Nanospheres of a Bisphosphonate Attenuate Intimal Hyperplasia

Abstract

The present study explored a novel strategy for attenuation of restenosis after arterial injury by a bisphosphonate encapsulated in polymeric nanoparticles (NP) for transient selective depletion of macrophages. A bisphosphonate (BP), 2-(2-Aminopyrimidino) ethyldiene-1,1-bisphosphonic acid betaine (ISA), was successfully formulated in 400 nm sized polylactide/glycolide-based NP with high yield (69%) and entrapment efficiency (60% w/w). ISA NP, but not blank NP or free ISA, exhibited specific and significant cytotoxic effect on macrophages-like RAW 264 cells, in a dose-dependent manner, with no inhibitory effect on the growth of smooth muscle cells (SMCs). Fluorescent pyrene-labeled NP were shown to be taken up by RAW 264 cells, but not by SMCs. Intravenously (i.v.) administered ISA NP (15 mg/kg, single dose on day-1) resulted in a significant attenuation of neointima to media area ratio (N/M) by 40% and stenosis by 45% 14 days after rat carotid injury, in comparison to animals treated with free ISA, buffer or blank NP. However, the effect was not preserved 30 days post injury, and an insignificant reduction of neointimal formation was observed. Neointimal hyperplasia was also significantly suppressed after subcutaneous (SC) injection of ISA NP (15 mg/kg, single dose on day-1), reducing both N/M and stenosis. Intraperitoneal (i.p.) injection of silica, a known selective toxin for macrophages, (1000 mg/kg), also resulted in a significant inhibition of N/M and stenosis, which further reinforces the cause-effect relationship of macrophage-inactivation and the prevention of neointima formation. Biocompatible and biodegradable NP loaded with ISA characterized by high colloidal stability, reproducible activity, and high drug entrapment warrant further consideration for restenosis therapy, and may be useful in other disease processes involving monocytes/macrophages.

Liposomal Simvastatin Attenuates Neointimal Hyperplasia in Rats

“…Long term inactivation of macrophages carries the danger of immunosuppression and infection. However, as in several studies in rabbits and rats, no overt infection was observed with partial and transient monocytes depletion (12)(13)(14)(15)(16)42,46,59).…”

“…Circulating blood monocytes fully recovered 7 days after injection. The effects of liposomal simvastatin are limited to cells with phagocytic capacity with no effect on other cells, such as SMC or endothelial cells, as has been demonstrated in animals treated with liposomal BPs (12)(13)(14)(15)(16)42,46). Simvastatin leaking from inactivated monocytes and the delivery system would accumulate mainly in the liver.…”

“…Macrophage content in atherectomy tissue and the activation status of blood monocytes correlate with an increased rate of restenosis in humans (57,58). Recently, we have shown that transient and partial depletion of circulating monocytes by particulate dosage forms such as polymeric NP and liposomes-laden BPs suppresses neointimal formation and reduces experimental restenosis (12)(13)(14)(15)(16). It is suggested that, similarly to liposomal BPs (14-16), the inhibition of stenosis was mediated via simvastatin liposomes accumulation in circulating monocytes and their inactivation.…”

“…The bisphosphonates (BPs), bone-seeking drugs, and osteoclasts inhibitors deplete circulating monocytes and inhibit macrophages when administered in a particulated dosage form, which is avidly phagocytosed by these cells. Recently, we have shown that partial and transient systemic inactivation of monocytes by polymeric nanoparticles (NP) and liposome-encapsulated BPs suppresses neointimal formation and reduces experimental restenosis (12)(13)(14)(15)(16).…”

Effect of nanoparticles binding ß-amyloid peptide on nitric oxide production by cultured endothelial cells and macrophages

“…Previously, Afergan et al and Cohen-Sela et al reported that RAW264.7 cells exposed to nanoparticles, including liposomes, were transiently inactivated, thereby compromising the function of cultured macrophages and leading to a diminished inflammatory response. 35,36 Overall, our results suggest that PA-LIP and CL-LIP could potentially be used in vivo without triggering a negative response in endothelial cells or macrophages, but this needs further confirmation.…”