Gut Check

Bile acids long have been known to play a role in human metabolism. Synthesized from cholesterol in the liver, bile acids are involved in digestive processes, particularly in absorbing fat. They also are modified by bacteria, which greatly expand the types of bile acids found in the host.

Deploying new technologies, a team led by Penn State researchers has uncovered the mechanism by which bacteria generate a wide variety of new bile acid species, the functions of which are not yet clear. The findings in some ways "upend" a century of thinking in the field, the scientists said.

The researchers, who published their results recently in Nature, identified a new role for an old bacterial enzyme known as bile salt hydrolase, or BSH. They found that the enzyme modifies human- and mouse-generated bile acids and changes their configurations by, for example, adding amino acids, leading to new molecules known as bacteria bile acid amidates, or BBAAs.

The team also showed, for the first time, that these BBAAs are made in humans at birth, coinciding with the establishment of the gut microbiome in newborns.

"The influence of bile acids on health and disease is well established," said corresponding author Andrew Patterson, professor of molecular toxicology and the John T. and Paige S. Smith Professor in the College of Agricultural Sciences. "But now we're finding that they can serve as signaling molecules between us and our microbial counterparts. It's like a communication network between us and microbes, with bile acids being the messenger."

Although the researchers are examining the long-term implications of their study, they pointed out that BSH and bile acids have been linked with many health conditions, such as inflammatory bowel disease, some cancers and obesity. Understanding their role eventually could lead to therapies, they noted.

"Teasing out the functions of these new bile acid species opens a lot of new doors to explore," Patterson said.

—Chuck Gill