MALDI Imaging Mass Spectrometry-A Mini Review of Methods and Recent Developments

Visualization of PFOA accumulation and its effects on phospholipid in zebrafish liver by MALDI Imaging

Exposure to poly- and perfluoroalkyl substances (PFASs) can result in bioaccumulation. Initial findings suggested that PFASs could accumulate in tissues rich in both phospholipids and proteins. However, our current understanding is limited to the average concentration of PFASs or phospholipid content across entire tissue matrices, leaving unresolved the spatial variations of lipid metabolism associated with PFOA in zebrafish tissue. To address gap, we developed a novel methodology for concurrent spatial profiling of perfluorooctanoic acid (PFOA) and individual phospholipids within zebrafish hepatic tissue sections, utilizing matrix-assisted laser desorption/ionization time of flight imaging mass spectrometry (MALDI-TOF-MSI). 5-diaminonapthalene (DAN) matrix and laser sensitivity of 50.0 were optimized for PFOA detection in MALDI-TOF-MSI analysis with high spatial resolution (25 μm). PFOA was observed to accumulate within zebrafish liver tissue. H&E staining results corroborating the damage inflicted by PFOA accumulation, consistent with MALDI MSI results. Significant up-regulation of 15 phospholipid species was observed in zebrafish groups exposed to PFOA, with these phospholipid demonstrating varied spatial distribution within the same tissue. Furthermore, co-localized imaging of distinct phospholipids and PFOA within identical tissue sections suggested there could be two distinct potential interactions between PFOA and phospholipids, which required further investigation. The MALDI-TOF-IMS provides a new tool to explore in situ spatial distributions and variations of the endogenous metabolites for the health risk assessment and ecotoxicology of emerging environmental pollutants.

Flexural Strength and Morphological Study of Different Multilayer Zirconia Dental Materials

Nowadays, yttria (Y3+)-stabilized ZrO2 (Y-TZP) is the most commonly used material in dental prosthetics. Y-TZP dental ceramics are mainly stabilized via the addition of 3 mol% yttrium oxide (Y2O3). These ceramics exhibit excellent mechanical properties, including high flexural strength, fracture toughness, elastic modulus, etc. Some manufacturers have recently introduced a new class of dental materials with multilayer composition with the aim of combining the advantages of adding more or less Y2O3 to the ceramic composition in one Y-TZP material. The flexural strength values of multilayer Y-TZP may vary depending on the dimensions of the specimen, layer distributions, and especially the layer exposed on the maximum tension side, i.e., loading configuration. Although previous studies have examined the flexural strength of separate Y-TZP layers, capturing the flexural strength of multilayer Y-TZP is still challenging. However, one should keep in mind that multilayer flexural strength is important for clinical indications. The objective of this study is to compare the flexural strength of three distinct multilayer translucent Y-TZP materials made up of layers with different Y3+ contents. Rectangular samples (2 mm × 2 mm × 16 mm) were prepared from CAD/CAM discs using the milling machine Programill PM7 (Ivoclar Vivadent AG). Milled bars were tested for flexural strength in a three-point bending test (ISO 6872:2015) using a universal testing machine (Inspekt Duo 5kN; Hegewald & Peschke, Nossen, Germany) at a crosshead speed of 0.5 mm/min. Representative samples of each type of material were selected for quantitative and qualitative analysis of the microstructure. Representative samples of each type of material were selected for structural, mechanical, and microstructural analyses.

Quantitative Analysis of the Concentration of Trifluridine in Tumor Hypoxic Regions Using a Novel Platform Combining Functional Endoscopy and Mass Spectrometry

Hypoxic regions in solid tumors are highly resistant to drugs and thus represents an obstacle in drug discovery. Currently, however, there are technical barriers in sampling human hypoxic tumors and examining drug delivery with high sensitivity and accuracy. Herein, we present a new platform combining functional endoscopy and highly sensitive liquid chromatography-mass spectrometry (LC-MS) to assess drug delivery to hypoxic regions. Because oxygen saturation endoscopic imaging (OXEI), a functional endoscopy, can evaluate lesions and hypoxia in real-time by simultaneously acquiring a pseudocolor map of oxygen saturation and conventional endoscopic images, this platform can be used to evaluate drug delivery with human samples from hypoxic regions. As the first clinical application of this platform, the relationship between hypoxic regions and the concentration of trifluridine (FTD) incorporated into DNA was evaluated in patients with advanced gastric cancer treated with FTD/tipiracil (FTD/TPI; n = 13) by obtaining and analysis of tissue samples by OXEI and LC-MS and vascular maturity index by CD31/α-SMA staining ex vivo. The results showed that the concentration of FTD was significantly higher in the normoxic region than in the hypoxic region (P < 0.05) and there were significantly more immature vessels in hypoxic regions than in normoxic regions (P < 0.05). These results indicate that the platform was sufficiently sensitive to evaluate differences in drug anabolism in different oxygenic regions of human tumor tissue. This new platform allows quantitative drug analysis in hypoxic regions and is expected to initiate a new era of drug discovery and development.

Chemical QuantArray: A Quantitative Tool for Mass Spectrometry Imaging

Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is a powerful analytical technique that provides spatially preserved detection and quantification of analytes in tissue specimens. However, clinical translation still requires improved throughput, precision, and accuracy. To accomplish this, we created "Chemical QuantArray", a gelatin tissue microarray (TMA) mold filled with serial dilutions of isotopically labeled endogenous metabolite standards. The mold is then cryo-sectioned onto a tissue homogenate to produce calibration curves. To improve precision and accuracy, we automatically remove pixels outside of each TMA well and investigated several intensity normalizations, including the utilization of a second stable isotope internal standard (IS). Chemical QuantArray enables the quantification of several endogenous metabolites over a wide dynamic range and significantly improve over current approaches. The technique reduces the space needed on the MALDI slides for calibration standards by approximately 80%. Furthermore, removal of empty pixels and normalization to an internal standard or matrix peak provided precision (<20% RSD) and accuracy (<20% DEV). Finally, we demonstrate the applicability of Chemical QuantArray by quantifying multiple purine metabolites in 14 clinical tumor specimens using a single MALDI slide. Chemical QuantArray improves the analytical characteristics and practical feasibility of MALDI-MSI metabolite quantification in clinical and translational applications.

Recent advances in mass spectrometry analysis of neuropeptides

Due to their involvement in numerous biochemical pathways, neuropeptides have been the focus of many recent research studies. Unfortunately, classic analytical methods, such as western blots and enzyme-linked immunosorbent assays, are extremely limited in terms of global investigations, leading researchers to search for more advanced techniques capable of probing the entire neuropeptidome of an organism. With recent technological advances, mass spectrometry (MS) has provided methodology to gain global knowledge of a neuropeptidome on a spatial, temporal, and quantitative level. This review will cover key considerations for the analysis of neuropeptides by MS, including sample preparation strategies, instrumental advances for identification, structural characterization, and imaging; insightful functional studies; and newly developed absolute and relative quantitation strategies. While many discoveries have been made with MS, the methodology is still in its infancy. Many of the current challenges and areas that need development will also be highlighted in this review.

Bacterial Volatile Isovaleric Acid Triggers Growth Alteration of Arabidopsis Seedlings

Bacterial volatile organic compounds (BVOCs) released from selected soil microbes have been shown to trigger the alteration of plant growth. However, the substances responsible for such bioactivity and the mechanism of how plants interpret and respond to BVOCs remain largely elusive. Here, we established a model bioassay system using Arabidopsis and Bacillus spp. and found that Bacillus BVOCs interfere with the normal growth of Arabidopsis seedlings. Moreover, through a bioassay-guided purification, we identified isovaleric acid (IVA) as a volatile compound that exhibits inhibitory growth activity towards Arabidopsis seedlings. Our data provide novel molecular insights into how short-chain fatty acids released from soil microbes can affect plant growth through interkingdom signals.

Discontinuously Dewetting Solvent Arrays: Droplet Formation and Poly-Synchronous Surface Extraction for Mass Spectrometry Imaging Applications

We describe a new liquid tissue stamping method called poly-synchronous surface extraction (PSSE) that utilizes an omniphobic substrate patterned with hydrophilic surface energy traps (SETs), which when wet with a solvent form a dense microdroplet array. When contacted with a tissue sample, each droplet locally extracts analytes from the tissue surface, which subsequentially can be analyzed by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-IMS) or ambient ionization-MS techniques. Optimization of the patterned surface with six different solvents was carried out to increase the droplet density, height, and reproducibility of volume deposition. Once optimized, sister slices of a strawberry (Fragaria × ananassa) were spatially extracted using the PSSE technique and the chemical distribution of selected compounds was analyzed with both MALDI-IMS and a lower resolution but faster ambient liquid microjunction surface sampling probe (LMJ-SSP) approach. Heat maps for target analytes for the PSSE approach are compared to those produced using traditional MALDI-IMS analysis. The PSSE method aligned well with direct analysis and demonstrated the potential to increase the speed of ambient MS tissue imaging techniques by decreasing the number of steps required for sample preparation.

Referenced Kendrick Mass Defect Annotation and Class-Based Filtering of Imaging MS Lipidomics Experiments

Because of their diverse functionalities in cells, lipids are of primary importance when characterizing molecular profiles of physiological and disease states. Imaging mass spectrometry (IMS) provides the spatial distributions of lipid populations in tissues. Referenced Kendrick mass defect (RKMD) analysis is an effective mass spectrometry (MS) data analysis tool for classification and annotation of lipids. Herein, we extend the capabilities of RKMD analysis and demonstrate an integrated method for lipid annotation and chemical structure-based filtering for IMS datasets. Annotation of lipid features with lipid molecular class, radyl carbon chain length, and degree of unsaturation allows image reconstruction and visualization based on each structural characteristic. We show a proof-of-concept application of the method to a computationally generated IMS dataset and validate that the RKMD method is highly specific for lipid components in the presence of confounding background ions. Moreover, we demonstrate an application of the RKMD-based annotation and filtering to matrix-assisted laser desorption/ionization (MALDI) IMS lipidomic data from human kidney tissue analysis.

Insights and prospects for ion mobility-mass spectrometry in clinical chemistry

INTRODUCTION

Ion mobility-mass spectrometry is an emerging technology in the clinical setting for high throughput and high confidence molecular characterization from complex biological samples. Ion mobility spectrometry can provide isomer separations on the basis of molecular structure, the ability of which is increasing through technological developments that afford enhanced resolving power. Integrating multiple separation dimensions, such as liquid chromatography-ion mobility-mass spectrometry (LC-IM-MS) provide dramatic enhancements in the mitigation of molecular interferences for high accuracy clinical measurements.

AREAS COVERED

Multidimensional separations with LC-IM-MS provide better selectivity and sensitivity in molecular analysis. Mass spectrometry imaging of tissues to inform spatial molecular distribution is improved by complementary ion mobility analyses. Biomarker identification in surgical environments is enhanced by intraoperative biochemical analysis with mass spectrometry and holds promise for integration with ion mobility spectrometry. New prospects in high resolving power ion mobility are enhancing analysis capabilities, such as distinguishing isomeric compounds.

EXPERT OPINION

Ion mobility-mass spectrometry holds many prospects for the field of isomer identification, molecular imaging, and intraoperative tumor margin delineation in clinical settings. These advantages are afforded while maintaining fast analysis times and subsequently high throughput. High resolving power ion mobility will enhance these advantages further, in particular for analyses requiring high confidence isobaric selectivity and detection.

Mass Spectrometry Imaging for Glycome in the Brain

Glycans are diverse structured biomolecules that play crucial roles in various biological processes. Glycosylation, an enzymatic system through which various glycans are bound to proteins and lipids, is the most common and functionally crucial post-translational modification process. It is known to be associated with brain development, signal transduction, molecular trafficking, neurodegenerative disorders, psychopathologies, and brain cancers. Glycans in glycoproteins and glycolipids expressed in brain cells are involved in neuronal development, biological processes, and central nervous system maintenance. The composition and expression of glycans are known to change during those physiological processes. Therefore, imaging of glycans and the glycoconjugates in the brain regions has become a “hot” topic nowadays. Imaging techniques using lectins, antibodies, and chemical reporters are traditionally used for glycan detection. However, those techniques offer limited glycome detection. Mass spectrometry imaging (MSI) is an evolving field that combines mass spectrometry with histology allowing spatial and label-free visualization of molecules in the brain. In the last decades, several studies have employed MSI for glycome imaging in brain tissues. The current state of MSI uses on-tissue enzymatic digestion or chemical reaction to facilitate successful glycome imaging. Here, we reviewed the available literature that applied MSI techniques for glycome visualization and characterization in the brain. We also described the general methodologies for glycome MSI and discussed its potential use in the three-dimensional MSI in the brain.

The human vermilion surface contains a rich amount of cholesterol sulfate than the skin

BACKGROUND

The vermilion of the human lip presents characteristic features and undergoes aging faster than the skin. Therefore, knowledge of the vermilion surface-specific functional molecules is important to understand lip aging and formulate lip care products. Previously, we analyzed the free fatty acids distributions and showed that docosahexaenoic acid highly accumulated in the vermilion's epithelium than in the skin.

OBJECTIVE

We aimed to explore the functional molecules other than the free fatty acids on the vermilion's surface.

METHODS

Human lip tissues from children and tape-stripped samples from smooth and rough lips of adults were measured by desorption electrospray ionization-mass spectrometry imaging (DESI-MSI).

RESULTS

DESI-MSI of children's lip sections revealed a major distribution of five phospholipid species in the viable layer, but not in the superficial area, of both the vermilion and the skin than that in the underlying tissue. Interestingly, a remarkably higher distribution of cholesterol sulfate was observed in the vermilion's superficial area compared to that in the skin in all subjects under this study. Furthermore, theDESI-MSI of tape-stripped lip sample showed an overall higher accumulation of cholesterol sulfate in the stratum corneum of the rough lip than that in the smooth lips showed an overall higher accumulation of cholesterol sulfate in the stratum corneum of the rough lips than that in the smooth lips.

CONCLUSION

Our study concluded that cholesterol sulfate has a characteristic distribution to the vermilion's surface and showed an association with the roughness of the lip.

Desorption ionization using through-hole alumina membrane offers higher reproducibility than 2,5-dihydroxybenzoic acid, a widely used matrix in Fourier transform ion cyclotron resonance mass spectrometry imaging analysis

RATIONALE

DIUTHAME (desorption ionization using through-hole alumina membrane), a recently developed matrix-free ionization-assisting substrate, was examined for reproducibility in terms of mass accuracy and intensity using standard lipid and mouse brain sections. The impregnation property of DIUTHAME significantly improved the reproducibility of mass accuracy and intensity compared with 2,5-dihydroxybenzoic acid (DHB).

METHODS

Frozen tissue sections were mounted on indium tin oxide-coated glass slides. DIUTHAME and DHB were applied to individual sections. Subsequently, a solution of a phosphatidylcholine standard, PC(18:2/18:2), was poured onto the DIUTHAME and matrix. Finally, the samples were subjected to laser desorption ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The reproducibility was tested by calculating the mean ± standard deviation values of mass errors and intensities of individual ion species.

RESULTS

Analysis of the PC(18:2/18:2) standard showed significantly (p < 0.01) lower mass error for DIUTHAME-MS than for MALDI-MS. Endogenous PC(36:4) analysis in mouse brain section also showed significantly (p < 0.05) lower mass errors for DIUTHAME-MS. Furthermore, we investigated the mass error of some abundant lipid ions in brain sections and observed similar results. DIUTHAME-MS displayed lower signal intensity in standard PC analysis. Interestingly, it offered higher signal intensities for all the endogenous lipid ions. Lower fluctuations of both mass accuracies and signal intensities were observed in DIUTHAME-MS.

CONCLUSIONS

Our results demonstrated that DIUTHAME-MS offers higher reproducibility for mass accuracies and intensities than MALDI-MS in both standard lipid and mouse brain tissue analyses. It can potentially be used instead of conventional MALDI-MS and mass spectrometry imaging analyses to achieve highly reproducible data for mass accuracy and intensity.

Impact of Sandblasting on Morphology, Structure and Conductivity of Zirconia Dental Ceramics Material

Over the last decade, zirconia (ZrO₂)-based ceramic materials have become more applicable to modern dental medicine due to the sustained development of diverse computer-aided design/computer-aided manufacturing (CAD/CAM) systems. However, before the cementation and clinical application, the freshly prepared zirconia material (e.g., crowns) has to be processed by sandblasting in the dental laboratory. In this work, the impact of the sandblasting on the zirconia is monitored as changes in morphology (i.e., grains and cracks), and the presence of impurities might result in a poor adhesive bonding with cement. The sandblasting is conducted by using Al₂O₃ powder (25, 50, 110 and 125 µm) under various amounts of air-abrasion pressure (0.1, 0.2, 0.4 and 0.6 MPa). There has been much interest in both the determination of the impact of the sandblasting on the zirconia phase transformations and conductivity. Morphology changes are observed by using Scanning Electron Microscope (SEM), the conductivity is measured by Impedance Spectroscopy (IS), and the phase transformation is observed by using Powder X-Ray Diffraction (PXRD). The results imply that even the application of the lowest amount of air-abrasion pressure and the smallest Al₂O₃ powder size yields a morphology change, a phase transformation and a material contamination.

Mass spectrometry-based phospholipid imaging: methods and findings

Introduction: Imaging is a technique used for direct visualization of the internal structure or distribution of biomolecules of a living system in a two-dimensional or three-dimensional fashion. Phospholipids are important structural components of biological membranes and have been reported to be associated with various human diseases. Therefore, the visualization of phospholipids is crucial to understand the underlying mechanism of cellular and molecular processes in normal and diseased conditions. Areas covered: Mass spectrometry imaging (MSI) has enabled the label-free imaging of individual phospholipids in biological tissues and cells. The commonly used MSI techniques include matrix-assisted laser desorption ionization-MSI (MALDI-MSI), desorption electrospray ionization-MSI (DESI-MSI), and secondary ion mass spectrometry (SIMS) imaging. This special report described those methods, summarized the findings, and discussed the future development for the imaging of phospholipids. Expert opinion: Phospholipids imaging in complex biological samples has been significantly benefited from the development of MSI methods. In MALDI-MSI, novel matrix that produces homogenous crystals exclusively with polar lipids is important for phospholipids imaging with greater efficiency and higher spatial resolution. DESI-MSI has the potential of live imaging of the biological surface while SIMS is expected to image at the subcellular level in the near future.

137Cs γ Ray and 28Si Irradiation Induced Murine Hepatocellular Carcinoma Lipid Changes in Liver Assessed by MALDI-MSI Combined with Spatial Shrunken Centroid Clustering Algorithm: A Pilot Study

Characterization of lipids by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is of great interest because not only are lipids important structural molecules in both the cell and internal organelle membranes, but they are also important signaling molecules. MALDI-MSI combined with spatial image segmentation has been previously used to identify tumor heterogeneities within tissues with distinct anatomical regions such as the brain. However, there has been no systematic study utilizing MALDI-MSI combined with spatial image segmentation to assess the tumor microenvironment in the liver. Here, we present that image segmentation can be used to evaluate the tumor microenvironment in the liver. In particular, to better understand the molecular mechanisms of irradiation-induced hepatic carcinogenesis, we used MALDI-MSI in the negative ion mode to identify lipid changes 12 months post exposure to low dose ²⁸Si and ¹³⁷Cs γ ray irradiation. We report here the changes in the lipid profiles of male C3H/HeNCrl mice liver tissues after exposure to irradiation and analyzed using the spatial shrunken centroid clustering algorithm. These findings provide valuable information as astronauts will be exposed to high-charge high-energy (HZE) particles and low-energy γ-ray irradiation during deep space travel. Even at low doses, exposure to these irradiations can lead to cancer. Previous studies infer that irradiation of mice with low-dose HZE particles induces oxidative damage and microenvironmental changes that are thought to play roles in the pathophysiology of hepatocellular carcinoma.

Region-specific effects of Scrapper on the abundance of glutamate and gamma-aminobutyric acid in the mouse brain

The brain consists of various areas with anatomical features. Neurons communicate with one another via excitatory or inhibitory synaptic transmission. Altered abundance of neurotransmitters, including glutamate and gamma-aminobutyric acid (GABA), in specific brain regions is closely involved in severe neurological diseases, such as schizophrenia and obsessive-compulsive disorder. SCRAPPER, a ubiquitin E3 ligase, regulates synaptic transmission. Scrapper gene deficiency results in defective neurotransmission due to excessive secretion of neurotransmitters. The present study employed matrix-assisted laser desorption/ionization imaging mass spectrometry to analyze the abundance of amino acid neurotransmitters in Scrapper knockout (SCR-KO) mice. SCR-KO mice exhibited significantly increased glutamate levels in the isocortex (CTX), corpus callosum (CC), thalamus (TH), midbrain (MB), cerebellar cortex (CBX), and caudoputamen (CP) and increased GABA levels in the CTX, CC, TH, MB, CBX and hypothalamus (HY) compared with wild-type mice. These findings indicate that Scrapper deficiency leads to upregulated glutamate and GABA levels in multiple regions. Our results show a differential, region-specific effect of Scrapper on the abundance of glutamate and GABA.

Modeling cardiac complexity: Advancements in myocardial models and analytical techniques for physiological investigation and therapeutic development in vitro

Cardiomyopathies, heart failure, and arrhythmias or conduction blockages impact millions of patients worldwide and are associated with marked increases in sudden cardiac death, decline in the quality of life, and the induction of secondary pathologies. These pathologies stem from dysfunction in the contractile or conductive properties of the cardiomyocyte, which as a result is a focus of fundamental investigation, drug discovery and therapeutic development, and tissue engineering. All of these foci require in vitro myocardial models and experimental techniques to probe the physiological functions of the cardiomyocyte. In this review, we provide a detailed exploration of different cell models, disease modeling strategies, and tissue constructs used from basic to translational research. Furthermore, we highlight recent advancements in imaging, electrophysiology, metabolic measurements, and mechanical and contractile characterization modalities that are advancing our understanding of cardiomyocyte physiology. With this review, we aim to both provide a biological framework for engineers contributing to the field and demonstrate the technical basis and limitations underlying physiological measurement modalities for biologists attempting to take advantage of these state-of-the-art techniques.

Simultaneous quantification of atropine and scopolamine in infusions of herbal tea and Solanaceae plant material by matrix-assisted laser desorption/ionization time-of-flight (tandem) mass spectrometry

RATIONALE

Atropine (Atr) and scopolamine (Scp) are toxic secondary plant metabolites of species within the Solanaceae genus that can accidentally or intentionally reach the food store chain by inaccurate harvesting of any plant material, e.g. for herbal tea infusions. Ingestion may cause severe anticholinergic poisoning thus requiring risk-oriented determination in food and beverages. The suitability of matrix-assisted laser desorption/ionization time-of-flight (tandem) mass spectrometry, MALDI-TOF MS(/MS), should be characterized for simultaneous analysis.

METHODS

We herein present the first MALDI-TOF MS(/MS) procedure for quantitative determination of both alkaloids in herbal tea infusions and Solanaceae plant material. A standard additions procedure using triply deuterated Atr as internal standard was developed and validated.

RESULTS

Tropane alkaloids were detected without interferences and the standard additions procedure allowed reliable quantification. Intraday and interday precision were less than 17% and corresponding accuracies were between 77% and 112%. Limits of detection in the spotting solution were found at 5 ng/mL (Atr) and 0.5 ng/mL (Scp). The assay was applied to diverse tea infusions as well as to berries and leaves of deadly nightshade and angel's trumpet.

CONCLUSIONS

The usefulness of MALDI-TOF MS(/MS) for investigations of plant-derived samples to prove contaminations by small basic compounds was demonstrated. The elaborate procedure is reliable but quite laborious to obtain quantitative results, but MALDI-TOF MS(/MS) was also shown to be a valuable tool for rapid qualitative screening for Atr and Scp in plant extracts.

Anatomical-Molecular Distribution of EphrinA1 in Infarcted Mouse Heart Using MALDI Mass Spectrometry Imaging

EphrinA1 is a tyrosine kinase receptor localized in the cellular membrane of healthy cardiomyocytes, the expression of which is lost upon myocardial infarction (MI). Intra-cardiac injection of the recombinant form of ephrinA1 (ephrinA1-Fc) at the time of ligation in mice has shown beneficial effects by reducing infarct size and myocardial necrosis post-MI. To date, immunohistochemistry and Western blotting comprise the only experimental approaches utilized to localize and quantify relative changes of ephrinA1 in sections and homogenates of whole left ventricle, respectively. Herein, we used matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) coupled with a time-of-flight mass spectrometer (MALDI/TOF MS) to identify intact as well as tryptic fragments of ephrinA1 in healthy controls and acutely infarcted murine hearts. The purpose of the present study was 3-fold: (1) to spatially resolve the molecular distribution of endogenous ephrinA1, (2) to determine the anatomical expression profile of endogenous ephrinA1 after acute MI, and (3) to identify molecular targets of ephrinA1-Fc action post-MI. The tryptic fragments detected were identified as the ephrinA1-isoform with 38% and 34% sequence coverage and Mascot scores of 25 for the control and MI hearts, respectively. By using MALDI-MSI, we have been able to simultaneously measure the distribution and spatial localization of ephrinA1, as well as additional cardiac proteins, thus offering valuable information for the elucidation of molecular partners, mediators, and targets of ephrinA1 action in cardiac muscle. Graphical Abstract ᅟ.

Mass Spectrometry Based Profiling and Imaging of Various Ginsenosides from Panax ginseng Roots at Different Ages

(1) Background: Panax ginseng root is one of the most important herbal products, and the profiling of ginsenosides is critical for the quality control of ginseng roots at different ages in the herbal markets. Furthermore, interest in assessing the contents as well as the localization of biological compounds has been growing. The objective of this study is to carry out the mass spectrometry (MS)-based profiling and imaging of ginsenosides to assess ginseng roots at different ages; (2) Methods: Optimal ultra performance liquid chromatography coupled to quadrupole time of flight/MS (UPLC-QTOF/MS) was used to profile various ginsenosides from P. ginseng roots. Matrix-assisted laser desorption ionization (MALDI)-time of flight (TOF)/MS-based imaging was also optimized to visualize ginsenosides in ginseng roots; (3) Results: UPLC-QTOF/MS was used to profile 30 ginsenosides with high mass accuracy, with an in-house library constructed for the fast and exact identification of ginsenosides. Using this method, the levels of 14 ginsenosides were assessed in P. ginseng roots cultivated for 4, 5, and 6 years. The optimal MALDI-imaging MS (IMS) was also applied to visualize the 14 ginsenosides in ginseng roots. As a result, the MSI cross sections showed the localization of 4 ginsenoside ions ([M + K]⁺) in P. ginseng roots at different ages; (4) Conclusions: The contents and localization of various ginsenosides differ depending on the cultivation years of P. ginseng roots. Furthermore, this study demonstrated the utility of MS-based profiling and imaging of ginsenosides for the quality control of ginseng roots.

Comparative mass spectrometry-based metabolomics strategies for the investigation of microbial secondary metabolites

Covering: 2000 to 2016The labor-intensive process of microbial natural product discovery is contingent upon identifying discrete secondary metabolites of interest within complex biological extracts, which contain inventories of all extractable small molecules produced by an organism or consortium. Historically, compound isolation prioritization has been driven by observed biological activity and/or relative metabolite abundance and followed by dereplication via accurate mass analysis. Decades of discovery using variants of these methods has generated the natural pharmacopeia but also contributes to recent high rediscovery rates. However, genomic sequencing reveals substantial untapped potential in previously mined organisms, and can provide useful prescience of potentially new secondary metabolites that ultimately enables isolation. Recently, advances in comparative metabolomics analyses have been coupled to secondary metabolic predictions to accelerate bioactivity and abundance-independent discovery work flows. In this review we will discuss the various analytical and computational techniques that enable MS-based metabolomic applications to natural product discovery and discuss the future prospects for comparative metabolomics in natural product discovery.

MALDI-imaging enables direct observation of kinetic and thermodynamic products of mixed peptide fiber assembly

The first use of MALDI-imaging, as a snapshot tool to characterize multicomponent self-assembling peptide fibers.

MALDI mass spectrometry imaging in rheumatic diseases

Mass spectrometry imaging (MSI) is a technique used to visualize the spatial distribution of biomolecules such as peptides, proteins, lipids or other organic compounds by their molecular masses. Among the different MSI strategies, MALDI-MSI provides a sensitive and label-free approach for imaging of a wide variety of protein or peptide biomarkers from the surface of tissue sections, being currently used in an increasing number of biomedical applications such as biomarker discovery and tissue classification. In the field of rheumatology, MALDI-MSI has been applied to date for the analysis of joint tissues such as synovial membrane or cartilage. This review summarizes the studies and key achievements obtained using MALDI-MSI to increase understanding on rheumatic pathologies and to describe potential diagnostic or prognostic biomarkers of these diseases. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Molecular imaging of brain localization of liposomes in mice using MALDI mass spectrometry

Phospholipids have excellent biocompatibility and are therefore often used as main components of liposomal drug carriers. In traditional bioanalytics, the in-vivo distribution of liposomal drug carriers is assessed using radiolabeled liposomal constituents. This study presents matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) as an alternative, label-free method for ex-vivo molecular imaging of liposomal drug carriers in mouse tissue. To this end, indocyanine green as cargo and two liposomal markers, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine conjugated with monodisperse polyethylene glycol (PEG36-DSPE) were incorporated into liposomal carriers and administered to mice. We used MALDI MSI of the two lipid markers in both positive and negative ion mode for visualization of liposome integrity and distribution in mouse organs. Additional MSI of hemoglobin in the same tissue slice and pixel-by-pixel computational analysis of co-occurrence of lipid markers and hemoglobin served as indicator of liposome localization either in parenchyma or in blood vessels. Our proof-of-concept study suggests that liposomal components and indocyanine green distributed into all investigated organs.

Protease-resistant modified human β-hexosaminidase B ameliorates symptoms in GM2 gangliosidosis model

GM2 gangliosidoses, including Tay-Sachs and Sandhoff diseases, are neurodegenerative lysosomal storage diseases that are caused by deficiency of β-hexosaminidase A, which comprises an αβ heterodimer. There are no effective treatments for these diseases; however, various strategies aimed at restoring β-hexosaminidase A have been explored. Here, we produced a modified human hexosaminidase subunit β (HexB), which we have termed mod2B, composed of homodimeric β subunits that contain amino acid sequences from the α subunit that confer GM2 ganglioside-degrading activity and protease resistance. We also developed fluorescent probes that allow visualization of endocytosis of mod2B via mannose 6-phosphate receptors and delivery of mod2B to lysosomes in GM2 gangliosidosis models. In addition, we applied imaging mass spectrometry to monitor efficacy of this approach in Sandhoff disease model mice. Following i.c.v. administration, mod2B was widely distributed and reduced accumulation of GM2, asialo-GM2, and bis(monoacylglycero)phosphate in brain regions including the hypothalamus, hippocampus, and cerebellum. Moreover, mod2B administration markedly improved motor dysfunction and a prolonged lifespan in Sandhoff disease mice. Together, the results of our study indicate that mod2B has potential for intracerebrospinal fluid enzyme replacement therapy and should be further explored as a gene therapy for GM2 gangliosidoses.

Proteomic MALDI-TOF/TOF-IMS examination of peptide expression in the formalin fixed brainstem and changes in sudden infant death syndrome infants

Matrix assisted laser desorption/ionisation imaging mass spectrometry (MALDI-IMS) has not previously been utilised to examine sudden infant death syndrome (SIDS). This study aimed to optimise MALDI IMS for use on archived formalin-fixed-paraffin-embedded human infant medulla tissue (n=6, controls; n=6, SIDS) to evaluate differences between multiple nuclei of the medulla by using high resolution IMS. Profiles were compared between SIDS and age/sex matched controls. LC-MALDI identified 55 proteins based on 321 peptides across all samples; 286 peaks were found using IMS, corresponding to these 55 proteins that were directly compared between controls and SIDS. Control samples were used to identify common peptides for neuronal/non-neuronal structures allowing identification of medullary regions. In SIDS, abnormal expression patterns of 41 peptides (p≤0.05) corresponding to 9 proteins were observed; these changes were confirmed with immunohistochemistry. The protein abnormalities varied amongst nuclei, with the majority of variations in the raphe nuclei, hypoglossal and pyramids. The abnormal proteins are not related to a previously identified neurological disease pathway but consist of developmental neuronal/glial/axonal growth, cell metabolism, cyto-architecture and apoptosis components. This suggests that SIDS infants have abnormal neurological development in the raphe nuclei, hypoglossal and pyramids of the brainstem, which may contribute to the pathogenesis of SIDS.

BIOLOGICAL SIGNIFICANCE

This study is the first to perform an imaging mass spectrometry investigation in the human brainstem and also within sudden infant death syndrome (SIDS). LC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue; with abnormal expression patterns present for 41/285 and 9/55 proteins in SIDS using IMS. The abnormal proteins are critical for neurological development; with the impairment supporting the hypothesis that SIDS may be due to delayed neurological maturation. The brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids. This study highlights that basic cyto-architectural proteins are affected in SIDS and that abnormal expression of these proteins in other CNS disorders should be examined.

KEY SENTENCES

LC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue. Abnormal expression patterns were present for 41/285 and 9/55 proteins in SIDS using IMS. Brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids.

Optimized Protocol To Analyze Changes in the Lipidome of Xenografts after Treatment with 2-Hydroxyoleic Acid

Xenografts are a popular model for the study of the action of new antitumor drugs. However, xenografts are highly heterogeneous structures, and therefore it is sometimes difficult to evaluate the effects of the compounds on tumor metabolism. In this context, imaging mass spectrometry (IMS) may yield the required information, due to its inherent characteristics of sensitivity and spatial resolution. To the best of our knowledge, there is still no clear analysis protocol to properly evaluate the changes between samples due to the treatment. Here we present a protocol for the evaluation of the effect of 2-hydroxyoleic acid (2-OHOA), an antitumor compound, on xenografts lipidome based on IMS. Direct treated/control comparison did not show conclusive results. As we will demonstrate, a more sophisticated protocol was required to evaluate these changes including the following: (1) identification of different areas in the xenograft, (2) classification of these areas (necrotic/viable) to compare similar types of tissues, (3) suppression of the effect of the variation of adduct formation between samples, and (4) normalization of the variables using the standard deviation to eliminate the excessive impact of the stronger peaks in the statistical analysis. In this way, the 36 lipid species that experienced the largest changes between treated and control were identified. Furthermore, incorporation of 2-hydroxyoleic acid to a sphinganine base was also confirmed by MS/MS. Comparison of the changes observed here with previous results obtained with different techniques demonstrates the validity of the protocol.

Review of matrix-assisted laser desorption ionization-imaging mass spectrometry for lipid biochemical histopathology

Matrix-Assisted Laser Desorption Ionization-Imaging Mass Spectrometry (MALDI-IMS) is a rapidly evolving method used for the in situ visualization and localization of molecules such as drugs, lipids, peptides, and proteins in tissue sections. Therefore, molecules such as lipids, for which antibodies and other convenient detection reagents do not exist, can be detected, quantified, and correlated with histopathology and disease mechanisms. Furthermore, MALDI-IMS has the potential to enhance our understanding of disease pathogenesis through the use of "biochemical histopathology". Herein, we review the underlying concepts, basic methods, and practical applications of MALDI-IMS, including post-processing steps such as data analysis and identification of molecules. The potential utility of MALDI-IMS as a companion diagnostic aid for lipid-related pathological states is discussed.

Imaging mass spectrometry increased resolution using 2-mercaptobenzothiazole and 2,5-diaminonaphtalene matrices: application to lipid distribution in human colon

Imaging mass spectrometry is becoming a reference technique in the field of lipidomics, due to its ability to map the distribution of hundreds of species in a single run, along a tissue section. The next frontier is now achieving increasing resolution powers to offer cellular (or even sub-cellular) resolution. Thus, the new spectrometers are equipped with sophisticated optical systems to decrease the laser spot to <30 μm. Here, we demonstrate that by using the correct matrix (i.e., a matrix that maximizes ion detection and forms small crystals) and a careful preparation, it is possible to achieve resolutions of ∼5-10 μm, even with spectrometers equipped with non-optimal optics, which produces laser spots of 50 μm or even larger. As a proof of concept, we present images of distributions of lipids, both in positive and negative ion mode, over human colon endoscopic sections, recorded using 2-mercaptobenzothiazole for positive ion mode and 2,5-diaminonaphtalene for negative ion mode and an LTQ-Orbitrap XL, equipped with a matrix-assisted laser desorption ionization (MALDI) source that produces astigmatic laser spots. Graphical Abstract Imaging mass spectrometry is becoming an invaluable technique to complement traditional histology, but still higher resolutions are required. Here we deal with such issue.

Imaging Mass Spectrometric Analysis of Neurotransmitters: A Review

Imaging mass spectrometry (IMS) is a toolbox of versatile techniques that enable us to investigate analytes in samples at molecular level. In recent years, IMS, and especially matrix-assisted laser desorption/ionisation (MALDI), has been used to visualise a wide range of metabolites in biological samples. Simultaneous visualisation of the spatial distribution of metabolites in a single sample with little tissue disruption can be considered as one important advantage of MALDI over other techniques. However, several technical hurdles including low concentrations and rapid degradation rates of small molecule metabolites, matrix interference of signals and poor ionisation, need to be addressed before MALDI can be considered as a reliable tool for the analysis of metabolites such as neurotransmitters in brain tissues from different sources including humans. In the present review we will briefly describe current MALDI IMS techniques used to study neurotransmitters and discuss their current status, challenges, as well as future prospects.

Characterization of lipidic markers of chondrogenic differentiation using mass spectrometry imaging

Mesenchymal stem cells (MSC) are an interesting alternative for cell-based therapy of cartilage defects attributable to their capacity to differentiate toward chondrocytes in the process termed chondrogenesis. The metabolism of lipids has recently been associated with the modulation of chondrogenesis and also with the development of pathologies related to cartilage degeneration. Information about the distribution and modulation of lipids during chondrogenesis could provide a panel of putative chondrogenic markers. Thus, the discovery of new lipid chondrogenic markers could be highly valuable for improving MSC-based cartilage therapies. In this work, MS imaging was used to characterize the spatial distribution of lipids in human bone marrow MSCs during the first steps of chondrogenic differentiation. The analysis of MSC micromasses at days 2 and 14 of chondrogenesis by MALDI-MSI led to the identification of 20 different lipid species, including fatty acids, sphingolipids, and phospholipids. Phosphocholine, several sphingomyelins, and phosphatidylcholines were found to increase during the undifferentiated chondrogenic stage. A particularly detected lipid profile was verified by TOF secondary ion MS. Using this technology, a higher intensity of phosphocholine-related ions was observed in the peripheral region of the micromasses collected at day 14.

MALDI mass spectrometric imaging meets “omics”: recent advances in the fruitful marriage

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI MSI) is a method that allows the investigation of the molecular content of surfaces, in particular, tissues, within its morphological context.

MALDI TOF imaging mass spectrometry in clinical pathology: a valuable tool for cancer diagnostics (review)

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) imaging mass spectrometry (IMS) is an evolving technique in cancer diagnostics and combines the advantages of mass spectrometry (proteomics), detection of numerous molecules, and spatial resolution in histological tissue sections and cytological preparations. This method allows the detection of proteins, peptides, lipids, carbohydrates or glycoconjugates and small molecules.Formalin-fixed paraffin-embedded tissue can also be investigated by IMS, thus, this method seems to be an ideal tool for cancer diagnostics and biomarker discovery. It may add information to the identification of tumor margins and tumor heterogeneity. The technique allows tumor typing, especially identification of the tumor of origin in metastatic tissue, as well as grading and may provide prognostic information. IMS is a valuable method for the identification of biomarkers and can complement histology, immunohistology and molecular pathology in various fields of histopathological diagnostics, especially with regard to identification and grading of tumors.

Mass spectrometry of natural products: current, emerging and future technologies

Although mass spectrometry is a century old technology, we are entering into an exciting time for the analysis of molecular information directly from complex biological systems. In this Highlight, we feature emerging mass spectrometric methods and tools used by the natural product community and give a perspective of future directions where the mass spectrometry field is migrating towards over the next decade.