In vivo detection of metabolic H-incorporation upon ingestion of HO

Objective:The aim of this work was to explore the feasibility of in vivo and non-invasive monitoring of deuterium/hydrogen (H/H) exchange at the metabolic level upon exposure to heavy water (HO).Methods:The healthy female mice were randomly assigned to two groups after day 0 when both mice received standard drinking water. The treated mouse was fed with HO (80%, v/v) and the control mouse fed with standard drinking water (HO) over next 13 days. Real-time mass spectrometric analysis of volatile metabolism emitted through breathing and the skin was performed on days 1, 2, 3, 10, 12, and 13. Animal experiment was approved by the Laboratory Animal Ethics Committee of Jinan University (approval No. 20161117163322) on October 29, 2021.Results:We observed a replacement of HbyH in 52 mass spectral features (60 H/ H isotopologue pairs) for the mouse fed with HO, but not for the control mouse. These included pyruvic acid and lactic acid, lysine and methyl-lysine as well as short-chain fatty acids comprising acetic acid, propionic acid, butyric acid and valeric acid.Conclusion:Secondary electrospray ionization-high resolution mass spectrometry allows monitoring in vivoH-incorporation of metabolites in a non-invasive and real-time setup and opens new opportunities to use H tracing to extend current metabolic studies, especially those with a focus on anaerobic glycolysis, lysine methylation and gut microbiome via monitoring of short-chain fatty acids.