Imbalance between low sod activity and excessive superoxide occurs in end-stage OA cartilage and synovium.

Purpose: Superoxide is a reactive oxygen species (ROS), which are harmful molecules mainly generated during mitochondrial respiration and metabolized by superoxide dismutase (SOD). We have previously concluded that excessive superoxide produced by SOD depletion in chondrocytes accelerates cartilage degeneration in mice. SOD activity is a key component of cellular antioxidant system to protect cells from oxidative stress. However, it has been unclear the alteration of superoxide and SOD activity in the end-stage human knee osteoarthritis (OA). The purpose of this study is to clarify the alteration of SOD activity in the end-stage knee OA cartilage and synovium. Methods: To evaluate superoxide generation using dihydroethidium (DHE) staining, cartilage and synovium samples were obtained from 6 subjects (age mean=72.6±7.03) with end-stage knee OA underwent total knee arthroplasty (TKA) and compared to cartilage and synovium from 6 subjects (age mean=31.6±13.2) with control underwent knee arthroscopy for meniscal tears or anterior cruciate ligament reconstruction. Next, to evaluate SOD activity in end-stage knee OA joint, cartilage and synovium samples were obtained from 18 subjects (age mean=76.6±8.88) with end-stage knee OA underwent TKA and compared to cartilage and synovium from 9 subjects (age mean=31.4±14.5) with control underwent knee arthroscopy for meniscal tears or anterior cruciate ligament reconstruction. SOD activity was analyzed using enzyme-linked immunosorbent assay (ELISA). To evaluate the correlation between age and SOD activity in chondrocytes, Pearson correlation method was used. Furthermore, to evaluate correlation between age and SOD activity in synovium, Spearman correlation method was used. In this study, all tests were conducted at the 5% significance level (P=0.05). A patient’s informed consent was obtained before enrolling in this study, which was approved by the ethics committee of Juntendo University. Results: The intensity of DHE staining was 1.94-fold increase in end-stage knee OA cartilage compared to control (p<0.001, student’s t test) and 1.26-fold increase in end-stage knee OA synovium compared to control (p<0.05, student’s t test). SOD activity in end-stage knee OA cartilage (mean=14.38 U/mg protein) was significantly decreased compared to control (mean=25.11 U/mg protein) (p<0.001, student’s t test). Surprisingly, SOD activity in end-stage knee OA synovium (mean=14.79 U/mg protein) was significantly decreased compared to control (mean=43.26 U/mg protein) (p<0.01, Mann-Whitney U test). SOD activity in cartilage showed a low negative correlation with age (r=-.381, p<0.05). However, the relationship of synovium between SOD activity and age was not significant (r=-.299, p>0.13). Conclusions: Not only end-stage knee OA cartilage but also end-stage knee OA synovium indicated imbalance between excessive oxidative stress (excessive superoxide generation) and low antioxidant capacity. These data showed that regulation of SOD activity in joint cavity might be able to prevent OA progression.