Dextromethorphan Exhibits Anti-inflammatory and Immunomodulatory Effects in a Murine Model of Collagen-Induced Arthritis and in Human Rheumatoid Arthritis

Dextromethorphan (d-3-methoxy-17-methylmorphinan, DXM) is a commonly used antitussive with a favorable safety profile. Previous studies have demonstrated that DXM has anti-inflammatory and immunomodulatory properties; however, the effect of DXM in rheumatoid arthritis (RA) remains unknown. Herein, we found that DXM treatment attenuated arthritis severity and proinflammatory cytokine expression levels, including TNF-α, IL-6, and IL-17A, in paw tissues of CIA mice. DXM treatment also reduced serum TNF-α, IL-6, and IL-17A levels of CIA mice and patients with RA. DXM further decreased the production of anti-CII IgG, IFN-γ, and IL-17A in collagen-reactive CD4(+) T cells extracted from the lymph nodes of CIA mice. In vitro incubation of bone marrow–derived dendritic cells with DXM limited CD4(+) T-cell proliferation and inflammatory cytokine secretion. In conclusion, our results showed that DXM attenuated arthritis symptoms in CIA mice and significantly reduced proinflammatory cytokines in patients with RA, suggesting that it can be used as an anti-arthritic agent.