The Role of Dietary Tryptophan on Aryl Hydrocarbon Receptor Activation

Study Overview
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Brief Summary
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This study evaluates the role of dietary L-tryptophan, an essential amino acid, in the activation of a specific cellular component: the aryl hydrocarbon receptor.

Detailed Description
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The Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor implicated in a range of key cellular events. In the gut, AHR is crucial for maintaining intestinal barrier immune homeostasis. The physiology of the AHR, however, is not completely understood; its precise gut luminal activators and functional consequences are unknown. Some AHR ligands originate from the diet. Commensals play crucial roles in metabolizing tryptophan and other amino acids such as tyrosine, with the subsequent production of tryptophan metabolites. Previous studies show that inflammatory bowel disease (IBD) patients have impaired production of AHR agonists by the microbiota. Furthermore, dietary supplementation with tryptophan ameliorates clinical parameters of colitis in rodent models. Whether these findings translate into human pathophysiology has not been explored. In the present study, the investigators will evaluate the effect of high- versus low-tryptophan diet on AHR activation in healthy participants. Briefly, participants will be instructed to follow a standardized low-tryptophan diet and will be randomized to a 3-week L-tryptophan supplement or placebo. Later, after a 2-week washout period, participants will crossover to the other arm. In addition, the effect of tryptophan and microbiota-derived metabolites on AHR activation will be analyzed.

Official Title
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The Role of Tryptophan on Aryl Hydrocarbon Receptor Activation: a Randomized, Double Blind, Placebo-controlled, Crossover Design Pilot Trial

Conditions
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Diet Modification

Intervention / Treatment
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* Dietary Supplement: L-tryptophan
* Dietary Supplement: Placebo


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy volunteer between 18 and 75 years of age. Exclusion Criteria: Rome IV criteria for any functional gastrointestinal disorder.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 75 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: All subjects will be following a standardized low-tryptophan diet and randomized to L-tryptophan supplements or placebo, for three weeks. After a 2 weeks washout period, subjects will crossover to the other arm.
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Low-tryptophan diet and L-tryptophan.<br>Standardized low-tryptophan diet (500-1000 mg of L-tryptophan and 1800 kcal) + L-tryptophan supplements (3 g/day). | Dietary Supplement: L-tryptophan<br>* 3 g/day of L-tryptophan added to the standardized low-tryptophan diet. Duration: 3 weeks.<br>|
| Placebo Comparator: Low-tryptophan diet and placebo<br>Standardized low-tryptophan diet (500-1000 mg of L-tryptophan and 1800 kcal) + placebo. | Dietary Supplement: Placebo<br>* A placebo will be added to the standardized low-tryptophan diet. Duration: 3 weeks.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| AHR activation levels in stool and duodenal content. | Changes in AHR activation levels will be assessed in stool and duodenal samples before and after the intervention (high- and low-tryptophan diets) using an AHR cell-reporter line. | three weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Bacterial and fungal microbiota composition in stool, duodenum and rectum/sigmoid biopsies. | Changes in bacterial and fungal microbiota composition will be assessed before and after the intervention in stool samples, duodenum and rectum biopsies. | Three weeks | 
| Tryptophan metabolites levels, including host and bacterial catabolites, in blood, urine and stool. | Changes in tryptophan metabolites leves will be compared before and after the intervention, in blood, urine and stool samples. | Three weeks | 
| mRNA levels in duodenal and rectum/sigmoid biopsies. | Changes in mRNA levels in duodenal and rectum/sigmoid biopsies will be assessed before and after the intervention. | three weeks | 
| Cytokines in serum. | Changes in cytokines in the serum (IL-22, IL-6, IL-2, IL-10, IL-12p70, IL-23p19, IFNγ, TNFα and CRP will be measured by ELISA in cell culture supernatants after stimulation with LPS, curdlan and ConA ) will be measured before and after the intervention and patients will be grouped into two categories for each measurement: high vs. low, according to the cutoff reference test value for each of the cytokines. | three weeks. | 
| Gastrointestinal symptoms | Changes in gastrointestinal symptoms before and after the intervention will be assessed using a validated questionnaire (The Gastrointestinal Symptoms Rating Scale) | three weeks. | 
| Mood | Changes in mood before and after the intervention will be assessed using a validated questionnaire (Hospital anxiety and depression scale) | three weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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immunity, Aryl-hydrocarbon receptor, immune homeostasis, microbiota, tryptophan