Lipoplex gene transfer of inducible nitric oxide synthase inhibits the reactive intimal hyperplasia after expanded polytetrafluoroethylene bypass grafting

ObjectiveIntimal hyperplasia (IH) is most commonly the cause of graft occlusion in infrainguinal bypass grafting for arterial occlusive disease. We investigated the influence of nitric oxide on the IH of the arterial vessel wall at the region of prosthetic bypass anastomoses.MethodsExperiments were performed in 10 Foxhound dogs. We used a technique of inducible nitric oxide synthase (iNOS) overexpression by a non–virus-mediated, liposome-based iNOS gene transfer. The plasmid pSCMV-iNOS, which drives the expression of iNOS under control of the cytomegalovirus promoter, was complexed with cationic liposomes (lipoplexes). Segments of both carotid arteries were pretreated by intramural injection of a lipoplex solution by using an infiltrator balloon catheter (Infiltrator Drug Delivery Balloon System). In each dog, iNOS was administered at one side, and a control vector (pSCMV2) was administered at the contralateral side. Carotid arteries were ligated, and bypass grafts (expanded polytetrafluoroethylene, 6-mm, ring enforced) were implanted on both sides. The proximal and distal anastomoses (end-to-side fashion; running nonabsorbable sutures) were placed in the pretreated regions. After 6 months, the prostheses were excised, and the intimal thicknesses of 50 cross sections (orcein staining) of each anastomosis were measured planimetrically.ResultsThe average reduction of the neointima thickness of the iNOS side in proximal anastomoses at the prosthetic wall, suture region, and arterial wall was 43%, 52%, and 81%, respectively. In distal anastomoses, the average reduction was 40%, 47%, and 52%, respectively. All differences of neointima thickness between the iNOS and control sides were statistically significant (Wilcoxon test; P ≤ .05).ConclusionsInducible NOS expression is an efficient approach for inhibition of IH. In contrast to earlier studies, which investigated the efficacy of gene therapeutic NOS expression at 3 to 4 weeks after intervention, the novelty of our findings is that a single local lipoplex-mediated transfection of the vascular wall with iNOS-expressing plasmids leads to a reduction of IH in a prosthetic in vivo model even after 6 months. Because all components can be manufactured under Good Manufacturing Practice conditions (the quality-management system of the European pharmaceutical industry based on ISO 9000), this approach is also amenable to human therapy.

Clinical RelevanceIntimal hyperplasia is a uniform adverse effect after vascular suture, endarterectomy, angioplasty, and stenting and is the most limiting factor with regard to long-term patency. Eradication of intimal hyperplasia by lipoplex gene transfer of inducible nitric oxide synthase would be a milestone in the development of vascular and endovascular procedures. The results of bypass grafting, as well as those of endarterectomies, patch plasties, angioplasties, and stents in supra-aortic, coronary, visceral, renal, and peripheral vessels, could thus be markedly improved. The manufacturing process of inducible nitric oxide synthase lipoplexes under Good Manufacturing Practice conditions is well established, but the substance is commercially not available yet. The promising results presented here should encourage the industry to commercialize inducible nitric oxide synthase lipoplexes and to foster necessary clinical and experimental studies within a wide range of possible applications.