Ex vivo metabolism kinetics of primary to secondary bile acids via a physiologically relevant human faecal microbiota model

• Published in: Chemico-biological interactions Vol. 399; p. 111140
• Main Authors: Ng, Daniel Zhi Wei, Low, Adrian, Tan, Amanda Jia Hui, Ong, Jia Hui, Kwa, Wit Thun, Lee, Jonathan Wei Jie, Chan, Eric Chun Yong
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 25.08.2024
• Subjects: Chenodeoxycholic acid; Cholic acid; Ex vivo faecal microbiota model; Gut microbiome; Hyocholic acid; Hyodeoxycholic acid; Cholic acid; Chenodeoxycholic acid; Hyocholic acid; Gut microbiome; Ex vivo faecal microbiota model; Hyodeoxycholic acid
• ISSN: 0009-2797; 1872-7786; 1872-7786
• DOI: 10.1016/j.cbi.2024.111140

Bile acids (BA) are synthesized in the human liver and undergo metabolism by host gut bacteria. In diseased states, gut microbial dysbiosis may lead to high primary unconjugated BA concentrations and significant perturbations to secondary BA. Hence, it is important to understand the microbial-mediated formation kinetics of secondary bile acids using physiologically relevant ex vivo human faecal microbiota models. Here, we optimized an ex vivo human faecal microbiota model to recapitulate the metabolic kinetics of primary unconjugated BA and applied it to investigate the formation kinetics of novel secondary BA metabolites and their sequential pathways. We demonstrated (1) first-order depletion of primary BA, cholic acid (CA) and chenodeoxycholic acid (CDCA), under non-saturable conditions and (2) saturable Michaelis-Menten kinetics for secondary BA metabolite formation with increasing substrate concentration. Notably, relatively lower Michaelis constants (Km) were associated with the formation of deoxycholic acid (DCA, 14.3 μM) and lithocholic acid (LCA, 140 μM) versus 3-oxo CA (>1000 μM), 7-keto DCA (443 μM) and 7-keto LCA (>1000 μM), thereby recapitulating clinically observed saturation of 7α-dehydroxylation relative to oxidation of primary BA. Congruently, metagenomics revealed higher relative abundance of functional genes related to the oxidation pathway as compared to the 7α-dehydroxylation pathway. In addition, we demonstrated gut microbial-mediated hyocholic acid (HCA) and hyodeoxycholic acid (HDCA) formation from CDCA. In conclusion, we optimized a physiologically relevant ex vivo human faecal microbiota model to investigate gut microbial-mediated metabolism of primary BA and present a novel gut microbial-catalysed two-step pathway from CDCA to HCA and, subsequently, HDCA. [Display omitted] •Ex vivo human faecal model for primary bile acid (BA) metabolism was optimized.•Concentration-dependent formation kinetics of secondary BA were recapitulated.•Novel gut microbial metabolism of chenodeoxycholic acid to 6α-hydroxylated BA.