Oxidative stress and haemodialysis: role of inflammation and duration of dialysis treatment

Inflammation and oxidative stress in patients on hemodiafiltration

BACKGROUND

Chronic inflammation and oxidative stress are common features in hemodialysis patients. However, research results on the long-term influence of hemodiafiltration (HDF) on oxidative stress and inflammation are limited.

METHODS

We studied changes of inflammatory and oxidative stress biomarkers in 9 stable patients on post-dilution HDF for 9 months. Total antioxidant capacity (TAC), reactive oxygen metabolites (d-ROMs) and superoxide dismutase (SOD) measured by spectrophotometry were used as oxidative stress biomarkers. High-sensitivity CRP (hs-CRP) and IL-6 measured by ELISA were used as inflammation biomarkers.

RESULTS

d-ROMs showed significant reduction at 3 months (323.0 +/- 81.9 vs. 275.0 +/- 62.0 U, p < 0.008) and remained low (267.9 +/- 45.8 U) to the end of the study. At the end of the study there was a significant increase in TAC levels (1.3 +/- 0.1 vs. 1.4 +/- 0.1 mmol/l, p < 0.03), while SOD rise did not reach statistical significance (13.1 +/- 9.8 vs. 18.7 +/- 9.4 U/ml, p = 0.06). hs-CRP values at the end of the study decreased significantly (16.3 +/- 11.4 vs. 6.0 +/- 5.1 microg/ml, p < 0.02), while IL-6 levels showed a non-significant reduction (16.9 +/- 9.3 vs. 12.0 +/- 7.3 pg/ml, p = 0.2).

CONCLUSION

Our results suggest that post-dilution HDF for 9 months suppresses oxidative stress by rapid lowering of d-ROMs and improves antioxidant capacity by increasing TAC, while it reduces inflammation by decreasing hs-CRP.

Lipid peroxidation in hemodialysis patients: effect of vitamin C supplementation

OBJECTIVES

Renal failure is associated with several metabolic disturbances and increasing evidences support a role of oxidative stress and impaired antioxidant defence in the pathologic mechanisms that may contribute to accelerated atherogenesis in these patients. Aim of the study was to further investigate the relationship between oxidative stress and chronic renal failure.

DESIGN AND METHODS

We compared the paraoxonase (PON1) activity, the levels of lipid hydroperoxides and AGE adducts in plasma of hemodialysis patients before and after intravenous administration of vitamin C.

RESULTS

An increase in lipid hydroperoxides, AGE adducts and a decrease in the activity of PON1 were observed in patients with respect to controls. The comparison before and after supplementation with vitamin C showed an increase of PON1 activity and a decrease of AGE and lipid hydroperoxides levels.

CONCLUSIONS

The results provide further evidence that lipid peroxidation and impairment of antioxidant system in plasma of patients may play a role in renal disease and suggest that evaluation of PON1 activity could represents an useful approach to monitor antioxidant treatment and new dialysis therapies.

Inflammatory syndrome in patients on hemodialysis

Mortality is markedly elevated in hemodialysis (HD) patients. Between 30 and 50% of prevalent patients have elevated serum levels of inflammatory markers such as C-reactive protein and IL-6. The presence of inflammation, chronic or episodic, has been found to be associated with increased mortality risk. The causes of inflammation are multifactorial and include patient-related factors, such as underlying disease, comorbidity, oxidative stress, infections, obesity, and genetic or immunologic factors, or on the other side, HD-related factors, mainly depending on the membrane biocompatibility and dialysate quality. The adequate knowledge of these causes and their prevention or treatment if possible may contribute to improving the inflammatory state of patients who are on HD and possibly their mortality.

Acute effect of standard heparin versus low molecular weight heparin on oxidative stress and inflammation in hemodialysis patients

OBJECTIVE

Atherosclerotic cardiovascular diseases caused by traditional and non-traditional risk factors are the most common cause of morbidity and mortality in hemodialysis patients. Recently, much interest has been focused on non-traditional factors, such as oxidative stress, inflammation, and endothelial dysfunction. Hemodialysis patients are not only exposed to oxidative stress but also to inflammation. Although anticoagulants are the most frequently used drugs in hemodialysis patients, their effect upon oxidative stress and inflammation in dialysis patients are still unknown.

METHODS

Thirty-three hemodialysis patients were randomized into three groups. Group 1 received standard heparin while group 2 received low molecular weight heparin during the dialysis therapy. Group 3 (control group) did not receive any anticoagulant agent. Investigators were blinded to the therapy. Serum concentrations of oxidative stress and inflammation markers, including C-reactive protein, tumor necrosis factor alpha, superoxide dismutase, and malondialdehyde, were measured before and after dialysis session.

RESULTS

The oxidative stress and inflammation markers were significantly increased in groups 1 and 3 (p < 0.05 for each) compared to their baseline values. In contrast, baseline and end-treatment values of the oxidative stress and inflammation markers were comparable in the group 2 (p > 0.05).

CONCLUSION

These findings indicate that the type of anticoagulants may take a role in the acute effect of hemodialysis upon oxidative stress and inflammation markers. A comparison of the groups revealed that low molecular weight heparin decreased the oxidative stress and inflammation, whereas standard heparin increased the oxidative stress and inflammation. Low molecular weight heparin appears to have an additive benefit for hemodialysis patients.

Pleiotropic effects of the non-calcium phosphate binder sevelamer

The number of chronic kidney disease (CKD) patients and related adverse outcomes has dramatically increased worldwide in the past decade. Therefore, numerous experimental and clinical studies have recently addressed the underlying mechanisms, in particular the marked increase in cardiovascular mortality. Hyperphosphatemia is a major problem in these patients with advanced stage of CKD. Its control by calcium-containing phosphate binders is effective, but at the price of potentially noxious calcium overload. Sevelamer hydrochloride is a phosphate binder that offers an effective control of hyperphosphatemia as calcium-rich binders but without increase of calcium load. Beyond the control of phosphate, sevelamer seems to exert pleiotropic effects which include the correction of lipid abnormalities and the clearance of some uremic toxins.

The Impact of Standard High-Flux Polysulfone Versus Novel High-Flux Polysulfone Dialysis Membranes on Inflammatory Markers: A Randomized, Single-Blinded, Controlled Clinical Trial

BACKGROUND

This study is a prospective, randomized, single-blind, clinical trial over 12 months involving 60 stable hemodialysis patients comparing standard high-flux polysulfone dialyzer membranes with a novel high-flux polysulfone dialyzer membrane (Helixone; Fresenius Medical Care, St Wendel, Germany) modified in the fiber-spinning process to enhance middle-molecule clearance through changing the distribution of pore size and increased filtration.

METHODS

Markers of protein and lipid oxidation and inflammatory markers, including proinflammatory cytokines and cell adhesion molecules, were compared. The hypothesis tested was that improved clearances of middle molecules with the FX80 membrane would lead to less oxidative stress and inflammation compared with the high-flux polysulfone (HF80) membrane.

RESULTS

Type of dialysis membrane used did not significantly affect lipid and protein peroxidation, C-reactive protein level, interleukin 6 level, or sgp130 level during 12 months. beta(2)-Microglobulin concentrations decreased significantly in the Helixone membrane group compared with those dialyzed using conventional polysulfone membranes during the study (-15%; 95% confidence interval, -20 to -10).

CONCLUSION

Long-term dialysis with a Helixone membrane did not modify any parameters of oxidative stress or inflammation in this stable hemodialysis population compared with a high-flux polysulfone dialysis membrane.

Selenium status indices, laboratory data, and selected biochemical parameters in end-stage renal disease patients

We investigated the relations between selenium status (SeS) parameters, indexes of nutrition, erythropoiesis, and uremic toxemia, serum electrolytes, and other biochemical markers in end-stage renal disease (ESRD) patients, as no multivariate statistical analysis concerning all of these parameters was performed so far. SeS was evaluated by plasma Se concentration (plSe) and glutathione peroxidase (plGSHPx) activity in 69 uremic patients treated with hemodialysis (HD) and 40 healthy controls. The hierarchical multivariate partial least squares model (PLS2) was employed to establish data structure and correlations between parameters investigated. plSe and plGSHPx activity were significantly lower in patients when compared with controls (p=0.000). plSe was positively associated with indexes of erythropoiesis and nutritional status, as well as serum electrolytes and parameters of uremic toxemia. plGSHPx was inversely dependent on the pair of parameters: intact parathyroid hormone (iPTH) and aluminum plasma concentration (Al). We conclude that (1) ESRD strongly decreases selenium status and (2) the PLS2 approach revealed the existence of significant interactions among plSe, plGSHPx, and selected biochemical parameters or groups of such parameters; some of these associations need further studies to be clarified.

Hemodialysis and Protein Oxidation Products

The presence of a chronic inflammatory state has also been widely documented in end-stage renal disease patients receiving maintenance hemodialysis (HD). It is commonly attributed to the constantly renewed activation of circulating neutrophils and monocytes following blood passage through dialysis circuits and subsequent generation of activated complement components due to contact of plasma with bioincompatible membranes and/or transfer of endotoxins from the dialyzate to the blood compartment. This conjunction leads to a massive generation of reactive oxygen species (ROS), for example, superoxide anion, hydrogen peroxide, hydroxyl radical, and chlorinated oxidants, such as hypochlorous acid by activated neutrophils. The exquisite vulnerability of proteins to ROS is now well documented. Oxidation of amino acid residues, such as tyrosine, leads to the formation of dityrosine, protein aggregation, cross-linking, and fragmentation. Dityrosine-containing protein cross-linking products in the plasma of dialysis patients are named as advanced oxidation protein products (AOPP). In addition, advanced glycation end-products (AGE) is a protein carbonyl compound and produced by protein-ROS interaction. We investigated both the effect of the renewed activation of the immune cells, due to blood-dialyzer interaction over protein oxidation products like AOPP and AGE, among chronic renal failure (CRF) patients receiving maintenance HD, and choice of dialyzers like high flux or the other group on protein oxidation product levels.

Chronic renal failure-induced multiple-organ injury in rats is alleviated by the selective CysLT1 receptor antagonist montelukast

Chronic renal failure (CRF) is associated with oxidative stress that promotes production of reactive oxygen species and cytokine release. We aimed to investigate the possible protective effect of montelukast, a CysLT1 receptor antagonist, against oxidative damage in a rat model of CRF, induced by 5/6 reduction of renal mass. Male Wistar albino rats were randomly assigned to either the CRF group or the sham-operated control group, which received saline or montelukast (10mg/kg, i.p.) for 4 weeks. At the end of the 4 weeks, rats were decapitated and trunk blood was collected. Creatinine, blood urea nitrogen and lactate dehydrogenase (LDH) activity were measured in the serum samples, while leukotriene B(4), TNF-alpha, IL-1 beta, IL-6, total antioxidant capacity (AOC) and leukocyte apoptosis were assayed in plasma samples. Kidney, lung, heart and brain tissue samples were taken for the determination of tissue malondialdehyde (MDA), glutathione (GSH) levels, and myeloperoxidase (MPO) activity. Oxidant-induced tissue fibrosis was determined by tissue collagen contents, and the extent of tissue injuries was analyzed microscopically. CRF caused significant decreases in tissue GSH and plasma AOC, which were accompanied with significant increases in MDA levels, MPO activities, and collagen contents of all the studied tissues, while the circulating levels of the pro-inflammatory mediators, LDH activity, creatinine and BUN were elevated. Montelukast treatment reversed all these biochemical indices, as well as histopathological alterations induced by CRF. Similarly, flow cytometric measurements revealed that leukocyte apoptosis was increased in CRF group, while montelukast reversed this effect. In conclusion, CRF-induced oxidative tissue injury occurs via the activation of pro-inflammatory mediators and by neutrophil infiltration into tissues, and that protective effects of montelukast on CRF-induced injury can be attributed to its ability to inhibit neutrophil infiltration and apoptosis, to balance oxidant-antioxidant status and to regulate the generation of pro-inflammatory mediators.

Reg2 inactivation increases sensitivity to Fas hepatotoxicity and delays liver regeneration post-hepatectomy in mice

Reg2/RegIIIbeta is the murine homologue of the human secreted HIP/PAP C-type lectin. HIP/PAP transgenic mice were protected against acetaminophen-induced acute liver failure and were stimulated to regenerate post-hepatectomy. To assess the role of Reg2, we used Reg2-/- mice in a model of fulminant hepatitis induced by Fas and in the post-hepatectomy regeneration. Within 4 hours of J0-2 treatment (0.5 microg/g), only 50% of the Reg2-/- mice were alive but with an increased sensitivity to Fas-induced oxidative stress and a decreased level of Bcl-xL. In contrast, HIP/PAP transgenic mice were resistant to Fas, with HIP/PAP serving as a sulfhydryl buffer to slow down decreases in glutathione and Bcl-xL. In Reg2-/- mice, liver regeneration was markedly impaired, with 29% mortality and delay of the S-phase and the activation of ERK1/2 and AKT. Activation of STAT3 began on time at 3 hours but persisted strongly up to 72 hours despite significant accumulation of SOCS3. Thus, Reg2 deficiency induced exaggerated IL-6/STAT-3 activation and mito-inhibition. Because the Reg2 gene was activated between 6 and 24 hours after hepatectomy in wild-type mice, Reg2 could mediate the TNF-alpha/IL-6 priming signaling by exerting a negative feed-back on STAT3/IL-6 activation to allow the hepatocytes to progress through the cell cycle. In conclusion, Reg2 deficiency enhanced liver sensitivity to Fas-induced oxidative stress and delayed liver regeneration with persistent TNF-alpha/IL6/STAT3 signaling. In contrast, overexpression of human HIP/PAP promoted liver resistance to Fas and accelerated liver regeneration with early activation/deactivation of STAT3. Reg2/HIP/PAP is therefore a critical mitogenic and antiapoptotic factor for the liver.

Paraoxonase, anti-oxidant response and oxidative stress in children with chronic renal failure

Increased oxidative stress is believed to contribute to an increased risk of cardiovascular disease in uraemia. In children with chronic renal failure (CRF), an anti-oxidant enzyme, paraoxonase (PON), that inhibits oxidation of LDL-cholesterol, has not been previously investigated. In this study we aimed to investigate PON activity, total anti-oxidant response (TAR), total peroxide (TPX), oxidative stress index (OSI) and some pro-oxidant cytokines in 29 children with CRF [mean age 10.2+/-3.5 years; 19 pre-dialysis, ten on continuous ambulatory peritoneal dialysis (CAPD)] and in 25 control subjects. Children with CRF had lower PON and TAR and higher TPX and OSI values than did controls (P<0.05). Except for lower TAR and serum albumin levels of the CAPD subgroup (P<0.05), other parameters were similar in non-dialysis and CAPD patients (P>0.05). Patients had significant positive correlation between TAR and serum albumin (P<0.05). Serum urea had significant positive correlation with TPX and OSI (P<0.05). Increased oxidative stress and decreased anti-oxidants measured by serum PON activity and TAR were found in children with CRF. We can hypothesize, on the basis of statistical correlations, that low levels of serum albumin and high levels of uraemic metabolites might be responsible for increased oxidative stress in children with CRF. Further studies with larger sample sizes are needed to verify these results.

Disruption of thiol homeostasis in plasma of terminal renal failure patients

BACKGROUND

The aim of the present studies was to investigate the changes in concentrations of different forms of thiols in plasma of terminal renal failure patients before and after hemodialysis.

METHODS

Total concentrations of thiols, their free forms and the level of their mixed disulfides with proteins were determined with HPLC.

RESULTS

In terminal renal failure patients before dialysis, total concentrations of cysteine, homocysteine and cysteinylglycine and their free and protein-bound fractions increased while level of all such forms of glutathione dropped. A single dialysis session caused short-lasting return of concentrations of all forms of thiols to the level equal or close to the control group. The changes observed in non-dialyzed patients were similar to those observed in dialyzed patients before single dialysis procedure.

CONCLUSIONS

The obtained results showed severe disturbance of thiol homeostasis in plasma of terminal renal failure patients. The following changes have to be emphasized: (1) high level of free cysteine (cystine) fraction, (2) strong tendency of homocysteine to form mixed disulfides with proteins, (3) drop of glutathione level. These observations confirm a suggestion that atherogenic action of homocysteine can be a result of S-homocysteinylation and N-homocysteinylation reactions, whereas toxic action of cysteine can result from auto-oxidation reaction.

[Comparative analysis of the efficacy and biocompatibility of various methods of dialysis]

BACKGROUND/AIM

The efficacy and biocompatibility of hemodialysis have a singnificant impact on dialysis patient morbidity and mortality rate. The aim of our study was to compare the efficacy and biocompatibility of different hemodialysis modalities in our patients.

METHODS

A total of 55 patients were included in the study, and on the basis of dialysis modality, they were divided in four groups: group I--post-dilution on-line hemodiafiltration (n=15), group II--bicarbonate high-flux polysulphone hemodialysis (n=15), group III--bicarbonate low-flux polysulphone hemodialysis (n=15), and groupe IV--bicarbonate cuprophane hemodialysis (n=10). The efficacy was evaluated on the basis of urea reduction rate (URR), urea Kt/V index and serum beta2-microglobuline reduction rate, and the biocompatibility was evaluated on the basis of the leukocyte count fall during the first fiftheen minutes of dialysis session, and of the serum C-reactive protein (CRP) level.

RESULTS

The highest mean URR was achieved in the group I (70.53 +/- 6.49%), and it was significantly higher in comparison with the average URR in the group IV (54.8 +/- 6.35%) (p = 0.001). The average value of urea Kt/V index in the group I (1.48 +/- 0.22) was significantly higher in comparison with the average value in the group II 1.30 +/- 0.22 (p < 0.05), group III (1.05 +/- 0.22), and group IV (0.98 + 0.22) (p = 0.001). Serum beta2-microglobuline reduction rate was 68.93 +/- 8.25% in the group I, and 58.86 +/- 7.98% in the groupe II (p = 0.01). During the first 15 minutes of hemodialysis the leukocyte number was decreased by 12.57 +/- 9.35% in the group 1, 13.61 +/- 9.64% in the group 11, 18.3 +/- 13.24 in the group III and 62.3 +/- 15.4 in the group IV, on average. The mean serum level of CRP was 9.4 +/- 6.47 mg/l in the group IV, and less than 3.5 mg/l in the group I of the patients (p = 0.001).

CONCLUSION

Postdilution on-line hemodiafiltration in comparison with standard hemodialysis provided the more effective elimination of small and middle uremic toxins molecules and a significantly higher degree of biocompatibility. The patients treated with standard hemodialysis frequently do not achieve the minimal value of urea Kt/V index prescribed by National Kidney Foundation-Dialysis Outcomes Quality Inatiatives standards. These patients also have significantly higher serum CRP values which suggest the state of chronic microinflammation.

Relevance of Oxidative Pathways in the Pathophysiology of Chronic Kidney Disease

Patients with uremia (whether requiring renal replacement therapy or not) have a greatly increased cardiovascular risk that cannot be explained entirely by traditional cardiovascular risk factors. An increase in oxidative stress has been proposed as a nontraditional cardiovascular risk factor in this patient population. Using a wide variety of different biomarkers of increased oxidative stress status, numerous laboratories around the world have now unequivocally demonstrated that uremia is a state of increased oxidative stress. Recent data also suggest linkages between oxidative stress inflammation, endothelial dysfunction, and malnutrition in the uremic population. These factors are probably synergistic in their effects on atherogenecity and risk of a cardiovascular event. The pathophysiology of increased oxidative stress in uremia is multifactorial, but the retention of oxidized solute by the loss of kidney function is probably a major contributor. Uremic oxidative stress can be characterized biologically by an increase in lipid per oxidation products and reactive aldehyde groups as well as by increased retention of oxidized thiols. Two recently published studies have suggested that antioxidative therapy may be particularly promising in reducing cardiovascular events in this patient population.Further definitive studies of antioxidant use are greatly needed.

Effects of oral vitamin C supplementation on oxidative stress and inflammation status in haemodialysis patients

BACKGROUND

There is increasing evidence for the presence of oxidative stress and vitamin C deficiency in dialysis patients. Limited data, however, are available regarding the effects of vitamin C supplementation on oxidative stress and inflammation markers in such patients.

METHODS

We ran a prospective, randomized, open-label trial to assess the effects of oral vitamin C supplementation (250 mg three times per week) for 2 months on well-defined oxidative and inflammatory markers in 33 chronic haemodialysis (HD) patients.

RESULTS

Normalization of plasma total vitamin C and ascorbate levels by oral vitamin C supplementation did not modify plasma levels of carbonyls, C-reactive protein and albumin, or erythrocyte concentrations of reduced and oxidized glutathione.

CONCLUSION

Short-term oral vitamin C supplementation did not modify well-defined oxidative/antioxidative stress and inflammation markers in HD patients. Whether a higher oral dose or the intravenous route can modify these markers remains to be determined.

Anti-inflammatory effects of alpha-tocopherol

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the western world. Its incidence has been increasing lately in the developing countries. Much evidence suggests a major role for inflammation in all phases of atherosclerosis. Cell adhesion molecules, cytokines, chemokines, and monocytes-macrophages as well as T lymphocytes play a pivotal role in atherogenesis. C-reactive protein (CRP), a downstream marker of inflammation, in addition to being a risk marker for CVD, could contribute to atherosclerosis. Dietary micronutrients with anti-inflammatory properties, specially alpha-tocopherol, may play an important role with regard to the prevention and treatment of CVD. alpha-Tocopherol has been shown to have anti-inflammatory effects both in vitro and in vivo. alpha-Tocopherol therapy, especially at high doses, has been shown to decrease release of pro-inflammatory cytokines (such as interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha) and the chemokine interleukin-8, and to decrease adhesion of monocytes to endothelium. In addition, alpha-tocopherol has been shown to decrease CRP levels in patients with CVD and having related risk factors for CVD (such as diabetes and smoking). Furthermore, pro-inflammatory cytokines and plasminogen activator inhibitor-1 (PAI-1) levels have also been shown to be decreased with alpha-tocopherol supplementation in vivo. In this review, our focus will be on anti-inflammatory effects of alpha-tocopherol reported in in vivo studies.

Influence of Epoietinum Therapy on the Oxidative Stress in Haemodialysis Patients

BACKGROUND

The causes of oxidative stress in haemodialysis (HD) patients are still controversial. Beside the uraemic state and dialysis-related factors, adjuvant drug therapies such as epoietinum (rHuEpo) and intravenous iron were involved.

METHODS

Several parameters related to oxidative stress were assessed by spectrophotometry in stable HD patients, treated for at least 2 months with epoietinum (n = 14; mean dose = 97.7 +/- 19.1 U/kg/week) or not (n = 15), none of them on iron therapy, and in 13 controls. Plasma thiobarbituric acid-reactive substances (TBARS) were used as markers of reactive species generation. Erythrocyte and plasma antioxidant systems, reflected by non-protein erythrocyte thiols, and erythrocyte enzyme activities -- superoxide dismutase (SOD), glutathione peroxidase, catalase and plasma total thiols, respectively -- were also investigated.

RESULTS

There were no differences between HD subgroups regarding haemoglobin levels. Plasma TBARS was increased in all HD patients as opposed to controls, irrespective of rHuEpo therapy. In addition, no change in antioxidant status parameters between rHuEpo-treated and -untreated patients was observed. Except for SOD, the other antioxidant indices were higher in all HD patients versus controls.

CONCLUSIONS

These results suggest that (1) chronic HD patients appear to have simultaneously enhanced reactive species generation and antioxidative systems efficiency, and (2) epoietinum therapy did not change their oxidative status, at least in the absence of concomitant iron supplementation and at similar haemoglobin levels.

Linking oxidative stress and inflammation in kidney disease: which is the chicken and which is the egg?

For end-stage renal disease (ESRD) patients, cardiovascular disease remains the single most common cause of excess morbidity and mortality. Furthermore, although the prevalence of traditional cardiovascular risk factors is high in the dialysis population, the extent and severity of associated cardiovascular morbidity and mortality remain disproportionate to traditional risk factor profiles. Consequently, considerable effort has been focused on "nontraditional" risk factors for cardiovascular events in this patient population. Among the examined nontraditional risk factors, increased oxidative stress as well as increased acute phase inflammation are postulated to be important contributors to uremic cardiovascular risk. Additional important uremic cardiovascular risk factors include malnutrition and endothelial dysfunction, both of which may be directly linked to the processes that cause increased oxidative stress and inflammation in uremia. In this context I review available data linking the pathogenesis of oxidative stress to acute phase inflammation and uremia. I also review data suggesting that oxidative stress in uremia directly contributes to the development of acute phase inflammation and that patients with higher levels of inflammation have higher levels of oxidative stress biomarkers. Similarly I review emerging data on the potential effects of antioxidant therapy on inflammatory biomarkers, as well as data suggesting that strategies to lower acute phase inflammation may also improve biomarkers of oxidative stress. Theoretical constructs evaluating the linkage of oxidative stress and inflammation in uremia and their contribution to the pathogenesis of atherosclerosis are suggested.

Low total vitamin C plasma level is a risk factor for cardiovascular morbidity and mortality in hemodialysis patients

Hemodialysis patients are prone to deficiency of vitamin C, which constitutes the most abundant nonenzymatic antioxidant in blood. Because antioxidants are involved in the pathogenesis of atherosclerosis, the authors examined the association of total vitamin C plasma level with cardiovascular outcomes in such patients. One hundred thirty-eight consecutive maintenance hemodialysis patients (median age 61 yr, 90 males) were enrolled in a single-center study. At baseline, routine laboratory parameters were recorded, and predialysis total vitamin C plasma levels were measured by high-pressure liquid chromatography. Patients were prospectively followed-up for the occurrence of a primary composite endpoint consisting of fatal and nonfatal major adverse cardiovascular events (MACE) and for all-cause and cardiovascular mortality. MACE occurred in 35 patients (25%) over a period of median 30 mo, and 42 patients (30%) died [29 cardiovascular deaths (21% of total)]. Using Cox proportional hazards modeling, adjusted hazard ratios for the occurrence of MACE were 3.90 (95% confidence interval [CI]: 1.42 to 10.67; P = 0.008) and 3.03 (95% CI: 1.03 to 8.92; P = 0.044) for patients in the lower (<32 micromol/L) and middle (32 to 60 micromol/L) tertile of total vitamin C levels, compared with patients in the upper tertile (>60 micromol/L). Hazard ratios for cardiovascular death were 3.79 (95% CI: 1.23 to 11.66; P = 0.020) and 2.89 (95% CI: 0.89 to 9.37; P = 0.076). Total vitamin C levels were not independently associated with all-cause mortality. This study concludes that low total vitamin C plasma levels predict adverse cardiovascular outcomes among maintenance hemodialysis patients. Future studies should address the potential protective effect of an adequate vitamin C supplementation.

Oxidative stress in uremia

PURPOSE OF REVIEW

Oxidative stress has been described as 'a disturbance in the prooxidant-antioxidant balance in favor of the former, leading to potential damage. In uremic patients, an increase in oxidative stress may occur because of the loss of residual renal function, and may be exacerbated by dialysis. This review will focus on the emerging biochemical evidence of an increase in oxidative stress in uremic patients, the relationship with renal replacement therapy, and the potential linkages to acute-phase inflammation, malnutrition, and adverse cardiovascular outcomes in uremic patients.

RECENT FINDINGS

Many studies from multiple research laboratories around the world have recently utilized in-vivo biomarkers to describe increased oxidative stress in uremic patients. An emerging literature suggests that there are links between an increase in oxidative stress, endothelial dysfunction, an increase in acute-phase inflammation, and an accelerated risk of cardiovascular complications in dialysis patients. Additional uremia-associated metabolic abnormalities, including hyperhomocysteinemia, intravenous iron exposure, and biocompatibility changes related to dialysis, may contribute to an increase in oxidative stress. Finally, two well-conducted pilot clinical randomized trials have suggested that antioxidant therapy may have efficacy in reducing cardiovascular events in uremic patients.

SUMMARY

The implications of the findings of a generalized increase in oxidative stress associated with uremia have led to the suggestion that antioxidative therapy may be efficacious in reducing cardiovascular complications. Pilot studies have suggested potential efficacy for this approach. However, further large-scale randomized clinical trials will be required to establish a compelling, evidence-based approach to the use of antioxidants in patients with uremia.

Does glucose present in the dialysate limit oxidative stress in patients undergoing regular hemodialysis?

BACKGROUND

Decreased glucose concentration in the blood causes the inhibition of the hexose monophosphate (HMP) cycle in the erythrocyte. NADPH, which is the source of the reductive equivalents necessary for the reproduction of glutathione (GSH), is not regenerated. The presence of glucose in dialysate should provide the stability of its concentration in the blood of patients undergoing hemodialysis (HD). The aim of the study was to assess the influence of glucose in the dialysate on the intensity of oxidative stress in patients undergoing regular HD.

METHODS

The study comprised 43 patients hemodialyzed with dialysate containing (HD-g(+)) or not containing glucose (HD-g(-)). The concentrations of the products of reaction with thiobarbituric acid-reactive substance (TBARS) and GSH as well as the activity of erythrocyte superoxide dismutase were determined. Glucose concentrations in the blood before and immediately after dialysis were also measured.

RESULTS

After flow-through dialysis the glucose concentration in the blood decreases both when dialysate does not contain glucose (4.8 vs. 1.6 mmol/l) and when dialysate contains glucose (6.6 vs. 5.8 mmol/l). HD caused changes in the TBARS concentration: in the HD-g(+) group the concentration decreased after HD, whereas in the HD-g(-) group it increased. In both groups of patients studied the GSH concentration changed after HD; in the HD-g(-) group it decreased and in the HD-g(+) group it increased. The results obtained in the groups of patients examined were confirmed by in vitro studies.

CONCLUSIONS

The presence of glucose in the dialysate guarantees the normal activity of the HMP cycle, which provides the production of reductive equivalents for the regeneration of reduced GSH - free radicals scavenger - and therefore the limitation of oxidative stress.

Neurological complications in renal failure: a review

Neurological complications whether due to the uremic state or its treatment, contribute largely to the morbidity and mortality in patients with renal failure. Despite continuous therapeutic advances, many neurological complications of uremia, like uremic encephalopathy, atherosclerosis, neuropathy and myopathy fail to fully respond to dialysis. Moreover, dialytic therapy or kidney transplantation may even induce neurological complications. Dialysis can directly or indirectly be associated with dialysis dementia, dysequilibrium syndrome, aggravation of atherosclerosis, cerebrovascular accidents due to ultrafiltration-related arterial hypotension, hypertensive encephalopathy, Wernicke's encephalopathy, hemorrhagic stroke, subdural hematoma, osmotic myelinolysis, opportunistic infections, intracranial hypertension and mononeuropathy. Renal transplantation itself can give rise to acute femoral neuropathy, rejection encephalopathy and neuropathy in graft versus host disease. The use of immunosuppressive drugs after renal transplantation can cause encephalopathy, movement disorders, opportunistic infections, neoplasms, myopathy and progression of atherosclerosis. We address the clinical, pathophysiological and therapeutical aspects of both central and peripheral nervous system complications in uremia.

Antioxidant therapy in uremia: evidence-based medicine?

Because of correlations between cardiovascular disease, inflammation, and renal failure, many investigators are pursuing nontraditional risk factors and therapies in order to reduce cardiovascular morbidity and mortality in the end-stage renal disease (ESRD) population. Despite the disappointing lack of clinical effects with antioxidative therapies seen in large studies of the general population, some studies suggest a diminished cardiovascular risk in individuals with renal failure. This expanding new line of evidence is promising as a method to help alleviate the more than 20-fold increase in risk of cardiovascular events in the ESRD population. Most of the current available studies have evaluated laboratory or physiologic endpoints, such as endothelial function and measures of oxidative burden, and have evaluated relatively small numbers of patients. However, it is currently premature to initiate widespread clinical therapy with antioxidants. Further investigation in this area should be supported to see if reported benefits can be duplicated in more widespread study populations, and to more accurately define the most appropriate choice of therapy, mode of therapy, and dose.

Effects of Intravenous Polymaltose Iron on Oxidant Stress and Non-Transferrin-Bound Iron in Hemodialysis Patients

BACKGROUND

The use of intravenous iron to correct anemia in end-stage renal diseases (ESRD) has been suspected of catalyzing the production of activated oxygen species and promoting oxidative damage. We investigated the pro-oxidative potential of injected iron in hemodialysis patients.

METHODS

In study A, 65 patients with ESRD were studied. 20 patients received weekly infusions of iron polymaltose (maltofer), whereas 45 patients had been off iron therapy for more than 2 months. In study B, 12 patients were investigated during two consecutive hemodialysis sessions, one session without and one session with infusion of 100 mg of maltofer over 4 h. Serum iron status, non-transferrin-bound iron (NTBI) and markers of oxidative stress were studied in blood samples from these patients.

RESULTS

In study A, NTBI was detected in 41% of the patients and the proportion of NTBI-positive patients was the same whether or not they received iron therapy. In study B, the serum iron and transferrin saturation index increased during iron infusion and NTBI transiently appeared in some patients but markers of oxidative stress were not significantly affected.

CONCLUSION

Although ESRD patients have a high prevalence of NTBI in their serum, no correlation could be established between the presence of NTBI and an increased oxidative stress. The slow infusion of maltofer does not promote a significant increase in the plasma concentration of oxidative stress markers. It may therefore be considered as a safe complement to erythropoietin therapy.

Advanced oxidation protein products as risk factors for atherosclerotic cardiovascular events in nondiabetic predialysis patients

BACKGROUND

Inflammation and oxidative stress are established risk factors for atherosclerosis, but whether they contribute to the accelerated atherogenesis associated with chronic kidney disease (CKD) remains to be assessed at the predialysis stage.

METHODS

We prospectively examined the relationship between plasma levels of C-reactive protein (CRP), fibrinogen, and advanced oxidation protein products (AOPPs), as selected markers of inflammation and oxidative stress, and incident first occlusive atherosclerotic cardiovascular (CV) events (ASCVEs) in a single-center cohort of 80 uremic predialysis patients without diabetes with a creatinine clearance ranging from 20 to 40 mL/min/1.73 m2 .

RESULTS

During follow-up (median, 7 years), 21 patients developed coronary, cerebral, or peripheral artery occlusive accidents, an incidence of 44/1,000 patient-years. Except for older age, their conventional risk factors did not differ compared with the 59 patients who remained free of such accidents. Conversely, plasma levels of CRP (4.3 +/- 2.7 versus 2.3 +/- 2 mg/L; P = 0.005), fibrinogen (5.6 +/- 1.4 versus 4.4 +/- 1.2 mg/L; P = 0.0009), and AOPPs (58 +/- 20 versus 42 +/- 14 micromol/L; P = 0.0002) were significantly greater at baseline, although serum creatinine levels did not differ between the 2 groups. By multivariate Cox regression analysis, age and CRP, fibrinogen, and AOPP levels were significant independent predictors of ASCVEs. Risk factor-adjusted hazard ratios were as follows: age, 1.13 (95% confidence interval, 1.04 to 1.22; P = 0.002); CRP level, 1.37 (95% confidence interval, 1.05 to 1.79; P = 0.02); fibrinogen level, 2.23 (95% confidence interval, 1.20 to 4.13; P = 0.011); and AOPP level, 1.68 (95% confidence interval, 1.12 to 2.51; P = 0.011).

CONCLUSION

CRP, fibrinogen, and AOPP levels independently predict ASCVEs in patients with CKD in the predialysis phase and might directly contribute to the uremia-associated accelerated atherogenesis.

F2-isoprostanes as biomarkers of lipid peroxidation in patients with chronic renal failure

Chronic renal failure patients on long-term hemolysis are found to be under increased oxidative stress, caused by antioxidant deficiency, neutrophil activation during hemodialysis (HD), platelet activation and/or chronic inflammation. Increased levels of oxidants (e.g. malondialdehyde, 4-hydroxynonenal, hydrocarbons, lipohydroperoxides, oxycholesterols, carbonyls) in HD patients are thought to play an important role in the development of endothelial dysfunction, atherogenesis and cardiovascular disease, which is a frequent condition in end-stage renal disease. F2-isoprostanes have been established as chemically stable, highly specific and reliable biomarkers of in vivo oxidative stress which can very sensitively measured by gas chromatography-mass spectrometry (Morrow et al. [17]). An up to 6-fold increase of plasma F2-isoprostanes in HD patients is accompanied by an enhanced formation of indicators of inflammation (e.g. C-reactive protein) and decreases of endogenous antioxidants (e.g. ascorbate, alpha-tocopherol). In their esterified form F2-isoprostanes may be a useful criteria to evaluate the effectiveness of clinical interventions to diminish oxidant stress and associated inflammation. Furthermore, F2-isoprostanes possess potent biological activities (e.g. 8-iso-PGF2alpha is known as a renal vasoconstrictor) suggesting that they may also act as mediators of the cellular effects of oxidative stress and inflammation.

Early prediction of IgA nephropathy progression: Proteinuria and AOPP are strong prognostic markers

BACKGROUND

Inflammation and oxidative stress have been incriminated in the pathogenesis of IgA nephropathy (IgAN). The aim of the present study was to assess whether markers reflecting these pathophysiologic processes, namely C-reactive protein (CRP) and advanced oxidation protein products (AOPP), would allow-in conjunction with clinical and histopathologic parameters-to predict disease progression.

METHODS

Between 1994 and 1997, 120 adult patients with biopsy-proven IgAN were included in a prospective cohort study, and followed until the end of 2002 or start of dialysis. In every patient, we determined plasma levels of CRP and AOPP. These parameters were included, together with clinical data, in a multivariate Cox proportional hazard regression analysis, with halving of baseline creatinine clearance as the primary renal end point.

RESULTS

A total of 51 patients reached the renal end point, including 30 who had to start dialysis. With multivariate analysis, the most potent independent risk factors of poor renal outcome were proteinuria > or =1 g/day [proportional hazard risk (HR) = 23.7, P= 0.0001], hypertension (HR = 8.13, P= 0.008), and AOPP plasma level (HR = 1.09 per 10 micromol/L, P= 0.042), whereas angiotensin II inhibitors were protective (HR = 0.19, P= 0.001).

CONCLUSION

Our data support the role of oxidative stress in the pathogenesis of IgAN and suggest that patients with proteinuria > or =1 g/day should be eligible for early implemented antioxidant and/or anti-inflammatory therapeutic strategies, with AOPP plasma level as a surrogate marker to evaluate their effects.

Pro-oxidative effect of α-tocopherol in the oxidation of LDL isolated from co-antioxidant-depleted non-diabetic hemodialysis patients

The association between the antioxidants in LDL and the oxidizability of LDL assessed by the oxidation lag time during copper ion-catalyzed oxidation was investigated in 69 non-diabetic hemodialysis patients and 23 healthy volunteers. The concentrations of co-antioxidants, including ubiquinol-10, lycopene and beta-carotene, in LDL were significantly lower in the hemodialysis patients than in the healthy volunteers, while there was no difference in the alpha-tocopherol concentration between the groups. The lag time showed a significantly positive correlation with the alpha-tocopherol level (r = 0.62, P < 0.01) in the healthy subjects, but a significantly negative correlation (r = -0.38, P < 0.05) in the hemodialysis patients. Furthermore, in vitro incubation of LDL with alpha-tocopherol prolonged the lag time in the healthy subjects, but shortened it in the hemodialysis patients. These results suggested that the alpha-tocopherol might exert the pro-oxidative effect in co-antioxidant-depleted LDL that was isolated from the hemodialysis patients. Despite such co-antioxidant depletion and the pro-oxidative effect of alpha-tocopherol, the lag time in the hemodialysis patients was not statistically different from that in the healthy volunteers. This might have been because the polyunsaturated fatty acids concentration, another determinant of the lag time, in LDL was less in the hemodialysis patients than in the healthy controls.

Serum malondialdehyde and coronary artery disease in hemodialysis patients

BACKGROUND/AIMS

It has been suggested that enhanced oxidative stress participates in the acceleration of coronary artery disease (CAD) in patients with end-stage renal disease (ESRD). The aim of this study was to investigate the relationship between the level of malondialdehyde (MDA), which is a marker of lipid peroxidation, and the severity of CAD in ESRD patients.

METHODS

We conducted a study of 39 hemodialysis patients (median age 58 years; 27 males and 12 females; diabetics 44%). In these patients, the predialysis serum concentrations of MDA and C-reactive protein (CRP) were measured. We performed multirow spiral computed tomography to derive coronary artery calcification (CAC) scores, as a marker of CAD severity.

RESULTS

Eleven of the 39 patients had minimal CAC (28%, CAC score <10), 10 patients had mild to moderate CAC (26%, 10-400), and 18 patients had severe CAC (46%, >400). The MDA levels increased (p < 0.05) with increasing CAC category and were correlated (r = 0.35, p < 0.05) with the CAC scores. The levels of MDA also correlated with the serum concentrations of CRP and albumin (r = 0.34, p < 0.05 and r = -0.32, p < 0.05, respectively). Patients in the highest tertile of MDA compared with the other patients were over four times as likely to have severe CAC, and the highest tertile of MDA was an independent predictor of severe CAC, along with a previous cardiovascular event.

CONCLUSION

An increased level of MDA, which was associated with inflammatory markers, was a predictive factor for severe CAC in ESRD patients.

Oxidative stress from rapid versus slow intravenous iron replacement in haemodialysis patients

METHODS AND RESULTS

Oxidative stress was examined in 19 erythropoietin-treated haemodialysis patients who were receiving 100 mg of iron sucrose every 2 weeks by two intravenous methods, rapid injection and slow infusion. There were no significant differences in incidence of iron oversaturation state between the two methods. Regarding oxidative stress markers, the values of plasma and red blood cell thiobarbituric acid reactive substances (TBARS) expressed in terms of malonyldialdehyde (MDA) equivalents following the two methods did not increase, and the values of area under the curve (AUC) of both markers were not different between both regimens. Also, there were no significant differences in the values of plasma and AUC of anti-oxidant markers including total anti-oxidant status, reduced thiols, and vitamin E among both periods treated with two intravenous iron methods.

CONCLUSION

As such, both intravenous iron methods could be safely used without enhancing oxidative stress in haemodialysis patients. The rapid injection method would be the preferred method of intravenous iron administration because it is more convenient while still retaining the safety profile.

Vascular biology in uremia: insights into novel mechanisms of vascular injury

Cardiovascular disease is the leading cause of death in patients with end-stage renal disease. Although the prevalence of traditional atherosclerotic risk factors is increased in patients with chronic kidney disease, these traditional risk factors alone do not seem to account for the increased cardiovascular mortality. It has been proposed that additional risk factors may play a role in vascular injury. Among nontraditional risk factors, chronic inflammation, oxidative stress, and vascular calcification have been implicated in the accelerated athersclerosis of chronic kidney disease. Uremia is a proinflammatory state. Elevated levels of the proinflammatory cytokine interleukin-6 and suppressed levels of the anti-inflammatory cytokine interleukin-10 are present in chronic kidney disease and have been implicated in accelerated atherosclerosis. Uremia also results in increased oxidative stress. Asymmetric dimethyl arginine and myeloperoxidase may be critical mediators of the endothelial damage that results from oxidative stress. Finally, the uremic milieu seems to promote vascular calcification. The abundance of proinflammatory cytokines, the possible deficiency in calcification inhibitory proteins and the high phosphorus that are often present in uremia contribute to vascular calcification. Smooth muscle cells in calcifying lesions undergo phenotypic changes and molecular reprogramming that are reminiscent of endochondral bone formation during embryogenesis.

The variability and accurate assessment of microinflammation in haemodialysis patients

BACKGROUND

Systemic microinflammation is correlated with atherosclerosis. It needs a reliable assessment. This study explores the temporal variations of three inflammatory indexes [C-reactive protein (CRP), serum amyloid A (SAA) and interleukin-6 (IL-6)] in a period free of clinical events and tests the reliability of their multiple measurements for the assessment of microinflammation in haemodialysis (HD) patients, a population at high risk of atherosclerotic cardiovascular disease.

METHODS

For 4 months, serum CRP, SAA and IL-6 were measured in 29 HD patients during the weeks they were free of inflammatory clinical events (> or =12 measurements for each index in every patient). The components of the variance as well as the reliability of two to five measurements for each index, aimed at assessing microinflammation precisely, were computed.

RESULTS

The median (interquartile range) of CRP was 2.3 (0.9-4.9) mg/l, of SAA 3.7 (2.1-9.3) mg/l and of IL-6 4.4 (2.2-7.7) pg/ml. Patients were approximately equally distributed between three groups of low, intermediate and high variability for each index. The contribution of intraindividual (biological) variation to the total of variance was 71.3%, 69.3% and 86.7% for CRP, SAA and IL-6, respectively (higher than in all other similar studies in healthy populations). Using two measurements, the estimated reliability was 57-68% for CRP in two-thirds of the patients (comparable with that found in healthy subjects) and 57% for SAA and IL-6 in only one-third of the patients. Increasing the number of measurements up to five did not change the reliability.

CONCLUSIONS

Individual factors significantly influence the levels of inflammatory indexes in HD patients in periods free of inflammatory clinical events. The mean of two weekly CRP measurements, but not of SAA or IL-6, seems to assess microinflammation in most patients with a sufficient reliability.

Increased hydrogen peroxide in the exhaled breath of uraemic patients unaffected by haemodialysis

BACKGROUND

Uraemia is accompanied by conditions favouring the rise of H2O2 activity in body fluids. This results from the increased release of H2O2 by polymorphonuclear leukocytes and decreased plasma glutathione peroxidase activity. The purpose of this study was to determine if patients on chronic haemodialysis (HD) exhale more H2O2 than healthy individuals, and if dialysis affects breath H2O2 content.

METHODS

We studied 29 chronic HD patients (mean age 49 +/- 11 years) and 40 healthy persons (mean age 44 +/- 9 years). H2O2, which is volatile, was measured fluorimetrically with the homovanillic acid method in the exhaled breath condensate (EBC) of the study cohort. EBC was collected immediately before and after the HD session and also at 20 and 60 min of HD treatment (n = 14) and once in controls. Peak expiratory flow (PEF), white blood cell (WBC) count, PaO(2) and circulatory cyclic guanosine monophosphate (cGMP), Il-6 and Il-8 concentrations were measured concomitantly. Finally, H2O2 diffusion through the dialyser cuprophane membrane was determined in an in vitro experiment.

RESULTS

At baseline, EBC H2O2 concentration was 22 times higher in HD patients than in controls (2.92 +/- 4.64 vs 0.16 +/- 0.13 microM, P < 0.001). Although the maximum decrease in PEF (431 +/- 52 vs 398 +/- 56 l/min, P < 0.01) and WBC count (6.72 +/- 1.02 vs 3.82 +/- 1.51 x 10(3)/ microl, P < 0.01) occurred at 20 min after the start of HD, no significant changes in breath H2O2 levels were noted throughout the session. Plasma IL-6 and IL-8 levels remained unchanged whereas cGMP rose 1.3 times at 60 min (P < 0.01). In vitro, H2O2 rapidly diffused through the cuprophane membrane.

CONCLUSION

Chronic HD patients exhale more H2O2 than healthy subjects. Although no change of breath H2O2 concentration was observed during HD, as H2O2 easily diffuses through the dialyser membrane, it is not possible to rule out that HD stimulates H2O2 generation.

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.

Linkage of hypoalbuminemia, inflammation, and oxidative stress in patients receiving maintenance hemodialysis therapy

BACKGROUND

Hypoalbuminemia is a powerful predictor of cardiovascular mortality in maintenance hemodialysis patients. Increased biomarkers of acute-phase inflammation and oxidative stress are highly prevalent and also correlate with cardiovascular morbidity and mortality. The extent to which hypoalbuminemia, biomarkers of inflammation, and biomarkers of oxidative stress are linked in this patient population is unknown. We hypothesized that a high proportion of hypoalbuminemic hemodialysis patients also would manifest increased levels of biomarkers of inflammation and oxidative stress.

METHODS

We surveyed 600 maintenance hemodialysis patients and identified 18 severely hypoalbuminemic patients (serum albumin level < 3.2 g/dL [32 g/L]) without recent infection or hospitalization. We then identified 18 age-, race-, sex-, and diabetes-matched normoalbuminemic hemodialysis patients, as well as 18 age-, race-, sex-, and diabetes-matched healthy subjects, for cohort comparison. Measurements of plasma interleukin-6 (IL-6) levels, plasma protein reduced thiol content, plasma protein carbonyl content, and plasma free F2-isoprostane levels, as well as serum concentrations of C-reactive protein (CRP) and prealbumin, were performed for study purposes.

RESULTS

Levels of serum CRP, IL-6, plasma protein thiol oxidation, and protein carbonyl formation were significantly elevated in both hypoalbuminemic and normoalbuminemic hemodialysis patients compared with healthy subjects and also were significantly different in hypoalbuminemic maintenance dialysis patients compared with normoalbuminemic hemodialysis patients. Prealbumin levels were significantly lower in hypoalbuminemic hemodialysis patients than in other groups.

CONCLUSION

There is a high prevalence of inflammation and oxidative stress in the maintenance hemodialysis population. Levels of inflammatory and oxidative stress biomarkers are increased further in hypoalbuminemic compared with normoalbuminemic dialysis patients. Hypoalbuminemia, acute-phase inflammation, and oxidative stress may act synergistically to increase cardiovascular morbidity and mortality risk in maintenance hemodialysis patients.

Total and corrected antioxidant capacity in hemodialyzed patients

BACKGROUND

Oxidative stress may play a critical role in the vascular disease of end stage renal failure and hemodialysis patients. Studies, analyzing either discrete analytes and antioxidant substances, or the integrated total antioxidant activity of human plasma during hemodialysis, give contradictory results.

METHODS

Recently, we have introduced a new automated method for the determination of Total Antioxidant Capacity (TAC) of human plasma. We have serially measured TAC and corrected TAC (cTAC: after subtraction of the interactions due to endogenous uric acid, bilirubin and albumin) in 10 patients before the onset of the dialysis session, 10 min, 30 min, 1 h, 2 h and 3 h into the procedure and after completion of the session.

RESULTS

Our results indicate that TAC decreases, reaching minimum levels at 2 h. However, corrected TAC increases with t1/2 of about 30 min. We then repeated the measurements in 65 patients undergoing dialysis with different filters (36 patients with ethylene vinyl alcohol copolymer resin filter -Eval-, 23 patients with two polysulfone filters -10 with F6 and 13 with PSN140-, and 6 patients with hemophan filters). Three specimens were collected (0, 30, 240 min). The results of this second group confirm our initial results, while no significant difference was observed using either filter.

CONCLUSIONS

Our results are discussed under the point of view of possible mechanisms of modification of endogenous antioxidants, and the interaction of lipid- and water-soluble antioxidants.

Dialysis filter type determines the acute effect of haemodialysis on endothelial function and oxidative stress

BACKGROUND

Endothelial function of large arteries is impaired in chronic haemodialysis patients and oxidative stress due to the dialysis procedure has been suggested as a causal factor. However, it is not clear whether different types of dialysis membranes affect endothelial function differently. Therefore we determined endothelium-dependent, flow-mediated dilatation (FMD) of the brachial artery as well as markers of oxidative stress immediately before and after haemodialysis (HD) with either a cellulosic cuprophane or a synthetic polysulphone dialyser in a blinded, randomized, cross-over study.

METHODS

Twelve haemodialysis patients (age 55+/-3 years, time on dialysis 20+/-2 months, mean fluid change -1782+/-21 ml, systolic/diastolic blood pressure 139/75 mmHg) were included. Using a multi-gate-pulsed Doppler system (echo-tracking device) brachial artery FMD and nitroglycerine-induced, endothelium-independent vasodilatation (NMD) were measured. Patients were randomized to HD with either a polysulphone or a cuprophane membrane and were crossed over to the other filter. Investigators were blinded to the type of membrane used. Serum concentrations of oxidized LDL (oxLDL) and alpha-tocopherol as markers of oxidative stress were measured before and after each dialysis session.

RESULTS

Data are given as mean+/-SEM. Treatment with polysulphone filter HD did not significantly affect FMD (baseline 9.3+/-2.0% vs after HD 9.6+/-1.8%). After dialysis with a cuprophane membrane FMD decreased from 9.4+/-2.1 to 7.4+/-1.8% (P<0.05). NMD was not significantly affected by HD irrespective of the membrane material used. Serum levels of oxLDL were not changed by either treatment; however, alpha-tocopherol concentrations fell significantly after dialysis with the cuprophane filter (baseline 18.0+/-2.3 after HD 16.6+/-1.3 micro g/ml, P<0.05), while alpha-tocopherol levels remained unchanged when the polysulphone membrane was used.

CONCLUSIONS

The type of dialysis filter membrane determines the acute effect of haemodialysis on arterial endothelial function. Differences in biocompatibility and oxidative stress may account for the observed differential effects, since the decrease of FMD after dialysis with a cellulosic cuprophane membrane-but not with a synthetic polysulphone membrane-was associated with a reduction in serum vitamin E.

Oxidative stress in end-stage renal disease: an emerging threat to patient outcome

INTRODUCTION

Patients affected by end-stage renal disease (ESRD) experience an excess of morbidity and mortality due to cardiovascular disease (CVD), which cannot be fully explained by the classical CVD risk factors. Among emerging CVD risk factors, oxidative stress is currently being given emphasis.

METHODS

We achieved a consensus on key points relating to oxidative stress in ESRD patients.

RESULTS

ESRD patients are subjected to enhanced oxidative stress, as a result of reduced anti-oxidant systems (vitamin C and selenium deficiency, reduced intracellular levels of vitamin E, reduced activity of the glutathione system) and increased pro-oxidant activity (advanced age, high frequency of diabetes, chronic inflammatory state, uraemic syndrome, bio-incompatibility of dialysis membranes and solutions). Oxidative stress and inflammation are deeply inter-related, as different oxidant free radicals are generated by phagocytic cells in response to inflammatory stimuli: both are related to endothelial dysfunction, as the endothelium is a source and a target of oxidants and participates in the inflammatory response. There is growing evidence, from experimental and clinical studies, that oxidative stress may be implicated in the pathogenesis of atherosclerosis and other complications of ESRD, namely dialysis-related amyloidosis, malnutrition and anaemia. Given that free radicals have very short half-lives (seconds), the clinical assessment of oxidative stress is based on the measurement of different stable oxidized compounds (such as lipid peroxidation products, advanced glycation and oxidation lipid and protein products, nucleic acid oxidation derivatives) or antibodies directed against oxidized epitopes (such as anti-oxidized low-density lipoprotein antibodies). At the same time, both enzymatic anti-oxidants (superoxide dismutase, catalase, glutathione peroxidase) and non-enzymatic anti-oxidants (glutathione, vitamin C, vitamin E, negative inflammatory proteins) can be evaluated. However, many laboratory methods assessing various oxidative stress components still have to be standardized. Moreover, it is still uncertain whether it is better measuring plasma and/or intracellular concentrations or activities of these components. The possibility of improving patient outcome by therapeutic interventions aimed at reducing oxidative stress, e.g. by vitamin C or vitamin E supplementation, currently is to the fore, but results so far have remained inconclusive.

CONCLUSIONS

It is important to consider oxidative stress as a potentially important source of patient morbidity and mortality, although this knowledge is not yet immediately applicable in the clinical arena. Further well-designed, randomized controlled clinical trials with anti-oxidants (e.g. vitamin E, vitamin C, N-acetyl cysteine, L-arginine) are required to establish evidence-based recommendations for clinical practice.

New insights into the effects of the protein moiety of oxidized LDL (oxLDL)

Oxidative stress has been implicated in the cardiovascular complications in chronic renal failure patients. Lipoprotein oxidation is involved in the genesis of atherosclerosis. Both the lipid and the protein moieties of low-density lipoproteins (LDL) are subject to oxidation. We have shown that oxidation of LDL by hypochlorous acid (HOCl) in vitro, reflecting increased myeloperoxidase (MPO) activity in vivo, leads mainly to modifications of apolipoproteins, such that the latter in turn induce high rates of apoptosis in a human monocytic cell line via a caspase-dependent pathway. These in vitro oxidative changes of LDL protein moiety, if shown to occur to a significant extent in uremic patients in vivo, may represent an important pathway in the pathogenesis of atherogenesis.

Blood 8-hydroxy-2'-deoxyguanosine is associated with erythropoietin resistance in haemodialysis patients

BACKGROUND

8-Hydroxy-2'-deoxyguanosine (8-OHdG), a product of oxidized DNA, is increased in haemodialysis (HD) patients, but the clinical relevance of enhanced 8-OHdG production in these patients remains unknown.

METHODS

We cross-sectionally measured serum 8-OHdG in 73 patients on maintenance HD (age 68+/-2 years, time on HD 85+/-11 months, male/female=42/31), and examined the relationship between blood 8-OHdG and the severity of renal anaemia and the weekly dosage of recombinant human erythropoietin (rHuEPO).

RESULTS

There was a significant increase in serum 8-OHdG in HD patients compared with normal subjects. Serum 8-OHdG was positively correlated with the patients' age (r=0.231, P<0.05) but not with the duration of HD. Serum 8-OHdG was significantly higher in diabetic subjects than in non-diabetic subjects (P<0.05). Serum 8-OHdG had a significant inverse correlation with haemoglobin (Hb) (r=-0.526, P<0.01) but a positive correlation with the rHuEPO dose (r=0.443, P<0.01) and the ratio of the weekly rHuEPO dose divided by Hb (r=0.487, P<0.01). Serum 8-OHdG was not correlated with inflammatory and nutritional parameters.

CONCLUSIONS

These findings suggest that the elevation of circulating 8-OHdG may be associated, at least in part, with rHuEPO resistance in HD patients.

Cardiac troponin T and malondialdehyde modified plasma lipids in haemodialysis patients

BACKGROUND

In patients with end-stage renal disease (ESRD), treated with haemodialysis, a high overall mortality is observed. A previous study showed that cardiac troponin T (cTnT) is a strong independent predictor of outcome in this population. In this study we investigated possible causes of cTnT increase and its relationship with a marker of oxidative stress.

METHODS

In a group of 71 haemodialysis patients (36 male, 35 female, mean age 68.7+/-1.5 years) we determined cTnT and compared its presence with several biochemical parameters and with malondialdehyde (MDA), which is an indicator of oxidative stress. None of the patients suffered an acute coronary event during the observation period. Three measurements of cTnT and MDA were performed with a 2-week interval. Forty-nine patients underwent a transthoracic echocardiography.

RESULTS

Twenty-nine patients (or 40.8%) had a positive cTnT determination (defined as cTnT >/=0.10 ng/ml). cTnT positive patients had significantly higher levels of MDA (P=0.0125), C-reactive protein (CRP) (P=0.04) and pre-dialysis urea (P=0.04). Regression analysis showed that both pre-dialysis urea and MDA independently influenced cTnT. No correlation was found with age, dialysis adequacy, post-dialysis urea, total cholesterol, white blood cell count, fibrinogen or any of the echocardiographical parameters. Presence of heart failure, diabetes or use of medication could not discriminate between cTnT positive and cTnT negative patients. MDA levels correlated positively with time on haemodialysis (P=0.0021). Echocardiography showed left ventricular hypertrophy in 88% of the examined patients and impaired wall motion in 35%. Patients with clinical signs of heart failure had a lower ejection fraction and worse wall motion score index. No correlation existed between echocardiographic findings and cTnT or MDA. Survival was independently predicted by cTnT (P=0.0025), MDA (P=0.0007), CRP (P=0.006) and age (P=0.0143). Patients with both cTnT and CRP increase had a survival of <50% at 1 year, compared with 90% in patients with both cTnT and CRP within the normal range and 80% when either CRP or cTnT was increased (chi(2)=12.127; P=0.0023).

CONCLUSIONS

This study confirms that the presence of cTnT predicts prognosis in ESRD. The presence of cTnT is linked to oxidative stress, inflammation and uraemia. The absence of specific findings on EKG and echocardiography points towards subclinical myocardial damage caused by endothelial disturbances.

Oxidant stress in hemodialysis patients: what are the determining factors?

Oxidant stress contributes to morbidity in hemodialysis patients. Three possible causes of oxidant stress have been suggested: the uremic state, the dialyzer membrane, and bacterial contaminants from the dialysate. Oxidant stress occurs in uremia before dialysis therapy is initiated, as evidenced by increased production of reactive oxygen species, increased levels of oxidized plasma proteins and lipids, and decreased antioxidant defenses. It has been proposed that increased production of reactive oxygen species during hemodialysis is also an important contributor to oxidant stress. Hemodialysis is associated with a transient increase in production of reactive oxygen species, particularly with cellulose membranes. In addition, surveys have shown widespread contamination of dialysate by endotoxin, which may cross membranes and prime production of reactive oxygen species by phagocytic cells. Recent studies, however, show a decrease in protein oxidation from pre- to post-dialysis and a normalization of neutrophil reactive oxygen species production. Taken together, these data suggest that uremia, per se, is the most important cause of oxidant stress in hemodialysis patients. Dialysate quality may also contribute to oxidant stress, but evidence that the dialyzer membrane plays a role is weak.

Vitamin C as an antioxidant: evaluation of its role in disease prevention

Vitamin C in humans must be ingested for survival. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans. Antioxidant effects of vitamin C have been demonstrated in many experiments in vitro. Human diseases such as atherosclerosis and cancer might occur in part from oxidant damage to tissues. Oxidation of lipids, proteins and DNA results in specific oxidation products that can be measured in the laboratory. While these biomarkers of oxidation have been measured in humans, such assays have not yet been validated or standardized, and the relationship of oxidant markers to human disease conditions is not clear. Epidemiological studies show that diets high in fruits and vegetables are associated with lower risk of cardiovascular disease, stroke and cancer, and with increased longevity. Whether these protective effects are directly attributable to vitamin C is not known. Intervention studies with vitamin C have shown no change in markers of oxidation or clinical benefit. Dose concentration studies of vitamin C in healthy people showed a sigmoidal relationship between oral dose and plasma and tissue vitamin C concentrations. Hence, optimal dosing is critical to intervention studies using vitamin C. Ideally, future studies of antioxidant actions of vitamin C should target selected patient groups. These groups should be known to have increased oxidative damage as assessed by a reliable biomarker or should have high morbidity and mortality due to diseases thought to be caused or exacerbated by oxidant damage.

Effects of high-flux hemodialysis on oxidant stress

BACKGROUND

Neutrophil oxygen radical production is increased in end-stage renal disease (ESRD) patients and it is further enhanced during dialysis with low-flux cellulosic membranes. This increased oxygen radical production may contribute to the protein and lipid oxidation observed in ESRD patients. We tested the hypothesis that high-flux hemodialysis does not increase oxygen radical production and that it is not associated with protein oxidation.

METHODS

Neutrophil oxygen radical production was measured during dialysis with high-flux dialyzers containing polysulfone and cellulose triacetate membranes. Free sulfhydryl and carbonyl groups and advanced oxidation protein products were measured to assess plasma protein oxidation.

RESULTS

Pre-dialysis, neutrophil oxygen radical production was significantly greater than normal and increased significantly as blood passed through the dialyzer in the first 30 minutes of dialysis. Post-dialysis, however, neutrophil oxygen radical production had decreased and was not different from normal. Pre-dialysis, significant plasma protein oxidation was evident from reduced free sulfhydryl groups, increased carbonyl groups, and increased advanced oxidation protein products. Post-dialysis, plasma protein free sulfhydryl groups had increased to normal levels, while plasma protein carbonyl groups increased slightly, and advanced oxidation protein products remained unchanged.

CONCLUSIONS

The results of this study show that neutrophil oxygen radical production normalizes during high-flux dialysis, despite a transient increase early in dialysis. This decrease in oxygen radical production is associated with an improvement in some, but not all, measures of protein oxidation.