Role of selenium in the pathophysiology of cardiorenal anaemia syndrome

Chronic kidney disease (CKD) and cardiovascular disease (CVD) have multiple bidirectional mechanisms, and anaemia is one of the critical factors that are associated with the progression of the two disorders [referred to as cardiorenal anaemia syndrome (CRAS)]. Several lines of evidence indicate that CRAS confers a worse prognosis, suggesting the need to clarify the underlying pathophysiology. Among the micronutrients (trace elements) that are essential to humans, inadequate iron status has previously been implicated in the pathogenesis of CRAS; however, the roles of other trace elements remain unclear. Selenium critically regulates the function of selenoproteins, in which selenocysteine is present at the active centres. The human genome encodes 25 selenoproteins, and accumulating data indicate that they regulate diverse physiological processes, including cellular redox homeostasis, calcium flux, thyroid hormone activity and haematopoiesis, all of which directly or indirectly influence cardiac function. The essential role of selenium in human health is underscored by the fact that its deficiency results in multiple disorders, among which are cardiomyopathy and abnormal erythrocyte morphology. Studies have shown that selenium deficiency is not uncommon in CKD patients with poor nutritional status, suggesting that it may be an under-recognized cause of anaemia and cardiovascular disorders in these patients. In this review, we discuss the role of selenium in the pathophysiology of CKD, particularly in the context of the interconnection among CKD, cardiac dysfunction and anaemia. Given that selenium deficiency is associated with treatment-resistant anaemia and an increased risk of CVD, its role as a key modulator of CRAS merits future investigation.

Micronutrients and Renal Outcomes: A Prospective Cohort Study

Background: Micronutrients are essential in maintaining normal human physiology. Data regarding the association between micronutrients and renal outcomes in chronic kidney disease (CKD) are lacking. Methods: This prospective observational cohort study enrolled 261 patients with CKD stages 1−5 and 30 subjects with normal renal function. Baseline serum zinc (Zn), selenium (Se), chromium, manganese, and copper, and laboratory tests were performed at enrolment. The primary endpoint was the presence of end-stage renal disease (ESRD) requiring long-term renal replacement therapy. Results: The median follow-up periods of renal and non-renal survivals were 67.78 and 29.03 months, respectively. Multiple linear regression showed that Zn and Se (β ± SE: 24.298 ± 8.616, p = 0.005; 60.316 ± 21.875, p = 0.006, respectively) levels were positively correlated with renal function. Time to ESRD was significantly longer for those with Zn levels ≥1287.24 ng/g and Se levels ≥189.28 ng/g (both p < 0.001). Cox regression analysis identified a higher Zn level as an independently negative predictor of ESRD after adjusting for renal function (hazard ratio, 0.450, p = 0.019). Conclusion: Serum Se and Zn concentrations are positively associated with renal function and better renal outcomes. A higher Zn concentration could independently predict better renal survival.

Selenium Nutritional Status and Glutathione Peroxidase Activity and Its Relationship with Hemodialysis Time in Individuals Living in a Brazilian Region with Selenium-Rich Soil

Suboptimal selenium status may impair the antioxidant defense system in patients undergoing hemodialysis, compromising the selenoenzyme glutathione peroxidase activity. To evaluate the association between the duration of hemodialysis, nutritional selenium status, glutathione peroxidase activity (GPx), and thiobarbituric acid reactive substance (TBARS) levels in patients with chronic renal failure undergoing hemodialysis in a region of selenium-rich soils (Ceará, Northeast Brazil). The case-control study of 75 individuals aged 18 to 88 years was allocated between two groups: hemodialysis (n = 41) and control (n = 34). Plasma and erythrocytes selenium levels were determined by inductively coupled plasma optical emission spectrometry. The GPx activity and TBARS levels were also evaluated. In addition, the hemodialysis group was stratified according to the duration of treatment (≤ 59 months and ≥ 60 months). The Mann-Whitney test, Student's t test, and Pearson's or Spearman's correlation were applied according to the data distribution. Moreover, a quantile regression was performed. The significance level (p) was < 0.05. The hemodialysis group had lower selenium levels in their plasma and erythrocytes than the control group (p < 0.001). However, there was no difference in the GPx activity between the groups. Furthermore, an association between the hemodialysis group and selenium levels in plasma (coefficient - 16,343, p < 0.001) and erythrocytes (coefficient - 7839, p = 0.003) was observed by quantile regression, independent of age, sex, and body-mass index. In individuals who had undergone treatment for 60 months or more, GPx activity was lower (p = 0.026) and TBARS levels higher (p = 0.011) than in those who had undergone treatment for less than 60 months. The status of selenium was reduced in the hemodialysis group compared to the control group. The lower GPx activity and higher levels of TBARS in individuals who had undergone treatment for 60 months or more correlated with greater oxidative stress.

Associations Between Blood Trace Element Levels and Nutritional Status in Maintenance Hemodialysis

OBJECTIVE(S)

We aimed to investigate the associations between blood trace element levels and nutritional status in patients undergoing maintenance hemodialysis (MHD).

METHODS

This cross-sectional study included patients undergoing MHD who were treated at our center in September 2019. Clinical and demographic data and blood samples were collected before hemodialysis sessions, and the levels of manganese, lead, selenium, zinc, and copper were measured by inductively coupled plasma mass spectrometry. The Simplified Nutritional Appetite Questionnaire scale was used to assess patient appetite. Skinfold thickness, bicep circumference, upper arm muscle circumference, 7-point Subjective Global Assessment, Nutritional Risk Screening 2002 (NRS 2002), and Geriatric Nutritional Risk Index (GNRI) were used to assess patient nutritional status. Univariate and multivariate logistic regression analyses were performed to study the relationship between trace elements and nutritional indicators.

RESULTS

In total, 118 patients (64 males and 54 females) were included, with a median dialysis vintage of 34.0 months (16.0-54.5 months) and an average age of 63.20 ± 14.26 years. Malnourished patients, as defined by the GNRI, Subjective Global Assessment, and NRS 2002, accounted for 28.0%, 49.2%, and 26.3% of enrolled patients, respectively. The multivariate binary logistic regression showed that higher blood copper levels were independently associated with nutritional risk defined as GNRI ≤91.2 (odds ratio [OR] = 1.003, 95% confidence interval [CI] = 1.000-1.006; P = .020), whereas lower blood zinc levels (OR = 0.634, 95% CI = 0.439-0.916; P = .015), blood zinc < 4.220 mg/L (OR = 3.723, 95% CI = 1.274-10.879; P = .016), lower blood selenium levels (OR = 0.959, 95% CI = 0.929-0.990; P = .010), and blood selenium < 85 μg/L (OR = 5.568, 95% CI = 1.039-29.840; P = .045) were independently associated with a nutritional risk defined as NRS 2002 ≥ 3.

CONCLUSION(S)

Higher levels of blood copper and lower levels of blood zinc and selenium were independently associated with higher nutritional risk in MHD patients.

Selenium Deficiency-Induced Damage and Altered Expression of Mitochondrial Biogenesis Markers in the Kidneys of Mice

Previous studies have raised concerns that kidney disease is often closely related to low serum Se levels in patients and that hyposelenemia may increase the vulnerability of patients to complications. However, few studies examining renal injury caused by Se deficiency have been conducted. To determine the effects of a selenium-deficient diet on renal function, a mouse model was fed a selenium-deficient diet (0.02 mg Se/kg) for 20 weeks. Meanwhile, mice in the control group (selenium-adequate) were fed a standard diet (0.18 mg Se/kg). The cellular models were established by lentiviral Trnau1ap-shRNA vectors transfected into mouse podocyte (MPC5) and mouse renal tubular epithelial (TCMK1) cell lines. Significant increases in serum creatinine levels and urinary protein/creatinine ratios were accompanied by increased MDA content in the Se-deficient group compared to the control group. The morphological observations of tissues showed widespread inflammation and ultrastructural changes in the Se-deficient group, such as swollen mitochondria and extensive podocyte fusion and renal tubular microvilli shedding. In addition, the expression of COXIV and cytochrome c was significantly downregulated in the Se-deficient group. Importantly, the mRNA levels of silent mating type information regulation 2 homolog 1 (SIRT1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and the protein levels of SIRT1 were increased in the Se-deficient group compared with the normal control group. Our data indicate that Se deficiency induces renal injury in mice. The elevated oxidative stress caused by Se deficiency may result in mitochondrial damage, which might affect renal function. Moreover, the SIRT1/PGC1α axis likely plays an important role in the compensatory mechanism of mitochondrial dysfunction.

A Clinical Tool to Predict Low Serum Selenium in Patients with Worsening Heart Failure

Selenium is an essential micronutrient, and a low selenium concentration (<100 µg/L) is associated with a poorer quality of life and exercise capacity, and an impaired prognosis in patients with worsening heart failure. Measuring selenium concentrations routinely is laborious and costly, and although its clinical utility is yet to be proven, an easy implemented model to predict selenium status is desirable. A stepwise multivariable logistic regression analysis was performed using routinely measured clinical factors. Low selenium was independently predicted by: older age, lower serum albumin, higher N-terminal pro-B-type natriuretic peptide levels, worse kidney function, and the presence of orthopnea and iron deficiency. A 10-points risk-model was developed, and a score of ≥6 points identified >80% of patients with low selenium (sensitivity of 44%, specificity of 80%). Given that selenium and iron overlap in their physiological roles, we evaluated the shared determinants and prognostic associates. Both deficiencies shared similar clinical characteristics, including the model risk factors and, in addition, a low protein intake and high levels of C-reactive protein. Low selenium was associated with a similar or worse prognosis compared to iron deficiency. In conclusion, although it is difficult to exclude low selenium based on clinical characteristics alone, we provide a prediction tool which identifies heart failure patients at higher risk of having a low selenium status.

Antioxidant Supplementation in Renal Replacement Therapy Patients: Is There Evidence?

The disruption of balance between production of reactive oxygen species and antioxidant systems in favor of the oxidants is termed oxidative stress (OS). To counteract the damaging effects of prooxidant free radicals, all aerobic organisms have antioxidant defense mechanisms that are aimed at neutralizing the circulating oxidants and repair the resulting injuries. Antioxidants are either endogenous (the natural defense mechanisms produced by the human body) or exogenous, found in supplements and foods. OS is present at the early stages of chronic kidney disease, augments progressively with renal function deterioration, and is further exacerbated by renal replacement therapy. End-stage renal disease patients, on hemodialysis (HD) or peritoneal dialysis (PD), suffer from accelerated OS, which has been associated with increased risk for mortality and cardiovascular disease. During HD sessions, the bioincompatibility of dialyzers and dialysate trigger activation of white blood cells and formation of free radicals, while a significant loss of antioxidants is also present. In PD, the bioincompatibility of solutions, including high osmolality, elevated lactate levels, low pH, and accumulation of advanced glycation end-products trigger formation of prooxidants, while there is significant loss of vitamins in the ultrafiltrate. A number of exogenous antioxidants have been suggested to ameliorate OS in dialysis patients. Vitamins B, C, D, and E, coenzyme Q10, L-carnitine, a-lipoic acid, curcumin, green tea, flavonoids, polyphenols, omega-3 polyunsaturated fatty acids, statins, trace elements, and N-acetylcysteine have been studied as exogenous antioxidant supplements in both PD and HD patients.

Efficacy of Nutritional Interventions on Inflammatory Markers in Haemodialysis Patients: A Systematic Review and Limited Meta-Analysis

Low-grade chronic inflammation is prevalent in patients undergoing haemodialysis (HD) treatment and is linked to the development of premature atherosclerosis and mortality. The non-pharmacological approach to treat inflammation in HD patients through nutritional intervention is well cited. We aimed to assess the efficacy of different nutritional interventions at improving inflammatory outcomes in HD patients, based on markers such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α). We searched PubMed, Cochrane Library, and Embase for randomized controlled trials (RCT) published before June 2017. Inclusion criteria included RCTs on adult patients on maintenance HD treatment with duration of nutritional interventions for a minimum 4 weeks. Risk of bias was assessed using the Jadad score. In total, 46 RCTs experimenting different nutritional interventions were included in the review and categorized into polyphenols rich foods, omega-3 fatty acids, antioxidants, vitamin D, fibres, and probiotics. Meta-analyses indicated significant reduction in CRP levels by omega-3 fatty acids (Random model effect: -0.667 mg/L, p < 0.001) and vitamin E (fixed model effect: -0.257 mg/L, p = 0.005). Evidence for other groups of nutritional interventions was inconclusive. In conclusion, our meta-analysis provided evidence that omega-3 fatty acids and vitamin E could improve inflammatory outcomes in HD patients.

Association of Depression With Selenium Deficiency and Nutritional Markers in the Patients With End-Stage Renal Disease on Hemodialysis

OBJECTIVE

Depression is considered as the most common psychological problem in hemodialysis (HD) patients. As there is little evidence regarding the association of depression with serum selenium level as an antioxidant in these patients, the current survey investigates the possible relationship between depression and nutritional status including serum selenium levels.

DESIGN

Cross-sectional study.

SETTING AND SUBJECTS

A total of 110 HD patients and 40 healthy controls were enrolled in the study. The patients were in the age range of 18 to 85 years, who had been on hemodialysis for at least 3 months without any acute illness.

MAIN OUTCOME MEASURE

Beck Depression Inventory was used for assessing the severity of depression. Malnutrition was evaluated through subjective global assessment (SGA) and malnutrition inflammation score (MIS). Serum selenium levels and routine laboratory markers were measured from fasting samples.

RESULTS

Sixty-two percent of the patients had some degree of depression based on Beck Depression Inventory score. HD patients were considered to be selenium deficient after comparing the mean value of serum selenium between the patients and controls (P < .001). No significant difference was found in serum selenium levels between depressed HD patients and the rest of patients without depression. The mean level of SGA and MIS in the depressed patients was significantly higher than the rest of patients (P = .03 and P = .04, respectively). Also lower levels of hemoglobin and serum albumin were significantly seen in depressed patients compared with nondepressed ones (P = .004 and P = .04, respectively).

CONCLUSIONS

Although the HD patients in this study were selenium deficient, no significant association was found between depression and selenium. In addition, depression was more prevalent in malnourished HD patients with higher SGA and MIS scores and lower serum albumin and hemoglobin levels.

Trace elements in dialysis

In end-stage chronic kidney disease (CKD), pediatric nephrologists must consider the homeostasis of the multiple water-soluble ions that are influenced by renal replacement therapy (RRT). While certain ions such as potassium and calcium are closely monitored, little is known about the handling of trace elements in pediatric dialysis. RRT may lead to accumulation of toxic trace elements, either due to insufficient elimination or due to contamination, or to excessive removal of essential trace elements. However, trace elements are not routinely monitored in dialysis patients and no mechanism for these deficits or toxicities has been established. This review summarizes the handling of trace elements, with particular attention to pediatric data. The best data describe lead and indicate that there is a higher prevalence of elevated lead (Pb, atomic number 82) levels in children on RRT when compared to adults. Lead is particularly toxic in neurodevelopment and lead levels should therefore be monitored. Monitoring of zinc (Zn, atomic number 30) and selenium (Se, atomic number 34) may be indicated in the monitoring of all pediatric dialysis patients to reduce morbidity from deficiency. Prospective studies evaluating the impact of abnormal trace elements and the possible therapeutic value of intervention are required.

[Importance of selenium homeostasis in chronic and end-stage kidney diseases]

Selenium is an essential trace element for the human body with a significant antioxidant effect. Selenium deficiency and excess are both detrimental for proper functioning of the human body. The possible association between selenium deficiency and acute or chronic renal disease, along with their complications has been less intensively investigated, however, there are firm data showing that selenium deficiency and renal failure increase the risk of both coronary artery disease and total mortality. Further studies revealed that selenium deficiency increases the risk of death due to infection in patients treated with hemodialysis through dysfunction of the immune system. However, there are no data whether the imbalance of selenium metabolism, especially selenium deficiency, could cause chronic kidney disease or renal failure. As far as results of selenium measurements, there is convincing evidence that protein loss and renal replacement treatment reduce serum selenium levels. Despite some contradictory results obtained from various studies regarding selenium deficiency in chronic kidney diseases, it seems that selenium supplementation may be beneficial in many patients with severe or end-stage kidney disease including those treated with dialysis.

Decreased serum selenium levels are correlated with diminished coronary flow reserve among hemodialysis patients

Cardiovascular diseases are the main reason of high mortality among hemodialysis patients. Decreased serum selenium levels may have a role in accelerated atherosclerosis in this patient group. The hypothesis of this study was to show a correlation between decreased serum selenium levels and coronary flow reserve as an indicator of endothelial dysfunction and atherosclerosis in HD patients. Seventy-one chronic hemodialysis patients and age 65 and sex-matched healthy controls were included in the study. Plasma selenium levels were measured by spectrophotometry, and coronary flow reserve was assessed by transthoracic Doppler echocardiography. Serum selenium levels (34.16 ± 6.15 ng/ml vs. 52.4 ± 5.51 ng/ml, P < 0.001) and coronary flow reserve values (1.73 ± 0.11 vs. 2.32 ± 0.28, P < 0.001) were significantly lower in hemodialysis patients compared with controls, respectively. There was a significant positive correlation between coronary flow reserve and serum levels of selenium (r = 0.676, P < 0.001). A linear regression analysis showed that serum levels of selenium were independently and positively correlated with coronary flow reserve (regression coefficient = 0.650, P < 0.05). This study was the first to show a positive and independent correlation between decreased selenium levels and diminished coronary flow reserve as an indicator of endothelial dysfunction and atherosclerosis in hemodialysis patients. Our data suggest that decreased serum selenium levels may facilitate the development of endothelial dysfunction and disruption of coronary flow reserve which occur before the development of overt atherosclerosis.

Zinc supplementation alters plasma aluminum and selenium status of patients undergoing dialysis: a pilot study

End stage renal disease patients undergoing long-term dialysis are at risk for abnormal concentrations of certain essential and non-essential trace metals and high oxidative stress. We evaluated the effects of zinc (Zn) supplementation on plasma aluminum (Al) and selenium (Se) concentrations and oxidative stress in chronic dialysis patients. Zn-deficient patients receiving continuous ambulatory peritoneal dialysis or hemodialysis were divided into two groups according to plasma Al concentrations (HA group, Al > 50 μg/L; and MA group, Al > 30 to ≤ 50 μg/L). All patients received daily oral Zn supplements for two months. Age- and gender-matched healthy individuals did not receive Zn supplement. Clinical variables were assessed before, at one month, and after the supplementation period. Compared with healthy subjects, patients had significantly lower baseline plasma Se concentrations and higher oxidative stress status. After two-month Zn treatment, these patients had higher plasma Zn and Se concentrations, reduced plasma Al concentrations and oxidative stress. Furthermore, increased plasma Zn concentrations were related to the concentrations of Al, Se, oxidative product malondialdehyde (MDA), and antioxidant enzyme superoxide dismutase activities. In conclusion, Zn supplementation ameliorates abnormally high plasma Al concentrations and oxidative stress and improves Se status in long-term dialysis patients.

Altered serum selenium and uric acid levels and dyslipidemia in hemodialysis patients could be associated with enhanced cardiovascular risk

In the present study, the first objective was to follow up serum selenium (Se) concentrations in 117 hemodialysis patients (HPs) during a 2-year longitudinal study, relating concentrations to biochemical indexes (n = 6; namely lipoprotein profile, uric acid, and total protein levels). It was also evaluated whether the disease is associated with an enhanced cardiovascular risk. A healthy control group (n = 50) was also studied. Mean serum Se levels were significantly lower in HPs than in the controls (p = 0.002); mean levels significantly increased from the first to third blood sampling (p < 0.001). HPs showed a marked dyslipidemia, with a significant reduction in total cholesterol, low-density lipoprotein, and high-density lipoprotein cholesterol levels and a significant increase in triglyceride levels (p < 0.001). HPs showed a marked hyperuricemia (p < 0.001). Serum selenium levels in HPs were correlated negatively with uric acid levels (inflammation biomarker; p < 0.01). In HPs, serum Se levels are reduced due to their disease (chronic renal failure). Serum Se levels rose until the third blood sampling. The marked dyslipidemia and hyperuricemia found in HPs and the negative correlation between the serum Se and uric acid levels in these patients could imply an enhanced cardiovascular risk.