Methylglyoxal-derived Advanced Glycation End-products Research Articles

421-P: Methylglyoxal-Derived Advanced Glycation End Products Are Prognostic Biomarkers for Diabetic Complications and Drivers of Endothelial Dysfunction

Diabetic kidney disease (DKD) affects over 30% of individuals with T1D, significantly increasing mortality risk in this population. Canonical tools to predict DKD such as glomerular filtration rate (GFR) or albumin excretion rate (AER) alone may not be sufficient to predict disease risk, as they often do not become apparent until significant kidney damage has already occurred. Therefore, there is an unmet need to identify additional clinically useful biomarkers to predict DKD risk. Methylglyoxal (MG) is an abundant, reactive electrophile produced during metabolic flux from glycolysis and protein and lipid metabolism. MG covalently modifies macromolecules such as DNA, RNA, and protein forming MG-advanced glycation end products (MG-AGEs). Both MG and MG-AGEs have been correlated with diabetes and cancer, but the ability of nucleoside MG-AGEs to predict DKD risk has not been examined. Using a novel mass spectrometry method, we measured levels of MG-AGEs in patient urinary samples collected from the DCCT/EDIC study and found MG-AGEs independently predicted DKD risk up to 16 years pre-diagnosis. This association was more significant than the association of AER, GFR, or HbA1c with DKD. In DKD, endothelial cells (ECs) become dysfunctional, which contributes to the development of the disease. To understand the extent to which MG-AGEs impact EC dysfunction, we synthesized pure MG-AGEs and exposed human umbilical vein endothelial cells (HUVECS) to these compounds. We found MG-AGEs activated pathways associated with the receptor for AGEs (RAGE) and EC dysfunction as evidenced by increased leukocyte adhesion, oxidative stress, pro-inflammatory gene expression, and NFkB activation. This suggests that MG-AGEs are not only predictive of DKD, but may also contribute to EC dysfunction preceding disease. Disclosure S.Lai: None. E.D.J.Lopez gonzalez: None. S.Shuck: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (X01DK118575); National Institutes of Health (1R21DK127285); Wanek Family Project to Cure T1D; Diabetes Complications Consortium

Analysis of Glyoxal- and Methylglyoxal-Derived Advanced Glycation End Products during Grilling of Porcine Meat.

The reaction of the N6-amino group of lysine residues and 1,2-dicarbonyl compounds during Maillard processes leads to advanced glycation end products (AGEs). In the present work, we deliver a comprehensive analysis of changes of carbohydrates, dicarbonyl structures, and 11 AGEs during the grilling of porcine meat patties. While raw meat contained mainly glyoxal-derived N6-carboxymethyl lysine (CML), grilling led to an increase of predominantly methylglyoxal-derived AGEs N6-carboxyethyl lysine (CEL), N6-lactoyl lysine, methylglyoxal lysine dimer (MOLD), and methylglyoxal lysine amide (MOLA). Additionally, we identified and quantitated a novel methylglyoxal-derived amidine compound N1,N2-di-(5-amino-5-carboxypentyl)-2-lactoylamidine (methylglyoxal lysine amide, MGLA) in heated meat. Analysis of carbohydrates suggested that approximately 50% of the methylglyoxal stemmed from the fragmentation of triosephosphates during the heat treatment. Surprisingly, N6-lactoyl lysine was the major AGE, and based on model incubations, we propose that approximately 90% must be explained by the nonenzymatic acylation of lysine through S-lactoylglutathione, which was quantitated for the first time in meat herein.

Methylglyoxal-Derived Advanced Glycation End Products (AGE4) Promote Cell Proliferation and Survival in Renal Cell Carcinoma Cells through the RAGE/Akt/ERK Signaling Pathways.

Advanced glycation end products (AGEs) are the products formed through a non-enzymatic reaction of reducing sugars with proteins or lipids. There is a potential for toxicity in the case of AGEs produced through glycation with dicarbonyl compounds including methylglyoxal, glyoxal, and 3-deoxyglucosone. The AGEs bind the receptor for advanced glycation end products (RAGE) and stimulate the mitogen-activated protein (MAP) kinase signaling pathway that can increase the production of matrix metalloproteinases (MMPs). In addition, AGE-induced protein kinase B (Akt) signaling can promote cancer cell proliferation and contribute to many diseases such as kidney cancer. In light of the lack of extensive study of the relationship between methylglyoxal-induced AGEs (AGE4) and renal cancer, we studied the proliferous and anti-apoptotic effects of AGE4 on renal cell carcinoma (RCC) in this study. AGE4 treatment was involved in the proliferation and migration of RCC cells in vitro by upregulating proliferating cell nuclear antigen (PCNA) and MMPs while suppressing apoptotic markers such as Bax and caspase 3. Moreover, Akt and extracellular-signal-regulated kinase (ERK) were phosphorylated in RCC cells with AGE4 treatment. As a result, this study demonstrated that AGE4-RAGE axis can promote the growth ability of RCC by inducing PCNA, MMPs, and inhibiting apoptosis in RCC via the Akt and ERK signaling pathways.

Methylglyoxal-Derived Advanced Glycation End Product (AGE4)-Induced Apoptosis Leads to Mitochondrial Dysfunction and Endoplasmic Reticulum Stress through the RAGE/JNK Pathway in Kidney Cells.

Advanced glycation end products (AGEs) are formed via nonenzymatic reactions between reducing sugars and proteins. Recent studies have shown that methylglyoxal, a potent precursor for AGEs, causes a variety of biological dysfunctions, including diabetes, inflammation, renal failure, and cancer. However, little is known about the function of methylglyoxal-derived AGEs (AGE4) in kidney cells. Therefore, we verified the expression of endoplasmic reticulum (ER) stress-related genes and apoptosis markers to determine the effects of AGE4 on human proximal epithelial cells (HK-2). Moreover, our results showed that AGE4 induced the expression of apoptosis markers, such as Bax, p53, and kidney injury molecule-1, but downregulated Bcl-2 and cyclin D1 levels. AGE4 also promoted the expression of NF-κB, serving as a transcription factor, and the phosphorylation of c-Jun NH2-terminal kinase (JNK), which induced cell apoptosis and ER stress mediated by the JNK inhibitor. Furthermore, AGE4 induced mitochondrial dysfunction by inducing the permeabilization of the mitochondrial membrane and ATP synthesis. Through in vitro and in vivo experiments, this study provides a new perspective on renal dysfunction with regard to the AGE4-induced RAGE /JNK signaling pathway, which leads to renal cell apoptosis via the imbalance of mitochondrial function and ER stress in kidney damage.

Sulforaphane and Vitamin E Protect From Glucotoxic Neurodegeneration and Lifespan Reduction In C. Elegans.

Caenorhabditis elegans is an established model organism in neurodegeneration and aging research. Oxidative stress and formation of advanced glycation endproducts (AGEs), as they occur under hyperglycemic conditions in diabetes mellitus, contribute to neuronal damage and lifespan reduction. Sulforaphane (SFN) is an indirect antioxidant, alpha-tocopherol (vitamin E) is a direct antioxidant that acts as a free radical scavenger. Aim of this study is to investigate the protective effects of SFN and vitamin E against glucotoxic damages to the neuronal system and lifespan in C. elegans. Culture conditions that mimic clinical hyperglycemia increased the formation of reactive oxygen species (ROS) (p<0.001) and the accumulation of methylglyoxal-derived advanced glycation endproducts (MG-derived AGEs) (p<0.01) with subsequent neuronal damage and neuronal dysfunction, ultimately leading to a significant shortening of lifespan (p<0.01). Treatment with both, 20 µmol/l SFN and 200 µg/ml vitamin E, completely prevented the increase in ROS and MG-derived AGEs, abolished the glucotoxic effects on neuronal structure and function, and preserved lifespan, resulting in a life expectancy similar to untreated controls. These data emphasize the relevance of indirect and direct antioxidants as potential therapeutic options for the prevention of glucotoxic pathologies.

Methylglyoxal-derived advanced glycation end products induce matrix metalloproteinases through activation of ERK/JNK/NF-κB pathway in kidney proximal epithelial cells.

The accumulation of reactive α-dicarbonyl leading to advanced glycation end products (AGEs) have been linked to pathophysiological diseases in many studies, such as atherosclerosis, cataract, cancer, and diabetic nephropathy. Glycation-generated AGEs increase the expression of inflammatory cytokines by transferring signals to the cell by binding them to the receptor for AGEs (RAGE) on their cell surface. The effect of methylglyoxal-derived AGEs (AGE-4) on the induction of matrix metalloproteinases (MMPs) in rat ordinary kidney cells (NRK-52E) was explored in this research, among other AGEs. The cell treated with 100μg/mL AGE-4 for 24h showed a substantial rise in MMP-2 and MMP-9 expression relative to BSA control only and other AGEs through ERK, JNK, and NF-B pathways. Our findings therefore suggest that AGE-4 expresses MMPs through the AGE-4-RAGE axis, activating MAPK signals that may contribute to dysfunction of the kidney cell.

Ethyl Pyruvate Prevents Renal Damage Induced by Methylglyoxal-Derived Advanced Glycation End Products.

The renal accumulation of advanced glycation end products (AGEs) is a causative factor of various renal diseases, including chronic kidney disease and diabetic nephropathy. AGE inhibitors, such as aminoguanidine and pyridoxamine, have the therapeutic activities for reversing the increase in renal AGE burden. This study evaluated the inhibitory effects of ethyl pyruvate (EP) on methylglyoxal- (MGO-) modified AGE cross-links with proteins in vitro. We also determined the potential activity of EP in reducing the renal AGE burden in exogenously MGO-injected rats. EP inhibited MGO-modified AGE-bovine serum albumin (BSA) cross-links to collagen (IC50 = 0.19 ± 0.03 mM) in a dose-dependent manner, and its activity was stronger than aminoguanidine (IC50 = 35.97 ± 0.85 mM). In addition, EP directly trapped MGO (IC50 = 4.41 ± 0.08 mM) in vitro. In exogenous MGO-injected rats, EP suppressed AGE burden and MGO-induced oxidative injury in renal tissues. These activities of EP on the MGO-mediated AGEs cross-links with protein in vitro and in vivo showed its pharmacological potential for inhibiting AGE-induced renal diseases.

Gene doubling increases glyoxalase 1 expression in RAGE knockout mice

BackgroundThe receptor for advanced glycation end-products (RAGE) is a multifunctional protein. Its function as pattern recognition receptor able to interact with various extracellular ligands is well described. Genetically modified mouse models, especially the RAGE knockout (RAGE-KO) mouse, identified the amplification of the immune response as an important function of RAGE. Pro-inflammatory ligands of RAGE are also methylglyoxal-derived advanced glycation end-products, which depend in their quantity, at least in part, on the activity of the methylglyoxal-detoxifying enzyme glyoxalase-1 (Glo1). Therefore, we studied the potential interaction of RAGE and Glo1 by use of RAGE-KO mice. MethodsVarious tissues (lung, liver, kidney, heart, spleen, and brain) and blood cells from RAGE-KO and wildtype mice were analyzed for Glo1 expression and activity by biochemical assays and the Glo1 gene status by PCR techniques. ResultsWe identified an about two-fold up-regulation of Glo1 expression and activity in all tissues of RAGE-KO mice. This was result of a copy number variation of the Glo1 gene on mouse chromosome 17. In liver tissue and blood cells, the Glo1 expression and activity was additionally influenced by sex with higher values for male than female animals. As the genomic region containing Glo1 also contains the full-length sequence of another gene, namely Dnahc8, both genes were duplicated in RAGE-KO mice. ConclusionA genetic variance in RAGE-KO mice falsely suggests an interaction of RAGE and Glo1 function. General significanceRAGE-independent up-regulation of Glo1 in RAGE-KO mice might be as another explanation for, at least some, effects attributed to RAGE before.

Methylglyoxal-Derived Advanced Glycation Endproducts Accumulate in Multiple Sclerosis Lesions.

Multiple sclerosis (MS) is a demyelinating autoimmune disease in which innate and adaptive immune cells infiltrate the central nervous system (CNS) and damage the myelin sheaths surrounding the axons. Upon activation, infiltrated macrophages, CNS-resident microglia, and astrocytes switch their metabolism toward glycolysis, resulting in the formation of α-dicarbonyls, such as methylglyoxal (MGO) and glyoxal (GO). These potent glycating agents lead to the formation of advanced glycation endproducts (AGEs) after reaction with amino acids. We hypothesize that AGE levels are increased in MS lesions due to the inflammatory activation of macrophages and astrocytes. First, we measured tissue levels of AGEs in brain samples of MS patients and controls. Analysis of MS patient and non-demented control (NDC) specimens showed a significant increase in protein-bound Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1), the major AGE, compared to white matter of NDCs (107 ± 11 vs. 154 ± 21, p < 0.05). In addition, immunohistochemistry revealed that MGO-derived AGEs were specifically present in astrocytes, whereas the receptor for AGEs, RAGE, was detected on microglia/macrophages. Moreover, in cerebrospinal fluid from MS patients, α-dicarbonyls and free AGEs correlated with their respective levels in the plasma, whereas this was not observed for protein-bound AGEs. Taken together, our data show that MG-H1 is produced by astrocytes. This suggests that AGEs secreted by astrocytes have paracrine effects on RAGE-positive macrophages/microglia and thereby contribute to the pathology of MS.

Enhanced Formation of Methylglyoxal-Derived Advanced Glycation End Products in Arabidopsis Under Ammonium Nutrition.

Nitrate (NO3–) and ammonium (NH4+) are prevalent nitrogen (N) sources for plants. Although NH4+ should be the preferred form of N from the energetic point of view, ammonium nutrition often exhibits adverse effects on plant physiological functions and induces an important growth-limiting stress referred as ammonium syndrome. The effective incorporation of NH4+ into amino acid structures requires high activity of the mitochondrial tricarboxylic acid cycle and the glycolytic pathway. An unavoidable consequence of glycolytic metabolism is the production of methylglyoxal (MG), which is very toxic and inhibits cell growth in all types of organisms. Here, we aimed to investigate MG metabolism in Arabidopsis thaliana plants grown on NH4+ as a sole N source. We found that changes in activities of glycolytic enzymes enhanced MG production and that markedly elevated MG levels superseded the detoxification capability of the glyoxalase pathway. Consequently, the excessive accumulation of MG was directly involved in the induction of dicarbonyl stress by introducing MG-derived advanced glycation end products (MAGEs) to proteins. The severe damage to proteins was not within the repair capacity of proteolytic enzymes. Collectively, our results suggest the impact of MG (mediated by MAGEs formation in proteins) in the contribution to NH4+ toxicity symptoms in Arabidopsis.

High-glucose toxicity is mediated by AICAR-transformylase/IMP cyclohydrolase and mitigated by AMP-activated protein kinase in Caenorhabditis elegans

The enzyme AICAR-transformylase/IMP cyclohydrolase (ATIC) catalyzes the last two steps of purine de novo synthesis. It metabolizes 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), which is an AMP analogue, leading to activation of AMP-activated kinase (AMPK). We investigated whether the AICAR-ATIC pathway plays a role in the high glucose (HG)-mediated DNA damage response and AICAR-mediated AMPK activation, explaining the detrimental effects of glucose on neuronal damage and shortening of the lifespan. HG up-regulated the expression and activity of the Caenorhabditis elegans homologue of ATIC, C55F2.1 (atic-1), and increased the levels of reactive oxygen species and methylglyoxal-derived advanced glycation end products. Overexpression of atic-1 decreased the lifespan and head motility and increased neuronal damage under both standard and HG conditions. Inhibition of atic-1 expression, by RNAi, under HG was associated with increased lifespan and head motility and reduced neuronal damage, reactive oxygen species, and methylglyoxal-derived advanced glycation end product accumulation. This effect was independent of an effect on DNA damage or antioxidant defense pathways, such as superoxide dismutase (sod-3) or glyoxalase-1 (glod-4), but was dependent on AMPK and accumulation of AICAR. Through AMPK, AICAR treatment also reduced the negative effects of HG. The mitochondrial inhibitor rotenone abolished the AICAR/AMPK-induced amelioration of HG effects, pointing to mitochondria as a prime target of the glucotoxic effects in C. elegans We conclude that atic-1 is involved in glucotoxic effects under HG conditions, either by blocked atic-1 expression or via AICAR and AMPK induction.

Proteomic identification and characterization of hepatic glyoxalase 1 dysregulation in non-alcoholic fatty liver disease

BackgroundNon-alcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide. However, its molecular pathogenesis is incompletely characterized and clinical biomarkers remain scarce. The aims of these experiments were to identify and characterize liver protein alterations in an animal model of early, diet-related, liver injury and to assess novel candidate biomarkers in NAFLD patients.MethodsLiver membrane and cytosolic protein fractions from high fat fed apolipoprotein E knockout (ApoE−/−) animals were analyzed by quantitative proteomics, utilizing isobaric tags for relative and absolute quantitation (iTRAQ) combined with nano-liquid chromatography and tandem mass spectrometry (nLC-MS/MS). Differential protein expression was confirmed independently by immunoblotting and immunohistochemistry in both murine tissue and biopsies from paediatric NAFLD patients. Candidate biomarkers were analyzed by enzyme-linked immunosorbent assay in serum from adult NAFLD patients.ResultsThrough proteomic profiling, we identified decreased expression of hepatic glyoxalase 1 (GLO1) in a murine model. GLO1 protein expression was also found altered in tissue biopsies from paediatric NAFLD patients. In vitro experiments demonstrated that, in response to lipid loading in hepatocytes, GLO1 is first hyperacetylated then ubiquitinated and degraded, leading to an increase in reactive methylglyoxal. In a cohort of 59 biopsy-confirmed adult NAFLD patients, increased serum levels of the primary methylglyoxal-derived advanced glycation endproduct, hydroimidazolone (MG-H1) were significantly correlated with body mass index (r = 0.520, p < 0.0001).ConclusionCollectively these results demonstrate the dysregulation of GLO1 in NAFLD and implicate the acetylation-ubquitination degradation pathway as the functional mechanism. Further investigation of the role of GLO1 in the molecular pathogenesis of NAFLD is warranted.

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.

Inhibitory Effect of Arachis hypogaea (Peanut) and Its Phenolics against Methylglyoxal-Derived Advanced Glycation End Product Toxicity.

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound that causes endothelial dysfunction and plays important roles in the development of diabetic complications. Peanuts are rich in energy, minerals, and antioxidants. Here, we report the potential beneficial effects of peanuts, and particularly the phenolic contents, against MGO-mediated cytotoxicity. Firstly, we optimized the extraction conditions for maximum yield of phenolics from peanuts by examining different processing methods and extraction solvents. To estimate the phenolic contents of peanut extracts, a simultaneous analysis method was developed and validated by ultra-high-performance liquid chromatography–tandem mass spectrometry. We found that roasted peanuts and their 80% methanol extracts showed the highest amount of total phenolics. Secondly, we evaluated the inhibitory effects of phenolics and peanut extracts against MGO-mediated cytotoxicity. Phenolics and peanut extracts were observed to inhibit advanced glycation end product (AGE) formation as well as to break preformed AGEs. Furthermore, pretreatment with peanut extracts significantly inhibited MGO-induced cell death and reactive oxygen species production in human umbilical vein endothelial cells. Peanut extracts prevented MGO-induced apoptosis by increasing Bcl-2 expression and decreasing Bax expression, and MGO-mediated activation of mitogen-activated protein kinases (MAPKs). In conclusion, the constituents of peanuts may prevent endothelial dysfunction and diabetic complications.

Methylglyoxal-derived advanced glycation end products contribute to negative cardiac remodeling and dysfunction post-myocardial infarction.

Advanced glycation end-products (AGEs) have been associated with poorer outcomes after myocardial infarction (MI), and linked with heart failure. Methylglyoxal (MG) is considered the most important AGE precursor, but its role in MI is unknown. In this study, we investigated the involvement of MG-derived AGEs (MG-AGEs) in MI using transgenic mice that over-express the MG-metabolizing enzyme glyoxalase-1 (GLO1). MI was induced in GLO1 mice and wild-type (WT) littermates. At 6h post-MI, mass spectrometry revealed that MG-H1 (a principal MG-AGE) was increased in the hearts of WT mice, and immunohistochemistry demonstrated that this persisted for 4weeks. GLO1 over-expression reduced MG-AGE levels at 6h and 4weeks, and GLO1 mice exhibited superior cardiac function at 4weeks post-MI compared to WT mice. Immunohistochemistry revealed greater vascular density and reduced cardiomyocyte apoptosis in GLO1 vs. WT mice. The recruitment of c-kit+ cells and their incorporation into the vasculature (c-kit+CD31+ cells) was higher in the infarcted myocardium of GLO1 mice. MG-AGEs appeared to accumulate in type I collagen surrounding arterioles, prompting investigation in vitro. In culture, the interaction of angiogenic bone marrow cells with MG-modified collagen resulted in reduced cell adhesion, increased susceptibility to apoptosis, fewer progenitor cells, and reduced angiogenic potential. This study reveals that MG-AGEs are produced post-MI and identifies a causative role for their accumulation in the cellular changes, adverse remodeling and functional loss of the heart after MI. MG may represent a novel target for preventing damage and improving function of the infarcted heart.

The specific localization of advanced glycation end-products (AGEs) in rat pancreatic islets

Advanced glycation end-products (AGEs) are produced by non-enzymatic glycation between protein and reducing sugar such as glucose. Although glyceraldehyde-derived AGEs (Glycer-AGEs), one of the AGEs subspecies, have been reported to be involved in the pathogenesis of various age-relating diseases such as diabetes mellitus or arteriosclerosis, little is known about the pathological and physiological mechanism of AGEs in vivo. In present study, we produced 4 kinds of polyclonal antibodies against AGEs subspecies and investigated the localization of AGEs-modified proteins in rat peripheral tissues, making use of these antibodies. We found that Glycer-AGEs and methylglyoxal-derived AGEs (MGO-AGEs) were present in pancreatic islets of healthy rats, distinguished clearly into the pancreatic α and β cells, respectively. Although streptozotocin-induced diabetic rats suffered from remarkable impairment of pancreatic islets, the localization and deposit levels of the Glycer- and MGO-AGEs were not altered in the remaining α and β cells. Remarkably, the MGO-AGEs in pancreatic β cells were localized into the insulin-secretory granules. These results suggest that the cell-specific localization of AGEs-modified proteins are presence generally in healthy peripheral tissues, involved in physiological intracellular roles, such as a post-translational modulator contributing to the secretory and/or maturational functions of insulin.

Methylglyoxal-Derived Advanced Glycation Endproducts in Multiple Sclerosis.

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS). The activation of inflammatory cells is crucial for the development of MS and is shown to induce intracellular glycolytic metabolism in pro-inflammatory microglia and macrophages, as well as CNS-resident astrocytes. Advanced glycation endproducts (AGEs) are stable endproducts formed by a reaction of the dicarbonyl compounds methylglyoxal (MGO) and glyoxal (GO) with amino acids in proteins, during glycolysis. This suggests that, in MS, MGO-derived AGEs are formed in glycolysis-driven cells. MGO and MGO-derived AGEs can further activate inflammatory cells by binding to the receptor for advanced glycation endproducts (RAGE). Recent studies have revealed that AGEs are increased in the plasma and brain of MS patients. Therefore, AGEs might contribute to the inflammatory status in MS. Moreover, the main detoxification system of dicarbonyl compounds, the glyoxalase system, seems to be affected in MS patients, which may contribute to high MGO-derived AGE levels. Altogether, evidence is emerging for a contributing role of AGEs in the pathology of MS. In this review, we provide an overview of the current knowledge on the involvement of AGEs in MS.

The role of fibrinogen glycation in ATTR: evidence for chaperone activity loss in disease.

Transthyretin amyloidosis (ATTR) belongs to a class of disorders caused by protein misfolding and aggregation. ATTR is a disabling disorder of autosomal dominant trait, where transthyretin (TTR) forms amyloid deposits in different organs, causing dysfunction of the peripheral nervous system. We previously discovered that amyloid fibrils from ATTR patients are glycated by methylglyoxal. Even though no consensus has been reached about the actual role of methylglyoxal-derived advanced glycation end-products in amyloid diseases, evidence collected so far points to a role for protein glycation in conformational abnormalities, being ubiquitously found in amyloid deposits in Alzheimer's disease, dialysis-related amyloidosis and Parkinson's diseases. Human fibrinogen, an extracellular chaperone, was reported to specifically interact with a wide spectrum of stressed proteins and suppress their aggregation, being an interacting protein with TTR. Fibrinogen is differentially glycated in ATTR, leading to its chaperone activity loss. Here we show the existence of a proteostasis imbalance in ATTR linked to fibrinogen glycation by methylglyoxal.

Inhibitory effect of herbal medicines and their trapping abilities against methylglyoxal-derived advanced glycation end-products.

BackgroundMethylglyoxal (MG) is one of the most reactive glycating agents, which result the formation of advanced glycation end-products (AGEs) that have been implicated in the progression of age-related diseases. Inhibition of MG-induced AGE formation is the imperative approach for alleviating diabetic complications. The objective of this study was to investigate the MG-trapping abilities of herbal medicines and their inhibitory activities on the formation of MG-derived AGEs.MethodsThe aqueous extract of herbal medicines was measured for the content of total phenolic compounds and the antioxidant activity by Folin-Ciocalteu assay and the 1,1-diphenyl 2-picrylhydrazyl (DPPH) radical scavenging activity, respectively. The extracts were investigated the MG-trapping ability by high performance liquid chromatography (HPLC). The extracts were incubated with BSA and MG at 37 °C for 1 day. The formation of MG-derived AGEs was measured.ResultsTotal phenolic compounds of eleven herbal medicines showed marked variations, ranging from 12.16 to 272.36 mg gallic acid equivalents/g extract. All extracts (1 mg/mL) markedly exhibited the DPPH radical scavenging activity (0.31–73.52 %) and the MG-trapping abilities (13.97–58.97 %). In addition, they also inhibited the formation of MG-derived AGEs by 4.01–79.98 %. The results demonstrated that Rhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus were the potent inhibitors against the formation of MG-derived AGEs. The positive correlations between the contents of phenolics and % MG trapping (r = 0.912, p < 0.01) and % inhibition of MG-derived AGEs (r = 0.716, p < 0.01) were observed in the study. Furthermore, there was a moderate positive correlation between % MG trapping and % inhibition of MG-derived AGEs (r =0.584, p < 0.01).ConclusionsRhinacanthus nasutus, Syzygium aromaticum, and Phyllanthus amarus could reduce the formation of MG-derived AGEs through their MG-trapping abilities. These findings are relevant for focusing on potential herbal medicines to prevent or ameliorate AGE-mediated diabetic complications.

Protective Effects of Liraglutide and Linagliptin in C. elegans as a New Model for Glucose-Induced Neurodegeneration.

Liraglutide and linagliptin are novel drugs for the treatment of diabetes. Antioxidative and neuroprotective effects have been described for both compounds. However, it is not yet known, whether these mechanisms are also protective against diabetic retinal neurodegeneration. We assessed the antioxidative and neuroprotective capabilities of liraglutide and linagliptin as well as the signaling pathways involved, by using C. elegans as a model for glucose-induced neurodegeneration. C. elegans were cultivated under conditions, which mimic clinical hyperglycemia, and treated with 160 μmol/l liraglutide or 13 μmol/l linagliptin. Oxidative stress was reduced by 29 or 78% and methylglyoxal-derived advanced glycation endproducts (AGEs) by 33 or 22%, respectively. This resulted in an improved neuronal function by 42 or 60% and an extended mean lifespan by 9 or 11%, respectively. Antioxidative and AGE reducing effects of liraglutide and linagliptin were not dependent on v-akt murine thymoma viral oncogene homologue 1/forkhead box O1 (AKT1/FOXO). Neuroprotection by liraglutide was AKT1/FOXO dependent, yet AKT1/FOXO independent upon linagliptin treatment. Both liraglutide and linagliptin exert neuroprotective effects in an experimental model for glucose-induced neurodegeneration, however, the signaling pathways differ in the present study. Further pharmacological intervention with these pathways may help to delay the clinical onset of diabetic retinopathy by preserving neuronal integrity.