Transforming growth factor-?1 incorporated during setting in calcium phosphate cement stimulates bone cell differentiationin vitro

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Abstract
Growth stimulation of periimplant tissues by growth factors like transforming growth factor-β1 (TGF-β1) may increase the indication for and success of implant use. Calcium phosphate as a material for implants or for coating of implants is known for its good biologic interaction with bone. Therefore, calcium phosphate implants combined with TGF-β1 might improve osseointegration. In this study we hypothesise that the addition of recombinant human TGF-β1 (rhTGF-β1) to calcium phosphate cement (CPC) affects the differentiation of bone cells growing on the cement layer. rhTGF-β1 incorporated during setting in a CPC layer at 20 ng rhTGF-β1/60 mg cement was found to be gradually released into tissue culturing medium leading to a 20% release after 24 h. Two cell populations were obtained from collagenase-treated fragments of adult rat long bones: preosteoblastic cells, which were released by the collagenase treatment, and osteoblastic cells, which grew from the collagenase-stripped bone fragments. Both cell populations were tested for their osteoblastic characteristic phenotype by measuring their alkaline phosphatase (ALP) activity after vitamin D treatment and cyclic AMP after parathyroid hormone stimulation. After preculture the cells were plated on a layer of CPC containing 0 (control), 10, or 20 ng rhTGF-β1/60 mg CPC. Bone cell differentiation was analyzed after 10 days by measuring the ALP activity, as well as the protein content of the cell layer. Incorporation of rhTGF-β1 in the CPC did not change the ALP activity in osteoblastic cells, but a significant (analyzed by multivariate analysis of variance) increase was observed in preosteoblastic cells. Incorporation of 10 ng of rhTGF-β1 in 60 mg of CPC increased the ALP activity in preosteoblastic cells by threefold and 20 ng rhTGF-β1/60 mg CPC increased it by fivefold. The total protein content was not affected by rhTGF-β1 in either of the cell populations. We conclude that rhTGF-β1 incorporated during setting in CPC stimulates the differentiation of preosteoblastic cells in vitro. These results provide a basis for further studies on the use of this combination as an implant material in vivo. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 50, 67–74, 2000.