Effect of glucosamine on c-jun DNA-binding activity in HPCs stimulated with 10 ng/ml IL-1β. Cells were pretreated with 2.5 and 10 mmol/l glucosamine (G2.5 and G10, respectively) for 2 hours and then stimulated with IL-1β for 15 minutes. Nuclear extract was prepared as described in Materials and methods. Results are expressed as optical density (OD) measured at 450 nm and represent the mean ± standard error of data obtained in six different experiments. *P ≤ 0.05. CTL, control; HPC, human primary chondrocyte.