To examine the nitric oxide (NO) production relevant to chondrocyte cell death in order to elucidate the mechanism of chondro-osteophyte formation in osteoarthrotic joints.
Human chondro-osteophytes were obtained during total hip arthroplasty. Expression of inducible nitric oxide synthase (iNOS) mRNA was determined by in-situ hybridization. Localization of iNOS and nitrotyrosine at protein level were examined by immunohistochemistry. Cell death of chondrocytes were confirmed by both TUNEL method and transmission electron microscopy.
The various populations of proliferative and hypertrophic chondrocytes expressed iNOS mRNA and iNOS as well as nitrotyrosine protein. Approximately 30% of hypertrophic chondrocytes forming chondro-osteophyte showed positive reaction to TUNEL staining. Electron microscopy confirmed both disintegrated and apoptotic chondrocytes in these zones. In the deep hypertrophic zone calcification was seen around each of the matrix vesicles and some masses of cell debris.
Chondro-osteophyte formation involves NO production by chondrocytes. The expression and localization of iNOS and nitrotyrosine in chondro-osteophytes suggest the significant role of NO in chondrocyte hypertrophy and apoptosis.