Stigmasterol mitigates rheumatoid arthritis progression by decreasing Nrf2/NLRP3-mediated pyroptosis in chondrocyte

Stigmasterol (Stig), a phytosterol with anti-inflammatory and antioxidant properties, has been shown to have potential therapeutic effects. In this study, we aimed to investigate whether Stig mitigates rheumatoid arthritis (RA) progression by reducing chondrocyte injury. A mouse model of RA was established by intradermally injecting type II collagen into the tail roots of mice. The arthritic score and spleen index were measured in RA mice to assess the effects of Stig on RA progression. Lipopolysaccharide (LPS)-treated chondrocytes were used as a cellular model of RA. The roles of Stig in chondrocyte viability, proliferation, migration, inflammation, and injury were assessed using Cell Counting Kit-8, EdU, Transwell assays, quantitative real-time PCR, and western blotting, respectively. The results demonstrated that Stig exhibited no significant cytotoxicity in CHON-001 chondrocytes. Interestingly, it effectively inhibited LPS-induced apoptosis and increased cell viability, proliferation, and migration. Stig also alleviated LPS-induced pro-inflammatory responses and CHON-001 cell injury. Mechanistically, Stig activated nuclear factor erythroid 2-related factor 2 (Nrf2) signaling, which led to the inactivation of the NOD-like receptor protein 3 (NLRP3) inflammasome and a subsequent decrease in CHON-001 cell pyroptosis. However, the protective effects of Stig were abrogated by ML385, a specific inhibitor Nrf2. Stig treatment further improved the clinical severity in RA mice. In summary, Stig reduces LPS-induced chondrocyte injury and mitigates RA progression by inhibiting Nrf2/NLRP3-mediated pyroptosis, offering a potential therapeutic approach for RA.