Angiogenesis with nanomolecular gene therapy vectors

Myocardial infarction often leads to left ventricular dysfunction, cardiomyopathy and heart failure through cell death resulting from lacking oxygen supply of the affected tissue. Revascularization of ischemic myocardium can significantly improve global ventricular function. However, coronary artery disease in patients with ischemic cardiomyopathy often is not amenable to either percutaneous revascularization or coronary artery bypass grafting. This has promoted extensive investigation in alternative revascularization strategies, such as attempts to exogenously induce angiogenesis using a variety of growth factors, such as fibroblast growth factor and vascular endothelial growth factor. Because of its potent angiogenic effects, we postulate that local secretoneurin therapy might be effective in treating ischemic cardiomyopathy. Recently, a gene therapy vector (plasmid) has been developed and characterized for this novel angiogenic neuropeptide and showed beneficial effects in the mouse hindlimb ischemia model. Secretoneurin gene therapy increased limb blood perfusion, density of capillaries and arteries and reduced foot necrosis. The aim of this study is to investigate the functional and biochemical effects of direct myocardial injection of different secretoneurin gene therapy vectors in a rat model of postinfarction heart failure. Besides the unpacked plasmid, nanoparticulate plasmid- formulations should be developed and investigated for their potency to increase cardiac cell transfection. For nanopariculate formulation, chitosan modified with thioglycolic acid as well as poly (lactic-co-glycolic)acid (PLGA) were chosen, as they allow formulation of stable complexes with plasmid structures and proved there transfection efficacy before. Following hypothesis shall be tested: Does Secretoneurin have beneficial effects on cardiac repair by inducing therapeutic angiogenesis in the hypoxic myocardium, leading to restoration of the left ventricle and prevention of cardiac dysfunction. In addition, the aim will be to develop nanomolecular structured plasmid carriers, based on the multifunctional polymers chitosan-thioglycolic acid as well as PLGA. In this part of the investigation, the hypothesis that nanomolecular plasmid carriers, which are more stable, allow sustained plasmid release and protection against enzymatic degredation, increase the efficacy of the beneficial effects of secretoneurin by facilitating cell transfection, should be ascertained.

Coronary heart disease represents a common disease and together with other vascular diseases is the most prominent cause of death in industrialized countries. Chronic ischemia or acute myocardial infarction, characterized by an acute occlusion of a large coronary vessel, might lead to reduced contractility of the ventricle and heart failure. A significant proportion of patients with coronary heart disease have no option of revascularization and this group of patients would profit from novel therapeutic approaches like therapeutic angiogenesis. Angiogenesis represents the growth of new blood vessels due to action of several cytokines known to moderate this effect. Vascular endothelial growth factor and fibroblast growth factor are the best characterized angiogenic cytokines. We recently described a novel angiogenic factor, the neuropeptide secretoneurin and tested the hypothesis that gene therapy with this factor improves outcome in the rat myocardial infarction model. Secretoneurin gene therapy improved left ventricular function after induction of infarction (as measured by Echocardiography and invasively by catheter) and reduced fibrosis. When the infarct border zone was analyzed for density of blood vessels secretoneurin induced significant increase of capillaries and arteries indicating induction of angiogenesis and arteriogenesis. We also could show that secretoneurin exerts positive effects on human coronary arterial endothelial cells (inhibition of apoptosis, stimulation of proliferation) and activates proteins of signal transduction like Akt or MAPkinases in these cells. Interestingly, these effects were blocked by a neutralizing antibody against vascular endothelial growth factor indicating that secretoneurin-induced effects are mediated by this prominent angiogenic factor. We also were able to dissect the mechanism of this interaction and could demonstrate that secretoneurin stimulates binding of vascular endothelial growth factor to its receptor. The results of this work were published recently in Circulation (Albrecht -Schgoer et al., 2012). We also investigated the effect of nanomolecular carriers on transfection efficacy of secretoneurin plasmid but unfortunately were not able to improve transfection efficacy. In summary, our data indicate that secretoneurin gene therapy improves function in an animal model of myocardial infarction and future studies aim to improve transfection efficacy of (viral) secretoneurin gene therapy vectors or slow release peptide formulations to ultimately apply this therapy in patients suffering from this disease.