Dysbiosis-Driven Reprogramming of Secondary Bile Acid Metabolism in Metabolic Dysfunction-Associated Steatotic Liver Disease: Insights from an <i>Ex Vivo</i> Human Fecal Microbiota Model

Gut microbial dysbiosis-induced perturbations in bile acid (BA) metabolism are implicated in metabolic dysfunction-associated steatotic liver disease (MASLD), yet evidence remains largely associative. Using an optimized <i>ex vivo</i> fecal microbiota model, we modeled the metabolism kinetics of conjugated- and primary-BA between MASLD and healthy donors. Enzymes for known BA metabolic reactions were inferred using functional metagenomics. MASLD cultures exhibited impaired deconjugation capacity but preserved downstream primary-BA clearance and demonstrated a substrate-independent shift that favored oxidative metabolism over 7α-dehydroxylation. This was marked by increased formation clearance of 7-keto-deoxycholic acid (175%) and 3-oxo-cholic acid (51.7%) from cholic acid (CA) and 7-keto-lithocholic acid (77.9%) from chenodeoxycholic acid (CDCA). C7-oxidized BA constituted the major proportion of total BA clearance (CA = 56.0%, CDCA = 72.3%) in MASLD cultures. Enrichment of C3- and C7-hydroxysteroid dehydrogenases in MASLD compared to control corroborated the differential secondary BA profiles. Together, microbes catalyzing C7-oxidation warrants further investigation as potential pharmacological targets of MASLD.