Enhancement of the in vivo osteogenic potential of marrow/hydroxyapatite composites by bovine bone morphogenetic protein

A composite of marrow mesenchymal stem cells and porous hydroxyapatite (HA) has in vivo osteogenic potential. To investigate factors enhancing the ost eogenic potential of marrow/HA composites, we prepared a bone morphogenetic protein (BMP) fraction from the 4M guanidine extract of bovine bone by hep arin-sepharose affinity chromatography. Marrow/HA composites or composites containing marrow mesenchymal stem cells, BMP, and HA (marrow/BMP/HA compos ites) were implanted subcutaneously in 7-week-old male Fischer rats. BMP/HA composites and HA alone were also implanted. The implants were harvested a fter 2, 4, or 8 weeks and were prepared for histological and biochemical st udies. Histological examination showed obvious de novo bone formation toget her with active osteoblasts at 2 weeks, as well as more extensive bone form ation at 4 and 8 weeks in many pores of the marrow, BMP/HA composites. The marrow/HA composites did not induce bone formation at 2 weeks, but there wa s moderate bone formation at 2 weeks. At 2 weeks, only marrow/BMP/ HA compo sites resulted in intensive osteogenic activity, judging from alkaline phos phatase and osteocalcin expression at both the protein and gene levels. The se results indicate that the combination of marrow mesenchymal stem cells, porous HA, and BMP synergistically enhances osteogenic potential, and may p rovide a rational basis for their clinical application, although further in vivo experiment is needed. (C) 2000 John Wiley & Sons, Inc.