Recent advances in on-site mass spectrometry analysis for clinical applications

In recent years, mass spectrometry (MS) is increasingly attracting interests for clinical applications, which also calls for technical innovations to make a transfer of MS from conventional analytical laboratories to clinics. The system design and analysis procedure should be friendly for novice users and appliable for on-site clinical diagnosis. In addition, the analysis result should be auto-interpreted and reported in formats much simpler than mass spectra. This motivates new ideas for developments in all the aspects of MS. In this review, we report recent advances of direct sampling ionization and miniature MS system, which have been developed targeting clinical and even point-of-care analysis. We also discuss the trend of the development and provide perspective on the technical challenges raised by diseases such as coronavirus SARS-CoV-2.

Matrix-Assisted Ionization and Tandem Mass Spectrometry Capabilities in Protein Biomarker Characterization-An Initial Study Using the Small Cell Lung Cancer Biomarker Progastrin Releasing Peptide as a Model Compound

This initial study evaluates vacuum matrix-assisted ionization (vMAI) mass spectrometry (MS) for identification and determination of tryptic peptides from the biomarker protein progastrin releasing peptide (ProGRP). Similar peptides and charge states were observed as in liquid chromatography (LC) electrospray ionization (ESI) MS. The prolonged ion duration in vMAI with similar charge states as in ESI was advantageous for determining the MS/MS fragmentation conditions compared to MAI. It is assumed that the vacuum ionization conditions lower the detection limits of the experiment. This may be the reason vMAI combined with high resolution MS enabled detection of tryptic peptides from more digested proteins than MAI selected reaction monitoring MS. Additionally, MAI ion mobility spectrometry MS (MAI-IMS-MS) was evaluated for differentiation of intact protein isoforms, successfully enabling differentiation of the isoforms by drift time selection. Examples are both shown for model proteins bovine serum albumin, cytochrome C, and lysozyme and the clinically relevant small cell lung cancer protein biomarker ProGRP, which exists in three isoforms. Coupling with the vacuum ionization conditions using a dedicated vacuum-probe source MAI enables information to be extracted readily as with conventional approaches, just faster.

Analysis of biofluids by paper spray-MS in forensic toxicology

Direct ambient ionization techniques have been developed with the aim to reduce the complexity of mass spectrometry analysis by minimizing sample preparation and chromatographic separation. In this context, paper spray-MS (PS-MS) is an innovative approach that provides faster and cheaper analysis of biofluids by the addition of the sample directly to a paper. In forensic toxicology, the analytical workflow for the detection and quantification of drugs of abuse is onerous, including sample treatment, extraction and clean up, especially regarding complex biological matrices. PS-MS allows the detection of analytes of toxicological interest in blood, plasma and urine using low sample volume. This review aims to discuss the potential use, advances and challenges of PS-MS in forensic toxicology.

Ambient ionisation mass spectrometry for in situ analysis of intact proteins

Ambient surface mass spectrometry is an emerging field which shows great promise for the analysis of biomolecules directly from their biological substrate. In this article, we describe ambient ionisation mass spectrometry techniques for the in situ analysis of intact proteins. As a broad approach, the analysis of intact proteins offers unique advantages for the determination of primary sequence variations and posttranslational modifications, as well as interrogation of tertiary and quaternary structure and protein-protein/ligand interactions. In situ analysis of intact proteins offers the potential to couple these advantages with information relating to their biological environment, for example, their spatial distributions within healthy and diseased tissues. Here, we describe the techniques most commonly applied to in situ protein analysis (liquid extraction surface analysis, continuous flow liquid microjunction surface sampling, nano desorption electrospray ionisation, and desorption electrospray ionisation), their advantages, and limitations and describe their applications to date. We also discuss the incorporation of ion mobility spectrometry techniques (high field asymmetric waveform ion mobility spectrometry and travelling wave ion mobility spectrometry) into ambient workflows. Finally, future directions for the field are discussed.

Rapid Quadrupole-Time-of-Flight Mass Spectrometry Method Quantifies Oxygen-Rich Lignin Compound in Complex Mixtures

Complex mixture analysis is a costly and time-consuming task facing researchers with foci as varied as food science and fuel analysis. When faced with the task of quantifying oxygen-rich bio-oil molecules in a complex diesel mixture, we asked whether complex mixtures could be qualitatively and quantitatively analyzed on a single mass spectrometer with mid-range resolving power without the use of lengthy separations. To answer this question, we developed and evaluated a quantitation method that eliminated chromatography steps and expanded the use of quadrupole-time-of-flight mass spectrometry from primarily qualitative to quantitative as well. To account for mixture complexity, the method employed an ionization dopant, targeted tandem mass spectrometry, and an internal standard. This combination of three techniques achieved reliable quantitation of oxygen-rich eugenol in diesel from 300 to 2500 ng/mL with sufficient linearity (R² = 0.97 ± 0.01) and excellent accuracy (percent error = 0% ± 5). To understand the limitations of the method, it was compared to quantitation attained on a triple quadrupole mass spectrometer, the gold standard for quantitation. The triple quadrupole quantified eugenol from 50 to 2500 ng/mL with stronger linearity (R² = 0.996 ± 0.003) than the quadrupole-time-of-flight and comparable accuracy (percent error = 4% ± 5). This demonstrates that a quadrupole-time-of-flight can be used for not only qualitative analysis but also targeted quantitation of oxygen-rich lignin molecules in complex mixtures without extensive sample preparation. The rapid and cost-effective method presented here offers new possibilities for bio-oil research, including: (1) allowing for bio-oil studies that demand repetitive analysis as process parameters are changed and (2) making this research accessible to more laboratories. Graphical Abstract ᅟ.

A Comparison of Tissue Spray and Lipid Extract Direct Injection Electrospray Ionization Mass Spectrometry for the Differentiation of Eutopic and Ectopic Endometrial Tissues

Recent research revealed that tissue spray mass spectrometry enables rapid molecular profiling of biological tissues, which is of great importance for the search of disease biomarkers as well as for online surgery control. However, the payback for the high speed of analysis in tissue spray analysis is the generally lower chemical sensitivity compared with the traditional approach based on the offline chemical extraction and electrospray ionization mass spectrometry detection. In this study, high resolution mass spectrometry analysis of endometrium tissues of different localizations obtained using direct tissue spray mass spectrometry in positive ion mode is compared with the results of electrospray ionization analysis of lipid extracts. Identified features in both cases belong to three lipid classes: phosphatidylcholines, phosphoethanolamines, and sphingomyelins. Lipids coverage is validated by hydrophilic interaction liquid chromatography with mass spectrometry of lipid extracts. Multivariate analysis of data from both methods reveals satisfactory differentiation of eutopic and ectopic endometrium tissues. Overall, our results indicate that the chemical information provided by tissue spray ionization is sufficient to allow differentiation of endometrial tissues by localization with similar reliability but higher speed than in the traditional approach relying on offline extraction. Graphical Abstract ᅟ.

Transferring Ions from Solution to the Gas Phase: The Two Basic Principles

The efficient formation of gaseous ions is the crucial step in all successful mass spectrometric experiments. The invention of electrospray ionization (ESI) has strongly facilitated this step by transferring preformed ions directly from solution to the gas phase - thereby circumventing the need to first convert analytes to the gas phase and then ionize them - and therefore ESI has become an extremely useful and widely applied MS technique. The invention of sonic spray ionization (SSI) has also allowed for the transfer of ions from solution into the gas phase, but without the assistance of a voltage or heating. Numerous ionization techniques, using similar principles to those applied in either ESI or SSI, have subsequently been developed. Although experimental conditions used in such techniques vary markedly, herein we argue that they are all based on either one of two basic principles by which ions can be transferred from solution to the gas phase, that is: via (1) neutralizing the counter ion, or (2) separating the ions. We have selected 35 such techniques and categorized them accordingly. This article thereby aims to establish the basic principles by which gaseous ions can be obtained from solvated ions. We further propose that any new ionization technique used to transfer solvated ions to the gas phase will similarly fall into one of these two mechanistic categories. Graphical abstract.

Ambient mass spectrometry in metabolomics

Since the introduction of desorption electrospray ionization (DESI) mass spectrometry (MS), ambient MS methods have seen increased use in a variety of fields from health to food science. Increasing its popularity in metabolomics, ambient MS offers limited sample preparation, rapid and direct analysis of liquids, solids, and gases, in situ and in vivo analysis, and imaging. The metabolome consists of a constantly changing collection of small (<1.5 kDa) molecules. These include endogenous molecules that are part of primary metabolism pathways, secondary metabolites with specific functions such as signaling, chemicals incorporated in the diet or resulting from environmental exposures, and metabolites associated with the microbiome. Characterization of the responsive changes of this molecule cohort is the principal goal of any metabolomics study. With adjustments to experimental parameters, metabolites with a range of chemical and physical properties can be selectively desorbed and ionized and subsequently analyzed with increased speed and sensitivity. This review covers the broad applications of a variety of ambient MS techniques in four primary fields in which metabolomics is commonly employed.

High-resolution mass spectra processing for the identification of different pathological tissue types of brain tumors

The purpose of the work is to demonstrate the possibilities of identifying the different types of pathological tissue identification directly through tissue mass spectrometry. Glioblastoma parts dissected during neurosurgical operation were investigated. Tumor fragments were investigated by the immunohistochemistry method and were identified as necrotic tissue with necrotized vessels, necrotic tissue with tumor stain, tumor with necrosis (tumor tissue as major), tumor, necrotized tumor (necrotic tissues as major), parts of tumor cells, boundary brain tissue, and brain tissue hyperplasia. The technique of classification of tumor tissues based on mass spectrometric profile data processing is suggested in this paper. Classifiers dividing the researched sample to the corresponding tissue type were created as a result of the processing. Classifiers of necrotic and tumor tissues are shown to yield a combined result when the tissue is heterogeneous and consists of both tumor cells and necrotic tissue.

Ambient Ionization and Miniature Mass Spectrometry Systems for Disease Diagnosis and Therapeutic Monitoring

Mass spectrometry has become a powerful tool in the field of biomedicine. The combination of ambient ionization and miniature mass spectrometry systems could most likely fulfill a significant need in medical diagnostics, providing highly specific molecular information in real time for clinical and even point-of-care analysis. In this review, we discuss the recent development of ambient ionization and miniature mass spectrometers as well as their potential in disease diagnosis and therapeutic monitoring, with an emphasis on their capability in analysis of biofluids and tissues. We also speculate the future development of the integrated, miniature MS systems and provide our perspectives on the challenges in technical development as well as possible solutions for path forward.

Present and foreseeable future of metabolomics in forensic analysis

The revulsive publications during the last years on the precariousness of forensic sciences worldwide have promoted the move of major steps towards improvement of this science. One of the steps (viz. a higher involvement of metabolomics in the new era of forensic analysis) deserves to be discussed under different angles. Thus, the characteristics of metabolomics that make it a useful tool in forensic analysis, the aspects in which this omics is so far implicit, but not mentioned in forensic analyses, and how typical forensic parameters such as the post-mortem interval or fingerprints take benefits from metabolomics are critically discussed in this review. The way in which the metabolomics-forensic binomial succeeds when either conventional or less frequent samples are used is highlighted here. Finally, the pillars that should support future developments involving metabolomics and forensic analysis, and the research required for a fruitful in-depth involvement of metabolomics in forensic analysis are critically discussed.

Laser dissection sampling modes for direct mass spectral analysis

RATIONALE

Laser microdissection coupled directly with mass spectrometry provides the capability of on-line analysis of substrates with high spatial resolution, high collection efficiency, and freedom on shape and size of the sampling area. Establishing the merits and capabilities of the different sampling modes that the system provides is necessary in order to select the best sampling mode for characterizing analytically challenging samples.

METHODS

The capabilities of laser ablation spot sampling, laser ablation raster sampling, and laser 'cut and drop' sampling modes of a hybrid optical microscopy/laser ablation liquid vortex capture electrospray ionization mass spectrometry system were compared for the analysis of single cells and tissue.

RESULTS

Single Chlamydomonas reinhardtii cells were monitored for their monogalactosyldiacylglycerol (MGDG) and diacylglyceryltrimethylhomo-Ser (DGTS) lipid content using the laser spot sampling mode, which was capable of ablating individual cells (~4-15 μm) even when agglomerated together. Turbid Allium Cepa cells (~150 μm) having unique shapes difficult to precisely measure using the other sampling modes could be ablated in their entirety using laser raster sampling. Intact microdissections of specific regions of a cocaine-dosed mouse brain tissue were compared using laser 'cut and drop' sampling. Since in laser 'cut and drop' sampling whole and otherwise unmodified sections are captured into the probe, 100% collection efficiencies were achieved. Laser ablation spot sampling has the highest spatial resolution of any sampling mode, while laser ablation raster sampling has the highest sampling area adaptability of the sampling modes.

CONCLUSIONS

Laser ablation spot sampling has the highest spatial resolution of any sampling mode, useful in this case for the analysis of single cells. Laser ablation raster sampling was best for sampling regions with unique shapes that are difficult to measure using other sampling modes. Laser 'cut and drop' sampling can be used for cases where the highest sensitivity is needed, for example, monitoring drugs present in trace amounts in tissue.

Toxoplasma gondii infection and testosterone congruently increase tolerance of male rats for risk of reward forfeiture

Decision making under risk involves balancing the potential of gaining rewards with the possibility of loss and/or punishment. Tolerance to risk varies between individuals. Understanding the biological basis of risk tolerance is pertinent because excessive tolerance contributes to adverse health and safety outcomes. Yet, not much is known about biological factors mediating inter-individual variability in this regard. We investigate if latent Toxoplasma gondii infection can cause risk tolerance. Using a rodent model of the balloon analogous risk task, we show that latent T. gondii infection leads to a greater tolerance of reward forfeiture. Furthermore, effects of the infection on risk can be recapitulated with testosterone supplementation alone, demonstrating that greater testosterone synthesis by the host post-infection is sufficient to change risk tolerance. T. gondii is a frequent parasite of humans and animals. Thus, the infection status can potentially explain some of the inter-individual variability in the risky decision making.

Atmospheric pressure thermal ionization ion source for peptide analysis

A novel atmospheric pressure thermal ionization (APTI) ion source was developed for the analysis of liquid samples. The feasibility of the ion source was demonstrated on peptides using two configurations-assisted by hot wire or hot surface. Microalloyed molybdenum, used as a thermal ion- emitter, notably facilitated the formation of multiply-charged ions, but fragmentation products were still observed. Peptide fragmentation accompanying thermal ionization can be used for peptide identification. The described method is promising for studies of biological samples with minimal pre-treatment.