Directly monitoring the dynamic in vivo metabolisms of hyperpolarized ¹³C-oligopeptides

Peptides play essential roles in biological phenomena, and, thus, there is a growing interest in detecting in vivo dynamics of peptide metabolisms. Dissolution-dynamic nuclear polarization (d-DNP) is a state-of-the-art technology that can markedly enhance the sensitivity of nuclear magnetic resonance (NMR), providing metabolic and physiological information in vivo. However, the hyperpolarized state exponentially decays back to the thermal equilibrium, depending on the spin-lattice relaxation time (T₁). Because of the limitation in T₁, peptide-based DNP NMR molecular probes applicable in vivo have been limited to amino acids or dipeptides. Here, we report the direct detection of in vivo metabolic conversions of hyperpolarized ¹³C-oligopeptides. Structure-based T₁ relaxation analysis suggests that the C-terminal [1-¹³C]Gly-d₂ residue affords sufficient T₁ for biological uses, even in relatively large oligopeptides, and allowed us to develop ¹³C-β-casomorphin-5 and ¹³C-glutathione. It was found that the metabolic response and perfusion of the hyperpolarized ¹³C-glutathione in the mouse kidney were significantly altered in a model of cisplatin-induced acute kidney injury.