A QUANTITATIVE ASSESSMENT OF OSTEOINDUCTIVITY OF HUMAN DEMINERALIZED BONE-MATRIX

DEMINERALIZED BONE MATRIX (DBM) is widely used in tile repair of patho logies associated with skeletal defects and periodontal. diseases. The present study was directed at establishing in vivo and in vitro model s fur a quantitative assessment of the osteoinductivity of DBM before clinical use. Athymic mice were used in an in vivo assay to overcome t he species limitations (for human DBM) found in xenogeneic animal mode ls. Calcium contents of explants. as an indicator of new bone formatio n, were assayed and expressed as a change in the weight percent calciu m in the explant as compared to the weight percent of calcium in the i mplanted material. A total of 82 mice (2 implants per mouse) were used in this study. Significant amounts of new bone were induced in this a nimal model in response to implantation of DBM. Muscular implantation was found to be more osteoinductive (increases of 10.0 +/- 0.4 calcium weight percent of explant) than subcutaneous implantation (increases of 1.62 +/- 0.21 calcium weight percent of explant) and new bone forma tion in muscular implantation sites of athymic mice mimics endochondra l bone formation. Between weeks 1 to 4, the weight of explanted materi als did not significantly differ from the weight of the implanted mate rial; however, by week 5 the explant weight began to increase. Calcium deposition over the 5 weeks Elf implantation increased in a nearly li near fashion. Consequently week 4 was chosen as the optimum time for e xplantation in the in vivo assay in that sufficient calcium levels had been achieved without a significant increase in explant dry weight. A liquots of 10, 20, 30, and 40 mg per implantation site were used in do se response studies in the in vivo bioassay, Dose response curves with DBM exhibited maximal activity at the 20 mg DBM implant dose in the i n vivo bioassay. An in vitro bioassay was also developed where human p eriosteal (HPO) cells were chosen because osteoprogenitor cells found in bone repair typically come from periosteal tissue. Alkaline phospha tase (ALP) activity in confluent cell cultures of HPO cells exposed to DBM, as an indicator of osteoblast induction, reached its highest lev el on day 50E DBM treatment. Aliquots of 2, 5, 10, 20, 30, and 40 mg D BM per flask were chosen in dose response studies using the in vitro b ioassay, These dose response studies with DBM revealed that quantities approximating 5 to 10 mg DBM in the in vitro model provided for maxim al levels of ALP in cell extracts. A linear correlation (R-2 = 0.7397) was demonstrated between the in vivo calcium remineralization assay a nd the in vitro ALP assay of osteoinductivity of DBM, suggesting that the in vitro assay can be used to quantitatively assess the osteoinduc tive potential of DBM where production and distribution of clinically usable DBM dictates rapid analysis.