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

Advanced Glycation End Products in Disease Development and Potential Interventions

Advanced glycation end products (AGEs) are a group of compounds formed through non-enzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs can be generated in the body or introduced through dietary sources and smoking. Recent clinical and animal studies have highlighted the significant role of AGEs in various health conditions. These compounds accumulate in nearly all mammalian tissues and are associated with a range of diseases, including diabetes and its complications, cardiovascular disease, and neurodegeneration. This review summarizes the major diseases linked to AGE accumulation, presenting both clinical and experimental evidence. The pathologies induced by AGEs share common mechanisms across different organs, primarily involving oxidative stress, chronic inflammation, and direct protein cross-linking. Interventions targeting AGE-related diseases focus on inhibiting AGE formation using synthetic or natural antioxidants, as well as reducing dietary AGE intake through lifestyle modifications. AGEs are recognized as significant risk factors that impact health and accelerate aging, particularly in individuals with hyperglycemia. Monitoring AGE level and implementing nutritional interventions can help maintain overall health and reduce the risk of AGE-related complications.

Soluble receptor for advanced glycation end products (sRAGE) is associated with obesity rates: a systematic review and meta-analysis of cross-sectional study

BACKGROUND

Several studies have highlighted the possible positive effects of soluble receptor for advanced glycation end products (sRAGE) against obesity. However, due to their inconsistent results, this systematic review and meta-analysis aimed to quantitatively evaluate and critically review the results of studies evaluating the relationship between sRAGE with obesity among adult population.

METHODS

In the systematic search, the eligibility criteria were as follows: studies conducted with a cross-sectional design, included apparently healthy adults, adults with obesity, or obesity-related disorders, aged over 18 years, and evaluated the association between general or central obesity indices with sRAGE.

RESULTS

Our systematic search in electronic databases, including PubMed, Scopus, and Embase up to 26 October, 2023 yielded a total of 21,612 articles. After removing duplicates, screening the titles and abstracts, and reading the full texts, 13 manuscripts were included in the final meta-analysis. According to our results, those at the highest category of circulating sRAGE concentration with median values of 934.92 pg/ml of sRAGE, had 1.9 kg/m2 lower body mass index (BMI) (WMD: -1.927; CI: -2.868, -0.986; P < 0.001) compared with those at the lowest category of sRAGE concentration with median values of 481.88 pg/ml. Also, being at the highest sRAGE category with the median values of 1302.3 pg/ml sRAGE, was accompanied with near 6 cm lower waist circumference (WC) (WMD: -5.602; CI: -8.820, -2.383; P < 0.001 with 86.4% heterogeneity of I2) compared with those at the lowest category of sRAGE concentration with median values of 500.525 pg/ml. Individuals with obesity had significantly lower circulating sRAGE concentrations (WMD: -135.105; CI: -256.491, -13.72; P = 0.029; with 79.5% heterogeneity of I2). According to the subgrouping and meta-regression results, country and baseline BMI were possible heterogeneity sources. According to Begg's and Egger's tests and funnel plots results, there was no publication bias.

CONCLUSION

According to our results, higher circulating sRAGE concentrations was associated with lower BMI and WC among apparently healthy adults. Further randomized clinical trials are warranted for possible identification of causal associations.

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

BACKGROUND AND AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The role of sRAGE in cardiovascular diseases

Advanced glycation end products (AGEs), by-products of glucose metabolism, have been linked to the emergence of cardiovascular disorders (CVD). AGEs can cause tissue damage in four different ways: (1) by altering protein function, (2) by crosslinking proteins, which makes tissue stiffer, (3) by causing the generation of free radicals, and (4) by activating an inflammatory response after binding particular AGE receptors, such as the receptor for advanced glycation end products (RAGE). It is suggested that the soluble form of RAGE (sRAGE) blocks ligand-mediated pro-inflammatory and oxidant activities by serving as a decoy. Therefore, several studies have investigated the possible anti-inflammatory and anti-oxidant characteristics of sRAGE, which may help lower the risk of CVD. According to the results of various studies, the relationship between circulating sRAGE, cRAGE, and esRAGE and CVD is inconsistent. To establish the potential function of sRAGE as a therapeutic target in the treatment of cardiovascular illnesses, additional studies are required to better understand the relationship between sRAGE and CVD. In this review, we explored the potential function of sRAGE in different CVD, highlighting unanswered concerns and outlining the possibilities for further investigation.

Altered expression of a disintegrin and metalloproteinase 10 in peripheral blood mononuclear cells in type 2 diabetes mellitus patients with the acute coronary syndrome: a pilot study

PURPOSE

Advanced glycation end products (AGEs) are responsible for the complications in type 2 diabetes mellitus (T2DM) patients by acting via its receptor (RAGE). The soluble form of RAGE (sRAGE) prevents the harmful effects of AGE-RAGE signalling. The sRAGE is produced either by alternate splicing (esRAGE) or proteolytic RAGE cleavage by a disintegrin and metalloproteinase 10 (ADAM10). Hence, the study aimed to compare the expression of ADAM10 in peripheral blood mononuclear cell (PBMC), serum sRAGE and esRAGE levels in T2DM patients with and without acute coronary syndrome (ACS).

METHODS

Forty-five T2DM patients with ACS and 45 age, gender and duration of DM-matched T2DM patients without ACS were recruited. Serum sRAGE and esRAGE levels were measured by enzyme-linked immunosorbent assay. The expression of ADAM10 in PBMC was determined by quantitative reverse transcription-polymerase chain reaction.

RESULTS

The expression of ADAM10 in PBMC and serum sRAGE levels were significantly lower in T2DM patients with ACS than in T2DM patients without ACS (p < 0.001). Serum sRAGE levels and expression of ADAM10 in PBMC were positively correlated with each other and negatively correlated with markers of cardiac injury and glycaemic status (p < 0.05). Simple logistic regression showed that the models containing the expression of ADAM10 and serum sRAGE level could predict the ACS risk among T2DM patients. ROC analysis showed that both might be used for ACS diagnosis in T2DM patients.

CONCLUSION

Reduced expression of ADAM10 in PBMC might be responsible for lower serum sRAGE levels, predisposing T2DM patients to high ACS risk.

Soluble RAGE in COPD, with or without coexisting obstructive sleep apnoea

BACKGROUND

Hypoxia can reduce the levels of soluble receptor for advanced glycation end-products (sRAGE), a new anti-inflammatory biomarker of COPD. We assessed sRAGE in patients with hypoxia-related diseases such as COPD, OSA and OSA-COPD overlap.

METHODS

Plasma levels of sRAGE were measured in 317 subjects at baseline (57 heathy nonsmokers [HNS], 84 healthy smokers [HS], 79 OSA, 62 COPD and 35 OSA-COPD overlap patients) and in 294 subjects after one year of follow-up (50 HNS, 74 HS, 77 OSA, 60 COPD and 33 overlap).

RESULTS

After adjusting for age, sex, smoking status and body mass index, sRAGE levels showed a reduction in OSA (- 12.5%, p = 0.005), COPD (- 14.8%, p < 0.001) and OSA-COPD overlap (- 12.3%, p = 0.02) compared with HNS. There were no differences when comparing sRAGE plasma levels between overlap patients and those with OSA or COPD alone. At follow-up, sRAGE levels did not change significantly in healthy subjects, COPD and OSA or OSA-COPD overlap nontreated with continuous positive airway pressure (CPAP). Moreover, in patients with OSA and OSA-COPD overlap who were treated with CPAP, sRAGE increased significantly.

CONCLUSIONS

The levels of sRAGE are reduced in COPD and OSA. Treatment with CPAP appears to improve sRAGE levels in patients with OSA who also had COPD.

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.

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.

Soluble Receptor for Advanced Glycation End-products (sRAGE) and Colorectal Cancer Risk: A Case-Control Study Nested within a European Prospective Cohort

BACKGROUND

Overexpression of the receptor for advanced glycation end-product (RAGE) has been associated with chronic inflammation, which in turn has been associated with increased colorectal cancer risk. Soluble RAGE (sRAGE) competes with RAGE to bind its ligands, thus potentially preventing RAGE-induced inflammation.

METHODS

To investigate whether sRAGE and related genetic variants are associated with colorectal cancer risk, we conducted a nested case-control study in the European Prospective Investigation into Cancer and Nutrition (EPIC). Plasma sRAGE concentrations were measured by ELISA in 1,361 colorectal cancer matched case-control sets. Twenty-four SNPs encoded in the genes associated with sRAGE concentrations were available for 1,985 colorectal cancer cases and 2,220 controls. Multivariable adjusted ORs and 95% confidence intervals (CIs) were computed using conditional and unconditional logistic regression for colorectal cancer risk and circulating sRAGE and SNPs, respectively.

RESULTS

Higher sRAGE concentrations were inversely associated with colorectal cancer (ORQ5vs.Q1, 0.77; 95% CI, 0.59-1.00). Sex-specific analyses revealed that the observed inverse risk association was restricted to men (ORQ5vs.Q1, 0.63; 95% CI, 0.42-0.94), whereas no association was observed in women (ORQ5vs.Q1, 1.00; 95% CI, 0.68-1.48; P heterogeneity for sex = 0.006). Participants carrying minor allele of rs653765 (promoter region of ADAM10) had lower colorectal cancer risk (C vs. T, OR, 0.90; 95% CI, 0.82-0.99).

CONCLUSIONS

Prediagnostic sRAGE concentrations were inversely associated with colorectal cancer risk in men, but not in women. An SNP located within ADAM10 gene, pertaining to RAGE shedding, was associated with colorectal cancer risk.

IMPACT

Further studies are needed to confirm our observed sex difference in the association and better explore the potential involvement of genetic variants of sRAGE in colorectal cancer development.

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

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

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

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

Quantification of Furosine (Nε-(2-Furoylmethyl)-l-lysine) in Different Parts of Velvet Antler with Various Processing Methods and Factors Affecting Its Formation

Furosine (Nε-(2-furoylmethyl)-l-lysine) is formed during the early stages of the Maillard reaction from a lysine Amadori compound and is frequently used as a marker of reaction progress. Furosine is toxic, with significant effects on animal livers, kidneys, and other organs. However, reports on the formation of furosine in processed velvet antler are scarce. In this study, we have quantified the furosine content in processed velvet antler by using UPLC-MS/MS. The furosine contents of velvet antler after freeze-drying, boiling, and processing without and with blood were 148.51–193.93, 168.10–241.22, 60.29–80.33, and 115.18–138.99 mg/kg protein, respectively. The factors affecting furosine formation in processed velvet antler, including reducing sugars, proteins, amino acids, and process temperature, are discussed herein. Proteins, amino acids, and reducing sugars are substrates for the Maillard reaction and most significantly influence the furosine content in the processed velvet antler. High temperatures induce the production of furosine in boiled velvet antler but not in the freeze-dried samples, whereas more furosine is produced in velvet antler processed with blood, which is rich in proteins, amino acids, and reducing sugars, than in the samples processed without blood. Finally, wax slices rich in proteins, amino acids, and reducing sugars produced more furosine than the other parts of the velvet antler. These data provide a reference for guiding the production of low-furosine velvet antler and can be used to estimate the consumer intake of furosine from processed velvet antler.

sRAGE and early signs of cardiac target organ damage in mild hypertensives

Background

Soluble Receptor for Advanced Glycation End Products (sRAGE) may be considered a marker inversely related to inflammation and its participation has been established in patients with advanced atherosclerotic vascular diseases. However, it is still unknown whether sRAGE reduction could be early metabolic change in the first stage of hypertension and initial hypertension-associated cardiac damage. We sought to determine the sRAGE values in otherwise healthy, untreated and recently diagnosed mild hypertensives and evaluate their association with blood pressure (BP) values, metabolic parameters, and with subclinical initial signs of cardiac target organ damage (TOD).

Methods

sRAGE were measured in 100 hypertensive and 100 normotensive subjects matched for age, gender and body mass index (BMI), submitted to a clinic visit and both ambulatory BP monitoring and echocardiography to determine the presence of initial cardiac TOD (presence of signs of left ventricular hypertrophy: left ventricular mass indexed for height^2.7 (LVMi) > 48 g/m^2.7 for men and > 44 g/m^2.7 for women and/or increased left atrial volume 4-chamber indexed for body surface area (LAVi) > 34 ml/m²).

Results

sRAGE levels were similar between hypertensive and normotensive subjects and were not significantly correlated with office and 24-h BPs values. However, when subgrouping the hypertensive patients in Hyp-TOD and Hyp-withoutTOD, sRAGE was found to be different among the three groups (p = 0.030), being lower in the Hyp-TOD group than the values of both Hyp-withoutTOD (p = 0.038) and normotensives (p = 0.038). In hypertensive patients sRAGE was negatively related with both LVMi (r = − 0.239, p = 0.034) and LAVi (r = − 0.315, p = 0.005) and was independently related to cardiac TOD also in multivariable analysis.

Conclusions

In this population of mild hypertensives, low circulating sRAGE may be a very early marker of initial TOD, suggesting the possible participation of oxidative stress in initial cardiac changes in human hypertension.

Electronic supplementary material

The online version of this article (10.1186/s12933-019-0821-5) contains supplementary material, which is available to authorized users.

Sympathoadrenergic suppression improves heart function by upregulating the ratio of sRAGE/RAGE in hypertension with metabolic syndrome

Receptors-for-Advanced-Glycation-End-products (RAGE) activate pro-inflammatory programs mediated by carboxymethyllysine (CML) and high-mobility-group-box1 protein (HMGB1). The soluble isoform sRAGE neutralizes RAGE-ligands preventing cardiovascular complications in conditions associated with increased sympathetic activation like hypertension and diabetes. The effects of sympathetic modulation on RAGE/sRAGE-balance and end-organ damage in metabolic syndrome on top of hypertension remains unknown. We hypothesized that increased sympathoadrenergic activity might lead to an unfavourable RAGE/sRAGE regulation. Renal denervation (RDN) was used to modulate sympathetic activation in obese spontaneously hypertensive rats (SHRobRDN) versus sham-operated obese spontaneously hypertensive rats (SHRob), their hypertensive lean controls (SHR) and non-hypertensive controls. Cardiac fibrosis was assessed by histological analysis and sRAGE/RAGE and ligand levels by Western blotting. Levels of CML and HMGB1 were highest in SHRob and were significantly lowered by RDN in serum (-44% and -45%) and myocardium (-25% and -52%). Myocardial RAGE was increased in SHR (+72% versus controls) and in SHRob (+68% versus SHR) while sRAGE decreased (-50% in SHR versus controls and -51% in SHRob versus SHR). RDN reduced myocardial RAGE expression. (-20%) and increased sRAGE levels in heart (+80%) and serum (+180%) versus sham-operated SHRob. Myocardial fibrosis correlated inversely with myocardial sRAGE content (r = -0.79; p = .004; n = 10). Myocardial sRAGE shedding active A-Disintegrin-And-Metalloprotease-10 (ADAM-10) was decreased in SHR (-33% versus controls) and in SHRob (-54% versus SHR), and was restored after RDN (+129% versus SHRob). Serum ADAM-10 activity was also decreased in SHRob (-66% versus SHR) and restored after RDN (+150% versus SHRob). In vitro, isoproterenol induced a ß1-adrenergic receptor mediated increase of RAGE expression in splenocytes (+200%) and decreased sRAGE secretion of splenocytes and cardiac fibroblasts (-50% and -49%) by ß2-adrenergic receptor stimulation mediated suppression of ADAM-10 activity. In conclusion, sympathetic activity affects sRAGE/RAGE-balance, which can be suppressed through sympathetic modulation by RDN, preventing RAGE-induced cardiac damage in hypertension with metabolic syndrome.

Endogenous Secretory Receptor for Advanced Glycation End Products Protects Endothelial Cells from AGEs Induced Apoptosis

Endogenous secretory receptor for advanced glycation end products (esRAGE) binds extracellular RAGE ligands and blocks RAGE activation on the cell surface, protecting endothelial cell function. However, the underlying mechanism remains unclear. Endothelial cells overexpressing the esRAGE gene were generated using a lentiviral vector. Then, quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) were used to assess esRAGE mRNA and protein levels, respectively. Hoechst-PI double staining was used to assess apoptosis. Western blot and qRT-PCR were used to assess the expression levels of apoptosis-related factors and the proinflammatory cytokine NF-кB. Compared with the control group, AGEs significantly induced endothelial cell apoptosis, which was significantly reduced by esRAGE overexpression. Incubation with AGEs upregulated the proapoptotic factor Bax and downregulated the antiapoptotic factor Bcl-2. Overexpression of esRAGE reduced Bax expression induced by AGEs and increased Bcl-2 levels. Furthermore, AGEs increased the expression levels of proinflammatory cytokine NF-кB, which were reduced after esRAGE overexpression. esRAGE protects endothelial cells from AGEs associated apoptosis, by downregulating proapoptotic (Bax) and inflammatory (NF-кB) factors and upregulating the antiapoptotic factor Bcl-2.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

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

BACKGROUND

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Glycation & the RAGE axis: targeting signal transduction through DIAPH1

INTRODUCTION

The consequences of chronic disease are vast and unremitting; hence, understanding the pathogenic mechanisms mediating such disorders holds promise to identify therapeutics and diminish the consequences. The ligands of the receptor for advanced glycation end products (RAGE) accumulate in chronic diseases, particularly those characterized by inflammation and metabolic dysfunction. Although first discovered and reported as a receptor for advanced glycation end products (AGEs), the expansion of the repertoire of RAGE ligands implicates the receptor in diverse milieus, such as autoimmunity, chronic inflammation, obesity, diabetes, and neurodegeneration. Areas covered: This review summarizes current knowledge regarding the ligand families of RAGE and data from human subjects and animal models on the role of the RAGE axis in chronic diseases. The recent discovery that the cytoplasmic domain of RAGE binds to the formin homology 1 (FH1) domain, DIAPH1, and that this interaction is essential for RAGE ligand-stimulated signal transduction, is discussed. Finally, we review therapeutic opportunities targeting the RAGE axis as a means to mitigate chronic diseases. Expert commentary: With the aging of the population and the epidemic of cardiometabolic disease, therapeutic strategies to target molecular pathways that contribute to the sequelae of these chronic diseases are urgently needed. In this review, we propose that the ligand/RAGE axis and its signaling nexus is a key factor in the pathogenesis of chronic disease and that therapeutic interruption of this pathway may improve quality and duration of life.

Role of RAGE in Alzheimer's Disease

Receptor for advanced glycation end products (RAGE) is a receptor of the immunoglobulin super family that plays various important roles under physiological and pathological conditions. Compelling evidence suggests that RAGE acts as both an inflammatory intermediary and a critical inducer of oxidative stress, underlying RAGE-induced Alzheimer-like pathophysiological changes that drive the process of Alzheimer's disease (AD). A critical role of RAGE in AD includes beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangles, failure of synaptic transmission, and neuronal degeneration. The steady-state level of Aβ depends on the balance between production and clearance. RAGE plays an important role in the Aβ clearance. RAGE acts as an important transporter via regulating influx of circulating Aβ into brain, whereas the efflux of brain-derived Aβ into the circulation via BBB is implemented by LRP1. RAGE could be an important contributor to Aβ generation via enhancing the activity of β- and/or γ-secretases and activating inflammatory response and oxidative stress. However, sRAGE-Aβ interactions could inhibit Aβ neurotoxicity and promote Aβ clearance from brain. Meanwhile, RAGE could be a promoting factor for the synaptic dysfunction and neuronal circuit dysfunction which are both the material structure of cognition, and the physiological and pathological basis of cognition. In addition, RAGE could be a trigger for the pathogenesis of Aβ and tau hyper-phosphorylation which both participate in the process of cognitive impairment. Preclinical and clinical studies have supported that RAGE inhibitors could be useful in the treatment of AD. Thus, an effective measure to inhibit RAGE may be a novel drug target in AD.

Soluble receptor for advanced glycation end products and increased aortic stiffness in the general population

It has been suggested that accumulation of advanced glycation end products (AGEs) is involved in several pathophysiological processes in the vessel wall. We hypothesized that low levels of the soluble receptor for AGEs (sRAGE) might be associated with increased arterial stiffness, a manifestation of vascular ageing in the general population. Using a cross-sectional design, we analyzed 1077 subjects from the Czech post-MONICA study. The aortic pulse wave velocity (aPWV) was measured using a Sphygmocor device. sRAGE concentrations were assessed in frozen samples using enzyme-linked immunosorbent assay methods (R&D Systems). aPWV significantly (P<0.0001) increased across the sRAGE quartiles. An aPWV of 1 m s(-1) was associated with a 37% increase in the risk of low sRAGE (<918 pg ml(-1), bottom quartile; P-value=0.018). In a categorized manner, subjects in the bottom sRAGE quartile had an odds ratio of an increased aPWV (⩾9.3 m s(-1)), adjusted for all potential confounders of 2.05 (95% confidence interval: 1.26-3.32; P=0.004), but this was only the case for non-diabetic hypertensive patients. In contrast, a low sRAGE was rejected as an independent predictor of an increased aPWV in normotensive or diabetic subjects using similar regression models. In conclusion, low circulating sRAGE was independently associated with increased arterial stiffness in a general population-based sample, but this was only observed in hypertensive non-diabetic patients.

Uremic Toxicity of Advanced Glycation End Products in CKD

Advanced glycation end products (AGEs), a heterogeneous group of compounds formed by nonenzymatic glycation reactions between reducing sugars and amino acids, lipids, or DNA, are formed not only in the presence of hyperglycemia, but also in diseases associated with high levels of oxidative stress, such as CKD. In chronic renal failure, higher circulating AGE levels result from increased formation and decreased renal clearance. Interactions between AGEs and their receptors, including advanced glycation end product-specific receptor (RAGE), trigger various intracellular events, such as oxidative stress and inflammation, leading to cardiovascular complications. Although patients with CKD have a higher burden of cardiovascular disease, the relationship between AGEs and cardiovascular disease in patients with CKD is not fully characterized. In this paper, we review the various deleterious effects of AGEs in CKD that lead to cardiovascular complications and the role of these AGEs in diabetic nephropathy. We also discuss potential pharmacologic approaches to circumvent these deleterious effects by reducing exogenous and endogenous sources of AGEs, increasing the breakdown of existing AGEs, or inhibiting AGE-induced inflammation. Finally, we speculate on preventive and therapeutic strategies that focus on the AGE-RAGE axis to prevent vascular complications in patients with CKD.

Glycated peptides are associated with the variability of endothelial dysfunction in the cerebral vessels and the kidney in type 2 diabetes mellitus patients: a cross-sectional study

BACKGROUND

Diabetic atherosclerosis and microangiopathy parallel diabetic nephropathy. The aim of our study was to evaluate the pattern of endothelial dysfunction in two vascular territories, the kidney and the brain, both affected by diabetic vasculopathic complications. The endothelial variability was evaluated in relation to advanced glycation end-products modified peptides.

METHODS

Seventy patients with type 2 diabetes mellitus and 11 healthy subjects were assessed concerning urine albumin: creatinine ratio, plasma and urinary advanced glycation end-products, plasma asymmetric dimethyl-arginine, serum cystatin C, intima-media thickness in the common carotid arteries, the pulsatility index, the resistance index in the internal carotid arteries and the middle cerebral arteries, the cerebrovascular reactivity through the breath-holding test.

RESULTS

The breath-holding index correlated with asymmetric dimethyl-arginine (R²=0.151; p<0.001), plasma advanced glycation end-products (R²=0.173; p<0.001), C-reactive protein (R²=0.587; p<0.001), duration of diabetes mellitus (R²=0.146; p=0.001), cystatin C (R²=0.220; p<0.001), estimated glomerular filtration rate (R²=0.237; p=0.001). Urine albumin: creatinine ratio correlated with urinary advanced glycation end-products (R²=0.257; p<0.001), but not with asymmetric dimethyl-arginine (R²=0.029; p=0.147).

CONCLUSIONS

In type 2 diabetic patients endothelial dysfunction in the cerebral vessels appears to be dissociated from glomerular endothelial dysfunction in early diabetic nephropathy. Advanced glycation end-products could impact both the cerebral vessels and the glomerular endothelium.

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.