Selenium in uremia

Selenium Metabolism in Patients on Continuous Ambulatory Peritoneal Dialysis

Background

Selenium is an essential trace element for living organisms. In many publications, researchers express concern about a possible Se deficiency in patients with end-stage chronic renal failure (ESCRF) undergoing continuous ambulatory peritoneal dialysis (CAPD). However, in a number of published articles, the data provide no evidence that patients under CAPD develop Se deficiency.

Objective

We investigated Se metabolism in ESCRF patients on CAPD.

Setting

The study was carried out at the Department of Propaedeutic Surgery, Athens University; the Laboratory for Material Analysis of the Nuclear Physics Institute; and the State General Hospital, Athens, Greece.

Patients and Methods

The study group included 24 patients on CAPD treatment, 14 ESCRF patients, and 17 healthy controls. We measured the Se and Fe content of serum, blood, and erythrocytes. We also measured hematocrit, serum total proteins and albumins, and Se in dialysate effluent.

Results

As compared with healthy subjects, the ESCRF and CAPD patients exhibited reduced serum concentrations of Se. However, considering the difference in hematocrit values, the total serum-transported Se per liter of blood was close to normal. Erythrocyte Se proved normal for both groups. The measured Se in the spent effluent indicates that patients under CAPD receive approximately 100 μg Se from their daily diet, as normal subjects do. The Se measurement data from the effluent indicate that 90% of the Se carried by the serum is bound to albumins and that only the remaining 10% is in the form of low molecular weight selenate, free to pass the peritoneal membrane. Of the 24 CAPD patients studied, 4 patients (all women) showed extremely low Se serum levels. Data suggest that those low levels are more likely due to the significantly lower serum albumin levels in the 4 patients than to an insufficient dietary intake.

Conclusions

Data from the present experimental work suggest that patients undergoing CAPD receive the necessary quantities of Se from their regular diet. The data contradict statements in the relevant literature that CAPD patients develop Se deficiency.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

Selenium and selenium-dependent antioxidants in chronic kidney disease

Oxidative stress plays a key role in numerous disease processes including chronic kidney disease (CKD). In general, oxygen metabolism leads to the formation of reactive oxygen species (ROS) dangerous to cells. Although enzymes and low-molecular-weight antioxidants protect against ROS, chronic imbalances of formation and elimination can eventually overwhelm endogenous defenses leading to deleterious consequences. In CKD, glutathione peroxidases (GSH-Px) play an important role in ROS metabolism. Plasma GSH-Px is synthesized in the kidney and requires selenium (Se) as a cofactor. Interestingly, Se and plasma GSH-Px are both significantly reduced in CKD, especially for those patients on hemodialysis. Supplementation of Se in these patients results in modest increases of GSH-Px, presumably from residual renal tissue. Kidney transplantation rapidly restores plasma GSH-Px. In this chapter, the relevance of these findings to CKD is explored with emphasis on renal disease processes and impact on attendant disorders including cancer and cardiovascular disease.

[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.

Oxidative stress and nucleic acid oxidation in patients with chronic kidney disease

Patients with chronic kidney disease (CKD) have high cardiovascular mortality and morbidity and a high risk for developing malignancy. Excessive oxidative stress is thought to play a major role in elevating these risks by increasing oxidative nucleic acid damage. Oxidative stress results from an imbalance between reactive oxygen/nitrogen species (RONS) production and antioxidant defense mechanisms and can cause vascular and tissue injuries as well as nucleic acid damage in CKD patients. The increased production of RONS, impaired nonenzymatic or enzymatic antioxidant defense mechanisms, and other risk factors including gene polymorphisms, uremic toxins (indoxyl sulfate), deficiency of arylesterase/paraoxonase, hyperhomocysteinemia, dialysis-associated membrane bioincompatibility, and endotoxin in patients with CKD can inhibit normal cell function by damaging cell lipids, arachidonic acid derivatives, carbohydrates, proteins, amino acids, and nucleic acids. Several clinical biomarkers and techniques have been used to detect the antioxidant status and oxidative stress/oxidative nucleic acid damage associated with long-term complications such as inflammation, atherosclerosis, amyloidosis, and malignancy in CKD patients. Antioxidant therapies have been studied to reduce the oxidative stress and nucleic acid oxidation in patients with CKD, including alpha-tocopherol, N-acetylcysteine, ascorbic acid, glutathione, folic acid, bardoxolone methyl, angiotensin-converting enzyme inhibitor, and providing better dialysis strategies. This paper provides an overview of radical production, antioxidant defence, pathogenesis and biomarkers of oxidative stress in patients with CKD, and possible antioxidant therapies.

The effect of selenium supplementation in the prevention of DNA damage in white blood cells of hemodialyzed patients: a pilot study

Patients with chronic kidney disease (CKD) have an increased incidence of cancer. It is well known that long periods of hemodialysis (HD) treatment are linked to DNA damage due to oxidative stress. In this study, we examined the effect of selenium (Se) supplementation to CKD patients on HD on the prevention of oxidative DNA damage in white blood cells. Blood samples were drawn from 42 CKD patients on HD (at the beginning of the study and after 1 and 3 months) and from 30 healthy controls. Twenty-two patients were supplemented with 200 μg Se (as Se-rich yeast) per day and 20 with placebo (baker's yeast) for 3 months. Se concentration in plasma and DNA damage in white blood cells expressed as the tail moment, including single-strand breaks (SSB) and oxidative bases lesion in DNA, using formamidopyrimidine glycosylase (FPG), were measured. Se concentration in patients was significantly lower than in healthy subjects (P < 0.0001) and increased significantly after 3 months of Se supplementation (P < 0.0001). Tail moment (SSB) in patients before the study was three times higher than in healthy subjects (P < 0.01). After 3 months of Se supplementation, it decreased significantly (P < 0.01) and was about 16% lower than in healthy subjects. The oxidative bases lesion in DNA (tail moment, FPG) of HD patients at the beginning of the study was significantly higher (P < 0.01) compared with controls, and 3 months after Se supplementation it was 2.6 times lower than in controls (P < 0.01). No changes in tail moment was observed in the placebo group. In conclusion, our study shows that in CKD patients on HD, DNA damage in white blood cells is higher than in healthy controls, and Se supplementation prevents the damage of DNA.

Euthyroid Sick Syndrome and Nutritional Status are Correlated with Hyposelenemia in Hemodialysis Patients

Background

Maintenance hemodialysis (HD) patients have altered levels of thyroid hormone (TH) in euthyroid sick syndrome, along with low T3 levels and several nutritional metabolic disturbances. Selenium (Se) is an essential trace element for living organisms, which has been shown to play a major role in thyroid hormone levels and the nutritional metabolism. The aims of the present study were to assess the changes in serum levels of selenium and their correlation with disorders of the endocrine and nutritional metabolism in HD patients.

Methods

Fifty-three uremic patients with hemodialysis were evaluated; 30 healthy volunteers served as controls. Baseline serum concentrations of total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4), and free thyroxine (FT4) were determined by radioimmunoassay (RIA). Serum levels of thyroid-stimulating hormone (TSH) and intact parathyroid hormone (iPTH) were measured by a sensitive immunoradiometric assay (IRMA). Serum selenium was analyzed using Hitachi Z- 2000 polarized Zeeman atomic absorption spectrometry. Other metabolic variables were measured in all patients and control subjects. Multiple correlation analysis was performed among variables.

Results

Higher serum triglyceride, LDL-C, ApoB and lower albumin, HDL-C levels were found in subjects with HD. Mean serum selenium concentration was significantly lower in the HD group than in the control group (p<0.01). The levels of serum TT3 and FT3 in HD patients were significantly lower than in healthy control subjects (p<0.01; p<0.05, respectively), but TT4, FT4 and TSH were not different. However, serum iPTH levels were significantly higher in patients than in controls (p<0.01). In the group of HD patients, serum selenium levels were significantly positively correlated with albumin, HDL-C, TT3 and FT3; and negatively correlated with triglyceride (TG), LDL-C, ApoB and iPTH. Both serum TT3 and FT3 levels were significantly positively correlated with HDL-C; and negatively correlated with TG, LDL-C and ApoB.

Conclusions

These data suggest that hyposelenemia in HD patients correlated with euthyroid sick syndrome with low T3 levels, and nutritional status with hyperlipidemia and hypoalbuminemia which might be involved in dysfunction in the endocrine and nutrition metabolism in dialysis patients.

Chronic treatment with statins increases the availability of selenium in the antioxidant defence systems of hemodialysis patients

PROJECT

Oxidative stress (OS) is enhanced in hemodialysis (HD) patients. Lipid peroxidation and oxidative damage to glycids, proteins and nucleic acids are the main consequences of OS and are associated with increased cardiovascular risk. Vitamin E and glutathione peroxidase (GSH-Px) represent the main antioxidant systems in human cells. Selenium (Se), bound to the active sites of GSH-Pxs, plays a critical role in this antioxidant defence system. Statins are widely used and extensively investigated in the prevention of cardiovascular disease, notably in high-risk subjects. Several studies show antioxidant effects of statins not related to their lipid-lowering action. Our study aimed to compare serum Se concentration in ESRD patients on maintenance HD and in homogeneous healthy subjects and to investigate whether chronic treatment with statins may interfere with serum Se concentration in HD patients.

PROCEDURE

A total of 103 HD patients and 69 healthy subjects were enrolled; HD patients were divided into patients who were not treated with statins (group A) and patients who assumed statins since 6 months at least (group B). Serum Se was determined by atomic absorption spectrometry.

RESULTS

Serum Se was significantly lower in HD patients of group A compared with healthy subjects (81.65+/-19.66 Vs. 96.47+/-15.62 mcg/L, p<0.0040). However, in HD patients who assumed statins serum, Se was significantly higher than in HD patients who did not (111.83+/-18.82 vs. 81.65+/-19.66 mcg/L, p<0.0001).

CONCLUSIONS

Our results suggest that in HD patients chronic treatment with statins is related to higher-serum Se concentration.

Overproduction of reactive oxygen species in end-stage renal disease patients: a potential component of hemodialysis-associated inflammation

During the past decade, hemodialysis (HD)-induced inflammation has been linked to the development of long-term morbidity in end-stage renal disease (ESRD) patients on regular renal replacement therapy. Because interleukins and anaphylatoxins produced during HD sessions are potent activators for nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, an example of an enzyme that is responsible for overproduction of reactive oxygen species (ROS), this may constitute a link between leukocyte activation and cell or organ toxicity. Oxidative stress, which results from an imbalance between oxidant production and antioxidant defense mechanisms, has been documented in ESRD patients using lipid and/or protein oxidative markers. Characterization of HD-induced oxidative stress has included identification of potential activators for NADPH oxidase. Uremia per se could prime phagocyte oxidative burst. HD, far from improving the oxidative status, results in an enhancement of ROS owing to hemoincompatibility of the dialysis system, hemoreactivity of the membrane, and trace amounts of endotoxins in the dialysate. In addition, the HD process is associated with an impairment in antioxidant mechanisms. The resulting oxidative stress has been implicated in long-term complications including anemia, amyloidosis, accelerated atherosclerosis, and malnutrition. Prevention of oxidative stress in HD might focus on improving the hemocompatibility of the dialysis system, supplementation of deficient patients with antioxidants, and modulation of NADPH oxidase by pharmacologic approaches.

Selenium and glutathione peroxidases in blood of patients with different stages of chronic renal failure

In patients with chronic renal failure (CRF) Se concentration in blood components is usually lower as compared with healthy controls. One of the five known forms of Se-dependent glutathione peroxidases (GSH-Px), the plasma GSH-Px, is synthesized primarily in the kidney. In CRF patients, plasma GSH-Px activity is reduced and the reduction increases with the progress of the disease. The Se concentration in blood components was measured spectrofluorometrically with 2,3-diaminonaphthalene as complexing reagent. Activities of GSH-Px in red cells and in plasma were assayed by the coupled method with t-butyl hydroperoxide as substrate. The study group consisted of 150 patients in different stages of CRF. The results were compared with the values for 30 healthy subjects. Se concentrations in whole blood and plasma of the entire group of patients were significantly lower (p < 0.01) as compared with the healthy subjects. In the incipient stage, however, the Se levels in all blood components were non-significantly lower. In whole blood and plasma the Se levels gradually decreased, reaching in the end stage values that were lower by 29 to 32% (p < 0.0001) as compared with the control group. Total protein and albumin levels in plasma of patients were significantly lower (p < 0.0001) as compared with healthy subjects and they decreased linearly with the progress of the disease. Positive and highly significant correlations were noted between total plasma protein and plasma Se concentrations (p < 0.0001) as well as between plasma albumin and plasma Se concentrations (p < 0.0001). Red cell GSH-Px activity in the entire group of patients was lower (p < 0.05) than in the control group and did not change significantly with the progress of the disease. In plasma, however, GSH-Px activity of the entire group was lower by 33% (p < 0.0001) as compared with healthy subjects and decreased gradually with increasing renal failure. Highly significant, inverse correlations were seen between creatinine levels and plasma GSH-Px activities (p < 0.0001) as well as between urea nitrogen levels and plasma GSH-Px activities (p < 0.0001) when all stages of the disease were included. In conclusion, patients with CRF exhibit lower Se levels in blood components as compared with healthy subjects. In whole blood and plasma these levels decrease with the progress of the disease. Plasma GSH-Px activity in patients was extremely reduced and it dramatically decreased with the progress of the illness.

Micronutrient status and glutathione peroxidase in bedridden patients on tube feeding

Deficiency of micronutrients, especially selenium, is common in critically ill patients. We investigated the micronutrient status (selenium, zinc, copper and manganese) and glutathione peroxidase (GSH-Px) activity in 30 tube-fed patients and 21 hospitalized non-tube-fed control patients. Serum levels of selenium, copper and manganese in tube-fed patients were significantly lower than in control patients (selenium: 4.85+/-1.38 microg/dl versus 8.67+/-1.45 pg/dl; copper: 44.7+/-36.9 microg/dl versus 92.1+/-21.2 microg/dl; manganese 0.59+/-0.41 microg/dl versus 1.52+/-0.59 microg/dl). However, zinc and log GSH-Px in the serum were similar in the two groups. Serum selenium concentration correlated with the daily intake of selenium in tube-fed patients, but zinc, copper and manganese concentrations did not correlate with the daily intake of the respective trace elements in tube-fed patients. Blood GSH-Px activity correlated positively with serum selenium concentrations in the control patients, but not in tube-fed patients. These results demonstrate that selenium content of enteral feed appears to be insufficient to maintain normal serum levels in elderly bedridden patients. Our findings emphasize the importance of monitoring micronutrient status in patients on enteral feeding to avoid trace element deficiencies.

Selenium, glutathione peroxidases, and some other antioxidant parameters in blood of patients with chronic renal failure

In the present study several parameters associated with oxidative stress were examined in the blood of 25 chronic renal failure (CRF) patients and the results were compared with 18 healthy subjects. Mean creatinine concentration in patients was 1,216 +/- 292 micromol/l. Selenium (Se) concentration in red cells, whole blood and in plasma of CRF patients (106 +/- 32.5, 59.0 +/- 16.7 and 42.4 +/- 13.8 ng/ml, respectively) was significantly (0.0001 < P 0.01) lower (by 20-42%) compared with the controls. Red cell and plasma glutathione peroxidase (GSH-Px) activities (16.6 +/- 3.4 U/g Hb and 93.7 +/- 32.9 U/l plasma) were lower by 12 and 53% (P < 0.05 and < 0.0001, respectively) in patients than in healthy subjects. GSH concentration in red cells of patients (2.81 +/- 0.45 mmol/l) was significantly (P < 0.001) higher (by 20%) than in control group. Malonyldialdehyde (MDA) concentration (expressed as thiobarbituric acid-reactive substances) in red cells of patients (725 +/- 155 nmol/g Hb) was significantly (P < 0.001) higher (by 28%) than in control group. No significant difference was observed in the activity of superoxide dismutase in pLasma between the two groups. In conclusion, our results confirm that the aLterations in Se levels in blood components and in GSH-Px activity in plasma show that the kidney plays an important role in Se homeostasis and in plasma GSH-Px synthesis.

Increased genomic damage in lymphocytes of patients before and after long-term maintenance hemodialysis therapy

This study investigates spontaneous genomic damage in peripheral lymphocytes of 19 patients with severe end-stage renal disease not enrolled onto a maintenance hemodialysis (MHD) program (creatinine level, 5.4 to 10.5 mg/dL) and 16 long-term MHD patients (111 to 282 months on MHD) and the possible association of genomic damage with the degree of renal insufficiency and duration of MHD. Genomic damage was assessed by evaluating the numbers of micronuclei (MN), which are cytoplasmic DNA-containing structures. The average number of MN in the control group of 23 healthy subjects was 15.3 +/- 4.7 MN/1,000 binucleate (BN) cells. The MN frequencies in the long-term MHD group were significantly greater (44.3 +/- 13.7 MN/1,000 BN) than the control frequencies. A significant increase in MN frequencies (28.2 +/- 9.4 MN/1,000 BN) was also seen in patients with advanced renal failure. The major findings of the study, high MN frequencies in long-term hemodialysis and advanced chronic renal failure patients, may result from decreased DNA repair previously shown and may contribute to the increased cancer incidence in these patients.

The role of selenium deficiency in dilated cardiomyopathy in Saudi Arabia

BACKGROUND

Selenium deficiency is implicated in the etiology of endemic juvenile dilated cardiomyopathy in China, and in sporadic cases in other countries. The aim of this study was to evaluate the role of selenium deficiency in the pathophysiology of dilated cardiomyopathy in the Saudi Arabian population.

PATIENTS AND METHODS

Plasma and urine selenium concentrations from 72 Saudi patients with confirmed dilated cardiomyopathy were compared with corresponding values from 70 control subjects of the same national origin who had normal ventricular function.

RESULTS

Plasma and urine selenium concentrations (mean+/-SD) were 1.347plusmn;0.45 and 0.49+/-0.37 micromol/L, respectively, for the patient group, and 1.32+/-0.41 and 0.60+/-0.41 micromol/L, respectively, for the control group. The differences in the values between the two groups were statistically insignificant.

CONCLUSION

In the Saudi population, dilated cardiomyopathy is not caused by selenium deficiency.

Redox regulation of renal DNA synthesis, transforming growth factor-beta1 and collagen gene expression

Growth and injury represent recurrent and related themes in the study of progressive renal disease. We have previously demonstrated that a prooxidant diet, one deficient in antioxidants, selenium and vitamin E, induces renal enlargement, proteinuria, mild tubulointerstitial disease and diminished glomerular filtration rate (GFR). Our present study represents continued examination of these processes. We demonstrate that these diets increase thymidine incorporation into DNA and net DNA content in renal tissue, and induce expression of the mRNA for the proto-oncogene, c-myc, and the histone, H2b. We localize increased DNA synthesis as occurring mainly in the distal renal tubular epithelium. These deficient kidneys also exhibit interstitial expansion that parallels the pattern of DNA synthesis in that both processes are more prominent in the medulla than in the cortex. mRNAs for collagens I, III and IV in conjunction with transforming growth factor-beta1 (TGF-beta1) are up-regulated in the kidney in rats maintained on the deficient diet. In complementary in vitro studies, the exposure of rat kidney fibroblasts, NRK 49F cells, to noncytolytic doses of hydrogen peroxide, induces collagen III, collagen IV and TGF-beta1 mRNA. Induction of these genes is also observed in mesangial cells so exposed to noncytolytic doses of hydrogen peroxide. A final aspect of our study was the examination of renal generation of hydrogen peroxide and the profile of the hydrogen peroxide-degrading enzymes. Deficient kidneys exhibit increased mitochondrial generation of hydrogen peroxide independent of oxygen consumption but in conjunction with suppression of glutathione peroxidase mRNA and activity. Lipid peroxidation was increased twofold in the cortex and medulla of the deficient kidneys. Surprisingly, catalase activity, measured in the cortex and medulla, and whole kidney catalase mRNA were also reduced in rats maintained on the antioxidant deficient diet, effects that may further compromise the clearance of hydrogen peroxide. These changes in catalase represent an adverse response to this dietary deficiency, and may be relevant to decreased catalase activity described in chronic renal insufficiency. Thus, a chronic prooxidant state, with features that mimic those of clinical uremia, increases DNA synthesis of renal tubular epithelium, induces mRNA expression for collagens I, III and IV in conjunction with the mRNA for the fibrogenic cytokine, TGF-beta1. Oxidants also induce collagen III, collagen IV and TGF-beta1 mRNA in vitro.

Serum and tissue selenium contents related to renal disease and colon cancer as determined by electrothermal atomic absorption spectrometry

Microwave digestion with nitric acid and hydrogen peroxide was applied to the determination of selenium in biological tissues by Electrothermal Atomic Absorption Spectrometry (ETAAS). Validation of this method is presented in terms of adequate recovery of selenium from standard reference materials and the method is applied to carcinogen human colon tissue. Ultramicrofiltration was used to study selenium protein binding and its fractionation and speciation in blood serum. These studies showed that 95% of the total selenium in serum seems to be bonded to high-molecular-weight proteins. Experiments with renal failure patients showed lower selenium levels than in the health population (0.57 +/- 0.23 mM versus 0.81 +/- 0.11 mM). A wider distribution pattern of total serum selenium concentration (from 0.1 to 1 mM) was clearly observed in renal failure patients. However, the ultramicrofiltrable selenium fraction was always constant, even in the presence of desferrioxamine (DFO).