Enrichment of hepatic glycogen and plasma glucose from H₂¹⁸O informs gluconeogenic and indirect pathway fluxes in naturally feeding mice

Abstract

Deuterated water ( 2 H 2 O) is a widely used tracer of carbohydrate biosynthesis in both preclinical and clinical settings, but the significant kinetic isotope effects (KIE) of 2 H can distort metabolic information and mediate toxicity. 18 O-water (H 2 18 O) has no significant KIE and is incorporated into specific carbohydrate oxygens via well-defined mechanisms, but to date it has not been evaluated in any animal model. Mice were given H 2 18 O during overnight feeding and 18 O-enrichments of liver glycogen, triglyceride glycerol (TG), and blood glucose were quantified by 13 C NMR and mass spectrometry (MS). Enrichment of oxygens 5 and 6 relative to body water informed indirect pathway contributions from the Krebs cycle and triose phosphate sources. Compared with mice fed normal chow (NC), mice whose NC was supplemented with a fructose/glucose mix (i.e., a high sugar [HS] diet) had significantly higher indirect pathway contributions from triose phosphate sources, consistent with fructose glycogenesis. Blood glucose and liver TG 18 O-enrichments were quantified by MS. Blood glucose 18 O-enrichment was significantly higher for HS versus NC mice and was consistent with gluconeogenic fructose metabolism. TG 18 O-enrichment was extensive for both NC and HS mice, indicating a high turnover of liver triglyceride, independent Abbreviations used: 2 H 2 O, water enriched with deuterium; DBS, dried blood spot; GC-MS, gas chromatography mass spectrometry; H 2 18 O, water enriched with oxygen-18; HS, chow supplemented with fructose/glucose mix (i.e., a high sugar diet); KIE, kinetic isotope effects; LC-MS/MS, liquid chromatography coupled to tandem mass spectrometry; MAG, monoacetone glucose; NC, normal chow; TAMAG, 3,5,6-tri-O-[1-13 C]acetyl monoacetone glucose. Margarida Coelho and Rohit Mahar are joint first authors.