Molecular histology analysis by matrix-assisted laser desorption/ionization imaging mass spectrometry using gold nanoparticles as matrix

Screening the Extract of Laportea bulbifera (Sieb. et Zucc.) Wedd. Based on Active Component Content, Its Antioxidant Capacity and Exploration of Hepatoprotective Activity in Rats

Laportea bulbifera (Sieb. et Zucc.) Wedd., a plant with a long history of medicinal use, possesses uncertainly defined medicament portions while its antioxidant capacity remains largely unexplored. To gain a better understanding of its medicinal value, this study focused on investigating the Laportea bulbifera aboveground part (LBAP) and the Laportea bulbifera root (LBR). Through an assessment of the bioactive compound content, a significant finding emerged: the LBR exhibited notably higher levels of these bioactive phytochemicals compared to the LBAP. This observation was further reinforced by the antioxidant assays, which demonstrated the superiority of the LBR's antioxidant capacity. The experimental results unequivocally indicate that the root is the optimal medicament portion for Laportea bulbifera. Furthermore, it was discovered that the presence of alcohol in the extraction solvent significantly enhanced the extraction of active ingredients, with the methanol extract of LBR performing the best among the extracts tested. Consequently, this extract was selected for further research. Leveraging cutting-edge UHPLC-ESI-Q-TOF-MS technology, the methanol extract of LBR was meticulously analyzed, revealing the presence of 41 compounds, primarily belonging to the phenolics and fatty acids. Remarkably, stability experiments demonstrated that the phenolics in the methanol extract maintained their stability across various pH values and during in vitro simulations of the human digestive system, albeit showing gradual degradation under high temperatures. Furthermore, the oxidative stability tests conducted on oils revealed the potential of the methanol extract as a stabilizer for olive oil and sunflower oil. Moreover, oral acute toxicity studies confirmed the low toxicity of the methanol extract, further supporting its safe use for medicinal purposes. Of particular note, histopathological examination and biochemical analysis affirmed the remarkable protective effects of the methanol extract against d-galactosamine-induced liver damage. These findings underscore the therapeutic potential of the methanol extract from the LBR in the treatment of diseases associated with oxidative imbalance.

Phytochemical Analysis, Antioxidant and Enzyme-Inhibitory Activities, and Multivariate Analysis of Insect Gall Extracts of Picea koraiensis Nakai

Picea koraiensis Nakai (PK) is an evergreen tree. It plays an important role in landscaping and road greening. Insect galls of PK are formed by parasitism of the adelgid Adelges laricis. Except for phenolics, other chemical constituents and biological activity of insect gall from PK are still unknown. Thus, here, we performed phytochemical and biological activity analyses of PK insect gall extracts, aiming to turn waste into treasure and serve human health. PK insect gall extracts were prepared using seven solvents. Antioxidant activities of the extracts were examined via antioxidant assays (radical and oxidizing substance quenching, metal chelating, and reducing power). The inhibitory activities of the extracts were determined toward the key human-disease-related enzymes α-glucosidase, α-amylase, cholinesterase, tyrosinase, urease, and xanthine oxidase. The content of numerous active constituents was high in the methanol and ethanol extracts of PK insect gall, and these extracts had the highest antioxidant and enzyme-inhibitory activities. They also showed excellent stability and low toxicity. These extracts have potential for use as stabilizers of olive and sunflower seed oils.

Surface-assisted laser desorption/ionization mass spectrometry imaging: A review

In the last decades, surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has attracted increasing interest due to its unique capabilities, achievable through the nanostructured substrates used to promote the analyte desorption/ionization. While the most widely recognized asset of SALDI-MS is the untargeted analysis of small molecules, this technique also offers the possibility of targeted approaches. In particular, the implementation of SALDI-MS imaging (SALDI-MSI), which is the focus of this review, opens up new opportunities. After a brief discussion of the nomenclature and the fundamental mechanisms associated with this technique, which are still highly controversial, the analytical strategies to perform SALDI-MSI are extensively discussed. Emphasis is placed on the sample preparation but also on the selection of the nanosubstrate (in terms of chemical composition and morphology) as well as its functionalization possibilities for the selective analysis of specific compounds in targeted approaches. Subsequently, some selected applications of SALDI-MSI in various fields (i.e., biomedical, biological, environmental, and forensic) are presented. The strengths and the remaining limitations of SALDI-MSI are finally summarized in the conclusion and some perspectives of this technique, which has a bright future, are proposed in this section.

Imaging of Neurotransmitters and Small Molecules in Brain Tissues Using Laser Desorption/Ionization Mass Spectrometry Assisted with Zinc Oxide Nanoparticles

Inorganic nanostructured materials such as silicon, carbon, metals, and metal oxides have been explored as matrices of low-background signals to assist the laser desorption/ionization (LDI) mass spectrometric (MS) analysis of small molecules, but their applications for imaging of small molecules in biological tissues remain limited in the literature. Titanium dioxide is one of the known nanoparticles (NP) that can effectively assist LDI MS imaging of low molecular weight molecules (LMWM). TiO₂ NP is commercially available as dispersions, which can be applied using a chemical solution sprayer. However, aggregation of NP can occur in the dispersions, and the aggregated NP can slowly clog the sprayer nozzle. In this work, the use of zinc oxide (ZnO) NP for LDI MS imaging is investigated as a superior alternative due to its dissolution in acidic pH. ZnO NP was found to deliver similar or better results in the imaging of LMWM in comparison to TiO₂ NP. The regular acid washes were effective in minimizing clogging and maintaining high reproducibility. High-quality images of mouse sagittal and rat coronal tissue sections were obtained. Ions were detected predominately as Na⁺ or K⁺ adducts in the positive ion mode. The number of LMWM detected with ZnO NP was similar to that obtained with TiO₂ NP, and only a small degree of specificity was observed.

Fe3O4-assisted laser desorption ionization mass spectrometry for typical metabolite analysis and localization: Influencing factors, mechanisms, and environmental applications

Fe₃O₄ has been suggested as an efficient matrix for small-molecule analysis by laser desorption ionization mass spectrometry (LDI-MS), but thus far there has been no systematic study exploring the influencing factors of nano-Fe₃O₄ on the detection of typical metabolites, or the mechanism by which nano-Fe₃O₄ assists the desorption and ionization of analytes after receiving laser energy. In this study, Fe₃O₄ nanoparticles with different physicochemical properties were synthesized and characterized. The results revealed that smaller particle size and greater surface hydroxyl amount of nano-spherical Fe₃O₄ could improve the intensity and relative standard deviation of typical metabolites by LDI-MS. The thermally driven desorption process played a vital role in LDI performance, but the chemical interactions between nano-Fe₃O₄ and analytes did not. Good intra- or inter-spot repeatability and linearity of analytes were obtained by the optimum Fe₃O₄-assisted LDI-MS. Finally, the developed method was successfully used for the rapid analysis and localization of endogenous metabolites in biofluids and whole zebrafish tissue section samples. Our results not only elucidate the influencing factors and mechanisms of nano-Fe₃O₄ for the detection of typical metabolites in LDI-MS but also reveal an innovative tool for the imaging of chemicals in the regions of interest in terms of eco-toxicological research.

A window into the brain: Tools to assess pre-clinical efficacy of biomaterials-based therapies on central nervous system disorders

Therapeutic conveyance into the brain is a cardinal requirement for treatment of diverse central nervous system (CNS) disorders and associated pathophysiology. Effectual shielding of the brain by the blood-brain barrier (BBB) sieves out major proportion of therapeutics with the exception of small lipophilic molecules. Various nano-delivery systems (NDS) provide an effective solution around this obstacle owing to their small size and targeting properties. To date, these systems have been used for several pre-clinical disease models including glioma, neurodegenerative diseases and psychotic disorders. An efficacy screen for these systems involves a test battery designed to probe into the multiple facets of therapeutic delivery. Despite their wide application in redressing various disease targets, the efficacy evaluation strategies for all can be broadly grouped into four modalities, namely: histological, bio-imaging, molecular and behavioural. This review presents a comprehensive insight into all of these modalities along with their strengths and weaknesses as well as perspectives on an ideal design for a panel of tests to screen brain nano-delivery systems.

Toward Mass Spectrometry Imaging in the Metabolomics Scale: Increasing Metabolic Coverage Through Multiple On-Tissue Chemical Modifications

Exploring the metabolic differences directly on tissues is essential for the comprehensive understanding of how multicellular organisms function. Mass spectrometry imaging (MSI) is an attractive technique toward this goal; however, MSI in metabolomics scale has been hindered by multiple limitations. This is most notable for single cell level high-spatial resolution imaging because of the limited number of molecules in small sampling size and the low ionization yields of many metabolites. Several on-tissue chemical derivatization approaches have been reported to increase MSI signals of targeted compounds, especially in matrix-assisted laser desorption/ionization (MALDI)-MSI. Herein, we adopt a combination of chemical derivatization reactions, to selectively enhance metabolite signals of a specific functional group for each consecutive tissue section. Three well-known on-tissue derivatization methods were used as a proof of concept experiment: coniferyl aldehyde for primary amines, Girard's reagent T for carbonyl groups, and 2-picolylamine for carboxylic acids. This strategy was applied to the cross-sections of leaves and roots from two different maize genotypes (B73 and Mo17), and enabled the detection of over six hundred new unique metabolite features compared to without modification. Statistical analysis indicated quantitative variation between metabolites in the tissue sections, while MS images revealed differences in localization of these metabolites. Combined, this untargeted approach facilitated the visualization of various classes of compounds, demonstrating the potential for untargeted MSI in the metabolomics scale.

Sputter-Coated Metal Screening for Small Molecule Analysis and High-Spatial Resolution Imaging in Laser Desorption Ionization Mass Spectrometry

Nanoparticles are efficient matrices in laser desorption/ionization (LDI) mass spectrometry (MS), especially for the profiling or imaging of small molecules. Recently, solvent-free physical vapor desorption (PVD), or sputter coating, was adopted as a homogenous method to rapidly apply metal nanoparticles (NPs) in situ to samples prior to LDI MS or MS imaging analysis. However, there has been no systematic study comparing different metal targets for the analysis of a variety of small molecule metabolites. Here, we present a screening and optimization of various sputter-coated metals, including Ag, Au, Cu, Pt, Ni, and Ti, for LDI analysis of small molecules in both positive and negative ion modes. Optimized sputter coating is then applied to high-spatial resolution LDI mass spectrometry imaging (MSI) of maize root and seed cross-sections. Noble metals, Ag, Au, and Pt, are found to be much more efficient than transition metals and organic matrices for most small metabolites. Sputter-coated metals are efficient for neutral lipids, such as triacylglycerols and diacylglycerols, but are very inefficient for most phospholipids. Graphical Abstract ᅟ.

Fluorinated Gold Nanoparticles for Nanostructure Imaging Mass Spectrometry

Nanostructure imaging mass spectrometry (NIMS) with fluorinated gold nanoparticles (f-AuNPs) is a nanoparticle assisted laser desorption/ionization approach that requires low laser energy and has demonstrated high sensitivity. Here we describe NIMS with f-AuNPs for the comprehensive analysis of metabolites in biological tissues. F-AuNPs assist in desorption/ionization by laser-induced release of the fluorocarbon chains with minimal background noise. Since the energy barrier required to release the fluorocarbons from the AuNPs is minimal, the energy of the laser is maintained in the low μJ/pulse range, thus limiting metabolite in-source fragmentation. Electron microscopy analysis of tissue samples after f-AuNP NIMS shows a distinct "raising" of the surface as compared to matrix assisted laser desorption ionization ablation, indicative of a gentle desorption mechanism aiding in the generation of intact molecular ions. Moreover, the use of perfluorohexane to distribute the f-AuNPs on the tissue creates a hydrophobic environment minimizing metabolite solubilization and spatial dislocation. The transfer of the energy from the incident laser to the analytes through the release of the fluorocarbon chains similarly enhances the desorption/ionization of metabolites of different chemical nature, resulting in heterogeneous metabolome coverage. We performed the approach in a comparative study of the colon of mice exposed to three different diets. F-AuNP NIMS allows the direct detection of carbohydrates, lipids, bile acids, sulfur metabolites, amino acids, nucleotide precursors as well as other small molecules of varied biological origins. Ultimately, the diversified molecular coverage obtained provides a broad picture of a tissue's metabolic organization.

Chemical Printing of Biological Tissue by Gold Nanoparticle-Assisted Laser Ablation

A chemical printing method based on gold nanoparticle (AuNP)-assisted laser ablation has been developed. By rastering a thin layer of AuNPs coated on a rat kidney tissue section with a UV laser, biomolecules are extracted and immediately transferred/printed onto a supporting glass substrate. The integrity of the printed sample is preserved, as revealed by imaging mass spectrometric analysis. By studying the mechanism of the extraction/printing process, transiently molten AuNPs were found to be involved in the process, as supported by the color and morphological changes of the AuNP thin film. The success of this molecular printing method was based on the efficient laser-nanomaterial interaction, that is, the strong photoabsorption, laser-induced heating, and phase-transition properties of the AuNPs. It is anticipated that the molecular printing method can be applied to perform site-specific printing, which extracts and transfers biochemicals from different regions of biological tissue sections to different types of supporting materials for subsequent biochemical analysis with the preservation of the original tissue samples.

Silver–gold alloy nanoparticles as tunable substrates for systematic control of ion-desorption efficiency and heat transfer in surface-assisted laser desorption/ionization

Laser energy conversion that controls heat transfer and ion desorption was systematically managed by tuning the composition of Ag–Au nanoparticles.

Direct Visualization of Neurotransmitters in Rat Brain Slices by Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI - MS)

Mass spectrometry imaging (MSI) of neurotransmitters has so far been mainly performed by matrix-assisted laser desorption/ionization (MALDI) where derivatization reagents, deuterated matrix and/or high resolution, or tandem MS have been applied to circumvent problems with interfering ion peaks from matrix and from isobaric species. We herein describe the application of desorption electrospray ionization mass spectrometry imaging (DESI)-MSI in rat brain coronal and sagittal slices for direct spatial monitoring of neurotransmitters and choline with no need of derivatization reagents and/or deuterated materials. The amino acids γ-aminobutyric (GABA), glutamate, aspartate, serine, as well as acetylcholine, dopamine, and choline were successfully imaged using a commercial DESI source coupled to a hybrid quadrupole-Orbitrap mass spectrometer. The spatial distribution of the analyzed compounds in different brain regions was determined. We conclude that the ambient matrix-free DESI-MSI is suitable for neurotransmitter imaging and could be applied in studies that involve evaluation of imbalances in neurotransmitters levels. Graphical Abstract ᅟ.

Enhancement of Image Contrast, Stability, and SALDI-MS Detection Sensitivity for Latent Fingerprint Analysis by Tuning the Composition of Silver-Gold Nanoalloys

Metal alloy nanoparticles (NPs) offer a new combination of unique physicochemical properties based on their pure counterparts, which can facilitate the development of novel analytical methods. Here, we demonstrated that Ag-Au alloy NPs could be utilized for optical and mass spectrometric imaging of latent fingerprints (LFPs) with improved image contrast, stability, and detection sensitivity. Upon deposition of Ag-Au alloy NPs (Ag:Au = 60:40 wt %), ridge regions of the LFP became amber colored, while the groove regions appeared purple-blue. The presence of Au in the Ag-Au alloy NPs suppressed aggregation behavior compared to pure AgNPs, thus improving the stability of the developed LFP images. In addition, the Ag component in the Ag-Au alloy NPs enhanced optical absorption efficiency compared to pure AuNPs, resulting in higher contrast LFP images. Moreover, varying the Ag-Au ratio could enable the tuning of the resulting surface plasmonic resonance absorption and hence affect image contrast. Furthermore, the Ag-Au alloy NPs assisted the surface-assisted laser desorption/ionization MS analysis of chemical and biochemical compounds in LFPs, with better detection sensitivity than either pure AgNPs or AuNPs.

Multivalent aptamer/gold nanoparticle-modified graphene oxide for mass spectrometry-based tumor tissue imaging

The protein mucin1 (MUC1) is an attractive target for cancer biomarkers because it is overexpressed in most adenocarcinomas. In this study, we exploited a MUC1-binding aptamer (Apt_MUC1) as a targeting agent for nanoparticle-based imaging systems coupled with laser desorption/ionization mass spectrometry (LDI-MS). We found that Apt_MUC1-conjugated gold nanoparticles immobilized, through hydrophobic and π–π interactions, on graphene oxide (Apt_MUC1–Au NPs/GO) bound effectively to MUC1 units on tumor cell membranes. The ultrahigh density and high flexibility of Apt_MUC1 on the GO surface enhanced the platform’s cooperative and multivalent binding affinity for MUC1 on cell membranes. After we had labeled MUC1-overexpressing MCF-7 cells (human breast adenocarcinoma cell line) with Apt_MUC1–Au NPs/GO, we used LDI-MS to monitor Au cluster ions ([Au_n]⁺; n = 1–3), resulting in the detection of as few as 100 MCF-7 cells. We also employed this Apt_MUC1–Au NPs/GO–LDI-MS system to analyze four different MUC1 expression cell lines. In addition, the Apt_MUC1–Au NPs/GO platform could be used further as a labeling agent for tumor tissue imaging when coupled with LDI-MS. Thus, Apt–Au NPs/GO can function as a highly amplified signal transducer through the formation of large Au clusters ions during LDI-MS analysis.

Monitoring Cluster Ions Derived from Aptamer-Modified Gold Nanofilms under Laser Desorption/Ionization for the Detection of Circulating Tumor Cells

In this paper, we describe the use of pulsed laser desorption/ionization mass spectrometry (LDI-MS) for the detection of tumor cells through the analysis of gold cluster ions [Aun](+) from aptamer-modified gold nanofilms (Au NFs). We observed not only the transformation of the Au NFs into gold nanoparticles (Au NPs) but also the formation of gaseous gold cluster ions ([Au(n)](+); n = 1-5) under irradiation with a nanosecond pulsed laser. The size and density of the formed Au NPs and the abundance of [Au(n)](+) ions were both highly dependent on the thickness of the Au NFs (10-100 nm). Thin Au NFs tended to form highly dense Au NPs on the substrate and favored the desorption and ionization of gold cluster ions. The signal intensities of the [Au(n)](+) species, monitoring using mass spectrometry, decreased upon increasing the thickness of the Au NF from 10 to 100 nm and after modification with thiolated DNA. Furthermore, we found that Au NFs modified with mucin1-binding aptamer (AptMUC1-Au NFs) could selectively enrich MCF-7 cells (human breast adenocarcinoma cell line) in blood samples; coupled with LDI-MS analysis of the [Au(n)](+) ions, we could detect MCF-7 cells selectively in blood samples at abundances as low as 10 cells. This approach offers the advantages of high sensitivity, selectivity, and throughput for the detection of circulating tumor cells, and has great potential for use as a powerful analytical platform for clinical diagnoses of tumor metastasis.

Challenges and recent advances in mass spectrometric imaging of neurotransmitters

Mass spectrometric imaging (MSI) is a powerful tool that grants the ability to investigate a broad mass range of molecules, from small molecules to large proteins, by creating detailed distribution maps of selected compounds. To date, MSI has demonstrated its versatility in the study of neurotransmitters and neuropeptides of different classes toward investigation of neurobiological functions and diseases. These studies have provided significant insight in neurobiology over the years and current technical advances are facilitating further improvements in this field. Herein, we briefly review new MSI studies of neurotransmitters, focusing specifically on the challenges and recent advances of MSI of neurotransmitters.

Current status and future perspectives of mass spectrometry imaging

Mass spectrometry imaging is employed for mapping proteins, lipids and metabolites in biological tissues in a morphological context. Although initially developed as a tool for biomarker discovery by imaging the distribution of protein/peptide in tissue sections, the high sensitivity and molecular specificity of this technique have enabled its application to biomolecules, other than proteins, even in cells, latent finger prints and whole organisms. Relatively simple, with no requirement for labelling, homogenization, extraction or reconstitution, the technique has found a variety of applications in molecular biology, pathology, pharmacology and toxicology. By discriminating the spatial distribution of biomolecules in serial sections of tissues, biomarkers of lesions and the biological responses to stressors or diseases can be better understood in the context of structure and function. In this review, we have discussed the advances in the different aspects of mass spectrometry imaging processes, application towards different disciplines and relevance to the field of toxicology.