Among the various treatments, induction of synoviocyte apoptosis by natural products during a rheumatoid arthritis (RA) pathological condition can be considered to have vast potential. However, it is unclear that liquiritin, a kind of natural flavonoid extracted from the roots of Glycyrrhiza uralensis, induced the apoptosis of the synovial membrane and its molecular mechanism. In this study, interleukin-1β (IL-1β)-RA-FLS cells were incubated with different concentrations of liquiritin. An MTT assay, Hoechst 33342 staining, JC-1 staining, and Western blot were used to check the viability, cell apoptosis, mitochondrial membrane potential changes, and the expression of related proteins, respectively. In vivo, a TUNEL assay and HE staining of tissue were used for histopathological evaluation. Our results showed that liquiritin significantly inhibited the proliferation of IL-1β-induced-RA-FLS, promoted nuclear DNA fragmentation, and changed the mitochondrial membrane potential to accelerate cell apoptosis. Liquiritin downregulated the ratio of Bcl-2/Bax and inhibited the VEGF expression and phosphorylation of JNK and P38. Moreover, liquiritin improved the clinical score of rheumatism, inflammatory infiltration, and angiogenesis and induced apoptosis of the synovial tissue in vivo. Hence, liquiritin ameliorates RA by reducing inflammation, blocking MAPK signaling, and restraining angiogenesis.
Keywords: MAPK signaling pathway; angiogenesis; inflammation; liquiritin; rheumatoid arthritis.