Soluble receptors for advanced glycation end-products prevent unilateral ureteral obstruction-induced renal fibrosis

Introduction: The receptor for advanced glycation end products (RAGE) and its ligands, such as high-mobility group protein box 1 (HMGB1), play an important role in the accumulation of extracellular matrix in chronic kidney diseases with tubulointerstitial fibrosis. Blocking RAGE signaling with soluble RAGE (sRAGE) is a therapeutic candidate for renal fibrosis. Methods: NRK-52E cells were stimulated with or without HMGB1 and incubated with sRAGE in vitro. Sprague-Dawley rats were intraperitoneally treated with sRAGE after unilateral ureteral obstruction (UUO) operation in vivo. Results: HMBG1-stimulated NRK-52E cells showed increased fibronectin expression, type I collagen, α-smooth muscle actin, and connective tissue growth factor, which were attenuated by sRAGE. The mitogen-activated protein kinase (MAPK) pathway and nuclear translocation of nuclear factor kappa B (NF-κB) were enhanced in NRK-52E cells exposed to HMBG1, and sRAGE treatment alleviated the activation of the MAPK and NF-κB pathways. In the UUO rat models, sRAGE significantly ameliorated the increased renal fibronectin, type I collagen, and α-smooth muscle actin expressions. Masson's trichrome staining confirmed the anti-fibrotic effect of sRAGE in the UUO rat model. RAGE also significantly attenuated the activation of the MAPK pathway and NF-κB, as well as the increased number of infiltrated macrophages within the tubulointerstitium in the kidney of the UUO rat models. Conclusion: These findings suggest that RAGE plays a pivotal role in the pathogenesis of renal fibrosis and that its inhibition by sRAGE may be a potential therapeutic approach for renal fibrosis.

RAGE Inhibitors in Neurodegenerative Diseases

Nonenzymatic reactions of reducing sugars with primary amino groups of amino acids, proteins, and nucleic acids, followed by oxidative degradations would lead to the formation of advanced glycation endproducts (AGEs). The AGEs exert multifactorial effects on cell damage leading to the onset of neurological disorders. The interaction of AGEs with the receptors for advanced glycation endproducts (RAGE) contribute to the activation of intracellular signaling and the expression of the pro-inflammatory transcription factors and various inflammatory cytokines. This inflammatory signaling cascade is associated with various neurological diseases, including Alzheimer's disease (AD), secondary effects of traumatic brain injury (TBI), amyotrophic lateral sclerosis (ALS), and diabetic neuropathy, and other AGE-related diseases, including diabetes and atherosclerosis. Furthermore, the imbalance of gut microbiota and intestinal inflammation are also associated with endothelial dysfunction, disrupted blood-brain barrier (BBB) and thereby the onset and progression of AD and other neurological diseases. AGEs and RAGE play an important role in altering the gut microbiota composition and thereby increase the gut permeability and affect the modulation of the immune-related cytokines. The inhibition of the AGE-RAGE interactions, through small molecule-based therapeutics, prevents the inflammatory cascade of events associated with AGE-RAGE interactions, and thereby attenuates the disease progression. Some of the RAGE antagonists, such as Azeliragon, are currently in clinical development for treating neurological diseases, including AD, although currently there have been no FDA-approved therapeutics based on the RAGE antagonists. This review outlines the AGE-RAGE interactions as a leading cause of the onset of neurological diseases and the current efforts on developing therapeutics for neurological diseases based on the RAGE antagonists.

A Study on the Protective Effect of sRAGE-MSCs in a Rodent Reperfusion Model of Myocardial Infarction

Acute myocardial infarction (AMI) is one of the major leading causes of death in humans globally. Recently, increased levels of recruited macrophages and AGE-albumin were observed in the hearts of humans and animals with acute myocardial infarction. Thus, the purposes of this study were to investigate whether the elevated levels of AGE-albumin from activated macrophage cells are implicated in ischemia-induced cardiomyocyte death and to develop therapeutic strategies for AMI based on its underlying molecular mechanisms with respect to AGEs. The present study demonstrated that activated macrophages and AGE-albumin were observed in heart tissues obtained from humans and rats with AMI incidences. In the cellular model of AMI, it was found that increased expression of AGE-albumin was shown to be co-localized with macrophages, and the presence of AGE-albumin led to increased expression of RAGE through the mitogen-activated protein kinase pathway. After revealing cardiomyocyte apoptosis induced by toxicity of the AGE-RAGE system, sRAGE-secreting MSCs were generated using the CRISPR/Cas9 platform to investigate the therapeutic effects of sRAGE-MSCs in an AMI rat model. Gene-edited sRAGE-MSCs showed greater therapeutic effects against AMI pathogenesis in rat models compared to mock MSCs, and promising results of the functional improvement of stem cells could result in significant improvements in the clinical management of cardiovascular diseases.

Reduced Circulating Soluble Receptor for Advanced Glycation End-products in Chronic Hepatitis B Are Associated with Hepatic Necroinflammation

The diagnosis and disease management of chronic hepatitis B (CHB) remain challenging due to the elusive assessment of disease severity. Recently, soluble receptor for advanced glycation end-products (sRAGE) has been implicated in the inflammatory-immune response initiated by liver injury. Nonetheless, its natural behavior and clinical importance in CHB remain elusive. One hundred and twenty CHB patients and forty healthy controls (HCs) were enrolled, and the serum sRAGE as well as RAGE expression in biopsy specimens from these subjects was analyzed, and correlation of sRAGE with clinical features as well as its potential predictive value for monitoring the CHB was also evaluated. Reduced serum sRAGE levels and decreased tissular RAGE expression were observed in CHB patients. sRAGE and RAGE were inversely correlated with gradually increased grades of hepatic necroinflammation as well as the routine indicator ALT. Furthermore, receiver operating characteristic (ROC) analysis showed that combination of ALT and sRAGE exerted better predictive power (area under the ROC curve (AUC) of 0.86) for hepatic necroinflammation than that of ALT (AUC of 0.82), sRAGE (AUC of 0.81), or sRAGE-to-ALT ratio (sRAGE/ALT) (AUC of 0.85) alone. More importantly, circulating sRAGE alone exerted valuable predictive power for hepatic moderate-to-severe necroinflammation in CHB patients but with normal ALT (AUC of 0.81) or minimally elevated ALT (AUC of 0.85). In conclusion, reduced serum sRAGE levels may imply an increased severity for necroinflammation, and it may serve as a potential alternative biomarker for monitoring hepatic necroinflammation in CHB.

Plasma advanced glycation end products and soluble receptor for advanced glycation end products as indicators of sterol content in human carotid atherosclerotic plaques

Advanced glycation end products (AGEs) are independently related to cardiovascular disease (CVD) and favor cholesterol and oxysterol accumulation in macrophage foam cells. Soluble RAGE (sRAGE) impairs cellular AGE signaling alleviating the deleterious effects of AGE in atherogenesis. The association between plasma AGEs and sRAGE with the content of cholesterol, markers of cholesterol synthesis and absorption, and oxysterols in atherosclerotic plaques was evaluated in subjects undergoing carotid endarterectomy.Plasma and carotid plaques were obtained from symptomatic (n = 23) and asymptomatic subjects (n = 40). Lipids from plaques were extracted and sterols (oxysterols, cholesterol, desmosterol, lathosterol, sitosterol, and campesterol) were determined by using gas chromatography/mass spectrometry. Plasma total AGEs and pentosidine were measured by using fluorimetry and sRAGE by using ELISA.In symptomatic subjects´ atherosclerotic plaques, an increased amount of cholesterol (3x) and oxysterols [7 α-hydroxycholesterol (1.4x); 7 β-hydroxycholesterol (1.2x); 25-hydroxycholesterol (1.3x); 24-hydroxycholesterol (2.7x), and 27-hydroxycholesterol, (1.15x)], with exception to 7 ketocholesterol, were found in comparison to asymptomatic individuals. Plasma total AGEs and pentosidine significantly and positively correlated to sterols accumulated in the atherosclerotic lesion, including cholesterol, desmosterol, campesterol, sitosterol, and oxysterols. On the other hand, sRAGE inversely correlated to total AGEs and pentosidine in plasma, and with major species of oxysterols, cholesterol, and markers of cholesterol synthesis and absorption in the atherosclerotic lesion. In multiple regression analyses, it was observed a significant inverse correlation between sRAGE and 24-hydroxycholesterol and desmosterol, and a positive significant correlation between pentosidine and 24-hydroxycholesterol, 27-hydroxycholesterol, and campesterol.In conclusion, the plasma concentration of AGEs and sRAGE is a tool to predict the accumulation of sterols in atherosclerotic lesions in symptomatic and asymptomatic individuals, helping to prevent and improve the management of acute cardiovascular complications.

Changes in Plasma Soluble Receptor for Advanced Glycation End-Products Are Associated with Survival in Patients with Acute Respiratory Distress Syndrome

The plasma soluble receptor for advanced glycation end-products (sRAGE) is a marker of lung epithelial injury with prognostic value when measured at baseline in acute respiratory distress syndrome (ARDS). However, whether changes in plasma sRAGE could inform prognosis in ARDS remains unknown. In this secondary analysis of the Lung Imaging for Ventilator Setting in ARDS (LIVE) multicenter randomized controlled trial, which evaluated a personalized ventilation strategy tailored to lung morphology, plasma sRAGE was measured upon study entry (baseline) and on days one, two, three, four and six. The association between changes in plasma sRAGE over time and 90-day survival was evaluated. Higher baseline plasma sRAGE (HR per-one log increment, 1.53; 95% CI, 1.16–2.03; p = 0.003) and an increase in sRAGE over time (HR for each one-log increment in plasma sRAGE per time unit, 1.01; 95% CI, 1.01–1.02; p < 10⁻³) were both associated with increased 90-day mortality. Each 100-unit increase in the plasma sRAGE level per unit of time increased the risk of death at day 90 by 1% in joint modeling. Plasma sRAGE increased over time when a strategy of maximal alveolar recruitment was applied in patients with focal ARDS. Current findings suggest that the rate of change in plasma sRAGE over time is associated with 90-day survival and could be helpful as a surrogate outcome in ARDS.

Low Soluble Receptor for Advanced Glycation End Products Precedes and Predicts Cardiometabolic Events in Women With Rheumatoid Arthritis

Background: Cardiovascular disease (CVD) causes premature mortality in rheumatoid arthritis (RA). Levels of soluble (s)RAGE change with aging, hypertension and hypercholesterolemia. We assessed whether sRAGE was associated with increased risk of CVD in RA patients.

Methods: Serum sRAGE was measured in 184 female RA patients and analyzed with respect to CVD risk estimated by the Framingham algorithm (eCVR), metabolic profile and inflammation. Levels of sRAGE in 13 patients with known cardio-metabolic morbidity defined the cut-off for low sRAGE. Prospective 5-year follow-up of new CV and metabolic events was completed.

Results: Low sRAGE was significantly associated with previous history and with new imminent cardiometabolic events in the prospective follow-up of RA patients. In both cases, low sRAGE reflected higher estimation of CVR in those patients. Low sRAGE was attributed to adverse metabolic parameters including high fasting plasma glucose and body fat content rather than inflammation. The association of sRAGE and poor metabolic profile was prominent in patients younger than 50 years.

Conclusions: This study points at low sRAGE as a marker of metabolic failure developed during chronic inflammation. It highlights the importance for monitoring metabolic health in female RA patients for timely prevention of CVD.

Trial registration:ClinicalTrials.gov with ID NCT03449589. Registered 28, February 2018.

AGE-RAGE Stress in the Pathophysiology of Atrial Fibrillation and Its Treatment

Atrial fibrillation (AF) is the most common of cardiac arrhythmias. Mechanisms such as atrial structural remodeling and electrical remodeling have been implicated in the pathogenesis of AF. The data to date suggest that advanced glycation end products (AGEs) and its cell receptor RAGE (receptor for AGE) and soluble receptor (sRAGE) are involved in the pathogenesis of AF. This review focuses on the role of AGE-RAGE axis in the pathogenesis of AF. Interaction of AGE with RAGE generates reactive oxygen species, cytokines, and vascular cell adhesion molecules. sRAGE is a cytoprotective agent. The data show that serum levels of AGE and sRAGE, and expression of RAGE, are elevated in AF patients. Elevated levels of sRAGE did not protect the development of AF. This might be due to greater elevation of AGE than sRAGE. Measurement of AGE-RAGE stress (AGE/sRAGE) would be appropriate as compared with measurement of AGE or RAGE or sRAGE alone in AF patients. AGE and its interaction with RAGE can induce AF through alteration in cellular protein and extracellular matrix. AGE and its interaction with RAGE induce atrial structural and electrical remodeling. The treatment strategy should be directed toward reduction in AGE levels, suppression of RAGE expression, blocking of binding of AGE to RAGE, and elevation of sRAGE and antioxidants. In conclusion, AGE-RAGE axis is involved in the development of AF through atrial structural and electrical remodeling. The treatment modalities for AF should include lowering of AGE, suppression of RAGE, elevation of sRAGE, and use of antioxidants.

AGE-RAGE Stress in the Pathophysiology of Pulmonary Hypertension and its Treatment

Pulmonary hypertension (PH) is a rare and fatal disease characterized by elevation of pulmonary artery pressure ≥ 25 mm Hg. There are five groups of PH: (1) pulmonary artery (PA) hypertension (PAH), (2) PH due to heart diseases, (3) PH associated with lung diseases/hypoxia, (4) PH associated with chronic obstruction of PA, and (5) PH due to unclear and/or multifactorial mechanisms. The pathophysiologic mechanisms of group 1 have been studied in detail; however, those for groups 2 to 5 are not that well known. PH pathology is characterized by smooth muscle cells (SMC) proliferation, muscularization of peripheral PA, accumulation of extracellular matrix (ECM), plexiform lesions, thromboembolism, and recanalization of thrombi. Advanced glycation end products (AGE) and its receptor (RAGE) and soluble RAGE (sRAGE) appear to be involved in the pathogenesis of PH. AGE and its interaction with RAGE induce vascular hypertrophy through proliferation of vascular SMC, accumulation of ECM, and suppression of apoptosis. Reactive oxygen species (ROS) generated by interaction of AGE and RAGE modulates SMC proliferation, attenuate apoptosis, and constricts PA. Increased stiffness in the artery due to vascular hypertrophy, and vasoconstriction due to ROS resulted in PH. The data also suggest that reduction in consumption and formation of AGE, suppression of RAGE expression, blockage of RAGE ligand binding, elevation of sRAGE levels, and antioxidants may be novel therapeutic targets for prevention, regression, and slowing of progression of PH. In conclusion, AGE-RAGE stress may be involved in the pathogenesis of PH and the therapeutic targets should be the AGE-RAGE axis.

Experimental Hyperglycemia Alters Circulating Concentrations and Renal Clearance of Oxidative and Advanced Glycation End Products in Healthy Obese Humans

The purpose of this investigation was to evaluate the effects of experimental hyperglycemia on oxidative damage (OX), advanced glycation end products (AGEs), and the receptor for AGEs (RAGE) through an in vivo approach. Obese subjects (n = 10; 31.2 ± 1.2 kg·m⁻²; 56 ± 3 years) underwent 24 h of hyperglycemic clamp (+5.4 mM above basal), where plasma at basal and after 2 h and 24 h of hyperglycemic challenge were assayed for OX (methionine sulfoxide, MetSO, and aminoadipic acid, AAA) and AGE-free adducts (N^e-carboxymethyllysine, CML; N^e-carboxyethyllysine, CEL; glyoxal hydroimidazolone-1, GH-1; methylglyoxal hydroimidazolone-1, MG-H1; and 3-deoxyglucosone hydroimidazolone, 3DG-H) via liquid chromatography–tandem mass spectrometry (LC–MS/MS). Urine was also analyzed at basal and after 24 h for OX and AGE-free adducts and plasma soluble RAGE (sRAGE) isoforms (endogenous secretory RAGE, esRAGE, and cleaved RAGE, cRAGE), and inflammatory markers were determined via enzyme-linked immunosorbent assay (ELISA). Skeletal muscle tissue collected via biopsy was probed at basal, 2 h, and 24 h for RAGE and OST48 protein expression. Plasma MetSO, AAA, CEL, MG-H1, and G-H1 decreased (−18% to −47%; p < 0.05), while CML increased (72% at 24 h; p < 0.05) and 3DG-H remained unchanged (p > 0.05) with the hyperglycemic challenge. Renal clearance of MetSO, AAA, and G-H1 increased (599% to 1077%; p < 0.05), CML decreased (−30%; p < 0.05), and 3DG-H, CEL, and MG-H1 remained unchanged (p > 0.05). Fractional excretion of MetSO, AAA, CEL, G-H1, and MG-H1 increased (5.8% to 532%; p < 0.05) and CML and 3DG-H remained unchanged (p > 0.05). Muscle RAGE and OST48 expression, plasma sRAGE, IL-1β, IL-1Ra, and TNFα remained unchanged (p > 0.05), while IL-6 increased (159% vs. basal; p > 0.05). These findings suggest that individuals who are obese but otherwise healthy have the capacity to prevent accumulation of OX and AGEs during metabolic stress by increasing fractional excretion and renal clearance.

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.

Role of Receptors for Advanced Glycation End Products and High-Mobility Group Box 1 in the Outcome of Human T Cell Lymphotropic Type 1 Infection

Human T cell lymphotropic type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic viral neuroinflammatory disease, which leads to damage of the central nervous system. Inflammatory responses and mediators are both involved in the pathogenesis of the disease and in determining its outcome. High-Mobility Group Box 1 (HMGB1) is a chromatin-associated nuclear protein acting as a signaling molecule in cells after binding to its receptors. Receptor for advanced glycation end products (RAGE) is a transmembrane multiligand receptor that binds to HMGB1. HMGB1-RAGE signaling has an important role in inflammatory and infectious diseases. Inhibition of HMGB1 activity reduces the inflammation in immune-associated diseases. In the present study, we examined the gene expressions and plasma levels of HMGB1 and its receptor RAGE in HAM/TSP patients, HTLV-1-infected asymptomatic carriers (ACs), and healthy controls. Peripheral blood mononuclear cells were collected from all the groups and complementary DNA (cDNA) was synthesized. HMGB-1 messenger RNA (mRNA) expression was quantified by real-time polymerase chain reaction (PCR) TaqMan method, and plasma levels of HMGB1 and soluble RAGE (sRAGE) were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA expression of HMGB1 was the same among the groups (p > 0.05). No significant difference in the plasma levels of HMGB1 was observed between the groups (p > 0.05). The plasma levels of sRAGE were higher in ACs than HAM/TSP patients, and a significant difference was observed between the two groups (p < 0.001). Our results showed that sRAGE could play a potential role in the control of inflammatory response in HTLV-1 carriers through the inhibition of HMGB1 signaling and potentially could be used as an indicator for evaluation of HAM/TSP developing in HTLV-1-infected individuals.

JNK and ATF4 as two important platforms for tumor necrosis factor-α-stimulated shedding of receptor for advanced glycation end products

Soluble receptor for advanced glycation end products (sRAGE), shed from cell surfaces, is found in human circulation and has been implicated in cardiovascular disease. Its pathophysiological regulation and underlying mechanisms are scarcely understood. In endothelium-specific human RAGE transgenic mice, human sRAGE was detected in circulation, whereas its level was markedly increased after LPS treatment. That increase was preceded by a rapid rise in TNF-α level. Treatment with TNF-α also significantly increased serum sRAGE. In human microvascular endothelial cells or human umbilical vein endothelial cells with RAGE overexpression, TNF-α markedly induced RAGE shedding, which was dependent on MMP9 and ADAM10. TNF-α-stimulated MMP9 expression was completely dependent on JNK activation, with its inhibition partially effective in suppressing TNF-α-induced RAGE shedding. In contrast, TNF-α transiently induced activation transcription factor (ATF)4, a major component in unfolded protein response (UPR), whereas knockdown of ATF4 abrogated TNF-α-stimulated RAGE shedding. Protein levels of the pro and activated forms of ADAM10 were also decreased by ATF4 knockdown, whereas inhibition of other components of UPR, including XBP1 and ATF6, failed to block TNF-α-stimulated RAGE shedding. Although the endoplasmic reticulum stressors thapsigargin and tunicamycin induced markedly and sustained expression of ATF4 and XBP-1, they did not induce RAGE shedding to the same level as TNF-α, suggesting that ATF4 is necessary but not sufficient alone for TNF-α-mediated RAGE shedding. ATF4 inhibition did not affect TNF-α-stimulated MMP9 expression, whereas inhibition of JNK activity did not influence ADAM10 activation. Thus, inflammatory cascades including TNF-α induced RAGE shedding in endothelial cells in vivo and in vitro. JNK and ATF4 may be 2 platforms for regulation of TNF-α-stimulated RAGE shedding.-Miyoshi, A., Koyama, S., Sasagawa-Monden, M., Kadoya, M., Konishi, K., Shoji, T., Inaba, M., Yamamoto, Y., Koyama, H. JNK and ATF4 as two important platforms for tumor necrosis factor-α-stimulated shedding of receptor for advanced glycation end products.

A drop in the circulating concentrations of soluble receptor for advanced glycation end products is associated with seroconversion to autoantibody positivity but not with subsequent progression to clinical disease in children en route to type 1 diabetes

BACKGROUND

Advanced glycation end products (AGEs) and their interaction with the receptor for AGEs (RAGE) have been studied for their role in the pathogenesis and complications of type 1 diabetes. Decreased concentrations of soluble RAGE (sRAGE) have been reported in acute autoimmune inflammation. We set out to analyze the changes in sRAGE concentration during preclinical diabetes in children seroconverting to islet autoantibody positivity.

METHODS

We measured serum concentrations of sRAGE in 168 children who progressed to clinical disease and 43 children who turned positive for at least 2 diabetes-associated autoantibodies but remained nondiabetic. We analyzed the sRAGE before seroconversion in the first autoantibody-positive sample and annually thereafter until the diagnosis of type 1 diabetes or end of follow-up.

RESULTS

Both groups had similar sRAGE before seroconversion, but subsequently, sRAGE concentrations were lower (P < .001) in the progressors. The progressors had significantly higher sRAGE concentrations before than after seroconversion (P < .001). The nonprogressors did not experience a similar decrease. The sRAGE concentrations remained stable after seroconversion in both groups.

CONCLUSIONS

These data indicate that sRAGE may be involved in the initiation of beta-cell autoimmunity but not in the progression from beta-cell autoimmunity to clinical disease.

Soluble RAGE Treatment Delays Progression of Amyotrophic Lateral Sclerosis in SOD1 Mice

The etiology of amyotrophic lateral sclerosis (ALS), a fatal motor neuron disorder characterized by progressive muscle weakness and spasticity, remains largely unknown. Approximately 5-10% of cases are familial, and of those, 15-20% are associated with mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Mutations of the SOD1 gene interrupt cellular homeostasis and contribute to cellular toxicity evoked by the presence of altered SOD1, along with other toxic species, such as advanced glycation end products (AGEs). AGEs trigger activation of their chief cell surface receptor, RAGE (receptor for advanced glycation end products), and induce RAGE-dependent cellular stress and inflammation in neurons, thereby affecting their function and leading to apoptosis. Here, we show for the first time that the expression of RAGE is higher in the SOD1 transgenic mouse model of ALS vs. wild-type mouse spinal cord. We tested whether pharmacological blockade of RAGE may delay the onset and progression of disease in this mouse model. Our findings reveal that treatment of SOD1 transgenic mice with soluble RAGE (sRAGE), a natural competitor of RAGE that sequesters RAGE ligands and blocks their interaction with cell surface RAGE, significantly delays the progression of ALS and prolongs life span compared to vehicle treatment. We demonstrate that in sRAGE-treated SOD1 transgenic animals at the final stage of the disease, a significantly higher number of neurons and lower number of astrocytes is detectable in the spinal cord. We conclude that RAGE antagonism may provide a novel therapeutic strategy for ALS intervention.

Elevated Circulating S100A12 Associates with Vascular Disease and Worse Clinical Outcome in Peritoneal Dialysis Patients

♦

BACKGROUND

The pro-inflammatory receptor of advanced glycation end-products (RAGE)-ligand S100A12 is thought to promote, whereas anti-inflammatory soluble RAGE (sRAGE) may protect against, vascular disease. We evaluated circulating S100A12 and sRAGE in relation to vascular disease, inflammation, nutritional status, and mortality risk in peritoneal dialysis (PD) patients. ♦

METHODS

Plasma S100A12 and sRAGE, biomarkers of inflammation, nutritional status, and comorbidities were analyzed in 82 prevalent PD patients (median age 65 years; 70% men; median vintage 12 months) and, for comparative analysis, also in 190 hemodialysis (HD) patients and 50 control subjects. Associations between mortality risk and concentrations of S100A12 and sRAGE were assessed in PD and HD patients after a mean follow-up period of 31 and 29 months respectively using a competing risk Cox regression model. ♦

RESULTS

In PD patients, median S100A12, sRAGE and S100A12/sRAGE were markedly higher than in controls, and S100A12 was 1.9 times higher and median sRAGE 14% lower compared with HD patients. In PD patients, S100A12 associated with C-reactive protein (ρ = 0.46; p < 0.001) and interleukin-6 (ρ = 0.38; p < 0.001), and, negatively, with s-albumin (ρ = -0.27; p < 0.05) whereas sRAGE associated negatively with body mass index (ρ = -0.37; p < 0.001), fat body mass index (ρ = -0.34; p < 0.001), and lean body mass index (ρ = -0.36; p < 0.001). Peripheral vascular disease or cerebrovascular disease (PCVD) was present in 28% of PD patients and, in multivariate analysis, associated mainly with high S100A12 (odds ratio [OR] 3.52, p = 0.04). In both PD and HD patients, the highest versus other tertiles of S100A12 associated with increased mortality. In contrast, sRAGE did not associate with PCVD or mortality in PD and HD patients. ♦

CONCLUSIONS

Plasma S100A12 and sRAGE are markedly elevated in PD patients. Soluble RAGE was inversely related to body mass indices while S100A12 associated with increased inflammation, PCVD, and mortality, suggesting that S100A12 may identify PD patients at high risk for vascular disease and increased mortality.

Glycation, carbonyl stress and AGEs inhibitors: a patent review

INTRODUCTION

The glycation process, comprising a series of reactions, results in the formation of heterogeneous adducts, known as advanced glycation end products (AGEs). AGEs are involved in several pathologies, including diabetes-associated late complications, atherosclerosis, Alzheimer's disease and inflammatory arthritis. Several inhibitors of AGEs and/or reactive carbonyl species have been identified from various sources, including natural products and synthetic molecules, and have been investigated for their mechanism of action.

AREAS COVERED

This review covers the literature on AGEs inhibitors published as patents between 2001 and 2014. Initially, the earlier reported molecules with AGEs inhibitory properties, their mechanism of actions and reported adverse effects are discussed. The main focus has been on the chemical structures, methods for evaluation of the activity, modes of action, pharmacokinetics and therapeutic outcomes. The potential of these AGEs inhibitors in the treatment and management of a number of diseases are also discussed in this review.

EXPERT OPINION

The reactive carbonyl species and AGEs have recently emerged as novel therapeutic targets for the prevention and treatment of several diseases. Currently, the major concerns with the use of AGEs inhibitors as therapeutic agents are low effectiveness, poor pharmacokinetics and undesirable side effects. Many of the AGEs inhibitors reviewed here possess potent antiglycation activity and are devoid of undesirable side effects. These small molecules inhibitors can, therefore, serve as scaffolds for the development and designing of new AGEs inhibitors as clinical agents.

The association between the RAGE G82S polymorphism, sRAGE and chronic periodontitis in Taiwanese individuals with and without diabetes

BACKGROUND AND OBJECTIVE

The present study investigated the association between the RAGE G82S polymorphism, the plasma levels of sRAGE and chronic periodontitis in subjects with and without diabetes mellitus (DM).

MATERIAL AND METHODS

A total of 230 patients with DM and 264 non-DM participants were recruited for this study. Genotyping of the RAGE G82S polymorphism was accomplished using polymerase chain reaction-restriction fragment length polymorphism, and associations were analyzed with the chi-squared test and logistic regression analysis.

RESULTS

In the non-DM group, the chi-squared test showed that the frequency distributions of the G82S polymorphism were significantly different between chronic periodontitis and non-chronic periodontitis subjects (χ(2) = 8.39, p = 0.02). A multivariate logistic regression model showed that the (G82S + S82S) genotypes were associated with a significantly increased risk of chronic periodontitis development compared to the G82G genotype (adjusted odds ratio = 2.06, 95% confidence interval: 1.08-4.07). In the DM group, there was no association between the G82S polymorphism and chronic periodontitis development when a multivariate logistic regression was performed. Plasma levels of sRAGE were significantly higher in subjects with the G82G genotype compared to those with the (G82S + S82S) genotypes in both the non-DM (856.6 ± 332.0 vs. 720.4 ± 311.4 pg/mL, p = 0.003) and DM groups (915.3 ± 497.1 vs. 603.5 ± 298.3 pg/mL, p < 0.0001). However, there was no difference in plasma sRAGE levels between chronic periodontitis and non-chronic periodontitis subjects in both the DM and non-DM groups. Moreover, when the subjects were further sub-divided by the G82S polymorphism, the difference in plasma levels of sRAGE between chronic periodontitis and non-chronic periodontitis subjects in the DM and non-DM groups remained statistically insignificant.

CONCLUSIONS

The present study revealed that the RAGE G82S polymorphism was associated with chronic periodontitis in the non-DM group but not in the DM group. Our results also showed that the plasma levels of sRAGE were significantly higher in subjects with the RAGE G82G genotype, and this correlation was not affected by the presence of chronic periodontitis in the DM and non-DM groups.

Expression of the receptor for advanced glycation end-products and frequency of polymorphism in lung cancer

Receptor for advanced glycation end products (RAGE) is associated with the pathogenesis of cancer progression. The pathological effects mediated through RAGE are physiologically inhibited by soluble RAGE (sRAGE). The aim of the present study was to identify the expression of the sRAGE, RAGE and RAGE ligands in serum samples and lung cancer tissue obtained from lung cancer patients. Using ELISA and immunohistochemistry, it was observed that the sRAGE levels were downregulated in the serum, the expression of RAGE was decreased in the lung cancer tissue and the RAGE ligands HMGB1 and S100 were upregulated in cancer tissue. Furthermore, the presence of several selected types of RAGE polymorphism that occur in lung cancers were measured in the tissue samples. An association between the -429T/C and 2184A/G polymorphisms of RAGE and the genesis and progression of lung cancer was identified. The comparison between various histological subtypes and stages of lung cancer was performed with the aim to clarify the biological role of the RAGE gene, and identify a biomarker to aid diagnosis and predict the prognosis for lung cancer patients.

Impact of hyperglycemia and acute pancreatitis on the receptor for advanced glycation endproducts

Since hyperglycemia aggravates acute pancreatitis and also activates the receptor for advanced glycation endproducts (RAGE) in other organs, we explored if RAGE is expressed in the pancreas and if its expression is regulated during acute pancreatitis and hyperglycemia. Acute pancreatitis was induced by cerulein in untreated and streptozotocin treated diabetic mice. Expression of RAGE was analyzed by Western blot and immunohistochemistry. To evaluate signal transduction the phosphorylation of ERK1/ERK2 was assessed by Western blot and the progression of acute pancreatitis was monitored by evaluation of lipase activity and the pancreas wet to dry weight ratio. RAGE is mainly expressed by acinar as well as interstitial cells in the pancreas. During acute pancreatitis infiltrating inflammatory cells also express RAGE. Using two distinct anti-RAGE antibodies six RAGE proteins with diverse molecular weight are detected in the pancreas, whereas just three distinct RAGE proteins are detected in the lung. Hyperglycemia, which aggravates acute pancreatitis, significantly reduces the production of two RAGE proteins in the inflamed pancreas.

Paradoxical function for the receptor for advanced glycation end products in mouse models of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with poor survival. The identification of therapeutic targets is essential to improving outcomes. Previous studies found that expression of the receptor for advanced glycation end products (RAGE) in the lung is significantly decreased in human IPF lungs and in two animal models of pulmonary fibrosis. In addition, RAGE-null mice spontaneously develop pulmonary fibrosis with age and more severe fibrosis when challenged with asbestos. In contrast to the findings that the lack of RAGE enhanced pulmonary fibrosis, He et al. found that RAGE null mice were protected from bleomycin-induced fibrosis and suggested the effect was due to a lack of HMGB1 induced RAGE signaling. The current study further tests this hypothesis by blocking RAGE signaling via administration of soluble RAGE, a decoy receptor, to determine if this will also protect against pulmonary fibrosis. Wild-type, RAGE(+/-), and RAGE(-/-) mice were treated with bleomycin and assessed for fibrosis. Wild-type mice were also treated with exogenous soluble RAGE or vehicle control. In addition, in vitro studies with primary alveolar epithelial cells from wild-type and RAGE null mice were used to investigate the effect of RAGE on cell viability and migration in response to injury. A lack of RAGE was found to be protective against bleomycin injury in both in vivo and in vitro studies. However, soluble RAGE administration was unable to ameliorate fibrosis. This study confirms paradoxical responses to two different models of pulmonary fibrosis and suggests a further role for RAGE in cellular migration.