Microbiology: Nicotine-degrading bacteria protects against smoking-related liver disease in mice

A gut bacterium capable of breaking down nicotine is identified in a Nature paper. The bacterium is also shown to protect against smoking-related fatty liver disease progression in a mouse model. The findings suggest a possible avenue for investigation to reduce the progression of some tobacco smoking-associated diseases.

Tobacco smoking is the leading cause of preventable death in the world, as described by the World Health Organization. Quitting smoking is the most effective way to extend life expectancy, but it is not easy to do because of the powerful addictive properties and withdrawal symptoms of nicotine. Smoking is associated with many diseases, including non-alcoholic fatty liver disease, which can lead to liver scarring and cancer. The underlying mechanisms between smoking and this disease remain unclear.

Frank Gonzalez and colleagues tested human stool and serum samples from 30 smokers and 30 non-smokers and found that high levels of nicotine accumulate in the gut following nicotine exposure. Similar results were observed in mouse models of nicotine exposure, and this accumulation was found to be associated with increased risk for developing non-alcoholic fatty liver disease in mice. Comparisons between germ-free mice (free of all microorganisms) and those with pre-specified gut microbiota revealed that nicotine levels were higher in germ-free mice, suggesting that specific gut bacteria might be able to regulate nicotine levels. The authors screened the microbiota of the mice in search of strains known to carry nicotine-degrading enzyme genes, and identified that the bacterium Bacteroides xylanisolvens reduced gut nicotine concentrations in mice exposed to nicotine, and reduced the severity of non-alcoholic fatty liver disease in these mice.

B. xylanisolvens is also found naturally in the human gut, but further research is required to understand the capacity of the gut microbiota to break down nicotine and prevent smoking-associated diseases in humans, the authors suggest.