Chondrocytes were pretreated with anti-TNF-α antibody (50 μg/ml), anti-IL-1β antibody (50 μg/ml), celecoxib (5 μM), or 1400W (50 μM) for 1 h and then stimulated with or without 10 ng/ml IL-1β for 30 min, followed by 10 ng/ml melatonin for 24 h. A. qPCR and B. and C. Western blot analyses were performed to determine the mRNA and protein expression of MMP-3 and MMP-13, respectively. GAPDH and β-actin were used as internal controls. D. Levels of MMP-3 and MMP-13 in the media were measured by ELISAs. Each value represents means ± SD of 3 replicates or representative of 3 independent experiments. *P < 0.05 compared with control; #P < 0.05 compared with IL-1β-treated group. Mel: melatonin; Cel: celecoxib.