Biomimetic Citrate-Coated Luminescent Apatite Nanoplatforms for Diclofenac Delivery in Inflammatory Environments

Luminescent nanoparticles are innovative tools for medicine, allowing the imaging of cells and tissues, and, at the same time, carrying and releasing different types of molecules. We explored and compared the loading/release ability of diclofenac (COX-2 antagonist), in both undoped- and luminescent Terbium³⁺ (Tb³⁺)-doped citrate-coated carbonated apatite nanoparticles at different temperatures (25, 37, 40 °C) and pHs (7.4, 5.2). The cytocompatibility was evaluated on two osteosarcoma cell lines and primary human osteoblasts. Biological effects of diclofenac-loaded-nanoparticles were monitored in an in vitro osteoblast's cytokine-induced inflammation model by evaluating COX-2 mRNA expression and production of PGE₂. Adsorption isotherms fitted the multilayer Langmuir-Freundlich model. The maximum adsorbed amounts at 37 °C were higher than at 25 °C, and particularly when using the Tb³⁺ -doped particles. Diclofenac-release efficiencies were higher at pH 5.2, a condition simulating a local inflammation. The luminescence properties of diclofenac-loaded Tb³⁺ -doped particles were affected by pH, being the relative luminescence intensity higher at pH 5.2 and the luminescence lifetime higher at pH 7.4, but not influenced either by the temperature or by the diclofenac-loaded amount. Both undoped and Tb³⁺-doped nanoparticles were cytocompatible. In addition, diclofenac release increased COX-2 mRNA expression and decreased PGE₂ production in an in vitro inflammation model. These findings evidence the potential of these nanoparticles for osteo-localized delivery of anti-inflammatory drugs and the possibility to localize the inflammation, characterized by a decrease in pH, by changes in luminescence.