Iguratimod ameliorated collagen-induced arthritis by suppressing TNF-α/NF-κB signaling pathway and enhancing lymphangiogenesis in a murine model.

Rheumatoid arthritis (RA) is a complex autoimmune joint disease characterized by persistent synovial inflammation and hyperplasia. The TNF-α/NF-κB signaling pathway is one of the most important inflammatory pathways involved in the onset and progression of RA. In addition, impaired lymphatic drainage plays a critical role in disease exacerbation. Iguratimod (IGU), a novel disease-modifying antirheumatic drug, has been shown to exert immunomodulatory effects. However, the precise mechanisms underlying its anti-inflammatory function remain unclear. Furthermore, whether IGU could restore lymphatic reflux function in inflammatory arthritis has yet to be determined. Therefore, the study aimed to elucidate the mechanisms underlying the therapeutic effects of IGU in RA. The therapeutic efficacy of IGU was evaluated in a collagen-induced arthritis (CIA) mouse model, with methotrexate used as a positive control. Histopathological analyses of footpad and ankle tissues were performed to asses of disease onset and progression. Levels of inflammatory cytokines (e.g., TNF-α, IFN-γ, IL-4, and IL-6) and IgG autoantibody (such as anti-CCP antibody) were determined using ELISA. Lymphangiogenic markers, including VEGF-C, VEGFR-3, and LYVE-1, were assessed in ankle joint tissues. The protein and mRNA expression levels of TNF-α and NF-κB in joint tissues were also evaluated. In addition, an in vitro tube formation assay was performed to examine the direct effects of IGU on lymphangiogenesis. IGU treatment significantly alleviated arthritis severity in CIA mice by reducing joint inflammation, minimizing tissue damage, and preserving bone integrity. Beyond its established anti-inflammatory properties, IGU could enhance lymphangiogenesis in inflamed joints. Mechanistically, IGU suppressed the TNF-α/NF-κB signaling pathway, thereby attenuating immune responses and inflammatory cytokine production. Furthermore, IGU directly promoted lymphatic vessel formation by upregulating LYVE-1, Prox-1, VEGF-C, and VEGFR-3 in lymphatic endothelial cells. The effect might contribute to the restoration of lymphatic drainage function. The study suggests that IGU exerts a dual therapeutic action by modulating inflammation and promoting lymphatic vessel formation, which might facilitate the restoration of lymphatic drainage and contribute to improved outcomes in RA.