Direct Intramuscular Gene Transfer of Naked DNA Encoding Vascular Endothelial Growth Factor Augments Collateral Development and Tissue Perfusion

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Abstract
Background Striated muscle has been shown to be capable of taking up and expressing foreign genes transferred in the form of naked plasmid DNA, although typically with a low level of gene expression. In the case of genes that encode secreted proteins, however, low transfection efficiency may not preclude bioactivity of the secreted gene product. Accordingly, we investigated the hypothesis that intramuscular (IM) gene therapy with naked plasmid DNA encoding vascular endothelial growth factor (VEGF) could augment collateral development and tissue perfusion in an animal model of hindlimb ischemia. Methods and Results Ten days after ischemia was induced in one rabbit hindlimb, 500 μg of phVEGF 165 , or the reporter gene LacZ , was injected IM into the ischemic hindlimb muscles. Thirty days later, angiographically recognizable collateral vessels and histologically identifiable capillaries were increased in VEGF transfectants compared with controls. This augmented vascularity improved perfusion to the ischemic limb, documented by a superior calf blood pressure ratio for phVEGF 165 (0.85±0.05) versus controls (0.64±0.05, P <.01), improved blood flow in the ischemic limb (measured with an intra-arterial Doppler wire) at rest (phVEGF 165 =21.3±3.9 mL/min, control=14.6±1.6 mL/min, P <.01) and after a vasodilator (phVEGF 165 =54.2±12.0 mL/min, control=37.3±8.9 mL/min, P <.01) and increased microspheres in the adductor (phVEGF 165 =4.3±1.6 mL·min −1 ·100 g of tissue −1 , control=2.9±1.2 mL·min −1 ·100 g of tissue −1 , P <.05) and gastrocnemius (phVEGF 165 =3.9±1.0 mL·min −1 ·100 g of tissue −1 , control=2.8±1.4 mL·min −1 ·100 g of tissue −1 , P <.05) muscles of the ischemic limb. Conclusions Ischemic skeletal muscle represents a promising target for gene therapy with naked plasmid DNA. IM transfection of genes encoding angiogenic cytokines, particularly those that are naturally secreted by intact cells, may constitute an alternative treatment strategy for patients with extensive peripheral vascular disease in whom the use of intravascular catheter–based gene transfer is compromised and/or prohibited.