Advanced Glycation End Products sRAGE Research Articles

Study the Effect of RAGE and HMGB1 Genes Polymorphism on Breast Cancer Susceptibility in Iraqi Female

Background: The most frequent malignancy among women globally is breast cancer (BC). Breast lobules or ducts are the genesis of breast cancer, which is an uncontrolled development of epithelial cells. High mobility group protein box 1 (HMGB1) possesses both pro- and anti-tumorigenic bioactivities, which contribute to its complicated function in carcinogenesis. Damage associated Molecular Pattern molecules (DAMPs) generated following tissue injury include HMGB1, many S100 proteins, and others. RAGE is thought to be a receptor for these moleculAim of the study: The study was aimed to find the High mobility group protein box 1 (HMGB1) HMGB1 (rs1412125) and Receptor for Advanced Glycation End Products RAGE (rs1800624) genotypic and allelic frequency. Using Allele Specefic polymerase chain reaction AC-PCR and Polymerase Chain Reaction Restriction Fragment Length Polymorphism RFLP-PCR in BC patients and healthy controls, as well as their correlation with breast cancer susceptibility.Material and methods :. Samples were taken at Marjan Cancer Hospital, Babylon. HMGB1 rs1412125 and RAGE rs18400624 polymorphisms were evaluated for patients and controls using the PCR-RFLP and allele-specific polymerase chain reaction (AS-PCR) method. SPSS software was used to perform the statistical analysis.Results : There is non-significant difference between patients and control in TT, AA, and TA genotyping of (rs1800624) in RAGE gene (p=0.22), non-significant difference between patients and control in TT, TC, and CC genotyping of (rs1412125) in HMGB1 gene (p=0.09).Conclusion : Our results showed no association between HMGB1 polymorphisms and RAGE and breast cancer risk.

The Effect of HMGB1 Protein and Its Truncated Form on the Expression of RAGE Variants in Breast Cancer Cells

HMGB1 protein is a DNA binding nuclear protein. Its properties to bind different non-B DNA conformations and also to bend linear DNA implicate the protein in many essential cellular processes as DNA replication, repair, transcription, remodelling, etc. HMGB1 plays important role outside the cell as it is passively released from necrotic cells and actively from apoptotic ones and binds its specific receptor for advanced glycation end products RAGE. HMGB1/RAGE interactin is implicated in various diseases including cancer. Different soluble RAGE forms were reported whose functional role is to serve as a decoy for the ligands and in this way to block the signalling pathway. How the ligands regulate the production of RAGE variants is a subject of great scientific interest. We studied the effect of HMGB1 and its truncated form lacking the C- terminus on the expression of full-length (flRAGE) and soluble RAGE (sRAGE) in breast cancer cell lines: MCF7 represents a hormone dependent cancer with better prognosis and MDA-MB-231 – hormone independent with substantial invasive capacity. HMGB1 stimulates the total RAGE expression in both breast cancer cells but in MCF7 the ratio changes and is in favour of the membrane fraction. The absence of the C-tail of HMGB1 provokes comparable changes in RAGE production in MCF7 cells as the whole HMGB1 molecule. In MDA-MB- 231cell line the total amount of RAGE was slightly affected but it is entirely represented by the membrane form and the soluble one is in negligible amounts.

Targeting extracellular matrix glycation to attenuate fibroblast activation

The extracellular matrix (ECM) of the tumor microenvironment undergoes constant remodeling that alters its biochemical and mechano-physical properties. Non-enzymatic glycation can induce the formation of advanced glycation end-products (AGEs), which may cause abnormal ECM turnover with excessively cross-linked collagen fibers. However, the subsequent effects of AGE-mediated matrix remodeling on the characteristics of stromal cells in tumor microenvironments remain unclear. Here, we demonstrate that AGEs accumulated in the ECM alter the fibroblast phenotype within a three-dimensional collagen matrix. Both the AGE interaction with its receptor (RAGE) and integrin-mediated mechanotransduction signaling were up-regulated in glycated collagen matrix, leading to fibroblast activation to acquire a cancer-associated fibroblast (CAF)-like phenotype. These effects were blocked with neutralizing antibodies against RAGE or the inhibition of focal adhesion (FA) signaling. An AGE cross-link breaker, phenyl-4,5-dimethylthiazolium bromide (ALT 711), also reduced the transformation of fibroblasts into the CAF-like phenotype because of its dual inhibitory role in the AGE-modified matrix. Apart from targeting the AGE–RAGE interaction directly, the decreased matrix stiffness attenuated fibroblast activation by inhibiting the downstream cellular response to matrix stiffness. Our results suggest that indirect/direct targeting of accumulated AGEs in the ECM has potential for targeting the tumor stroma to improve cancer therapy. Statement of significanceAdvanced glycated end-products (AGEs)-modified extracellular matrix (ECM) is closely associated with pathological states and is recognized as a critical factor that precedes tumorigenesis. While increased matrix stiffness is known to induce fibroblast activation, less is known about how both biochemical and mechano-physical changes in AGE-mediated matrix-remodeling cooperate to produce a myofibroblastic cancer-associated fibroblast (CAF)-like phenotype. For the first time, we found that both the AGE interaction with its receptor (RAGE) and integrin-mediated mechanotransduction were up-regulated in glycated collagen matrix, leading to fibroblast activation. We further demonstrated that an AGE cross-link breaker, ALT-711, reduced the CAF-like transformation because of its dual inhibitory role in the AGE-modified matrix. Our findings offer promising extracellular-reversion strategies targeting the non-enzymatic ECM glycation, to regulate fibroblast activation.

Impact of Gut Microbiome Manipulation in 5xFAD Mice on Alzheimer's Disease-Like Pathology.

The gut brain axis seems to modulate various psychiatric and neurological disorders such as Alzheimer’s disease (AD). Growing evidence has led to the assumption that the gut microbiome might contribute to or even present the nucleus of origin for these diseases. In this regard, modifiers of the microbial composition might provide attractive new therapeutics. Aim of our study was to elucidate the effect of a rigorously changed gut microbiome on pathological hallmarks of AD. 5xFAD model mice were treated by antibiotics or probiotics (L. acidophilus and L. rhamnosus) for 14 weeks. Pathogenesis was measured by nest building capability and plaque deposition. The gut microbiome was affected as expected: antibiotics significantly reduced viable commensals, while probiotics transiently increased Lactobacillaceae. Nesting score, however, was only improved in antibiotics-treated mice. These animals additionally displayed reduced plaque load in the hippocampus. While various physiological parameters were not affected, blood sugar was reduced and serum glucagon level significantly elevated in the antibiotics-treated animals together with a reduction in the receptor for advanced glycation end products RAGE—the inward transporter of Aβ peptides of the brain. Assumedly, the beneficial effect of the antibiotics was based on their anti-diabetic potential.

Thrombin/PAR-1 activation induces endothelial damages via NLRP1 inflammasome in gestational diabetes

Gestational diabetes mellitus (GDM) is associated with an increased risk of progressing to type 2 DM and cardiovascular disease; however, the pathogenesis is still poorly understood. This study was to investigate roles of thrombin and its receptor protease-activated receptor 1 (PAR-1) and NLRP1 inflammasome in endothelial injury in GDM condition. Umbilical cord and plasma of GDM patients and high glucose (HG) cultured human umbilical vein endothelial cells (HUVECs) were used to examine the pathological changes of these pathways. Meanwhile, ameliorative effects and potential mechanisms of a natural product sarsasapogenin (Sar) were investigated in HUVECs. Thrombin/PAR-1 pathway, advanced glycation endproducts (AGEs) and their receptor (RAGE) axis, and the nucleotide-binding domain and leucine-rich repeat containing protein 1 (NLRP1) inflammasome were activated in GDM condition and HG-cultured HUVECs, accompanied by endothelial injury (decreased cell viability and increased lactate dehydrogenase release). Nevertheless, thrombin inhibition or PAR-1 antagonism caused decreases in AGEs formation and RAGE expression in HG-cultured HUVECs, while AGEs inhibition or RAGE antagonism declined PAR-1 expression not thrombin activity. Furthermore, thrombin inhibition or PAR-1 antagonism restrained NLRP1 inflammasome activation in HG-cultured HUVECs; meanwhile, NLRP1 expression and interleukin 18 levels were remarkably reduced in HG-cultured HUVECs after PAR-1 knockdown. Interestingly, Sar co-treatment could suppress thrombin/PAR-1 pathway, NLRP1 inflammasome, and AGEs/RAGE axis. Together, endothelial damages in GDM were likely due to enhanced interaction between AGEs/RAGE axis and thrombin/PAR-1 pathway, followed by NLRP1 inflammasome activation. Moreover, Sar may act as a protective agent against endothelial injury in chronic HG condition.

The impact of chronic blackberry intake on the neuroinflammatory status of rats fed a standard or high-fat diet

Neuroinflammation has been suggested as a central mediator of central nervous system dysfunction, including in dementia and neurodegenerative disease. Flavonoids have emerged as promising candidates for the prevention of neurodegenerative diseases and are thought to be capable of antiinflammatory effects in the brain. In the present study, the impact of a chronic intake of an anthocyanin extract from blackberry (BE) on brain inflammatory status in the presence or absence of a high-fat diet was investigated. Following intake of the dietary regimes for 17weeks neuroinflammatory status in Wistar rat cortex, hippocampus and plasma were assessed using cytokine antibody arrays. In the cortex, intake of the high-fat diet resulted in an increase of at least 4-fold, in expression of the cytokine-induced neutrophil chemoattractant CINC-3, the ciliary neurotrophic factor CNTF, the platelet-derived growth factor PDGF-AA, IL-10, the tissue inhibitor of metalloproteinase TIMP-1 and the receptor for advanced glycation end products RAGE. BE intake partially decreased the expression of these mediators in the high-fat challenged brain. In standard-fed animals, BE intake significantly increased cortical levels of fractalkine, PDGF-AA, activin, the vascular endothelial growth factor VEGF and agrin expression, suggesting effects as neuronal growth and synaptic connection modulators. In hippocampus, BE modulates fractalkine and the thymus chemokine TCK-1 expression independently of diet intake and, only in standard diet, increased PDGF-AA. Exploring effects of anthocyanins on fractalkine transcription using the neuronal cell line SH-SY5Y suggested that other cell types may be involved in this effect. This is the first evidence, in in vivo model, that blackberry extract intake may be capable of preventing the detrimental effects of neuroinflammation in a high-fat challenged brain. Also, fractalkine and TCK-1 expression may be specific targets of anthocyanins and their metabolites on neuroinflammation.

Targeting advanced glycation endproducts and mitochondrial dysfunction in cardiovascular disease

Cardiovascular disease (CVD) is a leading cause of mortality in the Western World. The development and onset of disease can be attributed to many risk factors including genetic susceptibility, diabetes, obesity and atherosclerosis. Numerous studies highlight the production of advanced glycation endproducts (AGEs) and interaction with their receptor (RAGE) as playing a key pathogenic role. The AGEs-RAGE axis is thought to contribute to a proinflammatory environment inducing cellular dysfunction which cascades towards pathology. Mitochondrial dysfunction concurrently plays a role in these proinflammatory responses presenting excess reactive oxygen species (ROS) production under pathological conditions. This ROS release can exacerbate the production of AGEs fuelling the fire somewhat. However, the AGEs-RAGE axis may influence mitochondrial function independently of inflammation. Therefore instigation of the AGEs-RAGE axis may facilitate spiralling towards pathology on many fronts including CVD development.

Inhibitory effect of soluble RAGE in disturbed flow-induced atherogenesis

Soluble receptor for advanced glycation end products RAGE (sRAGE), a secretory form of RAGE, plays an important role in suppressing RAGE signals that induce pro-inflammatory gene activation in a range of inflammatory diseases, such as Alzheimer's disease, complications of diabetes mellitus and atherosclerosis. Recent studies have suggested that fluid shear stress generated by laminar blood flow protects blood vessels from atherosclerosis, whereas low and oscillatory shear stress (OSS) generated by disturbed blood flow causes atherosclerosis. Although RAGE levels are increased in atherosclerotic plaque, the regulatory mechanisms of sRAGE in the occurrence of atherosclerotic plaque induced by disturbed blood flow remain largely unknown. This study aimed to determine the effects of sRAGE as a competitive inhibitor of RAGE in atherogenesis induced by disturbed blood flow. To determine the role of sRAGE in atherosclerosis induced by disturbed blood flow, we used a mouse model of partial carotid artery ligation using ApoE(-/-) and C57BL/6 mice. Our results revealed that the expression of RAGE was significantly increased in the region of atherosclerotic plaque and that treatment with sRAGE attenuated the development of plaque formation. We found that the expression levels of RAGE and high mobility group box 1 (HMGB1), the agonistic ligand of RAGE, were significantly increased in human umbilical vein endothelial cells (HUVECs) under shear stress conditions induced by disturbed blood flow and suppressed following treatment with sRAGE. We further observed that treatment with sRAGE decreased the expression of vascular cell adhesion molecule‑1 (VCAM-1) and markedly attenuated monocyte-endothelial cell adhesion. Taken together, our results reveal that sRAGE exerts anti-atherogenic effects by blocking the activation of the RAGE signaling pathway induced by disturbed blood flow and may thus be a potential therapeutic target for the prevention of atherosclerosis.

Statins modulate feedback regulation mechanisms between advanced glycation end-products and C-reactive protein: Evidence in patients with acute myocardial infarction

ObjectiveHigh sensitivity C-reactive protein (hsCRP) and advanced glycation end-products (AGEs) have been proposed as mediators in inflammation and atherosclerosis. Therefore, we studied the relation between AGE and hsCRP in patients with acute myocardial infarction (AMI). MethodsPatients with AMI diagnosis and satisfying our inclusion criteria were included during 2009–2011 in an unicentre registry of AMI patients for a cross-sectional study. The final cohort was composed of 156 patients (46.2% STEMI and 27.6% with type-2 diabetes). AGE and hsCRP were measured in plasma. ResultsDiabetic patients were older than non-diabetics (68.6±10.6 vs. 60.4±13.9years; p<0.05), presented more incidence of hypertension (62.8 vs. 36.3%; p<0.05) and were in a higher Killip class (p<0.05). The mean values of fluorescent AGE and hsCRP levels were 61.3±49.8 AU and 2.4±4.0mg/L, respectively, and there were no differences in these parameters between diabetic and non-diabetic patients. A direct association between AGE and hsCRP levels was observed, mainly in diabetic patients (r=0.258; p=0.018). Importantly, this association disappeared in patients who had been treated with statins before their AMI (r=−0.055; p=0.845), but it was maintained in non-diabetic patients naïve for statins treatment (r=0.634; p<0.001), independently of other treatments and confounding parameters. ConclusionsThis is the first evidence in humans of a feedback regulation mechanism between CRP and the AGE–RAGE axis modulated by statins.

AGEs–RAGE mediated up-regulation of connexin43 in activated human microglial CHME-5 cells

Microglial activation is a significant contributor to the pathogenesis of many neurodegenerative diseases. Microglia respond to a range of stimuli including pathogenic protein deposits such as advanced glycation endproducts (AGEs). AGEs are prominent inflammatory stimuli that accumulate in the ageing brain. AGEs can activate microglia, leading to the production of excessive amounts of inflammatory cytokines and coupling via gap junction proteins especially connexin43 (Cx43). The literature on the expression of microglial Cx43 during inflammation is controversial. Many cellular effects of AGEs are thought to be mediated by the receptor RAGE. There is however, no evidence suggesting Cx43 is a downstream effector of AGEs–RAGE interaction in microglia. In addition, most of the AGEs-related studies have been undertaken using rodent microglia; the information on human microglia is sparse. Microglia of human and rodent origin respond differently to certain stimuli. The aims of this study were to investigate the AGEs–RAGE-mediated activation of human microglia and establish if Cx43 is one of the downstream effectors of AGEs–RAGE interaction in these cells. Human microglial CHME-5 cells were treated with different doses of AGEs for a selected time-period and microglial activation studied using specific markers. The protein expression of RAGE, Cx43 and TNF-α-receptors (RI and RII) was analysed in response to AGEs in the absence/presence of various doses of anti-RAGE Fabs. TNF-α levels in media were measured using ELISA. TNF-α-induced opening of gap junctional channels was assessed by dye uptake assays and the effect of neutralising TNFRII on Cx43 levels was also studied. CHME-5 cells showed an up-regulation of RAGE, TNF-α, TNFRs (especially TNFRII) and Cx43 upon AGEs treatment and a significant dose-dependent drop in the levels of TNF-α, TNFRII and Cx43 in the presence of anti-RAGE Fabs. TNF-α induced gap junctional/hemichannel opening whereas blocking TNFRII inhibited TNF-α-induced increase in Cx43 levels. Results suggested that TNF-α, TNFRII and Cx43 are downstream effectors of the AGEs–RAGE interaction in human microglial CHME-5 cells.

Evidence for a role of advanced glycation end products in atrial fibrillation

BackgroundRecent studies suggested that advanced glycation end-products (AGEs) and their receptor (RAGE) interaction may be promoted by inflammation and oxidative stress. These processes could also contribute to the pathogenesis of atrial fibrillation (AF), but their roles remain poorly defined. We studied the association of AGE–RAGE axis with AF in diabetic and non-diabetic patients, since the axis appears to play a key role in the process. MethodsNinety-seven consecutive outpatients were included in this transversal study. Fifty-nine patients were in sinus rhythm (SR) and 38 in permanent AF. Plasma fluorescent AGEs and soluble RAGE (sRAGE) were measured and comparisons between patients with and without AF were performed. A multivariate logistic regression analysis was made to define the independent factors associated with AF. ResultsFluorescent AGEs and sRAGE were higher in AF group (74.9±25.6 vs. 61.8±20.1a.u. for fluorescent AGEs, p=0.006; 1714.2±1105.5 vs. 996.1±820.7pg/mL for sRAGE, p=0.001). These differences were specially marked in non-diabetic patients. Both AGEs and sRAGE directly correlated with left atrial dimensions (r=0.496; r=0.536 for atrial area and r=0.491; r=0.511 for atrial volume, for fluorescent AGEs and sRAGE, respectively, p<0.001). In a multivariate analysis, fluorescent AGEs and sRAGE resulted as markers of AF independent of left atrial distension, diabetes and other confounding variables. ConclusionsAGEs and sRAGE plasma levels were higher in patients with AF, independently of diabetes mellitus, and they positively correlated with atrial dimensions, indicating a role for the AGE–RAGE axis in the arrhythmogenic structural atrial remodelling.

Aldose Reductase and AGE–RAGE pathways: central roles in the pathogenesis of vascular dysfunction in aging rats

Aging is inevitably accompanied by gradual and irreversible innate endothelial dysfunction. In this study, we tested the hypothesis that accentuation of glucose metabolism via the aldose reductase (AR) pathway contributes to age-related vascular dysfunction. AR protein and activity levels were significantly increased in aged vs. young aortic homogenates from Fischer 344 rats. Immunostaining revealed that the principal site of increased AR protein was the aortic endothelium as well as smooth muscle cells. Studies revealed that endothelial-dependent relaxation (EDR) in response to acetylcholine was impaired in aged rats compared to young rats and that treatment with the AR inhibitor (ARI) zopolrestat significantly improved EDR in aged rats. Methylglyoxal (MG), a key precursor of advanced glycation endproducts (AGEs), was significantly increased in the aortas of aged rats vs. young rats. Consistent with central roles for AR in generation of MG in aging, ARI treatment significantly reduced MG levels in aged rat aorta to those in young rats. Treatment of aged rats with soluble(s) RAGE, a soluble form of the chief signal transduction receptor for AGEs, RAGE, significantly improved EDR in aged rats, thus establishing the contribution of age-related increases in AGEs to endothelial dysfunction. These findings reveal that significant increases in AR expression and activity in aged rat vasculature linked to endothelial dysfunction may be mitigated, at least in part, via ARI and that aging-linked increased flux via AR generates AGEs; species which transduce endothelial injury consequent to their interaction with RAGE. These data demonstrate for the first time that AR mediates aging-related vascular dysfunction, at least in part, via RAGE.

Soluble form of a receptor for advanced glycation end products sRAGE as a biomarker

There is a growing body of evidence that advanced glycation end products (AGEs) and their receptor (RAGE) system are implicated in various disorders, including vascular complications in diabetes, cardiovascular disease, neurodegenerative diseases, inflammatory and autoimmune disorders, and cancer growth and metastasis. Indeed, the engagement of RAGE with AGEs elicits oxidative stress generation and evokes inflammatory and thrombogenic responses, thus playing an important role in these devastating disorders. Moreover, since administration of a recombinant soluble form of RAGE (sRAGE), has been shown to block the AGE-RAGE signaling pathway in animal models, exogenously administered sRAGE may capture and eliminate circulating AGEs, thus protecting against the AGE-elicited tissue damage by acting as a decoy receptor for AGEs. Recently, sRAGE has been identified in humans. However, there are a few comprehensive papers about the regulation and role of sRAGE in humans. Therefore, in this paper, we review the kinetics, regulation and pathophysiological role of sRAGE in humans. We further discuss the potential clinical utility of measuring sRAGE in various disorders as a biomarker.

RAGE expression in the human peritoneal membrane

Experimental animal models have demonstrated that the interaction of advanced glycation end-products (AGE) with their receptor RAGE is, at least in part, responsible for peritoneal damage. This study investigates the in vivo expression of RAGE in the peritoneal membrane of uraemic human patients. Peritoneal biopsies of 89 subjects (48 uraemic and 41 healthy age-matched patients) were examined. The expression of CD3, IL-6, activated NFkappaBp65, VEGF, transforming growth factor (TGF)-beta1, smooth-muscle actin (SMA), methylglyoxal (MGO) and RAGE was analysed immunohistochemically. Additionally, in 4 of the 48 uraemic patients, peritoneal biopsies were repeated after 15 months at the time of catheter removal to analyse the above parameters and the extent of NFkappaB-binding activity determined by electrophoretic mobility shift assay (EMSA) in the long-term follow-up. In comparison to the healthy controls, uraemic patients showed a significant increase in fibrosis, angiogenesis, submesothelial thickness, MGO-derived protein adducts, RAGE, IL-6, VEGF, TGF-beta1, SMA and NFkappaBp65 in their peritonea. Four patients, followed up longitudinally from peritoneal dialysis (PD) catheter insertion to removal, demonstrated further significant increase in the above parameters, particularly in RAGE expression and NFkappaB activation. Along with a higher expression of several indicators for inflammation, angiogenesis, fibrosis and AGE accumulation, the peritoneal membrane of the uraemic patients showed an increased submesothelial thickness and a marked induction of RAGE expression and NFkappaB-binding activity, which both further increased after PD treatment. These findings in human peritoneum support the concept of the AGE-RAGE interaction being crucial in peritoneal damage due to uraemia and PD.

THE AGE/RAGE AXIS IN DIABETES‐ACCELERATED ATHEROSCLEROSIS

1. There is increasing evidence that advanced glycation end-products (AGEs) and their interaction with the receptor RAGE play a pivotal role in atherosclerosis, in particular in the setting of diabetes. 2. Previous studies have shown that inhibition of AGE accumulation and RAGE expression in diabetes by either reduction of the formation of AGEs or cross-link breakers was associated with reduced atherosclerosis and renal disease. Advanced glycation end-products bind to RAGE, thereby leading to activation of a range of inflammatory and fibrotic pathways causing tissue injury. Different splice variants of RAGE exist, including a soluble form that lacks the intracellular domain and fails to induce signal transduction. Therapeutic approaches using soluble RAGE as a decoy binding protein for circulating AGE have been effective in preventing externally induced arterial injury and atherosclerosis in the absence and presence of diabetes. 3. In order to delineate the role of RAGE in vascular disease in more detail, it was necessary to create RAGE(-/-) mice, as well as transgenic mice overexpressing RAGE in endothelial cells. It was shown that RAGE overexpression was associated with increased vascular injury, nephropathy and retinopathy. 4. In contrast, RAGE deletion was associated with partial vascular protection, such as reduced neointima formation after arterial denudation, as well as protection from diabetic nephropathy. The present review summarizes the evidence for RAGE being a pro-inflammatory and pro-fibrotic receptor. 5. Further studies are needed to delineate the effect of RAGE deletion and overexpression in diabetic macrovascular disease. Based on these findings, RAGE could be a potential therapeutic target in combating inflammatory vascular diseases, including diabetes-associated atherosclerosis.

A novel mechanism of action of atorvastatin against cardiovascular risk: A commentary on “Decreased plasma soluble RAGE in patients with hypercholesterolemia: effects of statins”

Growing evidence derived from clinical studies has recentlyfostered the idea that the soluble form of the receptor foradvanced glycation endproducts (sRAGE) might serve as avaluable risk marker for several RAGE-mediated disorders.Accordingly, circulating levels of sRAGE have been found tobe reduced in a number of diverse clinical conditions, includingcoronary atherosclerosis [1], hypertension [2], type 2 diabetes[3],Alzheimerdisease[4],andrheumatoidarthritis[5].BecauseRAGE has been shown to act as a decoy binding inflammatoryRAGE ligands like advanced glycation endproducts (AGEs)[6], it has been speculated that RAGE might counteractinflammatory reflexes triggered by RAGE ligands such asAGEs, S100 proteins, and HMGB1 [7].The potential therapeutic usefulness of genetically engi-neeredsRAGEforpreventionandtreatmentofRAGE-mediateddisorders has been demonstrated in numerous animal studies[8]. Thus far, however, the limited data on the pathophysiolo-gical mechanisms regulating sRAGE production in humanshave hampered the therapeutic application of soluble RAGE inhuman disease states. To gain more insight into this crucialchallenge, first it would be necessary to shed more light on howcurrent pharmacological agents could modulate circulatinglevels of sRAGE in human beings. In this regard, Forbes et al.[9] have previously shown that inhibition of angiotensin-converting enzyme increased plasma sRAGE levels in bothdiabetic rats and humans with type 1 diabetes.A new intriguing paper by Santilli and colleagues [10] takesthe next step in showing how sRAGE levels might actually bemodulated by cardiovascular drugs. In a sample of Italiannondiabetic subjects with hypercholesterolemia, these authorsshowlowerendogenouslevelsofsRAGEthatweresignificantlyreversed after 8 weeks of statin treatment with atorvastatin(20 mg/day) but not with pravastatin (40 mg/day). Notably, thiseffect seemed to occur independent of LDL-cholesterolimprovement, which was virtually equal in both treatmentgroups. It is now well recognized that the beneficial effects ofstatins are not entirely related to their lipid-lowering effects, butrather to a number of diverse actions [11]. In this regard, thework of Santilli and colleagues provides a new mechanism ofaction for statins with the observation that atorvastatin mightelevate levels of sRAGE in hypercholesterolemic subjects,regardless of its lipid-lowering effect. Of great interest, we havepreviously shown that a reduced level of sRAGE may act as animportant risk factor for cardiovascular disease even in normo-cholesterolemic subjects [1]. The question as to whetheratorvastatin administration to patients with normocholesterole-mia may reduce cardiovascular risk through an elevation ofplasma sRAGE levels remains open, but future clinical studiesare certainly warranted to address this issue.In addition to confirming preclinical studies showing thatstatins might modulate the AGE–RAGE system in culture[12,13], the work of Santilli et al. might carry another importantimplication for studies focusing on circulating sRAGE levels inpatients with cardiovascular diseases. By showing that statinscanelevatelevelsofsRAGE,theauthors’findingsimplicatethatthe use of these drugs may act as an important confounder inclinical reports investigating circulating sRAGE concentrationsincohortsofpatientswithcardiovascularormetabolicdisorders.It follows that results of cross-sectional and prospectiveinvestigations on sRAGE as a biomarker should be statisticallyadjusted for statin use to yield reliable information.Whataboutthemolecular mechanismsof actionofstatins onsRAGE levels? A previous report has suggested that statinsmight inhibit RAGE activation by reducing myeloperoxidase-

Telmisartan, an Angiotensin II Type 1 Receptor Blocker, Inhibits Advanced Glycation End-product (AGE)-induced Monocyte Chemoattractant Protein-1 Expression in Mesangial Cells through Downregulation of Receptor for AGEs via Peroxisome Proliferator-activated Receptor-γ Activation

Interaction between advanced glycation end-products (AGEs) and their receptor (RAGE) plays a central role in diabetic nephropathy pathogenesis. Pathophysiological crosstalk between the AGEs-RAGE system and angiotensin II (Ang II) is also involved in this disease. This study investigated the role of proliferator-activated receptor-gamma (PPAR-gamma)-modulating activity on inhibition of monocyte chemoattractant protein (MCP-1) expression. Telmisartan, an Ang II type 1 receptor blocker, downregulated RAGE mRNA and inhibited superoxide generation and MCP-1 gene expression in mesangial cells; these processes were blocked by GW9662, a PPAR-gamma inhibitor. Candesartan, an Ang II type 1 receptor blocker, did not suppress AGEs-induced superoxide generation. Telmisartan and the antioxidant, N-acetylcysteine, completely inhibited AGEs-induced MCP-1 overproduction by mesangial cells. These results suggest that telmisartan inhibits AGEs-signalling to MCP-1 expression in mesangial cells by downregulating RAGE gene expression and subsequent oxidative stress generation via PPAR-gamma activation. This study has demonstrated a unique benefit of telmisartan in that it may function as an anti-inflammatory agent against AGEs via PPAR-gamma activation and may play a protective role in diabetic nephropathy.

Pathogenesis of diabetic nephropathy: a radical approach.

factors, extracellular matrix (ECM ) proteins and Introduction inflammatory cytokines, as well as to stimulate cell proliferation [8,9]. AGEs have also been shown to Diabetes is on the rise and diabetic kidney disease has quench nitric oxide, and have been implicated in the emerged as a leading cause for end-stage renal failure pathogenesis of atherosclerosis [11,12]. The cellular in certain parts of the world [1]. Although data from and molecular mechanisms responsible for AGE-medithe Diabetes Control and Complication Trial establish ated cellular effects have not yet been fully defined. a central role for hyperglycaemia in diabetic complicaRecent studies suggest that a central pathway through tions [2], strict control of glucose in diabetics can be which AGEs mediate their cellular effects may involve difficult, and some times dangerous. Understanding the interaction of AGEs with their cellular binding the distal pathway of glucose toxicity therefore has sites, the best characterized is the Receptor for AGE clinical significance. Although during chronic hyper(RAGE ) [13,14]. glycaemia multiple glucose metabolites and reaction products accumulate, accruing evidence supports a key role for advanced glycation end-products (AGEs) in diabetic complications [3–10]. There are several theorAGE–RAGE interaction etical reasons and experimental evidence that suggest an important role for AGEs and oxidative stress in RAGE is expressed on a number of cell types that are the pathogenesis of diabetic nephropathy. relevant to the pathogenesis of diabetic complications. These include endothelial, mesangial and vascular smooth muscle cells and macrophages [15]. Based on AGEs in diabetic nephropathy preliminary reports, the activation of NF-kB by AGEs appears to be mediated through a signalling mechanism AGEs are formed from the non-enzymatic glycation/ involving p21ras and MAP kinase [16]. AGE–RAGE oxidation not only of amino acids of proteins, but also interactions may be a potential pathway for the extraof lipids and lipoproteins [11,12]. In patients with cellular protein gene activation during diabetes based diabetic nephropathy, high levels of AGEs accumulate on the following observation. AGE albumin when in the plasma, and importantly, within the sclerosing perfused in situ interacted with vascular wall, via glomeruli [3,4]. The latter has been noted to precede binding to RAGE. AGE–RAGE interaction was the onset of diabetic renal disease, and correlate with accompanied by activation of IL-6 and VCAM-1 genes the course of the disease [10]. In animals, chronic [17,18]; the latter may explain the elevated plasma administration of advanced glycated albumin to nonsoluble VCAM-1 (sVCAM ) reported in human diadiabetic rats led to proteinuria and glomerular changes betics [19]. Such upregulation of VCAM-1 expression, similar to those seen in diabetic nephropathy, and in theory, can contribute to the diabetic vascular these changes were associated with activation of lesions, since VCAM-1 is a cell–cell recognition protein collagen, laminin, and TGF-b genes [9,11]. on the endothelial cell surface, which promotes interTissue accumulation of AGEs is associated with a action between circulating monocytes and endothelnumber of toxic effects. These include cross-linking of ium. long-lived proteins such as collagens and other matrix Since many effects of AGEs such as cross-linking of proteins, increasing of vascular permeability, and proproteins, increased vascular permeability, induction of motion of mononuclear cell influx [8,9]. Additionally lipid peroxidation, quenching of nitric oxide, and accelAGEs have been shown to induce genes for growth eration of atherosclerosis can also be duplicated by the effects of free radicals, attention has recently been Correspondence and offprint requests to: Abdulla K. Salahudeen MD focused on examining whether AGE–RAGE interFRCP, Renal Division, Department of Medicine, University of action can indeed lead to increased free radical Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216–4505, USA. production.