Iguratimod, a Disease-Modifying Anti-Rheumatic Drug, Inhibits Osteoclastogenesis and Bone Resorption through Suppression of the Nuclear Factor of Activated T Cells Signaling Pathway

Introduction: The aim of this study was to observe an inhibition of bone resorptionand osteoclastogenesis by iguratimod (IGU, T-614), a disease-modifyinganti-rheumatic drug, using adjuvant-induced arthritis (AIA) rats and receptoractivator of nuclear factor kappa-B ligand (RANKL)-stimulated RAW264.7 cells. Methods:The bone mineral density and 3D morphometric parameters of hind paws in AIArats were measured using micro computed tomography (μCT) imaging. The activityof osteoclast cells was estimated based on tartrate-resistant acid phosphatase(TRAP) staining in specimens from the rats. Invitro TRAP activity was investigated using RANKL-stimulated RAW264.7 cells.The amount of nuclear factor of activated T-cells, cytoplasmic,calcineurin-dependent 1 (NFATc1) protein was measured by western blot analysis.The expression of Nfatc1, itsregulator genes, its upstream factors, and osteoclast-functional genes wereinvestigated. Results: In addition to the suppression of bone resorptionand lesions of bone trabeculae of AIA rats, IGU significantly decreased thenumber of TRAP-positive cells in the calcaneal bones. Moreover, this druginhibited the differentiation of RANKL-stimulated RAW264.7 cells into osteoclasts,which were identified morphologically and functionally. IGU decreased theamount of NFATc1 protein and improved the altered expression ofNFATc1-associated genes and osteoclast-functional genes. Conclusions: IGUsuppressed osteoclastogenesis and bone resorption via the RANKL-NFATc1 pathway, suggesting such effect would beexpected in clinical use.