High-resolution Mass Spectrometry Imaging Research Articles

High spatial resolution imaging mass spectrometry of human optic nerve lipids and proteins.

The human optic nerve carries signals from the retina to the visual cortex of the brain. Each optic nerve is comprised of approximately one million nerve fibers that are organized into bundles of 800-1200 fibers surrounded by connective tissue and supportive glial cells. Damage to the optic nerve contributes to a number of blinding diseases including: glaucoma, neuromyelitis optica, optic neuritis, and neurofibromatosis; however, the molecular mechanisms of optic nerve damage and death are incompletely understood. Herein we present high spatial resolution MALDI imaging mass spectrometry (IMS) analysis of lipids and proteins to define the molecular anatomy of the human optic nerve. The localization of a number of lipids was observed in discrete anatomical regions corresponding to myelinated and unmyelinated nerve regions as well as to supporting connective tissue, glial cells, and blood vessels. A protein fragment from vimentin, a known intermediate filament marker for astrocytes, was observed surrounding nerved fiber bundles in the lamina cribrosa region. S100B was also found in supporting glial cell regions in the prelaminar region, and the hemoglobin alpha subunit was observed in blood vessel areas. The molecular anatomy of the optic nerve defined by MALDI IMS provides a firm foundation to study biochemical changes in blinding human diseases.

High resolution mass spectrometry imaging of plant tissues: towards a plant metabolite atlas.

Mass spectrometry (MS) imaging provides spatial and molecular information for a wide range of compounds. This tool can be used to investigate metabolic changes in plant physiology and environmental interactions. A major challenge in our study was to prepare tissue sections that were compatible with high spatial resolution analysis and therefore dedicated sample preparation protocols were established and optimized for the physicochemical properties of all major plant organs. We combined high spatial resolution (5 μm), in order to detect cellular features, and high mass accuracy (<2 ppm root mean square error), for molecular specificity. Mass spectrometry imaging experiments were performed in positive and negative ion mode. Changes in metabolite patterns during plant development were investigated for germination of oilseed rape. The detailed localization of more than 90 compounds allowed assignment to metabolic processes and indicated possible functions in plant tissues. The 'untargeted' nature of MS imaging allows the detection of marker compounds for the physiological status, as demonstrated for plant-pathogen interactions. Our images show excellent correlation with optical/histological examination. In contrast to previous MS imaging studies of plants, we present a complete workflow that covers multiple species, such as oilseed rape, wheat seed and rice. In addition, different major plant organs and a wide variety of compound classes were analyzed. Thus, our method could be used to develop a plant metabolite atlas as a reference to investigate systemic and local effects of pathogen infection or environmental stress.

Abstract 2064: Mass Spectrometry Imaging of therapeutic antibodies: Distribution of unlabeled trastuzumab in CB.17 SCID mice implanted with the human breast BT474 xenograft

Abstract Introduction Mass Spectrometry Imaging (MSI) is an emerging technique in preclinical analysis that allows for analysis of the distribution and the quantification of target molecules in tissue sections. The main advantage of this imaging technology is the detection of the molecule of interest in tissues without labelling and with high specificity. MSI is now routinely used for small molecule distribution analysis in lead optimization process, and in PK/PD or toxicity studies. Due to the mass range limitation of the instrument analyzer one of the main challenges is the detection of administered large molecules such as therapeutic antibodies. . In this study, we describe the detection and the distribution of trastuzumab, a monoclonal antibody that recognizes the HER2/neu receptor, in a BT474 human breast xenograft model. Experimental procedures BT474 tumor fragments are implanted in female CB.17 SCID mice. When the tumors reach 80-120 mm3, the trastuzumab treatment of 20mg/kg with eight bi-weekly intraperitoneal injections was initiated. The endpoint was fixed at day 30 post first administration. At 50 hours post 1st, 5th and 8th doses vehicle and trastuzumab treated animals were sacrificed and tumor, plasma and carcass were collected. One section of each tumor tissue was first digested with a proteolytic enzyme deposited with a dedicated device onto the tissue. After the proteolytic digestion, the selected MALDI matrix is sprayed onto the tissue and then the distribution of the Trastuzumab is determined based on its specific peptide mass fingerprint (PMF) by high resolution mass spectrometry imaging with a MALDI-FTICR instrument (SolariX FTICR 7.0T from Bruker). The images are obtained with Quantinetix software dedicated to the MSI data set. Novel Aspect We describe a process which combines MSI and bottom-up proteomics approach directly on tissue to follow the distribution of a therapeutic antibody without any labelling. Until now, mass spectrometry imaging was used to study some biomarkers' (proteins) distribution on tissue. This work describes a novel MSI application for analysis of a dosed therapeutic antibody. Data collection is ongoing. Conclusions We have adapted the use of Mass Spectrometry Imaging to follow the distribution of a non-labeled therapeutic antibody based on its peptide mass fingerprint in dosed tissues. This opens the use of this technology to other large molecules, such as therapeutic proteins or Antibody-Drug Conjugates (ADCs) in a variety of therapeutic fields (Oncology, Immunology, CNS, etc.) In addition to the distribution of the target therapeutic antibody, Mass Spectrometry Imaging could also allow the detection of other important endogenous molecules in the same or adjacent tissue section, such as specific disease markers, thus allowing further understanding of PK/PD relationships. Citation Format: David Bonnel, Chassidy Hall, Robert J. Mullin, Kathryn A. Simon, Jonathan Stauber. Mass Spectrometry Imaging of therapeutic antibodies: Distribution of unlabeled trastuzumab in CB.17 SCID mice implanted with the human breast BT474 xenograft. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2064. doi:10.1158/1538-7445.AM2014-2064

Abstract 4959: High-resolution MALDI imaging mass spectrometry demonstrated the correlation between phosphatidylinositol profiles and invasion/metastasis in human breast cancer

Abstract High-resolution matrix-assisted laser desorption/ionization imaging mass spectrometry (HR-MALDI IMS) is an emerging application for lipid research that provides a detailed histological distribution of ionized lipids within tissue section. Phosphatidylinositol (PI) is one of the major classes of membrane phospholipid. The cellular membrane fluidity and signal transduction activity could be modulated by the alteration of fatty acid composition of PIs. Especially, PI-3kinase pathway, which can be activated by the phosphorylation of PIs, has become a great concern in breast cancer treatment. Although the amount of PIs is known to increase in human breast cancer tissues, it remains unclear how PIs are distributed in cancerous tissues. In this study, we investigated the detailed spatial distribution of PIs in breast tissues obtained from 24 patients, including 23 invasive ductal carcinoma (IDC), 4 ductal carcinoma in situ (DCIS), and 4 fibrocystic change lesions by using HR-MALDI IMS. The distribution of PIs was visualized at the resolution of 10um. 10 PIs with different fatty acid composition were detected in breast tissues. High-resolution analysis revealed the fatty acid composition of PIs was altered specifically in cancer cell clusters compared to stromal cells and non-malignant epithelia. PIs carrying monounsaturated fatty acid (MUFA) and PIs carrying polyunsaturated fatty acid (PUFA) showed the specific localization to cancer cell clusters. However, the proportion of PIs carrying MUFA and PIs carrying PUFA showed a clear inverse correlation in cancer cells. When we compared the PI profiles of IDC, DCIS, and FC, it was suggested that the accumulation of PIs carrying PUFA was occurred during the step of invasion. Moreover, lymph node metastasis well correlated with the accumulation of PIs carrying PUFA in cancer cells. HR-MALDI IMS firstly demonstrated the possible association between the PI profiles of breast cancer cells and their invasion/metastasis ability. Although this is a preliminary study, HR-MALDI IMS could be a useful modality to visualize the reprogramming of the lipid metabolism which reflects the cancer cell phenotype. Citation Format: Masahiro Kawashima, Nobuko Kawaguchi-Sakita, Masahiro Sugimoto, Taka-Aki Sato, Koichi Tanaka, Masakazu Toi. High-resolution MALDI imaging mass spectrometry demonstrated the correlation between phosphatidylinositol profiles and invasion/metastasis in human breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4959. doi:10.1158/1538-7445.AM2014-4959

Natural products in Glycyrrhiza glabra (licorice) rhizome imaged at the cellular level by atmospheric pressure matrix-assisted laser desorption/ionization tandem mass spectrometry imaging.

The rhizome of Glycyrrhiza glabra (licorice) was analyzed by high-resolution mass spectrometry imaging and tandem mass spectrometry imaging. An atmospheric pressure matrix-assisted laser desorption/ionization imaging ion source was combined with an orbital trapping mass spectrometer in order to obtain high-resolution imaging in mass and space. Sections of the rhizome were imaged with a spatial resolution of 10 μm in the positive ion mode, and a large number of secondary metabolites were localized and identified based on their accurate mass and MS/MS fragmentation patterns. Major tissue-specific metabolites, including free flavonoids, flavonoid glycosides and saponins, were successfully detected and visualized in images, showing their distributions at the cellular level. The analytical power of the technique was tested in the imaging of two isobaric licorice saponins with a mass difference of only 0.02 Da. With a mass resolving power of 140 000 and a bin width of 5 ppm in the image processing, the two compounds were well resolved in full-scan mode, and appeared with different distributions in the tissue sections. The identities of the compounds and their distributions were validated in a subsequent MS/MS imaging experiment, thereby confirming their identities and excluding possible analyte interference. The use of high spatial resolution, high mass resolution and tandem mass spectrometry in imaging experiments provides significant information about the biosynthetic pathway of flavonoids and saponins in legume species, combing the spatially resolved chemical information with morphological details at the microscopic level. Furthermore, the technique offers a scheme capable of high-throughput profiling of metabolites in plant tissues.

Secondary ion mass spectrometry imaging of Dictyostelium discoideum aggregation streams.

High resolution imaging mass spectrometry could become a valuable tool for cell and developmental biology, but both, high spatial and mass spectral resolution are needed to enable this. In this report, we employed Bi3 bombardment time-of-flight (Bi3 ToF-SIMS) and C60 bombardment Fourier transform ion cyclotron resonance secondary ion mass spectrometry (C60 FTICR-SIMS) to image Dictyostelium discoideum aggregation streams. Nearly 300 lipid species were identified from the aggregation streams. High resolution mass spectrometry imaging (FTICR-SIMS) enabled the generation of multiple molecular ion maps at the nominal mass level and provided good coverage for fatty acyls, prenol lipids, and sterol lipids. The comparison of Bi3 ToF-SIMS and C60 FTICR-SIMS suggested that while the first provides fast, high spatial resolution molecular ion images, the chemical complexity of biological samples warrants the use of high resolution analyzers for accurate ion identification.

110 The expression profile of phosphatidylinositol in high resolution imaging mass spectrometry is a potential biomarker for prostate cancer

110 The expression profile of phosphatidylinositol in high resolution imaging mass spectrometry is a potential biomarker for prostate cancer

The Expression Profile of Phosphatidylinositol in High Spatial Resolution Imaging Mass Spectrometry as a Potential Biomarker for Prostate Cancer

High-resolution matrix-assisted laser desorption/ionization imaging mass spectrometry (HR-MALDI-IMS) is an emerging application for the comprehensive and detailed analysis of the spatial distribution of ionized molecules in situ on tissue slides. HR-MALDI-IMS in negative mode in a mass range of m/z 500–1000 was performed on optimal cutting temperature (OCT) compound-embedded human prostate tissue samples obtained from patients with prostate cancer at the time of radical prostatectomy. HR-MALDI-IMS analysis of the 14 samples in the discovery set identified 26 molecules as highly expressed in the prostate. Tandem mass spectrometry (MS/MS) showed that these molecules included 14 phosphatidylinositols (PIs), 3 phosphatidylethanolamines (PEs) and 3 phosphatidic acids (PAs). Among the PIs, the expression of PI(18:0/18:1), PI(18:0/20:3) and PI(18:0/20:2) were significantly higher in cancer tissue than in benign epithelium. A biomarker algorithm for prostate cancer was formulated by analyzing the expression profiles of PIs in cancer tissue and benign epithelium of the discovery set using orthogonal partial least squares discriminant analysis (OPLS-DA). The sensitivity and specificity of this algorithm for prostate cancer diagnosis in the 24 validation set samples were 87.5 and 91.7%, respectively. In conclusion, HR-MALDI-IMS identified several PIs as being more highly expressed in prostate cancer than benign prostate epithelium. These differences in PI expression profiles may serve as a novel diagnostic tool for prostate cancer.

Towards Lipidomics of Low-Abundant Species for Exploring Tumor Heterogeneity Guided by High-Resolution Mass Spectrometry Imaging

Many studies have evidenced the main role of lipids in physiological and also pathological processes such as cancer, diabetes or neurodegenerative diseases. The identification and the in situ localization of specific low-abundant lipid species involved in cancer biology are still challenging for both fundamental studies and lipid marker discovery. In this paper, we report the identification and the localization of specific isobaric minor phospholipids in human breast cancer xenografts by FTICR MALDI imaging supported by histochemistry. These potential candidates can be further confirmed by liquid chromatography coupled with electrospray mass spectrometry (LC-ESI-MS) after extraction from the region of interest defined by MALDI imaging. Finally, this study highlights the importance of characterizing the heterogeneous distribution of low-abundant lipid species, relevant in complex histological samples for biological purposes.

Surface-Transfer Mass Spectrometry Imaging on a Monoisotopic Silver Nanoparticle Enhanced Target

A new method for both high-resolution laser desorption/ionization mass spectrometry and mass spectrometry imaging is described. The method could be considered as matrix-less because no additional matrix is needed for MS measurements and also because of surface-assisted laser desorption/ionization due to the nanoparticle-rich surface. The standard matrix-assisted laser desorption/ionization target containing unique monoisotopic cationic (109)Ag nanoparticles ((109)AgNPs) was used for high-resolution mass spectrometry imaging of fingermarks and also plant flower and plant stem cross sections with high mass accuracy. The methodology presented in this work allowed visualization of two drugs--anti-inflammatory ibuprofen and anticancer 5-fluorouracil--along with many other compounds found on the finger. Moreover, visualization of herbicide localization inside of the plant stem is also shown. The simple inorganic ions ionized by silver nanoparticles were also found and may be used for their localization in biological material. In addition, the methodology presented here does not require freezing of species or slice-making equipment.

Correlated SEM, FIB-SEM, TEM, and NanoSIMS Imaging of Microbes from the Hindgut of a Lower Termite: Methods forIn SituFunctional and Ecological Studies of Uncultivable Microbes

The hindguts of lower termites harbor highly diverse, endemic communities of symbiotic protists, bacteria, and archaea essential to the termite's ability to digest wood. Despite over a century of experimental studies, ecological roles of many of these microbes are unknown, partly because almost none can be cultivated. Many of the protists associate with bacterial symbionts, but hypotheses for their respective roles in nutrient exchange are based on genomes of only two such bacteria. To show how the ecological roles of protists and nutrient transfer with symbiotic bacteria can be elucidated by direct imaging, we combined stable isotope labeling (13C-cellulose) of live termites with analysis of fixed hindgut microbes using correlated scanning electron microscopy, focused ion beam-scanning electron microscopy (FIB-SEM), transmission electron microscopy, and high resolution imaging mass spectrometry (NanoSIMS). We developed methods to prepare whole labeled cells on solid substrates, whole labeled cells milled with a FIB-SEM instrument to reveal cell interiors, and ultramicrotome sections of labeled cells for NanoSIMS imaging of 13C enrichment in protists and associated bacteria. Our results show these methods have the potential to provide direct evidence for nutrient flow and suggest the oxymonad protist Oxymonas dimorpha phagocytoses and enzymatically degrades ingested wood fragments, and may transfer carbon derived from this to its surface bacterial symbionts.

Abstract 3932: High resolution imaging mass spectrometry reveals the breast cancer cell-related profiles of phosphatidylinositol unsaturation.

Abstract Lipid metabolism is supposed to be altered in breast cancer, and several literatures have suggested the possible compositional change of phospholipids in breast cancer tissues and its correlations with the tumor grade, sex hormone receptor status and patient's prognosis. However, the breast cancer cell-related alteration of phospholipid profiles and its underlying metabolic change remain unclear. The aim of this study is to investigate the cancer cell-related phospholipid alteration by using high resolution matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). We evaluated the spatial distributions and the proportions of phosphatidylinositols (PIs) in seven breast cancer tissues (three luminal cases and four non-luminal cases including one Her2 positive case) and one normal breast tissue. MS images of PIs and their mass spectra showed that the fatty acyl chain compositions of observed PIs remarkably changed in cancer cell region, compared with those in normal duct epithelium or surrounding stromal cells. PIs containing polyunsaturated fatty acid (PUFA) were the major components in normal duct epithelium. In five of seven cancer cases, PIs containing monounsaturated fatty acid (MUFA) were the most dominant in the observed PIs and specifically upregulated in cancer cells. In the rest of the cases, the MUFA upregulation was less obvious than the aforementioned five cases, and PIs containing PUFA still constituted a large percentage of observed PIs. In non-luminal cases, the MUFA upregulation in cancer cells was well correlated with the expression level of stearoyl CoA desaturase 1 (SCD1), a key enzyme in de novo MUFA synthesis. This observation suggested that the upregulation of de novo MUFA synthesis in cancer cells could contribute to the increase of PIs containing MUFA. In conclusion, high resolution MALDI-IMS revealed the breast cancer cell-related changes of PI profiles according to the degree of the fatty acyl chain unsaturation, which implied the existence of cancer cell-related PI remodeling process. Citation Format: Masahiro Kawashima, Noriko Iwamoto, Nobuko Kawaguchi-Sakita, Masahiro Sugimoto, Takayuki Ueno, Kazuya Terasawa, Taka-Aki Sato, Koichi Tanaka, Kazuharu Shimizu, Masakazu Toi. High resolution imaging mass spectrometry reveals the breast cancer cell-related profiles of phosphatidylinositol unsaturation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3932. doi:10.1158/1538-7445.AM2013-3932

Molecular histology with high resolution imaging mass spectrometry

Imaging mass spectrometry (IMS) compliments traditional histopathology by illuminating the biochemical processes that accompany visual changes in cellular structure. As an imaging technique, IMS is characterized by spatial resolution, but as a mass spectrometry technique IMS is characterized by the range of compounds detected. In an effort to improve the performance of IMS for high‐resolution, label‐free molecular histology we investigated two key aspects of IMS: instrumentation (laser focus) and sample processing (analyte diffusion).Using a solvent‐free preparation, images of phospholipids acquired from rat brain exhibit virtually no analyte diffusion and allow the laser focus to be reduced to cellular dimensions. For imaging larger proteins, however, solvent‐free conditions are not effective and traditional solvent‐based preparations induce substantial analyte diffusion thereby limiting resolution. Rat brain sections were processed in a high‐humidity atmosphere instead of using liquid solvent and a large number of high resolution protein images were collected. This shows that such conditions provide efficient analyte extraction with minimal migration. High resolution IMS images viewed in conjunction with histopathology show a more detailed picture of cellular processes and promises a better understanding of mechanisms of disease progression and treatment response.

MSiReader: An Open-Source Interface to View and Analyze High Resolving Power MS Imaging Files on Matlab Platform

During the past decade, the field of mass spectrometry imaging (MSI) has greatly evolved, to a point where it has now been fully integrated by most vendors as an optional or dedicated platform that can be purchased with their instruments. However, the technology is not mature and multiple research groups in both academia and industry are still very actively studying the fundamentals of imaging techniques, adapting the technology to new ionization sources, and developing new applications. As a result, there important varieties of data file formats used to store mass spectrometry imaging data and, concurrent to the development of MSi, collaborative efforts have been undertaken to introduce common imaging data file formats. However, few free software packages to read and analyze files of these different formats are readily available. We introduce here MSiReader, a free open source application to read and analyze high resolution MSI data from the most common MSi data formats. The application is built on the Matlab platform (Mathworks, Natick, MA, USA) and includes a large selection of data analysis tools and features. People who are unfamiliar with the Matlab language will have little difficult navigating the user-friendly interface, and users with Matlab programming experience can adapt and customize MSiReader for their own needs.

Silver-Assisted Laser Desorption Ionization For High Spatial Resolution Imaging Mass Spectrometry of Olefins from Thin Tissue Sections

Silver has been demonstrated to be a powerful cationization agent in mass spectrometry (MS) for various olefinic species such as cholesterol and fatty acids. This work explores the utility of metallic silver sputtering on tissue sections for high resolution imaging mass spectrometry (IMS) of olefins by laser desorption ionization (LDI). For this purpose, sputtered silver coating thickness was optimized on an assorted selection of mouse and rat tissues including brain, kidney, liver, and testis. For mouse brain tissue section, the thickness was adjusted to 23 ± 2 nm of silver to prevent ion suppression effects associated with a higher cholesterol and lipid content. On all other tissues, a thickness of at 16 ± 2 nm provided the best desorption/ionization efficiency. Characterization of the species by MS/MS showed a wide variety of olefinic compounds allowing the IMS of different lipid classes including cholesterol, arachidonic acid, docosahexaenoic acid, and triacylglyceride 52:3. A range of spatial resolutions for IMS were investigated from 150 μm down to the high resolution cellular range at 5 μm. The applicability of direct on-tissue silver sputtering to LDI-IMS of cholesterol and other olefinic compounds presents a novel approach to improve the amount of information that can be obtained from tissue sections. This IMS strategy is thus of interest for providing new biological insights on the role of cholesterol and other olefins in physiological pathways or disease.

Host-compound foraging by intestinal microbiota revealed by single-cell stable isotope probing

The animal and human intestinal mucosa secretes an assortment of compounds to establish a physical barrier between the host tissue and intestinal contents, a separation that is vital for health. Some pathogenic microorganisms as well as members of the commensal intestinal microbiota have been shown to be able to break down these secreted compounds. Our understanding of host-compound degradation by the commensal microbiota has been limited to knowledge about simplified model systems because of the difficulty in studying the complex intestinal ecosystem in vivo. In this study, we introduce an approach that overcomes previous technical limitations and allows us to observe which microbial cells in the intestine use host-derived compounds. We added stable isotope-labeled threonine i.v. to mice and combined fluorescence in situ hybridization with high-resolution secondary ion mass spectrometry imaging to characterize utilization of host proteins by individual bacterial cells. We show that two bacterial species, Bacteroides acidifaciens and Akkermansia muciniphila, are important host-protein foragers in vivo. Using gnotobiotic mice we show that microbiota composition determines the magnitude and pattern of foraging by these organisms, demonstrating that a complex microbiota is necessary in order for this niche to be fully exploited. These results underscore the importance of in vivo studies of intestinal microbiota, and the approach presented in this study will be a powerful tool to address many other key questions in animal and human microbiome research.

Direct chemical evidence for sphingolipid domains in the plasma membranes of fibroblasts

Sphingolipids play important roles in plasma membrane structure and cell signaling. However, their lateral distribution in the plasma membrane is poorly understood. Here we quantitatively analyzed the sphingolipid organization on the entire dorsal surface of intact cells by mapping the distribution of (15)N-enriched ions from metabolically labeled (15)N-sphingolipids in the plasma membrane, using high-resolution imaging mass spectrometry. Many types of control experiments (internal, positive, negative, and fixation temperature), along with parallel experiments involving the imaging of fluorescent sphingolipids--both in living cells and during fixation of living cells--exclude potential artifacts. Micrometer-scale sphingolipid patches consisting of numerous (15)N-sphingolipid microdomains with mean diameters of ∼200 nm are always present in the plasma membrane. Depletion of 30% of the cellular cholesterol did not eliminate the sphingolipid domains, but did reduce their abundance and long-range organization in the plasma membrane. In contrast, disruption of the cytoskeleton eliminated the sphingolipid domains. These results indicate that these sphingolipid assemblages are not lipid rafts and are instead a distinctly different type of sphingolipid-enriched plasma membrane domain that depends upon cortical actin.

Nano-scale investigation of the association of microbial nitrogen residues with iron (hydr)oxides in a forest soil O-horizon

Amino sugars in fungal cell walls (such as chitin) represent an important source of nitrogen (N) in many forest soil ecosystems. Despite the importance of this material in soil nitrogen cycling, comparatively little is known about abiotic and biotic controls on and the timescale of its turnover. Part of the reason for this lack of information is the inaccessibility of these materials to classic bulk extraction methods. To address this issue, we used advanced visualization tools to examine transformation pathways of chitin-rich fungal cell wall residues as they interact with microorganisms, soil organic matter and mineral surfaces. Our goal was to document initial micro-scale dynamics of the incorporation of 13C- and 15N-labeled chitin into fungi-dominated microenvironments in O-horizons of old-growth forest soils. At the end of a 3-week incubation experiment, high-resolution secondary ion mass spectrometry imaging of hyphae-associated soil microstructures revealed a preferential association of 15N with Fe-rich particles. Synchrotron-based scanning transmission X-ray spectromicroscopy (STXM/NEXAFS) of the same samples showed that thin organic coatings on these soil microstructures are enriched in aliphatic C and amide N on Fe (hydr)oxides, suggesting a concentration of microbial lipids and proteins on these surfaces. A possible explanation for the results of our micro-scale investigation of chemical and spatial patterns is that amide N from chitinous fungal cell walls was assimilated by hyphae-associated bacteria, resynthesized into proteinaceous amide N, and subsequently concentrated onto Fe (hydr)oxide surfaces. If confirmed in other soil ecosystems, such rapid association of microbial N with hydroxylated Fe oxide surfaces may have important implications for mechanistic models of microbial cycling of C and N.

High-Resolution Multi-isotope Imaging Mass Spectrometry Enables Visualisation of Stem Cell Division and Metabolism

MIMS visualises metabolism: A recent publication by Steinhauser and co-workers presents a novel application of multi-isotope mass spectrometry (MIMS) to visualise physiological metabolism in live mammalian organisms, and validate the "immortal strand hypothesis" of asymmetric chromosomal division of stem cells in the small intestine.

Sublimation of New Matrix Candidates for High Spatial Resolution Imaging Mass Spectrometry of Lipids: Enhanced Information in Both Positive and Negative Polarities after 1,5-Diaminonapthalene Deposition

Matrix sublimation has demonstrated to be a powerful approach for high-resolution matrix-assisted laser desorption ionization (MALDI) imaging of lipids, providing very homogeneous solvent-free deposition. This work presents a comprehensive study aiming to evaluate current and novel matrix candidates for high spatial resolution MALDI imaging mass spectrometry of lipids from tissue section after deposition by sublimation. For this purpose, 12 matrices including 2,5-dihydroxybenzoic acid (DHB), sinapinic acid (SA), α-cyano-4-hydroxycinnamic acid (CHCA), 2,6-dihydroxyacetphenone (DHA), 2',4',6'-trihydroxyacetophenone (THAP), 3-hydroxypicolinic acid (3-HPA), 1,8-bis(dimethylamino)naphthalene (DMAN), 1,8,9-anthracentriol (DIT), 1,5-diaminonapthalene (DAN), p-nitroaniline (NIT), 9-aminoacridine (9-AA), and 2-mercaptobenzothiazole (MBT) were investigated for lipid detection efficiency in both positive and negative ionization modes, matrix interferences, and stability under vacuum. For the most relevant matrices, ion maps of the different lipid species were obtained from tissue sections at high spatial resolution and the detected peaks were characterized by matrix-assisted laser desorption ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry. First proposed for imaging mass spectrometry (IMS) after sublimation, DAN has demonstrated to be of high efficiency providing rich lipid signatures in both positive and negative polarities with high vacuum stability and sub-20 μm resolution capacity. Ion images from adult mouse brain were generated with a 10 μm scanning resolution. Furthermore, ion images from adult mouse brain and whole-body fish tissue sections were also acquired in both polarity modes from the same tissue section at 100 μm spatial resolution. Sublimation of DAN represents an interesting approach to improve information with respect to currently employed matrices providing a deeper analysis of the lipidome by IMS.