Osteopontin and bone metabolism in healing cranial defects in rabbits

Non-collagen proteins such as bone sialoprotein and osteopontin (OPN) form 10% of the extracellular bone matrix. In this study, the influence of OPN on bone repair was investigated. Human OPN (Innogenetics) was produced by a recombinant technique and bonded onto the surface of hydroxyapatite (Interpore 200). Thirty rabbits were divided into six equal groups. A circular defect (10mm) was prepared in each parietal bone. In four rabbits of each group the left and right defects were filled with either OPN-coated hydroxyapatite (OPN-HA) or non-coated hydroxyapatite (HA). One sham animal of each group received no implants. The animals were killed after 1, 2, 6, 12, 18 and 30 weeks. The histological sections were scanned and analysed digitally. There were no statistically significant differences in total bone formation between defects filled with OPN-HA and HA. Bone formation at the borders of the healing area was significantly higher in defects filled with OPN-HA than in those filled with HA. Less bone formation was noted in the OPN-HA and HA groups at the centre of the healing area than at the borders of the healing area and the dural area. Although some animals in the sham group showed a high level of bone formation in the dural area, this was not significantly different to that in the dural area of the other groups. There was no sign of infection or tissue rejection of the graft.