The Many Neuroprogressive Actions of Tryptophan Catabolites (TRYCATs) that may be Associated with the Pathophysiology of Neuro-Immune Disorders.
Level 5 - mechanism / opinion, no new human data
Narrative review of biological mechanisms without systematic methodology or primary empirical data
PubMed 26667000 · doi:10.2174/1381612822666151215102420
What was done
This narrative review synthesizes literature on how chronic immune activation, systemic inflammation, and oxidative and nitrosative stress upregulate indoleamine 2,3-dioxygenase (IDO) and shift tryptophan metabolism toward the tryptophan catabolite (TRYCAT) pathway. The authors describe the biological actions of specific catabolites and their proposed involvement in schizophrenia, Alzheimer's disease, and chronic fatigue syndrome.
What was found
The abstract provides qualitative mechanistic descriptions without quantitative data or effect sizes. It details that upregulated IDO activity makes the TRYCAT pathway the primary route for tryptophan breakdown. Quinolinic acid functions as an NMDA receptor agonist, inhibits mitochondrial ATP production, elevates oxidative stress, impairs glial-neuronal signaling, compromises blood-brain barrier integrity, and induces glial apoptosis. Kynurenic acid antagonizes NMDA, AMPA, and kainate receptors and interacts with alpha7 nicotinic acetylcholine and aryl hydrocarbon receptors; while neuroprotective, elevated levels are linked to impaired neurocognitive function and emotional processing.
Why it matters
The paper outlines the dual neurotoxic and neuromodulatory actions of tryptophan breakdown products, offering a conceptual framework for how chronic peripheral and central inflammation may drive neuroprogressive illness.
Limits
The abstract reports a narrative review with no systematic search criteria, quality appraisal of cited literature, or quantitative synthesis. No primary human or clinical trial data are presented, and direct causal roles in human disease states cannot be confirmed from these proposed pathways alone.
Cited by
- supports Kynurenic acid acts as an NMDA receptor antagonist, whereas quinolinic acid acts as an NMDA receptor agonist with neurotoxic properties.