In Vivo Ultraslow MAS ²H/¹³C NMR Emphasizes Metabolites in Dynamic Flux

NMR spectroscopy is a powerful tool for metabolite screening, and owing to its noninvasive nature, it can be applied in vivo. However, the magnetic susceptibility mismatches within the intact organisms, lead to broad signals and loss of spectral information. Magic-angle spinning (MAS) is the most robust way to reduce these distortions, enhancing line shapes and providing a wealth of metabolic information, in vivo. Unfortunately, mainly due to overlapping water sidebands, relatively fast spinning is required (∼2500 Hz), which induces stress on the organism, leading to mortality within a relatively short time frame. Here, a novel approach is introduced utilizing 2H/13C isotopic enrichment that demonstrates the following advantages. (1) 2H is a quadrupolar nucleus; hence, in 2H/13C two-dimensional (2D) NMR only the most dynamic molecules (mobile metabolites) are observed in vivo, whereas structural components are broadened beyond detection. In turn, this results in a well-resolved and unique window into the dynamic metabolite pool that includes newly released or synthesized molecules correlated to a biological response/process. (2) 2H shares the same chemical shift window as 1H, making assignment relatively easy. (3) 2H detection reduces problems associated with the water peak, and as the dynamic molecules are selectively detected, no sidebands are observed. (4) As such, samples can be spun slowly (50 Hz), reducing the stress and increasing 100% survivability to 24 h for Daphnia magna and 48 h for Hyalella azteca. To our knowledge, this represents the only MAS-based NMR approach that can provide high-resolution 2D NMR in vivo metabolic fingerprint at slow spinning rates