A novel combination of astilbin and low-dose methotrexate respectively targeting AAR and its ligand adenosine for the treatment of collagen-induced arthritis.

Methotrexate (MTX) is widely used for rheumatoid arthritis (RA) treatment with frequently serious adverse effects. Therefore, combination of low-dose MTX with other drugs is often used in clinic. In this study, we investigated the improvement of astilbin and low-dose MTX combination on collagen-induced arthritis in DBA/1J mice. Results showed that the clinic score, incidence rate, paw swelling, pathological changes of joints and rheumatoid factors were more alleviated in combination therapy than MTX or astilbin alone group. Elevated antibodies (IgG, IgG1, IgG2a, IgM and anti-collagen IgG) and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-γ and IL-17A) in serum were significantly inhibited, while anti-inflammatory cytokine, IL-10, was enhanced by combination therapy. Further studies indicated that combination therapy significantly decreased Th1 and Th17 cell differentiation and increased Treg cell differentiation. Mechanisms analysis demonstrated combination therapy greatly inhibited Con A-activated MAPK and inflammatory transcriptional signals. Moreover, MTX activated adenosine release and astilbin specifically up-regulated A adenosine receptor (AAR) expression simultaneously, which most probably contributed to the synergistic efficacy of combination therapy. ZM241385, a specific antagonist of AAR, greatly blocked the effects of combination therapy on T cell functions and downstream pathways. All these findings suggest that astilbin is a valuable candidate for low-dose MTX combined therapy in RA via increasing AAR/adenosine system and decreasing ERK/NFκB/STATs signals.