A Stable Isotope Tracing Primer for the Mass Spectrometrist.

Metabolic function plays a key role in our understanding of both biological and pathophysiological processes. Metabolism is a complex combination of intrinsic processes and environmental cues across a heterogeneous mix of cell types. To investigate metabolism, stable isotope tracing is a versatile approach to assess metabolism across scales, including in cultured cells, animal models, and humans. From the first tracing studies over a century ago, the development and utility of these studies have gone hand-in-hand with technological advances in detecting these labeled atoms, particularly with mass spectrometry. In this review, we describe the instrumentation used to measure isotopically labeled metabolites and approaches to analyze and interpret stable isotope tracing data, and discuss current challenges and opportunities for discovery with these methods.