Modulation of CD36 protein expression by AGEs and insulin in aortic VSMCs from diabetic and non-diabetic rats

Background and aimIn type 2 diabetes, the interplay between cells and inflammatory mediators up-regulates CD36 expression in macrophages. The aim of this work was to investigate advanced glycation end products (AGE)-induced CD36 expression and its regulation by insulin in aortic vascular smooth muscle cells (VSMCs) from Goto–Kakisaki (GK) rats, a non-obese insulin model of both insulin resistance and type 2 diabetes. The context of overexpression of CD36 in aortas was also evaluated.Methods and resultsVSMCs were isolated and cultured from the aortas of GK rats and non-diabetic rats. The expression of proteins was evaluated by Western blot. The aortic production of superoxide anion (O₂^·−) was measured by luminescence on isolated tissue. AGEs and advanced oxidation protein products (AOPPs) were determined in plasma by fluorescence spectroscopy and spectrophotometry, respectively.AGE receptor (RAGE), NF-κB, and CD36 protein expression as well as O₂^·− production were higher in GK aortas than in control aortas, and AGEs and AOPPs were higher in GK plasma. In VSMCs from non-diabetic rats, insulin was able to reduce (10 nM) or suppress (100 nM) the protein overexpression of CD36 induced by AGEs–BSA. In contrast, in VSMCs from GK rats, insulin was unable to reduce AGEs–BSA-induced CD36 overexpression.ConclusionsThe results suggest an overexpression of CD36 in VSMCs from GK rats and impaired control by insulin. In the context of increased plasma AGEs, aortic RAGE overexpression and increased oxidative stress markers, the data are compatible with an AGEs induced CD36 overexpression in diabetes.     

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.     

Hypothalamic serotonin-insulin signaling cross-talk and alterations in a type 2 diabetic model

Serotonin and insulin are key regulators of homeostatic mechanisms in the hypothalamus. However, in type 2 diabetes, the hypothalamic responsiveness to serotonin is not clearly established. We used a diabetic model, the Goto Kakizaki (GK) rats, to explore insulin receptor expression, insulin and serotonin efficiency in the hypothalamus and liver by means of Akt phosphorylation. Insulin or dexfenfluramine (stimulator of serotonin) treatment induced Akt phosphorylation in Wistar rats but not in GK rats that exhibit down-regulated insulin receptor. Studies in a neuroblastoma cell line showed that serotonin-induced Akt phosphorylation is PI3-kinase dependent. Finally, in response to food intake, hypothalamic serotonin release was reduced in GK rats, indicating impaired responsiveness of this neurotransmitter. In conclusion, hypothalamic serotonin as insulin efficiency is impaired in diabetic GK rats. The insulin-serotonin cross-talk and impairment observed is one potential key modification in the brain during the onset of diabetes.     

Endothelial dysfunction in type 2 diabetes: effect of antioxidants.

Individuals with insulin resistance and diabetes mellitus have increased cardiovascular morbidity and mortality, caused in part by vascular complications. Endothelial dysfunction has been implicated in the pathogenesis of vascular diabetic disease. This abnormal function of the vasculature precedes cardiovascular disease and is associated with impaired endothelium-dependent vasorelaxation. The main etiology of the increased mortality and morbidity of type 2 diabetic patients is atherosclerosis. Increased production of free radicals is associated with the pathophysiology of diabetes, resulting in oxidative damage to lipids and proteins. Reduction of oxidative stress in diabetic patients may delay the onset of atherogenesis and the appearance of micro- and macrovascular complications. Alpha-lipoic acid (LA) is a multifunctional antioxidant that has been shown to have beneficial effects on polyneuropathy and on markers of oxidative stress in various tissues. This study was conducted to investigate the effects of LA on endothelial function in diabetic and hyperlipidemic animal models. Carbohydrate and lipid metabolism, endothelial function, plasma malondialdehyde (MDA) and urinary 8-hydroxydeoxyguanosine (8-OHdG) were assessed in non-diabetic controls (Wistar rats), untreated diabetic Goto-Kakizaki (GK) rats and, atherogenic diet (AD)-fed GK rats (fed with atherogenic diet only, treated with alpha-lipoic acid and treated with vehicle, for 3 months). AD resulted in a 3-fold increase in both total and non-HDL serum cholesterol levels and in a 2-fold increase triglyceride levels while endothelial function was significantly reduce MDA and 8-OHdG levels were higher in the GK and GK hyperlipidemic groups and were completely reversed by the antioxidant. Hyperlipidemic GK diabetic rats showed significantly reduced endothelial function that was partially improved with LA. Furthermore, lipoic acid significantly reduced serum cholesterol levels, without lowering HDL cholesterol. Alpha-lipoic acid supplementation represents an achievable adjunct therapy to improve endothelial function and reduce oxidative stress, factors that are implicated in the pathogenesis of atherosclerosis in diabetes.     

Circulating glycotoxins and dietary advanced glycation endproducts: two links to inflammatory response, oxidative stress, and aging

BACKGROUND: Oxidative stress (OS) and inflammatory mediators increase with aging. The levels of advanced glycation endproducts (AGEs), prooxidant factors linked to chronic diseases such as diabetes, cardiovascular disease, and renal disease, also increase with aging. AGEs are readily derived from heat-treated foods. We propose that the excess consumption of certain AGEs via the diet enhances OS and inflammatory responses in healthy adults, especially in elderly persons. METHODS: We examined 172 young (<45 years old) and older (>60 years old) healthy individuals to determine whether the concentration of specific serum AGEs (N(epsilon)-carboxymethyl-lysine [CML] or methylglyoxal [MG] derivatives) were higher in older compared to younger persons and whether, independent of age, they correlated with the intake of dietary AGEs, as well as with circulating markers of OS and inflammation. RESULTS: Body weight, body mass index (BMI), and serum AGE, CML, and MG derivatives were higher in older participants, independent of gender. Serum CML correlated with levels of 8-isoprostanes (r = 0.448, p =.0001) as well as with Homeostasis Model Assessment index (HOMA), an index of insulin resistance (r = 0.247, p =.044). The consumption of dietary AGEs, but not of calories, correlated independently with circulating AGEs (CML: r = 0.415, p =.0001 and MG: r = 0.282, p =.002) as well as with high sensitivity C-reactive protein (hsCRP) (r = 0.200, p =.042). CONCLUSIONS: Circulating indicators of AGEs (CML and MG derivatives), although elevated in older participants, correlate with indicators of inflammation and OS across all ages. Indicators of both AGEs and OS are directly influenced by the intake of dietary AGEs, independent of age or energy intake. Thus, reduced consumption of these oxidants may prove a safe economic policy to prevent age-related diseases, especially in an aging population.     

Ischaemic preconditioning does not protect the heart in obese and lean animal models of Type 2 diabetes

Aims/hypothesis The prevalence of Type 2 diabetes mellitus is increasing worldwide with obese diabetic patients constituting the majority of this population. Type 2 diabetes is associated with increased morbidity and mortality after acute myocardial infarction. Previous experimental studies of ischaemia-reperfusion tolerance in diabetes have only been performed in animal models of Type 1 diabetes mellitus, yielding conflicting data. The aim of the present study was to characterise and compare the tolerance to ischaemia and effects of ischaemic preconditioning (IPC) in hearts from obese Zucker diabetic fatty (ZDF) and lean Goto-Kakizaki (GK) Type 2 diabetic rats, using non-obese Zucker and Wistar rats as respective controls.Methods The two rat strains were divided into 8 groups. The ZDF study (n=47) consisted of: Control –IPC, Control +IPC, ZDF –IPC and ZDF +IPC. The GK study (n=38) consisted of: Control –IPC, Control +IPC, GK –IPC and GK +IPC. Hearts, which were studied in a Langendorff preparation perfused with Krebs-Henseleit buffer, were subjected or not to IPC (+IPC, –IPC) before 50 minutes of regional ischaemia and 120 minutes reperfusion.Results Ischaemic reperfusion injury was smaller in obese (p<0.05) and lean (p<0.05) Type 2 diabetic animals than in their respective control animals. IPC reduced ischaemic reperfusion injury during reperfusion in non-diabetic control rats (p<0.01), but failed to protect hearts from both diabetic animal models. Post-ischaemic haemodynamic recovery was impaired in the ZDF rats compared to both control and GK rats (p<0.05).Conclusions/interpretation Ischaemic preconditioning does not protect hearts from obese or lean Type 2 diabetic animals. However, the susceptibility of the Type 2 diabetic myocardium to ischaemic damage is lower than in non-diabetic hearts. The method described here could be used as a tool to study the pathogenesis of increased cardiovascular morbidity and mortality in Type 2 diabetes.     

Association of dietary factors with insulin resistance and inflammatory markers in subjects with diabetes mellitus and coronary artery disease in Indian population

BackgroundInsulin resistance (IR) and inflammation have been implicated in pathogenesis of diabetes and cardiovascular disease. Dietary factors have been reported to be associated to insulin resistance and inflammation. Hence, we studied the association of dietary factors with IR and inflammation in known patients with diabetes mellitus and coronary artery disease with the hypothesis that carbohydrate and fat will be positively; and protein, fiber and mineral will be negatively associated with IR and inflammatory markers.MethodsThree hundred patients (M: 216; F: 84, age: 25–92) who had coronary disease on angiography were included in this study consecutively. All patients were evaluated for anthropometry and cardiovascular risk factors, and blood samples were collected for biochemical and inflammatory markers. Nutrition assessment was done once at the time of recruitment, based on 24 h dietary recall.Results and ConclusionsDiabetic patients had significantly lower protein and total dietary fiber intake as compared to non diabetics. Diabetic patients had lower intake of vitamin A, riboflavin and vitamin B12. There was significantly lower intake of minerals by diabetic patients. Dietary carbohydrate and fat were positively, and protein and dietary fiber intakes were negatively correlated with HOMA-IR and IL-6. There was no correlation of individual amino acids with HOMA-IR but showed strong negative correlation with inflammatory markers (hsCRP; IL-6 and TNF-α). Intake of vitamins and minerals was negatively correlated with HOMA-IR and inflammatory markers. There is a strong correlation between dietary factors, insulin resistance and inflammatory markers.     

Decreased blood levels of glyoxalase I and diabetic complications

The formation of Advanced Glycation Endproducts (AGEs) has been found to play a role in the development of diabetic symptoms. Production of methylglyoxal (MG), a highly cytotoxic and crosslinking aldehyde, is elevated among patients with type 2 diabetes mellitus (T2DM) and is a precursor to AGEs. The ubiquitous glyoxalase system is one of several defense mechanisms involved in MG metabolism and the protection against the production of AGEs. The system is a complex of two enzymes: glyoxalase I (GloI) that converts MG and reduced glutathione (GSH) to S-lactoylglutathione which is converted to D-lactic acid by glyoxalase II, regenerating GSH in the process. The malfunctioning of the glyoxalase system results in the accumulation of MG. The present study was performed to explore the relationship between the decreased activity of GloI and the complications associated to T2DM. The activities of the GloI, GloII and the concentration of GSH were measured in blood samples of 203 volunteers: 75 controls, 60 non-insulino-dependent diabetes mellitus (NIDDM) individuals and 68 NIDDM patients with complications as follow: 18 with nephropathy, 15 with retinopathy, 15 with neuropathy and 20 with macroangiopathy. All individuals were from the northen region of Morocco. We also evaluated the relationships between GloI levels and the pathogenesis of micro- and macrovascular complications of diabetes. We found a significant decrease in the GloI activity and GSH levels in patients with diabetes compared to controls. GloI activity was further reduced in samples from diabetes patients with complications. The levels of GloI were markedly lower in blood samples from patients with nephropathy than in uncomplicated patients and normal subjects. In contrast, there was no significant change in the activity of GloII in NIDDM patients compared to controls. This study suggests that the low level of GloI activity in T2DM patients is most probably due to decreased level of GSH content and reflects the role of GloI enzyme in protecting T2DM patients from AGEs accumulation and further complications.

     

Glycation and cardiovascular disease in diabetes: A perspective on the concept of metabolic memory

Epidemiological studies have suggested that cumulative diabetic exposure, namely prolonged exposure to chronic hyperglycemia, contributes to the increased risk of cardiovascular disease (CVD) in diabetes. The formation and accumulation of advanced glycation end‐products (AGEs) have been known to progress under hyperglycemic conditions. Because AGEs‐modified collagens are hardly degraded and remain in diabetic vessels, kidneys and the heart for a long time, even after glycemic control has been achieved, AGEs could become a marker reflecting cumulative diabetic exposure. Furthermore, there is a growing body of evidence that an interaction between AGEs and the receptor for AGEs (RAGE) plays a role in the pathogenesis of CVD. In addition, AGEs induce the expression of RAGE, thus leading to sustained activation of the AGEs–RAGE axis in diabetes. Herein we review the pathological role of the AGEs–RAGE axis in CVD, focusing particularly on the phenomenon of metabolic memory, and discuss the potential clinical usefulness of measuring circulating and tissue levels of AGEs accumulation to evaluate diabetic macrovascular complications.     

Initial steps of insulin signaling and glucose transport are defective in the type 2 diabetic rat heart

OBJECTIVE: Whole body insulin resistance and diabetes are risk factors for cardiovascular diseases, yet little is known about insulin resistance in the diabetic heart. The aim of this work was to define the insulin response in hearts of the Goto-Kakizaki (GK) rat, a polygenic model of spontaneous type 2 diabetes. METHODS: We measured D[2-3H]glucose uptake before and after insulin stimulation, plus initial steps of the insulin signaling pathway after insulin infusion via the caudal vena cava in hearts from the male Wistar and spontaneously diabetic GK rats. RESULTS: Despite normal basal D[2-3H]glucose uptake, insulin-stimulated glucose uptake was 50% (p<0.03) lower in GK rat hearts compared with their Wistar controls. Total GLUT4 protein was depleted by 28% (p<0.01) in GK rat hearts. We found 31% (p<0.0001) and 38% (p<0.001) decreased protein levels of insulin receptor beta (IRbeta)-subunit and insulin receptor substrate-1 (IRS-1), respectively, in GK rat hearts with 37% (p<0.02) and 45% (p<0.01) lower insulin-stimulated tyrosine phosphorylation of these proteins. Owing to the decreased IRS-1 protein levels, GK rat hearts had a 41% (p<0.0001) decrease in insulin-stimulated IRS-1 protein association with the p85 subunit of phosphatidylinositol 3-kinase, despite normal phosphatidylinositol 3-kinase protein expression. Insulin-stimulated serine phosphorylation of protein kinase B was the same in all hearts, as was protein kinase B expression. CONCLUSION: We conclude that decreased insulin receptor beta, IRS-1 and GLUT4 proteins are associated with insulin resistance in type 2 diabetic rat hearts.     

A quick,simple method for detecting circulating fluorescent advanced glycation end-products: Correlation with in vitro and in vivo non-enzymatic glycation

ObjectiveAdvanced glycation end-products (AGEs) constitute a highly heterogeneous family of compounds, relevant in the pathogenesis of diabetic complications, which could represent efficient biomarkers of disease progression and drug response. Unfortunately, due to their chemical heterogeneity, no method has been validated to faithfully monitor their levels in the course of the disease. In this study, we refine a procedure to quantitatively analyze fluorescent AGEs (fAGEs), a subset considered remarkably representative of the entire AGE family, and measure them in in vitro glycated BSA (gBSA) and in plasma and vitreous of diabetic rats, for testing its use to possibly quantify circulating AGEs in patients, as markers of metabolic control.MethodsfAGE levels were evaluated by spectrofluorimetric analysis in in vitro and in vivo experimental models. BSA was glycated in vitro with increasing D-glucose concentrations for a fixed time or with a fixed D-glucose concentration for increasing time. In in vivo experiments, streptozotocin-induced diabetic rats were studied at 1, 3, 6 and 12 weeks to analyze plasma and vitreous. To confirm the presence of AGEs in our models, non-diabetic rat retinal explants were exposed to high glucose (HG), to reproduce short-term effects, or in vitro gBSA, to reproduce long-term effects of elevated glucose concentrations. Rat retinal explants and diabetic retinal tissues were evaluated for the receptor for advanced glycation end-product (RAGE) by Western blot analysis.ResultsIn in vitro experiments, fluorescence emission showed glucose concentration- and time-dependent increase of fAGEs in gBSA (p ≤ 0.05). In streptozotocin-induced diabetic rats, fAGE in plasma and vitrei showed an increase at 6 (p ≤ 0.005) and 12 (p ≤ 0.05) weeks of diabetes, with respect to control. RAGE was time-dependently upregulated in retinas incubated with gBSA, but not with HG, and in diabetic retinal tissue, substantiating exposure to AGEs.ConclusionsApplying the proposed technique, we could show that fAGEs levels increase with glucose concentration and time of exposure in vitro. Furthermore, in diabetic rats, it showed that circulating fAGEs are similarly upregulated as those in vitreous, suggesting a correlation between circulating and tissue AGEs. These results support the use of this method as a simple and reliable test to measure circulating fAGEs and monitor diabetes progression.     

Glycated proteins and cardiovascular disease in glucose intolerance and type 2 diabetes

Individuals with diabetes have more atherosclerosis and cardiovascular events and a higher complication rate from cardiovascular events than nondiabetic individuals. Also, lesions from diabetic patients are more prone to rupture and exhibit more intravascular thrombosis than those from nondiabetic patients. Glucose modification of circulating proteins and matrix proteins mediates the activation of the inflammatory pathways critical in diabetes-associated atherosclerosis. Extracellular matrix proteins containing advanced glycation end products (AGEs) serve as ligands for scavenger receptors and the receptor for AGEs. Ligation of the receptor for AGEs activates inflammatory pathways and destabilizes atherosclerotic plaques in diabetic patients. Clinically, researchers have used concentrations of fructosamine and glycosylated hemoglobin to investigate the relationships among glycemia, glucose-modified proteins, and cardiovascular risk. They found that increased levels of fructosamine and hemoglobin A_1c are associated with a significantly increased multivariable-adjusted risk of cardiovascular events.     

Advanced glycation end‐products are a risk for muscle weakness in Japanese patients with type 1 diabetes

Accumulation of advanced glycation end‐products (AGEs) is thought to contribute to muscle weakness in a diabetic animal model. Skin autofluorescence is a proposed marker for accumulation of AGEs in the skin. We aimed to investigate the relationship between AGEs accumulation, sarcopenia and muscle function of Japanese patients with type 1 diabetes. A total of 36 patients with type 1 diabetes participated in the present cross‐sectional study. Sarcopenia parameters (skeletal muscle mass index and knee extension strength) were compared with subcutaneous AGEs accumulation using skin autofluorescence. The prevalence of sarcopenia and impaired knee extension strength was 16.6% (men 0.0%, women 22.2%) and 47.2% (men 22.2%, women 55.6%), respectively. Knee extension strength was negatively correlated with skin autofluorescence (r² = 0.14, P < 0.05), but not with skeletal muscle mass index. In conclusion, the AGEs accumulation might be one of the reasons of impaired lower limb muscle function in Japanese patients with type 1 diabetes.     

Inhibitors of advanced glycation end products (AGEs): potential utility for the treatment of cardiovascular disease

Accelerated atherosclerosis and microvascular complications are the leading causes of coronary heart disease, stroke, blindness, and end-stage renal failure, which could account for disabilities and high mortality rates in patients with diabetes. Recent clinical studies have substantiated the concept of "hyperglycemic memory" in the pathogenesis of cardiovascular disease (CVD) in diabetes. Indeed, the Diabetes Control and Complications Trial-Epidemiology of Diabetes Interventions and Complications (DCCT-EDIC) Research, has revealed that intensive therapy during the DCCT reduces the risk of cardiovascular events by about 50% in type 1 diabetic patients 11 years after the end of the trial. Among various biochemical pathways activated under diabetic conditions, the process of formation and accumulation of advanced glycation end products (AGEs) and their mode of action are most compatible with the theory "hyperglycemic memory." Further, there is a growing body of evidence that AGEs play an important role in CVD in diabetes. These observations suggest that the inhibition of AGEs formation may be a promising target for therapeutic intervention in diabetic vascular complications. Therefore, in this article, we review several agents with inhibitory effects on AGEs formation and their therapeutic implications in CVD in diabetes.     

Metformin protects the ischemic heart by the Akt-mediated inhibition of mitochondrial permeability transition pore opening

Background In the majority of studies, metformin has been demonstrated to cardioprotect diabetic patients, the mechanism of which is unclear. We hypothesized that metformin cardioprotects the ischemic heart through the Akt-mediated inhibition of mitochondrial permeability transition pore (mPTP) opening. Materials and methods Isolated perfused hearts from normoglycemic Wistar or from diabetic Goto-Kakizaki (GK) rats (N ≥ 6/group) were subjected to 35 min ischemia and 120 min of reperfusion. Metformin (50 μmol/l) was added for 15 min at reperfusion, alone or with LY294002 (15 μmol/l), a PI3K inhibitor. Infarct size and Akt phosphorylation were measured. Furthermore, the effect of metformin on mPTP opening in adult cardiomyocytes isolated from both strains was determined. Results Metformin reduced infarct size in both Wistar (35 ± 2.7% metformin vs. 62 ± 3.0% control: P < 0.05) and GK hearts (43 ± 4.7% metformin vs. 60 ± 3.8% control: P < 0.05). This protection was accompanied by a significant increase in Akt phosphorylation. LY294002 abolished the metformin-induced Akt phosphorylation and the infarct-limiting effect of metformin in Wistar (61 ± 6.7% metformin + LY294002 vs. 35 ± 2.7% metformin: P < 0.05) and GK rats (56 ± 5.7% metformin + LY294002 vs. 43 ± 4.7% metformin: P < 0.05). In addition, metformin significantly inhibited mPTP opening and subsequent rigor contracture in both Wistar and GK cardiomyocytes subjected to oxidative stress, in a LY-sensitive manner. Conclusions We report that metformin given at the time of reperfusion reduces myocardial infarct size in both the non-diabetic and diabetic heart and this protective effect is mediated through PI3K and is associated with Akt phosphorylation. Furthermore, cardioprotection appears to be executed through a PI3K-mediated inhibition of mPTP opening. These findings may explain in part the cardioprotective properties of metformin observed in clinical studies of diabetic patients. Returned for 1. Revision: 14 May 2007 1. Revision received: 18 May 2007 Returned for 2. Revision: 4 June 2007 2. Revision received: 23 October 2007     

The effects of the receptor for advanced glycation end products (RAGE) on bone metabolism under physiological and diabetic conditions

It has been reported that AGEs and the receptor for AGEs (RAGEs) have been linked to the pathogenesis of diabetic microangiopathy. However, the relationship between RAGE and alteration in bone metabolism is unclear. Therefore, in order to determine the role of RAGE in bone metabolism, we investigated the effects of RAGE deletion on bone metabolism under physiological and diabetic conditions using RAGE knockout mice (RAGE-KO). Eight-week-old male RAGE-KO and wild-type littermates (WT) were intraperitoneally injected with either streptozotocin or vehicle. Mice were classified into four groups: (1) nondiabetic WT; (2) nondiabetic RAGE-KO; (3) diabetic WT; and (4) diabetic RAGE-KO. After 12 weeks of streptozotocin or vehicle treatment, the physical properties of femora and the static and dynamic parameters of bone histomorphometry of tibiae were assessed. The deletion of RAGE affected neither body weights nor hemoglobin A1c levels. RAGE deletion resulted in increased bone mineral density due to decreased osteoclast function under physiological conditions that is no accumulation of AGEs. In contrast, lacking RAGE did not affect the alteration in bone metabolism under diabetic conditions, suggesting that AGEs-RAGE interaction may not be involved in the pathogenesis of diabetic osteopenia, although RAGE plays a crucial role in bone metabolism.     

Accumulation of tissue advanced glycation end products correlated with glucose exposure dose and associated with cardiovascular morbidity in patients on peritoneal dialysis

ObjectivesAccumulation of tissue advanced glycation end products (AGEs) is a marker of cumulative glycemic and/or oxidative stress. Cutaneous AGEs levels measured by skin autofluorescence correlate well with cardiovascular outcomes in diabetes and hemodialysis (HD) patients. The present study aimed to compare tissue AGEs levels with peritoneal dialysis (PD) and HD patients and to evaluate the relationship between skin autofluorescence and cardiovascular morbidity in patients on PD.MethodsA total of 2388 maintenance dialysis patients (613 PD and 1775 HD) were enrolled in this cross-sectional study. Skin autofluorescence was measured non-invasively with an autofluorescence reader. Cardiovascular morbidity was defined as clinically diagnosed ischemic heart disease, heart failure, stroke or peripheral vascular disease from initiation of dialysis.ResultsMore than 90% of patients on both PD and HD had met current dialysis adequacy targets. Compared to HD group, PD patients receiving conventional glucose-containing dialyzate had significantly higher skin autofluorescence values in each category of age and dialysis duration, irrespective of the presence or absence of diabetes. In PD patients, skin autofluorescence values were strongly correlated with the duration of PD and glucose exposure dose and independently associated with cardiovascular morbidity. Multivariate analysis revealed that glucose exposure dose and skin autofluorescence were the strongest risk factors for cardiovascular morbidity in PD patients after adjustment by age, gender, and other classic- or uremic-related risk factors.ConclusionsAccumulation of tissue AGEs provides a potential link between PD exposure of metabolic stress and progression of cardiovascular disease in patients on PD.     

Diminished penile expression of vascular endothelial growth factor and its receptors at the insulin-resistant stage of a type II diabetic rat model: a possible cause for erectile dysfunction in diabetes

Erectile dysfunction (ED) is commonly experienced in men with diabetes mellitus. Vascular endothelial growth factor (VEGF) has been extensively documented for its pathogenic significance in different complications of diabetes. We hypothesized that expressions of VEGF, its receptors and its signaling pathway Akt may be drastically altered in diabetic penile tIssues and their alterations may modulate penile expression of the molecules that are believed to play a role in diabetic ED. Otsuka Long-Evans Fatty (OLETF) rats, a type II (non-insulin-dependent) diabetes mellitus, were used at the insulin-resistant stage of type II diabetes (20 weeks of age). We determined protein and mRNA expressions of VEGF, its receptors, Akt, nitric oxide synthase isoforms, and apoptosis-related molecules in the penis using immunohistochemistry, Western blotting, in situ hybridization, and real-time quantitative PCR analyses. The penile sections were also submitted to the Tdt-mediated dUTP nick end labeling assay for apoptosis. OLETF rats showed marked reductions in penile expression of VEGF, its two receptors and Akt. In OLETF rat penises, endothelial and neuronal nitric oxide synthase isoforms were expressed less abundantly. Furthermore, while anti-apoptotic markers, Bcl-2 and phosphorylated Bad, were down-regulated, pro-apoptotic markers, active caspase-3 and Bax, were up-regulated, resulting in the appearance of apoptotic cells in the penile tIssues of OLETF rats. The VEGF signaling system would work less well in diabetic penile tIssues as a result of the reduced expression, leading to diminished endothelial production of nitric oxide and apoptosis-related erectile tIssue damage. We propose that the abnormalities of the VEGF signaling system in the penis may play a role in the pathophysiology of diabetic ED.     

Role of advanced glycation end product (AGE)-induced receptor (RAGE) expression in diabetic vascular complications

AimsVascular complications are the major causes of morbidity and mortality in diabetic subjects. Interaction of advanced glycation end products (AGEs) with their receptor (RAGE) induces signal transduction that culminates in vascular complications. Therefore, in the present study we investigated the dependence of RAGE expression on circulating AGEs and evaluated the outcome of AGE–RAGE interaction by the oxidative stress and nature of vascular complications in type 2 diabetes mellitus (T2DM) patients.MethodsRAGE expression was determined by quantitative real-time PCR and western blotting, serum AGEs were estimated by ELISA and spectrofluorometry and oxidative stress markers namely protein carbonyl (PCO), advanced oxidation protein products (AOPP) and lipid peroxidation (MDA) were assayed spectrophotometerically in 75 T2DM patients (DM without vascular complication n = 25; DM with microvascular complications n = 25; DM with macrovascular complications n = 25) and 25 healthy controls.ResultsSerum AGE level was significantly higher in diabetic patients having vascular complications as compared to T2DM without complications (p < 0.01). RAGE m-RNA expression level in PBMCs assayed by quantitative real time PCR was four times higher in diabetic subjects without vascular complications while DM patients having microvascular and macrovascular complications showed 12 fold and 8 fold higher RAGE m-RNA expression respectively compared to healthy controls. Circulating AGE level showed significant positive correlation with RAGE m-RNA expression and oxidative stress markers.ConclusionAGE-mediated exacerbation of RAGE expression may contribute to oxidative stress generation that plays a key role in pathogenesis of vascular complications in diabetes.