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

Functional resilience of C57BL/6J mouse heart to dietary fat overload

Molecular mechanisms underlying cardiac dysfunction and subsequent heart failure in diabetic cardiomyopathy are incompletely understood. Initially we intended to test the role of G protein-coupled receptor kinase 2 (GRK2), a potential mediator of cardiac dysfunction in diabetic cardiomyopathy, but found that control animals on HFD did not develop cardiomyopathy. Cardiac function was preserved in both wild-type and GRK2 knockout animals fed high-fat diet as indicated by preserved left ventricular ejection fraction (LVEF) although heart mass was increased. The absence of cardiac dysfunction led us to rigorously evaluate the utility of diet-induced obesity to model diabetic cardiomyopathy in mice. Using pure C57BL/6J animals and various diets formulated with different sources of fat-lard (32% saturated fat, 68% unsaturated fat) or hydrogenated coconut oil (95% saturated fat), we consistently observed left ventricular hypertrophy, preserved LVEF, and preserved contractility measured by invasive hemodynamics in animals fed high-fat diet. Gene expression patterns that characterize pathological hypertrophy were not induced, but a modest induction of various collagen isoforms and matrix metalloproteinases was observed in heart with high-fat diet feeding. PPARα-target genes that enhance lipid utilization such as Pdk4, CD36, AcadL, and Cpt1b were induced, but mitochondrial energetics was not impaired. These results suggest that although long-term fat feeding in mice induces cardiac hypertrophy and increases cardiac fatty acid metabolism, it may not be sufficient to activate pathological hypertrophic mechanisms that impair cardiac function or induce cardiac fibrosis. Thus, additional factors that are currently not understood may contribute to the cardiac abnormalities previously reported by many groups.NEW & NOTEWORTHY Dietary fat overload (DFO) is widely used to model diabetic cardiomyopathy but the utility of this model is controversial. We comprehensively characterized cardiac contractile and mitochondrial function in C57BL6/J mice fed with lard-based or saturated fat-enriched diets initiated at two ages. Despite cardiac hypertrophy, contractile and mitochondrial function is preserved, and molecular adaptations likely limit lipotoxicity. The resilience of these hearts to DFO underscores the need to develop robust alternative models of diabetic cardiomyopathy.

Chronic metformin treatment decreases cardiac injury during ischemia-reperfusion by attenuating endoplasmic reticulum stress with improved mitochondrial function

Aging impairs mitochondrial function that leads to greater cardiac injury during ischemia and reperfusion. Cardiac endoplasm reticulum (ER) stress increases with age and contributes to mitochondrial dysfunction. Metformin is an anti-diabetic drug that protects cardiac mitochondria during acute ER stress. We hypothesized that metformin treatment would improve preexisting mitochondrial dysfunction in aged hearts by attenuating ER stress, followed by a decrease in cardiac injury during subsequent ischemia and reperfusion.

Male young (3 mo.) and aged mice (24 mo.) received metformin (300 mg/kg/day) dissolved in drinking water with sucrose (0.2 g/100 ml) as sweetener for two weeks versus sucrose vehicle alone. Cytosol, subsarcolemmal (SSM), and interfibrillar mitochondria (IFM) were isolated. In separate groups, cardioprotection was evaluated using ex vivo isolated heart perfusion with 25 min. global ischemia and 60 min. reperfusion. Infarct size was measured.

The contents of CHOP and cleaved ATF6 were decreased in metformin-treated 24 mo. mice compared to vehicle, supporting a decrease in ER stress. Metformin treatment improved OXPHOS in IFM in 24 mo. using a complex I substrate. Metformin treatment decreased infarct size following ischemia-reperfusion. Thus, metformin feeding decreased cardiac injury in aged mice during ischemia-reperfusion by improving pre-ischemic mitochondrial function via inhibition of ER stress.

Xbp1s-FoxO1 axis governs lipid accumulation and contractile performance in heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) is now the dominant form of heart failure and one for which no efficacious therapies exist. Obesity and lipid mishandling greatly contribute to HFpEF. However, molecular mechanism(s) governing metabolic alterations and perturbations in lipid homeostasis in HFpEF are largely unknown. Here, we report that cardiomyocyte steatosis in HFpEF is coupled with increases in the activity of the transcription factor FoxO1 (Forkhead box protein O1). FoxO1 depletion, as well as over-expression of the Xbp1s (spliced form of the X-box-binding protein 1) arm of the UPR (unfolded protein response) in cardiomyocytes each ameliorates the HFpEF phenotype in mice and reduces myocardial lipid accumulation. Mechanistically, forced expression of Xbp1s in cardiomyocytes triggers ubiquitination and proteasomal degradation of FoxO1 which occurs, in large part, through activation of the E3 ubiquitin ligase STUB1 (STIP1 homology and U-box-containing protein 1) a novel and direct transcriptional target of Xbp1s. Our findings uncover the Xbp1s-FoxO1 axis as a pivotal mechanism in the pathogenesis of cardiometabolic HFpEF and unveil previously unrecognized mechanisms whereby the UPR governs metabolic alterations in cardiomyocytes.

Diabetic cardiomyopathy: molecular mechanisms, detrimental effects of conventional treatment, and beneficial effects of natural therapy

ABSTARCT

Diabetic complications are among the largely exigent health problems currently. Cardiovascular complications, including diabetic cardiomyopathy (DCM), account for more than 80% of diabetic deaths. Investigators are exploring new therapeutic targets to slow or abate diabetes because of the growing occurrence and augmented risk of deaths due to its complications. Research on rodent models of type 1 and type 2 diabetes mellitus, and the use of genetic engineering techniques in mice and rats have significantly sophisticated for our understanding of the molecular mechanisms in human DCM. DCM is featured by pathophysiological mechanisms that are hyperglycemia, insulin resistance, oxidative stress, left ventricular hypertrophy, damaged left ventricular systolic and diastolic functions, myocardial fibrosis, endothelial dysfunction, myocyte cell death, autophagy, and endoplasmic reticulum stress. A number of molecular and cellular pathways, such as cardiac ubiquitin proteasome system, FoxO transcription factors, hexosamine biosynthetic pathway, polyol pathway, protein kinase C signaling, NF-κB signaling, peroxisome proliferator-activated receptor signaling, Nrf2 pathway, mitogen-activated protein kinase pathway, and micro RNAs, play a major role in DCM. Currently, there are a few drugs for the management of DCM and some of them have considerable adverse effects. So, researchers are focusing on the natural products to ameliorate it. Hence, in this review, we discuss the pathogical, molecular, and cellular mechanisms of DCM; the current diagnostic methods and treatments; adverse effects of conventional treatment; and beneficial effects of natural product-based therapeutics, which may pave the way to new treatment strategies. Graphical Abstract.

The Effect of a High-Fat Diet on the Fatty Acid Composition in the Hearts of Mice

The Western diet can lead to alterations in cardiac function and increase cardiovascular risk, which can be reproduced in animal models by implementing a high-fat diet (HFD). However, the mechanism of these alterations is not fully understood and may be dependent on alterations in heart lipid composition. The aim of this study was to evaluate the effect of an HFD on the fatty acid (FA) composition of total lipids, as well as of various lipid fractions in the heart, and on heart function. C57BL/6 mice were fed an HFD or standard laboratory diet. The FA composition of chow, serum, heart and skeletal muscle tissues was measured by gas chromatography–mass spectrometry. Cardiac function was evaluated by ultrasonography. Our results showed an unexpected increase in polyunsaturated FAs (PUFAs) and a significant decrease in monounsaturated FAs (MUFAs) in the heart tissue of mice fed the HFD. For comparison, no such effects were observed in skeletal muscle or serum samples. Furthermore, we found that the largest increase in PUFAs was in the sphingolipid fraction, whereas the largest decrease in MUFAs was in the phospholipid and sphingomyelin fractions. The hearts of mice fed an HFD had an increased content of triacylglycerols. Moreover, the HFD treatment altered aortic flow pattern. We did not find significant changes in heart mass or oxidative stress markers between mice fed the HFD and standard diet. The above results suggest that alterations in FA composition in the heart may contribute to deterioration of heart function. A possible mechanism of this phenomenon is the alteration of sphingolipids and phospholipids in the fatty acid profile, which may change the physical properties of these lipids. Since phospho- and sphingolipids are the major components of cell membranes, alterations in their structures in heart cells can result in changes in cell membrane properties.

MD1 Deficiency Promotes Inflammatory Atrial Remodelling Induced by High-Fat Diets

BACKGROUND

Myeloid differentiation protein 1 (MD1) is expressed in various tissues, including the heart. However, the role of MD1 in obesity-related atrial remodelling remains incompletely understood. Here, this study intends to determine the regulatory role and underlying mechanisms of MD1 in obesity-related atrial remodelling.

METHODS

A high-fat diet (HFD) feeding was performed in 6-week-old MD1-knockout (MD1-KO) mice and wild-type (WT) littermates for 20 weeks. Morphological, biochemical, functional, histological, and electrophysiological studies were conducted at the age of 26 weeks.

RESULTS

Our results revealed that the MD1 expression levels were downregulated in the atrium of the HFD-fed induced obesity mice. An increase in body weight, glucose intolerance, hyperlipidemia, and adverse atrial remodelling, such as atrial inflammation and fibrosis, were induced by HFD feeding in WT mice. Vulnerability to atrial fibrillation (AF) was also significantly increased by HFD feeding in WT mice. In addition, these adverse effects caused by HFD-fed induced obesity were further exaggerated in MD1-KO mice compared with WT mice. Mechanistically, MD1-KO activated TLR4/NF-κB signaling pathways, which led to atrial remodelling in mice fed by HFD by increasing the phosphorylation of p65 and IκBα.

CONCLUSIONS

Our data suggested that MD1 deficiency played an important role in accelerating the development of inflammatory atrial fibrosis and increasing vulnerability to AF in mice with HFD-fed induced obesity, providing an essential target for improving HFD-induced atrial remodelling.

Nox4 reprograms cardiac substrate metabolism via protein O-GlcNAcylation to enhance stress adaptation

Cardiac hypertrophic remodeling during chronic hemodynamic stress is associated with a switch in preferred energy substrate from fatty acids to glucose, usually considered to be energetically favorable. The mechanistic interrelationship between altered energy metabolism, remodeling, and function remains unclear. The ROS-generating NADPH oxidase-4 (Nox4) is upregulated in the overloaded heart, where it ameliorates adverse remodeling. Here, we show that Nox4 redirects glucose metabolism away from oxidation but increases fatty acid oxidation, thereby maintaining cardiac energetics during acute or chronic stresses. The changes in glucose and fatty acid metabolism are interlinked via a Nox4-ATF4–dependent increase in the hexosamine biosynthetic pathway, which mediates the attachment of O-linked N-acetylglucosamine (O-GlcNAcylation) to the fatty acid transporter CD36 and enhances fatty acid utilization. These data uncover a potentially novel redox pathway that regulates protein O-GlcNAcylation and reprograms cardiac substrate metabolism to favorably modify adaptation to chronic stress. Our results also suggest that increased fatty acid oxidation in the chronically stressed heart may be beneficial.

Nox4 reprograms intermediary metabolism in the heart through an ATF4-mediated enhancement of protein O-GlcNAcylation, and the resulting switch to increased fatty acid oxidation protects the overloaded heart.

Molecular mechanisms of cardiac pathology in diabetes - Experimental insights

Diabetic cardiomyopathy is a distinct pathology independent of co-morbidities such as coronary artery disease and hypertension. Diminished glucose uptake due to impaired insulin signaling and decreased expression of glucose transporters is associated with a shift towards increased reliance on fatty acid oxidation and reduced cardiac efficiency in diabetic hearts. The cardiac metabolic profile in diabetes is influenced by disturbances in circulating glucose, insulin and fatty acids, and alterations in cardiomyocyte signaling. In this review, we focus on recent preclinical advances in understanding the molecular mechanisms of diabetic cardiomyopathy. Genetic manipulation of cardiomyocyte insulin signaling intermediates has demonstrated that partial cardiac functional rescue can be achieved by upregulation of the insulin signaling pathway in diabetic hearts. Inconsistent findings have been reported relating to the role of cardiac AMPK and β-adrenergic signaling in diabetes, and systemic administration of agents targeting these pathways appear to elicit some cardiac benefit, but whether these effects are related to direct cardiac actions is uncertain. Overload of cardiomyocyte fuel storage is evident in the diabetic heart, with accumulation of glycogen and lipid droplets. Cardiac metabolic dysregulation in diabetes has been linked with oxidative stress and autophagy disturbance, which may lead to cell death induction, fibrotic 'backfill' and cardiac dysfunction. This review examines the weight of evidence relating to the molecular mechanisms of diabetic cardiomyopathy, with a particular focus on metabolic and signaling pathways. Areas of uncertainty in the field are highlighted and important knowledge gaps for further investigation are identified. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Metabolic Remodeling in Diabetic Cardiomyopathy

Diabetes is a risk factor for heart failure and cardiovascular mortality with specific changes to myocardial metabolism, energetics, structure, and function. The gradual impairment of insulin production and signalling in diabetes is associated with elevated plasma fatty acids and increased myocardial free fatty acid uptake and activation of the transcription factor PPARα. The increased free fatty acid uptake results in accumulation of toxic metabolites, such as ceramide and diacylglycerol, activation of protein kinase C, and elevation of uncoupling protein-3. Insulin signalling and glucose uptake/oxidation become further impaired, and mitochondrial function and ATP production become compromised. Increased oxidative stress also impairs mitochondrial function and disrupts metabolic pathways. The diabetic heart relies on free fatty acids (FFA) as the major substrate for oxidative phosphorylation and is unable to increase glucose oxidation during ischaemia or hypoxia, thereby increasing myocardial injury, especially in ageing female diabetic animals. Pharmacological activation of PPARγ in adipose tissue may lower plasma FFA and improve recovery from myocardial ischaemic injury in diabetes. Not only is the diabetic heart energetically-impaired, it also has early diastolic dysfunction and concentric remodelling. The contractile function of the diabetic myocardium negatively correlates with epicardial adipose tissue, which secretes proinflammatory cytokines, resulting in interstitial fibrosis. Novel pharmacological strategies targeting oxidative stress seem promising in preventing progression of diabetic cardiomyopathy, although clinical evidence is lacking. Metabolic agents that lower plasma FFA or glucose, including PPARγ agonism and SGLT2 inhibition, may therefore be promising options.

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.

Hearts from mice fed a non-obesogenic high-fat diet exhibit changes in their oxidative state, calcium and mitochondria in parallel with increased susceptibility to reperfusion injury

Rationale

High-fat diet with obesity-associated co-morbidities triggers cardiac remodeling and renders the heart more vulnerable to ischemia/reperfusion injury. However, the effect of high-fat diet without obesity and associated co-morbidities is presently unknown.

Objectives

To characterize a non-obese mouse model of high-fat diet, assess the vulnerability of hearts to reperfusion injury and to investigate cardiac cellular remodeling in relation to the mechanism(s) underlying reperfusion injury.

Methods and Results

Feeding C57BL/6J male mice high-fat diet for 20 weeks did not induce obesity, diabetes, cardiac hypertrophy, cardiac dysfunction, atherosclerosis or cardiac apoptosis. However, isolated perfused hearts from mice fed high-fat diet were more vulnerable to reperfusion injury than those from mice fed normal diet. In isolated cardiomyocytes, high-fat diet was associated with higher diastolic intracellular Ca²⁺ concentration and greater damage to isolated cardiomyocytes following simulated ischemia/reperfusion. High-fat diet was also associated with changes in mitochondrial morphology and expression of some related proteins but not mitochondrial respiration or reactive oxygen species turnover rates. Proteomics, western blot and high-performance liquid chromatography techniques revealed that high-fat diet led to less cardiac oxidative stress, higher catalase expression and significant changes in expression of putative components of the mitochondrial permeability transition pore (mPTP). Inhibition of the mPTP conferred relatively more cardio-protection in the high-fat fed mice compared to normal diet.

Conclusions

This study shows for the first time that high-fat diet, independent of obesity-induced co-morbidities, triggers changes in cardiac oxidative state, calcium handling and mitochondria which are likely to be responsible for increased vulnerability to cardiac insults.

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.

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.

High-fat feeding-induced hyperinsulinemia increases cardiac glucose uptake and mitochondrial function despite peripheral insulin resistance

In obesity, reduced cardiac glucose uptake and mitochondrial abnormalities are putative causes of cardiac dysfunction. However, high-fat diet (HFD) does not consistently induce cardiac insulin resistance and mitochondrial damage, and recent studies suggest HFD may be cardioprotective. To determine cardiac responses to HFD, we investigated cardiac function, glucose uptake, and mitochondrial respiration in young (3-month-old) and middle-aged (MA) (12-month-old) male Ldlr(-/-) mice fed chow or 3 months HFD to induce obesity, systemic insulin resistance, and hyperinsulinemia. In MA Ldlr(-/-) mice, HFD induced accelerated atherosclerosis and nonalcoholic steatohepatitis, common complications of human obesity. Surprisingly, HFD-fed mice demonstrated increased cardiac glucose uptake, which was most prominent in MA mice, in the absence of cardiac contractile dysfunction or hypertrophy. Moreover, hearts of HFD-fed mice had enhanced mitochondrial oxidation of palmitoyl carnitine, glutamate, and succinate and greater basal insulin signaling compared with those of chow-fed mice, suggesting cardiac insulin sensitivity was maintained, despite systemic insulin resistance. Streptozotocin-induced ablation of insulin production markedly reduced cardiac glucose uptake and mitochondrial dysfunction in HFD-fed, but not in chow-fed, mice. Insulin injection reversed these effects, suggesting that insulin may protect cardiac mitochondria during HFD. These results have implications for cardiac metabolism and preservation of mitochondrial function in obesity.

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.

Ceramide synthase 5 mediates lipid-induced autophagy and hypertrophy in cardiomyocytes

Diabetic cardiomyopathy (DbCM), which consists of cardiac hypertrophy and failure in the absence of traditional risk factors, is a major contributor to increased heart failure risk in type 2 diabetes patients. In rodent models of DbCM, cardiac hypertrophy and dysfunction have been shown to depend upon saturated fatty acid (SFA) oversupply and de novo sphingolipid synthesis. However, it is not known whether these effects are mediated by bulk SFAs and sphingolipids or by individual lipid species. In this report, we demonstrate that a diet high in SFA induced cardiac hypertrophy, left ventricular systolic and diastolic dysfunction, and autophagy in mice. Furthermore, treatment with the SFA myristate, but not palmitate, induced hypertrophy and autophagy in adult primary cardiomyocytes. De novo sphingolipid synthesis was required for induction of all pathological features observed both in vitro and in vivo, and autophagy was required for induction of hypertrophy in vitro. Finally, we implicated a specific ceramide N-acyl chain length in this process and demonstrated a requirement for (dihydro)ceramide synthase 5 in cardiomyocyte autophagy and myristate-mediated hypertrophy. Thus, this report reveals a requirement for a specific sphingolipid metabolic route and dietary SFAs in the molecular pathogenesis of lipotoxic cardiomyopathy and hypertrophy.

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.

Cardiac-specific deletion of acetyl CoA carboxylase 2 prevents metabolic remodeling during pressure-overload hypertrophy

RATIONALE

Decreased fatty acid oxidation (FAO) with increased reliance on glucose are hallmarks of metabolic remodeling that occurs in pathological cardiac hypertrophy and is associated with decreased myocardial energetics and impaired cardiac function. To date, it has not been tested whether prevention of the metabolic switch that occurs during the development of cardiac hypertrophy has unequivocal benefits on cardiac function and energetics.

OBJECTIVE

Because malonyl CoA production via acetyl CoA carboxylase 2 (ACC2) inhibits the entry of long chain fatty acids into the mitochondria, we hypothesized that mice with a cardiac-specific deletion of ACC2 (ACC2H-/-) would maintain cardiac FAO and improve function and energetics during the development of pressure-overload hypertrophy.

METHODS AND RESULTS

ACC2 deletion led to a significant reduction in cardiac malonyl CoA levels. In isolated perfused heart experiments, left ventricular function and oxygen consumption were similar in ACC2H-/- mice despite an ≈60% increase in FAO compared with controls (CON). After 8 weeks of pressure overload via transverse aortic constriction (TAC), ACC2H-/- mice exhibited a substrate utilization profile similar to sham animals, whereas CON-TAC hearts had decreased FAO with increased glycolysis and anaplerosis. Myocardial energetics, assessed by 31P nuclear magnetic resonance spectroscopy, and cardiac function were maintained in ACC2H-/- after 8 weeks of TAC. Furthermore, ACC2H-/--TAC demonstrated an attenuation of cardiac hypertrophy with a significant reduction in fibrosis relative to CON-TAC.

CONCLUSIONS

These data suggest that reversion to the fetal metabolic profile in chronic pathological hypertrophy is associated with impaired myocardial function and energetics and maintenance of the inherent cardiac metabolic profile and mitochondrial oxidative capacity is a viable therapeutic strategy.

Dietary linoleate preserves cardiolipin and attenuates mitochondrial dysfunction in the failing rat heart

AIMS

Cardiolipin (CL) is a tetra-acyl phospholipid that provides structural and functional support to several proteins in the inner mitochondrial membrane. The majority of CL in the healthy mammalian heart contains four linoleic acid acyl chains (L(4)CL). A selective loss of L(4)CL is associated with mitochondrial dysfunction and heart failure in humans and animal models. We examined whether supplementing the diet with linoleic acid would preserve cardiac L(4)CL and attenuate mitochondrial dysfunction and contractile failure in rats with hypertensive heart failure.

METHODS AND RESULTS

Male spontaneously hypertensive heart failure rats (21 months of age) were administered diets supplemented with high-linoleate safflower oil (HLSO) or lard (10% w/w; 28% kilocalorie fat) or without supplemental fat (control) for 4 weeks. HLSO preserved L(4)CL and total CL to 90% of non-failing levels (vs. 61-75% in control and lard groups), and attenuated 17-22% decreases in state 3 mitochondrial respiration observed in the control and lard groups (P < 0.05). Left ventricular fractional shortening was significantly higher in HLSO vs. control (33 ± 2 vs. 29 ± 2%, P < 0.05), while plasma insulin levels were lower (5.4 ± 1.1 vs. 9.1 ± 2.3 ng/mL; P < 0.05), with no significant effect of lard supplementation. HLSO also increased serum concentrations of several eicosanoid species compared with control and lard diets, but had no effect on plasma glucose or blood pressure.

CONCLUSION

Moderate consumption of HLSO preserves CL and mitochondrial function in the failing heart and may be a useful adjuvant therapy for this condition.

Differential effects of high-fat diet on myocardial lipid metabolism in failing and nonfailing hearts with angiotensin II-mediated cardiac remodeling in mice

Normal myocardium adapts to increase of nutritional fatty acid supply by upregulation of regulatory proteins of the fatty acid oxidation pathway. Because advanced heart failure is associated with reduction of regulatory proteins of fatty acid oxidation, we hypothesized that failing myocardium may not be able to adapt to increased fatty acid intake and therefore undergo lipid accumulation, potentially aggravating myocardial dysfunction. We determined the effect of high-fat diet in transgenic mice with overexpression of angiotensinogen in the myocardium (TG1306/R1). TG1306/R1 mice develop ANG II-mediated left ventricular hypertrophy, and at one year of age approximately half of the mice present heart failure associated with reduced expression of regulatory proteins of fatty acid oxidation and reduced palmitate oxidation during ex vivo working heart perfusion. Hypertrophied hearts from TG1306/R1 mice without heart failure adapted to high-fat feeding, similarly to hearts from wild-type mice, with upregulation of regulatory proteins of fatty acid oxidation and enhancement of palmitate oxidation. There was no myocardial lipid accumulation or contractile dysfunction. In contrast, hearts from TG1306/R1 mice presenting heart failure were unable to respond to high-fat feeding by upregulation of fatty acid oxidation proteins and enhancement of palmitate oxidation. This resulted in accumulation of triglycerides and ceramide in the myocardium, and aggravation of contractile dysfunction. In conclusion, hearts with ANG II-induced contractile failure have lost the ability to enhance fatty acid oxidation in response to increased fatty acid supply. The ensuing accumulation of lipid compounds may play a role in the observed aggravation of contractile dysfunction.

Aldehyde stress and up-regulation of Nrf2-mediated antioxidant systems accompany functional adaptations in cardiac mitochondria from mice fed n-3 polyunsaturated fatty acids

Diets replete with n-3 PUFAs (polyunsaturated fatty acids) are known to have therapeutic potential for the heart, although a specifically defined duration of the n-3 PUFA diet required to achieve these effects remains unknown, as does their mechanism of action. The present study was undertaken to establish whether adaptations in mitochondrial function and stress tolerance in the heart is evident following short- (3 weeks) and long- (14 weeks) term dietary intervention of n-3 PUFAs, and to identify novel mechanisms by which these adaptations occur. Mitochondrial respiration [mO2 (mitochondrial O2)], H2O2 emission [mH2O2 (mitochondrial H2O2)] and Ca2+-retention capacity [mCa2+ (mitochondrial Ca2+)] were assessed in mouse hearts following dietary intervention. Mice fed n-3 PUFAs for 14 weeks showed significantly lower mH2O2 and greater mCa2+ compared with all other groups. However, no significant differences were observed after 3 weeks of the n-3 PUFA diet, or in mice fed on an HFC (high-fat control) diet enriched with vegetable shortening, containing almost no n-3 PUFAs, for 14 weeks. Interestingly, expression and activity of key enzymes involved in antioxidant and phase II detoxification pathways, all mediated by Nrf2 (nuclear factor E2-related factor 2), were elevated in hearts from mice fed the n-3 PUFA diet, but not hearts from mice fed the HFC diet, even at 3 weeks. This increase in antioxidant systems in hearts from mice fed the n-3 PUFA diet was paralleled by increased levels of 4-hydroxyhexenal protein adducts, an aldehyde formed from peroxidation of n-3 PUFAs. The findings of the present study demonstrate distinct time-dependent effects of n-3 PUFAs on mitochondrial function and antioxidant response systems in the heart. In addition, they are the first to provide direct evidence that non-enzymatic oxidation products of n-3 PUFAs may be driving mitochondrial and redox-mediated adaptations, thereby revealing a novel mechanism for n-3 PUFA action in the heart.

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.

A high fat diet increases mitochondrial fatty acid oxidation and uncoupling to decrease efficiency in rat heart

Elevated levels of cardiac mitochondrial uncoupling protein 3 (UCP3) and decreased cardiac efficiency (hydraulic power/oxygen consumption) with abnormal cardiac function occur in obese, diabetic mice. To determine whether cardiac mitochondrial uncoupling occurs in non-genetic obesity, we fed rats a high fat diet (55% kcal from fat) or standard laboratory chow (7% kcal from fat) for 3 weeks, after which we measured cardiac function in vivo using cine MRI, efficiency in isolated working hearts and respiration rates and ADP/O ratios in isolated interfibrillar mitochondria; also, measured were medium chain acyl-CoA dehydrogenase (MCAD) and citrate synthase activities plus uncoupling protein 3 (UCP3), mitochondrial thioesterase 1 (MTE-1), adenine nucleotide translocase (ANT) and ATP synthase protein levels. We found that in vivo cardiac function was the same for all rats, yet oxygen consumption was 19% higher in high fat-fed rat hearts, therefore, efficiency was 21% lower than in controls. We found that mitochondrial fatty acid oxidation rates were 25% higher, and MCAD activity was 23% higher, in hearts from rats fed the high fat diet when compared with controls. Mitochondria from high fat-fed rat hearts had lower ADP/O ratios than controls, indicating increased respiratory uncoupling, which was ameliorated by GDP, a UCP3 inhibitor. Mitochondrial UCP3 and MTE-1 levels were both increased by 20% in high fat-fed rat hearts when compared with controls, with no significant change in ATP synthase or ANT levels, or citrate synthase activity. We conclude that increased cardiac oxygen utilisation, and thereby decreased cardiac efficiency, occurs in non-genetic obesity, which is associated with increased mitochondrial uncoupling due to elevated UCP3 and MTE-1 levels.

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.

Metabolic therapy at the crossroad: how to optimize myocardial substrate utilization?

There has been growing interest in targeting myocardial substrate metabolism for the therapy of cardiovascular and metabolic diseases. This is largely based on the observation that cardiac metabolism undergoes significant changes during both physiologic and pathologic stresses. In search for an effective therapeutic strategy, recent studies have focused on the functional significance of the substrate switch in the heart during stress conditions, such as cardiac hypertrophy and failure, using both pharmacologic and genetic approaches. The results of these studies indicate that both the capacity and the flexibility of the cardiac metabolic network are essential for normal function; thus, their maintenance should be the primary goal for future metabolic therapy.

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.

Creating and curing fatty hearts

PURPOSE OF REVIEW

Diseases associated with ectopic disposition of lipids are becoming an increasingly important medical problem as the incidence of type 2 diabetes and obesity increases. One of the organs affected by lipotoxicity is the heart and this review presents an update on human and animal studies of this problem.

RECENT FINDINGS

Human studies have clearly correlated heart dysfunction with the content of triglyceride. More recently human heart samples have been used to assess gene changes associated with altered lipid accumulation. Genetically altered mice have been created that develop lipotoxic cardiomyopathies and newer investigations are attempting to delineate curative therapies.

SUMMARY

Human studies will confirm the metabolic changes associated with lipotoxic cardiomyopathy and, hopefully, animal studies will guide treatment options.

Critical role of complex III in the early metabolic changes following myocardial infarction

AIMS

The chronically infarcted rat heart has multiple defects in metabolism, yet the location of the primary metabolic abnormality arising after myocardial infarction is unknown. Therefore, we investigated cardiac mitochondrial metabolism shortly after infarction.

METHODS AND RESULTS

Myocardial infarctions (n = 11) and sham operations (n = 9) were performed on Wistar rats, at 2 weeks cardiac function was assessed using echocardiography, and rats were grouped into failing (ejection fraction < or =45%), moderately impaired (46-60%), and sham-operated (>60%). Respiration rates were decreased by 28% in both subsarcolemmal and interfibrillar mitochondria isolated from failing hearts, compared with sham-operated controls. However, respiration rates were not impaired in mitochondria from hearts with moderately impaired function. The mitochondrial defect in the failing hearts was located within the electron transport chain (ETC), as respiration rates were suppressed to the same extent when fatty acids, ketone bodies, or glutamate were used as substrates. Complex III protein levels were decreased by 46% and complex III activity was decreased by 26%, in mitochondria from failing hearts, but all other ETC complexes were unchanged. Decreased complex III activity was accompanied by a three-fold increase in complex III-derived H(2)O(2) production, decreased cardiolipin content, and a 60% decrease in mitochondrial cytochrome c levels from failing hearts. Respiration rates, complex III activity, cardiolipin content, and reactive oxygen species generation rates correlated with ejection fraction.

CONCLUSION

In conclusion, a specific defect in complex III occurred acutely after myocardial infarction, which increased oxidative damage and impaired mitochondrial respiration. The extent of mitochondrial dysfunction in the failing heart was proportional to the degree of cardiac dysfunction induced by myocardial infarction.

Rodent models of diabetic cardiomyopathy

Diabetic cardiomyopathy increases the risk of heart failure in individuals with diabetes, independently of co-existing coronary artery disease and hypertension. The underlying mechanisms for this cardiac complication are incompletely understood. Research on rodent models of type 1 and type 2 diabetes, and the use of genetic engineering techniques in mice, have greatly advanced our understanding of the molecular mechanisms responsible for human diabetic cardiomyopathy. The adaptation of experimental techniques for the investigation of cardiac physiology in mice now allows comprehensive characterization of these models. The focus of the present review will be to discuss selected rodent models that have proven to be useful in studying the underlying mechanisms of human diabetic cardiomyopathy, and to provide an overview of the characteristics of these models for the growing number of investigators who seek to understand the pathology of diabetes-related heart disease.

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.