Changes in the sedimentation profile of proteoglycan aggregates in early experimental canine osteoarthritis

Osteoarthritis was induced in 12 normal dogs by severing of the anterior cruciate ligament of the right knees, the left knees serving as sham operated controls. The animals were killed at 7 and 14 weeks postsurgery. The total hexuronate, and thus proteoglycan, content of the articular cartilage of operated knees remained unaltered during the period of study. After pretreatment with a highly purified collagenase and in the presence of selected protease inhibitors, a higher proportion of the tissue hexuronate could be extracted from the different topographical areas of osteoarthritic joints under non dissociative conditions (70-75% versus 55-65% for control knees). The nondissociatively recovered osteoarthritic proteoglycans (a-A1 preparations) displayed progressive and consistent changes in their sedimentation profile. First, the size of the fast sedimenting or more saturated aggregates appeared to be reduced in the different regions of osteoarthritic joints at 7 weeks postoperatively. The disappearance of the faster sedimenting mode as well as a dramatic increase in the proportion of monomers were only detected in the topographical zones exhibiting the most severe surface damage and histologic abnormalities at 14 weeks postsurgery. The proteoglycan molecules present as "free" or "nonaggregated" monomers in a-A1 preparations recovered from normal and osteoarthritic cartilage at different time periods after surgery were separated from their corresponding aggregates by rate zonal centrifugation in isokinetic cesium sulfate gradient. Although they were severely depleted in keratan sulfate, the purified "free" and "aggregated" osteoarthritic monomers appeared to be normal in terms of aggregating capacity and size distribution, and were therefore not degraded. This progressive changes in size distribution of proteoglycan aggregates in the early stages of experimental canine osteoarthritis could contribute significantly to the biochemical and biomechanical alterations of osteoarthritic cartilage.