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 precursors that circulate in the monocyte fraction. This study has determined the effect of phagocytosis of metal particles on 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-dihydroxyvitamin D3, dexamethasone, and human macophage colony-stimulating factor. Cobalt-chrome alloy (CoCr), stainless steel (316L-SS), titanium alloy (TiAlV), and commercially pure titanium (cpTi) particles (size range, 0.5-3.0 μm) and 1.0-μm latex particles were added to the cocultures as a single dose at the beginning of each experiment. All 5 types of particles were readily phagocytosed by the monocytes. After 4 days’ exposure to high concentrations of all the metal particles, some cell death was found in the cocultures. After 14 days, a reduction in the number of CD14⁺ cells was seen in cocultures exposed to high concentrations of metal particles, particularly CoCr and 316L-SS particles. Phagocytosis of latex particles by osteoclast precursors did not affect the ability of these cells to undergo osteoclast differentiation. In contrast, exposure to metal wear particle preparations caused a dose-dependent reduction in the number of vitronectin receptor-positive osteoclastic cells formed and a dose-dependent reduction in the bone resorption produced by these cells. This decrease in resorption was greater after exposure to CoCr and 316L-SS particles compared with TiAlV and cpTi particles. This in vitro cell culture system may provide a useful model to compare the effect of different prosthetic materials on human osteoclast formation and bone resorption.