Articular chondrocytes and synoviocytes in a co-culture system: influence on reactive oxygen species-induced cytotoxicity and lipid peroxidation

Objective: A new co-culture system of rat articular chondrocytes and synovi ocytes (HIG-82; cell line) was incubated with phorbol myristate acetate (PM A), H2O2 or a combination of Fe2+ and ascorbic acid to simulate inflammatio n-like radical attacks in articular joints. Methods: Chondrocytes were char acterized by immunocytochemistry against collagen type II, transmission ele ctron (TEM) and light microscopy. Lipid peroxidation was investigated by me asuring thiobarbituric-acid-reactive material in the supernatants, cytotoxi city by determining release of lactate dehydrogenase and proliferation by m easuring [H-3]thymidine incorporation, culture protein and DNA. Results: PM A or Fe2+ and ascorbic acid induced lipid peroxidation in chondrocytes and synoviocytes that was decreased significantly in co-cultures. PMA and H2O2, dose dependently induced release of lactate dehydrogenase in chondrocytes, which was lowered in co-cultures or in previously co-cultured chondrocytes to a nearly basal level. In contrast, conditioned media of synoviocyte cul tures showed no lowering effect on the radical-induced toxicity. Protection against H2O2-induced damage of cellular membranes by co-culturing was also shown by TEM. Synoviocytes released chondrocyte-stimulating growth factors spontaneously without previous interaction. Conclusion: Chondrocytes estab lish protective mechanisms against reactive oxygen species via an interacti on with synoviocytes. Our co-culture model presents a possible way to study mechanisms of inflammation in articular joints under defined conditions.