The effect of particle phagocytosis and metallic wear particles on osteoclast formation and bone resorption in vitro

Osteoclasts are multinucleated bone-resorbing cells that are formed from pr ecursors that circulate in the monocyte fraction. This study has determined the effect of phagocytosis of metal particles an osteoclast formation and bone resorption in vitro. Human peripheral blood monocytes were cocultured for 21 days with osteoblast-like UMR 106 cells, in the presence of 1,25-dih ydroxyvitamin D-3, dexamethasone, and human macophage colony-stimulating fa ctor. Cobalt-chrome alloy (CoCr), stainless steel (316L-SS), titanium alloy (TiAlV), and commercially pure titanium (cpTi) particles (size range, 0.5- 3.0 mu m) and 1.0-mu m latex particles were added to the cocultures as a si ngle dose at the beginning of each experiment. All 5 types of particles wer e readily phagocytosed by the monocytes. After 4 days' exposure to high con centrations of all the metal particles, some cell death was found in the co cultures. After 14 days, a reduction in the number of CD14(+) cells was see n in cocultures exposed to high concentrations of metal particles, particul arly CoCr and 316L-SS particles. Phagocytosis of latex particles by osteocl ast precursors did not affect the ability of these cells to undergo osteocl ast differentiation. Ln contrast, exposure to metal wear particle preparati ons caused a dose-dependent reduction in the number of vitronectin receptor -positive osteoclastic cells formed and a dose-dependent reduction in the b one resorption produced by these cells. This decrease in resorption was gre ater after exposure to CoCr and 316L-SS particles compared with TiAlV and c pTi particles. This in vitro cell culture system may provide a useful model to compare the effect of different prosthetic materials on human osteoclas t formation and bone resorption.