Increased serum levels of the specific AGE-compound methylglyoxal-derived hydroimidazolone in patients with type 2 diabetes

A map of glycation and glycoxidation sites in collagen I of human cortical bone: Effects of sex and type 2 diabetes

Complications of diabetes is a major health problem affecting multiple organs including bone, where the chronic disease increases the risk of fragility fractures. One hypothesis suggests a pathogenic role for hyperglycemia-induced modification of proteins, a.k.a. advanced glycation end products (AGEs), resulting in structural and functional damage to bone extracellular matrix (ECM). Evidence supporting this hypothesis has been limited by the lack of comprehensive information about the location of AGEs that accumulate in vivo at specific sites within the proteins of bone ECM. Analyzing extracts from cortical bone of cadaveric femurs by liquid chromatography tandem mass spectrometry, we generated a quantitative AGE map of human collagen I for male and female adult donors with and without diabetes. The map describes the chemical nature, sequence position, and levels of four major physiological AGEs, e.g. carboxymethyllysine, and an AGE precursor fructosyllysine within the collagen I triple-helical region. The important features of the map are: 1) high map reproducibility in the individual bone extracts, i.e. 20 male and 20 female donors; 2) localization of modifications to distinct clusters: 10 clusters containing 34 AGE sites in male donors and 9 clusters containing 28 sites in female donors; 3) significant increases in modification levels in diabetes at multiple sites: 26 out of 34 sites in males and in 17 out of 28 sites in females; and 4) generally higher modification levels in male vs. female donors. Moreover, the AGE levels at multiple individual sites correlated with total bone pentosidine levels in male but not in female donors. Molecular dynamics simulations and molecular modeling predicted significant impact of modifications on solvent exposure, charge distribution, and hydrophobicity of the triple helix as well as disruptions to the structure of collagen I fibril. In summary, the AGE map of collagen I revealed diabetes-induced, sex-specific non-enzymatic modifications at distinct triple helical sites that can disrupt collagen structure, thus proposing a specific mechanism of AGE contribution to diabetic complications in human bone.

Diabetes and Parkinson's Disease: Understanding Shared Molecular Mechanisms

Aging is a major risk factor for Parkinson's disease (PD). Genetic mutations account for a small percentage of cases and the majority appears to be sporadic, with yet unclear causes. However, various environmental factors have been linked to an increased risk of developing PD and, therefore, understanding the complex interplay between genetic and environmental factors is crucial for developing effective disease-modifying therapies. Several studies identified a connection between type 2 diabetes (T2DM) and PD. T2DM is characterized by insulin resistance and failure of β-cells to compensate, leading to hyperglycemia and serious comorbidities. Both PD and T2DM share misregulated processes, including mitochondrial dysfunction, oxidative stress, chronic inflammation, altered proteostasis, protein aggregation, and misregulation of glucose metabolism. Chronic or recurring hyperglycemia is a T2DM hallmark and can lead to increased methylglyoxal (MGO) production, which is responsible for protein glycation. Glycation of alpha-synuclein (aSyn), a central player in PD pathogenesis, accelerates the deleterious aSyn effects. Interestingly, MGO blood plasma levels and aSyn glycation are significantly elevated in T2DM patients, suggesting a molecular mechanism underlying the T2DM - PD link. Compared to high constant glucose levels, glycemic variability (fluctuations in blood glucose levels), can be more detrimental for diabetic patients, causing oxidative stress, inflammation, and endothelial damage. Accordingly, it is imperative for future research to prioritize the exploration of glucose variability's influence on PD development and progression. This involves moving beyond the binary classification of patients as diabetic or non-diabetic, aiming to pave the way for the development of enhanced therapeutic interventions.

Mechanism of peroxidasin inactivation in hyperglycemia: Heme damage by reactive oxygen species

Diabetic complications present a serious health problem. Functional damage to proteins due to post-translational modifications by glycoxidation reactions is a known factor contributing to pathology. Extracellular proteins are especially vulnerable to diabetic damage because robust antioxidant defenses are lacking outside the cell. We investigated glucose-induced inactivation of peroxidasin (PXDN), a heme protein catalyzing sulfilimine crosslinking of collagen IV that reinforce the basement membranes (BM). Experiments using physiological diabetic glucose levels were carried out to exclude several potential mechanisms of PXDN inactivation i.e., direct adduction of glucose, reactive carbonyl damage, steric hindrance, and osmotic stress. Further experiments established that PXDN activity was inhibited via heme degradation by reactive oxygen species. Activity of another extracellular heme protein, myeloperoxidase, was unaffected by glucose because its heme was resistant to glucose-induced oxidative degradation. Our findings point to specific mechanisms which may compromise BM structure and stability in diabetes and suggest potential modes of protection.

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

The effect of GLP-1 receptor agonist lixisenatide on experimental diabetic retinopathy

AIMS

Glucagon-like peptide-1 receptor agonists are effective treatments for type 2 diabetes, effectively lowering glucose without weight gain and with low risk for hypoglycemia. However, their influence on the retinal neurovascular unit remains unclear. In this study, we analyzed the effects of the GLP-1 RA lixisenatide on diabetic retinopathy.

METHODS

Vasculo- and neuroprotective effects were assessed in experimental diabetic retinopathy and high glucose-cultivated C. elegans, respectively. In STZ-diabetic Wistar rats, acellular capillaries and pericytes (quantitative retinal morphometry), neuroretinal function (mfERG), macroglia (GFAP western blot) and microglia (immunohistochemistry) quantification, methylglyoxal (LC-MS/MS) and retinal gene expressions (RNA-sequencing) were determined. The antioxidant properties of lixisenatide were tested in C. elegans.

RESULTS

Lixisenatide had no effect on glucose metabolism. Lixisenatide preserved the retinal vasculature and neuroretinal function. The macro- and microglial activation was mitigated. Lixisenatide normalized some gene expression changes in diabetic animals to control levels. Ets2 was identified as a regulator of inflammatory genes. In C. elegans, lixisenatide showed the antioxidative property.

CONCLUSIONS

Our data suggest that lixisenatide has a protective effect on the diabetic retina, most likely due to a combination of neuroprotective, anti-inflammatory and antioxidative effects of lixisenatide on the neurovascular unit.

Evidence that methylglyoxal and receptor for advanced glycation end products are implicated in bladder dysfunction of obese diabetic ob/ob mice

Glycolytic overload in diabetes causes large accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO) and overproduction of advanced glycation end products (AGEs), which interact with their receptors (RAGE), leading to diabetes-associated macrovascular complications. The bladder is an organ that stays most in contact with dicarbonyl species, but little is known about the importance of the MGO-AGEs-RAGE pathway to diabetes-associated bladder dysfunction. Here, we aimed to investigate the role of the MGO-AGEs-RAGE pathway in bladder dysfunction of diabetic male and female ob/ob mice compared with wild-type (WT) lean mice. Diabetic ob/ob mice were treated with the AGE breaker alagebrium (ALT-711, 1 mg/kg) for 8 wk in drinking water. Compared with WT animals, male and female ob/ob mice showed marked hyperglycemia and insulin resistance, whereas fluid intake remained unaltered. Levels of total AGEs, MGO-derived hydroimidazolone 1, and RAGE in bladder tissues, as well as fluorescent AGEs in serum, were significantly elevated in ob/ob mice of either sex. Collagen content was also markedly elevated in the bladders of ob/ob mice. Void spot assays in filter paper in conscious mice revealed significant increases in total void volume and volume per void in ob/ob mice with no alterations of spot number. Treatment with ALT-711 significantly reduced the levels of MGO, AGEs, RAGE, and collagen content in ob/ob mice. In addition, ALT-711 treatment normalized the volume per void and increased the number of spots in ob/ob mice. Activation of AGEs-RAGE pathways by MGO in the bladder wall may contribute to the pathogenesis of diabetes-associated bladder dysfunction.NEW & NOTEWORTHY The involvement of methylglyoxal (MGO) and advanced glycation end products (AGEs) in bladder dysfunction of diabetic ob/ob mice treated with the AGE breaker ALT-711 was investigated here. Diabetic mice exhibited high levels of MGO, AGEs, receptor for AGEs (RAGE), and collagen in serum and/or bladder tissues along with increased volume per void, all of which were reduced by ALT-711. Activation of the MGO-AGEs-RAGE pathway in the bladder wall contributes to the pathogenesis of diabetes-associated bladder dysfunction.

Advanced glycation end products: Key mediator and therapeutic target of cardiovascular complications in diabetes

The incidence of type 2 diabetes mellitus is growing in epidemic proportions and has become one of the most critical public health concerns. Cardiovascular complications associated with diabetes are the leading cause of morbidity and mortality. The cardiovascular diseases that accompany diabetes include angina, myocardial infarction, stroke, peripheral artery disease, and congestive heart failure. Among the various risk factors generated secondary to hyperglycemic situations, advanced glycation end products (AGEs) are one of the important targets for future diagnosis and prevention of diabetes. In the last decade, AGEs have drawn a lot of attention due to their involvement in diabetic patho-physiology. AGEs can be derived exogenously and endogenously through various pathways. These are a non-homogeneous, chemically diverse group of compounds formed non-enzymatically by condensation between carbonyl groups of reducing sugars and free amino groups of protein, lipids, and nucleic acid. AGEs mediate their pathological effects at the cellular and extracellular levels by multiple pathways. At the cellular level, they activate signaling cascades via the receptor for AGEs and initiate a complex series of intracellular signaling resulting in reactive oxygen species generation, inflammation, cellular proliferation, and fibrosis that may possibly exacerbate the damaging effects on cardiac functions in diabetics. AGEs also cause covalent modifications and cross-linking of serum and extracellular matrix proteins; altering their structure, stability, and functions. Early diagnosis of diabetes may prevent its progression to complications and decrease its associated comorbidities. In the present review, we recapitulate the role of AGEs as a crucial mediator of hyperglycemia-mediated detrimental effects in diabetes-associated complications. Furthermore, this review presents an overview of future perspectives for new therapeutic interventions to ameliorate cardiovascular complications in diabetes.

Subendothelial Matrix Stiffening by Lysyl Oxidase Enhances RAGE-Mediated Retinal Endothelial Activation in Diabetes

Endothelial cell (EC) activation is a crucial determinant of retinal vascular inflammation associated with diabetic retinopathy (DR), a major microvascular complication of diabetes. We previously showed that, similar to abnormal biochemical factors, aberrant mechanical cues in the form of lysyl oxidase (LOX)-dependent subendothelial matrix stiffening also contribute significantly to retinal EC activation in diabetes. Yet, how LOX is itself regulated and precisely how it mechanically controls retinal EC activation in diabetes is poorly understood. Here, we show that high-glucose-induced LOX upregulation in human retinal ECs (HRECs) is mediated by proinflammatory receptor for advanced glycation end products (RAGE). HRECs treated with methylglyoxal (MGO), an active precursor to the advanced glycation end product (AGE) MG-H1, exhibited LOX upregulation that was blocked by a RAGE inhibitor, thus confirming the ability of RAGE to promote LOX expression. Crucially, as a downstream effector of RAGE, LOX was found to mediate both the proinflammatory and matrix remodeling effects of AGE/RAGE, primarily through its ability to crosslink or stiffen matrix. Finally, using decellularized HREC-derived matrices and a mouse model of diabetes, we demonstrate that LOX-dependent matrix stiffening feeds back to enhance RAGE, thereby achieving its autoregulation and proinflammatory effects. Collectively, these findings provide fresh mechanistic insights into the regulation and proinflammatory role of LOX-dependent mechanical cues in diabetes while simultaneously implicating LOX as an alternative (downstream) target to block AGE/RAGE signaling in DR.

ARTICLE HIGHLIGHTS

We investigated the regulation and proinflammatory role of retinal endothelial lysyl oxidase (LOX) in diabetes. Findings reveal that LOX is upregulated by advanced glycation end products (AGE) and receptor for AGE (RAGE) and mediates AGE/RAGE-induced retinal endothelial cell activation and subendothelial matrix remodeling. We also show that LOX-dependent subendothelial matrix stiffening feeds back to enhance retinal endothelial RAGE. These findings implicate LOX as a key proinflammatory factor and an alternative (downstream) target to block AGE/RAGE signaling in diabetic retinopathy.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Identification of biomarkers in diabetic nails by Raman spectroscopy

BACKGROUND

The growth of Diabetes Mellitus (DM) is a serious public health issue which is more prevalent in developing countries. The main problems related to DM are the gradual changes in the structural and functional integrity of tissues caused by hyperglycemia, which calls for early diagnosis and periodic monitoring exams. Recent studies suggest that the quality of the nail plate has great potential to assess the secondary complications of DM. Hence, this study aimed to determine the biochemical characteristics of the nails of individuals with DM2 by Raman confocal spectroscopy (CRS).

METHODS

We collected fragments from the distal region of the fingernails of 30 healthy volunteers and 30 volunteers with DM2. The samples were analyzed by CRS (Xplora - Horiba) coupled to a 785 nm laser.

RESULTS

Alterations in different biochemical components, such as proteins, lipids, amino acids, and final agents of advanced glycation, and alterations in the disulfide bridges, which are important in stabilizing keratin in nails were identified.

CONCLUSION

The spectral signatures and new DM2 markers in nails were identified. Therefore, the possibility of acquiring biochemical information by evaluating the nails of diabetics, a simple and easily acquired material associated with the CRS technique, may allow health complications to be detected quickly.

Anti-Glucotoxicity Effect of Phytoconstituents via Inhibiting MGO-AGEs Formation and Breaking MGO-AGEs

The therapeutic benefits of phytochemicals in the treatment of various illnesses and disorders are well documented. They show significant promise for the discovery and creation of novel medications for treating a variety of human diseases. Numerous phytoconstituents have shown antibiotic, antioxidant, and wound-healing effects in the conventional system. Traditional medicines based on alkaloids, phenolics, tannins, saponins, terpenes, steroids, flavonoids, glycosides, and phytosterols have been in use for a long time and are crucial as alternative treatments. These phytochemical elements are crucial for scavenging free radicals, capturing reactive carbonyl species, changing protein glycation sites, inactivating carbohydrate hydrolases, fighting pathological conditions, and accelerating the healing of wounds. In this review, 221 research papers have been reviewed. This research sought to provide an update on the types and methods of formation of methylglyoxal-advanced glycation end products (MGO-AGEs) and molecular pathways induced by AGEs during the progression of the chronic complications of diabetes and associated diseases as well as to discuss the role of phytoconstituents in MGO scavenging and AGEs breaking. The development and commercialization of functional foods using these natural compounds can provide potential health benefits.

In Vitro Antiglycation and Methylglyoxal Trapping Effect of Peppermint Leaf (Mentha × piperita L.) and Its Polyphenols

The most significant reactive α-dicarbonyl RCS involved in the pathomechanism of glycation and related diseases is methylglyoxal (MGO). Hyperglycemia promotes the generation of MGO and leads to the formation of advanced glycation end products (AGEs). Therefore, MGO trapping and glycation inhibition appear to be important therapeutic targets in prediabetes, diabetes, and in the early prevention of hyperglycemic complications. Peppermint leaf is commonly used as herbal tea, rich in polyphenols. Eriocitrin, its predominant component, in a double-blind, randomized controlled study reversed the prediabetic condition in patients. However, the antiglycation activity of this plant material and its polyphenols has not been characterized to date. Therefore, the aim of this study was to evaluate the ability of a peppermint leaf dry extract and its polyphenols to inhibit non-enzymatic protein glycation in a model with bovine serum albumin (BSA) and MGO as a glycation agent. Peppermint polyphenols were also evaluated for their potential to trap MGO in vitro, and the resulting adducts were analyzed by UHPLC-ESI-MS. To relate chemical composition to glycation inhibitory activity, the obtained peppermint extract was subjected to qualitative and quantitative analysis. The capability of peppermint leaf polyphenols to inhibit glycation (27.3-77.2%) and form adducts with MGO was confirmed. In the case of flavone aglycones, mono- and di-adducts with MGO were observed, while eriodictyol and eriocitrin effectively produced only mono-adducts. Rosmarinic acid and luteolin-7-O-glycosides did not reveal this action. IC₅₀ of the peppermint leaf dry extract was calculated at 2 mg/mL, equivalent to a concentration of 1.8 μM/mL of polyphenols, including ~1.4 μM/mL of flavonoids and ~0.4 μM/mL of phenolic acids. The contribution of the four major components to the anti-AGE activity of the extract was estimated at 86%, including eriocitrin 35.4%, rosmarinic acid 25.6%, luteolin-7-O-rutinoside 16.9%, luteolin-7-O-β-glucuronoside 8.1%, and others 14%. The effect of peppermint dry extract and polyphenols in inhibiting MGO-induced glycation in vitro was comparable to that of metformin used as a positive control.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

Causative or associative: A critical review of the role of advanced glycation end-products in bone fragility

The accumulation of advanced glycation end-products (AGEs) in the organic matrix of bone with aging and chronic disease such as diabetes is thought to increase fracture risk independently of bone mass. However, to date, there has not been a clinical trial to determine whether inhibiting the accumulation of AGEs is effective in preventing low-energy, fragility fractures. Moreover, unlike with cardiovascular or kidney disease, there are also no pre-clinical studies demonstrating that AGE inhibitors or breakers can prevent the age- or diabetes-related decrease in the ability of bone to resist fracture. In this review, we critically examine the case for a long-standing hypothesis that AGE accumulation in bone tissue degrades the toughening mechanisms by which bone resists fracture. Prior research into the role of AGEs in bone has primarily measured pentosidine, an AGE crosslink, or bulk fluorescence of hydrolysates of bone. While significant correlations exist between these measurements and mechanical properties of bone, multiple AGEs are both non-fluorescent and non-crosslinking. Since clinical studies are equivocal on whether circulating pentosidine is an indicator of elevated fracture risk, there needs to be a more complete understanding of the different types of AGEs including non-crosslinking adducts and multiple non-enzymatic crosslinks in bone extracellular matrix and their specific contributions to hindering fracture resistance (biophysical and biological). By doing so, effective strategies to target AGE accumulation in bone with minimal side effects could be investigated in pre-clinical and clinical studies that aim to prevent fragility fractures in conditions that bone mass is not the underlying culprit.

Methylglyoxal and glyoxalase 1-a metabolic stress pathway-linking hyperglycemia to the unfolded protein response and vascular complications of diabetes

The study of the glyoxalase system by Thornalley and co-workers in clinical diabetes mellitus and correlation with diabetic complications revealed increased exposure of patients with diabetes to the reactive, dicarbonyl metabolite methylglyoxal (MG). Twenty-eight years later, extended and built on by Thornalley and co-workers and others, the glyoxalase system is an important pathway contributing to the development of insulin resistance and vascular complications of diabetes. Other related advances have been: characterization of a new kind of metabolic stress—‘dicarbonyl stress’; identification of the major physiological advanced glycation endproduct (AGE), MG-H1; physiological substrates of the unfolded protein response (UPR); new therapeutic agents—‘glyoxalase 1 (Glo1) inducers’; and a refined mechanism underlying the link of dysglycemia to the development of insulin resistance and vascular complications of diabetes.

Enhanced RAGE Expression and Excess Reactive-Oxygen Species Production Mediates Rho Kinase-Dependent Detrusor Overactivity After Methylglyoxal Exposure

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound implicated in diabetes-associated diseases. In vascular tissues, MGO induces the formation of advanced glycation end products (AGEs) that bounds its receptor RAGE, initiating the downstream tissue injury. Outside the cardiovascular system, MGO intake produces mouse voiding dysfunction and bladder overactivity. We have sought that MGO-induced bladder overactivity is due to activation of AGE-RAGE-reactive-oxygen species (ROS) signaling cascade, leading to Rho kinase activation. Therefore, female mice received 0.5% MGO orally for 12 weeks, after which in vitro bladder contractions were evaluated in the presence or not of superoxide dismutase (PEG-SOD) or the Rho kinase inhibitor Y27632. Treatment with MGO significantly elevated the serum levels of MGO and fluorescent AGEs, as well as the RAGE immunostaining in the urothelium, detrusor, and vascular endothelium. RAGE mRNA expression in the bladder was also higher in the MGO group. Methylglyoxal significantly increased the ROS production in both urothelium and detrusor smooth muscle, with the increases in detrusor markedly higher than urothelium. The bladder activity of superoxide dismutase (SOD) was significantly reduced in the MGO group. Gene expressions of L-type Ca²⁺ channels, RhoA, ROCK-1, and ROCK-2 in bladder tissues were significantly elevated in the MGO group. Increased bladder contractions to electrical-field stimulation, carbachol α,β-methylene ATP, and extracellular Ca²⁺ were observed after MGO exposure, which was significantly reduced by prior incubation with either PEG-SOD or Y27632. Overall, our data indicate serum MGO accumulation elevates the AGEs levels and activates the RAGE-ROS signaling leading to Rho kinase-induced muscle sensitization, ultimately leading to detrusor overactivity.

ApoA-I Nanoparticles as Curcumin Carriers for Cerebral Endothelial Cells: Improved Cytoprotective Effects against Methylglyoxal

Methylglyoxal (MGO) is a highly reactive metabolite of glucose present at elevated levels in diabetic patients. Its cytotoxicity is associated with endothelial dysfunction, which plays a role in cardiovascular and cerebrovascular complications. Although curcumin has many therapeutic benefits, these are limited due to its low bioavailability. We aimed to improve the bioavailability of curcumin and evaluate a potential synergistic effect of curcumin and reconstituted high-density lipoprotein (rHDL) nanoparticles (Cur-rHDLs) on MGO-induced cytotoxicity and oxidative stress in murine cerebrovascular endothelial cells (bEnd.3). Cur-rHDL nanoparticles (14.02 ± 0.95 nm) prepared by ultracentrifugation and containing curcumin were quantified by LC–MS/MS. The synergistic effect of cur-rHDL nanoparticles was tested on bEnd.3 cytotoxicity, reactive oxygen species (ROS) production, chromatin condensation, endoplasmic reticulum (ER) stress, and endothelial barrier integrity by impedancemetry. The uptake of curcumin, alone or associated with HDLs, was also assessed by mass spectrometry. Pretreatment with Cur-rHDLs followed by incubation with MGO showed a protective effect on MGO-induced cytotoxicity and chromatin condensation, as well as a strong protective effect on ROS production, endothelial cell barrier integrity, and ER stress. These results suggest that Cur-rHDLs could be used as a potential therapeutic agent to limit MGO-induced dysfunction in cerebrovascular endothelial cells by enhancing the bioavailability and protective effects of curcumin.

Plasma advanced glycation end products and the subsequent risk of microvascular complications in type 1 diabetes in the DCCT/EDIC

INTRODUCTION

To assess impact of glycemic control on plasma protein-bound advanced glycation end products (pAGEs) and their association with subsequent microvascular disease.

RESEARCH DESIGN AND METHODS

Eleven pAGEs were measured by liquid chromatography-mass spectrometry in banked plasma from 466 participants in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study at three time points (TPs): DCCT year 4 (TP1) and year 8 (TP2) and EDIC year 5/6 (TP3). Correlation coefficients assessed cross-sectional associations, and Cox proportional hazards models assessed associations with subsequent risk of microvascular complications through EDIC year 24.

RESULTS

Glucose-derived glycation products fructose-lysine (FL), glucosepane (GSPN) and carboxymethyl-lysine (CML) decreased with intensive glycemic control at both TP1 and TP2 (p<0.0001) but were similar at TP3, and correlated with hemoglobin A1c (HbA1c). At TP1, the markers were associated with the subsequent risk of several microvascular outcomes. These associations did not remain significant after adjustment for HbA1c, except methionine sulfoxide (MetSOX), which remained associated with diabetic kidney disease. In unadjusted models using all 3 TPs, glucose-derived pAGEs were associated with subsequent risk of proliferative diabetic retinopathy (PDR, p<0.003), clinically significant macular edema (CSME, p<0.015) and confirmed clinical neuropathy (CCN, p<0.018, except CML, not significant (NS)). Adjusted for age, sex, body mass index, diabetes duration and mean updated HbA1c, the associations remained significant for PDR (FL: p<0.002, GSPN: p≤0.02, CML: p<0.003, pentosidine: p<0.02), CMSE (CML: p<0.03), albuminuria (FL: p<0.02, CML: p<0.03) and CCN (FL: p<0.005, GSPN : p<0.003).

CONCLUSIONS

pAGEs at TP1 are not superior to HbA1c for risk prediction, but glucose-derived pAGEs at three TPs and MetSOX remain robustly associated with progression of microvascular complications in type 1 diabetes even after adjustment for HbA1c and other factors.

Isolation of Anti-Diabetic Active Compounds from Benincasae Exocarpium and Development of Simultaneous Analysis by HPLC-PDA

Diabetes is a chronic metabolic disease that is a constant problem. Previous studies have reported that Benincasa cerifera Savi. extracts are effective in treating diabetes and its complications. Benincasae Exocarpium (BE) is a fruit peel of B. cerifera that has been reported to be used for the prevention and treatment of metabolic diseases such as hyperglycemia, obesity, and hyperlipidemia. However, there are not enough studies on the compounds and bioassays to support the efficacy of BE. The inhibitory activity of the BE extracts and fractions against advanced glycation end-products (AGE) formation and α-glucosidase activity was evaluated. These assays are relevant for the treatment of type 2 diabetes and its complications. Based on these results, compounds 1-11 were isolated through bioassay-guided isolation. In addition, we developed a high-performance liquid chromatography (HPLC) method that can simultaneously analyze these 11 compounds. Activity evaluation of the compounds was also conducted, and eight compounds exhibited significant activity. Among these, flavonoid compounds showed strong activity. A quantitative evaluation of eight bioactive compounds (2, 5-11) was conducted. In conclusion, this study demonstrated the potential of BE for prevention and treatment of type 2 diabetes and its complications.

Association between glucose intolerance and chemotherapy-induced lung injury in patients with lung cancer and interstitial lung disease

PURPOSE

Cytotoxic chemotherapy-induced lung injury is a fatal complication in patients with lung cancer and interstitial lung disease (ILD). We aimed to evaluate the association between hyperglycemia and this form of lung injury in patients with lung cancer concomitant with ILD.

METHODS

From 1147 patients with advanced lung cancer, we retrospectively enrolled 98 patients with ILD whose hemoglobin A1c (HbA1c) levels were measured, and investigated the association between HbA1c levels and cytotoxic chemotherapy-induced lung injury. In 73 patients whose serum samples were retained, we measured serum levels of advanced glycation end products (AGE) and assessed the association of AGE levels with HbA1c levels and cytotoxic chemotherapy-induced lung injury.

RESULTS

The incidence of cytotoxic chemotherapy-induced lung injury was significantly higher in patients with HbA1c levels ≥ 5.8% than in those with HbA1c levels < 5.8%, but not in those with HbA1c levels ≥ 6.5% than in those with HbA1c levels < 6.5%. The multivariate logistic regression model revealed that HbA1c level ≥ 5.8% was a significant risk factor for this complication [odds ratio 3.178 (95% confidence interval 1.057-9.556), P = 0.040]. In addition, serum AGE levels were significantly higher in patients with HbA1c levels ≥ 5.8% than in those with HbA1c levels < 5.8% [median (interquartile range); 0.129 (0.023-0.290) and 0.474 (0.213-1.109) μg/mL, P = 0.001].

CONCLUSION

Glucose intolerance (e.g., HbA1c level ≥ 5.8%) may be a risk factor of cytotoxic chemotherapy-induced lung injury, which might be associated with elevated AGE production due to hyperglycemia.

Methylglyoxal-derived hemoglobin advanced glycation end products induce apoptosis and oxidative stress in human umbilical vein endothelial cells

The presence of excess glucose promotes hemoglobin glycation via the biochemical modification of hemoglobin by dicarbonyl products. However, the precise effects of Hb-AGEs in human umbilical vein endothelial cells (HUVECs) are not known to date. Therefore, we investigated the tentative effects of Hb-AGEs in HUVECs. Initially, we used the AGE formation assay to examine the selectivity of MGO toward various proteins. Among all proteins, MGO-Hb-AGEs formation was higher compared to the formation of other dicarbonyl-mediated AGEs. Our next data demonstrated that treatment with 0.5 mg/mL of Hb-AGEs-4w significantly reduced cell viability in HUVECs. Further, we evaluated the role of MGO in conformational and structural changes in Hb. The results showed that Hb demonstrated a highly altered conformation upon incubation with MGO. Moreover, Hb-AGEs-4w treatment strongly increased ROS production, and decreased mitochondrial membrane potential in HUVECs, and moderately reduced the expression of phosphorylated forms of p-38 and JNK. We observed that Hb-AGEs-4w treatment increased the number of apoptotic cells and the Bax/Bcl-2 ratio and cleaved the nuclear enzyme PARP in HUVECs. Finally, Hb-AGEs also inhibited migration and proliferation of HUVECs, thus be physiologically significant in endothelial dysfunction. Taken together, our data suggest that Hb-AGEs may play a critical role in inducing vascular endothelial cell damage. Therefore, this study may provide a plausible explanation for the potential Hb-AGEs in human endothelial cell dysfunction of diabetic patients.

Protective Effects of Swertiamarin against Methylglyoxal-Induced Epithelial-Mesenchymal Transition by Improving Oxidative Stress in Rat Kidney Epithelial (NRK-52E) Cells

Increased blood glucose in diabetic individuals results in the formation of advanced glycation end products (AGEs), causing various adverse effects on kidney cells, thereby leading to diabetic nephropathy (DN). In this study, the antiglycative potential of Swertiamarin (SM) isolated from the methanolic extract of E. littorale was explored. The effect of SM on protein glycation was studied by incubating bovine serum albumin with fructose at 60 °C in the presence and absence of different concentrations of swertiamarin for 24 h. For comparative analysis, metformin was also used at similar concentrations as SM. Further, to understand the role of SM in preventing DN, in vitro studies using NRK-52E cells were done by treating cells with methylglyoxal (MG) in the presence and absence of SM. SM showed better antiglycative potential as compared to metformin. In addition, SM could prevent the MG mediated pathogenesis in DN by reducing levels of argpyrimidine, oxidative stress and epithelial mesenchymal transition in kidney cells. SM also downregulated the expression of interleukin-6, tumor necrosis factor-α and interleukin-1β. This study, for the first time, reports the antiglycative potential of SM and also provides novel insights into the molecular mechanisms by which SM prevents toxicity of MG on rat kidney cells.

Suicidal Erythrocyte Death in Metabolic Syndrome

Eryptosis is a coordinated, programmed cell death culminating with the disposal of cells without disruption of the cell membrane and the release of endocellular oxidative and pro-inflammatory milieu. While providing a convenient form of death for erythrocytes, dysregulated eryptosis may result in a series of detrimental and harmful pathological consequences highly related to the endothelial dysfunction (ED). Metabolic syndrome (MetS) is described as a cluster of cardiometabolic factors (hyperglycemia, dyslipidemia, hypertension and obesity) that increases the risk of cardiovascular complications such as those related to diabetes and atherosclerosis. In the light of the crucial role exerted by the eryptotic process in the ED, the focus of the present review is to report and discuss the involvement of eryptosis within MetS, where vascular complications are utterly relevant. Current knowledge on the mechanisms leading to eryptosis in MetS-related conditions (hyperglycemia, dyslipidemia, hypertension and obesity) will be analyzed. Moreover, clinical evidence supporting or proposing a role for eryptosis in the ED, associated to MetS cardiovascular complications, will be discussed.

Inhibitors of Advanced Glycation End Product (AGE) Formation and Accumulation

A range of chemically different compounds are known to inhibit the formation and accumulation of advanced glycation end products (AGEs) or disrupt associated signalling pathways. There is evidence that some of these agents can provide end-organ protection in chronic diseases including diabetes. Whilst this group of therapeutics are structurally and functionally different and have a range of mechanisms of action, they ultimately reduce the deleterious actions and the tissue burden of advanced glycation end products. To date it remains unclear if this is due to the reduction in tissue AGE levels per se or the modulation of downstream signal pathways. Some of these agents either stimulate antioxidant defence or reduce the formation of reactive oxygen species (ROS), modify lipid profiles and inhibit inflammation. A number of existing treatments for glucose lowering, hypertension and hyperlipidaemia are also known to reduce AGE formation as a by-product of their action. Targeted AGE formation inhibitors or AGE cross-link breakers have been developed and have shown beneficial effects in animal models of diabetic complications as well as other chronic conditions. However, only a few of these agents have progressed to clinical development. The failure of clinical translation highlights the importance of further investigation of the advanced glycation pathway, the diverse actions of agents which interfere with AGE formation, cross-linking or AGE receptor activation and their effect on the development and progression of chronic diseases including diabetic complications. Advanced glycation end products (AGEs) are (1) proteins or lipids that become glycated as a result of exposure to sugars or (2) non-proteinaceous oxidised lipids. They are implicated in ageing and the development, or worsening, of many degenerative diseases, such as diabetes, atherosclerosis, chronic kidney and Alzheimer's disease. Several antihypertensive and antidiabetic agents and statins also indirectly lower AGEs. Direct AGE inhibitors currently investigated include pyridoxamine and epalrestat, the inhibition of the formation of reactive dicarbonyls such as methylglyoxal as an important precursor of AGEs via increased activation of the detoxifying enzyme Glo-1 and inhibitors of NOX-derived ROS to reduce the AGE/RAGE signalling.

Long-term methylglyoxal intake aggravates murine Th2-mediated airway eosinophil infiltration

Asthma outcomes is aggravated in obese patients. Excess of methylglyoxal (MGO) in obese/diabetic patients has been associated with diverse detrimental effects on cell function. This study aimed to evaluate the effects of long-term oral intake of MGO on ovalbumin-induced eosinophil inflammation. Male C57/Bl6 mice received 0.5% MGO in the drinking water for 12 weeks. Mice were sensitized and challenged with ovalbumin (OVA), and at 48 h thereafter, bronchoalveolar lavage (BAL) fluid and lungs were collected for cell counting, morphological analysis, and ELISA, mRNA expressions and DHE assays. In MGO-treated mice, OVA challenge significantly increased the peribronchiolar infiltrations of inflammatory cells and eosinophils compared with control group. Higher levels of IL-4, IL-5, and eotaxin in BAL fluid were also detected in MGO compared with control group. In addition, lung tissue of MGO-treated mice displayed significant increases in mRNA expressions of NF-κB and iNOS whereas COX-2 expression remained unchanged. The high TNF-α mRNA expression observed in lungs of OVA-challenged control mice was not further increased by MGO treatment. In MGO group, OVA-challenge increased significantly the NOX-2 and NOX-4 mRNA expressions, without affecting the NOX-1 expression. Levels of reactive-oxygen species (ROS) were significantly higher in lungs of MGO-treated mice, and no further increase by OVA-challenge was observed. In conclusion, 12-week intake of MGO exacerbates Th2-mediated airway eosinophil infiltration by activation of NF-kB/iNOS-dependent signaling pathway and positive regulation of NOX-2 and NOX-4 in the lung tissues. Scavengers of MGO could be an option to prevent obesity-related asthma.

Ginsenoside Rb1 mitigates oxidative stress and apoptosis induced by methylglyoxal in SH-SY5Y cells via the PI3K/Akt pathway

Diabetic encephalopathy is a severe diabetic complication characterized by cognitive dysfunction and neuropsychiatric disability. Methylglyoxal (MGO), a highly reactive metabolite of hyperglycemia, serves as a major precursor of advanced glycation end products that play key roles in diabetic complications. Ginsenoside Rb1 (abbreviated as Rb1) has received extensive attention due to its potential therapeutic effects on diabetes and neurodegeneration. Therefore, this study aimed to investigate the effects of Rb1 on MGO-induced damage in SH-SY5Y cells and the related mechanism. SH-SY5Y cells were pretreated with Rb1 for 8 h and then exposed to MGO (0.5 mM) for 24 h. Cell survival was assessed by the MTT assay. Cell apoptosis was assessed using Hoechst 33342/propidium iodide (PI) staining and an Annexin-V/PI kit. The activities of oxidative stress markers were examined using commercial kits. Reactive oxygen species (ROS) staining and JC-1 staining were used to evaluate mitochondria injury. In addition, protein levels were measured by Western blot analysis. As a result, Rb1 alleviated the injury induced by MGO by increasing the activities of superoxide dismutase, catalase and total glutathione, decreasing the level of malondialdehyde, and alleviating mitochondrial damage and ROS production. Furthermore, Rb1 could enhance the Bcl-2/Bax ratio, inhibit the expression of cleaved caspase-3 and cleaved caspase-9, and enhance the levels of phosphorylated Akt. Moreover, the protective effects of Rb1 against MGO-induced apoptosis were partly abolished by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation. Our results demonstrated that Rb1 ameliorated MGO-induced oxidative stress and apoptosis in SH-SY5Y cells via activating the PI3K/Akt signaling pathway.

A review of the putative causal mechanisms associated with lower macular pigment in diabetes mellitus

Macular pigment (MP) confers potent antioxidant and anti-inflammatory effects at the macula, and may therefore protect retinal tissue from the oxidative stress and inflammation associated with ocular disease and ageing. There is a body of evidence implicating oxidative damage and inflammation as underlying pathological processes in diabetic retinopathy. MP has therefore become a focus of research in diabetes, with recent evidence suggesting that individuals with diabetes, particularly type 2 diabetes, have lower MP relative to healthy controls. The present review explores the currently available evidence to illuminate the metabolic perturbations that may possibly be involved in MP's depletion. Metabolic co-morbidities commonly associated with type 2 diabetes, such as overweight/obesity, dyslipidaemia, hyperglycaemia and insulin resistance, may have related and independent relationships with MP. Increased adiposity and dyslipidaemia may adversely affect MP by compromising the availability, transport and assimilation of these dietary carotenoids in the retina. Furthermore, carotenoid intake may be compromised by the dietary deficiencies characteristic of type 2 diabetes, thereby further compromising redox homeostasis. Candidate causal mechanisms to explain the lower MP levels reported in diabetes include increased oxidative stress, inflammation, hyperglycaemia, insulin resistance, overweight/obesity and dyslipidaemia; factors that may negatively affect redox status, and the availability, transport and stabilisation of carotenoids in the retina. Further study in diabetic populations is warranted to fully elucidate these relationships.

Methylglyoxal-Induced Retinal Angiogenesis in Zebrafish Embryo: A Potential Animal Model of Neovascular Retinopathy

Methylglyoxal (MG) is an intermediate of glucose metabolism and the precursor of advanced glycation end products (AGEs) found in high levels in blood or tissue of diabetic patients. MG and AGEs are thought to play a major role in the pathogenesis of diabetic retinopathy. In order to determine if zebrafish is valuable to help us understand more about retinopathy, we evaluate if MG induces abnormal vascular change and angiogenesis in zebrafish in a short incubation period. We also used an inhibitor of VEGFR (PTK787) to explore the mechanistic role of VEGF in MG-induced pathogenesis. A transgenic Tg(flk1:GFP) zebrafish line was used, and the embryos were incubated with MG solution and in combination with glucose (to mimic hyperglycemia). Retinal vascular structure visible with fluorescence signal was imaged using fluorescence microscopy. The percentage of vascular area was calculated and found elevated in the MG treatment groups than that in the control group (p < 0.01) which indicated increased angiogenesis induced by MG treatment. PTK787 blocked the proangiogenic effects of MG treatment. This study suggests that MG has a potential proangiogenic effect via VEGF signaling in the retina of zebrafish embryos. Therefore, this zebrafish model may be used to study neovascular retinopathy.

Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model

The aim of this study was to evaluate whether damage to the neurovascular unit in diabetes depends on reactive metabolites such as methylglyoxal (MG), and to assess its impact on retinal gene expression. Male Wistar rats were supplied with MG (50 mM) by drinking water and compared with age-matched streptozotocin-diabetic animals and untreated controls. Retinal damage was evaluated for the accumulation of MG-derived advanced glycation end products, changes in hexosamine and PKC pathway activation, microglial activation, vascular alterations (pericyte loss and vasoregression), neuroretinal function assessed by electroretinogram, and neurodegeneration. Retinal gene regulation was studied by microarray analysis, and transcription factor involvement was identified by upstream regulator analysis. Systemic application of MG by drinking water increased retinal MG to levels comparable with diabetic animals. Elevated retinal MG resulted in MG-derived hydroimidazolone modifications in the ganglion cell layer, inner nuclear layer, and outer nuclear layer, a moderate activation of the hexosamine pathway, a pan-retinal activation of microglia, loss of pericytes, increased formation of acellular capillaries, decreased function of bipolar cells, and increased expression of the crystallin gene family. MG mimics important aspects of diabetic retinopathy and plays a pathogenic role in microglial activation, vascular damage, and neuroretinal dysfunction. In response to MG, the retina induces expression of neuroprotective crystallins.-Schlotterer, A., Kolibabka, M., Lin, J., Acunman, K., Dietrich, N., Sticht, C., Fleming, T., Nawroth, P., Hammes, H.-P. Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model.

Migratory, metabolic and functional alterations of fibrocytes in type 2 diabetes

Fibrocytes are bloodborne mesenchymal progenitor cells that are recruited to injured tissue sites and contribute to the repair process by acquiring a myofibroblast-like phenotype and producing extracellular matrix components and growth factors. Treatment with normal fibrocytes or their exosomes restores the ability of genetically diabetic mice to heal skin wounds, suggesting the existence of dysfunctional alterations in diabetic fibrocytes. This study compared the migratory, metabolic and functional characteristics of fibrocytes from patients with type 2 diabetes (T2DPs) and healthy controls (HCs). It was found that the frequency of these cells was abnormally low in the peripheral blood of T2DPs. Diabetic fibrocytes showed reduced expression of the C-X-C motif and C-C motif chemokine receptors (CXCR)4, (CCR)5, and CCR7, and demonstrated reduced migration in response to their ligands (CXCL)12, (CCL)5, and CCL21. They exhibited increased expression of the receptor for advanced glycation end product, suppression of the alternative AGE receptor 1, increased intracellular concentrations of AGEs, decreased expression of sirtuin-1 and elevated oxidative stress. In short-term cultures, fibrocytes from T2DPs released larger amounts of proinflammatory cytokines than those from HCs. Unlike normal fibrocytes, diabetic fibrocytes did not exhibit increased expression of type I collagen and α-smooth muscle actin on stimulation with transforming growth factor (TGF)-β1 and this abnormal response was associated with downregulation of TGF-β1 type II receptor on the cell surface. Study findings uncover multiple migratory and functional alterations of diabetic fibrocytes that may contribute to explain why T2DPs experience impaired wound healing and chronic ulcers. © 2018 IUBMB Life, 70(11):1122-1132, 2018.

Inhibition of Methylglyoxal-Induced Histone H1 Nε-Carboxymethyllysine Formation by (+)-Catechin

Reactive dicarbonyl species (RCS) such as methylglyoxal (MGO) and glyoxal (GO) are common intermediates in protein damage, leading to the formation of advanced glycation end products (AGEs) through nonenzymatic glycation. (+)-Catechin, a natural plant extract from tea, has been evaluated for its ability in trapping GO and MGO. However, (+)-catechin is also reported to have both antioxidant ability and pro-oxidant properties. Until now, whether (+)-catechin can inhibit the formation of nonenzymatic glycation and the mechanism of the inhibition in nucleoprotein nonenzymatic glycation is still unclear. In the present study, histone H1 and MGO were used to establish an in vitro (100 mM phosphate buffer solution (PBS), pH 7.4, 37 °C) protein glycation model to study the trapping ability of (+)-catechin. Our data show that MGO caused dose-dependent protein damage, and the content of MGO-induced Schiff base formation was inhibited by (+)-catechin when the molecular ratio of catechin:MGO was 1:6. The formation of N^ε-carboxymethyllysine (CML) was reduced significantly when the ratio of (+)-catechin and MGO was 1:1, which was similar to the inhibition effect of aminoguanidine (AG). The formation of CML under in vitro conditions can be inhibited by low concentration (12.5-100 μM) of (+)-catechin but not with high concentration (200-800 μM) of (+)-catechin. The reason is that the high concentration of (+)-catechin did not inhibit CML formations due to H₂O₂ produced by (+)-catechin. In the presence of catalase, catechin can inhibit MGO-induced CML formation. In conclusion, the trapping ability of (+)-catechin may be more effective at the early stage of nonenzymatic glycation. However, a high concentration (200-800 μM) of (+)-catechin may not inhibit the formation of CML because it induced the increase of H₂O₂ formation.

Inhibition of advanced glycation endproduct (AGE) rescues against streptozotocin-induced diabetic cardiomyopathy: Role of autophagy and ER stress

Diabetes mellitus leads to oxidative stress and contractile dysfunction in the heart. Although several rationales have been speculated, the precise mechanism behind diabetic cardiomyopathy remains elusive. This study was designed to assess the role of inhibition of advanced glycation endproducts (AGE) in streptozotocin (STZ)-induced diabetic cardiac dysfunction. Cardiac contractile function was assessed in normal C57BL/6 and STZ (200mg/kg, single injection and maintained for 2 wks)-induced diabetic mice treated with or without the AGE inhibitor aminoguanidine (50mg/kg/d in drinking water) for 2 weeks using echocardiography and IonOptix MyoCam techniques. Diabetes compromised cardiac contractile function shown as reduced fractional shortening and ejection fraction, enlarged left ventricular end systolic/diastolic diameters, decreased peak shortening, maximal velocity of shortening/relengthening, prolonged shortening and relengthening duration as well as impaired intracellular Ca²⁺ homeostasis, the effects of which were alleviated or reversed by aminoguanidine treatment. Diabetes also inhibited autophagy, increased ER stress and phosphorylation of pro-hypertrophic signaling molecules Akt and mTOR, the effect of which was reversed by aminoguanidine. In vitro study revealed that methylglyoxal-derived AGE (MG-AGE) incubation in isolated cardiomyocytes promoted oxidation of sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA2a) and production of superoxide, the effects of which were negated by the autophagy inducer rapamycin, the ER stress chaperone TUDCA or the antioxidant N-acetylcysteine. Taken together, these data revealed that inhibition of AGE formation rescues against experimental diabetes-induced cardiac remodeling and contractile dysfunction possible through regulation of autophagy and ER stress.

A Hypothesis: Moderate Consumption of Alcohol Contributes to Lower Prevalence of Type 2 Diabetes Due to the Scavenging of Alpha-Dicarbonyls by Dietary Polyphenols

The world is experiencing an epidemic of type-2-diabetes mellitus (T2DM). This has led to increased morbidity and mortality, explosive growth in health care budgets, and an even greater adverse, if indirect, impact on societies and economies of affected countries. While genetic susceptibility to T2DM is a major determinant of its prevalence, changes in lifestyles also play a role. One such change has been a transition from traditional diets characterized by low caloric and high nutrient density to calorie-rich but nutrient-poor Western diets. Given this, one solution to the epidemic of T2DM would be to abandon Western diets and revert to traditional eating patterns. However, traditional diets cannot provide enough calories for the increasing global population, so transition from traditional to Western foodstuffs appears to be irreversible. Consequently, the only practical solution to problems caused by these changes is to modify Western diets, possibly by supplementing them with functional foods containing nutrients that would compensate for these dietary deficits. I present in this study a hypothesis to explain why shifts from traditional to Western diets have been so problematic and to suggest nutrients that may counteract these adverse effects. I postulate that the components of traditional diets that may compensate for deficiencies of Westerns diets are scavengers of reactive α-dicarbonyls produced as unavoidable by-products of glucose and lipid metabolism. Most important among these scavengers are some plant secondary metabolites: polyphenols, phlorotannins, and carotenoids. They are found in alcoholic beverages and are abundant in seasonings, cocoa, coffee, tea, whole grains, pigmented vegetables, fruits, and berries.

Dicarbonyl stress and glyoxalase enzyme system regulation in human skeletal muscle

Skeletal muscle insulin resistance is a hallmark of Type 2 diabetes (T2DM) and may be exacerbated by protein modifications by methylglyoxal (MG), known as dicarbonyl stress. The glyoxalase enzyme system composed of glyoxalase 1/2 (GLO1/GLO2) is the natural defense against dicarbonyl stress, yet its protein expression, activity, and regulation remain largely unexplored in skeletal muscle. Therefore, this study investigated dicarbonyl stress and the glyoxalase enzyme system in the skeletal muscle of subjects with T2DM (age: 56 ± 5 yr.; BMI: 32 ± 2 kg/m²) compared with lean healthy control subjects (LHC; age: 27 ± 1 yr.; BMI: 22 ± 1 kg/m²). Skeletal muscle biopsies obtained from the vastus lateralis at basal and insulin-stimulated states of the hyperinsulinemic (40 mU·m^-2·min^-1)-euglycemic (5 mM) clamp were analyzed for proteins related to dicarbonyl stress and glyoxalase biology. At baseline, T2DM had increased carbonyl stress and lower GLO1 protein expression (-78.8%), which inversely correlated with BMI, percent body fat, and HOMA-IR, while positively correlating with clamp-derived glucose disposal rates. T2DM also had lower NRF2 protein expression (-31.6%), which is a positive regulator of GLO1, while Keap1 protein expression, a negative regulator of GLO1, was elevated (207%). Additionally, insulin stimulation during the clamp had a differential effect on NRF2, Keap1, and MG-modified protein expression. These data suggest that dicarbonyl stress and the glyoxalase enzyme system are dysregulated in T2DM skeletal muscle and may underlie skeletal muscle insulin resistance. Whether these phenotypic differences contribute to the development of T2DM warrants further investigation.

Identification of an argpyrimidine-modified protein in human red blood cells from schizophrenic patients: A possible biomarker for diseases involving carbonyl stress

Argpyrimidine (ARP) is an advanced glycation end product thought to be generated from a reaction between methylglyoxal and arginine residues in proteins. In this study, we observed marked accumulation of an approximately 56 kD protein, reactive to anti-ARP antibodies, in the red blood cells (RBCs) of some patients with refractory schizophrenia. This ARP-modified protein was purified from the blood of schizophrenic patients and identified as selenium binding protein 1 (SBP1) by LC-MS/MS. This is the first report of ARP-modified proteins accumulating in RBCs of patients with diseases involving carbonyl stress. We also observed high accumulation of ARP-modified SBP1 in the RBCs of patients with chronic kidney disease. Therefore, this modified protein may be a novel marker of carbonyl stress.

An insight on the association of glycation with hepatocellular carcinoma

Hepato-cellular carcinoma (HCC) is one of the frequent cause of cancer-related death worldwide and dominant form of primary liver cancer. However, the reason behind a steady increase in the incidence of this form of cancer remains elusive. Glycation has been reported to play a significant role in the induction of several chronic diseases including cancer. Several risk factors that could induce HCC have been reported in the literature. Deciphering the complex patho-physiology associated with HCC is expected to provide new targets for the early detection, prevention, progression and recurrence. Even-though, some of the causative aspects of HCC is known, the advanced glycation end products (AGEs) related mechanism still needs further research. In the current manuscript, we have tried to uncover the possible role of glycation in the induction of HCC. In the light of the available scientific literature, we advocate in-depth comprehensive studies which will shed light towards mechanistic association of glycation with HCC.

Advanced glycation end products in children with type 1 diabetes and early reduced diastolic heart function

BACKGROUND

Reduced diastolic function is an early sign of diabetes cardiomyopathy in adults and is associated with elevated levels of HbA1c and advanced glycation end products (AGEs).

OBJECTIVE

To assess the associations between early reduced diastolic function and elevated levels of HbA1c and AGEs in children and adolescents with type 1 diabetes (T1D).

METHODS

One hundred fourty six T1D patients (age 8-18 years) without known diabetic complications were examined with tissue Doppler imaging and stratified into two groups according to diastolic function. A clinical examination and ultrasound of the common carotid arteries were performed. Methylglyoxal-derived hydroimidazolone-1 (MG-H1) was measured by immunoassay.

RESULTS

At inclusion, 36 (25%) participants were stratified into a low diastolic function group (E'/A'-ratio < 2.0). Compared to the rest of the T1D children, these participants had higher body mass index (BMI), 22.8 (SD = 4.0) vs. 20.1 (SD = 3.4) kg/m², p < 0.001, higher systolic blood pressure 104.2 (SD = 8.7) vs. 99.7 (SD = 9.3) mmHg, p = 0.010, and higher diastolic blood pressure, 63.6 (SD = 8.3) vs. 59.9 (SD = 7.9) mmHg, p = 0.016. The distensibility coefficient was lower, 0.035 (SD = 0.010) vs. 0.042 (SD = 0.02) kPa^-1, p = 0.013, Young's modulus higher, 429 (SD = 106) vs. 365 (SD = 143), p = 0.009, and MG-H1 higher, 163.9 (SD = 39.2) vs. 150.3 (SD = 33.4) U/ml, p = 0.046. There was no difference in carotid intima-media thickness between the groups. There were no associations between reduced diastolic function and years from diagnosis, HBA1c, mean HBA1c, CRP or calculated glycemic burden. Logistic regression analysis showed that BMI was an independent risk factor for E'/A'-ratio as well as a non-significant, but relatively large effect size for MG-H1, indicating a possible role for AGEs.

CONCLUSIONS

Early signs of reduced diastolic function in children and adolescents with T1D had higher BMI, but not higher HbA1c. They also had elevated serum levels of the advanced glycation end product MG-H1, higher blood pressure and increased stiffness of the common carotid artery, but these associations did not reach statistical significance when tested in a logistic regression model.

Very High Prevalence of Frozen Shoulder in Patients With Type 1 Diabetes of ≥45 Years' Duration: The Dialong Shoulder Study

OBJECTIVES

To compare the prevalence of shoulder disorders and self-reported shoulder disability in patients with long-term type 1 diabetes mellitus and diabetes-free subjects; and to explore the association between the long-term glycemic burden and shoulder disability in the diabetes group.

DESIGN

Cross-sectional study of shoulder diagnoses with 30 years' historical data on glycemic burden in patients with diabetes.

SETTING

Diabetics center and a university hospital.

PARTICIPANTS

Subjects attending the Norwegian Diabetics Center in 2015 with type 1 diabetes since 1970 or earlier were eligible (N=136). One hundred and five patients were included, and 102 (50% women; mean age, 61.9y) completed the study together with 73 diabetes-free subjects (55% women; mean age, 62.5y).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Shoulder diagnoses decided through clinical examination according to scientific diagnostic criteria.

RESULTS

Frozen shoulder was diagnosed in 60 (59%) patients with diabetes and 0 diabetes-free subjects, with a lifetime prevalence of 76% in the diabetes group versus 14% in the diabetes-free subjects. Patients with diabetes had higher disability and higher mean QuickDASH scores (23.0±19.9) than diabetes-free subjects (8.9±12.0), with a mean difference of -14.2 (95% confidence interval, -19.3 to -9.0) points (P<.001). We found an association between chronic hyperglycemia and QuickDASH scores, with a 6.16-point increase in QuickDASH scores per unit increase in glycated hemoglobin A_1c (HbA_1c) (P=.014).

CONCLUSIONS

The point prevalence of frozen shoulder in patients with long-lasting type 1 diabetes was 59%, and the lifetime prevalence was 76%. The diabetes group had more shoulder disability than diabetes-free subjects. The historical HbA_1c level was associated with increased shoulder disability.

Advanced glycation end products mediated cellular and molecular events in the pathology of diabetic nephropathy

Diabetic nephropathy (DN) is a major cause of morbidity and mortality in diabetic patients and a leading cause of end-stage renal disease (ESRD). Degenerative changes such as glomerular hypertrophy, hyperfiltration, widening of basement membranes, tubulointerstitial fibrosis, glomerulosclerosis and podocytopathy manifest in various degrees of proteinuria in DN. One of the key mechanisms implicated in the pathogenesis of DN is non-enzymatic glycation (NEG). NEG is the irreversible attachment of reducing sugars onto free amino groups of proteins by a series of events, which include the formation of Schiff’s base and an Amadori product to yield advanced glycation end products (AGEs). AGE modification of client proteins from the extracellular matrix induces crosslinking, which is often associated with thickening of the basement membrane. AGEs activate several intracellular signaling cascades upon interaction with receptor for AGEs (RAGE), which manifest in aberrant cellular responses such as inflammation, apoptosis and autophagy, whereas other receptors such as AGE-R1, AGE-R3 and scavenger receptors also bind to AGEs and ensue endocytosis and degradation of AGEs. Elevated levels of both serum and tissue AGEs are associated with adverse renal outcome. Increased evidence supports that attenuation of AGE formation and/or inhibition of RAGE activation manifest(s) in improving renal function. This review provides insights of NEG, discusses the cellular and molecular events triggered by AGEs, which manifest in the pathogenesis of DN including renal fibrosis, podocyte epithelial-mesenchymal transition and activation of renin-angiotensin system. Therapies designed to target AGEs, such as inhibitors of AGEs formation and crosslink breakers, are discussed.

Mass spectrometric determination of early and advanced glycation in biology

Protein glycation in biological systems occurs predominantly on lysine, arginine and N-terminal residues of proteins. Major quantitative glycation adducts are found at mean extents of modification of 1-5 mol percent of proteins. These are glucose-derived fructosamine on lysine and N-terminal residues of proteins, methylglyoxal-derived hydroimidazolone on arginine residues and N(ε)-carboxymethyl-lysine residues mainly formed by the oxidative degradation of fructosamine. Total glycation adducts of different types are quantified by stable isotopic dilution analysis liquid chromatography-tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring mode. Metabolism of glycated proteins is followed by LC-MS/MS of glycation free adducts as minor components of the amino acid metabolome. Glycated proteins and sites of modification within them - amino acid residues modified by the glycating agent moiety - are identified and quantified by label-free and stable isotope labelling with amino acids in cell culture (SILAC) high resolution mass spectrometry. Sites of glycation by glucose and methylglyoxal in selected proteins are listed. Key issues in applying proteomics techniques to analysis of glycated proteins are: (i) avoiding compromise of analysis by formation, loss and relocation of glycation adducts in pre-analytic processing; (ii) specificity of immunoaffinity enrichment procedures, (iii) maximizing protein sequence coverage in mass spectrometric analysis for detection of glycation sites, and (iv) development of bioinformatics tools for prediction of protein glycation sites. Protein glycation studies have important applications in biology, ageing and translational medicine - particularly on studies of obesity, diabetes, cardiovascular disease, renal failure, neurological disorders and cancer. Mass spectrometric analysis of glycated proteins has yet to find widespread use clinically. Future use in health screening, disease diagnosis and therapeutic monitoring, and drug and functional food development is expected. A protocol for high resolution mass spectrometry proteomics of glycated proteins is given.

Strong inhibition of the polyol pathway diverts glucose flux to protein glycation leading to rapid establishment of secondary complications in diabetes mellitus

BACKGROUND

Polyol pathway and protein glycation are implicated in establishing secondary complications in diabetes. Their relative contribution to the process needs to be evaluated. It is essential to understand why some aldose reductase inhibitors (ARIs) trials are successful while some have failed and to study their effect on protein glycation.

METHODS

Aldose reductase (AR) was assayed using xylose as substrate; protein glycation was evaluated using total and specific fluorescence, fructoseamine and protein bound carbonyl content (PCO) measurements. Long term studies were carried out on streptozotocin induced diabetic rats for evaluation of urine parameters, tissue fluorescence. Anti-cataract action was studied by lens culture studies.

RESULTS

Epalrestat, a commercial ARI was also found to possess potent glycation inhibitory action. Long term experiments revealed strong protein glycation with higher concentration of citronellol (ARI) demonstrating shift in glucose flux. Treatment with epalrestat and limonene revealed improved urine parameters and tissue fluorescence. Lens culture studies revealed cataract formation at higher inhibition of AR while no lens opacity was observed at lower citronellol concentration and with limonene and epalrestat.

CONCLUSION

Strong inhibition of AR shifts the glucose flux to protein glycation causing damage. ARIs possessing protein glycation inhibition are more useful in amelioration of secondary complications.

Plasma Proteins Modified by Advanced Glycation End Products (AGEs) Reveal Site-specific Susceptibilities to Glycemic Control in Patients with Type 2 Diabetes

Protein glycation refers to the reversible reaction between aldoses (or ketoses) and amino groups yielding relatively stable Amadori (or Heyns) products. Consecutive oxidative cleavage reactions of these products or the reaction of amino groups with other reactive substances (e.g. α-dicarbonyls) yield advanced glycation end products (AGEs) that can alter the structures and functions of proteins. AGEs have been identified in all organisms, and their contents appear to rise with some diseases, such as diabetes and obesity. Here, we report a pilot study using highly sensitive and specific proteomics approach to identify and quantify AGE modification sites in plasma proteins by reversed phase HPLC mass spectrometry in tryptic plasma digests. In total, 19 AGE modification sites corresponding to 11 proteins were identified in patients with type 2 diabetes mellitus under poor glycemic control. The modification degrees of 15 modification sites did not differ among cohorts of normoglycemic lean or obese and type 2 diabetes mellitus patients under good and poor glycemic control. The contents of two amide-AGEs in human serum albumin and apolipoprotein A-II were significantly higher in patients with poor glycemic control, although the plasma levels of both proteins were similar among all plasma samples. These two modification sites might be useful to predict long term, AGE-related complications in diabetic patients, such as impaired vision, increased arterial stiffness, or decreased kidney function.

Soluble RAGE and atherosclerosis in youth with type 1 diabetes: a 5-year follow-up study

BACKGROUND

Advanced glycation end products (AGEs) play a role in the development of late complications and atherosclerosis in diabetes by engaging the receptor for advanced glycation end products, RAGE. Receptor binding leads to activation of the vascular endothelium and increased inflammation in the vessel wall. The soluble variants of the receptor, endogenous secretory RAGE (esRAGE) and the cleaved cell-surface part of RAGE, which together comprise soluble RAGE (sRAGE), are suggested to have a protective effect acting as decoys for RAGE. We aimed to test whether high levels of soluble variants of RAGE could be protective against atherosclerosis development.

METHODS

Participants in the prospective atherosclerosis and childhood diabetes study were examined at baseline (aged 8-18) and at follow-up after 5 years. Both sRAGE and esRAGE were measured by immunoassay in 299 patients with type 1 diabetes and 112 healthy controls at baseline and 241 patients and 128 controls at follow-up. The AGEs methylglyoxal-derived hydroimidazolone-1 (MG-H1) and carboxymethyllysine (CML) were measured by immunoassay. The surrogate markers of atherosclerosis assessed were carotid intima-media thickness (cIMT), C-reactive protein (CRP) and Young's modulus, measures of arterial wall thickness, inflammation and arterial stiffness, respectively.

RESULTS

Levels of sRAGE and esRAGE correlated strongly both at baseline and at follow-up in both diabetes patients and controls. With increasing age, mean values of both variants declined, independent of gender, diabetes or pubertal stage. In the diabetes group, multiple regression analysis showed a positive association between both variants of soluble RAGE and cIMT. There was no significant relationship with Young's modulus, but a negative association between sRAGE at baseline and CRP at follow-up. The ratios between the AGEs and the variants of soluble RAGE were increased in diabetes patients compared to controls.

CONCLUSIONS

The results show a possible protective effect of high levels of sRAGE at baseline against inflammation 5 years later, but not on arterial stiffness or wall thickness, in this cohort of adolescents and young adults with T1D.