A naturally occurring coumestan dolichosin A targets Syk kinase to dually inhibit macrophage inflammation and osteoclast formation for anti-arthritic therapy

Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by synovial inflammation and osteoclast-mediated bone destruction. Current therapeutic strategies often lack dual efficacy in targeting both inflammatory and bone-eroding pathways. In this study, we investigated the anti-arthritic properties and underlying mechanisms of dolichosin A (DoA), a naturally occurring coumestan derived from Glycine tabacina (Labill.) Benth. DoA administration was found to significantly block lipopolysaccharide (LPS)-induced inflammatory activation of macrophages and inhibit receptor activator of nuclear factor kappa B (NF-κB) ligand (RANKL)-induced formation of osteoclasts. This dual effect significantly contributed to the alleviation of inflammation and bone destruction in collagen-induced arthritis (CIA) mice treated with DoA. DoA directly targeted spleen tyrosine kinase (Syk), with hydrogen bonds formed with Glu452, Asn499, and Asp512 playing a critical role in its binding to Syk. DoA inhibited the autophosphorylation of Syk and activation of downstream signaling pathways, including phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), mitogen-activated protein kinase (MAPK), and calcium oscillations, thereby exerting inhibitory effects on macrophage inflammation and osteoclast formation. Additionally, it was found that the combination of the natural Syk inhibitor DoA with the Janus kinase (JAK) inhibitor tofacitinib (TOF) resulted in an enhanced anti-arthritic effect in the CIA mice. Furthermore, DoA was loaded into a folic acid (FA)-functionalized liposomal delivery system (DoA@FA-Lips), which significantly enhanced the pharmacological effects of DoA with low cytotoxicity. Our findings highlight DoA as a novel dual-functional agent targeting Syk to concurrently mitigate macrophage-driven inflammation and osteoclast-mediated bone resorption, offering a promising strategy for RA therapy.