PTGS2 and osteoarthritis: Chow et al. demonstrated that the nitric oxide route (inducible nitric oxide synthase (iNOS), nitric oxide (NO)) and the prostacyclin pathway (cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2)) are essential to the pathophysiology of osteoarthritis (Chow and Chin, 2020[8]).