Researchers have successfully isolated a microbial metabolite (Urolithin A or UroA) responsible for protecting the integrity of the gut lining. Leakage of toxins and bacteria leading to inflammatory bowel diseases such as colitis occurs when the integrity of the gut lining is compromised.

However, not everyone has the gut microbes essential for converting the polyphenols present in berries and pomegranates into UroA metabolite. Besides isolating the metabolite, a multi-institutional team co-led by Dr. Praveen Kumar Vemula from the Institute for Stem Cell Biology and Regenerative Medicine (inStem), Bengaluru, synthesised an analogue by chemically modifying the naturally occurring metabolite.

The integrity of the gut barrier is maintained by tight junction proteins. Colitis and other inflammatory bowel diseases cause a significant reduction in the levels of the junction proteins, leading to leakage of microbes and toxins from the gut causing acute or chronic inflammation. Restoring the integrity of the gut barrier is therefore essential for treating colitis.

The natural and synthetic metabolites have anti-inflammatory property and also increase the production of tight junction proteins. “But the synthetic metabolite was more stable and more effective in treating and preventing colitis in mice model than the natural metabolite. It was able to prevent and repair the damaged gut barrier and reduce inflammation. Synthetic metabolite even in nanomolar range was sufficient to treat or prevent colitis,” says Dr. Sandeep Chandrashekharappa from inStem and a co-author of a paper published in Nature Communications.

The metabolite (both natural and synthetic) repairs the gut barrier by activating a particular pathway (AhR-nrf2) leading to excess production of the tight junction proteins.

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In vitro studies

Two different cell lines of the colon and another of immune cells (macrophages) were used for the study. A monolayer of colon cells mimicking the gut lining was treated with lipopolysaccharide to induce inflammation and breakage of the monolayer. While lipopolysaccharide destroyed the integrity of the monolayer, there was only minimal inflammation. Both metabolites were able to repair monolayer leakage with the synthetic one being more efficient than the natural metabolite.

In the case of immune cells, lipopolysaccharide treatment caused inflammation and excess production of inflammatory cytokines. Treatment with the metabolites stopped cytokine production and reduced the inflammation. Again, the synthetic metabolite outperformed the natural one.

Animal studies

The researchers induced acute colitis in mice by using a chemical (dextran sodium sulphate). There was increased inflammation and gut barrier leakage. Metabolites given orally led to complete reduction in inflammation and gut leakage repair. To mimic chronic colitis, the chemical was given to the mice for a prolonged period of ten weeks with two weeks of break after each week of chemical exposure. “The animals treated with the metabolites showed no inflammation and gut leakage even during the course of the treatment. We saw the leakage being repaired after two cycles of chemical treatment,” says Dr. Vemula.

Acute colitis in mice was produced by using a single dose of a different chemical followed by metabolite treatment. There was much lower inflammation and leakage after treatment. “The colon which had shrunk in length due to colitis regained its original length after treatment,” says Dr. Vemula.

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Prophylactic property

To test the prophylactic property of the metabolite, mice were given one dose of the metabolite each day for seven days and a chemical was used to cause colitis on the seventh day. The ability of the metabolite to render protection was tested on day 11. “The animals did not develop colitis while the mice in the control group showed full-blown colitis,” says Anikita A. Hiwale from inStem and one of the authors of the paper.

“We are now making a library of analogues to come up with a synthetic metabolite that is even better than the one currently tested. We are planning for a start-up company for clinical development,” says Dr. Vemula.



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