Glucose-induced pseudohypoxia and advanced glycosylation end products explain peritoneal damage in long-term peritoneal dialysis

Long-term peritoneal dialysis is associated with the development of peritoneal membrane alterations, both in morphology and function. Impaired ultrafiltration (UF) is the most important functional change, and peritoneal fibrosis is the major morphological alteration. Both are caused by the continuous exposure to dialysis solutions that are different from plasma water with regard to the buffer substance and the extremely high-glucose concentrations. Glucose has been incriminated as the major cause of long-term peritoneal membrane changes, but the precise mechanism has not been identified. We argue that glucose causes the membrane alterations by peritoneal pseudohypoxia and by the formation of advanced glycosylation end products (AGEs). After a summary of UF kinetics including the role of glucose transporters (GLUT), and a discussion on morphologic alterations, relationships between function and morphology and a survey of the pathogenesis of UF failure (UFF), it will be argued that impaired UF is partly caused by a reduction in small pore fluid transport as a consequence of AGE-related vasculopathy and - more importantly - in diminished free water transport due to pseudohypoxia, caused by increased peritoneal cellular expression of GLUT-1. The metabolism of intracellular glucose will be reviewed. This occurs in the glycolysis and in the polyol/sorbitol pathway, the latter is activated in case of a large supply. In both pathways the ratio between the reduced and oxidised form of nicotinamide dinucleotide (NADH/NAD+ ratio) will increase, especially because normal compensatory mechanisms may be impaired, and activate expression of hypoxia-inducible factor-1 (HIF-1). The latter gene activates various profibrotic factors and GLUT-1. Besides replacement of glucose as an osmotic agent, medical treatment/prevention is currently limited to tamoxifen and possibly Renin/angiotensis/aldosteron (RAA) inhibitors.

Apolipoprotein A-I attenuates peritoneal fibrosis associated with peritoneal dialysis by inhibiting oxidative stress and inflammation

Apolipoprotein A-I (apoA-I), 90% of which is present in high-density lipoprotein (HDL), is the main constituent of HDL, has anti-inflammatory and anti-oxidant properties, and has received extensive attention in anti-atherosclerosis. Yet little is known about apoA-I 's role in peritoneal dialysis. In this study, by analyzing PD patients (n = 81), we found that decreased apoA/HDL-C ratio is significantly associated with rapid decline in peritoneal function. Further studies were performed in animal experiments to determine the ascendancy of apolipoprotein A-I mimetic peptide (D-4F) on peritoneum, we found that D-4F administration reduced peritoneal fibrosis and peritoneal endothelial mesenchymal transformation (EMT) induced by high glucose peritoneal dialysate, such as N-cadherin, Fibronectin, Vimentin, and α-smooth muscle actin (α-SMA) expression decreased. In mechanism, D-4F can significantly inhibit Smad2/3 phosphorylation, which is the major pathway leading to fibrosis. Furthermore, D-4F treatment inhibited NADPH oxidase and thiobarbituric acid reactive substances (TBARS) expression, increased the activity of certain enzymes, such as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Finally, treatment with D-4F inhibits the expression of interleukins-6(IL-6), Interleukin-1β(IL-1β), and tumor necrosis factor-α(TNF-α). Taken together, based on the above research evidence, apoA-I and its peptide mimic may regulate the oxidative stress, TGF- β1/Smads signaling pathway and inflammatory response to reduce peritoneal fibrosis due to peritoneal dialysis.

Novel oxidized LDL-based clinical markers in peritoneal dialysis patients for atherosclerosis risk assessment

Maintenance peritoneal dialysis (PD) is commonly associated with cardiovascular diseases (CVDs), whose risk is assessed via LDL-C. Nonetheless, oxidized LDL (oxLDL), as being a key component of atherosclerotic lesions, could be also associated with atherosclerosis and related CVDs. However, its predictive value for CVDs risk assessment is subject of research studies due to the lack of specific methods to measure oxLDL status from its individual lipid/protein components. In the present study, six novel oxLDL markers, representative of certain oxidative modifications on the LDL protein and lipid components, are measured in atherosclerosis-prone PD patients (39) versus those in chronic kidney disease patients (61) under hemodialysis (HD) and healthy controls (40). LDL from serum of PD, HD and control subjects were isolated and fractionated into cholesteryl esters, triglycerides, free cholesterol, phospholipids and apolipoprotein B100 (apoB100). Subsequently the oxLDL markers cholesteryl ester hydroperoxides (-OOH), triglyceride-OOH, free cholesterol-OOH, phospholipid-OOH, apoB100 malondialdehyde and apoB100 dityrosines were measured. LDL carotenoid levels and LDL particle serum concentration were also measured. The levels of all oxLDL lipid-OOH markers were significantly elevated in PD patients versus control, while the levels of cholesteryl ester-/triglyceride-/free cholesterol-OOH were significantly elevated in PD versus HD patients, regardless of patients' underlying medical conditions, sex, age, PD type, clinical biochemical markers and medication. It should be noted that all fractionated lipid-OOH levels were inversely correlated with LDL-P concentration, while LDL-P concentration was not correlated with LDL-C in PD patients. Moreover, LDL carotenoids were significantly lower in PD patients versus control. The increased levels of oxLDL status specific markers in both PD and HD patients (compared to control), support a potential prognostic value of oxLDL regarding CVD risk assessment in both patient groups. Lastly, the study introduces the oxLDL peroxidation markers free cholesterol-OOH and cholesteryl ester-OOH as complementary to LDL-P number, and as possible alternatives to LDL-C.

Reduced Oxidative Stress in Hypoalbuminemic CAPD Patients

Objective

Albumin is one of the plasma antioxidants. The higher incidence of cardiovascular disease in dialysis patients with hypoalbuminemia may be related to decreased antioxidant capacity resulting from low serum albumin. We evaluated malondialdehyde (MDA), a marker of oxidative stress, and total antioxidant capacity (TAC) in relation to serum albumin in continuous ambulatory peritoneal dialysis (CAPD) patients.

Patients and Methods

In this cross-sectional study, we measured MDA, TAC, albumin, uric acid (another important plasma antioxidant), prealbumin, and C-reactive protein (CRP) in the blood of 66 CAPD patients and 30 normal controls. Twenty-two CAPD patients with albumin less than or equal to 3.5 g/dL were divided into two groups: In the experimental group ( n = 11), MDA, TAC, and CRP were measured before and after repeated infusion of 20% albumin 100 mL daily for 7 days. In the control group ( n = 11), the same parameters were measured without albumin infusion.

Results

CAPD patients had lower albumin and higher MDA, TAC, and uric acid than normal controls. There were positive correlations between albumin and TAC or uric acid in CAPD patients. Contrary to our expectation, there was also positive correlation between albumin and MDA in CAPD patients ( r = 0.37, p = 0.004). MDA showed a positive correlation with TAC. Uric acid was correlated with TAC. It did not, however, show correlation with MDA. Log CRP was negatively correlated with albumin, but did not show correlation with MDA or TAC. Prealbumin was correlated with MDA, TAC, albumin, and uric acid. Serum albumin in the experimental group increased from 2.5 ± 0.3 g/dL to 3.6 ± 0.2 g/dL ( p < 0.001) at the end of repeated infusions. No changes were seen in MDA, TAC, and CRP in either group.

Conclusions

The present study suggests that lipid peroxidation is increased in CAPD patients and that this is not due to weakening of antioxidant defenses of plasma. Increased TAC was mainly caused by a higher level of uric acid. Reduced, rather than increased, MDA in hypoalbuminemic patients and lack of effects of albumin infusion on levels of MDA suggest that the frequent occurrence of cardiovascular disease in dialysis patients with hypoalbuminemia is not due to the decrease in antioxidant capacity resulting from low serum albumin.

Oxidative Stress in Peritoneal Dialysis Patients: Association with the Dialysis Adequacy and Technique Survival

Introduction:

Increased oxidative stress is suggested as one of the possible mechanisms of structural and functional damage to the peritoneal membrane in peritoneal dialysis patients. But there are few available data on the association of oxidative stress with peritoneal dialysis adequacy and technique survival. The present study was undertaken to investigate the association of oxidative stress biomarkers with the peritoneal dialysis adequacy and technique survival.

Methods:

This prospective single-center observational study was conducted between January 2010 and May 2015. Adequacy of dialysis, malondialdehyde levels in the serum and erythrocytes (as an indicator of lipid peroxidation), the concentration of ceruloplasmin, transferrin, and sulfhydryl groups in the blood, and total peroxidase activity in erythrocyte (as indicators of antioxidant system) were determined in 44 stable ambulatory non-diabetic peritoneal dialysis patients.

Results:

The follow-up period was 3 years. We identified a negative correlation between the serum level of malondialdehyde in the patients and total weekly Kt/V. Peritoneal weekly CrCl was positively correlated with the levels of transferrin, total peroxidase activity, and SH– groups. Daily peritoneal ultrafiltration had a positive correlation with the total peroxidase activity and the serum transferrin levels. The results of the Kaplan–Meier analysis and the log-rank test also demonstrated a significant difference in the cumulative technique survival rate between the patients with ceruloplasmin level ≤0.19 g/l and ≥0.2 g/l.

Conclusions:

The results mentioned above could be considered as one of the ways to explain better technique survival in PD patients.

Oxidative Stress in Patients Undergoing Peritoneal Dialysis: A Current Review of the Literature

Peritoneal dialysis (PD) patients manifest excessive oxidative stress (OS) compared to the general population and predialysis chronic kidney disease patients, mainly due to the composition of the PD solution (high-glucose content, low pH, elevated osmolality, increased lactate concentration and glucose degradation products). However, PD could be considered a more biocompatible form of dialysis compared to hemodialysis (HD), since several studies showed that the latter results in an excess accumulation of oxidative products and loss of antioxidants. OS in PD is tightly linked with chronic inflammation, atherogenesis, peritoneal fibrosis, and loss of residual renal function. Although exogenous supplementation of antioxidants, such as vitamins E and C, N-acetylcysteine, and carotenoids, in some cases showed potential beneficial effects in PD patients, relevant recommendations have not been yet adopted in everyday clinical practice.

Human Peritoneal Mesothelial Cell Death Induced by High-Glucose Hypertonic Solution Involves Ca2+ and Na+ Ions and Oxidative Stress with the Participation of PKC/NOX2 and PI3K/Akt Pathways

Chronic peritoneal dialysis (PD) therapy is equally efficient as hemodialysis while providing greater patient comfort and mobility. Therefore, PD is the treatment of choice for several types of renal patients. During PD, a high-glucose hyperosmotic (HGH) solution is administered into the peritoneal cavity to generate an osmotic gradient that promotes water and solutes transport from peritoneal blood to the dialysis solution. Unfortunately, PD has been associated with a loss of peritoneal viability and function through the generation of a severe inflammatory state that induces human peritoneal mesothelial cell (HPMC) death. Despite this deleterious effect, the precise molecular mechanism of HPMC death as induced by HGH solutions is far from being understood. Therefore, the aim of this study was to explore the pathways involved in HGH solution-induced HPMC death. HGH-induced HPMC death included influxes of intracellular Ca²⁺ and Na⁺. Furthermore, HGH-induced HPMC death was inhibited by antioxidant and reducing agents. In line with this, HPMC death was induced solely by increased oxidative stress. In addition to this, the cPKC/NOX2 and PI3K/Akt intracellular signaling pathways also participated in HGH-induced HPMC death. The participation of PI3K/Akt intracellular is in agreement with previously shown in rat PMC apoptosis. These findings contribute toward fully elucidating the underlying molecular mechanism mediating peritoneal mesothelial cell death induced by high-glucose solutions during peritoneal dialysis.

Correlation of bioelectrical impedance analysis phase angle with changes in oxidative stress on end-stage renal disease patients, before, during, and after dialysis

Chronic kidney disease is a condition that promotes oxidative stress. There are conflicting evidence about the role of hemodialysis on oxidative stress, that are mostly related with the various types of membrane materials used, the quality and type of dialysate, the method used, etc. The phase angle (PhA), which is determined with bioelectrical impedance analysis (BIA), measures the functionality of cell membranes. In this study, the correlation of the PhA with parameters of oxidative stress is attempted for the first time. We evaluated parameters of oxidative status as total antioxidant capacity (TAC) in erythrocytes (RBCs) and plasma of patients with ESRD undergoing hemodialysis with low flux synthetic polysulfone membranes. Measurements were recorded from 30 patients (16 men and 14 women) aged 64 ± 14 years before, during, and after dialysis, and in 15 healthy volunteers aged 56 ± 12 years The PhA was obtained by BIA. The plasma TAC increased significantly (41%, p < 0.05). Intracellular TAC noted a non-significant increase. Total antioxidant capacity of the patients before and after hemodialysis was significantly lower from the healthy volunteers (p < 0.05) showing that ESRD patients are at the state of increased oxidative stress. The PhA increased in significantly positive correlation with plasma TAC at the end of hemodialysis. The process of hemodialysis with biocompatible synthetic membranes and bicarbonate dialysate improved plasma TAC. The positive correlation of PhA with extracellular TAC could evolve to a method of oxidative stress estimation by BIA but further research is needed.

Influence of Hemodialysis on Lipid Peroxidation, Enzymatic and Non-Enzymatic Antioxidant Capacity in Chronic Renal Failure Patients

BACKGROUND

Free radical induced damages are thought to be involved in chronic kidney disease (CKD), especially in patients who are on hemodialysis (HD) for prolonged periods. Hemodialysis can influence multiple biochemical factors, several of which are useful, although the rest can be harmful and increase the severity of disease.

OBJECTIVES

The purpose of this study was to evaluate the effect of the HD membrane polysulfone on oxidative stress markers, by measuring the level of lipid peroxidation and total antioxidant activity (TAC), in the blood of HD patients.

PATIENTS AND METHODS

This study was carried out on 31 HD patients and 31 healthy persons, matched for age and sex, as control group. Blood samples were drawn before and after HD from arteriovenous fistulas, and once from the controls. Superoxide dismutase (SOD), catalase (CAT) and thiobarbituric acid-reactive substance (TBARS) in blood hemolyzate, Glutathione peroxidase (GpX) of whole blood and TAC of plasma were measured, respectively. Then, we investigated the association between TAC of plasma, measured by ferric reducing antioxidant power (FRAP), and lipid peroxidation level with its related parameters, in HD patients.

RESULTS

The SOD, GpX and CAT were decreased after HD (P < 0.05). Also, FRAP was shown to decrease after HD (P < 0.05). However, erythrocyte TBARS levels (μmol/gr of Hb) were increased after HD, in comparison with controls, and before HD (P < 0.05). There was a significant negative correlation between TBARS and antioxidant indices, such as SOD (r = -0.67, P = 0.001), GpX (r = -0.76, P = 0.001), CAT (r = -0.63, P = 0.001) and FRAP (r = -0.84, P = 0.001). The FRAP was significantly and directly correlated with uric acid (r = +0.62, P = 0.001), SOD (r = +0.72, P = 0.001), GpX (r = +0.87, P = 0.001) and CAT (r = +0.84, P = 0.001).

CONCLUSIONS

The results of our study proposed that there is a loss or inactivation of antioxidant factors, coupled with increased lipid peroxidation during the procedure of HD, possibly through the dialyzer membrane, with probable consequences on the severity of illness.

Linkage of some trace elements, peripheral blood lymphocytes, inflammation, and oxidative stress in patients undergoing either hemodialysis or peritoneal dialysis

BACKGROUND

Changes in essential trace elements may affect the inflammatory and immunological state of patients on hemodialysis (HD) or peritoneal dialysis (PD). Therefore, we aimed to determine trace element content and markers of oxidative stress, inflammation, and immune status in HD and PD patients and to assess the relationships among these parameters.

METHODS

Patients on either HD (n = 20) or PD (n = 20) and age-, sex-, body mass index-matched healthy individuals (n = 20) were enrolled in the study. The trace elements zinc, copper, selenium, and iron; markers of oxidative stress thiobarbituric acid reactive substances (TBARS) and protein carbonyl levels; activities of antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase; percentages of CD3 T lymphocytes and the subsets CD4 and CD8; the CD4/CD8 ratio; and C-reactive protein (CRP) were measured.

RESULTS

All dialysis patients had low levels of albumin and hemoglobin. Significantly decreased percentages of CD3 and CD4 T lymphocytes and increased levels of CRP, TBARS, and carbonyl compounds were observed in HD patients. HD patients also had elevated erythrocyte SOD, lower GPx and catalase activities, and decreased levels of Se, Zn, and Fe in comparison to PD patients and healthy subjects. In addition, CRP was positively associated with TBARS and carbonyl levels, but was significantly inversely associated with Zn and Se levels. Positive correlations were found between T lymphocyte CD3 and CD4 percentages and Zn, Se, and Fe levels.

CONCLUSIONS

There were significant decreases in T lymphocyte-related immunological regulation and increased inflammation and oxidative stress in dialysis patients. Essential trace element status was independently related to immune status, inflammation, and oxidative damage.

Advanced oxidative protein products are independently associated with endothelial function in peritoneal dialysis patients

AIM

Oxidative stress (OS) and asymmetric dimethylarginine (ADMA) are accepted as non-classical cardiovascular risk factors in end-stage renal disease patients. To clarify the role of these factors in the atherosclerotic process, we investigated if OS and ADMA are associated with endothelial function (EF) in peritoneal dialysis (PD) patients.

METHODS

Fifty-two non-diabetic PD patients without known atherosclerotic disease as well as 30 age- and sex-matched healthy individuals were included. We measured serum thiobarbituric acid-reactive substances (TBARS), malondialdehyde (MDA), advanced glycation end-product (AGE), pentosidine, advanced oxidation protein products (AOPP), ADMA and EF as described by Celermejer et al. in all subjects.

RESULTS

TBARS, MDA, AOPP, AGE, pentosidine and ADMA levels were significantly higher in PD patients than in controls (P < 0.001). Flow-mediated dilatation (FMD)% and nitrate mediated dilatation (NMD)% in PD patients were lower than in the control group (7.7 +/- 4.0% vs 11.70 +/- 5.50%, P < 0.01 and 17.6 +/- 8.3% vs 26.4 +/- 4.6%, P < 0.01). Additionally, it was found that AOPP are independently correlated with FMD% and NMD% in PD patients (beta = -463, P < 0.01 and beta = -420, P < 0.05).

CONCLUSION

This study shows that PD patients without known atherosclerotic disease can also be characterized by endothelial dysfunction and AOPP levels independently predict endothelial function level in PD patients.

Oxidative stress and asymmetric dimethylarginine is independently associated with carotid intima media thickness in peritoneal dialysis patients

BACKGROUND

Oxidative stress (OS) and asymmetric dimethylarginine (ADMA) are accepted as nonclassical cardiovascular risk factors in end-stage renal disease patients. To clarify the role of these factors in the atherosclerotic process, we investigated if OS and ADMA are associated with common carotid artery intima media thickness (CIMT) in peritoneal dialysis (PD) patients.

METHODS

Thirty PD patients without known atherosclerotic disease and classical cardiovascular risk factors as well as age- and gender-matched 30 healthy individuals were included. We measured serum thiobarbituric acid-reactive substances (TBARS), malondialdehyde (MDA), advanced glycation end product (AGE), pentosidine, advanced oxidation protein products (AOPP), ADMA and CIMT in each subjects.

RESULTS

TBARS, MDA, AOPP, AGE, pentosidine and ADMA levels were significantly higher in PD patients than in controls (p < 0.001). CIMT in patients was higher than in the control group (0.83 +/- 0.09 vs. 0.77 +/- 0.06 mm; p < 0.01). CIMT was independently correlated with TBARS (beta = 0.33, p < 0.01), MDA (beta = 0.27, p < 0.01), AOPP (beta = 0.22, p < 0.02), AGE (beta = 0.45, p < 0.01), pentosidine (beta = 0.56, p < 0.01) and ADMA (beta = 0.54, p < 0.01).

CONCLUSIONS

OS markers and serum ADMA levels independently predict the CIMT level in PD patients.

Reactive oxygen species amplify protein kinase C signaling in high glucose-induced fibronectin expression by human peritoneal mesothelial cells

BACKGROUND

We previously demonstrated that high glucose up-regulates fibronectin mRNA and protein expression by human peritoneal mesothelial cells (HPMC) through activation of protein kinase C (PKC). PKC is known to induce cellular reactive oxygen species (ROS) and PKC-dependent activation of the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has recently been shown to be responsible, in part, for increased oxidative stress in diabetes. On the other hand, high glucose-induced mitochondrial overproduction of superoxide anion was found to activate PKC. We, therefore, hypothesized that high glucose-induced activation of PKC in HPMC may increase cellular ROS and ROS, in turn, may activate PKC and thus provide signal amplification in high glucose-induced fibronectin up-regulation in HPMC.

METHODS

The role of ROS in high glucose- and PKC-induced fibronectin expression was examined by quantification of cellular ROS after stimulation with high glucose and phorbol 12-myristate 13-acetate (PMA), by the effect of hydrogen peroxide (H(2)O(2)) and PMA on fibronectin expression, and finally by inhibition of ROS and PKC. The source of cellular ROS was further examined by inhibition of NADPH oxidase and mitochondrial metabolism.

RESULTS

D-glucose increased dichlorofluorescein (DCF)-sensitive cellular ROS in HPMC in a dose-dependent manner. l-glucose did not induce ROS generation and cytochalasin B completely blocked high glucose-induced ROS generation, suggesting that glucose uptake, but not media hyperosmolality, is required in ROS generation in HPMC. PMA increased cellular ROS and fibronectin secretion. A single dose of H(2)O(2) or H(2)O(2) continuously generated by glucose oxidase up-regulated fibronectin expression [corrected]. Antioxidants trolox and catalase inhibited high glucose- and PMA-induced fibronectin mRNA and protein expression. Inhibition of PKC inhibited high glucose-and H(2)O(2)-induced fibronectin secretion. NADPH oxidase inhibitors (diphenyleneiodinium and apocynin) and an inhibitor of mitochondrial electron transport chain subunit I (rotenone) all effectively inhibited high glucose-induced cellular ROS generation and fibronectin secretion.

CONCLUSION

The present data demonstrate that high glucose increases cellular ROS in HPMC through activation of PKC, NADPH oxidase, and mitochondrial metabolism and that ROS, thus generated, up-regulate fibronectin expression by HPMC. ROS are not only downstream but also upstream signaling molecules to PKC and provide signal amplification in high glucose-induced fibronectin expression by HPMC. The present data imply that cellular ROS may be potential therapeutic targets in progressive accumulation of extracellular matrix in the peritoneal tissue of long-term peritoneal dialysis patients using high glucose-containing peritoneal dialysis solutions.

Assessment of DNA strand breakage by the alkaline COMET assay in dialysis patients and the role of Vitamin E supplementation

Although the role of reactive oxygen species (ROS) in chronic renal failure (CRF) is not definitely demonstrated, a consistent number of observations has provided evidence for the presence of oxidative stress in uremic patients undergoing maintenance dialysis. In order to investigate this hypothesis further and to understand the role of antioxidant supplementation, peripheral blood lymphocytes were taken from 36 dialysis patients before and after Vitamin E supplementation in a dosage of 600 mg per day (2x300 mg) for 14 weeks and examined in the alkaline Comet assay for DNA strand breakage. The results were also compared with those of 36 controls with comparable age, sex, and smoking habits, and with no history of renal disease. The DNA breakage observed in the lymphocytes of patients before Vitamin E supplementation was significantly higher than in the controls (P<0.001) but a clear protective effect of Vitamin E supplementation were observed after 14 weeks of therapy.

Increased oxidative damage to peripheral blood leukocyte DNA in chronic peritoneal dialysis patients

This study focuses on the extent of oxidative DNA damage in peripheral blood leukocytes of chronic peritoneal dialysis (CPD) patients. 8-Hydroxy 2'-deoxyguanosine (8-OHdG) contents in peripheral leukocyte DNA were measured by an HPLC-electrochemical detection method in 24 age- and sex-matched healthy subjects, 22 nondialyzed patients with advanced renal failure, and 42 CPD patients. Mean 8-OHdG content was the highest in CPD patients, followed by the nondialyzed patients, and then by the healthy subjects (19.4 versus 11.9 versus 8.3/10(6) dG; ANOVA P < 0.001). In nondialyzed subjects, peripheral leukocyte 8-OHdG contents inversely correlated with renal creatinine clearance (r = -0.772; P < 0.001). Deficiency of blood antioxidants in CPD and nondialyzed patients was expressed by the lower plasma levels of ascorbate, cholesterol-standardized alpha-tocopherol and whole-blood reduced glutathione, and the higher levels of whole-blood oxidized glutathione as compared with healthy subjects (ANOVA P < 0.05). Mean serum ferritin and iron levels and transferrin saturation were higher in the CPD patients than those in the nondialyzed patients and controls (ANOVA P < 0.05). Flow cytometric analyses of intracellular reactive oxygen species production of peripheral leukocytes showed that spontaneous production by granulocytes, as well as phorbol-12-myristate-13-acetate (PMA)-induced production by granulocytes, lymphocytes and monocytes, were the highest from CPD patients, followed by nondialyzed patients, and then by the healthy subjects (ANOVA P < 0.05). Forward stepwise multiple regression disclosed that uremia, PD treatment, spontaneous and PMA-induced reactive oxygen species production in leukocytes, and serum iron were the independent determinants of peripheral leukocyte 8-OHdG content (R(2) = 0.769; P < 0.001). In conclusion, profound increased 8-OHdG levels in peripheral leukocyte DNA occur in the course of chronic renal failure, gradually increase with its progression, and are further exacerbated by PD treatment.

Vitamin E as an antioxidant agent in CAPD patients

Oxidative stress, increased lipid peroxidation and decreased activity of antioxidant systems may contribute to the accelerated development of atherosclerosis in chronic renal failure patients during renal replacement therapy. The aim of the study was to investigate the influence of vitamin E (400 mg/day) on some antioxidant defense parameters in CAPD patients. In fourteen CAPD patients, erythrocyte antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT), the concentration of plasma malondialdehyde (MDA), vitamin A, vitamin C and vitamin E were investigated. The study was divided into two periods. Each period lasted six weeks. In the first period patients received orally vitamin E 400 mg/day, in the second period they did not receive vitamin E or other antioxidant drugs. Each parameter was determined at the beginning of the study and at the end of each period. Six CAPD patients were treated by erythropoietin (EPO) and received orally pyridoxine 20 mg/day and the others without EPO treatment received pyridoxine 5 mg/day. Six-week treatment by vitamin E (400 mg/day) led to the significant increase of serum vitamin E (from 33.6+/-9.0 to 49.3+/-15.5 micromol/L) and to the significant decrease of MDA (from 2.62+/-0.5 to 2.36+/-0.4 micromol/L). The mean values of erythrocyte enzymes were in or under the lower margin of normal range and were not influenced by vitamin E in CAPD patients. The results of our study showed that orally administered vitamin E is a very important antioxidant agent for CAPD patients.

Do different dialytic techniques have different atherosclerotic and antioxidant activities?

To compare the chronic effect of several dialytic techniques (bicarbonate dialysis, BHD; acetate free biofiltration, AFB; hemodiafiltration, HDF; paired filtration dialysis, PFD) on atherosclerosis and antioxidant activity, three different indices were created. The first (atherosclerotic index = AI) is formed using the sum of three plasma substances: MDA, Hcy, and Cys (malondialdehyde, homocysteine, cysteine). The second (antioxidant activity index = AOAI) is the sum of five erythrocyte (E) parameters: E-GSH, GPx, CAT, SOD, GR (E-glutathione, E-glutathione peroxidase, E-catalase, E-superoxide dismutase, E-glutathione reductase). The third (defense index = DI) is derived from the previous two: (AOAI - AI). The indices were so expressed as AI in mmol/L, AOAI in U/g hemoglobin (Hb), and DI in arbitrary units. These indices were calculated in 20 controls and 51 chronic HD patients (26 female, 25 male) before, during, and after the first session of the week. HD patients were divided according to their dialytic technique: BHD, n = 35; AFB, n = 5 patients; HDF, n = 7 patients; or PFD = 4 patients. All patients had been treated with a given technique for at least 12 months, before entering the study. As expected, HD patients had AI values higher than controls, both before and after the session, with a mean value of 541 (before) and 331 (after), whereas controls had a mean value of 205. The AOAI was lower than controls, both before and after the session, the mean value being 1,122 (before) and 1,582 (after), that of controls being 2,424. In all cases, PFD gave the best "acute" results; at the end of a PFD session, near normal values of AI, AOAI, and DI (defensive index = AOAI - AI) were obtained.

Ex vivo low-density lipoprotein oxidizability and in vivo lipid peroxidation in patients on CAPD

BACKGROUND

Chronic renal failure is associated with accelerated atherosclerosis and a high incidence of cardiovascular disease. Oxidative modification of low-density lipoprotein (LDL) is considered a key event in atherogenesis.

METHODS

We studied the ex vivo oxidizability of LDL exposed to Cu2+ ions (lag time, rate of propagation, maximum conjugated diene formation) and its relationship with LDL density, fatty acids, and antioxidants, along with plasma malondialdehyde (MDA) and autoantibodies against Cu2+-, MDA-, and hypochlorous acid-modified LDL and plasma antioxidants in 17 continuous ambulatory peritoneal dialysis (CAPD) patients and 21 healthy control subjects.

RESULTS

LDL alpha- and gamma-tocopherol and total polyunsaturated fatty acid (PUFA) concentrations were significantly higher in the CAPD patients. LDL density was shifted to small, dense LDL. LDL oxidizability was comparable to that of healthy subjects. Lag time correlated positively with LDL alpha-tocopherol and inversely with both total PUFA concentrations and density; the rate of oxidation and LDL density correlated positively with total PUFA and total fatty acid concentrations, respectively. Ratios of autoantibody titers against oxidized to native LDL did not differ between the two groups. While plasma alpha- and gamma-tocopherol concentrations and tocopherol to cholesterol ratios were significantly higher, vitamin C concentrations were very low in the CAPD patients. MDA concentrations were 1.7 times higher than in healthy subjects.

CONCLUSIONS

(1) Ex vivo LDL oxidizability is normal in CAPD patients as a result of efficient protection by LDL-associated lipophilic antioxidants, although the LDL composition is altered toward high oxidizability; and (2) the plasma antioxidant screen is insufficient due to impaired vitamin C status.

Role of cellulosic and noncellulosic membranes in hyperhomocysteinemia and oxidative stress

Hyperhomocysteinemia is an independent risk factor for cardiovascular morbidity and mortality in end-stage renal disease (ESRD) with an increased relative risk (RR) of 1% per micromol/L in total homocysteine concentration. In ESRD patients who undergo hemodialysis (HD), the antioxidant system is largely inadequate in correcting the imbalance between generation and scavenging of reactive oxygen species (ROS). To clarify the role of several cellulosic (CMs) and noncellulosic of synthetic membranes (NCMs) upon hyperhomocysteinemia and the oxidative stress, we measured plasma (P) homocysteine (t-HCY), plasma lipid peroxidation (LPO), and erythrocyte (E) concentration of several antioxidant enzymes in 20 normal subjects, in 35 HD patients treated with CMs, and in 29 patients treated with NCMs. Before, during, and after the first session of the week (at times 0', 120', end, 30' after HD end), blood samples were drawn. Plasma (P) homocysteine (t-HCY), cysteine (CYS), malondialdehyde (MDA), erythrocyte (E)-glutathione (GSH), glucose-6-phosphodehydrogenase (G6PD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), and superoxide-dismutase (SOD) were determined. The dialytic procedure significantly decreased the three plasma parameters, but none normalized (as a mean). The E-enzymes scavenging ROS (lower than normal before session) increased throughout the session, but the normal range of activity was never reached. Different membranes have shown different effects. When these effects on P and E spaces were pooled, we were able to classify the membranes as follows. In a general sense, cellulosic membranes are less effective than synthetic membranes both on lipoperoxides (LPO) and antioxidant activity (AOA). Among synthetic membranes, PMMA is the best membrane both for plasma values and lesser enzymatic derangement during the session. A practical system for classifying the anti-atherosclerotic action and antioxidant activity of dialytic membranes is proposed.

Analysis of 7-ketocholesterol in low density lipoprotein and fatty acid composition in erythrocyte membranes of patients on maintenance hemodialysis and healthy controls

We established a method to quantify 7-ketocholesterol (7-KC) in low density lipoprotein by using the heparin-citrate method and gas chromatography-mass spectrometry. We examined the concentration of 7-ketocholesterol in LDL using this method to assess the pathological conditions in uremic patients with hemodialysis and healthy controls. We also examined the fatty acid composition in erythrocyte membranes to estimate the modification of biological membranes. We showed that the concentrations of 7-KC/cholesterol in LDL were significantly increased in hemodialysis patients compared to healthy controls (3.68+/-0.45 vs. 2.41+/-0.19, P<0.05) and the ratio of polyunsaturated fatty acids to saturated fatty acids in erythrocyte membranes was significantly decreased in hemodialysis patients compared to healthy controls (0.499+/-0.014 vs. 0.655+/-0. 017, P<0.001). There was no significant difference in 7-KC concentration in LDL or fatty acid composition in erythrocyte membranes between pre- and post-intervention of hemodialysis. We concluded that hemodialysis patients are under oxidative stress, which modifies LDL and erythrocyte membranes and we speculated these modifications may participate in the process of atherosclerosis. We believe that the method to quantify 7-KC in this study is concise and reliable and may be used to investigate various diseases.

Enhanced oxidative stress in haemodialysis patients receiving intravenous iron therapy

BACKGROUND

Iron balance is critical for adequate erythropoiesis and there remains much debate concerning the optimal timing and dosage of iron therapy for haemodialysis patients receiving recombinant human erythropoietin therapy.

METHODS

In this study, we examined the influence of baseline ferritin level and intravenous infusion of 100 mg ferric saccharate on the oxidative status of the patients on maintenance haemodialysis. The levels of antioxidant enzymes and lipid peroxides were determined in erythrocytes and plasma of 50 uraemic patients on haemodialysis. These patients were divided into groups 1, 2, and 3, based on their baseline serum ferritin levels of <300, 301-600, and >601 microg/l, respectively.

RESULTS

We found that the mean superoxide dismutase (SOD) activities in the erythrocytes were similar in the three groups of patients and did not differ from those of the age-matched controls. On the other hand, all the haemodialysis patients showed significantly higher plasma SOD activity as compared to controls. After intravenous iron infusion, group 3 patients showed the largest decrease in plasma SOD activity. The plasma glutathione peroxidase (GSHPx) activities of the patients in all three groups and the erythrocyte GSHPx activities of the patients in the groups 2 and 3 were lower than those of the healthy controls. In all three groups of patients, no difference in GSHPx activity was found before and after intravenous iron infusion. On the other hand, we found that the average baseline levels of plasma lipid peroxides of all three groups of patients were significantly higher than that of the controls. The patients in group 3 with the highest serum ferritin levels showed the highest levels of plasma lipid peroxides. More importantly, we found that after iron infusion, the patients in all three groups, particularly those in group 3, showed significantly elevated levels of plasma lipid peroxides.

CONCLUSION

We demonstrated that increased oxidative stress in the blood circulation of the uraemic patients on haemodialysis is exacerbated by the elevated baseline serum ferritin levels and intravenous iron infusion. The resultant oxidative damage may contribute to the increased incidence of atherosclerosis in the patients with end-stage renal disease on long-term haemodialysis.

Oxidative stress in cyclosporin and azathioprine treated renal transplant patients

The major cause of death following transplantation is cardiovascular disease. Among the many processes involved in atherogenesis, oxidative stress and modification of low density lipoprotein has been assigned a major role. This in turn may be affected by the immunosuppressive regime used. We studied oxidative stress in 40 renal transplant patients receiving two different immunosuppressive regimens (20 on cyclosporin, 20 on azathioprine/prednisolone), and 19 normal controls. Changes in lipid peroxidation (assessed as thiobarbituric acid reacting substances, TBARS), antioxidant enzyme activities (glutathione reductase GSHPx, glutathione peroxidase GSHPx and superoxide dismutase SOD) vitamin E and antioxidant associated trace metals (selenium, copper, zinc) were studied. Alteration of erythrocyte membrane fluidity was examined using the fluorescent probe 1,6 diphenyl-1,3,5-hexatriene (DPH). Both transplant groups showed no difference in TBARS, lipid standardised vitamin E, copper or selenium compared to controls. Zinc was significantly increased in both the cyclosporin and azathioprine groups compared to controls (P < 0.05). SOD was reduced in both transplant groups compared to controls (P < 0.001). GSHPx was elevated in both groups compared to controls but only reached significance in the azathioprine treated group (P < 0.005). GSHRx was slightly elevated in both transplant groups but did not reach significance. Erythrocyte membrane anisotropy was decreased in the cyclosporin treated group (P < 0.05). There was no difference in the azathioprine group compared to controls. The present results suggest an adaptive response to increased oxidative stress in both transplant groups sufficient to minimise markers of oxidative stress (TBARS and anisotropy). The results also suggest no significant difference between the two immunosuppressive regimes with regard to oxidative stress.

Antioxidant enzymes and trace elements in hemodialyzed patients

Antioxidant enzymes together with trace elements in 26 patients with chronic renal failure treated with hemodialysis and 25 healthy subjects were investigated. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSHPx) in plasma and erythrocytes were examined immediately before and after hemodialysis. The results are summarized as follows: 1. A significant decrease in plasma SOD, CAT, and GSHPx and erythrocyte GSHPx were found in patients before hemodialysis. 2. Erythrocyte CAT and GSHPx were significantly lower in the patients after hemodialysis than in the controls. 3. Plasma GSHPx was significantly higher after a single hemodialysis than before hemodialysis. 4. A good correlation between erythrocyte SOD and copper (Cu) in patients before hemodialysis was found. 5. A good correlation of GSHPx in erythrocytes and plasma was found before hemodialysis, whereas an even better correlation was found after hemodialysis. 6. Abnormalities of trace elements were found in hemodialyzed patients. 7. There is indirect evidence for increased oxidizing stress in uremic patients with hemodialysis. Dialysis treatment may improve some abnormalities (e.g., Hb, P), but may also induce some deleterious effects of free radicals or lipid peroxidation.

Oxidation of low density lipoprotein in hemodialysis patients: effect of dialysis and comparison with matched controls

End stage renal failure is associated with lipoprotein abnormalities and a high prevalence of premature atherosclerosis. Oxidative modification of low density lipoprotein (LDL) may be promoted by hemodialysis increasing its atherogenicity. The oxidative status of LDL was therefore examined in female subjects before and after routine hemodialysis (HD; n = 10) and compared with women of similar age without significant renal disease (n = 19). There were no significant differences between the groups in the LDL fatty acid composition, or in the content of reactive amino acid groups (lysine) before or after exposure to Cu2+. The kinetics of LDL oxidation by Cu2+ showed no significant differences between the groups with respect to the lag time, the level of conjugated dienes before and after oxidation, or the maximal rate of oxidation during the propagation phase. No acute effects of HD were demonstrated. The present study provides no evidence that circulating LDL isolated from HD patients is more extensively modified or more susceptible to oxidation in vitro than gender-matched controls without renal failure.

Plasma ubiquinol/cholesterol ratios in patients with hyperlipidaemia, those with diabetes mellitus and in patients requiring dialysis

Plasma ubiquinol was measured in diabetics, patients on haemodialysis (HD) therapy, patients maintained by continuous ambulatory peritoneal dialysis (CAPD), hyperlipidaemic patients and control subjects. Ubiquinol values were standardized using total cholesterol (mumol/mmol). Diabetics, HD and CAPD patients were found to have plasma ubiquinol levels which were lower than the control subjects. There was no difference in values between the control subjects and hyperlipidaemic patients. Values for diabetics with poor metabolic control were similar to those with good control, and patients with diabetic complications had values which were not significantly different from those for patients with no complications. IDDM patients were found to have values which were lower than the control group, whereas values for the NIDDM patients were not significantly different. These results suggest that increased oxidative stress in certain patient groups may be the result of, and/or the cause of, decreased plasma ubiquinol. This could be due to increased demand or to decreased ability to regenerate the effective form of antioxidant.

Lipid abnormalities of erythrocyte membranes in hemodialysis patients with chronic renal failure

Lipids in erythrocyte membranes from 16 hemodialysis patients and 16 healthy volunteers were studied using gas chromatographic mass spectrometry. 7-keto cholestadiene was first reported in this study. The ratios of 7-keto cholestadiene to cholesterol, the ratios of arachidonate to cholesterol and the ratios of dochosahexanate to cholesterol in peak heights of chromatograms were measured in both groups as the markers of lipid peroxidation. Higher 7-keto cholestadiene/cholesterol ratios and lower arachidonate/cholesterol and dochosahexanate/cholesterol ratios were significantly observed in hemodialysis patients compared with healthy subjects. Our results are evidence that hemodialysis patients are exposed to much oxidative stress. It has been suggested that, during hemodialysis, leukocytes are activated by contract with non-physiological surfaces of the blood line tubing and produce oxygen free radicals. Oxygen free radicals attach cholesterol, arachidonate and dochosahexanate to produce lipid peroxides. In this study, this cell activation may be responsible for the increased lipid peroxidation of hemodialysis patients, 7-Keto cholestadiene, arachidonate and dochosahexanate can be used as markers of lipid peroxidation in hemodialysis patients.

Lipid peroxidation and antioxidant enzymes in CAPD patients

The mechanisms of free-radical injury include reactions with proteins, nucleic acids, and polysaccharides; and covalent binding to membrane components and initiation of lipid peroxidation. Cells have developed antioxidant defense to prevent free-radical injury including superoxide dismutase (SOD) and glutathione peroxidase (GPx). Significantly higher concentrations of total malondialdehyde (MDA) in plasma (1.22 +/- 0.42 vs. 0.64 +/- 0.22 micromol/L, p < 0.0001) as well as erythrocytes (2.56 +/- 1.28 vs. 1.03 +/- 0.44 micromol/L, p < 0.0001) of the CAPD patients were found when compared to the control group. The free MDA in plasma and the erythrocytes do not differ significantly in continuous ambulatory peritoneal dialysis (CAPD) patients and the control group. A significantly lower activity of GPx in erythrocytes of CAPD patients (17.85 +/- 2.63 U/g Hb vs. 23.26 +/- 3.61 U/g Hb, p < 0.0001) was found when compared to the control group, but the SOD activity in erythrocytes is not different (2272.36 +/- 579.92 U/g Hb vs. 2347.13 +/- 502.51 U/g Hg, NS). Our results show an increase of total MDA in erythrocytes and plasma. MDA is the product of lipid peroxidation with decreasing activity of GPx, which is capable of detoxifying peroxides. The activity of SOD did not change in CAPD patients. These results propose a possible role of free radicals with reduced antioxidant activity of GPx in CAPD patients and indicate that they could play some role in other pathological conditions such as atherogenesis and hemolysis.

Glutathione antioxidant system as a marker of oxidative stress in chronic renal failure

A profound imbalance between oxidants and antioxidants has been suggested in uremic patients on maintenance hemodialysis. However, the respective influence of uremia and dialysis procedure has not been evaluated. Circulating levels of copper-zinc superoxide dismutase (CuZn SOD), glutathione peroxidase (GSH-Px), and reductase (GSSG-Rd), total GSH and GSSG were determined in a large cohort of 233 uremic patients including 185 undialyzed patients with mild to severe chronic renal failure, and 48 patients treated by peritoneal dialysis or hemodialysis. Compared to controls, erythrocyte GSH-Px and GSSG-Rd activities were significantly increased at the mild stage of chronic uremia (p < .001), whereas erythrocyte CuZn SOD activity was unchanged, total level of GSH and plasma GSH-Px activity were significantly decreased, and GSSG level and GSSG-Rd activity were unchanged. Positive Spearman rank correlations were observed between creatinine clearance and plasma levels of GSH-Px (r = .65, p < .001), selenium (r = .47, p < .001), and GSH (r = .41, p < .001). Alterations in antioxidant systems gradually increased with the degree of renal failure, further rose in patients on peritoneal dialysis and culminated in hemodialysis patients in whom an almost complete abolishment of GSH-Px activity was observed. In conclusion, such disturbances in antioxidant systems that occur from the early stage of chronic uremia and are exacerbated by dialysis provide additional evidence for a resulting oxidative stress that could contribute to the development of accelerated atherosclerosis and other long-term complications in uremic patients.

No evidence for systemic oxidant stress in Parkinson's or Alzheimer's disease

Oxidant stress secondary to dopamine metabolism has been proposed as a pathogenic factor in the development of Parkinson's disease. Biochemical abnormalities extending beyond the central nervous system have been identified in patients with this condition. Previous investigators have found abnormally elevated concentrations of the lipid peroxidation product, malondialdehyde, in the plasma and serum of patients with Parkinson's disease. We attempted to replicate these findings but controlled for other factors that could influence malondialdehyde levels. We detected no significant elevations in mean serum malondialdehyde concentrations in either levodopa-treated or untreated patients with Parkinson's disease, compared to normal controls; similarly, no elevation was found in a group of patients with dementia of Alzheimer's type. On the other hand, a group of subjects with diabetes mellitus but no neurodegenerative disease had significantly elevated mean serum malondialdehyde levels, consistent with previous studies of diabetic patients. Autoxidation is one of the two major routes by which dopamine and dopa metabolism may generate oxygen free radicals. We analyzed the autoxidation product of dopa, 5-S-cysteinyl-dopa, in the plasma of these same groups of patients with neurodegenerative disease and normal controls; no significant differences were identified. Serum concentrations of two other antioxidant substances, alpha-tocopherol and uric acid, were also statistically similar in these groups. In conclusion, analysis of several blood products relevant to oxidant stress, including malondialdehyde, 5-S-cysteinyl-dopa, alpha-tocopherol, and uric acid, failed to distinguish patients with Parkinson's disease or dementia of Alzheimer's type from controls.

Oxidative stress and erythrocyte membrane fluidity in patients undergoing regular dialysis

Oxidative damage due to free radical production is increased in uraemic patients and has been suggested as a possible factor contributing to the anaemia of chronic renal failure (CRF) and the pathogenesis of atherosclerosis. Oxidative stress was assessed in 40 patients with CRF maintained by either haemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) and in 18 healthy controls. Lipid peroxidation (assessed as malondialdehyde, MDA), total glutathione (TG), antioxidant enzyme (glutathione reductase (GSHRx), glutathione peroxidase (GSHPx) and superoxide dismutase (SOD)) activity and antioxidant associated trace metal (selenium, copper, zinc) levels were studied. Erythrocyte membrane fluidity was examined using the fluorescent probe 1,6 diphenyl-1,3,5-hexatriene (DPH). The results indicate increased levels of oxidative stress and altered erythrocyte membrane fluidity in patients treated with CAPD compared with controls and patients treated with HD. Only minor changes were observed in patients treated with HD. Altered free radical activity, oxidative stress and altered erythrocyte membrane fluidity observed in patients with CRF may contribute to the increase in vascular disease in such patients and to the anaemia of CRF.

Redox state, antioxidative activity and lipid peroxidation in erythrocytes and plasma of chronic ambulatory peritoneal dialysis patients

Red blood cells and plasma reduced and oxidized glutathione levels, glutathione peroxidase (GSH-Px) activity, thiobarbituric acid reactants (TBAR) of both chronic ambulatory peritoneal dialysis (CAPD) patients and a matched control group were investigated in this study. Oxidized and reduced pyridinic nucleotides in red blood cells (RBC), in which NADPH is a direct expression of hexose monophosphate shunt function, were also studied. The results obtained indicate that RBC and plasma are exposed to oxidative stress in CAPD. This condition is characterized by a decreased GSH/GSSG ratio, particularly evident in RBC as a consequence of the GSSG accumulation. Lipid peroxidation is increased, as indicated by raised TBAR levels, and reduced pyridinic nucleotides are decreased. Increased GSH-Px levels and unmodified or slightly increased GSH content were observed in the RBC but not in plasma, which showed decreased GSH and unmodified peroxidase activity. Peroxidase correlated positively with TBAR levels in the RBC lysates. In a subgroup of patients treated with erythropoietin (vs. untreated patients and controls) no differences were observed in the glutathione-related parameters studied. These data suggest that a mechanism for adaptation to oxidative conditions may be present in CAPD and its effects on RBC integrity are discussed in comparison with the hemodialysis conditions previously studied.