Research News

At least half of the cells in and on the human body are not human at all. Trillions of microbes (bacteria, viruses, fungi and other single-celled organisms) colonize in and on the various organs of the human body – including the skin, the gut and even the nasal cavity. These small communities form microbiomes, and their peaceful existence with each other and with the human body plays many important roles in our overall health.

The careful balance of the microbiome depends on both microbial species and quantity. In the human body, healthy microbiomes assist with development and digestion. Unbalanced microbiomes have been linked to cancer, heart disease, kidney disease, and urinary and fertility problems.

New research findings published in PLOS One by Charis Eng, MD, PhD, Chair of The Genomic Medicine Institute and of the Center for Personalized Genetic Healthcare, as well as Hardis Endowed Chair of Cancer Genomic Medicine, and Alok Khorana, MD, Director of the Gastrointestinal Cancers Program, and Hardis Endowed Chair of Oncology Research, have uncovered yet another potential link between the microbes within us and human disease – specifically within our bile tracts.

The biliary tract, also known as the pancreaticobiliary system, connects the liver to the small intestine. It includes the gallbladder, pancreas, and biliary ducts, highlighted here in yellow.

Moving away from the gut 

While the best-understood human microbiome system is the gut microbiome, or the community of microbes that live in our intestines, the microbiomes in other parts of the digestive system are still relatively unknown. 

The biliary tract, called the body's "plumbing system," is a connected group of organs and tubes that aid digestion. Any disease affecting a component of this bile pipeline, from the gallbladder to the bile ducts to the pancreas, is referred to as a pancreaticobiliary or biliary tract disease.

Due to its physical anatomy and its role in the digestive process, it was only recently discovered that this important body system actually has its own microbiome. 

Drs. Eng and Khorana led a novel study to determine whether microbes in the pancreaticobiliary (or bile) microbiome – play a role in human disease, specifically in cancer. "The majority of microbiome studies are based on the gut microbiome, represented by stool samples, or on microbes within a tumor," says Dr. Eng, "Ours is one of the more unusual studies that looks at the local environment microbiome – in this case, the bile microbiome." 

Promising findings for the future of patient care 

Physicians collected bile samples from individuals with and without different pancreaticobiliary diseases, and scientists in the Eng lab compared the bacterial genetic signatures between the different groups.

The study revealed that pancreaticobiliary microbiomes differ in healthy people and those with diseases. In addition, cancerous diseases had different microbial signatures from noncancerous diseases, and the microbiomes from people with pancreatic cancer were easily distinguishable from people with cancer of the gallbladder or bile ducts. 

The findings, Dr. Eng says, reveal one of two hypotheses: Either the microbes are causing disease, or the disease affects the microbes. Regardless, she says, more research into the bile microbiome is needed. "Depending on what's happening in the bile tract, we might be able to use the microbial signatures in bile as a diagnostic aid, or to manipulate the pancreaticobiliary microbiome to directly treat a tumor. We are very hopeful about the future."

Dr. Khorana agrees. "Diseases of the biliary tract, especially cancers like pancreatic cancer, are typically detected late and associated with poor outcomes. Learning more about the microbial communities in this system helps us better understand how diseases of the pancreas and biliary system develop, and may even someday help us intervene and prevent malignancy from occurring."