Bone homeostasis plays a major role in supporting and protecting various organs as well as a body structure by maintaining the balance of activities of the osteoblasts and osteoclasts. Unbalanced differentiation and functions of these cells result in various skeletal diseases, such as
osteoporosis,
osteopetrosis, and Paget's disease. Although various synthetic nanomaterials have been developed for bone imaging and
therapy through the chemical conjugation, they are associated with serious drawbacks, including heterogeneity and random orientation, in turn resulting in low efficiency. Here, we report the synthesis of bone-targeting
ferritin nanoparticles for bone imaging.
Ferritin, which is a globular
protein composed of 24 subunits, was employed as a carrier molecule. Bone-targeting
peptides that have been reported to specifically bind to osteoblast and
hydroxyapatite were genetically fused to the N-terminus of the heavy subunit of human
ferritin in such a way that the
peptides faced outwards.
Ferritin nanoparticles with fused bone-targeting
peptides were also conjugated with
fluorescent dyes to assess their binding ability using osteoblast imaging and a
hydroxyapatite binding assay; the results showed their specific binding with osteoblasts and
hydroxyapatite. Using in vivo analysis, a specific fluorescent signal from the lower limb was observed, demonstrating a highly selective affinity of the modified nanoparticles for the bone tissue. These promising results indicate a specific binding ability of the nanoscale targeting system to the bone tissue, which might potentially be used for
bone disease therapy in future clinical applications.