Protein glycation: a firm link to endothelial cell dysfunction

Distribution of the receptor for advanced glycation end products in the human male reproductive tract: prevalence in men with diabetes mellitus

BACKGROUND

Diabetics have a significantly higher percentage of sperm with nuclear DNA (nDNA) fragmentation and increased levels of advanced glycation end products (AGEs), in their testis, epididymis and sperm. As the receptor for AGEs (RAGE) is important to oxidative stress and cell dysfunction, we hypothesise, that it may be involved in sperm nDNA damage.

METHODS

Immunohistochemistry was performed to determine the presence of RAGE in the human testis and epididymis. A comparison of the receptor's incidence and localization on sperm from 10 diabetic and 11 non-diabetic men was conducted by blind semi-quantitative assessment of the immunostaining. Enzyme-linked immunosorbent assay analysis ascertained RAGE levels in seminal plasma and sperm from 21 diabetic and 31 non-diabetic subjects. Dual labelling immunolocalization was employed to evaluate RAGE's precise location on the sperm head.

RESULTS

RAGE was found throughout the testis, caput epididymis, particularly the principle cells apical region, and on sperm acrosomes. The number of sperm displaying RAGE and the overall protein amount found in sperm and seminal plasma were significantly higher in samples from diabetic men (P < 0.01, P < 0.0001 and P < 0.0001, respectively).

CONCLUSIONS

The presence of RAGE implies that it may play a central role in sperm nDNA damage particularly in diabetic men where the levels are elevated.

Role of Krüppel-Like Transcription Factors in Endothelial Biology

Krüppel-like factors are members of the zinc finger family of transcription factors that have been implicated as playing key roles in regulating cellular differentiation and tissue development. Studies over the past several years support an important role for this family of factors in vascular biology. This review summarizes the role of Krüppel-like factors in endothelial cell biology.

High serum level of pentosidine, an advanced glycation end product (AGE), is a risk factor of patients with heart failure

BACKGROUND

Pentosidine, one of the advanced glycation end products (AGE), is generated by nonenzymatic glycation and oxidation of proteins. The receptor of AGE (RAGE) is expressed in a variety of tissue, and interaction of AGE with RAGE induces oxidative stress and activation of intracellular signaling, causing production of cytokines and mediators of inflammation. We investigated whether serum pentosidine is a risk factor for heart failure.

METHODS AND RESULTS

Serum pentosidine concentration was measured in 141 patients with heart failure and 18 control subjects by a competitive enzyme-linked immunosorbent assay. Patients were prospectively followed during a median follow-up period of 479 days with end points of cardiac death or rehospitalization. Serum concentration of pentosidine was significantly higher in New York Heart Association (NYHA) Class III/IV patients than in NYHA class I/II patients (P < .0001). Serum pentosidine was also higher in patients with cardiac events than in event-free patients (P < .001). In the univariate Cox proportional hazard analysis, age, NYHA class, pentosidine, creatinine, uric acid, B-type natriuretic peptide, left ventricular end-systolic volume, and left ventricular mass were significant risk factors to predict cardiac events. In the multivariate Cox analysis, serum pentosidine concentration was an independent risk factor for cardiac events (hazard ratio 1.88, 95% confidence interval 1.23-2.69, P = .002). The highest 4th quartile of pentosidine was associated with the highest risk of cardiac events (4.52-fold).

CONCLUSIONS

Serum pentosidine concentration is an independent prognostic factor for heart failure, and this new marker may be useful for risk stratification of patients with heart failure. Patients were divided into 4 groups based on the serum pentosidine levels.

Novel inhibitors of glycation and AGE formation

Accelerated formation of advanced glycation/lipoxidation and endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several natural and synthetic compounds have been proposed and tested as inhibitors of AGE/ALE formation. We have previously reported the therapeutic effects of several new AGE/ALE inhibitors on the prevention of nephropathy and dyslipidemia in streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the effects of various concentrations of a compound, LR-90, on the progression of renal disease and its effects on AGE and receptor for AGE (RAGE) protein expression on the kidneys of diabetic STZ-rats. Diabetic male Sprague-Dawley rats were treated with or without LR-90 (0, 5, 20, 25, and 50 mg/l of drinking water). After 32 weeks, body weight, glycemic status, renal function, and plasma lipids were measured. Kidney histopathology and AGE/ALE accumulation and RAGE protein expression in tissues were also determined. In vitro studies were also performed to determine the possible mechanism of action of LR-90 in inhibiting AGE formation and AGE-protein cross-linking. LR-90 protected the diabetic kidneys by inhibiting the increase in urinary albumin-to-creatinine ratio and ameliorated hyperlipidemia in diabetic rats in a concentration-dependent fashion without any effects on hyperglycemia. LR-90 treatment also reduced kidney AGE/ALE accumulation and RAGE protein expression in a concentration-dependent manner. In vitro, LR-90 exhibited general antioxidant properties by inhibiting metal-catalyzed reactions and reactive oxygen species (OH radical) and reactive carbonyl species (methlyglyoxal, glyoxal) generations without any effect on pyridoxal 5' phosphate. The compound also prevents AGE-protein cross-linking reactions. These findings demonstrate the bioefficacy of LR-90 in treating nephropathy and hyperlipidemia in diabetic animals by inhibiting AGE accumulation, RAGE protein expression, and protein oxidation in the diabetic kidney. Additionally, our study suggests that LR-90 may be useful also to delay the onset and progression of diabetic atherosclerosis as the compound can inhibit the expression of RAGE and inflammation-related pathology, as well as prevent lipid peroxidation reactions.

PKC delta and NADPH oxidase in AGE-induced neuronal death

Advanced glycation end product (AGE) accumulation in brain is believed to contribute to neuronal death in several neurodegenerative diseases. Neurons exposed to AGEs undergo oxidative stress, but the molecular mechanisms able to induce ROS generation and cell death are not yet clear. In this work, we exposed SH-SY5Y neuroblastoma cells to glycated albumin, as a model of AGE-modified protein, and we observed that cells differentiated by retinoic acid died after AGE exposure, through anion superoxide and peroxide generation, while undifferentiated cells resulted resistant. Retinoic acid induced marked increase in p47phox expression and in catalytic activity of PKC delta: the upregulation of a pathway involving NADPH oxidase and PKC delta is likely to be responsible for neuronal susceptibility to AGE. This hypothesis is confirmed by the fact that pre-treatments of differentiated cells with DPI, an inhibitor of NADPH oxidase, or with rottlerin, an inhibitor of PKC delta, were able to prevent AGE-induced neuronal death.

Oxidatively-modified and glycated proteins as candidate pro-inflammatory toxins in uremia and dialysis patients

End stage renal disease (ESRD) patients accumulate blood hallmarks of protein glycation and oxidation. It is now well established that these protein damage products may represent a heterogeneous class of uremic toxins with pro-inflammatory and pro-oxidant properties. These toxins could be directly involved in the pathogenesis of the inflammatory syndrome and vascular complications, which are mainly sustained by the uremic state and bioincompatibility of dialysis therapy. A key underlying event in the toxicity of these proteinaceous solutes has been identified in scavenger receptor-dependent recognition and elimination by inflammatory and endothelial cells, which once activated generate further and even more pronounced protein injuries by a self-feeding mechanism based on inflammation and oxidative stress-derived events. This review examines the literature and provides original information on the techniques for investigating proteinaceous pro-inflammatory toxins. We have also evaluated therapeutic - either pharmacological or dialytic - strategies proposed to alleviate the accumulation of these toxins and to constrain the inflammatory and oxidative burden of ESRD.

Advanced glycation end products and receptors in Fuchs' dystrophy corneas undergoing Descemet's stripping with endothelial keratoplasty

PURPOSE

To describe the histopathologic features of Descemet's membrane (DM) obtained from Fuchs' endothelial corneal dystrophy (FECD) corneas undergoing Descemet's stripping with endothelial keratoplasty (DSEK) and to assess the presence of advanced glycation end products (AGEs) and their receptors in FECD endothelium and DM.

DESIGN

Prospective observational case series.

PARTICIPANTS

Five eyes of 5 patients undergoing DSEK for FECD and 4 normal control eyebank corneas.

METHODS

Descemet's membrane and corneal endothelium from FECD patients undergoing DSEK were assessed with hematoxylin-eosin staining and immunohistochemistry for AGEs, receptor of AGEs (RAGE), and galectin 3 (AGE-R3).

MAIN OUTCOME MEASURES

Histopathologic abnormalities and presence of AGEs, RAGE, and AGE-R3 in DSEK specimens.

RESULTS

Histopathologic assessment of DSEK specimens from FECD patients disclosed thickening and nodularity of DM and loss of endothelial cells. Immunohistochemical staining of FECD DM for AGE, RAGE, and AGE-R3 showed an abundance of AGEs in the anterior portion of DM, mild positivity for RAGE, and moderate positivity for AGE-R3.

CONCLUSIONS

Tissue quality after DSEK is sufficient to allow detailed histopathologic analysis. The presence of AGEs, RAGE, and AGE-R3 in DM and corneal endothelium of FECD patients supports a link between accumulation of AGEs, oxidative stress, and corneal endothelial cell apoptosis in the pathogenesis of FECD.

Altered phenotype and gene transcription in endothelial cells, induced by Plasmodium falciparum-infected red blood cells: pathogenic or protective?

Severe malaria is associated with sequestration of Plasmodium falciparum-infected red blood cells (PRBC) in the microvasculature and elevation of intercellular adhesion molecule-1 (ICAM-1) and TNF. In vitro co-culture of human umbilical vein endothelial cells (HUVEC), with either PRBC or uninfected RBC, required the presence of low level TNF (5 pg/ml) for significant up-regulation of ICAM-1, which may contribute to increased cytoadhesion in vivo. These effects were independent of P. falciparum erythrocyte membrane protein-1 (PfEMP-1)-mediated adhesion but critically dependent on cell–cell contact. Further changes included increases in IL8 release and soluble TNF receptor shedding. Microarray analysis of HUVEC transcriptome following co-culture, using a human Affymetrix microarray chip, showed significant differential regulation of genes which defined gene ontologies such as cell communication, cell adhesion, signal transduction and immune response. Our data demonstrate that endothelial cells have the ability to mobilise immune and pro-adhesive responses when exposed to both PRBC and TNF. In addition, there is also a previously un-described positive regulation by RBC and TNF and a concurrent negative regulation of a range of genes involved in inflammation and cell-death, by PRBC and TNF. We propose that the balance between positive and negative regulation demonstrated in our study will determine endothelial pathology during a malaria infection.

Oral adsorbent AST-120 decreases serum levels of AGEs in patients with chronic renal failure

Advanced glycation end products (AGEs) are senescent macroprotein derivatives that are formed at an accelerated rate in patients with chronic renal failure (CRF). AGE formation and accumulation in plasma and vascular tissues contribute to accelerated atherosclerosis in this devastating disorder. AST-120 is an oral adsorbent that attenuates the progression of CRF by removing uremic toxins. Recently, AST-120 has been reported to reduce the progression of atherosclerosis as well. However, whether AST-120 decreases serum levels of AGEs and subsequently exerts atheroprotective properties remains to be elucidated. Ten nondiabetic CRF patients were enrolled in this study. All patients were kept on regular therapeutic diet and medications throughout the study. Serum AGE levels before and after AST-120 treatments were measured using enzyme-linked immunosorbent assay. Effects of patient-derived serum on atherosclerosis-related gene expression in cultured human umbilical vein endothelial cells (HUVECs) were analyzed by semiquantitative RT-PCR. Administration of AST-120 (6 g/day) for 3 months significantly decreased serum levels of AGEs in nondiabetic CRF patients, whereas AGE levels remained unchanged in age- and renal function-matched CRF patients without AST-120 treatment (n = 6). Patient serum after AST-120 treatment significantly reduced mRNA levels of receptor for AGEs, monocyte chemoattractant protein-1, and vascular adhesion molecule-1 in HUVECs compared with serum before treatment. Moreover, in vitro, AST-120 was found to adsorb carboxymethyllysine (CML), one of the well-characterized, digested food-derived AGEs. This study suggests that atheroprotective properties of AST-120 can be ascribed, at least in part, to its AGE-lowering ability via absorption of CML.

Oral adsorbent AST-120 decreases serum levels of AGEs in patients with chronic renal failure

Advanced glycation end products (AGEs) are senescent macroprotein derivatives that are formed at an accelerated rate in patients with chronic renal failure (CRF). AGE formation and accumulation in plasma and vascular tissues contribute to accelerated atherosclerosis in this devastating disorder. AST-120 is an oral adsorbent that attenuates the progression of CRF by removing uremic toxins. Recently, AST-120 has been reported to reduce the progression of atherosclerosis as well. However, whether AST-120 decreases serum levels of AGEs and subsequently exerts atheroprotective properties remains to be elucidated. Ten nondiabetic CRF patients were enrolled in this study. All patients were kept on regular therapeutic diet and medications throughout the study. Serum AGE levels before and after AST-120 treatments were measured using enzyme-linked immunosorbent assay. Effects of patient-derived serum on atherosclerosis-related gene expression in cultured human umbilical vein endothelial cells (HUVECs) were analyzed by semiquantitative RT-PCR. Administration of AST-120 (6 g/day) for 3 months significantly decreased serum levels of AGEs in nondiabetic CRF patients, whereas AGE levels remained unchanged in age- and renal function-matched CRF patients without AST-120 treatment (n = 6). Patient serum after AST-120 treatment significantly reduced mRNA levels of receptor for AGEs, monocyte chemoattractant protein-1, and vascular adhesion molecule-1 in HUVECs compared with serum before treatment. Moreover, in vitro, AST-120 was found to adsorb carboxymethyllysine (CML), one of the well-characterized, digested food-derived AGEs. This study suggests that atheroprotective properties of AST-120 can be ascribed, at least in part, to its AGE-lowering ability via absorption of CML.

Hypochlorite-modified albumin colocalizes with RAGE in the artery wall and promotes MCP-1 expression via the RAGE-Erk1/2 MAP-kinase pathway

Signal transduction via the endothelial receptor for advanced glycation end products (RAGE) plays a key role in vascular inflammation. Recent observations have shown that the myeloperoxidase-H2O2-chloride system of activated phagocytes is highly up-regulated under inflammatory conditions where hypochlorous acid (HOCl) is formed as the major oxidant. Albumin, an in vivo carrier for myeloperoxidase is highly vulnerable to oxidation and a major representative of circulating advanced oxidized proteins during inflammatory diseases. Immunohistochemical studies performed in the present study revealed marked colocalization of HOCl-modified epitopes with RAGE and albumin in sections of human atheroma, mainly at the endothelial lining. We show that albumin modified with physiologically relevant concentrations of HOCl, added as reagent or generated by the myeloperoxidase-H2O2-chloride system, is a high affinity ligand for RAGE. Albumin, modified by HOCl in the absence of free amino acids/carbohydrates/lipids to exclude formation of AGE-like structures, induced a rapid, RAGE-dependent activation of extracellular signal-regulated kinase 1/2 and up-regulation of the proinflammatory mediator monocyte chemoattractant protein-1. Cellular activation could be blocked either by a specific polyclonal anti-RAGE IgG and/or a specific mitogen-activated protein-kinase kinase inhibitor. The present study demonstrates that HOCl-modified albumin acts as a ligand for RAGE and promotes RAGE-mediated inflammatory complications.

HUVECs from newborns with a strong family history of diabetes show diminished ROS synthesis in the presence of high glucose concentrations

BACKGROUND

A family history of type 2 diabetes mellitus (DM) increases the probability to develop DM and endothelial dysfunction. The probable mechanism involves augmented reactive oxygen species (ROS) synthesis. The aim of this study was to evaluate the synthesis of ROS in human umbilical vein endothelial cells (HUVECs) obtained from healthy newborns with (experimental) and without (control) a strong family history of type 2 DM, exposed to different glucose concentrations.

METHODS

HUVECs were exposed to various glucose concentrations for 24 and 48 h periods, before cell proliferation, mitochondrial activity, and mitochondrial membrane potential were determined. Intracellular ROS synthesis in the presence or absence of the mitochondrial uncoupler CCCP, cytochalasin B, or diphenyleneiodonium (DPI) was also evaluated.

RESULTS

As opposed to control HUVECs, we found that experimental HUVECs exposed to 30 mmol/L glucose showed a 50% decrease in cell proliferation, a 90% reduction in mitochondrial activity, and a statistically significant inhibition of ROS synthesis in the presence of CCCP or cytochalasin B; DPI had no effect.

CONCLUSIONS

Our results suggest that mitochondria and NAD(P)H-oxidase from HUVECs obtained from healthy newborns with a family history of DM have an innate deficient response to high glucose concentrations.

Aging, smooth muscle cells and vascular pathobiology: Implications for atherosclerosis

Epidemiological and autopsy studies suggest a close link between aging and the clinical manifestation of atherosclerosis. Several experiments show increased arterial susceptibility to atherogenetic stimuli in aged subjects. All together, these findings support the concept that aging represents an independent atherogenetic risk factor, intimately associated to other parietal, microenvironmental and systemic noxae. Smooth muscle cells (SMCs) represent the major arterial cell population. As aging occurs, SMCs progressively migrate from the tunica media and accumulate into the tunica intima. Myointimal thickening may represent the site where low-grade atherogenic stimuli cause early development and more severe lesion progression. Intimal SMC accumulation is characterized from a switch, from a differentiated to a synthetic phenotype, with reduced myocytic cytoskeletal markers and the expression of new proteins. Aging also associates to changes of SMC proliferative and apoptotic behavior and response to growth factors, such as transforming growth factor-beta1. The alteration of SMC properties represents a crucial event in the pathobiology of arterial wall, since it contributes to the vascular remodeling and decline of function with aging and favors the progression of atherosclerosis. Increased knowledge of biomolecular mechanisms regulating these events helps to develop new strategies aimed at contrasting the adverse effect of vascular aging.

Cellular mechanisms and signalling pathways activated by high glucose and AGE-albumin in the aortic endothelium

This review summarizes evidence on the effect of excess circulating glucose concentration and AGE-albumin on the aortic endothelial cells (ECs) phenotype, transport function, and expression of signalling molecules. The recent reports on the ECs dysfunction in diabetes are briefly reviewed, to provide a broader view on the link between ECs structural changes, functional alterations, and the underlying biochemical mechanisms. The original results emerging from streptozotocin-injected mice and human aortic endothelial cells grown in high (25 mM) glucose concentration are presented. Compared to physiological condition, in diabetes aortic ECs switch to a biosynthetic phenotype, present an increased number of caveolae, and enhance (by approximately 20%) transcytosis of AGE-albumin (AGE-Alb). In cultured ECs, 25 mM glucose induces approximately 2.6 fold increase in pSTAT-3 and pERK1 and approximately 1.8 fold increase in pERK2; further exposure to 5 microM AGE-Alb causes approximately 4.3 fold increase in pERK1/2 (vs. 5 mM glucose). Together, these data may explain the phenotypic change, enhanced permeability, and proliferation of aortic ECs in diabetic conditions.

Endothelial nitric oxide synthase deficiency produces accelerated nephropathy in diabetic mice

Functionally significant polymorphisms in endothelial nitric oxide synthase (eNOS) and reduced vascular eNOS activity have been associated with increased human diabetic nephropathy (DN), but the pathogenic role of eNOS deficiency in the development of DN has not yet been confirmed. This study characterizes the severity of DN in eNOS(-/-) mice that were backcrossed to C57BLKS/J db/db mice. Although the severity of hyperglycemia was similar to C57BLKS/J db/db mice, by 26 wk, eNOS(-/-) C57BLKS/J db/db mice exhibited dramatic albuminuria, arteriolar hyalinosis, increased glomerular basement membrane thickness, mesangial expansion, mesangiolysis, and focal segmental and early nodular glomerulosclerosis. Even more remarkable, eNOS(-/-) C57BLKS db/db exhibited decreases in GFR to levels <50% of that in eNOS(+/+) C57BLKS db/db, as confirmed by increased serum creatinine. In summary, eNOS(-/-) db/db mice provide the most robust model of type II DN that has been described to date and support a role for deficient eNOS-derived NO production in the pathogenesis of DN.

Postprandial hyperglycemia alters inflammatory and hemostatic parameters

Glucose or glucose derived products are increased in blood during the postprandial phase and are, to a certain extent, related to meal composition. Glucose and glucose derived products such as advanced glycation end products (AGEs) can be formed in the intracellular compartment but can also be absorbed as AGEs or AGE precursors present in food. Glucose, glucose metabolites and AGEs alter endothelial cell functions, induce adhesion molecule overexpression (ICAM-1, VCAM), cytokine release (IL-6, MCP-1) and tissue factor production. Tumor necrosis factor alpha systemic level is increased during the postprandial phase as are augmented C reactive protein and fibrinogen level. Hyperglycemia induced an increase in plasminogen activator inhibitor, and shortened fibrinogen half life. Hyperglycemia and AGEs provoked an oxidant stress. The formation of reactive oxygen intermediates perturbates NO (Nitric oxide) formation and are deleterious for cell functions. All the modifications observed in the postprandial phase are not too deleterious but their iterative characteristics may lead to vascular dysfunction.

Accelerated atherosclerosis in patients with systemic autoimmune diseases

Systemic autoimmune diseases such as systemic lupus erythematosus and Wegener's granulomatosis are associated with a significantly increased prevalence of cardiovascular disease (CVD) compared with age- and sex-matched controls. Many risk factors are involved in the pathogenesis of atherosclerosis, the major underlying cause of CVD. In patients with systemic autoimmune diseases, it has been shown that traditional risk factors for CVD cannot completely explain the prevalence of atherosclerosis. Therefore, in addition to these traditional factors, nontraditional risk factors are suggested to contribute to atherogenesis. All risk factors, traditional and nontraditional, contribute to endothelial activation that, followed by endothelial dysfunction, is seen as one of the first steps in this process. This review updates information on the factors that contribute to accelerated atherosclerosis in patients with systemic autoimmune diseases, such as disease-related factors, inflammatory mediators, and advanced glycation end products.

Aldose reductase pathway inhibition improved vascular and C-fiber functions, allowing for pressure-induced vasodilation restoration during severe diabetic neuropathy

Pressure-induced vasodilation, a neurovascular mechanism relying on the interaction between mechanosensitive C-fibers and vessels, allows skin blood flow to increase in response to locally nonnociceptive applied pressure that in turn may protect against pressure ulcers. We expected that severe neuropathy would dramatically affect pressure-induced vasodilation in diabetic mice, and we aimed to determine whether pressure-induced vasodilation alteration could be reversed in 8-week diabetic mice. Control and diabetic mice received no treatment or sorbinil, an aldose reductase inhibitor, or alagebrium, an advanced glycation end product breaker, the last 2 weeks of diabetes. Laser Doppler flowmetry was used to evaluate pressure-induced vasodilation and endothelium-dependent vasodilation after iontophoretic delivery of acetylcholine (ACh). We assessed the nervous function with measurements of motor nerve conduction velocity (MNCV) as well as the C-fiber-mediated nociception threshold. Pressure-induced vasodilation, endothelial response, C-fiber threshold, and MNCV were all altered in 8-week diabetic mice. None of the treatments had a significant effect on MNCV. Although sorbinil and alagebrium both restored ACh-dependent vasodilation, sorbinil was the sole treatment to restore the C-fiber threshold as well as pressure-induced vasodilation development. Therefore, the inhibition of aldose reductase pathway by sorbinil improved vascular and C-fiber functions that allow pressure-induced vasodilation restoration that could limit neuropathic diabetic cutaneous pressure ulcers.

Amadori-modified glycated albumin predominantly induces E-selectin expression on human umbilical vein endothelial cells through NADPH oxidase activation

BACKGROUND

Protein glycation is closely linked to endothelial-cell dysfunction and vascular complications in diabetes. Glycated albumin is reported to induce cellular signaling similar to advanced glycation endoproducts (AGEs), however, cellular signaling remains obscure.

METHOD

We stimulated human umbilical vein endothelial cells (HUVECs) by glycated human serum albumin (Glc-HSA), determined E-selectin expression by real-time PCR and immunometric methods, and estimated cellular signaling by using various signaling molecule inhibitors and confocal microscopy.

RESULTS

Glc-HSA-induced E-selectin expression was 10 or 20 times more than that induced with 3 kinds of AGEs-HSAs, which was not suppressed by anti-receptor for AGEs (RAGE) antibody. Glc-HSA-induced E-selectin expression was completely suppressed by the NADPH oxidase inhibitor diphenylene iodonium chloride and the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine. Confocal microscopic analysis also revealed intracellular accumulation of ROS. Glc-HSA-induced E-selectin expression was suppressed by the phosphatidylinositol 3 kinase (PI3K) inhibitors wortmannin and LY294002, the protein kinase B (PKB) inhibitor ML-9, the IkappaB kinase (IKK) inhibitor BAY117082, and the Jun N-terminal kinase (JNK) inhibitor SP600125, On the other hand, the protein kinase C inhibitors calphostin C and H-7 did not suppress Glc-HSA-induced E-selectin expression.

CONCLUSION

Glc-HSA induces activation of NADPH oxidase, PKB-IKK and JNK, then E-selectin gene transcription is upregulated by nuclear-translocated NF-kappaB and AP-1.

Elevation of circulating endothelial microparticles in patients with chronic renal failure

BACKGROUND

Chronic renal failure patients are at high risk of cardiovascular events and display endothelial dysfunction, a critical element in the pathogenesis of atherosclerosis. Upon activation, the endothelium sheds microparticles, considered as markers of endothelial dysfunction that also behave as vectors of bioactive molecules.

AIM

To measure plasma levels of endothelial microparticles (EMPs) in chronic renal failure patients (CRF), either undialyzed or hemodialyzed (HD), and to investigate the ability of uremic toxins to induce EMP release in vitro.

METHODS

Circulating EMPs were numerated by flow cytometry, after staining of platelet-free plasma with phycoerythrin (PE)-conjugated anti-CD144 (CD144+ EMP) or anti-CD146 (CD146+ EMP) monoclonal antibodies. Platelet MP (CD41+ PMP), leukocyte MP (CD45+ leukocyte microparticles (LMP)), and annexin-V+ MPs were also counted. In parallel, MPs were counted in supernatant of human umbilical vein endothelial cells incubated with uremic toxins [oxalate, indoxyl sulfate, p-cresol, and homocysteine (Hcy)], at concentrations found in patients.

RESULTS AND CONCLUSIONS

CD144+ EMP and CD146+ EMP levels were significantly higher in CRF and HD patients than in healthy subjects. Furthermore, annexin-V+ MPs were elevated in both groups of uremic patients, and CD41+ PMP and CD45+ LMP were increased in CRF and HD patients, respectively. In vitro, p-cresol and indoxyl sulfate significantly increased both CD146+ and annexin-V+ EMP release. Increased levels of circulating EMP in CRF and HD patients represent a new marker of endothelial dysfunction in uremia. The ability of p-cresol and indoxyl sulfate to increase EMP release in vitro suggests that specific uremic factors may be involved in EMP elevation in patients.

The RAGE axis and endothelial dysfunction: maladaptive roles in the diabetic vasculature and beyond

Receptor for advanced glycation end product (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules. The ligand-RAGE axis is emerging as a central mechanism linked to vascular injury and atherosclerosis in diabetes and in euglycemia. The repertoire of RAGE ligands, including advanced glycation end products, S100/calgranulins, high-mobility group box 1, amyloid-beta peptide, and Mac-1, transcends RAGE biology from specifically the science of diabetic complications to central aspects of the inflammatory response and oxidative stress. Experiments in cell culture and in vivo support the notion that interaction of RAGE ligands with RAGE activates key signal transduction pathways that modulate fundamental cellular properties, thereby leading to vascular and inflammatory cell perturbation. These considerations support the premise that the ligand-RAGE axis may be an important target for therapeutic intervention in cardiovascular disease and, fundamentally, in initiation and amplification of inflammatory responses.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

Advanced glycation end-product peptides are associated with impaired renal function, but not with biochemical markers of endothelial dysfunction and inflammation, in non-diabetic individuals

BACKGROUND

Patients with end-stage renal disease as well as mild renal impairment have an increased risk for the development of cardiovascular disease. It has been suggested that advanced glycation end-products (AGEs) are involved in atherogenesis, possibly through induction of endothelial dysfunction and low-grade inflammation.

METHODS

In a cross-sectional, single-centre study, we investigated four groups of 20 non-diabetic subjects with a creatinine clearance ranging from normal (> 90 ml/min/1.73 m2) to < 31 ml/min/1.73 m2. We measured AGE-peptides, markers of endothelial dysfunction (von Willebrand factor, soluble E-selectin, plasminogen activator inhibitor-1, tissue-type plasminogen activator, soluble vascular cell adhesion molecule-1) and markers of inflammatory activity (soluble intercellular adhesion molecule-1, C-reactive protein, secretory phospholipase A2). We constructed composite endothelial dysfunction and inflammatory activity Z-scores using these markers.

RESULTS

AGE-peptides were independently related to creatinine clearance (standardized beta -0.55, 95% confidence interval (CI) -0.77 to -0.34, P < 0.001). AGE-peptides were not independently related to the individual markers of endothelial dysfunction and inflammation, nor to the composite endothelial dysfunction Z-score (standardized beta 0.08, 95% CI -0.14 to -0.30, P = 0.48) or the inflammatory activity Z-score (standardized beta -0.05, 95% CI -0.25 to -0.16, P = 0.66).

CONCLUSIONS

Plasma concentrations of AGE-peptides are associated with creatinine clearance but not with biochemical markers of endothelial dysfunction and inflammatory activity in non-diabetic patients over a wide range of renal function. This suggests that the atherogenic effects of AGE-peptides in individuals with renal functional impairment are not mediated by endothelial dysfunction or inflammatory activity as estimated by the markers used.

Decreased endogenous secretory advanced glycation end product receptor in type 1 diabetic patients: its possible association with diabetic vascular complications

OBJECTIVE

The binding of advanced glycation end products (AGEs) to their receptor (RAGE) plays an important role in the development of diabetic vascular complications. In the present study, we examined circulating endogenous secretory RAGE (esRAGE) levels in subjects with type 1 diabetes and explored the possible association between esRAGE levels and the severity of diabetic vascular complications.

RESEARCH DESIGN AND METHODS

Circulating esRAGE levels in serum were examined in 67 Japanese type 1 diabetic patients (22 men and 45 women, age 24.0 +/- 4.4 years [means +/- SD]) and 23 age-matched healthy nondiabetic subjects (10 men and 13 women aged 24.9 +/- 1.4 years). Daily urinary albumin excretion, the presence of retinopathy, and intima-media thickness (IMT) of the carotid artery were also evaluated. We further explored the association between esRAGE levels and severity of diabetic vascular complications.

RESULTS

Circulating esRAGE levels were significantly lower in subjects with type 1 diabetes than in nondiabetic subjects (0.266 +/- 0.089 vs. 0.436 +/- 0.121 ng/ml, respectively, P < 0.0001) and was inversely correlated with HbA(1c) (A1C) levels (r = -0.614, P < 0.0001). In addition, multivariate regression analysis demonstrated that A1C was an independent risk factor for a low esRAGE value. Furthermore, circulating esRAGE levels were inversely correlated with carotid IMT (r = -0.325, P = 0.0017) and was one of the independent risk factors for IMT thickening. Furthermore, there was a significant difference (P = 0.0124) in esRAGE levels between patients without retinopathy (0.286 +/- 0.092 ng/ml) and those with retinopathy (0.230 +/- 0.074 ng/ml).

CONCLUSIONS

Circulating esRAGE levels were significantly lower in type 1 diabetic patients than in nondiabetic subjects and were inversely associated with the severity of some diabetic vascular complications.

The discovery of glycated hemoglobin: a major event in the study of nonenzymatic chemistry in biological systems

Glycated hemoglobins are minor components of human hemoglobin (Hb). These are formed nonenzymatically by condensation of glucose or other reducing sugars with alpha- and beta-chains of hemoglobin A. The subfraction HbA1c, a nonenzymatic glycation at the amino-terminal valines of the beta-chain, was identified by the author in the 1960s as a minor "abnormal fast-moving hemoglobin band" in diabetic patients during routine screening for hemoglobin variants. This finding later turned out to be an important biomolecular marker with clinical and pathological applications. Measurement of HbA1c in diabetic patients is an established procedure for evaluating long-term control of diabetes, and the introduction of this measurement represents an outstanding contribution to the quality of care of diabetic patients in this century. More importantly, HbA1c is the first example of in vivo nonenzymatic glycation of proteins, and its discovery opened new and still-growing avenues of research on Maillard reactions in biological systems, including the concept of advanced glycation/lipoxidation end products (AGEs/ALEs) and the development of diabetic complications and various diseases associated with aging. Although interest in the Maillard reaction is growing rapidly, much remains to be done in this field, including detection and characterization of all in vivo AGEs/ALEs, development and clinical applications of AGE inhibitors and breakers, as well as investigations into the possible roles of the Maillard reaction in regulatory biology and carcinogenesis.

Advanced glycation end products and the kidney

Advanced glycation end products (AGEs) are a heterogeneous group of protein and lipids to which sugar residues are covalently bound. AGE formation is increased in situations with hyperglycemia (e.g., diabetes mellitus) and is also stimulated by oxidative stress, for example in uremia. It appears that activation of the renin-angiotensin system may contribute to AGE formation through various mechanisms. Although AGEs could nonspecifically bind to basement membranes and modify their properties, they also induce specific cellular responses including the release of profibrogenic and proinflammatory cytokines by interacting with the receptor for AGE (RAGE). However, additional receptors could bind AGEs, adding to the complexity of this system. The kidney is both: culprit and target of AGEs. A decrease in renal function increases circulating AGE concentrations by reduced clearance as well as increased formation. On the other hand, AGEs are involved in the structural changes of progressive nephropathies such as glomerulosclerosis, interstitial fibrosis, and tubular atrophy. These effects are most prominent in diabetic nephropathy, but they also contribute to renal pathophysiology in other nondiabetic renal diseases. Interference with AGE formation has therapeutic potential for preventing the progression of chronic renal diseases, as shown from data of animal experiments and, more recently, the first clinical trials.

Advanced-glycation end products in insulin-resistant states

Insulin resistance is a central component of a number of clinical conditions, including the metabolic syndrome, diabetes, and hypertension. There is emerging evidence that the consequent hyperinsulinemia and visceral adiposity may be directly responsible for the excess cardiovascular morbidity and mortality seen in these conditions. Advanced-glycation end products, a chemically diverse group of compounds found in higher levels in insulin-resistant states, have also been shown to adversely affect endothelial function as well as activate numerous intracellular signaling pathways implicated in the atherosclerotic pathway. In this review, we summarize the factors thought to be important in both the initiation and exacerbation of the insulin-resistant state, and directly examine the potential role of advanced-glycation end products in this process.

Arterial aging: is it an immutable cardiovascular risk factor?

Age is the dominant risk factor for cardiovascular diseases. However, until recently, convincing mechanistic or molecular explanations for the increased cardiovascular risks conferred by aging have been elusive. Aging is associated with alterations in a number of structural and functional properties of large arteries, including diameter, wall thickness, wall stiffness, and endothelial function. Emerging evidence indicates that these age-associated changes are also accelerated in the presence of cardiovascular diseases, and that these changes are themselves risk factors for the appearance or progression of these diseases. In this review, the evidence demonstrating that arterial aging is accelerated in cardiovascular diseases and that accelerated arterial aging is a risk factor for adverse cardiovascular outcomes is briefly reviewed, and selected advances in vascular biology that provide insights into the mechanisms that may underlie the increased risks conferred by arterial aging are summarized. Remarkably, a host of biochemical, enzymatic, and cellular alterations that are operative in accelerated arterial aging have also been implicated in the pathogenesis and progression of arterial diseases. These vascular alterations are thus putative candidates that could be targeted by interventions aimed at attenuating arterial aging, similar to the lifestyle and pharmacological interventions that have already been proven effective. Therefore, the notion that aging is a chronological process and that its risky components cannot be modulated is no longer tenable. It is our hope that a greater appreciation of the links between arterial aging and cardiovascular diseases will stimulate further investigation into strategies aimed at preventing or retarding arterial aging.

Rho GTPases and leucocyte-induced endothelial remodelling

Leucocytes in the bloodstream respond rapidly to inflammatory signals by crossing the blood vessel wall and entering the tissues. This process involves adhesion to, and subsequent transmigration across, the endothelium, mediated by a cascade of interactions between adhesion molecules and stimulation of intracellular signalling pathways in both leucocytes and endothelial cells. This leads to changes in endothelial cell morphology that assist leucocyte extravasation, including endothelial cell contraction, intercellular junction disruption, increased permeability, remodelling of the endothelial apical surface and alterations in vesicle trafficking. Rho GTPases play a central role in many of the endothelial responses to leucocyte interaction. In this review, we discuss recent findings on leucocyte-induced alterations to endothelial cells, and the roles of Rho GTPases in these responses.

Palmitate-induced apoptosis in cultured bovine retinal pericytes: roles of NAD(P)H oxidase, oxidant stress, and ceramide

Apoptosis of pericytes (PCs) is an early event in diabetic retinopathy. It is generally thought to be a consequence of sustained hyperglycemia. In keeping with this, long-term (>7 days) incubation of cultured PCs in a high-glucose media has been shown to increase apoptosis. We examine here whether the saturated free fatty acid palmitate, the concentration of which is often elevated in diabetes, has similar effects on cultured PCs. Incubation with 0.4 mmol/l palmitate for 24 h induced both oxidant stress and apoptosis, as evidenced by a sixfold increase in DCF fluorescence and a twofold increase in caspase-3 activation, respectively. NAD(P)H oxidase appeared to be involved in these responses, since overexpression of dominant-negative subunits of NAD(P)H oxidase, such as phox47(DN), diminished oxidant stress, and phox67(DN) and N-17 RAC1(DN) prevented the increase in caspase-3 activity. Likewise, overexpression of vRAC, a constitutively active RAC1, increased caspase-3 activity to the same extent as palmitate alone. The effects of vRAC and palmitate were not additive. In parallel with the increases in oxidative stress, the redox-sensitive transcription factor nuclear factor-kappaB (NF-kappaB) was activated in cells incubated with 0.4 mmol/l palmitate. Furthermore, inhibition of NF-kappaB activation by various means inhibited caspase-3 activation. Finally, incubation with palmitate increased the cellular content of ceramide, a molecule linked to apoptosis and increases in oxidative stress and NF-kappaB activation in other cells. In keeping with such a role, in PCs both coincubation with fumonisin B1 (a ceramide synthase inhibitor) and overexpression of ceramidase I reversed the proapoptotic effect of palmitate. On the other hand, they increased rather than decreased DCF fluorescence. In conclusion, the results suggest that palmitate-induced apoptosis in PCs is associated with activation of NAD(P)H oxidase and NF-kappaB and an increase in ceramide. The precise interactions between these molecules in causing apoptosis and the importance of oxidant stress as a contributory factor remain to be determined.

Advanced glycation end products and RAGE: a common thread in aging, diabetes, neurodegeneration, and inflammation

The products of nonenzymatic glycation and oxidation of proteins and lipids, the advanced glycation end products (AGEs), accumulate in a wide variety of environments. AGEs may be generated rapidly or over long times stimulated by a range of distinct triggering mechanisms, thereby accounting for their roles in multiple settings and disease states. A critical property of AGEs is their ability to activate receptor for advanced glycation end products (RAGE), a signal transduction receptor of the immunoglobulin superfamily. It is our hypothesis that due to such interaction, AGEs impart a potent impact in tissues, stimulating processes linked to inflammation and its consequences. We hypothesize that AGEs cause perturbation in a diverse group of diseases, such as diabetes, inflammation, neurodegeneration, and aging. Thus, we propose that targeting this pathway may represent a logical step in the prevention/treatment of the sequelae of these disorders.

Roles of the receptor for advanced glycation endproducts in diabetes-induced vascular injury

Diabetic patients have shorter life span and poorer Quality of Life mainly due to diabetic vascular complications. Recent in vitro and in vivo studies have shown that advanced glycation endproducts (AGE) account for diabetic vascular complications through their engagement of the receptor for AGE (RAGE). In this review, we summarize our recent studies on the roles of the AGE-RAGE system in diabetes-induced vascular injury. In vitro experiments showed that AGE engagement of RAGE leads to changes in endothelial cells (EC) and pericytes, which are characteristic of diabetic microangiopathy. Diabetic RAGE transgenic mice that overexpress RAGE in vascular cells exhibited the exacerbation of the indices of nephropathy and retinopathy, and this was prevented by the inhibition of AGE formation. RAGE overexpression also caused calcium handling impairment in cardiac myocytes. In contrast to the RAGE-overexpressing mice, diabetic RAGE knockout mice showed marked improvement of nephropathy. We found that human vascular cells express a novel splice variant coding for a soluble RAGE protein and named it endogenous secretory RAGE (esRAGE). The esRAGE neutralizes AGE actions on EC and is present in human sera. Individual variations in circulating esRAGE could be a determinant for individual differences in susceptibility or resistance to the development of diabetic vascular complications. The AGE-RAGE system should be, therefore, a candidate molecular target for overcoming diabetic vascular complications.

Cellular mechanisms and treatment of diabetes vascular complications converge on reactive oxygen species

High glucose activates a myriad of signaling and gene expression pathways in non-insulin-dependent target cells causing diabetes complications. One of the earliest responses to high glucose by vascular cells is the generation of reactive oxygen species (ROS) that act directly on intracellular proteins and DNA, or indirectly as second messengers, transforming these cells into disease phenotypes. ROS are produced by mitochondria and/or NADPH oxidase in all target cells exposed to high glucose studied to date. Reports using cell cultures and diabetic animal models indicate that inhibition of ROS generation prevents the amplification of signaling and gene expression that are implicated in vascular complications. These models convincingly demonstrate that maneuvers preventing ROS production attenuate or completely abrogate early micro- and macrovascular end-organ damage of diabetes, including nephropathy, retinopathy, and large-vessel atherosclerosis. Attention now turns to the development of more effective antioxidants that could be used in clinical trials in the prevention and treatment of diabetes complications.