Advanced glycation end products in renal failure

Non-enzymatic modification of aminophospholipids induces angiogenesis, inflammation, and insulin signaling dysregulation in human renal glomerular endothelial cells in vitro

AIMS/HYPOTHESIS

Advanced glycation end-products (AGEs) formation in proteins are involved in healthy aging and a variety of diseases including Alzheimer's disease, atherosclerosis, and diabetic complications. However, the biological effects of the non-enzymatic modification of aminophospholipids (lipid-AGEs) at cellular level are poorly understood. This study aimed to investigate the effects of lipid-AGEs on angiogenesis, inflammation, insulin signaling, and mitochondrial function in human renal glomerular endothelial cells (HRGEC), exploring their potential role in the pathophysiology of diabetic nephropathy (DN).

METHODS

HRGEC cells were exposed to non-enzymatically modified phosphatidylethanolamine (PE) by AGEs (lipid-AGEs), non-modified PE (nmPE) (aminophospholipid without modification), employed as a negative control, and lipopolysaccharides (LPS) as a positive control. Angiogenesis was assessed through vascular network formation metrics, including capillary area, junction density, and endpoints, under different extracellular matrices. Gene expression of inflammatory and angiogenic markers was quantified by RT-qPCR. Insulin signaling components, including IRS1 and AKT phosphorylation, were evaluated by immunoblotting. Mitochondrial function was assessed using high-resolution respirometry to determine ATP production rates from glycolysis and oxidative phosphorylation.

RESULTS

Lipid-AGEs induced dose-, time-, and matrix-dependent angiogenesis, with effects comparable to LPS, particularly in Engelbreth-Holm-Swarm extracellular matrix (ECM) (capillary area increase: 25 %, p < 0.05). Lipid-AGEs significantly upregulated the expression of inflammatory genes IL8 and NFKB (p < 0.05), and the angiogenesis-related markers TGFB1 and ANGPT2 (p < 0.05). Insulin signaling was disrupted, as lipid-AGEs enhanced inhibitory phosphorylation of IRS1 (Ser-1101, 1.8-fold increase, p < 0.01) and modulated AKT (Ser-473) and p42/p44 ERK activation. At lower doses, lipid-AGEs reduced eNOS phosphorylation (p < 0.05) impairing insulin responsiveness. High-resolution respirometry revealed that lipid-AGEs reduced basal oxygen consumption rates (OCR) by 20 % (p < 0.05), with no significant changes in glycolytic ATP production.

CONCLUSION

Lipid-AGEs induce angiogenesis, inflammation, and insulin signaling disruption in HRGEC, contributing to endothelial dysfunction. These findings underscore the potential role of lipid-AGEs in age-related decline of renal function, as well as the pathogenic potential in DN highlighting their relevance as therapeutic targets for mitigating vascular and metabolic complications in diabetes.

The Potential Role of Advanced Glycation End Products in the Development of Kidney Disease

Advanced glycation end products (AGEs) represent a class of toxic and irreversible compounds formed through non-enzymatic reactions between proteins or lipids and carbonyl compounds. AGEs can arise endogenously under normal metabolic conditions and in pathological states such as diabetes, kidney disease, and inflammatory disorders. Additionally, they can be obtained exogenously through dietary intake, particularly from foods high in fat or sugar, as well as grilled and processed items. AGEs accumulate in various organs and have been increasingly recognized as significant contributors to the progression of numerous diseases, particularly kidney disease. As the kidney plays a crucial role in AGE metabolism and excretion, it is highly susceptible to AGE-induced damage. In this review, we provide a comprehensive discussion on the role of AGEs in the onset and progression of various kidney diseases, including diabetic nephropathy, chronic kidney disease, and acute kidney injury. We explore the potential biological mechanisms involved, such as AGE accumulation, the AGEs-RAGE axis, oxidative stress, inflammation, gut microbiota dysbiosis, and AGE-induced DNA damage. Furthermore, we discuss recent findings on the metabolic characteristics of AGEs in vivo and their pathogenic impact on renal function. Additionally, we examine the clinical significance of AGEs in the early diagnosis, treatment, and prognosis of kidney diseases, highlighting their potential as biomarkers and therapeutic targets. By integrating recent advancements in AGE research, this review aims to provide new insights and strategies for mitigating AGE-related renal damage and improving kidney disease management.

The receptor for advanced glycation end products and its ligands' expression in OVE26 diabetic sciatic nerve during the development of length-dependent neuropathy

Type 1 diabetes (T1D) may affect the peripheral nervous system and alter the expression of proteins contributing to inflammation and cellular cytoskeleton dysfunction, in most cases leading to the development of diabetic length-dependent neuropathy (DLDN). In the present study, we performed immunohistochemistry (IHC) to probe the expression of the receptor for advanced glycation end products (RAGE); its key ligands, high-mobility group box 1 (HMGB1), S100 calcium-binding protein B (S100B), and carboxymethyl-lysine (CML - advanced glycation end products (AGE)); and its cytoplasmic tail-binding partner, diaphanous related formin 1 (DIAPH1) and associated molecules, beta-actin (ACTB) and profilin 1 (PFN1) proteins in sciatic nerves harvested from seven-month old FVB/OVE26 mice with genetically-mediated T1D. We found that the amount of RAGE, HMGB1, and S100B proteins was elevated in diabetic vs the non-diabetic groups, while the amount of DIAPH1, ACTB, as well as PFN1 proteins did not differ between these groups. Moreover, our data revealed linear dependence between RAGE and HMGB1 proteins. Interaction criss-cross of selected sets of proteins in the sciatic nerve revealed that there were connected in a singular network. Our results indicate that T1D may alter expression patterns of RAGE axis proteins and thus contribute to DLDN.

The Role of Advanced Glycation End Products and Its Soluble Receptor in Kidney Diseases

Patients with chronic kidney disease (CKD) are more prone to oxidative stress and chronic inflammation, which may lead to an increase in the synthesis of advanced glycation end products (AGEs). Because AGEs are mostly removed by healthy kidneys, AGE accumulation is a result of both increased production and decreased kidney clearance. On the other hand, AGEs may potentially hasten decreasing kidney function in CKD patients, and are independently related to all-cause mortality. They are one of the non-traditional risk factors that play a significant role in the underlying processes that lead to excessive cardiovascular disease in CKD patients. When AGEs interact with their cell-bound receptor (RAGE), cell dysfunction is initiated by activating nuclear factor kappa-B (NF-κB), increasing the production and release of inflammatory cytokines. Alterations in the AGE-RAGE system have been related to the development of several chronic kidney diseases. Soluble RAGE (sRAGE) is a decoy receptor that suppresses membrane-bound RAGE activation and AGE-RAGE-related toxicity. sRAGE, and more specifically, the AGE/sRAGE ratio, may be promising tools for predicting the prognosis of kidney diseases. In the present review, we discuss the potential role of AGEs and sRAGE as biomarkers in different kidney pathologies.

Use of Continuous Glucose Monitoring in the Assessment and Management of Patients With Diabetes and Chronic Kidney Disease

In developed countries, diabetes is the leading cause of chronic kidney disease (CKD) and accounts for 50% of incidence of end stage kidney disease. Despite declining prevalence of micro- and macrovascular complications, there are rising trends in renal replacement therapy in diabetes. Optimal glycemic control may reduce risk of progression of CKD and related death. However, assessing glycemic control in patients with advanced CKD and on dialysis (G4-5) can be challenging. Laboratory biomarkers, such as glycated haemoglobin (HbA_1c), may be biased by abnormalities in blood haemoglobin, use of iron therapy and erythropoiesis-stimulating agents and chronic inflammation due to uraemia. Similarly, glycated albumin and fructosamine may be biased by abnormal protein turnover. Patients with advanced CKD exhibited heterogeneity in glycemic control ranging from severe insulin resistance to 'burnt-out' beta-cell function. They also had high risk of hypoglycaemia due to reduced renal gluconeogenesis, frequent use of insulin and dysregulation of counterregulatory hormones. Continuous glucose monitoring (CGM) systems measure glucose in interstitial fluid every few minutes and provide an alternative and more reliable method of glycemic assessment, including asymptomatic hypoglycaemia and hyperglycaemic excursions. Recent international guidelines recommended use of CGM-derived Glucose Management Index (GMI) in patients with advanced CKD although data are scarce in this population. Using CGM, patients with CKD were found to experience marked glycemic fluctuations with hypoglycemia due to loss of glucose and insulin during haemodialysis (HD) followed by hyperglycemia in the post-HD period. On the other hand, during peritoneal dialysis, patients may experience glycemic excursions with influx of glucose from dialysate solutions. These undesirable glucose exposure and variability may accelerate decline of residual renal function. Although CGM may improve the quality of glycemic monitoring and control in populations with CKD, further studies are needed to confirm the accuracy, optimal mode and frequency of CGM as well as their cost-effectiveness and user-acceptability in patients with advanced CKD and dialysis.

Glyoxal-Lysine Dimer, an Advanced Glycation End Product, Induces Oxidative Damage and Inflammatory Response by Interacting with RAGE

The glyoxal-lysine dimer (GOLD), which is a glyoxal (GO)-derived advanced glycation end product (AGE), is produced by the glycation reaction. In this study, we evaluated the effect of GOLD on the oxidative damage and inflammatory response in SV40 MES 13 mesangial cells. GOLD significantly increased the linkage with the V-type immunoglobulin domain of RAGE, a specific receptor of AGE. We found that GOLD treatment increased RAGE expression and reactive oxygen species (ROS) production in mesangial cells. GOLD remarkably regulated the protein and mRNA expression of nuclear factor erythroid 2-related factor 2 (NRF2) and glyoxalase 1 (GLO1). In addition, mitochondrial deterioration and inflammation occurred via GOLD-induced oxidative stress in mesangial cells. GOLD regulated the mitogen-activated protein kinase (MAPK) and the release of proinflammatory cytokines associated with the inflammatory mechanism of mesangial cells. Furthermore, oxidative stress and inflammatory responses triggered by GOLD were suppressed through RAGE inhibition using RAGE siRNA. These results demonstrate that the interaction of GOLD and RAGE plays an important role in the function of mesangial cells.

Dietary Quercetin Reduces Plasma and Tissue Methylglyoxal and Advanced Glycation End Products in Healthy Mice Treated with Methylglyoxal

BACKGROUND

Methylglyoxal (MGO), a precursor of advanced glycation end products (AGEs), has been linked to AGEs-associated diseases.

OBJECTIVES

This study investigated the efficacy and mechanisms of dietary quercetin in decreasing plasma and tissue concentrations of MGO and AGEs in MGO-administered mice.

METHODS

Male, 6-wk-old CD-1 mice were administered AIN-93G diet and water (Con) or 0.12% MGO in water (MGO) or MGO plus 0.2% (0.2Q) dietary quercetin for 1 wk (n = 5) (experiment 1), and water (Con), 0.12% MGO (MGO), or MGO plus 0.1% (0.1Q), 0.2% (0.2Q), or 0.4% (0.4Q) dietary quercetin for 6 wk (n = 10) (experiment 2). The plasma, kidney, and liver concentrations of MGO, quercetin, and isorhamnetin and their trapping adducts with MGO were determined by LC-MS, and AGE concentrations were measured by the fluorescent method. Furthermore, the expressions of glyoxalase I/II (GLO I/II) and aldose reductase (AR), MGO detoxification enzymes, were determined by Western blot. One-factor ANOVA and post hoc Dunnett's or Tukey's test were used to analyze the data.

RESULTS

After 1 wk of treatment, the MGO concentrations in plasma (20.2%) and kidney (29.9%) in 0.2Q mice were significantly lower than those in MGO mice. After 6 wk of treatment, the concentrations of MGO in the plasma (14.7-18.6%), kidney (20-20.8%), liver (15.4-18.6%), and tissue AGEs (28-36.8%) in 0.1Q, 0.2Q, and 0.4Q mice were significantly lower than those in MGO mice. The plasma concentrations of quercetin, isorhamnetin, and their MGO adducts were dose-dependently increased after quercetin administration. In addition, after 6 wk of quercetin administration, the expressions of GLO I/II and AR in the liver and kidney were significantly upregulated to promote MGO detoxification compared with MGO-treated mice.

CONCLUSIONS

Quercetin reduced plasma and tissue MGO concentrations and inhibited AGE formation by trapping MGO and regulating the MGO detoxification systems in MGO-administered healthy mice.

The cross-talk between RAGE and DIAPH1 in neurological complications of diabetes: A review

Neuropathy, or dysfunction of peripheral nerve, is one of the most common neurological manifestation in patients with diabetes mellitus (DM). DM is typically associated with a hyperglycaemic milieu, which promotes non-enzymatic glycation of proteins. Proteins with advanced glycation are known to engage a cell-surface receptor called the receptor for advanced glycation end products (RAGE). Thus, it is reasonable to assume that RAGE and its associated molecule-mediated cellular signalling may contribute to DM-induced symmetrical axonal (length-dependent) neuropathy. Of particular interest is diaphanous related formin 1 (DIAPH1), a cytoskeletal organizing molecule, which interacts with the cytosolic domain of RAGE and whose dysfunction may precipitate axonopathy/neuropathy. Indeed, it has been demonstrated that both RAGE and DIAPH1 are expressed in the motor and sensory fibres of nerve harvested from DM animal models. Although the detailed molecular role of RAGE and DIAPH1 in diabetic neurological complications remains unclear, here we will discuss available evidence of their involvement in peripheral diabetic neuropathy. Specifically, we will discuss how a hyperglycaemic environment is not only likely to elevate advanced glycation end products (ligands of RAGE) and induce a pro-inflammatory environment but also alter signalling via RAGE and DIAPH1. Further, hyperglycaemia may regulate epigenetic mechanisms that interacts with RAGE signalling. We suggest the cumulative effect of hyperglycaemia on RAGE-DIAPH1-mediated signalling may be disruptive to axonal cytoskeletal organization and transport and is therefore likely to play a key role in pathogenesis of diabetic symmetrical axonal neuropathy.

Diabetes mellitus in chronic kidney disease: Biomarkers beyond HbA1c to estimate glycemic control and diabetes-dependent morbidity and mortality

Diabetes mellitus (DM) is the leading cause of chronic kidney disease (CKD). Optimal glycemic control contributes to improved outcomes in patients with DM, particularly for microvascular damage, but blood glucose levels are too variable to provide an accurate assessment and instead markers averaging long-term glycemic load are used. The most established glycemic biomarker of long-term glycemic control is HbA1c. Nevertheless, HbA1c has pitfalls that limit its accuracy to estimate glycemic control, including the presence of altered red blood cell survival, hemoglobin glycation and suboptimal performance of HbA1c assays. Alternative methods to evaluate glycemic control in patients with DM include glycated albumin, fructosamine, 1-5 anhydroglucitol, continuous glucose measurement, self-monitoring of blood glucose and random blood glucose concentration measurements. Accordingly, our aim was to review the advantages and pitfalls of these methods in the context of CKD.

AcDCXR Is a Cowpea Aphid Effector With Putative Roles in Altering Host Immunity and Physiology

Cowpea, Vigna unguiculata, is a crop that is essential to semiarid areas of the world like Sub-Sahara Africa. Cowpea is highly susceptible to cowpea aphid, Aphis craccivora, infestation that can lead to major yield losses. Aphids feed on their host plant by inserting their hypodermal needlelike flexible stylets into the plant to reach the phloem sap. During feeding, aphids secrete saliva, containing effector proteins, into the plant to disrupt plant immune responses and alter the physiology of the plant to their own advantage. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify the salivary proteome of the cowpea aphid. About 150 candidate proteins were identified including diacetyl/L-xylulose reductase (DCXR), a novel enzyme previously unidentified in aphid saliva. DCXR is a member of short-chain dehydrogenases/reductases with dual enzymatic functions in carbohydrate and dicarbonyl metabolism. To assess whether cowpea aphid DCXR (AcDCXR) has similar functions, recombinant AcDCXR was purified and assayed enzymatically. For carbohydrate metabolism, the oxidation of xylitol to xylulose was tested. The dicarbonyl reaction involved the reduction of methylglyoxal, an α-β-dicarbonyl ketoaldehyde, known as an abiotic and biotic stress response molecule causing cytotoxicity at high concentrations. To assess whether cowpea aphids induce methylglyoxal in plants, we measured methylglyoxal levels in both cowpea and pea (Pisum sativum) plants and found them elevated transiently after aphid infestation. Agrobacterium-mediated transient overexpression of AcDCXR in pea resulted in an increase of cowpea aphid fecundity. Taken together, our results indicate that AcDCXR is an effector with a putative ability to generate additional sources of energy to the aphid and to alter plant defense responses. In addition, this work identified methylglyoxal as a potential novel aphid defense metabolite adding to the known repertoire of plant defenses against aphid pests.

Advanced Glycated apoA-IV Loses Its Ability to Prevent the LPS-Induced Reduction in Cholesterol Efflux-Related Gene Expression in Macrophages

We addressed how advanced glycation (AGE) affects the ability of apoA-IV to impair inflammation and restore the expression of genes involved in cholesterol efflux in lipopolysaccharide- (LPS-) treated macrophages. Recombinant human apoA-IV was nonenzymatically glycated by incubation with glycolaldehyde (GAD), incubated with cholesterol-loaded bone marrow-derived macrophages (BMDMs), and then stimulated with LPS prior to measurement of proinflammatory cytokines by ELISA. Genes involved in cholesterol efflux were quantified by RT-qPCR, and cholesterol efflux was measured by liquid scintillation counting. Carboxymethyllysine (CML) and pyrraline (PYR) levels, determined by Liquid Chromatography-Mass Spectrometry (LC-MS/MS), were greater in AGE-modified apoA-IV (AGE-apoA-IV) compared to unmodified-apoA-IV. AGE-apoA-IV inhibited expression of interleukin 6 (Il6), TNF-alpha (Tnf), IL-1 beta (Il1b), toll-like receptor 4 (Tlr4), tumor necrosis factor receptor-associated factor 6 (Traf6), Janus kinase 2/signal transducer and activator of transcription 3 (Jak2/Stat3), nuclear factor kappa B (Nfkb), and AGE receptor 1 (Ddost) as well as IL-6 and TNF-alpha secretion. AGE-apoA-IV alone did not change cholesterol efflux or ABCA-1 levels but was unable to restore the LPS-induced reduction in expression of Abca1 and Abcg1. AGE-apoA-IV inhibited inflammation but lost its ability to counteract the LPS-induced changes in expression of genes involved in macrophage cholesterol efflux that may contribute to atherosclerosis.

Hemodialysis biomarkers: total advanced glycation end products (AGEs) against oxidized human serum albumin (HSAox)

AIMS

Nephropathic patients show higher levels of advanced glycation end products (AGEs) and oxidized human serum albumin (HSAox) compared to healthy subjects. These two classes of compounds are formed as the result of oxidative insults; for this reason, they can be useful oxidative stress biomarkers. The present study examines the variation of AGEs and HSAox in hemodialysis (HD) patients before and after dialysis session, evaluating the impact of different dialytic techniques and filters on their removal.

METHODS

A total of 50 healthy subjects (control group) and 130 HD patients were enrolled in the study. Hemodialysis patients were subdivided based on dialytic techniques: 109 in diffusive technique and 22 in convective technique. We monitored HSAox, AGEs and other laboratory parameters at early morning in healthy subjects and in HD patients before and after the dialysis procedures.

RESULTS

The level of HSAox decreases after a single dialytic session (from 58.5 ± 8.8% to 41.5 ± 11.1%), but the concentration of total AGEs increases regardless of adopted dialytic techniques (from 6.8 ± 5.2 µg/ml to 9.2 ± 4.4 µg/ml). In our study, levels of HSAox and total AGEs are similar in diabetic and non-diabetic HD patients. The increase in total AGEs after dialysis was only observed using polysulfone filters but was absent with polymethacrylate filters.

CONCLUSIONS

HSAox is a simple and immediate method to verify the beneficial effect of a single dialysis session on the redox imbalance, always present in HD patients. Total AGEs assayed by ELISA procedure seem to be a less reliable biomarker in this population.

Glycation Damage: A Possible Hub for Major Pathophysiological Disorders and Aging

Glycation is both a physiological and pathological process which mainly affects proteins, nucleic acids and lipids. Exogenous and endogenous glycation produces deleterious reactions that take place principally in the extracellular matrix environment or within the cell cytosol and organelles. Advanced glycation end product (AGE) formation begins by the non-enzymatic glycation of free amino groups by sugars and aldehydes which leads to a succession of rearrangements of intermediate compounds and ultimately to irreversibly bound products known as AGEs. Epigenetic factors, oxidative stress, UV and nutrition are important causes of the accumulation of chemically and structurally different AGEs with various biological reactivities. Cross-linked proteins, deriving from the glycation process, present both an altered structure and function. Nucleotides and lipids are particularly vulnerable targets which can in turn favor DNA mutation or a decrease in cell membrane integrity and associated biological pathways respectively. In mitochondria, the consequences of glycation can alter bioenergy production. Under physiological conditions, anti-glycation defenses are sufficient, with proteasomes preventing accumulation of glycated proteins, while lipid turnover clears glycated products and nucleotide excision repair removes glycated nucleotides. If this does not occur, glycation damage accumulates, and pathologies may develop. Glycation-induced biological products are known to be mainly associated with aging, neurodegenerative disorders, diabetes and its complications, atherosclerosis, renal failure, immunological changes, retinopathy, skin photoaging, osteoporosis, and progression of some tumors.

The Role of Advanced Glycation End Products in Aging and Metabolic Diseases: Bridging Association and Causality

Accumulation of advanced glycation end products (AGEs) on nucleotides, lipids, and peptides/proteins are an inevitable component of the aging process in all eukaryotic organisms, including humans. To date, a substantial body of evidence shows that AGEs and their functionally compromised adducts are linked to and perhaps responsible for changes seen during aging and for the development of many age-related morbidities. However, much remains to be learned about the biology of AGE formation, causal nature of these associations, and whether new interventions might be developed that will prevent or reduce the negative impact of AGEs-related damage. To facilitate achieving these latter ends, we show how invertebrate models, notably Drosophila melanogaster and Caenorhabditis elegans, can be used to explore AGE-related pathways in depth and to identify and assess drugs that will mitigate against the detrimental effects of AGE-adduct development.

Circulating Concentrations of Advanced Glycation end Products, its Association With the Development of Diabetes Mellitus

BACKGROUND

Diabetes Mellitus (DM) is characterized by the production and accumulation of advanced glycation end products (AGEs), which are one of the key mechanisms in the development of its chronic complications.

AIMS OF THE STUDY

To assess the serum AGEs concentration by a radioimmunoassay (RIA) developed in our laboratory, to establish reference values in healthy population and to evaluate the diagnostic potential of measuring longitudinal changes in circulating AGEs concentrations to predict the development of DM.

METHODS

Clinical and metabolic parameters were obtained from a cohort of 781 Mexican people, initially and then seven years later. AGEs were quantified by a specific RIA. Associations of the changes in circulating levels of AGEs with the appearance of impaired fasting glucose (IFG), and the development of DM were evaluated.

RESULTS

Diabetic subjects had higher circulating levels of AGEs than normoglycemic subjects or individuals with IFG in both samples studied (471 vs. 246 and 342 μU/mL, p <0.001; and 912 vs. 428 and 519 μU/mL, p <0.001; respectively). A multinomial logistic regression analysis showed that subjects who had AGEs concentration ≥400 μU/mL in the baseline sample had a relative risk ratio of 1.98 to develop IFG seven years later (p = 0.003). While the subjects who had AGEs concentration ≥450 μU/mL in the baseline sample had a relative risk ratio of 10.7 to develop DM seven years later (p <0.001).

CONCLUSIONS

Circulating AGEs concentration is a good early marker to predict risk of developing DM.

Increased Levels of sRAGE in Diabetic CKD-G5D Patients: A Potential Protective Mechanism against AGE-Related Upregulation of Fibroblast Growth Factor 23 and Inflammation

Advanced glycation end products (AGEs) may induce cardiac remodeling in kidney disease by promoting fibroblast growth factor 23 (FGF-23) expression. Since AGEs are increased in diabetes mellitus (DM), our first aim was to evaluate the existence of any potential association between AGEs, FGF-23, inflammation, and increased cardiovascular risk in DM patients on dialysis (CKD-G5D). Secondarily, we explored the potential role of the soluble receptor for AGEs (sRAGE) as a marker of heart failure. Levels of glycated albumin (GA), sRAGE, c-terminal FGF-23 (cFGF-23), brain natriuretic peptide (BNP), and inflammatory mediators were compared between DM and non-DM CKD-G5D patients. The levels of sRAGE, cFGF-23, BNP, and proinflammatory markers were over the ranges of normality in both DM and non-DM groups. Only GA and sRAGE levels were increased in DM compared to non-DM patients. Plasma levels of sRAGE and CRP were the only independent predictors of BNP concentration. In conclusion, in DM CKD-G5D patients, sRAGE appeared to be a marker of cardiac remodeling. Indeed, its increase could be a potential protective mechanism against the increased risk of cardiovascular complications related to AGEs and inflammation. The causal relationship between sRAGE and cardiovascular risk in these patients needs to be further confirmed by mechanistic studies.

An association of cognitive impairment with diabetes and retinopathy in end stage renal disease patients under peritoneal dialysis

Background

Diabetes and retinopathy have been considered as risk factors of cognitive impairment (CI) in previous studies. We investigated both of these two factors and their relationship with global and specific cognitive functions in end stage renal disease patients under peritoneal dialysis (PD).

Methods

In this multicenter cross-sectional study, 424 clinically stable patients were enrolled from 5 PD units, who performed PD for at least three months and completed fundoscopy examination if they had diabetes. Global cognitive function was measured using the Modified Mini-Mental State Examination (3MS), Trail-Making Test forms A and B for executive function, and subtests of the Battery for the Assessment of Neuropsychological Status for immediate and delayed memory, visuospatial skills, and language ability.

Results

PD Patients with DM and Retinopathy had significantly higher prevalence of CI, executive dysfunction, impaired immediate memory and visuospatial skill, compared with patients in non-DM group. By multivariate logistic regression analyses, DM and retinopathy rather than DM only were significantly associated with increased risk for CI, executive dysfunction, impaired immediate memory and visuospatial skill, odds ratios(ORs) and 95% confidence intervals were 2.09[1.11,3.92], 2.89[1.55,5.37], 2.16 [1.15,4.06] and 2.37[1.32,4.22], respectively (all P < 0.05).

Conclusions

Diabetic PD patients with retinopathy were at two times risk for overall cognitive impairment, executive dysfunction, impaired immediate memory and visuospatial skill as compared to non-diabetic PD patients.

Co-Expression Analysis of Blood Cell Genome Expression to Preliminary Investigation of Regulatory Mechanisms in Uremia

Background

Uremia involves a series of clinical manifestations and is a common syndrome that occurs in nearly all end-stage kidney diseases. However, the exact genetic and/or molecular mechanisms that underlie uremia remain poorly understood.

Material/Methods

In this case-control study, we analyzed whole-genome microarray of 75 uremia patients and 20 healthy controls to investigate changes in gene expression and cellular mechanisms relevant to uremia. Gene co-expression network analysis was performed to construct co-expression networks using differentially expressed genes (DEGs) in uremia. We then determined hub models of co-expressed gene networks by MCODE, and we used miRNA enrichment analysis to detect key miRNAs in each hub module.

Results

We found nine co-expressed hub modules implicated in uremia. These modules were enriched in specific biological functions, including “proteolysis”, “membrane-enclosed lumen”, and “apoptosis”. Finally, miRNA enrichment analysis to detect key miRNAs in each hub module found 15 miRNAs that were specifically targeted to uremia-related hub modules. Of these, miRNA-21-3p and miRNA-210-3p have been identified in other studies as being important for uremia.

Conclusions

In summary, our study connected biological functions, genes, and miRNAs that underpin the network modules that can be used to elucidate the molecular mechanisms involved in uremia.

Dietary consumption of advanced glycation end products and risk of metabolic syndrome

Metabolic syndrome (MetS) is a complex disorder which has become one of the major public health challenges worldwide. This study was conducted to evaluate the association between dietary advanced glycation end products (AGEs) and risk of MetS and its components. This cross-sectional study was conducted in a representative sample of 5848 adults, aged 19-70 years. Daily consumption of carboxymethyl lysine, a major type of AGEs, was determined using a validated semi-quantitative food frequency questionnaire. Across increasing trend of AGEs consumption, the percentage of fat intake increased and that of carbohydrate significantly decreased (p < 0.001). Subjects in the highest (>10,506 kU/d) compared to the lowest (<6673 kU/d) quartile category of AGEs had higher risk of abdominal obesity (OR: 1.19, 95% CI: 1.01-1.39) and hypertriglyceridemia (OR: 1.26, 95% CI: 1.07-1.49). Therefore, recommendation on restriction of AGEs intake could be a practical approach to prevent metabolic abnormalities.

Aging Biology in the Kidney

The notion that kidney function declines with age in the general population is well known in the Nephrology community and the average loss of glomerular filtration rate (GFR) about 1ml per year in most longitudinal studies. There is much debate within the community about whether this represents "normal aging" or whether this constitutes a form of renal disease. However this debate turns out, the real question is whether this decline is preventable - can it be modified or slowed? Efforts to find drivers of this decline are still in the very earliest stages, but have shown some promise at elucidating some of the pathologies involved. This article will address both the wider issue of the biology of aging as well as the specific pathologies of the aging kidney.

Low glucose degradation product peritoneal dialysis regimen is associated with lower plasma EN-RAGE and HMGB-1 proinflammatory ligands of receptor for advanced glycation end products

Intraperitoneal glucose degradation products (GDP) load influences systemic advanced glycation end products (AGEs) but the effects on soluble receptor for AGEs (s-RAGE) and its proinflammatory ligands: extracellular newly identified receptor for advanced glycation end-products binding protein(EN-RAGE) and high mobility group box-1 protein (HMGB-1) are unknown. We aimed to compare plasma and peritoneal s-RAGE, EN-RAGE and HMGB-1 between three peritoneal dialysis (PD) prescription regimens with different intraperitoneal GDP loads. High GDP load (glucose-lactate PD fluid, D; N = 8) was compared with a low (glucose-bicarbonate/lactate with icodextrin for overnight dwell, E; N = 9) and a very low GDP load (glucose-bicarbonate/lactate, P; N = 16). D group demonstrated higher plasma EN-RAGE, 77.8 ng/mL, vs. both E, 11.2, P < 0.001 and P, 27.0, P < 0.001 as well as higher plasma HMGB-1, 2.2 ng/mL vs. both E, 1.1, P < 0.01 and P, 1.5, P < 0.01. Plasma s-RAGE, which did not differ between D, E and P, correlated with its effluent levels. Patients with faster peritoneal transport (D/Pcr > 0.65) tended to have higher plasma s-RAGE compared to slow transporters (2300 vs. 1762 pg/mL, P = 0.056). Peritoneal clearance of s-RAGE and EN-RAGE was higher with E compared to both D and P (P < 0.001 resp. P < 0.01). Subgroup of PD patients with CRP above median demonstrated higher plasma HMGB-1 and EN-RAGE, P < 0.05 for both. A lower intraperitoneal GDP load is associated with decreased plasma levels of EN-RAGE and HMGB-1. Peritoneal transport, microinflammation and the capability of icodextrin to increase peritoneal clearance of middle molecular weight substances might also exert an effect on plasma s-RAGE and its proinflammatory ligands levels.

Dietary consumption of advanced glycation end products and pancreatic cancer in the prospective NIH-AARP Diet and Health Study

BACKGROUND

Advanced glycation end products (AGEs) are a heterogeneous group of compounds present in uncooked foods as well as in foods cooked at high temperatures. AGEs have been associated with insulin resistance, oxidative stress, and chronic inflammation in patients with diabetes. Dietary AGEs are an important contributor to the AGE pool in the body. N(ϵ)-(carboxymethyl)lysine (CML) AGE is one of the major biologically and chemically well-characterized AGE markers. The consumption of red meat, which is CML-AGE rich, has been positively associated with pancreatic cancer in men.

OBJECTIVES

With the use of a published food CML-AGE database, we estimated the consumption of CML AGE in the prospective NIH-AARP Diet and Health Study and evaluated the association between CML-AGE consumption and pancreatic cancer and the mediating effect of CML AGE on the association between red meat consumption and pancreatic cancer.

DESIGN

Multivariate Cox proportional hazard regression models were used to estimate HRs and 95% CIs for pancreatic cancer.

RESULTS

During an average of 10.5 y of follow-up, we identified 2193 pancreatic cancer cases (1407 men and 786 women) from 528,251 subjects. With the comparison of subjects in the fifth and the first quintiles of CML-AGE consumption, we observed increased pancreatic cancer risk in men (HR: 1.43; 95% CI: 1.06, 1.93, P-trend = 0.003) but not women (HR: 1.14; 95% CI: 0.76, 1.72, P-trend = 0.42). Men in the highest quintile of red meat consumption had higher risk of pancreatic cancer (HR: 1.35; 95% CI: 1.07, 1.70), which attenuated after adjustment for CML-AGE consumption (HR: 1.20; 95% CI: 0.95, 1.53).

CONCLUSION

Dietary CML-AGE consumption was associated with modestly increased risk of pancreatic cancer in men and may partially explain the positive association between red meat and pancreatic cancer.

Influence of nonenzymatic posttranslational modifications on constitution, oligomerization and receptor binding of S100A12

This study examined the effect of methylglyoxal (MGO)-derived nonenzymatic posttranslational modifications (nePTMs) on the binding affinity of S100A12 to its natural receptor for advanced glycation end-products (RAGE). Binding of MGO-modified S100A12 to RAGE decreased significantly with increasing MGO concentration and incubation time. Ca²⁺-induced S100A12 hexamerization was impaired only at higher MGO concentrations indicating that the loss of affinity is not predominantly caused by disturbance of ligand oligomerization. nePTM mapping showed carboxyethylation of lysine (CEL) and the N-terminus without preferential modification sites. Besides, hydroimidazolone, hemiaminals, argpyrimidine, and tetrahydropyrimidine rapidly formed at R21. Even at the highest modification rate, hexamerization of synthesized CEL-S100A12 was unaffected and RAGE-binding only slightly impaired. Thus, nePTMs at R21 seem to be the major cause of MGO-induced impairment of S100A12 oligomerization and RAGE binding.

The axis AGE-RAGE-soluble RAGE and oxidative stress in chronic kidney disease

Chronic kidney disease (CKD) has been shown to be associated with high oxidative stress and cardiovascular disease. In this chapter our focus will be on the role of advanced glycation end products (AGE) and their receptor, RAGE in CKD progression and their role on cardiovascular complications. We provide a succinct, yet comprehensive summary of the current knowledge, the challenges and the future therapeutic avenues that are stemming out from novel recent findings. We first briefly review glycation and AGE formation and the role of the kidney in their metabolism. Next, we focus on the RAGE, its signaling and role in oxidative stress. We address the possible role of soluble RAGEs as decoys and the controversy regarding this issue. We then provide the latest information on the specific role of both AGE and RAGE in inflammation and perpetuation of kidney damage in diabetes and in CKD without diabetes, which is the main purpose of the review. Finally, we offer an update on new avenues to target the AGE-RAGE axis in CKD.

Cyclooxygenase-2 and vascular endothelial growth factor expressions are involved in ultrafiltration failure

BACKGROUND

Long-term peritoneal dialysis (PD) is associated with ultrafiltration failure (UFF). The aim of the study was to investigate changes in cyclooxygenase-2 (COX-2), vascular endothelial growth factor A (VEGF-A), and vascular endothelial growth factor C (VEGF-C) expressions in a rat model of UFF induced by PD solution.

METHODS

Sprague-Dawley rats were divided into six groups (n = 8/group): normal untreated control group, sham operation group, uremic group (nephrectomy without PD), uremic 2-wk PD group (PD solution for 2 wk), uremic 4-wk PD group (PD solution for 4 wk), and uremic 4-wk PD + celecoxib group (PD solution plus COX-2 inhibitor celecoxib 20 mg/kg for 4 wk). Peritoneal function was determined by peritoneal equilibration test. Peritoneal morphology was determined by hematoxylin and eosin and Masson staining. Microvessel and lymphatic microvessel formation was determined by immunohistochemistry. COX-2, VEGF-A, and VEGF-C expressions were determined by real-time polymerase chain reaction and immunohistochemistry.

RESULTS

Uremic rat model was successfully established. PD-induced peritoneal morphologic changes associated with UFF, characterized by inflammation, edema, and collagen accumulation. PD solution increased the density of microvessels marked by CD31 (microvessel density) and lymphatic microvessels marked by LYVE-1 (lymphatic vessel density) in peritoneum. COX-2, VEGF-A, and VEGF-C expression levels in the uremic 4-wk PD group were higher than those in the uremic group (all P < 0.05). All these changes were partially reversed by celecoxib. VEGF-A and VEGF-C protein expressions were positively correlated with microvessel density and lymphatic vessel density formation.

CONCLUSIONS

COX-2 could increase VEGF-A and VEGF-C expressions in peritoneal tissue, resulting in increased formation of peritoneal microvessels and lymphatic microvessels, playing pivotal roles in the development of UFF.

Placental growth factor, pregnancy-associated plasma protein-A, soluble receptor for advanced glycation end products, extracellular newly identified receptor for receptor for advanced glycation end products binding protein and high mobility group box 1 levels in patients with acute kidney injury: a cross sectional study

BACKGROUND

Placental growth factor (PlGF), pregnancy-associated plasma protein-A (PAPP-A), soluble receptor for advanced glycation end products (sRAGE), extracellular newly identified receptor for RAGE binding protein (EN-RAGE) and high mobility group box 1 (HMGB-1) are novel biomarkers in chronic kidney disease (CKD). However, their clinical significance in acute kidney injury (AKI) is unknown. The aim of this cross-sectional study was to determine whether selected biomarkers are changed in AKI patients.

METHODS

Serum PlGF, PAPP-A, sRAGE, EN-RAGE and HMGB-1 levels were assessed in 40 patients with AKI, 42 CKD 5 patients, 31 haemodialysis patients (HD) and 39 age-matched healthy controls.

RESULTS

PAPP-A was elevated in AKI (20.6 ± 16.9 mIU/L) compared with controls (9.1 ± 2.3 mIU/L, p < 0.001). PlGF was not increased in AKI (11.7 ± 7.4 pg/mL) versus controls (8.5 ± 2.4 pg/mL, n.s.), as well as sRAGE was not elevated in AKI (2400 ± 1400 pg/mL) compared with controls (1760 ± 730 pg/mL, n.s), but was lower compared with CKD 5 (3200 ± 1500 pg/mL, p < 0.05); EN-RAGE was elevated in AKI 480 ± 450 ng/mL in comparison with controls (60 ± 62 ng/mL), CKD 5 (190 ± 120 ng/mL), and HD (120 ± 100 ng/mL), all p < 0.001. Similarly, HMGB-1 was increased in AKI (5.8 ± 7.5 ng/mL) versus controls (1.7 ± 1.4 ng/mL), CKD 5 (3.2 ± 3.1 ng/mL) and HD (2.5 ± 2.1 ng/mL), all p < 0.001.In AKI group, in multivariate regression analysis: PAPP-A levels were associated with transferrin (p <0.001), negatively with albumin (p < 0.01) and prealbumin (p < 0.05); PlGF levels were associated with C--reactive protein (p < 0.001). EN-RAGE levels were associated with ferritin (p < 0.01) and orosomucoid (p = 0.02), and HMGB-1 levels with leukocyte count (p < 0.01) and negatively with proteinuria (p = 0.02).

CONCLUSIONS

In AKI patients, PAPP-A, EN-RAGE and HMGB1 are elevated, but sRAGE and PlGF are not increased. Whereas PAPP-A correlates with markers of nutrition; PlGF, EN-RAGE and HMGB-1 are related to inflammatory parameters.

Dietary consumption of meat, fat, animal products and advanced glycation end-products and the risk of Barrett's oesophagus

BACKGROUND

Advanced glycation end-products (AGEs) are found in high quantity in high-fat foods and meat cooked at high temperature. AGEs have been shown to contribute to chronic inflammation and oxidative stress in humans.

AIM

To investigate the associations between consumption of meat, fat and AGEs, and the risk of Barrett's oesophagus (BO).

METHODS

We conducted a case-control study using data from the patients who were scheduled for elective esophagogastroduodenoscopy (EGD) and from a random sample of patients who were identified at primary care clinics. Daily consumption of meat, fat and Nε-(carboxymethyl) lysine (CML), a major type of AGEs, was derived from the food frequency questionnaire (FFQ). Multivariate logistic regression models were used to estimate the odds ratio (OR) and its 95% confidence interval (CI) for BO.

RESULTS

A total of 151 cases with BO and 777 controls without BO completed the FFQ. The multivariate OR (95% CI) for BO was 1.91 (1.07-3.38) for total meat, 1.80 (1.02-3.16) for saturated fat and 1.63 (0.96-2.76) for CML-AGE, when the highest tertile of intake was compared with the lowest. The association for total meat was attenuated to 1.61 (0.82-3.16), and that for saturated fat to 1.54 (0.81-2.94) after adjusting for CML-AGE.

CONCLUSIONS

Higher consumption of total meat, saturated fat or possibly CML-AGE was associated with an increased risk of Barrett's oesophagus. CML-AGE may partly explain the association between total meat and saturated fat consumption and the risk of Barrett's oesophagus.

Circulating soluble receptor for advanced glycation end product (sRAGE) and left ventricular hypertrophy in patients with chronic kidney disease (CKD)

BACKGROUND AND AIM

A decoy receptor for advanced glycation end product (soluble RAGE or sRAGE) is involved in left ventricular hypertrophy (LVH), and cardiomyopathy myocardial damage in experimental models and observational studies in patients with heart failure support the hypothesis that sRAGE attenuates the progression of heart disease and prevents death. Since sRAGE accumulates in patients with chronic kidney disease (CKD) we studied the relationship between plasma sRAGE with LVH in CKD patients.

METHODS AND RESULTS

We enrolled 142 patients with an average estimated glomerular filtration rate (eGFR) of 32 ml/min/1.73 m(2) and 49 healthy control individuals matched for age and gender. Plasma sRAGE was significantly higher in CKD patients than in healthy controls. Significant inverse relationships were found between sRAGE with left ventricular mass index (LVMI) and mean wall thickness (MWT) but no such associations were found in controls. A bootstrap re-sampling validation study confirmed the estimates of the link between sRAGE and these variables. On covariance analysis, the slopes of LVMI and MWT to sRAGE were significantly steeper in CKD patients than in the controls. On logistic regression analysis 1 log unit increase in sRAGE was associated with a 82% decrease in the odds for LVH in CKD patients.

CONCLUSIONS

sRAGE is an inverse marker of LVH in CKD patients. This association generates the hypothesis that the RAGE pathway could be a causal risk factor for LVH in this population and that blockade of this pathway by the endogenous decoy receptor sRAGE could attenuate LVH in the same population.

Nonenzymatic Post-Translational Modification Derived Products: New Biomarkers of Protein Aging

During their biological life, proteins are exposed in a cumulative way to irreversible nonenzymatic post-translational modifications that are responsible for their molecular aging and generate specific by-products called »post-translational modification derived products« (PTMDPs). PTMDPs are involved in the pathogenesis of various diseases such as diabetes mellitus, renal insufficiency and atherosclerosis, and are potential biomarkers in clinical practice. Nonenzymatic glycation refers to the spontaneous binding of glucose and reducing sugars to free amino groups and is amplified by oxidative processes (referred to as »glycoxidation«). It generates many reactive by-products such as aldehydes and leads to the formation of »advanced glycation end products« (AGEs). AGEs accumulatein vivo, alter tissue organization and activate membrane receptors such as RAGE, which triggers inflammatory responses. Carbamylation is due to the binding of isocyanic acid, formedin vivoeither by spontaneous dissociation of urea or by action of myeloperoxidase on thiocyanate, and generates homocitrulline from lysine groups. Carbamylation leads to alteration of the structural and biological properties of proteins, and favors inflammation and atherosclerosis. PTMDPs may be assayed by different methods, among others LC-MS/MS or immuno assays, constitute a promising field of investigation in basic research and are potential major biomarkers in laboratory medicine.

Effect of circulating soluble receptor for advanced glycation end products (sRAGE) and the proinflammatory RAGE ligand (EN-RAGE, S100A12) on mortality in hemodialysis patients

BACKGROUND AND OBJECTIVES

The soluble receptor of advanced glycation end products (sRAGE) may exert anti-inflammatory protective roles on the vasculature. In contrast, the RAGE ligand S100A12 (also known as EN-RAGE) contributes to inflammation and the development of atherosclerosis in animal models. Whether alterations at this level contribute to the increased mortality observed in patients on dialysis is currently unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Prospective study including 184 prevalent hemodialysis patients and 50 healthy controls matched for age and gender. Plasma concentrations of S100A12 and sRAGE were studied in relation to risk profile and mortality after a median follow-up period of 41 months.

RESULTS

S100A12 and sRAGE levels were significantly elevated in hemodialysis patients compared with healthy controls. S100A12 had a strong positive correlation with C-reactive protein and IL-6, whereas sRAGE negatively associated with C-reactive protein. S100A12, but not sRAGE, was independently and positively associated with clinical cardiovascular disease (CVD). During follow-up, 85 (33 cardiovascular-related) deaths occurred. Whereas sRAGE did not predict mortality, S100A12 was associated with both all-cause (per log(10) ng/ml hazard ratio [HR] 1.93, 95% confidence interval [CI] 1.18 to 3.15) and CVD-related (HR 3.23, 95% CI 1.48 to 7.01) mortality, even after adjustment for age, sex, vintage, and comorbidities. Further adjustment for inflammation made the predictive value of S100A12 disappear for all-cause mortality, but still persisted in CVD-related mortality.

CONCLUSIONS

Circulating S100A12 and sRAGE are both elevated in hemodialysis patients. However, only S100A12 associates with mortality, partly explained by its links with inflammation.

Anaerobic vs aerobic pathways of carbonyl and oxidant stress in human lens and skin during aging and in diabetes: A comparative analysis

The effects of anaerobic (lens) vs aerobic (skin) environment on carbonyl and oxidant stress are compared using de novo and existing data on advanced glycation and oxidation products in human crystallins and collagen. Almost all modifications increase with age. Methylglyoxal hydroimidazolones, carboxymethyllysine, and carboxyethyllysine are severalfold higher in lens than in skin and markedly increase upon incubation of lens crystallins with 5mM ascorbic acid. In contrast, fructose-lysine, glucosepane crosslinks, glyoxal hydroimidazolones, metal-catalyzed oxidation (allysine), and H(2)O(2)-dependent modifications (2-aminoapidic acid and methionine sulfoxide) are markedly elevated in skin, but relatively suppressed in the aging lens. In both tissues ornithine is the dominant modification, implicating arginine residues as the principal target of the Maillard reaction in vivo. Diabetes (here mostly type 2 studied) increases significantly fructose-lysine and glucosepane in both tissues (P<0.001) but has surprisingly little effect on the absolute level of most other advanced glycation end products. However, diabetes strengthens the Spearman correlation coefficients for age-related accumulation of hydrogen peroxide-mediated modifications in the lens. Overall, the data suggest that oxoaldehyde stress involving methylglyoxal from either glucose or ascorbate is predominant in the aging noncataractous lens, whereas aging skin collagen undergoes combined attack by nonoxidative glucose-mediated modifications, as well as those from metal-catalyzed oxidation and H(2)O(2).

Evaluation of nonenzymatic posttranslational modification-derived products as biomarkers of molecular aging of proteins

BACKGROUND

During their biological life, proteins are exposed in a cumulative fashion to irreversible nonenzymatic, late posttranslational modifications that are responsible for their molecular aging. It is now well established that these damaged proteins constitute a molecular substratum for many dysfunctions described in metabolic and age-related diseases, such as diabetes mellitus, renal insufficiency, atherosclerosis, or neurodegenerative diseases. Accordingly, the specific end products derived from these reactions are considered potentially useful biomarkers for these diseases.

CONTENT

The aim of this review is to give an overview of nonenzymatic posttranslational modifications of proteins and their influence in vivo, take inventory of the analytical methods available for the measurement of posttranslational modification-derived products, and assess the potential contribution of new technologies for their clinical use as biological markers of protein molecular aging.

SUMMARY

Despite their clinical relevance, biomarkers of posttranslational modifications of proteins have been studied only in the context of experimental clinical research, owing to the analytical complexity of their measurement. The recent implementation in clinical chemistry laboratories of mass spectrometry-based methods that provide higher specificity and sensitivity has facilitated the measurement of these compounds. These markers are not used currently by clinicians in routine practice, however, and many challenges, such as standardization, have to be confronted before these markers can be used as efficient tools in the detection and monitoring of long-term complications of metabolic and age-related diseases.

Poly(Adenosine 5'-diphosphate-ribose) polymerase inhibition counteracts multiple manifestations of experimental type 1 diabetic nephropathy

This study was aimed at evaluating the role for poly(ADP-ribose) polymerase (PARP) in early nephropathy associated with type 1 diabetes. Control and streptozotocin-diabetic rats were maintained with or without treatment with one of two structurally unrelated PARP inhibitors, 1,5-isoquinolinediol (ISO) and 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de] anthracen-3-one (GPI-15427), at 3 mg/kg(-1) x d(-1) ip and 30 mg/kg(-1) x d(-1), respectively, for 10 wk after the first 2 wk without treatment. PARP activity in the renal cortex was assessed by immunohistochemistry and Western blot analysis of poly(ADP-ribosyl)ated proteins. Variables of diabetic nephropathy in urine and renal cortex were evaluated by ELISA, Western blot analysis, immunohistochemistry, and colorimetry. Urinary albumin excretion was increased about 4-fold in diabetic rats, and this increase was prevented by ISO and GPI-15427. PARP inhibition counteracted diabetes-associated increase in poly(ADP-ribose) immunoreactivities in renal glomeruli and tubuli and poly(ADP-ribosyl)ated protein level. Renal concentrations of TGF-beta(1), vascular endothelial growth factor, endothelin-1, TNF-alpha, monocyte chemoattractant protein-1, lipid peroxidation products, and nitrotyrosine were increased in diabetic rats, and all these changes as well as an increase in urinary TNF-alpha excretion were completely or partially prevented by ISO and GPI-15427. PARP inhibition counteracted diabetes-induced up-regulation of endothelin (B) receptor, podocyte loss, accumulation of collagen-alpha1 (IY), periodic acid-Schiff-positive substances, fibronectin, and advanced glycation end-products in the renal cortex. In conclusion, PARP activation is implicated in multiple changes characteristic for early nephropathy associated with type 1 diabetes. These findings provide rationale for development and further studies of PARP inhibitors and PARP inhibitor-containing combination therapies.

Circulating soluble receptor of advanced glycation end product inversely correlates with atherosclerosis in patients with chronic kidney disease

The soluble receptor of advanced glycation end product (sRAGE) prevents vascular damage in experimental animal models, and observational studies in the general population support the hypothesis that sRAGE may exert a protective role on the vasculature. To test this in patients with chronic kidney disease, we determined the relationship between plasma sRAGE and carotid atherosclerosis in 142 patients with an average estimated glomerular filtration rate (eGFR) of 32 ml/min per 1.73 m(2) and 49 healthy control individuals matched for age and gender. Plasma sRAGE was significantly higher in patients with chronic kidney disease than in the control cohort. In an aggregate analysis of the patients and controls, there was a significant inverse relationship between eGFR and sRAGE, with a breakpoint in the regression line at 64 ml/min per 1.73 m(2). Significant inverse relationships were found for sRAGE to intima-media thickness and plaque number in the patients with chronic kidney disease, but no such associations were found in the controls. On covariance analysis, the slopes of intima-media thickness and plaque number to sRAGE were significantly steeper in patients with chronic kidney disease than in the controls. Furthermore, a significant interaction was found between sRAGE and smoking for predicting atherosclerotic plaques in patients with chronic kidney disease. The pathophysiological significance of this correlation will have to await more mechanistic studies.

Advanced glycation end product accumulation in rho0 cells without a functional respiratory chain

Advanced glycation end products (AGEs) accumulate during ageing with reactive oxygen species from the mitochondrial respiratory chain discussed as a driving force. To determine the role of mitochondrial activity for AGE formation, a rho0 derivative of the 143B.TK- osteosarcoma cell line lacking the respiratory chain, was analysed. These cells exhibit decreased superoxide formation but unchanged mitochondrial SOD expression as well as unchanged antioxidative free sulfhydryl (SH) levels. Whereas total protein content shows no differences in AGE levels, cell fractionation and Western blotting demonstrates some changes in the AGE pattern. Thus, the absence of functional respiration has only a negligible impact on AGE accumulation.

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.

Modification of vimentin: a general mechanism of nonenzymatic glycation in human skin

In a recent study, we were able to show that the intermediate filament protein vimentin aggregates in human dermal fibroblasts because of modification by the advanced glycation endproduct carboxymethyllysine (CML). In this work, we investigated the formation of intracellular CML in relation to the concentration of glucose in the culture medium. The natural degradation product of glucose, methylglyoxal, was able to induce the aggregation of vimentin. This dicarbonyl leads to the formation of the modifications MG-H1 and carboxyethyllysine (CEL) as a result of the reaction with arginine and lysine residues of proteins. Furthermore, we found that the protein vimentin was modified, not only by CML and CEL, but also by pentosidine and pyrraline. These findings underline the special position of vimentin as a preferential target of the Maillard reaction in human skin.

Dietary advanced glycation end products--a risk to human health? A call for an interdisciplinary debate

Physiological consequences resulting from protein-bound Maillard compounds in foods must be discussed carefully. This was the idea behind the debate, which is put for discussion by the papers by Sebekova and Somoza, who argued for the motion that dietary advanced glycation end products (AGEs) are a health risk, and by Ames, who provided evidence against the motion. In this two excellent reviews, numerous arguments based on papers published in high-impact journals are given for each of the opinions. The fact that no final conclusion can be drawn, may reflect the need for a more comprehensive examination of this issue in the future. For a deeper understanding of biological consequences resulting from heated foods, the relationships between well-defined biological effects and well-characterized chemical structures must be studied. Prerequisite for this is profound chemistry--pure compounds, exact concentrations, and unambiguous analytical techniques. A real "risk assessment" is much too complex than to leave it up to one discipline alone. It must be a comprehensive and interdisciplinary approach, joining the resources of biology, medicine, and chemistry.

Increased serum glycated albumin level is associated with the presence and severity of coronary artery disease in type 2 diabetic patients

BACKGROUND

Glycated albumin is the predominant circulating Amadori-type glycated protein in vivo and plays a major role in the development of diabetic vascular complications. The aim of this study was to assess the relationship between increased serum glycated albumin level and the presence and severity of coronary artery disease (CAD) in patients with type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

In a total of 320 consecutive patients with T2DM, coronary angiography revealed normal coronary arteries in 83 patients (control group) and significant coronary stenosis (> or = 70% luminal diameter narrowing) in 237, of whom 51 patients had 1-vessel disease (Group I), 80 had 2-vessel disease (Group II), and 106 had 3-vessel disease (Group III). Serum glycated albumin, hemoglobin A(1c) (HbA(1c)) and tumor necrosis factor (TNF)-alpha levels, lipid profile, and renal function were measured. Logistic regression analysis was performed to determine the relative risk of serum glycated albumin level for the presence and severity of CAD. Multivariate stepwise linear regression analysis was done to identify independent determinants of the glycated albumin level. Serum glycated albumin (21.2+/-5.3% vs 19.4+/-4.3%, p=0.005) and TNF-alpha levels (123 +/-115 pg/ml vs 65+/-59 pg/ml, p<0.001) were significantly higher in patients with CAD than in controls, but serum HbAlc level did not significantly differ between them (7.6+/-1.3% vs 7.4+/-1.2%, p=0.19). There was a significant difference in serum glycated albumin level between Groups I and III (19.5+/-3.3% vs 21.8+/-5.7%, p<0.001). The serum glycated albumin level correlated with the number of diseased arteries (Spearman r=0.205, p<0.001), and was closely related to serum levels on admission of glucose (r=0.495, p<0.001), TNF-alpha (r=0.123, p=0.028), blood urea nitrogen (r=0.167, p=0.004), triglycerides (r=0.129, p=0.021), and HbA(1c) (r=0.795, p<0.001). Multivariate analysis indicated that serum levels of glucose (p<0.0001), TNF-alpha (p=0.001), blood urea nitrogen (p=0.004) and triglycerides (p=0.035) were independent determinants for glycated albumin. Logistic regression analysis revealed that glycated albumin > or = 19% (odds ratio (OR) 2.9, p<0.001) was an independent predictor for CAD and glycated albumin > or = 21% (OR 2.3, p=0.032) for 3-vessel disease prediction. The area under the receiver-operating characteristic curve for glycated albumin (0.620, 95% confidence interval (CI) 0.548 to 0.691, p=0.001) was superior to that for HbA(1c) (0.543, 95% CI 0.473 to 0.613, p=0.243).

CONCLUSIONS

An increased serum level of glycated albumin is associated with the presence and severity of CAD, and may be useful in screening patients with T2DM.

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.

Paraoxonase-1 concentrations in end-stage renal disease patients increase after hemodialysis: correlation with low molecular AGE adduct clearance

BACKGROUND

Hemorrhagic stroke and ischemic heart disease continue to be key problems in patients with end stage renal failure. Reduced serum paraoxonase (PON-1) activity has been described in these patients, which could contribute to the accelerated development of atherosclerosis. We hypothesized that retention of uremic toxins and or "middle molecules" including advanced glycation (AGE) free adducts and peptides could play a mechanistic role in decreasing PON-1 activity.

METHODS

We enrolled 22 ESRD patients undergoing hemodialysis in whom paired pre- and post-dialysis samples were studied along with 30 age-matched control subjects.

RESULTS

ESRD patients showed a 76% decrease in PON-1 activity. As expected, ESRD patients had an increase in lipoperoxides and advanced oxidation protein products (AOPP). Our patients had a 3-fold increase in serum AGEs and a striking 10-fold increase in low molecular weight (<10 kDa) AGEs. Post-dialysis samples in all patients displayed an increase in PON-1 activity, which ranged from 4 to 40% of the predialysis value. HDL-cholesterol, apoAI, free cholesterol (as a LCAT surrogate), HDL-subclasses and TG did not change significantly after dialysis. Changes in PON-1 activity display a good correlation (r=0.66, p<0.001) with rates in which creatinine and urea are cleared. Clearance of low molecular weight AGEs after hemodialysis explains 79% of the changes in PON-1 activity and are hence a much better predictor than creatinine changes (r=0.89, p<0.00). In vitro incubation of paraoxonase with serum ultrafiltrates show a time and concentration dependent inhibition of PON-1 by the ultrafiltrates, an inhibition that is up to 3 times higher (from 8 to 24%) when chronic renal failure patients are the source of the ultrafiltrate.

CONCLUSION

We showed that HD results in a significant, consistent increase in the activity of the antioxidant enzyme PON-1. The effect, correlates with the effectiveness of dialysis to clear creatinine and urea, and with the clearance of AGE adducts of low molecular weight. This effect was replicated in vitro, showing time and dose dependency. Our results suggest that another cause for the observed lower PON-1 concentrations in CRF are the retention of low-middle molecules and demonstrate a positive effect of hemodialysis in the delicate oxidant-antioxidant state of these patients, that should be weighted against other pro-oxidant effects that have also been shown to occur previously. If the hypothesis that AGEs are the main culprits is proved in further research, this opens a putative therapeutic avenue for AGE blockers in ESRD.