BMP-2 gene-fibronectin-apatite composite layer enhances bone formation

An apatite composite layer was evaluated to determine the efficiency of gene transfer to cells cultured on it. Cells were cultured on a composite layer including the BMP-2 gene and FB, and BMP-2 gene expression, BMP-2 protein concentrations, alkaline phosphatase (ALP) activity, and osteocalcin (OC) concentrations were measured. A bone defect on the cranium of rats was treated with hydroxyapatite (HAP)-coated ceramic buttons with the apatite composite layer including the BMP-2 gene and FB (HAP-BMP-FB). The tissue concentration of BMP-2, bone formation, and the expression levels of the BMP-2, ALP, and OC genes were all quantified.The apatite composite layer provided more efficient gene transfer for the cultured cells than an apatite composite layer without FB. The BMP-2 concentration was approximately 100~600 pg/mL in the cell-culture medium. Culturing the cells on the apatite composite layer for 27 days increased ALP activity and OC concentrations. In animal experiments, the tissue concentrations of BMP-2 were over 100 pg/mg in the HAP-BMP-FB group and approximately 50 pg/mg in the control groups. Eight weeks later, bone formation was more enhanced in the HAP-BMP-FB group than in the control groups. In the tissues surrounding the HAP button, the gene expression levels of ALP and OC increased.The BMP-2 gene-FB-apatite composite layer might be useful for bone engineering.Some gene therapy systems have been reported for bone and cartilage tissue engineering in animal models [1-9]. Bone morphogenetic protein (BMP) genes have often been applied for bone repair, and their usefulness has been reported in various animal experiments [1-5,8]. BMP-2 is a potent osteoinductive factor shown to induce the osteogenic differentiation of mesenchymal cells [10], and treatment systems using recombinant BMP-2 protein show promise for the future. However, these systems using recombinant proteins have several problems, including high doses that range from micrograms up to milligrams (whic