Xanthones from antagonized the antirheumatic effects of methotrexate by promoting its secretion into urine.

Background: This study was designed to characterize the interaction between Hassk. derived xanthones and methotrexate (MTX).

Methods: Collagen-induced arthritis (CIA) was induced in rats, which were treated with MTX, a xanthone-rich fraction (XRF), or MTX+XRF by gavage for 30 days. Clinical efficacy was assessed based on arthritis scores, serological analysis, and histological examination. Protein expression was investigated by either immunohistochemical or immunoblotting methods. MTX concentrations were determined by HPLC or LC-MS methods. Obtained results were further validated by assays using 1,7-dihydroxy-3,4-dimethoxyxanthone and HEK 293 T cells.

Results: XRF antagonized the antirheumatic effects of MTX , suggested by higher levels of proinflammatory cytokines, and severer swelling and deformation of joints in CIA rats in the MTX+XRF group compared with MTX monotherapy. XRF reduced MTX concentration in plasma and promoted its excretion into urine. As a result, XRF attenuated MTX-induced edema of the proximal tubule. Furthermore, XRF restored the decreased expression of organic anion transporter three (OAT3), which accounts for MTX secretion in the kidney. Consistently, 1,7-dihydroxy-3,4-dimethoxyxanthone promoted the cellular intake of MTX by increasing OTA3 expression.

Conclusion: It is suggested that the combined use of with MTX should be optimized to avoid the antagonistic effects and improve the safety of the MTX regimen.