SPHK1 and rheumatoid arthritis: Additionally, lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage model was used as an in vitro inflammation model to examine the direct effects of SIE on the production of inflammatory factors and the activity of the SphK1/S1P signaling pathway, which is closely related to the pathophysiological process of RA and sphingolipid metabolism (Wang et al., 2021).