Bile acids are amphipathic molecules synthesized from cholesterol in the liver and transported to the gut where they aid in the digestion of dietary fat. Due to their roles in gastrointestinal and human health, their identification and quantitation is essential. However, bile acids are extremely difficult to analyze due to their numerous isomers resulting from just small linkage and stereochemical changes around their steroid ring. Recently, these analytical challenges have been further compounded by the discovery of bile acid conjugates with linked amino acids beyond just glycine and taurine which were previously thought to be the only ones of importance. To address these analysis and identification challenges, we coupled liquid chromatography, ion mobility spectrometry and mass spectrometry (LC-IMS-MS) separations to analyze 176 new bile acid conjugates plus the traditional bile acids. All bile acid species studied where separable using one of the 4 measurement dimensions, however removing any one dimension resulted in identification overlap. Since there has been question of how common these bile acids are in real samples, we then created a Skyline library with all the bile acid characteristics and used it to evaluate 202 bacterial strains from the Human Microbiome Project (HMP) cultured in the presence of excess primary bile acids. From these analyses, we confirmed the microbial origin of &gt;100 bile acid species as well as phylogenetic correlations in the production of these new bile acid conjugates, confirming that the newly discovered bile acids are commonly present.

Multidimensional LC-IMS-MS Profiling Confirms Expanded Bile Acid Pool from Gut Bacteria Enzymatic Modifications

ACS Fall 2021

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