You Are What You Smoke
Written by Sarena Yang
Edited by Priya Ram
February 9th, 2023
Edited by Priya Ram
February 9th, 2023
Research
Our intestines play such an important role in our everyday lives – they provide us with nutrients and digest our food. Unfortunately, a common type of cancer can occur in the intestines, specifically in the colon and the rectum. Colorectal cancer (CRC) is when cells in the colon or rectum grow out of control (What Is Colorectal Cancer?). It typically begins as harmless growths called polyps; however, in certain cases they can grow uncontrollably (What Is Colorectal Cancer?). Certain genetic factors and lifestyle choices increase risk for CRC, including lack of regular exercise, a diet low in fiber or fruit, heavy alcohol usage, and smoking (What Is Colorectal Cancer?). Previous research has shown that CRC, and more specifically cigarette smoking, is associated with an altered gut microbiome (Yu et al.). Bai et al. seeks to discover the mechanism behind how cigarette smoking promotes CRC.
In this study, Bai et al. performed experiments on mice which are model organisms whose genetics can be easily manipulated. Typical first-hand or second-hand smoking conditions were simulated by exposing them to cigarette smoke for 2 hours a day. The control group were in clean air conditions with no exposure to cigarette smoke. Their experiment spanned over 28 weeks and in the end they studied the mice’s tumor number and size, their gut microbiota, and more.
At the end of the experiment, they found that the cigarette smoke-exposed mice had significantly larger colorectal tumor size and a higher number of tumors (Bai et al.). Not only that, but the growth of the epithelial cells that line the colon increased significantly. When studying the stool of the mice to learn more about their gut microbiota, they found that 20 bacterial strains experienced significant changes in population (Bai et al.). There are both beneficial and harmful bacteria that live in the colon. The researchers found that the harmful bacteria, E. lenta, increased. E. lenta participates in bile acid synthesis, and an overabundance can contribute to tumor growth. In addition, the beneficial bacteria Lactobacillus decreased. This bacteria plays a role in suppressing infection of the gut with pathogenic bacteria. The increase of harmful bacteria and decrease in beneficial bacteria in the microbiome caused by smoking may contribute to tumor growth in CRC (Bai et al.).
Bai et al. was able to learn more about how the gut microbiota plays a role in tumor growth when exposed to cigarette smoking. In the future, researchers may investigate whether cessation of smoking can be beneficial in once again balancing the gut microbiome, and lowering risk for CRC.