The Elution Kinetics of BMP-2, BMP-4, and BMP-7 From a Commercial Human Demineralized Bone Matrix Putty

Bone morphogenetic proteins (BMPs) are associated with bone extracellular matrix and impart osteoinductive properties to demineralized bone matrix (DBM) grafts. The first step of the osteoinductive process is BMP release from DBM in situ; however, this has not been characterized for human DBM. The authors investigated the release of BMPs 2, 4, and 7 from a clinical human DBM putty (Bonus II DBM, Biomet Inc, Warsaw, IN). The DBM was placed in Sorensen buffer and the BMP concentrations in the Sorensen buffer and guanidine extracts of the DBM were measured concurrently by enzymelinked immunosorbant assay for up to 7 days. The baseline DBM concentrations were BMP-2: 28.1 ± 1.3 ng/g DBM, BMP-4: 0.577 ± 0.056 ng/g DBM, and BMP-7: 92.9 ± 7.5 ng/g DBM. Relative to baseline, the proportions released by 7 days were 11.1%, 3.9%, and 29.3%, respectively. The early (0-8 hour) and late (8-168 hours) elution rates were BMP-2: 0.16 ± 0.24 and 0.0089 ± 0.012 ng/(g DBM hr), and BMP-7: 1.29 ± 2.1 and 0.086 ± 0.039 ng/(g DBM hr), respectively. Little BMP-4 elution occurred over the first 24 hours, with the rate for the remaining interval being 0.00014 ± 0.00021 ng/(g DBM hr). The apparent DBM BMP profiles were counterintuitive in that the concentrations increased from baseline for some, or all, of the 7 days instead of monotonically decreasing. Similar behavior has previously been reported in bovine studies. This provides further evidence that BMPs are associated with at least 2 compartments in DBM differing by their affinity for BMPs and that guanidine extraction of BMPs is not 100% efficient.