What Exactly is Bile?

A study from Michigan State University (MSU) has shed new light on bile, an acidic body fluid that's produced in the liver and released into the intestine during food consumption. The findings were published in the journal Nature and explain how the team discovered a new strain of bile acids produced not by enzymes but by microbes in the gut.

Bile acid was first discovered in 1848 by German scientist Heinrich Otto Wieland, who was awarded a Nobel Prize in 1928 for his research into the molecular structure of the fluid. Over the following decades researchers such as Robert Quinn, lead author of the study and assistant professor of biochemistry and molecular biology at MSU, have continued to explore the properties and functions of bile.

"Since then, our understanding of the chemistry of bile production in the liver was that the cholesterol backbone of the bile acid structure is linked to the amino acids glycine or taurine to produce our primary bile acids," says Quinn. "It begs the question of how the new bile acids we've discovered have remained hidden during the last 170 years of bile acid chemical research."

New bile acids produced by gut microbes

Unlike the bile discovered by Wieland, the new bile acids are created by microbes in the gut. The study explains how the cholesterol backbone conjugates with other amino acids in the gut to exchange genetic material create unique bile acids. For Quinn and his team, the discovery unlocks new insight into how the digestive system works and highlights the importance of the gut microbiome.

"These molecules can alter signalling pathways in the human gut that result in a reduction of overall bile acid production, representing a new mechanism where our gut bacteria can manipulate our own physiology," says Quinn.

Paving the way for new gastrointestinal disease research

Levels of the new bile acids were higher in the guts of patients suffering from gastrointestinal diseases such as cystic fibrosis and Crohn's disease, suggesting the study could be used to develop new treatments. "Clearly, our understanding of these compounds is in its infancy," says Quinn. "This exciting new discovery opens more questions than answers about these compounds and their role in our health."

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