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Study decoded · health · Emerging
Tryptophan Byproduct Kynurenic Acid Calms Allergic Rhinitis In Rats
Rat study, 48 animalsAhR receptor restoredMatched antihistamine14-day treatment
A tryptophan-derived compound called kynurenic acid reduced allergic rhinitis symptoms in rats as effectively as the antihistamine desloratadine, according to a study published October 1, 2026 in PLOS One.
Researchers sensitized 48 adult male rats to ovalbumin, then split them into six groups of 8: control, untreated allergic rhinitis, vehicle, kynurenic acid, desloratadine (a standard antihistamine), and kynurenic acid plus an AhR-blocking drug. From day 15 to day 29, treated rats got daily kynurenic acid (10 mg/kg, injected) or desloratadine (5 mg/kg, oral). After an ovalbumin nasal challenge on day 30, untreated allergic rats showed sharply increased sneezing and nasal scratching, along with elevated blood levels of IgE, IL-4 and IL-6, all markers of allergic inflammation.
Kynurenic acid reduced nasal scratching and sneezing compared with untreated allergic rats, and cut serum IgE, IL-4 and IL-6 to levels statistically indistinguishable from desloratadine. Kynurenic acid produced a bigger improvement than desloratadine on nasal scratching specifically, and reduced spleen tissue damage scores where desloratadine showed no measurable improvement. The spleen-to-body-weight ratio, a marker of systemic immune activation, dropped with kynurenic acid but not with desloratadine.
Kynurenic acid is a naturally occurring breakdown product of tryptophan, an amino acid from protein-rich food. In these rats, it restored two nasal tissue proteins, AhR and CYP1A1, that had dropped sharply with allergic rhinitis, and raised two immune-calming signals, IL-10 and TGF-beta, that had also fallen. AhR is a receptor in nasal lining cells and immune cells that helps keep inflammation in check at mucosal surfaces; when researchers blocked it with a drug called CH223191, much of kynurenic acid's benefit in these rats disappeared, pointing to AhR signaling as a key part of the mechanism, the study authors report.
Treatment dose parameters, 14-day protocol
Data Panel
- Who
- 48 adult male Wistar rats, ovalbumin-induced allergic rhinitis model, divided into 6 groups of 8
- Design
- Randomized controlled animal study with control, allergic rhinitis, vehicle, kynurenic acid, desloratadine and kynurenic acid plus AhR-blocker groups
- Dose
- Kynurenic acid 10 mg/kg/day injected; desloratadine 5 mg/kg/day oral; AhR blocker CH223191 10 mg/kg/day injected, all for 14 days (days 15-29)
- Primary result
- Kynurenic acid reduced nasal scratching and sneezing versus untreated allergic rats and matched desloratadine on serum IgE, IL-4 and IL-6 reduction; kynurenic acid showed greater improvement than desloratadine on nasal scratching and spleen histopathology score
- Secondary
- Nasal AhR and CYP1A1 protein levels, both reduced in allergic rats, were restored by kynurenic acid beyond desloratadine's effect; nasal IL-10 and TGF-beta, immune-regulating signals, increased with kynurenic acid more than desloratadine; blocking AhR with CH223191 partly reversed these gains
- Funding / conflicts
- Funded by a research grant from Alborz University of Medical Sciences; funders had no role in study design, data collection, analysis or the decision to publish; no conflicts of interest declared
This was conducted in rats, not humans, using one dose and one two-week schedule, so the findings cannot be assumed to apply to people with seasonal or pet allergies. The AhR-blocking drug used to test the mechanism can have effects beyond AhR itself.
Dr. Axe's Take
This rat study points at the aryl hydrocarbon receptor, a sensor cells use to read environmental and metabolic signals, as a piece of the chronic nasal allergy puzzle worth watching. Rats are not people, and I would not treat kynurenic acid as a human allergy therapy based on this alone. What I would do this week is support the pathway that feeds this receptor naturally: cruciferous vegetables like broccoli and Brussels sprouts supply compounds that activate AhR signaling, and adequate dietary protein supplies the tryptophan this whole system runs on. Anyone managing seasonal allergies now should keep using what their doctor prescribed, including antihistamines, and watch the kynurenine pathway as a research direction, not a reason to change today's protocol.
— Dr. Axe