Non-invasive panel tests for gastrointestinal motility monitoring within the MARS-500 Project.

Aim: To develop an integrated approach for monitoring gastrointestinal motility and inflammation state suitable for application in long-term spaceflights.

Methods: Breath tests based on the oral administration of ¹³C-labeled or hydrogen-producing substrates followed by the detection of their metabolites (¹³CO₂ or H₂) in breath were used to measure gastrointestinal motility parameters during the 520-d spaceflight ground simulation within the MARS-500 Project. In particular, the gastric emptying rates of solid and liquid contents were evaluated by ¹³C-octanoic acid and ¹³C-acetate breath tests, respectively, whereas the orocecal transit time was assessed by an inulin H₂-breath test, which was performed simultaneously with the ¹³C-octanoic acid breath test. A ready-to-eat, standardized pre-packaged muffin containing 100 mg of ¹³C-octanoic acid was used in the ¹³C-octanoic acid breath test to avoid the extemporaneous preparation of solid meals. In addition, a cassette-type lateral flow immunoassay was employed to detect fecal calprotectin, a biomarker of intestinal inflammation. Because no items could be introduced into the simulator during the experiment, all materials and instrumentation required for test performance during the entire mission simulation had to be provided at the beginning of the experiment.

Results: The experiments planned during the simulation of a manned flight to Mars could be successfully performed by the crewmembers without any external assistance. No evident alterations (i.e., increasing or decreasing trends) in the gastric emptying rates were detected using the ¹³C-breath tests during the mission simulation, as the gastric emptying half-times were in the range of those reported for healthy subjects. In contrast to the ¹³C-breath tests, the results of the inulin H₂-breath test were difficult to interpret because of the high variability of the H₂ concentration in the breath samples, even within the same subject. This variability suggested that the H₂-breath test was strongly affected by external factors, which may have been related to the diet of the crewmembers or to environmental conditions (e.g., the accumulation of hydrogen in the simulator microenvironment). At least in closed microenvironments such as the MARS-500 simulator, ¹³C-breath tests should therefore be preferred to H₂-breath tests. Finally, the fecal calprotectin test showed significant alterations during the mission simulation: all of the crewmembers were negative for the test at the beginning of the simulation but showed various degrees of positivity in at least one of the subsequent tests, thus indicating the onset of an intestinal inflammation.

Conclusion: Breath tests, especially those ¹³C-based, proved suitable for monitoring gastrointestinal motility in the 520-d isolation experiment within MARS-500 project and can be applied in long-term spaceflights.