Carbon monoxide foam in the rectum eases bowel disease in mice

It’s best known as a deadly poison, but in low doses, carbon monoxide can have therapeutic benefits for conditions like inflammatory bowel disease and cancer. Now, researchers may have found a way to deliver the treatment safely in a foam

By Grace Wade

Carbon monoxide foam delivered via the rectum can reduce inflammation and speed tissue recovery in mice and rats.

The colourless, odourless gas is most widely known as a dangerous poison, capable of causing coma, convulsions and eventually death when it reaches concentrations of 50 per cent or more in the blood.

But it isn’t always harmful. Our bodies actually produce small amounts routinely, and about 20 years ago, Leo Otterbein at Harvard Medical School noticed that production ramps up when we are sick.

Since then, several studies, mostly in animals, have found that low doses of carbon monoxide can help treat conditions such as cardiovascular disease and even cancer, primarily by reducing inflammation.

The challenge, though, is developing a safe and effective way to administer it. Dosing and safe storage can be problematic with delivery methods such as inhalation and infusion.

Now, it turns out whipping the gas into a foam may do the trick.

“We wanted to try an approach that was really out of the box,” says James Byrne at the University of Iowa Health Care, a co-author of the new study along with Otterbein and Giovanni Traverso at the Massachusetts Institute of Technology. “So, we looked to molecular gastronomy and what they’ve done in terms of pushing the physical boundaries of food,” he says.

The researchers placed ingredients commonly found in processed foods, like xanthan gum, inside pressurised vessels containing carbon monoxide. They then entrapped the gas inside these materials by whipping them at high speeds. The resulting concoction looks like a dollop of frothed milk. Since all the materials are food grade and the concentration of carbon monoxide is very low, there are no risks of handling the material, Byrne says.

Next, they inserted the foam into the rectums of about 40 mice and rats with symptoms of one of three conditions: inflammatory bowel disease, radiation-induced gut damage or liver failure related to an overdose of acetaminophen. Across all three, the treated rodents had significant reductions in inflammation and tissue injury compared with those given a control foam or no treatment at all.

The benefits seen in the liver indicate that once the carbon monoxide is released from the foam, it enters the bloodstream where it can access other organs, says Otterbein. This means the foam could potentially treat a wide range of conditions like cardiovascular, kidney or lung diseases.

“I don’t know if there is another foam out there used to deliver therapeutic gases,” says Traverso. “This opens up a whole new way of how we think about therapeutics.”

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.abl4135

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