Effect of exercise intervention on endothelial function and incidence of cardiovascular disease in patients with type 2 diabetes.

AIM: The effects of exercise intervention and to assess its long-term efficacy in preventing subsequent cardiovascular events in patients with type 2 diabetes were little known on randomized controlled trial. METHODS: Thirty-eight type 2 diabetic patients (21 men and 17 women) were assigned to either the exercise group (n=21) or the control group without exercise training (n=17) by simple randomization. The exercise training group was scheduled for aerobic and resistance exercise programs for 3 months. After the 3-month, we investigated endothelial function, insulin resistance, adipocytokines and inflammatory markers. The endothelial function was evaluated by examining a flow-mediated endothelium-dependent vasodilatation (FMD). Furthermore, we followed the incidence of cardiovascular events for 24 months. RESULTS: After 3-month, HbA1C was decreased significantly in both groups. FMD was increased from 7.3+/-4.7% to 10.9+/-6.2% only in the exercise group (p<0.05). Long-term follow-up data showed that the control group developed cardiovascular events more frequently than did the exercise group (p<0.05). CONCLUSIONS: Exercise improves endothelial dysfunction independently of glycemic control and insulin sensitivity in patients with type 2 diabetes. The beneficial effects of 3-month exercise to reduce cardiovascular events persist for 24 months.

Reciprocal regulation of natriuretic peptide receptors by insulin in adipose cells.

Atrial- and brain-type natriuretic peptides (ANP and BNP, respectively) have been shown to exert potent lipolytic action in adipocytes. A family of natriuretic peptide receptors (NPRs), NPR-1, NPR-2, and NPR-3, mediates their physiologic effects. NPR-1 and NPR-2 are receptor guanylyl cyclases, while NPR-3 lacks enzymatic activity and functions primarily as a clearance receptor for natriuretic peptides. ANP has a high affinity for NPR-1 and NPR-3 than other natriuretic peptides. There is a possibility that ANP may exhibit its lipolytic effect through the balance of NPR-1 and NPR-3 expressions in adipocytes. However, the regulation of adipose NPRs has not been fully elucidated. We here examined the regulation of mouse adipose NPRs by insulin, an anti-lipolytic hormone. Among the insulin target organs, NPR-1 mRNA levels were higher in white adipose tissue (WAT) than in liver and skeletal muscle. NPR-3 mRNA was expressed most abundantly in WAT. Fasting condition induced NPR-1 mRNA level while suppressed NPR-3 mRNA level in WAT. Administration of streptozotocin resulted in the increase of NPR-1 mRNA level while the decrease of NPR-3 mRNA level in WAT. In ob/ob mice, hyperinsulinemic model, NPR-1 mRNA level was lower whereas NPR-3 mRNA level was higher compared to lean control mice. In 3T3-L1 adipocytes, insulin significantly reduced NPR-1 mRNA level while increased NPR-3 mRNA levels both through phosphatidylinositol 3-kinase (PI3-kinase) pathway. In summary, NPR-1 and NPR-3 were highly expressed in WAT and adipose NPR-1 and NPR-3 were reciprocally regulated by insulin. This study suggests that insulin may efficiently promote lipogenesis partly by reducing the lipolytic action of ANP through the opposite regulation of NPR-1 and NPR-3.

Blockade of mineralocorticoid receptor reverses adipocyte dysfunction and insulin resistance in obese mice.

AIMS: In obesity, chronic low-grade inflammation and overproduction of reactive oxygen species (ROS) in fat contribute to the development of metabolic syndrome. Suppression of inflammation and ROS production in fat may attenuate the metabolic syndrome. Activation of mineralocorticoid receptor (MR) promotes inflammation in heart, kidney, and vasculature via ROS generation. However, the significance of MR in fat remains elusive. Here we investigated whether MR blockade attenuates obesity-related insulin resistance and improves adipocyte dysfunction. METHODS AND RESULTS: Obese ob/ob and db/db mice were treated with eplerenone, a MR antagonist, for 3 weeks. 3T3-L1 adipocytes were treated with aldosterone or H2O2, with and without eplerenone or MR-siRNA. High levels of MR mRNA were detected in adipose tissue of obese ob/ob and db/db mice. Eplerenone treatment significantly reduced insulin resistance, suppressed macrophage infiltration and ROS production in adipose tissues, and corrected the mRNA levels of obesity-related genes in obese mice. In 3T3-L1 adipocytes, aldosterone and H2O2 increased intracellular ROS levels and MR blockade inhibited such increases. H2O2 and aldosterone resulted in dysregulation of mRNAs of various genes related to ROS and cytokines, whereas MR blockade corrected such changes. CONCLUSION: MR blockade attenuates obesity-related insulin resistance partly through reduction of fat ROS production, inflammatory process, and induction of cytokines.

[Human genetic mutations and polymorphisms of adipocytokines relating to obesity].

Human gene mutations and polymorphisms of adipocytokines, adipocyte-derived bioactive molecules, have been reported to be implicated in the pathogenesis of obesity. Leptin and its receptor gene mutations are well-established in the development of severe obesity. Among early onset severe obese patients, the prevalence of various leptin-receptor gene mutations was about 3%. The polymorphisms of adiponectin, another important adipocytokine with anti-atherogenic and anti-diabetic properties, are reported to associate with the pathophysiology but not with the severity of obesity. Adipocytokine dysregulation due to lifestyle-mediated obesity would be common at this stage, although further study of adipocytokine mutation should be necessary.

Adiponectin protects against angiotensin II-induced cardiac fibrosis through activation of PPAR-alpha.

OBJECTIVE: Adiponectin is recognized as an antidiabetic, antiatherosclerotic, and anti-inflammatory protein derived from adipocytes. However, the role of adiponectin in cardiac fibrosis remains uncertain. We herein explore the effects of adiponectin on cardiac fibrosis induced by angiotensin II (Ang II). METHODS AND RESULTS: Wild-type (WT), adiponectin knockout (Adipo-KO), and PPAR-alpha knockout (PPAR-alpha-KO) mice were infused with Ang II at 1.2 mg/kg/d. Severe cardiac fibrosis and left ventricular dysfunction were observed in Ang II-infused Adipo-KO mice compared to WT mice. Adenovirus-mediated adiponectin treatment improved the above phenotypes and the dysregulation of reactive oxygen species (ROS)-related mRNAs in Adipo-KO mice, whereas such amelioration was not observed in PPAR-alpha-KO mice despite adiponectin accumulation in heart tissue. In cultured cardiac fibroblasts, adiponectin improved the reduction of AMP-activated protein kinase (AMPK) activity and elevation of extracellular signal-regulated kinase 1/2 (ERK1/2) activity induced by Ang II. Adiponectin significantly enhanced PPAR-alpha activity, whereas the adiponectin-dependent PPAR-alpha activation was diminished by Compound C, an inhibitor of AMPK. CONCLUSIONS: The present study suggests that adiponectin protects against Ang II-induced cardiac fibrosis possibly through AMPK-dependent PPAR-alpha activation.

Clinical significance of high-molecular weight form of adiponectin in male patients with coronary artery disease.

BACKGROUND: It has been reported previously that the measurement of plasma total adiponectin level is clinically useful to estimate the risk of coronary artery disease (CAD). Here, the relevance of high molecular weight (HMW) adiponectin with risk factors for atherosclerosis is investigated METHODS AND RESULTS: A total of 186 consecutive male CAD patients participated in the study and were categorized into quartiles based on their total adiponectin level. The interquartile cut-off points were 4.0, 5.5 and 7.0 microg/ml. The HMW adiponectin levels were significantly lower in the quartile of lower total adiponectin levels both in non-diabetic and diabetic patients. In contrast, low molecular weight adiponectin levels (which were calculated as the Total - HMW) were constant. In univariate analysis, total adiponectin correlated negatively with body mass index and hemoglobin (Hb) A1c, and HMW adiponectin correlated negatively with HbA1c in non-diabetic patients. On the other hand, total and HMW adiponectin correlated positively with high-density lipoprotein-cholesterol (HDL-C) in diabetic patients. Multiple regression analysis revealed that HMW adiponectin correlated negatively with HbA1c in non-diabetic patients, and total and HMW adiponectin correlated positively with HDL-C in diabetic patients. CONCLUSIONS: Change in the HMW isoform reflects a change in total adiponectin level. Measurement of total and HMW adiponectin were equally useful in assessing metabolic risk in CAD patients.

Impaired flow-mediated vasodilatation and insulin resistance in type 2 diabetic patients with albuminuria.

An elevated urinary albumin excretion is associated with an increased risk of cardiovascular disease due to atherosclerosis, but the pathophysiological mechanism underlying this association is poorly understood. We studied 217 diabetic patients, that is, 121 normoalbuminuric patients, 71 microalbuminuric patients, and 25 macroalbuminuric patients. We evaluated flow-mediated dilatation of brachial artery (%FMD, one endothelial function marker associated with endogenous NO production), von Willebrand factor (vWF, endothelial activation marker), high-sensitive CRP (hsCRP, a low-grade inflammation marker), asymmetric dimethyl arginine (ADMA, an endogenous inhibitor of NO synthesis), and insulin sensitivity by steady-state plasma glucose method. %FMD was apparently decreased in microalbuminuric and macroalbuminuric patients compared with normoalbuminuric patients (p<0.001). Moreover, %FMD was significantly correlated with the degree of albuminuria (r=-0.38, p<0.05). On the other hand, vWF and hsCRP did not show significant difference between normoalbuminuric patients and microalbuminuric patients. In diabetic patients with macroalbuminuria, ADMA was significantly elevated compared to those with normoalbuminuria. Insulin sensitivity was significantly associated with urinary albumin excretion rate. These results suggested that endothelial dysfunction which may be due to impaired NO production and insulin resistance underlie the association between diabetic nephropathy and atherosclerosis in diabetic patients.

Effects of peroxisome proliferator-activated receptor ligands, bezafibrate and fenofibrate, on adiponectin level.

OBJECTIVE: Adiponectin is adipose-specific secretory protein and acts as anti-diabetic and anti-atherosclerotic molecule. We previously found peroxisome proliferators response element in adiponectin promoter region, suggesting that peroxisome proliferator-activated receptor (PPAR) ligands elevate adiponectin. Fibrates are known to be PPARalpha ligands and were shown to reduce risks of diabetes and cardiovascular disease. Effect of fibrates on adiponectin has not been clarified, whereas thiazolidinediones enhance adiponectin. Thus, we explored the possibility and mechanism that fibrates enhance adiponectin in humans, mice, and cells. METHODS AND RESULTS: Significant increase of serum adiponectin was observed in bezafibrate-treated subjects compared with placebo group in patients enrolled in The Bezafibrate Infarction Prevention study. Higher baseline adiponectin levels were strongly associated with reduced risk of new diabetes. Fibrates, bezafibrate and fenofibrate, significantly elevated adiponectin levels in wild-type mice and 3T3-L1 adipocytes. Such an effect was not observed in PPARalpha-deficient mice and adipocytes. Fibrates activated adiponectin promoter but failed to enhance its activity when the point mutation occurred in peroxisome proliferators response element site and the endogenous PPARalpha was knocked down by PPARalpha-RNAi. CONCLUSIONS: Our results suggest that fibrates enhance adiponectin partly through adipose PPARalpha and measurement of adiponectin might be a useful tool for searching subjects at high risk for diabetes.

Adiponectin replenishment ameliorates obesity-related hypertension.

Patients with obesity are susceptible to hypertension. We have reported that the plasma adiponectin levels are decreased in obesity and that adiponectin has many defensive properties against obesity-related diseases, such as type 2 diabetes and coronary artery disease. The aim of this study was to determine the relationship between adiponectin and hypertension in mice. We measured blood pressure and heart rate directly by a catheter in the carotid artery and indirectly by automatic sphygmomanometer at the tail artery. Obese KKAy mice had significantly lower plasma adiponectin levels and higher systolic blood pressure than control C57BL/6J mice at 21 weeks of age. Adenovirus-delivered adiponectin significantly decreased blood pressure in KKAy mice. The direct role of adiponectin on blood pressure regulation under insulin resistance-free state was investigated in adiponectin-knockout (KO) mice. Adiponectin KO mice developed hypertension when maintained on a high-salt diet (8% NaCl) without insulin resistance. The hypertension of salt-fed adiponectin KO mice was associated with reduced mRNA levels of endothelial NO synthase (eNOS) and prostaglandin I(2) synthase in aorta and low metabolite levels of endothelial NO synthase and prostaglandin I(2) synthase in plasma. Adiponectin therapy lowered the elevated blood pressure and corrected the above mRNA levels to those of the wild type. Our results suggest that hypoadiponectinemia contributes to the development of obesity-related hypertension, at least in part, directly, in addition to its effect via insulin resistance, and that adiponectin therapy can be potentially useful for hypertension in patients with the metabolic syndrome.

Pioglitazone-induced insulin sensitization improves vascular endothelial function in nondiabetic patients with essential hypertension.

BACKGROUND: It has been suggested that insulin resistance is involved in the impaired vascular endothelial function not only in diabetic patients but also in hypertensive patients. The present study assessed the hypothesis that primary treatment of insulin resistance may reverse endothelial dysfunction in hypertensive subjects. METHODS: Fifteen nondiabetic patients with essential hypertension were enrolled in this study. An oral glucose tolerance test (OGTT) and insulin sensitivity test were performed. Insulin sensitivity was determined with the steady-state plasma glucose (SSPG) method. Only subjects with insulin resistance (SSPG > or =8.3 mmol/L) were included. Endothelium-dependent vasodilation during reactive hyperemia (flow-mediated dilation) was evaluated using ultrasonography. Six months after treatment with the insulin-sensitizing agent pioglitazone (30 mg/day), these examinations were repeated in all subjects. RESULTS: Pioglitazone did not decrease fasting plasma glucose and hemoglobin A1c (HbA1c) in the nondiabetic subjects, although the area under the curve for glucose and insulin on OGTT significantly decreased. A marked decrease in SSPG was observed after pioglitazone treatment (10.7 +/- 1.4 to 7.9 +/- 2.1 mmol/L, P < .001). Endothelium-dependent vasodilation evaluated by flow-mediated dilation was also improved by pioglitazone (5.0% +/- 2.2% to 6.3% +/- 2.4%, P = .023). Furthermore, the increase in flow-mediated dilation was closely correlated with the decrease in SSPG (r = 0.72, P = .002) but not with the decrease in area under the curve for glucose or insulin on OGTT. Endothelium-independent dilation induced by glyceryl trinitrate was not altered by pioglitazone. CONCLUSIONS: The present findings demonstrate that pioglitazone improves endothelial function in nondiabetic hypertensive individuals with insulin resistance, and that the improvement is associated with the amelioration of insulin resistance itself rather than that of hyperglycemia or hyperinsulinemia.

Pioglitazone improves left ventricular diastolic function in patients with essential hypertension.

BACKGROUND: Left ventricular (LV) hypertrophy and diastolic dysfunction, which are common cardiac consequences of hypertension, are modified by insulin resistance. The present study assessed the hypothesis that primary treatment of insulin resistance may reverse such cardiac changes in hypertensive patients. METHODS: A total of 30 patients with essential hypertension were enrolled in this study. In echocardiographic examinations, LV mass index, the peak velocity ratio of early diastolic to atrial filling (E/A), and the E-wave deceleration time (DcT) were determined. Insulin sensitivity test with steady-state plasma glucose (SSPG) method, oral glucose tolerance test, and blood samplings for measurement of adiponectin and matrix metalloproteinase (MMP)-2 were also performed. Six months after treatment with pioglitazone (30 mg/day), an insulin sensitizer, these examinations were repeated. RESULTS: Pioglitazone significantly increased E/A and decreased DcT, without a change in LV mass index. These improvements in diastolic properties were much greater in subjects with a marked (>or==3.3 mmol/L) decrease in SSPG (n=11) than the others (n=19), although the decrease in glucose levels did not differ between the two groups. In addition, the changes in E/A and DcT were closely correlated with the decrease in SSPG. Pioglitazone treatment significantly elevated plasma adiponectin and MMP-2 levels, and the increase in MMP-2 was positively correlated with the increase in adiponectin. CONCLUSIONS: The present findings demonstrate that pioglitazone improves LV diastolic function without LV mass regression in hypertensive patients in proportion to the amelioration of insulin resistance. These findings suggest that increased adiponectin and MMP may be involved in the beneficial effect of pioglitazone on diastolic function.

Plasma asymmetric dimethylarginine and coronary and peripheral endothelial dysfunction in hypertensive patients.

BACKGROUND: The attenuation of coronary flow reserve (CFR) and endothelium-mediated vasodilation of the brachial artery (EMV-BA) have been frequently reported in hypertensive patients. The present study investigated the link between CFR and EMV-BA in hypertensive patients. We hypothesized that changes in serum asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, and concomitant insulin resistance may be underlying factors connecting the two pathologic alterations. METHODS: A total of 75 patients (30 men and 45 women, 61.5 +/- 10.1 years of age) with essential hypertension and without coronary artery disease and diabetes mellitus were included in the study. Measurements of CFR were made using adenosine-triphosphate stress transthoracic Doppler echocardiography, and forearm EMV-BA was measured by venous occlusion strain gauge plethysmography. A plasma ADMA assay and a 75-g oral glucose tolerance test were also performed. RESULTS: Average CFR and EMV-BA values were 2.54 +/- 0.63 and 86.0 +/- 54.7%, respectively. A significant correlation was found between CFR and EMV-BA (r = 0.493, P <.001). Both CFR and EMV-BA were also significantly correlated with age and plasma ADMA concentration, but were not correlated with insulin resistance, plasma insulin, or left ventricular mass. Multiple regression analysis revealed that ADMA was the only statistically independent parameter associated with CFR and EMV-BA. CONCLUSIONS: The similar deterioration in endothelial function in coronary and peripheral vascular territories may be mainly due to increased plasma ADMA concentration. Plasma ADMA appears to play a major role in endothelial dysfunction in hypertensive patients, independent of insulin resistance or left ventricular hypertrophy.

Close association of endothelial dysfunction with insulin resistance and carotid wall thickening in hypertension.

BACKGROUND: Endothelial dysfunction has been regarded as an early stage in the atherosclerotic process. Endothelial dysfunction and insulin resistance were observed in hypertensive subjects and were associated with carotid wall thickening. METHODS: We examined the determinants of endothelial dysfunction including insulin sensitivity and carotid wall thickening. A total of 41 subjects with nondiabetic essential hypertension were studied. Endothelial function of brachial artery and carotid wall thickening were assessed noninvasively using ultrasound technique. In brachial artery, we measured flow-mediated endothelium-dependent vasodilation (FMD) and glyceryl trinitrate-induced endothelium-independent vasodilation (GTN). We estimated intima-media thickness of the common carotid artery (IMT). Insulin sensitivity was measured according to the steady-state plasma glucose (SSPG) method. High SSPG levels indicated insulin resistance. RESULTS: On univariate analysis, there were significant negative correlations between FMD and SSPG (r = -0.695, P <.0001) or IMT (r = -0.449, P <.004). The FMD was negatively correlated significantly with age and with systolic and diastolic blood pressures (BP). A significant negative correlation was observed between GTN and SSPG. There was a significant positive relation between SSPG and IMT. On multiple regression analysis including systolic BP, SSPG, and age as independent variables and FMD as a dependent variable, FMD was independently related to SSPG (P <.03) and systolic BP (P <.02). If the presence of SSPG, diastolic BP, and age were entered as independent variables against FMD, FMD was independently related to SSPG (P <.002). CONCLUSIONS: One of the major determinants of endothelial function was insulin resistance. Our findings suggest that endothelial dysfunction and early structural vascular changes were related to insulin resistance.