Autoxidation products of both carbohydrates and lipids are increased in uremic plasma: is there oxidative stress in uremia?

Biological autoluminescence as a perturbance-free method for monitoring oxidation in biosystems

Biological oxidation processes are in the core of life energetics, play an important role in cellular biophysics, physiological cell signaling or cellular pathophysiology. Understanding of biooxidation processes is also crucial for biotechnological applications. Therefore, a plethora of methods has been developed for monitoring oxidation so far, each with distinct advantages and disadvantages. We review here the available methods for monitoring oxidation and their basic characteristics and capabilities. Then we focus on a unique method - the only one that does not require input of additional external energy or chemicals - which employs detection of biological autoluminescence (BAL). We highlight the pros and cons of this method and provide an overview of how BAL can be used to report on various aspects of cellular oxidation processes starting from oxygen consumption to the generation of oxidation products such as carbonyls. This review highlights the application potential of this completely non-invasive and label-free biophotonic diagnostic method.

Lipid Peroxidation Has Major Impact on Malondialdehyde-Derived but Only Minor Influence on Glyoxal and Methylglyoxal-Derived Protein Modifications in Carbohydrate-Rich Foods

In the present work, the contribution of lipid peroxidation on modifications of lysine and arginine residues of proteins was investigated. Lipid peroxidation had a major impact on malondialdehyde-derived protein modifications; however, the influence on glyoxal and methylglyoxal-derived modifications in flat wafers was negligible. Therefore, vegetable oils (either linseed oil, sunflower oil, or coconut oil) were added to respective batters, and flat wafers were baked (150 °C, 3-10 min). Analysis of malondialdehyde indicated oxidation in linseed wafers, which was supported by the direct quantitation of three malondialdehyde protein adducts in the range of 0.09-23.5 mg/kg after enzymatic hydrolysis. In contrast, levels of free glyoxal and methylglyoxal were independent of the type of oil added, which was in line with the analysis of 13 advanced glycation end products. Comprehensive incubations of 40 mM N²-t-Boc-lysine (100 mM phosphate buffer, pH 7.4) with either 10% oil or an equimolar concentration of carbohydrates led to magnitudes higher (10³-10⁵) amounts of N⁶-carboxymethyl lysine, N⁶-glycolyl lysine, and N⁶-carboxyethyl lysine in the latter. Furthermore, malondialdehyde exceeded glyoxal and methylglyoxal in incubations of pure oils at 150 °C by factors of 30 and 100, respectively.

The Advanced Lipoxidation End-Product Malondialdehyde-Lysine in Aging and Longevity

The nonenzymatic adduction of malondialdehyde (MDA) to the protein amino groups leads to the formation of malondialdehyde-lysine (MDALys). The degree of unsaturation of biological membranes and the intracellular oxidative conditions are the main factors that modulate MDALys formation. The low concentration of this modification in the different cellular components, found in a wide diversity of tissues and animal species, is indicative of the presence of a complex network of cellular protection mechanisms that avoid its cytotoxic effects. In this review, we will focus on the chemistry of this lipoxidation-derived protein modification, the specificity of MDALys formation in proteins, the methodology used for its detection and quantification, the MDA-lipoxidized proteome, the metabolism of MDA-modified proteins, and the detrimental effects of this protein modification. We also propose that MDALys is an indicator of the rate of aging based on findings which demonstrate that (i) MDALys accumulates in tissues with age, (ii) the lower the concentration of MDALys the greater the longevity of the animal species, and (iii) its concentration is attenuated by anti-aging nutritional and pharmacological interventions.

Carbonyl Stress: Increased Carbonyl Modification of Tissue and Cellular Proteins in Uremia

Advanced glycation end-products (AGEs) are formed during non enzymatic glycation and oxidation (glycoxidation) reactions. This process is accelerated in diabetics owing to hyperglycemia, and it has been implicated in the pathogenesis of diabetic complications. Surprisingly, AGEs increase in normoglycemic uremic patients to a much greater extent than in diabetics. AGE accumulation in uremia cannot be attributed to hyperglycemia nor simply to a decreased removal by glomerular filtration. Recently gathered evidence has suggested that, in uremia, the increased carbonyl compounds derived from carbohydrates and lipids modify proteins not only by glycoxidation reaction but also by lipoxidation reaction (“carbonyl stress”).

Carbonyl stress has been implicated in the pathogenesis of long-term uremic complications such as dialysisrelated amyloidosis. With regard to continuous ambulatory peritoneal dialysis (CAPD), the peritoneal cavity appears to be in a state of severe overload of carbonyl compounds derived from CAPD solution containing high glucose, from heat sterilization of the solution, and from uremic circulation. Carbonyl stress might modify not only peritoneal matrix proteins and alter their structures, but also react with mesothelial and endothelial cell surface proteins and initiate a range of inflammatory responses. Carbonyl stress might therefore contribute to the development of peritoneal sclerosis in patients with long-term CAPD.

β2-Microglobulin and Renal Bone Disease

Dialysis-related amyloidosis (DRA) is characterized by amyloid deposition mainly in bone and joint structures, presenting as carpal tunnel syndrome, destructive arthropathy, and subchondral bone erosions and cysts. β2-microglobulin has been demonstrated to be a major constituent of amyloid fibrils. DRA occurs not only in patients undergoing long-term hemodialysis, but also in patients undergoing continuous ambulatory peritoneal dialysis. The incidence of this complication increases with the duration of dialytic therapy and the age of the patient. While a definitive diagnosis of DRA can be made only by histological findings, various imaging techniques often support diagnosis. The molecular pathogenesis of this complication remains unknown. Recent studies have, however, suggested a pathogenic role of a new modification of β2-microglobulin in amyloid fibrils -that is, the advanced glycation end-products (AGEs) formed with carbonyl compounds derived from autoxidation of both carbohydrates and lipids (“carbonyl stress”). Therapy for DRA is limited to symptomatic approaches and surgical removal of amyloid deposits. High-flux biocompatible dialysis membranes could be used to delay DRA development.

Glucoselysine is derived from fructose and accumulates in the eye lens of diabetic rats

Prolonged hyperglycemia generates advanced glycation end-products (AGEs), which are believed to be involved in the pathogenesis of diabetic complications. In the present study, we developed a polyclonal antibody against fructose-modified proteins (Fru-P antibody) and identified its epitope as glucoselysine (GL) by NMR and LC-electrospray ionization (ESI)- quadrupole TOF (QTOF) analyses and evaluated its potential role in diabetes sequelae. Although the molecular weight of GL was identical to that of fructoselysine (FL), GL was distinguishable from FL because GL was resistant to acid hydrolysis, which converted all of the FLs to furosine. We also detected GL in vitro when reduced BSA was incubated with fructose for 1 day. However, when we incubated reduced BSA with glucose, galactose, or mannose for 14 days, we did not detect GL, suggesting that GL is dominantly generated from fructose. LC-ESI-MS/MS experiments with synthesized [¹³C₆]GL indicated that the GL levels in the rat eye lens time-dependently increase after streptozotocin-induced diabetes. We observed a 31.3-fold increase in GL 8 weeks after the induction compared with nondiabetic rats, and Nϵ-(carboxymethyl)lysine and furosine increased by 1.7- and 21.5-fold, respectively, under the same condition. In contrast, sorbitol in the lens levelled off at 2 weeks after diabetes induction. We conclude that GL may be a useful biological marker to monitor and elucidate the mechanism of protein degeneration during progression of diabetes.

Mitochondria as a Source and a Target for Uremic Toxins

Elucidation of molecular and cellular mechanisms of the uremic syndrome is a very challenging task. More than 130 substances are now considered to be "uremic toxins" and represent a very diverse group of molecules. The toxicity of these molecules affects many cellular processes, and expectably, some of them are able to disrupt mitochondrial functioning. However, mitochondria can be the source of uremic toxins as well, as the mitochondrion can be the site of complete synthesis of the toxin, whereas in some scenarios only some enzymes of the pathway of toxin synthesis are localized here. In this review, we discuss the role of mitochondria as both the target and source of pathological processes and toxic compounds during uremia. Our analysis revealed about 30 toxins closely related to mitochondria. Moreover, since mitochondria are key regulators of cellular redox homeostasis, their functioning might directly affect the production of uremic toxins, especially those that are products of oxidation or peroxidation of cellular components, such as aldehydes, advanced glycation end-products, advanced lipoxidation end-products, and reactive carbonyl species. Additionally, as a number of metabolic products can be degraded in the mitochondria, mitochondrial dysfunction would therefore be expected to cause accumulation of such toxins in the organism. Alternatively, many uremic toxins (both made with the participation of mitochondria, and originated from other sources including exogenous) are damaging to mitochondrial components, especially respiratory complexes. As a result, a positive feedback loop emerges, leading to the amplification of the accumulation of uremic solutes. Therefore, uremia leads to the appearance of mitochondria-damaging compounds, and consecutive mitochondrial damage causes a further rise of uremic toxins, whose synthesis is associated with mitochondria. All this makes mitochondrion an important player in the pathogenesis of uremia and draws attention to the possibility of reducing the pathological consequences of uremia by protecting mitochondria and reducing their role in the production of uremic toxins.

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.

RAGE-mediated inflammation in patients with septic shock

BACKGROUND

The receptor for advanced glycation end-products (RAGE)-pathway is described to be a crucial component of the innate immune response in sepsis. The aims of the present study were, therefore, to delineate the kinetics of membrane-bound RAGE expression, to quantify its soluble isoforms, and to determine the extent of metabolic (e.g., AGE-CML) as well as immunologic (e.g., S100A8/A9) ligands in different inflammatory settings in humans.

MATERIALS AND METHODS

The presented data result from secondary analyses of an observational clinical pilot study, including patients with septic shock (n = 60), postoperative controls (n = 30), and healthy volunteers (n = 30). Surface-bound expression of RAGE by peripheral blood leukocytes was determined by flow cytometry. In addition, plasma levels of sRAGE, esRAGE, AGE-CML, S100A8/A9, S100A8/A9-CML, RBP, RBP-CML, HSA-CML, HMBG-1, and ß-Amyloid were measured using ELISA.

RESULTS

In patients with septic shock, RAGE expression was significantly increased in comparison to both control groups, which was paralleled by a significant increase in sRAGE plasma levels. Formation of AGE-CML was shown to be dependent on the availability of the unmodified protein. However, the total amount of AGE-CML did not differ significantly between septic patients and healthy volunteers at early stages or was even lower in patients with sepsis at later stages. In contrast, immunologic ligands (e.g., S100A8/A9) were shown to be significantly elevated in septic patients within the entire study period.

CONCLUSIONS

Activation of the RAGE-pathway was shown to be of relevance in patients with septic shock, mainly driven by an increase in immunologic (e.g., S100A8/A9) rather than metabolic ligands (e.g., CML-derived AGE-formation).

The balance of powers: Redox regulation of fibrogenic pathways in kidney injury

Oxidative stress plays a central role in the pathogenesis of diverse chronic inflammatory disorders including diabetic complications, cardiovascular disease, aging, and chronic kidney disease (CKD). Patients with moderate to advanced CKD have markedly increased levels of oxidative stress and inflammation that likely contribute to the unacceptable high rates of morbidity and mortality in this patient population. Oxidative stress is defined as an imbalance of the generation of reactive oxygen species (ROS) in excess of the capacity of cells/tissues to detoxify or scavenge them. Such a state of oxidative stress may alter the structure/function of cellular macromolecules and tissues that eventually leads to organ dysfunction. The harmful effects of ROS have been largely attributed to its indiscriminate, stochastic effects on the oxidation of protein, lipids, or DNA but in many instances the oxidants target particular amino acid residues or lipid moieties. Oxidant mechanisms are intimately involved in cell signaling and are linked to several key redox-sensitive signaling pathways in fibrogenesis. Dysregulation of antioxidant mechanisms and overproduction of ROS not only promotes a fibrotic milieu but leads to mitochondrial dysfunction and further exacerbates kidney injury. Our studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues such as the kidney activate fibrogenic pathways and promote end-organ damage. The ability to quantify these changes and assess response to therapies will be pivotal in understanding disease mechanisms and monitoring efficacy of therapy.

Advanced glycation/glycoxidation endproduct carboxymethyl-lysine and incidence of coronary heart disease and stroke in older adults

BACKGROUND

Advanced glycation/glycoxidation endproducts (AGEs) accumulate in settings of increased oxidative stress--such as diabetes, chronic kidney disease and aging--where they promote vascular stiffness and atherogenesis, but the prospective association between AGEs and cardiovascular events in elders has not been previously examined.

METHODS

To test the hypothesis that circulating levels of N(ɛ)-carboxymethyl-lysine (CML), a major AGE, increase the risk of incident coronary heart disease and stroke in older adults, we measured serum CML by immunoassay in 2111 individuals free of prevalent cardiovascular disease participating in a population-based study of U.S. adults ages 65 and older.

RESULTS

During median follow-up of 9.1 years, 625 cardiovascular events occurred. CML was positively associated with incident cardiovascular events after adjustment for age, sex, race, systolic blood pressure, anti-hypertensive treatment, diabetes, smoking status, triglycerides, albumin, and self-reported health status (hazard ratio [HR] per SD [0.99 pmol/l] increase=1.11, 95% confidence interval [CI]=1.03-1.19). This association was not materially attenuated by additional adjustment for C-reactive protein, estimated glomerular filtration rate (eGFR), and urine albumin/creatinine ratio. Findings were similar for the component endpoints of coronary heart disease and stroke.

CONCLUSIONS

In this large older cohort, CML was associated with an increased risk of cardiovascular events independent of a wide array of potential confounders and mediators. Although the moderate association limits CML's value for risk prediction, these community-based findings provide support for clinical trials to test AGE-lowering therapies for cardiovascular prevention in this population.

Skin autofluorescence is associated with the progression of chronic kidney disease: a prospective observational study

Background

Advanced glycation end product (AGE) accumulation is thought to be a measure of cumulative metabolic stress that has been reported to independently predict cardiovascular disease in diabetes and renal failure. The aim of this study was to evaluate the association between AGE accumulation, measured as skin autofluorescence, and the progression of renal disease in pre-dialysis patients with chronic kidney disease (CKD).

Methods

Skin autofluorescence was measured noninvasively with an autofluorescence reader at baseline in 449 pre-dialysis patients with CKD. The primary end point was defined as a doubling of serum creatinine and/or need for dialysis.

Results

Thirty-three patients were lost to follow-up. Forty six patients reached the primary end point during the follow-up period (Median 39 months). Kaplan-Meier analysis showed a significantly higher risk of development of the primary end points in patients with skin autofluorescence levels above the optimal cut-off level of 2.31 arbitrary units, derived by receiver operator curve analysis. Cox regression analysis revealed that skin autofluorescence was an independent predictor of the primary end point, even after adjustment for age, gender, smoking history, diabetes, estimated glomerular filtration rate and proteinuria (adjusted hazard ratio 2.58, P = 0.004).

Conclusions

Tissue accumulation of AGEs, measured as skin autofluorescence, is a strong and independent predictor of progression of CKD. Skin autofluorescence may be useful for risk stratification in this group of patients; further studies should clarify whether AGE accumulation could be one of the therapeutic targets to improve the prognosis of CKD.

Skin autofluorescence is associated with severity of vascular complications in Japanese patients with Type 2 diabetes

AIMS

Skin autofluorescence, a non-invasive measure of the accumulation for advanced glycation end products, has been reported to be a useful marker for diabetic vascular risks in the Caucasian population. The aim of this study was to evaluate associations between skin autofluorescence and vascular complications in non-Caucasian patients with Type 2 diabetes.

METHODS

Subjects in this cross-sectional study comprised 130 Japanese patients with Type 2 diabetes. Skin advanced glycation end products were assessed by skin autofluorescence using an autofluorescence reader. Association between skin autofluorescence and severity of vascular complications was evaluated.

RESULTS

Of the 130 patients, 60 (46.2%) had microvascular complications such as diabetic retinopathy, neuropathy and nephropathy, 10 (7.7%) had macrovascular complications and 63 (48.5%) had micro- and/or macrovascular complications. Skin autofluorescence increased with severity of vascular complications. Independent determinants of skin autofluorescence were age (β = 0.24, P < 0.01), mean HbA(1c) in previous year (β = 0.17, P = 0.03), microvascular complications (β = 0.44, P < 0.01) and macrovascular complications (β = 0.27, P < 0.01). Multiple logistic regression analysis revealed that diabetes duration (odds ratio 1.15, P < 0.01), systolic blood pressure (odds ratio 1.04, P = 0.01), skin autofluorescence (odds ratio 3.62, P = 0.01) and serum albumin (odds ratio 0.84, P < 0.01) were independent factors for the presence of vascular complications in these patients.

CONCLUSIONS

Skin autofluorescence had independent effects on vascular complications in Japanese patients with Type 2 diabetes. This indicates that skin advanced glycation end products are a surrogate marker for vascular risk and a non-invasive autofluorescence reader may be a useful tool to detect high-risk cases in non-Caucasian patients with diabetes.

Protein conjugated with aldehydes derived from lipid peroxidation as an independent parameter of the carbonyl stress in the kidney damage

BACKGROUND

One of the well-defined and characterized protein modifications usually produced by oxidation is carbonylation, an irreversible non-enzymatic modification of proteins. However, carbonyl groups can be introduced into proteins by non-oxidative mechanisms. Reactive carbonyl compounds have been observed to have increased in patients with renal failure. In the present work we have described a procedure designed as aldehyde capture to calculate the protein carbonyl stress derived solely from lipid peroxidation.

METHODS

Acrolein-albumin adduct was prepared as standard at alkaline pH. Rat liver microsomal membranes and serum samples from patients with diabetic nephropathy were subjected to the aldehyde capture procedure and aldol-protein formation. Before alkalinization and incubation, samples were precipitated and redisolved in 6M guanidine. The absorbances of the samples were read with a spectrophotometer at 266 nm against a blank of guanidine.

RESULTS

Evidence showed abundance of unsaturated aldehydes derived from lipid peroxidation in rat liver microsomal membranes and in the serum of diabetic patients with advanced chronic kidney disease. Carbonyl protein and aldol-proteins resulted higher in the diabetic nephropathy patients (p < 0.004 and p < 0.0001 respectively).

CONCLUSION

The aldehyde-protein adduct represents a non oxidative component of carbonyl stress, independent of the direct amino acid oxidation and could constitute a practical and novelty strategy to measure the carbonyl stress derived solely from lipid peroxidation and particularly in diabetic nephropathy patients. In addition, we are in a position to propose an alternative explanation of why alkalinization of urine attenuates rhabdomyolysis-induced renal dysfunction.

Effect of sevelamer and calcium-based phosphate binders on coronary artery calcification and accumulation of circulating advanced glycation end products in hemodialysis patients

BACKGROUND

Some trials have indicated that coronary artery calcification progresses more slowly in sevelamer-treated dialysis patients than in those using calcium-based binders. Effects of phosphate binders on circulating advanced glycation end products (AGEs) are unknown.

STUDY DESIGN

Randomized trial with parallel-group design.

SETTING & PARTICIPANTS

183 adult (aged >20 years) patients on maintenance hemodialysis therapy at 12 dialysis facilities with a mean vintage of 118 ± 89 (median, 108) months. Dialysate calcium concentration was 2.5 mEq/L, and dietary calcium was not controlled.

INTERVENTION

Patients were randomly assigned to 12 months of treatment with sevelamer (n = 91) or calcium carbonate (n = 92).

OUTCOMES & MEASUREMENTS

Primary outcome measures were change from baseline in coronary artery calcification score (CACS) determined at study entry and completion using multislice computed tomography and the proportion of patients with a ≥ 15% increase in CACS. Blood parameters were determined at study entry and 2-week intervals, and levels of plasma pentosidine, a representative AGE, were determined at study entry, 6 months, and study completion.

RESULTS

79 (86.8%) and 84 (91.3%) patients in the sevelamer and calcium-carbonate arms completed the treatment, respectively. Both binders were associated with an increase in mean CACS: 81.8 (95% CI, 42.9-120.6) and 194.0 (139.7-248.4), respectively (P < 0.001 for both). After adjustment for baseline values, the increase in the sevelamer group was 112.3 (45.8-178) less (P < 0.001). Percentages of patients with a ≥ 15% increase in CACS were 35% of the sevelamer group and 59% of the calcium-carbonate group (P = 0.002). Plasma pentosidine levels increased with calcium carbonate but not [corrected] sevelamer treatment (P < 0.001). Sevelamer use was associated with decreased risk of a ≥ 15% increase in CACS regardless of baseline blood parameters, pentosidine level, and CACS.

LIMITATIONS

Treatment duration was relatively short, some sevelamer-treated patients (7 of 79) received calcium carbonate, and washout could not be performed.

CONCLUSIONS

The data suggest that sevelamer treatment slowed the increase in CACS and suppressed AGE accumulation.

Glycation and biomarkers of vascular complications of diabetes

Propensity to diabetic nephropathy (DN), retinopathy (DR), and cardiovascular disease (CVD) varies between individuals. Current biomarkers such as indicators of glycemia (HbA1c), retinal examinations, and albuminuria, cannot detect early tissue damage. HbAIc also doesn't reflect most glycative and oxidative chemical pathways that cause complications, and studies of new biomarkers to measure their end-products are needed. This review proposes the study of advanced glycation end products (AGEs) and oxidation end-products (OPs) in long-term diabetes outcome studies. AGEs integrate the activity of glycation pathways that form dicarbonyls, while OPs reflect superoxides, hydroxyl radicals, and peroxides. We discuss using these biomarkers to predict risk of development and progression of DN, DR, and CVD, and to determine if they confer risk independently of the level of HbA1c. We also discuss methods and guidelines to document sample quality in such studies. These studies have the potential to validate unique biomarkers during the early stages of diabetes in those who are at high risk of diabetic complications. Information on basic mechanisms responsible for complications could also stimulate development of therapeutic approaches to delay or arrest them. The ultimate goal is to predict those requiring aggressive therapies during the earliest stages, when prevention or reversal of complications is still possible.

AGEs/RAGE in CKD: irreversible metabolic memory road toward CVD?

BACKGROUND

Cardiovascular disease is the major cause of death in patients with renal insufficiency, accounting for 50% of all deaths in renal replacement therapy patients. Mortality from cardiovascular diseases in these patients is approximately 9% per year, which is about 30 times the risk in the general population. So far, intensive interventions to the general risk factors, such as high LDL-cholesterol or C-reactive protein, have not been successful in improving their cardiovascular outcomes, suggesting that the beneficial effect of risk reduction may be overwhelmed by accumulated risk memorized by long-term exposure to oxidative stress during the progression of renal failure.

DESIGN

In this review, we propose that this irreversible memory effect in renal failure may be mediated by advanced glycation end-products (AGEs).

RESULTS

The generation of AGEs has been implicated to be deeply associated with increased oxidative stress. Moreover, interaction of the receptor for AGEs (RAGE) with AGEs leads to crucial biomedical pathway generating intracellular oxidative stress and inflammatory mediators, which could result in further amplification of the pathway involved in AGE generation. Several lines of evidence suggest that AGEs/RAGE axis can profoundly be involved in cardiovascular diseases. Recent advances in AGEs and RAGE measurements led us to be capable of understanding more about the role of AGEs/RAGE axis as a risk for cardiovascular diseases in patients with renal failure.

CONCLUSION

AGEs/RAGE axis could be a crucial mediator of oxidative stress in renal failure. RAGE could be not only a useful biomarker, but also a potentially therapeutic target to overcome the accumulated adverse metabolic memory in renal failure.

Skin autofluorescence is associated with renal function and cardiovascular diseases in pre-dialysis chronic kidney disease patients

BACKGROUND

Tissue accumulation of advanced glycation end-products (AGE) is thought to be a contributing factor to the progression of cardiovascular disease (CVD). Skin autofluorescence, a non-invasive measure of AGE accumulation using autofluorescence of the skin under ultraviolet light, has shown associations with CVD in haemodialysis patients. The present study aimed to evaluate relationships of skin autofluorescence to renal function as well as CVD in pre-dialysis patients with chronic kidney disease (CKD).

METHODS

Subjects in this cross-sectional analysis comprised 304 pre-dialysis CKD patients [median age, 62.0 years; median estimated glomerular filtration rate (eGFR), 54.3 mL/min/1.73 m(2); diabetes, n = 81 (26.6%)]. AGE accumulation in skin was assessed by skin autofluorescence using an autofluorescence reader. Relationships between skin autofluorescence, eGFR, CVD history and other parameters were evaluated.

RESULTS

Skin autofluorescence correlated negatively with eGFR (r = -0.42, P < 0.01) and increased as CKD stage advanced. Multiple regression analysis revealed significant correlations of skin autofluorescence with age, presence of diabetes, eGFR and CVD history in CKD patients (R(2) = 30%). Age, male gender, smoking history, skin autofluorescence and eGFR were significantly correlated with CVD history, and multiple logistic regression analysis identified age [odds ratio (OR), 1.09; 95% confidence interval (CI), 1.03-1.15; P < 0.01], history of smoking (OR, 6.50; 95%CI, 1.94-21.83; P < 0.01) and skin autofluorescence (OR, 3.74; 95%CI, 1.54-9.24; P < 0.01) as independent factors.

CONCLUSIONS

Tissue AGE accumulation measured as skin autofluorescence increased as GFR decreased and was related to CVD history in CKD patients. Non-invasive autofluorescence readers may provide potential markers for clinical risk assessment in pre-dialysis CKD patients.

Glyoxalase I Glu111Ala polymorphism in patients with breast cancer

Effect of advanced glycation end products (AGEs) in the pathogenesis of cancer could be diminished by interaction with soluble RAGE or by reducing AGE-precursors via glyoxalase I. Glu111Ala polymorphism of glyoxalase I gene, AGEs, and sRAGE serum levels were studied in 113 breast cancer patients and in 58 controls. Higher frequency of the mutated C allele was found in patients with negative estrogen receptors and in patients in clinical stage III compared to controls (P< 0.05). The presence of the C allele could represent a negative prognostic factor; however, further studies are needed to confirm this hypothesis.

Serum Protein-Bound 3,4-Dihydroxyphenylalanine and Related Products of Protein Oxidation and Chronic Hemodialysis

INTRODUCTION

Protein-bound dihydroxyphenylalanine (PB-DOPA) and its oxidation products are formed by free radical and oxidative attack on proteins. Hemodialysis and uremic toxins can activate leukocytes leading to overproduction of reactive oxygen species such as hydrogen peroxide and hypochlorous acid (HOCl) that increases protein oxidation.

METHODS

We have used a sensitive fluorometric method to measure PB-DOPA and its oxidation products in proteins after gamma-irradiation and incubation with HOCl and in serum from hemodialysis patients and healthy controls. These PB-DOPA concentrations were compared with those measured by HPLC (PB-DOPAHPLC).

RESULTS

Fluorescent PB-DOPA increased linearly with increasing amounts of human serum and with increasing amounts of gamma-irradiated bovine serum albumin. Concentrations of fluorescent PB-DOPA paralleled PB-DOPAHPLC levels but were approximately 60-70 times higher. Incubation of BSA and human serum albumin (HSA) with HOCl (39.4 mM) significantly (P < 0.0001) increased fluorescent PB-DOPA by 5 fold and 10 fold respectively and PB-DOPAHPLC by 6-fold for both proteins Fluorescent PB-DOPA concentration increased significantly (P < 0.0001) by 16-fold in human serum incubated with HOCl (39.4 mM). Mean serum fluorescent PB-DOPA was significantly (P < 0.0001) higher in 19 hemodialysis patients (57.7 +/- 16.1 microM) compared with 21 healthy controls (33.5 +/- 3.7 microM). Mean PB-DOPAHPLC was 4.45 +/- 1.63 microM in the healthy controls and 12 hemodialysis patients had values within the range of values in these controls while five patients had values that were outside eight SDs of the mean for healthy subjects. Serum fluorescent PB-DOPA was not correlated significantly with PB-DOPAHPLC in these subjects.

CONCLUSIONS

The results of this study suggest that fluorophores of the type, which are derived from DOPA can be reproducibly measured in delipidated serum protein and that HOCl can increase levels of these fluorophores-generating proteins and may potentially contribute to the high levels in serum from hemodialysis patients. This high level of fluorescent PB-DOPA compounds is only partially due to authentic PB-DOPA and might also be derived from other related protein oxidation products including those from DOPA oxidation.

Free and total plasma malondialdehyde in chronic renal insufficiency and in dialysis patients

BACKGROUND

Available data about oxidative status in patients with end-stage renal disease (ESRD) or on dialysis are contradictory. The present cross-sectional study aimed to investigate the role of renal insufficiency and dialysis on lipid peroxidation. To separate the effects of uraemia from dialysis-induced stress, we enrolled 26 patients with renal insufficiency on conservative treatment (ESRD), 23 on peritoneal dialysis (PD), 30 on haemodialysis (HD) and 30 controls.

METHODS

Plasma malondialdehyde (MDA) levels, both total (tMDA) and free (fMDA), were measured as indexes of oxidative stress by gas chromatography-mass spectrometry. Bound MDA (bMDA) levels were calculated as the difference between tMDA and fMDA.

RESULTS

Total and bMDA concentrations were significantly higher in patients than in controls (ESRD > HD > PD). In PD and HD patients, fMDA levels were similar and significantly higher than in ESRD. Multivariate analysis, with tMDA, fMDA and bMDA as dependent variables, showed similar and significant tMDA and bMDA relations with residual renal function (t = -2.160, P = 0.035) and albumin (t = -2.049, P = 0.045). Erythropoietin dose affected only fMDA values (t = -2.178, P = 0.034).

CONCLUSIONS

Free and bMDA concentrations identified different MDA patterns. Bound MDA, not excreted by kidneys, accounts alone for high tMDA concentrations in ESRD patients, while both fMDA and bMDA contribute to tMDA values in dialysis patients. These findings show that increased tMDA could be indicative not only of recent lipid peroxidation, and they also highlight the importance of evaluating free, bound and total MDA in patients with reduced renal function in order to assess their oxidative status.

Mass spectrometric quantification of amino acid oxidation products identifies oxidative mechanisms of diabetic end-organ damage

Diabetes mellitus is increasingly prevalent worldwide. Diabetic individuals are at markedly increased risk for premature death due to cardiovascular disease. Furthermore, substantial morbidity results from microvascular complications which include retinopathy, nephropathy, and neuropathy. Clinical studies involving diabetic patients have suggested that degree of diabetic hyperglycemia correlates with risk of complications. Recent evidence implicates a central role for oxidative stress and vascular inflammation in all forms of insulin resistance, obesity, diabetes and its complications. Although, glucose promotes glycoxidation reactions in vitro and products of glycoxidation and lipoxidation are elevated in plasma and tissue in diabetics, the exact relationships among hyperglycemia, the diabetic state, and oxidative stress are not well-understood. Using a combination of in vitro and in vivo experiments, we have identified amino acid oxidation markers that serve as molecular fingerprints of specific oxidative pathways. Quantification of these products utilizing highly sensitive and specific gas chromatography/mass spectrometry in animal models of diabetic complications and in humans has provided insights in oxidative pathways that result in diabetic complications. Our studies strongly support the hypothesis that unique oxidants are generated in the microenvironment of tissues vulnerable to diabetic damage. Potential therapies interrupting these reactive pathways in target tissue are likely to be beneficial in preventing diabetic complications.

Diabetic threesome (hyperglycaemia, renal function and nutrition) and advanced glycation end products: evidence for the multiple-hit agent?

Complex chemical processes termed non-enzymic glycation that operate in vivo and similar chemical interactions between sugars and proteins that occur during thermal processing of food (known as the Maillard reaction) are one of the interesting examples of a potentially-harmful interaction between nutrition and disease. Non-enzymic glycation comprises a series of reactions between sugars, alpha-oxoaldehydes and other sugar derivatives and amino groups of amino acids, peptides and proteins leading to the formation of heterogeneous moieties collectively termed advanced glycation end products (AGE). AGE possess a wide range of chemical and biological properties and play a role in diabetes-related pathology as well as in several other diseases. Diabetes is, nevertheless, of particular interest for several reasons: (1) chronic hyperglycaemia provides the substrates for extracellular glycation as well as intracellular glycation; (2) hyperglycaemia-induced oxidative stress accelerates AGE formation in the process of glycoxidation; (3) AGE-modified proteins are subject to rapid intracellular proteolytic degradation releasing free AGE adducts into the circulation where they can bind to several pro-inflammatory receptors, especially receptor of AGE; (4) kidneys, which are principally involved in the excretion of free AGE adducts, might be damaged by diabetic nephropathy, which further enhances AGE toxicity because of diminished AGE clearance. Increased dietary intake of AGE in highly-processed foods may represent an additional exogenous metabolic burden in addition to AGE already present endogenously in subjects with diabetes. Finally, inter-individual genetic and functional variability in genes encoding enzymes and receptors involved in either the formation or the degradation of AGE could have important pathogenic, nutrigenomic and nutrigenetic consequences.

Proinflammatory effects of advanced lipoxidation end products in monocytes

OBJECTIVE

The reactions of carbohydrate- or lipid-derived intermediates with proteins lead to the formation of Maillard reaction products, which subsequently leads to the formation of advanced glycation/lipoxidation end products (AGE/ALEs). Levels of AGE/ALEs are increased in diseases like diabetes. Unlike AGEs, very little is known about ALE effects in vitro. We hypothesized that ALEs can have proinflammatory effects in monocytes.

RESEARCH DESIGN AND METHODS

In a profiling approach, conditioned media from THP-1 cells either cultured in normal glucose (5.5 mmol/l) or treated with MDA-Lys or MDA alone were hybridized to arrays containing antibodies to 120 known human cytokines/chemokines. Pathway analyses with bioinformatics software were used to identify signalling networks.

RESULTS

Synthetic ALE (malondialdehyde-lysine [MDA-Lys]) (50 micromol/l) could induce oxidant stress and also activate the transcriptional factor nuclear factor-kappaB (NF-kappaB) in THP-1 monocytes. MDA-Lys also significantly increased the expression of key candidate proinflammatory genes, interferon-gamma-inducible protein-10, beta1- and beta2-integrins, cyclooxygenase-2 (COX-2), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 and -8, and inducible nitric-oxide synthase, which are also associated with monocyte dysfunction. Several key target proinflammatory proteins were significantly induced by MDA-Lys relative to normal glucose or MDA alone, including MCP-1; tumor necrosis factor ligand superfamily member-14; chemokine CC motif ligand-11 (CCL11); growth-related oncogene-alpha, -beta, and -gamma; and chemokine CXC motif ligand-13. Bioinformatics analyses identified a network of chemokine signaling among MDA-Lys-regulated genes. MDA-Lys also increased monocyte binding to vascular smooth muscle and endothelial cells. Furthermore, plasma from diabetic rats showed significantly higher levels of MDA-Lys and CCL11.

CONCLUSIONS

These new results suggest that ALEs can promote monocyte activation and vascular complications via induction of inflammatory pathways and networks.

Evidence for increased risk of prediabetes in the uremic patient

A prediabetic state is defined as a higher than normal blood glucose level but not yet high enough to meet the diagnosis of overt diabetes mellitus. While patients with advanced diabetic nephropathy are vulnerable to hypoglycemia, we believe that there is sufficient evidence that uremic nondiabetic patients are susceptible to hyperglycemia, which calls for more attention that uremia is a prediabetic state. It is, therefore, intriguing to identify these uremic factors which lead to prediabetes. Such a study may have significance to improve uremic patients' outcomes. To raise the awareness of the uremic prediabetic state, this review will, therefore, elaborate on the analysis of factors important in the development of prediabetes in uremia and will delineate whether their modification leads to an improved patient outcome.

Advanced glycation end products and the absence of premature atherosclerosis in glycogen storage disease Ia

INTRODUCTION

Despite their unfavourable cardiovascular risk profile, patients with glycogen storage disease type Ia (GSD Ia) do not develop premature atherosclerosis. We hypothesized that this paradox might be related to a decreased formation of advanced glycation end products (AGEs) resulting from lifetime low plasma glucose levels and decreased oxidative stress.

METHODS

In 8 GSD Ia patients (age 20-34 years) and 30 matched controls we measured carotid intima-media thickness (IMT), skin autofluorescence (AF; a non-invasive index for AGEs), and specific AGEs (pentosidine, N-(carboxymethyl)lysine (CML), N-(carboxyethyl)lysine (CEL)) and collagen linked fluorescence (CLF, measured at excitation/emission wavelength combinations of 328/378 and 370/440 nm) in skin samples.

RESULTS

Carotid IMT was significantly lower in GSD Ia patients. Skin AF did not differ between patients and controls. The skin samples showed higher CEL levels in the patient group (p = 0.008), but similar levels of pentosidine, CML, and CLF. In the total group, skin AF correlated with CML (r = 0.39, p = 0.031), CLF 328/378 nm (r = 0.53; p = 0.002) and CLF 370/440 nm (r = 0.60; p = 0.001). In the control group, AF also correlated with the maximum carotid IMT (r = 0.6; p = 0.004).

CONCLUSION

Although our data confirm that GSD Ia patients present with a reduced burden of atherosclerosis, this phenomenon cannot be explained by differences in AGE accumulation as measured in the skin.

Mechanisms for oxidative stress in diabetic cardiovascular disease

Obesity, metabolic syndrome, and diabetes are increasingly prevalent in Western society, and they markedly increase the risk for atherosclerotic vascular disease, the major cause of death in diabetics. Although recent evidence suggests a causal role for oxidative stress in insulin resistance, diabetes, and atherosclerosis, there is considerable controversy regarding its nature, magnitude, and underlying mechanisms. Glucose promotes glycoxidation reactions in vitro, and products of glycoxidation and lipoxidation are elevated in plasma and tissue from humans suffering from diabetes, but the exact relationships between hyperglycemia and oxidative stress are poorly understood. This review focuses on molecular mechanisms of increased oxidative stress in diabetes, the relationship of oxidant production to hyperglycemia, and the potential interaction of reactive carbonyls and lipids in oxidant generation. Using highly sensitive and specific gas chromatography-mass spectrometry, molecular signatures of specific oxidation pathways were identified in tissues of diabetic humans and animals. These studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues promote diabetic damage. Therapies interrupting these reactive pathways in vascular tissue might help prevent cardiovascular disease in this high-risk population.

PON1 status in haemodialysis patients and the impact of hepatitis C infection

OBJECTIVES

Paraoxonase-1 (PON1) activity has been reported to decrease in both haemodialysis patients and patients with HCV infection. We aimed to investigate paraoxonase and arylesterase activities, and lipid hydroperoxide levels (LOOH) in haemodialysis patients with or without hepatitis C infection, and to find out whether PON1 activity is affected further by the presence of HCV infection in HD patients.

DESIGN AND METHODS

Twenty HCV (+) haemodialysis patients, 26 HCV (-) haemodialysis patients, and 26 controls were enrolled. Paraoxonase and arylesterase activities were measured spectrophotometrically. LOOH levels were measured by ferrous oxidation with xylenol orange assay.

RESULTS

Haemodialysis patients with or without HCV infection had lower paraoxonase and arylesterase activities than controls (all p<0.001), while higher LOOH levels (both p<0.001). Paraoxonase and arylesterase activities, and LOOH levels were comparable between haemodialysis patients with or without HCV infection (p>0.05). Significant inverse correlation was observed between paraoxonase or arylesterase activities, and LOOH levels (p<0.05, beta=-0.319 and p<0.05, beta=-0.348, respectively).

CONCLUSION

We concluded that PON1 activity significantly decreases in both haemodialysis patients with or without HCV infection. Nevertheless, PON1 activity is not affected further by the presence of HCV infection in haemodialysis patients.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Genomic Damage and Malignancy in End-Stage Renal Failure: Do Advanced Glycation End Products Contribute?

In end-stage renal disease (ESRD) there is not only excessive morbidity and mortality due to cardiovascular disease but also an enhanced occurrence of various types of cancer. Both are characterized by oxidative stress and inflammation as two of the central underlying causes of the disease states. In cancer, genomic damage has been demonstrated to be of high pathogenetic relevance. DNA lesions may induce mutations of oncogenes and tumor-suppressor genes which, in the long-run, may lead to malignancies if mutagenicity is not mitigated by repair mechanisms. A high incidence of genomic damage in ESRD patients has been validated by various biomarkers of DNA lesions. We reviewed the mechanisms of DNA damage, focusing in particular on the role of advanced glycation end products (AGEs) which accumulate markedly in renal insufficiency. Considering the in vitro and in vivo findings to date, one has to assume a significant role of AGEs in DNA damage and the potential development of cancer.

Vitamin C mediates chemical aging of lens crystallins by the Maillard reaction in a humanized mouse model

Senile cataracts are associated with progressive oxidation, fragmentation, cross-linking, insolubilization, and yellow pigmentation of lens crystallins. We hypothesized that the Maillard reaction, which leads browning and aroma development during the baking of foods, would occur between the lens proteins and the highly reactive oxidation products of vitamin C. To test this hypothesis, we engineered a mouse that selectively overexpresses the human vitamin C transporter SVCT2 in the lens. Consequently, lenticular levels of vitamin C and its oxidation products were 5- to 15-fold elevated, resulting in a highly compressed aging process and accelerated formation of several protein-bound advanced Maillard reaction products identical with those of aging human lens proteins. These data strongly implicate vitamin C in lens crystallin aging and may serve as a model for protein aging in other tissues particularly rich in vitamin C, such as the hippocampal neurons and the adrenal gland. The hSVCT2 mouse is expected to facilitate the search for drugs that inhibit damage by vitamin C oxidation products.

The Advanced Glycation End Product Nε-Carboxymethyllysine Is Not a Predictor of Cardiovascular Events and Renal Outcomes in Patients With Type 2 Diabetic Kidney Disease and Hypertension

BACKGROUND

Advanced glycation end products (AGEs) are implicated in the pathogenesis of vascular damage, especially in patients with diabetes and renal insufficiency. The oxidatively formed AGE N(epsilon)-carboxymethyllysine (CML) is thought to be a marker of oxidative stress.

METHODS

Four hundred fifty patients with type 2 diabetes and nephropathy from the Irbesartan in Diabetic Nephropathy Trial cohort (mean age, 58 +/- 8.2 years; 137 women, 313 men) with a mean glomerular filtration rate of 48.2 mL/min (0.80 mL/s; Modification of Diet in Renal Disease formula) were followed up for 2.6 years. Serum CML was measured by using an enzyme-linked immunosorbent assay. Relationships between CML levels, traditional risk factors, and cardiovascular and renal events were tested in Cox proportional hazards models.

RESULTS

Mean serum CML level was 599.9 +/- 276.0 ng/mL, and mean hemoglobin A1c level was 7.5% +/- 1.6%. One hundred forty-three first cardiovascular events occurred during follow-up; 74 patients died, 44 of cardiovascular causes. Final multivariate analysis showed age (relative risk [RR], 1.87; confidence interval [CI], 1.13 to 3.11; P = 0.016 for the highest compared with lowest quartile), history of prior cardiovascular events (RR, 1.96; CI, 1.35 to 2.85; P < 0.0005), and 24-hour urinary albumin-creatinine ratio (RR, 1.29; CI, 1.11 to 1.50 per doubling; P < 0.0005) to be independent risk factors for a first cardiovascular event, but not CML level. CML level also did not correlate significantly with renal outcome.

CONCLUSION

Serum CML level could not be identified as an independent risk factor for cardiovascular or renal outcomes in the examined population. This suggests that traditional risk factors might have a more important role for these end points or that other AGE compounds, as well as tissue AGE levels, might be of greater relevance compared with serum levels, which remains open to further study.

Impaired Muscle Oxygen Metabolism in Uremic Children: Improved After Renal Transplantation

BACKGROUND

The purpose of this study is to clarify skeletal muscle oxidative metabolism in children with end-stage renal disease (ESRD) before and after renal transplantation.

METHODS

We examined muscle oxygenation and metabolism by using noninvasive near-infrared spectroscopy in 10 patients (age, 12.4 +/- 3.1 years) 1 week before and 4 weeks after renal transplantation and in 10 controls (age, 12.8 +/- 2.6 years) during submaximal hand-grip exercise using the flexor digitorum superficialis muscle. We used 2 indicators to evaluate muscle metabolism. The rate of initial decrease in hemoglobin/myoglobin deoxygenation during arterial occlusion after exercise relative to the value at rest (S2/S1) was used as an indicator of mitochondrial oxygen consumption, whereas recovery time (TR) after exercise was used as an indicator of oxygen delivery to the muscle and aerobic capacity.

RESULTS

S2/S1 and TR after exercise were significantly lower in patients before renal transplantation compared with the control group (P < 0.05). S2/S1 and TR after exercise improved significantly after renal transplantation (P < 0.01, P < 0.05) and were not significantly different from those of controls.

CONCLUSION

Oxidative metabolism in skeletal muscle during exercise is impaired in children with ESRD and recovers after renal transplantation.

The role of mass spectrometry in the study of non-enzymatic protein glycation in diabetes: an update

Recent studies on non-enzymatic protein glycation are reviewed, and results are critically discussed. Advanced glycation end products (AGE) levels in the body reflect a balance between their formation and catabolism. AGE proteolysis leads to the formation of low-molecular-weight AGE (AGE peptides) that are normally excreted in urine. In the case of diabetic disease and/or renal failure, AGE peptides accumulate in plasma. Because of their high reactivity, these compounds have been thought to play a role in the progression of chronic complications. The structural identification of these compounds is particularly important, and a strategy has been designed for their possible definition. A series of experiments has been devoted to the study of the enzymatic degradation products of in vitro glycated human serum albumin (HSA). This approach, based on different MS methods (LC/ESI/MS, LC/ESI/FTMS, MALDI), led to the detection of the glycated peptides generated by digestion of HSA. A further study was devoted to the possible identification of the peptides identified in the glycated HSA digestion products in the plasma of diabetic and nephropatic subjects. No glycated HSA digestion products were found in plasma samples of the subjects under investigation even if clear differences were found among the LC runs from populations of healthy, diabetic, and nephropatic subjects. Parallel investigations were devoted to the evaluation of glyoxal and methylglyoxal-dicarbonyl compounds that originate at the intermediate stage of the Maillard reaction. This evaluation was performed in diabetic patients, before and after the achievement of good metabolic control, and in nephropatic patients subjected to peritoneal dialysis (PD). In the latter case, results indicated that these dicarbonyl compounds, already present in the dialysis fluids, show a decrease in plasma and in dialysis fluids; those data suggested their reaction at peritoneal membrane level.

Oxidative stress in hepatitis C infected end-stage renal disease subjects

BACKGROUND

Both uremia and hepatitis C infection is associated with increased oxidative stress. In the present study, we aimed to find out whether hepatitis C infection has any impact on oxidative stress in hemodialysis subjects.

METHODS

Sixteen hepatitis C (+) hemodialysis subjects, 24 hepatitis C negative hemodialysis subjects and 24 healthy subjects were included. Total antioxidant capacity, total peroxide level and oxidative stress index were determined in all subjects.

RESULTS

Total antioxidant capacity was significantly higher in controls than hemodialysis subjects with or without hepatitis C infection (all p < 0.05/3), while total peroxide level and oxidative stress index were significantly lower (all p < 0.05/3). Hepatitis C (-) hemodialysis subjects had higher total antioxidant capacity compared to hepatitis C (+) hemodialysis subjects (all p < 0.05/3). Total peroxide level and oxidative stress index was comparable between hemodialysis subjects with or without hepatitis C infection (p > 0.05/3).

CONCLUSION

Oxidative stress is increased in both hepatitis C (+) and hepatitis C (-) hemodialysis subjects. However, hepatitis C infection seems to not cause any additional increase in oxidative stress in hemodialysis subjects and it may be partly due to protective effect of dialysis treatment on hepatitis C infection.

Association of advanced glycoxidation end products and inflammation markers with thrombosis of arteriovenous grafts in hemodialysis patients

BACKGROUND/AIMS

Intimal hyperplasia at the venous anastomosis of arteriovenous dialysis grafts (AVGs) is a common and costly complication in hemodialysis (HD) patients. Previous studies have shown significant accumulation of advanced glycation end products (AGEs) within the lesions, suggesting a pathogenic role for these compounds in this condition.

METHODS

We retrospectively analyzed data from 139 HD patients, including 58 subjects with AVGs, to determine any relationship between serum AGEs and other circulating markers, e.g. C-reactive protein (CRP), tumor necrosis factor (TNF-alpha), vascular cell adhesion molecule-1 (VCAM-1), plasminogen activator inhibitor type 1 and vascular endothelial growth factor, with the presence of graft thrombosis, an index of venous intimal hyperplasia.

RESULTS

Patients with previously thrombosed AVGs exhibited significantly higher levels of serum AGEs (42 +/- 18 vs. 28+/- 8 U/ml), CRP (1.4 +/- 1.1 vs. 0.6 +/- 0.4 mg/dl) and VCAM-1 (3,172 +/- 696 vs. 2,447 +/- 1,101 ng/ml) than those with uncomplicated AVGs, variances that were mostly attributed to diabetes difference. There was no difference regarding the levels of the parameters studied between patients with AVGs and other forms of vascular access.

CONCLUSIONS

These results support an association between circulating AGEs, markers of inflammation and endothelial function and intimal hyperplasia at the venous anastomosis of AVGs in HD patients. The implication is that there may be a therapeutic role for anti-AGE interventions in the management of this common clinical condition.

Evaluation of Glyoxal and Methylglyoxal Levels in Uremic Patients under Peritoneal Dialysis

Advanced glycation end products (AGEs) accumulate in serum and tissues of patients with chronic renal failure, even in the absence of diabetes, and a different clearance of these species has been observed by hemodialysis and peritoneal dialysis (CAPD). Furthermore, it has been shown that not only AGE but also 1,2-dicarbonyl compounds are formed during heat sterilization of glucose-based peritoneal dialysis fluids. Therefore, we investigated the level of some AGEs (pentosidine and free pentosidine) and dicarbonyl compounds (glyoxal and methylglyoxal) in end-stage renal disease patients subjected to peritoneal dialysis. Samples (20 from healthy subjects, 16 from uremic patients before and after 12 h of peritoneal dialysis) were analyzed, and the plasma and dialysate levels of glyoxal, methylglyoxal, pentosidine, and free pentosidine were determined. In plasma of uremic patients, mean values of pentosidine showed a small decrease after dialysis and were always higher than those of healthy control subjects. An analogous trend was observed for free pentosidine. In the case of peritoneal dialysate, no pentosidine and free pentosidine were found at time zero, whereas both compounds were detected after 12 h of dialysis. Glyoxal and methylglyoxal mean levels showed a decrease in plasma after dialysis even if their values were always higher than those of healthy control subjects. Surprisingly, an analogous trend was observed also in dialysate. These results might indicate that glyoxal and methylglyoxal already present in the dialysis fluid react with the peritoneal matrix proteins, accounting for the gradual loss of peritoneal membrane function that is often observed in patients subjected to CAPD for a long time.

Pentosidine and Its Deposition in Renal Tissue in Renal Transplantation

BACKGROUND

Advanced glycation end products (AGEs) accumulate in lesions of arteriosclerosis, Alzheimer's disease, rheumatoid arthritis, diabetic retinopathy, and diabetic nephropathy. Among AGEs, chemical quantification and immunohistologic methods for pentosidine have been established. Free pentosidine-eliminated by renal excretion- is mainly affected by renal function. In this study, we measured concentrations of plasma free and total pentosidine and immunohistologically investigated kidney graft biopsy specimens in patients after renal transplantation to investigate the renal function, plasma free and total pentosidine, and its relationship with deposition in the renal tissue.

PATIENTS AND METHODS

In 28 patients who underwent renal transplantation from 1996 to 2003, we measured the time course of plasma concentrations of free pentosidine, total pentosidine, and serum creatinine starting right after renal transplantation. Thirty-four graft biopsy specimens were immunohistologically investigated using anti-pentosidine antibody. Plasma free and total pentosidine, and serum creatinine were measured at the same time.

RESULTS

Plasma free and total pentosidine were positively correlated with serum creatinine. Plasma free pentosidine and serum creatinine reached nadir values on day 34.2 +/- 14.2, when the blood concentrations were 5.1 +/- 1.6 pmol/mL and 1.7 +/- 0.7 mg/dL, respectively. Plasma total pentosidine reached a nadir on day 116.5 +/- 39.7 when the plasma concentration was 4.0 +/- 1.5 pmol/mg. We correlated the time required to reach the nadir of plasma free and total pentosidine concentrations. However, neither the concentration of plasma free nor plasma total pentosidine at nadir correlated with serum creatinine. The intensity of immunostaining with anti-pentosidine antibody in proximal tubular cells was graded as weakly positive, positive, or strongly positive. Significant differences were obtained among plasma free pentosidine values between the weakly positive and strongly positive groups.

CONCLUSIONS

Renal transplantation improves renal function and decreases renal excretion of free pentosidine. Accordingly, total pentosidine also decreases. However, the concentrations of plasma free and total pentosidine at nadir varied among individuals; the blood concentrations were not determined by renal function alone. It was suggested that deposition of pentosidine in proximal tubular cells was more severe among patients with higher plasma free pentosidine and serum creatinine values.