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

Roles of MicroRNAs in Glucose and Lipid Metabolism in the Heart

MicroRNAs (miRNAs) are small non-coding RNAs that participate in heart development and pathological processes mainly by silencing gene expression. Overwhelming evidence has suggested that miRNAs were involved in various cardiovascular pathological processes, including arrhythmias, ischemia-reperfusion injuries, dysregulation of angiogenesis, mitochondrial abnormalities, fibrosis, and maladaptive remodeling. Various miRNAs could regulate myocardial contractility, vascular proliferation, and mitochondrial function. Meanwhile, it was reported that miRNAs could manipulate nutrition metabolism, especially glucose and lipid metabolism, by regulating insulin signaling pathways, energy substrate transport/metabolism. Recently, increasing studies suggested that the abnormal glucose and lipid metabolism were closely associated with a broad spectrum of cardiovascular diseases (CVDs). Therefore, maintaining glucose and lipid metabolism homeostasis in the heart might be beneficial to CVD patients. In this review, we summarized the present knowledge of the functions of miRNAs in regulating cardiac glucose and lipid metabolism, as well as highlighted the miRNA-based therapies targeting cardiac glucose and lipid metabolism.

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

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

Long-Term High-Fat Diet Inhibits the Recovery of Myocardial Mitochondrial Function After Chronic Hypoxia Reoxygenation in Rats

Yan, Jun, Kang Song, Sisi Zhou, and Ri-Li Ge. Long-term high-fat diet inhibits the recovery of myocardial mitochondrial function after chronic hypoxia reoxygenation in rats. High Alt Med Biol. 16:000-000, 2021. Aims: A high-fat diet (HFD) is associated with cardiovascular diseases and mitochondrial dysfunction. Obesity incidence is low at high altitudes, but the impact of HFD, which is closely associated with obesity at high altitudes, and the effects of reoxygenation on the heart are unclear. In this study, we investigated the effects of long-term HFD consumption on mitochondrial function in the myocardium after chronic hypoxia reoxygenation. Main Methods: Sprague-Dawley rats were randomized into the following six groups: normoxia groups, including a control group and HFD group; chronic hypoxia groups, including a normal chow diet (CH-CD) group and an HFD (CH-HFD) group; and hypoxic-reoxygenated (HR) groups, including a hypoxia-reoxygenation normal chow diet (HR-CD) group and a hypoxia-reoxygenation HFD (HR-HFD) group. All rats were euthanized in this study. Results: We found that chronic hypoxia aggravated myocardial mitochondrial dysfunction. The Flameng score (in which the higher the score, the more severe the mitochondrial damage) was used to assess the extent of mitochondrial structural damage. Compared with the control group and HFD group, the Flameng scores of the CH-CD and CH-HFD groups were significantly increased, respectively [1.260 ± 0.063 vs. 0.68 ± 0.05 (p < 0.05); 2.03 ± 0.07 vs. 1.48 ± 0.05 (p < 0.05)]. Moreover, progressive reoxygenation facilitated the recovery of myocardial mitochondrial function; this process was inhibited by long-term HFD. After reoxygenation, the Flameng scores in the HR-CD group became comparable to those in the CH-CD group [0.86 ± 0.05 vs. 1.26 ± 0.06 (p < 0.05)]. However, no significant changes were observed in the Flameng score between the HR-HFD and CH-HFD groups. Significance: Long-term HFD consumption inhibits myocardial mitochondrial function after reoxygenation. This finding may be helpful for the prevention and control of risk factors related to cardiovascular diseases in plateau residents.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Energy metabolism disorders and potential therapeutic drugs in heart failure

Heart failure (HF) is a global public health problem with high morbidity and mortality. A large number of studies have shown that HF is caused by severe energy metabolism disorders, which result in an insufficient heart energy supply. This deficiency causes cardiac pump dysfunction and systemic energy metabolism failure, which determine the development of HF and recovery of heart. Current HF therapy acts by reducing heart rate and cardiac preload and afterload, treating the HF symptomatically or delaying development of the disease. Drugs aimed at cardiac energy metabolism have not yet been developed. In this review, we outline the main characteristics of cardiac energy metabolism in healthy hearts, changes in metabolism during HF, and related pathways and targets of energy metabolism. Finally, we discuss drugs that improve cardiac function via energy metabolism to provide new research ideas for the development and application of drugs for treating HF.

Barth syndrome-related cardiomyopathy is associated with a reduction in myocardial glucose oxidation

Heart failure presents as the leading cause of infant mortality in individuals with Barth syndrome (BTHS), a rare genetic disorder due to mutations in the tafazzin (TAZ) gene affecting mitochondrial structure and function. Investigations into the perturbed bioenergetics in the BTHS heart remain limited. Hence, our objective was to identify the potential alterations in myocardial energy metabolism and molecular underpinnings that may contribute to the early cardiomyopathy and heart failure development in BTHS. Cardiac function and myocardial energy metabolism were assessed via ultrasound echocardiography and isolated working heart perfusions, respectively, in a mouse model of BTHS [doxycycline-inducible Taz knockdown (TazKD) mice]. In addition, we also performed mRNA/protein expression profiling for key regulators of energy metabolism in hearts from TazKD mice and their wild-type (WT) littermates. TazKD mice developed hypertrophic cardiomyopathy as evidenced by increased left ventricular anterior and posterior wall thickness, as well as increased cardiac myocyte cross-sectional area, though no functional impairments were observed. Glucose oxidation rates were markedly reduced in isolated working hearts from TazKD mice compared with their WT littermates in the presence of insulin, which was associated with decreased pyruvate dehydrogenase activity. Conversely, myocardial fatty acid oxidation rates were elevated in TazKD mice, whereas no differences in glycolytic flux or ketone body oxidation rates were observed. Our findings demonstrate that myocardial glucose oxidation is impaired before the development of overt cardiac dysfunction in TazKD mice, and may thus represent a pharmacological target for mitigating the development of cardiomyopathy in BTHS.NEW & NOTEWORTHY Barth syndrome (BTHS) is a rare genetic disorder due to mutations in tafazzin that is frequently associated with infantile-onset cardiomyopathy and subsequent heart failure. Although previous studies have provided evidence of perturbed myocardial energy metabolism in BTHS, actual measurements of flux are lacking. We now report a complete energy metabolism profile that quantifies flux in isolated working hearts from a murine model of BTHS, demonstrating that BTHS is associated with a reduction in glucose oxidation.

Reactive oxygen species produced by altered tumor metabolism impacts cancer stem cell maintenance

Controlling reactive oxygen species (ROS) at sustainable levels can drive multiple facets of tumor biology, including within the cancer stem cell (CSC) population. Tight regulation of ROS is one key component in CSCs that drives disease recurrence, cell signaling, and therapeutic resistance. While ROS are well-appreciated to need oxygen and are a product of oxidative phosphorylation, there are also important roles for ROS under hypoxia. As hypoxia promotes and sustains major stemness pathways, further consideration of ROS impacts on CSCs in the tumor microenvironment is important. Furthermore, glycolytic shifts that occur in cancer and may be promoted by hypoxia are associated with multiple mechanisms to mitigate oxidative stress. This altered metabolism provides survival advantages that sustain malignant features, such as proliferation and self-renewal, while producing the necessary antioxidants that reduce damage from oxidative stress. Finally, disease recurrence is believed to be attributed to therapy resistant CSCs which can be quiescent and have changes in redox status. Effective DNA damage response pathways and/or a slow-cycling state can protect CSCs from the genomic catastrophe induced by irradiation and genotoxic agents. This review will explore the delicate, yet complex, relationship between ROS and its pleiotropic role in modulating the CSC.

Role of Warburg Effect in Cardiovascular Diseases: A Potential Treatment Option

Background:

Under normal conditions, the heart obtains ATP through the oxidation of fatty acids, glucose, and ketones. While fatty acids are the main source of energy in the heart, under certain conditions, the main source of energy shifts to glucose where pyruvate converts into lactate, to meet the energy demand. The Warburg effect is the energy shift from oxidative phosphorylation to glycolysis in the presence of oxygen. This effect is observed in tumors as well as in diseases, including cardiovascular diseases. If glycolysis is more dominant than glucose oxidation, the two pathways uncouple, contributing to the severity of the heart condition. Recently, several studies have documented changes in metabolism in several cardiovascular diseases; however, the specific mechanisms remain unclear.

Methods:

This literature review was conducted by an electronic database of Pub Med, Google Scholar, and Scopus published until 2020. Relevant papers are selected based on inclusion and exclusion criteria.

Results:

A total of 162 potentially relevant articles after the title and abstract screening were screened for full-text. Finally, 135 papers were included for the review article.

Discussion:

This review discusses the effects of alterations in glucose metabolism, particularly the Warburg effect, on cardiovascular diseases, including heart failure, atrial fibrillation, and cardiac hypertrophy.

Conclusion:

Reversing the Warburg effect could become a potential treatment option for cardiovascular diseases.

Short-term administration of C. aronia stimulates insulin signaling, suppresses fatty acids metabolism, and increases glucose uptake and utilization in the hearts of healthy rats

This study evaluated the effect of Crataegus aronia (C. aronia) aqueous extract on cardiac substrate utilization and insulin signaling in adult male healthy Wistar rats. Rats (n = 18/group) were either administered normal saline (vehicle) or treated with C. aronia aqueous extract (200 mg/kg) for 7 days, daily. Fasting plasma glucose and insulin levels were not significantly changed in C. aronia-treated rats but were significantly reduced after both the intraperitoneal glucose or insulin tolerance tests. Besides, C. aronia significantly increased the left ventricular (LV) activities of phosphofructokinase (PFK) and pyruvate dehydrogenase (PDH), two markers of glycolysis and glucose oxidation, respectively, and suppressed the levels of pyruvate dehydrogenase kinase 4 (PDK4), an inhibitor of PDH. Concomitantly, it significantly reduced the LV levels of carnitine palmitoyltransferase 1 (CPT1) and PPARα, two markers of fatty acid (FAs) oxidations. Under basal and insulin stimulation, C. aronia aqueous extract boosted insulin signaling in the LV of rats by increasing the protein levels of p-IRS (Tyr⁶¹²) and p-Akt (Ser⁴⁷³) and suppressing protein levels of p-mTOR (Ser 2448) and p-IRS (Ser³⁰⁷). In parallel, C. aronia also increased the protein levels of GLUT-4 in the membrane fraction of the treated LVs. All these effects were also associated with a significant increase in AMPK activity (phosphorylation at Thr¹⁷²), a major energy modulator that stimulates glucose utilization. In conclusion, short-term administration of C. aronia aqueous extract shifts the cardiac metabolism toward glucose utilization, thus making this plant a potential therapeutic medication in cardiac disorders with impaired metabolism.

Applications of Metabolomics in Forensic Toxicology and Forensic Medicine

Forensic toxicology and forensic medicine are unique among all other medical fields because of their essential legal impact, especially in civil and criminal cases. New high-throughput technologies, borrowed from chemistry and physics, have proven that metabolomics, the youngest of the “omics sciences”, could be one of the most powerful tools for monitoring changes in forensic disciplines. Metabolomics is a particular method that allows for the measurement of metabolic changes in a multicellular system using two different approaches: targeted and untargeted. Targeted studies are focused on a known number of defined metabolites. Untargeted metabolomics aims to capture all metabolites present in a sample. Different statistical approaches (e.g., uni- or multivariate statistics, machine learning) can be applied to extract useful and important information in both cases. This review aims to describe the role of metabolomics in forensic toxicology and in forensic medicine.

Harnessing the Benefits of Endogenous Hydrogen Sulfide to Reduce Cardiovascular Disease

Cardiovascular disease is the leading cause of death in the U.S. While various studies have shown the beneficial impact of exogenous hydrogen sulfide (H₂S)-releasing drugs, few have demonstrated the influence of endogenous H₂S production. Modulating the predominant enzymatic sources of H₂S-cystathionine-β-synthase, cystathionine-γ-lyase, and 3-mercaptopyruvate sulfurtransferase-is an emerging and promising research area. This review frames the discussion of harnessing endogenous H₂S within the context of a non-ischemic form of cardiomyopathy, termed diabetic cardiomyopathy, and heart failure. Also, we examine the current literature around therapeutic interventions, such as intermittent fasting and exercise, that stimulate H₂S production.

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

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

Inhibiting Cardiac Mitochondrial Fatty Acid Oxidation Attenuates Myocardial Injury in a Rat Model of Cardiac Arrest

Mitochondrial fatty acid oxidation (FAO) is involved in myocardial damage after cardiopulmonary resuscitation (CPR). This study is aimed at investigating the effect of inhibiting mitochondrial FAO on myocardial injury and the underlying mechanisms of postresuscitation myocardial dysfunction. Rats were induced, subjected to 8 min of ventricular fibrillation, and underwent 6 min of CPR. Rats with return of spontaneous circulation (ROSC) were randomly divided into the Sham group, CPR group, and CPR + Trimetazidine (TMZ) group. Rats in the CPR + TMZ group were administered TMZ (10 mg/kg) at the onset of ROSC via the right external jugular vein, while rats in the CPR group were injected with equivalent volumes of vehicle. The sham rats were only administered equivalent volumes of vehicle. We found that the activities of enzymes related to cardiac mitochondrial FAO were partly improved after ROSC. TMZ, as a reversible inhibitor of 3-ketoacyl CoA thiolase, inhibited myocardial mitochondrial FAO after ROSC. In the CPR + TMZ group, the levels of mitochondrial injury in cardiac tissue were alleviated following attenuated myocardial damage and oxidative stress after ROSC. In addition, the disorder of cardiac mitochondrial metabolism was ameliorated, and specifically, the superfluous succinate related to mitochondrial reactive oxygen species (ROS) generation was decreased by inhibiting myocardial mitochondrial FAO with TMZ administration after ROSC. In conclusion, in the early period after ROSC, inhibiting cardiac mitochondrial FAO attenuated excessive cardiac ROS generation and preserved myocardial function, probably by alleviating the dysfunction of cardiac mitochondrial metabolism in a rat model of cardiac arrest.

Energy substrate metabolism and mitochondrial oxidative stress in cardiac ischemia/reperfusion injury

The heart is the most metabolically flexible organ with respect to the use of substrates available in different states of energy metabolism. Cardiac mitochondria sense substrate availability and ensure the efficiency of oxidative phosphorylation and heart function. Mitochondria also play a critical role in cardiac ischemia/reperfusion injury, during which they are directly involved in ROS-producing pathophysiological mechanisms. This review explores the mechanisms of ROS production within the energy metabolism pathways and focuses on the impact of different substrates. We describe the main metabolites accumulating during ischemia in the glucose, fatty acid, and Krebs cycle pathways. Hyperglycemia, often present in the acute stress condition of ischemia/reperfusion, increases cytosolic ROS concentrations through the activation of NADPH oxidase 2 and increases mitochondrial ROS through the metabolic overloading and decreased binding of hexokinase II to mitochondria. Fatty acid-linked ROS production is related to the increased fatty acid flux and corresponding accumulation of long-chain acylcarnitines. Succinate that accumulates during anoxia/ischemia is suggested to be the main source of ROS, and the role of itaconate as an inhibitor of succinate dehydrogenase is emerging. We discuss the strategies to modulate and counteract the accumulation of substrates that yield ROS and the therapeutic implications of this concept.

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.

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.

1H NMR-based metabolomics study of the dynamic effect of Xue-Fu-Zhu-Yu capsules on coronary heart disease rats induced by high-fat diet, coronary artery ligation

An ¹H NMR-based metabolomics approach was conducted to holisticly explore the effect of Xue Fu Zhu Yu (XFZY) capsule (a well-known Chinese herbal medicine) on high-fat diets combined with coronary artery ligation induced coronary heart disease (CHD) model rats. 1H NMR-based metabolomics approach combined with multivariate analysis was performed to explore potential biomarkers, a total of 20 metabolites were confirmed as contributors to the discrimination of model group and sham group. We investigated the dynamic metabolic characteristics of XFZY capsule on CHD rats, lactate, glutamine, pyruvate, citrate, choline and taurine were potential biomarkers of early effect. More potential biomarkers changed after 28 days of medication, XFZY capsules primarily influenced the taurine and hypotaurine metabolism, glycine, serine and threonine metabolism, glyoxylate and dicarboxylate metabolism, purine metabolism, glycolysis/gluconeogenesis, amino sugar and nucleotide sugar metabolism, primary bile acid biosynthesis.

Bioinformatic analysis of membrane and associated proteins in murine cardiomyocytes and human myocardium

In the current study we examined several proteomic- and RNA-Seq-based datasets of cardiac-enriched, cell-surface and membrane-associated proteins in human fetal and mouse neonatal ventricular cardiomyocytes. By integrating available microarray and tissue expression profiles with MGI phenotypic analysis, we identified 173 membrane-associated proteins that are cardiac-enriched, conserved amongst eukaryotic species, and have not yet been linked to a 'cardiac' Phenotype-Ontology. To highlight the utility of this dataset, we selected several proteins to investigate more carefully, including FAM162A, MCT1, and COX20, to show cardiac enrichment, subcellular distribution and expression patterns in disease. We performed three-dimensional confocal imaging analysis to validate subcellular localization and expression in adult mouse ventricular cardiomyocytes. FAM162A, MCT1, and COX20 were expressed differentially at the transcriptomic and proteomic levels in multiple models of mouse and human heart diseases and may represent potential diagnostic and therapeutic targets for human dilated and ischemic cardiomyopathies. Altogether, we believe this comprehensive cardiomyocyte membrane proteome dataset will prove instrumental to future investigations aimed at characterizing heart disease markers and/or therapeutic targets for heart failure.

PCSK9 in Myocardial Infarction and Cardioprotection: Importance of Lipid Metabolism and Inflammation

Extensive evidence from epidemiologic, genetic, and clinical intervention studies has indisputably shown that elevated low-density lipoprotein cholesterol (LDL-C) concentrations play a central role in the pathophysiology of atherosclerotic cardiovascular disease. Apart from LDL-C, also triglycerides independently modulate cardiovascular risk. Reduction of proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a therapeutic target for reducing plasma LDL-C, but it is also associated with a reduction in triglyceride levels potentially through modulation of the expression of free fatty acid transporters. Preclinical data indicate that PCSK9 is up-regulated in the ischaemic heart and decreasing PCSK9 expression impacts on infarct size, post infarct inflammation and remodeling as well as cardiac dysfunction following ischaemia/reperfusion. Clinical data support that notion in that PCSK9 inhibition is associated with reductions in the incidence of myocardial infarction, stroke, and coronary revascularization and an improvement of endothelial function in subjects with increased cardiovascular risk. The aim of the current review is to summarize the current knowledge on the importance of free fatty acid metabolism on myocardial ischaemia/reperfusion injury and to provide an update on recent evidence on the role of hyperlipidemia and PCSK9 in myocardial infarction and cardioprotection.

Forces, fluxes, and fuels: tracking mitochondrial metabolism by integrating measurements of membrane potential, respiration, and metabolites

Assessing mitochondrial function in cell-based systems is a central component of metabolism research. However, the selection of an initial measurement technique may be complicated given the range of parameters that can be studied and the need to define the mitochondrial (dys)function of interest. This methods-focused review compares and contrasts the use of mitochondrial membrane potential measurements, plate-based respirometry, and metabolomics and stable isotope tracing. We demonstrate how measurements of 1) cellular substrate preference, 2) respiratory chain activity, 3) cell activation, and 4) mitochondrial biogenesis are enriched by integrating information from multiple methods. This manuscript is meant to serve as a perspective to help choose which technique might be an appropriate initial method to answer a given question, as well as provide a broad "roadmap" for designing follow-up assays to enrich datasets or resolve ambiguous results.

Altered Acylcarnitine Metabolism Is Associated With an Increased Risk of Atrial Fibrillation

Background Atrial fibrillation (AF) is the most common cardiac arrhythmia, but the pathogenesis is not completely understood. The application of metabolomics could help in discovering new metabolic pathways involved in the development of the disease. Methods and Results We measured 112 baseline fasting metabolites of 3770 participants in the Malmö Diet and Cancer Study; these participants were free of prevalent AF. Incident cases of AF were ascertained through previously validated registers. The associations between baseline levels of metabolites and incident AF were investigated using Cox proportional hazard models. During 23.1 years of follow-up, 650 cases of AF were identified (incidence rate: 8.6 per 1000 person-years). In Cox regression models adjusted for AF risk factors, 7 medium- and long-chain acylcarnitines were associated with higher risk of incident AF (hazard ratio [HR] ranging from 1.09; 95% CI, 1.00-1.18 to 1.14, 95% CI, 1.05-1.24 per 1 SD increment of acylcarnitines). Furthermore, caffeine and acisoga were also associated with an increased risk (HR, 1.17; 95% CI, 1.06-1.28 and 1.08; 95% CI, 1.00-1.18, respectively), while beta carotene was associated with a lower risk (HR, 0.90; 95% CI, 0.82-0.99). Conclusions For the first time, we show associations between altered acylcarnitine metabolism and incident AF independent of traditional AF risk factors in a general population. These findings highlight metabolic alterations that precede AF diagnosis by many years and could provide insight into the pathogenesis of AF. Future studies are needed to replicate our finding in an external cohort as well as to test whether the relationship between acylcarnitines and AF is causal.

Cardioprotective GLP-1 metabolite prevents ischemic cardiac injury by inhibiting mitochondrial trifunctional protein-α

Mechanisms mediating the cardioprotective actions of glucagon-like peptide 1 (GLP-1) were unknown. Here, we show in both ex vivo and in vivo models of ischemic injury that treatment with GLP-1(28-36), a neutral endopeptidase-generated (NEP-generated) metabolite of GLP-1, was as cardioprotective as GLP-1 and was abolished by scrambling its amino acid sequence. GLP-1(28-36) enters human coronary artery endothelial cells (caECs) through macropinocytosis and acts directly on mouse and human coronary artery smooth muscle cells (caSMCs) and caECs, resulting in soluble adenylyl cyclase Adcy10-dependent (sAC-dependent) increases in cAMP, activation of protein kinase A, and cytoprotection from oxidative injury. GLP-1(28-36) modulates sAC by increasing intracellular ATP levels, with accompanying cAMP accumulation lost in sAC-/- cells. We identify mitochondrial trifunctional protein-α (MTPα) as a binding partner of GLP-1(28-36) and demonstrate that the ability of GLP-1(28-36) to shift substrate utilization from oxygen-consuming fatty acid metabolism toward oxygen-sparing glycolysis and glucose oxidation and to increase cAMP levels is dependent on MTPα. NEP inhibition with sacubitril blunted the ability of GLP-1 to increase cAMP levels in coronary vascular cells in vitro. GLP-1(28-36) is a small peptide that targets novel molecular (MTPα and sAC) and cellular (caSMC and caEC) mechanisms in myocardial ischemic injury.

Phosphatidylinositol 4-kinase IIIβ mediates contraction-induced GLUT4 translocation and shows its anti-diabetic action in cardiomyocytes

In the diabetic heart, long-chain fatty acid (LCFA) uptake is increased at the expense of glucose uptake. This metabolic shift ultimately leads to insulin resistance and a reduced cardiac function. Therefore, signaling kinases that mediate glucose uptake without simultaneously stimulating LCFA uptake could be considered attractive anti-diabetic targets. Phosphatidylinositol-4-kinase-IIIβ (PI4KIIIβ) is a lipid kinase downstream of protein kinase D1 (PKD1) that mediates Golgi-to-plasma membrane vesicular trafficking in HeLa-cells. In this study, we evaluated whether PI4KIIIβ is involved in myocellular GLUT4 translocation induced by contraction or oligomycin (an F₁F₀-ATP synthase inhibitor that activates contraction-like signaling). Pharmacological targeting, with compound MI14, or genetic silencing of PI4KIIIβ inhibited contraction/oligomycin-stimulated GLUT4 translocation and glucose uptake in cardiomyocytes but did not affect CD36 translocation nor LCFA uptake. Addition of the PI4KIIIβ enzymatic reaction product phosphatidylinositol-4-phosphate restored oligomycin-stimulated glucose uptake in the presence of MI14. PI4KIIIβ activation by PKD1 involves Ser294 phosphorylation and altered its localization with unchanged enzymatic activity. Adenoviral PI4KIIIβ overexpression stimulated glucose uptake, but did not activate hypertrophic signaling, indicating that unlike PKD1, PI4KIIIβ is selectively involved in GLUT4 translocation. Finally, PI4KIIIβ overexpression prevented insulin resistance and contractile dysfunction in lipid-overexposed cardiomyocytes. Together, our studies identify PI4KIIIβ as positive and selective regulator of GLUT4 translocation in response to contraction-like signaling, suggesting PI4KIIIβ as a promising target to rescue defective glucose uptake in diabetics.

Cardioprotective Natural Compound Pinocembrin Attenuates Acute Ischemic Myocardial Injury via Enhancing Glycolysis

Purpose

Emerging evidence has shown that pinocembrin protects the myocardium from ischemic injury in animals. However, it is unknown whether it has cardioprotection when given at the onset of reperfusion. Also, mechanisms mediating the cardioprotective actions of pinocembrin were largely unknown. Thus, this study is aimed at investigating the effects of pinocembrin postconditioning on ischemia-reperfusion (I/R) injury and the underlying mechanisms.

Methods

The in vivo mouse model of myocardial I/R injury, ex vivo isolated rat heart with global I/R, and in vitro hypoxia/reoxygenation (H/R) injury model for primary cardiomyocytes were used.

Results

We found that pinocembrin postconditioning significantly reduced the infarct size and improved cardiac contractile function after acute myocardial I/R. Mechanically, in primary cardiomyocytes, we found that pinocembrin may confer protection in part via direct stimulation of cardiac glycolysis via promoting the expression of the glycolytic enzyme, PFKFB3. Besides, PFKFB3 inhibition abolished pinocembrin-induced glycolysis and protection in cardiomyocytes. More importantly, PFKFB3 knockdown via cardiotropic adeno-associated virus (AAV) abrogated cardioprotective effects of pinocembrin. Moreover, we demonstrated that HIF1α is a key transcription factor driving pinocembrin-induced PFKFB3 expression in cardiomyocytes.

Conclusions

In conclusion, these results established that the acute cardioprotective benefits of pinocembrin are mediated in part via enhancing PFKFB3-mediated glycolysis via HIF1α, which may provide a new therapeutic target to impede the progression of myocardial I/R injury.

Oleic Acid Prevents Isoprenaline-Induced Cardiac Injury: Effects on Cellular Oxidative Stress, Inflammation and Histopathological Alterations

The present study was designed to assess the cardio-protective role of oleic acid in myocardial injury (MI) induced by intra-peritoneal injection of isoprenaline (ISO) in rats for 2 consecutive days. Oleic acid (OA) was administered orally (@ 5 mg/kg b.wt and 10 mg/kg b.wt) for 21 days before inducing MI. Pre-exposure to OA at higher dose significantly improved the HW/BW ratio, myocardial infarct size, lipid profiles (total cholesterol, HDL-C) and cardiac injury biomarkers (LDH, CK-MB, cardiac troponin-I, MMP-9), thus suggesting its cardio-protective role. The ameliorative potential of the higher dose of OA was further substantiated by its ability to reduce the cardiac oxidative stress as evidenced by significant decrease in lipid peroxidation coupled with increase in superoxide dismutase activity and reduced glutathione level. Significant decrease in heart rate as well as increase in RR and QT intervals in oleic acid pre-exposed rats were also observed. OA pre-treatment also reduced the histopathological alterations seen in myocardial injury group rats. The mRNA expression of cardiac UCP-2 gene, a regulator of reactive oxygen species (ROS) generation, was significantly increased in oleic acid pre-exposure group compared to the ISO-induced myocardial injury group. Thus increase in expression of UCP-2 gene in cardiac tissue seems to be one of the protective measures against myocardial injury. Based on the above findings, it may be inferred that oleic acid possesses promising cardio-protective potential against myocardial injury due to its anti-oxidative property and ability to modulate cardiac metabolic processes.

Myocardial Energy Metabolism in Non-ischemic Cardiomyopathy

As the most metabolically demanding organ in the body, the heart must generate massive amounts of energy adenosine triphosphate (ATP) from the oxidation of fatty acids, carbohydrates and other fuels (e.g., amino acids, ketone bodies), in order to sustain constant contractile function. While the healthy mature heart acts omnivorously and is highly flexible in its ability to utilize the numerous fuel sources delivered to it through its coronary circulation, the heart’s ability to produce ATP from these fuel sources becomes perturbed in numerous cardiovascular disorders. This includes ischemic heart disease and myocardial infarction, as well as in various cardiomyopathies that often precede the development of overt heart failure. We herein will provide an overview of myocardial energy metabolism in the healthy heart, while describing the numerous perturbations that take place in various non-ischemic cardiomyopathies such as hypertrophic cardiomyopathy, diabetic cardiomyopathy, arrhythmogenic cardiomyopathy, and the cardiomyopathy associated with the rare genetic disease, Barth Syndrome. Based on preclinical evidence where optimizing myocardial energy metabolism has been shown to attenuate cardiac dysfunction, we will discuss the feasibility of myocardial energetics optimization as an approach to treat the cardiac pathology associated with these various non-ischemic cardiomyopathies.

Ketone metabolism in the failing heart

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

Glucose transporters in cardiovascular system in health and disease

Glucose transporters are essential for the heart to sustain its function. Due to its nature as a high energy-consuming organ, the heart needs to catabolize a huge quantity of metabolic substrates. For optimized energy production, the healthy heart constantly switches between various metabolites in accordance with substrate availability and hormonal status. This metabolic flexibility is essential for the maintenance of cardiac function. Glucose is part of the main substrates catabolized by the heart and its use is fine-tuned via complex molecular mechanisms that include the regulation of the glucose transporters GLUTs, mainly GLUT4 and GLUT1. Besides GLUTs, glucose can also be transported by cotransporters of the sodium-glucose cotransporter (SGLT) (SLC5 gene) family, in which SGLT1 and SMIT1 were shown to be expressed in the heart. This SGLT-mediated uptake does not seem to be directly linked to energy production but is rather associated with intracellular signalling triggering important processes such as the production of reactive oxygen species. Glucose transport is markedly affected in cardiac diseases such as cardiac hypertrophy, diabetic cardiomyopathy and heart failure. These alterations are not only fingerprints of these diseases but are involved in their onset and progression. The present review will depict the importance of glucose transport in healthy and diseased heart, as well as proposed therapies targeting glucose transporters.

Diet-induced obese mouse hearts tolerate an acute high-fatty acid exposure that also increases ischemic tolerance

An ischemic insult is accompanied by an acute increase in circulating fatty acid (FA) levels, which can induce adverse changes related to cardiac metabolism/energetics. Although chronic hyperlipidemia contributes to the pathogenesis of obesity-/diabetes-related cardiomyopathy, it is unclear how these hearts are affected by an acute high FA-load. We hypothesize that adaptation to chronic FA exposure enhances the obese hearts' ability to handle an acute high FA-load. Diet-induced obese (DIO) and age-matched control (CON) mouse hearts were perfused in the presence of low- or high FA-load (0.4 and 1.8 mM, respectively). Left ventricular (LV) function, FA oxidation rate, myocardial oxygen consumption, and mechanical efficiency were assessed, followed by analysis of myocardial oxidative stress, mitochondrial respiration, protein acetylation, and gene expression. Finally, ischemic tolerance was determined by examining LV functional recovery and infarct size. Under low-FA conditions, DIO hearts showed mild LV dysfunction, oxygen wasting, mechanical inefficiency, and reduced mitochondrial OxPhos. High FA-load increased FA oxidation rates in both groups, but this did not alter any of the above parameters in DIO hearts. In contrast, CON hearts showed FA-induced mechanical inefficiency, oxidative stress, and reduced OxPhos, as well as enhanced acetylation and activation of PPARα-dependent gene expression. While high FA-load did not alter functional recovery and infarct size in CON hearts, it increased ischemic tolerance in DIO hearts. Thus, this study demonstrates that acute FA-load affects normal and obese hearts differently and that chronically elevated circulating FA levels render the DIO heart less vulnerable to the disadvantageous effects of an acute FA-load.NEW & NOTEWORTHY An acute myocardial fat-load leads to oxidative stress, oxygen wasting, mechanical inefficiency, hyperacetylation, and impaired mitochondrial function, which can contribute to reduced ischemic tolerance. Following obesity/insulin resistance, hearts were less affected by a high fat-load, which subsequently also improved ischemic tolerance. This study highlights that an acute fat-load affects normal and obese hearts differently and that obesity renders hearts less vulnerable to the disadvantageous effects of an acute fat-load.

α1-Adrenergic receptors increase glucose oxidation under normal and ischemic conditions in adult mouse cardiomyocytes

The role of catecholamine receptors in cardiac energy metabolism is unknown. α₁-adrenergic receptors (α₁-ARs) have been identified to play a role in whole body metabolism but its role in cardiac energy metabolism has not been explored. We used freshly prepared primary adult mouse cardiomyocytes and incubated with either ¹⁴C-palmitate or ¹⁴C-glucose tracers to measure oxidation rates in the presence or absence of phenylephrine, an α₁-AR agonist (with β and α₂-AR blockers) under normal cell culture conditions. ¹⁴CO₂ released was collected over a 10 min period in covered tissue culture plates using a 1 M hyamine hydroxide solution placed in well cups, counted by scintillation and converted into nmoles/hr. We found that phenylephrine stimulated glucose oxidation but not fatty acid oxidation in adult primary cardiomyocytes. α₁-AR stimulated glucose oxidation was blocked by the AMPK inhibitor, dorsomorphin dihydrochloride, and the PKC inhibitor, rottlerin. Ischemic conditions were induced by lowering the glucose concentration from 22.5 mM to 1.375 mM. Under ischemic conditions, we found that phenylephrine also increased glucose oxidation. We report a direct role of α₁-ARs in regulating glucose oxidation under normal and ischemic conditions that may lead to new therapeutic approaches in treating ischemia.

Extracellular vesicles derived from microRNA-150-5p-overexpressing mesenchymal stem cells protect rat hearts against ischemia/reperfusion

An intriguing area of research has demonstrated the ability of extracellular vesicles (EVs) as biological vehicles for microRNAs (miRNAs) transfer. Mesenchymal stem cells (MSCs) produce large amounts of EVs. Rat models of ischemia/reperfusion (I/R) were established to explore the expression profile of thioredoxin-interacting protein (TXNIP), which was then knocked-down to investigate its effects on myocardial remodeling, followed by detection on myocardial infarction size (MIS), myocardial collagen volume fraction (CVF) and cardiomyocyte apoptosis. MSCs-derived EVs carrying miR-150-5p were cultured with neonatal cardiomyocytes under hypoxia/hypoglycemia condition for in vitro exploration and intramyocardially injected into I/R rats for in vivo exploration. I/R-induced rats presented higher TXNIP levels and lower miR-150-5p levels, along with increased cardiomyocyte apoptosis. miR-150-5p in MSCs was transferred through EVs to cardiomyocytes, leading to suppressed myocardial remodeling, as reflected by smaller MIS and CVF and suppressed cardiomyocyte apoptosis. I/R-treated rats injected with MSCs-derived EVs containing miR-150-5p showed a reduction in myocardial remodeling associated with the downregulation of TXNIP, which may be clinically applicable for treatment of I/R.

Trimetazidine improves hepatic lipogenesis and steatosis in non‑alcoholic fatty liver disease via AMPK‑ChREBP pathway

Clinical studies have demonstrated that trimetazidine (TMZ) possesses a synergistic hypolipidemic effect together with statins, but the underlying mechanism remains to be elucidated. The present study aimed to investigate the role of TMZ in non-alcoholic fatty liver disease (NAFLD). By investigating the TMZ treatment of NAFLD, it was identified that high-fat diet (HFD) mice exhibit significant changes in several physiologic indices, including body weight, plasma lipids and glucose tolerance. Notably, hepatocyte bullous steatosis and fibrosis in HFD mice are greatly attenuated by 8 weeks of TMZ treatments. The results of the present study also indicated that the expression of carbohydrate-responsive element-binding protein (ChREBP), fatty acid synthase and acetyl-CoA carboxylase were all significantly reduced in the HFD + TMZ group compared with the HFD group. In order to confirm the hypothesis in vitro, the palmitate-treated liver cancer cell line (HepG2) was employed and similar results were obtained in TMZ-treated HepG2 cells. Furthermore, TMZ markedly upregulated the AMP-activated protein kinase (AMPK) signaling pathway and reduced the expression of forkhead box O1 (FOXO1) in the cells, while these effects controlled by TMZ were abolished by the AMPK inhibitor Compound C. The present study reported that knockdown of FOXO1 expression by FOXO1 small interfering RNA resulted in a reduction of ChREBP protein expression and post-transcriptional activity. In summary, for the first time, to the best of the authors' knowledge, the present study revealed a novel role of TMZ in hepatic steatosis; TMZ ameliorated ChREBP-induced de novo lipogenesis by activating the AMPK-FOXO1 pathway.

Changes in Myocardial Metabolism Preceding Sudden Cardiac Death

Heart disease is widely recognized as a major cause of death worldwide and is the leading cause of mortality in the United States. Centuries of research have focused on defining mechanistic alterations that drive cardiac pathogenesis, yet sudden cardiac death (SCD) remains a common unpredictable event that claims lives in every age group. The heart supplies blood to all tissues while maintaining a constant electrical and hormonal feedback communication with other parts of the body. As such, recent research has focused on understanding how myocardial electrical and structural properties are altered by cardiac metabolism and the various signaling pathways associated with it. The importance of cardiac metabolism in maintaining myocardial function, or lack thereof, is exemplified by shifts in cardiac substrate preference during normal development and various pathological conditions. For instance, a shift from fatty acid (FA) oxidation to oxygen-sparing glycolytic energy production has been reported in many types of cardiac pathologies. Compounded by an uncoupling of glycolysis and glucose oxidation this leads to accumulation of undesirable levels of intermediate metabolites. The resulting accumulation of intermediary metabolites impacts cardiac mitochondrial function and dysregulates metabolic pathways through several mechanisms, which will be reviewed here. Importantly, reversal of metabolic maladaptation has been shown to elicit positive therapeutic effects, limiting cardiac remodeling and at least partially restoring contractile efficiency. Therein, the underlying metabolic adaptations in an array of pathological conditions as well as recently discovered downstream effects of various substrate utilization provide guidance for future therapeutic targeting. Here, we will review recent data on alterations in substrate utilization in the healthy and diseased heart, metabolic pathways governing cardiac pathogenesis, mitochondrial function in the diseased myocardium, and potential metabolism-based therapeutic interventions in disease.

Cardiac metabolism as a driver and therapeutic target of myocardial infarction

Reducing infarct size during a cardiac ischaemic-reperfusion episode is still of paramount importance, because the extension of myocardial necrosis is an important risk factor for developing heart failure. Cardiac ischaemia-reperfusion injury (IRI) is in principle a metabolic pathology as it is caused by abruptly halted metabolism during the ischaemic episode and exacerbated by sudden restart of specific metabolic pathways at reperfusion. It should therefore not come as a surprise that therapy directed at metabolic pathways can modulate IRI. Here, we summarize the current knowledge of important metabolic pathways as therapeutic targets to combat cardiac IRI. Activating metabolic pathways such as glycolysis (eg AMPK activators), glucose oxidation (activating pyruvate dehydrogenase complex), ketone oxidation (increasing ketone plasma levels), hexosamine biosynthesis pathway (O-GlcNAcylation; administration of glucosamine/glutamine) and deacetylation (activating sirtuins 1 or 3; administration of NAD+ -boosting compounds) all seem to hold promise to reduce acute IRI. In contrast, some metabolic pathways may offer protection through diminished activity. These pathways comprise the malate-aspartate shuttle (in need of novel specific reversible inhibitors), mitochondrial oxygen consumption, fatty acid oxidation (CD36 inhibitors, malonyl-CoA decarboxylase inhibitors) and mitochondrial succinate metabolism (malonate). Additionally, protecting the cristae structure of the mitochondria during IR, by maintaining the association of hexokinase II or creatine kinase with mitochondria, or inhibiting destabilization of FO F1 -ATPase dimers, prevents mitochondrial damage and thereby reduces cardiac IRI. Currently, the most promising and druggable metabolic therapy against cardiac IRI seems to be the singular or combined targeting of glycolysis, O-GlcNAcylation and metabolism of ketones, fatty acids and succinate.

Pathogenesis and pathophysiology of heart failure with reduced ejection fraction: translation to human studies

Heart failure represents the end result of different pathophysiologic processes, which culminate in functional impairment. Regardless of its aetiology, the presentation of heart failure usually involves symptoms of pump failure and congestion, which forms the basis for clinical diagnosis. Pathophysiologic descriptions of heart failure with reduced ejection fraction (HFrEF) are being established. Most commonly, HFrEF is centred on a reactive model where a significant initial insult leads to reduced cardiac output, further triggering a cascade of maladaptive processes. Predisposing factors include myocardial injury of any cause, chronically abnormal loading due to hypertension, valvular disease, or tachyarrhythmias. The pathophysiologic processes behind remodelling in heart failure are complex and reflect systemic neurohormonal activation, peripheral vascular effects and localised changes affecting the cardiac substrate. These abnormalities have been the subject of intense research. Much of the translational successes in HFrEF have come from targeting neurohormonal responses to reduced cardiac output, with blockade of the renin-angiotensin-aldosterone system (RAAS) and beta-adrenergic blockade being particularly fruitful. However, mortality and morbidity associated with heart failure remains high. Although systemic neurohormonal blockade slows disease progression, localised ventricular remodelling still adversely affects contractile function. Novel therapy targeted at improving cardiac contractile mechanics in HFrEF hold the promise of alleviating heart failure at its source, yet so far none has found success. Nevertheless, there are increasing calls for a proximal, 'cardiocentric' approach to therapy. In this review, we examine HFrEF therapy aimed at improving cardiac function with a focus on recent trials and emerging targets.

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.

Human-induced pluripotent stem cells for modelling metabolic perturbations and impaired bioenergetics underlying cardiomyopathies

Normal cardiac contractile and relaxation functions are critically dependent on a continuous energy supply. Accordingly, metabolic perturbations and impaired mitochondrial bioenergetics with subsequent disruption of ATP production underpin a wide variety of cardiac diseases, including diabetic cardiomyopathy, dilated cardiomyopathy, hypertrophic cardiomyopathy, anthracycline cardiomyopathy, peripartum cardiomyopathy, and mitochondrial cardiomyopathies. Crucially, there are no specific treatments for preventing the onset or progression of these cardiomyopathies to heart failure, one of the leading causes of death and disability worldwide. Therefore, new treatments are needed to target the metabolic disturbances and impaired mitochondrial bioenergetics underlying these cardiomyopathies in order to improve health outcomes in these patients. However, investigation of the underlying mechanisms and the identification of novel therapeutic targets have been hampered by the lack of appropriate animal disease models. Furthermore, interspecies variation precludes the use of animal models for studying certain disorders, whereas patient-derived primary cell lines have limited lifespan and availability. Fortunately, the discovery of human-induced pluripotent stem cells has provided a promising tool for modelling cardiomyopathies via human heart tissue in a dish. In this review article, we highlight the use of patient-derived iPSCs for studying the pathogenesis underlying cardiomyopathies associated with metabolic perturbations and impaired mitochondrial bioenergetics, as the ability of iPSCs for self-renewal and differentiation makes them an ideal platform for investigating disease pathogenesis in a controlled in vitro environment. Continuing progress will help elucidate novel mechanistic pathways, and discover novel therapies for preventing the onset and progression of heart failure, thereby advancing a new era of personalized therapeutics for improving health outcomes in patients with cardiomyopathy.

The Role of Nonglycolytic Glucose Metabolism in Myocardial Recovery Upon Mechanical Unloading and Circulatory Support in Chronic Heart Failure

BACKGROUND

Significant improvements in myocardial structure and function have been reported in some patients with advanced heart failure (termed responders [R]) following left ventricular assist device (LVAD)-induced mechanical unloading. This therapeutic strategy may alter myocardial energy metabolism in a manner that reverses the deleterious metabolic adaptations of the failing heart. Specifically, our previous work demonstrated a post-LVAD dissociation of glycolysis and oxidative-phosphorylation characterized by induction of glycolysis without subsequent increase in pyruvate oxidation through the tricarboxylic acid cycle. The underlying mechanisms responsible for this dissociation are not well understood. We hypothesized that the accumulated glycolytic intermediates are channeled into cardioprotective and repair pathways, such as the pentose-phosphate pathway and 1-carbon metabolism, which may mediate myocardial recovery in R.

METHODS

We prospectively obtained paired left ventricular apical myocardial tissue from nonfailing donor hearts as well as R and nonresponders at LVAD implantation (pre-LVAD) and transplantation (post-LVAD). We conducted protein expression and metabolite profiling and evaluated mitochondrial structure using electron microscopy.

RESULTS

Western blot analysis shows significant increase in rate-limiting enzymes of pentose-phosphate pathway and 1-carbon metabolism in post-LVAD R (post-R) as compared with post-LVAD nonresponders (post-NR). The metabolite levels of these enzyme substrates, such as sedoheptulose-6-phosphate (pentose phosphate pathway) and serine and glycine (1-carbon metabolism) were also decreased in Post-R. Furthermore, post-R had significantly higher reduced nicotinamide adenine dinucleotide phosphate levels, reduced reactive oxygen species levels, improved mitochondrial density, and enhanced glycosylation of the extracellular matrix protein, α-dystroglycan, all consistent with enhanced pentose-phosphate pathway and 1-carbon metabolism that correlated with the observed myocardial recovery.

CONCLUSIONS

The recovering heart appears to direct glycolytic metabolites into pentose-phosphate pathway and 1-carbon metabolism, which could contribute to cardioprotection by generating reduced nicotinamide adenine dinucleotide phosphate to enhance biosynthesis and by reducing oxidative stress. These findings provide further insights into mechanisms responsible for the beneficial effect of glycolysis induction during the recovery of failing human hearts after mechanical unloading.

Intralipid Increases Nitric Oxide Release from Human Endothelial Cells During Oxidative Stress

BACKGROUND

Intralipid (ILP), a lipid emulsion, protects organs against ischemia/reperfusion (IR) injury. We hypothesized that ILP activates endothelial nitric oxide synthase (eNOS) and increases NO release from endothelial cells (ECs) through a fatty-acid translocase cluster of differentiation (CD36) mediated endocytotic mechanism, acting as a potentially protective paracrine signal during oxidative stress.

METHODS

Human umbilical-vein ECs were exposed to 1% ILP for 2 hours followed by oxidative stress with 0.2-mM hydrogen peroxide for 2 hours. Western blots were conducted with anti-CD36, dynamin-2, src-kinase-1, eNOS, and phospho-eNOS; equal protein loading was confirmed with β-actin. CD36 immunoprecipitation was probed for caveolin-1 to determine if CD36 and caveolin-1 were complexed on the cell membrane. NO was measured by fluorescence of ECs.

RESULTS

ILP caused a 227% increase in CD36 expression vs controls. Immunoprecipitation indicated a CD36/caveolin-1 complex on ECs' membrane with exposure to ILP. Dynamin-2 increased 52% and src-kinase-1 340% after ILP treatment vs control cells. eNOS phosphorylation was confirmed by a 63% increase in the phospho-eNOS/eNOS ratio in ILP-treated cells, and NO fluorescence increased 102%.

CONCLUSION

ILP enters ECs via endocytosis by a CD36/caveolin-1 cell membrane receptor complex, which in turn is pulled into the cell by dynamin-2 activity. Upregulation of src-kinase-1 and eNOS phosphorylation suggest downstream mediators. Subsequent NO release from ECs serve as a paracrine signal to neighboring cells for protection against IR injury. Student t-test was utilized for single comparisons and analysis of variance with Bonferroni-Dunn post hoc modification for multiple comparisons; P < .05 was considered statistically significant.

Exogenous Oleic Acid and Palmitic Acid Improve Boar Sperm Motility via Enhancing Mitochondrial Β-Oxidation for ATP Generation

Simple Summary

Sperm requires ATP production for maintaining motility. In boar sperm, it is not clear whether the mitochondrial β-oxidation pathway for ATP generation is active or not. We found that boar sperm could utilize oleic acid and palmitic acid during the liquid storage. Addition of oleic acid and palmitic acid to extender improved the sperm quality. Using the incubation model, we found that boar sperm utilized oleic acid and palmitic acid as the energy substrates for ATP generation via mitochondrial β-oxidation pathway. We suggest that addition of fatty acids to the extender would be beneficial to improve boar sperm quality.

Abstract

It takes several hours for mammalian sperm to migrate from the ejaculation or insemination site to the fertilization site in the female reproductive tract in which glucose, amino acids, and fatty acids are regarded as the primary substrates for ATP generation. The present study was designed to investigate whether oleic acid and palmitic acid were beneficial to boar sperm in vitro; and if yes, to elucidate the mechanism that regulates sperm motility. Therefore, the levels of oleic acid and palmitic acid, motility, membrane integrity, acrosome integrity, and apoptosis of sperm were evaluated. Moreover, the enzymes involved in mitochondrial β-oxidation (CPT1: carnitine palmitoyltransferase 1; ACADVL: long-chain acyl-coenzyme A dehydrogenase) were detected with immunofluorescence and Western blotting. Consequently, the ATP content and the activities of CPT1, ACADVL, malate dehydrogenase (MDH), and succinate dehydrogenase (SDH) were also measured. We observed that CPT1 and ACADVL were expressed in boar sperm and localized in the midpiece. The levels of oleic acid and palmitic acid were decreased during storage at 17 °C. The addition of oleic acid and palmitic acid significantly increased sperm motility, progressive motility, straight-line velocity (VSL), membrane integrity, and acrosome integrity with a simultaneous decrease in sperm apoptosis after seven days during storage. When sperm were incubated with oleic acid and palmitic acid at 37 °C for 3 h, the activities of CPT1 and ACADVL, the ATP level, the mitochondrial membrane potential, the activities of MDH and SDH, as well as sperm motility patterns were significantly increased compared to the control (p < 0.05). Moreover, the addition of etomoxir to the diluted medium in the presence of either oleic acid or palmitic acid and the positive effects of oleic acid and palmitic acid were counteracted. Together, these data suggest that boar sperm might utilize oleic acid and palmitic acid as energy substrates for ATP production via β-oxidation. The addition of these acids could improve sperm quality.

Mechanisms of Anthracycline-Induced Cardiotoxicity: Is Mitochondrial Dysfunction the Answer?

Cardiac side effects are a major drawback of anticancer therapies, often requiring the use of low and less effective doses or even discontinuation of the drug. Among all the drugs known to cause severe cardiotoxicity are anthracyclines that, though being the oldest chemotherapeutic drugs, are still a mainstay in the treatment of solid and hematological tumors. The recent expansion of the field of Cardio-Oncology, a branch of cardiology dealing with prevention or treatment of heart complications due to cancer treatment, has greatly improved our knowledge of the molecular mechanisms behind anthracycline-induced cardiotoxicity (AIC). Despite excessive generation of reactive oxygen species was originally believed to be the main cause of AIC, recent evidence points to the involvement of a plethora of different mechanisms that, interestingly, mainly converge on deregulation of mitochondrial function. In this review, we will describe how anthracyclines affect cardiac mitochondria and how these organelles contribute to AIC. Furthermore, we will discuss how drugs specifically targeting mitochondrial dysfunction and/or mitochondria-targeted drugs could be therapeutically exploited to treat AIC.

Human pluripotent stem cell-derived cardiomyocytes for studying energy metabolism

Cardiomyocyte energy metabolism is altered in heart failure, and primary defects of metabolic pathways can cause heart failure. Studying cardiac energetics in rodent models has principal shortcomings, raising the question to which extent human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) can provide an alternative. As metabolic maturation of CM occurs mostly after birth during developmental hypertrophy, the immaturity of hiPSC-CM is an important limitation. Here we shortly review the physiological drivers of metabolic maturation and concentrate on methods to mature hiPSC-CM with the goal to benchmark the metabolic state of hiPSC-CM against in vivo data and to see how far known abnormalities in inherited metabolic disorders can be modeled in hiPSC-CM. The current data indicate that hiPSC-CM, despite their immature, approximately mid-fetal state of energy metabolism, faithfully recapitulate some basic metabolic disease mechanisms. Efforts to improve their metabolic maturity are underway and shall improve the validity of this model.

Circadian-Hypoxia Link and its Potential for Treatment of Cardiovascular Disease

Throughout the evolutionary time, all organisms and species on Earth evolved with an adaptation to consistent oscillations of sunlight and darkness, now recognized as 'circadian rhythm.' Single-cellular to multisystem organisms use circadian biology to synchronize to the external environment and provide predictive adaptation to changes in cellular homeostasis. Dysregulation of circadian biology has been implicated in numerous prevalent human diseases, and subsequently targeting the circadian machinery may provide innovative preventative or treatment strategies. Discovery of 'peripheral circadian clocks' unleashed widespread investigations into the potential roles of clock biology in cellular, tissue, and organ function in healthy and diseased states. Particularly, oxygen-sensing pathways (e.g. hypoxia inducible factor, HIF1), are critical for adaptation to changes in oxygen availability in diseases such as myocardial ischemia. Recent investigations have identified a connection between the circadian rhythm protein Period 2 (PER2) and HIF1A that may elucidate an evolutionarily conserved cellular network that can be targeted to manipulate metabolic function in stressed conditions like hypoxia or ischemia. Understanding the link between circadian and hypoxia pathways may provide insights and subsequent innovative therapeutic strategies for patients with myocardial ischemia. This review addresses our current understanding of the connection between light-sensing pathways (PER2), and oxygen-sensing pathways (HIF1A), in the context of myocardial ischemia and lays the groundwork for future studies to take advantage of these two evolutionarily conserved pathways in the treatment of myocardial ischemia.

CaMKII and GLUT1 in heart failure and the role of gliflozins

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

Serum metabolite profiling of ST-segment elevation myocardial infarction using liquid chromatography quadrupole time-of-flight mass spectrometry

ST segment elevation myocardial infarction (STEMI) is one of the most common global causes of cardiovascular disease-related death. Several metabolites may change during STEMI. Hence, analysis of metabolites in body fluid may be considered as a rapid and accurate test for initial diagnosis. This study has therefore attempted to determine the variation in metabolites identified in the serum of STEMI patients (n = 20) and 15 controls. Samples collected from the Cardiology Department, Medical Faculty, Ataturk University, were extracted by liquid-liquid extraction and analysed using liquid chromatography quadrupole time-of-flight mass spectrometry. The METLIN database was used for the identification and characterization of metabolites. According to Q-TOF/MS measurements, 231 m/z values, which were significantly different between groups (P < 0.01 and fold analysis >1.5) were detected. Metabolite identification was achieved via the Human Metabolome database. According to the multivariate data analysis, leucine, isoleucine, l-proline, l-alanine, glycine, fumaric acid, citrate, succinate and carnitine levels were decreased, whereas levels of propionic acid, maleic acid, butyric acid, urea, oleic acid, palmitic acid, lysoPC [18:2(9Z)], glycerol, phoshpatidylethanolamine, caffeine and l-lactic acid were increased in STEMI patients compared with controls. In conclusion, malonic acid, maleic acid, fumaric acid and palmitic acid can be used as biomarkers for early risk stratification of patients with STEMI.

Myocardial Adaptation in Pseudohypoxia: Signaling and Regulation of mPTP via Mitochondrial Connexin 43 and Cardiolipin

Therapies intended to mitigate cardiovascular complications cannot be applied in practice without detailed knowledge of molecular mechanisms. Mitochondria, as the end-effector of cardioprotection, represent one of the possible therapeutic approaches. The present review provides an overview of factors affecting the regulation processes of mitochondria at the level of mitochondrial permeability transition pores (mPTP) resulting in comprehensive myocardial protection. The regulation of mPTP seems to be an important part of the mechanisms for maintaining the energy equilibrium of the heart under pathological conditions. Mitochondrial connexin 43 is involved in the regulation process by inhibition of mPTP opening. These individual cardioprotective mechanisms can be interconnected in the process of mitochondrial oxidative phosphorylation resulting in the maintenance of adenosine triphosphate (ATP) production. In this context, the degree of mitochondrial membrane fluidity appears to be a key factor in the preservation of ATP synthase rotation required for ATP formation. Moreover, changes in the composition of the cardiolipin’s structure in the mitochondrial membrane can significantly affect the energy system under unfavorable conditions. This review aims to elucidate functional and structural changes of cardiac mitochondria subjected to preconditioning, with an emphasis on signaling pathways leading to mitochondrial energy maintenance during partial oxygen deprivation.

[Dysfunctions of mitochondrial fatty acid β-oxidation in rare and common diseases]

Dysfunctions of mitochondrial fatty acid ß-oxidation (ß-FAO) in various tissues represent a hallmark of many common disorders, and are acknowledged to play an essential role in the pathogenesis of diabetes, obesity, and cardiac diseases. Moreover, inborn defects in ß-FAO form a large family of rare diseases with variable phenotypes, ranging from fatal multi-organ failure in the newborn to isolated adult onset myopathy. These pathologies highlight the critical role of ß-FAO in many tissues with high-energy demand (heart, muscle, liver, kidney). Furthermore, and unexpectedly, very recent data unveiled the possible involvement of ß-FAO in instructing complex non energy-related functions, such as chromatin modification, control of neural stem cell activity, or survival and fate of cancer cells. Pharmacological targeting of ß-FAO by small molecules might therefore open new avenues for the treatment of various rare or common diseases.

Insights from Exercise-induced Cardioprotection-from Clinical Application to Basic Research

Exercise has long been recognized as a beneficial living style for cardiovascular health. It has been applied to be a central component of cardiac rehabilitation for patients with chronic heart failure (CHF), coronary heart disease (CHD), post-acute coronary syndrome (ACS) or primary percutaneous coronary intervention (PCI), post cardiac surgery or transplantation. Although the effect of exercise is multifactorial, in this review, we focus on the specific contribution of regular exercise on the heart and vascular system. We will summarize the known result of clinical findings and possible mechanisms of chronic exercise on the cardiovascular system.