Keywords: magnetic nanoparticles, magnetic targeting, in-stent restenosis, endothelium, cell therapy, vascular healing
Summary:The advent of percutaneous transluminal angioplasty with stent implantation and the even more recent use of drug-eluting stents have resulted in a paradigm shift in the care of obstructive vascular disease. However, deleterious sequelae of endovascular interventions are the result of unavoidable mechanical damage to the vessel wall. Disruption of the endothelial monolayer exposes the underlying media and induces a cascade of cellular and biological events, resulting in abnormal vascular wall function. Current standards of clinical care focus on inhibition of smooth muscle cells using drug-eluting stents that release nonselective antiproliferative drugs, which also affect endothelial cells, the important modulators of vascular hemostasis, fibrinolysis, and proliferative state of the smooth muscle cells. Alternatively, the promotion of healing in the vascular endothelium may be a more natural and consequently safer approach in the prevention of vascular restenosis and thrombosis. Therefore, strategies that promote recovery of endothelial cells in the vessel wall following injury may limit complications such as thrombosis, vasospasm, and neointimal formation, through the reconstitution of a luminal barrier and cellular secretion of paracrine factors. The present study assessed the potential of magnetically mediated delivery of endothelial cells (ECs) to inhibit in-stent stenosis induced by mechanical injury in a rat carotid artery stent angioplasty model. Syngeneic ECs loaded (25pg magnetite/cell) with polylactide-based magnetic nanoparticles (MNPs) and transduced with luciferase gene were administered at the distal end of the stented artery using a brief exposure (12 min) to a uniform magnetic field (1.4-kOe). Bioluminescent imaging was used to demonstrate successful localization of the ECs to the stented artery segment and assess the viability of the delivered cells over two months. The therapeutic effect of the magnetic cell delivery was assessed by quantitative ultrasonic imaging measuring morphological (lumen diameter) and hemodynamic changes (peak systolic velocity) in the targeted and non-targeted (control) animals. After two months, magnetic localization of ECs demonstrated significant protection from stenosis at the distal part of the stent in the cell therapy group compared to both the proximal part of stent in the cell therapy group and the control (stented, nontreated) group: 1.7-fold (p < 0.001) less reduction in lumen diameter as measured by B-mode and color Doppler ultrasound, 2.3-fold (p < 0.001) less reduction in the ratios of peak systolic velocities as measured by pulsed wave Doppler ultrasound, and 2.1-fold (p < 0.001) attenuation of stenosis as determined through end point morphometric analysis, which correlated with the detected traces of MNPs found only at the distal end of the stented artery. This work demonstrates that magnetically mediated targeting of nonmodified endothelial cells prevented the development of in-stent stenosis nearly 2-fold earlier and with a 2-fold greater magnitude in treated animals in comparison to untreated controls. In the future, addressing uniformity of cell delivery, choice of stent material, cell source and considering enhancement of EC function via genetic manipulation, the methodology investigated here may provide the basis for designing the next generation of cell-based therapy for vascular healing after stent angioplasty.