Chondroitin sulfate concentration and protein-polysaccharide composition of articular cartilage in osteoarthritis.

In osteoarthritis the articular cartilage becomes roughened, fibrillar, softened, thinned, and finally eroded, with secondary changes occurring in the underlying bone. Histologically, early cartilage lesions in osteoarthritis are characterized by loss of metachromasia in the matrix, and it has been postulated that the initial disturbance involves the intercellular substance (1, 2). The decrease in metachromatic material in the matrix apparently is not due to degenerative changes in the cartilage cells; on the contrary, areas of osteoarthritis usually show proliferation of chondrocytes and increased radiosulfate uptake (2). The loss of metachromasia has been attributed to a diminution in chondroitin sulfate content. Hirsch has shown a decreased sulfate concentration in chondromalacia of the patella, associated with loss of metachromatic staining and loss of elasticity of the cartilage (3). Matthews (4) reported a fall in hexosamine-hydroxyproline ratio in fibrillar osteoarthritic cartilage, and Kuhn and Leppelmann (5) showed a fall in galactosamine and glucosamine concentration of femoral articular cartilage in individuals with "arthrosis deformans." Such observations suggest that metabolic changes occur in the cartilage lesions of osteoarthritis. In the studies to be reported, chondroitin sulfate concentration was determined as glucuronic acid, a more specific assay for this polysaccharide than hexosamine, since the latter is also present in the keratosulfate in cartilage; for example, the hexosamine concentration of adult rib cartilage is four times greater than can be accounted for as chondroitin sulfate (6). A decrease in chondroitin sulfate concentration was found in osteoarthritic cartilage, most marked in the more advanced lesions. In addition, qualitative changes in the polysaccharide-protein complex of osteoarthritic cartilage