Academic literature on the topic 'MALDI-MS Imaging'

AbstractBackgroundMatrix-assisted laser desorption ionisation (MALDI) mass spectrometry (MS) has been used for more than 30 years. Compared with other analytical techniques, it offers ease of use, high throughput, robustness, cost-effectiveness, rapid analysis and sensitivity. As advantages, current clinical techniques (e.g. immunoassays) are unable to directly measure the biomarker; rather, they measure secondary signals. MALDI-MS has been extensively researched for clinical applications, and it is set for a breakthrough as a routine tool for clinical diagnostics.ContentThis review reports on the principles of MALDI-MS and discusses current clinical applications and the future clinical prospects for MALDI-MS. Furthermore, the review assesses the limitations currently experienced in clinical assays, the advantages and the impact of MALDI-MS to transform clinical laboratories.SummaryMALDI-MS is widely used in clinical microbiology for the screening of microbial isolates; however, there is scope to apply MALDI-MS in the diagnosis, prognosis, therapeutic drug monitoring and biopsy imaging in many diseases.OutlookThere is considerable potential for MALDI-MS in clinic as a tool for screening, profiling and imaging because of its high sensitivity and specificity over alternative techniques.

Food contains various compounds, and there are many methods available to analyze each of these components. However, the large amounts of low-molecular-weight metabolites in food, such as amino acids, organic acids, vitamins, lipids, and toxins, make it difficult to analyze the spatial distribution of these molecules. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging is a two-dimensional ionization technology that allows the detection of small metabolites in tissue sections without requiring purification, extraction, separation, or labeling. The application of MALDI-MS imaging in food analysis improves the visualization of these compounds to identify not only the nutritional content but also the geographical origin of the food. In this review, we provide an overview of some recent applications of MALDI-MS imaging, demonstrating the advantages and prospects of this technology compared to conventional approaches. Further development and enhancement of MALDI-MS imaging is expected to offer great benefits to consumers, researchers, and food producers with respect to breeding improvement, traceability, the development of value-added foods, and improved safety assessments.

Coupling laser post-ionisation with a high resolving power MALDI Orbitrap mass spectrometer has realised an up to ∼100-fold increase in the sensitivity and enhanced the chemical coverage for MALDI-MS imaging of lipids relative to conventional MALDI.

MALDI Imaging has gained huge interest in the past few years with an ever increasing population of specialists choosing to investigate samples using MALDI imaging, including growing interest and financial backing from pharma and contract research organisations. Presented within this thesis is the development and application of MALDI imaging techniques for a variety of analytical problems. The use of various software packages have been employed in the interpretation of the data acquired from MALDI experiments including, the use of statistical analysis for the identification of ion of interest from 6 distinct brain regions and also for the identification of ions of interest associated with small molecule tumour markers. The advantages of MALDI-IMS-MSI as a further separation stage within MALDI-MSI have been shown. Demonstrated is a method for MALDI-IMS-MS imaging of endogenous lipids in healthy tissue and tumours, also demonstrated is the application of MALDI-IMS-MS to xenobiotic distribution studies, it has been clearly shown that ion mobility separation within MALDI-MSI experiments can improve the analysis of xenobiotics by removing any interfering ions. With instrumentation development for MALDI a high repetition rate Nd:YVO4 laser has been assessed as a possible method for decreasing acquisition time.

The diverse applications of MALDI MSI are explored in this thesis with an emphasis on the sample preparation procedure and method development for small molecule analysis for a range of samples. The two main themes that have been focussed on are the pharmaceutical and metabolomic applications of this state of the art technique. MALDI MSI has been evaluated as a technique for the detection and imaging of antiasthmatic compounds in lung tissue. Four compounds were assessed initially with conventional MALDI MS experiments, followed by both direct and indirect tissue imaging experiments. Pharmaceutical tablet formulations have also been assessed using MALDI MSI to map the active component throughout the excipients contained within the tablet providing information that is critical to the manufacturing process such as the homogeneity of the active pharmaceutical ingredient (API) throughout the tablet. MALDI MSI has been applied to the relatively new addition to the 'omics sciences, metabolomics. A non-targeted metabolomics approach has been used to study both plant and animal tissue in an attempt to gain a greater understanding of the complex biological processes that occur within both types of tissue. Wheat grain was used as the model system to conduct the experiments and evaluate the application of both UV MALDI MS and IR LDI MS for plant metabolomics. These techniques provided complementary information to published literature, however the novel aspect of this study was the incorporation of imaging experiments for UV MALDI MS; this allowed the metabolites to be visualised in the wheat grain section. MALDI MSI was also used to explore the differences between mice with chronic relapsing experimental autoimmune encephalomyelitis; the animal model of multiple sclerosis alongside healthy controls. Spinal cord samples were analysed and the main difference was tentatively attributed to choline levels.

Mass spectrometric techniques have been developed recently for the examination of biological tissue samples. Tandem mass spectrometry has been employed for the detection of pharmaceutical compounds and also mass spectrometric 'images' have been produced which show the spatial distribution of peptides, proteins and drugs in tissue. In this thesis, a programme of method development for the detection and imaging of topically applied pharmaceutical compounds in porcine epidermal tissue by MALDI-TOF-MS is presented. Direct analysis of fresh tissue sections was compared with the analysis of tissue imprints formed by blotting onto a variety of substrates. The samples were coated with matrix material by a prototype electrospray deposition device. Analyses were performed on a linear time-of-flight (LaserTOF 1500, SAI) mass spectrometer. Direct analysis of tissue and analysis of the C18 blots gave irreproducible data. Problems with matrix layer in-homogeneity were experienced with nitrocellulose and polyvinyl difluoride (PVDF) membranes. Reproducible data were obtained by analysis of tissue imprints created on carbon and cellulose membranes. All subsequent work was conducted using an Applied Biosystem Qstar pulsar i hybrid quadrupole time-of-flight mass spectrometer fitted with an orthogonal MALDI ion source and ion imaging software. The advantages of superior mass accuracy and resolution with such an instrument configuration were investigated. Electrospray and airspray methods were compared for analysis of tissue imprinted carbon and cellulose membranes. A novel method of pre-coating cellulose membranes in matrix by airspray prior to the blotting procedure was developed. The method was found to retain the expected distribution of the analyte. Ion images demonstrating the permeation of the applied compound into the skin were achieved by imaging a cross sectional imprint of treated tissue on a cellulose membrane precoated in matrix material. A calibration graph for the determination of ketoconazole was prepared using the sodium adduct of the matrix ion as an internal standard. This enabled construction of a quantitative profile of drug in skin. Conventional haematoxylin and eosin staining and microscopy methods were employed to obtain a histological image of the porcine epidermal tissue. Super imposing the mass spectrometric and histological images revealed drug permeation into the dermal tissue layer. A quantitative corneum tape stripping/HPLC method was developed for comparison. Useful data was acquired and further work suggested to facilitate a full validation of the methods presented in this thesis.

Matrix-assisted laser desorption/ionisation-mass spectrometry imaging (MALDI-MSI) has been extensively applied to monitoring the distribution of pharmaceutical compounds in tissues. The main aim of the work reported in this thesis is to monitor the distribution of respiratory compounds in the lungs following inhaled delivery. Glucocorticoids that contain multiple carbonyl functionalities are not easily protonated/de-protonated to form charged species due to the poor ionisation efficiencies of the carbonyl functionalities. Derivatisation with hydrazine based reagents has been proposed as a solution to this problem. These reagents have been employed for the in-solution and on-tissue derivatisation of a range of glucocorticoids to form their respective hydrazones improving their mass spectral ionisation efficiency and detection. MALDI-MSI has been used to screen a set of respiratory compounds in order to determine their on-tissue limit of detection. The distribution of a Tiotropium Bromide was monitored throughout the lungs following inhaled delivery. High spatial resolution imaging enabled a detailed view of the distribution of Tiotropium in the trachea and major airways. Quantitative mass spectrometry imaging is a new field that has recently gained a lot of attention especially in pharmaceutical research. The ability to obtain quantitative information as well as the distribution of pharmaceutical compounds and associated metabolites offers a distinct advantage over traditional quantitative methods such as LC-MS/MS and QWBA. The current methods of generating quantification information from MALDI-MS images has been evaluated, which let development of a method for the preparation of standards for use in the quantification of drugs in tissue sections. MALDI-MSI has been used to acquire data from serial sections obtained at equal intervals through control mouse lung tissue, homogenate registration markers were incorporated in order to aid the final 3D image construction. Using two 3D imaging software packages were used to reconstruct the images were stacked together to enable the 3D distribution of a particular endogenous species throughout the lungs to be displayed.

The overall aim of this work described in this thesis was to apply MALDI-MS and imaging MALDI-MS (MALDI-MSI) to the analysis of compounds of interest in occupational hygiene monitoring. Isocyanates are highly reactive compounds with a wide variety of industrial uses. MALDI-MS and MS/MS were used to investigate diisocyanate stability and reactivity. A monoisocyanate intermediate product was observed from the hydrolysis of both an aromatic and also an aliphatic diisocyanate. The stability of this product was assessed over a 14 day experimental period. Ethanol was used to derivatise hexamethylene diisocyanate (HDI) and the resulting urethane was observed to be stable over 14 days. This derivatisation method was incorporated into a surface swab technique for sampling of HDI from work surfaces. Industrial diisocyanates have been reported to penetrate through skin and to be excreted as diamine metabolites in urine. A LC-MS method for the determination of free toluene diamine (TDA) monomer formed by biotransformation of toluene diisocyanate (TDI) when applied to HaCaT cells was developed. In the two experiments performed, TDA was only observed at low levels after spiking with high concentrations of TDI. This appeared to be due to most of the isocyanate becoming conjugated to proteins within the cell and thus not being extracted during the extraction procedure. A novel ethanol-saturated cellulose membrane blotting technique was developed for the extraction and ethanol-derivatisation of HDI from the surface of skin. However, not all of the HDI present on the membrane reacted with the ethanol. Increasing the amount of ethanol on the membrane did increase the amount of derivatised HDI monomer observed although this occurred at the expense of spatial information. The technique was also applied for analysis of the insecticide chlorpyrifos, for both skin surface sampling and permeation studies. From the images obtained, chlorpyrifos was observed to readily penetrate through the stratum corneum and reach a depth of 1.7mm. The highest amount was located in the dermis after the 1 hour exposure time. The dermal absorption of HDI was monitored after 1 hour exposure by mapping HDI monoamine penetration through the skin via indirect blotting and novel direct skin analysis methods. Similar profiles were observed from both methods. Penetration depths of 2.3 and 2.6 mm were observed for the direct skin and indirect blotting methods respectively. The highest level of HDI monoamine was located in the dermis.

Water is essential for life, human activities and ecosystems. The global climate change together the population increase causes an imbalance between the demand of water and the available water resources.. All these factors lead to a increasing deterioration of human health and aquatic ecosystems. The characterization of aquatic systems includes structural and functional aspects. In addition, it is necessary to emphasize the degradation of natural and anthropogenic organic matter Aquatic ecosystem ecology, to study the loss of organic matter, uses the weight loss of natural organic devices such as dry leaves or fragments of standardized wood that has been exposed to the environment. Bearing this in mind, the main objective of this thesis was to add more chemistry knowledge into the river ecology by using of a synthetic material probe to study its degradation in natural and engineering aquatic environments. The device is based on a commercial polymer exposed for a while to different aquatic environments. The degradation of the synthetic material probe is collected and analyzed by using advanced mass spectrometry techniques such HPLC-MS, MALDI-TOF/MS and MALDI IMAGING. Chapter 1 (Introduction) is distributed into three parts. The first presents the problems associated with the quality of the aquatic environment, their effects on ecosystems and succinctly describes the biotic and abiotic processes of degradation of organic matter and its application in WWTPs. In the second part there is a brief description of the polymers, their uses and degradation, as well as the analytical techniques used for their characterization. In the third part, we describe the mass spectrometry analytical techniques used in this thesis, emphasizing those that allow the study of space in two dimensions, through the corresponding generation of images (IMAGING). The main objectives of the thesis are described in Chapter 2. Chapter 3 describes the selection of possible polymers to be used, and the optimization of the analytical methodologies used by MALDI-TOF/MS. The chosen polymer was (polycaprolactone 1250). Probes consisting of a plastic capsule-piston with a sample of the polymer were prepared. Exposure experiments were carried out at various points of the Ebro River. The results obtained showed different types of degradation. Finally, these results were compared with those obtained in parallel using classical methods (using tree leaves). Chapter 4 describes laboratory-scale experiments performed with the selected polymer. These experiments consisted in exposing polymer samples for a time in aqueous systems, in sterile, aerobic and denitrifying conditions. The use of the novel MALDI IMAGING technique allowed the observation of degradation differences along the surface of the sample between the three types of conditions tested, obtaining images of the most interesting ions. Likewise, the statistical treatment of the results obtained was confirmed by the results of the images. The success of the previous laboratory-scale experiment drove it to the next level and this experiment was applied it to wastewater samples. The WWTP El Prat de Llobregat was the site chosen, placing polymer probes in the secondary reactor, where the aerobic and denitrification (anaerobic) treatment are performed. The MALDI IMAGING technique was used to analyze the samples and high-resolution liquid chromatography coupled to mass spectrometry (HPLC-MS) was used as a complementary technique to elucidate the structures of the degradation compounds. The results obtained allowed to establish the degradation mechanisms and corresponding transformation products differentiated between the two types of environments studied. The description and results of this study is presented in Chapter 5. Finally, in chapter 6 contains a general discussion of each experiment of this thesis.
El agua es esencial para la vida y las actividades del ser humano y de los ecosistemas. El cambio global climático junto al incremento constante de población hace que el desequilibrio entre la demanda de agua y los recursos hídricos disponibles se incremente. Todo ello redunda en un impacto creciente sobre la salud humana y los ecosistemas acuáticos. La caracterización de los sistemas acuáticos incluye tanto aspectos estructurales como funcionales. Entre estos últimos hay que destacar la degradación de la materia orgánica, tanto natural como de origen antropogénico. La ecología de sistemas acuáticos utiliza la pérdida de peso de soportes orgánicos naturales como hojas secas o fragmentos de madera estandarizados expuestos al medio para calcular la pérdida de materia orgánica. Partiendo de esta idea el objetivo principal de esta tesis ha sido introducir más conocimiento químico dentro de la ecología de ríos utilizando una sonda basada en material sintético para estudiar su degradación en ambientes acuáticos, tanto naturales como ingenieriles. El dispositivo contiene un polímero comercial, el cual después de estar expuesto un tiempo en diferentes entornos acuáticos se recoge y se analiza su degradación utilizando técnicas avanzadas de espectrometría de masas, como son HPLC-MS, MALDI-TOF/MS y MALDI IMAGING. El capítulo 1 (Introducción) está dividido en tres partes. En la primera se presenta la problemática asociada a la calidad del medio acuático, sus efectos sobre los ecosistemas y se describen sucintamente los procesos bióticos y abióticos de degradación de la materia orgánica y su aplicación en las EDAR. En la segunda parte se realiza una breve descripción de los polímeros, sus usos y degradación, así como las técnicas analíticas que se usan para caracterizarlos. En la tercera parte, se describen las técnicas analíticas de espectrometría de masas empleadas en esta tesis, haciendo énfasis en aquellas que permiten el estudio espacial en dos dimensiones, mediante la correspondiente generación de imágenes (IMAGING). Los objetivos principales de la tesis se detallan en el capítulo 2. En el capítulo 3 se describe la selección de posibles polímeros a utilizar, así como la optimización de los correspondientes métodos de análisis mediante MALDI-TOF/MS. Con el polímero finalmente elegido (policaprolactonadiol 1250) se prepararon sondas poliméricas y se realizaron experimentos de exposición en diversos puntos del río Ebro. Los resultados obtenidos evidenciaron diferentes tipos de degradación. Finalmente, éstos se compararon con los obtenidos en paralelo mediante métodos clásicos, empleando hojas de árbol. Con el polímero seleccionado se realizaron experimentos a escala de laboratorio, que se describen en el capítulo 4, consistentes en la exposición de muestras de polímero durante un tiempo concreto en sistemas acuosos en condiciones estériles, aeróbicas y desnitrificantes. El uso de la novedosa técnica MALDI IMAGING, permitió observar diferencias de degradación a lo largo de la superficie de la muestra entre los tres tipos de condiciones ensayadas, obteniendo imágenes de los iones más interesantes. Así mismo, el tratamiento estadístico de los resultados obtenidos confirmó las imágenes adquiridas. El éxito del experimento anterior a escala de laboratorio, impulsó llevarlo al siguiente nivel y aplicarlo en muestras de aguas residuales. Así pues, las sondas de polímero se instalaron en el reactor secundario de la EDAR del Prat de Llobregat, donde se realiza un tratamiento de nitrificación (aerobio) y uno de desnitrificación (anaerobio). Para analizar las muestras se utilizó la técnica MALDI IMAGING y HPLC-MS para elucidar las estructuras de los compuestos de degradación y establecer los mecanismos de degradación correspondientes productos de transformación en función de las condiciones estudiadas. Finalmente en el capítulo 6 se comenta la discusión general de cada experimento realizado extrayéndose unas conclusiones finales.

Massenspektrometrisches Imaging (MSI) ist unverzichtbar für die Untersuchung der räumlichen Verteilung von Molekülen in einer Vielzahl von biologischen Proben. Seit seiner Einführung hat sich MALDI zu einer dominierenden Bildgebungsmethode entwickelt, die sich als nützlich erwiesen hat, um die Komplexität von Lipidstrukturen in biologischen Geweben zu bestimmen. Einerseits ist die Rolle von Cisplatin bei der Behandlung von menschlichen malignen Erkrankungen gut etabliert, jedoch ist Nephrotoxizität eine limitierende Nebenwirkung, die Veränderungen des renalen Lipidprofils beinhaltet. Dies führte zu der Motivation, die Lipidzusammensetzung des Nierengewebes in mit Cisplatin behandelten Ratten zu untersuchen, um die involvierten Lipid-Signalwege aufzuklären. Es wurde eine Methode zur Kartierung der Lipidzusammensetzung in Nierenschnitten unter Verwendung von MALDI MSI entwickelt. Die Verteilung von Nierenlipiden in Cisplatin-behandelten Proben zeigte deutliche Unterschiede in Bezug auf die Kontrollgruppen. Darüber hinaus wurde die Beurteilung der Ionenbilder von Lipiden in Cisplatin-behandelten Nieren meist als qualitative Aspekte betrachtet. Relative quantitative Vergleiche wurden durch den variablen Einfluss von experimentellen und instrumentellen Bedingungen begrenzt. Daher bestand die Notwendigkeit, ein Normalisierungsverfahren zu entwickeln, das einen Vergleich der Lipidintensität verschiedener Proben ermöglicht. Das Verfahren verwendete einen Tintenstrahldrucker, um eine Mischung der MALDI-Matrix und der internen internen Lipid-Metall-Standards aufzubringen. Unter Verwendung von ICP-MS erlaubte der interne Metallstandard, die Konsistenz der Matrix und der internen Standards zu bestätigen. Die Anwendung der Methode zur Normalisierung von Ionenintensitäten von Nierenlipiden zeigte eine ausgezeichnete Bildkorrektur und ermöglichte einen relativen quantitativen Vergleich von Lipidbildern in Cisplatin-behandelten Proben.
Mass spectrometry imaging is indispensable for studying the spatial distribution of molecules within a diverse range of biological samples. Since its introduction, MALDI has become a dominant imaging method, which proved useful to sort out the complexity of lipid structures in biological tissues. The role of cisplatin in the treatment of human malignancies is well-established. However, nephrotoxicity is a limiting side effect that involves an acute injury of the proximal tubule and alterations in the renal lipid profile. This evolved the motivation to study the spatial distribution of lipids in the kidney tissue of cisplatin-treated rats to shed light on the lipid signaling pathways involved. A method for mapping of lipid distributions in kidney sections using MALDI-LTQ-Orbitrap was developed, utilizing the high performance of orbitrap detection. The distribution of kidney lipids in cisplatin-treated samples revealed clear differences with respect to control group, which could be correlated to the proximal tubule injury. The findings highlight the usefulness of MALDI MSI as complementary tool for clinical diagnostics. Furthermore, assessment of the ion images of lipids in cisplatin-treated kidney mostly considered qualitative aspects. Relative quantitative comparisons were limited by the variable influence of experimental and instrumental conditions. Hence, the necessity developed to establish a normalization method allowing comparison of lipid intensity in MALDI imaging measurements of different samples. The method employed an inkjet printer to apply a mixture of the MALDI matrix and dual lipid-metal internal standards. Using ICP-MS, the metal internal standard allowed to confirm the consistency of the matrix and internal standards application. Applying the method to normalize ion intensities of kidney lipids demonstrated excellent image correction and successfully enabled relative quantitative comparison of lipid images in control and cisplatin-treated samples.