Biochemical Findings in Normal and Osteoarthritic Articular Cartilage. II. Chondroitin Sulfate Concentration and Chain Length, Water, and Ash Content*

Abstract

Softening and erosion of cartilage, the charac-teristic early lesions of osteoarthritis, occur in sites of decreased chondroitin sulfate concentra-tion. The role of aging and the specific biochemi-cal events that produce this alteration in glycos-aminoglycan composition have been under study in several laboratories. Collins and McElligott found increased radiosulfate fixation in these le-sions compared with normal articular cartilage from the same individuals, suggesting increased synthesis of polysaccharide (1). These observa-tions indicated an increased turnover of chon-droitin sulfate in osteoarthritic cartilage lesions, and attention has become focused on the mecha-nism responsible for breakdown of this glycos-aminoglycan. As reported previously (2), when the cartilage proteinpolysaccharide complex was extracted from human articular cartilage obtained at autopsy, a decrease in the concentration of chondroitin sulfate but not protein was found in the areas of erosion. This observation pointed to a specific breakdown of the glycosaminoglycan, since proteolysis might be expected to cause removal of both components such as occurs after papain injection into rabbits (3). An enzyme resembling testicular hyalu-ronidase could be responsible, but reports of the presence of hyaluronidase in tissues other than testis were unconvincing or unconfirmed. urine, plasma, liver, spleen, kidney, synovial tissue, and synovial fluid, but no hyaluronidase activity was detected in articular or costal cartilage (4). On the other hand, a proteolytic enzyme capable of degrading cartilage proteinpolysaccharide is present in chondrocytes (5-7). Whether protease or an enzyme resembling testicular hyaluronidase is responsible for the increased turnover of chon-droitin sulfate in osteoarthritic cartilage matrix requires more definitive analysis. Cartilage proteinpolysaccharide probably con-sists of multiple chondroitin sulfate chains at-tached to a central protein core (8). One could, therefore, predict that proteolysis would release part of the protein and associated polysaccharide from the molecule, but the chondroitin sulfate remaining would be qualitatively unchanged. On the other hand, hyaluronidase would specifically attack and degrade the chondroitin sulfate chains, leaving behind polysaccharide of lower average chain length in the zones of decreased chondroitin sulfate concentration. In addition, keratan sulfate is probably attached to the same or a similar pro-tein core; hyaluronidase, which does not digest keratan sulfate, would cause loss of only the chondroitin sulfate, whereas protease would cause both glycosaminoglycans to be lost from the car-tilage matrix. Similar glycoproteins, which are also present in cartilage matrix, are not affected by hyaluronidase. This paper reports studies of the chain length of chondroitin sulfate and the rela-tive concentrations of chondroitin sulfate and neu-tral sugar in keratan sulfate and glycoprotein in human osteoarthritic and normal articular carti-lage; in addition, we studied the synthesis of chondroitin sulfate in these lesions by cartilage samples in vitro and determined their water and ash content. We also analyzed the influence of 1170