Myocardial Insulin Resistance Research Articles

Maternal Obesity and Cardiac Development in the Offspring: Study in Human Neonates and Minipigs

ObjectivesThe aim of this study was to investigate the consequences of maternal overweight on cardiac development in offspring in infants (short term) and minipigs (short and longer term). BackgroundThe epidemic of overweight involves pregnant women. The uterine environment affects organ development, modulating disease susceptibility. Offspring of obese mothers have higher rates of cardiovascular events and mortality. MethodsEchocardiography was performed in infants born to lean and overweight mothers at birth and at 3, 6, and 12 months of age. In minipigs born to mothers fed a high-fat diet or a normal diet, cardiac development (echocardiography, histology), glucose metabolism and perfusion (positron emission tomography), triglyceride and glycogen content, and myocardial enzymes regulating metabolism (mass spectrometry) were determined from birth to adulthood. ResultsIn neonates, maternal overweight, especially in the last trimester, predicted a thicker left ventricular posterior wall at birth (4.1 ± 0.3 vs. 3.3 ± 0.2 mm; p < 0.05) and larger end-diastolic and stroke volumes at 1 year. Minipigs born to mothers fed a high-fat diet showed greater left ventricular mass (p = 0.0001), chambers (+100%; p < 0.001), stroke volume (+75%; p = 0.001), cardiomyocyte nuclei (+28%; p = 0.02), glucose uptake, and glycogen accumulation at birth (+100%; p < 0.005), with lower levels of oxidative enzymes, compared with those born to mothers fed a normal diet. Subsequently, they developed myocardial insulin resistance and glycogen depletion. Late adulthood showed elevated heart rate (111 ± 5 vs. 84 ± 8 beats/min; p < 0.05) and ejection fraction and deficient fatty acid oxidative enzymes. ConclusionsNeonatal changes in cardiac morphology were explained by late-trimester maternal body mass index; myocardial glucose overexposure seen in minipigs can justify early human findings. Longer term effects in minipigs consisted of myocardial insulin resistance, enzymatic alterations, and hyperdynamic systolic function.

Abstract 273: Pressure Overload Induces Cardiac Insulin Resistance in an Angiotensin II-Independent Manner

Aims: Pressure overload is able to provoke the cardiac insulin resistance via angiotensin II (AngII). However, the direct effect of pressure overload on the myocardial insulin sensitivity was poorly understood. This study was aimed to explore whether and how pressure overload impairs myocardial insulin sensitivity independent of AngII. Methods and Results: To mimic cardiac pressure overload, C57BL/6 mice were subjected to transverse aortic constriction (TAC) for 2 weeks in vivo . Cultured neonatal rat cardiomyocytes (NRCMs) were imposed with mechanical stretch for 24 hours in vitro . Although pressure overload dramatically restrained the glucose uptake and expression of glucose transporter 4 (GLUT4) in the myocardial membrane, it didn’t increase the local expression of AngII in TAC mouse hearts and mechanically-stretched NRCMs. C57BL/6 mice were treated with Enalapril and then subjected to TAC for 2 weeks. The glucose uptake and expression of GLUT4 in the myocardial membrane were dramatically restrained in the left ventricles (LVs) of 2 week TAC mice, which were preserved in mice treated with Enalapril. Angiotensinogen knock out ( ATG -/- ) mice were subjected to TAC for 2 weeks. Angiotensin converting enzyme (ACE)-deficient NRCMs were mechanically stretched. Insulin sensitivity was significantly impaired by TAC in ATG -/- mouse hearts and mechanical stretch in NRCMs evidenced by a notably decreased glucose uptake and expression of GLUT4 in myocardial membrane. Pressure overload impaired the myocardial insulin signals including decreased phosphorylation of insulin receptor, insulin receptor substrate 1 and Akt. Candesartan, an AngII receptor 1 (AT1R) blocker, partly attenuated the myocardial insulin resistance induced by mechanical stress in vivo and in vitro . Conclusion: In conclusion, we unraveled that pressure overload is able to provoke myocardial insulin resistance independent of AngII which was partly mediated by AT1R.

Empagliflozin Improves Left Ventricular Diastolic Dysfunction in a Genetic Model of Type 2 Diabetes.

Cardiovascular (CV) diseases in type 2 diabetes (T2DM) represent an enormous burden with high mortality and morbidity. Sodium-glucose cotransporter 2 (SGLT2) inhibitors have recently emerged as a new antidiabetic class that improves glucose control, as well as body weight and blood pressure with no increased risk of hypoglycemia. The first CV outcome study terminated with empagliflozin, a specific SGLT2 inhibitor, has shown a reduction in CV mortality and in heart failure hospitalization, suggesting a beneficial impact on cardiac function which remains to be demonstrated. This study was designed to examine the chronic effect of empagliflozin on left ventricular (LV) systolic and diastolic functions in a genetic model of T2DM, ob/ob mice. Cardiac phenotype was characterized by echocardiography, in vivo hemodynamics, histology, and molecular profiling. Our results demonstrate that empagliflozin significantly lowered HbA1c and slightly reduced body weight compared to vehicle treatment with no obvious changes in insulin levels. Empagliflozin also improved LV maximum pressure and in vivo indices of diastolic function. While systolic function was grossly not affected in both groups at steady state, response to dobutamine stimulation was significantly improved in the empagliflozin-treated group, suggesting amelioration of contractile reserve. This was paralleled by an increase in phospholamban (PLN) phosphorylation and increased SERCA2a/PLN ratio, indicative of enhanced SERCA2a function, further supporting improved cardiac relaxation and diastolic function. In addition, empagliflozin reconciled diabetes-associated increase in MAPKs and dysregulated phosphorylation of IRS1 and Akt, leading to improvement in myocardial insulin sensitivity and glucose utilization. The data show that chronic treatment with empagliflozin improves diastolic function, preserves calcium handling and growth signaling pathways and attenuates myocardial insulin resistance in ob/ob mice, findings suggestive of a potential clinical utility for empagliflozin in the treatment of diastolic dysfunction.

RISK OF HOSPITALIZATION OR DEATH DUE TO HEART FAILURE WITH INTENSIVE GLUCOSE-LOWERING THERAPY IN DIABETIC WOMEN: SUBGROUP ANALYSES BY HISTORY OF CARDIOVASCULAR DISEASE IN THE ACCORD TRIAL

Background: Patients with type 2 diabetes (T2D) and cardiovascular disease (CVD) often exhibit myocardial insulin resistance, potentially contributing to morbidity and mortality. In a prior secondary analysis of publicly available ACCORD data, we noted increased hospitalization or death due to heart

Fenofibrate Therapy Restores Antioxidant Protection and Improves Myocardial Insulin Resistance in a Rat Model of Metabolic Syndrome and Myocardial Ischemia: The Role of Angiotensin II.

Renin-angiotensin system (RAS) activation promotes oxidative stress which increases the risk of cardiac dysfunction in metabolic syndrome (MetS) and favors local insulin resistance. Fibrates regulate RAS improving MetS, type-2 diabetes and cardiovascular diseases. We studied the effect of fenofibrate treatment on the myocardic signaling pathway of Angiotensin II (Ang II)/Angiotensin II type 1 receptor (AT1) and its relationship with oxidative stress and myocardial insulin resistance in MetS rats under heart ischemia. Control and MetS rats were assigned to the following groups: (a) sham; (b) vehicle-treated myocardial infarction (MI) (MI-V); and (c) fenofibrate-treated myocardial infarction (MI-F). Treatment with fenofibrate significantly reduced triglycerides, non-high density lipoprotein cholesterol (non-HDL-C), insulin levels and insulin resistance index (HOMA-IR) in MetS animals. MetS and MI increased Ang II concentration and AT1 expression, favored myocardial oxidative stress (high levels of malondialdehyde, overexpression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4), decreased total antioxidant capacity and diminished expression of superoxide dismutase (SOD)1, SOD2 and catalase) and inhibited expression of the insulin signaling cascade: phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PkB, also known as Akt)/Glut-4/endothelial nitric oxide synthase (eNOS). In conclusion, fenofibrate treatment favors an antioxidant environment as a consequence of a reduction of the Ang II/AT1/NOX4 signaling pathway, reestablishing the cardiac insulin signaling pathway. This might optimize cardiac metabolism and improve the vasodilator function during myocardial ischemia.

203 - Evaluation of Serum Redox Homeosthasis of AAS Abusers

Introduction The administration of anabolic-androgenic steroids (AAS) for improvement of athletic performance has increased notably during the past three decades, even among non-athletes. Beyond the desired effects for these individuals, these high dosages provoke a series of adverse effect, such as: dyslipidemia, atherosclerosis, hypertension, cardiac hypertrophy, ischemia and acute myocardial infarction, insulin resistance and development of cancer. Interestingly, many AAS-side effects have redox imbalance in their etiology. Objective To evaluate redox homeosthasis in the blood of AAS abusers. Method A total of 30 men who regularly engaged in both resistance and aerobic exercise at fitness academies volunteered for the study (control group: n = 15, age=26.93 ± 1.820 years; AAS group: n = 15, age=30.13 ± 1.762 years). Serum Gluthatione Peroxidase (GPx) and Superoxide Dismutase (SOD) activities were evaluated through Elisa Cayman’s kit, while serum Oxidized Low Density Lipoprotein (OxLDL) was evaluated by enzyme-linked immunosorbent Assay kit (Cloud-Clone Corporation). Testosterone, free testosterone, sex hormone-binding globulin (SHBG), Luteinizing hormone (LH), Follicle-stimulating hormone (FSH) and Estradiol were evaluated by electrochemiluminescence immunoassay (Roche). Data were analyzed by software Graph-Pad Prism 5.0, unpaired t test. Results Serum testosterone (C=579.7 ± 45.16 ng/dL n=15; AAS=989.5 ± 145.5 ng/dL n=15,p=0,0119), free testosterone (C=437.6 ± 33.68 pmol/L n=15; AAS=1104 ± 202.2 pmol/L n=13,p=0,0017) and estradiol (C=27.07 ± 2.634 pg/mL n=15; AAS=92.60 ± 25.46 pg/mL n=15,p=0,0161) were higher in AAS group when compared to C group. Moreover, serum AAS (C=3.267 ± 0.3160 mUl/mL, n=15; AAS= 0.7000 ± 0.2640 mUl/mL n=15,p , LH (C=4.693 ± 0.4076 mUI/mL, n=15; AAS=1.060 ± 0.4985 mUl/mL n=15,p Conclusion Our data shows that redox homeostasis is not affected by AAS abuse.

Direct Evidence that Myocardial Insulin Resistance following Myocardial Ischemia Contributes to Post-Ischemic Heart Failure.

A close link between heart failure (HF) and systemic insulin resistance has been well documented, whereas myocardial insulin resistance and its association with HF are inadequately investigated. This study aims to determine the role of myocardial insulin resistance in ischemic HF and its underlying mechanisms. Male Sprague-Dawley rats subjected to myocardial infarction (MI) developed progressive left ventricular dilation with dysfunction and HF at 4 wk post-MI. Of note, myocardial insulin sensitivity was decreased as early as 1 wk after MI, which was accompanied by increased production of myocardial TNF-α. Overexpression of TNF-α in heart mimicked impaired insulin signaling and cardiac dysfunction leading to HF observed after MI. Treatment of rats with a specific TNF-α inhibitor improved myocardial insulin signaling post-MI. Insulin treatment given immediately following MI suppressed myocardial TNF-α production and improved cardiac insulin sensitivity and opposed cardiac dysfunction/remodeling. Moreover, tamoxifen-induced cardiomyocyte-specific insulin receptor knockout mice exhibited aggravated post-ischemic ventricular remodeling and dysfunction compared with controls. In conclusion, MI induces myocardial insulin resistance (without systemic insulin resistance) mediated partly by ischemia-induced myocardial TNF-α overproduction and promotes the development of HF. Our findings underscore the direct and essential role of myocardial insulin signaling in protection against post-ischemic HF.

Regulation of B-type natriuretic peptide synthesis by insulin in obesity in male mice.

Human studies suggest that insulin resistance and obesity are associated with a decrease in B-type natriuretic peptide (BNP) plasma concentrations. The objective of the study was to gain insights into the mechanisms involved in the association between insulin resistance and decreased BNP plasma concentrations. Mice fed a high-fat, high-fructose (HFHF) diet for 4 weeks developed mild obesity and systemic insulin resistance. Elevated plasma concentrations of insulin, glucose and triglycerides were noted. The HFHF diet was also associated with myocardial insulin resistance, characterized by an impaired response of the phosphoinositide 3-kinase-AKT (PI3K-AKT) pathway to insulin in the left ventricle. Myocardial BNP expression and protein were decreased in HFHF-fed mice compared with control animals. Exposure of cardiomyocytes to 100 nm insulin activated PI3K-AKT signalling (15 min) and induced a 1.9 ± 0.3-fold increase in BNP gene expression (6 h). Prolonged exposure of cardiomyocytes to a high insulin concentration (100 nm) for 48 h induced insulin resistance, characterized by an impaired response of the PI3K-AKT signalling pathway and a decreased response of the BNP gene expression to insulin. The decreased response in BNP gene expression was reproduced by treating cardiomyocytes for 7 h with a PI3-kinase inhibitor (wortmannin). In conclusion, HFHF diet in vivo, prolonged exposure to an elevated concentration of insulin or inhibition of the PI3K-AKT pathway in vitro all decrease BNP mRNA levels; this decrease may in turn contribute to the decreased BNP peptide concentrations in plasma observed in insulin-resistant individuals.

Abstract 16485: Hyperinsulinemia Reduces Autophagy in Insulin Resistant Hearts Through Insulin Growth Factor 1 Receptor (IGF-1R) Signaling

Introduction: Diabetes is a leading cause of mortality and morbidity worldwide with over 50% of deaths in diabetic patients being caused by cardiovascular complications. The mechanisms underlying the high incidence of diabetic cardiac dysfunction remain relatively obscure but may involve altered autophagy. Macro-autophagy (referred to as autophagy) is a regulated intracellular catabolic pathway for the turnover of long-lived proteins, macromolecular aggregates, and damaged organelles. Hypothesis: Taking advantage TIRKO mice (a mouse model of total cardiac ablation of insulin receptors [IRs]), we aimed to investigate the impact of myocardial insulin resistance and systemic hyperinsulinemia (SH) on cardiac autophagy. Results: Basal and fasting-induced autophagy were significantly reduced in TIRKO hearts, as evidenced by reduced LC3II/LC3I ratios and increased P62 accumulation. As TIRKO mice develop SH, we next sought to determine whether this reduces autophagy independently of the absence of IRs. Thus, we used mice with cardiomyocytes-specific deletion of IRs (CIRKO mice) but without SH or (ob/ob) mice that have IRs in the heart but develop SH. We demonstrated that cardiac autophagy reduction is indeed caused by systemic SH as its level was unaltered in CIRKO hearts but reduced in (ob/ob) hearts. Because of the absence of IRs in TIRKO hearts and the degree of insulin resistance in (ob/ob) hearts, we hypothesized that the reduction of cardiac autophagy by SH is mediated by the IGF-1R signaling. Indeed, IGF-1R phosphorylation was enhanced in both TIRKO and (ob/ob) hearts but not in CIRKO hearts. To begin to understand the functional role of attenuated autophagy in TIRKO hearts, we further decreased autophagosomes clearance by treating mice with the lysosomal clearance inhibitor chloroquine. Treatment of TIRKO mice with chloroquine for 4 hours massively increased LC3I and P62 levels, promoted cells death and decreased mitochondrial clearance. Conclusions: Taken together, these results suggest that hyperinsulinemia-mediated reduction in cardiac autophagy can be adaptive to suppress sustained autophagy activation by insulin resistance but can become maladaptive if the heart is challenged by a reduction in lysosomal degradation.

ACE2 Deficiency Worsens Epicardial Adipose Tissue Inflammation and Cardiac Dysfunction in Response to Diet-Induced Obesity.

Obesity is increasing in prevalence and is strongly associated with metabolic and cardiovascular disorders. The renin-angiotensin system (RAS) has emerged as a key pathogenic mechanism for these disorders; angiotensin (Ang)-converting enzyme 2 (ACE2) negatively regulates RAS by metabolizing Ang II into Ang 1-7. We studied the role of ACE2 in obesity-mediated cardiac dysfunction. ACE2 null (ACE2KO) and wild-type (WT) mice were fed a high-fat diet (HFD) or a control diet and studied at 6 months of age. Loss of ACE2 resulted in decreased weight gain but increased glucose intolerance, epicardial adipose tissue (EAT) inflammation, and polarization of macrophages into a proinflammatory phenotype in response to HFD. Similarly, human EAT in patients with obesity and heart failure displayed a proinflammatory macrophage phenotype. Exacerbated EAT inflammation in ACE2KO-HFD mice was associated with decreased myocardial adiponectin, decreased phosphorylation of AMPK, increased cardiac steatosis and lipotoxicity, and myocardial insulin resistance, which worsened heart function. Ang 1-7 (24 µg/kg/h) administered to ACE2KO-HFD mice resulted in ameliorated EAT inflammation and reduced cardiac steatosis and lipotoxicity, resulting in normalization of heart failure. In conclusion, ACE2 plays a novel role in heart disease associated with obesity wherein ACE2 negatively regulates obesity-induced EAT inflammation and cardiac insulin resistance.

Antioxidant treatment normalizes mitochondrial energetics and myocardial insulin sensitivity independently of changes in systemic metabolic homeostasis in a mouse model of the metabolic syndrome

Cardiac dysfunction in obesity is associated with mitochondrial dysfunction, oxidative stress and altered insulin sensitivity. Whether oxidative stress directly contributes to myocardial insulin resistance remains to be determined. This study tested the hypothesis that ROS scavenging will improve mitochondrial function and insulin sensitivity in the hearts of rodent models with varying degrees of insulin resistance and hyperglycemia. The catalytic antioxidant MnTBAP was administered to the uncoupling protein-diphtheria toxin A (UCP-DTA) mouse model of insulin resistance (IR) and obesity, at early and late time points in the evolution of IR, and to db/db mice with severe obesity and type-two diabetes. Mitochondrial function was measured in saponin-permeabilized cardiac fibers. Aconitase activity and hydrogen peroxide emission were measured in isolated mitochondria. Insulin-stimulated glucose oxidation, glycolysis and fatty acid oxidation rates were measured in isolated working hearts, and 2-deoxyglucose uptake was measured in isolated cardiomyocytes. Four weeks of MnTBAP attenuated glucose intolerance in 13-week-old UCP-DTA mice but was without effect in 24-week-old UCP-DTA mice and in db/db mice. Despite the absence of improvement in the systemic metabolic milieu, MnTBAP reversed cardiac mitochondrial oxidative stress and improved mitochondrial bioenergetics by increasing ATP generation and reducing mitochondrial uncoupling in all models. MnTBAP also improved myocardial insulin mediated glucose metabolism in 13 and 24-week-old UCP-DTA mice. Pharmacological ROS scavenging improves myocardial energy metabolism and insulin responsiveness in obesity and type 2 diabetes via direct effects that might be independent of changes in systemic metabolism.

Exercise Training Activations PI3K/Akt/eNOS Signalling Improves Insulin Resistance in Post‐Myocardial Infarction Rats

Myocardial infarction (MI) has been shown to induce cardiac dysfunction and insulin resistance. This study was designed to examine the effects of MI‐related insulin resistance on vaso relaxation function and its underlying mechanisms, with specific focus on the role of exercise in reversing vasorelaxation response. Adult male Sprague‐Dawley rats were divided into three groups: Sham, MI, and MI+Exercise. MI+Exercise rats were subjected to 8 weeks of treadmill training (50 min/day, 5 days/week). Myocardial infarction caused significant impairments in endothelial structure and vasodilation (P &lt; 0.05‐0.01), which was evidenced by decreased arterial vasorelaxation to ACh and insulin. Myocardial infarction attenuated myocardial contractile response to insulin, decreased PI3K/Akt/eNOS expression and its phosphorylation by insulin, and increased IL‐1β, IL‐6, and TNF‐α (P &lt; 0.05‐0.01). Exercise improved insulin sensitivity, facilitated arterial vasorelaxation to ACh and insulin, and increased arterial PI3K/Akt/eNOS activation in post‐MI rats. Inhibition of PI3K with LY294002, and eNOS with L‐NAME significantly blocked exercise‐facilitated arterial vasorelaxation and PI3K/Akt/eNOS activation response to insulin. In conclusion, these results demonstrate that endothelial dysfunction in response to insulin plays an important role in the development of myocardial infarction‐related insulin resistance. The reversal of insulin resistance by exercise is most likely associated with normalizes inflammatory cytokines, and PI3K/Akt/eNOS‐dependent improvement in insulin sensitivity.

Marine omega-3 fatty acids prevent myocardial insulin resistance and metabolic remodeling as induced experimentally by high insulin exposure.

Insulin resistance is an important risk factor for the development of several cardiac pathologies, thus advocating strategies for restoring insulin sensitivity of the heart in these conditions. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), mainly eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3), have been shown to improve insulin sensitivity in insulin-sensitive tissues, but their direct effect on insulin signaling and metabolic parameters in the myocardium has not been reported previously. The aim of this study was therefore to examine the ability of EPA and DHA to prevent insulin resistance in isolated rat cardiomyocytes. Primary rat cardiomyocytes were made insulin resistant by 48 h incubation in high insulin (HI) medium. Parallel incubations were supplemented by 200 μM EPA or DHA. Addition of EPA or DHA to the medium prevented the induction of insulin resistance in cardiomyocytes by preserving the phosphorylation state of key proteins in the insulin signaling cascade and by preventing persistent relocation of fatty acid transporter CD36 to the sarcolemma. Only cardiomyocytes incubated in the presence of EPA, however, exhibited improvements in glucose and fatty acid uptake and cell shortening. We conclude that ω-3 PUFAs protect metabolic and functional properties of cardiomyocytes subjected to insulin resistance-evoking conditions.

Abstract 15225: Post-ischemic Myocardial Insulin Resistance Induced by Tnf-α Overproduction Precipitates the Development of Heart Failure After Myocardial Infarction

Objectives: Clinical evidence has demonstrated a decreased myocardial insulin response in HF patients. However, the role of myocardial insulin resistance and the underlying mechanisms in HF are largely unclear. Methods and Results: Sprague Dawley rats subjected to myocardial infarction (MI) resulted in a progressive left ventricular (LV) remodeling and dysfunction. Echocardiographic assessment showed preserved LV end-systolic dimension (LVESD 0.453 ± 0.027 cm) and ejection fraction (EF 57.03 ± 2.35%) at 1 wk after MI, and evident LV dilation (LVESD 0.612 ± 0.026 cm) and dysfunction (EF 40.21 ± 3.09%) at 4 wk after MI. Myocardial insulin sensitivity decreased significantly at 1 wk after MI as evidenced by reduced insulin-stimulated myocardial fluorodeoxyglucose uptake (Standardized Uptake Value: 2.71 ± 0.42 vs. 5.13 ± 0.51 of sham+insulin, n=6, P &lt;0.01) and GLUT-4 translocation and altered insulin signaling, whereas systemic insulin sensitivity remained unchanged. Mechanistically, myocardial TNF-α production was increased following MI. Treatment with etanercept (a TNF-α inhibitor) post-MI improved myocardial insulin sensitivity, while adenovirus-mediated overexpression of TNF-α resulted in myocardial insulin resistance in non-MI hearts. In addition, TNF-α overexpressed rat hearts exhibited LV dysfunction (EF 41.32 ± 4.21%) and LV dilation as early as 1 wk after MI. Moreover, insulin treatment during the first week following MI suppressed myocardial TNF-α production and increased myocardial insulin sensitivity, resulting in alleviated cardiac dysfunction and remodeling at 4 wk after MI. Importantly, in a separate experiment, cardiomyocyte-specific insulin receptor knockout mice exhibited aggravated post-ischemic LV remodeling and dysfunction compared with littermate controls. Conclusions: Our data provide novel insights that myocardial insulin resistance, independently of systemic insulin resistance, precipitates the development of post-ischemic HF. Myocardial insulin resistance is an early event partly attributed to myocardial TNF-α overproduction following MI. This finding indicates the essential role of myocardial insulin signaling in protection against ischemic HF.

Abstract 18910: Angiotensin Converting Enzyme 2 Deficiency Results in Cardiac Insulin Resistance in Response to High-Fat Diet

Background: Activation of the renin-angiotensin system (RAS) can alter the cardiac energy substrate preference, thereby contributing to the progression of heart failure. Angiotensin converting enzyme (ACE) 2 is a key negative regulator of the RAS where it metabolizes angiotensin (Ang) II into Ang (1-7). Hypothesis: Myocardial ACE2 was upregulated in response to high-fat diet in wildtype (WT) mice. We hypothesize that ACE2 upregulation is a compensatory response and loss of ACE2 will worsened obesity and its associated cardiomyopathy. Methods and Results: ACE2-null (ACE2-/y; ACE2KO) and WT litter-mate control mice were fed with high-fat diet (HFD; 45 kcal%) or control diet (10 kcal%) and studied at 6-months of age. In contrast to our hypothesis, loss of ACE2 resulted in decreased obesity in response to HFD compared to WT mice (body weight at 6-months: 45.9±4.3 in ACE2KO-HFD vs 51.4±1.55 in WT-HFD; p&lt;0.05). Conversely, ACE2KO-HFD mice showed increased fasting plasma glucose levels (6.76±0.7 in ACE2KO-HFD vs 5.11±0.6 in WT-HFD; p&lt;0.05) with worsened whole-body insulin resistance. We subjected hearts to ex vivo aerobic perfusions to measure cardiac energy metabolism. ACE2KO-HFD hearts showed markedly decreased cardiac work along with reduced insulin response suggesting increased myocardial insulin resistance. ACE2KO-HFD hearts relied predominantly on fat metabolism as the energy source, a feature observed in cardiomyopathy. Pressure-volume analysis showed worsened diastolic dysfunction in the ACE2KO hearts compared to WT hearts in response to HFD, which was primarily due to impaired active relaxation (Tau(Weiss): 7.41±0.4 in ACE2KO-HFD vs 6.26±0.52 in WT-HFD; p&lt;0.05). Metabolic and functional changes in the ACE2KO-HFD were associated with impaired insulin signaling (decreased p-Akt) and decreased phosphorylation of AMPK. ACE2KO-HFD hearts also showed increased pyruvate dehydrogenase kinase 4 expression and phosphorylation of pyruvate dehydrogenase. Conclusions: Renin-angiotensin system plays an important role in cardiac metabolism. We found a novel role of ACE2 in cardiac insulin signaling, where ACE2 negatively regulates obesity and hyperglycemia induced cardiac insulin-resistance and alterations in cardiac metabolism.

GW25-e4230 Post-ischemic myocardial insulin resistance induced by TNF-α overproduction precipitates the development of heart failure after myocardial infarction

Objectives: Clinical evidence has demonstrated a decreased myocardial insulin response in HF patients. However, the role of myocardial insulin resistance and the underlying mechanisms in HF are lar...

The hexosamine biosynthetic pathway induces gene promoter activity of acetyl-CoA carboxylase beta

The cardiac isoform of acetyl-CoA carboxylase (ACCβ) produces malonyl-CoA, a potent inhibitor of mitochondrial fatty acid (FA) uptake. Higher ACCβ activity decreases FA utilization, potentially leading to intracellular myocardial lipid accumulation and insulin resistance (IR). Since increased hexosamine biosynthetic pathway (HBP) flux is linked to IR onset, we hypothesized that HBP activation leads to the induction of ACCβ gene promoter activity. Rat H9c2 cardio-myoblasts were transiently transfected with a 1317bp human ACCβ promoter-luciferase construct (pPIIβ−1317)±an expression construct encoding the HBP rate-limiting step, i.e., glutamine:fructose 6-phosphate amidotransferase (GFAT)±various HBP modulators. The administration of l-glutamine (HBP substrate) dose-dependently increased, while HBP inhibitors attenuated pPIIβ−1317 activity. Co-transfections with dominant-negative GFAT constructs diminished pPIIβ−1317 activity. To explore underlying transcriptional mechanisms, we co-transfected with upstream stimulatory factor (USF) expression constructs and found that USF2 induced pPIIβ−1317 activity vs. controls. Moreover, co-transfection of a GFAT expression construct+USF reporter-promoter construct (with consensus USF binding elements) led to induction of pPIIβ−1317 activity vs. controls. We next performed transfections with GFAT±full length ACCβ and seven truncated promoter-luciferase constructs, respectively. Here GFAT-mediated ACCβ promoter induction was blunted when co-transfected with the pPIIβ−38/+65 deletion construct indicating that USF2 binds to the proximal ACCβ promoter region (near start codon). Our study demonstrates that HBP activation induces ACCβ gene promoter activity in H9c2 cells via USF2. We propose that such ACCβ induction may elicit serious downstream effects, e.g. the inhibition of FA β-oxidation and the onset of IR.

GLP-1 (7-36) amide restores myocardial insulin sensitivity and prevents the progression of heart failure in senescent beagles.

BackgroundWe previously demonstrated that older beagles have impaired whole body and myocardial insulin responsiveness (MIR), and that glucagon-like peptide-1 (GLP-1 [7–36] amide) improves MIR in young beagles with dilated cardiomyopathy (DCM). Here, we sought to determine if aging alone predisposes to an accelerated course of DCM, and if GLP-1 [7–36] amide would restore MIR and impact the course of DCM in older beagles.MethodsEight young beagles (Young-Control) and sixteen old beagles underwent chronic left ventricle (LV) instrumentation. Seven old beagles were treated with GLP-1 (7–36) amide (2.5 pmol/kg/min) for 2 weeks prior to instrumentation and for 35 days thereafter (Old + GLP-1), while other 9 served as control (Old-Control). All dogs underwent baseline metabolic determinations and LV biopsy for mitochondria isolation prior to the development of DCM induced by rapid pacing (240 min−1). Hemodynamic measurements were performed routinely as heart failure progressed.ResultsAt baseline, all old beagles had elevated non-esterifed fatty acids (NEFA), and impaired MIR. GLP-1 reduced plasma NEFA (Old-Control: 853 ± 34; Old + GLP-1: 531 ± 33 μmol/L, p < 0.02), improved MIR (Old-Control: 289 ± 54; Old + GLP-1: 512 ± 44 mg/min/100 mg, p < 0.05), and increased uncoupling protein-3 (UCP-3) expression in isolated mitochondria. Compared to the Young-Control, the Old-Controls experienced an accelerated course of DCM (7 days versus 29 days, p < 0.005) and excess mortality, while the Old + GLP-1 experienced increased latency to the onset of DCM (7 days versus 23 days, p < 0.005) and reduced mortality.ConclusionAging is associated with myocardial insulin resistance, which predispose to an accelerated course of DCM. GLP-1 treatment is associated with increased MIR and protection against an accelerated course of DCM in older beagles.

Independent effects of circulating glucose, insulin and NEFA on cardiac triacylglycerol accumulation and myocardial insulin resistance in a swine model.

Cardiac steatosis and myocardial insulin resistance elevate the risk of cardiac complications in obesity and diabetes. We aimed to disentangle the effects of circulating glucose, insulin and NEFA on myocardial triacylglycerol (TG) content and myocardial glucose uptake. Twenty-two pigs were stratified according to four protocols: low NEFA + low insulin (nicotinic acid), high NEFA + low insulin (fasting) and high insulin + low NEFA ± high glucose (hyperinsulinaemia-hyperglycaemia or hyperinsulinaemia-euglycaemia). Positron emission tomography, [U-(13)C]palmitate enrichment techniques and tissue biopsies were used to assess myocardial metabolism. Heart rate and rate-pressure product (RPP) were monitored. Myocardial glucose extraction was increased by NEFA suppression and was similar in the hyperinsulinaemia-hypergylcaemia, hyperinsulinaemia-euglycaemia and nicotinic acid groups. Hyperglycaemia enhanced myocardial glucose uptake due to a mass action. Myocardial TG content was greatest in the fasting group, whereas hyperinsulinaemia had a mild effect. Heart rate and RPP increased in hyperinsulinaemia-euglycaemia, in which cardiac glycogen content was reduced. Heart rate correlated with myocardial TG and glycogen content. Elevated NEFA levels represent a powerful, self-sufficient promoter of cardiac TG accumulation and are a downregulator of myocardial glucose uptake, indicating that the focus of treatment should be to 'normalise' adipose tissue function to lower the risk of cardiac TG accumulation and myocardial insulin resistance. The observation that hyperinsulinaemia and nicotinic acid led to myocardial fuel deprivation provides a potential explanation for the cardiovascular outcomes reported in recent intensive glucose-lowering and NEFA-lowering clinical trials.

Metabolomic analysis of pressure-overloaded and infarcted mouse hearts.

Cardiac hypertrophy and heart failure are associated with metabolic dysregulation and a state of chronic energy deficiency. Although several disparate changes in individual metabolic pathways have been described, there has been no global assessment of metabolomic changes in hypertrophic and failing hearts in vivo. Hence, we investigated the impact of pressure overload and infarction on myocardial metabolism. Male C57BL/6J mice were subjected to transverse aortic constriction or permanent coronary occlusion (myocardial infarction [MI]). A combination of LC/MS/MS and GC/MS techniques was used to measure 288 metabolites in these hearts. Both transverse aortic constriction and MI were associated with profound changes in myocardial metabolism affecting up to 40% of all metabolites measured. Prominent changes in branched-chain amino acids were observed after 1 week of transverse aortic constriction and 5 days after MI. Changes in branched-chain amino acids after MI were associated with myocardial insulin resistance. Longer duration of transverse aortic constriction and MI led to a decrease in purines, acylcarnitines, fatty acids, and several lysolipid and sphingolipid species but a marked increase in pyrimidines as well as ascorbate, heme, and other indices of oxidative stress. Cardiac remodeling and contractile dysfunction in hypertrophied hearts were associated with large increases in myocardial, but not plasma, levels of the polyamines putrescine and spermidine as well as the collagen breakdown product prolylhydroxyproline. These findings reveal extensive metabolic remodeling common to both hypertrophic and failing hearts that are indicative of extracellular matrix remodeling, insulin resistance and perturbations in amino acid, and lipid and nucleotide metabolism.