Of the cancers that affect both men and women, colorectal cancer is the third most common cancer in the United States and the second leading cause of cancer-related death. New research - published in the journal Cancer Research - suggests a very common food additive might play a role in its development.
What IBD and colorectal cancer have in common is an alteration in the gut microbiota.
An overview of recent scientific literature shows that changes in the microbiota have become increasingly associated with colorectal cancer.
This is why Dr. Emilie Viennois, assistant professor at the Georgia State University Institute for Biomedical Sciences, Atlanta, believes there might be a connection between a common food additive that alters intestinal microbiota and colorectal cancer.
"The incidence of colorectal cancer has been markedly increasing since the mid-20th century. A key feature of this disease is the presence of an altered intestinal microbiota that creates a favorable niche for tumorigenesis."
Dr. Emilie Viennois
Dr. Viennois has led a team of researchers to examine the effect of certain dietary changes in mice and cancer tumor development.
The role of intestinal microbiota in colorectal cancer
There are over 100 trillion microorganisms living in the gut, including bacteria, viruses, and fungi. The microbiota is made of the physiological interaction between the host's microorganisms and the ones introduced from the environment.
The microbiota is acquired during the first stages of life and varies with every individual. Having a diverse and balanced microbiota is crucial in keeping a healthy immune system.
Severe changes in the microbiota, either as a result of changing one's diet, lifestyle, or because of an infection, can alter the symbiotic relationship between the host microorganisms and the environmental ones, leading to IBD.
IBD promotes the formation of tumors in the colon. Low-grade inflammation, which has been associated with changes in the microbiota and metabolic disease, has also been observed in many cases of colorectal cancer.
Emulsifiers and IBD
Previous studies have hypothesized that since the mid-20th century, dietary emulsifiers might have been responsible for IBD.
Research by the team at Georgia State University research labs showed that low concentrations of two common emulsifiers - carboxymethylcellulose and polysorbate-80 - induced low-grade inflammation and obesity/metabolic syndrome in mice.
Normally the intestine is protected from a variety of harmful bacteria via the mucus structures that cover the intestines, keeping the harmful bacteria away from the epithelial cells that line the intestine.
But emulsifiers seem to help transport bacteria across epithelial cells.
Emulsifiers are detergent-like molecules added to modern processed food, and they are used to help water and oil mix, giving processed food a smooth texture.
Assessing the effects of emulsifiers in mice
A new study - led by some of the same researchers at the Institute for Biomedical Sciences at Georgia State University - hypothesized that emulsifiers affect the gut microbiota in a way that promotes colorectal cancer.
"The dramatic increase in [colorectal cancer] has occurred amidst constant human genetics, suggesting a pivotal role for an environmental factor," says Benoit Chassaing, assistant professor at the Institute for Biomedical Sciences.
The team fed mice the two most common additives have also been linked to low-grade bowel inflammation and metabolic disease: polysorbate 80 and carboxymethylcellulose.
The doses were replicated so as to mirror the proportions these emulsifiers are commonly added to human processed food.
Emulsifiers alter gut bacteria composition
Researchers found that an intake of emulsifiers severely alters the composition of the gut microbiota, and it does so in a way that promotes inflammation and creates an environment favorable for the development of cancer.
After suffering emulsifier-induced alterations, the bacteria in the gut displayed more flagellin and lipopolysaccharide. These two substances activate pro-inflammatory gene expression in the immune system.
Not only did emulsifiers alter the microbiotic environment in a way that is pro-inflammatory, but it also changed the balance between cell proliferation and cell death, which enhances tumor development.
The negative effects of consuming emulsifiers disappeared completely in mice that had no germs and therefore no microbiota. Researchers also transplanted microbiota from mice that consumed emulsifiers to germ-free mice, and this was enough to change the balance in the intestine's epithelial cells.
This further reinforces the central role that the microbiota plays in tumor induction and development.
This study demonstrates that emulsifiers induce alterations in the microbiome. These alterations are both necessary and sufficient for changing the balance in the intestinal epithelial cells.
Changes in epithelial cells are thought to cause the appearance and development of tumors.
These findings support the notion that changing the composition of gut microbiota causes low-grade inflammation in a way that promotes colorectal cancer.
The researchers are now further investigating specifically which microbiota are responsible for this effect, as well as the precise mechanism that promotes cancer.