Great increase in bone 66 kDa protein and osteocalcin at later stages with healing rat fractures: Effect of zinc treatment

Fracture healing has been demonstrated to increase production of bone growth factors, and this elevation has been shown to be enhanced by zinc treatment. Moreover, the effect of zinc treatment on production of bone osteocalcin, which is a kind of Ca2+-binding protein localized in bone matrix, at the later stages with bone fracture was investigated. Rats were sacrificed 7 (earlier stage) or 21 (later stage) days after fracture of femoral diaphysis. Femoral-diaphyseal tissues with fracture healing were cultured in a serum-free medium for 24 h. Many proteins in the bone tissues were released into the medium. Bone protein production was markedly elevated 21 days after bone fracture as compared with that of 7 days. A ≈66 kDa protein molecule, a major protein component which was produced by the diaphyseal tissues during fracture healing, was predominantly increased at the later stages with fracture healing. Bone osteocalcin production was significantly increased during fracture healing. This increase was enhanced at the later stages with fracture healing. The presence of zinc acexamate (10−4 M) in culture medium caused a significant increase in bone protein and osteocalcin production at 7 or 21 days after bone fracture. The effect of zinc acexamate in increasing bone total protein and osteocalcin production was remarkable at the later stages with fracture healing. Moreover, zinc treatment caused a significant increase in alkaline phosphatase activity, deoxyribonucleic acid (DNA) and calcium content in the femoral-diaphyseal tissues of the later stages with fracture healing in vitro. The present study demonstrates that bone protein production is markedly increased at the later stages with fracture healing, and that zinc treatment can enhance production of bone protein components including osteocalcin in vitro. Zinc treatment may stimulate the healing of femoral fracture at earlier and later stages.