Pharmacologic Approaches Against Advanced Glycation End Products (AGEs) in Diabetic Cardiovascular Disease

Mitigating diabetes associated with reactive oxygen species (ROS) and protein aggregation through pharmacological interventions

Diabetes mellitus, a complex metabolic disorder, presents a growing global health challenge. In 2021, there were 529 million diabetics worldwide. At the super-regional level, Oceania, the Middle East, and North Africa had the highest age-standardized rates. The majority of cases of diabetes in 2021 (>90.0%) were type 2 diabetes, which is largely indicative of the prevalence of diabetes in general, particularly in older adults (K. L. Ong, et al., Global, regional, and national burden of diabetes from 1990 to 2021, with projections of prevalence to 2050: a systematic analysis for the Global Burden of Disease Study 2021, Lancet, 2023, 402(10397), 203-234). Nowadays, slowing the progression of diabetic complications is the only effective way to manage diabetes with the available therapeutic options. However, novel biomarkers and treatments are urgently needed to control cytokine secretion, advanced glycation end products (AGEs) production, vascular inflammatory effects, and cellular death. Emerging research has highlighted the intricate interplay between reactive oxygen species (ROS) and protein aggregation in the pathogenesis of diabetes. In this scenario, the main aim of this paper is to provide a comprehensive review of the current understanding of the molecular mechanisms underlying ROS-induced cellular damage and protein aggregation, specifically focusing on their contribution to diabetes development. The role of ROS as key mediators of oxidative stress in diabetes is discussed, emphasizing their impact on cellular components and signaling. Additionally, the involvement of protein aggregation in impairing cellular function and insulin signaling is explored. The synergistic effects of ROS and protein aggregation in promoting β-cell dysfunction and insulin resistance are examined, shedding light on potential targets for therapeutic intervention.

An overview on glycation: molecular mechanisms, impact on proteins, pathogenesis, and inhibition

The formation of a heterogeneous set of advanced glycation end products (AGEs) is the final outcome of a non-enzymatic process that occurs in vivo on long-life biomolecules. This process, known as glycation, starts with the reaction between reducing sugars, or their autoxidation products, with the amino groups of proteins, DNA, or lipids, thus gaining relevance under hyperglycemic conditions. Once AGEs are formed, they might affect the biological function of the biomacromolecule and, therefore, induce the development of pathophysiological events. In fact, the accumulation of AGEs has been pointed as a triggering factor of obesity, diabetes-related diseases, coronary artery disease, neurological disorders, or chronic renal failure, among others. Given the deleterious consequences of glycation, evolution has designed endogenous mechanisms to undo glycation or to prevent it. In addition, many exogenous molecules have also emerged as powerful glycation inhibitors. This review aims to provide an overview on what glycation is. It starts by explaining the similarities and differences between glycation and glycosylation. Then, it describes in detail the molecular mechanism underlying glycation reactions, and the bio-molecular targets with higher propensity to be glycated. Next, it discusses the precise effects of glycation on protein structure, function, and aggregation, and how computational chemistry has provided insights on these aspects. Finally, it reports the most prevalent diseases induced by glycation, and the endogenous mechanisms and the current therapeutic interventions against it.

Advanced glycation end product (AGE) targeting antibody SIWA318H is efficacious in preclinical models for pancreatic cancer

SIWA318H is a novel monoclonal antibody that selectively targets an advanced glycation end product biomarker found in damaged/dysfunctional cells exhibiting (a) aerobic glycolysis, and (b) oxidative stress. Cells with this biomarker are dysfunctional and are associated with stresses and/or damages relating to aging, cancer and other disease processes. In this study, we evaluated the biological effects and antitumor activity of SIWA318H in preclinical models for pancreatic cancer. SIWA318H binds to pancreatic cancer cells and cancer-associated fibroblasts, as well as tumor xenografts derived from pancreatic cancer patients. Furthermore, SIWA318H induced significant antibody-dependent cell-mediated cytotoxicity (ADCC) against pancreatic cancer cells. In a humanized CD34+ NSG mouse xenograft model for pancreatic cancer, tumors in mice treated with SIWA318H grew significantly slower compared to those in control mice (p < 0.001). After 3 weeks of treatment with SIWA318H, the tumor growth was suppressed by 68.8% and 61.5% for the high and low dose regimens, respectively, when compared to the isotype antibody control (ANOVA p < 0.002). Moreover, a significant increase in complete remission (CR) rate was observed in mice receiving the high dose (60%, p < 0.04) or low dose (77.8%, p < 0.02) of SIWA318H treatment compared with control mice (6.7%). Immunohistochemical analyses of the tumor tissues showed a significant decrease in senescent cells in the tumor microenvironment of SIWA318H treated mice compared to that of control treated mice (p < 0.05). These results provide compelling evidence that SIWA318H is a promising novel therapeutic against pancreatic cancer.

Continuous low serum levels of advanced glycation end products and low risk of cardiovascular disease in patients with poorly controlled type 2 diabetes

BACKGROUND

Type 2 diabetes is associated with an increased risk of developing cardiovascular events. Previous studies have reported that advanced glycation end products (AGEs) were related to cardiovascular events in type 2 diabetes. However, data on associations between long-term AGEs and cardiovascular events in type 2 diabetes are lacking. This study aimed to determine whether a long-time shift in the levels of serum AGEs is associated with cardiovascular events in patients with poorly controlled type 2 diabetes.

METHODS

Two-time serum methyl-glyoxal-hydroimidazoline (MG-H1) levels were measured in 138 patients with type 2 diabetes whose mean glycated hemoglobin level was 10.1%. We categorized patients whose serum MG-H1 levels were < 2.8 µg/mL at both times as the continuous low MG-H1 group. The primary endpoints of this study were combined cardiovascular events, which were defined as heart disease, peripheral arterial disease, stroke, and all-cause death. Hazard ratios (HRs) for combined cardiovascular events with 95% confidence intervals (CIs) were calculated using the Cox proportional hazard models to compare the outcomes between the continuous low MG-H1 group and others.

RESULTS

The continuous low MG-H1 group was associated with a significantly lower risk than others in combined cardiovascular events after adjusting for possible confounders (HR: 0.50; 95% CI, 0.28-0.87; P = 0.02). Furthermore, the same relationship was observed in patients without a history of cardiovascular events.

CONCLUSIONS

Continuous low serum MG-H1 levels are associated with a low frequency of diabetes-related complications in patients with poorly controlled type 2 diabetes.

Accelerated AGEing: The Impact of Advanced Glycation End Products on the Prognosis of Chronic Kidney Disease

Advanced glycation end products (AGEs) are aging products. In chronic kidney disease (CKD), AGEs accumulate due to the increased production, reduced excretion, and the imbalance between oxidant/antioxidant capacities. CKD is therefore a model of aging. The aim of this review is to summarize the present knowledge of AGEs in CKD onset and progression, also focusing on CKD-related disorders (cardiovascular diseases, sarcopenia, and nutritional imbalance) and CKD mortality. The role of AGEs as etiopathogenetic molecules, as well as potential markers of disease progression and/or therapeutic targets, will be discussed.

Diabetic hyperglycemia promotes primary tumor progression through glycation-induced tumor extracellular matrix stiffening

Diabetes mellitus is a complex metabolic disorder that is associated with an increased risk of breast cancer. Despite this correlation, the interplay between tumor progression and diabetes, particularly with regard to stiffening of the extracellular matrix, is still mechanistically unclear. Here, we established a murine model where hyperglycemia was induced before breast tumor development. Using the murine model, in vitro systems, and patient samples, we show that hyperglycemia increases tumor growth, extracellular matrix stiffness, glycation, and epithelial-mesenchymal transition of tumor cells. Upon inhibition of glycation or mechanotransduction in diabetic mice, these same metrics are reduced to levels comparable with nondiabetic tumors. Together, our study describes a novel biomechanical mechanism by which diabetic hyperglycemia promotes breast tumor progression via glycating the extracellular matrix. In addition, our work provides evidence that glycation inhibition is a potential adjuvant therapy for diabetic cancer patients due to the key role of matrix stiffening in both diseases.

Endogenous advanced glycation end products in the pathogenesis of chronic diabetic complications

Diabetes is a common metabolic illness characterized by hyperglycemia and is linked to long-term vascular problems that can impair the kidney, eyes, nerves, and blood vessels. By increasing protein glycation and gradually accumulating advanced glycation end products in the tissues, hyperglycemia plays a significant role in the pathogenesis of diabetic complications. Advanced glycation end products are heterogeneous molecules generated from non-enzymatic interactions of sugars with proteins, lipids, or nucleic acids via the glycation process. Protein glycation and the buildup of advanced glycation end products are important in the etiology of diabetes sequelae such as retinopathy, nephropathy, neuropathy, and atherosclerosis. Their contribution to diabetes complications occurs via a receptor-mediated signaling cascade or direct extracellular matrix destruction. According to recent research, the interaction of advanced glycation end products with their transmembrane receptor results in intracellular signaling, gene expression, the release of pro-inflammatory molecules, and the production of free radicals, all of which contribute to the pathology of diabetes complications. The primary aim of this paper was to discuss the chemical reactions and formation of advanced glycation end products, the interaction of advanced glycation end products with their receptor and downstream signaling cascade, and molecular mechanisms triggered by advanced glycation end products in the pathogenesis of both micro and macrovascular complications of diabetes mellitus.

Dicarbonyl Stress in Diabetic Vascular Disease

Late vascular complications play a prominent role in the diabetes-induced increase in morbidity and mortality. Diabetes mellitus is recognised as a risk factor driving atherosclerosis and cardiovascular mortality; even after the normalisation of blood glucose concentration, the event risk is amplified-an effect called "glycolytic memory". The hallmark of this glycolytic memory and diabetic pathology are advanced glycation end products (AGEs) and reactive glucose metabolites such as methylglyoxal (MGO), a highly reactive dicarbonyl compound derived mainly from glycolysis. MGO and AGEs have an impact on vascular and organ structure and function, contributing to organ damage. As MGO is not only associated with hyperglycaemia in diabetes but also with other risk factors for diabetic vascular complications such as obesity, dyslipidaemia and hypertension, MGO is identified as a major player in the development of vascular complications in diabetes both on micro- as well as macrovascular level. In diabetes mellitus, the detoxifying system for MGO, the glyoxalase system, is diminished, accounting for the increased MGO concentration and glycotoxic load. This overview will summarise current knowledge on the effect of MGO and AGEs on vascular function.

Dietary Advanced Glycation End Products in an Elderly Population with Diabetic Nephropathy: An Exploratory Investigation

Advanced glycation end products (AGEs) are important in pathophysiology of type 2 diabetes mellitus (T2DM) and diabetic kidney disease (DKD). Dietary AGEs (dAGEs) contribute to the overall AGE pool in the body. Forty elderly T2DM patients with DKD were randomly allocated to a low-AGE (n = 20) or regular diabetic (n = 20) diet group. A three-day meal questionnaire was used to estimate average quantity of dAGEs. AGE accumulation was measured using skin autofluorescence and urine spectroscopy. sRAGE (soluble receptor AGE) was quantified using ELISA. After 8 weeks, the mean consumption of dAGEs was considerably reduced, both in the low-AGE diet (p = 0.004) and the control (p = 0.019) group. The expected urinary emission peak at 490 nm was shifted to 520 nm in some spectra. dAGEs did not correspond with urine AGE output. An AGE-limited diet for two months did not affect AGE content in skin and urine, or sRAGE concentration in the blood. The role of glycemia is likely to be greater than the impact of dAGE consumption. The unique observation of a fluorescence pattern at 520 nm warrants further examination, since it might point to genetic differences in AGE regulation, which could have clinical consequences, as AGE content depends on its formation and elimination.

Insulin Resistance Is Cheerfully Hitched with Hypertension

Cardiovascular diseases and type 2 diabetes mellitus (T2DM) have risen steadily worldwide, particularly in low-income and developing countries. In the last hundred years, deaths caused by cardiovascular diseases increased rapidly to 35-40%, becoming the most common cause of mortality worldwide. Cardiovascular disease is the leading cause of morbidity and mortality in type 2 diabetes mellitus (T2DM), which is aggravated by hypertension. Hypertension and diabetes are closely interlinked since they have similar risk factors such as endothelial dysfunction, vascular inflammation, arterial remodeling, atherosclerosis, dyslipidemia, and obesity. Patients with high blood pressure often show insulin resistance and have a higher risk of developing diabetes than normotensive individuals. It has been observed that over the last 30 years, the prevalence of insulin resistance (IR) has increased significantly. Accordingly, hypertension and insulin resistance are strongly related to an increased risk of impaired glucose tolerance, diabetes, cardiovascular diseases (CVD), and endocrine disorders. Common mechanisms, for instance, upregulation of the renin-angiotensin-aldosterone system, oxidative stress, inflammation, and activation of the immune system, possibly have a role in the association between diabetes and hypertension. Altogether these abnormalities significantly increase the risk of developing type 2 diabetes.

Understanding diabetes-induced cardiomyopathy from the perspective of renin angiotensin aldosterone system

Experimental and clinical evidence suggests that diabetic subjects are predisposed to a distinct cardiovascular dysfunction, known as diabetic cardiomyopathy (DCM), which could be an autonomous disease independent of concomitant micro and macrovascular disorders. DCM is one of the prominent causes of global morbidity and mortality and is on a rising trend with the increase in the prevalence of diabetes mellitus (DM). DCM is characterized by an early left ventricle diastolic dysfunction associated with the slow progression of cardiomyocyte hypertrophy leading to heart failure, which still has no effective therapy. Although the well-known "Renin Angiotensin Aldosterone System (RAAS)" inhibition is considered a gold-standard treatment in heart failure, its role in DCM is still unclear. At the cellular level of DCM, RAAS induces various secondary mechanisms, adding complications to poor prognosis and treatment of DCM. This review highlights the importance of RAAS signaling and its major secondary mechanisms involving inflammation, oxidative stress, mitochondrial dysfunction, and autophagy, their role in establishing DCM. In addition, studies lacking in the specific area of DCM are also highlighted. Therefore, understanding the complex role of RAAS in DCM may lead to the identification of better prognosis and therapeutic strategies in treating DCM.

Potential of Vasoprotectives to Inhibit Non-Enzymatic Protein Glycation, and Reactive Carbonyl and Oxygen Species Uptake

Reactive carbonyl species (RCS) such as methylglyoxal (MGO) or glyoxal (GO) are the main precursors of the formation of advanced glycation end products (AGEs). AGEs are a major factor in the development of vascular complications in diabetes. Vasoprotectives (VPs) exhibit a wide range of activities beneficial to cardiovascular health. The present study aimed to investigate selected VPs and their structural analogs for their ability to trap MGO/GO, inhibit AGE formation, and evaluate their antioxidant potential. Ultra-high-performance liquid chromatography coupled with an electrospray ionization mass spectrometer (UHPLC-ESI-MS) and diode-array detector (UHPLC-DAD) was used to investigate direct trapping capacity and kinetics of quenching MGO/GO, respectively. Fluorimetric and colorimetric measurements were used to evaluate antiglycation and antioxidant action. All tested substances showed antiglycative effects, but hesperetin was the most effective in RCS scavenging. We demonstrated that rutin, diosmetin, hesperidin, and hesperetin could trap both MGO and GO by forming adducts, whose structures we proposed. MGO-derived AGE formation was inhibited the most by hesperetin, and GO-derived AGEs by diosmetin. High reducing and antiradical activity was confirmed for quercetin, rutin, hesperetin, and calcium dobesilate. Therefore, in addition to other therapeutic applications, some VPs could be potential candidates as antiglycative agents to prevent AGE-related complications of diabetes.

Effects of an equol-containing supplement on advanced glycation end products, visceral fat and climacteric symptoms in postmenopausal women: A randomized controlled trial

INTRODUCTION

Equol, an isoflavone derivative whose chemical structure is similar to estrogen, is considered a potentially effective agent for relieving climacteric symptoms, for the prevention of lifestyle-related diseases, and for aging care in postmenopausal women. We investigated the effect of an equol-containing supplement on metabolism and aging and climacteric symptoms with respect to internally produced equol in postmenopausal women.

METHODS

A single-center, randomized controlled trial (registration number: UMIN000030975) on 57 postmenopausal Japanese women (mean age: 56±5.37 years) was conducted. Twenty-seven women received the equol supplement, while the remaining received control. Metabolic and aging-related biomarkers were compared before and after the 3-month intervention. Climacteric symptoms were assessed every month using a validated self-administered questionnaire in Japanese postmenopausal women.

RESULTS

Three months post-intervention, the treatment group showed significant improvement in climacteric symptoms compared to the control group (81% vs. 53%, respectively, p = 0.045). We did not observe any beneficial effect on metabolic and aging-related biomarkers in the intervention group. However, in certain populations, significant improvement in skin autofluorescence, which is a measurement of AGE skin products, and visceral fat area was observed, especially among equol producers.

CONCLUSION

Women receiving equol supplementation showed improved climacteric symptoms. This study offered a new hypothesis that there may be a synergy between supplemented equol and endogenously produced equol to improve skin aging and visceral fat in certain populations.

Influence of SGLT2 Inhibitor Treatment on Urine Antioxidant Status in Type 2 Diabetic Patients: A Pilot Study

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) have been recognized as potent antioxidant agents. Since SGLT2i are nephroprotective drugs, we aimed to examine the urine antioxidant status in patients with type 2 diabetes mellitus (T2DM). One hundred and one subjects participated in this study, including 37 T2DM patients treated with SGLT2i, 31 T2DM patients not using SGLT2i, and 33 healthy individuals serving as a control group. Total antioxidant capacity (TAC), superoxide dismutase (SOD), manganese superoxide dismutase (MnSOD), free thiol groups (R-SH, sulfhydryl groups), and catalase (CAT) activity, as well as glucose concentration, were assessed in the urine of all participants. Urine SOD and MnSOD activity were significantly higher among T2DM patients treated with SGLT2i than T2DM patients without SGLT2i treatment (p = 0.009 and p = 0.003, respectively) and to the healthy controls (p = 0.002 and p = 0.001, respectively). TAC was significantly lower in patients with T2DM treated with SGLT2i when compared to those not treated and healthy subjects (p = 0.036 and p = 0.019, respectively). It could be hypothesized that the mechanism by which SGLT2i provides nephroprotective effects involves improvement of the SOD antioxidant activity. However, lower TAC might impose higher OS (oxidative stress), and elevation of SOD activity might be a compensatory mechanism.

Advanced Glycation End Products: New Clinical and Molecular Perspectives

Diabetes mellitus (DM) is considered one of the most massive epidemics of the twenty-first century due to its high mortality rates caused mainly due to its complications; therefore, the early identification of such complications becomes a race against time to establish a prompt diagnosis. The research of complications of DM over the years has allowed the development of numerous alternatives for diagnosis. Among these emerge the quantification of advanced glycation end products (AGEs) given their increased levels due to chronic hyperglycemia, while also being related to the induction of different stress-associated cellular responses and proinflammatory mechanisms involved in the progression of chronic complications of DM. Additionally, the investigation for more valuable and safe techniques has led to developing a newer, noninvasive, and effective tool, termed skin fluorescence (SAF). Hence, this study aimed to establish an update about the molecular mechanisms induced by AGEs during the evolution of chronic complications of DM and describe the newer measurement techniques available, highlighting SAF as a possible tool to measure the risk of developing DM chronic complications.

The AGE receptor, OST48 drives podocyte foot process effacement and basement membrane expansion (alters structural composition)

AIMS

The accumulation of advanced glycation end products is implicated in the development and progression of diabetic kidney disease. No study has examined whether stimulating advanced glycation clearance via receptor manipulation is reno-protective in diabetes. Podocytes, which are early contributors to diabetic kidney disease and could be a target for reno-protection.

MATERIALS AND METHODS

To examine the effects of increased podocyte oligosaccharyltransferase-48 on kidney function, glomerular sclerosis, tubulointerstitial fibrosis and proteome (PXD011434), we generated a mouse with increased oligosaccharyltransferase-48kDa subunit abundance in podocytes driven by the podocin promoter.

RESULTS

Despite increased urinary clearance of advanced glycation end products, we observed a decline in renal function, significant glomerular damage including glomerulosclerosis, collagen IV deposition, glomerular basement membrane thickening and foot process effacement and tubulointerstitial fibrosis. Analysis of isolated glomeruli identified enrichment in proteins associated with collagen deposition, endoplasmic reticulum stress and oxidative stress. Ultra-resolution microscopy of podocytes revealed denudation of foot processes where there was co-localization of oligosaccharyltransferase-48kDa subunit and advanced glycation end-products.

CONCLUSIONS

These studies indicate that increased podocyte expression of oligosaccharyltransferase-48 kDa subunit results in glomerular endoplasmic reticulum stress and a decline in kidney function.

Polymers and Nanoparticles for Statin Delivery: Current Use and Future Perspectives in Cardiovascular Disease

Atherosclerosis-related coronary artery disease (CAD) is one of the leading sources of mortality and morbidity in the world. Primary and secondary prevention appear crucial to reduce CAD-related complications. In this scenario, statin treatment was shown to be clinically effective in the reduction of adverse events, but systemic administration provides suboptimal results. As an attempt to improve bioavailability and effectiveness, polymers and nanoparticles for statin delivery were recently investigated. Polymers and nanoparticles can help statin delivery and their effects by increasing oral bioavailability or enhancing target-specific interaction, leading to reduced vascular endothelial dysfunction, reduced intimal hyperplasia, reduced ischemia-reperfusion injury, increased cardiac regeneration, positive remodeling in the extracellular matrix, reduced neointimal growth and increased re-endothelization. Moreover, some innovative aspects described in other cardiovascular fields could be translated into the CAD scenario. Recent preclinical studies are underlining the effect of statins in the stimulation and differentiation of endogenous cardiac stem cells, as well as in targeting of local adverse conditions implicated in atherosclerosis, and statin delivery through poly-lactic-co-glycolic acid (PLGA) appears the most promising aspect of current research to enhance drug activity. The present review intends to summarize the current evidence about polymers and nanoparticles for statin delivery in the field of cardiovascular disease, trying to shed light on this topic and identify new avenues for future studies.

A review on mechanism of inhibition of advanced glycation end products formation by plant derived polyphenolic compounds

Advanced glycation end products (AGEs) are naturally occurring biomolecules formed by interaction of reducing sugars with biomolecules such as protein and lipids etc., Long term high blood sugar level and glycation accelerate the formation of AGEs. Unchecked continuous formation and accumulation of AGEs are potential risks for pathogenesis of various chronic diseases. Current mode of antidiabetic therapy is based on synthetic drugs that are often linked with severe adverse effects. Polyphenolic compounds derived from plants are supposed to inhibit glycation and formation of AGEs at multiple levels. Some polyphenolic compounds regulate the blood glucose metabolism by amplification of cell insulin resistance and activation of insulin like growth factor binding protein signaling pathway. Their antioxidant nature and metal chelating activity, ability to trap intermediate dicarbonyl compounds could be possible mechanisms against glycation and AGEs formation and hence, against AGEs induced health complications. Although, few species of polyphenolic compounds are being used in in vitro trials and their in vivo study is still in progress, increasing the area of research in this field may produce a fruitful approach in management of overall diabetic complications.

Autophagic receptor p62 protects against glycation-derived toxicity and enhances viability

Diabetes and metabolic syndrome are associated with the typical American high glycemia diet and result in accumulation of high levels of advanced glycation end products (AGEs), particularly upon aging. AGEs form when sugars or their metabolites react with proteins. Associated with a myriad of age-related diseases, AGEs accumulate in many tissues and are cytotoxic. To date, efforts to limit glycation pharmacologically have failed in human trials. Thus, it is crucial to identify systems that remove AGEs, but such research is scanty. Here, we determined if and how AGEs might be cleared by autophagy. Our in vivo mouse and C. elegans models, in which we altered proteolysis or glycative burden, as well as experiments in five types of cells, revealed more than six criteria indicating that p62-dependent autophagy is a conserved pathway that plays a critical role in the removal of AGEs. Activation of autophagic removal of AGEs requires p62, and blocking this pathway results in accumulation of AGEs and compromised viability. Deficiency of p62 accelerates accumulation of AGEs in soluble and insoluble fractions. p62 itself is subject to glycative inactivation and accumulates as high mass species. Accumulation of p62 in retinal pigment epithelium is reversed by switching to a lower glycemia diet. Since diminution of glycative damage is associated with reduced risk for age-related diseases, including age-related macular degeneration, cardiovascular disease, diabetes, Alzheimer's, and Parkinson's, discovery of methods to limit AGEs or enhance p62-dependent autophagy offers novel potential therapeutic targets to treat AGEs-related pathologies.

Advanced Glycation End Products: Potential Mechanism and Therapeutic Target in Cardiovascular Complications under Diabetes

The occurrence and development of cardiovascular complications are predominantly responsible for the increased morbidity and mortality observed in patients with diabetes. Oxidative stress under hyperglycemia is currently considered the initial link to diabetic cardiovascular complications and a key node for the prevention and treatment of diabetes-related fatal cardiovascular events. Numerous studies have indicated that the common upstream pathway in the context of oxidative stress in the cardiovascular system under diabetic conditions is the interaction of advanced glycation end products (AGEs) with their receptors (RAGEs). Therefore, a further understanding of the relationship between oxidative stress and AGEs is of great significance for the prevention and treatment of cardiovascular complications in patients with diabetes. In this review, we will briefly summarize the recent research advances in diabetes with an emphasis on oxidative stress and its association with AGEs in diabetic cardiovascular complications.

Alagebrium and Complications of Diabetes Mellitus

Glycation is the process of linking a sugar and free amino groups of proteins. Cross-linking of glycation products to proteins results in the formation of cross-linked proteins that inhibit the normal functioning of the cell. Advanced glycation end products (AGEs) are risk molecules for the cell aging process. These ends products are increasingly synthesized in diabetes and are essentially responsible for diabetic complications. They accumulate in the extracellular matrix and bind to receptors (receptor of AGE [RAGE]) to generate oxidative stress and inflammation. particularly in the cardiovascular system. Treatment methods targeting the AGE system may be of clinical importance in reducing and preventing the complications induced by AGEs in diabetes and old age. The AGE cross-link breaker alagebrium (a thiazolium derivative) is the most studied anti-AGE compound in the clinical field. Phase III clinical studies with alagebrium have been successfully conducted, and this molecule has positive effects on cardiovascular hypertrophy, diabetes, hypertension, vascular sclerotic pathologies, and similar processes. However, the mechanism is still not fully understood. The primary mechanism is that alagebrium removes newly formed AGEs by chemically separating α-dicarbonyl carbon-carbon bonds formed in cross-linked structures. However, it is also reported that alagebrium is a methylglyoxal effective inhibitor. It is not yet clear whether alagebrium inhibits copper-catalyzed ascorbic acid oxidation through metal chelation or destruction of the AGEs. It is not known whether alagebrium has a direct association with RAGEs. The safety profile is favorably in humans, and studies have been terminated due to financial insufficiency and inability to license as a drug.

Cognitive dysfunction in diabetic rats is prevented by pyridoxamine treatment. A multidisciplinary investigation

OBJECTIVE

The impact of diabetes mellitus on the central nervous system is less widely studied than in the peripheral nervous system, but there is increasing evidence that it elevates the risk of developing cognitive deficits. The aim of this study was to characterize the impact of experimental diabetes on the proteome and metabolome of the hippocampus. We tested the hypothesis that the vitamin B6 isoform pyridoxamine is protective against functional and molecular changes in diabetes.

METHODS

We tested recognition memory using the novel object recognition (NOR) test in streptozotocin (STZ)-induced diabetic, age-matched control, and pyridoxamine- or insulin-treated diabetic male Wistar rats. Comprehensive untargeted metabolomic and proteomic analyses, using gas chromatography-mass spectrometry and iTRAQ-enabled protein quantitation respectively, were utilized to characterize the molecular changes in the hippocampus in diabetes.

RESULTS

We demonstrated diabetes-specific, long-term (but not short-term) recognition memory impairment and that this deficit was prevented by insulin or pyridoxamine treatment. Metabolomic analysis showed diabetes-associated changes in 13/82 identified metabolites including polyol pathway intermediates glucose (9.2-fold), fructose (4.9-fold) and sorbitol (5.2-fold). We identified and quantified 4807 hippocampal proteins; 806 were significantly altered in diabetes. Pathway analysis revealed significant alterations in cytoskeletal components associated with synaptic plasticity, glutamatergic signaling, oxidative stress, DNA damage and FXR/RXR activation pathways in the diabetic rat hippocampus.

CONCLUSIONS

Our data indicate a protective effect of pyridoxamine against diabetes-induced cognitive deficits, and our comprehensive 'omics datasets provide insight into the pathogenesis of cognitive dysfunction enabling development of further mechanistic and therapeutic studies.

Poorly controlled type 2 diabetes with no progression of diabetes-related complications and low levels of advanced glycation end products: A Case report

RATIONALE

Previous studies have suggested that increased levels of advanced glycation end products (AGEs) and soluble receptor for AGE (sRAGE) are associated with diabetes-related complications. However, there is little evidence on the association between long-term levels of AGEs and sRAGE and progression of diabetes-related complications.

PATIENT CONCERNS

A 64-year-old man had poorly controlled type 2 diabetes, obesity, smoking, hypertension, and dyslipidemia. He had many risk factors for diabetes-related complications.

DIAGNOSIS

Despite poor glycemic control over 15 years, the patient did not exhibit diabetes-related complications.

INTERVENTIONS

We examined serum AGEs (CEL and MG-H1) and sRAGE levels in this patient over the past 10 years.

OUTCOMES

The patient maintained low serum AGEs and sRAGE levels.

LESSONS

AGEs and sRAGE levels may be associated with long-term development of diabetes-related complications.

The role of advanced glycation end-products in the development of coronary artery disease in patients with and without diabetes mellitus: a review

Background

Traditional risk factors are insufficient to explain all cases of coronary artery disease (CAD) in patients with diabetes mellitus (DM). Advanced glycation end-products (AGEs) and their receptors may play important roles in the development and progression of CAD.

Body

Hyperglycemia is the hallmark feature of DM. An increase in the incidence of both micro-and macrovascular complications of diabetes has been observed with increased duration of hyperglycemia. This association persists even after glycemic control has been achieved, suggesting an innate mechanism of “metabolic memory.” AGEs are glycated proteins that may serve as mediators of metabolic memory due to their increased production in the setting of hyperglycemia and generally slow turnover. Elevated AGE levels can lead to abnormal cross linking of extracellular and intracellular proteins disrupting their normal structure and function. Furthermore, activation of AGE receptors can induce complex signaling pathways leading to increased inflammation, oxidative stress, enhanced calcium deposition, and increased vascular smooth muscle apoptosis, contributing to the development of atherosclerosis. Through these mechanisms, AGEs may be important mediators of the development of CAD. However, clinical studies regarding the role of AGEs and their receptors in advancing CAD are limited, with contradictory results.

Conclusion

AGEs and their receptors may be useful biomarkers for the presence and severity of CAD. Further studies are needed to evaluate the utility of circulating and tissue AGE levels in identifying asymptomatic patients at risk for CAD or to identify patients who may benefit from invasive intervention.

Caloric restriction improves the redox homeostasis in the aging male rat heart even when started in middle-adulthood and when the body weight is stable

Evidence indicates that maintenance of redox homeostasis is fundamental for cellular longevity. Caloric-restriction (CR) is said to decrease the formation of oxidatively modified cellular macromolecules and improve health. On the other hand, some studies indicate that many CR studies are flawed, because ad libitum fed rats are not well-controlled. Thus, it is claimed that purported beneficial effects of CR could be not due to real CR effect, but due to control animals going obese. Also, it remains to be elucidated whether effects of CR could be observed even when CR is started in mid-adulthood. Male Sprague-Dawley rats were grouped as: non-CR 6-month-old rats (n = 7), 24-month-old rats subjected to 40% CR for 6 months between 18th and 24th months (n = 8), and non-CR 24-month-old animals (n = 8). We investigated 16 previously validated biomarkers of macromolecular redox homeostasis, ranging from protein and lipid oxidation to glycation and antioxidative capacity. In the present study, the protein, lipid and antioxidant capacity redox homeostasis biomarkers overwhelmingly indicate that, CR, even though not started very early in adulthood, could still offer potential therapeutic effects and it could significantly improve various redox homeostasis biomarkers associated with disease reliably in the heart tissue of aging male Sprague-Dawley rats. Therefore, the effects of CR likely operate through similar mechanisms throughout adulthood and CR seems to have real ameliorative effects on organisms that are not due to confounding factors that come from ad libitum fed rats.

Advanced glycation end products (AGEs) estimated by skin autofluorescence are related with cardiovascular risk in renal transplant

Background

Advanced glycation end products (AGEs) accumulation, a measure of cumulative metabolic stress, constitute a novel pathogenic mechanism involved in aging, diabetes, cardiovascular (CVD) and chronic kidney disease (CKD). Despite removal of uremic toxins and AGEs after a successful renal transplant (RT), CVD remains the leading cause of mortality. We hypothesized that AGEs measurement by Skin Autofluorescence (SAF) might be useful even after a successful RT and thus reflect the high cardiovascular risk burden of these patients.

Methods

189 stable RT (61% men, aged 56±13.0 years), CKD stages 1–4 and >12 months since RT were enrolled. Variables collected comprised comorbid history, medication use, smoking habit, routine biochemistry, subclinical atheromatosis by ankle-brachial-index (ABI) and allograft resistivity index (RI), 24-h ABPM, anthropometry and handgrip strength. AGEs were measured by SAF and expressed in arbitrary units (AU). Vascular age was estimated by Koetsier´s formula (SAF-0.83/0.024) and expected 10-years cardiovascular death risk was calculated with the REGICOR score.

Results

Mean SAF was 3.00±0.83 AU and estimated vascular age 90±34.7 years (30 years above biological age). SAF was higher among men (3.10±0.91 vs 2.81±0.66), diabetic nephropathy (3.49±0.75 vs 2.96±0.83) and steroid users (3.14±0.86 vs 2.71±0.69). We observed a positive correlation of SAF with night-systolic blood pressure (r = 0.25, p = 0.001), parathormone (r = 0.20, p<0.01), phosphate (r = 0.28, p<0.001) and negative with hemoglobin (r = -0.29, p<0.001), CKD-EPI (r = -0.32, p<0.001), albumin (r = -0.17, p<0.05), and dynamometry (r = -0.20, p<0.01). Subclinical vascular atheromatosis (ABI and RI) as well as the REGICOR scale (r = 0.35 p<0.001) were also correlated with SAF. In multivariable analysis age, gender, steroid use, serum phosphate and handgrip strength remained independently associated with SAF.

Conclusions

SAF levels are elevated in RT patients and correlate with CVD risk. Besides age and male sex, our results suggest that phosphate overload, steroid use and nutritional status are important factors linking to AGEs accumulation.

Diabetes, Hypertension, and Cardiovascular Disease: Clinical Insights and Vascular Mechanisms

Hypertension and type 2 diabetes are common comorbidities. Hypertension is twice as frequent in patients with diabetes compared with those who do not have diabetes. Moreover, patients with hypertension often exhibit insulin resistance and are at greater risk of diabetes developing than are normotensive individuals. The major cause of morbidity and mortality in diabetes is cardiovascular disease, which is exacerbated by hypertension. Accordingly, diabetes and hypertension are closely interlinked because of similar risk factors, such as endothelial dysfunction, vascular inflammation, arterial remodelling, atherosclerosis, dyslipidemia, and obesity. There is also substantial overlap in the cardiovascular complications of diabetes and hypertension related primarily to microvascular and macrovascular disease. Common mechanisms, such as upregulation of the renin-angiotensin-aldosterone system, oxidative stress, inflammation, and activation of the immune system likely contribute to the close relationship between diabetes and hypertension. In this article we discuss diabetes and hypertension as comorbidities and discuss the pathophysiological features of vascular complications associated with these conditions. We also highlight some vascular mechanisms that predispose to both conditions, focusing on advanced glycation end products, oxidative stress, inflammation, the immune system, and microRNAs. Finally, we provide some insights into current therapies targeting diabetes and cardiovascular complications and introduce some new agents that may have vasoprotective therapeutic potential in diabetes.

Salidroside Protects Against Advanced Glycation End Products-Induced Vascular Endothelial Dysfunction

Background

Salidroside, the major active compound in Rhodiola, has been reported to provide beneficial effects on cardiovascular diseases, but its effects on diabetes-induced vascular endothelial dysfunction are less known. Here, we examined the protective effects of salidroside on endothelial function in diabetes and explored the potential underlying mechanism.

Material/Methods

First, we assessed the endothelium-dependent relaxation response to acetylcholine, with or without salidroside treatment, in aortas isolated from Sprague-Dawley rats. Then, cell viability, oxidative biomarkers, and protein expression were tested to determine the effect of salidroside treatment on human umbilical vein endothelial cells (HUVECs) in vitro.

Results

Advanced glycation end product (AGE)-induced endothelial dysfunction was significantly improved by salidroside treatment (P<0.05), as shown by a reduced relaxation response to the vasodilator acetylcholine. Further, incubation with salidroside restored NO levels and reduced reactive oxygen species formation in AGE-stimulated HUVECs in a concentration-dependent manner (P<0.05). We also showed that nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/heme oxygenase 1 (HO-1) and nuclear factor kappa B (NF-κB) signaling was critical for the salidroside-mediated beneficial regulation.

Conclusions

Our results demonstrate that salidroside protects against AGE-induced endothelial dysfunction, and its effects may be in part attributed to the induction of HO-1 and attenuation of phosphorylated NF-κB p65.

Alpha-Synuclein Glycation and the Action of Anti-Diabetic Agents in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder with complex etiology and variable pathology. While a subset of cases is associated with single-gene mutations, the majority originates from a combination of factors we do not fully understand. Thus, understanding the underlying causes of PD is indispensable for the development of novel therapeutics. Glycation, the non-enzymatic reaction between reactive dicarbonyls and amino groups, gives rise to a variety of different reaction products known as advanced glycation end products (AGEs). AGEs accumulate over a proteins life-time, and increased levels of glycation reaction products play a role in diabetic complications. It is now also becoming evident that PD patients also display perturbed sugar metabolism and protein glycation, including that of alpha-synuclein, a key player in PD. Here, we hypothesize that anti-diabetic drugs targeting the levels of glycation precursors, or promoting the clearance of glycated proteins may also prove beneficial for PD patients.

Kidney, heart and brain: three organs targeted by ageing and glycation

Advanced glycation end-product (AGE) is the generic term for a heterogeneous group of derivatives arising from a non-enzymatic reaction between reducing sugars and proteins. In recent years, evidence has accumulated that incriminates AGEs in pathogenic processes associated with both chronic hyperglycaemia and age-related diseases. Regardless of their exogenous or endogenous origin, the accumulation of AGEs and their derivatives could promote accelerated ageing by leading to protein modifications and activating several inflammatory signalling pathways via AGE-specific receptors. However, it remains to be demonstrated whether preventing the accumulation of AGEs and their effects is an important therapeutic option for successful ageing. The present review gives an overview of the current knowledge on the pathogenic role of AGEs by focusing on three AGE target organs: kidney, heart and brain. For each of these organs we concentrate on an age-related disease, each of which is a major public health issue: chronic kidney disease, heart dysfunction and neurodegenerative diseases. Even though strong connections have been highlighted between glycation and age-related pathogenesis, causal links still need to be validated. In each case, we report evidence and uncertainties suggested by animal or epidemiological studies on the possible link between pathogenesis and glycation in a chronic hyperglycaemic state, in the absence of diabetes, and with exogenous AGEs alone. Finally, we present some promising anti-AGE strategies that are currently being studied.

The Association between Diffuse Myocardial Fibrosis on Cardiac Magnetic Resonance T1 Mapping and Myocardial Dysfunction in Diabetic Rabbits

The objective of this study was to assess the relationship between imaging surrogates for diffuse fibrosis and myocardial dysfunction. Thirty-six New Zealand white rabbits were classified into two groups: a control group (n = 18) and an alloxan-induced diabetes mellitus (DM) group (n = 18). For all rabbits, conventional ultrasonography, two-dimensional speckle tracking, and cardiac magnetic resonance (CMR) T1 mapping were performed; all of the rabbits were then sacrificed for Masson’s staining. The extracellular volume (ECV) was calculated from pre- and post-contrast T1 values and compared with myocardial function measured by echocardiography using Pearson’s correlation. In the DM group, ECV increased as the duration of diabetes increased, consistent with the changes in myocardial fibrosis verified by pathology. Moreover, ECV was strongly correlated with the early diastolic strain rate (r = −0.782, p < 0.001) and moderately correlated with the radial systolic peak strain (r = 0.478, p = 0.045). Thus, ECV is an effective surrogate for myocardial diffuse fibrosis on CMR imaging, and higher ECV values are associated with an increased impairment of myocardial diastolic function.

Computational approaches in the rational design of improved carbonyl quenchers: focus on histidine containing dipeptides

AIM

The inhibition of protein carbonylation can play therapeutic roles in several oxidative-based diseases and direct carbonyl quenching appears the most effective inhibition strategies. l-carnosine derivatives are effective and selective quenchers toward 4-hydroxy-2-nonenal even though their activity was never investigated in a fully comparable way.

RESULTS

The reported results revealed that anserine, homocarnosine and carnosinamide retain a remarkable quenching activity combined with a satisfactory selectivity. In silico analyses confirmed the key role of flexibility, lipophilicity and nucleophilicity parameters in rationalizing the measured reactivity.

CONCLUSION

This study confirms that in silico approaches can be successfully used in the rational design of improved carbonyl quenchers. Physicochemical and stereoelectronic descriptors appear really informative especially when explored by their corresponding property spaces.

Cellular mechanisms and consequences of glycation in atherosclerosis and obesity

Post-translational modification of proteins imparts diversity to protein functions. The process of glycation represents a complex set of pathways that mediates advanced glycation endproduct (AGE) formation, detoxification, intracellular disposition, extracellular release, and induction of signal transduction. These processes modulate the response to hyperglycemia, obesity, aging, inflammation, and renal failure, in which AGE formation and accumulation is facilitated. It has been shown that endogenous anti-AGE protective mechanisms are thwarted in chronic disease, thereby amplifying accumulation and detrimental cellular actions of these species. Atop these considerations, receptor for advanced glycation endproducts (RAGE)-mediated pathways downregulate expression and activity of the key anti-AGE detoxification enzyme, glyoxalase-1 (GLO1), thereby setting in motion an interminable feed-forward loop in which AGE-mediated cellular perturbation is not readily extinguished. In this review, we consider recent work in the field highlighting roles for glycation in obesity and atherosclerosis and discuss emerging strategies to block the adverse consequences of AGEs. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Metabolomics in diabetic complications

With a global prevalence of 9%, diabetes is the direct cause of millions of deaths each year and is quickly becoming a health crisis. Major long-term complications of diabetes arise from persistent oxidative stress and dysfunction in multiple metabolic pathways. The most serious complications involve vascular damage and include cardiovascular disease as well as microvascular disorders such as nephropathy, neuropathy, and retinopathy. Current clinical analyses like glycated hemoglobin and plasma glucose measurements hold some value as prognostic indicators of the severity of complications, but investigations into the underlying pathophysiology are still lacking. Advancements in biotechnology hold the key to uncovering new pathways and establishing therapeutic targets. Metabolomics, the study of small endogenous molecules, is a powerful toolset for studying pathophysiological processes and has been used to elucidate metabolic signatures of diabetes in various biological systems. Current challenges in the field involve correlating these biomarkers to specific complications to provide a better prediction of future risk and disease progression. This review will highlight the progress that has been made in the field of metabolomics including technological advancements, the identification of potential biomarkers, and metabolic pathways relevant to macro- and microvascular diabetic complications.

Antioxidant, antiglycation and insulinotrophic properties of Coccinia grandis (L.) in vitro: Possible role in prevention of diabetic complications

In an attempt to develop Complementary and Alternative Medicine (CAM) for the treatment of diabetes and related complications, the antidiabetic potential of the mature unripe fruits of Coccinia grandis (CGF) was evaluated. Oxidative stress and glycation plays an important role in manifesting of diabetes and vascular complications. Agents with antioxidant and antiglycation properties may retard these pathological alterations. In this study, the edible plant Coccinia grandis was assessed for in vitro estimation of antioxidant and antiglycation potential and its insulinotrophic properties in RINm5F cells. Antioxidant activity was evaluated as DPPH (1,1-diphenyl-2-picrylhydrazyl), hydrogen peroxide and superoxide anion scavenging activities, whereas the protein glycation inhibitory potential was evaluated using in vitro albumin-fructose glycation model. Glycation inhibition was estimated by different biochemical parameters viz. fructosamine, protein carbonyl group and protein aggregation using thioflavin T fluorescence. C. grandis extract exerted a dose dependent radical scavenging activity and exhibited a significant antiglycation potential. The extract also showed a significant insulinotrophic property with 1.28 and 1.71-fold increase in insulin release when compared to control at 0.25 and 0.50 mg/mL, respectively. These data suggest the possible antidiabetic role of CGF extract, presumably by its antioxidant, antiglycation and insulin secretory effects. Present findings provide experimental evidence that the fruits of C. grandis have potential antidiabetic activity which might be used as a functional food and safe remedy for the treatment of diabetes and associated complications. This study also revealed that the plant can be a promising source for development of natural antiglycating agents and novel insulin secretagogues.

Cells and extracellular matrix interplay in cardiac valve disease: because age matters

Cardiovascular aging is a physiological process affecting all components of the heart. Despite the interest and experimental effort lavished on aging of cardiac cells, increasing evidence is pointing at the pivotal role of extracellular matrix (ECM) in cardiac aging. Structural and molecular changes in ECM composition during aging are at the root of significant functional modifications at the level of cardiac valve apparatus. Indeed, calcification or myxomatous degeneration of cardiac valves and their functional impairment can all be explained in light of age-related ECM alterations and the reciprocal interplay between altered ECM and cellular elements populating the leaflet, namely valvular interstitial cells and valvular endothelial cells, is additionally affecting valve function with striking reflexes on the clinical scenario. The initial experimental findings on this argument are underlining the need for a more comprehensive understanding on the biological mechanisms underlying ECM aging and remodeling as potentially constituting a pharmacological therapeutic target or a basis to improve existing prosthetic devices and treatment options. Given the lack of systematic knowledge on this topic, this review will focus on the ECM changes that occur during aging and on their clinical translational relevance and implications in the bedside scenario.