Gut bacteria may reduce harmful effects of nicotine on the liver

Smokers with a certain bacterium in their gut that breaks down nicotine have less severe liver disease, and tests in mice suggest this microbe can prevent liver damage

By Carissa Wong

Smokers with a certain bacterium in their gut had less severe liver disease

Doucefleur/Shutterstock

Altering the gut microbiome could help reduce the harmful effects of nicotine on the liver.

Previous studies suggest that smoking tobacco or using nicotine patches can lead to a build-up of nicotine in the gut, which has been linked to more severe non-alcoholic fatty liver disease. This condition can lead to liver failure due to scarring and harmful inflammation resulting from high levels of fat in the organ.

Now, research on mice has found that a gut bacterium that degrades nicotine can reduce the severity of this condition.

Frank Gonzalez and Lulu Sun at the National Institutes of Health in Maryland and their colleagues first gave water containing nicotine to six mice with gut bacteria and six mice without gut bacteria to compare how they were affected. In mice without gut bacteria, the levels of nicotine in the gut were higher than in mice with such bacteria.

Next, the team identified a species of bacterium called Bacteroides xylanisolvens that could degrade nicotine in a lab dish using an enzyme called NicX.

To see if the microbe could reduce the severity of non-alcoholic fatty liver disease, the researchers fed 12 further mice with gut bacteria a diet high in sugar and cholesterol along with water containing nicotine for 20 weeks to induce the condition. Some of the mice were also given a dose of B. xylanisolvens every three days via a tube into the stomach, and these mice had roughly half as much nicotine in their intestines.

What’s more, the livers of mice given the bacterium had less scarring and inflammation than other mice, suggesting the microbe counteracted nicotine’s harmful effects.

The researchers also analysed stool samples from 41 smokers with non-alcoholic fatty liver disease, and found that people with higher levels of B. xylanisolvens in their faeces had less severe liver disease.

Sun suggests that a probiotic containing the NicX enzyme could be developed for use in people, to decrease nicotine levels and ward off fatty liver disease.

However, more research is needed to see if this would work and it shouldn’t be seen as a way to keep smoking, says Gonzalez. “It’s very hard to actually alter the human microbiome long term, limiting such an approach,” he says.

Journal reference: Nature, DOI: 10.1038/s41586-022-05299-4

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