51
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Jackson SN, Baldwin K, Muller L, Womack VM, Schultz JA, Balaban C, Woods AS. Imaging of lipids in rat heart by MALDI-MS with silver nanoparticles. Anal Bioanal Chem 2013; 406:1377-86. [PMID: 24309627 DOI: 10.1007/s00216-013-7525-6] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Revised: 10/14/2013] [Accepted: 11/19/2013] [Indexed: 12/21/2022]
Abstract
Lipids are a major component of heart tissue and perform several important functions such as energy storage, signaling, and as building blocks of biological membranes. The heart lipidome is quite diverse consisting of glycerophospholipids such as phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidylinositols (PIs), phosphatidylglycerols (PGs), cardiolipins (CLs), and glycerolipids, mainly triacylglycerols (TAGs). In this study, mass spectrometry imaging (MSI) enabled by matrix implantation of ionized silver nanoparticles (AgNP) was used to map several classes of lipids in heart tissue. The use of AgNP matrix implantation was motivated by our previous work showing that implantation doses of only 10(14)/cm(2) of 2 nm gold nanoparticulates into the first 10 nm of the near surface of the tissue enabled detection of most brain lipids (including neutral lipid species such as cerebrosides) more efficiently than traditional organic MALDI matrices. Herein, a similar implantation of 500 eV AgNP(-) across the entire heart tissue section results in a quick, reproducible, solvent-free, uniform matrix concentration of 6 nm AgNP residing near the tissue surface. MALDI-MSI analysis of either positive or negative ions produce high-quality images of several heart lipid species. In negative ion mode, 24 lipid species [16 PEs, 4 PIs, 1 PG, 1 CL, 2 sphingomyelins (SMs)] were imaged. Positive ion images were also obtained from 29 lipid species (10 PCs, 5 PEs, 5 SMs, 9 TAGs) with the TAG species being heavily concentrated in vascular regions of the heart.
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Affiliation(s)
- Shelley N Jackson
- Structural Biology Unit, NIDA IRP, NIH, 333 Cassell Drive, Room 1120, Baltimore, MD, 21224, USA
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52
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Griffiths RL, Sarsby J, Guggenheim EJ, Race AM, Steven RT, Fear J, Lalor PF, Bunch J. Formal lithium fixation improves direct analysis of lipids in tissue by mass spectrometry. Anal Chem 2013; 85:7146-53. [PMID: 23879734 DOI: 10.1021/ac400737z] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Mass spectrometry imaging is a powerful method for imaging and in situ characterization of lipids in thin tissue sections. Structural elucidation of lipids is often achieved via collision induced dissociation, and lithium-lipid adducts have been widely reported as providing the most structurally informative fragment ions. We present a method for the incorporation of lithium salts into tissue imaging experiments via fixation of samples in formal lithium solutions. The method is suitable for preparation of single tissue sections, or as an immersion fixation method for whole tissue blocks or organs prior to sectioning. We compare lithium adduct detection and MALDI-MSI of murine brain from analysis of tissues prepared in different ways. Tissues prepared in formal solutions containing lithium or sodium salts before coating in matrix via air-spray deposition are compared with fresh samples coated in lithium-doped matrix preparations by either dry-coating or air-spray deposition. Sample preparation via fixation in formal lithium is shown to yield the highest quality images of lithium adducts, resulting in acquisition of more informative product ion spectra in MALDI MS/MS profiling and imaging experiments. Finally, the compatibility of formal lithium solutions with standard histological staining protocols (hemotoxylin and eosin, Van Giessen and Oil Red O) is demonstrated in a study of human liver tissue.
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Affiliation(s)
- Rian L Griffiths
- School of Chemistry, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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53
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Steven RT, Palmer AD, Bunch J. Fluorometric beam profiling of UV MALDI lasers. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1146-1152. [PMID: 23709039 DOI: 10.1007/s13361-013-0650-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 04/08/2013] [Accepted: 04/21/2013] [Indexed: 06/02/2023]
Abstract
The photon distribution (beam profile) of the laser as projected onto the sample is an important variable in matrix assisted laser desorption ionization mass spectrometry (MALDI-MS). Measurement of the beam profile is, therefore, an important factor within MALDI-MS. In this study a simple, low-cost fluorometric laser beam profiling technique is presented and applied in conjunction with MALDI-MS experiments. A comparison of the beam profile information afforded by a commercial system and the fluorometric method is carried out to determine the variation of beam profile for an Nd:YVO4 laser operated between 1 and 25 kHz. The beam profile information can be used, in conjunction with corresponding ion yields, to inform MALDI-MS experiments. The fluorometric beam profiling technique is used to obtain information about the beam dimensions as incident upon the MALDI-MS sample plate in-source. These values are compared with equivalent information obtained from ablation of thin film α-cyano-4-hydroxycinnamic acid (CHCA). In this study, area estimation by ablation provided a value 1.6 times smaller than that obtained by the fluorometric method, demonstrating the need for caution when measuring beam profile and, therefore, fluence, in MALDI-MS. ᅟ
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Affiliation(s)
- Rory T Steven
- PSIBS Doctoral Training Centre, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
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54
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Steven RT, Race AM, Bunch J. para-Nitroaniline is a promising matrix for MALDI-MS imaging on intermediate pressure MS systems. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:801-804. [PMID: 23456890 DOI: 10.1007/s13361-013-0586-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 01/11/2013] [Accepted: 01/15/2013] [Indexed: 06/01/2023]
Abstract
para-Nitroaniline (PNA) is presented as a promising matrix for matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) on an intermediate-pressure ion source (~1 Torr) QqTOF instrument using an Nd:YVO4 laser operated at 5 kHz. An imaging study was carried out to determine the utility of PNA at this pressure by analyzing 14 tissue sections. We demonstrate acquisition of high-quality imaging data over a 6-h period in the ion source. In this study, comparisons were made between PNA and α-cyano-4-hydroxycinnamic acid (CHCA) in positive ion mode to demonstrate the utility of PNA in these circumstances. PNA performed as well as or better than CHCA in terms of lipid ion intensities, resulting in lower levels of ion fragmentation and in lower incidences of analyte migration at the edges of the tissue sections when using airspray matrix deposition.
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Affiliation(s)
- Rory T Steven
- PSIBS Centre, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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55
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Eriksson C, Masaki N, Yao I, Hayasaka T, Setou M. MALDI Imaging Mass Spectrometry-A Mini Review of Methods and Recent Developments. Mass Spectrom (Tokyo) 2013; 2:S0022. [PMID: 24349941 DOI: 10.5702/massspectrometry.s0022] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2012] [Accepted: 01/23/2013] [Indexed: 12/16/2022] Open
Abstract
As the only imaging method available, Imaging Mass Spectrometry (IMS) can determine both the identity and the distribution of hundreds of molecules on tissue sections, all in one single run. IMS is becoming an established research technology, and due to recent technical and methodological improvements the interest in this technology is increasing steadily and within a wide range of scientific fields. Of the different IMS methods available, matrix-assisted laser desorption/ionization (MALDI) IMS is the most commonly employed. The course at IMSC 2012 in Kyoto covered the fundamental principles and techniques of MALDI-IMS, assuming no previous experience in IMS. This mini review summarizes the content of the one-day course and describes some of the most recent work performed within this research field.
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Affiliation(s)
- Cecilia Eriksson
- Department of Cell Biology and Anatomy, Hamamatsu University School of Medicine ; Medical Mass Spectrometry, Department of Pharmaceutical Biosciences, Uppsala University
| | - Noritaka Masaki
- Department of Cell Biology and Anatomy, Hamamatsu University School of Medicine
| | - Ikuko Yao
- Department of Medical Chemistry, Kansai Medical University
| | - Takahiro Hayasaka
- Department of Cell Biology and Anatomy, Hamamatsu University School of Medicine
| | - Mitsutoshi Setou
- Department of Cell Biology and Anatomy, Hamamatsu University School of Medicine
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56
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Repeat MALDI MS imaging of a single tissue section using multiple matrices and tissue washes. Anal Bioanal Chem 2013; 405:4719-28. [DOI: 10.1007/s00216-013-6899-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 02/28/2013] [Accepted: 03/05/2013] [Indexed: 01/03/2023]
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57
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Race AM, Steven RT, Palmer AD, Styles IB, Bunch J. Memory efficient principal component analysis for the dimensionality reduction of large mass spectrometry imaging data sets. Anal Chem 2013; 85:3071-8. [PMID: 23394348 DOI: 10.1021/ac302528v] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A memory efficient algorithm for the computation of principal component analysis (PCA) of large mass spectrometry imaging data sets is presented. Mass spectrometry imaging (MSI) enables two- and three-dimensional overviews of hundreds of unlabeled molecular species in complex samples such as intact tissue. PCA, in combination with data binning or other reduction algorithms, has been widely used in the unsupervised processing of MSI data and as a dimentionality reduction method prior to clustering and spatial segmentation. Standard implementations of PCA require the data to be stored in random access memory. This imposes an upper limit on the amount of data that can be processed, necessitating a compromise between the number of pixels and the number of peaks to include. With increasing interest in multivariate analysis of large 3D multislice data sets and ongoing improvements in instrumentation, the ability to retain all pixels and many more peaks is increasingly important. We present a new method which has no limitation on the number of pixels and allows an increased number of peaks to be retained. The new technique was validated against the MATLAB (The MathWorks Inc., Natick, Massachusetts) implementation of PCA (princomp) and then used to reduce, without discarding peaks or pixels, multiple serial sections acquired from a single mouse brain which was too large to be analyzed with princomp. Then, k-means clustering was performed on the reduced data set. We further demonstrate with simulated data of 83 slices, comprising 20,535 pixels per slice and equaling 44 GB of data, that the new method can be used in combination with existing tools to process an entire organ. MATLAB code implementing the memory efficient PCA algorithm is provided.
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Affiliation(s)
- Alan M Race
- Physical Sciences of Imaging in the Biomedical Sciences Doctoral Training Centre, School of Chemistry, University of Birmingham, Edgbaston, Birmingham, United Kingdom
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58
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Fonville JM, Carter CL, Pizarro L, Steven RT, Palmer AD, Griffiths RL, Lalor PF, Lindon JC, Nicholson JK, Holmes E, Bunch J. Hyperspectral visualization of mass spectrometry imaging data. Anal Chem 2013; 85:1415-23. [PMID: 23249247 DOI: 10.1021/ac302330a] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The acquisition of localized molecular spectra with mass spectrometry imaging (MSI) has a great, but as yet not fully realized, potential for biomedical diagnostics and research. The methodology generates a series of mass spectra from discrete sample locations, which is often analyzed by visually interpreting specifically selected images of individual masses. We developed an intuitive color-coding scheme based on hyperspectral imaging methods to generate a single overview image of this complex data set. The image color-coding is based on spectral characteristics, such that pixels with similar molecular profiles are displayed with similar colors. This visualization strategy was applied to results of principal component analysis, self-organizing maps and t-distributed stochastic neighbor embedding. Our approach for MSI data analysis, combining automated data processing, modeling and display, is user-friendly and allows both the spatial and molecular information to be visualized intuitively and effectively.
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Affiliation(s)
- Judith M Fonville
- Biomolecular Medicine, Department of Surgery and Cancer, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom
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59
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60
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Sample preparation for mass spectrometry imaging: Small mistakes can lead to big consequences. J Proteomics 2012; 75:4893-4911. [DOI: 10.1016/j.jprot.2012.04.012] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Revised: 04/11/2012] [Accepted: 04/12/2012] [Indexed: 12/13/2022]
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61
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Crecelius AC, Steinacker R, Meier A, Alexandrov T, Vitz J, Schubert US. Application of Matrix-Assisted Laser Desorption/Ionization Mass Spectrometric Imaging for Photolithographic Structuring. Anal Chem 2012; 84:6921-5. [DOI: 10.1021/ac301616v] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Anna C. Crecelius
- Laboratory of Organic
and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, 07743 Jena, Germany
- Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany
- Dutch Polymer Institute (DPI), John F. Kennedylaan
2, 5612 AB Eindhoven, The Netherlands
| | - Ralf Steinacker
- Laboratory of Organic
and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, 07743 Jena, Germany
- Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany
| | - Alexander Meier
- Laboratory of Organic
and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, 07743 Jena, Germany
- Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany
| | - Theodore Alexandrov
- Steinbeis Innovation Center for Scientific Computing in Life Sciences (SCiLS), Bremen, Germany
- Center for Industrial Mathematics, University of Bremen, Bremen, Germany
- MALDI Imaging Lab, University of Bremen, Bremen, Germany
| | - Jürgen Vitz
- Laboratory of Organic
and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, 07743 Jena, Germany
- Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany
- Dutch Polymer Institute (DPI), John F. Kennedylaan
2, 5612 AB Eindhoven, The Netherlands
| | - Ulrich S. Schubert
- Laboratory of Organic
and Macromolecular Chemistry (IOMC), Friedrich-Schiller-University Jena, Humboldtstrasse 10, 07743 Jena, Germany
- Jena Center for Soft Matter (JCSM), Friedrich-Schiller-University Jena, Humboldtstrasse
10, 07743 Jena, Germany
- Dutch Polymer Institute (DPI), John F. Kennedylaan
2, 5612 AB Eindhoven, The Netherlands
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62
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Conductive carbon tape used for support and mounting of both whole animal and fragile heat-treated tissue sections for MALDI MS imaging and quantitation. J Proteomics 2012; 75:4912-4920. [PMID: 22796569 DOI: 10.1016/j.jprot.2012.07.006] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Revised: 06/22/2012] [Accepted: 07/04/2012] [Indexed: 11/21/2022]
Abstract
Analysis of whole animal tissue sections by MALDI MS imaging (MSI) requires effective sample collection and transfer methods to allow the highest quality of in situ analysis of small or hard to dissect tissues. We report on the use of double-sided adhesive conductive carbon tape during whole adult rat tissue sectioning of carboxymethyl cellulose (CMC) embedded animals, with samples mounted onto large format conductive glass and conductive plastic MALDI targets, enabling MSI analysis to be performed on both TOF and FT-ICR MALDI mass spectrometers. We show that mounting does not unduly affect small molecule MSI detection by analyzing tiotropium abundance and distribution in rat lung tissues, with direct on-tissue quantitation achieved. Significantly, we use the adhesive tape to provide support to embedded delicate heat-stabilized tissues, enabling sectioning and mounting to be performed that maintained tissue integrity on samples that had previously been impossible to adequately prepare section for MSI analysis. The mapping of larger peptidomic molecules was not hindered by tape mounting samples and we demonstrate this by mapping the distribution of PEP-19 in both native and heat-stabilized rat brains. Furthermore, we show that without heat stabilization PEP-19 degradation fragments can detected and identified directly by MALDI MSI analysis.
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63
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Sparvero L, Amoscato A, Dixon C, Long J, Kochanek P, Pitt B, Bayir H, Kagan V. Mapping of phospholipids by MALDI imaging (MALDI-MSI): realities and expectations. Chem Phys Lipids 2012; 165:545-62. [PMID: 22692104 PMCID: PMC3642772 DOI: 10.1016/j.chemphyslip.2012.06.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Revised: 05/30/2012] [Accepted: 06/01/2012] [Indexed: 02/07/2023]
Abstract
Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has emerged as a novel powerful MS methodology that has the ability to generate both molecular and spatial information within a tissue section. Application of this technology as a new type of biochemical lipid microscopy may lead to new discoveries of the lipid metabolism and biomarkers associated with area-specific alterations or damage under stress/disease conditions such as traumatic brain injury or acute lung injury, among others. However there are limitations in the range of what it can detect as compared with liquid chromatography-MS (LC-MS) of a lipid extract from a tissue section. The goal of the current work was to critically consider remarkable new opportunities along with the limitations and approaches for further improvements of MALDI-MSI. Based on our experimental data and assessments, improvements of the spectral and spatial resolution, sensitivity and specificity towards low abundance species of lipids are proposed. This is followed by a review of the current literature, including methodologies that other laboratories have used to overcome these challenges.
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Affiliation(s)
- L.J. Sparvero
- Center for Free Radical and Antioxidant Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Departments of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - A.A. Amoscato
- Center for Free Radical and Antioxidant Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Departments of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - C.E. Dixon
- Safar Center for Resuscitation Research, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Neurosurgery, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - J.B. Long
- Center for Military Psychiatry and Neuroscience, Walter Reed Army Institute of Research, Silver Spring, MD 21910, USA
| | - P.M. Kochanek
- Safar Center for Resuscitation Research, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - B.R. Pitt
- Departments of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - H. Bayir
- Center for Free Radical and Antioxidant Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Safar Center for Resuscitation Research, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Departments of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - V.E. Kagan
- Center for Free Radical and Antioxidant Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Departments of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
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64
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Palmer AD, Griffiths R, Styles I, Claridge E, Calcagni A, Bunch J. Sucrose cryo-protection facilitates imaging of whole eye sections by MALDI mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2012; 47:237-241. [PMID: 22359334 DOI: 10.1002/jms.2049] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Sucrose is used as a cryo-preservation agent on large mammalian eyes post formalin fixation and is shown to reduce freezing artefacts allowing the collection of 12-µm thick sections from these large aqueous samples. The suitability of this technique for use in MALDI imaging experiments is demonstrated by the acquisition of the first images of lipid distributions within whole sagittal porcine eye sections.
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Affiliation(s)
- Andrew D Palmer
- PSIBS Doctoral Training Centre, University of Birmingham, Birmingham, UK
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65
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Fonville JM, Carter C, Cloarec O, Nicholson JK, Lindon JC, Bunch J, Holmes E. Robust data processing and normalization strategy for MALDI mass spectrometric imaging. Anal Chem 2012; 84:1310-9. [PMID: 22148759 DOI: 10.1021/ac201767g] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) provides localized information about the molecular content of a tissue sample. To derive reliable conclusions from MSI data, it is necessary to implement appropriate processing steps in order to compare peak intensities across the different pixels comprising the image. Here, we review commonly used normalization methods, and propose a rational data processing strategy, for robust evaluation and modeling of MSI data. The approach includes newly developed heuristic methods for selecting biologically relevant peaks and pixels to reduce the size of a data set and remove the influence of the applied MALDI matrix. The methods are demonstrated on a MALDI MSI data set of a sagittal section of rat brain (4750 bins, m/z = 50-1000, 111 × 185 pixels) and the proposed preferred normalization method uses the median intensity of selected peaks, which were determined to be independent of the MALDI matrix. This was found to effectively compensate for a range of known limitations associated with the MALDI process and irregularities in MS image sampling routines. This new approach is relevant for processing of all MALDI MSI data sets, and thus likely to have impact in biomarker profiling, preclinical drug distribution studies, and studies addressing underlying molecular mechanisms of tissue pathology.
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Affiliation(s)
- Judith M Fonville
- Biomolecular Medicine, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, Sir Alexander Fleming Building, South Kensington, London SW7 2AZ, United Kingdom
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