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

Blockade of endogenous cytokines mitigates neointimal formation in obese Zucker rats

BACKGROUND

It is well known that diabetes mellitus is a major risk factor for vascular diseases such as atherosclerosis and restenosis after angioplasty. It has become clear that advanced glycation end products (AGE) and their receptor (RAGE) are implicated in vascular diseases, especially in diabetes mellitus. Nevertheless, the mechanisms by which diabetes mellitus is often associated with vascular diseases remain unclear.

METHODS AND RESULTS

To study the role of endogenous cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 in the development of vascular diseases and in the expression of RAGE, we used semapimod, a pharmacological inhibitor of cytokine production, and examined its effect on neointimal formation in the femoral artery of obese Zucker (OZ) rats. We also used an adenovirus construct expressing a dominant negative mutant of the receptor for TNF-alpha (AdTNFRDeltaC) to block the action of endogenous TNF-alpha. Semapimod significantly suppressed neointimal formation and RAGE expression in OZ rats compared with untreated OZ rats. This inhibitory effect of semapimod on neointimal formation was overcome by infection of an adenovirus expressing RAGE into the femoral artery of OZ rats. Furthermore, AdTNFRDeltaC infection significantly suppressed neointimal formation and RAGE expression in the femoral artery of OZ rats.

CONCLUSIONS

These results suggest that endogenous cytokines, especially TNF-alpha, were implicated in neointimal formation in OZ rats and that RAGE was a mediator of the effect of these cytokines on neointimal formation.

Bridging advanced glycation end product, receptor for advanced glycation end product and nitric oxide with hormonal replacement/estrogen therapy in healthy versus diabetic postmenopausal women: A perspective

Cardiovascular diseases (CVD) are the most significant cause of death in postmenopausal women. The loss of estrogen biosynthesis with advanced age is suggested as one of the major causes of higher CVD in postmenopausal women. While some studies show beneficial effects of estrogen therapy (ET)/hormonal replacement therapy (HRT) in the cardiovascular system of healthy postmenopausal women, similar studies in diabetic counterparts contradict these findings. In particular, ET/HRT in diabetic postmenopausal women results in a seemingly detrimental effect on the cardiovascular system. In this review, the comparative role of estrogens is discussed in the context of CVD in both healthy and diabetic postmenopausal women in regard to the synthesis or expression of proinflammatory molecules like advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGEs), inducible nitric oxide synthases (iNOS) and the anti-inflammatory endothelial nitric oxide synthases (eNOS). The interaction of AGE-RAGE signaling with molecular nitric oxide (NO) may determine the level of reactive oxygen species (ROS) and influence the overall redox status of the vascular microenvironment that may further determine the ultimate outcome of the effects of estrogens on the CVD in healthy versus diabetic women.

Diabetes, prediabetes, and cardiovascular risk: shifting the paradigm

As the prevalence of diabetes continues to increase worldwide, diabetes-related macrovascular morbidity and mortality are becoming major health care problems. Epidemiologic evidence suggests this relationship begins early in the progression from normal glucose tolerance to frank diabetes. This report reviews this epidemiologic evidence linking early stages of glucose dysregulation with cardiovascular disease and discusses the results of major clinical trials demonstrating that lifestyle or pharmacologic intervention can reduce the incidence of diabetes in high-risk individuals. These observations indicate that early identification and aggressive treatment of subjects with impaired fasting glucose or impaired glucose tolerance have the potential to reduce both the incidence of diabetes and its related cardiovascular disease. Three clinical trials are being conducted to test whether early pharmacotherapy can reduce or delay the incidence of diabetes, and their results may well begin to shift the treatment paradigm toward earlier intervention.

The RAGE pathway in inflammatory myopathies and limb girdle muscular dystrophy

Oxidative stress and nuclear factor-kappaB (NF-kappaB) activation are linked to the pathogenesis of many metabolic, degenerative, and chronic inflammatory diseases. Activation of the receptor for advanced glycation end products (RAGE) by its specific ligand N(epsilon)-carboxymethyllysine (CML) results in the activation of NF-kappaB and the production of proinflammatory cytokines. To determine whether engagement of RAGE contributes to the pathogenesis of inflammatory myopathies, we performed immunohistochemical studies on the presence of CML-modified proteins, RAGE and activated NF-kappaB in muscle biopsies of patients with polymyositis (PM, n=10), dermatomyositis (DM, n=10), limb girdle muscular dystrophy (LGMD, n=10) and in 10 controls with normal muscle biopsy results. In inflammatory myopathies CML, RAGE and NF-kappaB were detected in mononuclear cells and in regenerating muscle fibers. CML, NF-kappaB and, to a lesser extent, RAGE were also found in degenerating muscle fibers, but colocalization of CML, RAGE and NF-kappaB was only seen in infiltrating mononuclear cells and regenerating muscle fibers. Immunofluorescence double labeling demonstrated an expression of CML, RAGE and NF-kappaB in CD4-, CD8-, CD22- and CD68-positive mononuclear cells. Western blot analysis showed an increased immunoreactivity for CML-modified proteins in PM and DM. In LGMD, CML, RAGE and NF-kappaB were found in regenerating muscle fibers and less frequently in degenerating muscle fibers, and with lower staining intensities than in inflammatory myopathies. Our data suggests that the CML-RAGE-NF-kappaB pathway is an evident proinflammatory pathomechanism in mononuclear effector cells in PM and DM. RAGE-mediated NF-kappaB activation may be involved in muscle fiber regeneration in inflammatory myopathies and LGMD.

Impact of rHuEPO therapy initiation on soluble adhesion molecule levels in haemodialysis patients

BACKGROUND

Increased levels of soluble adhesion molecules have been reported in haemodialysis (HD) patients. Recent studies have shown that recombinant human erythropoietin (rHuEPO) elicits proliferation and migration of endothelial cells and modifies endothelial function. The present study was design to explore the effects of rHuEPO on serum levels of soluble adhesion molecules in HD patients.

METHODS

Soluble serum levels of E-selectin (sE-selectin), intracellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1) were measured by ELISA in 29 rHuEPO naïve HD patients (20 males, 9 females) and 10 control subjects at baseline and second month. The HD patients with a haemoglobin level lower than 10.0 mg/dL (n = 19) were administered rHuEPO therapy and other HD patients (n = 10) were followed as a placebo group.

RESULTS

Serum levels of soluble adhesion molecules were significantly higher in HD patients compared with the control group. A significant rise from the baseline in sE-selectin levels (77 +/- 70 vs 100 +/- 86 ng/mL, P < 0.05) was observed 2 months after rHuEPO initiation, while sICAM-1 and sVCAM-1 levels decreased (271 +/- 261 vs 197 +/- 89 and 1043 +/- 243 vs 990 +/- 236 ng/mL, respectively, P < 0.05).

CONCLUSIONS

The present data indicate that rHuEPO could have an important action on serum levels of soluble adhesion molecules in HD patients. rHuEPO might modify the expression of adhesion molecules from endothelial cells either. However, the exact mechanism responsible for the serum elevation of these molecules in HD patients is yet to be fully elucidated.

RAGE modulates vascular inflammation and atherosclerosis in a murine model of type 2 diabetes

Previous studies demonstrated that induction of diabetes with streptozotocin (stz) accelerated atherosclerosis in hyperlipidemic apo E null (-/-) mice. Blockade of the Receptor for Advanced Glycation Endproducts (RAGE) in those animals suppressed acceleration of atherosclerotic lesion area, in a manner independent of changes in levels of glucose, insulin or lipids. In the present studies, we extended these concepts to a murine model of type 2 diabetes, and bred apo E -/- mice into the db/db background. Db/db mice are a model of obesity and insulin resistance-mediated hyperglycemia. Compared to apo E -/- m/db (non-diabetic) mice, apo E -/- db/db (diabetic) mice displayed accelerated atherosclerosis at the aortic sinus. Consistent with an important role for RAGE in this process, administration of soluble (s) RAGE, the extracellular ligand-binding domain of RAGE, resulted in significantly reduced atherosclerotic lesion area in a glycemia- and lipid-independent manner. In parallel, apo E -/- db/db mice displayed RAGE-dependent enhanced expression of Vascular Cell Adhesion Molecule-1, tissue factor and matrix metalloproteinase (MMP)-9 antigen/activity in aortae compared to non-diabetic animals. In addition, consistent with the premise that upregulation of RAGE ligands and RAGE occurs even in the non-diabetic, hyperlipidemic state, albeit to lesser degrees than in diabetes, administration of sRAGE to apo E -/- m/db mice resulted in decreased atherosclerotic lesion area at the aortic sinus. Taken together, these findings establish a new murine model for the study of atherosclerosis in type 2 diabetes and highlight important roles for RAGE in proatherogenic mechanisms in hyperglycemia triggered by insulin resistance.

Mesangial accumulation of GA-pyridine, a novel glycolaldehyde-derived AGE, in human renal disease

BACKGROUND

Advanced glycation end products (AGEs) contribute to diabetic and atherosclerotic end-organ damage, but the mechanisms of AGE-formation and AGE-induced damage are unclear. Glycolaldehyde (GA) is a Maillard-reaction intermediate and can be formed by reaction of L-serine with the myeloperoxidase-system. GA reacts with proteins to form AGEs, such as GA-pyridine, which is specific for protein modification by GA. GA-pyridine accumulates in human atherosclerotic lesions. As atherosclerosis and progressive glomerulosclerosis share many similarities, we hypothesized that GA-pyridine accumulates in renal diseases, especially those with prominent mesangial involvement.

METHODS

Paraffin-embedded renal biopsies from 55 patients with various renal diseases, as well as control tissue, obtained from the unaffected part of kidneys from 10 patients with renal cell carcinoma were immunohistochemically stained with a monoclonal antibody directed against GA-pyridine and were scored semiquantitatively. Additional sections were scored for mesangial matrix expansion (MME) and focal glomerular sclerosis (FGS).

RESULTS

In normal human kidneys, GA-pyridine was mainly localized in tubular epithelial cells, but not in the glomerular mesangium. Significant mesangial GA-pyridine accumulation was found in disorders with mesangial involvement as a common denominator. In contrast, mesangial GA-pyridine accumulation was less prominent in renal diseases without prominent mesangial involvement. Moreover, mesangial GA-pyridine accumulation was more pronounced in kidneys with higher MME and FGS scores across the different diagnoses.

CONCLUSION

GA-pyridine accumulates in the mesangium in human renal disease, in particular in disorders with mesangial involvement. Further studies should elucidate whether mesangial GA-pyridine plays a role in the progression of glomerular damage.

Glyco-oxidation in diabetes and related diseases

BACKGROUND

Recent evidence has shown that hyperglycemia is able to cause increased production of superoxide on the mitochondrial transport chain, and that this is the key event which activates some events such as increased AGE formation, increased hexosamine and polyol flux, and activation of PKC, all believed to be important for the development of the chronic complications of diabetes, aging and uremia. In this context, non-enzymatic protein glyco-oxidation leads to the formation of a series of products whose intra- and extra-cellular accumulation is of key importance in the pathogenesis of these chronic diseases.

METHODS

Various spectrometric approaches, such as matrix-assisted laser desorption ionisation (MALDI), and liquid chromatography-electrospray ionisation (ESI) were used.

RESULTS AND CONCLUSIONS

The latest mass spectrometric approaches have shown their power in proteomics, and we report here some applications of this technique in the study of in vitro and in vivo non-enzymatic protein glyco-oxidation.

Race-specific differences in antioxidant enzyme activity in patients with type 2 diabetes: a potential association with the risk of developing nephropathy

OBJECTIVE

Lipid hydroperoxide, a marker of oxidative stress, is linked to the development of nephropathy and is reportedly higher in patients of African origin compared with Caucasians. This may be relevant to race-specific differences in susceptibility to nephropathy. We investigated whether alterations in antioxidant enzyme activity could account for this biochemical phenotype and examined the relationship with conventional markers of renal disease.

RESEARCH DESIGN AND METHODS

Two hundred seventeen individuals were studied. Patients with type 2 diabetes (n = 75) of African and Caucasian origin were matched by sex and racial origin with healthy control subjects (n = 142). Plasma total superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity were spectrophotometrically measured, and total cholesterol and triglycerides were measured by enzymatic methods.

RESULTS

SOD activity was higher and GPx activity lower in patients with diabetes than in healthy control subjects (573 +/- 515 vs. 267 +/- 70 units/l, P < 0.001 and 150 +/- 93 vs. 178 +/- 90 units/l, P = 0.019, respectively). Patients of African origin with diabetes had lower GPx and higher SOD activity compared with Caucasian patients (126 +/- 82 vs. 172 +/- 97 units/l, P = 0.03 and 722 +/- 590 vs. 445 +/- 408 units/l, P = 0.002, respectively). Patients of African origin with normal urinary albumin excretion had significantly higher plasma creatinine concentrations (100.7 +/- 14.2 vs. 88.1 +/- 14.9 micromol/l, P = 0.007) and lower GPx activity (99.0 +/- 72.4 vs. 173.7 +/- 107.4 units/l, P = 0.02) compared with those of Caucasian origin. African origin was an independent predictor of elevated SOD (P = 0.007) and reduced GPx activity (P = 0.02) in regression analysis.

CONCLUSIONS

SOD and GPx enzyme activities vary according to race and could account for differences in lipid hydroperoxide. In patients of African origin, susceptibility to renal disease may be associated with lowered GPx activity.

Sophorae radix extract inhibits high glucose-induced vascular cell adhesion molecule-1 up-regulation on endothelial cell line

BACKGROUND

Sophorae radix (SR) has been used for various diseases including atherosclerosis and arrhythmias. Atherosclerosis induced by hyperglycemia is an important factor in the promotion of diabetic complications. An early event in atherosclerosis is the adhesion of monocytes to endothelium via adhesion molecules. Among them, vascular cell adhesion molecule-1 (VCAM-1) expression mediates the binding of monocytes and lymphocytes to vascular endothelial cells.

METHODS

The study was performed on vascular endothelial cells (ECV304 cells) that were pretreated with various concentrations of SR extract for 3 h before exposure with high glucose (55.5 mmol/l) for 48 h. The protein expression of VCAM-1 was measured by enzyme-linked immunosorbent assay (ELISA) and its mRNA expression was by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

SR extract significantly inhibited high glucose-induced expression of VCAM-1 in a dose-dependent manner and reduced the level of VCAM-1 mRNA through interfering with translocation of nuclear factor-kappaB (NF-kappaB). Decreased VCAM-1 expression by SR extract was associated reduction of adherence between high glucose-stimulated ECV304 cells and human monocyte-like HL-60 cells.

CONCLUSIONS

These data suggest that SR extract inhibits high glucose-mediated monocytes-endothelial cells adhesions and expression of VCAM-1 via inhibition of NF-kappaB translocation.

Development of capture assays for different modifications of human low-density lipoprotein

Antibodies to malondialdehyde (MDA)-modified low-density lipoprotein (LDL), copper-oxidized LDL (oxLDL), Nepsilon(carboxymethyl) lysine (CML)-modified LDL, and advanced glycosylation end product (AGE)-modified LDL were obtained by immunization of rabbits with in vitro-modified human LDL preparations. After absorption of apolipoprotein B (ApoB) antibodies, we obtained antibodies specific for each modified lipoprotein with unique patterns of reactivity. MDA-LDL antibodies reacted strongly with MDA-LDL and also with oxLDL. CML-LDL antibodies reacted strongly with CML-LDL and also AGE-LDL. oxLDL antibodies reacted with oxLDL but not with MDA-LDL, and AGE-LDL antibodies reacted with AGE-LDL but not with CML-LDL. Capture assays were set with each antiserum, and we tested their ability to capture ApoB-containing lipoproteins isolated from precipitated immune complexes (IC) and from the supernatants remaining after IC precipitation (free lipoproteins). All antibodies captured lipoproteins contained in IC more effectively than free lipoproteins. Analysis of lipoproteins in IC by gas chromatography-mass spectrometry showed that they contained MDA-LDL and CML-LDL in significantly higher concentrations than free lipoproteins. A significant correlation (r=0.706, P<0.019) was obtained between the MDA concentrations determined by chemical analysis and by the capture assay of lipoproteins present in IC. In conclusion, we have developed capture assays for different LDL modifications in human ApoB/E lipoprotein-rich fractions isolated from precipitated IC. This approach obviates the interference of IC in previously reported modified LDL assays and allows determination of the degree of modification of LDL with greater accuracy.

Feasibility of using hyperosmolar mannitol as a liquid tumor embolization agent

BACKGROUND AND PURPOSE

This study assesses the cytotoxicity of hyperosmolar mannitol on human endothelial and meningioma cells in vitro and summarizes the initial clinical experience of using mannitol as a liquid tumor embolization agent.

METHODS

Human umbilical vein endothelial cells and primary meningioma cells from surgical specimens were treated with 300, 600, 900, and 1200 mOsm of mannitol, mannitol and iohexol mixture, saline, and iohexol alone. Cell death was evaluated with a Live/Dead kit and quantified with thymidine incorporation. From 1998 to 2004, 23 patients with meningioma were treated with mannitol and 31 patients were treated with polyvinyl alcohol (PVA) particles alone. Angiographic results, procedural complications, intraoperative observation, and estimated blood loss during surgical resection were retrospectively evaluated.

RESULTS

Minimal endothelial cell death was seen after incubation with 300 mOsm of mannitol for 15 minutes, but 43 +/- 2% of endothelial cells were damaged by 1200 mOsm of mannitol after 30 minutes. Five meningioma cell lines exhibited significant cell death (22 +/- 2%; P < .05) after incubation with mannitol. Satisfactory angiographic results were obtained in all 23 patients. Tumor necrosis was observed intraoperatively and confirmed pathologically. There was no significant difference in estimated blood loss between mannitol- and PVA-embolized patients (407 +/- 64 mL vs 381 +/- 50 mL; P > .75).

CONCLUSION

High concentration of mannitol can injure endothelial cells and meningioma cells in a short period of time. It is feasible to use mannitol as a liquid embolic agent to treat meningioma.

At least 2 distinct pathways generating reactive oxygen species mediate vascular cell adhesion molecule-1 induction by advanced glycation end products

OBJECTIVE

The interaction of advanced glycation end products (AGEs) with their main receptor RAGE in endothelial cells induces intracellular generation of reactive oxygen species (ROS) and the expression of vascular cell adhesion molecule (VCAM)-1. We investigated the role of distinct sources of ROS, including the mitochondrial electron transport chain, NAD(P)H oxidase, xanthine oxidase, and arachidonic acid metabolism, in AGE-induced VCAM-1 expression.

METHODS AND RESULTS

The induction of ROS and VCAM-1 by AGEs in cultured human umbilical vein endothelial cells was specifically blocked by an anti-RAGE antibody. The inhibition of NAD(P)H oxidase by apocynin and diphenylene iodonium, and of the mitochondrial electron transport system at complex II by thenoyltrifluoroacetone (TTFA), significantly inhibited both AGE-induced ROS production and VCAM-1 expression, whereas these effects were potentiated by rotenone and antimycin A, specific inhibitors of mitochondrial complex I and III, respectively. The inhibition of Cu/Zn superoxide dismutase inhibited both ROS and VCAM-1 induction, indicating that H2O2 by this source is involved as a mediator of VCAM-1 expression by AGEs.

CONCLUSIONS

Altogether, these results demonstrate that ROS generated by both NAD(P)H-oxidase and the mitochondrial electron transport system are involved in AGE signaling through RAGE, and indicate potential targets for the inhibition of the atherogenic signals triggered by AGE-RAGE interaction.

Monocytes promote natural killer cell interferon gamma production in response to the endogenous danger signal HMGB1

Substantial attention has been paid to the role of the toll-like receptor (TLR) ligands of late and their role in regulating the innate immune response. They serve as exogenous danger signals important in informing and driving the distal adaptive immune response to pathogens. Less clear has been the role of the nominal endogenous danger signals released and recognized in stressed cells following genotoxic or metabolic stress as occurs in progressively growing tumors. HMGB1 (high-mobility group B1) is a nuclear protein well characterized for its ability to modify DNA access to transcriptional proteins that is released from necrotic cells as well as secreted through the endosomal route from hematopoietic cells, serving as a late mediator of sepsis. It interacts with high-affinity RAGE (receptor for advanced glycation end products) and TLR2 receptors. Here we show that HMGB1 enhances interferon gamma release from macrophage (but not dendritic cell)-stimulated NK cells. This is effective only when coupled with other pro-inflammatory cytokines particularly with IL-2 in combination with IL-1 or IL-12. We have used this information to suggest that HMGB1, which also promotes epithelial migration and proliferation, drives repair in the absence or inhibition of other factors but enhances inflammation in their presence. The implications for tumorigenesis and tumor progression are quite important as they may be for other states of chronic inflammation.

Circulating soluble vascular cell adhesion molecule 1: Relationships with residual renal function, cardiac hypertrophy, and outcome of peritoneal dialysis patients

BACKGROUND

Vascular cell adhesion molecule 1 (VCAM-1) is involved in leukocyte-endothelial cell interaction and has a pivotal role in inflammation. Whether it contributes to excessive mortality in dialysis patients remains uncertain. In this study, we examined circulating soluble VCAM-1 (sVCAM-1) in relation to different clinical and biochemical parameters, as well as mortality and cardiovascular events, in peritoneal dialysis (PD) patients.

METHODS

Values for serum sVCAM-1, together with C-reactive protein (CRP), homocysteine, albumin, lipid profile, blood hemoglobin, and indices of dialysis adequacy, were determined at study baseline, and echocardiography was performed in 160 long-term PD patients. Patients were followed up for a mean of 35 +/- 16 (SD) months.

RESULTS

Serum sVCAM-1 levels were elevated in our continuous ambulatory PD (CAPD) patients and showed a negative correlation with residual glomerular filtration rate (GFR; P < 0.001) and low-density lipoprotein (LDL) cholesterol level (P = 0.004), but a positive correlation with left ventricular mass index (P = 0.025). Using Kaplan-Meier analysis, overall survival rates at 2 years were 96.2%, 75.2%, and 50.6% for patients in the lower, middle, and upper tertiles of sVCAM-1 levels, respectively (P < 0.0001). Fatal and nonfatal cardiovascular event-free survival rates were 58.2%, 56.9%, and 19.4% for patients in the lower, middle, and upper tertiles, respectively (P < 0.0001). Using Cox regression analysis with adjustment for confounding covariates, every 100-ng/mL increase in sVCAM-1 level was associated with 8% (95% confidence interval, 1.03 to 1.13) and 5% (95% confidence interval, 1.00 to 1.10) increases in risk for death and fatal and nonfatal cardiovascular events, respectively. Its significance for all-cause mortality remained with additional adjusting for LDL cholesterol level, but was lost when adjusting for residual GFR. Its association with cardiovascular events became insignificant when adjusting for LDL cholesterol level or residual GFR. Furthermore, patients with both sVCAM-1 and CRP levels elevated at the 50th percentile or greater were associated with the greatest death and fatal and nonfatal cardiovascular event rates compared with those with either CRP or sVCAM-1 level elevated at the 50th percentile or greater.

CONCLUSION

Circulating sVCAM-1 levels show an important link with residual renal function, LDL cholesterol level, and cardiac hypertrophy in CAPD patients. Furthermore, residual renal function, which correlates inversely with circulating sVCAM-1 level, shows an important association with all-cause mortality and cardiovascular events and displaces sVCAM-1 level from the models for all-cause mortality and future cardiovascular events in CAPD patients. Additional study is needed to explore possible mechanistic links between inflammation, soluble adhesion molecules, residual renal function, and cardiac hypertrophy in CAPD patients.

Angiotensin II suppresses growth arrest specific homeobox (Gax) expression via redox-sensitive mitogen-activated protein kinase (MAPK)

Oxidative stress is known to be involved in growth control of vascular smooth muscle cells (VSMCs). We and others have demonstrated that angiotensin II (Ang II) has an important role in vascular remodeling. Several reports suggested that VSMC growth induced by Ang II was elicited by oxidative stress. Gax, growth arrest-specific homeobox is a homeobox gene expressed in the cardiovascular system. Over expression of Gax is demonstrated to inhibit VSMC growth. We previously reported that Ang II down-regulated Gax expression. To address the regulatory mechanism of Gax, we investigated the significance of oxidative stress in Ang II-induced suppression of Gax expression. We further examined the involvement of mitogen-activated protein kinases (MAPKs), which is crucial for cell growth and has shown to be activated by oxidative stress, on the regulation of Gax expression by Ang II. Ang II markedly augmented intracellular H2O2 production which was decreased by pretreatment with N-acetylcystein (NAC), an anti-oxidant. Ang II and H2O2 decreased Gax expression dose-dependently and these effects were blocked by administration of both NAC and pyrrolidine dithiocarbamate (PDTC), another anti-oxidant. Ang II and H2O2 induced marked activation of extracellular signal-responsive kinase1/2 (ERK1/2), which was blocked by NAC. Ang II and H2O2 also activated p38MAPK, and they were blocked by pre-treatment with NAC. However, the level of activated p38MAPK was quite low in comparison with ERK1/2. Ang II- or H2O2 -induced Gax down-regulation was significantly inhibited by PD98059, an ERK1/2 inhibitor but not SB203580, a p38MAPK inhibitor. The present results demonstrated the significance of regulation of Gax expression by redox-sensitive ERK1/2 activation.

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.

Influence of Different Haemodialysis Modalities on AGE Peptide Levels: Intradialytic versus Long-Term Results

BACKGROUND

Peptide-linked degradation products of advanced glycation end products (AGE peptides) accumulate in chronic haemodialysis (HD) patients and may contribute to a number of HD-related long-term complications, such as accelerated atherosclerosis.

METHODS

The influence of a single HD session versus long-term HD on serum AGE peptides was determined. The patients were randomized to HD with a low-flux polysulfone (PS; F 6HPS), a high-flux PS (F 60S), a superflux PS (F 500S), or a superflux cellulose triacetate (CTA; Tricea 150G) dialyzer.

RESULTS

During a single HD session, both AGE peptides and reference peptides decreased significantly (AGE peptides: Tricea 150G -37.0 +/- 2.9%; F 6HPS -35.5 +/- 2.4%; F 60S -39.5 +/- 4.7%, and F 500S -43.3 +/- 2.1%, p = 0.005; reference peptides: Tricea 150G -73.2 +/- 8.8%; F 6HPS -73.2 +/- 7.9%; F 60S -72.5 +/- 8.2%, and F 500S -74.1 +/- 7.3%, p = 0.005). After 12 weeks of HD with the superflux CTA, the AGE peptide levels decreased significantly (week 1: 2.7 +/- 1.1 arbitrary units, week 12: 2.5 +/- 1.2 arbitrary units, decrease 7.4%; p = 0.01), whereas the AGE peptide levels remained unchanged after HD with each of the other three modalities. The reference peptide levels did not change after 12 weeks of HD.

CONCLUSION

Although AGE peptides can be effectively removed during a single HD session, superflux CTA seems to be the only modality capable of reducing AGE peptides in the long term.

Nuclear factor kappaB signaling in atherogenesis

Atherosclerosis is an inflammatory disease, characterized by the accumulation of macrophage-derived foam cells in the vessel wall and accompanied by the production of a wide range of chemokines, cytokines, and growth factors. These factors regulate the turnover and differentiation of immigrating and resident cells, eventually influencing plaque development. One of the key regulators of inflammation is the transcription factor nuclear factor kappaB (NF-kappaB), which, for a long time, has been regarded as a proatherogenic factor, mainly because of its regulation of many of the proinflammatory genes linked to atherosclerosis. NF-kappaB may play an important role in guarding the delicate balance of the atherosclerotic process as a direct regulator of proinflammatory and anti-inflammatory genes and as a regulator of cell survival and proliferation. Here we address recent literature on the function of NF-kappaB in inflammatory responses and its relation to atherosclerosis.

High serum levels of advanced glycation end products predict increased coronary heart disease mortality in nondiabetic women but not in nondiabetic men: a population-based 18-year follow-up study

BACKGROUND

Advanced glycation end products (AGEs), modification products of glycation or glycoxidation of proteins and lipids, have been linked to premature atherosclerosis in patients with diabetes as well as in nondiabetic subjects.

METHODS AND RESULTS

Serum levels of AGEs were measured with an immunoassay in samples obtained at baseline examination of a random sample of 1141 nondiabetic individuals (535 men and 606 women), aged 45 to 64 years, living in Kuopio, East Finland, or Turku, West Finland in 1982 to 1984. After 18 years of follow-up, all-cause mortality, cardiovascular disease (CVD), and coronary heart disease (CHD) mortality were registered on the basis of copies of death certificates. Multivariate Cox regression model showed a significant association of serum AGEs with all-cause (P=0.012), CVD (P=0.018), and CHD (P=0.008) mortality in women but not in men. Fasting serum AGEs in the highest quartile were an independent risk factor for all-cause (hazards ratio [HR], 1.90; 95% CI, 1.16 to 3.11; P=0.011) and CHD (HR, 6.51; 95% CI, 1.78 to 23.79; P=0.005) mortality in women, even after the adjustment for confounding factors, including highly sensitive C-reactive protein.

CONCLUSIONS

The present study is the first to show that serum levels of AGEs can predict total, CVD, and CHD mortality in nondiabetic women.

Markers of inflammation are cross-sectionally associated with microvascular complications and cardiovascular disease in type 1 diabetes--the EURODIAB Prospective Complications Study

AIMS/HYPOTHESIS

The pathogenesis of vascular complications in type 1 diabetes is poorly understood, but may involve chronic, low-grade inflammation. We investigated the association of markers of inflammation with vascular complications in type 1 diabetes.

METHODS

A cross-sectional nested case-control study of the follow-up data of the EURODIAB Prospective Complications Study. This study included 543 individuals (278 men) with type 1 diabetes diagnosed at <36 years of age. Cases (n=348) had complications of diabetes, controls (n=195) had no complications.

RESULTS

C-reactive protein, interleukin-6 and tumour necrosis factor-alpha levels, which were combined in an inflammatory marker Z-score, were associated with albuminuria, retinopathy and cardiovascular disease. Calculated means (95% confidence intervals) of the marker Z-score were -0.15 (-0.22 to -0.07), 0.10 (-0.05 to 0.25), and 0.28 (0.15 to 0.41), p for trend <0.0001, in individuals with normo-, micro- and macroalbuminuria; -0.23 (-0.33 to -0.13), 0.14 (0.02 to 0.25) and 0.20 (0.07 to 0.32), p for trend <0.0001, in individuals with no, non-proliferative and proliferative retinopathy; and -0.28 (-0.39 to -0.18) and 0.06 (-0.08 to 0.20), p<0.001, in individuals without and with cardiovascular disease. Per 1 SD increase of the inflammatory marker Z-score, GFR decreased by -4.6 (-6.6 to -2.6) ml per min per 1.73 m(2) (p<0.001).

CONCLUSIONS/INTERPRETATION

We have shown that markers of inflammation are strongly and independently associated with microvascular complications and cardiovascular disease in type 1 diabetes. These data suggest that strategies to decrease inflammatory activity may help to prevent the development of vascular complications in type 1 diabetes.

Quantification of carbamylated LDL in human sera by a new sandwich ELISA

BACKGROUND

We previously suggested that increased carbamylated LDL (cLDL), a product of nonenzymatic modification of LDL in human serum by urea-derived cyanate, may cause cardiovascular complications in patients with chronic renal insufficiency. An assay for precise measurement of cLDL in serum was not previously available.

METHODS

Polyclonal antibodies against human cLDL and nonmodified, native LDL (nLDL) were raised in rabbits and extensively purified by affinity chromatography. New sandwich ELISAs to measure cLDL and nLDL with use of these antibodies were developed. Serum concentrations of cLDL and nLDL were measured by the sandwich ELISAs in 41 patients with end-stage renal disease (ESRD) and 40 healthy controls.

RESULTS

Both assays showed satisfactory reproducibility, linearity, and recovery. The assays could detect 2.7 mg/L cLDL with a linear detection range of 5-1000 mg/L and 5 mg/L nLDL with a linear detection range of 50-1000 mg/L. These measurements showed that patients with ESRD have significantly increased serum cLDL [281.5 (46.9) mg/L compared with 86.1 (29.7) mg/L in a control group; P <0.001]. There was no significant difference in nLDL concentrations between the groups.

CONCLUSIONS

These assays are a potentially valuable tool for cardiovascular research in renal patients and healthy individuals. The cLDL concentration appears to be the highest among all previously described modified LDL isoforms in both controls and ESRD patients.

Expression of the receptor of advanced glycation end products in gingival tissues of type 2 diabetes patients with chronic periodontal disease: a study utilizing immunohistochemistry and RT-PCR

OBJECTIVES

Relationship between diabetes and periodontal disease is well established. It has been shown that advanced glycation end-products (AGEs) might exert noxious effects on gingival tissues through its receptor. Evidence for the role of receptors of AGE (RAGE) in periodontal disease was verified in a murine model for diabetes. However, the presence of RAGE in human gingival tissues has not been demonstrated previously. In this study we demonstrate the presence of RAGE in human periodontium in patients with chronic periodontitis with and without type 2 diabetes.

MATERIAL AND METHODS

Gingival biopsies from eight patients with both type 2 diabetes and chronic periodontitis and 14 healthy control subjects with chronic periodontitis were immunohistochemically stained for RAGE. Five samples from the study groups and four controls were subjected to reverse transcriptase coupled to polymerase chain reaction (RT-PCR) for quantitative determination of mRNA for RAGE.

RESULTS

On immunohistochemistry, positive staining for RAGE was seen in the endothelium and the basal and spinous layer of the inflamed gingival epithelium in both type 2 diabetes and non-diabetes tissue with no statistically significant difference between both groups. RT-PCR, however, showed a 50% increase in mRNA for RAGE in the gingiva of diabetic patients when compared with controls (p<0.05).

CONCLUSIONS

Although there was no change in the staining intensity for RAGE between both groups, the increase in the mRNA for RAGE in the type 2 diabetes gingival epithelium may indicate a possible involvement of this receptor in the periodontal destruction in type 2 diabetes.

Two immunochemical assays to measure advanced glycation end-products in serum from dialysis patients

Advanced glycation end-products are uremic toxins that accumulate in the serum and tissues of patients with chronic renal failure. Here, we established two enzyme-linked immunosorbent assays (ELISAs) for N

a-Series gangliosides mediate the effects of advanced glycation end products on pericyte and mesangial cell proliferation: a common mediator for retinal and renal microangiopathy?

Advanced glycation end products (AGEs) are involved in the development of microvascular complications, including alterations of retinal pericyte and renal mesangial cell growth occurring during diabetic retinopathy and diabetic nephropathy, respectively. Because gangliosides are implicated in the regulation of cell proliferation, we hypothesized that AGEs could exert cellular effects in part by modulating ganglioside levels. Results of the present study indicate that AGEs caused an inhibition of both bovine retinal pericyte (BRP) and rat renal mesangial cell (RMC) proliferation, associated with an increase of a-series gangliosides consecutive to GM3 synthase activity increase and GD3 synthase activity inhibition. Similar modifications were also found in the renal cortex of diabetic db/db mice compared with controls. Treatment of BRP and RMC with exogenous a-series gangliosides decreased proliferation and blockade of a-series gangliosides with specific antibodies partially protecting the two cell types from the AGE-induced proliferation decrease. Further, inhibition of GM3 synthase using specific SiRNA partially reversed the AGE effects on mesangial cell proliferation. These results suggest that a-series gangliosides are mediators of the adverse AGE effects on BRP and RMC proliferation. They also raise the hypothesis of common mechanisms involved in the development of diabetic retinopathy and diabetic nephropathy.

Advanced glycation and endothelial functions: a link towards vascular complications in diabetes

The formation of advanced glycation end-products (AGEs), also called the Maillard reaction, occurs ubiquitously and irreversibly in patients with diabetes mellitus, and its consequences are especially relevant to vascular dysfunctions. The interaction of AGEs with their receptors (RAGE) has been implicated in the development of vascular complications. This interaction elicits remarkable vascular cell changes analogous to those observed in diabetes mellitus, including angiogenic and thrombogenic responses of endothelial cells, increased oxidative stress, and functional alterations in vascular tone control. This review focuses on AGEs formation, the interaction with their specific receptors and how the triggered intracellular events determine functional alterations of vascular endothelium. Finally, some potential pharmacological approaches undertaken to circumvent the deleterious effects of AGEs are also discussed.

Activation of nuclear factor-kappaB by hyperglycemia in vascular smooth muscle cells is regulated by aldose reductase

Activation of the polyol pathway has been linked to the development of secondary diabetic complications. However, the underlying molecular mechanisms remain unclear. To probe the contribution of this pathway, we examined whether inhibition of aldose reductase, which catalyzes the first step of the pathway, affects hyperglycemia-induced activation of the inflammatory transcription factor nuclear factor (NF)-kappaB. Treatment of vascular smooth muscle cells with the aldose reductase inhibitors tolrestat and sorbinil prevented high-glucose-induced protein kinase C (PKC) activation, nuclear translocation of NF-kappaB, phosphorylation of IKK, and the increase in the expression of intracellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and aldose reductase. High-glucose-induced NF-kappaB activation was also prevented by the PKC inhibitors chelerythrine and calphostin C. Ablation of aldose reductase by small interference RNA (siRNA) prevented high-glucose-induced NF-kappaB and AP-1 activation but did not affect the activity of SP-1 or OCT-1. Stimulation with iso-osmotic mannitol activated NF-kappaB and increased the expression of aldose reductase but not ICAM-1 and VCAM-1. Treatment with aldose reductase inhibitors or aldose reductase siRNA did not affect mannitol-induced NF-kappaB or AP-1 activation. Administration of tolrestat (15 mg . kg(-1) . day(-1)) decreased the abundance of activated NF-kappaB in balloon-injured carotid arteries of diabetic rats. Collectively, these results suggest that inhibition of aldose reductase, which prevents PKC-dependent nonosmotic NF-kappaB activation, may be a useful approach for treating vascular inflammation caused by diabetes.

AMPK inhibits fatty acid-induced increases in NF-κB transactivation in cultured human umbilical vein endothelial cells

The fuel sensing enzyme AMP-activated protein kinase (AMPK) enhances processes that generate ATP when stresses such as exercise or glucose deprivation make cells energy deficient. We report here a novel role of AMPK, to prevent the activation of NF-kappaB in endothelial cells exposed to the fatty acid palmitate or the cytokine TNF-alpha. Incubation of cultured human umbilical vein endothelial cells (HUVEC) with elevated levels of palmitate (0.4mM) increased NF-kappaB reporter gene expression by 2- to 4-fold within 8h and caused a 7-fold increase in VCAM-1 mRNA expression at 24h. In contrast, no increase in reporter gene expression was detected for AP-1, glucocorticoid-, cyclic AMP-, or serum response elements. Similar increases in NF-kappaB activation and VCAM-1 expression were not observed in cells incubated with an elevated concentration of glucose (25mM). The increases in NF-kappaB activation and VCAM-1 expression caused by palmitate were markedly inhibited by co-incubation with the AMPK activator AICAR and, where studied, by expression of a constitutively active AMPK. Likewise, AMPK activation inhibited the increase in NF-kappaB reporter gene expression observed in HUVEC incubated with TNF-alpha. The results suggest that AMPK inhibits the activation of NF-kappaB caused by both palmitate and TNF-alpha. The mechanism responsible for this action, as well as its relevance to the reported anti-atherogenic actions of exercise, metformin, thiazolidinediones, and adiponectin, all of which have been shown to activate AMPK, remains to be determined.

Thiazolidinediones reduce endothelial expression of receptors for advanced glycation end products

Advanced glycation end products (AGEs) are critically involved in atherogenesis in diabetes by binding to receptors for AGE (RAGEs) in vascular cells, thus inducing the expression of proinflammatory mediators. In animal models, interruption of the AGE-RAGE interaction reduces lesion size and plaque development. Therefore, limiting RAGE expression might be an intriguing concept to modulate vascular disease in diabetic patients. The present study investigated whether thiazolidinediones (TZDs), antidiabetic agents clinically used to treat patients with type 2 diabetes, might modulate endothelial RAGE expression. Stimulation of human endothelial cells with rosiglitazone or pioglitazone decreased basal as well as tumor necrosis factor-alpha-induced RAGE cell surface and total protein expression. In addition, TZDs reduced RAGE mRNA expression in endothelial cells. These effects on RAGE expression were caused by an inhibition of nuclear factor-kappaB (NF-kappaB) activation at the proximal NF-kappaB site of the RAGE promoter. The functional relevance of reduced RAGE expression was demonstrated by showing that pretreatment of endothelial cells with TZDs decreased AGE- as well as beta-amyloid-induced monocyte chemoattractant protein-1 expression. In conclusion, TZDs reduce RAGE expression in human endothelial cells, thus limiting the cells' susceptibility toward proinflammatory AGE effects. These data provide new insight on how TZDs, in addition to their metabolic effects, might modulate the development of vascular dysfunction in diabetic patients.

Characterisation of advanced glycation endproducts in saliva from patients with diabetes mellitus

Patients with diabetes mellitus are prone to develop increased advanced glycation endproducts causing local complications and increased overall morbidity and mortality. Nuclear magnetic resonance spectra were determined in saliva of 52 consecutive patients with diabetes mellitus and 47 age-matched healthy control subjects. Resonance spectra showed specific peaks at 2.3, 7.3, and 8.4 ppm in saliva from patients with diabetes mellitus. These peaks could be generated by incubation of saliva from healthy control subjects with hypochloric acid in vitro, indicating the presence of advanced glycation endproducts. The presence of advanced glycation endproducts in patients with diabetes mellitus was associated with approximal plaque index, indicating increased periodontal damage. The study indicates that increased advanced glycation endproducts are involved in the pathogenesis of diabetic complications.

Blockade of late stages of autoimmune diabetes by inhibition of the receptor for advanced glycation end products

Ligation of the receptor for advanced glycation end products (RAGE) occurs during inflammation. Engagement of RAGE results in enhanced expression of addressins and it is therefore, not surprising that previous studies have shown a role of RAGE/ligand interactions in immune responses including cell/cell contact but the role of RAGE in spontaneous autoimmunity has not been clearly defined. To study the role of RAGE/ligand interactions in autoimmune diabetes, we tested the ability of soluble RAGE, a scavenger of RAGE ligands, in late stages of diabetes development in the NOD mouse-disease transferred with diabetogenic T cells and recurrent disease in NOD/scid recipients of syngeneic islet transplants. RAGE expression was detected on CD4(+), CD8(+), and B cells from diabetic mice and transferred to NOD/scid recipients. RAGE and its ligand, S100B, were found in the islets of NOD/scid mice that developed diabetes. Treatment of recipient NOD/scid mice with soluble RAGE prevented transfer of diabetes and delayed recurrent disease in syngeneic islet transplants. RAGE blockade was associated with increased expression of IL-10 and TGF-beta in the islets from protected mice. RAGE blockade reduced the transfer of disease with enriched T cells, but had no effect when diabetes was transferred with the activated CD4(+) T cell clone, BDC2.5. We conclude that RAGE/ligand interactions are involved in the differentiation of T cells to a mature pathogenic phenotype during the late stages of the development of diabetes.

[Diabetes mellitus, oxidative stress and advanced glycation endproducts]

Chronic hyperglycemia in diabetes mellitus is an oxidative stress created by an imbalance of prooxidants over antioxidant defenses. The pathogenesis would involve several mechanisms including glucose autoxidation, protein glycation, the polyol pathway, and overproduction of superoxide radicals in mitochondria and via NAD(P)H oxidase. Glycemic equilibrium plays a very important role in the prooxidant/antioxidant balance. Macromolecules such as found in the extracellular matrix, lipoproteins, and deoxyribonucleic acid also constitute targets for free radicals in diabetes mellitus. This oxidative tress is involved in the pathophysiology of diabetes complications. The chronic hyperglycemic status also favors glycation reactions (irreversible glucose binding on protein amino groups), thereby leading to advanced glycation endproducts. Via their recognition by cell receptors, advanced glycation endproducts also participate in the development of oxidative stress and the inflammatory status. Involvement of oxidative stress and advanced glycation endproducts in diabetes complications is the basis of the development of adjunct therapies with antioxidant and/or anti)advanced glycation endproducts molecules.

Reduced cell replication and induction of apoptosis by advanced glycation end products in rat Schwann cells

We investigated the effects of advanced glycation end products (AGEs) derived from glucose, glyceraldehyde, and glycolaldehyde (designated as AGE-1, -2, and -3, respectively) on the viability, replication rate, and cytokine production of cultured Schwann cells. AGE-2 and -3, but not AGE-1, induced apoptosis, and significantly decreased the viability measured by MTT assay. The decrease was prevented completely by antioxidant alpha-lipoic acid and was prevented partially by p38 mitogen-activated protein kinase inhibitor SB202190. The decrease in mitochondrial membrane potential by AGE-2 and -3 was also observed. In addition, AGE-2 and -3 significantly suppressed the replication rate as shown by reduced bromodeoxyuridine uptake, whereas they enhanced the release of TNF-alpha and IL-1beta into the medium and activated nuclear factor-kappaB. The effects of AGE-1 on these measures were equivocal. The series of events elicited by AGE-2 and -3 may be responsible for some of the aspects of pathogenetic mechanisms in patients with diabetic neuropathy.

Definition of the immunogenic forms of modified human LDL recognized by human autoantibodies and by rabbit hyperimmune antibodies

Humans and laboratory animals recognize human modified LDL as immunogenic. Immune complexes (ICs) isolated from human sera contain malondialdehyde-modified LDL (MDA-LDL) and N (epsilon)(carboxymethyl)lysine-modified LDL (CML-LDL) as well as antibodies reacting with MDA-LDL, copper-oxidized LDL (OxLDL), CML-LDL, and advanced glycosylation end product (AGE)-modified LDL. OxLDL and AGE-LDL antibodies isolated from human sera recognize the same LDL modifications and do not react with modified non-LDL proteins. Rabbit antibodies have different reactivity patterns: MDA-LDL antibodies react strongly with MDA-LDL and MDA-BSA but weakly with OxLDL; OxLDL antibodies react strongly with OxLDL and weakly with MDA-LDL; CML-LDL antibodies react with CML-LDL > CML-BSA > AGE-LDL > OxLDL; AGE-LDL antibodies react strongly with AGE-LDL, react weakly with OxLDL, and do not react with CML-LDL. Thus, human and rabbit antibodies seem to recognize different epitopes. Capture assays carried out with all rabbit antibodies showed binding of apolipoprotein B-rich lipoproteins isolated from ICs, suggesting that laboratory-generated epitopes are expressed by in vivo-modified LDL, although they are not necessarily recognized by the human immune system. Thus, the definition of immunogenic forms of modified LDL eliciting human autoimmune responses requires the isolation and characterization of autoantibodies and modified LDL from human samples, whereas rabbit antibodies can be used to detect in vivo-modified human LDL.

High levels of dietary advanced glycation end products transform low-density lipoprotein into a potent redox-sensitive mitogen-activated protein kinase stimulant in diabetic patients

BACKGROUND

LDL modification by endogenous advanced glycation end products (AGEs) is thought to contribute to cardiovascular disease of diabetes. It remains unclear, however, whether exogenous (diet-derived) AGEs influence glycoxidation and endothelial cell toxicity of diabetic LDL.

METHODS AND RESULTS

Twenty-four diabetic subjects were randomized to either a standard diet (here called high-AGE, HAGE) or a diet 5-fold lower in AGE (LAGE diet) for 6 weeks. LDL pooled from patients on HAGE diet (Db-HAGE-LDL) was more glycated than LDL from the LAGE diet group (Db-LAGE-LDL) (192 versus 92 AGE U/mg apolipoprotein B) and more oxidized (5.7 versus 1.5 nmol malondialdehyde/mg lipoprotein). When added to human endothelial cells (ECV 304 or human umbilical vein endothelial cells), Db-HAGE-LDL promoted marked ERK1/2 phosphorylation (pERK1/2) (5.5- to 10-fold of control) in a time- and dose-dependent manner compared with Db-LAGE-LDL or native LDL. In addition, Db-HAGE-LDL stimulated NF-kappaB activity significantly in ECV 304 and human umbilical vein endothelial cells (2.3-fold above baseline) in a manner inhibitable by a MEK inhibitor PD98059 (10 micromol/L), the antioxidant N-acetyl-l-cysteine, NAC (30 mmol/L), and the NADPH oxidase inhibitor DPI (20 micromol/L). In contrast to Db-LAGE-LD and native LDL, Db-HAGE-LDL induced significant soluble vascular cell adhesion molecule-1 production (2.3-fold), which was blocked by PD98059, NAC, and DPI.

CONCLUSIONS

Exposure to daily dietary glycoxidants enhances LDL-induced vascular toxicity via redox-sensitive mitogen-activated protein kinase activation. This can be prevented by dietary AGE restriction.

Advanced glycation end product interventions reduce diabetes-accelerated atherosclerosis

Advanced glycation end product (AGE) formation may contribute to the progression of atherosclerosis, particularly in diabetes. The present study explored atherosclerosis in streptozotocin-induced diabetic apolipoprotein E-deficient (apoE-/-) mice that were randomized (n = 20) to receive for 20 weeks no treatment, the AGE cross-link breaker ALT-711, or the inhibitor of AGE formation aminoguanidine (AG). A sixfold increase in plaque area with diabetes was attenuated by 30% with ALT-711 and by 40% in AG-treated mice. Regional distribution of plaque demonstrated no reduction in plaque area or complexity within the aortic arch with treatment, in contrast to the thoracic and abdominal aortas, where significant attenuation was seen. Diabetes-associated accumulation of AGEs in aortas and plasma and decreases in skin collagen solubility were ameliorated by both treatments, in addition to reductions in the vascular receptor for AGE. Collagen-associated reductions in the AGEs carboxymethyllysine and carboxyethyllysine were identified with both treatments. Diabetes was also accompanied by aortic accumulation of total collagen, specifically collagens I, III, and IV, as well as increases in the profibrotic cytokines transforming growth factor-beta and connective tissue growth factor and in cellular alpha-smooth muscle actin. Attenuation of these changes was seen in both treated diabetic groups. ALT-711 and AG demonstrated the ability to reduce vascular AGE accumulation in addition to attenuating atherosclerosis in these diabetic mice.

Lipid inflammatory mediators in diabetic vascular disease

Type 2 diabetes is associated with significantly accelerated rates of macrovascular complications such as atherosclerosis. Emerging evidence now indicates that atherosclerosis is an inflammatory disease and that certain inflammatory markers may be key predictors of diabetic atherosclerosis. Proinflammatory cytokines and cellular adhesion molecules expressed by vascular and blood cells during stimulation by growth factors and cytokines seem to play major roles in the pathophysiology of atherosclerosis and diabetic vascular complications. However, more recently, data suggest that inflammatory responses can also be elicited by smaller oxidized lipids that are components of atherogenic oxidized low-density lipoprotein or products of phospholipase activation and arachidonic acid metabolism. These include oxidized lipids of the lipoxygenase and cyclooxygenase pathways of arachidonic acid and linoleic acid metabolism. These lipids have potent growth, vasoactive, chemotactic, oxidative, and proinflammatory properties in vascular smooth muscle cells, endothelial cells, and monocytes. Cellular and animal models indicate that these enzymes are induced under diabetic conditions, have proatherogenic effects, and also mediate the actions of growth factors and cytokines. This review highlights the roles of the inflammatory cyclooxygenase and 12/15-lipoxygenase pathways in the pathogenesis of diabetic vascular disease. Evidence suggests that inflammatory responses in the vasculature can be elicited by small oxidized lipids that are components of oxidized low-density lipoprotein or products of the lipoxygenase and cyclooxygenase pathways of arachidonic and linoleic acid metabolism. This review evaluates these inflammatory and proatherogenic pathways in the pathogenesis of diabetic vascular disease.

Obesity, glucose intolerance and diabetes and their links to cardiovascular disease. Implications for laboratory medicine

This article provides an overview of the role of metabolite toxicity, low-grade inflammation and disturbed cellular signaling in obesity, glucose intolerance and diabetes. It also highlights links between this continuum of deteriorating glucose tolerance and atherosclerosis. Obesity, diabetes mellitus, and cardiovascular disease are all related to diet and to the level of physical activity. They have reached epidemic proportions worldwide. Glucose intolerance and diabetes increase the risk of atherosclerotic events. Moreover, obesity, and glucose intolerance or diabetes, are components of the metabolic syndrome, which also imparts an increased cardiovascular risk. There is increasing recognition that common mechanisms contribute to diabetes and cardiovascular disease. Following increased calorie intake and/or decreased physical activity, fuel metabolism generates excess of 'toxic' metabolites, particularly glucose and fatty acids. Homeostasis is affected by the endocrine output from the adipose tissue. Reactive oxygen species are generated, creating oxidative stress, which exerts major effects on signaling pathways, further affecting cellular metabolism and triggering low-grade inflammatory reaction. This perspective on the diabetic syndrome has been reflected in the approach to its treatment, which integrates maintenance of glycemic control with primary and secondary cardiovascular prevention. Laboratory medicine should support diabetes care with an integrated package of tests which, in addition to glycemic control, enable assessment and monitoring of the risk of microvascular complications as well as cardiovascular disease.

Accumulation of advanced glycation end products as a molecular mechanism for aging as a risk factor in osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is one of the most prevalent and disabling chronic conditions affecting the elderly. Its etiology is largely unknown, but age is the most prominent risk factor. The current study was designed to test whether accumulation of advanced glycation end products (AGEs), which are known to adversely affect cartilage turnover and mechanical properties, provides a molecular mechanism by which aging contributes to the development of OA.

METHODS

The hypothesis that elevated AGE levels predispose to the development of OA was tested in the canine anterior cruciate ligament transection (ACLT) model of experimental OA. Cartilage AGE levels were enhanced in young dogs by intraarticular injections of ribose. This mimics the accumulation of AGEs without the interference of other age-related changes. The severity of OA was then assessed 7 weeks after ACLT surgery in dogs with normal versus enhanced AGE levels.

RESULTS

Intraarticular injections of ribose enhanced cartilage AGE levels approximately 5-fold, which is similar to the normal increase that is observed in old dogs. ACLT surgery resulted in more-pronounced OA in dogs with enhanced AGE levels. This was observed as increased collagen damage and enhanced release of proteoglycans. The attempt to repair the matrix damage was impaired; proteoglycan synthesis and retention were decreased at enhanced AGE levels. Mankin grading of histology sections also revealed more-severe OA in animals with enhanced AGE levels.

CONCLUSION

These findings demonstrate increased severity of OA at higher cartilage AGE levels and provide the first in vivo experimental evidence for a molecular mechanism by which aging may predispose to the development of OA.

Binding of receptor for advanced glycation end products (RAGE) ligands is not sufficient to induce inflammatory signals: lack of activity of endotoxin-free albumin-derived advanced glycation end products

AIMS/HYPOTHESIS

Activation of the receptor for advanced glycation end products (RAGE) reportedly triggers cellular responses implicated in the pathogenesis of diabetes, such as increasing vascular cell adhesion molecule-1 (VCAM-1) expression on vascular endothelial cells and inducing TNF-alpha secretion by mononuclear cells. The objective of this study was to evaluate whether RAGE binding affinity of AGE-BSAs and cellular activation correlate.

METHODS

To produce AGEs with varying glycation, bovine albumin AGEs were prepared with 500 mmol/l of glucose, fructose or ribose at times of incubation from 1 to 12 weeks. In addition, AGE-BSA was generated using either glyoxylic acid or glycolaldehyde. Cellular binding of the AGE-BSAs and the effect on endothelial cell VCAM-1 expression were studied in RAGE-expressing human microvascular endothelial cell line-4 cells. Induction of TNF-alpha secretion was assessed using RAGE-expressing human peripheral blood mononuclear cells (PBMCs).

RESULTS

Cellular binding of the different AGE preparations correlated well with RAGE affinity. Interestingly, we found that the AGE preparations, which were essentially endotoxin free (< or =0.2 ng/mg protein), were incapable of inducing VCAM-1 or TNF-alpha secretion regardless of RAGE binding affinity, AGE concentration or incubation time. In contrast, the reported RAGE ligand S100b was confirmed to induce VCAM-1 expression on endothelial cells and TNF-alpha secretion by PBMCs after 24 h of treatment.

CONCLUSIONS/INTERPRETATION

The results of this study suggest that AGE modification and high RAGE binding affinity are not sufficient to generate pro-inflammatory signalling molecules. Thus, RAGE binding affinity of AGE-BSAs does not seem to correlate with cellular activation. Our findings using AGEs with strong RAGE-binding properties indicate that AGEs may not uniformly play a role in cellular activation.

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel 'remember'? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic 'memory'. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

PPARgamma agonists ameliorate endothelial cell activation via inhibition of diacylglycerol-protein kinase C signaling pathway: role of diacylglycerol kinase

Subject- Peroxisome proliferator-activated receptor (PPAR)-gamma agonists are emerging as potential protectors against inflammatory cardiovascular diseases including atherosclerosis and diabetic complications. However, their molecular mechanism of action within vasculature remains unclear. We report here that PPARgamma agonists, thiazolidinedione class drugs (TZDs), or 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) were capable of activating diacylglycerol (DAG) kinase (DGK), resulting in attenuation of DAG levels and inhibition of protein kinase C (PKC) activation. The PPARgamma agonist-induced DGK was completely blocked by a dominant-negative mutant of PPARgamma, indicating an essential receptor-dependent action. Importantly, the suppression of DAG-PKC signaling pathway was functional linkage to the anti-inflammatory properties of PPARgamma agonists in endothelial cells (EC), characterized by the inhibition of proinflammatory adhesion molecule expression and adherence of monocytes to the activated EC induced by high glucose. These findings thus demonstrate a novel molecular action of PPARgamma agonists to suppress the DAG-PKC signaling pathway via upregulation of an endogenous attenuator, DGK.

Receptor for advanced glycation endproduct (RAGE)-mediated nuclear factor-κB activation in vasculitic neuropathy

Binding of ligands to the receptor for advanced glycation endproducts (RAGE) results in activation of the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) and subsequent expression of NF-kappaB-regulated cytokines. In order to determine whether engagement of RAGE contributes to the pathogenesis of vasculitic neuropathy, we studied the presence of the RAGE ligand N(epsilon)-(carboxymethyl)lysine (CML), the receptor itself, NF-kappaB, and interleukin-6 (IL-6) in sural nerve biopsies of 12 patients with vasculitic neuropathies and 12 controls. In the patients, CML, RAGE, NF-kappaB, and IL-6 were localized in mononuclear cells, epineurial and endoneurial vessels and the perineurium. CML, RAGE, NF-kappaB, and IL-6 were expressed by CD4(+), CD8(+), and CD68(+) cells invading the nerves. Controls showed only weak staining. These data suggest that the RAGE pathway plays a critical proinflammatory role in vasculitic neuropathy.

Divergent pathways of gene expression are activated by the RAGE ligands S100b and AGE-BSA

Activation of the receptor for advanced glycation end products (RAGE) reportedly triggers a variety of proinflammatory responses. However, our previous work revealed that RAGE-binding AGEs free of endotoxin were incapable of inducing vascular cell adhesion molecule-1 (VCAM-1) or tumor necrosis factor-alpha (TNF-alpha) expression. Thus, the objective of this study was to clarify the role of AGEs in cell activation through gene expression profiling using both in vitro and in vivo model systems. Endothelial cells treated with AGE-BSA, previously shown to bind RAGE with high affinity, did not show gene expression changes indicative of an inflammatory response. In contrast, the alternate RAGE ligand, S100b, triggered an increase in endothelial mRNA expression of a variety of immune-related genes. The effects of AGEs were studied in vivo using healthy mice exposed to two different treatment conditions: 1) intravenous injection of a single dose of model AGEs or 2) four intraperitoneal injections of model AGEs (once per day). In both cases, the liver was extracted for gene expression profiling. Both of the short-term AGE treatments resulted in a moderate increase in liver mRNA levels for genes involved in macrophage-based clearance/detoxification of foreign agents. Our findings using AGEs with strong RAGE-binding properties indicate that AGEs may not uniformly play a role in cellular activation.

Amphoterin as an extracellular regulator of cell motility: from discovery to disease

Amphoterin is a ubiquitous and highly conserved protein previously considered solely as a chromatin-associated, nuclear molecule. Amphoterin is released into the extracellular space by various cell types, and plays an important role in the regulation of cell migration, differentiation, tumorigenesis and inflammation. This paper reviews recent research on the mechanistic background underlying the biology of secreted amphoterin, with an emphasis on the role of amphoterin as an autocrine/paracrine regulator of cell migration.

Involvement of Toll-like Receptors 2 and 4 in Cellular Activation by High Mobility Group Box 1 Protein

High mobility group box 1 (HMGB1) protein, originally described as a DNA-binding protein that stabilizes nucleosomes and facilitates transcription, can also be released extracellularly during acute inflammatory responses. Exposure of neutrophils, monocytes, or macrophages to HMGB1 results in increased nuclear translocation of NF-kappaB and enhanced expression of proinflammatory cytokines. Although the receptor for advanced glycation end products (RAGE) has been shown to interact with HMGB1, other putative HMGB1 receptors are known to exist but have not been characterized. In the present experiments, we explored the role of RAGE, Toll-like receptor (TLR) 2, and TLR 4, as well as associated kinases, in HMGB1-induced cellular activation. Culture of neutrophils or macrophages with HMGB1 produced activation of NF-kappaB through TLR 4-independent mechanisms. Unlike lipopolysaccharide (LPS), which primarily increased the activity of IKKbeta, HMGB1 exposure resulted in activation of both IKKalpha and IKKbeta. Kinases and scaffolding proteins downstream of TLR 2 and TLR 4, but not TLR/interleukin-1 receptor (IL-1R)-independent kinases such as tumor necrosis factor receptor-associated factor 2, were involved in the enhancement of NF-kappaB-dependent transcription by HMGB1. Transfections with dominant negative constructs demonstrated that TLR 2 and TLR 4 were both involved in HMGB1-induced activation of NF-kappaB. In contrast, RAGE played only a minor role in macrophage activation by HMGB1. Interactions of HMGB1 with TLR 2 and TLR 4 may provide an explanation for the ability of HMGB1 to generate inflammatory responses that are similar to those initiated by LPS.

The pattern recognition receptor (RAGE) is a counterreceptor for leukocyte integrins: a novel pathway for inflammatory cell recruitment

The pattern recognition receptor, RAGE (receptor for advanced glycation endproducts), propagates cellular dysfunction in several inflammatory disorders and diabetes. Here we show that RAGE functions as an endothelial adhesion receptor promoting leukocyte recruitment. In an animal model of thioglycollate-induced acute peritonitis, leukocyte recruitment was significantly impaired in RAGE-deficient mice as opposed to wild-type mice. In diabetic wild-type mice we observed enhanced leukocyte recruitment to the inflamed peritoneum as compared with nondiabetic wild-type mice; this phenomenon was attributed to RAGE as it was abrogated in the presence of soluble RAGE and was absent in diabetic RAGE-deficient mice. In vitro, RAGE-dependent leukocyte adhesion to endothelial cells was mediated by a direct interaction of RAGE with the beta2-integrin Mac-1 and, to a lower extent, with p150,95 but not with LFA-1 or with beta1-integrins. The RAGE-Mac-1 interaction was augmented by the proinflammatory RAGE-ligand, S100-protein. These results were corroborated by analysis of cells transfected with different heterodimeric beta2-integrins, by using RAGE-transfected cells, and by using purified proteins. The RAGE-Mac-1 interaction defines a novel pathway of leukocyte recruitment relevant in inflammatory disorders associated with increased RAGE expression, such as in diabetes, and could provide the basis for the development of novel therapeutic applications.