Cardiac gene therapy: are we there yet?

The incidence of cardiovascular disease (CVD) is increasing throughout the world and is associated with elevated morbidity and mortality. Gene therapy to treat cardiac dysfunction is gaining importance because of the limited therapeutic benefit offered by pharmacotherapies. The growing knowledge of the complex signaling pathways and the development of sophisticated vectors and delivery systems, are facilitating identification and targeting of specific molecular candidates involved in initiation and progression of CVDs. Several preclinical and clinical studies have shown the therapeutic efficiency of gene therapy in different disease models and patients. Hence, gene therapy might plausibly become an unconventional treatment modality for CVD patients. In this review, we summarize the gene delivery carriers, modes of delivery, recent preclinical/clinical studies and potential therapeutic targets. We also briefly discuss the existing limitations of gene therapy, technical challenges surrounding gene carriers and delivery systems, and some approaches to overcome these limitations for bringing CVD gene therapy one step closer to reality.

Quantitative assessment of brain microvascular and tissue oxygenation during cardiac arrest and resuscitation in pigs.

Cardiac arrest is associated with a very high rate of mortality, in part due to inadequate tissue perfusion during attempts at resuscitation. Parameters such as mean arterial pressure and end-tidal carbon dioxide may not accurately reflect adequacy of tissue perfusion during cardiac resuscitation. We hypothesised that quantitative measurements of tissue oxygen tension would more accurately reflect adequacy of tissue perfusion during experimental cardiac arrest. Using oxygen-dependent quenching of phosphorescence, we made measurements of oxygen in the microcirculation and in the interstitial space of the brain and muscle in a porcine model of ventricular fibrillation and cardiopulmonary resuscitation. Measurements were performed at baseline, during untreated ventricular fibrillation, during resuscitation and after return of spontaneous circulation. After achieving stable baseline brain tissue oxygen tension, as measured using an Oxyphor G4-based phosphorescent microsensor, ventricular fibrillation resulted in an immediate reduction in all measured parameters. During cardiopulmonary resuscitation, brain oxygen tension remained unchanged. After the return of spontaneous circulation, all measured parameters including brain oxygen tension recovered to baseline levels. Muscle tissue oxygen tension followed a similar trend as the brain, but with slower response times. We conclude that measurements of brain tissue oxygen tension, which more accurately reflect adequacy of tissue perfusion during cardiac arrest and resuscitation, may contribute to the development of new strategies to optimise perfusion during cardiac resuscitation and improve patient outcomes after cardiac arrest.

BRCA1 gene therapy reduces systemic inflammatory response and multiple organ failure and improves survival in experimental sepsis.

Sepsis-related complications and mortality remain a major clinical problem. Increased cell death and unresolved cellular repair have been implicated as key upstream mediators of sepsis-induced organ dysfunction and death. We hypothesised that gene therapy with BRCA1, a critical regulator of DNA damage repair and cell survival, would attenuate the sequelae of sepsis and peritonitis in mice subjected to caecal ligation and perforation (CLP) and thioglycollate stimulation. C57Bl/6J mice underwent sham or CLP surgery 3 days following treatment with either human BRCA1 adenovirus (AdBRCA1) or the adeno-CMV-null vector (Adnull). The 24-h post-CLP mortality was 2.8% vs 17.9% (P<0.001) and the median post-CLP survival was 50.5 vs 33 h (P<0.05) for AdBRCA1- vs Adnull-treated mice, respectively. AdBRCA1 therapy blunted CLP-associated cardiac, pulmonary, hepatic and renal dysfunction and also reduced CLP-elicited double strand breaks and apoptosis in the liver. BRCA1 gene therapy was associated with lower CLP-evoked cardiac and hepatic superoxide generation that in the liver was in part due to improved reactive oxygen species removal. CLP also elevated mesenteric arteriolar and serum intercellular adhesion molecule-1, both of which were partially abrogated with AdBRCA1 administration. Thioglycollate-challenged AdBRCA1-treated mice displayed reduced peritoneal neutrophil recruitment and dampened cytokine elaboration relative to their Adnull-treated counterparts. Taken together, we report a novel role of BRCA1 gene therapy in limiting systemic inflammation, multiple-organ failure and mortality in experimental sepsis.

Mast cells promote lung vascular remodelling in pulmonary hypertension.

Left heart disease (LHD) frequently causes lung vascular remodelling and pulmonary hypertension (PH). Yet pharmacological treatment for PH in LHD is lacking and its pathophysiological basis remains obscure. We aimed to identify candidate mechanisms of PH in LHD and to test their relevance and therapeutic potential. In rats, LHD was induced by supracoronary aortic banding. Whole genome microarray analyses were performed, candidate genes were confirmed by RT-PCR and Western blots and functional relevance was tested in vivo by genetic and pharmacological strategies. In lungs of LHD rats, mast cell activation was the most prominently upregulated gene ontology cluster. Mast cell gene upregulation was confirmed at RNA and protein levels and remodelled vessels showed perivascular mast cell accumulations. In LHD rats treated with the mast cell stabiliser ketotifen, or in mast cell deficient Ws/Ws rats, PH and vascular remodelling were largely attenuated. Both strategies also reduced PH and vascular remodelling in monocrotaline-induced pulmonary arterial hypertension, suggesting that the role of mast cells extends to non-cardiogenic PH. In PH of different aetiologies, mast cells accumulate around pulmonary blood vessels and contribute to vascular remodelling and PH. Mast cells and mast cell-derived mediators may present promising targets for the treatment of PH.

S100B interaction with the receptor for advanced glycation end products (RAGE): a novel receptor-mediated mechanism for myocyte apoptosis postinfarction.

RATIONALE: Post-myocardial infarction ventricular remodeling is associated with the expression of a variety of factors including S100B that can potentially modulate myocyte apoptosis. OBJECTIVE: This study was undertaken to investigate the expression and function of S100B and its receptor, the receptor for advanced glycation end products (RAGE) in both postinfarction myocardium and in a rat neonatal myocyte culture model. METHODS AND RESULTS: In a rat model of myocardial infarction following coronary artery ligation, we demonstrate in periinfarct myocytes, upregulation of RAGE, induction of S100B, and release into plasma with consequent myocyte apoptosis. Using a coimmunoprecipitation strategy, we demonstrate a direct interaction between S100B and RAGE. In rat neonatal cardiac myocyte cultures, S100B at concentrations > or = 50 nmol/L induced myocyte apoptosis, as evidenced by increased terminal DNA fragmentation, TUNEL, cytochrome c release from mitochondria to cytoplasm, phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p53, increased expression and activity of proapoptotic caspase-3, and decreased expression of antiapoptotic Bcl-2. Transfection of a full-length cDNA of RAGE or a dominant-negative mutant of RAGE resulted in increased or attenuated S100B-induced myocyte apoptosis, respectively. Inhibition of ERK1/2 by U0126/PD-98059 or overexpression of a dominant negative p53 comparably inhibited S100B-induced myocyte apoptosis. CONCLUSIONS: These results suggest that interaction of RAGE and its ligand S100B after myocardial infarction may play a role in myocyte apoptosis by activating ERK1/2 and p53 signaling. This receptor-mediated mechanism is uniquely amenable to therapeutic intervention.

CCS/CAR/CANM/CNCS/CanSCMR joint position statement on advanced noninvasive cardiac imaging using positron emission tomography, magnetic resonance imaging and multidetector computed tomographic angiography in the diagnosis and evaluation of ischemic heart disease--executive summary.

BACKGROUND: Over the past few decades, advanced imaging modalities with excellent diagnostic capabilities have emerged. The aim of the present position statement was to systematically review existing literature to define Canadian recommendations for their clinical use. METHODS: A systematic literature review to 2005 was conducted for positron emission tomography (PET), multidetector computed tomographic angiography and magnetic resonance imaging (MRI) in ischemic heart disease. Papers that met the criteria were reviewed for accuracy, prognosis data and study quality. Recommendations were presented to primary and secondary panels of experts, and consensus was achieved. RESULTS: Indications for PET include detection of coronary artery disease (CAD) with perfusion imaging, and defining viability using fluorodeoxyglucose to determine left ventricular function recovery and/or prognosis after revascularization (class I). Detection of CAD in patients, vessel segments and grafts using computed tomographic angiography was considered class IIa at the time of the literature review. Dobutamine MRI is class I for CAD detection and, along with late gadolinium enhancement MRI, class I for viability detection to predict left ventricular function recovery. Imaging must be performed at institutions and interpreted by physicians with adequate experience and training. CONCLUSIONS: Cardiac imaging using advanced modalities (PET, multidetector computed tomographic angiography and MRI) is useful for CAD detection, viability definition and, in some cases, prognosis. These modalities complement the more widespread single photon emission computed tomography and echocardiography. Given the rapid evolution of technology, initial guidelines for clinical use will require regular updates. Evaluation of their integration in clinical practice should be ongoing; optimal use will require proper training. A joint effort among specialties is recommended to achieve these goals.

Quantification of myocardial perfusion and determination of coronary stenosis severity during hyperemia using real-time myocardial contrast echocardiography.

Although regional myocardial perfusion can be currently quantified with myocardial contrast echocardiography (MCE) by using intermittent harmonic imaging (IHI), the method is tedious and time-consuming in the clinical setting. We hypothesized that regional myocardial perfusion can be quantified and the severity of coronary stenosis determined during hyperemia with MCE using real-time imaging (RTI) where microbubbles are not destroyed. Six open-chest dogs were studied during maximal hyperemia induced by adenosine in the absence or presence of coronary stenoses varying from mild to severe. Myocardial blood flow (MBF) was measured at each stage by using radiolabeled microspheres. MCE was performed using both IHI and RTI. Data for the latter were acquired in both end-systole and end-diastole. No differences were found between myocardial flow velocity (MFV) derived from IHI and RTI when end-systolic frames were used for the latter. MFV was consistently higher for RTI (P <.01) when end-diastolic frames were used. A linear relation was noted between MFV and radiolabeled microsphere-derived MBF ratios from the stenosed and the normal beds when end-systolic frames were used for RTI (r = 0.78, P <.001), whereas no relation was found when end-diastolic frames were used (r = 0.08, P =.78). The scatter for assessing MBF (A.beta) was minimal for IHI and RTI (9%-10%) with end-systolic frames, whereas that for RTI with end-diastolic frames was large (30%). Furthermore the correlation with radiolabeled microsphere-derived MBF was significantly (P <.01) weaker with RTI when end-diastolic frames were used (r = 0.53) than when end-systolic frames (r = 0.94) or IHI was used (r = 0.99). Data acquisition for IHI was 10 minutes, whereas it was 8 seconds for RTI. Thus, RTI can be used to quantify regional myocardial perfusion and stenosis severity during MCE. Only end-systolic frames, however, provide accurate data. RTI offers a rapid and easy means of assessing regional myocardial perfusion with MCE.

Decrease in coronary blood flow reserve during hyperlipidemia is secondary to an increase in blood viscosity.

BACKGROUND: During maximal hyperemia, capillaries provide the greatest resistance to flow. A major determinant of capillary resistance is viscosity. We, therefore, hypothesized that abnormal coronary blood flow (CBF) reserve observed during hyperlipidemia is secondary to increased blood viscosity and not abnormal coronary vasomotion. METHODS AND RESULTS: Maximal hyperemia was induced in 9 dogs using adenosine. Serum triglyceride levels were increased by incremental doses of Intralipid. A good correlation was noted between serum triglyceride levels and blood viscosity (r=0.82). Neither total coronary blood volume nor myocardial blood volume changed with increasing serum triglyceride levels, indicating lack of vasomotion. Myocardial vascular resistance (MVR) increased with increasing triglyceride levels (r=0.84), while hyperemic myocardial blood flow (MBF) decreased (r=-0.64). The decrease in hyperemic MBF was associated with a decrease in blood velocity (r=-0.56). These findings were confirmed with direct intravital microscopic observations in the mice cremaster muscle. CONCLUSIONS: Increasing lipid levels in a fully dilated normal coronary bed causes no change in large or small vessel dimensions. Instead, the increase in blood viscosity causes capillary resistance to rise, which attenuates hyperemic CBF. Therefore, the abnormal CBF reserve associated with hyperlipidemia is due to increase blood viscosity and not abnormal vascular function.

Quantification of cerebral perfusion with "Real-Time" contrast-enhanced ultrasound.

BACKGROUND: No noninvasive technique is currently capable of "real-time" assessment and monitoring of cerebral blood flow (CBF). We hypothesized that cerebral perfusion could be accurately measured and monitored in "real time" with contrast-enhanced ultrasound (CEU). METHODS AND RESULTS: Cerebral perfusion was assessed in 9 dogs through a craniotomy with CEU at baseline and during hypercapnia and hypocapnia while normoxia was maintained. Cerebral microvascular blood volume (A), microbubble velocity (beta), and blood flow (Axbeta) were calculated from time-versus-acoustic intensity relations. Compared with baseline, hypercapnia and hypocapnia significantly increased and decreased CBF, respectively, as measured by CEU. These changes in blood flow were mediated by changes in both A and beta. A good correlation was found between Axbeta derived from CEU and CBF measured by radiolabeled microspheres (y=0.67x-0.04, r=0.91, P<0.001). CONCLUSIONS: Changes in both cerebral microvascular blood volume and red blood cell velocity can be accurately assessed with CEU. Thus, CEU has the potential for bedside measurement and monitoring of cerebral perfusion in real time in patients with craniotomies or burr holes.