Joint Synovial Fluid Metabolomics Method to Decipher the Metabolic Mechanisms of Adjuvant Arthritis and Geniposide Intervention

Rheumatoid arthritis (RA), a chronic systemic autoimmune disease, is mainly characterized by joint lesions and permanent loss of joint function. To discover the metabolic characteristics of RA and the underlying mechanisms in treatment with geniposide (GE), untargeted metabolomic analysis based on hydrophilic interaction liquid chromatography coupled to high-resolution mass spectrometry (HILIC–HRMS) was performed using the joint synovial fluid samples from adjuvant arthritis (AA) rats. Microdialysis (MD) was utilized to collect the dialysate samples precisely from the articular cavity of AA rats. Multivariate statistical analysis was then conducted to discover the metabolite changes induced by AA and to differentiate GE-related biomarkers. The mass spectrometry data are available on the Chorus website (https://chorusproject.org/pages/index.html) with the data set identifier 1680. The results showed that 20 metabolites differed significantly between AA rats and normal rats. GE treatment recovered the altered levels of the 13 metabolites mentioned above, such as palmitoylethanolamide (PEA), Cer (d18:0/22:0), and PC (18:1(11Z)/16:1(9Z)), and normalized glycerophospholipid metabolism. As evidenced by western blotting, the changes in PEA levels adjusted by GE were associated with the down-regulated expression of N-acylethanolamine-hydrolyzing acid amidase (NAAA) in synovial tissues. Taken together, the elucidation of metabolic changes of joint synovial fluid and how this is influenced by GE will promote future therapeutic interventions of RA.