Cathepsin activity in conditioned media of human chondrocytes and explant cultures. Human chondrocytes were isolated from intact regions of osteoarthritis (OA)-derived cartilage and plated at passage 0. Following confluence the cells were treated with (A) 50 ng/mL TNFα and 5 ng/mL IL1β for 24 h or (B) 5 ng/mL IL1β. Conditioned media were labeled with GB123, concentrated and run on PAGE, and labeled cathepsins were detected by on gel-fluorescent scan (n = 4). Plots of band intensity (imageJ software) show standard deviation surrounding an average data point. Statistical analysis was obtained using non-parametric Mann-Whitney analysis, assuming P <0.05 to be statistically significant.