Angela Sciacqua

Angiotensin II impairs the insulin signaling pathway promoting production of nitric oxide by inducing phosphorylation of insulin receptor substrate-1 on Ser312 and Ser616 in human umbilical vein endothelial cells

It has been suggested that serine (Ser) phosphorylation of insulin receptor substrate-1 (IRS-1) decreases the ability of IRS-1 to be phosphorylated on tyrosine, thereby attenuating insulin signaling. There is evidence that angiotensin II (AII) may impair insulin signaling to the IRS-1/phosphatydilinositol 3-kinase (PI 3-kinase) pathway by enhancing Ser phosphorylation. Insulin stimulates NO production by a pathway involving IRS-1/PI3-kinase/Akt/endo-thelial NO synthase (eNOS). We addressed the question of whether AII affects insulin signaling involved in NO production in human umbilical vein endothelial cells and tested the hypothesis that the inhibitory effect of AII on insulin signaling was caused by increased site-specific Ser phosphorylation in IRS-1. Exposure of human umbilical vein endothelial cells to AII resulted in inhibition of insulin-stimulated production of NO. This event was associated with impaired IRS-1 phosphorylation at Tyr612 and Tyr632, two sites essential for engaging the p85 subunit of PI3-kinase, resulting in defective activation of PI 3-kinase, Akt, and eNOS. This inhibitory effect of AII was reversed by the type 1 receptor antagonist losartan. AII increased c-Jun N-terminal kinase (JNK) and extracellular signal–regulated kinase (ERK) 1/2 activity, which was associated with a concomitant increase in IRS-1 phosphorylation at Ser312 and Ser616, respectively. Inhibition of JNK and ERK1/2 activity reversed the negative effects of AII on insulin-stimulated NO production. Our data suggest that AII, acting via the type 1 receptor, increases IRS-1 phosphorylation at Ser312 and Ser616 via JNK and ERK1/2, respectively, thus impairing the vasodilator effects of insulin mediated by the IRS-1/PI 3-kinase/Akt/eNOS pathway.

Elevated one-hour post-load plasma glucose levels identifies subjects with normal glucose tolerance but early carotid atherosclerosis

OBJECTIVE To examine whether individuals with normal glucose tolerance (NGT), whose 1-h post-load plasma glucose is >or=155 mg/dl, or with impaired glucose tolerance (IGT) have an increased carotid intima-media thickness (IMT), as compared with NGT individuals with 1-h post-load plasma <155 mg/dl. METHODS Atherosclerosis risk factors, oral glucose tolerance test (OGTT), and ultrasound manual measurement of IMT were analyzed in 400 non-diabetic Caucasians. RESULTS As compared with individuals with a 1-h post-load plasma glucose <155 mg/dl, NGT individuals with a 1-h post-load plasma glucose >or=155 mg/dl exhibited higher hsCRP (2.0+/-1.5 vs. 1.5+/-1.0, P=0.008), and IMT (0.82+/-0.20 vs. 0.71+/-0.16; P=0.006), and lower insulin sensitivity (71+/-39 vs. 105+/-57; P<0.0001), and IGF-1 levels (214+/-88 vs. 176+/-49; P<0.03). No significant differences were observed in metabolic and cardiovascular risk factors between IGT and NGT subjects with a 1-h post-load glucose >or=155 mg/dl. Of the three glycemic parameters, 1-h and 2-h post-load glucose, but not fasting glucose, were significantly correlated with IMT. In a stepwise multivariate regression analysis in a model including age, gender, and a variety of atherosclerosis risk factors, the three variables that remained significantly associated with IMT were age (P<0.0001), BMI (P<0.0001), and 1-h post-load glucose (P=0.02) accounting for 20.2% of its variation. CONCLUSIONS NGT subjects with a 1-h post-load glucose >or=155 mg/dl have an atherogenic profile similar to IGT individuals. These data suggest that a cutoff point of 155 mg/dl for the 1-h post-load glucose during OGTT may be helpful in the identification of NGT subjects at increased risk for cardiovascular disease.

Pulse pressure and endothelial dysfunction in never-treated hypertensive patients.

OBJECTIVES This study sought to investigate whether pulse pressure (PP) is associated with endothelium-dependent vasodilation in a group of never-treated hypertensives. BACKGROUND Pulse pressure represents a well-established independent predictor for cardiovascular morbidity and mortality. Forearm endothelial dysfunction, defined as impaired vasodilating response to acetylcholine (ACh), may be associated with several cardiovascular risk factors. Recently, the prognostic value of coronary and forearm endothelial dysfunction has been demonstrated. METHODS All patients underwent measurement of blood pressure (BP) both clinically and in an ambulatory setting. Endothelium-dependent and -independent vasodilation was investigated by strain-gauge plethysmography in 262 hypertensive patients (age 30 to 55 years) during intra-arterial infusion of increasing doses of ACh and sodium nitroprusside. RESULTS We observed that systolic BP rather than diastolic BP significantly induces the PP increase. Linear regression analysis revealed a significant inverse correlation between ACh-stimulated forearm blood flow (FBF) and age, body mass index, clinic and monitored systolic BP, and clinic and monitored PP. However, stepwise multivariate analysis showed that monitored PP was the strongest independent predictor of ACh-stimulated FBF, accounting for 33.6% of the variation. After adjustment for other covariates, ACh-stimulated FBF decreases by 8.7% for each mm Hg increment in monitored PP. CONCLUSIONS Our data indicate that monitored PP is inversely correlated with ACh-stimulated vasodilation. It is possible to hypothesize that elevation in PP reduces FBF by increasing oxidative stress and reducing production of nitric oxide caused by reduced shear stress. In addition, the present findings demonstrate the accuracy of ambulatory BP as a prognostic predictor of hypertension-associated endothelial dysfunction.

Interleukin-6 Impairs the Insulin Signaling Pathway, Promoting Production of Nitric Oxide in Human Umbilical Vein Endothelial Cells

ABSTRACT Interleukin 6 (IL-6) is an independent predictor of type 2 diabetes and cardiovascular disease and is correlated with insulin resistance. Insulin stimulates nitric oxide (NO) production through the IRS-1/PI3-kinase/Akt/eNOS pathway (where IRS-1 is insulin receptor substrate 1, PI3-kinase is phosphatidylinositol 3-kinase, and eNOS is endothelial NO synthase). We asked if IL-6 affects insulin vasodilator action both in human umbilical vein endothelial cells (HUVEC) and in the aortas of C57BL/6J mice and whether this inhibitory effect was caused by increased Ser phosphorylation of IRS-1. We observed that IL-6 increased IRS-1 phosphorylation at Ser312 and Ser616; these effects were paralleled by increased Jun N-terminal protein kinase (JNK) and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and reversed by JNK and ERK1/2 inhibition. In addition, IL-6 treatment resulted in impaired IRS-1 phosphorylation at Tyr612, a site essential for engaging PI3-kinase. Furthermore, IL-6 treatment reduced insulin-stimulated phosphorylation of eNOS at the stimulatory Ser1177 site and impaired insulin-stimulated eNOS dephosphorylation at the inhibitory Thr495 site. Insulin-stimulated eNOS activation and NO production were also inhibited by IL-6; these effects were reversed by inhibition of JNK and ERK1/2. Treatment of C57BL/6J mice with IL-6 resulted in impaired insulin-dependent activation of the Akt/eNOS pathway in the aorta as a result of JNK and ERK1/2 activation. Our data suggest that IL-6 impairs the vasodilator effects of insulin that are mediated by the IRS-1/PI3-kinase/Akt/eNOS pathway through activation of JNK and ERK1/2.

Endothelial Dysfunction and Subsequent Decline in Glomerular Filtration Rate in Hypertensive Patients

Background— Chronic kidney disease is a risk factor for cardiovascular disease, increasing all-cause mortality. Some evidence suggests that endothelial dysfunction is present in the early stages of renal insufficiency, but no data exist about its possible role in the progression of renal disease. Thus, we prospectively evaluated the effect of endothelial function on estimated glomerular filtration rate (eGFR) in essential hypertension. Methods and Results— We enrolled 500 never-treated uncomplicated hypertensive subjects with serum creatinine ≤1.5 mg/dL. Endothelial function was measured by strain-gauge plethysmography during intra-arterial infusion of acetylcholine and sodium nitroprusside. eGFR was calculated by use of the Chronic Kidney Disease Epidemiology Collaboration equation. The annual rate of decline of eGFR (&Dgr;eGFR/y) was determined as the difference between the follow-up and baseline eGFR values, with this value divided by the time interval in years. During follow-up (92.3±36.2 months), mean &Dgr;eGFR/y was 1.49±1.65 mL · min−1 · 1.73 m−2, with no significant differences between men and women (1.55±1.72 versus 1.43±1.58 mL · min−1 · 1.73 m−2, respectively; P=0.455). This was correlated with acetylcholine-stimulated forearm blood flow (r=−0.256, P<0.0001), creatinine (r=0.141, P=0.001), systolic blood pressure (r=−0.103, P=0.01), and eGFR (r=0.092, P=0.020). In multivariable regression analysis, forearm blood flow and systolic blood pressure remained associated with change in eGFR. On average, eGFR changed by 0.37 mL · min−1 · 1.73 m−2 for each 100% change in forearm blood flow (P<0.001) and by 0.1 mL · min−1 · 1.73 m−2 for each difference of 10 mm Hg in systolic blood pressure (P=0.032). Conclusions— We demonstrated that acetylcholine-stimulated vasodilation and systolic blood pressure were associated with eGFR loss after adjustment for other cardiovascular risk factors and antihypertensive treatment.

Endothelial dysfunction, ADMA and insulin resistance in essential hypertension

BACKGROUND Endothelial dysfunction and insulin resistance (IR) are associated with essential hypertension and other cardiovascular risk factors. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, induces endothelial dysfunction in different setting of patients. However, at this moment no data are available about the role of ADMA and IR to induce endothelial dysfunction in an independent way or combined between them. In this study, we investigated, in 63 hypertensives and 21 normotensive healthy subjects, the relationship between ADMA and IR and their possible interaction on endothelial function. METHODS ADMA plasma levels were measured by high-performance liquid chromatography, and IR by homeostasis model assessment (HOMA). Endothelial function was estimated by intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside at increasing doses. RESULTS Hypertensive patients had significantly higher ADMA, insulin, HOMA and C-reactive protein (CRP) values than normotensive controls (P<0.0001). There were no significant differences in mean l-arginine/ADMA ratio between groups. ACh-stimulated forearm blood flow (FBF) was significantly reduced in hypertensive patients (P<0.0001). In hypertensive group, HOMA was the strongest determinant of FBF, accounting for the 45.5% of its variation. ADMA and gender were the independent determinants of HOMA, accounting for 12.3% and 8.3% of its variation, respectively. CONCLUSIONS The association between ADMA and IR contributes to identify a possible novel mechanism by which ADMA promotes vascular damage, increasing individual cardiovascular risk in hypertensive patients. However, this hypothesis should be tested in a larger study group.

Cardiometabolic Risk Profiles and Carotid Atherosclerosis in Individuals With Prediabetes Identified by Fasting Glucose, Postchallenge Glucose, and Hemoglobin A1c Criteria

OBJECTIVE We evaluated whether cardiometabolic risk profiles differ for subjects identified as having prediabetes by A1C, fasting glucose (FPG), or 2-h postchallenge glucose (2-PG) criteria. RESEARCH DESIGN AND METHODS Atherosclerosis risk factors, oral glucose tolerance test, and ultrasound measurement of carotid intima–media thickness (IMT) were analyzed in 780 nondiabetic individuals. RESULTS Poor agreement existed for A1C and FPG criteria for identification of subjects with prediabetes (κ coefficient = 0.332). No differences in cardiometabolic risk profiles were observed among the three groups of individuals with prediabetes by A1C only, FPG only, and both A1C and FPG. Poor agreement also existed for A1C and 2-PG criteria for identification of individuals with prediabetes (κ coefficient = 0.299). No significant differences in cardiometabolic risk factors were observed between IGT-only and individuals with prediabetes by A1C and 2-PG. Compared with subjects with prediabetes identified by A1C only, IGT-only individuals exhibited a worse cardiometabolic risk profile, with significantly higher systolic blood pressure, pulse pressure, 2-h postchallenge insulin, triglycerides, high-sensitivity C-reactive protein, and carotid IMT, and lower HDL cholesterol levels and insulin sensitivity. CONCLUSIONS These results suggest that considerable discordance between A1C, FPG, and 2-PG exists for the identification of individuals with prediabetes and that the cardiometabolic risk profile of these individuals varies by metabolic parameter, with 2-PG showing the stronger association with cardiometabolic risk factors and subclinical atherosclerosis than FPG or A1C.

Nonalcoholic Fatty Liver Disease Is Associated with Low Circulating Levels of Insulin-Like Growth Factor-I

CONTEXT Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease and is associated with insulin resistance and cardiovascular disease. Among the potential factors that may account for the increased cardiometabolic risk, IGF-I is a plausible candidate because the liver is the main site of its production. OBJECTIVE Our objective was to examine the relationship between NAFLD and IGF-I levels and to test the hypothesis that free fatty acids-induced insulin resistance might impair insulin-induced increase of GH receptor (GHR) expression in human hepatoma cells. SUBJECTS, DESIGN, AND SETTING: Five hundred three nondiabetic Caucasians participated in this ambulatory-care cross-sectional study. MAIN OUTCOME MEASURES Cardiometabolic risk factors and liver ultrasound scanning were assessed. Insulin-induced expression of GHR in HuH7 human hepatoma cells exposed for 24 h to palmitate was determined by Western blotting and real-time PCR. RESULTS After adjustment for age and gender, individuals with NAFLD had significantly higher body mass index, waist circumference, fasting insulin, triglycerides, homeostasis model assessment index, liver enzymes, and lower high-density lipoprotein cholesterol compared with control subjects. IGF-I levels were significantly lower in individuals with NAFLD (P = 0.001). Exposure of HuH7 hepatoma cells to palmitate caused a dose-dependent reduction in the insulin-induced increase of GHR expression. CONCLUSIONS These data show that IGF-I levels are reduced in subjects with NAFLD and suggest that hepatic insulin resistance may affect IGF-I levels by modulating GH-stimulated synthesis of hepatic IGF-I.

One-hour postload plasma glucose levels and left ventricular mass in hypertensive patients.

OBJECTIVE Left ventricular hypertrophy (LVH), an independent risk factor for cardiovascular (CV) morbidity and mortality, recognizes a multifactorial pathogenesis. A plasma glucose value ≥155 mg/dL for the 1-h postload plasma glucose during an oral glucose tolerance test (OGTT) identifies subjects with normal glucose tolerance (NGT) at high risk for type 2 diabetes. We addressed the question if glucose tolerance status, particularly 1-h postload plasma glucose levels, affects left ventricular mass (LVM) and cardiac geometry in essential hypertension. RESEARCH DESIGN AND METHODS We enrolled 767 never-treated hypertensive subjects, 393 women and 374 men (mean age 49.6 ± 8.5 years). All patients underwent an OGTT for the evaluation of glucose tolerance and standard echocardiography. LVM was calculated using the Devereux formula and normalized by body surface area (LVM index [LVMI]). Insulin sensitivity was assessed by the Matsuda index. Among all participants, 514 had NGT, 168 had impaired glucose tolerance (IGT), and 85 had type 2 diabetes. According to the 1-h postload plasma glucose cutoff point of 155 mg/dL, we divided normotolerant subjects into two groups: NGT <155 mg/dL (n = 356) and NGT ≥155 mg/dL (n = 158). RESULTS Subjects in the NGT ≥155 mg/dL group had worse insulin sensitivity than subjects in the NGT <155 mg/dL group (Matsuda index 63.9 vs. 88.8; P < 0.0001). Men with NGT ≥155 mg/dL had a higher LVMI than men with NGT <155 mg/dL (126.6 vs. 114.3 g/m2; P = 0.002) and a different LVH prevalence (41.1 vs. 25.8%; P < 0.0001). At multiple regression analysis, 1-h glucose resulted in the major determinant of LVMI in normotolerant, IGT, and diabetic groups. CONCLUSIONS These data show that NGT ≥155 mg/dL subjects, compared with NGT <155 mg/dL subjects, have a higher LVMI and a greater prevalence of LVH similar to that of IGT and diabetic patients.

One-Hour Postload Plasma Glucose Levels Are Associated with Kidney Dysfunction

BACKGROUND AND OBJECTIVES A cutoff of 155 mg/dl for 1-hour postload plasma glucose (1hPG) during the oral glucose tolerance test (OGTT) is able to identify patients who are at high risk for type 2 diabetes and vascular atherosclerosis. We aimed to examine whether individuals with 1hPG ≥155 mg/dl are also at increased risk for chronic kidney disease (CKD). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Atherosclerosis risk factors, OGTT, and estimated GFR by Chronic Kidney Disease Epidemiology Collaboration equation were analyzed in 1075 white individuals without diabetes. RESULTS The area under the receiver operating characteristic curve for 1hPG was the highest (0.700) compared with the areas under the receiver operating characteristic curve of 0, 30-minute, and 2-hour glucose concentrations. Individuals with 1hPG ≥155 mg/dl had a worse cardiometabolic risk profile, exhibiting significantly higher body mass index, BP, triglycerides, and fasting insulin levels and lower HDL, IGF-1 levels, and insulin sensitivity, than individuals with 1hPG <155 mg/dl. Estimated GFR was significantly lower in individuals with 1hPG ≥155 mg/dl. In a logistic regression model adjusted for age and gender, individuals with 1hPG ≥155 mg/dl showed an increased risk for CKD compared with individuals with 1hPG <155 mg/dl. When the logistic regression analysis was restricted to individuals who had normal glucose tolerance, those with 1hPG ≥155 mg/dl showed a higher risk for CKD compared with individuals with 1hPG <155 mg/dl. CONCLUSIONS These data suggest that a cutoff point of 155 mg/dl for the 1hPG during OGTT may be helpful in the identification of individuals who are at increased risk for CKD.