Periprosthetic osteolysis: characterizing the innate immune response to titanium wear-particles.

Osteolysis of bone following total hip replacement is a major clinical problem. Examination of the areas surrounding failed implants has indicated an increase in the bone-resorption-inducing cytokine, interleukin 1β (IL-1β). NALP3, a NOD-like receptor protein located in the cytosol of macrophages, signals the cleavage of pro-IL-1β into its mature, secreted form, IL-1β. Here we showed that titanium particles stimulate the NALP3 inflammasome. We demonstrated that titanium induces IL-1β secretion from macrophages. This response depended on the expression of components of the NALP3 inflammasome, including NALP3, ASC, and Caspase-1. We also showed that titanium particles trigger the recruitment of neutrophils and that this acute inflammatory response depends on the expression of the IL-1 receptor and IL-1α/β. Moreover, administration of the IL-1 receptor antagonist (IL-1Ra) diminished neutrophil recruitment in response to titanium particles. Together, these results suggest that titanium particle-induced acute inflammation is due to activation of the NALP3 inflammasome, which leads to increased IL-1β secretion and IL-1-associated signaling, including neutrophil recruitment. Efficacy of IL-1Ra treatment introduces the potential for antagonist-based therapies for implant osteolysis.