Recombinant human bone morphogenetic protein-2 promotes osteogenesis within atelopeptide type I collagen solution by combination with rat cultured marrow cells

We evaluated the combination effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) and cultured rat bone marrow mesenchymal stem cells (MSCs) in atelopeptide type I collagen (AC) solution on osteogenesis in a diffusion chamber (DC) to develop a bone substitute having consistent osteogenic capability for clinical applications. The cultured MSCs were obtained by 10-day primary culture of fresh bone marrow cells of Fischer rats. We prepared three groups of DCs: AC solution with rhBMP-2, AC solution with cultured MSCs, and AC solution with rhBMP-2 and cultured MSCs. The prepared combined solutions were injected into DCs, which were subcutaneously implanted into the backs of syngeneic rats. DCs were harvested after 2, 4, or 8 weeks and analyzed for bone-forming capability by determining histological and osteoblastic biochemical markers. De novo bone formation was observed both inside and outside of the membrane filter of DCs in the group of AC solution with rhBMP-2 and cultured MSCs. The alkaline phosphatase activity and osteocalcin content in the group of AC solution with rhBMP-2 and cultured MSCs were significantly higher than those in the group of AC solution with cultured MSCs at any time. These findings indicate that AC aqueous solution is a useful material not only as a carrier of rhBMP-2 but also as a cell-anchorage for differentiation and proliferation of MSCs. Therefore, this study suggests that clinical repairs of bone defects are feasible using injectable AC solution with rhBMP-2 and cultured MSCs as a bone substitute. (C) 2002 John Wiley & Sons, Inc. J Biomed Mater Res 60: 61-69, 2002.