Tryptophan metabolites clearance in hemodialyzed patients

Hemodialysis (HD) and hemodiafiltration (HDF) procedures have limited efficacy regarding removal of selected toxins. Tryptophan (Trp) metabolites formed through the kynurenine (KYN) pathway are known to contribute to kidney failure (KF) complications, some of which may affect the survival of neurons. The aim of this study was to investigate the removal of Trp and its metabolites, KYN, kynurenic acid (KYNA) and 3-hydroxykynurenine (3-OHKYN) in patients treated by HD or HDF and the impact of patients' comorbidities on toxins removal. The study was conducted in 50 patients with KF. Serum level of free fractions of Trp and its metabolites were measured before and after a dialysis session through high performance liquid chromatography. The serum concentration of Trp, as well as 3-OHKYN/KYN ratio remained unchanged, whereas the concentration of KYN, KYNA, 3-OHKYN, together with KYN/Trp ratio significantly decreased after dialysis procedures. The indices KYNA/KYN and KYNA/3-OHKYN increased. In patients with heart failure, higher reduction ratio (RR) of KYN was found, whereas in patients with diabetes higher KYN RR and lower KYNA RR was observed. In patients without residual kidney function, KYNA RR was significantly higher compared to patients with preserved diuresis. RR of all tested metabolites did not differ between HD and HDF treated patients. In KF, Trp metabolites were removed from the blood during dialysis procedures with different efficacies. Targeted strategies to lower KYN pathway metabolites concentration may be beneficial in patients with KF and selected comorbidities.