RAGE axis: Animal models and novel insights into the vascular complications of diabetes

Mechanism of Zhishi Xiebai Guizhi decoction to treat atherosclerosis: Insights into experiments, network pharmacology and molecular docking

ETHNOPHARMACOLOGICAL RELEVANCE

Zhishi Xiebai Guizhi Decoction (ZSXBGZD) is a traditional herbal manuscript used to treat cardiovascular disease, including atherosclerosis and coronary heart disease. The decoction has demonstrated its capability to protect arteries and resist atherosclerosis. Its mechanisms for anti-atherosclerosis effect, nevertheless, remain unknown.

AIMS OF THE STUDY

The goal of the present study is to explore the effectiveness of ZSXBGZD acting on atherosclerosis and its key components based on experimental verification and network pharmacology analysis.

MATERIALS AND METHODS

The ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and databases were used to identify chemical components in ZSXBGZD. Network pharmacological analysis and molecular docking were implemented in order to reveal the possible therapeutic targets of ZSXBGZD. To form the model of atherosclerosis, we gave Apolipoprotein E knocked out mice a high-fat diet. H&E staining was performed to observe the effects of ZSXBGZD on atherosclerosis. Immunofluorescence and Western blot were used to investigate whether ZSXBGZD could affect autophagy, apoptosis, AGE-RAGE signaling pathway and other related mechanisms.

RESULTS

In total, 30 core compounds were screened through intersecting UPLC-Q-TOF-MS and the databases. The anti-atherosclerotic effect of ZSXBGZD might relate to the AGE-RAGE signaling pathway via network pharmacology analysis. ZSXBGZD could inhibit apoptosis, activate autophagy and ease inflammation by modifying AGE-RAGE signaling pathway to reduce the area of atherosclerotic plaque.

CONCLUSION

ZSXBGZD could treat atherosclerosis by regulating autophagy and apoptosis via adjusting the AGE-RAGE signaling pathway.

The role of sRAGE in cardiovascular diseases

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

Receptors for Advanced Glycation End Products (RAGE): Promising Targets Aiming at the Treatment of Neurodegenerative Conditions

Advanced glycation end products (AGEs) are compounds formed after the non-enzymatic addition of reducing sugars to lipids, proteins, and nucleic acids. They are associated with the development of various clinical complications observed in diabetes and cardiovascular diseases, such as retinopathy, nephropathy, diabetic neuropathy, and others. In addition, compelling evidence indicates that these molecules participate in the progression of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Multiple cellular and molecular alterations triggered by AGEs that could alter homeostasis have been identified. One of the main targets for AGE signaling is the receptor for advanced glycation end-products (RAGE). Importantly, this receptor is the target of not only AGEs, but also amyloid β peptides, HMGB1 (high-mobility group box-1), members of the S100 protein family, and glycosaminoglycans. The activation of this receptor induces intracellular signaling cascades that are involved in pathological processes and cell death. Therefore, RAGE represents a key target for pharmacological interventions in neurodegenerative diseases. This review will discuss the various effects of AGEs and RAGE activation in the pathophysiology of neurodegenerative diseases, as well as the currently available pharmacological tools and promising drug candidates.

Cognitive decline in heart failure: Biomolecular mechanisms and benefits of exercise

By definition, heart failure (HF) is a human pathological condition affecting the structure and function of all organs in the body, and the brain is not an exception to that. Failure of the heart to pump enough blood centrally and peripherally is at the foundation of HF patients' inability to attend even the most ordinary daily activities and progressive deterioration of their cognitive capacity. What is more, between heart and brain exists a bidirectional relationship that goes well beyond hemodynamics and concerns bioelectric and endocrine signaling. This increasingly consolidated evidence makes the scenario even more complex. Studies have mainly chased how HF impairs cognition without focusing much on preventive measures, notably cardio-cerebral health proxies. Here, we aim to provide a brief account of known and hypothetical factors that may explain how exercise can help obviate cognitive dysfunction associated with HF in its different forms. As we shall see, there is a stringent need for a deeper grasp of such mechanisms. Indeed, gaining this new knowledge will automatically shed new light on the inner workings of HF itself, thus resulting in more effective prevention and treatment of this escalating syndrome.

Does dietary fat affect advanced glycation end products and their receptors? A systematic review of clinical trials

CONTEXT

Dietary fat seems to affect advanced glycation end products (AGEs) and their receptors. This systematic review assesses studies that evaluated the effect of dietary fat on markers of glycation.

OBJECTIVE

The aim of this systematic review was to analyze the effect of dietary fat on markers of glycation and to explore the mechanisms involved.

DATA SOURCES

This study was conducted according to PRISMA guidelines. PubMed, Cochrane, and Scopus databases were searched, using descriptors related to dietary fat, AGEs, and the receptors for AGEs.

STUDY SELECTION

Studies were selected independently by the 3 authors. Divergent decisions were resolved by consensus. All studies that evaluated the effects of the quantity and quality of dietary fat on circulating concentrations of AGEs and their receptors in adults and elderly adults with or without chronic diseases were included. Initially, 9 studies met the selection criteria.

DATA EXTRACTION

Three authors performed data extraction independently. Six studies were included.

RESULTS

Consumption of a Mediterranean diet rich in monounsaturated fatty acids (MUFAs) and low in dietary AGEs reduced serum concentrations of AGEs, reduced expression of the receptor for AGE (RAGE), and increased expression of the AGE receptor 1 (AGER1) when compared with consumption of a Western diet rich in saturated fatty acids and dietary AGEs. Supplementation with omega-3 polyunsaturated fatty acids (PUFAs) resulted in decreased concentrations of fluorescent AGEs and decreased expression of RAGE as well as increased expression of AGER1.

CONCLUSIONS

Increased consumption of MUFAs and omega-3 PUFAs and reduced consumption of saturated fatty acids seem to be effective strategies to beneficially affect glycation markers, which in turn may prevent and control chronic diseases.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42021220489.

Collagen crosslinking: effect on structure, mechanics and fibrosis progression

Biophysical properties of extracellular matrix (ECM), such as matrix stiffness, viscoelasticity and matrix fibrous structure, are emerging as important factors that regulate progression of fibrosis and other chronic diseases. The biophysical properties of the ECM can be rapidly and profoundly regulated by crosslinking reactions in enzymatic or non-enzymatic manners, which further alter the cellular responses and drive disease progression. In-depth understandings of crosslinking reactions will be helpful to reveal the underlying mechanisms of fibrosis progression and put forward new therapeutic targets, whereas related reviews are still devoid. Here, we focus on the main crosslinking mechanisms that commonly exist in a plethora of chronic diseases (e.g. fibrosis, cancer, osteoarthritis) and summarize current understandings including the biochemical reaction, the effect on ECM properties, the influence on cellular behaviors, and related studies in disease model establishment. Potential pharmaceutical interventions targeting the crosslinking process and relevant clinical studies are also introduced. Limitations of pharmaceutical development may be due to the lack of systemic investigations related to the influence on crosslinking mechanism from micro to macro level, which are discussed in the last section. We also propose the unclarified questions regarding crosslinking mechanisms and potential challenges in crosslinking-targeted therapeutics development.

Inhibitory effect of Salvia coccinea on inflammatory responses through NF-κB signaling pathways in THP-1 cells and acute rat diabetes mellitus

Hyperglycemia-induced oxidative stress has been implicated in diabetes and its complications. Medicinal plants possessing antioxidant activity may decrease oxidative stress by scavenging radicals and reducing power activity and would be a promising strategy for the treatment of inflammatory disorders like diabetes. This study was designed to evaluate the antioxidant effect of Aqueous Extract of  S.coccinea leaf (AESL) in HG treated THP-1 cells and streptozotocin (STZ)-induced diabetic Wistar rats. AESL and the standard antidiabetic drug glibenclamide were administered orally by intragastric tube for 14 days and pre-treated HG grown THP-1 cells. AESL treatment reduced HG induced increase in ROS production, NF-κB dependent proinflammatory gene expression by influencing NF-κB nuclear translocation in THP-1 cells. Oral administration of AESL inhibited STZ-induced increase in serum lipid peroxidation, aspartate transaminase, alanine transaminase, and Lactate dehydrogenase of diabetic rats. Significant increase in activity of superoxide dismutase, catalase and glutathione peroxidase, and a reduced level of glutathione, were observed in AESL treatment. The results demonstrate that AESL is useful in controlling blood glucose and also has antioxidant potential to influence the translocation of NF-κB, protect damage caused by hyperglycemia-induced inflammation.

Intensity of Glycemic Exposure in Early Adulthood and Target Organ Damage in Middle Age: The CARDIA Study

AIM

To determine whether long-term intensity of glycemic exposure (IGE) during young adulthood is associated with multiple target organs function at midlife independent of single fasting glucose (FG) measurement.

METHODS

We included 2,859 participants, aged 18-30 years at Y0, in the Coronary Artery Risk Development in Young Adults (CARDIA) Study. IGE was calculated as the sum of (average FG of two consecutive examinations × years between the examinations) over 25 years. Target organs function was indicated by cardiac structure, left ventricular (LV) systolic function, LV diastolic function, coronary artery calcium (CAC), and urine albumin-to-creatinine ratio (UACR) at Y25. We evaluated the associations between IGE with target organs function using linear regression models and estimated the associations between IGE with numbers of organs involved (0, 1, or ≥ 2 organs) using multinomial logistic regression models.

RESULTS

A 1-SD increment of IGE was significantly associated with worse target organs function after multivariable adjustment: left ventricular mass (β [SE], 5.468 [1.175]); global longitudinal strain (β [SE], 0.161 [0.071]); E/e' ratio (β[SE], 0.192 [0.071]); CAC score (β [SE], 27.948 [6.116]); and log UACR (β [SE], 0.076 [0.010]). Besides, IGE was independently associated with having ≥ 2 organs involved in both overall population (OR [95% CI], 1.48 [1.23, 1.41], P < 0.001) and subgroups stratified by diabetes at Y25.

CONCLUSION

Higher intensity of glycemic exposure during young adulthood was independently associated with subclinical alterations of target organs function at midlife. Our findings highlight the importance of early screening and management of IGE in youth.

Epigenetic Mechanisms in Diabetic Vascular Complications and Metabolic Memory: The 2020 Edwin Bierman Award Lecture

Macrovascular complications such as atherosclerosis, myocardial infarction and stroke, and microvascular complications such as nephropathy, retinopathy, and neuropathy are the major causes of increased morbidity and mortality in both type 1 and type 2 diabetes. Increased inflammation, oxidative stress, and fibrosis are common features in most diabetes complications. Although extensive studies have examined the biochemical pathways leading to the expression of inflammatory, profibrotic, and other pathological genes, as well as genetic factors related to diabetes and associated complications, much less is known about the contribution of epigenetic changes that occur without alterations in the DNA sequence. Environmental factors, lifestyles, and improper diet implicated in diabetes can affect epigenetic states. Epigenetic modifications, including DNA methylation and histone modifications, can alter gene transcription in response to environmental stimuli and cooperate with noncoding RNAs. These epigenetic modifications have been observed in various target cells under diabetic conditions. Moreover, epigenetics has also been implicated in the phenomenon of metabolic memory observed in clinic trials and animal studies, in which prior episodes of poor glycemic control can confer continued risk of complications despite subsequent glucose normalization. Epigenome-wide association studies in cohorts with diabetes are uncovering epigenotype variations that provide new insights into diabetic vascular complications. Here, I discuss the role of epigenetics and noncoding RNAs in diabetes complications and metabolic memory, and their translation potential to serve as biomarkers and drug targets to improve clinical management of diabetic vascular complications.

Molecular complexities underlying the vascular complications of diabetes mellitus - A comprehensive review

Diabetes is a chronic disease, characterized by hyperglycemia, which refers to the elevated levels of glucose in the blood, due to the inability of the body to produce or use insulin effectively. Chronic hyperglycemia levels lead to macrovascular and microvascular complications. The macrovascular complications consist of peripheral artery disease (PAD), cardiovascular diseases (CVD) and cerebrovascular diseases, while the microvascular complications comprise of diabetic microangiopathy, diabetic nephropathy, diabetic retinopathy and diabetic neuropathy. Vascular endothelial dysfunction plays a crucial role in mediating both macrovascular and microvascular complications under hyperglycemic conditions. In diabetic microvasculature, the intracellular hyperglycemia causes damage to the vascular endothelium through - (i) activation of four biochemical pathways, namely the Polyol pathway, protein kinase C (PKC) pathway, advanced glycation end products (AGE) pathway and hexosamine pathway, all of which commutes glucose and its intermediates leading to overproduction of reactive oxygen species, (ii) dysregulation of growth factors and cytokines, (iii) epigenetic changes which concern the changes in DNA as a response to intracellular changes, and (iv) abnormalities in non-coding RNAs, specifically microRNAs. This review will focus on gaining an understanding of the molecular complexities underlying the vascular complications in diabetes mellitus, to increase our understanding towards the development of new mechanistic therapeutic strategies to prevent or treat diabetes-induced vascular complications.

Integral role of receptor for advanced glycation end products (RAGE) in nondiabetic atherosclerosis

An advanced glycation end products (AGE)/a receptor for AGE (RAGE) axis plays a central role in the pathogenesis of diabetic vascular remodeling. This study was conducted to clarify the role of RAGE in nondiabetic atherosclerosis. We used the aortic and coronary atherosclerotic lesions of Watanabe heritable hyperlipidemic (WHHL) rabbits prone to myocardial infarction (WHHLMI) at 1 to 14 months. Immunohistochemistry demonstrated the significant expression of RAGE as early as at 1 month with the stronger expression at 3 and 7 months, which was remarkably diminished at 14 months. RAGE expression was concordant with AGE accumulation. The major original sources of RAGE expression were macrophages and smooth muscle cells in addition to endothelial cells, and RAGE expression was distributed in the areas of phospholipid products, a component of oxidized LDL and nitrotyrosine. The concentrations of serum AGE did not alter significantly with aging. These findings suggested the expression of RAGE was induced by hyperlipidemia and oxidative stress independent of diabetes in WHHLMI rabbits. Additionally, our in vitro study showed that silencing of RAGE tended to attenuate oxidized-LDL-triggered PAI-1 expression in human cultured macrophages, as well as oxidized-LDL-induced tissue factor expression in peritoneal macrophages, suggesting a possible role of RAGE in prothrombogenic molecular regulation. In conclusion, the present study provides in vivo evidence that RAGE plays an integral role in the initiation and progression of nondiabetic atherosclerosis, suggesting that RAGE may be a novel target for treating not only diabetic but also nondiabetic vascular complications.

Methylglyoxal and soluble RAGE in type 2 diabetes mellitus: Association with oxidative stress

Purpose

Methylglyoxal (MGO) and MGO related advance end product (AGE) are thought to contribute to the development of diabetes and its complications. The present study was intended to determine plasma MGO and sRAGE levels in T2DM patients and to assess the relationship between MGO and other parameters, such as sRAGE and oxidative markers.

Methods

The study was carried out in 100 control and T2DM subjects. Methylglyoxal, sRAGE, HbA1c, and other markers were measured by using a standard protocol and the relationship between variables was analyzed using Spearman's correlation analysis.

Results

Plasma MGO levels in patients with T2DM (221.1 ± 9.50 ng/mL) were significantly higher than in control subjects (121.1 ± 6.52 ng/mL, P < 0.001). The plasma level of MGO was positively correlated with glycosylated hemoglobin (HbA1c, r = 0.50, P < 0.001). Plasma soluble form of RAGE (sRAGE) was significantly decreased in T2DM subjects (5.3 ± 0.64 ng/mL) as compared to the control group (7.7 ± 0.86 ng/mL, p < 0.05). However, at increased level of glycation (HbA1c > 10%), the sRAGE level was 6.2 ± 0.42 ng/mL and was not statistically significant as compared to control healthy group (> 0.05). Moreover, we have not found any correlation between MGO and other markers (p > 0.05).

Conclusions

The findings of the present study showed that increased plasma MGO level is significantly associated with the HbA1c levels in T2DM patients. Moreover, the study shows that plasma sRAGE level is significantly augmented at increased level of glycation (HbA1c > 10%) in T2DM patients.

The Active Compounds of Yixin Ningshen Tablet and Their Potential Action Mechanism in Treating Coronary Heart Disease- A Network Pharmacology and Proteomics Approach

Yixin Ningshen tablet is a CFDA-approved TCM formula for treating coronary heart disease (CHD) clinically. However, its active compounds and mechanism of action in treating CHD are unknown. In this study, a novel strategy with the combination of network pharmacology and proteomics was proposed to identify the active components of Yixin Ningshen tablet and the mechanism by which they treat CHD. With the application of network pharmacology, 62 active compounds in Yixin Ningshen tablet were screened out by text mining, and their 313 potential target proteins were identified by a tool in SwissTargetPrediction. These data were integrated with known CHD-related proteomics results to predict the most possible targets, which reduced the 313 potential target proteins to 218. The STRING database was retrieved to find the enriched pathways and related diseases of these target proteins, which indicated that the Calcium, MAPK, PI3K-Akt, cAMP, Rap1, AGE-RAGE, Relaxin, HIF-1, Prolactin, Sphingolipid, Estrogen, IL-17, Jak-STAT signaling pathway, necroptosis, arachidonic acid metabolism, insulin resistance, endocrine resistance, and steroid hormone biosynthesis might be the main pathways regulated by Yixin Ningshen tablet for the treatment of CHD. Through further enrichment analysis and literature study, EGFR, ERBB2, VGFR2, FGF1, ESR1, LOX15, PGH2, HMDH, ADRB1, and ADRB2 were selected and then validated to be the target proteins of Yixin Ningshen tablet by molecular docking, which indicated that Yixin Ningshen tablet might treat CHD mainly through promoting heart regeneration, new vessels' formation, and the blood supply of the myocardial region and reducing cardiac output, oxygen demand, and inflammation as well as arteriosclerosis (promoting vasodilation and intraplaque neoangiogenesis, lowering blood lipid). This study is expected to benefit the clinical application of Yixin Ningshen tablet for the treatment of CHD.

The Role of Advanced Glycation End Products in Diabetic Vascular Complications

In cases of chronic hyperglycemia, advanced glycation end-products (AGEs) are actively produced and accumulated in the circulating blood and various tissues. AGEs also accelerate the expression of receptors for AGEs, and they play an important role in the development of diabetic vascular complications through various mechanisms. Active interventions for glucose and related risk factors may help improve the clinical course of patients by reducing AGEs. This review summarizes recent updates on AGEs that have a significant impact on diabetic vascular complications.

Duration of Diabetes and Prediabetes During Adulthood and Subclinical Atherosclerosis and Cardiac Dysfunction in Middle Age: The CARDIA Study

OBJECTIVE

To determine whether the duration of diabetes and duration of prediabetes estimated during a 25-year period in early adulthood are each independently associated with coronary artery calcified plaque (CAC) and abnormalities in left ventricular structure and function later in life.

RESEARCH DESIGN AND METHODS

Participants were 3,628 white and black adults aged 18-30 years without diabetes or prediabetes at baseline (1985-1986) in the Coronary Artery Risk Development in Young Adults (CARDIA) Study. Durations of diabetes and prediabetes were estimated based on their identification at examinations 7, 10, 15, 20, and 25 years later. CAC was identified by computed tomography at years 15, 20, and 25. Left ventricular structure and function were measured via echocardiogram at year 25.

RESULTS

Of the 3,628 individuals, 12.7% and 53.8% developed diabetes and prediabetes, respectively; average (SD) duration was 10.7 (10.7) years and 9.5 (5.4) years. After adjustment for sociodemographic characteristics and other cardiovascular risk factors, and mutual adjustment for each other, the hazard ratio for the presence of CAC was 1.15 (95% CI 1.06, 1.25) and 1.07 (1.01, 1.13) times higher for each 5-year-longer duration of diabetes and prediabetes, respectively. Diabetes and prediabetes duration were associated with worse subclinical systolic function (longitudinal strain [Ptrend < 0.001 for both]) and early diastolic relaxation (e' [Ptrend 0.004 and 0.002, respectively]). Duration of diabetes was also associated with a higher diastolic filling pressure (E-to-e' ratio [Ptrend 0.001]).

CONCLUSIONS

Durations of diabetes and prediabetes during adulthood are both independently associated with subclinical atherosclerosis and left ventricular systolic and diastolic dysfunction in middle age.

Cellular and Molecular Mechanisms of Diabetic Atherosclerosis: Herbal Medicines as a Potential Therapeutic Approach

An increasing number of patients diagnosed with diabetes mellitus eventually develop severe coronary atherosclerosis disease. Both type 1 and type 2 diabetes mellitus increase the risk of cardiovascular disease associated with atherosclerosis. The cellular and molecular mechanisms affecting the incidence of diabetic atherosclerosis are still unclear, as are appropriate strategies for the prevention and treatment of diabetic atherosclerosis. In this review, we discuss progress in the study of herbs as potential therapeutic agents for diabetic atherosclerosis.

Effects of pomegranate juice consumption on oxidative stress in patients with type 2 diabetes: a single-blind, randomized clinical trial

Increased free radicals production due to hyperglycemia produces oxidative stress in patients with diabetes. Pomegranate juice (PJ) has antioxidant properties. This study was conducted to determine the effects of PJ consumption in oxidative stress in type 2 diabetic patients. This study was a randomized clinical trial performed on 60, 40-65 years old diabetic patients. The patients were randomly allocated either to PJ consumption group or control. Patients in PJ group consumed 200 ml of PJ daily for six weeks. Sex distribution and the mean age were not different between two groups. After six weeks intervention, oxidized LDL and anti-oxidized LDL antibodies decreased and total serum antioxidant capacity and arylesterase activity of paraoxonase increased significantly in the PJ-treated group compared to the control group. Our data have shown that six weeks supplementation of PJ could have favorable effects on oxidative stress in patients with type 2 diabetes (T2D).

Skin Autofluorescence is Associated with Early-stage Atherosclerosis in Patients with Type 1 Diabetes

AIM

Accumulation level of fluorescent advanced glycation end products (AGEs) in the skin can be measured non-invasively as skin autofluorescence (skin AF) by autofluorescence reader. The aim of this study was to assess possible associations between skin AF and diabetic complications, especially early-stage atherosclerosis, in Japanese type 1 diabetic patients.

METHODS

Skin AF was measured by AGE reader® in 105 Japanese type 1 diabetic patients (34 men and 71 women, aged 37.4±12.4 years (±SD)) and 23 age-matched healthy non-diabetic subjects. Ultrasonic carotid intima-media thickness (IMT), ankle-brachial index (ABI), and brachial ankle pulse wave velocity (baPWV) were evaluated as indices of early-stage diabetic macroangiopathy. Urinary albumin-to-creatinine ratio (UACR), the coefficient of variation of R-R intervals (CVR-R), and presence of retinopathy were also evaluated.

RESULTS

Skin AF values were significantly higher in type 1 diabetic patients than in healthy controls (2.07±0.50 (mean±SD) and 1.90±0.26, respectively, p=0.024). Skin AF was associated with carotid IMT (r=0.446, p＜0.001) and baPWV (r=0.450, p＜0.001), but not with ABI (r=－0.019, p=0.8488). Notably, skin AF was an independent risk factor for IMT thickening. Similarly, skin AF was associated with log (UACR) (r=0.194, p=0.049) and was an independent risk factor for UACR. Furthermore, skin AF values were significantly higher in patients with diabetic retinopathy than in those without (2.21±0.08 and 1.97±0.06, respectively, p=0.020).

CONCLUSIONS

Skin AF was significantly associated with the presence and/or severity of diabetic complications and was an independent risk factor for carotid atherosclerosis.

RAGE and AGEs in Mild Cognitive Impairment of Diabetic Patients: A Cross-Sectional Study

OBJECTIVE

Receptor for advanced glycation end products (AGEs; RAGE) binds to both AGEs and amyloid-beta peptides. RAGE is involved in chronic complications of type 2 diabetes and Alzheimer's disease. We aimed to investigate the roles of RAGE, AGEs and the Gly82Ser polymorphism of RAGE in mild cognitive impairment (MCI) among type 2 diabetes patients.

METHODS

Of the 167 hospitalized type 2 diabetes patients recruited, 82 satisfied the diagnostic criteria for MCI, and 85 matched control individuals were classified as non-MCI. Demographic data were collected, and the soluble RAGE (sRAGE) concentrations, serum AGE-peptide (AGE-P) levels, RAGE Gly82Ser genotype and neuropsychological test results were examined.

RESULTS

The MCI group exhibited a decreased sRAGE level (0.87±0.35 vs. 1.05±0.52 ng/ml, p<0.01) and an increased serum AGE-P level (3.54±1.27 vs. 2.71±1.18 U/ml, p<0.01) compared with the control group. Logistic regression analysis indicated that each unit reduction in the sRAGE concentration increased the MCI risk by 54% (OR 0.46[95% CI 0.22-0.96], p = 0.04) and that each unit increase in the AGE-P level increased the MCI risk by 72% in the type 2 diabetes patients (OR 1.72[95% CI 1.31-2.28], p<0.01). The serum sRAGE level was negatively correlated with the score on the trail making test-B (TMT-B) (r = -0.344, p = 0.002), which indicates early cognitive deficits related to diabetes. Moreover, the AGE-P level was positively correlated with multiple cognitive domains (all p<0.05). No significant differences in the neuropsychological test results or serum RAGE concentrations between the different RAGE genotypes or in the RAGE genotype frequencies between the MCI and control groups were identified (all p>0.05).

CONCLUSIONS

The RAGE pathway partially mediates AGE-induced MCI in diabetic patients. The serum AGE-P level may serve as a serum biomarker of MCI in these individuals, and sRAGE represents a predictor and even a potential intervention target of early cognitive decline in type 2 diabetes patients.

TRIAL REGISTRATION

Advanced Glycation End Products Induced Cognitive Impairment in Diabetes: BDNF Signal Meditated Hippocampal Neurogenesis ChiCTR-OCC-15006060.

Elevated glycated albumin and reduced endogenous secretory receptor for advanced glycation endproducts levels in serum predict major adverse cardio-cerebral events in patients with type 2 diabetes and stable coronary artery disease

BACKGROUND AND AIM

Glycated albumin (GA) and the endogenous secretory receptor for advanced glycation endproducts (esRAGE) may modulate risk related to atherosclerosis. We tested the hypothesis that elevated GA and reduced esRAGE in serum are associated with adverse clinical outcomes in patients with type 2 diabetes and stable coronary artery disease (CAD).

METHODS

We determined GA and esRAGE serum levels in 576 consecutive patients with type 2 diabetes and stable CAD undergoing sirolimus-eluting stent (SES)-PCI. The primary endpoint was the incidence of major adverse cardio-cerebral events (MACCE) including cardiac death, non-fatal myocardial infarction, and non-fatal stroke during a 2-year follow-up. The secondary endpoint was the occurrence of clinically driven repeat revascularization during a 2-year follow-up. The prognostic value of GA and esRAGE was determined with the Cox-proportional hazard model after adjustment for covariates.

RESULTS

A total 40 patients (6.9%) experienced MACCE, and 108 (18.8%) patients underwent repeat coronary revascularization during the follow-up. Serum GA (HR=1.22, 95% CI 1.16-1.28; HR=1.15, 95% CI 1.11-1.19, respectively; for both p<0.001) and esRAGE (HR=0.60, 95% CI 0.40-0.87; HR=0.75, 95% CI 0.61-0.92, respectively; for both p<0.01) levels remained independent predictors of the primary and secondary endpoints after adjustment for possible confounders.

CONCLUSIONS

Serum GA and esRAGE are novel predictors of long-term clinical outcomes in patients with type 2 diabetes and stable CAD. Increased serum GA and decreased esRAGE are associated with a poor prognosis in such patients.

Mechanisms linking brain insulin resistance to Alzheimer's disease

Several studies have indicated that Diabetes Mellitus (DM) can increase the risk of developing Alzheimer's disease (AD). This review briefly describes current concepts in mechanisms linking DM and insulin resistance/deficiency to AD. Insulin/insulin-like growth factor (IGF) resistance can contribute to neurodegeneration by several mechanisms which involve: energy and metabolism deficits, impairment of Glucose transporter-4 function, oxidative and endoplasmic reticulum stress, mitochondrial dysfunction, accumulation of AGEs, ROS and RNS with increased production of neuro-inflammation and activation of pro-apoptosis cascade. Impairment in insulin receptor function and increased expression and activation of insulin-degrading enzyme (IDE) have also been described. These processes compromise neuronal and glial function, with a reduction in neurotransmitter homeostasis. Insulin/IGF resistance causes the accumulation of AβPP-Aβ oligomeric fibrils or insoluble larger aggregated fibrils in the form of plaques that are neurotoxic. Additionally, there is production and accumulation of hyper-phosphorylated insoluble fibrillar tau which can exacerbate cytoskeletal collapse and synaptic disconnection.

Nuclear DAMP complex-mediated RAGE-dependent macrophage cell death

High mobility group box 1 (HMGB1), histone, and DNA are essential nuclear components involved in the regulation of chromosome structure and function. In addition to their nuclear function, these molecules act as damage-associated molecular patterns (DAMPs) alone or together when released extracellularly. The synergistic effect of these nuclear DNA-HMGB1-histone complexes as DAMP complexes (nDCs) on immune cells remains largely unexplored. Here, we demonstrate that nDCs limit survival of macrophages (e.g., RAW264.7 and peritoneal macrophages) but not cancer cells (e.g., HCT116, HepG2 and Hepa1-6). nDCs promote production of inflammatory tumor necrosis factor α (TNFα) release, triggering reactive oxygen species-dependent apoptosis and necrosis. Moreover, the receptor for advanced glycation end products (RAGE), but not toll-like receptor (TLR)-4 and TLR-2, was required for Akt-dependent TNFα release and subsequent cell death following treatment with nDCs. Genetic depletion of RAGE by RNAi, antioxidant N-Acetyl-l-cysteine, and TNFα neutralizing antibody significantly attenuated nDC-induced cell death. These findings provide evidence supporting novel signaling mechanisms linking nDCs and inflammation in macrophage cell death.

Microvascular perfusion heterogeneity contributes to peripheral vascular disease in metabolic syndrome

A major challenge facing public health is the increased incidence and prevalence of the metabolic syndrome, a clinical condition characterized by excess adiposity, impaired glycaemic control, dyslipidaemia and moderate hypertension. The greatest concern for this syndrome is the profound increase in risk for development of peripheral vascular disease (PVD) in afflicted persons. However, ongoing studies suggest that reductions in bulk blood flow to skeletal muscle may not be the primary contributor to the premature muscle fatigue that is a hallmark of PVD. Compelling evidence has been provided suggesting that an increasingly spatially heterogeneous and temporally stable distribution of blood flow at successive arteriolar bifurcations in metabolic syndrome creates an environment where a large number of the pre-capillary arterioles have low perfusion, low haematocrit, and are increasingly confined to this state, with limited ability to adapt perfusion in response to a challenged environment. Single pharmacological interventions are unable to significantly restore function owing to a divergence in their spatial effectiveness, although combined therapeutic approaches to correct adrenergic dysfunction, elevated oxidant stress and increased thromboxane A2 improve perfusion-based outcomes. Integrated, multi-target therapeutic interventions designed to restore healthy network function and flexibility may provide for superior outcomes in subjects with metabolic syndrome-associated PVD.

Molecular mechanisms of AGE/RAGE-mediated fibrosis in the diabetic heart

Chronic hyperglycemia is one of the main characteristics of diabetes. Persistent exposure to elevated glucose levels has been recognized as one of the major causal factors of diabetic complications. In pathologies, like type 2 diabetes mellitus (T2DM), mechanical and biochemical stimuli activate profibrotic signaling cascades resulting in myocardial fibrosis and subsequent impaired cardiac performance due to ventricular stiffness. High levels of glucose nonenzymatically react with long-lived proteins, such as collagen, to form advanced glycation end products (AGEs). AGE-modified collagen increase matrix stiffness making it resistant to hydrolytic turnover, resulting in an accumulation of extracellular matrix (ECM) proteins. AGEs account for many of the diabetic cardiovascular complications through their engagement of the receptor for AGE (RAGE). AGE/RAGE activation stimulates the secretion of numerous profibrotic growth factors, promotes increased collagen deposition leading to tissue fibrosis, as well as increased RAGE expression. To date, the AGE/RAGE cascade is not fully understood. In this review, we will discuss one of the major fibrotic signaling pathways, the AGE/RAGE signaling cascade, as well as propose an alternate pathway via Rap1a that may offer insight into cardiovascular ECM remodeling in T2DM. In a series of studies, we demonstrate a role for Rap1a in the regulation of fibrosis and myofibroblast differentiation in isolated diabetic and non-diabetic fibroblasts. While these studies are still in a preliminary stage, inhibiting Rap1a protein expression appears to down-regulate the molecular switch used to activate the ζ isotype of protein kinase C thereby promote AGE/RAGE-mediated fibrosis.

Local and systemic RAGE axis changes in pulmonary hypertension: CTEPH and iPAH

OBJECTIVE

The molecular determinants of chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (iPAH) remain poorly understood. The receptor for advanced glycation endproducts (RAGE) and its ligands: HMGB1 and S100A9 are involved in inflammatory disorders. We sought to investigate the role of the RAGE axis in patients with CTEPH undergoing pulmonary endarterectomy (PEA), iPAH undergoing lung transplantation (LuTX). The high pulmonary vascular resistance in CTEPH/iPAH results in pressure overload of the right ventricle. We compared sRAGE measurements to that of patients with aortic valve stenosis (AVS) - pressure overload of the left ventricle.

METHODS

We enrolled patients with CTEPH(26), iPAH(15), AVS(15) and volunteers(33). Immunohistochemistry with antibodies to RAGE and HMGB1 was performed on PEA specimens and lung tissues. We employed enzyme-linked immunosorbent assays to determine the concentrations of sRAGE, esRAGE, HMGB1 and S100A9 in serum of volunteers and patients with CTEPH, iPAH, AVS before and after PEA, LuTX and aortic valve replacement (AVR).

RESULTS

In endarterectomised tissues from patients with CTEPH RAGE and HMGB1 were identified in myofibroblasts (α-SMA+vimentin+CD34-), recanalizing vessel-like structures of distal myofibrotic tissues and endothelium of neointima. RAGE was differentially expressed in prototypical Heath Edwards lesions in iPAH. We found significantly increased serum concentrations of sRAGE, esRAGE and HMGB1 in CTEPH. In iPAH, sRAGE and esRAGE were significantly higher than in controls. Serum concentrations of sRAGE were significantly elevated in iPAH(p<0.001) and CTEPH(p = 0.001) compared to AVS. Serum sRAGE was significantly higher in iPAH compared to CTEPH(p = 0.042) and significantly reduced in AVS compared to controls(p = 0.001). There were no significant differences in sRAGE serum concentrations before and after surgical therapy for CTEPH, iPAH or AVS.

CONCLUSIONS

Our data suggest a role for the RAGE pathway in the pathophysiology of CTEPH and iPAH. PEA improves the local control of disease but may not influence the systemic inflammatory mechanisms in CTEPH patients through the RAGE pathway.

Extracellular S100A4 induces smooth muscle cell phenotypic transition mediated by RAGE

We identified S100A4 as a marker of rhomboid (R) smooth muscle cells (SMCs) in vitro (the synthetic phenotype, typical of intimal SMCs) in the porcine coronary artery and of intimal SMCs in vivo in both pigs and humans. S100A4 is an intracellular Ca²⁺ signaling protein and can be secreted; it has extracellular functions via the receptor for advanced glycation end products (RAGE). Our objective was to explore the role of S100A4 in SMC phenotypic change, a phenomenon characteristic of atherosclerotic plaque formation. Transfection of a human S100A4-containing plasmid in spindle-shaped (S) SMCs (devoid of S100A4) led to approximately 10% of S100A4-overexpressing SMCs, S100A4 release, and a transition towards a R-phenotype of the whole SMC population. Furthermore treatment of S-SMCs with S100A4-rich conditioned medium collected from S100A4-transfected S-SMCs induced a transition towards a R-phenotype, which was associated with decreased SMC differentiation markers and increased proliferation and migration by activating the urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). It yielded NF-κB activation in a RAGE-dependent manner. Blockade of extracellular S100A4 in R-SMCs with S100A4 neutralizing antibody induced a transition from R- to S-phenotype, decreased proliferative activity and upregulation of SMC differentiation markers. By contrast, silencing of S100A4 mRNA in R-SMCs did not change the level of extracellular S100A4 or SMC morphology in spite of decreased proliferative activity. Our results show that extracellular S100A4 plays a pivotal role in SMC phenotypic changes. It could be a new target to prevent SMC accumulation during atherosclerosis and restenosis. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

Role of multiligand/RAGE axis in platelet activation

In the context of plaque progression, platelet hyperactivity associated with hyperlipidemia contributes to the development of a pro-thrombotic state. In this context, it has been demonstrated that advanced glycation end products (AGEs) significantly increases platelet activation and receptor for AGEs (RAGE) expression at the platelet surface membrane. In addition to AGEs, other ligands (S100, HMGB1 and amyloid β, among others) of RAGE have raised particular attention in platelet activation. Therefore, in this article we describe platelet hyperactivity by AGEs via RAGE-independent and RAGE-dependent pathways.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

EGCG-rich green tea extract stimulates sRAGE secretion to inhibit S100A12-RAGE axis through ADAM10-mediated ectodomain shedding of extracellular RAGE in type 2 diabetes

The receptor for advanced glycation of end products (RAGE) plays a critical role in the progression of type 2 diabetes (T2D). Soluble RAGE (sRAGE) is one of the RAGE variants, which acts as a decoy domain receptor and competes with RAGE, thus contributing to prevention of T2D. In this study, we conducted clinical trials of (-)-epigallocatechin-3-gallate (EGCG) rich green tea extract (300-900 mg/day) to investigate the effect of EGCG on relationship between S100A12 RAGE ligand and diverse sRAGE in T2D. Moreover, mechanism of sRAGE production also confirmed in vitro. Our data indicated that EGCG could stimulate sRAGE circulation but inhibited RAGE ligand in T2D, and ADAM10-mediated ectodomain shedding of extracellular RAGE was mainly involved in EGCG-stimulated sRAGE circulation. The present evidence indicates that EGCG has a potential to block S100A12-RAGE axis by stimulating sRAGE production through ADAM10-mediated ectodomain shedding of extracellular RAGE. Therefore, EGCG contributes to nutritional strategies for diabetes, not only because of its efficient antioxidant activity to scavenge free radicals, but also because of its ability stimulating sRAGE release in the circulation. Additionally, ADAM10-induced ectodomain shedding of extracellular RAGE leading to sRAGE circulation should be a potential of passive mechanism of sRAGE production to block S100A12-RAGE axis-related pathogenesis of proinflammation and diabetes.

RAGE-mediated cell signaling

RAGE (receptor for advanced glycation end products) is a multi-ligand receptor that belongs to the immunoglobulin superfamily of transmembrane proteins. RAGE binds AGEs (advanced glycation end products), HMGB1 (high-mobility group box-1; also designated as amphoterin), members of the S100 protein family, glycosaminoglycans and amyloid β peptides. Recent studies using tools of structural biology have started to unravel common molecular patterns in the diverse set of ligands recognized by RAGE. The distal Ig domain (V1 domain) of RAGE has a positively charged patch, the geometry of which fits to anionic surfaces displayed at least in a proportion of RAGE ligands. Association of RAGE to itself, to HSPGs (heparan sulfate proteoglycans), and to Toll-like receptors in the cell membrane plays a key role in cell signaling initiated by RAGE ligation. Ligation of RAGE activates cell signaling pathways that regulate migration of several cell types. Furthermore, RAGE ligation has profound effects on the transcriptional profile of cells. RAGE signaling has been mainly studied as a pathogenetic factor of several diseases, where acute or chronic inflammation plays a role. Recent studies have suggested a physiological role for RAGE in normal lung function and in neuronal signaling.

Advanced-glycation-end-product-induced formation of immunoproteasomes: involvement of RAGE and Jak2/STAT1

AGEs (advanced glycation-end products) accumulate during aging and several pathologies such as Alzheimer's disease and diabetes. These protein products are known to inhibit proteolytic pathways. Moreover, AGEs are known to be involved in the activation of immune responses. In the present study we demonstrate that AGEs induce the expression of immunoproteasomal subunits. To elucidate a molecular basis underlying the observed effects we were able to demonstrate an activation of the Jak2 (Janus kinase 2)/STAT1 (signal transducer and activator of transcription 1) pathway. Inhibition of Jak2 by AG-490 and STAT1 by specific siRNA (small interfering RNA) abolished AGE-induced expression of immunoproteasomal subunits. Furthermore, silencing of RAGE (receptor for AGEs) revealed that AGE-induced up-regulation of the immunoproteasome is mediated by a RAGE signalling process. Thus we have described for the first time that the signalling pathway of Jak2 and STAT1 activated by AGEs via RAGE is involved in the induction of the immunoproteasome.

Vascular calcification: pathophysiology and risk factors

Vascular calcification can occur in nearly all arterial beds and in both the medial and intimal layers. The initiating factors and clinical consequences depend on the underlying disease state and location of the calcification. The best studied manifestation is coronary artery calcification, in part because of the obvious clinical consequences, but also because of CT-based imaging modalities. In the general population, the presence of coronary artery calcification increases cardiovascular risk above that predicted by traditional Framingham risk factors, suggesting the presence of nontraditional risk factors. In patients with chronic kidney disease (CKD), coronary artery calcification is more prevalent and markedly more severe than in the general population. In these CKD patients, nontraditional risk factors such as oxidative stress, advanced glycation end products, and disordered mineral metabolism are also more prevalent and more severe and offer mechanistic insight into the pathogenesis of vascular calcification.

Consequences of Aberrant Insulin Regulation in the Brain: Can Treating Diabetes be Effective for Alzheimer's Disease

There is an urgent need for new ways to treat Alzheimer’s disease (AD), the most common cause of dementia in the elderly. Current therapies are modestly effective at treating the symptoms, and do not significantly alter the course of the disease. Over the years, a range of epidemiological and experimental studies have demonstrated interactions between diabetes mellitus and AD. As both diseases are leading causes of morbidity and mortality in the elderly and are frequent co-morbid conditions, it has raised the possibility that treating diabetes might be effective in slowing AD. This is currently being attempted with drugs such as the insulin sensitizer rosiglitazone. These two diseases share many clinical and biochemical features, such as elevated oxidative stress, vascular dysfunction, amyloidogenesis and impaired glucose metabolism suggesting common pathogenic mechanisms. The main thrust of this review will be to explore the evidence from a pathological point of view to determine whether diabetes can cause or exacerbate AD. This was supported by a number of animal models of AD that have been shown to have enhanced pathology when diabetic conditions were induced. The one drawback in linking diabetes and insulin to AD has been the postmortem studies of diabetic brains demonstrating that AD pathology was not increased; in fact decreased pathology has often been reported. In addition, diabetes induces its own distinct features of neuropathology different from AD. There are common pathological features to be considered including vascular abnormalities, a major feature arising from diabetes; there is increasing evidence that vascular abnormalities can contribute to AD. The most important common mechanism between insulin-resistant (type II) diabetes and AD could be impaired insulin signaling; a form of toxic amyloid can damage neuronal insulin receptors and affect insulin signaling and cell survival. It has even been suggested that AD could be considered as “type 3 diabetes” since insulin can be produced in brain. Another common feature of diabetes and AD are increased advanced glycation endproduct-modified proteins are found in diabetes and in the AD brain; the receptor for advanced glycation endproducts plays a prominent role in both diseases. In addition, a major role for insulin degrading enzyme in the degradation of Aβ peptide has been identified. Although clinical trials of certain types of diabetic medications for treatment of AD have been conducted, further understanding the common pathological processes of diabetes and AD are needed to determine whether these diseases share common therapeutic targets.

The receptor of advanced glycation end products plays a central role in advanced oxidation protein products-induced podocyte apoptosis

The accumulation of plasma advanced oxidation protein products (AOPPs) is prevalent in chronic kidney disease. We previously showed that accumulation of AOPPs resulted in podocyte apoptosis and their deletion by a cascade of signaling events coupled with intracellular oxidative stress. The transmembrane receptor that specifically transmits the AOPPs' signals to elicit cellular activity, however, remains unknown. Using co-immunoprecipitation and immunofluorescence, we found that AOPPs colocalized and interacted with the receptor of advanced glycation end products (RAGE) on podocytes. Blocking RAGE by anti-RAGE immunoglobulin G or its silencing by siRNA significantly protected podocytes from AOPPs-induced apoptosis both in vitro and in vivo and ameliorated albuminuria in AOPPs-challenged mice. AOPPs-induced activation of nicotinamide adenine dinucleotide phosphate oxidase and the excessive generation of intracellular superoxide were largely inhibited by anti-RAGE immunoglobulin G or RAGE siRNA. Moreover, blockade of RAGE decreased the activation of the p53/Bax/caspase-dependent proapoptotic pathway induced by AOPPs. Thus, AOPPs interact with RAGE to induce podocyte apoptosis and this, in part, may contribute to the progression of chronic kidney disease.

Advanced glycation end products induce moesin phosphorylation in murine retinal endothelium

Increase in vascular permeability is the most important pathological event during the development of diabetic retinopathy. Deposition of advanced glycation end products (AGEs) plays a crucial role in the process of diabetes. This study was to investigate the role of moesin and its underlying signal transduction in retinal vascular hyper-permeability induced by AGE-modified mouse serum albumin (AGE-MSA). Female C57BL/6 mice were used to produce an AGE-treated model by intraperitoneal administration of AGE-MSA for seven consecutive days. The inner blood-retinal barrier was quantified by Evans blue leakage assay. Endothelial F-actin cytoskeleton in retinal vasculature was visualized by fluorescence probe staining. The expression and phosphorylation of moesin in retinal vessels were detected by RT-PCR and western blotting. Further studies were performed to explore the effects of Rho kinase (ROCK) and p38 MAPK pathway on the involvement of moesin in AGE-induced retinal vascular hyper-permeability response. Treatment with AGE-MSA significantly increased the permeability of the retinal microvessels and induced the disorganization of F-actin in retinal vascular endothelial cells. The threonine (T558) phosphorylation of moesin in retinal vessels was enhanced remarkably after AGE administration. The phosphorylation of moesin was attenuated by inhibitions of ROCK and p38 MAPK, while this treatment also prevented the dysfunction of inner blood-retinal barrier and the reorganization of F-actin in retinal vascular endothelial cells. These results demonstrate that moesin is involved in AGE-induced retinal vascular endothelial dysfunction and the phosphorylation of moesin is triggered via ROCK and p38 MAPK activation.

AGE formation blockade with aminoguanidine does not ameliorate chronic allograft nephropathy

AIMS

Advanced glycation end products (AGEs) are produced by glycoxidation and lipid peroxidation. AGEs induce oxidative stress and inflammation, and accumulate in tubular cells after kidney transplantation. We hypothesize that the AGE formation blocker aminoguanidine (AG) reduces AGE formation and improves renal transplant function.

MAIN METHODS

Fisher 344 kidneys were orthotopically transplanted into Lewis recipients. Recipients were treated with AG (100 mg/kg/day), candesartan (CAND; 5mg/kg/day), or vehicle (VEH) for 24 weeks. The major non-cross linking AGE N(ε)-carboxymethyllysine (CML) was measured post-transplantation with gas chromatography-tandem mass spectrometry or immunohistochemistry. As a marker of systemic lipid peroxidation 8-isoprostane was measured by ELISA. We determined intra-arterial blood pressure, heart weight/body weight ratio, size of cardiomyocytes and cardiac hypertrophy as assessed by echocardiography. For biochemical evaluation of cardiac and renal fibrosis we measured hydroxyproline content.

KEY FINDINGS

AG significantly reduced serum CML and 8-isoprostane, but did not reduce signs of chronic allograft nephropathy (CAN) or blood pressure. AG did not alter tubular AGE accumulation. AG reduced heart weight/body weight ratio (AG: 2.7 ± 0.1g/kg; CAND: 2.2 ± 0.1, VEH: 3.0 ± 0.4 g/kg), size of cardiomyocytes (P < 0.05) and showed a tendency to reduce cardiac hypertrophy (wall volume average radial AG 7.072 ± 0.83 cm(3) vs. CAND 6.841 ± 0.66 cm(3) vs. VEH 7.839 ± 0.74 cm(3)).

SIGNIFICANCE

Despite effective reduction of serum CML and 8-isoprostane, AG did not ameliorate CAN or reduce renal AGE accumulation. On the other hand AG reduced cardiac size suggesting a supportive cardio-protective action which is blood pressure independent.

The antioxidant N-acetylcysteine promotes atherosclerotic plaque stabilization through suppression of RAGE, MMPs and NF-κB in ApoE-deficient mice

AIMS

N-acetylcysteine (NAC) has antioxidant and anti-inflammatory properties. To explore the mechanisms underlying atherosclerotic plaque stabilization induced by NAC, we examined the effects of NAC administration in apoE-deficient mice on the expression of the receptor of advanced glycation end products (RAGE), matrix metalloproteinases (MMPs) and the activation of nuclear factor kappa B (NF-κB) in atherosclerotic plaques.

METHODS

10-week-old ApoE(-/-) mice fed with atherogenic diet were treated with NAC (200 mg/kg/ day) for 8 weeks. Serum lipid, glucose and malondialdehyde (MDA) were detected. The size and composition of atherosclerotic plaques were measured by en face analysis, Movat staining, immunofluorescence and immunohistochemistry, respectively. Reactive oxygen species (ROS) generation in aortic root was tested by DHE staining. The levels of vascular cell adhesion molecule-1(VCAM-1), NF-κB, phosphor-NF-κB, I-κB, phosphor-I-κB, RAGE, MMP2 and MMP9 in descending arteries were analyzed by Western blot.

RESULTS

ApoE(-/-) mice administrated with NAC displayed reduced serum MDA level and impaired ROS generation in aortic root. However, NAC did not affect the levels of plasma glucose, lipids and the size of atherosclerotic lesions. Analysis of plaque composition showed decreased amounts of macrophages, lipid deposition, but not smooth muscle cells, and increased collagen content in atherosclerotic lesions in apoE(-/-) mice administered with NAC. Moreover, we found that NAC down-regulated the expression of VCAM-1, MMP2 and MMP9, accompanied by inhibition of NF-κB activation and reduced expression of RAGE.

CONCLUSION

In the present study, we show novel data to suggest that NAC promotes atherosclerotic plaque stabilization through suppression of RAGE, MMPs and NF-κB in apoE(-/-) mice.

RAGE-dependent activation of the oncoprotein Pim1 plays a critical role in systemic vascular remodeling processes

OBJECTIVE

Vascular remodeling diseases (VRD) are mainly characterized by inflammation and a vascular smooth muscle cells (VSMCs) proproliferative and anti-apoptotic phenotype. Recently, the activation of the advanced glycation endproducts receptor (RAGE) has been shown to promote VSMC proliferation and resistance to apoptosis in VRD in a signal transducer and activator of transcription (STAT)3-dependant manner. Interestingly, we previously described in both cancer and VRD that the sustainability of this proproliferative and antiapoptotic phenotype requires activation of the transcription factor NFAT (nuclear factor of activated T-cells). In cancer, NFAT activation is dependent of the oncoprotein provirus integration site for Moloney murine leukemia virus (Pim1), which is regulated by STAT3 and activated in VRD. Therefore, we hypothesized that RAGE/STAT3 activation in VSMC activates Pim1, promoting NFAT and thus VSMC proliferation and resistance to apoptosis. Methods/Results- In vitro, freshly isolated human carotid VSMCs exposed to RAGE activator Nε-(carboxymethyl)lysine (CML) for 48 hours had (1) activated STAT3 (increased P-STAT3/STAT3 ratio and P-STAT3 nuclear translocation); (2) increased STAT3-dependent Pim1 expression resulting in NFATc1 activation; and (3) increased Pim1/NFAT-dependent VSMC proliferation (PCNA, Ki67) and resistance to mitochondrial-dependent apoptosis (TMRM, Annexin V, TUNEL). Similarly to RAGE inhibition (small interfering RNA [siRNA]), Pim1, STAT3 and NFATc1 inhibition (siRNA) reversed these abnormalities in human carotid VSMC. Moreover, carotid artery VSMCs isolated from Pim1 knockout mice were resistant to CML-induced VSMC proliferation and resistance to apoptosis. In vivo, RAGE inhibition decreases STAT3/Pim1/NFAT activation, reversing vascular remodeling in the rat carotid artery-injured model.

CONCLUSIONS

RAGE activation accounts for many features of VRD including VSMC proliferation and resistance to apoptosis by the activation of STAT3/Pim1/NFAT axis. Molecules aimed to inhibit RAGE could be of a great therapeutic interest for the treatment of VRD.

Advanced glycation end products and its receptor (RAGE) are increased in patients with COPD

Advanced Glycation End products (AGEs) are the products of nonenzymatic glycation and oxidation of proteins and lipids. Formation of AGEs is increased in response to hyperglycaemia, reactive oxygen species and ageing. AGEs are proinflammatory and can modify the extracellular matrix. RAGE (Receptor for Advanced Glycation End Products) mediates some of the effects of AGEs.

METHODS

Formalin-fixed lung tissue from patients who had lobectomy for bronchial carcinoma was used to investigate the presence of AGEs and RAGE. Subjects were divided into those with COPD and controls. Immunostaining for AGEs and RAGE was performed and the intensity of staining measured.

RESULTS

Subjects with COPD and controls were similar in age and smoking history but FEV(1)% predicted was lower for COPD than controls. Intensity of staining for AGEs was greater in the airways (p = 0.025) and alveolar walls (p = 0.004) in COPD. Intensity of staining for RAGE was also significantly increased in alveolar walls (p = 0.03) but not the airways. FEV(1)% predicted was correlated with the intensity of staining for AGEs in the airways and alveoli.

CONCLUSIONS

The increased staining for both AGEs and RAGE in COPD lung raises the possibility that the RAGE-AGEs interaction may have a role in the pathogenesis of COPD.

Alagebrium chloride, a novel advanced glycation end-product cross linkage breaker, inhibits neointimal proliferation in a diabetic rat carotid balloon injury model

Background and Objectives

Vascular perturbation induced by advanced glycation end-products (AGEs) leads to progression of atherosclerosis, plaque instability, and vascular inflammation, which results in a higher risk of neointimal proliferation. Here we investigated the inhibitory effect of alagebrium chloride (ALT-711), a breaker of AGE-based cross links, on neointimal proliferation in a carotid artery balloon injury model in diabetic rats induced by streptozotocin (STZ).

Materials and Methods

Rat aortic vascular smooth muscle cells (RASMCs) were treated with 1-100 µM of alagebrium added 24 hours before the addition of AGEs. This in vivo study was done using 8-week-old male rats that were injected intraperitoneally with 80 mg/kg STZ. Sixteen weeks later, the diabetic rats were treated with 10 mg/kg alagebrium for 4 weeks, after which carotid artery balloon injury was induced. After 4 weeks, the animals were sacrificed for histological analysis.

Results

Proliferation of RASMCs was significantly inhibited in alagebrium-treated cells. Alagebrium dose-dependently inhibited AGE-mediated formation of reactive oxygen species (ROS), extracellular signal-regulated kinase phosphorylation, and cyclooxygenase-2 expression. The cellular mechanisms of AGE-induced connective tissue and extracellular matrix expression were decreased in the alagebrium-treated group. This in vivo study shows that expression of AGE receptors and neointima hyperplasia are significantly suppressed in balloon-injured rats treated with alagebrium.

Conclusion

Alagebrium treatment in diabetic rats significantly inhibits neointimal hyperplasia after carotid balloon injury due to its inhibition of intracellular ROS synthesis, which results in inhibition of RASMCs proliferation.

Combined immunoelectron microscopic and computer-assisted image analyses to detect advanced glycation end-products in human myocardium

Advanced glycation end-products (AGEs) result from oxidation-reduction reactions that ensue when a sugar becomes adducted to a protein. AGEs cause various complications of diabetes mellitus (DM). Experimental and clinical evidence suggest that AGEs also contribute to the complications of hypertension (HTN). Little is known about the abundance and localization of AGEs in human myocardium. In a few light microscopic studies, the AGE carboxymethyl lysine (CML) has been immunolabeled and localized virtually exclusively to the walls of small arteries. To more precisely delineate the abundance and localization of CML, we developed an immunoelectron microscopic (IEM) detection method using anti-CML monoclonal antibody 6D12 in conjunction with computer-assisted image analysis. Antibody was pre-absorbed with purified AGE-bovine serum albumin to assure specificity. Antigen-antibody (ag-ab) complexes were individually identified with protein A-conjugated colloidal gold and counted with an automated system. We applied this method in 21 patients (pts) undergoing epicardial biopsy during coronary bypass grafting (CBG) [20 M, 1 F; mean age 65 +/- 7.4 (+/- SEM) years]. Seven pts had neither DM nor HTN, seven had HTN, and seven had DM + HTN. In contrast to the prior light microscopic studies, we detected CML scattered throughout the cardiomyocyte in all pts, but in widely varying amounts. Ag-ab complexes were abundant in sections through myofilaments (mean count 23.6 +/- 9.2 per microm(2), range 9.4-48) and even more so in mitochondria (mean count 34.4 +/- 11.9 per microm(2), range 14.1-68.2, P < 0.001 vs. myofilaments). CML was also detected in vascular endothelial cells. There were no statistically significant differences based on presence or absence of HTN or DM. In conclusion, our IEM method is the first to provide detailed delineation of the localization and abundance of CML in myocardium. CML is very prevalent in CBG pts, suggesting that AGEs could play a role in abnormal cardiomyocyte function, including altered energy metabolism.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Anti-receptor for advanced glycation end products therapies as novel treatment for abdominal aortic aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms (AAA) is a devastating event potentially preventable by therapies that inhibit growth of small aneurysms. Receptor of advanced glycation end products (RAGE) has been implicated in age related diseases including atherosclerosis and Alzheimer. Consequently, we explored whether RAGE may also contribute to the formation of AAAs.

RESULTS

Implicating a role for RAGE in AAA, we found the expression of RAGE and its ligand AGE were highly elevated in human aneurysm specimens as compared with normal aortic tissue. In a mouse model of AAA, RAGE gene deletion (knockout) dramatically reduced the incidence of AAA to 1/3 of control (AAAs in 75.0% of controls vs. 25.0% knockouts). Moreover, aortic diameter was markedly reduced in RAGE knockout animals versus controls. As to mechanism, we found that RAGE was coexpressed in AAA macrophages with MMP-9, a promoter of matrix degradation, which is known to induce AAA. In vitro, AGE induced the production of MMP-9 in macrophages in a dose-dependent manner while blocking RAGE signaling with a soluble AGE inhibitor prevented MMP-9 expression. In vivo, RAGE gene deficiency eliminated MMP-9 activity that was prevalent in aneurismal wall of the wild-type mice.

CONCLUSIONS

RAGE promotes the development of AAA by inducing MMP-9 expression. Blocking RAGE in a mouse aneurysm model has a dramatic inhibitory effect on the formation of aneurysms. These data suggest that larger animal and eventually human trials should be designed to test oral RAGE inhibitors and their potential to prevent progression of small aneurysms.

Association of arterial stiffness with HbA1c in 1,000 type 2 diabetic patients with or without hypertension

The objective is to evaluate the association of arterial stiffness [brachial-ankle pulse wave velocity (ba-PWV)] with glycemic control and duration of type 2 diabetes in diabetic subjects with or without hypertension. One thousand Chinese diabetic patients (562 with hypertension, 438 without hypertension) were included in this study. All patients underwent ba-PWV and biochemical measurements. Ba-PWV was significantly higher in diabetic subjects with hypertension than those without hypertension (1779 +/- 341 vs. 1691 +/- 342 cm/s, P < 0.0001), and these subjects were under similar glycemic control (6.9 +/- 1.5 vs. 6.9 +/- 1.3, P = 0.86). In diabetic and hypertensive subjects, ba-PWV was positively associated with HbA1c (1715 +/- 314 vs. 1851 +/- 335 cm/s, in subjects with HbA1c < 6.5% and with HbA1c > 7.0%, respectively, P < 0.0001), as well as duration of diabetes (1671 +/- 342 vs. 1791 +/- 313 vs. 1861 +/- 338 cm/s, in subjects with duration of diabetes <5 years, 5-10 years, and >10 years, respectively, P all < 0.05). In diabetic subjects without hypertension, ba-PWV was not associated with HbA1c (P = 0.47), but associated with duration of diabetes (1503 +/- 272 vs. 1692 +/- 354 cm/s, in subjects with duration of diabetes <5 years and >10 years, respectively, P = 0.0013). Ba-PWV was higher in diabetic subjects with hypertension than in diabetic subjects without hypertension, suggesting the independent effect of hypertension on arterial stiffness in diabetic subjects. Ba-PWV positively correlated with HbA1c and duration of diabetes in subjects with diabetes and hypertension, suggesting the importance of early glycemic control in the prevention of arterial stiffness and vascular complications.