Right ventricular targeted gene transfer of a beta-adrenergic receptor kinase inhibitor improves ventricular performance after pulmonary artery banding

Model-specific selection of molecular targets for heart failure gene therapy

Heart failure (HF) is a complex multifaceted problem of abnormal ventricular function and structure. In recent years, new information has been accumulated allowing for a more detailed understanding of the cellular and molecular alterations that are the underpinnings of diverse causes of HF, including myocardial ischemia, pressure-overload, volume-overload or intrinsic cardiomyopathy. Modern pharmacological approaches to treat HF have had a significant impact on the course of the disease, although they do not reverse the underlying pathological state of the heart. Therefore gene-based therapy holds a great potential as a targeted treatment for cardiovascular diseases. Here, we survey the relative therapeutic efficacy of genetic modulation of β-adrenergic receptor signaling, Ca(2+) handling proteins and angiogenesis in the most common extrinsic models of HF.

AAV6-βARKct gene delivery mediated by molecular cardiac surgery with recirculating delivery (MCARD) in sheep results in robust gene expression and increased adrenergic reserve

OBJECTIVE

Genetic modulation of heart function is a novel therapeutic strategy. We investigated the effect of molecular cardiac surgery with recirculating delivery (MCARD)-mediated carboxyl-terminus of the β-adrenergic receptor kinase (βARKct) gene transfer on cardiac mechanoenergetics and β-adrenoreceptor (βAR) signaling.

METHODS

After baseline measurements, sheep underwent MCARD-mediated delivery of 10(14) genome copies of self-complimentary adeno-associated virus (scAAV6)-βARKct. Four and 8 weeks after MCARD, mechanoenergetic studies using magnetic resonance imaging were performed. Tissues were analyzed with real-time quantitative polymerase chain reaction (RT-qPCR) and Western blotting. βAR density, cyclic adenosine monophosphate levels, and physiologic parameters were evaluated.

RESULTS

There was a significant increase in dP/dt(max) at 4 weeks: 1384 ± 76 versus 1772 ± 182 mm Hg/s; and the increase persisted at 8 weeks in response to isoproterenol (P < .05). Similarly, the magnitude of dP/dt(min) increased at both 4 weeks and 8 weeks with isoproterenol stimulation (P < .05). At 8 weeks, potential energy was conserved, whereas in controls there was a decrease in potential energy (P < .05) in response to isoproterenol. RT-qPCR confirmed robustness of βARKct expression throughout the left ventricle and undetectable expression in extracardiac tissues. Quantitative Western blot data confirmed higher expression of βARKct in the left ventricle: 0.46 ± 0.05 versus 0.00 in lung and liver (P < .05). Survival was 100% and laboratory parameters of major organ function were within normal limits.

CONCLUSIONS

MCARD-mediated βARKct delivery is safe, results in robust cardiac-specific gene expression, enhances cardiac contractility and lusitropy, increases adrenergic reserve, and improves energy utilization efficiency in a preclinical large animal model.

GRK2 as a novel gene therapy target in heart failure

Despite significant advances in pharmacological and clinical treatment, heart failure (HF) remains a leading cause of morbidity and mortality worldwide. HF is a chronic and progressive clinical syndrome characterized by a reduction in left ventricular (LV) ejection fraction and adverse remodeling of the myocardium. The past several years have seen remarkable progress using animal models in unraveling the cellular and molecular mechanisms underlying HF pathogenesis and progression. These studies have revealed potentially novel therapeutic targets/strategies. The application of cardiac gene transfer, which allows for the manipulation of targets in cardiomyocytes, appears to be a promising therapeutic tool in HF. β-adrenergic receptor (βAR) dysfunction represents a hallmark abnormality of chronic HF, and increased G protein-coupled receptor kinase 2 (GRK2) levels/activity in failing myocardium is among these alterations. In the past 15years, several animal studies have shown that expression of a peptide inhibitor of GRK2 (βARKct) can improve the contractile function of failing myocardium including promoting reverse remodeling of the LV. Therefore, data support the use of the βARKct as a promising candidate for therapeutic application in human HF. Importantly, recent studies in cardiac-specific GRK2 knockout mice have corroborated GRK2 being pathological in failing myocytes. The purpose of this review is to discuss: 1) the alterations of βAR signaling that occur in HF, 2) the evidence from transgenic mouse studies investigating the impact of GRK2 manipulation in failing myocardium, 3) the therapeutic efficacy of in vivo βARKct gene therapy in HF, and 4) the intriguing possibility of lowering HF-related sympathetic nervous system hyperactivity by inhibiting GRK2 activity in the adrenal gland. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Right ventricular beneficial effects of beta adrenergic receptor kinase inhibitor (betaARKct) gene transfer in a rat model of severe pressure overload

Heart failure is associated with abnormalities in betaAR cascade regulation, calcium cycling, expression of inflammatory mediators and apoptosis. Adenoviral mediated gene transfer of betaARKct has beneficial indirect effects on these pathologic processes upon the left ventricular myocardium. The concomitant biochemical changes that occur in the right ventricle have not been well characterized. Sprague-Dawley rats underwent aortic banding and were followed by echocardiography. After a decrease in fractional shortening of 25% from baseline, intracoronary injection of adenoviral-betaARKct (n=14) or adenoviral-beta-galactosidase (control, n=13) was performed. Rats were randomly euthanized on post-operative day 7, 14 or 21. Protein analysis including RV myocardial levels of betaARKct, betaARK1, SERCA(2a), inflammatory tissue mediators (IL-1, IL-6 and TNF-alpha), apoptotic markers (bax and bak), and MAP kinases (jnk, p38 and erk) was performed. ANOVA was employed for group comparison. Adenoviral-betaARKct treated animals showed increased expression of betaARKct and decreased levels of betaARK1 compared with controls. This treatment group also demonstrated normalization of SERCA(2a) expression and decreased levels of the inflammatory markers IL-1, IL-6 and TNF-alpha. The pro-apoptotic markers bax and bak were similarly improved. Ventricular levels of the MAP kinase jnk were increased. Differences were most significant 7 days after gene transfer, but the majority of these changes persisted at 21 days. These results suggest that attenuation of the pathologic mechanisms of beta adrenergic receptor desensitization, SERCA(2a) expression, inflammation and apoptosis, not only occur in the left ventricle but also in the right ventricular myocardium after intracoronary gene transfer of betaARKct during heart failure.

Molecular and physiological characterization of RV remodeling in a murine model of pulmonary stenosis

Right ventricular (RV) dysfunction is a common long-term complication in patients after the repair of congenital heart disease. Previous investigators have examined the cellular and molecular mechanisms of left ventricular (LV) remodeling, but little is known about the stressed RV. Our purpose was to provide a detailed physiological characterization of a model of RV hypertrophy and failure, including RV-LV interaction, and to compare gene alterations between afterloaded RV versus LV. Pulmonary artery constriction was performed in 86 mice. Mice with mild and moderate pulmonary stenosis (PS) developed stable hypertrophy without decompensation. Mice with severe PS developed edema, decreased RV function, and high mortality. Tissue Doppler imaging demonstrated septal dyssynchrony and deleterious RV-LV interaction in the severe PS group. Microarray analysis showed 196 genes with increased expression and 1,114 with decreased expression. Several transcripts were differentially increased in the afterloaded RV but not in the afterloaded LV, including clusterin, neuroblastoma suppression of tumorigenicity 1, Dkk3, Sfrp2, formin binding protein, annexin A7, and lysyl oxidase. We have characterized a murine model of RV hypertrophy and failure, providing a platform for studying the physiological and molecular events of RV remodeling. Although the molecular responses of the RV and LV to afterload stress are mostly concordant, there are several key differences, which may represent targets for RV failure-specific therapy.

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.

Decreased left ventricular function, myocarditis, and coronary arteriolar medial thickening following monocrotaline administration in adult rats

Decreased right as well as left ventricular function can be associated with pulmonary hypertension (PH). Numerous investigations have examined cardiac function following induction of pulmonary hypertension with monocrotaline (MCT) assuming that MCT has no direct cardiac effect. We tested this assumption by examining left ventricular function and histology of isolated and perfused hearts from MCT-treated rats. Experiments were performed on 50 male Sprague-Dawley rats [348 +/- 6 g (SD)]. Thirty-seven rats received MCT (50 mg/kg sc; MCT group) while the remainder did not (Control group). Three weeks later, pulmonary artery pressure was assessed echocardiographically in 20 MCT and 8 Control rats. The hearts were then excised and perfused in the constant pressure Langendorff mode to determine peak left ventricular pressure (LVP), the peak instantaneous rate of pressure increase (+dP/dtmax) and decrease (-dP/dtmax), as well as the rate pressure product (RPP). Histological sections were subsequently examined. Pulmonary artery pressure was higher in the MCT-treated group compared with the Control group [12.9 +/- 6 vs. 51 +/- 35.3 mmHg (P < 0.01)]. Left ventricular systolic function and diastolic relaxation were decreased in the MCT group compared with the Control group (+dP/dtmax 4,178 +/- 388 vs. 2,801 +/- 503 mmHg/s, LVP 115 +/- 11 vs. 83 +/- 14 mmHg, RPP 33,688 +/- 1,910 vs. 23,541 +/- 3,858 beats x min(-1) x mmHg(-1), -dP/dtmax -3,036 +/- 247 vs. -2,091 +/- 389 mmHg/s; P < 0.0001). The impairment of cardiac function was associated with myocarditis and coronary arteriolar medial thickening. Similarly depressed ventricular function and inflammatory infiltration was seen in 12 rats 7 days after MCT administration. Our findings appear unrelated to the degree of PH and indicate a direct cardiotoxic effect of MCT.

Catheter-mediated subselective intracoronary gene delivery to the rabbit heart: introduction of a novel method

BACKGROUND

Recent studies suggest that gene therapy using replication-deficient adenoviruses will benefit treatment of cardiovascular diseases including heart failure. A persistent hurdle is the effective and reproducible delivery of a transgene to the myocardium with minimal iatrogenic morbidity. In this study, we sought to design a relatively non-invasive percutaneous gene delivery system that would maximize cardiac transgene expression and minimize mortality after intracoronary adenovirus injection.

METHODS

Adult rabbits received a left circumflex coronary artery (LCx) infusion of 5x10(11) total viral particles of an adenovirus containing the marker transgene beta-galactosidase (Adeno-betaGal) via either a continuous infusion method utilizing an oxygenated, normothermic, physiologic pH Krebs solution driven by a Langendorff apparatus (n=12) or a timed bolus and set concentration at a constant infusion rate to the LCx (n=12). Six rabbits underwent global transgene delivery via an invasive method involving intraventricular delivery and aortic root cross-clamping. The efficacy of transgene expression via these three distinct delivery methods was determined in the left ventricle at 5 days by histological staining and colorimetric quantification assay.

RESULTS

While the open-chest, aortic cross-clamping method provides the highest level of gene expression throughout the heart, the morbidity of this procedure is clinically prohibitive. Percutaneous LCx delivery of Adeno-betaGal using the Langendorff apparatus was associated with the lowest morbidity and mortality while still supporting significant myocardial gene expression.

CONCLUSIONS

Percutaneous delivery of an adenovirus solution using a continuous infusion of oxygenated Krebs solution via a Langendorff apparatus appears to be a gene delivery modality offering the best compromise of gene expression and clinical utility to maximize any potential therapeutic outcome.

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.