Role of iNOS in osteoarthritis: Pathological and therapeutic aspects

Accumulating evidence suggests that inflammation has a key role in the pathogenesis of osteoarthritis (OA). Nitric oxide (NO) has been established as one of the major inflammatory mediators in OA and drives many pathological changes during the development and progression of OA. Excessive production of NO in chondrocytes promotes cartilage destruction and cellular injury. The synthesis of NO in chondrocytes is catalyzed by inducible NO synthase (iNOS), which is thereby an attractive therapeutic target for the treatment of OA. A number of direct and indirect iNOS inhibitors, bioactive compounds, and plant-derived small molecules have been shown to exhibit chondroprotective effects by suppressing the expression of iNOS. Many of these iNOS inhibitors hold promise for the development of new, disease-modifying therapies for OA; however, attempts to demonstrate their success in clinical trials are not yet successful. Many plant extracts and plant-derived small molecules have also shown promise in animal models of OA, though further studies are needed in human clinical trials to confirm their therapeutic potential. In this review, we discuss the role of iNOS in OA pathology and the effects of various iNOS inhibitors in OA.