Biomedical subjects

Michael J Quon

Publications and source records attributed to Michael J Quon.

At least 19 recordsLinked to original sources

PubMed2007

EGCG, a green tea polyphenol, improves endothelial function and insulin sensitivity, reduces blood pressure, and protects against myocardial I/R injury in SHR.

Epigallocatechin gallate (EGCG), a bioactive polyphenol in green tea, may augment metabolic and vascular actions of insulin. Therefore, we investigated effects of EGCG treatment to simultaneously improve cardiovascular and metabolic function in spontaneously hypertensive rats (SHR; model of metabolic syndrome with hypertension, insulin resistance, and overweight). In acute studies, EGCG (1-100 microM) elicited dose-dependent vasodilation in mesenteric vascular beds (MVB) isolated from SHR ex vivo that was inhibitable by N(omega)-nitro-L-arginine methyl ester (L-NAME; nitric oxide synthase antagonist) or wortmannin [phosphatidylinositol (PI) 3-kinase inhibitor]. In chronic studies, 9-wk-old SHR were treated by gavage for 3 wk with EGCG (200 mg.kg(-1).day(-1)), enalapril (30 mg.kg(-1).day(-1)), or vehicle. A separate group of SHR receiving L-NAME (80 mg/l in drinking water) was treated for 3 wk with either EGCG or vehicle. Vasodilator actions of insulin were significantly improved in MVB from EGCG- or enalapril-treated SHR (when compared with vehicle-treated SHR). Both EGCG and enalapril therapy significantly lowered systolic blood pressure (SBP) in SHR. EGCG therapy of SHR significantly reduced infarct size and improved cardiac function in Langendorff-perfused hearts exposed to ischemia-reperfusion (I/R) injury. In SHR given L-NAME, beneficial effects of EGCG on SBP and I/R were not observed. Both enalapril and EGCG treatment of SHR improved insulin sensitivity and raised plasma adiponectin levels. We conclude that acute actions of EGCG to stimulate production of nitric oxide from endothelium using PI 3-kinase-dependent pathways may explain, in part, beneficial effects of EGCG therapy to simultaneously improve metabolic and cardiovascular pathophysiology in SHR. These findings may be relevant to understanding potential benefits of green tea consumption in patients with the metabolic syndrome.

Animals↗

PubMed2007

Reciprocal relationships between abnormal metabolic parameters and endothelial dysfunction.

PURPOSE OF REVIEW: Endothelial dysfunction plays a crucial role in the pathogenesis of atherosclerosis and related cardiovascular diseases. Glucotoxicity, lipotoxicity, and inflammation all independently contribute to development of both endothelial dysfunction and insulin resistance. We review pathophysiological mechanisms underlying reciprocal relationships between endothelial dysfunction and insulin resistance and recent insights from therapeutic interventions to improve both metabolic and vascular function. RECENT FINDINGS: Shared causal factors such as glucotoxicity, lipotoxicity, and inflammation interact at multiple levels creating reciprocal relationships between insulin resistance and endothelial dysfunction that help to explain frequent clustering of metabolic and cardiovascular disorders. Metabolic abnormalities implicated in the development of insulin resistance, including hyperglycemia, elevated levels of free fatty acids, accumulation of advanced glycation end products, dyslipidemias, and decreased levels of adiponectin, also contribute importantly to endothelial dysfunction. Diet, exercise, cardiovascular drugs, and insulin sensitizers simultaneously improve endothelium-dependent vascular function, reduce inflammation, and improve insulin sensitivity by both distinct and interrelated mechanisms. SUMMARY: Pathophysiological mechanisms underlying reciprocal relationships between endothelial dysfunction and insulin resistance contribute to clustering of metabolic and cardiovascular diseases represented by the metabolic syndrome. Therapeutic interventions that target endothelial dysfunction or insulin resistance often simultaneously improve both metabolic and vascular function.

Diet↗

PubMed2006

Predicted effects of hemoglobin A1c assay precision on a patient population distribution of serial hemoglobin A1c difference values.

BACKGROUND: Interpretation of serial measurements of % hemoglobin A1c includes an assessment of differences from preceding values (DHbA1c). We examined predicted effects of different assay precisions on an observed population distribution for DHbA1c. METHODS: Primary data were 5260 DHbA1c values from sequential HbA1c measurement pairs obtained within 1 calendar year. Each DHbA1c was replaced by a distribution obtained from sampling each component HbA1c value according to a normal distribution characterized by a fixed coefficient of variation (CV) of either 1%, 3% or 5% (forming data sets A, B and C, respectively). Data sets B and C, with inferior precision, were compared with the reference data set A (highest precision). RESULTS: Using DHbA1c bin widths of 0.5% HbA1c, differences in assay precision caused significant redistribution of numbers within bins. For instance, for CV=5%, there was a 7.2% decrease in the number of results within the DHbA1c bin=(-0.5 to 0.5. CONCLUSION: Different HbA1c assay CVs can significantly affect the fraction of patients within different clinical categorizations for DHbA1c and consequently may differently influence patient care recommendations.

Female↗

PubMed2006

Ghrelin has novel vascular actions that mimic PI 3-kinase-dependent actions of insulin to stimulate production of NO from endothelial cells.

Ghrelin is an orexigenic peptide hormone secreted by the stomach. In patients with metabolic syndrome and low ghrelin levels, intra-arterial ghrelin administration acutely improves their endothelial dysfunction. Therefore, we hypothesized that ghrelin activates endothelial nitric oxide synthase (eNOS) in vascular endothelium, resulting in increased production of nitric oxide (NO) using signaling pathways shared in common with the insulin receptor. Similar to insulin, ghrelin acutely stimulated increased production of NO in bovine aortic endothelial cells (BAEC) in primary culture (assessed using NO-specific fluorescent dye 4,5-diaminofluorescein) in a time- and dose-dependent manner. Production of NO in response to ghrelin (100 nM, 10 min) in human aortic endothelial cells was blocked by pretreatment of cells with NG-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor), wortmannin [phosphatidylinositol (PI) 3-kinase inhibitor], or (D-Lys3)-GHRP-6 (selective antagonist of ghrelin receptor GHSR-1a), as well as by knockdown of GHSR-1a using small-interfering (si) RNA (but not by mitogen/extracellular signal-regulated kinase inhibitor PD-98059). Moreover, ghrelin stimulated increased phosphorylation of Akt (Ser473) and eNOS (Akt phosphorylation site Ser1179) that was inhibitable by knockdown of GHSR-1a using siRNA or by pretreatment of cells with wortmannin but not with PD-98059. Ghrelin also stimulated phosphorylation of mitogen-activated protein (MAP) kinase in BAEC. However, unlike insulin, ghrelin did not stimulate MAP kinase-dependent secretion of the vasoconstrictor endothelin-1 from BAEC. We conclude that ghrelin has novel vascular actions to acutely stimulate production of NO in endothelium using a signaling pathway that involves GHSR-1a, PI 3-kinase, Akt, and eNOS. Our findings may be relevant to developing novel therapeutic strategies to treat diabetes and related diseases characterized by reciprocal relationships between endothelial dysfunction and insulin resistance.

Animals↗

PubMed2006

Combined therapy with ramipril and simvastatin has beneficial additive effects on tissue factor activity and prothrombin fragment 1+2 in patients with type 2 diabetes.

Tissue factor (TF) plays a pivotal role in thrombus formation. Statins and angiotensin converting enzyme inhibitors attenuate expression of TF by distinct mechanism. Therefore, we hypothesized that combined therapy with simvastatin and ramipril may have additive beneficial anti-atherogenic effects to lower TF activity when compared with either drug alone. This was a randomized, double-blind, placebo-controlled cross-over trial with three treatment arms (each 2 months) and two washout periods (each 2 months). Fifty patients with type 2 diabetes were given simvastatin 20 mg and placebo, simvastatin 20 mg and ramipril 10 mg, or ramipril 10 mg and placebo daily during each treatment period. Simvastatin and ramipril monotherapy tended to reduce TF activity (0.53 to 0.46 nM, P=0.056; 0.54 to 0.50 nM, P=0.167, respectively) while combined therapy had a significant effect (0.64 to 0.43 nM, P<0.001). All three therapies significantly reduced prothrombin fragment 1+2 (F1+2) levels from their respective baselines (P=0.037, P<0.001, and P=0.057, respectively). Combined therapy significantly reduced TF activity and F1+2 levels to a greater extent than either simvastatin or ramipril alone (P=0.029 and P=0.040 by ANOVA, respectively). Percent changes in TF activity and percent changes in F1+2 levels were significantly correlated. All three therapies reduced CD40 ligand levels from their respective baselines (P=0.098, P<0.001, and P=0.002, respectively) with no significant differences among these three therapies (P=0.204 by ANOVA). Ramipril combined with simvastatin significantly reduces plasma TF activity and F1+2 levels to a greater extent than monotherapy with either drug in patients with type 2 diabetes.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed2006

PKCdelta-mediated IRS-1 Ser24 phosphorylation negatively regulates IRS-1 function.

The IRS-1 PH and PTB domains are essential for insulin-stimulated IRS-1 Tyr phosphorylation and insulin signaling, while Ser/Thr phosphorylation of IRS-1 disrupts these signaling events. To investigate consensus PKC phosphorylation sites in the PH-PTB domains of human IRS-1, we changed Ser24, Ser58, and Thr191 to Ala (3A) or Glu (3E), to block or mimic phosphorylation, respectively. The 3A mutant abrogated the inhibitory effect of PKCdelta on insulin-stimulated IRS-1 Tyr phosphorylation, while reductions in insulin-stimulated IRS-1 Tyr phosphorylation, cellular proliferation, and Akt activation were observed with the 3E mutant. When single Glu mutants were tested, the Ser24 to Glu mutant had the greatest inhibitory effect on insulin-stimulated IRS-1 Tyr phosphorylation. PKCdelta-mediated IRS-1 Ser24 phosphorylation was confirmed in cells with PKCdelta catalytic domain mutants and by an RNAi method. Mechanistic studies revealed that IRS-1 with Ala and Glu point mutations at Ser24 impaired phosphatidylinositol-4,5-bisphosphate binding. In summary, our data are consistent with the hypothesis that Ser24 is a negative regulatory phosphorylation site in IRS-1.

Amino Acid Sequence↗

PubMed2006

FOXO1 represses peroxisome proliferator-activated receptor-gamma1 and -gamma2 gene promoters in primary adipocytes. A novel paradigm to increase insulin sensitivity.

FOXO1 and peroxisome proliferator-activated receptor-gamma (PPARgamma) are crucial transcription factors that regulate glucose metabolism and insulin responsiveness in insulin target tissues. We have shown that, in primary rat adipocytes, both factors regulate transcription of the insulin-responsive GLUT4 gene and that PPARgamma2 detachment from the GLUT4 promoter upon thiazolidinedione binding up-regulates GLUT4 gene expression, thus increasing insulin sensitivity (Armoni, M., Kritz, N., Harel, C., Bar-Yoseph, F., Chen, H., Quon, M. J., and Karnieli, E. (2003) J. Biol. Chem. 278, 30614-30623). However, the mechanisms regulating PPARgamma gene transcription are largely unknown. We studied the effects of FOXO1 on human PPARgamma gene expression in primary rat adipocytes and found that both genes are endogenously expressed. FOXO1 coexpression dose-dependently repressed transcription from either the PPARgamma 1 or PPARgamma2 promoter reporter by 65%, whereas insulin (100 nm, 20-24 h) either partially or completely reversed this effect. Phosphorylation-defective FOXO1 mutants T24A, S256A, S319A, and T24A/S256A/S319A still repressed the PPARgamma1 promoter and partially lost their effects on the PPARgamma2 promoter in either basal or insulin-stimulated cells. Use of DNA binding-defective FOXO1 (H215R) indicated that this domain is crucial for FOXO1 repression of the PPARgamma2 (but not PPARgamma1) promoter. Progressive 5'-deletion and gel retardation analyses revealed that this repression involves direct and specific binding of FOXO1 to the PPARgamma2 promoter; chromatin immunoprecipitation analysis confirmed that this binding occurs in cellulo. We suggest a novel paradigm to increase insulin sensitivity in adipocytes in which FOXO1 repression of PPARgamma, the latter being a repressor of the GLUT4 promoter, consequently leads to GLUT4 derepression/up-regulation, thus enhancing cellular insulin sensitivity. The newly identified FOXO1-binding site on the PPARgamma2 promoter may serve as a therapeutic target for type 2 diabetes.

Adipocytes↗

PubMed2006

Reciprocal relationships between insulin resistance and endothelial dysfunction: molecular and pathophysiological mechanisms.

Endothelial dysfunction contributes to cardiovascular diseases, including hypertension, atherosclerosis, and coronary artery disease, which are also characterized by insulin resistance. Insulin resistance is a hallmark of metabolic disorders, including type 2 diabetes mellitus and obesity, which are also characterized by endothelial dysfunction. Metabolic actions of insulin to promote glucose disposal are augmented by vascular actions of insulin in endothelium to stimulate production of the vasodilator nitric oxide (NO). Indeed, NO-dependent increases in blood flow to skeletal muscle account for 25% to 40% of the increase in glucose uptake in response to insulin stimulation. Phosphatidylinositol 3-kinase-dependent insulin-signaling pathways in endothelium related to production of NO share striking similarities with metabolic pathways in skeletal muscle that promote glucose uptake. Other distinct nonmetabolic branches of insulin-signaling pathways regulate secretion of the vasoconstrictor endothelin-1 in endothelium. Metabolic insulin resistance is characterized by pathway-specific impairment in phosphatidylinositol 3-kinase-dependent signaling, which in endothelium may cause imbalance between production of NO and secretion of endothelin-1, leading to decreased blood flow, which worsens insulin resistance. Therapeutic interventions in animal models and human studies have demonstrated that improving endothelial function ameliorates insulin resistance, whereas improving insulin sensitivity ameliorates endothelial dysfunction. Taken together, cellular, physiological, clinical, and epidemiological studies strongly support a reciprocal relationship between endothelial dysfunction and insulin resistance that helps to link cardiovascular and metabolic diseases. In the present review, we discuss pathophysiological mechanisms, including inflammatory processes, that couple endothelial dysfunction with insulin resistance and emphasize important therapeutic implications.

Animals↗

PubMed2006

The effects of simvastatin, losartan, and combined therapy on soluble CD40 ligand in hypercholesterolemic, hypertensive patients.

The proinflammatory mediator CD40 ligand plays an important role in atherogenesis. Biological mechanisms underlying statin and angiotensin II type 1 receptor blocker therapies differ. Therefore, we compared the effects of these therapies either alone or in combination on plasma soluble CD40 ligand (sCD40L). This was a randomized, double-blind, placebo-controlled cross-over trial with three treatment arms (each 2 months) and two washout periods (each 2 months). Forty-seven hypertensive, hypercholesterolemic patients were given simvastatin 20mg and placebo, simvastatin 20mg and losartan 100mg, or losartan 100mg and placebo daily during each 2 month treatment period. Simvastatin alone did not significantly reduce sCD40L levels relative to baseline measurements when the entire cohort was analyzed. However, simvastatin significantly reduced sCD40L levels from 5.10+/-0.34 to 3.07+/-0.43ng/ml (P=0.002) in a subgroup of 18 patients with high baseline sCD40L levels >2.95ng/ml. Combined therapy or losartan alone significantly decreased plasma sCD40L levels relative to baseline measurements by 14+/-7% (P=0.001) and 13+/-10% (P=0.001), respectively. These decreases were significantly greater than those observed with simvastatin alone (P=0.023 by ANOVA). Significant inverse correlations between baseline sCD40L levels and percent changes in sCD40L levels were observed (r=-0.456, P=0.001 after simvastatin alone; r=-0.476, P<0.001 after combined therapy; r=-0.451, P=0.002 after losartan alone). Losartan alone or combined therapy significantly reduced plasma sCD40L levels more than simvastatin alone in our subjects. Simvastatin, losartan and combined therapy significantly reduced sCD40L to the greatest extent in patients with high baseline sCD40L levels.

Antihypertensive Agents↗

PubMed2006

MKR mice are resistant to the metabolic actions of both insulin and adiponectin: discordance between insulin resistance and adiponectin responsiveness.

Most rodent models of insulin resistance are accompanied by decreased circulating adiponectin levels. Adiponectin treatment improves the metabolic phenotype by increasing fatty acid oxidation in skeletal muscle and suppressing hepatic glucose production. Muscle IGF-I receptor (IGF-IR)-lysine-arginine (MKR) mice expressing dominant-negative mutant IGF-IRs in skeletal muscle are diabetic with insulin resistance in muscle, liver, and adipose tissue. Adiponectin levels are elevated in MKR mice, suggesting an unusual discordance between insulin resistance and adiponectin responsiveness. Therefore, we investigated the metabolic actions of adiponectin in MKR mice. MKR and ob/ob mice were treated both acutely (28 microg/g) and chronically (for 2 wk) with full-length adiponectin. Acute hypoglycemic effects of adiponectin were evident only in ob/ob mice but not in MKR mice. Chronic adiponectin treatment significantly improved both insulin sensitivity and glucose tolerance in ob/ob but not in MKR mice. Adiponectin receptor mRNA levels and adiponectin-stimulated phosphorylation of AMPK in skeletal muscle and liver were similar among MKR, wild-type, and ob/ob mice. Thus MKR mice are adiponectin resistant despite normal expression of adiponectin receptors and normal AMPK phosphorylation in muscle and liver. MKR mice may be a useful model for dissecting relationships between insulin resistance and adiponectin action in regulation of glucose homeostasis.

Adiponectin↗

PubMed2006

Vascular and metabolic effects of candesartan: insights from therapeutic interventions.

BACKGROUND: Effects of angiotensin II type 1 receptor blockers (ARBs) to improve endothelial dysfunction may be due to mechanisms in addition to the reduction of high blood pressure per se. Endothelial dysfunction is characterized by vascular inflammation that contributes to clinically significant atherosclerosis and by an increased tendency for thrombus formation. Hypertensive patients have impaired endothelial functions that have positive predictive power with respect to future cardiovascular events. OBJECTIVES: The present review will focus on multiple mechanisms underlying vascular and metabolic effects of ARBs that may synergize to prevent or regress atherosclerosis, onset of diabetes, and coronary heart disease. CONCLUSIONS: Angiotensin II accelerates the development of atherosclerosis by activating angiotensin II type 1 receptors that then promote superoxide anion generation and oxidative stress, leading to activation of nuclear transcription factor and endothelial dysfunction. Activation of angiotensin II type 1 receptors also stimulates increased expression of plasminogen activator inhibitor type 1 and tissue factor. Endothelial dysfunction associated with the metabolic syndrome and other insulin-resistant states is characterized by impaired insulin-stimulated production of nitric oxide from the endothelium and decreased blood flow to skeletal muscle. Increasing insulin sensitivity therefore improves endothelial function, and this may be an additional mechanism whereby ARBs decrease the incidence of coronary heart disease and the onset of diabetes. Adiponectin serves to link obesity with insulin resistance. In addition, adiponectin has anti-atherogenic properties.

Adiponectin↗

PubMed2006

Treatment of spontaneously hypertensive rats with rosiglitazone and/or enalapril restores balance between vasodilator and vasoconstrictor actions of insulin with simultaneous improvement in hypertension and insulin resistance.

Spontaneously hypertensive rats (SHRs) exhibit endothelial dysfunction and insulin resistance. Reciprocal relationships between endothelial dysfunction and insulin resistance may contribute to hypertension by causing imbalanced regulation of endothelial-derived vasodilators (e.g., nitric oxide) and vasoconstrictors (e.g., endothelin-1 [ET-1]). Treatment of SHRs with rosiglitazone (insulin sensitizer) and/or enalapril (ACE inhibitor) may simultaneously improve hypertension, insulin resistance, and endothelial dysfunction by rebalancing insulin-stimulated production of vasoactive mediators. When compared with WKY control rats, 12-week-old vehicle-treated SHRs were hypertensive, overweight, and insulin resistant, with elevated fasting levels of insulin and ET-1 and reduced serum adiponectin levels. In mesenteric vascular beds (MVBs) isolated from vehicle-treated SHRs and preconstricted with norepinephrine (NE) ex vivo, vasodilator responses to insulin were significantly impaired, whereas the ability of insulin to oppose vasoconstrictor actions of NE was absent (versus WKY controls). Three-week treatment of SHRs with rosiglitazone and/or enalapril significantly reduced blood pressure, insulin resistance, fasting insulin, and ET-1 levels and increased adiponectin levels to values comparable with those observed in vehicle-treated WKY controls. By restoring phosphatidylinositol 3-kinase-dependent effects, rosiglitazone and/or enalapril therapy of SHRs also significantly improved vasodilator responses to insulin in MVB preconstricted with NE ex vivo. Taken together, our data provide strong support for the existence of reciprocal relationships between endothelial dysfunction and insulin resistance that may be relevant for developing novel therapeutic strategies for the metabolic syndrome.

Adiponectin↗

PubMed2006

Oral glucosamine for 6 weeks at standard doses does not cause or worsen insulin resistance or endothelial dysfunction in lean or obese subjects.

Glucosamine is a popular nutritional supplement used to treat osteoarthritis. Intravenous administration of glucosamine causes insulin resistance and endothelial dysfunction. However, rigorous clinical studies evaluating the safety of oral glucosamine with respect to metabolic and cardiovascular pathophysiology are lacking. Therefore, we conducted a randomized, placebo-controlled, double-blind, crossover trial of oral glucosamine at standard doses (500 mg p.o. t.i.d.) in lean (n = 20) and obese (n = 20) subjects. Glucosamine or placebo treatment for 6 weeks was followed by a 1-week washout and crossover to the other arm. At baseline, and after each treatment period, insulin sensitivity was assessed by hyperinsulinemic-isoglycemic glucose clamp (SI(Clamp)) and endothelial function evaluated by brachial artery blood flow (BAF; Doppler ultrasound) and forearm skeletal muscle microvascular recruitment (ultrasound with microbubble contrast) before and during steady-state hyperinsulinemia. Plasma glucosamine pharmacokinetics after oral dosing were determined in each subject using a high-performance liquid chromatography method. As expected, at baseline, obese subjects had insulin resistance and endothelial dysfunction when compared with lean subjects (SI(Clamp) [median {25th-75th percentile}] = 4.3 [2.9-5.3] vs. 7.3 [5.7-11.3], P < 0.0001; insulin-stimulated changes in BAF [% over basal] = 12 [-6 to 84] vs. 39 [2-108], P < 0.04). When compared with placebo, glucosamine did not cause insulin resistance or endothelial dysfunction in lean subjects or significantly worsen these findings in obese subjects. The half-life of plasma glucosamine after oral dosing was approximately 150 min, with no significant changes in steady-state glucosamine levels detectable after 6 weeks of therapy. We conclude that oral glucosamine at standard doses for 6 weeks does not cause or significantly worsen insulin resistance or endothelial dysfunction in lean or obese subjects.

Administration, Oral↗

PubMed2006

Additive beneficial effects of fenofibrate combined with candesartan in the treatment of hypertriglyceridemic hypertensive patients.

OBJECTIVE: Mechanisms underlying fibric acid and angiotensin II type 1 receptor blocker therapies differ. Signaling from peroxisome proliferator-activated receptor alpha may cross-talk with the angiotensin II system. We investigated vascular and metabolic responses to these therapies either alone or in combination in hypertriglyceridemic hypertensive patients. RESEARCH DESIGN AND METHODS: This was a randomized, double-blind, placebo-controlled, cross-over trial with three treatment arms (each 2 months) and two washout periods (each 2 months). Forty-four patients were given 200 mg fenofibrate and placebo, 200 mg fenofibrate and 16 mg candesartan, or 16 mg candesartan and placebo daily during each treatment period. RESULTS: Fenofibrate, combined therapy, or candesartan therapy significantly reduced blood pressure. However, combined therapy significantly reduced blood pressure more than fenofibrate or candesartan alone (P < 0.001 by ANOVA). When compared with candesartan, fenofibrate or combined therapy significantly improved the lipoprotein profile. All three treatment arms significantly improved flow-mediated dilator response to hyperemia. Combined therapy significantly decreased plasma malondialdehyde, high-sensitivity C-reactive protein, and soluble CD40L levels relative to baseline measurements. Importantly, these parameters were changed to a greater extent with combined therapy when compared with monotherapy (P < 0.001, P = 0.002, P = 0.050, and P = 0.032 by ANOVA, respectively). Fenofibrate, combined therapy, and candesartan significantly increased plasma adiponectin levels and insulin sensitivity relative to baseline measurements. However, the magnitude of these increases were not significantly different among the three therapies (P = 0.246 and P = 0.153 by ANOVA, respectively). CONCLUSIONS: Fenofibrate combined with candesartan improves endothelial function and reduces inflammatory markers to a greater extent than monotherapy in hypertriglyceridemic hypertensive patients.

Adiponectin↗

PubMed2006

Reciprocal relationships between insulin resistance and endothelial dysfunction: insights from therapeutic interventions.

Endothelial dysfunction contributes to cardiovascular diseases that are also characterized by insulin resistance. Insulin resistance is a hallmark of metabolic disorders including Type 2 diabetes, obesity, and the metabolic syndrome that are also characterized by endothelial dysfunction. Metabolic actions of insulin to promote glucose disposal are augmented by vascular actions of insulin in endothelium to stimulate production of the vasodilator nitric oxide (NO). Indeed, NO-dependent increases in blood flow to skeletal muscle account for 25% to 40% of the increase in glucose uptake in response to insulin stimulation. PI 3-kinase-dependent insulin signaling pathways in endothelium related to production of NO share striking similarities with metabolic pathways in skeletal muscle that promote glucose uptake. Other distinct non-metabolic branches of insulin signaling pathways regulate secretion of the vasoconstrictor endothelin-1 (ET-1) in endothelium. Metabolic insulin resistance is characterized by pathway-specific impairment in PI 3-kinase-dependent signaling that in endothelium may cause imbalance between production of NO and secretion of ET-1 leading to decreased blood flow that worsens insulin resistance. Therapeutic interventions in both animal models and human studies demonstrate that improving endothelial function ameliorates insulin resistance while improving insulin sensitivity ameliorates endothelial dysfunction. Taken together, cellular, physiological, clinical, and epidemiological studies strongly support a reciprocal relationship between endothelial dysfunction and insulin resistance that helps to link cardiovascular and metabolic diseases. In this review, pathophysiological mechanisms that couple endothelial dysfunction with insulin resistance will be discussed with an emphasis on important therapeutic implications for the metabolic syndrome.

Animals↗

PubMed2005

Dehydroepiandrosterone mimics acute actions of insulin to stimulate production of both nitric oxide and endothelin 1 via distinct phosphatidylinositol 3-kinase- and mitogen-activated protein kinase-dependent pathways in vascular endothelium.

Dehydroepiandrosterone (DHEA) is an adrenal steroid and nutritional supplement that may improve insulin sensitivity. Although steroid hormones classically act by regulating transcription, they may also signal through cell surface receptors to mediate nongenomic actions. Because DHEA may augment insulin sensitivity, we hypothesized that DHEA mimics vascular actions of insulin to acutely activate signaling pathways in endothelium-mediating production of nitric oxide (NO) and endothelin 1 (ET-1). Treatment of bovine aortic endothelial cells with either insulin or DHEA (100 nm, 5 min) stimulated significant increases in NO production (assessed with NO-selective fluorescent dye diaminofluorescein 2). These responses were abolished by pretreatment of cells with L-NAME (nitro-L-arginine methyl ester; NO synthase inhibitor) or wortmannin [phosphatidylinositol (PI) 3-kinase inhibitor]. Under similar conditions, insulin- or DHEA-stimulated phosphorylation of Akt (Ser473) and endothelial nitric oxide synthase (Ser1179) was inhibited by pretreatment of cells with wortmannin (but not MAPK kinase inhibitor PD98059). Acute DHEA treatment also caused phosphorylation of MAPK (Thr202/Tyr204) that was inhibitable by PD98059 (but not wortmannin). DHEA treatment of bovine aortic endothelial cells (100 nM, 5 min) stimulated a 2-fold increase in ET-1 secretion that was abolished by pretreatment of cells with PD98059 (but not wortmannin). We conclude that DHEA has acute, nongenomic actions in endothelium to stimulate production of the vasodilator NO via PI 3-kinase-dependent pathways and secretion of the vasoconstrictor ET-1 via MAPK-dependent pathways. Altering the balance between PI 3-kinase- and MAPK-dependent signaling in vascular endothelium may determine whether DHEA has beneficial or harmful effects relevant to the pathophysiology of diabetes.

Animals↗

PubMed2005

Inflammatory markers and the metabolic syndrome: insights from therapeutic interventions.

Inflammation in the vasculature might be an important pathogenic link between cardiovascular diseases and the metabolic syndrome. Inflammation can be reduced by a variety of approaches including diet, exercise, cardiovascular drugs, and insulin sensitizers. Importantly, these different measures improve vascular function and reduce inflammation by distinct mechanisms. Therefore, combination therapy including lifestyle modifications and multiple drugs from separate classes might produce additive beneficial outcomes. We review plausible mechanisms for effects of combination therapy to reduce inflammation, improve endothelial dysfunction, and decrease insulin resistance in atherosclerosis, coronary heart disease, and hypertension in the context of insulin-resistant states including diabetes, obesity, and the metabolic syndrome.

Adiponectin↗

PubMed2005

Anti-inflammatory and metabolic effects of candesartan in hypertensive patients.

BACKGROUND: Angiotensin II type 1 (AT1) receptor blocker therapy prevented or retarded the progression of coronary heart disease. The mechanisms of this benefit may relate to the ability of AT1 receptor blockers to reduce inflammation and insulin resistance. METHODS: We administered placebo or candesartan 16 mg daily during 2 months to 45 patients with mild to moderate hypertension. This study was randomized, double-blind, placebo-controlled, crossover in design. RESULTS: Candesartan therapy significantly lowered both systolic and diastolic blood pressure. Compared with placebo, candesartan therapy significantly lowered plasma hsCRP levels relative to baseline measurements from 1.10 to 0.70 mg/l (P=0.024) and soluble CD40 ligand levels by 30+/-11% (P<0.001). There were significant inverse correlations between body mass index and baseline plasma adiponectin levels (r=-0.480, P=0.009). There were significant correlations between baseline adiponectin levels and baseline insulin (r=-0.317, P=0.034) or baseline Quantitative Insulin-Sensitivity Check Index (QUICKI), a surrogate index of insulin sensitivity (r=0.371, P=0.012). Compared with placebo, candesartan therapy significantly lowered fasting insulin levels (P=0.011) and increased plasma levels of adiponectin by 15+/-4% (P=0.012) and increased QUICKI by 8+/-2% (P=0.007). There were significant correlations between percent changes in adiponectin levels and percent changes in insulin (r=-0.340, P=0.022) or QUICKI (r=0.325, P=0.029). CONCLUSIONS: Candesartan therapy significantly reduced inflammation and increased adiponectin levels and improved insulin sensitivity in hypertensive patients.

Adiponectin↗