LUCIGENIN-DEPENDENT CHEMILUMINESCENCE IN ARTICULAR CHONDROCYTES

We were recently able to measure intracellular levels of hydrogen pero xide within normal articular chondrocytes using the trapped indicator 2',7-dichlorofluorescein diacetate. Further studies have shown that st imulated chondrocytes produce luminol-dependent chemiluminescence, sug gesting that these cells produce hydrogen peroxide and singlet oxygen. In the present study, we have investigated the lucigenin-dependent ch emiluminescence response in normal articular chondrocytes. Chondrocyte s either in suspension or adhered to cover slips showed lucigenin-depe ndent chemiluminescence. There was a dose-dependent increase in chemil uminescence response when chondrocytes were incubated with soluble sti muli like phorbol-myristate-acetate, concanavalin A, and f-met-leu-phe . Catalase and the metabolic inhibitor, sodium azide, which inhibits t he enzyme myeloperoxidase, had no inhibitory effect on lucigenin-depen dent chemiluminescence production. Only the antioxidant, superoxide di smutase, prevented lucigenin-dependent chemiluminescence, indicating t hat this assay measures the production of superoxide anions by chondro cytes. We confirmed that chondrocytes release superoxide radicals usin g the biochemical assay of ferricytochrome c reduction. Since cartilag e tissue is semitransparent, we were able to measure chemiluminescence response in live cartilage tissue, showing that chondrocytes which ar e embedded within the matrix can also generate superoxide anion radica ls. Reactive oxygen intermediates have been shown to play a significan t role in the degradation of matrix in arthritis. Our previous and pre sent studies suggest that oxygen radicals produced by chondrocytes may be an important mechanism by which chondrocytes induce cartilage matr ix degradation.