Regulation of endothelial constitutive nitric oxide synthase gene expression in endothelial cells and in vivo : a specific vascular action of insulin

TLR4 at the Crossroads of Nutrients, Gut Microbiota, and Metabolic Inflammation

Obesity is accompanied by the activation of low-grade inflammatory activity in metabolically relevant tissues. Studies have shown that obesity-associated insulin resistance results from the inflammatory targeting and inhibition of key proteins of the insulin-signaling pathway. At least three apparently distinct mechanisms-endoplasmic reticulum stress, toll-like receptor (TLR) 4 activation, and changes in gut microbiota-have been identified as triggers of obesity-associated metabolic inflammation; thus, they are expected to represent potential targets for the treatment of obesity and its comorbidities. Here, we review the data that place TLR4 in the center of the events that connect the consumption of dietary fats with metabolic inflammation and insulin resistance. Changes in the gut microbiota can lead to reduced integrity of the intestinal barrier, leading to increased leakage of lipopolysaccharides and fatty acids, which can act upon TLR4 to activate systemic inflammation. Fatty acids can also trigger endoplasmic reticulum stress, which can be further stimulated by cross talk with active TLR4. Thus, the current data support a connection among the three main triggers of metabolic inflammation, and TLR4 emerges as a link among all of these mechanisms.

Does Insulin Like Growth Factor-1 (IGF-1) Deficiency Have a "Protective" Role in the Development of Diabetic Retinopathy in Thalassamia Major Patients?

RATIONALE

Both insulin and IGF-1 have been implicated in the control of retinal endothelial cell growth, neovascularization and diabetic retinopathy. Recent findings have established an essential role for IGF-1 in angiogenesis and demonstrated a new target for control of retinopathy that explains why diabetic retinopathy initially increases with the onset of insulin treatment.

OBJECTIVE

This cross-sectional study was designed to give insights into relationship between Insulin-Growth-Factor 1 (IGF-1) levels and diabetic retinopathy (DR) in a sample of thalassemia major (TM) patients with insulin dependent diabetes mellitus (IDDM). This relation was not previously evaluated, despite the fact that both diseases co-exist in the same patient. The study also describes the clinical and biochemical profile of the associated complications in TM patients with and without IDDM.

DESIGN

A population-based cross-sectional study.

PARTICIPANTS

The study includes 19 consecutive TM patients with IDDM and 31 age- and sex-matched TM patients without IDDM who visited our out-patient clinics for an endocrine assessment.

METHODS

An extensive medical history, with data on associated complications and current medications, was obtained. Blood samples were drawn in the morning after an overnight fast to measure the serum concentrations of IGF-1, glucose, fructosamine, free thyroxine (FT4), thyrotropin (TSH) and biochemical analysis. Serologic screening assays for hepatitis C virus seropositivity (HCVab and HCV-RNA) were also evaluated; applying routine laboratory methods. Plasma total IGF-1 was measured by a chemiluminescent immunometric assay (CLIA) method. Ophthalmology evaluation was done by the same researcher using stereoscopic fundus biomicroscopy through dilated pupils. DR was graded using the scale developed by the Global Diabetic Retinopathy Group. Iron stores were assessed by direct and indirect methods.

RESULTS

Eighteen TM patients with IDDM (94.7 %) and ten non-diabetic patients (32.2 %) had IGF-1 levels below the 2.5(th) percentile of the normal values for the Italian population. The mean serum IGF-1 concentrations were significantly lower in the diabetic versus the non-diabetic TM groups (p < 0.001). DR was present in 4 (21 %) of 19 TM patients with IDDM and was associated with the main classical risk factors, namely inefficient glycemic control and duration of the disease but not hypertension. Using the scale developed by the Global Diabetic Retinopathy Group, the DR in our patients was classified as non proliferative diabetic retinopathy (NPDR). Only a few numbers of microaneurysms [1-3] were detected. Our data also confirm the strong association of IDDM in TM patients with other endocrine and non-endocrine complications.

Vascular and hepatic impact of short-term intermittent hypoxia in a mouse model of metabolic syndrome

Background

Experimental models of intermittent hypoxia (IH) have been developed during the last decade to investigate the consequences of obstructive sleep apnea. IH is usually associated with detrimental metabolic and vascular outcomes. However, paradoxical protective effects have also been described depending of IH patterns and durations applied in studies. We evaluated the impact of short-term IH on vascular and metabolic function in a diet-induced model of metabolic syndrome (MS).

Methods

Mice were fed either a standard diet or a high fat diet (HFD) for 8 weeks. During the final 14 days of each diet, animals were exposed to either IH (1 min cycle, FiO₂ 5% for 30s, FiO₂ 21% for 30s; 8 h/day) or intermittent air (FiO₂ 21%). Ex-vivo vascular reactivity in response to acetylcholine was assessed in aorta rings by myography. Glucose, insulin and leptin levels were assessed, as well as serum lipid profile, hepatic mitochondrial activity and tissue nitric oxide (NO) release.

Results

Mice fed with HFD developed moderate markers of dysmetabolism mimicking MS, including increased epididymal fat, dyslipidemia, hepatic steatosis and endothelial dysfunction. HFD decreased mitochondrial complex I, II and IV activities and increased lactate dehydrogenase (LDH) activity in liver. IH applied to HFD mice induced a major increase in insulin and leptin levels and prevented endothelial dysfunction by restoring NO production. IH also restored mitochondrial complex I and IV activities, moderated the increase in LDH activity and liver triglyceride accumulation in HFD mice.

Conclusion

In a mouse model of MS, short-term IH increases insulin and leptin levels, restores endothelial function and mitochondrial activity and limits liver lipid accumulation.

Arg972 insulin receptor substrate-1 enhances tumor necrosis factor-α-induced apoptosis in osteoblasts

The presence of Arg972 insulin receptor substrate-1 (IRS-1) is associated with impaired insulin/IRS-1 signaling to activate phosphatidylinositol-3 kinase (PI3K). Tumor necrosis factor-α (TNF-α), an inflammatory cytokine with a central role in the pathogenesis of rheumatoid arthritis (RA), induces apoptosis in osteoblasts, which are the principal cell type responsible for bone loss in RA. In our previous study, an association between Arg972 IRS-1 and a high risk and severity of RA was identified. In the present study, the effects of Arg972 IRS-1 and IRS-1 on TNF-α-induced apoptosis in human osteoblasts were examined. Normal and RA osteoblasts were stably transfected with Arg972 IRS-1 and IRS-1. In addition, cells were stably transduced with IRS-1-shRNA to knock down IRS1. Following stimulation with 10 nM insulin for 30 min, the stable overexpression of Arg972 IRS-1 and knock down of IRS-1 significantly decreased IRS-1-associated PI3K activity and Akt activation/phosphorylation at serine 473 (ser473) and enhanced TNF-α-induced apoptosis in normal and in RA osteoblasts. By contrast, the stable overexpression of IRS-1 significantly increased the levels of IRS-1-associated PI3K activity and Akt phosphorylation (ser473) and inhibited TNF-α-induced apoptosis, which was eliminated by pretreatment with 50 µn BJM120, a selective PI3K inhibitor, for 30 min. In conclusion, the present study provided the first evidence, to the best of our knowledge, that insulin stimulation of Arg972 IRS-1 and IRS-1 enhanced and inhibited TNF-α-induced apoptosis, respectively in normal and RA osteoblasts by a PI3K‑dependent mechanism. These findings suggest that insulin/IRS-1 signaling is important in the pathogenesis of RA.

Oxidative stress in obesity: a critical component in human diseases

Obesity, a social problem worldwide, is characterized by an increase in body weight that results in excessive fat accumulation. Obesity is a major cause of morbidity and mortality and leads to several diseases, including metabolic syndrome, diabetes mellitus, cardiovascular, fatty liver diseases, and cancer. Growing evidence allows us to understand the critical role of adipose tissue in controlling the physic-pathological mechanisms of obesity and related comorbidities. Recently, adipose tissue, especially in the visceral compartment, has been considered not only as a simple energy depository tissue, but also as an active endocrine organ releasing a variety of biologically active molecules known as adipocytokines or adipokines. Based on the complex interplay between adipokines, obesity is also characterized by chronic low grade inflammation with permanently increased oxidative stress (OS). Over-expression of oxidative stress damages cellular structures together with under-production of anti-oxidant mechanisms, leading to the development of obesity-related complications. The aim of this review is to summarize what is known in the relationship between OS in obesity and obesity-related diseases.

Insulin regulates nitric oxide production in the kidney collecting duct cells

The kidney is an important organ for arterial blood pressure (BP) maintenance. Reduced NO generation in the kidney is associated with hypertension in insulin resistance. NO is a critical regulator of vascular tone; however, whether insulin regulates NO production in the renal inner medullary collecting duct (IMCD), the segment with the greatest enzymatic activity for NO production in kidney, is not clear. Using an NO-sensitive 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) fluorescent dye, we found that insulin increased NO production in mouse IMCD cells (mIMCD) in a time- and dose-dependent manner. A concomitant dose-dependent increase in the NO metabolite (NOx) was also observed in the medium from insulin-stimulated cells. NO production peaked in mIMCD cells at a dose of 100 nm insulin with simultaneously increased NOx levels in the medium. At this dose, insulin significantly increased p-eNOS(Ser1177) levels in mIMCD cells. Pretreatment of cells with a PI 3-kinase inhibitor or insulin receptor silencing with RNA interference abolished these effects of insulin, whereas insulin-like growth factor-1 receptor (IGF-1R) silencing had no effect. We also showed that chronic insulin infusion to normal C57BL/6J mice resulted in increased endothelial NOS (eNOS) protein levels and NO production in the inner medulla. However, insulin-infused IRKO mice, with targeted deletion of insulin receptor from tubule epithelial cells of the kidney, had ∼50% reduced eNOS protein levels in their inner medulla along with a significant rise in BP relative to WT littermates. We have previously reported increased baseline BP and reduced urine NOx in IRKO mice. Thus, reduced insulin receptor signaling in IMCD could contribute to hypertension in the insulin-resistant state.

Hepatic protein tyrosine phosphatase 1B (PTP1B) deficiency protects against obesity-induced endothelial dysfunction

Growing evidence suggests that hepatic-insulin resistance is sufficient to promote progression to cardiovascular disease. We have shown previously that liver-specific protein-tyrosine-phosphatase 1B (PTP1B) deficiency improves hepatic-insulin sensitivity and whole-body glucose homeostasis. The aim of this study was to investigate the impact of liver-specific PTP1B-deficiency (L-PTP1B-/-) on cardiac and peripheral vascular function, with special emphasis on endothelial function in the context of high-fat diet (HFD)-induced obesity. L-PTP1B-/- mice exhibited an improved glucose and lipid homeostasis and increased insulin sensitivity, without changes in body weight. HFD-feeding increased systolic blood pressure (BP) in both L-PTP1B-/- and control littermates; however, this was significantly lower in L-PTP1B-/- mice. HFD-feeding increased diastolic BP in control mice only, whilst the L-PTP1B-/- mice were completely protected. The analysis of the function of the left ventricle (LV) revealed that HFD-feeding decreased LV fractional shortening in control animals, which was not observed in L-PTP1B-/- mice. Importantly, HFD feeding significantly impaired endothelium-dependent vasorelaxation in response to acetylcholine in aortas from control mice, whilst L-PTP1B-/- mice were fully protected. This was associated with alterations in eNOS phosphorylation. Selective inhibition of COX-2, using NS-398, decreased the contractile response in response to serotonin (5-HT) only in vessels from control mice. HFD-fed control mice released enhanced levels of prostaglandin E, a vasoconstrictor metabolite; whilst both chow- and HFD-fed L-PTP1B-/- mice released higher levels of prostacylin, a vasorelaxant metabolite. Our data indicate that hepatic-PTP1B inhibition protects against HFD-induced endothelial dysfunction, underscoring the potential of peripheral PTP1B inhibitors in reduction of obesity-associated cardiovascular risk in addition to its anti-diabetic effects.

Targeting inflammation in diabetes: Newer therapeutic options

Inflammation has been recognised to both decrease beta cell insulin secretion and increase insulin resistance. Circulating cytokines can affect beta cell function directly leading to secretory dysfunction and increased apoptosis. These cytokines can also indirectly affect beta cell function by increasing adipocyte inflammation.The resulting glucotoxicity and lipotoxicity further enhance the inflammatory process resulting in a vicious cycle. Weight reduction and drugs such as metformin have been shown to decrease the levels of C-Reactive Protein by 31% and 13%, respectively. Pioglitazone, insulin and statins have anti-inflammatory effects. Interleukin 1 and tumor necrosis factor-α antagonists are in trials and NSAIDs such as salsalate have shown an improvement in insulin sensitivity. Inhibition of 12-lipo-oxygenase, histone de-acetylases, and activation of sirtuin-1 are upcoming molecular targets to reduce inflammation. These therapies have also been shown to decrease the conversion of pre-diabetes state to diabetes. Drugs like glicazide, troglitazone, N-acetylcysteine and selective COX-2 inhibitors have shown benefit in diabetic neuropathy by decreasing inflammatory markers. Retinopathy drugs are used to target vascular endothelial growth factor, angiopoietin-2, various proteinases and chemokines. Drugs targeting the proteinases and various chemokines are pentoxifylline, inhibitors of nuclear factor-kappa B and mammalian target of rapamycin and are in clinical trials for diabetic nephropathy. Commonly used drugs such as insulin, metformin, peroxisome proliferator-activated receptors, glucagon like peptide-1 agonists and dipeptidyl peptidase-4 inhibitors also decrease inflammation. Anti-inflammatory therapies represent a potential approach for the therapy of diabetes and its complications.

Role of microangiopathy in diabetic cardiomyopathy

Although heart disease due to diabetes is mainly associated with complications of the large vessels, microvascular abnormalities are also considered to be involved in altering cardiac structure and function. Three major defects, such as endothelial dysfunction, alteration in the production/release of hormones, and shift in metabolism of smooth muscle cells, have been suggested to produce damage to the small arteries and capillaries (microangiopathy) due to hyperglycemia, and promote the development of diabetic cardiomyopathy. These factors may either act alone or in combination to produce oxidative stress as well as changes in cellular signaling and gene transcription, which in turn cause vasoconstriction and structural remodeling of the coronary vessels. Such alterations in microvasculature produce hypoperfusion of the myocardium and thereby lower the energy status resulting in changes in Ca(2+)-handling, apoptosis, and decreased cardiac contractile force. This article discusses diabetes-induced mechanisms of microvascular damage leading to cardiac dysfunction that is characterized by myocardial dilatation, cardiac hypertrophy as well as early diastolic and late systolic defects. Metabolic defects and changes in neurohumoral system due to diabetes, which promote disturbances in vascular homeostasis, are highlighted. In addition, increase in the vulnerability of the diabetic heart to the development of heart failure and the signaling pathways integrating nuclear factor κB and protein kinase C in diabetic cardiomyopathy are also described for comparison.

Pioglitazone and Endothelial Dysfunction: Pleiotropic Effects and Possible Therapeutic Implications

The vascular endothelium has a central role in the modulation of vascular tone with associated antioxidant, anti-inflammatory, pro-fibrinolytic, anti-adhesive, and anticoagulant effects. This is primarily accomplished by the timely release of endothelial autacoids. On the other hand, endothelial dysfunction (ED) provoked by insulin resistance has been linked with reduced nitric oxide bioavailability, increased production of reactive oxygen species, and alterations of endothelial regeneration. Pioglitazone is classified as an insulin-sensitizing, anti-hyperglycemic agent. The mechanism of action associated with pioglitazone includes the activation of peroxisome proliferator-activated receptor-gamma with stable improvement in glycemic control in diabetic patients. Today, it is known that apart from the beneficial effects on glucose homeostasis, pioglitazone exerts several pleiotropic effects, including the improvement of ED. Thus, the aim of this article was to summarize the current knowledge related to signaling mechanisms of the pioglitazone-induced improvement or reversal of ED. The relevant clinical studies and possible therapeutic implications connected to pioglitazone-related action on the endothelium were analyzed too.

Associations between different types of hypoglycemic agents and the clinical outcome of percutaneous coronary intervention in diabetic patients-From the FU-Registry

BACKGROUND

It is not clear whether it is reasonable to use particular drugs for glycemic control in preference to other hypoglycemic agents in terms of the clinical outcome of percutaneous coronary intervention (PCI) in patients with diabetes mellitus (DM).

METHODS AND RESULTS

Among 2148 patients (2568 lesions) in the FU-Registry, DM patients who underwent PCI (n=758; 922 lesions) were investigated to clarify the effects of various drugs for glycemic control on the clinical outcome [major adverse cardiac events (MACEs): death, myocardial infarction (MI), and target lesion revascularization (TLR)] over approximately 300 days of follow-up (UMIN000005679). The MACEs(+) group (n=165) had a higher usage of insulin (p<0.001) and a lower usage of biguanides (BG, p<0.05) and dipeptidyl peptidase-IV inhibitors (p<0.05) at PCI, compared to the MACEs(-) group (n=593). A multivariate logistic regression analysis showed that low-density lipoprotein cholesterol, insulin use, atherosclerosis obliterans, and lesion reference might be significantly associated with MACEs, while BG use was negatively correlated with MACEs (p=0.04). The cumulative frequency of MACEs in the insulin-treated group was significantly higher (p<0.05) than that in the non-insulin group, and the strongest association between insulin with MACEs was seen in the hemoglobin (Hb) A1c 6.5-7.5% group. There tended to be a negative correlation between the use of insulin and MACEs, with risk ratios of <1, for the HbA1c >8.5% groups.

CONCLUSIONS

Among different hypoglycemic agents, treatment with insulin was associated with poor mid-term clinical outcomes in DM patients who underwent PCI, while BG use was negatively correlated with MACEs. It may be reasonable for patients with HbA1c >8.5% to avoid hyperglycemia and glucotoxicity, even through the use of insulin.

Oxidative stress: implications for the development of diabetic retinopathy and antioxidant therapeutic perspectives

In recent decades, localized tissue oxidative stress has been implicated as a key component in the development of diabetic retinopathy (DR). Increasing evidence shows that oxidative stress caused by diabetes-induced metabolic abnormalities is the most common mechanism associated with the pathogenesis of DR for both type 1 and type 2 diabetes. Increase in intracellular reactive oxygen species (ROS) concentrations results in the activation of several mechanisms involved in the pathogenesis of DR. In particular, damage or dysfunction caused by oxidative stress still persists even after glycemia has been normalized. Despite considerable evidence showing the beneficial effects of antioxidants in preventing the development of retinopathy, results from large-scale clinical trials on classic antioxidants are somewhat ambiguous. Scavenging reactive radicals may not be the most ideal antioxidant strategy in DR. Advances in understanding the function of ROS in the development of DR can lead to the development of new therapeutic strategies based on the mechanisms of ROS generation and scavenging. Increasing amounts of data have demonstrated the promising prospect of antioxidant therapy and its beneficial effects in vision protection. Therefore, new strategies that utilize antioxidants as additive therapy should be implemented in the treatment of DR.

Role of red grape polyphenols as antidiabetic agents

The worldwide incidence of diabetes mellitus has reached alarming proportions. Persistent hyperglycemia due to impaired insulin activity and/or insulin resistance inversely affects the retina, cerebrovascular system, kidney, peripheral limbs, and other parts of the body, which leads to life-threatening complications. The causal role of oxidative stress in the development and progression of diabetic complications has been emphasized. Polyphenols present in natural products have gained much attention in recent decades in preventive studies against diabetes-associated pathologies. In the present review, we provide a comparative update on the role of quercetin, myricetin, and resveratrol—the major polyphenols present in red grapes—in intervening with diabetic complications, and a brief highlight on the molecular mechanisms underlying oxidative stress mediated hyperglycemia.

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

Intraoperative maintenance of normoglycemia with insulin and glucose preserves verbal learning after cardiac surgery

Objective

The hyperglycemic response to surgery may be a risk factor for cognitive dysfunction. We hypothesize that strict maintenance of normoglycemia during cardiac surgery preserves postoperative cognitive function.

Methods

As part of a larger randomized, single-blind, interventional efficacy study on the effects of hyperinsulinemic glucose control in cardiac surgery (NCT00524472), consenting patients were randomly assigned to receive combined administration of insulin and glucose, titrated to preserve normoglycemia (3.5–6.1 mmol L⁻¹; experimental group), or standard metabolic care (blood glucose 3.5–10 mmol L⁻¹; control group), during open heart surgery. The patients’ cognitive function was assessed during three home visits, approximately two weeks before the operation, and two months and seven months after surgery. The following tests were performed: Rey Auditory Verbal Learning Task (RAVLT for verbal learning and memory), Digit Span Task (working memory), Trail Making A & B (visuomotor tracking and attention), and the Word Pair Task (implicit memory). Questionnaires measuring specific traits known to affect cognitive performance, such as self-esteem, depression, chronic stress and social support, were also administered. The primary outcome was to assess the effect of hyperinsulinemic-normoglycemic clamp therapy versus standard therapy on specific cognitive parameters in patients receiving normoglycemic clamp, or standard metabolic care.

Results

Twenty-six patients completed the study with 14 patients in the normoglycemia and 12 patients in the control group. Multiple analysis of covariance (MANCOVA) for the RAVLT showed a significant effect for the interaction of group by visit (F = 4.07, p = 0.035), and group by visit by recall (F = 2.21, p = 0.04). The differences occurred at the second and third visit. MANCOVA for the digit span task, trail making and word pair association test showed no significant effect.

Conclusions

Preserving intraoperative normoglycemia by intravenous insulin and glucose may prevent the impairment of memory function, both short and long-term, after cardiac surgery.

Exercise protects against chronic β-adrenergic remodeling of the heart by activation of endothelial nitric oxide synthase

Extensive data have shown that exercise training can provide cardio-protection against pathological cardiac hypertrophy. However, how long the heart can retain cardio-protective phenotype after the cessation of exercise is currently unknown. In this study, we investigated the time course of the loss of cardio-protection after cessation of exercise and the signaling molecules that are responsible for the possible sustained protection. Mice were made to run on a treadmill six times a week for 4 weeks and then rested for a period of 0, 1, 2 and 4 weeks followed by isoproterenol injection for 8 days. Morphological, echocardiographic and hemodynamic changes were measured, gene reactivation was determined by real-time PCR, and the expression and phosphorylation status of several cardio-protective signaling molecules were analyzed by Western-blot. HW/BW, HW/TL and LW/BW decreased significantly in exercise training (ER) mice. The less necrosis and lower fetal gene reactivation induced by isoproterenol injection were also found in ER mice. The echocardiographic and hemodynamic changes induced by β-adrenergic overload were also attenuated in ER mice. The protective effects can be sustained for at least 2 weeks after the cessation of the training. Western-blot analysis showed that the alterations in the phosphorylation status of endothelial nitric oxide synthase (eNOS) (increase in serine 1177 and decrease in threonine 495) continued for 2 weeks after the cessation of the training whereas increases of the phosphorylation of Akt and mTOR disappeared. Further study showed that L-NG-Nitroarginine methyl ester (L-NAME) treatment abolished the cardio-protective effects of ER. Our findings demonstrate that stimulation of eNOS in mice through exercise training provides acute and sustained cardioprotection against cardiac hypertrophy.

Arg972 insulin receptor substrate-1 polymorphism and risk and severity of Alzheimer's disease

We explored the association between the Arg972 insulin receptor substrate-1 (IRS1) polymorphism and the risk and severity of Alzheimer's disease (AD). We genotyped the Arg972 IRS1 (rs1801278) polymorphism in 1123 pairs of age, sex, body mass index, residence area and education level-matched Han Chinese AD patients and controls. AD severity was assessed with Mini-Mental State Examination (MMSE) scores. The AA (homozygous Arg972 IRS1) and GA (heterozygous Arg972 IRS1) genotypes were associated with an increased risk of AD after adjustment for comorbidities including type 2 diabetes mellitus, coronary heart disease, and hypertension (p<0.001; adjusted odds ratio [OR] 3.93 and 2.90, respectively). The A allele was associated with an increased risk of AD after adjustment for comorbidities (p<0.001; adjusted OR 2.26; 95% confidence interval 1.92-2.80). The percentage of Arg972 IRS1 AA homozygotes was higher in the MMSE score ⩽14 category than in the MMSE score 15-26 category overall and in each age group (p<0.001), while the wild type IRS1 GG homozygotes were predominantly found in the MMSE score 15-26 category overall and in each age group. The GG homozygote group had higher MMSE score than the GA heterozygote group, which in turn had higher MMSE score than the AA homozygote group overall and in each age group (p<0.05). In conclusion, the Arg972 IRS1 polymorphism is an independent risk factor for AD and the A allele has a gene dosage effect on AD severity in Han Chinese. This study adds fresh insights into the pathogenesis of AD.

Validation of surrogate indexes of insulin sensitivity in acute phase of myocardial infarction based on euglycemic-hyperinsulinemic clamp

The decrease in insulin sensitivity (IS) during myocardial infarction (MI) is recognized as a possible contributor to poor patient outcomes. Despite its potential relevance, a standardized and convenient IS assessment tool has yet to be established for said clinical scenarios. This study aimed to validate the accuracy of surrogate indexes in determining IS in acute MI patients by comparison with the gold standard reference method for measuring IS, the euglycemic-hyperinsulinemic clamp (EHC). We performed EHCs in 31 consecutive nondiabetic patients who were admitted within the first 24 h of symptoms of ST-segment elevation MI. Patients with prior diagnosis of diabetes, use of hypoglycemic agents, or a glycosylated hemoglobin ≥6.5% were excluded. EHCs were performed at the second day (D2) and sixth day (D6) post-MI. Basal (12-h fasting) blood samples from D2 and D6 were used to evaluate patient blood glucose and insulin levels. We then calculated the following surrogate indexes: homeostatic model assessment of insulin sensitivity (HOMA2S), homeostatic model assessment of insulin resistance (HOMA-IR), and quantitative insulin sensitivity check index (QUICKI). The IS index measured by EHC (ISiclamp) was correlated to HOMA2S, HOMA-IR, and QUICKI at D2 (r = 0.485, P = 0.009; r = -0.384, P = 0.048; r = 0.479, P = 0.01, respectively) and D6 (r = 0.621, P = 0.002; r = -0.576, P = 0.006; r = 0.626, P = 0.002, respectively). Receiver operator characteristic curves made for discrimination of ISiclamp above the median in D2 and D6 depicted areas under the curve of 0.740, 0.734, and 0.760 for HOMA2S, HOMA-IR, and QUICKI, respectively. Bland-Altman plots displayed no apparent systematic error for indexes, but a propensity for proportional error, particularly with HOMA-IR. Thus, based on EHC, these simple surrogate indexes are feasible for assessing IS during MI.

The endocrine role between β cells and intra-islet endothelial cells

The islets of Langerhans is the endocrine function region of pancreas, which exist in five cell types. The majority of endocrine cells are insulin-secreting β cells, mixed up with glucagon-secreting α-cells. The islets of Langerhans are highly vascularized, and the capillary network around the islet is about five times denser than that in the exocrine tissues. It guarantees endocrine cells adequately contact with the capillary networks. Above mentioned is the basis of deep study the interaction between β cells and capillary. Increasing number of studies contribute to the consensus that endothelial cells have positive effects in the islet microenvironment. Endothelial cells can act as endocrine cells which release many active substances, such as hepatocyte growth factors (HGF), thrombospondin-1(TSP-1), laminins, and collagens by means of different molecule pathways, inducing β cells differentiation, proliferation, survivor, and insulin release next to the vessels. Apart from the effect of endothelial cells on β cells by paracrine fashion, the islets can utilize VEGF-A, angiopoietin-1 and insulin signaling to increase the interaction with endothelial cells. As the endocrine role of endothelial cells to β cells, it may be a novel target to stimulate β cells regeneration, promote vascularization post islet transplantation strategy in the treatment of diabetes mellitus.

The β-cell/EC axis: how do islet cells talk to each other?

Within the pancreatic islet, the β-cell represents the ultimate biosensor. Its central function is to accurately sense glucose levels in the blood and consequently release appropriate amounts of insulin. As the only cell type capable of insulin production, the β-cell must balance this crucial workload with self-preservation and, when required, regeneration. Evidence suggests that the β-cell has an important ally in intraislet endothelial cells (ECs). As well as providing a conduit for delivery of the primary input stimulus (glucose) and dissemination of its most important effector (insulin), intraislet blood vessels deliver oxygen to these dense clusters of metabolically active cells. Furthermore, it appears that ECs directly impact insulin gene expression and secretion and β-cell survival. This review discusses the molecules and pathways involved in the crosstalk between β-cells and intraislet ECs. The evidence supporting the intraislet EC as an important partner for β-cell function is examined to highlight the relevance of this axis in the context of type 1 and type 2 diabetes. Recent work that has established the potential of ECs or their progenitors to enhance the re-establishment of glycemic control following pancreatic islet transplantation in animal models is discussed.

Insulin resistance is an independent determinate of ED in young adult men

Background

Insulin resistance (IR) triggers endothelial dysfunction, which contributes to erectile dysfunction (ED) and cardiovascular disease.

Aim

To evaluate whether IR was related to ED in young adult patients.

Methods

A total of 283 consecutive men complaining of ED at least six months were enrolled, with a full medical history, physical examination, and laboratory tests collected. Quantitative Insulin Sensitivity Check Index (QUICKI) was used to determine IR. The severity of ED was assessed by IIEF-5 questionnaire. Endothelial function was assessed by ultrasonographic examination of brachial artery flow mediated dilation (FMD).

Results

IR was detected in 52% patients. Subjects with IR had significant higher total cholesterol, triglycerides, low density lipoprotein-cholesterol (LDL-c), glycated haemoglobin (HBA1c), high sensitivity C-reactive protein (hs-CRP) and body mass index (BMI), but showed significant lower IIEF-5 score, FMD%, high density lipoprotein -cholesterol (HDL-c), testosterone, sex hormone binding globulin (SHBG) levels than patients without IR. Multiple regression analysis showed QUICKI and testosterone were independent predictors of IIEF-5 score. Furthermore, the incidence of IR was correlated with the severity of ED.

Conclusions

Compared with other CVFs, IR was found as the most prevalent in our subjects. Besides, IR was independently associated with ED and its severity, suggesting an adverse effect of insulin resistance on erectile function.

Interaction between the NOS3 gene and obesity as a determinant of risk of type 2 diabetes: the Atherosclerosis Risk in Communities study

Endothelial nitric oxide synthase 3 (NOS3) catalyzes the production of nitric oxide from L-arginine in endothelial cells. Obesity is a modifiable risk factor for diabetes, and obese individuals have been reported to have reduced nitric oxide availability compared to controls whose weight is in the normal range. Since homozygous carriers of the NOS3 G894T variant are predicted to have decreased enzyme activity, the association between NOS3 genotype and type 2 diabetes, and possible effect modification by body mass index (BMI) were evaluated. The prevalence of diabetes and BMI was determined at baseline in 14,374 participants 45-66 years of age from the prospective biracial population-based Atherosclerosis Risk in Communities (ARIC) Study of the development of atherosclerosis in four communities in the United States. Individuals with a BMI ≥30 kg/m(2) were considered obese. Those subjects not meeting the case definition were the comparison groups for the 728 African American and 980 white participants with diabetes. Multivariable logistic regression models adjusted for age, sex, and field center were used to test for main genetic effects and interaction with obesity. Although the NOS3 G894T variant was not independently associated with diabetes in either African Americans or whites, significant interaction between BMI and the NOS3 polymorphism indicated that obesity was an effect modifier of diabetes risk for white individuals with the TT genotype (odds ratio (OR) for interaction = 1.65, p = 0.04). In stratified analyses, homozygosity for the NOS3 T allele in obese white participants but not in those whose BMI <30 kg/m(2) was associated with an elevated risk of diabetes (OR = 1.47, p = 0.02) when compared to the common GG genotype. These results suggest that interaction between obesity and NOS3 genotype may be a determinant of diabetes case status in whites in the ARIC cohort. Replication in other populations will be required to confirm these observations.

Brain expansion in patients with type II diabetes following insulin therapy: a preliminary study with longitudinal voxel-based morphometry

OBJECTIVE

We performed a longitudinal analysis based on magnetic resonance (MR) imaging to investigate the brain structural and perfusion changes caused by insulin therapy in patients with type II diabetes.

METHODS

High resolution three-dimensional T1-weighted fast spoiled gradient recalled echo images and flow-sensitive alternating inversion recovery (FAIR) images were obtained from 11 patients with type II diabetes before and 1 year after initiation of insulin therapy and 11 normal controls. Brain volume changes were investigated by a longitudinal voxel-based morphometry (VBM), and perfusion changes were evaluated by FAIR imaging between baseline and follow-up data.

RESULTS

Significant regional gray matter (GM) expansion located in bilateral frontal, parietal, and left occipital lobes, and regional white matter (WM) expansion was shown in left precentral subcortical WM and right angular subcortical WM after insulin therapy (P < .05 with FDR correction). Brain hyperperfusion was detected in bilateral frontal cortex, left occipital cortex, and right temporal cortex after insulin therapy (P < .05).

CONCLUSIONS

In patients with type II diabetes, brain expansion and hyperperfusion were demonstrated 1 year after initiation of insulin therapy, and insulin therapy could contribute to the brain volume gainment in the patients with type II diabetes.

A review of the mechanisms and effectiveness of dietary polyphenols in reducing oxidative stress and thrombotic risk

Dietary sources of polyphenols, which are derivatives and/or isomers of flavones, isoflavones, flavonols, catechins and phenolic acids, possess antioxidant properties and therefore might be important in preventing oxidative-stress-induced platelet activation and attenuating adverse haemostatic function. Free radicals, including reactive oxygen and nitrogen species, promote oxidative stress, leading to platelet hyperactivation and the risk of thrombosis. The consumption of antioxidant/polyphenol rich foods might therefore impart anti-thrombotic and cardiovascular protective effects via their inhibition of platelet hyperactivation or aggregation. Most commonly-used anti-platelet drugs such as aspirin block the cyclooxygenase (COX)-1 pathway of platelet activation, similar to the action of antioxidants with respect to neutralising hydrogen peroxide (H2 O2 ), with a similar effect on thromboxane production via the COX-1 pathway. Polyphenols also target various additional platelet activation pathways (e.g. by blocking platelet-ADP, collagen receptors); thus alleviating fibrinogen binding to platelet surface (GPIIb-IIIa) receptors, reducing further platelet recruitment for aggregation and inhibiting platelet degranulation. As a result of the ability of polyphenols to target additional pathways of platelet activation, they may have the potential to substitute or complement currently used anti-platelet drugs in sedentary, obese, pre-diabetic or diabetic populations who can be resistant or sensitive to pharmacological anti-platelet therapy.

Cellular and molecular mechanisms of endothelial dysfunction in diabetes

In healthy individuals, the vascular endothelium regulates an intricate balance of factors that maintain vascular homeostasis and normal arterial function. Functional disruption of the endothelium is known to be an early event that underlies the development of subsequent cardiovascular disease (CVD) including atherosclerosis and coronary heart disease. In addition, the rising global epidemic of type 2 diabetes is a significant problem conferring a significantly higher risk of CVD to individuals in whom endothelial dysfunction is also notable. This review first summarises the role of endothelium in health and explores and evaluates the impact of diabetes on endothelial function. The characteristic features of insulin resistance and other metabolic disturbances that may underlie long-term changes in vascular endothelial function (metabolic memory) are described along with proposed cellular, molecular and epigenetic mechanisms. Through understanding the underlying mechanisms, novel targets for future therapies to restore endothelial homeostasis and 'drive' a reparative cellular phenotype are explored.

Insulin resistance and atherosclerosis: convergence between metabolic pathways and inflammatory nodes

For some time now it has been known that diabetes and atherosclerosis are chronic inflammatory diseases that are closely associated with one another and often develop together. In both there is an increase in tissue-wide inflammation that is exhibited by the infiltration of immune cells into the adipose tissue and the vascular walls respectively. The monocyte/macrophage populations that are recruited in these seemingly different settings also display a high similarity by exhibiting similar phenotypes in both conditions. In the insulin resistant as well as the atherosclerotic setting there is a distinct switch in the macrophage populations present from an anti-inflammatory (M2) population to an inflammatory (M1) population, which releases cytokines and chemotactic factors with the ability to worsen the local environment and thus aggravate the situation by creating a vicious circle. However, although some discoveries suggest that preventing the development of M1 macrophages reduces inflammation and thereby aggravation of these diseases, there are currently no clear-cut opinions on how to achieve a switch from M2 to M1.

Arg972 Insulin receptor substrate-1 is associated with decreased serum angiotensin-converting enzyme 2 levels in acute myocardial infarction patients: in vivo and in vitro evidence

Background

Activation of the renin-angiotensin system (RAS) plays a critical role in the pathophysiology of myocardial infarction (MI) and the development of heart failure. Both angiotensin-converting enzyme 2 (ACE2) and insulin/insulin receptor substrate-1 (IRS-1) show cardioprotective effects after acute MI. The Arg⁹⁷² IRS-1 polymorphism is associated with diminished activity of insulin. In the present study, we explored the association among Arg⁹⁷² IRS-1, acute MI, and serum levels of ACE2.

Methods

A total of 711 subjects, including 351 subjects with first-time acute MI and 360 subjects without a history of MI were genotyped for Arg⁹⁷² IRS-1 polymorphism. Serum levels of ACE2 and MI severity scores were determined. Primary human cardiomyocytes with overexpression of wild type IRS-1 or Arg⁹⁷² IRS-1 or knockdown of endogenous IRS-1 were exposed to normoxia and hypoxia, and the expression levels of ACE2 were determined.

Results

The serum ACE2 level was significantly increased in acute MI patients compared with that of non-MI controls. Compared with wild type IRS-1 carriers, Arg⁹⁷² IRS-1 carriers exhibited decreased serum ACE2 levels and increased MI severity scores after MI. Our in vitro data demonstrate that impairment of insulin/IRS-1/PI3K signaling by overexpression of Arg⁹⁷²-IRS-1, knockdown of endogenous IRS-1, or PI3K inhibitor can abolish hypoxia-induced IRS-1-associated PI3K activity and ACE2 expression in human cardiomyocytes, which suggests a causal relationship between Arg⁹⁷²-IRS-1 and decreased serum ACE2 levels in acute MI patients. Our in vitro data also indicate that insulin/IRS-1/PI3K signaling is required for ACE2 expression in cardiomyocytes, and that hypoxia can enhance the induction effect of insulin/IRS-1/PI3K signaling on ACE2 expression in cardiomyocytes.

Conclusions

This study provides the first evidence of crosstalk between insulin/IRS-1/PI3K signaling and RAS after acute MI, thereby adding fresh insights into the pathophysiology and treatment of acute MI.

Sirtuin 1 is upregulated in young obese Zucker rat cerebral arteries

Many diseases, including metabolic syndrome, are characterised by endothelial dysfunction mediated by reduced nitric oxide bioavailability and oxidative stress. Sirtuin 1 is a protein deacetylase that targets endothelial nitric oxide synthase resulting in enhanced nitric oxide bioavailability. Although it has been highlighted as a potential therapeutic target, we still have no understanding of vascular SIRT1 changes during obesity. Therefore, the aim of the present study was to measure vascular function, SIRT1 protein levels of expression and markers of oxidative stress in obese Zucker rats. Middle cerebral arteries from nondiabetic obese and lean Zucker rats were mounted in a pressure myograph to assess nitric oxide-dependent dilations. Western blotting was used to measure protein levels of SIRT1, p53, acetylated p53, eNOS, phosphorylated eNOS and markers of oxidative stress (nitrotyrosine, Nox4 and SOD2) in cerebral vascular tissue. SIRT1 expression was two-fold greater in both cerebral arteries and aorta from obese compared to lean Zucker rats. Acetylation of p53 at the SIRT1-specific lysine 379 site was markedly decreased. At the same time, there was noted cerebral vascular impairment however markers of oxidative stress were not increased. In fact, Nox4 appeared to be downregulated in obesity. Thus, SIRT1 protein levels within the vasculature are greater in obese compared to lean Zucker rats and are associated with higher SIRT1 activity and lower Nox4 expression. We propose that the increased expression and activity of SIRT1 may be a vascular adaptive mechanism in obesity, aiming to prevent oxidative stress.

Diabetic nephropathy: protective factors and a new therapeutic paradigm

Diabetic nephropathy (DN) is the most common cause of chronic kidney disease (CKD) and its number has been increasing. CKD is a worldwide threat to health but the precise mechanism of this problem is not fully appreciated. It is believed that hyperglycemia is one of the most important metabolic factors in the development of DN. Multiple molecular mechanisms have been proposed to mediate hyperglycemia's adverse effects on kidney. To identify targets for therapeutic intervention, most studies have focused on understanding how abnormal levels of such metabolities cause DN. However, there have been few reports regarding endogenous renal protective factors. Thus, recognition of the importance of this could be providing a new perspective for understanding the development of DN and a new therapeutic paradigm to combat DN.

Improvement of β-cell function after achievement of optimal glycaemic control via long-term continuous subcutaneous insulin infusion therapy in non-newly diagnosed type 2 diabetic patients with suboptimal glycaemic control

BACKGROUND

Achieving euglycaemia by continuous subcutaneous insulin infusion (CSII) therapy alone has been shown to restore β-cell function in patients with newly diagnosed type 2 diabetes. However, the efficacy has not been evaluated in patients with non-newly diagnosed type 2 diabetes and suboptimal glycaemic control.

METHODS

Of the 1220 patients with type 2 diabetes who began CSII therapy from March 2000 to March 2007, we retrospectively selected patients using the following inclusion criteria: glycosylated haemoglobin (HbA1c ) ≥ 7.0%, diabetes duration ≥ 1 year before CSII therapy, and duration of CSII therapy ≥ 6 months. We evaluated sequential changes in HbA1c and serum C-peptide levels measured at a 6- to 12-month intervals during CSII therapy.

RESULTS

In the 521 subjects included in this study [median diabetes duration 10 years; interquartile range (IQR) 6.0-17.0; CSII therapy ≤ 30 months], median HbA1c decreased from 8.7% (IQR 7.7-10.0) at baseline to 6.3% (IQR 5.9-6.9) after 6 months of CSII therapy (p < 0.0001). During the subsequent 24 months, median HbA1c levels were maintained between 6.3% and 6.5% (p < 0.0001 for all time points vs baseline). At 12 months after CSII therapy, median C-peptide levels began to increase compared with baseline (fasting level 23% increase, p < 0.0001; 2-h postprandial level 26% increase, p = 0.022), and the increase was maintained at 30 months (fasting level 39%; 2-h postprandial level 53%; p < 0.0001 for all vs baseline).

CONCLUSIONS

β-Cell function was significantly improved in patients with non-newly diagnosed and suboptimally controlled type 2 diabetes after achieving and maintaining optimal glycaemic control with long-term CSII therapy alone.

Impairment of endothelial-myocardial interaction increases the susceptibility of cardiomyocytes to ischemia/reperfusion injury

Endothelial-myocardial interactions may be critically important for ischemia/reperfusion injury. Tetrahydrobiopterin (BH4) is a required cofactor for nitric oxide (NO) production by endothelial NO synthase (eNOS). Hyperglycemia (HG) leads to significant increases in oxidative stress, oxidizing BH4 to enzymatically incompetent dihydrobiopterin. How alterations in endothelial BH4 content impact myocardial ischemia/reperfusion injury remains elusive. The aim of this study was to examine the effect of endothelial-myocardial interaction on ischemia/reperfusion injury, with an emphasis on the role of endothelial BH4 content. Langendorff-perfused mouse hearts were treated by triton X-100 to produce endothelial dysfunction and subsequently subjected to 30 min of ischemia followed by 2 h of reperfusion. The recovery of left ventricular systolic and diastolic function during reperfusion was impaired in triton X-100 treated hearts compared with vehicle-treated hearts. Cardiomyocytes (CMs) were co-cultured with endothelial cells (ECs) and subsequently subjected to 2 h of hypoxia followed by 2 h of reoxygenation. Addition of ECs to CMs at a ratio of 1∶3 significantly increased NO production and decreased lactate dehydrogenase activity compared with CMs alone. This EC-derived protection was abolished by HG. The addition of 100 µM sepiapterin (a BH4 precursor) or overexpression of GTP cyclohydrolase 1 (the rate-limiting enzyme for BH4 biosynthesis) in ECs by gene trasfer enhanced endothelial BH4 levels, the ratio of eNOS dimer/monomer, eNOS phosphorylation, and NO production and decreased lactate dehydrogenase activity in the presence of HG. These results demonstrate that increased BH4 content in ECs by either pharmacological or genetic approaches reduces myocardial damage during hypoxia/reoxygenation in the presence of HG. Maintaining sufficient endothelial BH4 is crucial for cardioprotection against hypoxia/reoxygenation injury.

Insulin resistance is associated with significant clinical atherosclerosis in nondiabetic patients with acute myocardial infarction

OBJECTIVE

The prevalence of insulin resistance (IR) is increasing worldwide because of increasing age, obesity, and physical inactivity. Emerging evidence supports a direct proatherogenic effect of IR on the coronary vasculature, but the relation between IR and angiographic atherosclerosis in a real-world clinical setting is uncertain. In this work, we assessed whether IR is independently associated with clinically significant angiographic atherosclerosis in nondiabetic individuals.

APPROACH AND RESULTS

We examined the association between IR and the extent of coronary atherosclerosis determined by angiography in 1073 nondiabetic patients surviving acute myocardial infarction. Patients were divided into quartiles on the basis of the homeostasis model assessment grading of IR, and associations between IR and multivessel coronary artery disease, defined as ≥ 2 arteries with ≥ 70% stenosis (or ≥ 50% left main stenosis), were analyzed in bivariate and multivariable modeling. Overall, the cohort had a median age of 56 years; 28.9% women and 21.8% nonwhite. The crude prevalence of multivessel coronary artery disease was 37.8%, 42.3%, 47.2%, and 48.0% for homeostasis model assessment grading of IR quartiles 1, 2, 3, and 4, respectively (P(trend) = 0.009). In multivariable modeling, compared with quartile 1, both quartile 3 (relative risk [95% confidence interval], 1.31 [1.07-1.60]) and quartile 4 (1.29 [1.03-1.60]) were independently associated with multivessel coronary artery disease. Covariates in the model included patient demographic and clinical characteristics and metabolic factors (low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, triglyceride, glycosylated hemoglobin, and high-sensitivity C-reactive protein).

CONCLUSIONS

We demonstrate an independent association between IR and multivessel coronary artery disease in nondiabetic postmyocardial infarction patients. Our findings strengthen the experimental evidence for a direct atherogenic effect of IR independent of glucose control and other components of the metabolic syndrome.

Nitric oxide regulates vascular adaptive mitochondrial dynamics

Cardiovascular disease risk factors, such as diabetes, hypertension, dyslipidemia, obesity, and physical inactivity, are all correlated with impaired endothelial nitric oxide synthase (eNOS) function and decreased nitric oxide (NO) production. NO-mediated regulation of mitochondrial biogenesis has been established in many tissues, yet the role of eNOS in vascular mitochondrial biogenesis and dynamics is unclear. We hypothesized that genetic eNOS deletion and 3-day nitric oxide synthase (NOS) inhibition in rodents would result in impaired mitochondrial biogenesis and defunct fission/fusion and autophagy profiles within the aorta. We observed a significant, eNOS expression-dependent decrease in mitochondrial electron transport chain (ETC) protein subunits from complexes I, II, III, and V in eNOS heterozygotes and eNOS null mice compared with age-matched controls. In response to NOS inhibition with NG-nitro-L-arginine methyl ester (L-NAME) treatment in Sprague Dawley rats, significant decreases were observed in ETC protein subunits from complexes I, III, and IV as well as voltage-dependent anion channel 1. Decreased protein content of upstream regulators of mitochondrial biogenesis, cAMP response element-binding protein and peroxisome proliferator-activated receptor-γ coactivator-1α, were observed in response to 3-day L-NAME treatment. Both genetic eNOS deletion and NOS inhibition resulted in decreased manganese superoxide dismutase protein. L-NAME treatment resulted in significant changes to mitochondrial dynamic protein profiles with decreased fusion, increased fission, and minimally perturbed autophagy. In addition, L-NAME treatment blocked mitochondrial adaptation to an exercise intervention in the aorta. These results suggest that eNOS/NO play a role in basal and adaptive mitochondrial biogenesis in the vasculature and regulation of mitochondrial turnover.

Beneficial effect of genistein on lowering blood pressure and kidney toxicity in fructose-fed hypertensive rats

The study evaluates the effects of genistein on blood pressure (BP) and ultrastructural changes in kidney of fructose-fed hypertensive rats. Male Wistar rats were fed a diet containing 60 % starch or 60 % fructose as the source of carbohydrate. After 15 d, rats in each dietary group were divided into two groups and were treated with either genistein (1 mg/kg per d) in dimethylsulfoxide (DMSO) or 30 % DMSO alone. BP, pressor mechanisms, protein kinase C-βII (PKC-βII) expression, endothelial NO synthase (eNOS) expression and renal ultrastructural changes were evaluated after 60 d. Fructose-fed rats displayed significant elevation in BP and heart rate. Significant increase in plasma angiotensin-converting enzyme (ACE) activity, alterations in renal lipid profile, nitrite and kallikrein activity, enhanced expression of membrane-associated PKC-βII and decreased expression of eNOS were observed in them. Histology and electron microscopic studies showed structural changes in the kidney. Genistein administration lowered BP, restored ACE, PKC-βII and eNOS expression and preserved renal ultrastructural integrity. These findings demonstrate that genistein has effects on eNOS activity in renal cells, leading to eNOS activation and NO synthesis. These effects could have been mediated by activation of PKC-βII. The observed benefits of genistein make it a promising candidate for therapy of diabetic kidney disease.

Insulin relaxes bladder via PI3K/AKT/eNOS pathway activation in mucosa: unfolded protein response-dependent insulin resistance as a cause of obesity-associated overactive bladder

We aimed to investigate the role of insulin in the bladder and its relevance for the development of overactive bladder (OAB) in insulin-resistant obese mice. Bladders from male individuals who were involved in multiple organ donations were used. C57BL6/J mice were fed with a high-fat diet for 10 weeks to induce insulin-resistant obesity. Concentration-response curves to insulin were performed in human and mouse isolated mucosa-intact and mucosa-denuded bladders. Cystometric study was performed in terminally anaesthetized mice. Western blot was performed in bladders to detect phosphorylated endothelial NO synthase (eNOS) (Ser1177) and the phosphorylated protein kinase AKT (Ser473), as well as the unfolded protein response (UPR) markers TRIB3, CHOP and ATF4. Insulin (1-100 nm) produced concentration-dependent mouse and human bladder relaxations that were markedly reduced by mucosal removal or inhibition of the PI3K/AKT/eNOS pathway. In mouse bladders, insulin produced a 3.0-fold increase in cGMP levels (P < 0.05) that was prevented by PI3K/AKT/eNOS pathway inhibition. Phosphoinositide 3-kinase (PI3K) inhibition abolished insulin-induced phosphorylation of AKT and eNOS in bladder mucosa. Obese mice showed greater voiding frequency and non-voiding contractions, indicating overactive detrusor smooth muscle. Insulin failed to relax the bladder or to increase cGMP in the obese group. Insulin-stimulated AKT and eNOS phosphorylation in mucosa was also impaired in obese mice. The UPR markers TRIB3, CHOP and ATF4 were increased in the mucosa of obese mice. The UPR inhibitor 4-phenyl butyric acid normalized all the functional and molecular parameters in obese mice. Our data show that insulin relaxes human and mouse bladder via activation of the PI3K/AKT/eNOS pathway in the bladder mucosa. Endoplasmic reticulum stress-dependent insulin resistance in bladder contributes to OAB in obese mice.

Mechanisms of lipotoxicity in the cardiovascular system

Cardiovascular diseases account for approximately one third of all deaths globally. Obese and diabetic patients have a high likelihood of dying from complications associated with cardiovascular dysfunction. Obesity and diabetes increase circulating lipids that upon tissue uptake, may be stored as triglyceride, or may be metabolized in other pathways, leading to the generation of toxic intermediates. Excess lipid utilization or activation of signaling pathways by lipid metabolites may disrupt cellular homeostasis and contribute to cell death, defining the concept of lipotoxicity. Lipotoxicity occurs in multiple organs, including cardiac and vascular tissues, and a number of specific mechanisms have been proposed to explain lipotoxic tissue injury. In addition, recent data suggests that increased tissue lipids may also be protective in certain contexts. This review will highlight recent progress toward elucidating the relationship between nutrient oversupply, lipotoxicity, and cardiovascular dysfunction. The review will focus in two sections on the vasculature and cardiomyocytes respectively.

Lipotoxicity contributes to endothelial dysfunction: a focus on the contribution from ceramide

Cardiovascular complications are the leading causes of morbidity and mortality in individuals with obesity, type 2 diabetes mellitus (T2DM), and insulin resistance. Complications include pathologies specific to large (atherosclerosis, cardiomyopathy) and small (retinopathy, nephropathy, neuropathy) vessels. Common among all of these pathologies is an altered endothelial cell phenotype i.e., endothelial dysfunction. A crucial aspect of endothelial dysfunction is reduced nitric oxide (NO) bioavailability. Hyperglycemia, oxidative stress, activation of the renin-angiotensin system, and increased pro-inflammatory cytokines are systemic disturbances in individuals with obesity, T2DM, and insulin resistance and each of these contribute independently and synergistically to decreasing NO bioavailability. This review will examine the contribution from elevated circulating fatty acids in these subjects that lead to lipotoxicity. Particular focus will be placed on the fatty acid metabolite ceramide.

Insulin resistance and atherosclerosis

Insulin resistance is a complex metabolic defect that has several causes dependent on an individual's genetic substrate and the underlying pathophysiologic state. Atherogenic dyslipidemia, hyperinsulinemia, dysglycemia, inflammation associated with obesity, and ectopic steatosis in liver and skeletal muscle all collude to facilitate endothelial dysfunction and predispose to the initiation and propagation of atherosclerosis. As aggressive management of the various risk factors does not seem to abrogate the so-called residual risk, more research is needed to define ways by which intervention can fundamentally alter the metabolic and vascular milieu and slow the pace of atherosclerosis, thus favorably affecting outcomes.

Insulin inhibits lipopolysaccharide-induced nitric oxide synthase expression in rat primary astrocytes

Excessive production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) from reactive astrocytes and microglia may contribute to the development of many types of neurological diseases. Insulin has been shown to inhibit the expression of iNOS, in several organs and cell types. Although insulin and its receptors are present in the central nervous system, the effects of insulin on the iNOS pathway in the brain have not been determined. In this study, using lipopolysaccharide (LPS)-stimulated astrocytes as a model of reactive astrocytes, we investigated the effects of insulin on iNOS expression in activated astrocytes and the mechanism involved. The expression of iNOS was significantly upregulated by LPS in astrocytes. Insulin applied prior to LPS, dose-dependently inhibited LPS-induced iNOS gene expression and iNOS protein levels. In agreement with the suppressive effects of insulin on iNOS expression, insulin also inhibited LPS-induced iNOS activity and NO production. Moreover, insulin was found to significantly inhibit LPS-induced IκB-α phosphorylation and degradation, which led to a decrease in levels of the p65 subunit of NF-κB in the nuclear fraction. Therefore, insulin inhibited LPS-induced iNOS expression via suppressing NF-κB pathway in astrocytes. In addition, treatment with insulin had no effect on LPS-induced PKB phosphorylation. Based on our results, it is plausible to speculate that insulin in the brain may play a neuroprotective role in neurological disorders by controlling the release of NO via the regulation of iNOS expression in astrocytes.

Insulin signalling to the kidney in health and disease

Ninety-one years ago insulin was discovered, which was one of the most important medical discoveries in the past century, transforming the lives of millions of diabetic patients. Initially insulin was considered only important for rapid control of blood glucose by its action on a restricted number of tissues; however, it has now become clear that this hormone controls an array of cellular processes in many different tissues. The present review will focus on the role of insulin in the kidney in health and disease.

Vascular complications of diabetes: mechanisms of injury and protective factors

In patients with diabetes, atherosclerosis is the main reason for impaired life expectancy, and diabetic nephropathy and retinopathy are the largest contributors to end-stage renal disease and blindness, respectively. An improved therapeutic approach to combat diabetic vascular complications might include blocking mechanisms of injury as well as promoting protective or regenerating factors, for example by enhancing the action of insulin-regulated genes in endothelial cells, promoting gene programs leading to induction of antioxidant or anti-inflammatory factors, or improving the sensitivity to vascular cell survival factors. Such strategies could help prevent complications despite suboptimal metabolic control.

Inflammation and oxidative stress in diabetic nephropathy: new insights on its inhibition as new therapeutic targets

Diabetes and insulin resistance can greatly increase microvascular complications of diabetes including diabetic nephropathy (DN). Hyperglycemic control in diabetes is key to preventing the development and progression of DN. However, it is clinically very difficult to achieve normal glucose control in individual diabetic patients. Many factors are known to contribute to the development of DN. These include diet, age, lifestyle, or obesity. Further, inflammatory- or oxidative-stress-induced basis for DN has been gaining interest. Although anti-inflammatory or antioxidant drugs can show benefits in rodent models of DN, negative evidence from large clinical studies indicates that more effective anti-inflammatory and antioxidant drugs need to be studied to clear this question. In addition, our recent report showed that potential endogenous protective factors could decrease inflammation and oxidative stress, showing great promise for the treatment of DN.

The risk for coronary heart disease according to insulin resistance with and without type 2 diabetes

OBJECTIVE

To examine the role of insulin resistance versus hyperglycemia in the risk for coronary heart disease (CHD) and to explore the interaction of insulin resistance with hyperglycemia.

METHODS

This is a cross-sectional study based on the National Health and Nutrition Examination Survey III (NHANES). 4,825 subjects were selected from 9,737 adults aged ³40 years excluding those with fasting <8 hours, type 1 diabetes, pregnancy, or missing data. Insulin resistance was calculated using the HOMA II and then log-transformed (log IR). Odds ratios (OR) of CHD was obtained with multiple logistic regression with reference to non-diabetics with log IR > 1.

RESULTS

CHD and type 2 diabetes were present in 9.1 % and 10.5%. Elevated insulin resistance was common; diabetics and non-diabetics with log IR > 1 constituted 6.3% and 12.1% of the population, respectively. ORs for CHD increased as insulin resistance increased in both non-diabetic and diabetics. When log IR > 1, the risk for CHD was not different between diabetics and non-diabetics (OR 1.12, 95% CI; 0.76-1.65). Furthermore, the risk for CHD was higher in non-diabetics with log IR > 1 than in diabetics with log IR1 (OR 0.55, 95% CI; 0.36-0.85).

CONCLUSIONS

Insulin resistance was a greater risk for CHD than type 2 diabetes. Non-diabetics can have a higher risk for CHD than diabetics when insulin resistance is elevated. More research is warranted to develop strategies to identify and treat insulin resistance.

The molecular mechanisms of offspring effects from obese pregnancy

The incidence of obesity, increased weight gain and the popularity of high-fat / high-sugar diets are seriously impacting upon the global population. Billions of individuals are affected, and although diet and lifestyle are of paramount importance to the development of adult obesity, compelling evidence is emerging which suggests that maternal obesity and related disorders may be passed on to the next generation by non-genetic means. The processes acting within the uteri of obese mothers may permanently predispose offspring to a diverse plethora of diseases ranging from obesity and diabetes to psychiatric disorders. This review aims to summarise some of the molecular mechanisms and active processes currently known about maternal obesity and its effect on foetal and neonatal physiology and metabolism. Complex and multifactorial networks of molecules are intertwined and culminate in a pathologically synergistic manner to cause disruption and disorganisation of foetal physiology. This altered phenotype may potentiate the cycle of intergenerational transmission of obesity and related disorders.