Intra-articular administration of interleukin-1 causes prolonged suppression of cartilage proteoglycan synthesis in rats.

The effect of IL-1 on proteoglycan synthesis was studied after intraarticular injection of IL-1 into the knee joints of rats. IL-1 reduced the sulfated glycosaminoglycan synthesis in the articular cartilage of rats in a dose-dependent fashion. Analysis of the sulfated molecules by chondroitinase ABC digestion followed by composite agarose/acrylamide gel electrophoresis confirmed the proteoglycan nature of the molecules. Immunoprecipitation of the methionine-labeled extracts with a polyclonal antibody against the core protein indicated that the reduction in glycosaminoglycan synthesis was due to an inhibition of the core protein synthesis after IL-1 treatment. IL-1 induced inhibition occurred in both young and old rats and was independent of the prostaglandin pathway, as non-steroidal anti-inflammatory drugs failed to block the inhibition of proteoglycan synthesis by IL-1. The cartilage of rats injected with IL-1 was able to recover with time and synthesize normal amounts of total proteoglycan. However, administration of successive doses resulted in a much delayed return to normal synthesis. These results suggest that IL-1, if available locally in a cyclical fashion, could significantly interfere with the ability of cartilage to repair by causing a prolonged suppression of proteoglycan synthesis.