Every year in the United States, over 600,000 surgeries are performed involving bone grafts, making bone the second most common transplanted tissue, after blood transfusions (1, 2). Many of these grafts are used in dental regenerative procedures to restore alveolar bone that was lost from periodontal disease, trauma, or long-term tooth loss. Autogenous bone is widely used as the gold standard in craniofacial regenerative medicine, but comes with increased morbidity to the patient (3). Therefore clinicians often turn to allograft and xenograft materials, but these may lose osteoinductivity due to processing (4). Re-establishing the osteoinductive potential in these grafts would be a major step forward in enhancing clinical outcomes. The incorporation of osteoinductive molecules represents a promising strategy for creating a substrate that matches the performance of autografted bone. Preliminary studies from our group utilized a hydroxyapatitie (HA) binding domain that comprised of a highly negative heptaglutamate sequence (E7) that can be added to synthetic peptides and recombinant proteins to achieve an increased concentration, as well as greater retention, of these agents on HA surfaces, thus enabling sustained delivery of osteoinductive factors within sites of bone regeneration (5-7). The goal of this proposal is to utilize a specific HA binding domain to achieve targeted coupling of osteoinductive factors to biologic HA within three different commercially available dental bone graft materials: 1) acellular allograft 2) acelluar anorganic bovine xenograft and 3) allograft wit endogenous MSCs and osteoprogenitor cells.
Specific Aim 1 : E7-directed anchoring of osteoinductive peptides/proteins to bone grafts to increase loading and retention of osteoinductive molecules: collagen mimetic peptide (DGEA), BMP2 peptide, and rBMP2 protein will be synthesized with E7 domains and evaluated for loading and retention on three commercially available bone grafts.
Specific Aim 2 : Determination of osteoinductive potential of the grafts anchored with osteoinductive peptides/protein (in vitro and in vivo): In vitro: Peptides or proteins with and without E domains will be anchored to grafts. The cellular bone matrix allograft will be cultured and MSCs will be seeded onto the acellular bone grafts and also cultured. Bone formation markers such as alkaline phosphatase and osteocalcin will be measured. In vivo we will evaluate the anchored grafts ability to form bone in a subcutaneous rat model. If bone can form in this environment we speculate that in bony lesions and/or deficiencies in the oral cavity the bone forming potential should be even greater. This will set th stage for utilizing this technology in Phase I clinical trials.
Alveolar bone loss occurs due to a number of conditions and there is a need to regain this lost bone either for tooth retention or tooth replacement by dental implants. Autogenous bone, often considered the gold standard for regenerative procedures, requires harvesting from the patient and increased morbidity;therefore allograft bone can be used as a substitute but due to processing and sterilization procedures it may have lost important proteins that help in bone formation. By developing a method of anchoring these important proteins back to this commercially available bone we hope to increase the regenerative capacity of allograft bone comparable to the level of autogenous bone.
|Bain, Jennifer L; Culpepper, Bonnie K; Reddy, Michael S et al. (2014) Comparing variable-length polyglutamate domains to anchor an osteoinductive collagen-mimetic peptide to diverse bone grafting materials. Int J Oral Maxillofac Implants 29:1437-45|