Positional Enrichment by Proton Analysis (PEPA): a One-Dimensional 1H-NMR Approach for 13C Stable Isotope Tracer Studies in Metabolomics

A novel metabolomics approach for NMR-based stable isotope tracer studies called PEPA is presented, and its performance validated using human cancer cells. PEPA detects the position of carbon label in isotopically enriched metabolites and quantifies fractional enrichment by indirect determination of 13C-satellite peaks using 1D-1H-NMR spectra. In comparison with 13C-NMR, TOCSY and HSQC, PEPA improves sensitivity, accelerates the elucidation of 13C positions in labeled metabolites and the quantification of the percentage of stable isotope enrichment. Altogether, PEPA provides a novel framework for extending the high-throughput of 1H-NMR metabolic profiling to stable isotope tracing in metabolomics, facilitating and complementing the information derived from 2D-NMR experiments and expanding the range of isotopically enriched metabolites detected in cellular extracts. The study also contains data, subjected to this technique, pertaining to exonuclease domain like 2 (EXD2), a nuclear encoded gene that we have found is targeted to the mitochondria and is critical for normal metabolism.