Effects of Glc, GlcN-S, GlcA and GlcN-HCl on the production of MMP-2. Porcine cartilage explants were cultured with IL-1β (25 ng/ml) in the absence and presence of each chemical (at varying concentrations of 20, 40, 80 mM) for 3 days. Media were collected and were then analyzed by gelatin zymography as described in the text. Three experiments were carried out independently and they were reproducible. *, ** Denotes a value that is significantly different (p < 0.05 and p < 0.01, respectively) from the IL-1β control.