High-fat diet postinfarction enhances mitochondrial function and does not exacerbate left ventricular dysfunction

Circulating sphingolipids in heart failure

Lack of significant advancements in early detection and treatment of heart failure have precipitated the need for discovery of novel biomarkers and therapeutic targets. Over the past decade, circulating sphingolipids have elicited promising results as biomarkers that premonish adverse cardiac events. Additionally, compelling evidence directly ties sphingolipids to these events in patients with incident heart failure. This review aims to summarize the current literature on circulating sphingolipids in both human cohorts and animal models of heart failure. The goal is to provide direction and focus for future mechanistic studies in heart failure, as well as pave the way for the development of new sphingolipid biomarkers.

Ketogenic Diet and Ketone Bodies against Ischemic Injury: Targets, Mechanisms, and Therapeutic Potential

The ketogenic diet (KD) has been used as a treatment for epilepsy since the 1920s, and its role in the prevention of many other diseases is now being considered. In recent years, there has been an intensive investigation on using the KD as a therapeutic approach to treat acute pathologies, including ischemic ones. However, contradictory data are observed for the effects of the KD on various organs after ischemic injury. In this review, we provide the first systematic analysis of studies conducted from 1980 to 2022 investigating the effects and main mechanisms of the KD and its mimetics on ischemia-reperfusion injury of the brain, heart, kidneys, liver, gut, and eyes. Our analysis demonstrated a high diversity of both the composition of the used KD and the protocols for the treatment of animals, which could be the reason for contradictory effects in different studies. It can be concluded that a true KD or its mimetics, such as β-hydroxybutyrate, can be considered as positive exposure, protecting the organ from ischemia and its negative consequences, whereas the shift to a rather similar high-calorie or high-fat diet leads to the opposite effect.

Nutrition in chronic heart failure patients: a systematic review

Nutrition is the primary source of energy production for myocardial contractility and to maintaining cardiac efficiency. Although many studies provided evidence of the benefits of nutritional intervention in chronic heart failure patients (CHF), these effects are not still completely understood. We searched in PubMed and Embase articles related to the following keywords: "chronic heart failure" with "diet," "nutrition," "insulin resistance," and "caloric restriction." Of the 975 retrieved articles, 20 have been selected. The primary endpoint was the left ventricular (LV) function and the secondary mortality rate in HF patients. Some studies showed that the Mediterranean diet (MedDiet) had a beneficial effect on cardiac function, while others did not find any positive impact. Nutritional supplements and hypercaloric intake had positive effects on underweight HF patients, while hypocaloric diet was beneficial in obese HF patients improving glucose control and cardiac function. The effect of MedDiet in HF patients showed conflicting results. Changes in the dietary pattern can reduce the evolution of HF, considering not only the quality of food but also the caloric intake. The discriminant factor to prescribe a diet regime in HF patients is represented by body mass index (BMI). A well-balanced caloric diet represents an effective therapy in overweight HF patients to reduce the mortality rate. Long-term studies evaluating cause-effect of energy and macronutrients intake on cardiac function in HF patients are necessary.

Short-term but not long-term high fat diet feeding protects against pressure overload-induced heart failure through activation of mitophagy

AIMS

Recent studies have shown that enhancement of fatty acid utilization through feeding animals a high fat diet (HFD) attenuated cardiac dysfunction in heart failure (HF). Here, we aimed to examine the temporal effects of HFD feeding on cardiac function in mice with heart failure and its underlying mechanism.

MAIN METHODS

Pressure overload-induced HF was established via transverse aortic constriction (TAC) surgery. After surgery, the mice were fed on either normal diet or HFD for 8 or 16 weeks.

KEY FINDINGS

HFD feeding exerted opposite effects on cardiac function at different time points post-surgery. Short-term HFD feeding (8 wk) protected the heart against pressure overload, inhibiting cardiac hypertrophy and improving cardiac function, while long-term HFD feeding (16 wk) aggravated cardiac dysfunction in TAC mice. Short-term HFD feeding elevated cardiac fatty acid utilization, while long-term HFD feeding showed no significant effects on cardiac fatty acid utilization in TAC mice. Specifically, an increase in cardiac fatty acid utilization was accompanied with activated mitophagy and improved mitochondrial function. Palmitic acid treatment (400 μM, 2 h) stimulated fatty acid oxidation and mitophagy in neonatal myocytes. Mechanistically, fatty acid utilization stimulated mitophagy through upregulation of Parkin. Cardiac-specific knockdown of Parkin abolished the protective effects of short-term HFD feeding on cardiac function in TAC mice.

SIGNIFICANCES

These results suggested that short-term but not long-term HFD feeding protects against pressure overload-induced heart failure through activation of mitophagy, and dietary fat intake should be used with caution in treatment of heart failure.

High-fat diet affects skeletal muscle mitochondria comparable to pressure overload-induced heart failure

In heart failure, high-fat diet (HFD) may exert beneficial effects on cardiac mitochondria and contractility. Skeletal muscle mitochondrial dysfunction in heart failure is associated with myopathy. However, it is not clear if HFD affects skeletal muscle mitochondria in heart failure as well. To induce heart failure, we used pressure overload (PO) in rats fed normal chow or HFD. Interfibrillar mitochondria (IFM) and subsarcolemmal mitochondria (SSM) from gastrocnemius were isolated and functionally characterized. With PO heart failure, maximal respiratory capacity was impaired in IFM but increased in SSM of gastrocnemius. Unexpectedly, HFD affected mitochondria comparably to PO. In combination, PO and HFD showed additive effects on mitochondrial subpopulations which were reflected by isolated complex activities. While PO impaired diastolic as well as systolic cardiac function and increased glucose tolerance, HFD did not affect cardiac function but decreased glucose tolerance. We conclude that HFD and PO heart failure have comparable effects leading to more severe impairment of IFM. Glucose tolerance seems not causally related to skeletal muscle mitochondrial dysfunction. The additive effects of HFD and PO may suggest accelerated skeletal muscle mitochondrial dysfunction when heart failure is accompanied with a diet containing high fat.

Trimetazidine inhibits cardiac fibrosis by reducing reactive oxygen species and downregulating connective tissue growth factor in streptozotocin-induced diabetic rats

Diabetes may affect myocardial fibrosis through oxidative stress. Trimetazidine (TMZ) is an anti-anginal agent. The present study aimed to determine the modulatory effect of TMZ on reactive oxygen species (ROS) and connective tissue growth factor (CTGF) expression and to evaluate the potential of TMZ to improve diastolic function in streptozotocin (STZ)-induced diabetic rats. After treating STZ-induced diabetic rats with TMZ for 16 weeks, a decrease in malondialdehyde levels, cardiac collagen volume fraction, left ventricular (LV) end-diastolic pressure and protein expression of collagen-I (Col I), Col III and CTGF compared with those in diabetic control rats was observed. In vitro, TMZ inhibited Col I, Col III and CTGF protein expression in cardiac fibroblasts treated with high glucose and decreased intracellular ROS generation and hydroxyproline content in the cell culture medium of cardiac fibroblasts. TMZ markedly improved cardiac fibrosis and diastolic function in diabetic rats. This effect was associated with a reduction in ROS production and CTGF expression in cardiac fibroblasts. The present study suggests that TMZ may be beneficial for protecting the hearts of diabetic patients.

Enhancing fatty acid utilization ameliorates mitochondrial fragmentation and cardiac dysfunction via rebalancing optic atrophy 1 processing in the failing heart

AIMS

Heart failure (HF) is characterized by reduced fatty acid (FA) utilization associated with mitochondrial dysfunction. Recent evidence has shown that enhancing FA utilization may provide cardioprotection against HF. Our aim was to investigate the effects and the underlying mechanisms of cardiac FA utilization on cardiac function in response to pressure overload.

METHODS AND RESULTS

Transverse aortic constriction (TAC) was used in C57 mice to establish pressure overload-induced HF. TAC mice fed on a high fat diet (HFD) exhibited increased cardiac FA utilization and improved cardiac function and survival compared with those on control diet. Such cardioprotection could also be provided by cardiac-specific overexpression of CD36. Notably, both HFD and CD36 overexpression attenuated mitochondrial fragmentation and improved mitochondrial function in the failing heart. Pressure overload decreased ATP-dependent metalloprotease (YME1L) expression and induced the proteolytic cleavage of the dynamin-like guanosine triphosphatase OPA1 as a result of suppressed FA utilization. Enhancing FA utilization upregulated YME1L expression and subsequently rebalanced OPA1 processing, resulting in restoration of mitochondrial morphology in the failing heart. In addition, cardiac-specific overexpression of YME1L exerted similar cardioprotective effects against HF to those provided by HFD or CD36 overexpression.

CONCLUSIONS

These findings demonstrate that enhancing FA utilization ameliorates mitochondrial fragmentation and cardiac dysfunction via rebalancing OPA1 processing in pressure overload-induced HF, suggesting a unique metabolic intervention approach to improving cardiac functions in HF.

Hydrochlorothiazide modulates ischemic heart failure-induced cardiac remodeling via inhibiting angiotensin II type 1 receptor pathway in rats

AIMS

Our previous study indicates that hydrochlorothiazide inhibits transforming growth factor (TGF)-β/Smad signaling pathway, improves cardiac function and reduces fibrosis. We determined whether these effects were common among the diuretics and whether angiotensin II receptor type 1 (AT1) signaling pathway played a role in these effects.

METHODS

Heart failure was produced by ligating the left anterior descending coronary artery in adult male Sprague Dawley rats. Two weeks after the ligation, 70 rats were randomly divided into five groups: sham-operated group, control group, valsartan group (80 mg/kg/d), hydrochlorothiazide group (12.5 mg/kg/d) and furosemide group (20 mg/kg/d). In addition, neonatal rat ventricular fibroblasts were treated with angiotensin II.

RESULTS

After eight-week drug treatment, hydrochlorothiazide group and valsartan group but not furosemide group had improved cardiac function (ejection fraction was 49.4±2.1%, 49.5±1.8% and 39.9±1.9%, respectively, compared with 40.1±2.2% in control group), reduced cardiac interstitial fibrosis and collagen volume fraction (9.7±1.2%, 10.0±1.3% and 14.1±0.8%, respectively, compared with 15.9±1.1% in control group), and decreased expression of AT1, TGF-β and Smad2 in the cardiac tissues. In addition, hydrochlorothiazide reduced plasma angiotensin II and aldosterone levels. Furthermore, hydrochlorothiazide inhibited angiotensin II-induced TGF-β1 and Smad2 protein expression in the neonatal rat ventricular fibroblasts.

CONCLUSIONS

Our study indicates that the cardiac function and remodeling improvement after ischemic heart failure may not be common among the diuretics. Hydrochlorothiazide may reduce the left ventricular wall stress and angiotensin II signaling pathway to provide these beneficial effects.

Gene Expressions Underlying Mishandled Calcium Clearance and Elevated Generation of Reactive Oxygen Species in the Coronary Artery Smooth Muscle Cells of Chronic Heart Failure Rats

BACKGROUND

The calcium clearance and reactive oxygen species (ROS) generations in the coronary artery smooth muscle cells in chronic heart failure (HF) have not been fully investigated. Therefore, we attempted to understand the gene expressions underlying the mishandling of calcium clearance and the accumulations of ROS.

METHODS

We initially established an animal model of chronic HF by making the left anterior descending coronary artery ligation (CAL) in rats, and then isolated the coronary artery vascular smooth muscle cells from the ischemic and the nonischemic parts of the coronary artery vessels in 12 weeks after CAL operation. The intracellular calcium concentration and ROS level were measured using flow cytometry, and the gene expressions of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a), encoding sarcoplasmic reticulum Ca2+-ATPase 2a, encoding sodium-calcium exchanger (NCX), and p47phox encoding a subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase were examined using real-time quantitative reverse transcription polymerase chain reaction and Western blotting, respectively.

RESULTS

We found that the calcium accumulation and ROS generation in the coronary artery smooth muscle cells isolated from either the ischemic or the nonischemic part of the CAL coronary artery vessel were significantly increased irrespective of blood supply (all P < 0.01). Moreover, these were accompanied by the increased expressions of NCX and p47phox, the decreased expression of SERCA2a, and the increased amount of phosphorylated forms of p47phox in NADPH oxidase (all P < 0.05).

CONCLUSIONS

Our results demonstrated that the disordered calcium clearance and the increased ROS generation occurred in the coronary artery smooth muscle cells in rats with chronic HF produced by ligation of the left anterior descending coronary artery (CAL), and which was found to be disassociated from blood supply, and the increased generation of ROS in the cells was found to make concomitancy to the increased activity of NADPH oxidase in cytoplasm.

A low-carbohydrate high-fat diet decreases lean mass and impairs cardiac function in pair-fed female C57BL/6J mice

Background

Excess body fat is a major health issue and a risk factor for the development of numerous chronic diseases. Low-carbohydrate diets like the Atkins Diet are popular for rapid weight loss, but the long-term consequences remain the subject of debate. The Scandinavian low-carbohydrate high-fat (LCHF) diet, which has been popular in Scandinavian countries for about a decade, has very low carbohydrate content (~5 E %) but is rich in fat and includes a high proportion of saturated fatty acids. Here we investigated the metabolic and physiological consequences of a diet with a macronutrient composition similar to the Scandinavian LCHF diet and its effects on the organs, tissues, and metabolism of weight stable mice.

Methods

Female C57BL/6J mice were iso-energetically pair-fed for 4 weeks with standard chow or a LCHF diet. We measured body composition using echo MRI and the aerobic capacity before and after 2 and 4 weeks on diet. Cardiac function was assessed by echocardiography before and after 4 weeks on diet. The metabolic rate was measured by indirect calorimetry the fourth week of the diet. Mice were sacrificed after 4 weeks and the organ weight, triglyceride levels, and blood chemistry were analyzed, and the expression of key ketogenic, metabolic, hormonal, and inflammation genes were measured in the heart, liver, and adipose tissue depots of the mice using real-time PCR.

Results

The increase in body weight of mice fed a LCHF diet was similar to that in controls. However, while control mice maintained their body composition throughout the study, LCHF mice gained fat mass at the expense of lean mass after 2 weeks. The LCHF diet increased cardiac triglyceride content, impaired cardiac function, and reduced aerobic capacity. It also induced pronounced alterations in gene expression and substrate metabolism, indicating a unique metabolic state.

Conclusions

Pair-fed mice eating LCHF increased their percentage of body fat at the expense of lean mass already after 2 weeks, and after 4 weeks the function of the heart deteriorated. These findings highlight the urgent need to investigate the effects of a LCHF diet on health parameters in humans.

Impact of high-fat, low-carbohydrate diet on myocardial substrate oxidation, insulin sensitivity, and cardiac function after ischemia-reperfusion

High-fat, low-carbohydrate Diet (HFLCD) impairs the myocardial response to ischemia-reperfusion, but the underlying mechanisms remain elusive. We sought to determine the magnitude of diet-induced alterations in intrinsic properties of the myocardium (including insulin sensitivity and substrate oxidation) and circulating substrate and insulin differences resulting from diet, leading to this impaired response. Rats were fed HFLCD (60% kcal from fat/30% protein/10% carbohydrate) or control diet (CONT) (16%/19%/65%) for 2 wk. Isolated hearts underwent global low-flow ischemia followed by reperfusion (I/R). Carbon-13 NMR spectroscopy was used to determine myocardial substrate TCA cycle entry. Myocardial insulin sensitivity was assessed as dose-response of Akt phosphorylation. There was a significant effect of HFLCD and I/R with both these factors leading to an increase in free fatty acid (FFA) oxidation and a decrease in carbohydrate or ketone oxidation. Following I/R, HFLCD led to decreased ketone and increased FFA oxidation; the recovery of left ventricular (LV) function was decreased in HFLCD and was negatively correlated with FFA oxidation and positively associated with ketone oxidation. HFLCD also resulted in reduced insulin sensitivity. Under physiologic ranges, there were no direct effects of buffer insulin and ketone levels on oxidation of any substrate and recovery of cardiac function after I/R. An insulin-ketone interaction exists for myocardial substrate oxidation characteristics. We conclude that the impaired recovery of function after ischemia-reperfusion with HFLCD is largely due to intrinsic diet effects on myocardial properties, rather than to diet effect on circulating insulin or substrate levels.

Fuel availability and fate in cardiac metabolism: A tale of two substrates

The heart's extraordinary metabolic flexibility allows it to adapt to normal changes in physiology in order to preserve its function. Alterations in the metabolic profile of the heart have also been attributed to pathological conditions such as ischemia and hypertrophy; however, research during the past decade has established that cardiac metabolic adaptations can precede the onset of pathologies. It is therefore critical to understand how changes in cardiac substrate availability and use trigger events that ultimately result in heart dysfunction. This review examines the mechanisms by which the heart obtains fuels from the circulation or from mobilization of intracellular stores. We next describe experimental models that exhibit either an increase in glucose use or a decrease in FA oxidation, and how these aberrant conditions affect cardiac metabolism and function. Finally, we highlight the importance of alternative, relatively under-investigated strategies for the treatment of heart failure. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

In vivo assessment of cardiac metabolism and function in the abdominal aortic banding model of compensated cardiac hypertrophy

Aims

Left ventricular hypertrophy is an adaptive response of the heart to chronic mechanical overload and can lead to functional deterioration and heart failure. Changes in cardiac energy metabolism are considered as key to the hypertrophic remodelling process. The concurrence of obesity and hypertrophy has been associated with contractile dysfunction, and this work therefore aimed to investigate the in vivo structural, functional, and metabolic remodelling that occurs in the hypertrophied heart in the setting of a high-fat, high-sucrose, Western diet (WD).

Methods and results

Following induction of cardiac hypertrophy through abdominal aortic banding, male Sprague Dawley rats were exposed to either a standard diet or a WD (containing 45% fat and 16% sucrose) for up to 14 weeks. Cardiac structural and functional characteristics were determined by CINE MRI, and in vivo metabolism was investigated using hyperpolarized ¹³C-labelled pyruvate. Cardiac hypertrophy was observed at all time points, irrespective of dietary manipulation, with no evidence of cardiac dysfunction. Pyruvate dehydrogenase flux was unchanged in the hypertrophied animals at any time point, but increased incorporation of the ¹³C label into lactate was observed by 9 weeks and maintained at 14 weeks, indicative of enhanced glycolysis.

Conclusion

Hypertrophied hearts revealed little evidence of a switch towards increased glucose oxidation but rather an uncoupling of glycolytic metabolism from glucose oxidation. This was maintained under conditions of dietary stress provided by a WD but, at this compensated phase of hypertrophy, did not result in any contractile dysfunction.

Differential PI3K signal transduction in obesity-associated cardiac hypertrophy and response to ischemia

OBJECTIVE

Elevated insulin and inflammatory cytokine levels in obesity may chronically activate signaling pathways regulating cardiac growth and contractility. Our aim was to examine the effect of obesity on cardiac PI3K isoform and Akt activation during left ventricular (LV) hypertrophy and heart failure.

METHODS

Wild-type mice were fed normal chow or high-fat diet (HFD) for 2, 4, or 6 months. A subset of mice was subjected to chronic myocardial ischemia (MI).

RESULTS

Echocardiography revealed a progressive increase in LV mass, wall thickness, and diameters in obese mice. Systolic pump function was not impaired. Increased cardiac levels of PI3Kγ, phosphorylated Akt, GSK3β, and Epac were observed after HFD for 2 months but gradually declined and were normal or reduced after 6 months, paralleled by elevated PP2A and SOCS3 levels. MI resulted in heart failure, independent of obesity, but compensatory LV hypertrophy was absent in obese mice. Histochemical analyses revealed similar increases in cardiac fibrosis, inflammation, apoptosis, and angiogenesis in lean and obese mice.

CONCLUSIONS

Our findings suggest that activation of Akt initially contributes to cardiac hypertrophy and that chronic metabolic and inflammatory stimulation and overexpression of inhibitory mediators decrease PI3Kγ-mediated Akt signaling and blunt compensatory hypertrophy after MI.

Chronic high-fat diet-induced obesity decreased survival and increased hypertrophy of rats with experimental eccentric hypertrophy from chronic aortic regurgitation

Background

The composition of a diet can influence myocardial metabolism and development of left ventricular hypertrophy (LVH). The impact of a high-fat diet in chronic left ventricular volume overload (VO) causing eccentric LVH is unknown. This study examined the effects of chronic ingestion of a high-fat diet in rats with chronic VO caused by severe aortic valve regurgitation (AR) on LVH, function and on myocardial energetics and survival.

Methods

Male Wistar rats were divided in four groups: Shams on control or high-fat (HF) diet (15 rats/group) and AR rats fed with the same diets (ARC (n = 56) and ARHF (n = 32)). HF diet was started one week before AR induction and the protocol was stopped 30 weeks later.

Results

As expected, AR caused significant LV dilation and hypertrophy and this was exacerbated in the ARHF group. Moreover, survival in the ARHF group was significantly decreased compared the ARC group. Although the sham animals on HF also developed significant obesity compared to those on control diet, this was not associated with heart hypertrophy. The HF diet in AR rats partially countered the expected shift in myocardial energy substrate preference usually observed in heart hypertrophy (from fatty acids towards glucose). Systolic function was decreased in AR rats but HF diet had no impact on this parameter. The response to HF diet of different fatty acid oxidation markers as well as the increase in glucose transporter-4 translocation to the plasma membrane compared to ARC was blunted in AR animals compared to those on control diet.

Conclusions

HF diet for 30 weeks decreased survival of AR rats and worsened eccentric hypertrophy without affecting systolic function. The expected adaptation of myocardial energetics to volume-overload left ventricle hypertrophy in AR animals seemed to be impaired by the high-fat diet suggesting less metabolic flexibility.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2261-14-123) contains supplementary material, which is available to authorized users.

Physiological and structural differences in spatially distinct subpopulations of cardiac mitochondria: influence of cardiac pathologies

Cardiac tissue contains discrete pools of mitochondria that are characterized by their subcellular spatial arrangement. Subsarcolemmal mitochondria (SSM) exist below the cell membrane, interfibrillar mitochondria (IFM) reside in rows between the myofibrils, and perinuclear mitochondria are situated at the nuclear poles. Microstructural imaging of heart tissue coupled with the development of differential isolation techniques designed to sequentially separate spatially distinct mitochondrial subpopulations have revealed differences in morphological features including shape, absolute size, and internal cristae arrangement. These findings have been complemented by functional studies indicating differences in biochemical parameters and, potentially, functional roles for the ATP generated, based upon subcellular location. Consequently, mitochondrial subpopulations appear to be influenced differently during cardiac pathologies including ischemia/reperfusion, heart failure, aging, exercise, and diabetes mellitus. These influences may be the result of specific structural and functional disparities between mitochondrial subpopulations such that the stress elicited by a given cardiac insult differentially impacts subcellular locales and the mitochondria contained within. The goal of this review is to highlight some of the inherent structural and functional differences that exist between spatially distinct cardiac mitochondrial subpopulations as well as provide an overview of the differential impact of various cardiac pathologies on spatially distinct mitochondrial subpopulations. As an outcome, we will instill a basis for incorporating subcellular spatial location when evaluating the impact of cardiac pathologies on the mitochondrion. Incorporation of subcellular spatial location may offer the greatest potential for delineating the influence of cardiac pathology on this critical organelle.

High-fat, low-carbohydrate diet promotes arrhythmic death and increases myocardial ischemia-reperfusion injury in rats

High-fat, low-carbohydrate diets (HFLCD) are often eaten by humans for a variety of reasons, but the effects of such diets on the heart are incompletely understood. We evaluated the impact of HFLCD on myocardial ischemia/reperfusion (I/R) using an in vivo model of left anterior descending coronary artery ligation. Sprague-Dawley rats (300 g) were fed HFLCD (60% calories fat, 30% protein, 10% carbohydrate) or control (CONT; 16% fat, 19% protein, 65% carbohydrate) diet for 2 wk and then underwent open chest I/R. At baseline (preischemia), diet did not affect left ventricular (LV) systolic and diastolic function. Oil red O staining revealed presence of lipid in the heart with HFLCD but not in CONT. Following I/R, recovery of LV function was decreased in HFLCD. HFLCD hearts exhibited decreased ATP synthase and increased uncoupling protein-3 gene and protein expression. HFLCD downregulated mitochondrial fusion proteins and upregulated fission proteins and store-operated Ca(2+) channel proteins. HFLCD led to increased death during I/R; 6 of 22 CONT rats and 16 of 26 HFLCD rats died due to ventricular arrhythmias and hemodynamic shock. In surviving rats, HFLCD led to larger infarct size. We concluded that in vivo HFLCD does not affect nonischemic LV function but leads to greater myocardial injury during I/R, with increased risk of death by pump failure and ventricular arrhythmias, which might be associated with altered cardiac energetics, mitochondrial fission/fusion dynamics, and store-operated Ca(2+) channel expression.

Alterations in mitochondrial function in cardiac hypertrophy and heart failure

Normal cardiac function requires high and continuous supply with ATP. As mitochondria are the major source of ATP production, it is apparent that mitochondrial function and cardiac function need to be closely related to each other. When subjected to overload, the heart hypertrophies. Initially, the development of hypertrophy is a compensatory mechanism, and contractile function is maintained. However, when the heart is excessively and/or persistently stressed, cardiac function may deteriorate, leading to the onset of heart failure. There is considerable evidence that alterations in mitochondrial function are involved in the decompensation of cardiac hypertrophy. Here, we review metabolic changes occurring at the mitochondrial level during the development of cardiac hypertrophy and the transition to heart failure. We will focus on changes in mitochondrial substrate metabolism, the electron transport chain and the role of oxidative stress. We will demonstrate that, with respect to mitochondrial adaptations, a clear distinction between hypertrophy and heart failure cannot be made because most of the findings present in overt heart failure can already be found in the various stages of hypertrophy.

Cardioprotective effects of dietary lipids evident in the time-dependent alterations of cardiac function and gene expression following myocardial infarction

We have previously shown that prolonged high–saturated fat feeding (SAT) for 8 weeks after myocardial infarction (MI) improves ventricular function and prevents the metabolic remodeling commonly observed in heart failure. The current study was designed to delineate the interplay between markers of energy metabolism and indices of cardiac remodeling with 2 and 4 weeks of post‐MI SAT in male Wistar rats. By 2 weeks, less remodeling was noted in MI‐SAT evidenced by diminished chamber dilation and greater ejection fraction assessed by echocardiography and hemodynamic measures. In addition, gene expression of energy metabolism targets involved in FA uptake, oxidation, and glucose oxidation regulation was increased in MI‐SAT with respect to MI alone, although no change in PDH phosphorylation was observed. The regulatory kinase, phosphoinositide 3 kinase (Pi3k), was strongly induced by 2 weeks in the MI‐SAT group, although AKT protein content (a primary downstream target of PI3K that affects metabolism) was decreased by both MI and SAT alone, indicating early involvement of cellular signaling pathways in lipid‐mediated cardioprotection. Our results demonstrate that cardioprotection occurs acutely with SAT following MI, with improvement in indices of both cardiac function and fatty acid oxidation, suggesting a mechanistic role for energy metabolism in the beneficial effects of high dietary fat following cardiac injury.

e12019

A diet rich in saturated fats is cardioprotective after myocardial infarction. The cardioprotective effect is noted by 2 weeks and includes functional and genomic changes indicative of a relationship with preservation of metabolic flexibility.

High fat feeding in mice is insufficient to induce cardiac dysfunction and does not exacerbate heart failure

Preclinical studies of animals with risk factors, and how those risk factors contribute to the development of cardiovascular disease and cardiac dysfunction, are clearly needed. One such approach is to feed mice a diet rich in fat (i.e. 60%). Here, we determined whether a high fat diet was sufficient to induce cardiac dysfunction in mice. We subjected mice to two different high fat diets (lard or milk as fat source) and followed them for over six months and found no significant decrement in cardiac function (via echocardiography), despite robust adiposity and impaired glucose disposal. We next determined whether antecedent and concomitant exposure to high fat diet (lard) altered the murine heart's response to infarct-induced heart failure; high fat feeding during, or before and during, heart failure did not significantly exacerbate cardiac dysfunction. Given the lack of a robust effect on cardiac dysfunction with high fat feeding, we then examined a commonly used mouse model of overt diabetes, hyperglycemia, and obesity (db/db mice). db/db mice (or STZ treated wild-type mice) subjected to pressure overload exhibited no significant exacerbation of cardiac dysfunction; however, ischemia-reperfusion injury significantly depressed cardiac function in db/db mice compared to their non-diabetic littermates. Thus, we were able to document a negative influence of a risk factor in a relevant cardiovascular disease model; however, this did not involve exposure to a high fat diet. High fat diet, obesity, or hyperglycemia does not necessarily induce cardiac dysfunction in mice. Although many investigators use such diabetes/obesity models to understand cardiac defects related to risk factors, this study, along with those from several other groups, serves as a cautionary note regarding the use of murine models of diabetes and obesity in the context of heart failure.

Cardiac metabolism and its interactions with contraction, growth, and survival of cardiomyocytes

The network for cardiac fuel metabolism contains intricate sets of interacting pathways that result in both ATP-producing and non-ATP-producing end points for each class of energy substrates. The most salient feature of the network is the metabolic flexibility demonstrated in response to various stimuli, including developmental changes and nutritional status. The heart is also capable of remodeling the metabolic pathways in chronic pathophysiological conditions, which results in modulations of myocardial energetics and contractile function. In a quest to understand the complexity of the cardiac metabolic network, pharmacological and genetic tools have been engaged to manipulate cardiac metabolism in a variety of research models. In concert, a host of therapeutic interventions have been tested clinically to target substrate preference, insulin sensitivity, and mitochondrial function. In addition, the contribution of cellular metabolism to growth, survival, and other signaling pathways through the production of metabolic intermediates has been increasingly noted. In this review, we provide an overview of the cardiac metabolic network and highlight alterations observed in cardiac pathologies as well as strategies used as metabolic therapies in heart failure. Lastly, the ability of metabolic derivatives to intersect growth and survival are also discussed.

Rescue of heart lipoprotein lipase-knockout mice confirms a role for triglyceride in optimal heart metabolism and function

Hearts utilize fatty acids as a primary source of energy. The sources of those lipids include free fatty acids and lipoprotein triglycerides. Deletion of the primary triglyceride-hydrolyzing enzyme lipoprotein lipase (LPL) leads to cardiac dysfunction. Whether heart LPL-knockout (hLPL0) mice are compromised due a deficiency in energetic substrates is unknown. To test whether alternative sources of energy will prevent cardiac dysfunction in hLPL0 mice, two different models were used to supply nonlipid energy. 1) hLPL0 mice were crossed with mice transgenically expressing GLUT1 in cardiomyocytes to increase glucose uptake into the heart; this cross-corrected cardiac dysfunction, reduced cardiac hypertrophy, and increased myocardial ATP. 2) Mice were randomly assigned to a sedentary or training group (swimming) at 3 mo of age, which leads to increased skeletal muscle production of lactate. hLPL0 mice had greater expression of the lactate transporter monocarboxylate transporter-1 (MCT-1) and increased cardiac lactate uptake. Compared with hearts from sedentary hLPL0 mice, hearts from trained hLPL0 mice had adaptive hypertrophy and improved cardiac function. We conclude that defective energy intake and not the reduced uptake of fat-soluble vitamins or cholesterol is responsible for cardiac dysfunction in hLPL0 mice. In addition, our studies suggest that adaptations in cardiac metabolism contribute to the beneficial effects of exercise on the myocardium of patients with heart failure.

Age-dependent effects of high fat-diet on murine left ventricles: role of palmitate

Obesity-associated heart disease results in myocardial lipid accumulation leading to lipotoxicity. However, recent studies are suggestive of protective effects of high-fat diets (HFD). To determine whether age results in differential changes in diet-induced obesity, we fed young and old (3 and 18 months) male C57Bl/6 mice control diet, low-fat diet (both 10 kcal% fat) or HFD (45 kcal% fat) for 16 weeks, after which we analyzed LV function, mitochondrial changes, and potential modifiers of myocardial structure. HFD or age did not change LV systolic function, although a mildly increased BNP was observed in all old mice. This was associated with increased myocardial collagen, triglyceride, diacylglycerol, and ceramide content as well as higher caspase 3 activation in old mice with highest levels in old HFD mice. Pyruvate-dependent respiration and mitochondrial biogenesis were reduced in all old mice and in young HFD mice. Activation of AMPK, a strong inducer of mitochondrial biogenesis, was reduced in both HFD groups and in old control or LFD mice. Cardiomyocytes from old rats demonstrated significantly reduced AMPK activation, impaired mitochondrial biogenesis, higher ceramide content, and reduced viability after palmitate (C16:0) in vitro, while no major deleterious effects were observed in young cardiomyocytes. Aged but not young cardiomyocytes were unable to respond to higher palmitate with increased fatty acid oxidation. Thus, HFD results in cardiac structural alterations and accumulation of lipid intermediates predominantly in old mice, possibly due to the inability of old cardiomyocytes to adapt to high-fatty acid load.

Dietary saturated fat and docosahexaenoic acid differentially effect cardiac mitochondrial phospholipid fatty acyl composition and Ca(2+) uptake, without altering permeability transition or left ventricular function

High saturated fat diets improve cardiac function and survival in rodent models of heart failure, which may be mediated by changes in mitochondrial function. Dietary supplementation with the n3-polyunsaturated fatty acid docosahexaenoic acid (DHA, 22:6n3) is also beneficial in heart failure and can affect mitochondrial function. Saturated fatty acids and DHA likely have opposing effects on mitochondrial phospholipid fatty acyl side chain composition and mitochondrial membrane function, though a direct comparison has not been previously reported. We fed healthy adult rats a standard low-fat diet (11% of energy intake from fat), a low-fat diet supplemented with DHA (2.3% of energy intake) or a high-fat diet comprised of long chain saturated fatty acids (45% fat) for 6 weeks. There were no differences among the three diets in cardiac mass or function, mitochondrial respiration, or Ca²⁺-induced mitochondrial permeability transition. On the other hand, there were dramatic differences in mitochondrial phospholipid fatty acyl side chains. Dietary supplementation with DHA increased DHA from 7% to ∼25% of total phospholipid fatty acids in mitochondrial membranes, and caused a proportional depletion of arachidonic acid (20:4n6). The saturated fat diet increased saturated fat and DHA in mitochondria and decreased linoleate (18:2n6), which corresponded to a decrease in Ca²⁺ uptake by isolated mitochondria compared to the other diet groups. In conclusion, despite dramatic changes in mitochondrial phospholipid fatty acyl side chain composition by both the DHA and high saturated fat diets, there were no effects on mitochondrial respiration, permeability transition, or cardiac function.

Diabetes, perioperative ischaemia and volatile anaesthetics: consequences of derangements in myocardial substrate metabolism

Volatile anaesthetics exert protective effects on the heart against perioperative ischaemic injury. However, there is growing evidence that these cardioprotective properties are reduced in case of type 2 diabetes mellitus. A strong predictor of postoperative cardiac function is myocardial substrate metabolism. In the type 2 diabetic heart, substrate metabolism is shifted from glucose utilisation to fatty acid oxidation, resulting in metabolic inflexibility and cardiac dysfunction. The ischaemic heart also loses its metabolic flexibility and can switch to glucose or fatty acid oxidation as its preferential state, which may deteriorate cardiac function even further in case of type 2 diabetes mellitus.Recent experimental studies suggest that the cardioprotective properties of volatile anaesthetics partly rely on changing myocardial substrate metabolism. Interventions that target at restoration of metabolic derangements, like lifestyle and pharmacological interventions, may therefore be an interesting candidate to reduce perioperative complications. This review will focus on the current knowledge regarding myocardial substrate metabolism during volatile anaesthesia in the obese and type 2 diabetic heart during perioperative ischaemia.

Intravenous glial growth factor 2 (GGF2) isoform of neuregulin-1β improves left ventricular function, gene and protein expression in rats after myocardial infarction

AIMS

Recombinant Neuregulin (NRG)-1β has multiple beneficial effects on cardiac myocytes in culture, and has potential as a clinical therapy for heart failure (HF). A number of factors may influence the effect of NRG-1β on cardiac function via ErbB receptor coupling and expression. We examined the effect of the NRG-1β isoform, glial growth factor 2 (GGF2), in rats with myocardial infarction (MI) and determined the impact of high-fat diet as well as chronicity of disease on GGF2 induced improvement in left ventricular systolic function. Potential mechanisms for GGF2 effects on the remote myocardium were explored using microarray and proteomic analysis.

METHODS AND RESULTS

Rats with MI were randomized to receive vehicle, 0.625 mg/kg, or 3.25 mg/kg GGF2 in the presence and absence of high-fat feeding beginning at day 7 post-MI and continuing for 4 weeks. Residual left ventricular (LV) function was improved in both of the GGF2 treatment groups compared with the vehicle treated MI group at 4 weeks of treatment as assessed by echocardiography. High-fat diet did not prevent the effects of high dose GGF2. In experiments where treatment was delayed until 8 weeks after MI, high but not low dose GGF2 treatment was associated with improved systolic function. mRNA and protein expression analysis of remote left ventricular tissue revealed a number of changes in myocardial gene and protein expression altered by MI that were normalized by GGF2 treatment, many of which are involved in energy production.

CONCLUSIONS

This study demonstrates that in rats with MI induced systolic dysfunction, GGF2 treatment improves cardiac function. There are differences in sensitivity of the myocardium to GGF2 effects when administered early vs. late post-MI that may be important to consider in the development of GGF2 in humans.

Enhanced resistance to permeability transition in interfibrillar cardiac mitochondria in dogs: effects of aging and long-term aldosterone infusion

Functional differences between subsarcolemmal and interfibrillar cardiac mitochondria (SSM and IFM) have been observed with aging and pathological conditions in rodents. Results are contradictory, and there is little information from large animal models. We assessed the respiratory function and resistance to mitochondrial permeability transition (MPT) in SSM and IFM from healthy young (1 yr) and old (8 yr) female beagles and in old beagles with hypertension and left ventricular (LV) wall thickening induced by 16 wk of aldosterone infusion. MPT was assessed in SSM and IFM by Ca(2+) retention and swelling. Healthy young and old beagles had similar mitochondrial structure, respiratory function, and Ca(2+)-induced MPT within SSM and IFM subpopulations. On the other hand, oxidative capacity and resistance to Ca(2+)-induced MPT were significantly greater in IFM compared with SSM in all groups. Old beagles treated with aldosterone had greater LV wall thickness and worse diastolic filling but normal LV chamber volume and systolic function. Treatment with aldosterone did not alter mitochondrial respiratory function but accelerated Ca(2+)-induced MPT in SSM, but not IFM, compared with healthy old and young beagles. In conclusion, in a large animal model, oxidative capacity and resistance to MPT were greater in IFM than in SSM. Furthermore, aldosterone infusion increased susceptibility to MPT in SSM, but not IFM. Together this suggests that SSM are less resilient to acute stress than IFM in the healthy heart and are more susceptible to the development of pathology with chronic stress.

Normalizing the metabolic phenotype after myocardial infarction: impact of subchronic high fat feeding

The normal heart relies primarily on the oxidation of fatty acids (FA) for ATP production, whereas during heart failure (HF) glucose utilization increases, implying pathological changes to cardiac energy metabolism. Despite the noted lipotoxic effects of elevating FA, our work has demonstrated a cardioprotective effect of a high fat diet (SAT) when fed after myocardial infarction (MI), as compared to normal chow (NC) fed cohorts. This data has suggested a mechanistic link to energy metabolism. The goal of this study was to determine the impact of SAT on the metabolic phenotype of the heart after MI. Male Wistar rats underwent coronary ligation surgery (MI) and were evaluated after 8 weeks of SAT. Induction of MI was verified by echocardiography. LV function assessed by in vivo hemodynamic measurements revealed improvements in the MI-SAT group as compared to MI-NC. Perfused working hearts revealed a decrease in cardiac work in MI-NC that was improved in MI-SAT. Glucose oxidation was increased and FA oxidation decreased in MI-NC compared to shams suggesting an alteration in the metabolic profile that was ameliorated by SAT. (31)P NMR analysis of Langendorff perfused hearts revealed no differences in PCr:ATP indicating no overt energy deficit in MI groups. Phospho-PDH and PDK(4) were increased in MI-SAT, consistent with a shift towards fatty acid oxidation (FAO). Overall, these results support the hypothesis that SAT post-infarction promotes a normal metabolic phenotype that may serve a cardioprotective role in the injured heart.

Dietary fat and heart failure: moving from lipotoxicity to lipoprotection

There is growing evidence suggesting that dietary fat intake affects the development and progression of heart failure. Studies in rodents show that in the absence of obesity, replacing refined carbohydrate with fat can attenuate or prevent ventricular expansion and contractile dysfunction in response to hypertension, infarction, or genetic cardiomyopathy. Relatively low intake of n-3 polyunsaturated fatty acids from marine sources alters cardiac membrane phospholipid fatty acid composition, decreases the onset of new heart failure, and slows the progression of established heart failure. This effect is associated with decreased inflammation and improved resistance to mitochondrial permeability transition. High intake of saturated, monounsaturated, or n-6 polyunsaturated fatty acids has also shown beneficial effects in rodent studies. The underlying mechanisms are complex, and a more thorough understanding is needed of the effects on cardiac phospholipids, lipid metabolites, and metabolic flux in the normal and failing heart. In summary, manipulation of dietary fat intake shows promise in the prevention and treatment of heart failure. Clinical studies generally support high intake of n-3 polyunsaturated fatty acids from marine sources to prevent and treat heart failure. Additional clinical and animals studies are needed to determine the optimal diet in terms of saturated, monounsaturated, and n-6 polyunsaturated fatty acids intake for this vulnerable patient population.

High intake of saturated fat, but not polyunsaturated fat, improves survival in heart failure despite persistent mitochondrial defects

AIMS

The impact of a high-fat diet on the failing heart is unclear, and the differences between polyunsaturated fatty acids (PUFA) and saturated fat have not been assessed. Here, we compared a standard low-fat diet to high-fat diets enriched with either saturated fat (palmitate and stearate) or PUFA (linoleic and α-linolenic acids) in hamsters with genetic cardiomyopathy.

METHODS AND RESULTS

Male δ-sarcoglycan null Bio TO2 hamsters were fed a standard low-fat diet (12% energy from fat), or high-fat diets (45% fat) comprised of either saturated fat or PUFA. The median survival was increased by the high saturated fat diet (P< 0.01; 278 days with standard diet and 361 days with high saturated fat)), but not with high PUFA (260 days) (n = 30-35/group). Body mass was modestly elevated (∼10%) in both high fat groups. Subgroups evaluated after 24 weeks had similar left ventricular chamber size, function, and mass. Mitochondrial oxidative enzyme activity and the yield of interfibrillar mitochondria (IFM) were decreased to a similar extent in all TO2 groups compared with normal F1B hamsters. Ca(2+)-induced mitochondrial permeability transition pore opening was enhanced in IFM in all TO2 groups compared with F1B hamsters, but to a significantly greater extent in those fed the high PUFA diet compared with the standard or high saturated fat diet.

CONCLUSION

These results show that a high intake of saturated fat improves survival in heart failure compared with a high PUFA diet or low-fat diet, despite persistent mitochondrial defects.

Glucose metabolism and cardiac hypertrophy

The most notable change in the metabolic profile of hypertrophied hearts is an increased reliance on glucose with an overall reduced oxidative metabolism, i.e. a reappearance of the foetal metabolic pattern. In animal models, this change is attributed to the down-regulation of the transcriptional cascades promoting gene expression for fatty acid oxidation and mitochondrial oxidative phosphorylation in adult hearts. Impaired myocardial energetics in cardiac hypertrophy also triggers AMP-activated protein kinase (AMPK), leading to increased glucose uptake and glycolysis. Aside from increased reliance on glucose as an energy source, changes in other glucose metabolism pathways, e.g. the pentose phosphate pathway, the glucosamine biosynthesis pathway, and anaplerosis, are also noted in the hypertrophied hearts. Studies using transgenic mouse models and pharmacological compounds to mimic or counter the switch of substrate preference in cardiac hypertrophy have demonstrated that increased glucose metabolism in adult heart is not harmful and can be beneficial when it provides sufficient fuel for oxidative metabolism. However, improvement in the oxidative capacity and efficiency rather than the selection of the substrate is likely the ultimate goal for metabolic therapies.

Effects of hydrochlorothiazide on cardiac remodeling in a rat model of myocardial infarction-induced congestive heart failure

Heart failure is a major cause of morbidity and mortality worldwide. Diuretics are regarded as the first-line treatment for patients with heart failure because they provide symptomatic relief. However, the specific benefits of diuretics and their effects on heart failure survival remain unclear. This study was designed to investigate the potential of hydrochlorothiazide to improve cardiac remodeling compared with spironolactone. Heart failure was produced by ligation of the left anterior descending coronary artery in male Sprague-Dawley rats. Two weeks after coronary artery ligation, 55 rats were randomly divided into four groups: sham-operated group (n=10), control group (n=15), hydrochlorothiazide group (12.5 mg/kg/day, n=15) and spironolactone group (20 mg/kg/day, n=15). Cardiac function was assessed by echocardiography and Millar catheter after treatment with drugs for 8 weeks. Compared with the control group, ejection fraction and left ventricular end-systolic pressure were significantly improved in the hydrochlorothiazide and spironolactone treatment groups (P<0.05). In addition, hydrochlorothiazide and spironolactone reduced collagen volume fraction and proinflammatory cytokine levels. Moreover, gene and protein expression of TGF-β1, Smad2, Smad3 and Smad7 (P<0.05) were also reduced. Nevertheless, no significant differences were observed between the hydrochlorothiazide and spironolactone groups. These results suggest that hydrochlorothiazide improves cardiac remodeling as effectively as spironolactone by reducing proinflammatory cytokine levels and inhibiting the TGF-β signaling pathway in post-myocardial infarction congestive heart failure. Moreover, the effects of the drugs on the TGF-β signaling pathway are likely to result from inhibited TGF-β and R-Smads expression rather than increased Inhibitory-Smad7 expression.

Myocardial insulin resistance induced by high fat feeding in heart failure is associated with preserved contractile function

Previous studies have reported that high fat feeding in mild to moderate heart failure (HF) results in the preservation of contractile function. Recent evidence has suggested that preventing the switch from fatty acid to glucose metabolism in HF may ameliorate dysfunction, and insulin resistance is one potential mechanism for regulating substrate utilization. This study was designed to determine whether peripheral and myocardial insulin resistance exists with HF and/or a high-fat diet and whether myocardial insulin signaling was altered accordingly. Rats underwent coronary artery ligation (HF) or sham surgery and were randomized to normal chow (NC; 14% kcal from fat) or a high-fat diet (SAT; 60% kcal from fat) for 8 wk. HF + SAT animals showed preserved systolic (+dP/dt and stroke work) and diastolic (-dP/dt and time constant of relaxation) function compared with HF + NC animals. Glucose tolerance tests revealed peripheral insulin resistance in sham + SAT, HF + NC, and HF + SAT animals compared with sham + NC animals. PET imaging confirmed myocardial insulin resistance only in HF + SAT animals, with an uptake ratio of 2.3 ± 0.3 versus 4.6 ± 0.7, 4.3 ± 0.4, and 4.2 ± 0.6 in sham + NC, sham + SAT, and HF + NC animals, respectively; the myocardial glucose utilization rate was similarly decreased in HF + SAT animals only. Western blot analysis of insulin signaling protein expression was indicative of cardiac insulin resistance in HF + SAT animals. Specifically, alterations in Akt and glycogen synthase kinase-3β protein expression in HF + SAT animals compared with HF + NC animals may be involved in mediating myocardial insulin resistance. In conclusion, HF animals fed a high-saturated fat exhibited preserved myocardial contractile function, peripheral and myocardial insulin resistance, decreased myocardial glucose utilization rates, and alterations in cardiac insulin signaling. These results suggest that myocardial insulin resistance may serve a cardioprotective function with high fat feeding in mild to moderate HF.

The myocardial contractile response to physiological stress improves with high saturated fat feeding in heart failure

Impaired myocardial contractile function is a hallmark of heart failure (HF), which may present under resting conditions and/or during physiological stress. Previous studies have reported that high fat feeding in mild to moderate HF/left ventricular (LV) dysfunction is associated with improved contractile function at baseline. The goal of this study was to determine whether myocardial function is compromised in response to physiological stress and to evaluate the global gene expression profile of rats fed high dietary fat after infarction. Male Wistar rats underwent ligation or sham surgery and were fed normal chow (NC; 10% kcal fat; Sham + NC and HF + NC groups) or high-fat chow (SAT; 60% kcal saturated fat; Sham + SAT and HF + SAT groups) for 8 wk. Myocardial contractile function was assessed using a Millar pressure-volume conductance catheter at baseline and during inferior vena caval occlusions and dobutamine stress. Steady-state indexes of systolic function, LV +dP/dt(max), stroke work, and maximal power were increased in the HF + SAT group versus the HF + NC group and reduced in the HF + NC group versus the Sham + NC group. Preload recruitable measures of contractility were decreased in HF + NC group but not in the HF + SAT group. beta-Adrenergic responsiveness [change in LV +dP/dt(max) and change in cardiac output with dobutamine (0-10 microg x kg(-1) x min(-1))] was reduced in HF, but high fat feeding did not further impact the contractile reserve in HF. The contractile reserve was reduced by the high-fat diet in the Sham + SAT group. Microarray gene expression analysis revealed that the majority of significantly altered pathways identified contained multiple gene targets correspond to cell signaling pathways and energy metabolism. These findings suggest that high saturated fat improves myocardial function at rest and during physiological stress in infarcted hearts but may negatively impact the contractile reserve under nonpathological conditions. Furthermore, high fat feeding-induced alterations in gene expression related to energy metabolism and specific signaling pathways revealed promising targets through which high saturated fat potentially mediates cardioprotection in mild to moderate HF/LV dysfunction.

Lipotoxicity in the heart

Obesity and insulin resistance are associated with ectopic lipid deposition in multiple tissues, including the heart. Excess lipid may be stored as triglycerides, but are also shunted into non-oxidative pathways that disrupt normal cellular signaling leading to organ dysfunction and in some cases apoptosis, a process termed lipotoxicity. Various pathophysiological mechanisms have been proposed to lead to lipotoxic tissue injury, which might vary by cell type. Specific mechanisms by which lipotoxicity alter cardiac structure and function are incompletely understood, but are beginning to be elucidated. This review will focus on mechanisms that have been proposed to lead to lipotoxic injury in the heart and will review the state of knowledge regarding potential causes and correlates of increased myocardial lipid content in animal models and humans. We will seek to highlight those areas where additional research is warranted.

Dietary omega-3 fatty acids alter cardiac mitochondrial phospholipid composition and delay Ca2+-induced permeability transition

Consumption of omega-3 fatty acids from fish oil, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), decreases risk for heart failure and attenuates pathologic cardiac remodeling in response to pressure overload. Dietary supplementation with EPA + DHA may also impact cardiac mitochondrial function and energetics through alteration of membrane phospholipids. We assessed the role of EPA + DHA supplementation on left ventricular (LV) function, cardiac mitochondrial membrane phospholipid composition, respiration, and sensitivity to mitochondrial permeability transition pore (MPTP) opening in normal and infarcted myocardium. Rats were subjected to sham surgery or myocardial infarction by coronary artery ligation (n=10-14), and fed a standard diet, or supplemented with EPA + DHA (2.3% of energy intake) for 12 weeks. EPA + DHA altered fatty acid composition of total mitochondrial phospholipids and cardiolipin by reducing arachidonic acid content and increasing DHA incorporation. EPA + DHA significantly increased calcium uptake capacity in both subsarcolemmal and intrafibrillar mitochondria from sham rats. This treatment effect persisted with the addition of cyclosporin A, and was not accompanied by changes in mitochondrial respiration or coupling, or cyclophilin D protein expression. Myocardial infarction resulted in heart failure as evidenced by LV dilation and contractile dysfunction. Infarcted LV myocardium had decreased mitochondrial protein yield and activity of mitochondrial marker enzymes, however respiratory function of isolated mitochondria was normal. EPA + DHA had no effect on LV function, mitochondrial respiration, or MPTP opening in rats with heart failure. In conclusion, dietary supplementation with EPA + DHA altered mitochondrial membrane phospholipid fatty acid composition in normal and infarcted hearts, but delayed MPTP opening only in normal hearts.

Increased myocardial NAD(P)H oxidase-derived superoxide causes the exacerbation of postinfarct heart failure in type 2 diabetes

Type 2 diabetes adversely affects the outcomes in patients with myocardial infarction (MI), which is associated with the development of left ventricular (LV) failure. NAD(P)H oxidase-derived superoxide (O(2)(-)) production is increased in type 2 diabetes. However, its pathophysiological significance in advanced post-MI LV failure associated with type 2 diabetes remains unestablished. We thus hypothesized that an inhibitor of NAD(P)H oxidase activation, apocynin, could attenuate the exacerbated LV failure after MI in high-fat diet (HFD)-induced obese mice with type 2 diabetes. Male C57BL/6J mice were fed on either HFD or normal diet (ND) for 8 wk. At 4 wk of feeding, MI was created in mice by ligating the left coronary artery. HFD-fed MI mice were treated with either 10 mmol/l apocynin or vehicle. HFD + MI had significantly greater LV end-diastolic diameter (LVEDD; 5.7 +/- 0.1 vs. 5.3 +/- 0.2 mm), end-diastolic pressure (12 +/- 2 vs. 8 +/- 1 mmHg), and lung weight/tibial length (10.1 +/- 0.3 vs. 8.7 +/- 0.7 mg/mm) than ND + MI, which was accompanied by an increased interstitial fibrosis of noninfarcted LV. Treatment of HFD + MI with apocynin significantly decreased LVEDD (5.4 +/- 0.1 mm), LV end-diastolic pressure (9.7 +/- 0.8 mmHg), lung weight/tibial length (9.0 +/- 0.3 mg/mm), and concomitantly interstitial fibrosis of noninfarcted LV to the ND + MI level without affecting body weight, glucose metabolism, and infarct size. NAD(P)H oxidase activity and O(2)(-) production were increased in noninfarcted LV tissues from HFD + MI, both of which were attenuated by apocynin to the ND + MI level. Type 2 diabetes was associated with the exacerbation of LV failure after MI via increasing NAD(P)H oxidase-derived O(2)(-), which may be a novel important therapeutic target in advanced heart failure with diabetes.

Prolonged exposure to high dietary lipids is not associated with lipotoxicity in heart failure

Previous studies have reported that elevated myocardial lipids in a model of mild-to-moderate heart failure increased mitochondrial function, but did not alter left ventricular function. Whether more prolonged exposure to high dietary lipids would promote a lipotoxic phenotype in mitochondrial and myocardial contractile function has not been determined. We tested the hypothesis that prolonged exposure to high dietary lipids, following coronary artery ligation, would preserve myocardial and mitochondrial function in heart failure. Rats underwent ligation or sham surgery and were fed normal (10% kcal fat) (SHAM, HF) or high fat diet (60% kcal saturated fat) (SHAM+FAT, HF+FAT) for sixteen weeks. Although high dietary fat was accompanied by myocardial tissue triglyceride accumulation (SHAM 1.47+/-0.14; SHAM+FAT 2.32+/-0.14; HF 1.34+/-0.14; HF+FAT 2.21+/-0.20 micromol/gww), fractional shortening was increased 16% in SHAM+FAT and 28% in HF+FAT compared to SHAM and HF, respectively. Despite increased medium-chain acyl-CoA dehydrogenase (MCAD) activity in interfibrillar mitochondria (IFM) of both SHAM+FAT and HF+FAT, dietary lipids also were associated with decreased state 3 respiration using palmitoylcarnitine (SHAM 369+/-14; SHAM+FAT 307+/-23; HF 354+/-13; HF+FAT 366+/-18 nAO min(-1) mg(-1)) in SHAM+FAT compared to SHAM and HF+FAT. State 3 respiration in IFM also was decreased in SHAM+FAT relative to SHAM using succinate and DHQ. In conclusion, high dietary lipids promoted myocardial lipid accumulation, but were not accompanied by alterations in myocardial contractile function typically associated with lipotoxicity. In normal animals, high dietary fat decreased mitochondrial respiration, but also increased MCAD activity. These studies support the concept that high fat feeding can modify multiple cellular pathways that differentially affect mitochondrial function under normal and pathological conditions.

Impaired insulin signaling accelerates cardiac mitochondrial dysfunction after myocardial infarction

Diabetes increases mortality and accelerates left ventricular (LV) dysfunction following myocardial infarction (MI). This study sought to determine the impact of impaired myocardial insulin signaling, in the absence of diabetes, on the development of LV dysfunction following MI. Mice with cardiomyocyte-restricted knock out of the insulin receptor (CIRKO) and wildtype (WT) mice were subjected to proximal left coronary artery ligation (MI) and followed for 14 days. Despite equivalent infarct size, mortality was increased in CIRKO-MI vs. WT-MI mice (68% vs. 40%, respectively). In surviving mice, LV ejection fraction and dP/dt were reduced by >40% in CIRKO-MI vs. WT-MI. Relative to shams, isometric developed tension in LV papillary muscles increased in WT-MI but not in CIRKO-MI. Time to peak tension and relaxation times were prolonged in CIRKO-MI vs. WT-MI suggesting impaired, load-independent myocardial contractile function. To elucidate mechanisms for impaired LV contractility, mitochondrial function was examined in permeabilized cardiac fibers. Whereas maximal ADP-stimulated mitochondrial O(2) consumption rates (V(ADP)) with palmitoyl carnitine were unchanged in WT-MI mice relative to sham-operated animals, V(ADP) was significantly reduced in CIRKO-MI (13.17+/-0.94 vs. 9.14+/-0.88 nmol O(2)/min/mgdw, p<0.05). Relative to WT-MI, expression levels of GLUT4, PPAR-alpha, SERCA2, and the FA-Oxidation genes MCAD, LCAD, CPT2 and the electron transfer flavoprotein ETFDH were repressed in CIRKO-MI. Thus reduced insulin action in cardiac myocytes accelerates post-MI LV dysfunction, due in part to a rapid decline in mitochondrial FA oxidative capacity, which combined with limited glucose transport capacity that may reduce substrate utilization and availability.

Myocardial ischemic-reperfusion injury in a rat model of metabolic syndrome

Hearts of NaCl-induced hypertensive-glucose intolerant (HGI) rats develop reduced infarcts after ischemia-reperfusion injury (IRI) than their hypertensive (H) counterparts. Because high intake of saturated fat is a major risk factor for ischemic heart disease, we tested the hypothesis that chronic (18 weeks) consumption of a high saturated fat diet increases susceptibility to IRI, an effect more marked in the HGI rats than in the H rats. The fat-fed H (HFAT) rat displayed significantly higher body weight and plasma leptin content compared to the H, HGI, or fat-fed HGI (HGIFAT) rats which all showed similar values. In contrast, plasma triglyceride concentration was significantly higher in the HGIFAT rat than in the other three groups. Plasma insulin concentration was similar in the two H groups but higher than that of the two HGI groups. Compared to the H rat, the HGI rat was markedly glucose intolerant, with fat feeding causing comparable worsening of glucose intolerance in each group. The HGIFAT rats displayed a reduction in baseline myocardial contractility and relaxation and a higher end-diastolic pressure compared to the other three groups. Infarct size was significantly lower in the HGI rats than in the H rats. Although fat feeding did not affect infarct size of the H rat, it worsened that of the HGIFAT rat thereby abrogating the differential that existed between the H and HGI rats. In conclusion, excess fat feeding impairs myocardial function of HGI rats and increases their susceptibility to IRI. These findings are of relevance to the metabolic syndrome that manifests as a cluster of insulin resistance, dyslipidemia, and systemic hypertension.

Hypertrophic cardiomyopathy in high-fat diet-induced obesity: role of suppression of forkhead transcription factor and atrophy gene transcription

Cellular hypertrophy is regulated by coordinated pro- and antigrowth machineries. Foxo transcription factors initiate an atrophy-related gene program to counter hypertrophic growth. This study was designed to evaluate the role of Akt, the forkhead transcription factor Foxo3a, and atrophy genes muscle-specific RING finger (MuRF)-1 and atrogin-1 in cardiac hypertrophy and contractile dysfunction associated with high-fat diet-induced obesity. Mice were fed a low- or high-fat diet for 6 mo along with a food-restricted high-fat weight control group. Echocardiography revealed decreased fractional shortening and increased end-systolic diameter and cardiac hypertrophy in high-fat obese but not in weight control mice. Cardiomyocytes from high-fat obese but not from weight control mice displayed contractile and intracellular Ca2+ defects including depressed maximal velocity of shortening/relengthening, prolonged duration of shortening/relengthening, and reduced intracellular Ca2+ rise and clearance. Caspase activities were greater in high-fat obese but not in weight control mouse hearts. Western blot analysis revealed enhanced basal Akt and Foxo3a phosphorylation and reduced insulin-stimulated phosphorylation of Akt and Foxo3a without changes in total protein expression of Akt and Foxo3a in high-fat obese hearts. RT-PCR and immunoblotting results displayed reduced levels of the atrogens atrogin-1 and MuRF-1, the upregulated hypertrophic markers GATA4 and ciliary neurotrophic factor receptor-alpha, as well as the unchanged calcineurin and proteasome ubiquitin in high-fat obese mouse hearts. Transfection of H9C2 myoblast cells with dominant-negative Foxo3a adenovirus mimicked palmitic acid (0.8 mM for 24 h)-induced GATA4 upregulation without an additive effect. Dominant-negative Foxo3a-induced upregulation of pAkt and repression of phosphatase and tensin homologue were abrogated by palmitic acid. These results suggest a cardiac hypertrophic response in high-fat diet-associated obesity at least in part through inactivation of Foxo3a by the Akt pathway.

Role of diet and fuel overabundance in the development and progression of heart failure

Under physiological conditions, the human heart derives energy from glucose, fatty acids, and/or lactate depending upon substrate availability, circulating hormone levels, and nutritional status. Circulating free fatty acid and glucose levels often exceed the normal range, as observed with type 2 diabetes, obesity, or physical inactivity. Chronic exposure of the heart to high plasma levels of free fatty acids may cause accumulation of toxic lipid intermediates within cardiomyocytes. Furthermore, suppression of glucose oxidation by increased fatty acid uptake shunts glucose into the oxidative pentose phosphate and hexosamine biosynthetic pathways, both of which yield potentially harmful products. Noxious derivatives of aberrant glucose and fatty acid oxidation can activate signalling cascades leading to myocyte dysfunction or death, processes termed 'glucotoxicity' and 'lipotoxicity'. This review discusses the effects of dietary extremes (e.g. high fat and high carbohydrate consumption) and substrate overabundance in the context of heart failure (HF) development and progression. Emerging data suggest that substrate excess leads to cardiac dysfunction and HF, which may be prevented or slowed by maintaining low body fat and high insulin sensitivity and consuming a diet of low glycaemic load that is high in mono- and polyunsaturated fatty acids.

Disruption of the circadian clock within the cardiomyocyte influences myocardial contractile function, metabolism, and gene expression

Virtually every mammalian cell, including cardiomyocytes, possesses an intrinsic circadian clock. The role of this transcriptionally based molecular mechanism in cardiovascular biology is poorly understood. We hypothesized that the circadian clock within the cardiomyocyte influences diurnal variations in myocardial biology. We, therefore, generated a cardiomyocyte-specific circadian clock mutant (CCM) mouse to test this hypothesis. At 12 wk of age, CCM mice exhibit normal myocardial contractile function in vivo, as assessed by echocardiography. Radiotelemetry studies reveal attenuation of heart rate diurnal variations and bradycardia in CCM mice (in the absence of conduction system abnormalities). Reduced heart rate persisted in CCM hearts perfused ex vivo in the working mode, highlighting the intrinsic nature of this phenotype. Wild-type, but not CCM, hearts exhibited a marked diurnal variation in responsiveness to an elevation in workload (80 mmHg plus 1 μM epinephrine) ex vivo, with a greater increase in cardiac power and efficiency during the dark (active) phase vs. the light (inactive) phase. Moreover, myocardial oxygen consumption and fatty acid oxidation rates were increased, whereas cardiac efficiency was decreased, in CCM hearts. These observations were associated with no alterations in mitochondrial content or structure and modest mitochondrial dysfunction in CCM hearts. Gene expression microarray analysis identified 548 and 176 genes in atria and ventricles, respectively, whose normal diurnal expression patterns were altered in CCM mice. These studies suggest that the cardiomyocyte circadian clock influences myocardial contractile function, metabolism, and gene expression.

Alterations in carbohydrate metabolism and its regulation in PPARalpha null mouse hearts

Although a shift from fatty acids (FAs) to carbohydrates (CHOs) is considered beneficial for the diseased heart, it is unclear why subjects with FA beta-oxidation defects are prone to cardiac decompensation under stress conditions. The present study investigated potential alterations in the myocardial utilization of CHOs for energy production and anaplerosis in 12-wk-old peroxisome proliferator-activating receptor-alpha (PPARalpha) null mice (a model of FA beta-oxidation defects). Carbon-13 methodology was used to assess substrate flux through energy-yielding pathways in hearts perfused ex vivo at two workloads with a physiological substrate mixture mimicking the fed state, and real-time RT-quantitative polymerase chain reaction was used to document the expression of selected metabolic genes. When compared with that from control C57BL/6 mice, isolated working hearts from PPARalpha null mice displayed an impaired capacity to withstand a rise in preload (mimicking an increased venous return as it occurs during exercise) as reflected by a 20% decline in the aortic flow rate. At the metabolic level, beyond the expected shift from FA (5-fold down) to CHO (1.5-fold up; P < 0.001) at both preloads, PPARalpha null hearts also displayed 1) a significantly greater contribution of exogenous lactate and glucose and/or glycogen (2-fold up) to endogenous pyruvate formation, whereas that of exogenous pyruvate remained unchanged and 2) marginal alterations in citric acid cycle-related parameters. The lactate production rate was the only measured parameter that was affected differently by preloads in control and PPARalpha null mouse hearts, suggesting a restricted reserve for the latter hearts to enhance glycolysis when the energy demand is increased. Alterations in the expression of some glycolysis-related genes suggest potential mechanisms involved in this defective CHO metabolism. Collectively, our data highlight the importance of metabolic alterations in CHO metabolism associated with FA oxidation defects as a factor that may predispose the heart to decompensation under stress conditions even in the fed state.

Glycemic control and treatment patterns in patients with heart failure

Patients with diabetes mellitus are more likely to develop heart failure and cardiac dysfunction (with or without coronary artery disease), and the combination portends a poorer prognosis. Although the majority of treatment options in heart failure appear to be as effective in those with diabetes as in those without, less is known about the safety and effectiveness of different antidiabetic medications in the setting of heart failure. Nevertheless, it is well recognized that many patients with diabetes mellitus may develop subclinical structural heart disease prior to overt clinical presentations. Therefore, the potential of early detection (or screening) is very important to prevent the significant disease burden of heart failure in the diabetic population. In-depth investigations of the role of current and emerging strategies of metabolic modulation are promising, although the precise therapeutic targets remain elusive.

Heart failure progression is accelerated following myocardial infarction in type 2 diabetic rats

Clinical studies have shown a greater incidence of myocardial infarction in diabetic patients, and following an infarction, diabetes is associated with an increased risk for the development of left ventricular (LV) dysfunction and heart failure. The goal of this study was to determine if the progression of heart failure following myocardial infarction in type 2 diabetic (T2D) rats is accelerated compared with nondiabetic rats. Male nondiabetic Wistar-Kyoto (WKY) and T2D Goto-Kakizaki (GK) rats underwent coronary artery ligation or sham surgery to induce heart failure. Postligation (8 and 20 wk), two-dimensional echocardiography and LV pressure measurements were made. Heart failure progression, as assessed by enhanced LV remodeling and contractile dysfunction, was accelerated 8 wk postligation in the T2D animals. LV remodeling was evident from increased end-diastolic and end-systolic diameters and areas in the GK compared with the WKY infarcted group. Furthermore, enhanced LV contractile dysfunction was evident from a greater deterioration in fractional shortening and enhanced myocardial performance index (an index of global LV dysfunction) in the GK infarcted group. This accelerated progression was accompanied by greater increases in atrial natriuretic factor and skeletal alpha-actin (gene markers of heart failure and hypertrophy) mRNA levels in GK infarcted hearts. Despite similar decreases in metabolic gene expression (i.e., peroxisome proliferator-activated receptor-alpha-regulated genes associated with fatty acid oxidation) between infarcted WKY and GK rat hearts, myocardial triglyceride levels were elevated in the GK hearts only. These results, demonstrating enhanced remodeling and LV dysfunction 8 wk postligation provide evidence of an accelerated progression of heart failure in T2D rats.