Focal modification of electrical conduction in the heart by viral gene transfer

AAV-Mediated Delivery of Plakophilin-2a Arrests Progression of Arrhythmogenic Right Ventricular Cardiomyopathy in Murine Hearts: Preclinical Evidence Supporting Gene Therapy in Humans

BACKGROUND

Pathogenic variants in PKP2 (plakophilin-2) cause arrhythmogenic right ventricular cardiomyopathy, a disease characterized by life-threatening arrhythmias and progressive cardiomyopathy leading to heart failure. No effective medical therapy is available to prevent or arrest the disease. We tested the hypothesis that adeno-associated virus vector-mediated delivery of the human PKP2 gene to an adult mammalian heart deficient in PKP2 can arrest disease progression and significantly prolong survival.

METHODS

Experiments were performed using a PKP2-cKO (cardiac-specific, tamoxifen-activated PKP2 knockout murine model). The potential therapeutic, adeno-associated virus vector of serotype rh.74 (AAVrh.74)-PKP2a (PKP2 variant A; RP-A601) is a recombinant AAVrh.74 gene therapy viral vector encoding the human PKP2 variant A. AAVrh.74-PKP2a was delivered to adult mice by a single tail vein injection either before or after tamoxifen-activated PKP2-cKO. PKP2 expression was confirmed by molecular and histopathologic analyses. Cardiac function and disease progression were monitored by survival analyses, echocardiography, and electrocardiography.

RESULTS

Consistent with prior findings, loss of PKP2 expression caused 100% mortality within 50 days after tamoxifen injection. In contrast, AAVrh.74-PKP2a-mediated PKP2a expression resulted in 100% survival for >5 months (at study termination). Echocardiographic analysis revealed that AAVrh.74-PKP2a prevented right ventricle dilation, arrested left ventricle functional decline, and mitigated arrhythmia burden. Molecular and histological analyses showed AAVrh.74-PKP2a-mediated transgene mRNA and protein expression and appropriate PKP2 localization at the cardiomyocyte intercalated disc. Importantly, the therapeutic benefit was shown in mice receiving AAVrh.74-PKP2a after disease onset.

CONCLUSIONS

These preclinical data demonstrate the potential for AAVrh.74-PKP2a (RP-A601) as a therapeutic for PKP2-related arrhythmogenic right ventricular cardiomyopathy in both early and more advanced stages of the disease.

The Autonomic Coumel Triangle: A New Way to Define the Fascinating Relationship between Atrial Fibrillation and the Autonomic Nervous System

Arrhythmogenic substrate, modulating factors, and triggering factors (the so-called Coumel's triangle concept) play a primary role in atrial fibrillation (AF) pathophysiology. Several years have elapsed since Coumel and co-workers advanced the concept of the relevance of autonomic nervous system (ANS) influences on atrial cells' electrophysiological characteristics. The ANS is not only associated with cardiac rhythm regulation but also exerts an important role in the triggering and maintenance of atrial fibrillation. This review aims to describe in detail the autonomic mechanisms involved in the pathophysiology of atrial fibrillation (AF), starting from the hypothesis of an "Autonomic Coumel Triangle" that stems from the condition of the fundamental role played by the ANS in all phases of the pathophysiology of AF. In this article, we provide updated information on the biomolecular mechanisms of the ANS role in Coumel's triangle, with the molecular pathways of cardiac autonomic neurotransmission, both adrenergic and cholinergic, and the interplay between the ANS and cardiomyocytes' action potential. The heterogeneity of the clinical spectrum of the ANS and AF, with the ANS playing a relevant role in situations that may promote the initiation and maintenance of AF, is highlighted. We also report on drug, biological, and gene therapy as well as interventional therapy. On the basis of the evidence reviewed, we propose that one should speak of an "Autonomic Coumel's Triangle" instead of simply "Coumel's Triangle".

G protein-coupled receptor signaling: transducers and effectors

G protein-coupled receptors (GPCRs) are of considerable interest due to their importance in a wide range of physiological functions and in a large number of Food and Drug Administration (FDA)-approved drugs as therapeutic entities. With continued study of their function and mechanism of action, there is a greater understanding of how effector molecules interact with a receptor to initiate downstream effector signaling. This review aims to explore the signaling pathways, dynamic structures, and physiological relevance in the cardiovascular system of the three most important GPCR signaling effectors: heterotrimeric G proteins, GPCR kinases (GRKs), and β-arrestins. We will first summarize their prominent roles in GPCR pharmacology before transitioning into less well-explored areas. As new technologies are developed and applied to studying GPCR structure and their downstream effectors, there is increasing appreciation for the elegance of the regulatory mechanisms that mediate intracellular signaling and function.

Gene therapy to terminate tachyarrhythmias

INTRODUCTION

To date, the treatment option for tachyarrhythmia is classified into drug therapy, catheter ablation, and implantable device therapy. However, the efficacy of the antiarrhythmic drugs is limited. Although the indication of catheter ablation is expanding, several fatal tachyarrhythmias are still refractory to ablation. Implantable cardioverter-defibrillator increases survival, but it is not a curable treatment. Therefore, a novel therapy for tachyarrhythmias refractory to present treatments is desired. Gene therapy is being developed as a promising candidate for this purpose, and basic research and translational research have been accumulated in recent years.

AREAS COVERED

This paper reviews the current state of gene therapy for arrhythmias, including susceptible arrhythmias, the route of administration to the heart, and the type of vector to use. We also discuss the latest progress in the technology of gene delivery and genome editing.

EXPERT OPINION

Gene therapy is one of the most promising technologies for arrhythmia treatment. However, additional technological innovation to achieve safe, localized, homogeneous, and long-lasting gene transfer is required for its clinical application.

Atrial Gene Painting in Large Animal Model of Atrial Fibrillation

Gene therapy appears promising as a targeted treatment of cardiac diseases. Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and also a major contributor to stroke, heart failure, and death. Mechanisms that initiate and sustain AF are associated with structural and electrophysiological remodeling in the whole atria. Selection of the appropriate gene delivery method is critical for transduction efficacy. The ideal gene delivery method to manage AF should provide widespread and sufficient exposure to the transgene in atria only that safely maintains the homeostasis of the heart without off-target expression. All these requirements can be achieved using atrial gene painting that is directly applied to the atrial epicardial surface. In this chapter, we present the advantages of atrial gene painting and the experimental method, as applied to a large animal model of AF.

Recent advances in gene therapy for atrial fibrillation

Atrial fibrillation (AF) is the most common heart rhythm disorder in adults and a major cause of stroke. Unfortunately, current treatments for AF are suboptimal as they are not targeting the molecular mechanisms underlying AF. In this regard, gene therapy is emerging as a promising approach for mechanism-based treatment of AF. In this review, we summarize recent advances and challenges in gene therapy for this important cardiovascular disease.

Atrial fibrillation and autonomic nervous system: A translational approach to guide therapeutic goals

The autonomic nervous system (ANS) is known to play an important role in the genesis and maintenance of atrial fibrillation (AF). Biomolecular and genetic mechanisms, anatomical knowledges with recent diagnostic techniques acquisitions, both invasive and non-invasive, have enabled greater therapeutic goals in patients affected by AF related to ANS imbalance. Catheter ablation of ganglionated plexi (GP) in the left and right atrium has been proposed in varied clinical conditions. Moreover interesting results arise from renal sympathetic denervation and vagal nerve stimulation. Despite all this, in the scenario of ANS modulation translational strategies we necessary must consider the treatment or correction of dynamic factors such as obesity, obstructive sleep apnea, lifestyle, food, and stress. Finally, new antiarrhythmic drugs, gene therapy and "ablatogenomic" could be represent exciting future therapeutic perspectives.

Autonomic Dysfunction and Neurohormonal Disorders in Atrial Fibrillation

Atrial fibrillation (AF) is the most commonly diagnosed arrhythmia and eludes an efficacious cure despite an increasing prevalence and a significant association with morbidity and mortality. In addition to an array of clinical sequelae, the origins and propagation of AF are multifactorial. In recent years, the contribution from the autonomic nervous system has been an area of particular interest. This review highlights the relevant physiology of autonomic and neurohormonal contributions to AF origin and maintenance, the current state of the literature on targeted therapies, and the path forward for clinical interventions.

Gene and Cell Therapy for Cardiac Arrhythmias

PURPOSE

In the last decade, interest in gene therapy as a therapeutic technology has increased, largely driven by an exciting yet modest number of successful applications for monogenic diseases. Setbacks in the use of gene therapy for cardiac disease have motivated efforts to develop vectors with enhanced tropism for the heart and more efficient delivery methods. Although monogenic diseases are the logical target, cardiac arrhythmias represent a group of conditions amenable to gene therapy because of focal targets (biological pacemakers, nodal conduction, or stem cell-related arrhythmias) or bystander effects on cells not directly transduced because of electrical coupling.

METHODS

This review provides a contemporary narrative of the field of gene therapy for experimental cardiac arrhythmias, including those associated with stem cell transplant. Recent articles published in the English language and available through the PubMed database and other prominent literature are discussed.

FINDINGS

The promise of gene therapy has been realized for a handful of monogenic diseases and is actively being pursued for cardiac applications in preclinical models. With improved vectors, it is likely that cardiac disease will also benefit from this technology. Cardiac arrhythmias, whether inherited or acquired, are a group of conditions with a potentially lower threshold for phenotypic correction and as such hold unique potential as targets for cardiac gene therapy.

IMPLICATIONS

There has been a proliferation of research on the potential of gene therapy for cardiac arrhythmias. This body of investigation forms a strong basis on which further developments, particularly with viral vectors, are likely to help this technology progress along its translational trajectory.

Real-Time Closed-Loop Suppression of Repolarization Alternans Reduces Arrhythmia Susceptibility In Vivo

BACKGROUND

Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death.

METHODS

We have developed a real-time, closed-loop system to record and analyze RA from multiple intracardiac leads, and deliver dynamically R-wave triggered pacing stimuli during the absolute refractory period. We have evaluated the ability of this system to control RA and reduce arrhythmia susceptibility, in vivo.

RESULTS

R-wave triggered pacing can induce RA, the magnitude of which can be modulated by varying the amplitude, pulse width, and size of the pacing vector. Using a swine model (n=9), we demonstrate that to induce a 1 µV change in the alternans voltage on the body surface, coronary sinus and left ventricle leads, requires a delivered charge of 0.04±0.02, 0.05±0.025, and 0.06±0.033 µC, respectively, while to induce a one unit change of the K_score, requires a delivered charge of 0.93±0.73, 0.32±0.29, and 0.33±0.37 µC, respectively. For all body surface and intracardiac leads, both Δ(alternans voltage) and ΔK_score between baseline and R-wave triggered paced beats increases consistently with an increase in the pacing pulse amplitude, pulse width, and vector spacing. Additionally, we show that the proposed method can be used to suppress spontaneously occurring alternans (n=7), in the presence of myocardial ischemia. Suppression of RA by pacing during the absolute refractory period results in a significant reduction in arrhythmia susceptibility, evidenced by a lower S_rank score during programmed ventricular stimulation compared with baseline before ischemia.

CONCLUSIONS

We have developed and evaluated a novel closed-loop method to dynamically modulate RA in a swine model. Our data suggest that suppression of RA directly reduces arrhythmia susceptibility and reinforces the concept that RA plays a critical role in the pathophysiology of arrhythmogenesis.

Muscarinic receptors promote pacemaker fate at the expense of secondary conduction system tissue in zebrafish

Deterioration or inborn malformations of the cardiac conduction system (CCS) interfere with proper impulse propagation in the heart and may lead to sudden cardiac death or heart failure. Patients afflicted with arrhythmia depend on antiarrhythmic medication or invasive therapy, such as pacemaker implantation. An ideal way to treat these patients would be CCS tissue restoration. This, however, requires precise knowledge regarding the molecular mechanisms underlying CCS development. Here, we aimed to identify regulators of CCS development. We performed a compound screen in zebrafish embryos and identified tolterodine, a muscarinic receptor antagonist, as a modifier of CCS development. Tolterodine provoked a lower heart rate, pericardiac edema, and arrhythmia. Blockade of muscarinic M3, but not M2, receptors induced transcriptional changes leading to amplification of sinoatrial cells and loss of atrioventricular identity. Transcriptome data from an engineered human heart muscle model provided additional evidence for the contribution of muscarinic M3 receptors during cardiac progenitor specification and differentiation. Taken together, we found that muscarinic M3 receptors control the CCS already before the heart becomes innervated. Our data indicate that muscarinic receptors maintain a delicate balance between the developing sinoatrial node and the atrioventricular canal, which is probably required to prevent the development of arrhythmia.

Utility of a Smartphone Based System (cvrPhone) to Predict Short-term Arrhythmia Susceptibility

Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. We developed a 12-lead, blue-tooth/Smart-Phone (Android) based electrocardiogram (ECG) acquisition and monitoring system (cvrPhone), and an application to estimate RA, in real-time. In in-vivo swine studies (N = 17), 12-lead ECG signals were recorded at baseline and following coronary artery occlusion. RA was estimated using the Fast Fourier Transform (FFT) method using a custom developed algorithm in JAVA. Underlying ischemia was detected using a custom developed ischemic index. RA from each lead showed a significant (p < 0.05) increase within 1 min of occlusion compared to baseline (n = 29). Following myocardial infarction, spontaneous ventricular tachycardia episodes (n = 4) were preceded by significant (p < 0.05) increase of RA prior to the onset of the tachy-arrhythmias. Similarly, the ischemic index exhibited a significant increase following myocardial infarction (p < 0.05) and preceding a tachy-arrhythmic event. In conclusion, RA can be effectively estimated using surface lead electrocardiograms by analyzing beat-to-beat variability in ECG morphology using a smartphone based platform. cvrPhone can be used to detect myocardial ischemia and arrhythmia susceptibility using a user-friendly, clinically acceptable, mobile platform.

Gene Therapy Approaches to Biological Pacemakers

Bradycardia arising from pacemaker dysfunction can be debilitating and life threatening. Electronic pacemakers serve as effective treatment options for pacemaker dysfunction. They however present their own limitations and complications. This has motivated research into discovering more effective and innovative ways to treat pacemaker dysfunction. Gene therapy is being explored for its potential to treat various cardiac conditions including cardiac arrhythmias. Gene transfer vectors with increasing transduction efficiency and biosafety have been developed and trialed for cardiovascular disease treatment. With an improved understanding of the molecular mechanisms driving pacemaker development, several gene therapy targets have been identified to generate the phenotypic changes required to correct pacemaker dysfunction. This review will discuss the gene therapy vectors in use today along with methods for their delivery. Furthermore, it will evaluate several gene therapy strategies attempting to restore biological pacing, having the potential to emerge as viable therapies for pacemaker dysfunction.

Direct Reprograming to Regenerate Myocardium and Repair Its Pacemaker and Conduction System

The regenerative medicine field has been revolutionized by the direct conversion of one cell type to another by ectopic expression of lineage-specific transcription factors. The direct reprogramming of fibroblasts to induced cardiac myocytes (iCMs) by core cardiac transcription factors (Gata4, Mef2c, Tbx5) both in vitro and in vivo has paved the way in cardiac regeneration and repair. Several independent research groups have successfully reported the direct reprogramming of fibroblasts in injured myocardium to cardiac myocytes employing a variety of approaches that rely on transcription factors, small molecules, and micro RNAs (miRNAs). Recently, this technology has been considered for local repair of the pacemaker and the cardiac conduction system. To address this, we will first discuss the direct reprograming advancements in the setting of working myocardium regeneration, and then elaborate on how this technology can be applied to repair the cardiac pacemaker and the conduction system.

Clinical Effects of "Selective Drug" Regulating Vagus Nerve Signal Pathway in Vagally-Mediated Atrial Fibrillation

Background

The cardiac autonomic nervous system plays a crucial role in genesis and development of atrial fibrillation (AF) through the G protein signal transduction pathway. Therefore, intervening in the G protein signal transduction pathway may be a new “selective drug” method to regulate autonomic nerve activity to prevent vagally-mediated AF.

Material/Methods

Seventeen adult beagles were randomized into 3 groups: shame-operation control group (group A, n=5), empty vector gene control group (group B, n=6), and Gα_i2ctp gene experimental group (group C, n=6). Group A was injected with normal saline into the anterior atrial wall, and group B and group C animals were injected with recombinant adenovirus with empty vector or Gα_i2ctp vector in the same region. AF was induced by the method of rapid atrial pacing in groups B and C. To determine the clinical effect of vagal modulation, the effective refractory periods (ERP) and field action potential duration (FAPD) were evaluated by electrophysiological study. The expression levels of tyrosine hydroxylase (TH) and choline acetyl transferase (CHAT) in different parts were determined with immunohistochemistry.

Results

After successful Gα_i2ctp gene transfer, in group B, the ERP and FAPD significantly decreased (P<0.05), and TH and CHAT expression observably increased (P<0.05), while those differences were absent between groups A and C (P>0.05).

Conclusions

Recombinant adenovirus-mediated overexpression of Gα_i2ctp in canine myocardial cells can interfere with the activity of the vagus nerve, reverse the development and progression of electrical remodeling, and reduce the incidence of AF.

Biological therapies targeting arrhythmias: are cells and genes the answer?

INTRODUCTION

Arrhythmias can cause symptoms ranging from simple dizziness to life-threatening circulatory collapse. Current management includes medical therapy and procedures such as catheter ablation or device implantation. However, these strategies still pose a risk of serious side effects, and some patients remain symptomatic. Advancement in our understanding of how arrhythmias develop on the cellular level has made more targeted approaches possible. In addition, contemporary studies have found that several genes are involved in the pathogenesis of arrhythmias.

AREAS COVERED

In the present review, the authors explore the cellular and genetic mechanisms leading to arrhythmias as well as the progress that has been made in using both gene and cell therapy to treat tachy- and bradyarrhythmias. They also consider why gene and cell therapy has resulted into a few clinical trials with promising results, however still not applicable in routine clinical practice.

EXPERT OPINION

The question currently is whether such biological therapies could replace current established approaches. The contemporary evidence suggests that despite recent advances in this field, it will need more work in experimental models before this is applied into clinical practice. Gene and cell studies targeting conduction and repolarization are promising, but still not ready for use in the clinical setting.

Improving Atrial Fibrillation Therapy: Is There a Gene for That?

Atrial fibrillation (AF) is an all-too-common and often challenging reality of clinical care. AF leads to significant morbidity and mortality; however, currently available treatments for AF have modest efficacy and high recurrence rates. In recent years, genetic therapy approaches have been explored in preclinical models of AF, and offer potential as a treatment modality with targeted delivery, tissue specificity, and therapy tailored to address mechanisms underlying the arrhythmia. However, many challenges remain before gene therapy can advance to a clinically relevant AF treatment. In this review, we summarize the available published data on gene therapy and discuss the challenges, opportunities, and limitations of this approach.

Biological Therapies for Atrial Fibrillation: Ready for Prime Time?

Atrial fibrillation is a prominent cause of morbidity and mortality in developed countries. Treatment strategies center on controlling atrial rhythm or ventricular rate. The need for anticoagulation is an independent decision from the rate versus rhythm control debate. This review discusses novel biological strategies that have potential utility in the management of atrial fibrillation. Rate controlling strategies predominately rely on G-protein gene transfer to enhance cholinergic or suppress adrenergic signaling pathways in the atrioventricular node. Calcium channel blocking gene therapy and fibrosis enhancing cell therapy have also been reported. Rhythm controlling strategies focus on disrupting reentry by enhancing conduction or suppressing repolarization. Efforts to suppress inflammation and apoptosis are also under study. Resistance to blood clot formation has been shown with thrombomodulin. These strategies are in various stages of preclinical development.

Antiarrhythmic gene therapy - will biologics replace catheters, drugs and devices?

The clinical management of heart rhythm disorders still constitutes a major challenge. The development of alternatives to current approaches is of significant interest in order to establish more effective therapies that increase quality of life and reduce symptoms and hospitalizations. Over the past two decades the mechanistic understanding of pathophysiological pathways underlying cardiac arrhythmias has advanced profoundly, opening up novel avenues for mechanism-based therapeutic approaches. In particular, gene therapy offers greater selectivity than small molecule-based or interventional treatment. The gene of interest is packaged into viral or non-viral carriers and delivered to the target area via direct injection or using catheter-based techniques, providing the advantage of site-restricted action in contrast to systemic application of drugs. This work summarizes the current knowledge on mechanistic background, application strategies, and preclinical outcome of antiarrhythmic gene therapy for atrial fibrillation, ventricular tachycardia, and modulation of sinus node function.

The Current and Future Landscape of SERCA Gene Therapy for Heart Failure: A Clinical Perspective

Gene therapy has been applied to cardiovascular disease for over 20 years but it is the application to heart failure that has generated recent interest in clinical trials. There is laboratory and early clinical evidence that delivery of sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) gene therapy is beneficial for heart failure and this therapy could become the first positive inotrope with anti-arrhythmic properties. In this review we will discuss the rationale for SERCA2a gene therapy as a viable strategy in heart failure, review the published data, and discuss the ongoing clinical trials, before concluding with comments on the future challenges and potential for this therapy.

Gene therapy to treat cardiac arrhythmias

Gene therapy to treat electrical dysfunction of the heart is an appealing strategy because of the limited therapeutic options available to manage the most-severe cardiac arrhythmias, such as ventricular tachycardia, ventricular fibrillation, and asystole. However, cardiac genetic manipulation is challenging, given the complex mechanisms underlying arrhythmias. Nevertheless, the growing understanding of the molecular basis of these diseases, and the development of sophisticated vectors and delivery strategies, are providing researchers with adequate means to target specific genes and pathways involved in disorders of heart rhythm. Data from preclinical studies have demonstrated that gene therapy can be successfully used to modify the arrhythmogenic substrate and prevent life-threatening arrhythmias. Therefore, gene therapy might plausibly become a treatment option for patients with difficult-to-manage acquired arrhythmias and for those with inherited arrhythmias. In this Review, we summarize the preclinical studies into gene therapy for acquired and inherited arrhythmias of the atria or ventricles. We also provide an overview of the technical advances in the design of constructs and viral vectors to increase the efficiency and safety of gene therapy and to improve selective delivery to target organs.

Gene therapy to restore electrophysiological function in heart failure

INTRODUCTION

Heart failure (HF) is a major public health epidemic and a leading cause of morbidity and mortality in the industrialized world. Existing treatments for patients with HF are often associated with pro-arrhythmic activity and risk of sudden cardiac death. Therefore, development of novel, effective and safe therapeutic options for HF patients is a critical area of unmet need.

AREAS COVERED

In this article, we review recent advances in the emerging field of cardiac gene therapy for the treatment of tachy- and bradyarrhythmias in HF. We provide an overview of gene-based approaches that modulate myocardial conduction, repolarization, calcium cycling and adrenergic signaling to restore heart rate and rhythm.

EXPERT OPINION

We highlight major advantages of gene therapy for arrhythmias, including the ability to selectively target specific cell populations and to limit the therapeutic effect to the region that requires modification. We illustrate how advances in our fundamental understanding of the molecular origins of arrhythmogenic disorders are allowing investigators to use targeted gene-based approaches to successfully correct abnormal excitability in the atria, ventricles and conduction system. Translation of various gene therapy approaches to humans may revolutionize our ability to combat lethal arrhythmias in HF patients.

The Use of Gene Therapy for Ablation of Atrial Fibrillation

Atrial fibrillation is the most common clinically significant cardiac arrhythmia, increasing the risk of stroke, heart failure and morbidity and mortality. Current therapies, including rate control and rhythm control by antiarrhythmic drugs or ablation therapy, are moderately effective but far from optimal. Gene therapy has the potential to become an attractive alternative to currently available therapies for atrial fibrillation. Various gene transfer vectors have been developed for cardiovascular disease with viral vectors being most widely used due to their high efficiency. Several gene delivery methods have been employed on different therapeutic targets. With increasing understanding of arrhythmia mechanisms, novel therapeutic targets have been discovered. This review will evaluate state-of-art gene therapy strategies and approaches including sinus rhythm restoration and ventricular rate control that could eventually prevent or eliminate atrial fibrillation in patients.

Cellular unfolded protein response against viruses used in gene therapy

Viruses are excellent vehicles for gene therapy due to their natural ability to infect and deliver the cargo to specific tissues with high efficiency. Although such vectors are usually "gutted" and are replication defective, they are subjected to clearance by the host cells by immune recognition and destruction. Unfolded protein response (UPR) is a naturally evolved cyto-protective signaling pathway which is triggered due to endoplasmic reticulum (ER) stress caused by accumulation of unfolded/misfolded proteins in its lumen. The UPR signaling consists of three signaling pathways, namely PKR-like ER kinase, activating transcription factor 6, and inositol-requiring protein-1. Once activated, UPR triggers the production of ER molecular chaperones and stress response proteins to help reduce the protein load within the ER. This occurs by degradation of the misfolded proteins and ensues in the arrest of protein translation machinery. If the burden of protein load in ER is beyond its processing capacity, UPR can activate pro-apoptotic pathways or autophagy leading to cell death. Viruses are naturally evolved in hijacking the host cellular translation machinery to generate a large amount of proteins. This phenomenon disrupts ER homeostasis and leads to ER stress. Alternatively, in the case of gutted vectors used in gene therapy, the excess load of recombinant vectors administered and encountered by the cell can trigger UPR. Thus, in the context of gene therapy, UPR becomes a major roadblock that can potentially trigger inflammatory responses against the vectors and reduce the efficiency of gene transfer.

Acute and chronic observations of complete atrioventricular block in rats

The mechanisms of production, and gross, microscopic and electrocardiograhic findings of surgically-induced complete heart block (CHB) in the adult rat are presented. This is an effective in vivo model for establishing alternative methods to electronic pacemakers and for providing detailed information aimed at replacement, reduction and refinement of the technique. Sternal thoracotomy was employed to identify the epicardial fat pad by the aortic root, used as a landmark for cauterization of the atrioventricular (AV) node. Stable CHB was produced in 60 rats with a 70% survival rate. The best survival rate was observed in 8-week-old animals weighing 221 ± 27.6 g. Heart rate before cauterization was 387 ± 55 bpm, reduced after cauterization to 126 ± 40 bpm in the survival and to 65 ± 19 bpm in the non-survival groups. At 30 days findings were: elevated left ventricular end-diastolic pressure (21 ± 5.4 mmHg, P < 0.05); maximal rate of rise of left ventricular pressure (LVP) during isovolumetric contraction (2192 ± 235 mmHg/s, P < 0.05); maximal rate of decrease of LVP (-1658 ± 191 mmHg/s, P < 0.05); isovolumetric relaxation constant (5.7 ± 0.8 ms, P < 0.05) with wet-to-dry lung-weight ratio (78.1 ± 0.4, P < 0.05); heart weight/body weight (0.6 ± 0.1, P < 0.05); heart volume (1.8 ± 0.3 mL, P < 0.05); longitudinal diameter (20.2 ± 1.91 mm, P < 0.05); and transversal diameter (17.0 ± 1.4 mm, P < 0.05) with supported dilated cardiomyopathy which culminated in chronic heart failure. CHB hearts had increased preload and replacement of myofibrils by collagen. CHB was achieved reproducibly by cauterization of the rat AV node and/or His bundle. This led to electrophysiological, hemodynamic, and structural remodeling, and could be useful in long-term cardiac remodeling assessments and potential therapy development.

Gene transfer for congestive heart failure: update 2013

Congestive heart failure is a major cause of morbidity and mortality with increasing social and economic costs. There have been no new high impact therapeutic agents for this devastating disease for more than a decade. However, many pivotal regulators of cardiac function have been identified using cardiac-directed transgene expression and gene deletion in preclinical studies. Some of these increase function of the failing heart. Altering the expression of these pivotal regulators using gene transfer is now either being tested in clinical gene transfer trials, or soon will be. In this review, we summarize recent progress in cardiac gene transfer for clinical congestive heart failure.

Cell and gene therapy for arrhythmias: Repair of cardiac conduction damage

Action potentials generated in the sinoatrial node (SAN) dominate the rhythm and rate of a healthy human heart. Subsequently, these action potentials propagate to the whole heart via its conduction system. Abnormalities of impulse generation and/or propagation in a heart can cause arrhythmias. For example, SAN dysfunction or conduction block of the atrioventricular node can lead to serious bradycardia which is currently treated with an implanted electronic pacemaker. On the other hand, conduction damage may cause reentrant tachyarrhythmias which are primarily treated pharmacologically or by medical device-based therapies, including defibrillation and tissue ablation. However, drug therapies sometimes may not be effective or are associated with serious side effects. Device-based therapies for cardiac arrhythmias, even with well developed technology, still face inadequacies, limitations, hardware complications, and other challenges. Therefore, scientists are actively seeking other alternatives for antiarrhythmic therapy. In particular, cells and genes used for repairing cardiac conduction damage/defect have been investigated in various studies both in vitro and in vivo. Despite the complexities of the excitation and conduction systems of the heart, cell and gene-based strategies provide novel alternatives for treatment or cure of cardiac arrhythmias. This review summarizes some highlights of recent research progress in this field.

Comparison of adeno-associated virus serotypes and delivery methods for cardiac gene transfer

Cardiac gene transfer is a potentially useful strategy for cardiovascular diseases. The adeno-associated virus (AAV) is a common vector to obtain transgene expression in the heart. Initial studies conducted in rodents used indirect intracoronary delivery for cardiac gene transfer. More recently AAV vectors with so-called cardiac tropism have enabled significant cardiac transgene expression following intravenous injection. However, a direct comparison of intravenous versus intracoronary delivery with rigorous quantification of cardiac transgene expression has not been conducted. In the present study we tested the hypothesis that intracoronary AAV delivery would be superior to intravenous delivery vis-à-vis cardiac transgene expression. We compared intravenous and intracoronary delivery of AAV5, AAV6, and AAV9 (5×10(11) genome copies per mouse). Using enhanced green fluorescent protein as a reporter, we quantified transgene expression by fluorescence intensity and Western blotting. Quantitative polymerase chain reaction (PCR) was also performed to assess vector DNA copies, employing primers against common sequences on AAV5, AAV6, and AAV9. Intracoronary delivery resulted in 2.6- to 28-fold higher transgene protein expression in the heart 3 weeks after AAV injection compared to intravenous delivery depending on AAV serotype. The highest level of cardiac gene expression was achieved following intracoronary delivery of AAV9. Intracoronary delivery of AAV9 is a preferred method for cardiac gene transfer.

Biological Heart Rate Reduction Through Genetic Suppression of Gα(s) Protein in the Sinoatrial Node

BACKGROUND

Elevated heart rate represents an independent risk factor for cardiovascular outcome in patients with heart disease. In the sinoatrial node, rate increase is mediated by β(1) adrenoceptor mediated activation of the Gα(s) pathway. We hypothesized that genetic inactivation of the stimulatory Gα(s) protein in the sinoatrial node would provide sinus rate control and would prevent inappropriate heart rate acceleration during β-adrenergic activation.

METHODS AND RESULTS

Domestic pigs (n=10) were evenly assigned to receive either Ad-small interfering RNA (siRNA)-Gα(s) gene therapy to inactivate Gα(s) or adenovirus encoding for green fluorescent protein (Ad-GFP) as control. Adenoviruses were applied through virus injection into the sinoatrial node followed by epicardial electroporation, and heart rates were evaluated for 7 days. Genetic inhibition of Gα(s) protein significantly reduced mean heart rates on day 7 by 16.5% compared with control animals (110±8.8 vs 131±9.4 beats per minute; P<0.01). On β-adrenergic stimulation with isoproterenol, we observed a tendency toward diminished rate response in the Ad-siRNA-Gα(s) group (Ad-siRNA-Gα(s), +79.3%; Ad-GFP, +61.7%; n=3 animals per group; P= 0.294). Adverse effects of gene transfer on left ventricular ejection fraction (LVEF) were not detected following treatment (LVEF(Ad-siRNA-Gαs), 66%; LVEF(Ad-GFP), 60%).

CONCLUSIONS

In this preclinical proof-of-concept study targeted Ad-siRNA-Gα(s) gene therapy reduced heart rates during normal sinus rhythm compared with Ad-GFP treatment and prevented inappropriate rate increase after β-adrenergic stimulation. Gene therapy may provide an additional therapeutic option for heart rate reduction in cardiac disease. (J Am Heart Assoc. 2012;1:jah3-e000372 doi: 10.1161/JAHA.111.000372).

Effects of sterol regulatory element-binding protein (SREBP) in chickens

Sterol regulatory element binding protein- 1 and -2 (SREBP-1 and -2) are key transcription factors involved in the biosynthesis of cholesterol and fatty acids. The SREBP have mostly been studied in rodents in which lipogenesis is regulated in both liver and adipose tissue. There is, though, a paucity of information on birds, in which lipogenesis occurs essentially in the liver as in humans. Since a prelude to the investigation of the role of SREBP in lipid metabolism regulation in chicken, we review Size and Tissue expression Pattern of SREBP and role of this protein in chickens.

Cardiac gene therapy in large animals: bridge from bench to bedside

Several clinical trials are evaluating gene transfer as a therapeutic approach to treat cardiac diseases. Although it has just started on the path to clinical application, recent advances in gene delivery technologies with increasing knowledge of underlying mechanisms raise great expectations for the cardiac gene therapy. Although in vivo experiments using small animals provide the therapeutic potential of gene transfer, there exist many fundamental differences between the small animal and the human hearts. Before applying the therapy to clinical patients, large animal studies are a prerequisite to validate the efficacy in an animal model more relevant to the human heart. Several key factors including vector type, injected dose, delivery method and targeted cardiac disease are all important factors that determine the therapeutic efficacy. Selecting the most optimal combination of these factors is essential for successful gene therapy. In addition to the efficacy, safety profiles need to be addressed as well. In this regard, large animal studies are best suited for comprehensive evaluation at the preclinical stages of therapeutic development to ensure safe and effective gene transfer. As the cardiac gene therapy expands its potential, large animal studies will become more important to bridge the bench side knowledge to the clinical arena.

The genetics of atrial fibrillation: from the bench to the bedside

Atrial fibrillation (AF) has become a growing global epidemic and a financial burden for society. The past 10 years have seen significant advances in our understanding of the genetic aspects of AF: At least 2 chromosomal loci and 17 causal genes have been identified in familial AF, and an additional 7 common variants and single-nucleotide polymorphisms in 11 different genes have been indicated in nonfamilial AF. However, the current management strategies for AF are suboptimal. The integration of genetic information into clinical practice may aid the early identification of AF patients who are at risk as well as the characterization of molecular pathways that culminate in AF, with the eventual result of better treatment. Never before has such an opportunity arisen to advance our understanding of the biology of AF through the translation of genetics findings from the bench to the bedside.

Genetic suppression of atrial fibrillation using a dominant-negative ether-a-go-go-related gene mutant

BACKGROUND

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Gene therapy-dependent modulation of atrial electrophysiology may provide a more specific alternative to pharmacological and ablative treatment strategies.

OBJECTIVE

We hypothesized that genetic inactivation of atrial repolarizing ether-a-go-go-related gene (ERG) K(+) currents using a dominant-negative mutant would provide rhythm control in AF.

METHODS

Ten domestic swine underwent pacemaker implantation and were subjected to atrial burst pacing to induce persistent AF. Animals were then randomized to receive either AdCERG-G627S to suppress ERG/I(Kr) currents or green fluorescent protein (AdGFP) as control. Adenoviruses were applied using a novel hybrid technique combining atrial virus injection and epicardial electroporation to increase transgene expression.

RESULTS

In pigs treated with AdCERG-G627S, the onset of persistent AF was prevented (n = 2) or significantly delayed compared with AdGFP controls (12 ± 2.1 vs. 6.2 ± 1.3 days; P < .001) during 14-day follow-up. Effective refractory periods were prolonged in the AdCERG-G627S group compared with AdGFP animals (221.5 ± 4.7 ms vs. 197.0 ± 4.7 ms; P < .006). Impairment of left ventricular ejection fraction (LVEF) during AF was prevented by AdCERG-G627S application (LVEF(CERG-G627S) = 62.1% ± 4.0% vs. LVEF(GFP) = 30.3% ± 9.1%; P < .001).

CONCLUSION

Inhibition of ERG function using atrial AdCERG-G627S gene transfer suppresses or delays the onset of persistent AF by prolongation of atrial refractoriness in a porcine model. Targeted gene therapy represents an alternative to pharmacological or ablative treatment of AF.

Targeted nonviral gene-based inhibition of Gα(i/o)-mediated vagal signaling in the posterior left atrium decreases vagal-induced atrial fibrillation

BACKGROUND

Pharmacologic and ablative therapies for atrial fibrillation (AF) have suboptimal efficacy. Newer gene-based approaches that target specific mechanisms underlying AF are likely to be more efficacious in treating AF. Parasympathetic signaling appears to be an important contributor to AF substrate.

OBJECTIVE

The purpose of this study was to develop a nonviral gene-based strategy to selectively inhibit vagal signaling in the left atrium and thereby suppress vagal-induced AF.

METHODS

In eight dogs, plasmid DNA vectors (minigenes) expressing Gα(i) C-terminal peptide (Gα(i)ctp) was injected in the posterior left atrium either alone or in combination with minigene expressing Gα(o)ctp, followed by electroporation. In five control dogs, minigene expressing scrambled peptide (Gα(R)ctp) was injected. Vagal- and carbachol-induced left atrial effective refractory periods (ERPs), AF inducibility, and Gα(i/o)ctp expression were assessed 3 days following minigene delivery.

RESULTS

Vagal stimulation- and carbachol-induced effective refractory period shortening and AF inducibility were significantly attenuated in atria receiving a Gα(i2)ctp-expressing minigene and were nearly eliminated in atria receiving both Gα(i2)ctp- and Gα(o1)ctp-expressing minigenes.

CONCLUSION

Inhibition of both G(i) and G(o) proteins is necessary to abrogate vagal-induced AF in the left atrium and can be achieved via constitutive expression of Gα(i/o)ctps expressed by nonviral plasmid vectors delivered to the posterior left atrium.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

The pathology and treatment of cardiac arrhythmias: focus on atrial fibrillation

Atrial fibrillation (AF) is the most frequently encountered sustained cardiac arrhythmia in clinical practice and a major cause of morbidity and mortality. Effective treatment of AF still remains an unmet medical need. Treatment of AF is based on drug therapy and ablative strategies. Antiarrhythmic drug therapy is limited by a relatively high recurrence rate and proarrhythmic side effects. Catheter ablation suppresses paroxysmal AF in the majority of patients without structural heart disease but is more difficult to achieve in patients with persistent AF or with concomitant cardiac disease. Stroke is a potentially devastating complication of AF, requiring anticoagulation that harbors the risk of bleeding. In search of novel treatment modalities, targeted pharmacological treatment and gene therapy offer the potential for greater selectivity than conventional small-molecule or interventional approaches. This paper summarizes the current understanding of molecular mechanisms underlying AF. Established drug therapy and interventional treatment of AF is reviewed, and emerging clinical and experimental therapeutic approaches are highlighted.

Randomized transcoronary delivery of CD34(+) cells with perfusion versus stop-flow method in patients with recent myocardial infarction: Early cardiac retention of ⁹⁹(m)Tc-labeled cells activity

BACKGROUND

For transcoronary progenitor cells' administration, injections under flow arrest (over-the-wire balloon technique, OTW) are used universally despite lack of evidence for being required for cell delivery or being effective in stimulating myocardial engraftment. Flow-mediated endothelial rolling is mandatory for subsequent cell adhesion and extravasation.

METHODS

To optimize cell directing toward the coronary endothelium under maintained flow, the authors developed a cell-delivery side-holed perfusion catheter (PC). Thirty-four patients (36-69 years, 30 men) with primary stent-assisted angioplasty-treated anterior MI (peak TnI 151 [53-356]ng/dL, mean[range]) were randomly assigned to OTW or PC autologous ⁹⁹Tc-extametazime-labeled bone marrow CD34(+) cells (4.34 [0.92-7.54] × 10⁶) administration at 6-14 days after pPCI (LVEF 37.1 [24-44]%). Myocardial perfusion (⁹⁹(m)Tc-MIBI) and labeled cells' activity were evaluated (SPECT) at, respectively, 36-48 h prior to and 60 min after delivery.

RESULTS

In contrast to OTW coronary occlusions, no intolerance or ventricular arrhythmia occurred with PC cells' administration (P < .001). One hour after delivery, 4.86 [1.7-7.6]% and 5.05 [2.2-9.9]% activity was detected in the myocardium (OTW and PC, respectively, P = .84). Labeled cell activity was clearly limited to the (viable) peri-infarct zone in 88% patients, indicating that the infarct core zone may be largely inaccessible to transcoronary-administered cells.

CONCLUSIONS

Irrespective of the transcoronary delivery method, only ≈ 5% of native (i.e., non-engineered) CD34(+) cells spontaneously home to the injured myocardium, and cell retention occurs preferentially in the viable peri-infarct zone. Although the efficacy of cell delivery is not increased with the perfusion method, by avoiding provoking ischemic episodes PC offers a rational alternative to the OTW delivery.

Regenerative therapies in electrophysiology and pacing: introducing the next steps

The morbidity and mortality of cardiac arrhythmias are major international health concerns. Drug and device therapies have made inroads but alternative approaches are still being sought. For example, gene and cell therapies have been explored for treatment of brady- and tachyarrhythmias, and proof of concept has been obtained for both biological pacing in the setting of heart block and gene therapy for ventricular tachycardias. This paper reviews the state of the art developments with regard to gene and cell therapies for cardiac arrhythmias and discusses next steps.