Adenovirus-mediated genetic manipulation of the myocardial beta-adrenergic signaling system in transplanted hearts

Graft preservation in heart transplantation: current approaches

Heart transplantation (HTx) represents the current best surgical treatment for patients affected by end-stage heart failure. However, with the improvement of medical and interventional therapies, the population of HTx candidates is increasingly old and at high-risk for mortality and complications. Moreover, the use of "extended donor criteria" to deal with the shortage of donors could increase the risk of worse outcomes after HTx. In this setting, the strategy of donor organ preservation could significantly affect HTx results. The most widely used technique for donor organ preservation is static cold storage in ice. New techniques that are clinically being used for donor heart preservation include static controlled hypothermia and machine perfusion (MP) systems. Controlled hypothermia allows for a monitored cold storage between 4°C and 8°C. This simple technique seems to better preserve the donor heart when compared to ice, probably avoiding tissue injury due to sub-zero °C temperatures. MP platforms are divided in normothermic and hypothermic, and continuously perfuse the donor heart, reducing ischemic time, a well-known independent risk factor for mortality after HTx. Also, normothermic MP permits to evaluate marginal donor grafts, and could represent a safe and effective technique to expand the available donor pool. However, despite the increasing number of donor hearts preserved with these new approaches, whether these techniques could be considered superior to traditional CS still represents a matter of debate. The aim of this review is to summarize and critically assess the available clinical data on donor heart preservation strategies employed for HTx.

A normothermic ex vivo organ perfusion delivery method for cardiac transplantation gene therapy

Clinically, both percutaneous and surgical approaches to deliver viral vectors to the heart either have resulted in therapeutically inadequate levels of transgene expression or have raised safety concerns associated with extra-cardiac delivery. Recent developments in the field of normothermic ex vivo cardiac perfusion storage have now created opportunities to overcome these limitations and safety concerns of cardiac gene therapy. This study examined the feasibility of ex vivo perfusion as an approach to deliver a viral vector to a donor heart during storage and the resulting bio distribution and expression levels of the transgene in the recipient post-transplant. The influence of components (proprietary solution, donor blood, and ex vivo circuitry tubing and oxygenators) of the Organ Care System (OC) (TransMedics, Inc., Andover MA) on viral vector transduction was examined using a cell-based luciferase assay. Our ex vivo perfusion strategy, optimized for efficient Adenoviral vector transduction, was utilized to deliver 5 × 10¹³ total viral particles of an Adenoviral firefly luciferase vector with a cytomegalovirus (CMV) promotor to porcine donor hearts prior to heterotopic implantation. We have evaluated the overall levels of expression, protein activity, as well as the bio distribution of the firefly luciferase protein in a series of three heart transplants at a five-day post-transplant endpoint. The perfusion solution and the ex vivo circuitry did not influence viral vector transduction, but the serum or plasma fractions of the donor blood significantly inhibited viral vector transduction. Thus, subsequent gene delivery experiments to the explanted porcine heart utilized an autologous blood recovery approach to remove undesired plasma or serum components of the donor blood prior to its placement into the circuit. Enzymatic assessment of luciferase activity in tissues (native heart, allograft, liver etc.) obtained post-transplant day five revealed wide-spread and robust luciferase activity in all regions of the allograft (right and left atria, right and left ventricles, coronary arteries) compared to the native recipient heart. Importantly, luciferase activity in recipient heart, liver, lung, spleen, or psoas muscle was within background levels. Similar to luciferase activity, the luciferase protein expression in the allograft appeared uniform and robust across all areas of the myocardium as well as in the coronary arteries. Importantly, despite high copy number of vector genomic DNA in transplanted heart tissue, there was no evidence of vector DNA in either the recipient’s native heart or liver. Overall we demonstrate a simple protocol to achieve substantial, global gene delivery and expression isolated to the cardiac allograft. This introduces a novel method of viral vector delivery that opens the opportunity for biological modification of the allograft prior to implantation that may improve post-transplant outcomes.

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.

Current strategies for myocardial gene delivery

Existing methods of cardiac gene delivery can be classified by the site of injection, interventional approach and type of cardiac circulation at the time of transfer. General criteria to assess the efficacy of a given delivery method include: global versus regional myocardial transduction, technical complexity and the pathophysiological effects associated with its use, delivery-related collateral expression and the delivery-associated inflammatory and immune response. Direct gene delivery (intramyocardial, endocardial, epicardial) may be useful for therapeutic angiogenesis and for focal arrhythmia therapy but with gene expression which is primarily limited to regions in close proximity to the injection site. An often unappreciated limitation of these techniques is that they are frequently associated with substantial systemic vector delivery. Percutaneous infusion of vector into the coronary arteries is minimally invasive and allows for transgene delivery to the whole myocardium. Unfortunately, efficiency of intracoronary delivery is highly variable and the short residence time of vector within the coronary circulation and significant collateral organ expression limit its clinical potential. Surgical techniques, including the incorporation of cardiopulmonary bypass with isolated cardiac recirculation, represent novel delivery strategies that may potentially overcome these limitations; yet, these techniques are complex with inherent morbidity that must be thoroughly evaluated before safe translation into clinical practice. Characteristics of the optimal technique for gene delivery include low morbidity, increased myocardial transcapillary gradient, extended vector residence time in the coronary circulation and exclusion of residual vector from the systemic circulation after delivery to minimize extracardiac expression and to mitigate a cellular immune response. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Cardiac gene therapy: optimization of gene delivery techniques in vivo

Vector-mediated cardiac gene therapy holds tremendous promise as a translatable platform technology for treating many cardiovascular diseases. The ideal technique is one that is efficient and practical, allowing for global cardiac gene expression, while minimizing collateral expression in other organs. Here we survey the available in vivo vector-mediated cardiac gene delivery methods--including transcutaneous, intravascular, intramuscular, and cardiopulmonary bypass techniques--with consideration of the relative merits and deficiencies of each. Review of available techniques suggests that an optimal method for vector-mediated gene delivery to the large animal myocardium would ideally employ retrograde and/or anterograde transcoronary gene delivery,extended vector residence time in the coronary circulation, an increased myocardial transcapillary gradient using physical methods, increased endothelial permeability with pharmacological agents, minimal collateral gene expression by isolation of the cardiac circulation from the systemic, and have low immunogenicity.

Modulation of phosphatidylinositol 3-kinase signaling reduces intimal hyperplasia in aortocoronary saphenous vein grafts

OBJECTIVES

Fifty percent of human aortocoronary saphenous vein grafts are occluded after 10 years. Intimal hyperplasia is an initial step in graft occlusion and consists of vascular smooth muscle cell proliferation. Phosphatidylinositol 3-kinase and its downstream regulator, the inositol 3-phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10), are important regulators of vascular smooth muscle cell proliferation, migration, and cell death. This study tests whether overexpression of PTEN in aortocoronary saphenous vein grafts can reduce intimal hyperplasia.

METHODS

Adult dogs underwent aortocoronary bypass grafting to the left anterior descending artery by using the autologous saphenous vein. Saphenous vein grafts were treated with phosphate-buffered saline (n = 9), empty adenovirus (n = 8), or adenovirus encoding for PTEN (n = 8). Arteriography at 30 and 90 days assessed saphenous vein graft patency. A subset received saphenous vein grafts treated with a marker transgene (beta-galactosidase, n = 3), empty adenovirus (n = 4), or adenovirus encoding for PTEN (n = 4) and were killed on postoperative day 3 to confirm expression. Vascular smooth muscle cells were isolated from canine saphenous vein infected with adenovirus encoding for PTEN, and immunoblotting and proliferation assays were performed.

RESULTS

Saphenous vein graft transgene expression was confirmed by means of immunohistochemistry, immunoblotting, and polymerase chain reaction. Arteriograms revealed all saphenous vein grafts to be patent. Saphenous vein grafts treated with adenovirus encoding for PTEN demonstrated reduced intimal area compared with those treated with empty adenovirus and phosphate-buffered saline (1.39 +/- 0.11 vs 2.35 +/- 0.3 and 2.57 +/- 0.4 mm 2 , P < .05), and the intima/media ratio was lower in saphenous vein grafts treated with adenovirus encoding for PTEN (0.50 +/- 0.05 vs 1.43 +/- 0.18 and 1.11 +/- 0.14, P < .005). PTEN overexpression in vascular smooth muscle cells inhibited platelet-derived growth factor-induced phosphorylation of Akt, a downstream effector of phosphatidylinositol 3-kinase. PTEN-treated vascular smooth muscle cells demonstrated decreased basal, platelet-derived growth factor-stimulated, and serum-stimulated proliferation.

CONCLUSION

This study demonstrates that PTEN overexpression in aortocoronary saphenous vein grafts reduces intimal hyperplasia. The mechanism of this antiproliferative effect in vascular smooth muscle cells is likely due to inhibition of phosphatidylinositol 3-kinase signaling through Akt, with resultant decreases in vascular smooth muscle cell growth and survival. Therefore modulation of the phosphatidylinositol 3-kinase pathway through PTEN overexpression might represent a novel therapy to prevent saphenous vein graft intimal hyperplasia after coronary artery bypass grafting.

Gene delivery approaches to heart failure treatment

Heart failure remains a leading cause of worldwide morbidity and mortality. Despite recent advances in treatment and our increasing knowledge of pathophysiology and the molecular derangements involved in the failing heart, our ability to affect the underlying cardiac disease processes is limited. In recent years, there has been considerable interest in myocardial gene transfer as both an investigational and potential therapeutic modality. Ultimately, the goal of any such strategy is to reprogramme failing cardiac myocytes and correct the aberrant molecular events causing heart failure. So far, viral vectors have been utilised with success more frequently than any other method of gene delivery in animal models. Studies in animal models and in failing human cardiomyocytes in culture targeting specific molecular pathways, including the beta-adrenergic receptor cascade and the myocyte intracellular calcium handling system, have shown encouraging results and offer hope that gene manipulation may provide novel adjunctive therapeutic modalities for human heart failure.

Viral-based myocardial gene therapy approaches to alter cardiac function

In recent years there has been a rapid expansion in our understanding of the molecular biology that underpins human physiology. In the heart, elegant molecular pathways have been elucidated, and derangements in these pathways have been identified as factors in cardiac disease. However, as our understanding has grown, we have recognized that there exist only relatively crude tools to effect changes in molecular pathophysiology. The ultimate promise of gene therapy is to correct the molecular derangements that cause illness. To bring this promise to fruition in the clinical arena, many problems need to be solved, and chief among these remains reliable and robust delivery of genes to the target organ. To this end, viral vectors have been utilized with success more frequently than any other method of gene delivery. The use of these vectors in the heart has already offered promising novel benefit for human ischemic heart disease, and studies in animal models have given glimpses of hope that gene therapy may provide future therapeutic benefit in heart failure by improving cardiac function.

Ventricular Assist Devices as a Bridge to Transplant or Recovery

Ventricular assist devices have emerged as the standard of care in treating end-stage heart failure. Their success in bridging patients to transplantation is well documented. The data supporting their ability to bridge patients to recovery is sparser. However, as technology continues to advance, these devices will offer a high quality of life both in and out of the hospital setting, making them options for a broader spectrum of heart failure patients.

Robust adenoviral and adeno-associated viral gene transfer to the in vivo murine heart: application to study of phospholamban physiology

BACKGROUND

Viral gene transfer to the whole heart in vivo has been achieved in several mammalian species but remained difficult to accomplish in murine hearts. We postulated that a key impediment derives from the use of proximal aortic occlusion during virus injection, because this eliminates coronary perfusion gradients in mice as aortic root and left ventricle pressures equalize.

METHODS AND RESULTS

Pressure-volume analysis confirmed these mechanics. In contrast, descending aortic occlusion with whole-body cooling (20 degrees C) preserved transmyocardial perfusion gradients and allowed for sustained (>10-minute) dwell times in an upper-body perfusion circuit. This approach yielded robust cardiac transfection with adenovirus (AdV) and adeno-associated virus (AAV) injected into the left ventricle cavity or more simply via a central vein. Cardio-specific expression was achieved with a myocyte-specific promotor. Optimal AdV transfection required 9-minute aortic occlusion, versus 5-minute occlusion for AAV. Using this method, we examined the in vivo function of phospholamban (PLB) by stably transfecting PLB-null mice with AAV encoding PLB (AAV(PLB)). AAV(PLB) restored PLB protein to near control levels that colocalized with SERCA2A in cardiomyocytes. At baseline, PLB-null hearts exhibited enhanced systolic and diastolic function, but frequency-dependent reserve was blunted versus wild-type controls. These properties, particularly the frequency response, returned toward control 3 months after AAV(PLB) transfection.

CONCLUSIONS

The new simplified approach for murine whole-heart viral transfection should assist molecular physiology studies.

Molecular mechanisms of reduced beta-adrenergic signaling in the aged heart as revealed by genomic profiling

Myocardial aging leads to a reduction of beta-adrenergic receptor-induced metabolic and contractile responsiveness. We hypothesize that a change in the patterns of gene expression is important in these age-related events. To test this, hearts were harvested from young and aged male rats (3-4 and 20-22 mo, respectively). Total mRNA was extracted and prepared for hybridization to Affymetrix U34A GeneChips. Filtering criteria, involving fold change and a statistical significance cutoff were employed, yielding 263 probe pairs exhibiting differential signals. Of the 163 annotated genes, at least 56 (34%) were classified as signaling/cell communication. Of these 56, approximately half were directly involved in G protein-coupled receptor signaling pathways. We next determined which of these changes might be involved in anti-adrenergic activity and identified 19 potentially important gene products. Importantly, we observed a decrease in beta1-adrenergic receptor and adenylyl cyclase mRNAs, whereas the mRNA encoding beta-arrestin increased. Furthermore, the results demonstrate an increase in mRNAs encoding the adenosine A1 receptor and phospholipase D, which could increase anti-adrenergic effects. Moreover, the mRNAs encoding the muscarinic M3 receptor, nicotinic acetylcholine receptor beta3, and nicotinic acetylcholine receptor-related protein were increased as was the mRNA encoding guanylate kinase-associated protein. Interestingly, we also observed eight mRNAs whose abundance changed three- to sixfold with aging that could be considered as being compensatory. Although these results do not prove causality, they demonstrate that cardiac aging is associated with changes in the profiles of gene expression and that many of these changes may contribute to reduced adrenergic signaling.

Gene interventions in the beta-adrenergic system for treating heart failure

Cardiovascular disease accounts for nearly 40% of all deaths annually in this country. Prevention management and advances in medical treatments have dramatically reduced the overall mortality rate due to heart disease. However, death due to chronic heart failure (HF) continues to rise, and effective therapy, particularly for end-stage HF, has been elusive. The myocardial beta-adrenergic receptor (betaAR) system is critical not only in chronic HF but also in acute settings where cardiac function is compromised. Adding to its importance is the fact that drugs that act by altering betaAR signal transduction are at the forefront of conventional HF therapeutic strategies. Accordingly, the ability to genetically manipulate betaAR signaling in the heart is of great interest since it may provide unique inotropic support and improve existing therapeutic strategies for HF.

Heterotopic transplantation as a model to study functional recovery of unloaded failing hearts

OBJECTIVES

Recent studies have demonstrated cardiac improvement in patients supported with a ventricular assist device, suggesting that reverse remodeling and myocardial recovery are possible. We developed an animal model of cardiac unloading by adapting a heterotopic transplantation technique and used it to examine the pattern of functional recovery in the left ventricle of the failing heart.

METHODS

Heart failure was induced in adult New Zealand rabbits by coronary artery ligation with subsequent myocardial infarction. Animals undergoing sham operation served as a control group. After 4 weeks or 3 months, failing hearts were transplanted into the necks of recipient rabbits. A left ventricular latex balloon connected to subcutaneous tubing allowed repeated physiologic analysis on days 1 and after transplantation and then every 5 days until day 30.

RESULTS

Contractility (left ventricular dP/dt(max)) and relaxation (left ventricular dP/dt(min)) were significantly lower in transplanted postinfarction hearts as compared to control hearts immediately after transplantation. Both left ventricular dP/dt(max) and left ventricular dP/dt(min) responses to increased preload and to beta-adrenergic stimulation progressively improved to a significantly higher level after 30 days of left ventricular unloading for the hearts that were transplanted 4 weeks after myocardial infarction. However, this functional improvement was not detected in failing hearts transplanted 3 months after infarction.

CONCLUSIONS

This model of cardiac unloading appears at least partially to mimic conditions of ventricular assist devices. If performed early in the development of heart failure, it permits improvement of contractile dysfunction and restoration of cardiac responsiveness to mechanical and beta-adrenergic stimulation. Therefore this model may constitute a novel alternative in the study of reverse remodeling in unloaded failing hearts.

Myocardial gene transfer and overexpression of beta2-adrenergic receptors potentiates the functional recovery of unloaded failing hearts

BACKGROUND

Mechanical assistance of the failing left ventricle (LV) can lead to functional recovery after a period of unloading, including restoration of beta-adrenergic receptor (betaAR) inotropic reserve. We tested whether prolonged LV unloading of failing rabbit hearts by use of a heterotopic transplantation technique could lead to recovery and whether adenoviral gene transfer of a beta2AR transgene (Adv-beta2AR) could alter this process.

METHODS AND RESULTS

Heart failure was induced by coronary artery ligation in adult New Zealand White rabbits. After 4 weeks, failing hearts were heterotopically transplanted into recipient rabbits, allowing normal coronary perfusion but complete LV unloading. We also placed an LV latex balloon for remote access and in vivo physiological analysis. We found that there was reversal of signaling and functional abnormalities after 30 days of unloading. In another set of failing hearts, we randomly delivered, at the time of transplantation, either 2x10(11) viral particles of Adv-beta2AR or saline via the coronary arteries. Sham-operated animals with nonfailing hearts served as controls. After 5 days of unloading, in vivo LV contractility (LV dP/dt(max)) and relaxation (LV dP/dt(min)) were significantly decreased in saline-treated failing hearts compared with control nonfailing hearts (P<0.05). In failing hearts treated with Adv-beta2AR, however, LV dP/dt(max) and LV dP/dt(min) were improved in response to higher preloads (P<0.05) and betaAR stimulation (P<0.01).

CONCLUSIONS

Heterotopic transplantation in the rabbit does allow recovery of the failing heart, and beta2AR overexpression acutely enhances this functional improvement. Accordingly, genetic manipulation of betaAR signaling may represent a novel molecular adjunct to mechanical assistance to facilitate functional myocardial recovery.

Ventricular dysfunction after cardioplegic arrest is improved after myocardial gene transfer of a beta-adrenergic receptor kinase inhibitor

BACKGROUND

Acute cardiac contractile dysfunction is common after cardiopulmonary bypass (CPB). A potential molecular mechanism is enhanced beta-adrenergic receptor kinase (betaARK1) activity, because beta-adrenergic receptor (betaAR) signaling is altered in cardiomyocytes after cardioplegia. Therefore, we examined whether adenovirus-mediated intracoronary delivery of a betaARK1 inhibitor (Adv-betaARKct) could prevent post-CPB dysfunction.

METHODS AND RESULTS

Rabbits were randomized to receive 5x10(11) total viral particles of Adv-betaARKct or PBS. After 5 days, hearts were arrested with University of Wisconsin solution, excised, and stored at 4 degrees C for 15 minutes or 4 hours before reperfusion on a Langendorff apparatus. Left ventricular (LV) function measured by end-diastolic pressure response to preload augmentation, contractility (LV dP/dt(max)), and relaxation (LV dP/dt(min)) was assessed by use of increasing doses of isoproterenol and compared with a control group of nonarrested hearts acutely perfused on the Langendorff apparatus. In the PBS-treated hearts, LV function decreased in a temporal manner and was significantly impaired compared with control hearts after 4 hours of cardioplegic arrest. LV function in Adv-betaARKct-treated hearts, however, was significantly enhanced compared with PBS treatment and was similar to control nonarrested hearts even after 4 hours of cardioplegia. Biochemically, several aspects of betaAR signaling were dysfunctional in PBS-treated hearts, whereas they were normalized in betaARKct-overexpressing hearts.

CONCLUSIONS

Myocardial gene transfer of Adv-betaARKct stabilizes betaAR signaling and prevents LV dysfunction induced by prolonged cardioplegic arrest. Thus, betaARK1 inhibition may represent a novel target in limiting depressed ventricular function after CPB.

Modification of the beta 2-adrenergic receptor to engineer a receptor-effector complex for gene therapy

Depressed G-protein-coupled receptor (GPCR) signaling has been implicated as a component of the pathophysiology of a number of complex diseases including heart failure and asthma, and augmentation or restoration of signaling by various means has been shown to improve organ function. Because some properties of native GPCRs are disadvantageous for ectopic therapeutic expression, we utilized the beta(2)-adrenergic receptor (beta(2)AR) as a scaffold to construct a highly modified therapeutic receptor-effector complex (TREC) suitable for gene therapy. Altogether, 19 modifications were made to the receptor. The ligand-binding site was re-engineered in TM-3 so that a beta-hydroxylmethyl side chain acts as a proton donor for the binding of a novel ligand. In addition, sites critical for agonist-promoted down-regulation in the amino terminus and for phosphorylation by GPCR kinases, and protein kinases A and C, in the third intracellular loop and the carboxyl terminus of the receptor were altered. These modifications of the receptor resulted in depressed agonist-stimulated adenylyl cyclase activity (26.8 +/- 2.1 versus 41.4 +/- 8 pmol/min/mg for wild-type beta(2)AR). This was fully restored by fusing the carboxyl terminus of the modified receptor to G alpha(s) (43.3 +/- 2.7 pmol/min/mg). The fully modified fused receptor was not activated by beta-agonists but rather by a nonbiogenic amine agonist that itself failed to activate the wild-type beta(2)AR. This two-way selectivity thus provides targeted activation based on physiologic status. Furthermore, the TREC did not display tachyphylaxis to prolonged agonist exposure (desensitization was 1 +/- 5% versus 55 +/- 4% for wild-type beta(2)AR). Thus, despite extensive alterations in regions of conformational lability, the beta(2)AR can be tailored to have optimal signaling characteristics for gene therapy. As a general paradigm, TRECs for enhancement of other G-protein signaling appear to be feasible for modification of other pathologic states.

Myocardial gene transfer

Recent improvements in both gene transfer vectors and in vivo gene delivery techniques have facilitated genetic manipulation of myocardial function and enabled targeted therapy of animal models of cardiac disease and, in particular, heart failure. Increases in myocardial perfusion, improved calcium handling, and enhanced beta-adrenergic receptor signaling have all been achieved by gene transfer in animal models, and appear to be important determinants of myocardial function. Increased understanding of the molecular etiologies of myocardial disease processes combined with advances in vectors and gene delivery will facilitate the development of novel therapies and represent important progress in the effort to make myocardial gene therapy a clinical reality beyond experimental protocols.