Several studies have also demonstrated NO and iNOS involvement in inflammatory arthritis, including increased circulating NO levels in serum, urine, and synovial fluid of patients with RA [24, 25], as well as higher iNOS levels in synovial tissues of RA joints than in osteoarthritic joints and absence of iNOS in normal joints [26–29]. Here, NOS2 is linked to rheumatoid arthritis.