Advanced glycation endproducts interacting with their endothelial receptor induce expression of vascular cell adhesion molecule-1 (VCAM-1) in cultured human endothelial cells and in mice. A potential mechanism for the accelerated vasculopathy of diabetes

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Impact of diabetic serum on endothelial cells: an in-vitro-analysis of endothelial dysfunction in diabetes mellitus type 2

Diabetic endothelial dysfunction was characterized by altered levels of adhesion molecules and cytokines. Aim of our study was to evaluate the effects of diabetic serum on cell-growth and proinflammatory markers in human saphenous vein endothelial cells (HSVEC) from diabetic and non-diabetic patients. Diabetic serum showed (1) complementary proliferative activity for non-diabetic and diabetic HSVEC, (2) unchanged surface expression of adhesion molecules, and (3) elevated levels of sICAM-1 in HSVEC of all donors. The concentration of sVCAM-1 was increased only in diabetic cells. The proinflammatory state of diabetic HSVEC characterized by increased levels of cytokines was compensated. We concluded that even under normoglycemic conditions the serum itself contains critical factors leading to abnormal regulation of inflammation in diabetics. We introduced an in vitro model of diabetes representing the endothelial situation at the beginning of diabetes (non-diabetic cells/diabetic serum) as well as the diabetic chronic state (diabetic cells/diabetic serum).

The extracellular region of the receptor for advanced glycation end products is composed of two independent structural units

The receptor for advanced glycation end products (RAGE) is an important cell surface receptor being pursued as a therapeutic target because it has been implicated in complications arising from diabetes and chronic inflammatory conditions. RAGE is a single membrane spanning receptor containing a very small approximately 40 residue cytosolic domain and a large extracellular region composed of 3 Ig-like domains. In this study, high level bacterial expression systems and purification protocols were generated for the extracellular region of RAGE (sRAGE) and the five permutations of single and tandem domain constructs to enable biophysical and structural characterization of its tertiary and quaternary structure. The structure and stability of each of these six protein constructs was assayed by biochemical methods including limited proteolysis, dynamic light scattering, CD, and NMR. A homology model of sRAGE was constructed to aid in the interpretation of the experimental data. Our results show that the V and C1 domains are not independent domains, but rather form an integrated structural unit. In contrast, C2 is attached to VC1 by a flexible linker and is fully independent. The interaction with a known RAGE ligand, Ca2+-S100B, was mapped to VC1, with the major contribution from the V domain but clearly defined secondary effects from the C1 domain. The implications of these results are discussed with respect to models for RAGE signaling.

Effect of Pentoxifylline on inflammatory burden, oxidative stress and platelet aggregability in hypertensive type 2 diabetes mellitus patients

OBJECTIVES

Inflammation and oxidative stress are main culprits behind atherosclerosis in diabetes mellitus. This study explores the effect of add-on Pentoxifylline on inflammatory burden and oxidative stress in hypertensive diabetic patients.

RESEARCH DESIGN AND METHODS

60 hypertensive type 2 diabetic, aged > or = 45 years were evaluated for anthropometry, clinical parameters, C-reactive protein, total leukocyte count, erythrocyte sedimentation rate, serum albumin, plasma malondialdehyde, blood reduced glutathione, platelet aggregation and clot retraction profile. With informed consent and randomization, Pentoxifylline (400 mg) was prescribed to 30 patients orally twice daily with meals as add-on therapy to the standard therapeutic regimen for one month. The particular parameters were repeated in 26 patients in control group and 25 patients in Pentoxifylline group who completed the follow up. The study was a randomized, open, add-on clinical trial with parallel controls.

RESULTS

At one-month follow-up, in the Pentoxifylline group, there was 20.9% decrease (p<0.001) in C-reactive protein, 18% reduction (p<0.001) in erythrocyte sedimentation rate, 11.1% reduction (p<0.001) in total leukocyte count and 5.8% increase (p=0.003) in serum albumin. Pentoxifylline showed 20.2% reduction in plasma malondialdehyde and 4.6% increase in blood reduced glutathione level. In therapeutic dose range, Pentoxifylline exerted a significant anti-aggregatory effect and a dose dependent decrease in clot retraction in-vitro but there was no significant change in ex-vivo clot retraction. The control group showed no statistically significant change in parameters assessed.

CONCLUSION

This study reveals improvements in inflammatory markers, oxidative stress and platelet-aggregation by Pentoxifylline, thus preventing atherosclerosis in diabetes mellitus.

Association of A1C with cardiovascular disease and metabolic syndrome in Asian Indians with normal glucose tolerance

OBJECTIVE

This study examines the association of A1C with cardiovascular disease (CVD) risk factors, coronary artery disease (CAD), and metabolic syndrome in Asian Indians with normal glucose tolerance (NGT).

RESEARCH DESIGN AND METHODS

This cross-sectional study recruited subjects from phase III of the Chennai Urban Rural Epidemiology Study (CURES), an epidemiological study in a representative population of Chennai (formerly Madras) in South India, conducted between January 2003 and June 2004. Included were 1,644 subjects with NGT, i.e., fasting plasma glucose <100 mg/dl (5.6 mmol/l) and 2-h postload plasma glucose <140 mg/dl (7.8 mmol/l). A1C was measured using the Biorad Variant machine. Metabolic syndrome was defined based on modified Adult Treatment Panel III guidelines.

RESULTS

The mean +/- SD A1C value in the study cohort was 5.5 +/- 0.4%. A1C showed a significant association with BMI (beta = 0.017, P < 0.001), systolic (beta = 0.002, P = 0.028) and diastolic (beta = 0.202, P = 0.017) blood pressure, waist circumference (beta = 0.007, P < 0.001), serum cholesterol (beta = 0.002, P < 0.001), triglycerides (beta = 0.001, P < 0.001), LDL cholesterol (beta = 0.002, P < 0.001), fasting insulin (beta = 0.009, P < 0.001), and homeostasis model assessment of insulin resistance (beta = 0.047, P < 0.001) after adjusting for age and sex. Regression analysis showed that A1C had a strong association with metabolic syndrome that persisted after adjusting for age and sex (odds ratio [OR] 2.9 [95% CI 2.08-4.00]; P < 0.001). A1C also had a strong association with CAD (2.6 [1.23-5.63]; P = 0.01), but the significance was lost when adjusted for age and sex.

CONCLUSIONS

There is a strong association of A1C with prevalent CVD risk factors in Asian-Indian subjects with NGT.

Receptor for advanced glycation end products (RAGE) in a dash to the rescue: inflammatory signals gone awry in the primal response to stress

The multiligand receptor for advanced glycation end products (RAGE) of the Ig superfamily transduces the biological impact of discrete families of ligands, including advanced glycation end products, certain members of the S100/calgranulin family, high mobility group box-1, Mac-1 (alpha(M)beta(2), CD11b/CD18), and amyloid-beta peptide and beta-sheet fibrils. Although structurally dissimilar, at least at the monomeric level, recent evidence suggests that oligomeric forms of these RAGE ligands may be especially apt to activate the receptor and up-regulate a program of inflammatory and tissue injury-provoking genes. The challenge in probing the biology of RAGE and its impact in acute responses to stress and the potential development of chronic disease is to draw the line between mechanisms that evoke repair versus those that sustain inflammation and tissue damage. In this review, we suggest the concept that the ligands of RAGE comprise a primal program in the acute response to stress. When up-regulated in environments laden with oxidative stress, inflammation, innate aging, or high glucose, as examples, the function of these ligand families may be transformed from ones linked to rapid repair to those that drive chronic disease. Identification of the threshold beyond which ligands of RAGE mediate repair versus injury is a central component in delineating optimal strategies to target RAGE in the clinic.

Do glucose and lipids exert independent effects on atherosclerotic lesion initiation or progression to advanced plaques?

It is becoming increasingly clear that suboptimal blood glucose control results in adverse effects on large blood vessels, thereby accelerating atherosclerosis and cardiovascular disease, manifested as myocardial infarction, stroke, and peripheral vascular disease. Cardiovascular disease is accelerated by both type 1 and type 2 diabetes. In type 1 diabetes, hyperglycemia generally occurs in the absence of elevated blood lipid levels, whereas type 2 diabetes is frequently associated with dyslipidemia. In this review article, we discuss hyperglycemia versus hyperlipidemia as culprits in diabetes-accelerated atherosclerosis and cardiovascular disease, with emphasis on studies in mouse models and isolated vascular cells. Recent studies on LDL receptor-deficient mice that are hyperglycemic, but exhibit no marked dyslipidemia compared with nondiabetic controls, show that diabetes in the absence of diabetes-induced hyperlipidemia is associated with an accelerated formation of atherosclerotic lesions, similar to what is seen in fat-fed nondiabetic mice. These effects of diabetes are masked in severely dyslipidemic mice, suggesting that the effects of glucose and lipids on lesion initiation might be mediated by similar mechanisms. Recent evidence from isolated endothelial cells demonstrates that glucose and lipids can induce endothelial dysfunction through similar intracellular mechanisms. Analogous effects of glucose and lipids are also seen in macrophages. Furthermore, glucose exerts many of its cellular effects through lipid mediators. We propose that diabetes without associated dyslipidemia accelerates atherosclerosis by mechanisms that can also be activated by hyperlipidemia.

Long-term effects of oral vitamin C supplementation on the endothelial dysfunction in the iris microvessels of diabetic rats

The current study was aimed to investigate effects of long-term supplementation of vitamin C on the iris microcirculation in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in male Wistar-Furth rats by intravenous injection of STZ (55 mg/kg b.w.). The rats were divided into three groups: control rats (CON), STZ-induced diabetic rats (STZ), and STZ rats supplemented with vitamin C (STZ-vitC). For supplementation of vitamin C, ascorbic acid (1 g/l) was added into the drinking water. The experiments were performed at different periods (8, 12, 24 and 36 weeks) after injection of STZ. Blood glucose, tissue lipid peroxidation and plasma vitamin C were measured. To examine the endothelial function, leukocyte adhesion to the venular endothelium was evaluated in the iris post-capillaries by means of counting the number of leukocytes labeled with rhodamine 6G. Blood flow perfusion in the iris was monitored using a laser Doppler flow meter. In the STZ rats, hyperglycemia was induced with an increase in HbA(1c) and lipid peroxidation but with a decrease in the plasma vitamin C level which improved by vitamin C supplementation. The number of adherent leukocytes increased significantly, associated with reduction in the iris blood flow perfusion, at 8, 12, 24 and 36 weeks after injection of STZ. In the STZ-vitC rats, the iris blood flow perfusion was significantly increased in comparison with the STZ rats, while the leukocyte adhesion was decreased at 24 and 36 weeks. The statistical analysis shows that the leukocyte adhesion decreased with increase in the iris blood flow perfusion in STZ and STZ-vitC rats. In conclusion, vitamin supplementation suppressed leukocyte adhesion and thus endothelial dysfunction, associated with increase in iris blood flow perfusion in diabetes. The antioxidant vitamin C may be a therapeutic agent for preventing diabetic retinopathy.

Receptor for advanced glycation endproducts mediates neutrophil migration across intestinal epithelium

Receptor for advanced glycation endproducts (RAGE) is an Ig superfamily cell surface receptor that interacts with a diverse array of ligands associated with inflammatory responses. In this study, we provide evidence demonstrating that RAGE is involved in inflammatory responses in the intestines. We showed that RAGE is expressed in intestinal epithelial cells, primarily concentrated at the lateral membranes close to the apical cell junction complexes. Although RAGE expression was low in epithelium under normal conditions, this protein was up-regulated after treatment with the inflammatory cytokines IFN-gamma and/or TNF-alpha. RAGE expression was also elevated in colon tissue samples from patients with inflammatory bowel diseases. Using in vitro transmigration assays, we found that RAGE mediates neutrophil (polymorphonuclear leukocytes (PMN)) adhesion to, and subsequent migration across, intestinal epithelial monolayers. This activity appears to be mediated by the binding of RAGE to the PMN-specific beta(2) integrin CD11b/CD18. Thus, these results provide a novel mechanism for the regulation of PMN transepithelial migration and may suggest a new therapeutic target for intestinal inflammation.

Mitochondrial dysfunction in atherosclerosis

Increased production of reactive oxygen species in mitochondria, accumulation of mitochondrial DNA damage, and progressive respiratory chain dysfunction are associated with atherosclerosis or cardiomyopathy in human investigations and animal models of oxidative stress. Moreover, major precursors of atherosclerosis-hypercholesterolemia, hyperglycemia, hypertriglyceridemia, and even the process of aging-all induce mitochondrial dysfunction. Chronic overproduction of mitochondrial reactive oxygen species leads to destruction of pancreatic beta-cells, increased oxidation of low-density lipoprotein and dysfunction of endothelial cells-factors that promote atherosclerosis. An additional mechanism by which impaired mitochondrial integrity predisposes to clinical manifestations of vascular diseases relates to vascular cell growth. Mitochondrial function is required for normal vascular cell growth and function. Mitochondrial dysfunction can result in apoptosis, favoring plaque rupture. Subclinical episodes of plaque rupture accelerate the progression of hemodynamically significant atherosclerotic lesions. Flow-limiting plaque rupture can result in myocardial infarction, stroke, and ischemic/reperfusion damage. Much of what is known on reactive oxygen species generation and modulation comes from studies in cultured cells and animal models. In this review, we have focused on linking this large body of literature to the clinical syndromes that predispose humans to atherosclerosis and its complications.

Effects of flavonoids on the expression of the pro-inflammatory response in human monocytes induced by ligation of the receptor for AGEs

Increasing evidence has shown advanced glycation end products (AGEs) receptor ligation (RAGE) to be an important part of complex interactions of the oxidative stress and pro-inflammatory responses. In this study, flavonoids were used to monitor the protective effects against the oxidative damage and inflammation mediated by AGEs in human monocytes. S100B (RAGE ligand) treatment in human THP-1 monocytic cells (THP-1) significantly increased gene expression of the pro-inflammatory cytokines TNF-alpha and IL-1beta; chemokines MCP-1 and IP-10; adhesion factors platelet endothelial cell adhesion molecule (PECAM-1) and beta2-integrin; and pro-inflammatory cyclooxygenase-2 (COX-2). S100B treatment with quercetin and catechin in THP-1 cells had inhibitory effects on the expression of pro-inflammatory genes and protein levels. Quercetin and catechin could regulate S100B-activated oxidant stress-sensitive pathways through blocking p47phox protein expression. Treatment with quercetin and catechin could eliminate reactive oxygen species (ROS) to reduce oxidative stress stimulated by S100B in THP-1 cells. Quercetin and catechin also showed different regulatory abilities on mitogen-activated protein kinase (MAPK) signaling pathways by inhibiting protein expression in S100B-stimulated inflammatory responses in THP-1 cells. This study suggests that quercetin and catechin may be of benefit for diabetic vascular complications due to its antioxidant abilities against AGE-mediated oxidative stress through oxidative stress-sensitive and oxidative stress-responsive signaling pathways, which lead to inflammation in human monocytes.

Renal microvascular injury in diabetes: RAGE and redox signaling

Diabetic nephropathy remains a major cause of morbidity and mortality in the diabetic population and is the leading cause of end-stage renal failure in the Western World. Despite current therapeutics including intensified glycemic control and blood pressure lowering agents, renal disease continues to progress relentlessly in diabetic patients, albeit at a lower rate. It is well recognized that metabolic and hemodynamic factors play a central role in accelerating renal disease in diabetes. However, recent experimental studies have suggested that increased generation of reactive oxygen species (ROS) as a result of the diabetic milieu may play a central role in the progression of diabetic microvascular complications. These ROS appear to be generated primarily from mitochondrial sources and via the enzyme, NADPH oxidase. This review focuses on how ROS play a deleterious role in the diabetic kidney and how they are involved in crosstalk among various signaling pathways, ultimately leading to renal dysfunction and structural injury.

Anti-inflammatory effects of the advanced glycation end product inhibitor LR-90 in human monocytes

Ligation of advanced glycation end products (AGEs) with their receptor (RAGE) plays an important role in the development of various diabetes complications, including atherosclerosis. Monocyte activation, adhesion, and migration are key events in the pathogenesis of atherosclerosis. Previous studies showed that AGEs and S100b, a specific RAGE ligand, could augment monocyte inflammatory responses via RAGE. In this study, we examined whether LR-90, a compound belonging to a new class of AGE inhibitor, could inhibit inflammatory responses in human monocytes. Human THP-1 cells were pretreated with LR-90 and then stimulated with S100b. LR-90 significantly inhibited S100b-induced expression of RAGE and other proinflammatory genes including monocyte chemoattractant protein-1, interferon-gamma-inducible protein-10, and cyclooxygenase-2 in a dose-dependent manner. These inhibitory effects may be exerted via inhibition of nuclear factor-kappaB (NF-kappaB) activation, as LR-90 suppressed both S100b-and tumor necrosis factor-alpha-induced IkappaB-alpha degradation as well as NF-kappaB promoter transcriptional activity. LR-90 also prevented oxidative stress in activated monocytes, as demonstrated by its inhibitory effects on S100b-induced expression of NADPH oxidase and intracellular superoxide production. In addition, LR-90 blocked S100b-induced monocyte adhesion to human umbilical vein endothelial cell. These new data show that, in addition to its AGE inhibitory effects, LR-90 has novel anti-inflammatory properties and might therefore have additional protective effects against diabetic vascular complications.

Pregnancy-associated plasma protein a and soluble receptor for advanced glycation end products after kidney transplantation

BACKGROUND

Pregnancy-associated plasma protein A (PAPP-A) and soluble receptor for advanced glycation end products (sRAGE) are new markers related to vascular damage.

METHODS

Thirty-one patients who had undergone kidney transplantation (TX) in the year 2005 under tacrolimus-based immunosuppression were included in this prospective single-center study. PAPP-A and sRAGE were determined before TX and 2 and 6 weeks and 3 months after TX. The results were correlated with the 3-month protocol kidney graft biopsy findings.

RESULTS

Both PAPP-A and sRAGE decreased after TX (mean values in serum: PAPP-A 20.8, 13.7, 12.1, and 10.7 mIU/l, respectively, before and 2 and 6 weeks and 3 months after TX, p < 0.001; sRAGE 4,403.4, 2,512.7, 1,909.0, and 1,817.6 pg/ml, respectively, before and 2 and 6 weeks and 3 months after TX, p < 0.001) and were correlated with the graft function (PAPP-A vs. modification of diet in renal disease formula r = -0.52, p < 0.001; sRAGE vs. modification of diet in renal disease formula r = -0.54, p < 0.001). Additionally, the PAPP-A levels correlated with interstitial inflammation (r = 0.57, p < 0.05) and vascular intimal thickening (r = 0.47, p < 0.05), while sRAGE correlated with arteriolar hyalinosis (r = 0.49, p < 0.05).

CONCLUSIONS

Our study demonstrates the role of the kidney in the metabolism and/or the removal of PAPP-A and sRAGE. After successful TX, these substances decrease, and, on the contrary, early chronic vascular changes in the kidney TX are associated with elevation of their serum levels.

Mesothelial RAGE activation by AGEs enhances VEGF release and potentiates capillary tube formation

Advanced glycation end-products (AGEs) inhibit ischemia-induced angiogenesis but are potential triggers of neoangiogenesis that occurs in peritoneal dialysis (PD) patients. We investigated whether the effect of glucose and AGEs on human peritoneal mesothelial cells (HPMCs) might alter the release of vascular endothelial growth factor (VEGF) and subsequently the formation of capillary tubes by human umbilical vein endothelial cells (HUVECs). HPMCs were exposed to glucose and the glycated protein Nvarepsilon-(carboxymethyl)lysine-human serum albumin (CML-HSA) and VEGF production was measured by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Capillary tube formation by HUVECs in presence of HPMC supernatant or co-cultured with HPMC was investigated. AGE and VEGF levels in PD effluents from 11 patients were measured. CML-HSA stimulated VEGF production by HPMCs, P<0.001. Glucose and AGE inhibited capillary tube formation by HUVECs, P<0.001. HPMC supernatant potentiated capillary tube formation, P<0.001. In co-culture with HPMC capillary tube formation was increased, especially by HPMCs stimulated by CML-HSA, P<0.001. Anti-VEGF antibody limited this effect, P<0.001. Preincubation of HPMCs with anti-receptor for AGEs (RAGE) antibody reduced capillary tube formation, P<0.001. AGE and VEGF levels in PD effluents were increased during long dwell time, P<0.05 and P<0.001, respectively. In a co-culture system, we showed that VEGF production by HPMC favors capillary tube formation through mesothelial RAGE activation and could explain neoangiogenesis in PD patient.

Advanced glycation end products induce actin rearrangement and subsequent hyperpermeability of endothelial cells�THIS ARTICLE HAS BEEN RETRACTED

This study aimed to determine the effects of advanced glycation end products (AGEs) on endothelial cytoskeleton morphology and permeability, and to detect the underlying signaling mechanisms involved in these responses. Cultured endothelial cells (ECs) were exposed to AGE-modified human serum albumin (AGE-HSA), and EC cytoskeletal changes were evaluated by observing fluorescence of F-actin following ligation with labeled antibodies. Endothelial permeability was detected by measuring the flux of TRITC-albumin across the EC monolayers. To explore the signaling pathways behind AGE-induced EC alteration, ECs were treated with either soluble anti-AGE receptor (RAGE) IgG, or the MAPK inhibitors PD98059 and SB203580 before AGE-HSA administration. To further elucidate possible involvement of the ERK and p38 pathways in AGE-induced EC changes, adenovirus-carried recombinant constitutive dominant-negative forms of upstream ERK and p38 kinases, namely MEK1(A) and MKK6b(A), were pre-infected into ECs 24 h prior to AGE-HSA exposure. AGE-HSA induced actin cytoskeleton rearrangement, as well as EC hyperpermeability, in a dose and time-dependent manner. The effects were attenuated in cells pretreated with anti-RAGE IgG, PD98059 or SB203580, respectively. EC pre-infection with MEK1(A) and MKK6b(A) also alleviated the effect of AGEs. Furthermore, adenovirus-mediated administration of activated forms of either MEK1 or MKK6b alone induced rearrangement of F-actin and hyperpermeability. The results indicate that ERK and p38 MAPK play important roles in the mediation of AGE-induced EC barrier dysfunction associated with morphological changes of the F-actin.

AGE-BSA decreases ABCG1 expression and reduces macrophage cholesterol efflux to HDL

BACKGROUND

Previous reports have suggested that advanced glycation end products (AGE) participate in the pathogenesis of diabetic macroangiopathy. However, current understanding of the mechanisms by which AGE may accelerate atherogenesis remains incomplete.

METHODS AND RESULTS

Microarray and reverse transcription real-time PCR analyses revealed that exposure to AGE-BSA (BSA, bovine serum albumin) reduced mRNA levels (60%) in the ATP-binding cassette transporter G1 (ABCG1) but not ABCA1 in human macrophages. AGE-BSA also reduced ABCG1 protein levels. These effects occurred mainly through the receptor for AGE (RAGE), as an anti-RAGE antibody significantly limited ABCG1 mRNA reduction. Functional studies demonstrated that exposure to AGE-BSA decreased cholesterol efflux to high-density lipoprotein (HDL) (P<0.05) but not to apolipoprotein AI, compared to BSA treatment. Although liver X receptors (LXR) augment ABCG1 expression, macrophages treated with AGE-BSA showed no reduction in LXR mRNA levels or in the binding of nuclear proteins to the LXR response element, compared with BSA.

CONCLUSIONS

Our data show that AGE-BSA can decrease cholesterol efflux from macrophages to HDL via an LXR-independent pathway. This novel mechanism may contribute to accelerated foam cell production and atherogenesis in diabetic patients.

Receptor for advanced glycation end products and the cardiovascular complications of diabetes and beyond: lessons from AGEing

The presence of elevated blood glucose levels characterizes the diabetic state. Hyperglycemia may be caused by a number of underlying factors; however, the consequences of chronically elevated glucose are similar. Both the macrovasculature and microvasculature are exquisitely sensitive to the long-term effects of elevated blood glucose. Cardiovascular disease remains the leading cause of morbidity and mortality in diabetes, regardless of the underlying cause of hyperglycemia. Although other substrates, such as DNA, are susceptible to glycation, this article addresses the impact of nonenzymatic glycation on the proteome. The impact of Advanced Glycation End products (AGEs) on alteration of protein function and signal transduction mechanisms contributes to the pathogenesis of diabetes complications. This suggests that blocking the generation or molecular impact of AGEs may modulate the complications of diabetes.

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

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

Gliclazide treatment lowers serum ICAM-1 levels in poorly controlled type 2 diabetic patients

OBJECTIVE

To investigate the potential effect of gliclazide on serum ICAM-1 (intercellular adhesion molecule-1) and VCAM-1 (vascular cell adhesion molecule-1) levels in poorly controlled type 2 diabetic patients.

PATIENTS AND METHODS

The study included 104 patients, randomly divided into two groups. Group A comprised 53 patients (26 men) treated with gliclazide with a mean age of 67.5+/-9.9 years, a mean diabetes duration of 13.4+/-5.4 years and a mean HbA1c of 8.6+/-1.1%. Group B comprised 51 patients (25 men) treated with glibenclamide with a mean age of 66.4+/-10.9 years, a mean diabetes duration of 13.2+/-6.1 years and a mean HbA1c of 8.4+/-1.3%. A third group of 30 healthy controls (15 men) with a mean age of 63.3+/-10.4 years was also included. Serum levels of ICAM-1 and VCAM-1 were measured at the beginning of the study and after six months of treatment.

RESULTS

Pretreatment serum ICAM-1 and VCAM-1 levels did not differ between groups A and B, while they were significantly higher (P=0.0001) than in healthy controls. No significant difference in HbA1c, body mass index, blood pressure control and lipid profile between the two groups was observed after the sixth month of treatment. In group A, serum ICAM-1 levels after six months of treatment were significantly reduced from 623.12+/-61.17 ng/ml to 370.14+/-49.92 ng/ml (P=0,01), while no reduction was found in VCAM-1 levels. In group B, no reduction was found in serum ICAM-1 and VCAM-1 levels after the end of the study.

CONCLUSIONS

Our results suggest that gliclazide treatment reduces serum ICAM-1 levels in poorly controlled type 2 diabetic patients. This reduction is independent of the hypoglycaemic action of gliclazide.

Susceptibility of brain microvascular endothelial cells to advanced glycation end products-induced tissue factor upregulation is associated with intracellular reactive oxygen species

There is accumulating evidence that advanced glycation end products (AGEs) are relevant to the formation of vascular complications in diabetes mellitus. The aim of this study was to investigate whether AGEs have a significant effect on tissue factor (TF) expression in brain microvascular endothelial cells compared with that in other arterial endothelial cells. Cultured bovine brain microvascular endothelial cells (BBMECs) and aortic endothelial cells (BAECs) were incubated in medium containing glyceraldehyde-derived AGE (glycer-AGE). TF mRNA expression, protein expression, and activity were measured at multiple time points after glycer-AGE incubation. Participation of reactive oxygen species (ROS) in the effect of glycer-AGE on TF expression was investigated by treatment with a free radical scavenger, edaravone, and intracellular ROS measurements with dihydroethidium (DHE). Basic TF mRNA expression was greater in BBMECs than in BAECs. Glycer-AGE significantly upregulated TF mRNA expression in both cells, and the upregulation was more prominent in BBMECs than in BAECs. TF protein expression and activity were also upregulated with a pattern of being greater in BBMECs than in BAECs. Edaravone significantly attenuated the AGE-induced upregulation of TF mRNA expression, protein expression, and activity. Intracellular ROS levels measured with DHE-stained fluorescent intensity were significantly upregulated by glycer-AGE with a pattern of being greater in BBMECs than in BAECs. AGE-induced ROS upregulation was attenuated by edaravone like AGE-induced TF upregulation. These results suggest that brain microvascular endothelial cells are more susceptible to AGE-induced TF upregulation than aortic endothelial cells, and that this susceptibility is associated with levels of intracellular ROS.

Advanced glycation end products: sparking the development of diabetic vascular injury

Advanced glycation end products (AGEs) are proteins or lipids that become glycated after exposure to sugars. AGEs are prevalent in the diabetic vasculature and contribute to the development of atherosclerosis. The presence and accumulation of AGEs in many different cell types affect extracellular and intracellular structure and function. AGEs contribute to a variety of microvascular and macrovascular complications through the formation of cross-links between molecules in the basement membrane of the extracellular matrix and by engaging the receptor for advanced glycation end products (RAGE). Activation of RAGE by AGEs causes upregulation of the transcription factor nuclear factor-kappaB and its target genes. Soluble AGEs activate monocytes, and AGEs in the basement membrane inhibit monocyte migration. AGE-bound RAGE increases endothelial permeability to macromolecules. AGEs block nitric oxide activity in the endothelium and cause the production of reactive oxygen species. Because of the emerging evidence about the adverse effects of AGEs on the vasculature of patients with diabetes, a number of different therapies to inhibit AGEs are under investigation.

Blockade of angiotensin II receptors reduces the expression of receptors for advanced glycation end products in human endothelial cells

OBJECTIVE

Receptors for advanced glycation end products (RAGEs) play crucial roles in atherogenesis. Because tumor necrosis factor alpha (TNFalpha) is expressed and upregulates RAGE expression in atherosclerotic lesions, the TNFalpha-RAGE interaction might be involved in the inflammatory process of atherogenesis. On the other hand, an angiotensin II type-1 receptor blocker (ARB), widely used as an antihypertensive drug, has been reported to have also antiatherosclerotic effects. Thus we investigated whether an ARB exerts antiatherosclerotic effects via inhibiting the TNFalpha-RAGE interaction.

METHODS AND RESULTS

Stimulation of human endothelial cells with candesartan as well as olmesartan decreased TNFalpha-induced RAGE expression in both mRNA and protein levels along with the decrease in the activity of nuclear factor kappaB and the expression of inflammatory mediators such as vascular cell adhesion molecule (VCAM)-1. Both candesartan and olmesartan inhibited the binding of nuclear factor kappaB to the RAGE gene promoter. Furthermore, gene silencing of RAGE by RNA interference decreased the expression of TNFalpha-induced VCAM-1 in both mRNA and protein levels.

CONCLUSIONS

RAGE contributes at least partially to the TNFalpha-induced VCAM-1 expression in both mRNA and protein levels. Blockade of angiotensin II receptors might exert antiatherosclerotic effects via reducing TNFalpha-RAGE interaction.

Receptor for advanced glycation end products is involved in impaired angiogenic response in diabetes

Angiogenic response is impaired in diabetes. Here, we examined the involvement of receptor for advanced glycation end products (RAGE) in diabetes-related impairment of angiogenesis in vivo. Angiogenesis was determined in reconstituted basement membrane protein (matrigel) plugs containing vascular endothelial growth factor (VEGF) implanted into nondiabetic or insulin-deficient diabetic wild-type or RAGE(-/-) mice. The total, endothelial, and smooth muscle (or pericytes) cells in the matrigel were significantly decreased in diabetes, with the regulation dependent on RAGE. In the matrigel, proangiogenic VEGF expression was decreased, while antiangiogenic thrombospondin-1 was upregulated in diabetic mice, regardless of the presence of RAGE. In wild-type mice, proliferating cell nuclear antigen (PCNA)-positive cells in the matrigel were significantly less in diabetic than in nondiabetic mice, while the numbers of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells were significantly higher. This alteration in PCNA- and TUNEL-positive cells in diabetes was not observed in RAGE(-/-) mice. Similarly, the percentage of nuclear factor kappaB-activated cells is enhanced in diabetes, with the regulation dependent on the presence of RAGE. Importantly, adenovirus-mediated overexpression of endogenous secretory RAGE, a decoy receptor for RAGE, restores diabetes-associated impairment of angiogenic response in vivo. Thus, RAGE appears to be involved in impairment of angiogenesis in diabetes, and blockade of RAGE might be a potential therapeutic target.

Diabetes, leukoencephalopathy and rage

Longstanding diabetes mellitus damages kidney, retina, peripheral nerve and blood vessels, but brain is not usually considered a primary target. We describe direct involvement of the brain, particularly white matter, in long-term (9 months) experimental diabetes of mice, not previously modeled, correlating magnetic resonance (MR) imaging with quantitative histological assessment. Leukoencephalopathy and cerebral atrophy, resembling that encountered in diabetic humans, developed in diabetic mice and was accompanied by time-related development of cognitive changes in behavioural testing. Increased RAGE (receptor for advanced glycation end products) expression, a mediator of widespread diabetic complications, increased dramatically at sites of white matter damage in regions of myelination. RAGE expression was also elevated within neurons, astrocytes and microglia in grey matter and within oligodendrocytes in white matter. RAGE null diabetic mice had significantly less neurodegenerative changes when compared to wild-type diabetic mice. Our findings identify a robust and novel model of cerebral, particularly white matter, involvement with diabetes associated with abnormal RAGE signaling.

Selective Inhibition by Grape Seed Proanthocyanidin Extracts of Cell Adhesion Molecule Expression Induced by Advanced Glycation End Products in Endothelial Cells

The interaction of advanced glycation end products (AGE) with their cell surface receptors for AGEs (RAGE) has been causally implicated in the pathogenesis of diabetic vascular complications and has been shown to stimulate cell adhesion molecule expression in endothelial cells via induction of reactive oxygen species (ROS). Alternatively, grape seed proanthocyanidin extracts (GSPE), which are naturally occurring polyphenolic compounds, have been reported to possess potent radical scavenging and antioxidant properties and to display significant cardiovascular protective action. In this study, we investigated whether GSPE could inhibit AGE-induced cell adhesion molecule expression through interference with ROS generations in human umbilical vein endothelial cells. AGE-modified bovine serum albumin (AGE-BSA) was prepared by incubating BSA with a high concentration of glucose. Stimulation of cultured human umbilical vein endothelial cells with 200 microg/mL of AGE-BSA significantly enhanced intracellular ROS formation and subsequently upregulated the expression of vascular cell adhesion molecule-1 (VCAM) and intercellular adhesion molecule-1 (ICAM-1), whereas both unmodified BSA and GSPE alone were without effect. However, preincubation of different concentrations of GSPE markedly downregulated AGE-BSA-induced VCAM-1 expression at the surface protein and mRNA level in a concentration-dependent manner, but the increased ICAM-1 expression was not affected by GSPE treatment. Meanwhile, the inhibition by GSPE of intracellular ROS generation was also observed at defined time periods. These results demonstrate that GSPE can inhibit the enhanced VCAM-1 expression but not ICAM-1 in AGE-exposed endothelial cells by suppressing ROS generation. Hence, GSPE may have therapeutic potential in the prevention and treatment of vascular complications in patients with diabetes.

Albumin inhibits adipogenesis and stimulates cytokine release from human adipocytes

Bovine serum albumin (BSA) is commonly used in adipocyte experiments as a binding protein for fat-soluble substances. Therefore, it is of interest to investigate whether BSA per se is influencing the functioning of human adipocytes in vitro. In the present study, we investigated the potential of BSA to affect the proliferation and differentiation capacity of human preadipocytes. BSA was found to inhibit adipose differentiation in a dose-dependent manner (being significant at concentrations of 2.5 μM), whereas proliferation was not affected. We further investigated the effect of BSA on the secretory function of adipocytes focusing on the release of selected cytokines. Preadipocytes and freshly isolated adipocytes incubated with BSA secreted significantly higher amounts of IL-6, -8, and -10, and TNF-α compared with cells incubated without BSA. The effects on cytokine secretion seemed to reside at the level of gene expression because BSA increased TNF-α and IL-6 mRNA in a dose-dependent manner. The results of the present study indicate that the presence of BSA in the culture medium has considerable effects on adipocyte function in vitro. These effects should be carefully considered for in vitro studies of adipose tissue.

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.

Upregulation of RAGE and its ligands in proliferative retinal disease

We sought to study the presence of the receptor for advanced glycation endproducts (RAGE) and its ligands, advanced glycation endproducts (AGEs), S100/calgranulins and amphoterin (high mobility group box 1 protein; HMGB1), in the vitreous cavity and epiretinal membranes (ERMs) of eyes of patients with proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Undiluted vitreous specimens were collected from 30 eyes of 30 patients undergoing pars plana vitrectomy for repair of retinal detachment (RD) secondary to PDR (n = 15) or PVR (n = 15). The vitreous samples obtained from 10 eyes undergoing macular hole repair were used as controls. Epiretinal membranes were obtained from eight eyes with PDR and from 10 eyes with PVR. The levels of AGEs in the vitreous were measured using ELISA. The vitreous levels of soluble RAGE (sRAGE), S100/calgranulins and amphoterin were measured using Western blot analyses. The localization of RAGE and its ligands in ERMs was determined with immunohistochemistry. The vitreous levels of sRAGE were significantly increased in both PDR and PVR (p < or = 0.05) compared to control vitreous. In both PDR and PVR, the vitreous levels of AGEs (p < or = 0.01), S100/calgranulins (p < or = 0.05), and amphoterin (p < or = 0.01) were also elevated compared to control eyes. Expression of RAGE was detected in six of eight ERMs from eyes with PDR and eight of 10 ERMs from eyes with PVR. Many cells expressing RAGE also expressed vimentin, suggesting a glial cell origin. Ligands for RAGE were also detected in ERMs, with AGEs detected in five eyes with PDR and eight eyes with PVR. Similarly, S100 and amphoterin ERM expression was observed in six eyes with PDR; these ligands were also expressed in ERMs from eyes with PVR (8 and 7 cases, respectively). We conclude that RAGE and its ligands are increased in the vitreous cavity of eyes with PDR and PVR and are present in ERMs of eyes with these proliferative retinal disorders. These findings suggest a role for the proinflammatory RAGE axis in the pathogenesis of proliferative retinal diseases.

Association of Advanced Glycation End Products with A549 Cells, a Human Pulmonary Epithelial Cell Line, Is Mediated by a Receptor Distinct from the Scavenger Receptor Family and RAGE

Cellular interactions with advanced glycation end products (AGE)-modified proteins are known to induce several biological responses, not only endocytic uptake and degradation, but also the induction of cytokines and growth factors, combined responses that may be linked to the development of diabetic vascular complications. In this study we demonstrate that A549 cells, a human pulmonary epithelial cell line, possess a specific binding site for AGE-modified bovine serum albumin (AGE-BSA) (K(d) = 27.8 nM), and additionally for EN-RAGE (extracellular newly identified RAGE binding protein) (K(d) = 118 nM). Western blot and RT-PCR analysis showed that RAGE (receptor for AGE) is highly expressed on A549 cells, while the expression of other known AGE-receptors such as galectin-3 and SR-A (class A scavenger receptor), are below the level of detection. The binding of (125)I-AGE-BSA to these cells is inhibited by unlabeled AGE-BSA, but not by EN-RAGE. In contrast, the binding of (125)I-EN-RAGE is significantly inhibited by unlabeled EN-RAGE and soluble RAGE, but not by AGE-BSA. Our results indicate that A549 cells possess at least two binding sites, one specific for EN-RAGE and the other specific for AGE-BSA. The latter receptor on A549 cells is distinct from the scavenger receptor family and RAGE.

The association of plasma adiponectin level with carotid arterial stiffness

Adiponectin plays important roles in protecting against both insulin resistance and the development of atherosclerosis. The aim of the present study was to investigate the clinical impact of plasma adiponectin on arterial stiffness, a functional property of atherosclerosis, in type 2 diabetic and nondiabetic subjects. We evaluated plasma adiponectin levels and stiffness index beta for the common carotid artery assessed by ultrasound using a phase-locked echo-tracking system for 98 type 2 diabetic subjects and 116 nondiabetic subjects as controls. Plasma adiponectin levels were significantly lower in the diabetic than in the nondiabetic group. The stiffness index beta was significantly higher in the diabetic than in the nondiabetic group. Plasma adiponectin level was significantly correlated with stiffness index beta in the group of all subjects (r=-0.189, P=.006) and the nondiabetic group (r=-0.187, P=.045), but not in the diabetic group (r=0.045, P=.665). On multiple regression analysis, plasma adiponectin level was found to be a significant independent contributor to stiffness index beta in the group of all subjects (beta=-0.232, P=.020) and the nondiabetic group (beta=-0.337, P=.016), but not in the diabetic group. In conclusion, adiponectin is significantly but weakly associated with carotid arterial stiffness independently of known atherogenic factors in the nondiabetic group and that of all subjects, although no significant association between these variables was found in the group of diabetic subjects.

Amelioration of oxidant stress by the defensin lysozyme

Reactive oxidant species (ROS), products of normal metabolism, cause oxidant injury if they accumulate in pathological amounts. Lysozyme (LZ) contains an 18-amino acid domain that binds agents such as advanced glycation end products (AGE) that generate ROS. We examined whether endogenous LZ affected physiological, or baseline, antioxidant balance and provided protection against both acute and chronic oxidant injury, using paraquat and H2O2 as agents of acute injury and AGE for chronic injury. Hen egg LZ-Tg mice had threefold higher serum LZ levels and decreased baseline AGE levels in serum and liver. These findings were linked to an enhanced baseline systemic GSH-to-GSSG ratio. Baseline levels of stress response genes p66(Shc) and c-Jun were also lower in liver tissue of LZ-Tg mice. Survival from severe oxidant injury induced by paraquat was twofold greater in LZ-Tg mice. In addition, LZ-Tg mice were resistant to chronic exogenous oxidant stress (OS) induced by AGE administration. Preincubation of hepatocytes (Hep G2) with LZ suppressed redox balance at baseline, as well as OS after added paraquat, AGE, or H2O2. LZ also ameliorated paraquat-enhanced cell apoptosis in a dose-dependent manner and suppressed AGE-induced p66(Shc) expression and c-Jun phosphorylation in Hep G2 cells. Thus LZ provides protection against acute and chronic oxidant injury by mechanisms involving suppression of ROS generation and of OS response genes.

Soluble receptor for advanced glycation end products in patients with decreased renal function

BACKGROUND

Advanced glycation end products (AGEs) accumulate in patients with decreased renal function and exert various toxic effects through the receptor for AGEs (RAGE). Soluble RAGE (sRAGE) is a naturally occurring inhibitor of AGE-RAGE action. The aim of the study is to describe the relationship of sRAGE to renal function and dialysis modalities.

METHODS

The studied group consisted of 81 patients: 25 patients with various degrees of decreased renal function, 20 long-term hemodialysis (HD) patients, 15 peritoneal dialysis (PD) patients, and 21 healthy age-matched subjects. sRAGE was assessed immunochemically (enzyme-linked immunosorbent assay), and routine biochemical parameters were measured by means of certified methods.

RESULTS

sRAGE level correlates positively with serum creatinine concentration (r = 0.50; P < 0.05), and its relationship to creatinine clearance is hyperbolic. sRAGE levels are elevated significantly, mainly in patients with end-stage renal disease (3,119.0 +/- 968.4 pg/mL in HD patients and 3,652.7 +/- 1,677.7 pg/mL in PD patients versus 1,405.1 +/- 426.1 pg/mL in controls; both P < 0.001 versus controls). In PD patients, sRAGE is detectable in spent dialysate (median, 75.8 pg/mL), correlates with its serum levels (r = 0.67; P < 0.05), and is related to protein losses in dialysate. In HD patients, sRAGE levels increase by 50% (P < 0.001) from 0 to 15 minutes during both HD and hemodiafiltration, and then decrease until the end of the session.

CONCLUSION

Serum sRAGE levels increase in patients with decreased renal function, mainly patients with end-stage renal disease. It remains to be elucidated whether the increase is caused just by decreased renal function or whether sRAGE is upregulated to protect against toxic effects of AGEs.

Insulin resistance reduces arterial prostacyclin synthase and eNOS activities by increasing endothelial fatty acid oxidation

Insulin resistance markedly increases cardiovascular disease risk in people with normal glucose tolerance, even after adjustment for known risk factors such as LDL, triglycerides, HDL, and systolic blood pressure. In this report, we show that increased oxidation of FFAs in aortic endothelial cells without added insulin causes increased production of superoxide by the mitochondrial electron transport chain. FFA-induced overproduction of superoxide activated a variety of proinflammatory signals previously implicated in hyperglycemia-induced vascular damage and inactivated 2 important antiatherogenic enzymes, prostacyclin synthase and eNOS. In 2 nondiabetic rodent models--insulin-resistant, obese Zucker (fa/fa) rats and high-fat diet-induced insulin-resistant mice--inactivation of prostacyclin synthase and eNOS was prevented by inhibition of FFA release from adipose tissue; by inhibition of the rate-limiting enzyme for fatty acid oxidation in mitochondria, carnitine palmitoyltransferase I; and by reduction of superoxide levels. These studies identify what we believe to be a novel mechanism contributing to the accelerated atherogenesis and increased cardiovascular disease risk occurring in people with insulin resistance.

How to revascularize patients with diabetes mellitus: bypass or stents and drugs?

The diabetic patient is at high risk for coronary artery disease. Incidence as well as severity of the disease is highly increased in comparison to non-diabetic patients. The revascularization of the diabetic patient is a great challenge, since the longterm results are disappointing when compared to non-diabetic patients. The success of coronary artery bypass grafting is limited by increased perioperative mortality and a faster occlusion of especially venous bypass grafts. In percutaneous interventions the excessive high restenosis rates worsen longterm results. Several clinical trials investigated the outcome of the two revascularization strategies and could demonstrate at least a tendency towards better results when the operative approach was chosen. Particularly, the BARI trial showed reduced mortality for surgery when compared to percutaneous coronary interventions. However, in this trial, in 87% of patients undergoing bypass surgery all stenoses were successfully treated, whereas in patients undergoing percutaneous coronary intervention only 76% of all stenoses were primarily successfully treated. In addition, no stents were used in this trial.Furthermore, the enrollment of the previous trials dates one decade ago. These trials do therefore not necessarily represent the current standard therapy, especially for percutaneous coronary interventions. The restenosis rate could be decreased in recent years by means of drug-eluting stents and an aggressive antiplatelet therapy from more than 50% to less than 10% leading to considerably improved long-term results. Therefore, percutaneous coronary interventions have developed to be a reasonable alternative to bypass surgery. Different clinical trials are currently underway (BARI 2D, CarDIA, FREEDOM) comparing the outcome of the two approaches.

Oral glycine administration attenuates diabetic complications in streptozotocin-induced diabetic rats

Diabetes mellitus is a disease characterized by impaired glucose metabolism that leads to retinopathy, brain micro-infarcts and other complications. We have previously shown that oral glycine administration to diabetic rats inhibits non-enzymatic glycation of hemoglobin and diminishes renal damage. In this work, we evaluated the capacity of the amino acid glycine (1% w/v, 130 mM) to attenuate diabetic complications in streptozotocin (STZ)-induced diabetic Wistar rats and compared them with non-treated or taurine-treated (0.5% w/v, 40 mM) diabetic rats. Glycine-treated diabetic rats showed an important diminution in the percentage of animals with opacity in lens and microaneurysms in the eyes. Interestingly, there was a diminished expression of O-acetyl sialic acid in brain vessels compared with untreated diabetic rats (P<0.05). Additionally, peripheral blood mononuclear cells isolated from glycine-treated diabetic rats showed a better proliferative response to PHA or ConA than those obtained from non-treated diabetic rats (P<0.05). Glycine-treated rats had a less intense corporal weight loss in comparison with non-treated animals. Our results suggest that administration of glycine attenuates the diabetic complications in the STZ-induced diabetic rat model, probably due to inhibition of the non-enzymatic glycation process.

Benfotiamine accelerates the healing of ischaemic diabetic limbs in mice through protein kinase B/Akt-mediated potentiation of angiogenesis and inhibition of apoptosis

AIMS/HYPOTHESIS

Benfotiamine, a vitamin B1 analogue, reportedly prevents diabetic microangiopathy. The aim of this study was to evaluate whether benfotiamine is of benefit in reparative neovascularisation using a type I diabetes model of hindlimb ischaemia. We also investigated the involvement of protein kinase B (PKB)/Akt in the therapeutic effects of benfotiamine.

METHODS

Streptozotocin-induced diabetic mice, given oral benfotiamine or vehicle, were subjected to unilateral limb ischaemia. Reparative neovascularisation was analysed by histology. The expression of Nos3 and Casp3 was evaluated by real-time PCR, and the activation state of PKB/Akt was assessed by western blot analysis and immunohistochemistry. The functional importance of PKB/Akt in benfotiamine-induced effects was investigated using a dominant-negative construct.

RESULTS

Diabetic muscles showed reduced transketolase activity, which was corrected by benfotiamine. Importantly, benfotiamine prevented ischaemia-induced toe necrosis, improved hindlimb perfusion and oxygenation, and restored endothelium-dependent vasodilation. Histological studies revealed the improvement of reparative neovascularisation and the inhibition of endothelial and skeletal muscle cell apoptosis. In addition, benfotiamine prevented the vascular accumulation of advanced glycation end products and the induction of pro-apoptotic caspase-3, while restoring proper expression of Nos3 and Akt in ischaemic muscles. The benefits of benfotiamine were nullified by dominant-negative PKB/Akt. In vitro, benfotiamine stimulated the proliferation of human EPCs, while inhibiting apoptosis induced by high glucose. In diabetic mice, the number of circulating EPCs was reduced, with the deficit being corrected by benfotiamine.

CONCLUSIONS/INTERPRETATION

We have demonstrated, for the first time, that benfotiamine aids the post-ischaemic healing of diabetic animals via PKB/Akt-mediated potentiation of angiogenesis and inhibition of apoptosis. In addition, benfotiamine combats the diabetes-induced deficit in endothelial progenitor cells.

Oxidative stress and diabetic cardiovascular complications

Diabetes diagnoses are increasing at an alarming rate worldwide. The majority of diabetes-related deaths arise from cardiovascular complications such as myocardial infarction, stroke, and peripheral vascular disease. Oxidative stress has been demonstrated to be present in animal models as well as in patients with diabetes and has been suggested as a possible contributor to the accelerated atherosclerosis seen in diabetics. The generation of reactive oxygen species in diabetes occurs via several mechanisms and is initiated not only by glucose, but also by other substances that are found at elevated levels in diabetic patients. The resulting oxidative stress leads to a number of proatherogenic events. The elucidation of the mechanisms of oxidative stress in diabetes and their relationship with atherosclerosis could potentially identify molecular targets of therapy for this condition and its cardiovascular consequences.

Inhibition of human endothelial cell nitric oxide synthesis by advanced glycation end-products but not glucose: relevance to diabetes

Endothelial dysfunction, with decreased NO (nitric oxide) biosynthesis, may play a pathophysiological role in diabetic vasculopathy. The aim of the present study was to determine the relative contributions of glucose and AGE (advanced glycation end-product) accumulation in suppressing NOS-3 (the endothelial isoform of NO synthase). Cultured HUVECs (human umbilical vein endothelial cells) were incubated with different concentrations of glucose, unmodified albumin or AGE-modified albumin for different times. NOS activity was measured from the conversion of L-[(3)H]arginine into L-[(3)H]citrulline, and the expression, serine phosphorylation and O-glycosylation of NOS-3 were determined by Western blotting. High (25 mmol/l) glucose, for up to 12 days of incubation, had no effect on the activity or expression of NOS-3, nor on its degree of serine phosphorylation or O-glycosylation, compared with physiological (5 mmol/l) glucose. By contrast, AGE-modified albumin exerted a concentration- and time-dependent suppression of NOS-3 expression in HUVECs at a range of concentrations (0-200 mg/l) found in diabetic plasma; this was evident after 24 h, whereas inhibition of NOS activity was seen after only 3 h incubation with AGE-modified albumin, consistent with our previous observations of rapid suppression of NOS-3 serine phosphorylation and NOS-3 activity by AGE-modified albumin. In conclusion, AGE-modified albumin suppresses NOS-3 activity in HUVECs through two mechanisms: one rapid, involving suppression of its serine phosphorylation, and another slower, involving a decrease in its expression. We also conclude that, in the context of the chronic hyperglycaemia in diabetes, the effects of AGEs on endothelial NO biosynthesis are considerably more important than those of glucose.

Manifestations of cutaneous diabetic microangiopathy

The etiologies of a variety of skin conditions associated with diabetes have not been fully explained. One possible etiological factor is diabetic microangiopathy, which is known to affect the eyes and kidneys in patients with diabetes. There are many mechanisms by which diabetes may cause microangiopathy. These include excess sorbitol formation, increased glycation end products, oxidative damage, and protein kinase C overactivity. All of these processes occur in the skin, and the existence of a cutaneous diabetic microangiopathy has been well demonstrated. These microangiopathic changes are associated with abnormalities of skin perfusion. Because the skin plays a thermoregulatory role, there is significant capillary redundancy in normal skin. In diabetic patients, loss of capillaries is associated with a decrease in perfusion reserve. This lost reserve is demonstrable under stressed conditions, such as thermal stimulation. The associated failure of microvascular perfusion to meet the requirements of skin metabolism may result in diverse skin lesions in patients with diabetes. Many skin conditions peculiar to diabetes are fairly rare. Necrobiosis lipoidica diabeticorum (NLD) and diabetic bullae occur very infrequently as compared with diabetic retinopathy and nephropathy. Conversely, there is a correlation between diabetic microvascular disease and NLD. This correlation also exists with more common skin conditions, such as diabetic dermopathy. This relationship suggests that diabetic microangiopathy may contribute to these conditions even if it is not primarily causal. Clinically, the major significance of diabetic cutaneous microangiopathy is seen in skin ulceration which is very common and has a major impact on diabetic patients. Many factors contribute to the development of diabetic foot ulcers. Neuropathy, decreased large vessel perfusion, increased susceptibility to infection, and altered biomechanics all play a role, but there is no doubt that inadequate small blood vessel perfusion is a major cause of the inability to heal small wounds that eventually results in ulcer formation. The accessibility of skin capillaries makes cutaneous diabetic microangiopathy an attractive model for research on the evolution of microvascular disease in diabetic patients.

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.

Argpyrimidine-modified Heat shock protein 27 in human non-small cell lung cancer: a possible mechanism for evasion of apoptosis

Tumors generally display a high glycolytic rate. One consequence of increased glycolysis is the non-enzymatic glycation of proteins leading to the formation of advanced glycation end-products (AGEs). Therefore, we studied the presence of AGEs in non-small cell lung cancer and consequences thereof. We show the presence of two AGEs, i.e. the major AGE N(epsilon)-(carboxymethyl)lysine (CML) and the methylglyoxal-arginine adduct argpyrimidine, in human non-small cell lung cancer tissues by immunohistochemistry. We found in squamous cell carcinoma and adenocarcinoma tissues a strong CML positivity in both tumour cells and tumour-surrounding stroma. In contrast, argpyrimidine positivity was predominantly found in tumor cells and was strong in squamous cell carcinomas, but only weak in adenocarcinomas (2.6+/-0.5 vs. 1.2+/-0.4, respectively; P<0.005). In accordance, argpyrimidine was found in the human lung squamous carcinoma cell line SW1573, while it was almost absent in the adenocarcinoma cell line H460. Heat shock protein 27 (Hsp27) was identified as a major argpyrimidine-modified protein. In agreement with a previously described anti-apoptotic activity of argpyrimidine-modified Hsp27, the percentage of active caspase-3 positive tumor cells in squamous cell carcinomas was significantly lower when compared to adenocarcinomas. In addition, incubation with cisplatin induced almost no caspase-3 activation in SW1573 cells while a strong activation was seen in H460 cells; which was significantly reduced by incubation with an inhibitor of glyoxalase I, the enzyme that catalyzes the conversion of methylglyoxal. These findings suggest that a high level of argpyrimidine-modified Hsp27 is a mechanism of cancer cells for evasion of apoptosis.

Association of mineral metabolism with an increase in cellular adhesion molecules: another link to cardiovascular risk in maintenance haemodialysis?

BACKGROUND

Abnormal mineral metabolism is associated with increased cardiovascular morbidity and mortality. The exact pathogenesis linking mineral metabolism to cardiovascular risk is unknown. This study was undertaken to investigate the association between serum phosphate and/or Ca x PO(4) product with serum levels of soluble E-selectin (sE-selectin), soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 and the degree of carotid artery atherosclerosis in patients on haemodialysis.

METHODS

Seventy-three patients (46 male, 27 female; mean age 48+/-13 years, on haemodialysis for 82+/-80 months) were included in the study. All patients were stable, had no evidence of vascular disease and/or active infection. Consecutive 6 months clinical and laboratory data were obtained for each patient from their medical records and mean values were used for analysis. Serum levels of soluble adhesion molecules were assayed by ELISA. All subjects underwent a detailed evaluation of the carotid arteries.

RESULTS

The percentage of patients who met all three targets of NKF-K/DOQI for phosphate, calcium and Ca x PO(4) product was 27.1%, whereas those who did not achieve the target in one, two or three parameters was 28.1, 17.7 and 14.6%, respectively. The sICAM-1 levels were significantly higher in patients who had hyperphosphataemia (serum phosphate >5.5 mg/dl; P = 0.044) and hypercalcaemia (serum calcium >9.5 mg/dl; P = 0.014), both sE-selectin and sICAM-1 levels were significantly higher in patients with Ca x PO(4) product levels above 55 mg(2)/dl(2) (P = 0.002 and P = 0.000, respectively). Soluble E-selectin and sICAM levels demonstrated a near-linear increase in parallel to the degree of deviation from mineral metabolism targets. Soluble E-selectin and sICAM levels were correlated with serum phosphate and Ca x PO(4) product, but there were no correlations between adhesion molecules and carotid measurements.

CONCLUSION

These findings suggest that in stable haemodialysis patients abnormal bone mineral metabolism was associated with increased soluble adhesion molecules. These alterations in adhesion molecules may favour the development of cardiovascular changes and contribute to high cardiovascular morbidity and mortality in patients with abnormal mineral metabolism.

Promotion of cell adherence and spreading: a novel function of RAGE, the highly selective differentiation marker of human alveolar epithelial type I cells

The receptor for advanced glycation endproducts (RAGE) is expressed under pathological conditions in many tissues and has been assigned many functions. We demonstrate, in normal human lung tissue, the preferential and highly abundant expression of RAGE by quantitative polymerase chain reaction. In addition, RAGE expression, as a specific differentiation marker of alveolar epithelial type I cells (AT I cells), and its localization to the basolateral plasma membrane have been confirmed by means of newly raised monoclonal antibodies. The physiological function of RAGE on AT I cells has previously remained elusive. By using HEK293 cells transfected with cDNA encoding for full-length RAGE, we show that RAGE enhances the adherence of epithelial cells to collagen-coated surfaces and has a striking capacity for inducing cell spreading. The preferential binding of RAGE to collagen has been confirmed by assaying the binding of soluble RAGE to various substrates. RAGE might thus assist AT I cells to acquire a spreading morphology, thereby ensuring effective gas exchange and alveolar stability.

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.