In 2013, Celastrol (9) (1–5 μM) was reported to be an active neutral compound that could dose-dependently induce apoptosis of RA-FLS, the possible mechanism is the induction of DNA damage, the G2/M phase of the cell cycle arrest and apoptosis related proteins (Bax/Bcl-2, Caspase-3 and -9) [138]. Here, BAX is linked to rheumatoid arthritis.