Tryptophan and Kynurenine Levels and Its Association With Sleep, Nonphysical Fatigue, and Depression in Chronic Hemodialysis Patients

Objective Sleep and mood disorders are common in hemodialysis (HD) patients and the pathophysiology is still unclear. Tryptophan (TRP) and its metabolites may play a prominent role in neural pathways related to sleep, fatigue, and depression. Here, we sought to compare the levels of TRP and its metabolites between HD patients and healthy subjects and examine their association with sleep, fatigue, and depression in HD patients. The design was cross-sectional analysis. Subjects Ninety-nine adult patients on stable thrice weekly HD schedule between September 2011 and March 2014 and 10 healthy controls. Intervention Venous blood samples were drawn in healthy subjects and immediately before dialysis in chronic HD patients. TRP and kynurenine (KYN) metabolites were measured by high-performance liquid chromatography. The Medical Outcomes Study Sleep Scale, the PROMIS Short form Fatigue, and the Patient Health Questionnaire were administered concurrently. Main Outcome Measure Sleep, fatigue, and depression as assessed by subjective questionnaire. Results TRP levels were significantly lower (52.4 ± 15.2 vs. 67.9 ± 3.1 μmol/L; P