Articular chondrocyte apoptosis in equine osteoarthritis

Osteoarthritis (OA) is the most common joint disease in horses. Chondrocyte apoptosis has been implicated as a major pathological OA change in humans and experimental animals but no studies have been performed on equine OA. Articular cartilage was collected from three normal and five OA horses. Histopathological changes were scored by a modified Mankin grading system. A terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay was performed to identify chondrocyte apoptosis. Nitric oxide (NO) production from chondrocytes was indirectly evaluated by immunohistochemistry with polyclonal antibody to nitrotyrosine. The histopathological score and percentage of chondrocyte apoptosis from the OA cartilages were significantly higher than from normal cartilages. There was a significant correlation between histopathological grade and the percentage of chondrocyte apoptosis. OA cartilages exhibited stronger immunoreactivity to nitrotyrosine than normal cartilage. Topographical distributions of chondrocyte apoptosis, cartilage matrix degeneration, and NO production overlapped in equine OA cartilages, suggesting that these pathological phenomena are closely interrelated.