Evaluation of a novel osteogenic factor, bone cell stimulating substance, in a rabbit cranial defect model

A novel osteogenic factor, bone cell stimulating substance (BCSS), was recently isolated from bovine bone. Unlike the bone morphogenetic proteins, which are generally 20- to 40-kDa glycoproteins belonging to the transforming growth factor-beta superfamily, BCSS is a 2.5-kDa, water-soluble polypeptide. This study evaluated the osteogenic potential of BCSS in combination with coralline-derived porous hydroxyapatite to reconstruct a large, nonhealing cranial defect in the rabbit. Twenty-four rabbits underwent a 16 X 20 mm full-thickness (extradural) excision of the parietal bones and were divided into six groups of four rabbits each. Groups 1 through 5 were reconstructed with 16 X 20 X 1.5 mm hydroxyapatite implants treated with: (1) 20 osteogenic units (424 mu g) BCSS, (2) 8 osteogenic units (170 mu g) BCSS, (3) 4 osteogenic units (85 mu g) BCSS, (4) 0 osteogenic units (424 mu g) inactive BCSS analog, or (5) left untreated. Group 6 was left unreconstructed. Implants were harvested at 12 weeks and analyzed for percentage of lamellar bone formation by a computerized microscope video image analysis system. Groups reconstructed with BCSS-treated hydroxyapatite implants demonstrated more bone ingrowth than did the control hydroxyapatite groups not treated with BCSS (inactive BCSS analog or untreated). Linear regression dose-response analysis indicated an average 3.2 percent increase in bone ingrowth for a 10-U increase in BCSS (p = 0.043). The unreconstructed control group demonstrated no healing. With a molecular mass of only 2.5 kDa and its identity not completely known, BCSS is a novel factor that seems to possess osteogenic potential similar to that of previously investigated osteogenic proteins.