Osteopontin and bone metabolism: a histology and scintigraphy study in rats

Osteopontin (OPN) is one of the major non-collagen proteins in extracellular bone matrix. To elucidate the function of OPN in bone metabolism, a cellular defect was created in parietal bone and tibia of 12 rats. In Group 1, the left defects were filled with OPN-coated hydroxyapatite (OPN-H). In Group 2, the right defects were filled with non-coated hydroxyapatite (N-H). In both groups, the contra lateral defects were used as control defects. In Group 3, OPN-H was inserted in the left defects and N-H in the right defects. Bone metabolism was measured by 45Ca and technetium-99m methylene diphosphonate scintigraphy for 4 weeks. Scintigraphy did not show any significant differences in bone metabolism between the defects filled with OPN-H and N-H. A higher bone metabolism was measured between the parietal defects filled with OPN-H or N-H in comparison with the parietal control defects. This difference, however, was not significant and was less for tibia defects. Histological observation (7th week) shows less inflammatory cells at the tibia defects filled with OPN-H compared to the tibia defects filled with N-H. This study did not show any acceleration or inhibition of bone metabolism in parietal or tibia bone in rats, but there is some evidence that OPN might influence inflammatory cells in bone matrix.