Tracing metabolic fluxes using mass spectrometry: Stable isotope-resolved metabolomics in health and disease

Tracing metabolic fluxes, defined as the reaction and transport rates in living cells, is essential to characterize metabolic phenotypes. One of the most informative methods to predict fluxes is stable isotope-resolved metabolomics (SIRM). In SIRM, a biological system is fed with substrates labeled with stable heavy isotopes. This isotopic label propagates along metabolic pathways and is incorporated into metabolites. After incubation, metabolites are extracted, and the incorporation of the isotopic label is quantified with isotope-sensitive analytical techniques, either mass spectrometry (MS) or nuclear magnetic resonance (NMR). Here we review the most suitable and widely-used MS platforms and methodologies for SIRM. We also provide an overview of state of the art in the analysis of SIRM data to trace metabolic fluxes, covering both local flux predictions and network-wide flux analysis. Finally, we highlight the role of SIRM in shaping our current understanding of metabolism in both health and pathological conditions.