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

RAGE/DIAPH1 and atherosclerosis through an evolving lens: Viewing the cell from the "Inside - Out"

Background and aims

In hyperglycemia, inflammation, oxidative stress and aging, Damage Associated Molecular Patterns (DAMPs) accumulate in conditions such as atherosclerosis. Binding of DAMPs to receptors such as the receptor for advanced glycation end products (RAGE) activates signal transduction cascades that contribute to cellular stress. The cytoplasmic domain (tail) of RAGE (ctRAGE) binds to the formin Diaphanous1 (DIAPH1), which is important for RAGE signaling. This Review will detail the evidence linking the RAGE/DIAPH1 signaling pathway to atherosclerosis and envisages future therapeutic opportunities from the "inside-out" point of view in affected cells.

Methods

PubMed was searched using a variety of search terms, including "receptor for advanced glycation end products" along with various combinations including "and atherosclerosis," "soluble RAGE and atherosclerosis," "statins and RAGE," "PPAR and RAGE" and "SGLT2 inhibitor and RAGE."

Results

In non-diabetic and diabetic mice, antagonism or global deletion of Ager (the gene encoding RAGE) retards progression and accelerates regression of atherosclerosis. Global deletion of Diaph1 in mice devoid of the low density lipoprotein receptor (Ldlr) significantly attenuates atherosclerosis; mice devoid of both Diaph1 and Ldlr display significantly lower plasma and liver concentrations of cholesterol and triglyceride compared to mice devoid of Ldlr. Associations between RAGE pathway and human atherosclerosis have been identified based on relationships between plasma/serum concentrations of RAGE ligands, soluble RAGEs and atherosclerosis.

Conclusions

Efforts to target RAGE/DIAPH1 signaling through a small molecule antagonist therapeutic strategy hold promise to quell accelerated atherosclerosis in diabetes and in other forms of cardiovascular disease.

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

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

Skin autofluorescence corresponds to microvascular reactivity in diabetes mellitus

Advanced glycation accelerated by chronic hyperglycaemia contributes to the development of diabetic vascular complications throughout several mechanisms. One of these mechanisms is supposed to be impaired microvascular reactivity, that precedes significant vascular changes. The aim of this study was to find an association between advanced glycation, the soluble receptor for AGEs (sRAGE), and microvascular reactivity (MVR) in diabetes. Skin autofluorescence (SAF), which reflects advanced glycation, was assessed by AGE-Reader, MVR was measured by laser Doppler fluxmetry and evaluated together with sRAGE in 43 patients with diabetes (25 Type 1 and 18 Type 2) and 26 healthy controls of comparable age. SAF was significantly higher in patients with diabetes compared to controls (2.4 ± 0.5 vs. 2.0 ± 0.5 AU; p < 0.01). Patients with diabetes with SAF > 2.3 AU presented significantly worse MVR in both post-occlusive reactive hyperaemia (PORH) on the finger and forearm, and thermal hyperaemia (TH), compared to patients with SAF < 2.3 AU. SAF was age dependent in both diabetes (r = 0.41, p < 0.01) and controls (r = 0.45, p < 0.05). There was no association between SAF and diabetes control expressed by glycated haemoglobin. A significant relationship was observed between SAF and sRAGE in diabetes (r = 0.56, p < 0.001), but not in controls. A significant inverse association was found between SAF and MVR on the forearm in diabetes (PORH: r = -0.42, p < 0.01; TH: r = -0.46, p < 0.005). Both advanced glycation expressed by higher SAF or sRAGE and impaired MVR are involved in the pathogenesis of vascular complications in diabetes, and we confirm a strong interplay of these processes in this scenario.

Association Between Soluble Receptor for Advanced Glycation End Product and Endogenous Secretory Soluble Receptor for Advanced Glycation End Product Levels and Carotid Atherosclerosis in Diabetes: A Systematic Review and Meta-analysis

BACKGROUND

The soluble receptor for advanced glycation end product (sRAGE) and endogenous secretory RAGE (esRAGE) are novel biomarkers that are associated with vascular disease. We carried out a systematic review to provide a more complete picture of sRAGE, esRAGE, carotid atherosclerosis and cardiovascular disease (CVD) in patients with diabetes.

METHODS

We searched the Cochrane Library, PubMed and Embase databases. Systematic review best practices were followed, and study quality was assessed.

RESULTS

Ultimately, 11 studies met all the inclusion criteria. Meta-analysis indicated that esRAGE was not significantly lower in patients with type 1 diabetes (T1D) (standardized mean difference [SMD], -0.76; 95% confidence interval [CI], -1.57 to 0.05; I²=90%; p=0.002), whereas it was significantly lower in patients with type 2 diabetes (T2D) (SMD, -1.08; 95% CI, -1.53 to -0.62; I²=80%; p=0.006). Meta-analysis suggested that sRAGE levels were not significantly lower or higher in T1D (SMD, 0.06; 95% CI, -0.14 to 0.26; I²=38%; p=0.20) or T2D (SMD, 0.00; 95% CI, -0.26 to 0.26; I²=0.00%; p=1.00) patients. The level of esRAGE was inversely correlated with carotid intima-media thickness (IMT) in T2D patients, whereas there was a contrasting relationship between sRAGE and carotid IMT in T1D patients. Higher sRAGE was associated with cardiovascular events.

CONCLUSION

Our meta-analysis showed that circulating esRAGE was lower and inversely correlated with IMT in T2D patients.

The role of soluble receptor for advanced glycation end-products (sRAGE) in the general population and patients with diabetes mellitus with a focus on renal function and overall outcome

Isoforms of the receptor for advanced glycation end-product (RAGE) protein, which lack the transmembrane and the signaling (soluble RAGE or sRAGE) domains are hypothesized to counteract the detrimental action of the full-length receptor by acting as a decoy, and they provide a potential tool to treat RAGE-associated diseases. Multiple studies have explored the relationship between sRAGE and endogenous secretory RAGE and its polymorphism and obesity, metabolic syndrome, atherosclerosis, kidney function, and increased mortality in the general population. In addition, sRAGE may be a key player in the pathogenesis of diabetes mellitus and its microvascular (e.g. kidney disease) as well as macrovascular (e.g. cardiovascular disease) complications. In this review, we focus on the role of sRAGE as a biomarker in these specific areas. As there is a lack of an underlying unifying hypothesis about how sRAGE changes according to the disease condition or risk factor, there is a call to incorporate all three players of the AGE-RAGE axis into a new universal biomarker/risk marker: (AGE + RAGE)/sRAGE. However, the measurement of RAGE in humans is not practical as it is a cell-bound receptor for which tissue is required for analysis. A high AGE/sRAGE ratio may be a valuable alternative and practical universal biomarker/risk marker for diseases associated with the AGE-RAGE axis, irrespective of low or high serum sRAGE concentrations.

Predictors of future microalbuminuria in children and adolescents with type 1 diabetes mellitus in Egypt

Introduction

The present study was designed to assess the validity and efficacy of urinary markers (NAG, RBP, transferrin, α1-microglobulin, and plasma homocysteine) as early predictors of microalbuminuria in diabetic nephropathy in children and adolescents with type-1 diabetes, and its relation with haemoglobin glycated (HbA_1c), serum lipid profile, and blood pressure.

Material and methods

This study is a follow-up study to the 2002 study by Salem et al. The present study included 35 type 1 diabetes mellitus (T1DM) children and adolescents recruited from regular attendees of the specialised Diabetology Clinic, Children’s hospital, Ain Shams University, with previously measured urinary N-acetyl-β-glucosaminidase (13) or homocysteine (11) or transferrin (28) or α1-microglobulin (27) or retinol binding protein (13) as an early predictor of diabetic nephropathy in T1DM. Thirty-five patients with type 1 diabetes mellitus were enrolled, and 24 patients were normoalbuminuric at baseline. The patients were tested for markers other than urinary microalbumin, to predict diabetic nephropathy and early renal impairment in children and adolescents with type 1 diabetes mellitus.

Results

Regarding the metabolic control between the studied groups, we found that there is significant difference in HbA_1c between the microalbuminuric patients and the normoalbuminuric patients. According to the number of positive markers of diabetic nephropathy, the only parameter that was higher in patients with more than one elevated marker was mean systolic blood pressure. Although mean diabetic blood pressure was higher, it was not statistically significant. Regarding to the predictability of urinary markers, urinary N-acetyl-β-glucosaminidase is the most predictable marker with high sensitivity and specificity. The least sensitivity noticed was urinary RBP and the least specificity noticed was urinary α1-microglobulin.

Conclusions

Regarding the predictability of urinary markers, urinary NAG is the most predictable marker with both high sensitivity and specificity, with a sensitivity of 60%, specificity 75%, positive predictive value 60%, negative predictive value 75%, and a diagnostic accuracy of 0.58%. Urinary RBP is another marker with low sensitivity but high specificity. Urinary α1-microglobulin is a valid marker with high sensitivity but low specificity. Contrary to previous markers, plasma homocysteine has high specificity but low sensitivity.

1 h Postload Glycemia Is Associated with Low Endogenous Secretory Receptor for Advanced Glycation End Product Levels and Early Markers of Cardiovascular Disease

We investigated the correlation of the soluble receptor for advanced glycation end products (sRAGE) and endogenous secretory RAGE (esRAGE) with markers of cardiovascular disease in subjects with normal glucose tolerance (NGT) and 1 h postload glucose ≥155 mg/dL after an oral glucose tolerance test. We stratified 282 subjects without a previous diagnosis of diabetes into three groups: 123 controls (NGT and 1 h postload glycemia <155 mg/dL), 84 NGT and 1 h postload glycemia ≥155 mg/dL (NGT 1 h high), and 75 subjects with impaired fasting glucose and/or impaired glucose tolerance (IFG/IGT). NGT 1 h high subjects exhibited lower esRAGE (0.36 ± 0.18 vs. 0.4 5 ± 0.2, p < 0.05) and higher S100A12 levels than controls (5684 (3193.2–8295.6) vs. 3960.1 (2101.8–7419), p < 0.05). Furthermore, they showed an increased pulse wave velocity (PWV) and intima–media thickness (IMT). No differences were found between the NGT 1 h high group and the IFG/IGT group regarding cardiometabolic profiles. After multiple regression analyses, esRAGE was associated with glycated hemoglobin (HbA_1c) and high-sensitivity C-reactive protein (hs-CRP). Age, HbA_1c, and esRAGE were the determinants of IMT, whereas S100A12 and systolic pressure were the determinants of PWV. The NGT 1 h high group exhibited low esRAGE levels and an altered cardiometabolic profile. HbA_1c, S100A12, and hs-CRP were associated with these alterations. In conclusion, subjects with NGT are not a homogeneous population, and they present different cardiovascular and glycometabolic risks.

Soluble Forms of the Receptor for Advanced Glycation Endproducts (RAGE) in Periodontitis

The receptor for advanced glycation endproducts (RAGE) is critically involved in the pathobiology of chronic inflammatory diseases. Soluble forms of RAGE have been proposed as biomarkers of severity in inflammatory and metabolic conditions, and in monitoring therapeutic responses. The aim of the present study was to determine circulating levels of the soluble forms of RAGE in periodontitis and to evaluate the expression of cell-bound, full-length RAGE and its antagonist AGER1 locally, in gingival tissues. Periodontitis patients and periodontally healthy, sex- and age-matched controls (50 per group) were included. Serum levels of total soluble RAGE and cleaved RAGE (cRAGE) were significantly lower in periodontitis patients. Levels of the endogenous secretory esRAGE were similar in the two groups. cRAGE remained significantly lower in the periodontitis group following multiple adjustments, and had a statistically significant inverse correlation with body mass index and all periodontal parameters. In periodontitis patients, gene expression of full-length RAGE and of AGER1 were significantly higher in periodontitis-affected gingival tissues compared to healthy gingiva. Soluble forms of RAGE, particularly cRAGE, may serve as biomarkers for the presence and severity/extent of periodontitis, and may be implicated in its pathogenesis and its role as a systemic inflammatory stressor.

Divergent Changes in Plasma AGEs and sRAGE Isoforms Following an Overnight Fast in T1DM

Advanced glycation end products (AGEs) promote the development of diabetic complications through activation of their receptor (RAGE). Isoforms of soluble RAGE (sRAGE) sequester AGEs and protect against RAGE-mediated diabetic complications. We investigated the effect of an overnight fast on circulating metabolic substrates, hormones, AGEs, and sRAGE isoforms in 26 individuals with type 1 diabetes (T1DM). Blood was collected from 26 young (18–30 years) T1DM patients on insulin pumps before and after an overnight fast. Circulating AGEs were measured via LC-MS/MS and sRAGE isoforms were analyzed via ELISA. Glucose, insulin, glucagon, and eGFR_cystatin-c decreased while cortisol increased following the overnight fast (p < 0.05). AGEs (CML, CEL, 3DG-H, MG-H1, and G-H1) decreased (21–58%, p < 0.0001) while total sRAGE, cleaved RAGE (cRAGE), and endogenous secretory RAGE (esRAGE) increased (22–24%, p < 0.0001) following the overnight fast. The changes in sRAGE isoforms were inversely related to MG-H1 (rho = −0.493 to −0.589, p < 0.05) and the change in esRAGE was inversely related to the change in G-H1 (rho = −0.474, p < 0.05). Multiple regression analyses revealed a 1 pg/mL increase in total sRAGE, cRAGE, or esRAGE independently predicted a 0.42–0.52 nmol/L decrease in MG-H1. Short-term energy restriction via an overnight fast resulted in increased sRAGE isoforms and may be protective against AGE accumulation.

Clinical relevance of cleaved RAGE plasma levels as a biomarker of disease severity and functional outcome in aneurysmal subarachnoid hemorrhage

BACKGROUND

Cleaved receptor for advanced glycation end-products (cRAGE) has been introduced as a new inflammatory marker. We clarified the associations between cRAGE levels, disease severity and functional outcome in aneurysmal subarachnoid hemorrhage (aSAH).

METHODS

In this prospective, observational study, plasma levels of total soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) were quantified in 108 aSAH patients and 108 controls. The level of cRAGE was calculated by subtracting the level of esRAGE from that of sRAGE. World Federation of Neurological Surgeons (WFNS) score, modified Fisher score, and Hunt Hess (HH) score were recorded to assess aSAH severity. Relationship between plasma cRAGE levels and 6-month poor outcome (Glasgow Outcome Scale score of 1-3) was assess using multivariate analysis.

RESULTS

Plasma cRAGE levels were significantly higher in patients than in controls. Its levels were significantly correlated with WNFS score, modified Fisher score and HH score of patients. Plasma cRAGE emerged as an independent predictor for 6-month poor outcome. Area under receiver operating characteristic curve (AUC) of this biomarker was similar to those of WNFS score, modified Fisher score and HH score. Moreover, it significantly improved AUCs of WNFS score, modified Fisher score and HH score.

CONCLUSIONS

Plasma cRAGE levels are highly associated with the severity and poor prognosis in aSAH.

Racial differences in circulating levels of the soluble receptor for advanced glycation endproducts in middle-aged and older adults

BACKGROUND

Low levels of the soluble receptor for advanced glycation endproducts (sRAGE) have been implicated in a number of chronic diseases. Previous studies indicate that sRAGE levels are ~30% lower in Blacks compared to Whites. However, the reasons for these differences are unclear.

PURPOSE

We aimed to identify predictors of circulating sRAGE biomarkers among Black and White adults at high cardiac risk.

METHODS

Serum levels of total sRAGE, endogenous secretory RAGE (esRAGE), carboxymethyl-lysine (CML, a major RAGE ligand), and their ratios were measured in 99 Blacks and 454 Whites.

RESULTS

Blacks had a more adverse cardiovascular risk profile, as well as lower median levels of total sRAGE (972 vs. 1564pg/ml) and esRAGE (474 vs. 710pg/ml) compared to Whites (p<0.0001). In addition, the proportion of esRAGE was higher in Blacks (47% vs. 44%, p=0.02), as were the CML/total sRAGE (0.89 vs. 0.56ng/pg) and CML/esRAGE (1.72 vs. 1.20ng/pg) ratios (p<0.0001). Racial differences persisted after adjustment for key covariates including age, gender, tobacco use, comorbidities, BMI, blood pressure, glucose, insulin, triglycerides, C-reactive protein, and renal function (p<0.05). Race alone accounted for nearly half of the variability in total sRAGE levels (10.6%; model explained 23.9%). In stratified analyses, gender and heart rate were independently associated with total sRAGE and esRAGE in Whites, while CML and C-reactive protein were associated with total sRAGE in Blacks.

CONCLUSIONS

We identified several independent predictors of sRAGE biomarkers. Notably, Black race was associated with an adverse AGE/RAGE profile, including lower sRAGE and higher CML/sRAGE ratios.

Elevated endogenous secretory receptor for advanced glycation end products (esRAGE) levels are associated with circulating soluble RAGE levels in diabetic children

BACKGROUND

Advanced glycation end products (AGEs) and the receptor for AGE (RAGE) play an important role in the development of diabetic vascular complications. This study aimed at investigating the relationship between the soluble form of RAGE (sRAGE), endogenous secretory RAGE (esRAGE), and pentosidine in childhood diabetes.

METHODS

The study included 18 children with type 1 diabetes mellitus (T1DM), 10 with type 2 DM (T2DM), and 22 age-matched, non-diabetic children (control).

RESULTS

Serum sRAGE levels in the T1DM (2557.7 pg/mL) were significantly higher than both T2DM (1956.4 pg/mL) and control (1658.5 pg/mL). The circulating levels of esRAGE in T1DM and T2DM children were similar, but significantly higher than those of control. Serum pentosidine levels in the T1DM group were positively correlated with serum sRAGE and esRAGE levels, but not with anthropometric or biochemical measurements. The duration of diabetes and esRAGE levels were independent predictors of the circulating sRAGE levels.

CONCLUSIONS

Unlike adults, children with diabetes exhibit high circulating esRAGE levels, and both sRAGE and esRAGE levels are correlated with pentosidine levels. These results suggest that circulating sRAGE and esRAGE in children may be surrogate markers for progressive glucose toxicity in pediatric patients with childhood-onset diabetes.

The effects of n-3 long-chain polyunsaturated fatty acid supplementation on AGEs and sRAGE in type 2 diabetes mellitus

In diabetes mellitus, chronic hyperglycemia leads to formation of advanced glycation end products (AGEs). Binding of AGEs to receptors of AGE (RAGE) causes deleterious effects. In populations with a high consumption of n-3 long-chain polyunsaturated fatty acids, a lower prevalence of diabetes mellitus has been reported. We aimed to investigate the effects of n-3 fatty acid (EPA and DHA) supplementation on the levels of AGEs (carboxymethyl lysine (CML) and pentosidine), sRAGE, and nuclear factor kappa B (NF-kB) in type 2 diabetes mellitus (T2DM). T2DM patients (n = 38) treated with oral hypoglycemic agents, without insulin were supplemented with n-3 fatty acids (1.2 g/day) for 2 months. Plasma CML, pentosidine, sRAGE, and NF-kB levels were measured by ELISA both before and after the supplementation. n-3 fatty acid supplementation significantly reduced fasting glucose (p < 0.01), glycated hemoglobin (HbA_1c) (p < 0.05), and pentosidine (p < 0.05) levels. The supplementation induced percentage changes in pentosidine and HbA_1c and in pentosidine and creatinine were observed to be correlated (r = 0.349, p < 0.05) and (r = 0.377, p < 0.05), respectively. Waist circumference and systolic and diastolic pressures were significantly decreased due to n-3 supplementation (p < 0.001, p < 0.01, p < 0.01), respectively. Our results show that supplementation with n-3 fatty acid has beneficial effects on waist circumference; systolic and diastolic blood pressures; and the levels of glucose, HbA_1c, and pentosidine in T2DM patients. However, the supplementation failed to decrease these parameters to the reference ranges for healthy subjects. In addition, the supplementation did not appear to induce any significant differences in CML, sRAGE, or NF-kB.

Cleaved but not endogenous secretory RAGE is associated with outcome in acute ischemic stroke

OBJECTIVE

To investigate the expression patterns of 2 soluble isoforms of receptor for advanced glycation end-product (RAGE), including endogenous secretory RAGE (esRAGE) and cleaved RAGE (cRAGE), and their associations with outcome in acute ischemic stroke (IS).

METHODS

Acute IS patients (n = 106) and age- and sex-matched controls (n = 150) were recruited. Plasma levels of total soluble RAGE (sRAGE) and esRAGE in patients at <48 hours and 48-72 hours after IS and in controls were measured by ELISA. The level of cRAGE was calculated by subtracting the level of sRAGE from that of esRAGE. Poor outcome was defined as modified Rankin Scale score >2 at 3 months after stroke.

RESULTS

The plasma levels of cRAGE were significantly higher and correlated to those of esRAGE (p < 0.001). The plasma levels of esRAGE and cRAGE were both significantly higher in IS patients <48 hours and 48-72 hours after onset than in controls, but only level of cRAGE at <48 hours was independently associated with poor outcome after adjusting for clinical variables (odds ratio 2.44; 95% confidence interval 1.16-5.16; p = 0.019).

CONCLUSION

The plasma level of cRAGE at <48 hours after IS, rather than esRAGE, is a significant predictor of acute IS outcome.

Soluble RAGE and atherosclerosis in youth with type 1 diabetes: a 5-year follow-up study

BACKGROUND

Advanced glycation end products (AGEs) play a role in the development of late complications and atherosclerosis in diabetes by engaging the receptor for advanced glycation end products, RAGE. Receptor binding leads to activation of the vascular endothelium and increased inflammation in the vessel wall. The soluble variants of the receptor, endogenous secretory RAGE (esRAGE) and the cleaved cell-surface part of RAGE, which together comprise soluble RAGE (sRAGE), are suggested to have a protective effect acting as decoys for RAGE. We aimed to test whether high levels of soluble variants of RAGE could be protective against atherosclerosis development.

METHODS

Participants in the prospective atherosclerosis and childhood diabetes study were examined at baseline (aged 8-18) and at follow-up after 5 years. Both sRAGE and esRAGE were measured by immunoassay in 299 patients with type 1 diabetes and 112 healthy controls at baseline and 241 patients and 128 controls at follow-up. The AGEs methylglyoxal-derived hydroimidazolone-1 (MG-H1) and carboxymethyllysine (CML) were measured by immunoassay. The surrogate markers of atherosclerosis assessed were carotid intima-media thickness (cIMT), C-reactive protein (CRP) and Young's modulus, measures of arterial wall thickness, inflammation and arterial stiffness, respectively.

RESULTS

Levels of sRAGE and esRAGE correlated strongly both at baseline and at follow-up in both diabetes patients and controls. With increasing age, mean values of both variants declined, independent of gender, diabetes or pubertal stage. In the diabetes group, multiple regression analysis showed a positive association between both variants of soluble RAGE and cIMT. There was no significant relationship with Young's modulus, but a negative association between sRAGE at baseline and CRP at follow-up. The ratios between the AGEs and the variants of soluble RAGE were increased in diabetes patients compared to controls.

CONCLUSIONS

The results show a possible protective effect of high levels of sRAGE at baseline against inflammation 5 years later, but not on arterial stiffness or wall thickness, in this cohort of adolescents and young adults with T1D.

Increased carotid intima-media thickness (CIMT) levels in patients with type 1 diabetes mellitus (T1DM): A meta-analysis

AIM

To derive a more precise estimation of carotid intima-media thickness (CIMT) levels in patients with type 1 diabetes mellitus (T1DM) by meta-analysis.

METHODS

PubMed and Embase databases were searched to identify all available studies comparing CIMT levels between T1DM group and control group. Meta-analysis was performed to compare the difference of overall mean CIMT levels between the two groups. Publication bias was evaluated by funnel plot, Begg' test and Egger' test. Meta-regression analysis was conducted to investigate the influential factors on CIMT difference. The meta-analysis was conducted by STATA 12.0 software.

RESULTS

A total of 1840 articles were obtained after searching databases; 47 studies were finally included in the meta-analysis. Significant heterogeneity was observed among these studies (Q = 768.75, P < 0.001, I(2) = 94.0%). Compared with the control group, the T1DM group had significantly higher CIMT levels (standardized mean difference: 1.01, 95% CI: 0.75-1.28; P < 0.001). A likely source of heterogeneity was Newcastle-Ottawa Scale (NOS) scores and sample size ratio of patents and controls. The funnel plot did not show a skewed or asymmetrical shape, and the result of Begg' test and Egger' test was P = 0.178 and P = 0.145 respectively. Accordingly, it could be assumed that publication bias was not present.

CONCLUSION

T1DM patients have significantly increased CIMT levels compared to control subjects.

Circulating HMGB1 and RAGE as Clinical Biomarkers in Malignant and Autoimmune Diseases

High molecular group box 1 (HMGB1) is a highly conserved member of the HMG-box-family; abundantly expressed in almost all human cells and released in apoptosis; necrosis or by activated immune cells. Once in the extracellular space, HMGB1 can act as a danger associated molecular pattern (DAMP), thus stimulating or inhibiting certain functions of the immune system; depending on the “combinatorial cocktail” of the surrounding milieu. HMGB1 exerts its various functions through binding to a multitude of membrane-bound receptors such as TLR-2; -4 and -9; IL-1 and RAGE (receptor for advanced glycation end products); partly complex-bound with intracellular fragments like nucleosomes. Soluble RAGE in the extracellular space, however, acts as a decoy receptor by binding to HMGB1 and inhibiting its effects. This review aims to outline today’s knowledge of structure, intra- and extracellular functions including mechanisms of release and finally the clinical relevance of HMGB1 and RAGE as clinical biomarkers in therapy monitoring, prediction and prognosis of malignant and autoimmune disease.

Relationship between serum levels of endogenous secretory RAGE and blood pressure in male nondiabetic patients with obstructive sleep apnea

The interaction of advanced glycation end products (AGE) and their specific cell-surface receptor (RAGE) has an important role in the pathogenesis of cardiovascular disease and diabetic complications. Two isoforms of C-truncated RAGE, soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE), may prevent activation of RAGE signaling by acting as decoys. This study investigated whether serum esRAGE and sRAGE levels are associated with blood pressure in nondiabetic patients with obstructive sleep apnea (OSA). Male nondiabetic patients (n=139) with OSA were enrolled. Serum esRAGE and sRAGE levels were examined using enzyme-linked immunosorbent assay. Three consecutive seated systolic blood pressure (SBP) and diastolic blood pressure (DBP) measurements were obtained at 5-min intervals in the morning. In univariate analysis, there was a significant correlation between serum esRAGE and SBP or DBP, but not between serum sRAGE and SBP or DBP. Multiple regression analysis showed that SBP was independently associated with waist circumference, HbA1c, minimum SaO2 and serum esRAGE, and that DBP was independently associated with low-density lipoprotein cholesterol, apnea-hypopnea index, serum AGE and body mass index, but not with serum esRAGE. These results indicated that serum esRAGE levels were inversely associated with blood pressure, especially SBP, in male nondiabetic patients with OSA. esRAGE may have a protective role against hypertension in patients with OSA, and it may be a novel biomarker for OSA patients at high risk of developing cardiovascular diseases.

Serum soluble RAGE levels and carotid atherosclerosis: the Northern Manhattan Study (NOMAS)

BACKGROUND

Recent cohort studies suggested that serum levels of soluble Receptor for Advanced Glycation End-products (sRAGE) are associated with the risk of cardiovascular disease. We hypothesized that sRAGE levels are associated with subclinical atherosclerosis in a racially and ethnically diverse population.

METHODS AND RESULTS

828 stroke-free participants from the Northern Manhattan Study (mean age 71.1±8.7yrs; 64% Hispanic, 19% black, and 17% white) underwent high-resolution carotid B-mode ultrasound to measure carotid plaque (present in 62% of subjects) and intima-media thickness (IMT) (mean Total=0.96±0.10 mm). Serum sRAGE was measured by ELISA and associations tested between sRAGE with IMT and plaque presence. Soluble RAGE levels were not associated with plaque presence or IMT after adjusting for sociodemographic, vascular risk factors and medication use. Stratification by race-ethnicity did not reveal any associations with carotid IMT or plaque.

CONCLUSION

In the present study, sRAGE levels were not associated with carotid atherosclerosis.

Two soluble isoforms of receptors for advanced glycation end products (RAGE) in carotid atherosclerosis: the difference of soluble and endogenous secretory RAGE

BACKGROUND

Advanced glycation end products (AGEs) promote atherosclerosis through binding to their receptor, RAGE. Since soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) may suppress AGEs-RAGE signaling, we examined the usefulness of sRAGE and esRAGE as biomarkers of early-stage atherosclerosis.

METHODS

Serum sRAGE and esRAGE levels were measured in 284 subjects with no history of atherothrombotic diseases. The subjects were divided into high-sRAGE and low-sRAGE groups and high-esRAGE and low-esRAGE groups based on respective median values. We investigated the relationships between these parameters and the following factors: number of metabolic components, maximum intima-media thickness of the common carotid artery (IMT Cmax), carotid plaque calcification, and asymptomatic cerebral white matter lesions.

RESULTS

The low-sRAGE and low-esRAGE groups exhibited significantly more components of metabolic syndrome than the high-sRAGE and high-esRAGE groups, respectively. IMT Cmax was significantly higher in the low-sRAGE and low-esRAGE groups. Low-sRAGE levels were significantly associated with carotid plaque calcification. Multiple linear regression analysis identified body mass index (BMI), age, and high-sensitivity C-reactive protein as determinants of sRAGE, whereas only BMI was identified as a determinant of esRAGE.

CONCLUSIONS

We demonstrated that sRAGE and esRAGE are associated with atherosclerotic risk factors in early-stage atherosclerosis, suggesting that their levels evolve in correlation with those of metabolic components and inflammation. Interestingly, low-sRAGE and esRAGE levels are associated with high IMT Cmax, but only low-sRAGE levels were associated with carotid plaque calcification. Thus, sRAGE and esRAGE may reflect different aspects of atherosclerosis in its early stage.

Cardiovascular risk profile in subjects with prediabetes and new-onset type 2 diabetes identified by HbA(1c) according to American Diabetes Association criteria

OBJECTIVE

We investigated the cardiovascular risk profile in subjects with prediabetes and new-onset type 2 diabetes identified by glycated hemoglobin A1c (HbA(1c)) according to the new American Diabetes Association criteria.

RESEARCH DESIGN AND METHODS

Arterial stiffness, intima-media thickness (IMT), soluble receptor for advanced glycation end products (sRAGEs), and oral glucose tolerance test (OGTT) were evaluated in 274 subjects without a previous history of diabetes. The subjects were stratified into three groups according to the HbA(1c) levels.

RESULTS

The subjects with prediabetes (n = 117, HbA(1c) 5.7-6.4% [39-46 mmol/mol]) showed a higher augmentation (Aug), augmentation index (AugI), and IMT compared with those with lower HbA1c; however, these values were similar to those of subjects with HbA(1c) >6.5% (48 mmol/mol). When we further analyzed the subjects with prediabetes but included only subjects with normal glucose tolerance (NT) in the analysis, AugI and IMT still remained significantly higher than their levels in control subjects with HbA(1c) <5.7% (39 mmol/mol). After multiple regression analyses including several cardiovascular risk factors, only HbA(1c), age, and sRAGE were significantly correlated with the IMT, whereas age and 1-h postload glucose were the major determinants of AugI.

CONCLUSIONS

Our data show that subjects with prediabetes according to HbA1c, but with both NT according to the OGTT and normal fasting glycemia, have an altered IMT and AugI. These data suggest that a simple, reproducible, and less expensive marker such as HbA1c may be better able to identify prediabetic subjects at high cardiovascular risk compared with fasting glycemia or OGTT alone.

The alarmin functions of high-mobility group box-1 and IL-33 in the pathogenesis of systemic lupus erythematosus

'Alarmins' are a group of endogenous proteins or molecules that are released from cells during cellular demise to alert the host innate immune system. Two of them, high-mobility group box-1 (HMGB1) and IL-33 shared many similarities of cellular localization, functions and involvement in various inflammatory diseases including systemic lupus erythematosus (SLE). The expressions of HMGB1 and IL-33, and their corresponding receptors RAGE (receptor for advanced glycation end products) and ST2, respectively, are substantially upregulated in patients with lupus nephritis (LN). This review highlights the emerging roles of alarmin proteins in various pathologies of LN, by focusing on classical HMGB1 and a newly discovered alarmin IL-33.

Decreased level of endogenous secretory receptor for advanced glycation end-products in diabetes with concomitant hyperlipidemia

Endogenous secretory receptor (esRAGE) for advanced glycation end-product (AGE) acts as decoy for AGEs. The AGE-to-esRAGE ratio was hypothesized to be implicated in diabetic vasculopathy. We investigated an association of esRAGE and methylglyoxal-adducts serum level, as well as AGE-to-esRAGE ratio in subpopulation of diabetic patients with or without concomitant hyperlipidemia and macrovascular disease in history. In diabetes with concomitant hyperlipidemia esRAGE was significantly decreased compared to hyperlipidemia with normal glucose metabolism (0.306+/-0.2 vs. 0.367+/-0.1; p=0.019) or diabetes alone (0.306+/-0.2 vs. 0.404+/-0.1; p=0.004). High AGE/esRAGE ratio, found in diabetic patients with hyperlipidemia, pointed to increased production of AGEs and low expression of esRAGE. In multivariable analysis adjusted for several confounding factors, increased AGE/esRAGE ratio was recognized as a high risk for vascular disease outcomes.

Potential of the angiotensin receptor blockers (ARBs) telmisartan, irbesartan, and candesartan for inhibiting the HMGB1/RAGE axis in prevention and acute treatment of stroke

Stroke is a major cause of mortality and disability worldwide. The main cause of stroke is atherosclerosis, and the most common risk factor for atherosclerosis is hypertension. Therefore, antihypertensive treatments are recommended for the prevention of stroke. Three angiotensin receptor blockers (ARBs), telmisartan, irbesartan and candesartan, inhibit the expression of the receptor for advanced glycation end-products (RAGE), which is one of the pleiotropic effects of these drugs. High mobility group box 1 (HMGB1) is the ligand of RAGE, and has been recently identified as a lethal mediator of severe sepsis. HMGB1 is an intracellular protein, which acts as an inflammatory cytokine when released into the extracellular milieu. Extracellular HMGB1 causes multiple organ failure and contributes to the pathogenesis of hypertension, hyperlipidemia, diabetes mellitus, atherosclerosis, thrombosis, and stroke. This is the first review of the literature evaluating the potential of three ARBs for the HMGB1-RAGE axis on stroke therapy, including prevention and acute treatment. This review covers clinical and experimental studies conducted between 1976 and 2013. We propose that ARBs, which inhibit the HMGB1/RAGE axis, may offer a novel option for prevention and acute treatment of stroke. However, additional clinical studies are necessary to verify the efficacy of ARBs.

Effect of insulin on the soluble receptor for advanced glycation end products (RAGE)

AIMS

The receptor for advanced glycation end products (RAGE) plays an important role in the pathogenesis of diabetic complications. RAGE transcript splicing generates a number of isoforms, including a full-length membrane-bound receptor and a soluble isoform, endogenous secretory RAGE (esRAGE). Soluble forms of the receptor (sRAGE) can also be formed by ectodomain shedding of the membrane-associated receptor. We have evaluated serum levels of sRAGE and esRAGE in Chinese patients with Type 1 diabetes and investigated the effect of insulin on the generation of esRAGE and sRAGE in vitro.

METHODS

Serum sRAGE and esRAGE were measured by ELISA. The in vitro effect of insulin was investigated by incubating THP-1 macrophages with insulin and RAGE isoforms in cell lysate and conditioned media determined.

RESULTS

In patients with diabetes, both serum esRAGE and sRAGE were significantly higher than in age-matched healthy subjects without diabetes. In vitro, insulin increased esRAGE and total RAGE isoform expression in cell lysate on a western blot, and reverse transcription-polymerase chain reaction showed an increase in esRAGE and full-length RAGE mRNA. This was accompanied by an increase in esRAGE and sRAGE in cell conditioned media. Pretreatment of THP-1 cells with a general metalloproteinase inhibitor GM6001 significantly reduced the production of sRAGE, suggesting that insulin also increased the cleavage of full-length cell surface RAGE to form sRAGE.

CONCLUSIONS

Chinese patients with Type 1 diabetes have higher serum levels of esRAGE and sRAGE. In vitro, insulin not only increases both full-length RAGE and esRAGE expression, but can also stimulate the shedding of sRAGE from the membrane-bound receptor.

Soluble receptor for advanced glycation end-product levels are related to albuminuria and arterial stiffness in essential hypertension

BACKGROUND AND AIMS

Emerging evidence suggests that the soluble receptor for advanced glycation end-products (sRAGE) is implicated in the development of vascular disease. We investigated the interrelationships of sRAGE with albumin to creatinine ratio (ACR) and arterial stiffness in essential hypertension.

METHODS AND RESULTS

In 309 untreated non-diabetic hypertensives, ACR values were determined as the mean of three non-consecutive morning spot urine samples and aortic stiffness was evaluated on the basis of carotid to femoral pulse wave velocity (c-f PWV). In all subjects, venous blood sampling was performed for the estimation of sRAGE levels. Patients with low (n = 155) compared to those with high sRAGE values (n = 154) had greater 24-h systolic BP (140 ± 8 vs. 134 ± 7 mmHg, p < 0.0001), exhibited higher ACR (36.3 ± 51.6 vs. 17.2 ± 1.2 mg g(-1), p < 0.0001) and c-f PWV (8.3 ± 1.5 vs. 7.8 ± 1.1 m s(-1), p = 0.003), independently of confounding factors. Multiple regression analyses revealed that age, male sex, 24-h systolic BP and sRAGE were the 'independent correlates' of ACR (R(2) = 0.493, p < 0.0001), while age, 24-h systolic BP and sRAGE were the 'independent correlates' of c-f PWV (R(2) = 0.428, p < 0.0001).

CONCLUSION

In hypertensives, decreased sRAGE levels are accompanied by pronounced albuminuria and arterial stiffening. The association of sRAGE with ACR and c-f PWV suggests involvement of sRAGE in the progression of hypertensive vascular damage.

Skin autofluorescence relates to soluble receptor for advanced glycation end-products and albuminuria in diabetes mellitus

The aim of this study was to compare skin autofluorescence caused by advanced glycation end-products (AGEs) with biochemical markers of endothelial dysfunction and soluble receptor for AGEs (sRAGE) in patients with diabetes. Skin autofluorescence (AF) assessed by AGE-Reader was evaluated with sRAGE and other biochemical parameters in 88 patients with diabetes (47 Type 1/T1DM/ and 41 Type 2/T2DM/) and 20 controls. Skin AF was significantly higher in T1DM and T2DM in comparison to controls (2.39 ± 0.54, 2.63 ± 0.73 versus 1.96 ± 0.33 AU; P < 0.0001). Positive correlation of AF with sRAGE was detected in T1DM and T2DM (r = 0.37, P < 0.02 and r = 0.60, P < 0.0001), but not in controls. Significantly higher AF values were found in patients with positive albuminuria as compared to those with normal albuminuria. Similarly, higher AF was detected in patients with endothelial dysfunction expressed by vWF, ICAM-1, and VCAM-1. Multiple regression analysis revealed independent association of skin AF with age, sRAGE, and albumin-creatinine ratio in patients with diabetes (R (2) = 0.38). Our study confirms that AF is elevated in patients with diabetes, especially with positive albuminuria and endothelial dysfunction. The strong and independent relationship between AF and sRAGE supports the idea that AF may reflect AGEs/RAGE interactions. The exact mechanism remains to be established.

Soluble RAGE and malondialdehyde in type 1 diabetes patients without chronic complications during the course of the disease

Malondialdehyde (MDA), an end product of lipid peroxidation and biomarker for oxidative stress, and its soluble receptor (sRAGE) were evaluated in 42 patients with type 1 diabetes mellitus, but without chronic complications, during the early years after diagnosis (0-10 years) and through the further progression of the disease (10-20 and > 20 years after diagnosis). Clinical and biochemical parameters of the cohort of diabetic patients were compared with those determined in 24 healthy individuals. The median levels of MDA in plasma were similar in type 1 diabetes patients and in healthy subjects. In contrast, statistically significant increases were detected in the median values of sRAGE in patients with type 1 diabetes compared with healthy subjects (2423.75 versus 1472.75 pg/ml; p=0.001, Mann-Whitney test). However, no significant between-group differences (p>0.05) were observed in levels of sRAGE when diabetic patients were grouped according to time elapsed after diagnosis. It is concluded that increased plasma levels of sRAGE in type 1 diabetes may provide protection against cell damage and may be sufficient to eliminate excessive circulating MDA during early years after disease onset.

An explorative analysis of secretory receptor for advanced glycation endproducts in primary focal segmental glomerulosclerosis

BACKGROUND

Despite remarkable medical progress, the main pathogenetic mechanisms of focal segmental glomerulosclerosis (FSGS) have not been fully delineated and its prognosis is poor at present. Recently, it was revealed that the receptor for advanced glycation endproducts (RAGE) was highly expressed at the base of podocytes with an up-regulation mainly in diabetic nephropathy. However, there is no report about the association between glomerulonephritis and RAGE. The aims of the current study were to explore the relationships between several clinical parameters and circulating soluble RAGE in primary FSGS and compare serum levels in primary FSGS with immunoglobulin A nephropathy (IgAN) and controls.

METHODS

A total of 35 subjects aged >18 years were enrolled. Thirty-five subjects consisted of three groups: primary FSGS (N = 15), IgAN (N = 10), and normal controls (N = 10). Laboratory measurements of serum carboxymethyl-lysin (CML), soluble RAGE (sRAGE), and endogenous secretory RAGE (esRAGE) were performed.

RESULTS

Serum esRAGE level in the FSGS group was higher than that in the IgAN group (0.55 ± 0.32 ng/mL vs. 0.27 ± 0.11 ng/mL, p = 0.013). There was no statistical difference between sRAGE and CML among the three groups. Within the FSGS group, esRAGE, but not sRAGE, was positively correlated with 24-h urinary protein (r = 0.553, p = 0.033) and negatively correlated with body mass index (r = -0.623, p = 0.013). In stepwise multiple regression analysis, body mass index and 24-h urinary protein were significant contributors to esRAGE within the FSGS group.

CONCLUSION

This study showed that only the serum level of esRAGE, not sRAGE, was higher in the FSGS group than in the IgAN and control groups. The amount of 24-h proteinuria was also related to the serum level of esRAGE in the FSGS group.

Clinical significance of serum sRAGE and esRAGE in women with normal pregnancy and preeclampsia

BACKGROUND

We determined serum endogenous secretory receptor of advanced glycation end products (esRAGE) and soluble RAGE (sRAGE) concentrations and the esRAGE/sRAGE ratio in normal pregnancy and preeclampsia because esRAGE and sRAGE have been negatively linked to components of metabolic syndromes and pathologic pregnancy including preeclampsia.

METHOD

Eighty-seven normal pregnant women and 28 with preeclampsia were recruited. Serum sRAGE and esRAGE levels were measured by enzyme-linked immunosorbent assay.

RESULTS

There were significant differences in esRAGE concentration and esRAGE/sRAGE ratio between 1(st) and 3(rd) trimester in normal pregnancy (P=0.007 and P=0.003). Serum esRAGE concentrations and esRAGE/sRAGE ratio in patients with preeclampsia significantly increased compared to controls (P=0.005 and P<0.001).

CONCLUSIONS

Maternal serum esRAGE concentration and esRAGE/sRAGE ratio (1) gradually decrease with gestational age in normal pregnancy; and (2) are higher in patients with preeclampsia than healthy pregnant controls, significantly. Serum esRAGE and esRAGE/sRAGE ratio might be associated with preeclampsia.

Association of serum soluble receptor for advanced glycation end-products with subclinical cerebrovascular disease: the Northern Manhattan Study (NOMAS)

OBJECTIVE

Serum levels of the soluble receptor for advanced glycation end-products (sRAGE) have been associated with risk of cardiovascular disease. We hypothesized that sRAGE levels are associated with subclinical cerebrovascular disease in an ethnically diverse population.

METHODS

Clinically stroke-free participants in the multi-ethnic Northern Manhattan Study (NOMAS) underwent brain MRI to quantify subclinical brain infarcts (SBI) and white matter hyperintensity volume (WMHV) (n = 1102). Serum levels of sRAGE were measured by ELISA. Logistic and multiple linear regression were employed to estimate associations of sRAGE with SBI and WMHV, after adjusting for demographics and vascular risk factors.

RESULTS

Median sRAGE levels were significantly lower in Hispanics (891.9 pg/ml; n = 708) and non-Hispanic blacks (757.4 pg/ml; n = 197) than in non-Hispanic whites (1120.5 pg/ml; n = 170), and these differences remained after adjusting for other risk factors. Interactions were observed by race-ethnicity between sRAGE levels and MRI measurements, including for SBI in Hispanics (p = 0.04) and WMHV among blacks (p = 0.03). In Hispanics, increasing sRAGE levels were associated with a lower odds of SBI, with those in the upper sRAGE quartile displaying a 50% lower odds of SBI after adjusting for sociodemographic and vascular risk factors (p = 0.05). Among blacks, those in the upper quartile of sRAGE had a similarly reduced increased risk of SBI (p = 0.06) and greater WMHV (p = 0.04).

CONCLUSION

Compared to whites, Hispanics and blacks have significantly lower sRAGE levels, and these levels were associated with more subclinical brain disease. Taken together, these findings suggest sRAGE levels may be significantly influence by ethnicity. Further studies of sRAGE and stroke risk, particularly in minorities, are warranted.

The Nε-(carboxymethyl)lysine-RAGE axis: putative implications for the pathogenesis of obesity-related complications

Obesity is an important contributor to the burden of insulin resistance, Type 2 diabetes and cardiovascular disease. An important mechanism by which excess adiposity causes obesity-associated complications is the dysregulated production and secretion of biologically active molecules derived from adipocytes. These adipokines affect the vascular wall and contribute to the development of insulin resistance and Type 2 diabetes. However, factors that cause an increased production of pro-inflammatory adipokines, while decreasing anti-inflammatory adipokines, have not been fully clarified. Owing to local conditions in adipose tissue, that is, increased fatty acids, hypoxia and oxidative stress, we speculate that an increased formation of the major advanced lipoxidation end product, N^ε-(carboxymethyl)lysine (CML), may play a role. CML-adducts in proteins are major ligands for the receptor for advanced glycation end products (RAGE). The consequence of RAGE activation by CML is the activation of important signaling inflammatory pathways. The putative role of CML-modified proteins in obesity is addressed in this article. The identification of this pathway may provide an important strategy for novel therapeutic approaches against obesity-associated complications.

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

BACKGROUND AND OBJECTIVES

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

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

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

RESULTS

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

CONCLUSIONS

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

Soluble receptor of advanced glycation end products levels are related to ischaemic aetiology and extent of coronary disease in chronic heart failure patients, independent of advanced glycation end products levels: New Roles for Soluble RAGE

AIMS

Knowledge of the role of advanced glycation end products (AGE), their receptor (RAGE), and the receptor's soluble form (sRAGE), in heart failure (HF) is very limited. We evaluated the clinical role of the AGE-RAGE system in HF and in particular any association it might have with ischaemic aetiology.

METHODS AND RESULTS

We measured fluorescent AGE, glycated albumin and sRAGE in 103 patients with chronic HF. We showed that sRAGE but not AGE was related to ischaemic aetiology (1638.3 ± 207.4 ischaemic vs. 1065.1 ± 94.2 pg/mL non-ischaemic group; P =0.016) independent of age, sex, diabetes, renal function, clinical severity, or other variables (OR: 1.091; 95% CI (confidence interval): 1.032-1.153; P =0.007). Moreover, sRAGE was directly associated with extent of coronary disease (OR for three vessel disease compared with non-coronary lesions: 1.186; 95% CI: 1.065-1.322; P =0.002). We also found a correlation between sRAGE and severity of HF, which increased with New York Heart Association (NYHA) class (741.9 ± 88.9 pg/mL in class 1, 1195.9 ± 113.2 pg/mL in class II, and 1724.8 ± 245.7 pg/mL in class III (P < 0.05)) and brain natriuretic peptide (BNP) levels (667.4 ± 68.0 vs. 1344.5 ± 126.0 pg/mL for BNP < and ≥400 pg/mL, respectively).

CONCLUSION

sRAGE is an indicator of chronic heart failure severity and an independent marker of coronary artery disease and its severity in patients with CHF.

Higher plasma soluble Receptor for Advanced Glycation End Products (sRAGE) levels are associated with incident cardiovascular disease and all-cause mortality in type 1 diabetes: a 12-year follow-up study

OBJECTIVE

To investigate the associations of plasma levels of soluble receptor for advanced glycation end products (sRAGE) with incident cardiovascular disease (CVD) and all-cause mortality in type 1 diabetes and the extent to which any such associations could be explained by endothelial and renal dysfunction, low-grade inflammation, arterial stiffness, and advanced glycation end products (AGEs).

RESEARCH DESIGN AND METHODS

We prospectively followed 169 individuals with diabetic nephropathy and 170 individuals with persistent normoalbuminuria who were free of CVD at study entry and in whom levels of sRAGE and other biomarkers were measured at baseline. The median follow-up duration was 12.3 years (7.6-12.5).

RESULTS

The incidence of fatal and nonfatal CVD and all-cause mortality increased with higher baseline levels of log-transformed sRAGE (Ln-sRAGE) independently of other CVD risk factors: hazard ratio (HR) 1.90 (95% CI 1.13-3.21) and 2.12 (1.26-3.57) per 1-unit increase in Ln-sRAGE, respectively. Adjustments for estimated glomerular filtration rate (eGFR(MDRD)), but not or to a smaller extent for markers of endothelial dysfunction, low-grade inflammation, arterial stiffness, and AGEs, attenuated these associations to HR 1.59 (95% CI 0.91-2.77) for fatal and nonfatal CVD events and to 1.90 (1.09-3.31) for all-cause mortality. In addition, in patients with nephropathy, the rate of decline of GFR was 1.38 ml/min/1.73 m(2) per year greater per 1-unit increase of Ln-sRAGE at baseline (P = 0.036).

CONCLUSIONS

Higher levels of sRAGE are associated with incident fatal and nonfatal CVD and all-cause mortality in individuals with type 1 diabetes. sRAGE-associated renal dysfunction may partially explain this association.

AGEs/RAGE in CKD: irreversible metabolic memory road toward CVD?

BACKGROUND

Cardiovascular disease is the major cause of death in patients with renal insufficiency, accounting for 50% of all deaths in renal replacement therapy patients. Mortality from cardiovascular diseases in these patients is approximately 9% per year, which is about 30 times the risk in the general population. So far, intensive interventions to the general risk factors, such as high LDL-cholesterol or C-reactive protein, have not been successful in improving their cardiovascular outcomes, suggesting that the beneficial effect of risk reduction may be overwhelmed by accumulated risk memorized by long-term exposure to oxidative stress during the progression of renal failure.

DESIGN

In this review, we propose that this irreversible memory effect in renal failure may be mediated by advanced glycation end-products (AGEs).

RESULTS

The generation of AGEs has been implicated to be deeply associated with increased oxidative stress. Moreover, interaction of the receptor for AGEs (RAGE) with AGEs leads to crucial biomedical pathway generating intracellular oxidative stress and inflammatory mediators, which could result in further amplification of the pathway involved in AGE generation. Several lines of evidence suggest that AGEs/RAGE axis can profoundly be involved in cardiovascular diseases. Recent advances in AGEs and RAGE measurements led us to be capable of understanding more about the role of AGEs/RAGE axis as a risk for cardiovascular diseases in patients with renal failure.

CONCLUSION

AGEs/RAGE axis could be a crucial mediator of oxidative stress in renal failure. RAGE could be not only a useful biomarker, but also a potentially therapeutic target to overcome the accumulated adverse metabolic memory in renal failure.

Soluble RAGE: therapy and biomarker in unraveling the RAGE axis in chronic disease and aging

The multi-ligand Receptor for Advanced Glycation Endproducts (RAGE) is implicated in the pathogenesis and progression of chronic diseases such as diabetes and immune/inflammatory disorders. Recent studies are uncovering the precise mechanisms by which distinct RAGE ligands bind the extracellular (soluble) domain of the receptor at the V-, C1- and/or C2-immunoglobulin like domains. Experiments using soluble RAGE in animals as a ligand decoy have illustrated largely beneficial effects in reducing vascular and inflammatory stress and, thereby, preventing long-term tissue damage in models of diabetes and immune/inflammatory disorders. Measurement of soluble RAGE levels in the human, both "total" soluble RAGE and a splice variant-derived product known as endogenous secretory or esRAGE, holds promise for the identification of potential therapeutic targets and/or biomarkers of RAGE activity in disease. In this article, we review the evidence from the rodent to the human implicating RAGE in the diverse disease states in which its ligands accumulate.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Association between serum levels of the soluble receptor (sRAGE) for advanced glycation endproducts (AGEs) and their receptor (RAGE) in peripheral blood mononuclear cells of children with type 1 diabetes mellitus

AIM

The binding of AGEs to RAGE is involved in diabetic vascular complications. We studied sRAGE levels and RAGE protein expression (P) together with N-carboxymethyl lysine (CML), a major AGE, in 74 patients with type 1 diabetes mellitus (DM1) and 43 healthy (C) children.

METHODS

sRAGE and CML levels were determined by ELISA and RAGE P was evaluated in mononuclear cells by Western immunoblotting.

RESULTS

Serum sRAGE was higher in DM1 than in C (1430 +/- 759 vs 1158 +/- 595 pg/ml, p = 0.047), inversely correlated to diabetes duration (r = -0.265, p = 0.037) and directly correlated to LDL-cholesterol levels (r = 0.224, p = 0.039). Diabetes duration correlated independently with sRAGE (p = 0.034). Circulating CML levels were not significantly different between DM1 and C groups (3.51 +/- 1.49 vs 3.59 +/- 1.83 ng/ml, p > 0.05) and RAGE P was lower in DM1 than in C (61 +/- 46 vs 102 +/- 63%, p = 0.0001).

CONCLUSIONS

Increased serum sRAGE in children with DM1 may provide temporary protection against cell damage and may be sufficient to eliminate excessive circulating CML.

Soluble forms of RAGE in internal medicine

The receptor for advanced glycation end-products (RAGE) and its ligands are intimately involved in the pathobiology of a wide range of diseases that share common features, such as enhanced oxidative stress, immune/inflammatory responses, and altered cell functions. Soluble forms of RAGE (sRAGE), including the splice variant endogenous secretory (es)RAGE, have been found circulating in plasma and tissues. Experimental data suggest that these isoforms may neutralize the ligand-mediated damage by acting as a decoy. Moreover, evidence is mounting to support a role for both sRAGE and esRAGE as biomarkers or endogenous protection factors against RAGE-mediated pathogenesis. In this review, we will focus on clinical and therapeutical implications arising from studies investigating the significance of soluble RAGE isoforms in several clinical settings, including cardiovascular disease, diabetes mellitus, hypercholesterolemia, chronic renal failure, immune/inflammatory diseases, pulmonary diseases, neurodegeneration, and cancer.

Levels of Soluble Receptor for Advanced Glycation End Products in Acute Ischemic Stroke without a Source of Cardioembolism

BACKGROUND AND PURPOSE

Low levels of soluble receptor for advanced glycation end products (sRAGE) are associated with three conventional vascular risk factors (3Fs: diabetes, hypertension, and hypercholesterolemia), nondiabetic coronary artery disease, and Alzheimer's disease. However, the association between sRAGE and acute ischemic stroke (AS), especially AS without a source of cardioembolism, has not yet been established.

METHODS

Patients with AS without a source of cardioembolism (n=259) and age-matched controls (n=300) were grouped according to the presence of 3Fs: AS patients with and without 3Fs (3Fs+ AS and 3Fs- AS, respectively) and controls with and without 3Fs (3Fs+ control and 3Fs- control, respectively). Levels of sRAGE were analyzed among the four groups.

RESULTS

sRAGE was significantly higher in the controls than in the AS patients (855 pg/mL vs. 690 pg/mL, p<0.01). sRAGE was significantly higher in 3Fs- controls (996 pg/mL, p<0.05) than in 3Fs+ controls (721 pg/mL), and in AS group regardless of the 3Fs (629 pg/mL in 3Fs- and 705 pg/mL in 3Fs+). The lowest tertile of sRAGE was associated with an increased risk of AS in the 3Fs- group [adjusted odds ratio (OR) 4.0, 95% confidence interval (CI) 1.6-10.3, p<0.01] but not in the 3Fs+ group. The level of sRAGE was also correlated with neurological severity in the 3Fs- AS group (r=-0.32, p<0.05) but not in the 3Fs+ AS group.

CONCLUSIONS

Low plasma levels of sRAGE is a potential biomarker for the risk of AS and may reflect the neurological severity of the condition, especially in subjects without identifiable conventional risk factors.

RAGE: therapeutic target and biomarker of the inflammatory response--the evidence mounts

The RAGE binds multiple ligand families linked to hyperglycemia, aging, inflammation, neurodegeneration, and cancer. Activation of RAGE by its ligands stimulates diverse signaling cascades. The recent observation that the cytoplasmic domain of RAGE interacts with diaphanous or mDia-1 links RAGE signal transduction to cellular migration and activation of the Rho GTPases, cdc42 and rac-1. Pharmacological blockade of RAGE or genetic deletion of RAGE imparts significant protection in murine models of diabetes, inflammatory conditions, Alzheimer's disease, and tumors. Intriguingly, soluble forms of RAGE, including the splice variant-derived esRAGE, circulate in human plasma. Studies in human subjects suggest that sRAGE levels may be modulated by the diseases impacted by RAGE and its ligands. Thus, in addition to being a potential therapeutic target in chronic disease, monitoring of plasma sRAGE levels may provide a novel biomarker platform for tracking chronic inflammatory diseases, their severity, and response to therapeutic intervention.

Levels of soluble receptor for AGE are cross-sectionally associated with cardiovascular disease in type 1 diabetes, and this association is partially mediated by endothelial and renal dysfunction and by low-grade inflammation: the EURODIAB Prospective Complications Study

AIMS/HYPOTHESIS

Plasma soluble receptor for AGE (sRAGE) may reflect the activity of the AGE-RAGE axis, which has been proposed as a potential mechanism linking hyperglycaemia to vascular complications in diabetes. We have therefore investigated: (1) whether sRAGE is associated with greater prevalence of cardiovascular disease (CVD) and microvascular complications in type 1 diabetic individuals; and (2) the extent to which any such associations are explained by markers of endothelial and renal dysfunction and inflammation.

METHODS

The study included 477 individuals (234 women; mean age 42 +/- 10 [SD] years) from the EURODIAB Prospective Complications Study. We used linear regression analyses to investigate the differences in sRAGE levels between individuals with and without vascular complications. All analyses were adjusted for age, sex, HbA(1c), duration of diabetes and other risk factors.

RESULTS

Individuals with CVD (n = 116) had higher levels of sRAGE than those without CVD or any microvascular complications (n = 178): beta = 0.15 (95% CI 0.04-0.27). Further adjustments for markers of endothelial (beta = 0.13 [0.02-0.24]) and renal dysfunction (beta = 0.10 [-0.01, 0.20]) and inflammation (beta = 0.12 [0.01-0.23]) attenuated these differences; altogether these variables explained about 50% of the association between sRAGE and prevalent CVD. sRAGE levels tended to be higher in the presence and across the levels of severity of albuminuria (p for trend = 0.087) and retinopathy (p for trend = 0.057); adjustments for endothelial and renal dysfunction and inflammation also attenuated these differences.

CONCLUSIONS/INTERPRETATION

sRAGE is associated with greater prevalence of CVD in type 1 diabetic individuals, and these associations may be partly explained by endothelial and renal dysfunction and low-grade inflammation.

RAGE: a novel biological and genetic marker for vascular disease

RAGE [receptor for AGEs (advanced glycation end-products)] plays an important role in the development and progression of vascular disease. Studies in cultured cells and small animal models of disease have clearly demonstrated that RAGE is central to the pathogenesis of vascular disease of the macro- and micro-vessels in both the diabetic and non-diabetic state. Emerging results from human clinical studies have revealed that levels of circulating soluble RAGE in the plasma may reflect the presence and/or extent of vascular disease state. Additionally, genetic variants of the RAGE gene (AGER in HUGO nomenclature) have been associated with vascular disease risk. Combining RAGE circulating protein levels and the presence of particular RAGE polymorphisms may be a useful clinical tool for the prediction of individuals at risk for vascular disease. Therapeutic intervention targeted at the RAGE gene may therefore be a useful means of treating pathologies of the vasculature.

Receptor for advanced glycation end products: its role in Alzheimer's disease and other neurological diseases

The receptor for advanced glycation end products (RAGE) has been demonstrated to play a central role in the pathogenic mechanisms of a growing number of important neurological diseases, including Alzheimer's disease (AD) and stroke. Two functional types of RAGE have been associated with neurological diseases: cell membrane-bound (full length) and soluble. In general, ligand binding to full-length RAGE initiates sustained cellular activation and receptor-dependent signaling resulting in inflammation and cellular stress, and is ultimately associated with increased RAGE expression. By comparison, soluble forms of RAGE, generated either by alternative splicing or by proteolysis, can reduce the severity of the consequence of ligand-membrane RAGE interactions by preventing ligands from binding to the full-length RAGE. This can inhibit the neurotoxic or proinflammatory responses involved in disease states. This article reviews the pathobiology of RAGE, with emphasis on soluble forms of RAGE, and discusses its relevance to AD and to other neurological diseases, as well as how manipulation of the different forms of RAGE is becoming a powerful therapeutic strategy.