Effect of glucosamine MAPK phosphorylation in HPCs stimulated with 10 ng/ml IL-1β. Cells were pretreated for 2 hours with 2.5 or 10 mmol/l glucosamine (G2.5 and G10, respectively), and then stimulated with IL-1β for 15 minutes. Whole cell extract was prepared as described in Materials and methods. Proteins were resolved on SDS-PAGE, electrotransferred and immunoblotted. Antibodies to (a) phosphorylated (p)-c-jun amino-terminal kinase (JNK) and total JNK, (b) p-p38 and total p38, and (c) p-extracellular signal-regulated kinase (ERK)1/2 and total ERK1/2 were used to visualize mitogen-activated protein kinase (MAPK) phosphorylation. Representative data from six independent experiments are shown. CTL, control; HPC, human primary chondrocyte.