In vitro mineralization studies with substrate-immobilized bone morphogenetic protein peptides.

Understanding the factors that control osteoblastic behavior is centrally important in establishment of successful osseointegration. Pharmacogenetic control of the osteoblast to increase the mineral content around dental implants may offer a unique advantage to clinicians in improving osseointegration success and decreasing time before mechanical loading. This in vitro pilot study has screened for bioactive peptides derived from bone morphogenetic protein 7 (BMP-7) (also called osteogenic protein 1 [OP-1]). Thirteen overlapping peptides of BMP-7 were synthesized and covalently coupled to glass coverslip substrates using silane chemistry. The rate and relative amount of mineralization were compared by von Kossa analysis using primary rat calvarial osteoblastic cell populations during a 7- to 21-day period. In addition, bone sialoprotein (BSP) and osteocalcin (OC) gene expression was measured from osteoblastic cells grown on peptide-immobilized glass coverslips by reverse transcriptase-polymerase chain reaction. Initial results from mineralization studies suggested the BMP-7-derived peptides were able to support mineralization to varying degrees with enhanced peptide-induced mineralization from the C-and N-termini of the BMP-7 molecule. Analysis of these peptide regions indicated that these peptides comprised the finger 1 and 2 domains of CP-1, which contribute toward ligand-receptor interaction. Further analysis of gene expression from select peptide-immobilized substrates indicated that peptides from the C-terminus of BMP-7 were capable of supporting BSP and OC messenger RNA expression. These studies indicate that BMP-7 peptides covalently bound to solid substrates may provide the biological basis to immobilize peptides to titanium implants to induce osteoblastic differentiation and mineralization in a more predictable fashion.