Interaction between a bisphosphonate, tiludronate and nanocrystalline apatite: in vitro viability and proliferation of HOP and HBMSC cells

Nanocrystalline apatites (NCA) are the inorganic components of mineralized tissues and they have been recently proposed as biomaterials for drug delivery systems. Bisphosphonates (BPs) are currently the reference drugs used to treat diseases involving bone disorders such as osteoporosis. Nevertheless, the interaction phenomena between BP molecules and apatite nanocrystals of bone are not well understood. Therefore, the adsorption characteristics have been examined and cellular activity of tiludronate molecules on NCA as models of bone mineral has been investigated. Adsorption experiments of tiludronate onto NCA were carried out and revealed a Langmuir-type adsorption isotherm. The uptake of tiludronate molecules is associated with a release of phosphate ions, indicating that the main reaction is an ion exchange process involving surface anions. The results evidence the strong affinity of BP molecules for the apatitic surface. The interactions of NCA–tiludronate associations with human osteoprogenitor cells and human bone marrow stromal cells do not reveal any cytotoxicity and evidence the activity of adsorbed tiludronate molecules. Moreover, an evolution of the physico-chemical characteristics of the apatitic substrate during biological study was observed, highlighting the existence of dynamic interactions. This work contributes to clarifying the reaction mechanisms between BPs and biomimetic apatites.