Breath water-based doubly labelled water method for the noninvasive determination of CO production and energy expenditure in mice.

We explored a novel doubly labelled water (DLW) method based on breath water (BW-DLW) in mice to determine whole body CO production and energy expenditure noninvasively. The BW-DLW method was compared to the DLW based on blood plasma. Mice (n = 11, 43.5 ± 4.6 g body mass (BM)) were administered orally a single bolus of doubly labelled water (1.2 g HO kg BM and 0.4 g HO kg BM, 99 atom% (AP) O or H). To sample breath water, the mice were placed into a respiration vessel. The exhaled water vapour was condensed in a cold-trap. The isotope enrichments of breath water were compared with plasma samples. The H/H and O/O isotope ratios were measured by means of isotope ratio mass spectrometry. The CO production (RCO) was calculated from the H and O enrichments in breath water and plasma over 5 days. The isotope enrichments of breath water vs. plasma were correlated (R = 0.89 for H and 0.95 for O) linearly. The RCO determined based on breath water and plasma was not different (113.2 ± 12.7 vs. 111.4 ± 11.0 mmol d), respectively. In conclusion, the novel BW-DLW method is appropriate to obtain reliable estimates of RCO avoiding blood sampling.