In vitro apatite induction by osteopontin: interfacial energy for hydroxyapatite nucleation on osteopontin.
Noncollagenous phosphoproteins that interact with type I collagen are thought to nucleate the mineral phase to the collagen fibril network of mineralized tissues. We previously reported that a specific dentin phosphoprotein, phosphophoryn, crosslinked to an insoluble substrate such as type I collagen fibrils, was an effective nucleator of apatite. In this study, we investigated the capacity of another phosphoprotein in dentin, osteopontin, for apatite nucleation in vitro. Osteopontin purified from bovine milk was either absorbed to agarose beads or crosslinked to agarose beads. Each preparation was incubated at 37 degrees C in metastable solutions. Apatite was induced by osteopontin that was crosslinked to agarose beads, whereas osteopontin adsorbed to agarose beads failed to induce apatite crystal formation. Using classical nucleation theory, the interfacial energy for hydroxyapatite nucleation on osteopontin crosslinked to agarose beads was determined to be 94.7 ergs/cm(2). This value is larger than that for phosphophoryn, though it is similar to that for hydroxyapatite. The present study indicates that osteopontin, like phosphophoryn, has a high potential to induce apatite formation when it is covalently bound to some substrate in vitro, and suggests the possibility that osteopontin bound to type I collagen may induce apatite formation in vivo.
Department of Operative Dentistry and Endodontology, School of Dentistry, Health Sciences University of Hokkaido, 1757 Tobetsu, Hokkaido 061-0293, Japan.
Shuichi
S
Ito
Takashi
T
Saito
Kaori
K
Amano
D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D002417:Cattle; D003432:Cross-Linking Reagents / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D053495:Osteopontin; D012685:Sepharose / Q000737:chemistry; D012795:Sialoglycoproteins / Q000737:chemistry* / Q000302:isolation & purification
D001672:Biocompatible Materials; D002130:Calcium Phosphates; D003432:Cross-Linking Reagents; D012795:Sialoglycoproteins; D053495:Osteopontin; D012685:Sepharose; D017886:Durapatite