Serum free amino acid levels in rheumatoid arthritis according to therapy and physical disability

Background: In presented study the amino acid analysis was performed in serum derived from rheumatoid arthritis patients (RA) according to undertaken therapy and classification of physical disability. The results were compared with previously published data. Methods: The levels of 31 free amino acids were determined in 50 serum samples derived from RA subjects and 51 controls. The RA patients were divided into two groups according to the therapy (methotrexate/leflunomide, infliximab/adalimumab/etanercept/tocilizumab, prednisolone/NSAID) and classification of physical disability of the patients. Levels of amino acids were measured by LC-MS/MS. The obtained results were subjected to multivariate statistical tests. Results: According to the therapy that was being used, threonine differentiated RA patients treated with methotrexate/leflunomide- infliximab/adalimumab/etanercept/tocilizumab (p = 0.00954) and infliximab/ adalimumab/etanercept/tocilizumab- prednisolone/NSAID (p = 0.03109), while tryptophan differentiated RA patients treated with methotrexate/leflunomide- infliximab/adalimumab/etanercept/tocilizumab (p = 0.01723). In the functional classification, arginine differentiated RA samples between class III and IV (p = 0.02332), while glycine differentiated them between class I + II and III of the Steinbrocker functional classification (p = 0.03366). Conclusions: An analysis of the metabolome profile requires the use of validated bioanalytical methods that are strictly dedicated for this purpose. The obtained results are not accidental (p value less than 0.05), and all of the selected amino acids play an important role in inflammation and immune response. It is suggested that studied amino acids can be considered as a markers for diagnosis of RA and monitoring pharmacotherapy of the disease.