Nitrite determination as a stable metabolite of nitric oxide in synovial fluid of equine metacarpophalangeal joint

Abstract

The striking feature of osteoarthritis (OA) is fibrilation and loss of articular cartilage. Nitric oxide (NO^•) has been involved as an important biological mediator of OA and its production is significantly higher in OA cartilage. NO^•suppresses cartilagenous matrix synthesis and induces condrocytes apoptosis in articular cartilage. The NO^•production was indirectly determined by measuring nitrite by Griess reaction. Nitrite concentration of synovial fluid was compared in different equine metacarpophalangic joint conditions. Joint classification and age determination were carried out by macroscopic examination. It was considered a normal joint group NN (n = 47) the one without any visual damage of articular structures. The damaged groups considered a) a group with a congestive synovial membrane without cartilage damage NA (n = 25), b) a group with damaged cartilage and normal synovial membrane AN (n=23) and c) a group with damaged cartilage and congestive synovial membrane AA (n = 15). A damaged cartilage showed erosions and multiple wear lines and a damaged synovial membrane showed a congestive appearance. There were no significant differences in nitrite concentration between the analyzed groups. Only in the NA group a non significant increase (44.4 ± 32.6 µmol/L) was detected, that was possibly associated to the absence of cartilage loss and so with a major response to proinflammatory stimulation originated in the congestive synovial membrane. Nitrite concentration decreased in a non significant way in the damaged cartilage and synovial membrane group AA (26.3 ± 22.1 µmol/L) which might be explained by cartilage loss in this in vivo model.