Advanced Glycation Endproducts Promote Adhesion Molecule (VCAM-1, ICAM-1) Expression and Atheroma Formation in Normal Rabbits

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Linking diabetes and atherosclerosis

Cardiovascular diseases are the major causes of morbidity and mortality in people with diabetes. Macroangiopathy in diabetes is manifested by more accelerated and progressive atherosclerosis, which is more widely distributed. The pathogenesis of this accelerated atherosclerosis is multifactorial and includes very complex interactions. Several abnormalities - such as hyperglycemia, dyslipidemia, hypertension, endothelial dysfunction, renin-angiotensin system activation and chronic subclinical inflammation - all appear to play important roles in the development of diabetes-induced atherosclerosis. Treatment of the residual risk, other than glycemia, blood pressure and low-density lipoprotein cholesterol, remains important as the rate of diabetes increases worldwide. A synergistic multifactorial approach against both conventional cardiovascular risk factors and emerging risk factors, such as vasoactive systems, the AGE-RAGE axis, novel proteins, such as TRAIL, and the complement system, as well as oxidative stress and inflammation, may be a promising way to prevent macrovascular disease in diabetes. In this review we focus on the major causes and mechanisms of atherosclerotic disease in patients with diabetes and highlight emerging targets for therapeutic intervention.

Atherosclerotic plaque development and instability: a dual role for VEGF

Vascular endothelial growth factor (VEGF), a potent growth factor for endothelial cells and inducer of angiogenesis, is important for endothelial integrity and thus for vascular function. On the other hand, VEGF may enhance the pathophysiologic mechanism of plaque formation and plaque destabilization. In this review we discuss the data available so far for VEGF as angiogenic and/or inflammatory cytokine in the vulnerable atherosclerotic plaque.

Calcitriol blunts the deleterious impact of advanced glycation end products on endothelial cells

Advanced glycation end products (AGEs), which are elevated in diabetic and uremic patients, may induce vascular dysfunctions, and calcitriol may improve the cardiovascular complications. Therefore, we examined whether calcitriol may modify the endothelial response to AGEs stimulation. Knowing the importance of nuclear factor-κB in endothelial inflammatory responses, the effect of AGEs and calcitriol on this pathway was also studied. Calcitriol was added to endothelial cells previously incubated with AGE-human serum albumin (HSA). AGE-HSA induced a decrease in endothelial nitric oxide synthase (eNOS) mRNA expression and enzyme activity. Addition of calcitriol to AGE-HSA-treated endothelial cells improved the decreased action of AGEs on the eNOS system. AGE-HSA increased the AGEs receptor mRNA and protein, which were both blunted by calcitriol. The parallel elevation of interleukin-6 mRNA in the presence of AGE-HSA was also blunted by calcitriol. The NF-κB-p65 DNA binding activity was enhanced and associated with a decrease in inhibitor κBα (IκBα) and an increase in phosphorylated (p)-IκBα levels. Addition of calcitriol blunted the AGEs-induced elevation of NF-κB-p65 DNA binding activity, a phenomenon related to an increased expression of IκBα. This increase was correlated to declined p-IκBα levels. The present results support the concept that calcitriol may act as a vascular protective agent counteracting the probable deleterious actions of AGEs on endothelial cell activities.

Advanced glycation end products, diabetes and ageing

Advanced glycation end products (AGEs) are formed in vivo by a non-enzymatic reaction of proteins with carbohydrates and accumulate in many tissues during ageing. They are discussed as being responsible for many age- and diabetes-related diseases. On the other hand, AGEs are formed by the heating of food and are taken up by the nutrition. The contribution of endogenously formed versus exogenous intake of AGEs to age-related diseases is still under discussion.

Advanced glycosylation end products and nutrition--a possible relation with diabetic atherosclerosis and how to prevent it

Advanced glycosylation end product (AGE) levels are elevated in diabetic patients and may contribute to the excessive cardiovascular disease in this population, promoting oxidant stress and chronic vascular inflammation. AGEs in people with diabetes mellitus are formed mainly by protein and lipid glucosylation in an environment of chronic hyperglycemia and also by prolonged thermal food processing (diet derived AGEs). This brief review summarizes current literature about food derived AGEs and their relationship with diabetic vascular disease and supports the importance of low AGE diet as an essential preventive or therapeutic intervention against atheromatosis progress.

Markers of endothelial activity are related to components of the metabolic syndrome, but not to circulating concentrations of the advanced glycation end-product Nɛ-carboxymethyl-lysine in healthy Swedish men

Endothelial function is considered important in the development of cardiovascular diseases and type 2 diabetes. Circulating advanced glycation end-products (AGEs) and dietary components have been shown to affect endothelial function in type 2 diabetics, but determinants of endothelial function in a non-diabetic population are more poorly investigated. Therefore, we investigated relationships between dietary habits, AGEs and endothelial activation in men with isolated metabolic disturbances. Circulating markers of endothelial activation (soluble forms of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, E-selectin and von Willebrand factor) and plasma N epsilon-carboxymethyl-lysine (CML, the predominant AGE in human plasma) were analyzed in a cross-sectional study of 294 healthy men. Individuals completed a 7-day dietary record, and metabolic and inflammatory parameters were determined. NCEP/ATPIII-criteria were used to define the metabolic syndrome. Endothelial activation was higher in individuals with the metabolic syndrome, and was positively related to certain features of the syndrome (insulin, glucose, inflammation and obesity), but not to others (triacylglycerol and blood pressure). Dietary factors were related to endothelial activation, but CML was not. Multivariate analysis revealed energy and alcohol intake, along with insulin and markers of oxidative stress and inflammation, to be positive predictors of endothelial activation. In this cohort of otherwise healthy men, endothelial activation was increased in individuals with the full metabolic syndrome, but not in those with only some of the components of the metabolic syndrome. Insulin resistance, inflammation, oxidative stress, the dietary intake of energy and alcohol, but not plasma CML, predicted endothelial activation in these men.

Ablation of the gene encoding p66Shc protects mice against AGE-induced glomerulopathy by preventing oxidant-dependent tissue injury and further AGE accumulation

AIMS/HYPOTHESIS

AGEs have been implicated in renal disease associated with ageing, diabetes and other age-related disorders. Reactive oxygen species (ROS) promote formation of AGEs, which cause AGE-receptor-mediated ROS generation with activation of signalling pathways leading to tissue injury and further AGE accumulation. ROS generation is regulated by the Src homology 2 domain-containing transforming protein C1 (Shc1) isoform p66(Shc), whose deletion has been shown to protect from tissue injury induced by ageing, diabetes, hyperlipidaemia and ischaemia-reperfusion by preventing oxidative stress. This study was aimed at assessing the role of p66(Shc) in the modulation of oxidative stress and oxidant-dependent renal injury induced by AGEs.

METHODS

For 10 weeks, male p66 (shc) knockout (KO) and wild-type (WT) mice were injected with 60 microg/day albumin modified or unmodified by N epsilon-(carboxymethyl) lysine (CML). Mice were then killed for the assessment of renal function and structure, as well as systemic and renal tissue oxidative stress.

RESULTS

Upon CML injection, KO mice, in contrast to WT mice, showed no or only mild forms of proteinuria, glomerular hypertrophy, mesangial expansion, glomerular sclerosis, renal/glomerular cell apoptosis and extracellular matrix upregulation. Moreover, KO mice had lower circulating and tissue AGEs than WT mice and unchanged plasma isoprostane 8-epi-prostaglandin-F(2alpha) levels, renal/glomerular CML, 4-hydroxy-2-nonenal, AGE receptor and NAD(P)H oxidase 4 (NOX4) content (and expression of the corresponding genes), and nuclear factor kappaB activation (NFkappaB). Mesangial cells from KO mice exposed to CML showed no or slight increase in ROS levels and NFkappaB activation, again at variance with WT cells.

CONCLUSIONS/INTERPRETATION

These data indicate that p66(Shc) participates in the pathogenesis of AGE-dependent glomerulopathy by mediating AGE-induced tissue injury and further AGE formation through ROS-dependent mechanisms involving NFkappaB activation and upregulation of Nox4 expression and NOX4 production.

Mechanism of high glucose induced angiotensin II production in rat vascular smooth muscle cells

Angiotensin II (Ang II), a circulating hormone that can be synthesized locally in the vasculature, has been implicated in diabetes-associated vascular complications. This study was conducted to determine whether high glucose (HG) (approximately 23.1 mmol/L), a diabetic-like condition, stimulates Ang II generation and the underlying mechanism of its production in rat vascular smooth muscle cells. The contribution of various enzymes involved in Ang II generation was investigated by silencing their expression with small interfering RNA in cells exposed to normal glucose (approximately 4.1 mmol/L) and HG. Angiotensin I (Ang I) was generated from angiotensinogen by cathepsin D in the presence of normal glucose or HG. Although HG did not affect the rate of angiotensinogen conversion, it decreased expression of angiotensin-converting enzyme (ACE), downregulated ACE-dependent Ang II generation, and upregulated rat vascular chymase-dependent Ang II generation. The ACE inhibitor captopril reduced Ang II levels in the media by 90% in the presence of normal glucose and 19% in HG, whereas rat vascular chymase silencing reduced Ang II production in cells exposed to HG but not normal glucose. The glucose transporter inhibitor cytochalasin B, the aldose reductase inhibitor alrestatin, and the advanced glycation end product formation inhibitor aminoguanidine attenuated HG-induced Ang II generation. HG caused a transient increase in extracellular signal-regulated kinase (ERK)1/2 phosphorylation, and ERK1/2 inhibitors reduced Ang II accumulation by HG. These data suggest that polyol pathway metabolites and AGE can stimulate rat vascular chymase activity via ERK1/2 activation and increase Ang II production. In addition, decreased Ang II degradation, which, in part, could be attributable to a decrease in angiotensin-converting enzyme 2 expression observed in HG, contributes to increased accumulation of Ang II in vascular smooth muscle cells by HG.

Increased serum levels of advanced glycation endproducts predict total, cardiovascular and coronary mortality in women with type 2 diabetes: a population-based 18 year follow-up study

AIMS/HYPOTHESIS

AGEs, modification products formed by glycation or glycoxidation of proteins and lipids, have been linked to premature atherosclerosis in patients with diabetes. We investigated whether increased serum levels of AGEs predict total, cardiovascular (CVD) or CHD mortality in a population-based study.

SUBJECTS AND METHODS

Serum levels of AGEs were determined by immunoassay in a random sample of 874 Finnish diabetic study participants (488 men, 386 women), aged 45-64 years. These participants were followed for 18 years for total, CVD and CHD mortality.

RESULTS

Multivariate Cox regression models revealed that serum levels of AGEs were significantly associated with total (p = 0.002) and CVD mortality (p = 0.021) in women, but not in men. Serum levels of AGEs in the highest sex-specific quartile predicted all-cause (hazards ratio [HR] 1.51; 95% confidence intervals [CI], 1.14-1.99; p = 0.004), CVD (HR 1.56; 95% CI 1.12-2.19; p = 0.009), and CHD (HR 1.68; 95% CI 1.11-2.52; p = 0.013) mortality in women, even after adjustment for confounding factors, including high-sensitivity C-reactive protein.

CONCLUSIONS/INTERPRETATION

Increased serum levels of AGEs predict total and CVD mortality in women with type 2 diabetes.

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

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

Advanced glycation endproducts: what is their relevance to diabetic complications?

Glycation is a major cause of spontaneous damage to proteins in physiological systems. This is exacerbated in diabetes as a consequence of the increase in glucose and other saccharides derivatives in plasma and at the sites of vascular complications. Protein damage by the formation of early glycation adducts is limited to lysine side chain and N-terminal amino groups whereas later stage adducts, advanced glycation endproducts (AGEs), modify these and also arginine and cysteine residues. Metabolic dysfunction in vascular cells leads to the increased formation of methylglyoxal which adds disproportionately to the glycation damage in hyperglycaemia. AGE-modified proteins undergo cellular proteolysis leading to the formation and urinary excretion of glycation free adducts. AGEs may potentiate the development of diabetic complications by activation of cell responses by AGE-modified proteins interacting with specific cell surface receptors, activation of cell responses by AGE free adducts, impairment of protein-protein and enzyme-substrate interactions by AGE residue formation, and increasing resistance to proteolysis of extracellular matrix proteins. The formation of AGEs is suppressed by intensive glycaemic control, and may in future be suppressed by thiamine and pyridoxamine supplementation, and several other pharmacological agents. Increasing expression of enzymes of the enzymatic defence against glycation provides a novel and potentially effective future therapeutic strategy to suppress protein glycation.

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

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

Vascular endothelial growth factor-A induces plaque expansion in ApoE knock-out mice by promoting de novo leukocyte recruitment

Vascular endothelial growth factor-A is widely used in clinical trials for the treatment of cardiac ischemia. VEGF-A was recently suggested to act in a proinflammatory manner, which could aggravate adjacent atherogenesis in VEGF-A–based therapy. To assess potential bystander effects, VEGF-A was focally overexpressed in advanced atherosclerotic plaques in ApoE−/− mice. Sheer-induced carotid artery plaques were transluminally incubated with Ad.hVEGF-A leading to neointimal overexpression of VEGF-A. Ad.hVEGF-A treatment of pre-existing lesions was seen to promote plaque expansion, with a concomitant increase in macrophage and lipid content, whereas it lowered collagen content. In general, Ad.hVEGF-A–treated plaques displayed a more vulnerable phenotype. VEGF-A overexpression was not accompanied by increased microvessel development in the neointima, suggesting that VEGF-A destabilizes atherosclerotic plaques through an angiogenesis-independent mechanism. Intravital microscopy confirmed that treatment with Ad.hVEGF-A led to an increased monocyte adhesion, which was mediated by a VCAM-1/PECAM-1–dependent pathway. VEGF-A indeed induced a differential expression of VCAM-1 and PECAM-1 in endothelial cells. Our data underline the importance of regular monitoring of stenotic vessels adjacent to the site of VEGF-A application. We propose that VCAM-1/PECAM-1–directed cotherapy may be an efficient strategy to prevent bystander effects of focal VEGF-A therapy in patients suffering from cardiovascular disease.

Glycaemic control, markers of endothelial cell activation and oxidative stress in children with type 1 diabetes mellitus

BACKGROUND

The aim of this study was to compare the effect of glycaemic control on oxidative stress and biochemical markers of endothelial activation in type 1 diabetic children.

METHODS

Serum total cholesterol, HDL cholesterol, VLDL cholesterol, apolipoprotein A1, apolipoprotein B, HbA(1c), MDA, VEGF, NO, ICAM levels were assessed in 100 children with type 1 DM aged 2-17 years. Study cases were evaluated in three groups in view of their mean HbA(1c) values, as metabolically well-controlled (HbA(1c)< or =8%) and poorly controlled (HbA(1c)>8%) patients with DM and 40 healthy children were included as normal controls.

RESULTS

Levels of MDA, NO, VEGF, ICAM, apolipoprotein A1 and apolipoprotein B in metabolically poorly controlled diabetic patients were significantly higher than control group (P<0.05). In correlation analysis of HbA(1c) to VEGF, no significant correlations were detected in metabolically well-controlled DM, but there were significant correlations between HbA(1c) and NO, MDA, ICAM levels. In correlation analysis of HbA(1c) to VEGF, NO, MDA and ICAM levels, significant correlations were detected in poorly controlled diabetics (P<0.05).

CONCLUSIONS

In the present study, increased levels of MDA, NO, ICAM-1 and VEGF levels showed that especially metabolically poorly controlled DM children are at high risk of atherosclerosis and vascular complications of DM and that there is a significant relationship between HbA(1c) and oxidative stress. It may be appropriate to evaluate levels of VEGF and sICAM-1 as well as markers of oxidative stress in addition to routine laboratory assessments in evaluation of type 1 DM pediatric patients.

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

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

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

BACKGROUND

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

METHOD

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

RESULTS

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

CONCLUSION

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

Advanced Oxidation Protein Products Accelerate Atherosclerosis Through Promoting Oxidative Stress and Inflammation

Objective— Increased level of plasma advanced oxidation protein products (AOPPs) has been found in patients with uremia and nonuremic subjects with coronary artery disease. This study was conducted to test the hypothesis that AOPPs play a causal role in atherosclerosis.

Methods and Results— Hypercholesterolemic (0.5% wt/wt diet) or normal rabbits received either repeated intravenous injections of AOPPs modified rabbit serum albumin (AOPPs-RSA) or unmodified RSA for 8 weeks. Compared with RSA- or vehicle-treated hypercholesterolemic rabbits, AOPPs-RSA–treated animals displayed increased atherosclerotic plaque area oxidized low-density lipoprotein (oxLDL) deposition, macrophage infiltration, and smooth muscle cell proliferation. Aortic sections from AOPPs-RSA–treated normal rabbits showed significant focal intima proliferation and mild Oil-Red-O staining lipid deposition in the affected areas, a phenomenon not observed in the RSA- or vehicle-treated controls. Plasma AOPPs levels in AOPPs-treated groups significantly increased in both hypercholesterolemic and normal rabbits compared with their relevant controls. Close correlations were found between plasma levels of AOPPs and the parameters of oxidative stress, eg, oxLDL and thiobarbituric acid reactive substances levels, or glutathione peroxidase activity. A highly significant correlation was also observed between plasma AOPPs and tumor necrosis factor (TNF)-α levels.

Conclusions— This study provides in vivo evidence for a causal relationship between chronic AOPPs accumulation and atherosclerosis.

Advanced glycation end products activate a chymase-dependent angiotensin II-generating pathway in diabetic complications

BACKGROUND

Angiotensin II is a key mediator of diabetes-related vascular disease. It is now recognized that in addition to angiotensin-converting enzyme, chymase is an important alternative angiotensin II-generating enzyme in hypertension and diabetes. However, the mechanism of induction of chymase in diabetes remains unknown.

METHODS AND RESULTS

Here, we report that chymase is upregulated in coronary and renal arteries in patients with diabetes by immunohistochemistry. Upregulation of vascular chymase is associated with deposition of advanced glycation end products (AGEs), an increase in expression of the receptor for AGEs (RAGE), and activation of ERK1/2 MAP kinase. In vitro, AGEs can induce chymase expression and chymase-dependent angiotensin II generation in human vascular smooth muscle cells via the RAGE-ERK1/2 MAP kinase-dependent mechanism. This is confirmed by blockade of AGE-induced vascular chymase expression with a neutralizing RAGE antibody and an inhibitor to ERK1/2 and by overexpression of the dominant negative ERK1/2. Compared with angiotensin-converting enzyme, chymase contributes to the majority of angiotensin II production (>70%, P<0.01) in response to AGEs. Furthermore, AGE-induced angiotensin II production is blocked by the anti-RAGE antibody and by inhibition of ERK1/2 MAP kinase activities.

CONCLUSIONS

AGEs, a hallmark of diabetes, induce chymase via the RAGE-ERK1/2 MAP kinase pathway. Chymase initiates an important alternative angiotensin II-generating pathway in diabetes and may play a critical role in diabetic vascular disease.

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

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

Rage gene promoter polymorphisms and diabetic retinopathy in a clinic-based population from South India

PURPOSE

The main objective of this study was to evaluate if the -429T/C, -374T/A and 63 bp deletion polymorphisms in the RAGE gene are associated with diabetic retinopathy (DR) among Type 2 diabetic subjects in a clinic-based population from South India.

METHODS

We screened 149 normal glucose tolerant subjects (NGT), 189 Type 2 diabetes subjects without retinopathy (DM) and 190 subjects with DR for these polymorphisms using the PCR-RFLP method. DR was diagnosed by grading color fundus photography. Logistic regression models were used to evaluate the association of individual polymorphisms with DR. Expectation-maximization algorithms were implemented in haplotype tests of association to examine the combined effects of -429T/C and -374T/A polymorphisms on DR.

RESULTS

The allelic frequencies of -429T are 0.83 in NGT, 0.84 in DM and 0.85 in DR subjects, and that of -374T are 0.93 in NGT, 0.92 in DM and 0.88 in DR subjects. The -374 polymorphism was found to be associated with non-proliferative retinopathy when this subgroup was compared to the DM group (OR=1.814, 95% CI=1.005-3.273). However, this association was not obvious when both the subphenotypes of DR (the nonproliferative and proliferative DR groups) were studied jointly. We found no evidence for associations between the -429T/C polymorphism and the DR phenotype. Finally, extension to a 2-SNP haplotype did not reveal any significant statistical difference between the groups (P=0.668).

CONCLUSION

In this study, we found a modest association with the -374T/A polymorphism in the nonproliferative DR subgroup.

Characterization of hearing loss in aged type II diabetics

Presbycusis - age-related hearing loss - is the number one communicative disorder and a significant chronic medical condition of the aged. Little is known about how type II diabetes, another prevalent age-related medical condition, and presbycusis interact. The present investigation aimed to comprehensively characterize the nature of hearing impairment in aged type II diabetics. Hearing tests measuring both peripheral (cochlea) and central (brainstem and cortex) auditory processing were utilized. The majority of differences between the hearing abilities of the aged diabetics and their age-matched controls were found in measures of inner ear function. For example, large differences were found in pure-tone audiograms, wideband noise and speech reception thresholds, and otoacoustic emissions. The greatest deficits tended to be at low frequencies. In addition, there was a strong tendency for diabetes to affect the right ear more than the left. One possible interpretation is that as one develops presbycusis, the right ear advantage is lost, and this decline is accelerated by diabetes. In contrast, auditory processing tests that measure both peripheral and central processing showed fewer declines between the elderly diabetics and the control group. Consequences of elevated blood sugar levels as possible underlying physiological mechanisms for the hearing loss are discussed.

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

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

High levels of pigment epithelium-derived factor in the retina of a rat model of type 2 diabetes

Spontaneously diabetic Torii (SDT) rats are a new animal model of diabetes. To investigate the mechanisms controlling diabetic retinopathy, we examined the retinal changes in SDT rats and determined the molecular balance between pigment epithelium-derived factor (PEDF), an angiogenic inhibitor, and vascular endothelial growth factor (VEGF), a major angiogenic stimulator. The retinopathy in SDT rats was characterized by a low incidence of neovascular formation and absence of non-perfused areas, and high levels of both PEDF and VEGF. Proliferative neovascular membranes, that are similar to that in human eyes with proliferative diabetic retinopathy, were found in the eyes of some of the SDT rats at >50-weeks-of-age, Immunoreactivity for VEGF was detected in the retina of SDT rats and the level of VEGF increased with the duration of diabetes. More importantly, immunoreactivity for PEDF was also increased in the retina of diabetic SDT rats. Western blot analysis showed that the level of VEGF in the retina was increased by 2.4 fold at 20-week-old, and by 6.8 fold at >40-week-old compared to that of 10-weeks old SDT rats. The levels of PEDF in the retina at 20-week- and at >40-week-old were significantly higher than that of 10-weeks old SDT rats (20-week-old; 13.5-fold increase, > 40-week-old; 10.3-fold increase). Earlier studies showed that the level of PEDF was decreased and VEGF was increased in proliferative diabetic retinopathy in human eyes. The high levels of PEDF in the retina of SDT rats may contribute to the low incidence of neovascular formation and absence of non-perfused areas that do not match the typical diabetic retinopathy in humans.

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

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

Advanced glycation end products in human cancer tissues: detection of Nepsilon-(carboxymethyl)lysine and argpyrimidine

Tumors are generally characterized by an increased glucose uptake and a high rate of glycolysis. Since one consequence of an elevated glycolysis is the nonenzymatic glycation of proteins, we studied the presence of advanced glycation end products (AGEs) in human cancer tissues. We detected the presence of the AGEs N(epsilon)-(carboxymethyl)lysine (CML) and argpyrimidine in several human tumors using specific antibodies. Because AGEs have been associated with the etiology of a variety of different diseases, these results suggest that CML and argpyrimidine could be implicated in the biology of human cancer.

Markers of endothelial dysfunction in the prediction of coronary artery disease in type 1 diabetes. The Pittsburgh Epidemiology of Diabetes Complications Study

Low-density lipoprotein (LDL) oxidation, the immune response it provokes, and lipoprotein subclasses measured by nuclear magnetic resonance (NMR) spectroscopy have explained some of the enhanced coronary artery disease (CAD) risks in Type 1 diabetes. We examined whether cellular adhesion molecules further improve CAD prediction. Participants were identified from the Epidemiology of Diabetes Complications (EDC) cohort, a 10-year prospective study of childhood-onset Type 1 diabetes. Mean age at baseline was 28 years, and diabetes duration was 19 years. CAD incidence was determined by EDC physician-diagnosed angina, confirmed myocardial infarction (MI), stenosis > or =50%, ischemic ECG, or revascularization. Cases were gender, age, and diabetes duration (+/-3 years) matched with the controls. The samples and risk factors used in the analyses were identified from the earliest exam prior to incidence in the cases. Sixty cases and 72 controls (including 43 pairs) had complete information on all covariates. Cox proportional hazard models with backward elimination and conditional logistic regression (for paired analyses) were conducted. Separate analyses were conducted to examine whether E-selectin related differently to soft (ischemic ECG and angina; n=68) or hard (revascularization, MI, and fatal events; n=37) CAD endpoints. Mean E-selectin concentration was elevated among cases (P=.0009) compared to controls. Adjusting for previously established CAD risk factors, E-selectin remained an independent predictor of CAD (HR=1.07, 95% Cl=1.01-1.15). Multivariable models confirmed the importance of E-selectin as a risk factor of soft (HR=1.13, 95% Cl=1.03-1.24; HRs are per standard deviation increase) but not hard CAD. Study results suggest that E-selectin may enhance CAD prediction beyond traditional risk factors or markers of oxidative stress in Type 1 diabetes.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Protein glycation: a firm link to endothelial cell dysfunction

The advanced glycation end products (AGEs) are a heterogeneous class of molecules, including the following main subgroups: bis(lysyl)imidazolium cross-links, hydroimidazolones, 3-deoxyglucosone derivatives, and monolysyl adducts. AGEs are increased in diabetes, renal failure, and aging. Microvascular lesions correlate with the accumulation of AGEs, as demonstrated in diabetic retinopathy or renal glomerulosclerosis. On endothelial cells, ligation of receptor for AGE (RAGE) by AGEs induces the expression of cell adhesion molecules, tissue factor, cytokines such as interleukin-6, and monocyte chemoattractant protein-1. A chief means by which AGEs via RAGE exert their effects is by generation of reactive oxygen species, at least in part via stimulation of NADPH oxidase. Diabetes-associated vascular dysfunction in vivo can be prevented by blockade of RAGE. Thus, agents that limit AGE formation, increase the catabolism of these species, or antagonize their binding to RAGE may provide new targets for vascular protection in diabetes.

Effect of advanced glycation end-products on gene expression and synthesis of TNF-alpha and endothelial nitric oxide synthase by endothelial cells

BACKGROUND

Advanced glycation end-products (AGEs), which are formed in aging, diabetes mellitus, and kidney failure are implicated in the occurrence of vascular complications. We, thus, evaluated in cultured endothelial cells, the AGEs' effect on gene expression and synthesis of tumor necrosis factor-alpha (TNF-alpha) and endothelial nitric oxide synthase (eNOS) mRNA and protein expression, which may be involved in vascular remodeling.

METHODS

Human umbilical vein cords endothelial cells (HUVEC) were stimulated with AGE-specific compounds [AGE-human serum albumin (AGE-HSA), N(epsilon)-carboxymethylysine (CML), AGE-beta2 microglobulin (AGE-beta2m)], and thereafter, incubated with interleukin1-alpha, lipopolysaccharide, and interferon-gamma.

RESULTS

mRNA expression and secretion of TNF-alpha were significantly enhanced after incubation with AGE-HSA, CML, and AGE-beta2m compared to that found in HUVEC incubated with HSA or beta2m. AGE-HSA, CML, and AGE-beta2m induced a significant decrease in eNOS protein and mRNA expression.

CONCLUSION

AGEs promote mRNA expression and secretion of TNF-alpha and reduce eNOS mRNA and protein expression in HUVEC. Such changes may play a role in the vascular dysfunction and the development of vasculopathy seen in diabetes, uremia, and old age.

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.

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

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

Application of stereological methods for the quantification of VCAM-1 and ICAM-1 expression in early stages of rabbit atherogenesis

Early stages of atherogenesis are characterized by the overexpression of cell adhesion molecules with the subsequent accumulation of macrophages, smooth muscle cells and proliferation of extracellular matrix in arterial intima. The quantification of atherogenic changes is necessary for the objective evaluation of the atherogenic process. The purpose of this study was to introduce stereological methods that may be used for the quantification of immunohistochemical staining, namely intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Twenty-four New Zealand White rabbits were subdivided into the three groups. Eighteen rabbits received a 0.4% cholesterol diet for 1, 2 and 3 months, respectively. Stereological principles of the systematic uniform random sampling and the point-counting method were applied for the quantification. Stereological analysis showed that VCAM-1 and ICAM-1 were upregulated during the consumption of high cholesterol diet and that VCAM-1, but not ICAM-1, has a considerable role in the formation of early atherosclerotic lesions. Stereological methods proved to be useful for the quantification of immunohistochemistry and can be used for an objective characterization of atherogenic changes in atherosclerosis.

Correlation between cardiovascular disease and diabetes mellitus: current concepts

Individuals exhibiting precursor symptoms of diabetes mellitus or reaching diagnostic thresholds for diabetes are at increased risk of death due to cardiovascular disease (CVD). Moreover, patients with diabetes alone, as well as those who have diabetes paired with established CVD, remain undertreated for cardiovascular risk factors. The clear correlation between these disease processes has led many to speculate that they share common pathogenetic processes. Recent research has made it increasingly evident that the core metabolic defects that mark diabetes, including impaired glucose tolerance, insulin resistance, and proinflammatory and prothrombotic states, lead to endothelial dysfunction and accelerate atherogenesis. Moreover, increases in sympathetic tone with diabetes are associated with changes in cardiac and vascular function that lead to hypertension, left ventricular dysfunction, and cardiac autonomic neuropathy; such changes set the stage for arrhythmia, silent infarction, and sudden death. Furthermore, diabetes-related changes in metabolic and autonomic functioning, as well as increases in inflammatory and thrombotic signaling, compromise the ability of myocardial and vascular tissue to remodel after injury and to recover and sustain functionality. Because potentiation of atherogenesis and cardiac dysfunction occurs in the presence of early diabetic symptoms as well as in the established disease, early implementation of strategies to reduce cardiovascular risk factors and to slow diabetes progression may help to improve long-term outcomes for at-risk individuals. Such interventions may include well-established treatments for hypertension and dyslipidemia, diet improvements, weight loss, and exercise as well as novel pharmacologic interventions aimed at newly identified therapeutic targets.

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

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

The role of advanced glycation end products in the development of atherosclerosis

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Atherosclerosis constitutes the main pattern of cardiovascular disease and leads to thickening of the intima with plaque formation and eventual occlusion of the arterial lumen. A large amount of evidence links advanced glycation end products (AGEs) with the development or progression of atherosclerosis, regardless of the diabetic status. AGEs are a heterogenous group of compounds formed by the nonenzymatic reaction of reducing sugars with proteins, lipids, and nucleic acids. Although AGEs are formed endogenously in the body, diet has recently been recognized as an important exogenous source. An increased understanding of the mechanisms of formation and interaction of AGEs has allowed the development of several potential anti-AGE approaches.

Adverse effects of dietary glycotoxins on wound healing in genetically diabetic mice

Advanced glycoxidation end products (AGEs) are implicated in delayed diabetic wound healing. To test the role of diet-derived AGE on the rate of wound healing, we placed female db/db (+/+) (n = 55, 12 weeks old) and age-matched control db/db (+/-) mice (n = 45) on two diets that differed only in AGE content (high [H-AGE] versus low [L-AGE] ratio, 5:1) for 3 months. Full-thickness skin wounds (1 cm) were examined histologically and for wound closure. Serum 24-h urine and skin samples were monitored for N(epsilon)-carboxymethyl-lysine and methylglyoxal derivatives by enzyme-linked immunosorbent assays. L-AGE-fed mice displayed more rapid wound closure at days 7 and 14 (P < 0.005) and were closed completely by day 21 compared with H-AGE nonhealed wounds. Serum AGE levels increased by 53% in H-AGE mice and decreased by 7.8% in L-AGE mice (P < 0.04) from baseline. L-AGE mice wounds exhibited lower skin AGE deposits, increased epithelialization, angiogenesis, inflammation, granulation tissue deposition, and enhanced collagen organization up to day 21, compared with H-AGE mice. Reepithelialization was the dominant mode of wound closure in H-AGE mice compared with wound contraction that prevailed in L-AGE mice. Thus, increased diet-derived AGE intake may be a significant retardant of wound closure in diabetic mice; dietary AGE restriction may improve impaired diabetic wound healing.

Intercellular adhesion molecule-1-deficient mice are resistant against renal injury after induction of diabetes

Diabetic nephropathy is a leading cause of end-stage renal failure. Several mechanisms, including activation of protein kinase C, advanced glycation end products, and overexpression of transforming growth factor (TGF)-beta, are believed to be involved in the pathogenesis of diabetic nephropathy. However, the significance of inflammatory processes in the pathogenesis of diabetic microvascular complications is poorly understood. Accumulation of macrophages and overexpression of leukocyte adhesion molecules and chemokines are prominent in diabetic human kidney tissues. We previously demonstrated that intercellular adhesion molecule (ICAM)-1 mediates macrophage infiltration into the diabetic kidney. In the present study, to investigate the role of ICAM-1 in diabetic nephropathy, we induced diabetes in ICAM-1-deficient (ICAM-1(-/-)) mice and ICAM-1(+/+) mice with streptozotocin and examined the renal pathology over a period of 6 months. The infiltration of macrophages was markedly suppressed in diabetic ICAM-1(-/-) mice compared with that of ICAM-1(+/+) mice. Urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion were significantly lower in diabetic ICAM-1(-/-) mice than in diabetic ICAM-1(+/+) mice. Moreover, expressions of TGF-beta and type IV collagen in glomeruli were also suppressed in diabetic ICAM-1(-/-) mice. These results suggest that ICAM-1 is critically involved in the pathogenesis of diabetic nephropathy.

A new En face method is useful to quantitate endothelial damage in vivo

Endothelial damage is considered to be an initial change in the atherosclerotic process. However, it has been difficult to detect this initial change in vivo. We established a modified En face immunostaining method that enabled us to obtain clear images of the entire endothelial surface, including at arterial bifurcations, and to quantitate the number of cells of interest in the endothelium. Using this method, we found that treatment with an atherogenic factor, albumin-derived advanced glycosylation end products, for only 2 weeks caused a significant increase in the number of proliferating cell nuclear antigen-positive endothelial cells and the number of macrophages adhering to the endothelium, suggesting that these changes might be relevant to the early events of endothelial dysfunction. In conclusion, the present modified En face immunostaining method may be a promising tool for understanding the pathophysiology of atherosclerosis.

Reduction of advanced glycation end product levels by on-line hemodiafiltration in long-term hemodialysis patients

BACKGROUND

Advanced glycation end products (AGEs) are thought to be involved in many complications of end-stage renal disease. This study analyzed serum AGE level reduction rates and corresponding long-term changes in serum levels among different dialysis modes.

METHODS

Eighty-one patients with chronic uremia were divided into 3 groups receiving conventional hemodialysis (HD), high-flux HD, or on-line hemodiafiltration (HDF). Serum AGE levels were measured by competitive enzyme-linked immunosorbent assay predialysis and postdialysis and after 6 months. Additionally, AGE clearance was measured in 11 uremic patients treated with alternative high-flux HD and on-line HDF.

RESULTS

Although predialysis serum AGE levels were similar, postdialysis levels were significantly lower in patients treated with on-line HDF (35.4 +/- 4.2 microg/mL) compared with those treated with conventional HD (82.2 +/- 11.4 microg/mL; P = 0.003), but not high-flux HD (56.7 +/- 5.9 microg/mL; P = 0.15). The serum AGE level reduction rate in on-line HDF (61.5% +/- 4.2%) was significantly greater than that in conventional HD (20.5% +/- 2.4%; P < 0.001) and high-flux HD patients (40.4% +/- 2.7%; P = 0.049). AGE clearance was increased 50% with on-line HDF compared with high-flux HD, reaching borderline significance (P = 0.07). In a 6-month study, predialysis serum AGE levels were significantly lower in patients treated with on-line HDF compared with those treated with conventional and high-flux HD.

CONCLUSION

On-line HDF may provide an improved form of treatment that achieves significantly better AGE level reduction than high-flux HD and conventional HD. Uremic patients treated with on-line HDF for longer than 6 months achieved a significant reduction in predialysis serum AGE levels.

Dietary glycotoxins promote diabetic atherosclerosis in apolipoprotein E-deficient mice

Hyperglycemia derived advanced glycation endproducts (AGE) have been implicated in diabetic atherosclerosis (AS) but the role of exogenous (dietary) AGE in the development of this serious complication is not known. This study evaluates the influence of diet-related AGE on AS in genetically hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)), streptozotocin-induced diabetic mice. Diabetic and non-diabetic apoE(-/-) mice (6-8 weeks old) were randomized into either a standard AIN-93G chow (AGE 12,500+/-700 U/mg, termed high-AGE diet, H-AGE), or the same chow having four to fivefold lower AGE level (L-AGE: 2,700+/-830 U/mg) based on ELISA. After 2 months of diabetes, compared to the diabetic mice fed standard (H-AGE) diet, the AS lesions at the aortic root of the L-AGE group were >50% smaller (0.17+/-0.03 vs. 0.31+/-0.05 mm(2), P<0.05). Serum AGE were lower in the diabetic L-AGE than in the H-AGE mice (by approximately 53%) (P<0.00001), as were in the non-diabetic L-AGE vs. H-AGE groups (P<0.05). No diet-related changes were noted in plasma glucose, triglycerides, or plasma cholesterol. Immunohistochemical comparisons showed markedly suppressed tissue AGE, AGE-Receptor-1, -2 and RAGE expression, reduced numbers of inflammatory cells, tissue factor, vascular cell adhesion molecule-1 and MCP-1 in the L-AGE diabetic group. The findings are supportive of an important link between dietary intake of pre-formed glycoxidation products, tissue-incorporated AGE, and diabetes-accelerated AS. The marked anti-atherogenic effects of an AGE-restricted diet in this model may provide the basis for relevant clinical studies.

Role of pro-atherogenic adhesion molecules and inflammatory cytokines in patients with coronary artery disease and diabetes mellitus type 2

Accelerated progression of atherosclerosis in coronary, carotid, cerebral, and peripheral arteries is a phenomenon observed in diabetes mellitus. Pathophysiologic mechanisms are slowly being understood. Pro-atherogenic adhesion molecules and inflammatory cytokines are involved in this process. This review addresses current concepts of atherogenesis and focuses on alterations of adhesion molecule and cytokine expression and their regulation in diabetic patients. Molecules are being discussed in both the normoglycemic and hyperglycemic states, with a focus on their atherogenic role in diabetes mellitus. Understanding the mechanisms that underlie disease progression will help to identify high-risk patients, which is a prerequisite for new treatment strategies aiming at an attenuation of disease progression in diabetic patients.

Atherothrombosis, inflammation, and diabetes

Diabetes represents a major cause of cardiovascular morbidity and mortality in developed countries, and atherothrombosis accounts for most deaths among diabetics. Recent evidence has reliably shown the relevant etiopathogenetic role of inflammation in atherothrombotic disease. This review summarizes and discusses the possible synergistic effects of diabetes and inflammation in promoting atherothrombosis and its complications, as well as potential avenues for diagnostic, preventive, and therapeutic benefits in the modulation of inflammatory mechanisms in diabetic atherothrombotic disease.