Effect of particle size on zinc release from zinc containing tricalcium phosphate (ZnTCP) in Zn-deficient osteoporosis rats.

The effect of particle size on in vivo and in vitro Zn release of ZnTCP was investigated for the purpose of understanding Zn release behavior from a sustained-release device. The tricalcium phosphate powders (Ca2.7 Zn0.3(PO4)2), with particle size of 7.5 and 553 microm (S-ZnTCP and L-ZnTCP), including a 10 mol% of Zn (6.17 w/w%), as new sustained-release preparations, were synthesized by heating, after then ground and sieved using 38 and 300 microm screens. The different powder samples were characterized by the X-ray powder diffractometry and scanning electron microscopy. The release rates from Zn-TCP powders (10 mg) were measured in 10 ml of simulated body fluid (SBF) containing 10 mg/100 ml Ca2+(SBF/H), SBF containing 5 mg/100 ml Ca2+ (SBF/L) or SBF without Ca2+ (SBF/-) at 37.0 degrees C. The in vitro Zn release profiles for the smallest and the largest particles size of ZnTCP powders (L-ZnTCP and S-ZnTCP) at various Ca concentrations in SBF were significantly higher in SBF/- and SBF/L than in SBF/H. The Zn release rate from ZnTCP with different particle sizes were found to be inversely proportional to the concentration of calcium in SBF. After injection of a ZnTCP suspension containing 30 mg of S-ZnTCP powder on the backs of the rats, the plasma Zn level increased rapidly, reaching a concentration range of around 2 microg/ml. The area under the curve values of the plasma Zn concentration (Zn-AUC) over 6 days post injection of S-ZnTCP and L-ZnTCP were significantly higher than that of the control experiment. After the injection of S-ZnTCP and L-ZnTCP suspension, the plasma alkaline phosphatase activity (AIP) levels increased to more than 300 IU/l. In contrast, the AIP for the control decreased after 2 days. The area under the curve of the AIP (AIP-AUC) for 6 days of S-ZnTCP was significantly higher than that of other groups.