Advances in mass spectrometry imaging for spatial cancer metabolomics

Mass spectrometry (MS) has become a central technique in cancer research. The ability to analyze various types of biomolecules in complex biological matrices makes it well suited for understanding biochemical alterations associated with disease progression. Different biological samples, including serum, urine, saliva, and tissues have been successfully analyzed using mass spectrometry. In particular, spatial metabolomics using MS imaging (MSI) allows the direct visualization of metabolite distributions in tissues, thus enabling in-depth understanding of cancer-associated biochemical changes within specific structures. In recent years, MSI studies have been increasingly used to uncover metabolic reprogramming associated with cancer development, enabling the discovery of key biomarkers with potential for cancer diagnostics. In this review, we aim to cover the basic principles of MSI experiments for the nonspecialists, including fundamentals, the sample preparation process, the evolution of the mass spectrometry techniques used, and data analysis strategies. We also review MSI advances associated with cancer research in the last 5 years, including spatial lipidomics and glycomics, the adoption of three-dimensional and multimodal imaging MSI approaches, and the implementation of artificial intelligence/machine learning in MSI-based cancer studies. The adoption of MSI in clinical research and for single-cell metabolomics is also discussed. Spatially resolved studies on other small molecule metabolites such as amino acids, polyamines, and nucleotides/nucleosides will not be discussed in the context.

Visualizing the Spatial Distribution of Arctium lappa L. Root Components by MALDI-TOF Mass Spectrometry Imaging

This study is aimed at developing novel analytical methods to accurately visualize the spatial distribution of various endogenous components in Arctium lappa L. (A. lappa) roots, and to precisely guide the setting of pre-treatment operations during processing technologies and understand plant metabolism process. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) imaging technology was used for visual demonstration of the in situ spatial distribution in A. lappa roots. This work consisted of four steps: matrix selection, section preparation, matrix coating, and MALDI-TOF MS imaging analysis. Consequently, eight saccharides, four caffeoylquinic acids, four flavonoids, six amino acids, one choline, and one phospholipid were imaged and four unidentified components were found. Saccharides were distributed in the center, whereas caffeoylquinic acids and flavonoids were mainly present in the epidermis and cortex. Furthermore, amino acids were mainly detected in the phloem, and choline in the cambium, while phosphatidylserine was found in the secondary phloem and cambium. This study demonstrated that MALDI-TOF MS imaging technology could provide a technical support to understand the spatial distribution of components in A. lappa roots, which would promote the processing technologies for A. lappa roots and help us to understand the plant metabolism process.

Synthesis and Investigation of Novel CHCA-Derived Matrices for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometric Analysis of Lipids

A significant area of study and upgrading for increasing sensitivity and general performances of matrix-assisted laser-desorption ionization (MALDI) mass spectrometry (MS) is related to matrix design. Several efforts have been made to address the challenge of low-mass-region interference-free for metabolomics analysis and specifically for lipidomics. To this aim, rationally designed matrices as 4-chloro-α-cyanocinnamic acid (ClCCA) were introduced and reported to provide enhanced analytical performances. We have taken this rational design one step further by developing and optimizing new MALDI matrices with a range of modifications on the CHCA core, involving different functionalities and substituents. Of particular interest was the understanding of the electron-withdrawing (e.g., nitro-) or donating (e.g., methoxy-) effects along with the extent of conjugation on the ionization efficiency. In the present work, ten matrices were designed on a reasonable basis, synthesized, and characterized by NMR and UV spectroscopies and laser desorption ionization. With the assistance of these putative MALDI matrices, samples containing phospholipids (PL), and neutral di-/tri-acylglycerols (DAG, TAG) were investigated using milk, fish, blood, and human plasma extracts. In comparison with CHCA and ClCCA, four of them, viz. [(2E,4E)-2-cyano-5-(4-methoxyphenyl)penta-2,4-dienoic acid] (1), [(2E,4E)-2-cyano-5-(4-nitrophenyl)penta-2,4-dienoic acid] (2), [(E)-2-cyano-3-(6-methoxynaphthalen-2-yl)acrylic acid] (6) and [(E)-2-cyano-3-(naphthalen-2-yl)acrylic acid] (7) displayed good to even excellent performances as MALDI matrices in terms of ionization capability, interference-free spectra, S/N ratio, and reproducibility. Especially compound 7 (cyano naphthyl acrylic acid, CNAA) was the election matrix for PL analysis and matrix 2 (cyano nitrophenyl dienoic acid, CNDA) for neutral lipids such as DAG and TAG in positive ion mode.

Mass Spectrometry Imaging of Biological Tissues by Laser Desorption Ionization from Silicon Nanopost Arrays

Mass spectrometry imaging (MSI) plays an expanding role in the label-free spatial mapping of hundreds of molecules simultaneously. Currently, matrix-assisted laser desorption ionization (MALDI) is among the most widely adopted MSI techniques. However, matrix application can impact the fidelity of spatial distributions, and matrix selection and related spectral interferences in the low mass range can lead to biased molecular coverage. Nanophotonic ionization from silicon nanopost arrays (NAPA) is an emerging matrix-free MSI platform with enhanced sensitivity for several molecular classes, for example, neutral lipids and biooligomers. Here, we describe a protocol with minimal sample preparation for NAPA-MSI of metabolites, lipids, and biooligomers from biological tissues.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

In Situ Localization of Plant Lipid Metabolites by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI)

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has emerged as a major analytical platform for the determination and localization of lipid metabolites directly from tissue sections. Unlike analysis of lipid extracts, where lipid localizations are lost due to homogenization and/ or solvent extraction, MALDI-MSI analysis is capable of revealing spatial localization of metabolites while simultaneously collecting high chemical resolution mass spectra. Important considerations for obtaining high quality MALDI-MS images include tissue preservation, section preparation, MS data collection and data processing. Errors in any of these steps can lead to poor quality metabolite images and increases the chance for metabolite misidentification and/ or incorrect localization. Here, we present detailed methods and recommendations for specimen preparation, MALDI-MS instrument parameters, software analysis platforms for data processing, and practical considerations for each of these steps to ensure acquisition of high-quality chemical and spatial resolution data for reconstructing MALDI-MS images of plant tissues.

Mass Spectrometry Imaging of Bio-oligomer Polydispersity in Plant Tissues by Laser Desorption Ionization from Silicon Nanopost Arrays

Mass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI-MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix-free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra-trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA-LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA-LDI-MSI.

A boronic acid modified binary matrix consisting of boron nitride and α-cyano-4-hydroxycinnamic acid for determination of cis-diols by MALDI-TOF MS

A MALDI-TOF mass spectrometric method is described for the determination of small molecule compounds with cis-diol. It is based on the use of a binary matrix consisting of boron nitride (BN) and α-cyano-4-hydroxycinnamic acid that was modified with the derivatization reagent of (3-(acridin-9-ylamino)phenyl)boronic acid which can recognize cis-diols. The binary matrix is used for desorption/ionization (DI) in the positive ion mode. The mechanism leading to DI enhancement was investigated. The results imply that BN is beneficial for the DI because it induces an enhancement in the positive ion mode. The boronic acid-functionalized binary matrix was successfully applied to capture the glucose, shikimic acid and quinic acid. The method was applied to the determination of 3-chloro-1,2-propanediol in plant oil. Graphical abstract Schematic representation of a method for detecting the cis-diol compounds on matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) using the binary matrix of boron nitride (BN)/α-cyano-4-hydroxycinnamic acid (CHCA) that was modified with (3-(acridin-9-ylamino)phenyl) boronic acid (AYPBA).

Sputter-Coated Metal Screening for Small Molecule Analysis and High-Spatial Resolution Imaging in Laser Desorption Ionization Mass Spectrometry

Nanoparticles are efficient matrices in laser desorption/ionization (LDI) mass spectrometry (MS), especially for the profiling or imaging of small molecules. Recently, solvent-free physical vapor desorption (PVD), or sputter coating, was adopted as a homogenous method to rapidly apply metal nanoparticles (NPs) in situ to samples prior to LDI MS or MS imaging analysis. However, there has been no systematic study comparing different metal targets for the analysis of a variety of small molecule metabolites. Here, we present a screening and optimization of various sputter-coated metals, including Ag, Au, Cu, Pt, Ni, and Ti, for LDI analysis of small molecules in both positive and negative ion modes. Optimized sputter coating is then applied to high-spatial resolution LDI mass spectrometry imaging (MSI) of maize root and seed cross-sections. Noble metals, Ag, Au, and Pt, are found to be much more efficient than transition metals and organic matrices for most small metabolites. Sputter-coated metals are efficient for neutral lipids, such as triacylglycerols and diacylglycerols, but are very inefficient for most phospholipids. Graphical Abstract ᅟ.

Cellular and Subcellular Level Localization of Maize Lipids and Metabolites Using High-Spatial Resolution MALDI Mass Spectrometry Imaging

Recent technological advances have pushed the achievable spatial resolution for mass spectrometry imaging (MSI) to cellular and subcellular levels. Direct visualization of maize tissues by this tool has provided key insights into the localization of metabolites and lipids. This chapter outlines methodology for sample preparation, data acquisition, and data analysis of maize tissue sections using high-spatial resolution matrix-assisted laser desorption ionization (MALDI)-MSI, as well as the incorporation of a multi-resolution optical system, which allows for simple inter-conversion between different resolution setups (5, 10, and 50 μm imaging).

3D MALDI Mass Spectrometry Imaging of a Single Cell: Spatial Mapping of Lipids in the Embryonic Development of Zebrafish

The zebrafish (Danio rerio) has been widely used as a model vertebrate system to study lipid metabolism, the roles of lipids in diseases, and lipid dynamics in embryonic development. Here, we applied high-spatial resolution matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI) to map and visualize the three-dimensional spatial distribution of phospholipid classes, phosphatidylcholine (PC), phosphatidylethanolamines (PE), and phosphatidylinositol (PI), in newly fertilized individual zebrafish embryos. This is the first time MALDI-MSI has been applied for three dimensional chemical imaging of a single cell. PC molecular species are present inside the yolk in addition to the blastodisc, while PE and PI species are mostly absent in the yolk. Two-dimensional MSI was also studied for embryos at different cell stages (1-, 2-, 4-, 8-, and 16-cell stage) to investigate the localization changes of some lipids at various cell developmental stages. Four different normalization approaches were compared to find reliable relative quantification in 2D- and 3D- MALDI MSI data sets.

High-Spatial Resolution Mass Spectrometry Imaging: Toward Single Cell Metabolomics in Plant Tissues

Mass spectrometry imaging (MSI) is a powerful tool that has advanced our understanding of complex biological processes by enabling unprecedented details of metabolic biology to be uncovered. Through the use of high-spatial resolution MSI, metabolite localizations can be obtained with high precision. Here we describe our recent progress to enhance the spatial resolution of matrix-assisted laser desorption/ionization (MALDI) MSI from ∼50 μm with the commercial configuration to ∼5 μm. Additionally, we describe our efforts to develop a 'multiplex MSI' data acquisition method to allow more chemical information to be obtained on a single tissue in a single instrument run, and the development of new matrices to improve the ionization efficiency for a variety of small molecule metabolites. In combination, these contributions, along with the efforts of others, will bring MSI experiments closer to achieving metabolomic scale.

Optimum Conditions for the Fabrication of Zein/Ag Composite Nanoparticles from Ethanol/H₂O Co-Solvents Using Electrospinning

The optimum conditions for the fabrication of zein/Ag composite nanoparticles from ethanol/H₂O cosolvents using electrospinning and the properties of the composite were investigated. The zein/Ag nanoparticles were characterized using field-emission scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis. The antibacterial activity of the zein/Ag composite nanoparticles was also investigated. The XRD patterns and TEM images indicate the coexistence of a zein matrix and well-distributed Ag nanoparticles.