Hydrocortisone Affects Fatigue and Physical Functioning Through Metabolism of Tryptophan: A Randomized Controlled Trial.

Abstract

Hydrocortisone (HC) treatment influences health-related quality of life (HRQOL) in secondary adrenal insufficiency (AI). Glucocorticoids regulate tryptophan metabolism through the kynurenine pathway, which modulates mood and energy homeostasis. This study investigated whether tryptophan metabolism mediated the effect of HC dose on HRQOL in patients with secondary AI. Forty-seven patients with secondary AI participated in this double-blind randomized controlled cross-over trial in the University Medical Center Groningen. Patients were treated for two 10-week periods with a daily HC dose of 0.2 to 0.3 mg/kg and 0.4 to 0.6 mg/kg body weight, respectively. Diary data and questionnaires were used to assess HRQOL. Tryptophan, kynurenine and 3-hydroxykynurenine were measured in serum and dialyzed plasma and the kynurenine-to-tryptophan ratio (Kyn/Trp ratio) ratio was calculated. A higher dose HC was associated with increased levels of tryptophan (95% CI for mean difference 0.37 to 12.5, P = 0.038), reduced levels of kynurenine (95% CI, -0.49 to -0.10, P = 0.004) and 3-hydroxykynurenine (95% CI, -10.6 to -2.35, P = 0.003), and a reduced Kyn/Trp ratio (95% CI, -0.84 to -0.50, P < 0.001). The Kyn/Trp ratio mediated the effect of a higher dose HC on fatigue (P = 0.041) and physical functioning (P = 0.005). Metabolism of tryptophan through the kynurenine pathway is reduced after a 10-week treatment with a higher dose HC and plays a role in the effect of HC on fatigue and physical functioning in patients with secondary AI.