Proteomics analyses of human plasma reveal triosephosphate isomerase as a potential blood marker of methotrexate resistance in rheumatoid arthritis

Objective The objective of this study was to assess differentially expressed blood proteins between patients with active RA and patients in remission after MTX treatment, with the aim of identifying a biomarker of MTX resistance (MTXR). Methods Two populations of RA patients treated with a stable dose of s.c. MTX for at least 3 months were constituted according to the DAS28: remission (DAS28 < 2.6; n = 24) and active disease (DAS28 > 3.2; n = 32). The two groups of RA patients were homogeneous regarding their epidemiological characteristics, except for the duration of treatment, which was longer in the remission group. After collection of a blood sample, plasma protein digestion was performed, followed by untargeted proteomics analysis. Then, a targeted analysis was performed to confirm the results of the untargeted approach. Results Untargeted proteomics analysis revealed eight plasma proteins that were differentially expressed between the two groups of patients. Among them, triosephosphate isomerase (TPI-1) and glucose-6-phosphate isomerase (GPI), which are main actors in glycolysis, were found down-regulated in the active group. This result was confirmed for TPI-1 in the targeted proteomics analysis. Conclusion A first step was achieved in the search for biomarkers of MTXR, with the identification of two actors in glycolysis (TPI-1 and GPI). The next step will be to confirm these results in a larger cohort, including samples from treatment-naive patients, to assess the predictive potential of these protein markers.