Guaianolide sesquiterpenoids from Chrysanthemum indicum L. alleviate rheumatoid arthritis by targeting of NLRP3 inflammasome pathway.

Thirteen undescribed guaianolide lactones chryguaialactones A-M (1-13), together with ten known analogues (14-23), were isolated from the flowers of Chrysanthemum indicum L. The previously unreported structures including their absolute configurations were determined through spectroscopic techniques, combined with DP4+ NMR analysis, X-ray crystallography and calculated ECD methods. All compounds were screened on their IL-1β inhibitory activity in THP-1 cells, and most of them (1, 3-5, 7-8, 10, 12-17, and 19-23) displayed inhibitory effects with IC50 values in the range 0.31-15.95 μM. Besides, compound 13 showed the most potential activity with IC50 value of 0.31 ± 0.15 μM. Mechanismly, 13 inhibited the NLRP3 assembly and the activation of its downstream proteins. Furthermore, 13 could interact with NLRP3 protein illustrated by CETSA, DARTS and IP assays. Molecular docking revealed the covalent binding between the α, β unsaturated ketone in 13 and the NACHT domain of NLRP3. The suppression of 13 on NLRP3 inflammasome pathway was further proved in HFLS-RA cells. Hence, these findings uncovered an unrecognized role of 13 exerting anti rheumatoid arthritis activity in the regulation of NLRP3 inflammasome pathway.