Clinical significance of plasma tryptophan, kynurenine, and kynurenine/tryptophan ratio in rheumatoid arthritis patients

A systematic review and meta-analysis of the kynurenine pathway of tryptophan metabolism in rheumatic diseases

“…Thus, 24 studies were selected for analysis ( Table 1 ) ( 26 – 49 ). The risk of bias, presented in Supplementary Table 3 , was moderate in 14 studies ( 26 – 35 , 37 , 41 , 44 , 45 , 47 ), and low in the remaining 10 ( 34 , 36 , 38 – 40 , 42 , 43 , 46 , 48 , 49 ). The initial certainty of evidence was low for all studies (rating 2, ⊕⊕⊝⊝) given their cross-sectional design.…”

“…Ten were conducted in Europe ( 26 – 29 , 32 – 37 ), and 11 in Asia ( 30 , 31 , 38 , 40 – 42 , 44 , 46 – 49 ). Six study groups included patients with RA ( 28 , 31 , 34 , 36 , 38 , 41 ), five with pSS ( 29 , 33 , 44 , 46 , 47 ), four with SLE ( 27 , 30 , 32 , 35 ), three with AS ( 38 , 40 ), two with SSc ( 26 , 37 ), and one with BD ( 42 ), FMF ( 48 ), and axSpA ( 49 ), respectively. Liquid chromatography was used in 21 study groups ( 27 – 38 , 40 – 42 , 44 , 46 , 48 , 49 ), a spectrofluorimetric assay in one ( 26 ), and an enzyme-linked immunosorbent assay (ELISA) in the remaining one ( 47 ).…”

“…Among the liquid chromatography-based assays, seven used fluorimetric detection ( 27 – 33 ), and the remaining 14 mass spectrometry ( 34 – 38 , 40 – 42 , 44 , 46 , 48 , 49 ). Measurements were conducted in serum in 17 study groups ( 26 – 33 , 36 , 38 , 40 , 42 , 46 – 48 ), and plasma in the remaining six ( 34 , 35 , 37 , 41 , 44 , 49 ). The risk of bias ( Supplementary Table 3 ) was moderate in 13 studies ( 26 – 33 , 35 , 37 , 41 , 44 , 47 ), and low in the remaining eight ( 34 , 36 , 38 , 40 , 42 , 46 , 48 , 49 ).…”

“…Measurements were conducted in serum in 17 study groups ( 26 – 33 , 36 , 38 , 40 , 42 , 46 – 48 ), and plasma in the remaining six ( 34 , 35 , 37 , 41 , 44 , 49 ). The risk of bias ( Supplementary Table 3 ) was moderate in 13 studies ( 26 – 33 , 35 , 37 , 41 , 44 , 47 ), and low in the remaining eight ( 34 , 36 , 38 , 40 , 42 , 46 , 48 , 49 ).…”

“…In liquid chromatography studies, seven used mass spectrometry ( 40 – 42 , 44 , 46 , 48 , 49 ), six ultraviolet ( 27 – 29 , 31 – 33 ), and one fluorimetric detection ( 30 ). Kynurenine was measured in serum in 14 study groups ( 27 – 33 , 40 , 42 , 45 – 48 ), and plasma in the remaining four ( 35 , 41 , 44 , 49 ). The risk of bias ( Supplementary Table 3 ) was moderate in 12 studies ( 27 – 33 , 35 , 41 , 44 , 45 , 47 ), and low in the remaining five ( 40 , 42 , 46 , 48 , 49 ).…”