Keratan sulfate content in the superficial and deep layers of osteophytic and nonfibrillated human articular cartilage in osteoarthritis

Very thin slices of the superficial and deep layers of osteophytic and apparently normal articular cartilage from six human osteoarthritic femoral heads were digested with papain. The digests were analyzed for keratin sulfate content using an enzyme-linked immunosorbent assay (ELISA) with inhibition step, and for chondroitin sulfate and collagen contents using biochemical assays. Although there were marked differences in Safranin-O staining of the superficial and deep layers of osteophytic cartilage, these two layers had identical high ratios of chondroitin sulfate/collagen. Keratan sulfate was present only in small amounts in osteophytic cartilage. However, the deeper layer contained significantly more of this glycosaminoglycan. The deeper layer of articular cartilage contained approximately twice as much chondroitin sulfate and six times more keratan sulfate relative to collagen than the superficial layer. The results of this study showed that this new sensitive approach, which requires as little as 200 micrograms wet cartilage as starting material, provides important qualitative and quantitative information about the major constituents of the matrix.