Histological investigation of osteoinductive properties of rh-BMP2 in a rat calvarial bone defect model.

INTRODUCTION: Recombinant human bone morphogenetic protein-2 (rh-BMP2) has osteoinductive properties. The sequence of osteogenesis induced by rh-BMP2 in a rat calvarial bone defect model was evaluated histologically.

MATERIAL AND METHODS: Atelopeptide type I collagen was selected as the carrier matrix for rh-BMP2. This collagen was mixed with 50 microg of rh-BMP2 and treated by lyophilization to make a suitable form for filling bone defects. Thirty Wistar rats (male; 10 weeks old) underwent craniotomy resulting in a round bone defect with a diameter of 4 mm. Three weeks after the operation, the defect site was exposed to implant collagen with rh-BMP2 in the experimental group and collagen only in the control group. Three, 6 and 9 weeks after implantation, calvarial specimens were harvested and stained with haematoxylin/eosin. In addition, bromodeoxyuridine (BrdU) immunohistochemical staining was performed.

RESULTS: In the experimental group, marked ossification was found. In contrast, there was no tendency towards osteogenesis in the control group, 9 weeks after collagen implantation. In BrdU immunohistochemical staining, the number of BrdU-positive cells was significantly higher in the experimental group than in the control group, and was significantly higher at the periosteal site than at other sites at 3 and 6 weeks after implantation.

CONCLUSIONS: rh-BMP2 exhibited osteoinductive properties, and markedly stimulated proliferation of periosteal cells.