Investigation of the laser fluence and wavelength dependence in surface-assisted laser desorption/ionization mass spectrometry using gold nanoparticles.

Rationale: Surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) builds on the use of nanostructured surfaces (e.g., coatings of colloidal nanoparticles) to promote analyte desorption and ionization.

Large-Scale Screening of Pharmaceutical Compounds to Explore the Application Space of On-Tissue MALDI and MALDI-2 Mass Spectrometry.

The successful application of matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) in pharmaceutical research is strongly dependent on the detection of the drug of interest at physiologically relevant concentrations. Here we explored how insufficient sensitivity due to low ionization efficiency and/or the interaction of the drug molecule with the local biochemical environment of the tissue can be mitigated for many compound classes using the recently introduced MALDI-MSI coupled with laser-induced postionization, known as MALDI-2-MSI. Leveraging a MALDI-MSI screen of about 1,200 medicines/drug-like compounds from a broad range of medicinal application areas, we demonstrate a significant improvement in drug detection and the degree of sensitivity uplift by using MALDI-2 versus traditional MALDI.

Visualization of metabolites and microbes at high spatial resolution using MALDI mass spectrometry imaging and in situ fluorescence labeling.

Label-free molecular imaging techniques such as matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) enable the direct and simultaneous mapping of hundreds of different metabolites in thin sections of biological tissues. However, in host-microbe interactions it remains challenging to localize microbes and to assign metabolites to the host versus members of the microbiome. We therefore developed a correlative imaging approach combining MALDI-MSI with fluorescence in situ hybridization (FISH) on the same section to identify and localize microbial cells.

Multiparametric chemical exchange saturation transfer MRI detects metabolic changes in breast cancer following immunotherapy.

Background: With metabolic alterations of the tumor microenvironment (TME) contributing to cancer progression, metastatic spread and response to targeted therapies, non-invasive and repetitive imaging of tumor metabolism is of major importance. The purpose of this study was to investigate whether multiparametric chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI) allows to detect differences in the metabolic profiles of the TME in murine breast cancer models with divergent degrees of malignancy and to assess their response to immunotherapy.

Methods: Tumor characteristics of highly malignant 4T1 and low malignant 67NR murine breast cancer models were investigated, and their changes during tumor progression and immune checkpoint inhibitor (ICI) treatment were evaluated.

Visualization of Differential Cardiolipin Profiles in Murine Retinal Cell Layers by High-Resolution MALDI Mass Spectrometry Imaging.

The precise fatty acyl chain configuration of cardiolipin (CL), a tetrameric mitochondrial-specific membrane lipid, exhibits dependence on cell and tissue types. A powerful method to map CL profiles in tissue sections in a spatially resolved manner is matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). To build on and explore this potential, we employed a quadrupole time-of-flight mass spectrometer along with optimized sample preparation protocols.

Negative Ion-Mode N-Glycan Mass Spectrometry Imaging by MALDI-2-TOF-MS.

Matrix-assisted laser desorption/ionization mass spectrometry imaging with laser-induced postionization (MALDI-2-MSI) has proven a powerful tool for the in situ analysis of N-linked glycosylation, or N-glycans, directly from clinical tissue samples. Here we describe a sample preparation protocol for the analysis of N-glycans from formalin-fixed, paraffin-embedded tissue sections.

Mass spectrometry imaging to explore molecular heterogeneity in cell culture.

Molecular analysis on the single-cell level represents a rapidly growing field in the life sciences. While bulk analysis from a pool of cells provides a general molecular profile, it is blind to heterogeneities between individual cells. This heterogeneity, however, is an inherent property of every cell population.

Single-Photon-Induced Post-Ionization to Boost Ion Yields in MALDI Mass Spectrometry Imaging.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a rapidly growing method in the life sciences. However, for many analyte classes, its sensitivity is limited due to poor ionization efficiencies. To mitigate this problem, we here introduce a novel post-ionization scheme based on single-photon induced chemical ionization using pulsed RF-Kr lamps.

Spatial distribution of isobaric androgens in target tissues using chemical derivatization and MALDI-2 on a trapped ion mobility quadrupole time-of-flight instrument.

Prostate cancer is initially treated androgen deprivation therapy (ADT), a highly successful treatment in the initial pursuit of tumour regression, but commonly restricted by the eventual emergence of a more lethal 'castrate resistant' (CRPC) form of the disease. Intracrine pathways that utilize dehydroepiandrosterone (DHEA) or other circulatory precursor steroids are thought to generate relevant levels of growth-stimulating androgens such as testosterone (T) and dihydrotestosterone (DHT). Decoding this tissue-specific metabolic pathway is key for the development of novel therapeutic treatments.

Mass Spectrometry Imaging Techniques Enabling Visualization of Lipid Isomers in Biological Tissues.

This Feature focuses on a review of recent developments in mass spectrometry imaging (MSI) of lipid isomers in biological tissues. The tandem MS techniques utilizing online and offline chemical derivatization procedures, ion activation techniques such as ozone-induced dissociation (OzID), ultraviolet photodissociation (UVPD), or electron-induced dissociation (EID), and other techniques such as coupling of ion mobility with MSI are discussed. The importance of resolving lipid isomers in diseases is highlighted.

Effect of the Laser Pulse Width in MALDI-2: A Comparative Study of Picosecond versus Nanosecond Wide Pulses for Laser Postionization.

MALDI-2 is a recently introduced technique for postionization (PI) in matrix-assisted laser desorption/ionization (MALDI). It is based on an initial photoionization of neutrally desorbed matrix molecules and subsequent charge-transfer reactions in a fine vacuum or atmospheric pressure ion source. MALDI-2 significantly increases the ion yields for numerous classes of analytes, including lipids, glycans, and a range of pharmaceuticals.

MALDI-2 and t-MALDI-2 Mass Spectrometry Imaging.

Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) combined with laser-induced postionization for MALDI-2 enables the simultaneous registration of numerous classes of small molecules (e.g., secondary metabolites including sterols) as well as phospholipids, glycolipids, and glycans from tissue sections and from cell cultures with strongly boosted ion yields.

Infrared MALDI Mass Spectrometry with Laser-Induced Postionization for Imaging of Bacterial Colonies.

Ultraviolet matrix-assisted laser desorption ionization mass spectrometry imaging (UV-MALDI-MSI) is a powerful tool to visualize bacterial metabolites in microbial colonies and in biofilms. However, a challenge for the method is the efficient extraction of analytes from deeper within the bacterial colonies and from the cytoplasm of individual cells during the matrix coating step. Here, we used a pulsed infrared (IR) laser of 2.

Transmission-Mode MALDI Mass Spectrometry Imaging of Single Cells: Optimizing Sample Preparation Protocols.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) makes it possible to simultaneously visualize the spatial distribution of dozens to hundreds of different biomolecules (, phospho- and glycolipids) in tissue sections and in cell cultures. The implementation of novel desorption and (post-)ionization techniques has recently pushed the pixel size of this imaging technique to the low micrometer scale and below and thus to a cellular and potentially sub-cellular level. However, to fully exploit this potential for cell biology and biomedicine, sample preparation becomes highly demanding.

Molecular insights into symbiosis-mapping sterols in a marine flatworm-algae-system using high spatial resolution MALDI-2-MS imaging with ion mobility separation.

Waminoa sp. acoel flatworms hosting Symbiodiniaceae and the related Amphidinium dinoflagellate algae are an interesting model system for symbiosis in marine environments. While the host provides a microhabitat and safety, the algae power the system by photosynthesis and supply the worm with nutrients.

MALDI-2 for the Enhanced Analysis of -Linked Glycans by Mass Spectrometry Imaging.

-glycans are important players in a variety of pathologies including different types of cancer, (auto)immune diseases, and also viral infections. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an important tool for high-throughput -glycan profiling and, upon use of tandem MS, for structure determination. By use of MALDI-MS imaging (MSI) in combination with PNGase F treatment, also spatially correlated -glycan profiling from tissue sections becomes possible.

Low-Pressure Photoionization in a Dual-Ion Funnel Injector Coupled to an Orbitrap Mass Spectrometer for Direct Analysis of Human Breath and Head-Space Sampled Coffee Roasts.

Low-pressure photoionization (LPPI) is a versatile tool for the mass spectrometric detection of (semi-)volatile organic compounds, (s)VOC. Here, a dual-ion funnel MALDI/ESI ion injector was equipped with a direct-inlet LPPI module. A radio-frequency (RF) drive enabled the implementation of three Kr discharge lamps in a novel design optimized for efficient photoionization and undisturbed ion trajectories.

Validation of MALDI-MS imaging data of selected membrane lipids in murine brain with and without laser postionization by quantitative nano-HPLC-MS using laser microdissection.

MALDI mass spectrometry imaging (MALDI-MSI) is a widely used technique to map the spatial distribution of molecules in sectioned tissue. The technique is based on the systematic generation and analysis of ions from small sample volumes, each representing a single pixel of the investigated sample surface. Subsequently, mass spectrometric images for any recorded ion species can be generated by displaying the signal intensity at the coordinate of origin for each of these pixels.

Detailed Characterization of the Postionization Efficiencies in MALDI-2 as a Function of Relevant Input Parameters.

A recently introduced technique based on MALDI with laser-induced postionization (PI), also named MALDI-2, increases the ion yields for numerous classes of lipids, metabolites, and carbohydrates in MALDI-MS imaging experiments under certain experimental conditions. Here, we used a semiautomatic LabVIEW-based protocol to investigate and optimize the efficiency of the PI process dependent on four relevant input parameters and a dense parameter grid: pulse energies of the two lasers, delay between the laser pulses, and buffer gas pressure in the ion source. All experiments were conducted with a modified MALDI-2 Synapt G2-S mass spectrometer (Waters) and use of a focal spot size on the sample of 15-17 μm.

MALDI-2 on a Trapped Ion Mobility Quadrupole Time-of-Flight Instrument for Rapid Mass Spectrometry Imaging and Ion Mobility Separation of Complex Lipid Profiles.

Matrix-assisted laser desorption/ionization combined with laser-induced postionization (MALDI-2) is a recently introduced method for enhanced mass spectrometry imaging of numerous classes of biomolecules, including phospho- and glycolipids in tissue sections at high lateral resolution. Here we describe the first adaptation of the technology to a Bruker timsTOF fleX mass spectrometer. Upon use of a 1 kHz postionization laser, MALDI-2 produces a sizable increase in the number of detected features as well as in ion signal intensities.

MALDI-2 Mass Spectrometry and Immunohistochemistry Imaging of Gb3Cer, Gb4Cer, and Further Glycosphingolipids in Human Colorectal Cancer Tissue.

The main cellular receptors of Shiga toxins (Stxs), the neutral glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer/CD77) and globotetraosylceramide (Gb4Cer), are significantly upregulated in about half of the human colorectal carcinomas (CRC) and in other cancers. Therefore, conjugates exploiting the Gb3Cer/Gb4Cer-binding B subunit of Stx (StxB) have attracted great interest for both diagnostic and adjuvant therapeutic interventions. Moreover, fucosylated GSLs were recognized as potential tumor-associated targets.

Ozonization of Tissue Sections for MALDI MS Imaging of Carbon-Carbon Double Bond Positional Isomers of Phospholipids.

Visualizing the differential distribution of carbon-carbon double bond (C═C db) positional isomers of unsaturated phospholipids (PL) in tissue sections by use of refined matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) technologies offers a high promise to deeper understand PL metabolism and isomer-specific functions in health and disease. Here we introduce an on-tissue ozonization protocol that enables a particular straightforward derivatization of unsaturated lipids in tissue sections. Collision-induced dissociation (CID) of MALDI-generated ozonide ions (with yields in the several ten percent range) produced the Criegee fragment ion pairs, which are indicative of C═C db position(s).

Charge Distribution between Different Classes of Glycerophospolipids in MALDI-MS Imaging.

Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is widely used to visualize and analyze the distribution of membrane lipids in an increasingly large number of applications. In this context, different lipoforms of glycerophospholipids (GPLs) are among the prime targets of interest. For this group of analytes, however, ion suppression effects have been described to strongly favor the detection of certain GPL classes over others, thereby hampering the analysis of suppressed species and greatly restraining quantitative analysis.

Advanced Methods for MALDI-MS Imaging of the Chemical Communication in Microbial Communities.

Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is increasingly used to visualize the chemical communication between microorganisms. However, to fully exploit the potential of this label-free technique, crucial methodological advances are still needed. In particular, with current microbial MALDI-MSI methods chemical coverage is strongly limited to well ionizing compounds and a safe MSI-compatible inactivation of microbial viability and quenching of metabolism is not possible.