Evidence linking chondrocyte lipid peroxidation to cartilage matrix protein degradation - Possible role in cartilage aging and the pathogenesis of osteoarthritis

Reactive oxygen species (ROS) are implicated in both cartilage aging and th e pathogenesis of osteoarthritis. We developed an in vitro model to study t he role of chondrocyte-derived ROS in cartilage matrix protein degradation. Matrix proteins in cultured primary articular chondrocytes were labeled wi th [H-3]proline, and the washed cell matrix was returned to a serum-free ba lanced salt solution. Exposure to hydrogen peroxide resulted in oxidative d amage to the cell matrix as established by monitoring the release of labele d material into the medium. Calcium ionophore treatment of chondrocytes, in a dose-dependent manner, significantly enhanced the release of labeled mat rix, suggesting a chondrocyte-dependent mechanism of matrix degradation. An tioxidant enzymes such as catalase or superoxide dismutase did not influenc e matrix release by the calcium ionophore-activated chondrocytes. However, vitamin E, at physiological concentrations, significantly diminished the re lease of labeled matrix by activated chondrocytes. The fact that vitamin E is a chain-breaking antioxidant indicates that the mechanism of matrix degr adation and release is mediated by the lipid peroxidation process. Lipid pe roxidation was measured in chondrocytes loaded with cis-parinaric acid. Bot h resting and activated cells showed constitutive and enhanced levels of li pid peroxidation activity, which were significantly reduced in the presence of vitamin E. In an immunoblot analysis, malondialdehyde and hydroxynonena l adducts were observed in chondrocyte-matrix extracts, and the amount of a dducts increased with calcium ionophore treatment, Furthermore, vitamin E d iminished aldehyde-protein adduct formation in activated extracts, which su ggests that vitamin E has an antioxidant role in preventing protein oxidati on, This study provides in vitro evidence linking chondrocyte lipid peroxid ation to cartilage matrix protein (collagen) oxidation and degradation and suggests that vitamin E has a preventive role. These observations indicate that chondrocyte lipid peroxidation may have a role in the pathogenesis of cartilage aging and osteoarthritis.