Glucosamine and its N-acetylphenyl-alanine derivative own regulate metalloprotease production in chondrocytes by affecting MAP kinase phosphrylation.

Glucosamine (GlcN), a symptom-control drug used in the treatment of osteoarthritis (OA), has been proved effective in slowing OA progression (Reginster et al., 2001). OA is characterized by a progressive degradation of cartilage due to an imbalance between synthesis and degradation of the extracellular matrix component. Production of proinflammatory cytokines stimulates chondrocytes to secrete an excess of proteases. We report the effects of GlcN and its N-acetyl phenylalanine derivative (NAPA) on metalloprotease (MMP) production in immortalized chondrocyte cell line, LBPVA55, stimulated with proinflammatory cytokine interleukin (IL)-1 β. We analyzed, by quantitative-real time-PCR, MMP-1, -2, -3, -8, -9, 13 mRNA expression level in cells treated with 2.5 and10 mM GlcN or with 2.5 and 10 mM NAPA, after stimulation with 10 ng/ml IL-1β. We found MMP-1, -3, and -13 upregulated by IL-1β stimulation and brought back by GlcN and NAPA. Same results were obtained when MMP-1, -3, and -13 protein levels were analyzed by ELISA. Mengshol et al. (2000), previously demonstrated that IL-1β induction of MMPs requires MAP kinases activation. To verify if GlcN and NAPA could affect p38, JNK, and ERK MAP kinases activity, we analyzed the whole cell extracts by Western blot analysis, using antiphospho-antibodies. We found phospho-p38, phospho-JNK, and phospho-ERK increased by IL-1β;phospho-JNK and phospho p38, but not phospho-ERK, were downregulated by GlcN and NAPA. Finally, we discovered that GlcN and NAPA, by affecting p38 and JNK kinases whose phosphorylation is requested to activate AP1 transcription factor, downregulated MMP-1, -3, and -13 production.