Cellular receptors for advanced glycation end products. Implications for induction of oxidant stress and cellular dysfunction in the pathogenesis of vascular lesions

Skin autofluorescence provides additional information to the UK Prospective Diabetes Study (UKPDS) risk score for the estimation of cardiovascular prognosis in type 2 diabetes mellitus

AIMS/HYPOTHESIS

The UK Prospective Diabetes Study (UKPDS) risk engine has become a standard for cardiovascular risk assessment in type 2 diabetes mellitus. Skin autofluorescence was recently introduced as an alternative tool for cardiovascular risk assessment in diabetes. We investigated the prognostic value of skin autofluorescence for cardiovascular events in combination with the UKPDS risk engine in a cohort of patients with type 2 diabetes managed in primary care.

METHODS

Clinical, UKPDS risk engine and skin autofluorescence data were obtained at baseline in 2001-2002 in the type 2 diabetes group (n = 973). Follow-up data concerning fatal and non-fatal cardiovascular events (primary endpoint) were obtained till 2005. Patients were classified as 'low risk' when their 10 year UKPDS risk score for fatal cardiovascular events was <10%, and 'high risk' if >10%. Skin autofluorescence was measured non-invasively with an autofluorescence reader. Skin autofluorescence was classified by the median (i.e. low risk < median, high risk > median).

RESULTS

The incidence of cardiovascular events was 119 (44 fatal, 75 non-fatal). In multivariate analysis, skin autofluorescence, age, sex and diabetes duration were predictors for the primary endpoint. Addition of skin autofluorescence information to that from the UKPDS risk engine resulted in re-classification of 55 of 203 patients from the low-risk to the high-risk group. The 10 year cardiovascular event rate was higher in patients with a UKPDS score >10% when skin autofluorescence was above the median (55.8% vs 38.9%).

CONCLUSIONS/INTERPRETATION

Skin autofluorescence provides additional information to the UKPDS risk engine which can result in risk re-classification of a substantial number of patients. It furthermore identifies patients who have a particularly high risk for developing cardiovascular events.

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.

Soluble receptor for advanced glycation end products (sRAGE) and endogenous secretory RAGE (esRAGE) in amniotic fluid: modulation by infection and inflammation

OBJECTIVE

The receptor for advanced glycation end products (RAGE) has been proposed to participate in the innate and adaptive immune responses. RAGE can induce production of pro-inflammatory cytokines and chemokines, as well as neutrophil chemotaxis in a manner that may be suppressed or stimulated by soluble, truncated forms of RAGE including the soluble form of RAGE (sRAGE) and endogenous secretory RAGE (esRAGE). The objective of this study was to determine whether intra-amniotic infection/inflammation (IAI) is associated with changes in the amniotic fluid concentration of sRAGE and esRAGE.

STUDY DESIGN

Amniotic fluid (AF) was retrieved from patients in the following groups: 1) mid-trimester (14-18 weeks of gestation; n=68); 2) term not in labor (n=24); 3) term in labor (n=51); 4) preterm labor and intact membranes (n=124); and 5) preterm PROM (n=80). Intra-amniotic infection and inflammation were defined as the presence of a positive amniotic fluid culture for microorganisms and an AF interleukin-6 concentration >or=2.6 ng/mL, respectively. The AF concentration of sRAGE and esRAGE were determined using specific and sensitive ELISAs which measured total immunoreactive sRAGE and esRAGE, respectively. Patients were matched for gestational age at amniocentesis to compare the AF concentration of sRAGE and esRAGE in patients with and without IAI. Non-parametric statistics were used for analysis and a P<0.05 was considered significant.

RESULTS

1) Patients at term not in labor had higher median AF concentrations of sRAGE and esRAGE than those in the mid-trimester (P<0.001 for both comparisons) and those at term in labor (P=0.03 and P=0.04, respectively); 2) patients with preterm labor and intact membranes with intra-amniotic infection/inflammation (IAI) had higher median AF concentrations of sRAGE and esRAGE than those without IAI (P=0.02 and P=0.005, respectively); 3) similarly, patients with preterm PROM with IAI had higher median AF concentrations of sRAGE and esRAGE than those without IAI (P=0.03 and P=0.02, respectively).

CONCLUSION

Intra-amniotic infection/inflammation is associated with increased amniotic fluid concentrations of sRAGE and esRAGE. Changes in the amniotic fluid concentration of sRAGE and esRAGE may represent part of the immune response to intra-amniotic infection/inflammation.

Receptor for advanced glycation end-products (RAGE) and soluble RAGE (sRAGE): cardiovascular implications

Disorders of glucose metabolism are associated with increased risk for cardiovascular disease (CVD) complications, including coronary, peripheral and cerebral arterial disease, that account for the majority of morbidity and mortality among patients with diabetes mellitus (DM). These associations between glucose and CVD risk extend continuously well below the glycaemic thresholds established for the diagnosis of diabetes, including significantly increased risk associated with impaired fasting glucose, impaired glucose tolerance, and even high normal glucose concentrations. While these epidemiological observations have established a clear association between cardiovascular disease and dysglycaemia and suggest a direct causal link, the mechanisms by which hyperglycaemia may contribute to the development, progression and instability of atherosclerosis remain unclear. A number of recent advances in the realm of vascular biology have identified several novel, plausible pathways that might link hyperglycaemia with atherosclerosis, individually or in aggregate. Key among them are the interaction between advanced glycation end-products (AGEs) and the receptor for AGEs (RAGE), which exists as a trans-membrane signalling receptor and as a circulating form, soluble RAGE (sRAGE). The purpose of this review is to provide an overview of the present understanding of RAGE and sRAGE, their plausible role linking perturbed glucose metabolism with the development, progression and instability of atherosclerosis, and the potential therapeutic implications of modulation of this biological system.

High glucose-induced Nox1-derived superoxides downregulate PKC-betaII, which subsequently decreases ACE2 expression and ANG(1-7) formation in rat VSMCs

In rat diabetic animal models, ANG(1-7) treatment prevents the development of cardiovascular complications. Angiotensin-converting enzyme (ACE)2 is a major ANG(1-7)-generating enzyme in vascular smooth muscle cells (VSMCs), and its expression is decreased by a prolonged exposure to high glucose (HG), which is reflected by lower ANG(1-7) levels. However, the underlying mechanism of its downregulation is unknown and was the subject of this study. Rat aortic VSMCs were maintained in normal glucose (NG) or HG ( approximately 4.1 and approximately 23.1 mmol/l, respectively) for up to 72 h. Several PKC and NADPH oxidase inhibitors and short interfering (si)RNAs were used to determine the mechanism of HG-induced ACE2 downregulation. Cell lysates were subjected to Western blot analysis, real-time quantitative PCR, and ANG(1-7) radioimmunodetection. At 72 h of HG exposure, ACE2 mRNA, protein, and ANG(1-7) levels were decreased (0.17 +/- 0.01-, 0.47 +/- 0.03-, and 0.16 +/- 0.01-fold, respectively), and the expression of NADPH oxidase subunit Nox1 was increased (1.70 +/- 0.2-fold). The HG-induced ACE2 decrease was reversed by antioxidants and Nox1 siRNA as well as by inhibitors of glycotoxin formation. ACE2 expression was PKC-betaII dependent, and PKC-betaII protein levels were reduced in the presence of HG (0.32 +/- 0.03-fold); however, the PKC-betaII inhibitor CG-53353 prevented the HG-induced ACE2 loss and Nox1 induction, suggesting a nonspecific effect of the inhibitor. Our data suggest that glycotoxin-induced Nox1 expression is regulated by conventional PKCs. ACE2 expression is PKC-betaII dependent. Nox1-derived superoxides reduce PKC-betaII expression, which lowers ACE2 mRNA and protein levels and consequently decreases ANG(1-7) formation.

In skeletal muscle advanced glycation end products (AGEs) inhibit insulin action and induce the formation of multimolecular complexes including the receptor for AGEs

Chronic hyperglycemia promotes insulin resistance at least in part by increasing the formation of advanced glycation end products (AGEs). We have previously shown that in L6 myotubes human glycated albumin (HGA) induces insulin resistance by activating protein kinase Calpha (PKCalpha). Here we show that HGA-induced PKCalpha activation is mediated by Src. Coprecipitation experiments showed that Src interacts with both the receptor for AGE (RAGE) and PKCalpha in HGA-treated L6 cells. A direct interaction of PKCalpha with Src and insulin receptor substrate-1 (IRS-1) has also been detected. In addition, silencing of IRS-1 expression abolished HGA-induced RAGE-PKCalpha co-precipitation. AGEs were able to induce insulin resistance also in vivo, as insulin tolerance tests revealed a significant impairment of insulin sensitivity in C57/BL6 mice fed a high AGEs diet (HAD). In tibialis muscle of HAD-fed mice, insulin-induced glucose uptake and protein kinase B phosphorylation were reduced. This was paralleled by a 2.5-fold increase in PKCalpha activity. Similarly to in vitro observations, Src phosphorylation was increased in tibialis muscle of HAD-fed mice, and co-precipitation experiments showed that Src interacts with both RAGE and PKCalpha. These results indicate that AGEs impairment of insulin action in the muscle might be mediated by the formation of a multimolecular complex including RAGE/IRS-1/Src and PKCalpha.

Distinct roles of heterogeneous nuclear ribonuclear protein K and microRNA-16 in cyclooxygenase-2 RNA stability induced by S100b, a ligand of the receptor for advanced glycation end products

Advanced glycation end products play major roles in diabetic complications. They act via their receptor RAGE to induce inflammatory genes such as cyclooxygenase-2 (COX-2). We examined the molecular mechanisms by which the RAGE ligand, S100b, induces COX-2 in monocytes. S100b significantly increased COX-2 mRNA accumulation in THP-1 monocytes at 2 h via mRNA stability. This was further confirmed by showing that S100b increased stability of luciferase-COX-2 3'-UTR mRNA. Chromatin immunoprecipitation and RNA immunoprecipitation revealed that S100b decreased occupancy of the DNA/RNA-binding protein, heterogeneous nuclear ribonuclear protein K (hnRNPK), at the COX-2 promoter but simultaneously increased its binding to the COX-2 3'-UTR. S100b treatment promoted the translocation of nuclear hnRNPK to cytoplasm, whereas a cytoplasmic translocation-deficient hnRNPK mutant inhibited S100b-induced COX-2 mRNA stability. Small interfering RNA-mediated specific knockdown of hnRNPK blocked S100b-induced COX-2 mRNA stability, whereas on the other hand, overexpression of hnRNPK increased S100b-induced COX-2 mRNA stability. S100b promoted the release of entrapped COX-2 mRNA from cytoplasmic processing bodies, sites of mRNA degradation. Furthermore, S100b significantly down-regulated the expression of a key microRNA, miR-16, which can destabilize COX-2 mRNA by binding to its 3'-UTR. MiR-16 inhibitor oligonucleotides increased, whereas, conversely, miR-16 mimic oligonucleotides decreased COX-2 mRNA stability in monocytes, further supporting the inhibitory effects of miR-16. Interestingly, hnRNPK knockdown increased miR-16 binding to COX-2 3'-UTR, indicating a cross-talk between them. These new results demonstrate that diabetic stimuli can efficiently stabilize inflammatory genes via opposing actions of key RNA-binding proteins and miRs.

Admission hyperglycemia and length of hospital stay in patients with diabetes and heart failure: a prospective cohort study

The authors assessed the relationship between glycemia and length of hospital stay (LOS) in a prospective cohort study of patients with diabetes mellitus and heart failure (HF). Of 212 patients with acute HF exacerbation, 119 (56%) also had diabetes. The mean age of the cohort was 63+/-0.87 years, and the mean body mass index was 29.3 kg/m2. Diabetic patients had significantly longer LOS compared with the nondiabetics (5.0+/-0.29 vs 3.4+/-0.19; P<.001). In patients with diabetes, the mean glycated hemoglobin A1c was 8.3%, admission blood glucose (BG) was 169+/-7.7 mg/dL, and average BG was 196+/-8.1 mg/dL. After adjusting for age, sex, weight, hypertension, renal function, and anemia, LOS was significantly correlated with admission BG (r=0.31; P<.001) and average BG (r=0.34; P=.001). In patients with acute HF exacerbation, diabetes significantly prolonged LOS. Hyperglycemia correlated with LOS.

Reduced expression of endogenous secretory receptor for advanced glycation endproducts in hippocampal neurons of Alzheimer's disease brains

The receptor for advanced glycation endproducts (RAGE) is a cell-surface multiligand receptor, which interacts with amyloid beta (Abeta), a key protein in Alzheimer's disease (AD). RAGE-Abeta interaction is thought to be associated with pathological progression in AD. A splice variant of RAGE, endogenous secretory RAGE (esRAGE) can act as a decoy receptor for RAGE ligands that would prevent the progression of some pathologic conditions. In this study, the expression of esRAGE in the hippocampal tissues from AD brains compared with control (non-AD) was examined by immunohistochemistry and Western blot analysis. Semiquantitative immunohistochemical analysis of hippocampal tissues using esRAGE-specific antibody revealed significantly decreased immunoreactivities in pyramidal cells in CA1 and CA3 regions of AD compared with non-AD. On the other hand, immunoreactivities of astrocytes for esRAGE significantly increased in those regions. Dentate granule cells and astrocytes showed essentially invariant immunoreactivities between AD and non-AD. Changes in esRAGE immunoreactivity in CA3 neurons and astrocytes were observed from the early pathological stages. Moreover, the esRAGE-immunoreactive bands of AD samples were weaker than those of non-AD samples in Western blot analysis. The results indicate that low expression of esRAGE in the hippocampus would be associated with the development of AD.

Advanced glycation end product homeostasis: exogenous oxidants and innate defenses

Increased oxidative stress (OS) underlies many chronic diseases prevalent in aging. Data in humans confirm the hypothesis that advanced glycation end products (AGEs) and other oxidants derived from the diet may be major contributors to increased OS in normal adults as well as those with diabetes mellitus or kidney failure. Mice fed a diet with a lowered (approximately 50%) content of AGEs or a typical calorie-restricted (CR) diet, accumulated a smaller amount of AGEs, maintained normal levels of AGE receptor-1 (AGER1), and did not have increased oxidant stress or cardiac or kidney fibrosis with aging. However, the findings in mice fed a CR diet with an increased content of AGEs resembled those in mice fed a nonrestricted diet that had the usual higher content of AGEs. Thus, there was an inverse correlation between the dietary AGE content, the AGER1 to receptor for AGE (RAGE) ratio, OS, organ damage, and life span. In both humans and mice, there was an inverse correlation between the AGER1 to RAGE ratio and the levels of OS.

Role of advanced glycation end products with oxidative stress in resistance artery dysfunction in type 2 diabetic mice

OBJECTIVE

Type 2 diabetes is associated with increased advanced glycation end product (AGE) formation and vasculopathy. We hypothesized that AGEs contribute to resistance artery dysfunction.

METHODS AND RESULTS

Type 2 diabetic db(-)/db(-) (diabetic) and nondiabetic db(-)/db(+) (control) mice were treated with the AGE inhibitor (aminoguanidine: 50 mg/Kg/d) for 3 months. Isolated mesenteric resistance arteries (MRAs) were mounted in an arteriograph. Pressure-induced myogenic tone (MT) was increased in diabetic mice but was unaffected by aminoguanidine treatment. Phenylephrine-induced contraction and nitric oxide donor-induced endothelium-independent relaxation were similar in all groups. In diabetic mice, endothelium-dependent relaxation in response to shear-stress or acetylcholine was altered and was associated with reduced eNOS protein and mRNA expression. Aminoguanidine treatment improved endothelial function and restored eNOS expression. AGE formation and hypoxia markers (plasminogen activator inhibitor 1 and Bnip3) were increased in MRA from diabetic mice and normalized with Aminoguanidine. Primary cultured endothelial cells (ECs) isolated from resistance arteries subjected to high glucose for 48 hours showed decreased eNOS expression and phosphorylation in response to calcium ionophore. High glucose decreased antioxidant protein (MnSOD) and increased prooxidant proteins (gp91phox) expression leading to increased oxidative stress generation, as assessed by DHE staining and endothelial NADH/NADPH oxidase activity. The preincubation of ECs with aminoguanidine restored eNOS-phosphorylation and expression as well as the balance between pro- and antioxidant factors induced by high glucose.

CONCLUSIONS

We provide evidence of a link between AGEs, oxidative stress, and resistance artery EC dysfunction in type 2 diabetic mice. Thus, AGEs and oxidative stress may be a potential target for overcoming diabetic microvessels complications.

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.

Priming of neutrophil oxidative burst in diabetes requires preassembly of the NADPH oxidase

Hyperglycemia associated with diabetes mellitus results in the priming of neutrophils leading to oxidative stress that is, in part, responsible for diabetic complications. p47phox, a NADPH oxidase cytosolic subunit, is a key protein in the assembly of the NADPH oxidase leading to superoxide generation. Little is known about the priming mechanism of oxidative pathways in neutrophils of people with diabetes. In this study, the kinetics of p47phox activation was investigated by comparing neutrophils from diabetic and healthy subjects, and the mechanism of hyperglycemia-induced changes was studied by using neutrophil-like HL-60 cells as a model. In resting neutrophils from diabetic subjects, p47phox prematurely translocates to the cell membrane and preassembles with p22phox, a NADPH oxidase membrane subunit. This premature p47phox translocation and preassembly with p22phox were also observed in HL-60 cells cultured with high glucose (HG; 25 mM) and with the specific ligand for the receptor for advanced glycation end products (RAGE), S100B. Phosphorylation of ERK1/2, but not p38 MAPK, was the primary signaling pathway, as evidenced by PD98059 suppressing the translocation of p47phox in HL-60 cells incubated with HG and S100B. HL-60 cells cultured in HG and S100B exhibited a 1.8-fold increase in fMLP-induced superoxide generation compared with those cultured in normal glucose (5.5 mM). These data suggest that HG and increased AGE prime neutrophils and increase oxidative stress inducing the translocation of p47phox to the cell membrane and preassembly with p22phox by stimulating a RAGE-ERK1/2 pathway.

Proinflammatory effects of advanced lipoxidation end products in monocytes

OBJECTIVE

The reactions of carbohydrate- or lipid-derived intermediates with proteins lead to the formation of Maillard reaction products, which subsequently leads to the formation of advanced glycation/lipoxidation end products (AGE/ALEs). Levels of AGE/ALEs are increased in diseases like diabetes. Unlike AGEs, very little is known about ALE effects in vitro. We hypothesized that ALEs can have proinflammatory effects in monocytes.

RESEARCH DESIGN AND METHODS

In a profiling approach, conditioned media from THP-1 cells either cultured in normal glucose (5.5 mmol/l) or treated with MDA-Lys or MDA alone were hybridized to arrays containing antibodies to 120 known human cytokines/chemokines. Pathway analyses with bioinformatics software were used to identify signalling networks.

RESULTS

Synthetic ALE (malondialdehyde-lysine [MDA-Lys]) (50 micromol/l) could induce oxidant stress and also activate the transcriptional factor nuclear factor-kappaB (NF-kappaB) in THP-1 monocytes. MDA-Lys also significantly increased the expression of key candidate proinflammatory genes, interferon-gamma-inducible protein-10, beta1- and beta2-integrins, cyclooxygenase-2 (COX-2), monocyte chemoattractant protein-1 (MCP-1), interleukin-6 and -8, and inducible nitric-oxide synthase, which are also associated with monocyte dysfunction. Several key target proinflammatory proteins were significantly induced by MDA-Lys relative to normal glucose or MDA alone, including MCP-1; tumor necrosis factor ligand superfamily member-14; chemokine CC motif ligand-11 (CCL11); growth-related oncogene-alpha, -beta, and -gamma; and chemokine CXC motif ligand-13. Bioinformatics analyses identified a network of chemokine signaling among MDA-Lys-regulated genes. MDA-Lys also increased monocyte binding to vascular smooth muscle and endothelial cells. Furthermore, plasma from diabetic rats showed significantly higher levels of MDA-Lys and CCL11.

CONCLUSIONS

These new results suggest that ALEs can promote monocyte activation and vascular complications via induction of inflammatory pathways and networks.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Glycated fetal calf serum affects the viability of an insulin-secreting cell line in vitro

The purpose of the present study was to evaluate the direct effects of advanced glycation end products (AGEs) on beta-cells by their exposure to a glycated serum to estimate the cellular viability and the related insulin secretion. Glycation of fetal calf serum was obtained by incubation with 50 mol/L ribose at 37 degrees C for 7 days; at the end of this incubation period, the pentosidine content ranged between 15 and 16 x 10(5) pmol/L. HIT-T15 cells, a pancreatic islet cell line, were grown and cultured for 5 days in Roswell Park Memorial Institute (RPMI) medium containing either not glycated (NGS) or glycated (GS) fetal calf serum. Cellular oxidative stress (ie, thiobarbituric acid-reactive substances) was assessed by high-performance liquid chromatography. Cellular viability was evaluated by detection of proliferation, cell necrosis, and cell apoptosis rate. The insulin secretion and the related intracellular content were evaluated by enzyme-linked immunosorbent assay. The present study reported, after 5 days of exposure to the glycation environment, a moderately reduced cellular proliferation (-20.44% +/- 2.92%) with a corresponding increase of cell necrosis (+67.7% +/- 1.56%) and cell apoptosis (+39.83% +/- 2.92%) rate in comparison with the untreated cells. Oxidative intracellular stress was higher in GS conditions compared with the NGS ones (+293.3% +/- 87.53%). Insulin release from GS-treated HIT-T15 cells was lower than that of NGS-treated cells both when cells were stimulated with low glucose concentration (2.8 mmol/L, -30.3% +/- 4.91%) or when they were challenged with high glucose concentration (16.7 mmol/L, -29.2% +/- 5.82%). Incubation of HIT-T15 cells with glycated serum also caused a significant decrease of insulin intracellular content (-44.47% +/- 9.98%). Thus, AGEs were shown to exert toxic effects on insulin-secreting cells. Chronically high intracellular oxidative stress, due to accumulation of AGEs, affects the insulin secretion machinery. The present data suggest a pivotal role of the non-enzymatic glycation process in the onset and progression of diabetes during aging and a direct adverse effect of a glycated environment on the pancreatic islet cells.

Oxidative stress: Does it play a role in the genesis of early glycated proteins?

Glycation and oxidative stress are two important processes known to play a key role in complications of many pathophysiological processes. The two traditional factors found to modulate the early glycation of proteins are the prevailing concentration of glucose and half life of the protein. But evidences in the literature have documented an increased glycated protein levels in some non-diabetic pathological states. So it stands to reason that hyperglycemia, while clearly the culprit in diabetes, is not the complete answer to the etiology of increased early glycated products in non-diabetic conditions. A common denominator in all these above mentioned non-diabetic pathological conditions is oxidative stress. Collective evidences from the literature reveal that malondialdehyde, reduced glutathione, vitamin C, vitamin E and drugs with antioxidant properties mitigate the process of protein glycation. Taking all the above factors into account, we hypothesis that oxidative stress either via increasing reactive oxygen species or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo.

Thiazolidinediones as anti-inflammatory and anti-atherogenic agents

In the last few years, there has been increasing focus on the impact of interventions on cardiovascular outcomes in patients with type 2 diabetes. Insulin resistance and hyperglycaemia often co-exist with a cluster of risk factors for coronary artery disease, but the underlying mechanisms leading to the development of such vascular complications are complex. The over-production of free radicals in patients suffering from diabetes results in a state of oxidative stress, which leads to endothelial dysfunction and a greater risk of atherosclerosis. Moreover, inflammatory factors which play a critical role in atherothrombosis and plaque rupture are often found to be at elevated levels in this patient population. Thiazolidinediones (TZDs) are now routinely used to manage glucose levels, and have been suggested to influence other cardiovascular risk factors and therefore the pathways leading to macrovascular events. Consequently, recent studies have investigated the anti-inflammatory and anti-atherogenic properties of TZDs. The data available up to the present time, in the context of the emerging cardiovascular outcome profiles of rosiglitazone and pioglitazone, will be discussed here.

Receptor for advanced glycation end product polymorphisms and type 2 diabetes: the CODAM study

Genetic variation in the receptor for advanced glycation end products (RAGE) gene may alter the expression and function of RAGE and affect disease development and outcome. We investigated whether single nucleotide polymorphisms (SNPs) in RAGE were associated with diabetes and parameters of glucose homeostasis. In total, nine SNPs of RAGE were analyzed in individuals with and without type 2 diabetes in CODAM: a cohort study of diabetes and atherosclerosis, Maastricht. A significant difference in genotype frequency of SNP rs3134945 was observed between the nondiabetic control subjects, subjects with impaired glucose metabolism, and diabetic patients. The C allele of this polymorphism was significantly associated with higher fasting glucose concentrations, 2-h postload glucose concentrations, insulin levels, and homeostasis model assessment of insulin resistance. These results indicate that SNP rs3134945 or a locus in linkage disequilibrium with this polymorphism may be involved in the development of insulin resistance and diabetes. Because the functionality of this polymorphism is not known, the mechanism whereby this polymorphism contributes to the development of insulin resistance and diabetes has to be further elucidated.

Vieillissement: rôle et contrôle de la glycation

PURPOSE

Advanced glycation end-products (AGEs) accumulate in aging tissues and organs during rheumatoid arthritis and Alzheimer disease. These aging toxins are especially involved in cell alteration during diabetes mellitus (glycotoxin) and renal failure (uremic toxin). AGEs participate to the endothelial dysfunction leading to diabetic macro but also micro-angiopathy. AGEs binding to cell receptors are critical steps in the deleterious consequences of AGE excess. AGE-receptor activation altered cell and organ functions by a pro-inflammatory, pro-coagulant and pro-fibrosis factors cell response.

CURRENT KNOWLEDGE AND KEY POINTS

Non-enzymatic glycation and glycoxidation with glucose auto-oxidation represent the two main pathways resulting in AGE formation. No exclusive AGE classification is actually available. Pathophysiological mechanisms are described to explain AGE toxicity. AGEs bind to cell receptors inducing deleterious consequences such as endothelial dysfunction after endothelial RAGE activation. AGEs can also have deleterious effects through glycated protein accumulation or in situ protein glycation.

FUTURE PROSPECTS AND PROJECTS

Many in vitro or animal studies demonstrated that AGE deleterious effects can be prevented by glycation inhibitors, AGE cross-link breakers or AGE-RAGE interaction inhibition. New molecules are actually studied as new strategy to prevent or treat the deleterious effects of these aging toxins.

Diagnostic utility of serum or cerebrospinal fluid levels of toxic advanced glycation end-products (TAGE) in early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are amyloid beta protein (A beta) and tau protein, respectively. Based on the disease pathology, numerous blood and cerebrospinal fluid (CSF) tests have been proposed for early detection of AD. However, there is no definite clinical method to determine in which patients with mild cognitive impairment will progress to AD with dementia. Therefore, to develop a novel promising biomarker for early diagnosis of AD is urgently needed. Several epidemiological studies have reported moderately increased risks for AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end-products (AGEs), senescent macroprotein derivatives, progress more rapidly. In addition, recent understanding of this process has confirmed that AGEs-their receptor (RAGE) interactions may play a role in the pathogenesis of neurodegenerative disorders including AD. In human AD brains, AGEs are distributed in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. In this paper, we discuss the pathophysiological role for toxic AGEs (TAGE) in AD. We further review here the possibility that serum or cerebrospinal fluid levels of TAGE could become a promising biomarker for early detection of AD.

Receptor for advanced glycation endproducts and atherosclerosis: From basic mechanisms to clinical implications

The receptor for advanced glycation endproducts (RAGE) is a member of the immunoglobulin superfamily of cell-surface molecules with a diverse repertoire of ligands. In the atherosclerotic milieu, three classes of RAGE ligands, i.e., products of non-enzymatic glycoxidation, S100 proteins and amphoterin, appear to drive receptor-mediated cellular activation and potentially, acceleration of vascular disease. The interaction of RAGE-ligands effectively modulates several steps of atherogenesis, triggering an inflammatory-proliferative process and furthermore, critically contributing to propagation of vascular perturbation, mainly in diabetes. RAGE has a circulating truncated variant isoform, soluble RAGE (sRAGE), corresponding to its extracellular domain only. By competing with cell-surface RAGE for ligand binding, sRAGE may contribute to the removal/neutralization of circulating ligands thus functioning as a decoy. The critical role of RAGE in the chronic vascular inflammation processes highlights this receptor-ligand axis as a possible and attractive candidate for therapeutic intervention to limit vascular damage and its associated clinical disorders.

Protective effects of an herbal formulation of Radix Astragali , Radix Codonopsis and Cortex Lycii on streptozotocin-induced apoptosis in pancreatic β -cells: an implication for its treatment of diabetes mellitus

Hyperglycemia is one of the main causes of oxidative stress in type 2 diabetes mellitus. During hyperglycemia, the increased level of various reducing sugars in the blood enhances the production of reactive oxygen species (ROS) and triggers tissue damage, especially in pancreatic beta-cells. Streptozotocin (STZ) is a diabetogen that causes diabetes mellitus via ROS-induced apoptosis in beta-cells. In this study, SR10, an herbal formulation consisting of the aqueous extracts of Radix Astragali, Radix Codonopsis and Cortex Lycii was examined for its antidiabetic effects in vitro. SR10 treatment resulted in significant enhancement of survival rate of rat pancreatic beta-cells which were treated by streptozotocin. SR10 apparently reduced apoptosis of streptozotocin-treated beta-cells by decreasing DNA fragmentation, sub-G(1) peak area and percentage of apoptotic cells. Nitric oxide (NO) production in streptozotocin-treated cells was inhibited by SR10 via the suppression of the expression of inducible nitric oxide synthase (iNOS). The implication of SR10 in treating type 2 diabetes mellitus was discussed.

Cardiovascular actions of insulin

Insulin has important vascular actions to stimulate production of nitric oxide from endothelium. This leads to capillary recruitment, vasodilation, increased blood flow, and subsequent augmentation of glucose disposal in classical insulin target tissues (e.g., skeletal muscle). Phosphatidylinositol 3-kinase-dependent insulin-signaling pathways regulating endothelial production of nitric oxide share striking parallels with metabolic insulin-signaling pathways. Distinct MAPK-dependent insulin-signaling pathways (largely unrelated to metabolic actions of insulin) regulate secretion of the vasoconstrictor endothelin-1 from endothelium. These and other cardiovascular actions of insulin contribute to coupling metabolic and hemodynamic homeostasis under healthy conditions. Cardiovascular diseases are the leading cause of morbidity and mortality in insulin-resistant individuals. Insulin resistance is typically defined as decreased sensitivity and/or responsiveness to metabolic actions of insulin. This cardinal feature of diabetes, obesity, and dyslipidemia is also a prominent component of hypertension, coronary heart disease, and atherosclerosis that are all characterized by endothelial dysfunction. Conversely, endothelial dysfunction is often present in metabolic diseases. Insulin resistance is characterized by pathway-specific impairment in phosphatidylinositol 3-kinase-dependent signaling that in vascular endothelium contributes to a reciprocal relationship between insulin resistance and endothelial dysfunction. The clinical relevance of this coupling is highlighted by the findings that specific therapeutic interventions targeting insulin resistance often also ameliorate endothelial dysfunction (and vice versa). In this review, we discuss molecular mechanisms underlying cardiovascular actions of insulin, the reciprocal relationships between insulin resistance and endothelial dysfunction, and implications for developing beneficial therapeutic strategies that simultaneously target metabolic and cardiovascular diseases.

Effects of Ginkgo biloba on prevention of development of experimental diabetic nephropathy in rats

AIM

To observe the preventive and therapeutic effects of Ginkgo biloba extract (GbE) on early experimental diabetic nephropathy (DN) in rats.

METHODS

After an early DN model was induced by streptozotocin, rats were administered GbE at 3 doses for 12 weeks. Fasting blood glucose, creatinine (Cr), blood urea nitrogen (BUN), urine protein, kidney index, anti-oxidase, advanced glycosylation end products (AGE), collagen IV and laminin, matrix metalloproteinases-2 (MMP-2) and the tissue inhibitor of metalloproteinase-2 (TIMP-2), connective tissue growth factor (CTGF), and transforming growth factor-beta1 (TGF-beta1) mRNA were measured by different methods. The ultrastructural morphology and the thickness of glomerular base membrane (GBM) were observed by a transmission electron microscope.

RESULTS

For the GbE-treated DN rats, when compared with the vehicle-treated DN rats, the fasting blood glucose level, Cr, BUN, urine protein level, and the intensity of oxidative stress were significantly decreased. The expression of MMP-2 greatly increased, and TIMP-2 decreased. Also, AGE, either in serum or in renal, the collagen IV, laminin, CTGF levels, and TGF-beta1 mRNA were reduced. Furthermore, both relative grades of mesangium hyperplasia by microscopical observation and the thickness of GBM by electron microscope measurement decreased significantly.

CONCLUSION

GbE has protective effects on several pharmacological targets in the progress of DN and is a potential drug for the prevention of early DN.

Glycotoxins in the diet promote diabetes and diabetic complications

Oxidant stress underlies diabetes and diabetic complications, including cardiovascular, renal, and retinal disease. Advanced glycation end products (AGEs), or glycotoxins, are a significant contributor to oxidant stress in diabetes. The diet is a major, unrecognized source of AGEs. Importantly, reduction of dietary AGEs decreases circulating inflammatory markers in both diabetic patients and prediabetic patients and complications in animal models. This beneficial outcome requires only a 50% decrease in dietary AGEs, making this necessary intervention practical and inexpensive.

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

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

Novel inhibitors of glycation and AGE formation

Accelerated formation of advanced glycation/lipoxidation and endproducts (AGEs/ALEs) has been implicated in the pathogenesis of various diabetic complications. Several natural and synthetic compounds have been proposed and tested as inhibitors of AGE/ALE formation. We have previously reported the therapeutic effects of several new AGE/ALE inhibitors on the prevention of nephropathy and dyslipidemia in streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the effects of various concentrations of a compound, LR-90, on the progression of renal disease and its effects on AGE and receptor for AGE (RAGE) protein expression on the kidneys of diabetic STZ-rats. Diabetic male Sprague-Dawley rats were treated with or without LR-90 (0, 5, 20, 25, and 50 mg/l of drinking water). After 32 weeks, body weight, glycemic status, renal function, and plasma lipids were measured. Kidney histopathology and AGE/ALE accumulation and RAGE protein expression in tissues were also determined. In vitro studies were also performed to determine the possible mechanism of action of LR-90 in inhibiting AGE formation and AGE-protein cross-linking. LR-90 protected the diabetic kidneys by inhibiting the increase in urinary albumin-to-creatinine ratio and ameliorated hyperlipidemia in diabetic rats in a concentration-dependent fashion without any effects on hyperglycemia. LR-90 treatment also reduced kidney AGE/ALE accumulation and RAGE protein expression in a concentration-dependent manner. In vitro, LR-90 exhibited general antioxidant properties by inhibiting metal-catalyzed reactions and reactive oxygen species (OH radical) and reactive carbonyl species (methlyglyoxal, glyoxal) generations without any effect on pyridoxal 5' phosphate. The compound also prevents AGE-protein cross-linking reactions. These findings demonstrate the bioefficacy of LR-90 in treating nephropathy and hyperlipidemia in diabetic animals by inhibiting AGE accumulation, RAGE protein expression, and protein oxidation in the diabetic kidney. Additionally, our study suggests that LR-90 may be useful also to delay the onset and progression of diabetic atherosclerosis as the compound can inhibit the expression of RAGE and inflammation-related pathology, as well as prevent lipid peroxidation reactions.

Genome-wide analysis of histone lysine methylation variations caused by diabetic conditions in human monocytes

Aberrant histone lysine methylation patterns that change chromatin structure can promote dysregulated gene transcription and disease progression. Diabetic conditions such as high glucose (HG) are known to alter key pathologic pathways. However, their impact on cellular histone lysine methylation is unknown. We hypothesized that chronic HG can induce aberrant changes in histone H3 lysine 4 and lysine 9 dimethylation (H3K4me2 and H3K9me2) within target cells. Chromatin immunoprecipitation linked to microarrays (ChIP-on-chip) is currently a widely used approach for acquiring genome-wide information on histone modifications. We adopted this approach to profile and compare the variations in H3K4me2 and H3K9me2 in human gene coding and CpG island regions in THP-1 monocytes cultured in normal glucose and HG. Subsequently, we identified key relevant candidate genes displaying differential changes in H3K4me2 and H3K9me2 in HG versus normal glucose and also validated them with follow-up conventional ChIPs. Relevance to human diabetes was demonstrated by noting that H3K9me2 at the coding and promoter regions of two candidate genes was significantly greater in blood monocytes of diabetic patients relative to normal controls similar to the THP-1 data. In addition, regular mRNA profiling with cDNA arrays revealed correlations between mRNA and H3K9me2 levels. These novel results show histone methylation variations, for the first time, under diabetic conditions at a genome-wide level.

Genes, ageing and longevity in humans: problems, advantages and perspectives

Many epidemiological data indicate the presence of a strong familial component of longevity that is largely determined by genetics, and a number of possible associations between longevity and allelic variants of genes have been described. A breakthrough strategy to get insight into the genetics of longevity is the study of centenarians, the best example of successful ageing. We review the main results regarding nuclear genes as well as the mitochondrial genome, focusing on the investigations performed on Italian centenarians, compared to those from other countries. These studies produced interesting results on many putative "longevity genes". Nevertheless, many discrepancies are reported, likely due to the population-specific interactions between gene pools and environment. New approaches, including large-scale studies using high-throughput techniques, are urgently needed to overcome the limits of traditional association studies performed on a limited number of polymorphisms in order to make substantial progress to disentangle the genetics of a trait as complex as human longevity.

Parathyroid hormone stimulates endothelial expression of atherosclerotic parameters through protein kinase pathways

Parathyroid hormone (PTH), the major systemic calcium-regulating hormone, has been linked to uremic vascular changes. Considering the possible deleterious action of PTH on vascular structures, it seemed logical to evaluate the impact of PTH on the receptor of advanced glycation end products (RAGE) and interleukin 6 (IL-6) mRNA and protein expression, taking into account that such parameters might be involved in the pathogenesis of vascular calcification, atherosclerosis, and/or arteriolosclerosis. Human umbilical vein cord endothelial cells (HUVEC) were stimulated for 24 h with 10(-12)-10(-10) mol/l PTH. The mRNA expression of RAGE and IL-6 was established by reverse transcriptase/PCR techniques. RAGE protein levels were determined by Western blot and IL-6 secretion was measured by ELISA. The pathways by which PTH may have an effect on HUVEC functions were evaluated. PTH (10(-11)-10(-10)mol/l) significantly increased RAGE mRNA and protein expression. PTH also significantly increased IL-6 mRNA expression without changes at protein levels. The addition of protein kinase (PKC or PKA) inhibitors or nitric oxide (NO) synthase inhibitors significantly reduced the RAGE and IL-6 mRNA expression and the RAGE protein expression. PTH stimulates the mRNA expressions of RAGE and IL-6 and the protein expression of RAGE. These stimulatory effects are probably through PKC and PKA pathways and are also NO dependent. Such data may explain the possible impact of PTH on the atherosclerotic and arteriosclerotic progression.

Toxicity of the AGEs generated from the Maillard reaction: On the relationship of food-AGEs and biological-AGEs

Advanced glycation end products (AGEs) are generated in the late stages of Maillard reaction in foods and biological systems. These products are mostly formed by the reactions of reducing sugar or degradation products of carbohydrates, lipids, and ascorbic acid. AGEs exist in high concentration in foods, but in relatively low concentrations in most of the biological systems. Recently, some AGEs have been reported to be toxic, and were proposed to be causative factors for various kinds of diseases, especially diabetes and kidney disorder, through the association with receptor of AGE (RAGE). It has also been reported that food-derived AGEs (food-AGEs) may not be a causative factor for pro-oxidation. However, the relationship of food-AGEs and biological-derived AGEs (biological-AGEs) is not clear. In this review, the following issues are discussed: the formation of AGEs in foods and biological systems; identification of the main AGEs in foods and biological systems; absorption of food-AGEs; the effects of AGEs in vivo; relationship between food-AGEs and biological-AGEs; possible defense mechanism against AGEs in vivo and finally, the problems to be solved concerning the toxicity of AGEs.

Cellular mechanisms and signalling pathways activated by high glucose and AGE-albumin in the aortic endothelium

This review summarizes evidence on the effect of excess circulating glucose concentration and AGE-albumin on the aortic endothelial cells (ECs) phenotype, transport function, and expression of signalling molecules. The recent reports on the ECs dysfunction in diabetes are briefly reviewed, to provide a broader view on the link between ECs structural changes, functional alterations, and the underlying biochemical mechanisms. The original results emerging from streptozotocin-injected mice and human aortic endothelial cells grown in high (25 mM) glucose concentration are presented. Compared to physiological condition, in diabetes aortic ECs switch to a biosynthetic phenotype, present an increased number of caveolae, and enhance (by approximately 20%) transcytosis of AGE-albumin (AGE-Alb). In cultured ECs, 25 mM glucose induces approximately 2.6 fold increase in pSTAT-3 and pERK1 and approximately 1.8 fold increase in pERK2; further exposure to 5 microM AGE-Alb causes approximately 4.3 fold increase in pERK1/2 (vs. 5 mM glucose). Together, these data may explain the phenotypic change, enhanced permeability, and proliferation of aortic ECs in diabetic conditions.

Enhanced proatherogenic responses in macrophages and vascular smooth muscle cells derived from diabetic db/db mice

Diabetes is associated with enhanced inflammatory responses and cardiovascular complications such as atherosclerosis. However, it is unclear whether similar responses are present in cells derived from experimental animal models of diabetes. We examined our hypothesis that macrophages and short-term cultured vascular smooth muscle cells (VSMCs) derived from obese, insulin-resistant, and diabetic db/db mice would exhibit increased proatherogenic responses relative to those from control db/+ mice. We observed that macrophages from db/db mice exhibit significantly increased expression of key inflammatory cytokines and chemokines as well as arachidonic acid-metabolizing enzymes cyclooxygenase-2 and 12/15-lipoxygenase that generate inflammatory lipids. Furthermore, VSMCs derived from db/db mice also showed similar enhanced expression of inflammatory genes. Expression of inflammatory genes was also significantly increased in aortas derived from db/db mice. Both macrophages and VSMCs from db/db mice demonstrated significantly increased oxidant stress, activation of key signaling kinases, and transcription factors cAMP response element-binding protein and nuclear factor-kappaB, involved in the regulation of atherogenic and inflammatory genes. Interestingly, VSMCs from db/db mice displayed enhanced migration as well as adhesion to WEHI mouse monocytes relative to db/+. Thus, the diabetic milieu and a potential hyperglycemic memory can induce aberrant behavior of vascular cells. These new results demonstrate that monocyte/macrophages and VSMCs derived from db/db mice display a "preactivated" and proinflammatory phenotype associated with the pathogenesis of diabetic vascular dysfunction and atherosclerosis.

Interferon-gamma-inducible protein (IP)-10 mRNA stabilized by RNA-binding proteins in monocytes treated with S100b

Chemokines mediate the recruitment and activation of blood monocyte/macrophages and lymphocytes to sites of inflammation. Expression of the chemokine IP-10 (interferon-gamma-inducible protein) has been documented in several inflammatory and autoimmune disorders including type 1 diabetes. However, the mechanism of its expression in monocytes or its functional role in diabetes is not known. Advanced glycation end products acting via their receptor, RAGE, play major roles in diabetic complications. In this study, we observed for the first time that S100b, an inflammatory protein as well as a specific RAGE ligand, significantly increased IP-10 mRNA and protein levels in THP-1 monocytes as well as peripheral blood monocytes. Promoter luciferase assays showed that IP-10 mRNA accumulation by S100b was not via increased transcription. On the other hand, S100b significantly increased IP-10 mRNA half-life and stability. This appeared to be mediated by S100b-induced binding of specific RNA-binding protein(s) to a 3'-untranslated region-responsive region of the IP-10 mRNA. Our results demonstrate for the first time that diabetic stimuli such as RAGE ligands can induce inflammatory gene expression in monocytes via increased message stability.

The influence of diabetes on gingival crevicular fluid beta-glucuronidase and interleukin-8

OBJECTIVES

Polymorphonuclear neutrophil (PMN) dysfunction is associated with diabetes. We examined the gingival crevicular fluid (GCF) beta-glucuronidase (BG) and interleukin-8 (IL-8) levels of periodontitis patients with and without type 2 diabetes mellitus (DM).

MATERIAL AND METHODS

Forty five adults with type 2 DM and 32 adults without DM, both with chronic periodontitis were enrolled. GCF was collected from eight posterior sites in each quadrant, and periodontal parameters were recorded. GCF was assayed for IL-8 by ELISA and BG by a fluorometric assay.

RESULTS

GCF IL-8 was positively correlated with probing depth (PD), and GCF BG but not clinical attachment level (CAL), bleeding on probing (BOP), or plaque index (PI). In contrast, GCF BG was strongly correlated with each of the clinical measures of periodontal disease. Subjects with DM significantly lower levels of both BG (73.0+/-44.8 versus 121.9+/-84.6 pg/sample; p=0.002) and IL-8 (32.1+/-33.1 versus 90.8+/-83.2 pg/sample; p<0.0001) even after adjustments for age, gender, PD, CAL, BOP, and PI. Neither BG nor IL-8 was correlated with HbA1c levels in subjects with DM.

CONCLUSION

These data suggest that an inadequate local response by PMN, partially explained by an altered chemokine gradient, may contribute to periodontal disease in patients with type 2 DM.

Percutaneous coronary revascularization in diabetics: from balloon angioplasty to drug-eluting stents

Diabetic patients may have aggressive coronary disease with an excessive rate of restenosis and accelerated atherosclerotic progression. This article reviews the different modalities of percutaneous treatment and their results in the diabetic population, from the early days of balloon angioplasty to the current implementation of drug-eluting stents. As restenosis may be virtually eradicated in the near future, plaque progression remains the cornerstone for interventional cardiologists and the medical community. In this regard, attempts to modify life habits, and a more accurate control of the components of the metabolic syndrome should be the main therapeutic objective.

Diabetic neuropathy and oxidative stress

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

Increased expression levels of monocyte CCR2 and monocyte chemoattractant protein-1 in patients with diabetes mellitus

Increased monocyte recruitment into subendothelial space in atherosclerotic lesions is one of the hallmarks of diabetic angiopathy. The aim of this study was to determine the state of peripheral blood monocytes in diabetes associated with atherosclerosis. Diabetic patients treated with/without an oral hypoglycemic agent and/or insulin for at least 1 year were recruited (n=106). We also included 24 non-diabetic control subjects. We measured serum levels of monocyte chemoattractant protein (MCP)-1, fasting plasma glucose (FPG), HbA1c, total cholesterol, triglyceride, body mass index (BMI), high sensitivity CRP (hs-CRP) and evaluated CCR2, CD36, CD68 expression on the surface of monocytes. Serum MCP-1 levels were significantly (p<0.05) higher in diabetic patients than in normal subjects. In diabetic patients, serum MCP-1 levels correlated significantly with FPG, HbA1c, triglyceride, BMI, and hs-CRP. The expression levels of CCR2, CD36, and CD68 on monocytes were significantly increased in diabetic patients and were more upregulated by MCP-1 stimulation. Our data suggest that elevated serum MCP-1 levels and increased monocyte CCR2, CD36, CD68 expression correlate with poor blood glucose control and potentially contribute to increased recruitment of monocytes to the vessel wall in diabetes mellitus.