Influence of hemodialysis membrane type on pentosidine plasma level, a marker of "carbonyl stress"

The Characteristics of Dialysis Membranes: Benefits of the AN69 Membrane in Hemodialysis Patients

Patients undergoing hemodialysis (HD) experience serious cardiovascular complications, through malnutrition, inflammation, and atherosclerosis. Amputation for peripheral arterial disease (PAD) is more prevalent in patients undergoing HD than in the general population. In addition, revascularization procedures in dialysis patients are often associated with subsequent amputation and high mortality rates. To improve the prognosis of dialysis patients, malnutrition and inflammation must be properly treated, which necessitates a better understanding of the characteristics of dialysis membranes. Herein, the characteristics of several dialysis membranes were studied, with a special reference to the AN69 membrane, noting several similarities to low-density lipoprotein (LDL)-apheresis, which is also applicable for the treatment of PAD. Both systems (LDL-apheresis and AN69) have anti-inflammatory and anti-thrombogenic effects because they use a negatively charged surface for extracorporeal adsorptive filtration from the blood/plasma, and contact phase activation. The concomitant use of both these therapeutic systems may have additive therapeutic benefits in HD patients. Here, we reviewed the characteristics of dialysis membranes and benefits of the AN69 membrane in dialysis patients.

Reduction of protein-bound uraemic toxins in plasma of chronic renal failure patients: A systematic review

BACKGROUND

Protein-bound uraemic toxins (PBUTs) accumulate in patients with chronic kidney disease and impose detrimental effects on the vascular system. However, a unanimous consensus on the most optimum approach for the reduction of plasma PBUTs is still lacking.

METHODS

In this systematic review, we aimed to identify the most efficient clinically available plasma PBUT reduction method reported in the literature between 1980 and 2020. The literature was screened for clinical studies describing approaches to reduce the plasma concentration of known uraemic toxins. There were no limits on the number of patients studied or on the duration or design of the studies.

RESULTS

Out of 1274 identified publications, 101 studies describing therapeutic options aiming at the reduction of PBUTs in CKD patients were included in this review. We stratified the studies by the PBUTs and the duration of the analysis into acute (data from a single procedure) and longitudinal (several treatment interventions) trials. Reduction ratio (RR) was used as the measure of plasma PBUTs lowering efficiency. For indoxyl sulphate and p-cresyl sulphate, the highest RR in the acute studies was demonstrated for fractionated plasma separation, adsorption and dialysis system. In the longitudinal trials, supplementation of haemodialysis patients with AST-120 (Kremezin®) adsorbent showed the highest RR. However, no superior method for the reduction of all types of PBUTs was identified based on the published studies.

CONCLUSIONS

Our study shows that there is presently no technique universally suitable for optimum reduction of all PBUTs. There is a clear need for further research in this field.

Estimated influence of a novel biocompatible dialysis membrane on vascular events in dialysis patients with diabetic nephropathy: a prospective randomized controlled pilot study

Background

Polysulfone (PS) dialyzers are most frequently used worldwide for chronic renal failure patients and they are produced by several manufacturers. Despite using the same materials, differences in biocompatibility among PS dialyzers have been reported. TORAYLIGHT NV (NV) is a PS dialyzer that was reported to have superior biocompatibility compared with other PS membranes (conventional PS membranes). Therefore, we examined whether biocompatibility of PS membranes would affect the occurrence of cardiovascular events in hemodialysis patients with diabetic nephropathy (DN).

Methods

Fifty hemodialysis patients with DN were enrolled. They were randomly divided into NV and PS groups and then followed up for 3 years. The number of patients who developed cardiovascular events and clinical data including laboratory tests and blood pressure was recorded.

Results

There were 13 and 14 patients who developed cardiovascular events during the 3-year follow-up of the NV and PS groups, respectively. There was no significant difference between the groups. There were no significant differences in most of the clinical data between the two groups. However, serum pentosidine concentrations in the PS group significantly increased throughout this study, while those in the NV group did not change. Additionally, the width of the systolic blood pressure drop, which was shown to be the difference between before and after dialysis session, in the PS group showed no change, while that in the NV group tended to decrease.

Conclusions

The superiority of using NV membrane compared with conventional PS membranes in reducing cardiovascular events in hemodialysis patients with DN remains unclear. However, our results suggested that PS membranes with superior biocompatibility would slow the progression of atherosclerosis and reduce the occurrence of intradialytic hypotension.

Trial registration

This study was retrospectively registered with the Clinical Trials Registry at the University Hospital Medical Information Network (UMIN-CTR) on March 17, 2017 (registration ID, UMIN 000026339). https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr.cgi?function=brows&action=brows&recptno=R000030259&type=summary&language=J

Endothelial dysfunction and low-grade inflammation in the transition to renal replacement therapy

Introduction

End-stage renal disease (ESRD) strongly associates with cardiovascular disease (CVD) risk. This risk is not completely mitigated by renal replacement therapy. Endothelial dysfunction (ED) and low-grade inflammation (LGI) may contribute to the increased CVD risk. However, data on serum biomarkers of ED and LGI during the transition to renal replacement therapy (dialysis and kidney transplantation) are scarce.

Methods

We compared serum biomarkers of ED and LGI between 36 controls, 43 participants with chronic kidney disease (CKD) stage 5 non-dialysis (CKD5-ND), 20 participants with CKD stage 5 hemodialysis (CKD5-HD) and 14 participants with CKD stage 5 peritoneal dialysis (CKD5-PD). Further, in 34 and 15 participants repeated measurements were available during the first six months following dialysis initiation and kidney transplantation, respectively. Serum biomarkers of ED (sVCAM-1, E-selectin, P-selectin, thrombomodulin, sICAM-1, sICAM-3) and LGI (hs-CRP, SAA, IL-6, IL-8, TNF-α) were measured with a single- or multiplex array detection system based on electro-chemiluminescence technology.

Results

In linear regression analyses adjusted for potential confounders, participants with ESRD had higher levels of most serum biomarkers of ED and LGI than controls. In addition, in CKD5-HD levels of serum biomarkers of ED and LGI were largely similar to those in CKD5-ND. In contrast, in CKD5-PD levels of biomarkers of ED were higher than in CKD5-ND and CKD5-HD. Similarly, in linear mixed model analyses sVCAM-1, thrombomodulin, sICAM-1 and sICAM-3 increased after PD initiation. In contrast, incident HD patients showed an increase in sVCAM-1, P-selectin and TNF-α, but a decline of hs-CRP, SAA and IL-6. Further, following kidney transplantation sVCAM-1, thrombomodulin, sICAM-3 and TNF-α were lower at three months post-transplantation and remained stable in the three months thereafter.

Conclusions

Levels of serum biomarkers of ED and LGI were higher in ESRD as compared with controls. In addition, PD initiation and, less convincingly, HD initiation may increase levels of selected serum biomarkers of ED and LGI on top of uremia per se. In contrast to dialysis, several serum biomarkers of ED and LGI markedly declined following kidney transplantation.

Pentosidine in chronic hemodialysis patients: relation with arteriovenous fistula morphology and function

PURPOSE

It has been suggested that advanced glycation end products (AGEs) are involved in atherogenesis, vascular calcification and remodeling, including neointimal hyperplasia, in renal and non-renal patients. Their relevance for arteriovenous fistula (AVF) function has been poorly studied to date, with only one clinical study addressing the issue of thrombosis of vascular access in relation to AGEs in dialysis patients. We aimed to evaluate the relationship between serum pentosidine and AVF morphology and function.

METHODS

Eighty-eighth hemodialysis patients with patent native AVF were included. Ultrasound examination of AVF evaluated blood flow in the brachial artery, resistivity index (RI), the diameter of the vessels and the presence of stenosis. AVF and cardiovascular history were recorded, routine clinical and laboratory evaluation was performed and serum pentosidine was assessed.

RESULTS

Forty-eight patients (54.54%) had AVF stenosis. Pentosidine correlated in univariate analysis with cholesterol (r = 0.270, p = 0.01), triglycerides (r = 0.309, p = 0.003), calcium (r = 0.040, p < 0.001) and inversely to dialysis vintage (r = - 0.453, p < 0.001), access vintage (r = - 0.432, p = 0.001), phosphate (r = - 0.211, p = 0.04), parathyroid hormone (r = - 0.211, p = 0.04), urea (r = - 0.230, p = 0.03), residual diameter of AVF (r = - 0.023, p = 0.03). In multivariate regression calcium (p = 0.006), access vintage (p = 0.03), and residual diameter of AVF vein (p = 0.02) remain significantly linked to pentosidine. Patients with pentosidine above median had higher cholesterol (179.91 vs. 160.97, p = 0.04), triglycerides (187.18 vs. 129.31, p = 0.002) and higher prevalence of hypertension (93.70% vs. 84.10%, p = 0.02).

CONCLUSIONS

Our study suggests that pentosidine could be associated to vascular access morphology and function in dialysis patients.

Review of pentosidine and pyrraline in food and chemical models: formation, potential risks and determination

Pyrraline and pentosidine are advanced Maillard reaction products derived from the reaction of glucose with the lysine amino group on proteins. They have been implicated in uremia, diabetes, and related complications, including inflammation, retinopathy, and nephropathy. This review focuses on the formation mechanism, human potential risks, and detections of pentosidine and pyrraline and lays the foundation for further study of pentosidine and pyrraline. © 2017 Society of Chemical Industry.

Advanced Glycation end Products: Specific Fluorescence Changes of Pentosidine-Like Compounds during Short Daily Hemodialysis

Background

Advanced glycation end products (AGE) accumulate in uremia and represent an important etiopathogenetic cause of morbidity in dialyzed patients. Conventional hemodialysis treatment seems to be ineffective in lowering AGE levels. We wished to investigate whether daily hemodialysis (DHD), a treatment that seems to result in better clinical condition in end-stage renal disease patients, is effective in the reduction of these compounds.

Methods

We evaluated 10 non-diabetic patients on standard hemodialysis (SHD = 3 × 4h/week) for more than 6 months by a crossover study. These patients were assigned randomly to 6 months of DHD (6 × 2h/week) or 6 months of SHD. Then, they were switched to 6 months of the alternative treatment. At the end of these two periods, we studied pentosidine-like AGE compounds by measuring the total fluorescence at a wavelength characteristic for these substances: Ex: 335nm / Em:385nm; we also measured protein-linked pentosidine at the same time points. Finally, we determined the AGE-related total fluorescence in the deproteinized serum of 13 uremic patients on peritoneal dialysis (CAPD) and of 10 healthy controls.

Results

Pre-HD AGE-related total fluorescence obtained after 6 months of DHD was significantly lower than that obtained with standard HD (DHD = 201.3 ± 36.4 AU/ml vs. SHD = 267.5 ± 141.4 AU/ml, p=0.03). The extraction rate per minute of dialysis was slightly, but not significantly higher during DHD than SHD (0.29 ± 0.11% vs. 0.23 ± 0.04, p = 0.07). AGE-related total fluorescence pre-HD values in patients treated by SHD and DHD were about 20-fold higher than in control subjects. They did not differ from CAPD patients. The pre-dialysis level of protein-linked pentosidine was significantly lower in DHD than in SHD (DHD = 16.12 ± 4.71 pmol/mg protein, SHD = 22.64 ± 6.86 pmol/mg protein, p < 0.01).

Conclusions

DHD showed a reduction in AGE-related total fluorescence, although the mean value remained higher than in control subjects. DHD is also accompanied by a decrease in protein-linked pentosidine.

Skin Autofluorescence Is Associated with Endothelial Dysfunction in Uremic Subjects on Hemodialysis

BACKGROUND

Elevated levels of advanced glycation end products (AGEs) within tissues may contribute to endothelial dysfunction, an early indicator of atherosclerosis. We aimed to investigate whether levels of skin AGEs could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.

METHODS AND RESULTS

One hundred and nineteen uremic patients on hemodialysis and 57 control subjects with moderate-to-high cardiovascular risk factors and without chronic kidney disease (CKD) were enrolled. We used ultrasound to measure flow-mediated vasodilation (FMD). An AGE reader measured skin autoflurorescence (AF). We then compared differences in FMD and skin AF values between the two groups. The uremic subjects had significantly higher levels of skin AF (3.47±0.76 AU vs. 2.21±0.45 arbitrary units; P<0.01) and significantly lower levels of FMD (4.79%±1.88% vs. 7.19%±2.17%; P<0.01) than the non-CKD subjects. After adjusting for all potential covariates, we found that skin AF level independently predicted FMD in both the hemodialysis and the non-CKD groups. In the hemodialysis group, skin AF ≥ 3.05 arbitrary units predicted abnormal FMD at a sensitivity of 87.9% and a specificity of 78.6% (P<0.01).

CONCLUSIONS

Skin AF could be a useful marker to predict endothelial dysfunction in uremic subjects on hemodialysis.

Uremic Toxicity of Advanced Glycation End Products in CKD

Advanced glycation end products (AGEs), a heterogeneous group of compounds formed by nonenzymatic glycation reactions between reducing sugars and amino acids, lipids, or DNA, are formed not only in the presence of hyperglycemia, but also in diseases associated with high levels of oxidative stress, such as CKD. In chronic renal failure, higher circulating AGE levels result from increased formation and decreased renal clearance. Interactions between AGEs and their receptors, including advanced glycation end product-specific receptor (RAGE), trigger various intracellular events, such as oxidative stress and inflammation, leading to cardiovascular complications. Although patients with CKD have a higher burden of cardiovascular disease, the relationship between AGEs and cardiovascular disease in patients with CKD is not fully characterized. In this paper, we review the various deleterious effects of AGEs in CKD that lead to cardiovascular complications and the role of these AGEs in diabetic nephropathy. We also discuss potential pharmacologic approaches to circumvent these deleterious effects by reducing exogenous and endogenous sources of AGEs, increasing the breakdown of existing AGEs, or inhibiting AGE-induced inflammation. Finally, we speculate on preventive and therapeutic strategies that focus on the AGE-RAGE axis to prevent vascular complications in patients with CKD.

Role of advanced glycation endproducts and potential therapeutic interventions in dialysis patients

It has been nearly 100 years since the first published report of advanced glycation end products (AGEs) by the French chemist Maillard. Since then, our understanding of AGEs in diseased states has dramatically changed. Especially in the last 25 years, AGEs have been implicated in complications related to aging, neurodegenerative diseases, diabetes, and chronic kidney disease. Although AGE formation has been well characterized by both in vitro and in vivo studies, few prospective human studies exist demonstrating the role of AGEs in patients on chronic renal replacement therapy. As the prevalence of end-stage renal disease (ESRD) in the United States rises, it is essential to identify therapeutic strategies that either delay progression to ESRD or improve morbidity and mortality in this population. This article reviews the role of AGEs, especially those of dietary origin, in ESRD patients as well as potential therapeutic anti-AGE strategies in this population.

Serum Carboxymethyllysine Predicts Mortality in Hemodialysis Patients

BACKGROUND

Hemodialysis patients show markedly elevated serum levels of advanced glycation end products (AGEs). AGEs have been implicated in the pathogenesis of vascular damage and are regarded as a class of uremic toxins. However, to date, serum AGE level could not be identified as an independent predictor of mortality. The aim of the present study is to test whether serum level of the AGE carboxymethyllysine (CML) predicts all-cause or cardiovascular mortality in hemodialysis patients.

METHODS

Serum total CML concentration was measured by means of enzyme-linked immunosorbent assay in 154 patients receiving long-term hemodialysis. Patients were divided into groups with serum CML levels less and greater than the median (23.8 ng/mg protein). All-cause and cardiovascular mortality were registered during a follow-up of 51 months. The relationship between serum CML level and mortality was tested by using Kaplan-Meier and Cox regression analyses.

RESULTS

In the group with low serum CML levels, 38% of patients died during the follow-up period; 23% had a cardiovascular cause of death. However, in the group with high CML levels, 58% died (P < 0.01) and 36% had a cardiovascular cause of death (P < 0.05). The following parameters proved to be independent risk factors of all-cause mortality: age (hazard ratio, 1.056; P < 0.001), preexisting vascular disease (hazard ratio, 2.53; P < 0.05), smoking (hazard ratio, 3.03; P < 0.005), high serum CML level (hazard ratio, 1.776; P < 0.05), and C-reactive protein level (hazard ratio, 1.017; P < 0.001).

CONCLUSION

The AGE CML may contribute to increased mortality in patients with uremia.

In a type 2 diabetic nephropathy rat model, the improvement of obesity by a low calorie diet reduces oxidative/carbonyl stress and prevents diabetic nephropathy

BACKGROUND

The present study has been undertaken to unravel the critical factors involved in the progression of diabetic nephropathy (DN).

METHODS

A unique type 2 diabetic rat model with a wide range of metabolic derangements and hypertension has been utilized, the spontaneously hypertensive/NIH-corpulent rat SHR/NDmcr-cp(cp/cp). It develops histologically evident glomerular injury and tubulointerstitial damage, including mesangial activation, podocyte injury, and inflammatory cell infiltration in the tubulointerstitium.

RESULTS

A low calorie diet for 22 weeks significantly improves obesity, proteinuria and renal morphological alterations. The correction of renal injury is independent of blood pressure control. Obesity correction, although partial, normalizes the renal content of pentosidine taken as a marker of oxidative stress and advanced glycation end products (AGEs). This occurs despite the fact that, in this model, improvement of glucose control and hyperlipidaemia is limited. Proteinuria and body weight are highly correlated with renal pentosidine content, while proteinuria and body weight are also correlated with each other. Diabetic renal injury is thus inhibited by a low calorie diet with an attendant reduction of oxidative stress and AGE formation, despite sustained hypertension.

CONCLUSION

The present findings suggest a direct role of obesity in the generation of a localized oxidative stress and AGE formation, directly responsible for DN.

Ultrapure dialysate reduces plasma levels of beta2-microglobulin and pentosidine in hemodialysis patients

BACKGROUND

beta2-Microglobulin (beta2MG) and carbonyl stress are reported to contribute to the development of dialysis-related amyloidosis. The aim of this study was to determine whether the purity of dialysate affects plasma levels of beta2MG and pentosidine (a surrogate marker of carbonyl stress) in hemodialysis patients.

METHODS

Sixteen patients on hemodialysis with a polysulfone membrane participated in this study. We switched the dialysate from conventional dialysate (endotoxin level 0.055-0.066 endotoxin units (EU)/ml) to ultrapure dialysate (endotoxin level <0.001 EU/ml), followed patients for 6 months, and then switched back to conventional dialysate once again. Plasma levels of beta2MG, pentosidine, CRP and interleukin-6 (IL-6) were determined before the switch to ultrapure dialysate, 1 and 6 months after the switch to ultrapure dialysate, and 1 month after the switch back to conventional dialysate.

RESULTS

The switch from conventional to ultrapure dialysate significantly decreased plasma levels of beta2MG, from 30.1 +/- 1.4 to 27.1 +/- 1.4 mg/dl (p < 0.05) and pentosidine, from 1,535.8 +/- 107.5 to 1,267.6 +/- 102.9 nmol/l (p < 0.01) after 1 month of use. The change of dialysate also significantly decreased plasma levels of CRP, from 0.28 +/- 0.09 to 0.14 +/- 0.05 mg/dl (p < 0.05) and IL-6, from 9.4 +/- 2.7 to 3.5 +/- 0.8 pg/ml (p < 0.01) over the 1-month period. These changes in plasma levels of beta2MG, pentosidine, CRP and IL-6 were maintained over 6 months after switching to ultrapure dialysate and returned to basal levels by switching back to a conventional dialysate.

CONCLUSIONS

Ultrapure dialysate decreases plasma levels of beta2MG, pentosidine and inflammatory markers in hemodialysis patients. The use of ultrapure dialysate might be useful in preventing and/or treating complications of dialysis, such as dialysis-related amyloidosis, atherosclerosis and malnutrition.

Glyoxal inactivates glutamate transporter-1 in cultured rat astrocytes

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by progressive motor paralysis and selective motor neuron death. There is increasing evidence that motor neuron death in ALS is mediated by glutamate toxicity resulting from reduced activity of astrocytic glutamate transporter-1 (GLT-1). Recent morphological studies have shown that Nepsilon-(carboxymethyl)lysine (CML) accumulates in reactive astrocytes of ALS spinal cords. CML is a product of post-translational protein modification by glyoxal, a reactive aldehydic intermediate. In considering these documents, it is important to determine whether GLT-1 protein modification by glyoxal might cause reduced GLT-1 activity. To address this issue, we investigated the effects of glyoxal on GLT-1 properties in cultured rat astrocytes. High performance liquid chromatography showed reduced glutamate uptake activity in the glyoxal-exposed cells. Immunocytochemical analysis displayed CML accumulation in the cytoplasm of astrocytes by glyoxal exposure. Immunoblots of immunoprecipitated GLT-1 disclosed GLT-1 CML adduct formation in the glyoxal-exposed cells. Our results indicate that glyoxal modifies GLT-1 to form CML and simultaneously deprives its glutamate uptake activity. Thus, these toxic effects of glyoxal on astrocytes might be implicated in motor neuron death in ALS.

Influence of Different Haemodialysis Modalities on AGE Peptide Levels: Intradialytic versus Long-Term Results

BACKGROUND

Peptide-linked degradation products of advanced glycation end products (AGE peptides) accumulate in chronic haemodialysis (HD) patients and may contribute to a number of HD-related long-term complications, such as accelerated atherosclerosis.

METHODS

The influence of a single HD session versus long-term HD on serum AGE peptides was determined. The patients were randomized to HD with a low-flux polysulfone (PS; F 6HPS), a high-flux PS (F 60S), a superflux PS (F 500S), or a superflux cellulose triacetate (CTA; Tricea 150G) dialyzer.

RESULTS

During a single HD session, both AGE peptides and reference peptides decreased significantly (AGE peptides: Tricea 150G -37.0 +/- 2.9%; F 6HPS -35.5 +/- 2.4%; F 60S -39.5 +/- 4.7%, and F 500S -43.3 +/- 2.1%, p = 0.005; reference peptides: Tricea 150G -73.2 +/- 8.8%; F 6HPS -73.2 +/- 7.9%; F 60S -72.5 +/- 8.2%, and F 500S -74.1 +/- 7.3%, p = 0.005). After 12 weeks of HD with the superflux CTA, the AGE peptide levels decreased significantly (week 1: 2.7 +/- 1.1 arbitrary units, week 12: 2.5 +/- 1.2 arbitrary units, decrease 7.4%; p = 0.01), whereas the AGE peptide levels remained unchanged after HD with each of the other three modalities. The reference peptide levels did not change after 12 weeks of HD.

CONCLUSION

Although AGE peptides can be effectively removed during a single HD session, superflux CTA seems to be the only modality capable of reducing AGE peptides in the long term.

Oxidative stress and uremia

Oxidative stress is a pathogenic element of great importance in uremic patients, with a great impact on their survival. The cause of oxidative stress in patients on hemodialysis is traditionally attributed to the recurrent activation of polymorphonucleate neutrophils and monocytes. The effects of oxidative stress are evident on all biochemical components of biological tissues: lipids, proteins, carbohydrates, and nucleic acids. This study briefly reviews the effects of different dialytic techniques and of kidney transplant on several parameters of oxidative stress. Many different modalities of pharmaceutical intervention are then analyzed, and the clinical evidences reported.

The influence of hepatitis C and iron replacement therapy on plasma pentosidine levels in haemodialysis patients

BACKGROUND

Chronic liver disease and intravenous (i.v.) iron therapy can enhance oxidative stress. The aim of this study was to assess the influence of hepatitis C virus (HCV) and i.v. iron administration on oxidative stress in chronic haemodialysis (HD) patients.

METHODS

A total of 115 HD patients (47% males, age 47 +/- 13 years) were placed in two groups according to the presence (HCV(+)) or absence (HCV(-)) of serum antibodies against HCV. Plasma pentosidine, high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6) and alanine aminotransferase (ALT) levels were measured. The patients were also analysed according to the tertiles of serum levels of ferritin: group 1 (ferritin <380 ng/ml), group 2 (ferritin 380-750 ng/ml) and group 3 (ferritin >750 ng/ml). The cumulative iron dose was recorded during 6 months prior to the study.

RESULTS

HCV(+) patients had significantly higher levels of plasma pentosidine and ALT than HCV(-) patients. Age, gender, serum albumin, IL-6 and hsCRP did not differ according to HCV serology. The levels of pentosidine were related to the ferritin levels and were significantly higher in group 3 compared with group 1. Moreover, the cumulative dose of iron was significantly higher in group 3 than in group 1. Plasma pentosidine showed a positive correlation with age, HCV and ferritin. In a stepwise backward multiple regression model, age and HCV were independent predictors of pentosidine levels.

CONCLUSION

HCV in HD patients is associated with increased pentosidine levels, possibly reflecting increased oxidative stress. The association between pentosidine and ferritin levels may suggest an impact of i.v. iron therapy.

Ultrapure dialysate decreases plasma pentosidine, a marker of “carbonyl stress”

BACKGROUND

Advanced glycation end products (AGEs) and their reactive carbonyl precursors accumulate in renal failure ("carbonyl stress"). Carbonyl stress derives from a broad derangement in the nonenzymatic biochemistry of both carbohydrates and lipids. We tested the influence of dialysate quality on plasma level of pentosidine, an AGE moiety taken as a surrogate marker of carbonyl stress, in hemodialysis patients.

METHODS

Plasma pentosidine is measured by means of high-performance liquid chromatography in patients hemodialyzed successively with a conventional and an ultrapure endotoxin-free dialysate.

RESULTS

Dialysate endotoxin level decreased from 0.040 +/- 0.017 EU/mL before the switch to the new water supply system to less than the detection limit (<0.001 EU/mL) after the switch. Plasma pentosidine levels decreased from 1.55 +/- 0.61 nmol/mL before the switch to 1.38 +/- 0.52 nmol/mL (P < 0.0001) and 1.31 +/- 0.50 nmol/mL (P < 0.0001) 3 and 6 months after the switch to an ultrapure dialysate, respectively. Decreases in plasma pentosidine levels were similar regardless of dialyzer membrane type; ie, high-flux polysulfone, high-flux polymethylmethacrylate, and low-flux cellulose acetate membranes. Unexpectedly, plasma triglyceride levels decreased from 150 +/- 116 mg/dL (1.69 +/- 1.31 mmol/L) before the switch to 124 +/- 79 mg/dL (1.40 +/- 0.89 mmol/L; P < 0.01) and 119 +/- 75 mg/dL (1.34 +/- 0.85 mmol/L; P < 0.01) 3 and 6 months after the switch despite unchanged total cholesterol levels, respectively. Changes in pentosidine levels were unrelated to those in triglycerides, and both were unrelated to C-reactive protein levels, which remained stable throughout the study.

CONCLUSION

Ultrapure dialysate reduces plasma pentosidine levels and improves plasma triglyceride levels in hemodialysis patients through still undefined mechanisms.

N -(carboxymethyl)lysine, N -(carboxyethyl)lysine and vascular cell adhesion molecule-1 (VCAM-1) in relation to peritoneal glucose prescription and residual renal function; a study in peritoneal dialysis patients

BACKGROUND

Advanced glycation end products (AGEs) may contribute to peritoneal and cardiovascular damage in peritoneal dialysis (PD) patients, possibly in part by over-expression of vascular cell adhesion molecule-1 (VCAM-1). It has been suggested that peritoneal glucose load, oxidative stress, as well as the uraemic state itself may lead to an increased formation of AGEs. Aims of the present study were first to investigate the relation between residual glomerular filtration rate (rGFR), malondialdehyde (MDA) as a marker of lipid peroxidation, and peritoneal glucose prescription and absorption with serum levels of VCAM-1 and with the well characterized AGEs N(epsilon)-(carboxymethyl)lysine (CML) and N(epsilon)-(carboxyethyl)lysine (CEL), as well as with CML and CEL in peritoneal effluent.

METHODS

CML and CEL were measured by tandem mass spectroscopy, MDA by HPLC, and VCAM-1 by ELISA in 37 stable PD patients (age 54 +/- 12 years; time on PD 25 +/- 18 months). CML and CEL were also measured after a 4-month interval.

RESULTS

rGFR was independently related to CML both in serum (r = -0.66; P<0.001) and effluent (r = -0.62; P<0.001), whereas peritoneal glucose prescription and absorption were, respectively, related to CML in serum and effluent (r = 0.49; P<0.001 and r = 0.44; P<0.01). Relationships were comparable when assessed after the follow-up period. Peritoneal glucose absorption (r = 0.37; P<0.05), but not rGFR, was related to CEL in serum. The relation between peritoneal glucose prescription and CML in effluent lost significance when rGFR was added to the multi-regression model. Both rGFR (r = -0.40; P<0.05) and peritoneal glucose absorption (r = 0.37; P<0.05) were associated with VCAM-1 expression, which was itself weakly related only to CML in effluent (r = 0.38; P<0.05). MDA was not related to any parameter.

CONCLUSION

Peritoneal glucose prescription and absorption, as well as rGFR are related to serum and effluent levels of CML and to VCAM-1 expression in serum, whereas peritoneal glucose absorption was related to serum levels of CEL. Still, the effect of rGFR, which does not appear to be mediated through lipid peroxidation pathways, on effluent levels of CML appears to outweigh the effect of the PD treatment. Even small differences in residual renal function in patients already on dialysis therapy are related to large variations of CML in serum and the peritoneal cavity.

Malnutrition in hemodialysis diabetic patients: evaluation and prognostic influence

BACKGROUND

This work aimed to evaluate the role of malnutrition in the increased mortality rate of hemodialysis diabetic patients from a French cooperative series.

METHODS

Body mass index (BMI), serum albumin, prealbumin, cholesterol, and pre-dialysis creatinine, normalized protein catabolic rate and lean body mass (LBM) were measured in 734 diabetic and 6389 non-diabetic patients (aged 63.4 +/- 12.2 and 62.0 +/- 15.9 years; 1.01 male to 1.40 female ratio). The outcome of 1610 of these patients, including 170 diabetics, was assessed during a 30-month follow-up.

RESULTS

Diabetic as compared to non-diabetic patients showed a significant (P < 10-4) increased BMI (25.9 +/- 5.2 vs. 23.1 +/- 4.3) and cholesterol (5.5 +/- 1.6 vs. 5.3 +/- 1.5 mmol/L), and decreased albumin (37.8 +/- 5.4 vs. 38.9 +/- 5.3 g/L), prealbumin (317 +/- 91 vs. 340 +/- 94 mg/L), creatinine (711 +/- 184 vs. 816 +/- 217 micromol/L) and LBM (76 +/- 18 vs. 87 +/- 21%). Normalized protein catabolic rate was similar in the two groups (1.11 +/- 0.31 vs. 1.13 +/- 0.32 g/kg/L). One and two-year survival was 83.7 +/- 2.9% and 65.5 +/- 3.8% in diabetic patients versus 90.3 +/- 0.8% and 79.9 +/- 1.1% in non-diabetics (relative risk 1.26, P < 0.01). Independent predictors of survival were age, albumin and prealbumin in non-diabetics and only age in diabetics.

CONCLUSION

Diabetic patients compared to non-diabetics were characterized by an increased incidence of protein malnutrition and decreased survival. However, the higher death risk associated with diabetes was not related to malnutrition.

Toward better dialysis compatibility: advances in the biochemistry and pathophysiology of the peritoneal membranes

Peritoneal dialysis (PD) has modified our concept of the peritoneal membrane, which is now a topic of active research. Peritoneal solute transport progressively increases with time on PD, enhances the dissipation of the osmotic gradient and, eventually, reduces ultrafiltration capacity. The causes of peritoneal membrane failure remain elusive. Recurrent episodes of peritonitis are not a prerequisite for the development of ultrafiltration failure. Functionally, the changes of the failing peritoneal membrane are best described as an increased functional area of exchange for small solutes between blood and dialysate. Histologically, these events are associated with vascular proliferation and structural changes of pre-existing vessels. Gathered evidence, including information on the composition of peritoneal cavity fluids and its dependence on the uremic environment, have cast a new light on the molecular mechanisms of decline in peritoneal membrane function. Chronic uremia per se modifies the peritoneal membrane and increases the functional area of exchange for small solutes. Biochemical alterations in the peritoneum inherent to uremia might be, at least in part, accounted for by severe reactive carbonyl compounds overload originating both from uremic circulation and PD fluid ("peritoneal carbonyl stress"). The molecular events associated with long-term PD are similar but more severe than those present in chronic uremia without PD, including modifications of nitric oxide synthase (NOS) and angiogenic growth factors expression, and advanced glycation and lipoxidation of the peritoneal proteins. This review focuses on reactive carbonyls and their association with a number of molecular changes observed in peritoneal tissues. This hypothetical approach will require further testing. Nevertheless, the insights gained on the peritoneal membrane offer a new paradigm to assess the effect of uremic toxins on serosal membranes. Furthermore, the progresses made in the dissection of the molecular events leading to peritoneal membrane failure open new avenues to develop safe, more biocompatible peritoneal dialysis technologies.

Hemodialysis Membranes: Interleukins, Biocompatibility, and Middle Molecules

ABSTRACT. Maintenance hemodialysis patients display evidence of elevated interleukin-1 (IL-1) and tumor necrosis factor alpha release after stimulation either by contaminated dialysate, bioincompatible membrane material, or both. This release is followed by the stimulated secretion of a large number of other interleukins, particularly IL-6, the cytokine principally responsible for acute-phase protein synthesis. It has been shown that high levels of the circulating proinflammatory cytokines IL-1, tumor necrosis factor alpha, IL-6, and IL-13 are associated with mortality in hemodialysis patients. Essential functions of polymorphonuclear leukocytes—that is, phagocytosis, oxygen species production, upregulation of specific cell surface receptor proteins, or apoptosis—are disturbed in patients with end-stage renal disease. These are further altered as a result of complement activation by the hemodialysis procedure, particularly if bioincompatible dialyzers are used. Polymorphonuclear leukocyte degranulation occurring during extracorporeal circulation does not depend on complement activation but rather on intracellular calcium and the presence or absence of the degranulation inhibitory proteins angiogenin and complement factor D. Clinical signs and symptoms of end-stage renal disease patients are at least in part related to the accumulation of middle molecules such as β2-microglobulin, parathyroid hormone, advanced glycation end products, advanced lipoxidation end products, advanced oxidation protein products (formed as a result of oxidative stress, carbonyl stress, or both), granulocyte inhibitory proteins, or leptin. Currently available membrane materials do not provide long-lasting, effective reduction of middle molecules in patients who require maintenance hemodialysis.

Filtration of native and glycated beta2-microglobulin by charged and neutral dialysis membranes

BACKGROUND

It has been postulated that protein glycation and formation of advanced glycation end products (AGE) are among toxic factors in chronic uremia, whether the renal disease is of diabetic or nondiabetic origin. In this setting, AGE-modified beta2-microglobulin (beta2m) may favor dialysis beta2m-related dialysis amyloidosis. Consequently, efficient removal of modified beta2m by highly permeable dialysis membranes is as important as removal of native beta2m to postpone the development of dialysis amyloidosis.

METHODS

To define the role of dialysis membrane surface electronegativity on plasma protein transfer, an in vitro model was used to test the interactions of native and glycated beta2m with various highly permeable dialysis membranes. An experimental circuit with minidialyzers was used. The neutral high-flux polysulfone membrane (PS), the electronegative polymethylmetacrylate membrane (PMMA), the electronegative AN69 membrane and a modified AN69 membrane, the surface of which was neutralized with polyethyleneimine (AN69-PEI), were tested using both native beta2m and the more acidic glycated beta2m. Protein mass transfer and binding to the membrane were measured.

RESULTS

Mass transfer of glycated beta2m was significantly decreased through all membranes tested when compared with native beta2m. This result was due to the increased molecular weight of beta2m, which became less permeable to porous membranes, whereas adsorption of both native and glycated beta2m to membranes, due to ionic interactions, decreased similarly with AN69 and AN69-PEI, but remained unchanged with PS and PMMA. Moreover, surface neutralization of AN69 membrane did not alter its core binding capacity, since beta2m absorption accounted for 98 and 97% and glycated beta2m for 83.7 and 81.4% of the protein removed with AN69 and AN69-PEI, respectively.

CONCLUSION

Clearance of glycated beta2m through highly permeable neutral and negatively charged membranes was lower than that of native beta2m, reflecting a decreased sieving coefficient for the neoformed higher molecular weight and conformationally altered molecule. The binding capacity of the neutral PS was roughly half that of the charged membranes. Neutralizing surface electronegativity of the AN69 membrane with PEI did not alter its binding capacity. These results suggest that it would be useful for dialysis protocols to include comparative studies of both serum native and modified beta2m in order to prevent beta2m-amyloidosis.

Oxidative stress is reduced by the long-term use of vitamin E-coated dialysis filters

BACKGROUND

Oxidative stress during hemodialysis is thought to promote the progression of vascular complications in hemodialysis patients. The protective role of vitamin E as a lipophilic antioxidant against oxidative stress has been widely investigated. Here we investigated the effects of a vitamin E-coated regenerated cellulose hollow fiber dialyzer (CL-EE) on oxidative stress compared with a polysulfone hollow fiber (CL-PS).

METHODS

For at least three months before beginning the protocol, 10 nondiabetic (NDM) patients (70.0 +/- 7.5 years; 6 males and 4 females) and 8 diabetic (DM) patients (65.0 +/- 7.4 years; 4 males, 4 females) were dialyzed with CL-PS. After that, we treated all of the patients with CL-EE for six months. Malondialdehyde (MDA), advanced glycation end products (AGEs), and 8-hydroxydeoxyguanosine (8-OHdG) were monitored as biomarkers for oxidative stress at the start and then at one, three, and six months into treatment with CL-EE.

RESULTS

Serum MDA, AGE, and 8-OHdG levels increased after the hemodialysis with CL-PS. The increase of the biomarkers was completely prevented by a single use of CL-EE. Long-term hemodialysis with CL-EE for six months significantly reduced the basal levels of the oxidant markers at one month for AGE and at six months for 8-OHdG in both DM and NDM patients. Serum MDA was reduced in only DM patients at three months. The improvement of the oxidative stress with CL-EE was more prominent in the DM patients.

CONCLUSIONS

Long-term treatment with CL-EE efficiently improves the oxidative stress associated with hemodialysis and potentially reduces dialysis complications due to oxidative stress.

Influence of dialysis modalities on serum AGE levels in end-stage renal disease patients

BACKGROUND

The accumulation of advanced glycation end-products (AGEs) in end-stage renal disease (ESRD) influenced by dialysis modalities is of current interest. Highly permeable membranes in haemodialysis or haemofiltration should be able to eliminate circulating AGEs as well as their AGE precursors more efficiently.

METHODS

In our study, 10 non-diabetic and 10 diabetic ESRD patients were on haemodialysis with low-flux membranes (LF) followed by a cross-over haemodialysis with high-flux or super-flux polysulfone membranes (HF, SF) for 6 months each. We measured the protein-bound pentosidine and free pentosidine serum levels by high-performance liquid chromatography (HPLC) as well as the serum AGE peptide, AGE-beta(2)-microglobulin and beta(2)-microglobulin concentrations, using ELISA assays.

RESULTS

All parameters investigated were significantly higher in dialysis patients than in healthy subjects. The reduction rates during a single dialysis session were found to be higher using the SF than those obtained with the HF (free pentosidine 82.4+/-7.3 vs 76.6+/- 8.7%; AGE peptides 79.7+/-7.7 vs 62.3+/-14.7%; AGE-beta(2)-microglobulin 64.0+/-16.5 vs 45.4+/-17.7%; beta(2)-microglobulin 70.5+/-5.6 vs 58.2+/-6.0%). The protein-bound pentosidine levels remained constant over the respective dialysis sessions. In the 6-month treatment period with the SF, decreased pre-dialysis serum levels of protein-bound pentosidine, free pentosidine and AGE peptides were observed in non-diabetics and diabetics as compared with values obtained with the LF. The respective pre-dialysis AGE-beta(2)-microglobulin concentrations decreased insignificantly, whereas those of beta(2)-microglobulin were significantly lower. Using the HF dialyser, only moderate changes of the parameters measured were noted.

CONCLUSION

Treatment with the biocompatible polysulfone SF dialyser seems to be better suited to lower serum AGE levels and to eliminate their precursors.

Renal versus continuous versus intermittent therapies for removal of uremic toxins

Uremic toxin removal by renal replacement therapies (RRTs) differs from the elimination of waste products by the native kidney in several ways. Specifically, uremic toxin removal by a RRT is achieved by a one-step membrane-based process, without the subsequent modifications that occur in the native kidney after a solute is filtered across the glomerular membrane. Another major difference relates to the continuous nature of native kidney function, which provides constant solute clearances and mass removal rates for a patient in steady state. This constancy of solute clearance, mass removal rate, and serum concentration does not exist for RRTs used in patients with end-stage renal disease (ESRD). The purpose of this review is first to compare solute removal by the native kidney with that by the various RRTs used for uremic patients. Subsequently, the therapy specificity of the relationship between solute clearance and mass removal rate is discussed, and the effective solute removal capabilities of different therapies compared.

Reactive carbonyl compounds related uremic toxicity ("carbonyl stress")

Many studies on uremic toxins have focused on enzymatic biochemistry. Recently, attention has turned to nonenzymatic biochemistry, especially progressive and irreversible modifications of proteins. Two different approaches opened the field of irreversible nonenzymatic modifications of proteins in uremia: the advanced glycation end products (AGEs) derived from the Maillard reaction and the advanced lipoxidation end products (ALEs) derived from lipid peroxidation. They have revealed the accumulation of reactive carbonyl compounds (RCOs) derived from carbohydrates and lipids and the subsequent carbonyl modifications of proteins ("carbonyl stress"). In this article, we describe the causal role of various RCOs and AGEs/ALEs accumulating in uremia, the clinical consequences of carbonyl stress in uremia, and finally, the therapeutic perspectives. We propose carbonyl stress as a new uremic toxicity.

Mixed predilution and postdilution online hemodiafiltration compared with the traditional infusion modes

BACKGROUND

On postdilution hemodiafiltration (post-HDF), convective removal of medium-high molecular weight solutes is, at the highest ultrafiltration rates, limited by high blood viscosity and protein concentration. Prefilter reinfusion (pre-HDF) may overcome this problem, but plasma dilution may affect the overall efficiency of the technique. In this study, an experimental system of online HDF with combined prefilter and postfilter infusion (mixed HDF) was evaluated and compared with the traditional predilution and postdilution modes.

METHODS

Removal of urea (U), creatinine (Cr), phosphate (Phos), and beta(2)-microglobulin (beta(2)m), ultrafiltration coefficients of the dialyzer (K(UF)), and rheologic conditions of the blood circuit were evaluated during the three infusion modes (a total of 36 runs lasting 180 min), performed with a polysulfone hemofilter 1.8 m(2), blood flow (Q(b)) 400 mL/min, dialysate flow (Q(d)) 700 mL/min, and infusion rate 120 mL/min (pre-HDF and post-HDF), or 60 + 60 mL/min (mixed HDF).

RESULTS

The mean effective U and Cr clearances and urea index of dialysis dose (eKt/V) were significantly higher on post-HDF than on pre-HDF (K(WB) (U) 210 vs. 193 mL/min, K(DQ) (Cr) 152 vs. 142 mL/min, eKt/V 1.41 vs. 1.30), while mixed HDF did not show significant differences versus post-HDF (K(WB) (U) 201 mL/min, K(DQ) (Cr) 149 mL/min). K(DQ) for Phos and beta(2)m were higher on post-HDF in only absolute values. Similar differences were found for instantaneous dialyzer clearances (K(I)) at 60, 120, and 180 minutes of the sessions, with a common trend to decrease with time. K(UF) and the apparent beta(2)m sieving coefficient showed their lowest values toward the end of post-HDF sessions. Increasing filtration fractions (FFs) were associated with increasing transmembrane pressure (TMP) and solute clearances up to FF values of 0.45. These were values achieved in only post-HDF, at which point the curve of the relationship between TMP and FF assumed its steepest exponential trend.

CONCLUSIONS

Mixed HDF, by better preserving the characteristics of water and solute transport of the membrane, ensured safer operating conditions than post-HDF, while achieving similar removal of small- and large-size solutes. Optimizing the ratio of prefilter/postfilter infusion and the total infusion according to the relationships found in our study between solute clearances, FF, and TMP, convective flux and transport may avoid excessive hemoconcentration and dangerous pressure gradients.

The quality of dialysate: an integrated approach

The role of bacterial contamination of dialysis water with respect to chronic inflammatory diseases associated with long-term hemodialysis therapy has been greatly underestimated in the last two decades. In the present article, recent multicenter studies assessing the bacteriological quality of water and dialysate are discussed. In addition, we describe that pyrogenic substances of bacterial origin derived from contaminated dialysate penetrate intact dialyzer membranes with the consequence of the induction of an inflammatory response in the patients. The influence of dialyzer membrane characteristics on the passage of bacterial substances from dialysate into blood are discussed. Reaching the patients blood, bacteria-derived substances activate circulating mononuclear cells to produce proinflammatory cytokines. Cytokines such as interleukin-1 beta and tumor necrosis factor-alpha are mediators of the acute phase response resulting in elevated levels of acute phase proteins (for example, C-reactive protein). The consequence is a state of microinflammation that may contribute to progressive inflammatory diseases in chronic renal failure such as beta2-microglobulin amyloidosis, protein catabolism, and atherosclerosis. The use of sterile dialysate reduces cytokine production and plasma levels of acute phase proteins, and may positively influence progressive inflammatory diseases in patients with end-stage renal failure.

Relevance of oxidative and carbonyl stress to long-term uremic complications

Oxidative stress is a disturbance of balance between oxidants and antioxidant species. The existence of an increased oxidative stress in chronic renal failure is supported by evidence of increased lipid, carbohydrate, and protein oxidation products in plasma and cell membrane. Recent studies have implicated the oxidative stress in the nonenzymatic biochemistry leading to irreversible protein modifications. Reactive oxygen species may directly alter proteins with the eventual formation of oxidized amino acids. Alternatively, reactive carbonyl compounds formed by the oxidation of carbohydrates and lipids may indirectly lead to advanced glycation or lipoxidation of proteins. Chronic uremia is associated with increased modification of protein caused by reactive carbonyl compounds derived from both carbohydrates and lipids. Increased carbonyl modification of proteins subsequently results in the rise of plasma and tissue contents of advanced glycation end products and advanced lipoxidation end products, in which the deleterious biological effects have been revealed. This article focuses on the irreversible nonenzymatic modification of proteins, which might, at least in part, contribute to the development of complications associated with chronic renal failure and long-term dialysis, such as atherosclerosis and dialysis-related amyloidosis.

Clinical manifestations of AB-amyloidosis: effects of biocompatibility and flux

BACKGROUND

Highly permeable biocompatible dialysis membranes may postpone the development of AB-amyloidosis, but the relative contribution of enhanced flux or reduced inflammation by highly biocompatible membranes and sterile dialysis fluid remains unknown.

METHODS

In this retrospective investigation, 89 patients with end-stage renal disease maintained on regular haemodialysis for at least 10 years and treated with one type of dialysis membrane exclusively were selected for analysis. They were divided into three groups: low-flux, bioincompatible cellulose (I), low-flux, intermediately biocompatible polysulphone or PMMA (II), or high-flux, highly biocompatible polysulphone or AN69 (III). In addition, the patients were analysed according to the microbiological quality of the dialysis fluid, which had been tested regularly and was classified either as standard or as intermittently contaminated. The clinical manifestations indicative of AB-amyloidosis, namely, carpal tunnel syndrome, arthropathy and bone cysts, were diagnosed after recruitment.

RESULTS

Clinical symptoms were most pronounced in group I, intermediate in group II, and lowest in group III. Patients treated with intermittently contaminated dialysis fluid showed a higher prevalence of AB-amyloidosis than patients with less contaminated dialysis fluid. Logistic regression analysis demonstrated that the flux characteristics of the dialyser and the microbiological quality of the dialysis fluid as well as the biocompatibility of the dialyser were independent determinants of AB-amyloidosis.

CONCLUSION

It would be prudent clinical practice to employ high-flux biocompatible membranes in conjunction with ultrapure dialysis fluid for the treatment of end-stage renal disease patients who need to remain on long-term haemodialysis.

Mechanisms for the formation of glycoxidation products in end-stage renal disease

BACKGROUND

Advanced glycation end products (AGEs) accumulate on tissue and plasma proteins in patients with renal failure far in excess of normal aging or diabetes. The aim of these studies was to elucidate the nature of the precursors and the pathways that lead to an accelerated formation of two structurally identified AGEs [pentosidine and Nepsilon(carboxymethyl)lysine (CML)] in the uremic milieu.

METHODS

Serum levels of the glycoxidation products, pentosidine and CML, were quantitated by high-performance liquid chromatography in uremic patients treated by dialysis. The formation of early glycation products (as furosine) and late glycoxidation products was modeled in uremic serum and in spent peritoneal dialysate.

RESULTS

Clinical factors that affect circulating levels of AGEs included dialysis clearance and dialyzer membrane pore size, but not the presence or absence of diabetes. Both pentosidine and CML form at an accelerated rate in serum from uremic patients. Chelating agents most effectively slow the formation in vitro. In uremic fluids, the primary mechanism of formation of pentosidine is through the Amadori pathway. The primary mechanism of formation of CML is through metal-chelated autoxidation of reducing sugars generating reactive carbonyl precursors. In uremic serum, the presence of an unidentified reactive low molecular weight precursor accelerates the formation of pentosidine.

CONCLUSIONS

The formation of the two glycoxidation products, pentosidine and CML, proceeds by different pathways and is enhanced by different precursors in the uremic milieu. The formation of both AGEs is markedly enhanced by metal-catalyzed reactions, evidence for the presence of increased metal-ion mediated oxidant stress in uremia.