Enhanced breakdown of bovine articular cartilage proteoglycans by conditioned synovial medium. The effect of serum and dextran sulphate.

Medium from cultured bovine synovial membrane when applied to articular cartilage from the same animal enhanced proteoglycan breakdown, as measured by the release of [35S]sulphate from prelabelled cartilage, principally by activating chondrocytes to secrete or activate their own enzymes. This effect persisted whether or not the synovium was cultured in medium containing fetal calf serum. The release of proteoglycans from cartilage was markedly enhanced when the synovium was cultured in the presence of dextran sulphate (200 micrograms/ml), while dextran sulphate had no effect upon cartilage alone or when added together with medium cultured in the absence of dextran sulphate. Since the release of the proteoglycan breakdown products from frozen and thawed cartilage was not stimulated by dextran sulphate, this agent appeared to be enhancing the indirect chondrocyte-mediated effect of synovial medium rather than the direct proteolytic enzyme-induced effect. A possible mechanism for the production of a substance responsible for the chondrocyte-mediated matrix degradation is proposed, involving monocyte-like or macrophage-like cells, either resident in the synovial tissue or derived from the circulation.