Global and targeted metabolomics of synovial fluid discovers special osteoarthritis metabolites

To identify special metabolites in synovial fluid of osteoarthritis (OA) via a metabolomics approach. Synovial fluid of 35 participants (25 OA patients and 10 controls) was detected by GC‐TOF/MS and multivariate data analysis was applied to analyze correlation among the observations. Different metabolites were screened by VIP value (VIP > 1), student t‐test (p < 0.05), and fold change (fold >1.5), and verified with the standard metabolites in the synovial fluid of 24 OA patients and 11 controls by LC/MS. The classification performance of different metabolites was analyzed by receiver operating characteristic (ROC) analysis. The results showed that six different metabolites (glutamine, 1,5‐anhydroglucitol, gluconic lactone, tyramine, threonine, and 8‐aminocaprylic acid) were strongly associated with OA in global metabolomics. Verified results of the first three metabolites were the same as the identified results using targeted metabolomics. ROC curve analysis demonstrated that their concentrations in synovial fluid were strongly correlated to OA. In addition, the concentrations of gluconic lactone were significantly different between OA and RA. Metabolites with altered levels may be contributors to OA pathogenesis and can be used as potential diagnosis criteria for OA. Gluconic lactone may prove to be a novel criterion for differential diagnosis of OA from RA.