Serum carboxymethyl-lysine, a dominant advanced glycation end product, is associated with chronic kidney disease: the Baltimore longitudinal study of aging

Circulating Concentrations of advanced Glycation end Products, Carboxymethyl Lysine and Methylglyoxal are Associated With Renal Function in Individuals With Diabetes

OBJECTIVE

Diabetic kidney disease (DKD) is one of the most severe chronic complications of diabetes and is associated with higher level of advanced glycation end products (AGEs). The aim of this study was to investigate the diagnostic potential of combined detection of multiple serum AGEs in diagnosing DKD.

METHODS

Serum AGEs, Nε-(carboxymethyl) lysine (CML), Nε-(carboxyethyl) lysine, and methylglyoxal (MGO) levels were measured by enzyme-linked immunosorbent assay in 176 individuals with type 2 diabetes. Participants were classified into normoalbuminuria, microalbuminuria, and macroalbuminuria group according to their urinary albumin to creatinine ratio (UACR).

RESULTS

Higher serum AGEs levels were found to be positively correlated with U-Alb, UACR, and blood urea nitrogen in the study of 176 individuals with type 2 diabetes. CML and MGO levels were positively correlated with U-Alb, UACR, blood urea nitrogen, Scr, and uric acid, and negatively correlated with estimated glomerular filtration rate (P < .05). Multivariate logistic regression analysis showed that elevated levels of AGEs, CML, and MGO were independent risk factors for the progression of DKD (odds ratio = 1.861, 1.016, 7.607, P < .01). The sensitivity, specificity, and area under receiver operating characteristic curve of combined detection of AGEs, MGO, and CML were higher than those of three individual detections (area under the curve = 0.952, 0.772, 0.868, 0905, respectively, P < .05).

CONCLUSION

The combined detection of AGEs, CML, and MGO may improve the reliability of early diagnosis of DKD.

A Role for Advanced Glycation End Products in Molecular Ageing

Ageing is a composite process that involves numerous changes at the cellular, tissue, organ and whole-body levels. These changes result in decreased functioning of the organism and the development of certain conditions, which ultimately lead to an increased risk of death. Advanced glycation end products (AGEs) are a family of compounds with a diverse chemical nature. They are the products of non-enzymatic reactions between reducing sugars and proteins, lipids or nucleic acids and are synthesised in high amounts in both physiological and pathological conditions. Accumulation of these molecules increases the level of damage to tissue/organs structures (immune elements, connective tissue, brain, pancreatic beta cells, nephrons, and muscles), which consequently triggers the development of age-related diseases, such as diabetes mellitus, neurodegeneration, and cardiovascular and kidney disorders. Irrespective of the role of AGEs in the initiation or progression of chronic disorders, a reduction in their levels would certainly provide health benefits. In this review, we provide an overview of the role of AGEs in these areas. Moreover, we provide examples of lifestyle interventions, such as caloric restriction or physical activities, that may modulate AGE formation and accumulation and help to promote healthy ageing.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Advanced Glycation End Products (AGEs) and Chronic Kidney Disease: Does the Modern Diet AGE the Kidney?

Since the 1980s, chronic kidney disease (CKD) affecting all ages has increased by almost 25%. This increase may be partially attributable to lifestyle changes and increased global consumption of a “western” diet, which is typically energy dense, low in fruits and vegetables, and high in animal protein and ultra-processed foods. These modern food trends have led to an increase in the consumption of advanced glycation end products (AGEs) in conjunction with increased metabolic dysfunction, obesity and diabetes, which facilitates production of endogenous AGEs within the body. When in excess, AGEs can be pathological via both receptor-mediated and non-receptor-mediated pathways. The kidney, as a major site for AGE clearance, is particularly vulnerable to AGE-mediated damage and increases in circulating AGEs align with risk of CKD and all-cause mortality. Furthermore, individuals with significant loss of renal function show increased AGE burden, particularly with uraemia, and there is some evidence that AGE lowering via diet or pharmacological inhibition may be beneficial for CKD. This review discusses the pathways that drive AGE formation and regulation within the body. This includes AGE receptor interactions and pathways of AGE-mediated pathology with a focus on the contribution of diet on endogenous AGE production and dietary AGE consumption to these processes. We then analyse the contribution of AGEs to kidney disease, the evidence for dietary AGEs and endogenously produced AGEs in driving pathogenesis in diabetic and non-diabetic kidney disease and the potential for AGE targeted therapies in kidney disease.

Plasma Catestatin Levels and Advanced Glycation End Products in Patients on Hemodialysis

Catestatin (CST) is a pleiotropic peptide involved in cardiovascular protection with its antihypertensive and angiogenic effects. Considering that patients with end-stage renal disease (ESRD) who are undergoing hemodialysis (HD) are associated with higher cardiovascular risk, the aim of this study was to investigate plasma CST levels in HD patients, compare them to healthy controls and evaluate possible CST associations with advanced glycation end products (AGEs) and laboratory, anthropometric and clinical parameters. The study included 91 patients on HD and 70 healthy controls. Plasma CST levels were determined by an enzyme-linked immunosorbent assay in a commercially available diagnostic kit, while AGEs were determined using skin autofluorescence. Plasma CST levels were significantly higher in the HD group compared to the controls (32.85 ± 20.18 vs. 5.39 ± 1.24 ng/mL, p < 0.001) and there was a significant positive correlation between CST and AGEs (r = 0.492, p < 0.001). Furthermore, there was a significant positive correlation between plasma CST levels with both the Dialysis Malnutrition Score (r = 0.295, p = 0.004) and Malnutrition-Inflammation Score (r = 0.290, p = 0.005). These results suggest that CST could be playing a role in the complex pathophysiology of ESRD/HD and that it could affect the higher cardiovascular risk of patients on HD.

Glycation of HDL blunts its anti-inflammatory and cholesterol efflux capacities in vitro, but has no effect in poorly controlled type 1 diabetes subjects

BACKGROUND

High-density lipoproteins (HDL) modified by glycation have been reported to be dysfunctional. Little is known regarding the anti-inflammatory effects on adipocytes of glycated HDL.

AIMS

We tested whether modification of HDL in vitro by glycolaldehyde (GAD), malondialdehyde (MDA) or glucose affected HDL's anti-inflammatory properties and ability to promote cholesterol efflux. To determine whether similar changes occur in vivo, we examined modifications of apolipoprotein A1 (APOA1) and APOA2 and anti-inflammatory and cholesterol efflux properties of HDL isolated from subjects with type 1 diabetes in poor glycemic control.

RESULTS

In vitro modification with both GAD and MDA blunted HDL's ability to inhibit palmitate-induced inflammation and cholesterol efflux in adipocytes. Modification of HDL by glucose had little impact on HDL function, like the response using HDL isolated from subjects with diabetes. Mass spectrophotometric analysis revealed that lysine residues in APOA1 and APOA2 of HDL modified by GAD and MDA in vitro differed from those modified by glucose, which resembled that seen with HDL from patients with type1 diabetes.

CONCLUSIONS

Modification of lysine residues in HDL by GAD and MDA in vitro does not mirror the HDL glycation in vivo in patients with diabetes, but resembles HDL modified in vitro by glucose.

Receptor for Advanced Glycation End Products is Involved in Platelet Hyperactivation and Arterial Thrombosis during Chronic Kidney Disease

BACKGROUND

 Chronic kidney disease (CKD) is associated with a high cardiovascular mortality due to increased rates of vascular lesions and thrombotic events, as well as serum accumulation of uremic toxins. A subgroup of these toxins (advanced glycation end products [AGEs] and S100 proteins) can interact with the receptor for AGEs (RAGE). In this study, we analyzed the impact of CKD on platelet function and arterial thrombosis, and the potential role of RAGE in this process.

METHODS

 Twelve weeks after induction of CKD in mice, platelet function and time to complete carotid artery occlusion were analyzed in four groups of animals (sham-operated, CKD, apolipoprotein E [Apoe]^-/-, and Apoe^-/-/Ager^-/- mice).

RESULTS

 Analysis of platelet function from whole blood and platelet-rich plasma showed hyperactivation of platelets only in CKD Apoe^-/- mice. There was no difference when experiments were done on washed platelets. However, preincubation of such platelets with AGEs or S100 proteins induced RAGE-mediated platelet hyperactivation. In vivo, CKD significantly reduced carotid occlusion times of Apoe^-/- mice (9.2 ± 1.1 vs. 11.1 ± 0.6 minutes for sham, p < 0.01). In contrast, CKD had no effect on occlusion times in Apoe^-/-/Ager^-/- mice. Moreover, carotid occlusion in Apoe^-/- CKD mice occurred significantly faster than in Apoe^-/-/Ager^-/- CKD mice (p < 0.0001).

CONCLUSION

 Our results show that CKD induces platelet hyperactivation, accelerates thrombus formation in a murine model of arterial thrombosis, and that RAGE deletion has a protective role. We propose that RAGE ligands binding to RAGE is involved in CKD-induced arterial thrombosis.

Novel associations between blood metabolites and kidney function among Bogalusa Heart Study and Multi-Ethnic Study of Atherosclerosis participants

INTRODUCTION

Chronic kidney disease (CKD) is a major public health challenge given its high global prevalence and associated risks of cardiovascular disease and progression to end stage renal disease. Although it is known that numerous metabolic changes occur in CKD patients, identifying novel metabolite associations with kidney function may enhance our understanding of the physiologic pathways relating to CKD.

OBJECTIVES

The objective of this study was to elucidate novel metabolite associations with kidney function among participants of two community-based cohorts with carefully ascertained metabolomics, kidney function, and covariate data.

METHODS

Untargeted ultrahigh-performance liquid chromatography-tandem mass spectrometry was used to detect and quantify blood metabolites. We used multivariate adjusted linear regression to examine associations between single metabolites and creatinine-based estimated glomerular filtration rate (eGFRcr) among 1243 Bogalusa Heart Study (BHS) participants (median eGFRcr: 94.4, 5th-95th percentile: 66.0-119.6 mL/min/1.73 m²). Replication, determined by statistical significance and consistent effect direction, was tested using gold standard measured glomerular filtration rate (mGFR) among 260 Multi-Ethnic Study of Atherosclerosis (MESA) participants (median mGFR: 72.0, 5th-95th percentile: 43.5-105.0 mL/min/1.73 m²). All analyses used Bonferroni-corrected alpha thresholds.

RESULTS

Fifty-one novel metabolite associations with kidney function were identified, including 12 from previously unrelated sub-pathways: N6-carboxymethyllysine, gulonate, quinolinate, gamma-CEHC-glucuronide, retinol, methylmalonate, 3-hydroxy-3-methylglutarate, 3-aminoisobutyrate, N-methylpipecolate, hydroquinone sulfate, and glycine conjugates of C₁₀H₁₂O₂ and C₁₀H₁₄O₂(1). Significant metabolites were generally inversely associated with kidney function and smaller in mass-to-charge ratio than non-significant metabolites.

CONCLUSION

The 51 novel metabolites identified may serve as early, clinically relevant, kidney function biomarkers.

Advanced glycation endproducts and dicarbonyls in end-stage renal disease: associations with uraemia and courses following renal replacement therapy

Background

End-stage renal disease (ESRD) is strongly associated with cardiovascular disease (CVD) risk. Advanced glycation endproducts (AGEs) and dicarbonyls, major precursors of AGEs, may contribute to the pathophysiology of CVD in ESRD. However, detailed data on the courses of AGEs and dicarbonyls during the transition of ESRD patients to renal replacement therapy are lacking.

Methods

We quantified an extensive panel of free and protein-bound serum AGEs [N^∈-(carboxymethyl)lysine (CML), N^∈-(carboxyethyl)lysine (CEL), N_δ-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine (MG-H1)], serum dicarbonyls [glyoxal (GO), methylglyoxal (MGO), 3-deoxyglucosone (3-DG)] and tissue AGE accumulation [estimated by skin autofluorescence (SAF)] in a combined cross-sectional and longitudinal observational study of patients with ESRD transitioning to dialysis or kidney transplantation (KTx), prevalent dialysis patients and healthy controls. Cross-sectional comparisons were performed with linear regression analyses, and courses following renal replacement therapy were analysed with linear mixed models.

Results

Free and protein-bound AGEs, dicarbonyls and SAF were higher in chronic kidney disease (CKD) Stage 5 non-dialysis (CKD 5-ND; n = 52) and CKD Stage 5 dialysis (CKD 5-D; n = 35) than in controls (n = 42). In addition, free AGEs, protein-bound CML, GO and SAF were even higher in CKD 5-D than in CKD5-ND. Similarly, following dialysis initiation (n = 43) free and protein-bound AGEs, and GO increased, whereas SAF remained similar. In contrast, following KTx (n = 21), free and protein-bound AGEs and dicarbonyls, but not SAF, markedly declined.

Conclusions

AGEs and dicarbonyls accumulate in uraemia, which is even exaggerated by dialysis initiation. In contrast, KTx markedly reduces AGEs and dicarbonyls. Given their associations with CVD risk in high-risk populations, lowering AGE and dicarbonyl levels may be valuable.

Biocatalytic Reversal of Advanced Glycation End Product Modification

Advanced glycation end products (AGEs) are a heterogeneous group of molecules that emerge from the condensation of sugars and proteins through the Maillard reaction. Despite a significant number of studies showing strong associations between AGEs and the pathologies of aging-related illnesses, it has been a challenge to establish AGEs as causal agents primarily due to the lack of tools in reversing AGE modifications at the molecular level. Herein, we show that MnmC, an enzyme involved in a bacterial tRNA-modification pathway, is capable of reversing the AGEs carboxyethyl-lysine (CEL) and carboxymethyl-lysine (CML) back to their native lysine structure. Combining structural homology analysis, site-directed mutagenesis, and protein domain dissection studies, we generated a variant of MnmC with improved catalytic properties against CEL in its free amino acid form. We show that this enzyme variant is also active on a CEL-modified peptidomimetic and an AGE-containing peptide that has been established as an authentic ligand of the receptor for AGEs (RAGE). Our data demonstrate that MnmC variants are promising lead catalysts toward the development of AGE-reversal tools and a better understanding of AGE biology.

Food advanced glycation end products as potential endocrine disruptors: An emerging threat to contemporary and future generation

Mankind exposure to chemicals in the past century has increased dramatically throughout environment. There is no question that chemicals interfere with the physiology of biological system. Abundance of chemicals is documented to be detrimental to human and wildlife. The mammalian endocrine system is comprised of many interacting tissues mediate themselves through hormones that are essential for metabolism, growth and development. Humans secrete over fifty different hormones to orchestrate major physiological functions however; these vital functions can be intervened by huge number of internal and external chemical stressors that are identified as endocrine disruptors. Advanced glycation end products (AGEs), familiarly known as Maillard products, formed through non-enzymatic glycation whose production is augmented on aging as well as environmental stressors. Processed foods have become very popular today due to their taste, convenience, and inexpensiveness. Manufacture of these day-to-day foods involves extreme temperatures on processing results in the formation of AGEs could independently promote oxidative stress, aging, diabetes, cancer, degenerative diseases, more fascinatingly hormonal disruption is the subject of interest of this review. Based on some substantial observations documented till time, we discuss the emergence of dietary AGEs as potential endocrine disruptors by emphasizing their occurrence, mechanisms and participation in endocrine interruption. Both economically and in terms of human life, AGEs may represent an enormous cost for the future society. Therefore, by explicating their novel role in endocrine diseases, the review strives to make an impact on AGEs and their exposure among public as well as scientific communities.

Oxidative stress, aging, and diseases

Reactive oxygen and nitrogen species (RONS) are produced by several endogenous and exogenous processes, and their negative effects are neutralized by antioxidant defenses. Oxidative stress occurs from the imbalance between RONS production and these antioxidant defenses. Aging is a process characterized by the progressive loss of tissue and organ function. The oxidative stress theory of aging is based on the hypothesis that age-associated functional losses are due to the accumulation of RONS-induced damages. At the same time, oxidative stress is involved in several age-related conditions (ie, cardiovascular diseases [CVDs], chronic obstructive pulmonary disease, chronic kidney disease, neurodegenerative diseases, and cancer), including sarcopenia and frailty. Different types of oxidative stress biomarkers have been identified and may provide important information about the efficacy of the treatment, guiding the selection of the most effective drugs/dose regimens for patients and, if particularly relevant from a pathophysiological point of view, acting on a specific therapeutic target. Given the important role of oxidative stress in the pathogenesis of many clinical conditions and aging, antioxidant therapy could positively affect the natural history of several diseases, but further investigation is needed to evaluate the real efficacy of these therapeutic interventions. The purpose of this paper is to provide a review of literature on this complex topic of ever increasing interest.

In vivo imaging of advanced glycation end products (AGEs) of albumin: first observations of significantly reduced clearance and liver deposition properties in mice

Advanced glycation end products (AGEs) are associated with various diseases, especially during aging and the development of diabetes and uremia. To better understand these biological processes, investigation of the in vivo kinetics of AGEs, i.e., analysis of trafficking and clearance properties, was carried out by molecular imaging. Following the preparation of Cy7.5-labeled AGE-albumin and intravenous injection in BALB/cA-nu/nu mice, noninvasive fluorescence kinetics analysis was performed. In vivo imaging and fluorescence microscopy analysis revealed that non-enzymatic AGEs were smoothly captured by scavenger cells in the liver, i.e., Kupffer and other sinusoidal cells, but were unable to be properly cleared from the body. Overall, these results highlight an important link between AGEs and various disorders associated with them, which may serve as a platform for future research to better understand the processes and mechanisms of these disorders.

Advanced Glycation End Products and Risks for Chronic Diseases: Intervening Through Lifestyle Modification

Advanced glycation end products (AGEs) are a family of compounds of diverse chemical nature that are the products of nonenzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs bind to one or more of their multiple receptors (RAGE) found on a variety of cell types and elicit an array of biologic responses. In this review, we have summarized the data on the nature of AGEs and issues associated with their measurements, their receptors, and changes in their expression under different physiologic and disease states. Last, we have used this information to prescribe lifestyle choices to modulate AGE-RAGE cycle for better health.

Stirring the Pot: Can Dietary Modification Alleviate the Burden of CKD?

Diet is one of the largest modifiable risk factors for chronic kidney disease (CKD)-related death and disability. CKD is largely a progressive disease; however, it is increasingly appreciated that hallmarks of chronic kidney disease such as albuminuria can regress over time. The factors driving albuminuria resolution remain elusive. Since albuminuria is a strong risk factor for GFR loss, modifiable lifestyle factors that lead to an improvement in albuminuria would likely reduce the burden of CKD in high-risk individuals, such as patients with diabetes. Dietary therapy such as protein and sodium restriction has historically been used in the management of CKD. Evidence is emerging to indicate that other nutrients may influence kidney health, either through metabolic or haemodynamic pathways or via the modification of gut homeostasis. This review focuses on the role of diet in the pathogenesis and progression of CKD and discusses the latest findings related to the mechanisms of diet-induced kidney disease. It is possible that optimizing diet quality or restricting dietary intake could be harnessed as an adjunct therapy for CKD prevention or progression in susceptible individuals, thereby reducing the burden of CKD.

Advanced Glycation End Products, Inflammation, and Chronic Metabolic Diseases: Links in a Chain?

Advanced glycation end products (AGEs) are a diverse group of compounds produced when reducing sugars react with proteins or other compounds to form glycosylated molecules. AGEs may form endogenously, and glycation of molecules may negatively affect their function. AGEs may also be consumed in food form with dietary AGEs reported to be particularly high in foods treated with high heat: baked, broiled, grilled, and fried foods. Whether dietary AGEs are absorbed in significant quantities and whether they are harmful if absorbed is a question under current debate. The American Diabetes Association makes no recommendation regarding avoidance of these foods, but many researchers are concerned that they may be pro-inflammatory and way worsen cardiac function, kidney function, diabetes and its complications and may even contribute to obesity.

Carboxymethyl lysine, an advanced glycation end product, and incident diabetes: a case-cohort analysis of the ARIC Study

AIMS

To verify whether elevated fasting levels of circulating carboxymethyl lysine (CML), an advanced glycation end product, predict the development of diabetes in middle-age adults.

METHODS

Using a stratified case-cohort design, we followed 543 middle-aged individuals who developed diabetes and 514 who did not over a median 9 years in the Atherosclerosis Risk in Communities Study. Weighted Cox proportional hazards analyses were used to account for the design.

RESULTS

In weighted analyses, correlation between CML levels and anthropometric, inflammatory or metabolic variables was minimal (Pearson correlations usually < 0.10). CML, when modelled as a continuous variable and after adjustment for age, sex, race, centre, parental history of diabetes, BMI, waist-to-hip ratio, non-esterified fatty acids, oxidized LDL-cholesterol, GFR, smoking, an inflammation score, adiponectin, leptin, insulin and glucose levels, was associated with an increased risk of diabetes [Hazard ratio (HR) = 1.35; 95% confidence interval (CI) 1.09-1.67, for each 100 ng/ml CML increment]. Baseline glucose level and race each modified the association (P < 0.05 for interaction), which was present only among those with impaired fasting glucose (≥ 5.6 mmol/l, HR = 1.61, 95% CI 1.26-2.05) and among white participants (HR = 1.50, 95% CI 1.13-1.99).

CONCLUSIONS

Elevated fasting CML, after adjustment for multiple risk factors for diabetes, predicts the development of incident diabetes, the association being present among those with impaired fasting glucose and in white participants. These prospective findings suggest that advanced glycation end products might play a role in the development of diabetes.

Association of Skin Autofluorescence Levels With Kidney Function Decline in Patients With Peripheral Artery Disease

Objective—

Skin autofluorescence (SAF), a measure of advanced glycation end product accumulation, is associated with kidney function. We investigated the association of SAF with rate of kidney function decline in a cohort of patients with peripheral artery disease.

Approach and Results—

We performed a post hoc analysis of an observational longitudinal cohort study. We included 471 patients with peripheral artery disease, and SAF was measured at baseline. Primary end point was rate of estimated glomerular filtration rate (eGFR) decline. Secondary end points were incidence of eGFR <60 and <45 mL/min/1.73 m 2 and rapid eGFR decline, defined as a decrease in eGFR of >5 mL/min/1.73 m 2 /y. During a median follow-up of 3 years, the mean change in eGFR per year was −1.8±4.4 mL/min/1.73 m 2 /y. No significant difference in rate of eGFR decline was observed per 1 arbitrary unit increase in SAF (−0.1 mL/min/1.73 m 2 /y; 95% confidence interval, −0.7 to 0.5; P =0.8). Analyses of the secondary end points showed that there was an association of SAF with incidence of eGFR <60 and <45 mL/min/1.73 m 2 (hazard ratio, 1.54; 95% confidence interval, 1.13–2.10; P =0.006 and hazard ratio, 1.76; 95% confidence interval, 1.20–2.59; P =0.004, respectively), but after adjustment for age and sex, significance was lost. There was no association of SAF with rapid eGFR decline.

Conclusions—

In conclusion, in this cohort of patients with peripheral artery disease, elevated SAF was associated with lower baseline eGFR. Although SAF has previously been established as a predictor for cardiovascular disease and mortality, it did not predict the rate of kidney function decline during follow-up in this study.

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).

Pathologic role of dietary advanced glycation end products in cardiometabolic disorders, and therapeutic intervention

Reactive derivatives from nonenzymatic glucose-protein condensation reactions, as well as lipids and nucleic acids exposed to reducing sugars, form a heterogeneous group of irreversible adducts called AGEs (advanced glycation end products). The glycation process begins with the conversion of reversible Schiff base adducts to more stable, covalently bound Amadori rearrangement products. Over the course of days to weeks, these Amadori products undergo further rearrangement and condensation reactions to form irreversibly cross-linked macroprotein derivatives known as AGEs. The formation and accumulation of AGEs have been known to progress in a physiological aging process and at an accelerated rate under hyperglycemic and oxidative stress conditions. There is growing evidence that AGEs play a pathologic role in numerous disorders. Indeed, glycation and/or cross-linking modification of circulating or organic matrix proteins by AGEs the senescence of moieties and deteriorate their physiological function and structural integrity in multiple organ systems. Moreover, AGEs elicit oxidative stress and inflammatory reactions through the interaction with the receptor for advanced glycation products in a variety of cells, thereby contributing to the development and progression of various aging- or diabetes-related disorders, such as cardiovascular disease, chronic kidney disease, insulin resistance, and Alzheimer's disease. Recently, diet has been recognized as a major environmental source of AGEs that could cause proinflammatory reactions and organ damage in vivo. Therefore, this review summarizes the pathophysiological role of dietary AGEs in health and disease, especially focusing on cardiometabolic disorders. We also discuss the potential utility in targeting exogenously derived AGEs for therapeutic intervention.

Determinants of concentrations of N(ε)-carboxymethyl-lysine and soluble receptor for advanced glycation end products and their associations with risk of pancreatic cancer

The soluble receptor for advanced glycation end-products (sRAGE) is shown to mitigate pro-inflammatory effects triggered by ligation of RAGE with N(ε)-carboxymethyl-lysine (CML)-AGE or other ligands. We examined the associations among host, lifestyle, and genetic determinants of CML-AGE or sRAGE and risk of pancreatic cancer in the prospective ATBC Study. We obtained baseline exposure information, data on serological and genetic biomarkers from 141 patients with pancreatic cancer and 141 subcohort controls. Stepwise linear and logistic regression models were used for data analysis. Multiple linear regression analyses showed that CML-AGE concentrations were independently inversely correlated with the minor allele of rs640742 of DDOST, physical activity, alcohol consumption, diastolic blood pressure (BP), and positively correlated with heart rate, serum sRAGE and HDL concentrations (P < 0.05). sRAGE concentrations were independently inversely correlated with the 82Ser allele of rs2070600 of RAGE, age, body mass index, heart rate, and serum HDL; and positively correlated with serum CML-AGE, sucrose consumption, and diastolic BP (P < 0.05). The minor allele of rs1035786 of RAGE was associated with reduced risk of pancreatic cancer (any T compared with CC: multivariate OR = 0.61, 95% CI: 0.38-0.98). We identified host metabolic profile, lifestyle and genetic factors that explained approximately 50% of variability of CML-AGE or sRAGE in Finnish men smokers. The association between RAGE SNPs and pancreatic cancer risk warrants further investigation.

The aging kidney revisited: a systematic review

As for the whole human body, the kidney undergoes age-related changes which translate in an inexorable and progressive decline in renal function. Renal aging is a multifactorial process where gender, race and genetic background and several key-mediators such as chronic inflammation, oxidative stress, the renin-angiotensin-aldosterone (RAAS) system, impairment in kidney repair capacities and background cardiovascular disease play a significant role. Features of the aging kidney include macroscopic and microscopic changes and important functional adaptations, none of which is pathognomonic of aging. The assessment of renal function in the framework of aging is problematic and the question whether renal aging should be considered as a physiological or pathological process remains a much debated issue. Although promising dietary and pharmacological approaches have been tested to retard aging processes or renal function decline in the elderly, proper lifestyle modifications, as those applicable to the general population, currently represent the most plausible approach to maintain kidney health.

A receptor-based bioadsorbent to target advanced glycation end products in chronic kidney disease

The accumulation of advanced glycation end products (AGEs) has been reported to be a major contributor to chronic systemic inflammation. AGEs are not efficiently removed by hemodialysis or the kidney of a chronic kidney disease (CKD) patient. The goal of this study was to develop a receptor for AGEs (RAGE)-based bioadsorbent device that was capable of removing endogenous AGEs from human blood. The extracellular domain of RAGE was immobilized onto agarose beads to generate the bioadsorbent. The efficacy of AGE removal from saline, serum, and whole blood; biological effects of AGE reduction; and hemocompatibility and stability of the bioadsorbent were investigated. The bioadsorbent bound AGE-modified bovine serum albumin (AGE-BSA) with a binding capacity of 0.73 ± 0.07 mg AGE-BSA/mL bioadsorbent. The bioadsorbent significantly reduced the concentration of total AGEs in serum isolated from end-stage kidney disease patients by 57%. AGE removal resulted in a significant reduction of vascular cell adhesion molecule-1 expression in human endothelial cells and abolishment of osteoclast formation in osteoclast progenitor cells. A hollow fiber device loaded with bioadsorbent-reduced endogenous AGEs from recirculated blood to 36% of baseline levels with no significant changes in total protein or albumin concentration. The bioadsorbent maintained AGE-specific binding capacity after freeze-drying and storage for 1 year. This approach provides the foundation for further development of soluble RAGE-based extracorporeal therapies to selectively deplete serum AGEs from human blood and decrease inflammation in patients with diabetes and/or CKD.

Validation study to compare effects of processing protocols on measured N (ε)-(carboxymethyl)lysine and N (ε)-(carboxyethyl)lysine in blood

Epidemiological studies show that elevated plasma levels of advanced glycation end products (AGEs) are associated with diabetes, kidney disease, and heart disease. Thus AGEs have been used as disease progression markers. However, the effects of variations in biological sample processing procedures on the level of AGEs in plasma/serum samples have not been investigated. The objective of this investigation was to assess the effect of variations in blood sample collection on measured N^ε-(carboxymethyl)lysine (CML), the best characterised AGE, and its homolog, N^ε-(carboxyethyl)lysine (CEL). The investigation examined the effect on CML and CEL of different blood collection tubes, inclusion of a stabilising cocktail, effect of freeze thaw cycles, different storage times and temperatures, and effects of delaying centrifugation on a pooled sample from healthy volunteers. CML and CEL were measured in extracted samples by ultra-performance liquid chromatography-tandem mass spectrometry. Median CML and CEL ranged from 0.132 to 0.140 mM/M lys and from 0.053 to 0.060 mM/M lys, respectively. No significant difference was shown CML or CEL in plasma/serum samples. Therefore samples collected as part of epidemiological studies that do not undergo specific sample treatment at collection are suitable for measuring CML and CEL.

Biodistribution and elimination study of fluorine-18 labeled Nε-carboxymethyl-lysine following intragastric and intravenous administration

Background

N^ε-carboxymethyl-lysine (CML) is a major advanced glycation end-product (AGEs) widely found in foods. The aim of our study was to evaluate how exogenous CML-peptide is dynamically absorbed from the gastrointestinal tract and eliminated by renal tubular secretion using microPET imaging.

Methods

The present study consisted of three investigations. In study I, we synthesized the imaging tracer ¹⁸F-CML by reacting N-succinimidyl 4-¹⁸F-fluorobenzoate (¹⁸F-SFB) with CML. In study II, the biological activity of ¹⁸F-CML was evaluated in RAW264.7 cells and HepG2 cells. In study III, the biodistribution and elimination of AGEs in ICR mice were studied in vivo following tail vein injection and intragastric administration of ¹⁸F-CML.

Result

The formation of ¹⁸F-CML was confirmed by comparing its retention time with the corresponding reference compound ¹⁹F-CML. The radiochemical purity (RCP) of ¹⁸F-CML was >95%, and it showed a stable character in vitro and in vivo. Uptake of ¹⁸F-CML by RAW264.7 cells and HepG2 cells could be inhibited by unmodified CML. ¹⁸F-CML was quickly distributed via the blood, and it was rapidly excreted through the kidneys 20 min after tail vein injection. However, ¹⁸F-CML was only slightly absorbed following intragastric administration. After administration of ¹⁸F-CML via a stomach tube, the radioactivity was completely localized in the stomach for the first 15 min. At 150 min post intragastric administration, intense accumulation of radioactivity in the intestines was still observed.

Conclusions

PET technology is a powerful tool for the in vivo analysis of the gastrointestinal absorption of orally administered drugs. ¹⁸F-CML is hardly absorbed by the gastrointestinal tract. It is rapidly distributed and eliminated from blood following intravenous administration. Thus, it may not be harmful to healthy bodies. Our study showed the feasibility of noninvasively imaging ¹⁸F-labeled AGEs and was the first to describe CML-peptide gastrointestinal absorption by means of PET.

Plasma glycation levels are associated with severity in sepsis

BACKGROUND

Advanced glycation end-products (AGE) have been involved in inflammatory diseases and may have an important role in the progression of symptoms. However, few studies have analysed the levels of glycated proteins in sepsis. In this study, we evaluated the levels of the well-known AGE (N(ε) -(carboxymethyl)lysine (CML) and N(ε) -(carboxyethyl)lysine (CEL)) in the plasma of septic patients.

MATERIAL AND METHODS

Plasma from 36 patients admitted to an adult intensive care unit and 6 healthy controls had the levels of CML/CEL measured by ELISA.

RESULTS

The level of AGE in plasma decreased with the increase of severity (1·40±0·46 nmol/mg of protein in sepsis, 0·58±0·23 nmol/mg of protein in severe sepsis and 0·31±0·12 nmol/mg of protein in septic shock). Control plasma presented low AGE concentration (0·06±0·01 nmol/mg protein). Also, we found a decrease in plasma AGE in those patients that died at the end of 28 days follow-up (0·80±0·50 nmol/mg of protein in survivors vs. 0·31±0·10 nmol/mg of protein in nonsurvivors), being associated with the renal component of sequential organ failure assessment (SOFA) score. In the same line, there was a decrease in plasma AGE with the increase in SOFA.

CONCLUSIONS

Our data demonstrate that plasma AGE levels are inversely associated with the severity of sepsis and may be associated with kidney dysfunction.

Natural history of age-related retinal lesions that precede AMD in mice fed high or low glycemic index diets

PURPOSE

Epidemiologic data indicate that people who consume low glycemic index (GI) diets are at reduced risk for the onset and progression of age-related macular degeneration (AMD). The authors sought corroboration of this observation in an animal model.

METHODS

Five- and 16-month-old C57BL/6 mice were fed high or low GI diets until they were 17 and 23.5 months of age, respectively. Retinal lesions were evaluated by transmission electron microscopy, and advanced glycation end products (AGEs) were evaluated by immunohistochemistry.

RESULTS

Retinal lesions including basal laminar deposits, loss of basal infoldings, and vacuoles in the retinal pigment epithelium were more prevalent in the 23.5- than in the 17-month-old mice. Within each age group, consumption of a high GI diet increased the risk for lesions and the risk for photoreceptor abnormalities and accumulation of AGEs.

CONCLUSIONS

Consuming high GI diets accelerates the appearance of age-related retinal lesions that precede AMD in mice, perhaps by increasing the deposition of toxic AGEs in the retina. The data support the hypothesis that consuming lower GI diets, or simulation of their effects with nutraceuticals or drugs, may protect against AMD. The high GI-fed C57BL/6 mouse is a new model of age-related retinal lesions that precede AMD and mimic the early stages of disease and may be useful for drug discovery.

Advanced glycation end products overload might explain intracellular cobalamin deficiency in renal dysfunction, diabetes and aging

Advanced glycation end products (AGEs) contribute to aging. Cobalamin (Cbl) is required for cell growth and functions, and its deficiency causes serious complications. Diabetics and renal patients show high concentrations of Cbl, but metabolic evidence of Cbl deficiency that is reversible after Cbl treatment. Cbl might be sequestered in blood and cannot be delivered to the cell. Megalin mediates the uptake of transcobalamin-Cbl complex into the proximal tubule cells. Megalin is involved in the uptake and degradation of AGEs. In aging, diabetes or renal dysfunction, AGEs might overload megalin thus lowering Cbl uptake. Transcobalamin-Cbl might retain in blood. Shedding of megalin and transcobalamin receptor under glycation conditions is also a possible mechanism of this phenomenon.

AGE restriction in diabetes mellitus: a paradigm shift

Persistently elevated oxidative stress and inflammation precede or occur during the development of type 1 or type 2 diabetes mellitus and precipitate devastating complications. Given the rapidly increasing incidence of diabetes mellitus and obesity in the space of a few decades, new genetic mutations are unlikely to be the cause, instead pointing to environmental initiators. A hallmark of contemporary culture is a preference for thermally processed foods, replete with pro-oxidant advanced glycation endproducts (AGEs). These molecules are appetite-increasing and, thus, efficient enhancers of overnutrition (which promotes obesity) and oxidant overload (which promotes inflammation). Studies of genetic and nongenetic animal models of diabetes mellitus suggest that suppression of host defenses, under sustained pressure from food-derived AGEs, may potentially shift homeostasis towards a higher basal level of oxidative stress, inflammation and injury of both insulin-producing and insulin-responsive cells. This sequence promotes both types of diabetes mellitus. Reducing basal oxidative stress by AGE restriction in mice, without energy or nutrient change, reinstates host defenses, alleviates inflammation, prevents diabetes mellitus, vascular and renal complications and extends normal lifespan. Studies in healthy humans and in those with diabetes mellitus show that consumption of high amounts of food-related AGEs is a determinant of insulin resistance and inflammation and that AGE restriction improves both. This Review focuses on AGEs as novel initiators of oxidative stress that precedes, rather than results from, diabetes mellitus. Therapeutic gains from AGE restriction constitute a paradigm shift.

Oxidative damage in the liver of rats treated with glycolaldehyde

Liver diseases are often associated with hyperglycemia, inflammation, and oxidative stress. These conditions, commonly associated with diabetes mellitus and obesity, facilitate the formation of advanced glycation end products (AGEs). These products are known to impair protein function and promote inflammation. Accumulation of AGEs such as N(ε)-(carboxymethyl)lysine (CML) is related to chronic liver diseases and their severity. Although several reports suggest a crucial role of AGEs in liver failure, there is little investigation on the direct effects of reducing sugars, precursors of AGEs, and on the onset and progression of liver failure. In this work, we investigate the effects of intravenously administrated glycolaldehyde (GA), a short-chain aldehyde, on oxidative parameters in the liver of Wistar rats. Animals received a single injection of GA (10, 50, or 100 mg/kg) and were sacrificed after 6, 12, or 24 hours. Levels of protein carbonyl, lipid peroxidation, and reduced thiol were quantified. The activities of catalase, superoxide dismutase, and glyoxalase I were also assessed. The amount of CML was quantified with specific antibody. There was an increase in oxidative stress markers in the liver of GA-treated rats. Glycolaldehyde induced a decrease in the activities of all enzymes assayed. Also, all tested doses led to an increase in CML content. Our data suggest that GA might play an important role in liver diseases through the impairment of antioxidant defenses and generation of AGEs.

Glycolaldehyde induces oxidative stress in the heart: a clue to diabetic cardiomyopathy?

Cardiovascular complications account for 80% of the mortality related to diabetes mellitus. Hyperglycemia is believed to be the major culprit of angiopathy and cardiomyopathy. High glucose levels and oxidative stress cause elevation of Advanced Glycation End-products that are known to contribute to diabetic complications and correlate with many diseases. However, there are few reports describing the effects of glycating agents other than glucose. Here, we aimed to evaluate the effects of glycolaldehyde (GA) on oxidative stress parameters in the heart of Wistar rats. Male Wistar rats received a single injection of GA (10, 50 or 100 mg/Kg) and were sacrificed 6, 12 or 24 h after injection. As indexes of oxidative stress, we quantified protein carbonylation, lipid peroxidation and total reduced thiols. The activities of superoxide dismutase, catalase and glyoxalase I were assayed. Also, the content of N (ɛ)-(carboxymethyl)lysine (CML) was quantified. Glycolaldehyde induced an imbalance in the redox status, with increased protein carbonylation and lipoperoxidation. Catalase and glyoxalase I had a decrease in their activities. Despite the oxidative stress, we observed no increase in CML content. These results suggest that short-chain aldehydes such as GA might have a significant role in the development of diabetic cardiomyopathy.

Advanced glycation end products on stored red blood cells increase endothelial reactive oxygen species generation through interaction with receptor for advanced glycation end products

BACKGROUND

Recent evidence suggests that storage-induced alterations of the red blood cell (RBC) are associated with adverse consequences in susceptible hosts. As RBCs have been shown to form advanced glycation end products (AGEs) after increased oxidative stress and under pathologic conditions, we examined whether stored RBCs undergo modification with the specific AGE N-(carboxymethyl)lysine (N(ε) -CML) during standard blood banking conditions.

STUDY DESIGN AND METHODS

Purified, fresh RBCs from volunteers were compared to stored RBCs (35-42 days old) obtained from the blood bank. N(ε) -CML formation was quantified using a competitive enzyme-linked immunosorbent assay. The receptor for advanced glycation end products (RAGE) was detected in human pulmonary microvascular endothelial cells (HMVEC-L) by real-time polymerase chain reaction, Western blotting, and flow cytometry. Intracellular reactive oxygen species (ROS) generation was measured by the use of 5-(and 6-)chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester-based assays.

RESULTS

Stored RBCs showed increased surface N(ε) -CML formation when compared with fresh RBCs. HMVEC-L showed detectable surface RAGE expression constitutively. When compared to fresh RBCs, stored RBCs triggered increased intracellular ROS generation in both human umbilical vein endothelial cells and HMVEC-L. RBC-induced endothelial ROS generation was attenuated in the presence of soluble RAGE or RAGE blocking antibody.

CONCLUSIONS

The formation of the AGE N(ε) -CML on the surface of stored RBCs is one functional consequence of the storage lesion. AGE-RAGE interactions may be one mechanism by which transfused RBCs cause endothelial cell damage.

Role of advanced glycation end products (AGEs) and receptor for AGEs (RAGE) in vascular damage in diabetes

A non-enzymatic reaction between ketones or aldehydes and the amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules and to the development and progression of various age-related disorders such as vascular complications of diabetes, Alzheimer's disease, cancer growth and metastasis, insulin resistance and degenerative bone disease. Under hyperglycemic and/or oxidative stress conditions, this process begins with the conversion of reversible Schiff base adducts, and then to more stable, covalently-bound Amadori rearrangement products. Over a course of days to weeks, these early glycation products undergo further reactions and rearrangements to become irreversibly crossed-linked, fluorescent protein derivatives termed advanced glycation end products (AGEs). There is a growing body of evidence that AGE and their receptor RAGE (receptor for AGEs) interaction elicits oxidative stress, inflammatory reactions and thrombosis, thereby being involved in vascular aging and damage. These observations suggest that the AGE-RAGE system is a novel therapeutic target for preventing diabetic vascular complications. In this paper, we review the pathophysiological role of the AGE-RAGE-oxidative stress system and its therapeutic intervention in vascular damage in diabetes. We also discuss here the potential utility of the restriction of food-derived AGEs in diabetic vascular complications.

Immunochemical and mass spectrometric analysis of Nε-(carboxymethyl)lysine content of AGE-BSA systems prepared with and without selected antiglycation agents

The present study was designed to compare surface plasmon resonance (SPR) biosensor, enzyme-linked immunosorbent assay (ELISA), and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) methods for the analysis of Nε-(carboxymethyl)lysine (CML) in glucose-bovine serum albumin (BSA) model systems and to investigate the possible inhibitory effect of selected compounds (α-tocopherol, ferulic acid, rutin, thiamin, thiamin monophosphate, and thiamin pyrophosphate) on CML formation. The reported levels of CML detected were dependent upon the method of analysis employed. The highest reported concentrations were obtained with the SPR biosensor, whereas the lowest were found by ELISA. However, a high correlation was observed between these two immunochemical procedures. CML concentrations were dependent upon the type and concentration of the candidate CML inhibitor. All inhibitory compounds investigated, with the exception of α-tocopherol, decreased the level of CML formation in the glucose-BSA system.

Atorvastatin reduces proteinuria in non-diabetic chronic kidney disease patients partly via lowering serum levels of advanced glycation end products (AGEs)

There is accumulating evidence that advanced glycation end products (AGEs) play a role in the development and progression of chronic kidney disease (CKD). We have previously found that atorvastatin treatment significantly reduces serum levels of AGEs in type 2 diabetic patients and subjects with non-alcoholic steatohepatitis in a cholesterol loweringindependent manner. In this study, we examined whether atorvastatin could reduce proteinuria partly via reduction of serum levels of AGEs in non-diabetic CKD patients. Ten non-diabetic normotensive stage I or II CKD patients with dyslipidemia were enrolled. Patients were treated with atorvastatin (10 mg/day) for one year. All subjects underwent determination of blood chemistries, proteinuria and serum levels of AGEs at baseline and after one year. Atorvastatin treatment for one year significantly decreased circulating levels of total cholesterol, LDL cholesterol, triglycerides and AGEs, while it increased HDL cholesterol levels. Further, although atorvastatin treatment did not affect estimated glomerular filtration rate, it significantly reduced proteinuria. In univariate analyses, proteinuria levels were correlated with total cholesterol, LDL cholesterol, triglycerides, HDL cholesterol (inversely) and AGEs. Multiple stepwise regression analysis revealed that AGE level was a sole independent correlate of proteinuria. In this initial examination of the patients in this study, our present study suggests that atorvastatin could decrease proteinuria in non-diabetic CKD patients with dyslipidemia partly via reduction of serum levels of AGEs. Atorvastatin may have AGE-lowering effects in CKD patients as well that could contribute to renoprotective properties of this agent.

Does accumulation of advanced glycation end products contribute to the aging phenotype?

BACKGROUND

Aging is a complex multifactorial process characterized by accumulation of deleterious changes in cells and tissues, progressive deterioration of structural integrity and physiological function across multiple organ systems, and increased risk of death.

METHODS

We conducted a review of the scientific literature on the relationship of advanced glycation end products (AGEs) with aging. AGEs are a heterogeneous group of bioactive molecules that are formed by the nonenzymatic glycation of proteins, lipids, and nucleic acids.

RESULTS

Humans are exposed to AGEs produced in the body, especially in individuals with abnormal glucose metabolism, and AGEs ingested in foods. AGEs cause widespread damage to tissues through upregulation of inflammation and cross-linking of collagen and other proteins. AGEs have been shown to adversely affect virtually all cells, tissues, and organ systems. Recent epidemiological studies demonstrate that elevated circulating AGEs are associated with increased risk of developing many chronic diseases that disproportionally affect older individuals.

CONCLUSIONS

Based on these data, we propose that accumulation of AGEs accelerate the multisystem functional decline that occurs with aging, and therefore contribute to the aging phenotype. Exposure to AGEs can be reduced by restriction of dietary intake of AGEs and drug treatment with AGE inhibitors and AGE breakers. Modification of intake and circulating levels of AGEs may be a possible strategy to promote health in old age, especially because most Western foods are processed at high temperature and are rich in AGEs.