In vitro osteogenic response of rat bone marrow cells to bFGF and BMP-2 treatments.

Basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) are actively pursued for stimulation of bone formation. To assess their promise for systemic therapy of osteoporosis, we ascertained the effects of bFGF and BMP-2 on bone marrow cells in vitro. Bone marrow cells were obtained from young (8 weeks) and adult (32 weeks) rats by femoral aspiration and were exposed to osteogenic medium (ie, basal medium with 10 mM -glycerolphosphate and 100 nM dexamethasone) containing the growth factors. The cell viability in osteogenic medium was reduced after 3 weeks but not if the concentration of -glycerolphosphate/dexamethasone was reduced to 3 mM/30 nM. Unlike BMP-2, bFGF at 2–50 ng/mL was capable of enhancing longterm cell viability. Continuous treatment of bone marrow cells for 3 weeks resulted in dose-dependent stimulation of mineralization by BMP-2, but not by bFGF, whose activity was optimal at 2–10 ng/mL. To explore the effect of shortterm exposure, bone marrow cells were treated with growth factors for 1 week and subsequent mineralization was investigated. BMP-2 exposure increased the extent of mineralization, but bFGF was not effective after the short exposure. We concluded bFGF was more potent (ie, required lower concentration) for stimulating osteogenic parameters, but BMP-2 effects were lasting on the bone marrow cells. Protein growth factors are endogenous regulators of cells responsible for mineralized tissue mass and are being explored therapeutically for bone tissue engineering. The growth factors have been used in clinics by implantation with biomaterial carriers for bone repair at a site of administration. The growth factors also have been administered systemically in preclinical models to stimulate bone deposition throughout the skeletal tissues. The growth factors particularly are attractive for systemic stimulation of bone formation in patients with osteoporosis. Unlike the osteoporosis drug bisphosphonates that inhibit osteoclastic activity, growth factors have the potential to directly enhance skeletal integrity by stimulating deposition of new mineralized tissue by bone marrow cells (BMC). Basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) are two growth factors that act as a prototypical mitogen and morphogen, respectively. The bFGF administered by intravenous route was shown to stimulate endocortical bone deposition in young (growing) and ovariectomized rats, the latter serving as a model of postmenopausal osteoporosis. Angiogenic and mitogenic effects of the bFGF have been attributed for the beneficial effects at bone sites. Systemic administration of BMP-2 was attempted in two osteoporotic mouse models, which led to increased trabecular bone volume at femurs. Human-derived BMC are sensitive to bFGF and BMP-2 treatments, but the reported osteogenic effects of these growth factors are conflicting. Lecanda et al reported a BMP-2 dependent matrix mineralization parallel with enhanced alkaline phosphatase (ALP) activity and increased deposition of the extracellular matrix proteins collagen(I), osteopontin, and decorin. Frank et al used a medium containing bFGF/dexamethasone combination and reported differences in some osteogenic markers (BMP-2, bone sialoprotein, and osteopontin expression), but not in others (ALP activity, collagen(I) expression, and mineralization); bFGF treatment reduced colony formation and ALP activity of the BMC, but acted as a mitogen From the *Department of Chemical and Materials Engineering, Faculty of Engineering; the †Department of Biomedical Engineering, Faculty of Medicine; and the ‡Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada; and the §Theodor-Boveri-Institut fur Biowissenschaften der Universitat of Wurzburg, Wurzburg, Germany. One or more of the authors (HU) has received funding from a Whitaker Biomedical Engineering Grant (HU; Grant No G700000178) and an Operating Grant from the Canadian Institutes of Health Research (HU; Grant No G118260007). Infrastructure support was provided by an Innovation Fund Grant from the Canadian Foundation of Innovation and an Opportunity Fund Grant from the Alberta Heritage Foundation for Medical Research (HU; G125000067). Each author certifies that his or her institution has approved the animal protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research. Correspondence to: Hasan Uludag, #526 Chemical & Materials Engineering Building, University of Alberta, Edmonton, Alberta T6G 2G6 Canada. Phone: 780-492-0988; Fax: 780-492-2881; E-mail: hasan.uludag@ualberta.ca. DOI: 10.1097/01.blo.0000200236.84189.87 CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 443, pp. 113–123 © 2006 Lippincott Williams & Wilkins