Efficient transgene expression from naked DNA delivered into an arterio-venous fistula model for kidney dialysis

Background: Patients with kidney failure frequently require the formation of an arterio-venous fistula (AVF) in which a vein is connected to an artery resulting in arterialization of the vein to allow adequate blood flow into an external 'artificial kidney'. In most patients, neo-intimal hyperplasia (NIH) ensues, causing narrowing and subsequent occlusion of the vein, leading to significant morbidity. The cellular events causing venous NIH may serve as ideal targets for molecular-based therapies. However, therapeutic gene delivery into the vascular system is seriously impeded by problems related to the low efficacy and toxicity of targeted viral vector delivery. Materials and methods: To explore the feasibility of a plasmid-based vascular gene delivery system, we established a rat AVF model that develops NIH. Plasmids encoding for reporter or therapeutic genes were delivered into the blood vessels at the time or after AVF formation. Results: Intra-luminal injection of plasmid into the AVF resulted in extensive and long-term reporter gene expression at the venous limb mainly at the site of NIH formation. Transgene expression was confined to endothelial cells and myofibroblasts that migrate inwards from the adventitia and form the NIH lesion. There was no detrimental tissue reaction to plasmid delivery, contrasting with the severe inflammatory response observed after adenovirus infection. Intra-vascular delivery of a plasmid carrying the endothelial nitric oxide synthase gene resulted in sustained production of nitric oxide, previously shown to mitigate NIH formation. Conclusions: These findings open the possibility of vascular transduction with naked DNA bearing therapeutic genes in areas prone to NIH to ameliorate vein graft pathologies using simple and clinically applicable vector delivery methods.