Hydroxyapatite nanoparticles: preparation, characterization, and evaluation of their potential use in bone targeting: an animal study.

Objective: Hydroxyapatite is used as a drug-delivery system for bone therapy applications because of its biocompatibility, bioactivity, and osteoconductive properties. In addition, hydroxyapatite nanoparticles (HApN) might be used as a theranostic probe. The aim of this study was to prepare and characterize hydroxyapatite mesoporous nanoparticles, and radiolabel these nanoparticles with technetium-99m (Tc). Moreover, biodistribution studies were carried out in healthy mice.
Materials and Methods: HApN were synthesized and characterized. Tc-HApN was prepared by adding Tc-pertechnetate to a dispersion of HApN in the presence of stannous chloride. Radiochemical purity and in-vitro stability were determined. The circulation time of Tc-HApN was determined by measuring blood radioactivity in healthy mice. In addition, biodistribution studies were carried out in healthy mice at 1 and 4 h after injection.
Results: Tc-HApN showed high radiochemical purity (98.7±0.2%) and in-vitro stability until 24 h. Tc-HApN levels in blood decreased in a biphasic manner, with an α half-life of 1.8 min and a β half-life of 126.9 min. High uptake was achieved in the liver and spleen because of the macrophage uptake. Furthermore, bone uptake was higher than that of the surrounding muscle, resulting in high bone-to-muscle ratios.
Conclusion: HApN were synthesized successfully with suitable characteristics for in-vivo applications. Tc-HApN was prepared and showed high stability. Tc-HApN presented increasing bone uptake over time, showing a higher affinity to bone tissues in contrast to surrounding muscle. The present results, together with further studies, may indicate a potential application of HApN as a nanocarrier for bone diseases.