Oxidative damage to RBC membranes and pentose phosphate shunt activity in hemodialysis patients after suspension of erythropoietin treatment

Role of alpha-lipoic acid in the management of anemia in patients with chronic renal failure undergoing hemodialysis

INTRODUCTION

Anemia associated with chronic kidney disease is a serious complication necessitating expenditure of huge medical efforts and resources. This study investigates the role of alpha-lipoic acid (ALA) in end stage renal disease patients undergoing hemodialysis. By the virtue of its antioxidative effects, ALA is expected to act as an erythropoietin (EPO) adjuvant, and also has extended beneficial effects on endothelial dysfunction.

METHODS

Forty-four patients undergoing hemodialysis and receiving EPO were randomized into two groups: the first group received ALA 600 mg once daily for 3 months; while the other group represented the control group. Parameters measured at baseline and at end of study were hemoglobin, EPO doses, EPO resistance index (ERI), iron store indices, malondialdehyde, oxidized low-density lipoprotein (ox-LDL), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and asymmetric dimethylarginine (ADMA), as well as routine laboratory follow-up.

RESULTS

EPO doses and ERI were significantly decreased in the treatment group, while they did not change in the control group. Hemoglobin, iron store indices, malondialdehyde, oxidized ox-LDL, IL-6, TNF-α, and ADMA were similar in both treatment and control groups at baseline, and did not change by the end of study period. Likewise, routine laboratory measures were not affected by the treatment.

CONCLUSION

ALA could be used in hemodialysis patients to reduce requirements for EPO. However, larger and longer term studies are required to clarify the exact role of ALA in hemodialysis as well as in pre-hemodialysis patients.

Global effect of an RNA polymerase β-subunit mutation on gene expression in the radiation-resistant bacterium Deinococcus radiodurans

The β-subunit of RNA polymerase, which is involved in rifampin binding, is highly conserved among prokaryotes, and Rifr mutants detected in many bacteria are the result of amino acid changes. Spontaneous rifampin resistance mutations resulting in amino acid replacement (L420R) and deletion (1258-66 9 bp deletion) have been previously isolated in the rpoB gene of Deinococcus radiodurans. In this study, a β-subunit mutation in D. radiodurans resulted in a unique effect on growth rate. We used DNA microarrays and biochemical assays to investigate how the Rifr mutation in the β-subunit led to changes in growth rate via altered regulation of multiple genes. The expression of genes with predicted functions in metabolism, cellular processes and signaling, and information storage and processing were significantly altered in the 9 bp-deletion rpoB mutant. The consensus promoter sequence of up-regulated genes in the 9 bp-deletion rpoB mutant was identified as an AT-rich sequence. Greater levels of reactive oxygen species accumulated in the L420R and 9 bp-deletion rpoB mutants compared with wild type. These results provide insight into the molecular mechanism of how the β-subunit Rifr mutation alters the regulation of multiple genes.

Enhanced methylglyoxal formation in the erythrocytes of hemodialyzed patients

Methylglyoxal (MG) contributes significantly to the carbonyl stress in uremia; however, the reason for its increased concentration is not clear. Thus, the present study was aimed to investigate the formation and degradation of MG in the erythrocytes of hemodialyzed (HD) patients with end-stage renal disease. In 22 nondiabetic patients on long-term HD, erythrocyte MG and d-lactate levels, glyoxalase activities, and whole blood reduced glutathione content were determined. The data were compared with those from 22 healthy controls. Erythrocyte MG and d-lactate production were also investigated in vitro under normoglycemic (5 mmol/L) and hyperglycemic (50 mmol/L) conditions. The erythrocyte MG levels were elevated (P < .001) in the HD patients. The blood reduced glutathione content and glyoxalase I activity were similar to the control levels, but the glyoxalase II activity was significantly (P < .005) increased. In the normoglycemic in vitro model, production of both MG (P < .001) and d-lactate (P < .002) was significantly enhanced in the HD erythrocytes relative to the controls. During hyperglycemia, the MG formation and degradation rates were further increased (P < .001). The present study demonstrated an increased formation of MG in the erythrocytes of HD patients. This seemed to be related to a glucose metabolism disturbance of the cells. The degradation system of MG was also activated; still, it was not able to counteract the high rate of MG formation. The alterations and imbalance of these metabolic processes may contribute to the carbonyl overload and stress in the HD patients.

Erythrocyte Antioxidant Defense System in Patients with Chronic Renal Failure According to the Hemodialysis Conditions

BACKGROUND

Patients suffering from chronic renal failure (CRF) are exposed to increased oxidative stress generated by uremic toxins, factors connected with hemodialysis, chronic inflammatory state, lack of vitamins A, E and selenium, advanced age, and parenteral iron administration. Their antioxidative system is inefficient. In erythrocytes, hexosemonophosphate (HMP) cycle does not assure an adequate amount of reductive equivalents (NADPH) necessary to restore reduced glutathione (GSH), an important free radical scavenger. Hemodialysis treatment also causes a large loss of glucose, which is the basic substrate for that metabolic pathway. The object of the research was to establish the influence of glucose present in dialysate on antioxidant defense system in red blood cells.

METHODS

A group of 51 patients undergoing regular hemodialysis using glucose (26 subjects, GL+ HD) or non-glucose fluid (25 subjects, GL- HD) was studied. The GSH concentration, glucose-6-phosphate dehydrogenase (G-6-P DH) and glutathione reductase (GSSG-R) activities were determined. Glucose concentration before and after the hemodialysis session was also measured.

RESULTS

The activity of G-6-P DH was significantly higher in GL+ HD both before (p = 0.000) and after (p = 0.0002) the dialysis treatment compared to GL- HD, respectively, and to the healthy subjects (p = 0.000). The hemodialysis session caused a decrease in the activity of the enzyme in GL+ HD from 4.91 +/- 1.53 to 4.42 +/- 1.40 U/g Hb (p = 0.004) as well as in GL- HD from 3.97 +/- 1.00 to 3.59 +/- 0.87 U/g Hb (p = 0.007). The GSSG-R showed an increase in activity in CRF patients before HD (in GL+ HD to 2.57 +/- 0.76 and in GL- HD to 2.82 +/- 0.98 U/gHb). After dialysis, lower values were observed, particularly in GL+ HD (2.05 +/- 0.59 U/g Hb, p = 0.004). GSH concentrations in the examined group were higher (in GL+ HD 0.0205 +/- 0.008 and in GL- HD 0.0196 +/- 0.008 mmol/g Hb) than in controlled subjects (0.0142 +/- 0.002 mmol/g Hb) and decreased during dialysis treatment (considerably only in GL- HD to 0.0183 +/- 0.007 mmol/g Hb, p = 0.056). Glucose concentrations in GL+ HD were significantly higher compared to GL- HD (p < 0.002).

CONCLUSIONS

Glucose presence in dialyzing fluid improves the HMP cycle activity as well as glutathione system reactions and determines a better antioxidant status of erythrocytes. It limits hemolysis and improves the hematological parameters in CRF.

The DNA excision repair system of the highly radioresistant bacterium Deinococcus radiodurans is facilitated by the pentose phosphate pathway

Deinococcus radiodurans is highly resistant to radiation and mutagenic chemicals. Mutants defective in the putative glucose-6-phosphate dehydrogenase gene (zwf-) and the aldolase gene (fda-) were generated by homologous recombination. These mutants were used to test the cells' resistance to agents that cause dimer formation and DNA strand breaks. The zwf - mutants were more sensitive to agents that induce DNA excision repair, such as UV irradiation and H2O2, but were as resistant to DNA strand break-causing agents such as methylmethanesulphonic acid (MMS) and mitomycin C (MMC) as the wild-type cells. Analysis of the cytoplasmic fraction of zwf- cells showed that the concentrations of inosine monophosphate (IMP) and uridine monophosphate (UMP) were only 30% of those found in the wild-type cells. The fda- mutants were slightly more resistant to UV light and H2O2. Results suggested that the deinococcal pentose phosphate pathway augmented the DNA excision repair system by providing cells with adequate metabolites for the DNA mismatch repair.

L-carnitine treatment of anemia

Recombinant human erythropoietin (rHuEPO) and iron supplementation have had a profoundly positive impact on the anemia of patients with chronic kidney disease. However, a significant number of patients remain hyporesponsive to rHuEPO, with hemoglobin values less than target levels. A suboptimal response to rHuEPO is associated with complications that can reduce quality of life and increase morbidity, mortality, and costs. There are a number of other metabolic derangements associated with uremia that can impact on the production and survival of red blood cells. Dialysis-related carnitine disorder is a functional metabolic deficiency, common in chronic dialysis patients, that can have a negative impact on erythrocyte production and survival. This article reviews the role of L-carnitine in the pathogenesis and adjunctive treatment of anemia associated with kidney failure. After a comprehensive database search, primary and secondary reports were analyzed. Laboratory studies examining the influence of carnitine on red blood cell function and clinical trials of L-carnitine in dialysis patients support the use of L-carnitine in the setting of rHuEPO hyporesponsiveness. Consensus groups, including the National Kidney Foundation-Kidney Disease Outcome Quality Initiative (K/DOQI), consider the use of L-carnitine for hyporesponsive rHuEPO-dependent anemia a promising application of this therapy, recommending an empiric trial of L-carnitine in these patients.

Oxidative cross-linking of ApoB100 and hemoglobin results in low density lipoprotein modification in blood. Relevance to atherogenesis caused by hemodialysis

Human blood contains a form of minimally modified low density lipoprotein (LDL), termed LDL-, whose origin remains unknown. Exploring the mechanism of formation, we found that LDL- can be produced in plasma in the absence of oxygen following LDL incubation with oxidized hemoglobin species. A high degree of apolipoprotein B100 modification results from covalent association of hemoglobin with LDL involving dityrosine formation but not due to the malonaldehyde epitope formation. This was evidenced by the cross-reactivity of oxidized LDL with antibodies against hemoglobin that was accompanied by a 60-fold increase in dityrosine levels. In this study we found significantly higher LDL- levels in the blood of hemodialysis patients, perhaps contributing to their greatly increased risk of atherosclerosis. The mechanism of LDL- formation was studied during ex vivo blood circulation using a model system resembling clinical hemodialysis in terms of the induction of inflammatory responses. This circulation increased free hemoglobin and LDL- levels compared with non-circulated blood without appreciable lipid peroxidation. Pronounced increases in LDL- were found also during circulation of plasma supplemented with nanomolar hemoglobin levels. The increase in dityrosine content and presence of heme in LDL after blood circulation suggest that LDL is modified, in part, by hemoglobin-LDL conjugates containing heme. Thus, hemoglobin-mediated reactions leading to LDL oxidation in plasma can account for high LDL- levels in hemodialysis patients.

Oxidative stress in hemodialysis patients treated with a dialysis membrane which has alpha-tocopherol bonded to its surface

BACKGROUND

MDA, a major product of LPO, was shown to be increased in plasma of patients with end-stage renal failure (ESRF) undergoing hemodialysis (HD). Elevated oxidative stress in ESRF patients is a result of multiple pathogenetic factors. HD treatment has been shown to be one important cause of accelerated radical generation. The aim of our study was to examine whether treatment with a dialysis membrane which has alpha-tocopherol hydrophobically bonded to its surface (Excebrane by Terumo, Japan) can decrease oxidative stress due to HD.

METHODS

10 ESRF patients undergoing HD three times weekly were examined. First, analysis was done when patients were still dialysed with the membranes used before the study. Thereafter, samples were taken when patients were dialysed first time with the Excebrane membrane, and six weeks after Excebrane treatment. Samples were collected always before and after HD session. A method with HPLC-separation and flourimetric detection was used to measure plasma concentration of MDA.

RESULTS

After HD with the regularly used membranes MDA was found significantly increased (before HD 1.92 [1.81-2.02] microM (median and interquartile ranges) vs. after HD 2.26 [2.02-2.60] microM, p < 0.05) suggesting that MDA was produced during HD. The first time Excebrane was used MDA was decreased significantly (before HD 2.04 [1.95-2.88] microM vs. after HD 1.35 [1.19-1.92] microM, p < 0.05). After six weeks of Excebrane treatment, plasma MDA did not change significantly during HD (before HD 2.01 [1.69-2.62] microM vs. after HD 1.95 [1.42-2.20] microM).

CONCLUSION

Oxidative stress due to HD might be significantly decreased by the Excebrane membrane. However, after six weeks of treatment with Excebrane no effect was seen on the initial plasma concentration of MDA compared to the time before.