Tissue derivatization for visualizing lactate and pyruvate in mouse testis tissues using matrix-assisted laser desorption/ionization-mass spectrometry imaging.

Pyruvate and lactate are the final metabolites of the glycolytic system that are formed under oxygen-rich and anaerobic conditions, respectively. They play an important role in energy metabolism. Obtaining a tissue distribution image of pyruvate and lactate holds great significance in molecular biology because the glycolytic system plays an essential role in diseases, such as tumors and diabetes; microbial activities, such as alcohol production and lactic acid fermentation; and maintaining homeostasis in the gut environment. However, it is difficult to obtain images of the distribution of in vivo metabolites because of the low detection sensitivities of current methods. In this study, a novel derivatization method for pyruvate and lactate was developed using matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) to detect pyruvate and lactate in vivo and obtain biodistribution images. We investigated derivatization methods using readily available 3-nitrophenylhydrazine (3NPH), the addition of which improves the sensitivity of pyruvate detection, and the distribution of pyruvate in mouse testes was successfully visualized. Furthermore, the distribution of lactate in the mouse testes could be visualized, and improved detection sensitivity for the main metabolites of the tricarboxylic acid cycle was demonstrated. This derivatization method can be used to detect carboxyl-containing metabolites, including pyruvate, via MALDI-MSI. Furthermore, 3NPH forms amide bonds with carbonyl, phosphate, and carboxyl groups, suggesting the possibility of visualizing its distribution in many metabolites.

Novel mimetic tissue standards for precise quantitative mass spectrometry imaging of drug and neurotransmitter concentrations in rat brain tissues.

Understanding the relationship between the concentration of a drug and its therapeutic efficacy or side effects is crucial in drug development, especially to understand therapeutic efficacy in central nervous system drug, quantifying drug-induced site-specific changes in the levels of endogenous metabolites, such as neurotransmitters. In recent times, evaluation of quantitative distribution of drugs and endogenous metabolites using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI) has attracted much attention in drug discovery research. However, MALDI-MSI quantification (quantitative mass spectrometry imaging, QMSI) is an emerging technique, and needs to be further developed for practicable and convenient use in drug discovery research. In this study, we developed a reliable QMSI method for quantification of clozapine (antipsychotic drug) and dopamine and its metabolites in the rat brain using MALDI-MSI. An improved mimetic tissue model using powdered frozen tissue for QMSI was established as an alternative method, enabling the accurate quantification of clozapine levels in the rat brain. Furthermore, we used the improved method to evaluate drug-induced fluctuations in the concentrations of dopamine and its metabolites. This method can quantitatively evaluate drug localization in the brain and drug-induced changes in the concentration of endogenous metabolites, demonstrating the usefulness of QMSI.

Probe oscillation control in tapping-mode scanning probe electrospray ionization for stabilization of mass spectrometry imaging.

Mass spectrometry imaging (MSI) is used for visualizing the distribution of components in solid samples, such as biological tissues, and requires a technique to ionize the components from local areas of the sample. Tapping-mode scanning probe electrospray ionization (t-SPESI) uses an oscillating capillary probe to extract components from a local area of a sample with a small volume of solvent and to perform electrospray ionization of those components at high speed. MSI can be conducted by scanning the sample surface with a capillary probe. To ensure stable extraction and ionization for MSI, the probe oscillation during measurements must be understood. In this study, we examined the changes in oscillation amplitude and phase due to the interaction between the oscillating probe and the brain tissue section when the probe tip was dynamically brought close to the sample surface. The changes in the probe oscillation depended on the oscillation frequency and polarity of the bias voltage applied to the solvent because an electrostatic force shifted the frequency of the probe oscillation. These findings suggest that controlling the probe oscillation frequency is important for stabilizing MSI by t-SPESI.

Analysis of the Correlation between Cholesterol Levels in Blood Using Clinical Data and Hair Using Mass Spectrometry Imaging.

Mass spectrometry imaging (MSI) is a technique that visualizes the distribution of molecules by ionizing the components on the surface of a sample and directly detecting them. Previously, MSI using hair has primarily been used in the forensic field to detect illegal drugs. On the other hand, there are few examples of using this technology for health monitoring. In this study, hair and clinical data were collected from 24 subjects, and the correlation between blood cholesterol levels and cholesterol detected from cross-sectional hair slices was analyzed. As a result, a positive correlation with a correlation coefficient of 0.43 was observed between blood cholesterol and cholesterol detected from hair. Furthermore, when comparing the results of fluorescence staining (FS) of hair cholesterol with Filipin III and the MSI results, it was found that while FS could visualize detailed hair structures, there were cases where the results differed from MSI, possibly due to some cholesterol loss during the staining process. In the future, if various disease biomarkers can be detected using hair MSI, it could potentially become a non-invasive diagnostic method.

Development of a Mass Spectrometry Imaging Method to Evaluate the Penetration of Moisturizing Components Coated on Surgical Gloves into Artificial Membranes.

Skin dryness and irritant contact dermatitis induced by the prolonged use of surgical gloves are issues faced by physicians. To address these concerns, manufacturers have introduced surgical gloves that incorporate a moisturizing component on their inner surface, resulting in documented results showing a reduction in hand dermatitis. However, the spatial distribution of moisturizers applied to surgical gloves within the integument remains unclear. Using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI), we investigated the spatial distribution of moisturizers in surgical gloves within artificial membranes. Recently, dermal permeation assessments using three-dimensional models, silicone membranes, and Strat-M have gained attention as alternative approaches to animal testing. Therefore, in this study, we established an in vitro dermal permeation assessment of commercially available moisturizers in surgical gloves using artificial membranes. In this study, we offer a methodology to visualize the infiltration of moisturizers applied to surgical gloves into an artificial membrane using MALDI-MSI, while evaluating commercially available moisturizer-coated surgical gloves. Using our penetration evaluation method, we confirmed the infiltration of the moisturizers into the polyethersulfone 2 and polyolefin layers, which correspond to the epidermis and dermis of the skin, after the use of surgical gloves. The MSI-based method presented herein demonstrated the efficacy of evaluating the permeation of samples containing active ingredients.

Rice grain structural characteristics of sake rice cultivar Hakutsurunishiki for daiginjo-shu brewing.

Hakutsurunishiki is a sake rice cultivar bred using Yamadabo (seed parent) and Wataribune 2 (pollen parent), equivalent to a Yamadanishiki sibling. This study evaluated the structural characteristics of the Hakutsurunishiki rice grain that contribute to the brewing characteristics of daiginjo-shu, via a comparison with Yamadanishiki. Hakutsurunishiki brown rice was a little heavy and had a large white core. Observing a cross-section of white rice after soaking revealed that the rice grain structure of Hakutsurunishiki was different from that of Yamadanishiki. Hakutsurunishiki white rice showed fewer voids than Yamadanishiki, promoting a slower water absorption rate. Glucose distribution in rice koji obtained by mass spectrometry imaging showed that Hakutsurunishiki rice koji, like Yamadanishiki, is tsuki-haze type, suggesting that its grain structure is suitable for making rice koji for daiginjo-shu. With these observations, we were able to clarify the structural characteristics of Hakutsurunishiki rice grain.

Improving the Signal Intensity of Cryosections Using a Conductive Adhesive Film in Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging.

The matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) technique was used to obtain the molecular images of cryosections without labeling. Although MALDI-MSI has been widely used to detect small molecules from biological tissues, issues remain due to the technical process of cryosectioning and limited mass spectrometry parameters. The use of a conductive adhesive film is a unique method to obtain high-quality sections from cutting tissue, such as bone, muscle, adipose tissue, and whole body of mice or fish, and we have reported the utilization of the film for MALDI-MSI in previous. However, some signal of the small molecules using the conductive adhesive films was still lower than on the indium tin oxide (ITO) glass slide. Here, the sample preparation and analytical conditions for MALDI-MSI using an advanced conductive adhesive film were optimized to obtain strong signals from whole mice heads. The effects of tissue thickness and laser ionization power on signal intensity were verified using MALDI-MSI. The phospholipid signal intensity was measured for samples with three tissue thicknesses (5, 10, and 20 µm); compared to the signals from the samples on the ITO glass slides, the signals with conductive adhesive films exhibited significantly higher intensities when a laser with a higher range of power was used to ionize the small molecules. Thus, the technique using the advanced conductive adhesive film showed an improvement in MALDI-MSI analysis.

Using Mass Spectrometry Imaging to Visualize Pesticide Accumulation and Time-Dependent Distribution in Fungicide-Coated Seeds.

Pesticide seed treatment provides efficient crop protection in the early season and enables a reduction in the quantity of fungicides used later. Hence, it has been a practical application for crop protection in major crop sectors such as corn, soybean, wheat, and cotton. The chemicals on pesticide-treated seeds may show different distributions depending on the structure of the seeds and the physical properties of the chemicals, but they have not been well studied because of a lack of versatile analytical tools. Here, we used mass spectrometry imaging to visualize the distribution of a fungicide (ethaboxam) in corn and soybean seeds coated with it. Contrasting distribution patterns were noted, which are likely dependent on the seed structure. We also obtained information on fungicide distribution after the seedings, which will contribute to a better understanding of the fungicide delivery pathway within plants. Using this new analytical method, we were able to obtain hitherto unavailable time-dependent, dynamic information on the ethaboxam. We expect that this method will be a useful tool with widespread applications in pesticide development and use. Copyright © 2023 Shuichi Shimma, Hiromi Saito, Takuya Inoue, and Fukumatsu Iwahashi. This is an open-access article distributed under the terms of Creative Commons Attribution Non-Commercial 4.0 International License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

An Alternative Method for Quantitative Mass Spectrometry Imaging (q-MSI) of Dopamine Utilizing Fragments of Animal Tissue.

Mass spectrometry imaging (MSI) is a well-known method for the ionization of molecules on tissue sections and the visualization of their localization. Recently, different sample preparation methods and new instruments have been used for MSI, and different molecules are becoming visible. On the other hand, although several quantification methods (q-MSI) have been proposed, there is still room for the development of a simplified procedure. Here, we have attempted to develop a reproducible and reliable quantification method using a calibration curve prepared from tissue debris of a frozen section of a sample when we trim the frozen blocks. We discuss the reproducibility of this method across different sample lots and the effect of the biological matrix (ion suppression) on our results. The quantitative performance was evaluated in terms of accuracy and relative standard deviation, and the reliability of the quantitative values obtained by matrix-assisted laser desorption/ionization-MSI was further evaluated by enzyme-linked immunosorbent assay (ELISA). Our q-MSI method for the quantification of dopamine in mouse brain tissue was found to be highly linear, accurate, and precise. The quantitative values obtained by MSI were found to be highly comparable (>85% similarity) to the results obtained by ELISA from the same tissue extracts.

Visualization of azoxystrobin penetration in wheat leaves using mass microscopy imaging.

Fungicides must penetrate the internal tissues of plants to kill pathogenic fungi. Mass spectrometers have been used to confirm this penetration, but conventional mass spectrometric methods cannot distinguish the fungicides in different internal tissues owing to the extraction steps. However, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can detect the penetration of fungicides into leaf sections through direct analysis of the sample surfaces. Therefore, the objective of this study was to establish a method for visualizing fungicide penetration in wheat leaf cross sections using MALDI-MSI. The penetration of azoxystrobin from the epidermal to the internal tissue of the leaves was observed. Moreover, azoxystrobin accumulates in the cells around the vascular bundle. This study suggests that MSI can be useful for the evaluation of fungicide penetration in plant leaves.

Phosphatidylinositol-3,4,5-trisphosphate interacts with alpha-synuclein and initiates its aggregation and formation of Parkinson's disease-related fibril polymorphism.

Lipid interaction with α-synuclein (αSyn) has been long implicated in the pathogenesis of Parkinson's disease (PD). However, it has not been fully determined which lipids are involved in the initiation of αSyn aggregation in PD. Here exploiting genetic understanding associating the loss-of-function mutation in Synaptojanin 1 (SYNJ1), a phosphoinositide phosphatase, with familial PD and analysis of postmortem PD brains, we identified a novel lipid molecule involved in the toxic conversion of αSyn and its relation to PD. We first established a SYNJ1 knockout cell model and found SYNJ1 depletion increases the accumulation of pathological αSyn. Lipidomic analysis revealed SYNJ1 depletion elevates the level of its substrate phosphatidylinositol-3,4,5-trisphosphate (PIP3). We then employed Caenorhabditis elegans model to examine the effect of SYNJ1 defect on the neurotoxicity of αSyn. Mutations in SYNJ1 accelerated the accumulation of αSyn aggregation and induced locomotory defects in the nematodes. These results indicate that functional loss of SYNJ1 promotes the pathological aggregation of αSyn via the dysregulation of its substrate PIP3, leading to the aggravation of αSyn-mediated neurodegeneration. Treatment of cultured cell line and primary neurons with PIP3 itself or with PIP3 phosphatase inhibitor resulted in intracellular formation of αSyn inclusions. Indeed, in vitro protein-lipid overlay assay validated that phosphoinositides, especially PIP3, strongly interact with αSyn. Furthermore, the aggregation assay revealed that PIP3 not only accelerates the fibrillation of αSyn, but also induces the formation of fibrils sharing conformational and biochemical characteristics similar to the fibrils amplified from the brains of PD patients. Notably, the immunohistochemical and lipidomic analyses on postmortem brain of patients with sporadic PD showed increased PIP3 level and its colocalization with αSyn. Taken together, PIP3 dysregulation promotes the pathological aggregation of αSyn and increases the risk of developing PD, and PIP3 represents a potent target for intervention in PD.

Solvent effects of N,N-dimethylformamide and methanol on mass spectrometry imaging by tapping-mode scanning probe electrospray ionization.

Mass spectrometry imaging (MSI) is an effective technique for visualizing the distribution of lipids in tissues. The direct extraction-ionization methods using minute volumes of solvent for local components have the advantage of rapid measurement without any sample pretreatment. For effective MSI of tissues, it is necessary to understand the effect of solvent physicochemical properties on ion images. In this study, we report solvent effects on the lipid imaging of mouse brain tissue by tapping-mode scanning probe electrospray ionization (t-SPESI) which is capable of extraction-ionization using sub-pL solvents. To precisely measure lipid ions, we developed a measurement system incorporating a quadrupole-time-of-flight mass spectrometer. The differences in signal intensity and spatial resolution of lipid ion images were investigated using N,N-dimethylformamide (non-protic polar solvent), methanol (protic polar solvent) and their mixture. The mixed solvent was suitable for the protonation of lipids, and it provided high spatial resolution MSI. Results indicate that the mixed solvent improves the extractant transfer efficiency and minimizes charged droplets from an electrospray. The solvent selectivity study revealed the importance of solvent selection based on physicochemical properties for the advancement of MSI by t-SPESI.

Visualization of Glutamate Decarboxylase Activity in Barley Seeds under Salinity Stress Using Mass Microscope.

γ-Aminobutyric acid (GABA) accumulates in plants in response to environmental stresses. The activity levels of glutamate decarboxylase (GAD), an enzyme involved in GABA biosynthesis, are reported to increase during germination under salinity stress. However, it is not clear which tissues of the plant seeds are affected by GAD activity in response to salinity stress. In this study, the effects of salinity stress on the distribution of barley seeds GAD activity during germination were investigated. The mass spectrometry imaging (MSI) method was optimized, and the distribution of GAD activity in germinated seeds exposed to salinity stress at different germination stages from 12 to 48 h after imbibition was investigated. In this study, MSI was successfully applied to enzyme histochemistry to visualize the relative GAD activity in germinating barley seeds for the first time. The salinity stress increased the GAD activity, mostly due to the increase in relative GAD activity in the embryo. Higher GAD activity was detected in seeds exposed to salinity stress in the scutellum or aleurone layer, which are difficult to separate for extraction. This method can be used to clarify the role of GABA shunts, including GAD enzyme responses, in barley seeds under stress.

MALDI Mass Spectrometry Imaging Reveals the Existence of an N-Acyl-homoserine Lactone Quorum Sensing System in Pseudomonas putida Biofilms.

Quorum sensing (QS) is generally used to describe the process involving the release and recognition of signaling molecules, such as N-acyl-homoserine lactones, by bacteria to coordinate their response to population density and biofilm development. However, detailed information on the heterogeneity of QS metabolites in biofilms remains largely unknown. Here, we describe the utilization of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) to follow the production of specific metabolites, including QS metabolites, during Pseudomonas putida biofilm development. To do so, a method to grow an agar-based biofilm was first established, and MALDI-MSI was used to detect and visualize the distribution of QS metabolites in biofilms at different cultivation times. This study demonstrated that N-acyl-homoserine lactones are homogeneously produced in the early stages of P. putida biofilm formation. In contrast, the spatial distribution of quinolones and pyochelin correlated with the swarming motility of P. putida in mature biofilms. These two metabolites are involved in the production of extracellular polymeric substances and iron chelators. Our study thus contributes to establishing the specific temporal regulation and spatial distribution of N-acyl-homoserine lactone-related metabolites and quinolone and pyochelin in P. putida biofilms.

Detection of Changes in Monoamine Neurotransmitters by the Neonicotinoid Pesticide Imidacloprid Using Mass Spectrometry.

Monoamine neurotransmitters (MAs), including dopamine (DA) and serotonin (5-HT), regulate brain functions such as behavior, memory, and learning. Neonicotinoids are pesticides that are being used more frequently. Neonicotinoid exposure has been observed to produce neurological symptoms, such as altered spontaneous movements and anxiety-like behaviors, which are suspected to be caused by altered MA levels. However, current neurotoxicity tests are not sufficiently sensitive enough to make these determinations. In this study, we performed some behavior tests, and derivatization reagents to improve the ionization efficiency, which was applied to liquid chromatography mass spectrometry (LC-MS/MS) to reveal the effect of neonicotinoid administration on MAs in the brain. We orally administered the neonicotinoid imidacloprid (0, 10, and 50 mg/kg body weight) to C57BL/6NCrSlc mice. In the behavior tests, a decrease in activity was observed. The LC-MS/MS quantification of MAs in various brain regions showed a decrease in some MA levels in the olfactory bulb and the striatum. These results showed, for the first time, that even a low dose of imidacloprid could alter MA levels in various parts of the brain.

Mass spectrometry imaging enables visualization of the localization of glutamate decarboxylase activity in germinating legume seeds.

Visualizing the distribution of enzymes is vital for understanding physiological phenomena. Enzyme histochemistry is a technique used to investigate the localization of enzyme activity. However, the target is restricted to enzymes with easy-to-design artificial substrates that can develop color through reactions. Mass spectrometry imaging (MSI)-based enzyme histochemistry has been developed as a novel method to visualize enzyme localization. It can be applied to enzyme histochemistry as it detects products from the supplied substrate using enzymes present on the tissue sections. However, enzyme histochemistry using MSI has not been applied to plant tissue samples yet. Glutamate decarboxylase (GAD, EC: 4.1.1.15) is an enzyme that catalyzes the decarboxylation reaction of l-glutamic acid to produce γ-aminobutyric acid (GABA). GABA biosynthesis is important both in the field of food chemistry and plant physiology. This study focused on GAD during the legume germination process and successfully visualized GAD activity in legume seeds using MSI for the first time. Furthermore, the localization of GAD activity in the embryonic axis of germinated soybean seeds and alfalfa seeds could be visualized.

Fusobacterium nucleatum Metabolically Integrates Commensals and Pathogens in Oral Biofilms.

Fusobacterium nucleatum is a common constituent of the oral microbiota in both periodontal health and disease. Previously, we discovered ornithine cross-feeding between F. nucleatum and Streptococcus gordonii, where S. gordonii secretes ornithine via an arginine-ornithine antiporter (ArcD), which in turn supports the growth and biofilm development of F. nucleatum; however, broader metabolic aspects of F. nucleatum within polymicrobial communities and their impact on periodontal pathogenesis have not been addressed. Here, we show that when cocultured with S. gordonii, F. nucleatum increased amino acid availability to enhance the production of butyrate and putrescine, a polyamine produced by ornithine decarboxylation. Coculture with Veillonella parvula, another common inhabitant of the oral microbiota, also increased lysine availability, promoting cadaverine production by F. nucleatum. We confirmed that ArcD-dependent S. gordonii-excreted ornithine induces synergistic putrescine production, and mass spectrometry imaging revealed that this metabolic capability creates a putrescine-rich microenvironment on the surface of F. nucleatum biofilms. We further demonstrated that polyamines caused significant changes in the biofilm phenotype of a periodontal pathogen, Porphyromonas gingivalis, with putrescine accelerating the biofilm life cycle of maturation and dispersal. This phenomenon was also observed with putrescine derived from S. gordonii-F. nucleatum coculture. Lastly, analysis of plaque samples revealed cooccurrence of P. gingivalis with genetic modules for putrescine production by S. gordonii and F. nucleatum. Overall, our results highlight the ability of F. nucleatum to induce synergistic polyamine production within multispecies consortia and provide insight into how the trophic web in oral biofilm ecosystems can eventually shape disease-associated communities. IMPORTANCE Periodontitis is caused by a pathogenic shift in subgingival biofilm ecosystems, which is accompanied by alterations in microbiome composition and function, including changes in the metabolic activity of the biofilm, which comprises multiple commensals and pathogens. While Fusobacterium nucleatum is a common constituent of the supra- and subgingival biofilms, its metabolic integration within polymicrobial communities and the impact on periodontal pathogenesis are poorly understood. Here, we report that amino acids supplied by other commensal bacteria induce polyamine production by F. nucleatum, creating polyamine-rich microenvironments. Polyamines reportedly have diverse functions in bacterial physiology and possible involvement in periodontal pathogenesis. We show that the F. nucleatum-integrated trophic network yielding putrescine from arginine through ornithine accelerates the biofilm life cycle of Porphyromonas gingivalis, a periodontal pathogen, from the planktonic state through biofilm formation to dispersal. This work provides insight into how cooperative metabolism within oral biofilms can tip the balance toward periodontitis.

Visualization of dipeptidyl peptidase B enzymatic reaction in rice koji using mass spectrometry imaging.

Enzyme histochemistry via mass spectrometry imaging (MSI) has garnered attention as a straightforward approach for visualizing enzymatic reactions. While several studies in the medical and physiological fields have shown its promising application potential, its applicability to agricultural or food studies has not yet been demonstrated. Rice koji, known as an enzyme source for various fermented products, is a suitable model for demonstrating the applicability of this method to food-related materials. In this study, the enzymatic reaction of dipeptidyl peptidase B (DppB) in rice koji was visualized using MSI for the first time. The method was optimized and applied to investigate the effects of rice variety, polishing ratio, and cultivation time on the location of the DppB reaction. The DppB enzymatic reaction was found to occur in different locations in each of the two rice varieties, Yamadanishiki and Hakutsurunishiki. The polishing ratio also affected the distribution of the DppB enzymatic reactions. Furthermore, a time-course investigation of rice koji cultivation revealed that while the location of the reaction was largely associated with mycelial penetration, the structure and features of the rice grain may also affect the location of the enzymatic reaction. In summary, these results demonstrate the applicability of enzyme histochemistry by MSI to food-related materials.

Mass Spectrometry Imaging.

Mass spectrometry imaging (MSI) is a technique for obtaining information on the distribution of various molecules by performing mass spectrometry directly on the sample surface. The applications range from small molecules such as lipids to large molecules such as proteins. It is also possible to detect pharmaceuticals and elemental isotopes in interstellar matter. This review will introduce various applications of MSI with examples.

Metabolite alteration analysis of acetaminophen-induced liver injury using a mass microscope.

Acetaminophen (APAP)-induced liver injury (APAP-ILI), which occurs during APAP overdose, has been extensively studied. The production of N-acetyl-p-benzoquinone imine (NAPQI), the reactive metabolite of APAP, primarily contributes to liver injury. However, the mechanism underlying APAP-ILI has not been fully characterized. For further clarification, it is important to consider drug localization and endogenous substances in the injured liver. Herein, we show the localization of NAPQI metabolites and the injury site-specific changes in endogenous substances in the rat liver following APAP overdose using a mass microscope. Our results of on-tissue derivatization matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) showed that the glutathione metabolite of APAP, a detoxified metabolite of NAPQI, localized in the damaged central vein region in the rat liver following APAP administration. Moreover, in the conventional MALDI-MSI, the intensities of some phospholipids, phosphocreatine, and ceramides decreased or increased in the damaged regions compared with those in non-damaged regions. Phosphocreatine was localized in the damaged cells, whereas its related mitochondrial creatine kinase was localized in the non-damaged cells. These results are expected to contribute to further elucidation of the mechanisms underlying APAP-ILI. Our findings illustrate the localization of NAPQI-related metabolites and endogenous molecules associated with APAP-ILI, which may be related to apoptosis or metabolic adaptation ultimately protecting the cells. As MALDI-MSI can analyze and differentiate regions with tissue damage, it is a valuable tool for analyzing the mechanism underlying drug-induced liver injury to identify novel biomarkers.