Influence of tissue maturation and antioxidants on the apoptotic response of articular cartilage after injurious compression

Objective. To study the influence of tissue maturation and antioxidants on apoptosis in bovine articular cartilage induced by injurious compression. Methods. Bovine articular cartilage disks were obtained from the femoropatellar groove of animals ages 0.5-23 months and placed in culture. Cartilage disks were preincubated overnight with the cell-permeable superoxide dismutase (SOD) mimetic Mn(III) porphyrin (0-12.5 muM) or alpha-tocopherol (0-50 muM) and then injured by a single unconfined compression to a final strain of 50% at a velocity of 1 mm/second. After 4 days of additional incubation, the disks were fixed and embedded for light and electron microscopy. Apoptotic cells were quantified morphologically by the appearance of nuclear blebbing on light microscopy. Biosynthetic activity was demonstrated by incorporation of radiolabeled proline. The antioxidative action of the SOD mimetic was confirmed by histologic examination of cartilage after incubation with nitroblue tetrazolium. Results. Injurious compression induced significantly more apoptosis in cartilage disks from newborn calves (22% of cells) than in cartilage from more mature cows (2-6%). In cartilage from 22-month-old animals, the SOD mimetic reduced the percentage of apoptotic cells induced by injury in a dose-dependent manner (complete inhibition with 2.5 muM), while alpha-tocopherol had no effect. Neither antioxidant altered protein biosynthesis or cellular ultrastructure. Conclusion. Our data suggest that the apoptotic response of articular cartilage to mechanical injury is affected by maturation and is mediated in part by reactive oxygen species. The antioxidative status of the tissue might be important for the prevention of mechanically induced cell death in articular cartilage.