Vascular Endoluminal Delivery of Mesenchymal Stem Cells Using Acoustic Radiation Force

Abstract

Restoration of functional endothelium is a requirement for preventing late stent thrombosis. We propose a novel method for targeted delivery of stem cells to a site of arterial injury using ultrasound-generated acoustic radiation force. Mesenchymal stem cells (MSCs) were surface-coated electrostatically with cationic gas-filled lipid microbubbles (mb-MSC). mb-MSC was characterized microscopically and by flow cytometry. The effect of ultrasound (5 MHz) on directing mb-MSC movement toward the vessel wall under physiologic flow conditions was tested in vitro in a vessel phantom. In vivo testing of acoustic radiation force-mediated delivery of mb-MSCs to ballooninjured aorta was performed in rabbits using intravascular ultrasound (1.7 MHz) during intra-aortic infusion of mb-MSCs. Application of ultrasound led to marginalization and adhesion of mb-MSCs to the vessel phantom wall, whereas no effect was observed on mb-MSCs in the absence of ultrasound. The effect was maximal when there were 7 -1 microbubbles/cell (n = 6). In rabbits (n = 6), adherent MSCs were observed in the ultrasound-treated aortic segment 20 min after the injection (334 -137 MSCs/cm 2 ), whereas minimal adhesion was observed in control segments not exposed to ultrasound (2 -1 MSCs/cm 2 , p < 0.05). At 24 h after mb-MSC injection and ultrasound treatment, the engrafted MSCs persisted and spread out on the luminal surface of the artery. The data demonstrate proof of principle that acoustic radiation force can target delivery of therapeutic cells to a specific endovascular treatment site. This approach may be used for endoluminal cellular paving and could provide a powerful tool for cell-based re-endothelialization of injured arterial segments.

Acoustic Radiation Force for Vascular Cell Therapy: In Vitro Validation

“…MSCs were mixed for 5 minutes with cationic MBs at a ratio of 1:40, previously experimentally shown by us to be optimal for achieving ARF-induced MB-MSC adhesion to a vascular surface (Toma et al 2011). The MB-MSC suspension was then diluted to a concentration of 5 × 10 3 cells/ml in a sample reservoir, with a solution of PVP and PBS adjusted to include 1 mM of calcium chloride (CaCl 2 ) and 0.5 mM of magnesium chloride (MgCl).…”

“…However, intra-arterially delivered cells would have to overcome significant hydrodynamic forces to adhere under flow, which is why experimental in vivo delivery of EPCs or MSCs to a specific vascular segment usually requires prolonged cessation of flow to that segment, an ineffective and impractical option from a clinical standpoint. We have previously reported a novel in vivo method for effective targeted delivery of stem cells to a site of arterial injury using ARF (Toma et al 2011). By tagging MSCs with gas-filled lipid MBs, the MB-cell complexes were selectively pushed with acoustic energy to the endoluminal surface of the arterial wall.…”

“…Therefore, the MBs themselves are not targeted, but they serve as carriers for MSCs. We have demonstrated previously that the MSCs could be successfully delivered to the endothelium in the abdominal aorta through in vivo experiments in a rabbit model (Toma et al, 2011). …”

Mechanistic Insights into Arterial Repair with Mesenchymal Stromal Cells

“…This could be achieved by direct infusion into the lumen of the target vessel, or by using novel approaches like magnetic tagging [25], ultrasound-generated acoustic radiation forces [26] or antibody capture to attract cells to the surface of the revascularized conduit (stent or graft). New catheter injection systems are also in development that will enable cells to be injected transluminally into the vascular adventitia and periadventitial space.…”

Reducing Neointima Formation in a Swine Model with IVUS and Sirolimus Microbubbles

“…Microbubbles, an ultrasound contrast agent and drug delivery vehicle, are comprised of a gas core surrounded by a lipid shell that can be loaded with molecules for delivery (e.g., fluorophores, drugs, genes, stem cells 55 ). Importantly, microbubble oscillations enhance drug deliver by causing the transient permeabilization of the cell membrane.…”