Cigarette smoke changes the gut microbiome

When we talk about smoking cigarettes, we usually discuss the harmful effects that it has on our lungs, mouth, skin, and other parts of the body. However, we don't often talk about the gut even though cigarette smoke is the best-known environmental risk factor for Inflammatory bowel diseases (IBD), Crohn’s disease and ulcerative colitis.  While the exact mechanism for why people get these diseases is not yet known, it is recognized that a dysbiosis of the gut plays a contributing role to the onset of these conditions. A research team in Germany investigated the effects that cigarette smoke exposure had on the mucus layer and the microbes in the gut.

The scientists exposed mice to cigarette smoke or air for a period of 24 weeks. They found there was a shift in the microbial community in the caecum and distal colon after exposure to smoke. Specifically, there was an increase in Lachnospiraceae in the colon however it remained the same in the ileum, the last part of the small intestine.

They also found that smoke exposure led to changes in mucin exposure. Mucin is a type of protein that is known for producing gels that act to lubricate and protect parts of the body, both internal and external. The most common mucins are Muc2, Muc3, and Muc4. Muc2 for example is a protein that is secreted onto the mucosal surfaces of the large intestine and serves as a protective barrier for the epithelium. In this study, they found that Muc2, Muc3, and Muc4 gene expression was altered after cigarette smoke exposure.

The authors hypothesize that cigarette smoke affects the immune system in the ileum and may lead to the inflammation associated with Crohn’s disease. Overall, this study found that exposure to cigarette smoke had a profound effect on the gut bacteria and mucin composition in the mouse. While this was not done in humans, the same effects would likely be seen.

Asthma, COPD, and the Microbiome

Asthma and chronic obstructive pulmonary disease (COPD) are both illnesses that are caused by chronic inflammation of the respiratory tract, and recent research suggests that the microbiota of the lower respiratory tract may influence the development of these two diseases.  The upper respiratory tract, though, remained unstudied, until a new article was recently published in PLoS ONE.  This article characterized the microbiome of the oropharynx (in the upper respiratory tract) to discover the association between these problems and the microbiome.

Samples were swabbed from the oropharynx of patients who were recently diagnosed with asthma and COPD, as well as from a healthy control group.  Researchers performed 16S rRNA gene sequencing of the bacteria collected from the patients, in order to determine which bacteria were present. They found that there are few differences in microbiome diversity between asthma and COPD patients, however there was a prevalent presence of the bacteria Lactobacillus (phylum Firmicutes) and Pseudomonas (phylum Proteobacteria) in both, which were identified in only very small amounts in healthy patients. On the contrary, the upper respiratory tract of healthy individuals was found to be dominated by Streptococcus, Veillonella, Prevotella, and Neisseria, from the phylum Bacteroidetes, compared to individuals with asthma and COPD.

This study showed distinct differences in the microbiomes of diseased and healthy individuals.  The researchers also note that the low abundance of Neisseria they observed in this study has also been seen in studies of smokers, meaning that this bacteria may be important to respiratory health.  Further work is still needed, though, to determine if the bacteria identified in this study are contributing to the diseased individuals.  Even if they are not, they could still potentially be used in diagnosis.