In a recent study published in the journal Nutrients, researchers used a mouse model to examine the effects of long-term consumption of a high-fat diet in the presence and absence of electronic cigarette (e-cigarette) vapor with and without nicotine on metabolic markers, gut microbiome, body weight, and systemic inflammation levels.
Study: E-Cigarette Vapour Alters High-Fat Diet-Induced Systemic Inflammatory Responses but Has No Effect on High-Fat Diet-Induced Changes in Gut Microbiota. Image Credit: Hazem.m.kamal/Shutterstock.com
Recent research indicates that the gut microbiome and its interaction with the lungs through the gut-lung axis could play a major role in developing lung diseases.
Cigarette smoking is known to cause changes in the gut microbiota, which is linked to several chronic lung diseases. However, while there is evidence of acute lung injury due to e-cigarette use that is comparable to smoking, the understanding of the long-term effects of exposure to e-vapor with and without nicotine on the gut microbiome is low.
Another factor that alters the gut microbiota is diet, with changes in the gut microbiome due to poor diet being linked to various metabolic conditions and obesity. Results from a population-based study on e-cigarette use also showed that individuals who were overweight or obese preferred e-cigarettes over tobacco cigarettes.
The impact of a prolonged high-fat diet and exposure to e-vapor on the gut microbiome and its link to metabolic and inflammatory disorders remains less explored.
About the study
In the present study, the researchers used mice models fed a high-fat diet and standard chow as the control for ten weeks, after which they were exposed to e-vapor with or without nicotine for half an hour, twice a day for the next six weeks. Body weight measurements were taken at the onset of the experiment and every week until the endpoint.
The euthanized mice were dissected, and epididymal and retroperitoneal fat pads were weighed. Blood and serum samples were also collected to test the levels of interleukin-1β (Il-1β), tumor necrosis factor-α (TNF-α), serum triglycerides, and serum non-esterified free fatty acids.
For the microbiome analysis, deoxyribonucleic acid (DNA) analysis was conducted at the end of the study on a single fecal pellet from each mouse, and the 16s ribosomal ribonucleic acid (rRNA) gene was amplified from the extracted DNA.
A phylogenetic tree was constructed from the sequences, and the significant differences in the amplicon sequence variants were determined. Additionally, UniFrac distances were calculated to compare natural gut microbiome communities and the Shannon diversity index.
The results reported that mice fed a high-fat diet had higher circulating levels of non-esterified fatty acids and triglycerides. Fat mass and body weight decreased when the mice were exposed to e-vapor, irrespective of nicotine content.
Similarly, in the control group, where the mice were fed standard chow, fat mass, body weight, and levels of non-esterified fatty acids were seen to reduce after exposure to e-vapor containing nicotine. While exposure to e-vapor without nicotine increased the serum levels of TNF-α in mice fed on a high-fat diet, the levels of IL-1β in the serum did not change.
Furthermore, while the high-fat diet significantly impacted the alpha and beta diversity of the gut microbiome, exposure to e-vapor had no significant effect on the gut microbiome, irrespective of the diet.
In the mice in the control group, exposure to e-vapor significantly impacted the UniFrac distances, indicating the presence or absence of certain operational taxonomic units based on exposure to e-vapor. However, the differences in the relative abundances of the gut microbiota were not significantly different.
The high-fat diet was shown to increase the relative abundance of groups such as Proteobacteria and Firmicutes and decrease the abundance of Tenericutes.
The reduction in body weight demonstrated the toxicity of e-vapor exposure and an increase in the inflammatory markers in circulation in the mice fed on a high-fat diet and the mice in the control group that were fed the standard chow.
Given the results from previous studies that e-cigarette use alters the oral microbiome and the epithelial barrier in the gut, the lack of changes in the gut microbiome after exposure to e-vapor was surprising. However, the researchers noted that the dose of e-vapor used in this study was low, and exposure to higher dosage and other flavors with different compositions, the results could vary.
Overall, the findings indicated that while exposure to e-vapor, irrespective of the nicotine content, caused a reduction in body weight and increased the circulating levels of TNF-α, it did not alter the gut microbiota composition.
The authors believe that it is likely that long-term e-cigarette use might not cause significant alterations in the gut microbiota.