In-vitro NMR Studies of Prostate Tumor Cell Metabolism by Means of Hyperpolarized [1-13C]Pyruvate Obtained Using the PHIP-SAH Method

A continuous flow bioreactor system for high-throughput hyperpolarized metabolic flux analysis

Hyperpolarized carbon-13 labeled compounds are increasingly being used in medical MR imaging (MRI) and MR imaging (MRI) and spectroscopy (MRS) research, due to its ability to monitor tissue and cell metabolism in real-time. Although radiological biomarkers are increasingly being considered as clinical indicators, biopsies are still considered the gold standard for a large variety of indications. Bioreactor systems can play an important role in biopsy examinations because of their ability to provide a physiochemical environment that is conducive for therapeutic response monitoring ex vivo. We demonstrate here a proof-of-concept bioreactor and microcoil receive array setup that allows for ex vivo preservation and metabolic NMR spectroscopy on up to three biopsy samples simultaneously, creating an easy-to-use and robust way to simultaneously run multisample carbon-13 hyperpolarization experiments. Experiments using hyperpolarized [1-13C]pyruvate on ML-1 leukemic cells in the bioreactor setup were performed and the kinetic pyruvate-to-lactate rate constants ( k PL ) extracted. The coefficient of variation of the experimentally found k PL s for five repeated experiments was C V = 35 % . With this statistical power, treatment effects of 30%-40% change in lactate production could be easily differentiable with only a few hyperpolarization dissolutions on this setup. Furthermore, longitudinal experiments showed preservation of ML-1 cells in the bioreactor setup for at least 6 h. Rat brain tissue slices were also seen to be preserved within the bioreactor for at least 1 h. This validation serves as the basis for further optimization and upscaling of the setup, which undoubtedly has huge potential in high-throughput studies with various biomarkers and tissue types.

Structural Elucidation of Agrochemical Metabolic Transformation Products Based on Infrared Ion Spectroscopy to Improve In Silico Toxicity Assessment

Toxicological assessments of newly developed agrochemical agents consider chemical modifications and their metabolic and biotransformation products. To carry out an in silico hazard assessment, understanding the type of chemical modification and its location on the original compound can greatly enhance the reliability of the evaluation. Here, we present and apply a method based on liquid chromatography-mass spectrometry (LC-MS) enhanced with infrared ion spectroscopy (IRIS) to better delineate the molecular structures of transformation products before in silico toxicology evaluation. IRIS facilitates the recording of IR spectra directly in the mass spectrometer for features selected by retention time and mass-to-charge ratio. By utilizing quantum-chemically predicted IR spectra for candidate molecular structures, one can either derive the actual structure or significantly reduce the number of (isomeric) candidate structures. This approach can assist in making informed decisions. We apply this method to a plant growth stimulant, digeraniol sinapoyl malate (DGSM), that is currently under development. Incubation of the compound in Caco-2 and HepaRG cell lines in multiwell plates and analysis by LC-MS reveals oxidation, glucuronidation, and sulfonation metabolic products, whose structures were elucidated by IRIS and used as input for an in silico toxicology assessment. The toxicity of isomeric metabolites predicted by in silico tools was also assessed, which revealed that assigning the right metabolite structure is an important step in the overall toxicity assessment of the agrochemical. We believe this identification approach can be advantageous when specific isomers are significantly more hazardous than others and can help better understand metabolic pathways.

Enzymatic Reactions Observed with Zero- and Low-Field Nuclear Magnetic Resonance

We demonstrate that enzyme-catalyzed reactions can be observed in zero- and low-field NMR experiments by combining recent advances in parahydrogen-based hyperpolarization methods with state-of-the-art magnetometry. Specifically, we investigated two model biological processes: the conversion of fumarate into malate, which is used in vivo as a marker of cell necrosis, and the conversion of pyruvate into lactate, which is the most widely studied metabolic process in hyperpolarization-enhanced imaging. In addition to this, we constructed a microfluidic zero-field NMR setup to perform experiments on microliter-scale samples of [1-13C]fumarate in a lab-on-a-chip device. Zero- to ultralow-field (ZULF) NMR has two key advantages over high-field NMR: the signals can pass through conductive materials (e.g., metals), and line broadening from sample heterogeneity is negligible. To date, the use of ZULF NMR for process monitoring has been limited to studying hydrogenation reactions. In this work, we demonstrate this emerging analytical technique for more general reaction monitoring and compare zero- vs low-field detection.

Enhancing Cancer Diagnosis with Real-Time Feedback: Tumor Metabolism through Hyperpolarized 1-13C Pyruvate MRSI

This review article discusses the potential of hyperpolarized (HP) ¹³C magnetic resonance spectroscopic imaging (MRSI) as a noninvasive technique for identifying altered metabolism in various cancer types. Hyperpolarization significantly improves the signal-to-noise ratio for the identification of ¹³C-labeled metabolites, enabling dynamic and real-time imaging of the conversion of [1-¹³C] pyruvate to [1-¹³C] lactate and/or [1-¹³C] alanine. The technique has shown promise in identifying upregulated glycolysis in most cancers, as compared to normal cells, and detecting successful treatment responses at an earlier stage than multiparametric MRI in breast and prostate cancer patients. The review provides a concise overview of the applications of HP [1-¹³C] pyruvate MRSI in various cancer systems, highlighting its potential for use in preclinical and clinical investigations, precision medicine, and long-term studies of therapeutic response. The article also discusses emerging frontiers in the field, such as combining multiple metabolic imaging techniques with HP MRSI for a more comprehensive view of cancer metabolism, and leveraging artificial intelligence to develop real-time, actionable biomarkers for early detection, assessing aggressiveness, and interrogating the early efficacy of therapies.

Missing Pieces in Structure Puzzles: How Hyperpolarized NMR Spectroscopy Can Complement Structural Biology and Biochemistry

Structure determination lies at the heart of many biochemical research programs. However, the "giants": X-ray diffraction, electron microscopy, molecular dynamics simulations, and nuclear magnetic resonance, among others, leave quite a few dark spots on the structural pictures drawn of proteins, nucleic acids, membranes, and other biomacromolecules. For example, structural models under physiological conditions or of short-lived intermediates often remain out of reach of the established experimental methods. This account frames the possibility of including hyperpolarized, that is, dramatically signal-enhanced NMR in existing workflows to fill these spots with detailed depictions. We highlight how integrating methods based on dissolution dynamic nuclear polarization can provide valuable complementary information about formerly inaccessible conformational spaces for many systems. A particular focus will be on hyperpolarized buffers to facilitate the NMR structure determination of challenging systems.

Exosome secretion and cellular response of DU145 and PC3 after exposure to alpha radiation

Exosomes are spherical membrane nanovesicles secreted from cells, and they play an important role in tumor immune response, metastasis, angiogenesis, and survival. Studies investigating exosomes isolated from cells exposed to photon radiation commonly used in conventional radiotherapy demonstrate the influence of this type of radiation on exosome characteristics and secretion. There is currently no research investigating the effects of densely ionizing particles such as protons and alpha radiation on exosomes. Thus we have evaluated the cellular response of human prostate cancer cells exposed to 0, 2, and 6 Gy of alpha radiation emitted from the Am-241 source. Irradiated PC3 and DU145 cell lines, characterized by differences in radiosensitivity, were studied using apoptosis, LDH, and IL-6 assays. Additionally, the corresponding concentration and size of isolated exosomes were measured using NTA. We found that exposure to ionizing radiation resulted in gross changes in viability and cell damage. There were increased amounts of apoptotic or necrotic cells as a function of radiation dose. We demonstrated that irradiated PC3 cells secrete higher quantities of exosomes compared to DU145 cells. Additionally, we also found no statistical difference in exosome size for control and irradiated cells.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

New tools to investigate tumor metabolism by NMR/MRI

Changes in metabolism is an hallmark that characterizes tumour cells from healthy ones. Their detection can be highly relevant for staging the tumor and for monitoring the response to therapeutic treatments. Herein it is shown the readout of these changes can be achieved either by assessing the pH of the extracellular space in the tumour region and by monitoring real time transformations of hyperpolarized C-13 labelled substrates. Mapping pH in a MR image is possible by measuring the CEST response of an administered contrast agent such as Iopamidol that can provide accurate measurements of the heterogeneity of tumour acidosis. Direct detection of relevant enzymatic activities have been acquired by using Pyruvate and Fumarate hyperpolarized by the incorporation of a molecule of para-H₂. Finally, it has been found that the tumour transformation involves an increase in the water exchange rate between the intra- and the extra-cellular compartments. A quantitative estimation of these changes can be obtained by acquiring the longitudinal relaxation times of tissue water protons at low magnetic field strength on Fast Field Cycling Relaxometers. This finding has been exploited in an application devoted to the assessment of the presence of residual tumour tissue in the margins of the resected mass in breast conservative surgery.

Radio Signals from Live Cells: The Coming of Age of In-Cell Solution NMR

A detailed knowledge of the complex processes that make cells and organisms alive is fundamental in order to understand diseases and to develop novel drugs and therapeutic treatments. To this aim, biological macromolecules should ideally be characterized at atomic resolution directly within the cellular environment. Among the existing structural techniques, solution NMR stands out as the only one able to investigate at high resolution the structure and dynamic behavior of macromolecules directly in living cells. With the advent of more sensitive NMR hardware and new biotechnological tools, modern in-cell NMR approaches have been established since the early 2000s. At the coming of age of in-cell NMR, we provide a detailed overview of its developments and applications in the 20 years that followed its inception. We review the existing approaches for cell sample preparation and isotopic labeling, the application of in-cell NMR to important biological questions, and the development of NMR bioreactor devices, which greatly increase the lifetime of the cells allowing real-time monitoring of intracellular metabolites and proteins. Finally, we share our thoughts on the future perspectives of the in-cell NMR methodology.

Determining the enantioselectivity of asymmetric hydrogenation through parahydrogen-induced hyperpolarization

Asymmetric hydrogenation plays an essential role for both academic research and industry to produce enantiomeric pure chiral molecules. Although nuclear magnetic resonance (NMR) is powerful in determining the yields of hydrogenation, it is still challenging to use NMR for chirality-related analysis. Herein, we applied parahydrogen-induced hyperpolarization (PHIP) NMR to determine the enantioselectivity of asymmetric hydrogenation and the absolute chirality of products. We hyperpolarized two types of unsaturated amino acid precursors, i.e., methyl-α-acetoamido cinnamate and (E)-ethyl 3-acetamidobut-2-enoate. Hydrogenation of prochiral substrates with parahydrogen gave temporary hyperpolarized diastereoisomers, which exhibit different PHIP patterns distinguishable in ¹H NMR. After assigning the NMR peaks by density functional theory calculations, we simulated the PHIP patterns of all the possible temporary hyperpolarized diastereoisomers and unambiguously assigned the chirality of the products and the enantioselectivity of asymmetric hydrogenation. Our work demonstrates the application and potential of PHIP in revealing the mechanism of asymmetric hydrogenation.

Parahydrogen-Induced Polarization of Amino Acids

Nuclear magnetic resonance (NMR) has become a universal method for biochemical and biomedical studies, including metabolomics, proteomics, and magnetic resonance imaging (MRI). By increasing the signal of selected molecules, the hyperpolarization of nuclear spin has expanded the reach of NMR and MRI even further (e.g. hyperpolarized solid-state NMR and metabolic imaging in vivo). Parahydrogen (pH2 ) offers a fast and cost-efficient way to achieve hyperpolarization, and the last decade has seen extensive advances, including the synthesis of new tracers, catalysts, and transfer methods. The portfolio of hyperpolarized molecules now includes amino acids, which are of great interest for many applications. Here, we provide an overview of the current literature and developments in the hyperpolarization of amino acids and peptides.

Discrimination of PHIP Signals Through their Evolution in Multipulse Sequences

The antiphase character of the PHIP associated signals after a hydrogenation reaction is particularly sensitive to line broadening introduced by magnetic field inhomogeneities and interferences by the presence of resonance lines steaming from a large amount of thermally polarized spins. These obstacles impose a limitation in the detection of reaction products as well as in the experimental setups. A simple way to overcome these impediments consists of acquiring the signal with a train of refocusing pulses instead of a single r.f. pulse. We present here a number of examples where this multipulse acquisition, denominated PhD-PHIP, displays its potentiality in improving the information related to hyperpolarized spins performed in a sample, where the former parahydrogen nuclei are part of a complex J-coupling network.

ParaHydrogen Polarized Ethyl-[1-13 C]pyruvate in Water, a Key Substrate for Fostering the PHIP-SAH Approach to Metabolic Imaging

An efficient synthesis of vinyl-[1-13 C]pyruvate has been reported, from which 13 C hyperpolarized (HP) ethyl-[1-13 C]pyruvate has been obtained by means of ParaHydrogen Induced Polarization (PHIP). Due to the intrinsic lability of pyruvate, which leads quickly to degradation of the reaction mixture even under mild reaction conditions, the vinyl-ester has been synthesized through the intermediacy of a more stable ketal derivative. 13 C and 1 H hyperpolarizations of ethyl-[1-13 C]pyruvate, hydrogenated using ParaHydrogen, have been compared to those observed on the more widely used allyl-derivative. It has been demonstrated that the spin order transfer from ParaHydrogen protons to 13 C, is more efficient on the ethyl than on the allyl-esterdue to the larger J-couplings involved. The main requirements needed for the biological application of this HP product have been met, i. e. an aqueous solution of the product at high concentration (40 mM) with a good 13 C polarization level (4.8 %) has been obtained. The in vitro metabolic transformation of the HP ethyl-[1-13 C]pyruvate, catalyzed by an esterase, has been observed. This substrate appears to be a good candidate for in vivo metabolic investigations using PHIP hyperpolarized probes.

Pd-based bimetallic catalysts for parahydrogen-induced polarization in heterogeneous hydrogenations

Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise H 2 addition required for the observation of parahydrogen-induced polarization (PHIP) effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for PHIP in heterogeneous hydrogenations (HET-PHIP). The dilution of catalytically active Pd with less active Ag or In atoms provides the formation of atomically dispersed Pd 1 sites on the surface of Pd-based bimetallic catalysts, which are significantly more selective toward pairwise H 2 addition compared to the monometallic Pd. Furthermore, the choice of the dilution metal (Ag or In) has a pronounced effect on the efficiency of bimetallic catalysts in HET-PHIP, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.

Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution

Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by polarization reagents. In this work we overcome these drawbacks in the production of PHIP-polarized [1-¹³C]fumarate, a biomarker of cell necrosis in metabolic ¹³C MRI.

Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at ¹³C polarization levels of 30–45%.

Hydrogenative-PHIP polarized metabolites for biological studies

ParaHydrogen induced polarization (PHIP) is an efficient and cost-effective hyperpolarization method, but its application to biological investigations has been hampered, so far, due to chemical challenges. PHIP is obtained by means of the addition of hydrogen, enriched in the para-spin isomer, to an unsaturated substrate. Both hydrogen atoms must be transferred to the same substrate, in a pairwise manner, by a suitable hydrogenation catalyst; therefore, a de-hydrogenated precursor of the target molecule is necessary. This has strongly limited the number of parahydrogen polarized substrates. The non-hydrogenative approach brilliantly circumvents this central issue, but has not been translated to in-vivo yet. Recent advancements in hydrogenative PHIP (h-PHIP) considerably widened the possibility to hyperpolarize metabolites and, in this review, we will focus on substrates that have been obtained by means of this method and used in vivo. Attention will also be paid to the requirements that must be met and on the issues that have still to be tackled to obtain further improvements and to push PHIP substrates in biological applications.