Protein release parameters estimated with a flow system on zinc-containing apatite

Abstract

Adsorption and desorption properties of proteins on zinc-containing apatite were successively monitored with a newly-developed flow system, and sustained-release ability of the apatite with different zinc contents was evaluated using protein release parameters we suggested. Three sustained-release parameters; initial desorption rate (rinit), time of desorption-completed (Tdes), and desorption constant (kd) were estimated with graphical analysis of dynamic desorption curves in a flow of 20 mM phosphate-buffered solution (PBS). Bovine serum albumin (BSA) of isoelectric point (pI) 4.8 and egg white lysozyme (LSZ) of pI 11.2 were employed as model protein drugs. Incorporation of zinc into hydroxyapatite changed desorption responses of the proteins. Zn(0.15), where the number in parentheses denoted the preparing molar ratio of Zn/Ca, showed the most sustained-release ability: less rinit, longer Tdes, and smaller kd. Furthermore, the adsorbed amounts of the proteins for Zn(0.15) were 1.5 ~ 4 times larger than Zn(0), which suggested that Zn(0.15) would be promising as a sustained-release carrier of protein drugs.