Casticin suppresses monoiodoacetic acid-induced knee osteoarthritis through inhibiting HIF-1α/NLRP3 inflammasome signaling

•Casticin ameliorates MIA-induced synovial inflammation and fibrosis in rats.•Castcin improves hypoxia and downregulates HIF-1α in synovium of rats.•Casticin inhibits the activation of the NLRP3 inflammasome in both rats and primary synovial fibroblasts. Knee osteoarthritis (KOA) is a disabling chronic inflammatory disease that is closely associated with synovium tissue hypoxia and synovial fibrosis. Casticin, a compound purified from the Chinese herb Viticis Fructus, has been proved effective in preventing inflammation and fibrosis in previous studies. However, the effect of casticin on synovial fibrosis in KOA is not clear. In present study, we aimed to investigate how did casticin affect synovial fibrosis on monoiodoacetic acid (MIA)-induced KOA in rats. The MIA-induced knee osteoarthritis model and lipopolysaccharide (LPS) stimulated primary synovial fibroblasts inflammation model were established. Pathological and morphological changes in synovial tissue were observed by H&E and sirius red staining. The hypoxia of synovium was detected by pimonidazole staining and immunohistochemistry of hypoxia-inducible factors 1α (HIF-1α). The levels of nucleotide oligomerization domain-like receptor protein 3 (NLRP3) inflammasome components, fibrogenic markers (TGF-β, COL1A1 and TIMP1) and inflammatory cytokines were examined by western blotting, qRT-PCR or ELISA in both KOA rat models and primary synovial fibroblasts. Our data suggested that casticin improved hypoxia and inflammation in synovium tissue, as well the synovial fibrosis in rats. Besides, casticin inhibited the activation of NLRP3 inflammasome in MIA-induced KOA rats and synovial fibroblasts. In conclusion, our findings demonstrated that casticin alleviated MIA-induced KOA by inhibiting of HIF-1α/NLRP3 inflammasome activation. Therefore, casticin could be a potential treatment strategy for KOA.