Investigation of Storage Conditions and Quality Control Markers for Metabolites and Lipids in Human Feces

Background/Objectives: The stability of metabolites and lipids in feces varies depending on the storage temperature and duration. Methods: We examined the stability of various metabolites and lipids in human feces under 10 different storage conditions (room temperature for 2, 6, 24, and 48 h, 4 °C for 6, 24, and 48 h, -20 °C for 1 week, 2 weeks and 1 month) and explored markers useful for quality control of fecal samples, using metabolites and lipids that vary depending on temperature and time. Results: There was generally more variation at 4 °C than at -20 °C, and more at room temperature than at 4 °C, and variation also increased as the storage duration was extended under each temperature condition. Some metabolites and lipids were found to be unstable, even over short periods (2 or 6 h) at room temperature or 4 °C storage. However, storage at -20 °C generally maintained the stability of most of them for up to two weeks. Our results suggest that the following ratios can serve as useful quality control markers: methionine to S-methyl-5-thioadenosine, xanthine to inosine and N-linoleoyl leucine to 1,2-dilinoleoyl-sn-glycerol. Conclusions: For comprehensive metabolite and lipid analysis, we recommend promptly transferring samples to -80 °C storage, except when stored at -20 °C for no longer than two weeks, with checks on markers for quality control. When measuring specific metabolites or lipids, our catalog data can be consulted to determine acceptable storage conditions.