Fig. 3
From: Bridging the gap between non-targeted stable isotope labeling and metabolic flux analysis
Effects of different oxygen levels on MIDs and metabolic fluxes in lung cancer cells fed with [1,2-13C2]glucose or [U-13C]glutamine. In total, 73 compounds were detected as isotopically enriched under at least one experimental condition. a Compounds with the highest variation in relative mass isotopomer abundances. Non-targeted analysis revealed that the MIDs of citric acid cycle-associated metabolites and an unidentified compound were most affected by changes in oxygen levels. Arrows indicate the mass isotopomers abundances with the highest variation. Unidentified compounds are named by their chromatographic retention index (RI). n.d.: not determinable. See also Additional file 1: Table S3. b Simplified model of how these strong changes in MIDs at low oxygen can be explained by the relative reduction of PDH flux and inversion of IDH flux directionality (see text). c NAA 2TMS can be used as a proxy to determine acetyl-CoA labeling under isotopic steady state conditions. Mass spectrometric fragmentation of NAA 2TMS allows to deconvolute the MIDs of the acetyl- and aspartyl-moiety (see also Additional file 1: Figure S5). Isotopic enrichment of the acetyl-moiety reflects changes in carbon origin of the acetyl-CoA pool from which NAA was synthesized. Contribution from [U-13C]glutamine (blue) or [1,2-13C2]glucose (red) as well as their summed contribution (grey) across different oxygen levels are shown. Enrichment was corrected for the applied tracer ratio and partial labeling in the case of [1,2-13C2]glucose. Data are represented as mean ±SD (3≤n≤4). Abbreviations: IDH/PDH isocitrate/pyruvate dehydrogenase, ACLY ATP-dependent citrate lyase, CS citrate synthase, Glc glucose, Pyr pyruvate, AcCoA acetyl-coenzyme A, Cit citrate, OAA oxaloacetate, Mal malate, NAA N-acetylaspartate