Harnessing ¹³C-labeled myo-inositol to interrogate inositol phosphate messengers by NMR

Inositol poly- and pyrophosphates (InsPs and PP-InsPs) are an important group of metabolites and mediate a wide range of processes in eukaryotic cells. To elucidate the functions of these molecules, robust techniques for the characterization of inositol phosphate metabolism are required, both at the biochemical and the cellular level. Here, a new tool-set is reported, which employs uniformly ¹³C-labeled compounds ([¹³C₆]myo-inositol, [¹³C₆]InsP₅, [¹³C₆]InsP₆, and [¹³C₆]5PP-InsP₅), in combination with commonly accessible NMR technology. This approach permitted the detection and quantification of InsPs and PP-InsPs within complex mixtures and at physiological concentrations. Specifically, the enzymatic activity of IP6K1 could be monitored in vitro in real time. Metabolic labeling of mammalian cells with [¹³C₆]myo-inositol enabled the analysis of cellular pools of InsPs and PP-InsPs, and uncovered high concentrations of 5PP-InsP₅ in HCT116 cells, especially in response to genetic and pharmacological perturbation. The reported method greatly facilitates the analysis of this otherwise spectroscopically silent group of molecules, and holds great promise to comprehensively analyze inositol-based signaling molecules under normal and pathological conditions.