Beta-receptor blockade decreases carnitine palmitoyl transferase I activity in dogs with heart failure

Metabolomics of repetitive myocardial stunning in chronic multivessel coronary artery stenosis: Effect of non-selective and selective β1-receptor blockers

Chronic coronary artery stenosis can lead to regional myocardial dysfunction in the absence of myocardial infarction by repetitive stunning, hibernation or both. The molecular mechanisms underlying repetitive stunning-associated myocardial dysfunction are not clear. We used non-targeted metabolomics to elucidate responses to chronically stunned myocardium in a canine model with and without β-adrenergic blockade treatment. After development of left ventricular systolic dysfunction induced by ameroid constrictors on the coronary arteries, animals were randomized to 3 months of placebo, metoprolol or carvedilol. We compared these two β-blockers with their different β-adrenergic selectivities on myocardial function, perfusion and metabolic pathways involved in tissue undergoing chronic stunning. Control animals underwent sham surgery. Dysfunction in stunned myocardium was associated with reduced fatty acid oxidation and enhanced ketogenic amino acid metabolism, together with alterations in mitochondrial membrane phospholipid composition. These changes were consistent with impaired mitochondrial function and were linked to reduced nitric oxide and peroxisome proliferator-activated receptor signalling, resulting in a decline in adenosine monophosphate-activated protein kinase. Mitochondrial changes were ameliorated by carvedilol more than metoprolol, and improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. In summary, repetitive myocardial stunning commonly seen in chronic multivessel coronary artery disease is associated with adverse metabolic remodelling linked to mitochondrial dysfunction and specific signalling pathways. These changes are reversed by β-blockers, with the non-selective inhibitor having a more favourable impact. This is the first investigation to demonstrate that β-blockade-associated improvement of ventricular function in chronic myocardial stunning is associated with restoration of mitochondrial function. KEY POINTS: The mechanisms responsible for the metabolic changes associated with repetitive myocardial stunning seen in chronic multivessel coronary artery disease have not been fully investigated. In a canine model of repetitive myocardial stunning, we showed that carvedilol, a non-selective β-receptor blocker, ameliorated adverse metabolic remodelling compared to metoprolol, a selective β1-receptor blocker, by improving nitric oxide synthase and adenosine monophosphate protein kinase function, enhancing calcium/calmodulin-dependent protein kinase, probably increasing hydrogen sulphide, and suppressing cyclic-adenosine monophosphate signalling. Mitochondrial fatty acid oxidation alterations were ameliorated by carvedilol to a larger extent than metoprolol; this improvement was linked to nitric oxide and possibly hydrogen sulphide signalling. Both β-blockers improved the cardiac energy imbalance by reducing metabolites in ketogenic amino acid and nucleotide metabolism. These results elucidated why metabolic remodelling with carvedilol is preferable to metoprolol when treating chronic ischaemic left ventricular systolic dysfunction caused by repetitive myocardial stunning.

Management of Chronic Congestive Heart Failure Caused by Myxomatous Mitral Valve Disease in Dogs: A Narrative Review from 1970 to 2020

Simple Summary

Myxomatous mitral valve disease (MMVD) is the most common acquired cardiovascular disease in dogs. The progression of the disease and the increasing severity of valvular regurgitation cause a volume overload of the left heart, leading to left atrial and ventricular remodeling and congestive heart failure (CHF). The treatment of chronic CHF secondary to MMVD in dogs has not always been the same over time. In the last fifty years, the drugs utilized have considerably changed, as well as the therapeutic protocols. Some drugs have also changed their intended use. An analysis of the literature concerning the therapy of chronic heart failure in dogs affected by this widespread degenerative disease is not available; a synthesis of the published literature on this topic and a description of its current state of art are needed. To the authors’ knowledge, a review of this topic has never been published in veterinary medicine; therefore, the aim of this study is to overview the treatments of chronic CHF secondary to MMVD in dogs from 1970 to 2020 using the general framework of narrative reviews.

Abstract

The treatment of chronic congestive heart failure (CHF), secondary to myxomatous mitral valve disease (MMVD) in dogs, has considerably changed in the last fifty years. An analysis of the literature concerning the therapy of chronic CHF in dogs affected by MMVD is not available, and it is needed. Narrative reviews (NRs) are aimed at identifying and summarizing what has been previously published, avoiding duplications, and seeking new study areas that have not yet been addressed. The most accessible open-access databases, PubMed, Embase, and Google Scholar, were chosen, and the searching time frame was set in five decades, from 1970 to 2020. The 384 selected studies were classified into categories depending on the aim of the study, the population target, the pathogenesis of MMVD (natural/induced), and the resulting CHF. Over the years, the types of studies have increased considerably in veterinary medicine. In particular, there have been 43 (24.29%) clinical trials, 41 (23.16%) randomized controlled trials, 10 (5.65%) cross-over trials, 40 (22.60%) reviews, 5 (2.82%) comparative studies, 17 (9.60%) case-control studies, 2 (1.13%) cohort studies, 2 (1.13%) experimental studies, 2 (1.13%) questionnaires, 6 (3.40%) case-reports, 7 (3.95%) retrospective studies, and 2 (1.13%) guidelines. The experimental studies on dogs with an induced form of the disease were less numerous (49–27.68%) than the studies on dogs affected by spontaneous MMVD (128–72.32%). The therapy of chronic CHF in dogs has considerably changed in the last fifty years: in the last century, some of the currently prescribed drugs did not exist yet, while others had different indications.

Metabolic Impairment in Coronary Artery Disease: Elevated Serum Acylcarnitines Under the Spotlights

Coronary artery disease (CAD) remains the leading cause of death worldwide. Expanding patients' metabolic phenotyping beyond clinical chemistry investigations could lead to earlier recognition of disease onset and better prevention strategies. Additionally, metabolic phenotyping, at the molecular species level, contributes to unravel the roles of metabolites in disease development. In this cross-sectional study, we investigated clinically healthy individuals (n = 116, 65% male, 70.8 ± 8.7 years) and patients with CAD (n = 54, 91% male, 67.0 ± 11.5 years) of the COmPLETE study. We applied a high-coverage quantitative liquid chromatography-mass spectrometry approach to acquire a comprehensive profile of serum acylcarnitines, free carnitine and branched-chain amino acids (BCAAs), as markers of mitochondrial health and energy homeostasis. Multivariable linear regression analyses, adjusted for confounders, were conducted to assess associations between metabolites and CAD phenotype. In total, 20 short-, medium- and long-chain acylcarnitine species, along with L-carnitine, valine and isoleucine were found to be significantly (adjusted p ≤ 0.05) and positively associated with CAD. For 17 acylcarnitine species, associations became stronger as the number of affected coronary arteries increased. This implies that circulating acylcarnitine levels reflect CAD severity and might play a role in future patients' stratification strategies. Altogether, CAD is characterized by elevated serum acylcarnitine and BCAA levels, which indicates mitochondrial imbalance between fatty acid and glucose oxidation.

Cyclic AMP-binding protein Epac1 acts as a metabolic sensor to promote cardiomyocyte lipotoxicity

Cyclic adenosine monophosphate (cAMP) is a master regulator of mitochondrial metabolism but its precise mechanism of action yet remains unclear. Here, we found that a dietary saturated fatty acid (FA), palmitate increased intracellular cAMP synthesis through the palmitoylation of soluble adenylyl cyclase in cardiomyocytes. cAMP further induced exchange protein directly activated by cyclic AMP 1 (Epac1) activation, which was upregulated in the myocardium of obese patients. Epac1 enhanced the activity of a key enzyme regulating mitochondrial FA uptake, carnitine palmitoyltransferase 1. Consistently, pharmacological or genetic Epac1 inhibition prevented lipid overload, increased FA oxidation (FAO), and protected against mitochondrial dysfunction in cardiomyocytes. In addition, analysis of Epac1 phosphoproteome led us to identify two key mitochondrial enzymes of the the β-oxidation cycle as targets of Epac1, the long-chain FA acyl-CoA dehydrogenase (ACADL) and the 3-ketoacyl-CoA thiolase (3-KAT). Epac1 formed molecular complexes with the Ca2+/calmodulin-dependent protein kinase II (CaMKII), which phosphorylated ACADL and 3-KAT at specific amino acid residues to decrease lipid oxidation. The Epac1-CaMKII axis also interacted with the α subunit of ATP synthase, thereby further impairing mitochondrial energetics. Altogether, these findings indicate that Epac1 disrupts the balance between mitochondrial FA uptake and oxidation leading to lipid accumulation and mitochondrial dysfunction, and ultimately cardiomyocyte death.

Remodeling after myocardial infarction and effects of heart failure treatment investigated by hyperpolarized [1-13 C]pyruvate magnetic resonance spectroscopy

PURPOSE

Hyperpolarized [1-¹³ C]pyruvate MRS can measure cardiac metabolism in vivo. We investigated whether [1-¹³ C]pyruvate MRS could predict left ventricular remodeling following myocardial infarction (MI), long-term left ventricular effects of heart failure medication, and could identify responders to treatment.

METHODS

Thirty-five rats were scanned with hyperpolarized [1-¹³ C]pyruvate MRS 3 days after MI or sham surgery. The animals were re-examined after 30 days of therapy with β-blockers and ACE-inhibitors (active group, n = 12), placebo treatment (placebo group, n = 13) or no treatment (sham group, n = 10). Furthermore, heart tissue mitochondrial respiratory capacity was assessed by high-resolution respirometry. Metabolic results were compared between groups, over time and correlated to functional MR data at each time point.

RESULTS

At 30 ± 0.5 days post MI, left ventricular ejection fraction (LVEF) differed between groups (sham, 77% ± 1%; placebo, 52% ± 3%; active, 63% ± 2%, P < .001). Cardiac metabolism, measured by both hyperpolarized [1-¹³ C]pyruvate MRS and respirometry, neither differed between groups nor between baseline and follow-up. Three days post MI, low bicarbonate + CO₂ /pyruvate ratio was associated with low LVEF. At follow-up, in the active group, a poor recovery of LVEF was associated with high bicarbonate + CO₂ /pyruvate ratio, as measured by hyperpolarized MRS.

CONCLUSION

In a rat model of moderate heart failure, medical treatment improved function, but did not on average influence [1-¹³ C]pyruvate flux as measured by MRS; however, responders to heart failure medication had reduced capacity for carbohydrate metabolism.

Impact of Aldosterone on the Failing Myocardium: Insights from Mitochondria and Adrenergic Receptors Signaling and Function

The mineralocorticoid aldosterone regulates electrolyte and blood volume homeostasis, but it also adversely modulates the structure and function of the chronically failing heart, through its elevated production in chronic human post-myocardial infarction (MI) heart failure (HF). By activating the mineralocorticoid receptor (MR), a ligand-regulated transcription factor, aldosterone promotes inflammation and fibrosis of the heart, while increasing oxidative stress, ultimately induding mitochondrial dysfunction in the failing myocardium. To reduce morbidity and mortality in advanced stage HF, MR antagonist drugs, such as spironolactone and eplerenone, are used. In addition to the MR, aldosterone can bind and stimulate other receptors, such as the plasma membrane-residing G protein-coupled estrogen receptor (GPER), further complicating it signaling properties in the myocardium. Given the salient role that adrenergic receptor (ARs)—particularly βARs—play in cardiac physiology and pathology, unsurprisingly, that part of the impact of aldosterone on the failing heart is mediated by its effects on the signaling and function of these receptors. Aldosterone can significantly precipitate the well-documented derangement of cardiac AR signaling and impairment of AR function, critically underlying chronic human HF. One of the main consequences of HF in mammalian models at the cellular level is the presence of mitochondrial dysfunction. As such, preventing mitochondrial dysfunction could be a valid pharmacological target in this condition. This review summarizes the current experimental evidence for this aldosterone/AR crosstalk in both the healthy and failing heart, and the impact of mitochondrial dysfunction in HF. Recent findings from signaling studies focusing on MR and AR crosstalk via non-conventional signaling of molecules that normally terminate the signaling of ARs in the heart, i.e., the G protein-coupled receptor-kinases (GRKs), are also highlighted.

Targeting Adrenergic Receptors in Metabolic Therapies for Heart Failure

The heart has a reduced capacity to generate sufficient energy when failing, resulting in an energy-starved condition with diminished functions. Studies have identified numerous changes in metabolic pathways in the failing heart that result in reduced oxidation of both glucose and fatty acid substrates, defects in mitochondrial functions and oxidative phosphorylation, and inefficient substrate utilization for the ATP that is produced. Recent early-phase clinical studies indicate that inhibitors of fatty acid oxidation and antioxidants that target the mitochondria may improve heart function during failure by increasing compensatory glucose oxidation. Adrenergic receptors (α1 and β) are a key sympathetic nervous system regulator that controls cardiac function. β-AR blockers are an established treatment for heart failure and α1A-AR agonists have potential therapeutic benefit. Besides regulating inotropy and chronotropy, α1- and β-adrenergic receptors also regulate metabolic functions in the heart that underlie many cardiac benefits. This review will highlight recent studies that describe how adrenergic receptor-mediated metabolic pathways may be able to restore cardiac energetics to non-failing levels that may offer promising therapeutic strategies.

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.

Circulating acylcarnitine profile in human heart failure: a surrogate of fatty acid metabolic dysregulation in mitochondria and beyond

Heart failure (HF) is associated with metabolic perturbations, particularly of fatty acids (FAs), which remain to be better understood in humans. This study aimed at testing the hypothesis that HF patients with reduced ejection fraction display systemic perturbations in levels of energy-related metabolites, especially those reflecting dysregulation of FA metabolism, namely, acylcarnitines (ACs). Circulating metabolites were assessed using mass spectrometry (MS)-based methods in two cohorts. The main cohort consisted of 72 control subjects and 68 HF patients exhibiting depressed left ventricular ejection fraction (25.9 ± 6.9%) and mostly of ischemic etiology with ≥2 comorbidities. HF patients displayed marginal changes in plasma levels of tricarboxylic acid cycle-related metabolites or indexes of mitochondrial or cytosolic redox status. They had, however, 22-79% higher circulating ACs, irrespective of chain length (P < 0.0001, adjusted for sex, age, renal function, and insulin resistance, determined by shotgun MS/MS), which reflects defective mitochondrial β-oxidation, and were significantly associated with levels of NH₂-terminal pro-B-type natriuretic peptide levels, a disease severity marker. Subsequent extended liquid chromatography-tandem MS analysis of 53 plasma ACs in a subset group from the primary cohort confirmed and further substantiated with a comprehensive lipidomic analysis in a validation cohort revealed in HF patients a more complex circulating AC profile. The latter included dicarboxylic-ACs and dihydroxy-ACs as well as very long chain (VLC) ACs or sphingolipids with VLCFAs (>20 carbons), which are proxies of dysregulated FA metabolism in peroxisomes. Our study identified alterations in circulating ACs in HF patients that are independent of biological traits and associated with disease severity markers. These alterations reflect dysfunctional FA metabolism in mitochondria but also beyond, namely, in peroxisomes, suggesting a novel mechanism contributing to global lipid perturbations in human HF.NEW & NOTEWORTHY Mass spectrometry-based profiling of circulating energy metabolites, including acylcarnitines, in two cohorts of heart failure versus control subjects revealed multiple alterations in fatty acid metabolism in peroxisomes in addition to mitochondria, thereby highlighting a novel mechanism contributing to global lipid perturbations in heart failure.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/acylcarnitines-in-human-heart-failure/.

Cardiac energetic impairment in heart disease and the potential role of metabolic modulators: a review for clinicians

Cardiac energetic impairment is a frequent finding in patients with both inherited and acquired diseases of heart muscle. In this review the mechanisms of energy generation in the healthy heart and their disturbances in heart muscle diseases are described. Therapeutic agents targeted at correcting cardiac energetic impairment are discussed.

Metabolic abnormalities of the heart in type II diabetes

Type 2 diabetes mellitus escalates the risk of heart failure partly via its ability to induce a cardiomyopathic state that is independent of coronary artery disease and hypertension. Although the pathogenesis of diabetic cardiomyopathy has yet to be fully elucidated, aberrations in cardiac substrate metabolism and energetics are thought to be key drivers. These aberrations include excessive fatty acid utilisation and storage, suppressed glucose oxidation and impaired mitochondrial oxidative phosphorylation. An appreciation of how these abnormalities arise and synergise to promote adverse cardiac remodelling is critical to their effective amelioration. This review focuses on disturbances in myocardial fuel (fatty acids and glucose) flux and energetics in type 2 diabetes, how these disturbances relate to the development of diabetic cardiomyopathy and the potential therapeutic agents that could be used to correct them.

Cardiac energy metabolic alterations in pressure overload-induced left and right heart failure (2013 Grover Conference Series)

Pressure overload of the heart, such as seen with pulmonary hypertension and/or systemic hypertension, can result in cardiac hypertrophy and the eventual development of heart failure. The development of hypertrophy and heart failure is accompanied by numerous molecular changes in the heart, including alterations in cardiac energy metabolism. Under normal conditions, the high energy (adenosine triphosphate [ATP]) demands of the heart are primarily provided by the mitochondrial oxidation of fatty acids, carbohydrates (glucose and lactate), and ketones. In contrast, the hypertrophied failing heart is energy deficient because of its inability to produce adequate amounts of ATP. This can be attributed to a reduction in mitochondrial oxidative metabolism, with the heart becoming more reliant on glycolysis as a source of ATP production. If glycolysis is uncoupled from glucose oxidation, a decrease in cardiac efficiency can occur, which can contribute to the severity of heart failure due to pressure-overload hypertrophy. These metabolic changes are accompanied by alterations in the enzymes that are involved in the regulation of fatty acid and carbohydrate metabolism. It is now becoming clear that optimizing both energy production and the source of energy production are potential targets for pharmacological intervention aimed at improving cardiac function in the hypertrophied failing heart. In this review, we will focus on what alterations in energy metabolism occur in pressure overload induced left and right heart failure. We will also discuss potential targets and pharmacological approaches that can be used to treat heart failure occurring secondary to pulmonary hypertension and/or systemic hypertension.

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.

Metabolic impairment in heart failure: the myocardial and systemic perspective

Although bioenergetic starvation is not a new concept in heart failure (HF), recent research has led to a growing appreciation of the complexity of metabolic aspects of HF pathophysiology. All steps of energy extraction, transfer, and utilization are affected, and structural metabolism is impaired, leading to compromised functional integrity of tissues. Not only the myocardium, but also peripheral tissues and organs are affected by metabolic failure, resulting in a global imbalance between catabolic and anabolic signals, leading to tissue wasting and, ultimately, to cachexia. Metabolic feedback signals from muscle and fat actively contribute to further myocardial strain, promoting disease progression. The prolonged survival of patients with stable, compensated HF will increasingly bring chronic metabolic complications of HF to the fore and gradually shift its clinical presentation. This paper reviews recent evidence on myocardial and systemic metabolic impairment in HF and summarizes current and emerging therapeutic concepts with specific metabolic targets.

Cardiac mitochondrial proteome dynamics with heavy water reveals stable rate of mitochondrial protein synthesis in heart failure despite decline in mitochondrial oxidative capacity

We recently developed a method to measure mitochondrial proteome dynamics with heavy water ((2)H2O)-based metabolic labeling and high resolution mass spectrometry. We reported the half-lives and synthesis rates of several proteins in the two cardiac mitochondrial subpopulations, subsarcolemmal and interfibrillar (SSM and IFM), in Sprague Dawley rats. In the present study, we tested the hypothesis that the mitochondrial protein synthesis rate is reduced in heart failure, with possible differential changes in SSM versus IFM. Six to seven week old male Sprague Dawley rats underwent transverse aortic constriction (TAC) and developed moderate heart failure after 22weeks. Heart failure and sham rats of the same age received heavy water (5% in drinking water) for up to 80days. Cardiac SSM and IFM were isolated from both groups and the proteins were separated by 1D gel electrophoresis. Heart failure reduced protein content and increased the turnover rate of several proteins involved in fatty acid oxidation, electron transport chain and ATP synthesis, while it decreased the turnover of other proteins, including pyruvate dehydrogenase subunit in IFM, but not in SSM. Because of these bidirectional changes, the average overall half-life of proteins was not altered by heart failure in both SSM and IFM. The kinetic measurements of individual mitochondrial proteins presented in this study may contribute to a better understanding of the mechanisms responsible for mitochondrial alterations in the failing heart.

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.

A "PET" area of interest: myocardial metabolism in human systolic heart failure

Myocardial substrate metabolism provides the energy needed for cardiac contraction and relaxation. The normal adult heart uses predominantly fatty acids (FAs) as its primary fuel source. However, the heart can switch and use glucose (and to a lesser extent, ketones, lactate, as well as endogenous triglycerides and glycogen), depending on the metabolic milieu and superimposed conditions. FAs are not a wholly better fuel than glucose, but they do provide more energy per mole than glucose. Conversely, glucose is the more oxygen-efficient fuel. Studies in animal models of heart failure (HF) fairly consistently demonstrate a shift away from myocardial fatty acid metabolism and toward glucose metabolism. Studies in humans are less consistent. Some show the same metabolic switch away from FA metabolism but not all. This may be due to differences in the etiology of HF, sex-related differences, or other mitigating factors. For example, obesity, insulin resistance, and diabetes are all related to an increased risk of HF and may complicate or contribute to its development. However, these conditions are associated with increased FA metabolism. This review will discuss aspects of human heart metabolism in systolic dysfunction as measured by the noninvasive, quantitative method-positron emission tomography. Continued research in this area is vital if we are to ameliorate HF by manipulating heart metabolism with the aim of increasing energy production and/or efficiency.

β1-Adrenergic receptor blockade extends the life span of Drosophila and long-lived mice

Chronic treatment with β-adrenergic receptor (βAR) agonists increases mortality and morbidity while βAR antagonists (β-blockers) decrease all-cause mortality for those at risk of cardiac disease. Levels of sympathetic nervous system βAR agonists and βAR activity increase with age, and this increase may hasten the development of age-related mortality. Here, we show that β-blockers extend the life span of healthy metazoans. The β-blockers metoprolol and nebivolol, administered in food daily beginning at 12 months of age, significantly increase the mean and median life span of isocalorically fed, male C3B6F1 mice, by 10 and 6.4%, respectively (P < 0.05). Neither drug affected the weight or food intake of the mice, indicating that induced CR is not responsible for these effects, and that energy absorption and utilization are not altered by the drugs. Both β-blockers were investigated to control for their idiosyncratic, off-target effects. Metoprolol and nebivolol extended Drosophila life span, without affecting food intake or locomotion. Thus, βAR antagonists are capable of directly extending the life span of two widely divergent metazoans, suggesting that these effects are phylogenetically highly conserved. Thus, long-term use of β-blockers, which are generally well-tolerated, may enhance the longevity of healthy humans.

Carnitine palmitoyltransferase-1b deficiency aggravates pressure overload-induced cardiac hypertrophy caused by lipotoxicity

BACKGROUND

Carnitine palmitoyltransferase-1 (CPT1) is a rate-limiting step of mitochondrial β-oxidation by controlling the mitochondrial uptake of long-chain acyl-CoAs. The muscle isoform, CPT1b, is the predominant isoform expressed in the heart. It has been suggested that inhibiting CPT1 activity by specific CPT1 inhibitors exerts protective effects against cardiac hypertrophy and heart failure. However, clinical and animal studies have shown mixed results, thereby creating concerns about the safety of this class of drugs. Preclinical studies using genetically modified animal models should provide a better understanding of targeting CPT1 to evaluate it as a safe and effective therapeutic approach.

METHODS AND RESULTS

Heterozygous CPT1b knockout (CPT1b(+/-)) mice were subjected to transverse aorta constriction-induced pressure overload. These mice showed overtly normal cardiac structure/function under the basal condition. Under a severe pressure-overload condition induced by 2 weeks of transverse aorta constriction, CPT1b(+/-) mice were susceptible to premature death with congestive heart failure. Under a milder pressure-overload condition, CPT1b(+/-) mice exhibited exacerbated cardiac hypertrophy and remodeling compared with wild-type littermates. There were more pronounced impairments of cardiac contraction with greater eccentric cardiac hypertrophy in CPT1b(+/-) mice than in control mice. Moreover, the CPT1b(+/-) heart exhibited exacerbated mitochondrial abnormalities and myocardial lipid accumulation with elevated triglycerides and ceramide content, leading to greater cardiomyocyte apoptosis.

CONCLUSIONS

CPT1b deficiency can cause lipotoxicity in the heart under pathological stress, leading to exacerbation of cardiac pathology. Therefore, caution should be exercised in the clinical use of CPT1 inhibitors.

Treatment of chronic heart failure with β-adrenergic receptor antagonists: a convergence of receptor pharmacology and clinical cardiology

Despite the absence of a systematic development plan, β-blockers have reached the top tier of medical therapies for chronic heart failure. The successful outcome was due to the many dedicated investigators who produced, over a 30-year period, increasing evidence that β-blocking agents should or actually did improve the natural history of dilated cardiomyopathies and heart failure. It took 20 years for supportive evidence to become undeniable, at which time in 1993 the formidable drug development resources of large pharmaceutical companies were deployed into Phase 3 trials. Success then came relatively quickly, and within 8 years multiple agents were on the market in the United States and Europe. Importantly, there is ample room to improve antiadrenergic therapy, through novel approaches exploiting the nuances of receptor biology and/or intracellular signaling, as well as through pharmacogenetic targeting.

Parallel effects of β-adrenoceptor blockade on cardiac function and fatty acid oxidation in the diabetic heart: Confronting the maze

Diabetic cardiomyopathy is a disease process in which diabetes produces a direct and continuous myocardial insult even in the absence of ischemic, hypertensive or valvular disease. The β-blocking agents bisoprolol, carvedilol and metoprolol have been shown in large-scale randomized controlled trials to reduce heart failure mortality. In this review, we summarize the results of our studies investigating the effects of β-blocking agents on cardiac function and metabolism in diabetic heart failure, and the complex inter-related mechanisms involved. Metoprolol inhibits fatty acid oxidation at the mitochondrial level but does not prevent lipotoxicity; its beneficial effects are more likely to be due to pro-survival effects of chronic treatment. These studies have expanded our understanding of the range of effects produced by β-adrenergic blockade and show how interconnected the signaling pathways of function and metabolism are in the heart. Although our initial hypothesis that inhibition of fatty acid oxidation would be a key mechanism of action was disproved, unexpected results led us to some intriguing regulatory mechanisms of cardiac metabolism. The first was upstream stimulatory factor-2-mediated repression of transcriptional master regulator PGC-1α, most likely occurring as a consequence of the improved function; it is unclear whether this effect is unique to β-blockers, although repression of carnitine palmitoyltransferase (CPT)-1 has not been reported with other drugs which improve function. The second was the identification of a range of covalent modifications which can regulate CPT-1 directly, mediated by a signalome at the level of the mitochondria. We also identified an important interaction between β-adrenergic signaling and caveolins, which may be a key mechanism of action of β-adrenergic blockade. Our experience with this labyrinthine signaling web illustrates that initial hypotheses and anticipated directions do not have to be right in order to open up meaningful directions or reveal new information.

Changes in myofilament proteins, but not Ca²⁺ regulation, are associated with a high-fat diet-induced improvement in contractile function in heart failure

Pathological conditions such as diabetes, insulin resistance, and obesity are characterized by elevated plasma and myocardial lipid levels and have been reported to exacerbate the progression of heart failure (HF). Alterations in cardiomyocyte Ca(2+) regulatory properties and myofilament proteins have also been implicated in contractile dysfunction in HF. However, our prior studies reported that high saturated fat (SAT) feeding improves in vivo myocardial contractile function, thereby exerting a cardioprotective effect in HF. Therefore, we hypothesized that SAT feeding improves contractile function by altering Ca(2+) regulatory properties and myofilament protein expression in HF. Male Wistar rats underwent coronary artery ligation (HF) or sham surgery (SH) and were fed normal chow (SHNC and HFNC groups) or a SAT diet (SHSAT and HFSAT groups) for 8 wk. Contractile properties were measured in vivo [echocardiography and left ventricular (LV) cannulation] and in isolated LV cardiomyocytes. In vivo measures of contractility (peak LV +dP/dt and -dP/dt) were depressed in the HFNC versus SHNC group but improved in the HFSAT group. Isolated cardiomyocytes from both HF groups were hypertrophied and had decreased percent cell shortening and a prolonged time to half-decay of the Ca(2+) transient versus the SH group; however, SAT feeding reduced in vivo myocyte hypertrophy in the HFSAT group only. The peak velocity of cell shortening was reduced in the HFNC group but not the HFSAT group and was positively correlated with in vivo contractile function (peak LV +dP/dt). The HFNC group demonstrated a myosin heavy chain (MHC) isoform switch from fast MHC-α to slow MHC-β, which was prevented in the HFSAT group. Alterations in Ca(2+) transients, L-type Ca(2+) currents, and protein expression of sarco(endo)plasmic reticulum Ca(2+)-ATPase and phosphorylated phospholamban could not account for the changes in the in vivo contractile properties. In conclusion, the cardioprotective effects associated with SAT feeding in HF may occur at the level of the isolated cardiomyocyte, specifically involving changes in myofilament function but not sarcoplasmic reticulum Ca(2+) regulatory properties.

Metabolic remodelling in human heart failure

In addition to the typical abnormalities in myocardial structure and function, it is well established that the cardiac metabolism is abnormal in patients with heart failure (HF). Insulin resistance is a common co-morbidity in HF patients and also modulates cardiac metabolism in HF. The notion that an altered myocardial metabolism may contribute to the disease pathogenesis and optimizing it may serve therapeutic purposes underscores the importance of identifying the metabolic characteristics of HF patients. In this paper, the literature on the metabolic changes in human HF is reviewed, and the effects of metabolic modulators on patients with HF are discussed.

Targeting fatty acid and carbohydrate oxidation--a novel therapeutic intervention in the ischemic and failing heart

Cardiac ischemia and its consequences including heart failure, which itself has emerged as the leading cause of morbidity and mortality in developed countries are accompanied by complex alterations in myocardial energy substrate metabolism. In contrast to the normal heart, where fatty acid and glucose metabolism are tightly regulated, the dynamic relationship between fatty acid β-oxidation and glucose oxidation is perturbed in ischemic and ischemic-reperfused hearts, as well as in the failing heart. These metabolic alterations negatively impact both cardiac efficiency and function. Specifically there is an increased reliance on glycolysis during ischemia and fatty acid β-oxidation during reperfusion following ischemia as sources of adenosine triphosphate (ATP) production. Depending on the severity of heart failure, the contribution of overall myocardial oxidative metabolism (fatty acid β-oxidation and glucose oxidation) to adenosine triphosphate production can be depressed, while that of glycolysis can be increased. Nonetheless, the balance between fatty acid β-oxidation and glucose oxidation is amenable to pharmacological intervention at multiple levels of each metabolic pathway. This review will focus on the pathways of cardiac fatty acid and glucose metabolism, and the metabolic phenotypes of ischemic and ischemic/reperfused hearts, as well as the metabolic phenotype of the failing heart. Furthermore, as energy substrate metabolism has emerged as a novel therapeutic intervention in these cardiac pathologies, this review will describe the mechanistic bases and rationale for the use of pharmacological agents that modify energy substrate metabolism to improve cardiac function in the ischemic and failing heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

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.

Energetics and metabolism in the failing heart: important but poorly understood

PURPOSE OF REVIEW

Profound abnormalities in myocardial energy metabolism occur in heart failure and correlate with clinical symptoms and survival. Available comprehensive human metabolic data come from small studies, enrolling patients across heart failure causes, at different disease stages, and using different methodologies, and is often contradictory. Remaining fundamental gaps in knowledge include whether observed shifts in cardiac substrate utilization are adaptive or maladaptive, causal or an epiphenomenon of heart failure.

RECENT FINDINGS

Recent studies have characterized the temporal changes in myocardial substrate metabolism involved in progression of heart failure, the role of insulin resistance, and the mechanisms of mitochondrial dysfunction in heart failure. The concept of metabolic inflexibility has been proposed to explain the lack of energetic and mechanical reserve in the failing heart.

SUMMARY

Despite current therapies, which provide substantial benefits to patients, heart failure remains a progressive disease, and new approaches to treatment are necessary. Developing metabolic interventions would be facilitated by systems-level integration of current knowledge on myocardial metabolic control. Although preliminary evidence suggests that metabolic modulators inducing a shift towards carbohydrate utilization seem generally beneficial in the failing heart, such interventions should be matched to the stage of metabolic deregulation in the progression of heart failure.

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.

Myocardial fatty acid metabolism in health and disease

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

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

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

Interaction between PPARA genotype and beta-blocker treatment influences clinical outcomes following acute coronary syndromes

AIMS

beta-blockers (BB) are strongly recommended after an acute coronary syndrome (ACS), although all patients may not benefit. Causes for variable patient responses to BB are unknown. Given that myocardial ischemia and BB influence metabolic processes regulated by peroxisome proliferator-activated receptor alpha (PPARalpha), we hypothesized that interactions between polymorphisms of the PPARalpha gene (PPARA) and BB treatment would influence clinical outcome following ACS.

PATIENTS & METHODS

Patients were prospectively enrolled into an ACS registry. A total of 735 ACS patients were genotyped. Mortality and cardiac rehospitalization through 1 year were analyzed in relation to PPARA genotype and BB prescription (597 BB; 138 no BB) at discharge.

RESULTS

Significantly different outcomes associated with BB therapy were observed according to PPARA IVS7 2498 genotype (p = 0.002 for interaction). PPARA IVS7 2498 GG homozygous patients discharged on BB had decreased cardiac rehospitalization (hazard ratio [HR]: 0.52; 95% CI: 0.32-0.86; p = 0.011), while C allele carriers discharged on BB had nearly threefold increased cardiac rehospitalization (HR: 2.92; 95% CI: 1.32-6.92; p = 0.015; genotype interaction p = 0.0005) compared with patients not on BB. PPARA genotype was also associated with differences in PPARalpha expression, with significantly increased mRNA levels in myocardial samples from normal hearts among GC heterozygotes compared with GG homozygotes (p = 0.04). Transgenic mice with cardiac-specific overexpression of PPARalpha showed significantly reduced myocardial contractile and chronotropic responses to the beta-sympathomimetic dobutamine (p < 0.05) compared with wild-type littermates, supporting the hypothesis that increased PPARalpha levels result in a blunted beta-adrenergic response.

CONCLUSIONS

PPARA IVS7 2498 genotype is associated with heterogeneity in 1-year outcome in response to BB among patients following ACS, and may predict which patients benefit from BB therapy, putatively related to the effect of myocardial PPARalpha expression on beta-adrenergic responsiveness.

High-sugar diets increase cardiac dysfunction and mortality in hypertension compared to low-carbohydrate or high-starch diets

OBJECTIVE

Sugar consumption affects insulin release and, in hypertension, may stimulate cardiac signaling mechanisms that accelerate left ventricular hypertrophy and the development of heart failure. We investigated the effects of high-fructose or sucrose diets on ventricular function and mortality in hypertensive Dahl salt-sensitive rats.

METHODS

Rats were fed chows that were either high starch (70% starch, 10% fat by energy), high fat (20% carbohydrates, 60% fat), high fructose (61% fructose, 9% starch, 10% fat), or high sucrose (61% sucrose, 9% starch, 10% fat). Hypertension was induced by adding 6% salt to the chow (n = 8-11/group).

RESULTS

After 8 weeks of treatment, systolic blood pressure and left ventricular mass were similarly increased in all rats that were fed high-salt diets. Hypertension caused a switch in mRNA myosin heavy chain isoform from alpha to beta, and this effect was greater in the high-salt sucrose and fructose groups than in starch and fat groups. The cardiac mRNA for atrial natriuretic factor was also increased in all high-salt groups compared to respective controls, with the increase being significantly greater in the hypertensive sucrose fed group. Mortality was greater in the sucrose group (44%) compared to all the other hypertensive groups (12-18%), as was cardiomyocyte apoptosis. Left ventricular ejection fraction was lower in the high-salt sucrose group, which was due to an increase in end-systolic volume, and not increased end-diastolic volume.

CONCLUSION

Diets high in sugar accelerated cardiac systolic dysfunction and mortality in hypertension compared to either a low-carbohydrate/high-fat or high-starch diet.

The antioxidant tempol attenuates pressure overload-induced cardiac hypertrophy and contractile dysfunction in mice fed a high-fructose diet

We have previously shown that high-sugar diets increase mortality and left ventricular (LV) dysfunction during pressure overload. The mechanisms behind these diet-induced alterations are unclear but may involve increased oxidative stress in the myocardium. The present study examined whether high-fructose feeding increased myocardial oxidative damage and exacerbated systolic dysfunction after transverse aortic constriction (TAC) and if this effect could be attenuated by treatment with the antioxidant tempol. Immediately after surgery, TAC and sham mice were assigned to a high-starch diet (58% of total energy intake as cornstarch and 10% fat) or high-fructose diet (61% fructose and 10% fat) with or without the addition of tempol [0.1% (wt/wt) in the chow] and maintained on the treatment for 8 wk. In response to TAC, fructose-fed mice had greater cardiac hypertrophy (55.1% increase in the heart weight-to-tibia length ratio) than starch-fed mice (22.3% increase in the heart weight-to-tibia length ratio). Treatment with tempol significantly attenuated cardiac hypertrophy in fructose-fed TAC mice (18.3% increase in the heart weight-to-tibia ratio). Similarly, fructose-fed TAC mice had a decreased LV area of fractional shortening (from 38+/-2% in sham to 22+/-4% in TAC), which was prevented by tempol treatment (33+/-3%). Markers of lipid peroxidation in fructose-fed TAC hearts were also blunted by tempol. In conclusion, tempol significantly blunted markers of cardiac hypertrophy, LV remodeling, contractile dysfunction, and oxidative stress in fructose-fed TAC mice.

Trimetazidine, a Metabolic Modulator, Has Cardiac and Extracardiac Benefits in Idiopathic Dilated Cardiomyopathy

Background— The anti-ischemic agent trimetazidine improves ejection fraction in heart failure that is hypothetically linked to inhibitory effects on cardiac free fatty acid (FFA) oxidation. However, FFA oxidation remains unmeasured in humans. We investigated the effects of trimetazidine on cardiac perfusion, efficiency of work, and FFA oxidation in idiopathic dilated cardiomyopathy.

Methods and Results— Nineteen nondiabetic patients with idiopathic dilated cardiomyopathy on standard medication were randomized to single-blind trimetazidine (n=12) or placebo (n=7) for 3 months. Myocardial perfusion, FFA, and total oxidative metabolism were measured using positron emission tomography with [ 15 O]H 2 O, [ 11 C]acetate, and [ 11 C]palmitate. Cardiac function was assessed echocardiographically; insulin sensitivity was assessed by the homeostasis model assessment index. Trimetazidine increased ejection fraction from 30.9±8.5% to 34.8±12% ( P =0.027 versus placebo). Myocardial FFA uptake was unchanged, and β-oxidation rate constant decreased only 10%. Myocardial perfusion, oxidative metabolism, and work efficiency remained unchanged. Trimetazidine decreased insulin resistance (glucose: 5.9±0.7 versus 5.5±0.6 mmol/L, P =0.047; insulin: 10±6.9 versus 7.6±3.6 mU/L, P =0.031; homeostasis model assessment index: 2.75±2.28 versus 1.89±1.06, P =0.027). The degree of β-blockade and trimetazidine interacted positively on ejection fraction. Plasma high-density lipoprotein concentrations increased 11% ( P <0.001).

Conclusions— In idiopathic dilated cardiomyopathy with heart failure, trimetazidine increased cardiac function and had both cardiac and extracardiac metabolic effects. Cardiac FFA oxidation modestly decreased and myocardial oxidative rate was unchanged, implying increased oxidation of glucose. Trimetazidine improved whole-body insulin sensitivity and glucose control in these insulin-resistant idiopathic dilated cardiomyopathy patients, thus hypothetically countering the myocardial damage of insulin resistance. Additionally, the trimetazidine-induced increase in ejection fraction was associated with greater β1-adrenoceptor occupancy, suggesting a synergistic mechanism.

Cardiac mitochondria in heart failure: decrease in respirasomes and oxidative phosphorylation

Aims

Mitochondrial dysfunction is a major factor in heart failure (HF). A pronounced variability of mitochondrial electron transport chain (ETC) defects is reported to occur in severe acquired cardiomyopathies without a consistent trend for depressed activity or expression. The aim of this study was to define the defect in the integrative function of cardiac mitochondria in coronary microembolization-induced HF.

Methods and results

Studies were performed in the canine coronary microembolization-induced HF model of moderate severity. Oxidative phosphorylation was assessed as the integrative function of mitochondria, using a comprehensive variety of substrates in order to investigate mitochondrial membrane transport, dehydrogenase activity and electron-transport coupled to ATP synthesis. The supramolecular organization of the mitochondrial ETC also was investigated by native gel electrophoresis. We found a dramatic decrease in ADP-stimulated respiration that was not relieved by an uncoupler. Moreover, the ADP/O ratio was normal, indicating no defect in the phosphorylation apparatus. The data point to a defect in oxidative phosphorylation within the ETC. However, the individual activities of ETC complexes were normal. The amount of the supercomplex consisting of complex I/complex III dimer/complex IV, the major form of respirasome considered essential for oxidative phosphorylation, was decreased.

Conclusions

We propose that the mitochondrial defect lies in the supermolecular assembly rather than in the individual components of the ETC.

Effects of a high saturated fat diet on cardiac hypertrophy and dysfunction in response to pressure overload

BACKGROUND

Dietary lipid content effects activation of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and may accelerate cardiac hypertrophy and dysfunction in response to pressure overload. This study investigated the effects of a high-fat diet on the development of cardiac hypertrophy.

METHODS AND RESULTS

C57BL/6J mice (n = 14-16/group) underwent transverse aortic constriction (TAC) or sham surgery and were fed either standard low-fat diet (STD; 10% fat) or a high-fat diet (HFD; 60% fat) for 16 weeks. Sham mice showed no differences between STD and HFD for heart mass or echocardiographic parameters despite greater plasma free fatty acid and leptin concentrations with HFD. TAC increased heart mass and decreased ejection fraction similarly in both groups. Left ventricular end systolic and diastolic diameters with TAC were increased compared with shams on the HFD (P < .05), but were not different from STD TAC mice. High-fat feeding increased expression of PPAR-alpha-regulated genes. The activity of medium chain acyl-coenzyme A dehydrogenase (MCAD), a marker of fatty acid oxidation capacity, was increased in HFD TAC mice compared with STD, consistent with PPAR-alpha activation.

CONCLUSIONS

Increased fat intake prevented the fall in MCAD activity and did not exacerbate the hypertrophic response to TAC compared with a low-fat diet.

Heart failure in the diabetic patient

This review examines the extent of the increased rate of heart failure (HF) in the diabetic patient, along with the possible causes for this increase and the poor prognosis associated with HF. Also reviewed are the therapies that are available for the treatment of diabetic HF and whether intensifying the use of these therapies might improve the worsened clinical outcomes for the patient who has diabetes.

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

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

Metoprolol improves cardiac function and modulates cardiac metabolism in the streptozotocin-diabetic rat

The effects of diabetes on heart function may be initiated or compounded by the exaggerated reliance of the diabetic heart on fatty acids and ketones as metabolic fuels. beta-Blocking agents such as metoprolol have been proposed to inhibit fatty acid oxidation. We hypothesized that metoprolol would improve cardiac function by inhibiting fatty acid oxidation and promoting a compensatory increase in glucose utilization. We measured ex vivo cardiac function and substrate utilization after chronic metoprolol treatment and acute metoprolol perfusion. Chronic metoprolol treatment attenuated the development of cardiac dysfunction in streptozotocin (STZ)-diabetic rats. After chronic treatment with metoprolol, palmitate oxidation was increased in control hearts but decreased in diabetic hearts without affecting myocardial energetics. Acute treatment with metoprolol during heart perfusions led to reduced rates of palmitate oxidation, stimulation of glucose oxidation, and increased tissue ATP levels. Metoprolol lowered malonyl-CoA levels in control hearts only, but no changes in acetyl-CoA carboxylase phosphorylation or AMP-activated protein kinase activity were observed. Both acute metoprolol perfusion and chronic in vivo metoprolol treatment led to decreased maximum activity and decreased sensitivity of carnitine palmitoyltransferase I to malonyl-CoA. Metoprolol also increased sarco(endo)plasmic reticulum Ca(2+)-ATPase expression and prevented the reexpression of atrial natriuretic peptide in diabetic hearts. These data demonstrate that metoprolol ameliorates diabetic cardiomyopathy and inhibits fatty acid oxidation in streptozotocin-induced diabetes. Since malonyl-CoA levels are not increased, the reduction in total carnitine palmitoyltransferase I activity is the most likely factor to explain the decrease in fatty acid oxidation. The metabolism changes occur in parallel with changes in gene expression.

Deleterious effects of sugar and protective effects of starch on cardiac remodeling, contractile dysfunction, and mortality in response to pressure overload

Little is known about the effects of the composition of dietary carbohydrate on the development of left ventricular (LV) hypertrophy (LVH) and heart failure (HF) under conditions of pressure overload. The objective of this study was to determine the effect of carbohydrate composition on LVH, LV function, and mortality in a mouse model of chronic pressure overload. Male C57BL/6J mice of 6 wk of age ( n = 14–16 mice/group) underwent transverse aortic constriction (TAC) or sham surgery and were fed either standard chow (STD; 32% corn starch, 35% sucrose, 3% maltodextrin, and 10% fat expressed as a percent of the total energy), high-starch chow (58% corn starch, 12% maltodextrin, and 10% fat), or high-fructose chow (9% corn starch, 61% fructose, and 10% fat). After 16 wk of treatment, mice with TAC fed the STD or high-fructose diets exhibited increased LV mass, larger end-diastolic and end-systolic diameters, and decreased ejection fraction compared with sham. The high-starch diet, in contrast, prevented changes in LV dimensions and contractile function. Cardiac mRNA for myosin heavy chain-β was increased dramatically in the fructose-fed banded animals, as was mortality (54% compared with 8% and 29% in the starch and STD banded groups, respectively). In conclusion, a diet high in simple sugar was deleterious, resulting in the highest mortality and expression of molecular markers of cardiac dysfunction in TAC animals compared with sham, whereas a high-starch diet blunted mortality, increases in cardiac mass, and contractile dysfunction.

Obesity cardiomyopathy: diagnosis and therapeutic implications

Obesity is associated with an increased risk of heart failure. Apparently healthy obese individuals can, however, exhibit subclinical left ventricular dysfunction. The use of myocardial imaging techniques to detect this subclinical change could have important management implications with respect to initiating prophylactic therapy. In this Review, we evaluate possible pharmacologic and nonpharmacologic strategies for treating obesity cardiomyopathy in the context of currently understood mechanisms, including myocardial remodeling and small vessel disease, and more speculative mechanisms such as insulin resistance, and activation of the renin-angiotensin-aldosterone and sympathetic nervous systems.

Fatty acid oxidation in cardiac and skeletal muscle mitochondria is unaffected by deletion of CD36

Recent studies found that the plasma membrane fatty acid transport protein CD36 also resides in mitochondrial membranes in cardiac and skeletal muscle. Pharmacological studies suggest that CD36 may play an essential role in mitochondrial fatty acid oxidation. We isolated cardiac and skeletal muscle mitochondria from wild type and CD36 knock-out mice. There were no differences between wild type and CD36 knock-out mice in mitochondrial respiration with palmitoyl-CoA, palmitoyl-carnitine or glutamate as substrate. We investigated a potential alternative role for CD36 in mitochondria, i.e. the export of fatty acids generated in the matrix. Palmitate export was not different between wild type and CD36 knock-out mice. Taken together, CD36 does not appear to play an essential role in mitochondrial uptake of fatty acids or export of fatty acid anions.

Dietary supplementation with omega-3 PUFA increases adiponectin and attenuates ventricular remodeling and dysfunction with pressure overload

OBJECTIVE

Epidemiological studies suggest that consumption of omega-3 polyunsaturated fatty acids (omega-3 PUFA) decreases the risk of heart failure. We assessed the effects of dietary supplementation with omega-3 PUFA from fish oil on the response of the left ventricle (LV) to arterial pressure overload.

METHODS

Male Wistar rats were fed a standard chow or a omega-3 PUFA-supplemented diet. After 1 week rats underwent abdominal aortic banding or sham surgery (n=9-12/group). LV function was assessed by echocardiography after 8 weeks. In addition, we studied the effect of omega-3 PUFA on the cardioprotective adipocyte-derived hormone adiponectin, which may alter the pro-growth serine-threonine kinase Akt.

RESULTS

Banding increased LV mass to a greater extent with the standard chow (31%) than with omega-3 PUFA (18%). LV end diastolic and systolic volumes were increased by 19% and 105% with standard chow, respectively, but were unchanged with omega-3 PUFA. The expression of adiponectin was up-regulated in adipose tissue, and the plasma adiponectin concentration was significantly elevated. Treatment with omega-3 PUFA increased total Akt protein expression in the heart, but decreased the fraction of Akt in the active phosphorylated form, and thus did not alter the amount of active phospho-Akt.

CONCLUSION

Dietary supplementation with omega-3 PUFA attenuated pressure overload-induced LV dysfunction, which was associated with elevated plasma adiponectin.

Mouse strain-specific differences in cardiac metabolic enzyme activities observed in a model of isoproterenol-induced cardiac hypertrophy

1. Alterations in myocardial energy metabolism accompany pressure overload-induced hypertrophy. We previously described a novel model of catecholamine-induced hypertrophy in which A/J mice exhibit more robust cardiac hypertrophy than B6 mice. Accordingly, we assessed the influence of mouse strain on the activities of key myocardial metabolic enzymes and whether there are strain-related metabolic adaptations to short-term, high-dose isoproterenol (ISO) administration. 2. Thirty-nine male mice (19 A/J mice, 20 B6 mice), aged 12-15 weeks, were randomly assigned to receive either ISO (100 mg/kg, s.c.) or vehicle (sterile water) daily for 5 days. On Day 6, all hearts were excised, weighed, freeze clamped and assayed for pyruvate dehydrogenase (PDH), medium chain acyl-CoA dehydrogenase, carnitine palmitoyl transferase I and citrate synthase activities. Plasma fatty acids (FA) were also measured. 3. The ISO-treated A/J mice demonstrated greater percentage increases in gravimetric heart weight/bodyweight ratio than ISO-treated B6 mice (24 vs 3%, respectively; P < 0.001). All enzyme activities were significantly greater in vehicle-treated B6 mice than in A/J mice, illustrating a greater capacity for aerobic metabolism in B6 mice. Administration of ISO reduced PDHa (active form) activity in B6 mice by 47% (P < 0.001), with no significant change seen in A/J mice. Free FA levels were not significantly different between groups; thus, the differences in PDHa were not due to changes in FA. 4. The basal activity of myocardial metabolic enzymes is greater in B6 mice than in A/J mice and ISO alters myocardial PDH activity in a mouse strain-dependent manner. Compared with A/J mice, B6 mice demonstrate less ISO-induced cardiac hypertrophy, but greater activity of key enzymes regulating FA and carbohydrate oxidation, which may protect against the development of hypertrophy. The metabolic adaptations associated with ISO-induced hypertrophy differ from those reported with pressure overload hypertrophy.

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

Lipid accumulation in nonadipose tissue due to enhanced circulating fatty acids may play a role in the pathophysiology of heart failure, obesity, and diabetes. Accumulation of myocardial lipids and related intermediates, e.g., ceramide, is associated with decreased contractile function, mitochondrial oxidative phosphorylation, and electron transport chain (ETC) complex activities. We tested the hypothesis that the progression of heart failure would be exacerbated by elevated myocardial lipids and an associated ceramide-induced inhibition of mitochondrial oxidative phosphorylation and ETC complex activities. Heart failure (HF) was induced by coronary artery ligation. Rats were then randomly assigned to either a normal (10% kcal from fat; HF, n = 8) or high saturated fat diet (60% kcal from saturated fat; HF + Sat, n = 7). Sham-operated animals (sham; n = 8) were fed a normal diet. Eight weeks postligation, left ventricular (LV) function was assessed by echocardiography and catheterization. Subsarcolemmal and interfibrillar mitochondria were isolated from the LV. Heart failure resulted in impaired LV contractile function [decreased percent fractional shortening and peak rate of LV pressure rise and fall (±dP/d t)] and remodeling (increased end-diastolic and end-systolic dimensions) in HF compared with sham. No further progression of LV dysfunction was evident in HF + Sat. Mitochondrial state 3 respiration was increased in HF + Sat compared with HF despite elevated myocardial ceramide. Activities of ETC complexes II and IV were elevated in HF + Sat compared with HF and sham. High saturated fat feeding following coronary artery ligation was associated with increased oxidative phosphorylation and ETC complex activities and did not adversely affect LV contractile function or remodeling, despite elevations in myocardial ceramide.