MALDI-LTQ-Orbitrap mass spectrometry imaging for lipidomic analysis in kidney under cisplatin chemotherapy

Untargeted metabolomics analysis of serum and urine unveils the protective effect of cilastatin on altered metabolic pathways during cisplatin-induced acute kidney injury

Acute kidney injury (AKI) is one of the most serious complications of cisplatin anticancer therapies. Cilastatin is a highly promising nephroprotective agent to eventually enter clinical use, but its biochemical mechanism is still not fully understood. We have employed an untargeted metabolomics approach based on capillary electrophoresis mass spectrometry (CE-MS) analysis of serum and urine from an in vivo rat model, to explore the metabolic pathways involved in cisplatin-induced AKI and cilastatin nephroprotection. A total of 155 and 76 identified metabolites were found to be significantly altered during cisplatin treatment in urine and serum, respectively. Most of these altered metabolites were either partially or totally recovered by cilastatin and cisplatin co-treatment. The main metabolic pathways disturbed by cisplatin during AKI involved diverse amino acids metabolism and biosynthesis, tricarboxylic acids (TCA) cycle, nicotinate and nicotinamide metabolism, among others. Cilastatin was proved to protect diverse cisplatin-altered pathways involving metabolites related to immunomodulation, inflammation, oxidative stress and amino acid metabolism in proximal tubules. However, cisplatin-altered mitochondrial metabolism (especially, the energy-producing TCA cycle) remained largely unprotected by cilastatin, suggesting an unresolved mitochondrial direct damage. Multivariate analysis allowed effective discrimination of cisplatin-induced AKI and cilastatin renoprotection based on metabolic features. A number of potential serum and urine biomarkers could also be foreseen for cisplatin-induced AKI detection and cilastatin nephroprotection.

Metabolomics unveils the exacerbating role of arachidonic acid metabolism in atherosclerosis

Atherosclerosis is a complex vascular disorder characterized by the deposition of lipids, inflammatory cascades, and plaque formation in arterial walls. A thorough understanding of its causes and progression is necessary to develop effective diagnostic and therapeutic strategies. Recent breakthroughs in metabolomics have provided valuable insights into the molecular mechanisms and genetic factors involved in atherosclerosis, leading to innovative approaches for preventing and treating the disease. In our study, we analyzed clinical serum samples from both atherosclerosis patients and animal models using laser desorption ionization mass spectrometry. By employing methods such as orthogonal partial least-squares discrimination analysis (OPLS-DA), heatmaps, and volcano plots, we can accurately classify atherosclerosis (AUC = 0.892) and identify key molecules associated with the disease. Specifically, we observed elevated levels of arachidonic acid and its metabolite, leukotriene B4, in atherosclerosis. By inhibiting arachidonic acid and monitoring its downstream metabolites, we discovered the crucial role of this metabolic pathway in regulating atherosclerosis. Metabolomic research provides detailed insights into the metabolic networks involved in atherosclerosis development and reveals the close connection between abnormal metabolism and the disease. These studies offer new possibilities for precise diagnosis, treatment, and monitoring of disease progression, as well as evaluating the effectiveness of therapeutic interventions.

A MALDI Mass Spectrometry Imaging Sample Preparation Method for Venous Thrombosis with Initial Lipid Characterization of Lab-Made and Murine Clots

Venous thromboembolism (VTE) and its complications affect over 900,000 people in the U.S. annually, with a third of cases resulting in fatality. Despite such a high incidence rate, venous thrombosis research has not led to significant changes in clinical treatments, with standard anti-coagulant therapy (heparin followed by a vitamin K antagonist) being used since the 1950s. Mechanical thrombectomy is an alternative strategy for treating venous thrombosis; however, clinical guidelines for patient selection have not been well-established or accepted. The effectiveness of both treatments is impacted by the heterogeneity of the thrombus, including the mechanical properties of its cellular components and its molecular makeup. A full understanding of the complex interplay between disease initiation and progression, biochemical molecular changes, tissue function, and mechanical properties calls for a multiplex and multiscale approach. In this work, we establish a protocol for using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging to characterize spatial heterogeneity of biomolecules in lab-made blood clots and ex vivo murine thrombi. In this work, we compared (1) tissue preservation and cryosectioning methods, (2) various matrixes, 9-aminoacridine hydrochloride monohydrate (9AA), 2,5-dihydroxybenzoic acid (DHB), and alpha-cyano-4-hydroxycinnamic acid matrix (CHCA), (3) plasma-rich versus red-blood-cell rich lab-made blood clots, and (4) lab-made blood clots versus ex vivo murine thrombi. This project is the first step in our work to combine mass spectrometry imaging with biomechanical testing of blood clots to improve our understanding of VTE.

Sublimation application of 5-chloro-2-mercaptobenzothiazole matrix for matrix-assisted laser desorption/ionization mass spectrometry imaging of mouse kidney

RATIONALE

Sublimation is a solvent-free technique used to apply a uniform matrix coating over a large sample plate, improving the matrix's purity and enhancing the analyte signal. Although the 5-chloro-2-mercaptobenzothiazole (CMBT) matrix was introduced years ago, there are no reports of its application via sublimation. We investigated the experimental parameters that are optimal for CMBT matrix sublimation on mouse kidney samples. We also evaluated the stability of the sublimed CMBT matrix under a vacuum environment. Using kidney samples prepared with a sublimated CMBT matrix, we conducted matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) analysis of specific phospholipids (phosphatidylcholine and phosphatidylglycerol in the positive ion mode and phosphatidylinositol in the negative ion mode). We also explored various spatial resolutions (50, 20, and 10 μm) and performed sequential MALDI-hematoxylin and eosin (H&E) staining.

METHODS

The CMBT matrix was applied to kidney samples using a sublimation apparatus connected to a vacuum pump to achieve a pressure of 0.05 Torr. The matrix was then subjected to different temperatures and sublimation times to determine the optimal conditions for matrix application. Subsequently, a Q-Exactive mass spectrometer equipped with a Spectroglyph MALDI ion source was employed for MALDI-MSI experiments. Standard protocols were followed for H&E staining after MALDI analysis.

RESULTS

A matrix thickness of 0.15 mg/cm² yielded high-quality images. The sublimated matrix exhibited minimal loss after approximately 20 h of exposure to a vacuum of 7 Torr, indicating its stability under these conditions. Ion images were successfully obtained at spatial resolutions of 50, 20, and 10 μm. Furthermore, orthogonal histological information was obtained through sequential MALDI-H&E staining.

CONCLUSIONS

We demonstrate that samples prepared for MALDI-MSI using sublimation to apply the CMBT matrix yield high-quality mass spectrometric images of mouse kidney sections. We also provide data for the impact of various experimental parameters on image quality (e.g., temperature, time, matrix thickness, and spatial resolution).

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

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.

In situ localization of lipids on mouse kidney tissues with acute cadmium toxicity using atmospheric pressure-MALDI mass spectrometry imaging

Cadmium-induced nephrotoxicity has been one of the major concerns for public health over the past century. Lipid peroxidation is a principal mechanism in its pathological process. Atmospheric pressure-MALDI mass spectrometry imaging (AP-MALDI MSI) enables direct mapping of lipids in the biological tissue sections. Considering the spatial visualization of lipids on mouse kidney tissues with acute cadmium toxicity is lacking, this study dedicates to filling the gap by using AP-MALDI MSI. Of the tested matrices, the optimized matrix for labeling lipids was 2,5-dihydroxyacetophenone (DHAP). A set of lipids including phosphatidylcholines (PC), phosphatidylglycerol (PG), lysophosphatidylcholine (LPC), sphingomyelin (SM), phosphatidic acid (PA), triglyceride (TG), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), etc. were identified and visualized. Accordingly, PC, PG, LPC, SM, PA and TG were down-regulated while PE and PI were up-regulated in the renal cortex or medulla regions in kidney tissues of the mouse with acute cadmium toxicity. Such in situ locations of lipids on mouse kidney tissues with acute cadmium toxicity could help discover tissue-specific nephrotoxic biomarkers and provide new insights into its renal toxicological mechanism.

Lipidomics Reveals Cisplatin-Induced Renal Lipid Alterations during Acute Kidney Injury and Their Attenuation by Cilastatin

Nephrotoxicity is a major complication of cisplatin-based chemotherapy, leading to acute kidney injury in ca. 30% of patients, with no preventive intervention or treatment available for clinical use. Cilastatin has proved to exert a nephroprotective effect for cisplatin therapies in in vitro and in vivo models, having recently entered clinical trials. A deeper understanding at the molecular level of cisplatin-induced renal damage and the effect of potential protective agents could be key to develop successful nephroprotective therapies and to establish new biomarkers of renal damage and nephroprotection. A targeted lipidomics approach, using LC-MS/MS, was employed for the quantification of 108 lipid species (comprising phospholipids, sphingolipids, and free and esterified cholesterol) in kidney cortex and medulla extracts from rats treated with cisplatin and/or cilastatin. Up to 56 and 63 lipid species were found to be altered in the cortex and medulla, respectively, after cisplatin treatment. Co-treatment with cilastatin attenuated many of these lipid changes, either totally or partially with respect to control levels. Multivariate analysis revealed that lipid species can be used to discriminate renal damage and nephroprotection, with cholesterol esters being the most discriminating species, along with sulfatides and phospholipids. Potential diagnostic biomarkers of cisplatin-induced renal damage and cilastatin nephroprotection were also found.

Innovation in drug toxicology: Application of mass spectrometry imaging technology

Mass spectrometry imaging (MSI) is a powerful molecular imaging technology that can obtain qualitative, quantitative, and location information by simultaneously detecting and mapping endogenous or exogenous molecules in biological tissue slices without specific chemical labeling or complex sample pretreatment. This article reviews the progress made in MSI and its application in drug toxicology research, including the tissue distribution of toxic drugs and their metabolites, the target organs (liver, kidney, lung, eye, and central nervous system) of toxic drugs, the discovery of toxicity-associated biomarkers, and explanations of the mechanisms of drug toxicity when MSI is combined with the cutting-edge omics methodologies. The unique advantages and broad prospects of this technology have been fully demonstrated to further promote its wider use in the field of pharmaceutical toxicology.

Comparative evaluation of phosphatidylcholine and phosphatidylserine with different fatty acids on nephrotoxicity in vancomycin-induced mice

Phospholipids reportedly alleviate drug-induced acute kidney injury. However, no study has compared the effect of phospholipids with different fatty acids and polar heads on drug-induced nephrotoxicity. In the present study, we aimed to compare the possible nephroprotection afforded by phosphatidylcholine and phosphatidylserine with different fatty acids in a mouse model of vancomycin-induced nephrotoxicity. Pretreatment with phospholipids rich in docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) doubled the survival time when compared with the model group. Moreover, phospholipids rich in DHA/EPA significantly reduced the serum levels of renal function biomarkers and ameliorated kidney pathologies. In terms of alleviating renal damage, no significant differences were observed between different polar heads in DHA-enriched phospholipids, while phosphatidylserine from soybean was better than phosphatidylcholine in mitigating renal injury. Furthermore, DHA/EPA-enriched phospholipids inhibited vancomycin-induced nephrotoxicity mainly by inhibiting apoptosis and oxidative stress. These results provide a scientific basis for phospholipids as potential ingredients to prevent acute kidney injury.

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.

Data Filtering and Its Prioritization in Pipelines for Spatial Segmentation of Mass Spectrometry Imaging

Mass spectrometry imaging (MSI) could provide vast amounts of data at the temporal-spatial scale in heterogeneous biological specimens, which challenges us to segment accurately suborgans/microregions from complex MSI data. Several pipelines had been proposed for MSI spatial segmentation in the past decade. More importantly, data filtering was found to be an efficient procedure to improve the outcomes of MSI segmentation pipelines. It is not clear, however, how the filtering procedure affects the MSI segmentation. An improved pipeline was established by elaborating the filtering prioritization and filtering algorithm. Lipidomic-characteristic-based MSI data of a whole-body mouse fetus was used to evaluate the established pipeline on localization of the physiological position of suborgans by comparing with three commonly used pipelines and commercial SCiLS Lab software. Two structural measurements were used to quantify the performances of the pipelines including the percentage of abnormal edge pixel (PAEP) and CHAOS. Our results demonstrated that the established pipeline outperformed the other pipelines in visual inspection, spatial consistence, time-cost, and robustness analysis. For example, the dorsal pallium (isocortex) and hippocampal formation (Hpf) regions, midbrain, cerebellum, and brainstem on the mouse brain were annotated and located by the established pipeline. As a generic pipeline, the established pipeline could help with the accurate assessment and screening of drug/chemical-induced targeted organs and exploration of the progression and molecular mechanisms of diseases. The filter-based strategy is expected to become a critical component in the standard operating procedure of MSI data sets.

Spatial evaluation of long-term metabolic changes induced by cisplatin nephrotoxicity

Cisplatin is a widely used chemotherapeutic agent. However, it is causing nephrotoxic side effects including a reduced glomerular filtration rate and acute kidney injury. Although kidneys can recover to an extent from the treatment, long-term damage is possible. While a lot of research is focusing on short-term effects, little is known about adverse metabolic effects in the process of recovery. In this study, male Han Wistar rats were dosed with a single intraperitoneal injection of 3 mg/kg cisplatin. Urine and kidney samples were harvested 3, 8 and 26 days after administration. Tubular injury was demonstrated through urinary biomarkers. Complementing this, mass spectrometry imaging gives insight on molecular alterations on a spatial level, thus making it well suited to analyze short- and long-term disturbances. Various metabolic pathways seem to be affected, as changes in a wide range of metabolites were observed between treated and control animals. Besides previously reported early changes in kidney metabolism, unprecedented long-term effects were detected including deviation in nucleotides, antioxidants, and phospholipids.

In situ metabolomics in nephrotoxicity of aristolochic acids based on air flow-assisted desorption electrospray ionization mass spectrometry imaging

Understanding of the nephrotoxicity induced by drug candidates is vital to drug discovery and development. Herein, an in situ metabolomics method based on air flow-assisted desorption electrospray ionization mass spectrometry imaging (AFADESI-MSI) was established for direct analysis of metabolites in renal tissue sections. This method was subsequently applied to investigate spatially resolved metabolic profile changes in rat kidney after the administration of aristolochic acid I, a known nephrotoxic drug, aimed to discover metabolites associated with nephrotoxicity. As a result, 38 metabolites related to the arginine–creatinine metabolic pathway, the urea cycle, the serine synthesis pathway, metabolism of lipids, choline, histamine, lysine, and adenosine triphosphate were significantly changed in the group treated with aristolochic acid I. These metabolites exhibited a unique distribution in rat kidney and a good spatial match with histopathological renal lesions. This study provides new insights into the mechanisms underlying aristolochic acids nephrotoxicity and demonstrates that AFADESI-MSI-based in situ metabolomics is a promising technique for investigation of the molecular mechanism of drug toxicity.

Across the spectrum: integrating multidimensional metal analytics for in situ metallomic imaging

To know how much of a metal species is in a particular location within a biological context at any given time is essential for understanding the intricate roles of metals in biology and is the fundamental question upon which the field of metallomics was born. Simply put, seeing is powerful. With the combination of spectroscopy and microscopy, we can now see metals within complex biological matrices complemented by information about associated molecules and their structures. With the addition of mass spectrometry and particle beam based techniques, the field of view grows to cover greater sensitivities and spatial resolutions, addressing structural, functional and quantitative metallomic questions from the atomic level to whole body processes. In this perspective, I present a paradigm shift in the way we relate to and integrate current and developing metallomic analytics, highlighting both familiar and perhaps less well-known state of the art techniques for in situ metallomic imaging, specific biological applications, and their use in correlative studies. There is a genuine need to abandon scientific silos and, through the establishment of a metallomic scientific platform for further development of multidimensional analytics for in situ metallomic imaging, we have an incredible opportunity to enhance the field of metallomics and demonstrate how discovery research can be done more effectively.

Advances in Toxicological Research of the Anticancer Drug Cisplatin

Cisplatin is one of the most widely used chemotherapeutic agents for various solid tumors in the clinic due to its high efficacy and broad spectrum. The antineoplastic activity of cisplatin is mainly due to its ability to cross-link with DNA, thus blocking transcription and replication. Unfortunately, the clinical use of cisplatin is limited by its severe, dose-dependent toxic side effects. There are approximately 40 specific toxicities of cisplatin, among which nephrotoxicity is the most common one. Other common side effects include ototoxicity, neurotoxicity, gastrointestinal toxicity, hematological toxicity, cardiotoxicity, and hepatotoxicity. These side effects together reduce the life quality of patients and require lowering the dosage of the drug, even stopping administration, thus weakening the treatment effect. Few effective measures exist clinically against these side effects because the exact mechanisms of various side effects from cisplatin remain still unclear. Therefore, substantial effort has been made to explore the complicated biochemical processes involved in the toxicology of cisplatin, aiming to identify effective ways to reduce or eradicate its toxicity. This review summarizes and reviews the updated advances in the toxicological research of cisplatin. We anticipate to provide insights into the understanding of the mechanisms underlying the side effects of cisplatin and designing comprehensive therapeutic strategies involving cisplatin.

Systematic evaluation of repeatability of IR-MALDESI-MS and normalization strategies for correcting the analytical variation and improving image quality

Mass spectrometry imaging is a powerful tool widely used in biological, clinical, and forensic research, but its often poor repeatability limits its application for quantitative and large-scale analysis. A systematic evaluation of infrared matrix-assisted laser desorption electrospray ionization mass spectrometry (IR-MALDESI-MS) repeatability in absolute ion abundances during short- and long-term experiments was carried out on liver slices from the same rat with minimal biological variability to be expected. Results of median %RSDs ranging from 14 to 45, pooled %RMADs ranging from 11 to 33, and Pearson correlation coefficients ranging from 0.83 to 1.00 demonstrated an acceptable repeatability of IR-MALDESI-MS. Normalization is commonly applied for the purpose of accounting for analytical variability of spectra generated from different runs so as to reveal real biological differences. Nine data normalization strategies were performed on the rat liver data sets to examine their effects on reducing analytical variation, and further on a hen ovary data set containing more morphological features for the investigation of their impact on ion images. Results demonstrated that the majority of normalization approaches benefit data quality to some extent, and local normalization methods significantly outperform their global counterparts, resulting in a reduction of median %RSD up to 22. Local median normalization was found to be promisingly robust for both homogeneous and heterogeneous samples.

Alterations in Lipid Profile of the Aging Kidney Identified by MALDI Imaging Mass Spectrometry

During aging, the kidney undergoes functional and physiological changes that are closely affiliated with chronic kidney disease (CKD). There is increasing evidence supporting the role of lipid or lipid-derived mediators in the pathogenesis of CKD and other aging-related diseases. To understand the role of lipids in various metabolic processes during kidney aging, we conducted matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) analysis in kidneys harvested from young (2 months old, n = 3) and old mice (24 months old, n = 3). MALDI-IMS analysis showed an increase in ceramide level and a decrease in sphingomyelin (SM) and phosphatidylcholine (PC) levels in kidneys of old mice. The increased expression of cPLA2 and SMPD1 protein in aged kidney was confirmed by immunohistochemistry and Western blot analysis. Our MALDI-IMS data showed the altered distribution of lipids in aged kidney as indicative of aging-related functional changes of the kidney. Combined analysis of MALDI-IMS and IHC confirmed lipidomic changes and expression levels of responsible enzymes as well as morphological changes.

MALDI-imaging of early stage Xenopus laevis embryos

Xenopus laevis is an important model organism for vertebrate development. An extensive literature has developed on changes in transcript expression during development of this organism, and there is a growing literature on the corresponding protein expression changes during development. In contrast, there is very little information on changes in metabolite expression during development. We present the first MALDI mass-spectrometry images of metabolites within the developing embryo. These images were generated for 142 metabolite ions. The images were subjected to an algorithm that revealed three spatially-resolved clusters of metabolites. One small cluster is localized near the outer membrane of the embryo. A large cluster of metabolites is found in cavities destined to form the neural tube and gut, and contains a number of ceramide species, which are associated with cellular signaling, including differentiation, proliferation, and programmed cell death. Another large cluster of metabolites is found in tissue and is dominated by phosphatidylcholines, which are common components of cell membranes. Surprisingly, no metabolites appear to be homogeneously distributed across the slices; metabolites are localized either within tissue or in cavities, but not both.

Whole-body spatially-resolved metabolomics method for profiling the metabolic differences of epimer drug candidates using ambient mass spectrometry imaging

Investigation of the in vivo drug action and metabolic differences of epimer drugs is challenging. Whole-body MSI analysis can visually present the stereoscopic distribution of molecules related to the interaction of drugs and organisms, and can provide more comprehensive organ-specific profiling information. Herein, we developed a whole-body spatially-resolved imaging metabolomics method based on an air flow-assisted ionisation desorption electrospray ionisation (AFADESI)-MSI system coupled with a high-resolution mass spectrometer and highly discriminating imaging software. The epimeric sedative-hypnotic drug candidates YZG-331 and YZG-330 were selected as examples, and rats administered normal or high oral doses were used. By performing multivariate statistical data-mining on the combined MSI data, organ-specific differential ions were screened. By comparing the variations in the relative contents of the drugs, their metabolites, and endogenous neurotransmitters throughout whole-body tissue sections of the rats, rich information that could potentially explain the more significant sedative-hypnotic effects of YZG-330 compared to YZG-331 was obtained. Such as the increased ratio of gamma-aminobutyric acid in the brain and stomach of the rats (0.25, 0.47, 0.68, 0.30, and 0.89 for the control and YZG-331-H, YZG-330-H, YZG-331-L, and YZG-330-L, respectively) were interesting. This study provided a convenient and visual method to investigate in vivo molecular metabolic differences and provide insight towards a better understanding of the pharmacodynamic mechanisms of these sedative-hypnotic drug-candidates.

Rapid Identification of Ischemic Injury in Renal Tissue by Mass-Spectrometry Imaging

The increasing analytical speed of mass-spectrometry imaging (MSI) has led to growing interest in the medical field. Acute kidney injury is a severe disease with high morbidity and mortality. No reliable cut-offs are known to estimate the severity of acute kidney injury. Thus, there is a need for new tools to rapidly and accurately assess acute ischemia, which is of clinical importance in intensive care and in kidney transplantation. We investigated the value of MSI to assess acute ischemic kidney tissue in a porcine model. A perfusion model was developed where paired kidneys received warm (severe) or cold (minor) ischemia ( n = 8 per group). First, ischemic tissue damage was systematically assessed by two blinded pathologists. Second, MALDI-MSI of kidney tissues was performed to study the spatial distributions and compositions of lipids in the tissues. Histopathological examination revealed no significant difference between kidneys, whereas MALDI-MSI was capable of a detailed discrimination of severe and mild ischemia by differential expression of characteristic lipid-degradation products throughout the tissue within 2 h. In particular, lysolipids, including lysocardiolipins, lysophosphatidylcholines, and lysophosphatidylinositol, were dramatically elevated after severe ischemia. This study demonstrates the significant potential of MSI to differentiate and identify molecular patterns of early ischemic injury in a clinically acceptable time frame. The observed changes highlight the underlying biochemical processes of acute ischemic kidney injury and provide a molecular classification tool that can be deployed in assessment of acute ischemic kidney injury.

Molecules and elements for quantitative bioanalysis: The allure of using electrospray, MALDI, and ICP mass spectrometry side-by-side

To understand biological processes, not only reliable identification, but quantification of constituents in biological processes play a pivotal role. This is especially true for the proteome: protein quantification must follow protein identification, since sometimes minute changes in abundance tell the real tale. To obtain quantitative data, many sophisticated strategies using electrospray and MALDI mass spectrometry (MS) have been developed in recent years. All of them have advantages and limitations. Several years ago, we started to work on strategies, which are principally capable to overcome some of these limits. The fundamental idea is to use elemental signals as a measure for quantities. We began by replacing the radioactive ³² P with the "cold" natural ³¹ P to quantify modified nucleotides and phosphorylated peptides and proteins and later used tagging strategies for quantification of proteins more generally. To do this, we introduced Inductively Coupled Plasma Mass Spectrometry (ICP-MS) into the bioanalytical workflows, allowing not only reliable and sensitive detection but also quantification based on isotope dilution absolute measurements using poly-isotopic elements. The detection capability of ICP-MS becomes particularly attractive with heavy metals. The covalently bound proteins tags developed in our group are based on the well-known DOTA chelate complex (1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid) carrying ions of lanthanoides as metal core. In this review, I will outline the development of this mutual assistance between molecular and elemental mass spectrometry and discuss the scope and limitations particularly of peptide and protein quantification. The lanthanoide tags provide low detection limits, but offer multiplexing capabilities due to the number of very similar lanthanoides and their isotopes. With isotope dilution comes previously unknown accuracy. Separation techniques such as electrophoresis and HPLC were used and just slightly adapted workflows, already in use for quantification in bioanalysis. Imaging mass spectrometry (MSI) with MALDI and laser ablation ICP-MS complemented the range of application in recent years.

Lipid imaging for visualizing cilastatin amelioration of cisplatin-induced nephrotoxicity

Nephrotoxicity is a major limitation to cisplatin antitumor therapies. Cilastatin, an inhibitor of renal dehydropeptidase-I, was recently proposed as a promising nephroprotector against cisplatin toxicity, preventing apoptotic cell death. In this work, cilastatin nephroprotection was further investigated in a rat model, with a focus on its effect on 76 renal lipids altered by cisplatin, including 13 new cisplatin-altered mitochondrial cardiolipin species. Lipid imaging was performed with MALDI mass spectrometry imaging (MALDI-MSI) in kidney sections from treated rats. Cilastatin was proved to significantly diminish the lipid distribution alterations caused by cisplatin, lipid levels being almost completely recovered to those of control samples. The extent of recovery of cisplatin-altered lipids by cilastatin turned out to be relevant for discriminating direct or secondary lipid alterations driven by cisplatin. Lipid peroxidation induced by cisplatin was also shown to be reduced when cilastatin was administered. Importantly, significant groups separation was achieved during multivariate analysis of cortex and outer-medullary lipids, indicating that damaged kidney can be discerned from the nephroprotected and healthy groups and classified according to lipid distribution. Therefore, we propose MALDI-MSI as a powerful potential tool offering multimolecule detection possibilities to visualize and evaluate nephrotoxicity and nephroprotection based on lipid analysis.

Towards enhanced metabolomic data analysis of mass spectrometry image: Multivariate Curve Resolution and Machine Learning

Large amounts of data are generally produced from mass spectrometry imaging (MSI) experiments in obtaining the molecular and spatial information of biological samples. Traditionally, MS images are constructed using manually selected ions, and it is very challenging to comprehensively analyze MSI results due to their large data sizes and highly complex data structures. To overcome these barriers, it is obligatory to develop advanced data analysis approaches to handle the increasingly large MSI data. In the current study, we focused on the method development of using Multivariate Curve Resolution (MCR) and Machine Learning (ML) approaches. We aimed to effectively extract the essential information present in the large and complex MSI data and enhance the metabolomic data analysis of biological tissues. Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) algorithm was used to obtain major patterns of spatial distribution and grouped metabolites with the same spatial distribution patterns. In addition, both supervised and unsupervised ML methods were established to analyze the MSI data. In the supervised ML approach, Random Forest method was selected, and the model was trained using the selected datasets based on the distribution pattern obtained from MCR-ALS analyses. In the unsupervised ML approach, both DBSCAN (Density-based Spatial Clustering of Applications with Noise) and CLARA (Clustering Large Applications) were applied to cluster the MSI datasets. It is worth noting that similar patterns of spatial distribution were discovered through MSI data analysis using MCR-ALS, supervised ML, and unsupervised ML. Our protocols of data analysis can be applied to process the data acquired using many other types of MSI techniques, and to extract the overall features present in MSI results that are intractable using traditional data analysis approaches.

MALDI-MS Imaging Reveals Asymmetric Spatial Distribution of Lipid Metabolites from Bisphenol S-Induced Nephrotoxicity

With the continuous exposure of environmental pollutants in organisms, determination of abundance variation and spatial distribution of lipids might expand our understanding of toxicological mechanisms occurring in the kidney. Herein, an integrated method involving mass spectrometry (MS)-based lipidomics and matrix-assisted laser desorption/ionization-MS imaging (MALDI-MSI) was developed for the study of nephrotoxicity in mice exposed to 10 and 100 μg bisphenol S (BPS)/kg body weight/day. The BPS exposure remarkable perturbed abundances of 91 potential markers that mainly involved in five metabolic pathways. We elucidated the lipids spatial heterogeneity by using morphological analysis, probabilistic latent semantic analysis, and coregistered multimodal three-dimensional (3D)-MSI. In morphological analysis, both 10 and 100 μg BPS induced significant nephrotoxicity to mice, including glomerular necrosis in renal cortex, cloudy swelling in renal medulla, and interstitial collapsing in renal pelvis. Significant differential signaling lipids such as sphingomyelin (SM) (d22:0/20:4), ceramide (Cer) (d18:2/24:1), and sphingosine (d18:0) related to inflammation were found to be up-regulated and colocalized in the renal cortex, medulla, and pelvis, respectively. Also, seven significant differential lipids, which are considered to be involved in membrane homeostasis and cellular function, were found to be colocalized in the renal cortex. The observed significant variations of morphology, lipid accumulation, and metabolism in the renal cortex implicated that lipids in the renal cortex were more sensitive to BPS exposure than those in the renal medulla and pelvis. Moreover, we reconstructed a 3D-MSI model of kidney and identified two heterogeneous-related substructures in the renal cortex and pelvis upon 100 μg BPS exposure. It might be used in novel specificity evaluation and early diagnosis for environmental pollutant-induced kidney diseases.

Single Cell Neurometabolomics

Metabolomics, the characterization of metabolites and their changes within biological systems, has seen great technological and methodological progress over the past decade. Most metabolomic experiments involve the characterization of the small-molecule content of fluids or tissue homogenates. While these microliter and larger volume metabolomic measurements can characterize hundreds to thousands of compounds, the coverage of molecular content decreases as sample sizes are reduced to the nanoliter and even to the picoliter volume range. Recent progress has enabled the ability to characterize the major molecules found within specific individual cells. Especially within the brain, a myriad of cell types are colocalized, and oftentimes only a subset of these cells undergo changes in both healthy and pathological states. Here we highlight recent progress in mass spectrometry-based approaches used for single cell metabolomics, emphasizing their application to neuroscience research. Single cell studies can be directed to measuring differences between members of populations of similar cells (e.g., oligodendrocytes), as well as characterizing differences between cell types (e.g., neurons and astrocytes), and are especially useful for measuring changes occurring during different behavior states, exposure to diets and drugs, neuronal activity, and disease. When combined with other omics approaches such as transcriptomics, and with morphological and physiological measurements, single cell metabolomics aids fundamental neurochemical studies, has great potential in pharmaceutical development, and should improve the diagnosis and treatment of brain diseases.

Quantitative analysis of drug distribution by ambient mass spectrometry imaging method with signal extinction normalization strategy and inkjet-printing technology

Quantitative mass spectrometry imaging (MSI) is a robust approach that provides both quantitative and spatial information for drug candidates' research. However, because of complicated signal suppression and interference, acquiring accurate quantitative information from MSI data remains a challenge, especially for whole-body tissue sample. Ambient MSI techniques using spray-based ionization appear to be ideal for pharmaceutical quantitative MSI analysis. However, it is more challenging, as it involves almost no sample preparation and is more susceptible to ion suppression/enhancement. Herein, based on our developed air flow-assisted desorption electrospray ionization (AFADESI)-MSI technology, an ambient quantitative MSI method was introduced by integrating inkjet-printing technology with normalization of the signal extinction coefficient (SEC) using the target compound itself. The method utilized a single calibration curve to quantify multiple tissue types. Basic blue 7 and an antitumor drug candidate (S-(+)-deoxytylophorinidine, CAT) were chosen to initially validate the feasibility and reliability of the quantitative MSI method. Rat tissue sections (heart, kidney, and brain) administered with CAT was then analyzed. The quantitative MSI analysis results were cross-validated by LC-MS/MS analysis data of the same tissues. The consistency suggests that the approach is able to fast obtain the quantitative MSI data without introducing interference into the in-situ environment of the tissue sample, and is potential to provide a high-throughput, economical and reliable approach for drug discovery and development.