UPLC-MS/MS-based metabolomics analysis identifies disease-associated metabolic signatures of B cells from patients with IgG4-RD

Background: Immunoglobulin G4-related disease (IgG4-RD) is an autoimmune-mediated fibro-inflammatory disorder. Enhanced B-cell differentiation, along with its contribution to inflammatory and fibrotic pathological processes, represents a core mechanism in IgG4-RD. However, the metabolic characteristics of B cells in these patients have yet to be systematically investigated. Methods: Targeted metabolomic analysis was performed on sorted B cells from 32 IgG4-RD patients and 31 healthy controls using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Differential metabolites between the two groups were identified using the Mann-Whitney U test and orthogonal partial least squares-discriminant analysis (OPLS-DA). Metabolic pathway enrichment analysis of differentially expressed metabolites was conducted using the MetaboAnalyst 6.0 platform. In an independent validation cohort, flow cytometry was employed to detect B-cell subpopulations, lipid content, and the expression of stearoyl-CoA desaturase 1 (SCD1). Results: Significant differences in metabolite profiles were observed between B cells from IgG4-RD patients and healthy controls. Compared to healthy controls, 24 metabolites were significantly upregulated and 124 metabolites were significantly downregulated in B cells from IgG4-RD patients. A panel of 14 metabolites demonstrated optimal performance in distinguishing IgG4-RD B cells from control B cells (AUC = 0.934). The upregulated metabolites were primarily enriched in pathways such as glutathione metabolism and unsaturated fatty acid biosynthesis, whereas various amino acid metabolism pathways were significantly downregulated. Lipid content was significantly elevated in B cells of IgG4-RD patients compared to healthy controls, with plasmablasts/plasma cells exhibiting the highest lipid content and fatty acid synthase expression among all B-cell subsets. The glutamate/glutamine ratio was significantly elevated in B cells of the fibrotic subgroup compared to the inflammatory subgroup of IgG4-RD. Taurocholic acid (TCA) and dimethylglycine showed correlations with serum IgG4 and IgE levels, respectively. Conclusion: This study reveals distinct metabolic features of pathogenic B cells in IgG4-RD, proposing the hypothesis that metabolic dysregulation contributes to their pathogenic alterations.