Hyperpolarized Multi-organ Spectroscopy of Liver and Brain Using 1-13C-Pyruvate Enhanced via Parahydrogen

Abstract

Hyperpolarization in nuclear magnetic resonance boosts the signals by several orders of magnitude. Using the singlet spin order of parahydrogen to create large non-equilibrium spin polarization is a fast approach to obtain hyperpolarized metabolites in seconds. In recent years, it has attracted particular interest in the field of biomedicine because signal-enhanced and 13C-enriched metabolites allow for real-time metabolic investigations in combination with imaging in vivo. With this, metabolism can be traced and characterized with spatial selectivity in the body. Here, we introduce a method to use signal-enhanced metabolites to study multiple organs in separate injections to obtain real-time kinetics in vivo of these organs. Using hyperpolarized 1-13C-pyruvate, we measured the kinetics of the conversion from pyruvate to lactate in the brain and the liver of mice. This we did by injecting the hyperpolarized pyruvate two times within half an hour and using each injection to measure the spectra of one region of interest. Organ cross-talk and especially how different organs affect each other in diseases is of major interest and poorly understood, because of the high complexity of biological systems. With the proof-of-principle study provided here, we are introducing a new tool to study organ-related interaction in vivo. It allows the characterization of different organs of the same animal within half an hour, which is enabled by the fast signal enhancement achieved with parahydrogen.

Molecular precursors to produce para‐hydrogen enhanced metabolites at any field

“…Previously, we have established that the cleavage of the labile ester bond between the cinnamyl sidearm and the molecule of interest followed by a fast purification method (developed in our group) releases the hyperpolarized metabolite in neat water solutions at physiological conditions. 32,33,51 These steps for full biocompatibility have been demonstrated for pyruvate recently. 32,33,51 To synthesize the sidearm, readily available benzaldehyde 1 (CAS 100-52-7, Scheme 1) was reacted with a Grignard reagent, which was obtained by the reaction of 13 C-methyl iodide (CAS 207507-22-0) and magnesium (CAS 7439-95-4), to obtain the secondary phenetylalcohol 2.…”

“…32,33,51 These steps for full biocompatibility have been demonstrated for pyruvate recently. 32,33,51 To synthesize the sidearm, readily available benzaldehyde 1 (CAS 100-52-7, Scheme 1) was reacted with a Grignard reagent, which was obtained by the reaction of 13 C-methyl iodide (CAS 207507-22-0) and magnesium (CAS 7439-95-4), to obtain the secondary phenetylalcohol 2. Because of availability, we used deuterated 13 C-labeled methyl iodide although that is not a requirement since all the protons or deuterons are going to be removed during the subsequent steps.…”

“…The results of these experiments are depicted in Figure 1b. Previously, we have established that the cleavage of the labile ester bond between the cinnamyl sidearm and the molecule of interest followed by a fast purification method (developed in our group) releases the hyperpolarized metabolite in neat water solutions at physiological conditions 32,33,51 . These steps for full biocompatibility have been demonstrated for pyruvate recently 32,33,51 …”

“…The latter is being used daily in many clinics around the world 1 . To overcome sensitivity challenges, signal‐enhancement or hyperpolarization approaches have been devised 2–51 . One important application of hyperpolarization is the real‐time monitoring of metabolites that can be converted in vitro and in vivo 3–7 .…”

“…The yielded polarized pyruvate in solution is afterwards injected for imaging. Para‐hydrogen‐based methods are other approaches to enhance the signals of metabolites 7–51 . Foremost, the para‐hydrogen‐induced polarization approach by means of sidearm hydrogenation (PHIP‐SAH) was the first to demonstrate signal‐enhanced metabolites 22 .…”