ANALYSIS OF GENE-EXPRESSION IN OSTEOGENIC CULTURED MARROW HYDROXYAPATITE CONSTRUCT IMPLANTED AT ECTOPIC SITES - A COMPARISON WITH THE OSTEOGENIC ABILITY OF CANCELLOUS BONE

We investigated the in vivo osteogenic ability of cultured marrow cell s subcultured in porous hydroxyapatite. This osteogenic ability was co mpared with that of cancellous bone grafts. Fresh marrow cells were ob tained from young adult rat femora and cultured in a standard medium f or 10 days, then trypsinized and used to make constructs of porous hyd roxyapatite (HA) and cultured marrow cells. An additional 2-week cultu re (subculture) was performed for the construct in standard medium wit h and without the addition of dexamethasone (Dex). The 2-week subcultu red constructs then were implanted into subcutaneous sites of syngenei c rats. These implants and the rat cancellous bone were harvested and prepared for gene expression analysis of alkaline phosphatase (ALP) an d osteocalcin (OC) as well as for histological analysis. ALP and OC mR NAs could be detected in Dex-treated subcultured constructs 1 week aft er implantation, with an increase at 2 weeks, comparable to the observ ation in cancellous bone. Histological analysis showed active bone for mation even 1 week postimplantation. In contrast, the subcultured cons tructs without the addition of Dex did not show bone formation, and on ly small levels of ALP and OC mRNAs were found. These results indicate that the bone tissue formed by grafting the Dex-treated construct of cultured marrow cells and hydroxyapatite possesses a high osteoblastic activity comparable to that of viable cancellous bone. Thus the prefa bricated osteogenic subcultured marrow/HA construct may be applicable in bone reconstructive surgery. (C) 1998 John Wiley & Sons, Inc. J Bio med Mater Res, 41, 568-573, 1998.