Immunological Detection of a Novel Advanced Glycation End-Product

Anhydrous microwave synthesis as efficient method for obtaining model advanced glycation end-products

Introduction

Advanced glycation end-products (AGEs) are capable of stimulating oxidative stress and inflammation. This study investigates the synthesis of medium crosslinked AGEs (the most optimal form of AGEs because of soluble in water, used in many assays as markers) and their biochemical properties.

Methods

One of model protein-myoglobin from horse heart muscle (MB) and a chosen respective glycation factor - D-melibiose (mel), acrolein (ACR), D-glucose (glc), 4-hydroksynonenal (4HNE), trans-2-nonenal (T2N), methylglyoxal (MGO) - were subjected to high temperature water synthesis (HTWS) and high temperature microwave synthesis in anhydrous conditions (HTMS). The syntheses were deliberately carried out in two different conditions to check whether adding an additional energy source (microwaves) while lowering the temperature and shortening the reaction time would allow for more effective obtaining of medium-cross-linked AGEs, monitored with SDS-PAGE. Products were analyzed using fluorescence measurements, Enzyme-Linked Immunosorbent Assay (ELISA) and immunoblotting tests and electrophoretic mobility shift assay to evaluate their ability to activate nuclear factor kappa-light-chain-enhancer (NF-κB).

Results

Medium cross-linked AGEs were more efficiently obtained in HTMS. Fluorescence was high for MB-ACR, MB-T2N and MB-glc products. Anti-MAGE antibodies showed reactivity towards MB-mels of HTMS and HTWS, and the MB-4HNEs from HTMS. HTWS products, apart from MB-ACR, did not activate NF-κB, whereas MB-ACR, MB-4HNE, MB-mel, and MB-T2N products of HTMS strongly activated this factor that indicates their strong pro-inflammatory properties.

Conclusion

HTMS is a fast and efficient method of synthesizing medium cross-linked AGEs.

Structures of Toxic Advanced Glycation End-Products Derived from Glyceraldehyde, A Sugar Metabolite

Advanced glycation end-products (AGEs) have recently been implicated in the onset/progression of lifestyle-related diseases (LSRDs); therefore, the suppression of AGE-induced effects may be used in both the prevention and treatment of these diseases. Various AGEs are produced by different biological pathways in the body. Glyceraldehyde (GA) is an intermediate of glucose and fructose metabolism, and GA-derived AGEs (GA-AGEs), cytotoxic compounds that accumulate and induce damage in mammalian cells, contribute to the onset/progression of LSRDs. The following GA-AGE structures have been detected to date: triosidines, GA-derived pyridinium compounds, GA-derived pyrrolopyridinium lysine dimers, methylglyoxal-derived hydroimidazolone 1, and argpyrimidine. GA-AGEs are a key contributor to the formation of toxic AGEs (TAGE) in many cells. The extracellular leakage of TAGE affects the surrounding cells via interactions with the receptor for AGEs. Elevated serum levels of TAGE, which trigger different types of cell damage, may be used as a novel biomarker for the prevention and early diagnosis of LSRDs as well as in evaluations of treatment efficacy. This review provides an overview of the structures of GA-AGEs.

Involvement of Intracellular TAGE and the TAGE-RAGE-ROS Axis in the Onset and Progression of NAFLD/NASH

The repeated excessive intake of sugar, a factor that contributes to the onset of nonalcoholic fatty liver disease (NAFLD) and its progression to the chronic form of nonalcoholic steatohepatitis (NASH), markedly increases the hepatocyte content of glyceraldehyde (GA), a glucose/fructose metabolic intermediate. Toxic advanced glycation end-products (toxic AGEs, TAGE) are synthesized by cross-linking reactions between the aldehyde group of GA and the amino group of proteins, and their accumulation has been implicated in the development of NAFLD/NASH and hepatocellular carcinoma (HCC). Our previous findings not only showed that hepatocyte disorders were induced by the intracellular accumulation of TAGE, but they also indicated that extracellular leakage resulted in elevated TAGE concentrations in circulating fluids. Interactions between extracellular TAGE and receptor for AGEs (RAGE) affect intracellular signaling and reactive oxygen species (ROS) production, which may, in turn, contribute to the pathological changes observed in NAFLD/NASH. RAGE plays a role in the effects of the extracellular leakage of TAGE on the surrounding cells, which ultimately promote the onset and progression of NAFLD/NASH. This review describes the relationships between intracellular TAGE levels and hepatocyte and hepatic stellate cell (HSC) damage as well as the TAGE-RAGE-ROS axis in hepatocytes, HSC, and HCC cells. The "TAGE theory" will provide novel insights for future research on NAFLD/NASH.

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.

Venestatin from parasitic helminths interferes with receptor for advanced glycation end products (RAGE)-mediated immune responses to promote larval migration

Parasitic helminths can reside in humans owing to their ability to disrupt host protective immunity. Receptor for advanced glycation end products (RAGE), which is highly expressed in host skin, mediates inflammatory responses by regulating the expression of pro-inflammatory cytokines and endothelial adhesion molecules. In this study, we evaluated the effects of venestatin, an EF-hand Ca²⁺-binding protein secreted by the parasitic helminth Strongyloides venezuelensis, on RAGE activity and immune responses. Our results demonstrated that venestatin bound to RAGE and downregulated the host immune response. Recombinant venestatin predominantly bound to the RAGE C1 domain in a Ca²⁺-dependent manner. Recombinant venestatin effectively alleviated RAGE-mediated inflammation, including footpad edema in mice, and pneumonia induced by an exogenous RAGE ligand. Infection experiments using S. venezuelensis larvae and venestatin silencing via RNA interference revealed that endogenous venestatin promoted larval migration from the skin to the lungs in a RAGE-dependent manner. Moreover, endogenous venestatin suppressed macrophage and neutrophil accumulation around larvae. Although the invasion of larvae upregulated the abundance of RAGE ligands in host skin tissues, mRNA expression levels of tumor necrosis factor-α, cyclooxygenase-2, endothelial adhesion molecules vascular cell adhesion protein-1, intracellular adhesion molecule-1, and E-selectin were suppressed by endogenous venestatin. Taken together, our results indicate that venestatin suppressed RAGE-mediated immune responses in host skin induced by helminthic infection, thereby promoting larval migration. The anti-inflammatory mechanism of venestatin may be targeted for the development of anthelminthics and immunosuppressive agents for the treatment of RAGE-mediated inflammatory diseases.

Parasitic helminths have evolved smart strategies to thrive in diverse hosts. For example, parasitic helminths secrete various immunomodulators in the host to establish successful tissue migration to their reproductive niche and chronic parasitism. Identification and functional analyses have revealed these immunomodulators may have potential therapeutic effects in the treatment of immune-related diseases. However, few immunomodulators from parasitic helminths have been identified and analyzed to date. In this study, we determined that venestatin, an EF-hand Ca²⁺-binding protein secreted by the parasitic nematode Strongyloides venezuelensis, bound to receptor for advanced glycation end products (RAGE), a host pro-inflammatory receptor, which downregulated RAGE-mediated inflammatory responses. S. venezuelensis larvae successfully migrated to their niche owing to the anti-inflammatory functions of venestatin. Venestatin could provide a novel therapeutic target for the treatment of RAGE-mediated inflammatory diseases, such as Alzheimer’s disease, rheumatoid arthritis, asthma, ulcerative colitis, and diabetes.

Toxic AGEs (TAGE) theory: a new concept for preventing the development of diseases related to lifestyle

BACKGROUND

The habitual excessive intake of sugar (i.e., sucrose and high-fructose corn syrup), which has been implicated in the onset of diabetes mellitus, induces excessive production of glyceraldehyde, a metabolite produced during glucose and fructose metabolism, in hepatocytes, neuronal cells, and cardiomyocytes.

MAIN TEXT

Toxic advanced glycation end-products (toxic AGEs, TAGE) are formed from reactions between glyceraldehyde and intracellular proteins, and their accumulation contributes to various cellular disorders. TAGE leakage from cells affects the surrounding cells and increases serum TAGE levels, promoting the onset and/or development of lifestyle-related diseases (LSRD). Therefore, serum TAGE levels have potential as a novel biomarker for predicting the onset and/or progression of LSRD, and minimizing the effects of TAGE might help to prevent the onset and/or progression of LSRD. Serum TAGE levels are closely related to LSRD associated with the excessive ingestion of sugar and/or dietary AGEs.

CONCLUSIONS

The TAGE theory is also expected to open new perspectives for research into numerous other diseases.

Receptor for Advanced Glycation End Products Acts as a Fuel to Colorectal Cancer Development

Receptor for advanced glycation end-products (RAGE) is a multiligand binding and single-pass transmembrane protein taken in diverse chronic inflammatory conditions. RAGE behaves as a pattern recognition receptor, which binds and is engaged in the cellular response to a variety of damage-associated molecular pattern molecules, as well as HMGB1, S100 proteins, and AGEs (advanced glycation end-products). The RAGE activation turns out to a formation of numerous intracellular signaling mechanisms, resulting in the progression and prolongation of colorectal carcinoma (CRC). The RAGE expression correlates well with the survival of colon cancer cells. RAGE is involved in the tumorigenesis, which increases and develops well in the stressed tumor microenvironment. In this review, we summarized downstream signaling cascade activated by the multiligand activation of RAGE, as well as RAGE ligands and their sources, clinical studies, and tumor markers related to RAGE particularly in the inflammatory tumor microenvironment in CRC. Furthermore, the role of RAGE signaling pathway in CRC patients with diabetic mellitus is investigated. RAGE has been reported to drive assorted signaling pathways, including activator protein 1, nuclear factor-κB, signal transducer and activator of transcription 3, SMAD family member 4 (Smad4), mitogen-activated protein kinases, mammalian target of rapamycin, phosphoinositide 3-kinases, reticular activating system, Wnt/β-catenin pathway, and Glycogen synthase kinase 3β, and even microRNAs.

Immunological evidence for in vivo production of novel advanced glycation end-products from 1,5-anhydro-D-fructose, a glycogen metabolite

The anhydrofructose pathway is an alternate pathway for glycogen degradation by α-1,4-glucan lyase. The sugar 1,5-anhydro-D-fructose (1,5-AF) acts as the central intermediate of this pathway, but its physiological role of in mammals is unclear. Glycation reactions forming advanced glycation end-products (AGEs) are important in the development of complications of diabetes mellitus. We hypothesized that 1,5-AF may contribute to cellular damage by forming 1,5-AF-derived AGEs (AF-AGEs) with intracellular proteins. To clarify the role of 1,5-AF in protein modification, we created a novel antibody targeting AF-AGEs. Serum albumin modified by AF-AGEs was prepared by incubating rabbit serum albumin (RSA) or bovine serum albumin (BSA) with 1,5-AF. After immunizing rabbits with AF-AGEs-RSA, affinity chromatography of anti-AF-AGE antiserum was performed on a Sepharose 4B column coupled with AF-AGEs-BSA or N-(carboxymethyl)/N-(carboxyethyl)lysine-BSA. A novel immunopurified anti-AF-AGE antibody was obtained and was characterized using a competitive enzyme-linked immunosorbent assay. Then an AF-AGEs assay was established using this immunopurified antibody. This assay was able to detect AF-AGEs in human and animal serum samples. Finally, intracellular accumulation of AF-AGEs was shown to be associated with damage to cultured hepatocytes (HepG2 cells). This is the first report about in vivo detection of AF-AGEs with a novel structural epitope.

Evaluation of Anti-glycation Activities of Phlorotannins in Human and Bovine Serum Albumin-glyceraldehyde Models

The anti-glycation activities of phlorotannins contained in the Japanese Lessoniaceae ( Ecklonia cava, Eck. kurome, Eck. stolonifera, Eisenia arborea, and Eis. bicyclis) were tested using serum albumin-glyceraldehyde (GA) models. In the human serum albumin (HSA)-GA model and the bovine serum albumin (BSA)-GA model, the concentrations of crude phlorotannins at 50% inhibition (IC50) of fluorescent advanced glycation end products (AGEs) formation was in the range of 0.48 to 0.70 mg/mL and 0.52 to 0.75 mg/mL, respectively. In tests using phloroglucinol and purified phlorotannins (eckol, fucofuroeckol A, phlorofucofuroeckol A, dieckol, and 8,8'-bieckol), dieckol had the highest inhibitory activity (IC50: 5.5 × 102 μM) against fluorescent AGEs formation in HSA-GA model and showed about 18 times inhibition compared with aminoguanidine hydrochloride of positive control. In the BSA albumin model, 8,8'-bieckol had about 27 times AGEs formation inhibitory activity (IC50: 6.2 × 102 μM) against aminoguanidine hydrochloride. In tests on GA scavenging activity, it was shown that compounds with phloroglucinol tetramer or higher had a scavenging rate of 70%, or more, with a reaction time of 120 minutes. These results suggest that among the phlorotannins, in particular the dimers of eckol (dieckol and 8,8'-bieckol), there are effective compounds for inhibiting the formation of AGEs derived from GA.

Glucose-derived AGEs enhance human gastric cancer metastasis through RAGE/ERK/Sp1/MMP2 cascade

Advanced glycation end products (AGEs) have been reported to take part in many cancer processes. Whether AGEs contribute to gastric cancer (GC) course and the underlying mechanism are still unclear. Here, glucose-derived AGEs are detected to be accumulated in tumor tissues and blood of patients with GC. As the receptor for AGEs, RAGE is highly expressed in cancer tissues, and closely associated with the depth of cancer invasion, lymph node metastasis and TNM stage. Both in vivo and in vitro treatment of AGEs accelerate the tumor invasion and metastasis, with upregualtion of RAGE, Specificity Protein 1 (Sp1), and MMP2 protein expression, as well as enhancement of MMP2 activity. Either RAGE-blocking antibody or Sp1-knockdown can partially block the AGEs-induced effects. Moreover, AGEs increased the phosphorylation of ERK, and reducing the phosphorylation level of ERK by MEK1/2 inhibitor decreased the expression of Sp1. These results indicate that accumulation of glucose-derived AGEs may act as one of potential risk factors for GC progression and promote the invasion and metastasis of gastric cancer partially through the activation of RAGE/ERK/Sp1/MMP2 pathway.

Comparative evaluation of three different ELISA assays and HPLC-ESI-ITMS/MS for the analysis of Nε-carboxymethyl lysine in food samples

N^ε-carboxymethyl-lysine (CML) is measured in food, but there is a controversy concerning the most convenient yet reliable method(s) for this task. This work compares three different ELISA assays and HPLC-ESI-ITMS/MS for the analysis of CML in several food items. The four methods showed the same decreasing order of CML concentration: beef, bacon>chicken > fish>dairy products>grain products>fruits/vegetables. HPLC-ESI-ITMS/MS results highly correlated with those obtained by ELISA performed with monoclonal CML-antibody (β=0.98, p<0.0001) whereas My Bio Source® kit results were not correlated with those provided by Lamider®. Small differences of CML concentrations in food items prepared by different culinary treatment were clearly distinguished by HPLC-ESI-ITMS/MS, but could not always be detected by ELISA. This work demonstrates a reasonable relationship between CM determined by ELISA and HPLC-ESI-ITMS/MS and therefore supports the implementation of ELISA in food CML/AGEs screening.

Toxic AGE (TAGE) Theory for the Pathophysiology of the Onset/Progression of NAFLD and ALD

Non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are among the most common causes of chronic liver diseases in the westernized world. NAFLD and ALD are frequently accompanied by extrahepatic complications, including hepatocellular carcinoma and cardiovascular diseases, which have a negative impact on patient survival. The chronic ingestion of an excessive daily diet containing sugar/high-fructose corn syrup increases the level of the fructose/glucose metabolite, glyceraldehyde (GA), while the chronic consumption of an excessive number of alcoholic beverages increases the level of the alcohol metabolite, acetaldehyde (AA) in the liver. GA and AA are known to react non-enzymatically with the ε- or α-amino groups of proteins, thereby generating advanced glycation end-products (AGEs, GA-AGEs, and AA-AGEs, respectively) in vivo. The interaction between GA-AGEs and the receptor for AGEs (RAGE) alters intracellular signaling, gene expression, and the release of pro-inflammatory molecules and also elicits the production of reactive oxygen species by human hepatocytes and hepatic stellate cells, all of which may contribute to the pathological changes associated with chronic liver diseases. We herein discuss the pathophysiological roles of GA-AGEs and AA-AGEs (toxic AGEs, TAGE) and a related novel theory for preventing the onset/progression of NAFLD and ALD.

Glucose-derived AGEs promote migration and invasion of colorectal cancer by up-regulating Sp1 expression

It is well established that the risk of colorectal cancer (CRC) is significantly increased in diabetic patients. As one of main forms of the advanced glycation end products (AGEs) that accumulate in vivo, glucose-derived AGEs play an important role in the pathogenesis of diabetic complications and may contribute to CRC progression. However, to date, both the contribution of glucose-derived AGEs to the course of CRC and the underlying mechanism are unclear. In the present study, the concentration of glucose-derived AGEs in the serum and tumor tissue of patients with CRC increased. A clinical data analysis demonstrated that the expression of the receptor for AGEs (RAGE), Specificity Protein 1 (Sp1), and matrix metallopeptidase -2 (MMP2) was significantly higher in cancerous tissues compared with non-tumor tissue in Chinese Han patients with CRC and that RAGE expression was closely associated with lymph node metastasis and TNM stage. Furthermore, in vivo and in vitro experiments showed that AGEs promoted invasion and migration of colorectal cancer, and the AGEs treatment increased the expression of RAGE, Sp1, and MMP2 in a dose-dependent manner. A RAGE blocking antibody and an Sp1-specific siRNA attenuated the AGE-induced effects. Moreover, the AGEs treatment increased the phosphorylation of ERK, and reducing the phosphorylation level of ERK by MEK1/2 inhibitor decreased the expression of Sp1. In conclusion, glucose-derived AGEs promote the invasion and metastasis of CRC partially through the RAGE/ERK/SP1/MMP2 cascade. These findings may provide an explanation for the poor prognoses of colorectal cancer in diabetic patients.

Serum Levels of Toxic AGEs (TAGE) May Be a Promising Novel Biomarker for the Onset/Progression of Lifestyle-Related Diseases

Advanced glycation end-products (AGEs) generated with aging or in the presence of diabetes mellitus, particularly AGEs derived from the glucose/fructose metabolism intermediate glyceraldehyde (Glycer-AGEs; termed toxic AGEs (TAGE)), were recently shown to be closely involved in the onset/progression of diabetic vascular complications via the receptor for AGEs (RAGE). TAGE also contribute to various diseases, such as cardiovascular disease; nonalcoholic steatohepatitis; cancer; Alzheimer's disease, and; infertility. This suggests the necessity of minimizing the influence of the TAGE-RAGE axis in order to prevent the onset/progression of lifestyle-related diseases (LSRD) and establish therapeutic strategies. Changes in serum TAGE levels are closely associated with LSRD related to overeating, a lack of exercise, or excessive ingestion of sugars/dietary AGEs. We also showed that serum TAGE levels, but not those of hemoglobin A1c, glucose-derived AGEs, or Nε-(carboxymethyl)lysine, have potential as a biomarker for predicting the progression of atherosclerosis and future cardiovascular events. We herein introduce the usefulness of serum TAGE levels as a biomarker for the prevention/early diagnosis of LSRD and the evaluation of the efficacy of treatments; we discuss whether dietary AGE/sugar intake restrictions reduce the generation/accumulation of TAGE, thereby preventing the onset/progression of LSRD.

Anti-glycation properties of the aqueous extract solutions of dried algae products and effect of lactic acid fermentation on the properties

The antioxidant and anti-glycation properties in aqueous extract solutions (AESs) of 11 dried algae products were investigated. AESs of brown algae Ecklonia kurome (kurome) and Ecklonia stolonifera (tsuruarame) showed a strong DPPH radical-scavenging capacity and Fe-reducing power with high total phenolic compound content. On the other hand, superoxide anion radical-scavenging capacities of Porphyra sp. (iwanori, red alga), sporophyll of Undaria pinnatifida (mekabu, brown alga), and Gelidiaceae sp. (tengusa, red alga) were also high. Anti-glycation activities in BSA-fructose and BSA-methylglyoxal glycation were also high in kurome, while iwanori showed high activity. Results of the BSA-fructose model agreed with those of superoxide anion radical-scavenging. On the other hand, those of the BSA-methylglyoxal model agreed with those of the phenolic content, DPPH radical-scavenging capacity, and Fe-reducing power. Anti-glycation activities of iwanori, U. pinnatifida (wakame), and mekabu in the BSA-fructose model were clearly increased by fermentation with Lactobacillus plantarum AN6.

Advanced Glycation End Products: A Molecular Target for Vascular Complications in Diabetes

A nonenzymatic reaction between reducing sugars and amino groups of proteins, lipids and nucleic acids contributes to the aging of macromolecules and subsequently alters their structural integrity and function. This process has been known to progress at an accelerated rate under hyperglycemic and/or oxidative stress conditions. Over a course of days to weeks, early glycation products undergo further reactions such as rearrangements and dehydration to become irreversibly cross-linked, fluorescent and senescent macroprotein derivatives termed advanced glycation end products (AGEs). There is a growing body of evidence indicating that interaction of AGEs with their receptor (RAGE) elicits oxidative stress generation and as a result evokes proliferative, inflammatory, thrombotic and fibrotic reactions in a variety of cells. This evidence supports AGEs' involvement in diabetes- and aging-associated disorders such as diabetic vascular complications, cancer, Alzheimer's disease and osteoporosis. Therefore, inhibition of AGE formation could be a novel molecular target for organ protection in diabetes. This report summarizes the pathophysiological role of AGEs in vascular complications in diabetes and discusses the potential clinical utility of measurement of serum levels of AGEs for evaluating organ damage in diabetes.

Generation and characterization of antibodies against arginine-derived advanced glycation endproducts

Although antibodies reagents have been widely employed for studying advanced glycation end-products (AGEs), these materials have been produced using complex mixtures of immunogens. Consequently, their epitope specificity remains unknown. Here we have generated the first antibodies capable of recognizing each of the three isomers of the methylglyoxal hydroimidazolones (MG-Hs) by using chemical synthesis to create homogenous immunogens. Furthermore, we have thoroughly characterized the epitope specificity of both our antibodies and that of two existing monoclonals by implementing a direct ELISA protocol employing synthetic MG-H antigens. Finally, we employed the reported anti-MG-H antibodies to the detection of MG-Hs in cellular systems using immunofluorescence microscopy. These studies have demonstrated that anti-MG-H1 and anti-MG-H3 staining is concentrated within the nucleus, while anti-MG-H2 affords only minimal signal. These observations are consistent with reported formation preferences for MG-Hs, and may suggest novel nuclear targets for non-enzymatic posttranslational modification. The antibody reagents reported herein, as well as the strategy employed for their creation, are likely to prove useful for the immunochemical study of AGEs in biological systems.

Assessment of the concentrations of various advanced glycation end-products in beverages and foods that are commonly consumed in Japan

Dietary consumption has recently been identified as a major environmental source of pro-inflammatory advanced glycation end-products (AGEs) in humans. It is disputed whether dietary AGEs represent a risk to human health. N^ε-(carboxymethyl)lysine (CML), a representative AGE compound found in food, has been suggested to make a significant contribution to circulating CML levels. However, recent studies have found that the dietary intake of AGEs is not associated with plasma CML concentrations. We have shown that the serum levels of glyceraldehyde-derived AGEs (Glycer-AGEs), but not hemoglobin A1c, glucose-derived AGEs (Glu-AGEs), or CML, could be used as biomarkers for predicting the progression of atherosclerosis and future cardiovascular events. We also detected the production/accumulation of Glycer-AGEs in normal rats administered Glu-AGE-rich beverages. Therefore, we assessed the concentrations of various AGEs in a total of 1,650 beverages and foods that are commonly consumed in Japan. The concentrations of four kinds of AGEs (Glu-AGEs, fructose-derived AGEs (Fru-AGEs), CML, and Glycer-AGEs) were measured with competitive enzyme-linked immunosorbent assays involving immunoaffinity-purified specific antibodies. The results of the latter assays indicated that Glu-AGEs and Fru-AGEs (especially Glu-AGEs), but not CML or Glycer-AGEs, are present at appreciable levels in beverages and foods that are commonly consumed by Japanese. Glu-AGEs, Fru-AGEs, CML, and Glycer-AGEs exhibited concentrations of ≥85%, 2–12%, <3%, and trace amounts in the examined beverages and ≥82%, 5–15%, <3%, and trace amounts in the tested foods, respectively. The results of the present study indicate that some lactic acid bacteria beverages, carbonated drinks, sugar-sweetened fruit drinks, sports drinks, mixed fruit juices, confectionery (snacks), dried fruits, cakes, cereals, and prepared foods contain markedly higher Glu-AGE levels than other classes of beverages and foods. We provide useful data on the concentrations of various AGEs, especially Glu-AGEs, in commonly consumed beverages and foods.

Longistatin in tick saliva blocks advanced glycation end-product receptor activation

Ticks are notorious hematophagous ectoparasites and vectors of many deadly pathogens. As an effective vector, ticks must break the strong barrier provided by the skin of their host during feeding, and their saliva contains a complex mixture of bioactive molecules that paralyze host defenses. The receptor for advanced glycation end products (RAGE) mediates immune cell activation at inflammatory sites and is constitutively and highly expressed in skin. Here, we demonstrate that longistatin secreted with saliva of the tick Haemaphysalis longicornis binds RAGE and modulates the host immune response. Similar to other RAGE ligands, longistatin specifically bound the RAGE V domain, and stimulated cultured HUVECs adhered to a longistatin-coated surface; this binding was dramatically inhibited by soluble RAGE or RAGE siRNA. Treatment of HUVECs with longistatin prior to stimulation substantially attenuated cellular oxidative stress and prevented NF-κB translocation, thereby reducing adhesion molecule and cytokine production. Recombinant longistatin inhibited RAGE-mediated migration of mouse peritoneal resident cells (mPRCs) and ameliorated inflammation in mouse footpad edema and pneumonia models. Importantly, tick bite upregulated RAGE ligands in skin, and endogenous longistatin attenuated RAGE-mediated inflammation during tick feeding. Our results suggest that longistatin is a RAGE antagonist that suppresses tick bite-associated inflammation, allowing successful blood-meal acquisition from hosts.

Post-ischemic inflammation regulates neural damage and protection

Post-ischemic inflammation is important in ischemic stroke pathology. However, details of the inflammation process, its resolution after stroke and its effect on pathology and neural damage have not been clarified. Brain swelling, which is often fatal in ischemic stroke patients, occurs at an early stage of stroke due to endothelial cell injury and severe inflammation by infiltrated mononuclear cells including macrophages, neutrophils, and lymphocytes. At early stage of inflammation, macrophages are activated by molecules released from necrotic cells [danger-associated molecular patterns (DAMPs)], and inflammatory cytokines and mediators that increase ischemic brain damage by disruption of the blood–brain barrier are released. After post-ischemic inflammation, macrophages function as scavengers of necrotic cell and brain tissue debris. Such macrophages are also involved in tissue repair and neural cell regeneration by producing tropic factors. The mechanisms of inflammation resolution and conversion of inflammation to neuroprotection are largely unknown. In this review, we summarize information accumulated recently about DAMP-induced inflammation and the neuroprotective effects of inflammatory cells, and discuss next generation strategies to treat ischemic stroke.

Amelioration of experimental autoimmune uveoretinitis by inhibition of glyceraldehyde-derived advanced glycation end-product formation

AGEs are permanently modified macromolecule derivatives that form through nonenzymatic glycation of amino groups of proteins. Glycer-AGEs are highly toxic and play an important role in the pathogenesis of chronic inflammatory diseases. However, the contribution of glycer-AGEs to the pathogenesis of uveitis is unclear. In this study, we measured serum levels of glycer-AGEs in 100 patients with endogenous uveitis (22 with HLA-B27-associated uveitis, 20 with VKH disease, 14 with Behçet's disease, and 44 with sarcoidosis) and 33 healthy volunteers. We then examined the effect of the AGE inhibitor in a mouse model of human endogenous uveitis (EAU) by continuous oral administration of pyridoxamine at 200 or 400 mg/kg/day. Regardless of the etiology, serum glycer-AGE levels were significantly higher in patients with uveitis than in healthy subjects. Treatment with 400 mg/kg pyridoxamine significantly reduced the clinical and histological severity of EAU and was accompanied by a significant decrease in serum and retinal glycer-AGE levels and suppression of translocation of NF-κB p65 into the nucleus of retinal cells. Serum glycer-AGE levels may therefore serve as a biomarker of human uveitis, as well as systemic inflammation, and may contribute to the progression of uveitis, including diabetic iritis, via the activation of NF-κB.

Advanced glycation end products increase carbohydrate responsive element binding protein expression and promote cancer cell proliferation

Diabetic patients have increased levels of advanced glycation end products (AGEs) and the role of AGEs in regulating cancer cell proliferation is unclear. Here, we found that treating colorectal and liver cancer cells with AGEs promoted cell proliferation. AGEs stimulated both the expression and activation of a key transcription factor called carbohydrate responsive element binding protein (ChREBP) which had been shown to promote glycolytic and anabolic activity as well as proliferation of colorectal and liver cancer cells. Using siRNAs or the antagonistic antibody for the receptor for advanced glycation end-products (RAGE) blocked AGEs-induced ChREBP expression or cell proliferation in cancer cells. Suppressing ChREBP expression severely impaired AGEs-induced cancer cell proliferation. Taken together, these results demonstrate that AGEs-RAGE signaling enhances cancer cell proliferation in which AGEs-mediated ChREBP induction plays an important role. These findings may provide new explanation for increased cancer progression in diabetic patients.

Non-enzymatic glycation and glycoxidation protein products in foods and diseases: an interconnected, complex scenario fully open to innovative proteomic studies

The Maillard reaction includes a complex network of processes affecting food and biopharmaceutical products; it also occurs in living organisms and has been strictly related to cell aging, to the pathogenesis of several (chronic) diseases, such as diabetes, uremia, cataract, liver cirrhosis and various neurodegenerative pathologies, as well as to peritoneal dialysis treatment. Dozens of compounds are involved in this process, among which a number of protein-adducted derivatives that have been simplistically defined as early, intermediate and advanced glycation end-products. In the last decade, various bottom-up proteomic approaches have been successfully used for the identification of glycation/glycoxidation protein targets as well as for the characterization of the corresponding adducts, including assignment of the modified amino acids. This article provides an updated overview of the mass spectrometry-based procedures developed to this purpose, emphasizing their partial limits with respect to current proteomic approaches for the analysis of other post-translational modifications. These limitations are mainly related to the concomitant sheer diversity, chemical complexity, and variable abundance of the various derivatives to be characterized. Some challenges to scientists are finally proposed for future proteomic investigations to solve main drawbacks in this research field.

Acetaldehyde-derived advanced glycation end-products promote alcoholic liver disease

Background

Chronic ingestion of ethanol increases acetaldehyde and leads to the production of acetaldehyde-derived advanced glycation end-products (AA-AGE). We evaluated the toxicity of AA-AGE on hepatocytes and studied the role of AA-AGE in the pathogenesis of alcoholic liver disease (ALD).

Methods

Rat hepatocyte cultures were treated with N-ethyllysine (NEL) or AA-AGE and the cell viability was evaluated using MTT assay. Male Wistar rats were fed with liquid diet containing 5% ethanol for 8 weeks following normal diet for another 12 weeks. A group of animals was sacrificed at 4th, 6th, and 8th week and the remaining animals at 12th, 14th, 16th, 18th, and 20th week. The liver sections were stained for AA-AGE and 4-hydroxy-2-nonenal (4-HNE). Liver biopsy obtained from ALD patients was also stained for AA-AGE and 4-HNE.

Results

Hepatocyte viability was significantly reduced in cultures treated with AA-AGE compared to NEL treated or control cultures. Severe fatty degeneration was observed during chronic administration of ethanol increasing from 4–8 weeks. The staining of AA-AGE and 4-HNE was correlated with the degree of ALD in both rat and human. In rats, hepatic fatty degeneration was completely disappeared and the staining for both AA-AGE and 4-HNE returned to normal at 12th week of abstinence. Staining for AA-AGE and 4-HNE was completely absent in normal human liver.

Conclusions

The data demonstrated that AA-AGE is toxic to hepatocytes, but not NEL. Chronic ethanol ingestion produces AA-AGE and reactive oxygen species that contribute to the pathogenesis of ALD. Abstinence of alcohol results in complete disappearance of both AA-AGE and 4-HNE along with fatty degeneration suggesting that AA-AGE plays a significant role in the pathogenesis of ALD.

Advanced glycation end products impair glucose-induced insulin secretion from rat pancreatic β-cells

BACKGROUND

Advanced glycation end products (AGEs) are derivative compounds generated from non-enzymatic glycosylation and oxidation. In comparison with glucose-derived AGEs (Glu-AGEs), glyceraldehyde-derived AGEs (Glycer-AGEs) have stronger toxicity to living systems. In this study, we compared the effects of Glu-AGE and Glycer-AGE on insulin secretion.

METHOD

Rat pancreatic islets were isolated by collagenase digestion and primary-cultured in the presence of 0.1 mg/ml bovine serum albumin (BSA) or 0.1 mg/ml Glu-AGE or Glycer-AGE-albumin. After 48 h of culture, we performed an insulin secretion test and identified the defects by a battery of rescue experiments [corrected]. Also, mRNA expression of genes associated with insulin secretion was measured.

RESULTS

Insulin secretion induced by a high glucose concentration was 164.1 ± 6.0, 124.4 ± 4.4 (P < 0.05) and 119.8 ± 7.1 (P < 0.05) μU/3 islets/h in the presence of BSA, Glu-AGE, and Glycer-AGE, respectively. Inhibition of insulin secretion by Glu-AGE or Glycer-AGE was rescued by a high extracellular potassium concentration, tolbutamide and α-ketoisocaproic acid, but not by glyceraldehyde, dihydroxacetone, methylpyruvate, glucagon-like peptide-1 and acetylcholine. Glu-AGE or Glycer-AGE reduced the expression of the malate dehydrogenase (Mdh1/2) gene, which plays a critical role in the nicotinamide adenine dinucleotide (NADH) shuttle.

CONCLUSION

Despite its reported cytotoxicity, the effects of Glycer-AGE on insulin secretion are similar to those of Glu-AGE.

Glucagon-like peptide-1 suppresses advanced glycation end product-induced monocyte chemoattractant protein-1 expression in mesangial cells by reducing advanced glycation end product receptor level

Advanced glycation end products (AGE) and receptor for AGE (RAGE) interaction elicits reactive oxygen species (ROS) generation and inflammatory reactions, thereby being involved in the development and progression of diabetic nephropathy. Recently, we, along with others, found that glucagon-like peptide-1 (GLP-1), one of the incretins and a gut hormone secreted from L cells in the intestine in response to food intake, could have anti-inflammatory and antithrombogenic properties in cultured endothelial cells. However, the effects of GLP-1 on renal mesangial cells are largely unknown. Therefore, to elucidate the role of GLP-1 in diabetic nephropathy, this study investigated whether and how GLP-1 blocked AGE-induced monocyte chemoattractant protein-1 expression in human cultured mesangial cells. Gene and protein expression was analyzed by quantitative real-time reverse transcription polymerase chain reactions, Western blots, and enzyme-linked immunosorbent assay. The ROS generation was measured with dihydroethidium staining. Glucagon-like peptide-1 receptor (GLP-1R) was expressed in mesangial cells. Glucagon-like peptide-1 inhibited RAGE gene expression in mesangial cells, which was blocked by small interfering RNAs raised against GLP-1R. Furthermore, GLP-1 decreased ROS generation and subsequently reduced monocyte chemoattractant protein-1 gene and protein expression in AGE-exposed mesangial cells. An analogue of cyclic adenosine monophosphate mimicked the effects of GLP-1 on mesangial cells. Our present study suggests that GLP-1 may directly act on mesangial cells via GLP-1R and that it could work as an anti-inflammatory agent against AGE by reducing RAGE expression via activation of cyclic adenosine monophosphate pathway.

Immunological detection of fructose-derived advanced glycation end-products

The advanced stage of non-enzymatic glycation (also called the Maillard reaction) that leads to the formation of advanced glycation end-products (AGEs) has an important function in the pathogenesis of angiopathy in diabetic patients. So far, most studies have been focused on the Maillard reaction by glucose. Although an elevated level of glucose had been thought to have a primary function in the Maillard reaction, on a molecular basis, glucose is among the least reactive sugars within biological systems. In addition to the extracellular formation of AGEs, rapid intracellular AGEs formation by various intracellular precursors (fructose, trioses, and dicarbonyl compounds) has recently attached attention. In this study, we considered the Maillard reaction with particular attention to the potential function of fructose. Fructose AGE-modified serum albumins were prepared by incubation of rabbit or bovine serum albumin (RSA or BSA) with D-fructose. After immunization of rabbits, fructose-derived AGEs (Fru-AGE) antiserum was subjected to affinity chromatography on a Sepharose 4B column coupled with Fru-AGE-BSA. Characterization of the novel anti-Fru-AGE antibody was performed with a competitive enzyme-linked immunosorbent assay and immunoblot analysis. The assay of Fru-AGE was established using the immunoaffinity-purified-specific antibody, and the presence of Fru-AGE in healthy and diabetic serum was shown (7.04+/-4.47 vs 29.13+/-18.08 U/ml). We also investigated whether high glucose treatment could stimulate intracellular Fru-AGE production in cultured pericytes, and we analyzed the amount of Fru-AGE contained in some common commercial beverages and condiments. It is possible that Fru-AGE formation by these endogenous and exogenous routes contributes importantly to the tissue pathology of diabetes and aging. This paper provides novel and clinically relevant information on the detection of Fru-AGE between fructose and proteins.

Involvement of TAGE-RAGE System in the Pathogenesis of Diabetic Retinopathy

Diabetic complications are a leading cause of acquired blindness, end-stage renal failure, and accelerated atherosclerosis, which are associated with the disabilities and high mortality rates seen in diabetic patients. Continuous hyperglycemia is involved in the pathogenesis of diabetic micro- and macrovascular complications via various metabolic pathways, and numerous hyperglycemia-induced metabolic and hemodynamic conditions exist, including increased generation of various types of advanced glycation end-products (AGEs). Recently, we demonstrated that glyceraldehyde-derived AGEs, the predominant structure of toxic AGEs (TAGE), play an important role in the pathogenesis of angiopathy in diabetic patients. Moreover, recent evidence suggests that the interaction of TAGE with the receptor for AGEs (RAGE) elicits oxidative stress generation in numerous types of cells, all of which may contribute to the pathological changes observed in diabetic complications. In this paper, we discuss the pathophysiological role of the TAGE-RAGE system in the development and progression of diabetic retinopathy.

Glucagon-like peptide-1 (GLP-1) inhibits advanced glycation end product (AGE)-induced up-regulation of VCAM-1 mRNA levels in endothelial cells by suppressing AGE receptor (RAGE) expression

Glucagon-like peptide-1 (GLP-1) is one of the incretins, a gut hormone secreted from L cells in the intestine in response to food intake. It has been proposed as a potential therapeutic target for the treatment of patients with type 2 diabetes. However, the direct effects of GLP-1 on vascular injury in diabetes are largely unknown. Since there is a growing body of evidence that advanced glycation end products (AGE) and their receptor RAGE axis plays an important role in vascular complications in diabetes, this study investigated whether and how GLP-1 blocked the deleterious effects of AGE on human umbilical vein endothelial cells (HUVEC). GLP-1 receptor (GLP-1R) was expressed in HUVEC. GLP-1 dose-dependently inhibited RAGE gene expression in HUVEC, which was blocked by small interfering RNAs raised against GLP-1R. An analogue of cyclic AMP also decreased RAGE mRNA level in HUVEC. Further, GLP-1 decreased reactive oxygen species generation and subsequently reduced vascular cell adhesion molecule-1 mRNA levels in AGE-exposed HUVEC. Our present study suggests that GLP-1 directly acts on HUVEC via GLP-1R and it could work as an anti-inflammatory agent against AGE by reducing RAGE expression via activation of cyclic AMP pathways.

Advanced glycation end products in senile diabetic and nondiabetic patients with cataract

BACKGROUND

Advanced glycation end products (AGE) have been reported to contribute to aging and cataract formation in the lens. In the present study, AGE immunoreactivity in human serum samples of normal senile subjects (n=31), senile diabetic patients without cataract (n=33), senile diabetic patients with cataract (n=30), senile nondiabetic with cataract (n=30), and normal young subjects (n=31) was investigated.

METHODS

A noncompetitive ELISA with polyclonal anti-AGE antibody was performed. The patients were selected on clinical grounds from Eye Ward, Jinnah Postgraduate Medical Centre, Karachi, Pakistan.

RESULTS

Fasting blood glucose, glycosylated hemoglobin, and serum fructosamine were estimated. Fasting blood glucose, HbA(1C), and serum fructosamine levels were significantly (P<.001) increased in senile diabetic patients with and without cataract as compared to nondiabetic senile patients with cataract and senile control subjects. However, the serum AGEs were found to be significantly (P<.001) increased in senile diabetic patients with cataract and senile nondiabetic patients with cataract followed by the diabetic patients without cataract as compared to senile control and young control subjects. In contrast to all four senile groups, the serum AGEs were significantly (P<.001) lower in young control subjects.

CONCLUSIONS

The AGE distribution in the senile groups corroborates the hypothesis that the advanced glycation process might have a role in cataract formation, which in diabetic patients occurs vigorously as compared with nondiabetic cataract patients.

Advanced glycation end products enhance the proliferation and activation of hepatic stellate cells

BACKGROUND

Advanced glycation end products (AGEs), final reaction products of protein with sugars, are known to contribute to diabetes-related complications. We have recently demonstrated high levels of serum AGEs in patients with nonalcoholic steatohepatitis (NASH). However, direct evidence for the participation of AGEs in hepatic inflammation and fibrosis has not been shown. To explore the pathogenesis of NASH, we examined the biological infl uence of AGEs on hepatic stellate cells (HSCs) in vitro.

METHODS

An established human HSC line, LI90, was exposed to a glyceraldehyde-derived-AGE (glycer-AGE), and the phenotypical changes of the LI90 cells were investigated. Intracellular formation of reactive oxygen species (ROS) was measured using a fl uorescent probe. Cell proliferation was examined by MTS assay. Fibrogenic marker gene expression was analyzed by quantitative real-time polymerase chain reaction. The production of monocyte chemoattractant protein 1 (MCP-1) was assessed by enzyme-linked immunosorbent assay.

RESULTS

The expression of AGE receptor was confirmed in LI90 cells at the mRNA and protein levels. In addition to increasing intracellular ROS generation, glycer-AGE upregulated fibrogenic genes such as those encoding for alpha-smooth muscle actin, transforming growth factor-beta1, and collagen type Ialpha2. The expression of MCP-1 mRNA in LI90 cells as well as its secretion into the culture medium was significantly increased in response to AGEs. These changes were attenuated by treatment with the antioxidant N-acetylcysteine.

CONCLUSIONS

These data indicate that AGEs induce ROS generation and intensify the proliferation and activation of HSCs, supporting the possibility that antioxidants may represent a promising treatment for prevention of the development of hepatic fibrosis in NASH.

Diagnostic utility of serum or cerebrospinal fluid levels of toxic advanced glycation end-products (TAGE) in early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are amyloid beta protein (A beta) and tau protein, respectively. Based on the disease pathology, numerous blood and cerebrospinal fluid (CSF) tests have been proposed for early detection of AD. However, there is no definite clinical method to determine in which patients with mild cognitive impairment will progress to AD with dementia. Therefore, to develop a novel promising biomarker for early diagnosis of AD is urgently needed. Several epidemiological studies have reported moderately increased risks for AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end-products (AGEs), senescent macroprotein derivatives, progress more rapidly. In addition, recent understanding of this process has confirmed that AGEs-their receptor (RAGE) interactions may play a role in the pathogenesis of neurodegenerative disorders including AD. In human AD brains, AGEs are distributed in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. In this paper, we discuss the pathophysiological role for toxic AGEs (TAGE) in AD. We further review here the possibility that serum or cerebrospinal fluid levels of TAGE could become a promising biomarker for early detection of AD.

Short-chain aldehyde-derived ligands for RAGE and their actions on endothelial cells

The formation and accumulation of advanced glycation endproducts (AGE) have been implicated in the development of diabetic vascular complications. Their biological responses are known to be mediated by the receptor for AGE (RAGE). Recently, AGE have been proposed to be derived not only from the classical Maillard reaction but also from other pathways of sugar autoxidation and metabolism. Here, we report the identification of glyceraldehydes (Gcer)- and glycolaldehyde (Gcol)-derived AGE as RAGE ligands and their presence in vivo. The apparent dissociation constants assessed by surface-plasmon resonance (SPR) analysis with purified human RAGE proteins were 360 nM for Gcer-AGE and 1.35 microM for Gcol-AGE. The radiolabeled-ligand binding assay with RAGE-expressing COS-7 cells revealed similar association kinetics. Competitive SPR assay with antibodies specific to the respective AGE fractions demonstrated abundant existence of both Gcer- and Gcol-AGE in RAGE affinity-purified proteins from human sera. The serum contents of Gcer- and Gcol-AGE in a diabetic patient were about twice as high as those in a healthy control. Functionally, Gcer- and Gcol-AGE upregulated the endothelial cell levels of mRNA for vascular endothelial growth factor (VEGF) and the secretion of its protein product into the culture media and DNA synthesis in a dose-dependent manner. Further, these endothelial responses were augmented by RAGE overexpression. The results suggest that RAGE engagement of Gcer- and Gcol-AGE may elicit angiogenesis through the induction of autocrine VEGF, thereby contributing to the development and progression of diabetic angiopathies.

De-N-glycosylation or G82S mutation of RAGE sensitizes its interaction with advanced glycation endproducts

Interactions between advanced glycation endproducts (AGE) and the receptor for AGE (RAGE) have been implicated in the development of diabetic vascular complications. RAGE has two N-glycosylation sites in and near the AGE-binding domain, and G82S mutation in the second N-glycosylation motif was recently reported in human. In this study, we examined whether de-N-glycosylation or G82S of RAGE affect its ability to bind AGE and cellular response to AGE. Recombinant wild-type, de-N-glycosylation and G82S RAGE proteins were produced in COS-7 cells, purified and assayed for ligand-binding abilities. De-N-glycosylation at N81 and G82S mutation decreased Kd for glycolaldehyde-derived AGE to three orders of magnitude lower levels compared with wild-type. AGE-induced upregulation of VEGF mRNA was significantly augmented in endothelial cell-derived ECV304 cells expressing de-N-glycosylated and G82S RAGE when compared with wild-type expressor. Exposure to low glucose resulted in the appearance of RAGE proteins of deglycosylated size in wild-type RAGE-expressing cells and significantly enhanced glycolaldehyde-derived AGE-induced VEGF mRNA expression. De-N-glycosylation or G82S mutation of RAGE increases affinity for AGE ligands, and may sensitize cells or conditions with it to AGE.

Elevated levels of serum advanced glycation end products in patients with non-alcoholic steatohepatitis

BACKGROUND AND AIM

Advanced glycation end products (AGE), senescent macroprotein derivatives formed at an accelerated rate in diabetes, play important roles in the pathogenesis of diabetic vascular complications. Recently, AGE have also been found to be involved in insulin resistance. Although non-alcoholic steatohepatitis (NASH) is generally considered a hepatic manifestation of insulin resistance, there are no reports showing the link of AGE to NASH. The aim of this study was to evaluate the clinical significance of AGE in patients with NASH.

METHODS

Glyceraldehyde-derived AGE levels were assayed from serum obtained from 106 patients: 66 with NASH, 10 with simple steatosis, and 30 controls.

RESULTS

Serum glyceraldehyde-derived AGE levels (U/mL) were significantly elevated in NASH patients (9.78 +/- 3.73) compared with simple steatosis (7.17 +/- 2.28, P = 0.018) or healthy controls (6.96 +/- 2.36, P = 0.003). Moreover, these were inversely correlated with adiponectin, an adipocytokine with insulin-sensitizing and anti-inflammatory properties. In addition, immunohistochemistry of glyceraldehyde-derived AGE showed intense staining in the livers of NASH patients.

CONCLUSION

The present data suggest that the sustained increase of glyceraldehyde-derived AGE could at least in part contribute to the pathogenesis of NASH. The serum glyceraldehyde-derived AGE level may be a useful biomarker for discriminating NASH from simple steatosis.

Diabetes mellitus exacerbates advanced glycation end product accumulation in the veins of end-stage renal failure patients

The excess accumulation of advanced glycation end products (AGEs) contributes to the chronic complications of type 2 diabetes mellitus (DM) and renal failure. Biopsy specimens (n = 184) of arterial (n = 92) and venous (n = 92) tissues were obtained (radial artery and cephalic vein) from end-stage renal disease (ESRD) patients with or without DM and normal healthy subjects (n = 12) requiring surgery (trauma patients). Immunohistochemical assessment of the blood vessels revealed the presence of pentosidine (AGE marker) in both veins and arteries in 72% of the ESRD patients. The percentage of arteries and veins that showed positive pentosidine staining in ESRD patients with type 2 DM alone was 100% and 92% respectively, in the non-diabetic ESRD patients it was < 70% (for arteries and veins), and in the ESRD patients with hypertension as an additional co-morbidity to type 2 DM it was 70% and 82%, respectively. The veins of ESRD patients with DM showed a strong (+++) positive staining and very strong (++++) positive staining was observed in the patients with DM and hypertension. Only mild (+) or moderate (++) pentosidine staining intensity was observed in the arteries of ESRD patients without or with comorbidities, respectively. The accumulation of AGE in the vein rather than the artery may be a better reflection of the extent of complications of ESRD.

Advanced glycation end-products downregulating intervertebral disc cell production of proteoglycans in vitro

Object

The authors sought to clarify the role, if any, of advanced glycation end-products (AGEs) in disc degeneration.

Methods

Intervertebral discs were analyzed for the presence of AGEs and of their receptor (RAGE) by immunohistochemical analysis. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to detect any RAGE gene expression, and real-time PCR was used to quantify messenger RNA (mRNA) levels of aggrecan and collagen types I and II in nucleus pulposus cells treated with AGEs. Aggrecan protein concentration was determined by enzyme-linked immunosorbent assay.

Immunohistochemical analysis revealed that AGEs and RAGE were localized in the nucleus pulposus of the intervertebral disc. Advanced glycation end-products were found to significantly suppress the expression of aggrecan at both mRNA and protein levels in a dose- and time-dependent manner. The levels of collagen types I and II remained unchanged after treatments with AGEs.

Conclusions

These results suggest that the accumulation of AGEs and their interaction with their receptor in the nucleus pulposus might result in the downregulation of aggrecan production responsible for disc degeneration.

RAGE control of diabetic nephropathy in a mouse model: effects of RAGE gene disruption and administration of low-molecular weight heparin

Diabetic nephropathy is a major microvascular complication in long-standing diabetic patients who eventually undergo renal dialysis or transplantation. To prevent development of this disease and to improve advanced kidney injury, effective therapies directed toward the key molecular target are required. In this study, we examined whether inhibition of the receptor for advanced glycation end products (RAGE) could attenuate changes in the diabetic kidney. Here, we show that inactivation of the RAGE gene in a mouse model of diabetic nephropathy results in significant suppression of kidney changes, including kidney enlargement, increased glomerular cell number, mesangial expansion, advanced glomerulosclerosis, increased albuminuria, and increased serum creatinine compared with wild-type diabetic mice. The degree of kidney injury was proportional to RAGE gene dosage. Furthermore, we show that low-molecular weight heparin (LMWH) can bind RAGE at a mean equilibrium dissociation constant (K(d)) value of approximately 17 nmol/l and act as an antagonist to RAGE. LMWH treatment of mice significantly prevented albuminuria and increased glomerular cell number, mesangial expansion, and glomerulosclerosis in a dose-dependent manner; it also significantly improved the indexes of advanced-stage diabetic nephropathy. This study provides insight into the pathological role of RAGE in both early- and advanced-phase diabetic nephropathy and suggests that RAGE antagonists will be a useful remedy in the treatment of diabetic nephropathy.

Development of an ELISA for esRAGE and its application to type 1 diabetic patients

We recently identified a naturally occurring soluble form of RAGE (the receptor for advanced glycation endproducts, receptor for AGE) in cultured human vascular cells, and named it endogenous secretory RAGE (esRAGE). esRAGE is generated by alternative RNA splicing and is able to capture AGE, and exerts protection against AGE-induced endothelial cell injury. In the present study, the presence of esRAGE in human circulation was demonstrated for the first time, and a highly sensitive and specific sandwich ELISA system for esRAGE was developed to see whether esRAGE could be related to an individual resistance to the development of diabetic vascular complications. Sera from 47 type 1 diabetic subjects without clinical nephropathy (urinary albumin excretion <300mg/g creatinine) and 55 healthy controls were analyzed by the ELISA. Circulating esRAGE concentrations in diabetic patients with simple and proliferative retinopathy (0.09+/-0.02ng/mL, n=16 and 0.08+/-0.02ng/mL, n=8, respectively) were significantly lower than in those without retinopathy (0.13+/-0.06ng/mL, n=23). The results indicate that esRAGE can be a useful biomarker to indicate individual variations in susceptibility to diabetic retinopathy.

Toxic advanced glycation end products (TAGE) theory in Alzheimer's disease

Several epidemiological studies have reported moderately increased risks of Alzheimer's disease (AD) in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress more rapidly. Recent understanding of this process has confirmed that interactions between AGEs and their receptor (RAGE) may play a role in the pathogenesis of diabetic complications and AD. The authors have recently found that glyceraldehyde-derived AGEs (AGE-2), which is predominantly the structure of toxic AGEs (TAGE), show significant toxicity on cortical neuronal cells and that the neurotoxic effect of diabetic serum is completely blocked by neutralizing antibody against the AGE-2 epitope. Moreover, in human AD brains, AGE-2 is distributed in the cytosol of neurons in the hippocampus and parahippocampal gyrus. These results suggest that TAGE is involved in the pathogenesis of AD as well as other age-related diseases. In this review, the authors discuss the molecular mechanisms of AD, especially focusing on TAGE-RAGE system.

Crotonaldehyde accumulates in glial cells of Alzheimer's disease brain

Several studies have documented the involvement of oxidative stress represented by lipid peroxidation in the pathogenesis of Alzheimer's disease (AD). To test whether the highly reactive carbonyl crotonaldehyde (CRA), generated during lipid peroxidation, is involved in AD, we performed an immunohistochemical analysis in AD and age-matched control hippocampi using a specific antibody against protein-bound CRA (P-CRA). In the AD cases, P-CRA immunoreactivity was preferentially localized in reactive astrocytes and microglia around senile plaques (SPs) and those present in the neuropil, while it was weakly detectable in neurons and neurofibrillary tangles. P-CRA immunoreactivity was also localized in all portions of diffuse SPs and the dystrophic neurites of neuritic and classical SPs, but was undetectable in amyloid cores. Age-matched controls showed P-CRA immunoreactivity only very weakly in neurons. In contrast to P-CRA, immunoreactivities for protein-bound acrolein and 4-hydroxy-2-nonenal were mainly localized to neurons and rarely seen in glial cells. Our results suggest that increased oxidative stress and CRA formation in glial cells is implicated in the disease processes of AD.

Cytotoxicity of acetaldehyde-derived advanced glycation end-products (AA-AGE) in alcoholic-induced neuronal degeneration

BACKGROUND

The Maillard reaction that leads to the formation of advanced glycation end-products (AGEs) plays an important role in the pathogenesis of angiopathy in diabetic patients, in aging and in neurodegenerative processes. We hypothesize that acetaldehyde (AA), one of the main metabolites of alcohol, may be involved in alcohol-induced neurotoxicity in vivo by formation of AA-derived AGEs (AA-AGE) with brain proteins.

METHODS

AA-AGE-bovine serum albumin (BSA) and AA-AGE-rabbit serum albumin (RSA) were prepared as described previously. Antibody specific for AA-AGE was isolated from rabbit antiserum by affinity chromatography. Primary cortical neuronal cell cultures were prepared as described previously.

RESULTS

Incubation of cortical neurons with AA-AGE produced a dose-dependent increase in neuronal cell-death, and the neurotoxicity of AA-AGE was neutralized by the addition of an anti-AA-AGE specific antibody, but not by anti-N-ethyllysine (NEL) antibody. The AA-AGE epitope was detected in human brain of alcoholism.

CONCLUSIONS

We propose that the structural epitope AA-AGE is an important toxic moiety for neuronal cells in alcoholism.

Characterization of advanced glycation end products for biochemical studies: side chain modifications and fluorescence characteristics

Advanced glycation end products (AGEs) are known to be involved in the pathogenesis of several diseases and therefore effects of AGEs on cells are the objective of numerous investigations. Since AGEs used in biochemical studies are usually not chemically characterized, comparison of data is difficult if not impossible. To find a suitable characterization protocol, human serum albumin was reacted with different concentrations of glucose, methyl glyoxal, and glyoxylic acid. The obtained AGEs were characterized with respect to the extent of side chain modifications (lysine and arginine), the carboxymethyl lysine and carbonyl content, and the fibrillar state. Additionally, their fluorescence and absorbance characteristics were extensively studied. Although we found significant differences in the degree of modification and in AGE-specific fluorescence when using different modifiers, the results provide important information and allow comparing AGEs derived from different modifier concentrations. The results also suggest strong conformational changes within the modified proteins. In the present paper we propose a set of parameters that is sufficient to partially characterize AGEs used for biochemical studies.