Metabolomics analysis revealed significantly higher synovial Phe/Tyr ratio in reactive arthritis and undifferentiated spondyloarthropathy.

To compare the synovial phenylalanine/tyrosine (Phe/Tyr) ratio between ReA/uSpA and RA and OA by NMR spectroscopy.Paired SF and serum of 30 patients with ReA/uSpA were collected and analysed using a 1D 1H Carr Purcell Meiboom Gill NMR spectra recorded on 800 MHz NMR spectrometer equipped with a TCI Cryoprobe (at 300 K). Phe and Tyr were quantified. SF from 25 patients with RA fulfilling ACR classification criteria and 21 patients with OA were taken as inflammatory and non-inflammatory controls.The synovial Phe/Tyr ratio was significantly higher in ReA/uSpA compared with RA and OA. Synovial Phe/Tyr ratios were comparable in RA and OA patients. Compared with serum, the Phe/Tyr was significantly higher in the SF in ReA/uSpA. The Phe/Tyr ratio was also found to be positively correlated between serum and SF samples, with a regression coefficient (r2) of 0.287.This NMR-based metabolomics study demonstrates that the synovial Phe/Tyr ratio is specifically elevated in ReA/uSpA.