Tumor necrosis factor-α/nuclear transcription factor-κB signaling in periprosthetic osteolysis

Due to irreversible joint destruction caused by the various arthritides, more than 400,000 total joint arthroplasties are performed each year in the United States. As many as 20% of these require revision surgery because of aseptic loosening. The current paradigm to explain aseptic loosening is that wear debris generated from the prosthesis stimulates the release of proinflammatory cytokines (i.e., tumor necrosis factor‐α and interleukins 1 and 6) following phagocytosis by resident macrophages. These cytokines, in turn, initiate an inflammatory response, with the development of an erosive pannus that stimulates bone resorption by osteoclasts. In support of this model, we have previously shown that human monocytes produce large quantities of tumor necrosis factor‐α in response to titanium particles in vitro. In the current study, we characterized the role of tumor necrosis factor‐α/nuclear transcription factor‐κB signaling in the proinflammatory response to titanium particles in vitro and in vivo. Using the mouse macrophage cell line J774, we showed that these cells produce an amount of tumor necrosis factor‐α in response to titanium particles similar to that produced by human peripheral blood monocytes. The production of tumor necrosis factor‐α was preceded by a drop in cellular levels of inhibitory factor‐κBα protein and translocation of p50/p65 nuclear transcription factor‐κB to the nucleus 30 minutes after stimulation. Levels of tumor necrosis factor‐α and inhibitory factor‐κBα mRNA increased 30 minutes after stimulation, consistent with the activation of nuclear transcription factor‐κB. Interleukin‐6 mRNA was first seen 4 hours after the addition of the titanium particles, indicating that the production of this cytokine is secondary to the immediate nuclear transcription factor‐κB response. To test the relevance of tumor necrosis factor‐α/nuclear transcription factor‐κB signaling in response to titanium particles in vivo, we adopted an animal model in which the particles were surgically implanted on the calvaria of mice. The animals displayed a dramatic histological response to the debris, with the formation of fibrous tissue and extensive bone resorption after only 1 week. With use of immunohistochemistry and tartrate‐resistant acid phosphatase staining, tumor necrosis factor‐α and osteoclasts were readily detected at the site of inflammation and bone resorption in the calvaria of the treated mice. By testing mice that genetically over‐produce tumor n