Repurposing monoamine oxidase inhibitors (MAOI) for the treatment of rheumatoid arthritis possibly through modulating reactive oxidative stress mediated inflammatory cytokines.

Monoamine oxidase inhibitors (MAOI) are presently used to treat depression, parkinsonian, and other psychiatric disorders. The present study was aimed to repurpose the use of MOAI in Rheumatoid Arthritis (RA). The animal model of RA was developed using collagen type II (CII) in Freund's complete adjuvant (FCA) followed by lipopolysaccharide (LPS) and a booster dose of CII in FCA. The effect of MAOI, Selegiline was evaluated whereas the indicators like paw thickness, arthritic score, and the splenic index were measured and compared with the standard drug Methotrexate. Further to explore the molecular mechanism, the expression of serum inflammatory cytokines (IL-6 and TNF-α), radiographical and histopathological study of hind paw were also checked and analyzed. Treatment with MAOI, Selegiline not only reduced the paw thickness, arthritic score, and the splenic index, but also greatly improved the inflammatory biochemical and hematologic parameters and improved the arthritis score. The serum level of IL-6 and TNF-α are considerably decreased dose dependently, however, the notable significant effect (**p < 0.01) observed at concentration of 30 mg/kg b.w. when the RA animals treated by Selegiline. Collectively, Selegiline improved the progression of RA possibly via decreased catecholamine breakdown at synovial fluid resulting decrease hydrogen peroxide (H 2 O 2 ) generation and inhibition of pro-inflammatory cytokines in situ. Thus, the finding support and indicate the repurposing of MAOI for the treatment of RA meriting further studies on synovial monoamine oxidase as a new therapeutic target to design a new drug for RA.