Tumor necrosis factor-alpha/nuclear transcription factor-kappa B signalingin periprosthetic osteolysis

Due to irreversible joint destruction caused by the various arthritides, mo re than 400,000 total joint arthroplasties are performed each year in the U nited States. As many as 20% of these require revision surgery because of a septic loosening. The current paradigm to explain aseptic loosening is that wear debris generated from the prosthesis stimulates the release of proinf lammatory cytokines (i.e., tumor necrosis factor-alpha and interleukins 1 a nd 6) following phagocytosis by resident macrophages. These cytokines, in t urn, initiate an inflammatory response, with the development of an erosive pannus that stimulates bone resorption by osteoclasts. In support of this m odel, we have previously shown that human monocytes produce large quantitie s of tumor necrosis factor-alpha in response to titanium particles in vitro . In the current study, we characterized the role of tumor necrosis factor- alpha/nuclear transcription factor-kappa B signaling in the proinflammatory response to titanium particles in vitro and in vivo. Using the mouse macro phage cell line J774, we showed that these cells produce an amount of tumor necrosis factor-alpha in response to titanium particles similar to that pr oduced by human peripheral blood monocytes. The production of tumor necrosi s factor-alpha was preceded by a drop in cellular levels of inhibitory fact or-kappa B alpha protein and translocation of p50/p65 nuclear transcription factor-kappa B to the nucleus 30 minutes after stimulation. Levels of tumo r necrosis factor-alpha and inhibitory factor-kappa B alpha mRNA increased 30 minutes after stimulation, consistent with the activation of nuclear tra nscription factor-kappa B. Interleukin-6 mRNA was first seen 4 hours after the addition of the titanium particles, indicating that the production of t his cytokine is secondary to the immediate nuclear transcription factor-kap pa B response. To test the relevance of tumor necrosis factor-alpha/nuclear transcription factor-kappa B signaling in response to titanium particles i n vivo, we adopted an animal model in which the particles were surgically i mplanted on the calvaria of mice. The animals displayed a dramatic histolog ical response to the debris, with the formation of fibrous tissue and exten sive bone resorption after only 1 week. With use of immunohistochemistry an d tartrate-resistant acid phosphatase staining, tumor necrosis factor-alpha and osteoclasts were readily detected at the site of inflammation and bone resorption in the calvaria of the treated mice. By testing mice that genet ically over-produce tumor necrosis factor-alpha (hTNF alpha-Tg), those defe ctive in tumor necrosis factor-alpha signaling (TNF-RI-/-), and those that are nuclear transcription factor-kappa B1-deficient (NF kappa B1-/-), we ev aluated the importance of tumor necrosis factor-alpha/nuclear transcription factor-kappa B signaling in the biological processes responsible for asept ic loosening. The hTNF alpha-Tg mice had a grossly exaggerated response, th e TNF-RI(-/-) mice showed little evidence of inflammation or bone resorptio n, and the nuclear transcription factor-kappa B1(-/-) mice had an inflammat ory response without bone resorption. On the basis of these results, we pro pose a model for periprosthetic osteolysis in which wear debris particles a re phagocytosed by macrophages, resulting in the activation of nuclear tran scription factor-kappa B and the production of tumor necrosis factor-alpha. Tumor necrosis factor-alpha directly induces fibroblast proliferation and tissue fibrosis and recruits or activates, or both, osteoclasts to resorb a djacent bone.