Vascular Gene Transfer of Phosphomimetic Endothelial Nitric Oxide Synthase (S1177D) Using Ultrasound-Enhanced Destruction of Plasmid-Loaded Microbubbles Improves Vasoreactivity

Abstract

Background — Local gene therapy has enormous potential for the treatment of vascular disease. We determined whether diagnostic ultrasound-mediated destruction of plasmid-loaded albumin microbubbles is a feasible and efficient technique for local vascular gene delivery. For gene transfer, we used a phosphomimetic, active endothelial nitric oxide synthase (eNOS) construct in which Ser1177 was replaced by aspartic acid (S1177D) and exhibits a 2-fold higher basal activity than the wild-type enzyme. Methods and Results — Gas-filled microbubbles (3.0±1.2 μm) were created by sonication of 5% human albumin in the presence of plasmid DNA encoding for LacZ or eNOS S1177D. Porcine coronary arteries were perfused with DNA-loaded albumin microbubbles in vitro, exposed to diagnostic ultrasound (5 seconds), and incubated for a further 24 hours. Detection of the β-galactosidase in LacZ -transfected vessels revealed a predominant staining of endothelial cells without any functional impairment of vasoreactivity. Western blotting demonstrated the expression of the eNOS S1177D construct in extracts from the transfected segments. Vascular responsiveness was tested with prostaglandin F 2α and the NOS inhibitor N ω nitro- l -arginine. Compared with segments treated with the expression plasmid alone, the contractile response to prostaglandin F 2α was impaired in segments transfected with eNOS S1177D, whereas the contractile response to the administration of N ω nitro- l -arginine was markedly enhanced. Conclusions — Ultrasound-mediated destruction of eNOS S1177D DNA-loaded albumin microbubbles is a feasible and efficient method for vascular gene transfection. Transfection resulted in significant protein expression and enhanced NO-mediated relaxation of bradykinin-stimulated porcine coronary arteries.