ReviewInternational journal of tryptophan research : IJTR2019
The Plasma [Kynurenine]/[Tryptophan] Ratio and Indoleamine 2,3-Dioxygenase: Time for Appraisal.
Review in International journal of tryptophan research : IJTR, 2019. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 147 papers, 4 of them syntheses that pooled it.
What it found
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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.
The trial behind it
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.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
147 citing papers in PubMed, 4 syntheses or guidelines pooled it.
- Pooled it
- Importance of the dysregulation of the kynurenine pathway on cognition in schizophrenia: a systematic review of clinical studies.European archives of psychiatry and clinical neuroscience · 2023Pooled it
- Ketamine's effect on inflammation and kynurenine pathway in depression: A systematic review.Journal of psychopharmacology (Oxford, England) · 2021Pooled it
- BrainFrontiers in immunology · 2021Pooled it
- Citalopram Neuroendocrine Challenge Shows Altered Tryptophan and Kynurenine Metabolism in Migraine.Cells · 2022Trial
- Dietary tryptophan mitigates lung ischemia-reperfusion injury in association with increased indole-3-propionate and aryl hydrocarbon receptor signaling.Gut microbes · 2026Article
- Tryptophan metabolism in colorectal cancer: From mechanistic insights to novel therapeutic strategies.Clinical and translational medicine · 2026Review
- Sex-specific association of IDO1 gene with schizophrenia and imbalanced levels of cytokines and neuroactive kynurenine metabolites in relapsed patients.European archives of psychiatry and clinical neuroscience · 2026Article
- Dietary Tryptophan Allocation in Depression: Serotonin-Kynurenine Balance, Microbial Indole Pathways, and Inflammatory Phenotypes.Nutrients · 2026Review
- The Kynurenine Pathway in Tuberculosis: Focus on Immunometabolic Regulation, Compartment-Specific Biology, and Therapeutic Potential.Life (Basel, Switzerland) · 2026Review
- Tracing NADCell reports · 2026Article
- Mechanism-First Psychobiotics: Fermented Vegetables, Dairy, and Soy for Depression and Anxiety.International journal of molecular sciences · 2026Review
- Disrupted glutathione homeostasis in the pathogenesis of TTR-V30M amyloidosis.Biomarker research · 2026Article
- The potential role of kynurenine pathway and inflammation in pediatric obsessive-compulsive disorder with and without major depressive disorder comorbidity.Journal of neural transmission (Vienna, Austria : 1996) · 2026Article
- The mediating role of the kynurenine pathway in longitudinal associations between dietary intake and quality of life in colorectal cancer survivors up to 12 months posttreatment.International journal of cancer · 2026Article
- Tryptophan Metabolism at the Crossroads of Immunity, Barrier Function, and the Microbiome in Atopic Dermatitis.Clinical reviews in allergy & immunology · 2026Review
- The Role of Kynurenine and 5-Hydroxytryptophan in Modulating Microbiota and Their Implications in Exudative Age-Related Macular Degeneration.Diagnostics (Basel, Switzerland) · 2026Article
- The Tryptophan Paradox: From Microbiome-Mediated Homeostasis to Tumor-Driven Immune Escape.International journal of molecular sciences · 2026Review
- A metabolic constraint in de novo NAD+ synthesis drives mucosal inflammation in IBD.Journal of Crohn's & colitis · 2026Article
- Stage-Dependent Changes in Kynurenine Pathway Enzyme Expression Suggest Immune-Related Involvement in Bladder Cancer Progression.International journal of urology : official journal of the Japanese Urological Association · 2026Article
87 more citing papers are in PubMed but not listed here.
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
2 authors.
Funding
No grant is acknowledged in the PubMed record.
Abstract
The plasma kynurenine to tryptophan ([Kyn]/[Trp]) ratio is frequently used to express or reflect the activity of the extrahepatic Trp-degrading enzyme indoleamine 2,3-dioxygenase (IDO). This ratio is increasingly used instead of measurement of IDO activity, which is often low or undetectable in immune and other cells under basal conditions, but is greatly enhanced after immune activation. The use of this ratio is valid in in vitro studies, eg, in cell cultures or isolated organs, but its 'blanket' use in in vivo situations is not, because of modulating factors, such as supply of nutrients; the presence of multiple cell types; complex structural and functional tissue arrangements; the extracellular matrix; and hormonal, cytokine, and paracrine interactions. Determinants other than IDO may therefore be involved in vivo. These are hepatic tryptophan 2,3-dioxygenase (TDO) activity and the flux of plasma-free Trp down the Kyn pathway. In addition, conditions leading to accumulation of Kyn, eg, inhibition of activities of Kyn monooxygenase and kynureninase, could lead to elevation of the aforementioned ratio. In this review, the origin of use of this ratio will be discussed, variations in extent of its elevation will be described, evidence against its indiscriminate use will be presented, and examining determinants other than IDO activity and their correlates will be proposed for future studies.
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Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.