Fig. 1.

Kynurenine pathway. Tryptophan is degraded by IDO or TDO to serotonin or N-formylKYN. Later on, the formed KYN can be catabolized into 3-OHKYN, KYNA or AA. The 3-OHKYN is converted into XA and QA, with the final product NAD. 3-OHKYN 3-hydroxykynurenine, AA anthranilic acid, HAAO 3-hydroxyanthranilic acid dioxygenase, IDO indoleamine 2,3-dioxygenase, KAT kynurenine aminotransferase, KMO kynurenine 3-monooxygenase (kynurenine 3-hydroxylase), KYN kynurenine, KYNA kynurenic acid, KZ kynureninase, NAD nicotinamide adenine dinucleotide, N-formylKYN N-formylkynurenine, QA quinolinic acid, QPRT quinolinic acid phosphoribosyltransferase, TDO tryptophan 2,3-dioxygenase, Trp tryptophan, XA xanthurenic acid. Created with BioRender.com