In vitro study of inhibitory millimeter wave treatment effects on the TNF-α-induced NF-κB signal transduction pathway

Abnormal activation of the nuclear factor-κB (NF-κB) in chondrocytes initiates the transcription of inflammatory mediators, promotes their generation and release, and amplifies initial inflammatory signals. This results in the release of chondral matrix-degrading enzymes and accelerates the degeneration of articular cartilage. As a non-pharmaceutical and non-invasive physical therapy regimen, millimeter wave treatment has been successfully used for the treatment of osteoarthritis. In this study, chondrocytes were derived from the cartilages of knee joints of 4-week-old male Sprague-Dawley rats and were mechanically digested by collagenase type II treatment for further culture in vitro. The third-passage chondrocytes were stained with toluidine blue and treated with a gradient of tumor necrosis factor-α (TNF-α) for various times. Chondrocytic activity was measured by MTT assay, and the apoptotic rate of the chondrocytes was determined with Hocehst 33342 staining to identify effective treatment concentrations and durations and to establish an apoptosis model for the chondrocytes in response to TNF-α. Using this model, the chondrocytes were randomly divided to receive millimeter wave treatment for various times. The apoptotic rate of the chondrocytes was measured by Annexin V-FITC staining and the protein expression levels of RIP, TAK1, IκB kinase (IKK)-ß, IκB-α and NF-κB, were determined by Western blotting. Chondrocytic structure was examined by transmission electronic microscopy. The apoptotic rates were significantly lower at 4 and 8 h of treatment than at 0 and 2 h. The expression levels of RIP, TAK1, IKK-ß and NF-κB were also significantly lower at 4 and 8 h than at 0 and 2 h, whereas that of IκB-α was significantly higher at 4 and 8 h than at 0 and 2 h. Therefore, we can conclude that millimeter wave treatment can inhibit the activation of the TNF-α-mediated NF-κB signal transduction pathway through the down-regulation of RIP, TAK1, IKK-ß and NF-κB, and the up-regulation of IkB-α, in chondrocytes.