Altered iso- and oxo-Fecal Bile Acid Concentrations in Dogs with Chronic Enteropathy

Bile acids (BAs) are important signaling molecules in the gastrointestinal (GI) tract and are associated with health and disease in humans and animals. Intestinal bacteria transform BA through deconjugation, dehydroxylation, and epimerization reactions, producing various isoforms, many of which have not been investigated in companion animal diseases. We aimed to develop and analytically validate a novel liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the quantification of 30 BAs in dog feces, with a simple extraction procedure and on-line solid-phase extraction. Validation demonstrated good accuracy, precision, sensitivity, spiking recovery, dilution, and stability for 29 BAs. The method was applied to fecal samples from healthy dogs (H; n = 121) and dogs with chronic enteropathy (CE; n = 58). The immediate and downstream products of bacterial 7α-dehydroxylation reactions with cholic acid were lower in concentration in dogs with CE when compared to healthy dogs (deoxycholic acid, 3-oxo-deoxycholic acid, and 12-oxo-lithocholic acid; q < 0.001). Across all fecal samples, the products of hydroxysteroid dehydrogenase (including oxo- and iso-BA) made up an average of 30% of the total measured fecal BA pool (glycine-BA, 0.1%; taurine-BA, 2.2%; unconjugated BA, 53%).