Heart failure gene therapy: the path to clinical practice

Deciphering the Basis of Molecular Biology of Selected Cardiovascular Diseases: A View on Network Medicine

Cardiovascular diseases are the leading cause of death across the world. For decades, researchers have been studying the causes of cardiovascular disease, yet many of them remain undiscovered or poorly understood. Network medicine is a recently expanding, integrative field that attempts to elucidate this issue by conceiving of disease as the result of disruptive links between multiple interconnected biological components. Still in its nascent stages, this revolutionary application of network science facilitated a number of important discoveries in complex disease mechanisms. As methodologies become more advanced, network medicine harbors the potential to expound on the molecular and genetic complexities of disease to differentiate how these intricacies govern disease manifestations, prognosis, and therapy. This is of paramount importance for confronting the incredible challenges of current and future cardiovascular disease research. In this review, we summarize the principal molecular and genetic mechanisms of common cardiac pathophysiologies as well as discuss the existing knowledge on therapeutic strategies to prevent, halt, or reverse these pathologies.

Gene Therapy With the N-Terminus of Junctophilin-2 Improves Heart Failure in Mice

BACKGROUND

Transcriptional remodeling is known to contribute to heart failure (HF). Targeting stress-dependent gene expression mechanisms may represent a clinically relevant gene therapy option. We recently uncovered a salutary mechanism in the heart whereby JP2 (junctophilin-2), an essential component of the excitation-contraction coupling apparatus, is site-specifically cleaved and releases an N-terminal fragment (JP2NT [N-terminal fragment of JP2]) that translocates into the nucleus and functions as a transcriptional repressor of HF-related genes. This study aims to determine whether JP2NT can be leveraged by gene therapy techniques for attenuating HF progression in a preclinical pressure overload model.

METHODS

We intraventricularly injected adeno-associated virus (AAV) (2/9) vectors expressing eGFP (enhanced green fluorescent protein), JP2NT, or DNA-binding deficient JP2NT (JP2NTΔbNLS/ARR) into neonatal mice and induced cardiac stress by transaortic constriction (TAC) 9 weeks later. We also treated mice with established moderate HF from TAC stress with either AAV-JP2NT or AAV-eGFP. RNA-sequencing analysis was used to reveal changes in hypertrophic and HF-related gene transcription by JP2NT gene therapy after TAC. Echocardiography, confocal imaging, and histology were performed to evaluate heart function and pathological myocardial remodeling following stress.

RESULTS

Mice preinjected with AAV-JP2NT exhibited ameliorated cardiac remodeling following TAC. The JP2NT DNA-binding domain is required for cardioprotection as its deletion within the AAV-JP2NT vector prevented improvement in TAC-induced cardiac dysfunction. Functional and histological data suggest that JP2NT gene therapy after the onset of cardiac dysfunction is effective at slowing the progression of HF. RNA-sequencing analysis further revealed a broad reversal of hypertrophic and HF-related gene transcription by JP2NT overexpression after TAC.

CONCLUSIONS

Our prevention- and intervention-based approaches here demonstrated that AAV-mediated delivery of JP2NT into the myocardium can attenuate stress-induced transcriptional remodeling and the development of HF when administered either before or after cardiac stress initiation. Our data indicate that JP2NT gene therapy holds great potential as a novel therapeutic for treating hypertrophy and HF.

Assessing the Effect of Cardiac Gene Therapy Using Catheter-Based Pressure-Volume Measurement in Large Animals

Gene therapy for heart failure targets various pathways that modulate cardiac function. Its detailed evaluation is crucial for proving the efficacy of cardiac gene therapies. Parameters that can be obtained by noninvasive approaches are generally influenced by loading conditions of the heart. In contrast, catheter-based left ventricular pressure-volume assessment provides a unique option to minimally invasively assess intrinsic myocardial function in a load-insensitive manner. In this chapter, we describe procedural steps for performing pressure-volume measurements and analysis in a preclinical large animal model.

Design and Production of Heart Chamber-Specific AAV9 Vectors

Adeno-associated virus serotype 9 (AAV9) is often used in heart research involving gene delivery due to its cardiotropism, high transduction efficiency, and little to no pathogenicity, making it highly applicable for gene manipulation, in vivo. However, current AAV9 technology is limited by the lack of strains that can selectively express and elucidate gene function in an atrial- and ventricular-specific manner. In fact, study of gene function in cardiac atria has been limited due to the lack of an appropriate tool to study atrial gene expression in vivo, hindering progress in the study of atrial-specific diseases such as atrial fibrillation, the most common cardiac arrhythmia in the USA.This chapter describes the method for the design and production of such chamber-specific AAV9 vectors, with the use of Nppa and Myl2 promoters to enhance atrial- and ventricular-specific expression. While several gene promoter candidates were considered and tested, Nppa and Myl2 were selected for use here because of their clearly defined regulatory elements that confer cardiac chamber-specific expression. Accordingly, Nppa (-425/+25) and Myl2 (-226/+36) promoter fragments are inserted into AAV9 vectors. The atrial- and ventricular-specific expression conferred by these new recombinant AAV9 was confirmed in a double-fluorescent Cre-dependent reporter mouse model. At only 450 and 262 base pairs of Nppa and Myl2 promoters, respectively, these AAV9 that drive chamber-specific AAV9 transgene expression address two major limitations of AAV9 technology, i.e., achieving chamber-specificity while maximizing space in the AAV genome for insertion of larger transgenes.

Direct reprogramming with Sendai virus vectors repaired infarct hearts at the chronic stage

Adult hearts have limited regenerative capacity. Hence, after acute myocardial infarction (MI), dead myocardial tissues are digested by immune cells and replaced by fibrosis, leading to ventricular remodeling and heart failure at the chronic stage. Direct reprogramming of the cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs) with cardiac transcription factors, including Gata4, Mef2c, and Tbx5 (GMT), may have significant potential for cardiac repair. Sendai virus (SeV) vectors expressing GMT have been reported to reprogram the mouse cardiac fibroblasts into iCMs without any risk of insertional mutagenesis. In vivo reprogramming improved the cardiac function after acute MI in immunodeficient mice. However, it is unknown whether the newly generated iCMs could exist in infarct hearts for a prolonged period and SeV-GMT can improve cardiac function after MI at the chronic stage in immunocompetent mice. Here, we show that SeV vectors efficiently infect CFs in vivo and reprogram them into iCMs, which existed for at least four weeks after MI, in fibroblast-linage tracing mice. Moreover, SeV-GMT improved cardiac function and reduced fibrosis and collagen I expression at 12 weeks after MI in immunocompetent mice. Thus, direct cardiac reprogramming with SeV vectors could be a promising therapy for MI.

Cardiac T-Tubule cBIN1-Microdomain, a Diagnostic Marker and Therapeutic Target of Heart Failure

Since its first identification as a cardiac transverse tubule (t-tubule) protein, followed by the cloning of the cardiac isoform responsible for t-tubule membrane microdomain formation, cardiac bridging integrator 1 (cBIN1) and its organized microdomains have emerged as a key mechanism in maintaining normal beat-to-beat heart contraction and relaxation. The abnormal remodeling of cBIN1-microdomains occurs in stressed and diseased cardiomyocytes, contributing to the pathophysiology of heart failure. Due to the homeostatic turnover of t-tubule cBIN1-microdomains via microvesicle release into the peripheral circulation, plasma cBIN1 can be assayed as a liquid biopsy of cardiomyocyte health. A new blood test cBIN1 score (CS) has been developed as a dimensionless inverse index derived from plasma cBIN1 concentration with a diagnostic and prognostic power for clinical outcomes in stable ambulatory patients with heart failure with reduced or preserved ejection fraction (HFrEF or HFpEF). Recent evidence further indicates that exogenous cBIN1 introduced by adeno-associated virus 9-based gene therapy can rescue cardiac contraction and relaxation in failing hearts. The therapeutic potential of cBIN1 gene therapy is enormous given its ability to rescue cardiac inotropy and provide lusitropic protection in the meantime. These unprecedented capabilities of cBIN1 gene therapy are shifting the current paradigm of therapy development for heart failure, particularly HFpEF.

Development of an AAV9-RNAi-mediated silencing strategy to abrogate TRPM4 expression in the adult heart

The cation channel transient receptor potential melastatin 4 (TRPM4) is a calcium-activated non-selective cation channel and acts in cardiomyocytes as a negative modulator of the L-type Ca²⁺ influx. Global deletion of TRPM4 in the mouse led to increased cardiac contractility under β-adrenergic stimulation. Consequently, cardiomyocyte-specific inactivation of the TRPM4 function appears to be a promising strategy to improve cardiac contractility in heart failure patients. The aim of this study was to develop a gene therapy approach in mice that specifically silences the expression of TRPM4 in cardiomyocytes. First, short hairpin RNA^miR30 (shRNA^miR30) sequences against the TRPM4 mRNA were screened in vitro using lentiviral transduction for a stable expression of the shRNA cassettes. Western blot analysis identified three efficient shRNA^miR30 sequences out of six, which reduced the endogenous TRPM4 protein level by up to 90 ± 6%. Subsequently, the most efficient shRNA^miR30 sequences were delivered into cardiomyocytes of adult mice using adeno-associated virus serotype 9 (AAV9)-mediated gene transfer. Initially, the AAV9 vector particles were administered via the lateral tail vein, which resulted in a downregulation of TRPM4 by 46 ± 2%. Next, various optimization steps were carried out to improve knockdown efficiency in vivo. First, the design of the expression cassette was streamlined for integration in a self-complementary AAV vector backbone for a faster expression. Compared to the application via the lateral tail vein, intravenous application via the retro-orbital sinus has the advantage that the vector solution reaches the heart directly and in a high concentration, and eventually a TRPM4 knockdown efficiency of 90 ± 7% in the heart was accomplished by this approach. By optimization of the shRNA^miR30 constructs and expression cassette as well as the route of AAV9 vector application, a 90% reduction of TRPM4 expression was achieved in the adult mouse heart. In the future, AAV9-RNAi-mediated inactivation of TRPM4 could be a promising strategy to increase cardiac contractility in preclinical animal models of acute and chronic forms of cardiac contractile failure.

Osteocrin attenuates inflammation, oxidative stress, apoptosis, and cardiac dysfunction in doxorubicin-induced cardiotoxicity

Background

Inflammation, oxidative stress, and apoptosis contribute to the evolution of doxorubicin (DOX)‐induced cardiotoxicity. Osteocrin (OSTN) is a novel secretory peptide mainly derived from the bone and skeletal muscle, and plays critical roles in regulating bone growth and physical endurance. Inspiringly, OSTN was also reported to be abundant in the myocardium that functioned as a therapeutic agent against cardiac rupture and congestive heart failure in mice after myocardial infarction. Herein, we investigated the role and potential mechanism of OSTN in DOX‐induced cardiotoxicity.

Methods

Cardiac‐restrict OSTN overexpression was performed by the intravenous injection of a cardiotropic AAV9 vector, and subsequently the mice received 15 mg/kg DOX injection (i.p., once) to induce acute cardiac injury. Besides, H9C2 cell lines were used to assess the possible role of OSTN in vitro by incubating with recombinant human OSTN or small interfering RNA against Ostn (siOstn). To clarify the involvement of protein kinase G (PKG), KT5823 and siPkg were used in vivo and in vitro. Mice were also administrated intraperitoneally with 5 mg/kg DOX weekly for consecutive 3 weeks at a cumulative dose of 15 mg/kg to mimic the cardiotoxic effects upon chronic DOX exposure.

Results

OSTN treatment notably attenuated, whereas OSTN silence exacerbated inflammation, oxidative stress, and cardiomyocyte apoptosis in DOX‐treated H9C2 cells. Besides, cardiac‐restrict OSTN‐overexpressed mice showed an alleviated cardiac injury and malfunction upon DOX injection. Mechanistically, we found that OSTN activated PKG, while PKG inhibition abrogated the beneficial effect of OSTN in vivo and in vitro. As expected, OSTN overexpression also improved cardiac function and survival rate in mice after chronic DOX treatment.

Conclusions

OSTN protects against DOX‐elicited inflammation, oxidative stress, apoptosis, and cardiac dysfunction via activating PKG, and cardiac gene therapy with OSTN provides a novel therapeutic strategy against DOX‐induced cardiotoxicity.

Novel approaches to the management of chronic systolic heart failure: future directions and unanswered questions

Despite improvements in outcomes in the last few decades for heart failure (HF) with reduced ejection fraction (HFrEF), there still remains a need for novel therapies as many patients incompletely recover with existing therapies and progress to advanced HF. In this review, we will discuss recent advances in the management of HFrEF with a focus on upcoming therapies that hold the greatest promise for clinical use. We will discuss novel pharmacological therapies and areas of uncertainty with existing therapies. We will also discuss the potential utility and controversy surrounding novel interventions for HF such as percutaneous mitral valve repair, atrial fibrillation ablation, and other emerging interventions with positive signals for benefit in HFrEF. Finally, we will summarize the current state of stem cell and gene therapy for HFrEF and future directions.

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Protease-Activatable Adeno-Associated Virus Vector for Gene Delivery to Damaged Heart Tissue

Adeno-associated virus (AAV) has emerged as a promising gene delivery vector because of its non-pathogenicity, simple structure and genome, and low immunogenicity compared to other viruses. However, its adoption as a safe and effective delivery vector for certain diseases relies on altering its tropism to deliver transgenes to desired cell populations. To this end, we have developed a protease-activatable AAV vector, named provector, that responds to elevated extracellular protease activity commonly found in diseased tissue microenvironments. The AAV9-based provector is initially inactive, but then it can be switched on by matrix metalloproteinases (MMP)-2 and -9. Cryo-electron microscopy and image reconstruction reveal that the provector capsid is structurally similar to that of AAV9, with a flexible peptide insertion at the top of the 3-fold protrusions. In an in vivo model of myocardial infarction (MI), the provector is able to deliver transgenes site specifically to high-MMP-activity regions of the damaged heart, with concomitant decreased delivery to many off-target organs, including the liver. The AAV provector may be useful in the future for enhanced delivery of transgenes to sites of cardiac damage.

The DWORF micropeptide enhances contractility and prevents heart failure in a mouse model of dilated cardiomyopathy

Calcium (Ca2+) dysregulation is a hallmark of heart failure and is characterized by impaired Ca2+ sequestration into the sarcoplasmic reticulum (SR) by the SR-Ca2+-ATPase (SERCA). We recently discovered a micropeptide named DWORF (DWarf Open Reading Frame) that enhances SERCA activity by displacing phospholamban (PLN), a potent SERCA inhibitor. Here we show that DWORF has a higher apparent binding affinity for SERCA than PLN and that DWORF overexpression mitigates the contractile dysfunction associated with PLN overexpression, substantiating its role as a potent activator of SERCA. Additionally, using a well-characterized mouse model of dilated cardiomyopathy (DCM) due to genetic deletion of the muscle-specific LIM domain protein (MLP), we show that DWORF overexpression restores cardiac function and prevents the pathological remodeling and Ca2+ dysregulation classically exhibited by MLP knockout mice. Our results establish DWORF as a potent activator of SERCA within the heart and as an attractive candidate for a heart failure therapeutic.

Non-invasive detection of adeno-associated viral gene transfer using a genetically encoded CEST-MRI reporter gene in the murine heart

Research into gene therapy for heart failure has gained renewed interest as a result of improved safety and availability of adeno-associated viral vectors (AAV). While magnetic resonance imaging (MRI) is standard for functional assessment of gene therapy outcomes, quantitation of gene transfer/expression relies upon tissue biopsy, fluorescence or nuclear imaging. Imaging of gene expression through the use of genetically encoded chemical exchange saturation transfer (CEST)-MRI reporter genes could be combined with clinical cardiac MRI methods to comprehensively probe therapeutic gene expression and subsequent outcomes. The CEST-MRI reporter gene Lysine Rich Protein (LRP) was cloned into an AAV9 vector and either administered systemically via tail vein injection or directly injected into the left ventricular free wall of mice. Longitudinal in vivo CEST-MRI performed at days 15 and 45 after direct injection or at 1, 60 and 90 days after systemic injection revealed robust CEST contrast in myocardium that was later confirmed to express LRP by immunostaining. Ventricular structure and function were not impacted by expression of LRP in either study arm. The ability to quantify and link therapeutic gene expression to functional outcomes can provide rich data for further development of gene therapy for heart failure.

Enhanced Cardiac S100A1 Expression Improves Recovery from Global Ischemia-Reperfusion Injury

Gene-targeted therapy with the inotropic Ca2 + -sensor protein S100A1 rescues contractile function in post-ischemic heart failure and is being developed towards clinical trials. Its proven beneficial effect on cardiac metabolism and mitochondrial function suggests a cardioprotective effect of S100A1 in myocardial ischemia-reperfusion injury (IRI). Fivefold cardiomyocyte-specific S100A1 overexpressing, isolated rat hearts perfused in working mode were subjected to 28 min ischemia (37 °C) followed by 60 min reperfusion. S100A1 overexpressing hearts showed superior hemodynamic recover: Left ventricular pressure recovered to 57 ± 7.3% of baseline compared to 51 ± 4.6% in control (p = 0.025), this effect mirrored in LV work and dP/dt(max). Troponin T and lactate dehydrogenase was decreased in the S100A1 group, as well as FoxO pro-apoptotic transcription factor, indicating less tissue necrosis, whereas phosphocreatine content was higher after reperfusion. This is the first report of a cardioprotective effect of S100A1 overexpression in a global IRI model.

Myocardial fibrosis: biomedical research from bench to bedside

Myocardial fibrosis refers to a variety of quantitative and qualitative changes in the interstitial myocardial collagen network that occur in response to cardiac ischaemic insults, systemic diseases, drugs, or any other harmful stimulus affecting the circulatory system or the heart itself. Myocardial fibrosis alters the architecture of the myocardium, facilitating the development of cardiac dysfunction, also inducing arrhythmias, influencing the clinical course and outcome of heart failure patients. Focusing on myocardial fibrosis may potentially improve patient care through the targeted diagnosis and treatment of emerging fibrotic pathways. The European Commission funded the FIBROTARGETS consortium as a multinational academic and industrial consortium with the primary aim of performing a systematic and collaborative search of targets of myocardial fibrosis, and then translating these mechanisms into individualized diagnostic tools and specific therapeutic pharmacological options for heart failure. This review focuses on those methodological and technological aspects considered and developed by the consortium to facilitate the transfer of the new mechanistic knowledge on myocardial fibrosis into potential biomedical applications.

Cardiac Myosin Activation with Gene Therapy Produces Sustained Inotropic Effects and May Treat Heart Failure with Reduced Ejection Fraction

Chronic inotropic therapy is effective for the treatment of heart failure with reduced ejection fraction, but has been limited by adverse long-term safety profiles, development of tolerance, and the need for chronic parenteral administration. A safe and convenient therapeutic agent that produces sustained inotropic effects could improve symptoms, functional capacity, and quality of life. Small amounts of 2-deoxy-adenosine triphosphate (dATP) activate cardiac myosin leading to enhanced contractility in normal and failing heart muscle. Cardiac myosin activation triggers faster myosin crossbridge cycling with greater force generation during each contraction. This paper describes the rationale and results of a translational medicine effort to increase dATP levels using a gene therapy strategy to deliver and upregulate ribonucleotide reductase (R1R2), the enzyme responsible for dATP synthesis, selectively in cardiomyocytes. In small and large animal models of heart failure, a single dose of this gene therapy has led to sustained inotropic effects with a benign safety profile. Further animal studies are appropriate with the goal of testing this agent in patients with heart failure.

Status of Therapeutic Gene Transfer to Treat Cardiovascular Disease in Dogs and Cats

Gene therapy is a procedure resulting in the transfer of a gene into an individual's cells to treat a disease. One goal of gene transfer is to express a functional gene when the endogenous gene is inactive. However, because heart failure is a complex disease characterized by multiple abnormalities at the cellular level, an alternate gene delivery approach is to alter myocardial protein levels to improve function. This article discusses background information on gene delivery, including packaging, administration, and a brief discussion of some of the candidate transgenes likely to alter the progression of naturally occurring heart disease in dogs and cats.

Cardiomyocyte Ca2+ homeostasis as a therapeutic target in heart failure with reduced and preserved ejection fraction

Heart failure is a highly prevalent syndrome of multiple etiologies and associated comorbidities, and aberrant intracellular Ca²⁺ homeostasis is a hallmark finding in heart failure patients. The cyclical changes in Ca²⁺ concentration within cardiomyocytes control cycles of cardiac contraction and relaxation, and dysregulation of Ca²⁺ handling processes leads to systolic dysfunction, diastolic dysfunction, and adverse remodeling. For this reason, greater understanding of Ca²⁺ handling mechanisms in heart failure is critical for selection of appropriate treatment strategies. In this review, we summarize the mechanisms of altered Ca²⁺ handling in two subsets of heart failure, heart failure with reduced ejection fraction and heart failure with preserved ejection fraction, and outline current and experimental treatments that target cardiomyocyte Ca²⁺ handling processes.

Sustained viral gene delivery from a micro-fibrous, elastomeric cardiac patch to the ischemic rat heart

Biodegradable and elastomeric patches have been applied to the surface of infarcted hearts as temporary mechanical supports to effectively alter adverse left ventricular remodeling processes. In this report, recombinant adeno-associated virus (AAV), known for its persistent transgene expression and low pathogenicity, was incorporated into elastomeric polyester urethane urea (PEUU) and polyester ether urethane urea (PEEUU) and processed by electrospinning into two formats (solid fibers and core-sheath fibers) designed to influence the controlled release behavior. The extended release of AAV encoding green fluorescent protein (GFP) was assessed in vitro. Sustained and localized viral particle delivery was achieved over 2 months in vitro. The biodegradable cardiac patches with or without AAV-GFP were implanted over rat left ventricular lesions three days following myocardial infarction to evaluate the transduction effect of released viral vectors. AAV particles were directly injected into the infarcted hearts as a control. Cardiac function and remodeling were significantly improved for 12 weeks after patch implantation compared to AAV injection. More GFP genes was expressed in the AAV patch group than AAV injection group, with both α-SMA positive cells and cardiac troponin T positive cells transduced in the patch group. Overall, the extended release behavior, prolonged transgene expression, and elastomeric mechanical properties make the AAV-loaded scaffold an attractive option for cardiac tissue engineering where both gene delivery and appropriate mechanical support are desired.

Cardiac molecular imaging to track left ventricular remodeling in heart failure

Cardiac left ventricular (LV) remodeling is the final common pathway of most primary cardiovascular diseases that manifest clinically as heart failure (HF). The more advanced the systolic HF and LV dysfunction, the worse the prognosis. The knowledge of the molecular, cellular, and neurohormonal mechanisms that lead to myocardial dysfunction and symptomatic HF has expanded rapidly and has allowed sophisticated approaches to understanding and management of the disease. New therapeutic targets for pharmacologic intervention in HF have also been identified through discovery of novel cellular and molecular components of membrane-bound receptor-mediated intracellular signal transduction cascades. Despite all advances, however, the prognosis of systolic HF has remained poor in general. This is, at least in part, related to the (1) relatively late institution of treatment due to reliance on gross functional and structural abnormalities that define the "heart failure phenotype" clinically; (2) remarkable genetic-based interindividual variations in the contribution of each of the many molecular components of cardiac remodeling; and (3) inability to monitor the activity of individual pathways to cardiac remodeling in order to estimate the potential benefits of pharmacologic agents, monitor the need for dose titration, and minimize side effects. Imaging of the recognized ultrastructural components of cardiac remodeling can allow redefinition of heart failure based on its "molecular phenotype," and provide a guide to implementation of "personalized" and "evidence-based" evaluation, treatment, and longitudinal monitoring of the disease beyond what is currently available through randomized controlled clinical trials.

Preventing antiblastic drug-related cardiomyopathy: old and new therapeutic strategies

Because of the recent advances in chemotherapeutic protocols, cancer survival has improved significantly, although cardiovascular disease has become a major cause of morbidity and mortality among cancer survivors: in addition to the well-known cardiotoxicity (CTX) from anthracyclines, biologic drugs that target molecules that are active in cancer biology also interfere with cardiovascular homeostasis.Pharmacological and non-pharmacological strategies to protect the cardiovascular structure and function are the best approaches to reducing the prevalence of cardiomyopathy linked to anticancer drugs. Extensive efforts have been devoted to identifying and testing strategies to achieve this end, but little consensus has been reached on a common and shared operability.Timing, dose and mode of chemotherapy administration play a crucial role in the development of acute or late myocardial dysfunction. Primary prevention initiatives cover a wide area that ranges from conventional heart failure drugs, such as β-blockers and renin-angiotensin-aldosterone system antagonists to nutritional supplementation and physical training. Additional studies on the pathophysiology and cellular mechanisms of anticancer-drug-related CTX will enable the introduction of novel therapies.We present various typologies of prevention strategies, describing the approaches that have already been used and those that could be effective on the basis of a better understanding of pharmacokinetic and pharmacodynamic CTX mechanisms.

Nucleoside Diphosphate Kinase-C Suppresses cAMP Formation in Human Heart Failure

BACKGROUND

Chronic heart failure (HF) is associated with altered signal transduction via β-adrenoceptors and G proteins and with reduced cAMP formation. Nucleoside diphosphate kinases (NDPKs) are enriched at the plasma membrane of patients with end-stage HF, but the functional consequences of this are largely unknown, particularly for NDPK-C. Here, we investigated the potential role of NDPK-C in cardiac cAMP formation and contractility.

METHODS

Real-time polymerase chain reaction, (far) Western blot, immunoprecipitation, and immunocytochemistry were used to study the expression, interaction with G proteins, and localization of NDPKs. cAMP levels were determined with immunoassays or fluorescent resonance energy transfer, and contractility was determined in cardiomyocytes (cell shortening) and in vivo (fractional shortening).

RESULTS

NDPK-C was essential for the formation of an NDPK-B/G protein complex. Protein and mRNA levels of NDPK-C were upregulated in end-stage human HF, in rats after long-term isoprenaline stimulation through osmotic minipumps, and after incubation of rat neonatal cardiomyocytes with isoprenaline. Isoprenaline also promoted translocation of NDPK-C to the plasma membrane. Overexpression of NDPK-C in cardiomyocytes increased cAMP levels and sensitized cardiomyocytes to isoprenaline-induced augmentation of contractility, whereas NDPK-C knockdown decreased cAMP levels. In vivo, depletion of NDPK-C in zebrafish embryos caused cardiac edema and ventricular dysfunction. NDPK-B knockout mice had unaltered NDPK-C expression but showed contractile dysfunction and exacerbated cardiac remodeling during long-term isoprenaline stimulation. In human end-stage HF, the complex formation between NDPK-C and Gα_i2 was increased whereas the NDPK-C/Gα_s interaction was decreased, producing a switch that may contribute to an NDPK-C-dependent cAMP reduction in HF.

CONCLUSIONS

Our findings identify NDPK-C as an essential requirement for both the interaction between NDPK isoforms and between NDPK isoforms and G proteins. NDPK-C is a novel critical regulator of β-adrenoceptor/cAMP signaling and cardiac contractility. By switching from Gα_s to Gα_i2 activation, NDPK-C may contribute to lower cAMP levels and the related contractile dysfunction in HF.

"Freeze, Don't Move": How to Arrest a Suspect in Heart Failure - A Review on Available GRK2 Inhibitors

Cardiovascular disease and heart failure (HF) still collect the largest toll of death in western societies and all over the world. A growing number of molecular mechanisms represent possible targets for new therapeutic strategies, which can counteract the metabolic and structural changes observed in the failing heart. G protein-coupled receptor kinase 2 (GRK2) is one of such targets for which experimental and clinical evidence are established. Indeed, several strategies have been carried out in place to interface with the known GRK2 mechanisms of action in the failing heart. This review deals with results from basic and preclinical studies. It shows different strategies to inhibit GRK2 in HF in vivo (βARK-ct gene therapy, treatment with gallein, and treatment with paroxetine) and in vitro (RNA aptamer, RKIP, and peptide-based inhibitors). These strategies are based either on the inhibition of the catalytic activity of the kinase (“Freeze!”) or the prevention of its shuttling within the cell (“Don’t Move!”). Here, we review the peculiarity of each strategy with regard to the ability to interact with the multiple tasks of GRK2 and the perspective development of eventual clinical use.

Translation of Cardiac Myosin Activation with 2-deoxy-ATP to Treat Heart Failure via an Experimental Ribonucleotide Reductase-Based Gene Therapy

Despite recent advances, chronic heart failure remains a significant and growing unmet medical need, reaching epidemic proportions carrying substantial morbidity, mortality, and costs. A safe and convenient therapeutic agent that produces sustained inotropic effects could ameliorate symptoms and improve functional capacity and quality of life. The authors discovered that small amounts of 2-deoxy-ATP (dATP) activate cardiac myosin leading to enhanced contractility in normal and failing heart muscle. Cardiac myosin activation triggers faster myosin cross-bridge cycling with greater force generation during each contraction. They describe the rationale and results of a translational medicine effort to increase dATP levels using a gene therapy strategy that up-regulates ribonucleotide reductase, the rate-limiting enzyme for dATP synthesis, selectively in cardiomyocytes. In small and large animal models of heart failure, a single dose of this gene therapy has led to sustained inotropic effects with no toxicity or safety concerns identified to date. Further animal studies are being conducted with the goal of testing this agent in patients with heart failure.

Gene therapy for heart failure

Novel strategies are needed to treat the growing population of heart failure patients. While new drug and device based therapies have improved outcomes over the past several decades, heart failure patients continue to experience amongst the lowest quality of life of any chronic disease, high likelihood of being hospitalized and marked reduction in survival. Better understanding of many of the basic mechanisms involved in the development of heart failure has helped identify abnormalities that could potentially be targeted by gene transfer. Despite success in experimental animal models, translating gene transfer strategies from the laboratory to the clinic remains at an early stage. This review provides an introduction to gene transfer as a therapy for treating heart failure, describes some of the many factors that need to be addressed in order for it to be successful and discusses some of the recent studies that have been carried out in heart failure patients. Insights from these studies highlight both the enormous promise of gene transfer and the obstacles that still need to be overcome for this treatment approach to be successful.

Novel Therapies for Heart Failure - Where Do They Stand?

Despite advances in therapy, patients with heart failure (HF) continue to experience unacceptably high rates of hospitalization and death, as well as poor quality of life. As a consequence, there is an urgent need for new treatments that can improve the clinical course of the growing worldwide population of HF patients. Serelaxin and ularatide, both based on naturally occurring peptides, have potent vasodilatory as well as other effects on the heart and kidneys. For both agents, phase 3 studies that are designed to determine whether they improve outcomes in patients with acute HF have completed enrollment. TRV027, a biased ligand for the type 1 angiotensin receptor with effects that extend beyond traditional angiotensin-receptor blockers is also being studied in the acute HF population. Omecamtiv mecarbil, an inotropic agent that improves myocardial contractility by a novel mechanism, and vericiguat, a drug that stimulates soluble guanylate cyclase, are both being developed to treat patients with chronic HF. Finally, despite the negative results of the CUPID study, gene transfer therapy continues to be explored as a means of improving the function of the failing heart. The basis for the use of these drugs and their current status in clinical trials are discussed. (Circ J 2016; 80: 1882-1891).

Pharmacology of heart failure: From basic science to novel therapies

Chronic heart failure is one of the leading causes for hospitalization in the United States and Europe, and is accompanied by high mortality. Current pharmacological therapy of chronic heart failure with reduced ejection fraction is largely based on compounds that inhibit the detrimental action of the adrenergic and the renin-angiotensin-aldosterone systems on the heart. More than one decade after spironolactone, two novel therapeutic principles have been added to the very recently released guidelines on heart failure therapy: the HCN-channel inhibitor ivabradine and the combined angiotensin and neprilysin inhibitor valsartan/sacubitril. New compounds that are in phase II or III clinical evaluation include novel non-steroidal mineralocorticoid receptor antagonists, guanylate cyclase activators or myosine activators. A variety of novel candidate targets have been identified and the availability of gene transfer has just begun to accelerate translation from basic science to clinical application. This review provides an overview of current pharmacology and pharmacotherapy in chronic heart failure at three stages: the updated clinical guidelines of the American Heart Association and the European Society of Cardiology, new drugs which are in clinical development, and finally innovative drug targets and their mechanisms in heart failure which are emerging from preclinical studies will be discussed.

Models of Heart Failure Based on the Cardiotoxicity of Anticancer Drugs

Heart failure (HF) is a complication of oncological treatments that may have dramatic clinical impact. It may acutely worsen a patient's condition or it may present with delayed onset, even years after treatment, when cancer has been cured or is in stable remission. Several studies have addressed the mechanisms of cancer therapy-related HF and some have led to the definition of disease models that hold valid for other and more common types of HF. Here, we review these models of HF based on the cardiotoxicity of antineoplastic drugs and classify them in cardiomyocyte-intrinsic, paracrine, or potentially secondary to effects on cardiac progenitor cells. The first group includes HF resulting from the combination of oxidative stress, mitochondrial dysfunction, and activation of the DNA damage response, which is typically caused by anthracyclines, and HF resulting from deranged myocardial energetics, such as that triggered by anthracyclines and sunitinib. Blockade of the neuregulin-1/ErbB4/ErbB2, vascular endothelial growth factor/vascular endothelial growth factor receptor and platelet-derived growth factor /platelet-derived growth factor receptor pathways by trastuzumab, sorafenib and sunitinib is proposed as paradigm of cancer therapy-related HF associated with alterations of myocardial paracrine pathways. Finally, anthracyclines and trastuzumab are also presented as examples of antitumor agents that induce HF by affecting the cardiac progenitor cell population.

Cardiomyocytes, endothelial cells and cardiac fibroblasts: S100A1's triple action in cardiovascular pathophysiology

Over the past decade, basic and translational research delivered comprehensive evidence for the relevance of the Ca(2+)-binding protein S100A1 in cardiovascular diseases. Aberrant expression levels of S100A1 surfaced as molecular key defects, driving the pathogenesis of chronic heart failure, arterial and pulmonary hypertension, peripheral artery disease and disturbed myocardial infarction healing. Loss of intracellular S100A1 renders entire Ca(2+)-controlled networks dysfunctional, thereby leading to cardiomyocyte failure and endothelial dysfunction. Lack of S100A1 release in ischemic myocardium compromises cardiac fibroblast function, entailing impaired damage healing. This review focuses on molecular pathways and signaling cascades regulated by S100A1 in cardiomyocytes, endothelial cells and cardiac fibroblasts in order to provide an overview of our current mechanistic understanding of S100A1's action in cardiovascular pathophysiology.

Prevalence of AAV1 neutralizing antibodies and consequences for a clinical trial of gene transfer for advanced heart failure

Adeno-associated virus serotype 1 (AAV1) has many advantages as a gene therapy vector, but the presence of pre-existing neutralizing antibodies (NAbs) is an important limitation. This study was designed to determine: (1) characteristics of AAV NAbs in human subjects, (2) prevalence of AAV1 NAbs in heart failure patients and (3) utility of aggressive immunosuppressive therapy in reducing NAb seroconversion in an animal model. NAb titers were assessed in a cohort of heart failure patients and in patients screened for a clinical trial of gene therapy with AAV1 carrying the sarcoplasmic reticulum calcium ATPase gene (AAV1/SERCA2a). AAV1 NAbs were found in 59.5% of 1552 heart failure patients. NAb prevalence increased with age (P=0.001) and varied geographically. The pattern of NAb titers suggested that exposure is against AAV2, with AAV1 NAb seropositivity due to crossreactivity. The effects of immunosuppression on NAb formation were tested in mini-pigs treated with immunosuppressant therapy before, during and after a single AAV1/SERCA2a infusion. Aggressive immunosuppression did not prevent formation of AAV1 NAbs. We conclude that immunosuppression is unlikely to be a viable solution for repeat AAV1 dosing. Strategies to reduce NAbs in heart failure patients are needed to increase eligibility for gene transfer using AAV vectors.

Shock Wave Treatment Protects From Neuronal Degeneration via a Toll-Like Receptor 3 Dependent Mechanism: Implications of a First-Ever Causal Treatment for Ischemic Spinal Cord Injury

Background

Paraplegia following spinal cord ischemia represents a devastating complication of both aortic surgery and endovascular aortic repair. Shock wave treatment was shown to induce angiogenesis and regeneration in ischemic tissue by modulation of early inflammatory response via Toll‐like receptor (TLR) 3 signaling. In preclinical and clinical studies, shock wave treatment had a favorable effect on ischemic myocardium. We hypothesized that shock wave treatment also may have a beneficial effect on spinal cord ischemia.

Methods and Results

A spinal cord ischemia model in mice and spinal slice cultures ex vivo were performed. Treatment groups received immediate shock wave therapy, which resulted in decreased neuronal degeneration and improved motor function. In spinal slice cultures, the activation of TLR3 could be observed. Shock wave effects were abolished in spinal slice cultures from TLR3^−/− mice, whereas the effect was still present in TLR4^−/− mice. TLR4 protein was found to be downregulated parallel to TLR3 signaling. Shock wave–treated animals showed significantly better functional outcome and survival. The protective effect on neurons could be reproduced in human spinal slices.

Conclusions

Shock wave treatment protects from neuronal degeneration via TLR3 signaling and subsequent TLR4 downregulation. Consequently, it represents a promising treatment option for the devastating complication of spinal cord ischemia after aortic repair.

Recent Advances on Pathophysiology, Diagnostic and Therapeutic Insights in Cardiac Dysfunction Induced by Antineoplastic Drugs

Along with the improvement of survival after cancer, cardiotoxicity due to antineoplastic treatments has emerged as a clinically relevant problem. Potential cardiovascular toxicities due to anticancer agents include QT prolongation and arrhythmias, myocardial ischemia and infarction, hypertension and/or thromboembolism, left ventricular (LV) dysfunction, and heart failure (HF). The latter is variable in severity, may be reversible or irreversible, and can occur soon after or as a delayed consequence of anticancer treatments. In the last decade recent advances have emerged in clinical and pathophysiological aspects of LV dysfunction induced by the most widely used anticancer drugs. In particular, early, sensitive markers of cardiac dysfunction that can predict this form of cardiomyopathy before ejection fraction (EF) is reduced are becoming increasingly important, along with novel therapeutic and cardioprotective strategies, in the attempt of protecting cardiooncologic patients from the development of congestive heart failure.

Intracoronary Cytoprotective Gene Therapy: A Study of VEGF-B167 in a Pre-Clinical Animal Model of Dilated Cardiomyopathy

BACKGROUND

Vascular endothelial growth factor (VEGF)-B activates cytoprotective/antiapoptotic and minimally angiogenic mechanisms via VEGF receptors. Therefore, VEGF-B might be an ideal candidate for the treatment of dilated cardiomyopathy, which displays modest microvascular rarefaction and increased rate of apoptosis.

OBJECTIVES

This study evaluated VEGF-B gene therapy in a canine model of tachypacing-induced dilated cardiomyopathy.

METHODS

Chronically instrumented dogs underwent cardiac tachypacing for 28 days. Adeno-associated virus serotype 9 viral vectors carrying VEGF-B167 genes were infused intracoronarily at the beginning of the pacing protocol or during compensated heart failure. Moreover, we tested a novel VEGF-B167 transgene controlled by the atrial natriuretic factor promoter.

RESULTS

Compared with control subjects, VEGF-B167 markedly preserved diastolic and contractile function and attenuated ventricular chamber remodeling, halting the progression from compensated to decompensated heart failure. Atrial natriuretic factor-VEGF-B167 expression was low in normally functioning hearts and stimulated by cardiac pacing; it thus functioned as an ideal therapeutic transgene, active only under pathological conditions.

CONCLUSIONS

Our results, obtained with a standard technique of interventional cardiology in a clinically relevant animal model, support VEGF-B167 gene transfer as an affordable and effective new therapy for nonischemic heart failure.

S100A1 DNA-based Inotropic Therapy Protects Against Proarrhythmogenic Ryanodine Receptor 2 Dysfunction

Restoring expression levels of the EF-hand calcium (Ca(2+)) sensor protein S100A1 has emerged as a key factor in reconstituting normal Ca(2+) handling in failing myocardium. Improved sarcoplasmic reticulum (SR) function with enhanced Ca(2+) resequestration appears critical for S100A1's cyclic adenosine monophosphate-independent inotropic effects but raises concerns about potential diastolic SR Ca(2+) leakage that might trigger fatal arrhythmias. This study shows for the first time a diminished interaction between S100A1 and ryanodine receptors (RyR2s) in experimental HF. Restoring this link in failing cardiomyocytes, engineered heart tissue and mouse hearts, respectively, by means of adenoviral and adeno-associated viral S100A1 cDNA delivery normalizes diastolic RyR2 function and protects against Ca(2+)- and β-adrenergic receptor-triggered proarrhythmogenic SR Ca(2+) leakage in vitro and in vivo. S100A1 inhibits diastolic SR Ca(2+) leakage despite aberrant RyR2 phosphorylation via protein kinase A and calmodulin-dependent kinase II and stoichiometry with accessory modulators such as calmodulin, FKBP12.6 or sorcin. Our findings demonstrate that S100A1 is a regulator of diastolic RyR2 activity and beneficially modulates diastolic RyR2 dysfunction. S100A1 interaction with the RyR2 is sufficient to protect against basal and catecholamine-triggered arrhythmic SR Ca(2+) leak in HF, combining antiarrhythmic potency with chronic inotropic actions.

Gene therapy for heart failure

Heart failure is a major public health problem throughout the world and it is likely that its prevalence will continue to grow over the next several decades. Despite advances in the treatment of heart failure, morbidity and mortality remain unacceptably high. Gene transfer therapy provides a novel strategy for targeting abnormalities in cardiac cells that adversely affect cardiac function. New vectors for gene delivery, mainly adeno-associated viruses (AAVs) that are preferentially taken up by cardiomyocytes, can result in sustained transgene expression. The cardiac isoform of sarco(endo)plasmic reticulum Ca(2+)ATPase (SERCA2a) plays a major role in regulating calcium levels in cardiomyocytes. Abnormal calcium handling by the failing heart caused by a reduction in SERCA2a activity adversely affects both systolic and diastolic function. The Calcium Upregulation by Percutaneous Administration of Gene Therapy in Cardiac Disease (CUPID) study was a Phase 2a double-blind, randomized, placebo-controlled, dose-finding study that was performed in patients with advanced heart failure due to systolic dysfunction. Eligible patients received AAV/SERCA2a or placebo by direct antegrade infusion into the coronary circulation. At the end of 12 months, patients receiving high-dose therapy (i.e. 1×10(13) DNase Resistant Particles) had evidence of favorable changes in several clinically relevant domains compared to patients treated with placebo. There were no safety concerns at any dose of AAV/SERCA2a. Patients treated with AAV/SERCA2a exhibited a striking reduction in cardiovascular events that persisted through 36 months of follow-up compared to patients who received placebo. Transgene expression was detected in the myocardium of patients receiving AAV/SERCA2a gene therapy as long as 31 months after delivery. A second Phase 2b study, CUPID 2, designed to confirm this favorable effect on heart failure events, is currently underway with the results expected to be presented later in 2015. Additional studies using other vectors and targets are in planning or underway making gene transfer therapy one of the most exciting new approaches under development for treating heart failure.

The war against heart failure: the Lancet lecture

Heart failure is a global problem with an estimated prevalence of 38 million patients worldwide, a number that is increasing with the ageing of the population. It is the most common diagnosis in patients aged 65 years or older admitted to hospital and in high-income nations. Despite some progress, the prognosis of heart failure is worse than that of most cancers. Because of the seriousness of the condition, a declaration of war on five fronts has been proposed for heart failure. Efforts are underway to treat heart failure by enhancing myofilament sensitivity to Ca(2+); transfer of the gene for SERCA2a, the protein that pumps calcium into the sarcoplasmic reticulum of the cardiomyocyte, seems promising in a phase 2 trial. Several other abnormal calcium-handling proteins in the failing heart are candidates for gene therapy; many short, non-coding RNAs--ie, microRNAs (miRNAs)--block gene expression and protein translation. These molecules are crucial to calcium cycling and ventricular hypertrophy. The actions of miRNAs can be blocked by a new class of drugs, antagomirs, some of which have been shown to improve cardiac function in animal models of heart failure; cell therapy, with autologous bone marrow derived mononuclear cells, or autogenous mesenchymal cells, which can be administered as cryopreserved off the shelf products, seem to be promising in both preclinical and early clinical heart failure trials; and long-term ventricular assistance devices are now used increasingly as a destination therapy in patients with advanced heart failure. In selected patients, left ventricular assistance can lead to myocardial recovery and explantation of the device. The approaches to the treatment of heart failure described, when used alone or in combination, could become important weapons in the war against heart failure.

Low energy shock wave therapy induces angiogenesis in acute hind-limb ischemia via VEGF receptor 2 phosphorylation

Objectives

Low energy shock waves have been shown to induce angiogenesis, improve left ventricular ejection fraction and decrease angina symptoms in patients suffering from chronic ischemic heart disease. Whether there is as well an effect in acute ischemia was not yet investigated.

Methods

Hind-limb ischemia was induced in 10–12 weeks old male C57/Bl6 wild-type mice by excision of the left femoral artery. Animals were randomly divided in a treatment group (SWT, 300 shock waves at 0.1 mJ/mm², 5 Hz) and untreated controls (CTR), n = 10 per group. The treatment group received shock wave therapy immediately after surgery.

Results

Higher gene expression and protein levels of angiogenic factors VEGF-A and PlGF, as well as their receptors Flt-1 and KDR have been found. This resulted in significantly more vessels per high-power field in SWT compared to controls. Improvement of blood perfusion in treatment animals was confirmed by laser Doppler perfusion imaging. Receptor tyrosine kinase profiler revealed significant phosphorylation of VEGF receptor 2 as an underlying mechanism of action. The effect of VEGF signaling was abolished upon incubation with a VEGFR2 inhibitor indicating that the effect is indeed VEGFR 2 dependent.

Conclusions

Low energy shock wave treatment induces angiogenesis in acute ischemia via VEGF receptor 2 stimulation and shows the same promising effects as known from chronic myocardial ischemia. It may therefore develop as an adjunct to the treatment armentarium of acute muscle ischemia in limbs and myocardium.

CaMKII inhibitors: from research tools to therapeutic agents

The cardiac field has benefited from the availability of several CaMKII inhibitors serving as research tools to test putative CaMKII pathways associated with cardiovascular physiology and pathophysiology. Successful demonstrations of its critical pathophysiological roles have elevated CaMKII as a key target in heart failure, arrhythmia, and other forms of heart disease. This has caught the attention of the pharmaceutical industry, which is now racing to develop CaMKII inhibitors as safe and effective therapeutic agents. While the first generation of CaMKII inhibitor development is focused on blocking its activity based on ATP binding to its catalytic site, future inhibitors can also target sites affecting its regulation by Ca²⁺/CaM or translocation to some of its protein substrates. The recent availability of crystal structures of the kinase in the autoinhibited and activated state, and of the dodecameric holoenzyme, provides insights into the mechanism of action of existing inhibitors. It is also accelerating the design and development of better pharmacological inhibitors. This review examines the structure of the kinase and suggests possible sites for its inhibition. It also analyzes the uses and limitations of current research tools. Development of new inhibitors will enable preclinical proof of concept tests and clinical development of successful lead compounds, as well as improved research tools to more accurately examine and extend knowledge of the role of CaMKII in cardiac health and disease.

The road ahead: working towards effective clinical translation of myocardial gene therapies

During the last two decades the fields of molecular and cellular cardiology, and more recently molecular cardiac surgery, have developed rapidly. The concept of delivering cDNA encoding a therapeutic gene to cardiomyocytes using a vector system with substantial cardiac tropism, allowing for long-term expression of a therapeutic protein, has moved from hypothesis to bench to clinical application. However, the clinical results to date are still disappointing. The ideal gene transfer method should be explored in clinically relevant animal models of heart disease to evaluate the relative roles of specific molecular pathways in disease pathogenesis, helping to validate the potential targets for therapeutic intervention. Successful clinical cardiovascular gene therapy also requires the use of nonimmunogenic cardiotropic vectors capable of expressing the requisite amount of therapeutic protein in vivo and in situ. Depending on the desired application either regional or global myocardial gene delivery is required. Cardiac-specific delivery techniques incorporating mapping technologies for regional delivery and highly efficient methodologies for global delivery should improve the precision and specificity of gene transfer to the areas of interest and minimize collateral organ gene expression.

Therapeutic safety of high myocardial expression levels of the molecular inotrope S100A1 in a preclinical heart failure model

Low levels of the molecular inotrope S100A1 are sufficient to rescue post-ischemic heart failure (HF). As a prerequisite to clinical application and to determine the safety of myocardial S100A1 DNA-based therapy, we investigated the effects of high myocardial S100A1 expression levels on the cardiac contractile function and occurrence of arrhythmia in a preclinical large animal HF model. At 2 weeks after myocardial infarction domestic pigs presented significant left ventricular (LV) contractile dysfunction. Retrograde application of AAV6-S100A1 (1.5 × 10(13) tvp) via the anterior cardiac vein (ACV) resulted in high-level myocardial S100A1 protein peak expression of up to 95-fold above control. At 14 weeks, pigs with high-level myocardial S100A1 protein overexpression did not show abnormalities in the electrocardiogram. Electrophysiological right ventricular stimulation ruled out an increased susceptibility to monomorphic ventricular arrhythmia. High-level S100A1 protein overexpression in the LV myocardium resulted in a significant increase in LV ejection fraction (LVEF), albeit to a lesser extent than previously reported with low S100A1 protein overexpression. Cardiac remodeling was, however, equally reversed. High myocardial S100A1 protein overexpression neither increases the occurrence of cardiac arrhythmia nor causes detrimental effects on myocardial contractile function in vivo. In contrast, this study demonstrates a broad therapeutic range of S100A1 gene therapy in post-ischemic HF using a preclinical large animal model.