To explore the metabolic mechanism of differential plasma interleukin (IL)-6 expression in patients with rheumatoid arthritis (RA). A total of 240 RA patients were enrolled in the non-target metabolomics study cohort and 69 healthy volunteers were included as healthy controls (HCs). Plasma IL-6 levels were detected by electrochemiluminescence assay. Plasma metabolites were detected by ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry. Patients with active RA (n = 20) and remissive RA (n = 20) and 20 HCs were enrolled in the targeted validation cohort. Metabolites identified by non-target metabolomics were quantitatively analyzed by ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometry. Effects of 1-oleoyl-sn-glycero-3-phosphocholine (OGPC) associated with IL-6 on MH7A cells were assessed. After 24-h or 48-h induction by TNF-α, the supernatants were collected for IL-6 quantification by enzyme-linked immunosorbent assay. Furthermore, Western blot was performed to investigate the relative JAK2 and p-JAK2 expressions. With an increasing IL-6 level, OGPC shown to be related to the glycerophospholipid metabolism pathway by Kyoto Encyclopedia of Genes and Genomes analysis displayed a significant decrease. In the validating RA cohort, the OGPC concentrations in remissive RA group and active RA group decreased compared with HC group. OGPC down-regulated IL-6 secretion and p-JAK2 expression in TNF-α-induced MH7A cells in vitro. In conclusion, glycerophospholipid metabolism is the main metabolic pathway associated with the differential IL-6 expression in RA patients. The down-regulated OGPC is a promoting factor for the increased IL-6 plasma level in RA patients, which further affects the downstream JAK signaling pathway.
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