Ability of deproteinized cancellous bovine bone to induce new bone formation

Background: Preclinical and clinical studies indicate that deproteinized cancellous bovine bone is osteoconductive and may be osteopromotive. Previous studies using commercial preparations failed to demonstrate the presence of protein, implicating bone-mineral composition and 3-dimensional structure as reasons for clinical success; however, these studies did not examine whether osteoinductive factors might be present in close association with the mineral phase. Methods: Deproteinized cancellous bovine bone was decalcified and any protein present released by chaotropic solvents using the protocol described for purification of bone morphogenetic proteins (BMPs). Three extracts were obtained and tested for their ability to support osteoinduction in the calf muscle of nude mice. Results: Protein content averaged 11 μg/g based on absorbance at 280 nm using bovine serum albumin as a standard. All extracts contained material that stained positively with silver stain after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Western blots of these gels indicated the presence of transforming growth factor-beta (TGF-β) and BMP-2. All 3 extracts were osteoinductive in the nude mouse model when combined with inactive DFDBA, and bone formation was comparable to that induced by active DFDBA. Deproteinized cancellous bovine bone by itself was not osteoinductive in the nude mouse, but in a clinical case, exhibited osteoclastic resorption with adjacent new bone formation. Conclusions: The results suggest that small amounts of protein are present in deproteinized cancellous bovine bone in close association with the mineral phase. Some of the extracted material has osteoinductive potential and may contain growth factors. This may explain the osteopromotive ability of deproteinized cancellous bovine bone clinically.