Suppression of Titanium Particle-Induced TNF-Alpha Expression and Apoptosis in Human U937 Macrophages by siRNA Silencing

Aseptic loosening of joint prosthetics is one of the most frequent reasons for the failure of total joint replacement surgeries. A major cause of the aseptic loosening is osteolysis caused by a periprosthetic inflammatory response to wear particles released from implanted prosthetics. Tumor necrosis factor (TNF)-α is thought to play a dominant role in wear-induced inflammation. It was shown previously by our group, as well as by other researchers, that macrophages produce abundant TNF-α when exposed to particulate titanium (Ti), which is widely used as a biomaterial in arthroplastic surgery. In the present study, we have tested the feasibility of using siRNA as a therapeutic intervention against wear-induced TNF-α production. Our data show that transfection of U937 macrophage cells with TNF-α siRNA inhibits Ti particle-induced expression of TNF-α mRNA and protein by >65%. Moreover, U937 cells transfected with TNF-α siRNA were significantly more resistant to Ti particle-induced apoptosis (>60%, p<0.05) and caspase-3 activation (>50%, p<0.05) compared with normal U937 cells. Collectively, our data show that siRNA can be an effective way to inhibit Ti particle-induced TNF-α expression and the activation of downstream pathways such as apoptosis in macrophages. These data provide a foundation for future studies to investigate the use of siRNA targeting inflammatory cytokines as a therapeutic modality for the treatment of aseptic loosening of prosthetic materials used in arthroplastic surgery.