NMR metabolomics study of chronic low-dose exposure to a cocktail of persistent organic pollutants.

Nowadays, exposure to endocrine-disrupting chemicals (EDCs), including persistent organic pollutants (POPs), is one of the most critical threats to public health. EDCs are chemicals that mimic, block, or interfere with hormones in the body's endocrine system and have been associated with a wide range of health issues. This innovative, untargeted metabolomics study investigates chronic low-dose internal exposure to a cocktail of POPs on multiple tissues that are known to accumulate these lipophilic compounds. Interestingly, the metabolic response differs among selected tissues/organs in mice. In the liver, we observed a dynamic effect according to the exposure time and the doses of POPs. In the brain tissue, the situation is the opposite, leading to the conclusion that the presence of POPs immediately gives a saturated effect that is independent of the dose and the duration of exposure studied. By contrast, for the adipose tissues, nearly no effect is observed. This metabolic profiling leads to a holistic and dynamic overview of the main metabolic pathways impacted in lipophilic tissues by a cocktail of POPs.

Present and future of pure shift NMR in metabolomics.

NMR is one of the most powerful techniques for the analysis of biological samples in the field of metabolomics. However, the high complexity of fluids, tissues, or other biological materials taken from living organisms is still a challenge for state-of-the-art pulse sequences, thereby limiting the detection, the identification, and the quantification of metabolites. In this context, the resolution enhancement provided by broadband homonuclear decoupling methods, which allows for simplifying 1 H multiplet patterns into singlets, has placed this so-called pure shift technique as a promising approach to perform metabolic profiling with unparalleled level of detail. In recent years, the many advances achieved in the design of pure shift experiments has paved the way to the analysis of a wide range of biological samples with ultra-high resolution. This review leads the reader from the early days of the main pure shift methods that have been successfully developed over the last decades to address complex samples, to the most recent and promising applications of pure shift NMR to the field of NMR-based metabolomics.

Ultrahigh-Resolution NMR with Water Signal Suppression for a Deeper Understanding of the Action of Antimetabolic Drugs on Diffuse Large B-Cell Lymphoma.

Ultrahigh-resolution NMR has recently attracted considerable attention in the field of complex samples analysis. Indeed, the implementation of broadband homonuclear decoupling techniques has allowed us to greatly simplify crowded 1H spectra, yielding singlets for almost every proton site from the analyzed molecules. Pure shift methods have notably shown to be particularly suitable for deciphering mixtures of metabolites in biological samples. Here, we have successfully implemented a new pure shift pulse sequence based on the PSYCHE method, which incorporates a block for solvent suppression that is suitable for metabolomics analysis. The resulting experiment allows us to record ultrahigh-resolution 1D NOESY 1H spectra of biofluids with suppression of the water signal, which is a crucial step for highlighting metabolite mixtures in an aqueous phase. We have successfully recorded pure shift spectra on extracellular media of diffuse large B-cell lymphoma (DLBCL) cells. Despite a lower sensitivity, the resolution of pure shift data was found to be better than that of the standard approach, which provides a more detailed vision of the exo-metabolome. The statistical analyses carried out on the resulting metabolic profiles allow us to successfully highlight several metabolic pathways affected by these drugs. Notably, we show that Kidrolase plays a major role in the metabolic pathways of this DLBCL cell line.

Characterizing extracellular diffusion properties using diffusion-weighted MRS of sucrose injected in mouse brain.

Brain water and some critically important energy metabolites, such as lactate or glucose, are present in both intracellular and extracellular spaces (ICS/ECS) at significant levels. This ubiquitous nature makes diffusion MRI/MRS data sometimes difficult to interpret and model. While it is possible to glean information on the diffusion properties in ICS by measuring the diffusion of purely intracellular endogenous metabolites (such as NAA), the absence of endogenous markers specific to ECS hampers similar analyses in this compartment. In past experiments, exogenous probes have therefore been injected into the brain to assess their apparent diffusion coefficient (ADC) and thus estimate tortuosity in ECS. Here, we use a similar approach in mice by injecting sucrose, a well-known ECS marker, in either the lateral ventricles or directly in the prefrontal cortex. For the first time, we propose a thorough characterization of ECS diffusion properties encompassing (1) short-range restriction by looking at signal attenuation at high b values, (2) tortuosity and long-range restriction by measuring ADC time-dependence at long diffusion times and (3) microscopic anisotropy by performing double diffusion encoding (DDE) measurements. Overall, sucrose diffusion behavior is strikingly different from that of intracellular metabolites. Acquisitions at high b values not only reveal faster sucrose diffusion but also some sensitivity to restriction, suggesting that the diffusion in ECS is not fully Gaussian at high b. The time evolution of the ADC at long diffusion times shows that the tortuosity regime is not reached yet in the case of sucrose, while DDE experiments suggest that it is not trapped in elongated structures. No major difference in sucrose diffusion properties is reported between the two investigated routes of injection and brain regions. These original experimental insights should be useful to better interpret and model the diffusion signal of molecules that are distributed between ICS and ECS compartments.

Metabolic NMR mapping with microgram tissue biopsy.

This study explores the potential of profiling a microgram-scale soft tissue biopsy by NMR spectroscopy. The important elements of high resolution and high sensitivity for the spectral data are achieved through a unique probe, HR-µMAS, which allowed comprehensive profiling to be performed on microgram tissue for the first time under MAS conditions. Thorough spatially resolved metabolic maps were acquired across a coronal brain slice of rat C6 gliomas, which rendered the delineation of the tumor lesion. The results present a unique ex vivo NMR possibility to analyze tissue pathology that cannot be fully explored by the conventional approach, HR-MAS and in vivo MRS. Aside from the capability of analyzing a small localized region to track its specific metabolism, it could also offer the possibility to carry out longitudinal investigations on live animals due to the feasibility of minimally invasive tissue excision.

Intact NMR spectroscopy: slow high-resolution magic angle spinning chemical shift imaging.

High-Resolution Magic-Angle Spinning Chemical Shift Imaging (HR-MAS CSI) has recently been explored for nuclear magnetic resonance (NMR) metabolomics and shows considerable promise in organism research. This is due to its ability to offer a supplemental dimension - spatial metabolic distribution - for profiling. However, HR-MAS CSI suffers from the large centrifugal stress exerted on the sample, which inevitably hinders the metabolic assessment. Herein, a slow sample spinning strategy was implemented and evaluated. The results demonstrate its potential as a highly informative profiling approach for intact specimens, with high quality data and feasibility.

General Guidelines for Sample Preparation Strategies in HR-µMAS NMR-based Metabolomics of Microscopic Specimens.

The study of the metabolome within tissues, organisms, cells or biofluids can be carried out by several bioanalytical techniques. Among them, nuclear magnetic resonance (NMR) is one of the principal spectroscopic methods. This is due to a sample rotation technique, high-resolution magic angle spinning (HR-MAS), which targets the analysis of heterogeneous specimens with a bulk sample mass from 5 to 10 mg. Recently, a new approach, high-resolution micro-magic angle spinning (HR-µMAS), has been introduced. It opens, for the first time, the possibility of investigating microscopic specimens (<500 µg) with NMR spectroscopy, strengthening the concept of homogeneous sampling in a heterogeneous specimen. As in all bioanalytical approaches, a clean and reliable sample preparation strategy is a significant component in designing metabolomics (or -omics, in general) studies. The sample preparation for HR-µMAS is consequentially complicated by the µg-scale specimen and has yet to be addressed. This report details the strategies for three specimen types: biofluids, fluid matrices and tissues. It also provides the basis for designing future µMAS NMR studies of microscopic specimens.

Current Developments in µMAS NMR Analysis for Metabolomics.

Analysis of microscopic specimens has emerged as a useful analytical application in metabolomics because of its capacity for characterizing a highly homogenous sample with a specific interest. The undeviating analysis helps to unfold the hidden activities in a bulk specimen and contributes to the understanding of the fundamental metabolisms in life. In NMR spectroscopy, micro(µ)-probe technology is well-established and -adopted to the microscopic level of biofluids. However, this is quite the contrary with specimens such as tissue, cell and organism. This is due to the substantial difficulty of developing a sufficient µ-size magic-angle spinning (MAS) probe for sub-milligram specimens with the capability of high-quality data acquisition. It was not until 2012; a µMAS probe had emerged and shown promises to µg analysis; since, a continuous advancement has been made striving for the possibility of µMAS to be an effective NMR spectroscopic analysis. Herein, the mini-review highlights the progress of µMAS development-from an impossible scenario to an attainable solution-and describes a few demonstrative metabolic profiling studies. The review will also discuss the current challenges in µMAS NMR analysis and its potential to metabolomics.

Simultaneous metabolic mapping of different anatomies by 1H HR-MAS chemical shift imaging.

Localized information on a specimen is considered indispensable for deciphering biological activity. Magnetic resonance spectroscopy is a notable method because of its versatility; however, one limitation is the spectral quality on a static sample. This study explores an amalgamated method with two magnetic resonance experiments: high-resolution magic-angle spinning (HR-MAS) for high-quality spectral acquisition from a spinning sample and chemical shift imaging (CSI) for spatial localization. The advantage of HR-MAS CSI is its amenity for simultaneously profiling the metabolome-with good spectral data-at different spatial regions in a single experiment. Herein, 1H HR-MAS CSI (including a T2-contrast CSI) was described and performed on various food tissues and an intact organism. Different data analyses such as multivariate and quantification were explored to identify the metabolic variants in different anatomical regions and in one case, to assist in a spatial allocation. The limitation and drawback of the experiment are also discussed. Graphical abstract.

HR-µMAS NMR-Based Metabolomics: Localized Metabolic Profiling of a Garlic Clove with µg Tissues.

The localization of metabolic profiles within a tissue sample is of particular interest when the sampling size is considerably small, i.e., in the order of a microgram (µg) scale. Small sampling size is inevitable when the sample availability is limited, or when different metabolic profiles are suspected in small disparate sample regions. Capitalizing a recently introduced high-resolution micro-MAS probe (HR-µMAS) for its capability of high-quality NMR data acquisition of µg samples, this study explores the localized metabolic NMR profiling of a single garlic clove and compares the methodology and results with the standard HR-MAS. One advantage of HR-µMAS is the feasibility of analyzing homogeneous µg samples within a large heterogeneous tissue. As a result, the sampling mass (<0.5 mg) allows to selectively profile four homogeneous anatomical garlic regions by HR-µMAS (skin, flesh, inner epidermis, and sprout), in contrast to three regions (skin, flesh, and core ≡ inner epidermis and sprout) by HR-MAS, with a sampling mass of ca. 8 mg. Discriminant analysis was carried out to identify the significant variables in the different regions. It found a significant presence of fructose in both skin and flesh, while sucrose and glucose are predominant in the core. Among the garlic characteristic sulfur compounds, allicin is dominant in the core and allyl mercaptan in both skin and flesh. Quantification analysis was conducted and demonstrated its potential by quantifying metabolites at the µg-level. This study offers an important basis for designing HR-µMAS NMR-based metabolomics studies that can benefit from profiling µg-scale samples.

Study by ³¹P NMR spectroscopy of the triacylglycerol degradation processes in olive oil with different heat-transfer mechanisms.

The thermal degradation of olive oil using conventional and microwave heating under the same experimental conditions were compared. A powerful identification and quantification technique based on (31)P NMR has been developed to characterise the differences between the minor components including diacylglycerol and free fatty acids in the heated samples. The (31)P NMR spectra of the degraded olive oils, which contain OH groups derivatised with a phosphorus reagent, showed that conventional heating is more detrimental to the oil than microwave technique. Conventional heating leads to a significant increase in the diacylglycerol and free fatty acid contents as well as in the number of degradation compounds, which damage the olive oil quality. However, the main process that takes place on using microwave heating is isomerisation between diacylglycerols, a change that could give a potential longer shelf life to the olive oil.