Electric pulses augment reporter gene expression in the beating heart

Background Gene therapy of the heart has been attempted in a number of clinical trials with the injection of naked DNA, although quantitative information on myocellular transfection rates is not available. The present study aimed to quantify the efficacy of electropulsing protocols that differ in pulse duration and number to stimulate transfection of cardiomyocytes and to determine the impact on myocardial integrity. Methods Reporter plasmid for constitutive expression of green fluorescent protein (GFP) was injected into the left ventricle of beating hearts of adult, male Lewis rats. Four electrotransfer protocols consisting of repeated long pulses (8 x 20 ms), trains of short pulses (eight trains of either 60 or 80 x 100 mu s) or their combination were compared with control procedures concerning the degree of GFP expression and the effect on infiltration, fibrosis and apoptosis. Results All tested protocols produced GFP expression at the site of plasmid injection. Continuous pulses were most effective and increased the number of GFP-positive cardiomyocytes by more than 300-fold compared to plasmid injection alone (p<0.05). Concomitantly, the incidence of macrophage infiltration, fibrosis and cell death was increased. Trains of short pulses reduced macrophage infiltration and fibrosis by four-and two-fold, respectively, although they were 20-fold less efficient in stimulating cardiomyocyte transfection. GFP expression co-related to delivered electric energy, infiltration and fibrosis, although not apoptosis. Conclusions The data imply that electropulsing of the myocardium promotes the overexpression of exogenous protein in mature cardiomyocytes in relation to an injury component. Fractionation of pulses is indicated as a option for sophisticated gene therapeutic approaches to the heart. Copyright (C) 2012 John Wiley & Sons, Ltd.