Role of advanced glycation end product (AGE)-induced receptor (RAGE) expression in diabetic vascular complications

AimsVascular complications are the major causes of morbidity and mortality in diabetic subjects. Interaction of advanced glycation end products (AGEs) with their receptor (RAGE) induces signal transduction that culminates in vascular complications. Therefore, in the present study we investigated the dependence of RAGE expression on circulating AGEs and evaluated the outcome of AGE–RAGE interaction by the oxidative stress and nature of vascular complications in type 2 diabetes mellitus (T2DM) patients.MethodsRAGE expression was determined by quantitative real-time PCR and western blotting, serum AGEs were estimated by ELISA and spectrofluorometry and oxidative stress markers namely protein carbonyl (PCO), advanced oxidation protein products (AOPP) and lipid peroxidation (MDA) were assayed spectrophotometerically in 75 T2DM patients (DM without vascular complication n = 25; DM with microvascular complications n = 25; DM with macrovascular complications n = 25) and 25 healthy controls.ResultsSerum AGE level was significantly higher in diabetic patients having vascular complications as compared to T2DM without complications (p < 0.01). RAGE m-RNA expression level in PBMCs assayed by quantitative real time PCR was four times higher in diabetic subjects without vascular complications while DM patients having microvascular and macrovascular complications showed 12 fold and 8 fold higher RAGE m-RNA expression respectively compared to healthy controls. Circulating AGE level showed significant positive correlation with RAGE m-RNA expression and oxidative stress markers.ConclusionAGE-mediated exacerbation of RAGE expression may contribute to oxidative stress generation that plays a key role in pathogenesis of vascular complications in diabetes.     

Up-Regulated Expression of Advanced Glycation End-Products and Their Receptor in the Small Intestine and Colon of Diabetic Rats

Background and Aims  

Gastrointestinal disorders and symptoms are common in diabetic patients. Advanced glycation end-products (AGEs) and their receptor (RAGE) have been proposed as an important pathological mechanism underlying diabetic complications, such as diabetic cardiopathy, retinopathy, nephropathy, etc. The aims were to study the distribution of AGE and RAGE in the normal and diabetic small intestine and colon in rats and the possible relationship between AGEs/RAGE and diabetes-induced intestinal structural remodeling.     

Modulation of CD36 protein expression by AGEs and insulin in aortic VSMCs from diabetic and non-diabetic rats

Background and aimIn type 2 diabetes, the interplay between cells and inflammatory mediators up-regulates CD36 expression in macrophages. The aim of this work was to investigate advanced glycation end products (AGE)-induced CD36 expression and its regulation by insulin in aortic vascular smooth muscle cells (VSMCs) from Goto–Kakisaki (GK) rats, a non-obese insulin model of both insulin resistance and type 2 diabetes. The context of overexpression of CD36 in aortas was also evaluated.Methods and resultsVSMCs were isolated and cultured from the aortas of GK rats and non-diabetic rats. The expression of proteins was evaluated by Western blot. The aortic production of superoxide anion (O₂^·−) was measured by luminescence on isolated tissue. AGEs and advanced oxidation protein products (AOPPs) were determined in plasma by fluorescence spectroscopy and spectrophotometry, respectively.AGE receptor (RAGE), NF-κB, and CD36 protein expression as well as O₂^·− production were higher in GK aortas than in control aortas, and AGEs and AOPPs were higher in GK plasma. In VSMCs from non-diabetic rats, insulin was able to reduce (10 nM) or suppress (100 nM) the protein overexpression of CD36 induced by AGEs–BSA. In contrast, in VSMCs from GK rats, insulin was unable to reduce AGEs–BSA-induced CD36 overexpression.ConclusionsThe results suggest an overexpression of CD36 in VSMCs from GK rats and impaired control by insulin. In the context of increased plasma AGEs, aortic RAGE overexpression and increased oxidative stress markers, the data are compatible with an AGEs induced CD36 overexpression in diabetes.     

Advanced glycation end products (AGEs) and their soluble receptors (sRAGE) as early predictors of reno-vascular complications in patients with uncontrolled type 2 diabetes mellitus

AimTo evaluate the role of advanced glycation end-products (AGEs) and their soluble receptors (sRAGE) expression levels as predictors of vascular complications in uncontrolled type 2 diabetes mellitus (T2DM).MethodsCross-sectional study was conducted on T2DM adults of both sexes who attended the outpatient service of Al-Karak Teaching Hospital, Jordan during the period from June 2017 to August 2018. Participants were categorized in two groups according to their glycemic control and the presence of reno-vascular complications. Twenty healthy subjects were recruited as control group. Blood sample was obtained from all participants and used for the assessment of FBG, HbA1c, serum AGEs and sRAGE, serum urea and creatinine; 24 h urine was also collected for the determination of urinary albumin.ResultsDiabetic subjects with vascular complication had a significantly higher serum AGEs 50.3 ± 13 vs. 28.9 ± 8 pg/ml) and AGEs/sRAGE ratio (0.058 ± 0.02 vs. 0.037 ± 0.02) associated with significantly lower serum sRAGE (868.7 ± 50.8 vs. 912.8 ± 294.3) compared to those with no complications. Serum AGEs and sRAGE showed weak negative and non-significant association in both groups of patients. However, the AGEs/sRAGE ration was inversely and significantly associated with the urinary albumin/creatinine ratio (r = − 0.51, P = 0.009) only in DM patients with reno-vascular complications.ConclusionWe found an association between AGEs/sRAGE ratio and urinary albumin/serum creatinine ratio in T2DM patients with reno-vascular complications; providing evidence that serum AGEs and sRAGE can be considered as predictors of vascular complications in uncontrolled T2DM patients.     

Plasma levels of advanced glycation end products are associated with haemolysis‐related organ complications in sickle cell patients

Oxidative stress plays an important role in the pathophysiology of sickle cell disease (SCD). Plasma levels of advanced glycation end products (AGEs) are increased under oxidative conditions and are associated with disease severity in diabetes and inflammatory diseases. We investigated whether AGEs are increased in sickle cell patients and whether they are associated with SCD‐related complications. Plasma levels of the AGEs pentosidine, N^ε‐(carboxymethyl)lysine (CML) and N^ε‐(carboxyethyl)lysine (CEL) were measured using single‐column high performance liquid chromatography with fluorescence detection (pentosidine) and ultra performance liquid chromatography‐tandem mass spectrometry (CML and CEL). Plasma levels of pentosidine and CML were increased in HbSS/HbSβ⁰‐thalassaemia (n = 60) and HbSC/HbSβ⁺‐thalassaemia (n = 42) patients during steady state as compared to healthy HbAA controls (n = 30) without increments during painful crisis. CEL levels were comparable between all groups. Pentosidine and CML levels correlated significantly to haemolytic rate during the clinically asymptomatic state while pentosidine was significantly related to the number of haemolysis‐related organ complications. The increased plasma AGE levels in sickle cell patients and their association with haemolysis and haemolysis‐related complications suggest AGEs might be implicated in the pathophysiology of the haemolytic phenotype of SCD. Measurement of AGEs might be useful in predicting organ complications in SCD.     

Association of glutathione-S-transferase with patients of type 2 diabetes mellitus with and without nephropathy

Statements of the problemHyperglycemia induced oxidative stress is implicated as a contributor to the onset and progression of type 2 diabetes mellitus (T2DM) and its complications like diabetic nephropathy (DN). Glutathione-S-transferase (GST) is primarily involved in the neutralization of reactive oxygen species (ROS) by enzymatic conjugation with the scavenger peptide glutathione (GSH). Therefore, present study was aimed to evaluate the role of GST along with oxidative stress markers and their correlation in patients with Type 2 diabetes mellitus with and without nephropathy.MethodsThis study comprised of 300 participants divided into three groups of 100 each: healthy controls (HC), T2DM without complications and DN. Plasma GST, malondialdehyde (MDA), reduced GSH levels and ferric reducing ability of plasma (FRAP) were estimated spectrophotometrically.ResultsHighest GST levels was observed in T2DM which was significantly higher (p < 0.05) as compared to DN and HC. However, GSH and FRAP levels were found to be significantly lowest whereas MDA levels were significantly highest in DN as compared to T2DM and HC. GST showed a significant negative correlation with GSH, FRAP and positive correlation with MDA in both patients groups.ConclusionsHighest activity of GST in T2DM might be as a compensatory mechanism in response to oxidative stress. GST is found to have significant negative association with decreased GSH. Altered redox milieu in DN collectively conspire to increase the risk of renal damage in T2DM.     

Relationship between advanced glycation end products and increased lipid peroxidation in semen of diabetic men

Aims

Majority of diabetic male patients have disturbances in their reproductive systems. However, the mechanisms underlying these disturbances are largely unknown. Since advanced glycation end products (AGE) have a key role in oxidative stress and cell damage in diabetic complications, we hypothesize that AGEs may be involved sperm lipid peroxidation.

Methods

Total AGEs in seminal plasma of 32 diabetic and 35 non-diabetic men was determined by spectrofluorimetric method and carboxy methyl lysine (CML) level was assayed using ELISA. Contents of lipid peroxidation in sperm and seminal plasma were determined by thiobarbituric acid reaction. Total antioxidant capacity (TAC) was measured by a colorimetric assay.

Results

Total AGEs were found significantly higher in seminal plasma of diabetic men than non-diabetic group (p < 0.001) whereas no significant differences in seminal plasma CML values between two groups was observed. Moreover, sperm and seminal plasma lipid peroxidation were significantly higher in diabetic subjects than non-diabetic men and a significantly lower TAC was detected in diabetic group compare to non-diabetics.

Conclusions

These results showed an increment in AGEs in seminal plasma of diabetic subjects and may suggest a key role for glycation process and increased oxidative stress in reproductive system dysfunction.     

Role of advanced glycation end products (AGEs) and receptor for AGEs (RAGE) in vascular damage in diabetes

A non-enzymatic reaction between ketones or aldehydes and the amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules and to the development and progression of various age-related disorders such as vascular complications of diabetes, Alzheimer's disease, cancer growth and metastasis, insulin resistance and degenerative bone disease. Under hyperglycemic and/or oxidative stress conditions, this process begins with the conversion of reversible Schiff base adducts, and then to more stable, covalently-bound Amadori rearrangement products. Over a course of days to weeks, these early glycation products undergo further reactions and rearrangements to become irreversibly crossed-linked, fluorescent protein derivatives termed advanced glycation end products (AGEs). There is a growing body of evidence that AGE and their receptor RAGE (receptor for AGEs) interaction elicits oxidative stress, inflammatory reactions and thrombosis, thereby being involved in vascular aging and damage. These observations suggest that the AGE-RAGE system is a novel therapeutic target for preventing diabetic vascular complications. In this paper, we review the pathophysiological role of the AGE-RAGE-oxidative stress system and its therapeutic intervention in vascular damage in diabetes. We also discuss here the potential utility of the restriction of food-derived AGEs in diabetic vascular complications.     

Advanced glycation end-products and methionine sulphoxide in skin collagen of patients with type 1 diabetes

Aims/hypothesis We determined whether oxidative damage in collagen is increased in (1) patients with diabetes; (2) patients with diabetic complications; and (3) subjects from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study, with comparison of subjects from the former standard vs intensive treatment groups 4 years after DCCT completion. Subjects, materials and methods We quantified the early glycation product fructose-lysine, the two AGEs N ^ε-(carboxymethyl)lysine (CML) and pentosidine, and the oxidised amino acid methionine sulphoxide (MetSO) in skin collagen from 96 patients with type 1 diabetes (taken from three groups: DCCT/EDIC patients and clinic patients from South Carolina and Scotland) and from 78 healthy subjects. Results Fructose-lysine was increased in diabetic patients (p<0.0001), both with or without complications (p<0.0001). Controlling for HbA_1c, rates of accumulation of AGEs were higher in diabetic patients than control subjects, regardless of whether the former had complications (CML and pentosidine given as log_e[pentosidine]) or not (CML only) (all p<0.0001). MetSO (log_e[MetSO]) also accumulated more rapidly in diabetic patients with complications than in controls (p<0.0001), but rates were similar in patients without complications and controls. For all three products, rates of accumulation with age were significantly higher in diabetic patients with complications than in those without (all p<0.0001). At 4 years after the end of the DCCT, no differences were found between the previous DCCT management groups for fructose-lysine, AGEs or MetSO. Conclusions/interpretation The findings suggest that in type 1 diabetic patients enhanced oxidative damage to collagen is associated with the presence of vascular complications.     

Advanced Glycation End Products and Receptor–Oxidative Stress System in Diabetic Vascular Complications

Reducing sugars can react non‐enzymatically with amino groups of protein to form Amadori products. These early glycation products undergo further complex reactions, such as rearrangement, dehydration, and condensation, to become irreversibly cross‐linked, heterogeneous fluorescent derivatives, termed advanced glycation end products (AGEs). The formation and accumulation of AGEs have been known to progress at an accelerated rate in patients with diabetes mellitus, thus being involved in the development and progression of diabetic micro‐ and macroangiopathy. Indeed, there is accumulating evidence that an interaction between an AGE and its receptor (RAGE) generates oxidative stress and subsequently evokes vascular inflammation and thrombosis, thereby playing a central role in diabetic vascular complications. In this paper, we review the pathophysiological role of AGE‐RAGE–oxidative stress system and its therapeutic interventions in diabetic micro‐ and macroangiopathy.     

晚期糖基化终末产物及其受体在原发性高血压中的作用机制

近年来研究发现晚期糖基化终末产物（advanced glycation end products,AGEs）在原发性高血压的发生、发展过程中起着一定的病理作用,AGEs主要通过直接修饰蛋白、结合受体RAGE并激活信号转导通路两条作用途径来发挥效应。此外AGEs—RAGE还与肾素-血管紧张素系统、氧化应激三者构成正反馈环路,共同参与了原发性高血压的进程。相信随着对AGEs—RAGE作剧机制及药物干预的进一步研究,抗AGEs的治疗策略将有望成为防治高血压及其并发症的新方向。     

Structural modifications of human albumin in diabetes

AimAlbumin, a major protein in the blood circulation, can undergo increased glycation in diabetes. From recent studies, it has become evident that glycation has important implications for albumin actions and impact on cell functioning. This study compares the structural and functional properties of albumin glycated by glucose and methylglyoxal (MGO) with those of albumin purified from diabetic patients.MethodsHuman serum albumin (HSA) was purified from diabetic patients and control subjects using affinity chromatography, and oxidation parameters in various albumin preparations were determined. Tryptophan and 1-anilino-8-naphthalene sulphonic acid (ANSA) probe fluorescence, redox state, antioxidant and copper-binding capacities of the different preparations of albumin were also determined and compared.ResultsOccurrence of oxidative modifications was enhanced in albumin whether purified from diabetic patients, or glycated by glucose or MGO, after determination of their fructosamine and free thiol and amino group contents, carbonyl content and antioxidant activities. Whereas more quantitative changes in oxidative and structural parameters were observed in the glucose- and MGO-modified albumins, significant impairment of albumin function (free-radical-scavenging and copper-binding capacities) were demonstrated in the HSA purified from diabetics. These findings reveal different structural and functional features of diabetic HSA compared with in vitro models.ConclusionThis study provides new information supporting albumin as an important biomarker for monitoring diabetic pathophysiology. In addition, it reconfirms the influence of experimental conditions in which advanced glycation end-products (AGEs) are generated in tests designed to mimic the pathological conditions of diabetes.     

Overexpression of RAGE Contributes to Cigarette Smoke-Induced Nitric Oxide Generation in COPD

Background

Receptor for advanced glycation end products (RAGE), a multiple-ligands receptor, is implicated in chronic obstructive pulmonary disease (COPD). This study was designed to investigate the potential role of RAGE in nitric oxide (NO) generation, an endogenous marker of nitrosative stress in COPD.

Methods

Lung tissues from COPD patients were used to describe the relationship between RAGE expression and NO level. RAGE expression was assessed by immunohistochemistry, western blot, and ELISA. Human bronchial epithelial cells (16HBE) were cultured with cigarette smoke extract (CSE). Neutralizing antibody against RAGE was used to detect the role of RAGE in CSE-induced NO generation by 16HBE cells.

Results

Compared with nonsmoker controls, overexpression of RAGE was significantly detected in COPD smokers (p < 0.01), but not healthy smokers and nonsmokers with COPD, which was dominantly expressed at bronchiolar epithelia. Correlation analysis showed that RAGE in COPD smokers was positively related to NO level, smoking status, and lung function decline. In cultured 16HBE cells treated with CSE, soluble RAGE was reduced; however, full-length RAGE was enhanced significantly as the same trend as NO generation. Moreover, increased NO level and NO synthase activity, decreased total glutathione (a major cellular antioxidant), enhanced nuclear translocation of p65 (a key molecule of nuclear factor (NF)-κB) and release of NF-κB-dependent proinflammatory cytokines were all reversed by pretreatment of anti-RAGE antibody.

Conclusions

These findings suggest that overexpression of RAGE contributes to CS-induced NO generation in COPD with involvement in NF-κB activation.     

Role of profilin-1 in vasculopathy induced by advanced glycation end products (AGEs)

AimsTo construct a simple and feasible rat model to mimic diabetic vasculopathy by chronic injection of advanced glycation end products (AGEs) and further determine the role of profilin-1 in vasculopathy in AGE-injection rats.MethodsSprague-Dawley rats were injected with AGEs-BSA (25 mg/kg/day) for 0, 20, 30, 40, and 60 days by caudal vein. Then, the morphological changes in the aorta, heart, and kidney and the expression of profilin-1 were assessed. In cultured endothelial cells, shRNA profilin-1 was used to clarify the role of profilin-1 in AGEs-induced vascular endothelial lesions and inflammatory reactions.ResultsThe aorta, heart, and kidney of the AGE-injection rats had obvious morphological changes. Also, the indicators of vascular remodeling in the aorta significantly increased, accompanied by the increased expression of profilin-1 in the aorta, heart, and kidney and polysaccharide content on the kidney basement membrane. In addition, the protein level of profilin-1 was markedly upregulated in the aorta of AGEs-injected rats and endothelial cells incubated with AGEs. shRNA profilin-1 markedly attenuated the upregulated expression of profilin-1, receptor for AGEs (RAGE), and NF-κB in endothelial cells incubated with AGEs, as well as reduced the high levels of ICAM-1, IL-8, TNF-α, ROS, and apoptosis induced by AGEs.ConclusionsExogenous AGEs can mimic diabetic vasculopathy in vivo to some extent and increase profilin-1 expression in the target organs of diabetic complications. Blockade of profilin-1 attenuates vascular lesions and inflammatory reactions, suggesting its critical role in the metabolic memory mediated by AGEs.     

Relationship between proinsulin-to-insulin ratio and advanced glycation endproducts in Japanese type 2 diabetic subjects

OBJECTIVE: Type 2 diabetes (T2DM) is characterized by increased proinsulin-to-insulin ratio (P/I ratio), increased glycation and oxidative stress, and beta-cell dysfunction. Previous reports implicated that increased P/I ratio, glycation and oxidative stress constitute markers of beta-cell dysfunction in T2DM. However, its clinical relevance remains to be elucidated. Therefore, in the present study we investigated the relationship between the P/I ratio, glycation and oxidative stress markers in patients with T2DM, using newly developed intact chemiluminescent immunoassay for proinsulin. METHODS: Fasting intact proinsulin, insulin, advanced glycation endproducts (AGEs), pentosidine, lipid peroxide and urine 8-isoprostane as well as other metabolic parameters were measured in 64 T2DM subjects. RESULTS: Using univariate analysis, P/I ratio showed significant positive correlations with plasma glucose (r=0.465), HbA1c (r=0.434) and AGEs (r=0.282), and significant negative correlations with insulin (r=-0.330) and HOMA-beta (r=-0.520) even after adjustment for age, sex, duration of diabetes, family history of diabetes, use of sulfonylureas, smoking and body mass index. Additionally, stepwise multiple regression analysis revealed that HOMA-beta, HbA1c and AGEs were independently and significantly correlated with P/I ratio. CONCLUSION: These findings suggest that not only hyperglycemia per se but also glycation is involved in beta-cell dysfunction in T2DM subjects.     

sRAGE与糖尿病及其并发症

晚期糖基化终末产物(AGEs)与其受体(RAGE)在糖尿病及其并发症的发生、发展中起重要作用.缺少胞内区的RAGE称为可溶性RAGE(sRAGE).其可阻断配体与RAGE的结合.糖尿病患者sRAGE水平明显降低,而他汀类、噻唑烷二酮类、血管紧张素转换酶抑制剂等药物可以提高血清sRAGE水平.对sRAGE的进一步研究有可...     

Glyco-oxidation and cardiovascular complications in type 2 diabetes: a clinical update

Diabetes is associated with a greatly increased risk of cardiovascular disease (CVD), which cannot be explained only by known risk factors, such as smoking, hypertension, and atherogenic dyslipidemia, so other factors, such as advanced glycation end-products (AGEs) and oxidative stress, may be involved. In this frame, hyperglycemia and an increased oxidative stress (AGE formation, increased polyol and hexosamine pathway flux, and protein kinase C activation) lead to tissue damage, thus contributing to the onset of cardiovascular complications. Several studies have identified in various cell systems, such as monocytes/macrophages and endothelial cells, specific cellular receptors (RAGE) that bind AGE proteins. The binding of AGEs on RAGE induces the production of cytokines and intracellular oxidative stress, thus leading to vascular damage. Soluble RAGE levels have been identified as hypothetical markers of CVD, but, in this regard, there are sparse and conflicting data in the literature. The purpose of this review was to examine all the available information on this issue with a view to clarifying or at least highlighting the points that are still weak, especially from the point of clinical view.