Noninvasive Detection of Early Metabolic Left Ventricular Remodeling in Systemic Hypertension

Role of Cardiac Energetics in Aortic Stenosis Disease Progression: Identifying the High-risk Metabolic Phenotype

BACKGROUND

Severe aortic stenosis (AS) is associated with left ventricular (LV) hypertrophy and cardiac metabolic alterations with evidence of steatosis and impaired myocardial energetics. Despite this common phenotype, there is an unexplained and wide individual heterogeneity in the degree of hypertrophy and progression to myocardial fibrosis and heart failure. We sought to determine whether the cardiac metabolic state may underpin this variability.

METHODS

We recruited 74 asymptomatic participants with AS and 13 healthy volunteers. Cardiac energetics were measured using phosphorus spectroscopy to define the myocardial phosphocreatine to adenosine triphosphate ratio. Myocardial lipid content was determined using proton spectroscopy. Cardiac function was assessed by cardiovascular magnetic resonance cine imaging.

RESULTS

Phosphocreatine/adenosine triphosphate was reduced early and significantly across the LV wall thickness quartiles (Q2, 1.50 [1.21-1.71] versus Q1, 1.64 [1.53-1.94]) with a progressive decline with increasing disease severity (Q4, 1.48 [1.18-1.70]; P=0.02). Myocardial triglyceride content levels were overall higher in all the quartiles with a significant increase seen across the AV pressure gradient quartiles (Q2, 1.36 [0.86-1.98] versus Q1, 1.03 [0.81-1.56]; P=0.034). While all AS groups had evidence of subclinical LV dysfunction with impaired strain parameters, impaired systolic longitudinal strain was related to the degree of energetic impairment (r=0.219; P=0.03). Phosphocreatine/adenosine triphosphate was not only an independent predictor of LV wall thickness (r=-0.20; P=0.04) but also strongly associated with myocardial fibrosis (r=-0.24; P=0.03), suggesting that metabolic changes play a role in disease progression. The metabolic and functional parameters showed comparable results when graded by clinical severity of AS.

CONCLUSIONS

A gradient of myocardial energetic deficit and steatosis exists across the spectrum of hypertrophied AS hearts, and these metabolic changes precede irreversible LV remodeling and subclinical dysfunction. As such, cardiac metabolism may play an important and potentially causal role in disease progression.

Progressive Cardiac Metabolic Defects Accompany Diastolic and Severe Systolic Dysfunction in Spontaneously Hypertensive Rat Hearts

Background Cardiac metabolic abnormalities are present in heart failure. Few studies have followed metabolic changes accompanying diastolic and systolic heart failure in the same model. We examined metabolic changes during the development of diastolic and severe systolic dysfunction in spontaneously hypertensive rats (SHR). Methods and Results We serially measured myocardial glucose uptake rates with dynamic 2-[18F] fluoro-2-deoxy-d-glucose positron emission tomography in vivo in 9-, 12-, and 18-month-old SHR and Wistar Kyoto rats. Cardiac magnetic resonance imaging determined systolic function (ejection fraction) and diastolic function (isovolumetric relaxation time) and left ventricular mass in the same rats. Cardiac metabolomics was performed at 12 and 18 months in separate rats. At 12 months, SHR hearts, compared with Wistar Kyoto hearts, demonstrated increased isovolumetric relaxation time and slightly reduced ejection fraction indicating diastolic and mild systolic dysfunction, respectively, and higher (versus 9-month-old SHR decreasing) 2-[18F] fluoro-2-deoxy-d-glucose uptake rates (Ki). At 18 months, only few SHR hearts maintained similar abnormalities as 12-month-old SHR, while most exhibited severe systolic dysfunction, worsening diastolic function, and markedly reduced 2-[18F] fluoro-2-deoxy-d-glucose uptake rates. Left ventricular mass normalized to body weight was elevated in SHR, more pronounced with severe systolic dysfunction. Cardiac metabolite changes differed between SHR hearts at 12 and 18 months, indicating progressive defects in fatty acid, glucose, branched chain amino acid, and ketone body metabolism. Conclusions Diastolic and severe systolic dysfunction in SHR are associated with decreasing cardiac glucose uptake, and progressive abnormalities in metabolite profiles. Whether and which metabolic changes trigger progressive heart failure needs to be established.

The Lure of Cardiac Metabolism in the Diagnosis, Prevention, and Treatment of Heart Failure

Energy substrate metabolism and contractile function are tightly coupled in the heart. Within this framework, heart failure may be viewed as a state of impaired energy transfer. The metabolic changes in the failing heart are linked to functional and structural changes. A worthwhile goal is to measure metabolic flux and its regulation quantitatively, and to do this in a manner that leads to targeted interventions. For several good reasons, this goal has been elusive until now. The development of new analytical and imaging techniques offers the potential of exploring the landscape of metabolic changes across the different stages of heart failure. In this Review Topic of the Month, we focus on concepts and brevity to provide a strategic overview of cardiac metabolism in the diagnosis, prevention, and treatment of nonischemic heart failure.

Diet-induced insulin resistance altered cardiac GLUT4 and FATP/CD36 expression in rats

Background

Altered substrate transport protein expression is central to the effect of insulin resistance on cardiac metabolism. The present study was thus designed to investigate the comparative effects of high fat, high sucrose and salt-induced IR on cardiac expression of fatty acid transporter (FATP) and glucose transporter (GLUT4) in rats.

Results

Rats fed with high fat, high sucrose and salt diets developed impaired glucose tolerance (p > 0.05) and hyperinsulinemia (p < 0.05) compared with control group. Myocardial glucose transporter expression was significantly increased (p < 0.001 for salt-induced IR; p < 0.01 for sucrose-induced IR; p < 0.01 for fat-induced IR) across all IR groups compared with control. Fatty acid transporter expression was also increased (p < 0.001) in high salt diet-induced IR rats, and high fat diet-induced IR rats (p < 0.05).

Conclusions

Our results demonstrate that salt and not caloric excess has a potential role in IR alteration of myocardial substrate transport protein expression in the rat.

Strategies for Imaging Metabolic Remodeling of the Heart in Obesity and Heart Failure

PURPOSE OF REVIEW

Define early myocardial metabolic changes among patients with obesity and heart failure, and to describe noninvasive methods and their applications for imaging cardiac metabolic remodeling.

RECENT FINDINGS

Metabolic remodeling precedes, triggers, and sustains functional and structural remodeling in the stressed heart. Alterations in cardiac metabolism can be assessed by using a variety of molecular probes. The glucose tracer analog, 18F-FDG, and the labeled tracer 11C-palmitate are still the most commonly used tracers to assess glucose and fatty acid metabolism, respectively. The development of new tracer analogs and imaging agents, including those targeting the peroxisome proliferator-activated receptor (PPAR), provides new opportunities for imaging metabolic activities at a molecular level. While the use of cardiac magnetic resonance spectroscopy in the clinical setting is limited to the assessment of intramyocardial and epicardial fat, new technical improvements are likely to increase its usage in the setting of heart failure. Noninvasive imaging methods are an effective tool for the serial assessment of alterations in cardiac metabolism, either during disease progression, or in response to treatment.

QiShenYiQi Pill Improves Myocardial Hypertrophy Caused by Pressure Overload in Rats

Pressure-overloaded myocardial hypertrophy is an independent risk factor for various cardiovascular diseases (CVDs), such as heart failure (HF), arrhythmia, and even sudden death. It is reported that QiShenYiQi pill (QSYQ) is widely used in the treatment of CVDs and can prevent pathological hypertrophy of myocardium, but its specific mechanism is still unclear. In this study, a rat model of myocardial hypertrophy was established through the pressure overload caused by abdominal aortic constriction in Wistar rats. The rats were randomly divided into model group, valsartan group, and QSYQ group, and sham-operated animals served as the control group. At the 4 and 8 weeks of intervention, the general morphology of the heart, myocardial collagen content, collagen volume factor (CVF), collagen type I, collagen type III, myocardial pathological changes, and the expression of ANP, β-MHC, TGF-β1, and CTGF were analyzed, respectively, in order to explore the possible effect of QSYQ on the mechanism of myocardial hypertrophy. We observed that QSYQ could effectively improve myocardial hypertrophy in pressure-overloaded rats, which was related to the regulatory mechanism of TGF-β1 and CTGF.

Metabolic remodeling precedes mTORC1-mediated cardiac hypertrophy

RATIONALE

The nutrient sensing mechanistic target of rapamycin complex 1 (mTORC1) and its primary inhibitor, tuberin (TSC2), are cues for the development of cardiac hypertrophy. The phenotype of mTORC1 induced hypertrophy is unknown.

OBJECTIVE

To examine the impact of sustained mTORC1 activation on metabolism, function, and structure of the adult heart.

METHODS AND RESULTS

We developed a mouse model of inducible, cardiac-specific sustained mTORC1 activation (mTORC1^iSA) through deletion of Tsc2. Prior to hypertrophy, rates of glucose uptake and oxidation, as well as protein and enzymatic activity of glucose 6-phosphate isomerase (GPI) were decreased, while intracellular levels of glucose 6-phosphate (G6P) were increased. Subsequently, hypertrophy developed. Transcript levels of the fetal gene program and pathways of exercise-induced hypertrophy increased, while hypertrophy did not progress to heart failure. We therefore examined the hearts of wild-type mice subjected to voluntary physical activity and observed early changes in GPI, followed by hypertrophy. Rapamycin prevented these changes in both models.

CONCLUSION

Activation of mTORC1 in the adult heart triggers the development of a non-specific form of hypertrophy which is preceded by changes in cardiac glucose metabolism.

Series of myocardial FDG uptake requiring considerations of myocardial abnormalities in FDG-PET/CT

Distinct from cardiac PET performed with preparation to control physiological FDG uptake in the myocardium, standard FDG-PET/CT performed with 4-6 h of fasting will show variation in myocardial FDG uptake. For this reason, important signs of myocardial and pericardial abnormality revealed by myocardial FDG uptake tend to be overlooked. However, recognition of possible underlying disease will support further patient management to avoid complications due to the disease. This review demonstrates the mechanism of FDG uptake in the myocardium, discusses the factors affecting uptake, and provides notable image findings that may suggest underlying disease.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

QiShenYiQi pill activates autophagy to attenuate reactive myocardial fibrosis via the PI3K/AKT/mTOR pathway

QiShenYiQi pill (QSYQ), a traditional Chinese medicine, is used to treat cardiovascular diseases. However, the dose-effect relationship of its intervention in the reactive myocardial fibrosis is elusive. In this work, rat models of reactive myocardial fibrosis induced by partial abdominal aortic coarctation were constructed and randomly classified into the model group, 3-methyladenine group, rapamycin group, QSYQ low-dose group, QSYQ medium-dose group, QSYQ high-dose group, and sham-operated rats (control group). We revealed that QSYQ lowered the heart mass index (HMI), left ventricular mass index (LVMI), and myocardial collagen volume fraction (CVF) levels in a dose-dependent mechanism. Additionally, QSYQ increased the number of autophagosomes, and the expression of myocardial Beclin-1 and LC3B. In contrast, it reduced the expression of myocardial p62 and decreased the ratios of myocardial p-PI3K/PI3K, p-Akt/Akt, and p-mTOR/mTOR. In conclusion, our results have revealed that QSYQ impacts anti-reactive myocardial fibrosis in a dose-dependent mechanism which is mediated by the activation of myocardial autophagy via the PI3K/AKT/mTOR pathway.

Mechanisms underlying the pathophysiology of heart failure with preserved ejection fraction: the tip of the iceberg

Heart failure with preserved ejection fraction (HFpEF) is a multifaceted syndrome with a complex aetiology often associated with several comorbidities, such as left ventricle pressure overload, diabetes mellitus, obesity, and kidney disease. Its pathophysiology remains obscure mainly due to the complex phenotype induced by all these associated comorbidities and to the scarcity of animal models that adequately mimic HFpEF. Increased oxidative stress, inflammation, and endothelial dysfunction are currently accepted as key players in HFpEF pathophysiology. However, we have just started to unveil HFpEF complexity and the role of calcium handling, energetic metabolism, and mitochondrial function remain to clarify. Indeed, the enlightenment of such cellular and molecular mechanisms represents an opportunity to develop novel therapeutic approaches and thus to improve HFpEF treatment options. In the last decades, the number of research groups dedicated to studying HFpEF has increased, denoting the importance and the magnitude achieved by this syndrome. In the current technological and web world, the amount of information is overwhelming, driving us not only to compile the most relevant information about the theme but also to explore beyond the tip of the iceberg. Thus, this review aims to encompass the most recent knowledge related to HFpEF or HFpEF-associated comorbidities, focusing mainly on myocardial metabolism, oxidative stress, and energetic pathways.

Variations in Energy Metabolism Precede Alterations in Cardiac Structure and Function in Hypertrophic Preconditioning

Recent studies have unveiled that myocardial hypertrophic preconditioning (HP), which is produced by de-banding (De-TAC) of short-term transverse aortic constriction (TAC), protects the heart against hypertrophic responses caused by subsequent re-constriction (Re-TAC) in mice. Although cardiac substrate metabolism is impaired in heart failure, it remains unclear about the role of HP-driven energetics in the development of cardiac hypertrophy. Here, we investigated energy metabolism, cardiac hypertrophy, and function following variational loading conditions, as well as their relationships in HP. Male C57BL/6J mice (10–12 weeks old) were randomly subjected to Sham, HP [TAC for 3days (TAC 3d), de-banding the aorta for 4 days (De-TAC 4d), and then re-banding the aorta for 4 weeks (Re-TAC 4W)], and TAC (TAC for 4 weeks without de-banding). Cardiac echocardiography, hemodynamics, and histology were utilized to evaluate cardiac remodeling and function. The mRNA expression levels of fetal genes (ANP and BNP), glucose metabolism-related genes (glut4, pdk4), and fatty acid oxidation-related genes (mcad, pgc1α, mcd, pparα) were quantitated by real-time quantitative PCR. Activation of hypertrophy regulators ERK1/2, a metabolic stress kinase AMP-activated protein kinase (AMPK), and its downstream target acetyl-coA carboxylase (ACC) were explored by western blot. Compared with TAC 4W mice, Re-TAC 4W mice showed less impairment in glucose and fatty acid metabolism, as well as less cardiac hypertrophy and dysfunction. Moreover, no significant difference was found in myocardial hypertrophy, fibrosis, and cardiac function in TAC 3d and De-TAC 4d groups compared with Sham group. However, glut4, pdk4, mcad, pgc1α, mcd, and pparα were all decreased, while AMPK and ACC were activated in TAC 3d and returned to Sham level in De-TAC 4d, suggesting that the change in myocardial energy metabolism in HP mice was earlier than that in cardiac structure and function. Collectively, HP improves energy metabolism and delays cardiac remodeling, highlighting that early metabolic improvements drive a potential beneficial effect on structural and functional restoration in cardiac hypertrophy.

Prdm16 Deficiency Leads to Age-Dependent Cardiac Hypertrophy, Adverse Remodeling, Mitochondrial Dysfunction, and Heart Failure

Hypertrophic cardiomyopathy (HCM) is a well-established risk factor for cardiovascular mortality worldwide. Although hypertrophy is traditionally regarded as an adaptive response to physiological or pathological stress, prolonged hypertrophy can lead to heart failure. Here we demonstrate that Prdm16 is dispensable for cardiac development. However, it is required in the adult heart to preserve mitochondrial function and inhibit hypertrophy with advanced age. Cardiac-specific deletion of Prdm16 results in cardiac hypertrophy, excessive ventricular fibrosis, mitochondrial dysfunction, and impaired metabolic flexibility, leading to heart failure. We demonstrate that Prdm16 and euchromatic histone-lysine N-methyltransferase factors (Ehmts) act together to reduce expression of fetal genes reactivated in pathological hypertrophy by inhibiting the functions of the pro-hypertrophic transcription factor Myc. Although young Prdm16 knockout mice show normal cardiac function, they are predisposed to develop heart failure in response to metabolic stress. Our study demonstrates that Prdm16 protects the heart against age-dependent cardiac hypertrophy and heart failure.

Effects of trimetazidine on ventricular remodeling in coronary artery disease patients with left ventricular hypertrophy: the rationale and design of a randomized controlled trial

Background

Trimetazidine is a metabolic anti-ischemic agent, which increases the tolerance of cardiomyocytes to ischemia. However, few studies have explored the effect of trimetazidine on ventricular remodeling in coronary artery disease (CAD) patients undergoing percutaneous coronary intervention (PCI) with left ventricular hypertrophy (LVH).

Methods

It is a randomized, placebo-controlled trial, and we propose to recruit one hundred and twenty-four CAD patients undergoing PCI with LVH during a 12-month period. They will be randomized to receive either trimetazidine (35 mg twice a day) or placebo in the following 12 months after PCI. Blood tests, echocardiography, symptom of angina and major adverse cardiovascular events (MACEs) will be collected at follow-up visit at 3 and 12 months. The primary end point will be the left ventricular remodeling measured by left ventricular mass index (LVMI) at 3- and 12-month follow-up compared with the baseline. The secondary end points will be the symptom of angina assessed by Seattle Angina Questionnaire, myocardial ischemia measured by 6-min walk test and exercise electrocardiography test, as well as MACEs (defined as a composite of death, myocardial infarction, stroke, recurrent angina, re-hospitalization, change of viable myocardium).

Discussion

This study aims to demonstrate the effect of trimetazidine on left ventricular remodeling and myocardial ischemia in CAD patients undergoing PCI with LVH. Trimetazidine treatment is likely to improve the left ventricular remodeling, symptoms of angina and myocardial ischemia. It might also reduce the risk of MACEs in CAD patients undergoing PCI with LVH.

Trial registration

http://www.chictr.org.cn, Chinese Clinical Trial Registry (ChiCTR1800017876). Registered on 19 Aug 2018.

How Hypertension Affects Heart Metabolism

Hypertension is one of the most frequently observed cardiovascular diseases, which precedes heart failure in 75% of its cases. It is well-established that hypertensive patients have whole body metabolic complications such as hyperlipidemia, hyperglycemia, decreased insulin sensitivity or diabetes mellitus. Since myocardial metabolism is strictly dependent on hormonal status as well as substrate milieu, the above mentioned disturbances may affect energy generation status in the heart. Interestingly, it was found that hypertension induces a shift in substrate preference toward increased glucose utilization in cardiac muscle, prior to structural changes development. The present work reports advances in the aspect of heart metabolism under high blood pressure conditions, including human and the most common animal models of hypertension.

Correlation of cardiomyocyte apoptosis with duration of hypertension, severity of hypertension and caspase-3 expression in hypertensive rats

Correlation of cardiomyocyte apoptosis with duration of hypertension, severity of hypertension and caspase-3 expression in hypertensive rats was analyzed. Sixty male Sprague-Dawley (SD) rats were selected and randomly divided into the observation group (n=30) and control group (n=30), and the rat models of hypertension were established by virtue of transverse aortic constriction (TAC). The rats in the two groups were further divided into the 7-day subgroup (n=10), 14-day subgroup (n=10) and 28-day subgroup (n=10), respectively according to their survival time after TAC. The blood pressure values of the rats in each group were measured through intubation of carotid artery to calculate the mean arterial pressure (MAP). The conditions of cardiomyocyte apoptosis were detected using terminal dexynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. Enzyme-linked immunosorbent assay (ELISA) was applied to measure the expression of caspase-3 in the myocardial tissues, and correlation analysis was performed. The MAPs in 7-, 14- and 28-day subgroups of the observation group were significantly higher than those in the corresponding subgroups of the control group (P<0.05). The 7-, 14- and 28-day subgroups of the observation group had remarkably elevated myocardial caspase-3 expression levels compared with the subgroups of the control group (P<0.05). The apoptosis rates of myocardial cells in the three subgroups of the observation group were obviously higher than those in the corresponding subgroups of the control group (P<0.05). Pearson's correlation analysis indicated that the cardiomyocyte apoptosis rate of hypertensive rats was positively correlated with the duration of hypertension, severity of hypertension and caspase-3 expression (P<0.05). Hypertension can induce apoptosis of myocardial cells, and the apoptosis becomes more serious with the constantly elevated level and prolonged duration of hypertension. In addition, the activity of caspase-3 has a close correlation with cardiomyocyte apoptosis.

Pet Imaging and its Application in Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading cause of death worldwide and represent a great challenge for modern research and medicine. Despite advances in preventing and treating CVD over the decades, there remains an urgent need to develop sensitive and safe methods for early detection and personalized treatment. With refinements of molecular imaging technologies such as positron emission tomography (PET), noninvasive imaging of CVDs is experiencing impressive progress in both preclinical and clinical settings. In this review, we summarize advances in cardiovascular PET imaging, highlight the latest development of CVD imaging probes, and illustrate the potential for individualized therapy based on metabolic phenotype.

Metabolic Recovery of the Failing Heart: Emerging Therapeutic Options

Heart failure has mortality rates that parallel those of breast cancer. Current management strategies include neurohormonal blockade, rate control measures, natriuretic peptide preservation, implantation of mechanical assist devices, and heart transplantation. Despite these strategies, however, the failing myocardium remains energy depleted. New strategies to promote metabolic recovery are being developed to potentially augment current treatment guidelines. For example, an unexpected finding of our own studies showed that mechanical unloading with assist devices in advanced-stage heart failure restored metabolic flux. Unfortunately, at that point it is too late for myocardial recovery. Traditional metabolic therapies addressing hyperglycemia have had limited long-term outcome benefit. Now, new therapeutic options are emerging based on increased understanding of the molecular mechanisms underlying energy depletion. Metabolic cardiac imaging combined with laboratory diagnostics could guide the design of individual therapeutic strategies. To date, agents that show benefit in select individuals include mimetics that stimulate glucagon-like peptide-1, inhibitors of sodium-glucose cotransporter receptors, drugs that limit fatty acid oxidation, and hormonal therapy in select individuals. This review will summarize mechanisms and investigations related to these metabolic approaches to heart failure.

Qiliqiangxin Enhances Cardiac Glucose Metabolism and Improves Diastolic Function in Spontaneously Hypertensive Rats

Cardiac diastolic dysfunction has emerged as a growing type of heart failure. The present study aims to explore whether Qiliqiangxin (QL) can benefit cardiac diastolic function in spontaneously hypertensive rat (SHR) through enhancement of cardiac glucose metabolism. Fifteen 12-month-old male SHRs were randomly divided into QL-treated, olmesartan-treated, and saline-treated groups. Age-matched WKY rats served as normal controls. Echocardiography and histological analysis were performed. Myocardial glucose uptake was determined by ¹⁸F-FDG using small-animal PET imaging. Expressions of several crucial proteins and key enzymes related to glucose metabolism were also evaluated. As a result, QL improved cardiac diastolic function in SHRs, as evidenced by increased E′/A′and decreased E/E′ (P < 0.01). Meanwhile, QL alleviated myocardial hypertrophy, collagen deposits, and apoptosis (P < 0.01). An even higher myocardial glucose uptake was illustrated in QL-treated SHR group (P < 0.01). Moreover, an increased CS activity and ATP production was observed in QL-treated SHRs (P < 0.05). QL enhanced cardiac glucose utilization and oxidative phosphorylation in SHRs by upregulating AMPK/PGC-1α axis, promoting GLUT-4 expression, and regulating key enzymes related to glucose aerobic oxidation such as HK2, PDK4, and CS (P < 0.01). Our data suggests that QL improves cardiac diastolic function in SHRs, which may be associated with enhancement of myocardial glucose metabolism.

Exercise Intolerance In Heart Failure With Preserved Ejection Fraction

More than 50% of Americans with heart failure have preserved ejection fraction (HFpEF). Exercise intolerance is a hallmark of HFpEF, but the pathophysiology is not well understood. Diverse etiologies and incomplete mechanistic understanding have resulted in ineffective management strategies to improve the outcomes of HFpEF. Traditional therapies that have been beneficial in the treatment of heart failure with reduced ejection fraction (HFrEF), neurohormonal blockade in particular, have not been effective in treating HFpEF. In this review, we address underlying mechanisms of HFpEF and present the rationale supporting exercise as a component of comprehensive management.

Trimetazidine attenuates pressure overload-induced early cardiac energy dysfunction via regulation of neuropeptide Y system in a rat model of abdominal aortic constriction

Background

Metabolism remodeling has been recognized as an early event following cardiac pressure overload. However, its temporal association with ventricular hypertrophy has not been confirmed. Moreover, whether trimetazidine could favorably affect this process also needs to be determined. The aim of the study was to explore the temporal changes of myocardial metabolism remodeling following pressure-overload induced ventricular hypertrophy and the potential favorable effect of trimetazidine on myocardial metabolism remodeling.

Methods

A rat model of abdominal aortic constriction (AAC)-induced cardiac pressure overload was induced. These rats were grouped as the AAC (no treatment) or TMZ group according to whether oral trimetazidine (TMZ, 40 mg/kg/d, for 5 days) was administered. Changes in cardiac structures were sequentially evaluated via echocardiography. The myocardial ADP/ATP ratio was determined to reflect the metabolic status, and changes in serum neuropeptide Y systems were evaluated.

Results

Myocardial metabolic disorder was acutely induced as evidenced by an increased ADP/ATP ratio within 7 days of AAC before the morphological changes in the myocardium, accompanied by up-regulation of serum oxidative stress markers and expression of fetal genes related to hypertrophy. Moreover, the serum NPY and myocardial NPY-1R, 2R, and 5R levels were increased within the acute phase of AAC-induced cardiac pressure overload. Pretreatment with TMZ could partly attenuate myocardial energy metabolic homeostasis, decrease serum levels of oxidative stress markers, attenuate the induction of hypertrophy-related myocardial fetal genes, inhibit the up-regulation of serum NPY levels, and further increase the myocardial expression of NPY receptors.

Conclusions

Cardiac metabolic remodeling is an early change in the myocardium before the presence of typical morphological ventricular remodeling following cardiac pressure overload, and pretreatment with TMZ may at least partly reverse the acute metabolic disturbance, perhaps via regulation of the NPY system.

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

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