Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

Swimming training attenuates the morphological reorganization of the myocardium and local inflammation in the left ventricle of growing rats with untreated experimental diabetes

Diabetic cardiomyopathy is associated with cardiac remodeling, myocardial dysfunction, low-grade inflammation, and reduced cardiac adiponectin in patients with type 1 diabetes mellitus (T1DM). Alternatively, physical exercise is an important strategy for the management of diabetes. This study aimed to investigate the influence of low-intensity swimming training in cardiac cytokines, structural remodeling, and cardiomyocyte contractile dysfunction in growing rats with untreated experimental DM. Thirty-day-old male Wistar rats were divided into four groups (n=14, per group): sedentary control (SC), exercised control (EC), sedentary diabetic (SD), and exercised diabetic (ED). Diabetes was induced by streptozotocin (60 mg kg(-1), i.p.). Animals from exercised groups swam (5 days/week, 90 min/day, loading up to 5% body weight around the animal's chest) for 8 weeks. The left ventricle (LV) was removed for molecular, morphological, and cardiomyocyte mechanical analysis. Diabetic animals presented cardiac remodeling with myocardial histoarchitectural disorganization, fibrosis, and necrosis. The capillary density was lower in diabetic animals. LV cardiomyocytes from diabetic animals exhibited more prolonged time to the peak of contraction and time to half relaxation than those from control animals. The cardiac levels of interleukin 10, nitric oxide, and total and high molecular weight (HMW) adiponectin were significantly decreased in diabetic animals. Exercise training reduced the level of TNF-α, increased capillary density, and attenuated the histopathological parameters assessed in diabetic rats. In conclusion, the cardiac structural remodeling coexists with reduced levels of total and HMW adiponectin, inflammation, and cardiomyocyte contractility dysfunction in experimental DM. More important, low-intensity swimming training attenuates part of these pathological changes, indicating the beneficial role for exercise in untreated T1DM.

PPARβ/δ and lipid metabolism in the heart

Cardiac lipid metabolism is the focus of attention due to its involvement in the development of cardiac disorders. Both a reduction and an increase in fatty acid utilization make the heart more prone to the development of lipotoxic cardiac dysfunction. The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR)β/δ modulates different aspects of cardiac fatty acid metabolism, and targeting this nuclear receptor can improve heart diseases caused by altered fatty acid metabolism. In addition, PPARβ/δ regulates glucose metabolism, the cardiac levels of endogenous antioxidants, mitochondrial biogenesis, cardiomyocyte apoptosis, the insulin signaling pathway and lipid-induced myocardial inflammatory responses. As a result, PPARβ/δ ligands can improve cardiac function and ameliorate the pathological progression of cardiac hypertrophy, heart failure, cardiac oxidative damage, ischemia-reperfusion injury, lipotoxic cardiac dysfunction and lipid-induced cardiac inflammation. Most of these findings have been observed in preclinical studies and it remains to be established to what extent these intriguing observations can be translated into clinical practice. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Abnormal Glucose Tolerance Is Associated with a Reduced Myocardial Metabolic Flexibility in Patients with Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is characterized by a metabolic shift from fat to carbohydrates and failure to increase myocardial glucose uptake in response to workload increments. We verified whether this pattern is influenced by an abnormal glucose tolerance (AGT). In 10 patients with DCM, 5 with normal glucose tolerance (DCM-NGT) and 5 with AGT (DCM-AGT), and 5 non-DCM subjects with AGT (N-AGT), we measured coronary blood flow and arteriovenous differences of oxygen and metabolites during Rest, Pacing (at 130 b/min), and Recovery. Myocardial lactate exchange and oleate oxidation were also measured. At Rest, DCM patients showed a reduced nonesterified fatty acids (NEFA) myocardial uptake, while glucose utilization increased only in DCM-AGT. In response to Pacing, glucose uptake promptly rose in N-AGT (from 72 ± 21 to 234 ± 73 nmol/min/g, p < 0.05), did not change in DCM-AGT, and slowly increased in DCM-NGT. DCM-AGT sustained the extra workload by increasing NEFA oxidation (from 1.3 ± 0.2 to 2.9 ± 0.1 μmol/min/gO2 equivalents, p < 0.05), while DCM-NGT showed a delayed increase in glucose uptake. Substrate oxidation rates paralleled the metabolites data. The presence of AGT in patients with DCM exacerbates both the shift from fat to carbohydrates in resting myocardial metabolism and the reduced myocardial metabolic flexibility in response to an increased workload. This trial is registered with ClinicalTrial.gov NCT02440217.

Cardiomyocyte VEGF Regulates Endothelial Cell GPIHBP1 to Relocate Lipoprotein Lipase to the Coronary Lumen During Diabetes Mellitus

Objective—

Lipoprotein lipase (LPL)–mediated triglyceride hydrolysis is the major source of fatty acid for cardiac energy. LPL, synthesized in cardiomyocytes, is translocated across endothelial cells (EC) by its transporter glycosylphosphatidylinositol-anchored high-density lipoprotein–binding protein 1 (GPIHBP1). Previously, we have reported an augmentation in coronary LPL, which was linked to an increased expression of GPIHBP1 following moderate diabetes mellitus. We examined the potential mechanism by which hyperglycemia amplifies GPIHBP1.

Approach and Results—

Exposure of rat aortic EC to high glucose induced GPIHBP1 expression and amplified LPL shuttling across these cells. This effect coincided with an elevated secretion of heparanase. Incubation of EC with high glucose or latent heparanase resulted in secretion of vascular endothelial growth factor (VEGF). Primary cardiomyocytes, being a rich source of VEGF, when cocultured with EC, restored EC GPIHBP1 that is lost because of cell passaging. Furthermore, recombinant VEGF induced EC GPIHBP1 mRNA and protein expression within 24 hours, an effect that could be prevented by a VEGF neutralizing antibody. This VEGF-induced increase in GPIHBP1 was through Notch signaling that encompassed Delta-like ligand 4 augmentation and nuclear translocation of the Notch intracellular domain. Finally, cardiomyocytes from severely diabetic animals exhibiting attenuation of VEGF were unable to increase EC GPIHBP1 expression and had lower LPL activity at the vascular lumen in perfused hearts.

Conclusion—

EC, as the first responders to hyperglycemia, can release heparanase to liberate myocyte VEGF. This growth factor, by activating EC Notch signaling, is responsible for facilitating GPIHBP1-mediated translocation of LPL across EC and regulating LPL-derived fatty acid delivery to the cardiomyocytes.

Present Insights on Cardiomyopathy in Diabetic Patients

The pathogenesis of diabetic cardiomyopathy (DCM) is partially understood and is likely to be multifactorial, involving metabolic disturbances, hypertension and cardiovascular autonomic neuropathy (CAN). Therefore, an important need remains to further delineate the basic mechanisms of diabetic cardiomyopathy and to apply them to daily clinical practice. We attempt to detail some of these underlying mechanisms, focusing in the clinical features and management. The novelty of this review is the role of CAN and reduction of blood pressure descent during sleep in the development of DCM. Evidence has suggested that CAN might precede left ventricular hypertrophy and diastolic dysfunction in normotensive patients with type 2 diabetes, serving as an early marker for the evaluation of preclinical cardiac abnormalities. Additionally, a prospective study demonstrated that an elevation of nocturnal systolic blood pressure and a loss of nocturnal blood pressure fall might precede the onset of abnormal albuminuria and cardiovascular events in hypertensive normoalbuminuric patients with type 2 diabetes. Therefore, existing microalbuminuria could imply the presence of myocardium abnormalities. Considering that DCM could be asymptomatic for a long period and progress to irreversible cardiac damage, early recognition and treatment of the preclinical cardiac abnormalities are essential to avoid severe cardiovascular outcomes. In this sense, we recommend that all type 2 diabetic patients, especially those with microalbuminuria, should be regularly submitted to CAN tests, Ambulatory Blood Pressure Monitoring and echocardiography, and treated for any abnormalities in these tests in the attempt of reducing cardiovascular morbidity and mortality.

Early impairment of coronary microvascular perfusion capacity in rats on a high fat diet

Background

It remains to be established if, and to what extent, the coronary microcirculation becomes compromised during the development of obesity and insulin resistance. Recent studies suggest that changes in endothelial glycocalyx properties contribute to microvascular dysfunction under (pre-)diabetic conditions. Accordingly, early effects of diet-induced obesity on myocardial perfusion and function were studied in rats under baseline and hyperaemic conditions.

Methods

Rats were fed a high fat diet (HFD) for 6 weeks and myocardial microvascular perfusion was determined using first-pass perfusion MRI before and after adenosine infusion. The effect of HFD on microcirculatory properties was also assessed by sidestream darkfield (SDF) imaging of the gastrocnemius muscle.

Results

HFD-fed rats developed central obesity and insulin sensitivity was reduced as evidenced by the marked reduction in insulin-induced phosphorylation of Akt in both cardiac and gastrocnemius muscle. Early diet-induced obesity did not lead to hypertension or cardiac hypertrophic remodeling. In chow-fed, control rats a robust increase in cardiac microvascular perfusion was observed upon adenosine infusion (+40 %; p < 0.05). In contrast, the adenosine response was abrogated in rats on a HFD (+8 %; N.S.). HFD neither resulted in rarefaction or loss of glycocalyx integrity in skeletal muscle, nor reduced staining intensity of the glycocalyx of cardiac capillaries.

Conclusions

Alterations in coronary microcirculatory function as assessed by first-pass perfusion MRI represent one of the earliest obesity-related cardiac adaptations that can be assessed non-invasively. In this early stage of insulin resistance, disturbances in glycocalyx barrier properties appeared not to contribute to the observed changes in coronary microvascular function.

Puerarin improves cardiac function through regulation of energy metabolism in Streptozotocin-Nicotinamide induced diabetic mice after myocardial infarction

It is well recognized that the incidence of heart failure and the risk of death is high in diabetic patients after myocardial infarction (MI). Accumulating evidence showed that puerarin (PUE) has protecting function on both cardiovascular disease and diabetes. The aim of this study is to explore whether puerarin could improve cardiac function in diabetic mice after MI and the underlying mechanism. The left anterior of Streptozotocin (STZ)-Nicotinamide (NA) induced diabetic mice were ligated permanently except for the Shame group. Then the operated mice were randomly treated with PUE or saline. Cardiac function was evaluated by echocardiograph before and at 1, 2, 4 weeks after MI. GLUT4/CD36/p-Akt/PPAR α of the heart was examined after treatment for 4 weeks. The results indicated that PUE significantly increased survival rate, improved cardiac function compared with MI group. Moreover, PUE increased expression and translocation of GLUT4 while attenuated expression and translocation of CD36. Western blot analysis showed that PUE enhanced phosphorylation of Akt and decreased PPAR α. This study demonstrated that PUE improved cardiac function after MI in diabetic mice through regulation of energy metabolism, the possible mechanism responsible for the effect of PUE was increasing the expression and translocation of GLUT4 while attenuating the expression and translocation of CD36.

High glucose induces mitochondrial dysfunction independently of protein O-GlcNAcylation

Diabetes is characterized by hyperglycaemia and perturbations in intermediary metabolism. In particular, diabetes can augment flux through accessory pathways of glucose metabolism, such as the hexosamine biosynthetic pathway (HBP), which produces the sugar donor for the β-O-linked-N-acetylglucosamine (O-GlcNAc) post-translational modification of proteins. Diabetes also promotes mitochondrial dysfunction. Nevertheless, the relationships among diabetes, hyperglycaemia, mitochondrial dysfunction and O-GlcNAc modifications remain unclear. In the present study, we tested whether high-glucose-induced increases in O-GlcNAc modifications directly regulate mitochondrial function in isolated cardiomyocytes. Augmentation of O-GlcNAcylation with high glucose (33 mM) was associated with diminished basal and maximal cardiomyocyte respiration, a decreased mitochondrial reserve capacity and lower Complex II-dependent respiration (P<0.05); however, pharmacological or genetic modulation of O-GlcNAc modifications under normal or high glucose conditions showed few significant effects on mitochondrial respiration, suggesting that O-GlcNAc does not play a major role in regulating cardiomyocyte mitochondrial function. Furthermore, an osmotic control recapitulated high-glucose-induced changes to mitochondrial metabolism (P<0.05) without increasing O-GlcNAcylation. Thus, increased O-GlcNAcylation is neither sufficient nor necessary for high-glucose-induced suppression of mitochondrial metabolism in isolated cardiomyocytes.

Intracellular diglycerides in relation to glycaemic control in the myocardium: A pilot study in humans

AIM

Intramyocellular diglycerides have been implicated in the development of insulin resistance in skeletal muscle. In the myocardium, excess lipid storage may also contribute to the appearance of diabetic cardiomyopathy, while diglycerides may have certain cardio-protective functions. However, little is known on intracellular diglyceride accumulation in the human heart. We aimed to determine diglyceride accumulation in the human myocardium in relation to diabetes status.

METHODS

Six diabetic and six non-diabetic aged human subjects undergoing by-pass surgery participated in the study. Subjects were matched for age and body mass index. Intracellular diglyceride levels were measured in heart biopsy samples. Additional samples were taken from pectoralis major muscle that served as control. Whole body glycaemic control was assessed as the percent glycated haemoglobin.

RESULTS

Intracellular diglycerides were significantly higher in the myocardium compared to pectoralis major (P<0.05). Although not statistically significant, diabetic subjects tended to accumulate smaller amounts of diglycerides compared to non-diabetic subjects in the myocardium. A linear negative correlation was observed between myocardial diglycerides and glycaemic control (r=0.632, P<0.05).

CONCLUSIONS

Our data suggest that poor glycaemic control and diabetes may be associated with a defective accumulation of myocardial diglycerides, possibly blunting intracellular processes and contributing to the development of cardiomyopathy.

Angiotensin-(1-7) treatment mitigates right ventricular fibrosis as a distinctive feature of diabetic cardiomyopathy

In diabetic patients, left ventricular (LV) remodeling is highly prevalent; however, little is known about the impact of diabetes on right ventricular (RV) structure and function. We recently found that overexpression of angiotensin (ANG)-converting enzyme 2 (ACE2), which metabolizes ANG-II to ANG-(1-7) and ANG-I to ANG-(1-9), may improve LV remodeling in diabetic cardiomyopathy (DCM). Here, we aimed to assess whether LV remodeling and dysfunction are paralleled by RV alterations and the effects of ANG-(1-7) on RV remodeling in DCM. After 12 wk of diabetes induced by a single intraperitoneal injection of streptozotocin, rats were treated with saline, ANG-(1-7), perindopril, ANG-(1-7) plus perindopril, ANG-(1-7) plus Mas receptor antagonist A779, or ANG-(1-7) plus ANG-II type 2 receptor antagonist PD123319 for 4 wk. RV remodeling in diabetic rats was indicated by fibrosis of the RV free wall in the absence of hypertrophy and apoptosis. Treatment with ANG-(1-7) prevented diabetes-induced RV fibrosis and dysfunction. ANG-(1-7) (800 ng·kg(-1)·min(-1)) was superior to perindopril in improving RV fibrosis. The major mechanisms involved a complex interaction of ANG-II type 2 and Mas receptors for subsequent downregulation of ACE expression and activity and ANG-II type 1 receptor expression, as well as upregulation of ACE2 expression and activity and the expression of ANG-II type 2 receptor and sarco(endo)plasmic reticulum Ca(2+)-ATPase. Thus RV fibrosis and dysfunction plays a central role in DCM, and ANG-(1-7) mitigates diabetes-induced RV alterations.

KLF15 and PPARα Cooperate to Regulate Cardiomyocyte Lipid Gene Expression and Oxidation

The metabolic myocardium is an omnivore and utilizes various carbon substrates to meet its energetic demand. While the adult heart preferentially consumes fatty acids (FAs) over carbohydrates, myocardial fuel plasticity is essential for organismal survival. This metabolic plasticity governing fuel utilization is under robust transcriptional control and studies over the past decade have illuminated members of the nuclear receptor family of factors (e.g., PPARα) as important regulators of myocardial lipid metabolism. However, given the complexity of myocardial metabolism in health and disease, it is likely that other molecular pathways are likely operative and elucidation of such pathways may provide the foundation for novel therapeutic approaches. We previously demonstrated that Kruppel-like factor 15 (KLF15) is an independent regulator of cardiac lipid metabolism thus raising the possibility that KLF15 and PPARα operate in a coordinated fashion to regulate myocardial gene expression requisite for lipid oxidation. In the current study, we show that KLF15 binds to, cooperates with, and is required for the induction of canonical PPARα-mediated gene expression and lipid oxidation in cardiomyocytes. As such, this study establishes a molecular module involving KLF15 and PPARα and provides fundamental insights into the molecular regulation of cardiac lipid metabolism.

The function of heparanase in diabetes and its complications

Heparan sulfate proteoglycans are ubiquitous glycoproteins that contain several heparan sulfate polysaccharide side chains attached to a core protein. They function not only as a primary structural component of the extracellular matrix, but also provide a storage depot for bioactive molecules, such as basic fibroblast growth factor, vascular endothelial growth factor and lipoprotein lipase. Heparanase is an endoglycosidase that specifically hydrolyzes heparan sulfate into oligosaccharides. Recent studies have indicated that heparanase is engaged in the initiation and progression of diabetes, in addition to its associated complications. This review focuses on the participation of heparanase in the cleavage of heparan sulfate proteoglycans in pancreatic islets promoting beta cell death, promotion of atherosclerosis, and its role in cardiac metabolic switching in the early stage of cardiomyopathy during diabetes. Understanding the mechanisms by which heparanase is regulated in diabetes could provide a drug target to prevent diabetes and its complications.

Comparison of Cardiomyocyte Differentiation Potential Between Type 1 Diabetic Donor- and Nondiabetic Donor-Derived Induced Pluripotent Stem Cells

Type 1 diabetes mellitus (T1DM) is the most common type of diabetes in children and adolescents. Diabetic subjects are more likely to experience a myocardial infarction compared to nondiabetic subjects. In recent years, induced pluripotent stem cells (iPSCs) have received increasing attention from basic scientists and clinicians and hold promise for myocardial regeneration due to their unlimited proliferation potential and differentiation capacity. However, cardiomyogenesis of type 1 diabetic donor-derived iPSCs (T1DM-iPSCs) has not been investigated yet. The aim of the study was to comparatively analyze cardiomyocyte (CM) differentiation capacity of nondiabetic donor-derived iPSCs (N-iPSCs) and T1DM-iPSCs. The differentiated CMs were confirmed by both expression of cardiac-specific markers and presence of cardiac action potential. Since mitochondrial bioenergetics is vital to every aspect of CM function, extracellular acidification rates and oxygen consumption rates were measured using Seahorse extracellular flux analyzer. The results showed that N-iPSCs and T1DM-iPSCs demonstrated similar capacity of differentiation into spontaneously contracting CMs exhibiting nodal-, atrial-, or ventricular-like action potentials. Differentiation efficiency was up to 90%. In addition, the CMs differentiated from N-iPSCs and T1DM-iPSCs (N-iPSC-CMs and T1DM-iPSC-CMs, respectively) showed 1) well-regulated glucose utilization at the level of glycolysis and mitochondrial oxidative phosphorylation and 2) the ability to switch metabolic pathways independent of extracellular glucose concentration. Collectively, we demonstrate for the first time that T1DM-iPSCs can differentiate into functional CMs with well-regulated glucose utilization as shown in N-iPSCs, suggesting that T1DM-iPSC-CMs might be a promising autologous cell source for myocardial regeneration in type 1 diabetes patients.

An altered pattern of myocardial histopathological and molecular changes underlies the different characteristics of type-1 and type-2 diabetic cardiac dysfunction

Increasing evidence suggests that both types of diabetes mellitus (DM) lead to cardiac structural and functional changes. In this study we investigated and compared functional characteristics and underlying subcellular pathological features in rat models of type-1 and type-2 diabetic cardiomyopathy. Type-1 DM was induced by streptozotocin. For type-2 DM, Zucker Diabetic Fatty (ZDF) rats were used. Left ventricular pressure-volume analysis was performed to assess cardiac function. Myocardial nitrotyrosine immunohistochemistry, TUNEL assay, hematoxylin-eosin, and Masson's trichrome staining were performed. mRNA and protein expression were quantified by qRT-PCR and Western blot. Marked systolic dysfunction in type-1 DM was associated with severe nitrooxidative stress, apoptosis, and fibrosis. These pathological features were less pronounced or absent, while cardiomyocyte hypertrophy was comparable in type-2 DM, which was associated with unaltered systolic function and increased diastolic stiffness. mRNA-expression of hypertrophy markers c-fos, c-jun, and β-MHC, as well as pro-apoptotic caspase-12, was elevated in type-1, while it remained unaltered or only slightly increased in type-2 DM. Expression of the profibrotic TGF-β 1 was upregulated in type-1 and showed a decrease in type-2 DM. We compared type-1 and type-2 diabetic cardiomyopathy in standard rat models and described an altered pattern of key pathophysiological features in the diabetic heart and corresponding functional consequences.

Inhibition of mitochondrial permeability transition pore restores the cardioprotection by postconditioning in diabetic hearts

Background

Cardiovascular risk factors, including diabetes mellitus may attenuate the cardioprotection by postconditioning. This study aimed to investigate the cardioprotective effect of ischemic-postconditioning (IPostC) against ischemia/reperfusion injury in normal and chronically type-1 diabetic rats and the effect of mitochondrial permeability transition pore (mPTP) inhibition in this field.

Methods

Diabetes was induced by a single intra-peritoneal injection of streptozotocin (50 mg/kg) in Wistar male rats (250-300 g). After 8 weeks, the hearts of control and diabetic animals were isolated and mounted on a constant-pressure Langendorff apparatus. All hearts were subjected to 30 min regional ischemia followed by 45 min reperfusion (by occluding and re-opening of LAD coronary artery, respectively). At the end of ischemia, the hearts received IPostC, cyclosporine-A, or both or none of them. Myocardial creatine-kinase (CK) release as an index of tissue injury was measured spectrophotometery in coronary effluent in reperfusion phase. Infarct size was identified by triphenyltetrazolium chloride staining. Heart rate, left ventricular end-diastolic pressure (LVEDP), LV systolic pressure (LVSP), rate-pressure product (RPP) and coronary flow were recorded throughout the experiment.

Results

IPostC, applied at the onset of reperfusion, failed to improve myocardial LVEDP and RPP, or reduce tissue damage indicated by infarct size and CK release in diabetic hearts, while it significantly recovered these parameters toward the pre-ischemic values in control hearts (P < 0.05). In contrast, with simultaneous inhibition of mPTP using cyclosporine-A, the cardioprotective effects of IPostC on myocardial hemodynamics, infarct size and CK release were significantly restored in diabetic hearts (P < 0.05).

Conclusions

The loss of cardioprotection by IPostC in diabetic state can be overcome by increasing the potency of protective IPostC through its co-application with mPTP inhibition.

Long-term inhibition of miR-21 leads to reduction of obesity in db/db mice

OBJECTIVE

To assess the effect of long-term pharmacological inhibition of miR-21 in a model of metabolic syndrome and obesity.

METHODS

Aged db/db mice were treated with locked nucleic acid-modified anti-miRs directed against miR-21 (LNA-21), control LNAs or PBS for 18 weeks. Cardiac function was assessed by echocardiography and the effect on body weight and white adipose tissue (WAT) was evaluated.

RESULTS

MiR-21 expression was efficiently inhibited in the heart and WAT with no apparent liver toxicity or deterioration of kidney function. MiR-21 inhibition had no effect on cardiac hypertrophy as well as systolic and diastolic cardiac functions. However, levels of cardiac collagen 1 were modestly reduced in LNA-21 treated mice. MiR-21 inhibition reduced body weight, as well as adipocyte size and serum triglycerides were significantly decreased. The miR-21 targets TGFβ-receptor 2 (TGFBR2) and phosphatase and tensin homolog (PTEN) were derepressed in WAT of LNA-21 treated mice and Sprouty1 and 2 were increased after miR-21 inhibition.

CONCLUSIONS

Long-term treatment with LNA-21 is safe and efficiently suppresses miR-21 expression. Cardiac function was not affected. LNA-21 treatment led to a significant weight loss and reduces adipocyte size as well as derepression of the targets TGFRB2, PTEN, and Sprouty1 and 2.

Adiponectin stimulates Rho-mediated actin cytoskeleton remodeling and glucose uptake via APPL1 in primary cardiomyocytes

OBJECTIVE

Adiponectin is known to confer its cardioprotective effects in obesity and type 2 diabetes, mainly by regulating glucose and fatty acid metabolism in cardiomyocytes. Dynamic actin cytoskeleton remodeling is involved in regulation of multiple biological functions, including glucose uptake. Here we investigated in neonatal cardiomyocytes whether adiponectin induced actin cytoskeleton remodeling and if this played a role in adiponectin-stimulated glucose uptake.

MATERIALS/METHODS

Primary cardiomyocytes were treated with full-length and globular adiponectin (fAd and gAd, respectively).

RESULTS

Both fAd and gAd increased RhoA activity, phosphorylation of the Rho/ROCK signaling target cofilin and actin polymerization to form filamentous actin as determined by rhodamine-phallodin immunofluorescence and quantitative analysis of filamentous to globular actin ratio. Scanning electron microscopy also demonstrated structural remodeling. Adiponectin stimulated glucose uptake, was significantly abrogated in the presence of inhibitors of actin cytoskeleton remodeling (cytochalasin D) and Rho/ROCK signaling (C3 transferase, Y27632). We showed that adiponectin increased colocalization of actin and APPL1 and that actin remodeling, phosphorylation of AMPK, p38MAPK and cofilin, glucose uptake and oxidation were all attenuated after siRNA-mediated knockdown of APPL1.

CONCLUSION

We show that adiponectin mediates Rho/ROCK-dependent actin cytoskeleton remodeling to increase glucose uptake and metabolism via APPL1 signaling.

Protocatechuic acid exerts a cardioprotective effect in type 1 diabetic rats

Oxidative stress has been shown to play an important role in the pathogenesis of diabetes-induced cardiac dysfunction. Protocatechuic acid (PCA) is a phenolic compound, a main metabolite of anthocyanin, which has been reported to display various pharmacological properties. We proposed the hypothesis that PCA exerts cardioprotection in type 1 diabetic (T1DM) rats. T1DM was induced in male Sprague-Dawley rats by a single i.p. injection of 50 mg/kg streptozotocin (STZ) and groups of these animals received the following treatments for 12 weeks: i) oral administration of vehicle, ii) oral administration of PCA at a dose of 50  mg/kg per day, iii) oral administration of PCA at a dose of 100 mg/kg per day, iv) s.c. injection of insulin at a dose of 4 U/kg per day, and v) a combination of PCA, 100 mg/kg per day and insulin, 4 U/kg per day. Metabolic parameters, results from echocardiography, and heart rate variability were monitored every 4 weeks, and the HbA1c, cardiac malondialdehyde (MDA), cardiac mitochondrial function, and cardiac BAX/BCL2 expression were evaluated at the end of treatment. PCA, insulin, and combined drug treatments significantly improved metabolic parameters and cardiac function as shown by increased percentage fractional shortening and percentage left ventricular ejection fraction and decreased low-frequency:high-frequency ratio in T1DM rats. Moreover, all treatments significantly decreased plasma HbA1c and cardiac MDA levels, improved cardiac mitochondrial function, and increased BCL2 expression. Our results demonstrated for the first time, to our knowledge, the efficacy of PCA in improving cardiac function and cardiac autonomic balance, preventing cardiac mitochondrial dysfunction, and increasing anti-apoptotic protein in STZ-induced T1DM rats. Thus, PCA possesses a potential cardioprotective effect and could restore cardiac function when combined with insulin treatment. These findings indicated that supplementation with PCA might be helpful for the prevention and alleviation of cardiovascular complications in T1DM.

New therapeutic options in heart failure. What's on the horizon? An overview

Heart failure is a complex clinical syndrome responsible for high morbidity and mortality in the world. Despite advances in the management of heart failure, the prognosis of these patients remains poor and there is a critical need for new treatment strategies improving the clinical outcomes. New approaches in heart failure therapies target cellular mechanisms, as well as mechanical and structural aspects of heart failure that are not addressed by recent therapies. These include abnormalities in molecular mechanisms, electrical conduction and ventricular remodeling. This review presents the pathophysiological basis, mechanisms of action and available clinical efficacy and safety data of drugs and mechanical therapies that are currently under development.

HMGB1 mediates hyperglycaemia-induced cardiomyocyte apoptosis via ERK/Ets-1 signalling pathway

Apoptosis is a key event involved in diabetic cardiomyopathy. The expression of high mobility group box 1 protein (HMGB1) is up-regulated in diabetic mice. However, the molecular mechanism of high glucose (HG)-induced cardiomyocyte apoptosis remains obscure. We aimed to determine the role of HMGB1 in HG-induced apoptosis of cardiomyocytes. Treating neonatal primary cardiomyocytes with HG increased cell apoptosis, which was accompanied by elevated levels of HMGB1. Inhibition of HMGB1 by short-hairpin RNA significantly decreased HG-induced cell apoptosis by reducing caspase-3 activation and ratio of Bcl2-associated X protein to B-cell lymphoma/leukemia-2 (bax/bcl-2). Furthermore, HG activated E26 transformation-specific sequence-1 (Ets-1), and HMGB1 inhibition attenuated HG-induced activation of Ets-1 via extracellular signal-regulated kinase 1/2 (ERK1/2) signalling. In addition, inhibition of Ets-1 significantly decreased HG-induced cardiomyocyte apoptosis. Similar results were observed in streptozotocin-treated diabetic mice. Inhibition of HMGB1 by short-hairpin RNA markedly decreased myocardial cell apoptosis and activation of ERK and Ets-1 in diabetic mice. In conclusion, inhibition of HMGB1 may protect against hyperglycaemia-induced cardiomyocyte apoptosis by down-regulating ERK-dependent activation of Ets-1.

Metabolic dysfunction in diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is defined as cardiac disease independent of vascular complications during diabetes. The number of new cases of DCM is rising at epidemic rates in proportion to newly diagnosed cases of diabetes mellitus (DM) throughout the world. DCM is a heart failure syndrome found in diabetic patients that is characterized by left ventricular hypertrophy and reduced diastolic function, with or without concurrent systolic dysfunction, occurring in the absence of hypertension and coronary artery disease. DCM and other diabetic complications are caused in part by elevations in blood glucose and lipids, characteristic of DM. Although there are pathological consequences to hyperglycemia and hyperlipidemia, the combination of the two metabolic abnormalities potentiates the severity of diabetic complications. A natural competition exists between glucose and fatty acid metabolism in the heart that is regulated by allosteric and feedback control and transcriptional modulation of key limiting enzymes. Inhibition of these glycolytic enzymes not only controls flux of substrate through the glycolytic pathway, but also leads to the diversion of glycolytic intermediate substrate through pathological pathways, which mediate the onset of diabetic complications. The present review describes the limiting steps involved in the development of these pathological pathways and the factors involved in the regulation of these limiting steps. Additionally, therapeutic options with demonstrated or postulated effects on DCM are described.

Impact of glucagon-like peptide-1 on myocardial glucose metabolism revisited

The gut hormone glucagon-like peptide-1 (GLP-1) is an insulinotropic incretin with significant cardiovascular impact. Two classes of medication, GLP-1 analogues and DPP-4 inhibitors, have been developed that circumvent the rapid degradation of GLP-1 by the enzyme dipeptidyl peptidase-4 (DPP-4), both enhance the incretin effect and were developed for the treatment of type 2 diabetes. Several mechanisms suggesting that DPP-4 inhibitors, GLP-1, and analogues could have a protective effect on the cardiovascular risk profile have been forwarded; e.g., reductions of blood glucose, body weight, blood pressure, improvement in left ventricular ejection fraction, myocardial perfusion, atherosclerosis development, and endothelial function. Despite this, the reasons for a decreased risk of developing cardiovascular disease and reduced post-ischaemia damage are still poorly understood. The potentially beneficial effect of GLP-1 stimulation may rely on, among others, improved myocardial glucose metabolism. This review focuses on the dogma that GLP-1 receptor stimulation may provide beneficial cardiovascular effects, possibly due to enhanced myocardial energetic efficiency, by increasing myocardial glucose uptake. The published literature was systematically reviewed and the applied models evaluated since the outcomes of varying studies differ substantially. Reports on the effect of GLP-1R stimulation on myocardial metabolism are conflicting and should be evaluated carefully. There is limited and conflicting information on the impact of these agents in real life patients and while clinical outcome studies investigating the cardiovascular effects of GLP-1 based therapies have been initiated, the first two studies, both on DPP-4 inhibitors, designed specifically to evaluate cardiac safety reported largely neutral outcomes.

Cardiac energy metabolism and oxidative stress biomarkers in diabetic rat treated with resveratrol

Resveratrol (RSV), polyphenol from grape, was studied to evaluate its effects on calorimetric parameters, energy metabolism, and antioxidants in the myocardium of diabetic rats. The animals were randomly divided into four groups (n = 8): C (control group): normal rats; C-RSV: normal rats receiving RSV; DM: diabetic rats; and DM-RSV: diabetics rats receiving RSV. Type 1 diabetes mellitus was induced with administration of streptozotocin (STZ; 60 mg⁻¹ body weight, single dose, i.p.). After 48 hours of STZ administration, the animals received RSV (1.0 mg/kg/day) for gavage for 30 days. Food, water, and energy intake were higher in the DM group, while administration of RSV caused decreases (p<0.05) in these parameters. The glycemia decreased and higher final body weight increased in DM-RSV when compared with the DM group. The diabetic rats showed higher serum-free fatty acid, which was normalized with RSV. Oxygen consumption (VO₂) and carbon dioxide production (VCO₂) decreased (p<0.05) in the DM group. This was accompanied by reductions in RQ. The C-RSV group showed higher VO₂ and VCO₂ values. Pyruvate dehydrogenase activity was lower in the DM group and normalizes with RSV. The DM group exhibited higher myocardial β-hydroxyacyl coenzyme-A dehydrogenase and citrate synthase activity, and RSV decreased the activity of these enzymes. The DM group had higher cardiac lactate dehydrogenase compared to the DM-RSV group. Myocardial protein carbonyl was increased in the DM group. RSV increased reduced glutathione in the cardiac tissue of diabetic animals. The glutathione reductase activity was higher in the DM-RSV group compared to the DM group. In conclusion, diabetes is accompanied by cardiac energy metabolism dysfunction and change in the biomarkers of oxidative stress. The cardioprotective effect may be mediated through RVS's ability to normalize free fatty acid oxidation, enhance utilization glucose, and control the biomarkers' level of oxidative stress under diabetic conditions.

Acute heart transplant graft failure in association with hyperosmolar hyperglycemia state

We report a 38-year-old male with end-stage ischemic cardiomyopathy requiring left ventricular assist device placement, followed by orthotopic heart transplantation, who presented 18 months post-orthotopic heart transplant with acute graft failure with estimated left ventricular ejection fraction of 5% to 10%, in association with a glucose level of 550 mg/dL, and hemoglobin A1C of 13.8% and a negative pathology for a graft cellular and humoral rejection and no vasculaopthy. His left ventricular ejection fraction improved significantly to 40% to 45% within three days of optimal glucose control.

Endothelial cells respond to hyperglycemia by increasing the LPL transporter GPIHBP1

In diabetes, when glucose uptake and oxidation are impaired, the heart is compelled to use fatty acid (FA) almost exclusively for ATP. The vascular content of lipoprotein lipase (LPL), the rate-limiting enzyme that determines circulating triglyceride clearance, is largely responsible for this FA delivery and increases following diabetes. Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein [GPIHBP1; a protein expressed abundantly in the heart in endothelial cells (EC)] collects LPL from the interstitial space and transfers it across ECs onto the luminal binding sites of these cells, where the enzyme is functional. We tested whether ECs respond to hyperglycemia by increasing GPIHBP1. Streptozotocin diabetes increased cardiac LPL activity and GPIHBP1 gene and protein expression. The increased LPL and GPIHBP1 were located at the capillary lumen. In vitro, passaging EC caused a loss of GPIHBP1, which could be induced on exposure to increasing concentrations of glucose. The high-glucose-induced GPIHBP1 increased LPL shuttling across EC monolayers. GPIHBP1 expression was linked to the EC content of heparanase. Moreover, active heparanase increased GPIHBP1 gene and protein expression. Both ECs and myocyte heparan sulfate proteoglycan-bound platelet-derived growth factor (PDGF) released by heparanase caused augmentation of GPIHBP1. Overall, our data suggest that this protein "ensemble" (heparanase-PDGF-GPIHBP1) cooperates in the diabetic heart to regulate FA delivery and utilization by the cardiomyocytes. Interrupting this axis may be a novel therapeutic strategy to restore metabolic equilibrium, curb lipotoxicity, and help prevent or delay heart dysfunction that is characteristic of diabetes.

Activation of angiotensin-converting enzyme 2 improves cardiac electrical changes in ventricular repolarization in streptozotocin-induced hyperglycaemic rats

AIMS

Diabetic patients present a high level of cardiac arrhythmias and risk of cardiac sudden death. The renin-angiotensin system (RAS) plays a key role in diabetes and cardiac diseases. The present study aimed to evaluate whether an angiotensin-converting enzyme 2 (ACE2) activator, diminazene aceturate (DIZE), could improve the streptozotocin (STZ)-induced electrical changes in ventricular repolarization in hyperglycaemic rats.

METHODS AND RESULTS

Hyperglycaemia was induced in Wistar male rats with STZ (60 mg/kg/iv). After 4 weeks of STZ injection, rats were daily treated with saline (control) or DIZE (1 mg/kg/gavage) for four consecutive weeks. The cardiac electrical function was evaluated in vivo by electrocardiogram and in vitro by cardiac action potential records in different pacing frequencies. Treatment with DIZE was not able to reverse hyperglycaemia nor body weight loss. However, DIZE reversed hyperglycaemia-induced cardiac electrical changes in ventricular repolarization. Specifically, animals treated with DIZE showed shorter QT and QTc intervals. In addition, ACE2 activation was capable to shorten the cardiac action potential and also reverse the arrhythmic markers. Diminazene aceturate treatment did not induce arrhythmic events in normal, as well as in hyperglycaemic animals.

CONCLUSION

Our data indicate that activation of ACE2 has a beneficial effect in hyperglycaemic rats, improving the cardiac electrical function. Thus, DIZE represents a promising new therapeutic agent to treat hyperglycaemia-induced cardiac electrical changes in ventricular repolarization.

Merit of ginseng in the treatment of heart failure in type 1-like diabetic rats

The present study investigated the merit of ginseng in the improvement of heart failure in diabetic rats and the role of peroxisome proliferator-activated receptors δ (PPAR δ ). We used streptozotocin-induced diabetic rat (STZ-rat) to screen the effects of ginseng on cardiac performance and PPAR δ expression. Changes of body weight, water intake, and food intake were compared in three groups of age-matched rats; the normal control (Wistar rats) received vehicle, STZ-rats received vehicle and ginseng-treated STZ-rats. We also determined cardiac performances in addition to blood glucose level in these animals. The protein levels of PPAR δ in hearts were identified using Western blotting analysis. In STZ-rats, cardiac performances were decreased but the food intake, water intake, and blood glucose were higher than the vehicle-treated control. After a 7-day treatment of ginseng in STZ-rats, cardiac output was markedly enhanced without changes in diabetic parameters. This treatment with ginseng also increased the PPAR δ expression in hearts of STZ-rats. The related signal of cardiac contractility, troponin I phosphorylation, was also raised. Ginseng-induced increasing of cardiac output was reversed by the cotreatment with PPAR δ antagonist GSK0660. Thus, we suggest that ginseng could improve heart failure through the increased PPAR δ expression in STZ-rats.

Reversible pulmonary trunk banding: IX. G6PD activity of adult goat myocardium submitted to ventricular retraining

Objective

Increased glucose 6-phosphate dehydrogenase activity has been demonstrated in heart failure. This study sought to assess myocardial glucose 6-phosphate dehydrogenase activity in retraining of the subpulmonary ventricle of adult goats.

Methods

Eighteen adult goats were divided into three groups: traditional (fixed banding), sham, and intermittent (adjustable banding, daily 12-hour systolic overload). Systolic overload (70% of systemic pressure) was maintained during a 4-week period. Right ventricle, pulmonary artery and aortic pressures were measured throughout the study. All animals were submitted to echocardiographic and hemodynamic evaluations throughout the protocol. After the study period, the animals were killed for morphological and glucose 6-phosphate dehydrogenase activity assessment.

Results

A 55.7% and 36.7% increase occurred in the intermittent and traditional right ventricle masses, respectively, when compared with the sham group (P<0.05), despite less exposure of intermittent group to systolic overload. No significant changes were observed in myocardial water content in the 3 groups (P=0.27). A 37.2% increase was found in right ventricle wall thickness of intermittent group, compared to sham and traditional groups (P<0.05). Right ventricle glucose 6-phosphate dehydrogenase activity was elevated in the traditional group, when compared to sham and intermittent groups (P=0.05).

Conclusion

Both study groups have developed similar right ventricle hypertrophy, regardless less systolic overload exposure of intermittent group. Traditional systolic overload for adult subpulmonary ventricle retraining causes upregulation of myocardial glucose 6-phosphate dehydrogenase activity. It may suggest that the undesirable "pathologic systolic overload" is influenced by activation of penthose pathway and cytosolic Nicotinamide adenine dinucleotide phosphate availability. This altered energy substrate metabolism can elevate levels of free radicals by Nicotinamide adenine dinucleotide phosphate oxidase, an important mechanism in the pathophysiology of heart failure.

Risk of postprandial insulin resistance: the liver/vagus rapport

Ingestion of a meal is the greatest challenge faced by glucose homeostasis. The surge of nutrients has to be disposed quickly, as high concentrations in the bloodstream may have pathophysiological effects, and also properly, as misplaced reserves may induce problems in affected tissues. Thus, loss of the ability to adequately dispose of ingested nutrients can be expected to lead to glucose intolerance, and favor the development of pathologies. Achieving interplay of several organs is of upmost importance to maintain effectively postprandial glucose clearance, with the liver being responsible of orchestrating global glycemic control. This dogmatic role of the liver in postprandial insulin sensitivity is tightly associated with the vagus nerve. Herein, we uncover the behaviour of metabolic pathways determined by hepatic parasympathetic function status, in physiology and in pathophysiology. Likewise, the inquiry expands to address the impact of a modern lifestyle, especially one's feeding habits, on the hepatic parasympathetic nerve control of glucose metabolism.

Cardiac autonomic neuropathy in patients with diabetes mellitus

Cardiac autonomic neuropathy (CAN) is an often overlooked and common complication of diabetes mellitus. CAN is associated with increased cardiovascular morbidity and mortality. The pathogenesis of CAN is complex and involves a cascade of pathways activated by hyperglycaemia resulting in neuronal ischaemia and cellular death. In addition, autoimmune and genetic factors are involved in the development of CAN. CAN might be subclinical for several years until the patient develops resting tachycardia, exercise intolerance, postural hypotension, cardiac dysfunction and diabetic cardiomyopathy. During its sub-clinical phase, heart rate variability that is influenced by the balance between parasympathetic and sympathetic tones can help in detecting CAN before the disease is symptomatic. Newer imaging techniques (such as scintigraphy) have allowed earlier detection of CAN in the pre-clinical phase and allowed better assessment of the sympathetic nervous system. One of the main difficulties in CAN research is the lack of a universally accepted definition of CAN; however, the Toronto Consensus Panel on Diabetic Neuropathy has recently issued guidance for the diagnosis and staging of CAN, and also proposed screening for CAN in patients with diabetes mellitus. A major challenge, however, is the lack of specific treatment to slow the progression or prevent the development of CAN. Lifestyle changes, improved metabolic control might prevent or slow the progression of CAN. Reversal will require combination of these treatments with new targeted therapeutic approaches. The aim of this article is to review the latest evidence regarding the epidemiology, pathogenesis, manifestations, diagnosis and treatment for CAN.

Bone marrow mesenchymal stromal cells rescue cardiac function in streptozotocin-induced diabetic rats

OBJECTIVES

In the present study, we investigated whether MSC-transplantation can revert cardiac dysfunction in streptozotocin-induced diabetic rats and the immunoregulatory effects of MSC were examined.

BACKGROUND

Cardiac complications are one of the main causes of death in diabetes. Several studies have shown anti-diabetic effects of bone marrow mesenchymal stromal cells (MSC).

METHODS/RESULTS

The rats were divided in three groups: Non-diabetic, Diabetic and Diabetic-Treated with 5 × 10(6) MSC 4 weeks after establishment of diabetes. Four weeks after MSC-therapy, systemic metabolic parameters, immunological profile and cardiac function were assessed. MSC-transplantation was able to revert the hyperglycemia and body weight loss of the animals. In addition, after MSC-transplantation a decrease in corticosterone and IFN-γ sera levels without restoration of insulin and leptin plasma levels was observed. Also, MSC-therapy improved electrical remodeling, shortening QT and QTc in the ECG and action potential duration of left ventricular myocytes. No arrhythmic events were observed after MSC-transplantation. MSC-therapy rescued the cardiac beta-adrenergic sensitivity by increasing beta-1 adrenergic receptor expression. Both alpha and beta cardiac AMPK and p-AMPK returned to baseline values after MSC-therapy. However, total ERK1 and p-ERK1/2 were not different among groups.

CONCLUSION

The results indicate that MSC-therapy was able to rescue cardiac impairment induced by diabetes, normalize cardiac AMPK subunit expression and activity, decrease corticosterone and glycemia and exert systemic immunoregulation.

Recurrence of left ventricular dysfunction in patients with restored idiopathic dilated cardiomyopathy

BACKGROUND

In some patients with nonischemic idiopathic dilated cardiomyopathy (DCM), left ventricular (LV) dysfunction improves spontaneously but can recur. The factors predicting recurrence of LV dysfunction in recovered idiopathic DCM are poorly defined. We investigated the clinical, echocardiographic, and laboratory variables affecting recurrence of LV dysfunction in patients who recovered from DCM.

HYPOTHESIS

The recurrence of LV dysfunction in recovered idiopathic DCM is impacted by clinical, echocardiographic, and laboratory variables.

METHODS

The study comprised 85 consecutively enrolled patients (62 males, age 57 ± 16 years) with DCM who achieved a restoration of LV systolic function. Patients were followed up for 50 ± 33 months after recovery from LV dysfunction without discontinuation of standard medication for heart failure with depressed ejection fraction. Clinical, echocardiographic, and laboratory variables were analyzed to identify factors independently associated with recurrence of LV dysfunction.

RESULTS

LV dysfunction recurred in 33 patients (23 males, age 64 ± 12 years). Univariate analysis revealed that age, duration from initial presentation to recovery time, diabetes, and LV end-diastolic dimension (LVEDD) at initial presentation were associated with recurrence of LV dysfunction. Multivariate analysis revealed that only age, diabetes, and LVEDD at initial presentation were independent predictors in patients who recovered from LV dysfunction.

CONCLUSIONS

The recurrence of LV dysfunction was significantly correlated with age, presence of diabetes, and LVEDD at initial presentation. Clinicians should consider maintenance of intensive care to patients who recovered from DCM with these factors.

Low molecular weight fucoidan alleviates cardiac dysfunction in diabetic Goto-Kakizaki rats by reducing oxidative stress and cardiomyocyte apoptosis

Diabetic cardiomyopathy (DCM) is characterized by cardiac dysfunction and cardiomyocyte apoptosis. Oxidative stress is suggested to be the major contributor to the development of DCM. This study was intended to evaluate the protective effect of low molecular weight fucoidan (LMWF) against cardiac dysfunction in diabetic rats. Type 2 diabetic goto-kakizaki rats were untreated or treated with LMWF (50 and 100 mg/kg/day) for three months. The establishment of DCM model and the effects of LMWF on cardiac function were evaluated by echocardiography and isolated heart perfusion. Ventricle staining with H-E or Sirius Red was performed to investigate the structural changes in myocardium. Functional evaluation demonstrated that LMWF has a beneficial effect on DCM by enhancing myocardial contractility and mitigating cardiac fibrosis. Additionally, LMWF exerted significant inhibitory effects on the reactive oxygen species production and myocyte apoptosis in diabetic hearts. The depressed activity of superoxide dismutase in diabetic heart was also improved by intervention with LMWF. Moreover, LMWF robustly inhibited the enhanced expression of protein kinase C β, an important contributor to oxidative stress, in diabetic heart and high glucose-treated cardiomyocytes. In conclusion, LMWF possesses a protective effect against DCM through ameliorations of PKCβ-mediated oxidative stress and subsequent cardiomyocyte apoptosis in diabetes.

Pro-HEART - a randomized clinical trial to test the effectiveness of a high protein diet targeting obese individuals with heart failure: rationale, design and baseline characteristics

There is ample research to support the potential benefits of a high protein diet on clinical outcomes in overweight/obese, diabetic subjects. However, nutritional management of overweight/obese individuals with heart failure (HF) and type 2 diabetes mellitus (DM) or metabolic syndrome (MS) is poorly understood and few clinical guidelines related to nutritional approaches exist for this subgroup. This article describes the design, methods, and baseline characteristics of study participants enrolled in Pro-HEART, a randomized clinical trial to determine the short term and long term effects of a high protein diet (30% protein [~110 g/day], 40% carbohydrates [150 g/day], 30% fat [~50 g/day]) versus a standard protein diet (15% protein [~55 g/day], 55% carbohydrates [~200 g/day], 30% fat [~50 g/day]) on body weight and adiposity, cardiac structure and function, functional status, lipid profile, glycemic control, and quality of life. Between August, 2009 and May, 2013, 61 individuals agreed to participate in the study; 52 (85%) - mean age 58.2 ± 9.8 years; 15.4% Blacks; 57.7% Whites; 19.2% Hispanics; 7.7% Asians; 73.1% male; weight 112.0 ± 22.6 kg - were randomized to a 3-month intensive weight management program of either a high protein or standard protein diet; data were collected at baseline, 3 months, and 15 months. This study has the potential to reveal significant details about the role of macronutrients in weight management of overweight/obese individuals with HF and DM or MS.

Hyperglycemia-induced secretion of endothelial heparanase stimulates a vascular endothelial growth factor autocrine network in cardiomyocytes that promotes recruitment of lipoprotein lipase

OBJECTIVE

During diabetes mellitus, coronary lipoprotein lipase increases to promote the predominant use of fatty acids. We have reported that high glucose stimulates active heparanase secretion from endothelial cells to cleave cardiomyocyte heparan sulfate and release bound lipoprotein lipase for transfer to the vascular lumen. In the current study, we examined whether heparanase also has a function to release cardiomyocyte vascular endothelial growth factor (VEGF), and whether this growth factor influences cardiomyocyte fatty acid delivery in an autocrine manner.

APPROACH AND RESULTS

Acute, reversible hyperglycemia was induced in rats, and a modified Langendorff heart perfusion was used to separate the coronary perfusate from the interstitial effluent. Coronary artery endothelial cells were exposed to high glucose to generate conditioned medium, and VEGF release from isolated cardiomyocytes was tested using endothelial cell conditioned medium or purified active and latent heparanase. Autocrine signaling of myocyte-derived VEGF on cardiac metabolism was studied. High glucose promoted latent and active heparanase secretion into endothelial cell conditioned medium, an effective stimulus for releasing cardiomyocyte VEGF. Intriguingly, latent heparanase was more efficient than active heparanase in releasing VEGF from a unique cell surface pool. VEGF augmented cardiomyocyte intracellular calcium and AMP-activated protein kinase phosphorylation and increased heparin-releasable lipoprotein lipase.

CONCLUSIONS

Our data suggest that the heparanase-lipoprotein lipase-VEGF axis amplifies fatty acid delivery, a rapid and adaptive mechanism that is geared to overcome the loss of glucose consumption by the diabetic heart. If prolonged, the resultant lipotoxicity could lead to cardiovascular disease in humans.

Rodent models of heart failure: an updated review

Heart failure (HF) is one of the major health and economic burdens worldwide, and its prevalence is continuously increasing. The study of HF requires reliable animal models to study the chronic changes and pharmacologic interventions in myocardial structure and function and to follow its progression toward HF. Indeed, during the past 40 years, basic and translational scientists have used small animal models to understand the pathophysiology of HF and find more efficient ways of preventing and managing patients suffering from congestive HF (CHF). Each species and each animal model has advantages and disadvantages, and the choice of one model over another should take them into account for a good experimental design. The aim of this review is to describe and highlight the advantages and drawbacks of some commonly used HF rodents models, including both non-genetically and genetically engineered models, with a specific subchapter concerning diastolic HF models.

Myocardial insulin resistance, metabolic stress and autophagy in diabetes

Clinical studies in humans strongly support a link between insulin resistance and non-ischaemic heart failure. The occurrence of a specific insulin-resistant cardiomyopathy, independent of vascular abnormalities, is now recognized. The progression of cardiac pathology linked with insulin resistance is poorly understood. Cardiac insulin resistance is characterized by reduced availability of sarcolemmal Glut-4 transporters and consequent lower glucose uptake. A shift away from glycolysis towards fatty acid oxidation for ATP supply is apparent and is associated with myocardial oxidative stress. Reliance of cardiomyocyte excitation-contraction coupling on glycolytically derived ATP supply potentially renders cardiac function vulnerable to the metabolic remodelling adaptations observed in diabetes development. Findings from Glut-4-knockout mice demonstrate that cardiomyocytes with extreme glucose uptake deficiency exhibit cardiac hypertrophy and marked excitation-contraction coupling abnormalities characterized by reduced sarcolemmal Ca(2+) influx and sarcoplasmic reticulum Ca(2+) uptake. The 'milder' phenotype fructose-fed mouse model of type 2 diabetes does not show evidence of cardiac hypertrophy, but cardiomyocyte loss linked with autophagic activation is evident. Fructose feeding induces a marked reduction in intracellular Ca(2+) availability with myofilament adaptation to preserve contractile function in this setting. The cardiac metabolic adaptations of two load-independent models of diabetes, namely the Glut-4-deficient mouse and the fructose-fed mouse are contrasted. The role of autophagy in diabetic cardiopathology is evaluated and anomalies of type 1 versus type 2 diabetic autophagic responses are highlighted.

Gene transfer of human neuregulin-1 attenuates ventricular remodeling in diabetic cardiomyopathy rats

Neuregulin-1 (NRG-1) is a cardioactive growth factor released from endothelial cells. However, the effect of NRG-1 on ventricular remodeling in diabetic cardiomyopathy (DCM) remains unclear. The aim of the present study was to investigate the pathophysiological role of NRG-1 in a rat model of DCM. Rat cardiac microvascular endothelial cells (CMECs) were transfected with human NRG-1 (hNRG-1) lentivirus. The hNRG-1 medium was utilized to culture rat cardiomyocytes. The cardiomyocytes were counted with a hemacytometer to determine the proliferation index and Annexin V/propidium iodide double staining was employed to examine the apoptotic rate. A rat model of DCM was induced by an intraperitoneal injection of streptozotocin. The hNRG-1 lentivirus was injected into the myocardium of the DCM model rats. Four weeks after the lentiviral injection, cardiac catheterization was performed to evaluate the cardiac function. Apoptotic cells were determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. Left ventricular sections were stained with Masson’s trichrome to investigate the myocardial collagen content. The expression levels of related genes and proteins were analyzed. The results indicated that hNRG-1 conditioned medium stimulated the proliferation and counteracted the apoptosis of cardiomyocytes in vitro. In the rats with DCM, gene transfer of hNRG-1 to the myocardium improved heart function, as indicated by invasive hemodynamic measurements. In addition, hNRG-1 reduced the number of apoptotic cells, decreased the expression of bax and increased the expression of bcl-2 in the myocardium of the DCM model rats. Myocardial fibrosis and type I and III pro-collagen mRNA levels in the myocardium were significantly reduced by hNRG-1. hNRG-1 also increased the expression of phospho-Akt and phospho-eNOS in the myocardium. In conclusion, the gene transfer of hNRG-1 ameliorates cardiac dysfunction in diabetes. Although further studies are required, NRG-1 appears to protect cardiomyocytes against apoptosis and to reduce the extent of myocardial interstitial fibrosis.

Left ventricular dysfunction and outcome at two-year follow-up in patients with type 2 diabetes: The DYDA study

AIMS

Left ventricular dysfunction (LVD) in type 2 diabetes mellitus (DM) (DYDA) study is a prospective investigation enrolling 960 with DM without overt cardiac disease. At baseline, a high prevalence of LVD was detected by analysing midwall shortening. We report here the incidence of clinical events in DYDA patients after 2-year follow-up and the frequency of LVD detected at baseline and 2-year evaluation.

METHODS

Systolic LVD was defined as midwall shortening ≤15%, diastolic LVD as any condition different from "normal diastolic function" identified as E/A ratio on Doppler mitral flow between 0.75 and 1.5 and deceleration time of E wave >140 ms. Major outcome was a composite of major events, including all-causes death and hospital admissions.

RESULTS

During the study period, any systolic/diastolic LVD was found in 616 of 699 patients (88.1%) in whom LVD function could be measured at baseline or at 2 years. Older age and high HbA1c predicted the occurrence of LVD. During the follow-up 15 patients died (1.6%), 3 for cardiovascular causes, 139 were hospitalized (14.5%, 43 of them for cardiovascular causes, 20 for a new cancer).

CONCLUSIONS

During a 2-year follow-up any LVD is detectable in a large majority of patients with DM without overt cardiac disease. Older age and higher HbA1c predict LVD. All-cause death or hospitalization occurred in 15% of patients, cardiovascular cause was uncommon. Independent predictors of events were older age, pathologic lipid profile, high HbA1c, claudicatio and repaglinide therapy. Echo-assessed LVD at baseline was not prognosticator of events.

AMPK-regulated and Akt-dependent enhancement of glucose uptake is essential in ischemic preconditioning-alleviated reperfusion injury

AIMS

Ischemic preconditioning (IPC) is a potent form of endogenous protection. However, IPC-induced cardioprotective effect is significantly blunted in insulin resistance-related diseases and the underlying mechanism is unclear. This study aimed to determine the role of glucose metabolism in IPC-reduced reperfusion injury.

METHODS

Normal or streptozotocin (STZ)-treated diabetic rats subjected to 2 cycles of 5 min ischemia/5 min reperfusion prior to myocardial ischemia (30 min)/reperfusion (3 h). Myocardial glucose uptake was determined by (18)F-fluorodeoxyglucose-positron emission tomography (PET) scan and gamma-counter biodistribution assay.

RESULTS

IPC exerted significant cardioprotection and markedly improved myocardial glucose uptake 1 h after reperfusion (P<0.01) as evidenced by PET images and gamma-counter biodistribution assay in ischemia/reperfused rats. Meanwhile, myocardial translocation of glucose transporter 4 (GLUT4) to plasma membrane together with myocardial Akt and AMPK phosphorylation were significantly enhanced in preconditioned hearts. Intramyocardial injection of GLUT4 siRNA markedly decreased GLUT4 expression and blocked the cardioprotection of IPC as evidence by increased myocardial infarct size. Moreover, the PI3K inhibitor wortmannin significantly inhibited activation of Akt and AMPK, reduced GLUT4 translocation, glucose uptake and ultimately, depressed IPC-induced cardioprotection. Furthermore, IPC-afforded antiapoptotic effect was markedly blunted in STZ-treated diabetic rats. Exogenous insulin supplementation significantly improved glucose uptake via co-activation of myocardial AMPK and Akt and alleviated ischemia/reperfusion injury as evidenced by reduced myocardial apoptosis and infarction size in STZ-treated rats (P<0.05).

CONCLUSIONS

The present study firstly examined the role of myocardial glucose metabolism during reperfusion in IPC using direct genetic modulation in vivo. Augmented glucose uptake via co-activation of myocardial AMPK and Akt in reperfused myocardium is essential to IPC-alleviated reperfusion injury. This intrinsic metabolic modulation and cardioprotective capacity are present in STZ-treated hearts and can be triggered by insulin.

Myocardial substrate metabolism in obesity

Obesity is linked to a wide variety of cardiac changes, from subclinical diastolic dysfunction to end-stage systolic heart failure. Obesity causes changes in cardiac metabolism, which make ATP production and utilization less efficient, producing functional consequences that are linked to the increased rate of heart failure in this population. As a result of the increases in circulating fatty acids and insulin resistance that accompanies excess fat storage, several of the proteins and genes that are responsible for fatty acid uptake and metabolism are upregulated, and the metabolic machinery responsible for glucose utilization and oxidation are inhibited. The resultant increase in fatty acid metabolism, and the inherent alterations in the proteins of the electron transport chain used to create the gradient needed to drive mitochondrial ATP production, results in a decrease in efficiency of cardiac work and a relative increase in oxygen usage. These changes in cardiac mitochondrial metabolism are potential therapeutic targets for the treatment and prevention of obesity-related heart failure.

Peroxisome proliferator-activated receptors modulate cardiac dysfunction in diabetic cardiomyopathy

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality among patients with diabetes mellitus (DM). Chronic inflammation and derangement of myocardial energy and lipid homeostasis are common features of DM. The transcription factors of peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor superfamily, which are important in regulating energy and lipid homeostasis. There are three PPAR isoforms, α, γ, and δ, and their roles have been increasingly recognized to be important in CVD. These three isoforms are expressed in the heart and play pivotal roles in myocardial lipid metabolism, as well as glucose and energy homeostasis, and contribute to extra metabolic roles with effects on inflammation and oxidative stress. Moreover, regulation of PPARs may have significant effects on cardiac electrical activity and arrhythmogenesis. This review describes the roles of PPARs and their agonists in DM cardiomyopathy, inflammation, and cardiac electrophysiology.