present study found that SeNPs could be reduced by the thioredoxin- or glutaredoxin-coupled glutathione system to generate ROS. Importantly, ROS production by SeNPs in these systems was more efficient than by selenite, which has been recognized as the most redox-active selenium compound for ROS production. This is because multiple steps of reduction from selenite to selenide anion are required; whereas only a single step reduction from the elemental selenium atom to selenide anion is needed to trigger redox cycling with oxygen to produce ROS. We thus speculated that accumulation of SeNPs in cancer cells would result in a strong therapeutic effect, rather than serves a detoxification function. Indeed, we showed herein that preformed SeNPs generated a potent therapeutic effect in a mouse model due to rapid, massive and selective accumulation of SeNPs in cancer cells. Overall, for the first time, we demonstrate that SeNPs have a stronger pro-oxidant property than selenite and hyper-accumulation of SeNPs in cancer cells can generate potent therapeutic effects.

Selenium Regulation of Selenoprotein Enzyme Activity and Transcripts in a Pilot Study with Founder Mouse Strains from the Collaborative Cross

Rodents and humans have 24–25 selenoproteins, and these proteins contain the 21st amino acid, selenocysteine, incorporated co‐translationally into the peptide backbone in a series of reactions dependent on at least 6 unique gene products. In selenium (Se) deficiency, there is differential regulation of selenoprotein expression, whereby levels of some selenoproteins and their transcripts decrease dramatically in Se deficiency, but other selenoprotein transcripts are spared this decrease; the underlying mechanism, however, is not fully understood. To begin explore the genetic basis for this variation in regulation by Se status in a pilot study, we fed Se‐deficient or Se‐adequate diets (0.005 or 0.2 μg Se/g, respectively) for eight weeks to the eight Founder strains of the Collaborative Cross. We found rather uniform expression of selenoenzyme activity for glutathione peroxidase (Gpx) 3 in plasma, Gpx1 in red blood cells, and Gpx1, Gpx4, and thioredoxin reductase in liver. In Founder mice, Se deficiency decreased each of these activities to a similar extent. Regulation of selenoprotein transcript expression by Se status was also globally retained intact, with dramatic down‐regulation of Gpx1, Selenow, and Selenoh transcripts in all 8 strains of Founder mice. These results indicate that differential regulation of selenoprotein expression by Se status is an essential aspect of Se metabolism and selenoprotein function. A few lone differences in Se regulation were observed for individual selenoproteins in this pilot study, but these differences did not single‐out one strain or one selenoprotein that consistently had unique Se regulation of selenoprotein expression. These differences should be affirmed in larger studies; use of the Diversity Outbred and Collaborative Cross strains may help to better define the functions of these selenoproteins.Support or Funding InformationSupported by the Wisconsin Alumni Foundation Selenium Nutrition Research Fund (No. 12046295)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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 17weeks, then repleted with graded levels of Se (0-0.3μg Se/g as Na2SeO3) for 7days, 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 7days; 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 (0.08-0.19μg 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 0.3μg Se/g. Plasma Gpx3 is secreted from kidney. In this short-term study, kidney Gpx3 mRNA reached plateau levels at 0.1μg Se/g, and other kidney selenoenzyme activities reached plateau levels at ≤0.2μg 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.

Interplay between Selenium Levels and Replicative Senescence in WI-38 Human Fibroblasts: A Proteomic Approach.

Selenoproteins are essential components of antioxidant defense, redox homeostasis, and cell signaling in mammals, where selenium is found in the form of a rare amino acid, selenocysteine. Selenium, which is often limited both in food intake and cell culture media, is a strong regulator of selenoprotein expression and selenoenzyme activity. Aging is a slow, complex, and multifactorial process, resulting in a gradual and irreversible decline of various functions of the body. Several cellular aspects of organismal aging are recapitulated in the replicative senescence of cultured human diploid fibroblasts, such as embryonic lung fibroblast WI-38 cells. We previously reported that the long-term growth of young WI-38 cells with high (supplemented), moderate (control), or low (depleted) concentrations of selenium in the culture medium impacts their replicative lifespan, due to rapid changes in replicative senescence-associated markers and signaling pathways. In order to gain insight into the molecular link between selenium levels and replicative senescence, in the present work, we have applied a quantitative proteomic approach based on 2-Dimensional Differential in-Gel Electrophoresis (2D-DIGE) to the study of young and presenescent cells grown in selenium-supplemented, control, or depleted media. Applying a restrictive cut-off (spot intensity ±50% and a p value < 0.05) to the 2D-DIGE analyses revealed 81 differentially expressed protein spots, from which 123 proteins of interest were identified by mass spectrometry. We compared the changes in protein abundance for three different conditions: (i) spots varying between young and presenescent cells, (ii) spots varying in response to selenium concentration in young cells, and (iii) spots varying in response to selenium concentration in presenescent cells. Interestingly, a 72% overlap between the impact of senescence and selenium was observed in our proteomic results, demonstrating a strong interplay between selenium, selenoproteins, and replicative senescence.

Selenium regulation of selenoprotein enzyme activity and transcripts in a pilot study with Founder strains from the Collaborative Cross.

Rodents and humans have 24–25 selenoproteins, and these proteins contain the 21st amino acid, selenocysteine, incorporated co-translationally into the peptide backbone in a series of reactions dependent on at least 6 unique gene products. In selenium (Se) deficiency, there is differential regulation of selenoprotein expression, whereby levels of some selenoproteins and their transcripts decrease dramatically in Se deficiency, but other selenoprotein transcripts are spared this decrease; the underlying mechanism, however, is not fully understood. To begin explore the genetic basis for this variation in regulation by Se status in a pilot study, we fed Se-deficient or Se-adequate diets (0.005 or 0.2 μg Se/g, respectively) for eight weeks to the eight Founder strains of the Collaborative Cross. We found rather uniform expression of selenoenzyme activity for glutathione peroxidase (Gpx) 3 in plasma, Gpx1 in red blood cells, and Gpx1, Gpx4, and thioredoxin reductase in liver. In Founder mice, Se deficiency decreased each of these activities to a similar extent. Regulation of selenoprotein transcript expression by Se status was also globally retained intact, with dramatic down-regulation of Gpx1, Selenow, and Selenoh transcripts in all 8 strains of Founder mice. These results indicate that differential regulation of selenoprotein expression by Se status is an essential aspect of Se metabolism and selenoprotein function. A few lone differences in Se regulation were observed for individual selenoproteins in this pilot study, but these differences did not single-out one strain or one selenoprotein that consistently had unique Se regulation of selenoprotein expression. These differences should be affirmed in larger studies; use of the Diversity Outbred and Collaborative Cross strains may help to better define the functions of these selenoproteins.

Identification of Genetic Disorders Causing Disruption of Selenoprotein Biosynthesis.

Disorders of selenoprotein biosynthesis in humans, due to mutations in three genes (SECISBP2, TRU-TCA1-1, and SEPSECS) involved in the selenocysteine insertion pathway, have been described. Patients with SECISBP2 and TRU-TCA1-1 defects manifest a multisystem disorder with a biochemical signature of abnormal thyroid function tests due to the impaired activity of deiodinase selenoenzymes, myopathic features linked to SEPN1 deficiency and phenotypes resulting from increased levels of reactive oxygen species attributable to lack of antioxidant selenoenzymes. In patients harboring SEPSECS mutations, severe, progressive, cerebello-cerebral atrophy (pontocerebellar hypoplasia type 2D) dominates the phenotype and it is not known whether the disorder is associated with thyroid dysfunction.

Superoxide-hydrogen peroxide genetic imbalance modulates differentially the oxidative metabolism on human peripheral blood mononuclear cells exposed to seleno-L-methionine

Superoxide-hydrogen peroxide (S-HP) imbalance genetically caused by a gene polymorphism in the human manganese superoxide dismutase enzyme (Val16Ala-MnSOD) is associated with several diseases. Into mitochondria, MnSOD catalyses superoxide radical producing HP and oxygen. Ala-MnSOD genotype presents a high MnSOD efficiency and generates the highest HP concentrations that has been associated with the risk of several cancer types. Cellular selenoenzymes glutathione peroxidase and thioredoxin reductase (TrxR) and catalase (CAT) are essential to HP removal produced in excess in cells. Since, synthesis and activities of selenoenzymes are selenium dependent, we hypothesized that AA-MnSOD cells could have an improvement on antioxidant status undergoing Seleno-L-methionine (SeMet) treatment. This study performed an in vitro protocol to evaluate the response of peripheral blood mononuclear cells (PBMC) carriers of different Val16Ala-MnSOD genotypes exposed to SeMet. SeMet effects on cell viability, apoptosis induction and modulation of oxidative variables were determined using spectrophotometric, flow cytometry, fluorimetric and immunoassays. Gene modulation of antioxidant enzymes was also performed by qRT-PCR. From an initial protocol using heterozygous (AV) cells was determined that 1nM SeMet presented a cytoprotective effect. However, whereas this concentration did not change AA viability, in VV cells it was cytotoxic by increasing necrosis events. SeMet induced higher selenoenzymes levels in AA and VV cells and decreased oxidative markers levels including DNA damage. The results suggest a pharmacogenetic positive response of SeMet effect on AA-cells. Future studies in vivo could be essential to evaluate the potential clinical impact of S-HP imbalance after use of foods or supplements containing SeMet.

Minimum Selenium Requirements Based on Muscle and Kidney Glutathione Peroxidase Activity in the Turkey

Liver and blood glutathione peroxidase (GPX) activities have been used extensively as biomarkers of selenium (Se) status in laboratory and livestock animals. In livestock species used for meat, selenoenzyme activity in the muscle should be considered when setting Se requirements. We recently reported that the Se requirement in rapidly growing young turkey poults is 0.3 μg Se/g diet, based on plasma and liver GPX activity (PLOS ONE 11:e0151665), vs. the published requirement of 0.2 μg Se/g diet (NRC 1994). To examine Se requirements based on breast and thigh muscle, cardiac muscle, and kidney (a tissue with high GPX activity), we fed day‐old male poults (n=50) 10 graded levels of Se (0–1.0 μg/g) for 28 d, and measured GPX1 and GPX4 activity, and transcript expression of all 24 turkey selenoproteins in each tissue. Se response curves and plateau breakpoints were plotted to determine extent of deficiency and minimum Se requirements for each biomarker. The minimum dietary Se requirement for growth was 0.05 μg Se/g. Poults receiving 0 μg Se/g diet had 1 and 8% of plateau GPX1 activity in kidney and heart, respectively, and minimum Se requirements were 0.30 and 0.34 μg Se/g diet, respectively. Breast and thigh GPX1 activity Se response curves were hyperbolic but did not reach well defined plateaus, as GPX1 activity was significantly higher in poults fed 1.0 μg Se/g vs. 0.4 μg Se/g. GPX4 activities in Se‐deficient poults were 9, 22, 8, and 27% of GPX4 plateau activities in kidney, heart, breast and thigh, respectively, and minimum Se requirements were 0.25, 0.31, 0.32 and 0.30 μg Se/g diet, respectively. qPCR of total RNA from each tissue showed that 2–6 transcripts out of 24 total selenoprotein transcripts were significantly downregulated by Se deficiency to 31–73% of Se‐adequate plateaus, with GPX1 and SELH transcripts downregulated in every tissue studied; minimum Se requirements based on transcript expression were 0.08–0.19 μg Se/g diet, and no selenoprotein transcript was up‐ or downregulated significantly by supernutritional Se. This study shows that the turkey minimum dietary Se requirement is 0.3 μg Se/g diet based on heart and kidney GPX activity and on breast and thigh GPX4 activity, just as determined previously based on gizzard, liver and plasma GPX activities. The hyperbolic Se response curves for breast and thigh GPX1 activity suggest that 0.4 μg Se/g diet may be warranted for the 0–4 wk old rapidly growing poult.Support or Funding InformationUSDA NIFA (Hatch 233618 and 1004389), and by the Wisconsin Alumni Foundation Selenium Nutrition Research Fund (No. 2046295).

Effects of Different Dietary Selenium Sources on Antioxidant Status and Blood Phagocytic Activity in Sheep.

The objective of this experiment was to investigate the effects of feed supplementation with equivalent doses of selenium from sodium selenite (SS) or selenized yeast (SY) on Se deposition, selenoenzyme activity and lipid peroxidation in tissues as well as in bacterial and protozoal fractions of rumen contents in sheep. The phagocytic activity of monocytes and neutrophils in whole blood was also assessed after 3months of dietary treatment. While animals in the control group were fed with unsupplemented basal diet (BD) containing only background Se (0.16mg/kg DM), the diet of the other two groups (n=6) consisted of identical BD enriched with 0.4mg Se/kg DM either from SS or SY. Concentrations of Se in blood and tissues were found to be significantly increased in both supplemented groups. No response in Se deposition was recorded in the musculus longissimus dorsi of sheep given dietary SS. The intake of SY resulted in a significantly higher Se level in the blood, kidney medulla, skeletal muscles, heart, intestinal and ruminal mucosa than in the case of SS supplementation. No differences appeared between tissue Se contents in the liver and kidney cortex due to the source of added Se. Regardless of source, Se supplementation to feeds significantly increased the glutathione peroxidase (GPx) activity in blood and tissues except the kidney medulla and jejunal mucosa. Supplementation with SY resulted in significantly higher activity of thioredoxin reductase in the liver and ileal mucosa, and also reduced malondialdehyde content in the liver and duodenal mucosa. Dietary Se intake increased Se concentrations in the total rumen contents and bacterial and protozoal fractions. The accumulation of Se in rumen microbiota was associated with increased GPx activity. Phagocytic cell activity was enhanced by Se supplementation. Our results indicate that Se from both sources has beneficial effects on antioxidant status in sheep and can be utilized by rumen microflora.

Selenium Requirements in Rats, Mice, Lambs, Chicks and Turkeys Based on Selenoprotein Enzyme Activity and Transcript Level

Over the past several years, my lab has conducted a series of studies to evaluate selenium (Se) status and requirements in rats, mice and lambs, all using virtually the same diets. These studies progressed from using glutathione peroxidase (GPX) activity as the primary biomarker, to use of GPX protein and GPX mRNA levels as biomarkers, and recently we expanded to include additional selenoenzyme activities as well as transcript levels for the full selenoproteome. Literature reports of Se requirements of turkeys have consistently indicated that turkeys have a markedly higher Se requirement than mammals (NRC: 0.2 μg Se/g). Thus we evaluated the Se requirements of turkey poults, and in parallel, of chicks. The objective here is to compare resulting requirements and to identify clues to better understand the underlying differences in Se requirements and in Se‐deficiency target tissues. For all studies, animals were fed a basal torula yeast diet (0.005–0.007 μg Se/g) with graded levels of Se supplemented as selenite for 4 weeks (lambs 8 wk). Se response curves result in well‐defined Se‐adequate plateaus for all biomarkers except RBC GPX1 activity. Based on plasma GPX3, liver GPX1, and RBC GPX1 activities, the mammalian minimal dietary Se requirement is uniformly 0.1 μg Se/g, whereas the turkey requirement is clearly 3‐times higher at 0.3 μg Se/g; the chick minimum Se requirement is 0.15 μg Se/g based on plasma GPX3 and GPX1 activities. Liver GPX4 activity is only modestly affected by Se deficiency in rats, but falls to ~10% of plateau levels in mice, chicks and poults. In contrast to selenoenzyme activity biomarkers, requirements based on liver GPX1 mRNA are uniformly 0.04–0.11 μg Se/g for rodents and avians, with GPX1 mRNA in Se deficiency falling more dramatically in rodents vs. avians. GPX4 mRNA is little affected by Se deficiency in rodents but falls to 30% in avians. Other unique species differences include high expression of GPX3 mRNA in avian liver; plasma GPX3 activity in Se deficiency falls to 1–3% of plateau levels in rats, chicks, poults and lambs and but only to 35% in mice. Sigmoidal Se response curves are observed for liver GPX1 activity in rats, chicks, turkeys and lambs, and for plasma GPX3 activity in mice, indicating that Se is preferentially directed to other selenoenzymes and/or tissues under Se‐deficient conditions. No mRNA response curves are markedly sigmoidal. Notably, there are no selenoprotein mRNAs that can be used as biomarkers for supernutritional Se status. These studies demonstrate that the minimum dietary Se requirement of young mammals falls over a narrow range, while the requirement of chicks is slightly higher, and turkey requirements are 3‐times that of mammals. Differences in these biomarker Se response curves may help to understand Se metabolism and targeting of tissues in Se deficiency, and thus help to better characterize Se requirements.Support or Funding InformationUSDA Hatch 233618 and 1004389, Northeast Agricultural Univ NECT‐1207‐02 and 1252‐ NCET‐009, and UW Selenium Nutrition Research Fund

Selenoprotein Transcript Level and Enzyme Activity as Biomarkers for Selenium Status and Selenium Requirements in the Turkey (Meleagris gallopavo).

The current National Research Council (NRC) selenium (Se) requirement for the turkey is 0.2 μg Se/g diet. The sequencing of the turkey selenoproteome offers additional molecular biomarkers for assessment of Se status. To determine dietary Se requirements using selenoprotein transcript levels and enzyme activities, day-old male turkey poults were fed a Se-deficient diet supplemented with 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 diet) as selenite, and 12.5X the vitamin E requirement. Poults fed less than 0.05 μg Se/g diet had a significantly reduced rate of growth, indicating the Se requirement for growth in young male poults is 0.05 μg Se/g diet. Se deficiency decreased plasma GPX3 (glutathione peroxidase), liver GPX1, and liver GPX4 activities to 2, 3, and 7%, respectively, of Se-adequate levels. Increasing Se supplementation resulted in well-defined plateaus for all blood, liver and gizzard enzyme activities and mRNA levels, showing that these selenoprotein biomarkers could not be used as biomarkers for supernutritional-Se status. Using selenoenzyme activity, minimum Se requirements based on red blood cell GPX1, plasma GPX3, and pancreas and liver GPX1 activities were 0.29–0.33 μg Se/g diet. qPCR analyses using all 10 dietary Se treatments for all 24 selenoprotein transcripts (plus SEPHS1) in liver, gizzard, and pancreas found that only 4, 4, and 3 transcripts, respectively, were significantly down-regulated by Se deficiency and could be used as Se biomarkers. Only GPX3 and SELH mRNA were down regulated in all 3 tissues. For these transcripts, minimum Se requirements were 0.07–0.09 μg Se/g for liver, 0.06–0.15 μg Se/g for gizzard, and 0.13–0.18 μg Se/g for pancreas, all less than enzyme-based requirements. Panels based on multiple Se-regulated transcripts were effective in identifying Se deficiency. These results show that the NRC turkey dietary Se requirement should be raised to 0.3 μg Se/g diet.

Selenium Health Benefit Values: Updated Criteria for Mercury Risk Assessments.

Selenium (Se)-dependent enzymes (selenoenzymes) protect brain tissues against oxidative damage and perform other vital functions, but their synthesis requires a steady supply of Se. High methylmercury (CH3Hg) exposures can severely diminish Se transport across the placenta and irreversibly inhibit fetal brain selenoenzymes. However, supplemental dietary Se preserves their activities and thus prevents pathological consequences. The modified Se health benefit value (HBVSe) is a risk assessment criterion based on the molar concentrations of CH3Hg and Se present in a fish or seafood. It was developed to reflect the contrasting effects of maternal CH3Hg and Se intakes on fetal brain selenoenzyme activities. However, the original equation was prone to divide-by-zero-type errors whereby the calculated values increased exponentially in samples with low CH3Hg contents. The equation was refined to provide an improved index to better reflect the risks of CH3Hg exposures and the benefits provided by dietary Se. The HBVSe provides a biochemically based perspective that confirms and supports the FDA/EPA advice for pregnant and breast-feeding women regarding seafoods that should be avoided vs. those that are beneficial to consume. Since Se can be highly variable between watersheds, further evaluation of freshwater fish is needed to identify locations where fish with negative HBVSe may arise and be consumed by vulnerable subpopulation groups.

Oxidant and antioxidant status in neonatal proven and clinical sepsis according to selenium status

Selenium is a trace element required for the functioning of the immune system. Neonatal sepsis is a serious condition leading to morbidity and mortality in neonates worldwide. The purpose of this study was to measure selenium and plasma selenoprotein P (SePP), selenoenzyme activity, and alterations in oxidant/antioxidant status with immune biomarkers in neonates with clinical (n = 27) and proven neonatal sepsis (n = 25). Erythrocyte selenium and SePP; plasma lipid peroxidation (LP), protein oxidation and total antioxidant capacity and erythrocyte total glutathione (GSH) concentration; erythrocyte glutathione peroxidase (GPx), thioredoxin reductase (TrxR), catalase (CAT) and total superoxide dismutase (SOD) activity were measured spectrophotometrically/spectrofluorometrically. Plasma interleukin 2 and 6 were also measured. Erythrocyte selenium and SePP were markedly lower both in the clinical and proven sepsis groups versus control. Erythrocyte GPx activity was higher only in the clinical sepsis group. TrxR activity was markedly lower in proven sepsis. SOD activity and GSH were markedly higher both in clinical sepsis and in proven sepsis. CAT activity was significantly higher both in clinical sepsis and in proven sepsis. LP and protein oxidation were significantly higher in both of the sepsis groups. Both selenium-dependent and selenium-independent blood redox systems were altered in sepsis, suggesting that sepsis causes an imbalance between cellular antioxidant and oxidant states.

Dietary Selenium Status Regulates the Transcriptions of Selenoproteome and Activities of Selenoenzymes in Chicken Kidney at Low or Super-nutritional Levels.

To determine dietary selenium (Se) status regulates the transcriptions of selenoproteome and activities of selenoenzymes in chicken kidney, 1-day-old chickens received low Se (0.028 mg Se per kg of diet) or super-nutritional Se (3.0 or 5.0 mg Se per kg of diet) in their diets for 8 weeks. It was observed that dietary low or super-nutritional Se did not make renal appearance pathological changes in chicken. Low Se significantly reduced total antioxidant capability (T-AOC), glutathione (GSH) content, but malondialdehyde (MDA) content in the kidney increased and decreased glutathione peroxidase (Gpx) and thioredoxin reductase (TrxR) activity with changes in their mRNA levels. Super-nutritional Se (3.0 mg/kg) increased T-AOC and GSH contents then made them reduce, but it reduced MDA content significantly, elevated then reduced Gpx activity, and decreased TrxR activity with changes in their mRNA levels. Dietary low Se downregulated the mRNA expressions of Gpx1-4, Txnrd3, Sepn1, Selw, Sepx1, Selh, and SEPSECS. At super-nutritional Se, most selenoproteins were upregulated in chicken kidney, but Sepp2 and Sep15 was only upregulated in Se excess (5.0 mg/kg) bird. These results indicated that dietary Se status stabilizes normal renal physiology function via regulation of the selenoprotemic transcriptions and selenoenzyme activities in avian.Electronic supplementary materialThe online version of this article (doi:10.1007/s12011-015-0470-9) contains supplementary material, which is available to authorized users.

Umbilical cord blood and placental mercury, selenium and selenoprotein expression in relation to maternal fish consumption

Seafood is an important source of nutrients for fetal neurodevelopment. Most individuals are exposed to the toxic element mercury through seafood. Due to the neurotoxic effects of mercury, United States government agencies recommend no more than 340g (12oz) per week of seafood consumption during pregnancy. However, recent studies have shown that selenium, also abundant in seafood, can have protective effects against mercury toxicity. In this study, we analyzed mercury and selenium levels and selenoprotein mRNA, protein, and activity in placenta of a cohort of women in Hawaii in relation to maternal seafood consumption assessed with dietary surveys. Fish consumption resulted in differences in mercury levels in placenta and cord blood. When taken as a group, those who consumed no fish exhibited the lowest mercury levels in placenta and cord blood. However, there were numerous individuals who either had higher mercury with no fish consumption or lower mercury with high fish consumption, indicating a lack of correlation. Placental expression of selenoprotein mRNAs, proteins and enzyme activity was not statistically different in any region among the different dietary groups. While the absence of seafood consumption correlates with lower average placental and cord blood mercury levels, no strong correlations were seen between seafood consumption or its absence and the levels of either selenoproteins or selenoenzyme activity.

Evaluation of Selenium, Redox Status and Their Association with Plasma Amyloid/Tau in Alzheimer’s Disease

The aim of the study was to evaluate blood selenium and antioxidants as possible oxidative stress markers in Alzheimer's disease (AD) along with amyloid β42 (Aβ42) and tau by comparing them with vascular dementia (VD) and age-matched healthy controls. Selenium, total tau, Aβ42, glutathione (GSH) and malondialdehyde (MDA) levels and the activities of antioxidant enzymes were analysed in the blood of AD patients (n = 30), VD patients (n = 35) and controls (n = 40) from South India. Plasma Aβ42 level was significantly higher (P < 0.001) in both AD and VD compared to controls. Total tau and tau-to-amyloid ratio were significantly lower in both AD and VD (P < 0.001), compared to controls, and a significant difference (P < 0.01 and P < 0.05, respectively) was also observed between AD and VD. The receiver operating characteristic (ROC) curve-derived cutoff values of <3.5 for tau-to-Aβ42 ratio and <520 pg/ml for total tau showed sensitivity and specificity of around 67-72 % for differentiating AD from VD and around 90 % for AD from controls, indicating that they could serve as reliable AD-specific markers. The MDA levels were significantly higher (P < 0.001) in both dementia groups along with a significant decrease (P < 0.001) in reduced GSH levels, indicating elevated oxidative stress and altered redox status in both forms of dementia. Selenium levels did not vary significantly between the three groups. The activity of glutathione peroxidase increased in both AD and VD compared to controls, with a concomitant decrease in glutathione reductase and glucose-6-phospate dehydrogenase (P < 0.001) activity. The activity of thioredoxin reductase was significantly lower in both patient groups (P < 0.001) compared to healthy controls. No correlation was observed between selenium and activities of selenoenzymes, tau, Aβ42 or tau-to-Aβ42 ratio, when analysing independently, indicating that blood selenium may not be directly involved in Aβ production and in regulating tau/Aβ42-mediated mechanism in AD. The present study emphasizes the enhanced oxidative stress in AD pathology and plasma tau and tau-to-amyloid ratio as possible markers to differentiate AD from VD. The study also points that blood selenium may not be involved in regulating oxidative stress in AD, and a longitudinal study correlating plasma and cerebrospinal fluid (CSF) selenium and selenoprotein levels is warranted.

Baseline Selenium and Prostate Cancer Risk: Comments and Open Questions

Baseline Selenium and Prostate Cancer Risk: Comments and Open Questions

Potential Role of Selenoenzymes and Antioxidant Metabolism in relation to Autism Etiology and Pathology.

Autism and autism spectrum disorders (ASDs) are behaviorally defined, but the biochemical pathogenesis of the underlying disease process remains uncharacterized. Studies indicate that antioxidant status is diminished in autistic subjects, suggesting its pathology is associated with augmented production of oxidative species and/or compromised antioxidant metabolism. This suggests ASD may result from defects in the metabolism of cellular antioxidants which maintain intracellular redox status by quenching reactive oxygen species (ROS). Selenium-dependent enzymes (selenoenzymes) are important in maintaining intercellular reducing conditions, particularly in the brain. Selenoenzymes are a family of ~25 genetically unique proteins, several of which have roles in preventing and reversing oxidative damage in brain and endocrine tissues. Since the brain's high rate of oxygen consumption is accompanied by high ROS production, selenoenzyme activities are particularly important in this tissue. Because selenoenzymes can be irreversibly inhibited by many electrophiles, exposure to these organic and inorganic agents can diminish selenoenzyme-dependent antioxidant functions. This can impair brain development, particularly via the adverse influence of oxidative stress on epigenetic regulation. Here we review the physiological roles of selenoproteins in relation to potential biochemical mechanisms of ASD etiology and pathology.

Can Recombinant Human Glutathione Peroxidase 1 with High Activity Be Efficiently Produced inEscherichia coli?

Cellular glutathione peroxidase 1 (GPx1) is an important antioxidant selenoenzyme. Due to the presence of selenocysteine (Sec) encoded by UGA, normally recognized as a stop codon, the expression of mammalian GPx with traditional recombinant DNA technology is extremely difficult. In this study, a series of human GPx1 (hGPx1) mutants with significantly high catalytic activities were produced for the first time in an Escherichia coli BL21(DE3)cys auxotrophic strain using the single-protein production system. Cys residues in hGPx1 were mutated to Ser in turn because untargeted substitution of Sec in place of Cys resulted in the decline of recombinant selenoenzyme activity. The results of this work showed that the catalytic activities of the mutants increased progressively with decreasing number of noncatalytic Sec residues. Seleno-hGPx1-C2/78/115/156/202S with all Cys residues changed to Ser showed the highest activity (21,268 U/μmol), which was more than 10-fold higher than bovine liver GPx. This increase could be explained by structural analysis of hGPx1 mutants based on homology modeling and binding site analysis. These results lead to the hypothesis that the conversion of noncatalytic Sec residues to Ser may optimize the structure of seleno-GPx in this expression system and consequently increase the catalytic efficiency.