A NUDE-MOUSE MODEL FOR HUMAN BONE-FORMATION IN UNLOADED CONDITIONS

We describe an experimental model for human bone formation in unloaded conditions. Bone formation has been assessed by implanting in vivo hu man bone marrow stromal cells (BMSC) on porous hydroxyapatite (HA) bio ceramics subcutaneously in nude mice, In this system, human bone forma tion and remodeling occurs and can be studied in unloaded conditions, i.e., with no influence of muscle tension. Using this model system, we have been also studying the effects of dexamethasone (Dex) in combina tion with fibroblast growth factor-2 (FGF-2) on the osteogenic potenti al of human BMSC. A colony-forming unit-fibroblastoid (CFU-F) formed i n clonal conditions were significantly larger when Dex/FGF-2 was prese nt in the culture medium. The cell proliferation rate was also increas ed by the combination Dex/FGF-2 at a higher extent than Dex or FGP-2 a lone. BMSC expanded with Dex/FGF-2 displayed alkaline phosphatase leve ls lower (56%) than Dex expanded cells, but significantly higher than FGF-2 expanded cells. Our results suggest that Dex/FGF-2 expanded BMSC are able to form more bone than BMSC expanded in the presence of FGF- 2 alone. (C) 1998 by Elsevier Science Inc. All rights reserved.