Effects of four types of hydroxyapatite nanoparticles with different nanocrystal morphologies and sizes on apoptosis in rat osteoblasts

ABSTRACT Hydroxyapatite nanoparticles (nano‐HAP) have been reported to cause inflammatory reactions. Here, we aimed to compare the effects of four types of nano‐HAP with different nanocrystal morphologies (short rod‐like, long rod‐like, spherical or needle‐shaped crystals) and sizes (10–20, 10–30 or 20–40 nm) on growth inhibition and apoptosis in primary cultured rat osteoblasts. The osteoblasts was treated with the four types of nano‐HAP at various concentrations (20, 40, 60, 80 or 100 mg l−1). The nano‐HAP specific surface area was detected using the Brunauer, Emmet and Teller method. The cell growth rate was detected using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay; apoptotic alterations and the level of reactive oxygen species in osteoblasts were measured using flow cytometry; and the amounts of apoptotic p53 and cytochrome c proteins were measured using western blotting. We observed that all four types of nano‐HAP inhibited the growth of osteoblasts in a dose‐dependent manner. These nano‐HAP significantly induced apoptosis in osteoblasts. Nano‐HAP with smaller specific surface areas induced lower apoptosis rates. The needle‐shaped and the short rod‐like particles induced greater cellular injury than the spherical and long rod‐like particles, respectively. The increased apoptosis rates were accompanied by increased p53 and cytochrome c expression. These findings indicate that nano‐HAP inhibit the activity of osteoblasts and also induce the apoptosis of osteoblasts in vitro. These findings also suggest that the nano‐HAP‐induced apoptotic pathway is mediated by a mitochondrial‐dependent pathway. Moreover, the sizes, morphologies and concentrations of nano‐HAP have significant effects on the apoptotic level. Copyright © 2011 John Wiley & Sons, Ltd. We aimed to compare the effects of four types of nano‐HAP with different nanocrystal morphologies and sizes on growth inhibition and apoptosis in primary cultured rat osteoblasts. And it was observed that all nano‐HAP inhibited the growth of osteoblasts and induced apoptosis in osteoblasts. The needle‐shaped and the short rod‐like particles induced greater cellular injury than the spherical and the long rod‐like particles respectively. The increased apoptosis rates were accompanied by increased p53 and cytochrome c expression.