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Tryptophan-Kynurenine Axis

Microbes shunt tryptophan toward indole metabolites; inflammation diverts host tryptophan to kynurenine.

A free, animated tryptophan-kynurenine axis you can read here or embed on any website, from Scrollchart.

Tryptophan-Kynurenine Axis

Tryptophan-Kynurenine AxisInflammation hijacks tryptophan toward kynurenine, depleting serotonin and gut-protective indolesTryptophandietary amino acid (1-2% of intake)IDO1/TDO activated byIFN-gamma, TNF-alphaSerotonin (5-HT)host TPH1/TPH2 (EC cells)KynurenineIDO1/TDO pathway (~95% flux)Indolesmicrobial (IAA, IPA, tryptamine)Quinolinic acid (QUIN)NMDA agonist, microglial activationneurotoxic; depressive phenotypeVagal tone, mood, motility90% gut-derived 5-HTactivates vagal afferentsAhR activation, IgA, IL-22barrier integrity, mucusanti-inflammatory, ILC3 supportTryptophan FluxKynurenine pathway95%liver + macrophagesSerotonin synthesis3%enterochromaffin cellsMicrobial indoles2%gut bacteria (Lactobacillus)Chronic inflammationfurther shifts flux to KYN;Kyn:Trp ratio = depression markerDysbiosis reduces microbial indoles; IDO1 activation by IFN-gamma diverts tryptophan toward neurotoxic quinolinic acid

Tryptophan branches: serotonin (host enterochromaffin), kynurenine (host IDO/TDO under inflammation), indoles (microbial). Imbalance toward kynurenine implicated in depression and inflammation.

Good for

  • Gut-brain axis and psychobiotic articles
  • Depression and inflammation mechanism explainers
  • Tryptophan supplement and mood science content

Source & accuracy

This tryptophan-kynurenine axis is an editorial illustration built to represent the concept accurately. Where it shows figures, they are typical or representative values chosen to make the relationship clear, not a single underlying dataset. The diagram and its explainer are reviewed and maintained centrally, and updated over time as understanding improves.

Three competing fates for dietary tryptophan

Tryptophan, an essential amino acid, can travel down several routes. Gut microbes convert a portion into indole and related metabolites that signal through the aryl hydrocarbon receptor and support the gut barrier. The host uses some for serotonin, and a large share enters the kynurenine pathway, the dominant route for tryptophan breakdown in the body.

These pathways compete for the same starting material, so shifts in one can change the supply available to the others.

How inflammation tips the balance

Inflammatory signals activate the enzyme IDO, which pushes more tryptophan into the kynurenine pathway. This both lowers the tryptophan available for serotonin and generates kynurenine metabolites, some of which influence immune tone and neuronal signaling. Microbial indole production can partly counterbalance this by supporting barrier integrity.

These mechanisms are studied intensively in mood, immunity, and metabolic research, but human findings are still emerging and not yet a basis for treatment. This is general educational information, not medical advice.

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Reference

What this is
A free, embeddable, animated tryptophan-kynurenine axis for any website.
Who uses it
Medical educators, Biohacker blogs, Psychology blogs.
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License
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URL
scrollchart.com/diagram/kynurenine-tryptophan

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Frequently asked questions

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Scrollchart provides "Tryptophan-Kynurenine Axis" as a free, embeddable animated diagram you can add to any website with one line of HTML. No signup is required and there is no watermark. The diagram and its explainer text are served from scrollchart.com, so the embed stays current without any maintenance on your end.
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