Association of RAGE gene Gly82Ser polymorphism with coronary artery disease and ischemic stroke: A systematic review and meta-analysis

BACKGROUND

The receptor for advanced glycosylation end products (RAGE) has been widely linked to diabetic atherosclerosis, but its effects on coronary artery disease (CAD) and ischemic stroke (IS) remain controversial. The Gly82Ser polymorphism is located in the ligand-binding V domain of RAGE, suggesting a possible influence of this variant on RAGE function. The aim of the present study is to clarify the association between the RAGE Gly82Ser polymorphism and susceptibility to CAD and IS.

METHODS

Eligible studies were identified through a comprehensive literature search. Odds ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the association of Gly82Ser polymorphism with CAD and IS risk. Fixed- or random-effects model was used depending on the heterogeneity between studies. A funnel plot and Egger linear regression test were applied to assess publication bias. We also performed subgroup analyses to investigate potential sources of heterogeneity.

RESULTS

A total of 16 eligible articles containing 18 studies were analyzed. The pooled analysis indicated that the Gly82Ser polymorphism significantly increased CAD risk in recessive and homozygous genetic models (SS vs GS + GG: OR = 1.34, 95% CI = 1.09-1.64; SS vs GG: OR = 1.38, 95% CI = 1.12-1.71). A significant association between the Gly82Ser polymorphism and IS risk was observed in all tested models except the heterozygous genetic model (GS + SS vs GG: OR = 1.20, 95% CI = 1.04-1.38; SS vs GS + GG: OR = 2.20, 95% CI = 1.74-2.78; SS vs GG: OR = 2.23, 95% CI = 1.72-2.91; S vs G: OR = 1.32, 95% CI = 1.05-1.65). Subgroup analysis suggested an association between CAD and IS risk and the Gly82Ser polymorphism in the Chinese population, but not in the non-Chinese population.

CONCLUSIONS

The current meta-analysis suggests that the RAGE Gly82Ser polymorphism is associated with an increased risk of CAD and IS, especially in the Chinese population. However, better-designed studies with larger sample sizes are needed to validate the results.

Plasma Levels of Pentosidine, Carboxymethyl-Lysine, Soluble Receptor for Advanced Glycation End Products, and Metabolic Syndrome: The Metformin Effect

Metabolic syndrome (MetS) is considered one of the most important public health problems. Several and controversial studies showed that the role of advanced glycation end products (AGEs) and their receptor in the development of metabolic syndrome and therapeutic pathways is still unsolved. We have investigated whether plasma pentosidine, carboxymethyl-lysine (CML), and soluble receptor for advanced glycation end products (sRAGE) levels were increased in patients with MetS and the effect of metformin in plasma levels of pentosidine, CML, and sRAGE. 80 control subjects and 86 patients were included in this study. Pentosidine, CML, and sRAGE were measured in plasma by enzyme-linked immunosorbent assay (ELISA). Plasma pentosidine, CML, and sRAGE levels were significantly increased in patients compared to control subjects (P < 0.001, P < 0.001, and P = 0.014, resp.). Plasma levels of pentosidine were significantly decreased in patients who received metformin compared to untreated patients (P = 0.01). However, there was no significant difference between patients treated with metformin and untreated patients in plasma CML levels. Plasma levels of sRAGE were significantly increased in patients who received metformin and ACE inhibitors (P < 0.001 and P = 0.002, resp.). However, in a multiple stepwise regression analysis, pentosidine, sRAGE, and drugs treatments were not independently associated. Patients with metabolic syndrome showed increased levels of AGEs such as pentosidine and CML. Metformin treatment showed a decreased level of pentosidine but not of CML. Therapeutic pathways of AGEs development should be taken into account and further experimental and in vitro studies merit for advanced research.

Coronary microvascular dysfunction after long-term diabetes and hypercholesterolemia

Coronary microvascular dysfunction (CMD) has been proposed as an important component of diabetes mellitus (DM)- and hypercholesterolemia-associated coronary artery disease (CAD). Previously we observed that 2.5 mo of DM and high-fat diet (HFD) in swine blunted bradykinin (BK)-induced vasodilation and attenuated endothelin (ET)-1-mediated vasoconstriction. Here we studied the progression of CMD after 15 mo in the same animal model of CAD. Ten male swine were fed a HFD in the absence (HFD, n = 5) or presence of streptozotocin-induced DM (DM + HFD, n = 5). Responses of small (∼300-μm-diameter) coronary arteries to BK, ET-1, and the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine were examined in vitro and compared with those of healthy (Normal) swine (n = 12). Blood glucose was elevated in DM + HFD (17.6 ± 4.5 mmol/l) compared with HFD (5.1 ± 0.4 mmol/l) and Normal (5.8 ± 0.6 mmol/l) swine, while cholesterol was markedly elevated in DM + HFD (16.8 ± 1.7 mmol/l) and HFD (18.1 ± 2.6 mmol/l) compared with Normal (2.1 ± 0.2 mmol/l) swine (all P < 0.05). Small coronary arteries showed early atherosclerotic plaques in HFD and DM + HFD swine. Surprisingly, DM + HFD and HFD swine maintained BK responsiveness compared with Normal swine due to an increase in NO availability relative to endothelium-derived hyperpolarizing factors. However, ET-1 responsiveness was greater in HFD and DM + HFD than Normal swine (both P < 0.05), resulting mainly from ET_B receptor-mediated vasoconstriction. Moreover, the calculated vascular stiffness coefficient was higher in DM + HFD and HFD than Normal swine (both P < 0.05). In conclusion, 15 mo of DM + HFD, as well as HFD alone, resulted in CMD. Although the overall vasodilation to BK was unperturbed, the relative contributions of NO and endothelium-derived hyperpolarizing factor pathways were altered. Moreover, the vasoconstrictor response to ET-1 was enhanced, involving the ET_B receptors. In conjunction with our previous study, these findings highlight the time dependence of the phenotype of CMD.

Advanced glycation end products impair the functions of saphenous vein but not thoracic artery smooth muscle cells through RAGE/MAPK signalling pathway in diabetes

Saphenous vein (SV) and internal thoracic artery (ITA) are commonly used bypass conduits. However, graft failure occurs in SV rather than in ITA, especially in diabetes (DM). The mechanism for this difference has not been fully understood. Accumulation of advanced glycation end products (AGEs) and activation of AGEs receptor (RAGE) could accelerate smooth muscle cells (SMC) proliferation in DM, we thus asked whether AGEs-RAGE could mediate the differences between SMC from SV (SMCV ) and from ITA (SMCA ). Twenty-five patients with DM and other 25 patients without DM were enclosed in DM and control group, respectively. AGEs (100 μg/ml) were added to cultured SMCA and SMCV obtained at coronary artery bypass graft (CABG) and proliferative rates were determined. Transcript expression, phosphorylation or protein expression levels of MAP kinase family (ERK, p38 and JNK), matrix metalloproteinases (MMP)-2 and MMP-9 were analysed by real-time PCR, Western-blot or immunofluorescence staining, respectively. Compared with paired SMCA , SMCV showed significantly increased proliferation rate, MAP kinase family phosphorylation, and MMP-2/9 expression in both groups, especially in DM group. The responses of SMCV induced by AGEs were significantly larger in DM than in control group, which could be suppressed by inhibition of RAGE and ERK. However, all the cellular events of SMCV were not found in paired SMCA . This study suggests that AGEs-RAGE could induce the proliferation of SMCV but not SMCA via MAP kinase pathway in DM. It is the intrinsic 'inactive' tendency of SMCA that contributes to the different rates of graft disease between SV and ITA after CABG.

Synthesis and Evaluation of [(18)F]RAGER: A First Generation Small-Molecule PET Radioligand Targeting the Receptor for Advanced Glycation Endproducts

The receptor for advanced glycation endproducts (RAGE) is a 35 kDa transmembrane receptor that belongs to the immunoglobulin superfamily of cell surface molecules. Its role in Alzheimer's disease (AD) is complex, but it is thought to mediate influx of circulating amyloid-β into the brain as well as amplify Aβ-induced pathogenic responses. RAGE is therefore of considerable interest as both a diagnostic and a therapeutic target in AD. Herein we report the synthesis and preliminary preclinical evaluation of [(18)F]RAGER, the first small molecule PET radiotracer for RAGE (Kd = 15 nM). Docking studies proposed a likely binding interaction between RAGE and RAGER, [(18)F]RAGER autoradiography showed colocalization with RAGE identified by immunohistochemistry in AD brain samples, and [(18)F]RAGER microPET confirmed CNS penetration and increased uptake in areas of the brain known to express RAGE. This first generation radiotracer represents initial proof-of-concept and a promising first step toward quantifying CNS RAGE activity using PET. However, there were high levels of nonspecific [(18)F]RAGER binding in vitro, likely due to its high log P (experimental log P = 3.5), and rapid metabolism of [(18)F]RAGER in rat liver microsome studies. Therefore, development of second generation ligands with improved imaging properties would be advantageous prior to anticipated translation into clinical PET imaging studies.

A method to produce fully characterized ubiquitin covalently modified by 4-hydroxy-nonenal, glyoxal, methylglyoxal, and malondialdehyde

Reactive carbonyl species (RCS) and the corresponding protein adducts (advanced glycoxidation or lipoxidation end products, i.e. AGEs and ALEs) are now widely studied from different points of view, since they can be considered as biomarkers, pathogenic factors, toxic mediators and drug targets. One of the main limits of the research in this field is the lack of standardized and fully characterized AGEs and ALEs to be used for biological, toxicological, and analytical studies. In this work, we set up a procedure to prepare and fully characterize a set of AGEs and ALEs by incubating ubiquitin - a model protein selected as target for carbonylation - with four different RCS: 4-hydroxy-trans-2-nonenal (HNE), methylglyoxal (MGO), glyoxal (GO), and malondialdehyde (MDA). After 24 h of incubation, the extent of protein carbonylation was estimated using a recently developed quantitative strategy based on high-resolution mass spectrometry. The resulting AGEs and ALEs were fully characterized by both intact protein and bottom-up analyses in terms of: stoichiometry of the total amount of modified protein, elucidation of the structure of the RCS-deriving adducts, and localization of the RCS-modified amino acids. Each RCS exhibited different reactivity toward ubiquitin, as detected by quantifying the extent of protein modification. The order of reactivity was MGO > GO > HNE > MDA. A variety of reaction products was identified and mapped on lysine, arginine, and histidine residues of the protein. In summary, a highly standardized and reproducible method to prepare fully characterized AGEs/ALEs is here presented.

Skin Autofluorescence in Systemic Sclerosis Is Related to the Disease and Vascular Damage: A Cross-Sectional Analytic Study of Comparative Groups

Skin autofluorescence (AF), a relatively simple and time saving procedure, measures the accumulation of advanced glycation end (AGE) products. The importance in autoimmune rheumatic diseases, particularly, systemic sclerosis (SSc), has not been evaluated yet. The aim of our study was to examine the skin AF in the context of SSc patients and to analyse the relations between skin AF and other surrogate measures of atherosclerosis. Forty-seven patients with SSc and 47 healthy volunteers were included in this study as controls. Patients and controls underwent common carotid artery wall assessment, arterial stiffness and wave reflection measurements, laser Doppler measurements of capillary flow, assessment of endothelial function by brachial ultrasound, peripheral arterial tonometry, and AGE measurement by skin AF. Wall properties of the common carotid arteries and wave reflection measurements were not affected in these study patients compared to controls while measures reflecting small capillary flow were altered. The accumulation of AGE products measured by skin AF was more prominent in SSc patients than in healthy controls. AGE products' score was significantly associated with carotid radial pulse wave velocity, intima media/carotid artery diameter ratio, capillary flow percentage change during occlusion, and the disease itself in a multivariate linear analysis model.

Ameliorating Effect of Akebia quinata Fruit Extracts on Skin Aging Induced by Advanced Glycation End Products

The accumulation of free radicals and advanced glycation end products (AGEs) in the skin plays a very important role in skin aging. Both are known to interact with each other. Therefore, natural compounds or extracts that possess both antioxidant and antiglycation activities might have great antiageing potential. Akebia quinata fruit extract (AQFE) has been used to treat urinary tract inflammatory disease in traditional Korean and Chinese medicines. In the present study, AQFE was demonstrated to possess antioxidant and antiglycation activity. AQFE protects human dermal fibroblasts (HDFs) from oxidative stress and inhibits cellular senescence induced by oxidative stress. We also found that AQFE inhibits glycation reaction between BSA and glucose. The antiglycation activity of AQFE was dose-dependent. In addition, the antiglycation activity of AQFE was confirmed in a human skin explant model. AQFE reduced CML expression and stimulated fibrillin-1 expression in comparison to the methyglyoxal treatment. In addition, the possibility of the extract as an anti-skin aging agent has also been clinically validated. Our analysis of the crow’s feet wrinkle showed that there was a decrease in the depth of deep furrows in RI treated with AQFE cream over an eight-week period. The overall results suggest that AQFE may work as an anti-skin aging agent by preventing oxidative stress and other complications associated with AGEs formation.

Musculoskeletal manifestations of diabetes mellitus

The prevalence of Type 1 and Type 2 diabetes are increasing significantly worldwide. Whilst vascular complications of diabetes are well recognized, and account for principle mortality and morbidity from the condition, musculoskeletal manifestations of diabetes are common and whilst not life threatening, are an important cause of morbidity, pain and disability. Joints affected by diabetes include peripheral joints and the axial skeleton. Charcot neuroarthropathy is an important cause of deformity and amputation associated with peripheral neuropathy. A number of fibrosing conditions of the hands and shoulder are recognized, including carpal tunnel syndrome, adhesive capsulitis, tenosynovitis and limited joint mobility. People with diabetes are more prone to gout and osteoporosis. Management of these conditions requires early recognition and close liaison between diabetes and rheumatology specialists.

Receptor for advanced glycation end products (RAGE) gene polymorphism and cardiovascular disease in end-stage renal disease patients

BACKGROUND/OBJECTIVES

Receptor for advanced glycation end products (RAGE) contributes to the pathogenesis of vascular and inflammatory diseases. We investigated whether the functional polymorphism in the promoter region of the RAGE gene (-374 T/A) influences development of cardiovascular disease in the end-stage renal disease (ESRD) patients.

METHODS

The cohorts of 1866 ESRD patients and 1143 healthy subjects were genotyped by polymerase chain reaction (PCR) for the RAGE variant rs1800624.

RESULTS

The genotype and allele frequencies did not differ significantly between ESRD patients and controls. There was no significant difference in the genotype distribution when patients with CVD were compared to those without it (p for A allele = 0.62). After stratifying CVD patients according to CVD clinical phenotype, the ESRD patients with stroke had a lower frequency of A allele than patients without CVD (0.12 vs. 0.21, p = 0.027). To confirm this finding, we genotyped 163 patients with ischemic stroke but without renal disease. In this group, the AA/TA genotypes were also significantly associated with lower risk of stroke (OR 0.46, p = 0.0002).

CONCLUSION

Our data suggest that the presence of the A allele of -374 T/A polymorphism in the RAGE gene has a protective effect against stroke.

Contribution of dietary advanced glycation end products (AGE) to circulating AGE: role of dietary fat

The purpose of this pilot study was to determine whether macronutrient content (low-fat v. high-fat diet) influences an indicator of advanced glycation end products (AGE), N(ε) carboxymethyl-lysine (CML), in the context of a 1-d, high-AGE diet. The effect of the diets on inflammatory markers was also assessed. A total of nineteen overweight and obese adults (nine men and ten women) without known disease were recruited to participate in a crossover challenge of a high-fat, high-AGE (HFHA) and low-fat, high-AGE (LFHA) diet. In each phase patients had fasting blood drawn, followed by consumption of a high-fat or low-fat breakfast test meal, then three postprandial blood draws at 1, 2 and 3 h after consuming the test meal. After consuming high-AGE meals for the remainder of the day, participants returned the next day for a follow-up analysis. A different pattern in the 3-h post-meal CML and soluble receptor for AGE response to the two diets was observed (P=0·01 and 0·05, respectively). No change in serum CML was observed following consumption of a LFHA breakfast (535 (25th-75th percentile 451-790) to 495 (25th-75th percentile 391-682) ng/ml; P=0·36), whereas a rise in CML occurred after the HFHA breakfast (463 (25th-75th percentile 428-664) to 578 (25th-75th percentile 474-865) ng/ml; P=0·05). High sensitivity C-reactive protein and high molecular weight adiponectin were not affected by either diet. These findings suggest that dietary CML may not be as important in influencing serum CML as other dietary factors. In addition, acute exposure to dietary CML may not influence inflammation in adults without diabetes or kidney disease. This is contrary to previous findings.

Serum Level of Soluble Receptor for Advanced Glycation End Products Is Associated with A Disintegrin And Metalloproteinase 10 in Type 1 Diabetes

BACKGROUND

The receptor for advanced glycation end products (RAGE) is involved in the pathogenesis of diabetic complications, and soluble forms of the receptor (sRAGE) can counteract the detrimental action of the full-length receptor by acting as decoy. Soluble RAGE is produced by alternative splicing [endogenous secretory RAGE (esRAGE)] and/or by proteolytic cleavage of the membrane-bound receptor. We have investigated the role of A Disintegrin And Metalloproteinase 10 (ADAM10) in the ectodomain shedding of RAGE.

METHODS

Constitutive and insulin-induced shedding of RAGE in THP-1 macrophages by ADAM10 was evaluated using an ADAM10-specific metalloproteinase inhibitor. Serum ADAM10 level was measured in type 1 diabetes and control subjects, and the association with serum soluble RAGE was determined. Serum total sRAGE and esRAGE were assayed by ELISA and the difference between total sRAGE and esRAGE gave an estimated measure of soluble RAGE formed by cleavage (cRAGE).

RESULTS

RAGE shedding (constitutive and insulin-induced) was significantly reduced after inhibition of ADAM10 in macrophages, and insulin stimulated ADAM10 expression and activity. Diabetic subjects have higher serum total sRAGE and esRAGE (p<0.01) than controls, and serum ADAM10 was also increased (p<0.01). Serum ADAM10 correlated with serum cRAGE in type 1 diabetes (r = 0.40, p<0.01) and in controls (r = 0.31. p<0.01) but no correlations were seen with esRAGE. The association remained significant after adjusting for age, gender, BMI, smoking status and HbA1c.

CONCLUSION

Our data suggested that ADAM10 contributed to the shedding of RAGE. Serum ADAM10 level was increased in type 1 diabetes and was a significant determinant of circulating cRAGE.

Brain-peripheral cell crosstalk in white matter damage and repair

White matter damage is an important part of cerebrovascular disease and may be a significant contributing factor in vascular mechanisms of cognitive dysfunction and dementia. It is well accepted that white matter homeostasis involves multifactorial interactions between all cells in the axon-glia-vascular unit. But more recently, it has been proposed that beyond cell-cell signaling within the brain per se, dynamic crosstalk between brain and systemic responses such as circulating immune cells and stem/progenitor cells may also be important. In this review, we explore the hypothesis that peripheral cells contribute to damage and repair after white matter damage. Depending on timing, phenotype and context, monocyte/macrophage can possess both detrimental and beneficial effects on oligodendrogenesis and white matter remodeling. Endothelial progenitor cells (EPCs) can be activated after CNS injury and the response may also influence white matter repair process. These emerging findings support the hypothesis that peripheral-derived cells can be both detrimental or beneficial in white matter pathology in cerebrovascular disease. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia, edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Human retinal pigment epithelial cell proliferation by the combined stimulation of hydroquinone and advanced glycation end-products via up-regulation of VEGF gene

Although recent research showed that advanced glycation endproduct (AGE) and hydroquinone (HQ) are related to the pathogenesis of age-related macular degeneration (AMD), the mechanism how AGE and HQ induce or accelerate AMD remains elusive. In the present study, we examined the effects of AGE and HQ on changes of human retinal pigment epithelial (RPE) cell numbers and found that the viable cell numbers were markedly reduced by HQ by apoptosis and that AGE prevented the decreases of HQ-treated cell numbers by increased replicative DNA synthesis of RPE cells without changing apoptosis. Real-time RT-PCR revealed that vascular endothelial growth factor (VEGF)-A mRNA was increased by HQ treatment and the addition of HQ+AGE resulted in a further increment. The increase of VEGF secretion was confirmed by ELISA, and inhibition of VEGF signaling by chemical inhibitors and small interfering RNA decreased the HQ+AGE-induced increases in RPE cell numbers. The deletion analysis demonstrated that -102 to -43 region was essential for the VEGF-A promoter activation. Site-directed mutaions of specificity protein 1 (SP1) binding sequences in the VEGF-A promoter and RNA interference of SP1 revealed that SP1 is an essential transcription factor for VEGF-A expression. These results indicate that HQ induces RPE cell apoptosis, leading to dry AMD, and suggest that AGE stimulation in addition to HQ enhances VEGF-A transcription via the AGE-receptor for AGE pathway in HQ-damaged cells. As a result, the secreted VEGF acts as an autocrine/paracrine growth factor for RPE and/or adjacent vascular cells, causing wet AMD.

Small interfering RNA targeting receptor for advanced glycation end products suppresses the generation of proinflammatory cytokines

The aim of the present study was to investigate the effect of receptor for advanced glycation end products (RAGE)-specific small interfering (si)RNA on the generation of proinflammatory cytokines in primary rat hepatic stellate cells (HSCs) and hepatic fibrotic (HF) rats. The RAGE-specific siRNA expression vector pAKD-GR126 was constructed, and then transfected into primary rat HSCs. Reverse transcription-quantitative polymerase chain reaction and western blot analyses were conducted to determine the mRNA and protein expression levels, respectively, of RAGE, tumor necrosis factor (TNF)-α and interleukin (IL)-6 in the primary HSCs. In addition, a CCl₄-induced Sprague Dawley (SD) rat model of hepatic fibrosis was established, and pAKD-GR126 was injected into the SD rats via the tail vein. Serum TNF-α and IL-6 concentrations were determined using radioimmunoassay. The mRNA and protein expression levels of RAGE (mRNA, F=7.791; protein, F=36.513), TNF-α (mRNA, F=474.568; protein, F=123.500) and IL-6 (mRNA, F=203.463; protein, F=320.555) in the pAKD-GR126-transfected primary HSCs were significantly reduced compared with those in the control and pAKD-NC groups (P<0.05). Serum TNF-α and IL-6 levels in the low-, medium- and high-dose pAKD-GR126 treatment groups were reduced compared with those in the fibrotic model group (TNF-α, F=416.397; IL-6, F=1,716.659; P<0.05). In summary, the RAGE-specific siRNA was able to effectively suppress the generation of the proinflammatory cytokines TNF-α and IL-6 in primary rat HSCs and HF rats.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.

Role of the receptor for advanced glycation endproducts (RAGE) in retinal vasodegenerative pathology during diabetes in mice

AIMS/HYPOTHESIS

The receptor for AGEs (RAGE) is linked to proinflammatory pathology in a range of tissues. The objective of this study was to assess the potential modulatory role of RAGE in diabetic retinopathy.

METHODS

Diabetes was induced in wild-type (WT) and Rage (-/-) mice (also known as Ager (-/-) mice) using streptozotocin while non-diabetic control mice received saline. For all groups, blood glucose, HbA1c and retinal levels of methylglyoxal (MG) were evaluated up to 24 weeks post diabetes induction. After mice were killed, retinal glia and microglial activation, vasopermeability, leucostasis and degenerative microvasculature changes were determined.

RESULTS

Retinal expression of RAGE in WT diabetic mice was increased after 12 weeks (p < 0.01) but not after 24 weeks. Rage (-/-) mice showed comparable diabetes but accumulated less MG and this corresponded to enhanced activity of the MG-detoxifying enzyme glyoxalase I in their retina when compared with WT mice. Diabetic Rage (-/-) mice showed significantly less vasopermeability, leucostasis and microglial activation (p < 0.05-0.001). Rage (-/-) mice were also protected against diabetes-related retinal acellular capillary formation (p < 0.001) but not against pericyte loss.

CONCLUSIONS/INTERPRETATION

Rage (-/-) in diabetic mice is protective against many retinopathic lesions, especially those related to innate immune responses. Inhibition of RAGE could be a therapeutic option to prevent diabetic retinopathy.

Design, synthesis, and biological evaluation of pyrimidine-2-carboxamide analogs: investigation for novel RAGE inhibitors with reduced hydrophobicity and toxicity

This paper describes an investigation of novel RAGE inhibitors with improved drug-like properties. To identify the improved drug-like RAGE inhibitor, we designed and synthesized pyrimidine-2-carboxamide analogs based on our previous work. Several potent analogs with improved hydrophilicity were identified by evaluation of RAGE inhibitory activity. In particular, one of the potent (diethylamino)ethoxymethoxy analogs did not exhibit undesired cytotoxicity in contrast with the parent RAGE inhibitors.

C-reactive protein stimulates RAGE expression in human coronary artery endothelial cells in vitro via ROS generation and ERK/NF-κB activation

AIM

The receptor for advanced glycation end-products (RAGE) plays an important role in development of atherosclerosis, and C-reactive protein (CRP) has been found to stimulate its expression in endothelial cells. In this study we investigated how CRP regulated the expression of RAGE in human coronary artery endothelial cells (HCAECs).

METHODS

HCAECs were treated in vitro with CRP (50 μg/mL) in combination with a variety of inhibitors. ROS generation was determined by immunocytochemistry and flow cytometry. The RAGE expression and phosphorylation of relevant signaling proteins were measured using Western blot analyses.

RESULTS

CRP stimulated the expression of RAGE in the cells, accompanied by markedly increased ROS generation, phosphorylation of ERK1/2 and NF-κB p65, as well as translocation of NF-κB p65 to the nuclei. CRP also stimulated phosphorylation of JNK and p38 MAPK. Pretreatment of the cells with the ROS scavenger N-acetyl-L-cysteine, ERK inhibitor PD98059 or NF-κB inhibitor PDTC blocked CRP-stimulated RAGE expression, but pretreatment with the NADPH oxidase inhibitor DPI, JNK inhibitor SP600125 or p38 MAPK inhibitor SB203580 did not significantly alter CRP-stimulated RAGE expression.

CONCLUSION

CRP stimulates RAGE expression in HCAECs in vitro via ROS generation and activation of the ERK/NF-κB signaling pathway.

Exenatide improves ovarian and endometrial injury and preserves ovarian reserve in streptozocin induced diabetic rats

We aimed to evaluate: (1) endometrial and ovarian tissue injury caused by the glucose toxicity in diabetic rat model and (2) the effect of GLP-1 analog (exenatide) on endometrial and ovarian diabetes induced injury with emphasizing the underlying mechanism. The study group composed of 24 female rats assigned randomly into 3 groups. Group 1 was the control group (n = 8) and received no treatment. Diabetes was induced by intraperitoneal injection of streptozocin for 16 rats which are further assigned randomly into 2 groups: 1 ml/kg intraperitoneal saline was given to Group-2 (diabetic non-treated control group, 8 rats) and 10 µg/kg/day of intraperitoneal exenatide was given to Group 3 (exenatide treated group, 8 rats) for four weeks. After four weeks, blood samples were collected and hysterectomy with bilateral oophorectomy was performed for histopathological examination. Diabetes caused endometrial and ovarian tissue injury in rats (p < 0.0001). Serum transforming growth factor beta (TGF-ß), malonylaldehyde (MDA), pentraxin-3 (PTX-3) levels were higher in diabetic rats (p < 0.0001), whereas antimullerian hormone (AMH) was lower (p < 0.001). Serum levels of these markers reflected that Diabetes induced injury in the reproductive tract occured via oxidative stress, fibrosis and severe inflammation. Diabetes diminished ovarian reserve. Exenatide treatment improved the histological degeneration and fibrosis in the endometrium and ovary with concomitant decrease in inflammatory and oxidative stress markers (p < 0.05). Exenatide also improved ovarian reserve (p < 0.05). Glucose toxicity occured severely in ovary and endometrium in DM. After exenatide treatment; ovarian and endometrial injury and fibrosis seems to decrease significantly. The effects of exenatide in rat models give hope to prevent the women with DM from premature ovarian failure and endometrial dysfunction.

Inhibitory effect of receptor for advanced glycation end product‑specific small interfering RNAs on the development of hepatic fibrosis in primary rat hepatic stellate cells

Specific small interfering RNAs (siRNAs) targeting receptor for advanced glycation end products (RAGE) inhibit the expression of RAGE, α-smooth muscle actin and type I collagen in the T6 hepatic stellate cells (HSCs), indicating that RAGE is important for the activation of HSCs and the expression of collagen. The present study aimed to investigate the effect of specific siRNAs targeting RAGE on the development of hepatic fibrosis (HF), using primary rat HSCs, which were isolated and cultured in vitro. The expression vectors for specific siRNAs targeting RAGE were constructed and transfected into primary rat HSCs. Untreated and nonspecific siRNA-transfected primary rat HSCs served as controls. The expression levels of RAGE, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), laminin (LN), hyaluronic acid (HA) and N-terminal procollagen III propeptide (PIIINP) in primary HSCs were detected by reverse transcription quantitative polymerase chain reaction and western blotting. The mRNA and 42 kD protein expression of RAGE in the pAKD-GR126-transfected primary HSCs were significantly downregulated compared with those in the untreated and the pAKD-negative control (NC)-transfected controls. The mRNA and protein expression levels of IL-6, TNF-α, TGF-β1, CTGF, LN, HA and PIIINP in the pAKD-GR126-transfected primary HSCs were also markedly downregulated compared with those in the untreated and pAKD-NC-transfected controls. Therefore, RAGE-specific siRNAs inhibited the expression of RAGE in primary rat HSCs and inhibited the development of HF.

Plasmatic isoforms of cytokeratin 18 and RAGE after severe trauma: a longitudinal cohort study

BACKGROUND

Life-threatening traumatic injuries lead to a complex inflammation-driven pathophysiology. Receptor of advanced glycation end product (RAGE) is a multiligand receptor of several endogenous alarmins, while cytokeratin 18 is a structural component of the filament of epithelial cells. Both proteins can be frequently found in plasma of patients with different diseases, whereby they have distinct underlying mechanism of formation. In this prospective observational study, we wanted to shed light on the kinetic of plasmatic RAGE and cytokeratin 18 isoforms after severe trauma, thereby also addressing the association of these markers with inflammation and their potential use as biomarkers.

METHODS

Plasma samples of 77 patients with severe multiple trauma as defined by an Injury Severity Score (ISS) 16 or greater were obtained from a local repository and levels of soluble RAGE, endogenous secretory RAGE, cytokeratin 18, cleaved cytokeratin 18, and interleukin 6 by enzyme-linked immunosorbent assay. Demographic and routine parameters of the cohort were extracted from an electronic patient data management system.

RESULTS

Both RAGE isoforms were transiently increased in plasma within 24 hours after trauma, while cytokeratin 18 levels were unchanged. Moreover, soluble RAGE concentrations in patients with thoracic injuries were higher compared with patients without injury, and both isoforms of RAGE discriminated between patients with most severe adult respiratory distress syndrome and patients with milder forms. In addition, cleaved and total cytokeratin 18 levels differ between patients with hepatic dysfunction and normal function, without possessing discriminatory power. RAGE and cytokeratin 18 isoforms correlated significantly but to a low extent with interleukin 6, while the isoforms of both parameters correlated to a high extent with one another.

CONCLUSION

The release of RAGE (but not cytokeratin 18) isoforms occurs early and transiently after trauma and is associated with the extent of injury and inflammatory response. RAGE and cytokeratin 18 isoforms have the potential to act as diagnostic or prognostic biomarkers of lung and hepatic dysfunction.

LEVEL OF EVIDENCE

Epidemiologic/prognostic study, level IV.

Genetic determinants of arterial stiffness

Stiffness of large arteries (called arteriosclerosis) is an independent predictor of cardiovascular morbidity and mortality. Although previous studies have shown that arterial stiffness is moderately heritable, genetic factors contributing to arterial stiffness are largely unknown. In this paper, we reviewed the available literature on genetic variants that are potentially related to arterial stiffness. Most variants have shown mixed depictions of their association with arterial stiffness across multiple studies. Various methods to measure arterial stiffness at different arterial sites can contribute to these inconsistent results. In addition, studies in patient populations with hypertension or atherosclerosis may overestimate the impact of genetic variants on arterial stiffness. Future studies are recommended to standardize current measures of arterial stiffness in different age groups. Studies conducted in normal healthy subjects may also provide better opportunities to find novel genetic variants of arterial stiffness.

Circulating soluble receptor for advanced glycation end product identifies patients with bicuspid aortic valve and associated aortopathies

OBJECTIVE

A total of 30% to 50% of patients with bicuspid aortic valve (BAV) require surgery for aortic valve replacement (AVR), ascending aortic replacement (AA), or both. To prevent adverse aortic events, they are risk stratified using imperfect criteria based on imaging modalities. As a result, a significant number of dissections occur outside of the parameters suggested by the guidelines. Advanced glycation end products (AGEs) are associated with valve and vascular remodeling and trigger the release of a soluble receptor (soluble receptor for advanced glycation end product [sRAGE]). This study aims to characterize sRAGE as a diagnostic and risk-stratification tool for patients with BAV referred for surgery.

APPROACH AND RESULTS

sRAGE was measured in 135 patients (BAV, n=74; tricuspid aortic valve, n=61) meeting inclusion criteria from 338 enrolled patients undergoing AVR and AA. Univariate and multivariate analyses were performed. sRAGE level was significantly associated with the presence of BAV, independent of age, sex, and common risk factors for vascular disease (P<0.001). Within the BAV cohort, patients referred for AA and AVR had higher sRAGE values than patients undergoing AVR only (P=0.002). Patients with BAV <60 years of age, presenting with both valve and aortic diseases (fast progressors), had higher sRAGE than older patients who only needed AVR (slow progressors). Histological analysis showed that sRAGE correlates with dysfunctional aortic microstructure and does not correlate with aortic diameter (R(2)=0.007; P=0.51) or diameter/body surface area (R(2)=0.011; P=0.42).

CONCLUSIONS

These results show that elevated level of circulating sRAGE is associated with the presence of BAV and associated aortopathies, independent of aortic diameter.

Role of bone-marrow- and non-bone-marrow-derived receptor for advanced glycation end-products (RAGE) in a mouse model of diabetes-associated atherosclerosis

RAGE (receptor for advanced glycation end-products) is expressed on multiple cell types implicated in the progression of atherosclerosis and plays a role in DAA (diabetes-associated atherosclerosis). The aim of the present study was to determine the relative role of either BM (bone marrow)- or non-BM-derived RAGE in the pathogenesis of STZ (streptozotocin)-induced DAA. Male ApoE (apolipoprotein E)-null (ApoE-/-:RAGE+/+) and ApoE:RAGE-null (ApoE-/-:RAGE-/-) mice at 7 weeks of age were rendered diabetic with STZ. At 8 weeks of age, ApoE-/- and ApoE-/-:RAGE-/- control and diabetic mice received BM from either RAGE-null or RAGE-bearing mice, generating various chimaeras. After 10 and 20 weeks of diabetes, mice were killed and gene expression and atherosclerotic lesion formation were evaluated respectively. Deletion of RAGE in either the BM cells or non-BM cells both resulted in a significant attenuation in DAA, which was associated with reduced VCAM-1 (vascular cell adhesion molecule-1) expression and translated into reduced adhesion in vitro. In conclusion, the results of the present study highlight the importance of both BM- and non-BM-derived RAGE in attenuating the development of DAA.

Metabolic dysfunction in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is defined as cardiac disease independent of vascular complications during diabetes. The number of new cases of DCM is rising at epidemic rates in proportion to newly diagnosed cases of diabetes mellitus (DM) throughout the world. DCM is a heart failure syndrome found in diabetic patients that is characterized by left ventricular hypertrophy and reduced diastolic function, with or without concurrent systolic dysfunction, occurring in the absence of hypertension and coronary artery disease. DCM and other diabetic complications are caused in part by elevations in blood glucose and lipids, characteristic of DM. Although there are pathological consequences to hyperglycemia and hyperlipidemia, the combination of the two metabolic abnormalities potentiates the severity of diabetic complications. A natural competition exists between glucose and fatty acid metabolism in the heart that is regulated by allosteric and feedback control and transcriptional modulation of key limiting enzymes. Inhibition of these glycolytic enzymes not only controls flux of substrate through the glycolytic pathway, but also leads to the diversion of glycolytic intermediate substrate through pathological pathways, which mediate the onset of diabetic complications. The present review describes the limiting steps involved in the development of these pathological pathways and the factors involved in the regulation of these limiting steps. Additionally, therapeutic options with demonstrated or postulated effects on DCM are described.

The interplay between hyperglycemia-induced oxidative stress markers and the level of soluble receptor for advanced glycation end products (sRAGE) in K562 cells

Formation and accumulation of advanced glycation end-products (AGE) and also generation of reactive oxygen species (ROS), the main causative players in the context of diabetes, are intensified under hyperglycemic condition. The consequences from AGE/RAGE interaction could be attenuated by the soluble form of RAGE, termed sRAGE. In the current study, we studied the link between hyperglycemia-induced oxidative stress and the level of soluble form of RAGE in K562 cells. Our data revealed a positive correlation between high glucose and/or AGE-modified albumin treatment and oxidative stress status. Besides, a significant decrease in soluble RAGE level following treatments with either AGE-modified albumin or high glucose was observed. However, pretreatment with an appropriate antioxidant such as Resveratrol, markedly elevated the sRAGE level. Hence, sRAGE therapy could be further evaluated as an effective therapeutical approach to attenuate some of the diabetes complications.

ENDOTHELIAL MECHANOTRANSDUCTION MECHANISMS FOR VASCULAR PHYSIOLOGY AND ATHEROSCLEROSIS

Vascular physiology and disease progression, such as atherosclerosis, are mediated by hemodynamic force generated from blood flow. The hemodynamic force exerts on vascular endothelial cells (ECs), which could perceive the mechanical signals and transmit them into cell interior by multiple potential shear sensors, collectively known as mechanotransduction. However, we do not understand completely how these shear-sensitive components orchestrate physiological and atherosclerotic responses to shear stress. In this review, we provide an overview of biomechanical mechanisms underlying vascular physiology and atherosclerotic progression. Additionally, we summarize current evidences to illustrate that atherosclerotic lesions preferentially develop in arterial regions experiencing disturbance in blood flow, during which endothelial dysfunction is the initial event of atherosclerosis, inflammation plays dominant roles in atherosclerotic progression, and angiogenesis emerges as compensatory explanation for atherosclerotic plaque rupture. Especially in the presence of systemic risk factors (e.g., hyperlipidaemia, hypertension and hyperglycemia), the synergy between these systemic risk factors with hemodynamic factors aggravates atherosclerosis by co-stimulating some of these biomechanical events. Given the hemodynamic environment of vasculature, understanding how the rapid shear-mediated signaling, particularly in combination with systemic risk factors, contribute to atherosclerotic progression through endothelial dysfunction, inflammation and angiogenesis helps to elucidate the role for atherogenic shear stress in specifically localizing atherosclerotic lesions in arterial regions with disturbed flow.

Research resource: Aorta- and liver-specific ERα-binding patterns and gene regulation by estrogen

Estrogen has vascular protective effects in premenopausal women and in women younger than 60 years who are receiving hormone replacement therapy. However, estrogen also increases the risks of breast and uterine cancers and of venous thromboses linked to up-regulation of coagulation factors in the liver. In mouse models, the vasculoprotective effects of estrogen are mediated by the estrogen receptor α (ERα) transcription factor. Here, through next-generation sequencing approaches, we show that almost all of the genes regulated by 17β-estradiol (E2) differ between mouse aorta and mouse liver, ex vivo, and that this difference is associated with a distinct genomewide distribution of ERα on chromatin. Bioinformatic analysis of E2-regulated promoters and ERα binding site sequences identify several transcription factors that may determine the tissue specificity of ERα binding and E2-regulated genes, including the enrichment of NF-κB, AML1, and AP1 sites in the promoters of E2 down-regulated inflammatory genes in aorta but not liver. The possible vascular-specific functions of these factors suggest ways in which the protective effects of estrogen could be promoted in the vasculature without incurring negative effects in other tissues.

Effect of natural flavonoids, stilbenes and caffeic acid oligomers on protein glycation

The aim of the present study was to identify the inhibitory activity of natural flavonoids, stilbenes and caffeic acid oligomers on protein glycation. Antioxidant activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity. The production of 3-deoxyglucosone (3-DG) and advanced glycation end products (AGEs) by glycation reactions were determined by high-performance liquid chromatography and fluorescence, respectively. Certain flavonoids, stilbenes and caffeic acid oligomers prevented AGE production and the IC₅₀ values of the compounds were compared. These examined compounds are assumed to suppress AGE generation by inhibiting the increase in 3-DG production through a specific unknown mechanism in the early phase of the Maillard reaction, by inhibiting the generation of active oxygen in the later phase and by suppressing the progression of the reaction. Regular, daily consumption of these compounds in the form of a food or extract is expected to aid in the prevention or inhibition of non-enzymatic amino acid glycation in the living body, which is possibly associated with aging, diabetic complications, arteriosclerotic diseases and Alzheimer's disease, and they may also be effective agents in cosmetics promoting anti-aging.

Controlling the receptor for advanced glycation end-products to conquer diabetic vascular complications

Diabetic vascular complications, such as cardiovascular disease, stroke and microangiopathy, lead to high rates of morbidity and mortality in patients with long‐term diabetes. Extensive intracellular and extracellular formation of advanced glycation end‐products (AGE) is considered a causative factor in vascular injuries in diabetes. Receptor‐dependent mechanisms are involved in AGE‐induced cellular dysfunction and tissue damage. The receptor for AGE (RAGE), originally an AGE‐binding receptor, is now recognized as a member of pattern‐recognition receptors and a pro‐inflammatory molecular device that mediates danger signals to the body. Previous animal studies have shown RAGE dependent of diabetic vascular injuries. Prophylactic and therapeutic strategies focusing on RAGE and its ligand axis will be of great importance in conquering diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00191.x, 2012)

Lifestyle and Advanced Glycation End Products (AGEs) Burden: Its Relevance to Healthy Aging

Uncontrolled continued exposure to oxidative stress is a precursor to many chronic diseases including cancer, diabetes, degenerative disorders and cardiovascular diseases. Of the many known mediators of oxidative stress, reactive oxygen species (ROS) and advanced glycation end products (AGEs) are the most studied. In the present review, we have summarized current data on the origin of circulating AGEs, discussed issues associated with reliable assessment of its steady state level, and changes in its level with age and select metabolic diseases. Lastly, we have made recommendations about life style changes that may decrease AGEs burden to promote healthy aging.

Endothelial dysfunction in metabolic and vascular disorders

Vascular endothelium has important regulatory functions in the cardiovascular system and a pivotal role in the maintenance of vascular health and metabolic homeostasis. It has long been recognized that endothelial dysfunction participates in the pathogenesis of atherosclerosis from early, preclinical lesions to advanced, thrombotic complications. In addition, endothelial dysfunction has been recently implicated in the development of insulin resistance and type 2 diabetes mellitus (T2DM). Considering that states of insulin resistance (eg, metabolic syndrome, impaired fasting glucose, impaired glucose tolerance, and T2DM) represent the most prevalent metabolic disorders and risk factors for atherosclerosis, it is of considerable scientific and clinical interest that both metabolic and vascular disorders have endothelial dysfunction as a common background. Importantly, endothelial dysfunction has been associated with adverse outcomes in patients with established cardiovascular disease, and a growing body of evidence indicates that endothelial dysfunction also imparts adverse prognosis in states of insulin resistance. In this review, we discuss the association of insulin resistance and T2DM with endothelial dysfunction and vascular disease, with a focus on the underlying mechanisms and prognostic implications of the endothelial dysfunction in metabolic and vascular disorders. We also address current therapeutic strategies for the improvement of endothelial dysfunction.

Glycation: the angiogenic paradox in aging and age-related disorders and diseases

Angiogenesis is generally a quiescent process which, however, may be modified by different physiological and pathological conditions. The "angiogenic paradox" has been described in diabetes because this disease impairs the angiogenic response in a manner that differs depending on the organs involved and disease evolution. Aging is also associated with pro- and antiangiogenic processes. Glycation, the post-translational modification of proteins, increases with aging and the progression of diabetes. The effect of glycation on angiogenesis depends on the type of glycated proteins and cells involved. This complex link could be responsible for the "angiogenic paradox" in aging and age-related disorders and diseases. Using diabetes as a model, the present work has attempted to review the age-related angiogenic paradox, in particular the effects of glycation on angiogenesis during aging.

Biological functions of histidine-dipeptides and metabolic syndrome

The rapid increase in the prevalence of metabolic syndrome, which is associated with a state of elevated systemic oxidative stress and inflammation, is expected to cause future increases in the prevalence of diabetes and cardiovascular diseases. Oxidation of polyunsaturated fatty acids and sugars produces reactive carbonyl species, which, due to their electrophilic nature, react with the nucleophilic sites of certain amino acids. This leads to formation of protein adducts such as advanced glycoxidation/lipoxidation end products (AGEs/ALEs), resulting in cellular dysfunction. Therefore, an effective reactive carbonyl species and AGEs/ALEs sequestering agent may be able to prevent such cellular dysfunction. There is accumulating evidence that histidine containing dipeptides such as carnosine (β-alanyl-L-histidine) and anserine (β-alanyl-methyl-L-histidine) detoxify cytotoxic reactive carbonyls by forming unreactive adducts and are able to reverse glycated protein. In this review, 1) reaction mechanism of oxidative stress and certain chronic diseases, 2) interrelation between oxidative stress and inflammation, 3) effective reactive carbonyl species and AGEs/ALEs sequestering actions of histidine-dipeptides and their metabolism, 4) effects of carnosinase encoding gene on the effectiveness of histidine-dipeptides, and 5) protective effects of histidine-dipeptides against progression of metabolic syndrome are discussed. Overall, this review highlights the potential beneficial effects of histidine-dipeptides against metabolic syndrome. Randomized controlled human studies may provide essential information regarding whether histidine-dipeptides attenuate metabolic syndrome in humans.

Advanced glycation end-products: a common pathway in diabetes and age-related erectile dysfunction

Reactive derivatives of non-enzymatic glucose-protein condensation reactions integrate a heterogeneous group of irreversible adducts called advanced glycation end-products (AGEs). Numerous studies have investigated the role of the AGEs in cardiovascular system; however, its contribution to erectile dysfunction (ED) that is an early manifestation of cardiovascular disease has been less intensively investigated. This review summarizes the most recent advances concerning AGEs effects in the cavernous tissue of the penis and in ED onset, particularly on diabetes and aging, conditions that not only favor AGEs formation, but also increase risk of developing ED. The specific contribution of AGE on intra- and extracellular deposition of insoluble complexes, interference in activity of endothelial nitric oxide (NO) synthase, NO bioavailability, endothelial-dependent vasodilatation, as well as molecular pathways activated by receptor of AGEs are presented. Finally, the interventional actions that prevent AGEs formation, accumulation or activity in the cavernous tissue and that include nutritional pattern modulation, nutraceuticals, exercise, therapeutic strategies (statins, anti-diabetics, inhibitors of phosphodiesterase-5, anti-hypertensive drugs) and inhibitors of AGEs formation and crosslink breakers, are discussed. From this review, we conclude that despite the experiments conducted in animal models pointing to the AGE/RAGE axis as a potential interventional target with respect to ED associated with diabetes and aging, the clinical data have been very disappointing and, until now, did not provide evidence of benefits of treatments directed to AGE inactivation.

Efficacy of alogliptin, a dipeptidyl peptidase-4 inhibitor, on glucose parameters, the activity of the advanced glycation end product (AGE) - receptor for AGE (RAGE) axis and albuminuria in Japanese type 2 diabetes

BACKGROUND

To examine the effects of alogliptin, a dipeptidyl peptidase-4 inhibitor, on glucose parameters, the advanced glycation end product (AGE)-receptor for AGE (RAGE) axis and albuminuria in Japanese type 2 diabetes patients.

METHODS

Sixty-one patients whose HbAlc  ≥ 6.1% (mean age 64.7 years; 67% men; mean HbAlc 7.4%; 57% were pharmacologically treated) underwent blood and urine sampling and analysis before and after 12 weeks of treatment with alogliptin (25 mg once daily).

RESULTS

Alogliptin treatment significantly reduced fasting glucose (160.3 mg/dL at baseline versus 138.0 mg/dL at 12 weeks), glycoalbumin (21.1% at baseline versus 18.9% at 12 weeks), HbAlc (7.4% at baseline versus 6.9% at 12 weeks), circulating soluble form of RAGE concentrations (847.3 pg/mL at baseline versus 791.4 pg/mL at 12 weeks) and urine albumin to creatinine ratio (31.6 mg/g Cr at baseline versus 26.5 mg/g Cr at 12 weeks), whereas 1,5-anhydroglucitol concentrations were significantly increased (7.5 µg/mL at baseline versus 11.6 µg/mL at 12 weeks; all P < 0.05). Circulating AGEs concentrations were reduced only in patients with baseline AGEs ≥7 U/mL (n = 33, from 8.2 U/mL to 7.2U /mL; p < 0.01) after alogliptin treatment. The treatment-induced change of soluble form of sRAGE concentrations was associated with changes of 1,5-anhydroglucitol and HbAlc concentrations (rho = -0.32 and 0.29, respectively). Meanwhile, the treatment-induced change of urine albumin to creatinine ratio was associated with a change in the fasting glucose concentration (rho = 0.25; all p < 0.05). During the intervention, alogliptin treatment was well tolerated without any hypoglycemia or side effects.

CONCLUSION

Alogliptin treatment improved the AGE-RAGE axis and reduced albuminuria in Japanese type 2 diabetes patients.

IL-1β, RAGE and FABP4: targeting the dynamic trio in metabolic inflammation and related pathologies

Within the past decade, inflammatory and lipid mediators, such as IL-1β, FABP4 and RAGE, have emerged as important contributors to metabolic dysfunction. As growing experimental and clinical evidence continues to tie obesity-induced chronic inflammation with dysregulated lipid, insulin signaling and related pathologies, IL-1β, FABP4 and RAGE each are being independently implicated as culprits in these events. There are also convincing data that molecular pathways driven by these molecules are interconnected in exacerbating metabolic consequences of obesity. This article highlights the roles of IL-1β, FABP4 and RAGE in normal physiology as well as focusing specifically on their contribution to inflammation, insulin resistance, atherosclerosis, Type 2 diabetes and cancer. Studies implicating the interconnection between these pathways, current and emerging therapeutics, and their use as potential biomarkers are also discussed. Evidence of impact of IL-1β, FABP4 and RAGE pathways on severity of metabolic dysfunction underlines the strong links between inflammatory events, lipid metabolism and insulin regulation, and offers new intriguing approaches for future therapies of obesity-driven pathologies.

EGCG-rich green tea extract stimulates sRAGE secretion to inhibit S100A12-RAGE axis through ADAM10-mediated ectodomain shedding of extracellular RAGE in type 2 diabetes

The receptor for advanced glycation of end products (RAGE) plays a critical role in the progression of type 2 diabetes (T2D). Soluble RAGE (sRAGE) is one of the RAGE variants, which acts as a decoy domain receptor and competes with RAGE, thus contributing to prevention of T2D. In this study, we conducted clinical trials of (-)-epigallocatechin-3-gallate (EGCG) rich green tea extract (300-900 mg/day) to investigate the effect of EGCG on relationship between S100A12 RAGE ligand and diverse sRAGE in T2D. Moreover, mechanism of sRAGE production also confirmed in vitro. Our data indicated that EGCG could stimulate sRAGE circulation but inhibited RAGE ligand in T2D, and ADAM10-mediated ectodomain shedding of extracellular RAGE was mainly involved in EGCG-stimulated sRAGE circulation. The present evidence indicates that EGCG has a potential to block S100A12-RAGE axis by stimulating sRAGE production through ADAM10-mediated ectodomain shedding of extracellular RAGE. Therefore, EGCG contributes to nutritional strategies for diabetes, not only because of its efficient antioxidant activity to scavenge free radicals, but also because of its ability stimulating sRAGE release in the circulation. Additionally, ADAM10-induced ectodomain shedding of extracellular RAGE leading to sRAGE circulation should be a potential of passive mechanism of sRAGE production to block S100A12-RAGE axis-related pathogenesis of proinflammation and diabetes.

Advanced glycation end products induce human corneal epithelial cells apoptosis through generation of reactive oxygen species and activation of JNK and p38 MAPK pathways

Advanced Glycation End Products (AGEs) has been implicated in the progression of diabetic keratopathy. However, details regarding their function are not well understood. In the present study, we investigated the effects of intracellular reactive oxygen species (ROS) and JNK, p38 MAPK on AGE-modified bovine serum albumin (BSA) induced Human telomerase-immortalized corneal epithelial cells (HUCLs) apoptosis. We found that AGE-BSA induced HUCLs apoptosis and increased Bax protein expression, decreased Bcl-2 protein expression. AGE-BSA also induced the expression of receptor for advanced glycation end product (RAGE). AGE-BSA-RAGE interaction induced intracellular ROS generation through activated NADPH oxidase and increased the phosphorylation of p47phox. AGE-BSA induced HUCLs apoptosis was inhibited by pretreatment with NADPH oxidase inhibitors, ROS quencher N-acetylcysteine (NAC) or neutralizing anti-RAGE antibodies. We also found that AGE-BSA induced JNK and p38 MAPK phosphorylation. JNK and p38 MAPK inhibitor effectively blocked AGE-BSA-induced HUCLs apoptosis. In addition, NAC completely blocked phosphorylation of JNK and p38 MAPK induced by AGE-BSA. Our results indicate that AGE-BSA induced HUCLs apoptosis through generation of intracellular ROS and activation of JNK and p38 MAPK pathways.