Myocardial Insulin Resistance Research Articles

Comparison of human and rodent cell models to study myocardial lipid-induced insulin resistance

Isolated or cultured cells have proven to be valuable model systems to investigate cellular (patho)biology and for screening of the efficacy of drugs or their possible side-effects. Pluripotent stem cells (PSC) can be readily obtained from healthy individuals as well as from diseased patients, and protocols have been developed to differentiate these cells into cardiomyocytes. Hence, these cellular models are moving center stage for a broader application. In this review, we focus on comparing mouse HL-1 cardiomyocytes, isolated adult rat cardiomyocytes, human embryonic stem cell-derived cardiomyocytes (hESC-CMs) and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for the study of metabolic aspects of cardiac functioning in health and disease. Various studies have reported that these cellular models are suitable for assessing substrate uptake and utilization, in that each display an adequate and similar response to physiological triggers, in particular the presence of insulin. Likewise, disease conditions, such as excess lipid supply, similarly affect each of these rodent and human cardiomyocyte models. It is concluded that PSC-CMs obtained from patients with cardiogenetic abnormalities are promising models to evaluate the functional consequence of gene variants with unknown significance.

Suppression of Myocardial Hypoxia-Inducible Factor-1α Compromises Metabolic Adaptation and Impairs Cardiac Function in Patients With Cyanotic Congenital Heart Disease During Puberty.

Cyanotic congenital heart disease (CCHD) is a complex pathophysiological condition involving systemic chronic hypoxia (CH). Some patients with CCHD are unoperated for various reasons and remain chronically hypoxic throughout their lives, which heightens the risk of heart failure as they age. Hypoxia activates cellular metabolic adaptation to balance energy demands by accumulating hypoxia-inducible factor 1-α (HIF-1α). This study aims to determine the effect of CH on cardiac metabolism and function in patients with CCHD and its association with age. The role of HIF-1α in this process was investigated, and potential therapeutic targets were explored. Patients with CCHD (n=25) were evaluated for cardiac metabolism and function with positron emission tomography/computed tomography and magnetic resonance imaging. Heart tissue samples were subjected to metabolomic and protein analyses. CH rodent models were generated to enable continuous observation of changes in cardiac metabolism and function. The role of HIF-1α in cardiac metabolic adaptation to CH was investigated with genetically modified animals and isotope-labeled metabolomic pathway tracing studies. Prepubertal patients with CCHD had glucose-dominant cardiac metabolism and normal cardiac function. In comparison, among patients who had entered puberty, the levels of myocardial glucose uptake and glycolytic intermediates were significantly decreased, but fatty acids were significantly increased, along with decreased left ventricular ejection fraction. These clinical phenotypes were replicated in CH rodent models. In patients with CCHD and animals exposed to CH, myocardial HIF-1α was upregulated before puberty but was significantly downregulated during puberty. In cardiomyocyte-specific Hif-1α-knockout mice, CH failed to initiate the switch of myocardial substrates from fatty acids to glucose, thereby inhibiting ATP production and impairing cardiac function. Increased insulin resistance during puberty suppressed myocardial HIF-1α and was responsible for cardiac metabolic maladaptation in animals exposed to CH. Pioglitazone significantly reduced myocardial insulin resistance, restored glucose metabolism, and improved cardiac function in pubertal CH animals. In patients with CCHD, maladaptation of cardiac metabolism occurred during puberty, along with impaired cardiac function. HIF-1α was identified as the key regulator of cardiac metabolic adaptation in animals exposed to CH, and pubertal insulin resistance could suppress its expression. Pioglitazone administration during puberty might help improve cardiac function in patients with CCHD.

MiR-155-5p alleviates ethanol-induced myocardial insulin resistance in H9C2 cells via regulating the mTOR signalling pathway.

Alcohol exposure impairs myocardium insulin sensitivity, which links to heart dysfunction. miR-155 regulates mTOR signaling pathway and is involved in multiple functions. However, the underlying mechanism of miR-155 in ethanol-induced myocardial insulin resistance remains unclear. Here, in this study we aimed to identify the role of miR-155 in myocardial insulin sensitivity and the involvement of mTOR pathway. H9C2 cells were cultured with or without 100mM ethanol for 24h. miR-155-5p inhibitor, miR-155-5p mimics or their respective negative control (inhibitor NC and mimic NC) were transfected to regulate miR-155-5p expression. mTOR signaling, including Ras homolog enriched in brain (Rheb), rapamycin insensitive companion of mTOR (Rictor) and ribosomal protein S6 kinase B2 (S6K2), was investigated by western blotting and qPCR, and insulin responsiveness was evaluated by glucose uptake and phosphorylation of insulin receptor substrate-1 (p-IRS1). The miR-155-5p level increased under ethanol exposure, accompanied by a decrease in glucose uptake, an increase in p-IRS1(ser 307) and activation of the mTOR signaling pathway in H9C2 cells. In addition, miR-155-5p downregulation decreased the glucose uptake, increased the p-IRS1(ser 307) level and activated the mTOR signaling pathway. miR-155-5p upregulation increased the glucose uptake, decreased the p-IRS1(ser 307) level and suppressed the mTOR signaling pathway. Collectively, these findings suggest miR-155-5p upregulation ameliorates myocardial insulin resistance via mTOR signaling in vitro, and miR-155-5p downregulation attenuates myocardial insulin resistance, which might become a potential therapeutic target for alcohol-induced cardiomyopathy.

Irisin Improves Myocardial Performance and Attenuates Insulin Resistance in Spontaneous Mutation (Leprdb ) Mice.

BackgroundIrisin, a newly identified peptide, is critical to regulating metabolism, thermogenesis, and reducing oxidative stresses. Our recent works demonstrated that irisin protected the heart against myocardial ischemic injury and preserved the function of mitochondria. However, whether irisin preserves myocardial performance and attenuates insulin resistance in type II diabetes remains unknown.ObjectiveEffects of irisin on type II diabetes-induced cardiac dysfty unction and insulin resistance in db/db mice were studied. Methods: Homozygous db/db mice (n=5/each group) for spontaneous mutation (Leprdb) and heterozygous (heterozygous) mice (n=5/each group) for control were used to assess for cardiac performance and impairment of insulin resistance. Homozygous and heterozygous controls received a treatment with either irisin (100 mg/kg, intraperitoneal injection, every other day) or vehicle control (PBS) for 4 weeks at 16 weeks of age. Insulin tolerance test and glucose tolerance test were employed to determine insulin resistance in mice. Cardiac function was assessed by echocardiography. Metabolic features including hyperglycemia and body growth were also examined. Immunohistochemical analysis was employed to determine myocardial hypertrophy and interstitial fibrosis. Immunoblots were employed to determine the signaling pathway associated with irisin treatment.ResultsHomozygous db/db mice developed an impairment in insulin sensitivity as indicated by Insulin tolerance test (ITT), glucose tolerance test (GTT) (p<0.05 vs non-irisin treatment), hyperglycemia (p<0.05 vs heterozygous control), and hyperinsulinemia (serum insulin: 0.81 ± 0.065 ng/ml in heterozygous control vs. 8.33 ± 0.69 ng/ml in homozygous db/db control, p<0.0001), which were attenuated by the administration of irisin (serum insulin 8.32 ± 0.68 ng/ml in homozygous db/db control vs 6.56 ± 0.38 ng/ml in homozygous db/db irisin treatment, p<0.0001). Furthermore, as compared to heterozygous control, db/db mice manifested a depression in cardiac performance [ejection fraction (EF): 91.9% ± 0.44 in heterozygous control vs 79.1% ± 2.0 in homozygous db/db control, p< 0.001] in associated myocardial remodeling (cardiac fibrosis 1.89% ± 0.09 in heterozygous control vs. 5.39% ± 0.22 in homozygous db/db control, p<0.001). Notably, the depression of cardiac function in EF (79.2% ± 2.0 homozygous db/db control vs. 88.6% ± 1.9 in homozygous db/db + irisin, p<0.01) and fractional shortening (FS) (42.2% ± 1.8 in homozygous db/db control vs. 53.2% ± 2.7 in homozygous db/db+irisin, p<0.01) and remodeling were markedly attenuated by the administration of irisin. Western blotting shows that irisin treatment prevented an approximate two-fold decrease in p38 phosphorylation and increase in histone deacetylase 4 (HDAC4) in the homozygous db/db myocardium (p<0.05 vs homozygous db/db control).ConclusionIrisin preserves myocardial performance and insulin resistance in db/db mice, which is related to p38 phosphorylation and HDAC reduction.

422-P: Association between Nonalcoholic Fatty Liver Disease and Diastolic Myocardial Dysfunction and Myocardial Insulin Resistance in Patients with Type 2 Diabetes

Nonalcoholic fatty liver disease (NAFLD) is highly prevalent in patients with type 2 diabetes and associated with cardiovascular risks. We investigated whether degree of NAFLD was associated with myocardial dysfunction in relation to myocardial glucose uptake in patients with type 2 diabetes. A total of 131 patients with type 2 diabetes were included from a tertiary care hospital. Myocardial glucose uptake was assessed using [18F]-FDG-PET scan. Hepatic steatosis and fibrosis were determined using transient liver elastography (Fibroscan). Echocardiogram was performed to evaluate cardiac structure and function. Patients with NAFLD revealed cardiac diastolic dysfunction with increased left ventricular filling pressure (E/e’ ratio) and left atrial volume index (LAVI) compared with patients without NAFLD (all p&amp;lt;0.05). Hepatic steatosis was correlated with E/e’ ratio and LAVI, and hepatic fibrosis was also correlated with E/e’ ratio (all p &amp;lt; 0.05). In linear regression analyses, degree of hepatic steatosis and fibrosis were independent determinant factors for a higher E/e’ ratio even after adjusting for confounding factors (r2=0.409, p=0.041 for steatosis and r2=0.423, p=0.009 for fibrosis). Higher degree of steatosis and fibrosis were associated with decreased myocardial glucose uptake (p for trends=0.084 and 0.012 for steatosis and fibrosis, respectively). Furthermore, decreased myocardial glucose uptake was an independent determinant factor for a higher E/e’ ratio (r2=0.409, p=0.04). In conclusion, hepatic steatosis and fibrosis are significantly associated with diastolic heart dysfunction in patients with type 2 diabetes coupled with decreased myocardial glucose uptake. Disclosure Y. Kim: None. M. Lee: None. S. Lee: None. B. Cha: None. E. Kang: None.

A PKB-SPEG signaling nexus links insulin resistance with diabetic cardiomyopathy by regulating calcium homeostasis

Diabetic cardiomyopathy is a progressive disease in diabetic patients, and myocardial insulin resistance contributes to its pathogenesis through incompletely-defined mechanisms. Striated muscle preferentially expressed protein kinase (SPEG) has two kinase-domains and is a critical cardiac regulator. Here we show that SPEG is phosphorylated on Ser2461/Ser2462/Thr2463 by protein kinase B (PKB) in response to insulin. PKB-mediated phosphorylation of SPEG activates its second kinase-domain, which in turn phosphorylates sarcoplasmic/endoplasmic reticulum calcium-ATPase 2a (SERCA2a) and accelerates calcium re-uptake into the SR. Cardiac-specific deletion of PKBα/β or a high fat diet inhibits insulin-induced phosphorylation of SPEG and SERCA2a, prolongs SR re-uptake of calcium, and impairs cardiac function. Mice bearing a Speg3A mutation to prevent its phosphorylation by PKB display cardiac dysfunction. Importantly, the Speg3A mutation impairs SERCA2a phosphorylation and calcium re-uptake into the SR. Collectively, these data demonstrate that insulin resistance impairs this PKB-SPEG-SERCA2a signal axis, which contributes to the development of diabetic cardiomyopathy.

The ACE-2 in COVID-19: Foe or Friend?

COVID-19 is a rapidly spreading outbreak globally. Emerging evidence demonstrates that older individuals and people with underlying metabolic conditions of diabetes mellitus, hypertension, and hyperlipidemia are at higher risk of morbidity and mortality. The SARS-CoV-2 infects humans through the angiotensin converting enzyme (ACE-2) receptor. The ACE-2 receptor is a part of the dual system renin-angiotensin-system (RAS) consisting of ACE-Ang-II-AT 1 R axis and ACE-2-Ang-(1–7)-Mas axis. In metabolic disorders and with increased age, it is known that there is an upregulation of ACE-Ang-II-AT 1 R axis with a downregulation of ACE-2-Ang-(1–7)-Mas axis. The activated ACE-Ang-II-AT1R axis leads to pro-inflammatory and pro-fibrotic effects in respiratory system, vascular dysfunction, myocardial fibrosis, nephropathy, and insulin secretory defects with increased insulin resistance. On the other hand, the ACE-2-Ang-(1–7)-Mas axis has anti-inflammatory and antifibrotic effects on the respiratory system and anti-inflammatory, antioxidative stress, and protective effects on vascular function, protects against myocardial fibrosis, nephropathy, pancreatitis, and insulin resistance. In effect, the balance between these two axes may determine the prognosis. The already strained ACE-2-Ang-(1–7)-Mas in metabolic disorders is further stressed due to the use of the ACE-2 by the virus for entry, which affects the prognosis in terms of respiratory compromise. Further evidence needs to be gathered on whether modulation of the renin angiotensin system would be advantageous due to upregulation of Mas activation or harmful due to the concomitant ACE-2 receptor upregulation in the acute management of COVID-19.

Targeting mir128-3p alleviates myocardial insulin resistance and prevents ischemia-induced heart failure.

Myocardial insulin resistance contributes to heart failure in response to pathological stresses, therefore, a therapeutic strategy to maintain cardiac insulin pathways requires further investigation. We demonstrated that insulin receptor substrate 1 (IRS1) was reduced in failing mouse hearts post-myocardial infarction (MI) and failing human hearts. The mice manifesting severe cardiac dysfunction post-MI displayed elevated mir128-3p in the myocardium. Ischemia-upregulated mir128-3p promoted Irs1 degradation. Using rat cardiomyocytes and human-induced pluripotent stem cell-derived cardiomyocytes, we elucidated that mitogen-activated protein kinase 7 (MAPK7, also known as ERK5)-mediated CCAAT/enhancer-binding protein beta (CEBPβ) transcriptionally represses mir128-3p under hypoxia. Therapeutically, functional studies demonstrated gene therapy-delivered cardiac-specific MAPK7 restoration or overexpression of CEBPβ impeded cardiac injury after MI, at least partly due to normalization of mir128-3p. Furthermore, inhibition of mir128-3p preserved Irs1 and ameliorated cardiac dysfunction post-MI. In conclusion, we reveal that targeting mir128-3p mitigates myocardial insulin resistance, thereafter slowing down the progression of heart failure post-ischemia.

Reduction in Global Myocardial Glucose Metabolism in Subjects With 1-Hour Postload Hyperglycemia and Impaired Glucose Tolerance.

Impaired insulin-stimulated myocardial glucose uptake has occurred in patients with type 2 diabetes with or without coronary artery disease. Whether cardiac insulin resistance is present remains uncertain in subjects at risk for type 2 diabetes, such as individuals with impaired glucose tolerance (IGT) or those with normal glucose tolerance (NGT) and 1-h postload glucose ≥155 mg/dL during an oral glucose tolerance test (NGT 1-h high). This issue was examined in this study. The myocardial metabolic rate of glucose (MRGlu) was measured by using dynamic 18F-fluorodeoxyglucose positron emission tomography combined with a euglycemic-hyperinsulinemic clamp in 30 volunteers without coronary artery disease. Three groups were studied: 1) those with 1-h postload glucose <155 mg/dL (NGT 1-h low) (n = 10), 2) those with NGT 1-h high (n = 10), 3) and those with IGT (n = 10). After adjusting for age, sex, and BMI, both subjects with NGT 1-h high (23.7 ± 6.4 mmol/min/100 mg; P = 0.024) and those with IGT (16.4 ± 6.0 mmol/min/100 mg; P < 0.0001) exhibited a significant reduction in global myocardial MRGlu; this value was 32.8 ± 9.7 mmol/min/100 mg in subjects with NGT 1-h low. Univariate correlations showed that MRGlu was positively correlated with insulin-stimulated whole-body glucose disposal (r = 0.441; P = 0.019) and negatively correlated with 1-h (r = -0.422; P = 0.025) and 2-h (r = -0.374; P = 0.05) postload glucose levels, but not with fasting glucose. This study shows that myocardial insulin resistance is an early defect that is already detectable in individuals with dysglycemic conditions associated with an increased risk of type 2 diabetes, such as IGT and NGT 1-h high.

Increased Drp1 Acetylation by Lipid Overload Induces Cardiomyocyte Death and Heart Dysfunction.

Lipid overload-induced heart dysfunction is characterized by cardiomyocyte death, myocardial remodeling, and compromised contractility, but the impact of excessive lipid supply on cardiac function remains poorly understood. To investigate the regulation and function of the mitochondrial fission protein Drp1 (dynamin-related protein 1) in lipid overload-induced cardiomyocyte death and heart dysfunction. Mice fed a high-fat diet (HFD) developed signs of obesity and type II diabetes mellitus, including hyperlipidemia, hyperglycemia, hyperinsulinemia, and hypertension. HFD for 18 weeks also induced heart hypertrophy, fibrosis, myocardial insulin resistance, and cardiomyocyte death. HFD stimulated mitochondrial fission in mouse hearts. Furthermore, HFD increased the protein level, phosphorylation (at the activating serine 616 sites), oligomerization, mitochondrial translocation, and GTPase activity of Drp1 in mouse hearts, indicating that Drp1 was activated. Monkeys fed a diet high in fat and cholesterol for 2.5 years also exhibited myocardial damage and Drp1 activation in the heart. Interestingly, HFD decreased nicotinamide adenine dinucleotide (oxidized) levels and increased Drp1 acetylation in the heart. In adult cardiomyocytes, palmitate increased Drp1 acetylation, phosphorylation, and protein levels, and these increases were abolished by restoration of the decreased nicotinamide adenine dinucleotide (oxidized) level. Proteomics analysis and in vitro screening revealed that Drp1 acetylation at lysine 642 (K642) was increased by HFD in mouse hearts and by palmitate incubation in cardiomyocytes. The nonacetylated Drp1 mutation (K642R) attenuated palmitate-induced Drp1 activation, its interaction with voltage-dependent anion channel 1, mitochondrial fission, contractile dysfunction, and cardiomyocyte death. These findings uncover a novel mechanism that contributes to lipid overload-induced heart hypertrophy and dysfunction. Excessive lipid supply created an intracellular environment that facilitated Drp1 acetylation, which, in turn, increased its activity and mitochondrial translocation, resulting in cardiomyocyte dysfunction and death. Thus, Drp1 may be a critical mediator of lipid overload-induced heart dysfunction as well as a potential target for therapy.

Metabolic markers of myocardium insulin resistance in dogs with heart failure.

Background:Heart failure syndrome is an aspect of primary or secondary heart disease and is associated with decompensation, formation, and activation of pathological interactions between regulation systems. This results in myocardial energy metabolism alteration. This study was carried out to defy some metabolic aspects of myocardial tissue insulin resistance (IRM) development in canine heart failure.Aim:To investigate the myocardial tissue concentration of adenosine triphosphate (ATP), glucose transporters 1 and 4, pyruvate dehydrogenase (PDH), hexokinase 2, insulin receptor (InsR), and adropin (ADR) protein and to screen metabolic changes and IRM in canine myocardium with heart failure.Methods:We studied 28 dogs of different sexes, ages, and breeds. Groups were formed according to primary pathology: apparently healthy dogs (HD, n = 6); dogs with CDVD (CDVDD, n = 8); dogs with DCM (DCMD, n = 6); and dogs with doxorubicin chemotherapy and doxorubicin-induced cardiomyopathy (DoxCMD, n = 8). Animals in the study were diagnosed for primary disease by standard methods and algorithms. Animals were euthanized due to incurable neurological disease, refractory heart failure, or by owners will. The material was obtained immediately after death, fixed in liquid nitrogen, and stored in −80°C refrigerator. Studied proteins concentrations were analyzed in a specialized research laboratory, using ELISA kits, provided by Cloud-Clone Corp.Results:ATP, GLUT1, and GLUT4 concentrations in myocardial tissue from the valvular disease group did not differ from the HD group. In CDVD, we found depression of PDH, hexokinase II (HX2), and ADR concentrations in comparison to HD. InsR was significantly lower in the CDVD and DoxCMD groups in comparison to the HD group, but in the DCM group, it was twofold higher than in the HD group. In the DCMD and DoxCMD groups, all parameters were lower than in the HD group. ATP, HX2, ADR, GLUT1, and GLUT4 were higher in the CDVD group, than in the DCM and DoxCM groups. PDH in the CDVD and DoxCM groups did not differ. PDH was depleted in the DCM to CDVD and DoxCM groups. InsR did not differ between the CDVD and DoxCM groups, but was upregulated in the DCM to CDVD and DoxCM groups.Conclusion:Development of myocardial tissue IRM is a part of the structural, functional and metabolic remodeling in dogs with heart failure of different etiology. At the late stages, we found significant changes in energy supply availability and production in the myocardium.

Abstract 279: Increased Drp1 Acetylation Mediates Lipid Overload-induced Cardiomyocyte Death &amp; Heart Dysfunction

Rationale: Lipid overload can cause diabetic cardiomyopathy (DCM), which is characterized by cardiomyocyte death, myocardial remodeling, and eventually contractile dysfunction. How excessive lipid supply impacts cardiac metabolism leading to DCM remains poorly understood. Objective: To investigate the role and mechanism of a mitochondrial fission protein, dynamin-related protein 1 (Drp1), in lipid overload-induced cardiomyocyte death and DCM. Methods and Results: Mice fed with high fat diet (HFD) for 18 weeks exhibited DCM phenotype including myocardial insulin resistance, fibrosis, hypertrophy, cardiomyocyte death and mild contractile dysfunction. Cultured adult cardiomyocytes incubated with high levels of palmitate also exhibited increased cell death and openings of the mitochondrial permeability transition pore. Mitochondrial fission was stimulated by HFD in the heart or by palmitate incubation in cultured adult cardiomyocytes. Mechanistically, lipid overload increased acetyl-CoA level and decreased NAD + level in the heart and in adult cardiomyocytes, leading to upregulation of Drp1 acetylation at lysine 642 (K642). Elevated Drp1 acetylation increased Drp1 protein level, its oligomerization and its phosphorylation at the activating serine 616 (S616) site. The excessively activated Drp1 translocated to mitochondria, induced fission, and bound with VDAC1 to promote cardiomyocyte death. Preventing Drp1 acetylation (K642R mutation), inhibiting Drp1 activity, or supplementing NAD + ameliorated palmitate-induced fission and cardiomyocyte death. In the hearts of HFD-fed monkeys, we observed increased Drp1 acetylation, oligomerization, and phosphorylation, which were accompanied with markers of DCM. Conclusions: These findings uncover a novel mechanism mediating lipid overload-induced heart hypertrophy and dysfunction. Excessive lipid supply created an intracellular environment that facilitated Drp1 acetylation, which increased its activity and mitochondrial translocation causing cardiomyocyte death. Thus, Drp1 could be a critical mediator for metabolic stress-induced heart dysfunction as well as a potential target for therapy.

Vitamin D Deficiency in Rats Causes Cardiac Dysfunction by Inducing Myocardial Insulin Resistance

Cause-effect relationship between vitamin D deficiency and cardiometabolic abnormalities remains undefined. The aim is to investigate the role of vitamin D deficiency in cardiac failure, through possible involvement in myocardial insulin signaling. Male SD rats (n = 6) are fed a normal diet (Con), vitamin D-deficient diet [Con(-)], or high-fat, high fructose diet (HFHFrD) for 20 weeks. Cardiac hypertrophy and fetal gene program are confirmed in Con(-) group. Cardiac dysfunction is assessed by echocardiography. Elevated renin, TGF-β and collagen-1α mRNAs, p-ERK1/2, and perivascular fibrosis indicate cardiac remodeling in Con(-) group. Increased serum insulin, triglycerides, and blood pressure, and decreased glucose tolerance and HDL cholesterol are observed in Con(-) rats. Decreased p-Akt/Akt, GLUT4, SOD2, and catalase, and increased NF-κB, TNF-α, and IL-6 are observed in Con(-) hearts. In H9c2 cells, calcitriol attenuates palmitate-induced insulin resistance. VDR-silenced H9c2 cells show reduced Akt phosphorylation, GLUT4 translocation, and 2-NBDG uptake. Findings in Con(-) and HFHFrD groups are comparable. Vitamin D deficiency in rats mimic high-fat-, high-fructose-induced metabolic syndrome and cardiac dysfunction. This study demonstrates that vitamin D deficiency is an independent risk factor for heart failure, at least in part, through induction of myocardial insulin resistance.

Role of Phosphorylated AMP-Activated Protein Kinase (AMPK) in Myocardial Insulin Resistance After Myocardial Ischemia-Reperfusion During Cardiopulmonary Bypass Surgery in Dogs.

BackgroundThe aim of this study was to determine the role of AMP-activated protein kinase (AMPK) in myocardial insulin resistance after myocardial ischemia-reperfusion during cardiopulmonary bypass surgery in dogs.Material/MethodsTwenty-four mongrel dogs were randomly assigned to 4 groups. The control group did not undergo aortic cross-clamping; the model group underwent 60 mins of aortic cross-clamping with 150 ml cardioplegic solution. The treatment group, the inhibition group respectively with 0.11mg/kg AICAR (AMPK agonist) in 150 ml cardioplegic solution and 0.11 mg/kg Compound C (AMPK inhibitor) in 150 ml cardioplegic solution. The blood flow was determined and left ventricular myocardial tissue were taken at pre-bypass, 15, 60, and 90 min after aorta declamping, respectively. Expression of AMPK mRNA, p-AMPK and GLUT-4 proteins was determined by RT-PCR, IHC and WB.ResultsCompared with the control group, receiving 60 min ischemia at 15 min after reperfusion, Myocardial Glucose Extraction Ratio were significantly decreased in the other 3 groups, it was significantly decreased from 20.0% to 1.2% at 60 min of reperfusion, and recovered to 6.1% after 90 min reperfusion in model group, while recovered to 4.1%, 12.0% after 90 min reperfusion respectively exposed to Compound C and AICAR. The expressions of p-AMPK, GLUT-4 protein and AMPK mRNA in myocardium were decreased in different experiment groups, but these changes occurred to a lesser extent in the treatment group.ConclusionsThe inability of GLUT-4 expression induced by the decreases in p-AMPK protein expression that may be one of the reasons for myocardial insulin resistance.

Myocardial mechano-energetic efficiency and insulin resistance in non-diabetic members of the Strong Heart Study cohort

BackgroundMyocardial energetic efficiency (MEE), is a strong predictor of CV events in hypertensive patient and is reduced in patients with diabetes and metabolic syndrome. We hypothesized that severity of insulin resistance (by HOMA-IR) negatively influences MEE in participants from the Strong Heart Study (SHS).MethodsWe selected non-diabetic participants (n = 3128, 47 ± 17 years, 1807 women, 1447 obese, 870 hypertensive) free of cardiovascular (CV) disease, by merging two cohorts (Strong Heart Study and Strong Heart Family Study, age range 18–93). MEE was estimated as stroke work (SW = systolic blood pressure [SBP] × stroke volume [SV])/“double product” of SBP × heart rate (HR), as an estimate of O2 consumption, which can be simplified as SV/HR ratio and expressed in ml/sec. Due to the strong correlation, MEE was normalized by left ventricular (LV) mass (MEEi).ResultsLinear trend analyses showed that with increasing quartiles of HOMA-IR patients were older, more likely to be women, obese and hypertensive, with a trend toward a worse lipid profile (all p for trend < 0.001), progressive increase in LV mass index, stroke index and cardiac index and decline of wall mechanics (all p < 0.0001). In multivariable regression, after adjusting for confounders, and including a kinship coefficient to correct for relatedness, MEEi was negatively associated with HOMA-IR, independently of significant associations with age, sex, blood pressure, lipid profile and central obesity (all p < 0.0001).ConclusionsSeverity of insulin resistance has significant and independent negative impact on myocardial mechano-energetic efficiency in nondiabetic individual from a population study of American Indians.Trial registration number NCT00005134, Name of registry: Strong Heart Study, URL of registry: https://clinicaltrials.gov/ct2/show/NCT00005134, Date of registration: May 25, 2000, Date of enrolment of the first participant to the trial: September 1988

Rare ginsenosides ameliorate lipid overload-induced myocardial insulin resistance via modulating metabolic flexibility

BackgroundRare ginsenosides are found in ginseng and notoginseng, two medicinal plants widely used in China for treatment of cardiovascular diseases and type 2 diabetes. However, their pharmacological studies regarding myocardial fuel metabolism and insulin signaling are not clear. PurposeTo explore the effect of a rare ginsenoside-standardized extract (RGSE), derived from steamed notoginseng, on cardiac fuel metabolism and insulin signaling. Study designWe used palmitic acid (PA) to treat H9c2 cells in vitro and high fat diet (HFD) to mice to induce insulin resistance in vivo. MethodsIn vitro, differentiated H9c2 cells were pretreated with RGSE, metformin, mildronate or dichloroacetate (DCA) and stimulated with PA. In vivo, mice were fed with HFD and received RGSE, metformin or DCA for 6 weeks. Protein expression was determined by Western blotting. Mitochondrial membrane potential (Δψm), glucose uptake and reactive oxygen species (ROS) production were measured by fluorescence labeling. Other assessments including oxygen consumption rate (OCR) were also performed. ResultsRGSE prevented PA-induced decrease in pyruvate dehydrogenase (PDH) activity and increase in carnitine palmitoyltransferase 1 (CPT1) expression, and ameliorated insulin-mediated glucose uptake and utilization in H9c2 cells. Metformin and mildronate exhibited similar effects. In vivo, RGSE counteracted HFD-induced increase in myocardial expression of p-PDH and CPT1 and ameliorated cardiac insulin signaling. Metformin and DCA also showed beneficial effects. Further study showed that RGSE decreased OCR and mitochondrial complex I activity in PA-treated H9c2 cells, reduced ROS production and relieved mitochondrial oxidative stress, thus decreased serine phosphorylation in IRS-1. ConclusionRGSE ameliorated myocardial insulin sensitivity under conditions of lipid overload, which was tightly associated with the decrease in mitochondrial oxidative stress via modulating glucose and fatty acid oxidation.

PO-273 Exercise, myocardial insulin resistance and myostatin

Objective Myostatin (MSTN) is a member of the TGF-β superfamily and is a negative regulator of skeletal muscle growth. MSTN is also expressed in other tissues such as heart and fat. The purpose of this study was to elucidate the occurrence of myocardial IR caused by myocardial MSTN expression, and to elucidate the regulation of MSTN expression by exercise and improve myocardial IR status and myocardial interstitial fibrosis.&#x0D; Methods The literatures on exercise, myocardial IR, and myocardial MSTN published in recent years were reviewed and summarized.&#x0D; Results 1.Myostatin, which is rarely expressed in myocardium under normal conditions, the appropriate amount of MSTN expression has anti-cardiac hypertrophy, and excessive MSTN expression can cause various cardiovascular diseases. In the IR state, the expression of myocardial inflammatory factors is increased, and MSTN is highly expressed. MSTN acts on the myocardium through various pathways, leading to the occurrence of myocardial fibrosis. In the IR state, possible pathways for inducing high expression of MSTN include: (1) inflammatory factor TNF-α is elevated, and MSTN expression is induced by P38MAPK and NF-KB; (2) The transcription factor Smad-2/3/4 up-regulates the MSTN promoter activity; (3) Glucocorticoid up-regulates MSTN expression; (4) IGF-1 up-regulates MSTN expression via p38MAPK and transcription factor MEF-2; (5) AngII up-regulates MSTN via Ang1 receptor, p38MAPK and MEF-2;(6) urotensin-II and urocortin can stimulate MSTN expression;(7) The ERK-1/2-MEF-2 pathway up-regulates MSTN expression. 3. Possible pathways by which MSTN acts on the myocardium include:(1) MSTN induces Smad2/3 overexpression; (2) MSTN activates the NF-KB pathway; (3) MSTN activates miR-1 expression, inhibits HSP70, and decreases pAkt levels; (4) MSTN inhibits the PI3K-Akt pathway, leading to induction or damage of the downstream pathway. Regular endurance exercise and resistance exercise improve myocardial IR and myocardial interstitial fibrosis involved in MSTN. This effect is mainly dependent on exercise can effectively improve the body's chronic inflammatory state, down-regulate the MSTN superior inducer, resulting in a series of cascade reactions.&#x0D; Conclusions 1.MSTN expression in myocardial tissue is dose-dependent,proper expression of MSTN in the myocardium can prevent cardiac hypertrophy, and overexpression of MSTN can lead to various cardiovascular diseases. 2.Under the hyperglycemia and inflammation state, it can induce high expression of MSTN. After high expression of myocardial MSTN, it can participate in myocardial IR and can lead to myocardial interstitial fibrosis. 3. Exercise can effectively improve the chronic inflammatory state of the body, down-regulate the level of MSTN induction, improve myocardial IR status and IR-induced myocardial interstitial fibrosis.&#x0D;

Free fatty acid can induce cardiac dysfunction and alter insulin signaling pathways in the heart

BackgroundInsulin resistance has been independently related to heart failure. However, the specific mechanisms of high FFA levels in the pathophysiology of heart failure in insulin-resistant states are remain largely unclear. This study investigated whether elevated circulating free fatty acids (FFA) levels result in impaired cardiac structure and function in vivo via insulin-related signaling pathways in myocardium.MethodsMale Wistar rats were randomly divided into the intralipid group (20% intralipid plus heparin infusion) and the control group (glycerol infusion). Blood samples were collected before and after 6-, 12-, and 24-h infusions. Cardiac structure and function were measured using echocardiography. Maximum velocity of myocardial contraction (+dP/dt max) and diastole (−dP/dt max) were measured using a physiological polygraph in vivo. Heart tissues were collected for western blotting.ResultsCompared with the control group, plasma FFA, plasma glucose, and serum insulin levels increased significantly in the intralipid group. With increasing infusion time, cardiac function in the intralipid group decreased gradually compared with the control group. After a 24-h infusion, early (E’, cm/s) diastolic peak velocities and (−dP/dt max) decreased significantly. Protein expression of phosphatidylinositol 3-kinase (PI3K), the serine/threonine kinase Akt, and phosphorylated Akt in myocardium increased after a 6-h infusion and decreased significantly after a 24-h infusion in the intralipid group. Protein expression of glucose transporter type 4 (GLUT4), Adenosine 5′-monophosphate -activated protein kinase (AMPK), phosphorylated AMPK(p-AMPK), and endothelial nitric oxide synthase (eNOS) in myocardium gradually decreased in the intralipid group.ConclusionsElevated FFA levels may impair cardiac function and cardiac dysfunction might result from myocardial insulin resistance with significant changes to PI3K-Akt-GLUT4 and AMPK-eNOS signaling pathways with increasing FFA levels.

Abstract 540: Magnesium Improves Cardiac Diastolic Function by Modulating Mitochondria

Rationale: A diet rich in saturated fat has been found to induce diabetes mellitus (DM) accompanied by myocardial mitochondrial dysfunction, insulin resistance, and magnesium (Mg) deficiency. The most prominent characteristic of diabetic cardiomyopathy is cardiac diastolic dysfunction (DD). Mg supplementation improves the heart rate variability and arterial elasticity in chronic heart failure. Recently, we have reported that mitochondrial reactive oxygen species (mitoROS) play a critical role in the progress of DD and diastolic heart failure. Therefore, we hypothesized that Mg supplementation would benefit diastolic function by improving mitochondrial function. Methods and Results: High fat diet (HFD)-induced diabetic mouse hearts showed cardiac DD with increased E/e’ (45±2 in DM mice vs. 32±2 in control mice), increased left ventricular diastolic volume (LVDV, 80±1 μL in DM vs. 61±4 μL in control), and increased incidence of DD (9 of 10 mice in DM vs 1 of 10 mice in control; P&lt;0.05 for all). DM mice also showed decreased plasma Mg concentration (0.80±0.04 mmol/L in DM vs. 0.98±0.03 mmol/L in control, P&lt;0.05). Ventricular cardiomyocytes isolated from DM mice exhibited decreased mitochondrial ATP production (75±11% of control), a 1.7±0.2-fold increase in mitoROS, significantly depolarized mitochondrial membrane potential, and mitochondrial Ca 2+ overload (3.7±1.3-fold; P&lt;0.05 vs. control for all). Dietary Mg administration (50 mg/mL, ≈6-8 g/kg/day) for 6 weeks corrected all these parameters with increased plasma Mg concentration (1.5±0.1 mmol/L), improved cardiac diastolic function (E/e’ 37±1; LVDV 54±5 μL; LVPWT 0.77±0.02 mm; the incidence of DD, 2 of 10 mice; P&lt;0.05 vs. DM for all). Mitochondrial function was improved significantly by Mg with increased ATP production, decreased mitoROS, repolarized mitochondrial membrane potential, and decreased mitochondrial Ca 2+ overload in DM mice. Conclusion: These results indicate that Mg supplementation improved mitochondrial function, reduced oxidative stress, and prevented diastolic dysfunction in DM.

Fatty acid binding protein 4 (FABP4) contributes to myocardial steatosis and insulin resistance in cardiac cells

Fatty acid binding protein 4 (FABP4) contributes to myocardial steatosis and insulin resistance in cardiac cells