Desorption Electrospray Ionization Mass Spectrometry Imaging Allows Spatial Localization of Changes in Acetaminophen Metabolism in the Liver after Intervention with 4-Methylpyrazole

High-Specificity Imaging Mass Spectrometry

Imaging mass spectrometry (IMS) enables highly multiplexed, untargeted tissue mapping for a broad range of molecular classes, facilitating in situ biological discovery. Yet, challenges persist in molecular specificity, which is the ability to discern one molecule from another, and spatial specificity, which is the ability to link untargeted imaging data to specific tissue features. Instrumental developments have dramatically improved IMS spatial resolution, allowing molecular observations to be more readily associated with distinct tissue features across spatial scales, ranging from larger anatomical regions to single cells. High-performance mass analyzers and systems integrating ion mobility technologies are also becoming more prevalent, further improving molecular coverage and the ability to discern chemical identity. This review provides an overview of recent advancements in high-specificity IMS that are providing critical biological context to untargeted molecular imaging, enabling integrated analyses, and addressing advanced biomedical research applications.

Spatial analysis of renal acetaminophen metabolism and its modulation by 4-methylpyrazole with DESI mass spectrometry imaging

Acute kidney injury (AKI) is a common complication in acetaminophen (APAP) overdose patients and can negatively impact prognosis. Unfortunately, N-acetylcysteine, which is the standard of care for the treatment of APAP hepatotoxicity does not prevent APAP-induced AKI. We have previously demonstrated the renal metabolism of APAP and identified fomepizole (4-methylpyrazole, 4MP) as a therapeutic option to prevent APAP-induced nephrotoxicity. However, the kidney has several functionally distinct regions, and the dose-dependent effects of APAP on renal response and regional specificity of APAP metabolism are unknown. These aspects were examined in this study using C57BL/6J mice treated with 300-1200 mg/kg APAP and mass spectrometry imaging (MSI) to provide spatial cues relevant to APAP metabolism and the effects of 4MP. We find that renal APAP metabolism and generation of the nonoxidative (APAP-GLUC and APAP-SULF) and oxidative metabolites (APAP-GSH, APAP-CYS, and APAP-NAC) were dose-dependently increased in the kidney. This was recapitulated on MSI which revealed that APAP overdose causes an accumulation of APAP and APAP GLUC in the inner medulla and APAP-CYS in the outer medulla of the kidney. APAP-GSH, APAP-NAC, and APAP-SULF were localized mainly to the outer medulla and the cortex where CYP2E1 expression was evident. Interestingly, APAP also induced a redistribution of reduced GSH, with an increase in oxidized GSH within the kidney cortex. 4MP ameliorated these region-specific variations in the formation of APAP metabolites in renal tissue sections. In conclusion, APAP metabolism has a distinct regional distribution within the kidney, the understanding of which provides insight into downstream mechanisms of APAP-induced nephrotoxicity.

Acetaminophen Hepatotoxicity: Paradigm for Understanding Mechanisms of Drug-Induced Liver Injury

Acetaminophen (APAP) overdose is the clinically most relevant drug hepatotoxicity in western countries, and, because of translational relevance of animal models, APAP is mechanistically the most studied drug. This review covers intracellular signaling events starting with drug metabolism and the central role of mitochondrial dysfunction involving oxidant stress and peroxynitrite. Mitochondria-derived endonucleases trigger nuclear DNA fragmentation, the point of no return for cell death. In addition, adaptive mechanisms that limit cell death are discussed including autophagy, mitochondrial morphology changes, and biogenesis. Extensive evidence supports oncotic necrosis as the mode of cell death; however, a partial overlap with signaling events of apoptosis, ferroptosis, and pyroptosis is the basis for controversial discussions. Furthermore, an update on sterile inflammation in injury and repair with activation of Kupffer cells, monocyte-derived macrophages, and neutrophils is provided. Understanding these mechanisms of cell death led to discovery of N-acetylcysteine and recently fomepizole as effective antidotes against APAP toxicity.

Recent developments and applications of ambient mass spectrometry imaging in pharmaceutical research: an overview

The application of ambient mass spectrometry imaging "MSI" is expanding in the areas of fundamental research on drug delivery and multiple phases of the process of identifying and developing drugs. Precise monitoring of a drug's pharmacological workflows, such as intake, distribution, metabolism, and discharge, is made easier by MSI's ability to determine the concentrations of the initiating drug and its metabolites across dosed samples without losing spatial data. Lipids, glycans, and proteins are just a few of the many phenotypes that MSI may be used to concurrently examine. Each of these substances has a particular distribution pattern and biological function throughout the body. MSI offers the perfect analytical tool for examining a drug's pharmacological features, especially in vitro and in vivo effectiveness, security, probable toxic effects, and putative molecular pathways, because of its high responsiveness in chemical and physical environments. The utilization of MSI in the field of pharmacy has further extended from the traditional tissue examination to the early stages of drug discovery and development, including examining the structure-function connection, high-throughput capabilities in vitro examination, and ex vivo research on individual cells or tumor spheroids. Additionally, an enormous array of endogenous substances that may function as tissue diagnostics can be scanned simultaneously, giving the specimen a highly thorough characterization. Ambient MSI techniques are soft enough to allow for easy examination of the native sample to gather data on exterior chemical compositions. This paper provides a scientific and methodological overview of ambient MSI utilization in research on pharmaceuticals.

Lack of mitochondrial Cyp2E1 drives acetaminophen-induced ER stress-mediated apoptosis in mouse and human kidneys: Inhibition by 4-methylpyrazole but not N-acetylcysteine

Acetaminophen (APAP) overdose causes liver injury and acute liver failure, as well as acute kidney injury, which is not prevented by the clinical antidote N-acetyl-L-cysteine (NAC). The absence of therapeutics targeting APAP-induced nephrotoxicity is due to gaps in understanding the mechanisms of renal injury. APAP metabolism through Cyp2E1 drives cell death in both the liver and kidney. We demonstrate that Cyp2E1 is localized to the proximal tubular cells in mouse and human kidneys. Virtually all the Cyp2E1 in kidney cells is in the endoplasmic reticulum (ER), not in mitochondria. By contrast, hepatic Cyp2E1 is in both the ER and mitochondria of hepatocytes. Consistent with this subcellular localization, a dose of 600 mg/kg APAP in fasted C57BL/6J mice induced the formation of APAP protein adducts predominantly in mitochondria of hepatocytes, but the ER of the proximal tubular cells of the kidney. We found that reactive metabolite formation triggered ER stress-mediated activation of caspase-12 and apoptotic cell death in the kidney. While co-treatment with 4-methylpyrazole (4MP; fomepizole) or the caspase inhibitor Ac-DEVD-CHO prevented APAP-induced cleavage of procaspase-12 and apoptosis in the kidney, treatment with NAC had no effect. These mechanisms are clinically relevant because 4MP but not NAC also significantly attenuated APAP-induced apoptotic cell death in primary human kidney cells. We conclude that reactive metabolite formation by Cyp2E1 in the ER results in sustained ER stress that causes activation of procaspase-12, triggering apoptosis of proximal tubular cells, and that 4MP but not NAC may be an effective antidote against APAP-induced kidney injury.

Detection of Distinct Distributions of Acetaminophen and Acetaminophen-Cysteine in Kidneys up to 10 μm Resolution and Identification of a Novel Acetaminophen Metabolite Using an AP-MALDI Imaging Mass Microscope

Drug distribution studies in tissue are crucial for understanding the pharmacokinetics and potential toxicity of drugs. Recently, matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) has gained attention for drug distribution studies due to its high sensitivity, label-free nature, and ability to distinguish between parent drugs, their metabolites, and endogenous molecules. Despite these advantages, achieving high spatial resolution in drug imaging is challenging. Importantly, many drugs and metabolites are rarely detectable by conventional vacuum MALDI-MSI because of their poor ionization efficiency. It has been reported that acetaminophen (APAP) and one of its major metabolites, APAP-Cysteine (APAP-CYS), cannot be detected by vacuum MALDI-MSI without derivatization. In this context, we showed the distribution of both APAP and APAP-CYS in kidneys at high spatial resolution (25 and 10 μm) by employing an atmospheric pressure-MALDI imaging mass microscope without derivatization. APAP was highly accumulated in the renal pelvis 1 h after drug administration, while APAP-CYS exhibited characteristic distributions in the outer medulla and renal pelvis at both 30 min and 1 h after administration. Interestingly, cluster-like distributions of APAP and APAP-CYS were observed in the renal pelvis at 10 μm spatial resolution. Additionally, a novel APAP metabolite, tentatively coined as APAP-butyl sulfate (APAP-BS), was identified in the kidney, brain, and liver by combining MSI and tandem MSI. For the first time, our study revealed differential distributions of APAP, APAP-CYS (in kidneys), and APAP-BS (in kidney, brain, and liver) and is believed to enhance the understanding of the pharmacokinetics and potential nephrotoxicity of this drug.

Applications of ambient ionization mass spectrometry in 2022: An annual review

The development of ambient ionization mass spectrometry (AIMS) has transformed analytical science, providing the means of performing rapid analysis of samples in their native state, both in and out of the laboratory. The capacity to eliminate sample preparation and pre-MS separation techniques, leading to true real-time analysis, has led to AIMS naturally gaining a broad interest across the scientific community. Since the introduction of the first AIMS techniques in the mid-2000s, the field has exploded with dozens of novel ion sources, an array of intriguing applications, and an evident growing interest across diverse areas of study. As the field continues to surge forward each year, ambient ionization techniques are increasingly becoming commonplace in laboratories around the world. This annual review provides an overview of AIMS techniques and applications throughout 2022, with a specific focus on some of the major fields of research, including forensic science, disease diagnostics, pharmaceuticals and food sciences. New techniques and methods are introduced, demonstrating the unwavering drive of the analytical community to further advance this exciting field and push the boundaries of what analytical chemistry can achieve.

Quantitative Mass Spectrometry Imaging of Bleomycin in Skin Using a Mimetic Tissue Model for Calibration

The aim of Quantitative mass spectrometry imaging (Q-MSI) is to provide distribution analysis and quantitation from one single mass-spectrometry-based experiment, and several quantitation methods have been devised for Q-MSI. Mimetic tissue models based on spiked tissue homogenates are considered one of the most accurate ways to perform Q-MSI, since the analyte is present in a well-defined concentration in a sample matrix highly similar to the one of the unknown sample to be analyzed. The delivery of drugs in skin is among the most frequent types of pharmaceutical MSI studies. Here, a mimetic tissue model is extended for use on the skin, which, due to its high collagen content, is different from most other tissue as the homogenates become extremely viscous. A protocol is presented which overcomes this by the addition of water and the handling of the homogenate at an elevated temperature where the viscosity is lower. Using a mimetic tissue model, a method was developed for the quantitative imaging of bleomycin in skin. To compensate for the signal drift and the inhomogeneities in the skin, an internal standard was included in the method. The method was tested on skin from a pig which had had an electropneumatic injection of bleomycin into the skin. Quantification was made at several regions in a cross section of the skin at the injection site, and the results were compared to the results of a quantitative LC-MS on a neighboring tissue biopsy from the same animal experiment. The overall tissue concentration determined by the LC-MS was within the range of the different regions quantified by the Q-MSI. As the model provides the results of the same order of magnitude as a LC-MS, it can either be used to replace LC-MS in skin studies where MSI and LC-MS are today carried out in combination, or it can add quantitative information to skin studies which are otherwise carried out by MSI alone.