Myocardial susceptibility to ischemic-reperfusion injury in a prediabetic model of dietary-induced obesity

Relationship of cardiac remodeling and perfusion alteration with hepatic lipid metabolism in a prediabetic high fat high sucrose diet female rat model

BACKGROUND AND AIMS

Cardiovascular disease (CVD) is known to be linked with metabolic associated fatty liver disease and type 2 diabetes, but few studies assessed this relationship in prediabetes, especially among women, who are at greater risk of CVD. We aimed to evaluate cardiac alterations and its relationship with hepatic lipid metabolism in prediabetic female rats submitted to high-fat-high-sucrose diet (HFS).

METHODS AND RESULTS

Wistar female rats were divided into 2 groups fed for 5 months with standard or HFS diet. We analyzed cardiac morphology, function, perfusion and fibrosis by Magnetic Resonance Imaging. Hepatic lipid contents along with inflammation and lipid metabolism gene expression were assessed. Five months of HFS diet induced glucose intolerance (p < 0.05), cardiac remodeling characterized by increased left-ventricular volume, wall thickness and mass (p < 0.05). No significant differences were found in left-ventricular ejection fraction and cardiac fibrosis but increased myocardial perfusion (p < 0.01) and reduced cardiac index (p < 0.05) were shown. HFS diet induced hepatic lipid accumulation with increased total lipid mass (p < 0.001) and triglyceride contents (p < 0.05), but also increased mitochondrial (CPT1a, MCAD; (p < 0.001; p < 0.05) and peroxisomal (ACO, LCAD; (p < 0.05; p < 0.001) β-oxidation gene expression. Myocardial wall thickness and perfusion were correlated with hepatic β-oxidation genes expression. Furthermore, myocardial perfusion was also correlated with hepatic lipid content and glucose intolerance.

CONCLUSION

This study brings new insights on the relationship between cardiac sub-clinical alterations and hepatic metabolism in female prediabetic rats. Further studies are warranted to explore its involvement in the higher CVD risk observed among prediabetic women.

Characterization and Comparison of the Divergent Metabolic Consequences of High-Sugar and High-Fat Diets in Male Wistar Rats

Diet-induced obesity (DIO) in laboratory rodents can serve as a model with which to study the pathophysiology of obesity, but obesogenic diets (high-sugar and/or high-fat) are often poorly characterised and simplistically aimed at inducing metabolic derangements for the purpose of testing the therapeutic capacity of natural products and other bioactive compounds. Consequently, our understanding of the divergent metabolic responses to different obesogenic diet formulations is limited. The aim of the present study was to characterise and compare differences in the metabolic responses induced by low-fat, medium-fat/high-sugar and high-fat diets in rats through multivariate statistical modelling. Young male Wistar rats were randomly assigned to CON (laboratory chow, low-fat), OB1 (high-sugar, medium-fat) or OB2 (high-fat) dietary groups (n = 24 each) for 17 weeks, after which metabolic responses were characterised. Projection-based multivariate analyses (principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA)) were used to explore the associations between measures of body composition and metabolism. Furthermore, we conducted a systematic literature survey to examine reporting trends in rat dietary intervention studies, and to determine how the metabolic responses observed in the present study compared to other recently published studies. The OB1 and OB2 dietary regimens resulted in distinct metabolic profiles, with OB1 characterised by perturbations in insulin homeostasis and adipose tissue secretory function, while OB2 was characterised by altered lipid and liver metabolism. This work therefore confirms, by means of direct comparison, that differences in dietary composition have a profound impact on metabolic and pathophysiological outcomes in rodent models of DIO. However, through our literature survey we demonstrate that dietary composition is not reported in the majority of rat dietary intervention studies, suggesting that the impact of dietary composition is often not considered during study design or data interpretation. This hampers the usefulness of such studies to provide enhanced mechanistic insights into DIO, and also limits the translatability of such studies within the context of human obesity.

Remodeling and Fibrosis of the Cardiac Muscle in the Course of Obesity-Pathogenesis and Involvement of the Extracellular Matrix

Obesity is a growing epidemiological problem, as two-thirds of the adult population are carrying excess weight. It is a risk factor for the development of cardiovascular diseases (hypertension, ischemic heart disease, myocardial infarct, and atrial fibrillation). It has also been shown that chronic obesity in people may be a cause for the development of heart failure with preserved ejection fraction (HFpEF), whose components include cellular hypertrophy, left ventricular diastolic dysfunction, and increased extracellular collagen deposition. Several animal models with induced obesity, via the administration of a high-fat diet, also developed increased heart fibrosis as a result of extracellular collagen accumulation. Excessive collagen deposition in the extracellular matrix (ECM) in the course of obesity may increase the stiffness of the myocardium and thereby deteriorate the heart diastolic function and facilitate the occurrence of HFpEF. In this review, we include a rationale for that process, including a discussion about possible putative factors (such as increased renin–angiotensin–aldosterone activity, sympathetic overdrive, hemodynamic alterations, hypoadiponectinemia, hyperleptinemia, and concomitant heart diseases). To address the topic clearly, we include a description of the fundamentals of ECM turnover, as well as a summary of studies assessing collagen deposition in obese individuals.

Stress-induced body weight loss and improvements in cardiometabolic risk factors do not translate to improved myocardial ischemic tolerance in western diet-fed mice

Although both diet-induced obesity and psychological stress are recognized as significant independent contributors to cardiometabolic and behavioral disorders, our understanding of how these two disorders interact and influence cardiometabolic risk and myocardial ischemic tolerance is limited. The aim of this study was to assess the combined effects of an obesogenic diet and psychological stress on cardiometabolic risk factors (body weight, dyslipidemia, insulin sensitivity) and postischemic cardiovascular outcomes. C57Bl/6J mice (n = 48) were subject to a combination of 22 weeks of western diet (WD) feeding and chronic restraint stress (CRS) for the last 4 weeks. Metabolic and behavioral changes were assessed using glucose tolerance tests and open field tests (OFTs), respectively. After 22 weeks, cardiac function and ischemic tolerance were assessed in Langendorff perfused hearts. WD feeding increased body weight and worsened blood lipids and insulin sensitivity. WD-fed mice also exhibited reduced exploratory behavior within the OFT. CRS reduced body weight and increased locomotion in both dietary groups and had differential effects on fasting glucose metabolism in the two dietary groups while not impacting non-fasting insulin. Although the WD only marginally reduced reperfusion left ventricular developed pressure recovery, CRS worsened reperfusion diastolic dysfunction in both dietary groups. Interestingly, despite WD+CRS animals exhibiting improved cardiometabolic parameters compared to the WD group, these changes did not translate to marked improvements to postischemic cardiac outcomes. In conclusion, in this study, combined WD feeding and CRS did not act synergistically to worsen cardiometabolic risk factors but instead improved them. Despite these cardiometabolic improvements, WD+CRS increased reperfusion end diastolic pressure which may be indicative of worsened ischemia/reperfusion injury.

Extracellular vesicle-based interorgan transport of mitochondria from energetically stressed adipocytes

Adipocytes undergo intense energetic stress in obesity resulting in loss of mitochondrial mass and function. We have found that adipocytes respond to mitochondrial stress by rapidly and robustly releasing small extracellular vesicles (sEVs). These sEVs contain respiration-competent, but oxidatively damaged mitochondrial particles, which enter circulation and are taken up by cardiomyocytes, where they trigger a burst of ROS. The result is compensatory antioxidant signaling in the heart that protects cardiomyocytes from acute oxidative stress, consistent with a preconditioning paradigm. As such, a single injection of sEVs from energetically stressed adipocytes limits cardiac ischemia/reperfusion injury in mice. This study provides the first description of functional mitochondrial transfer between tissues and the first vertebrate example of "inter-organ mitohormesis." Thus, these seemingly toxic adipocyte sEVs may provide a physiological avenue of potent cardio-protection against the inevitable lipotoxic or ischemic stresses elicited by obesity.

TAT delivery of a PTEN peptide inhibitor has direct cardioprotective effects and improves outcomes in rodent models of cardiac arrest

We have recently shown that pharmacologic inhibition of PTEN significantly increases cardiac arrest survival in a mouse model, however, this protection required pretreatment 30 min before the arrest. To improve the onset of PTEN inhibition during cardiac arrest treatment, we have designed a TAT fused cell-permeable peptide (TAT-PTEN9c) based on the C-terminal PDZ binding motif of PTEN for rapid tissue delivery and protection. Western blot analysis demonstrated that TAT-PTEN9c peptide significantly enhanced Akt activation in mouse cardiomyocytes in a concentration- and time-dependent manner. Mice were subjected to 8 min asystolic arrest followed by CPR, and 30 mice with successful CPR were then randomly assigned to receive either saline or TAT-PTEN9c treatment. Survival was significantly increased in TAT-PTEN9c-treated mice compared with that of saline control at 4 h after CPR. The treated mice had increased Akt phosphorylation at 30 min resuscitation with significantly decreased sorbitol content in heart or brain tissues and reduced release of taurine and glutamate in blood, suggesting improved glucose metabolism. In an isolated rat heart Langendorff model, direct effects of TAT-PTEN9c on cardiac function were measured for 20 min following 20 min global ischemia. Rate pressure product was reduced by >20% for both TAT vehicle and nontreatment groups following arrest. Cardiac contractile function was completely recovered with TAT-PTEN9c treatment given at the start of reperfusion. We conclude that TAT-PTEN9c enhances Akt activation and decreases glucose shunting to the polyol pathway in critical organs, thereby preventing osmotic injury and early cardiovascular collapse and death.NEW & NOTEWORTHY We have designed a cell-permeable peptide, TAT-PTEN9c, to improve cardiac arrest survival. It blocked endogenous PTEN binding to its adaptor and enhanced Akt signaling in mouse cardiomyocytes. It improved mouse survival after cardiac arrest, which is related to improved glucose metabolism and reduced glucose shunting to sorbitol in critical organs.

Influence of cardiometabolic comorbidities on myocardial function, infarction, and cardioprotection: Role of cardiac redox signaling

The morbidity and mortality from cardiovascular diseases (CVD) remain high. Metabolic diseases such as obesity, hyperlipidemia, diabetes mellitus (DM), non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) as well as hypertension are the most common comorbidities in patients with CVD. These comorbidities result in increased myocardial oxidative stress, mainly from increased activity of nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, mitochondria as well as downregulation of antioxidant defense systems. Oxidative and nitrosative stress play an important role in ischemia/reperfusion injury and may account for increased susceptibility of the myocardium to infarction and myocardial dysfunction in the presence of the comorbidities. Thus, while early reperfusion represents the most favorable therapeutic strategy to prevent ischemia/reperfusion injury, redox therapeutic strategies may provide additive benefits, especially in patients with heart failure. While oxidative and nitrosative stress are harmful, controlled release of reactive oxygen species is however important for cardioprotective signaling. In this review we summarize the current data on the effect of hypertension and major cardiometabolic comorbidities such as obesity, hyperlipidemia, DM, NAFLD/NASH on cardiac redox homeostasis as well as on ischemia/reperfusion injury and cardioprotection. We also review and discuss the therapeutic interventions that may restore the redox imbalance in the diseased myocardium in the presence of these comorbidities.

Synergistic effects of low-level stress and a Western diet on metabolic homeostasis, mood, and myocardial ischemic tolerance

How low-level psychological stress and overnutrition interact in influencing cardiometabolic disease is unclear. Mechanistic overlaps suggest potential synergies; however, findings are contradictory. We test whether low-level stress and Western diet (WD) feeding synergistically influence homeostasis, mood, and myocardial ischemic tolerance. Male C57BL6/J mice were fed a control diet or WD (32%/57%/11% calories from fat/carbohydrates/protein) for 12 wk, with subgroups restrained for 30 min/day over the final 3 wk. Metabolism, behavior, tolerance of perfused hearts to ischemia-reperfusion (I/R), and cardiac “death proteins” were assessed. The WD resulted in insignificant trends toward increased body weight (+5%), glucose (+40%), insulin (+40%), triglycerides (+15%), and cholesterol (+20%) and reduced leptin (−20%) while significantly reducing insulin sensitivity [100% rise in homeostasis model assessment of insulin resistance (HOMA-IR), P < 0.05]. Restraint did not independently influence metabolism while increasing HOMA-IR a further 50% (and resulting in significant elevations in insulin and glucose to 60–90% above control) in WD mice ( P < 0.05), despite blunting weight gain in control and WD mice. Anxiogenesis with restraint or WD was nonadditive, whereas anhedonia (reduced sucrose consumption) only arose with their combination. Neuroinflammation markers (hippocampal TNF-α, Il-1b) were unchanged. Myocardial I/R tolerance was unaltered with stress or WD alone, whereas the combination worsened dysfunction and oncosis [lactate dehydrogenase (LDH) efflux]. Apoptosis (nucleosome accumulation) and death protein expression (BAK, BAX, BCL-2, RIP-1, TNF-α, cleaved caspase-3, and PARP) were unchanged. We conclude that mild, anxiogenic yet cardio-metabolically “benign” stress interacts synergistically with a WD to disrupt homeostasis, promote anhedonia (independently of neuroinflammation), and impair myocardial ischemic tolerance (independently of apoptosis and death protein levels).

Diet-induced obese mouse hearts tolerate an acute high-fatty acid exposure that also increases ischemic tolerance

An ischemic insult is accompanied by an acute increase in circulating fatty acid (FA) levels, which can induce adverse changes related to cardiac metabolism/energetics. Although chronic hyperlipidemia contributes to the pathogenesis of obesity-/diabetes-related cardiomyopathy, it is unclear how these hearts are affected by an acute high FA-load. We hypothesize that adaptation to chronic FA exposure enhances the obese hearts' ability to handle an acute high FA-load. Diet-induced obese (DIO) and age-matched control (CON) mouse hearts were perfused in the presence of low- or high FA-load (0.4 and 1.8 mM, respectively). Left ventricular (LV) function, FA oxidation rate, myocardial oxygen consumption, and mechanical efficiency were assessed, followed by analysis of myocardial oxidative stress, mitochondrial respiration, protein acetylation, and gene expression. Finally, ischemic tolerance was determined by examining LV functional recovery and infarct size. Under low-FA conditions, DIO hearts showed mild LV dysfunction, oxygen wasting, mechanical inefficiency, and reduced mitochondrial OxPhos. High FA-load increased FA oxidation rates in both groups, but this did not alter any of the above parameters in DIO hearts. In contrast, CON hearts showed FA-induced mechanical inefficiency, oxidative stress, and reduced OxPhos, as well as enhanced acetylation and activation of PPARα-dependent gene expression. While high FA-load did not alter functional recovery and infarct size in CON hearts, it increased ischemic tolerance in DIO hearts. Thus, this study demonstrates that acute FA-load affects normal and obese hearts differently and that chronically elevated circulating FA levels render the DIO heart less vulnerable to the disadvantageous effects of an acute FA-load.NEW & NOTEWORTHY An acute myocardial fat-load leads to oxidative stress, oxygen wasting, mechanical inefficiency, hyperacetylation, and impaired mitochondrial function, which can contribute to reduced ischemic tolerance. Following obesity/insulin resistance, hearts were less affected by a high fat-load, which subsequently also improved ischemic tolerance. This study highlights that an acute fat-load affects normal and obese hearts differently and that obesity renders hearts less vulnerable to the disadvantageous effects of an acute fat-load.

Emerging Role of mTOR Signaling-Related miRNAs in Cardiovascular Diseases

Mechanistic/mammalian target of rapamycin (mTOR), an atypical serine/threonine kinase of the phosphoinositide 3-kinase- (PI3K-) related kinase family, elicits a vital role in diverse cellular processes, including cellular growth, proliferation, survival, protein synthesis, autophagy, and metabolism. In the cardiovascular system, the mTOR signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of both physiological and pathological processes. MicroRNAs (miRs), a class of short noncoding RNA, are an emerging intricate posttranscriptional modulator of critical gene expression for the development and maintenance of homeostasis across a wide array of tissues, including the cardiovascular system. Over the last decade, numerous studies have revealed an interplay between miRNAs and the mTOR signaling circuit in the different cardiovascular pathophysiology, like myocardial infarction, hypertrophy, fibrosis, heart failure, arrhythmia, inflammation, and atherosclerosis. In this review, we provide a comprehensive state of the current knowledge regarding the mechanisms of interactions between the mTOR signaling pathway and miRs. We have also highlighted the latest advances on mTOR-targeted therapy in clinical trials and the new perspective therapeutic strategies with mTOR-targeting miRs in cardiovascular diseases.

Pravastatin improves risk factors but not ischaemic tolerance in obese rats

Statins are effective in management of dyslipidaemia, and a cornerstone of CVD prevention strategies. However, the impacts of their pleiotropic effects on other cardiovascular risk factors and myocardial responses to infarction are not well characterised. We hypothesised that pravastatin treatment in obesity improves lipid profiles, insulin-resistance and myocardial resistance to ischaemia/reperfusion (I/R) injury. Wistar rats were fed a control (C) chow or high carbohydrate and fat diet (HCFD) for 16 weeks with vehicle or pravastatin (prava 7.5 mg/kg/day) treatment for 8 weeks. At 16 weeks HOMAs were performed, blood samples collected and hearts excised for Langendorff perfusions/biochemical analyses. Anti-oxidant activity and proteins regulating mitochondrial fission/fusion and apoptosis were assessed. The HCFD increased body weight (736±15 vs. 655±12 g for C; P<0.001), serum triglycerides (2.91±0.52 vs. 1.64±0.26 mmol/L for C; P<0.001) and insulin-resistance (HOMA- 6.9±0.8 vs. 4.2±0.5 for C; P<0.05) while prava prevented diet induced changes and paradoxically increased lipid peroxidation. The HCFD increased infarct size (34.1±3.1% vs. 18.8±3.0% of AAR for C; P<0.05), which was unchanged by prava in C and HCFD animals. The HCFD decreased cardiac TxR activity and mitochondrial MFN-1 and increased mitochondrial DRP-1 (reducing MFN-1:DRP-1 ratio) and Bax expression, with the latter changes prevented by prava. While unaltered by diet, cytosolic levels of Bax and caspase-3 were reduced by prava in C and HCFD hearts (without changes in cleaved caspase-3). We conclude that obesity, hyper-triglyceridemia and impaired glycemic control in HCFD rats are countered by prava. Despite improved risk factors, prava did not reduce myocardial infarct size, potentially reflecting its complex pleiotropic impacts on cardiac GPX activity and MFN-1, DRP-1, caspase-3 and Bcl-2 proteins.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

Review of a causal role of fructose-containing sugars in myocardial susceptibility to ischemia/reperfusion injury

In 2012, the World Health Organization Global Status Report on noncommunicable diseases showed that 7.4 million deaths were due to ischemic heart disease. Consequently, cardiovascular disease is a significant health burden, especially when partnered with comorbidities such as obesity, metabolic syndrome, and type 2 diabetes mellitus. Of note, these diseases can all be induced or exacerbated by diet. Carbohydrates, in particular, fructose and glucose, generally form the largest part of the human diet. Accumulating evidence from animal studies suggests that if large amounts of fructose are consumed either in isolation or in combination with glucose (fructose-containing sugars), myocardial susceptibility to ischemia/reperfusion (I/R) injury increases. However, the underlying mechanisms that predisposes the myocardium to I/R injury in the fructose model are not elucidated, and no single mechanistic pathway has been described. Based on all available data on this topic, this review describes previously investigated mechanisms and highlights 3 main mechanistic pathways whereby fructose has shown to increase myocardial susceptibility to I/R injury. These pathways include (1) increased reactive oxygen species, resulting in reduced nitric oxide synthase and coronary flow; (2) elevated plasma fatty acids and insulin, leading to increased cardiac triglyceride content and lipotoxicity; and (3) disrupted myocardial calcium handling/homeostasis. Moreover, we highlight various factors that should be taken into account when the fructose animal model is used, such as rat strain, treatment periods, and doses. We argue that failure to do so would result in erratic inferences drawn from the existing body of evidence on fructose animal models.

Reducing Caloric Intake Prevents Ischemic Injury and Myocardial Dysfunction and Affects Anesthetic Cardioprotection in Type 2 Diabetic Rats

Background. Type 2 diabetes mellitus (T2DM) increases the risk of myocardial ischemia, followed by increased perioperative risk of cardiovascular morbidity. We investigated whether reducing caloric intake reduces ischemic injury and myocardial dysfunction and affects the protective effects of the volatile anesthetic sevoflurane in diet-induced T2DM rats. Methods. Rats received a western (WD) or control diet (CD). Caloric intake was reduced by reversing WD-fed rats to CD. Myocardial function was determined with echocardiography. After 8 weeks of diet feeding, myocardial infarction was induced and the effect of sevoflurane was studied on myocardial function and ischemia/reperfusion injury. Results. WD-feeding resulted in a mild T2DM phenotype and myocardial dysfunction. Sevoflurane further impaired systolic function in WD-fed rats. Unexpectedly, WD-feeding reduced infarct size compared to CD-feeding. Sevoflurane reduced infarct size in CD-fed rats; however it enlarged infarct size in WD-fed rats. Caloric reduction restored myocardial dysfunction and the protective effect of sevoflurane against ischemia compared to WD-fed rats, whereas the protective effects of WD-feeding persisted. Conclusion. Caloric reduction restored the T2DM phenotype and myocardial function, while the cardioprotective properties of WD-feeding or sevoflurane persisted. Our data suggest that reducing caloric intake in T2DM might be a possible intervention to reduce perioperative risk of cardiovascular morbidity.

Diastolic dysfunction in prediabetic male rats: Role of mitochondrial oxidative stress

Although incidence and prevalence of prediabetes are increasing, little is known about its cardiac effects. Therefore, our aim was to investigate the effect of prediabetes on cardiac function and to characterize parameters and pathways associated with deteriorated cardiac performance. Long-Evans rats were fed with either control or high-fat chow for 21 wk and treated with a single low dose (20 mg/kg) of streptozotocin at week 4 High-fat and streptozotocin treatment induced prediabetes as characterized by slightly elevated fasting blood glucose, impaired glucose and insulin tolerance, increased visceral adipose tissue and plasma leptin levels, as well as sensory neuropathy. In prediabetic animals, a mild diastolic dysfunction was observed, the number of myocardial lipid droplets increased, and left ventricular mass and wall thickness were elevated; however, no molecular sign of fibrosis or cardiac hypertrophy was shown. In prediabetes, production of reactive oxygen species was elevated in subsarcolemmal mitochondria. Expression of mitofusin-2 was increased, while the phosphorylation of phospholamban and expression of Bcl-2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3, a marker of mitophagy) decreased. However, expression of other markers of cardiac auto- and mitophagy, mitochondrial dynamics, inflammation, heat shock proteins, Ca²⁺/calmodulin-dependent protein kinase II, mammalian target of rapamycin, or apoptotic pathways were unchanged in prediabetes. This is the first comprehensive analysis of cardiac effects of prediabetes indicating that mild diastolic dysfunction and cardiac hypertrophy are multifactorial phenomena that are associated with early changes in mitophagy, cardiac lipid accumulation, and elevated oxidative stress and that prediabetes-induced oxidative stress originates from the subsarcolemmal mitochondria.

Trenbolone Improves Cardiometabolic Risk Factors and Myocardial Tolerance to Ischemia-Reperfusion in Male Rats With Testosterone-Deficient Metabolic Syndrome

The increasing prevalence of obesity adds another dimension to the pathophysiology of testosterone (TEST) deficiency (TD) and potentially impairs the therapeutic efficacy of classical TEST replacement therapy. We investigated the therapeutic effects of selective androgen receptor modulation with trenbolone (TREN) in a model of TD with the metabolic syndrome (MetS). Male Wistar rats (n=50) were fed either a control standard rat chow (CTRL) or a high-fat/high-sucrose (HF/HS) diet. After 8 weeks of feeding, rats underwent sham surgery or an orchiectomy (ORX). Alzet miniosmotic pumps containing either vehicle, 2-mg/kg·d TEST or 2-mg/kg·d TREN were implanted in HF/HS+ORX rats. Body composition, fat distribution, lipid profile, and insulin sensitivity were assessed. Infarct size was quantified to assess myocardial damage after in vivo ischaemia reperfusion, before cardiac and prostate histology was performed. The HF/HS+ORX animals had increased sc and visceral adiposity; circulating triglycerides, cholesterol, and insulin; and myocardial damage, with low circulating TEST compared with CTRLs. Both TEST and TREN protected HF/HS+ORX animals against sc fat accumulation, hypercholesterolaemia, and myocardial damage. However, only TREN protected against visceral fat accumulation, hypertriglyceridaemia, and hyperinsulinaemia and reduced myocardial damage relative to CTRLs. TEST caused widespread cardiac fibrosis and prostate hyperplasia, which were less pronounced with TREN. We propose that TEST replacement therapy may have contraindications for males with TD and obesity-related MetS. TREN treatment may be more effective in restoring androgen status and reducing cardiovascular risk in males with TD and MetS.

A refined high carbohydrate diet is associated with changes in the serotonin pathway and visceral obesity

Consumption of palatable foods high in refined carbohydrate has been implicated as a contributing factor to the epidemic levels of obesity. Such foods may disrupt appetite regulation in the hypothalamus through alterations in hunger and satiety signalling. This investigation examined whether a palatable high refined carbohydrate (HRC) diet with the potential to induce obesity was linked to modulation of serotonin and dopamine signalling within the hypothalamus of rats. Male Wistar rats were allowed ad libitum access to either a palatable refined carbohydrate enriched (HRC) diet or standard chow (SC). Visceral fat percentage was used as a measure of the animals' weight gain during the trial. Real-time PCR was applied to determine any variation in levels of expression of the serotonin (Slc6A4 or Sert) and dopamine transporter (Slc6A3 or Dat) genes. After 29 weeks, the HRC group showed a significant increase in visceral fat percentage accompanied by increased expression of Sert. Higher levels of circulating triglycerides were also seen. This investigation determined that a refined high carbohydrate diet is associated with visceral obesity, increased circulating lipids in the blood and distorted serotonergic signalling, which possibly alters satiety and hunger signals.

Impact of Diet-Induced Obesity and Testosterone Deficiency on the Cardiovascular System: A Novel Rodent Model Representative of Males with Testosterone-Deficient Metabolic Syndrome (TDMetS)

INTRODUCTION

Current models of obesity utilise normogonadic animals and neglect the strong relationships between obesity-associated metabolic syndrome (MetS) and male testosterone deficiency (TD). The joint presentation of these conditions has complex implications for the cardiovascular system that are not well understood. We have characterised and investigated three models in male rats: one of diet-induced obesity with the MetS; a second using orchiectomised rats mimicking TD; and a third combining MetS with TD which we propose is representative of males with testosterone deficiency and the metabolic syndrome (TDMetS).

METHODS

Male Wistar rats (n = 24) were randomly assigned to two groups and provided ad libitum access to normal rat chow (CTRL) or a high fat/high sugar/low protein "obesogenic" diet (OGD) for 28 weeks (n = 12/group). These groups were further sub-divided into sham-operated or orchiectomised (ORX) animals to mimic hypogonadism, with and without diet-induced obesity (n = 6/group). Serum lipids, glucose, insulin and sex hormone concentrations were determined. Body composition, cardiovascular structure and function; and myocardial tolerance to ischemia-reperfusion were assessed.

RESULTS

OGD-fed animals had 72% greater fat mass; 2.4-fold greater serum cholesterol; 2.3-fold greater serum triglycerides and 3-fold greater fasting glucose (indicative of diabetes mellitus) compared to CTRLs (all p<0.05). The ORX animals had reduced serum testosterone and left ventricle mass (p<0.05). In addition to the combined differences observed in each of the isolated models, the OGD, ORX and OGD+ORX models each had greater CK-MB levels following in vivo cardiac ischemia-reperfusion insult compared to CTRLs (p<0.05).

CONCLUSION

Our findings provide evidence to support that the MetS and TD independently impair myocardial tolerance to ischemia-reperfusion. The combined OGD+ORX phenotype described in this study is a novel animal model with associated cardiovascular risk factors and complex myocardial pathology which may be representative of male patients presenting with TDMetS.

Obesity induced by high fat diet attenuates postinfarct myocardial remodeling and dysfunction in adult B6D2F1 mice

Obesity is a major risk factor for cardiovascular morbidity and mortality. However, some studies suggest that among patients with established cardiovascular disease, obesity is associated with better prognosis, a phenomenon described as the obesity paradox. In this study we tested the hypothesis that obesity with hyperinsulinemia and without hyperglycemia attenuates the impact of transient coronary occlusion on left ventricular remodeling and function. B6D2F1 mice from both genders fed with a high fat diet (HFD) or control diet for 6 months were subjected to 45 min of coronary occlusion and 28 days of reperfusion. Left ventricular dimensions and function were assessed by serial echocardiography, and infarct size was determined by Picrosirius red staining. HFD mice developed obesity with hypercholesterolemia and hyperinsulinemia in the absence of hyperglycemia or hypertension. During the period of feeding, no changes were observed in ventricular mass, volume or function, or in vascular reactivity. HFD attenuated the consequences of transient coronary occlusion as shown by a marked reduction in infarct size (51%, P = 0.021) and cardiac dilation, as well as improved left ventricular function as compared to control diet animals. These effects were associated with enhanced reperfusion injury salvage kinases (RISK) pathway function in HFD hearts shown as increased Akt and GSK3β phosphorylation. These results demonstrate that dietary obesity without hyperglycemia or hypertension attenuates the impact of ischemia/reperfusion injury in association with increased insulin signaling and RISK activation. This study provides experimental support to the controversial concept of the obesity paradox in humans.

Improvements in body composition, cardiometabolic risk factors and insulin sensitivity with trenbolone in normogonadic rats

Trenbolone (TREN) is used for anabolic growth-promotion in over 20 million cattle annually and continues to be misused for aesthetic purposes in humans. The current study investigated TREN's effects on body composition and cardiometabolic risk factors; and its tissue-selective effects on the cardiovascular system, liver and prostate. Male rats (n=12) were implanted with osmotic infusion pumps delivering either cyclodextrin vehicle (CTRL) or 2mg/kg/day TREN for 6 weeks. Dual-energy X-ray Absorptiometry assessment of body composition; organ wet weights and serum lipid profiles; and insulin sensitivity were assessed. Cardiac ultrasound examinations were performed before in vivo studies assessed myocardial susceptibility to ischemia-reperfusion (I/R) injury. Circulating sex hormones and liver enzyme activities; and prostate and liver histology were examined. In 6 weeks, fat mass increased by 34±7% in CTRLs (p<0.01). Fat mass decreased by 37±6% and lean mass increased by 11±4% with TREN (p<0.05). Serum triglycerides, HDL and LDL were reduced by 62%, 57% and 78% (p<0.05) respectively in TREN rats. Histological examination of the prostates from TREN-treated rats indicated benign hyperplasia associated with an increased prostate mass (149% compared to CTRLs, p<0.01). No evidence of adverse cardiac or hepatic effects was observed. In conclusion, improvements in body composition, lipid profile and insulin sensitivity (key risk factors for cardiometabolic disease) were achieved with six-week TREN treatment without evidence of adverse cardiovascular or hepatic effects that are commonly associated with traditional anabolic steroid misuse. Sex hormone suppression and benign prostate hyperplasia were confirmed as adverse effects of the treatment.

Short-term melatonin consumption protects the heart of obese rats independent of body weight change and visceral adiposity

Chronic melatonin treatment has been shown to prevent the harmful effects of diet-induced obesity and reduce myocardial susceptibility to ischaemia-reperfusion injury (IRI). However, the exact mechanism whereby it exerts its beneficial actions on the heart in obesity/insulin resistance remains unknown. Herein, we investigated the effects of relatively short-term melatonin treatment on the heart in a rat model of diet-induced obesity. Control and diet-induced obese Wistar rats (fed a high calorie diet for 20 wk) were each subdivided into three groups receiving drinking water with or without melatonin (4 mg/kg/day) for the last 6 or 3 wk of experimentation. A number of isolated hearts were perfused in the working mode, subjected to regional or global ischaemia-reperfusion; others were nonperfused. Metabolic parameters, myocardial infarct sizes (IFS), baseline and postischaemic activation of PKB/Akt, ERK42/44, GSK-3β and STAT-3 were determined. Diet-induced obesity caused increases in body weight gain, visceral adiposity, fasting blood glucose, serum insulin and triglyceride (TG) levels with a concomitant cardiac hypertrophy, large postischaemic myocardial IFSs and a reduced cardiac output. Melatonin treatment (3 and 6 wk) decreased serum insulin levels and the HOMA index (P < 0.05) with no effect on weight gain (after 3 wk), visceral adiposity, serum TG and glucose levels. It increased serum adiponectin levels, reduced myocardial IFSs in both groups and activated baseline myocardial STAT-3 and PKB/Akt, ERK42/44 and GSK-3β during reperfusion. Overall, short-term melatonin administration to obese/insulin resistant rats reduced insulin resistance and protected the heart against ex vivo myocardial IRI independently of body weight change and visceral adiposity.

Combined vildagliptin and metformin exert better cardioprotection than monotherapy against ischemia-reperfusion injury in obese-insulin resistant rats

BACKGROUND

Obese-insulin resistance caused by long-term high-fat diet (HFD) consumption is associated with left ventricular (LV) dysfunction and increased risk of myocardial infarction. Metformin and vildagliptin have been shown to exert cardioprotective effects. However, the effect of these drugs on the hearts under obese-insulin resistance with ischemia-reperfusion (I/R) injury is unclear. We hypothesized that combined vildagliptin and metformin provide better protective effects against I/R injury than monotherapy in obese-insulin resistant rats.

METHODOLOGY

Male Wistar rats were fed either HFD or normal diet. Rats in each diet group were divided into 4 subgroups to receive vildagliptin, metformin, combined vildagliptin and metformin, or saline for 21 days. Ischemia due to left anterior descending artery ligation was allowed for 30-min, followed by 120-min reperfusion. Metabolic parameters, heart rate variability (HRV), LV function, infarct size, mitochondrial function, calcium transient, Bax and Bcl-2, and Connexin 43 (Cx43) were determined. Rats developed insulin resistance after 12 weeks of HFD consumption. Vildagliptin, metformin, and combined drugs improved metabolic parameters, HRV, and LV function. During I/R, all treatments improved LV function, reduced infarct size and Bax, increased Bcl-2, and improved mitochondrial function in HFD rats. However, only combined drugs delayed the time to the first VT/VF onset, reduced arrhythmia score and mortality rate, and increased p-Cx43 in HFD rats.

CONCLUSION

Although both vildagliptin and metformin improved insulin resistance and attenuate myocardial injury caused by I/R, combined drugs provided better outcomes than single therapy by reducing arrhythmia score and mortality rate.

High carbohydrate and high fat diets protect the heart against ischaemia/reperfusion injury

Background

Although obesity is still considered a risk factor in the development of cardiovascular disorders, recent studies suggested that it may also be associated with reduced morbidity and mortality, the so-called “obesity paradox”. Experimental data on the impact of diabetes, obesity and insulin resistance on myocardial ischaemia/reperfusion injury are controversial. Similar conflicting data have been reported regarding the effects of ischaemic preconditioning on ischaemia/reperfusion injury in hearts from such animals. The aim of the present study was to evaluate the susceptibility to myocardial ischaemia/reperfusion damage in two models of diet-induced obesity as well as the effect of ischaemic and pharmacological preconditioning on such hearts.

Methods

Three groups of rats were fed with: (i) normal rat chow (controls) (ii) a sucrose-supplemented diet (DIO) (iii) a high fat diet (HFD). After 16 weeks, rats were sacrificed and isolated hearts perfused in the working mode and subjected to 35 min regional ischaemia/60 min reperfusion. Endpoints were infarct size and functional recovery. Infarct size was determined, using tetrazolium staining. Activation of PKB/Akt and ERKp44/p42 (RISK pathway) during early reperfusion was determined using Western blot. Statistical evaluation was done using ANOVA and the Bonferroni correction.

Results

Infarct sizes of non-preconditioned hearts from the two obese groups were significantly smaller than those of the age-matched controls. Ischaemic as well as pharmacological (beta-adrenergic) preconditioning with a beta2-adrenergic receptor agonist, formoterol, caused a significant reduction in infarct size of the controls, but were without effect on infarct size of hearts from the obese groups. However, ischaemic as well as beta-preconditioning caused an improvement in functional performance during reperfusion in all three groups. A clear-cut correlation between the reduction in infarct size and activation of ERKp44/p42 and PKB/Akt was not observed: The reduction in infarct size observed in the non-preconditioned hearts from the obese groups was not associated with activation of the RISK pathway. However, beta-adrenergic preconditioning caused a significant activation of ERKp44/p42, but not PKB/Akt, in all three groups.

Conclusions

Relatively long-term administration of the two obesity-inducing diets resulted in cardioprotection against ischaemia/reperfusion damage. Further protection by preconditioning was, however, without effect on infarct size, while an improvement in functional recovery was observed.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Myocardial structure, function and ischaemic tolerance in a rodent model of obesity with insulin resistance

Obesity and its comorbidities (dyslipidaemia, insulin resistance and hypertension) that together constitute the metabolic syndrome are all risk factors for ischaemic heart disease. Although obesity has been reported to be an independent risk factor for congestive heart failure, whether obesity-induced heart failure develops in the absence of increased afterload (induced by hypertension) is not clear. We have previously shown that obesity with insulin resistance decreases myocardial tolerance to ischaemia-reperfusion, but the mechanism for this decreased tolerance remains unclear. We hypothesize that obesity with insulin resistance induces adverse cardiac remodelling and pump dysfunction, as well as adverse changes in myocardial prosurvival reperfusion injury salvage kinase (RISK) pathway signalling to reduce myocardial tolerance to ischaemia-reperfusion. Wistar rats were fed an obesogenic (obese group) or a standard rat chow diet (control group) for 32 weeks. Echocardiography was performed over the 32 weeks before isolated Langendorff-perfused hearts were subjected to 40 min coronary artery ligation followed by reperfusion, and functional recovery (rate-pressure product), infarct size and RISK pathway function were assessed (Western blot analysis). Obesity with insulin resistance increased myocardial lipid accumulation but had no effect on in vivo or ex vivo left ventricular structure/function. Hearts from obese rats had lower reperfusion rate-pressure products (13115 ± 562 beats min(-1) mmHg for obese rats versus 17781 ± 1109 beats min(-1) mmHg for control rats, P < 0.05) and larger infarcts (36.3 ± 5.6% of area at risk in obese rats versus 14.1 ± 2.8% of area at risk in control rats, P < 0.01) compared with control hearts. These changes were associated with reductions in RISK pathway function, with 30-50 and 40-60% reductions in Akt and glycogen synthase kinase 3 beta (GSK-3β) expression and phosphorylation, respectively, in obese rat hearts compared with control hearts. Total endothelial nitric oxide synthase expression was reduced by 25% in obese rats. We conclude that obesity with insulin resistance had no effect on basal cardiac structure or function but decreased myocardial tolerance to ischaemia-reperfusion. This reduction in ischaemic tolerance was likely to be due to compromised RISK pathway function in obese, insulin-resistant animals.

Obesity improves myocardial ischaemic tolerance and RISK signalling in insulin-insensitive rats

Obesity with associated metabolic disturbances worsens ischaemic heart disease outcomes, and rodent studies confirm that obesity with insulin-resistance impairs myocardial resistance to ischemia-reperfusion (I-R) injury. However, the effects of obesity per se are unclear, with some evidence for paradoxic cardioprotection (particularly in older subjects). We tested the impact of dietary obesity on I-R tolerance and reperfusion injury salvage kinase (RISK) signalling in hearts from middle-aged (10 months old) insulin-insensitive rats. Hearts from Wistar rats on either a 32-week control (CD) or high carbohydrate obesogenic (OB) diet were assessed for I-R resistance in vivo (45 minutes left anterior descending artery occlusion and 120 minutes reperfusion) and ex vivo (25 minutes ischemia and 60 minutes reperfusion). Expression and δ-opioid receptor (δ-OR) phospho-regulation of pro-survival (Akt/PKB, Erk1/2, eNOS) and pro-injury (GSK3β) enzymes were also examined. OB rats were heavier (764±25 versus 657±22 g for CD; P<0.05), hyperleptinaemic (11.1±0.7 versus 5.0±0.7 for CD; P<0.01) and comparably insulin-insensitive (HOMA-IR of 63.2±3.3 versus 63.2±1.6 for CD). In vivo infarction was more than halved in OB (20±3%) versus CD rats (45±6% P<0.05), as was post-ischaemic lactate dehydrogenase efflux (0.4±0.3 mU/ml versus 5.6±0.5 mU/ml; P<0.02) and ex vivo contractile dysfunction (62±2% versus 44±6% recovery of ventricular force; P<0.05). OB hearts exhibited up to 60% higher Akt expression, with increased phosphorylation of eNOS (+100%), GSK3β (+45%) and Erk1/2 (+15%). Pre-ischaemic δ-OR agonism with BW373U86 improved recoveries in CD hearts in association with phosphorylation of Akt (+40%), eNOS (+75%) and GSK3β (+30%), yet failed to further enhance RISK-NOS activation or I-R outcomes in OB hearts. In summary, dietary obesity in the context of age-related insulin-insensitivity paradoxically improves myocardial I-R tolerance, in association with moderate hyperleptinaemic and enhanced RISK expression and phospho-regulation. However, OB hearts are resistant to further RISK modulation and cardioprotection via acute δ-OR agonism.

Effect of chronic CPT-1 inhibition on myocardial ischemia-reperfusion injury (I/R) in a model of diet-induced obesity

PURPOSE

By increasing circulating free fatty acids and the rate of fatty acid oxidation, obesity decreases glucose oxidation and myocardial tolerance to ischemia. Partial inhibition of fatty acid oxidation may improve myocardial tolerance to ischemia/reperfusion (I/R) in obesity. We assessed the effects of oxfenicine treatment on post ischemic cardiac function and myocardial infarct size in obese rats.

METHODS

Male Wistar rats were fed a control diet or a high calorie diet which resulted in diet induced obesity (DIO) for 16 weeks. Oxfenicine (200 mg/kg/day) was administered to control and DIO rats for the last 8 weeks. Isolated hearts were perfused and infarct size and post ischemic cardiac function was assessed after regional or global ischemia and reperfusion. Cardiac mitochondrial function was assessed and myocardial expression and activity of CPT-1 (carnitine palmitoyl transferase-1) and IRS-1 (insulin receptor substrate-1) was assessed using Western blot analysis.

RESULTS

In the DIO rats, chronic oxfenicine treatment improved post ischemic cardiac function and reduced myocardial infarct size after I/R but had no effect on the cardiac mitochondrial respiration. Chronic oxfenicine treatment worsened post ischemic cardiac function, myocardial infarct size and basal mitochondrial respiration in control rat hearts. Basal respiratory control index (RCI) values, state 2 and state 4 respiration rates and ADP phosphorylation rates were compromised by oxfenicine treatment.

CONCLUSION

Chronic oxfenicine treatment improved myocardial tolerance to I/R in the obese rat hearts but decreased myocardial tolerance to I/R in control rat hearts. This decreased tolerance to ischemia of oxfenicine treated controls was associated with adverse changes in basal and reoxygenation mitochondrial function. These changes were absent in oxfenicine treated hearts from obese rats.

Rheb is a critical regulator of autophagy during myocardial ischemia: pathophysiological implications in obesity and metabolic syndrome

BACKGROUND

Rheb is a GTP-binding protein that promotes cell survival and mediates the cellular response to energy deprivation (ED). The role of Rheb in the regulation of cell survival during ED has not been investigated in the heart.

METHODS AND RESULTS

Rheb is inactivated during cardiomyocyte (CM) glucose deprivation (GD) in vitro, and during acute myocardial ischemia in vivo. Rheb inhibition causes mTORC1 inhibition, because forced activation of Rheb, through Rheb overexpression in vitro and through inducible cardiac-specific Rheb overexpression in vivo, restored mTORC1 activity. Restoration of mTORC1 activity reduced CM survival during GD and increased infarct size after ischemia, both of which were accompanied by inhibition of autophagy, whereas Rheb knockdown increased autophagy and CM survival. Rheb inhibits autophagy mostly through Atg7 depletion. Restoration of autophagy, through Atg7 reexpression and inhibition of mTORC1, increased cellular ATP content and reduced endoplasmic reticulum stress, thereby reducing CM death induced by Rheb activation. Mice with high-fat diet-induced obesity and metabolic syndrome (HFD mice) exhibited deregulated cardiac activation of Rheb and mTORC1, particularly during ischemia. HFD mice presented inhibition of cardiac autophagy and displayed increased ischemic injury. Pharmacological and genetic inhibition of mTORC1 restored autophagy and abrogated the increase in infarct size observed in HFD mice, but they failed to protect HFD mice in the presence of genetic disruption of autophagy.

CONCLUSIONS

Inactivation of Rheb protects CMs during ED through activation of autophagy. Rheb and mTORC1 may represent therapeutic targets to reduce myocardial damage during ischemia, particularly in obese patients.

Depot-specific and hypercaloric diet-induced effects on the osteoblast and adipocyte differentiation potential of adipose-derived stromal cells

Adipose-derived stromal cells (ADSCs) can be differentiated in vitro into several mesenchyme-derived cell types. We had previously described depot-specific differences in the adipocyte differentiation of ADSCs, and consequently we hypothesized that there may also be depot-specific differences in osteoblast differentiation of ADSCs. For this study, the osteoblast differentiation potential of rat subcutaneous ADSCs (scADSCs) and perirenal visceral ADSCs (pvADSCs) was compared. Osteoblast differentiation media (OM) induced markers of the osteoblastic phenotype in scADSCs, but not in pvADSCs. ADSCs harvested from rats with diet-induced visceral obesity (DIO) exhibited reduced osteoinduction, compared to lean controls, but adipocyte differentiation was not affected. Expression of the pro-osteogenic transcription factor Msx2 was significantly higher in naïve scADSCs from lean and DIO rats than in pvADSCs. Our findings indicate that ADSCs from different anatomical sites are uniquely pre-programmed in vivo in a depot-specific manner, and that diet-induced metabolic disturbances translate into reduced osteoblast differentiation of ADSCs.

The Effects of Gender and Obesity on Myocardial Tolerance to Ischemia

Obesity is increasing at an alarming rate globally. Several studies have shown that premenopausal women have a reduced risk of CV disease and a reduced myocardial susceptibility to ischemia/reperfusion injury. The effect of obesity on myocardial tolerance to ischemia in women has not been established. To determine how obesity affects myocardial susceptibility to ischemia/reperfusion injury in both males and females, we fed male and female Wistar rats a high caloric diet (HCD) or a control rat chow diet (CD) for 18 weeks. Rats were subsequently fasted overnight, anesthetized and blood was collected. In separate experiments, 18-week-fed (HCD and CD) rats underwent 45 min in vivo coronary artery ligation (CAL) followed by 2 hours reperfusion. Hearts were stained with TTC and infarct size determined. Both male and female HCD fed rats had increased body and visceral fat weights. Homeostasis model assessment (HOMA) index values were 13.95±3.04 for CD and 33.58±9.39 for HCD male rats (p<0.01) and 2.98±0.64 for CD and 2.99±0.72 for HCD fed female rats. Male HCD fed rats had larger infarct sizes than CD fed littermates (43.2±9.3 % vs. 24.4±7.6 %, p<0.05). Female HCD and CD diet fed rats had comparable infarct sizes (31.8±4.3 % vs. 23.9±3.3 %). We conclude that male rats on the HCD became viscerally obese, dyslipidemic and insulin-resistant, while female HCD fed rats became viscerally obese without developing dyslipidemia or insulin resistance. Obesity increased myocardial infarct size in males but not the females.

Chronic melatonin consumption prevents obesity-related metabolic abnormalities and protects the heart against myocardial ischemia and reperfusion injury in a prediabetic model of diet-induced obesity

Obesity, a major risk factor for ischemic heart disease, is associated with increased oxidative stress and reduced antioxidant status. Melatonin, a potent free radical scavenger and antioxidant, has powerful cardioprotective effects in lean animals but its efficacy in obesity is unknown. We investigated the effects of chronic melatonin administration on the development of the metabolic syndrome as well as ischemia-reperfusion injury in a rat model of diet-induced obesity (DIO). Male Wistar rats received a control diet, a control diet with melatonin, a high-calorie diet, or a high-calorie diet with melatonin (DM). Melatonin (4 mg/kg/day) was administered in the drinking water. After 16 wk, biometric and blood metabolic parameters were measured. Hearts were perfused ex vivo for the evaluation of myocardial function, infarct size (IFS) and biochemical changes [activation of PKB/Akt, ERK, p38 MAPK, AMPK, and glucose transporter (GLUT)-4 expression). The high-calorie diet caused increases in body weight (BW), visceral adiposity, serum insulin and triglycerides (TRIG), with no change in glucose levels. Melatonin treatment reduced the BW gain, visceral adiposity, blood TRIG, serum insulin, homeostatic model assessment index and thiobarbituric acid reactive substances in the DIO group. Melatonin reduced IFS in DIO and control groups and increased percentage recovery of functional performance of DIO hearts. During reperfusion, hearts from melatonin-treated rats had increased activation of PKB/Akt, ERK42/44 and reduced p38 MAPK activation. Chronic melatonin treatment prevented the metabolic abnormalities induced by DIO and protected the heart against ischemia-reperfusion injury. These beneficial effects were associated with activation of the reperfusion injury salvage kinases pathway.

Diet-induced obesity alters signalling pathways and induces atrophy and apoptosis in skeletal muscle in a prediabetic rat model

Pro-inflammatory and stress-activated signalling pathways are important role players in the pathogenesis of obesity and insulin resistance. Obesity and type II diabetes are associated with chronic, low-grade inflammation and elevated tumour necrosis factor-α (TNF-α) levels. There is increasing evidence that TNF-α may play a critical role in skeletal muscle atrophy. However, the effects of obesity-induced insulin resistance on these signalling pathways are poorly understood in skeletal muscle. Therefore, the present study addressed the effects of obesity-induced insulin resistance on the activity of the ubiquitin ligases, nuclear factor-B, p38 MAPK and phosphoinositide 3-kinase signalling pathways in the gastrocnemius muscle and compared these with muscle of standard chow-fed control rats. Male Wistar rats were randomly allocated to a control diet group (standard commercial chow; 60% carbohydrates, 30% protein and 10% fat) or a cafeteria diet group (65% carbohydrates, 19% protein and 16% fat) for 16 weeks. Blood analysis was conducted to determine the impact of the model of obesity on circulating insulin, glucose, free fatty acids, TNF-α and angiotensin II concentrations. The experimental animals were 18% heavier and had 68% greater visceral fat mass than their control counterparts and were dyslipidaemic. Significant increases in the ubiquitin ligase and MuRF-1, as well as in caspase-3 and poly-ADP-ribose polymerase cleavage were observed in the muscle of obese animals compared with the control rats. We propose that dyslipidaemia may be a mechanism for the activation of inflammatory/stress-activated signalling pathways in obesity and type II diabetes, which will lead to apoptosis and atrophy in skeletal muscle.

A high-fat diet increases risk of ventricular arrhythmia in female rats: enhanced arrhythmic risk in the absence of obesity or hyperlipidemia

Obesity increases the incidence of cardiac arrhythmias and impairs wound healing. However, it is presently unknown whether a high-fat diet affects arrhythmic risk or wound healing before the onset of overt obesity or hyperlipidemia. After 8 wk of feeding a high-fat diet to adult female rats, a nonsignificant increase in body weight was observed and associated with a normal plasma lipid profile. Following ischemia/reperfusion injury, scar length (standard diet 0.29 +/- 0.09 vs. high-fat 0.32 +/- 0.13 cm), thickness (standard diet 0.047 +/- 0.02 vs. high-fat 0.059 +/- 0.01 cm), and collagen alpha(1) type 1 content (standard diet 0.21 +/- 0.04 vs. high-fat 0.20 +/- 0.04 arbitrary units/mm(2)) of infarcted hearts were not altered by the high-fat diet. However, the mortality rate was greatly increased 24 h postinfarction (from 5% to 46%, P < 0.01 for ischemia/reperfusion rats; from 20% to 89%, P < 0.0001, in complete-occlusion rats) in high-fat fed rats, in association with a higher prevalence of ventricular arrhythmias. Ventricular arrhythmia inducibility was also significantly increased in noninfarcted rats fed a high-fat diet. In the hearts of rats fed a high-fat diet, connexin-40 expression was absent, connexin-43 was hypophosphorylated and lateralized, and neurofilament-M immunoreactive fiber density (standard diet 2,020 +/- 260 vs. high-fat diet 2,830 +/- 250 microm(2)/mm(2)) and tyrosine hydroxylase protein expression were increased (P < 0.05). Thus, in the absence of overt obesity and hyperlipidemia, sympathetic hyperinnervation and an aberrant pattern of gap junctional protein expression and regulation in the heart of female rats fed a high-fat diet may have contributed in part to the higher incidence of inducible cardiac arrhythmias.

Impaired contractile function and mitochondrial respiratory capacity in response to oxygen deprivation in a rat model of pre-diabetes

AIM

Obesity is a major contributor to the global burden of disease and is closely associated with the development of type 2 diabetes and cardiovascular diseases. This study tested the hypothesis that mitochondrial respiratory capacity of the pre-diabetic heart is decreased leading to impaired contractile function and tolerance to ischaemia/reperfusion.

METHODS

Eight-week-old male Wistar rats were fed a high caloric diet for 16 weeks after which anthropometric, metabolic, cardiac and mitochondrial parameters were evaluated vs. age-matched lean controls. Cardiac function (working heart perfusions) and mitochondrial respiratory capacity were assessed at baseline and in response to acute oxygen deprivation.

RESULTS

Rats fed the high caloric diet exhibited increased body weight and visceral fat vs. the control group. Heart weights of obese rats were also increased. Triglyceride, fasting plasma insulin and free fatty acid levels were elevated, while high-density lipoprotein cholesterol levels were reduced in the obese group. Contractile function was attenuated at baseline and further decreased after subjecting hearts to ischaemia-reperfusion. Myocardial infarct sizes were increased while ADP phosphorylation rates were diminished in obese rats. However, no differences were found for mtDNA levels and the degree of oxidative stress-induced damage.

CONCLUSIONS

These data show that decreased mitochondrial bioenergetic capacity in pre-diabetic rat hearts may impair respiratory capacity and reduce basal contractile function and tolerance to acute oxygen deprivation.

Evaluation of the relationship between hyperinsulinaemia and myocardial ischaemia/reperfusion injury in a rat model of depression

Major depression is associated with medical co-morbidity, such as ischaemic heart disease and diabetes, but the underlying pathophysiological mechanisms remain unclear. The FSL (Flinders Sensitive Line) rat is a genetic animal model of depression exhibiting features similar to those of depressed individuals. The aim of the present study was to compare the myocardial responsiveness to I/R (ischaemia/reperfusion) injury and the effects of IPC (ischaemic preconditioning) in hearts from FSL rats using SD (Sprague-Dawley) rats as controls and to characterize differences in glucose metabolism and insulin sensitivity between FSL and SD rats. Hearts were perfused in a Langendorff model and were subjected or not to IPC before 40 min of global ischaemia, followed by 120 min of reperfusion. Myocardial infarct size was found to be significantly larger in the FSL rats than in the SD rats following I/R injury (62.4+/-4.2 compared with 46.9+/-2.9%; P<0.05). IPC reduced the infarct size (P<0.01) and improved haemodynamic function (P<0.01) in both FSL and SD rats. No significant difference was found in blood glucose levels between the two groups measured after 12 h of fasting, but fasting plasma insulin (70.1+/-8.9 compared with 40.9+/-4.7 pmol/l; P<0.05) and the HOMA (homoeostatic model assessment) index (P<0.01) were significantly higher in FSL rats compared with SD rats. In conclusion, FSL rats had larger infarct sizes following I/R injury and were found to be hyperinsulinaemic compared with SD rats, but appeared to have a maintained cardioprotective mechanism against I/R injury, as IPC reduced infarct size in these rats. This animal model may be useful in future studies when examining the mechanisms that contribute to the cardiovascular complications associated with depression.

Dietary-induced obesity hastens the progression from concentric cardiac hypertrophy to pump dysfunction in spontaneously hypertensive rats

We explored whether dietary-induced obesity hastens the transition from concentric left ventricular (LV) hypertrophy to pump dysfunction in spontaneously hypertensive rats (SHRs) and the mechanisms thereof. After feeding rats a diet for 4 to 5 months, obesity was induced in SHRs and Wistar-Kyoto (WKY) control rats. Obesity was not associated with abnormal blood glucose control (glycosylated hemoglobin) or with increases in systolic blood pressure. However, in SHRs, but not in WKY rats, obesity was associated with a reduced LV chamber systolic function, as determined by echocardiography, and in isolated perfused heart studies. A marked increase in LV end diastolic diameter and a right shift in the LV diastolic pressure-volume relation were noted in obese SHRs but not in obese WKY rats. Moreover, LV intrinsic myocardial systolic function, as determined from the slope of the linearized LV systolic stress-strain relationship (LV myocardial end systolic elastance), was markedly reduced in obese as compared with lean SHRs, whereas LV myocardial end systolic elastance was maintained in obese WKY rats. Obesity increased LV weight, cardiomyocyte width, cardiomyocyte apoptosis (TUNEL), the activity of myocardial matrix metalloproteinases (zymography), and serum leptin concentrations in SHRs but not in WKY rats. In conclusion, SHRs are susceptible to the adverse effects of dietary-induced obesity on the heart, an effect that hastens the progression from concentric LV hypertrophy to pump dysfunction independent of blood pressure changes or alterations in glycosylated hemoglobin. This effect may be mediated through a proclivity of SHRs to developing both obesity-induced effects on cardiomyocyte apoptosis and activation of myocardial collagenases through leptin resistance and obesity-induced hypertrophy.

Developmental programming resulting from maternal obesity in mice: effects on myocardial ischaemia-reperfusion injury

A comprehensive number of epidemiological and animal studies suggest that prenatal and early life events are important determinants for disorders later in life. Among them, prenatal stress (i.e. stress experienced by the pregnant mother with impact on the fetal ontogeny) has clear programming effects on the cardiovascular system. A fetus developing in adverse conditions becomes an adult who is susceptible to disease, which may include hypertension, insulin resistance, altered blood lipid levels and cardiovascular disease. Recent evidence demonstrates that maternal programming can occur in the absence of other adverse environmental factors. Obesity, which is becoming a problem of large proportions in Western countries, is a possible cause of programming. With over 30% of the population of the USA currently obese, many mothers suffer from obesity during their child-bearing years (in fact, these conditions are often aggravated during pregnancy). One of the targets of programming is the cardiovascular system, and reported consequences include hypertension, endothelial dysfunction and vascular abnormalities. The overall goal of our study was to investigate the susceptibility of the heart to ischaemia-reperfusion in an animal model of maternal obesity. Our data demonstrate that normal (non-mutant) offspring from obese agouti mouse dams had an increased susceptibility to ischaemia-reperfusion injury. These data may provide insights into the long-term cardiovascular consequences of programming.

Myocardial ischemic postconditioning against ischemia-reperfusion is impaired in ob/ob mice

Ischemic postconditioning (IPCD) significantly reduces infarct size in healthy animals and protects the human heart. Because obesity is a major risk factor of cardiovascular diseases, the effects of IPCD were investigated in 8- to 10-wk-old leptin-deficient obese (ob/ob) mice and compared with wild-type C57BL/6J (WT) mice. All animals underwent 30 min of coronary artery occlusion followed by 24 h of reperfusion associated or not with IPCD (6 cycles of 10-s occlusion, 10-s reperfusion). Additional mice were killed at 10 min of reperfusion for Western blotting. IPCD reduced infarct size by 58% in WT mice (33+/-1% vs. 14+/-3% for control and IPCD, respectively, P<0.05) but failed to induce cardioprotection in ob/ob mice (53+/-4% vs. 56+/-5% for control and IPCD, respectively). In WT mice, IPCD significantly increased the phosphorylation of Akt (+77%), ERK1/2 (+41%), and their common target p70S6K1 (+153% at Thr389 and +57% at Thr421/Ser424). In addition, the phosphorylated AMP-activated protein kinase (AMPK)-to-total AMPK ratio was also increased by IPCD in WT mice (+64%, P<0.05). This was accompanied by decreases in phosphatase and tensin homolog deleted on chromosome 10 (PTEN), MAP kinase phosphatase (MKP)-3, and protein phosphatase (PP)2C levels. In contrast, IPCD failed to increase the phosphorylation state of all these kinases in ob/ob mice, and the level of the three phosphatases was significantly increased. Thus, although IPCD reduces myocardial infarct size in healthy animals, its cardioprotective effect vanishes with obesity. The lack of enhanced phosphorylation by IPCD of Akt, ERK1/2, p70S6K1, and AMPK might partly explain the loss of cardioprotection in this experimental model of obese mice.