Chondrons From Articular Cartilage (II): Analysis of the Glycosaminoglycans in the Cellular Microenvironment of Isolated Canine Chondrons

A chondron rich preparation was isolated from mature canine tibial cartilage using low-speed homogenization techniques. Proteoglycans were extracted from this preparation by exhaustive treatment with 4M guanidine-HCl. A significant proportion of the total proteoglycan, measured as uronic acid, was resistant to extraction and represented 27.9% in intact cartilage chips and 18.6% in the chondron fraction. Histochemical examination of chondrons confirmed that extraction resistant proteoglycans remained within the capsule of the chondron after 4M guanidine-HCl treatment. Electrophoretic analysis of the glycosaminoglycans extracted from intact cartilage chips and the chondron fraction showed approximately equivalent amounts of chondroitin sulphate (79.3%), keratan sulphate (16.3%) and hyaluronic acid (4.3%) present. In contrast, the extraction resistant residue in the chondron fraction was significantly enriched for hyaluronic acid (10.5%, p less than 0.05) but was depleted of chondroitin sulphate (70.9%, p less than 0.05). The major chondroitin sulphate isomer in the resistant fraction was chondroitin 6-sulphate while in the soluble fraction, the quantities of the two isomers were approximately equivalent. Comparison with previously published data suggests a role for minor collagens in the retention of proteoglycans in the cellular microenvironment.