Kynurenic pathway of tryptophan metabolism and insulin resistance. Abbreviations: TRP: tryptophan; IFNG: interferon gamma; IDO: indoleamine 2,3-dioxygenase; TDO: TRP 2,3-dioxygenase; KYN: kynurenine; 3-HK: 3-hydroxyKYN; P5P: pyridoxal 5′-phosphate; NAD+: nicotinamide adenine dinucleotide; KYNA: kynurenic acid; XA: xanthurenic acid; IR: insulin resistance.