Atherogenesis and advanced glycation: promotion, progression, and prevention

Advanced glycation end products and insulin resistance in diabetic nephropathy

Insulin resistance is a central hallmark that connects the metabolic syndrome and diabetes to the resultant formation of advanced glycation end products (AGEs), which further results in the complications of diabetes, including diabetic nephropathy. Several factors play an important role as an inducer to diabetic nephropathy, and AGEs elicit their harmful effects via interacting with the receptor for AGEs Receptor for AGEs, by induction of pro-inflammatory cytokines, oxidative stress, endoplasmic reticulum stress and fibrosis in the kidney tissues leading to the loss of renal function. Insulin resistance results in the activation of other alternate pathways governed by insulin, which results in the hypertrophy of the renal cells and tissue remodeling. Apart from the glucose uptake and disposal, insulin dependent PI3K and Akt also upregulate the expression of endothelial nitric oxide synthase, that results in increasing the bioavailability of nitric oxide in the vascular endothelium, which further results in tissue fibrosis. Considering the global prevalence of diabetic nephropathy, and the impact of protein glycation, various inhibitors and treatment avenues are being developed, to prevent the progression of diabetic complications. In this chapter, we discuss the role of glycation in insulin resistance and further its impact on the kidney.

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.

RAGE is a critical factor of sex-based differences in age-induced kidney damage

Introduction: Advanced glycation end products (AGEs) are a heterogeneous group of molecules with potential pathophysiological effects on the kidneys. Fibrosis together with the accumulation of AGEs has been investigated for its contribution to age-related decline in renal function. AGEs mediate their effects in large parts through their interactions with the receptor for AGEs (RAGE). RAGE is a transmembrane protein that belongs to the immunoglobulin superfamily and has the ability to interact with multiple pro-inflammatory/pro-oxidative ligands. The role of RAGE in aging kidneys has not been fully characterized, especially for sex-based differences.

Methods: Therefore, we analyzed constitutive RAGE knockout (KO) mice in an age- and sex-dependent manner. Paraffin-embedded kidney sections were used for histological analysis and protein expression of fibrosis and damage markers. RNA expression analysis from the kidney cortex was done by qPCR for AGE receptors, kidney damage, and early inflammation/fibrosis factors. FACS analysis was used for immune cell profiling of the kidneys.

Results: Histological analysis revealed enhanced infiltration of immune cells (positive for B220) in aged (>70 weeks old) KO mice in both sexes. FACS analysis revealed a similar pattern of enhanced B-1a cells in aged KO mice. There was an age-based increase in pro-fibrotic and pro-inflammatory markers (IL-6, TNF, TGF-β1, and SNAIL1) in KO male mice that presumably contributed to renal fibrosis and renal damage (glomerular and tubular). In fact, in KO mice, there was an age-dependent increase in renal damage (assessed by NGAL and KIM1) that was accompanied by increased fibrosis (assessed by CTGF). This effect was more pronounced in male KO mice than in the female KO mice. In contrast to the KO animals, no significant increase in damage markers was detectable in wild-type animals at the age examined (>70 weeks old). Moreover, there is an age-based increase in AGEs and scavenger receptor MSR-A2 in the kidneys.

Discussion: Our data suggest that the loss of the clearance receptor RAGE in male animals further accelerates age-dependent renal damage; this could be in part due to an increase in AGEs load during aging and the absence of protective female hormones. By contrast, in females, RAGE expression seems to play only a minor role when compared to tissue pathology.

Advanced Glycation End-Products (AGEs): Formation, Chemistry, Classification, Receptors, and Diseases Related to AGEs

Advanced glycation end-products (AGEs) constitute a non-homogenous, chemically diverse group of compounds formed either exogeneously or endogeneously on the course of various pathways in the human body. In general, they are formed non-enzymatically by condensation between carbonyl groups of reducing sugars and free amine groups of nucleic acids, proteins, or lipids, followed by further rearrangements yielding stable, irreversible end-products. In the last decades, AGEs have aroused the interest of the scientific community due to the increasing evidence of their involvement in many pathophysiological processes and diseases, such as diabetes, cancer, cardiovascular, neurodegenerative diseases, and even infection with the SARS-CoV-2 virus. They are recognized by several cellular receptors and trigger many signaling pathways related to inflammation and oxidative stress. Despite many experimental research outcomes published recently, the complexity of their engagement in human physiology and pathophysiological states requires further elucidation. This review focuses on the receptors of AGEs, especially on the structural aspects of receptor-ligand interaction, and the diseases in which AGEs are involved. It also aims to present AGE classification in subgroups and to describe the basic processes leading to both exogeneous and endogeneous AGE formation.

Advanced Glycation End-Products Can Activate or Block Bitter Taste Receptors

Bitter taste receptors (T2Rs) are expressed in several tissues of the body and are involved in a variety of roles apart from bitter taste perception. Advanced glycation end-products (AGEs) are produced by glycation of amino acids in proteins. There are varying sources of AGEs, including dietary food products, as well as endogenous reactions within our body. Whether these AGEs are T2R ligands remains to be characterized. In this study, we selected two AGEs, namely, glyoxal-derived lysine dimer (GOLD) and carboxymethyllysine (CML), based on their predicted interaction with the well-studied T2R4, and its physiochemical properties. Results showed predicted binding affinities (K_d) for GOLD and CML towards T2R4 in the nM and μM range, respectively. Calcium mobilization assays showed that GOLD inhibited quinine activation of T2R4 with IC₅₀ 10.52 ± 4.7 μM, whilst CML was less effective with IC₅₀ 32.62 ± 9.5 μM. To characterize whether this antagonism was specific to quinine activated T2R4 or applicable to other T2Rs, we selected T2R14 and T2R20, which are expressed at significant levels in different human tissues. A similar effect of GOLD was observed with T2R14; and in contrast, GOLD and CML activated T2R20 with an EC₅₀ of 79.35 ± 29.16 μM and 65.31 ± 17.79 μM, respectively. In this study, we identified AGEs as novel T2R ligands that caused either activation or inhibition of different T2Rs.

PredGly: predicting lysine glycation sites for Homo sapiens based on XGboost feature optimization

Motivation

Protein glycation is a familiar post-translational modification (PTM) which is a two-step non-enzymatic reaction. Glycation not only impairs the function but also changes the characteristics of the proteins so that it is related to many human diseases. It is still much more difficult to systematically detect glycation sites due to the glycated residues without crucial patterns. Computational approaches, which can filter supposed sites prior to experimental verification, can extremely increase the efficiency of experiment work. However, the previous lysine glycation prediction method uses a small number of training datasets. Hence, the model is not generalized or pervasive.

Results

By searching from a new database, we collected a large dataset in Homo sapiens. PredGly, a novel software, can predict lysine glycation sites for H.sapiens, which was developed by combining multiple features. In addition, XGboost was adopted to optimize feature vectors and to improve the model performance. Through comparing various classifiers, support vector machine achieved an optimal performance. On the basis of a new independent test set, PredGly outperformed other glycation tools. It suggests that PredGly can provide more instructive guidance for further experimental research of lysine glycation.

Availability and implementation

https://github.com/yujialinncu/PredGly

Supplementary information

Supplementary data are available at Bioinformatics online.

Investigating the Glycating Effects of Glucose, Glyoxal and Methylglyoxal on Human Sperm

Glycation is the non-enzymatic reaction between reducing sugars, such as glucose, and proteins, lipids or nucleic acids, producing Advanced Glycation End (AGE) products. AGEs, produced during natural senescence as well as through lifestyle factors such as diet and smoking, are key pathogenic compounds in the initiation and progression of diabetes. Importantly, many of these factors and conditions also have influence on male fertility, affecting sperm count and semen quality, contributing to the decreasing trend in male fertility. This study investigated the impact of AGEs on sperm damage. In vitro sperm glycation assays were used to determine the levels and localization of the potent AGE compound, carboxymethyl-lysine (CML) in response to treatment with the glycating compounds glucose, glyoxal and methylglyoxal. Sperm function assays were then used to assess the effects of glycation on motility and hyaluronan binding, and levels of oxidative DNA damage were analyzed through measurement of the marker, 8-oxoguanine. Results showed that glyoxal, but not glucose or methylglyoxal, induced significant increases in CML levels on sperm and this correlated with an increase in 8-oxoguanine. Immunocytochemistry revealed that AGEs were located on all parts of the sperm cell and most prominently on the head region. Sperm motility and hyaluronidase activity were not adversely affected by glycation. Together, the observed detrimental effects of the increased levels of AGE on DNA integrity, without an effect on motility and hyaluronidase activity, suggest that sperm may retain some fertilizing capacity under these adverse conditions.

Ratio of serum levels of AGEs to soluble RAGE is correlated with trimethylamine-N-oxide in non-diabetic subjects

Trimethylamine (TMA), an intestinal microflora-dependent metabolite formed from phosphatidylcholine- and L-carnitine-rich food, such as red meat, is further converted to trimethylamine-N-oxide (TMAO), which could play a role in cardiometabolic disease. Red meat-derived products are one of the major environmental sources of advanced glycation end products (AGEs) that may also contribute to the pathogenesis of cardiometabolic disorders through the interaction with receptor for AGEs (RAGE). However, the relationship among AGEs, soluble form of RAGE (sRAGE) and TMAO in humans remains unclear. Non-diabetic subjects underwent a physical examination, determination of blood chemistry and anthropometric variables, including AGEs, sRAGE, TMA and TMAO. Multiple regression analyses revealed that HbA1c, uric acid and AGEs were independently associated with log TMA, whereas log AGEs to sRAGE ratio and statin non-use were independently correlated with log TMAO. Our present findings indicated that AGEs to sRAGE ratio was correlated with log TMAO, a marker of cardiometabolic disorders.

N-butanol extracts of Morinda citrifolia suppress advanced glycation end products (AGE)-induced inflammatory reactions in endothelial cells through its anti-oxidative properties

Background

Advanced glycation end products (AGEs), senescent macroprotein derivatives formed during a normal aging process and acceleratedly under diabetic conditions, play a role in atherosclerotic cardiovascular disease. AGEs cause endothelial cell (EC) damage, an initial trigger for atherosclerosis through the interaction with a receptor for AGEs (RAGE). We have previously shown that n-butanol extracts of Morinda citrifolia (noni), a plant belonging to the family Rubiaceae, block the binding of AGEs to RAGE in vitro. In this study, we examined the effects of n-butanol extracts of noni on reactive oxygen species (ROS) generation and inflammatory reactions on AGE-exposed human umbilical vein ECs (HUVECs).

Methods

HUVECs were treated with 100 μg/ml AGE-bovine serum albumin (AGE-BSA) or non-glycated BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni for 4 h. Then ROS generation and inflammatory and gene expression in HUVECs were evaluated by dihydroethidium staining and real-time reverse transcription-polymerase chain reaction analyses, respectively. THP-1 cell adhesion to HUVECs was measured after 2-day incubation of AGE-BSA or BSA in the presence or absence of 670 ng/ml n-butanol extracts of noni.

Results

N-butanol extracts of noni at 670 ng/ml significantly inhibited the AGE-induced ROS generation and RAGE, intercellular adhesion molecule-1 and plasminogen activator inhibitor-1 gene expressions in HUVECs. AGEs significantly increased monocytic THP-1 cell adhesion to HUVECs, which was also prevented by 670 ng/ml n-butanol extracts of noni.

Conclusions

The present study demonstrated for the first time that N-butanol extracts of noni could suppress the AGE-induced inflammatory reactions in HUVECs through its anti-oxidative properties via blocking of the interaction of AGEs with RAGE. Inhibition of the AGE-RAGE axis by n-butanol extracts of noni may be a novel nutraceutical strategy for the treatment of cardiovascular disease.

Advanced glycation end products mediated cellular and molecular events in the pathology of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetic patients and a leading cause of end-stage renal disease (ESRD). Degenerative changes such as glomerular hypertrophy, hyperfiltration, widening of basement membranes, tubulointerstitial fibrosis, glomerulosclerosis and podocytopathy manifest in various degrees of proteinuria in DN. One of the key mechanisms implicated in the pathogenesis of DN is non-enzymatic glycation (NEG). NEG is the irreversible attachment of reducing sugars onto free amino groups of proteins by a series of events, which include the formation of Schiff’s base and an Amadori product to yield advanced glycation end products (AGEs). AGE modification of client proteins from the extracellular matrix induces crosslinking, which is often associated with thickening of the basement membrane. AGEs activate several intracellular signaling cascades upon interaction with receptor for AGEs (RAGE), which manifest in aberrant cellular responses such as inflammation, apoptosis and autophagy, whereas other receptors such as AGE-R1, AGE-R3 and scavenger receptors also bind to AGEs and ensue endocytosis and degradation of AGEs. Elevated levels of both serum and tissue AGEs are associated with adverse renal outcome. Increased evidence supports that attenuation of AGE formation and/or inhibition of RAGE activation manifest(s) in improving renal function. This review provides insights of NEG, discusses the cellular and molecular events triggered by AGEs, which manifest in the pathogenesis of DN including renal fibrosis, podocyte epithelial-mesenchymal transition and activation of renin-angiotensin system. Therapies designed to target AGEs, such as inhibitors of AGEs formation and crosslink breakers, are discussed.

Sulforaphane reduces advanced glycation end products (AGEs)-induced inflammation in endothelial cells and rat aorta

BACKGROUND AND AIMS

Advanced glycation end products (AGEs)-receptor RAGE interaction evokes oxidative stress and inflammatory reactions, thereby being involved in endothelial cell (EC) damage in diabetes. Sulforaphane is generated from glucoraphanin, a naturally occurring isothiocyanate found in widely consumed cruciferous vegetables, by myrosinase. Sulforaphane has been reported to protect against oxidative stress-mediated cell and tissue injury. However, effects of sulforaphane on AGEs-induced vascular damage remain unclear.

METHODS AND RESULTS

In this study, we investigated whether and how sulforaphane could inhibit inflammation in AGEs-exposed human umbilical vein ECs (HUVECs) and AGEs-injected rat aorta. Sulforaphane treatment for 4 or 24 h dose-dependently inhibited the AGEs-induced increase in RAGE, monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecular-1 (VCAM-1) gene expression in HUVECs. AGEs significantly stimulated MCP-1 production by, and THP-1 cell adhesion to, HUVECs, both of which were prevented by 1.6 μM sulforaphane. Sulforaphane significantly suppressed oxidative stress generation and NADPH oxidase activation evoked by AGEs in HUVECs. Furthermore, aortic RAGE, ICAM-1 and VCAM-1 expression in AGEs-injected rats were increased, which were suppressed by simultaneous infusion of sulforaphane.

CONCLUSION

The present study demonstrated for the first time that sulforaphane could inhibit inflammation in AGEs-exposed HUVECs and AGEs-infused rat aorta partly by suppressing RAGE expression through its anti-oxidative properties. Inhibition of the AGEs-RAGE axis by sulforaphane might be a novel therapeutic target for vascular injury in diabetes.

Combined therapy with metformin and insulin attenuates systemic and hepatic alterations in a model of high-fat diet-/streptozotocin-induced diabetes

In this study we have explored the pathogenesis of the hepatic alterations which occur in diabetes and the modulation of these complications by the combination of metformin adjunct treatment and insulin monotherapy. For this purpose, diabetic rats were treated with insulin (DM + Ins) or metformin plus insulin (DM + Met + Ins). Biochemical and cardiometabolic parameters were analysed by spectrophotometry. Intravital microscopy was used to study the hepatic microcirculation. In the liver tissue, real-time PCR was used to analyse oxidative stress enzymes, inflammatory markers and receptors for advanced glycation end products (AGE) (RAGE) gene expression. Lipid peroxidation was assessed by thiobarbituric acid reactive species (TBARs) analyses. AGE deposition and RAGE protein expression were studied by fluorescence spectrophotometry and Western blot respectively. Body weight, %HbA1c , urea, total proteins and oxidative stress parameters were found to be similarly improved by insulin or Met + Ins treatments. On the other hand, Met + Ins treatment showed a more pronounced effect on fasting blood glucose level than insulin monotherapy. Fructosamine, uric acid, creatinine, albumin and amylase levels and daily insulin dose requirements were found to be only improved by the combined Met + Ins treatment. Liver, renal and pancreatic dysfunction markers were found to be more positively affected by metformin adjunct therapy when compared to insulin treatment. Liver microcirculation damage was found to be completely protected by Met + Ins treatment, while insulin monotherapy showed no effect. Our results suggest that oxidative stress, microcirculatory damage and glycated proteins could be involved in the aetiology of liver disease due to diabetes. Additionally, metformin adjunct treatment improved systemic and liver injury in induced diabetes and showed a more pronounced effect than insulin monotherapy.

Fructated apolipoprotein A-I exacerbates cellular senescence in human umbilical vein endothelial cells accompanied by impaired insulin secretion activity and embryo toxicity

Glycation of apolipoproteins is a major feature of the production of dysfunctional high-density lipoprotein (HDL), which is associated with the incidence of several metabolic diseases such as coronary artery disease and diabetes. In this report, fructated apoA-I (fA-I) induced by fructose treatment showed a covalently multimerized band without cross-linking, and lysine residues were irreversibly modified to prevent crosslinking. Using pancreatic β-cells, insulin secretion was impaired by fA-I in the lipid-free and reconstituted HDL (rHDL) states, by up to 35%, and 40%, respectively, under hyperglycemic conditions (25 mmol/L glucose). Treatment of human umbilical vein endothelial cells (HUVECs) with fA-I and HDL from elderly patients caused a 1.8-fold and 1.5-fold increased cellular senescence, respectively, along with increased lysosomal enlargement. In the lipid-free and rHDL states, fA-I increased embryo death by 1.5-fold and 2.5-fold, respectively, along with the production of oxidized species. Furthermore, rHDL containing fA-I (fA-I-rHDL) showed a higher isoelectric point (pI, approximately 8.5), whereas rHDL containing nA-I (nA-I-rHDL) showed a narrow band range with lower pI (around 8.0) as well as a much smaller particle size than that of nA-I-rHDL. In conclusion, fructose-mediated apoA-I fructation resulted in the severe loss of several beneficial functions of apoA-I and HDL, including anti-senescence and insulin secretion activities, accompanied with increased susceptibility to protein degradation and structural modification.

Genetic analysis of advanced glycation end products in the DHS MIND study

Advanced glycation end-products (AGEs) are a diverse group of molecules produced by the non-enzymatic addition of glucose to proteins, lipids, and nucleic acids. AGE levels have been associated with hyperglycemia and diabetic complications, especially in animal models, but less clearly in human studies. We measured total serum AGEs using an enzyme linked immunosorbant assay (ELISA) in 506 subjects from 246 families in the Diabetes Heart Study (DHS)/DHS MIND Study (n=399 type 2 diabetes (T2D)-affected). Single nucleotide polymorphisms (SNPs) in several candidate genes, including known AGE receptors, were tested for their influence on circulating AGE levels. The genetic analysis was expanded to include an exploratory genome-wide association study (GWAS) and exome chip analysis of AGEs (≈440,000 SNPs). AGEs were found to be highly heritable (h(2)=0.628, p=8.96 × 10(-10)). While no SNPs from candidate genes were significantly associated after Bonferroni correction, rs1035798 in the gene AGER was the most significantly associated (p=0.007). Additionally, rs7198427, in MT1A, showed a nominally significant p-value (p=0.0099). No SNPs from the GWAS or exome studies were identified after correction for multiple comparisons; however, rs17054480 in the PALLD2 gene on chromosome 4 showed the strongest association (p=7.77 × 10(-7)). Five SNPs at two loci (ISCA2/NPC2 and FBXO33) had p-values of less than 2.0 × 10(-5) and three additional SNPs (rs716326 in MACROD2, and rs6795197 and rs6765857 in ZBTB38) showed a nominal association with p-values of less than 1.0 × 10(-5).These findings provide a foundation for further investigation into the genetic component of circulating AGEs.

RAGE and AGEs in Mild Cognitive Impairment of Diabetic Patients: A Cross-Sectional Study

OBJECTIVE

Receptor for advanced glycation end products (AGEs; RAGE) binds to both AGEs and amyloid-beta peptides. RAGE is involved in chronic complications of type 2 diabetes and Alzheimer's disease. We aimed to investigate the roles of RAGE, AGEs and the Gly82Ser polymorphism of RAGE in mild cognitive impairment (MCI) among type 2 diabetes patients.

METHODS

Of the 167 hospitalized type 2 diabetes patients recruited, 82 satisfied the diagnostic criteria for MCI, and 85 matched control individuals were classified as non-MCI. Demographic data were collected, and the soluble RAGE (sRAGE) concentrations, serum AGE-peptide (AGE-P) levels, RAGE Gly82Ser genotype and neuropsychological test results were examined.

RESULTS

The MCI group exhibited a decreased sRAGE level (0.87±0.35 vs. 1.05±0.52 ng/ml, p<0.01) and an increased serum AGE-P level (3.54±1.27 vs. 2.71±1.18 U/ml, p<0.01) compared with the control group. Logistic regression analysis indicated that each unit reduction in the sRAGE concentration increased the MCI risk by 54% (OR 0.46[95% CI 0.22-0.96], p = 0.04) and that each unit increase in the AGE-P level increased the MCI risk by 72% in the type 2 diabetes patients (OR 1.72[95% CI 1.31-2.28], p<0.01). The serum sRAGE level was negatively correlated with the score on the trail making test-B (TMT-B) (r = -0.344, p = 0.002), which indicates early cognitive deficits related to diabetes. Moreover, the AGE-P level was positively correlated with multiple cognitive domains (all p<0.05). No significant differences in the neuropsychological test results or serum RAGE concentrations between the different RAGE genotypes or in the RAGE genotype frequencies between the MCI and control groups were identified (all p>0.05).

CONCLUSIONS

The RAGE pathway partially mediates AGE-induced MCI in diabetic patients. The serum AGE-P level may serve as a serum biomarker of MCI in these individuals, and sRAGE represents a predictor and even a potential intervention target of early cognitive decline in type 2 diabetes patients.

TRIAL REGISTRATION

Advanced Glycation End Products Induced Cognitive Impairment in Diabetes: BDNF Signal Meditated Hippocampal Neurogenesis ChiCTR-OCC-15006060.

Advanced glycation End-products (AGEs): an emerging concern for processed food industries

The global food industry is expected to increase more than US $ 7 trillion by 2014. This rise in processed food sector shows that more and more people are diverging towards modern processed foods. As modern diets are largely heat processed, they are more prone to contain high levels of advanced glycation end products (AGEs). AGEs are a group of complex and heterogeneous compounds which are known as brown and fluorescent cross-linking substances such as pentosidine, non-fluorescent cross-linking products such as methylglyoxal-lysine dimers (MOLD), or non-fluorescent, non-cross linking adducts such as carboxymethyllysine (CML) and pyrraline (a pyrrole aldehyde). The chemistry of the AGEs formation, absorption and bioavailability and their patho-biochemistry particularly in relation to different complications like diabetes and ageing discussed. The concept of AGEs receptor - RAGE is mentioned. AGEs contribute to a variety of microvascular and macrovascular complications through the formation of cross-links between molecules in the basement membrane of the extracellular matrix and by engaging the receptor for advanced glycation end products (RAGE). Different methods of detection and quantification along with types of agents used for the treatment of AGEs are reviewed. Generally, ELISA or LC-MS methods are used for analysis of foods and body fluids, however lack of universally established method highlighted. The inhibitory effect of bioactive components on AGEs by trapping variety of chemical moieties discussed. The emerging evidence about the adverse effects of AGEs makes it necessary to investigate the different therapies to inhibit AGEs.

Dipeptidyl peptidase-4 deficiency protects against experimental diabetic nephropathy partly by blocking the advanced glycation end products-receptor axis

Advanced glycation end products (AGEs) and their receptor (RAGE) have a role in diabetic nephropathy. We have recently found that linagliptin, an inhibitor of dipeptidyl peptidase-4 (DPP-4), could inhibit renal damage in type 1 diabetic rats by suppressing the AGE-RAGE axis. However, it remains unclear whether DPP-4 deficiency could also have beneficial effects on experimental diabetic nephropathy. To address the issue, we rendered wild-type F344/NSlc and DPP-4-deficient F344/DuCrl/Crlj rats diabetic by injection of streptozotocin, and then investigated whether DPP-4 deficiency could block the activation of AGE-RAGE axis in the diabetic kidneys and resultantly ameliorate renal injury in streptozotocin-induced diabetic rats. Compared with control rats at 9 and 11 weeks old, body weight and heart rates were significantly lower, while fasting blood glucose was higher in wild-type and DPP-4-deficient diabetic rats at the same age. There was no significant difference of body weight, fasting blood glucose and lipid parameters between the two diabetic rat strains. AGEs, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and nitrotyrosine levels in the kidney, renal gene expression of RAGE and intercellular adhesion molecule-1, glomerular area, urinary excretion of 8-OHdG and albumin, and the ratio of renal to body weight were increased in wild-type diabetic rats at 9 and/or 11 weeks old compared with age-matched control rats, all of which except for urinary 8-OHdG levels at 11 weeks old were significantly suppressed in DPP-4-deficient diabetic rats. Our present study suggests that DPP-4 deficiency could exert beneficial actions on type 1 diabetic nephropathy partly by blocking the AGE-RAGE axis. DPP-4 might be a novel therapeutic target for preventing diabetic nephropathy.

Switching to multiple daily injection therapy with glulisine improves glycaemic control, vascular damage and treatment satisfaction in basal insulin glargine-injected diabetic patients

BACKGROUND

Basal and bolus insulin therapy is required for strict blood control in diabetic patients, which could lead to prevention of vascular complications in diabetes. However, the optimal combination regimen is not well established.

METHODS

Fifty-nine diabetic patients (49 type 1 and 10 type 2; 52.9 ± 13.3 years old) whose blood glucose levels were uncontrolled (HbA1c  > 6.2%) by combination treatment of basal insulin glargine with multiple daily pre-meal injections of bolus short-acting insulin [aspart (n = 19), lispro (n = 37) and regular human insulin (n = 3)] for at least 8 weeks were enrolled in this study. We examined whether glycaemic control and vascular injury were improved by replacement of short-acting insulin with glulisine. Patient satisfaction was assessed with Diabetes Treatment Satisfaction Questionnaire.

RESULTS

Although bolus and basal insulin doses were almost unchanged before and after replacement therapy, switching to glulisine insulin for 24 weeks significantly decreased level of HbA1c , advanced glycation end products (AGEs), soluble receptor for AGEs (sRAGE), monocyte chemoattractant protein-1 (MCP-1) and urinary albumin excretion. In multiple stepwise regression analysis, change in MCP-1 values from baseline (ΔMCP-1) was a sole determinant of log urinary albumin excretion. ΔAGEs and ΔsRAGE were independently correlated with each other. The relationship between ΔMCP-1 and ΔsRAGE was marginally significant (p = 0.05). Replacement of short-acting insulin by glulisine significantly increased Diabetes Treatment Satisfaction Questionnaire scores.

CONCLUSIONS

Our present study suggests that combination therapy of glargine with multiple daily pre-meal injections of glulisine might show superior efficacy in controlling blood glucose, preventing vascular damage and improving treatment satisfaction in diabetic patients.

Advanced glycation end products: role in pathology of diabetic cardiomyopathy

Increasing evidence demonstrates that advanced glycation end products (AGEs) play a pivotal role in the development and progression of diabetic heart failure, although there are numerous other factors that mediate the disease response. AGEs are generated intra- and extracellularly as a result of chronic hyperglycemia. Then, following the interaction with receptors for advanced glycation end products (RAGEs), a series of events leading to vascular and myocardial damage are elicited and sustained, which include oxidative stress, increased inflammation, and enhanced extracellular matrix accumulation resulting in diastolic and systolic dysfunction. Whereas targeting glycemic control and treating additional risk factors, such as obesity, dyslipidemia, and hypertension, are mandatory to reduce chronic complications and prolong life expectancy in diabetic patients, drug therapy tailored to reducing the deleterious effects of the AGE-RAGE interactions is being actively investigated and showing signs of promise in treating diabetic cardiomyopathy and associated heart failure. This review shall discuss the formation of AGEs in diabetic heart tissue, potential targets of glycation in the myocardium, and underlying mechanisms that lead to diabetic cardiomyopathy and heart failure along with the use of AGE inhibitors and breakers in mitigating myocardial injury.

DNA aptamer raised against advanced glycation end products inhibits melanoma growth in nude mice

Epidemiological studies have suggested that diabetes is associated with an increased risk of cancer. However, the underlying molecular mechanism remains unclear. We investigated here whether DNA aptamer directed against advanced glycation end products (AGE-aptamer) inhibited melanoma growth in nude mice. G361 melanoma cells were injected intradermally into the upper flank of athymic nude mice. Mice received continuous intraperitoneal infusion (0.136 μg/day) of either AGE-aptamer (n=9) or Control-aptamer (n=8) by an osmotic mini pump. Tumor volume was measured at 4-day interval, and G361 melanoma was excised at day 43 after the aptamer treatment. We further examined the effects of AGE-aptamer on proliferation of AGE-exposed endothelial cells and G361 cells. AGE-aptamer significantly inhibited the in vivo-tumor growth of G361 melanoma. Immunohistochemical and western blotting analyses of G361 melanoma revealed that AGE-aptamer decreased expression levels of proliferating nuclear antigen, CD31 and Mac-3, markers of endothelial cells and macrophages, respectively. AGE-aptamer significantly decreased the number of tumor-associated vessels. AGE, receptor for AGE (RAGE) and vascular endothelial growth factor levels were also reduced in AGE-aptamer-treated G361 melanoma. AGE-aptamer inhibited the AGE-induced proliferation and tube formation of endothelial cells as well as the growth of G361 cells in vitro. The present findings suggest that AGE-aptamer could inhibit the AGE-RAGE axis in G361 melanoma and resultantly suppress the tumor growth in nude mice by blocking the angiogenesis. AGE-aptamer might be a novel therapeutic strategy for preventing the progression of malignant melanoma in diabetes.

Advanced glycation end products play adverse proinflammatory activities in osteoporosis

Osteoporosis is a major public health burden that is expected to further increase as the global population ages. In the last twenty years, advanced glycation end products (AGEs) have been shown to be critical mediators both in the pathogenesis and development of osteoporosis and other chronic degenerative diseases related to aging. The accumulation of AGEs within the bone induces the formation of covalent cross-links with collagen and other bone proteins which affects the mechanical properties of tissue and disturbs bone remodelling and deterioration, underlying osteoporosis. On the other hand, the gradual deterioration of the immune system during aging (defined as immunosenescence) is also characterized by the generation of a high level of oxidants and AGEs. The synthesis and accumulation of AGEs (both localized within the bone or in the systemic circulation) might trigger a vicious circle (in which inflammation and aging merged in the word "Inflammaging") which can establish and sustain the development of osteoporosis. This narrative review will update the molecular mechanisms/pathways by which AGEs induce the functional and structural bone impairment typical of osteoporosis.

Role of advanced glycation end products in cellular signaling

Improvements in health care and lifestyle have led to an elevated lifespan and increased focus on age-associated diseases, such as neurodegeneration, cardiovascular disease, frailty and arteriosclerosis. In all these chronic diseases protein, lipid or nucleic acid modifications are involved, including cross-linked and non-degradable aggregates, such as advanced glycation end products (AGEs). Formation of endogenous or uptake of dietary AGEs can lead to further protein modifications and activation of several inflammatory signaling pathways. This review will give an overview of the most prominent AGE-mediated signaling cascades, AGE receptor interactions, prevention of AGE formation and the impact of AGEs during pathophysiological processes.

Telmisartan inhibits AGE-induced podocyte damage and detachment

Advanced glycation end products (AGE) formed at an accelerated rate under diabetes, could cause podocyte apoptosis, thereby being involved in the development and progression of diabetic nephropathy. Renin-angiotensin system (RAS) plays a role in diabetic nephropathy as well. However, it remains unknown whether there exists a pathophysiological crosstalk between the RAS and AGE in podocyte damage in diabetic nephropathy. Therefore, this study investigated the effects of telmisartan, an angiotensin II (Ang II) type 1 receptor (AT1R) blocker on AGE or Ang II-induced podocyte damage in vitro. We further examined here the effects of AGE on AT1R expression levels in podocytes. AGE or Ang II not only increased DNA damage of podocytes which was evaluated by comet assay, but also induced cell detachment, both of which were significantly blocked by the treatment with telmisartan. AGE significantly increased AT1R levels in podocytes, whereas podocyte Ang II production was modestly stimulated by AGE. Telmisartan alone did not affect the release of lactate dehydrogenase from podocytes. Our present study suggests that AGE could induce podocyte DNA damage and detachment partly via stimulation of the Ang II-AT1R axis, thus providing a novel beneficial aspect of telmisartan in diabetic nephropathy.

Advanced glycation end products augment experimental hepatic fibrosis

BACKGROUND AND AIMS

Advanced glycation end products (AGEs) are nonenzymatic modifications of proteins by reducing sugars. These compounds accumulate in a number of chronic disease states, contributing to tissue injury via several mechanisms, including activation of the receptor for advanced glycation end products (RAGE). We aimed to investigate whether AGEs can exacerbate chronic liver injury and contribute to hepatic fibrosis.

METHODS

We initially studied the effects of chronic hepatic exposure to high levels of AGEs given intraperitoneally as AGE-rat serum albumin. In a separate experiment, we examined the impact of high AGE exposure in rats following bile duct ligation (BDL).

RESULTS

In normal rats, chronic AGE-rat serum albumin administration induced significant increases in α-smooth muscle actin gene and protein expression but did not induce fibrosis or biochemical evidence of liver injury. However, in BDL animals, AGE-bovine serum albumin administration significantly increased hepatic fibrosis as evidenced by increased collagen content and α-smooth muscle actin expression, compared with BDL alone. Furthermore, AGEs increased hepatic oxidative stress and receptor for advanced glycation end products gene expression.

CONCLUSIONS

These findings suggest that AGEs may contribute to the pathogenesis of chronic liver injury and fibrosis.

Potential clinical utility of advanced glycation end product cross-link breakers in age- and diabetes-associated disorders

Reducing sugars can react nonenzymatically with the amino groups of proteins to form Amadori products. These early glycation products undergo further complex reactions, such as rearrangement, dehydration, and condensation, to become irreversibly cross-linked, heterogeneous fluorescent derivatives, termed advanced glycation end products (AGEs). The formation and accumulation of AGEs have been known to progress in a normal aging process and at an accelerated rate under diabetes. Nonenzymatic glycation and cross-linking of proteins not only leads to an increase in vascular and myocardial stiffness, but also deteriorates structural integrity and physiological function of multiple organ systems. Furthermore, there is accumulating evidence that interaction of AGEs with a cell-surface receptor, receptor for AGEs (RAGE), elicits oxidative stress generation and subsequently evokes inflammatory, thrombogenic, and fibrotic reactions, thereby being involved in atherosclerosis, diabetic microvascular complications, erectile dysfunction, and pancreatic β-cell apoptosis. Recently, AGE cross-link breakers have been discovered. Therefore, removal of the preexisting AGEs by the breakers has emerged as a novel therapeutic approach to various types of diseases that develop with aging. This article summarizes the potential clinical utility of AGE cross-link breakers in the prevention and management of age- and diabetes-associated disorders.

Involvement of TAGE-RAGE System in the Pathogenesis of Diabetic Retinopathy

Diabetic complications are a leading cause of acquired blindness, end-stage renal failure, and accelerated atherosclerosis, which are associated with the disabilities and high mortality rates seen in diabetic patients. Continuous hyperglycemia is involved in the pathogenesis of diabetic micro- and macrovascular complications via various metabolic pathways, and numerous hyperglycemia-induced metabolic and hemodynamic conditions exist, including increased generation of various types of advanced glycation end-products (AGEs). Recently, we demonstrated that glyceraldehyde-derived AGEs, the predominant structure of toxic AGEs (TAGE), play an important role in the pathogenesis of angiopathy in diabetic patients. Moreover, recent evidence suggests that the interaction of TAGE with the receptor for AGEs (RAGE) elicits oxidative stress generation in numerous types of cells, all of which may contribute to the pathological changes observed in diabetic complications. In this paper, we discuss the pathophysiological role of the TAGE-RAGE system in the development and progression of diabetic retinopathy.

From hyperglycemia to AGE-RAGE interaction on the cell surface: a dangerous metabolic route for diabetic patients

BACKGROUND

Diabetes mellitus constitutes a serious public health problem. Recent advances in therapies are unable to control its vascular complications. New medications have been suggested but without comprehensive knowledge of the signaling pathways induced by hyperglycemia.

OBJECTIVE

To review the mechanisms of the inducer and effector phases of the metabolic cascade in diabetes, with emphasis on the steps that have been targeted to date The route from hyperglycemia to advanced glycation end products (AGE)-receptor of advanced glycation end products (RAGE) complex formation is suggested as a target for new therapies.

METHODS

A review of literature, including historical papers and recent manuscripts.

RESULTS

All the components of the suggested route are initially activated or indirectly formed due to hyperglycemia via a two-phase cascade that represents a dangerous metabolic route, especially for diabetics. Recent experiments with new drugs and clinical trials targeting this pathway are examined.

CONCLUSIONS

In order to control vascular injury in diabetes, several steps in the cascade need to be inhibited simultaneously together with aggressive glycemic control.

Advanced glycation end products and diabetic foot disease

Diabetic foot disease is an important complication of diabetes. The development and outcome of foot ulcers are related to the interplay between numerous diabetes-related factors such as nerve dysfunction, impaired wound healing and microvascular and/or macrovascular disease.The formation of advanced glycation end products (AGEs) has been recognized as an important pathophysiological mechanism in the development of diabetic complications. Several mechanisms have been proposed by which AGEs lead to diabetic complications such as the accumulation of AGEs in the extracellular matrix causing aberrant cross-linking, the binding of circulating AGEs to the receptor of AGEs (RAGE) on different cell types and activation of key cell signalling pathways with subsequent modulation of gene expression, and intracellular AGE formation leading to quenching of nitric oxide and impaired function of growth factors. In the last decade, many experimental studies have shown that these effects of AGE formation may play a role in the pathogenesis of micro- and macrovascular complications of diabetes, diabetic neuropathy and impaired wound healing. In recent years also, several clinical studies have shown that glycation is an important pathway in the pathophysiology of those complications that predispose to the development of foot ulcers. Currently, there are a number of ways to prevent or decrease glycation and glycation-induced tissue damage. Although not in the area of neuropathy or wound healing, recent clinical studies have shown that the AGE-breakers may be able to decrease adverse vascular effects of glycation with few side effects.

Glycated LDL increases monocyte CC chemokine receptor 2 expression and monocyte chemoattractant protein-1-mediated chemotaxis

BACKGROUND

Previous reports have suggested that levels of advanced glycation end product-modified LDL (AGE-LDL) increase in patients with diabetes due to elevated plasma glucose. However, understanding of the mechanisms by which AGE-LDL may accelerate atherogenesis remains incomplete.

METHODS AND RESULTS

Microarray and reverse transcription real-time PCR (RT-PCR) analyses revealed that AGE-LDL significantly increased levels of CC chemokine receptor 2 (CCR2) mRNA in human macrophages compared with LDL, an effect accompanied by increased levels of CCR2 protein. Flow cytometry also showed that AGE-LDL increases CCR2 expression on the cell surface following stimulation (48h) (P<0.05). This effect appeared to depend on the receptor for AGE (RAGE), since an anti-RAGE antibody significantly blocked increased CCR2 mRNA. Functional studies demonstrated that exposure of THP-1 monocytoid cells to AGE-LDL increases chemotaxis mediated by monocyte chemoattractant protein-1 (MCP-1) up to 3-fold compared to LDL treatment (P<0.05).

CONCLUSIONS

These data show that AGE-LDL can increase CCR2 expression in macrophages and stimulate the chemotactic response elicited by MCP-1. This novel mechanism may contribute to accelerated atherogenesis in diabetic patients.

Diagnostic utility of serum or cerebrospinal fluid levels of toxic advanced glycation end-products (TAGE) in early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are amyloid beta protein (A beta) and tau protein, respectively. Based on the disease pathology, numerous blood and cerebrospinal fluid (CSF) tests have been proposed for early detection of AD. However, there is no definite clinical method to determine in which patients with mild cognitive impairment will progress to AD with dementia. Therefore, to develop a novel promising biomarker for early diagnosis of AD is urgently needed. Several epidemiological studies have reported moderately increased risks for AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end-products (AGEs), senescent macroprotein derivatives, progress more rapidly. In addition, recent understanding of this process has confirmed that AGEs-their receptor (RAGE) interactions may play a role in the pathogenesis of neurodegenerative disorders including AD. In human AD brains, AGEs are distributed in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. In this paper, we discuss the pathophysiological role for toxic AGEs (TAGE) in AD. We further review here the possibility that serum or cerebrospinal fluid levels of TAGE could become a promising biomarker for early detection of AD.

Photosensitizing Activity of Advanced Glycation Endproducts on Tryptophan, Glucose 6-phosphate Dehydrogenase, Human Serum Albumin and Ascorbic Acid Evaluated at Low Oxygen Pressure†

A comparative study of the photosensitizing activity of advanced glycation endproducts (AGEs) prepared by incubating glucose (Glc), threose (Threo) and ascorbate (AH-) in the presence of lysine (Lys) was performed. Photochemical activity was evaluated under low oxygen pressure with the aim to simulate the conditions of the eye lens. AGE-sensitized tryptophan and AH- photodecomposition and glucose 6-phosphate dehydrogenase inactivation were studied. In all systems, glucose-derived AGEs showed the highest photosensitizing efficiency, followed by ascorbate and threose. The presence of different sensitizers in glycation products mixtures was investigated. For this purpose, Trp decomposition quantum yields were determined at 344 and 367 nm. The values obtained at 344 nm are between three and six times higher than those observed at 367 nm, confirming the presence of at least two compounds with different photosensitizing activities in the mixtures. The chemiluminescence associated with the AGE-mediated oxidation of free Trp and Trp residues in human serum albumin was also studied, and a good correlation between the emission of light and the extent of Trp decomposition was found. In conclusion, it is demonstrated that glucose derived AGEs, which can be formed in vivo in the eye lens of diabetic patients and are accumulated in elderly lenses, have a higher photosensitizing efficiency, at low oxygen pressure, than those arising from ascorbate and threose. This high efficiency is especially significant when proteins are employed as photochemical targets, indicating that protein-sensitizer interaction and the local environment around the sensitizers play an important role.

Advanced glycation end products: sparking the development of diabetic vascular injury

Advanced glycation end products (AGEs) are proteins or lipids that become glycated after exposure to sugars. AGEs are prevalent in the diabetic vasculature and contribute to the development of atherosclerosis. The presence and accumulation of AGEs in many different cell types affect extracellular and intracellular structure and function. AGEs contribute to a variety of microvascular and macrovascular complications through the formation of cross-links between molecules in the basement membrane of the extracellular matrix and by engaging the receptor for advanced glycation end products (RAGE). Activation of RAGE by AGEs causes upregulation of the transcription factor nuclear factor-kappaB and its target genes. Soluble AGEs activate monocytes, and AGEs in the basement membrane inhibit monocyte migration. AGE-bound RAGE increases endothelial permeability to macromolecules. AGEs block nitric oxide activity in the endothelium and cause the production of reactive oxygen species. Because of the emerging evidence about the adverse effects of AGEs on the vasculature of patients with diabetes, a number of different therapies to inhibit AGEs are under investigation.

Toxic advanced glycation end products (TAGE) theory in Alzheimer's disease

Several epidemiological studies have reported moderately increased risks of Alzheimer's disease (AD) in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress more rapidly. Recent understanding of this process has confirmed that interactions between AGEs and their receptor (RAGE) may play a role in the pathogenesis of diabetic complications and AD. The authors have recently found that glyceraldehyde-derived AGEs (AGE-2), which is predominantly the structure of toxic AGEs (TAGE), show significant toxicity on cortical neuronal cells and that the neurotoxic effect of diabetic serum is completely blocked by neutralizing antibody against the AGE-2 epitope. Moreover, in human AD brains, AGE-2 is distributed in the cytosol of neurons in the hippocampus and parahippocampal gyrus. These results suggest that TAGE is involved in the pathogenesis of AD as well as other age-related diseases. In this review, the authors discuss the molecular mechanisms of AD, especially focusing on TAGE-RAGE system.

Telmisartan inhibits expression of a receptor for advanced glycation end products (RAGE) in angiotensin-II-exposed endothelial cells and decreases serum levels of soluble RAGE in patients with essential hypertension

There is a growing body of evidence that the advanced glycation end product (AGE)-their receptor (RAGE) system plays a central role in the pathogenesis of diabetic vascular complication. The renin-angiotensin system (RAS) contributes to the development and progression of diabetic angiopathy as well. However, the cross-talk between the AGE-RAGE system and the RAS is not fully understood. In this study, we examined the role of angiotensin II (Ang II) type 1 receptor system for RAGE expression in cultured endothelial cells (ECs) and in patients with essential hypertension. Ang II up-regulated RAGE mRNA levels of microvascular ECs and subsequently increased the soluble form of RAGE (sRAGE) expression in the medium of ECs, both of which were completely blocked by telmisartan, a commercially available Ang II type 1 receptor antagonist. Furthermore, telmisartan was found to decrease serum levels of sRAGE in patients with essential hypertension. These results demonstrate that sRAGE is released from the cell surface of Ang-II-exposed ECs. Our present study indicates that a cross-talk exists between the AGE-RAGE system and the RAS and suggests that serum levels of sRAGE may reflect endothelial RAGE expression.

Angiotensin II augments advanced glycation end product-induced pericyte apoptosis through RAGE overexpression

Advanced glycation end product (AGE)-their receptor (RAGE) and angiotensin II (AII) are implicated in diabetic retinopathy. However, a crosstalk between the two is not fully understood. In vivo, AGE injection stimulated RAGE expression in the eye of spontaneously hypertensive rats, which was blocked by an AII-type 1 receptor blocker, telmisartan. In vitro, AII-type 1 receptor-mediated reactive oxygen species generation elicited RAGE gene expression in pericytes through NF-kappaB activation. Further, AII augmented AGE-induced pericyte apoptosis, the earliest hallmark of diabetic retinopathy. Our present study may implicate a crosstalk between AGE-RAGE system and AII in diabetic retinopathy.

Chronic Renal Failure Accelerates Atherogenesis in Apolipoprotein E–Deficient Mice

ABSTRACT. Cardiovascular mortality is 10 to 20 times increased in patients with chronic renal failure (CRF). Risk factors for atherosclerosis are abundant in patients with CRF. However, the pathogenesis of cardiovascular disease in CRF remains to be elucidated. The effect of CRF on the development of atherosclerosis in apolipoprotein E–deficient male mice was examined. Seven-week-old mice underwent 5/6 nephrectomy (CRF, n = 28), unilateral nephrectomy (UNX, n = 24), or no surgery (n = 23). Twenty-two weeks later, CRF mice showed increased aortic plaque area fraction (0.266 ± 0.033 versus 0.045 ± 0.006; P < 0.001), aortic cholesterol content (535 ± 62 versus 100 ± 9 nmol/cm2 intimal surface area; P < 0.001), and aortic root plaque area (205,296 ± 22,098 versus 143,662 ± 13,302 μm2; P < 0.05) as compared with no-surgery mice; UNX mice showed intermediate values. The plaques from uremic mice contained CD11b-positive macrophages and showed strong staining for nitrotyrosine. Systolic BP and plasma homocysteine concentrations were similar in uremic and nonuremic mice. Plasma urea and cholesterol concentrations were elevated 2.6-fold (P < 0.001) and 1.5-fold (P < 0.001) in CRF compared with no-surgery mice. Both variables correlated with aortic plaque area fraction (r2 = 0.5, P < 0.001 and r2 = 0.3, P < 0.001, respectively) and with each other (r2 = 0.5, P < 0.001). On multiple linear regression analysis, only plasma urea was a significant predictor of aortic plaque area fraction. In conclusion, the present findings suggest that uremia markedly accelerates atherogenesis in apolipoprotein E–deficient mice. This effect could not be fully explained by changes in BP, plasma homocysteine levels, or total plasma cholesterol concentrations. Thus, the CRF apolipoprotein E–deficient mouse is a new model for studying the pathogenesis of accelerated atherosclerosis in uremia. E-mail: susannebro@dadlnet.dk

The role of advanced glycation in the pathogenesis of diabetic retinopathy

Retinopathy is one of the commonest microvascular complications of diabetes and is still the prevailing cause of registerable blindness in the working population of developed countries. The clinicopathology of microvascular lesions and the dysregulation of an array of biochemical pathways in the diabetic retina have been extensively studied, although the relative contribution of various biochemical sequelae of hyperglycaemia remains ill- defined. There is little doubt that the pathogenesis of this diabetic complication is highly complex and there is a pressing need to establish new therapeutic regimens that can effectively prevent or retard the initiation and progression of retinal microvascular cell dysfunction and death which is characteristic of the vasodegenerative stages of diabetic retinopathy. Among the several pathogenic mechanisms that may contribute to diabetic retinopathy are the formation and accumulation of advanced glycation endproducts (AGEs). AGEs can form on the amino groups of proteins, lipids, and DNA through a number of complex pathways, including nonenzymatic glycation by glucose and reaction with metabolic intermediates and reactive dicarbonyl intermediates. These reactions not only modify the structure and function of proteins, but also cause intramolecular and intermolecular cross-link formation. AGEs are known to accumulate in the diabetic retina where they may have important effects on retinal vascular cell function in vitro and in vivo. Evidence now points toward a pathogenic role for advanced glycation in the initiation and progression of diabetic retinopathy. This review will examine the basis of AGE-related pathology in the diabetic retina at cellular and molecular levels. It will also outline how recent strategies to inhibit AGE formation or limit their pathogenic influence during chronic diabetes may have an important role to play in the treatment of retinopathy.

Atherothrombosis, inflammation, and diabetes

Diabetes represents a major cause of cardiovascular morbidity and mortality in developed countries, and atherothrombosis accounts for most deaths among diabetics. Recent evidence has reliably shown the relevant etiopathogenetic role of inflammation in atherothrombotic disease. This review summarizes and discusses the possible synergistic effects of diabetes and inflammation in promoting atherothrombosis and its complications, as well as potential avenues for diagnostic, preventive, and therapeutic benefits in the modulation of inflammatory mechanisms in diabetic atherothrombotic disease.

STAT5 activation induced by diabetic LDL depends on LDL glycation and occurs via src kinase activity

Advanced glycation end products (AGEs) have been implicated in the accelerated vascular injury occurring in diabetes. We recently reported that LDL prepared from type 2 diabetic patients (dm-LDL), but not normal LDL (n-LDL) triggered signal transducers and activators of transcription STAT5 activation and p21(waf) expression in endothelial cells (ECs). The aims of the present study were to investigate the role of LDL glycation in dm-LDL- mediated signals and to analyze the molecular mechanisms leading to STAT5 activation. We found that glycated LDL (gly-LDL) triggered STAT5 activation, the formation of a prolactin inducible element (PIE)-binding complex containing STAT5, and increased p21(waf) expression through the activation of the receptor for AGE (RAGE). We also demonstrated that dm-LDL and gly-LDL, but not n-LDL treatment induced the formation of a stable complex containing the activated STAT5 and RAGE. Moreover, gly-LDL triggered src but not JAK2 kinase activity. Pretreatment with the src kinase inhibitor PP1 abrogated both STAT5 activation and the expression of p21(waf) induced by gly-LDL. Consistently, gly-LDL failed to activate STAT5 in src(-/-) fibroblasts. Collectively, our results provide evidence for the role of glycation in dm-LDL-mediated effects and for a specific role of src kinase in STAT5-dependent p21(waf) expression.

Damaging effects of advanced glycation end-products in the murine macrophage cell line J774A.1

The interaction of reducing sugars, such as aldose, with proteins and the subsequent molecular rearrangements, produces irreversible advanced glycation end-products (AGEs), a heterogeneous class of non-enzymatic glycated proteins or lipids. AGEs form cross-links, trap macromolecules and release reactive oxygen intermediates. AGEs are linked to aging, and increase in several related diseases. The aim of this study was to assess, in a murine macrophage cell line, J774A.1, the effects of 48 h of exposure to glycated serum containing a known amount of pentosidine, a well-known AGE found in the plasma and tissues of diabetic and uremic subjects. Fetal bovine serum was incubated with ribose (50 mM) for 7 days at 37 degrees C to obtain about 10 nmol/ml of pentosidine. The cytotoxic parameters studied were cell morphology and viability by neutral red uptake, lactate dehydrogenase release and tetrazolium salt test. In the medium and in the intracellular compartment, bound and free pentosidine were evaluated by HPLC, as sensitive and specific glycative markers, and thiobarbituric acid reactive substances (TBARs), as index of the extent of lipid peroxidation. Our results confirm that macrophages are able to take up pentosidine. It is conceivable that bound pentosidine is degraded and free pentosidine is released inside the cell and then into the medium. The AGE increase in the medium was combined with an increase in TBARs, meaning that an oxidative stress occurred; marked cytotoxic effects were observed, and were followed by the release of free pentosidine and TBARs into the culture medium.

Antibodies to advanced glycation end products in children with diabetes mellitus

The tissue accumulation of advanced glycation end products (AGE) alters the structure and function of long-lived proteins. A number of studies have shown that tissue accumulation of AGE correlates with the severity of diabetic complications. Proteins containing AGE are highly immunogenic and anti-AGE antibodies were found in sera of diabetic rats and human. Considering the potential use of anti-AGE antibodies as a marker of AGE deposition during diabetes, we have investigated, by competitive ELISA, the presence of anti-AGE antibodies in sera of 58 children with Type 1 diabetes mellitus. The patients were studied for the period of 5 years. Positive for anti-AGE antibodies were 19 children with diabetes. Fourteen of them showed initial data for vascular complications. Anti-AGE antibodies were related to age (r = .25, P = .024), duration of diabetes (r = .41, P = .0001), HbA1c (r = .27, P = .016), microalbuminuria (r = .41, P = .0001), retinopathy (r = .35, P = .001), triglycerides (r = .27, P = .016), and total cholesterol (r = .19, P = .05). In conclusion, our study showed that the investigation of the levels and dynamics of anti-AGE antibodies might give the possibility for early diagnosis and prognosis of the severity of diabetic late complications.

Diabetes and advanced glycation endproducts

Bio-reactive advanced glycation endproducts (AGE) alter the structure and function of molecules in biological systems and increase oxidative stress. These adverse effects of both exogenous and endogenously derived AGE have been implicated in the pathogenesis of diabetic complications and changes associated with ageing including atherosclerosis, renal, eye and neurological disease. Specific AGE receptors and nonreceptor mechanisms contribute to these processes but also assist in the removal and degradation of AGE. The final disposal of AGE depends on renal clearance. Promising pharmacologic strategies to prevent AGE formation, reduce AGE toxicity, and/or inactivate AGE are under investigation.