[The mechanism of articular cartilage degeneration in osteoarthritis]

Immunohistochemical and biochemical studies were undertaken in order to investigate the mechanism of articular cartilage degeneration in human osteoarthritis. Polyclonal antibodies [anti-CB (cyanogen bromide) peptide antibodies] that specifically reacted with unwound alpha-chains and CNBr-derived peptides of human Type II collagen were utilized to identify degradation of Type II collagen fibers in articular cartilage. In the case of human osteoarthritic cartilage with mild degeneration, the most prominent staining by the anti-CB peptide antibodies was found in the superficial fibrillation and in the inter-territorial matrix of the superficial and mid-zones. In contrast, these regions showed weak staining by both anti-Type II collagen antibodies and anti-proteoglycan antibodies. Moreover, staining by anti-fibronectin antibodies and anti-dermatan sulfate proteoglycan antibodies was observed around cell clusters in the superficial zone. Synthesis of Type II collagen and proteoglycans was also investigated using cultured human chondrocytes obtained from mildly or moderately osteoarthritic cartilage. Chondrocytes from mildly degenerated cartilage showed increased synthetic activity, while cells from moderately degenerated cartilage showed decreased activity. These findings indicated that degeneration in osteoarthritic cartilage was initiated in the superficial zone and then gradually progressed to the mid and deep zones.