Effect of glycated collagen on proliferation of human smooth muscle cells in vitro

Reduced coronary reserve in response to short-term ischaemia and vasoactive drugs in ex vivo hearts from diabetic mice

AIM

The aim of the present study was to compare the coronary flow (CF) reserve of ex vivo perfused hearts from type 2 diabetic (db/db) and non-diabetic (db/+) mice.

METHODS

The hearts were perfused in the Langendorff mode with Krebs-Henseleit bicarbonate buffer (37 degrees C, pH 7.4) containing 11 mmol L(-1) glucose as energy substrate. The coronary reserve was measured in response to three different interventions: (1) administration of nitroprusside (a nitric oxide donor), (2) administration of adenosine and (3) production of reactive hyperaemia by short-term ischaemia.

RESULTS

Basal CF was approximately 15% lower in diabetic when compared with non-diabetic hearts (2.1 +/- 0.1 vs. 2.6 +/- 0.2 mL min(-1)). The maximum increase in CF rate in response to sodium nitroprusside and adenosine was significantly lower in diabetic (0.6 +/- 0.1 and 0.9 +/- 0.1 mL min(-1) respectively) than in non-diabetic hearts (1.2 +/- 0.1 and 1.4 +/- 0.1 mL min(-1) respectively). Also, there was a clear difference in the rate of return to basal CF following short-term ischaemia between diabetic and non-diabetic hearts. Thus, basal tone was restored 1-2 min after the peak hyperaemic response in non-diabetic hearts, whereas it took approximately 5 min in diabetic hearts.

CONCLUSION

These results show that basal CF, as well as the CF reserve, is impaired in hearts from type 2 diabetic mice. As diabetic and non-diabetic hearts were exposed to the same (maximum) concentrations of NO or adenosine, it is suggested that the lower coronary reserve in type 2 diabetic hearts is, in part, because of a defect in the intracellular pathways mediating smooth muscle relaxation.

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.

Oleate, not ligands of the receptor for advanced glycation end-products, promotes proliferation of human arterial smooth muscle cells

AIMS/HYPOTHESIS

Diabetes accelerates cardiovascular disease caused by atherosclerosis. Accordingly, diabetes accelerates atherosclerotic lesion progression and increases arterial smooth muscle cell proliferation. We hypothesized that diabetes can exert growth-promoting effects on smooth muscle cells via increased advanced glycation end-products or by dyslipidaemia.

METHODS

Primary human arterial smooth muscle cells were stimulated with advanced glycation end-products, other ligands of the receptor for advanced glycation end-products or fatty acids common in triglycerides. Cell proliferation was measured as DNA synthesis, cell cycle distribution and cell number. Effects of oleate on cellular phospholipids, diacylglycerol, triglycerides and cholesterol esters were analyzed by thin-layer chromatography, and oleate accumulation into diacylglycerol was confirmed by gas chromatography.

RESULTS

Human arterial smooth muscle cells express the receptor for advanced glycation end-products, but its ligands N(epsilon)-(carboxymethyl)lysine-modified proteins, methylglyoxal-modified proteins, S100B polypeptide and amyloid-beta (1-40) peptide, exert no mitogenic action. Instead, oleate, one of the most common fatty acids in triglycerides, enhances platelet-derived growth factor-BB-mediated proliferation and oleate-containing 1,2-diacylglycerol formation in smooth muscle cells. This mitogenic effect of oleate depends on phospholipase D activity and is associated with an increased formation of oleate-enriched 1,2-diacylglycerol.

CONCLUSION/INTERPRETATION

Oleate, not ligands of the receptor for advanced glycation end-products, acts as an enhancer of human smooth muscle cell proliferation. Thus, lipid abnormalities, rather than hyperglycaemia, could be a major factor promoting proliferation of smooth muscle cells in atherosclerotic lesions.

Aortic distensibility is reduced in subjects with type 2 diabetes and cardiac autonomic neuropathy

BACKGROUND

Reduced aortic distensibility predicts cardiovascular mortality in patients with type 2 diabetes and impaired glucose tolerance. Cardiac autonomic neuropathy is common in subjects with diabetes. However, the relationship between the elastic properties of the aorta and autonomic neuropathy has not been studied to date in subjects with type 2 diabetes.

MATERIALS AND METHODS

In this cross-sectional study, a total of 87 subjects with type 2 diabetes (27 with and 60 without cardiac autonomic neuropathy) as well as 60 healthy individuals, matched for age and sex with the diabetic subjects, were examined. Cardiac autonomic neuropathy was diagnosed on the basis of the battery of the classic cardiovascular autonomic function tests. Aortic distensibility was assessed by high-resolution ultrasonography.

RESULTS

Diabetic patients had reduced aortic distensibility in comparison with the control subjects: 1.81 +/- 0.58 vs. 2.53 +/- 0.34 10-6 cm2 dyn-1, respectively (P < 0.0001). In addition, diabetic individuals with cardiac autonomic neuropathy had reduced aortic distensibility as compared with patients without this complication: 1.60 +/- 0.72 vs. 1.90 +/- 0.48 10-6 cm2 dyn-1, respectively (P = 0.02). Multivariate linear regression analysis in the diabetic group, after controlling for a number of confounding factors such as age, systolic and diastolic blood pressure, duration of diabetes and presence as well as severity of cardiac autonomic neuropathy, demonstrated a significant and independent association between duration of diabetes [B = -0.02, SE(B) = 0.01, P = 0.01] and presence of cardiac autonomic neuropathy [B = -0.29, SE(B) = 0.14, P = 0.03] with aortic distensibility.

CONCLUSION

Type 2 diabetes is associated with a significant reduction in the elastic properties of the aorta. In addition, known duration of diabetes and presence of cardiac autonomic neuropathy are the main predictors of aortic distensibility in subjects with type 2 diabetes.

Glycohistochemical characterization of vascular muscle cell destruction in CADASIL subjects by lectins, neoglycoconjugates and galectin-specific antibodies

CADASIL (Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) is a type of small-artery stroke and vascular dementia-inducing pathology of the brain. In order to explain the molecular mechanisms behind the alterations to the blood vessels in CADASIL subjects, we scrutinized the expression of glycan and glycan-binding sites in the wall of vessels taken from five such subjects (vs. five control subjects matched for age and sex). Specimens were taken from the brain, heart, kidney, liver and lung. Although the main vessel lesions were observed in the tissues depending on the blood-brain barrier, alterations to systemic vessels were also observed despite the absence of any symptoms. The histochemical expression of a panel of 10 biotinylated neoglycoconjugates [Gal-beta(1-4)-D-Glc, Galbeta(1-3)GalNAc, alpha-D-GalNAc, beta-D-GalNAc, GalNAcalpha(1-3)-D-GalNAcalpha, GalNAcalpha(1-3)-D-GalNAcbeta, beta-D-Glc, alpha-D-Man, l-Fucose and D-Glcalpha(1-4)-D-Glc], eight plant lectins (PNA, MAA, SNA, DBA, WGA, ConA, GNA and UEA-1) and two antigalectin antibodies was monitored by means of semiquantitative and quantitative computer-assisted microscopy. The data show the altered histochemical binding of plant lectins, such as UEA-1 and ConA, in the vessel walls of CADASIL subjects. The present work, based upon staining by a panel of neoglycoconjugates, provides a biochemical characterization of the alteration of vessel walls in the brain compared to other organs including the heart, kidney, lung and liver in CADASIL as opposed to control subjects. These glycohistochemical results suggest a functional relevance of protein-carbohydrate interactions in this disease.

Semicarbazide-sensitive amine oxidase in aortic smooth muscle cells mediates synthesis of a methylglyoxal-AGE: implications for vascular complications in diabetes

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes formation of methylglyoxal (MG) from aminoacetone; MG then reacts with proteins to form advanced glycation end products or AGEs. Because of its potential to generate MG, SSAO may contribute to AGE-associated vascular complications of aging and diabetes. We developed a method to measure SSAO activity in bovine aortic smooth muscle cells (BASMC) based on the oxidation of 2',7'-dichlorofluorescin by hydrogen peroxide and horseradish peroxidase. The SSAO activity was completely inhibited by 10 mM semicarbazide. Argpyrimidine is a readily detectable fluorescent product of the reaction between MG and arginine. Cell lysates incubated with aminoacetone formed argpyrimidine in a reaction that was inhibited by 20 mM semicarbazide. Immunostaining of tissue sections showed that aminoacetone-treated rats (normal as well as diabetic) formed more argpyrimidine in aortic smooth muscle than untreated controls. We believe that SSAO can enhance AGE synthesis in the macrovasculature of diabetic individuals by production of MG.

Evaluation of glycated glucagon-like peptide-1(7-36)amide in intestinal tissue of normal and diabetic animal models

Glucagon-like peptide-1(7-36)amide (tGLP-1) is an important insulin-releasing hormone of the enteroinsular axis which is secreted by endocrine L-cells of the small intestine following nutrient ingestion. The present study has evaluated tGLP-1 in the intestines of normal and diabetic animal models and estimated the proportion present in glycated form. Total immunoreactive tGLP-1 levels in the intestines of hyperglycaemic hydrocortisone-treated rats, streptozotocin-treated mice and ob/ob mice were similar to age-matched controls. Affinity chromatographic separation of glycated and non-glycated proteins in intestinal extracts followed by radioimmunoassay using a fully cross-reacting anti-serum demonstrated the presence of glycated tGLP-1 within the intestinal extracts of all control animals (approximately 19% of total tGLP-1 content). Chemically induced and spontaneous animal models of diabetes were found to possess significantly greater levels of glycated tGLP-1 than controls, corresponding to between 24--71% of the total content. These observations suggest that glycated tGLP-1 may be of physiological significance given that such N-terminal modification confers resistance to DPP IV inactivation and degradation, extending the very short half-life (<3 min) and bioactivity of the native peptide.

Detection of glycated gastric inhibitory polypeptide within the intestines of diabetic obese (ob/ob) mice

Gastric inhibitory polypeptide (GIP) is produced within endocrine cells of the small intestine and released into the circulation upon nutrient ingestion. This study has quantified the levels of this insulinotropic peptide in the intestines of lean and diabetic obese ob/ob mice and estimated the proportion that is glycated. The total intestinal GIP concentration and content of the diabetic mice were significantly greater (p < 0.01) than that of control animals. Affinity chromatographic separation and side-viewing GIP radioimmunoassay demonstrated that approx 20% of the GIP extracted from intestines of ob/ob mice was present in glycated form. Less than 2% of intestinal GIP was glycated in lean mice. In conclusion substantial quantities of glycated GIP exist within the intestines of diabetic ob/ob mice, suggesting that this may be a contributing factor to the physiological disarray of this syndrome.

Advanced glycation end products impair protein turnover in LLC-PK1: amelioration by trypsin

BACKGROUND

Advanced glycation end products (AGEs) are assumed to play a key role in the pathogenesis of diabetic nephropathy (DN) and other diabetic complications. While AGEs have been shown to exert marked effects on mesangial and endothelial cells as well as on monocytes/macrophages, little is known about their effects on tubule cells. Therefore, we addressed the questions of (1) whether AGE-bovine serum albumin (AGE-BSA) impairs the protein metabolism in the tubule cells, and if so, (2) whether the AGE-induced effects are mediated via a protease sensitive mechanism.

METHODS

Arrested LLC-PK1 cells were exposed to a medium containing the vehicle (control, serum free), AGE-BSA (38 micromol/L), or BSA (38 micromol/L) in the presence or absence of trypsin (2.5 microg/mL) for 24 hours. We evaluated cell number, cell size, and cell protein content, as well as protein synthesis and protein degradation.

RESULTS

After an incubation period of 24 hours, AGE-BSA decreased the cell number to 84.5 +/- 5.5% of control and 82.5 +/- 5.6% of BSA-treated cells (P < 0.05). [3H]-thymidine incorporation declined to 66% of control (P < 0.05), while BSA was without any effect. The same AGE-BSA dose reduced protein degradation (P < 0.05) and stimulated total protein synthesis slightly, as determined by L-[14C]Phe incorporation into acidic-insoluble proteins. These effects resulted in a rise in cell protein content (AGE-BSA vs. control, 21.9 +/- 6.7%; AGE-BSA vs. BSA, 11.1 +/- 6.0%, P < 0.05) and cell volume (AGE-BSA vs. control 9.4 +/- 3.2%, AGE-BSA vs. BSA 18.4 +/- 3.7%, P < 0.05). Coincubation with AGE-BSA and trypsin was associated with an amelioration of all investigated parameters concerning cell number, cell proliferation, raised cell protein content, decreased protein degradation, and enhanced protein synthesis.

CONCLUSION

These data indicate that AGE-BSA impairs cell proliferation and protein turnover in LLC-PK1 cells with a consequent rise in cell protein. Since these alterations were abrogated by coincubation with trypsin, an interference of this serine protease with the AGE-binding proteins on cell surfaces is assumed.

Phytoestrogens attenuate oxidative DNA damage in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats

OBJECTIVES

A recent study demonstrated that reactive oxygen species (ROS) were involved in the maintenance of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). However, the role of oxidative stress in hypertension and its related diseases in SHRSP remains unknown. To determine whether phytoestrogens attenuate oxidative DNA damage in vascular smooth muscle cells (VSMC) from SHRSP and Wistar-Kyoto (WKY) rats, we investigated the effect of daidzein, genistein and resveratrol on oxidative DNA damage in VSMC, induced by advanced glycation end-products (AGEs).

METHODS

VSMC were treated with AGEs in the presence or absence of phytoestrogens for the indicated time. Cellular degeneration induced by AGEs was characterized in terms of intracellular oxidant levels, intracellular total glutathione (GSH) levels, mRNA expression for gamma-glutamylcysteine synthetase (GCS), and a new marker of oxidative stress, 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents.

RESULTS

AGEs stimulated 8-OHdG formation in VSMC in a time- and dose-dependent manner. We also confirmed that VSMC from SHRSP were more vulnerable to oxidative stress induced by AGEs, than VSMC from WKY rats. Daidzein, genistein or resveratrol reduced AGEs-induced 8-OHdG formation in a dose-dependent manner. The preventive effects of phytoestrogens on 8-OHdG formation remarkably paralleled changes in the intracellular oxidant levels in VSMC following AGEs treatment. We further demonstrated that phytoestrogens increase intracellular total GSH level in VSMC. Increased GSH synthesis was due to enhanced expression of the rate-limiting enzyme for GSH synthesis, GCS. Phytoestrogens-stimulated total GSH level in VSMC could lead to decreased intracellular oxidant levels, and thus prevent oxidative DNA damage, induced by AGEs. The phytoestrogens are powerful antioxidants able to interfere with AGEs-mediated oxidative DNA damage of VSMC, and are potentially useful against vascular diseases where ROS are involved in hypertension.

Protective effect of inducible type nitric oxide synthase against intracellular oxidative stress caused by advanced glycation end-products in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats

OBJECTIVE

A recent study demonstrated that free radicals were involved in the maintenance of hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). However, the role of oxidative stress in hypertension and its related diseases in SHRSP remains unknown. On the other hand, advanced glycation end-products (AGEs) accumulate progressively in the vasculature with ageing, and have been identified to be as relevant mediators for various vascular complications. To elucidate whether nitric oxide (NO) produced by inducible type NO synthase (iNOS) in vascular smooth muscle cells (VSMC) taken from SHRSP and Wistar-Kyoto rats (WKY) attenuate AGEs-induced oxidative stress, we investigated the effect of NO donors and iNOS-induction in VSMC on intracellular oxidant level caused by AGEs.

METHODS

The cells preincubated with or without NO donor, S-nitroso-n-acetylpenicillamine (SNAP) or 3-morpholinosydnonimine (SIN-1), IL-1beta and/or N(G)-monomethyl-L-arginine monoacetate (L-NMMA), were treated with AGEs, and the intracellular oxidant levels, total glutathione (GSH) levels, and gamma-glutamylcysteine synthetase (GCS) mRNA were determined. We also determined the expression of an iNOS in VSMC from SHRSP and WKY.

RESULTS

The intracellular oxidant level of VSMC was induced by AGEs in a dose-dependent manner. NO donor dose-dependently reduced AGEs-stimulated intracellular oxidant level. Treatment with IL-1beta reduced the AGEs-stimulated intracellular oxidant level through increased NO production, whilst inhibition of NO production by L-NMMA reduced the inhibitory effect of IL-1beta. We also confirmed that NO production as well as the expression of iNOS mRNA and the protein itself were significantly decreased in response to IL-1beta in VSMC from SHRSP compared with WKY. We also confirmed that total GSH levels, decreased by AGEs, were restored by stimulation with IL-1beta. Increased GSH synthesis was due to enhanced expression of the rate-limiting enzyme for GSH synthesis, GCS. These results indicate that NO release, produced by iNOS in VSMC in response to cytokines, might play a protective role against AGEs-stimulated oxidative stress in VSMC. This protective effect of NO is decreased in SHRSP compared to WKY.

Bovine beta-lactoglobulin receptors on transformed mammalian cells (hybridomas MARK-3): characterization by flow cytometry

Flow cytometry was used to demonstrate the presence of beta-lactoglobulin (betaLG) receptors on living murine hybridoma MARK-3 cells using a fluorescein isothiocyanate-betaLG conjugate (FITC-betaLG: molar ratio of 5:1). A site occupation curve was produced using a shift in the mean channel fluorescence at various concentrations of FITC-betaLG. The binding of labelled ligand was concentration dependent and was inhibited by unlabelled betaLG. The on-rate constant was 3.2x10(2) M(-1) min(-1) and the off-rate constant was 0.002 min(-1). Scatchard plot analysis gave a dissociation constant (K(d)) of 44+/-21x10(-7) and 39+/-24x10(-5) M (n=3). Flow cytometry indicated that at least 15% of the FITC-betaLG were internalized for 5 min and that internalization was temperature- and time-dependent. The internalization was confirmed by 3-D fluorescence microscopy (CELLScan system).

Reaction monitoring of succinylation of collagen with matrix-assisted laser desorption/ionization mass spectrometry

Succinylated collagen was synthesized by the reaction of collagen with succinic anhydride under basic conditions for one hour. Using the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) technique, the reaction products were directly identified without multi-step separation processes. MALDI-MS monitored the reaction more accurately than the conventional method of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). From the change in molecular mass during the reaction, it is observed that about 28 succinyl groups are attached to the collagen strand.

Extracellular matrix concentration exerts selection pressure on invasive cells

The mortality associated with cancer depends upon the ability of malignant cells to invade and metastasise into adjacent and distant regions. Such malignant spread is caused by the acquisition of an invasive phenotype which involves variable changes in cell-cell adhesion, proteolysis of adjoining extracellular matrix molecules, and the ability to move in a directed fashion in response to fixed and soluble gradients. Whilst the degree of variability in the pattern of metastasis is large, several cancers show regional predilections for invasion. Tumour cell heterogeneity and extracellular matrix composition have been shown to account for some regional variations. In this study, an invasion assay was used to assess the invasiveness of HT1080 tumour cells migrating through a collagen gel. Our experiments showed that, in the absence of externally imposed chemical gradients, HT1080 invasiveness was related in a biphasic manner to collagen concentration. Using a mathematical model, developed to study this phenomenon, we predicted that tumour cell proliferation may also be related in a biphasic manner to collagen concentration. This model prediction was confirmed using a combination of collagen gel invasion and proliferation assays. Investigation of the mathematical model suggests that interactions between haptotaxis and proliferation of the HT1080 cells may be responsible for the biphasic dependence of the penetration depth and proliferation on collagen gel concentration. In conclusion, we showed how mathematical methods can be combined with experimental work to provide new and valuable insight into important biological issues.

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.

Increased adhesion of lymphoid cells to glycated proteins

BACKGROUND AND AIMS

The advanced glycation end-products are involved in the pathogenesis of vascular damages and other clinical complications in diabetic patients. The aim of this study was to investigate the adhesion of lymphoid cells to nonenzymatically glycated proteins in comparison with the unmodified substances.

METHODS

Two cell lines (monocyte-macrophage line U937 and the T-cell line Jurkat) were used throughout the experiments. The cells were left to adhere to nonenzymatically glycated and native proteins coated on a 96-well flat-bottom plates and the cellular adhesion was registered as absorption at 550 nm following the method described by Ivanov and Kyurkchiev [G. Ivanov, S. Kyurkchiev, Effect of advanced glycosylation end-products on the activity of integrins expressed on U937 cells, Hum. Immunol. 59 (1998) 325-330.].

RESULTS

It was found that the monocytes had increased adhesion to nonenzymatically glycated proteins such as collagen, fibronectin and bovine serum albumin, whereas the T-cells had increased adhesion to the glycated collagen and bovine serum albumin but reduced adhesion to advanced glycated fibronectin. Experiments with different stimulating agents showed that phorbol-myriastate, acetate (A550 = 0.672 +/- 0.068, S.E.M., n = 40), glucose (A550 = 0.593 +/- 0.051, S.E.M., n = 40) and TNF-alpha (A550 = 0.580 +/- 0.042, S.E.M., n = 40) increased the adhesion of U937 cells to advanced glycated bovine serum albumin in comparison with the adhesion of the untreated cells (A550 = 0.260 +/- 0.046, S.E.M., n = 40). This is probably due to an upregulation of the expression or the activity of the receptors for the advanced glycation end-products.

CONCLUSION

Based on the results obtained it is concluded that the receptors for nonenzymatically glycated proteins expressed on the surface of lymphoid cells could act also as cell adhesion molecules.

Mechanical properties of mesenteric arteries in diabetic rats: consequences of outward remodeling

Diabetes induces hemodynamic and biochemical changes that can influence mechanical properties of arteries. Structure and mechanics of mesenteric small arteries were investigated in rats with streptozotocin-induced diabetes (duration 7-9 wk). The external diameter of mesenteric artery branches was measured in control (n = 9) and diabetic (n = 7) Wistar Rp rats at baseline and during pressurization in situ (0-150 mmHg) under normal and passive smooth muscle conditions. Mean arterial pressure and mesenteric artery pressure were not significantly different. Baseline mesenteric artery diameter was larger in the diabetes-induced group (439 +/- 12 vs. 388 +/- 18 micrometers, P < 0.05). Media cross-sectional area of arteries from diabetic rats was not significantly increased (0.0149 +/- 0.0015 vs. 0.0122 +/- 0.0007 mm2). Cross-sectional compliance was significantly increased in diabetic rats at intraluminal pressures ranging from 25 to 75 mmHg (P < 0.005), whereas cross-sectional distensibility was not modified. Wall tension and circumferential wall stress were increased in diabetes. These results indicate that mesenteric small arteries of diabetic rats display eutrophic outward remodeling associated with increased wall tension and circumferential wall stress.

Vascular smooth muscle cell hypertrophy induced by glycosylated human oxyhaemoglobin

1. Nonenzymatic protein glycosylation is a possible mechanism contributing to oxidative stress and vascular disease in diabetes. In this work, the influence of 14%-glycosylated human oxyhaemoglobin (GHHb), compared to the non-glycosylated protein (HHb), was studied on several growth parameters of rat cultured vascular smooth muscle cells (VSMC). A role for reactive oxygen species was also analysed. 2. Treatment of VSMC for 48 h with GHHb, but not with HHb, increased planar cell surface area in a concentration dependent manner. The threshold concentration was 10 nM, which increased cell size from 7965+/-176 to 9411+/-392 microm2. Similarly, only GHHb enhanced protein content per well in VSMC cultures. 3. The planar surface area increase induced by 10 nM GHHb was abolished by superoxide dismutase (SOD; 50 200 u ml(-1)), deferoxamine (100 nM-100 microM), or dimethylthiourea (1 mM), while catalase (50 200 u ml(-1)) or mannitol (1 mM) resulted in a partial inhibition of cell size enhancement. 4. When a known source of oxygen free radicals was administered to VSMC, the xanthine/xanthine oxidase system, the results were analogous to those produced by GHHb. Indeed, enhancements of cell size were observed, which were inhibited by SOD, deferoxamine, or catalase. 5. These results indicate that, at low concentrations, GHHb induces hypertrophy in VSMC, this effect being mediated by superoxide anions, hydrogen peroxide, and/or hydroxyl radicals. Therefore, glycosylated proteins can have a role in the development of the structural vascular alterations associated to diabetes by enhancing oxidative stress.

Breakers of advanced glycation end products restore large artery properties in experimental diabetes

Glucose and other reducing sugars react with proteins by a nonenzymatic, posttranslational modification process called nonenzymatic glycation. The formation of advanced glycation end products (AGEs) on connective tissue and matrix components accounts largely for the increase in collagen crosslinking that accompanies normal aging and which occurs at an accelerated rate in diabetes, leading to an increase in arterial stiffness. A new class of AGE crosslink "breakers" reacts with and cleaves these covalent, AGE-derived protein crosslinks. Treatment of rats with streptozotocin-induced diabetes with the AGE-breaker ALT-711 for 1-3 weeks reversed the diabetes-induced increase of large artery stiffness as measured by systemic arterial compliance, aortic impedance, and carotid artery compliance and distensibility. These findings will have considerable implications for the treatment of patients with diabetes-related complications and aging.