Functional Role of Mitochondria in Arrhythmogenesis

Calcium signaling from sarcoplasmic reticulum and mitochondria contact sites in acute myocardial infarction

Acute myocardial infarction (AMI) is a serious condition that occurs when part of the heart is subjected to ischemia episodes, following partial or complete occlusion of the epicardial coronary arteries. The resulting damage to heart muscle cells have a significant impact on patient's health and quality of life. About that, recent research focused on the role of the sarcoplasmic reticulum (SR) and mitochondria in the physiopathology of AMI. Moreover, SR and mitochondria get in touch each other through multiple membrane contact sites giving rise to the subcellular region called mitochondria-associated membranes (MAMs). MAMs are essential for, but not limited to, bioenergetics and cell fate. Disruption of the architecture of these regions occurs during AMI although it is still unclear the cause-consequence connection and a complete overview of the pathological changes; for sure this concurs to further damage to heart muscle. The calcium ion (Ca2+) plays a pivotal role in the pathophysiology of AMI and its dynamic signaling between the SR and mitochondria holds significant importance. In this review, we tried to summarize and update the knowledge about the roles of these organelles in AMI from a Ca2+ signaling point of view. Accordingly, we also reported some possible cardioprotective targets which are directly or indirectly related at limiting the dysfunctions caused by the deregulation of the Ca2+ signaling.

Traditional Chinese medicine and mitophagy: A novel approach for cardiovascular disease management

BACKGROUND

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality worldwide, imposing an enormous economic burden on individuals and human society. Laboratory studies have identified several drugs that target mitophagy for the prevention and treatment of CVD. Only a few of these drugs have been successful in clinical trials, and most studies have been limited to animal and cellular models. Furthermore, conventional drugs used to treat CVD, such as antiplatelet agents, statins, and diuretics, often result in adverse effects on patients' cardiovascular, metabolic, and respiratory systems. In contrast, traditional Chinese medicine (TCM) has gained significant attention for its unique theoretical basis and clinical efficacy in treating CVD.

PURPOSE

This paper systematically summarizes all the herbal compounds, extracts, and active monomers used to target mitophagy for the treatment of CVD in the last five years. It provides valuable information for researchers in the field of basic cardiovascular research, pharmacologists, and clinicians developing herbal medicines with fewer side effects, as well as a useful reference for future mitophagy research.

METHODS

The search terms "cardiovascular disease," "mitophagy," "herbal preparations," "active monomers," and "cardiac disease pathogenesis" in combination with "natural products" and "diseases" were used to search for studies published in the past five years until January 2024.

RESULTS

Studies have shown that mitophagy plays a significant role in the progression and development of CVD, such as atherosclerosis (AS), heart failure (HF), myocardial infarction (MI), myocardial ischemia/reperfusion injury (MI/RI), cardiac hypertrophy, cardiomyopathy, and arrhythmia. Herbal compound preparations, crude extracts, and active monomers have shown potential as effective treatments for these conditions. These substances protect cardiomyocytes by inducing mitophagy, scavenging damaged mitochondria, and maintaining mitochondrial homeostasis. They display notable efficacy in combating CVD.

CONCLUSION

TCM (including herbal compound preparations, extracts, and active monomers) can treat CVD through various pharmacological mechanisms and signaling pathways by inducing mitophagy. They represent a hotspot for future cardiovascular basic research and a promising candidate for the development of future cardiovascular drugs with fewer side effects and better therapeutic efficacy.

Transient receptor potential vanilloid type 1: cardioprotective effects in diabetic models

Cardiovascular disease, especially heart failure (HF) is the leading cause of death in patients with diabetes. Individuals with diabetes are prone to a special type of cardiomyopathy called diabetic cardiomyopathy (DCM), which cannot be explained by heart diseases such as hypertension or coronary artery disease, and can contribute to HF. Unfortunately, the current treatment strategy for diabetes-related cardiovascular complications is mainly to control blood glucose levels; nonetheless, the improvement of cardiac structure and function is not ideal. The transient receptor potential cation channel subfamily V member 1 (TRPV1), a nonselective cation channel, has been shown to be universally expressed in the cardiovascular system. Increasing evidence has shown that the activation of TRPV1 channel has a potential protective influence on the cardiovascular system. Numerous studies show that activating TRPV1 channels can improve the occurrence and progression of diabetes-related complications, including cardiomyopathy; however, the specific mechanisms and effects are unclear. In this review, we summarize that TRPV1 channel activation plays a protective role in the heart of diabetic models from oxidation/nitrification stress, mitochondrial function, endothelial function, inflammation, and cardiac energy metabolism to inhibit the occurrence and progression of DCM. Therefore, TRPV1 may become a latent target for the prevention and treatment of diabetes-induced cardiovascular complications.

NADPH Oxidases and Oxidative Stress in the Pathogenesis of Atrial Fibrillation

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and its prevalence increases with age. The irregular and rapid contraction of the atria can lead to ineffective blood pumping, local blood stasis, blood clots, ischemic stroke, and heart failure. NADPH oxidases (NOX) and mitochondria are the main sources of reactive oxygen species in the heart, and dysregulated activation of NOX and mitochondrial dysfunction are associated with AF pathogenesis. NOX- and mitochondria-derived oxidative stress contribute to the onset of paroxysmal AF by inducing electrophysiological changes in atrial myocytes and structural remodeling in the atria. Because high atrial activity causes cardiac myocytes to expend extremely high energy to maintain excitation-contraction coupling during persistent AF, mitochondria, the primary energy source, undergo metabolic stress, affecting their morphology, Ca2+ handling, and ATP generation. In this review, we discuss the role of oxidative stress in activating AF-triggered activities, regulating intracellular Ca2+ handling, and functional and anatomical reentry mechanisms, all of which are associated with AF initiation, perpetuation, and progression. Changes in the extracellular matrix, inflammation, ion channel expression and function, myofibril structure, and mitochondrial function occur during the early transitional stages of AF, opening a window of opportunity to target NOX and mitochondria-derived oxidative stress using isoform-specific NOX inhibitors and mitochondrial ROS scavengers, as well as drugs that improve mitochondrial dynamics and metabolism to treat persistent AF and its transition to permanent AF.

Mitochondrial Calcium Overload Plays a Causal Role in Oxidative Stress in the Failing Heart

Heart failure is a serious global health challenge, affecting more than 6.2 million people in the United States and is projected to reach over 8 million by 2030. Independent of etiology, failing hearts share common features, including defective calcium (Ca2+) handling, mitochondrial Ca2+ overload, and oxidative stress. In cardiomyocytes, Ca2+ not only regulates excitation-contraction coupling, but also mitochondrial metabolism and oxidative stress signaling, thereby controlling the function and actual destiny of the cell. Understanding the mechanisms of mitochondrial Ca2+ uptake and the molecular pathways involved in the regulation of increased mitochondrial Ca2+ influx is an ongoing challenge in order to identify novel therapeutic targets to alleviate the burden of heart failure. In this review, we discuss the mechanisms underlying altered mitochondrial Ca2+ handling in heart failure and the potential therapeutic strategies.

Myocardial RNA Sequencing Reveals New Potential Therapeutic Targets in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) represents a global health challenge, with limited therapies proven to enhance patient outcomes. This makes the elucidation of disease mechanisms and the identification of novel potential therapeutic targets a priority. Here, we performed RNA sequencing on ventricular myocardial biopsies from patients with HFpEF, prospecting to discover distinctive transcriptomic signatures. A total of 306 differentially expressed mRNAs (DEG) and 152 differentially expressed microRNAs (DEM) were identified and enriched in several biological processes involved in HF. Moreover, by integrating mRNA and microRNA expression data, we identified five potentially novel miRNA-mRNA relationships in HFpEF: the upregulated hsa-miR-25-3p, hsa-miR-26a-5p, and has-miR4429, targeting HAPLN1; and NPPB mRNA, targeted by hsa-miR-26a-5p and miR-140-3p. Exploring the predicted miRNA-mRNA interactions experimentally, we demonstrated that overexpression of the distinct miRNAs leads to the downregulation of their target genes. Interestingly, we also observed that microRNA signatures display a higher discriminative power to distinguish HFpEF sub-groups over mRNA signatures. Our results offer new mechanistic clues, which can potentially translate into new HFpEF therapies.

Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?

INTRODUCTION

Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. Currently, many therapeutic strategies have been implemented to improve mitochondrial function, but their effectiveness varies widely.

AREAS COVERED

This review focuses on new models of therapeutic strategies targeting mitochondrial function in the treatment of heart failure.

EXPERT OPINION

Therapeutic strategies targeting mitochondria appear to be a valuable option for treating heart failure. Currently, the greatest challenge is to develop new research models that could restore the disrupted metabolic processes in mitochondria as comprehensively as possible. Only the development of therapies that focus on improving as many dysregulated mitochondrial processes as possible in patients with heart failure will be able to bring the expected clinical improvement, along with inhibition of disease progression. Combined strategies involving the reduction of the effects of oxidative stress and mitochondrial dysfunction, appear to be a promising possibility for developing new therapies for a complex and multifactorial disease such as heart failure.

Small-conductance calcium-activated potassium channels in the heart: expression, regulation and pathological implications

Ca2+-activated K+ channels are critical to cellular Ca2+ homeostasis and excitability; they couple intracellular Ca2+ and membrane voltage change. Of these, the small, 4-14 pS, conductance SK channels include three, KCNN1-3 encoded, SK1/KCa2.1, SK2/KCa2.2 and SK3/KCa2.3, channel subtypes with characteristic, EC50 ∼ 10 nM, 40 pM, 1 nM, apamin sensitivities. All SK channels, particularly SK2 channels, are expressed in atrial, ventricular and conducting system cardiomyocytes. Pharmacological and genetic modification results have suggested that SK channel block or knockout prolonged action potential durations (APDs) and effective refractory periods (ERPs) particularly in atrial, but also in ventricular, and sinoatrial, atrioventricular node and Purkinje myocytes, correspondingly affect arrhythmic tendency. Additionally, mitochondrial SK channels may decrease mitochondrial Ca2+ overload and reactive oxygen species generation. SK channels show low voltage but marked Ca2+ dependences (EC50 ∼ 300-500 nM) reflecting their α-subunit calmodulin (CaM) binding domains, through which they may be activated by voltage-gated or ryanodine-receptor Ca2+ channel activity. SK function also depends upon complex trafficking and expression processes and associations with other ion channels or subunits from different SK subtypes. Atrial and ventricular clinical arrhythmogenesis may follow both increased or decreased SK expression through decreased or increased APD correspondingly accelerating and stabilizing re-entrant rotors or increasing incidences of triggered activity. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

From Obesity-Induced Low-Grade Inflammation to Lipotoxicity and Mitochondrial Dysfunction: Altered Multi-Crosstalk between Adipose Tissue and Metabolically Active Organs

Obesity is a major risk factor for several metabolic diseases, including type 2 diabetes, hyperlipidemia, cardiovascular diseases, and brain disorders. Growing evidence suggests the importance of inter-organ metabolic communication for the progression of obesity and the subsequent onset of related disorders. This review provides a broad overview of the pathophysiological processes that from adipose tissue dysfunction leading to altered multi-tissue crosstalk relevant to regulating energy homeostasis and the etiology of obesity. First, a comprehensive description of the role of adipose tissue was reported. Then, attention was turned toward the unhealthy expansion of adipose tissue, low-grade inflammatory state, metabolic inflexibility, and mitochondrial dysfunction as root causes of systemic metabolic alterations. In addition, a short spot was devoted to iron deficiency in obese conditions and the role of the hepcidin-ferroportin relationship in the management of this issue. Finally, different classes of bioactive food components were described with a perspective to enhance their potential preventive and therapeutic use against obesity-related diseases.

Modeling Duchenne Muscular Dystrophy Cardiomyopathy with Patients' Induced Pluripotent Stem-Cell-Derived Cardiomyocytes

Duchenne muscular dystrophy (DMD) is an X-linked progressive muscle degenerative disease caused by mutations in the dystrophin gene, resulting in death by the end of the third decade of life at the latest. A key aspect of the DMD clinical phenotype is dilated cardiomyopathy, affecting virtually all patients by the end of the second decade of life. Furthermore, despite respiratory complications still being the leading cause of death, with advancements in medical care in recent years, cardiac involvement has become an increasing cause of mortality. Over the years, extensive research has been conducted using different DMD animal models, including the mdx mouse. While these models present certain important similarities to human DMD patients, they also have some differences which pose a challenge to researchers. The development of somatic cell reprograming technology has enabled generation of human induced pluripotent stem cells (hiPSCs) which can be differentiated into different cell types. This technology provides a potentially endless pool of human cells for research. Furthermore, hiPSCs can be generated from patients, thus providing patient-specific cells and enabling research tailored to different mutations. DMD cardiac involvement has been shown in animal models to include changes in gene expression of different proteins, abnormal cellular Ca²⁺ handling, and other aberrations. To gain a better understanding of the disease mechanisms, it is imperative to validate these findings in human cells. Furthermore, with the recent advancements in gene-editing technology, hiPSCs provide a valuable platform for research and development of new therapies including the possibility of regenerative medicine. In this article, we review the DMD cardiac-related research performed so far using human hiPSCs-derived cardiomyocytes (hiPSC-CMs) carrying DMD mutations.

Mitochondrial Dysfunction in Cardiac Arrhythmias

Electrophysiological and structural disruptions in cardiac arrhythmias are closely related to mitochondrial dysfunction. Mitochondria are an organelle generating ATP, thereby satisfying the energy demand of the incessant electrical activity in the heart. In arrhythmias, the homeostatic supply-demand relationship is impaired, which is often accompanied by progressive mitochondrial dysfunction leading to reduced ATP production and elevated reactive oxidative species generation. Furthermore, ion homeostasis, membrane excitability, and cardiac structure can be disrupted through pathological changes in gap junctions and inflammatory signaling, which results in impaired cardiac electrical homeostasis. Herein, we review the electrical and molecular mechanisms of cardiac arrhythmias, with a particular focus on mitochondrial dysfunction in ionic regulation and gap junction action. We provide an update on inherited and acquired mitochondrial dysfunction to explore the pathophysiology of different types of arrhythmias. In addition, we highlight the role of mitochondria in bradyarrhythmia, including sinus node dysfunction and atrioventricular node dysfunction. Finally, we discuss how confounding factors, such as aging, gut microbiome, cardiac reperfusion injury, and electrical stimulation, modulate mitochondrial function and cause tachyarrhythmia.

Comprehensive Analysis of Mitochondrial Dynamics Alterations in Heart Diseases

The most common alterations affecting mitochondria, and associated with cardiac pathological conditions, implicate a long list of defects. They include impairments of the mitochondrial electron transport chain activity, which is a crucial element for energy formation, and that determines the depletion of ATP generation and supply to metabolic switches, enhanced ROS generation, inflammation, as well as the dysregulation of the intracellular calcium homeostasis. All these signatures significantly concur in the impairment of cardiac electrical characteristics, loss of myocyte contractility and cardiomyocyte damage found in cardiac diseases. Mitochondrial dynamics, one of the quality control mechanisms at the basis of mitochondrial fitness, also result in being dysregulated, but the use of this knowledge for translational and therapeutic purposes is still in its infancy. In this review we tried to understand why this is, by summarizing methods, current opinions and molecular details underlying mitochondrial dynamics in cardiac diseases.

Role of non-cardiomyocytes in anticancer drug-induced cardiotoxicity: A systematic review

Cardiotoxicity induced by anticancer drugs interferes with the continuation of optimal treatment, inducing life-threatening risks or leading to long-term morbidity. The heart is a complex pluricellular organ comprised of cardiomyocytes and non-cardiomyocytes. Although the study of these cell populations has been often focusing on cardiomyocytes, the contributions of non-cardiomyocytes to development and disease are increasingly being appreciated as both dynamic and essential. This review summarized the role of non-cardiomyocytes in anticancer drug-induced cardiotoxicity, including the mechanism of direct damage to resident non-cardiomyocytes, cardiomyocytes injury caused by paracrine modality, myocardial inflammation induced by transient cell populations and the protective agents that focused on non-cardiomyocytes.

Silica nanoparticles induce cardiac injury and dysfunction via ROS/Ca2+/CaMKII signaling

Interest is growing to better comprehend the interaction of silica nanoparticles (SiNPs) with the cardiovascular system. In particular, the extremely small size, relatively large surface area and associated unique properties may greatly enhance its toxic potentials compared to larger-sized counterparts. Nevertheless, the underlying mechanisms still need to be evaluated. In this context, the cardiotoxicity of nano-scale (Si-60; particle diameter about 60 nm) and submicro-scale silica particles (Si-300; 300 nm) were examined in ApoE^-/- mice via intratracheal instillation, 6.0 mg/kg·bw, once per week for 12 times. The echocardiography showed that the sub-chronic exposure of Si-60 declined cardiac output (CO) and stroke volume (SV), shorten LVIDd and LVIDs, and thickened LVAWs of ApoE^-/- mice in compared to the control and Si-300 groups. Histological investigations manifested Si-60 enhanced inflammatory infiltration, myocardial fiber arrangement disorder, hypertrophy and fibrosis in the cardiac tissue, as well as mitochondrial ultrastructural injury. Accordingly, the serum cTnT, cTnI and ANP were significantly elevated by Si-60, as well as cardiac ANP content. In particular, Si-60 greatly increased cardiac ROS, Ca²⁺ levels and CaMKII activation in comparison with Si-300. Further, in vitro investigations revealed silica particles induced a dose- and size-dependent activation of oxidative stress, mitochondrial membrane permeabilization, intracellular Ca²⁺ overload, CaMKII signaling activation and ensuing myocardial apoptosis in human cardiomyocytes (AC16). Mechanistic analyses revealed SiNPs induced myocardial apoptosis via ROS/Ca²⁺/CaMKII signaling, which may contribute to the abnormalities in cardiac structure and function in vivo. In summary, our research revealed SiNPs caused myocardial impairments, dysfunction and even structural remodeling via ROS/Ca²⁺/CaMKII signaling. Of note, a size-dependent myocardial toxicity was noticed, that is, Si-60 greater than Si-300.

Bioenergetic and Metabolic Impairments in Induced Pluripotent Stem Cell-Derived Cardiomyocytes Generated from Duchenne Muscular Dystrophy Patients

Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene and dilated cardiomyopathy (DCM) is a major cause of morbidity and mortality in DMD patients. We tested the hypothesis that DCM is caused by metabolic impairments by employing induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) generated from four DMD patients; an adult male, an adult female, a 7-year-old (7y) male and a 13-year-old (13y) male, all compared to two healthy volunteers. To test the hypothesis, we measured the bioenergetics, metabolomics, electrophysiology, mitochondrial morphology and mitochondrial activity of CMs, using respirometry, LC–MS, patch clamp, electron microscopy (EM) and confocal microscopy methods. We found that: (1) adult DMD CMs exhibited impaired energy metabolism and abnormal mitochondrial structure and function. (2) The 7y CMs demonstrated arrhythmia-free spontaneous firing along with “healthy-like” metabolic status, normal mitochondrial morphology and activity. In contrast, the 13y CMs were mildly arrhythmogenic and showed adult DMD-like bioenergetics deficiencies. (3) In DMD adult CMs, mitochondrial activities were attenuated by 45–48%, whereas the 7y CM activity was similar to that of healthy CMs. (4) In DMD CMs, but not in 7y CMs, there was a 75% decrease in the mitochondrial ATP production rate compared to healthy iPSC-CMs. In summary, DMD iPSC-CMs exhibit bioenergetic and metabolic impairments that are associated with rhythm disturbances corresponding to the patient’s phenotype, thereby constituting novel targets for alleviating cardiomyopathy in DMD patients.

Mitochondrial Dysfunction and Cardiovascular Disease: Pathophysiology and Emerging Therapies

Mitochondria ensure the supply of cellular energy through the production of ATP via oxidative phosphorylation. The alteration of this process, called mitochondrial dysfunction, leads to a reduction in ATP and an increase in the production of reactive oxygen species (ROS). Mitochondrial dysfunction can be caused by mitochondrial/nuclear DNA mutations, or it can be secondary to pathological conditions such as cardiovascular disease, aging, and environmental stress. The use of therapies aimed at the prevention/correction of mitochondrial dysfunction, in the context of the specific treatment of cardiovascular diseases, is a topic of growing interest. In this context, the data are conflicting since preclinical studies are numerous, but there are no large randomized studies.

Anti-Arrhythmic Effects of Sodium-Glucose Co-Transporter 2 Inhibitors

Arrhythmias are clinically prevalent with a high mortality rate. They impose a huge economic burden, thereby substantially affecting the quality of life. Sodium-glucose co-transporter 2 inhibitor (SGLT2i) is a new type of hypoglycemic drug, which can regulate blood glucose level safely and effectively. Additionally, it reduces the occurrence and progression of heart failure and cardiovascular events significantly. Recently, studies have found that SGLT2i can alleviate the occurrence and progression of cardiac arrhythmias; however, the exact mechanism remains unclear. In this review, we aimed to discuss and summarize new literature on different modes in which SGLT2i ameliorates the occurrence and development of cardiac arrhythmias.

Impaired Myocardial Mitochondrial Function in an Experimental Model of Anaphylactic Shock

Anaphylactic shock (AS) is associated with a profound vasodilation and cardiac dysfunction. The cellular mechanisms underlying AS-related cardiac dysfunction are unknown. We hypothesized that myocardial mitochondrial dysfunction may be associated with AS cardiac dysfunction. In controls and sensitized Brown Norway rats, shock was induced by ovalbumin i.v bolus, and abdominal aortic blood flow (ABF), systemic mean arterial pressure (MAP), and lactatemia were measured for 15 min. Myocardial mitochondrial function was assessed with the evaluation of mitochondrial respiration, oxidative stress production by reactive oxygen species (ROS), reactive nitrogen species (RNS), and the measurement of superoxide dismutases (SODs) activity. Oxidative damage was assessed by lipid peroxidation. The mitochondrial ultrastructure was assessed using transmission electronic microscopy. AS was associated with a dramatic drop in ABF and MAP combined with a severe hyperlactatemia 15 min after shock induction. CI-linked substrate state (197 ± 21 vs. 144 ± 21 pmol/s/mg, p < 0.05), OXPHOS activity by complexes I and II (411 ± 47 vs. 246 ± 33 pmol/s/mg, p < 0.05), and OXPHOS activity through complex II (316 ± 40 vs. 203 ± 28 pmol/s/mg, p < 0.05) were significantly impaired. ROS and RNS production was not significantly increased, but SODs activity was significantly higher in the AS group (11.15 ± 1.02 vs. 15.50 ± 1.40 U/mL/mg protein, p = 0.02). Finally, cardiac lipid peroxidation was significantly increased in the AS group (8.50 ± 0.67 vs. 12.17 ± 1.44 µM/mg protein, p < 0.05). No obvious changes were observed in the mitochondrial ultrastructure between CON and AS groups. Our experimental model of AS results in rapid and deleterious hemodynamic effects and was associated with a myocardial mitochondrial dysfunction with oxidative damage and without mitochondrial ultrastructural injury.

Diminazene Aceturate, an angiotensin converting enzyme 2 (ACE2) activator, promotes cardioprotection in ischemia/reperfusion-induced cardiac injury

This study aimed to investigate whether the Diminazene Aceturate (DIZE), an angiotensin-converting enzyme 2 (ACE2) activator, can revert cardiac dysfunction in ischemia reperfusion-induced (I/R) injury in animals and examine the mechanism underlying this effect. Wistar rats systemically received DIZE (1 mg/kg) for thirty days. Cardiac function in isolated rat hearts was evaluated using the Langendorff technique. After I/R, ventricular non-I/R and I/R samples were used to evaluate ATP levels. Mitochondrial function was assessed using cardiac permeabilized fibers and isolated cardiac mitochondria. Cardiac cellular electrophysiology was evaluated using the patch clamp technique. DIZE protected the heart after I/R from arrhythmia and cardiac dysfunction by preserving ATP levels, independently of any change in coronary flow and heart rate. DIZE improved mitochondrial function, increasing the capacity for generating ATP and reducing proton leak without changing the specific citrate synthase activity. The activation of the ACE2 remodeled cardiac electrical profiles, shortening the cardiac action potential duration at 90 % repolarization. Additionally, cardiomyocytes from DIZE-treated animals exhibited reduced sensibility to diazoxide (K_ATP agonist) and a higher K_ATP current compared to the controls. DIZE was able to improve mitochondrial function and modulate cardiac electrical variables with a cardio-protective profile, resulting in direct myocardial cell protection from I/R injury.

Empagliflozin Ameliorates Diabetic Cardiomyopathy via Attenuating Oxidative Stress and Improving Mitochondrial Function

Diabetic cardiomyopathy (DCM) is considered to be a critical contributor to the development of heart failure. Empagliflozin (EMPA), a sodium-glucose cotransporter 2 inhibitor, has been shown to prevent cardiovascular events and reduce the incidence of heart failure in randomized clinical trials. However, the mechanism of how EMPA prevents DCM is poorly understood. To study the potential mechanisms involved in the therapeutic effects of EMPA, we assessed the protective effects of EMPA on myocardial injury in type 2 diabetic db/db mice and H9C2 cardiomyocytes. 9-10-week-old male db/db mice were treated with EMPA (10 mg/kg) via oral gavage daily for 20 weeks. Afterward, cardiac function of treated mice was evaluated by echocardiography, and pathological changes in heart tissues were determined by histopathological examination and western blot assay. EMPA markedly reduced blood glucose levels, improved insulin tolerance, and enhanced insulin sensitivity of db/db mice. In addition, EMPA significantly prevented cardiac dysfunction, inhibited cardiac hypertrophy and fibrosis, and reduced glycogen deposition in heart tissues. Furthermore, EMPA improved diabetes-induced oxidative stress and mitochondrial dysfunction in both heart tissues of db/db mice and palmitate exposed H9C2 cells. EMPA significantly increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream genetic targets in cardiac tissue of type 2 diabetic db/db mice and H9C2 cells. EMPA also downregulated the expression of mitochondrial fission-related proteins and upregulated the expression of mitochondrial fusion-related proteins. Collectively, these findings indicate that EMPA may prevent DCM via attenuating oxidative stress and improving mitochondrial function in heart tissue.

Heart Mitochondrial Metabolic Flexibility and Redox Status Are Improved by Donkey and Human Milk Intake

The biological mechanisms linking nutrition and antioxidants content of the diet with cardiovascular protection are subject of intense investigation. It has been demonstrated that dietary supplementation with cow, donkey or human milk, characterized by distinct nutritional properties, triggers significant differences in the metabolic and inflammatory status through the modulation of hepatic and skeletal muscle mitochondrial functions. Cardiac mitochondria play a key role for energy-demanding heart functions, and their disfunctions is leading to pathologies. Indeed, an altered heart mitochondrial function and the consequent increased reactive oxygen species (ROS) production and inflammatory state, is linked to several cardiac diseases such as hypertension and heart failure. In this work it was investigated the impact of the milk consumption on heart mitochondrial functions, inflammation and oxidative stress. In addition, it was underlined the crosstalk between mitochondrial metabolic flexibility, lipid storage and redox status as control mechanisms for the maintenance of cardiovascular health.

Human myocardial mitochondrial oxidative capacity is impaired in mild acute heart transplant rejection

Aims

Acute cellular rejection (ACR) following heart transplantation (HTX) is associated with long‐term graft loss and increased mortality. Disturbed mitochondrial bioenergetics have been identified as pathophysiological drivers in heart failure, but their role in ACR remains unclear. We aimed to prove functional disturbances of myocardial bioenergetics in human heart transplant recipients with mild ACR by assessing myocardial mitochondrial respiration using high‐resolution respirometry, digital image analysis of myocardial inflammatory cell infiltration, and clinical assessment of HTX patients. We hypothesized that (i) mild ACR is associated with impaired myocardial mitochondrial respiration and (ii) myocardial inflammation, systemic oxidative stress, and myocardial oedema relate to impaired mitochondrial respiration and myocardial dysfunction.

Methods and results

We classified 35 HTX recipients undergoing endomyocardial biopsy according International Society for Heart and Lung Transplantation criteria to have no (0R) or mild (1R) ACR. Additionally, we quantified immune cell infiltration by immunohistochemistry and digital image analysis. We analysed mitochondrial substrate utilization in myocardial fibres by high‐resolution respirometry and performed cardiovascular magnetic resonance (CMR). ACR (1R) was diagnosed in 12 patients (34%), while the remaining 23 patients revealed no signs of ACR (0R). Underlying cardiomyopathies (dilated cardiomyopathy 50% vs. 65%; P = 0.77), comorbidities (type 2 diabetes mellitus: 50% vs. 35%, P = 0.57; chronic kidney disease stage 5: 8% vs. 9%, P > 0.99; arterial hypertension: 59% vs. 30%, P = 0.35), medications (tacrolimus: 100% vs. 91%, P = 0.54; mycophenolate mofetil: 92% vs. 91%, P > 0.99; prednisolone: 92% vs. 96%, P > 0.99) and time post‐transplantation (21.5 ± 26.0 months vs. 29.4 ± 26.4 months, P = 0.40) were similar between groups. Mitochondrial respiration was reduced by 40% in ACR (1R) compared with ACR (0R) (77.8 ± 23.0 vs. 128.0 ± 33.0; P < 0.0001). Quantitative assessment of myocardial CD3⁺‐lymphocyte infiltration identified ACR (1R) with a cut‐off of >14 CD3⁺‐lymphocytes/mm² (100% sensitivity, 82% specificity; P < 0.0001). Myocardial CD3⁺ infiltration (r = −0.41, P < 0.05), systemic oxidative stress (thiobarbituric acid reactive substances; r = −0.42, P < 0.01) and myocardial oedema depicted by global CMR derived T2 time (r = −0.62, P < 0.01) correlated with lower oxidative capacity and overt cardiac dysfunction (global longitudinal strain; r = −0.63, P < 0.01).

Conclusions

Mild ACR with inflammatory cell infiltration associates with impaired mitochondrial bioenergetics in cardiomyocytes. Our findings may help to identify novel checkpoints in cardiac immune metabolism as potential therapeutic targets in post‐transplant care.

The Role of Mitochondrial Dysfunction in Atrial Fibrillation: Translation to Druggable Target and Biomarker Discovery

Atrial fibrillation (AF) is the most prevalent and progressive cardiac arrhythmia worldwide and is associated with serious complications such as heart failure and ischemic stroke. Current treatment modalities attenuate AF symptoms and are only moderately effective in halting the arrhythmia. Therefore, there is an urgent need to dissect molecular mechanisms that drive AF. As AF is characterized by a rapid atrial activation rate, which requires a high energy metabolism, a role of mitochondrial dysfunction in AF pathophysiology is plausible. It is well known that mitochondria play a central role in cardiomyocyte function, as they produce energy to support the mechanical and electrical function of the heart. Details on the molecular mechanisms underlying mitochondrial dysfunction are increasingly being uncovered as a contributing factor in the loss of cardiomyocyte function and AF. Considering the high prevalence of AF, investigating the role of mitochondrial impairment in AF may guide the path towards new therapeutic and diagnostic targets. In this review, the latest evidence on the role of mitochondria dysfunction in AF is presented. We highlight the key modulators of mitochondrial dysfunction that drive AF and discuss whether they represent potential targets for therapeutic interventions and diagnostics in clinical AF.

Mitochondrial and Sarcoplasmic Reticulum Interconnection in Cardiac Arrhythmia

Ca²⁺ plays a pivotal role in mitochondrial energy production, contraction, and apoptosis. Mitochondrial Ca²⁺-targeted fluorescent probes have demonstrated that mitochondria Ca²⁺ transients are synchronized with Ca²⁺ fluxes occurring in the sarcoplasmic reticulum (SR). The presence of specialized proteins tethering SR to mitochondria ensures the local Ca²⁺ flux between these organelles. Furthermore, communication between SR and mitochondria impacts their functionality in a bidirectional manner. Mitochondrial Ca²⁺ uptake through the mitochondrial Ca²⁺ uniplex is essential for ATP production and controlled reactive oxygen species levels for proper cellular signaling. Conversely, mitochondrial ATP ensures the proper functioning of SR Ca²⁺-handling proteins, which ensures that mitochondria receive an adequate supply of Ca²⁺. Recent evidence suggests that altered SR Ca²⁺ proteins, such as ryanodine receptors and the sarco/endoplasmic reticulum Ca²⁺ ATPase pump, play an important role in maintaining proper cardiac membrane excitability, which may be initiated and potentiated when mitochondria are dysfunctional. This recognized mitochondrial role offers the opportunity to develop new therapeutic approaches aimed at preventing cardiac arrhythmias in cardiac disease.

Mitochondrial Dysfunction and Heart Disease: Critical Appraisal of an Overlooked Association

The myocardium is among the most energy-consuming tissues in the body, burning from 6 to 30 kg of ATP per day within the mitochondria, the so-called powerhouse of the cardiomyocyte. Although mitochondrial genetic disorders account for a small portion of cardiomyopathies, mitochondrial dysfunction is commonly involved in a broad spectrum of heart diseases, and it has been implicated in the development of heart failure via maladaptive circuits producing and perpetuating mitochondrial stress and energy starvation. In this bench-to-bedside review, we aimed to (i) describe the key functions of the mitochondria within the myocardium, including their role in ischemia/reperfusion injury and intracellular calcium homeostasis; (ii) examine the contribution of mitochondrial dysfunction to multiple cardiac disease phenotypes and their transition to heart failure; and (iii) discuss the rationale and current evidence for targeting mitochondrial function for the treatment of heart failure, including via sodium-glucose cotransporter 2 inhibitors.

Melatonin as a therapy in cardiac ischemia-reperfusion injury: Potential mechanisms by which MT2 activation mediates cardioprotection

Introduction

Previous studies reported the beneficial effects of pretreatment with melatonin on the heart during cardiac ischemia/reperfusion (I/R) injury. However, the effects of melatonin given after cardiac ischemia, as well as its comparative temporal effects are unknown. These include pretreatment, during ischemia, and at the onset of reperfusion. Also, the association between melatonin receptors and cardiac arrhythmias, mitochondrial function and dynamics, autophagy, and mitophagy during cardiac I/R have not been investigated.

Objectives

We tested two major hypotheses in this study. Firstly, the temporal effect of melatonin administration exerts different cardioprotective efficacy during cardiac I/R. Secondly, melatonin provides cardioprotective effects via MT2 activation, leading to improvement in cardiac mitochondrial function and dynamics, reduced excessive mitophagy and autophagy, and decreased cardiac arrhythmias, resulting in improved LV function.

Methods

Male rats were subjected to cardiac I/R, and divided into 4 intervention groups: vehicle, pretreatment with melatonin, melatonin given during ischemia, and melatonin given at the onset of reperfusion. In addition, either a non-specific melatonin receptor (MT) blocker or specific MT2 blocker was given to rats.

Results

Treatment with melatonin at all time points alleviated cardiac I/R injury to a similar extent, quantified by reduction in infarct size, arrhythmia score, LV dysfunction, cardiac mitochondrial dysfunction, imbalance of mitochondrial dynamics, excessive mitophagy, and a decreased Bax/Bcl2 ratio. In H9C2 cells, melatonin increased %cell viability by reducing mitochondrial dynamic imbalance and a decrease in Bax protein expression. The cardioprotective effects of melatonin were dependent on MT2 activation.

Conclusion

Melatonin given before or after ischemia exerted equal levels of cardioprotection on the heart with I/R injury, and its beneficial effects on cardiac arrhythmias, cardiac mitochondrial function and dynamics were dependent upon the activation of MT2.

Mitochondrial dysfunction in cardiovascular disease: Current status of translational research/clinical and therapeutic implications

Mitochondria provide energy to the cell during aerobic respiration by supplying ~95% of the adenosine triphosphate (ATP) molecules via oxidative phosphorylation. These organelles have various other functions, all carried out by numerous proteins, with the majority of them being encoded by nuclear DNA (nDNA). Mitochondria occupy ~1/3 of the volume of myocardial cells in adults, and function at levels of high-efficiency to promptly meet the energy requirements of the myocardial contractile units. Mitochondria have their own DNA (mtDNA), which contains 37 genes and is maternally inherited. Over the last several years, a variety of functions of these organelles have been discovered and this has led to a growing interest in their involvement in various diseases, including cardiovascular (CV) diseases. Mitochondrial dysfunction relates to the status where mitochondria cannot meet the demands of a cell for ATP and there is an enhanced formation of reactive-oxygen species. This dysfunction may occur as a result of mtDNA and/or nDNA mutations, but also as a response to aging and various disease and environmental stresses, leading to the development of cardiomyopathies and other CV diseases. Designing mitochondria-targeted therapeutic strategies aiming to maintain or restore mitochondrial function has been a great challenge as a result of variable responses according to the etiology of the disorder. There have been several preclinical data on such therapies, but clinical studies are scarce. A major challenge relates to the techniques needed to eclectically deliver the therapeutic agents to cardiac tissues and to damaged mitochondria for successful clinical outcomes. All these issues and progress made over the last several years are herein reviewed.

Pathological Responses of Cardiac Mitochondria to Burn Trauma

Despite advances in treatment and care, burn trauma remains the fourth most common type of traumatic injury. Burn-induced cardiac failure is a key factor for patient mortality, especially during the initial post-burn period (the first 24 to 48 h). Mitochondria, among the most important subcellular organelles in cardiomyocytes, are a central player in determining the severity of myocardial damage. Defects in mitochondrial function and structure are involved in pathogenesis of numerous myocardial injuries and cardiovascular diseases. In this article, we comprehensively review the current findings on cardiac mitochondrial pathological changes and summarize burn-impaired mitochondrial respiration capacity and energy supply, induced mitochondrial oxidative stress, and increased cell death. The molecular mechanisms underlying these alterations are discussed, along with the possible influence of other biological variables. We hope this review will provide useful information to explore potential therapeutic approaches that target mitochondria for cardiac protection following burn injury.

The Mitochondria: A Target of Polyphenols in the Treatment of Diabetic Cardiomyopathy

Diabetic cardiomyopathy (DCM) is a constellation of symptoms consisting of ventricular dysfunction and cardiomyocyte disarray in the presence of diabetes. The exact cause of this type of cardiomyopathy is still unknown; however, several processes involving the mitochondria, such as lipid and glucose metabolism, reactive oxygen species (ROS) production, apoptosis, autophagy and mitochondrial biogenesis have been implicated. In addition, polyphenols have been shown to improve the progression of diabetes. In this review, we discuss some of the mechanisms by which polyphenols, particularly resveratrol, play a role in slowing the progression of DCM. The most important intermediates by which polyphenols exert their protective effect include Bcl-2, UCP2, SIRT-1, AMPK and JNK1. Bcl-2 acts to attenuate apoptosis, UCP2 decreases oxidative stress, SIRT-1 increases mitochondrial biogenesis and decreases oxidative stress, AMPK increases autophagy, and JNK1 decreases apoptosis and increases autophagy. Our dissection of these molecular players aims to provide potential therapeutic targets for the treatment of DCM.

Role of Mitophagy in Cardiovascular Disease

Cardiovascular disease is the leading cause of mortality worldwide, and mitochondrial dysfunction is the primary contributor to these disorders. Recent studies have elaborated on selective autophagy-mitophagy, which eliminates damaged and dysfunctional mitochondria, stabilizes mitochondrial structure and function, and maintains cell survival and growth. Numerous recent studies have reported that mitophagy plays an important role in the pathogenesis of various cardiovascular diseases. This review summarizes the mechanisms underlying mitophagy and advancements in studies on the role of mitophagy in cardiovascular disease.

Modulation of SERCA in Patients with Persistent Atrial Fibrillation Treated by Epicardial Thoracoscopic Ablation: The CAMAF Study

OBJECTIVES

To evaluate atrial fibrillation (AF) recurrence and Sarcoplasmic Endoplasmic Reticulum Calcium ATPase (SERCA) levels in patients treated by epicardial thoracoscopic ablation for persistent AF.

BACKGROUND

Reduced levels of SERCA have been reported in the peripheral blood cells of patients with AF. We hypothesize that SERCA levels can predict the response to epicardial ablation.

METHODS

We designed a prospective, multicenter, observational study to recruit, from October 2014 to June 2016, patients with persistent AF receiving an epicardial thoracoscopic pulmonary vein isolation.

RESULTS

We enrolled 27 patients. Responders (n = 15) did not present AF recurrence after epicardial ablation at one-year follow-up; these patients displayed a marked remodeling of the left atrium, with a significant reduction of inflammatory cytokines, B type natriuretic peptide (BNP), and increased levels of SERCA compared to baseline and to nonresponders (p < 0.05). Furthermore, mean AF duration (Heart rate (HR) 1.235 (1.037-1.471), p < 0.05), Left atrium volume (LAV) (HR 1.755 (1.126-2.738), p < 0.05), BNP (HR 1.945 (1.895-1.999), p < 0.05), and SERCA (HR 1.763 (1.167-2.663), p < 0.05) were predictive of AF recurrence.

CONCLUSIONS

Our data indicate for the first time that baseline values of SERCA in patients with persistent AF might be predictive of failure to epicardial ablative approach. Intriguingly, epicardial ablation was associated with increased levels of SERCA in responders. Therefore, SERCA might be an innovative therapeutic target to improve the response to epicardial ablative treatments.

Mitochondrial Dysfunction as Substrate for Arrhythmogenic Cardiomyopathy: A Search for New Disease Mechanisms

Arrhythmogenic cardiomyopathy (ACM) is a familial heart disease, associated with ventricular arrhythmias, fibrofatty replacement of the myocardial mass and an increased risk of sudden cardiac death (SCD). Malignant ventricular arrhythmias and SCD largely occur in the pre-clinical phase of the disease, before overt structural changes occur. To prevent or interfere with ACM disease progression, more insight in mechanisms related to electrical instability are needed. Currently, numerous studies are focused on the link between cardiac arrhythmias and metabolic disease. In line with that, a potential role of mitochondrial dysfunction in ACM pathology is unclear and mitochondrial biology in the ACM heart remains understudied. In this review, we explore mitochondrial dysfunction in relation to arrhythmogenesis, and postulate a link to typical hallmarks of ACM. Mitochondrial dysfunction depletes adenosine triphosphate (ATP) production and increases levels of reactive oxygen species in the heart. Both metabolic changes affect cardiac ion channel gating, electrical conduction, intracellular calcium handling, and fibrosis formation; all well-known aspects of ACM pathophysiology. ATP-mediated structural remodeling, apoptosis, and mitochondria-related alterations have already been shown in models of PKP2 dysfunction. Yet, the limited amount of experimental evidence in ACM models makes it difficult to determine whether mitochondrial dysfunction indeed precedes and/or accompanies ACM pathogenesis. Nevertheless, current experimental ACM models can be very useful in unraveling ACM-related mitochondrial biology and in testing potential therapeutic interventions.

Pathophysiology of Calcium Mediated Ventricular Arrhythmias and Novel Therapeutic Options with Focus on Gene Therapy

Cardiac arrhythmias constitute a major health problem with a huge impact on mortality rates and health care costs. Despite ongoing research efforts, the understanding of the molecular mechanisms and processes responsible for arrhythmogenesis remains incomplete. Given the crucial role of Ca²⁺-handling in action potential generation and cardiac contraction, Ca²⁺ channels and Ca²⁺ handling proteins represent promising targets for suppression of ventricular arrhythmias. Accordingly, we report the different roles of Ca²⁺-handling in the development of congenital as well as acquired ventricular arrhythmia syndromes. We highlight the therapeutic potential of gene therapy as a novel and innovative approach for future arrhythmia therapy. Furthermore, we discuss various promising cellular and mitochondrial targets for therapeutic gene transfer currently under investigation.

Mitochondrial Dysfunction Underlies Cardiomyocyte Remodeling in Experimental and Clinical Atrial Fibrillation

Atrial fibrillation (AF), the most common progressive tachyarrhythmia, results in structural remodeling which impairs electrical activation of the atria, rendering them increasingly permissive to the arrhythmia. Previously, we reported on endoplasmic reticulum stress and NAD⁺ depletion in AF, suggesting a role for mitochondrial dysfunction in AF progression. Here, we examined mitochondrial function in experimental model systems for AF (tachypaced HL-1 atrial cardiomyocytes and Drosophila melanogaster) and validated findings in clinical AF. Tachypacing of HL-1 cardiomyocytes progressively induces mitochondrial dysfunction, evidenced by impairment of mitochondrial Ca²⁺-handling, upregulation of mitochondrial stress chaperones and a decrease in the mitochondrial membrane potential, respiration and ATP production. Atrial biopsies from AF patients display mitochondrial dysfunction, evidenced by aberrant ATP levels, upregulation of a mitochondrial stress chaperone and fragmentation of the mitochondrial network. The pathophysiological role of mitochondrial dysfunction is substantiated by the attenuation of AF remodeling by preventing an increased mitochondrial Ca²⁺-influx through partial blocking or downregulation of the mitochondrial calcium uniporter, and by SS31, a compound that improves bioenergetics in mitochondria. Together, these results show that conservation of the mitochondrial function protects against tachypacing-induced cardiomyocyte remodeling and identify this organelle as a potential novel therapeutic target.

Transcriptomics of cardiac biopsies reveals differences in patients with or without diagnostic parameters for heart failure with preserved ejection fraction

Heart failure affects 2–3% of adult Western population. Prevalence of heart failure with preserved left ventricular (LV) ejection fraction (HFpEF) increases. Studies suggest HFpEF patients to have altered myocardial structure and functional changes such as incomplete relaxation and increased cardiac stiffness. We hypothesised that patients undergoing elective coronary bypass surgery (CABG) with HFpEF characteristics would show distinctive gene expression compared to patients with normal LV physiology. Myocardial biopsies for mRNA expression analysis were obtained from sixteen patients with LV ejection fraction ≥45%. Five out of 16 patients (31%) had echocardiographic characteristics and increased NTproBNP levels indicative of HFpEF and this group was used as HFpEF proxy, while 11 patients had Normal LV physiology. Utilising principal component analysis, the gene expression data clustered into two groups, corresponding to HFpEF proxy and Normal physiology, and 743 differentially expressed genes were identified. The associated top biological functions were cardiac muscle contraction, oxidative phosphorylation, cellular remodelling and matrix organisation. Our results also indicate that upstream regulatory events, including inhibition of transcription factors STAT4, SRF and TP53, and activation of transcription repressors HEY2 and KDM5A, could provide explanatory mechanisms to observed gene expression differences and ultimately cardiac dysfunction in the HFpEF proxy group.

The machineries, regulation and cellular functions of mitochondrial calcium

Calcium ions (Ca²⁺) are some of the most versatile signalling molecules, and they have many physiological functions, prominently including muscle contraction, neuronal excitability, cell migration and cell growth. By sequestering and releasing Ca²⁺, mitochondria serve as important regulators of cellular Ca²⁺. Mitochondrial Ca²⁺ also has other important functions, such as regulation of mitochondrial metabolism, ATP production and cell death. In recent years, identification of the molecular machinery regulating mitochondrial Ca²⁺ accumulation and efflux has expanded the number of (patho)physiological conditions that rely on mitochondrial Ca²⁺ homeostasis. Thus, expanding the understanding of the mechanisms of mitochondrial Ca²⁺ regulation and function in different cell types is an important task in biomedical research, which offers the possibility of targeting mitochondrial Ca²⁺ machinery for the treatment of several disorders.

L-Carnitine: An Antioxidant Remedy for the Survival of Cardiomyocytes under Hyperglycemic Condition

BACKGROUND

Metabolic alterations as hyperglycemia and inflammation induce myocardial molecular events enhancing oxidative stress and mitochondrial dysfunction. Those alterations are responsible for a progressive loss of cardiomyocytes, cardiac stem cells, and consequent cardiovascular complications. Currently, there are no effective pharmacological measures to protect the heart from these metabolic modifications, and the development of new therapeutic approaches, focused on improvement of the oxidative stress condition, is pivotal. The protective effects of levocarnitine (LC) in patients with ischemic heart disease are related to the attenuation of oxidative stress, but LC mechanisms have yet to be fully understood.

OBJECTIVE

The aim of this work was to investigate LC's role in oxidative stress condition, on ROS production and mitochondrial detoxifying function in H9c2 rat cardiomyocytes during hyperglycemia.

METHODS

H9c2 cells in the hyperglycemic state (25 mmol/L glucose) were exposed to 0.5 or 5 mM LC for 48 and 72 h: LC effects on signaling pathways involved in oxidative stress condition were studied by Western blot and immunofluorescence analysis. To evaluate ROS production, H9c2 cells were exposed to H₂O₂ after LC pretreatment.

RESULTS

Our in vitro study indicates how LC supplementation might protect cardiomyocytes from oxidative stress-related damage, preventing ROS formation and activating antioxidant signaling pathways in hyperglycemic conditions. In particular, LC promotes STAT3 activation and significantly increases the expression of antioxidant protein SOD2. Hyperglycemic cardiac cells are characterized by impairment in mitochondrial dysfunction and the CaMKII signal: LC promotes CaMKII expression and activation and enhancement of AMPK protein synthesis. Our results suggest that LC might ameliorate metabolic aspects of hyperglycemic cardiac cells. Finally, LC doses herein used did not modify H9c2 growth rate and viability.

CONCLUSIONS

Our novel study demonstrates that LC improves the microenvironment damaged by oxidative stress (induced by hyperglycemia), thus proposing this nutraceutical compound as an adjuvant in diabetic cardiac regenerative medicine.

Arrhythmias and Heart Rate: Mechanisms and Significance of a Relationship

The occurrence of arrhythmia is often related to basic heart rate. Prognostic significance is associated with such a relationship; furthermore, heart rate modulation may result as an ancillary effect of therapy, or be considered as a therapeutic tool. This review discusses the cellular mechanisms underlying arrhythmia occurrence during tachycardia or bradycardia, considering rate changes per se or as a mirror of autonomic modulation. Besides the influence of steady-state heart rate, dynamic aspects of changes in rate and autonomic balance are considered. The discussion leads to the conclusion that the prognostic significance of arrhythmia relationship with heart rate, and the consequence of heart rate on arrhythmogenesis, may vary according to the substrate present in the specific case and should be considered accordingly.

Pulmonary hypertension as a manifestation of mitochondrial disease: A case report and review of the literature

BACKGROUND

Mitochondrial diseases are a group of multisystem heterogeneous diseases caused by pathologic dysfunction of the mitochondrial respiratory chain. A wide range of clinical expression has been described. However, pulmonary hypertension has rarely been described in association with mitochondrial disease until the past decade, and there is no currently recognized treatment for the pulmonary hypertension complicated with mitochondrial disorder.

PATIENT CONCERNS

We reported the case of a 15-year-old boy who presented with shortness of breath and exercise limitation after a cold, and the diagnosis of pulmonary hypertension was confirmed by right heart catheter. Other examinations, such as blood tests, high- resolution chest computed tomography scan, and pulmonary function test, excluded other associated diseases as causes of pulmonary hypertension.

DIAGNOSES AND OUTCOMES

The initial diagnosis was idiopathic pulmonary arterial hypertension and an injection of vasodilator (Treprostinil) was given. However, the dyspnea and fatigue subsequently got worsened. Tracing back his family history, together with the electromyography, nerve conduction studies, and the result of muscle biopsy, mitochondrial disease was confirmed. After treatment with vitamin E, vitamin B2, ATP, and coenzyme Q10, the patient's condition improved.

CONCLUSION

Pulmonary hypertension should be considered as another potential manifestation of mitochondrial disease. Both mechanism and treatment for pulmonary hypertension complicated with mitochondrial disease are unclear. Further study is necessary.

Cardiac Nonmyocyte Cell Functions and Crosstalks in Response to Cardiotoxic Drugs

The discovery of the molecular mechanisms involved in the cardiac responses to anticancer drugs represents the current goal of cardio-oncology research. The oxidative stress has a pivotal role in cardiotoxic responses, affecting the function of all types of cardiac cells, and their functional crosstalks. Generally, cardiomyocytes are the main target of research studies on cardiotoxicity, but recently the contribution of the other nonmyocyte cardiac cells is becoming of growing interest. This review deals with the role of oxidative stress, induced by anticancer drugs, in cardiac nonmyocyte cells (fibroblasts, vascular cells, and immune cells). The alterations of functional interplays among these cardiac cells are discussed, as well. These interesting recent findings increase the knowledge about cardiotoxicity and suggest new molecular targets for both diagnosis and therapy.

New Insights in Cardiac Calcium Handling and Excitation-Contraction Coupling

Excitation-contraction (EC) coupling denotes the conversion of electric stimulus in mechanic output in contractile cells. Several studies have demonstrated that calcium (Ca²⁺) plays a pivotal role in this process. Here we present a comprehensive and updated description of the main systems involved in cardiac Ca²⁺ handling that ensure a functional EC coupling and their pathological alterations, mainly related to heart failure.