Selenium deficiency, thyroid hormone metabolism, and thyroid hormone deiodinases

Nutritional Supplementation and Enhanced Antioxidant Function by Dietary Intake of Selenoneine and Other Selenium Compounds in Red Seabream Pagrus major

Selenoneine, 2-selenyl-Nα, Nα, Nα-trimethyl-L-histidine, is the major organic selenium compound in marine fish. To characterize biological antioxidant function of selenoneine in fish, the accumulation of selenoneine and other selenium compounds, i. e., sodium selenite and selenomethionine, in the muscle and other tissues of red seabream. We reared red seabream by feeding of 1% dry pellet containing of sodium selenite, selenomethionine, or selenoneine of body weight twice a day for 4 weeks. After that, we replaced to 1% of normal commercial dry pellet of body weight twice a day for 1 week from the selenium supplementation, and tissue distribution of total selenium was determined. Selenium supplementation with selenoneine, selenomethionine, and sodium selenite enhanced selenium accumulation in the white muscle, kidney, and hepatopancreas in comparison with the control group. By the dietary intake of selenoneine, total selenium concentrations were increased in the white muscle, heart, kidney, spleen, hepatopancreas, brain, and blood cells in a dose-dependent manner during the trials after 2 weeks. Dietary intake of selenoneine as well as sodium selenite and selenomethionine reduced oxidation-reduction potential (ORP). Selenoneine concentrations in the white muscle and blood cells were accumulated for 4 weeks by the selenoneine intake, whereas selenoneine concentration was not elevated by the intake of selenomethionine and sodium selenite, suggesting that tissue selenoneine levels might be derived from only selenoneine-containing diet. The uptake factor of selenoneine from the artificial feed containing selenoneine was calculated to be 0.0062 in the white muscle and 4.0 in the blood. The half-life of total selenium in the blood cells and white muscle were estimated to be 60 days in the white muscle and 30 days in the blood.

Associations of serum zinc, copper, and selenium with sleep disorders in the American adults: Data from NHANES 2011-2016

BACKGROUND

Even though various studies have been conducted to investigate the relationship between trace metals and sleep, few epidemiological studies have evaluated the relationship between trace metals and sleep disorders in American adults.

OBJECTIVE

This study intended to evaluate the associations of serum zinc (Zn), copper (Cu), selenium (Se), Zn/Cu, Zn/Se, and Cu/Se ratios with sleep disorders in American adults.

METHODS

We conducted a cross-sectional analysis of 3660 adults aged ≥18 years old who participated in the National Health and Nutrition Examination Survey (NHANES) 2011-2016. Binary logistic regression was employed to calculate the odds ratio (OR) and 95 % confidence interval (CI) of either serum trace metals or serum trace metals ratios with risks among sleep disorder phenotypes. The restricted cubic spline (RCS) model was additionally utilized to check the dose-response relationships between serum trace metals, serum trace metals ratios, and sleep disorders.

RESULTS

Logistic regression demonstrated that higher serum Zn (OR: 0.70, 95 % CI: 0.51-0.97, p = 0.035), Zn/Cu (OR: 0.62, 95 % CI: 0.45-0.87, p = 0.007), and Zn/Se (OR: 0.68, 95 % CI: 0.49-0.95, p = 0.025) were related to a decreased likelihood of self-reported sleep disorders, and dose-response relationships were detected by the RCS models, after adjustment for sociodemographic, behavioral, and health characteristics. No associations between serum Cu, Se, Cu/Se, and sleep disorders were observed. The findings in the sensitivity analyses were consistent with these results.

CONCLUSION

Our study revealed that serum Zn, Zn/Cu, and Zn/Se were inversely associated with the risk of self-reported sleep disorders in US adults.

Is Glucose-6-Phosphate Dehydrogenase Deficiency a Risk Factor for Autoimmune Thyroid Disease? A Retrospective Case-Control Study

BACKGROUND

The risk of developing thyroid disorders (TDs) in subjects with inherited glucose-6-phosphate dehydrogenase (G6PD) deficiency is unknown. The aim of this study was to explore the association between autoimmune (AITD) and G6PD deficiency in Northern Sardinia, in a population with a high frequency of these two conditions.

METHODS

In this retrospective single-center case-control study, demographic and clinical data were collected from patients examined in a tertiary referral Gastroenterology Section of a teaching hospital.

RESULTS

In 8894 subjects examined (64.7% females), 1218 patients were diagnosed with TDs; more specifically, 767 were diagnosed with AITD and 451 were not (non-AITD). Overall, G6PD deficiency was more prevalent in TD patients compared with patients without TD (controls) (16.7% vs. 11.2%; p < 0.0001). Multivariable logistic regression analysis (after adjusting for age, sex, excess weight and smoking habits), confirmed a higher risk of AITD among G6PD deficient patients with an odds ratio (OR) of 1.36 and 95% confidence interval (CI) of 1.11-1.6, female patients (OR 1.33, 95% CI 1.07-1.65) and overweight patients (OR 1.22, 95% CI 1.03-1.44).

CONCLUSIONS

The risk of AITD is increased in carriers of G6PD deficiency. A careful assessment of thyroid function is advisable in patients with inherited G6PD defects.

Effect of Selenium on the Iron Homeostasis and Oxidative Damage in Brain and Liver of Mice

Selenium is an essential trace element that maintains normal brain function, mainly due its antioxidant properties. Although the amount of Se in the body is tightly regulated by the liver, both an excess of and deficiency in Se can modulate the cellular redox status and affect the homeostasis of other essential elements for both humans and animals. The aim of this study was to determine the effect of inorganic selenium excess on oxidative stress and iron homeostasis in brain and liver of laboratory BALB/c mice, which were supplemented with Na₂SeO₃ solution (0.2 mg and 0.4 mg Se/kg body weight) for 8 weeks. The content of the lipid peroxidation product malondialdehyde and antioxidant enzyme catalase activity/gene expression were used as markers of oxidative damage and were evaluated by spectrophotometric assays. Selenium and iron concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Catalase gene expression was analyzed by qRT-PCR and ΔΔCt methods. Our results showed that doses of 0.2 mg Se and 0.4 mg Se caused a relatively low accumulation of Se in the brain of mice; however, it induced a 10-fold increase in its accumulation in the liver and also increased iron accumulation in both tested organs. Both doses of Se increased the content of malondialdehyde as well as decreased catalase activity in the liver, while the 0.4 mg Se dose has also activated catalase gene expression. Brain of mice exposed to 0.2 mg Se showed reduced lipid peroxidation; however, the exposure to 0.4 mg of Se increased the catalase activity as well as gene expression. One may conclude that exposure to both doses of Se caused the accumulation of this micronutrient in mice brain and liver and have also provided a disrupting effect on the levels of iron. Both doses of Se have triggered oxidative liver damage. In the brain, the effect of Se was dose dependent, where −0.2 mg of Se provided antioxidant activity, which was observed through a decrease in lipid peroxidation. On the contrary, the 0.4 mg dose increased brain catalase activity as well as gene expression, which may have contributed to maintaining brain lipid peroxidation at the control level.

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

Selenium (Se) is an essential element with application in manufacturing from food to medical industries. Water contamination by Se is of concern due to anthropogenic activities. Recently, Se remediation has received increasing attention. Hence, different types of remediation techniques are listed in this work, and their potential for Se recovery is evaluated. Sorption, co-precipitation, coagulation and precipitation are effective for low-cost Se removal. In photocatalytic, zero-valent iron and electrochemical systems, the above mechanisms occur with reduction as an immobilization and detoxification process. In combination with magnetic separation, the above techniques are promising for Se recovery. Biological Se oxyanions reduction has been widely recognized as a cost-effective method for Se remediation, simultaneously generating biosynthetic Se nanoparticles (BioSeNPs). Increasing the extracellular production of BioSeNPs and controlling their morphology will benefit its recovery. However, the mechanism of the microbial production of BioSeNPs is not well understood. Se containing products from both microbial reduction and abiotic methods need to be refined to obtain pure Se. Eco-friendly and cost-effective Se refinery methods need to be developed. Overall, this review offers insight into the necessity of shifting attention from Se remediation to Se recovery.

Unravelling the molecular interaction of diselenodipropionic acid (DSePA) with human serum albumin (HSA)

DSePA, a pharmacologically efficient selenium compound shows strong binding with extracellular carrier protein, Human Serum Albumin.

Chromatographic Determination of Total Selenium in Biofortified Allium sp. following Piazselenol Formation and Micro-Solid-Phase Extraction

Herein, a method based on selective piazselenol formation is applied for total selenium determination in biofortified Allium species. Piazselenol is formed by reacting Se(IV) with an aromatic diamine, namely 4-nitro-1,2-phenylenediamine, in acidic medium. Samples were digested in a nitric acid/hydrogen peroxide open system, followed by selenate reduction in hydrochloric acid. Reaction conditions were optimized in terms of pH, temperature, reaction time, and other auxiliary reagents for interference removal, namely, EDTA and hydroxylamine. For the extraction of the selectively formed 4-nitro-piazselenol, micro-solid-phase extraction (μSPE) was applied, and the analysis and detection of the corresponding complex was performed by HPLC coupled with DAD. An external standard calibration curve was developed (R² = 0.9994) with good sensitivity, and was used to calculate the total selenium content from several Allium plants material, with good intermediate precision (RSD% < 16%). The accuracy of the method was evaluated using both, a comparison with an accepted reference method from our previously published data, as well as three certified reference material with recoveries between 84-126%. The limit of detection was determined to be 0.35 μg/g (in solids) and 1.1 μg/L (in solution), while the limit of quantification was 1.07 μg/g and 3.4 μg/L (in solution). Using the proposed method, selenium content can be quickly and accurately determined in several types of samples. In addition, this study present experimental conditions for overcoming the interferences that might be encountered in selenium determination using piazselenol.

Prenatal Maternal Low Selenium, High Thyrotropin, and Low Birth Weights

In consideration of the potential roles of selenoproteins in thyroid function, we aimed to evaluate the association of low selenium status with hypothyroidism during pregnancy and the association of maternal low thyroid function with infant birth size. We conducted a prospective birth cohort study in Shanghai in 2010 and investigated 1931 pregnant mothers of gestational weeks 28-36. Maternal serum selenium and thyrotropin (TSH) levels were determined and birth weights and lengths of newborns were measured. Other covariates were obtained through maternal interviews and medical records. A non-linear association was observed between maternal selenium and TSH levels. Two-piecewise multivariable linear regression models were therefore applied to assess the association of serum selenium with TSH levels, and multivariable linear regression models were applied to assess the association of TSH levels with birth weight/length. Adjusting for potential confounders, when maternal serum selenium levels < 103.7 μg/L (P25th), each unit increase in selenium levels (μg/L) was significantly associated with a decrease of 0.014 μIU/mL in TSH levels (β = - 0.014, 95%CI - 0.025, - 0.002, P = 0.023). However, when selenium levels ≥ 103.7 μg/L, there were no significant relationships between selenium and TSH (β = 0.000, 95%CI - 0.001, 0.002, P = 0.859). Maternal TSH levels were significantly inversely associated with infant birth weight (β = - 0.060, 95%CI - 0.100, - 0.010, P = 0.010). We observed a non-linear association between maternal selenium status and TSH levels. Low selenium status during pregnancy may associate with low thyroid function that was related with low birth weights. Graphical abstract .

Organic selenium supplement partially alleviated diquat-induced oxidative insults and hepatic metabolic stress in nursery pigs

The study investigated antioxidant effects of Se on resilience to diquat-induced oxidative stress in nursery pigs. Thirty-five weaned pigs were individually housed and randomly assigned to one of the five treatments. Pigs were (1) fed a basal diet and intraperitoneally injected with sterile saline (negative control), (2) fed the basal diet and injected with diquat solution (positive control, PC), or fed the basal diet supplemented with 0·3 mg Se/kg as (3) sodium selenite (SS), (4) soyabean protein-chelated Se (SC) or (5) selenised yeast (SY) and intraperitoneally injected with diquat. Pigs were fed the experimental diets for 17 d and injected with diquat at 10 mg/kg body weight or saline on the 11th day of the study (day 0 post-injection (PI)). Diquat exposure induced acute stress and innate immune activation (P < 0·05) at 6 h PI and compromised (P < 0·05) plasma glutathione peroxidase activity on day 2 PI, which was accompanied by an increase in plasma malondialdehyde at 6 h and day 2 PI (P < 0·10). Organic Se, particularly SY, enhanced (P < 0·05) endogenous antioxidant activity in various aspects compared with the PC group. The growth rate and feed intake from day 0 to day 7 PI were significantly lower in the PC, SS and SC groups than the NC group (P < 0·05). Untargeted metabolomics analysis revealed that twenty-two hepatic metabolites (false discovery rate < 0·15) associated with lipid and cellular antioxidant metabolism were altered by diquat. SY restored hepatic metabolic profiles in some but not all samples.

Association of circulating selenium concentration with dyslipidemia: Results from the NHANES

BACKGROUND

Observational studies have suggested that selenium levels might associate with the risk of cardio-metabolic diseases, but how circulating selenium is related to dyslipidemia remains inconclusive.

OBJECTIVES

To investigate the association of circulating selenium levels with lipid profiles and dyslipidemia among US adults.

METHODS

Using the data collected from the National Health and Nutrition Examination Survey (NHANES 1999-2006), we performed multivariate logistic regression to examine the association of circulating selenium levels (in quartiles) with total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), non-HDL-C, and atherogenic index (AI).

RESULTS

We included 2903 adults (49.3 % male) (average age: 61.9) for analysis. Circulating selenium had non-linear association with TC, LDL-C, HDL-C, and AI (all p < 0.05). When comparing with the lowest quartile, subjects with the highest quartile of circulating selenium (>147.00 μg/L) had the higher odds of elevated TG (OR: 1.75, 95% CI = 1.14, 2.68), TC (OR: 2.47, 95% CI = 1.62, 3.76), LDL-C (OR: 2.52, 95% CI = 1.60, 3.96), non-HDL-C (OR: 2.17, 95% CI = 1.41, 3.33), AI (OR: 1.20, 95% CI = 0.73, 1.97) and low-HDL-C (OR: 2.10, 95% CI = 1.19, 3.72). Similar patterns were observed in subgroup analysis.

CONCLUSIONS

Higher circulating selenium levels had non-linear association with lipid profiles and the increased odds of dyslipidemia.

Screening and evaluating of long non-coding RNAs in prenatal and postnatal pituitary gland of sheep

Long non-coding RNAs are transcribed into RNA molecules that are >200 nucleotides in length. However, the expression and function analysis of lncRNAs in the sheep pituitary gland are still lacking. In this study, we identified 1755 lncRNAs (545 annotated lncRNAs and 1210 novel lncRNAs) from RNA-seq data in the pituitary gland of embryonic and adult sheep. A total of 235 lncRNAs were differentially expressed between embryonic and adult group. We verified the presence of some lncRNAs using RT-PCR and DNA sequencing, and identified some differentially expressed lncRNAs using qPCR. We also investigated the role of cis-acting lncRNAs on target genes. GO and KEGG enrichment analysis revealed that the target genes of lncRNAs were involved in the regulation of hormones secretion and some signaling pathways in the sheep pituitary gland. Our study provides comprehensive expression profiles of lncRNAs and valuable resource for understanding their function in the pituitary gland.

Is selenium supplementation in autoimmune thyroid diseases justified?

PURPOSE OF REVIEW

This review provides an appraisal of recent evidence for or against selenium supplementation in patients with autoimmune thyroid diseases, and discusses possible effect mechanisms.

RECENT FINDINGS

Epidemiological data suggest an increased prevalence of autoimmune thyroid diseases under conditions of low dietary selenium intake. Two systematic reviews have evaluated controlled trials among patients with autoimmune thyroiditis and report that selenium supplementation decreases circulating thyroid autoantibodies. The immunomodulatory effects of selenium might involve reducing proinflammatory cytokine release. However, clinically relevant effects of selenium supplementation, including improvement in quality of life, are more elusive. In Graves' disease, some, but not all, trials indicate that adjuvant selenium supplementation enhances the restoration of biochemical euthyroidism, and might benefit patients with mild Graves' orbitopathy.

SUMMARY

The use of selenium supplementation as adjuvant therapy to standard thyroid medication may be widespread, but a growing body of evidence yields equivocal results. The available evidence from trials does not support routine selenium supplementation in the standard treatment of patients with autoimmune thyroiditis or Graves' disease. However, correction of moderate to severe selenium deficiency may offer benefits in preventing, as well as treating, these disorders. Molecular mechanisms have been proposed, but further studies are needed.

Selenium Enrichment of Horticultural Crops

The ability of some crops to accumulate selenium (Se) is crucial for human nutrition and health. Selenium has been identified as a cofactor of the enzyme glutathione peroxidase, which is a catalyzer in the reduction of peroxides that can damage cells and tissues, and can act as an antioxidant. Plants are the first link in the food chain, which ends with humans. Increasing the Se quantity in plant products, including leafy and fruity vegetables, and fruit crops, without exceeding the toxic threshold, is thus a good way to increase animal and human Se intake, with positive effects on long-term health. In many Se-enriched plants, most Se is in its major organic form. Given that this form is more available to humans and more efficient in increasing the selenium content than inorganic forms, the consumption of Se-enriched plants appears to be beneficial. An antioxidant effect of Se has been detected in Se-enriched vegetables and fruit crops due to an improved antioxidative status and to a reduced biosynthesis of ethylene, which is the hormone with a primary role in plant senescence and fruit ripening. This thus highlights the possible positive effect of Se in preserving a longer shelf-life and longer-lasting quality.

Systematic review and meta-analysis shows a specific micronutrient profile in people with Down Syndrome: Lower blood calcium, selenium and zinc, higher red blood cell copper and zinc, and higher salivary calcium and sodium

Different metabolic profiles as well as comorbidities are common in people with Down Syndrome (DS). Therefore it is relevant to know whether micronutrient levels in people with DS are also different. This systematic review was designed to review the literature on micronutrient levels in people with DS compared to age and sex-matched controls without DS. We identified sixty nine studies from January 1967 to April 2016 through main electronic medical databases PubMed, Scopus, and Web of knowledge. We carried out meta-analysis of the data on four essential trace elements (Cu, Fe, Se, and Zn), six minerals (Ca, Cl, K, Mg, Na, and P), and five vitamins (vitamin A, B9, B12, D, and E). People with DS showed lower blood levels of Ca (standard mean difference (SMD) = -0.63; 95% confidence interval (CI): -1.16 to -0.09), Se (SMD = -0.99; 95% CI: -1.55 to -0.43), and Zn (SMD = -1.30; 95% CI: -1.75 to -0.84), while red cell levels of Zn (SMD = 1.88; 95% CI: 0.48 to 3.28) and Cu (SMD = 2.77; 95% CI: 1.96 to 3.57) were higher. They had also higher salivary levels of Ca (SMD = 0.85; 95% CI: 0.38 to 1.33) and Na (SMD = 1.04; 95% CI: 0.39 to 1.69). Our findings that micronutrient levels are different in people with DS raise the question whether these differences are related to the different metabolic profiles, the common comorbidities or merely reflect DS.

Does selenium supplementation affect thyroid function? Results from a randomized, controlled, double-blinded trial in a Danish population

OBJECTIVE

Selenium is present in the active site of proteins important for thyroid hormone synthesis and metabolism. The objective of this study is to investigate the effect of selenium supplementation in different doses on thyroid function, under conditions of suboptimal dietary selenium intake.

DESIGN

The Danish PREvention of Cancer by Intervention with SElenium pilot study (DK-PRECISE) is a randomized, double-blinded, placebo-controlled trial. A total of 491 males and females aged 60-74 years were randomized to 100 μg (n=124), 200 μg (n=122), or 300 μg (n=119) selenium-enriched yeast or matching yeast-based placebo tablets (n=126). A total of 361 participants, equally distributed across treatment groups, completed the 5-year intervention period.

METHODS

Plasma samples were analyzed for selenium and serum samples for TSH, free triiodothyronine (FT3), and free thyroxine (FT4) at baseline, and after 6 months, and 5 years of supplementation.

RESULTS

Plasma selenium concentrations increased significantly and dose-dependently in treatment groups receiving selenium (P<0.001). Serum TSH and FT4 concentrations decreased significantly and dose-dependently by 0.066 mIU/l (P=0.010) and 0.11 pmol/l (P=0.015), respectively, per 100 μg/day increase, with insignificant differences between 6 months and 5 years. No significant effects were found for FT3 and FT3:FT4 ratio.

CONCLUSIONS

In euthyroid subjects, selenium supplementation minutely and dose-dependently affects thyroid function, when compared with placebo, by decreasing serum TSH and FT4 concentrations. Based on these findings, selenium supplementation is not warranted under conditions of marginal selenium deficiency. However, a role for selenium supplementation in the treatment of autoimmune thyroid diseases is still unresolved.

Selenium as a feed supplement for heat-stressed poultry: a review

Heat stress is associated with compromised performance and productivity in poultry due to declines in feed intake, nutrient utilization, growth rate, egg production and quality, and feed efficiency. Emerging evidences have shown that acute heat exposure results in increased production of free radicals and causes oxidative damage to lipids, proteins, and DNA. Additionally, heat stress can influence immune response by changing the expression of cytokines and by making the immune cells more susceptible to oxidative stress. Selenium, as a part of specific selenoproteins, can help to maintain antioxidant defenses, thereby preventing damages to tissues. An optimum response with supplementation of selenium in diet has been found to improve feed intake, body weight gain, feed efficiency, egg production and quality, and antioxidant status in heat-stressed poultry. Selenium compounds are also known to improve immune responses by altering the production of certain cytokines secreted by cells of the immune system and by enhancing the resistance of the immune cells to oxidative stress. It was reported that selenium supplementation had inhibitory effects on tumor necrosis factor alpha levels in heat-stressed broiler chicks, but the details are not completely elucidated. In the present review, the effect of selenium on production performance, nutrient utilization, antioxidative status, and immune responses of heat-stressed poultry is summarized.

Roles of selenoprotein antioxidant protection in zebrafish, Danio rerio, subjected to dietary oxidative stress

In vertebrates, selenium (Se) is an essential micronutrient for vertebrates that is involved in antioxidant protection and thyroid hormone regulation among other roles and functions through its incorporation into proteins, the selenoproteins. Long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA), are essential nutrients for fish although high dietary levels may lead to increased oxidative stress due to the high degree of unsaturation. The present study investigated the effects of Se supplementation on zebrafish, Danio rerio, oxidative status together with selenoprotein expression profiles when subjected to a high-DHA diet. Fish were fed for 8 weeks with one of the four experimental diets, containing high or low DHA in combination with or without organic Se (7 mg/kg). Fish performance, Se content, fatty acid composition and TBARS of zebrafish were determined, as well as gene expression of selected selenoproteins in liver and muscle. The Se levels in whole fish reflected dietary content. High dietary DHA increased oxidative stress as indicated by reduced growth and high TBARS content, although Se supplementation reduced oxidation. The expression patterns of selenoproteins varied between liver and muscle with only deiodinase type II displaying a transcriptional response when high dietary Se was supplied. High dietary DHA decreased selenoprotein W expression in muscle and sps2 expression in liver regardless of the dietary Se content. These data suggest that oxidative stress protection associated with a high dietary intake of Se may not be solely mediated by transcriptional changes in teleost selenoprotein expression.

Role of selenium in male reproduction - a review

The role of Se and various selenoproteins in male reproductive performance is reviewed. Development of male reproductive tissue requires an optimal level of Se in testis, and a small deviation, either deficiency or excess, leads to abnormal development. Selenium is a constituent of selenoproteins including GPx1, GPx3, mGPx4, cGPx4, and GPx5 that protect against oxidative damage to spermatozoa throughout the process of sperm maturation, whereas selenoproteins, such as mGPx4 and snGPx4, serve as structural components of mature spermatozoa. Thus Se and selenoproteins ensure viability of spermatozoa as well as providing protection against reactive oxygen species. Gene knock-out studies of selenoproteins revealed that their absence during spermatogenesis results in abnormal spermatozoa, which in turn affects semen quality and fertility. Deviation from the optimal quantities of dietary Se, both above or below, may cause multiple abnormalities of spermatozoa and affect motility and fertility. Libido may also be increased by Se. Dietary Se should be in optimal quantity to maintain reproductive function in males and to avoid infertility.

Selenium supplementation for sepsis: a meta-analysis of randomized controlled trials

BACKGROUND

Recently, several studies were conducted to investigate the effect of selenium supplementation in septic patients. However, no consistent conclusion was made. Thus, we aimed to systematically summarize the available randomized controlled trials (RCTs) to evaluate the effect of selenium supplementation on important clinical outcomes in septic patients.

METHODS

A systematic literature search of Pubmed, Embase, and the Cochrane Central Register of Controlled Trials was conducted (up to August 25, 2012). RCTs were included if they reported the effect of selenium supplementation on the treatment of septic patients. A fixed-effect model was used, and in the case of significant heterogeneity, a random-effects model was employed.

RESULTS

Five studies with a total of 530 patients were included. Pooled analysis showed that selenium supplementation did not reduce all-cause mortality (relative risk [RR] = 0.89, 95% confidence interval [CI]: 0.73-1.07, P = .21), hospital-acquired pneumonia (RR = 1.15, 95% CI: 0.73-1.82, P = .55), or length of intensive care unit stay (weighted mean differences = 2.32 days, 95% CI: -0.05 to 4.69; P = .05). In addition, no significant difference was observed regarding adverse events between groups (RR = 0.97, 95% CI: 0.72-1.33, P = .87).

CONCLUSIONS

The present meta-analysis showed no benefit of selenium supplementation in patients with sepsis. Due to the limited number of RCTs included, more prospective multicenter clinical trials on selenium therapy in septic patients are warranted in the future.

Effect of mineral mixture and antioxidant supplementation on growth, reproductive performance and adaptive capability of Malpura ewes subjected to heat stress

This study was conducted to evaluate the effect of mineral and antioxidant supplementation on growth, reproductive performance and physiological adaptability of heat-stressed Malpura ewes. The study was conducted for a period of 21 days in 21 adult Malpura ewes. The ewes were randomly divided into three groups with seven animals each viz. GI (control; n = 7), GII (heat stress; n = 7) and GIII (heat stress + mineral and antioxidant supplementation; n = 7). The animals were stall fed ad libitum with the diet consisting of 70% roughage and 30% concentrate. GI ewes were maintained under normal controlled condition in the shed, while GII and GIII ewes were subjected to heat stress by exposing them to 42 °C in the climatic chamber. The parameters studied were feed intake (FI), water intake (WI), body weight, body condition score (BCS), physiological, biochemical and endocrine responses. Heat stress significantly altered FI, water intake, BCS, respiration rate and rectal temperature in the afternoon, oestrus duration, estradiol, progesterone, Hb, PCV, plasma glucose, total protein, cortisol, T3 and T4 levels while mineral and antioxidant supplementation ameliorated this heat stress effect on the parameters studied. Further, the adverse effect of heat stress on the productive and reproductive efficiency of Malpura ewes was reduced considerably by mineral mixture and antioxidant supplementation. This is evident from the non-significant difference in BCS, oestrus duration and plasma estradiol between GI and GIII in this study. Hence, it is very pertinent to conclude from this study that mineral mixture and antioxidant supplementation were able to protect Malpura ewes against heat stress.

Investigation of glutathione peroxidase activity in chicken meat under different experimental conditions

Due to the fact that previous studies on the enzymatic activity of Glutathione peroxidase (GSH-Px) diverge widely in their methodology and results, this study aimed to investigate the influence of different analytical conditions on GSH-Px activity in chicken thighs from broilers that were fed different diets with different sources and concentrations of selenium. GSH-Px activity was evaluated six hours after slaughter and 120 days after frozen storage at -18 ºC. The different analytical conditions included time of pre-incubation (0, 10 and 30 minutes), reaction medium, types of substrate (H2O2 (0.72 mM, 7.2 mM, and 72 mM) and Terc-butil hydroperoxide 15 mM), and different buffer concentrations (buffer 1, potassium phosphate 50 mM pH 7.0 + EDTA 1 mM + mercaptoethanol 1 mM, and buffer 2, tris-HCl 50 mM pH 7.6 + EDTA 1 mM + mercapthanol 5 mM). The results show that the highest GSH-Px activity was observed when enzyme and substrate were in contact at 22 ºC without any pre-incubation, and that, when used at concentrations above 0.72 mM, hydrogen peroxide saturated the GSH-Px enzyme and inhibited its activity. The enzyme presented higher affinity to hydrogen peroxide when compared to terc-butil peroxide, and the addition of a buffer containing mercaptoethanol did not increase GSH-Px enzymatic activity. The activity of GSH-Px was not influenced by the source and concentration of selenium in the diet either. The obtained results allowed the determination of the best temperature of contact between the enzyme and substrate (22 ºC), the optimum concentration, and the type of substrate and buffer to be used. This information is extremely useful for future studies on GSH-Px activity in meat due to the divergence and little information found in the literature.

Supplemental selenium alleviates the toxic effects of excessive iodine on thyroid

As excessive iodine intake is associated with a decrease of the activities of selenocysteine-containing enzymes, supplemental selenium was hypothesized to alleviate the toxic effects of excessive iodine. In order to verify this hypothesis, Balb/C mice were tested by giving tap water with or without potassium iodate and/or sodium selenite for 16 weeks, and the levels of iodine in urine and thyroid, the hepatic selenium level, the activities of glutathione peroxidase (GSHPx), type 1 deiodinase (D1), and thyroid peroxidase (TPO) were assayed. It had been observed in excessive iodine group that hepatic selenium, the activities of GSHPx, D1, and TPO decreased, while in the groups of 0.2 mg/L, 0.3 mg/L and 0.4 mg/L supplemental selenium, the urinary iodine increased significantly. Compared with the group of excessive iodine intake alone, supplemental selenium groups had higher activities of GSHPx, D1, and TPO. We could draw the conclusion that supplemental selenium could alleviate toxic effect of excessive iodine on thyroid. The optimal dosage of selenium ranges from 0.2 to 0.3 mg/L which can protect against thyroid hormone dysfunction induced by excessive iodine intake.

Effect of zinc supplementation on the status of thyroid hormones and Na, K, And Ca levels in blood following ethanol feeding

The influence of zinc (Zn) on the serum levels of triiodothyronine (T(3)), thyroxine (T(4)), thyroid-stimulating hormone (TSH) and sodium (Na), potassium (K), and calcium (Ca) was evaluated following ethanol toxicity to the rats. To achieve this, male Wistar rats (150-195 g) were given 3 ml of 30% ethanol orally, and zinc was given in the form of zinc sulfate (227 mg/l) in their drinking water daily for 8 weeks. Ethanol feeding resulted in a slight decrease in T(3) and T(4) levels and a significant increase in thyroid-stimulating hormone concentration, which may be due to the direct stimulatory effect of ethanol on thyroid. Interestingly, when zinc was given to these rats, all the above levels were brought quite close to their normal levels, thus indicating the positive role of zinc in thyroid hormone metabolism. Serum Zn and Ca levels were found to be reduced, but Na levels were raised upon ethanol feeding. Restoration of normal levels of these metals upon zinc supplementation to ethanol fed rats confirms that zinc has potential in alleviating some of the altered thyroid functions following ethanol administration.

Selenium bioavailability: current knowledge and future research requirements

Information on selenium bioavailability is required to derive dietary recommendations and to evaluate and improve the quality of food products. The need for robust data is particularly important in light of recent suggestions of potential health benefits associated with different intakes of selenium. The issue is not straightforward, however, because of large variations in the selenium content of foods (determined by a combination of geologic/environmental factors and selenium supplementation of fertilizers and animal feedstuffs) and the chemical forms of the element, which are absorbed and metabolized differently. Although most dietary selenium is absorbed efficiently, the retention of organic forms is higher than that of inorganic forms. There are also complications in the assessment and quantification of selenium species within foodstuffs. Often, extraction is only partial, and the process can alter the form or forms present in the food. Efforts to improve, standardize, and make more widely available techniques for species quantification are required. Similarly, reliable and sensitive functional biomarkers of selenium status are required, together with improvements in current biomarker methods. This requirement is particularly important for the assessment of bioavailability, because some functional biomarkers respond differently to the various selenium species. The effect of genotype adds a potential further dimension to the process of deriving bioavailability estimates and underlines the need for further research to facilitate the process of deriving dietary recommendations in the future.

Identification of a novel selenium-containing compound, selenoneine, as the predominant chemical form of organic selenium in the blood of bluefin tuna

A novel selenium-containing compound having a selenium atom in the imidazole ring, 2-selenyl-N(alpha),N(alpha),N(alpha)-trimethyl-L-histidine, 3-(2-hydroseleno-1H-imidazol-5-yl)-2-(trimethylammonio)propanoate, was identified from the blood and other tissues of the bluefin tuna, Thunnus orientalis. The selenium-containing compound was purified from the tuna blood in several chromatographic steps. High resolution mass spectrometry and nuclear magnetic resonance spectroscopy showed that the exact mass of the [M+H](+) ion of the compound was 533.0562 and the molecular formula was C(18)H(29)N(6)O(4)Se(2). Its gross structure was assigned as the oxidized dimeric form of an ergothioneine selenium analog in which the sulfur of ergothioneine is replaced by selenium. Therefore, we named this novel selenium-containing compound "selenoneine." By speciation analysis of organic selenium compounds using liquid chromatography inductively coupled plasma mass spectrometry, selenoneine was found widely distributed in various tissues of the tuna, with the highest concentration in blood; mackerel blood contained similar levels. Selenoneine was measurable at 2-4 orders of magnitude lower concentration in a limited set of tissues from squid, tilapia, pig, and chicken. Quantitatively, selenoneine is the predominant form of organic selenium in tuna tissues.

Assessment of serum thyroid hormone concentrations in lambs with selenium deficiency myopathy

OBJECTIVE

To assess changes in serum concentrations of thyroid hormones associated with selenium deficiency myopathy in lambs.

ANIMALS

35 lambs with selenium deficiency myopathy and 30 healthy lambs.

PROCEDURES

Blood samples were collected via jugular venipuncture from lambs with selenium deficiency myopathy and healthy lambs. Activities of markers of selenium deficiency myopathy (erythrocyte glutathione peroxidase [GSH-Px] and plasma creatine kinase [CK]) and serum thyroid-stimulating hormone (TSH) and total thyroxine (tT(4)) and total triiodothyronine (tT(3)) concentrations were assessed; values in affected lambs were compared with those in healthy lambs. Correlations of erythrocyte GSH-Px and plasma CK activities with serum concentrations of TSH, tT(4), and tT(3) were investigated, and the tT(3):tT(4) concentration ratio was evaluated.

RESULTS

Compared with findings in healthy lambs, erythrocyte GSH-Px activity, serum tT(3) concentration, and tT(3):tT(4) concentration ratio were significantly decreased and serum concentrations of tT(4) and TSH and the activity of plasma CK were significantly increased in affected lambs. Analysis revealed a significant negative correlation in the affected group between erythrocyte GSH-Px activity and each of the following: plasma CK activity (r = -0.443), serum TSH concentration (r = -0.599), serum tT(4) concentration (r = -0.577), and serum tT(3) concentration (r = -0.621).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that notable changes in circulating amounts of thyroid hormones develop in association with selenium deficiency in lambs. Such alterations in thyroid hormone metabolism may be involved in the high incidence of disorders, such as stillbirths and neonatal deaths, in selenium-deficient flocks.

Paliperidone as a mood stabilizer: a pre-frontal cortex synaptoneurosomal proteomics comparison with lithium and valproic acid after chronic treatment reveals similarities in protein expression

A series of recent studies has demonstrated that the molecules involved in regulation of neuronal plasticity are also involved in the mode of action of antidepressants and mood stabilizer drugs. Intracellular calcium signaling, energy metabolism, and neuronal plasticity can be influenced by inducing axonal remodeling and increasing levels of certain synaptic proteins. Because antipsychotic drugs are used as mood stabilizers our studies focused on a newly-marketed antipsychotic drug, paliperidone. We determined changes in rat synaptoneurosomal proteins after chronic treatment with paliperidone, lithium salt, or valproic acid in order to find similarities or differences between the mode of action of paliperidone and these two classical mood stabilizers. We determined differential protein expression profiles in prefrontal cortex (PFC) of male Sprague-Dawley rats (n = 4/group). Synaptoneurosomal-enriched preparations were obtained from PFC after chronic treatment with these three drugs. Proteins were separated by 2D-DIGE and identified by nano-LC-MS/MS. We observed similar protein expression profiles at the synaptoneurosomal level, suggesting that the mode of action for paliperidone is similar to that of lithium and valproic acid. However, the expression profile for paliperidone was more similar to that of lithium. Pathways affected in common by these two drugs included oxidative phosphorylation, electron transport, carbohydrate metabolism, and post-synaptic cytokinesis implicating the effects of these drugs in signaling pathways, energy metabolism, and synaptic plasticity.

Associations of blood selenium and serum lipid levels in Japanese premenopausal and postmenopausal women

OBJECTIVE

The purpose of this study was to investigate whether the level of selenium in serum or the level of selenium in erythrocytes (E-Se) was associated with serum lipid parameters (total cholesterol [TC], triglycerides, and high-density and low-density lipoprotein cholesterol [LDL-C]) in pre- and postmenopausal women.

DESIGN

Healthy female workers aged 35 to 60 years were recruited, and TC, triglycerides, high-density lipoprotein cholesterol, LDL-C, E-Se, and serum-Se levels were measured in 68 premenopausal and 59 postmenopausal women after excluding those who were treated for hyperlipidemia, receiving hormone therapy, had previous gynecological surgeries, or had irregular menstrual cycles. Information on these women, such as smoking status, current status of menstruation, and current or previous medical treatments, was obtained from a self-administered questionnaire. Correlation analyses and stepwise multiple regression analysis were applied to reveal the interrelationship between serum lipids and Se levels after adjusting for age, body mass index, smoking, and menopause status.

RESULTS

Postmenopausal women had significantly higher levels of TC, triglycerides, and LDL-C and lower levels of E-Se than premenopausal women. TC and LDL-C levels after menopause correlated negatively with E-Se. These associations were also statistically significant after controlling for age, smoking status, and body mass index. E-Se was selected as a significant related variable to explain TC and LDL-C levels as well as body mass index by multiple regression analysis.

CONCLUSION

E-Se may be one of the possible associated factors that decrease the levels of TC and LDL-C after menopause. Further studies are needed to clarify the cause-and-effect relationship of nutritional Se status and lipid profile.

Effect of Iodine Status and other Nutritional Factors on Psychomotor and Cognitive Performance of Filipino Schoolchildren

Background

Until 1998, iodine deficiency was a public health problem in the Philippines. A law entitled “An Act Promoting Salt Iodization Nationwide” (ASIN) has been passed and implemented by the government to eliminate iodine deficiency. The contribution of salt iodization, as well as dietary, health, and environmental factors, to improving the intellectual performance of Filipino schoolchildren remains to be determined.

Objective

The objectives of the study were to determine the relationship between iodine status and levels of psychomotor and cognitive performance in first-grade children aged 6 to 10 years, and to examine the extent to which dietary, biochemical, health, and environmental factors contribute to children's mental performance.

Methods

Two hundred ninety children in six classroom sections from a public school in Manila were examined by measurement of urinary iodine excretion (UIE) and thyroid palpation. The median UIE level for each section was determined. Sixty-five children classified as iodine deficient (UIE < 90 μg/L with grade 1 goiter, n = 34) and non-iodine deficient (UIE > 100 μg/L without goiter, n = 31) were given psychomotor and cognitive function tests (Bender–Gestalt and Raven's Colored Progressive Matrices). Scores from the two tests were used to determine each child's general ability percentile rank. Other variables examined were dietary intake (% RDA of nutrients ingested based on two nonconsecutive 24-hour recalls); deficiencies in iron, vitamin A, and selenium; parasitic infection; coliform contamination of drinking water; household use of iodized salt; illness in the past 2 weeks; and wasting and stunting.

Results

Children whose general ability scores were at or above the 50th percentile had higher UIE levels, but the relationship was not significant. Children from sections with higher median UIE levels had higher percentile ranks for general ability (p =.002). Backward logistic regression showed that the variance in deficient and adequate mental performance was explained by dietary intakes that met ≥ 80% of the RDA for energy, protein, thiamin, and riboflavin; the use of iodized salt; child's iodine status; and stunting (R2 =.520, p =.0016). Higher class median UIE was associated with better psychomotor and cognitive performance in children who were tested. Factors that contributed to better performance include higher intakes of energy, protein, thiamin, and riboflavin; household use of iodized salt; normal iodine status; and absence of stunting or chronic malnutrition.

Conclusions

Salt iodization, accompanied by adequate intakes of energy, protein, and foods rich in thiamin and riboflavin, can contribute to improved mental performance in Filipino schoolchildren. Longer-term factors that can contribute to improved performance are achievement of normal iodine status and elimination of protein–energy malnutrition.

Selenium in global food systems

Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 μg/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 μg/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Se-containing enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

Selenium influences growth via thyroid hormone status in broiler chickens

As there is a possibility that Se influences the growth of animals via thyroid hormone metabolism, the following three experiments were undertaken in order to determine the effects of dietary Se on growth, skeletal muscle protein turnover and thyroid hormone status in broiler chickens. Broiler chickens were raised on a Se-deficient diet until 12 d of age and then used for the experiments. In Experiment 1, twenty-eight birds were randomly assigned to four groups and fed purified diets with the following amounts of Se supplementation: 0·0, 0·1, 0·3 and 0·5 mg Se/kg diet. Dietary Se supplementation significantly increased plasma 3,5,3′-triiodothyronine (T3) concentration and improved growth, while plasma thyroxine (T4) concentration was decreased. In Experiment 2, twenty-eight birds were assigned to four groups and fed either a Se-deficient diet or a Se-supplemented diet (0·3 mg Se/kg diet) with or without the supplementation of iopanoic acid, a specific inhibitor of 5′-deiodinase (5 mg/kg diet). The growth was promoted and feed efficiency was improved by dietary Se supplementation as was also observed in Experiment 1. However, this effect of Se was halted by iopanoic acid supplementation. Hepatic 5′-deiodinase activity was elevated by Se and inhibited by iopanoic acid. In Experiment 3, birds were fed on the following diets to show that Se influences growth of birds via thyroid hormone metabolism: Se-deficient diet, Se-supplemented diets (0·1 and 0·3 mg/kg) and T3 supplemented diets (0·1 and 0·3 mg/kg diet). Lower dietary T3 supplementation (0·1 mg/kg diet) resulted in growth promotion similar to Se supplementation, while higher level of T3 caused growth depression. Furthermore, it was observed that the rate of skeletal muscle protein breakdown tended to be increased by Se similarly to the effect of T3. In conclusion, it was shown in the present study that Se deficiency depresses growth of broilers by inhibiting hepatic 5′-deiodinase activity which causes lower plasma T3 concentration.

Selenium status in Southern Tasmania

OBJECTIVE

To assess the selenium status of Southern Tasmanians.

DESIGN

Cross-sectional.

SETTINGS

One thousand and five hundred adults randomly selected from the electoral roll living in the Greater Hobart region of Southern Tasmania, Australia, were invited to participate.

SUBJECTS

The overall response rate was 22% (335/1500).

INTERVENTIONS

A venous blood sample was collected and a questionnaire administered (consisting of brief demographic details and health questions) to subjects who granted informed consent. A previously validated assay using magnetic sector ICP-MS was employed for plasma analysis.

RESULTS

Total plasma selenium levels for this sample population were normally distributed with a mean level of 110 microg/l (range 67-268 microg/l) indicating that the majority of the subjects were not selenium-depleted (71% with levels greater than 100 microg/l). Adjustment for differential age/gender response rates produced similar values. More women under 50 (42%) and men over 50 (32%) had selenium levels <100 microg/l with the potential for sub-optimal selenoprotein activity. Low education attainment was associated with low total selenium level (P<0.02).

CONCLUSIONS

The majority of participants were not deficient in selenium. Given the narrow therapeutic window of supplementation, dietary advice to increase foods rich in selenium, particularly to higher risk groups, may be an effective means of increasing plasma selenium toward target levels.

Attenuation of LDL receptor gene expression by selenium deficiency during hypercholesterolemia

Selenium deficiency has been associated with hypercholesterolemia. Present study was aimed to determine the effect of selenium (Se) deficiency on LDL receptor (LDL-R) activity as well as mRNA expression during experimental hypercholesterolemia in SD male rats. Animals were fed Se adequate (0.2 ppm) and deficient (0.02 ppm) control diet as well as high cholesterol (2%) diet (HCD) for 1 and 2 months. LDL-R activity was measured in vivo by injecting radiolabeled LDL to rats and percent decrease in cpm with time was taken as a measure of LDL clearance and in turn LDL-R activity. LDL-R mRNA expression was studied by RT-PCR. LDL-R activity and mRNA expression decreased significantly on HCD feeding in both Se deficient and adequate diet fed rats after 2 months. In Se deficiency receptor activity and mRNA expression decreased significantly. After 2 months LDL-R activity and expression decreased in both the Se deficient groups and in Se adequate HCD fed group in comparison to 1 month data. But after 4 month there was no significant difference observed in LDL-R activity and mRNA expression in selenium deficiency as well as on HCD feeding. So the present results demonstrate that Se deficiency act synergistically with hypercholesterolemia to downregulate LDL-R activity as well as mRNA expression.

Hypercholesterolemia and apolipoprotein B expression: regulation by selenium status

BACKGROUND

Apolipoprotein B (apoB) contains ligand-binding domain for the binding of LDL to LDL-R site, which enables the removal of LDL from circulation. Our recent data showed that selenium (Se) is involved in the lipid metabolism. The present study was aimed to understand the effect of Se deficiency (0.02 ppm) and selenium supplementation (1 ppm) on apoB expression in liver during hypercholesterolemia in male Sprague Dawley rats. Animals were fed with control and high cholesterol diet (2%) for 1 and 2 months. ApoB levels by ELISA and protein expression by western blot was done. Hepatic LDL receptor (LDL-R) activity (in vivo) and mRNA expression by RT-PCR was monitored.

RESULTS

In selenium deficiency and on high cholesterol diet (HCD) feeding apoB levels increased and LDL-R expression decreased significantly after 2 months. On 1 ppm selenium supplementation apoB expression significantly decreased and LDL-R expression increased after 2 months. But after one month of treatment there was no significant change observed in apoB and LDL-R expression.

CONCLUSION

So the present study demonstrates that Se deficiency leads to up regulation of apoB expression during experimental hypercholesterolemia. Selenium supplementation upto 1 ppm leads to downregulation of apoB expression. Further, this study will highlight the nutritional value of Se supplementation in lipid metabolism.

Selenium and the control of thyroid hormone metabolism

Thyroid hormone synthesis, metabolism and action require adequate availability of the essential trace elements iodine and selenium, which affect homeostasis of thyroid hormone-dependent metabolic pathways. The three selenocysteine-containing iodothyronine deiodinases constitute a novel gene family. Selenium is retained and deiodinase expression is maintained at almost normal levels in the thyroid gland, the brain and several other endocrine tissues during selenium deficiency, thus guaranteeing adequate local and systemic levels of the active thyroid hormone T(3). Due to their low tissue concentrations and their mRNA SECIS elements deiodinases rank high in the cellular and tissue-specific hierarchy of selenium distribution among various selenoproteins. While systemic selenium status and expression of abundant selenoproteins (glutathione peroxidase or selenoprotein P) is already impaired in patients with cancer, disturbed gastrointestinal resorption, unbalanced nutrition or patients requiring intensive care treatment, selenium-dependent deiodinase function might still be adequate. However, disease-associated alterations in proinflammatory cytokines, growth factors, hormones and pharmaceuticals modulate deiodinase isoenzyme expression independent from altered selenium status and might thus pretend causal relationships between systemic selenium status and altered thyroid hormone metabolism. Limited or inadequate supply of both trace elements, iodine and selenium, leads to complex rearrangements of thyroid hormone metabolism enabling adaptation to unfavorable conditions.

Effect of grazing pasture with a low selenium content on the concentrations of triiodothyronine and thyroxine in serum, and GSH-Px activity in erythrocytes in cows in Chile

AIM

To determine the effect of grazing pasture that had a low selenium (Se) concentration on serum concentrations of triiodothyronine (T3) and thyroxine (T4), and erythrocyte glutathione peroxidase (GSH-Px) activity in dairy cows.

METHODS

Forty pregnant Friesian cows were grazed on pasture that contained 0.03-0.04 ppm Se on a dry matter (DM) basis. Two months before parturition, 20 cows were randomly selected and treated with 1 mg Se/kg bodyweight subcutaneously, as barium selenate (Group Se-S). The other group (Se-D) was not supplemented. Blood samples were taken before supplementation (-60 days) and 30, 60, 90, 180 and 270 days after parturition, for determination of concentrations of T3 and T4 in serum, and GSH-Px activity in erythrocytes.

RESULTS

Erythrocyte GSH-Px activity in the Se-D group was <60 U/g haemoglobin (Hb) throughout the experiment. Supplementation increased (p<0.05) activities to >130 U/g Hb throughout lactation. Mean serum concentrations of T4 in Se-D and Se-S cows increased from 23.7 (SEM 0.7) and 23.4 (SEM 0.8) nmol/L, respectively, in the prepartum period to 69.6 (SEM 0.1) and 67.6 (SEM 0.2) nmol/L, respectively, at 180 days of lactation (p<0.01), and no effect of Se supplementation was evident. Serum concentrations of T3 in Se-D cows decreased (p<0.05) from 1.6 (SEM 0.1) nmol/L prepartum to 1.0 (SEM 0.2) nmol/L at the beginning of lactation, and remained lower (p<0.05) than those in the Se-S cows which did not decrease after calving and ranged from 1.9 (SEM 0.1) to 2.4 (SEM 0.2) nmol/L throughout lactation.

CONCLUSIONS

Serum T3 concentrations decreased during early lactation in unsupplemented cows grazing pastures low in Se (0.03-0.04 ppm) and both serum T3 and erythrocyte GSHPx activities were consistently lower throughout lactation compared with Se-supplemented cows. Se supplementation had no effect on serum T4 concentrations.

Biogeochemistry of selenium and its impact on food chain quality and human health

In areas where soils are low in bioavailable selenium (Se), potential Se deficiencies cause health risks for humans. Though higher plants have been considered not to require this element, the experience with low-Se soils in Finland has provided evidence that the supplementation of commercial fertilizers with sodium selenate affects positively not only the nutritive value of the whole food chain from soil to plants, animals and humans but also the quantity of plant yields. The level of Se addition has been optimal, and no abnormally high concentrations in plants or in foods of animal origin have been observed. Se levels in serum and human milk indicate that the average daily intake has been within limits considered to be safe and adequate. In fact, plants act as effective buffers, because their growth is reduced at high Se levels. They also tend to synthesize volatile compounds in order to reduce excess Se. On the other hand, when added at low concentrations, Se exerts a beneficial effect on plant growth via several mechanisms. As in humans and animals, Se strengthens the capacity of plants to counteract oxidative stress caused by oxygen radicals produced by internal metabolic or external factors. At proper levels it also delays some of the effects of senescence and may improve the utilization of short-wavelength light by plants. High additions are toxic and may trigger pro-oxidative reactions. Thus, the present supplementation of fertilizers with Se can be considered a very effective and readily controlled way to increase the average daily Se intake nationwide.

Effects of 17beta-estradiol and tamoxifen on the selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) mRNA expression in male reproductive organs of rats

The selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx) is highly expressed in testes under gonadotropin control. The expression patterns of PHGPx mRNA by 17beta-estradiol (E2) as an estrogen and tamoxifen (Tam) as an estrogen antagonist were investigated in the reproductive organs of male rats. Twelve-week-old male Sprague-Dawley rats were subcutaneously injected with E2 (7.5 microg/kg/day) or Tam (5 mg/kg/day) for 1 week. The E2 treatment significantly increased the levels of PHGPx mRNA in both testes and prostates, whereas the Tam treatment significantly decreased the levels of PHGPx mRNA, compared to the vehicle control (p<0.01). The treatment with E2 or Tam slightly decreased the levels of PHGPx mRNA in epididymides. In histopathological examination, severe vacuolization and depletion of germ cells in the seminiferous tubules, cell debris in the tubular lumen, and mild proliferative changes in interstitial tissues were observed in the testes of Tam-treated rats, whereas only mild spermatogonial proliferation was observed in the seminiferous tubules of E2-treated rats. There were no typical histopathological changes in the epididymides of any of the laboratory rats but mild epithelial proliferation in the prostates of E2- and Tam-treated rats. These results suggest that PHGPx mRNA expression may be influenced by estrogen in the male reproductive organs.

The role of essential trace elements in embryonic and fetal development in livestock

This review addresses the concept that essential trace minerals play a vital role in many enzymatic and metabolic pathways that are critical for conceptus development during pregnancy in livestock species. The conceptus relies entirely on the maternal system for a sufficient supply of trace minerals and other nutrients needed for normal development. If this supply is inadequate, growth and/or health of the conceptus can be affected adversely, and many of these effects carry over into the neonatal period. Information, accumulated in our laboratory and presented herein, indicates that zinc, copper and manganese are among the trace minerals that have the greatest impact on reproduction. For example, levels of zinc, copper and manganese were several fold greater in the conceptus than in other reproductive tissues, indicating that the conceptus preferentially accumulates these minerals, an action that may be important for conceptus development, growth and survival. Moreover, some recent results indicate that increasing the biological availability of zinc, copper and manganese, by attachment to short peptide chains (i.e., proteinated trace minerals) can enhance reproductive performance of swine. Mineral concentrations in conceptuses from female pigs consuming proteinated trace minerals were greater than those from females that consumed only inorganic mineral salts. Elucidating the mechanisms whereby conceptus development and survival are enhanced by essential trace minerals may lead to development of specific feeding programs to increase the number and health of offspring at parturition, thereby allowing for further improvements in production efficiency in animal agriculture.

Essentiality and toxicity of selenium and its status in Australia: a review

Selenium (Se) is an essential trace element for animals and humans because of its role in an antioxidant enzyme glutathione peroxidase. This enzyme protects cell membranes from damage caused by the peroxidation of lipids. The paper provides an overview of the effects of Se toxicity and deficiency in humans and animals. It is well established that Se deficiency causes health implications in humans and animals. Se is also very toxic and can cause Se poisoning (selenosis) in humans and animals. In Australia, Se deficiency has caused health problem to livestock; however, the problems were eliminated after the introduction of Se supplementation. Se toxicity has also been reported in some regions of Australia as a result of livestock feeding on Se accumulative plant species. The major source of Se is diet, and in many regions of the world the levels of Se in the soils generally reflect the Se status in human populations. In foods, the bioavailability and toxicity of Se depend on its chemical forms. Generally, organic forms of Se are more bioavailable and less toxic than the inorganic forms (selenites, selenates). The Se status in the Australian population and how this is compared with the rest of the world is also discussed.

Choice feeding of selenium-deficient laying hens affects diet selection, selenium intake and body weight

Inadequate selenium (Se) supply often in combination with low vitamin E status causes deficiency symptoms in many species. It is likely that a vague discomfort or sickness is perceived before clear deficiency signs become apparent. We investigated whether Se-deficient hens reduce their Se deficit by selecting a diet containing more selenium when offered two diets with different Se concentrations. A Low-Se diet (0.07 mg Se/kg) was supplemented with Se-enriched yeast (Sel-Plex 50) to produce Medium-Se (0.20 mg Se/kg) and High-Se (1.50 mg Se/kg) diets. Each of two consecutive study parts (I and II) with the same hens and treatments began with a 6-wk baseline period (Medium-Se diet), subsequently followed a 9-wk depletion period (Low-Se diet or Medium-Se diet), then a 6-wk choice feeding period in which two diets with different Se concentrations (Low-Se and Medium-Se, Medium-Se and High-Se, or Low-Se and High-Se) were offered. A control group received the Medium-Se diet throughout the study. Daily Se intake, calculated from daily feed intake, followed similar patterns in both parts of the study, but Se-deficient hens preferred (P < 0.05) the High-Se diet to the Low-Se diet during the first 3 wk of choice feeding only in part I. We conclude that young Se-deficient laying hens reduce their Se deficit if they have a choice between a Low-Se and a High-Se diet by preferentially selecting the High-Se diet, possibly based on learned place preference and/or learned taste aversion to the Low-Se diet, presumably in response to discomfort due to Se-deficiency.

Urinary selenium and iodine during pregnancy and lactation

The New Zealand environment is low in selenium and iodine, and is therefore ideally suited for the study of these anionic trace elements. The aim of this study was to determine urinary excretion of selenium and iodine during pregnancy and postpartum as part of an investigation of the influence of pregnancy and lactation on selenium metabolism in women of low selenium status. In a double-blind placebo-controlled study, 35 women in the earliest stages of pregnancy and 17 non-pregnant women were recruited in Dunedin, New Zealand. Eighteen pregnant women received 50 microg selenium as L-selenomethionine, while the others received a placebo daily during pregnancy and 12 months postpartum. The non-pregnant women received the supplement, serving as a positive control. Blood samples and twenty-four hour urine samples were collected monthly during pregnancy and at 3, 6, and 12 months postpartum for analysis of selenium and iodine. Selenium content in plasma and urinary excretion of selenium fell during pregnancy; however, total excretion of selenium was greater during pregnancy than postpartum. Urinary iodine excretion was much lower than reported previously in New Zealand. Due to large intra- and inter-subject variability, no trends in iodide excretion were observed. Factors which influence urinary excretion of selenium include dietary intake, but more closely, plasma concentrations of selenium (which is probably related to total selenium pool), creatinine excretion and therefore lean body mass, and glomerular filtration rate. The exact mechanism and sequence of events remains unclear and future studies incorporating new speciation techniques are necessary.