What do poultry, chocolate, bananas and cruciferous vegetables such as broccoli, cabbage and cauliflower have in common? They all contain an essential amino acid called tryptophan, which launches a biochemical chain reaction in the body that controls intestinal inflammation and keeps the gut barrier healthy.
In people with celiac disease though, that reaction is impaired, according to a study published in October by an international team of researchers led by McMaster University.
Yet this finding could actually be good news. Not only does it suggest a target for therapy, the team has a good idea of what that therapy might look like – combining tryptophan-rich foods with a probiotic that can act as a catalyst for that all-important chain reaction.
As lead researcher Elena Verdu explains, our bodies don’t produce tryptophan and it must be consumed through food. Tryptophan’s indole metabolites have many important roles to play, including activating receptors in the gut lining.
One of these receptors is the aryl hydrocarbon receptor, or AhR, and poor activation of AhR has been implicated in chronic intestinal inflammation. Activation of AhR by tryptophan metabolites in turn controls inflammation, says Verdu, professor of medicine at McMaster’s Farncombe Family Digestive Health Research Institute and a Canada Research Chair in Nutrition, Inflammation and Microbiota.
So Verdu and her collaborator, Farncombe Institute research associate Heather Galipeau, set out to investigate whether the breakdown of tryptophan by gut bacteria was altered in celiac disease and whether this pathway could be targeted as a potential therapy.
Next step: clinical trials
Using mice that express genes for celiac disease, she found adding some probiotic lactobacilli bacteria to their diet helped them metabolize tryptophan. This in turn allowed the amino acid to carry out its role in promoting a healthy gut barrier and reducing inflammation.
“Our theory is that in some patients with celiac disease and persistent inflammation despite the gluten-free diet, the capacity of their gut bacteria to metabolize tryptophan and produce these barrier-protecting and anti-inflammatory effects, is diminished,” says Verdu.
That said, she’s not ready to recommend people with celiac disease take lactobacilli bacteria probiotics. Human clinical trials must first test the safety and efficacy of such supplements in people with the disease, particularly in those with persistent symptoms despite a gluten-free diet. In any case, the particular strains of lactobacilli bacteria Verdu used are not yet available in stores.
University of Manitoba gastroenterologist Donald Duerksen agrees the study supports the potential role of tryptophan and its metabolites in modulating inflammation in celiac disease. Like Verdu, he is eager to see it put to the test with human clinical trials.
“Currently the only treatment for celiac disease is a gluten free diet,” says Dr. Duerksen, chair of the Canadian Celiac Association Professional Advisory Council. “This can be very difficult to achieve and therefore finding additional treatments for celiac disease could be very helpful for individuals with this condition.”