Xanthones from Securidaca inappendiculata Hassk. attenuate collagen-induced arthritis in rats by inhibiting the nicotinamide phosphoribosyltransferase/glycolysis pathway and macrophage polarization

Securidaca inappendiculata (SI) Hassk. is a traditional medicine used to treat rheumatoid arthritis. Recent studies have reported that macrophages are the primary regulators of joint homeostasis and their polarization is closely related to their metabolic mode. Here, we aimed to investigate the relationship between the joint protective effect of SI's xanthone-rich fraction (XRF) on collagen-induced arthritis (CIA) in rats and the nicotinamide phosphoribosyltransferase (NAMPT)-glycolysis-polarization axis of macrophages. CIA model rats were treated with oral XRF and therapeutic efficacy was assessed based on arthritis score, degree of paw swelling, histological examination, and immunohistochemical analysis. Serum levels of cytokines, cellular metabolite concentrations, and protein and mRNA expression were determined by enzyme-linked immunosorbent assay (ELISA), western blotting (WB), and quantitative real-time PCR (RT-qPCR), respectively. The effects of dihydroxy-3,4-dimethoxyxanthone (XAN), a representative SI-derived compound, on RAW264.7 macrophages was analyzed in vitro using confocal laser scanning and flow cytometry. We found that XRF treatment significantly alleviated disease severity in CIA model rats. Levels of pro-inflammatory cytokines in the serum and M1 markers in synovium were reduced after XRF treatment, accompanied by an increase in the levels of anti-inflammatory cytokines and M2 markers. Further, XRF significantly suppressed synovial glycolysis by regulating NAMPT. In vitro studies further showed that XAN induced repolarization of lipopolysaccharide (LPS)-induced RAW264.7 macrophages with M1-M2 phenotype. Moreover, XAN negatively regulated glycolysis in the LPS-induced RAW264.7 macrophages in correlation with changes in NAMPT expression. Overall, the findings of this study suggest that the joint protective effects of XRF are achieved by inhibiting the NAMPT/glycolysis pathway and thereby regulating macrophage polarization.