Plasma levels of soluble receptor for advanced glycation end products and coronary artery disease in nondiabetic men

Clinical relevance of advanced glycation endproducts for vascular surgery

Atherosclerosis is the main contributor to cardiovascular disease and leads to intimal plaque formation, which may progress to plaque rupture with subsequent thromboembolic events and/or occlusion of the arterial lumen. There is increasing evidence that the development or progression of atherosclerosis is associated with advanced glycation endproducts (AGEs). AGEs are a heterogeneous group of compounds formed by the non-enzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids. An increased understanding of the mechanisms of formation and interaction of AGEs has allowed the development of several potential anti-AGE strategies. This review summarizes AGE formation and biochemistry, the pathogeneic role of AGEs in cardiovascular disease, anti-AGE therapies and clinical relevance to vascular surgery.

Skin autofluorescence is elevated in patients with stable coronary artery disease and is associated with serum levels of neopterin and the soluble receptor for advanced glycation end products

AIMS

To investigate whether skin autofluorescence (AF), a non-invasive marker for advanced glycation end products (AGEs), is elevated in stable coronary artery disease (sCAD) and to investigate its relationship with serum levels of the soluble receptor for AGEs (sRAGE), neopterin and C-reactive protein (CRP).

METHODS AND RESULTS

Skin AF and serum levels of sRAGE, neopterin and CRP were assessed in 63 sCAD patients (mean age: 64.7+/-10.5 years), comprising 78% males, 19% subjects with diabetes, and 22% current smokers and in 33 (mean age: 63.4+/-10.0 years) healthy non-diabetic and non-smoking age and gender matched controls. Skin AF was significantly increased in sCAD compared with controls, irrespective of diabetes, current smoking and renal function. Levels of sRAGE (standardized beta: 0.43 (explaining 17% of variance in skin AF); P<0.001), neopterin (beta: 0.36 (11%); P=0.003) and glucose (beta: 0.29 (8%); P=0.0011) as well as current smoking (beta: 0.26 (6%); P=0.024) were independently associated with skin AF (R(2) 0.42), whereas the association of gender, former smoking, body mass index, CRP, lipids, creatinine clearance and pulse pressure with skin AF was not significant in this model.

CONCLUSION

These data demonstrate that skin AF is elevated in sCAD and is related to sRAGE and neopterin, making it an easily applicable tool to improve our understanding of inflammatory and oxidative stress in cardiovascular disease.

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.

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.

Receptor for advanced glycation end products (RAGE)--soluble form (sRAGE) and gene polymorphisms in patients with breast cancer

Receptor for advanced glycation end products (RAGE) may be involved in the pathogenesis of the cancer progression and metastasis. Pathological effects mediated via RAGE are physiologically inhibited by soluble RAGE (sRAGE), so the higher sRAGE levels may confer the patients with cancer with better outcome. The aim was to study sRAGE and RAGE gene polymorphisms in patients with breast cancer. The authors studied sRAGE and RAGE polymorphisms in 120 patients with breast cancer (subdivided based on the clinical stage, histologic grading, expression of hormonal and Her2/neu receptors) and in 92 healthy controls. Despite higher serum concentrations of AGEs, serum concentrations of sRAGE were lower in patients with breast cancer compared to healthy controls (1581 +/- 777 versus 1803 +/- 632 ng/mL, p < 0.05). Serum levels of sRAGE were higher in patients with advanced breast cancer (stage III), lower grade and positive estrogen receptors, and intermediate positivity of Her2/neu receptors and were also influenced genetically (Gly82Ser and 2184 AG polymorphisms of the RAGE gene). Decreased sRAGE levels in patients with breast cancer may contribute to the progression of the disease. Patients with better outcome (low grade and positive estrogen receptors) have higher sRAGE levels. Progression of the disease, may, however, increase sRAGE levels, possibly as a compensatory mechanism to counteract further progression.

Identification, classification, and expression of RAGE gene splice variants

The receptor for advanced glycation end-products (RAGE) is a single-transmembrane, multiligand receptor of the immunoglobulin superfamily. RAGE up-regulation is implicated in numerous pathological states including vascular disease, diabetes, cancer, and neurodegeneration. The understanding of the regulation of RAGE is important in both disease pathogenesis and normal homeostasis. Here, we demonstrate the characterization and identification of human RAGE splice variants by analysis of RAGE cDNA from tissue and cells. We identified a vast range of splice forms that lead to changes in the protein coding region of RAGE, which we have classified according to the Human Gene Nomenclature Committee (HGNC). These resulted in protein changes in the ligand-binding domain of RAGE or the removal of the transmembrane domain and cytosolic tail. Analysis of splice variants for premature termination codons reveals approximately 50% of identified variants are targeted to the nonsense-mediated mRNA decay pathway. Expression analysis revealed the RAGE_v1 variant to be the primary secreted soluble isoform of RAGE. Taken together, identification of functional splice variants of RAGE underscores the biological diversity of the RAGE gene and will aid in the understanding of the gene in the normal and pathological state.

Serum and mucosal S100 proteins, calprotectin (S100A8/S100A9) and S100A12, are elevated at diagnosis in children with inflammatory bowel disease

OBJECTIVE

Various markers characterize the complex inflammatory processes seen in chronic inflammatory bowel disease (IBD) including calprotectin, a complex of two S100 proteins, which has been evaluated and validated as a faecal marker of inflammation. However, the systemic and mucosal expression patterns of calprotectin and related S100 proteins are not well characterized in this disease. The objective of this study was to assess serum and mucosal levels of calprotectin, S100A12 and soluble receptor for advanced glycation end products (sRAGE), a putative S100 ligand, in a paediatric population with IBD.

MATERIAL AND METHODS

Children were enrolled at diagnosis of IBD, along with groups of children without IBD. Standard inflammatory markers and disease activity scores were collated. Calprotectin, S100A12 and sRAGE levels in serum and biopsy culture supernatants were measured by ELISA and tissue distribution of S100 proteins was investigated by immunohistochemistry.

RESULTS

Serum and mucosal calprotectin and S100A12 levels were increased in children with IBD as compared with non-IBD controls. Serum calprotectin levels correlated with S100A12 levels and with disease activity scores in children with IBD. sRAGE levels were not increased in IBD. S100A8, S100A9 and S100A12 were abundantly expressed throughout the lamina propria and epithelium in inflamed mucosa. In contrast, these proteins were present in the lamina propria, but not the epithelium, in non-inflamed mucosa.

CONCLUSIONS

Serum calprotectin and S100A12 are increased in children with IBD and indicate disease activity. Elevated levels of these proteins are present in the colonic mucosa and may contribute to the pathogenesis of IBD. Furthermore, an imbalance between sRAGE and S100A12 may contribute to inflammatory changes present in IBD.

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.

Decreased plasma soluble RAGE in patients with hypercholesterolemia: effects of statins

The receptor for advanced glycation endproducts (RAGE) is overexpressed at sites of vascular pathology. A soluble RAGE isoform (sRAGE) neutralizes the ligand-mediated damage by acting as a decoy. We hypothesized that in hypercholesterolemia up-regulation of the ligand-RAGE axis may bridge impairment of nitric oxide biosynthesis with oxidative stress. We measured in 60 hypercholesterolemic patients and 20 controls plasma total sRAGE levels, urinary 8-iso-prostaglandin (PG) F(2alpha) excretion, and plasma levels of asymmetric dimethylarginine (ADMA). The effects of two structurally different statins (pravastatin and atorvastatin) on these parameters were analyzed in 20 hypercholesterolemic subjects free of vascular disease. Plasma sRAGE was significantly lower, ADMA and urinary 8-iso-PGF(2alpha) were higher, in hypercholesterolemic versus normocholesterolemic patients. Patients on statin treatment with previous myocardial infarction had lower 8-iso-PGF(2alpha), higher sRAGE, and unchanged ADMA levels compared to subjects free of vascular disease. On multivariate regression analysis only 8-iso-PGF(2alpha) and ADMA predicted sRAGE levels. An 8-week treatment with either statin was associated with a significant reduction in urinary 8-iso-PGF(2alpha), whereas only atorvastatin raised sRAGE levels near to normal values, with no change in ADMA levels. sRAGE might serve as an endogenous protecting factor for accelerated atherosclerosis mediated by oxidative stress and endothelial dysfunction in hypercholesterolemia.

Low levels of sRAGE are associated with increased risk for mortality in renal transplant recipients

OBJECTIVE

Infusion of the soluble form of the receptor for advanced glycation end-products (sRAGE) was protective against atherosclerosis and nephropathy in animal models. In this study we investigated determinants of endogenous sRAGE in renal transplant recipients and whether sRAGE was associated with mortality and graft loss.

METHODS AND RESULTS

A total of 591 patients participated at a median time of 6 years after transplantation. Independent determinants of sRAGE were mycophenolate mofetil medication (beta=-0.21, P<0.001), creatinine clearance (beta=-0.15, P<0.001), BMI (beta=-0.12, P=0.003) and fasting insulin concentration (beta=-0.14, P=0.001). Low sRAGE levels were associated with a 2-3 times higher risk for mortality especially after correction for creatinine clearance (P=0.006).

CONCLUSION

A lack of sRAGE is a risk factor for mortality in renal transplant recipients. The putatively protective role of sRAGE and in particular its association with mycophenolate mofetil usage needs further investigation.

The mechanism by which dietary AGEs are a risk to human health is via their interaction with RAGE: Arguing against the motion

We are interested in the regulation of intracellular calcium and the various diseases associated with an altered regulation of this second messenger. More recently, we also became interested in pathologies involving the Ca2+-binding S100 proteins and AGEs and their association with the multifunctional Receptor for Advanced Glycation Endproducts (RAGE).

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.

Percutaneous treatment of peripheral vascular disease: the role of diabetes and inflammation

Peripheral arterial disease (PAD) is a growing health problem for many Americans and often occurs along with other cardiovascular risk factors, including diabetes mellitus (DM), low-grade inflammation, hypertension, and lipid disorders. Intermittent claudication (IC), an early manifestation of PAD, commonly leads to reduced quality of life for patients who are limited in their ambulation. While recent wide adoption of percutaneous peripheral interventional (PPI) techniques has increased the number patients being aggressively treated for IC, the overall effectiveness of PPI for the treatment of IC is not well known, especially for DM patients who have both hemodynamic and functional obstacles to treatment success. This review is designed to illustrate how treatment outcomes for IC can be measured by different modalities and how diabetes and inflammation can influence those outcomes. In the setting of greater concern for health care resources and clinical accountability, better understanding of treatment outcomes and efficacy will help us manage these complex challenges.

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.

Elevation of soluble form of receptor for advanced glycation end products (sRAGE) in diabetic subjects with coronary artery disease

BACKGROUND

Advanced glycation end products (AGEs)-receptor (RAGE) axis is implicated in diabetic vascular complication. Since a soluble form of RAGE (sRAGE) could be generated from the cleavage of cell surface RAGE in endothelial cells (ECs), serum sRAGE levels may be elevated in diabetes consequent to EC damage. In this study, we examined whether sRAGE levels were elevated in type 2 diabetic patients compared with non-diabetic healthy subjects.

METHODS

Serum sRAGE levels were examined in 75 Japanese type 2 diabetic patients (29 men and 46 women; mean age 66 +/- 11 years) and 75 age- and sex-matched non-diabetic healthy control subjects. We explored the association between sRAGE levels and coronary artery disease (CAD) in diabetic patients.

RESULTS

Serum sRAGE levels were significantly higher in diabetic patients than in non-diabetic subjects (965.3 +/- 544.2 vs 415 +/- 150.4 pg/mL, p < 0.001). In the univariate analysis, diastolic blood pressure (inversely), LDL cholesterol, triglycerides, HDL cholesterol, hemoglobin A(1c), and creatinine were significantly associated with sRAGE. After performing multivariate analyses, the presence of diabetes (p < 0.0001) was a sole independent determinant of sRAGE. Furthermore, there was a significant difference in sRAGE levels between diabetic patients with CAD and those without CAD (1680.6 +/- 891.1 vs 855.2 +/- 372.1 pg/mL, p < 0.001). Multiple stepwise regression analysis revealed that sRAGE and creatinine levels were independent determinants of CAD.

CONCLUSIONS

The present study demonstrated that serum sRAGE levels were significantly higher in type 2 diabetic patients than in non-diabetic subjects and positively associated with the presence of CAD.

Preventing macrovascular complications in type 2 diabetes mellitus: glucose control and beyond

Patients with type 2 diabetes mellitus are at increased risk for macrovascular disease complications. Hyperglycemia and atherosclerotic disease clearlyare associated, andbiologic intermediates mediated by hyperglycemia exist. Our understanding of the pathobiology linking hyperglycemia and atherosclerotic disease continues to evolve. Modulation of the advanced glycation end product (AGE) receptor for AGE (RAGE)/soluble RAGE (sRAGE) system, the thromboxane receptor, and C-peptide comprise just a few of the plausible links between dysglycemia and atherosclerosis. It seems intuitive, therefore, that therapeutic management of blood glucose in patients with diabetes should reduce macrovascular disease and related deaths. However, studies of glucose-lowering therapies performed to date yield qualitatively and quantitatively different results. No definitive proof of the concept is yet available, although it remains probable, with investigations presently under way. Numerous interventions extending beyond glucose control, including lifestyle modification, pharmacologic therapy with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins), aspirin, and angiotensin-converting enzyme inhibitors, as well as aggressive blood pressure control independent of blood pressure levels, have proved to be of cardiovascular benefit in the high-risk population of patients with diabetes. Thus, all of these interventions should be used in addition to glucose management in all patients with diabetes who are at increased risk for cardiovascular disease.

Pulmonary biomarkers based on alterations in protein expression after exposure to arsenic

OBJECTIVE

Environmental exposure to arsenic results in multiple adverse effects in the lung. Our objective was to identify potential pulmonary protein biomarkers in the lung-lining fluid of mice chronically exposed to low-dose As and to validate these protein changes in human populations exposed to As.

METHODS

Mice were administered 10 or 50 ppb As (sodium arsenite) in their drinking water for 4 weeks. Proteins in the lung-lining fluid were identified using two-dimensional gel electrophoresis (n = 3) or multidimensional protein identification technology (MUDPIT) (n = 2) coupled with mass spectrometry. Lung-induced sputum samples were collected from 57 individuals (tap water As ranged from ~ 5 to 20 ppb). Protein levels in sputum were determined by ELISA, and As species were analyzed in first morning void urine.

RESULTS

Proteins in mouse lung-lining fluid whose expression was consistently altered by As included glutathione-S-transferase (GST)-omega-1, contraspin, apolipoprotein A-I and A-IV, enolase-1, peroxiredoxin-6, and receptor for advanced glycation end products (RAGE). Validation of the putative biomarkers was carried out by evaluating As-induced alterations in RAGE in humans. Regression analysis demonstrated a significant negative correlation (p = 0.016) between sputum levels of RAGE and total urinary inorganic As, similar to results seen in our animal model.

CONCLUSION

Combinations of proteomic analyses of animal models followed by specific analysis of human samples provide an unbiased determination of important, previously unidentified putative biomarkers that may be related to human disease.

Soluble RAGE but not endogenous secretory RAGE is associated with albuminuria in patients with type 2 diabetes

Background

Total circulating soluble receptor for advanced glycation endproducts (sRAGE) and a more defined endogenous secretory splice variant of the receptor (esRAGE) were shown to be associated with different markers of cardiovascular risk in patients with diabetes. Since previous data were partly divergent, the aim of this study was to compare sRAGE and esRAGE in a head-to-head analysis in patients with type 2 diabetes (T2DM) with albuminuria.

Methods

sRAGE and esRAGE were studied in plasma of 110 T2DM patients using enzyme-linked immunosorbant assays (ELISA) detecting either sRAGE or esRAGE only. Both sRAGE and esRAGE were compared with regard to applicability as markers for vascular disease and glucose control in T2DM.

Results

In bivariate analysis, sRAGE correlated with age (R = 0.22, p = 0.02) and the 24 hour albumin excretion rate (R = 0.18, p = 0.05), while esRAGE correlated positively with age only (R = 0.23, p = 0.02). In contrast to previous reports, neither sRAGE nor esRAGE correlated with glucose control or intima-media-thickness (IMT) as a predictor of macrovascular disease. In multivariate regression models, the associations between sRAGE and albuminuria as well as esRAGE and age were shown to be independent of glucose control, diabetes duration, body-mass index, glomerular filtration rate, blood pressure and gender.

Conclusion

This is the first study comparing sRAGE and esRAGE as markers of vascular complications in patients with T2DM. sRAGE but not esRAGE is independently associated with albuminuria in these patients while neither sRAGE nor esRAGE are associated with markers of glucose control or macrovascular disease.

Soluble receptor for advanced glycation end products triggers a proinflammatory cytokine cascade via beta2 integrin Mac-1

OBJECTIVE

Receptor for advanced glycation end products (RAGE) is a cell surface molecule that binds a variety of ligands, including high mobility group box chromosomal protein 1 (HMGB-1), a potent proinflammatory cytokine. RAGE-ligand interaction leads to an inflammatory response. A truncated form of the receptor, soluble RAGE (sRAGE), has been suggested to function as a decoy abrogating cellular activation, but its endogenous activity is not fully understood. We undertook this study to assess the properties of sRAGE in vivo and in vitro and to analyze the role of sRAGE in HMGB-1-induced arthritis.

METHODS

Mice were injected intraarticularly with HMGB-1 and treated systemically with sRAGE prior to histologic joint evaluation. All animals were subjected to peritoneal lavage to assess the local effect of sRAGE treatment. For in vitro studies, mouse splenocytes were incubated with sRAGE followed by assessment of NF-kappaB activation and cytokine production. The chemotactic properties of sRAGE were investigated using in vitro migration assay.

RESULTS

Soluble RAGE was determined to have proinflammatory properties since it gave rise to production of interleukin-6, tumor necrosis factor alpha, and macrophage inflammatory protein 2. This effect was triggered by interaction with leukocyte beta2 integrin Mac-1 and was mediated via NF-kappaB. Systemic treatment with sRAGE significantly down-regulated HMGB-1-triggered arthritis, but the observed effect was due to a deviation of the inflammatory response from the joint to the peritoneal cavity rather than a genuine antiinflammatory effect. Apart from its proinflammatory properties, sRAGE was proven to act as a chemotactic stimulus for neutrophils.

CONCLUSION

We conclude that sRAGE interacts with Mac-1, thereby acting as an important proinflammatory and chemotactic molecule.

Association of the Gly82Ser polymorphism in the receptor for advanced glycation end products (RAGE) gene with circulating levels of soluble RAGE and inflammatory markers in nondiabetic and nonobese Koreans

We investigated the association between the Gly82Ser (G82S) polymorphism in the receptor for advanced glycation end products (RAGE) gene and circulating levels of soluble RAGE (sRAGE), advanced glycation end products (AGEs), and inflammatory markers in nondiabetic/nonobese Koreans. A total of 1096 men and 580 women aged 30 to 69 years and with body mass index of 18.5 to 29.9 kg/m(2) were recruited. Anthropometrics, lipid profiles, glucose, insulin, insulin resistance (IR), RAGE G82S polymorphism, sRAGE, AGEs, and inflammatory markers were measured. There was a significant association between G82S genotypes and plasma sRAGE concentrations (P < .001). sRAGE concentrations were significantly higher in subjects with the G/G genotype (1038 +/- 33 pg/mL) than in those with the G/S (809 +/- 19 pg/mL) or the S/S (428 +/- 43 pg/mL) genotype. Furthermore, the G82S genotypes in the RAGE gene were associated with serum AGE (P = .033), homeostasis model assessment for insulin resistance (HOMA-IR) (P < .001), plasma tumor necrosis factor alpha (TNF-alpha) (P = .033), serum C-reactive protein (CRP) (P= .002), and urinary excretion of 8-epi-prostaglandin F(2alpha) (P = .028) after adjusting for sex, age, body mass index, cigarette smoking, and alcohol drinking. Subjects with the S/S genotype showed higher levels of serum AGE, HOMA-IR, plasma TNF-alpha, serum CRP, and 8-epi-prostaglandin F(2alpha) than those with the G/G or G/S combination. The sRAGE levels showed a negative relation with high-sensitivity CRP (r = -0.250; P < .001). The AGE concentrations showed a positive relation with TNF-alpha levels (r = 0.398; P < .001). Subjects with homozygosity for the minor S allele (S/S) of the G82S polymorphism had higher risk factors for cardiovascular disease, such as low sRAGE levels, inflammation, oxidative stress, and IR, compared with those bearing at least one G allele.

Pregnancy-associated plasma protein a and soluble receptor for advanced glycation end products after kidney transplantation

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A) and soluble receptor for advanced glycation end products (sRAGE) are new markers related to vascular damage.

METHODS

Thirty-one patients who had undergone kidney transplantation (TX) in the year 2005 under tacrolimus-based immunosuppression were included in this prospective single-center study. PAPP-A and sRAGE were determined before TX and 2 and 6 weeks and 3 months after TX. The results were correlated with the 3-month protocol kidney graft biopsy findings.

RESULTS

Both PAPP-A and sRAGE decreased after TX (mean values in serum: PAPP-A 20.8, 13.7, 12.1, and 10.7 mIU/l, respectively, before and 2 and 6 weeks and 3 months after TX, p < 0.001; sRAGE 4,403.4, 2,512.7, 1,909.0, and 1,817.6 pg/ml, respectively, before and 2 and 6 weeks and 3 months after TX, p < 0.001) and were correlated with the graft function (PAPP-A vs. modification of diet in renal disease formula r = -0.52, p < 0.001; sRAGE vs. modification of diet in renal disease formula r = -0.54, p < 0.001). Additionally, the PAPP-A levels correlated with interstitial inflammation (r = 0.57, p < 0.05) and vascular intimal thickening (r = 0.47, p < 0.05), while sRAGE correlated with arteriolar hyalinosis (r = 0.49, p < 0.05).

CONCLUSIONS

Our study demonstrates the role of the kidney in the metabolism and/or the removal of PAPP-A and sRAGE. After successful TX, these substances decrease, and, on the contrary, early chronic vascular changes in the kidney TX are associated with elevation of their serum levels.

The ligand/RAGE axis: lighting the fuse and igniting vascular stress

Vascular inflammation contributes critically to the initiation and progression of atherosclerosis. These processes are accelerated in hyperglycemia and play key roles in the increased incidence and severity of myocardial infarction and stroke observed in diabetes. Evidence suggests that the ligands of the receptor for advanced glycation endproducts (RAGE), a multiligand member of the immunoglobulin superfamily, interact with this receptor to play important roles in both early development and progression of atherosclerosis and vascular inflammation. Studies in animal models of vascular injury underscored the potent impact of RAGE blockade; administration of ligand-binding decoys of RAGE or antibodies to the receptor reduced the consequences of diabetes, hyperlipidemia, and physical injury to the vessel wall. This review focuses on the ligand repertoire of RAGE, the impact of ligand-RAGE interaction, and the potent effect of RAGE blockade in rodent models of vascular injury.

Low Circulating Endogenous Secretory Receptor for AGEs Predicts Cardiovascular Mortality in Patients With End-Stage Renal Disease

OBJECTIVE

Receptor for advanced glycation end-products (RAGE) is involved in diabetic vascular complications. We have recently shown that plasma endogenously secretory RAGE (esRAGE), an alternatively spliced form of RAGE, is closely associated with metabolic syndrome and atherosclerosis. Here, we evaluated if plasma esRAGE is a predictor of cardiovascular mortality in a cohort of 206 (171 nondiabetic) patients with end-stage renal diseases (ESRD).

METHODS AND RESULTS

The cohort was followed for a median of 111 months, and 74 deaths including 34 cardiovascular deaths were recorded. Plasma esRAGE was measured at baseline. Cumulative incidence of cardiovascular death by Kaplan-Meier estimation was significantly higher in subjects in the lowest tertile of plasma esRAGE than those in the middle or the highest tertile both in all and nondiabetic subjects alone. In all subjects, as compared with the lowest tertile of plasma esRAGE, the hazards ratios for the highest and middle tertile were 0.40 (95% CI, 0.18 to 0.89) and 0.26 (0.10 to 0.66), respectively. The higher risk for lower esRAGE was still significant even after adjusted either with body mass index, hypertension, dyslipidemia and vascular complications, but was confounded by age and diabetes.

CONCLUSIONS

Low circulating esRAGE is a predictor for cardiovascular mortality in ESRD patients.

Circulating soluble receptor for advanced glycation end products is inversely associated with glycemic control and S100A12 protein

CONTEXT

The interaction of advanced glycation end products, including Nepsilon-(carboxymethyl)lysine-protein adducts (CML) and S100A12 protein, with their cellular receptor (RAGE) is implicated in the pathogenesis of diabetic vascular complications. RAGE has a circulating secretory receptor form, soluble RAGE (sRAGE), which, by neutralizing the action of advanced glycation end products, might exert a protective role against the development of cardiovascular disease.

OBJECTIVE

The objective of the study was to investigate whether plasma sRAGE levels are associated with glycemic control, proinflammatory factors, or circulating ligands of RAGE such as plasma CML and S100A12 protein.

STUDY DESIGN

We studied 160 subjects, 84 subjects with type 2 diabetes (aged 60 +/- 7 yr) and 76 nondiabetic controls (aged 45 +/- 10 yr).

RESULTS

Plasma sRAGE was lower in diabetic patients than controls [141 (53-345) vs. 735 (519-1001) pg/ml, median (interquartile range), P < 0.0001], whereas CML levels were higher in diabetic patients than controls [67.9 (46.0-84.7) vs. 43.4 (28.0-65.0) microg/ml, P < 0.0001]. In stepwise regression analysis of the whole data set, hemoglobin A1c, insulin resistance (as homeostasis model assessment), and C-reactive protein were independently associated with plasma sRAGE, whereas age was not. In a subgroup of 26 diabetic and 24 nondiabetic subjects of similar age (54 +/- 3 yr), plasma S100A12 levels were higher in diabetic subjects [49 (39-126) vs. 28 (21-39) ng/ml]. Moreover, low sRAGE and high S100A12 were strongly associated with increased risk for cardiovascular disease (Framingham score). In this subgroup, the plasma S100A12 level was the only determinant of plasma sRAGE concentration.

CONCLUSION

Plasma level of sRAGE is down-regulated in chronic hyperglycemia; among its ligands, S100A12 protein, but not CML, appears to be associated with this effect.

Association between serum levels of soluble receptor for advanced glycation end products and circulating advanced glycation end products in type 2 diabetes

AIMS/HYPOTHESIS

Activation of the receptor for advanced glycation end products (RAGE, also known as AGE-specific receptor [AGER]) has been implicated in the development of diabetic vascular complications. Blockade of RAGE using a soluble form of the receptor (sRAGE) suppressed vascular hyperpermeability and atherosclerosis in animal models. Since little is known about the regulation of endogenous sRAGE levels, we determined whether serum sRAGE is influenced by circulating AGEs and the severity of nephropathy in type 2 diabetic patients.

MATERIALS AND METHODS

We recruited 150 healthy control and 318 diabetic subjects. Diabetic subjects were subdivided into those with proteinuria, microalbuminuria or normoalbuminuria. Serum sRAGE was assayed by ELISA and serum AGEs by competitive ELISA using a polyclonal rabbit antiserum raised against AGE-RNase.

RESULTS

Diabetic subjects had higher sRAGE (1,029.5 pg/ml [766.1-1,423.0] interquartile range vs 1,002.6 [726.5-1,345.3], p<0.05) and AGEs (4.07+/-1.13, SD, unit/ml vs 3.39+/-1.05, p<0.01) than controls. Proteinuric subjects had the highest sRAGE levels and there was a significant trend between the severity of nephropathy and sRAGE (p=0.01). In diabetic subjects, serum log(sRAGE) correlated with AGEs (r=0.27, p<0.001), log(plasma creatinine) (r=0.31, p<0.001), log(urine AER) (r=0.24, p<0.01) and log(triglycerides) (r=0.15, p<0.01). On stepwise linear regression analysis, AGEs and creatinine levels were the main independent determinants of sRAGE concentration.

CONCLUSIONS/INTERPRETATION

Serum sRAGE levels and circulating AGEs are associated with the severity of nephropathy in type 2 diabetic patients. Prospective studies are required to determine whether endogenous sRAGE potentially influences the development of diabetic vascular complications.

Advanced glycation end products and vascular structure and function

Diabetes mellitus has now reached epidemic proportions in the Western world. The associated microvascular and macrovascular complications are a result of severe metabolic derangement, which leads to chronic tissue injury. Although there are a number of proposed pathophysiologic mechanisms for the vascular complications associated with diabetes, this review focuses predominantly on the role of advanced glycation end products (AGEs) in the pathogenesis of diabetes-associated atherosclerosis. The potential role of AGEs in enhancing arterial stiffness, an entity occurring with a greater prevalence in populations known to have higher-than-normal AGE levels, is also examined. Pharmacologic interventions aimed at reducing the level of these chemical compounds or interrupting their action provide hope for the future treatment of both atherosclerotic vascular disease and systolic hypertension, particularly in the setting of diabetes.

Skin autofluorescence, a novel marker for glycemic and oxidative stress-derived advanced glycation endproducts: an overview of current clinical studies, evidence, and limitations

BACKGROUND

Advanced glycation endproducts (AGEs) predict long-term complications in agerelated diseases. However, there are no clinically applicable markers for measuring AGEs in vivo.

METHODS

We have recently introduced the AGE-Reader (DiagnOptics B.V., Groningen, The Netherlands) to noninvasively measure AGE accumulation in the human skin of the forearm, making use of the characteristic autofluorescence (AF) pattern that AGEs encompass. Skin AF is calculated as a ratio of mean intensities detected from the skin between 420-600 nm and 300-420 nm. It correlates with collagen-linked fluorescence and specific skin AGE levels from skin biopsies in diabetes, renal failure, and control subjects. Skin AF levels are increased in patients with diabetes and renal failure and are associated with the presence of vascular complications. Additionally, skin AF is strongly related to the progression of coronary heart disease and mortality, independently of traditional risk factors. Since skin pigmentation might influence skin AF, we have investigated the relation of relative skin reflectance (R%) to skin AF in subjects with varying skin phototypes (SPT).

RESULTS

The data presented in this article suggest that only in subjects with an SPT of V and VI or R% <12%, no reliable measurement can be performed. Therefore, the current prototype of the AGE-Reader is suitable for subjects with SPT I-IV or R% >12%, and more research is needed for a broader application.

CONCLUSION

The AGE-Reader is useful as a noninvasive clinical tool for assessment of risk for long-term vascular complications in diabetes and in other conditions associated with AGE accumulation.

Receptor for advanced glycation end products and the cardiovascular complications of diabetes and beyond: lessons from AGEing

The presence of elevated blood glucose levels characterizes the diabetic state. Hyperglycemia may be caused by a number of underlying factors; however, the consequences of chronically elevated glucose are similar. Both the macrovasculature and microvasculature are exquisitely sensitive to the long-term effects of elevated blood glucose. Cardiovascular disease remains the leading cause of morbidity and mortality in diabetes, regardless of the underlying cause of hyperglycemia. Although other substrates, such as DNA, are susceptible to glycation, this article addresses the impact of nonenzymatic glycation on the proteome. The impact of Advanced Glycation End products (AGEs) on alteration of protein function and signal transduction mechanisms contributes to the pathogenesis of diabetes complications. This suggests that blocking the generation or molecular impact of AGEs may modulate the complications of diabetes.

Positive association between serum levels of advanced glycation end products and the soluble form of receptor for advanced glycation end products in nondiabetic subjects

The advanced glycation end products (AGEs)-receptor for AGE (RAGE) axis is implicated in diabetic vascular complications. Administration of soluble form of RAGE (sRAGE) to mice has been shown to block the AGE-elicited tissue damage by acting as a decoy. These observations suggest that endogenous sRAGE may capture and eliminate circulating AGEs and decrease its serum levels. However, because AGEs up-regulate tissue RAGE expression and endogenous sRAGE could be generated from the cleavage of cell surface RAGE, sRAGE may be positively, rather than inversely, associated with circulating AGEs by reflecting tissue RAGE expression. In this study, we investigated the association of sRAGE with serum levels of AGEs in humans. Data for fasting serum sRAGE and AGE levels of 184 nondiabetic subjects were obtained from a general population in Japan. We also measured body mass index (BMI), waist circumference, blood pressure, and blood biochemistries in this population. Uni- and multivariate analyses were applied for the determinants of serum sRAGE levels. The average sRAGE levels were 0.40 +/- 0.17 ng/mL in males and 0.43 +/- 0.14 ng/mL in females, respectively. In the univariate analysis, BMI (P < .05, inversely), waist circumference (P < .05, inversely), AGEs (P < .05), and alcohol intake (P < .05, inversely) were significantly associated with sRAGE levels. After performing multivariate analyses, BMI (P < .05, inversely) and AGEs (P < .05) still remained significant independently. The present study is the first demonstration that serum sRAGE levels were positively associated with circulating AGEs in the nondiabetic general population. Endogenous sRAGE levels are elevated in parallel with serum AGE levels.

Receptor for advanced glycation end products is involved in impaired angiogenic response in diabetes

Angiogenic response is impaired in diabetes. Here, we examined the involvement of receptor for advanced glycation end products (RAGE) in diabetes-related impairment of angiogenesis in vivo. Angiogenesis was determined in reconstituted basement membrane protein (matrigel) plugs containing vascular endothelial growth factor (VEGF) implanted into nondiabetic or insulin-deficient diabetic wild-type or RAGE(-/-) mice. The total, endothelial, and smooth muscle (or pericytes) cells in the matrigel were significantly decreased in diabetes, with the regulation dependent on RAGE. In the matrigel, proangiogenic VEGF expression was decreased, while antiangiogenic thrombospondin-1 was upregulated in diabetic mice, regardless of the presence of RAGE. In wild-type mice, proliferating cell nuclear antigen (PCNA)-positive cells in the matrigel were significantly less in diabetic than in nondiabetic mice, while the numbers of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells were significantly higher. This alteration in PCNA- and TUNEL-positive cells in diabetes was not observed in RAGE(-/-) mice. Similarly, the percentage of nuclear factor kappaB-activated cells is enhanced in diabetes, with the regulation dependent on the presence of RAGE. Importantly, adenovirus-mediated overexpression of endogenous secretory RAGE, a decoy receptor for RAGE, restores diabetes-associated impairment of angiogenic response in vivo. Thus, RAGE appears to be involved in impairment of angiogenesis in diabetes, and blockade of RAGE might be a potential therapeutic target.

Upregulation of RAGE and its ligands in proliferative retinal disease

We sought to study the presence of the receptor for advanced glycation endproducts (RAGE) and its ligands, advanced glycation endproducts (AGEs), S100/calgranulins and amphoterin (high mobility group box 1 protein; HMGB1), in the vitreous cavity and epiretinal membranes (ERMs) of eyes of patients with proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Undiluted vitreous specimens were collected from 30 eyes of 30 patients undergoing pars plana vitrectomy for repair of retinal detachment (RD) secondary to PDR (n = 15) or PVR (n = 15). The vitreous samples obtained from 10 eyes undergoing macular hole repair were used as controls. Epiretinal membranes were obtained from eight eyes with PDR and from 10 eyes with PVR. The levels of AGEs in the vitreous were measured using ELISA. The vitreous levels of soluble RAGE (sRAGE), S100/calgranulins and amphoterin were measured using Western blot analyses. The localization of RAGE and its ligands in ERMs was determined with immunohistochemistry. The vitreous levels of sRAGE were significantly increased in both PDR and PVR (p < or = 0.05) compared to control vitreous. In both PDR and PVR, the vitreous levels of AGEs (p < or = 0.01), S100/calgranulins (p < or = 0.05), and amphoterin (p < or = 0.01) were also elevated compared to control eyes. Expression of RAGE was detected in six of eight ERMs from eyes with PDR and eight of 10 ERMs from eyes with PVR. Many cells expressing RAGE also expressed vimentin, suggesting a glial cell origin. Ligands for RAGE were also detected in ERMs, with AGEs detected in five eyes with PDR and eight eyes with PVR. Similarly, S100 and amphoterin ERM expression was observed in six eyes with PDR; these ligands were also expressed in ERMs from eyes with PVR (8 and 7 cases, respectively). We conclude that RAGE and its ligands are increased in the vitreous cavity of eyes with PDR and PVR and are present in ERMs of eyes with these proliferative retinal disorders. These findings suggest a role for the proinflammatory RAGE axis in the pathogenesis of proliferative retinal diseases.

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.

Soluble receptor for advanced glycation end products in patients with decreased renal function

BACKGROUND

Advanced glycation end products (AGEs) accumulate in patients with decreased renal function and exert various toxic effects through the receptor for AGEs (RAGE). Soluble RAGE (sRAGE) is a naturally occurring inhibitor of AGE-RAGE action. The aim of the study is to describe the relationship of sRAGE to renal function and dialysis modalities.

METHODS

The studied group consisted of 81 patients: 25 patients with various degrees of decreased renal function, 20 long-term hemodialysis (HD) patients, 15 peritoneal dialysis (PD) patients, and 21 healthy age-matched subjects. sRAGE was assessed immunochemically (enzyme-linked immunosorbent assay), and routine biochemical parameters were measured by means of certified methods.

RESULTS

sRAGE level correlates positively with serum creatinine concentration (r = 0.50; P < 0.05), and its relationship to creatinine clearance is hyperbolic. sRAGE levels are elevated significantly, mainly in patients with end-stage renal disease (3,119.0 +/- 968.4 pg/mL in HD patients and 3,652.7 +/- 1,677.7 pg/mL in PD patients versus 1,405.1 +/- 426.1 pg/mL in controls; both P < 0.001 versus controls). In PD patients, sRAGE is detectable in spent dialysate (median, 75.8 pg/mL), correlates with its serum levels (r = 0.67; P < 0.05), and is related to protein losses in dialysate. In HD patients, sRAGE levels increase by 50% (P < 0.001) from 0 to 15 minutes during both HD and hemodiafiltration, and then decrease until the end of the session.

CONCLUSION

Serum sRAGE levels increase in patients with decreased renal function, mainly patients with end-stage renal disease. It remains to be elucidated whether the increase is caused just by decreased renal function or whether sRAGE is upregulated to protect against toxic effects of AGEs.

The RAGE axis and endothelial dysfunction: maladaptive roles in the diabetic vasculature and beyond

Receptor for advanced glycation end product (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules. The ligand-RAGE axis is emerging as a central mechanism linked to vascular injury and atherosclerosis in diabetes and in euglycemia. The repertoire of RAGE ligands, including advanced glycation end products, S100/calgranulins, high-mobility group box 1, amyloid-beta peptide, and Mac-1, transcends RAGE biology from specifically the science of diabetic complications to central aspects of the inflammatory response and oxidative stress. Experiments in cell culture and in vivo support the notion that interaction of RAGE ligands with RAGE activates key signal transduction pathways that modulate fundamental cellular properties, thereby leading to vascular and inflammatory cell perturbation. These considerations support the premise that the ligand-RAGE axis may be an important target for therapeutic intervention in cardiovascular disease and, fundamentally, in initiation and amplification of inflammatory responses.

Decreased plasma levels of soluble receptor for advanced glycation end-products in patients with essential hypertension

OBJECTIVES

Advanced glycation end-products (AGE) may cause vascular stiffening by forming crosslinks through the collagen molecule or by interaction with their cellular transductional receptor (RAGE). A secreted isoform of RAGE, termed soluble RAGE (sRAGE), may contribute to the removal/detoxification of AGE by acting as a decoy. Here we studied the plasma sRAGE levels in hypertensive and normotensive human subjects. We also investigated the relationship between blood pressure parameters and plasma sRAGE concentrations.

DESIGN

A cross-sectional case-control study.

SETTING AND PARTICIPANTS

The outpatient clinic of a university teaching hospital. Participants were 147 never-treated patients with essential hypertension (87 men and 60 women, aged 50 +/- 10 years) and 177 normotensive controls (118 men and 59 women, aged 49 +/- 10 years).

MAIN OUTCOME MEASURES

Plasma sRAGE levels determined by enzyme-linked immunosorbent assay, systolic blood pressure (SBP), diastolic blood pressure, pulse pressure (PP) and mean arterial pressure.

RESULTS

The plasma concentration of sRAGE [median (interquartile range)] was 1206 (879-1658) pg/ml in hypertensive subjects and 1359 (999-2198) pg/ml in normotensive controls (P = 0.002). Simple correlation analysis revealed that log-transformed sRAGE levels were inversely correlated with SBP (r = -0.11; P < 0.001) and PP (r = -0.23; P < 0.001). Forward-selection multiple regression analysis revealed that log-transformed sRAGE levels were determined more strongly by PP (F = 3.127, P < 0.001).

CONCLUSIONS

Plasma sRAGE levels are decreased in patients with essential hypertension and are inversely related to PP. Our results raise the possibility that sRAGE may play a role in arterial stiffening and its complications.

Plasma level of endogenous secretory RAGE is associated with components of the metabolic syndrome and atherosclerosis

OBJECTIVE

Advanced glycation endproducts, AGEs, and its specific receptor, RAGE, are involved in diabetic vascular complications. Endogenous secretory RAGE, esRAGE, has been identified as an alternatively spliced form of RAGE, and shown to act as a decoy receptor for AGE. Here, we measured plasma esRAGE level with a recently developed enzyme-linked immunosorbent assay (ELISA) and examined its association with atherosclerosis in age- and gender-matched 203 type 2 diabetic and 134 nondiabetic subjects.

METHODS AND RESULTS

Plasma esRAGE was inversely associated with carotid or femoral atherosclerosis, as quantitatively measured as intimal-medial thickness (IMT) by arterial ultrasound. Stepwise regression analyses revealed that plasma esRAGE was the third strongest and independent factor associated with carotid IMT, following age and systolic blood pressure. Plasma esRAGE was significantly lower in diabetic patients (0.176+/-0.092 ng/mL) than nondiabetic controls (0.253+/-0.111). Of note, in all, diabetic or nondiabetic group, plasma esRAGE was significantly and inversely correlated with components of the metabolic syndrome including body mass index, blood pressure, triglyceride, HbA1c, or an insulin resistance index. Stepwise regression analyses showed that body mass index or insulin resistance index was the major factor determining plasma esRAGE in all, nondiabetic or diabetic population.

CONCLUSIONS

esRAGE is a novel and potential protective factor for the metabolic syndrome and atherosclerosis.

Evaluation of rage isoforms, ligands, and signaling in the brain

Since the identification of the receptor for advanced glycosylation end products (RAGE) in 1992, there have been tremendous strides made in our understanding of the role RAGE receptors play in a variety of physiological and pathological processes. Despite such progress, several fundamental aspects of RAGE expression and RAGE function remain largely unanswered. In particular, while multiple forms of the RAGE receptor are known to exist, little is known with regards to how these different isoforms of the RAGE receptor work together to mediate RAGE signaling. For example, some forms of the RAGE receptor may promote deleterious feed-forward pathways, while others may serve to inhibit deleterious activation of the RAGE receptor. Additionally, important questions remain with regards to the intracellular domain of the full-length RAGE receptor, and the specifics surrounding how intracellular signaling pathways become activated via the RAGE family of receptors. The focus of this review is to address each of these important issues, as well as other key aspects of RAGE biology, and discuss how they are important for both our understanding of the physiological and pathological roles of RAGE signaling within the brain.

RAGE modulates vascular inflammation and atherosclerosis in a murine model of type 2 diabetes

Previous studies demonstrated that induction of diabetes with streptozotocin (stz) accelerated atherosclerosis in hyperlipidemic apo E null (-/-) mice. Blockade of the Receptor for Advanced Glycation Endproducts (RAGE) in those animals suppressed acceleration of atherosclerotic lesion area, in a manner independent of changes in levels of glucose, insulin or lipids. In the present studies, we extended these concepts to a murine model of type 2 diabetes, and bred apo E -/- mice into the db/db background. Db/db mice are a model of obesity and insulin resistance-mediated hyperglycemia. Compared to apo E -/- m/db (non-diabetic) mice, apo E -/- db/db (diabetic) mice displayed accelerated atherosclerosis at the aortic sinus. Consistent with an important role for RAGE in this process, administration of soluble (s) RAGE, the extracellular ligand-binding domain of RAGE, resulted in significantly reduced atherosclerotic lesion area in a glycemia- and lipid-independent manner. In parallel, apo E -/- db/db mice displayed RAGE-dependent enhanced expression of Vascular Cell Adhesion Molecule-1, tissue factor and matrix metalloproteinase (MMP)-9 antigen/activity in aortae compared to non-diabetic animals. In addition, consistent with the premise that upregulation of RAGE ligands and RAGE occurs even in the non-diabetic, hyperlipidemic state, albeit to lesser degrees than in diabetes, administration of sRAGE to apo E -/- m/db mice resulted in decreased atherosclerotic lesion area at the aortic sinus. Taken together, these findings establish a new murine model for the study of atherosclerosis in type 2 diabetes and highlight important roles for RAGE in proatherogenic mechanisms in hyperglycemia triggered by insulin resistance.

Soluble RAGE: a hot new biomarker for the hot joint?

The receptor for advanced glycation endproducts (RAGE) interacts with distinct ligand families linked to the inflammatory response. Studies in animal models suggest that RAGE is upregulated in the inflamed joint and that blockade of the receptor, using a ligand decoy soluble form of RAGE (sRAGE), attenuates joint inflammation and expression of inflammatory and tissue-destructive mediators. In this issue of Arthritis Research & Therapy, Rille Pullerits and colleagues reported that plasma levels of sRAGE were reduced in subjects with rheumatoid arthritis compared with healthy controls or subjects with non-inflammatory joint disease. These findings suggest the possibility that levels of sRAGE might be a biomarker of inflammation. Not resolved by these studies, however, is the intriguing possibility that endogenously higher levels of sRAGE might be linked to a lower incidence of arthritis or to the extent of inflammation. Nevertheless, although 'cause or effect' relationships may not be established in this report, fascinating insights into RAGE, inflammation and human arthritis emerge from these studies.