Comparative Analysis of Tryptophan and Downstream Metabolites in Patients With Rheumatoid Arthritis and Healthy Controls

Relevance. The main goal of treating rheumatoid arthritis (RA) is to achieve remission or low disease activity. In recent decades, research has focused on the pathogenesis and discovery of potential biomarkers using new and highly precise methods, particularly metabolomics. The aim of this study was to conduct a comparative analysis of tryptophan metabolites in patients with rheumatoid arthritis and healthy volunteers. Materials and Methods. The main study group consisted of 37 patients diagnosed with RA – "de novo" RA. A control group was formed from 31 healthy volunteers. The levels of tryptophan and its metabolites in venous blood plasma were assessed using high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). The comparative analysis of patients with RA and healthy volunteers revealed the most significant tryptophan metabolites playing an important role in the pathogenesis of RA: tryptophan (p < 0.001), hydroxyindoleacetic acid (HIAA) (p < 0.05), quinolinic acid (p < 0.05), kynurenic acid (p < 0.00001), kynurenine (p < 0.05), the ratio of kynurenic acid to quinolinic acid (p < 0.05), xanthurenic acid (p < 0.0001), and the ratio of quinolinic acid to HIAA (p < 0.01). Changes in the levels of these metabolites may be considered as biomarkers for diagnosis and therapeutic targets in RA.