Peripheral Kynurenine Pathway Metabolites in Patients with Psoriasis

Psoriasis is a systemic disease affecting 2-3% of the general population. Tryptophan (TRP) is an amino acid metabolized in the kynurenine pathway (KP). The aim of this study was to assess the kynurenine pathway's metabolites in serum and urine of psoriatic patients and explore the possible interplay with the disease's pathogenesis and its comorbidities. The study involved 60 patients with plaque psoriasis and 30 healthy volunteers matched for gender, age, and BMI. Serum and urine samples were taken from the participants and tested for TRP, indoleamine 2,3-dioxygenase (IDO), 2,3-tryptophan dioxygenase (TDO), kynurenine (KYN), kynurenic acid (KYNA), quinolinic acid (QUIN), and numerous laboratory parameters. Correlations between the metabolites' levels and clinical, laboratory parameters and depression occurrence were statistically evaluated. Concentrations of tryptophan, kynurenic acid, and quinolinic acid in serum and urine were significantly higher among patients with psoriasis (p < 0.05 and p < 0.001, p < 0.05 and p < 0.05 and p < 0.001 and p < 0.001, respectively). A significant stimulation of the kynurenine pathway in serum and urine of patients with psoriasis suggests its role in its pathogenesis and interplay between chronic inflammation or comorbidities. Further research is needed to discover whether the increase in KP metabolites is an indicator of inflammation or a compensatory mechanism in psoriasis.