In 1848, Germany’s Heinrich Otto Wieland discovered and investigated the role of bile acids in the human body. In 1927, Wieland was recognized for those efforts with a Nobel Prize in Chemistry. Our knowledge of bile has remained essentially unchanged since then, however—that is, until now. Robert Quinn, a biochemistry professor at Michigan State University, has published a new study that will literally rewrite the textbook on the chemistry of bile acids.
Quinn and his team have identified a hidden pool of unique bile acids that have never been detected before.
“These bile acids are made by the microbiome,” Quinn told Laboratory Equipment. “For over 170 years, we thought that mammalian bile acids were only conjugated with the amino acids glycine or taurine. A convention that has seen little challenge in the extensive bile literature through that time. In this paper, we show that microbes in our guts conjugate our bile acids with other amino acids, which totally changes our understanding of the chemistry of mammalian bile.”
While the largest implication of these findings falls on the microbiome—and personalized medicine by extension—the research also affects what we know, and don’t know, about human digestion. According to Quinn, it is very likely that these new compounds contribute to the metabolism of dietary fat. Bile acids are designed by nature as detergents—they help emulsify digested fats to facilitate their uptake into the bloodstream for use as energy.
The new molecules are likely to perform the same function, but they do display different properties than conventional bile produced in the liver. Quinn hypothesizes that the different amino acids may contribute to different solubilization efficiencies of fat particles; but there is still an immense amount of research left to understand their functional role in the human gut.
Moreover, Quinn’s research especially contributes to an ever-growing body of knowledge supporting the importance of the microbiome, the collective community of bacteria and other microorganisms living in human guts. Recently, microbiomes have been linked to overall human wellness, affecting everything from diabetes to depression and autism. In line with this, Quinn found the new bile acids particularly abundant in the guts of those suffering with gastrointestinal diseases, such as Crohn's disease and cystic fibrosis.
“We know that some bile acids inhibit the growth of the pathogen Clostridium difficile, for example, which can cause horrible infections and even death,” Quinn said. “We are very interested in how these compounds may affect that bacterium and many others in the gut. Bile acids are inherently antimicrobial, as such, they are a major mediator of which bacteria can exist in your microbiome. How these molecules may also impact the structure and function of other bacteria in our gut is of major interest.”
Importantly, in their study, Quinn and his team confirmed there are most certainly therapeutic implications for the discovery of these new bile molecules.
“Bile acids are some of the most abundant compounds in the human gut,” Quinn said. “We now realize that we were missing a major part of the story of bile. The implications for future research on these molecules are almost limitless.”