Microbial metabolism of mannitol as a tracer for the non-invasive measurement of oral-cecal transit

The timing of digestion after a meal reveals information essential for evaluating gastrointestinal function and overall digestive health. Alterations in transit time through the GI tract can reveal abnormalities such as delayed gastric emptying and provide critical insights into nutrient absorption dynamics. This information is particularly valuable for optimizing dietary interventions, managing metabolic conditions such as diabetes, and improving personalized nutrition strategies. Methods for measuring the oral to cecal transit time (OCTT) in murine models have significant limitations. We demonstrate a non-invasive approach in freely-moving non-anesthetized mice which quantifies the microbial digestion of the non-nutritive sweetener mannitol to CO ₂ . We monitor cage air for the production of ¹³ CO ₂ from ¹³ C-enriched mannitol using Off-Axis Integrated Cavity Output Spectroscopy integrated with multiplexes indirect calorimetry. With this approach, we find mannitol oxidation is absent in mice following commensal depletion of the microbiota. In mice with conventional microbiota, the peak ¹³ C-mannitol oxidation occurs proximal to the mouse cecum, allowing the quantitation of OCTT in mice. By tracking the output of ¹³ CO ₂ , this method provides highly granular, real-time data. We detect delayed OCTT with the use of pharmacological transit-altering compounds loperamide, a gut restricted opioid receptor agonist and also semaglutide, a GLP-1 receptor agonist. This approach may provide more physiologically relevant results in a range of genetic, environmental, and pharmacological research models.