Gastrointestinal Bile Salt Concentrations in Healthy Adults Under Fasted and Fed Conditions: A Systematic Review and Meta-Analysis for Mechanistic Physiologically-Based Pharmacokinetic (PBPK) Modelling.

Bile salts are biosurfactants released into the intestinal lumen which play an important role in the solubilisation of fats and certain drugs. Their concentrations vary along the gastrointestinal tract (GIT). This is significant for implementation in physiologically based pharmacokinetic (PBPK) modelling to mechanistically capture drug absorption. The aims of this meta-analysis were to collate all appropriate data on intestinal bile salt concentrations in healthy adults across all GIT segments in fasted and fed states for the purpose of PBPK modelling. Terms relating to bile composition were searched in PubMed and Google Scholar from inception to May 2024. Selected studies included aspirated intestinal fluid collected via gastric tubes or colonoscopy. Results showed high variability across studies and a time-dependency for the fed state. Data were rich for the duodenum, which showed a two-fold increase for the fed state versus the fasted state within multiple studies. Peaks and troughs in bile salt concentrations along the GIT were observed for both fasted and fed states, likely due to segmental water absorption differences. The highest between subject variability was observed for the duodenum in the fasted and fed state and the fed proximal jejunum, distal ileum, and colon. The findings from this meta-analysis can be used for the purpose of PBPK modelling to capture segmental drug solubilisation and absorption in fasted and fed states. However, data are lacking under different fed conditions, especially following low-fat meals, so the impact of different fat content associated with different meals on bile salt concentrations cannot be discerned.