Adenovirus-mediated gene transfer of the beta2-adrenergic receptor to donor hearts enhances cardiac function

betaARKct: a therapeutic approach for improved adrenergic signaling and function in heart disease

One of the most powerful regulators of cardiovascular function is catecholamine-stimulated adrenergic receptor (AR) signaling. The failing heart is characterized by desensitization and impaired beta-AR responsiveness as a result of upregulated G protein-coupled receptor kinase-2 (GRK2) present in injured myocardium. Deterioration of cardiac function is progressively enhanced by chronic adrenergic over-stimulation due to increased levels of circulating catecholamines. Increased GRK2 activity contributes to this pathological cycle of over-stimulation but lowered responsiveness. Over the past two decades the GRK2 inhibitory peptide betaARKct has been identified as a potential therapy that is able to break this vicious cycle of self-perpetuating deregulation of the beta-AR system and subsequent myocardial malfunction, thus halting development of cardiac failure. The betaARKct has been shown to interfere with GRK2 binding to the betagamma subunits of the heterotrimeric G protein, therefore inhibiting its recruitment to the plasma membrane that normally leads to phosphorylation and internalization of the receptor. In this article we summarize the current data on the therapeutic effects of betaARKct in cardiovascular disease and report on recent and ongoing studies that may pave the way for this peptide towards therapeutic application in heart failure and other states of cardiovascular disease.

Designing heart performance by gene transfer

The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.

Uncoupling of myocardial beta-adrenergic receptor signaling during coronary artery bypass grafting: the role of GRK2

BACKGROUND

Cardiopulmonary bypass (CPB) and cardioplegic arrest during cardiac surgery leads to desensitization of myocardial beta-adrenergic receptors (beta-ARs). Impaired signaling through this pathway can have a detrimental effect on ventricular function and increased need for inotropic support. The mechanism of myocardial beta-AR desensitization during cardiac surgery has not been defined. This study investigates the role of G protein-coupled receptor kinase-2 (GRK2), a serine-threonine kinase which phosphorylates and desensitizes agonist-occupied beta-ARs, as a primary mechanism of beta-AR uncoupling during coronary artery bypass grafting (CABG) with CPB and cardioplegic arrest.

METHODS

Forty-eight patients undergoing elective CABG were enrolled in this study. Myocardial beta-AR signaling was assessed by measuring total beta-AR density and adenylyl cyclase activity in right atrial biopsies obtained before CPB and just before weaning from CPB. Myocardial GRK2 expression and activity were also measured before CPB and just before weaning from CPB.

RESULTS

Myocardial beta-AR signaling was significantly impaired after CPB and cardioplegic arrest during CABG. Cardiac GRK2 expression was not altered; however, there was a twofold increase in GRK2 activity during CABG. There was an even greater elevation in cardiac GRK2 activity in patients with severely depressed ventricular function.

CONCLUSIONS

Increased myocardial GRK2 activity appears to be the primary mechanism of impaired beta-AR signaling during CABG with CPB and cardioplegic arrest. This may contribute to the greater need for inotropic support in patients with severe ventricular dysfunction. Strategies to inhibit activation of GRK2 during CABG may decrease morbidity in this patient population.

Gene therapy in heart failure

With increasing knowledge of basic molecular mechanisms governing the development of heart failure (HF), the possibility of specifically targeting key pathological players is evolving. Technology allowing for efficient in vivo transduction of myocardial tissue with long-term expression of a transgene enables translation of basic mechanistic knowledge into potential gene therapy approaches. Gene therapy in HF is in its infancy clinically with the predominant amount of experience being from animal models. Nevertheless, this challenging and promising field is gaining momentum as recent preclinical studies in larger animals have been carried out and, importantly, there are 2 newly initiated phase I clinical trials for HF gene therapy. To put it simply, 2 parameters are needed for achieving success with HF gene therapy: (1) clearly identified detrimental/beneficial molecular targets; and (2) the means to manipulate these targets at a molecular level in a sufficient number of cardiac cells. However, several obstacles do exist on our way to efficient and safe gene transfer to human myocardium. Some of these obstacles are discussed in this review; however, it primarily focuses on the molecular target systems that have been subjected to intense investigation over the last decade in an attempt to make gene therapy for human HF a reality.

RNA Interference and MicroRNA Modulation for the Treatment of Cardiac Disorders

The current status and challenges of RNA interference (RNAi) and microRNA modulation strategies for the treatment of myocardial disorders are discussed and related to the classical gene therapeutic approaches of the past decade. Section 2 summarizes the key issues of current vector technologies which determine if they may be suitable for clinical translation of experimental RNAi or microRNA therapeutic protocols. We then present and discuss examples dealing with the potential of cardiac RNAi therapy. First, an approach to block a key early step in the pathogenesis of a virus-induced cardiomyopathy by RNAi targeting of a cellular receptor for cardiopathogenic viruses (Section 3). Second, an approach to improve cardiac function by RNAi targeting of late pathway of heart failure pathogenesis common to myocardial disorders of multiple etiologies. This strategy is directed at myocardial Ca²⁺ homeostasis which is disturbed in heart failure due to coronary heart disease, heart valve dysfunction, cardiac inflammation, or genetic defects (Section 4). Whereas the first type of strategies (directed at early pathogenesis) need to be tailor-made for each different type of pathomechanism, the second type (targeting late common pathways) has a much broader range of application. This advantage of the second type of approaches is of key importance since enormous efforts need to be undertaken before any regulatory RNA therapy enters the stage of possible clinical translation. If then the number of patients eligible for this protocol is large, the actual transformation of the experimental therapy into a new therapeutic option of clinical importance is far more likely to occur.

Targeting myocardial beta-adrenergic receptor signaling and calcium cycling for heart failure gene therapy

Heart failure (HF) is a leading cause of morbidity and mortality in Western countries and projections reveal that HF incidence in the coming years will rise significantly because of an aging population. Pharmacologic therapy has considerably improved HF treatment during the last 2 decades, but fails to rescue failing myocardium and to increase global cardiac function. Therefore, novel therapeutic approaches to target the underlying molecular defects of ventricular dysfunction and to increase the outcome of patients in HF are needed. Failing myocardium generally exhibits distinct changes in beta-adrenergic receptor (betaAR) signaling and intracellular Ca2+-handling providing opportunities for research. Recent advances in transgenic and gene therapy techniques have presented novel therapeutic strategies to alter myocardial function and to target both betaAR signaling and Ca2+-cycling. In this review, we will discuss functional alterations of the betaAR system and Ca2+-handling in HF as well as corresponding therapeutic strategies. We will then focus on recent in vivo gene therapy strategies using the targeted inhibition of the betaAR kinase (betaARK1 or GRK2) and the restoration of S100A1 protein expression to support the injured heart and to reverse or prevent HF.

Heterotopic transplantation of the failing rat heart as a model of left ventricular mechanical unloading toward recovery

The left ventricular assist device (LVAD) is usually used in patients with end-stage heart failure as a bridge to transplantation. Recently, some studies have reported functional recovery with the use of an LVAD, although the mechanisms responsible for recovery are not fully understood. We investigated the functional recovery of the infarcted, failing rat heart in response to mechanical unloading after heterotopic transplantation. Heart failure was induced in Lewis rats by ligating the left anterior descending artery. After 4 weeks, the infarcted hearts were harvested and heterotopically transplanted. The transplanted infarcted heart was removed after 2 weeks of unloading and examined for hypertrophy and fibrosis, as well as for mRNA levels encoding for brain natriuretic peptide, sarco(endo)plasmic reticulum Ca(2+)-ATPase2a (SERCA2a), and beta1- and beta2-adrenergic receptors. Normal and infarcted rats without transplantation served as control animals. The infarcted heart was hypertrophied as evidenced by an increase in heart weight and myocyte diameter. After unloading the infarcted heart for 2 weeks, there was a decrease in heart weight and myocyte diameter. However, the percentage of myocardial fibrosis increased after unloading. The mRNA expression of brain natriuretic peptide and the beta2-adrenergic receptor significantly improved after mechanical unloading. The levels of SERCA2a mRNA tended to increase after unloading. In conclusion, unloading the failing, infarcted heart can help normalize left ventricular hypertrophy and cardiac gene expression. This unloading model appears to partially mimic the conditions of hemodynamic support with an LVAD in heart failure patients and potentially offers insights into the mechanisms of functional recovery.

Nitroprusside increases gene transfer associated with intracoronary delivery of adenovirus

Efficient gene transfer by vectors that can be easily delivered to target organs is desirable in clinical gene therapy. We tested the hypothesis that intracoronary infusion of the nitric oxide donor nitroprusside would increase the efficiency of adenovirus vector-mediated gene transfer to the heart. Intracoronary delivery of an adenovirus encoding murine adenylyl cyclase type VI (Ad.AC(VI)) was performed in adult pigs with and without simultaneous intracoronary infusion of nitroprusside. Animals were killed 12-14 days after Ad.AC(VI) delivery and myocardial adenylyl cyclase activity was measured. Addition of nitroprusside during intracoronary infusion of Ad.AC(VI) was associated with a 4-fold increase in cAMP-generating capacity in the left ventricle. Transgene expression was confirmed by immunoblotting. Intracoronary nitroprusside produced mild dose-dependent changes in blood pressure and heart rate during infusion. Intracoronary nitroprusside infusion is a safe and effective means to increase the extent of cardiac gene transfer with intracoronary delivery of adenovirus vectors.

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.

Efficiency of adenovirus-mediated gene transduction in heart grafts in rats

AIM

We determined the characteristics of transgene expression of heart grafts following ex vivo gene transfer using an adenovirus vector. Transgene expression was assessed periodically in the same animals by a non-invasive bioimaging system.

METHODS

Rat heterotopic heart transplantation was performed in a syngenic combination. We infused 1 x 10(9) plaque-forming units of adenovirus vectors containing firefly luciferase gene into the heart graft via the coronary artery, with preservation at 4 degrees C and transplanted into the cervix of the recipient. Transgene expression was periodically visualized and quantified by a noninvasive bioimaging system without sacrificing experimental animals.

RESULTS

Transgene expression in the graft peaked at day 7 and then fell gradually. Transgene expression was also observed in the recipient liver.

CONCLUSIONS

We have determined the time course of transgene expression in the heart graft. This constitutes important information about ex vivo gene therapy for heart grafts.

Dose dependent effects of cardiac β2 adrenoceptor gene therapy1

BACKGROUND

Adenoviral-mediated gene transfer during cardiopulmonary bypass (CPB) achieves efficient myocardial transgene expression. The optimal vector dose required to produce not only increased beta adrenoceptor (betaAR) density but, more importantly, enhanced left ventricular (LV) function is unknown. In addition, it is unclear if absent extracardiac expression in preliminary studies represented cardiac specific, as opposed to selective gene delivery, as a consequence of low vector doses.

MATERIALS AND METHODS

Adenoviral vector encoding the human beta(2) adrenoceptor (Adeno-beta(2)AR) was delivered to cardioplegic arrested hearts of neonatal piglets during CPB in three doses ranging from 5 x 10(11) total viral particles (tvp) to 2 x 10(12) tvp. Control animals received adenoviral vector encoding beta galactosidase (Adeno-betagal) or PBS (PBS). LV and liver betaAR density and in vivo LV function were assessed 5 days later.

RESULTS

Elevated LV betaAR density was present after delivery of Adeno-beta(2)AR at all doses. Piglets which received 5 x 10(11) tvp and 1 x 10(12) tvp Adeno-beta(2)AR demonstrated enhanced LV dP/dt(max) but in those receiving 2 x 10(12) tvp LV dP/dt(max) was unchanged. Moreover, at this higher dose of adenoviral vector the detrimental effects of cardiac inflammation and extracardiac gene overexpression became apparent.

CONCLUSIONS

Although the highest increase in cardiac betaAR density occurred after high-dose Adeno-beta(2)AR, LV dP/dt(max) was not enhanced. Moreover, significant extracardiac gene expression was present at this dose, emphasizing the need for careful dose response studies in gene therapy. However, cardiac selective beta(2)AR overexpression does occur following adenoviral vector delivery during CPB and cardioplegic arrest resulting in enhanced LV dP/dt(max).

Molecular Restoration of β-Adrenergic Receptor Signaling Improves Contractile Function of Failing Hearts

beta-adrenergic receptor (betaAR) antagonists, or beta blockers, are now a part of the standard therapeutic arsenal in the medical management of chronic heart failure (HF). Conversely, betaAR stimulation remains the most efficient way to enhance cardiac contractile function acutely, although long-term inotropic therapy based on enhanced betaAR stimulation is likely detrimental. Although altered betaAR signaling plays a pivotal role in the genesis of HF, the choice to therapeutically agonize or antagonize this receptor pathway remains an area of ongoing investigation. Research from the authors' laboratory as well as other research conducted over the last 10 years has produced evidence to support the fact that "normalizing" the betaAR system at a molecular level and improving signaling, instead of blocking it, leads to significant enhancement of cardiac contractile function and prevents ventricular remodeling in HF. This review summarizes the extensive in vivo animal model experimentation that supports the still-controversial hypothesis that increasing the myocardial density of beta(2)-ARs or, more effectively, inhibiting the activity of the betaAR kinase (also referred to as G-protein-coupled receptor kinase 2), represent potential novel therapeutic strategies for HF.

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.

A minimally invasive approach for efficient gene delivery to rodent hearts

Transcoronary gene delivery represents a desirable option to achieve global myocardial transgene expression but still requires aggressive surgical preparation in rodents. We therefore developed a catheter-based approach for cardiac gene transfer in the closed chest rat. A double-lumen balloon catheter was used to create aortic occlusion for specific infusion of adenoviral vectors carrying a beta-galactosidase transgene (1 x 10(11) PFU) into the coronaries. Simultaneously, venous return was obstructed by a second balloon catheter in the right atrium. To prolong viral incubation time, we induced a transient cardiac arrest (2 and 5 min) by a combination of acetylcholine and the beta-receptor antagonist, esmolol. At 72 h after transfection, the hearts showed a homogeneous and widespread beta-galactosidase expression, and the transduction efficiency increased and up to about 43% of cardiac myocytes (histochemistry) with a 400-fold increase of beta-galactosidase activity (luminescence assay) compared to sham-operated hearts. Pharmacological treatment aimed at increasing vascular permeability (SNAP and histamine) did not bring about synergistic effects on transfection efficiency. In addition, the method using high intracoronary pressure delivery (>300 mmHg) in a single-pass manner resulted in rather sparse beta-galactosidase expression in the myocardium (3-5% of cardiac myocytes). Therefore, the percutaneous gene delivery system described here provides a simple and minimally invasive procedure that represents a novel strategy for a homogeneous and highly efficient in vivo gene transfer to rodent hearts. Our results also suggest that prolongation of viral incubation time is an effective means for achieving highly efficient myocardial gene transduction.

Gene therapy for heart failure

Despite our continued advances in the management of coronary artery disease, there have been no significant reductions in the morbidity or mortality related to end-stage heart failure. The syndrome of heart failure represents a common endpoint for several disease processes, however, at the molecular level there are certain biochemical similarities common to all failing myocardium. Targeting these derangements with gene therapy represents a promising option in the treatment of heart failure. In this review, we will discuss the common biochemical changes that occur in the failing heart, novel therapeutic targets, including the beta-adrenergic receptor system and intracellular calcium regulation, and the vectors and transfer methodology responsible for delivering these transgenes to the myocardium.

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.

Positive inotropic stimulation

Adrenergic receptors transduce signals through the G proteins to regulate cardiac function. The catecholamines, via alpha- and beta-adrenergic receptor (beta-AR) stimulation, may play a role in the development of heart failure. Norepinephrine and isoproterenol can induce cardiac myocyte apoptosis. Studies suggest that alpha-, beta1-, and beta2-adrenergic pathways differentially regulate cardiac myocyte apoptosis. The stimulation of beta1-AR leads to cyclic AMP-dependent apoptosis, whereas that of the beta2-AR elicits concurrent apoptosis and survival signals in cardiac myocytes coupled to Gs protein. Overexpression of alpha1-adrenergic receptors does not induce apoptosis in wild-type mice. In contrast, the heart failure observed in some murine models has to be related to an enhanced beta-AR kinase expression. These recent advances make it possible to understand the beneficial effects of beta-blockers in the treatment of chronic heart failure and provide novel therapeutic modalities through the stimulation of beta2-ARs or the inhibition of beta-AR kinase expression.

New molecular insights into heart failure and cardiomyopathy: potential strategies and therapies

BACKGROUND

In the most severely affected patients the mortality for congestive heart failure exceeds that of many cancers. While therapies are largely aimed at attenuating neurohumoral responses recent molecular insights reveal other potential targets for therapy.

AIMS

To summarise some of the recent developments in the management of heart failure and provide the clinician who treats heart failure with new insights into emerging approaches.

METHODS

A literature review was conducted of the recent literature together with personal research data.

RESULTS

Large randomised trials will provide a more comprehensive understanding of the interaction of beta-blockers and other heart failure therapies with gene polymorphisms. Cytokines are important in the progression of heart failure, yet therapy aimed at blocking cytokine effects has not been successful. More selective use of anti-cytokine therapy may have beneficial effects. Gene therapy to improve heart failure has not yet reached clinical trials. The molecular genetics of hypertrophic and dilated cardiomyopathy is rapidly improving our understanding so that genetic diagnostics and counselling may soon be performed for patients and families.

CONCLUSIONS

The emergence of a molecular based understanding of heart failure will hopefully improve therapy of this common condition.

Genetic manipulation of beta-adrenergic signalling in heart failure

Heart failure (HF) represents one of the leading causes for hospitalization in developed nations. Despite advances in the management of coronary artery disease, no significant improvements in prognosis have been achieved for HF over the last several decades. Heart failure itself represents a final common endpoint for several disease entities, including hypertension, coronary artery disease, and cardiomyopathy. However, certain biochemical features remain common to the failing myocardium. Foremost amongst these are alterations in the beta-adrenergic receptor signalling cascade. Recent advances in transgenic and gene therapy techniques have presented novel therapeutic strategies for the management of HF via enhancement of beta-adrenergic signalling. In this review, we will discuss the biochemical changes that accompany HF as well as corresponding therapeutic strategies. We will then review the evidence from transgenic mouse work supporting the use of adrenergic receptor augmentation in the failing heart and more recent in vivo applications of gene therapy directed at reversing or preventing HF.

How to optimize in vivo gene transfer to cardiac myocytes: mechanical or pharmacological procedures?

An efficient gene delivery system is a prerequisite for myocardial gene therapy. Among the various procedures studied so far, catheter-based percutaneous gene delivery to the myocardium through the coronary vessels seems the most relevant to routine clinical practice; however, the optimal conditions remain to be determined. We selectively infused adenoviral vectors encoding luciferase (1 x 10(9) PFU) or beta-galactosidase (1 x 10(10) PFU) into coronary arteries of adult rabbits in various experimental conditions. Coronary artery occlusion for 30 sec, during and after adenovirus delivery, was required to observe luciferase activity in the target area of the circumflex artery (4.0 +/- 1.0 x 10(5) vs. 1.1 +/- 0.2 x 10(4) RLU/mg with and without coronary occlusion, respectively, p < 0.01, and 1.0 +/- 0.1 x 10(3) RLU/mg using nonselective infusion). When adenoviruses were delivered using high-pressure infusion (82 +/- 12 vs. 415 +/- 25 mmHg before and during infusion, respectively, p < 0.01), luciferase activity increased to 8.5 +/- 2.5 x 10(5) RLU/mg (p < 0.05 vs coronary occlusion alone). Coronary venous sinus occlusion with saline buffer retroinfusion starting before and during anterograde adenovirus delivery resulted in a further 4.7-fold increase in luciferase activity (4.4 +/- 0.8 x 10(6) RLU/mg, p < 0.01) with 5-25% blue-stained myocytes in the target area, compared with 0-5% with the other procedures. Histamine or VEGF-A(165) pretreatment, used to increase vascular permeability, slightly increased gene transfer efficiency (8.5 +/- 2.0 x 10(5) and 9.0 +/- 2.5 x 10(5) RLU/mg respectively, p < 0.05 vs. coronary occlusion alone). We conclude that catheter-mediated adenoviral gene transfer to cardiac myocytes through coronary vessels can be a very efficient procedure for myocardial gene therapy, particularly when the vector residence time and perfusion pressure in the vessels are increased.

Human coxsackie-adenovirus receptor is colocalized with integrins alpha(v)beta(3) and alpha(v)beta(5) on the cardiomyocyte sarcolemma and upregulated in dilated cardiomyopathy: implications for cardiotropic viral infections

BACKGROUND

The coxsackievirus and adenovirus receptor (CAR) was identified as a common cellular receptor for both viruses, but its biological and pathogenic relevance is uncertain. Knowledge of CAR localization in the human cardiovascular system is limited but important with respect to CAR-dependent viral infections and gene transfer using CAR-dependent viral vectors.

METHODS AND RESULTS

Explanted failing hearts from 13 patients (8 with dilated cardiomyopathy [DCM] and 5 with other heart diseases [non-DCM]) and normal donor hearts (n=7) were investigated for the expression levels and subcellular localization of CAR and the adenovirus coreceptors alpha(v)beta(3) and alpha(v)beta(5) integrins. CAR immunoreactivity was very low in normal and non-DCM hearts, whereas strong CAR signals occurred at the intercalated discs and sarcolemma in 5 of the 8 DCM hearts (62.5%); these strong signals colocalized with both integrins. In all hearts, CAR was detectable in subendothelial layers of the vessel wall, but not on the luminal endothelial surface, and on interstitial cells. Human CAR (hCAR) expressed in rat cardiomyocytes was targeted to cell-cell contacts, which resembled CAR localization in DCM hearts and resulted in 15-fold increased adenovirus uptake.

CONCLUSIONS

Low hCAR abundance may render normal human myocardium resistant to CAR-dependent viruses, whereas re-expression of hCAR, such as that observed in DCM, may be a key determinant of cardiac susceptibility to viral infections. Asymmetric expression of hCAR in the vessel wall may be an important determinant of adenovirus tropism in humans. hCAR subcellular localization in human myocardium and hCAR targeting to cell-cell contacts in cardiomyocyte cultures suggest that hCAR may play a role in cell-cell contact formation.

Gene therapeutic approaches to oxidative stress-induced cardiac disease: principles, progress, and prospects

Heart and vascular diseases continue to rank among the most frequent and devastating disorders to affect adults in many parts of the world. Increasing evidence from a variety of experimental models indicates that reactive oxygen species can play a key role in the development of myocardial damage from ischemia/reperfusion, the development of cardiac hypertrophy, and the transition of hypertrophy to cardiac failure. The recent dramatic increase in availability of genomic data has included information on the genetic modulation of reactive oxygen species and the antioxidant systems that normally prevent damage from these radicals. Nearly simultaneously, progressively more sophisticated and powerful methods for altering the genetic complement of selected tissues and cells have permitted application of gene therapeutic methods to understand better the pathophysiology of reactive oxygen species-mediated myocardial damage and to attenuate or treat that damage. Although exciting and promising, gene therapy approaches to these common disorders are still in the experimental and developmental stages. Improved understanding of pathophysiology, better gene delivery systems, and specific gene therapeutic strategies will be needed before gene therapy of oxyradical-mediated myocardial damage becomes a clinical reality.

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.

Direct intra-cardiomuscular transfer of beta2-adrenergic receptor gene augments cardiac output in cardiomyopathic hamsters

In chronic heart failure, down-regulation of beta-adrenergic receptor (beta-AR) occurs in cardiomyocytes, resulting in low catecholamine response and impaired cardiac function. To correct the irregularity in the beta-AR system, beta-AR gene was transduced in vivo into failing cardiomyocytes. The Epstein-Barr virus (EBV)-based plasmid vector carrying human beta2-AR gene was injected into the left ventricular muscle of Bio14.6 cardiomyopathic hamsters whose beta-AR is down-regulated in the cardiomyocytes. The echocardiographic examinations revealed that stroke volume (SV) and cardiac output (CO) were significantly elevated at 2 to 4 days after the beta2-AR gene transfer. Systemic loading of isoproterenol increased the cardiac parameters more significantly on day 2 to day 7, indicating that the adrenergic response was augmented by the genetic transduction. The same procedure did not affect the cardiac function of normal hamsters. Immunohistochemical examinations demonstrated human beta2-AR expression in failing cardiomyocytes transduced with the gene. RT-PCR analysis detected mRNA for the transgene in the heart but not in the liver, spleen, or kidney. The procedures may provide a feasible strategy for gene therapy of severe heart failure. Gene Therapy (2000) 7, 2087-2093.

DNA/dendrimer complexes mediate gene transfer into murine cardiac transplants ex vivo

Starburst polyamidoamine dendrimers are synthetic polymers with unique structural and physical characteristics suitable for DNA gene transfer. Our previous studies demonstrated that Starburst dendrimers augment plasmid-mediated gene transfer efficiency in a nonvascularized, cardiac transplantation model. In this study, the fifth generation of ethylenediamine core dendrimer was investigated for its ability to enhance gene transfer and expression in a clinically relevant murine vascularized heart transplantation model. The plasmid pMP6A-beta-gal, encoding beta-galactosidase (beta-Gal), was incubated with dendrimers to form complexes. The complexes were perfused via the coronary arteries during donor graft harvesting, and reporter gene expression was determined by quantitative evaluation of X-Gal staining. The grafts infused with pMP6A-beta-gal/dendrimer complexes showed beta-Gal expression in myocytes from 7 to 14 days. A number of variables for transfer of the DNA/dendrimer complexes were tested, including DNA:dendrimer charge ratios, concentrations of DNA and dendrimer, preservation solutions, ischemic time, and enhancement of vascular permeability by serotonin, papaverine, and VEGF administration. The results showed that DNA/dendrimer complexes containing 20 microg of DNA and 260 microg of dendrimer (1:20 charge ratio) in a total volume of 200 microl resulted in highest gene expression in the grafts. The results also showed that prolonged incubation (cold ischemic time) to 2 h and pretreatment with serotonin further enhanced gene expression.

Recent developments in gene therapy for cardiac disease

Cardiovascular[TRACE;del] disease is the leading cause of death in the US and world-wide. Advances in molecular biology and the human genome project have revealed opportunities for novel strategies for cardiac gene therapy. This review discusses general and specific aspects of gene transfer strategies in cardiac tissues. These include 1) the selection and/or optimization of the vector for gene transfer; 2) the identification of the target gene(s); 3) the use of cardiac-specific promoters; and 4) the use of an appropriate delivery system for administration. Currently, several vectors (e.g., viral and nonviral vectors) have been developed and many target genes have been identified (e.g., VEGF, FGF, beta-AR, etc.). Many investigations have provided experimental models for gene delivery systems but the most efficient cardiac gene transfer was obtained from intramyocardial injection or perfusion of explanted myocardium. The data available thus far have suggested favorable immediate effects following gene transfer, but long-term value of cardiac gene therapy has not been proven. Further refinements in appropriate vectors that provide cell or tissue selectivity and long-lasting effects are necessary as well as the development of minimally invasive procedures for gene transfer.

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

OBJECTIVES

Ex vivo perfusion of the cardiac allograft during organ procurement is an ideal environment for adenoviral vectors with transgenes that target improving graft contractility. One such target is the beta-adrenergic receptor-signaling system, in which alterations in transgenic mice have elucidated novel means to improve the function of the heart in vivo. The purpose of the current study was to determine the functional consequences of beta-adrenergic receptor manipulation in a rabbit model of cardiac allograft transplantation.

METHODS

New Zealand White rabbits weighing 3 kg served as recipients to 1-kg outbred donors. Donor hearts were arrested and harvested, and 1 of 3 adenoviral constructs was administered into the aortic root perfusing the graft. Transgenes delivered encoded either the human beta(2)-adrenergic receptor, a peptide inhibitor of beta-adrenergic receptor densensitization, or the marker transgene beta-galactosidase.

RESULTS

Five days after cervical heterotopic transplantation, left ventricular performance was measured on a Langendorff apparatus. A moderate pattern of rejection was seen in all grafts. Biventricular myocyte expression of beta-galactosidase was observed, and beta(2)-adrenergic receptor density was elevated 10-fold in grafts that received adeno-beta(2)-adrenergic receptor. Left ventricular systolic and diastolic performance was significantly increased in grafts transfected with either adeno-beta(2)-adrenergic receptor or adeno-beta-adrenergic receptor densensitization compared with control grafts that received adeno-beta-galactosidase.

CONCLUSIONS

Ex vivo adenovirus-mediated gene transfer is feasible in a rabbit allograft model and, more important, genetic manipulation of beta-adrenergic receptor signaling either by increasing beta(2)-adrenergic receptor density or blocking endogenous receptor desensitization improves graft function acutely in this allograft model.

Highly efficient adenovirus-mediated gene transfer to cardiac myocytes after single-pass coronary delivery

Efficient and homogeneous gene transfer to cardiac myocytes is a major target in myocardial gene therapy. The aim of this study was to determine the conditions permitting efficient, homogeneous, adenovirus-mediated gene transfer to cardiac myocytes, with a view to application during coronary artery catheterization. Gene transfer to adult rat ventricular myocytes was conducted using type 5 adenoviruses carrying the lacZ reporter gene. Adenovirus delivery via coronary arteries was performed on isolated perfused rat hearts, and gene transfer efficiency was analyzed on whole ventricles, freshly isolated myocytes, and cultured myocytes. Single-pass delivery of 1 X 10(9) PFU associated with 1 min of no-flow yielded only 1 +/- 0.5% of positive myocytes. Pretreatment by histamine perfusion (10(-5) M final concentration) increased this value to 30 +/- 9% (p < 0.001), and pretreatment by Ca2+-free buffer perfusion increased it to 67 +/- 8% (p < 0.001). Combination of the two pretreatments had no additional effect. Increasing the viral dose to 3 X 10(9) PFU increased transfection efficiency only in permeabilized vessels. The 1-min no-flow period after adenovirus delivery was crucial for efficient gene transfer: despite histamine pretreatment, only 2 +/- 1% positive myocytes were observed without flow interruption (p < 0.05 versus 1 min of no-flow). Gene transfer was shown to occur in situ during cardiac perfusion, rather than during heart digestion or myocyte isolation. This study shows that highly efficient adenovirus-mediated gene transfer to cardiac myocytes in situ can be achieved by single-pass intracoronary vector delivery, provided that vascular permeability is first increased and coronary flow is briefly interrupted.

Beta-Adrenergic gene therapy for cardiovascular disease

Gene therapy using in vivo recombinant adenovirus-mediated gene transfer is an effective technique that offers great potential to improve existing drug treatments for the complex cardiovascular diseases of heart failure and vascular smooth muscle intimal hyperplasia. Cardiac-specific adenovirus-mediated transfer of the carboxyl-terminus of the beta-adrenergic receptor kinase (betaARKct), acting as a Gbetagamma-beta-adrenergic receptor kinase (betaARK)1 inhibitor, improves basal and agonist-induced cardiac performance in both normal and failing rabbit hearts. In addition, betaARKct adenovirus infection of vascular smooth muscle is capable of significantly diminishing neointimal proliferation after angioplasty. Therefore, further investigation is warranted to determine whether inhibition of betaARK1 activity and sequestration of Gbetagamma via an adenovirus that encodes the betaARKct transgene might be a useful clinical tool for the treatment of cardiovascular pathologies.

Enhancement of cardiac function after adenoviral-mediated in vivo intracoronary beta2-adrenergic receptor gene delivery

Exogenous gene delivery to alter the function of the heart is a potential novel therapeutic strategy for treatment of cardiovascular diseases such as heart failure (HF). Before gene therapy approaches to alter cardiac function can be realized, efficient and reproducible in vivo gene techniques must be established to efficiently transfer transgenes globally to the myocardium. We have been testing the hypothesis that genetic manipulation of the myocardial beta-adrenergic receptor (beta-AR) system, which is impaired in HF, can enhance cardiac function. We have delivered adenoviral transgenes, including the human beta2-AR (Adeno-beta2AR), to the myocardium of rabbits using an intracoronary approach. Catheter-mediated Adeno-beta2AR delivery produced diffuse multichamber myocardial expression, peaking 1 week after gene transfer. A total of 5 x 10(11) viral particles of Adeno-beta2AR reproducibly produced 5- to 10-fold beta-AR overexpression in the heart, which, at 7 and 21 days after delivery, resulted in increased in vivo hemodynamic function compared with control rabbits that received an empty adenovirus. Several physiological parameters, including dP/dtmax as a measure of contractility, were significantly enhanced basally and showed increased responsiveness to the beta-agonist isoproterenol. Our results demonstrate that global myocardial in vivo gene delivery is possible and that genetic manipulation of beta-AR density can result in enhanced cardiac performance. Thus, replacement of lost receptors seen in HF may represent novel inotropic therapy.