Tissue culture of articular cartilage tissue. (a) Representative immunohistochemical staining for nitrotyrosine in cartilage explants treated with reactive oxygen species (ROS) or an antioxidative agent in tissue culture. Osteoarthritis (OA) cartilage explant from a 67-year-old donor was cut and divided into three groups: control group, H2O2 treated group, and antioxidative agent (ascorbic acid-2-O-phosphate [Asc2P]) treated group. After the end of the incubation period (48 hours of incubation), the cartilage sections were immunostained with anti-nitrotyrosine antibody. Original magnifications are given in parentheses. (b) The number of nitrotyrosine positive cells were counted in the 20 areas of tissue-cultured cartilage at 200× magnification (0.785 mm2/field). A statistical analysis of immunostaining was performed. *P < 0.05, **P < 0.01, versus control group.