Background: Ischemic skeletal muscle has been shown to be advantageous for taking up and expressing genes transferred in the form of naked plasmid DNA. Therefore, acutely ischemic skeletal muscle may represent a potential target for IM gene therapy with naked DNA. Accordingly, we investigated the impact of IM injection of plasmid DNA encoding the secreted angiogenic growth factor, vascular endothelial growth factor (VEGF), on collateral vessel development in an animal model of acute hindlimb ischemia.
Methods and results: After ligation of distal external iliac artery in New Zealand White rabbits, we directly injected 500 microg of phVEGF165 into the ischemic thigh muscles. At 30 days posttransfection, VEGF-transfected animals had more angiographically recognizable collateral vessels (angiographic score=0.72+/-0.06 versus 0.48+/-0.10; P<.01) as well as histologically assessed capillaries (248+/-37 versus 180+/-32/mm2, P<.01) compared to controls. Hemodynamic deficit was less severe in VEGF-transfected animals by calf systolic blood pressure ratio (0.80+/-0.09 versus 0.56+/-0.10, P<.01) and by flow to the ischemic limb measured with Doppler guidewire (resting flow=22+/-5 versus 14+/-4; P<.01; hyperemic flow=59+/-17 versus 39+/-12 mL/min; P<.05). Human VEGF mRNA was expressed in the transfected ischemic muscles as long as 14 days after gene transfer. Based on reporter plasmid expression, transfection efficiency was sixfold higher in ischemic muscles than in nonischemic control muscles.
Conclusions: These results suggest the feasibility of employing direct IM transfer of naked VEGF plasmid DNA to optimize treatment of acute limb ischemia.