Sphingolipidomic Profiling of Rat Serum by UPLC-Q-TOF-MS: Application to Rheumatoid Arthritis Study

Sphingolipids (SPLs) are biologically important molecules, but the structural diversity and complexity of SPLs brings significant analytical challenges for their study. In this paper, we have developed an UPLC-Q-TOF-MS-based sphingolipidomic approach for the comprehensive identification and quantification of SPLs in rat serum. A total of 120 SPLs covering seven subcategories were identified for the first time. Method validations including linearity, sensitivity, reproducibility, and recovery were also evaluated. This method was exemplarily applied to characterize the SPL alterations in rheumatoid arthritis (RA) rats and the intervention effects of indomethacin (IDM). Partial least squares-discriminant analysis (PLS-DA) showed that the model group was well separated from the control group, whereas the IDM-treated group exhibited a trend to recover the controls. Twenty-six significantly changed SPL markers were explored, and the levels of ceramides (Cers) and their metabolites were found to be reversed by IDM treatment. These results indicate that IDM exerts anti-arthritic effects through the suppression of Cer-mediated COX-2 activation and resulting PEG₂ liberation. The present study demonstrates a promising potential of this method for the understanding of RA and the anti-arthritic mechanisms of relevant drugs.

The structure and function of the S1P1 receptor

Sphingosine 1-phosphate (S1P) receptors (S1PRs) belong to the class A family of G protein-coupled receptors (GPCRs). S1PRs are widely expressed on many cell types, including those of the immune, cardiovascular, and central nervous systems. The S1PR family is rapidly gaining attention as an important mediator of many cellular processes, including cell differentiation, migration, survival, angiogenesis, calcium homeostasis, inflammation and immunity. Importantly, S1PRs are known drug targets for multiple sclerosis (MS), for which the newly developed oral therapy fingolimod, an S1PR modulator, has recently been approved for clinical use. Much progress has also recently been made in the field of structural biology and in the modeling of heterotrimeric GPCRs allowing the crystal structure of the S1PR1 subtype to be elucidated and key interactions defined. Here, we outline the structure and function of S1PR1, highlighting the key residues involved in receptor activation, signaling, transmembrane interactions, ligand binding, post-translational modification, and protein-protein interactions.