Total-body and myocardial substrate oxidation in congestive heart failure

Human cardiac metabolism

The heart is the most metabolically active organ in the human body, and cardiac metabolism has been studied for decades. However, the bulk of studies have focused on animal models. The objective of this review is to summarize specifically what is known about cardiac metabolism in humans. Techniques available to study human cardiac metabolism are first discussed, followed by a review of human cardiac metabolism in health and in heart failure. Mechanistic insights, where available, are reviewed, and the evidence for the contribution of metabolic insufficiency to heart failure, as well as past and current attempts at metabolism-based therapies, is also discussed.

Mitochondrial Dysfunction in Heart Failure: From Pathophysiological Mechanisms to Therapeutic Opportunities

Mitochondrial dysfunction, a feature of heart failure, leads to a progressive decline in bioenergetic reserve capacity, consisting in a shift of energy production from mitochondrial fatty acid oxidation to glycolytic pathways. This adaptive process of cardiomyocytes does not represent an effective strategy to increase the energy supply and to restore the energy homeostasis in heart failure, thus contributing to a vicious circle and to disease progression. The increased oxidative stress causes cardiomyocyte apoptosis, dysregulation of calcium homeostasis, damage of proteins and lipids, leakage of mitochondrial DNA, and inflammatory responses, finally stimulating different signaling pathways which lead to cardiac remodeling and failure. Furthermore, the parallel neurohormonal dysregulation with angiotensin II, endothelin-1, and sympatho-adrenergic overactivation, which occurs in heart failure, stimulates ventricular cardiomyocyte hypertrophy and aggravates the cellular damage. In this review, we will discuss the pathophysiological mechanisms related to mitochondrial dysfunction, which are mainly dependent on increased oxidative stress and perturbation of the dynamics of membrane potential and are associated with heart failure development and progression. We will also provide an overview of the potential implication of mitochondria as an attractive therapeutic target in the management and recovery process in heart failure.

Myocardial Metabolism in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is increasingly prevalent and now accounts for half of all heart failure cases. This rise is largely attributed to growing rates of obesity, hypertension, and diabetes. Despite its prevalence, the pathophysiological mechanisms of HFpEF are not fully understood. The heart, being the most energy-demanding organ, appears to have a compromised bioenergetic capacity in heart failure, affecting all phenotypes and aetiologies. While metabolic disturbances in heart failure with reduced ejection fraction (HFrEF) have been extensively studied, similar insights into HFpEF are limited. This review collates evidence from both animal and human studies, highlighting metabolic dysregulations associated with HFpEF and its risk factors, such as obesity, hypertension, and diabetes. We discuss how changes in substrate utilisation, oxidative phosphorylation, and energy transport contribute to HFpEF. By delving into these pathological shifts in myocardial energy production, we aim to reveal novel therapeutic opportunities. Potential strategies include modulating energy substrates, improving metabolic efficiency, and enhancing critical metabolic pathways. Understanding these aspects could be key to developing more effective treatments for HFpEF.

Cardiac Metabolism, Reprogramming, and Diseases

Cardiovascular diseases (CVD) account for the largest bulk of deaths worldwide, posing a massive burden on societies and the global healthcare system. Besides, the incidence and prevalence of these diseases are on the rise, demanding imminent action to revert this trend. Cardiovascular pathogenesis harbors a variety of molecular and cellular mechanisms among which dysregulated metabolism is of significant importance and may even proceed other mechanisms. The healthy heart metabolism primarily relies on fatty acids for the ultimate production of energy through oxidative phosphorylation in mitochondria. Other metabolites such as glucose, amino acids, and ketone bodies come next. Under pathological conditions, there is a shift in metabolic pathways and the preference of metabolites, termed metabolic remodeling or reprogramming. In this review, we aim to summarize cardiovascular metabolism and remodeling in different subsets of CVD to come up with a new paradigm for understanding and treatment of these diseases.

Insulin resistance and metabolic flexibility as drivers of liver and cardiac disease in T2DM

Metabolic flexibility refers to the ability of tissues to adapt their use of energy sources according to substrate availability and energy demands. This review aims to disentangle the emerging mechanisms through which altered metabolic flexibility and insulin resistance promote NAFLD and heart disease progression. Insulin resistance and metabolic inflexibility are central drivers of hepatic and cardiac diseases in individuals with type 2 diabetes. Both play a critical role in the complex interaction between glucose and lipid metabolism. Disruption of metabolic flexibility results in hyperglycemia and abnormal lipid metabolism, leading to increased accumulation of fat in the liver, contributing to the development and progression of NAFLD. Similarly, insulin resistance affects cardiac glucose metabolism, leading to altered utilization of energy substrates and impaired cardiac function, and influence cardiac lipid metabolism, further exacerbating the progression of heart failure. Regular physical activity promotes metabolic flexibility by increasing energy expenditure and enabling efficient switching between different energy substrates. On the contrary, weight loss achieved through calorie restriction ameliorates insulin sensitivity without improving flexibility. Strategies that mimic the effects of physical exercise, such as pharmacological interventions or targeted lifestyle modifications, show promise in effectively treating both diabetes and NAFLD, finally reducing the risk of advanced liver disease.

Novelties in the pharmacological approaches for chronic heart failure: new drugs and cardiovascular targets

Despite recent advances in chronic heart failure (HF) management, the prognosis of HF patients is poor. This highlights the need for researching new drugs targeting, beyond neurohumoral and hemodynamic modulation approach, such as cardiomyocyte metabolism, myocardial interstitium, intracellular regulation and NO-sGC pathway. In this review we report main novelties on new possible pharmacological targets for HF therapy, mainly on new drugs acting on cardiac metabolism, GCs-cGMP pathway, mitochondrial function and intracellular calcium dysregulation.

Targeting Myocardial Substrate Metabolism in the Failing Heart: Ready for Prime Time?

PURPOSE OF REVIEW

We review the clinical benefits of altering myocardial substrate metabolism in heart failure.

RECENT FINDINGS

Modulation of cardiac substrates (fatty acid, glucose, or ketone metabolism) offers a wide range of therapeutic possibilities which may be applicable to heart failure. Augmenting ketone oxidation seems to offer great promise as a new therapeutic modality in heart failure. The heart has long been recognized as metabolic omnivore, meaning it can utilize a variety of energy substrates to maintain adequate ATP production. The adult heart uses fatty acid as a major fuel source, but it can also derive energy from other substrates including glucose and ketone, and to some extent pyruvate, lactate, and amino acids. However, cardiomyocytes of the failing heart endure remarkable metabolic remodeling including a shift in substrate utilization and reduced ATP production, which account for cardiac remodeling and dysfunction. Research to understand the implication of myocardial metabolic perturbation in heart failure has grown in recent years, and this has raised interest in targeting myocardial substrate metabolism for heart failure therapy. Due to the interdependency between different pathways, the main therapeutic metabolic approaches include inhibiting fatty acid uptake/fatty acid oxidation, reducing circulating fatty acid levels, increasing glucose oxidation, and augmenting ketone oxidation.

Heart Failure and Drug Therapies: A Metabolic Review

Cardiovascular disease is the leading cause of mortality globally with at least 26 million people worldwide living with heart failure (HF). Metabolism has been an active area of investigation in the setting of HF since the heart demands a high rate of ATP turnover to maintain homeostasis. With the advent of -omic technologies, specifically metabolomics and lipidomics, HF pathologies have been better characterized with unbiased and holistic approaches. These techniques have identified novel pathways in our understanding of progression of HF and potential points of intervention. Furthermore, sodium-glucose transport protein 2 inhibitors, a drug that has changed the dogma of HF treatment, has one of the strongest types of evidence for a potential metabolic mechanism of action. This review will highlight cardiac metabolism in both the healthy and failing heart and then discuss the metabolic effects of heart failure drugs.

Lactate and Myocadiac Energy Metabolism

The myocardium is capable of utilizing different energy substrates, which is referred to as “metabolic flexibility.” This process assures ATP production from fatty acids, glucose, lactate, amino acids, and ketones, in the face of varying metabolic contexts. In the normal physiological state, the oxidation of fatty acids contributes to approximately 60% of energy required, and the oxidation of other substrates provides the rest. The accumulation of lactate in ischemic and hypoxic tissues has traditionally be considered as a by-product, and of little utility. However, recent evidence suggests that lactate may represent an important fuel for the myocardium during exercise or myocadiac stress. This new paradigm drives increasing interest in understanding its role in cardiac metabolism under both physiological and pathological conditions. In recent years, blood lactate has been regarded as a signal of stress in cardiac disease, linking to prognosis in patients with myocardial ischemia or heart failure. In this review, we discuss the importance of lactate as an energy source and its relevance to the progression and management of heart diseases.

Heart Metabolism in Sepsis-Induced Cardiomyopathy-Unusual Metabolic Dysfunction of the Heart

Due to the need for continuous work, the heart uses up to 8% of the total energy expenditure. Due to the relatively low adenosine triphosphate (ATP) storage capacity, the heart's work is dependent on its production. This is possible due to the metabolic flexibility of the heart, which allows it to use numerous substrates as a source of energy. Under normal conditions, a healthy heart obtains approximately 95% of its ATP by oxidative phosphorylation in the mitochondria. The primary source of energy is fatty acid oxidation, the rest of the energy comes from the oxidation of pyruvate. A failed heart is characterised by a disturbance in these proportions, with the contribution of individual components as a source of energy depending on the aetiology and stage of heart failure. A unique form of cardiac dysfunction is sepsis-induced cardiomyopathy, characterised by a significant reduction in energy production and impairment of cardiac oxidation of both fatty acids and glucose. Metabolic disorders appear to contribute to the pathogenesis of cardiac dysfunction and therefore are a promising target for future therapies. However, as many aspects of the metabolism of the failing heart remain unexplained, this issue requires further research.

Mitochondrial Bioenergetics and Dynamism in the Failing Heart

The heart is responsible for pumping blood, nutrients, and oxygen from its cavities to the whole body through rhythmic and vigorous contractions. Heart function relies on a delicate balance between continuous energy consumption and generation that changes from birth to adulthood and depends on a very efficient oxidative metabolism and the ability to adapt to different conditions. In recent years, mitochondrial dysfunctions were recognized as the hallmark of the onset and development of manifold heart diseases (HDs), including heart failure (HF). HF is a severe condition for which there is currently no cure. In this condition, the failing heart is characterized by a disequilibrium in mitochondrial bioenergetics, which compromises the basal functions and includes the loss of oxygen and substrate availability, an altered metabolism, and inefficient energy production and utilization. This review concisely summarizes the bioenergetics and some other mitochondrial features in the heart with a focus on the features that become impaired in the failing heart.

Role of mitochondrial quality surveillance in myocardial infarction: From bench to bedside

Myocardial infarction (MI) is the irreversible death of cardiomyocyte secondary to prolonged lack of oxygen or fresh blood supply. Historically considered as merely cardiomyocyte powerhouse that manufactures ATP and other metabolites, mitochondrion is recently being identified as a signal regulator that is implicated in the crosstalk and signal integration of cardiomyocyte contraction, metabolism, inflammation, and death. Mitochondria quality surveillance is an integrated network system modifying mitochondrial structure and function through the coordination of various processes including mitochondrial fission, fusion, biogenesis, bioenergetics, proteostasis, and degradation via mitophagy. Mitochondrial fission favors the elimination of depolarized mitochondria through mitophagy, whereas mitochondrial fusion preserves the mitochondrial network upon stress through integration of two or more small mitochondria into an interconnected phenotype. Mitochondrial biogenesis represents a regenerative program to replace old and damaged mitochondria with new and healthy ones. Mitochondrial bioenergetics is regulated by a metabolic switch between glucose and fatty acid usage, depending on oxygen availability. To maintain the diversity and function of mitochondrial proteins, a specialized protein quality control machinery regulates protein dynamics and function through the activity of chaperones and proteases, and induction of the mitochondrial unfolded protein response. In this review, we provide an overview of the molecular mechanisms governing mitochondrial quality surveillance and highlight the most recent preclinical and clinical therapeutic approaches to restore mitochondrial fitness during both MI and post-MI heart failure.

Identifying functional metabolic shifts in heart failure with the integration of omics data and a heart-specific, genome-scale model

In diseased states, the heart can shift to use different carbon substrates, measured through changes in uptake of metabolites by imaging methods or blood metabolomics. However, it is not known whether these measured changes are a result of transcriptional changes or external factors. Here, we explore transcriptional changes in late-stage heart failure using publicly available data integrated with a model of heart metabolism. First, we present a heart-specific genome-scale metabolic network reconstruction (GENRE), iCardio. Next, we demonstrate the utility of iCardio in interpreting heart failure gene expression data by identifying tasks inferred from differential expression (TIDEs), which represent metabolic functions associated with changes in gene expression. We identify decreased gene expression for nitric oxide (NO) and N-acetylneuraminic acid (Neu5Ac) synthesis as common metabolic markers of heart failure. The methods presented here for constructing a tissue-specific model and identifying TIDEs can be extended to multiple tissues and diseases of interest.

Ketone Ester Treatment Improves Cardiac Function and Reduces Pathologic Remodeling in Preclinical Models of Heart Failure

Supplemental Digital Content is available in the text.

Accumulating evidence suggests that the failing heart reprograms fuel metabolism toward increased utilization of ketone bodies and that increasing cardiac ketone delivery ameliorates cardiac dysfunction. As an initial step toward development of ketone therapies, we investigated the effect of chronic oral ketone ester (KE) supplementation as a prevention or treatment strategy in rodent heart failure models.

Metabolic effects of carvedilol through β-arrestin proteins: investigations in a streptozotocin-induced diabetes rat model and in C2C12 myoblasts

BACKGROUND AND PURPOSE

Carvedilol is a third-generation β-adrenoceptor antagonist, which also stimulates β-arrestins. β-arrestins initiate intracellular signalling and are involved in insulin release and sensitivity. Carvedilol is superior in effectiveness to other drugs that are used for similar indications and does not cause insulin resistance or diabetes, which can occur with other β-antagonists. We have shown that carvedilol increased glucose usage in C2C12 cells. We investigate the biased agonist efficacy of carvedilol on β-arrestins.

EXPERIMENTAL APPROACH

Streptozotocin (STZ)-induced diabetes rat model was used to induce metabolic and cardiac disorders. After 8 weeks of diabetes, animals were treated with carvedilol or vehicle for another 4 weeks. In vitro heart function was evaluated at baseline as well as with increasing concentrations of isoprenaline. Effects of diabetes and carvedilol treatment on β-arrestins, ERK, PPARα, CD36 proteins and pyruvate kinase activity were evaluated. β-arrestins were silenced in C2C12 cells by using siRNA. Acute effects of carvedilol on ERK, CD36, mitochondrial transcription factor A, cardiolipin proteins and citrate synthase activity were investigated.

KEY RESULTS

Carvedilol reversed the deterioration of cardiac function in diabetes and diabetes-induced decrease in β-arrestins in rats. Carvedilol decreased the expression of CD36 in diabetes and increased mitochondrial transcription factor A and cardiolipin proteins. Silencing of β-arrestins in cells prevented the effects of carvedilol on these proteins.

CONCLUSION AND IMPLICATIONS

The metabolic effects of carvedilol seem to be related to biased activation of β-arrestins. Patients with cardiovascular and metabolic disorders may benefit from new compounds that selectively act on β-arrestins.

Ketone metabolism in the failing heart

The high energy demands of the heart are met primarily by the mitochondrial oxidation of fatty acids and glucose. However, in heart failure there is a decrease in cardiac mitochondrial oxidative metabolism and glucose oxidation that can lead to an energy starved heart. Ketone bodies are readily oxidized by the heart, and can provide an additional source of energy for the failing heart. Ketone oxidation is increased in the failing heart, which may be an adaptive response to lessen the severity of heart failure. While ketone have been widely touted as a "thrifty fuel", increasing ketone oxidation in the heart does not increase cardiac efficiency (cardiac work/oxygen consumed), but rather does provide an additional fuel source for the failing heart. Increasing ketone supply to the heart and increasing mitochondrial ketone oxidation increases mitochondrial tricarboxylic acid cycle activity. In support of this, increasing circulating ketone by iv infusion of ketone bodies acutely improves heart function in heart failure patients. Chronically, treatment with sodium glucose co-transporter 2 inhibitors, which decreases the severity of heart failure, also increases ketone body supply to the heart. While ketogenic diets increase circulating ketone levels, minimal benefit on cardiac function in heart failure has been observed, possibly due to the fact that these dietary regimens also markedly increase circulating fatty acids. Recent studies, however, have suggested that administration of ketone ester cocktails may improve cardiac function in heart failure. Combined, emerging data suggests that increasing cardiac ketone oxidation may be a therapeutic strategy to treat heart failure.

Increased ketone body oxidation provides additional energy for the failing heart without improving cardiac efficiency

AIMS

The failing heart is energy-starved and inefficient due to perturbations in energy metabolism. Although ketone oxidation has been shown recently to increase in the failing heart, it remains unknown whether this improves cardiac energy production or efficiency. We therefore assessed cardiac metabolism in failing hearts and determined whether increasing ketone oxidation improves cardiac energy production and efficiency.

METHODS AND RESULTS

C57BL/6J mice underwent sham or transverse aortic constriction (TAC) surgery to induce pressure overload hypertrophy over 4-weeks. Isolated working hearts from these mice were perfused with radiolabelled β-hydroxybutyrate (βOHB), glucose, or palmitate to assess cardiac metabolism. Ejection fraction decreased by 45% in TAC mice. Failing hearts had decreased glucose oxidation while palmitate oxidation remained unchanged, resulting in a 35% decrease in energy production. Increasing βOHB levels from 0.2 to 0.6 mM increased ketone oxidation rates from 251 ± 24 to 834 ± 116 nmol·g dry wt-1 · min-1 in TAC hearts, rates which were significantly increased compared to sham hearts and occurred without decreasing glycolysis, glucose, or palmitate oxidation rates. Therefore, the contribution of ketones to energy production in TAC hearts increased to 18% and total energy production increased by 23%. Interestingly, glucose oxidation, in parallel with total ATP production, was also significantly upregulated in hearts upon increasing βOHB levels. However, while overall energy production increased, cardiac efficiency was not improved.

CONCLUSIONS

Increasing ketone oxidation rates in failing hearts increases overall energy production without compromising glucose or fatty acid metabolism, albeit without increasing cardiac efficiency.

Myocardial Ketones Metabolism in Heart Failure

Ketone bodies can become a major source of adenosine triphosphate production during stress to maintain bioenergetic homeostasis in the brain, heart, and skeletal muscles. In the normal heart, ketone bodies contribute from 10% to 15% of the cardiac adenosine triphosphate production, although their contribution during pathologic stress is still not well-characterized and currently represents an exciting area of cardiovascular research. This review focuses on the mechanisms that regulate circulating ketone levels under physiologic and pathologic conditions and how this impacts cardiac ketone metabolism. We also review the current understanding of the role of augmented ketone metabolism as an adaptive response in different types and stages of heart failure. This analysis includes the emerging experimental and clinical evidence of the potential favorable effects of boosting ketone metabolism in the failing heart and the possible mechanisms of action through which these interventions may mediate their cardioprotective effects. We also critically appraise the emerging data from animal and human studies which characterize the role of ketones in mediating the cardioprotection established by the new class of antidiabetic drugs, namely sodium-glucose co-transporter inhibitors.

Mitochondrial membrane transporters and metabolic switch in heart failure

Mitochondrial dysfunction is widely recognized as a major factor for the progression of cardiac failure. Mitochondrial uptake of metabolic substrates and their utilization for ATP synthesis, electron transport chain activity, reactive oxygen species levels, ion homeostasis, mitochondrial biogenesis, and dynamics as well as levels of reactive oxygen species in the mitochondria are key factors which regulate mitochondrial function in the normal heart. Alterations in these functions contribute to adverse outcomes in heart failure. Iron imbalance and oxidative stress are also major factors for the evolution of cardiac hypertrophy, heart failure, and aging-associated pathological changes in the heart. Mitochondrial ATP-binding cassette (ABC) transporters have a key role in regulating iron metabolism and maintenance of redox status in cells. Deficiency of mitochondrial ABC transporters is associated with an impaired mitochondrial electron transport chain complex activity, iron overload, and increased levels of reactive oxygen species, all of which can result in mitochondrial dysfunction. In this review, we discuss the role of mitochondrial ABC transporters in mitochondrial metabolism and metabolic switch, alterations in the functioning of ABC transporters in heart failure, and mitochondrial ABC transporters as possible targets for therapeutic intervention in cardiac failure.

Metabolomic Profiling of Left Ventricular Diastolic Dysfunction in Women With or at Risk for HIV Infection: The Women's Interagency HIV Study

Background People living with HIV have an increased risk of left ventricular diastolic dysfunction (LVDD) and heart failure. HIV-associated LVDD may reflect both cardiomyocyte and systemic metabolic derangements, but the underlying pathways remain unclear. Methods and Results To explore such pathways, we conducted a pilot study in the Bronx and Brooklyn sites of the WIHS (Women's Interagency HIV Study) who participated in concurrent, but separate, metabolomics and echocardiographic ancillary studies. Liquid chromatography tandem mass spectrometry-based metabolomic profiling was performed on plasma samples from 125 HIV-infected (43 with LVDD) and 35 HIV-uninfected women (9 with LVDD). Partial least squares discriminant analysis identified polar metabolites and lipids in the glycerophospholipid-metabolism and fatty-acid-oxidation pathways associated with LVDD. After multivariable adjustment, LVDD was significantly associated with higher concentrations of diacylglycerol 30:0 (odds ratio [OR], 1.60, 95% CI [1.01-2.55]); triacylglycerols 46:0 (OR 1.60 [1.04-2.48]), 48:0 (OR 1.63 [1.04-2.54]), 48:1 (OR 1.62 [1.01-2.60]), and 50:0 (OR 1.61 [1.02-2.53]); acylcarnitine C7 (OR 1.88 [1.21-2.92]), C9 (OR 1.99 [1.27-3.13]), and C16 (OR 1.80 [1.13-2.87]); as well as lower concentrations of phosphocholine (OR 0.59 [0.38-0.91]). There was no evidence of effect modification of these relationships by HIV status. Conclusions In this pilot study, women with or at risk of HIV with LVDD showed alterations in plasma metabolites in the glycerophospholipid-metabolism and fatty-acid-oxidation pathways. Although these findings require replication, they suggest that improved understanding of metabolic perturbations and their potential modification could offer new approaches to prevent cardiac dysfunction in this high-risk group.

CaMKII and GLUT1 in heart failure and the role of gliflozins

Empagliflozin, a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, has been shown to reduce mortality and hospitalization for heart failure in diabetic patients in the EMPA-REG-OUTCOME trial (Zinman et al., 2015). Surprisingly, dapagliflozin, another SGLT2 inhibitor, exerted comparable effects on clinical endpoints even in the absence of diabetes mellitus (DAPA-HF trial) (McMurray et al., 2019). There is a myriad of suggested underlying mechanisms ranging from improved glycemic control and hemodynamic effects to altered myocardial metabolism, inflammation, neurohumoral activation and intracellular ion homeostasis. Here, we review the effects of gliflozins on cardiac electro-mechanical coupling with an emphasis on novel CaMKII-mediated pathways and on cardiac glucose and ketone metabolism in the failing heart. We focus on empagliflozin as it is the gliflozin with the most abundant experimental evidence for direct effects on the heart. Where useful, we aim to compare empagliflozin to other gliflozins. To facilitate understanding of empagliflozin-induced alterations, we first give a short summary of the pathophysiological role of CaMKII in heart failure, as well as cardiac changes of glucose and ketone body metabolism in the failing heart.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

Increased Cardiac Uptake of Ketone Bodies and Free Fatty Acids in Human Heart Failure and Hypertrophic Left Ventricular Remodeling

BACKGROUND

Deranged energy metabolism contributes to the pathophysiology of heart failure (HF). Recent studies showed diminished free fatty acid (FFA) oxidation in experimental HF models with a shift towards oxidation of ketone bodies. However, conflicting clinical data on FFA metabolism and limited knowledge on ketone body metabolism in human HF mandate additional metabolic profiling studies. We, therefore, investigated cardiac uptake of FFAs and ketone bodies (β-hydroxybutyrate and acetoacetate) in patients with HF with reduced ejection fraction (HFrEF) or with aortic stenosis (AS)-induced left ventricular hypertrophy. We hypothesized that FFA oxidation is impaired in HFrEF and in AS and results in decreased concentrations of free carnitine, the necessary carrier for mitochondrial entry of activated FFAs, and in accumulation of metabolic intermediates.

METHODS AND RESULTS

We collected arterial and coronary sinus blood samples in patients with HFrEF (n=15), in AS patients with preserved systolic function (n=15), and in control patients (n=15). Plasma concentration gradients across the heart show significantly greater uptake of ketone bodies in patients with HFrEF than in controls. Patients with AS show significantly increased uptake of β-hydroxybutyrate and FFAs. Free carnitine concentration and concentration gradients of intermediates of FFA oxidation were comparable between groups.

CONCLUSIONS

In conclusion, our results show significantly increased cardiac uptake of ketone bodies in patients with stable HFrEF and AS and increased uptake of FFAs in AS compared with control patients. The lack of myocardial release of acyl-carnitine species or change in free carnitine uptake suggests no impairment of FFA oxidation.

Cardiac Resynchronisation Therapy and Cellular Bioenergetics: Effects Beyond Chamber Mechanics

Cardiac resynchronisation therapy is a cornerstone in the treatment of advanced dyssynchronous heart failure. However, despite its widespread clinical application, precise mechanisms through which it exerts its beneficial effects remain elusive. Several studies have pointed to a metabolic component suggesting that, both in concert with alterations in chamber mechanics and independently of them, resynchronisation reverses detrimental changes to cellular metabolism, increasing energy efficiency and metabolic reserve. These actions could partially account for the existence of responders that improve functionally but not echocardiographically. This article will attempt to summarise key components of cardiomyocyte metabolism in health and heart failure, with a focus on the dyssynchronous variant. Both chamber mechanics-related and -unrelated pathways of resynchronisation effects on bioenergetics – stemming from the ultramicroscopic level – and a possible common underlying mechanism relating mechanosensing to metabolism through the cytoskeleton will be presented. Improved insights regarding the cellular and molecular effects of resynchronisation on bioenergetics will promote our understanding of non-response, optimal device programming and lead to better patient care.

Adaptations in Protein Expression and Regulated Activity of Pyruvate Dehydrogenase Multienzyme Complex in Human Systolic Heart Failure

Pyruvate dehydrogenase (PDH) complex, a multienzyme complex at the nexus of glycolytic and Krebs cycles, provides acetyl-CoA to the Krebs cycle and NADH to complex I thus supporting a critical role in mitochondrial energy production and cellular survival. PDH activity is regulated by pyruvate dehydrogenase phosphatases (PDP1, PDP2), pyruvate dehydrogenase kinases (PDK 1-4), and mitochondrial pyruvate carriers (MPC1, MPC2). As NADH-dependent oxidative phosphorylation is diminished in systolic heart failure, we tested whether the left ventricular myocardium (LV) from end-stage systolic adult heart failure patients (n = 26) exhibits altered expression of PDH complex subunits, PDK, MPC, PDP, and PDH complex activity, compared to LV from nonfailing donor hearts (n = 21). Compared to nonfailing LV, PDH activity and relative expression levels of E2, E3bp, E1α, and E1β subunits were greater in LV failure. PDK4, MPC1, and MPC2 expressions were decreased in failing LV, whereas PDP1, PDP2, PDK1, and PDK2 expressions did not differ between nonfailing and failing LV. In order to examine PDK4 further, donor human LV cardiomyocytes were induced in culture to hypertrophy with 0.1 μM angiotensin II and treated with PDK inhibitors (0.2 mM dichloroacetate, or 5 mM pyruvate) or activators (0.6 mM NADH plus 50 μM acetyl CoA). In isolated hypertrophic cardiomyocytes in vitro, PDK activators and inhibitors increased and decreased PDK4, respectively. In conclusion, in end-stage failing hearts, greater expression of PDH proteins and decreased expression of PDK4, MPC1, and MPC2 were evident with higher rates of PDH activity. These adaptations support sustained capacity for PDH to facilitate glucose metabolism in the face of other failing bioenergetic pathways.

Loss of Metabolic Flexibility in the Failing Heart

To maintain its high energy demand the heart is equipped with a highly complex and efficient enzymatic machinery that orchestrates ATP production using multiple energy substrates, namely fatty acids, carbohydrates (glucose and lactate), ketones and amino acids. The contribution of these individual substrates to ATP production can dramatically change, depending on such variables as substrate availability, hormonal status and energy demand. This "metabolic flexibility" is a remarkable virtue of the heart, which allows utilization of different energy substrates at different rates to maintain contractile function. In heart failure, cardiac function is reduced, which is accompanied by discernible energy metabolism perturbations and impaired metabolic flexibility. While it is generally agreed that overall mitochondrial ATP production is impaired in the failing heart, there is less consensus as to what actual switches in energy substrate preference occur. The failing heart shift toward a greater reliance on glycolysis and ketone body oxidation as a source of energy, with a decrease in the contribution of glucose oxidation to mitochondrial oxidative metabolism. The heart also becomes insulin resistant. However, there is less consensus as to what happens to fatty acid oxidation in heart failure. While it is generally believed that fatty acid oxidation decreases, a number of clinical and experimental studies suggest that fatty acid oxidation is either not changed or is increased in heart failure. Of importance, is that any metabolic shift that does occur has the potential to aggravate cardiac dysfunction and the progression of the heart failure. An increasing body of evidence shows that increasing cardiac ATP production and/or modulating cardiac energy substrate preference positively correlates with heart function and can lead to better outcomes. This includes increasing glucose and ketone oxidation and decreasing fatty acid oxidation. In this review we present the physiology of the energy metabolism pathways in the heart and the changes that occur in these pathways in heart failure. We also look at the interventions which are aimed at manipulating the myocardial metabolic pathways toward more efficient substrate utilization which will eventually improve cardiac performance.

Longitudinal Evaluation of Myocardial Fatty Acid and Glucose Metabolism in Fasted and Nonfasted Spontaneously Hypertensive Rats Using MicroPET/CT

Using longitudinal micro positron emission tomography (microPET)/computed tomography (CT) studies, we quantified changes in myocardial metabolism and perfusion in spontaneously hypertensive rats (SHRs), a model of left ventricular hypertrophy (LVH). Fatty acid and glucose metabolism were quantified in the hearts of SHRs and Wistar-Kyoto (WKY) normotensive rats using long-chain fatty acid analog ¹⁸F-fluoro-6-thia heptadecanoic acid (¹⁸F-FTHA) and glucose analog ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) under normal or fasting conditions. We also used ¹⁸F-fluorodihydrorotenol (¹⁸F-FDHROL) to investigate perfusion in their hearts without fasting. Rats were imaged at 4 or 5 times over their life cycle. Compartment modeling was used to estimate the rate constants for the radiotracers. Blood samples were obtained and analyzed for glucose and free fatty acid concentrations. SHRs demonstrated no significant difference in ¹⁸F-FDHROL wash-in rate constant (P = .1) and distribution volume (P = .1), significantly higher ¹⁸F-FDG myocardial influx rate constant (P = 4×10⁻⁸), and significantly lower ¹⁸F-FTHA myocardial influx rate constant (P = .007) than WKYs during the 2009-2010 study without fasting. SHRs demonstrated a significantly higher ¹⁸F-FDHROL wash-in rate constant (P = 5×10⁻⁶) and distribution volume (P = 3×10⁻⁸), significantly higher ¹⁸F-FDG myocardial influx rate constant (P = 3×10⁻⁸), and a higher trend of ¹⁸F-FTHA myocardial influx rate constant (not significant, P = .1) than WKYs during the 2011–2012 study with fasting. Changes in glucose plasma concentrations were generally negatively correlated with corresponding radiotracer influx rate constant changes. The study indicates a switch from preferred fatty acid metabolism to increased glucose metabolism with hypertrophy. Increased perfusion during the 2011-2012 study may be indicative of increased aerobic metabolism in the SHR model of LVH.

Cardiac metabolism - A promising therapeutic target for heart failure

Both heart failure with reduced ejection fraction (HFrEF) and with preserved ejection fraction (HFpEF) are associated with high morbidity and mortality. Although many established pharmacological interventions exist for HFrEF, hospitalization and death rates remain high, and for those with HFpEF (approximately half of all heart failure patients), there are no effective therapies. Recently, the role of impaired cardiac energetic status in heart failure has gained increasing recognition with the identification of reduced capacity for both fatty acid and carbohydrate oxidation, impaired function of the electron transport chain, reduced capacity to transfer ATP to the cytosol, and inefficient utilization of the energy produced. These nodes in the genesis of cardiac energetic impairment provide potential therapeutic targets, and there is promising data from recent experimental and early-phase clinical studies evaluating modulators such as carnitine palmitoyltransferase 1 inhibitors, partial fatty acid oxidation inhibitors and mitochondrial-targeted antioxidants. Metabolic modulation may provide significant symptomatic and prognostic benefit for patients suffering from heart failure above and beyond guideline-directed therapy, but further clinical trials are needed.

Pediatric and adult dilated cardiomyopathy represent distinct pathological entities

Pediatric dilated cardiomyopathy (DCM) is the most common indication for heart transplantation in children. Despite similar genetic etiologies, medications routinely used in adult heart failure patients do not improve outcomes in the pediatric population. The mechanistic basis for these observations is unknown. We hypothesized that pediatric and adult DCM comprise distinct pathological entities, in that children do not undergo adverse remodeling, the target of adult heart failure therapies. To test this hypothesis, we examined LV specimens obtained from pediatric and adult donor controls and DCM patients. Consistent with the established pathophysiology of adult heart failure, adults with DCM displayed marked cardiomyocyte hypertrophy and myocardial fibrosis compared with donor controls. In contrast, pediatric DCM specimens demonstrated minimal cardiomyocyte hypertrophy and myocardial fibrosis compared with both age-matched controls and adults with DCM. Strikingly, RNA sequencing uncovered divergent gene expression profiles in pediatric and adult patients, including enrichment of transcripts associated with adverse remodeling and innate immune activation in adult DCM specimens. Collectively, these findings reveal that pediatric and adult DCM represent distinct pathological entities, provide a mechanistic basis to explain why children fail to respond to adult heart failure therapies, and suggest the need to develop new approaches for pediatric DCM.

Proteomics of acute heart failure in a rat post-myocardial infarction model

The aim of the present study was to identify the mechanisms underlying the development of post-myocardial infarction (post-MI) heart failure. The left anterior descending coronary artery of rats was occluded to mimic human ischemic heart disease. Linear Trap Quadropole OrbiTrap mass spectrometry was used to profile the expressions of energy metabolism‑associated and calcium‑binding proteins in the post‑MI and control groups. Using the online Protein Analysis Through Evolutionary Relationships classification system, 78 differentially expressed proteins were identified, including 50 downregulated proteins and 28 upregulated proteins in post‑MI group when compared with the control group. The differentially expressed proteins were closely associated with energy metabolism, contractile function, calcium handling, pathological hypertrophy and cardiac remodeling. These results were further validated using western blotting. At different postoperative time points (1st and 14th day following surgery) during the progression of advanced heart failure post‑MI, dynamic alterations in differential protein expression were identified. The expression of the vitamin D protein was significantly upregulated on the 1st day post‑MI however, was then downregulated with progression of the disease on the 14th day post‑MI. These results identified various target proteins associated with the disease, which may be used as diagnostic markers.

Cardiac metabolic imaging: current imaging modalities and future perspectives

In this review, current imaging techniques and their future perspectives in the field of cardiac metabolic imaging in humans are discussed. This includes a range of noninvasive imaging techniques, allowing a detailed investigation of cardiac metabolism in health and disease. The main imaging modalities discussed are magnetic resonance spectroscopy techniques for determination of metabolite content (triglycerides, glucose, ATP, phosphocreatine, and so on), MRI for myocardial perfusion, and single-photon emission computed tomography and positron emission tomography for quantitation of perfusion and substrate uptake.

Mitochondrial remodeling: Rearranging, recycling, and reprogramming

Mitochondria are highly dynamic and responsive organelles that respond to environmental cues with fission and fusion. They undergo mitophagy and biogenesis, and are subject to extensive post-translational modifications. Calcium plays an important role in regulating mitochondrial functions. Mitochondria play a central role in metabolism of glucose, fatty acids, and amino acids, and generate ATP with effects on redox poise, oxidative stress, pH, and other metabolites including acetyl-CoA and NAD(+) which in turn have effects on chromatin remodeling. The complex interplay of mitochondria, cytosolic factors, and the nucleus ensure a well-coordinated response to environmental stresses.

Effects of the Novel Long-Acting GLP-1 Agonist, Albiglutide, on Cardiac Function, Cardiac Metabolism, and Exercise Capacity in Patients With Chronic Heart Failure and Reduced Ejection Fraction

OBJECTIVES

This study sought to determine if glucagon-like peptide (GLP)-1 ameliorates myocardial metabolic abnormalities in chronic heart failure.

BACKGROUND

Albiglutide (GSK716155) is a GLP-1 agonist indicated for type 2 diabetes.

METHODS

We performed a randomized, placebo-controlled study evaluating 12 weeks of albiglutide in New York Heart Association II or III subjects with ejection fraction <40%. Subjects received weekly placebo (n = 30) or albiglutide 3.75 mg (n = 12), 15 mg (n = 13), or 30 mg (n = 27). The primary comparison was between albiglutide 30 mg and placebo. Assessments included echocardiography, 6-minute-walk test, and peak oxygen consumption. In a subgroup of patients, myocardial glucose and oxygen use were assessed. Endpoints are reported as change from baseline ± SE.

RESULTS

Albiglutide 30 mg compared with placebo did not improve change from baseline in left ventricular ejection fraction (2.4% [1.1%] vs. 4.4% [1.1%]; p = 0.22), 6-min walk test (18 [12] m vs. 9 [11] m; p = 0.58), myocardial glucose use (p = 0.59), or oxygen use (p = 0.25). In contrast, albiglutide 30 mg versus placebo improved change from baseline in peak oxygen consumption (0.9 [0.5] ml/kg/min vs. -0.6 [0.5] ml/kg/min; p = 0.02). Albiglutide was well tolerated.

CONCLUSIONS

Although there was no detectable effect of albiglutide on cardiac function or myocardial glucose use, there was a modest increase in peak oxygen consumption, which could have been mediated by noncardiac effects. (A Multi-center, Placebo-controlled Study to Evaluate the Safety of GSK716155 and Its Effects on Myocardial Metabolism, Myocardial Function, and Exercise Capacity in Patients With NYHA Class II/III Congestive Heart Failure; NCT01357850).

Exhaled Acetone Concentration Is Related to Hemodynamic Severity in Patients With Non-Ischemic Chronic Heart Failure

BACKGROUND

We hypothesized that exhaled acetone concentration (EAC), reflecting altered blood ketone body metabolism and increased acetone exhaust because of pulmonary congestion in heart failure (HF), would correlate with hemodynamic parameters in patients with non-ischemic chronic HF.

METHODS AND RESULTS

We prospectively enrolled 102 non-ischemic HF patients with New York Heart Association (NYHA) class I-III. Exhaled breath was collected after an overnight fast. Echocardiography and cardiac catheterization were performed in all patients. We also enrolled 17 control patients without HF. EAC in the HF patients was significantly higher than that in the control patients (median EAC; 0.53 vs. 0.38 ppm, P=0.012). EAC positively correlated with blood total ketone bodies (r=0.454, P<0.001), NYHA class (r=0.489, P<0.001), and plasma B-type natriuretic peptide (r=0.316, P=0.001). Right heart catheterization revealed that EAC significantly correlated with pulmonary capillary wedge pressure (PCWP, r=0.377, P<0.001). Receiver-operating characteristic analysis revealed that EAC >1.05 ppm was associated with PCWP ≥18 mmHg (area under the curve [AUC] 0.726, sensitivity 50%, specificity 89%). EAC was shown to be a comparable diagnostic biomarker for HF to BNP (AUC 0.760, sensitivity 80%, specificity 70%).

CONCLUSIONS

EAC may be a novel noninvasive biomarker that correlates hemodynamic severity in non-ischemic chronic HF. (Circ J 2016; 80: 1178-1186).

Normalization of cardiac substrate utilization and left ventricular hypertrophy precede functional recovery in heart failure regression

AIMS

Impaired cardiac substrate metabolism plays an important role in heart failure (HF) pathogenesis. Since many of these metabolic changes occur at the transcriptional level of metabolic enzymes, it is possible that this loss of metabolic flexibility is permanent and thus contributes to worsening cardiac function and/or prevents the full regression of HF upon treatment. However, despite the importance of cardiac energetics in HF, it remains unclear whether these metabolic changes can be normalized. In the current study, we investigated whether a reversal of an elevated aortic afterload in mice with severe HF would result in the recovery of cardiac function, substrate metabolism, and transcriptional reprogramming as well as determined the temporal relationship of these changes.

METHODS AND RESULTS

Male C57Bl/6 mice were subjected to either Sham or transverse aortic constriction (TAC) surgery to induce HF. After HF development, mice with severe HF (% ejection fraction < 30) underwent a second surgery to remove the aortic constriction (debanding, DB). Three weeks following DB, there was a near complete recovery of systolic and diastolic function, and gene expression of several markers for hypertrophy/HF were returned to values observed in healthy controls. Interestingly, pressure-overload-induced left ventricular hypertrophy (LVH) and cardiac substrate metabolism were restored at 1-week post-DB, which preceded functional recovery.

CONCLUSIONS

The regression of severe HF is associated with early and dramatic improvements in cardiac energy metabolism and LVH normalization that precede restored cardiac function, suggesting that metabolic and structural improvements may be critical determinants for functional recovery.

Mitochondrial protein hyperacetylation in the failing heart

Myocardial fuel and energy metabolic derangements contribute to the pathogenesis of heart failure. Recent evidence implicates posttranslational mechanisms in the energy metabolic disturbances that contribute to the pathogenesis of heart failure. We hypothesized that accumulation of metabolite intermediates of fuel oxidation pathways drives posttranslational modifications of mitochondrial proteins during the development of heart failure. Myocardial acetylproteomics demonstrated extensive mitochondrial protein lysine hyperacetylation in the early stages of heart failure in well-defined mouse models and the in end-stage failing human heart. To determine the functional impact of increased mitochondrial protein acetylation, we focused on succinate dehydrogenase A (SDHA), a critical component of both the tricarboxylic acid (TCA) cycle and respiratory complex II. An acetyl-mimetic mutation targeting an SDHA lysine residue shown to be hyperacetylated in the failing human heart reduced catalytic function and reduced complex II-driven respiration. These results identify alterations in mitochondrial acetyl-CoA homeostasis as a potential driver of the development of energy metabolic derangements that contribute to heart failure.

The Failing Heart Relies on Ketone Bodies as a Fuel

BACKGROUND

Significant evidence indicates that the failing heart is energy starved. During the development of heart failure, the capacity of the heart to utilize fatty acids, the chief fuel, is diminished. Identification of alternate pathways for myocardial fuel oxidation could unveil novel strategies to treat heart failure.

METHODS AND RESULTS

Quantitative mitochondrial proteomics was used to identify energy metabolic derangements that occur during the development of cardiac hypertrophy and heart failure in well-defined mouse models. As expected, the amounts of proteins involved in fatty acid utilization were downregulated in myocardial samples from the failing heart. Conversely, expression of β-hydroxybutyrate dehydrogenase 1, a key enzyme in the ketone oxidation pathway, was increased in the heart failure samples. Studies of relative oxidation in an isolated heart preparation using ex vivo nuclear magnetic resonance combined with targeted quantitative myocardial metabolomic profiling using mass spectrometry revealed that the hypertrophied and failing heart shifts to oxidizing ketone bodies as a fuel source in the context of reduced capacity to oxidize fatty acids. Distinct myocardial metabolomic signatures of ketone oxidation were identified.

CONCLUSIONS

These results indicate that the hypertrophied and failing heart shifts to ketone bodies as a significant fuel source for oxidative ATP production. Specific metabolite biosignatures of in vivo cardiac ketone utilization were identified. Future studies aimed at determining whether this fuel shift is adaptive or maladaptive could unveil new therapeutic strategies for heart failure.

Heart failure and loss of metabolic control

Heart failure is a leading cause of morbidity and mortality worldwide, currently affecting 5 million Americans. A syndrome defined on clinical terms, heart failure is the end result of events occurring in multiple heart diseases, including hypertension, myocardial infarction, genetic mutations and diabetes, and metabolic dysregulation, is a hallmark feature. Mounting evidence from clinical and preclinical studies suggests strongly that fatty acid uptake and oxidation are adversely affected, especially in end-stage heart failure. Moreover, metabolic flexibility, the heart's ability to move freely among diverse energy substrates, is impaired in heart failure. Indeed, impairment of the heart's ability to adapt to its metabolic milieu and associated metabolic derangement are important contributing factors in the heart failure pathogenesis. Elucidation of molecular mechanisms governing metabolic control in heart failure will provide critical insights into disease initiation and progression, raising the prospect of advances with clinical relevance.

Resveratrol treatment of mice with pressure-overload-induced heart failure improves diastolic function and cardiac energy metabolism

BACKGROUND

Although resveratrol has multiple beneficial cardiovascular effects, whether resveratrol can be used for the treatment and management of heart failure (HF) remains unclear. In the current study, we determined whether resveratrol treatment of mice with established HF could lessen the detrimental phenotype associated with pressure-overload-induced HF and identified physiological and molecular mechanisms contributing to this.

METHODS AND RESULTS

C57Bl/6 mice were subjected to either sham or transverse aortic constriction surgery to induce HF. Three weeks post surgery, a cohort of mice with established HF (% ejection fraction <45) was administered resveratrol (≈320 mg/kg per day). Despite a lack of improvement in ejection fraction, resveratrol treatment significantly increased median survival of mice with HF, lessened cardiac fibrosis, reduced gene expression of several disease markers for hypertrophy and extracellular matrix remodeling that were upregulated in HF, promoted beneficial remodeling, and improved diastolic function. Resveratrol treatment of mice with established HF also restored the levels of mitochondrial oxidative phosphorylation complexes, restored cardiac AMP-activated protein kinase activation, and improved myocardial insulin sensitivity to promote glucose metabolism and significantly improved myocardial energetic status. Finally, noncardiac symptoms of HF, such as peripheral insulin sensitivity, vascular function, and physical activity, were improved with resveratrol treatment.

CONCLUSIONS

Resveratrol treatment of mice with established HF lessens the severity of the HF phenotype by lessening cardiac fibrosis, improving molecular and structural remodeling of the heart, and enhancing diastolic function, vascular function, and energy metabolism.

Cardiac metabolism in hypertrophy and heart failure: implications for therapy

The heart consumes huge amounts of energy to fulfil its function as a relentless pump. A highly sophisticated system of energy generation based on flexibility of substrate use and efficient energy production, effective energy sensing and energy transfer ensures function of the healthy heart across a range of physiological situations. In left ventricular hypertrophy and heart failure, these processes become disturbed, leading as will be discussed to impaired cardiac energetic status and to further impairment of cardiac function. These metabolic disturbances form a potential target for therapy.

Metabolomic analysis of pressure-overloaded and infarcted mouse hearts

BACKGROUND

Cardiac hypertrophy and heart failure are associated with metabolic dysregulation and a state of chronic energy deficiency. Although several disparate changes in individual metabolic pathways have been described, there has been no global assessment of metabolomic changes in hypertrophic and failing hearts in vivo. Hence, we investigated the impact of pressure overload and infarction on myocardial metabolism.

METHODS AND RESULTS

Male C57BL/6J mice were subjected to transverse aortic constriction or permanent coronary occlusion (myocardial infarction [MI]). A combination of LC/MS/MS and GC/MS techniques was used to measure 288 metabolites in these hearts. Both transverse aortic constriction and MI were associated with profound changes in myocardial metabolism affecting up to 40% of all metabolites measured. Prominent changes in branched-chain amino acids were observed after 1 week of transverse aortic constriction and 5 days after MI. Changes in branched-chain amino acids after MI were associated with myocardial insulin resistance. Longer duration of transverse aortic constriction and MI led to a decrease in purines, acylcarnitines, fatty acids, and several lysolipid and sphingolipid species but a marked increase in pyrimidines as well as ascorbate, heme, and other indices of oxidative stress. Cardiac remodeling and contractile dysfunction in hypertrophied hearts were associated with large increases in myocardial, but not plasma, levels of the polyamines putrescine and spermidine as well as the collagen breakdown product prolylhydroxyproline.

CONCLUSIONS

These findings reveal extensive metabolic remodeling common to both hypertrophic and failing hearts that are indicative of extracellular matrix remodeling, insulin resistance and perturbations in amino acid, and lipid and nucleotide metabolism.

Metabolic remodeling in chronic heart failure

Although the management of chronic heart failure (CHF) has made enormous progress over the past decades, CHF is still a tremendous medical and societal burden. Metabolic remodeling might play a crucial role in the pathophysiology of CHF. The characteristics and mechanisms of metabolic remodeling remained unclear, and the main hypothesis might include the changes in the availability of metabolic substrate and the decline of metabolic capability. In the early phases of the disease, metabolism shifts toward carbohydrate utilization from fatty acids (FAs) oxidation. Along with the progress of the disease, the increasing level of the hyperadrenergic state and insulin resistance cause the changes that shift back to a greater FA uptake and oxidation. In addition, a growing body of experimental and clinical evidence suggests that the improvement in the metabolic capability is likely to be more significant than the selection of the substrate.

Longitudinal evaluation of left ventricular substrate metabolism, perfusion, and dysfunction in the spontaneously hypertensive rat model of hypertrophy using small-animal PET/CT imaging

Myocardial metabolic and perfusion imaging is a vital tool for understanding the physiologic consequences of heart failure. We used PET imaging to examine the longitudinal kinetics of (18)F-FDG and 14(R,S)-(18)F-fluoro-6-thia-heptadecanoic acid ((18)F-FTHA) as analogs of glucose and fatty acid (FA) to quantify metabolic substrate shifts with the spontaneously hypertensive rat (SHR) as a model of left ventricular hypertrophy (LVH) and failure. Myocardial perfusion and left ventricular function were also investigated using a newly developed radiotracer (18)F-fluorodihydrorotenol ((18)F-FDHROL).

METHODS

Longitudinal dynamic electrocardiogram-gated small-animal PET/CT studies were performed with 8 SHR and 8 normotensive Wistar-Kyoto (WKY) rats over their life cycle. We determined the myocardial influx rate constant for (18)F-FDG and (18)F-FTHA (Ki(FDG) and Ki(FTHA), respectively) and the wash-in rate constant for (18)F-FDHROL (K1(FDHROL)). (18)F-FDHROL data were also used to quantify left ventricular ejection fraction (LVEF) and end-diastolic volume (EDV). Blood samples were drawn to independently measure plasma concentrations of glucose, insulin, and free fatty acids (FFAs).

RESULTS

Ki(FDG) and Ki(FTHA) were higher in SHRs than WKY rats (P < 3 × 10(-8) and 0.005, respectively) independent of age. A decrease in Ki(FDG) with age was evident when models were combined (P = 0.034). The SHR exhibited higher K1(FDHROL) (P < 5 × 10(-6)) than the control, with no age-dependent trends in either model (P = 0.058). Glucose plasma concentrations were lower in SHRs than controls (P < 6 × 10(-12)), with an age-dependent rise for WKY rats (P < 2 × 10(-5)). Insulin plasma concentrations were higher in SHRs than controls (P < 3 × 10(-3)), with an age-dependent decrease when models were combined (P = 0.046). FFA levels were similar between models (P = 0.374), but an increase with age was evident only in SHR (P < 7 × 10(-6)).

CONCLUSION

The SHR exhibited alterations in myocardial substrate use at 8 mo characterized by increased glucose and FA utilizations. At 20 mo, the SHR had LVH characterized by decreased LVEF and increased EDV, while simultaneously sustaining higher glucose and similar FA utilizations (compared with WKY rats), which indicates maladaptation of energy substrates in the failing heart. Elevated K1(FDHROL) in the SHR may reflect elevated oxygen consumption and decreased capillary density in the hypertrophied heart. From our findings, metabolic changes appear to precede mechanical changes of LVH progression in the SHR model.

Persistent overexpression of phosphoglycerate mutase, a glycolytic enzyme, modifies energy metabolism and reduces stress resistance of heart in mice

BACKGROUND

Heart failure is associated with changes in cardiac energy metabolism. Glucose metabolism in particular is thought to be important in the pathogenesis of heart failure. We examined the effects of persistent overexpression of phosphoglycerate mutase 2 (Pgam2), a glycolytic enzyme, on cardiac energy metabolism and function.

METHODS AND RESULTS

Transgenic mice constitutively overexpressing Pgam2 in a heart-specific manner were generated, and cardiac energy metabolism and function were analyzed. Cardiac function at rest was normal. The uptake of analogs of glucose or fatty acids and the phosphocreatine/βATP ratio at rest were normal. A comprehensive metabolomic analysis revealed an increase in the levels of a few metabolites immediately upstream and downstream of Pgam2 in the glycolytic pathway, whereas the levels of metabolites in the initial few steps of glycolysis and lactate remained unchanged. The levels of metabolites in the tricarboxylic acid (TCA) cycle were altered. The capacity for respiration by isolated mitochondria in vitro was decreased, and that for the generation of reactive oxygen species (ROS) in vitro was increased. Impaired cardiac function was observed in response to dobutamine. Mice developed systolic dysfunction upon pressure overload.

CONCLUSIONS

Constitutive overexpression of Pgam2 modified energy metabolism and reduced stress resistance of heart in mice.