Formation Of Advanced Glycation End Research Articles

Advanced glycation end products and their receptors in serum of patients with type 2 diabetes

Glycation is a non-enzymatic process involving the reaction of reducing sugars or reactive oxoaldehyde with proteins, lipids or nucleic acids, which results in the formation of advanced glycation end products (AGEs). The presented work discusses the glycation process in people with advanced stage of type 1 or type 2 diabetes. The concentration of different AGEs and their receptors for 58 serum samples was determined by ELISA and by spectrofluorimetric methods. In addition to fluorescent low molecular weight and protein-bound AGEs, we have also marked a new class of AGEs: melibiose-derived glycation product (MAGE). Our attention was also focused on the two groups of AGEs receptors: scavenger receptors (SR-A and SR-B) and RAGE. The correlation between the SR-AI scavenging receptors concentration and the fluorescence of AGEs as well as diabetes biological markers: GFR, creatinine contentration and HbA1c was demonstrated. A relationship between the concentration of AGEs and their receptors was also found in serum sample of patients treated with the metformin and aspirin. Furthermore, the concentration of SR-AI scavenger and the fluorescence of total AGEs was significantly lower in treated patients than in non treated patients. AGEs have also been found to contribute to the development of cardiovascular disease, atherosclerosis and diabetic complications, what could be deduced from the correlation of AGEs level and HDL cholesterol or uric acid level. Thus, it was confirmed that AGEs are involved in the pathomechanism of diabetes and other degenerative diseases. Nowadays, it is believed that AGEs due to the long time remaining in the body may be an important diagnostic marker. Their determination may allow monitoring the progression of the disease and the effectiveness of the therapy.

Anti-Diabetic Effects of Different Phenolic-Rich Fractions from Rhus Chinensis Mill. Fruits in vitro

This study investigated the inhibitory effects of the Ethanol Extract (EE), Free Phenolic (TF), Esterified Phenolic (TE) and Insoluble-bound Phenolic (TI) from Rhus chinensis Mill. fruits on α-glucosidase, Dipeptidyl Peptidase-4 (DPP-IV), and the formation of Advanced Glycation End (AGE) products. Results showed that the TF had the strongest inhibition against α-glucosidase and DPP-IV with IC50 of 0.56 ± 0.04 and 66.08 ± 1.36 μg/mL, respectively (p < 0.05). TI exhibited the strongest inhibitory effect on the formation of AGEs with IC50 of 0.43 ± 0.03 mg/mL (p < 0.05). Two major compounds (myricetin-3-O-rhamnoside and quercetin-3-O-rhamnoside) showed additive or synergistic effects on α-glucosidase inhibition, while displayed antagonistic effect on DPP-IV inhibition. Correlation analysis indicated that myricetin-3-O-(6″-galloyl) glycoside and myricetin O-gallate contributed significantly on α-glucosidase inhibition, while di-O-galloyl-glucoside and its isomer may contribute remarkably toward DPP-IV inhibition. Protocatechuic acid and myricetin-3-O-rhamnoside showed a positive correlation with the suppression of AGEs formation. Those results may provide some scientific information for exploring R. chinensis fruits as nutraceuticals and/or functional foods to prevent or improve diabetes.

The Effects of Metformin, Aminoguanidine, and Pyridoxamine on Methylglyoxal Induced Cardiac Myocytes Injury

In diabetics, formation of advanced glycation end (AGE) products has been closely associated with cardiovascular complications. In order to mitigate the injury caused by AGEs, it is critical to understand the influence of the AGE precursor methylglyoxal. Methylglyoxal is a glycation intermediate and it has been found to be elevated in the blood of diabetic patients. The impact of methylglyoxal on cardiac cells is not well elucidated. In this study, the effects of methylglyoxal on H9C2 myoblast cell viability were evaluated. Thereafter, methylglyoxal induced cell injury was investigated by co‐treatment of methylglyoxal with metformin, aminoguanidine hydrochloride, or pyridoxamine dihydrochloride. Cell viability was evaluated after incubation of drugs for 24 hours by measuring absorbance at 450 nm by using tetrazolium to differentiate metabolically active and inactive cells (e.g., CCK‐8 kit). We found that methylglyoxal (1200 μM) significantly reduced cell viability by 72±6% when compared to the untreated control (n=4, p&lt;0.05). By contrast, co‐treatment of metformin (1–80 mM) significantly reduced methylglyoxal‐induced cell injury and increased cell viability to 69% – 122± 6% (n=4, p&lt;0.05 vs. methylglyoxal) when compared to the untreated control. Similarly, aminoguanidine hydrochloride (250–1000 μM) treated cells significantly increased cell viability to 77% – 109±10% (n=4, p&lt;0.05 vs. methylglyoxal) when compared to the untreated control. Additionally, pyridoxamine dihydrochloride (0.1–15 μM, n=4) showed dose‐dependent protection to increase cell viability. Highest pyridoxamine (15 μM) treated cells completely abolished methylglyoxal induced cell injury by increasing cell viability to 99± 4% (p&lt;0.05 vs. methylglyoxal) when compared to the untreated control. However, when the three drugs were washed out from the medium prior to the addition of the methylglyoxal, the protective effects were lost and cell viability was reduced similarly as methylglyoxal (n=1). Administration of all three drugs alone did not affect cell viability after incubation for 24 hours. The preliminary data suggests that metformin, aminoguanidine hydrochloride, or pyridoxamine dihydrochloride, when incubated concurrently with a high concentration of methylglyoxal, protect cardiac cells from methylglyoxal‐induced cell injury. The mechanism underlying the protective effects will be further investigated.Support or Funding InformationThis study was supported by the Center for Chronic Disorders of Aging, the Division of Research and the Department of Bio‐Medical Sciences at Philadelphia College of Osteopathic Medicine.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Гликирование белков при сахарном диабете и возможности его фармакологической коррекции (обзор)

Процесс неферментативного взаимодействия восстанавливющих сахаров со свободными аминогруппами белков (реакция Майяра), приводящий к образованию конечных продуктов гликирования, считают важным фактором патогенеза таких заболеваний, как атеросклероз, сердечная недостаточность, воспаление, ревматоидный артрит, нейродегенеративные заболевания. Особенно интенсивно он протекает при гипергликемии и лежит в основе патогенеза микро- и макрососудистых осложнений сахарного диабета. В обзоре описаны основные этапы реакции Майяра, патофизиологическая роль ее продуктов в развитии осложнений сахарного диабета, возможные пути фармакологической коррекции данного процесса и основные представители ингибиторов гликирования белков, известные на сегодняшний день.

Glycation abolishes the cardioprotective effects of albumin during ex vivo ischemia‐reperfusion

Hyperglycemia‐induced oxidative stress plays a key role in the onset/progression of cardiovascular diseases. For example, it can trigger formation of advanced glycation end (AGE) products with ischemia‐reperfusion performed under hyperglycemic conditions. For this study, we hypothesized that albumin modified by glycation loses its unique cardioprotective properties in the setting of ischemia‐reperfusion under high glucose conditions. Here, ex vivo rat heart perfusions were performed under simulated normo‐ and hyperglycemic conditions, that is Krebs‐Henseleit buffer containing 11 mmol/L and 33 mmol/L glucose, respectively, ± normal or glycated albumin preparations. The perfusion protocol consisted of a 60 min stabilization step that was followed by 20 min of global ischemia and 60 min reperfusion. Additional experiments were completed to determine infarct sizes in response to 20 min regional ischemia and 120 min reperfusion. At the end of perfusions, heart tissues were isolated and evaluated for activation of the AGE pathway, oxidative stress, and apoptosis. Our data reveal that native bovine serum albumin treatment elicited cardioprotection (improved functional recovery, decreased infarct sizes) under high glucose conditions together with enhanced myocardial antioxidant capacity. However, such protective features are lost with glycation where hearts displayed increased infarct sizes and poor functional recovery versus native albumin treatments. Myocardial antioxidant capacity was also lowered together with activation of the intracellular AGE pathway. These data therefore show that although albumin acts as a cardioprotective agent during ischemia‐reperfusion, it loses its cardioprotective and antioxidant properties when modified by glycation.

High glucose activates HIF-1-mediated signal transduction in glomerular mesangial cells through a carbohydrate response element binding protein

High glucose evokes a variety of signals in mesangial cells that alter cellular functions responsible for the development of diabetic glomerulopathy. The hypoxia-inducible factor-1alpha (HIF-1alpha) regulates cellular homeostasis under hypoxic conditions, but it also has pleiotropic effects in response to cellular stresses at normoxia. Here we determined whether HIF-1alpha has a role in the regulation of mesangial cells in hyperglycemia. In the streptozotocin-induced diabetic mouse model, glomerular mesangial cells had a significant increase in HIF-1alpha expression in the nucleus. In cultured mesangial cells, high glucose enhanced the expression of HIF-1alpha and its target genes known to be involved in the development of diabetic glomerulopathy. A glucose-responsive carbohydrate response element binding protein (ChREBP) was found to have a critical role in the transcriptional upregulation of HIF-1alpha and downstream gene expression in mesangial cells exposed to high glucose. Knockdown of HIF-1alpha or ChREBP in mesangial cells abrogated the high glucose-mediated perturbation of gene expression. Our results show that ChREBP and HIF-1alpha mediate gene regulation in mesangial cells. Further studies will be needed to find out whether these findings are relevant to the development of the diabetic nephropathy.

Inhibition of Protein Glycation by Skins and Seeds of the Muscadine Grape

The formation of advanced glycation end (AGE) products, mediated in part by oxidative processes, has been linked to the pathogenesis of diabetic complications. In this study, the effect of the seed and skin extracts of the muscadine grape on AGE product formation was examined. Seeds and skins were extracted (10% w/v) with 50% ethanol and incubated at 37°C with a solution containing 250 mM fructose and 10 mg/ml albumin in 200 mM potassium phosphate buffer, pH 7.4. After 4 days, fluorescence was measured at the wavelength pair of 370 and 440 nm as an index of the formation of AGE products. Both seed and skin extracts were found to be efficacious inhibitors of AGE product formation. A 1:300 dilution of the seed extract decreased fluorescence by approximately 90% while muscadine grape skin extract produced a 75 % lowering. This difference correlates with the greater antioxidant activity found in muscadine seeds in comparison to skins. The three major polyphenols in the seeds, gallic acid, catechin and epicatechin all decreased the AGE product related fluorescence by 85% at a concentration of 100 uM. These results suggest that consumption of the muscadine grape may provide beneficial, protective effects against the development of diabetic complications.

Human neutrophils employ the myeloperoxidase-hydrogen peroxide-chloride system to convert hydroxy-amino acids into glycolaldehyde, 2-hydroxypropanal, and acrolein. A mechanism for the generation of highly reactive alpha-hydroxy and alpha,beta-unsaturated aldehydes by phagocytes at sites of inflammation.

Reactive aldehydes derived from reducing sugars and lipid peroxidation play a critical role in the formation of advanced glycation end (AGE) products and oxidative tissue damage. We have recently proposed another mechanism for aldehyde generation at sites of inflammation that involves myeloperoxidase, a heme enzyme secreted by activated phagocytes. We now demonstrate that human neutrophils employ the myeloperoxidase-H202-chloride system to produce alpha-hydroxy and alpha,beta-unsaturated aldehydes from hydroxy-amino acids in high yield. Identities of the aldehydes were established using mass spectrometry and high performance liquid chromatography. Activated neutrophils converted L-serine to glycolaldehyde, an alpha-hydroxyaldehyde which mediates protein cross-linking and formation of Nepsilon-(carboxymethyl)lysine, an AGE product. L-Threonine was similarly oxidized to 2-hydroxypropanal and its dehydration product, acrolein, an extremely reactive alpha,beta-unsaturated aldehyde which alkylates proteins and nucleic acids. Aldehyde generation required neutrophil activation and a free hydroxy-amino acid; it was inhibited by catalase and heme poisons, implicating H202 and myeloperoxidase in the cellular reaction. Aldehyde production by purified myeloperoxidase required H202 and chloride, and was mimicked by reagent hypochlorous acid (HOCl) in the absence of enzyme, suggesting that the reaction pathway involves a chlorinated intermediate. Collectively, these results indicate that the myeloperoxidase-H202-chloride system of phagocytes converts free hydroxy-amino acids into highly reactive alpha-hydroxy and alpha,beta-unsaturated aldehydes. The generation of glycolaldehyde, 2-hydroxypropanal, and acrolein by activated phagocytes may thus play a role in AGE product formation and tissue damage at sites of inflammation.

Formation of advanced glycation end (AGE) products in diabetes: prevention by pyruvate and alpha-keto glutarate.

Glycation of proteins and their subsequent structural and functional modifications have been ascribed to play a prominent role in the pathogenesis of several secondary complications of diabetes, such as cataract and retinopathy. In addition, it plays a role in the generalized ageing process as well. Investigations have been conducted to explore the possibility of preventing the above process by use of pyruvate and alpha-keto glutarate as representatives of physiologically compatible keto acids. The results demonstrate that both these compounds are effective in preventing the initial glycation reaction as well as the formation of AGE products. Both these compounds also inhibit the generation of high molecular weight aggregates associated with cataract formation. Mechanistically, the preventive effects appear to be due to (1) competitive inhibition of glycation by the keto acids and (2) the antioxidant (radical scavenging) properties of these compounds. The results are hence considered useful from the point of view of developing these and other keto acid derivatives as pharmacological agents useful in preventing glycation related protein changes and consequent tissue pathological manifestations.