The Efficacy of Porous Hydroxyapatite Granule as a Carrier of E.coli-derived Recombinant Human Bone Morphogenetic Protein-2

Porous hydroxyapatite (HA) has great osteoconductivity, which allows it to be used as a bone graft extender. Porous HA enables bone formation by binding with recombinant human bone morphogenetic protein-2 (rhBMP-2). This research is to assess the capability of porous HA granules as a carrier of E.coli-derived rhBMP-2 (E.BMP-2). We compared the release of E.BMP-2 from porous HA of both block and granular forms for 120 min by using an ELISA. Using alkaline phosphatase (ALP) activity assay of human mesenchymal stem cells (hMSC), and the rat abdominal ectopic bone formation model, we also examined the osteogenic capacity of granular HA containing E.BMP-2.The result has shown that the rate of E.BMP-2 released from porous HA for 120 min indicated 42% of HA granules and 27.9% of HA block; the amount of HA granules was larger than HA block. At each set time interval of 10 min, 20 min, 40 min, 80 min, and 120 min, the amount of E.BMP-2 released from HA granules were significantly higher than those from HA block. The ALP activity on the third day of porous HA granules treated with 100 mu g E.BMP-2 was significantly higher than that of pure HA granules. In addition, in the rat in vivo model, bony tissue was confirmed in the all of the cases in the E.BMP-HA group but not in the pure HA group, according to the micro-CT and the histology 8 weeks after the surgery. Moreover, in contrast to the pure HA group, the E.BMP-HA group showed a higher level of bone volume, percent bone volume, structure model index, trabecular thickness, and trabecular number in the micro-CT scan. In conclusion, porous HA granules can be bound with E.BMP-2 and can properly release E.BMP-2, so that it can increase the osteoblastic differentiation of hMSC and induce the ectopic bone formation, consequently qualifying as a carrier of E.BMP-2.