VSL#3 Co-Administration Is Associated with Altered Early-Phase Obeticholic Acid Exposure in MASLD Mice

Background/Objectives: Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most prevalent chronic liver disease, and its global incidence continues to increase. MASLD can progress from simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. However, effective preventive and therapeutic options remain limited. In this study, obeticholic acid (OCA) and the probiotic mixture VSL#3 were co-administered to a mouse model of MASLD to modulate gut microbiota and bile acid metabolism. Methods: Male C57BL/6 mice were fed a WD to induce MASLD and treated with OCA, VSL#3, or both. Gut microbiota was analyzed by 16S rRNA sequencing, bile acid (BA) composition was assessed by LC–MS/MS, hepatic and intestinal gene expression was determined by quantitative real-time PCR (qPCR) and immunohistochemistry, and unconjugated OCA pharmacokinetics (PK) were evaluated. Results: VSL#3-containing groups showed differences in selected taxa with reported bile salt hydrolase (BSH) potential and in BA composition, including a numerical shift toward higher levels of deconjugated BAs. Co-administration of OCA and VSL#3 was accompanied by lower hepatic steatosis, numerically favorable serum markers of liver injury, and lower cholesterol and total bilirubin levels. In addition, mice receiving VSL#3 showed numerically higher early plasma concentrations of unconjugated OCA. Lower intestinal ATP-binding cassette subfamily C member 2 (Abcc2) expression was also observed as a separate exploratory finding. Conclusions: The co-administration of VSL#3 with OCA was accompanied by exploratory differences in selected biological parameters and early-phase unconjugated OCA exposure. Lower intestinal Abcc2/Mrp2 expression was observed as a separate exploratory finding, and no functional relationship between intestinal transporter expression and OCA pharmacokinetics was established.