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Addition of conditioned synovial medium (SM) from cultured calf knee-joint synovium to cultures of articular cartilage from the same animal resulted in a significant increase in breakdown of cartilage proteoglycans. Culturing the synovium in the presence of glucocorticoids (hydrocortisone, dexamethasone, prednisolone) or protein synthesis inhibitors (cycloheximide or actinomycin D) reduced the breakdown effect. In contrast, enhancement of proteoglycan breakdown was observed when the cartilage was exposed to glucocorticoids in the presence of SM from synovium cultured without these drugs (control SM). The stimulatory effect on cartilage breakdown of control SM or control SM + glucocorticoids was markedly reduced in the presence of actinomycin D or cycloheximide. The authors conclude that glucocorticoids under certain conditions enhance cartilage degradation and therefore, although they exert the temporary anti-inflammatory effects, treatment of joint diseases with glucocorticoids may not be beneficial in the long-term.

The black-pigmented Bacteroides gingivalis has previously been isolated from periodontal pockets and been shown capable of inflicting advanced tissue damage. Its effect on the degradation of articular cartilage proteoglycans has not previously been known. In these experiments it was demonstrated that under aerobic conditions the anaerobic microbe B. gingivalis is very potent in degrading the proteoglycans of fresh articular cartilage. It is even more potent in the presence of fetal calf serum (FCS) than in its absence. When the cartilage has been frozen/thawed there is still a slight enhancement of the degradation by B. gingivalis, but when the cartilage has been devitalized and de-enzymed by heat, the cartilage-degrading capacity of B. gingivalis is totally abolished. However, addition to the cartilage cultures of filtered conditioned medium from B. gingivalis inhibits in some degree the degradation of articular cartilage proteoglycans. It is therefore suggested that the great cartilage-degrading ability of Bacteroides gingivalis shown in this culture system could be due to its ability to degrade proteinase inhibitors.

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