Search

Summary: Monitoring and localizing molecules on living plants is critical for understanding their growth, development and disease. However, current techniques for molecular imaging of living plants often lack spatial information or require tedious pre‐labelling. Here, we proposed a novel molecular imaging platform that combines sliver nanowire‐doped Ti3C2 MXene (Ag NWs@MXene) flexible film substrate with laser desorption/ionization mass spectrometry imaging (AMF‐LDI‐MSI) to study the spatial distribution of biomolecules on the surface of living plants. This platform overcomes the MSI challenges posed by difficult‐to‐slice plant tissues (e.g., tough or water‐rich roots and fragile flowers) and enables precisely transfer and visualize the molecule. Comparisons of the measurement results to those from matrix‐assisted LDI‐MSI (MALDI‐MSI) technology demonstrate the accuracy and reliability of the platform. Biocompatibility evaluations indicated that the platform without observable adverse effects on the health of living plants. The distribution of growth and disease‐associated signalling molecules, such as choline, organic acids and carbohydrates, can be in situ non‐destructively detected on the surfaces of living plants, which is important for tracking the health of plants and their diseased areas. AMF‐LDI‐MSI platform can serve as a promising tool for label‐free, in situ and non‐destructive monitoring of functional biomolecules and plant growth from a spatial perspective. [ABSTRACT FROM AUTHOR]

Metabolic abnormalities in mammalian joint tissues are closely linked to various diseases, including rheumatoid arthritis and osteoarthritis. The variations of small molecule metabolites within bone joint tissues can affect cell proliferation, drive the secretion of inflammatory mediators, mediate leukocyte infiltration, and consequently induce synovial inflammation and cartilage damage. Therefore, the development of novel mass spectrometry imaging (MSI) methods for visualizing metabolites in joint tissues is crucial for comprehensively understanding the metabolic characteristics of different microregions under both physiological and pathological conditions. In this study, an airflow-assisted desorption electrospray ionization (AFADESI)-MSI was used to establish an ambient MSI method for rat joint tissues. To ensure the effectiveness of the method, dynamic range, sensitivity, and imaging effect were selected as the primary evaluation criteria. The tissue preparation, section thickness, and spray solvent systems were systematically optimized. Compared to the AB glue transfer method, the tape adhesion method can obtain complete bone joint tissue sections and clearer images. A section thickness of 20 μm, as opposed to 15 μm, provides higher ion intensity in the m/z 600-900 range. Among the tested spray solvent systems, compared with methanol-water (8:2, V/V), acetonitrile-water (8:2, V/V), and the acetonitrile-isopropanol-water (6:2:2, V/V/V), the acetonitrile-isopropanol-water (4:4:2, V/V/V) prove to be the most effective, detecting the highest number of metabolites and lipids when employed as the spray solvent. The precision of this method was evaluated on six adjacent rat knee sections under positive and negative ion modes, with the relative standard deviation (RSD) for the ion intensity of representative metabolites being less than 20%. Subsequently, this method was utilized for spatially resolved metabolomics analysis of rat knee tissues. A total of 613 metabolites are annotated in the overall knee tissues. Based on the optical images, the rat knee tissues were segmented into three microregions for bone, marrow, and cartilage. 452, 418, and 451 metabolites in these microregions are identified, respectively. In bone, the pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, and the TCA cycle are more prominent. In bone marrow, ascorbate and purine metabolism pathways are more significant. In cartilage, arginine and proline metabolism, as well as lysine degradation, are more pronounced. These findings highlight significant metabolic heterogeneity across different microregions of rat knee joint tissues. Overall, this study develops an AFADESI-MSI method for in-depth profiling of metabolites within rat joint tissues, providing a powerful tool for in situ visualization of metabolites in metabolic studies of joint tissues.

Copyright of Journal of Chinese Mass Spectrometry Society is the property of Journal of Chinese Mass Spectrometry Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Matrix selection and application is a crucial step in obtaining meaningful results with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). Most instruments have a large spatial, and data with adequate spatial resolution can frequently be obtained on a benchtop instrument. The matrix application workflow has been optimized for the imaging of the earthworm (Eisenia hortensis), after exposure to various statins, a class of blood lipid-lowering agents. Lipids are nonpolar, often neutral molecules, making them difficult to ionize, and heightening the need for matrix optimization. The matrices 2,5-dihydroxybenzoic acid (DHB), a-cyano-4- hydroxycinammic acid (CHCA), 1,5-diaminonaphthalene (DAN), and 3,5- dimethoxy-4-hydroxycinnamic acid (sinapinic acid; SA) were studied. Samples were also washed in the ammonium salts of acetate, bicarbonate, formate, sulfate, or water as a control to enhance ionization and improve spatial resolution. A successful matrix for MSI is one that demonstrates homogenous tissue coverage, ionization of the analytes of interest, and does not require excessive laser power for ionization. All matrices showed sufficient tissue coverage; however, CHCA yielded unambiguous images of cholesterol and yielded sufficient signal over the lipid mass range (400-1,000m/z), indicating that it successfully ionized endogenous lipids. Following additional optimization, the application of 50 mL of 10 mg/mL CHCA following a 5 s salt ammonium sulfate salt wash proved most successful for improving lipid ionization and enhancing spatial resolution. [ABSTRACT FROM AUTHOR]

ABSTRACT Trichodesmium, a globally significant N2-fixing marine cyanobacterium, forms extensive surface blooms in nutrient-poor ocean regions. These blooms consist of a dynamic assemblage of Trichodesmium species that form distinct colony morphotypes and are inhabited by diverse microorganisms. Trichodesmium colony morphotypes vary in ecological niche, nutrient uptake, and organic molecule release, differentially impacting ocean carbon and nitrogen biogeochemical cycles. Here, we assessed the poorly studied spatial abundance of metabolites within and between three morphologically distinct Trichodesmium colonies collected from the Red Sea. We also compared these results with two morphotypes of the cultivable Trichodesmium strain IMS101. Using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) coupled with liquid extraction surface analysis (LESA) tandem mass spectrometry (MS2), we identified and localized a wide range of small metabolites associated with single-colony Trichodesmium morphotypes. Our untargeted MALDI-MSI approach revealed 80 unique features (metabolites) shared between Trichodesmium morphotypes. Discrimination analysis showed spatial variations in 57 shared metabolites, accounting for 62% of the observed variation between morphotypes. The greatest variations in metabolite abundance were observed between the cultured morphotypes compared to the natural colony morphotypes, suggesting substantial differences in metabolite production between the cultivable strain IMS101 and the naturally occurring colony morphotypes that the cultivable strain is meant to represent. This study highlights the variations in metabolite abundance between natural and cultured Trichodesmium morphotypes and provides valuable insights into metabolites common to morphologically distinct Trichodesmium colonies, offering a foundation for future targeted metabolomic investigations.IMPORTANCEThis work demonstrates that the application of spatial mass spectrometry imaging at single-colony resolution can successfully resolve metabolite differences between natural and cultured Trichodesmium morphotypes, shedding light on their distinct biochemical profiles. Understanding the morphological differences between Trichodesmium colonies is crucial because they impact nutrient uptake, organic molecule production, and carbon and nitrogen export, and subsequently influence ocean biogeochemical cycles. As such, our study serves as an important initial assessment of metabolite differences between distinct Trichodesmium colony types, identifying features that can serve as ideal candidates for future targeted metabolomic studies.

Mass spectrometry imaging (MSI) has emerged as an invaluable analytical technique for investigating the spatial distribution of molecules within biological systems. In the realm of plant science, MSI is increasingly employed to explore metabolic processes across a wide array of plant tissues, including those in leaves, fruits, stems, roots, and seeds, spanning various plant systems such as model species, staple and energy crops, and medicinal plants. By generating spatial maps of metabolites, MSI has elucidated the distribution patterns of diverse metabolites and phytochemicals, encompassing lipids, carbohydrates, amino acids, organic acids, phenolics, terpenes, alkaloids, vitamins, pigments, and others, thereby providing insights into their metabolic pathways and functional roles. In this review, we present recent MSI studies that demonstrate the advances made in visualizing the plant spatial metabolome. Moreover, we emphasize the technical progress that enhances the identification and interpretation of spatial metabolite maps. Within a mere decade since the inception of plant MSI studies, this robust technology is poised to continue as a vital tool for tackling complex challenges in plant metabolism. [ABSTRACT FROM AUTHOR]

Given the complexity of nervous tissues, understanding neurochemical pathophysiology puts high demands on bioanalytical techniques with respect to specificity and sensitivity. Mass spectrometry imaging (MSI) has evolved to become an important, biochemical imaging technology for spatial biology in biological and translational research. The technique facilitates comprehensive, sensitive elucidation of the spatial distribution patterns of drugs, lipids, peptides, and small proteins in situ. Matrix‐assisted laser desorption ionization (MALDI)‐based MSI is the dominating modality due to its broad applicability and fair compromise of selectivity, sensitivity price, throughput, and ease of use. This is particularly relevant for the analysis of spatial lipid patterns, where no other comparable spatial profiling tools are available. Understanding spatial lipid biology in nervous tissue is therefore a key and emerging application area of MSI research. The aim of this review is to give a concise guide through the MSI workflow for lipid imaging in central nervous system (CNS) tissues and essential parameters to consider while developing and optimizing MSI assays. Further, this review provides a broad overview of key developments and applications of MALDI MSI‐based spatial neurolipidomics to map lipid dynamics in neuronal structures, ultimately contributing to a better understanding of neurodegenerative disease pathology. [ABSTRACT FROM AUTHOR]

Matrix selection and application is a crucial step in obtaining meaningful results with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). Most instruments have a large spatial, and data with adequate spatial resolution can frequently be obtained on a benchtop instrument. The matrix application workflow has been optimized for the imaging of the earthworm (Eisenia hortensis), after exposure to various statins, a class of blood lipid-lowering agents. Lipids are nonpolar, often neutral molecules, making them difficult to ionize, and heightening the need for matrix optimization. The matrices 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinammic acid (CHCA), 1,5-diaminonaphthalene (DAN), and 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid; SA) were studied. Samples were also washed in the ammonium salts of acetate, bicarbonate, formate, sulfate, or water as a control to enhance ionization and improve spatial resolution. A successful matrix for MSI is one that demonstrates homogenous tissue coverage, ionization of the analytes of interest, and does not require excessive laser power for ionization. All matrices showed sufficient tissue coverage; however, CHCA yielded unambiguous images of cholesterol and yielded sufficient signal over the lipid mass range (400–1,000 m/z), indicating that it successfully ionized endogenous lipids. Following additional optimization, the application of 50 mL of 10 mg/mL CHCA following a 5 s salt ammonium sulfate salt wash proved most successful for improving lipid ionization and enhancing spatial resolution.

Mass spectrometry imaging（MSI）based on spatially resolved metabolomics（SRM）has been recently developed to be a powerful technology. SRM can not only directly identify and quantify the metabolites in animal and plant tissues or cells in situ, but also use overall or local features of the image to determine the structure, content, spatiotemporal dynamic change, and spatial distribution of metabolites. It also may identify potential metabolic biomarkers. This technology has the advantages of high sensitivity, high resolution, judicious visualization and label-free, and therefore has been more and more widely applied in clinical disease diagnosis and research. This review summarizes some of the technological advances of SRM in recent years, and its emerging application in the fields of tumor, neuropsychiatric disorder, diabetes mellitus, among others, in an attempt to guide future application of SRM in disease diagnosis. [ABSTRACT FROM AUTHOR]

Triclosan (TCS), an antimicrobial additive, has been widely used in many daily consumer products. Although it is banned from using in soap products in 2016 by the USA Food and Drug Administration, it still can be used in many other products such as cosmetics, toys, mouthwash and toothpaste. Because of its ubiquitous characteristics, there is a growing concern over the impact of TCS on human health. Previous studies have reported that exposure to TCS could promote the development of hepatocellular carcinoma. However, little is known about the related mechanisms at the metabolic levels. In cancer research, multicellular tumor spheroids (MCTSs) are sphere-shaped cellular colonies, and which are considered to be the most appropriate in vitro cell model to test toxicities of chemicals because of their ability to mimic the main characteristics of solid tumors. To the best of our knowledge, no studies have tested the effect of TCS on the development of liver MCTS. Hence, in this work, liver MCTSs were exposed to TCS, and mass spectrometry imaging (MSI) was used to explore the variations of abundance and distribution of lipids in MCTS between exposure and control groups. The results revealed that treatment of 6 μmol/L TCS could significantly promote the growth of liver MCTS and induce the lipid disorders in MCTS. Segmentation analysis of MCTS showed that there were three microregions including the outer proliferative area, the middle quiescent area and the inner necrotic area in MCTS. Further MSI data revealed that the abundance of 27 lipids including 19 glycerophospholipids (GPs), 3 glycerolipids (GLs) and 5 sphingolipids (SPs) significantly changed in MCTS between treated and untreated groups. In GPs, a total of 16 up-regulated lipids located in the outer proliferative area of MCTS. In GLs, two up-regulated lipids located in the outer proliferative area, while one down-regulated lipid distributed in the inner area. In SPs, all five lipids with decreased levels located in the inner area. All these data suggested that the enhanced growth of liver MCTS induced by treatment of TCS may through promoting the growth of cells in the outer region of MCTS and inhibiting the death of cells in the inner region of MCTS. This result may offer a better understanding for the mechanisms of the effects of environmental pollutants on cancer progression.

Zebrafish (ZF; Danio rerio) larvae have emerged as a promising in vivo model in drug metabolism studies. Here, we set out to ready this model for integrated mass spectrometry imaging (MSI) to comprehensively study the spatial distribution of drugs and their metabolites inside ZF larvae. In our pilot study with the overall goal to improve MSI protocols for ZF larvae, we investigated the metabolism of the opioid antagonist naloxone. We confirmed that the metabolic modification of naloxone is in high accordance with metabolites detected in HepaRG cells, human biosamples, and other in vivo models. In particular, all three major human metabolites were detected at high abundance in the ZF larvae model. Next, the in vivo distribution of naloxone was investigated in three body sections of ZF larvae using LC-HRMS/MS showing that the opioid antagonist is mainly present in the head and body sections, as suspected from published human pharmacological data. Having optimized sample preparation procedures for MSI (i.e., embedding layer composition, cryosectioning, and matrix composition and spraying), we were able to record MS images of naloxone and its metabolites in ZF larvae, providing highly informative distributional images. In conclusion, we demonstrate that all major ADMET (absorption, distribution, metabolism, excretion, and toxicity) parameters, as part of in vivo pharmacokinetic studies, can be assessed in a simple and cost-effective ZF larvae model. Our established protocols for ZF larvae using naloxone are broadly applicable, particularly for MSI sample preparation, to various types of compounds, and they will help to predict and understand human metabolism and pharmacokinetics. [ABSTRACT FROM AUTHOR]

Abstract Background To adapt to life on land, Asiatic toads (Bufo gargarizans) must remodel their bodies and refine their chemical defenses in water. The full scope of the mechanisms underlying these processes has yet to be revealed. Bufadienolides (BDs) are chemical defense substances secreted by toads when they are in danger, and they have high medicinal value in treating heart failure, cancer, and hepatitis. However, the artificial breeding of toads to increase BDs has been unsuccessful due to the high mortality of toad larvae during metamorphosis. Method Toad larvae at different growth stages were selected to study the changes in the metamorphosis process under the same growth conditions. The differences of tadpoles were explored, including body remodeling, energy metabolism, synthesis and regulation of BDs, through lipidomic technology, transcriptomic technology, and mass spectrometry imaging technology during metamorphosis. Results During metamorphosis, tadpoles underwent significant changes in lipid metabolism due to body remodeling to adapt to terrestrial life, which involved ketosis, lipogenesis, cholesterol metabolism, and fatty acid oxidation. The accumulation trend of BDs was observed. “Pentose phosphate pathway” and “Aromatase activity” may be the critical pathway and GO term in BD synthesis, involving 16 genes predominantly expressed in the liver. The involved genes were mainly expressed in the liver, consistent with the synthetic site observed by mass spectrometry imaging. Conclusion Together, our findings presented the changes in the toad larvae during metamorphosis and highlighted the accumulation process of BDs as well as the regulatory pathways and synthetic site, providing research and theoretical basis for future development of the toad resources.

Copyright of Journal of Chinese Mass Spectrometry Society is the property of Journal of Chinese Mass Spectrometry Society and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To understand biological functions in organisms, it is important to investigate what is happening in different locations in cells and tissues. The conventional approach is to extract compounds from whole tissue, and then to measure their concentrations or other characteristics using equipment tailored to the different molecules. Recent advances in mass spectrometry have made it possible to measure trace amounts of compounds. Mass spectrometry imaging (MSI), which uses positional information and mass spectrometry data to show where and how much of each compound is present in tissues, has been in the spotlight. Improvements in MSI over the past few decades have enabled its use for visualizing the localization of small molecules including drugs, lipids, and many other compounds in a range of organisms. MSI has also been used to clarify the localization of natural products in plant tissues. This review summarizes the recent research related to MSI technology in Japan. • MSI shows where and how much of each compound is present in tissues. • MALDI-MSI has been used to visualize small molecules in plant tissues in Japan. • SIMS, DESI, and MALDI-2 are also used for MSI. [ABSTRACT FROM AUTHOR]

Background: To adapt to life on land, Asiatic toads (Bufo gargarizans) must remodel their bodies and refine their chemical defenses in water. The full scope of the mechanisms underlying these processes has yet to be revealed. Bufadienolides (BDs) are chemical defense substances secreted by toads when they are in danger, and they have high medicinal value in treating heart failure, cancer, and hepatitis. However, the artificial breeding of toads to increase BDs has been unsuccessful due to the high mortality of toad larvae during metamorphosis. Method: Toad larvae at different growth stages were selected to study the changes in the metamorphosis process under the same growth conditions. The differences of tadpoles were explored, including body remodeling, energy metabolism, synthesis and regulation of BDs, through lipidomic technology, transcriptomic technology, and mass spectrometry imaging technology during metamorphosis. Results: During metamorphosis, tadpoles underwent significant changes in lipid metabolism due to body remodeling to adapt to terrestrial life, which involved ketosis, lipogenesis, cholesterol metabolism, and fatty acid oxidation. The accumulation trend of BDs was observed. "Pentose phosphate pathway" and "Aromatase activity" may be the critical pathway and GO term in BD synthesis, involving 16 genes predominantly expressed in the liver. The involved genes were mainly expressed in the liver, consistent with the synthetic site observed by mass spectrometry imaging. Conclusion: Together, our findings presented the changes in the toad larvae during metamorphosis and highlighted the accumulation process of BDs as well as the regulatory pathways and synthetic site, providing research and theoretical basis for future development of the toad resources. [ABSTRACT FROM AUTHOR]

Glycosylation plays an important role in the progression of esophageal adenocarcinoma (EAC). Being able to image these glycosylation changes directly in endoscopic resection specimens could provide useful insights into the molecular mechanisms of the disease progression and potential markers for EACstaging. For this purpose, both3Dand 2.5D matrix-assisted laser/desorption ionization (MALDI) mass spectrometry imaging (MSI) have been employed in this study to investigate glycosidase-cleaved N-glycans in a total of24 formalin-fixed paraffin-embedded esophageal local excision specimens spanning all stages of disease progression, namely from non-dysplastic Barrett's esophagus to metastatic EAC. 3D-MSI was first used to estimate the number of sections needed to sufficiently cover the molecular heterogeneity of each stage of progression. This analysis showed that a total of four sections out of 20 were sufficient. This subset of four sections was measured for all remaining specimens and is called 2.5D-MSI. Subsequent analyses of the 2.5D-MSI datasets revealed significant elevations offivehigh-mannoseN-glycans (Man3,Man4,Man6,Man7, and Man8) in EAC and three complex (Hex6HexNAc5, Hex6HexNAc5NeuAc1, Hex7HexNAc6) N-glycans in metastatic EAC as compared to previous stages of the disease. The augmented levels of these glycans in EAC could be explained by publically available gene expression data of enzymes involved in glycan synthesis and processing. As the role of glycosylation is gaining more interest in MSI and cancer research, our results show the added value of combining localized N-glycan levels, as provided by MSI, with gene expression to gain a deeper understanding of the mechanisms behind N-glycan changes. This gives evidence at multiple levels that specific N-glycosylation plays an important role during progression of dysplasia to EAC and could play a role in patient surveillance. [ABSTRACT FROM AUTHOR]

For a long history, herbal medicines have made significant contributions to human health all around the world. However, the exploration of an effective approach to illustrate their inner quality remains a challenge. So, it is imperative to develop new methods and technologies to characterize and identify quality markers of herbal medicines. Taking Isatidis Radix, the dried root of Isatis indigotica as an example, desorption electrospray ionization (DESI), in combination with quadrupole-time-of-flight mass spectrometry (Q-TOF/MS), was applied in this work for the first time to reveal the comprehensive spatial distribution of metabolites and, further, to illustrate quality characters of this herbal medicine. After simple pretreatment, 102 metabolites including alkaloids, sulfur-containing compounds, phenylpropanoids, nucleosides, amino acids, organic acids, flavonoids, phenols, terpenes, saccharides, peptides, and sphingolipids were characterized, some of which were successfully localized and visualized in the transverse section of the root. Based on the ion images, samples with different quality characters were distinguished unambiguously by the pattern recognition method of orthogonal partial least squares discrimination analysis (OPLS-DA). Simultaneously, 11 major influencing components exerting higher ion intensities in superior samples were identified as the potential quality markers of Isatidis Radix. Desorption electrospray ionization (DESI) mass spectrometry imaging (MSI), together with chemometric analysis could not only improve the understanding of the plant biology of herbal medicines but also be beneficial in the identification of quality markers, so as to carry out better quality control of herbal medicines. [ABSTRACT FROM AUTHOR]

For a long history, herbal medicines have made significant contributions to human health all around the world. However, the exploration of an effective approach to illustrate their inner quality remains a challenge. So, it is imperative to develop new methods and technologies to characterize and identify quality markers of herbal medicines. Taking Isatidis Radix, the dried root of Isatis indigotica as an example, desorption electrospray ionization (DESI), in combination with quadrupole-time-of-flight mass spectrometry (Q-TOF/MS), was applied in this work for the first time to reveal the comprehensive spatial distribution of metabolites and, further, to illustrate quality characters of this herbal medicine. After simple pretreatment, 102 metabolites including alkaloids, sulfur-containing compounds, phenylpropanoids, nucleosides, amino acids, organic acids, flavonoids, phenols, terpenes, saccharides, peptides, and sphingolipids were characterized, some of which were successfully localized and visualized in the transverse section of the root. Based on the ion images, samples with different quality characters were distinguished unambiguously by the pattern recognition method of orthogonal partial least squares discrimination analysis (OPLS-DA). Simultaneously, 11 major influencing components exerting higher ion intensities in superior samples were identified as the potential quality markers of Isatidis Radix. Desorption electrospray ionization (DESI) mass spectrometry imaging (MSI), together with chemometric analysis could not only improve the understanding of the plant biology of herbal medicines but also be beneficial in the identification of quality markers, so as to carry out better quality control of herbal medicines.

Changes in overall bile acid (BA) levels and specific BA metabolites are involved in metabolic diseases, gastrointestinal, and liver cancer. BAs have become established as important signaling molecules that enable fine-tuned inter-tissue communication within the enterohepatic circulation. The liver, BAs site of production, displayed physiological and functional zonal differences in the periportal zone versus the centrilobular zone. In addition, BA metabolism shows regional differences in the intestinal tract. However, there is no available method to detect the spatial distribution and molecular profiling of BAs within the enterohepatic circulation. Herein, we demonstrated the application in mass spectrometry imaging (MSI) with a high spatial resolution (3 μm) plus mass accuracy matrix-assisted laser desorption ionization (MALDI) to imaging BAs and N-1-naphthylphthalamic acid (NPA). Our results could clearly determine the zonation patterns and regional difference characteristics of BAs on mouse liver, ileum, and colon tissue sections, and the relative content of BAs based on NPA could also be ascertained. In conclusion, our method promoted the accessibility of spatial localization and quantitative study of BAs on gastrointestinal tissue sections and demonstrated that MALDI-MSI was a valuable tool to investigate and locate several BA molecules in different tissue types leading to a better understanding of the role of BAs behind the gastrointestinal diseases.

Phosphatidylethanolamine (PE) is a major phospholipid in pork and a determinant of its quality. PE is classified into diacyl, alkylacyl, and plasmalogen types. Plasmalogens have antioxidant activity and are believed to have beneficial health properties. However, their presence in pork tissues have not been fully elucidated. Here, we analyzed their distribution in longissimus thoracis et lumborum (loin) muscle, spinalis muscle, intermuscular fat, and transparent tissue of pork chops. Liquid chromatography-electrospray ionization-mass spectrometry (LC–ESI–MS) revealed 14 diacyl-PEs, 10 alkylacyl-PEs, and 24 plasmalogen-PEs, suggesting that plasmalogen-PEs are a dominant type, and a major reservoir of eicosapentaenoic and docosahexaenoic acids. Matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI–MSI) revealed that the distributions of PEs among tissues depended on fatty acid compositions at sn-1 and sn-2 positions. Interestingly, diacyl-PEs were most abundant in intermuscular fat tissue; whereas alkylacyl-PEs and plasmalogen-PEs were highest in transparent tissue. To the best of our knowledge, this is the first report showing tissue-specific distributions of the three types of PEs in meat using MALDI-MSI. These results suggest that MALDI-MSI with LC-ESI-MS is a useful tool for distribution analysis of the three types of PEs in pork tissues. [ABSTRACT FROM AUTHOR]

• Conventional diagnostic modalities focus on tumor phenotypic attributes, limiting utility for early cancer detection. • In situ analysis by MSI offers new perspectives for the diagnosis of pulmonary disorders and biomarker discovery. • MSIcan provide a comprehensive view of the spatial and temporal distribution of drugs in the organism. Mass Spectrometry Imaging (MSI) represents a novel and advancing technology that offers unparalleled in situ characterization of tissues. It provides comprehensive insights into the chemical structures, relative abundances, and spatial distributions of a vast array of both identified and unidentified endogenous and exogenous compounds, a capability not paralleled by existing analytical methodologies. Recent scholarly endeavors have increasingly explored the utility of MSI in the adjunct diagnosis and biomarker research of pulmonary disorders, including but not limited to lung cancer. Concurrently, MSI has proven instrumental in elucidating the spatiotemporal dynamics of various pharmacological agents. This review concisely delineates the fundamental principles underpinning MSI, its applications in pulmonary disease diagnosis, biomarker discovery, and drug distribution investigations. Additionally, it presents a forward-looking perspective on the prospective trajectories of MSI technological advancements. [ABSTRACT FROM AUTHOR]

Stromal corneal dystrophies are a group of hereditary disorders caused by mutations in the TGFBI gene. The mutant TGFBIp is prone to protein aggregation and the mutant protein gets deposited in the cornea, leading to severe visual impairment. The mutations lead to a corneal specific protein aggregation suggesting the involvement of tissue-specific factors. The exact molecular mechanism of the process of tissue-specific protein aggregation remains to be elucidated. Differential proteolysis of mutant TGFBIp is a critical component of the disease pathology. The differential proteolysis gives rise to shorter peptides that are highly aggregation-prone and initiate the aggregation cascade. Analyzing the proteolytic processing of the different TGFBIp mutant may provide insight to aid in understanding the amyloid aggregation mechanism. We developed a MALDI-MSI methodology to identify expression and spatial localization of TGFBIp peptides in the cornea. Corneal tissue samples were collected from both control and dystrophic patients (with 2 different mutations), embedded in OCT and sectioned. The sections were trypsin digested and subjected to mass spectrometry imaging using a targeted approach to detect TGFBIp. MALDI-MSI identified peptides from TGFBIp that co-localized with the amyloid corneal deposits. In addition to the relative abundance data, the specific location of the peptides across the corneal sections as molecular signatures was also identified. Spatial distribution and intensity of the TGFBIp peptides showed differences between diseased and control models but also between the two LCD phenotypes. The TGFBIp peptide with m/z of 787.474 and m/z of 1179.579 showed increased expression in both LCD mutants compared to the controls. The peptide with m/z of 929.5 showed increased expression in the LCD phenotype with H626R mutation while the peptide with m/z of 1315.802 was abundant in the sample with R124C mutation. This initial report of 2D spatial protein signature and localization of TGFBIp may be expanded to other mutations to understand the proteolytic patterns of TGFBIp in different mutations. [ABSTRACT FROM AUTHOR]

Mass spectrometry imaging (MSI) is a promising method for characterizing the spatial distribution of compounds. Given the diversified development of acquisition methods and continuous improvements in the sensitivity of this technology, both the total amount of generated data and complexity of analysis have exponentially increased, rendering increasing challenges of data postprocessing, such as large amounts of noise, background signal interferences, as well as image registration deviations caused by sample position changes and scan deviations, and etc. Deep learning (DL) is a powerful tool widely used in data analysis and image reconstruction. This tool enables the automatic feature extraction of data by building and training a neural network model, and achieves comprehensive and in-depth analysis of target data through transfer learning, which has great potential for MSI data analysis. This paper reviews the current research status, application progress and challenges of DL in MSI data analysis, focusing on four core stages: data preprocessing, image reconstruction, cluster analysis, and multimodal fusion. The application of a combination of DL and mass spectrometry imaging in the study of tumor diagnosis and subtype classification is also illustrated. This review also discusses trends of development in the future, aiming to promote a better combination of artificial intelligence and mass spectrometry technology.

A drug delivery system (DDS) is a method for delivering a drug to its site of action in the body, with the goal of achieving therapeutic benefits while reducing adverse effects. Pharmacokinetics (PK) and pharmacodynamics (PD) studies have been conducted to evaluate drug delivery, but these approaches are rarely used in the early stages of drug discovery and development. We demonstrated that the tumor stromal barrier inhibits drug distribution within tumor tissue, especially in refractory cancers such as pancreatic cancer. This poses an obstacle to the discovery of new drugs, and is difficult to overcome using conventional in vitro drug discovery methods. In addition, we are also developing new DDS drugs and antibody-drug conjugates (ADCs). These agents act via four steps: Systemic circulation, the enhanced permeability and retention (EPR) effect, penetration within the tumor tissue, and action on cells including controlled drug release. Most of these activities can be evaluated by conventional biological or pharmacological assays. However, it is difficult to examine drug distribution and controlled drug release within targeted tissues. Recent advances in mass spectrometry imaging (MSI) allow examining drug delivery much more conveniently with the off-labeling. A mass microscope, a new type of matrix-associated laser desorption/ionization (MALDI)-MSI analyzer, is a microscope coupled with an atmospheric MALDI and quadruple ion trap time-of-flight (TOF) mass spectrometer, and can provide imaging data with enhanced resolution and high sensitivity. Using a mass microscope, we succeeded in visualizing the EPR effect of a polymeric micelle drug and controlled drug release by an ADC. Currently, we are developing a new drug imaging method using electrospray ionization (ESI)-MSI. Here, we review the use of MSI in early stages of drug discovery and development, as well as our related recent work.

Summary: Understanding when and where metabolites accumulate provides important cues to the gene function. Mass spectrometry imaging (MSI) enables in situ temporal and spatial measurement of a large assortment of metabolites, providing mapping information regarding their cellular distribution.To describe the current state and technical advances using MSI in plant sciences, we employed MSI to demonstrate its significant contribution to the study of plant specialised metabolism.We show that coupling MSI with: (1) RNA interference (RNAi), (2) virus induced gene silencing (VIGS), (3) agroinfiltration or (4) samples derived from plant natural variation provides great opportunities to understand the accurate gene–metabolite relationship and discover novel gene‐associated metabolites. This was exemplified in three plant species (i.e. tomato, tobacco and wheat) by mapping the distribution of metabolites possessing a range of polarities. In particular, we demonstrated that MSI is able to spatially map an entire metabolic pathway, including intermediates and final products, in the intricate biosynthetic route to tomato fruit steroidal glycoalkaloids.We therefore envisage MSI as a key component of the metabolome analysis arsenal employed in plant gene discovery strategies. [ABSTRACT FROM AUTHOR]

• Long-term metabolic alterations are visible 26 days after cisplatin treatment. • Cisplatin induces metabolic disturbances mainly in the corticomedullary boundary. • Core metabolic pathways, antioxidants and phospholipids are affected. Cisplatin is a widely used chemotherapeutic agent. However, it is causing nephrotoxic side effects including a reduced glomerular filtration rate and acute kidney injury. Although kidneys can recover to an extent from the treatment, long-term damage is possible. While a lot of research is focusing on short-term effects, little is known about adverse metabolic effects in the process of recovery. In this study, male Han Wistar rats were dosed with a single intraperitoneal injection of 3 mg/kg cisplatin. Urine and kidney samples were harvested 3, 8 and 26 days after administration. Tubular injury was demonstrated through urinary biomarkers. Complementing this, mass spectrometry imaging gives insight on molecular alterations on a spatial level, thus making it well suited to analyze short- and long-term disturbances. Various metabolic pathways seem to be affected, as changes in a wide range of metabolites were observed between treated and control animals. Besides previously reported early changes in kidney metabolism, unprecedented long-term effects were detected including deviation in nucleotides, antioxidants, and phospholipids. [ABSTRACT FROM AUTHOR]

Introduction: Three-dimensional (3D) cell cultures have become increasingly important materials to investigate biological processes and drug efficacy and toxicity. The ability of 3D cultures to mimic the physiology of primary tissues and organs in the human body enables further insight into cellular behavior and is hence highly desirable in early-stage drug development. Analyzing the spatial distribution of drug compounds and endogenous molecules provides an insight into the efficacy of a drug whilst simultaneously giving information on biological responses. Areas Covered: In this review we will examine the main 3D cell culture systems employed and applications, which describe their integration with mass spectrometry imaging (MSI). Expert Opinion: MSI is a powerful technique that can map a vast range of molecules simultaneously in tissues without the addition of labels that can provide insights into the efficacy and safety of a new drug. The combination of MSI and 3D cell cultures has emerged as a promising tool in early-stage drug analysis. However, the most common administration route for pharmaceutical drugs is via oral delivery. The use of MSI in combination with models of the GI tract is an area that has been little explored to date, the reasons for this are discussed. [ABSTRACT FROM AUTHOR]

Purpose: Desorption electrospray ionization mass spectrometry imaging (DESI-MSI) coupled with gas-phase ion mobility spectrometry was used to characterize the drug distribution in polymeric implants before and after exposure to accelerated in vitro release (IVR) media. DESI-MSI provides definitive chemical identification and localization of formulation components, including 2D chemical mapping of individual components with essentially no sample preparation. Methods: Polymeric implants containing 40% (w/w) entecavir and poly(D,L-lactide) (PLA) were prepared and then exposed to either acidified PBS (pH 2.5) or MeOH:H2O (50:50, v/v) medias during a 7-day IVR test using continuous flow-through (CFT) cell dissolution. The amount of drug released from the polymer matrix during the 7-day IVR test was monitored by online-ultraviolet spectroscopy (UV) and HPLC-UV. After that period, intact implants and radial sections of implants were analyzed by DESI-MSI with ion mobility spectrometry. The active ingredient along with impurities and contaminants were used to generate chemical maps before and after exposure to the release medias. Results: Bi-phasic release profiles were observed for implants during IVR release using both medias. During the second phase of release, implants exposed to PBS, pH 2.5, released the entecavir faster than the implants exposed to MeOH:H2O (50:50, v/v). Radial images of the polymer interior show that entecavir is localized along the central core of the implant after exposure to MeOH:H2O (50:50, v/v) and that the drug is more uniformly distributed throughout the implant after exposure to acidified PBS (pH 2.5). Conclusions: DESI-MSI coupled with ion mobility analysis produced chemical images of the drug distribution on the exterior and interior of cylindrical polymeric implants before and after exposure to various release medias. These results demonstrated the utility of this technique for rapid characterization of drug and impurity/degradant distribution within polymeric implants with direct implications for formulation development as well as analytical method development activities for various solid parenteral and oral dosage forms. These results are especially meaningful since samples were analyzed with essentially no preparative procedures. [ABSTRACT FROM AUTHOR]

• Amitriptyline induced alterations can be demonstrated via MALDI-MSI in rat liver. • Amitriptyline and its metabolites accumulate throughout the liver tissue. • Phosphatidylcholine (PC) species are increased in abundance upon Amitriptyline treatment. • Histological findings and Oil Red O staining revealed macrovesicular steatosis. • Two detected bile acids are decreased in Amitriptyline treatment group compared to control. As a consequence of the detoxification process, drugs and drug related metabolites can accumulate in the liver, resulting in drug induced liver injury (DILI), which is the major cause for dose limitation. Amitriptyline, a commonly used tricyclic anti-depressant, is known to cause DILI. The mechanism of Amitriptyline induced liver injury is not yet completely understood. However, as it undergoes extensive hepatic metabolism, unraveling the molecular changes in the liver upon Amitriptyline treatment can help understand Amitriptyline's mode of toxicity. In this study, Amitriptyline treated male rat liver tissue was analyzed using Matrix Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging (MALDI-MSI) to investigate the spatial abundances of Amitriptyline, lipids, and bile acids. The metabolism of Amitriptyline in liver tissue was successfully demonstrated, as the spatial distribution of Amitriptyline and its metabolites localize throughout treatment group liver samples. Several lipids appear upregulated, from which nine were identified as distinct phosphatidylcholine (PC) species. The detected bile acids were found to be lower in Amitriptyline treatment group. The combined results from histological findings, Oil Red O staining, and lipid zonation by MSI revealed lipid upregulation in the periportal area indicating drug induced macrovesicular steatosis (DIS). [ABSTRACT FROM AUTHOR]

Common traumas to the skeletal system are bone fractures and injury-related articular cartilage damage. The healing process can be impaired resulting in non-unions in 5–10% of the bone fractures and in post-traumatic osteoarthritis (PTOA) in up to 75% of the cases of cartilage damage. Despite the amount of research performed in the areas of fracture healing and cartilage repair as well as non-unions and PTOA, still, the outcome of a bone fracture or articular cartilage damage cannot be predicted. Here, we discuss known risk factors and key molecules involved in the repair process, together with the main challenges associated with the prediction of outcome of these injuries. Furthermore, we review and discuss the opportunities for mass spectrometry (MS) – an analytical tool capable of detecting a wide variety of molecules in tissues – to contribute to extending molecular understanding of impaired healing and the discovery of predictive biomarkers. Therefore, the current knowledge and challenges concerning MS imaging of bone and cartilage tissue as well as in vivo MS are discussed. Finally, we explore the possibilities of in situ, real-time MS for the prediction of outcome during surgery of bone fractures and injury-related articular cartilage damage. [ABSTRACT FROM AUTHOR]

Zebrafish (ZF; Danio rerio) larvae have become a popular in vivo model in drug metabolism studies. Here, we investigated the metabolism of methyl 2-[1-(4-fluorobutyl)-1H-indazole-3-carboxamido]-3,3-dimethylbutanoate (4F-MDMB-BINACA) in ZF larvae after direct administration of the cannabinoid via microinjection, and we visualized the spatial distributions of the parent compound and its metabolites by mass spectrometry imaging (MSI). Furthermore, using genetically modified ZF larvae, the role of cannabinoid receptor type 1 (CB1) and type 2 (CB2) on drug metabolism was studied. Receptor-deficient ZF mutant larvae were created using morpholino oligonucleotides (MOs), and CB2-deficiency had a critical impact on liver development of ZF larva, leading to a significant reduction of liver size. A similar phenotype was observed when treating wild-type ZF larvae with 4F-MDMB-BINACA. Thus, we reasoned that the cannabinoid-induced impaired liver development might also influence its metabolic function. Studying the metabolism of two synthetic cannabinoids, 4F-MDMB-BINACA and methyl 2-(1-(5-fluoropentyl)-1H-pyrrolo[2,3-b]pyridine-3-carboxamido)-3,3-dimethylbutanoate (7′N-5F-ADB), revealed important insights into the in vivo metabolism of these compounds and the role of cannabinoid receptor binding.

The identification of biomarkers through Mass spectrometry imaging (MSI) is gaining popularity in the clinical field. However, considering the complexity of spectral and spatial variables faced, data mining of the hyperspectral images can be troublesome. The discovery of markers generally depends on the creation of classification models which should be validated to ensure the statistical significance of the discriminants m / z detected. Internal validation using resampling methods such as cross validation (CV) are widely used for model selection, the estimation of its generalization performance and biomarker discovery when sample sizes are limited and an independent test set is not available. Here, we introduce for first time the use of Constrained Repeated Random Subsampling CV (CORRS-CV) on multi-images for the validation of classification models on MSI. Although several aspects must be taken into account (e.g. image size, CORRS-CV∂value, the similarity across spatially close pixels, the total computation time), CORRS-CV provides more accurate estimates of the model performance than k -fold CV using of biological replicates to define the data split when the number of biological replicates is scarce and holding images back for testing is a waste of valuable information. Besides, the combined use of CORRS-CV and rank products increases the robustness of the selection of discriminant features as candidate biomarkers which is an important issue due to the increased biological, environmental and technical variabilities when analysing multiple images, especially from human tissues collected in clinical studies. Image 1 • The validation of MSI biomarkers is challenging due to correlation among pixels. • CV based on pixels provide over-optimistic results. • CV based on biological replicates improves reliability, but it is no viable at small sample sizes. • CORSSCV provides a suitable alternative, providing trustworthiness to the biomarkers found. [ABSTRACT FROM AUTHOR]

Abstract Micropollutants and emerging organic contaminants (EOCs) have been widely studied in terms of persistance, removal, human risk assessment, toxicology, etc. Mass spectrometry imaging (MSI) offers the possibility of following the fate of a single pesticide in a plant leaf or a drug in the whole body of an animal, organ by organ. However, the admissibility of chronic low doses of complex mixtures for the ecosystem has not been assessed. How do micropollutants diffuse in the environment? How do living organisms cope with chronic exposure to a low dose of diverse micropollutants? Is there a cocktail effect or a chance for hormesis? Combining mass spectrometry imaging (MSI) and targeted and nontargeted liquid chromatography coupled to mass spectrometry (LC-MS), we attempt to answer these questions. We investigate the diversity of micropollutants at the exit of a water treatment facility, their diffusion in sludge and black poplar (Populus nigra), and their impact on a living organism. We reveal a specific tissue localization of micropollutants in peripheral leaf tissues, and an associated stress response from the plant, with stress hormones and tissue degradation markers induced in the plant growing near the water efflux. Graphical abstract Unlabelled Image Highlights • Differential micropollutants distribution in wetland water, sludge and poplar leaves • A specific tissue localization of micropollutants occurs in polluted poplar leaves. • Chronical exposure to treated wastewater induces a stress response in Poplar. • Stress hormones and degradation markers are induced in leaves accumulating pollutants. [ABSTRACT FROM AUTHOR]

Mass spectrometry imaging is a powerful tool for analyzing the different kinds of molecules in tissue sections, but some substances cannot be measured easily, due to their physicochemical properties. In such cases, chemical derivatization could be applied to introduce the charge into the molecule and facilitate its detection. Here, we study cholesterol derivatization with betaine aldehyde from tissue slices and evaluate how different sample preparation methods influence the signal from the derivatization product. In this study, we have tested different solutions for betaine aldehyde, different approaches to betaine aldehyde deposition (number of layers, deposition nozzle height), and different MALDI matrices for its analysis. As a result, we proved that the proposed approach could be used for the analysis of cholesterol in different tissues.

The study of biological specimens by mass spectrometry imaging (MSI) has had a profound influence in the various forms of spatial-omics over the past two decades including applications for the identification of clinical biomarker analysis; the metabolic fingerprinting of disease states; treatment with therapeutics; and the profiling of lipids, peptides and proteins. No singular approach is able to globally map all biomolecular classes simultaneously. This led to the development of many complementary multimodal imaging approaches to solve analytical problems: fusing multiple ionization techniques, imaging microscopy or spectroscopy, or local extractions into robust multimodal imaging methods. However, each fusion typically requires the melding of analytical information from multiple commercial platforms, and the tandem utilization of multiple commercial or third-party software platforms—even in some cases requiring computer coding. Herein, we report the use of matrix-assisted laser desorption/ionization (MALDI) in tandem with desorption electrospray ionization (DESI) imaging in the positive ion mode on a singular commercial orthogonal dual-source Fourier transform ion cyclotron resonance (FT-ICR) instrument for the complementary detection of multiple analyte classes by MSI from tissue. The DESI source was 3D printed and the commercial Bruker Daltonics software suite was used to generate mass spectrometry images in tandem with the commercial MALDI source. This approach allows for the generation of multiple modes of mass spectrometry images without the need for third-party software and a customizable platform for ambient ionization imaging. Highlighted is the streamlined workflow needed to obtain phospholipid profiles, as well as increased depth of coverage of both annotated phospholipid, cardiolipin, and ganglioside species from rat brain with both high spatial and mass resolution.

Zebrafish (Danio rerio) larvae have gained attention as a valid model to study in vivo drug metabolism and to predict human metabolism. The microinjection of compounds, oligonucleotides, or pathogens into zebrafish embryos at an early developmental stage is a well-established technique. Here, we investigated the metabolism of zebrafish larvae after microinjection of methyl 2-(1-(5-fluoropentyl)-1H-pyrrolo[2,3-b]pyridine-3-carboxamido)-3,3-dimethylbutanoate (7′N-5F-ADB) as a representative of recently introduced synthetic cannabinoids. Results were compared to human urine data and data from the in vitro HepaRG model and the metabolic pathway of 7′N-5F-ADB were reconstructed. Out of 27 metabolites detected in human urine samples, 19 and 15 metabolites were present in zebrafish larvae and HepaRG cells, respectively. The route of administration to zebrafish larvae had a major impact and we found a high number of metabolites when 7′N-5F-ADB was microinjected into the caudal vein, heart ventricle, or hindbrain. We further studied the spatial distribution of the parent compound and its metabolites by mass spectrometry imaging (MSI) of treated zebrafish larvae to demonstrate the discrepancy in metabolite profiles among larvae exposed through different administration routes. In conclusion, zebrafish larvae represent a superb model for studying drug metabolism, and when combined with MSI, the optimal administration route can be determined based on in vivo drug distribution.

Flavan-3-ols, procyanidins and their monomers are major flavonoids present in peanuts that show a wide range of biological properties and health benefits, based on their potent antioxidant activity. Procyanidin oligomers, especially A-type, are reportedly abundant in peanut skin; however, their localization in the raw peanut testa remains poorly understood. Therefore, we performed matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to investigate the localization of flavan-3-ols in peanut testa. 1,5-Diaminonaphthalene was coated onto the peanut section by matrix vapor deposition/recrystallization, and MALDI-MSI measurements were performed in the negative-ion mode. Peaks matching the m/z values of flavan-3-ol [M − H]− ions were observed in the mass spectrum extracted from the outer epidermis of the peanut testa, using the region of interest function. Catechin and/or epicatechin, five A-type, and one B-type procyanidins were assigned by the fragment ions generated by retro-Diels-Alder, heterocyclic ring fission, and quinone methide reactions detected in MALDI-tandem MS spectra. These flavan-3-ols were localized in the outer epidermis of the peanut testa. This information will contribute to improving the extraction and purification efficiencies of flavan-3-ols from peanut testa. As flavan-3-ols display anti-microbial activity, it is speculated that flavan-3-ols present in the outer epidermis of peanut testa act to prevent pathogen infection.

Environmental exposures have significant impacts on human health and can contribute to the occurrence and development of diseases. Pollutants can enter the body through ingestion, inhalation, dermal absorption, or mother-to-child transmission, and can metabolize and/or accumulate in different tissues and organs. These pollutants can recognize and interact with various biomolecules, including DNA, RNA, proteins, and metabolites, disrupting biological processes and leading to adverse effects in living organisms. Thus, it is crucial to analysis the exogenous pollutants in the body, identify potential biomarkers and investigate their toxic effects. Numerous studies have shown that the metabolism rate of environmental pollutants greatly differs in various tissues and organs, their accumulation is also heterogeneous and dynamically changing. Moreover, the synthesis and accumulation of endogenous metabolites exhibit precise spatial distributions in tissues and cells. Mapping the spatial distributions of both pollutants and endogenous metabolites can discover relevant exposure biomarkers and provide a better understanding of their toxic effects and molecular mechanisms. Mass spectrometry is currently the preferred method for the qualitative and quantitative analysis of various compounds, and has been extensively utilized in pollutant and metabolomics analyses. Mass spectrometry imaging (MSI) is an emerging technology for molecular imaging that combines the information obtained by mass spectrometry with the visualization of the two- and three-dimensional spatial distributions of various molecular species in thin sample sections. Unlike other molecular imaging techniques, MSI can perform the label-free and untargeted analysis of thousands of molecules, such as elements, metabolites, lipids, peptides, proteins, pollutants, and drugs, in a single experiment with high sensitivity and throughput. Different MSI technologies, such as matrix-assisted laser desorption ionization mass spectrometry imaging, secondary ion mass spectrometry imaging, desorption electrospray ionization mass spectrometry imaging, and laser ablation inductively coupled plasma mass spectrometry imaging, have been introduced for the mapping of compounds and elements in biological, medical, and clinical research. MSI technologies have recently been utilized to characterize the spatial distribution of pollutants in the whole body and specific tissues of organisms, assess the toxic effects of pollutants at the molecular level, and identify exposure biomarkers. Such developments have brought new perspectives to investigate the toxicity of environmental pollutants. In this review, we provide an overview of the principles, characteristics, mass analyzers, and workflows of different MSI techniques and introduce their latest application advances in the analysis of environmental pollutants and their toxic effects.

Environmental factors, such as environmental pollutants, behaviors, and lifestyles, are the leading causes of chronic noncommunicable diseases. Estimates indicate that approximately 50% of all deaths worldwide can be attributed to environmental factors. The exposome is defined as the totality of human environmental (i.e., all nongenetic) exposures from conception, including general external exposure (e.g., climate, education, and urban environment), specific external exposure (e.g., pollution, physical activity, and diet), and internal exposure (e.g., metabolic factors, oxidative stress, inflammation, and protein modification). As a new paradigm, this concept aims to comprehensively understand the link between human health and environmental factors. Therefore, a comprehensive measurement of the exposome, including accurate and reliable measurements of exposure to the external environment and a wide range of biological responses to the internal environment, is of great significance. The measurement of the general external exposome depends on advances in environmental sensors, personal-sensing technologies, and geographical information systems. The determination of exogenous chemicals to which individuals are exposed and endogenous chemicals that are produced or modified by external stressors relies on improvements in methodology and the development of instrumental approaches, including colorimetric, chromatographic, spectral, and mass-spectrometric methods. This article reviews the research strategies for chemical exposomes and summarizes existing exposome-measurement methods, focusing on mass spectrometry (MS)-based methods. The top-down and bottom-up approaches are commonly used in exposome studies. The bottom-up approach focuses on the identification of chemicals in the external environment (e.g., soil, water, diet, and air), whereas the top-down approach focuses on the evaluation of endogenous chemicals and biological processes in biological samples (e.g., blood, urine, and serum). Low- and high-resolution MS (LRMS and HRMS, respectively) have become the most popular methods for the direct measurement of exogenous and endogenous chemicals owing to their superior sensitivity, specificity, and dynamic range. LRMS has been widely applied in the targeted analysis of expected chemicals, whereas HRMS is a promising technique for the suspect and unknown screening of unexpected chemicals. The development of MS-based multiomics, including proteomics, metabolomics, epigenomics, and spatial omics, provides new opportunities to understand the effects of environmental exposure on human health. Metabolomics involves the sum of all low-molecular-weight metabolites in a living system. Nontargeted metabolomics can measure both endogenous and exogenous chemicals, which would directly link exposure to biological effects, internal dose, and disease pathobiology, whereas proteomics could play an important role in predicting potential adverse health outcomes and uncovering molecular mechanisms. MS imaging (MSI) is an emerging technique that provides unlabeled in-depth measurements of endogenous and exogenous molecules directly from tissue and cell sections without changing their spatial information. MSI-based spatial omics, which has been widely applied in biomarker discovery for clinical diagnosis, as well as drug and pollutant monitoring, is expected to become an effective method for exposome measurement. Integrating these response measurements from metabolomics, proteomics, spatial omics, and epigenomics will enable the generation of new hypotheses to discover the etiology of diseases caused by chemical exposure. Finally, we highlight the major challenges in achieving chemical exposome measurements.

Over the last two decades, mass spectrometry imaging (MSI) has been increasingly employed to investigate the spatial distribution of a wide variety of molecules in complex biological samples. MSI has demonstrated its potential in numerous applications from drug discovery, disease state evaluation through proteomic and/or metabolomic studies. Significant technological and methodological advancements have addressed natural limitations of the techniques, i.e., increased spatial resolution, increased detection sensitivity especially for large molecules, higher throughput analysis and data management. One of the next major evolutions of MSI is linked to the introduction of imaging mass cytometry (IMC). IMC is a multiplexed method for tissue phenotyping, imaging signalling pathway or cell marker assessment, at sub-cellular resolution (1 μm). It uses MSI to simultaneously detect and quantify up to 30 different antibodies within a tissue section. The combination of MSI with other molecular imaging techniques can also provide highly relevant complementary information to explore new scientific fields. Traditionally, classical histology (especially haematoxylin and eosin-stained sections) is overlaid with molecular profiles obtained by MSI. Thus, MSI-based molecular histology provides a snapshot of a tissue microenvironment and enables the correlation of drugs, metabolites, lipids, peptides or proteins with histological/pathological features or tissue substructures. Recently, many examples combining MSI with other imaging modalities such as fluorescence, confocal Raman spectroscopy and MRI have emerged. For instance, brain pathophysiology has been studied using both MRI and MSI, establishing correlations between in and ex vivo molecular imaging techniques. Endogenous metabolite and small peptide modulation were evaluated depending on disease state. Here, we review advanced 'hot topics' in MSI development and explore the combination of MSI with established molecular imaging techniques to improve our understanding of biological and pathophysiological processes. [ABSTRACT FROM AUTHOR]

Mass spectrometry imaging (MSI) is a technique that can map analyte spatial distribution directly onto a tissue section. This enables the spatial correlation of molecular entities with a tissue morphology to be investigated. Analyte annotation in MSI is intrinsically linked to the mass accuracy of the data. Mass accuracy and analyte identification are determined by such factors as the experimental set up and the data processing workflow. We present an MSI data processing workflow that uses a label-free approach to compensate for mass shifts. The algorithms developed were designed to perform efficiently even for datasets much larger than computer's memory. Herein, we present the application of the developed processing workflow to a dataset with more than 13.000 pixels and ∼50.000 mass channels. We assessed the overall mass accuracy in the range m/z 400 to 1200 using silver and gold sputtered nanolayers. With our novel processing workflow we were able to obtain mass errors as low as 5 ppm using a TOF instrument. [ABSTRACT FROM AUTHOR]

Mass spectrometry imaging (MSI) is a label‐free analytical technique capable of molecularly characterizing biological samples, including tissues and cell lines. The constant development of analytical instrumentation and strategies over the previous decade makes MSI a key tool in clinical research. Nevertheless, most MSI studies are limited to targeted analysis or the mere visualization of a few molecular species (proteins, peptides, metabolites, or lipids) in a region of interest without fully exploiting the possibilities inherent in the MSI technique, such as tissue classification and segmentation or the identification of relevant biomarkers from an untargeted approach. MSI data processing is challenging due to several factors. The large volume of mass spectra involved in a MSI experiment makes choosing the correct computational strategies critical. Furthermore, pixel to pixel variation inherent in the technique makes choosing the correct preprocessing steps critical. The primary aim of this review was to provide an overview of the data‐processing steps and tools that can be applied to an MSI experiment, from preprocessing the raw data to the more advanced strategies for image visualization and segmentation. This review is particularly aimed at researchers performing MSI experiments and who are interested in incorporating new data‐processing features, improving their computational strategy, and/or desire access to data‐processing tools currently available. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 37:281–306, 2018 [ABSTRACT FROM AUTHOR]

Phosphatidylcholine (PC) is the major phospholipid in meat and influences meat qualities, such as healthiness. PC is classified into three groups based on the bond at the sn-1 position: Diacyl, alkylacyl, and alkenylacyl. To investigate their composition and distribution in pork tissues, including longissimus thoracis et lumborum (loin) spinalis muscles, intermuscular fat, and transparent tissues, we performed matrix-assisted laser desorption/ionization−mass spectrometry imaging (MALDI−MSI). Eleven diacyl-, seven alkylacyl-, and six alkenylacyl-PCs were identified using liquid chromatography (LC)-tandem MS (MS/MS) analysis. Despite many alkylacyl- and alkenylacyl-PC species sharing identical m/z values, we were able to visualize these PC species using MALDI−MSI. Diacyl- and alkylacyl- and/or alkenylacyl-PC species showed unique distribution patterns in the tissues, suggesting that their distribution patterns were dependent on their fatty acid compositions. PCs are a major dietary source of choline in meat, and the amount was significantly higher in the muscle tissues. Consumption of choline mitigates age-related memory decline and neurodegenerative diseases; therefore, the consumption of pork muscle tissues could help to mitigate these diseases. These results support the use of MALDI−MSI analysis for assessing the association between PC species and the quality parameters of meat.

Flavan-3-ols, which comprise proanthocyanidins and their monomers, are major flavonoids in strawberries, and they have a wide range of biological activities and health benefits. However, their spatial distribution in strawberry fruit remains poorly understood. Therefore, we performed matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI), to visualize flavan-3-ols in ripe strawberry fruit. Peaks matching the m/z values of flavan-3-ols [M − H]− ions were detected in the negative ion mode using 1,5-diaminonaphthalene as matrix. Catechin and/or epicatechin, three B-type procyanidins, and two B-type propelargonidins were identified by MALDI-tandem MS. These flavan-3-ols were mainly distributed in the calyx, in and around the vascular bundles, and in the skin. In-source fragmentation of proanthocyanidins was determined using their standards, suggesting their distribution was mixed ion images of themselves, and fragment ions generated from those had a higher degree of polymerization. B-type procyanidins were predominantly distributed in the vascular bundles than in the skin, whereas B-type propelargonidins were almost equally distributed between the vascular bundles and skin, suggesting that their distribution patterns are different from the type of their flavan-3-ol monomers. Flavan-3-ols, especially B-type procyanidins, may help prevent pathogen infection not only in the skin but also in and around the vascular bundles.

Lignans are a major class of secondary metabolites distributed widely in the plant kingdom that are derived from coupling of phenylpropanoid (C6-C3) units. Most lignans are 8–8'-linked, and are often found in their glycosylated forms, which are catalyzed by UDP-dependent glycosyltransferase (UGT). Up to now, all UGTs involved in lignans biosynthesis are determined with substrate promiscuity. Here, IiUGT71B2 is reported from Isatis indigotica that specific catalyzes 4- O and 4′- O glycosylation of furan (lariciresinol) and dibenzylbutyrolactone (matairesinol) type lignans. Transcriptional profile of IiUGT71B2 indicates its involvement in lignan glycosides biosynthesis, which is co-expressed with other lignan biosynthetic genes, and is consistent with metabolic distribution of lignans in organs and tissues as well. Both in vitro and in vivo experiments demonstrate IiUGT71B2 catalyzes the mono- and di- glycosylation of lariciresinol and mono-glycosylation of matairesinol. The ligand docking and site-directed mutagenesis suggest Asn261, Ser289, Ala356, and Tyr395 as key residues, which may determine its catalytic efficiency together with the narrow binding pocket of IiUGT71B2. This study provides insights into lignan metabolism and functional diversity of plant UGTs. [Display omitted] • IiUGT71B2 specifically catalyzes glycosylation of lariciresinol and matairesinol. • The substrates promiscuity of lignan UGTs is driven by positive selection. • A precise metabolic distribution of lignans in roots section was visualized. [ABSTRACT FROM AUTHOR]