Background-Innate immunity is of major importance in vascular repair. The present study evaluated whether systemic and transient depletion of monocytes and macrophages with liposome-encapsulated bisphosphonates inhibits experimental in-stent neointimal formation. Methods and Results-Rabbits fed on a hypercholesterolemic diet underwent bilateral iliac artery balloon denudation and stent deployment. Liposomal alendronate (3 or 6 mg/kg) was given concurrently with stenting. Monocyte counts were reduced by Ͼ90% 24 to 48 hours after a single injection of liposomal alendronate, returning to basal levels at 6 days. This treatment significantly reduced intimal area at 28 days, from 3.88Ϯ0.93 to 2.08Ϯ0.58 and 2.16Ϯ0.62 mm 2 . Lumen area was increased from 2.87Ϯ0.44 to 3.57Ϯ0.65 and 3.45Ϯ0.58 mm 2 , and arterial stenosis was reduced from 58Ϯ11% to 37Ϯ8% and 38Ϯ7% in controls, rabbits treated with 3 mg/kg, and rabbits treated with 6 mg/kg, respectively (meanϮSD, nϭ8 rabbits/group, PϽ0.01 for all 3 parameters). No drug-related adverse effects were observed. Reduction in neointimal formation was associated with reduced arterial macrophage infiltration and proliferation at 6 days and with an equal reduction in intimal macrophage and smooth muscle cell content at 28 days after injury. Conversely, drug regimens ineffective in reducing monocyte levels did not inhibit neointimal formation.
Conclusions-Systemic
Systemic transient inactivation of monocytes and macrophages by LBPs reduced macrophage infiltration and neointimal formation in the rat carotid injury model. The findings demonstrate a BP potency-effect relationship, and highlight the role of circulating monocytes in vascular injury and repair.
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