Proteome analysis of rat serum proteins adsorbed onto synthetic octacalcium phosphate crystals

The present study was designed to determine which proteins are selectively adsorbed onto two bone substitute materials, octacalcium phosphate (OCP) and hydroxyapatite (HA) crystals, from rat serum by proteome analysis. Ground crystals of synthetic OCP and commercially available sintered HA, with the same surface area, were incubated in rat serum proteins at 37 °C for 24 h. The proteins from the crystals extracted with guanidine-HCl-EDTA were listed on the basis of the results of liquid chromatography tandem mass spectrometry (LC/MS/MS). A total of 138 proteins were detected from OCP; 103 proteins were detected from HA. Forty-eight proteins were from both crystals. A quantitative analysis of the proteins detected was performed for the extracted two bone formation-related proteins apolipoprotein E (Apo E), a protein known to promote osteoblast differentiation, and complement 3 (C3). HA adsorbed C3 (3.98 ± 0.03 fmol/μg protein) more than OCP (1.81 ± 0.07 fmol/μg protein) did, while OCP adsorbed Apo E (2.42 ± 0.03 fmol/μg protein) more than HA (1.21 ± 0.01 fmol/μg protein) did even after deleting the high-abundance proteins, such as albumin. The results demonstrated that OCP exhibits a similar property but distinct capacity with HA in adsorbing bone formation-related proteins from the serum constituents.