Background: Nanoparticles possess several advantages as a carrier system for intracellular delivery of therapeutic agents. Rapamycin is an immunosuppressive agent which also exhibits marked antiproliferative properties. We investigated whether rapamycin-loaded nanoparticles(NPs) can reduce neointima formation in a rat model of vein graft disease.
Methods: Poly(lactic-co-glycolic acid) (PLGA) NPs containing rapamycin was prepared using an oil/water solvent evaporation technique. Nanoparticle size and morphology were determined by dynamic light scattering methodology and electron microscopy. In vitro cytotoxicity of blank, rapamycin-loaded PLGA (RPLGA) NPs was studied using MTT Assay. Excised rat jugular vein was treated ex vivo with blank-NPs, or rapamycin-loaded NPs, then interposed back into the carotid artery position using a cuff technique. Grafts were harvested at 21 days and underwent morphometric analysis as well as immunohistochemical analysis.
Results: Rapamycin was efficiently loaded in PLGA nanoparticles with an encapsulation efficiency was 87.6%. The average diameter of NPs was 180.3 nm. The NPs-containing rapamycin at 1 ng/ml significantly inhibited vascular smooth muscular cells proliferation. Measurement of rapamycin levels in vein grafts shown that the concentration of rapamycin in vein grafts at 3 weeks after grafting were 0.9 ± 0.1 μg/g. In grafted veins without treatment intima-media thickness was 300.4 ± 181.5 μm after grafting 21 days. Whereas, Veins treated with rapamycin-loaded NPs showed a reduction of intimal-media thickness of 150.2 ± 62.5 μm (p = 0.001). CD-31 staining was used to measure luminal endothelial coverage in grafts and indicated a high level of endothelialization in 21 days vein grafts with no significant effect of blank or rapamycin-loaded NPs group.
Conclusions: We conclude that sustained-release rapamycin from rapymycin loaded NPs inhibits vein graft thickening without affecting the reendothelialization in rat carotid vein-to-artery interposition grafts and this may be a promising therapy for the treatment of vein graft disease.