Adsorption of Serum Fetuin onto Octacalcium Phosphate and Its Relation to Osteogenic Property

This study aimed to investigate how the chemical elements in relation to octacalcium phosphate (OCP) hydrolysis affect the osteoblastic differentiation in the presence of serum fetuin. The adsorption of fetuin onto OCP was examined in buffers having different degrees of supersaturation (DS) with respect to OCP and hydroxyapatite (HA) at pH 7.4 and 37 °C. The osteoblastic differentiation of mesenchymal stem cells (MSCs) was evaluated in cultures with OCP and 0 to 0.8 mg/mL of fetuin. The amount of fetuin adsorbed increased with increasing DS in the buffer. In the MSC culture, the coexistence of OCP and 0.2-0.4 mg/mL of fetuin close to serum level increased alkaline phosphatase activity; however, the activity was suppressed by 0.2-0.8 mg/mL of fetuin. Transmission electron microscopy revealed de novo crystal formation on OCP in supersaturated buffer and culture media with respect to OCP and HA at lower fetuin concentrations. Infrared spectroscopy and DS estimation indicate that the hydrolysis of OCP with de novo apatite formation was promoted in the culture media at 0.2-0.4 mg/mL of fetuin. These results suggest that OCP may promote osteoblastic differentiation if the suitable conditions are attained regarding the chemical elements and fetuin adsorption around OCP.