Nitric oxide sustains nuclear factor kappaB activation in cytokine-stimulated chondrocytes

Objective: In the current studies we have examined the effects of nitric oxide, and its redox derivatives peroxynitrite and S-nitrosothiol, S-nitrosocysteine, on nuclear factor kappaB (NF-kappaB) activation in cytokine-stimulated bovine chondrocytes. Methods: The kinetics of NF-kappaB activation (p65 nuclear translocation) were assessed by immunofluorescence and immunoblot assays. Results: We observed that the two nitric oxide redox species, peroxynitrite and S-nitrosocysteine, exert opposing effects on NF-kappaB activation. However, in lipopolysaccharicle (LPS)/cytokine-stimulated chondrocytes (LPS, IL-1beta and TNF-alpha (LIT)) in the presence or absence of the NOS inhibitor L-NG-monomethyl arginine citrate (L-NMMA), the results indicate that nitric oxide causes persistent activation of NF-kappaB, most likely via generation of the free radical derivative peroxynitrite. Conclusion: The studies indicate that while nitric oxide is not required for immediate NF-kappaB activation in cytokine-stimulated chondrocytes, its effect is to sustain nuclear translocation of p65 and thereby provide a persistent "on signal" to NF-kappaB dependent gene transcription. Persistent activation of NF-kappaB may represent a mechanism by which nitric oxide sustains catabolic processes and promotes cartilage degeneration in osteoarthritis. (C) 2004 OsteoArthritis Research Society International. Published by Elsevier Ltd. All rights reserved.