Various distribution of BMPs in different periosteal layers contributing to inconsistent osteoinductivity of DBM-based products.

As a native carrier of bone morphogenetic proteins (BMPs), demineralized bone matrix (DBM) has excellent osteoinductivity and is commonly used in clinical repair of bone defects. However, commercially DBM-based products present different osteoinductive potential. The purpose of this study were to compare the quantity of BMPs in DBM preparations harvested from different periosteal layers, as well as to evaluate the extraction efficiency of guanidine and collagenase. Three cortical bone particals were harvested from outer 1/3 cortical layer, middle 1/3 cortical layer and inner 1/3 cortical layer of single femoral shaft and were partly demineralized. Proteins were extracted from each sample separately with guanidine and collagenase, and the amounts of BMP-2 and BMP-7 were determined using enzyme-linked immunosorbent assay. After demineralization, the amounts of BMP-2 and BMP-7 in DBM were greater than cortical particles (p < 0.001). In general, the content of BMP-7 varied linearly with the content of BMP-2 independent of extraction method and the outer 1/3 cortical layer contained highest level of BMP-2 and BMP-7, while the inner 1/3 cortical layer contained lowest level (p < 0.05). In terms of extraction efficiency, guanidine significantly increased the extractable content of BMPs in all samples compared to collagenase. The considerable increasing multiples of extraction efficiency of GuHCl for BMP-2 and BMP-7 ranged from 13.3 to 23.7 times and from 2.8 to 126 times, respectively. This variability of BMP-2 and BMP-7 resulting from origin of periosteal layer of long bone is a potential reason for inconsistent osteoinductivity of DBM-based products.