Exposure to particles stimulates superoxide production by human THP-1 macrophages and avian HD-11EM osteoclasts activated by tumor necrosis factor-α and PMA

Wear of orthopaedic implants generates particles capable of inducing bone resorption and aseptic loosening of the implant. The present study shows the combined effect of particles and cell activation on macrophage (THP-1) and osteoclast (HD-11EM) release of reactive oxygen and nitrogen species, providing insight into mechanisms that can lead to osteolysis. In the absence of cell activation, exposure of either cell type to submicron zirconia or latex particles did not elicit an increase in reactive oxygen and nitrogen species production. Suboptimal stimulation with 4β-phorbol-12-myristate-13-acetate (PMA) plus particles resulted in a synergistic release of superoxide (O₂⁻), however, and a low-level production of nitric oxide · by THP-1 macrophages. Similarly, particle stimulation of tumor necrosis factor-α–activated THP-1 cells increased O₂⁻ release. Our findings show the synergistic effect of cell activation and wear particles on O₂⁻ production by activated macrophages and osteoclasts, suggesting O₂⁻ involvement in mediating osteolysis.