As researchers learn more about the gut microbiome, they have focused attention on the interactions between the individual bacteria, the body, and immunity. Researchers recently published work in Science sharing findings of a connection between the gut microbiome and liver tumor growth.
The gut microbiome, or gut microbiota, describes the diverse environment of microorganisms in the human and animal digestive tract. Many studies have looked at the connections between the gut microbiome and human health and disease. Its role is critical for human metabolism and affects nutrition, physiology and immune function. It is widely accepted that there are hundreds of different species of bacteria that can make up an individual’s gut microbiota; in fact, at least a third are shared amongst a majority of people with the other two thirds being unique to each individual. Our individual gut microbiome is like a fingerprint on the inside.
The murine study published in Science focused on the effects of antibiotics and gut microbiota in the presence of liver tumors. The group used three different liver cancer types and reduced gastrointestinal bacteria with a combination of antibiotics. The researchers found that by treating mice with liver tumors with antibiotics, they decreased particular bacteria and in turn, changed the make-up of immune cells in the liver. The decreased number of bacteria induced an increase in natural killer T-cells which actually shrunk the liver tumors and acted as tumor suppressors. In exploring this finding, the researchers determined that the accumulation of natural killer cells in the liver occurred due to increased expression of CXCL16, a protein found on the lining cells of liver capillaries. In examining the role of CXCL16, the protein expression patterns were regulated by bile acids. Increasing bile acids in mice changed the number of natural killer cells found in the liver and, therefore, could decrease the number of tumors in the liver.
The last connection made in this publication was that one specific bacterial species in the mouse microbiome controls metabolism of bile acids. Clostridium scindens moderates CXCL16 expression, affects natural killer cell presence, and tumor cell growth within the environment of the liver.
The authors recognize that these results are just the beginning but lay the groundwork for future discoveries connecting the gut microbiome to key processes in our bodies that are, as of yet, unknown.