Leonie Jt Balter, Xueqi Li, Lilly Schwieler, Sophie Erhardt, John Axelsson, Mats J Olsson, Julie Lasselin, Mats Lekander
Abstract
["Metabolites of the kynurenine pathway are hypothesized to be implicated in inflammation-associated depression, but there is a lack of experimental studies in humans assessing the kinetics of kynurenine metabolites in relation to experimentally-induced sickness. The aim of the present study was to assess changes in the kynurenine pathway and to explore its relation to symptoms of sickness behavior during an acute experimental immune challenge. This double-blind placebo-controlled randomized cross-over study included 22 healthy human participants (n\u00a0=\u00a021 both sessions, M = 23.4, SD = 3.6, nine women) who received an intravenous injection of 2.0\u00a0ng\/kg lipopolysaccharide (LPS) and saline (placebo) on two different occasions in a randomized order. Blood samples (0\u00a0h, 1\u00a0h, 1.5\u00a0h, 2\u00a0h, 3\u00a0h, 4\u00a0h, 5\u00a0h, 7\u00a0h post-injection) were analyzed for kynurenine metabolites and inflammatory cytokines. The intensity of symptoms of sickness behavior was assessed using the 10-item Sickness Questionnaire at 0\u00a0h, 1.5\u00a0h, 3\u00a0h, 5\u00a0h, and 7\u00a0h post-injection. LPS induced significantly lower concentrations of plasma tryptophan (at 2\u00a0h, 4\u00a0h, 5\u00a0h, and 7\u00a0h post-injection), kynurenine (at 2\u00a0h, 3\u00a0h, 4\u00a0h, and 5\u00a0h post-injection), nicotinamide (at 4\u00a0h, 5\u00a0h, and 7\u00a0h post-injection), and higher levels for quinolinic acid at 5\u00a0h post-injection as compared to placebo. LPS did not affect kynurenic acid, 3-hydroxykynurenine, and picolinic acid. The development of the sickness symptoms was largely similar across items, with the highest levels around 1.5-3\u00a0h post-injection. Changes in plasma levels of kynurenine metabolites seem to coincide rather than precede or follow changes in subjective sickness. Exploratory analyses indicate that higher Sickness Questionnaire total scores at 1.5-5\u00a0h post-injection were correlated with lower kynurenic acid and nicotinamide levels. These results lend further support for LPS-induced changes in the kynurenine pathway, but may not, as interpreted from blood levels, causally link to LPS-induced acute symptoms of sickness behavior. Future research may consider a larger sample to further scrutinize the role of the kynurenine pathway in the sickness response.",{"copyright":"Copyright \u00a9 2023 The Authors. Published by Elsevier Ltd.. All rights reserved."}]
Address:
Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden; Stress Research Institute, Department of Psychology, Stockholm University, Stockholm, Sweden. Electronic address:
[email protected].; Department of Physiology, Karolinska Institutet, Stockholm, Sweden.; Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden; Stress Research Institute, Department of Psychology, Stockholm University, Stockholm, Sweden.; Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden.; Department of Clinical Neuroscience, Division of Psychology, Karolinska Institutet, Stockholm, Sweden; Stress Research Institute, Department of Psychology, Stockholm University, Stockholm, Sweden; Osher Center for Integrative Health, Department of Clinical Neuroscience, Karolinska Institutet, Sweden.
