Studies into the influence of carrageenan-induced inflammation on articular cartilage degradation using implantation into air pouches

We describe a novel system for examining the degradation of articular cartilage in vivo. Implantation of rat femoral head cartilage into six day old subcutaneous air pouches allows the examination of the degradation of cartilage in contact with a synovial lining-like structure. Femoral head cartilage was removed 1, 2 or 3 weeks after implantation and the proteoglycan content measured using 1,9-dimethyl methylene blue. Chondrocyte viability was confirmed using 35S sulphate incorporation. Increasing proteoglycan loss was observed over 3 weeks. Loss was similar in transplants between inbred and between outbred animals, suggesting that allograft rejection did not contribute significantly. Introduction of the irritant carrageenan into pouches produced a massive and prolonged inflammatory response characterized by exudation of leucocyte-rich fluid. Induction of inflammation with carrageenan did not alter the profile of proteoglycan loss from whole, minced, live or dead cartilage, as compared to that seen in non-inflamed pouches. These results indicate that when the relationship between articular cartilage and its normal tissue surroundings is disturbed, rapid proteoglycan loss may occur. The conditions induced by carrageenan inflammation have, in comparison, little or no effect on cartilage degradation. This raises the possibility that the direct effects of inflammatory products are of relatively minor importance to cartilage destruction in human arthritis.