Characterization of bioactive substances involved in the induction of bone augmentation using demineralized bone sheets

Purpose To investigate the bone augmentation ability of demineralized bone sheets mixed with allogeneic bone with protein fractions containing bioactive substances and the interaction between coexisting bioactive substances and proteins. Methods Four types of demineralized bone sheets mixed with allogeneic bone in the presence or absence of bone proteins were created. Transplantation experiments using each demineralized bone sheet were performed in rats, and their ability to induce bone augmentation was analysed by microcomputed tomography images. Bioactive substances in bone proteins were isolated by heparin affinity chromatography and detected by the measurement of alkaline phosphatase activity in human periodontal ligament cells and dual luciferase assays. Noncollagenous proteins (NCPs) coexisting with the bioactive substances were identified by mass spectrometry, and their interaction with bioactive substances was investigated by in vitro binding experiments. Results Demineralized bone sheets containing bone proteins possessed the ability to induce bone augmentation. Bone proteins were isolated into five fractions by heparin affinity chromatography, and transforming growth factor-beta (TGF-beta) was detected in the third fraction (Hep-c). Dentin matrix protein 1 (DMP1), matrix extracellular phosphoglycoprotein (MEPE), and biglycan (BGN) also coexisted in Hep-c, and the binding of these proteins to TGF-beta increased TGF-beta activity by approximately 14.7% to 32.7%. Conclusions Demineralized bone sheets are capable of inducing bone augmentation, and this ability is mainly due to TGF-beta in the bone protein mixed with the sheets. The activity of TGF-beta is maintained when binding to bone NCPs such as DMP1, MEPE, and BGN in the sheets.