A peptidyl-glucosamine derivative affects IKK alpha kinase activity in human chondrocytes

Introduction: Nuclear factor-kappa B (NF-kappa B) transcription factor regulates several cell signaling pathways, such as differentiation and inflammation, which are both altered in osteoarthritis. Inhibitor kappa B kinase (IKK)alpha and IKK beta are kinases involved in the activation of the NF-kappa B transcription factor. The aim of the present study was to determine the effects of glucosamine (GlcN), which is administered in the treatment of osteoarthritis, and of its 2-(N-Acetyl)-L-phenylalanylamido-2-deoxy-beta-D-glucose (NAPA) derivative on IKK kinases and, consequently, on NF-kappa B activation in human chondrocytes. Methods: The human chondrosarcoma cell line HTB-94 and human primary chondrocytes were stimulated with tumor necrosis factor (TNF)alpha after pre-treatment with GlcN or NAPA. Gene mRNA expression level was evaluated by real-time PCR. Inhibitor kappa B protein (I kappa B)alpha phosphorylation and p65 nuclear re-localization were analyzed by Western blotting; IKK alpha nuclear re-localization was also investigated by immunocytochemistry and Western blotting. IKK kinase activity was studied by in vitro kinase assay. Results: After TNF alpha stimulation, the mRNA expression level of some of the genes under NF-kappa B control, such as interleukin (IL)-6 and IL-8, increased, while treatment with GlcN and NAPA reverted the effect. We investigated the possibility that GlcN and NAPA inhibit IKK kinase activity and found that NAPA inhibits the IKKa kinase activity, whereas GlcN does not. Interestingly, both GlcN and NAPA inhibit IKKa nuclear re-localization. Conclusions: Our results demonstrate that glucosamine and its peptidyl derivative can interfere with NF-kappa B signaling pathway by inhibiting IKK alpha activity in human chondrocytes. However, the mechanism of action of the two molecules is not completely overlapping. While NAPA can both specifically inhibit the IKK alpha kinase activity and IKK alpha nuclear re-localization, GlcN only acts on IKK alpha nuclear re-localization.