Liquid extraction surface analysis mass spectrometry (LESA-MS) as a novel profiling tool for drug distribution and metabolism analysis: the terfenadine example

Mass Spectrometry Imaging Techniques: Non-Ambient and Ambient Ionization Approaches

Molecular information can be acquired from sample surfaces in real time using a revolutionary molecular imaging technique called mass spectrometry imaging (MSI). The technique can concurrently provide high spatial resolution information on the spatial distribution and relative proportion of many different compounds. Thus, many scientists have been drawn to the innovative capabilities of the MSI approach, leading to significant focus in various fields during the past few decades. This review describes the sampling protocol, working principle and applications of a few non-ambient and ambient ionization mass spectrometry imaging techniques. The non-ambient techniques include secondary ionization mass spectrometry and matrix-assisted laser desorption ionization, while the ambient techniques include desorption electrospray ionization, laser ablation electrospray ionization, probe electro-spray ionization, desorption atmospheric pressure photo-ionization and femtosecond laser desorption ionization. The review additionally addresses the advantages and disadvantages of ambient and non-ambient MSI techniques in relation to their suitability, particularly for biological samples used in tissue diagnostics. Last but not least, suggestions and conclusions are made regarding the challenges and future prospects of MSI.

Spatial Proteomics toward Subcellular Resolution by Coupling Deep Ultraviolet Laser Ablation with Nanodroplet Sample Preparation

Multiplexed molecular profiling of tissue microenvironments, or spatial omics, can provide critical insights into cellular functions and disease pathology. The coupling of laser microdissection with mass spectrometry-based proteomics has enabled deep and unbiased mapping of >1000 proteins. However, the throughput of laser microdissection is often limited due to tedious two-step procedures, sequential laser cutting, and sample collection. The two-step procedure also hinders the further improvement of spatial resolution to <10 μm as needed for subcellular proteomics. Herein, we developed a high-throughput and high-resolution spatial proteomics platform by seamlessly coupling deep ultraviolet (DUV) laser ablation (LA) with nanoPOTS (Nanodroplet Processing in One pot for Trace Samples)-based sample preparation. We demonstrated the DUV-LA system can quickly isolate and collect tissue samples at a throughput of ∼30 spots/min and a spatial resolution down to 2 μm from a 10 μm thick human pancreas tissue section. To improve sample recovery, we developed a proximity aerosol collection approach by placing DMSO droplets close to LA spots. We demonstrated the DUV-LA-nanoPOTS platform can detect an average of 1312, 1533, and 1966 proteins from ablation spots with diameters of 7, 13, and 19 μm, respectively. In a proof-of-concept study, we isolated and profiled two distinct subcellular regions of the pancreas tissue revealed by hematoxylin and eosin (H&E) staining. Quantitative proteomics revealed proteins specifically enriched to subcellular compartments.

Imaging of N-Linked Glycans in Biological Tissue Sections Using Nanospray Desorption Electrospray Ionization (nano-DESI) Mass Spectrometry

N-linked glycans are complex biomolecules vital to cellular functions that have been linked to a wide range of pathological conditions. Mass spectrometry imaging (MSI) has been used to study the localization of N-linked glycans in cells and tissues. However, their structural diversity presents a challenge for MSI techniques, which stimulates the development of new approaches. In this study, we demonstrate for the first time spatial mapping of N-linked glycans in biological tissues using nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI). Nano-DESI MSI is an ambient ionization technique that has been previously used for imaging of metabolites, lipids, and proteins in biological tissue samples without special sample pretreatment. N-linked glycans are released from glycoproteins using an established enzymatic digestion with peptide N-glycosidase F, and their spatial localization is examined using nano-DESI MSI. We demonstrate imaging of N-linked glycans in formalin-fixed paraffin-embedded human hepatocellular carcinoma and human prostate tissues in both positive and negative ionization modes. We examine the localization of 38 N-linked glycans consisting of high mannose, hybrid fucosylated, and sialyated glycans. We demonstrate that negative mode nano-DESI MSI is well-suited for imaging of underivatized sialylated N-linked glycans. On-tissue MS/MS of different adducts of N-linked glycans proves advantageous for elucidation of the glycan sequence. This study demonstrates the applicability of liquid extraction techniques for spatial mapping of N-linked glycans in biological samples, providing an additional tool for glycobiology research.

Label-free Chemical Characterization of Polarized Immune Cells in vitro and Host Response to Implanted Bio-instructive Polymers in vivo Using 3D OrbiSIMS

The Three-dimensional OrbiTrap Secondary Ion Mass Spectrometry (3D OrbiSIMS) is a secondary ion mass spectrometry instrument, a combination of a Time of Flight (ToF) instrument with an Orbitrap analyzer. The 3D OrbiSIMS technique is a powerful tool for metabolic profiling in biological samples. This can be achieved at subcellular spatial resolution, high sensitivity, and high mass-resolving power coupled with MS/MS analysis. Characterizing the metabolic signature of macrophage subsets within tissue sections offers great potential to understand the response of the human immune system to implanted biomaterials. Here, we describe a protocol for direct analysis of individual cells after in vitro differentiation of naïve monocytes into M1 and M2 phenotypes using cytokines. As a first step in vivo, we investigate explanted silicon catheter sections as a medical device in a rodent model of foreign body response. Protocols are presented to allow the host response to different immune instructive materials to be compared. The first demonstration of this capability illustrates the great potential of direct cell and tissue section analysis for in situ metabolite profiling to probe functional phenotypes using molecular signatures. Details of the in vitro cell approach, materials, sample preparation, and explant handling are presented, in addition to the data acquisition approaches and the data analysis pipelines required to achieve useful interpretation of these complex spectra. This method is useful for in situ characterization of both in vitro single cells and ex vivo tissue sections. This will aid the understanding of the immune response to medical implants by informing the design of immune-instructive biomaterials with positive interactions. It can also be used to investigate a broad range of other clinically relevant therapeutics and immune dysregulations. Graphical overview.

Mass Spectrometry-Based High-Throughput Quantification of Bioproducts in Liquid Culture

To meet the ever-increasing need for high-throughput screening in metabolic engineering, information-rich, fast screening methods are needed. Mass spectrometry (MS) provides an efficient and general approach for metabolite screening and offers the capability of characterizing a broad range of analytes in a label-free manner, but often requires a range of sample clean-up and extraction steps. Liquid extraction surface analysis (LESA) coupled MS is an image-guided MS surface analysis approach that directly samples and introduces metabolites from a surface to MS. Here, we combined the advantages of LESA-MS and an acoustic liquid handler with stable isotope-labeled internal standards. This approach provides absolute quantitation of target chemicals from liquid culture-dried droplets and enables high-throughput quantitative screening for microbial metabolites. In this study, LESA-MS was successfully applied to quantify several different metabolites (itaconic acid, triacetic acid lactone, and palmitic acid) from different yeast strains in different mediums, demonstrating its versatility, accuracy, and efficiency across a range of microbial engineering applications.

The development and application of matrix assisted laser desorption electrospray ionization: The teenage years

In the past 15 years, ambient ionization techniques have witnessed a significant incursion into the field of mass spectrometry imaging, demonstrating their ability to provide complementary information to matrix-assisted laser desorption ionization. Matrix-assisted laser desorption electrospray ionization is one such technique that has evolved since its first demonstrations with ultraviolet lasers coupled to Fourier transform-ion cyclotron resonance mass spectrometers to extensive use with infrared lasers coupled to orbitrap-based mass spectrometers. Concurrently, there have been transformative developments of this imaging platform due to the high level of control the principal group has retained over the laser technology, data acquisition software (RastirX), instrument communication, and image processing software (MSiReader). This review will discuss the developments of MALDESI since its first laboratory demonstration in 2005 to the most recent advances in 2021.

Advances in mass spectrometry imaging for toxicological analysis and safety evaluation of pharmaceuticals

Safety issues caused by pharmaceuticals have frequently occurred worldwide, posing a tremendous threat to human health. As an essential part of drug development, the toxicological analysis and safety evaluation is of great significance. In addition, the risk of pharmaceuticals accumulation in the environment and the monitoring of the toxicity from natural medicines have also received ongoing concerns. Due to a lack of spatial distribution information provided by common analytical methods, analyses that provide spatial dimensions could serve as complementary safety evaluation methods for better prediction and evaluation of drug toxicity. With advances in technical solutions and software algorithms, mass spectrometry imaging (MSI) has received increasing attention as a popular analytical tool that enables the simultaneous implementation of qualitative, quantitative, and localization without complex sample pretreatment and labeling steps. In recent years, MSI has become more attractive, powerful, and sensitive and has been applied in several scientific fields that can meet the safety assessment requirements. This review aims to cover a detailed summary of the various MSI technologies utilized in the biomedical and pharmaceutical area, including technical principles, advantages, current status, and future trends. Representative applications and developments in the safety-related issues of different pharmaceuticals and natural medicines are also described to provide a reference for pharmaceutical research, improve rational clinical medicine use, and ensure public safety.

On-tissue chemical derivatization in mass spectrometry imaging

Mass spectrometry imaging (MSI) combines molecular and spatial information in a valuable tool for a wide range of applications. Matrix-assisted laser desorption/ionization (MALDI) is at the forefront of MSI ionization due to its wide availability and increasing improvement in spatial resolution and analysis speed. However, ionization suppression, low concentrations, and endogenous and methodological interferences cause visualization problems for certain molecules. Chemical derivatization (CD) has proven a viable solution to these issues when applied in mass spectrometry platforms. Chemical tagging of target analytes with larger, precharged moieties aids ionization efficiency and removes analytes from areas of potential isobaric interferences. Here, we address the application of CD on tissue samples for MSI analysis, termed on-tissue chemical derivatization (OTCD). MALDI MSI will remain the focus platform due to its popularity, however, alternative ionization techniques such as liquid extraction surface analysis and desorption electrospray ionization will also be recognized. OTCD reagent selection, application, and optimization methods will be discussed in detail. MSI with OTCD is a powerful tool to study the spatial distribution of poorly ionizable molecules within tissues. Most importantly, the use of OTCD-MSI facilitates the analysis of previously inaccessible biologically relevant molecules through the adaptation of existing CD methods. Though further experimental optimization steps are necessary, the benefits of this technique are extensive.

What are we imaging? Software tools and experimental strategies for annotation and identification of small molecules in mass spectrometry imaging

Mass spectrometry imaging (MSI) has become a widespread analytical technique to perform nonlabeled spatial molecular identification. The Achilles' heel of MSI is the annotation and identification of molecular species due to intrinsic limitations of the technique (lack of chromatographic separation and the difficulty to apply tandem MS). Successful strategies to perform annotation and identification combine extra analytical steps, like using orthogonal analytical techniques to identify compounds; with algorithms that integrate the spectral and spatial information. In this review, we discuss different experimental strategies and bioinformatics tools to annotate and identify compounds in MSI experiments. We target strategies and tools for small molecule applications, such as lipidomics and metabolomics. First, we explain how sample preparation and the acquisition process influences annotation and identification, from sample preservation to the use of orthogonal techniques. Then, we review twelve software tools for annotation and identification in MSI. Finally, we offer perspectives on two current needs of the MSI community: the adaptation of guidelines for communicating confidence levels in identifications; and the creation of a standard format to store and exchange annotations and identifications in MSI.

Liquid extraction surface analysis-mass spectrometry: An advanced and environment-friendly analytical tool in modern analysis

The Liquid Extraction Surface Analysis technique is a new high-throughput instrument for ambient mass spectrometry. The benefits of the Liquid Extraction Surface Analysis-Mass Spectrometry approach are the high throughput screening of samples and the absence of sample preparation. Liquid Extraction Surface Analysis-Mass Spectrometry also consumes less solvent for extraction, making it more environmentally friendly and there is no substrate restriction. It utilizes advanced instrumentation like the use of robotic pipettes, nanoelectrospray systems, electronspray ionization chips which makes it highly efficient. In recent years, Liquid Extraction Surface Analysis-Mass Spectrometry has seen widespread use in a variety of analytical fields including drug metabolite analysis, mapping drug distribution in tissues, protein and lipid characterization etc. In this review, we have summarized the basic working principles of the Liquid Extraction Surface Analysis-Mass Spectrometry approach in detail along with a detailed description of the recently reported applications in the analysis of proteins, lipids, drugs and foods. The investigated analytes along with detection methodologies and significant outcomes of various research reports have been presented with the help of tables. This tool has also been utilized in clinical investigations of biological fluids, fingerprint analysis and authentication of agarwood. This article is protected by copyright. All rights reserved.

Development and Application of DropletProbe Mass Spectrometry for Examining Biodistribution of Therapeutics

dropletProbe mass spectrometry is a novel technique for molecular characterization of surfaces. It can be used for rapid ex vivo analysis of therapeutics from thin animal tissue sections and has been shown to improve understanding of a drug's absorption, distribution, metabolism and excretion (ADME) properties. Here, we describe the tissue distribution analysis of diclofenac from a dosed whole-body mouse thin tissue section using a dropletProbe mass spectrometry system.

High-Spatial Resolution Atmospheric Pressure Mass Spectrometry Imaging Using Fiber Probe Laser Ablation-Dielectric Barrier Discharge Ionization

Atmospheric pressure mass spectrometry imaging (AP-MSI) is a powerful tool in many fields; however, there are still some difficulties to achieve high spatial resolution for AP-MSI, one of them being the need for a small ablation crater. Here, a fiber probe laser ablation (FPLA) system is introduced that uses an etched optical fiber with a sharp tip (o.d. 200 nm) to deliver ablation laser pulses to a sample surface to ablate materials with high spatial resolution. The tip-to-sample distance was adjusted to ∼10 μm using a micro-actuator having a stepping motor with submicron accuracy. The laser-ablated neutrals were post-ionized using a home-built in-line dielectric barrier discharge source, which can be interfaced to any mass spectrometer with an AP interface. Using MSI on a standard sample with a striped pattern and sections of fingernails treated with the drug methyl green zinc chloride salt, a FPLA-DBDI-MSI spatial resolution of ≈5 μm was demonstrated.

The liquid micro junction-surface sampling probe (LMJ-SSP); a versatile ambient mass spectrometry interface

Ambient ionization methods have become important tools in mass spectrometry. The LMJ-SSP can significantly simplify/reduce lengthy sample preparation requirements associated with mass spectrometry analysis. Samples may be introduced through direct contact, insertion and droplet injection, enabling applications from drug discovery and surface analysis to tissue profiling and metabolic mapping. This review examines the underlying principles associated with the LMJ-SSP interface and highlights modifications of the original design that have extended its capability. We summarize different application areas that have exploited the method and describe potential future directions for the adaptable ambient ionization source.

Spatially resolved absolute quantitation in thin tissue by mass spectrometry

Mass spectrometry (MS) has become the de facto tool for routine quantitative analysis of biomolecules. MS is increasingly being used to reveal the spatial distribution of proteins, metabolites, and pharmaceuticals in tissue and interest in this area has led to a number of novel spatially resolved MS technologies. Most spatially resolved MS measurements are qualitative in nature due to a myriad of potential biases, such as sample heterogeneity, sampling artifacts, and ionization effects. As applications of spatially resolved MS in the pharmacological and clinical fields increase, demand has become high for quantitative MS imaging and profiling data. As a result, several varied technologies now exist that provide differing levels of spatial and quantitative information. This review provides an overview of MS profiling and imaging technologies that have demonstrated quantitative analysis from tissue. Focus is given on the fundamental processes affecting quantitative analysis in an array of MS imaging and profiling technologies and methods to address these biases.Graphical abstract.

Sample Preparation Free Mass Spectrometry Using Laser-Assisted Rapid Evaporative Ionization Mass Spectrometry: Applications to Microbiology, Metabolic Biofluid Phenotyping, and Food Authenticity

Mass spectrometry has established itself as a powerful tool in the chemical, biological, medical, environmental, and agricultural fields. However, experimental approaches and potential application areas have been limited by a traditional reliance on sample preparation, extraction, and chromatographic separation. Ambient ionization mass spectrometry methods have addressed this challenge but are still somewhat restricted in requirements for sample manipulation to make it suitable for analysis. These limitations are particularly restrictive in view of the move toward high-throughput and automated analytical workflows. To address this, we present what we consider to be the first automated sample-preparation-free mass spectrometry platform utilizing a carbon dioxide (CO₂) laser for sample thermal desorption linked to the rapid evaporative ionization mass spectrometry (LA-REIMS) methodology. We show that the pulsatile operation of the CO₂ laser is the primary factor in achieving high signal-to-noise ratios. We further show that the LA-REIMS automated platform is suited to the analysis of three diverse biological materials within different application areas. First, clinical microbiology isolates were classified to species level with an accuracy of 97.2%, the highest accuracy reported in current literature. Second, fecal samples from a type 2 diabetes mellitus cohort were analyzed with LA-REIMS, which allowed tentative identification of biomarkers which are potentially associated with disease pathogenesis and a disease classification accuracy of 94%. Finally, we showed the ability of the LA-REIMS system to detect instances of adulteration of cooking oil and determine the geographical area of production of three protected olive oil products with 100% classification accuracy.

THE SPACE DIMENSION AT THE MICRO LEVEL: MASS SPECTROMETRY IMAGING OF DRUGS IN TISSUES

Mass spectrometry imaging (MSI) has seen remarkable development in recent years. The possibility of getting quantitative or semiquantitative data, while maintaining the spatial component in the tissues has opened up unique study possibilities. Now with a spatial window of few tens of microns, we can characterize the events occurring in tissue subcompartments in physiological and pathological conditions. For example, in oncology-especially in preclinical models-we can quantitatively measure drug distribution within tumors, correlating it with pharmacological treatments intended to modify it. We can also study the local effects of the drug in the tissue, and their effects in relation to histology. This review focuses on the main results in the field of drug MSI in clinical pharmacology, looking at the literature on the distribution of drugs in human tissues, and also the first preclinical evidence of drug intratissue effects. The main instrumental techniques are discussed, looking at the different instrumentation, sample preparation protocols, and raw data management employed to obtain the sensitivity required for these studies. Finally, we review the applications that describe in situ metabolic events and pathways induced by the drug, in animal models, showing that MSI makes it possible to study effects that go beyond the simple concentration of the drug, maintaining the space dimension. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Breaking Through the Barrier: Regulatory Considerations Relevant to Ambient Mass Spectrometry at the Bedside

Rapid characterization of tissue disorder using ambient mass spectrometry (MS) techniques, requiring little to no preanalytical preparations of sampled tissues, has been shown using a variety of ion sources and with many disease classes. A brief overview of ambient MS in clinical applications, the state of the art in regulatory affairs, and recommendations to facilitate adoption for use at the bedside are presented. Unique challenges in the validation of untargeted MS methods and additional safety and compliance requirements for deployment within a clinical setting are further discussed. Development of a harmonized validation strategy for ambient MS methods is emphasized.

Results of the first and second British Mass Spectrometry Society interlaboratory studies on ambient mass spectrometry

RATIONALE

As the popularity of ambient ionisation grows, so too does the importance of understanding its capabilities and limitations. The British Mass Spectrometry Society Special Interest Group on Ambient Ionisation has carried out two studies into the use of ambient ionisation, the results of which are presented here.

METHODS

The first study (study 1) examined the detection and quantitation capabilities of ambient ionisation while the second examined repeatability and robustness. For study 1 participants were sent a range of samples including two calibration sample sets and asked to analyse them. For study 2, two samples containing the same eight-component mixture were provided (one in solvent, one in matrix); participants were asked to analyse these samples multiple times, over multiple days to allow assessment of repeatability.

RESULTS

Study 1 showed that small, polar compounds were well detected by the participants while lower polarity compounds were less well detected. For many samples the introduction method appeared to be a significant factor in the observed spectra. The quantitation study gave good results but revealed significant variability. For study 2 the mean repeatabilities were 65% in solvent and 88% in matrix. The inclusion of an internal standard was shown to greatly improve repeatability.

CONCLUSIONS

Ambient ionisation is capable of ionising a wide range of compounds with good precision and excellent repeatability; however, in order to obtain such data care must be taken with the experimental design. The data can be significantly improved with a well-chosen internal standard.

Absolute quantitation of propranolol from 200-μm regions of mouse brain and liver thin tissues using laser ablation-dropletProbe-mass spectrometry

RATIONALE

The ability to quantify drugs and metabolites in tissue with sub-mm resolution is a challenging but much needed capability in pharmaceutical research. To fill this void, a novel surface sampling approach combining laser ablation with the commercial dropletProbe automated liquid surface sampling system (LA-dropletProbe) was developed and is presented here.

METHODS

Parylene C-coated 200 × 200 μm tissue regions of mouse brain and kidney thin tissue sections were analyzed for propranolol by laser ablation of tissue directly into a preformed liquid junction. Propranolol was detected by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) in positive electrospray ionization mode. Quantitation was achieved via application of a stable-isotope-labeled internal standard and an external calibration curve.

RESULTS

The absolute concentrations of propranolol determined from 200 × 200 μm tissue regions were compared with the propranolol concentrations obtained from 2.3-mm-diameter tissue punches of adjacent, non-coated sections using standard bulk tissue extraction protocols followed by regular HPLC/MS/MS analysis. The average concentration of propranolol in both organs determined by the two employed methods agreed to within ±12%. Furthermore, the relative abundances of phase II hydroxypropranolol glucuronide metabolites were recorded and found to be consistent with previous results.

CONCLUSIONS

This work illustrates that depositing a thin layer of parylene C onto thin tissue prior to analysis, which seals the surface and prevents direct liquid extraction of the drug from the tissue, coupled to the novel LA-dropletProbe surface sampling system is a viable approach for sub-mm resolution quantitative drug distribution analysis.

Design and Evaluation of a Tethered, Open Port Sampling Interface for Liquid Extraction-Mass Spectrometry Chemical Analysis

Presented is a tethered, liquid-extraction-sampling interface designed for the mass spectrometric surface sampling/analysis of 3D objects. The tethered, open port sampling interface (TOPSI) incorporates a vacuum line between the sampling probe and ionization source, which enables the ability for an extended, tethered sample transfer line. Herein, several designs of the hand-held TOPSI are presented and evaluated on the basis of the analytical metrics of analyte transport time, peak width, and analyte sensitivity. The best analytical metrics were obtained with capillary flow resistances arranged in a particular order and the vacuum region set at 6.2 kPa. This TOPSI design incorporated a transfer capillary 1 m in length, while retaining a fast analyte transport time (12 s), short signal peak width (5 s baseline-to-baseline), and high analyte signal at 90% of that obtained with a regular open port sampling interface (OPSI). The hand-held TOPSI was demonstrated for the characterization of extracted small molecules and metabolites from the surface of mint and rosemary leaves.

Integrated laser ablation-dropletProbe-mass spectrometry for absolute drug quantitation, metabolite detection, and distribution in tissue

RATIONALE

Spatially resolved and accurate quantitation of drug-related compounds in tissue is a much-needed capability in drug discovery research. Here, application of an integrated laser ablation-dropletProbe-mass spectrometry surface sampling system (LADP-MS) is reported, which achieved absolute quantitation of propranolol measured from <500 × 500 μm thin tissue samples.

METHODS

Mouse liver and kidney thin tissue sections were coated with parylene C and analyzed for propranolol by a laser ablation/liquid extraction workflow. Non-coated adjacent sections were microdissected for validation and processed using standard bulk tissue extraction protocols. High-performance liquid chromatography with positive ion mode electrospray ionization tandem mass spectrometry was applied to detect the drug and its metabolites.

RESULTS

Absolute propranolol concentration in ~500 × 500 μm tissue regions measured by the two methods agreed within ±8% and had a relative standard deviation within ±17%. Quantitation down to ~400 × 400 μm tissue regions was shown, and this resolution was also used for automated mapping of propranolol and phase II hydroxypropranolol glucuronide metabolites in kidney tissue.

CONCLUSIONS

This study exemplifies the capabilities of integrated laser ablation-dropletProbe-mass spectrometry (LADP-MS) for high resolution absolute drug quantitation analysis of thin tissue sections. This capability will be valuable for applications needing to quantitatively understand the spatial distribution of small molecules in tissue.

Probe Electrospray Ionization (PESI) and Its Modified Versions: Dipping PESI (dPESI), Sheath-Flow PESI (sfPESI) and Adjustable sfPESI (ad-sfPESI)

In 2007, probe electrospray ionization/mass spectrometry (PESI/MS) was developed. In this technique, the needle is moved down along a vertical axis and the tip of the needle touched to the sample. After capturing the sample at the needle tip, the needle is then moved up and a high voltage is applied to the needle at the highest position to generate electrospray. Due to the discontinuous sampling followed by the generation of spontaneous electrospray, sequential and exhaustive electrospray takes place depending on the surface activity of the analytes. As modified versions of PESI, dipping PESI (dPESI), sheath-flow PESI (sfPESI) and adjustable sfPESI (ad-sfPESI) have been developed. These methods are complementary to each other and they can be applicable to surface and bulk analysis of various biological samples. In this article, the characteristics of these methods and their applications to real samples will be reviewed.

Multimodal Imaging Mass Spectrometry: Next Generation Molecular Mapping in Biology and Medicine

Imaging mass spectrometry has become a mature molecular mapping technology that is used for molecular discovery in many medical and biological systems. While powerful by itself, imaging mass spectrometry can be complemented by the addition of other orthogonal, chemically informative imaging technologies to maximize the information gained from a single experiment and enable deeper understanding of biological processes. Within this review, we describe MALDI, SIMS, and DESI imaging mass spectrometric technologies and how these have been integrated with other analytical modalities such as microscopy, transcriptomics, spectroscopy, and electrochemistry in a field termed multimodal imaging. We explore the future of this field and discuss forthcoming developments that will bring new insights to help unravel the molecular complexities of biological systems, from single cells to functional tissue structures and organs.

Integrating ion mobility and imaging mass spectrometry for comprehensive analysis of biological tissues: A brief review and perspective

Imaging mass spectrometry (IMS) technologies are capable of mapping a wide array of biomolecules in diverse cellular and tissue environments. IMS has emerged as an essential tool for providing spatially targeted molecular information due to its high sensitivity, wide molecular coverage, and chemical specificity. One of the major challenges for mapping the complex cellular milieu is the presence of many isomers and isobars in these samples. This challenge is traditionally addressed using orthogonal liquid chromatography (LC)-based analysis, though, common approaches such as chromatography and electrophoresis are not able to be performed at timescales that are compatible with most imaging applications. Ion mobility offers rapid, gas-phase separations that are readily integrated with IMS workflows in order to provide additional data dimensionality that can improve signal-to-noise, dynamic range, and specificity. Here, we highlight recent examples of ion mobility coupled to IMS and highlight their importance to the field.

Rapid authentication of agarwood by using liquid extraction surface analysis mass spectrometry (LESA-MS)

INTRODUCTION

Agarwood is a highly valuable fragrant resinous wood which is widely used as traditional Chinese medicines, perfumes, incense and decorations. Due to its high economic value and excessive demand, this leads to a rising price and proliferation of fake commodities. Thus, strict authenticity identification and quality evaluation of agarwood are of great significance.

OBJECTIVE

To establish a simple, rapid and non-destructive technique for identifying the authenticity of agarwood.

METHODS

Liquid extraction surface analysis mass spectrometry (LESA-MS) was firstly proposed to identify the authenticity of 62 agarwood samples without sample preparation. In addition, multivariate statistical models and thin-layer chromatography (TLC) method were used to analyse and verify the results of LESA-MS.

RESULTS

Representative compounds of agarwood were detected by LESA-MS. A characteristic 2-(2-phenylethyl)chromone compound (m/z 319.1) was treated as a key chemical marker to identify agarwood and its counterfeits rapidly. Several other chromones ions were identified and used as additional evidence for authentic samples. A total of 62 samples were visually discriminated as two groups by principal component analysis (PCA) and orthogonal projection to latent structures discriminant analysis (OPLS-DA), and the specific characteristic marker was highlighted. Moreover, the qualitative results of the conventional TLC method were in agreement with the LESA-MS approach.

CONCLUSION

The proposed LESA-MS method was successfully applied in the direct qualitative analysis of agarwood from different sources. This study indicated great feasibility and practicality of LESA-MS in the rapid identification of agarwood, and provided a non-destructive and meaningful preliminary screening tool for the agarwood industry.

Mapping chemotherapeutic drug distribution in cancer cell spheroids using 2D-TOF-SIMS and LESA-TIMS-MS

Three-dimensional (3D) cancer cell cultures grown in the form of spheroids are effective models for the study of in vivo-like processes simulating cancer tumor pharmacological dynamics and morphology. In this study, we show the advantages of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) combined with in situ Liquid Extraction Surface Analysis coupled to trapped Ion Mobility Spectrometry Mass Spectrometry (LESA-TIMS-TOF MS) for high spatial resolution mapping and quantitation of ABT-737, a chemotherapeutic drug, at the level of single human colon carcinoma cell spheroids (HCT 116 MCS). 2D-TOF-SIMS studies of consecutive sections (∼16 μm thick slices) showed that ABT-737 is homogenously distributed in the outer layers of the HCT 116 MCS. Complementary in situ LESA-TIMS-TOF MS/MS measurements confirmed the presence of the ABT-737 drug in the MCS slides by the observation of the molecular ion [M + H]+m/z and mobility, and the charateristic fragmentation pattern. LESA-TIMS-TOF MS allowed a quantitative assessment of the ABT-737 drug of the control MCS slice spiked with ABT-737 standard over the 0.4-4.1 ng range and MCS treated starting at 10 μM for 24 h. These experiments showcase an effective protocol for unambigous characterization and 3D mapping of chemotherapeutic drug distribution at the single MCS level.

Distribution Analysis of Salvianolic Acids in Myocardial Ischemic Pig Tissues by Automated Liquid Extraction Surface Analysis Coupled with Tandem Mass Spectrometry

The distribution of active compounds of traditional Chinese medicine Salvia miltiorrhiza Bunge (Chinese name: Danshen) in vivo was determined by establishing a liquid extraction surface analysis coupled with the tandem mass spectrometry (LESA-MS/MS) method. Stability analysis and distribution analysis were designed in the present study using normal animals or a myocardial ischemia model. The model assessment was performed four weeks after surgery, and then three groups were created: a normal-dose group, a model-blank group, and a model-dose group. Meanwhile, Danshen decoction administration began in dose groups and lasted for four weeks. In stability analysis, four salvianolic acids—Danshensu (DSS), caffeic acid (CAA), rosmarinic acid (RA), and salvianolic acid A (SAA)—in kidney tissues from the normal-dose group were detected by LESA-MS/MS under four conditions, and then distribution analysis was conducted in different tissues using the same method. Ejection fraction (EF) and fractional shortening (FS) in animals from two model groups decreased significantly four weeks after surgery (P < 0.01) and were improved after four weeks of Danshen decoction administration (P < 0.01). Results of stability analysis demonstrated that this method was basically stable since there were no significant differences in signal intensities of DSS, CAA, and SAA under four conditions (P > 0.05). Distribution analysis showed the signal intensities of DSS in the liver and kidney and SAA in the heart were higher in the model-dose group than in the normal-dose group (P < 0.05 or P < 0.01). Signal intensities of RA in the liver and kidney, and SAA in the liver were lower in the model-dose group compared with the normal-dose group (P < 0.05 or P < 0.01). In conclusion, Danshen decoction has the effect of improving the ischemic condition in a chronic myocardial ischemia model, and the content of two active compounds increased in the targets. These findings contribute to an understanding of the therapeutic role of Danshen in cardiovascular disease.

A Critical and Concise Review of Mass Spectrometry Applied to Imaging in Drug Discovery

During the past decade, mass spectrometry imaging (MSI) has become a robust and versatile methodology to support modern pharmaceutical research and development. The technologies provide data on the biodistribution, metabolism, and delivery of drugs in tissues, while also providing molecular maps of endogenous metabolites, lipids, and proteins. This allows researchers to make both pharmacokinetic and pharmacodynamic measurements at cellular resolution in tissue sections or clinical biopsies. Despite drug imaging within samples now playing a vital role within research and development (R&D) in leading pharmaceutical companies, however, the challenges in turning compounds into medicines continue to evolve as rapidly as the technologies used to discover them. The increasing cost of development of new and emerging therapeutic modalities, along with the associated risks of late-stage program attrition, means there is still an unmet need in our ability to address an increasing array of challenging bioanalytical questions within drug discovery. We require new capabilities and strategies of integrated imaging to provide context for fundamental disease-related biological questions that can also offer insights into specific project challenges. Integrated molecular imaging and advanced image analysis have the opportunity to provide a world-class capability that can be deployed on projects in which we cannot answer the question with our battery of established assays. Therefore, here we will provide an updated concise review of the use of MSI for drug discovery; we will also critically consider what is required to embed MSI into a wider evolving R&D landscape and allow long-lasting impact in the industry.

Robotic sheath-flow probe electrospray ionization/mass spectrometry (sfPESI/MS): development of a touch sensor for samples in a multiwell plastic plate

In the previous work, sheath-flow probe electrospray ionization (sfPESI) equipped with a touch sensor was developed for conducting samples. In this work, a capacitiance-sensitive touch sensor that can be applicable to samples prepared in a nonconducting plastic multiwell plate was developed. The radiofrequency with 5 kHz and 4.5 Vpp was applied to the metal substrate on which the plastic plate was placed. The probe tip stopped at the position where it touched the surface of the liquid solution prepared in the plastic multiwell plate by detecting the displacement current flowing through the capacitance of the circuit. By coupling a nondisposable sfPESI probe with a table-top 3-axis robot, consecutive analysis of peptides, proteins, drugs, and real samples was performed. The carry-over by the consecutive analyses was suppressed to minimal by cleansing the probe tip using the solvent of water/methanol/acetonitrile (1/1/1).

LESA Cyclic Ion Mobility Mass Spectrometry of Intact Proteins from Thin Tissue Sections

Liquid extraction surface analysis (LESA) is an ambient surface sampling technique that allows the analysis of intact proteins directly from tissue samples via mass spectrometry. Integration of ion mobility separation to LESA mass spectrometry workflows has shown significant improvements in the signal-to-noise ratios of the resulting protein mass spectra and hence the number of proteins detected. Here, we report the use of a quadrupole–cyclic ion mobility–time-of-flight mass spectrometer (Q-cIM-ToF) for the analysis of proteins from mouse brain and rat kidney tissues sampled via LESA. Among other features, the instrument allows multiple pass cyclic ion mobility separation, with concomitant increase in resolving power. Single-pass experiments enabled the detection of 30 proteins from mouse brain tissue, rising to 44 when quadrupole isolation was employed. In the absence of ion mobility separation, 21 proteins were detected in rat kidney tissue including the abundant α- and β-globin chains from hemoglobin. Single-pass cyclic ion mobility mass spectrometry enabled the detection of 60 additional proteins. Multipass experiments of a narrow m/z range (m/z 870–920) resulted in the detection of 24 proteins (one pass), 37 proteins (two passes) and 54 proteins (three passes), thus demonstrating the benefits of improved mobility resolving power.

Application of 3D printed tools for customized open port probe-electrospray mass spectrometry

Three dimensional printed open port probe (3DP-OPP) and air displacement based liquid handler, were designed and optimized using fused deposition modeling (FDM) and stereolitography (SLA) 3D printing. The performance of the devices were investigated for the analysis of solid and liquid samples with electrospray ionization mass spectrometry (ESI-MS). Direct analysis in less than 1 min and without any sample preparation, enabled detection of pesticides (azoxtystrobin/imazalil) on fruits peel surface and illegal substances (MDMA/MDEA) in home-made pills. Conjunction of OPP in the overspill mode with a customized autosampler, equipped with disposable pipette tips, enables direct quantitative analysis of drugs of abuse in urine and plasma, with minimized carry-over and reduced matrix effect compared to flow injection analysis.

Point Analysis of Foods by Sheath-Flow Probe Electrospray Ionization/Mass Spectrometry (sfPESI/MS) Coupled with a Touch Sensor

For quick, noninvasive, and high-sensitivity surface analysis of foods and agricultural products, a touch sensor was developed and applied to sheath-flow probe electrospray ionization/mass spectrometry (sfPESI/MS). Upon making contact with the sample, the probe stopped by detecting the current flowing through the circuit and analytes on the sample surface were extracted in the solvent preloaded in the plastic capillary. By lifting up the probe to the default position, an electrospray ionization mass spectrum of the sample was obtained. By scanning the sample stage using a programming tool, a point analysis of targeted positions of biological samples with a spot diameter of ≤0.3 mm was achieved. It took less than 10 s for one sample spot. This method was applied to various plants and animal tissues.

Off-Colony Screening of Biosynthetic Libraries by Rapid Laser-Enabled Mass Spectrometry

By leveraging advances in DNA synthesis and molecular cloning techniques, synthetic biology increasingly makes use of large construct libraries to explore large design spaces. For biosynthetic pathway engineering, the ability to screen these libraries for a variety of metabolites of interest is essential. If the metabolite of interest or the metabolic phenotype is not easily measurable, screening soon becomes a major bottleneck involving time-consuming culturing, sample preparation, and extraction. To address this, we demonstrate the use of automated laser-assisted rapid evaporative ionization mass spectrometry (LA-REIMS)-a form of ambient laser desorption ionization mass spectrometry-to perform rapid mass spectrometry analysis direct from agar plate yeast colonies without sample preparation or extraction. We use LA-REIMS to assess production levels of violacein and betulinic acid directly from yeast colonies at a rate of 6 colonies per minute. We then demonstrate the throughput enabled by LA-REIMS by screening over 450 yeast colonies within <4 h, while simultaneously generating recoverable glycerol stocks of each colony in real time. This showcases LA-REIMS as a prescreening tool to complement downstream quantification methods such as liquid chromatography-mass spectroscopy (LCMS). By prescreening several hundred colonies with LA-REIMS, we successfully isolate and verify a strain with a 2.5-fold improvement in betulinic acid production. Finally, we show that LA-REIMS can detect 20 out of a panel of 27 diverse biological molecules, demonstrating the broad applicability of LA-REIMS to metabolite detection. The rapid and automated nature of LA-REIMS makes this a valuable new technology to complement existing screening technologies currently employed in academic and industrial workflows.

Review and perspectives on the applications of mass spectrometry imaging under ambient conditions

Ambient mass spectrometry (AMS)-based techniques are performed under ambient conditions in which the ionization and desorption occur in the open environment allowing the direct analysis of molecules with minimal or no sample preparation. A selected group of AMS techniques demonstrate imaging capabilities that can provide information about the localization of molecules on complex sample surfaces such as biological tissues. 2D, 3D, and multimodal imaging have unlocked an array of applications to systematically address complex problems in many areas of research such as drug monitoring, natural products, forensics, and cancer diagnostics. In the present review, we summarize recent advances in the field with respect to the implementation of new ambient ionization techniques and current applications in the last 5 years. In more detail, we mainly focus on imaging applications in topics related to animal whole bodies and tissues, single cells, cancer diagnostics and biomarkers, microbial cultures and co-cultures, plant and natural product metabolomics, and forensic applications. Finally, we discuss new areas of research, future perspectives, and the overall direction that the field may take in the years to come.

The exploration of effect of terfenadine on Ca2+ signaling in renal tubular cells

Terfenadine, an antihistamine used for the treatment of allergic conditions, affected Ca²⁺-related physiological responses in various models. However, the effect of terfenadine on cytosolic free Ca²⁺ levels ([Ca²⁺]_i) and its related physiology in renal tubular cells is unknown. This study examined whether terfenadine altered Ca²⁺ signaling and caused cytotoxicity in Madin-Darby canine kidney (MDCK) renal tubular cells. The Ca²⁺-sensitive fluorescent dye fura-2 was used to measure [Ca²⁺]_i. Cell viability was measured by the fluorescent reagent 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay. Terfenadine at concentrations of 100-1000 μM induced [Ca²⁺]_i rises concentration dependently. The response was reduced by approximately 35% by removing extracellular Ca²⁺. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) partly inhibited terfenadine-evoked [Ca²⁺]_i rises. Conversely, treatment with terfenadine abolished BHQ-evoked [Ca²⁺]_i rises. Inhibition of phospholipase C (PLC) with U73122 inhibited 95% of terfenadine-induced Ca²⁺ release. Terfenadine-induced Ca²⁺ entry was supported by Mn²⁺-caused quenching of fura-2 fluorescence. Terfenadine-induced Ca²⁺ entry was partly inhibited by an activator of protein kinase C (PKC), phorbol 12-myristate 13 acetate (PMA) and by three modulators of store-operated Ca²⁺ channels (nifedipine, econazole, and SKF96365). Terfenadine at 200-300 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in MDCK cells, terfenadine induced [Ca²⁺]_i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Furthermore, terfenadine caused cell death that was not triggered by preceding [Ca²⁺]_i rises.

Potential of Liquid Extraction Surface Analysis Mass Spectrometry (LESA-MS) for the Characterization of Polymer-Based Materials

Liquid extraction surface analysis mass spectrometry (LESA -MS) is a direct analysis method suitable for the analysis of polymers. It is based on a fast and efficient extraction of polymer components, such as non-intentionally added species (NIAS), post-polymerization residues, or additives, and residues resulting from specific uses followed by their MS detection. In comparison with batch methods, it is a “green” method, using negligible volumes of organic solvents, and it is cost-effective, avoiding lengthy sample preparation procedures. It can be used for the detection of known molecules (targeted analysis), identification of unknown species (exploratory analysis requiring MS/MS) and semi-quantative analysis, if standards are available. The to-date applications of LESA-MS in the field of polymer science are reviewed and critically discussed taking into account the hands-on experience from the authors’ laboratory. Future possibilities of LESA applications are highlighted.

Component Profiling in Agricultural Applications Using an Adjustable Acupuncture Needle for Sheath-Flow Probe Electrospray Ionization/Mass Spectrometry

In previous work, probe electrospray ionization/mass spectrometry (PESI/MS) and sheath-flow probe electrospray ionization/mass spectrometry (sfPESI/MS) were reported for the rapid and minimally invasive analysis of food. In this work, a modified version of sfPESI will be reported. The sample surface was pricked with an acupuncture needle inserted in the sfPESI probe that protruded from the terminus of the tip by 5 mm. The invasion depth of the needle into the sample was ∼1 mm. After sampling, the needle was retracted into the solvent-preloaded capillary with a protrusion length of 0.1-0.2 mm from the tip. A mass spectrum of the sample captured on the needle was obtained by applying a high voltage to the needle. This method could be applicable to profiling analyses of plants with the epicuticular wax covering on the surfaces that are difficult to analyze by sf-PESI. The on-site mass spectrometric analysis for a growing apricot in the field was performed to monitor the developing stage of the fruit.

Direct sampling mass spectrometry for clinical analysis

Direct sampling mass spectrometry (MS) has been advancing aggressively, showing immense potential in translating MS into the clinical field. Unlike traditional MS analysis involving extensive sample preparation and chromatographic separation, quick and simple procedures with minimal sample pretreatment or purification became available with direct sampling. An overview of the development in this field is provided, including some representative ambient ionization and fast extraction methods. Quantitative applications of these methods are emphasized and their efficacy are highlighted from a clinical aspect; non-quantitative applications in clinical analysis are also discussed. This review also discusses the integration of direct sampling MS with miniature mass spectrometers and its future outlook as an emerging clinical tool for point-of-care analysis.

Direct screening of food packaging materials for post-polymerization residues, degradation products and additives by liquid extraction surface analysis nanoelectrospray mass spectrometry (LESA-nESI-MS)

Materials in direct contact with food should be monitored for the presence of species able to migrate into food. A direct method based on liquid extraction surface analysis nanoelectrospray mass spectrometry (LESA-nanoESI-MS) was developed for the analysis of the migrating species from a polymer film. Different types of molecules: post-polymerization residues, degradation products (oligomers resulting from polymer recycling, products of polymer oxidative degradation) and anti-oxidant additives (vitamin E) were demonstrated to be detected and identified, and determined quantitatively if relevant calibration standards are available. The method was validated by a comparison a standard method based on with bulk extraction mass spectrometry. It offers considerable advantages over the latter in terms of drastically reduced analysis time and solvent consumption. Also, LESA-nanoESI-MS produced simpler spectra (limited to compounds able to migrate into food) than Direct Analysis in Real Time (DART).

Towards resolving the spatial metabolome with unambiguous molecular annotations in complex biological systems by coupling mass spectrometry imaging with structures for lossless ion manipulations

We demonstrate the coupling of liquid extraction surface analysis (LESA) to structures for lossless ion manipulations in conjunction with serpentine ultralong path with extending routing (SLIM SUPER) ion mobility-mass spectrometry (IM-MS) for the unambiguous annotation of important isomeric glycoforms in carbon-fixing communities.

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.

Imaging and spatially resolved quantification of drug distribution in tissues by mass spectrometry

Mass spectrometry imaging (MSI) is a powerful label-free technique for visualizing drug and metabolite distributions in biological tissues. In this review, we discuss recent developments in MSI and spatial profiling technologies to visualize and quantify drug distributions in tissues. We also present recent examples of applications of these technologies for assessing drug distribution within tissues and individual cells. Finally, we focus on an emerging technique coupling laser capture microdissection (LCM) to quantitative mass spectrometry, which combines the respective advantages of imaging and conventional liquid chromatography mass spectrometry, and thus enables spatially resolved drug quantification.