Comparing Effects of Ca(OH)₂ and BMP2 on Promoting Bone Repair

Objectives: Bone has been reported to contain numerous growth factors which are proposed to be released from the matrix following chemical treatment with calcium hydroxide Ca(OH)₂. It is hypothesised that the use of combinations of growth factors, such as the combinations found in the bone matrix, may be effective in promoting bone healing compared with single growth factor therapy such as bone morphogenic protein-2 (BMP2), which has found clinical application, but requires high doses to be effective. This study aims to compare the effect of bone matrix derived growth factor combinations and recombinant-BMP2 on cellular behaviour in mediating bone repair processes.
Methods: Using an “organotypic” model, fractures were made within slices of rat mandibles to further mimic bone fracture repair scenario. Fracture sites were treated with either 10µl Ca(OH)₂ (0.4 mM, pH11) or 100ng/ml BMP2 applied by agarose beads. Tissues were embedded in a semi-solid agar based medium and cultured in Trowel type cultures for 7 days. Following culture, tissues were fixed and demineralised prior to histological examination. Cellular characteristics within the fracture site in response to endogenous or exogenous growth factors were assessed by immunohistochemistry for proliferating cell nuclear antigen (PCNA) and bone matrix protein osteopontin (OSP). TGF-β1, BMP2 and VEGF levels in condition media were quantified by ELISA.
Results: Fractured mandible slices treated with Ca(OH)₂ exhibited a significant increase in cell number adjacent to the fracture site when compared with BMP2-slices. Ca(OH)₂ treated slices demonstrated increased immunopositivity for PCNA and OPN within the fracture site when compared with BMP2. Release of VEGF, TGF-β1 and BMP2 from treated surfaces were greater when compared with control slices
Conclusions: Ca(OH)₂ may release growth factors from bone surfaces which influences cellular reparative processes more than BMP-2. The clinical endpoint of this project will be development of new therapeutic approaches which utilise growth factors entrapped in bone matrix to stimulate bone regineration and avoid issues regard single growth factor therapy.