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

beta2-microglobulin induces MMP-1 but not TIMP-1 expression in human synovial fibroblasts

BACKGROUND

beta2-Microglobulin (beta2m) amyloidosis is a destructive articular disease that causes significant morbidity in patients undergoing hemodialysis. The amyloid deposits contain beta2m, some of which is altered with advanced glycation end products (AGE-beta2m). The deposits are located principally in joint structures, with adjacent degradation of cartilage and bone. We hypothesized that one of the mechanisms by which beta2m induces joint destruction is to induce the release of matrix metalloproteinase-1 (MMP-1), but not tissue inhibitor of metalloproteinase-1 (TIMP-1), from synovial fibroblasts.

METHODS

To test this hypothesis and determine the role of AGE-beta2m, we incubated human osteoarthritic synovial fibroblasts in the presence and absence of beta2m and AGE-beta2m and measured the release of interstitial collagenase (MMP-1) and/or TIMP-1 by enzyme-linked immunosorbent assay and Northern blot analysis.

RESULTS

beta2m and AGE-beta2m at 10 and 25 microg/mL induced the release of MMP-1 from human osteoarthritic synovial fibroblasts at 24 hours. In contrast, there was no increased release of TIMP-1, leading to an increase in the MMP-1/TIMP-1 ratio indicative of uncontrolled collagenolysis. A similar dose response was observed at 48 hours, except that AGE-beta2m had no effect over control cultures. MMP-1 mRNA expression by Northern blot analysis paralleled these findings. The source of the fibroblasts did not alter the results. Finally, we demonstrated that doxycycline, a treatment for arthritis, can inhibit the release of MMP-1 from synovial fibroblasts incubated with beta2m.

CONCLUSION

beta2m, at physiologically relevant concentrations, induces the release of MMP-1 without concomitant release of TIMP-1 from human synovial fibroblasts, leading to uncontrolled collagenolysis. The alteration of beta2m with AGE did not alter this effect at 24 hours, but blocked the effect at 48 hours. These findings may account for the tissue destruction seen in beta2m amyloidosis.

Gliclazide decreases low-density lipoprotein oxidation and monocyte adhesion to the endothelium

Increasing evidence implicates oxidized low-density lipoprotein (LDL) and advanced glycation end products (AGE) in the atherogenesis associated with diabetes mellitus. In the present study, we examined the in vitro effects of gliclazide on LDL oxidation and monocyte adhesion to endothelial cells induced by oxidized LDL and glycated albumin. To assess the clinical relevance of our in vitro findings, we also measured the effect on monocyte adhesion of gliclazide administration to type 2 diabetic patients. Incubation of human monocytes and endothelial cells with increasing concentrations of gliclazide (0 to 10 microg/mL) and native LDL (100 microg/mL) induced a dose-dependent diminution of cell-mediated LDL oxidation. Pretreatment of endothelial cells with gliclazide (0 to 10 microg/mL) before addition of native LDL (100 microg/mL) or glycated albumin (100 microg/mL) resulted in a dose-dependent diminution of oxidized LDL- and glycated albumin-induced monocyte adhesion to endothelial cells. In type 2 diabetic patients, administration of gliclazide inhibits the increased adhesiveness of monocytes to levels similar to those observed in control subjects. These results indicate that gliclazide is an antioxidant and suggest a beneficial effect of this drug in the prevention of atherosclerosis associated with type 2 diabetes.

Endothelial dysfunctions: common denominators in vascular disease

The past 20 years have witnessed enormous progress in our understanding of the biology of vascular endothelium and its role in cardiovascular disease. Stemming from the seminal observations of Furchgott, the concept of a continuous regulation of vascular tone by normal endothelium and alterations of such control in disease states has become one of the most enlightening concepts of cardiovascular research. This review covers a few updates on the topic, illustrating selective areas of recent progress in our understanding of endothelial function in the control of leucocyte adhesion, atherogenesis and vascular tone, as well as the alterations that cause and accompany vascular disease.

Negative consequences of glycation

The Diabetes Control and Complications Trial (DCCT) established unequivocally that the effects of inadequate insulin action (as monitored by the level of hyperglycemia) are associated with the incidence and progression of diabetic retinopathy, nephropathy, and neuropathy. How does hyperglycemia induce the functional and morphologic changes that characterize diabetic complications? Increasing evidence points to a major role for sugar-derived advanced glycation end products (AGEs), which form inside and outside cells as a function of glucose concentration. Recent work in this area supports a central role for reactive oxygen species (ROS) in both the formation of AGEs, and in AGE-induced pathologic alterations in gene expression. Inhibition of ROS may also be centrally important in the action of drugs that prevent complications in diabetic animal models.

Stress-associated endoplasmic reticulum protein 1 (SERP1)/Ribosome-associated membrane protein 4 (RAMP4) stabilizes membrane proteins during stress and facilitates subsequent glycosylation

Application of differential display to cultured rat astrocytes subjected to hypoxia allowed cloning of a novel cDNA, termed stress-associated endoplasmic reticulum protein 1 (SERP1). Expression of SERP1 was enhanced in vitro by hypoxia and/or reoxygenation or other forms of stress, causing accumulation of unfolded proteins in endoplasmic reticulum (ER) stress, and in vivo by middle cerebral artery occlusion in rats. The SERP1 cDNA encodes a 66-amino acid polypeptide which was found to be identical to ribosome-associated membrane protein 4 (RAMP4) and bearing 29% identity to yeast suppressor of SecY 6 protein (YSY6p), suggesting participation in pathways controlling membrane protein biogenesis at ER. In cultured 293 cells subjected to ER stress, overexpression of SERP1/RAMP4 suppressed aggregation and/or degradation of newly synthesized integral membrane proteins, and subsequently, facilitated their glycosylation when the stress was removed. SERP1/RAMP4 interacted with Sec61alpha and Sec61beta, which are subunits of translocon, and a molecular chaperon calnexin. Furthermore, Sec61alpha and Sec61beta, but not SERP1/RAMP4, were found to associate with newly synthesized integral membrane proteins under stress. These results suggest that stabilization of membrane proteins in response to stress involves the concerted action of a rescue unit in the ER membrane comprised of SERP1/RAMP4, other components of translocon, and molecular chaperons in ER.

Abnormal markers of endothelial cell activation and oxidative stress in children, adolescents and young adults with type 1 diabetes with no clinical vascular disease

BACKGROUND

Endothelial cell dysfunction is an early feature of vascular disease and oxidative stress may be involved in its pathogenesis.

METHODS

Fifty-one children, adolescents and young people with Type 1 diabetes with no clinical diabetic angiopathy, mean age+/-SD of 16+/-4 years, diabetes duration of 8+/-5 years, and HbA(1c) of 8.5+/-1.6%, and 29 age, sex matched normal controls had blood samples assayed for E-selectin, intercellular cell adhesion molecule-1, von Willebrand Factor, red cell superoxide dismutase, plasma thiol and red cell glutathione.

RESULTS

E-selectin and ICAM-1 levels were significantly higher in the diabetic patients at 72+/-24 ng/ml and 287+/-57 ng/ml, respectively vs 43+/-16 ng/ml and 248+/-71 ng/ml in the normal controls (p<0.0002 and p<0.013). Von Willebrand Factor levels were not different between the two groups. Superoxide dismutase activity was significantly higher in the diabetic group at 220+/-58 micro/ml vs 175+/-24 micro/ml in the normal controls p<0.001, and those of plasma thiol and red cell glutathione were significantly lower in the diabetic group, at 1267+/-202 micromol/l and 458+/-38 micromol/l, respectively vs 1403+/-278 micromol/l and 487+/-70 micromol/l in the controls p<0.02 and p<0.03. Levels of superoxide dismutase correlated negatively with plasma thiol, age and diabetes duration r=-0.318, p<0.02; r=-0. 328, p<0.02; and r=-0.286, p<0.05, respectively.

CONCLUSION

These results confirm evidence of endothelial perturbation in young people with diabetes mellitus, and they also suggest that free radical generation may contribute to this dysfunction. This supports the hypothesis that vascular disease starts early in the course of childhood diabetes, akin to the situation in adults with diabetes.

Effects of diet and of dietary components on endothelial leukocyte adhesion molecules

Endothelial-leukocyte adhesion molecules are involved in processes regulating the selective attachment of leukocytes to the vessel wall, which participate in tissue inflammation, atherogenesis, and immunity. There has been recent appreciation that diet or specific dietary components may modulate such processes. Highly unsaturated-- particularly omega-3 -- fatty acids and antioxidants are receiving increasing attention in this regard as potential antiatherogenic and anti-inflammatory agents. The vascular surface expression of endothelial leukocyte molecules can also be reflected by plasma levels of "soluble" adhesion molecules, thus allowing the assessment of the effects of diet and selected dietary components on these processes in vivo.

N(epsilon)-(carboxymethyl)lysine adducts of proteins are ligands for receptor for advanced glycation end products that activate cell signaling pathways and modulate gene expression

Recent studies suggested that interruption of the interaction of advanced glycation end products (AGEs), with the signal-transducing receptor receptor for AGE (RAGE), by administration of the soluble, extracellular ligand-binding domain of RAGE, reversed vascular hyperpermeability and suppressed accelerated atherosclerosis in diabetic rodents. Since the precise molecular target of soluble RAGE in those settings was not elucidated, we tested the hypothesis that predominant specific AGEs within the tissues in disorders such as diabetes and renal failure, N(epsilon)-(carboxymethyl)lysine (CML) adducts, are ligands of RAGE. We demonstrate here that physiologically relevant CML modifications of proteins engage cellular RAGE, thereby activating key cell signaling pathways such as NF-kappaB and modulating gene expression. Thus, CML-RAGE interaction triggers processes intimately linked to accelerated vascular and inflammatory complications that typify disorders in which inflammation is an established component.

Oxidative stress as a regulator of gene expression in the vasculature

Oxidative stress and the production of intracellular reactive oxygen species (ROS) have been implicated in the pathogenesis of a variety of diseases. In excess, ROS and their byproducts that are capable of causing oxidative damage may be cytotoxic to cells. However, it is now well established that moderate amounts of ROS play a role in signal transduction processes such as cell growth and posttranslational modification of proteins. Oxidants, antioxidants, and other determinants of the intracellular reduction-oxidation (redox) state play an important role in the regulation of gene expression. Recent insights into the etiology and pathogenesis of atherosclerosis suggest that this disease may be viewed as an inflammatory disease linked to an abnormality in oxidation-mediated signals in the vasculature. In this review, we summarize the evidence supporting the notion that oxidative stress and the production of ROS function as physiological regulators of vascular gene expression mediated via specific redox-sensitive signal transduction pathways and transcriptional regulatory networks. Elucidating, at the molecular level, the regulatory processes involved in redox-sensitive vascular gene expression represents a foundation not only for understanding the pathogenesis of atherosclerosis and other inflammatory diseases but also for the development of novel therapeutic treatment strategies.

Endothelial α2,6-Linked Sialic Acid Inhibits VCAM-1- Dependent Adhesion Under Flow Conditions

We have previously shown that costimulation of endothelial cells with IL-1 + IL-4 markedly inhibits VCAM-1-dependent adhesion under flow conditions. We hypothesized that sialic acids on the costimulated cell surfaces may contribute to the inhibition. Northern blot analyses showed that Galβ1-4GlcNAc α2,6-sialyltransferase (ST6N) mRNA was up-regulated in cultured HUVEC by IL-1 or IL-4 alone, but that the expression was enhanced by costimulation, whereas the level of Galβ1-4GlcNAc/Galβ1-3GalNAc α2,3-sialyltransferase (ST3ON) mRNA was unchanged. Removing both α2,6- and α2,3-linked sialic acids from IL-1 + IL-4-costimulated HUVEC by sialidase significantly increased VCAM-1-dependent adhesion, whereas removing α2,3-linked sialic acid alone had no effect; adenovirus-mediated overexpression of ST6N with costimulation almost abolished the adhesion, which was reversible by sialidase. The same treatments of IL-1-stimulated HUVEC had no effect. Lectin blotting showed that VCAM-1 is decorated with α2,6- but not α2,3-linked sialic acids. However, overexpression of α2,6-sialyltransferase did not increase α2,6-linked sialic acid on VCAM-1 but did increase α2,6-linked sialic acids on other proteins that remain to be identified. These results suggest that α2,6-linked sialic acids on a molecule(s) inducible by costimulation with IL-1 + IL-4 but not IL-1 alone down-regulates VCAM-1-dependent adhesion under flow conditions.

Endothelial adhesion molecule expression is enhanced in the aorta and internal mammary artery of diabetic patients

BACKGROUND

Diabetes mellitus is a major risk factor for the development of atherosclerosis but the mechanisms involved remain unclear. The expression of leukocyte adhesion molecules at the endothelial surface is a primary step in the recruitment of leukocytes into the intima and the subsequent development of lipid-containing foam cell lesions. Increased levels of circulating adhesion molecules have been identified in diabetic patients, but the distribution in the arterial wall has not been described.

MATERIALS AND METHODS

Frozen sections were prepared from aorta and internal mammary artery obtained during bypass surgery from 12 diabetic and 16 nondiabetic patients. Adhesion molecules (intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-Selectin), macrophages, and lymphocytes were identified and quantified using immunohistochemistry; intimal hyperplasia was quantified.

RESULTS

Endothelial expression of VCAM-1 and intimal smooth muscle cell expression of both VCAM-1 and ICAM-1 was increased in the aortas from diabetic patients. Intimal hyperplasia in aorta and internal mammary artery sections was significantly greater in diabetic tissue. Macrophages, T-lymphocytes, oil-red-O-stained lipid, glycated albumin, and glycated LDL were observed in the aorta of both diabetic and nondiabetic samples.

CONCLUSIONS

The increased incidence of VCAM-1 and ICAM-1 in the aorta may partly explain the enhanced atherosclerosis associated with diabetes mellitus, and their presence in established lesions may emphasize their long-term importance. The intimal hyperplasia observed in the bypass vessel may be a contributing factor to the increased incidence of restenosis in diabetic patients.

Receptor for advanced glycation end products (RAGE)-mediated neurite outgrowth and activation of NF-kappaB require the cytoplasmic domain of the receptor but different downstream signaling pathways

Receptor for advanced glycation end products (RAGE) mediates neurite outgrowth in vitro on amphoterin-coated substrates. Ligation of RAGE by two other ligands, advanced glycation end products or amyloid beta-peptide, is suggested to play a role in cell injury mechanisms involving cellular oxidant stress and activation of the transcription factor NF-kappaB. However, the RAGE signaling pathways in neurite outgrowth and cell injury are largely unknown. Here we show that transfection of RAGE to neuroblastoma cells induces extension of filopodia and neurites on amphoterin-coated substrates. Furthermore, ligation of RAGE in transfected cells enhances NF-kappaB-dependent transcription. Both the RAGE-mediated neurite outgrowth and activation of NF-kappaB are blocked by deletion of the cytoplasmic domain of RAGE. Moreover, dominant negative Rac and Cdc42 but not dominant negative Ras inhibit the extension of neurites induced by RAGE-amphoterin interaction. In contrast, the activation of NF-kappaB is inhibited by dominant negative Ras but not Rac or Cdc42. These data suggest that distinct signaling pathways are used by RAGE to induce neurite outgrowth and regulate gene expression through NF-kappaB.

Periodontal ligament cells from insulin-dependent diabetics exhibit altered alkaline phosphatase activity in response to growth factors

BACKGROUND

Insulin-dependent or Type 1 diabetes mellitus (IDDM) has been associated with an increased severity of periodontal disease. Because periodontal ligament (PDL) cells play a significant role in maintenance and regeneration of mineralized tissue, the success of procedures, such as guided tissue regeneration, is directly related to the ability of these cells to augment mineralized tissue. The objective of this study was to examine the ability of PDL cells from long-standing IDDM patients to form mineralized tissue and to determine whether these cells would exhibit altered responses to exogenously added growth factors.

METHODS

PDL cells were isolated from 4 patients with IDDM treated with insulin for at least 5 years and from systemically healthy donors. The cell isolates were tested for their ability to form mineralized nodules in vitro and to express alterations in alkaline phosphatase activity in response to exogenously added growth factors (transforming growth factor-beta (TGF-beta), platelet-derived growth factor-BB (PDGF-BB), and insulin-like growth factor-1 (IGF-1). Alkaline phosphatase activity was determined spectrophotometrically.

RESULTS

Although all PDL cell isolates formed mineralized nodules in vitro, PDL cells from diabetics formed mineralized nodules more slowly than did the controls. Alkaline phosphatase activity was not altered by exposure of diabetic PDL cells to TGF-beta for 9 days. In contrast, non-diabetic isolates exhibited increased levels of activity with increasing concentrations, from 0.5 to 1.0 ng/ml. Alkaline phosphatase activity was significantly higher in non-diabetic, but not in diabetic, cell isolates exposed to TGF-beta at 1.0 ng/ml, when compared to non-treated controls. Diabetic cell isolates exhibited significantly lower alkaline phosphatase activity than the non-diabetic isolates when exposed to either TGF-beta, PDGF-BB, IGF-1 or a combination of PDGF-BB and IGF-1.

CONCLUSIONS

These results suggest that the populations of PDL cells in insulin-dependent diabetics may be altered in their ability to form mineralized tissue and to respond to growth factors, functions affecting the maintenance and regeneration of the periodontium.

MMP-mediated events in diabetes

Both Type I and Type II diabetes mellitus (DM) have been associated with unusually aggressive periodontitis. Accordingly, rat models of both types of DM were used to study (i) mechanisms mediating this systemic/local interaction and (ii) new pharmacologic approaches involving a series of chemically modified tetracyclines (CMTs) that have lost their antimicrobial but retained their host-modulating (e.g., MMP-inhibitory) properties. In vitro experiments on tissues from Type I DM rats demonstrated that several of these CMTs were better matrix metalloproteinase (MMP) inhibitors than was antibacterial doxycycline (doxy), except for CMT-5, which, unlike the other MMP inhibitors, was found not to react with zinc. Data from in vivo studies on the same rat model generally supported the relative efficacy of these compounds: the CMTs and doxy were found to inhibit MMP activity, enzyme expression, and alveolar bone loss. To examine other long-term complications such as nephropathy and retinopathy, a Type II (ZDF) model of DM was studied. Treatment of these DM rats with CMT-8 produced a 37% (p < 0.05), 93% (p < 0.001), and 50% (p < 0.01) reduction in the incidence of cataract development, proteinuria, and tooth loss, respectively; whereas the doxy-treated ZDF rats showed little or no effect on these parameters. CMT treatment decreased mortality of the Type II ZDF diabetic animals, clearly indicating that CMTs, but not commercially available antibiotic tetracyclines (TCs), may have therapeutic applications for the long-term management of diabetes.

RAGE mediates a novel proinflammatory axis: a central cell surface receptor for S100/calgranulin polypeptides

S100/calgranulin polypeptides are present at sites of inflammation, likely released by inflammatory cells targeted to such loci by a range of environmental cues. We report here that receptor for AGE (RAGE) is a central cell surface receptor for EN-RAGE (extracellular newly identified RAGE-binding protein) and related members of the S100/calgranulin superfamily. Interaction of EN-RAGEs with cellular RAGE on endothelium, mononuclear phagocytes, and lymphocytes triggers cellular activation, with generation of key proinflammatory mediators. Blockade of EN-RAGE/RAGE quenches delayed-type hypersensitivity and inflammatory colitis in murine models by arresting activation of central signaling pathways and expression of inflammatory gene mediators. These data highlight a novel paradigm in inflammation and identify roles for EN-RAGEs and RAGE in chronic cellular activation and tissue injury.

Membrane proteins of human erythrocytes are modified by advanced glycation end products during aging in the circulation

Recent immunological studies demonstrated that proteins in vivo in several diseases are subjected to post-translational modification by advanced glycation end products (AGEs), suggesting a potential role of AGEs in aging and age-enhanced disease processes such as diabetic complications, atherosclerosis and Alzheimer's disease. Nvarepsilon-(Carboxymethyl)lysine (CML) is one of the major AGE-structures demonstrated in vivo so far. In the present study, membrane proteins from young erythrocyte population were compared with those from senescent erythrocytes separated from the same individual in their CML-contents using a monoclonal antibody for CML (6D12). SDS-polyacrylamide gel electrophoresis and subsequent Western blot showed that 6D12 bound to the band 1, 2, 3, 4.2, 5, 6 and 7 proteins from senescent erythrocytes, but not to those from young erythrocytes. Furthermore, quantitative estimation of the reactivity of 6D12 to these erythrocyte membranes by ELISA showed that the reactivity of 6D12 to senescent erythrocyte membranes was 3- to 6-fold higher than that of young erythrocyte membranes. These results indicate that membrane proteins of circulating erythrocytes undergo CML-modification, and the modified proteins accumulated in an age-dependent manner during the life span of erythrocytes.

Characterization of the advanced glycation end-product receptor complex in human vascular endothelial cells

Advanced glycation end products (AGEs) have been implicated as causal factors in the vascular complications of diabetes and it is known that these products interact with cells through specific receptors. The AGE-receptor complex, originally described as p60 and p90, has been characterised in hemopoietic cells and the component proteins identified and designated AGE-R1, -R2 and -R3. In the current study we have characterised this receptor in human umbilical vein endothelial cells (HUVECs) and elucidated several important biological properties which may impact on AGE mediated vascular disease. 125I-AGE-BSA binding to HUVEC monolayers was determined with and without various cold competitors. The synthetic AGE, 2-(2-furoyl)-4(5)-furanyl-1H-imidazole (FFI)-BSA, failed to compete with AGE-BSA binding unlike observations already reported in hemopoietic cells. The ability of 125I-AGE-BSA to bind to separated HUVEC plasma membrane (PM) proteins was also examined and the binding at specific bands inhibited by antibodies to each component of the AGE-receptor complex. Western blotting of whole cell and PM fractions, before and after exposure to AGE-BSA, revealed that AGE-R1, -R2 and -R3 are subject to upregulation upon exposure to their ligand, a phenomenon which was also demonstrated by immunofluorescence of non-permeabilised cells. mRNA expression of each AGE-receptor component was apparent in HUVECs, with the AGE-R2 and -R3 gene expression being upregulated upon exposure to AGEs in a time-dependent manner. A phosporylation assay in combination with AGE-R2 immunoprecipitation demonstrated that this component of the receptor complex is phosphorylated by acute exposure to AGE-BSA. These results indicate the presence of a conserved AGE-receptor complex in vascular endothelium which demonstrates subtle differences to other cell-types. In response to AGE-modified molecules, this complex is subject to upregulation, while the AGE-R2 component also displays increased phosphorylation possibly leading to enhanced signal transduction.

Activation of receptor for advanced glycation end products: a mechanism for chronic vascular dysfunction in diabetic vasculopathy and atherosclerosis

Receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules and engages diverse ligands relevant to distinct pathological processes. One class of RAGE ligands includes glycoxidation products, termed advanced glycation end products, which occur in diabetes, at sites of oxidant stress in tissues, and in renal failure and amyloidoses. RAGE also functions as a signal transduction receptor for amyloid beta peptide, known to accumulate in Alzheimer disease in both affected brain parenchyma and cerebral vasculature. Interaction of RAGE with these ligands enhances receptor expression and initiates a positive feedback loop whereby receptor occupancy triggers increased RAGE expression, thereby perpetuating another wave of cellular activation. Sustained expression of RAGE by critical target cells, including endothelium, smooth muscle cells, mononuclear phagocytes, and neurons, in proximity to these ligands, sets the stage for chronic cellular activation and tissue damage. In a model of accelerated atherosclerosis associated with diabetes in genetically manipulated mice, blockade of cell surface RAGE by infusion of a soluble, truncated form of the receptor completely suppressed enhanced formation of vascular lesions. Amelioration of atherosclerosis in these diabetic/atherosclerotic animals by soluble RAGE occurred in the absence of changes in plasma lipids or glycemia, emphasizing the contribution of a lipid- and glycemia-independent mechanism(s) to atherogenesis, which we postulate to be interaction of RAGE with its ligands. Future studies using mice in which RAGE expression has been genetically manipulated and with selective low molecular weight RAGE inhibitors will be required to definitively assign a critical role for RAGE activation in diabetic vasculopathy. However, sustained receptor expression in a microenvironment with a plethora of ligand makes possible prolonged receptor stimulation, suggesting that interaction of cellular RAGE with its ligands could be a factor contributing to a range of important chronic disorders.

Receptors for proteins modified by advanced glycation endproducts (AGE)--their functional role in atherosclerosis

Long-term incubation of proteins with glucose leads, through the formation of early stage products such as Schiff base and Amadori rearrangement products, to the formation of advanced glycation end products (AGE). Recent studies of AGE-structures as well as the receptor for AGE-proteins (AGE-receptors) have emphasized the involvement of protein modification by AGE in aging and age-enhanced disease processes. Immunohistochemical analyses of human atherosclerotic lesions using a monoclonal anti-AGE antibody have demonstrated diffuse extracellular AGE-deposition as well as dense intracellular AGE-deposition in macrophage- and vascular smooth muscle cell (SMC)-derived foam cells. In vitro experiments using both CHO cells overexpressing macrophage scavenger receptor-A (MSR-A) and peritoneal macrophages from MSR-A-knockout mice have shown that the MSR-A plays a major role in endocytic uptake of AGE-proteins by macrophages. Furthermore, in vitro experiments with rabbit arterial SMCs demonstrated a novel AGE-receptor mediating endocytosis of AGE-proteins. These in vivo and in vitro experiments suggest that AGE-proteins formed extracellularly in atherosclerotic lesions are endocytosed by macrophages through MSR-A in the early stage, and by SMCs through the novel AGE-receptor in the advanced stage, implicating functional contribution of the AGE-receptor-mediated interaction of AGE-proteins with these cells to atherosclerotic processes in arterial walls.

Effect of diabetes and aminoguanidine therapy on renal advanced glycation end-product binding

BACKGROUND

Advanced glycation end-products (AGEs) have been implicated in the pathogenesis of diabetic nephropathy, and aminoguanidine (AG) has been shown to decrease the accumulation of AGEs in the diabetic kidney.

METHODS

This study investigates changes in AGE binding associated with diabetes in the rat kidney using in vitro and in vivo autoradiographic techniques. Male Sprague-Dawley rats were randomized into control and diabetic groups with and without AG treatment and were sacrificed after three weeks. Frozen kidney sections (20 microm) were incubated with [125I]-AGE-RNase or [125I]-AGE-BSA. To localize the AGE binding site, in vivo autoradiography was performed by injection of 15 microCi of [125I]-AGE-BSA into the abdominal aorta of the rat.

RESULTS

Low-affinity binding sites specific for AGEs in the renal cortex (IC50 = 0.28 microm) were detected by in vitro autoradiography. There was a significant increase in [125I]-AGE binding in the diabetic kidney, which was prevented by AG treatment. Emulsion autoradiography revealed that binding was localized primarily to proximal tubules in the renal cortex. Renal AGE levels, as assessed by fluorescence or by radioimmunoassay, were increased after three weeks of diabetes. This increase was attenuated by AG therapy.

CONCLUSIONS

AGE binding sites are present within the proximal tubules of the kidney and appear to be modulated by endogenous AGE levels. It remains to be determined if these binding sites represent receptors involved in clearance of AGEs or are linked to pathogenic pathways that lead to the development of diabetic nephropathy.

Gliclazide reduces the induction of human monocyte adhesion to endothelial cells by glycated albumin

OBJECTIVE

To examine the kinetic of human monocyte adhesion to endothelial cells stimulated by glycated albumin, the contributive role of cell adhesion molecules to this effect, and the effect of gliclazide--an hypoglycemic drug with antioxidant properties--on these parameters.

METHODS

In-vitro experiments performed in the presence and absence of gliclazide consisted of: (1) time-dependent determination of human monocyte adhesion to human endothelial cells (ECs) pre-exposed to glycated albumin; (2) evaluation of adhesion after incubation of ECs with antibodies against cell surface adhesion molecules; and (3) determination of EC surface adhesion molecules and of the activity of the transcription factor NF-kappaB.

RESULTS

Exposition of human ECs for 1-48 h to 100 microg/ml glycated albumin led to a time-dependent increase in human monocyte adhesion to endothelium. Pretreatment of ECs with 10 microg/ml gliclazide significantly decreased the glycated albumin-stimulated monocyte adhesion to these cells. Anti-antibodies against E-selectin (ELAM-1), vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) also reduced the stimulatory effect of glycated albumin on monocyte adhesion. In glycated albumin-treated ECs, an induction of both soluble and cell associated expression of ELAM-1, VCAM-1 and ICAM-1, an augmentation in the levels of these molecule transcripts and an increase in the DNA binding activity for NF-kappaB in the promoters of these antigens were observed. Gliclazide markedly inhibited the induction of all these parameters.

CONCLUSIONS

Glycated albumin stimulates human monocyte adhesion to ECs by inducing cell associated ELAM-1, ICAM-1 and VCAM-1. Gliclazide effectively inhibits monocyte adhesion to ECs by reducing glycated albumin induction of EC adhesion molecules and NF-kappaB activation. These results suggest that gliclazide may be beneficial in the prevention of endothelial disturbances associated with hyperglycemia in diabetic patients.

Binding of long-term glycated low density lipoprotein and AGE-albumin by peripheral monocytes and endothelial cells

Modification of low density lipoprotein (LDL) and plasma or tissue proteins by non-enzymatic glycation culminating in the formation of advanced glycation endproducts (AGEs) is one of the essential pathomechanisms leading to diabetes-associated long-term complications. We compared binding of glycated, glycoxidated and oxidated LDL by peripheral monocytes in activated and quiescent form. Interaction via specific receptors was different for glycated as compared to (glyc)oxidated LDL-modifications. In addition, binding of glycated LDL to quiescent and activated human umbilical vein endothelial cells was studied. In patients with insulin-dependent diabetes mellitus (IDDM), AGE-binding was significantly increased as compared to healthy individuals. Specific and non-specific monocyte binding mechanisms were detected, and both were significantly increased in IDDM patients. Specific and non-specific binding strategies possibly act in concert to eliminate circulating AGEs, which are instrumental in the development and progress of microangiopathic and macroangiopathic complications of diabetes mellitus.

The role of oxidative stress and NF-kappaB activation in late diabetic complications

A common endpoint of hyperglycemia dependent cellular changes is the generation of reactive oxygen intermediates (ROIs) and the presence of elevated oxidative stress. Therefore, oxidative stress is supposed to play an important role in the development of late diabetic complications. Formation of advanced glycation end products (AGE's) due to elevated nonenzymatic glycation of proteins, lipids and nucleic acids is accompanied by oxidative, radical-generating reactions and thus represents a major source for oxygen free radicals under hyperglycemic conditions. Once formed, AGE's can influence cellular function by binding to several binding sites including the receptor for AGE's, RAGE. Binding of AGE's (and other ligands) to RAGE results in generation of intracellular oxidative stress and subsequent activation of the redox-sensitive transcription factor NF-kappaB in vitro and in vivo. Consistently, activation of NF-kappaB in diabetic patients correlates with the quality of glycemic control and can be reduced by treatment with the antioxidant alpha-lipoic acid. The development of techniques allowing for a tissue culture independent measurement of NF-kappaB activation in patients with diabetes mellitus gives insights into the molecular mechanisms linking diabetes mellitus and hyperglycemia with formation of advanced glycated endproducts and generation of oxidative stress finally resulting in oxidative stress mediated cellular activation.

Mechanisms of maturation and ageing of collagen

The deleterious age-related changes in collagen that manifest in the stiffening of the joints, the vascular system and the renal and retinal capillaries are primarily due to the intermolecular cross-linking of the collagen molecules within the tissues. The formation of cross-links was elegantly demonstrated by Verzar over 40 years ago but the nature and mechanisms are only now being unravelled. Cross-linking involves two different mechanisms, one a precise enzymically controlled cross-linking during development and maturation and the other an adventitious non-enzymic mechanism following maturation of the tissue. It is this additional non-enzymic cross-linking, known as glycation, involving reaction with glucose and subsequent oxidation products of the complex, that is the major cause of dysfunction of collagenous tissues in old age. The process is accelerated in diabetic subjects due to the higher levels of glucose. The effect of glycation on cell-matrix interactions is now being studied and may be shown to be an equally important aspect of ageing of collagen. An understanding of these mechanisms is now leading to the development of inhibitors of glycation and compounds capable of cleaving the cross-links, thus alleviating the devastating effects of ageing.

Sp1-binding elements in the promoter of RAGE are essential for amphoterin-mediated gene expression in cultured neuroblastoma cells

Receptor for AGE (RAGE) and the polypeptide amphoterin are highly expressed and co-localized in neurons of the developing central nervous system of the rat. In vitro, the interaction of amphoterin with neuronal RAGE induces neurite outgrowth. We tested the hypothesis that interaction of amphoterin with neuronal cells enhances RAGE expression, thereby providing a mechanism by which amphoterin-mediated regulation of RAGE might contribute to promotion of neurite growth and spreading. Incubation of cultured neuroblastoma cells with amphoterin resulted in increased transcription and translation of RAGE, a process largely inhibited in the presence of anti-RAGE IgG but not by nonimmune IgG. To begin to delineate molecular mechanisms underlying these findings, we identified multiple putative binding elements within the 5'-flanking region of the RAGE gene for Sp1, a transcription factor that has been critically linked to the process of normal development. DNase I footprinting and electrophoretic mobility shift assays demonstrated multiple functional Sp1-binding sites within the region -245 to -40 of the RAGE promoter. Transient transfection of cultured SK-N-SH neuroblastoma cells with chimeric 5'-deletion constructs linked to luciferase reporter revealed that the region containing Sp1-binding elements did not contribute uniquely to basal expression of the RAGE gene. Simultaneous mutation of the multiple Sp1-binding elements in this region did not affect basal promoter function; however, promoter responsiveness to amphoterin was markedly attenuated. These results point to Sp1-dependent mechanisms underlying amphoterin-mediated increases in RAGE expression in neuroblastoma cells and further link amphoterin-RAGE interaction to development of the nervous system.

Endothelial cell adhesion molecule and PMNL response to inflammatory stimuli and AGE-modified fibronectin

BACKGROUND

Atherosclerotic vascular disease is the leading cause of death in patients with diabetes mellitus and end-stage renal disease. Advanced glycation end products (AGEs) are strongly suggested to be involved in the pathogenesis of atherosclerosis in these patients who also frequently experience infectious complications. We hypothesized that the interaction of AGEs and inflammatory mediators contributes to the up-regulation of endothelial cell activation.

METHODS

We investigated the effect of advanced glycated fibronectin in the presence or absence of inflammatory stimuli on the endothelial cell surface and mRNA expression of cell adhesion molecules. Furthermore, the influence of advanced glycated fibronectin on the transendothelial migration pattern of polymorphonuclear cells was analyzed.

RESULTS

Exposure to advanced glycated fibronectin together with inflammatory stimuli such as interleukin (IL)-1alpha, tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS) led to a significant increase in the surface expression of the cell adhesion molecules E-selectin, ICAM-1, VCAM-1 and PECAM-1 on endothelial cells. Soluble AGEs in combination with advanced glycated fibronectin significantly enhanced the endothelial cell surface expression of ICAM-1, VCAM-1 and PECAM-1, whereas this was not the case for E-selectin. At the transcriptional level short-time exposure of endothelial cells to advanced glycated fibronectin and inflammatory mediators resulted in an increased expression of E-selectin, ICAM-1 and VCAM-1 mRNA levels, whereas PECAM-1 repeatedly showed a significant decrease of gene transcript levels. An increase of mRNA levels was also observed for E-selectin, ICAM-1, VCAM-1 and PECAM-1 following incubation with a combination of advanced glycated fibronectin and soluble advanced glycation end-products. Furthermore, polymorphonuclear cells responded with a sevenfold increase in transendothelial migration following exposure of endothelial cells to advanced glycated fibronectin and inflammatory mediators.

CONCLUSIONS

These results suggest that the combination of matrix glycation and inflammation up-regulates the activation of the endothelial cell adhesion cascade, a mechanism that might contribute to the increased burden of atherosclerotic morbidity and mortality in patients suffering from diabetes mellitus or chronic renal failure.

A murine model of accelerated periodontal disease in diabetes

Diabetes is a risk factor for periodontal disease in humans. In hyperglycemia, glycoxidation of proteins and lipids results in the formation of advanced glycation endproducts, or AGEs. The accumulation of AGEs in the plasma and tissues, and their interaction with their cellular receptor for AGE (RAGE), has been implicated in diabetic complications. In order to establish a model with which to delineate the specific host response factors that underlie the development of periodontal disease in diabetes, male C57BL/6J mice were rendered diabetic with streptozotocin. One month after documentation of diabetes or control state, mice were inoculated with the human periodontal pathogen Porphyromonas gingivalis, strain 381 (P. gingivalis) or treated with vehicle. Infection with P. gingivalis was achieved, as demonstrated by infiltration of gingival tissue with granulocytes, presence of DNA specific for P. gingivalis as well as increased serum antibody titer to P. gingivalis. At 2 and 3 months after infection, increased alveolar bone loss was demonstrated in P. gingivalis-inoculated diabetic vs. non-diabetic mice, along with enhanced tissue-destructive capacity, as demonstrated by increased collagenolytic activity in gingival extracts. Consistent with an important role for AGE-RAGE interaction, increased AGE deposition and expression of vascular and monocyte RAGE were demonstrated in diabetic gingiva compared with non-diabetic controls. Taken together, these data indicate that we have established a murine model of enhanced periodontal disease in diabetes. This model will serve to delineate molecular mechanisms which account for the increased susceptibility of diabetic patients to periodontal disease.

Elevated serum levels of soluble vascular cell adhesion molecule-1 in NIDDM patients with proliferative diabetic retinopathy

We studied 68 Japanese NIDDM patients (38 men and 30 women), aged 56.9+/-1.2 years (range 33-75 years), with a BMI of 23.1+/-0.5 kg/m2 without hypertension, dyslipidemia, and diabetic macroangiopathy for evaluating the relationship between serum soluble vascular cell adhesion molecule-1 (sVCAM-1) levels and the severity of diabetic retinopathy. Fundus examination was performed by an ophthalmologist using an ophthalmoscope, and the findings were graded as: (1) no signs of diabetic retinopathy (NDR), (2) background diabetic retinopathy (BDR), or (3) proliferative diabetic retinopathy (PDR). Serum sVCAM-1 levels were measured in duplicate by enzyme-linked immunosorbent assay using the soluble VCAM-1 KIT (R&D Systems Ltd., Ablingdon, Oxfordshire, UK). There was no difference in serum sVCAM-1 levels between patients with BDR (n = 17) and patients with NDR (n = 40) (1035.3+/-104.4 and 978.8+/-48.9 ng/ml, respectively, P = 0.8), but patients with PDR (n = 11) showed a significant increase of serum sVCAM-1 levels compared with patients with NDR (1281.8+/-166.3 and 978.8+/-48.9 ng/ml, respectively, P = 0.02). Although serum sVCAM-1 levels were correlated, not only with age but also with the known diabetic duration (r = 0.39, P = 0.001, and r = 0.40, P = 0.0007, respectively), age-adjusted sVCAM-1 levels were still significantly higher in the PDR group than in the NDR group. In contrast. serum sVCAM-1 levels were not related to the presence of diabetic nephropathy or HbA1c levels. Our results suggest that sVCAM-1 might be implicated in the development of the diabetic retinopathy, and measurement of serum sVCAM-1 levels in NIDDM patients maybe clinically useful for assessing the severity and possibly the activity of diabetic retinopathy.

Suppression of accelerated diabetic atherosclerosis by the soluble receptor for advanced glycation endproducts

Accelerated atherosclerosis in patients with diabetes is a major cause of their morbidity and mortality, and it is unresponsive to therapy aimed at restoring relative euglycemia. In hyperglycemia, nonenzymatic glycation and oxidation of proteins and lipids results in the accumulation of irreversibly formed advanced glycation endproducts. These advanced glycation endproducts engage their receptor in cells of the blood vessel wall, thereby activating mechanisms linked to the development of vascular lesions. We report here a model of accelerated and advanced atherosclerosis in diabetic mice deficient for apolipoprotein E. Treatment of these mice with the soluble extracellular domain of the receptor for advanced glycation endproducts completely suppressed diabetic atherosclerosis in a glycemia- and lipid-independent manner. These findings indicate interaction between the advanced glycation endproducts and their receptor is involved in the development of accelerated atherosclerosis in diabetes, and identify this receptor as a new therapeutic target in diabetic macrovascular disease.

Chronic hyperglycemia increases arterial low-density lipoprotein metabolism and atherosclerosis in cynomolgus monkeys

Diabetes mellitus confers a threefold to fivefold increased risk of mortality from vascular disease. The primary cause of this increased incidence of vascular disease is atherosclerosis, but the mechanisms accounting for the increase are unclear. Chronic hyperglycemia is a common feature of all forms of diabetes mellitus and may contribute greatly to the increased incidence of atherosclerosis, via promotion of both lipoprotein and tissue glycation, which may have atherogenic effects. The present study investigated the effect of chronic hyperglycemia on measures of low-density lipoprotein (LDL) metabolism and atherosclerosis in streptozotocin-induced diabetic (STZ-DM) and control cynomolgus monkeys after 6 months of study. Consistent with a chronic hyperglycemic state, diabetic monkeys had significant increases in glycated hemoglobin (GHb) and glycated plasma LDL concentrations, but had minimal changes in total plasma cholesterol (TPC) or triglyceride (TG) concentrations during the study. Forty-eight hours before necropsy, control and in vitro-glycated LDL were differentially radiolabeled and coinjected into diabetic and control monkeys. There was a significant increase in arterial LDL accumulation in femoral arteries from diabetic monkeys compared with controls, with similar trends in other arterial sites. The effect of LDL glycation on arterial LDL accumulation was minimal in both groups. Arterial segments from diabetic monkeys also had greater amounts of arterial cholesterol content compared with controls. Histomorphometric analyses showed that diabetic monkeys had significantly greater intimal areas in the femoral artery and abdominal aorta compared with controls. Diabetic monkeys also had reduced arterial remodeling, or compensation, in the femoral artery and abdominal aorta. However, there was no difference in advanced glycation end products (AGE) in arterial collagen between groups. In conclusion, experimentally induced diabetes mellitus increases arterial LDL accumulation and atherosclerosis extent in cynomolgus monkeys before changes in AGE formation. The increased atherogenesis may be due to changes in lipoproteins or direct effects of hyperglycemia on the artery wall.

Enhanced interaction of advanced glycation end products with their cellular receptor RAGE: implications for the pathogenesis of accelerated periodontal disease in diabetes

The prevalence and severity of periodontal disease is increased in patients with both insulin-deficient and insulin-resistant forms of diabetes. While a number of underlying factors likely contribute to enhanced periodontal inflammation and alveolar bone loss in diabetes, a common characteristic of these disorders, regardless of etiology, is the presence of hyperglycemia. A critical consequence of hyperglycemia is non-enzymatic glycation and oxidation of proteins and lipids. After a series of reversible reactions which lead to the generation of Schiff bases/Amadori products, a further series of complex molecular rearrangements ensues which results in the formation of the irreversible advanced glycation end products, or AGEs. AGEs accumulate during the process of normal aging in the plasma and tissues, but to an accelerated degree in patients with diabetes. A central means by which AGEs are believed to impart their pathogenic effects is via interaction with specific cellular receptors; the best-characterized of these is receptor for AGE, or RAGE. RAGE, a member of the immunoglobulin superfamily of cell surface molecules, is present in increased levels on target cells in diabetes, such as endothelial cells and monocytes. One consequence of AGE-RAGE interaction is the generation of enhanced cellular oxidant stress, a means by which cell signaling pathways may be activated, thereby resulting in altered cellular phenotype and cellular dysfunction. In this report, we will review our studies to date on AGEs and RAGE and consider the implications of their enhanced interaction in the pathogenesis of accelerated periodontal disease in diabetes.

Effect of advanced glycosylation end products on the activity of integrins expressed on U937 cells

Advanced glycosylation end products (AGEs) are formed both in healthy old persons and diabetic patients by nonenzymatic glycosylation. However, AGEs are supposed to be a major factor in the vascular damages associated with diabetes. The aim of this study was to assess the effect of AGEs on the activity of cell adhesion molecules expressed on lymphoid cells. Human serum albumin (HSA) was glycosylated in vitro and used as a specific stimulating agent with U937 cells. The effect of glc-HSA was evaluated by the method of homotypic adhesion and adhesion to immunoplate coated with fibronectin. Specific monoclonal antibodies against integrins and ICAM-1 were applied in these studies. It was shown that glc-HSA enhanced the homotypic adhesion. The latter was mediaced via beta2-integrins as the effect was recorded after 15 min. incubation. The homotypic adhesion for the cells treated with glc-HSA followed the same kinetics as the cells incubated with phorbol myriastate acetate, which was used as a positive control. An anti-CD18 antibody inhibited the adhesion of U937 cells which indicated that the glc-HSA had a positive effect on the activity of beta2-integrins. Treatment with glc-HSA did not interfere with the adhesion of the referent cells to fibronectin coated plate. Based on these results the conclusion was drawn that the advanced glycosylation end products have a differential effect on the activity of integrin subfamilies expressed on cells of monocyte-macrophage origin.

Interaction of diabetes and hypertension on determinants of endothelial adhesiveness

Epidemiological studies have established that diabetes mellitus and hypertension are independent risk factors for atherosclerosis. One of the earliest abnormalities seen in atherogenesis is enhanced monocyte adherence to the endothelium. The mechanisms by which diabetes mellitus or hypertension enhances monocyte-endothelial cell interactions are incompletely characterized. It is not known whether there are additive interactions between these risk factors on endothelial adhesiveness for monocytes. Male Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were fed a normal or fructose-enriched diet. In some cases, animals were injected with streptozotocin (35 mg/kg body weight) to induce diabetes. After 2 weeks, plasma was drawn for biochemical measurements, and thoracic aortas were harvested, opened longitudinally, and exposed to fluorescently labeled mouse monocytoid cells (WEHI 78/24, 2 x 10(6)/mL) for 30 minutes on a rocking platform. Adherent cells were counted by epifluorescence microscopy. WEHI 78/24 binding to aortic segments from SHR animals was elevated compared with segments from WKYs. Fructose feeding alone had no effect on endothelial adhesiveness. When WKYs were made hyperglycemic by STZ injection, monocyte binding was 160% of the control value. Elevated monocyte binding was also observed in aortas derived from SHR animals injected with STZ, indicating an additive effect of hypertension and hyperglycemia. To determine whether alterations in oxidative state played a role in the endothelial adhesiveness, aortic segments were exposed to lucigenin (250 micromol/L) for measurement of superoxide anion. Aortic segments from SHR elaborated 120% more superoxide anion than did controls. Elevated free-radical production was also observed in aortas from diabetic WKYs. Furthermore, thoracic aortas derived from diabetic SHR animals elaborated more superoxide anion than did any of the other groups (374%, P<0.05). Immunohistochemical staining for monocyte chemotactic protein-1 demonstrated increased expression in aortas isolated from diabetic WKY and SHR compared with control vessels. These studies demonstrate that both diabetes and hypertension lead to increased monocyte adherence to the endothelium. This abnormality is associated with increased vascular superoxide production and monocyte chemotactic protein-1 expression. Furthermore, there appears to be an additive interaction between hyperglycemia and hypertension in their effects on endothelial adhesiveness and its determinants.

Vasculopathy and insulin resistance in the JCR:LA-cp rat

The JCR:LA-cp rat is one of a number of strains incorporating the autosomal recessive cp gene that induces obesity. This strain is unique in the development of not only a profound insulin resistance, but an accompanying cardiovascular disease that correlates strongly with hyperinsulinemia. The hyperinsulinemia develops rapidly after 4 weeks of age, with an age at half-maximum of 5.5 weeks. This reflects postprandial plasma insulin levels that peak at 1000 mU/l in a standardized meal tolerance test. Defective acetylcholine-mediated vascular relaxation develops with a 1-week lag over the developing hyperinsulinemia. The frequency of staining for the vascular adhesion molecules, VCAM-1 and ICAM, does not show either age or genotype variation, although plasma levels do show an age variation. Treatment of the rats with the alpha-glucosidase inhibitor, miglitol (Bay m1099), obviates the exaggerated postprandial glucose and, especially, the insulin responses of the cp/cp rat. This causes an improvement in insulin sensitivity, prevention of the impaired vascular relaxation, and reduction in plasma levels of advanced glycated end-products. Arterial wall morphology, as visualized by both scanning and transmission electron microscopy, shows abnormal endothelium, adherent macrophages, and activated migrating smooth muscle cells in the intima. Oil-Red-O staining reveals lipid deposits in the intimal spaces, as confirmed by the presence of foam cells. The lesions resemble fatty streaks or modest atherosclerosis in man, rather than the extensive cholesterol-laden lesions seen in familial hypercholesterolemia or cholesterol-fed rabbit models. The lean rats of the strain show similar, but less marked, intimal abnormalities. The vasculopathy in this animal model appears to be precipitated by the developing hyperinsulinemia, but also requires an underlying abnormality of vascular smooth muscle and possibly also of the endothelium.

Leukocyte-endothelial interaction is augmented by high glucose concentrations and hyperglycemia in a NF-kB-dependent fashion

We addressed the role of hyperglycemia in leukocyte-endothelium interaction under flow conditions by exposing human umbilical vein endothelial cells for 24 h to normal (5 mM), high concentration of glucose (30 mM), advanced glycosylation end product-albumin (100 microg/ml), or hyperglycemic (174-316 mg/dl) sera from patients with diabetes and abnormal hemoglobin A1c (8.1+/-1.4%). At the end of incubation endothelial cells were perfused with total leukocyte suspension in a parallel plate flow chamber under laminar flow (1.5 dyn/cm2). Rolling and adherent cells were evaluated by digital image processing. Results showed that 30 mM glucose significantly (P < 0. 01) increased the number of adherent leukocytes to endothelial cells in respect to control (5 mM glucose; 151+/-19 versus 33+/-8 cells/mm2). A similar response was induced by endothelial stimulation with IL-1beta, here used as positive control (195+/-20 cells/mm2). The number of rolling cells on endothelial surface was not affected by high glucose level. Stable adhesion of leukocytes to glucose-treated as well as to IL-1beta-stimulated endothelial cells was preceded by short interaction of leukocytes with the endothelial surface. The distance travelled by leukocytes before arrest on 30 mM glucose, or on IL-1beta-treated endothelial cells, was significantly (P < 0.01) higher than that observed for leukocytes adhering on control endothelium (30 mM glucose: 76.7+/-3.5; IL1beta: 69.7+/-4 versus 5 mM glucose: 21.5+/-5 microm). Functional blocking of E-selectin, intercellular cell adhesion molecule-1, and vascular cell adhesion molecule-1 on endothelial cells with the corresponding mouse mAb significantly inhibited glucose-induced increase in leukocyte adhesion (67+/-16, 83+/-12, 62+/-8 versus 144+/-21 cells/ mm2). Confocal fluorescence microscopy studies showed that 30 mM glucose induced an increase in endothelial surface expression of E-selectin, intercellular cell adhesion molecule-1, and vascular cell adhesion molecule-1. Electrophoretic mobility shift assay of nuclear extracts of human umbilical vein endothelial cells (HUVEC) exposed for 1 h to 30 mM glucose revealed an intense NF-kB activation. Treatment of HUVEC exposed to high glucose with the NF-kB inhibitors pyrrolidinedithiocarbamate (100 microM) and tosyl-phe-chloromethylketone (25 microM) significantly reduced (P < 0.05) leukocyte adhesion in respect to HUVEC treated with glucose alone. A significant (P < 0.01) inhibitory effect on glucose-induced leukocyte adhesion was observed after blocking protein kinase C activity with staurosporine (5 nM). When HUVEC were treated with specific antisense oligodesoxynucleotides against PKCalpha and PKCepsilon isoforms before the addition of 30 mM glucose, a significant (P < 0.05) reduction in the adhesion was also seen. Advanced glycosylation end product-albumin significantly increased the number of adhering leukocytes in respect to native albumin used as control (110+/-16 versus 66+/-7, P < 0.01). Sera from diabetic patients significantly (P < 0.01) enhanced leukocyte adhesion as compared with controls, despite normal levels of IL-1beta and TNFalpha in these sera. These data indicate that high glucose concentration and hyperglycemia promote leukocyte adhesion to the endothelium through upregulation of cell surface expression of adhesive proteins, possibly depending on NF-kB activation.

The free radical theory of aging matures

The free radical theory of aging, conceived in 1956, has turned 40 and is rapidly attracting the interest of the mainstream of biological research. From its origins in radiation biology, through a decade or so of dormancy and two decades of steady phenomenological research, it has attracted an increasing number of scientists from an expanding circle of fields. During the past decade, several lines of evidence have convinced a number of scientists that oxidants play an important role in aging. (For the sake of simplicity, we use the term oxidant to refer to all "reactive oxygen species," including O2-., H2O2, and .OH, even though the former often acts as a reductant and produces oxidants indirectly.) The pace and scope of research in the last few years have been particularly impressive and diverse. The only disadvantage of the current intellectual ferment is the difficulty in digesting the literature. Therefore, we have systematically reviewed the status of the free radical theory, by categorizing the literature in terms of the various types of experiments that have been performed. These include phenomenological measurements of age-associated oxidative stress, interspecies comparisons, dietary restriction, the manipulation of metabolic activity and oxygen tension, treatment with dietary and pharmacological antioxidants, in vitro senescence, classical and population genetics, molecular genetics, transgenic organisms, the study of human diseases of aging, epidemiological studies, and the ongoing elucidation of the role of active oxygen in biology.

Aminoguanidine has an anti-atherogenic effect in the cholesterol-fed rabbit

Advanced glycosylation endproducts (AGEs) which result from the non-enzymatic interaction of proteins and glucose are implicated in the vasculopathy of diabetes and aging. Since aminoguanidine (A) inhibits the accumulation of AGEs, we explored its effects on the development of atherosclerosis. Male New Zealand white cross rabbits fed a high cholesterol (1%) diet were randomized to control (C) or increasing doses of A treatment (25, 50 and 100 mg/kg A body weight). The animals were sacrificed after 12 weeks. Sudan IV was used to stain the lipid containing plaques of the aortic arch, thoracic and abdominal aorta and the surface area occupied by atheroma was assessed. Increasing doses of A treatment were associated with reduction in plaque formation in the aorta. At a dose of 100 mg/kg A, there was a 30, 49 and 48% reduction in plaque formation in the aortic arch, thoracic and abdominal aorta, respectively. There was a correlation between AGE levels and the degree of atheroma in these cholesterol fed rabbits (control, r = 0.75, P < 0.01; 100 mg/kg A, r = 0.59, P = 0.02). These data suggest that advanced glycation may participate in atherogenesis and raise the possibility that inhibitors of advanced glycation may retard this process.

Microglia, scavenger receptors, and the pathogenesis of Alzheimer's disease

The senile plaque is the pathological hallmark of Alzheimer's disease. Senile plaques are composed of beta amyloid fibrils, associated with activated microglia, astrocytes, and dystrophic neurons. We have recently identified class A scavenger receptors as the main receptors mediating the interaction of microglia with beta amyloid fibrils. Adhesion of microglia to beta amyloid fibrils leads to immobilization of these cells on the fibrils, and induces them to produce reactive oxygen species. We propose that interactions of microglial scavenger receptors with fibrillar beta amyloid may stimulate the microglia to secrete apolipoprotein E and complement proteins, which may further contribute to neurotoxicity and neuronal degeneration. Therefore, microglial scavenger receptors may be novel targets for therapeutic interventions in Alzheimer's disease.

Atherosclerosis as disease of redox-sensitive genes

Accumulating evidence provides a compelling case that one of the major pathophysiologic mechanisms involved in the pathogenesis of atherosclerosis is enhanced oxidative stress and that the most important manifestation of this altered redox state is the modulation of a set(s) of proinflammatory genes that are regulated directly or indirectly by reactive oxygen species. Viewed in this perspective the oxidation of LDL is but one important consequence of a generalized metabolic abnormality of the arterial wall in atherosclerosis rather than being the core pathophysiological feature. The fact that hypercholesterolemia, hypertension, and AGEs related to diabetes mellitus all activate similar redox-sensitive proinflammatory genes associated with the pathogenesis of atherosclerosis provides the potential for the development of unifying concepts concerning the etiology of the disease. These concepts also provide additional evidence that antioxidants may be potentially attractive therapeutic agents.

Persistent elevation and metabolic dependence of circulating E-selectin after delivery in women with gestational diabetes mellitus

The increased risk of premature atherosclerosis in noninsulin-dependent diabetes mellitus (NIDDM) might be related in part to augmented expression of endothelial adhesion molecules (AMs). So far it is, however, unknown whether increased circulating (c) AMs in NIDDM are only a consequence of this disease or also involved in its sequelae. To determine the presence of cAMs in a population at increased risk for subsequent development of NIDDM, we analyzed fasting and postprandial [oral glucose tolerance test (OGTT): 100 g] serum concentrations of circulating E-selectin, vascular cell adhesion molecule-1 (cVCAM-1), and intercellular adhesion molecule-1 (cICAM-1) in pregnant women with either gestational diabetes (GDM) or normal glucose tolerance (NT) before and after delivery vs. nonpregnant healthy women (C). During pregnancy cE-selectin and cVCAM-1 were elevated in both GDM and NT vs. nonpregnant females (P < 0.01 vs. C). Following delivery, all GDM females regained normal glucose tolerance according to OGTT criteria, but showed slightly higher postprandial [area under the curve (AUC)180 min] glycemia and HbA1c values than nonpregnant healthy women (P < 0.05), indicating persisting subtle abnormalities in carbohydrate metabolism. cE-selectin and cVCAM-1 remained increased in GDM (P < 0.01 vs.C) after delivery, but fell to normal in NT (P < 0.05 before vs. after delivery). Furthermore, a correlation was seen in GDM females between cE-selectin and HbA1c (P < 0.005), fasting glucose (P < 0.01), and insulin (P < 0.05) as well as postprandial (AUC180 min) glucose and insulin concentrations (P < 0.05) during OGTTs, both before and after delivery. ICAM-1, however, did not differ significantly between groups. In summary, GDM is characterized by persistently raised levels of cE-selectin and cVCAM-1 12 weeks after delivery. Whether these persistent elevations of cE-selectin and cVCAM-1 reflect early vascular injury or represent a risk factor for atherosclerosis in women at increased risk for NIDDM remains to be determined.

Future horizons in cardiovascular molecular therapeutics

In the past 2 decades, significant progress has been made in cardiovascular therapeutics. Effective drug therapies have been developed for hypertension, hypercholesterolemia, coronary artery disease, myocardial infarction, and congestive heart failure. Novel therapeutic strategies to treat cardiovascular disease consist of 3 major approaches: (1) changing the biology of vascular disease; (2) intervening in the ischemic event; or (3) modifying the post-ischemic course. The development of future therapies depends on continuing advancements in our understanding of the molecular mechanisms of vascular pathobiology. Novel therapies are aimed at the critical steps in vascular disease progression, which include reversing endothelial cell dysfunction, modulating thrombosis and inflammation, correcting dysregulated cell growth and apoptosis, modulating vascular phenotype, and modifying mechanicotransduction in vascular remodeling. Targeting these steps at the molecular level will stimulate the development of numerous therapeutic agents. Ongoing research will further define the role of the agents in the treatment of cardiovascular disease.

Soluble vascular cell adhesion molecule-1 as a biohumoral correlate of atherosclerosis

Vascular cell adhesion molecule-1 (VCAM-1) is a protein expressed on the surface of activated endothelial cells and expressed in early atherosclerosis. Because part of the protein is shed in the circulation and can be detected in peripheral plasma [soluble (s) VCAM-1], we hypothesized that sVCAM-1 may be a circulating marker of the presence and severity of atherosclerosis in humans. We selected 11 patients with essential hypertension plus peripheral vascular disease (PVD) and matched them for age, gender, body mass index, and smoking habits with 11 patients with uncomplicated essential hypertension (UH) and 11 healthy controls. We evaluated plasma concentrations of sVCAM-1 along with those of the soluble form of two other endothelial leukocyte adhesion molecules [sE-selectin and s-intercellular adhesion molecule-1 (sICAM-1)] and other markers of endothelial dysfunction/ damage [s-thrombomodulin, plasminogen activator inhibitor type I, and von Willebrand factor (vWF)]. We also measured insulin, glucose, fibrinogen, total and HDL cholesterol, and the urinary albumin excretion (UAE), which may also be related to atherosclerosis. Results of these assays were related to the echographic assessment of the maximum intima-media thickness (IMTmax) at the carotid bifurcation, as an index of atherosclerosis in the carotids. PVD patients had a clearly elevated IMTmax [2.7 (1.1-3.1) mm, median (range)] compared with both UH patients [1.2 (0.8-2.4) mm] and controls [1 (0.6-2) mm]. sVCAM-1 was clearly higher in PVD patients [990 (273-1808) ng/mL, median (range)] versus 340 (236-975) ng/mL in UH and 386 (204-835) ng/mL in controls, and it separated clinical categories better than sICAM-1, vWF, glucose, insulin, UAE, triglycerides, or total, LDL or HDL cholesterol, sVCAM-1 was also the best biohumoral correlate of IMTmax (R = .59; P < .001) in univariate analysis. Because many of the biohumoral variables assessed were mutually intercorrelated, they were entered in a multivariate analysis to assess their contribution in explaining IMTmax variability. sVCAM-1 remained the only independent predictor of IMTmax and totally abolished the contribution of other variables to IMTmax variability. Thus, sVCAM-1 is a good biohumoral correlate of overt atherosclerosis, independent of underlying hypertension, and may be an in vivo marker of endothelial activation. Its potential value as a surrogate for global risk assessment and its behavior in intervention studies remain to be determined.