• Basic Science

Bone tissue has been shown to contain numerous cell-to-cell signalling peptides called growth factors. These growth factors are thought to have important regulating effects for bone remodeling and bone healing, due to their potent effects on bone cell metabolism. In vivo studies over the last half decade have demonstrated that growth factors can stimulate bone formation and bone healing. These results have made bone growth factors candidates for future clinical use in orthopedic surgery. In numerous clinical situations enhanced bone formation and bone healing could lead to improved results of surgical procedures. This thesis describes the most important bone growth factors and their actions in vitro and in vivo. In vitro investigations of growth factor effects ¬on osteoblast chemotaxis and metabolism are described as well as in vivo studies with growth factor stimulation of fracture healing and bone healing to prosthetic-like implants. In vitro results. Several growth factors exhibited chemotactic effects towards human osteoblasts. TGF-ß1 and PDGF-BB had the strongest chemotactic effects, whereas PDGF-AA, IGF-1, and IGF-2 had less but significant chemotactic effects towards human osteoblasts. TGF-ß1 exhibited the highest chemotactic potency with maximal activity at 100 pg/ml, whereas the other growth factors had maximal effects at 10-100 ng/ml. BMP-2 was found to have chemotactic effects toward human osteoblasts, human bone marrow osteoprogenitor cells, and U2-OS osteosarcoma cells. BMP-4 and BMP-6 were without any chemotactic effects towards these cell¬types. Human bone marrow osteoprogenitor cells were the most responsive celltype to BMP-2 stimulation. Growth factor combinations resulted in synergic stimulative effects on different metabolic functions on human osteoblasts. Combinations with TGF-ß1 and PDGF-BB strongly stimulated proliferation and chemotaxis. Combinations with TGF-ß1, PDGF-BB and BMP-2 strongly stimulated an osteoblast differentiation parame¬ter (alkaline phosphatase activity). The different growth factor combinations had no effect on collagen synthesis in human osteoblasts. In vivo results: Continuous application of 1 and 10 μg natural TGF-ß to a plated tibial osteotomy in rabbits increased mechanical bending strength and callus formation at 6 weeks observation. Diaphyseal cortical bone remodeling was not affected by the local growth factor application.