Background: To investigate nitrite and inducible nitric oxide synthase (iNOS) levels in the plasma and synovial fluid of patients with primary knee osteoarthritis (OA) and to determine protein nitrotyrosine in synovial tissue of OA patients.
Material and Method: Thirty patients and 30 healthy controls were recruited into the present study. Plasma and synovial fluid
nitrite levels were measured using Griess reaction. Plasma and synovial fluid iNOS concentrations were analyzed by enzymelinked immunosorbent assay. Nitrotyrosine was detected immunohistochemically in synovial tissue of OA patients.
Results: Plasma and synovial fluid nitrite concentration in the OA group were significantly higher than those in the healthy control group were (p = 0.007 and p = 0.012). Furthermore, plasma iNOS levels were significantly higher in the OA group than those in healthy control group were (p = 0.04). Moreover, nitrotyrosine was detected immunohistochemically in
macrophages, synovial lining layer and synoviocytes of synovial tissue in the OA group.
Conclusion: These findings indicate that reactive nitrogen species and nitrotyrosine-containing proteins may be involved in
the joint destruction process, and play a potential role in the pathogenesis of knee osteoarthritis.

Keywords: Inducible nitric oxide synthase, Knee osteoarthritis, Nitrite, Nitrotyrosine