Real-Time Untargeted Monitoring of Intracellular Metabolism in Live Cells Using ¹ H NMR and Extracellular Signal Suppression

Nuclear magnetic resonance (NMR) spectroscopy is ideally suited for observing atomic-level phenomena in living cells. However, the measurement of intracellular signals using untargeted, highly sensitive ¹H NMR is impeded by the simultaneous detection of overwhelming signals from the extracellular media. To circumvent this limitation, we developed extracellular signal suppression (ExSS)-NMR, an in-cell NMR approach that enables the untargeted, real-time detection of intracellular ¹H NMR signals. This is primarily accomplished using a <i>T</i>₂ relaxation compound (α-Fe₂O₃ nanorods) that suppresses extracellular signals (348× at 600 MHz; 15,737× at 900 MHz) with no detectable reduction in cell viability. We present here the potential of this approach for: high temporal resolution (1 min time increments) metabolomics, mitochondrial function/dysfunction monitoring, native-state lipid droplet characterization, and xenobiotic uptake in HepG2 cells. We also report its suitability for use with adherent human cell lines established from the brain, breast, and prostate, indicating its potential for deriving novel insights from an array of cell types.