SPHK1 and rheumatoid arthritis: As the most effective SphK1 inhibitor so far, PF-543 can inhibit inflammation in RA model (Deng et al., 2021), ulcerative colitis model (Liu and Jiang, 2020) and mouse pulmonary hypertension hypoxia model (Ha et al., 2020) in vivo and in vitro, mainly by inhibiting the release of inflammatory cytokines and the change of cell biological function.