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

The interplay between hyperglycemia-induced oxidative stress markers and the level of soluble receptor for advanced glycation end products (sRAGE) in K562 cells

Formation and accumulation of advanced glycation end-products (AGE) and also generation of reactive oxygen species (ROS), the main causative players in the context of diabetes, are intensified under hyperglycemic condition. The consequences from AGE/RAGE interaction could be attenuated by the soluble form of RAGE, termed sRAGE. In the current study, we studied the link between hyperglycemia-induced oxidative stress and the level of soluble form of RAGE in K562 cells. Our data revealed a positive correlation between high glucose and/or AGE-modified albumin treatment and oxidative stress status. Besides, a significant decrease in soluble RAGE level following treatments with either AGE-modified albumin or high glucose was observed. However, pretreatment with an appropriate antioxidant such as Resveratrol, markedly elevated the sRAGE level. Hence, sRAGE therapy could be further evaluated as an effective therapeutical approach to attenuate some of the diabetes complications.

Plasma advanced glycation end products (AGEs) and NF-κB activity are independent determinants of diastolic and pulse pressure

BACKGROUND

High levels of circulating advanced glycation end products (AGEs) can initiate chronic low-grade activation of the immune system (CLAIS) with each of these factors independently associated with cardiovascular (CV) morbidity and mortality. Therefore, our objective was to characterize the relationship between serum AGEs, CLAIS and other risk factors for CV disease in normotensive non-diabetic individuals.

METHODS

We measured body mass index (BMI), waist-to-hip ratio (WHR), blood pressure, lipid and glucose profile in 44 non-diabetic volunteers (17 female, 27 males). Carboxymethyl-lysine (CML) was measured by ELISA as a marker for circulating AGEs and NF-κB p65 activity as an inflammatory marker by DNA-binding in peripheral blood mononuclear cells lysates (PBMC).

RESULTS

Plasma CML concentrations were related to diastolic blood pressure (r=-0.51, p<0.01) independently of age, sex, BMI and WHR (p<0.05). Diastolic blood pressure was also related to NF-κB activity in PBMC (r=0.47, p<0.01) before and after adjustment for age, sex, BMI and WHR (p<0.05). Plasma CML concentrations were related to the pulse pressure before (r=0.42; p<0.05) and after adjustment for age, sex, BMI and waist (p<0.05). Neither CML nor NF-κB activity were related to systolic blood pressure (both p=ns). Plasma CML concentrations were not associated with plasma lipid or glucose concentrations (all p=ns).

CONCLUSIONS

Plasma AGE levels and NF-κB activity in PBMC were independent determinants of diastolic and pulse pressure in healthy normotensive individuals. This association suggests a role for AGEs in the etiology of hypertension, possibly via the initiation of CLAIS and aortic stiffening.

Soluble RAGE plasma levels in patients with coronary artery disease and peripheral artery disease

The objective of the present study was define in a relatively large patient population with coronary artery disease (CAD) whether the concomitant presence of peripheral artery disease (PAD), which is known to convey additional cardiovascular risk, was associated with different circulating levels of sRAGE with respect to CAD alone and control subjects. Clinical and laboratory parameters including the ankle brachial index (ABI) and sRAGE (enzyme-linked immunosorbent assay kit) were investigated in 544 patients with angiographically documented CAD and 328 control subjects. 213/554 CAD patients (39%) showed an ABI <0.9 associated with typical symptoms (group CAD + PAD), whereas 331 patients were free from PAD. The concentration of plasma sRAGE was significantly lower (P < 0.0001) in CAD population, with and without PAD, than in control subjects. Among CAD patients, those with PAD showed lower levels of sRAGE. The distribution of the three groups (CAD, CAD + PAD, and controls) according to sRAGE tertiles showed that lower levels were more frequent in patients with CAD and CAD + PAD, whereas higher levels were more frequently found in controls. CAD patients presenting with PAD have lower sRAGE levels than CAD patients without peripheral atherosclerosis showing that stable atherosclerotic lesions in different vascular districts are inversely related to soluble decoy receptor sRAGE.

Fluorescent advanced glycation end products and their soluble receptor: the birth of new plasmatic biomarkers for risk stratification of acute coronary syndrome

Objective

Advanced glycation end products (AGEs) have pathophysiological implications in cardiovascular diseases. The aim of our study was to evaluate the prognostic value of fluorescent AGEs and its soluble receptor (sRAGE) in the context of acute coronary syndrome (ACS), both in-hospital phase and follow-up period.

Methods

A prospective clinical study was performed in patients with debut’s ACS. The endpoints were the development of cardiac events (cardiac deaths, re-infarction and new-onset heart failure) during in-hospital phase and follow-up period (366 days, inter-quartile range: 273–519 days). 215 consecutive ACS patients admitted to the coronary care unit (62.7±13.0 years, 24.2% female) were included. 47.4% had a diagnosis of ST segment elevation myocardial infarction. AGEs and sRAGE were analysed by fluorescence spectroscopy and competitive ELISA, respectively. Risk scores (GRACE, TIMI, PURSUIT) were calculated retrospectively using prospective data. The complexity of coronary artery disease was evaluated by SYNTAX score.

Results

The mean fluorescent AGEs and sRAGE levels were 57.7±45.1 AU and 1045.4±850.0 pg/mL, respectively. 19 patients presented cardiac events during in-hospital phase and 29 during the follow-up. In-hospital cardiac events were significantly associated with higher sRAGE levels (p = 0.001), but not long-term cardiac events (p = 0.365). Regarding fluorescent AGE the opposite happened. After multivariate analysis correcting by gender, left ventricular ejection fraction, glucose levels, haemoglobin, GRACE and SYNTAX scores, sRAGE was significantly associated with in-hospital prognosis, whereas fluorescent AGEs was significantly associated with long-term prognosis.

Conclusions

We conclude that elevated values of sRAGE are associated with worse in-hospital prognosis, whereas high fluorescent AGE levels are associated with more follow-up events.

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.

Molecular strategies to prevent, inhibit, and degrade advanced glycoxidation and advanced lipoxidation end products

The advanced glycoxidation end products (AGEs) and lipoxidation end products (ALEs) contribute to the development of diabetic complications and of other pathologies. The review discusses the possibilities of counteracting the formation and stimulating the degradation of these species by pharmaceuticals and natural compounds. The review discusses inhibitors of ALE and AGE formation, cross-link breakers, ALE/AGE elimination by enzymes and proteolytic systems, receptors for advanced glycation end products (RAGEs) and blockade of the ligand-RAGE axis.

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.

Functional role of soluble receptor for advanced glycation end products in stroke

OBJECTIVE

Little is known about the involvement of the soluble form of receptor for advanced glycation end products (sRAGE) in acute ischemic stroke (IS). Here, we aim to identify the role of plasma sRAGE and high mobility group box 1 (HMGB1) in imaging-confirmed IS patients, as well as mice subjected to focal ischemic stroke.

METHODS AND RESULTS

IS patients were recruited and plasma samples were collected for the measurement of sRAGE and HMGB1 after stroke. The relation of sRAGE and HMGB1 with acute IS was also investigated in a C57BL/6J mouse model of focal ischemic stroke and primary cortical neurons subjected to oxygen and glucose deprivation. Plasma levels of sRAGE and HMGB1 were both significantly increased within 48 hours after IS, and the sRAGE level was an independent predictor of functional outcome at 3 months poststroke. Immunoprecipitation assays revealed that the binding of plasma HMGB1 to sRAGE increased progressively after IS both in patients and mice. Administration of recombinant sRAGE significantly reduced infiltrating immune cells and improved the outcome of injury in mice, protected cultured neurons against oxygen and glucose deprivation-induced cell death, and ameliorated the detrimental effect of recombinant HMGB1.

CONCLUSIONS

Early poststroke plasma sRAGE may play a protective role in IS by capturing HMGB1. Hence, recombinant sRAGE is a potential therapeutic agent in acute IS.

Low levels of soluble receptor for advanced glycation end products in non-ST elevation myocardial infarction patients

BACKGROUND

Interaction of the receptors for advanced glycation end products (RAGEs) with advanced glycation end products (AGEs) results in expression of inflammatory mediators (tumor necrosis factor-alpha [TNF-α] and soluble vascular cell adhesion molecule-1 [sVCAM-1]), activation of nuclear factor-kappa B and induction of oxidative stress - all of which have been implicated in atherosclerosis. Soluble RAGE (sRAGE) acts as a decoy for the RAGE ligand and is protective against atherosclerosis.

OBJECTIVES

To determine whether levels of serum sRAGE are lower, and whether levels of serum AGEs, TNF-α and sVCAM-1 are higher in non-ST elevation myocardial infarction (NSTEMI) patients than in healthy control subjects; and whether sRAGE or the ratio of AGEs to sRAGE (AGEs/sRAGE) is a predictor/biomarker of NSTEMI.

METHODS

Serum levels of sRAGE, AGEs, TNF-α and sVCAM-1 were measured in 46 men with NSTEMI and 28 age- and sex-matched control subjects. Angiography was performed in the NSTEMI patients.

RESULTS

sRAGE levels were lower, and levels of AGEs, TNF-α, sVCAM-1 and AGEs/sRAGE were higher in NSTEMI patients than in control subjects. sRAGE levels were negatively correlated with the number of diseased coronary vessels, serum AGEs, AGEs/sRAGE, TNF-α and sVCAM-1. The sensitivity of the AGEs/sRAGE test is greater than that of the sRAGE test, while the specificity and predictive values of the sRAGE test are greater than those of the AGEs/sRAGE test for identifying NSTEMI patients.

CONCLUSIONS

Serum levels of sRAGE were low in NSTEMI patients, and were negatively correlated with extent of lesion, inflammatory mediators, AGEs and AGEs/sRAGE. Both sRAGE and AGEs/sRAGE may serve as biomarkers/predictors for identifying NSTEMI patients.

An update on advanced glycation endproducts and atherosclerosis

Advanced glycation endproducts (AGEs) are a group of modified molecular species formed by nonenzymatic reactions between the aldehydic group of reducing sugars with proteins, lipids, or nucleic acids. Formation and accumulation of AGEs are related to the aging process and are accelerated in diabetes. AGEs are generated in hyperglycemia, but their production also occurs in settings characterized by oxidative stress and inflammation. These species promote vascular damage and acceleration of atherosclerotic plaque progression mainly through two mechanisms: directly, altering the functional properties of vessel wall extracellular matrix molecules, or indirectly, through activation of cell receptor-dependent signaling. Interaction between AGEs and the key receptor for AGEs (RAGE), a transmembrane signaling receptor which is present in all cells relevant to atherosclerosis, alters cellular function, promotes gene expression, and enhances the release of proinflammatory molecules. The importance of the AGE-RAGE interaction and downstream pathways, leading to vessel wall injury and plaque development, has been amply established in animal studies. Moreover, the deleterious link of AGEs with diabetic vascular complications has been suggested in many human studies. Blocking the vicious cycle of AGE-RAGE axis signaling may be essential in controlling and preventing cardiovascular complications. In this article, we review the pathogenetic role of AGEs in the development, progression and instability of atherosclerosis, and the potential targets of this biological system for the prevention and treatment of cardiovascular disease.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Opposing roles of membrane and soluble forms of the receptor for advanced glycation end products in primary respiratory syncytial virus infection

Respiratory syncytial virus (RSV), a common respiratory pathogen in infants and the older population, causes pulmonary inflammation and airway occlusion that leads to impairment of lung function. Here, we have established a role for receptor for advanced glycation end products (RAGE) in RSV infection. RAGE-deficient (ager(-/-)) mice were protected from RSV-induced weight loss and inflammation. This protection correlated with an early increase in type I interferons, later decreases in proinflammatory cytokines, and a reduction in viral load. To assess the contribution of soluble RAGE (sRAGE) to RSV-induced disease, wild-type and ager(-/-) mice were given doses of sRAGE following RSV infection. Of interest, sRAGE treatment prevented RSV-induced weight loss and neutrophilic inflammation to a degree similar to that observed in ager(-/-) mice. Our work further elucidates the roles of RAGE in the pathogenesis of respiratory infections and highlights the opposing roles of membrane and sRAGE in modulating the host response to RSV infection.

Total soluble and endogenous secretory receptor for advanced glycation end products as predictive biomarkers of coronary heart disease risk in patients with type 2 diabetes: an analysis from the CARDS trial

OBJECTIVE

Circulating levels of soluble receptor for advanced glycation end products (sRAGE) likely comprise both a secreted isoform (esRAGE) and wild-type RAGE cleaved from the cell membrane. Both sRAGE and esRAGE have been proposed as biomarkers of cardiovascular disease (CVD), but prospective data are limited. We examined the relationship of sRAGE and esRAGE to incident coronary heart disease (CHD) and stroke in type 2 diabetic patients followed for 3.9 years in a trial of atorvastatin: the Collaborative Atorvastatin Diabetes Study (CARDS).

RESEARCH DESIGN AND METHODS

We used a nested case-control design sampling all incident cases of CVD with available plasma and randomly selecting three control subjects, who were free of CVD throughout follow-up, per case. Analysis was by Cox regression with adjustment for treatment allocation and relevant covariates.

RESULTS

sRAGE and esRAGE were strongly correlated (ρ = 0.88) and were both higher in those with lower BMI (P < 0.001), higher adiponectin (P < 0.001), lower estimated glomerular filtration rate (P = 0.009), and white ethnicity (P < 0.001). Both sRAGE and esRAGE were associated with incident CHD events, independently of treatment allocation and the above factors; hazard ratio (HR) = 1.74 (95% CI 1.25-2.41; P = 0.002) for a doubling of the sRAGE level; HR = 1.45 (1.11-1.89; P = 0.006) for a doubling of the esRAGE level. There was no significant association with stroke; HR for sRAGE = 0.66 (0.38-1.14). Atorvastatin, 10 mg daily, did not alter sRAGE.

CONCLUSIONS

Higher levels of sRAGE and esRAGE are associated with incident CHD but not stroke in type 2 diabetes.

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

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSIONS

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

Soluble receptor of advanced glycated endproducts is associated with plaque vulnerability in patients with acute myocardial infarction

BACKGROUND

The roles of soluble and endogenous secretory receptors for advanced glycation endproducts (sRAGE and esRAGE, respectively) in plaque vulnerability are unknown in patients with acute myocardial infarction (AMI).

METHODS AND RESULTS

We enrolled 54 patients with AMI (27 patients had type 2 diabetes mellitus [DM]) who had undergone primary percutaneous coronary intervention, and 54 controls who were matched for age, gender and the presence of DM. Plasma levels of s/esRAGE and matrix metalloproteinase (MMP)-9 were measured at the time of coronary angiography. There were no significant differences in the baseline characteristics of the AMI and control groups, except for the C-reactive protein levels (CRP: 14.1 ± 14.2 mg/L vs. 3.7 ± 5.2 mg/L, P < 0.001). The plasma levels of MMP-9 (28.6 ± 21.4 vs. 14.3 ± 8.5 ng/ml P < 0.001) and sRAGE (0.61 ± 0.28 vs. 0.41 ± 0.17 ng/ml, P < 0.001) were higher in the AMI group than in the controls. In multivariate logistic regression analysis, the plasma levels of MMP-9 and sRAGE above the median (odds ratio [OR], 2.39; 95% confidence interval [CI], 1.02-5.58; P = 0.044; OR, 2.47; 95%CI, 1.05-5.80; P = 0.039, respectively) were independent predictors of AMI, as well as being a current smoker (OR, 2.98; 95%CI, 1.18-7.55; P = 0.021) and CRP ≥ 3.0 mg/L (OR, 3.08; 95%CI, 1.25-7.59; P = 0.015).

CONCLUSIONS

An elevated plasma level of sRAGE might be independently associated with plaque vulnerability, as well as MMP-9, in patients with AMI.

Soluble receptor for advanced glycation end products is associated with in-stent restenosis in patients with type 2 diabetes with drug-eluting coronary stents

BACKGROUND

The levels of soluble receptor for advanced glycation end products (sRAGE) may reflect the activity of the advanced glycation end products-RAGE axis, which has been proposed as a potential mechanism of vascular inflammation in patients with type 2 diabetes (T2D). However, the role of sRAGE in in-stent restenosis (ISR) is not yet known in patients with T2D with drug-eluting stent (DES) implantation.

METHODS AND RESULTS

We enrolled 35 patients with T2D with ISR (T2D-ISR) and 35 patients with age-matched T2D without ISR (T2D-control) at the time of follow-up coronary angiography after DES implantation. Plasma levels of glycosylated hemoglobin (HbA(1c)), C-reactive protein (CRP), insulin-like growth factor-1 (IGF-1), and sRAGE were measured in blood samples obtained at the time of the index procedure. Baseline characteristics showed no difference between the groups. Plasma levels of sRAGE were significantly higher in the T2D-ISR group than in the T2D-control group (7.29 ± 2.91 vs. 5.36 ± 2.20 ng/ml, P= 0.003), but levels of HbA(1c) (7.65 ± 1.59% vs. 7.60 ± 1.65%, P = 0.89), CRP (8.15 ± 13.82 vs. 5.59 ± 7.68 mg/l, P = 0.34), and IGF-1 (0.93 ± 0.37 vs. 0.99 ± 0.30 ng/ml, P = 0.42) did not differ significantly between the two study groups. In multivariate logistic regression analysis, elevated plasma level of sRAGE (above the median) was a significant predictor of ISR [odds ratio (OR): 4.33, 95% confidence interval (CI): 1.38–13.59, P = 0.01], followed by mean stent diameter less than 3.0mm (OR: 3.35, CI: 0.98–11.46, P = 0.05).

CONCLUSION

Plasma level of sRAGE may be positively associated with ISR and RAGE-dependent inflammatory responses may contribute more to ISR development than IGF-1-dependent proliferative responses in patients with T2D with DES implantation.

Calcium channel blocker inhibition of AGE and RAGE axis limits renal injury in nondiabetic patients with stage I or II chronic kidney disease

BACKGROUND

There is a growing body of evidence that advanced glycation end products (AGE) and their receptor (RAGE) system are implicated in chronic kidney disease (CKD). We have previously found that a long-acting calcium channel blocker, azelnidipine, but not amlodipine, improves renal injury in CKD patients. However, little is known about the effect of azelnidipine on the AGE-RAGE axis in humans. In this study, we examined whether azelnidipine addition could have renoprotective properties in hypertensive CKD patients by reducing serum levels of AGE and soluble form of RAGE (sRAGE). Thirty nondiabetic stage I or II CKD patients who had already been treated with angiotensin II receptor blockers were enrolled in this study.

HYPOTHESIS

We hypothesized that azelnidipine treatment could limit renal injury partly by blocking the AGE-RAGE axis.

METHODS

Patients were randomly divided into 2 groups; one group was treated with 16 mg azelnidipine and the other with 5 mg amlodipine once daily. They were followed up for 6 months.

RESULTS

Proteinuria was positively correlated with circulating AGE and sRAGE levels in our subjects. Both drugs exhibited comparable and significant blood pressure (BP)-lowering effects. Although neither of them affected glucose, glycated hemoglobin, lipid levels, and estimated glomerular filtration rate, treatment with azelnidipine, but not amlodipine, decreased circulating AGE, sRAGE, proteinuria, and urinary levels of liver-type fatty acid binding protein, a marker of tubular injury, in a BP-lowering-independent manner.

CONCLUSIONS

Our present results suggest that azelnidipine may exert renoprotective properties in nondiabetic hypertensive CKD patients via its unique inhibitory effects on the AGE-RAGE axis.

THE AUTODIGESTION HYPOTHESIS AND RECEPTOR CLEAVAGE IN DIABETES AND HYPERTENSION

One of the key features of cardiovascular complications, such as hypertension or diabetes, is that they often appear at the same time in the same individual together with other forms of co-morbidities. While clinically a recognized phenomenon, no molecular mechanism for such co-morbidities has received universal acceptance. We propose a new hypothesis that provides a molecular basis for co-morbidities in hypertension due to unchecked proteolytic activity and receptor destruction. Testing of the hypothesis in the spontaneously hypertensive rat reveals an unchecked matrix metalloproteinase and serine protease activity in plasma and on several cardiovascular and parenchymal cells. The elevated proteolytic activity causes extracellular cleavage of multiple receptor types, such that cleavage of one receptor type leads to loss of the function carried out by this receptor. Proteolytic cleavage of the extracellular domain of the β(2) adrenergic receptor in arteries and arterioles causes vasoconstriction and elevation of the central blood pressure while cleavage of the extracellular domain of the insulin receptor leads to insulin resistance and lack of transmembrane glucose transport. A diverse set of cell dysfunctions in the spontaneously hypertensive rat are accompanied by cleavage of the membrane receptors that are involved in these functions. Chronic inhibition of the unchecked protease activity in the spontaneously hypertensive rat serves to restore the extracellular receptor density and alleviates the corresponding cell dysfunctions. The mild unchecked proteolytic activity in the spontaneously hypertensive rat points towards a chronic autodigestion process as a contributor to the end organ injury encountered in this rat strain. The presence of various soluble receptors, which consist of extracellular fragments of membrane receptors, in the plasma of hypertensive and diabetic patients suggest that the autodigestion process may also be present in man.

Enhanced expression of receptor for advanced glycation end-products is associated with low circulating soluble isoforms of the receptor in Type 2 diabetes

The sRAGE [soluble RAGE (receptor for advanced glycation end-products)] lack the transmembrane and cytoplasmic domain of the full-length receptor and can function as a decoy for RAGE ligands. Recent evidence suggests that sRAGE may be a potential biomarker of RAGE-mediated pathology. The present study aimed to examine the relationship between RAGE expression in peripheral blood monocytes and circulating sRAGE and esRAGE (endogenous sRAGE, a splice variant of sRAGE) in Type 2 diabetes. Protein expression of RAGE and esRAGE in monocyte cell lysate was determined by Western blot in 53 diabetic patients and 52 controls. Monocyte cell-surface-bound full-length RAGE expression was measured using flow cytometry. Serum sRAGE, esRAGE and AGE (advanced glycation end products) were assayed by ELISA. The mean HbA1c (glycated haemoglobin) of the diabetic patients was 9.74% and serum AGEs was increased. Monocyte full-length RAGE expression was significantly higher in diabetic patients whereas esRAGE expression was reduced, and serum AGEs concentration was an independent determinant of monocyte cell surface full-length RAGE expression. Serum levels of sRAGE [573.3 (375.7-754.3) compared with 608.1 (405.3-940.8) pg/ml, P<0.05] and esRAGE [241.8 (154.6-356.6) compared with 286.5 (202.6-390.0) pg/ml, P<0.05; values are medians (interquartile range)] were decreased. There was an inverse association between monocyte RAGE expression and log(serum sRAGE) (r=-0.34, P=0.01) but not with esRAGE. In conclusion, despite an increase in full-length RAGE expression, esRAGE expression was down-regulated in the diabetic patients, and serum sRAGE and esRAGE was also reduced. Hence increased full-length RAGE levels are not associated with a similar increase in sRAGE isoforms levels.

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

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

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSION

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

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Involvement of TAGE-RAGE System in the Pathogenesis of Diabetic Retinopathy

Diabetic complications are a leading cause of acquired blindness, end-stage renal failure, and accelerated atherosclerosis, which are associated with the disabilities and high mortality rates seen in diabetic patients. Continuous hyperglycemia is involved in the pathogenesis of diabetic micro- and macrovascular complications via various metabolic pathways, and numerous hyperglycemia-induced metabolic and hemodynamic conditions exist, including increased generation of various types of advanced glycation end-products (AGEs). Recently, we demonstrated that glyceraldehyde-derived AGEs, the predominant structure of toxic AGEs (TAGE), play an important role in the pathogenesis of angiopathy in diabetic patients. Moreover, recent evidence suggests that the interaction of TAGE with the receptor for AGEs (RAGE) elicits oxidative stress generation in numerous types of cells, all of which may contribute to the pathological changes observed in diabetic complications. In this paper, we discuss the pathophysiological role of the TAGE-RAGE system in the development and progression of diabetic retinopathy.

Plasma sRAGE is independently associated with high sensitivity C-reactive protein in type 2 diabetes without coronary artery disease

Our studies suggest that plasma soluble advanced glycation end products (sRAGEs) has significantly negative association with high sensitivity C-reactive protein (hs-CRP) in 245 type 2 diabetes patients without diagnosed coronary artery disease (CAD). sRAGE maybe act as a novel biomarker for predicting the atherosclerosis in diabetes at the early stage.

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

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

High plasma levels of the soluble receptor for advanced glycation endproducts in patients with symptomatic carotid atherosclerosis

BACKGROUND

Advanced glycation endproducts (AGEs), particularly carboxymethyl(lysine)-adducts (CML), exert part of their cellular effects by binding to a receptor, named receptor for AGEs (RAGE). The soluble form of this receptor (sRAGE) has been shown to have an athero-protective role. We hypothesized the existence of a relationship between the AGE-RAGE axis and the occurrence of symptoms related to carotid atherosclerosis in nondiabetic conditions.

MATERIALS AND METHODS

We evaluated plasma levels of CML and sRAGE (by ELISA), and tissue levels (tAGEs and tRAGE, semiquantitatively, by immunohistochemistry) in endarterectomy carotid plaque tissue in 29 nondiabetic patients. At the time of surgery, 10 patients were asymptomatic and 19 were symptomatic.

RESULTS

Plasma levels of sRAGE were higher in symptomatic patients than in asymptomatic patients [median (interquartile range): 676 (394-858) pg mL(-1) vs. 347 (284-479) pg mL(-1), P = 0.009]. In symptomatic patients, plasma levels of sRAGE correlated positively with CML (r = 0.60, P < 0.01), C-reactive protein (CRP) (r = 0.618, P < 0.01) and fibrinogen (r = 0.522, P<0.005), while in asymptomatic patients, no correlation was observed. Although tissue and plasma levels of AGEs and RAGE did not correlate between each other, tAGEs and tRAGE were also positively correlated only in symptomatic patients (chi(2) = 8.93, P = 0.003).

CONCLUSIONS

Plasma levels of sRAGE are higher in symptomatic than asymptomatic carotid atherosclerosis. Higher levels of sRAGE in symptomatic patients may be markers of a higher degree of vascular inflammation in such patients.

Positive association of serum levels of advanced glycation end products and high mobility group box-1 with asymmetric dimethylarginine in nondiabetic chronic kidney disease patients

There is accumulating evidence that engagement of the receptor for advanced glycation end products (RAGE) with ligands such as advanced glycation end products (AGEs) and high mobility group box-1 (HMGB-1) elicits vascular inflammation, thus contributing to the increased risk for cardiovascular disease. Furthermore, enhanced accumulation of asymmetric dimethylarginine (ADMA) plays a role in cardiovascular disease in chronic kidney disease (CKD) patients. However, the relationships among serum levels of AGEs, HMGB-1, soluble form of RAGE (sRAGE), and ADMA are largely unknown. The aim of the present study is to determine their relationships in CKD patients. Twenty nondiabetic normotensive CKD patients with dyslipidemia and 20 age- and sex-matched healthy controls were enrolled. All subjects underwent determination of blood chemistries; urinary proteinuria; and serum levels of AGEs, HMGB-1, sRAGE, and ADMA. Serum AGE, HMGB-1, sRAGE, and ADMA levels in CKD patients were significantly higher than those in control subjects. Circulating levels of AGEs in CKD patients were positively associated with sRAGE and ADMA, and HMGB-1 with ADMA, but not sRAGE. There were no significant associations among these markers and serum creatinine, estimated glomerular filtration rate, proteinuria, and lipid levels. In multiple regression analyses, AGEs and HMGB-1 were independently correlated with ADMA. The present study demonstrated that AGE and sRAGE levels were correlated with each other and that AGEs and HMGB-1 were independently associated with ADMA in nondiabetic CKD patients. Elevation of the RAGE ligands may enhance ADMA levels, suggesting the active involvement of AGE/HMGB-1-RAGE-ADMA axis in CKD patients.

Circulating levels of a soluble form of receptor for advanced glycation end products and high-mobility group box chromosomal protein 1 in patients with acute pancreatitis

OBJECTIVES

To study in patients with acute pancreatitis (AP) the plasma soluble form of the receptor for advanced glycation end products (sRAGE) and high-mobility group box chromosomal protein 1 (HMGB1) levels, followed-up for 12 days after hospitalization, in relation to the occurrence of organ failure and mortality.

METHODS

Thirty-eight patients with severe AP and organ failure (grade 2). A control group (127 patients) consisted of 38 patients with severe AP without organ failure (grade 1) and 89 patients with mild AP (grade 0). Plasma samples for determination of HMGB1 and sRAGE levels were collected on admission and on days 1 and 2, days 3 and 4, and days 7 and 12 after admission.

RESULTS

The median of the highest sRAGE levels was higher in grade 2 patients (472 pg/mL; interquartile range [IQR], 259-912) than in grade 0 plus grade 1 patients (349 pg/mL; IQR, 209-544; P = 0.024). Among the patients with detectable HMGB1, the median of the highest HMGB1 levels was 117 ng/mL (IQR, 56-212; n = 24) in grade 2 patients and 87 ng/mL (IQR, 54-161; n = 62) in grade 0 plus grade 1 patients (P = 0.310).

CONCLUSIONS

We demonstrate that sRAGE level, but not HMGB1 level, is significantly higher in AP patients who develop organ failure than in AP patients without organ failure who recover.

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

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Reduced endogenous secretory receptor for advanced glycation end products (esRAGE) in young people with Type 1 diabetes developing microalbuminuria

AIMS

The endogenous secretory receptor for advanced glycation end products (esRAGE) appears to work as a scavenger for AGEs and it has been implicated in the pathogenesis of diabetic complications. The aim of the present study was to perform a longitudinal evaluation of esRAGE in young people with Type 1 diabetes (T1D) in relation to the development of microalbuminuria (MA).

METHODS

Serum esRAGE levels were measured in longitudinally collected blood samples from 49 T1D patients with MA (MA+) and 49 matched normoalbuminuric patients (MA-), followed in the Oxford Regional Prospective Study. esRAGE levels were compared between MA+ and MA- subjects in relation to the time of MA onset.

RESULTS

Overall, esRAGE levels were significantly lower in MA+ than in MA- subjects (0.727 +/- 0.396 vs. 0.936 +/- 0.433 ng/ml; P = 0.015). These differences between the two groups were present both before (0.725 +/- 0.410 vs. 0.956 +/- 0.505 ng/ml, P = 0.038) and after the onset of MA (0.750 +/- 0.433 vs. 0.948 +/- 0.418 ng/ml, P = 0.04). In a longitudinal analysis there was no effect of age, duration, glycated haemoglobin (HbA(1c)) or body mass index standard deviation scores on esRAGE levels (all P > 0.05). In a Cox model, esRAGE levels significantly contributed to the probability of developing MA [Exp(B)(95% confidence interval): 0.34(0.12-0.98); P = 0.04), independently of HbA(1c).

CONCLUSIONS

In this longitudinal study of young people with T1D, esRAGE levels were reduced in MA+ subjects, even before the onset of MA, and appeared to be related to its development, thus suggesting a potential role of esRAGE in the pathogenesis of this complication. Diabet. Med. 26, 815-819 (2009).

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

AIMS/HYPOTHESIS

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

METHODS

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

RESULTS

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

CONCLUSIONS/INTERPRETATION

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

RAGE: a novel biological and genetic marker for vascular disease

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

Serum levels of soluble receptor for advanced glycation end products and of S100 proteins are associated with inflammatory, autoantibody, and classical risk markers of joint and vascular damage in rheumatoid arthritis

INTRODUCTION

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface receptor molecules. High concentrations of three of its putative proinflammatory ligands, S100A8/A9 complex (calprotectin), S100A8, and S100A12, are found in rheumatoid arthritis (RA) serum and synovial fluid. In contrast, soluble RAGE (sRAGE) may prevent proinflammatory effects by acting as a decoy. This study evaluated the serum levels of S100A9, S100A8, S100A12 and sRAGE in RA patients, to determine their relationship to inflammation and joint and vascular damage.

METHODS

Serum sRAGE, S100A9, S100A8 and S100A12 levels from 138 patients with established RA and 44 healthy controls were measured by ELISA and compared by unpaired t test. In RA patients, associations with disease activity and severity variables were analyzed by simple and multiple linear regressions.

RESULTS

Serum S100A9, S100A8 and S100A12 levels were correlated in RA patients. S100A9 levels were associated with body mass index (BMI), and with serum levels of S100A8 and S100A12. S100A8 levels were associated with serum levels of S100A9, presence of anti-citrullinated peptide antibodies (ACPA), and rheumatoid factor (RF). S100A12 levels were associated with presence of ACPA, history of diabetes, and serum S100A9 levels. sRAGE levels were negatively associated with serum levels of C-reactive protein (CRP) and high-density lipoprotein (HDL), history of vasculitis, and the presence of the RAGE 82Ser polymorphism.

CONCLUSIONS

sRAGE and S100 proteins were associated not just with RA inflammation and autoantibody production, but also with classical vascular risk factors for end-organ damage. Consistent with its role as a RAGE decoy molecule, sRAGE had the opposite effects to S100 proteins in that S100 proteins were associated with autoantibodies and vascular risk, whereas sRAGE was associated with protection against joint and vascular damage. These data suggest that RAGE activity influences co-development of joint and vascular disease in rheumatoid arthritis patients.

Independent determinants of soluble form of receptor for advanced glycation end products in elderly hypertensive patients

Advanced glycation end product receptor (RAGE) interaction plays an important role in atherosclerosis. Although exogenously administered soluble form of RAGE (sRAGE) has been shown to suppress the development and progression of atherosclerosis in animals, the kinetics and role of endogenous sRAGE in humans are not fully understood. In this study, to clarify whether endogenous sRAGE could capture and efficiently eliminate RAGE ligands such as circulating AGEs and high-mobility group box-1 (HMGB-1), we investigated the correlation between sRAGE and RAGE ligands and examined independent determinants of serum levels of sRAGE in hypertensive humans. Two-hundred seventy-one consecutive nondiabetic outpatients with essential hypertension (83 male and 188 female; mean age, 76.5 +/- 9.2 years) underwent a complete history, physical examination, and determination of blood chemistries, including serum levels of sRAGE, AGEs, and HMGB-1. Univariate regression analysis showed that serum levels of sRAGE were associated with body mass index (r = -0.313, P < .0001), waist (r = -0.214, P < .0001), alanine aminotransferase (r = -0.172, P = .005), gamma-glutamyltranspeptidase (r = -0.213, P < .0001), 24-hour creatinine clearance (r = -0.348, P < .0001), B-type natriuretic peptide (r = 0.138, P = .027), tumor necrosis factor-alpha (r = 0.138, P = .002), and alcohol intake (r = -0.155, P = .010). By the use of multiple stepwise regression analyses, 24-hour creatinine clearance (P < .0001), gamma-glutamyltranspeptidase (P < .001), body mass index (P = .007), and tumor necrosis factor-alpha (P = .024) remained significant independently. The present study demonstrated for the first time that there was no significant correlation between serum levels of sRAGE and RAGE ligands such as circulating AGEs and HMGB-1 in hypertensive patients. Anthropometric and inflammatory variables and liver and renal function may be the determinants of endogenous sRAGE levels in nondiabetic hypertensive patients.

Elevated serum advanced glycation end products and poor grip strength in older community-dwelling women

BACKGROUND

Advanced glycation end products (AGEs) have been implicated in the pathogenesis of diabetes, heart disease, and kidney failure and may potentially affect skeletal muscle. Whether AGEs are associated with poor muscle strength is unknown.

METHODS

Serum carboxymethyl-lysine (CML), a dominant AGE, circulating soluble form of receptor for advanced glycation end products (sRAGE), and endogenous secretory receptor for advanced glycation end product (esRAGE) and grip strength were measured in 559 moderately to severely disabled women, age 65 and older, in the Women's Health and Aging Study I in Baltimore, Md.

RESULTS

Mean (standard deviation) grip strength among women in the highest quartile of serum CML compared with women in the lower three quartiles was 18.6 and 20.0 kg, respectively (p = .002), adjusting for age, race, body mass index, cognitive dysfunction, depression, and diabetes. Serum sRAGE and esRAGE were not significantly associated with grip strength.

CONCLUSIONS

Women with high serum AGEs have greater muscle weakness. Further studies are needed to determine whether AGEs, a potentially modifiable risk factor, are associated with physical performance and disability in older adults.

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

Advanced glycation end-products (AGEs) and the receptor for AGEs (RAGE) system play an important role in the development of diabetic complications. The soluble form of RAGE (sRAGE) that potentially counteracts AGEs consists of several forms, including endogenous secretory RAGE (esRAGE; a splice variant of RAGE) and cleaved-type soluble RAGE derived from cell-surface RAGE. The aim of this study was to compare sRAGE and esRAGE directly in patients with type 1 diabetes. The associations of both total sRAGE and esRAGE with markers of glycaemic control and with carotid intima-media thickness (IMT) as a marker of atherosclerosis were examined in 130 type 1 diabetes patients (aged 23.6+/-4.9 years) and 22 age-matched non-diabetic subjects. IMT was inversely correlated with esRAGE (r=-0.254, p=0.0015) but neither with sRAGE nor subtracted soluble RAGE values (that is, circulating total sRAGE values - circulating esRAGE values). Furthermore, a stepwise multivariate regression analysis revealed that esRAGE (F=7.3), but not sRAGE, was a variable that interacted independently of IMT. It is likely that circulating sRAGE and esRAGE are distinct markers and that circulating esRAGE levels, but not sRAGE levels, are associated with the status of early-stage atherosclerosis.

Dietary fructose and the metabolic syndrome

PURPOSE OF REVIEW

Fructose, a naturally found sugar in many fruits, is now commonly used as an industrial sweetener and is excessively consumed in Western diets. High fructose intake is increasingly recognized as causative in development of prediabetes and metabolic syndrome. The mechanisms underlying fructose-induced metabolic disturbances are unclear but are beginning to be unravelled. This review presents recent findings in this field and an overall mechanistic insight into the metabolic effects of dietary fructose and its role in metabolic syndrome.

RECENT FINDINGS

Recent animal studies have confirmed the link between fructose feeding and increased plasma uric acid, a potentially causative factor in metabolic syndrome. Advanced glycation end products are also implicated because of their direct protein modifications and indirect effects on inflammation and oxidative stress. Human studies have demonstrated fructose's ability to change metabolic hormonal response, possibly contributing to decreased satiety.

SUMMARY

There is much evidence from both animal models and human studies supporting the notion that fructose is a highly lipogenic nutrient that, when consumed in high quantities, contributes to tissue insulin insensitivity, metabolic defects, and the development of a prediabetic state. Recently evidence has helped to decipher the mechanisms involved in these metabolic changes.

Circulating advanced glycation end products (AGEs) and soluble form of receptor for AGEs (sRAGE) are independent determinants of serum monocyte chemoattractant protein-1 (MCP-1) levels in patients with type 2 diabetes

BACKGROUND

Atherosclerosis is an inflammatory disease. Monocyte chemoattractant protein-1 (MCP-1) is an essential chemokine responsible for the recruitment of monocytes to inflammatory lesions in the vasculature, an initial step of atherosclerosis. Since serum levels of MCP-1 are higher in patients with type 2 diabetes, inhibition of MCP-1 may be a novel therapeutic target for prevention of accelerated atherosclerosis in diabetes. However, little is known about the regulation and determinants of serum MCP-1 levels in patients with diabetes. In this study, we examined the determinants of serum MCP-1 levels in type 2 diabetic patients.

METHODS

Eighty-six consecutive outpatients with type 2 diabetes (36 male and 50 female; mean age 68.4+/-9.6) underwent a complete history and physical examination, determination of blood chemistries, MCP-1, tumour necrosis factor-alpha, adiponectin, advanced glycation end products (AGEs), and soluble form of receptor for AGEs (sRAGE). We examined the association between MCP-1 levels and those in anthropometric, metabolic and inflammatory variables in these subjects.

RESULTS

Univariate regression analysis showed that serum levels of MCP-1 were positively associated with AGEs (r=0.386, p<0.001) and sRAGE (r=0.315, p<0.001). After adjusting for age and sex, AGEs (p<0.001) and sRAGE (p<0.05) still remained significant.

CONCLUSION

The results demonstrate for the first time that circulating levels of AGEs and sRAGE are independent determinants of serum MCP-1 levels in patients with type 2 diabetes. Our present observations suggest the AGEs-RAGE system may be mainly involved in the elevation of MCP-1 in type 2 diabetic patients.

Clinical significance of HbA1c as a marker of circulating lipids in male and female type 2 diabetic patients

Diabetic patients with accompanied (but often unnoticed) dyslipidemia are soft targets of cardiovascular deaths. An early intervention to normalize circulating lipids has been shown to reduce cardiovascular complications and mortality. Glycated hemoglobin (HbA(1c)) is a routinely used marker for long-term glycemic control. This investigation is an attempt to evaluate the diagnostic value of HbA(1c) in predicting diabetic dyslipidemia. Venous blood samples were collected from 2,220 type 2 diabetic patients (ages, 35-91 years; male/female ratio, 1.07). The sera were analyzed for HbA(1c), fasting blood glucose (FBG), total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL) and low-density lipoprotein cholesterol (LDL). The levels of HbA(1c) did not differ significantly between males (8.33 +/- 0.06%) and females (8.47 +/- 0.07%), whereas female patients had significantly higher FBG (10.01 +/- 0.13 mmol/l) than males (9.31 +/- 0.11 mmol/l). HbA(1c) showed direct and significant correlations with cholesterol, triglycerides and LDL and inverse correlation with HDL. Female diabetic patients had significantly higher levels of serum cholesterol (5.42 +/- 0.03 vs. 5.18 +/- 0.03 mmol/l) and HDL (1.32 +/- 0.01 vs. 1.12 +/- 0.01 mmol/l) as compared to males. There was no significant difference in triglycerides and LDL between the two genders. Older patients (>70 years) had significantly lower FBG, cholesterol, triglycerides and LDL. There was a linear and significant increase in triglycerides in the patients of both genders with impaired glycemic control. Both male and female patients with worse glycemic control (HbA(1c) > 9%) had significantly high cholesterol and LDL levels. Serum HDL showed a significant and inverse relationship with uncontrolled hyperglycemia in females but not in males. These findings clearly suggest that HbA(1c) can provide valuable supplementary information about the extent of circulating lipids besides its primary role in monitoring long-term glycemic control. Further studies are warranted to reinforce the potential of HbA(1c) as a biomarker for screening of high-risk diabetic patients.

RAGE and soluble RAGE: potential therapeutic targets for cardiovascular diseases

Receptor for advanced glycation end-products (RAGE) is known to be involved in microvascular complications in diabetes. RAGE is also profoundly associated with macrovascular complications in diabetes through regulation of atherogenesis, angiogenic response, vascular injury, and inflammatory response. The potential significance of RAGE in the pathogenesis of cardiovascular disease appears not to be confined solely to nondiabetic rather than diabetic conditions. Numerous truncated forms of RAGE have recently been described, and the C-terminally truncated soluble form of RAGE has received much attention. Soluble RAGE consists of several forms, including endogenous secretory RAGE (esRAGE), which is a spliced variant of RAGE, and a shedded form derived from cell-surface RAGE. These heterogeneous forms of soluble RAGE, which carry all of the extracellular domains but are devoid of the transmembrane and intracytoplasmic domains, bind ligands including AGEs and can antagonize RAGE signaling in vitro and in vivo. ELISA systems have been developed to measure plasma esRAGE and total soluble RAGE, and the pathophysiological roles of soluble RAGE have begun to be unveiled clinically. In this review, we summarize recent findings regarding pathophysiological roles in cardiovascular disease of RAGE and soluble RAGE and discuss their potential usefulness as therapeutic targets and biomarkers for the disease.

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

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

Receptor for advanced glycation endproducts and atherosclerosis: From basic mechanisms to clinical implications

The receptor for advanced glycation endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules with a diverse repertoire of ligands. In the atherosclerotic milieu, three classes of RAGE ligands, i.e., products of non-enzymatic glycoxidation, S100 proteins and amphoterin, appear to drive receptor-mediated cellular activation and potentially, acceleration of vascular disease. The interaction of RAGE-ligands effectively modulates several steps of atherogenesis, triggering an inflammatory-proliferative process and furthermore, critically contributing to propagation of vascular perturbation, mainly in diabetes. RAGE has a circulating truncated variant isoform, soluble RAGE (sRAGE), corresponding to its extracellular domain only. By competing with cell-surface RAGE for ligand binding, sRAGE may contribute to the removal/neutralization of circulating ligands thus functioning as a decoy. The critical role of RAGE in the chronic vascular inflammation processes highlights this receptor-ligand axis as a possible and attractive candidate for therapeutic intervention to limit vascular damage and its associated clinical disorders.