Values of cytokines and tryptophan metabolites over a 12 weeks time course in patients with depression and somatoform disorder
Daniela Krause 1*, Verena B Kirnich 2, Theresa M Stapf 2, Anika Hennings 3, Sabine Riemer 3, Michael Riedel 2, Ralf Schmidmaier 4, Francisco Pedrosa Gil 5, Winfried Rief 3, Markus J Schwarz 2
1Department of Psychiatry, Ludwig-Maximilians University, Munich, Germany, 2Department of Laboratory Medicine, Ludwig Maximilians University, Munich, Germany, 3Division of Clinical Psychology and Psychotherapy, Philipps University of Marburg, Germany , 4Department of Hematology and Oncology, Ludwig Maximilians University, Munich, Germany , 5Department of Psychiatry, Vogtland Hospital, Plauen, Germany
Received: April 22, 2017; Revised: September 28, 2017; Accepted: October 24, 2017; Published online: October 24, 2017.
© The Korean College of Neuropsychopharmacology. All rights reserved.

Objective: Previous studies have suggested alterations in the kynurenine pathway as a major link between cytokine and neurotransmitter abnormalities in psychiatric disorders. Most of these studies used a cross-sectional case-control study design. However, knowledge is still lacking regarding the stability over time of kynurenine pathway metabolites and the functionally related cytokines. Therefore, we studied the stability of cytokines and tryptophan parameters over a period of 12 weeks.
Methods: A total of 117 participants—39 with major depression (MD), 27 with somatoform disorder (SFD), and 51 healthy controls (HC)—were enrolled. Four evaluations, including blood withdrawal and psychometric testing, were performed over a period of 12 weeks. We used ELISA to measure IL-6, TNF α, and IL-1 RA, and HPLC to analyze neurotransmitter variables, i.e. tryptophan (TRP), 5-HIAA, kynurenine (KYN), 3-OH-kynurenine (3-HK), and kynurenic acid (KYNA).
Results: We found no significant fluctuations of TRP, its metabolites (5-HIAA, KYN, KYNA, and 3-HK), or the cytokines (IL-1 RA, IL-6, and TNF α) in any of the groups over the 12 weeks
Conclusion: To our knowledge, this is the first longitudinal study performed in psychiatric patients to verify the stability and consequently the reliability of the biological parameters we investigated. Our data indicate that tryptophan metabolites and cytokines are reliable biological parameters in psychiatric research because they do not fluctuate significantly over time.
Keywords: cytokines, tryptophan, depression, somatoform disorder, stability, longitudinal