Would three BMPs at low concentration be better than one at high concentration? An experimental study with rat osteoprogenitor cells.

Background: Bone morphogenetic proteins (BMPs) are used in clinical practice for stimulation of bone formation, but often evoke serious complications. Recent studies demonstrated that BMPs involved in early stages of bone formation are species specific. In cattle dominate BMP7, growth differentiation factor 5 (GDF5) and NEL-like protein 1 (NELL1) while in rats BMP2, BMP5 and BMP6. The purpose of the study was to compare the action of the species specific BMPs on the osteoprogenitor cells. Thus, rat osteoprogenitor cells were exposed to one BMP in a high dose and three of them at 1/3 of the former.

Materials And Methods: Isolated rat osteoprogenitor cells were treated in culture with different concentrations of BMP2, BMP5 and BMP6 or with lower concentration of combinations of these cytokines. Activity of alkaline phosphatase, calcium deposition and mRNA level for transcription factor SP7 (osterix) and tissue non-specific alkaline phosphatase (TNAP) served as indicators of BMPs effect.

Results: BMPs stimulated all studied parameters in comparison with control cultures, but no statistically significant differences were observed between the action of a large dose of one cytokine and a combination of cytokines given at lower concentrations.

Conclusions: Three BMPs used in a low dose exert similar effect as the one used at high dose. Since the BMPs stimulate different receptors and activate different signaling pathways the use of the mixture of properly chosen BMPs at low concentration may give better results than the single one at high concentration and may avoid untoward effects.