Oxidative stress in haemodialysis--intradialytic changes

Telomere shortening in patients on long-term hemodialysis

Background

Leukocyte telomere length shortening is a characteristic of premature senescence, a process that can be accelerated by oxidative stress. In general, patients with end-stage renal disease undergoing regular hemodialysis (HD) are repeatedly exposed to oxidative stress. Patients undergoing HD tend to have cardiovascular diseases associated with oxidative stress and inflammation. Therefore, we assumed that telomere length is associated with HD vintage and the degree of vascular calcification.

Methods

A total of 144 patients undergoing regular HD before kidney transplantation and 62 patients on hemodialysis, but not undergoing kidney transplantation, were enrolled. We measured common laboratory values, such as calcium, phosphate, and hemoglobin levels, and assessed the degree of vascular calcification in the patients. The leukocyte telomere length was measured using reverse transcription polymerase chain reaction, and Spearman correlation was used for correlation analysis.

Results

The leukocyte telomere length was negatively associated with age (rho = −0.306, P＜0.01); it was shorter in middle-aged patients than in young patients (13.48 ± 4.80 vs. 15.86 ± 4.51, P < 0.01). The telomere length was significantly different among patients aged 52–74 years in groups with different HD vintages. Additionally, the telomere length was positively associated with serum hemoglobin (Hb) levels in all patients (rho = 0.290, P < 0.01). There was a significant difference among patients divided into three groups according to the degree of anemia (17.09 ± 5.64 vs. 14.40 ± 4.07 vs. 13.99 ± 3.95, P < 0.01). Further, a significant difference was observed in the telomere length among patients with different degrees of vascular calcification (16.79 ± 4.91 vs. 13.61 ± 2.82 vs. 14.62 ± 3.63 vs. 10.71 ± 3.74, P < 0.01). The telomere length was shorter in the patients on hemodialysis who did not receive a kidney transplant than in the surgical patients (8.12 ± 1.83 vs. 14.33 ± 4.63, P < 0.01).

Conclusion

This study demonstrated that the telomere length was significantly correlated with HD vintage in patients of a certain age group. The telomere length was shorter in patients on hemodialysis who matched for age and dialysis vintage with kidney transplant patients. It was also associated with vascular calcification and serum Hb levels in all patients undergoing HD.

Elimination of lipid peroxide during hemodialysis

BACKGROUND/AIMS

This study is aimed to show the antioxidative effect of hemodialysis (HD) by demonstrating the elimination of toxic lipid peroxides.

METHODS

Blood samples were obtained from patients on regular maintenance HD before and 15, 30, 60, 120 and 240 min after the start of each HD session. Plasma cholesteryl ester hydroperoxide (CE-OOH), phosphatidylcholine hydroperoxide (PC-OOH), and eliminators of lipid peroxides (LOOH) such as apolipoprotein A-I (apoA-I) and lecithin:cholesterol acyltransferase (LCAT) were investigated. The hydroxyl radical scavenging activity was measured for the evaluation of the pro-oxidative side.

RESULTS

CE-OOH and PC-OOH were elevated in patients with chronic kidney disease both on and not on HD, while these values were much higher in HD patients. CE-OOH quickly dropped during the first 30 min of HD, then gradually decreased until 240 min. CE-OOH concentrations were related to those of apoA-I. In contrast, PC-OOH showed an increase 30 min after the start of HD, a change which resembled that of LCAT and was the reverse of the hydroxyl radical scavenging activity.

CONCLUSION

These results demonstrate the antioxidative action through CE-OOH elimination involving apoA-I. The pro- and antioxidative effects of HD on LOOH are not uniform but PC-OOH is mainly influenced prooxidatively.

Telomere Shortening and Haemodialysis

BACKGROUND

Increased oxidative stress is a well described feature of haemodialysis (HD). This is secondary to an increase in the production of reactive oxygen species and impaired antioxidant mechanisms. Telomeres are the specialized ends of eukaryotic chromosomes and consist of tandemly repeated DNA sequences. Telomeres shorten with each cell division and it is well known that telomere length in peripheral blood mononuclear cells (PBMCs) decreases with age. Telomere shortening rate is increased by oxidative stress. In this study we have examined a possible relationship between oxidative stress and telomere shortening in haemodialysis.

METHODS

20 control subjects, 20 non-diabetic and 18 diabetic HD patients were studied. Peripheral blood mononuclear cell telomere length, plasma malondialdehyde plus 4-hydroxyalkenal (MDA+4-HAE) concentration (a marker of oxidative stress) and C-reactive protein (CRP) concentration were measured.

RESULTS

MDA+4-HAE and CRP were significantly higher in the HD patients (CRP, controls 7.5 +/- 1.5, HD patients 16.4 +/- 3.1 mg/l, p < 0.05). There was no difference in mean telomere length between the HD patients and controls (control, 8,283 +/- 179 bp; non-diabetic HD, 7,966 +/- 160 bp; diabetic HD, 8,033 +/- 197 bp) but age adjusted residual telomere length was inversely associated with the length of time on dialysis (r = -0.35, p = 0.03).

CONCLUSION

These results suggest that length of time on dialysis is independently associated with increased telomere shortening in HD patients. We hypothesise that this reflects cumulative DNA exposure to oxidative stress.

Vitamins A, E and C as non-enzymatic antioxidants and their relation to lipid peroxidation in children with chronic renal failure

BACKGROUND

Increased lipid peroxidation (LP) and reduced enzymatic antioxidant defense have been observed in predialysis patients with advanced chronic renal failure (CRF) and in patients on maintenance hemodialysis (HD). To extend these observations, we evaluated the plasma, erythrocyte and dialysate levels of vitamins A and E and the plasma and dialysate levels of vitamin C as exogenous non-enzymatic antioxidants in children with CRF treated conservatively and on HD. The data obtained were related to LP monitored by erythrocyte malonyldialdehyde (E-MDA) and plasma organic hydroperoxide (OHP) concentrations.

PATIENTS

Forty-six predialysis children were enrolled in the study and divided into 2 groups: group I = moderate CRF (plasma creatinine < 265.3 micromol/l), and group II = plasma creatinine > or = 265.3 micromol/l. Group III consisted of 21 HD children. 27 age-matched healthy subjects served as a control group.

RESULTS

The plasma levels of vitamin A and vitamin C were significantly reduced in all CRF patients when compared to the controls, with the lowest values observed in children on maintenance HD (group III). Significant differences were also noted between the moderate CRF (group I) and HD (group III). Plasma levels of vitamin E were significantly decreased in moderate CRF (group I) and HD (group III) as compared to controls. In contrast, the erythrocyte vitamin A and vitamin E levels of predialysis children and HD patients were not different from the controls. The E-MDA and OHP concentrations in the 3 groups of CRF children were significantly higher than in healthy subjects. The concentration of plasma vitamin C was significantly inversely correlated with E-MDA, plasma OHP and creatinine in group I. In group II we found a significant correlation of plasma vitamin E levels with creatinine and E-MDA and a correlation of the plasma vitamin C concentration with E-MDA.

CONCLUSION

CRF in children is associated with decreased concentrations of plasma antioxidant vitamins. This reduction is most expressed in children on maintenance HD and particularly concerns plasma vitamin C and erythrocyte vitamin E concentrations. The low levels of plasma vitamin A, E and C might result in reduced activity of the non-enzymatic antioxidant defense system and might be responsible for increased oxidative stress occurring in children with CRF.

Changes in serum markers of oxidative stress with varying periods of haemodialysis

BACKGROUND AND AIMS

Oxidative stress possibly helps promote the progression and complications of chronic renal failure (CRF). Haemodialysis (HD) may aggravate oxidative stress. This controlled, cross-sectional clinical study with blind outcome assessment evaluated the effect of prolonged HD treatment on oxidative stress.

METHODS AND RESULTS

Seventy patients (M/F = 33/37) with CRF and who were on HD were divided into six groups with differing treatment periods of HD; from 3 to 12 months to 85-120 months. Twelve healthy subjects acted as controls. The serum levels of thiobarbituric acid reactive substances (TBARS), total sulfhydryl (SH) groups and protein carbonyls (PCs) were determined. Compared with controls, PCs were increased in patients, and this positively correlated with the duration of HD. Treatment for more than 24 months caused the most striking increases in PCs, with relevant differences as compared to those on HD for a maximum of 12 months. Increasing periods of HD were associated with increases in TBARS and similar decreases in SH as compared with controls; the differences between the SH levels of those on HD for more than 84 months and those on HD for up to 24 months were significant.

CONCLUSION

Our results indicate that HD continued for more than 2 years aggravates the latter. Decreased potential for oxygen-radical-scavenger activity becomes pronounced after 7 years of HD treatment.

Dyslipidemia, oxidative stress and cardiac dysfunction in children with chronic renal failure: effects of L-carnitine supplementation

BACKGROUND

Secondary carnitine deficiency may develop in chronic renal failure (CRF) patients undergoing long-term hemodialysis (HD), with a resulting higher incidence of cardiovascular diseases, dyslipidemia and oxidative stress. We studied the efficacy of 12 months of L-carnitine supplementation on the amelioration of dyslipidemia, oxidative stress and cardiac dysfunction in 24 CRF children undergoing long-term HD compared with 24 age- and sex-matched controls.

METHODS

Plasma samples were analyzed spectrophotometerically before and after dialysis sessions and after 2-month supplementation with oral L-carnitine (50 mg/kg/day) for free carnitine (FC), the lipid profile, and oxidative stress markers. Echocardiography the day following dialysis measured cardiac diameters, wall thicknesses, left ventricular mass index (MI), end diastole and systole volume indices and functions.

RESULTS

The pre-dialysis FC concentration was substantially lower than controls and decreased significantly at the end of the dialysis session. Pre- and post-dialysis plasma levels of free fatty acids (FFAs), trigyleride (TG), total cholesterol (TC) and oxidative stress markers significantly increased while high-density lipoprotein cholesterol (HDL-C) and phospholipids significantly decreased compared to controls. Echocardiography detected a significant increase in cardiac diameters and thickness, and systolic and diastolic cardiac dysfunction. After L-carnitine supplementation, plasma levels of FC increased to normal levels. FFAs, TC and HDL-C returned to control levels while TG, phospholipids, and the oxidative stress markers decreased but remained significantly higher than controls. There was a significant decrease in cardiac diameters and an increase in left ventricular diastolic function (E/A ratio), but no correlation between FC levels and echocardiographic parameters. Pre-dialysis, post-dialysis and after treatment, plasma FC level showed a significant positive correlation with HDL-C and phospholipids and a significant negative correlation with each of oxidative stress markers, FFAs, TG and TC. On the other hand, FFAs showed a significant positive correlation with TG, TC, DC, NO and a significant negative correlation with HDL-C and phospholipids.

CONCLUSION

This study demonstrates that CRF children under regular HD suffer from a decrease in the level of plasma FC, dyslipidemia, oxidative stress, and an increase in cardiac diameters and thickness with impairment of cardiac functions. Oral L-carnitine supplementation at a dose of 50 mg/kg for 2 months can increase plasma FC level, improve dyslipidemia, decrease oxidative stress with reduction of cardiac diameters and increase in diastolic function.

Effect of hemodialysis on the antioxidative properties of serum

In patients with chronic renal failure undergoing regular hemodialysis (HD), oxidative stress is involved in the development of dialysis-related pathologies. The aim of the study was to measure the effect of HD treatment on the general antioxidative status of serum with special consideration of the specific oxidizability of lipids and proteins. Indicators for the oxidative/antioxidative status of plasma were monitored at the beginning and at the end of a dialysis session on the arterial and venous side of the dialyzer. A decrease in the antioxidant status was accompanied by an increased oxidizability of proteins as well as lipids during HD treatment. During the first passage of the dialyzer, the lag time of lipid oxidation decreased from 114.0+/-19.8 to 81.5+/-18.9 min, the lag time of protein oxidation decreased from 105.0+/-24.6 to 72.9+/-21.3 min and the total antioxidative status decreased from 518+/-24 to 252+/-124 microM trolox equivalents. The carbonyl content of serum proteins was high in patients with end stage renal disease (ESRD) (3.9+/-1.1 vs. 0.9+/-0.1 nmol/mg in controls) but did not change significantly during dialysis procedure. Our data demonstrate that the susceptibility of serum lipids and proteins to oxidative modification is severely increased by HD treatment.