Effect of glucosamine on MMP-1 and MMP-13 expression in HPCs stimulated with 10 ng/ml IL-1β. Cells were pretreated for 2 hours with 2.5 and 10 mmol/l glucosamine (G2.5 and G10, respectively), and then stimulated with IL-1β for 22 hours. mRNA was extracted and analyzed by quantitative real-time PCR, and cell supernatant was analyzed by ELISA. Shown are (a) matrix metalloprotease (MMP)-1 and (b) MMP-13 mRNA levels, and (c) MMP-1 and (d) MMP-13 protein amounts. Quantitative real-time PCR results are expressed in relative arbitrary units (AU) and ELISA results are expressed in ng/ml or pg/ml. Results are expressed as mean ± standard error, obtained in six different experiments. *P ≤ 0.05. CTL, control; HPC, human primary chondrocyte.