Critically elucidating the role of selenium

The Effect of Parenteral Selenium Therapy on Serum Concentration of Inflammatory Mediators: a Systematic Review and Dose-Response Meta-Analysis of Randomized Clinical Trials

Selenium can protect against inflammation through its incorporation in selenoenzymes; therefore, in this study, we assessed the effect of parenteral selenium on C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) through a systematic review and meta-analysis on randomized controlled trials (RCTs). A systematic search was performed in the databases, including PubMed, Scopus, Cochrane, clinicaltrials.gov, and ISI Web of Science, up to October 2022, with no limitation in study location or publication time. We calculated the effect size by the mean change from baseline in serum concentration of selected inflammatory mediators and their standard deviations. DerSimonian and Laird random effects model was used to estimate the heterogeneity and summary of the overall effects. Included studies in this systematic review and meta-analysis were 10 and 8 RCTs, respectively. Our results revealed parenteral selenium significantly decreased serum IL-6 (Weighted Mean Difference (WMD) = -3.85 pg/ml; 95% confidence interval (CI) = -7.37, -0.34 pg/ml; p = 0.032) but did not significantly change serum levels of CRP (WMD = 4.58 mg/L; 95% CI = -6.11, 15.27 mg/L; P = 0.401) compared to the comparison groups. According to our results, parenteral selenium supplementation might reduce serum levels of inflammatory mediators.

Assessment of trace elements in critically ill patients with systemic inflammatory response syndrome: A systematic review

BACKGROUND

Zinc (Zn), copper (Cu), and selenium (Se) are involved in immune and antioxidant defense. Their role in systemic inflammatory response syndrome (SIRS) treatment and outcomes remains unclear. This systematic review aimed to describe trace element concentrations in different types of biological samples and their relationship with morbidity and mortality in patients with SIRS.

METHODS

Literature was systematically reviewed according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA). The search results were screened and evaluated for eligibility, and data were extracted and summarized in tables and figures.

RESULTS

Most of the 38 included studies evaluated Se (75%), followed by Zn (42%) and Cu (22%). Plasma was the main biological sample evaluated (58%). Thirteen studies found lower plasma/serum concentrations of Zn, Se, and Cu in SIRS patients than in controls upon admission, 11 studies on adults (intensive care unit-ICU) and two in pediatric ICU (PICU). Three ICU studies found no difference in erythrocyte trace element concentrations in patients with SIRS. In all studies, the two main outcomes investigated were organ failure and mortality. In seven ICU studies, patients with lower plasma or serum Zn/Se levels had higher mortality rates. A study conducted in the PICU reported an association between increased Se variation and lower 28-day mortality. In an ICU study, lower erythrocyte selenium levels were associated with higher ICU/hospital mortality, after adjustment. Five ICU studies associated lower plasma/serum Zn/Se levels with higher organ failure scores and one PICU study showed an association between higher erythrocyte Se levels and lower organ dysfunction scores.

CONCLUSION

There was no difference in erythrocyte Se levels in patients with SIRS. Serum/Plasma Zn and serum/plasma/erythrocyte Se are associated with organ dysfunction, mortality, and inflammation. Trace element deficiencies should be diagnosed by erythrocyte, or complementary measurements in the presence of inflammation.

Erythrocyte and plasma selenium in children with acute inflammatory response

OBJECTIVES

Plasma selenium may not reflect selenium status in critically ill patients because it transiently decreases inversely with the magnitude of the systemic inflammatory response. The decision to supplement selenium should ideally be based on laboratory measurements that reliably reflect selenium status. We hypothesized that erythrocyte selenium, unlike plasma selenium, is not affected by the systemic inflammatory response in critically ill children.

METHODS

In a prospective study of 109 critically ill children, plasma and erythrocyte selenium concentrations were evaluated on admission, and plasma selenoprotein P was evaluated on days 1, 2, and 3 of the ICU stay. The main outcome was the effect of systemic inflammation on the erythrocyte and plasma selenium concentrations. The magnitude of the systemic inflammatory response was measured using serum C-reactive protein (CRP) and procalcitonin levels. The covariates were age, sex, anthropometric nutritional status, diagnosis of severe sepsis/septic shock, and clinical severity on admission. Multiple linear regression and generalized estimating equations were used for statistical analysis.

RESULTS

Erythrocyte selenium levels were not influenced by the magnitude of the inflammatory response or by the patient's clinical severity. Procalcitonin (β coefficient=-0.99; 95%CI: -1.64; -0.34, p = 0.003) and clinical severity (β coefficient= -11.13; 95%CI: -21.6; -0.63), p = 0.038) on admission were associated with decreased plasma selenium concentrations. Erythrocyte selenium was associated with selenoprotein P in the first three days of ICU stay (β coefficient=0.32; 95%CI: 0.20; 0.44, p < 0.001).

CONCLUSION

Unlike plasma selenium, erythrocyte selenium does not change in children with an acute systemic inflammatory response and is associated with selenoprotein P concentrations. Erythrocyte selenium is probably a more reliable marker than plasma selenium for evaluating the selenium status in critically ill children.

Factors Affecting Selenium Status in Infants on Parenteral Nutrition Therapy

INTRODUCTION

Selenium is an essential micronutrient that must be supplemented in infants and young children on exclusive parenteral nutrition (PN). We examined selenium status and clinical factors associated with a deficiency in infants on PN.

METHODS

This was a retrospective cohort study of pediatric patients receiving PN with routine monitoring of selenium status. Deficiency was diagnosed using age-based norms of plasma selenium status. Associations between selenium deficiency and the following clinical factors were examined: birthweight status: extremely low birthweight (ELBW) versus very low birthweight (VLBW) versus low birthweight (LBW) versus normal birthweight (NBW), serum albumin status, presence of cholestasis, and co-administration of enteral feeds.

RESULTS

A total of 42 infants were included with gestational age [median (interquartile range)] 28 weeks (25,34). The prevalence of selenium deficiency was 80% and the prevalence of albumin deficiency was 87.5%. The odds of selenium deficiency were higher in ELBW infants (odds ratio = 17.84, 95% confidence interval [4.04-78.72], P < 0.001) and VLBW infants (odds ratio = 16.26, 95% confidence interval [1.96-135.04], P < 0.001) compared to NBW infants. The odds of selenium deficiency were 5-fold higher in patients with low serum albumin (odds ratio = 5.33, 95% confidence interval [1.39-20.42], P = 0.015). There were no associations seen between selenium status and presence of cholestasis or co-administration of enteral feeds.

CONCLUSION

In this cohort of infants on PN therapy, the main clinical factors associated with selenium deficiency were presence of hypoalbuminemia and history of ELBW or VLBW. These findings support dual measurement of serum albumin and serum selenium to improve interpretation of selenium status.

Serum selenium in critically ill patients: Profile and supplementation in a depleted region

BACKGROUND

General selenium supplementation to intensive care unit (ICU) patients in regions with selenium-rich soil does not improve outcomes. Still selenium supplementation may reduce morbidity and mortality in patients with low-serum selenium concentration (S-Se) in selenium-poor areas who respond to treatment. The primary aim of this observational study was to investigate S-Se in a selenium-deficient region at time of intensive care admission, and in addition to monitor S-Se during high-dose selenium supplementation for safety.

METHODS

We measured S-Se in 100 consecutive patients admitted to a tertiary general ICU. After initial sampling, high-dose intravenous (iv) selenium supplementation was administered up to 20 days.

RESULTS

At admission, in 95% of the cases, S-Se was below the saturation level for selenoenzymes, in 91%, below the Swedish reference level, and in 71%, below the level where selenoenzyme function may be impaired. At day 5 of substitution, all patients still remaining in the ICU (n = 26) were within the range for enzyme function, 12% were below reference, and 24% did not reach full enzymatic saturation. At day 10 and forward, all patients were within target for treatment. No patients were at risk for toxic S-Se concentration.

CONCLUSIONS

S-Se concentration was substantially lower compared to normal values at ICU admission in this cohort of unselected Swedish critical care patients. Selenium supplementation restituted S-Se to levels corresponding to enzymatic saturation and the Swedish reference interval for all subjects remaining in the ICU on day 5.

Does infusion time affect the retention of parenteral trace elements?

When readymade parenteral nutrition in multi-chamber bags is supplied without vitamins and minerals, these have to be added or given separately. Separate rapid infusion has logistical advantages but has been claimed to saturate tissue mechanisms, potentially increasing urine micronutrient losses. The present study compared urinary losses after fast (1 h) v. slow (10 h) trace elements infusion. The study enrolled thirty-nine consecutive patients who were starting parenteral nutrition postoperatively. One day’s dose of a complete intravenous micronutrient product was infused over 1 h and over 10 h, in random order, with a washout day after each infusion day. Urinary Zn, Mn, Se, Cr, Cu and Fe losses were measured by 24-h urine collection, recorded for each infusion day and subsequent washout day. For Zn, a dose of 100 μmol was given, and total urinary loss over the next 2 d was mean 40·6 (sd 23·8) μmol after the fast (1 h) infusion v. 33·4 (sd 25·4) μmol after the slow (10 h) infusion, that is, 7 % more of the 1-d dose was lost after fast infusion (P = 0·01). For Mn, after a dose of 1000 nmol, losses were 9·8 (sd 23·9) nmol after the fast infusion v. 22·1 (sd 47·2) nmol after the slow infusion, that is, 1 % more of the 1-d dose was lost after slow infusion (P = 0·04). There were no other significant differences: after 1 μmol Se, the losses were 1·5 (sd 0·6) μmol fast v. 1·3 (sd 0·5) μmol slow; after 200 nmol Cr, 257 (sd 92) μmol fast v. 246 (sd 107) nmol slow; after 8 μmol Cu, 1·6 (sd 1·4) μmol fast v. 1·5 (sd 1·3) μmol slow; and after 20 μmol Fe, 0·6 (sd 1·1) μmol fast v. 0·8 (sd 1·6) μmol slow (P > 0·05 for all). Overall, trace element retention appears to be minimally affected by infusion time.

Selenium and selenoproteins: from endothelial cytoprotection to clinical outcomes

The role of the vascular endothelium in inflammation was demonstrated experimentally through biomarkers of endothelial dysfunction and cytoprotection. Selenium is a trace element essential for cell protection against oxidative lesions triggered by reactive oxygen species or inflammatory responses. Preclinical studies have demonstrated a relationship between adhesion molecules as biomarkers of endothelial dysfunction and selenoproteins as biomarkers of selenium status under conditions that mimic different diseases. Most studies in humans indicate an association between selenium deficiency and increased risk of morbidity and mortality, yet the pathophysiology of selenium in endothelial activation remains unknown. Here, we summarize selenium-dependent endothelial function evaluation techniques and focus on the role of selenium in endothelial cytoprotection according to current scientific knowledge. Most studies on the role of selenium in endothelial processes show selenium-dependent endothelial functions and explain how cells and tissues adapt to inflammatory insults. Taken together, these studies show an increase in adhesion molecules and a decrease in the expression of selenoproteins following a decreased exposure to selenium. Few clinical trials have enough methodological quality to be included in meta-analysis on the benefits of selenium supplementation. Furthermore, the methodology adopted in many studies does not consider the relevant findings on the pathophysiology of endothelial dysfunction. Preclinical studies should be more frequently integrated into clinical studies to provide clearer views on the role of selenium status in endothelial cytoprotection.

Selenium supplementation of lung epithelial cells enhances nuclear factor E2-related factor 2 (Nrf2) activation following thioredoxin reductase inhibition

The trace element selenium (Se) contributes to redox signaling, antioxidant defense, and immune responses in critically ill neonatal and adult patients. Se is required for the synthesis and function of selenoenzymes including thioredoxin (Trx) reductase-1 (TXNRD1) and glutathione peroxidases (GPx). We have previously identified TXNRD1, primarily expressed by airway epithelia, as a promising therapeutic target to prevent lung injury, likely via nuclear factor E2-related factor 2 (Nrf2)-dependent mechanisms. The present studies utilized the TXNRD1 inhibitor auranofin (AFN) to test the hypothesis that Se positively influences Nrf2 activation and selenoenzyme responses in lung epithelial cells. Murine transformed Club cells (mtCCs) were supplemented with 0, 10, 25, or 100 nM Na2SeO3 to create a range of Se conditions and were cultured in the presence or absence of 0.5 μM AFN. TXNRD1 and GPX2 protein expression and enzymatic activity were significantly greater upon Se supplementation (p < 0.05). AFN treatment (0.5 μM AFN for 1 h) significantly inhibited TXNRD1 but not GPx activity (p < 0.001). Recovery of TXNRD1 activity following AFN treatment was significantly enhanced by Se supplementation (p < 0.041). Finally, AFN-induced Nrf2 transcriptional activation was significantly greater in mtCCs supplemented in 25 or 100 nM Na2SeO3 when compared to non-supplemented controls (p < 0.05). Our novel studies indicate that Se levels positively influence Nrf2 activation and selenoenzyme responses following TXNRD1 inhibition. These data suggest that Se status significantly influences physiologic responses to TXNRD1 inhibitors. In conclusion, correction of clinical Se deficiency, if present, will be necessary for optimal therapeutic effectiveness of TXNRD1 inhibitors in the prevention of lung disease.

Assessment of Micronutrient Status in Critically Ill Children: Challenges and Opportunities

Micronutrients refer to a group of organic vitamins and inorganic trace elements that serve many functions in metabolism. Assessment of micronutrient status in critically ill children is challenging due to many complicating factors, such as evolving metabolic demands, immature organ function, and varying methods of feeding that affect nutritional dietary intake. Determination of micronutrient status, especially in children, usually relies on a combination of biomarkers, with only a few having been established as a gold standard. Almost all micronutrients display a decrease in their serum levels in critically ill children, resulting in an increased risk of deficiency in this setting. While vitamin D deficiency is a well-known phenomenon in critical illness and can predict a higher need for intensive care, serum concentrations of many trace elements such as iron, zinc, and selenium decrease as a result of tissue redistribution in response to systemic inflammation. Despite a decrease in their levels, supplementation of micronutrients during times of severe illness has not demonstrated clear benefits in either survival advantage or reduction of adverse outcomes. For many micronutrients, the lack of large and randomized studies remains a major hindrance to critically evaluating their status and clinical significance.

Selenium Deficiency Induced Injury in Chicken Muscular Stomach by Downregulating Selenoproteins

The aim of the present study was to examine the effect of selenium (Se) deficiency on the expression of selenoproteins in chicken muscular stomach and to detect the correlation of selenoproteins with muscular stomach injuries. One-day-old broiler chickens were maintained for 55 days on a normal diet (0.2 mg/kg) or a Se-deficient diet (0.033 mg Se/kg). The expression levels of 25 selenoproteins, heat shock proteins (HSPs), and inflammatory factors were then examined by real-time PCR. Following this, the correlation between selenoproteins, HSPs, and inflammatory factors was analyzed by principal component analysis (PCA). The results showed that Se deficiency decreased the expression of 25 selenoproteins (P < 0.05), but increased the expression of HSP27, HSP40, HSP60, HSP70, and HSP90, and NF-κB, iNOS, TNF-α, COX-2, and HO-1 (P < 0.05). Selenoproteins showed a high negative correlation with HSPs and inflammatory factors. Thus, the results suggested that Se deficiency induced muscular stomach injuries by decreasing the expression of selenoproteins. In addition, selenoproteins play an important role in regulating HSPs and inflammatory response. The muscular stomach is a key target of Se deficiency and may play a special role in response to Se deficiency.

Low serum selenium is associated with the severity of organ failure in critically ill children

BACKGROUND & AIMS

Low concentration of serum selenium is associated with the inflammatory response and multiple organ failure in adult ICU-patients. Critically ill children are less well characterized. In this study, serum selenium concentration and its possible relation to multiple organ failure as well as glutathione status was investigated in pediatric intensive care (PICU) patients.

METHODS

A prospective consecutive cohort of critically ill children (n = 100) admitted to the PICU of a tertiary university hospital, and in addition an age stratified reference group of healthy children (n = 60) were studied. The concentrations of serum selenium and reduced and total glutathione were determined at admission and at day 5 for patients still in the PICU.

RESULTS

Low concentration of serum selenium as well as a high-reduced fraction of glutathione (GSH/tGSH) was associated with multiple organ failure (p < 0.001 and p < 0.01) respectively. A correlation between low serum selenium concentration and high-reduced fraction of glutathione (GSH/tGSH) was also seen (r = -0.19 and p = 0.03). The serum selenium concentrations in the pediatric reference group in a selenium poor area were age dependent with lower concentrations in infants as compared to older children (p < 0.001).

CONCLUSIONS

Both low serum selenium concentration and high reduced fraction of glutathione (GSH/tGSH) were associated with the development of multiple organ failure. The association between low serum selenium concentration and high fraction of reduced glutathione in whole blood favour the hypothesis that selenium is of critical importance for the scavenge capacity of glutathione peroxidase (GPX).

High-dose intravenous selenium does not improve clinical outcomes in the critically ill: a systematic review and meta-analysis

Background

Selenium (Se) is an essential trace element with antioxidant, anti-inflammatory, and immunomodulatory effects. So far, several randomized clinical trials (RCTs) have demonstrated that parenteral Se may improve clinical outcomes in intensive care unit (ICU) patients. Since publication of our previous systematic review and meta-analysis on antioxidants in the ICU, reports of several trials have been published, including the largest RCT on Se therapy. The purpose of the present systematic review was to update our previous data on intravenous (IV) Se in the critically ill.

Methods

We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials. We included RCTs with parallel groups comparing parenteral Se as single or combined therapy with placebo. Potential trials were evaluated according to specific eligibility criteria, and two reviewers abstracted data from original trials in duplicate independently. Overall mortality was the primary outcome; secondary outcomes were infections, ICU length of stay (LOS), hospital LOS, ventilator days, and new renal dysfunction.

Results

A total of 21 RCTs met our inclusion criteria. When the data from these trials were aggregated, IV Se had no effect on mortality (risk ratio [RR] 0.98, 95 % CI 0.90–1.08, P = 0.72, heterogeneity I² = 0 %). In addition, when the results of ten trials in which researchers reported on infections were statistically aggregated, there was no significant treatment effect of parenteral Se (RR 0.95, 95 % CI 0.88–1.02, P = 0.15, I² = 0 %). There was no positive or negative effect of Se therapy on ICU and hospital LOS, renal function, or ventilator days.

Conclusions

In critically ill patients, IV Se as monotherapy does not improve clinical outcomes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1529-5) contains supplementary material, which is available to authorized users.

Low preoperative selenium is associated with post-operative atrial fibrillation in patients having intermediate-risk coronary artery surgery

BACKGROUND/OBJECTIVES

Post-operative atrial fibrillation (POAF) is a frequent complication of cardiac surgery. Oxidative stress and reduced antioxidant function have major roles in its development. Selenium is a key to normal antioxidant function, and levels are often low before cardiac surgery. This study investigated whether low preoperative selenium levels were associated with POAF in cardiac surgical patients.

SUBJECTS/METHODS

Using the Society of Thoracic Surgeons (STS) Mortality risk score, 50 patients having primary coronary artery bypass grafts (CABG) surgery were divided into two groups: (i) low-risk group (STS ⩽0.5%; n=26) and (ii) intermediate-risk group (STS ⩾2.0%; n=24). Plasma levels of selenium, glutathione peroxidase (GPx) and malondialdehyde (MDA) were measured in all patients at anaesthetic induction, after aortic cross-clamp removal, 3 h post cardiopulmonary bypass and on post-operative days 1 and 5. Multiple logistic regression was used to assess whether selenium levels were associated with POAF development.

RESULTS

Seventeen patients developed POAF (14 patients in the intermediate-risk group and 3 patients in the low-risk group). Preoperative selenium was lower in patients who developed POAF compared with those with normal sinus rhythm (0.73±0.16 vs 0.89±0.13 μmol/l, P=0.005), and this was independently associated with POAF (PR 0.32; 95% confidence credible interval (95%cI) 0.06-0.85, P=0.016). Regardless of POAF, preoperative selenium was lower in the intermediate-risk patients than in the low-risk patients (0.77±0.15 vs 0.89±0.14 μmol/l; P=0.004).

CONCLUSIONS

Intermediate-risk patients with low preoperative selenium levels may be at a greater risk of developing POAF following CABG. This raises the question of whether selenium supplementation in select cardiac surgical patients may reduce their POAF risk.

Selenium Deficiency Affects the mRNA Expression of Inflammatory Factors and Selenoprotein Genes in the Kidneys of Broiler Chicks

The aim of this study was to investigate the influence of Se deficiency on the transcription of inflammatory factors and selenoprotein genes in the kidneys of broiler chicks. One hundred fifty 1-day-old broiler chicks were randomly assigned to two groups fed with either a low-Se diet (L group, 0.033 mg/kg Se) or an adequate Se diet (C group, 0.2 mg/kg Se). The levels of uric acid (UA) and creatinine (Cr) in the serum and the mRNA levels of 6 inflammatory factors and 25 selenoprotein genes in the kidneys were measured as the clinical signs of Se deficiency occurred at 20 days old. The results indicated that the contents of UA and Cr in the serum increased in L group (p < 0.05), and the mRNA levels of the inflammatory factors (NF-κB, iNOS, COX-2, and TNF-α) increased in L group (p < 0.05). Meanwhile, the mRNA levels of PTGEs and HO-1 were not changed. In addition, 25 selenoprotein transcripts displayed ubiquitous expression in the kidneys of the chicks. The mRNA levels of 14 selenoprotein genes (Dio1, Dio2, GPx3, Sepp1, SelH, SelI, SelK, Sepn1, SelO, SelW, Sep15, SelT, SelU, and SelS) decreased, and 9 selenoprotein genes (GPx1, GPx2, GPx4, SelPb, Txnrd1, Txnrd2, Txnrd3, SPS2, and SelM) increased in L group (p < 0.05), but the Dio3 and Sepx1 mRNA levels did not change. The results indicated that Se deficiency resulted in kidney dysfunction, activation of the NF-κB pathway, and a change in selenoprotein gene expression. The changes of inflammatory factor and selenoprotein gene expression levels were directly related to the abnormal renal functions induced by Se deficiency.

Assessment of serum zinc, selenium, and prolactin concentrations in critically ill children

Background

In critically ill patients, there are reduced stores of antioxidants, which are associated with increased organ failure and even higher mortality. Trace elements, especially zinc and selenium, are the cornerstone of the antioxidant defense in acute systemic inflammatory response syndrome. Prolactin (PRL) is the counterregulatory stress hormone that prevents cortisol/stress-induced lymphocyte apoptosis. The aim of our study is to detect the serum levels of zinc, selenium, and PRL hormone as important immunomodulators in critically ill children and to investigate the relationship between these immunomodulators and the severity of illness.

Subjects and methods

This was a prospective study that included two groups; group 1: 50 critically ill children within 72 hours of intensive care unit admission, and group 2: 30 healthy children as controls. Blood samples were collected from the two groups for zinc, selenium, and PRL level measurement.

Results

Zinc and PRL levels were found to be decreased in critically ill children compared to control group, and these levels were inversely correlated with organ failure index and pediatric logistic organ dysfunction scores. Selenium levels were decreased in patients with sepsis and in patients with multiple organ failure.

Conclusion

Serum concentrations of zinc and PRL are generally low in critically ill children, with a greater decrease in patients with sepsis and in the presence of multiple organ failure. The levels of zinc and PRL are inversely correlated with severity of illness. Selenium levels were decreased in patients with sepsis and in patients with multiple organ failure.

Impact of the Nationwide Intravenous Selenium Product Shortage on the Development of Selenium Deficiency in Infants Dependent on Long-Term Parenteral Nutrition

BACKGROUND

For patients dependent on parenteral nutrition (PN), selenium must be supplemented intravenously. A nationwide intravenous selenium shortage began in April 2011. The impact of this shortage on PN-dependent infants was evaluated by examining the provision of selenium, development of biochemical deficiency, and costs associated with the shortage.

MATERIALS AND METHODS

This single-center, retrospective study included PN-dependent infants aged ≤1 year who weighed ≤30 kg, received PN for ≥1 month, and had ≥1 serum selenium measurement. The primary outcome was the incidence of biochemical selenium deficiency. Secondary outcomes included severity of biochemical deficiency, clinical manifestations, costs, and relationship between serum selenium levels and selenium dose.

RESULTS

The average selenium dose decreased 2-fold during the shortage (2.1 ± 1.2 µg/kg/d; range, 0.2-4.6 µg/kg/d) versus the nonshortage period (3.8 ± 1 µg/kg/d; range, 2.4-6 µg/kg/d; P < .001). A linear relationship between serum selenium concentration and selenium dose was observed (r(2) = 0.42), with a dose of 6 µg/kg/d expected to result in normal serum levels in most cases. Similar proportions of patients developed biochemical deficiency in both groups: shortage period, 59.1%; nonshortage, 66.7%; P = .13. The severity of biochemical deficiency was similar between groups. A significant increase in incremental cost during the shortage was observed.

CONCLUSION

This is the first study examining the impact of the intravenous selenium shortage on PN-dependent infants. Both groups exhibited similarly high incidences of biochemical selenium deficiency, suggesting higher empiric doses may benefit this population. However, ongoing shortages limit the ability to provide supplementation.

Selenium speciation in tea by dispersive liquid-liquid microextraction coupled to high-performance liquid chromatography after derivatization with 2,3-diaminonaphthalene

Selenium is an important element for human health, and it is present in many natural drinks and foods. Present study described a new method using dispersive liquid-liquid microextraction prior to high-performance liquid chromatography with a UV variable wavelength detector for the determination of the total selenium, Se(IV), Se(VI), and total organoselenium in tea samples. In the procedure, 2,3-diaminonaphthalene was used as the chelating reagent, 400 μL acetonitrile was used as the disperser solvent and 60 μL chlorobenzene was used as the extraction solvent. The complex of Se(IV) and 2,3-diaminonaphthalene in the final extracted phase was analyzed by high-performance liquid chromatography. The factors influencing the derivatization and microextraction were investigated. Under the optimal conditions, the limit of detection was 0.11 μg/L for Se(IV) and the linearity range was in the range of 0.5-40 μg/L. This method was successfully applied to the determination of selenium in four tea samples with spiked recoveries ranging from 91.3 to 100%.

Pharmaconutrition with selenium in critically ill patients: what do we know?

Selenium is a component of selenoproteins with antioxidant, anti-inflammatory, and immunomodulatory properties. Systemic inflammatory response syndrome (SIRS), multiorgan dysfunction (MOD), and multiorgan failure (MOF) are associated with an early reduction in plasma selenium and glutathione peroxidase activity (GPx), and both parameters correlate inversely with the severity of illness and outcomes. Several randomized clinical trials (RCTs) evaluated selenium therapy as monotherapy or in antioxidant cocktails in intensive care unit (ICU) patient populations, and more recently several meta-analyses suggested benefits with selenium therapy in the most seriously ill patients. However, the largest RCT on pharmaconutrition with glutamine and antioxidants, the REducing Deaths due to Oxidative Stress (REDOXS) Study, was unable to find any improvement in clinical outcomes with antioxidants provided by the enteral and parenteral route and suggested harm in patients with renal dysfunction. Subsequently, the MetaPlus study demonstrated increased mortality in medical patients when provided extra glutamine and selenium enterally. The treatment effect of selenium may be dependent on the dose, the route of administration, and whether administered with other nutrients and the patient population studied. Currently, there are few small studies evaluating the pharmacokinetic profile of intravenous (IV) selenium in SIRS, and therefore more data are necessary, particularly in patients with MOD, including those with renal dysfunction. According to current knowledge, high-dose pentahydrate sodium selenite could be given as an IV bolus injection (1000-2000 µg), which causes transient pro-oxidant, cytotoxic, and anti-inflammatory effects, and then followed by a continuous infusion of 1000-1600 µg/d for up to 10-14 days. Nonetheless, the optimum dose and efficacy still remain controversial and need to be definitively established.

Increased plasma selenium is associated with better outcomes in children with systemic inflammation

OBJECTIVE

The aim of this study was to assess the effects of changes in plasma selenium on the outcome of critically ill children.

METHODS

Plasma selenium was prospectively measured in 99 children with acute systemic inflammation. The exposure variables were selenium level on admission and on day 5 of stay in the intensive care unit (ICU) and the difference in selenium concentrations between day 5 post-admission and the ICU admission (delta selenium). Selenium was given only as part of enteral diets. Age, malnutrition, red cell glutathione peroxidase-1 activity, serum C-reactive protein, Pediatric Index of Mortality 2, and Pediatric Logistic Organ Dysfunction scores were analyzed as covariates. The outcome variables were ventilator-free days, ICU-free days, and 28-d mortality.

RESULTS

Plasma selenium concentrations increased from admission (median 23.4 μg/L, interquartile range 12.0-30.8) to day 5 (median 25.1 μg/L, interquartile range 16.0-39.0; P = 0.018). After adjustment for confounding factors, a delta selenium increase of 10 μg/L was associated with reductions in ventilator days (1.3 d; 95% confidence interval [CI], 0.2-2.3; P = 0.017) and ICU days (1.4 d; 95% CI, 0.5-2.3; P < 0.01). Delta selenium >0 was associated with decreased 28-d mortality on a univariate model (odds ratio, 0.67; 95% CI, 0.46-0.97; P = 0.036). The mean daily selenium intake (6.82 μg; range 0-48.66 μg) was correlated with the increase in selenium concentrations on day 5.

CONCLUSIONS

An increase in plasma selenium is independently associated with shorter times of ventilation and ICU stay in children with systemic inflammation. These findings raise the hypothesis that selenium supplementation could be beneficial in children with critical illnesses.

SodiUm SeleniTe Adminstration IN Cardiac Surgery (SUSTAIN CSX-trial): study design of an international multicenter randomized double-blinded controlled trial of high dose sodium-selenite administration in high-risk cardiac surgical patients

Background

Cardiac surgery has been shown to result in a significant decrease of the antioxidant selenium, which is associated with the development of multiorgan dysfunction and increased mortality. Thus, a large-scale study is needed to investigate the effect of perioperative selenium supplementation on the occurrence of postoperative organ dysfunction.

Methods/Design

We plan a prospective, randomized double-blind, multicenter controlled trial, which will be conducted in North and South America and in Europe. In this trial we will include 1,400 high-risk patients, who are most likely to benefit from selenium supplementation. This includes patients scheduled for non-emergent combined and/or complex procedures, or with a predicted operative mortality of ≥5% according to the EuroSCORE II. Eligible patients will be randomly assigned to either the treatment group (bolus infusion of 2,000 μg sodium selenite immediately prior to surgery, followed by an additional dosage of 2,000 μg at ICU admission, and a further daily supplementation of 1,000 μg up to 10 days or ICU discharge) or to the control group (placebo administration at the same time points).

The primary endpoint of this study is a composite of 'persistent organ dysfunction’ (POD) and/or death within 30 days from surgery (POD + death). POD is defined as any need for life-sustaining therapies (mechanical ventilation, vasopressor therapy, mechanical circulatory support, continuous renal replacement therapy, or new intermittent hemodialysis) at any time within 30 days from surgery.

Discussion

The SUSTAIN-CSX™ study is a multicenter trial to investigate the effect of a perioperative high dosage sodium selenite supplementation in high-risk cardiac surgical patients.

Trial registration

This trial was registered at Clinicaltrials.gov (identifier: NCT02002247) on 28 November 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/1745-6215-15-339) contains supplementary material, which is available to authorized users.

Elements of margin of safety, toxicity and action of sodium selenite in a lipopolysaccharide rat model

PROJECT

Both septic shock and sodium selenite (Na2SeO3) lead to multiple organ failure through oxidation. Na2SeO3 has direct oxidant effects above the nutritional level and indirect anti-oxidant properties. In a lipopolysaccharide (LPS) rat model we assessed margin of safety, toxicity and beneficial effect of pentahydrate Na2SeO3 (5H2O·Na2SeO3) at oxidant doses.

PROCEDURE

In a three-step study on 204 rats we: (i) observed toxic effects of Na2SeO3 injected intraperitoneously (IP) and determined its Minimum Dose Without Toxic effect (MDWT) 0.25-0.35 mg/kg selenium (Se) content; (ii) injected IP LPS at 70% lethal dose (LD) followed, or not, one hour later by IP Na2SeO3 at MDWT and (iii) by doses>MDWT. At 48 h, in survivors, we measured plasma creatinine, lactate, aspartate and alanine aminotransferase (AST, ALT), nitric oxide (NO) and Se concentrations.

RESULTS

(i) Na2SeO3 alone did not increase NO and lactate. Encephalopathy appeared at 1mg Se/kg. Creatinine increased at 1-1.75 mg Se/kg, AST, ALT at 3-4.5 mg Se/kg, and the minimum LD was 3 mg Se/kg. (ii) Mortality after LPS was 37/50 (74%, [62-86%]) vs. 20/30 (67%, [50-84%]) when followed by Na2SeO3 at MDWT (p=0.483) with a decreased in NO (-31%, p=0.038) a trend for lactate decrease (-19%, p=0.068) and an increased Se in plasma of survivals. (iii) All rats died at doses ≥0.6 mg/kg (p<0.001).

CONCLUSION

Mechanisms of LPS and Na2SeO3 toxicity differ (i.e. NO, lactate). In septic shock 5H2O·Na2SeO3 toxicity increased, margin of safety decrease, but IP administration of dose considered as oxidant of 5H2O·Na2SeO3 showed beneficial effects.

Low plasma selenium concentrations in critically ill children: the interaction effect between inflammation and selenium deficiency

Introduction

Low plasma selenium concentrations are frequent in critically ill patients. However, whether this is due to systemic inflammation, a deficient nutritional state or both is still not clear. We aimed to determine the factors associated with low plasma selenium in critically ill children while considering the inflammatory response and nutritional status.

Method

A prospective study was conducted in 173 children (median age 34 months) with systemic inflammatory response who had plasma selenium concentrations assessed 48 hours after admission and on the 5th day of ICU stay. The normal reference range was 0.58 μmol/L to 1.6 μmol/L. The outcome variable was ‘low plasma selenium’, which was defined as plasma selenium values below the distribution median during this period. The main explanatory variables were age, malnutrition, sepsis, C-reactive protein (CRP), and clinical severity scores. The data were analyzed using a Binomial Generalized Estimating Equations model, which includes the correlation between admission and 5th day responses.

Results

Malnutrition and CRP were associated with low plasma selenium. The interaction effect between these two variables was significant. When CRP values were less than or equal to 40 mg/L, malnutrition was associated with low plasma selenium levels (odds ratio (OR) = 3.25, 95% confidence interval (CI) 1.39 to 7.63, P = 0.007; OR = 2.98, 95% CI 1.26 to 7.06, P = 0.013; OR = 2.49, 95% CI 1.01 to 6.17, P = 0.049, for CRP = 10, 20 and 40 mg/L, respectively). This effect decreased as CRP concentrations increased and there was loose significance when CRP values were >40 mg/L. Similarly, the effect of CRP on low plasma selenium was significant for well-nourished patients (OR = 1.13; 95% CI 1.06 to 1.22, P <0.001) but not for the malnourished (OR = 1.03; 95% CI 0.99 to 1.08, P = 0.16).

Conclusions

There is a significant interaction between the magnitude of the inflammatory response and malnutrition on low plasma selenium. This interaction should be considered when interpreting plasma concentrations as an index of selenium status in patients with systemic inflammation as well as in the decision on selenium supplementation.

Erythrocyte selenium concentration predicts intensive care unit and hospital mortality in patients with septic shock: a prospective observational study

Introduction

Selenoenzymes can modulate the extent of oxidative stress, which is recognized as a key feature of septic shock. The pathophysiologic role of erythrocyte selenium concentration in patients with septic shock remains unknown. Therefore, the objective of this study was to evaluate the association of erythrocyte selenium concentration with glutathione peroxidase (GPx1) activity, GPx1 polymorphisms and with ICU and hospital mortality in septic shock patients.

Methods

This prospective study included all patients older than 18 years with septic shock on admission or during their ICU stay, admitted to one of the three ICUs of our institution, from January to August 2012. At the time of the patients’ enrollment, demographic information was recorded. Blood samples were taken within the first 72 hours of the patients’ admission or within 72 hours of the septic shock diagnosis for determination of selenium status, protein carbonyl concentration, GPx1 activity and GPx1 Pro198Leu polymorphism (rs 1050450) genotyping.

Results

A total of 110 consecutive patients were evaluated. The mean age was 57.6 ± 15.9 years, 63.6% were male. Regarding selenium status, only erythrocyte selenium concentration was lower in patients who died in the ICU. The frequencies for GPx1 Pro198Leu polymorphism were 55%, 38% and 7% for Pro/Pro, Pro/Leu and Leu/Leu, respectively. In the logistic regression models, erythrocyte selenium concentration was associated with ICU and hospital mortality in patients with septic shock even after adjustment for protein carbonyl concentration and acute physiology and chronic health evaluation II score (APACHE II) or sequential organ failure assessment (SOFA).

Conclusions

Erythrocyte selenium concentration was a predictor of ICU and hospital mortality in patients with septic shock. However, this effect was not due to GPx1 activity or Pro198Leu polymorphism.

[Significance of selenium in the pathogenesis and therapy of cardiovascular diseases and those requiring intensive care]

Selenium deficiency results in profound changes in cellular defence mechanisms against oxidative stress, which plays an important role in the development of cardiovascular disease and the associated risk factors. Increased formation and decreased elimination of reactive oxygen radicals contribute to the complicated mechanisms of sepsis and related disorders. Use of selenium in prevention and treatment of the above mentioned conditions is not a new idea, but controversial data were published in relation to both fields recently. The aim of the present review is to summarize the most important results related to this area.

Heavy metal in the intensive care unit: a review of current literature on trace element supplementation in critically ill patients

Trace elements are essential for many physiologic processes. In recent years, supplementation has been studied for a variety of indications, including glycemic control, wound healing, antioxidant effect, and anemia. Critical illness, especially states such as burns, traumas, and septic shock, is associated with inflammatory and oxidative stress, immune dysfunction, and malnutrition. In these patients, enteral and parenteral nutrition or pharmaceutical supplementation is used to provide essential macronutrients, including trace elements. The purpose of this review is to describe trace element supplementation, including iron, copper, chromium, manganese, selenium, and zinc, and highlight their mechanism, pharmacology, outcome data, and adverse effects.

Plasma selenium status in a group of Australian blood donors and fresh blood components

The purpose of this study was to assess plasma selenium levels in an Australian blood donor population and measure extra-cellular selenium levels in fresh manufactured blood components. Selenium levels were measured using graphite furnace atomic absorption spectrometry with Zeeman background correction. The mean plasma selenium level in healthy plasmapharesis donors was 85.6±0.5 μg/L and a regional difference was observed between donors in South East Queensland and Far North Queensland. Although participants had selenium levels within the normal range (55.3-110.5 μg/L), 88.5% had levels below 100 μg/L, a level that has been associated with sub-optimal activity of the antioxidant enzyme glutathione peroxidase (GPx). Extra-cellular selenium levels in clinical fresh frozen plasma (cFFP) and apheresis-derived platelets (APH Plt) were within the normal range. Packed red blood cells (PRBC) and pooled buffy coat-derived platelets (BC Plt) had levels at the lower limit of detection, which may have clinical implications to the massively transfused patient.

[Pharmaconutrition with parenteral selenium in sepsis]

Critical illness is characterized by oxidative stress which leads to multiple organ failure, and sepsis-related organ dysfunction remains the most common cause of death in the intensive care unit. Over the last 2 decades, different antioxidant therapies have been developed to improve outcomes in septic patients. According to recent evidence, selenium therapy should be considered the cornerstone of the antioxidant strategies. Selenium given as selenious acid or sodium selenite should be considered as a drug or pharmaconutrient with prooxidant and cytotoxic effects when a loading dose in intravenous bolus form is administered, particularly in the early stage of severe sepsis/septic shock. To date, several phase ii trials have demonstrated that selenium therapy may be able to decrease mortality, improve organ dysfunction and reduce infections in critically ill septic patients. The effect of selenium therapy in sepsis syndrome must be confirmed by large, well designed phase iii clinical trials. The purpose of this review is to discuss current evidence on selenium pharmaconutrition in sepsis syndrome.

The effect of selenium therapy on mortality in patients with sepsis syndrome: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Patients with sepsis syndrome commonly have low serum selenium levels. Several randomized controlled trials have examined the efficacy of selenium supplementation on mortality in patients with sepsis.

OBJECTIVE

To determine the efficacy and safety of high-dose selenium supplementation compared to placebo for the reduction of mortality in patients with sepsis.

SOURCES OF DATA

We searched Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, SciFinder, and Clinicaltrials.gov.

SELECTION CRITERIA

Randomized controlled parallel group trials comparing selenium supplementation in doses greater than daily requirement to placebo on the outcome of mortality in patients with sepsis syndrome.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied eligibility criteria, assessed quality, and extracted data. The primary outcome was mortality; secondary outcomes were ICU length of stay, nosocomial pneumonia, and adverse events. Trial authors were contacted for additional or clarifying information.

RESULTS

Nine trials enrolling a total of 792 patients were included. Selenium supplementation in comparison to placebo was associated with lower mortality (odds ratio, 0.73; 95% CI, 0.54, 0.98; p = 0.03; I = 0%). Among patients receiving and not receiving selenium, there was no difference in ICU length of stay (mean difference, 2.03; 95% CI, -0.51, 4.56; p = 0.12; I = 0%) or nosocomial pneumonia (odds ratio, 0.83; 95% CI, 0.28, 2.49; p = 0.74; I = 56%). Significant heterogeneity among trials in adverse event reporting precluded pooling of results.

CONCLUSIONS

In patients with sepsis, selenium supplementation at doses higher than daily requirement may reduce mortality. We observed no impact of selenium on ICU length of stay or risk of nosocomial pneumonia.

Baseline serum concentrations of zinc, selenium, and prolactin in critically ill children

OBJECTIVES

To describe serum concentrations of zinc, selenium, and prolactin in critically ill children within 72 hours of PICU admission, and to investigate relationships between these immunomodulators and lymphopenia.

DESIGN

An analysis of baseline data collected as part of the multicenter Critical Illness Stress Induced Immune Suppression (CRISIS) Prevention Trial.

SETTING

PICUs affiliated with the Collaborative Pediatric Critical Care Research Network.

PATIENTS

All children enrolled in the CRISIS Prevention Trial that had baseline serum samples available for analysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of 293 critically ill children enrolled in the CRISIS Prevention Trial, 284 had baseline serum samples analyzed for prolactin concentration, 280 for zinc concentration, and 278 for selenium concentration within 72 hours of PICU admission. Lymphocyte counts were available for 235 children. Zinc levels ranged from nondetectable (< 0.1 μg/mL) to 2.87 μg/mL (mean 0.46 μg/mL and median 0.44 μg/mL) and were below the normal reference range for 235 (83.9%) children. Selenium levels ranged from 26 to 145 ng/mL (mean 75.4 ng/mL and median 74.5 ng/mL) and were below the normal range for 156 (56.1%) children. Prolactin levels ranged from nondetectable (< 1 ng/mL) to 88 ng/mL (mean 12.2 ng/mL and median 10 ng/mL). Hypoprolactinemia was present in 68 (23.9%) children. Lymphopenia was more likely in children with zinc levels below normal than those with zinc levels within or above the normal range (82 of 193 [42.5%] vs. 10 of 39 [25.6%], p = 0.0498). Neither selenium nor prolactin concentrations were associated with lymphopenia (p = 1.0 and p = 0.72, respectively).

CONCLUSIONS

Serum concentrations of zinc, selenium, and prolactin are often low in critically ill children early after PICU admission. Low serum zinc levels are associated with lymphopenia, whereas low selenium and prolactin levels are not. The implications of these findings and the mechanisms by which they occur merit further study.

Antioxidant micronutrients in the critically ill: a systematic review and meta-analysis

INTRODUCTION

Critical illness is characterized by oxidative stress, which is a major promoter of systemic inflammation and organ failure due to excessive free radical production, depletion of antioxidant defenses, or both. We hypothesized that exogenous supplementation of trace elements and vitamins could restore antioxidant status, improving clinical outcomes.

METHODS

We searched computerized databases, reference lists of pertinent articles and personal files from 1980 to 2011. We included randomized controlled trials (RCTs) conducted in critically ill adult patients that evaluated relevant clinical outcomes with antioxidant micronutrients (vitamins and trace elements) supplementation versus placebo.

RESULTS

A total of 21 RCTs met inclusion criteria. When the results of these studies were statistically aggregated (n = 20), combined antioxidants were associated with a significant reduction in mortality (risk ratio (RR) = 0.82, 95% confidence interval (CI) 0.72 to 0.93, P = 0.002); a significant reduction in duration of mechanical ventilation (weighed mean difference in days = -0.67, 95% CI -1.22 to -0.13, P = 0.02); a trend towards a reduction in infections (RR= 0.88, 95% CI 0.76 to 1.02, P = 0.08); and no overall effect on ICU or hospital length of stay (LOS). Furthermore, antioxidants were associated with a significant reduction in overall mortality among patients with higher risk of death (>10% mortality in control group) (RR 0.79, 95% CI 0.68 to 0.92, P = 0.003) whereas there was no significant effect observed for trials of patients with a lower mortality in the control group (RR = 1.14, 95% 0.72 to 1.82, P = 0.57). Trials using more than 500 μg per day of selenium showed a trend towards a lower mortality (RR = 0.80, 95% CI 0.63 to 1.02, P = 0.07) whereas trials using doses lower than 500 μg had no effect on mortality (RR 0.94, 95% CI 0.67 to 1.33, P = 0.75).

CONCLUSIONS

Supplementation with high dose trace elements and vitamins may improve outcomes of critically ill patients, particularly those at high risk of death.

Review of Intravenous Selenium Infusions for the Critically III Patient

Attempts to improve mortality for patients with sepsis, severe sepsis, systemic inflammatory response syndrome, and septic shock continue to challenge health care professionals. This review will explore how the antioxidant, and possibly pro-oxidant, properties of selenium may benefit critically ill patients. Literature examining improvements in clinical outcomes from intravenous (IV) selenium infusion therapy will be discussed. Although there is not an overwhelming amount of knowledge about IV selenium and its effect on morbidity and mortality, this review will outline recent research evaluating the use of IV selenium infusions and its potential to decrease morbidity and mortality for different critically ill patient populations.

Protective effects of ebselen on sodium-selenite-induced experimental cataract in rats

PURPOSE

To determine whether ebselen has a protective effect or antioxidative potential in a sodium-selenite-induced experimental cataract model.

SETTING

Fırat University, Elazığ, Turkey.

DESIGN

Experimental study.

METHODS

Twenty-one Sprague-Dawley rat pups were randomly divided into a control group, a sodium-selenite-induced-cataract group, and an ebselen-treated group; each group contained 7 rat pups. Rats in the control group received dimethyl sulfoxide (DMSO) intraperitoneally only and rats in the sodium-selenite-induced-cataract group received 30 nmol/g body weight sodium selenite subcutaneously and DMSO intraperitoneally 10 days postpartum. Rats in the ebselen group received 30 nmol/g body weight sodium selenite subcutaneously 10 days postpartum and were treated with 5 mg/kg body weight ebselen once a day for 4 consecutive days. Cataract development was assessed weekly for 3 weeks by slitlamp examination and graded using a scale. Reduced glutathione (GSH), total nitrite, and malondialdehyde (MDA) levels in lens supernatants were measured at the end of 3 weeks.

RESULTS

In the control group, all lenses were clear. In the ebselen-treated group, the mean cataract stage was significantly lower than in the sodium-selenite-induced-cataract group (P = .022). The GSH levels were significantly lower in the sodium-selenite-induced-cataract group than in the control and ebselen groups (P < .001). The MDA levels were lower in the ebselen group than in the sodium-selenite-induced-cataract group (P < .001). The mean total nitrite level was significantly lower in the sodium-selenite-induced-cataract group than in the ebselen group (P = .001).

CONCLUSIONS

Ebselen had a protective effect on cataract development in a sodium-selenite-induced experimental model. The protective effect of ebselen appears to be due to inhibition of oxidative stress.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Selenium supplementation in the critically ill

Selenium (Se) is an essential trace element with antioxidant, immunological, and anti-inflammatory properties, which are attributed to its presence in selenoproteins, as the 21st amino acid selenocysteine. These selenoenzymes are involved in redox signaling, antioxidant defense, thyroid hormone metabolism, and immune responses. Dietary intakes differ considerably between geographical regions, due to variability of the Se food content, leading to differences in dietary reference intakes and toxicity cautions. Critical illness with systemic inflammatory response syndrome (SIRS) is characterized by Se depletion with high morbidity and mortality. Se status correlates well with clinical outcome in SIRS and may be useful as an early predictor of survival. Several investigators have evaluated the benefits of Se supplementation for the critically ill, either as monotherapy or in an antioxidant micronutrient combination. Pharmaconutrition, with high-dose Se (from 500-1600 µg/d) involving an initial loading bolus, followed by continuous infusion, appears to be safe and efficacious, with evidence that it can improve clinical outcome by reducing illness severity, infectious complications, and decreasing mortality in the intensive care unit (ICU). We now have a clearer understanding of the pharmacokinetics of the initial and transient pro-oxidant effect of an intravenous bolus of selenite and the antioxidant effect of continuous infusion. Better biomarkers to ascertain optimum Se requirements for individual patients are now needed, and clinical practice guidelines need improvement. Nevertheless, sufficient evidence is available to consider initiating high-dose intravenous Se therapy routinely in critically ill SIRS patients, immediately on admission to the ICU.

The role of selenium in inflammation and immunity: from molecular mechanisms to therapeutic opportunities

Dietary selenium (]Se), mainly through its incorporation into selenoproteins, plays an important role in inflammation and immunity. Adequate levels of Se are important for initiating immunity, but they are also involved in regulating excessive immune responses and chronic inflammation. Evidence has emerged regarding roles for individual selenoproteins in regulating inflammation and immunity, and this has provided important insight into mechanisms by which Se influences these processes. Se deficiency has long been recognized to negatively impact immune cells during activation, differentiation, and proliferation. This is related to increased oxidative stress, but additional functions such as protein folding and calcium flux may also be impaired in immune cells under Se deficient conditions. Supplementing diets with above-adequate levels of Se can also impinge on immune cell function, with some types of inflammation and immunity particularly affected and sexually dimorphic effects of Se levels in some cases. In this comprehensive article, the roles of Se and individual selenoproteins in regulating immune cell signaling and function are discussed. Particular emphasis is given to how Se and selenoproteins are linked to redox signaling, oxidative burst, calcium flux, and the subsequent effector functions of immune cells. Data obtained from cell culture and animal models are reviewed and compared with those involving human physiology and pathophysiology, including the effects of Se levels on inflammatory or immune-related diseases including anti-viral immunity, autoimmunity, sepsis, allergic asthma, and chronic inflammatory disorders. Finally, the benefits and potential adverse effects of intervention with Se supplementation for various inflammatory or immune disorders are discussed.

Relevance of selenoprotein transcripts for selenium status in humans

The most commonly used methods for assessing the selenium (Se) status in humans involve analysis of Se concentration, selenoprotein activity, and concentration in the blood and its compartments. Recently, it has been suggested that the expression of selenoprotein mRNA in circulating blood leukocytes could differently reflect Se status, due to prioritization of specific selenoprotein synthesis in response to dietary Se supply. Whereas the Se levels required for optimization of selenoprotein P level and plasma glutathione peroxidise activity are well known, estimation of Se level that is required for maximal mRNA expression of selenoprotein in humans is the subject of current investigations. Studies on rats suggest that whole blood selenoprotein mRNA level can be used as the relevant molecular biomarker for assessing Se status, and suboptimal Se intake may be sufficient to achieve effective expression. Human studies, however, did not confirm this hypothesis. According to studies on rodents and humans discussed in this review, it appears that suboptimal Se intake may be sufficient to satisfy molecular requirements of Se and it is lower than current recommended dietary intake in humans. The use of selenoprotein transcripts as a molecular biomarker of Se status requires further studies on a large group of healthy individuals with different baseline Se, including data regarding genetic polymorphism of selenoproteins and data regarding potential modifiers of Se metabolism.

Hydroxyl radical and its scavengers in health and disease

It is generally believed that diseases caused by oxidative stress should be treated with antioxidants. However, clinical trials with such antioxidants as ascorbic acid and vitamin E, failed to produce the expected beneficial results. On the other hand, important biomolecules can be modified by the introduction of oxygen atoms by means of non-oxidative hydroxyl radicals. In addition, hydroxyl radicals can reduce disulfide bonds in proteins, specifically fibrinogen, resulting in their unfolding and scrambled refolding into abnormal spatial configurations. Consequences of this reaction are observed in many diseases such as atherosclerosis, cancer and neurological disorders, and can be prevented by the action of non-reducing substances. Moreover, many therapeutic substances, traditionally classified as antioxidants, accept electrons and thus are effective oxidants. It is described in this paper that hydroxyl radicals can be generated by ferric ions without any oxidizing agent. In view of the well-known damaging effect of poorly chelated iron in the human body, numerous natural products containing iron binding agents can be essential in the maintenance of human health. However, beneficial effects of the great number of phytochemicals that are endowed with hydroxyl radical scavenging and/or iron chelating activities should not be considered as a proof for oxidative stress.