Issue 6, 2016

Simultaneous tracing of carbon and nitrogen isotopes in human cells


Stable isotope tracing is a powerful method for interrogating metabolic enzyme activities across the metabolic network of living cells. However, most studies of mammalian cells have used 13C-labeled tracers only and focused on reactions in central carbon metabolism. Cellular metabolism, however, involves other biologically important elements, including nitrogen, hydrogen, oxygen, phosphate and sulfur. Tracing stable isotopes of such elements may help shed light on poorly understood metabolic pathways. Here, we demonstrate the use of high-resolution mass spectrometry to simultaneously trace carbon and nitrogen metabolism in human cells cultured with 13C- and 15N-labeled glucose and glutamine. To facilitate interpretation of the complex isotopomer data generated, we extend current methods for metabolic flux analysis to handle multivariate mass isotopomer distributions (MMIDs). We find that observed MMIDs are broadly consistent with known biochemical pathways. Whereas measured 13C MIDs were informative for central carbon metabolism, 15N isotopes provided evidence for nitrogen-carrying reactions in amino acid and nucleotide metabolism. This computational and experimental methodology expands the scope of metabolic flux analysis beyond carbon metabolism, and may prove important to understanding metabolic phenotypes in health and disease.

Graphical abstract: Simultaneous tracing of carbon and nitrogen isotopes in human cells

Supplementary files

Article information

Article type
05 Jan 2016
12 Apr 2016
First published
13 Apr 2016
This article is Open Access
Creative Commons BY license

Mol. BioSyst., 2016,12, 1929-1937

Author version available

Simultaneous tracing of carbon and nitrogen isotopes in human cells

R. Nilsson and M. Jain, Mol. BioSyst., 2016, 12, 1929 DOI: 10.1039/C6MB00009F

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