How gut breaks down common compound in meat, dairy key to understanding arthritis, finds study

New Delhi: How a common compound present in protein-rich foods like meat and dairy products gets broken down during digestion could be key to understanding how one develops inflammatory diseases such as rheumatoid arthritis, new research has found.

The compound, called tryptophan, helps the body produce proteins, muscles, enzymes, and neurotransmitters. It is not produced within the body, but is received through the diet we consume.

Researchers have found in mice that the byproducts formed when the compound tryptophan is broken down depends on the type of cells in the gut doing the ‘breaking down’ — body cells or bacterial cells.

While the body cells broke down tryptophan to produce anti-inflammatory products, bacterial cells broke the compound down to produce indoles, which triggered the body into producing the more inflammatory autoreactive T-cells, according to Kristine Kuhn, Head of the Division of Rheumatology, University of Colorado, US.

Further, the kind of diet we consume regularly was found to be important in governing how tryptophan got broken down.

“A diet that’s rich in plant-based fibres and lean meats — this whole Mediterranean diet — seems to push the microbiome into a healthier state, so that you are getting the anti-inflammatory properties of tryptophan, whereas the typical western diet seems to go more toward the inflammatory pathway,” said Kuhn, a co-author of the study published in the Journal of Clinical Investigation.

“That’s all about finding the right path for the body’s tryptophan,” she added.

Kuhn said the study built upon previous research which had linked changes in the gut microbiome with an increased production of indoles in patients with spondyloarthritis — different from rheumatoid arthritis which causes inflammation in joints, but a closely related condition affecting joints in spine.

Similar results were found in arthritis studies involving mice, she said.

For this study, the researchers put mice on antibiotics to wipe out their microbiome, and found that they neither got arthritis, nor did they had indoles.

So they tried to find out what would happen if the mice were put on a diet with little tryptophan.

“The microbiome can’t break down tryptophan into indole, and the mice didn’t get arthritis. So two different ways, we showed that it’s tryptophan that’s broken down by the microbiome into indole,” said Kuhn.

The paper concluded that blocking indole production may present unique pathways for therapies for rheumatoid arthritis and spondyloarthritis, which Kuhn said is what the team is interested in digging deeper into.

“How do you keep that balance tipped so that tryptophan goes towards that anti-inflammatory pathway? How can you manipulate intestinal bacteria to tip that balance? That’s where we’re interested in going in the future,” said Kuhn.