Many imaging methods have been proposed to act as surrogate markers of organ damage, yet for many candidates the essential biomarkers characteristics of the injured organ have not yet been described. Hyperpolarized [1-13C]pyruvate allows real time monitoring of metabolism in vivo. ParaHydrogen Induced Polarization (PHIP) is a portable, cost effective technique able to generate 13C MR hyperpolarized molecules within seconds. The introduction of the Side Arm Hydrogenation (SAH) strategy offered a way to widen the field of PHIP generated systems and to make this approach competitive with the currently applied dissolution-DNP (Dynamic Nuclear Polarization) method. Herein, we describe the first in vivo metabolic imaging study using the PHIP-SAH hyperpolarized [1-13C]pyruvate. In vivo maps of pyruvate and of its metabolic product lactate have been acquired on a 1 T MRI scanner. By comparing pyruvate/lactate 13C label exchange rate in a mouse model of dilated cardiomyopathy, it has been found that the metabolic dysfunction occurring in the cardiac muscle of the diseased mice can be detected well before the disease can be assessed by echocardiographic investigations.

Hyperpolarization of (13)C carboxylate signals of metabolically relevant molecules, such as acetate and pyruvate, was recently obtained by means of ParaHydrogen Induced Polarization by Side Arm Hydrogenation (PHIP-SAH). This method relies on functionalization of the carboxylic acid with an unsaturated alcohol (side arm), hydrogenation of the unsaturated alcohol using parahydrogen, and polarization transfer to the target (13)C signal. In this case, parahydrogen protons are added three to four bonds away from the target (13)C nucleus, while biologically relevant molecules had been hyperpolarized, using parahydrogen, through hydrogenation of an unsaturated bond adjacent to the target (13)C signal. The herein reported results show that the same polarization level can be obtained on the (13)C carboxylate signal of an ester by means of addition of parahydrogen to the acidic or to the alcoholic moiety and successive application of magnetic field cycle (MFC). Experimental results are supported by calculations that allow one to predict that, upon accurate control of magnetic field strength and speed of the passages, more than 20% polarization can be achieved on the (13)C-carboxylate resonance of the esters by means of side arm hydrogenation and MFC.

Cell‐tracking experiments by MRI are possible with a novel class of Tb and Eu paramagnetic imaging agents, with which contrast is generated upon irradiation at a specific frequency (see picture). Middle: A) unlabeled; B) Tb‐labeled; C) Eu‐labeled; D) Tb‐ and Eu‐labeled cells. Left: irradiation at ±180 kHz (Tb‐agent‐specific). Right: irradiation at ±15 kHz (Eu‐agent‐specific).

The use of [1-C]pyruvate, hyperpolarized by dissolution-Dynamic Nuclear Polarization (d-DNP), in in vivo metabolic studies has developed quickly, thanks to the imaging probe's diagnostic relevance. Nevertheless, the cost of a d-DNP polarizer is quite high and the speed of hyperpolarization process is relatively slow, meaning that its use is limited to few research laboratories. ParaHydrogen Induced Polarization Side Arm Hydrogenation (PHIP-SAH) (Reineri et al., 2015) is a cost effective and easy-to-handle method that produces C-MR hyperpolarization in [1-C]pyruvate and other metabolites. This work aims to identify the main determinants of the hyperpolarization levels observed in C13-pyruvate using this method. By dissecting the various steps of the PHIP-SAH procedure, it has been possible to assess the role of several experimental parameters whose optimization must be pursued if this method is to be made suitable for future translational steps. The search for possible solutions has led to improvements in the polarization of sodium [1-C]pyruvate from 2% to 5%. Moreover, these results suggest that observed polarization levels could be increased considerably by an automatized procedure which would reduce the time required for the work-up passages that are currently carried out manually. The results reported herein mean that the attainment of polarization levels suitable for the metabolic imaging applications of these hyperpolarized substrates show significant promise.

Hyperpolarized fumarate can be used as a probe of real-time metabolism in vivo, using carbon-13 magnetic resonance imaging. Dissolution dynamic nuclear polarization is commonly used to produce hyperpolarized fumarate, but a cheaper and faster alternative is to produce hyperpolarized fumarate via PHIP (parahydrogen induced polarization). In this work we trans-hydrogenate [1-13 C]acetylene dicarboxylate with para-enriched hydrogen using a commercially available Ru catalyst in water to produce hyperpolarized [1-13 C]fumarate. We show that fumarate is produced in 89% yield, with succinate as a side product in 11% yield. The proton polarization is converted into 13 C magnetization using a constant adiabaticity field cycle, and a polarization level of 25% is achieved using 86% para-enriched hydrogen gas. We inject the hyperpolarized [1-13 C]fumarate into cell suspensions and track the metabolism. This work opens the path to greatly accelerated preclinical studies using fumarate as a biomarker.

Abstract:Hyperpolarization of the 13C magnetic resonance signal of L-[1-13C]Lactate has been obtained using the chemically based, cost-effective method named ParaHydrogen Induced Polarization by means of Side Arm Hydrogenation (PHIP-SAH). Two ester derivatives of lactate have been tested and the factors that determine the polarization level on the product have been investigated into details. The metabolic conversion of hyperpolarized L-[1-13C]Lactate into Pyruvate has been observed in vitro using lactate dehydrogenase (LDH) and in a cells lysate. From the acquisition of a series of 13C-NMR spectra, the metabolic build-up of the [1-13C]Pyruvate signal has been observed. These studies demonstrate that, even if the experimental set-up used for these PHIP-SAH hyperpolarization studies is still far from optimal, the attained polarization level is already sufficient to carry out in vitro metabolic studies.Author Comments: Dear editor, enclosed please find the manuscript entitled "13C-MR Hyperpolarization of Lactate using ParaHydrogen and metabolic transformation in vitro " to be considered for publication in Chemistry, a European Journal. A previous version of the manuscript had been submitted to this journal and one of the two referees evaluated it a highly important manuscript, while the other considered it too specialized for publication, than the manuscript was rejected. Nevertheless, the editor suggested that an appropriately supplemented manuscript should be reconsidered.Here is submitted a deeply revised version of the manuscript. New experiments have been added, in accordance with the reviewers' suggestions, and new results have been obtained. The whole text has been extensively edited and integrated. We hope that, with the integration of the new results, the manuscript will be considered worth of publication in Chemistry. C]Pyruvate signal has been observed. These studies demonstrate that, even if the experimental set-up used for these PHIP-SAH hyperpolarization studies is still far from optimal, the attained polarization level is already sufficient to carry out in vitro metabolic studies. Yours sincerely Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation

The kinetics of metabolic processes can be assessed, in real time by means of MR hyperpolarized (HP) metabolites. [1‐13C]pyruvate, hyperpolarized by means of d‐DNP, is, by far, the substrate most widely applied to the investigation of several pathologies characterized by deregulated glycolytic metabolic networks, including cancer. Hyperpolarization of [1‐13C]pyruvate by means of the cost effective, fast and easy to handle PHIP‐SAH (para‐hydrogen induced polarization‐side arm hydrogenation) method opens‐up a pathway for the application of HP metabolites to a wide range of cancer‐related studies. Herein, we report the first application of PHIP‐SAH hyperpolarized [1‐13C]pyruvate in the investigation of upregulated glycolysis in two murine breast cancer cell lines (168FARN and 4T1). The results obtained using HP pyruvate have been validated with a conventional biochemical assay and are coherent with previously‐reported lactate dehydrogenase activity measured in those cells.

Honey, I shrunk the …︁ The chemical shift of intraliposomal water protons of LIPOCEST MRI agents may be enhanced by exploiting a contribution arising from bulk magnetic susceptibility. The effect was attained by osmotically shrinking liposomes to attain nonspherical compartments, with the largest shifts observed for systems containing paramagnetic Tm or Dy complexes either entrapped in the inner cavity or incorporated in the liposome membrane (see picture).