Sphingosine-1-phosphate is involved in inflammatory reactions in patients with Graves’ orbitopathy

Objective: Graves’ orbitopathy (GO) is initiated by excessive amount of various inflammatory mediators produced by orbital fibroblasts. This study aimed to assess the crucial role of sphingosine-1-phosphate (S1P) in the inflammatory process of GO. Methods: Orbital adipose/connective tissue samples were obtained from 10 GO patients and 10 normal control individuals during surgery. Primary orbital fibroblast culture was done. After the expression of S1P receptors and sphingosine kinase (SphK) was assessed with the treatment of interleukin (IL)-1β, we evaluated the expression of pro-inflammatory factors [intercellular adhesion molecule-1 (ICAM-1), cyclooxygenase-2 (COX-2) and IL-6] after treating S1P. S1P receptor antagonists and SphK 1 inhibitor were pretreated and the expression of the pro-inflammatory factors was assessed. Results: IL-1β exacerbated the inflammatory process by enhancing the expression of S1P receptors and SphK in GO orbital fibroblasts. IL-1β also induced the expressions of ICAM-1, COX-2, and IL-6 in GO orbital fibroblasts, and these expressions were effectively inhibited by S1P receptor antagonists and SphK1 inhibitor. Conclusion: S1P has an important role in the pathological inflammatory process of GO, which is mediated through the SphK1-S1P- S1P receptor pathway. SphK1 inhibitors and S1P receptors or antagonists could be potential approaches for controlling the inflammatory process of GO.