Stabilizing Peri-Stent Restenosis Using a Novel Therapeutic Carrier

Abstract

Late in-stent restenosis remains a significant problem. Bare-metal stents were implanted into peripheral arteries in miniature swine, followed by direct intra-arterial infusion of nitric oxide-loaded echogenic liposomes (ELIPs) and anti-intercellular adhesion molecule-1 conjugated ELIPs loaded with pioglitazone exposed to an endovascular catheter with an ultrasonic core. Ultrasound-facilitated delivery of ELIP formulations into stented peripheral arteries attenuated neointimal growth. Local atheroma-targeted, ultrasound-triggered delivery of nitric oxide and pioglitazone, an anti-inflammatory peroxisome proliferator-activated receptor-γ agonist, into stented arteries has the potential to stabilize stent-induced neointimal growth and obviate the need for long-term antiplatelet therapy.

Keywords: ELIP, echogenic liposome; ICAM, intercellular adhesion molecule; IVUS, intravascular ultrasound; NO, nitric oxide; PGN, pioglitazone; SPDP, 3-(2-pyridyldithio propionic acid)-N-hydroxysuccinimide ester; atherosclerosis; in-stent restenosis; nitric oxide; pioglitazone; ultrasound contrast agent.

Graphical abstract

Figure 1

Physical Properties and Localization of Pioglitazone in ELIPs Transmission electron micrographs of (A) empty echogenic liposomes (ELIPs) and (B) ELIPs loaded with pioglitazone shown as an electron-lucency within the lipid bilayers. (C, D, and E) Fluorescein isothiocyanate–labeled pioglitazone (green) appeared to distribute within the lipid shell of the ELIPs (red).

Figure 2

Ultrasound Facilitated the Delivery of Pioglitazone Into the Arterial Wall Representative images of the peripheral arteries demonstrating EKOS ultrasound-facilitated delivery of fluorescently labeled anti–intercellular adhesion molecule (ICAM)-1/pioglitazone (PGN)–echogenic liposomes (ELIPs) into the arterial wall. Multispectral imaging and secondary labeling were used with a goat anti-mouse immunoglobulin G antibody conjugated to AlexaFluor-488. Magnified sections are specified with selection boxes. Scale bars denote 20 μm. The extent of ELIP distribution is indicated by the white arrows. Without EKOS ultrasound activation (middle), anti–ICAM-1/PGN-ELIPs were localized to the endothelial surface, as indicated by the white arrows. With EKOS ultrasound activation, anti–ICAM-1/PGN-ELIPs were seen infiltrating to at least 60 μm into the arterial wall; the arrowheads indicate the extent of ELIP distribution from the superficial to the deeper layers of the artery. NO = nitric oxide.

Figure 3

Ultrasound-Facilitated Delivery of Pioglitazone Reduced Neointimal Atheroma Volume Neointimal atheroma volume within stented segments as determined by using intravascular ultrasound (IVUS). Ultrasound-facilitated delivery of ELIP payload was effective in attenuating neointimal growth within the stented arterial segments (3 stented arteries in each treatment arm). Representative IVUS images of stented segments treated with and without ultrasound are shown (inset figure). Abbreviations as in Figure 2.

Figure 4

Ultrasound-Facilitated Delivery of Pioglitazone Reduced Neointimal Hyperplasia and In-Stent Restenosis The degree of neointimal hyperplasia within stented segments was quantitated as the intima:media ratio in histological sections. Ultrasound-facilitated delivery of ELIP payload was effective in reducing neointimal growth within the stented arterial segments (9 sections from the control arteries vs. 9 sections from the treated cohort). Representative histological images of stented segments treated with and without ultrasound are shown. The arrows indicate the extent of neointimal formation. Abbreviations as in Figure 2.