Prostaglandin E-1 and recombinant bone morphogenetic protein effect on strength of hydroxyapatite implants

Although combinations of hydroxyapatite (HAP) and bone morphogenetic protei n (BMP) are expected to provide potent alternatives to autogenous bone graf ts, it is still anticipated that substances that act synergistically with B MP will be found because the inducing potential of purified BMP in bone is not strong enough. We already have shown that prostaglandin (PG) E-1 has a strong and dose-dependent synergistic effect on the osteoinductive activity induced by recombinant human (rh) BMP and that it enhances osteoconduction even when used alone. In this study, porous HAP rods were treated as follo ws: (1) without PGE(1) or rhBMP (control group); (2) with varying concentra tions of PGE(1); and (3) with varying concentrations of PGE, combined with 1 mu g of rhBMP-2. The rods were subperiosteally implanted on the cranial b one of rabbits to evaluate the effect of these treatments on the mechanical strength of the implanted HAP rods. The HAP rods were removed 3, 6, or 9 w eeks after implantation and subjected to mechanical strength determinations . The control group (no addition of BMP to the rods) showed no significant increase in three-point bending strength or in compression strength compare d to pre-implantation. On the other hand, PGE(1) combined with rhBMP had a strong and dose-dependent effect on the mechanical strength of HAP, increas ing it significantly, especially compression strength. PGE(1) also increase d mechanical strength even when used alone. Histological examination reveal ed that PGE(1), whether or not it was combined with rhBMP, increased bone f ormation into the pores of HAP and consequently increased the mechanical st rength of porous HAP. (C) 1999 John Wiley & Sons, Inc.