Nanosuspensions of alendronate with gallium or gadolinium attenuate neointimal hyperplasia in rats

Abstract

Monocytes/macrophages play a pivotal role in the formation of neointinal hyperplasia following vascular injury. Transient depletion of circulating monocytes by particulate delivery systems containing bisphosphonates, such as alendronate, results in restenosis inhibition. We hypothesized that a self-suspendable nanoparticulate dosage form, with a minimum amount of expients, could be formulated by complexing the negatively charged alendronate with gallium or gadolinium. We further hypothesized that a synergistic biological effect could be obtained by nanosuspensions of alendronate with these counter ions. Nanosuspensions (150-250 nm) of alendronate-gallium and alendronate-gadolinium were successfully formulated with no additives except for the active agents and HCl for pH adjustment. Both nanosuspensions exhibited macrophage cell line growth inhibition in a dose-response relationship in comparison to the various agents in solution and in liposomes. A synergistic effect of the nanosuspensions was observed in the inhibition of raw264 macrophages, and in reducing IL-1beta and TNF-alpha secretion in cell culture. Single IV administration at the time of injury, of alendronate-gallium or alendronate-gadolinium nanosuspensions resulted in inhibition of neointimal hyperplasia and stenosis in the rat model of vascular injury. The results correlated with the significant reduction of circulating monocytes. The nanosuspensions possess the advantages of no additives for minimal provocation of side effects, and the potential of immunomodulating inflammatory disorders.