ArticlePharmaceuticals (Basel, Switzerland)2022
Tryptophan Challenge in Healthy Controls and People with Schizophrenia: Acute Effects on Plasma Levels of Kynurenine, Kynurenic Acid and 5-Hydroxyindoleacetic Acid.
Article in Pharmaceuticals (Basel, Switzerland), 2022. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 12 papers, 1 of them a synthesis that pooled it.
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The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
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Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
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Who cites it
12 citing papers in PubMed, 1 synthesis or guideline pooled it, 17 citations in OpenAlex.
- Discovery of biological markers for schizophrenia based on metabolomics: a systematic review.Frontiers in psychiatry · 2025Pooled it
- Harnessing Dietary Tryptophan: Bridging the Gap Between Neurobiology and Psychiatry in Depression Management.International journal of molecular sciences · 2026Review
- An LC-MS/MS-based approach for monitoring monoaminergic status in lizard brains: method development and real-samples application.Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology · 2025Article
- Article
- KMO Inhibition Improves Seizures and Depressive-like Behaviors Without Aggravating Cognitive Impairment in Epileptic Mice.Current issues in molecular biology · 2025Article
- The effect of dietary tryptophan supplementation, and an oral tryptophan challenge, on urinary excretion of 5-hydroxyindoleacetic acid in domestic dogs.Frontiers in veterinary science · 2025Article
- Microbiota, Tryptophan and Aryl Hydrocarbon Receptors as the Target Triad in Parkinson's Disease-A Narrative Review.International journal of molecular sciences · 2024Review
- Article
- Kynurenine, Kynurenic Acid, Quinolinic Acid and Interleukin-6 Levels in the Serum of Patients with Autism Spectrum Disorder.Medicina (Kaunas, Lithuania) · 2023Article
- The Tryptophan and Kynurenine Pathway Involved in the Development of Immune-Related Diseases.International journal of molecular sciences · 2023Review
- Analysis of Intestinal Metabolites in SR-B1 Knockout Mice via Ultra-Performance Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry.Molecules (Basel, Switzerland) · 2023Article
- Review
Corrections and comments
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Authors and funding
9 authors at 1 institution in 1 country.
Funding
Abstract
The pivotal tryptophan (TRP) metabolite kynurenine is converted to several neuroactive compounds, including kynurenic acid (KYNA), which is elevated in the brain and cerebrospinal fluid of people with schizophrenia (SZ) and may contribute to cognitive abnormalities in patients. A small proportion of TRP is metabolized to serotonin and further to 5-hydroxyindoleacetic acid (5-HIAA). Notably, KP metabolism is readily affected by immune stimulation. Here, we assessed the acute effects of an oral TRP challenge (6 g) on peripheral concentrations of kynurenine, KYNA and 5-HIAA, as well as the cytokines interferon-γ, TNF-α and interleukin-6, in 22 participants with SZ and 16 healthy controls (HCs) using a double-blind, placebo-controlled, crossover design. TRP raised the levels of kynurenine, KYNA and 5-HIAA in a time-dependent manner, causing >20-fold, >130-fold and 1.5-fold increases in kynurenine, KYNA and 5-HIAA concentrations, respectively, after 240 min. According to multivariate analyses, neither baseline levels nor the stimulating effects of TRP differed between participants with SZ and HC. Basal cytokine levels did not vary between groups, and remained unaffected by TRP. Although unlikely to be useful diagnostically, measurements of circulating metabolites following an acute TRP challenge may be informative for assessing the in vivo efficacy of drugs that modulate the neosynthesis of KYNA and other products of TRP degradation.
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Registered trials
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