Advanced glycation endproducts interacting with their endothelial receptor induce expression of vascular cell adhesion molecule-1 (VCAM-1) in cultured human endothelial cells and in mice. A potential mechanism for the accelerated vasculopathy of diabetes

Detection of feto-maternal infection/inflammation by the soluble receptor for advanced glycation end products (sRAGE): results of a pilot study

OBJECTIVE

The receptor for advanced glycation end products, RAGE, plays an important role in the pathogenesis of several diseases. sRAGE, soluble receptor for advanced glycation end products, is an inhibitor of the pathological effect mediated via RAGE. The aim of this study was to assess the usefulness of measuring sRAGE concentration in pregnant women with threatening preterm labor.

METHODS

Serum levels of sRAGE, interleukin-6 (IL-6) and routine markers of inflammation were determined in 46 pregnant women with threatening preterm labor, 35 healthy pregnant women and 15 non-pregnant controls.

RESULTS

Serum levels of sRAGE in healthy pregnant women were significantly lower than in non-pregnant controls (669+/-296 vs. 1929+/-727 pg/mL, P<0.05). Women with threatening preterm birth had a significantly higher concentration of serum sRAGE in comparison with healthy pregnant women (819+/-329 pg/mL vs. 669+/-296 pg/mL, P<0.05). Conversely, patients with PPROM had significantly lower levels of sRAGE compared with patients with threatening premature labor (600+/-324 pg/mL, P<0.05). sRAGE correlated negatively with leukocyte counts (r=-0.325, P<0.05).

CONCLUSIONS

sRAGE might be a new and promising marker of premature labor, especially with the symptoms of PPROM.

Tempering the wrath of RAGE: an emerging therapeutic strategy against diabetic complications, neurodegeneration, and inflammation

The multiligand receptor RAGE (receptor for advanced glycation end-products) is emerging as a central mediator in the immune/inflammatory response. Epidemiological evidence accruing in the human suggests upregulation of RAGE's ligands (AGEs, S100/calgranulins, high mobility group box-1 (HMGB1), and amyloid beta-peptide and beta-sheet fibrils) and the receptor itself at sites of inflammation and in chronic diseases such as diabetes and neurodegeneration. The consequences of ligand-RAGE interaction include upregulation of molecules implicated in inflammatory responses and tissue damage, such as cytokines, adhesion molecules, and matrix metalloproteinases. In this review, we discuss the localization of RAGE and its ligand families and the biological impact of this axis in multiple cell types implicated in chronic diseases. Lastly, we consider findings from animal model studies suggesting that although tissue-damaging effects ensue from recruitment of the ligand-RAGE interaction, in distinct settings, adaptive and repair/regeneration outcomes appear to override detrimental effects of RAGE. As RAGE blockade moves further into clinical development, clarifying the biology of RAGE garners ever-increasing importance.

N(epsilon)-(Carboxymethyl)lysine and Coronary Atherosclerosis-Associated Low Density Lipoprotein Abnormalities in Type 2 Diabetes: Current Status

In comparison to the general population, individuals with diabetes suffer a 3- to 4-fold increased risk for developing complications of atherosclerosis and vascular insufficiency. This fact should be taken into account to develop a suitable determinant for the early detection of these complications and subsequently reduce the adverse effect of type 2 diabetes. In vitro experiments have shown that the products of glucose auto-oxidation and Amadori adducts are both potential sources of N(epsilon)-(carboxymethyl)lysine (CML). Excessive formation of CML on low density lipoprotein (LDL) has been proposed to be an important mechanism for the dyslipidemia and accelerated atherogenesis observed in patients with type 2 diabetes. It has been postulated that the uptake of CML-LDL by LDL receptors is impaired, thereby decreasing its clearance from the blood circulation. Alternatively, the uptake of these modified LDL particles by scavenger receptors on macrophages and vascular smooth muscle cells (SMCs) and by AGE receptors on endothelial cells, SMCs, and monocytes is highly enhanced and this, in turn, is centrally positioned to contribute to the pathogenesis of diabetic vascular complications especially coronary artery disease. The present review summarizes the up-to-date information on effects and mechanism of type 2 diabetes-associated coronary atherosclerosis induced by CML-LDL modification.

RAGE polymorphisms, renal function and histological finding at 12 months after renal transplantation

OBJECTIVES

Rage (receptor for advanced glycation end products) is involved in pathogenesis of many diseases. The aim of the study was to test whether polymorphisms of RAGE gene are associated with the outcome of kidney transplantation.

DESIGN AND METHODS

Four polymorphisms of the RAGE gene (-429T/C, -374T/A, Gly82Ser and 2184A/G) were assessed in 145 renal transplant recipients and their relationship to histological changes in 12 months protocol kidney graft biopsy and renal function was examined.

RESULTS

Genotype frequencies of each polymorphism corresponded to expected frequencies according to Hardy-Weinberg equilibrium. No differences between allelic and genotype frequencies among patients with normal histological findings, chronic allograft nephropathy and subclinical rejection were observed.

CONCLUSION

This is the first study on polymorphisms of the RAGE gene in patients with the transplanted kidney. No association of RAGE selected gene polymorphisms with 12-months outcome of renal transplants was shown in study.

Binding of S100 proteins to RAGE: an update

The Receptor for Advanced Glycation Endproducts (RAGE) is a multi-ligand receptor of the immunoglobulin family. RAGE interacts with structurally different ligands probably through the oligomerization of the receptor on the cell surface. However, the exact mechanism is unknown. Among RAGE ligands are members of the S100 protein family. S100 proteins are small calcium binding proteins with high structural homology. Several members of the family have been shown to interact with RAGE in vitro or in cell-based assays. Interestingly, many RAGE ligands appear to interact with distinct domains of the extracellular portion of RAGE and to trigger various cellular effects. In this review, we summarize the modes of S100 protein-RAGE interaction with regard to their cellular functions.

Advanced oxidation protein products activate vascular endothelial cells via a RAGE-mediated signaling pathway

The accumulation of advanced oxidation protein products (AOPPs) has been linked to vascular lesions in diabetes, chronic renal insufficiency, and atherosclerosis. However, the signaling pathway involved in AOPPs-induced endothelial cells (ECs) perturbation is unknown and was investigated. AOPPs modified human serum albumin (AOPPs-HSA) bound to the receptor for advanced glycation end products (RAGE) in a dose-dependent and saturable manner. AOPPs-HSA competitively inhibited the binding of soluble RAGE (sRAGE) with its preferential ligands advanced glycation end products (AGEs). Incubation of AOPPs, either prepared in vitro or isolated from uremic serum, with human umbilical vein ECs induced superoxide generation, activation of NAD(P)H oxidase, ERK 1/2 and p38, and nuclear translocation of NF-kappaB. Activation of signaling pathway by AOPPs-ECs interaction resulted in overexpression of VCAM-1 and ICAM-1 at both gene and protein levels. This AOPPs-triggered biochemical cascade in ECs was prevented by blocking RAGE with either anti-RAGE IgG or excess sRAGE, but was not affected by the neutralizing anti-AGEs IgG. These data suggested that AOPPs might be new ligands of endothelial RAGE. AOPPs-HSA activates vascular ECs via RAGE-mediated signals.

Cardiovascular risk evaluated by C-reactive protein levels in diabetic and obese Mexican subjects

BACKGROUND

Previous studies have reported elevated levels of C-reactive protein (CRP) in obese and diabetic subjects, but it is unclear whether both these conditions have an additive effect on the variability of serum CRP levels.

METHODS AND RESULTS

The study enrolled 385 men and women who were classified into 4 groups: (1) diabetes (n=97), (2) obesity (n=108), (3) diabetes/obesity (n=78), and (4) healthy (n=102). All were Mexican subjects from Guerrero State. Serum high-sensitivity CRP (hs-CRP) levels were higher in both type 2 diabetes mellitus (T2DM)/obesity and obesity (5.1 mg/L) groups than in the diabetics (1.8 mg/L) without obesity. Only the measurements of obesity were strongly related to hs-CRP (body mass index, r=0.46 and waist circumference, r=0.41). The presence of T2DM and obesity explain 20% of the circulating hs-CRP level, following waist circumference (16%), leukocyte count (10%), diastolic blood pressure (6%), and female gender (4%). Obese subjects (odds ratio (OR)=6.3) and T2DM/obesity patients (OR=6.9) showed high risk for coronary disease and this effect was increased in T2DM/obesity women (OR=9.9). Also, abdominal obesity was associated with high coronary disease risk (OR=5.4), showing an increase in women (OR=7.3).

CONCLUSION

High hs-CRP levels are related to obesity and central distribution of body fat, leading to a higher cardiovascular risk among Mexican subjects.

Endothelial dysfunction: from molecular mechanisms to measurement, clinical implications, and therapeutic opportunities

Endothelial dysfunction has been implicated as a key factor in the development of a wide range of cardiovascular diseases, but its definition and mechanisms vary greatly between different disease processes. This review combines evidence from cell-culture experiments, in vitro and in vivo animal models, and clinical studies to identify the variety of mechanisms involved in endothelial dysfunction in its broadest sense. Several prominent disease states, including hypertension, heart failure, and atherosclerosis, are used to illustrate the different manifestations of endothelial dysfunction and to establish its clinical implications in the context of the range of mechanisms involved in its development. The size of the literature relating to this subject precludes a comprehensive survey; this review aims to cover the key elements of endothelial dysfunction in cardiovascular disease and to highlight the importance of the process across many different conditions.

Endogenous secretory RAGE but not soluble RAGE is associated with carotid atherosclerosis in type 1 diabetes patients

Advanced glycation end-products (AGEs) and the receptor for AGEs (RAGE) system play an important role in the development of diabetic complications. The soluble form of RAGE (sRAGE) that potentially counteracts AGEs consists of several forms, including endogenous secretory RAGE (esRAGE; a splice variant of RAGE) and cleaved-type soluble RAGE derived from cell-surface RAGE. The aim of this study was to compare sRAGE and esRAGE directly in patients with type 1 diabetes. The associations of both total sRAGE and esRAGE with markers of glycaemic control and with carotid intima-media thickness (IMT) as a marker of atherosclerosis were examined in 130 type 1 diabetes patients (aged 23.6+/-4.9 years) and 22 age-matched non-diabetic subjects. IMT was inversely correlated with esRAGE (r=-0.254, p=0.0015) but neither with sRAGE nor subtracted soluble RAGE values (that is, circulating total sRAGE values - circulating esRAGE values). Furthermore, a stepwise multivariate regression analysis revealed that esRAGE (F=7.3), but not sRAGE, was a variable that interacted independently of IMT. It is likely that circulating sRAGE and esRAGE are distinct markers and that circulating esRAGE levels, but not sRAGE levels, are associated with the status of early-stage atherosclerosis.

Effects of thiamine and benfotiamine on intracellular glucose metabolism and relevance in the prevention of diabetic complications

Thiamine (vitamin B1) is an essential cofactor in most organisms and is required at several stages of anabolic and catabolic intermediary metabolism, such as intracellular glucose metabolism, and is also a modulator of neuronal and neuro-muscular transmission. Lack of thiamine or defects in its intracellular transport can cause a number of severe disorders. Thiamine acts as a coenzyme for transketolase (TK) and for the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes, enzymes which play a fundamental role for intracellular glucose metabolism. In particular, TK is able to shift excess fructose-6-phosphate and glycerhaldeyde-3-phosphate from glycolysis into the pentose-phosphate shunt, thus eliminating these potentially damaging metabolites from the cytosol. Diabetes might be considered a thiamine-deficient state, if not in absolute terms at least relative to the increased requirements deriving from accelerated and amplified glucose metabolism in non-insulin dependent tissues that, like the vessel wall, are prone to complications. A thiamine/TK activity deficiency has been described in diabetic patients, the correction of which by thiamine and/or its lipophilic derivative, benfotiamine, has been demonstrated in vitro to counteract the damaging effects of hyperglycaemia on vascular cells. Little is known, however, on the positive effects of thiamine/benfotiamine administration in diabetic patients, apart from the possible amelioration of neuropathic symptoms. Clinical trials on diabetic patients would be necessary to test this vitamin as a potential and inexpensive approach to the prevention and/or treatment of diabetic vascular complications.

Periodontal disease: associations with diabetes, glycemic control and complications

OBJECTIVE

This report reviews the evidence for adverse effects of diabetes on periodontal health and periodontal disease on glycemic control and complications of diabetes.

DESIGN

MEDLINE search of the English language literature identified primary research reports published on (a) relationships between diabetes and periodontal diseases since 2000 and (b) effects of periodontal infection on glycemic control and diabetes complications since 1960.

RESULTS

Observational studies provided consistent evidence of greater prevalence, severity, extent, or progression of at least one manifestation of periodontal disease in 13/17 reports reviewed. Treatment and longitudinal observational studies provided evidence to support periodontal infection having an adverse effect on glycemic control, although not all investigations reported an improvement in glycemic control after periodontal treatment. Additionally, evidence from three observational studies supported periodontal disease increasing the risk for diabetes complications and no published reports refuted the findings.

CONCLUSION

The evidence reviewed supports diabetes having an adverse effect on periodontal health and periodontal infection having an adverse effect on glycemic control and incidence of diabetes complications. Further rigorous study is necessary to establish unequivocally that treating periodontal infections can contribute to glycemic control management and to the reduction of the burden of diabetes complications.

Oxidative stress as a major culprit in kidney disease in diabetes

It is postulated that localized tissue oxidative stress is a key component in the development of diabetic nephropathy. There remains controversy, however, as to whether this is an early link between hyperglycemia and renal disease or develops as a consequence of other primary pathogenic mechanisms. In the kidney, a number of pathways that generate reactive oxygen species (ROS) such as glycolysis, specific defects in the polyol pathway, uncoupling of nitric oxide synthase, xanthine oxidase, NAD(P)H oxidase, and advanced glycation have been identified as potentially major contributors to the pathogenesis of diabetic kidney disease. In addition, a unifying hypothesis has been proposed whereby mitochondrial production of ROS in response to chronic hyperglycemia may be the key initiator for each of these pathogenic pathways. This postulate emphasizes the importance of mitochondrial dysfunction in the progression and development of diabetes complications including nephropathy. A mystery remains, however, as to why antioxidants per se have demonstrated minimal renoprotection in humans despite positive preclinical research findings. It is likely that the utility of current study approaches, such as vitamin use, may not be the ideal antioxidant strategy in human diabetic nephropathy. There is now an increasing body of data to suggest that strategies involving a more targeted antioxidant approach, using agents that penetrate specific cellular compartments, may be the elusive additive therapy required to further optimize renoprotection in diabetes.

Effects of cross-link breakers, glycation inhibitors and insulin sensitisers on HDL function and the non-enzymatic glycation of apolipoprotein A-I

AIMS/HYPOTHESIS

Hyperglycaemia, a key feature of diabetes, is associated with non-enzymatic glycation of plasma proteins. We have shown previously that the reactive alpha-oxoaldehyde, methylglyoxal, non-enzymatically glycates apolipoprotein (Apo)A-I, the main apolipoprotein of HDL, and prevents it from activating lecithin:cholesterol acyltransferase (LCAT), the enzyme that generates almost all of the cholesteryl esters in plasma. This study investigates whether the glycation inhibitors aminoguanidine and pyridoxamine, the insulin sensitiser metformin and the cross-link breaker alagebrium can inhibit and/or reverse the methylglyoxal-mediated glycation of ApoA-I and whether these changes can preserve or restore the ability of ApoA-I to activate LCAT.

METHODS

Inhibition of ApoA-I glycation was assessed by incubating aminoguanidine, pyridoxamine, metformin and alagebrium with mixtures of methylglyoxal and discoidal reconstituted HDL (rHDL) containing phosphatidylcholine and ApoA-I, ([A-I]rHDL). Glycation was assessed as the modification of ApoA-I arginine, lysine and tryptophan residues, and by the extent of ApoA-I cross-linking. The reversal of ApoA-I glycation was investigated by pre-incubating discoidal (A-I)rHDL with methylglyoxal, then incubating the modified rHDL with aminoguanidine, pyridoxamine or alagebrium.

RESULTS

Aminoguanidine, pyridoxamine, metformin and alagebrium all decreased the methylglyoxal-mediated glycation of the ApoA-I in discoidal rHDL and conserved the ability of the particles to act as substrates for LCAT. However, neither aminoguanidine, pyridoxamine nor alagebrium could reverse the glycation of ApoA-I or restore its ability to activate LCAT.

CONCLUSIONS/INTERPRETATION

Glycation inhibitors, insulin sensitisers and cross-link breakers are important for preserving normal HDL function in diabetes.

Oxidative stress induces vascular calcification through modulation of the osteogenic transcription factor Runx2 by AKT signaling

Oxidative stress plays a critical role in the pathogenesis of atherosclerosis including the formation of lipid laden macrophages and the development of inflammation. However, oxidative stress-induced molecular signaling that regulates the development of vascular calcification has not been investigated in depth. Osteogenic differentiation of vascular smooth muscle cells (VSMC) is critical in the development of calcification in atherosclerotic lesions. An important contributor to oxidative stress in atherosclerotic lesions is the formation of hydrogen peroxide from diverse sources in vascular cells. In this study we defined molecular signaling that is operative in the H2O2-induced VSMC calcification. We found that H2O2 promotes a phenotypic switch of VSMC from contractile to osteogenic phenotype. This response was associated with an increased expression and transactivity of Runx2, a key transcription factor for osteogenic differentiation. The essential role of Runx2 in oxidative stress-induced VSMC calcification was further confirmed by Runx2 depletion and overexpression. Inhibition of Runx2 using short hairpin RNA blocked VSMC calcification, and adenovirus-mediated overexpression of Runx2 alone induced VSMC calcification. Inhibition of H2O2-activated AKT signaling blocked VSMC calcification and Runx2 induction concurrently. This blockage did not cause VSMC apoptosis. Taken together, our data demonstrate a critical role for AKT-mediated induction of Runx2 in oxidative stress-induced VSMC calcification.

Exploration of hematological and immunological changes associated with the severity of type 2 diabetes mellitus in Japan

It has been postulated that immune modulation and activation play an important role in the pathogenesis of type 2 diabetes mellitus (T2DM), but evidence for this has not yet been well documented. We explored the changes in peripheral immunocompetent cells in relationship to the severity of T2DM in 142 patients, and 34 healthy individuals in Japan. A severity index with 0-12 grades was derived based on the HbA1c level and the number of complications. By multiple regression analysis, the severity index was positively associated with neutrophil counts and negatively associated with platelet and CD19+ lymphocyte counts. However, we did not observe any significant changes in other lymphocyte subsets such as CD4+, CD8+, and CD56+. These results suggest that poor diabetic control may be marked by changes in some blood cell types.

Soluble adhesion molecules levels in patients with Cushing's syndrome before and after cure

OBJECTIVE

Patients with Cushing's syndrome (CS) show a high prevalence of cardiovascular risk factors and atherosclerosis, persisting even after cure. Soluble intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1) are surrogate markers of endothelial function involved in the initiation of atherosclerosis. This study aimed to evaluate sICAM-1 and sVCAM-1 levels in patients with CS before and after successful cure.

SUBJECTS AND METHODS

sICAM-1 and sVCAM-1 levels were evaluated in 28 patients with active CS and in 12 patients with Cushing's disease (CD), 6-12 months after disease remission. Body mass index (BMI), blood pressure, glucose, serum lipids, ACTH, cortisol and urinary free cortisol (UFC) were measured in basal conditions in all patients.

RESULTS

At baseline, sICAM-1 levels positively correlated with BMI (r=0.443, p<0.01), while no correlations between sICAM/sVCAM levels and ACTH, cortisol or UFC were found. Plasma ACTH, serum cortisol, and UFC levels significantly decreased in 12 cured patients, but ICAM-1 and VCAM-1 levels were unchanged (12.7+/-1.8 vs 10.1+/-0.9 ng/ml and 33.5+/-4.4 vs 35.8+/-4.0 ng/ml, respectively). Obesity, hypertension, and impaired glucose metabolism persisted 1 yr after the biochemical cure of hypercortisolism. A significant reduction in ICAM-1 levels was observed in 4 out of 12 cured patients as well as a remission from diabetes, hypertension or obesity.

CONCLUSIONS

ICAM/VCAM-1 levels show a great variability in patients with active CS, not correlated with cortisol levels, and are slightly modified in some cured patients with CD. The persistence of obesity, hypertension, and impaired glucose metabolism may be responsible for the maintenance of a subclinical endothelial dysfunction, making these subjects still at high cardiovascular risk and needing a long-term follow-up.

Calcitriol blunts the deleterious impact of advanced glycation end products on endothelial cells

Advanced glycation end products (AGEs), which are elevated in diabetic and uremic patients, may induce vascular dysfunctions, and calcitriol may improve the cardiovascular complications. Therefore, we examined whether calcitriol may modify the endothelial response to AGEs stimulation. Knowing the importance of nuclear factor-κB in endothelial inflammatory responses, the effect of AGEs and calcitriol on this pathway was also studied. Calcitriol was added to endothelial cells previously incubated with AGE-human serum albumin (HSA). AGE-HSA induced a decrease in endothelial nitric oxide synthase (eNOS) mRNA expression and enzyme activity. Addition of calcitriol to AGE-HSA-treated endothelial cells improved the decreased action of AGEs on the eNOS system. AGE-HSA increased the AGEs receptor mRNA and protein, which were both blunted by calcitriol. The parallel elevation of interleukin-6 mRNA in the presence of AGE-HSA was also blunted by calcitriol. The NF-κB-p65 DNA binding activity was enhanced and associated with a decrease in inhibitor κBα (IκBα) and an increase in phosphorylated (p)-IκBα levels. Addition of calcitriol blunted the AGEs-induced elevation of NF-κB-p65 DNA binding activity, a phenomenon related to an increased expression of IκBα. This increase was correlated to declined p-IκBα levels. The present results support the concept that calcitriol may act as a vascular protective agent counteracting the probable deleterious actions of AGEs on endothelial cell activities.

Cellular signaling and potential new treatment targets in diabetic retinopathy

Dysfunction and death of microvascular cells and imbalance between the production and the degradation of extracellular matrix (ECM) proteins are a characteristic feature of diabetic retinopathy (DR). Glucose-induced biochemical alterations in the vascular endothelial cells may activate a cascade of signaling pathways leading to increased production of ECM proteins and cellular dysfunction/death. Chronic diabetes leads to the activation of a number of signaling proteins including protein kinase C, protein kinase B, and mitogen-activated protein kinases. These signaling cascades are activated in response to hyperglycemia-induced oxidative stress, polyol pathway, and advanced glycation end product formation among others. The aberrant signaling pathways ultimately lead to activation of transcription factors such as nuclear factor-κB and activating protein-1. The activity of these transcription factors is also regulated by epigenetic mechanisms through transcriptional coactivator p300. These complex signaling pathways may be involved in glucose-induced alterations of endothelial cell phenotype leading to the production of increased ECM proteins and vasoactive effector molecules causing functional and structural changes in the microvasculature. Understanding of such mechanistic pathways will help to develop future adjuvant therapies for diabetic retinopathy.

Mechanisms of disease: advanced glycation end-products and their receptor in inflammation and diabetes complications

Many important biochemical mechanisms are activated in the presence of high levels of glucose, which occur in diabetes. Elevated levels of glucose accelerate the formation of advanced glycation end-products (AGEs). Via their chief signaling receptor-the AGE-specific receptor (commonly abbreviated as RAGE)-AGEs generate reactive oxygen species and activate inflammatory signaling cascades. Consequently, AGEs have key roles in the pathogenesis of diabetic complications. Two discoveries have advanced our knowledge of the roles of RAGE in inflammation. First, this receptor has multiple ligands and binds not only AGEs but also proinflammatory, calcium-binding S100 proteins (also known as calgranulins) and nuclear high mobility group protein box-1. Second, RAGE is expressed on T lymphocytes, monocytes and macrophages; RAGE expression on T lymphocytes is essential for effective priming of immune responses in vivo. In this Review, we chronicle roles for RAGE in the pathogenesis of diabetic complications and develop the hypothesis that, in addition to RAGE's central role in the inflammatory response, it is critically linked to the pathogenesis of types 1 and 2 diabetes.

Receptor for advanced glycation end products expression on T cells contributes to antigen-specific cellular expansion in vivo

Receptor for advanced glycation end products (RAGE) is an activation receptor triggered by inflammatory S100/calgranulins and high mobility group box-1 ligands. We have investigated the importance of RAGE on Ag priming of T cells in murine models in vivo. RAGE is inducibly up-regulated during T cell activation. Transfer of RAGE-deficient OT II T cells into OVA-immunized hosts resulted in reduced proliferative responses that were further diminished in RAGE-deficient recipients. Examination of RAGE-deficient dendritic cells did not reveal functional impairment in Ag presentation, maturation, or migratory capacities. However, RAGE-deficient T cells showed markedly impaired proliferative responses in vitro to nominal and alloantigens, in parallel with decreased production of IFN-gamma and IL-2. These data indicate that RAGE expressed on T cells is required for efficient priming of T cells and elucidate critical roles for RAGE engagement during cognate dendritic cell-T cell interactions.

Advanced glycation end products, diabetes and ageing

Advanced glycation end products (AGEs) are formed in vivo by a non-enzymatic reaction of proteins with carbohydrates and accumulate in many tissues during ageing. They are discussed as being responsible for many age- and diabetes-related diseases. On the other hand, AGEs are formed by the heating of food and are taken up by the nutrition. The contribution of endogenously formed versus exogenous intake of AGEs to age-related diseases is still under discussion.

Endothelial dysfunction in patients with chronic kidney disease results from advanced glycation end products (AGE)-mediated inhibition of endothelial nitric oxide synthase through RAGE activation

BACKGROUND AND OBJECTIVES

Advanced glycation end products, known pro-inflammatory and pro-oxidative compounds that accumulate in patients with chronic kidney disease, may play a major role in their high prevalence of endothelial dysfunction and subsequent cardiovascular disease. This study examined the association of advanced glycation end product accumulation with cellular receptor for advanced glycation end product expression and endothelial dysfunction as well as the mechanisms of this association in chronic kidney disease.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cross-sectional study was conducted of ambulatory patients without diabetes and with different stages of chronic kidney disease (n = 51), compared with gender- and age-matched healthy subjects. Fasting blood was obtained for measurement of advanced glycation end products and mRNA receptor for advanced glycation end product expression in peripheral blood mononuclear cells. Endothelial reactivity was assessed by the microcirculatory response to local ischemia (postocclusive reactive hyperemia) and local hyperthermia (thermal hyperemia). Sera were pooled and passed through affinity columns to separate advanced glycation end product-rich fractions, which were incubated with human aortic endothelial cells, with or without blockade of receptor for advanced glycation end product, to measure their effect on endothelial nitric oxide synthase.

RESULTS

Glomerular filtration rate correlated with serum advanced glycation end product, mRNA receptor for advanced glycation end product levels, postocclusive reactive hyperemia, and thermal hyperemia. Serum advanced glycation end product correlated with receptor for advanced glycation end product and inversely with postocclusive reactive hyperemia. Advanced glycation end product-rich fractions from chronic kidney disease sera suppressed endothelial nitric oxide synthase expression of human aortic endothelial cells compared with sera from healthy subjects, an effect abrogated by receptor for advanced glycation end product blockade.

CONCLUSIONS

This study demonstrates for the first time an association of excess advanced glycation end product burden with increased peripheral blood mononuclear cell mRNA receptor for advanced glycation end product and in vivo endothelial dysfunction in patients with chronic kidney disease. Endothelial dysfunction in chronic kidney disease may be partly mediated by advanced glycation end product-induced inhibition of endothelial nitric oxide synthase through receptor for advanced glycation end product activation.

Advanced glycosylation end products and nutrition--a possible relation with diabetic atherosclerosis and how to prevent it

Advanced glycosylation end product (AGE) levels are elevated in diabetic patients and may contribute to the excessive cardiovascular disease in this population, promoting oxidant stress and chronic vascular inflammation. AGEs in people with diabetes mellitus are formed mainly by protein and lipid glucosylation in an environment of chronic hyperglycemia and also by prolonged thermal food processing (diet derived AGEs). This brief review summarizes current literature about food derived AGEs and their relationship with diabetic vascular disease and supports the importance of low AGE diet as an essential preventive or therapeutic intervention against atheromatosis progress.

The grateful dead: damage-associated molecular pattern molecules and reduction/oxidation regulate immunity

The response to pathogens and damage in plants and animals involves a series of carefully orchestrated, highly evolved, molecular mechanisms resulting in pathogen resistance and wound healing. In metazoans, damage- or pathogen-associated molecular pattern molecules (DAMPs, PAMPs) execute precise intracellular tasks and are also able to exert disparate functions when released into the extracellular space. The emergent consequence for both inflammation and wound healing of the abnormal extracellular persistence of these factors may underlie many clinical disorders. DAMPs/PAMPs are recognized by hereditable receptors including the Toll-like receptors, the NOD1-like receptors and retinoic-acid-inducible gene I-like receptors, as well as the receptor for advanced glycation end products. These host molecules 'sense' not only pathogens but also misfolded/glycated proteins or exposed hydrophobic portions of molecules, activating intracellular cascades that lead to an inflammatory response. Equally important are means to not only respond to these molecules but also to eradicate them. We have speculated that their destruction through oxidative mechanisms normally exerted by myeloid cells, such as neutrophils and eosinophils, or their persistence in the setting of pathologic extracellular reducing environments, maintained by exuberant necrotic cell death and/or oxidoreductases, represent important molecular means enabling chronic inflammatory states.

Soluble form of vascular cell adhesion molecule 1 induces migration and proliferation of vascular smooth muscle cells

BACKGROUND

Serum levels of soluble vascular cell adhesion molecule 1 (sVCAM-1) shed from its membrane-bound form are elevated in hypertension. This study clarified the effects of sVCAM-1 on vascular responses in rat aortic smooth muscle cells (RASMCs).

METHODS

Boyden chamber, 5-bromo-2'-deoxyuridine incorporation and ex vivo aortic ring assays for migration and proliferation, and Western blot for the kinase activity were used.

RESULTS

Spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats were compared functionally. sVCAM-1 increased RASMC migration and proliferation, which were greater in SHR compared with WKY rats. RASMCs expressed the very late antigen 4alpha receptor integrin with no difference between SHR and WKY rats. Inhibitors of phosphoinositide kinase 3 (PI3K) and spleen tyrosine kinase (Syk) and small interference RNA-Syk abolished the sVCAM-1-induced migration, proliferation and phosphorylation of focal adhesion kinase. The phosphorylation of Syk was significantly greater in RASMCs from SHR than from WKY rats. sVCAM-1 increased aortic sprout outgrowth, which was inhibited by inhibitors of PI3K and Syk.

CONCLUSIONS

This study suggests that sVCAM-1 promotes the RASMC migration and proliferation via the focal adhesion kinase pathway regulated by Syk and PI3K, and the altered sVCAM-1-induced responses during hypertension are closely associated with the increments in intracellular signal transmission.

Association between endogenous secretory RAGE, inflammatory markers and arterial stiffness

BACKGROUND

Advanced glycation end products (AGEs) and its receptor (RAGE) were known to play a pivotal role in the development of cardiovascular complications of diabetes. We investigated the association between circulating endogenous secretory RAGE (esRAGE) levels, inflammatory markers and arterial stiffness measured using brachial-ankle pulse wave velocity (baPWV).

METHODS

The study subjects were composed of 76 type 2 diabetic patients and 78 age- and sex-matched non-diabetic subjects.

RESULTS

Circulating esRAGE levels were significantly lower in subjects with type 2 diabetes (0.237+/-0.123 ng/ml vs. 0.307+/-0.177 ng/ml, p=0.005), and those levels were inversely correlated with body mass index (BMI), waist circumference, blood pressure, triglyceride, fasting glucose level and insulin resistance. Furthermore, esRAGE levels were significantly associated with adiponectin (r=0.164, p=0.044), interleukin-6 (IL-6) (r=-0.242, p=0.009) levels and baPWV (r=-0.296, p<0.001). Multiple regression analysis showed that fasting insulin, IL-6, glucose level and insulin resistance are major factor determining esRAGE (R(2)=0.186). Moreover, baPWV was found to be associated with age, systolic blood pressure, triglyceride, sex, BMI, fasting insulin and esRAGE level (R(2)=0.583).

CONCLUSIONS

Circulating esRAGE levels were significantly lower in type 2 diabetic patients, and were associated with inflammation and arterial stiffness. These results suggest that esRAGE may play an important role on ligand-RAGE interaction propagated inflammation and atherosclerosis.

Diabetes and the heart: could the diabetic myocardium be protected by preconditioning?

Both type 1 and type 2 diabetes (insulin-dependent and non-insulin dependent diabetes, respectively) are associated with increased risk for microvascular and macrovascular complications including retinopathy, neuropathy, nephropathy and atherosclerosis. Type 2 diabetes markedly increases the risk for cardiovascular morbidity and mortality, which has major public health implications. In this review, molecular mechanisms pertaining to diabetes-induced heart pathology are addressed.

Acute hyperglycaemia induces an inflammatory response in young patients with type 1 diabetes

BACKGROUND

Patients with type 1 diabetes (T1D) are at a substantially increased risk of cardiovascular disease. Stress-induced hyperglycaemia in turn is shown to worsen the prognosis of patients suffering from an acute myocardial infarction. However, the mechanisms behind these findings are incompletely known.

AIM

To investigate whether markers of chronic inflammation, and oxidative stress respond to acute hyperglycaemia in patients with T1D.

METHODS

The plasma glucose concentration was rapidly raised from 5 to 15 mmol/L in 35 males (22 men with T1D and 13 age-matched non-diabetic volunteers) and maintained for 2 h. All participants were young non-smokers without any signs of diabetic or other complications. Markers of chronic inflammation, and oxidative stress were analysed in serum/plasma samples drawn at base-line and after 120 min of hyperglycaemia.

RESULTS

Compared to normoglycaemia, acute hyperglycaemia increased the interleukin (IL)-6 concentrations by 39% in patients with T1D (P<0.01) and 26% in healthy volunteers (P<0.05). During hyperglycaemia the superoxide dismutase concentration was increased by 17% in the healthy volunteers (P<0.01) and 5% in the patients with type 1 diabetes (P=NS). The increase in tumour necrosis factor (TNF)-alpha was larger in patients with type 1 diabetes than in non-diabetic volunteers (35% versus -10%, P<0.05).

CONCLUSIONS

This study shows that acute hyperglycaemia induces an inflammatory response in patients with type 1 diabetes.

Arguing for the motion: yes, RAGE is a receptor for advanced glycation endproducts

Advanced glycation endproducts (AGEs) are an heterogenous class of compounds formed by diverse stimuli, including hyperglycemia, oxidative stress, inflammation, renal failure, and innate aging. Recent evidence suggests that dietary sources of AGE may contribute to pathology. AGEs impart diverse effects in cells; evidence strongly suggests that crosslinking of proteins by AGEs may irrevocably alter basement membrane integrity and function. In addition, the ability of AGEs to bind to cells and activate signal transduction, thereby affecting broad properties in the cellular milieu, indicates that AGEs are not innocent bystanders in the diseases of AGEing. Here, we present evidence that receptor for AGE (RAGE) is a receptor for AGEs.

Regulation of Src homology 2-containing protein tyrosine phosphatase by advanced glycation end products: the role on atherosclerosis in diabetes

Advanced glycation end products (AGEs), among the most important causes of atherosclerosis in diabetes mellitus, stimulate the proliferation of smooth muscle cells (SMCs). Smooth muscle cells are central in the formation of atherosclerotic lesions, where they show both increased migration and accelerated proliferation. In investigating how AGEs stimulate SMC proliferation, we focused on protein tyrosine phosphatase, especially Src homology 2-containing protein tyrosine phosphatase (SHP2), which is considered important in regulating cell proliferation. Advanced glycation end products increased activity of SHP2 in the membrane fraction of rat aortic SMCs compared with control bovine serum albumin (P < .05). Upon characterizing the genomic and promoter structure of SHP2, we detected nuclear factor-kappaB (NF-kappaB) binding sites in the promoter area. Advanced glycation end product stimulation increased luciferase activity in cells transfected with SHP2 promoter region including NF-kappaB binding sites (P < .05) and increased SHP2 expression (P < .05). These data indicate that AGE stimulation appears to activate NF-kappaB. Activated NF-kappaB binds to sites on the SHP2 promoter, resulting in increased SHP2 expression, SHP2 activity, and, ultimately, SMC proliferation. It suggests that AGE stimulation induces SMC proliferation via SHP2, underscoring the importance of control of AGE for suppressing macroangiopathy in diabetes mellitus.

RAGE and soluble RAGE: potential therapeutic targets for cardiovascular diseases

Receptor for advanced glycation end-products (RAGE) is known to be involved in microvascular complications in diabetes. RAGE is also profoundly associated with macrovascular complications in diabetes through regulation of atherogenesis, angiogenic response, vascular injury, and inflammatory response. The potential significance of RAGE in the pathogenesis of cardiovascular disease appears not to be confined solely to nondiabetic rather than diabetic conditions. Numerous truncated forms of RAGE have recently been described, and the C-terminally truncated soluble form of RAGE has received much attention. Soluble RAGE consists of several forms, including endogenous secretory RAGE (esRAGE), which is a spliced variant of RAGE, and a shedded form derived from cell-surface RAGE. These heterogeneous forms of soluble RAGE, which carry all of the extracellular domains but are devoid of the transmembrane and intracytoplasmic domains, bind ligands including AGEs and can antagonize RAGE signaling in vitro and in vivo. ELISA systems have been developed to measure plasma esRAGE and total soluble RAGE, and the pathophysiological roles of soluble RAGE have begun to be unveiled clinically. In this review, we summarize recent findings regarding pathophysiological roles in cardiovascular disease of RAGE and soluble RAGE and discuss their potential usefulness as therapeutic targets and biomarkers for the disease.

Methotrexate reduces the levels of pentosidine and 8-hydroxy-deoxy guanosine in patients with rheumatoid arthritis

This study was performed to investigate whether methotrexate (MTX) affects the levels of oxidative stress markers, including pentosidine one of the glycation end products (AGEs) or 8-hydroxy-deoxy guanosine (8-OHdG). These stress markers represent DNA damage; 19 rheumatoid arthritis (RA) patients underwent MTX treatment. The levels of serum total, urinary total, urinary-free pentosidine and also urinary 8-OHdG, as well as clinical parameters, including disease activity scores for 28 joints (DAS28) were measured at baseline and at 3 and 6 months after the initial treatment with MTX. After the initial treatment with MTX, serum total and urinary total pentosidine levels were reduced at 6 months, and urinary-free pentosidine levels were reduced at 3 and 6 months. Urinary 8-OHdG levels also were significantly reduced at 6 months after the initial treatment with MTX. This study demonstrated that MTX plays a role as a regulator against pentosidine formation and oxidative DNA damage in RA patients.

Endogenous Secretory RAGE as a Novel Biomarker for Metabolic Syndrome and Cardiovascular Diseases

Receptor for advanced glycation end-products (RAGE) is known to be involved in both micro- and macro-vascular complications in diabetes. Among numerous truncated forms of RAGE recently described, the C-terminally truncated form of RAGE has received much attention. This form of RAGE, carrying all of the extracellular domains but devoid of the transmembrane and intracytoplasmic domains, is released outside from cells, binds ligands including AGEs, and is capable of neutralizing RAGE signaling on endothelial cells in culture. This form of RAGE is generated as a splice variant and is named endogenous secretory RAGE (esRAGE). Adenoviral overexpression of esRAGE reverses diabetic impairment of vascular dysfunction, suggesting that esRAGE may be an important inhibitor of RAGE signaling in vivo and potentially be useful for prevention of diabetic vascular complications. An ELISA system to measure plasma esRAGE was recently developed, and the pathophysiological roles of esRAGE have begun to be unveiled clinically. Plasma esRAGE levels are decreased in patients with several metabolic diseases including type 1 and type 2 diabetes, metabolic syndrome and hypertension. In cross-sectional analysis, plasma esRAGE levels are inversely correlated with carotid or femoral atherosclerosis. In an observational cohort of patients with end-stage renal disease, cumulative incidence of cardiovascular death was significantly higher in subjects with lower plasma esRAGE levels. These findings suggest that plasma esRAGE may act as a protective factor against and a novel biomarker for the occurrence of metabolic syndrome and cardiovascular diseases.

Receptor for advanced glycation endproducts and atherosclerosis: From basic mechanisms to clinical implications

The receptor for advanced glycation endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules with a diverse repertoire of ligands. In the atherosclerotic milieu, three classes of RAGE ligands, i.e., products of non-enzymatic glycoxidation, S100 proteins and amphoterin, appear to drive receptor-mediated cellular activation and potentially, acceleration of vascular disease. The interaction of RAGE-ligands effectively modulates several steps of atherogenesis, triggering an inflammatory-proliferative process and furthermore, critically contributing to propagation of vascular perturbation, mainly in diabetes. RAGE has a circulating truncated variant isoform, soluble RAGE (sRAGE), corresponding to its extracellular domain only. By competing with cell-surface RAGE for ligand binding, sRAGE may contribute to the removal/neutralization of circulating ligands thus functioning as a decoy. The critical role of RAGE in the chronic vascular inflammation processes highlights this receptor-ligand axis as a possible and attractive candidate for therapeutic intervention to limit vascular damage and its associated clinical disorders.

Dietary AGEs and ALEs and risk to human health by their interaction with the receptor for advanced glycation endproducts (RAGE)--an introduction

The receptor for advanced glycation endproducts (RAGE) has a well-substantiated role in cell dysfunction and mechanisms of inflammatory disease. The physiological agonists of RAGE are less certain: S100/calgranulin proteins, high mobility group-1 protein HMGB1 and other proteins are candidate agonists. It increasingly appears unlikely proteins modified by advanced glycation endproducts are effective agonists in vivo. In the following debate, Professors Ann Marie Schmidt and Claus Heizmann gave arguments and evidences for and against the motion. Recent evidence suggesting the activation of RAGE impairs the enzymatic defence against glycation provided by glyoxalase 1 (Glo 1) suggests that studies of RAGE will continue to be of importance to our understanding of the physiological significance of protein glycation.

Soluble RAGE in type 2 diabetes: association with oxidative stress

Advanced glycation end products (AGEs) contribute to diabetic vascular complications by engaging the AGE receptor (RAGE). A soluble RAGE form (sRAGE) acts as a decoy domain receptor, thus decreasing AGE cellular binding. A cross-sectional comparison of sRAGE, asymmetric dimethylarginine (ADMA) plasma levels (index of endothelial dysfunction), and urinary 8-iso-prostaglandin (PG)F(2alpha) (marker of oxidative stress) was performed between 86 diabetic patients and 43 controls. Plasma sRAGE levels were significantly lower and ADMA levels were significantly higher in diabetic patients as compared to controls (P<0.0001). HbA1c and urinary 8-iso-PGF(2alpha) were correlated inversely with sRAGE and directly with ADMA. On multivariate analysis HbA1c was independently related to sRAGE levels in diabetic patients. Twenty-four of 86 patients with newly diagnosed diabetes and 12 patients in poor metabolic control were reevaluated after treatment with a hypoglycemic agent or insulin, respectively. Improvement in metabolic control by oral agents or insulin resulted in a significant increase in sRAGE and decrease in ADMA levels (P<0.0001). Thus, poor glycemic control reduces sRAGE levels, in association with enhanced oxidative stress and endothelial dysfunction in diabetes. These abnormalities are susceptible to modulation by improvement in metabolic control.

Diabetes mellitus and the peripheral nervous system: manifestations and mechanisms

Diabetes targets the peripheral nervous system with several different patterns of damage and several mechanisms of disease. Diabetic polyneuropathy (DPN) is a common disorder involving a large proportion of diabetic patients, yet its pathophysiology is controversial. Mechanisms considered have included polyol flux, microangiopathy, oxidative stress, abnormal signaling from advanced glycation endproducts and growth factor deficiency. Although some clinical trials have demonstrated modest benefits in disease stabilization or pain therapy in DPN, robust therapy capable of reversing the disease is unavailable. In this review, general aspects of DPN and other diabetic neuropathies are examined, including a summary of recent therapeutic trials. A particular emphasis is placed on the evidence that the neurobiology of DPN reflects a unique yet common and disabling neurodegenerative disorder.

Increased serum levels of advanced glycation endproducts predict total, cardiovascular and coronary mortality in women with type 2 diabetes: a population-based 18 year follow-up study

AIMS/HYPOTHESIS

AGEs, modification products formed by glycation or glycoxidation of proteins and lipids, have been linked to premature atherosclerosis in patients with diabetes. We investigated whether increased serum levels of AGEs predict total, cardiovascular (CVD) or CHD mortality in a population-based study.

SUBJECTS AND METHODS

Serum levels of AGEs were determined by immunoassay in a random sample of 874 Finnish diabetic study participants (488 men, 386 women), aged 45-64 years. These participants were followed for 18 years for total, CVD and CHD mortality.

RESULTS

Multivariate Cox regression models revealed that serum levels of AGEs were significantly associated with total (p = 0.002) and CVD mortality (p = 0.021) in women, but not in men. Serum levels of AGEs in the highest sex-specific quartile predicted all-cause (hazards ratio [HR] 1.51; 95% confidence intervals [CI], 1.14-1.99; p = 0.004), CVD (HR 1.56; 95% CI 1.12-2.19; p = 0.009), and CHD (HR 1.68; 95% CI 1.11-2.52; p = 0.013) mortality in women, even after adjustment for confounding factors, including high-sensitivity C-reactive protein.

CONCLUSIONS/INTERPRETATION

Increased serum levels of AGEs predict total and CVD mortality in women with type 2 diabetes.

Oxidant stress, immune dysregulation, and vascular function in type I diabetes

Although high glucose is an important contributor to diabetic vasculopathies, complications still occur in spite of tight glycemic control, suggesting that some critical event prior to or concurrent with hyperglycemia may contribute to early vascular changes. Utilizing previously published and new experimental evidence, this review will discuss how prior to the hyperglycemic state, an imbalance between oxidants and antioxidants may contribute to early vascular dysfunction and set in motion proinflammatory insults that are further amplified as the diabetes develops. This imbalance results from the resetting of the equilibrium between vessel superoxide/H(2)O(2) production and/or decreased antioxidant defenses. Such an imbalance may cause endothelial dysfunction, characterized by abnormal endothelium-dependent vasoreactivity, as the first sign of blood vessel damage, followed by morphological changes of the vessel wall and inflammation. As such, increased oxidant stress in preglycemic states may be a critically central initiating event that underlies the pathogenesis of life-threatening vascular diseases in autoimmune diabetes. This review focuses on the relationship between oxidative stress, immune dysregulation, and vascular injury in type 1 diabetes, and how the discovery of novel pathways of vascular disease in nonobese diabetic mice may direct future studies in patients with type 1 diabetes.