Conditioned media from organ cultures of cartilage obtained from treated joints contained higher levels of nitric oxide than did the media of organ cultures of cartilage obtained from control joints. The prevalence of apoptotic cells correlated with the levels of nitrite production and the grade of the osteoarthritis. These observations indicate an increase in chondrocyte apoptosis in cartilage in humans with osteoarthritis and in animals with experimentally osteoarthritis. Chondrocyte apoptosis and proteoglycan depletion are anatomically linked and may be mechanistically related. Thus, inhibitors of the production of nitric oxide synthesis or chondrocyte apoptosis may be of therapeutic value after cartilage injury and in osteoarthritis.
Articular cartilage has several features that affect the fate of apoptotic bodies.
This tissue is not vascularized and does not contain mononuclear phagocytes. Furthermore, chondrocytes are anchored in the extracellular matrix, are surrounded by a pericellular matrix, and are not known to migrate within cartilage. Thus, no apparent mechanism exists for the clearance of apoptotic bodies. Electron microscopy of apoptotic chondrocytes suggested a similarity between apoptotic bodies and matrix vesicles, which are essential in cartilage calcification during the formation of endochondral bone. We examined structural and functional properties of chondrocyte-derived apoptotic bodies.