Elevated serum levels of kynurenine pathway metabolites in Behçet's patients

Abstract Behçet's disease (BD) is a inflammatory, multisystemic vasculitis of unknown etiopathogenesis. However, innate and adaptive immune system involvement and immune-mediated networks play a key role in the inflammatory cascade. Studies have shown that both indoleamine 2,3-dioxygenase enzyme, which is induced in inflammatory conditions and catalyzes the first and rate-limiting step in the tryptophan (TRP) metabolism by the kynurenine pathway (KP), and downstream metabolites have immunomodulatory properties. The study was aimed to measure KP metabolites levels in patients with BD and to investigate the relationship between disease activity and clinical findings with these metabolites. The study included 120 patients with BD and 120 healthy volunteers. Serum TRP, kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxyanthranilic acid (3HAA), 3-hydroxykynurenine (3HK), quinolinic acid (QUIN) levels were analyzed with tandem mass spectrometric method. Demographic data, clinical manifestations and disease activity score (BDCAF) were recorded. Serum KYN, KYNA, 3HK, 3HAA, QUIN levels and KYN/TRP ratio were higher (p<0.05) in patients with BD compared to the control group, while TRP levels were lower (p<0.05). KYN/TRP ratio and QUIN levels were significantly higher in the presence of neurobehçet's while serum KYN levels were significantly higher in the presence of arthritis (p<0.05). Also, serum QUIN levels were significantly higher in the presence of thrombosis (p<0.05). BDCAF score positively correlated with KYN/TRP ratio and QUIN levels. Our findings showed that serum KP metabolite levels were elevated in patients with BD and there is a relationship between these metabolites with disease activity, clinical findings and inflammatory burden.