Release of cell surface proteoglycan from chondrocytes by interleukin-1

A cell culture model was developed to assess factors that can protect cartilage from recombinant human interleukin-1 alpha (IL-1)-induced breakdown. IL-1 (0.01-10 ng/ml) caused a dose-dependent release of cell surface proteoglycan into the medium of bovine and rabbit articular chondrocytes. Sulfated glycosaminoglycan (S-GAG) was detected in the medium and on the cell surface by a dimethlymethylene blue assay. The redistribution of the cell surface S-GAG to the medium compartment required protein synthesis because it was inhibited by cycloheximide and was time-dependent (> 5 h). Although the release was most likely due to de novo synthesis of proteases, standard protease inhibitors failed to prevent the release even when used in combination. TGF-beta and IGF-I increased the amount of S-GAG in both the medium and cell surface compartments, but did not protect from IL-1-induced release. This method has an advantage over a cartilage model of IL-1-induced matrix release because the drug and cytokine exposure time is reduced and the variability is less.