Multifunctional hydroxyapatite and poly(d,l-lactide-co-glycolide) nanoparticles for the local delivery of cholecalciferol

Cholecalciferol, vitamin D₃, plays an important role in bone metabolism by regulating extracellular levels of calcium. Presented here is a study on the effects of the local delivery of cholecalciferol (D₃) using nanoparticulate carriers composed of hydroxyapatite (HAp) and poly(d,l-lactide-co-glycolide) (PLGA). Multifunctional nanoparticulate HAp-based powders were prepared for the purpose of: (a) either fast or sustained, local delivery of cholecalciferol, and (b) the secondary, osteoconductive and defect-filling effect of the carrier itself. Two types of HAp-based powders with particles of narrowly dispersed sizes in the nano range were prepared and tested in this study: HAp nanoparticles as direct cholecalciferol delivery agents and HAp nanoparticles coated with cholecalciferol-loaded poly(d,l)-lactide-co-glycolide (HAp/D₃/PLGA).Satisfying biocompatibility of particulate systems, when incubated in contact with MC3T3-E1 osteoblastic cells in vitro, was observed for HAp/D₃/PLGA and pure HAp. In contrast, an extensively fast release of cholecalciferol from the system comprising HAp nanoparticles coated with cholecalciferol (HAp/D3) triggered necrosis of the osteoblastic cells in vitro. Artificial defects induced in the osteoporotic bone of the rat mandible were successfully reconstructed following implantation of cholecalciferol-coated HAp nanoparticles as well as those comprising HAp nanoparticles coated with cholecalciferol-loaded PLGA (HAp/D₃/PLGA). The greatest levels of enhanced angiogenesis, vascularization, osteogenesis and bone structure differentiation were achieved upon the implementation of HAp/D₃/PLGA systems.