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

Association of Incident Stroke Risk With an IL-18-Centered Inflammatory Network Biomarker Composite

BACKGROUND

A coordinated network of circulating inflammatory molecules centered on the pleotropic pro-atherogenic cytokine interleukin-18 (IL-18) is linked to cerebral small vessel disease. We sought to validate the association of this inflammatory biomarker network with incident stroke risk, cognitive impairment, and imaging metrics in a sample of the Framingham Offspring Cohort.

METHODS

Using available baseline measurements of serum levels of IL-18, GDF (growth and differentiation factor)-15, soluble form of receptor for advanced glycation end products, myeloperoxidase, and MCP-1 (monocyte chemoattractant protein-1) from Exam 7 of the Framingham Offspring Cohort (1998-2001), we constructed a population-normalized, equally weighted log-transformed mean Z-score value representing the average level of each serum analyte to create an inflammatory composite score (ICS5). Multivariable regression models were used to determine the association of ICS5 with incident stroke, brain magnetic resonance imaging features, and cognitive testing performance.

RESULTS

We found a significant association between ICS5 score and increased risk for incident all-cause stroke (hazard ratio, 1.48 [95% CI, 1.05-2.08]; P=0.024) and ischemic stroke (hazard ratio, 1.51 [95% CI, 1.03-2.21]; P=0.033) in the Exam 7 cohort of 2201 subjects (mean age 62±9 years; 54% female) aged 45+ years with an all-cause incident stroke rate of 6.1% (135/2201) and ischemic stroke rate of 4.9% (108/2201). ICS5 and its component serum markers are all associated with the Framingham Stroke Risk Profile score (β±SE, 0.19±0.02; P<0.0001). In addition, we found a significant inverse association of ICS5 with a global cognitive score, derived from a principal components analysis of the neuropsychological battery used in the Framingham cohort (-0.08±0.03; P=0.019). No association of ICS5 with magnetic resonance imaging metrics of cerebral small vessel disease was observed.

CONCLUSIONS

Circulating serum levels of inflammatory biomarkers centered on IL-18 are associated with an increased risk of stroke and cognitive impairment in the Framingham Offspring Cohort. Linking specific inflammatory pathways to cerebral small vessel disease may enhance individualized quantitative risk assessment for future stroke and vascular cognitive impairment.

Unveiling the molecular basis of inflamm-aging induced by advanced glycation end products (AGEs)-modified human serum albumin (AGE-HSA) in patients with different immune-mediated diseases

Increased serum advanced glycation end products (AGEs) are commonly found in the patients with Diabetes mellitus (DM), aging-related diseases, and immune-mediated diseases. These diseases are notorious for vasculopathy, immune dysfunctions, and low-grade inflammation mimicking inflamm-aging. However, the molecular basis of inflamm-aging related to AGEs remains elucidation. In this study, we incubated human serum albumin (HSA) and glucose at 37 °C in 5% CO₂ incubator for 0-180 days to generate AGE-HSA. We found the mixture gradually changing the color from transparancy to brown color and increased molecular weight during incubation. The pH value also gradually decreased from 7.2 to 5.4 irrelevant to ionic charge or [Ca²⁺] concentration, but dependent on gradual glycation of the alkaline amino acids, lysine and arginine. Functionally, 40 μg/mL of AGE-HSA decreased IL-2 production from human Jurkat T cell line via suppressing p-STAT3, p-STAT4, and p-STAT6 with an increased tendency of senescence-associated β-galactosidase (SA-βgal) expression but irrelevant to change of Th1/Th2/Treg subpopulations. In contrast, AGE-HSA enhanced CC motif chemokine ligand 5 (CCL-5), IL-8, macrophage migration inhibitor factor (MIF), and interleukin 1 receptor antagonist (IL-1Ra) but suppressed SA-βgal expression by human macrophage-like THP-1 cells. Interestingly, AGE-HSA abrogated the HSA-induced soluble intercellular adhesion molecules 1 (sICAM-1), sE-selectin and endothelin release from human coronary artery endothelial cells (HCAEC) and enhanced SA-βgal expression. The accelerated and increased HSA glycations by individual inflammation-related cytokine such as IL-2, IL-6, IL-17, TGF-β, or TNF-α in the in vitro study reflect increased serum AGE levels in patients with immune-mediated diseases . In conclusion, AGE-HSA can exert immunosuppresive, inflammatory and vasculopathic effects mimicking inflamm-aging in these patients.

Emerging markers of inflammation and oxidative stress as potential predictors of coronary artery disease

BACKGROUND AND AIMS

The multi-ligand receptor for advanced glycation end products (RAGE) and its ligands AGEs and S100/calgranulin proteins are important mediators of inflammation and oxidative stress whereas the soluble form of RAGE (sRAGE) by acting as a decoy and the antioxidant PARK7/DJ-1 exert antiatherogenic effects. We examined whether sRAGE and its ligands AGEs, S100A8/A9, S100B, S100A12 and DJ-1 are associated with the presence of angiographic coronary artery disease (CAD) in asymptomatic patients with and without diabetes.

METHODS AND RESULTS

Plasma levels of RAGE ligands, sRAGE and DJ-1 were determined in 50 patients with angiographically proven CAD and in 50 age-matched healthy controls. In the whole cohort, lower levels of sRAGE and higher levels of interleukin-6 (IL-6), the RAGE ligands S100B, S100A12 and the AGEs/sRAGE ratio were associated with CAD. In patients without diabetes (n = 72), lower levels of sRAGE and DJ-1 and higher levels of IL-6 and AGEs/sRAGE ratio were associated with CAD. In multivariable analysis, AGEs/sRAGE ratio was an independent predictor of CAD both in the whole cohort (p = 0.034, OR = 1.247, [95%CI: 1.024, 1.0519]) and in the subgroup of patients without diabetes (p = 0.021, OR = 1.363, 95%CI [1.048, 1.771]) on top of established cardiovascular risk factors.

CONCLUSION

Alterations in plasma RAGE axis inflammatory mediators are associated with atherosclerosis, and higher levels of AGEs/sRAGE ratio are independently associated with CAD in asymptomatic patients and may act as a novel biomarker for predicting CAD. DJ-1 emerges as promising marker of oxidative stress in CAD patients without diabetes, a finding that deserves further study.

The use of the soluble receptor for advanced glycation-end products (sRAGE) as a potential biomarker of disease risk and adverse outcomes

The soluble receptor for advanced glycation end-products (sRAGE) has been classically considered a sink for pro-inflammatory RAGE ligands and as such has been associated with protection from inflammatory stress and disease. An alternative, though not mutually exclusive view is that high levels of sRAGE in circulation reflect the overstimulation of cell surface RAGE which if persistent, lead to the amplification of pro-inflammatory processes and the exacerbation of pathological states. With these two scenarios in mind this review focuses on the potential role of sRAGE as a prospective biomarker of disease risk and adverse outcomes.

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The prognostic value of measuring sRAGE levels in blood is subjected to debate.

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Raised sRAGE levels may result from the overstimulation of cell surface RAGE.

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Raised sRAGE may reflect chronic inflammation and multimorbidity rather than a healthy state.

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sRAGE is a promising biomarker of disease risk and adverse outcomes.

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 potential role of dietary advanced glycation endproducts in the development of chronic non-infectious diseases: a narrative review

Increasing clinical and experimental evidence accumulated during the past few decades supports an important role for dietary advanced glycation endproducts (AGE) in the pathogenesis of many chronic non-infectious diseases, such as type 2 diabetes, CVD and others, that are reaching epidemic proportions in the Western world. Although AGE are compounds widely recognised as generated in excess in the body in diabetic patients, the potential importance of exogenous AGE, mostly of dietary origin, has been largely ignored in the general nutrition audience. In the present review we aim to describe dietary AGE, their mechanisms of formation and absorption into the body as well as their main mechanisms of action. We will present in detail current evidence of their potential role in the development of several chronic non-infectious clinical conditions, some general suggestions on how to restrict them in the diet and evidence regarding the potential benefits of lowering their consumption.

Soluble Receptor for Advanced Glycation End Products and Its Forms in COVID-19 Patients with and without Diabetes Mellitus: A Pilot Study on Their Role as Disease Biomarkers

The receptor for advanced glycation end products (RAGE), a well-known player of diabetes mellitus (DM)-related morbidities, was supposed to be involved in coronavirus disease-19 (COVID-19), but no data exist about COVID-19, DM, and the soluble RAGE (sRAGE) forms. We quantified total sRAGE and its forms, the endogenously secretory esRAGE and the membrane-cleaved cRAGE, in COVID-19 patients with and without DM and in healthy individuals to explore how COVID-19 may affect these molecules and their potential role as biomarkers. Circulating sRAGE and esRAGE were quantified by enzyme-linked-immunosorbent assays. cRAGE was obtained by subtracting esRAGE from total sRAGE. sRAGE, esRAGE, cRAGE, and the cRAGE/esRAGE ratio did not differ between DM and non-DM patients and had the same trend when compared to healthy individuals. Levels of total sRAGE, cRAGE, and cRAGE/esRAGE ratio were upregulated, while esRAGE was downregulated. The lack of difference between DM and non-DM COVID-19 patients in the levels of sRAGE and its forms supports the hypothesis that in COVID-19 the RAGE system is modulated regardless of glycemic control. Identifying how sRAGE and its forms associate to COVID-19 prognosis and the potential of RAGE as a therapeutic target to control inflammatory burden seem of relevance to help treatment of COVID-19.

Circulating Ligands of the Receptor for Advanced Glycation End Products and the Soluble Form of the Receptor Modulate Cardiovascular Cell Apoptosis in Diabetes

We determined whether plasma concentrations of the receptor for advanced glycation end products (RAGE) and the soluble (s) form of RAGE (sRAGE) in healthy individuals and patients with type 2 diabetes (T2D) modulate vascular remodeling. Healthy individuals and patients with T2D were divided into two age groups: young = <35 years old or middle-aged (36-64 years old) and stratified based on normal glucose tolerance (NGT), impaired (IGT), and T2D. Plasma titers of sRAGE, the RAGE ligands, AGEs, S100B, S100A1, S100A6, and the apoptotic marker Fas ligand Fas(L) were measured by enzyme-linked immunosorbent assay (ELISA). The apoptotic potential of the above RAGE ligands and sRAGE were assessed in cultured adult rat aortic smooth muscle cells (ASMC). In NGT individuals, aging increased the circulating levels of AGEs and S100B and decreased sRAGE, S100A1 and S100A6. Middle-aged patients with T2D presented higher levels of circulating S100B, AGEs and FasL, but lower levels of sRAGE, S100A1 and S100A6 than individuals with NGT or IGT. Treatment of ASMC with either AGEs or S100B at concentrations detected in T2D patients increased markers of inflammation and apoptosis. Responses attenuated by concomitant administration of sRAGE. In middle-aged patients with T2D, lower circulating plasma levels of sRAGE may limit decoy and exogenous trapping of deleterious pro-apoptotic/pro-inflammatory RAGE ligands AGEs and S100B, increasing the risk for diabetic complications.

Advanced glycation end products increased placental vascular permeability of human BeWo cells via RAGE/NF-kB signaling pathway

OBJECTIVE

This study aimed to investigate the mechanisms of advanced glycation end products (AGEs) on cell tight conjunction and placental vascular permeability in BeWo cells.

STUDY DESIGN

Monolayer permeability assay and transmission electron microscopy were employed to reveal the transformation of the placental vascular permeability and cell tight conjunction. Immunofluorescence, western blot and RT-qPCR were adopted to determine the protein and mRNA levels. Anti-RAGE and NF-kB inhibitor (PDTC) were used to inactivate the RAGE/NF-kB signaling pathway.

RESULTS

AGEs significantly decreased trans-epithelial electrical resistance (TEER), while increased paracellular permeability (P <  0.05). TEM showed that AGEs made cell junction loose. AGEs inhibited ZO-1 and Occludin expressions, while anti-RAGE or PDTC partially restored their levels. AGEs also significantly increased mRNA RAGE and NF-kB expressions in BeWo cells (P <  0.05), and their expressions were inhibited by anti-RAGEy or PDTC.

CONCLUSION

AGEs could reduce the expressions of ZO-1 and Occludin by activating RAGE/NF-kB signaling pathway, thus increasing placental vascular permeability.

High Plasma sRAGE (Soluble Receptor for Advanced Glycation End Products) Is Associated With Slower Carotid Intima-Media Thickness Progression and Lower Risk for First-Time Coronary Events and Mortality

Objective- RAGE (receptor for advanced glycation end products) and EMMPRIN (extracellular matrix metalloproteinase inducer) are immune receptors for proinflammatory mediators. These receptors can also be found in a soluble form in the circulation. Soluble RAGE (sRAGE) has shown atheroprotective properties in animal studies, possibly by acting as a decoy receptor for its ligands. Whether sEMMPRIN (soluble EMMPRIN) has similar roles is unknown. We hypothesized that sRAGE and sEMMPRIN might be associated with vascular disease progression, incident coronary events, and mortality. Approach and Results- We measured baseline sRAGE and sEMMPRIN in 4612 cardiovascular disease-free individuals from the population-based Malmö Diet and Cancer cohort. Measurements of intima-media thickness in the common carotid artery were performed at inclusion and after a median of 16.5 years. sRAGE was negatively correlated with carotid intima-media thickness progression, independently of traditional cardiovascular risk factors, kidney function, and hsCRP (high sensitive C-reactive protein). Additionally, sRAGE was associated with decreased risk for major adverse coronary events (hazard ratio=0.90 [0.82-0.97]; P=0.009) and mortality (hazard ratio=0.93 [0.88-0.99]; P=0.011) during a follow-up period of 21 years. The relationship with mortality was independent of all considered potential confounders. We found no correlations between EMMPRIN, intima-media thickness progression, or prognosis. Conclusions- Individuals with high levels of circulating sRAGE have a slower rate of carotid artery disease progression and a better prognosis. Although its predictive value was too weak to promote sRAGE as a useful clinical biomarker in the population, the findings support further research into the potential anti-inflammatory and atheroprotective properties of this soluble receptor.

An IL-18-centered inflammatory network as a biomarker for cerebral white matter injury

Chronic systemic sterile inflammation is implicated in the pathogenesis of cerebrovascular disease and white matter injury. Non-invasive blood markers for risk stratification and dissection of inflammatory molecular substrates in vivo are lacking. We sought to identify whether an interconnected network of inflammatory biomarkers centered on IL-18 and all previously associated with white matter lesions could detect overt and antecedent white matter changes in two populations at risk for cerebral small vessel disease. In a cohort of 167 older adults (mean age: 76, SD 7.1, 83 females) that completed a cognitive battery, physical examination, and blood draw in parallel with MR imaging including DTI, we measured cerebral white matter hyperintensities (WMH) and free water (FW). Concurrently, serum levels of a biologic network of inflammation molecules including MPO, GDF-15, RAGE, ST2, IL-18, and MCP-1 were measured. The ability of a log-transformed population mean-adjusted inflammatory composite score (ICS) to associate with MR variables was demonstrated in an age and total intracranial volume adjusted model. In this cohort, ICS was significantly associated with WMH (β = 0.222, p = 0.013), FW (β = 0.3, p = 0.01), and with the number of vascular risk factor diagnoses (r = 0.36, p<0.001). In a second cohort of 131 subjects presenting for the evaluation of acute neurologic deficits concerning for stroke, we used serum levels of 11 inflammatory biomarkers in an unbiased principal component analysis which identified a single factor significantly associated with WMH. This single factor was strongly correlated with the six component ICS identified in the first cohort and was associated with WMH in a generalized linear regression model adjusted for age and gender (p = 0.027) but not acute stroke. A network of inflammatory molecules driven by IL-18 is associated with overt and antecedent white matter injury resulting from cerebrovascular disease and may be a promising peripheral biomarker for vascular white matter injury.

The Relationship between the Soluble Receptor for Advanced Glycation End Products and Oxidative Stress in Patients with Palmoplantar Warts

Background and objectives: Warts are the most common lesions caused by human papillomavirus (HPV). Recent research suggests that oxidative stress and inflammation are involved in the pathogenesis of HPV-related lesions. It has been shown that the soluble receptor for advanced glycation end products (sRAGE) may act as a protective factor against the deleterious effects of inflammation and oxidative stress, two interconnected processes. However, in HPV infection, the role of sRAGE, constitutively expressed in the skin, has not been investigated in previous studies. Materials and Methods: In order to analyze the role of sRAGE in warts, we investigated the link between sRAGE and the inflammatory response on one hand, and the relationship between sRAGE and the total oxidant/antioxidant status (TOS/TAS) on the other hand, in both patients with palmoplantar warts (n = 24) and healthy subjects as controls (n = 28). Results: Compared to the control group, our results showed that patients with warts had lower levels of sRAGE (1036.50 ± 207.60 pg/mL vs. 1215.32 ± 266.12 pg/mL, p < 0.05), higher serum levels of TOS (3.17 ± 0.27 vs. 2.93 ± 0.22 µmol H2O2 Eq/L, p < 0.01), lower serum levels of TAS (1.85 ± 0.12 vs. 2.03 ± 0.14 µmol Trolox Eq/L, p < 0.01) and minor variations of the inflammation parameters (high sensitivity-CRP, interleukin-6, fibrinogen, and erythrocyte sedimentation rate). Moreover, in patients with warts, sRAGE positively correlated with TAS (r = 0.43, p < 0.05), negatively correlated with TOS (r = −0.90, p < 0.01), and there was no significant correlation with inflammation parameters. There were no significant differences regarding the studied parameters between groups when we stratified the patients according to the number of the lesions and disease duration. Conclusions: Our results suggest that sRAGE acts as a negative regulator of oxidative stress and could represent a mediator involved in the development of warts. However, we consider that the level of sRAGE cannot be used as a biomarker for the severity of warts. To the best of our knowledge, this is the first study to demonstrate that sRAGE could be involved in HPV pathogenesis and represent a marker of oxidative stress in patients with warts.

Detection of the receptor for advanced glycation endproducts in neuronally-derived exosomes in plasma

Exosomes are nanovesicles that participate in cell-to-cell communication and are secreted by a variety of cells including neurons. Recent studies suggest that neuronally-derived exosomes are detectable in plasma and that their contents likely reflect expression of various biomarkers in brain tissues. The receptor for advanced glycation endproducts (RAGE) has been implicated in the pathophysiology of Alzheimer's disease (AD) and is increased in brain regions affected by AD. The goal of our project was to determine whether RAGE is present in plasma exosomes, and specifically exosomes derived from neurons. Exosomes were isolated from plasma samples (n = 8) by precipitation (ExoQuick) and ultracentrifugation methods. Neuronally-derived exosomes were isolated using a biotin-tagged L1 Cell Adhesion Molecule (L1CAM) specific antibody and streptavidin-tagged agarose resin. RAGE expression was measured by Western blots and ELISA. Western Blotting showed that RAGE is present in L1CAM-positive exosomes isolated using both methods. Mean (SD) exosomal RAGE levels were 164 (60) pg/ml by ExoQuick and were highly correlated with plasma sRAGE levels (r = 0.87, p = 0.005), which were approximately 7.5-fold higher than exosomal levels. Weak to moderate correlations were found between exosomal RAGE and age, BMI, and cognitive function. These results show for the first time that RAGE is present in neuronally-derived plasma exosomes, and suggest that exosomal RAGE may be a novel biomarker that reflects pathophysiological processes in the brain.

AGE-RAGE Stress, Stressors, and Antistressors in Health and Disease

Adverse effects of advanced glycation end-products (AGEs) on the tissues are through nonreceptor- and receptor-mediated mechanisms. In the receptor-mediated mechanism, interaction of AGEs with its cell-bound receptor of AGE (RAGE) increases generation of oxygen radicals, activates nuclear factor-kappa B, and increases expression and release of pro-inflammatory cytokines resulting in the cellular damage. The deleterious effects of AGE and AGE-RAGE interaction are coined as "AGE-RAGE stress." The body is equipped with defense mechanisms to counteract the adverse effects of AGE and RAGE through endogenous enzymatic (glyoxalase 1, glyoxalase 2) and AGE receptor-mediated (AGER1, AGER2) degradation of AGE, and through elevation of soluble receptor of AGE (sRAGE). Exogenous defense mechanisms include reduction in consumption of AGE, prevention of AGE formation, and downregulation of RAGE expression. We have coined AGE and RAGE as "stressors" and the defense mechanisms as "anti-stressors." AGE-RAGE stress is defined as a shift in the balance between stressors and antistressors in the favor of stressors. Measurements of stressors or antistressors alone would not assess AGE-RAGE stress. For true assessment of AGE-RAGE stress, the equation should include all the stressors and antistressors. The equation for AGE-RAGE stress, therefore, would be the ratio of AGE + RAGE/sRAGE + glyoxalase1 + glyoxalase 2 + AGER1 +AGER2. This is, however, not practical in patients. AGE-RAGE stress may be assessed simply by the ratio of AGE/sRAGE. A high ratio of AGE/sRAGE indicates a relative shift in stressors from antistressors, suggesting the presence of AGE-RAGE stress, resulting in tissue damage, initiation, and progression of the diseases and their complications.

Diabetic Microvascular Disease: An Endocrine Society Scientific Statement

Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.

Advanced glycation end-product (AGE)-albumin from activated macrophage is critical in human mesenchymal stem cells survival and post-ischemic reperfusion injury

Post-ischemic reperfusion injury (PIRI) triggers an intense inflammatory response which is essential for repair but is also implicated in pathogenesis of post-ischemic remodeling in several organs in human. Stem cell therapy has recently emerged as a promising method for treatment of PIRI in human. However, satisfactory results have not been reported due to severe loss of injected stem cells in PIRI including critical limb ischemia (CLI). For investigating the advanced glycation end-product-albumin (AGE-albumin) from activated macrophages is critical in both muscle cell and stem cell death, we evaluated the recovery of PIRI-CLI by injection of human bone marrow derived mesenchymal stem cells (hBD-MSCs) with or without soluble receptor for AGEs (sRAGE). Our results showed that activated M1 macrophages synthesize and secrete AGE-albumin, which induced the skeletal muscle cell death and injected hBD-MSCs in PIRI-CLI through RAGE increase. Combined injection of sRAGE and hBD-MSCs resulted in enhanced survival of hBD-MSCs and angiogenesis in PIRI-CLI mice. Taken together, AGE-albumin from activated macrophages is critical for both skeletal muscle cell and hBD-MSCs death in PIRI-CLI. Therefore, the inhibition of AGE-albumin from activated macrophages could be a successful therapeutic strategy for treatment of PIRI including CLI with or without stem cell therapy.

Serum soluble receptor of advanced glycation end products and risk of metabolic syndrome in Egyptian obese women

Obesity is one of the diagnostic criteria of metabolic syndrome (MS). It is correlated with insulin resistance (IR) and high vascular risk as well. Advanced glycation end products (AGEs) and their receptor (RAGE) play an important role in abnormal metabolic components in obese women. This study aimed to explore the serum levels of sRAGE in Egyptian obese women and compare with healthy non-obese controls and investigate the relationship between serum sRAGE, metabolic parameters, and obesity complications. The soluble form of receptor for advanced glycation end products (sRAGE), anthropometry, metabolic and biochemical biomarkers were measured in 100 obese women and 100 age-matched healthy control non-obese women. The homeostasis model assessment estimate of insulin resistance (HOMA-IR) has been determined from serum insulin and glucose values. Serum sRAGE levels were significantly lower in obese cases than controls and inversely correlated with obesity and metabolic parameters. Results of univariate and multivariate analyses for determinants of serum sRAGE levels in obese cases showed that parameters statistically and significantly related were body mass index (BMI), waist circumference (WC), LDL-C, TG, BP, HOMA-IR, ALT and AST. sRAGE is a novel biomarker for metabolic dysfunction in Egyptian obese women and might predict the future cardio-metabolic events.

Evaluation of circulating sRAGE in osteoporosis according to BMI, adipokines and fracture risk: a pilot observational study

Background

Osteoporosis is a systemic metabolic disease based on age-dependent imbalance between the rates of bone formation and bone resorption. Recent studies on the pathogenesis of this disease identified that bone remodelling impairment, at the base of osteoporotic bone fragility, could be related to protein glycation, in association to oxidative stress. The glycation reactions lead to the generation of glycation end products (AGEs) which, in turn, accumulates into bone, where they binds to the receptor for AGE (RAGE). The aim of this study is to investigate the potential role of circulating sRAGE in osteoporosis, in particular evaluating the correlation of sRAGE with the fracture risk, in association with bone mineral density, the fracture risk marker FGF23, and lipid metabolism.

Results

Circulating level of soluble RAGE correlate with osteopenia and osteoporosis level. Serum sRAGE resulted clearly associated on the one hand to bone fragility and, on the other hand, with BMI and leptin. sRAGE is particularly informative because serum sRAGE is able to provide, as a single marker, information about both the aspects of osteoporotic disease, represented by bone fragility and lipid metabolism.

Conclusions

The measure serum level of sRAGE could have a potential diagnostic role in the monitoring of osteoporosis progression, in particular in the evaluation of fracture risk, starting from the prevention and screening stage, to the osteopenic level to osteoporosis.

Mouse RAGE Variant 4 Is a Dominant Membrane Receptor that Does Not Shed to Generate Soluble RAGE

The receptor for advanced glycation end products (RAGE) is a multi-ligand, immunoglobulin-like receptor that has been implicated in aging-associated diseases. Recent studies have demonstrated that both human and murine Ager genes undergo extensive alternative splicing that generates multiple putative transcripts encoding different receptor isoforms. Except for the soluble isoform (esRAGE), the majority of putative RAGE isoforms remain unstudied. Profiling of murine Ager transcripts showed that variant transcript 4 (mRAGE_v4), the second most abundant transcript in lungs and multiple other tissues, encodes a receptor that lacks nine residues located within the C2 extracellular section close to the trans-membrane domain. We therefore characterized mRAGEV4 isoreceptor in comparison with the full-length mRAGE (mRAGEFL). Although differing in only nine residues, mRAGEFL and mRAGEV4 display very different cellular behaviors. While mRAGEFL undergoes constitutive, extensive shedding in the cell to generate sRAGE, mRAGEV4 hardly sheds. In addition, we found that while mRAGEFL can localize to both the plasma membrane and the endosome, mRAGEV4 is exclusively localized to the plasma membrane. These very different cellular localization patterns suggest that, in addition to their roles in sRAGE production, mRAGEFL and mRAGEV4 may play distinct, spatiotemporal roles in signaling and innate immune responses. Compared to mice, humans do not have the v4 transcript. Although hRAGE, like mRAGEFL, also localizes to the plasma membrane and the endosome, its rate of constitutive shedding is significantly lower. These observations provide valuable information regarding RAGE biology, and serve as a reference by which to create mouse models relating to human diseases.

The Receptor for Advanced Glycation End Products (RAGE) Is Associated with Persistent Atrial Fibrillation

Objective

Upregulation of the receptor for advanced glycation end products (RAGE) has been proposed as a pathophysiological mechanism underlying the development of atrial fibrillation (AF). We sought to investigate if soluble RAGE levels are associated with AF in Caucasian patients.

Methods

Patients (n = 587) were prospectively recruited and serum levels of soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) measured. The patients included 527 with sinus rhythm, 32 with persistent AF (duration >7 days, n = 32) and 28 with paroxysmal AF (duration <7 days, n = 28).

Results

Patients with AF were older and had a greater prevalence of heart failure than patients in sinus rhythm. Circulating RAGE levels were higher in patients with persistent AF [median sRAGE 1190 (724–2041) pg/ml and median esRAGE 452 (288–932) pg/ml] compared with paroxysmal AF [sRAGE 799 (583–1033) pg/ml and esRAGE 279 (201–433) pg/ml, p ≤ 0.01] or sinus rhythm [sRAGE 782 (576–1039) pg/ml and esRAGE 289 (192–412) pg/ml, p < 0.001]. In multivariable logistic regression analysis, independent predictors of persistent AF were age, heart failure, sRAGE [odds ratio 1.1 per 100 pg/ml, 95% confidence interval (CI) 1.0–1.1, p = 0.001] and esRAGE [odds ratio 1.3 per 100 pg/ml, 95% CI 1.1–1.4, p < 0.001]. Heart failure and age were the only independent predictors of paroxysmal AF. In AF patients, sRAGE [odds ratio 1.1 per 100 pg/ml, 95% CI 1.1–1.2, p = 0.007] and esRAGE [odds ratio 1.3 per 100 pg/ml, 95% CI 1.0–1.5, p = 0.017] independently predicted persistent compared with paroxysmal AF.

Conclusions

Soluble RAGE is elevated in Caucasian patients with AF, and both sRAGE and esRAGE predict the presence of persistent AF.

Regulation of Receptor for Advanced Glycation End Products (RAGE) Ectodomain Shedding and Its Role in Cell Function

The receptor for advanced glycation end products (RAGE) is a multiligand transmembrane receptor that can undergo proteolysis at the cell surface to release a soluble ectodomain. Here we observed that ectodomain shedding of RAGE is critical for its role in regulating signaling and cellular function. Ectodomain shedding of both human and mouse RAGE was dependent on ADAM10 activity and induced with chemical activators of shedding (ionomycin, phorbol 12-myristate 13-acetate, and 4-aminophenylmercuric acetate) and endogenous stimuli (serum and RAGE ligands). Ectopic expression of the splice variant of RAGE (RAGE splice variant 4), which is resistant to ectodomain shedding, inhibited RAGE ligand dependent cell signaling, actin cytoskeleton reorganization, cell spreading, and cell migration. We found that blockade of RAGE ligand signaling with soluble RAGE or inhibitors of MAPK or PI3K blocked RAGE-dependent cell migration but did not affect RAGE splice variant 4 cell migration. We finally demonstrated that RAGE function is dependent on secretase activity as ADAM10 and γ-secretase inhibitors blocked RAGE ligand-mediated cell migration. Together, our data suggest that proteolysis of RAGE is critical to mediate signaling and cell function and may therefore emerge as a novel therapeutic target for RAGE-dependent disease states.

Blood and CSF biomarkers in brain subcortical ischemic vascular disease: Involved pathways and clinical applicability

Vascular dementia is the second most common type of dementia after Alzheimer’s disease (AD). Subcortical ischemic vascular disease refers to a form of vascular cognitive impairment characterized by the presence of diffuse white matter hyperintensities (WMHs) and multiple lacunar infarcts. These neuroimaging findings are mainly caused by cerebral small-vessel disease (cSVD) and relate to aging and cognitive impairment, but they can also be silent and highly prevalent in otherwise healthy individuals. We aimed to review studies on blood and cerebrospinal fluid (CSF) markers related to the presence of WMHs and lacunar infarcts that have been conducted in the past in large population-based studies and in high-risk selected patients (such as those with vascular risk factors, vascular cognitive impairment, or AD). Relevant associations with the presence and progression of cSVD have been described in the blood for markers related to inflammatory processes, endothelial damage and coagulation/fibrinolysis processes, etc. Also, different combinations of CSF markers might help to differentiate between etiologic types of dementia. In the future, to translate these findings into clinical practice and use biomarkers to early diagnosis and monitoring vascular cognitive impairment would require the replication of candidate markers in large-scale, multicenter, and prospectively designed studies.

Soluble Receptor for Advanced Glycation End Product: A Biomarker for Acute Coronary Syndrome

The receptor of advanced glycation end products (RAGE) and its ligands are linked to the pathogenesis of coronary artery disease (CAD), and circulating soluble receptor of advanced glycation end products (sRAGE), reflecting the RAGE activity, is suggested as a potential biomarker. Elevated sRAGE levels are reported in relation to acute ischemia and this review focuses on the role of sRAGE as a biomarker for the acute coronary syndrome (ACS). The current studies demonstrated that sRAGE levels are elevated in relation to ACS, however during a very narrow time period, indicating that the time of sampling needs attention. Interestingly, activation of RAGE may influence the pathogenesis and reflection in sRAGE levels in acute and stable CAD differently.

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.

Emerging Targets for Therapeutic Development in Diabetes and Its Complications: The RAGE Signaling Pathway

Types 1 and 2 diabetes are on the rise worldwide. Although the treatment of hyperglycemia has benefited from recent advances, aggressive efforts to maintain euglycemia may be fraught with risk, especially in older subjects or in subjects vulnerable to hypoglycemic unawareness. Hence, strategies to prevent and treat the complications of hyperglycemia are essential. In this review we summarize recent updates on the biology of the receptor for advanced glycation endproducts (RAGE) in the pathogenesis of both micro- and macrovascular complications of diabetes, insights from the study of mouse models of obesity and diabetic complications, and from associative studies in human subjects. The study of the mechanisms and consequences of the interaction of the RAGE cytoplasmic domain with the formin, mDia1, in RAGE signal transduction, will be discussed. Lastly, we review the "state-of-the-art" on RAGE-directed therapeutics. Tackling RAGE/mDia1 may identify a novel class of therapeutics preventing diabetes and its complications.

Genetics of Plasma Soluble Receptor for Advanced Glycation End-Products and Cardiovascular Outcomes in a Community-based Population: Results from the Atherosclerosis Risk in Communities Study

Plasma soluble Receptor for Advanced Glycation End-products (sRAGE) is a strong marker of vascular outcomes although evidence on the direction of association is mixed. Compared to whites, blacks have lower levels of sRAGE. We hypothesized that genetic determinants of sRAGE would help clarify the causal role of sRAGE and the black-white difference in sRAGE levels. We conducted a genome-wide analysis of sRAGE in whites and blacks from the Atherosclerosis Risk in Communities Study. Median plasma sRAGE levels were lower in blacks than whites (728 vs. 1067 pg/ml; P<0.0001). The T (vs. C) allele of rs2070600, a missense variant in AGER, the gene encoding RAGE, was associated with approximately 50% lower sRAGE levels in both whites (N = 1,737; P = 7.26x10^-16; minor allele frequency (MAF) = 0.04) and blacks (N = 581; P = 0.02; MAF = 0.01). In blacks, the T (vs. C) allele of rs2071288, intronic to AGER, was associated with 43% lower sRAGE levels (P = 2.22x10^-8; MAF = 0.10) and was nearly absent in whites. These AGER SNPs explained 21.5% and 26% of the variation in sRAGE in blacks and whites, respectively, but did not explain the black-white difference in sRAGE. These SNPs were not significantly associated with incident death, coronary heart disease, diabetes, heart failure, or chronic kidney disease in whites (N = 8,130–9,017) or blacks (N = 2,293–2,871) (median follow up ~20 years). We identified strong genetic determinants of sRAGE that did not explain the large black-white difference in sRAGE levels or clearly influence risk of clinical outcomes, suggesting that sRAGE may not be a causal factor in development of these outcomes.

Role of Advanced Glycation End Products and Its Receptors in the Pathogenesis of Cigarette Smoke-Induced Cardiovascular Disease

The interaction of advanced glycation end products (AGEs) with its cell-bound receptor RAGE increases gene expression and release of proinflammatory cytokines and increase generation of reactive oxygen species (ROS). Circulating receptors, soluble RAGE (sRAGE), and endosecretory RAGE (esRAGE) by binding with RAGE ligands have protective effects against AGE-RAGE interaction. Cigarette smoking is a risk factor for coronary artery disease, stroke, and peripheral vascular disease. This article reviews; if the AGE-RAGE axis is involved in the cigarette smoke-induced cardiovascular diseases. There are various sources of AGEs in smokers including, gas/tar of cigarette, activation of macrophages and polymorphonuclear leukocytes, uncoupling of endothelial isoform of nitric oxide synthase (eNOS) and xanthine oxidase. The levels of AGEs are elevated in smokers. Serum levels of sRAGE have been reported to be reduced, elevated, or unchanged in smokers. Mostly the levels are reduced. There is one article which shows an elevation of levels of sRAGE in smokers. Serum levels of esRAGE are unaltered in smokers. Mechanism of AGE-RAGE-induced atherosclerosis has been discussed. Atherosclerosis leads to the cardiovascular diseases. It has been suggested that ratio of AGE/sRAGE or AGE/esRAGE is useful in determining the deleterious effects of AGE-RAGE interaction in smokers. sRAGE alone is not a good marker for smoke-induced cardiovascular disease. In conclusion cigarette smoke induces formation of AGEs and reduces sRAGE resulting in the development of atherosclerosis and related coronary heart disease, stroke, and peripheral vascular disease. Ratio of AGEs/sRAGE is a better marker for cardiovascular disease than AGEs or sRAGE alone in smokers.

Altered serum glyceraldehyde-derived advanced glycation end product (AGE) and soluble AGE receptor levels indicate carbonyl stress in patients with schizophrenia

Recent cross-sectional and longitudinal studies indicate that measurements of peripheral blood carbonyl stress markers such as the advanced glycation end product (AGE) pentosidine and the reactive carbonyl-detoxifying B6 vitamin pyridoxal could be used as therapeutic biological markers in subpopulations of schizophrenia patients. Glyceraldehyde-derived AGEs (Glycer-AGE) have strong neurotoxicity, and soluble receptors for AGEs (sRAGE) may ameliorate the effects of AGEs. In the present study, we measured Glycer-AGEs and sRAGE levels to determine their potential as diagnostic, therapeutic, or clinical biological markers in patients with schizophrenia. After enrollment of 61 admitted Japanese patients with acute schizophrenia and 39 healthy volunteers, 54 patients were followed up from the acute stage to remission. Serum biomarkers were measured in blood samples taken before breakfast using competitive enzyme-linked immunosorbent assays, and Glycer-AGEs were significantly higher and sRAGE levels were significantly lower in patients with acute schizophrenia than in healthy controls. Glycer-AGEs/sRAGE ratios were also higher in schizophrenia patients and were stable during the clinical course. Furthermore, discriminant analyses confirmed that Glycer-AGEs and Glycer-AGEs/sRAGE ratios are significant diagnostic markers for schizophrenia, and distinguished between patients and healthy controls in 70.0% of cases. However, these markers of carbonyl stress were not correlated with clinical features, including disease severity, or with daily chlorpromazine doses. These data indicate the potential of Glycer-AGEs, RAGEs, and their relative ratios as diagnostic markers for patients with schizophrenia.

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.

Serum levels of soluble receptor for advanced glycation end-products and metabolic syndrome: the Northern Manhattan Study

OBJECTIVE

Recent studies have shown a strong link between serum soluble receptor for advanced glycation end-products (sRAGE) levels and cardiovascular risk factors and disease. What is less clear is the relationship between metabolic risk factors and sRAGE levels. Here, we tested the hypothesis that lower sRAGE levels may be associated with the metabolic syndrome (MetS) in an urban multi ethnic population.

MATERIALS/METHODS

From the Northern Manhattan Study (NOMAS), we included 1101 stroke-free participants (mean age: 71 ± 9 years, 60% women, 64% Hispanic, 18% black, 16% white). Serum sRAGE was measured by ELISA. Quantile regression analysis was performed to evaluate the association between sRAGE and MetS components and MetS, after adjusting for sociodemographics, smoking status and kidney function.

RESULTS

The median (interquartile) sRAGE was 899 pg/ml (647-1248 pg/ml), 42% had metabolic syndrome. The prevalence of unfavorable metabolic factors was 50% for waist circumference (WC), 81% for blood pressure, 39% for fasting glucose, 35% for reduced high density lipoproteins (HDL), and 23% for triglycerides. After adjustment, the median sRAGE levels were at least 120 pg/ml lower in those who had elevated WC (p<0.0001), blood pressure (p=0.0014), and fasting glucose (p<0.0001), and those who had 2 or more unfavorable metabolic factors. No relationship was seen between sRAGE levels and elevated triglycerides or reduced HDL levels. Interaction and stratified analyses revealed that the association of sRAGE with MetS was more prominent in Hispanics compared to whites, and displaying no association with components of MetS in blacks.

CONCLUSIONS

sRAGE levels were mainly associated with MetS factors related to obesity, diabetes and hypertension, and displayed variation with ethnicity in a multi-ethnic population. Further studies of sRAGE, MetS and their relationship to cardiovascular disease are warranted.

Association of plasma levels of soluble receptor for advanced glycation end products and risk of kidney disease: the Atherosclerosis Risk in Communities study

BACKGROUND

Advanced glycation end products and their cell-bound receptors are thought to mediate the adverse effects of vascular disease through oxidative stress, inflammation and endothelial dysfunction. We examined the association between the soluble form of receptor for advanced glycation end products (sRAGE) and kidney disease.

METHODS

In this case-cohort study nested within the Atherosclerosis Risk in Communities (ARIC) study, baseline sRAGE levels were measured in a cohort random sample of participants without kidney disease (n= 1218), and among participants who developed incident chronic kidney disease (CKD) [estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2) and ≥25% eGFR decline, n = 151] and end-stage renal disease (ESRD) [entry in the US Renal Data System (USRDS) registry, n = 152].

RESULTS

Baseline sRAGE levels were inversely related to baseline eGFR (r = -0.13). After adjusting for age, sex and race, one interquartile range higher log10-transformed sRAGE was associated with development of CKD [odds ratio: 1.39; 95% confidence interval (95% CI) 1.06-1.83; P = 0.02] and ESRD (hazard ratio: 1.97; 95% CI 1.47-2.64; P < 0.001). These associations were not significant after eGFR adjustment.

CONCLUSIONS

High sRAGE levels are associated with incident CKD and ESRD risk, but not after adjustment for kidney function at baseline. Future studies are needed to investigate specific mechanisms underlying the association of sRAGE with kidney disease risk.

Plasma advanced glycation end products (AGEs), receptors for AGEs and their correlation with inflammatory markers in middle school-age children

AIM

Advanced glycation end products (AGEs) and/or their receptors (RAGE) are significantly positively correlated with adiposity, inflammation, dyslipidemia, and insulin resistance in adults. However, the relationships between AGEs, RAGE, and adiposity-related comorbidites in children have not been well studied.

METHODS

In a cross-sectional study of 88 children (age 11-15 years) from the New York area enrolled in the Reduce Obesity and Diabetes (ROAD) study, we examined the correlation of the AGE N(ε)-(carboxymethyl)lysine (CML), soluble RAGE (sRAGE), and endogenous secretory RAGE (esRAGE) with adiposity, inflammatory markers [interleukin-6 (IL-6), C-reactive protein, tumor necrosis factor-α], adiponectin, lipids, insulin sensitivity, and insulin secretory capacity.

RESULTS

Pediatric CML levels were ~20% below average adult levels. CML was significantly (p < 0.05) positively correlated with age and insulin sensitivity and negatively with adiposity, dyslipidemia and IL-6. sRAGE correlated positively with esRAGE and negatively with adiposity and IL-6. Both sRAGE and esRAGE correlated negatively with insulin secretory capacity.

CONCLUSION

Our findings suggest that unlike adults, CML is negatively associated with adiposity and adiposity-related comorbidity risk in children. As in adults, sRAGE and esRAGE were, to varying degrees, negatively correlated with body fatness and risk factors for adiposity-related comorbidities.

Sleep duration is associated with white matter hyperintensity volume in older adults: the Northern Manhattan Study

Self-reports of long or short sleep durations have indicated an association with cardiovascular morbidity and mortality, but there are limited data evaluating their association with white matter hyperintensity volume (WMHV), a marker of cerebral small vessel disease. We conducted a cross-sectional analysis of self-reported sleep duration to test for a correlation with white matter hyperintensities, measured by quantitative magnetic resonance imaging (MRI), in the Northern Manhattan Study. We used multivariable linear regression models to assess associations between both short (<6 h) and long (≥9 h) sleep durations and log-transformed WMHV, adjusting for demographic, behavioural and vascular risk factors. A total of 1244 participants, mean age 70 ± 9 years, 61% women and 68% Hispanics were analysed with magnetic resonance brain imaging and self-reported sleep duration. Short sleep was reported by 23% (n = 293) and long sleep by 10% (n = 121) of the sample. Long sleep (β = 0.178; P = 0.035), but not short sleep (β = -0.053; P = 0.357), was associated with greater log-WMHV in fully adjusted models. We observed an interaction between sleep duration, diabetes mellitus and log-WMHV (P = 0.07). In fully adjusted models, stratified analysis showed that long sleep duration was associated with greater WMHV only in those with diabetes (β = 0.78; P = 0.0314), but not in those without diabetes (β = 0.022; P = 0.2), whereas short sleep was not associated with white matter hyperintensities in those with or without diabetes. In conclusion, long sleep duration was associated with a greater burden of white matter lesions in this stroke-free urban sample. The association was seen mainly among those with diabetes mellitus.

Low levels of serum soluble receptors for advanced glycation end products, biomarkers for disease state: myth or reality

Advanced glycation end products (AGEs) interact with the receptor for AGEs (RAGE) on the membrane and induce deleterious effects via activation of nuclear factor kappa-B, and increased oxidative stress and inflammatory mediators. AGEs also combine with circulating soluble receptors (endogenous secretory RAGE [esRAGE] and soluble receptor for RAGE [sRAGE]) and sequester RAGE ligands and act as a cytoprotective agent. esRAGE is secreted from the cells and is a spliced variant of RAGE. The sRAGE on the other hand is proteolytically cleaved from cell surface receptor via matrix metalloproteinase (MMPs). sRAGE is elevated in type 1 and type 2 diabetes and in patients with decreased renal function. Serum levels of sRAGE are reduced in diseases including coronary artery disease, atherosclerosis, essential hypertension, chronic obstructive lung disease, heart failure, and hypercholesterolemia. Serum levels of AGEs are elevated in patients with coronary artery disease and atherosclerosis. However, the increases in serum AGEs are very high in patients with diabetes and renal disease. There is a positive correlation between serum levels of AGEs and RAGE and sRAGE. The elevated levels of sRAGE in patients with diabetes and impaired renal function may be due to increased levels of MMPs. AGEs increase in the expression and production of MMPs, which would increase the cleavage of sRAGE from cell surface. In conclusion, low level of serum sRAGE is a good biomarker for disease other than diabetes and renal disease. A unified formula that takes into consideration of AGEs, sRAGE, and esRAGE such as AGE/sRAGE or AGEs/esRAGE would be better biomarker than sRAGE or esRAGE for all AGE-RAGE-associated diseases including diabetes and renal disease.

Total soluble and endogenous secretory receptor for advanced glycation endproducts (RAGE) in IBD

BACKGROUND AND AIMS

Recruitment and activation of neutrophils, with release of specific proteins such as S100 proteins, is a feature of inflammatory bowel disease (IBD). Soluble forms of the receptor for advanced glycation endproducts (sRAGE), and variants such as endogenous secretory (esRAGE), can act as decoy receptors by binding ligands, including S100A12. The aims of this study were to determine total sRAGE and esRAGE concentrations in patients with IBD and correlate these with C-reactive protein (CRP), endoscopic scores and clinical disease activity scores.

METHODS

EDTA-plasma was collected from patients undergoing colonoscopy including those with Crohn's disease (CD: n=125), ulcerative colitis (UC: n=79) and control patients without endoscopic signs of inflammation (non-IBD: n=156). Concentrations of sRAGE and esRAGE were determined by enzyme-linked immunosorbent assay and plasma CRP concentrations measured. Standard clinical disease activity and endoscopic severity scores were defined for all subjects.

RESULTS

Plasma sRAGE concentrations were lower in UC (but not CD) than non-IBD subjects (p<0.01). Whilst sRAGE concentrations correlated negatively with endoscopic activity in UC (p<0.05), this was not seen in CD. In contrast, esRAGE correlated negatively with disease activity in both UC (p=0.002) and CD (p=0.0001). Furthermore, sRAGE and esRAGE concentrations correlated inversely with CRP values (p<0.0001).

CONCLUSIONS

Although total sRAGE varied with activity in UC, esRAGE concentrations correlated inversely with endoscopic disease activity and CRP levels in both UC and CD. Additional studies are required to further define the significance of sRAGE and esRAGE in IBD.

Soluble form of receptor for advanced glycation end-products (sRAGE): do sRAGE ligands or anti-sRAGE auto-antibodies interfere with sRAGE quantification?

Background

The soluble form of the receptor for advanced glycation end-products (sRAGE) has been studied in various diseases. It is not clear why sRAGE levels vary between studies, with controversial results. What also remains to be determined is whether receptor for advanced glycation end-products (RAGE) ligands could affect sRAGE assessment by epitope masking. Recently described anti-sRAGE autoantibodies may play an interfering role. The aim of this study was therefore to investigate the influence of RAGE ligands and anti-sRAGE autoantibodies on sRAGE quantification.

Methods

The RAGE ligands carboxymethyllysine (CML; AGEs with a high affinity for RAGE), S100 proteins, high-mobility group protein B1 (HMGB1) and β-amyloid peptide (aβ) were tested by enzyme-linked immunosorbent assay (ELISA) with recombinant sRAGE (rHu-sRAGE) or serum from healthy controls. Using ELISA, anti-sRAGE autoantibodies (IgGs) were identified in haemodialysis (HD) patients, then purified and incubated with rHu-sRAGE or serum to investigate their effects on sRAGE levels.

Results

RAGE ligands, either alone at three different concentrations (CML was also tested at different glycation levels) or a mixture of all these ligands, did not affect sRAGE levels when incubated with rHu-sRAGE or control serum. Compared with healthy controls, HD patients had higher levels of sRAGE ( P < 0.001) and anti-sRAGE IgGs ( P < 0.05). However, incubation of rHu-sRAGE with purified IgGs from HD patients had no effect on sRAGE quantification.

Conclusions

RAGE ligands or anti-sRAGE autoantibodies did not interfere with sRAGE quantification. Further studies are required to elucidate the variability in sRAGE levels reported in the literature and to define the potential of sRAGE for use as a reliable biomarker.

Statins stimulate the production of a soluble form of the receptor for advanced glycation end products

The beneficial effects of statin therapy in the reduction of cardiovascular pathogenesis, atherosclerosis, and diabetic complications are well known. The receptor for advanced glycation end products (RAGE) plays an important role in the progression of these diseases. In contrast, soluble forms of RAGE act as decoys for RAGE ligands and may prevent the development of RAGE-mediated disorders. Soluble forms of RAGE are either produced by alternative splicing [endogenous secretory RAGE (esRAGE)] or by proteolytic shedding mediated by metalloproteinases [shed RAGE (sRAGE)]. Therefore we analyzed whether statins influence the production of soluble RAGE. Lovastatin treatment of either mouse alveolar epithelial cells endogenously expressing RAGE or HEK cells overexpressing RAGE caused induction of RAGE shedding, but did not influence secretion of esRAGE from HEK cells overexpressing esRAGE. Lovastatin-induced secretion of sRAGE was also evident after restoration of the isoprenylation pathway, demonstrating a correlation of sterol biosynthesis and activation of RAGE shedding. Lovastatin-stimulated induction of RAGE shedding was completely abolished by a metalloproteinase ADAM10 inhibitor. We also demonstrate that statins stimulate RAGE shedding at low physiologically relevant concentrations. Our results show that statins, due to their cholesterol-lowering effects, increase the soluble RAGE level by inducing RAGE shedding, and by doing this, might prevent the development of RAGE-mediated pathogenesis.

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.

sRAGE and risk of diabetes, cardiovascular disease, and death

Advanced glycation end products (AGEs) and their receptors are strongly implicated in the development of diabetes complications. When stimulated by AGEs, the receptors for AGEs (RAGEs) induce inflammation and are thought to fuel disease progression. Soluble circulating RAGE (sRAGE) may counteract the detrimental effects of RAGE. We measured sRAGE in stored plasma from a random sample of 1,201 participants in the Atherosclerosis Risk in Communities (ARIC) Study who were aged 47-68 years, had normal kidney function, and had no history of cardiovascular disease. In cross-sectional analyses, black race, male sex, higher BMI, and higher C-reactive protein were independently associated with low sRAGE. The racial difference was striking, with blacks approximately three times more likely to have low sRAGE compared with whites even after adjustment. During ~18 years of follow-up, there were 192 incident coronary heart disease events, 53 ischemic strokes, 213 deaths, and 253 cases of diabetes (among the 1,057 persons without diabetes at baseline). In multivariable Cox models comparing risk in the first quartile with that in the fourth quartile of baseline sRAGE, low levels of sRAGE were significantly associated with risk of diabetes (hazard ratio 1.64 [95% CI 1.10-2.44]), coronary heart disease (1.82 [1.17-2.84]), and mortality (1.72 [1.11-2.64]) but not ischemic stroke (0.78 [0.34-1.79]). In conclusion, we found that low levels of sRAGE were a marker of future chronic disease risk and mortality in the community and may represent an inflammatory state. Racial differences in sRAGE deserve further examination.

Circulating soluble RAGE as a predictive biomarker of cardiovascular event risk in patients with type 2 diabetes

It is still controversial whether circulating soluble form of receptor for AGE (sRAGE) is associated with atherosclerosis in diabetic patients. In this study, we enrolled 276 Japanese type 2 diabetic subjects without history of cardiovascular disease (CVD), assessed their baseline clinical and biochemical data including serum sRAGE levels, and prospectively evaluated the association between these parameters and CVD events. The median follow-up period was 5.6 years and there were 25 new CVD events. The tertile analysis showed that the risk for CVD events was higher as serum sRAGE levels were increased (p for trend = 0.046). A multivariate Cox proportional hazards regression analysis revealed that serum sRAGE levels were independently associated with CVD (HR per 1SD = 1.59, 95% CI 1.04-2.45, p = 0.034), even after adjusting for conventional coronary risk factors. In summary, elevated sRAGE levels were associated with the increased risk of CVD in Japanese type 2 diabetic subjects.

Clinically asymptomatic vascular brain injury: a potent cause of cognitive impairment among older individuals

Cerebrovascular risk factors and stroke are highly prevalent with advancing age, and stroke may be more common than Alzheimer's disease, particularly among older men. While stroke mortality continues to decline, the prevalence of individuals with various vascular risk factors continues to rise and many are undiagnosed or undertreated. Asymptomatic cerebrovascular brain injury that includes asymptomatic brain infarction and white matter hyperintensities as well as accelerated brain atrophy is even more frequent than clinical stroke. Moreover, the impact of cerebrovascular risk factors on brain injury appears to begin in middle life and additively increases the likelihood of later life dementia. This review focuses on the use of neuroimaging and genetics to understand the impact of asymptomatic vascular risk factors on the trajectories of cognitive aging as well as incident cognitive impairment, stroke, and mortality. Results of this review emphasize the need for early detection and treatment of vascular risk factors to improve the cognitive health of our rapidly aging population.

Genetic variation in the receptor for advanced glycation end-products (RAGE) gene and ischaemic stroke

BACKGROUND AND PURPOSE

The multi-ligand receptor for advanced glycation end-products (RAGE, alias AGER) is suggested to contribute to the pathogenesis of vascular disease, but its potential role in stroke is unclear. The aim of this study was to investigate whether genetic variation in RAGE gene is associated with ischaemic stroke (IS).

METHODS

The Sahlgrenska Academy Study on Ischaemic Stroke comprises 844 Caucasian patients with first ever (n = 732) and recurrent (n = 112) IS, and 668 Caucasian controls. Three tagSNPs were selected to capture genetic variation in the RAGE gene. IS subtypes were determined using TOAST criteria.

RESULTS

One SNP, rs1035798, showed significant association with the subtype of small-vessel disease (SVD) after correction for multiple testing (OR 1.56, 95% CI 1.16-2.09), adjusted P-value < 0.05). This association was independent of hypertension, diabetes and smoking. None of the SNPs was associated with overall IS.

CONCLUSION

In this sample of patients with IS, genetic variation in RAGE is associated with the IS subtype SVD, but not overall IS.

The soluble form of the receptor of advanced glycation endproducts increases after bariatric surgery in morbid obesity

OBJECTIVE

The increased cardiovascular (CV) disease risk in patients with morbid obesity (MO) cannot be fully explained by traditional CV risk factors. Activation of the receptor of Advanced Glycation Endproducts (RAGE) leads to inflammation via the NF κβ (nuclear factor κβ) pathway. The soluble form of RAGE (sRAGE), which is present in plasma, can bind to ligands of RAGE and avoids interaction of RAGE with proinflammatory ligands. We investigated sRAGE levels in patients with MO and compared them with healthy lean controls (CO), before and after bariatric surgery.

DESIGN

We conducted a cross-sectional study and a 24-month longitudinal study.

SUBJECTS

We included 85 patients (mean age: 41 ± 12 years; mean body mass index (BMI): 45.4 ± 7.9 kg m(-2)) with MO in comparison with 40 CO (mean age: 42 ± 13 years; mean BMI: 26.0 ± 5.5 kg m(-2)). All patients were investigated before and 2 years after bariatric surgery. Apart from weight and CV risk markers (blood pressure, lipids), a glucose tolerance test (75 g), renal and inflammation parameters were assessed. sRAGE levels were assessed by a commercial ELISA. To investigate the associations of the observed reductions of values, delta (Δ) of parameters were calculated.

RESULTS

Patients with MO had significant lower sRAGE levels than CO: 1010 ± 514 vs 1501 ± 674 pg ml(-1); P<0.001. In the longitudinal study, sRAGE levels increased significantly after bariatric surgery from 1010 ± 514 to 1261 ± 710 pg ml(-1); P=0.008. In the correlation analysis, ΔsRAGE levels were associated with Δ1-h and Δ2-h postprandial glucose, Δfasting insulin, Δ2-h postprandial insulin, ΔHOMA (homeostatic model assessment)-insulin resistance (ΔHOMA-IR), Δγ-glutamyl transferase and Δtriglycerides. In a multivariate model, Δ1-h and Δ2-h postprandial glucose, Δ2-h postprandial insulin and ΔHOMA-IR predicted ΔsRAGE.

CONCLUSION

Patients with MO have significantly lower sRAGE levels compared with non-obese CO, but sRAGE levels increase significantly after weight loss induced by bariatric surgery. As high sRAGE levels inhibit the activation of inflammatory pathways, our results might help understand the beneficial effects of bariatric surgery regarding CV morbidity and mortality.

Serum levels of soluble receptor for advanced glycation endproducts (sRAGE) are higher in ulcerative colitis and correlate with disease activity

Interaction of the receptor for advanced glycation endproducts (RAGE) with its ligands results in expression of inflammatory mediators, activation of NF-κB, and induction of oxidative stress, all of which have been implicated in the pathogenesis of inflammatory bowel diseases (IBD). Soluble receptor for advanced glycation endproducts (sRAGE) has recently emerged as a reliable biomarker of inflammation in numerous RAGE-mediated disorders.

OBJECTIVE

To assess sRAGE levels in adult patients with IBD.

METHOD

Serum was collected from adult patients with Crohn's disease (CD, 56 patients), ulcerative colitis (UC, 60 patients), and healthy controls (HC, 113 subjects). Levels of sRAGE were determined by enzyme-linked immunosorbent assay.

RESULTS

Serum sRAGE levels were elevated in IBD compared to HC and were higher in UC patients compared to CD and HC. Levels of sRAGE were significantly higher in the serum of UC patients with active disease compared to patients with inactive disease, but no association with the Montreal Classification was evident. Serum sRAGE was lower in CD patients with biological therapies.

CONCLUSIONS

These findings suggest that serum levels of sRAGE are altered in patients with intestinal inflammation and may reflect distinct immunoinflammatory pathogenesis of UC and CD.