Hyperglycemia inhibits endothelial nitric oxide synthase activity by posttranslational modification at the Akt site

Association between fasting blood glucose and outcomes and mortality in acute ischaemic stroke patients with diabetes mellitus: a retrospective observational study in Wuhan, China

OBJECTIVE

To evaluate the predictive value of fasting blood glucose (FBG) on unfavourable outcomes and mortality in diabetes mellitus (DM) patients after acute ischaemic stroke (AIS).

STUDY DESIGN

A hospital-based observational cohort study was conducted. Clinical data, including sex, age, body mass index, vascular risk factors and systolic/diastolic blood pressure, were routinely collected. National Institutes of Health Stroke Scale score was used to assess stroke severity on admission. FBG was determined on the first day after fasting for at least 8 hours. The modified Rankin Scale was used to assess functional outcome at 90 days: 3-6, unfavourable outcome and 6, death.

SETTING

Renmin Hospital of Wuhan University, Wuhan, China.

PARTICIPANTS

Patients who had AIS with DM, who were consecutively admitted within 24 hours of onset from January 2018 to June 2019.

RESULTS

For the 568 patients, the median age was 65 years (IQR, 55-74 years). There were 377 (66.4%) men. The median FBG values were 7.37 mmol/L (IQR, 5.99-10.10 mmol/L), and the median glycated haemoglobin (HbA1c) values were 6.6 (IQR, 5.8-8.3). Multivariable logistic and Cox regression analysis of confounding factors showed that FBG at the time of admission was an independent predictor of unfavourable outcome (OR, 1.25 (1.14-1.37); p<0.0001) and mortality (HR, 1.10 (1.03-1.15); p<0.05) at 90 days after onset. Time to death was analysed by Kaplan-Meier curves based on FBG quartiles. The risk of death in the two highest quartile groups (FBG, 7.38-10.10 mmol/L; FBG, ≥10.11 mmol/L) was significantly higher than that in the two lowest quartile groups (FBG, ≤6.00 mmol/L; FBG, 6.01-7.37 mmol/L; p<0.0001).

CONCLUSIONS

Higher FBG levels are associated with unfavourable outcomes and mortality in Chinese patients who had AIS with DM. Our data contribute to the knowledge regarding the relationship between FBG and prognosis in patients with DM who had AIS.

Macrovascular Complications in Patients with Diabetes and Prediabetes

Diabetes is a significant health problem worldwide, and its association with cardiovascular disease (CVD) was reported in several studies. Hyperglycemia and insulin resistance seen in diabetes and prediabetes lead to an increase in reactive oxygen species, which triggers intracellular molecular signaling. The resulting prothrombotic state and increase in inflammatory mediators expedite atherosclerotic changes and the development of macrovascular complications. Individuals with diabetes or prediabetes have a higher risk of developing myocardial infarction, stroke, and peripheral artery disease. However, no significant difference in cardiovascular morbidity has been observed with tight glycemic control despite a reduction in some CVD outcomes, and the risk of adverse outcomes such as hypoglycemia was increased. Recently, some GLP-1 receptor agonists and SGLT-2 inhibitors have been shown to reduce cardiovascular events and mortality. In this review we give an overview of the risk and pathogenesis of cardiovascular disease among diabetic and prediabetic patients, as well as the implication of recent changes in diabetes management.

Oxidative stress and metabolic pathologies: from an adipocentric point of view

Oxidative stress plays a pathological role in the development of various diseases including diabetes, atherosclerosis, or cancer. Systemic oxidative stress results from an imbalance between oxidants derivatives production and antioxidants defenses. Reactive oxygen species (ROS) are generally considered to be detrimental for health. However, evidences have been provided that they can act as second messengers in adaptative responses to stress. Obesity represents a major risk factor for deleterious associated pathologies such as type 2 diabetes, liver, and coronary heart diseases. Many evidences regarding obesity-induced oxidative stress accumulated over the past few years based on established correlations of biomarkers or end-products of free-radical-mediated oxidative stress with body mass index. The hypothesis that oxidative stress plays a significant role in the development of metabolic disorders, especially insulin-resistance state, is supported by several studies where treatments reducing ROS production reverse metabolic alterations, notably through improvement of insulin sensitivity, hyperlipidemia, or hepatic steatosis. In this review, we will develop the mechanistic links between oxidative stress generated by adipose tissue in the context of obesity and its impact on metabolic complications development. We will also attempt to discuss potential therapeutic approaches targeting obesity-associated oxidative stress in order to prevent associated-metabolic complications.

Podocyte-specific VEGF-a gain of function induces nodular glomerulosclerosis in eNOS null mice

VEGF-A and nitric oxide are essential for glomerular filtration barrier homeostasis and are dysregulated in diabetic nephropathy. Here, we examined the effect of excess podocyte VEGF-A on the renal phenotype of endothelial nitric oxide synthase (eNOS) knockout mice. Podocyte-specific VEGF(164) gain of function in eNOS(-/-) mice resulted in nodular glomerulosclerosis, mesangiolysis, microaneurysms, and arteriolar hyalinosis associated with massive proteinuria and renal failure in the absence of diabetic milieu or hypertension. In contrast, podocyte-specific VEGF(164) gain of function in wild-type mice resulted in less pronounced albuminuria and increased creatinine clearance. Transmission electron microscopy revealed glomerular basement membrane thickening and podocyte effacement in eNOS(-/-) mice with podocyte-specific VEGF(164) gain of function. Furthermore, glomerular nodules overexpressed collagen IV and laminin extensively. Biotin-switch and proximity ligation assays demonstrated that podocyte-specific VEGF(164) gain of function decreased glomerular S-nitrosylation of laminin in eNOS(-/-) mice. In addition, treatment with VEGF-A decreased S-nitrosylated laminin in cultured podocytes. Collectively, these data indicate that excess glomerular VEGF-A and eNOS deficiency is necessary and sufficient to induce Kimmelstiel-Wilson-like nodular glomerulosclerosis in mice through a process that involves deposition of laminin and collagen IV and de-nitrosylation of laminin.

O-GlcNAc cycling: a link between metabolism and chronic disease

To maintain homeostasis under variable nutrient conditions, cells rapidly and robustly respond to fluctuations through adaptable signaling networks. Evidence suggests that the O-linked N-acetylglucosamine (O-GlcNAc) posttranslational modification of serine and threonine residues functions as a critical regulator of intracellular signaling cascades in response to nutrient changes. O-GlcNAc is a highly regulated, reversible modification poised to integrate metabolic signals and acts to influence many cellular processes, including cellular signaling, protein stability, and transcription. This review describes the role O-GlcNAc plays in governing both integrated cellular processes and the activity of individual proteins in response to nutrient levels. Moreover, we discuss the ways in which cellular changes in O-GlcNAc status may be linked to chronic diseases such as type 2 diabetes, neurodegeneration, and cancers, providing a unique window through which to identify and treat disease conditions.

Propyl gallate plays a nephroprotective role in early stage of diabetic nephropathy associated with suppression of glomerular endothelial cell proliferation and angiogenesis

There is growing evidence suggesting that glomerular endothelial cell proliferation and angiogenesis may be responsible for the pathophysiological events in the early stage of diabetic nephropathy. This study was designed to investigate the factors related to glomerular endothelial cell proliferation and glomerular angiogenesis and assess the effect of propyl gallate on preventing these disorders in diabetic rats. We found that glomerular hypertrophy, glomerular mesangial matrix expansion, and albuminuria were significantly increased in DN rats. CD31+ endothelial cells significantly increased in glomerulus of diabetic rats. Double immunofluorescence staining showed some structurally defective vasculus tubes in glomerulus. Real-time PCR and western blot demonstrated the glomerular eNOS expression remained at the same level, while remarkable decreased NO productions and suppressed eNOS activities were observed in diabetic rats. Treatment with propyl gallate improved glomerular pathological changes, reduced endothelial cell proliferation, decreased albuminuria, and restored eNOS activity, but did not alter eNOS expression. These data suggest that endothelial cell proliferation and immature angiogenesis may be the contributors to progression of DN. Propyl gallate is a potential novel therapeutic agent on prevention of diabetic nephropathy.

Diabetic peripheral neuropathy: should a chaperone accompany our therapeutic approach?

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes that is associated with axonal atrophy, demyelination, blunted regenerative potential, and loss of peripheral nerve fibers. The development and progression of DPN is due in large part to hyperglycemia but is also affected by insulin deficiency and dyslipidemia. Although numerous biochemical mechanisms contribute to DPN, increased oxidative/nitrosative stress and mitochondrial dysfunction seem intimately associated with nerve dysfunction and diminished regenerative capacity. Despite advances in understanding the etiology of DPN, few approved therapies exist for the pharmacological management of painful or insensate DPN. Therefore, identifying novel therapeutic strategies remains paramount. Because DPN does not develop with either temporal or biochemical uniformity, its therapeutic management may benefit from a multifaceted approach that inhibits pathogenic mechanisms, manages inflammation, and increases cytoprotective responses. Finally, exercise has long been recognized as a part of the therapeutic management of diabetes, and exercise can delay and/or prevent the development of painful DPN. This review presents an overview of existing therapies that target both causal and symptomatic features of DPN and discusses the role of up-regulating cytoprotective pathways via modulating molecular chaperones. Overall, it may be unrealistic to expect that a single pharmacologic entity will suffice to ameliorate the multiple symptoms of human DPN. Thus, combinatorial therapies that target causal mechanisms and enhance endogenous reparative capacity may enhance nerve function and improve regeneration in DPN if they converge to decrease oxidative stress, improve mitochondrial bioenergetics, and increase response to trophic factors.

Telmisartan improves kidney function through inhibition of the oxidative phosphorylation pathway in diabetic rats

Telmisartan provides renal benefit at all stages of the renal continuum in patients with type 2 diabetes mellitus. This research is to investigate the effect of telmisartan on kidney function in diabetic rats and to identify the underlying molecular mechanisms. Diabetic rats were divided into vehicle group, low dosage (TeL) group, and high dosage of telmisartan (TeH) group. We performed Illumina RatRef-12 Expression BeadChip gene array experiments. We found 3-months of treatment with telmisartan significantly decreased 24-h urinary albumin, serum creatinine, blood urea nitrogen, and increased creatinine clearance rate. Kidney hypertrophy and glomerular mesangial matrix expansion were ameliorated. The glomeruli from the TeH group had 1541 genes with significantly changed expression (554 increased, 987 decreased). DAVID (Database for annotation, visualization and Integrated discovery) analyses showed that the most enriched term was 'mitochondrion' (Gene Ontology (GO:0005739)) in all 67 GO functional categories. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that all differentially expressed genes included seven KEGG pathways. Of those pathways, four are closely related to the oxidative phosphorylation pathway. Quantitative real-time PCR verified that the H+ transporting mitochondrial F1 complex, beta subunit (Atp5b), cytochrome c oxidase subunit VIc (Cox6c), and NADH dehydrogenase (ubiquinone) Fe-S protein 3 (Ndufs3) were significantly downregulated both in TeL and TeH groups, while nephrosis 1 homolog (Nphs1) and nephrosis 2 homolog (Nphs2) were significantly upregulated. The increased expression of malonaldehyde and NDUFS3 in the glomeruli of diabetic rats was attenuated by telmisartan. The other significantly changed pathway we found was the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Our data suggest that telmisartan can improve kidney function in diabetic rats. The mechanism may be involved in mitochondrion oxidative phosphorylation, the PPAR-γ pathway, and the slit diaphragm.

Mitochondrial dysfunction and mitochondrial DNA mutations in atherosclerotic complications in diabetes

Mitochondrial DNA (mtDNA) is particularly prone to oxidation due to the lack of histones and a deficient mismatch repair system. This explains an increased mutation rate of mtDNA that results in heteroplasmy, e.g., the coexistence of the mutant and wild-type mtDNA molecules within the same mitochondrion. In diabetes mellitus, glycotoxicity, advanced oxidative stress, collagen cross-linking, and accumulation of lipid peroxides in foam macrophage cells and arterial wall cells may significantly decrease the mutation threshold required for mitochondrial dysfunction, which in turn further contributes to the oxidative damage of the diabetic vascular wall, endothelial dysfunction, and atherosclerosis.

The role of glucosamine-induced ER stress in diabetic atherogenesis

Cardiovascular disease (CVD) is the major cause of mortality in individuals with diabetes mellitus. However the molecular and cellular mechanisms that predispose individuals with diabetes to the development and progression of atherosclerosis, the underlying cause of most CVD, are not understood. This paper summarizes the current state of our knowledge of pathways and mechanisms that may link diabetes and hyperglycemia to atherogenesis. We highlight recent work from our lab, and others', that supports a role for ER stress in these processes. The continued investigation of existing pathways, linking hyperglycemia and diabetes mellitus to atherosclerosis, and the identification of novel mechanisms and targets will be important to the development of new and effective antiatherosclerotic therapies tailored to individuals with diabetes.

Hyperglycemia and endothelial dysfunction in atherosclerosis: lessons from type 1 diabetes

A clear relationship between diabetes and cardiovascular disease has been established for decades. Despite this, the mechanisms by which diabetes contributes to plaque formation remain in question. Some of this confusion derives from studies in type 2 diabetics where multiple components of metabolic syndrome show proatherosclerotic effects independent of underlying diabetes. However, the hyperglycemia that defines the diabetic condition independently affects atherogenesis in cell culture systems, animal models, and human patients. Endothelial cell biology plays a central role in atherosclerotic plaque formation regulating vessel permeability, inflammation, and thrombosis. The current paper highlights the mechanisms by which hyperglycemia affects endothelial cell biology to promote plaque formation.

Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by inappropriate hyperglycemia due to lack of or resistance to insulin. Patients with DM are frequently afflicted with ischemic vascular disease or wound healing defect. It is well known that type 2 DM causes amplification of the atherosclerotic process, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. These complications ultimately lead to impairment of neovascularization and diabetic wound healing. Therapeutic angiogenesis remains an attractive treatment modality for chronic ischemic disorders including PAD and/or diabetic wound healing. Many experimental studies have identified better approaches for diabetic cardiovascular complications, however, successful clinical translation has been limited possibly due to the narrow therapeutic targets of these agents or the lack of rigorous evaluation of pathology and therapeutic mechanisms in experimental models of disease. This paper discusses the current body of evidence identifying endothelial dysfunction and impaired angiogenesis during diabetes.

Cross talk between O-GlcNAcylation and phosphorylation: roles in signaling, transcription, and chronic disease

O-GlcNAcylation is the addition of β-D-N-acetylglucosamine to serine or threonine residues of nuclear and cytoplasmic proteins. O-linked N-acetylglucosamine (O-GlcNAc) was not discovered until the early 1980s and still remains difficult to detect and quantify. Nonetheless, O-GlcNAc is highly abundant and cycles on proteins with a timescale similar to protein phosphorylation. O-GlcNAc occurs in organisms ranging from some bacteria to protozoans and metazoans, including plants and nematodes up the evolutionary tree to man. O-GlcNAcylation is mostly on nuclear proteins, but it occurs in all intracellular compartments, including mitochondria. Recent glycomic analyses have shown that O-GlcNAcylation has surprisingly extensive cross talk with phosphorylation, where it serves as a nutrient/stress sensor to modulate signaling, transcription, and cytoskeletal functions. Abnormal amounts of O-GlcNAcylation underlie the etiology of insulin resistance and glucose toxicity in diabetes, and this type of modification plays a direct role in neurodegenerative disease. Many oncogenic proteins and tumor suppressor proteins are also regulated by O-GlcNAcylation. Current data justify extensive efforts toward a better understanding of this invisible, yet abundant, modification. As tools for the study of O-GlcNAc become more facile and available, exponential growth in this area of research will eventually take place.

[O-GlcNAc glycosylation and regulation of cell signaling]

O-GlcNAcylation corresponds to the addition of N-acetylglucosamine on serine and threonine residues of cytosolic and nuclear proteins. O-GlcNAcylation is a dynamic post-translational modification, analogous to phosphorylation, that regulates the stability, the activity or the sub-cellular localisation of proteins. This reversible modification depends on the availability of glucose and therefore constitutes a powerful means by which cellular activities are regulated according to the nutritional environment of the cell. O-GlcNAcylation has been implicated in important human pathologies including Alzheimer disease and type-2 diabetes. Only two enzymes, OGT and O-GlcNAcase, control the O-GlcNAcylation level on proteins, and thereby regulate signaling pathways. Several lines of evidence indicate that OGT attenuates insulin signal by O-GlcNAcylation of proteins involved in proximal and distal steps in the signaling pathway. This negative feedback may be exacerbated when cells are exposed to elevated glucose concentrations as observed in diabetic patients, and could thereby contribute to insulin resistance and worsening of hyperglycaemia. double dagger.

Polymorphisms of eNOS gene are associated with diabetic nephropathy: a meta-analysis

The aim of the current study is to assess the association between the alleles of endothelial nitric oxide synthases (eNOS) gene 4b/a, G894T, T786C polymorphisms and diabetic nephropathy (DN) through meta-analyses. We also performed a subgroup analysis based on ethnicity (Caucasians, East-Asian and other populations). A total of 3793 patients (DN) and 3161 controls (diabetes without nephropathy) for 4b/a, 2654 patients and 1993 controls for G894T and 1348 patients and 1175 controls for T786C were included in our analysis. Overall, allele contrast (4a versus 4b) of 4b/a polymorphism produced significant results in the global population [random effects model (RE) odds ratio (OR) = 1.33; 95% confidence interval (CI) = 1.10-1.61, P = 0.003] and East-Asian population (RE OR = 1.68; 95% CI = 1.23-2.30, P = 0.001), but not in the Caucasian population. In allele contrast of G894T, an obvious significant result was observed in the East-Asian population [fixed effects model OR = 1.69; 95% CI = 1.37-2.08, P < 0.0001], but not in the Caucasian population. Sensitivity analyses generated similar results to those of the primary analyses. The evidence accumulated suggested that 4b/a and G894T polymorphisms in the eNOS gene were associated with susceptibility to DN in Asian populations, but not in Caucasian populations.

Inhibition of phospholamban phosphorylation by O-GlcNAcylation: implications for diabetic cardiomyopathy

Cardiac-type sarco(endo)plasmic reticulum Ca(2)-ATPase (SERCA2a) plays a major role in cardiac muscle contractility. Phospholamban (PLN) regulates the function of SERCA2a via its Ser(16)-phosphorylation. Since it has been proposed that the Ser/Thr residues on cytoplasmic and nuclear proteins are modified by O-linked N-acetylglucosamine (O-GlcNAc), we examined the effect of O-GlcNAcylation on PLN function in rat adult cardiomyocytes. Studies using enzymatic labeling and co-immunoprecipitation of wild type and a series of mutants of PLN showed that PLN was O-GlcNAcylated and Ser(16) of PLN might be the site for O-GlcNAcylation. In cardiomyocytes treated with O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc), the O-GlcNAcylation was significantly increased compared to non-treated cells. Simultaneously, Ser(16)-phosphorylation of PLN was reduced. In Chinese hamster ovary cells where PLN cDNA and O-GlcNAc transferase siRNA were co-transfected, the Ser(16)-phosphorylation of PLN was significantly increased compared to controls. The same results were observed in heart homogenates from diabetic rats. In a co-immunoprecipitation of PLN with SERCA2a, the physical interaction between the two proteins was increased in PUGNAc-treated cardiomyocytes. Unlike non-treated cells, the activity of SERCA2a and the profiles of calcium transients in PUGNAc-treated cardiomyocytes were not significantly changed even after treatment with catecholamine. These data suggest that PLN is O-GlcNAcylated to induce the inhibition of its phosphorylation, which correlates to the deterioration of cardiac function. This might define a novel mechanism by which PLN regulation of SERCA2a is altered under conditions where O-GlcNAcylation is increased, such as those occurring in diabetes.

Aldose reductase deficiency improves Wallerian degeneration and nerve regeneration in diabetic thy1-YFP mice

This study examined the role of aldose reductase (AR) in diabetes-associated impaired nerve regeneration using thy1-YFP (YFP) mice. Sciatic nerves of nondiabetic and streptozotocin-induced diabetic AR(+/+)YFP and AR(-/-)YFP mice were transected after 4 weeks of diabetes. Wallerian degeneration and nerve regeneration were evaluated at 1 and 2 weeks postaxotomy by fluorescence microscopy. Motor nerve conduction velocity recovery and regenerating nerve morphometric parameters were determined at 10 and 20 weeks, respectively. There was no difference in the extent of Wallerian degeneration, size of regenerating stump, motor nerve conduction velocity recovery, or caliber of regenerating fibers between nondiabetic AR(+/+)YFP and AR(-/-)YFP mice. In diabetic AR(+/+)YFP mice, Wallerian degeneration was delayed, associated with slower macrophage invasion and abnormal vascularization. Those mice had smaller regenerating stumps, slower motor nerve conduction velocity, and smaller regenerating fibers compared with nondiabetic mice. These features of impaired nerve regeneration were largely attenuated in diabetic AR(-/-)YFP mice. Retarded macrophage invasion and vascularization associated with Wallerian degeneration were normalized in diabetic AR(-/-)YFP mice. These results indicate that AR plays an important role in diabetes-associated impaired nerve regeneration, in part by affecting vascularization and macrophage invasion during Wallerian degeneration. The thy1-YFP mice are valuable tools for further investigation of the mechanism of diabetes-associated nerve regeneration.

Effects of the Cellcultured Acanthopanax senticosus Extract on Antioxidative Defense System and Membrane Fluidity in the Liver of Type 2 Diabetes Mouse

This study examined the effect of cellcultured Acanthopanax senticosus (A. senticosus) extract on the antioxidative defense system, oxidative stress and cell membrane fluidity in the liver of type 2 diabetes in the C57BL/6J mouse as an animal which is genetically prone to develop insulin resistance and obesity/diabetes. C57BL/6J mice were randomly divided, control diet (N-C), high fat diet (DM-C), control diet plus A. senticosus extract (N-CASM), and high fat diet plus A. senticosus extract (DM-CASM). The mice were orally administered an A. senticosus extract (0.5 g/kg body weight) in the N-CASM and DM-CASM groups once a day for 12 weeks, and distilled water in the N-C and DM-C groups. Cellcultured A. senticosus extract was found to be excellent for strengthening the antioxidative defense system, reducing the generation of reactive oxygen species (ROS) and damaging oxidative substances, and maintaing membrane fluidity (MF) in the liver of type 2 diabetes mouse.

Phosphoinositide 3-kinase signalling in the vascular system

Phosphoinositide 3-kinases (PI3Ks) are protein and lipid kinases activated by different classes of membrane receptors, including G-protein coupled and tyrosine kinase receptors. Several lines of evidence have uncovered specific roles for distinct PI3K isoforms in the vascular system in both physiology and disease. The present review will summarize and discuss the most recent advances regarding PI3K-Akt signalling in endothelial cells, vascular smooth muscle cells, platelets, and inflammatory cells involved in the atherosclerotic process. Of interest, the development of novel isoform-selective PI3K inhibitor drugs offers a unique opportunity to selectively and differentially target PI3K-driven pathways in the vascular system and may give rise to new strategies for the treatment of cardiovascular diseases.

Arterial stiffness and cognition in elderly persons with impaired glucose tolerance and microalbuminuria

BACKGROUND

Cognitive decline that occurs frequently in impaired glucose tolerance (IGT) may be largely due to endothelial dysfunction. We assessed: (i) the relationships between impact of urinary albumin excretion rate (UAER), as marker of generalized endothelial dysfunction, and cognition; (ii) if cognitive decline could be explained by arterial stiffening using pulse wave velocity (PWV).

METHODS

One hundred forty older patients (age range 70-85 years) with IGT and no dementia were selected. Patients were classified according to 24-hour UAER: normoalbuminuric (NA) (UAER<20 microg/min) or microalbuminuric (MA) (UAER between 20 and 199 microg/min). Cognitive abilities were assessed by the Mini-Mental State Examination (MMSE) and a composite score of executive and attention functioning (CCS) at baseline and after 12 months of follow-up.

RESULTS

In MA patients (n=80), increased UAERs correlated with intimal media thickness (IMT) (r=0.268; p=02) and PWV (r=0.310; p=004). In the same group, increased UAERs were correlated with MMSE and CCS even after adjusting for age and mean arterial blood pressure (MABP). After adding PWV, the associations among UAERs, MMSE, and CCS were no longer significant. In MA patients, PWV correlated with IMT, MMSE, and CCS. In NA patients, no significant correlations were found among UAERs, MMSE, and CCS. At follow-up, baseline UAERs predicted an approximately 20% risk of poor cognition (according to MMSE and CCS) after adjusting for confounders. After adding PWV, UAERs no longer predicted cognitive performance.

CONCLUSIONS

MA older persons with IGT showed a decline in cognition performance that may be partially explained by arterial stiffness.

Overexpression of calmodulin in pancreatic beta cells induces diabetic nephropathy

Recently, endothelial dysfunction induced by an uncoupling of vascular endothelial growth factor (VEGF) and nitric oxide has been implicated in the pathogenesis of diabetic nephropathy (DN). Investigating the pathogenesis of DN has been limited, however, because of the lack of animal models that mimic the human disease. In this report, pancreatic beta cell-specific calmodulin-overexpressing transgenic (CaMTg) mice, a potential new model of DN, are characterized with particular emphasis on VEGF and related molecules. CaMTg mice developed hyperglycemia at 3 wk and persistent proteinuria by 3 mo. Morphometric analysis showed considerable increases in the glomerular and mesangial areas with deposition of type IV collagen. Moreover, the pathologic hallmarks of human DN (mesangiolysis, Kimmelstiel-Wilson-like nodular lesions, exudative lesions, and hyalinosis of afferent and efferent arteries with neovascularization) were observed. In addition, increased VEGF expression was associated with an increased number of peritubular capillaries. Expression of endothelial nitric oxidase synthase was reduced and that of VEGF was markedly elevated in CaMTg mice kidney compared with nontransgenic mice. No differences in VEGF receptor-1 or VEGF receptor-2 expression were observed between CaMTg mice and nontransgenic kidneys. In summary, CaMTg mice develop most of the distinguishing lesions of human DN, and the elevated VEGF expression in the setting of diminished endothelial nitric oxide synthase expression may lead to endothelial proliferation and dysfunction. This model may prove useful in the study of the pathogenesis and treatment of DN.

Evaluation of the hemodialysis-induced changes in plasma glucose and insulin concentrations in diabetic patients: comparison between the hemodialysis and non-hemodialysis days

Often, well-controlled plasma glucose levels but high hemoglobin A(1c) levels have been observed at prehemodialysis in diabetic patients. The present study aimed to evaluate this difference between fasting glucose and hemoglobin A(1c) levels. We investigated hemodialysis-induced alterations in the plasma glucose and insulin levels. Based on their glycemic control level at inclusion, subjects were divided into poor control (hemoglobin A(1c)> or =7.0%; n = 8) and good control groups (hemoglobin A(1c) <7.0%; n = 8). We measured their plasma glucose and immunoreactive insulin levels at arterial and venous sites at three time points (predialysis, 2 h and 4 h after starting dialysis); we also studied their daily plasma glucose profiles. In both the groups, the V-site plasma glucose and immunoreactive insulin levels were significantly decreased compared to the A-site levels at each time point. The A-site plasma immunoreactive insulin levels 4 h after dialysis were significantly decreased compared to the levels 2 h after dialysis. Comparison between hemodialysis and non-hemodialysis days revealed that the plasma glucose levels decreased significantly during hemodialysis and significantly increased between predinner and bedtime in the poor control group. The present study confirmed that hemodialysis decreased the plasma glucose and immunoreactive insulin levels. In the poor control group, hyperglycemia appeared posthemodialysis; this was attributed partly to the hemodialysis-induced decrease in the plasma immunoreactive insulin levels. These results suggest that although diet therapy has been effective in diabetic hemodialysis patients, hemodialysis caused hyperglycemia by absolute or relative plasma immunoreactive insulin deficiency.

17Beta-oestradiol partially attenuates the inhibition of nitric oxide synthase-3 by advanced glycation end-products in human platelets

1. Diabetes mellitus predisposes to and female sex protects against arterial thrombosis. The aim of the present study was to determine whether advanced glycation end-products (AGE), which accumulate in diabetes, impair platelet function through effects on platelet nitric oxide (NO) generation and whether this can be prevented by 17beta-oestradiol. 2. Aggregation responses of human platelet-rich plasma to ADP were determined in the absence or presence of 200 mg/L AGE-modified albumin (AGE-albumin), 10(-5) mol/L 17beta-oestradiol and 10(-5) mol/L ICI 182 780 (the pure oestrogen receptor antagonist). 3. Intraplatelet cGMP, an index of bioactive NO, was measured by radioimmunoassay and expression of nitric oxide synthase (NOS)-3, phosphoserine-1177-NOS-3 and O-glycosylated NOS-3 was quantified by western blotting in response to these same treatments. 4. Advanced glycation end-products-albumin increased platelet aggregatory responses to ADP. This increase was largely prevented by 17beta-oestradiol. Advanced glycation end-products-albumin decreased and 17beta-oestradiol increased intraplatelet NO-attributable cGMP and 17beta-oestradiol attenuated the AGE-albumin-induced decrease in NO-attributable cGMP. Despite no effect on NOS-3 expression, AGE-albumin decreased and 17beta-oestradiol increased phosphoserine-1177-NOS-3 and 17beta-oestradiol largely prevented the decrease in phosphoserine-1177-NOS-3 induced by AGE-albumin. Alone, AGE-albumin increased O-glycosylation of NOS-3 by N-acetylglucosamine, an effect largely inhibited by 17beta-oestradiol. 5. In conclusion, AGE-albumin inhibits platelet NO biosynthesis through effects on serine phosphorylation and O-glycosylation of platelet NOS-3 and this may explain, at least in part, the increase in platelet aggregability induced by AGE-albumin. These effects of AGE-albumin are largely prevented by 17beta-oestradiol. These actions may contribute to the effects of diabetes and sex on arterial thrombosis in vivo.

Plasma Insulin is Removed by Hemodialysis: Evaluation of the Relation Between Plasma Insulin and Glucose by Using a Dialysate With or Without Glucose

The aim of the present study was to evaluate the alteration in plasma immunoreactive insulin (IRI) and glucose concentrations due to hemodialysis (HD) treatment by using a dialysate with or without glucose in HD patients. We divided the patients into three groups: non-diabetic patients (n-DM group), well-controlled diabetic patients (HbA(1c) <7.0% [w-DM group]), and poorly-controlled diabetic patients (HbA(1c) > or = 7.0% [p-DM group]). Using a dialysate with a glucose concentration of 100 mg/dL (glu(+)-dialysate) and a glucose-free dialysate (glu(-)-dialysate), we studied the daily profiles of plasma glucose in the three groups. We measured the levels of plasma glucose and IRI at three time points (predialysis and 2 h and 4 h after the initiation of dialysis) at pre(A) and postdialyzer (V) sites in HD patients. There was a significant increase in the daily profiles of the plasma glucose level from the time before dinner until bedtime in both the w-DM and p-DM groups, when comparing the values on an HD day with those on a non-HD day. In the p-DM group, the use of the glu(-)-dialysate resulted in a significant hyperglycemia in the evening hours when compared with the use of the glu(+)-dialysate. In the DM group, the use of the glu(+)-dialysate resulted in a significant decrease in the plasma glucose and IRI levels during HD. However, in the n-DM group, there was no difference in the plasma glucose levels during HD. On the other hand, the use of a glucose-free dialysate led to a significant decrease in the plasma glucose and IRI levels during HD in all groups. The plasma IRI levels decreased significantly between the A and V sites at each point in all groups irrespective of the glucose concentration of the dialysate. The present study confirmed that the concentration of not only glucose but also IRI had decreased during the passage of the plasma through the dialyzer. In HD patients with diabetes, the glucose content of the hemodialysis solution plays an important role in preventing acute hypoglycemia and hyperglycemia on HD days.

Atherosclerosis in diabetes and insulin resistance

Atherosclerosis and cardiovascular disease are the major causes of morbidity and mortality in patients with diabetes and those with insulin resistance and the metabolic syndrome. Both conditions profoundly accelerate the development of atherosclerosis and increase the morbidity and mortality of cardiovascular events. The question, therefore, is what are the molecular/biochemical mechanisms that underlie the potentiating influence of diabetes, the metabolic syndrome and/or insulin resistance on the development and progression of atherosclerosis? The following review will focus on the molecular mechanism whereby hyperglycaemia and/or hyperinsulinemia either directly or indirectly promote atherosclerosis.

Diabetic impairments in NO-mediated endothelial progenitor cell mobilization and homing are reversed by hyperoxia and SDF-1 alpha

Endothelial progenitor cells (EPCs) are essential in vasculogenesis and wound healing, but their circulating and wound level numbers are decreased in diabetes. This study aimed to determine mechanisms responsible for the diabetic defect in circulating and wound EPCs. Since mobilization of BM EPCs occurs via eNOS activation, we hypothesized that eNOS activation is impaired in diabetes, which results in reduced EPC mobilization. Since hyperoxia activates NOS in other tissues, we investigated whether hyperoxia restores EPC mobilization in diabetic mice through BM NOS activation. Additionally, we studied the hypothesis that impaired EPC homing in diabetes is due to decreased wound level stromal cell-derived factor-1alpha (SDF-1alpha), a chemokine that mediates EPC recruitment in ischemia. Diabetic mice showed impaired phosphorylation of BM eNOS, decreased circulating EPCs, and diminished SDF-1alpha expression in cutaneous wounds. Hyperoxia increased BM NO and circulating EPCs, effects inhibited by the NOS inhibitor N-nitro-L-arginine-methyl ester. Administration of SDF-1alpha into wounds reversed the EPC homing impairment and, with hyperoxia, synergistically enhanced EPC mobilization, homing, and wound healing. Thus, hyperoxia reversed the diabetic defect in EPC mobilization, and SDF-1alpha reversed the diabetic defect in EPC homing. The targets identified, which we believe to be novel, can significantly advance the field of diabetic wound healing.

Chemokines, cytokines, and growth factors in keratinocytes and dermal endothelial cells in the margin of chronic diabetic foot ulcers

Keratinocytes and dermal endothelial cells, excluding leukocytes that infiltrate wounds, are the main source of soluble factors regulating healing of skin ulcers. We used immunohistochemistry to analyze the expression of various chemotactic and growth factors and their receptors in the margin of diabetic foot ulcers and in normal nondiabetic foot skin. Our study found significantly elevated expression of transforming growth factor-beta1 (TGF-beta1) and type I TGF-beta receptors (TGFbetaR1), granulocyte macrophage colony-stimulating factor (GM-CSF), and epidermal growth factor (EGF) in keratinocytes in the ulcer margin (p < 0.05). Significantly increased expression of monocyte chemotactic protein-1, GM-CSF, CXCR1, and TGFbetaRI and decreased expression of interleukin (IL)-10, IL-15, and TGF-beta1 were observed in ulcer dermal endothelial cells (p < 0.05). There was a lack of up-regulation of IL-8, CCR2A, IL-10 receptor, GM-CSF receptor, platelet-derived growth factors and their receptors, vascular endothelial growth factor and its type II receptor, EGF receptor, insulin-like growth factor-1, and nitric oxide synthase-2 in both KCs and endothelial cells in the ulcer. Finally, there was a lack of up-regulation of IL-10 and IL-15 in keratinocytes and of EGF, basic fibroblast growth factor, and nitric oxide synthase-3 in endothelial cells in the ulcer margins. The enhanced expression of some factors responsible for KC behavior could suggest an unimpaired capacity of keratinocytes to reepithelialize the margin of diabetic foot ulcers. However, lack of up-regulation of some angiogenic and leukocyte chemotactic factors, associated with the reduced influx of immune cells, may account for a poor formation of granulation tissue and chronicity of ulcer epithelialization.

Antioxidants and CVD in diabetes: where do we stand now

Diabetes is an oxidative stress disorder as a result of both hyperglycemia and increased levels of free fatty acids. Oxidative stress has been implicated in the pathogenesis of diabetes-related complications, and treatment with antioxidants seemed to be a promising therapeutic option. Although animal studies and preliminary human studies were initially encouraging, subsequent human studies have failed to show a clear benefit of antioxidants, whereas some studies have even suggested that they can be potentially harmful. Therefore, treatment with antioxidants cannot be currently recommended as a therapeutic option.

17beta-estradiol antagonizes the down-regulation of endothelial nitric-oxide synthase and GTP cyclohydrolase I by high glucose: relevance to postmenopausal diabetic cardiovascular disease

In postmenopausal women, the risk of diabetic cardiovascular disease drastically increases compared with that of men or premenopausal women. However, the mechanism of this phenomenon has not yet been clarified. We hypothesized that the beneficial effects of estrogen on endothelial function may be relevant to protection against hyperglycemia-induced vascular derangement. Bovine aortic endothelial cells were incubated for 72 h in the presence and absence of the physiological concentration of 17beta-estradiol (17beta-E2) under normal and high-glucose conditions. The presence of 17beta-E2 significantly counteracted the reduction in basal nitric oxide production under high-glucose conditions. This finding was associated with the recovery of endothelial nitric-oxide synthase (eNOS) protein expression, tetrahydrobiopterin (BH4) levels, and the activity and gene expression of GTP cyclohydrolase I (GTPCH-I), a rate-limiting enzyme for BH4 synthesis. Both the gene transfer of estrogen receptor alpha using adenovirus and treatment with the protein kinase C inhibitor bisindolylmaleimide I significantly enhanced the effects of 17beta-E2 treatment under high-glucose conditions, whereas these effects were abolished by the estrogen receptor antagonist ICI 182,780 (faslodex). Transfection of small-interfering RNA targeting eNOS resulted in a marked reduction in GTPCH-I mRNA under both normal and high-glucose conditions, but this reduction was strongly reversed by 17beta-E2. These results suggest that the activation of ERalpha with 17beta-E2 can counteract high-glucose-induced down-regulation of eNOS and GTPCH-I in endothelial cells. Therefore, estrogen deficiency may result in an exaggeration of hyperglycemia-induced endothelial dysfunction, leading to the development of cardiovascular disease in postmenopausal diabetic women.

Diabetic endothelial nitric oxide synthase knockout mice develop advanced diabetic nephropathy

The pathogenesis of diabetic nephropathy remains poorly defined, and animal models that represent the human disease have been lacking. It was demonstrated recently that the severe endothelial dysfunction that accompanies a diabetic state may cause an uncoupling of the vascular endothelial growth factor (VEGF)-endothelial nitric oxide (eNO) axis, resulting in increased levels of VEGF and excessive endothelial cell proliferation. It was hypothesized further that VEGF-NO uncoupling could be a major contributory mechanism that leads to diabetic vasculopathy. For testing of this hypothesis, diabetes was induced in eNO synthase knockout mice (eNOS KO) and C57BL6 controls. Diabetic eNOS KO mice developed hypertension, albuminuria, and renal insufficiency with arteriolar hyalinosis, mesangial matrix expansion, mesangiolysis with microaneurysms, and Kimmelstiel-Wilson nodules. Glomerular and peritubular capillaries were increased with endothelial proliferation and VEGF expression. Diabetic eNOS KO mice showed increased mortality at 5 mo. All of the functional and histologic changes were improved with insulin therapy. Inhibition of eNO predisposes mice to classic diabetic nephropathy. The mechanism likely is due to VEGF-NO uncoupling with excessive endothelial cell proliferation coupled with altered autoregulation consequent to the development of preglomerular arteriolar disease. Endothelial dysfunction in human diabetes is common, secondary to effects of glucose, advanced glycation end products, C-reactive protein, uric acid, and oxidants. It was postulated that endothelial dysfunction should predict nephropathy and that correction of the dysfunction may prevent these important complications.

Respiration under control of uncoupling proteins: Clinical perspective

The term 'uncoupling protein' was originally used for the mitochondrial membrane protein UCP1, which is uniquely present in mitochondria of brown adipocytes, thermogenic cells that regulate body temperature in small rodents, hibernators and mammalian newborns. In these cells, UCP1 acts as a proton carrier activated by free fatty acids and creates a shunt between complexes of the respiratory chain and ATP-synthase resulting in a futile proton cycling and dissipation of oxidation energy as heat. Recent identification of new homologues to UCP1 expressed in brown and white adipose tissue, muscle, brain and other tissues together with the hypothesis that these novel uncoupling proteins (UCPs) may regulate thermogenesis and/or fatty acid metabolism and furthermore may protect against free radical oxygen species production have generated considerable optimism for rapid advances in the identification of new targets for pharmacological management of complex pathological syndromes such as obesity, type 2 diabetes or chronic inflammatory diseases. However, since the physiological and biochemical roles of the novel UCPs are not yet clear, the main challenge today consists first of all in providing mechanistic explanation for their functions in cellular physiology. This lively awaited information may be the basis for potential pharmacological targeting of the UCPs in future.

Fluid shear stress-induced nitric oxide production in human cavernosal endothelial cells: inhibition by hyperglycaemia

OBJECTIVE

To investigate whether fluid shear stress (FSS) induces endothelial nitric oxide synthase (eNOS) activity and NO production in isolated human corpus cavernosal endothelial cells (HCCECs), and whether this response is altered during hyperglycaemia in vitro, as haemodynamic signalling during penile erection induces eNOS-mediated NO production in vivo.

MATERIALS AND METHODS

ECs were cultured from HCC and characterized by the uptake of acetylated low-density lipoprotein and the expression of von Willebrand factor, VE-cadherin, CD31 and eNOS. HCCECs were exposed to FSS (1.2 Pa (12 dynes/cm2), 5 min) using a cone-and-plate viscometer in the presence or absence of high glucose (30 mm, 48 h). The phosphorylation of ser1177 on eNOS and total eNOS protein expression after FSS was examined by Western blot. NO in the conditioned media was assessed by measuring nitrate and nitrite levels.

RESULTS

Compared to static conditions, FSS induced a significant increase in the phosphorylation of eNOS on ser1177 in HCCECs, and the release of NO to the conditioned media. Treatment of HCCECs with high glucose levels did not alter the ratio FSS-induced phosphorylated eNOS/total eNOS, but did result in the down-regulation of total eNOS and significantly attenuated FSS-induced NO release.

CONCLUSION

These in vitro data suggest that FSS contributes to eNOS activation and NO release in HCCECs, and supports in vivo reports suggesting a role for haemodynamic signalling in the erectile response. Treatment with high glucose levels prevented FSS-induced NO release, suggesting a mechanism that may contribute to decreased erectile function associated with diabetes.

L-Arginine Supplementation Prevents the Development of Endothelial Dysfunction in Hyperglycaemia

Diabetes mellitus leads to the development of endothelial dysfunction which finally contributes to diabetic angiopathy. We investigated the effects of hyperglycaemia on nitric oxide (NO) liberation and a possible influence of L-arginine supplementation. Porcine endothelial aortic cells (PAEC) were cultured in Medium 199 containing 0.33 mmol/l L-arginine. During the entire third culture passage (= 4 days) cells were either exposed to 5 or 20 mmol/l D-glucose with or without additional 3 mmol/l L-arginine. For osmotic control, cells were exposed to 15 mmol/l mannitol. NO liberation was measured under basal conditions and after stimulation with 1 mmol/l ATP using the spectrophotometrical methemoglobin assay. Cells released 35 +/- 8 pmol NO/1 x 10(6) cells/10 min under basal conditions while hyperglycaemia led to a significant reduction in NO release to 16 +/- 6 pmol/1 x 10(6) cells/10 min. In osmotic control, NO release was unchanged (37 +/- 10 pmol/1 x 10(6) cells/10 min). Stimulation with 1 mmol/l ATP led to a significant increase in NO release to 103 +/- 11 pmol/1 x 10(6) cells/10 min (normoglycaemia) which was unchanged in osmotic controls. Under normoglycaemic conditions, additional L-arginine supplementation did not influence NO release from PAEC. In hyperglycaemia (0.33 mmol/l L-arginine) ATP stimulated NO release was reduced (48 +/- 8 pmol/1 x 10(6) cells/10 min, p < 0.05), which was completely prevented by 3 mmol/l L-arginine treatment (98 +/- 15 pmol/ 1 x 10(6) cells/10 min). Hyperglycaemia (but not enhanced osmotic pressure) leads to endothelial dysfunction with reduced NO release which is completely prevented by L-arginine. L-Arginine utilisation may be impaired in hyperglycaemia and L-arginine supplementation might be an interesting additional therapeutic tool in diabetic patients.

The regulation and pharmacology of endothelial nitric oxide synthase

Nitric oxide (NO) is a small, diffusible, lipophilic free radical gas that mediates significant and diverse signaling functions in nearly every organ system in the body. The endothelial isoform of nitric oxide synthase (eNOS) is a key source of NO found in the cardiovascular system. This review summarizes the pharmacology of NO and the cellular regulation of endothelial NOS (eNOS). The molecular intricacies of the chemistry of NO and the enzymology of NOSs are discussed, followed by a review of the biological activities of NO. This information is then used to develop a more global picture of the pharmacological control of NO synthesis by NOSs in both physiologic conditions and pathophysiologic states.

Insulin resistance reduces arterial prostacyclin synthase and eNOS activities by increasing endothelial fatty acid oxidation

Insulin resistance markedly increases cardiovascular disease risk in people with normal glucose tolerance, even after adjustment for known risk factors such as LDL, triglycerides, HDL, and systolic blood pressure. In this report, we show that increased oxidation of FFAs in aortic endothelial cells without added insulin causes increased production of superoxide by the mitochondrial electron transport chain. FFA-induced overproduction of superoxide activated a variety of proinflammatory signals previously implicated in hyperglycemia-induced vascular damage and inactivated 2 important antiatherogenic enzymes, prostacyclin synthase and eNOS. In 2 nondiabetic rodent models--insulin-resistant, obese Zucker (fa/fa) rats and high-fat diet-induced insulin-resistant mice--inactivation of prostacyclin synthase and eNOS was prevented by inhibition of FFA release from adipose tissue; by inhibition of the rate-limiting enzyme for fatty acid oxidation in mitochondria, carnitine palmitoyltransferase I; and by reduction of superoxide levels. These studies identify what we believe to be a novel mechanism contributing to the accelerated atherogenesis and increased cardiovascular disease risk occurring in people with insulin resistance.

Uncoupling of vascular endothelial growth factor with nitric oxide as a mechanism for diabetic vasculopathy

The role of VEGF in vascular disease is complicated. Vascular endothelial growth factor (VEGF) expression can be deleterious in diabetic vasculopathy, especially in kidney and retina. In contrast, VEGF seems to be renoprotective in nondiabetic renal disease. VEGF exerts it biologic effects in association with nitric oxide (NO), yet it is known that NO bioavailability is reduced in diabetes. Thus, it was hypothesized that this diverse biologic effect of VEGF on diabetic vasculopathy is due to uncoupling of VEGF with NO. VEGF stimulated NO production in a dose-dependent manner in bovine aortic endothelial cells (BAEC), and this was inhibited by either high glucose or Nomega-nitro-l-arginine methyl ester (L-NAME) treatment. Endothelial NO synthase phosphorylation by VEGF was also inhibited by high glucose. It is interesting that both high glucose and L-NAME enhanced the proliferative response of endothelial cells, which was prevented by an NO donor. Furthermore, high glucose as well as L-NAME stimulated VEGF and kinase-insert domain receptor (KDR) (VEGF receptor 2) mRNA expression in BAEC. These data suggest that the uncoupling of VEGF with NO enhances endothelial cell proliferation via the KDR pathway. Compatible with these findings, a KDR antagonist blocked this response. In addition, a VEGF mutant, which binds only KDR, induced extracellular signal-regulated kinase (ERK) activation, and inhibition of ERK completely blocked endothelial cell proliferation under this condition, suggesting a role of the KDR-ERK1/2 pathway on endothelial cell proliferation. In conclusion, high glucose causes an uncoupling of VEGF with NO, which enhances endothelial cell proliferation via activation of the KDR-ERK1/2 pathway. These results may provide new insights into the understanding of the mechanism of diabetic vascular disease.

CONVERGENCE OF GLUCOSE- AND FATTY ACID-INDUCED ABNORMAL MYOCARDIAL EXCITATION-CONTRACTION COUPLING AND INSULIN SIGNALLING

1. Myocardial insulin resistance and abnormal Ca(2+) regulation are hallmarks of hypertrophic and diabetic hearts, but deprivation of energetic substrates does not tell the whole story. Is there a link between the aetiology of these dysfunctions? 2. Diabetic cardiomyopathy is defined as phenotypic changes in the heart muscle cell independent of associated coronary vascular disease. The cellular consequences of diabetes on excitation-contraction (E-C) coupling and insulin signalling are presented in various models of diabetes in order to set the stage for exploring the pathogenesis of heart disease. 3. Excess glucose or fatty acids can lead to augmented flux through the hexosamine biosynthesis pathway (HBP). The formation of uridine 5 cent-diphosphate-hexosamines has been shown to be involved in abnormal E-C coupling and myocardial insulin resistance. 4. There is growing evidence that O-linked glycosylation (downstream of HBP) may regulate the function of cytosolic and nuclear proteins in a dynamic manner, similar to phosphorylation and perhaps involving reciprocal or synergistic modification of serine/threonine sites. 5. This review focuses on the question of whether there is a role for HBP and dynamic O-linked glycosylation in the development of myocardial insulin resistance and abnormal E-C coupling. The emerging concept that O-linked glycosylation is a regulatory, post-translational modification of cytosolic/nuclear proteins that interacts with phosphorylation in the heart is explored.

The hexosamine signaling pathway: deciphering the "O-GlcNAc code"

A dynamic cycle of addition and removal of O-linked N-acetylglucosamine (O-GlcNAc) at serine and threonine residues is emerging as a key regulator of nuclear and cytoplasmic protein activity. Like phosphorylation, protein O-GlcNAcylation dramatically alters the posttranslational fate and function of target proteins. Indeed, O-GlcNAcylation may compete with phosphorylation for certain Ser/Thr target sites. Like kinases and phosphatases, the enzymes of O-GlcNAc metabolism are highly compartmentalized and regulated. Yet, O-GlcNAc addition is subject to an additional and unique level of metabolic control. O-GlcNAc transfer is the terminal step in a "hexosamine signaling pathway" (HSP). In the HSP, levels of uridine 5'-diphosphate (UDP)-GlcNAc respond to nutrient excess to activate O-GlcNAcylation. Removal of O-GlcNAc may also be under similar metabolic regulation. Differentially targeted isoforms of the enzymes of O-GlcNAc metabolism allow the participation of O-GlcNAc in diverse intracellular functions. O-GlcNAc addition and removal are key to histone remodeling, transcription, proliferation, apoptosis, and proteasomal degradation. This nutrient-responsive signaling pathway also modulates important cellular pathways, including the insulin signaling cascade in animals and the gibberellin signaling pathway in plants. Alterations in O-GlcNAc metabolism are associated with various human diseases including diabetes mellitus and neurodegeneration. This review will focus on current approaches to deciphering the "O-GlcNAc code" in order to elucidate how O-GlcNAc participates in its diverse functions. This ongoing effort requires analysis of the enzymes of O-GlcNAc metabolism, their many targets, and how the O-GlcNAc modification may be regulated.

NADPH oxidase inhibitor, apocynin, restores the impaired endothelial-dependent and -independent responses and scavenges superoxide anion in rats with type 2 diabetes complicated by NO dysfunction

OBJECTIVE

We investigated the effect of apocynin, an NADPH oxidase inhibitor, in the impairment of vascular responses in Otsuka Long-Evans Tokushima Fatty (OLETF) rats (type 2 diabetic rat model) with or without (w/wo) N-nitro-l-arginine methyl ester treatment.

METHODS

Male OLETF and littermate Long-Evans Tokushima Otsuka (LETO) (28 weeks old) rats were separated as follows: LETO w/wo apocynin (Gp C, Gp C-apo), OLETF w/wo apocynin (Gp DM, Gp DM-apo) and OLETF plus l-nitro arginine acetate ester w/wo apocynin (Gp DMLN, Gp DMLN-apo). Five days after, peritoneal macrophages were stimulated with thioglycolate. Two days after, they were evaluated.

RESULTS

Plasma glucose and lipid levels remained unchanged. Acetylcholine-induced nitric oxide-dependent (NO-dependent) relaxation and nitroglycerin-induced NO-independent relaxation were improved in the Gp DMLN-apo, compared with that in Gp DMLN. Tone-related basal NO release and plasma NO(2) (-) and NO(3) (-) tended to be lower in Gp DM and Gp DMLN groups. The increased amount of superoxide anion released from macrophages in Gp DM and Gp DMLN was restored by apocynin. Intimal thickening was observed in aortae of Gp DM and Gp DMLN animals; however, there was little in aortae of Gp DM-apo and Gp DMLN(-) apo rats. Increased tumour necrosis factor-alpha (TNF-alpha) in the Gp DM and Gp DMLN was also restored by apocynin treatment.

CONCLUSION

Apocynin restores the impairment of endothelial and non-endothelial function in diabetic angiopathy in OLETF without changing plasma glucose and lipid levels. NO and O(2) (-) may play a role in this process by decreasing TNF-alpha levels.

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

Macro- and microvascular disease states currently represent the principal causes of morbidity and mortality in patients with type I or type II diabetes mellitus. Abnormal vasomotor responses and impaired endothelium-dependent vasodilation have been demonstrated in various beds in different animal models of diabetes and in humans with type I or type II diabetes. Several mechanisms leading to endothelial dysfunction have been reported, including changes in substrate avail ability, impaired release of NO, and increased destruction of NO. The principal mediators of diabetes-associated endothelial dysfunction are (a) increases in oxidized low density lipoprotein, endothelin-1, angiotensin II, oxidative stress, and (b) decreases in the actions of insulin or growth factors in endothelial cells. An accumulating body of evidence indicates that abnormal regulation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway may be one of several factors contributing to vascular dysfunction in diabetes. The PI3-K pathway, which activates serine/threonine protein kinase Akt, enhances NO synthase phosphorylation and NO production. Several studies suggest that in diabetes the relative ineffectiveness of insulin and the hyperglycemia act together to reduce activity in the insulin-receptor substrates (IRS)/PI3-K/Akt pathway, resulting in impairments of both IRS/PI3-K/Akt-mediated endothelial function and NO production. This article summarizes the PI3-K/Akt pathway-mediated contraction and relaxation responses induced by various agents in the blood vessels of diabetic animals.

The protective effect of aminoguanidine on erectile function in diabetic rats is not related to the timing of treatment

OBJECTIVE

To assess the accumulation of advanced glycation end products (AGEs) in streptozotocin (STZ)-induced diabetic rat cavernosal tissue, and to determine whether the protective effect of aminoguanidine (AG) on erectile function is related to the timing of treatment, as the accumulation of AGEs in the penis may be important in the pathogenesis of diabetes mellitus-induced erectile dysfunction, and prolonged treatment with AG (a selective AGE inhibitor), prevents erectile dysfunction in this situation.

MATERIALS AND METHODS

Harlan Sprague-Dawley rats were divided into groups 1-4, i.e. age-matched controls; STZ diabetic rats (60 mg/kg intraperitoneal) given free access to water; STZ diabetic rats treated with AG (1 g/L per day in the drinking water) immediately after inducing diabetes; and STZ-diabetic rats treated with AG 1 month after inducing diabetes, respectively. Two months after inducing diabetes the intracavernosal pressure was measured after cavernosal nerve stimulation, and cavernosal AGE (5-hydroxy methyl furfural, 5-HMF) levels assessed.

RESULTS

Cavernosal tissue 5-HMF levels from groups 2 and 4 were significantly higher than in group 1 (control). The expression of 5-HMF in group 3 was similar to that in group 1. Diabetic rats had significantly lower erectile function than controls, while groups 3 and 4 (treated with AG) had normal erectile function, as measured by cavernosal nerve stimulation.

CONCLUSIONS

The effect of AG on AGE levels seems to be time-dependent; that the 1-month treatment with AG improved erectile function with no change in AGEs suggests that AG has protective effects on the penile vasculature through alternative pathways.

Effect of a beta 2-adrenoceptor stimulation on hyperglycemia-induced endothelial dysfunction

To investigate whether beta(2)-adrenoceptors exist on endothelial cells and whether a beta(2)-adrenoceptor stimulation might prevent the development of hyperglycemia-induced endothelial dysfunction, porcine aortic endothelial cells (PAECs) were cultured and chronically exposed to either 5 mM D-glucose ("normoglycemia") or 20 mM D-glucose ("hyperglycemia"), with or without 100 nM salbutamol in absence or presence of beta(2)-adrenoceptor antagonist ICI 118,551 [1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxyl]-3-[(1-methylethyl)-amino]-2-butanol] or beta(1)-antagonist metoprolol. For osmotic control, PAECs were exposed to 15 mM L-glucose. We measured nitric oxide release using the met-hemoglobin assay and assessed beta-adrenoceptor density and subtypes by radioligand binding. Furthermore, we determined intracellular NADH and NADPH using high-performance liquid chromatography. High D-glucose concentrations but not L-glucose led to significantly reduced basal and stimulated nitric oxide release. Chronic salbutamol treatment significantly antagonized the impairment of the nitric oxide response, which was inhibited by ICI 118,551 but not by metoprolol. The number of giant cells was significantly increased in hyperglycemia, which could be prevented by salbutamol. Binding of the radioligand (-)-[(125)I]iodocyanopindolol revealed a total beta-adrenoceptor density of 29.8 +/- 3.7 (normoglycemic) and 30.3 +/- 3.6 (hyperglycemic) fmol/mg protein. Displacement by ICI 118,551 revealed beta-adrenoceptor subtype distribution with 30.3 +/- 4.4 (normoglycemic) and 29.1 +/- 3.8% beta(2)-adrenoceptors. NADH production increased in hyperglycemia, which was completely prevented by salbutamol. We conclude that hyperglycemia in PAEC induces endothelial dysfunction with impaired nitric oxide release and that this can be prevented by beta(2)-adrenoceptor stimulation.

Effect of chronic treatment with vitamin E on endothelial dysfunction in a type I in vivo diabetes mellitus model and in vitro

Diabetes mellitus often leads to generalized vasculopathy. Because of the pathophysiological role of free radicals we investigated the effects of vitamin E. Twenty-eight rats were rendered diabetic by streptozotocin injection and were fed either with a diet with low (10 mg/kg of chow), medium (75 mg/kg of chow) or high amounts of vitamin E (1300 mg/kg of chow). Nine age-matched nondiabetic rats receiving 75 mg of vitamin E/kg chow served as controls. After 7 months, mesenteric microcirculation was investigated. Smooth muscle contractile function was not altered in diabetic versus nondiabetic vessels. Endothelial function was significantly reduced in diabetics; relaxation upon 1 micro M acetylcholine was reduced by 50% in diabetics with a medium and high vitamin E diet. In vitamin E-deprived rats, a complete loss of endothelium-dependent relaxation was observed, and instead, acetylcholine elicited vasoconstriction. L-N(G)-Nitro-arginine-induced vasoconstriction was reduced in small arteries in diabetics, which was not prevented by vitamin E, but was aggravated by vitamin E deprivation. In a subchronic endothelial cell culture model, cells were cultivated with 5 or 20 mM D-glucose for an entire cell culture passage (4 days) with or without vitamin E (20 mg/l versus 0.01 mg/l). Hyperglycemia led to significant reduction in basal and ATP-stimulated nitric oxide (NO)-production. Hyperglycemia-induced reduction in basal NO-release was significantly prevented by vitamin E, whereas reduction in stimulated NO-release was not influenced. NADPH-diaphorase activity was reduced by 40% by hyperglycemia, which was completely prevented by vitamin E. We conclude that 1) vitamin E has a potential to prevent partially hyperglycemia-induced endothelial dysfunction, 2) under in vivo conditions vitamin E deficiency enhanced diabetic endothelial dysfunction dramatically, and 3) positive effects of vitamin E may be attenuated with a longer disease duration.

Regulation of nitric oxide synthesis by dietary factors

Nitric oxide (NO) is synthesized from L-arginine by NO synthase (NOS). As an endothelium-derived relaxing factor, a mediator of immune responses, a neurotransmitter, a cytotoxic free radical, and a signaling molecule, NO plays crucial roles in virtually every cellular and organ function in the body. The discovery of NO synthesis has unified traditionally diverse research areas in nutrition, physiology, immunology, pathology, and neuroscience. Increasing evidence over the past decade shows that many dietary factors, including protein, amino acids, glucose, fructose, cholesterol, fatty acids, vitamins, minerals, phytoestrogens, ethanol, and polyphenols, are either beneficial to health or contribute to the pathogenesis of chronic diseases partially through modulation of NO production by inducible NOS or constitutive NOS. Although most published studies have focused on only a single nutrient and have generated new and exciting knowledge, future studies are necessary to investigate the interactions of dietary factors on NO synthesis and to define the underlying molecular mechanisms.