Southern blot analysis of chondrocyte telomere lengths in cultured chondrocytes at each passage under the different oxidative conditions. (a) Representative image of Southern blot analysis. Telomere lengths in chondrocytes (1 × 106 cells/dish, initial subculture at the start of the experiment: chondrocytes at passage 3 or 4) were determined using the terminal restriction fragment (TRF) assay. (b) The mean lengths of the chondrocytes were calculated by densitometric molecular weight analysis and were plotted against the number of cell population doublings. *P < 0.05, versus control group at each incubation time. ROS, reactive oxygen species.