Effect of phosphophoryn on rhBMP-2-induced bone formation

In the present study, dentin phosphophoryn (DPP) derived from fresh bovine dentin was evaluated as a co-factor for recombinant human bone morphogenetic protein-2 (rhBMP-2) in rhBMP-2-induced bone formation in rats. A 5 μg amount of Escherichia coli-derived rhBMP-2 variant was combined with DPP cross-linked to type I collagen (2.4 μg DPP/360 μg collagen), acting as carrier. Next, rhBMP-2/DPP/collagen composites were implanted by onlay-grafting beneath the cranial periosteum in 4-week-old Wistar rats. Rats were sacrificed at 2 and 3 weeks after implantation. Throughout the experimental period, rhBMP-2/DPP/collagen composite induced more bone formation than the rhBMP-2/collagen composite. Moreover, the degradation rate of rhBMP-2/DPP/collagen composite in rat was faster than that of rhBMP-2/collagen composite. Neither DPP/collagen composite nor collagen alone conducted bone formation even at 3 weeks postimplantation. These results indicate that the bone-inducing activity of rhBMP-2 is enhanced by DPP as a co-factor of rhBMP-2 in vivo.