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

Spatial metabolomics reveal metabolic alternations in the injured mice kidneys induced by triclocarban treatment

Triclocarban (TCC) is a common antimicrobial agent that has been widely used in medical care. Given the close association between TCC treatment and metabolic disorders, we assessed whether long-term treatment to TCC at a human-relevant concentration could induce nephrotoxicity by disrupting the metabolic levels in a mouse model. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was applied to investigate the alterations in the spatial distributions and abundances of TCC, endogenous and exogenous metabolites in the kidney after TCC treatment. The results showed that TCC treatment induced the changes in the organ weight, organ coefficient and histopathology of the mouse kidney. MSI data revealed that TCC accumulated in all regions of the kidney, while its five metabolites mainly distributed in the cortex regions. The abundances of 79 biomolecules associated with pathways of leukotriene E4 metabolism, biosynthesis and degradation of glycerophospholipids and glycerolipids, ceramide-to-sphingomyelin signaling were significantly altered in the kidney after TCC treatment. These biomolecules showed distinctive distributions in the kidney and displayed a favorable spatial correlation with the pathological damage. This work offers new insights into the related mechanisms of TCC-induced nephrotocicity and exhibits the potential of MALDI-MSI-based spatial metabolomics as a promising approach for the risk assessment of agents in medical care.

eLIMS: Ensemble Learning-Based Spatial Segmentation of Mass Spectrometry Imaging to Explore Metabolic Heterogeneity

Spatial segmentation is an essential processing method for image analysis aiming to identify the characteristic suborgans or microregions from mass spectrometry imaging (MSI) data, which is critical for understanding the spatial heterogeneity of biological information and function and the underlying molecular signatures. Due to the intrinsic characteristics of MSI data including spectral nonlinearity, high-dimensionality, and large data size, the common segmentation methods lack the capability for capturing the accurate microregions associated with biological functions. Here we proposed an ensemble learning-based spatial segmentation strategy, named eLIMS, that combines a randomized unified manifold approximation and projection (r-UMAP) dimensionality reduction module for extracting significant features and an ensemble pixel clustering module for aggregating the clustering maps from r-UMAP. Three MSI datasets are used to evaluate the performance of eLIMS, including mouse fetus, human adenocarcinoma, and mouse brain. Experimental results demonstrate that the proposed method has potential in partitioning the heterogeneous tissues into several subregions associated with anatomical structure, i.e., the suborgans of the brain region in mouse fetus data are identified as dorsal pallium, midbrain, and brainstem. Furthermore, it effectively discovers critical microregions related to physiological and pathological variations offering new insight into metabolic heterogeneity.

Analysis of cantharidin-induced kidney injury and the protective mechanism of resveratrol in mice determined by liquid chromatography/mass spectrometry-based metabonomics

Cantharidin (CTD) is the main active component in the traditional Chinese medicine Mylabris and an effective anti-tumor agent. However, it is relatively toxic and exhibits nephrotoxicity, which limits its clinical use. However, its toxic mechanism is not clear. The toxic effects of CTD exposure on the kidney and the protective effect of resveratrol (RES) were studied in a mouse model, by determination of serum biochemical and renal antioxidant indicators, histopathological and ultrastructural observation, and metabonomics. After CTD exposure, serum uric acid, creatinine, and tissue oxidative stress indicators increased, and the renal glomerular and tubular epithelial cells showed clear pathological damage. Ultrastructure observation revealed marked mitochondrial swelling, endoplasmic reticulum dilation, and the presence of autophagy lysosomes in glomerular epithelial cells. RES ameliorated the renal injury induced by CTD. Metabonomics analysis indicated that CTD can induce apoptosis and oxidative damage in kidney cells, mainly by disrupting sphingolipid and glutathione metabolism, increasing sphingosine and sphingomyelin levels, and decreasing glutathione levels. RES counteracts these effects by regulating renal cell proliferation, the inflammatory response, oxidative stress, and apoptosis, by improving the levels of phosphatidylcholine (PC), LysoPC, and lysophosphatidyl glycerol in the glycerophospholipid metabolism pathway, thereby reducing CTD-induced nephrotoxicity. The mechanisms of CTD-induced renal injury and the protective effect of RES were revealed by metabonomics, providing a basis for evaluating clinical treatment regimens to reduce CTD-induced nephrotoxicity.

A NiO-nanostructure-based electrochemical sensor functionalized with supramolecular structures for the ultra-sensitive detection of the endocrine disruptor bisphenol S in an aquatic environment

Herein, NiO nanoparticles (NPs) functionalized with a para-hexanitrocalix[6]arene derivative (p-HNC6/NiO) were synthesized by using a facile method and applied as a selective electrochemical sensor for the determination of bisphenol S (BPS) in real samples. Moreover, the functional interactions, phase purities, surface morphologies and elemental compositions of the synthesized p-HNC6/NiO NPs were investigated via advanced analytical tools, such as Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Additionally, the synthesized p-HNC6/NiO NPs were cast on the surface of a bare glassy carbon electrode (GCE) via a drop casting method, which resulted in uniform deposition of p-HNC6/NiO/GCE over the surface of the GCE. Additionally, the developed p-HNC6/NiO/GCE sensor demonstrated an outstanding electrochemical response to BPS under optimized conditions, including a supporting electrolyte, a Briton-Robinson buffer electrolyte at pH 4, a scan rate of 110 mV s-1 and a potential window of between -0.2 and 1.0 V. The wide linear dynamic range was optimized to 0.8-70 μM to obtain a brilliant linear calibration curve for BPS. The limit of detection (LOD) and limit of quantification (LOQ) of the developed sensor were estimated to be 0.0059 and 0.019 μM, respectively, which are lower than those of reported sensors for BPS. The feasibility of the developed method was successfully assessed by analyzing the content of BPS in waste water samples, and good recoveries were achieved.

Advances in mass spectrometry imaging for spatial cancer metabolomics

Mass spectrometry (MS) has become a central technique in cancer research. The ability to analyze various types of biomolecules in complex biological matrices makes it well suited for understanding biochemical alterations associated with disease progression. Different biological samples, including serum, urine, saliva, and tissues have been successfully analyzed using mass spectrometry. In particular, spatial metabolomics using MS imaging (MSI) allows the direct visualization of metabolite distributions in tissues, thus enabling in-depth understanding of cancer-associated biochemical changes within specific structures. In recent years, MSI studies have been increasingly used to uncover metabolic reprogramming associated with cancer development, enabling the discovery of key biomarkers with potential for cancer diagnostics. In this review, we aim to cover the basic principles of MSI experiments for the nonspecialists, including fundamentals, the sample preparation process, the evolution of the mass spectrometry techniques used, and data analysis strategies. We also review MSI advances associated with cancer research in the last 5 years, including spatial lipidomics and glycomics, the adoption of three-dimensional and multimodal imaging MSI approaches, and the implementation of artificial intelligence/machine learning in MSI-based cancer studies. The adoption of MSI in clinical research and for single-cell metabolomics is also discussed. Spatially resolved studies on other small molecule metabolites such as amino acids, polyamines, and nucleotides/nucleosides will not be discussed in the context.

Assessment of MALDI matrices for the detection and visualization of phosphatidylinositols and phosphoinositides in mouse kidneys through matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI)

Phosphatidylinositols and their phosphorylated derivatives, known as phosphoinositides, are crucial in cellular processes, with their abnormalities linked to various diseases. Thus, identifying and measuring phosphoinositide levels in tissues are crucial for understanding their contributions to cellular processes and disease development. One powerful technique for mapping the spatial distribution of molecules in biological samples is matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). This technique allows for the simultaneous detection and analysis of multiple lipid classes in situ, making it invaluable for unbiased lipidomic studies. However, detecting phosphoinositides with MALDI-MSI is challenging due to their relatively low abundance in tissues and complex matrix effects. Addressing this, our study focused on optimizing matrix selection and thickness for better detection of phosphatidylinositols and their phosphorylated forms in mouse kidney tissues. Various matrices were assessed, including 9AA, DAN, CMBT, and DHA, adjusting their coating to improve ionization efficiency. Our results demonstrate that DAN, DHA, and CMBT matrices produced high-intensity chemical images of phosphatidylinositol distributions within kidney sections. These matrices, particularly DAN, DHA, and CMBT, allowed the identification of even low-abundance phosphoinositides, through tentative identifications. Notably, DAN and DHA served as optimal candidates due to their prominent detection and ability to map a majority of phosphatidylinositol species, while CMBT showed potential detection capability for phosphatidylinositol triphosphate compounds. These findings not only provide valuable insights for future research on the involvement of phosphoinositides in kidney pathophysiology, but also propose the use of the identified optimal matrices, particularly DAN and DHA, as the preferred choices for enhanced detection and mapping of these lipid species in future studies.

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.

Chronic cadmium exposure triggered ferroptosis by perturbing the STEAP3-mediated glutathione redox balance linked to altered metabolomic signatures in humans

Cadmium (Cd), a predominant environmental pollutant, is a canonical toxicant that acts on the kidneys. However, the nephrotoxic effect and underlying mechanism activated by chronic exposure to Cd remain unclear. In the present study, male mice (C57BL/6J, 8 weeks) were treated with 0.6 mg/L cadmium chloride (CdCl2) administered orally for 6 months, and tubular epithelial cells (TCMK-1 cells) were treated with low-dose (1, 2, and 3 μM) CdCl2 for 72 h (h). Our study results revealed that environmental Cd exposure triggered ferroptosis and renal dysfunction. Spatially resolved metabolomics enabled delineation of metabolic profiles and visualization of the disruption to glutathione homeostasis related to ferroptosis in mouse kidneys. Multiomics analysis revealed that chronic Cd exposure induced glutathione redox imbalance that depended on STEAP3-driven lysosomal iron overload. In particular, glutathione metabolic reprogramming linked to ferroptosis emerged as a metabolic hallmark in the blood of Cd-exposed workers. In conclusion, this study provides the first evidence indicating that chronic Cd exposure triggers ferroptosis and renal dysfunction that depend on STEAP3-mediated glutathione redox imbalance, greatly increasing our understanding of the metabolic reprogramming induced by Cd exposure in the kidneys and providing novel clues linking chronic Cd exposure to nephrotoxicity.

State-of-the-art mass spectrometry imaging applications in biomedical research

Mass spectrometry imaging has advanced from a niche technique to a widely applied spatial biology tool operating at the forefront of numerous fields, most notably making a significant impact in biomedical pharmacological research. The growth of the field has gone hand in hand with an increase in publications and usage of the technique by new laboratories, and consequently this has led to a shift from general MSI reviews to topic-specific reviews. Given this development, we see the need to recapitulate the strengths of MSI by providing a more holistic overview of state-of-the-art MSI studies to provide the new generation of researchers with an up-to-date reference framework. Here we review scientific advances for the six largest biomedical fields of MSI application (oncology, pharmacology, neurology, cardiovascular diseases, endocrinology, and rheumatology). These publications thereby give examples for at least one of the following categories: they provide novel mechanistic insights, use an exceptionally large cohort size, establish a workflow that has the potential to become a high-impact methodology, or are highly cited in their field. We finally have a look into new emerging fields and trends in MSI (immunology, microbiology, infectious diseases, and aging), as applied MSI is continuously broadening as a result of technological breakthroughs.

Mass Spectrometry Detects Sphingolipid Metabolites for Discovery of New Strategy for Cancer Therapy from the Aspect of Programmed Cell Death

Sphingolipids, a type of bioactive lipid, play crucial roles within cells, serving as integral components of membranes and exhibiting strong signaling properties that have potential therapeutic implications in anti-cancer treatments. However, due to the diverse group of lipids and intricate mechanisms, sphingolipids still face challenges in enhancing the efficacy of different therapy approaches. In recent decades, mass spectrometry has made significant advancements in uncovering sphingolipid biomarkers and elucidating their impact on cancer development, progression, and resistance. Primary sphingolipids, such as ceramide and sphingosine-1-phosphate, exhibit contrasting roles in regulating cancer cell death and survival. The evasion of cell death is a characteristic hallmark of cancer cells, leading to treatment failure and a poor prognosis. The escape initiates with long-established apoptosis and extends to other programmed cell death (PCD) forms when patients experience chemotherapy, radiotherapy, and/or immunotherapy. Gradually, supportive evidence has uncovered the fundamental molecular mechanisms underlying various forms of PCD leading to the development of innovative molecular, genetic, and pharmacological tools that specifically target sphingolipid signaling nodes. In this study, we provide a comprehensive overview of the sphingolipid biomarkers revealed through mass spectrometry in recent decades, as well as an in-depth analysis of the six main forms of PCD (apoptosis, autophagy, pyroptosis, necroptosis, ferroptosis, and cuproptosis) in aspects of tumorigenesis, metastasis, and tumor response to treatments. We review the corresponding small-molecule compounds associated with these processes and their potential implications in cancer therapy.

Adverse effects of triclosan on kidney in mice: Implication of lipid metabolism disorders

Triclosan (TCS) is a ubiquitous antimicrobial used in daily consumer products. Previous reports have shown that TCS could induce hepatotoxicity, endocrine disruption, disturbance on immune function and impaired thyroid function. Kidney is critical in the elimination of toxins, while the effects of TCS on kidney have not yet been well-characterized. The aim of the present study was to investigate the effects of TCS exposure on kidney function and the possible underlying mechanisms in mice. Male C57BL/6 mice were orally exposed to TCS with the doses of 10 and 100 mg/(kg•day) for 13 weeks. TCS was dissolved in dimethyl sulfoxide (DMSO) and diluted by corn oil for exposure. Corn oil containing DMSO was used as vehicle control. Serum and kidney tissues were collected for study. Biomarkers associated with kidney function, oxidative stress, inflammation and fibrosis were assessed. Our results showed that TCS could cause renal injury as was revealed by increased levels of renal function markers including serum creatinine, urea nitrogen and uric acid, as well as increased oxidative stress, pro-inflammatory cytokines and fibrotic markers in a dose dependent manner, which were more significantly in 100 mg/(kg•day) group. Mass spectrometry-based analysis of metabolites related with lipid metabolism demonstrated the occurrence of lipid accumulation and defective fatty acid oxidation in 100 mg/(kg•day) TCS-exposed mouse kidney. These processes might lead to lipotoxicity and energy depletion, thus resulting in kidney fibrosis and functional decline. Taken together, the present study demonstrated that TCS could induce lipid accumulation and fatty acid metabolism disturbance in mouse kidney, which might contribute to renal function impairment. The present study further widens our insights into the adverse effects of TCS.

Divide and Conquer: A Flexible Deep Learning Strategy for Exploring Metabolic Heterogeneity from Mass Spectrometry Imaging Data

Research on metabolic heterogeneity provides an important basis for the study of the molecular mechanism of a disease and personalized treatment. The screening of metabolism-related sub-regions that affect disease development is essential for the more focused exploration on disease progress aberrant phenotypes, even carcinogenesis and metastasis. The mass spectrometry imaging (MSI) technique has distinct advantages to reveal the heterogeneity of an organism based on in situ molecular profiles. The challenge of heterogeneous analysis has been to perform an objective identification among biological tissues with different characteristics. By introducing the divide-and-conquer strategy to architecture design and application, we establish here a flexible unsupervised deep learning model, called divide-and-conquer (dc)-DeepMSI, for metabolic heterogeneity analysis from MSI data without prior knowledge of histology. dc-DeepMSI can be used to identify either spatially contiguous regions of interest (ROIs) or spatially sporadic ROIs by designing two specific modes, spat-contig and spat-spor. Comparison results on fetus mouse data demonstrate that the dc-DeepMSI outperforms state-of-the-art MSI segmentation methods. We demonstrate that the novel learning strategy successfully obtained sub-regions that are statistically linked to the invasion status and molecular phenotypes of breast cancer as well as organizing principles during developmental phase.

Relationship between emergent BPA-substitutes and renal and cardiovascular diseases in adult population

Plastic waste pollution is one of the leading environmental problems of modern society. Its use, disposal, and recycling lead to the release of xenobiotic compounds such as bisphenol A (BPA), a known endocrine disruptor related to numerous pathologies. Due to the new restrictions on its use, it is gradually being replaced by derived molecules, such as bisphenol F or S (BPF or BPS), whose health risks have not yet been adequately studied. In the present work, significant relationships between the new BPA substitute molecules and renal and cardiovascular diseases have been detected by performing binomial and multinomial logistic regressions in one of the world's largest cohorts of urinary phenols. The results have shown a significant relationship between urinary BPF and renal function or heart disease (specifically congestive heart failure). Urinary BPS has shown a positive relationship with the risk of hypertension and a negative relationship with kidney disease. Consequently, applying new substitute molecules could imply potential health risks equivalent to BPA.

iSegMSI: An Interactive Strategy to Improve Spatial Segmentation of Mass Spectrometry Imaging Data

Spatial segmentation is a critical procedure in mass spectrometry imaging (MSI)-based biochemical analysis. However, the commonly used unsupervised MSI segmentation methods may lead to inappropriate segmentation results as the MSI data is characterized by high dimensionality and low signal-to-noise ratio. This process can be improved by the incorporation of precise prior knowledge, which is hard to obtain in most cases. In this study, we show that the incorporation of partial or coarse prior knowledge from different sources such as reference images or biological knowledge may also help to improve MSI segmentation results. Here, we propose a novel interactive segmentation strategy for MSI data called iSegMSI, which incorporates prior information in the form of scribble-regularization of the unsupervised model to fine-tune the segmentation results. By using two typical MSI data sets (including a whole-body mouse fetus and human thyroid cancer), the present results demonstrate the effectiveness of the iSegMSI strategy in improving the MSI segmentations. Specifically, the method can be used to subdivide a region into several subregions specified by the user-defined scribbles or to merge several subregions into a single region. Additionally, these fine-tuned results are highly tolerant to the imprecision of the scribbles. Our results suggest that the proposed iSegMSI method may be an effective preprocessing strategy to facilitate the analysis of MSI data.

iMS2Net: A multiscale networking methodology to decipher metabolic synergy of organism

The metabolic responses of organism to external stimuli are characterized by the multicellular- and multiorgan-based synergistic regulation. Network analysis is a powerful tool to investigate this multiscale interaction. The imaging mass spectrometry (iMS)-based spatial omics provides multidimensional and multiscale information, thus offering the possibility of network analysis to investigate metabolic response of organism to environmental stimuli. We present iMS dataset-sourced multiscale network (iMS2Net) strategy to uncover prenatal environmental pollutant (PM2.5)-induced metabolic responses in the scales of cell and organ from metabolite abundances and metabolite-metabolite interaction using mouse fetal model, including metabotypic similarity, metabolic vulnerability, metabolic co-variability and metabolic diversity within and between organs. Furthermore, network-based analysis results confirm close associations between lipid metabolites and inflammatory cytokine release. This networking methodology elicits particular advantages for modeling the dynamic and adaptive processes of organism under environmental stresses or pathophysiology and provides molecular mechanism to guide the occurrence and development of systemic diseases.

Spatially revealed perfluorooctane sulfonate-induced nephrotoxicity in mouse kidney using atmospheric pressure MALDI mass spectrometry imaging

Perfluorooctane sulfonate (PFOS), an emerging environmental persistent pollutant, has attracted extensive attention due to its potential nephrotoxicity. However, little is known about the spatial variations of lipid metabolism associated with PFOS exposure. In this study, atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-MALDI MSI) was used to reveal the spatial distributions of PFOS and its adverse effect on lipid metabolism directly in mouse kidney sections. We have observed that PFOS accumulated in the renal pelvis and outer cortex regions, with some found in the medulla and inner cortex regions. Hematoxylin and eosin (H&E) staining results also demonstrated that the accumulation of PFOS caused damage to the mouse kidney, which was consistent with AP-MALDI MSI results. Furthermore, a total of 42 lipids were shown to be significantly different in the spatial distribution patterns and variations between control and PFOS exposure mice groups, including the significant down-regulation of lyso-glycerophospholipids (Lyso-GPs), phosphatidic acids (PA), phosphatidylcholines (PC), phosphatidylethanolamines (PE), phosphatidylserines (PS) sphingomyelins (SM) and sulfatides (ST) in renal medulla or cortex region of mouse kidney sections, and remarkable up-regulation of cholesterol and phosphatidylinositols (PI) in the cortex regions of mouse kidney sections. The AP-MALDI MSI provides a new tool to explore spatial distributions and variations of the endogenous metabolites for the risk assessment of environmental pollutants.

Laser Ablation Electrospray Ionization Achieves 5 μm Resolution Using a Microlensed Fiber

A pulsed (10 Hz) infrared (IR) (1064 nm) laser is focused on a sample surface by means of a microlensed fiber. Analytes desorbed from the surface are captured by charged microdroplets before entering a mass spectrometer. By translating the sample surface, a chemical map is generated with a resolution of 5 μm, defined as the change from 20 to 80% of the analyte signal intensity. As a demonstration of the power of this new imaging technique, analytes from a parsnip root section are imaged and compared with that obtained from conventional laser ablation electrospray ionization mass spectrometry. The improvement in spatial resolution is about a factor of 20.

A study on bisphenol S induced nephrotoxicity and assessment of altered downstream kidney metabolites using gas chromatography-mass spectrometry based metabolomics

The global use of bisphenol S (BPS) has now been significantly increased for commensurate utilization as a substitute for BPA for its regulatory concerns. Though, previous reports indicated that BPS been also appeared as a toxic congener comparable to BPA. In the present study, we determined nephrotoxicity condition induced due to BPS exposure. Results indicated that BPS significantly promoted histopathological disturbance in the kidney, and altered the levels of biomarkers of kidney damage in serum and urine samples of Wistar rats. It is also indicated that BPS altered the expression of kidney damage biomarkers associated with glomerular and tubular injury. Additionally, we determined the perturbation of kidney metabolites in the underlying pathophysiological response of kidney injury due to BPS exposure. Gas chromatography-mass spectrometry based untargeted metabolomics exhibited 20 significantly perturbed metabolites. Moreover, metabolic pathway analysis revealed significant disturbance in the TCA cycle and pyruvate metabolism pathways.

Maltose-functional metal-organic framework assisted laser desorption/ionization mass spectrometry for small biomolecule determination

A series of functional metal-organic frameworks (MOFs) were facilely prepared through an one-pot procedure or post-synthetic modification strategy and used as matrices in laser desorption ionization mass spectrometry (LDI-MS). Compared with traditional organic matrices and other MOFs, maltose-functional MOF MIL-101-maltose demonstrated ultrahigh ionization efficiency, free matrix background, uniform crystallization, and good dispersibility. A simple, general, and efficient LDI-MS platform was developed for rapid detection of various small biomolecules using MIL-101-maltose as matrix, providing several advantages including low sample consumption of 500 nL, short analysis time of few seconds, strong salt tolerance (500 mM NaCl), and satisfactory reproducibility. The MIL-101-maltose matrix was used for serum glucose determination and successfully distinguished the diabetic patients from the healthy controls. This work provides a generic LDI-MS platform for fast determination of small biomolecules with high potential in clinical diagnosis and disease monitoring.

MALDI mass spectrometry imaging workflow for the aquatic model organisms Danio rerio and Daphnia magna

Lipids play various essential roles in the physiology of animals. They are also highly dependent on cellular metabolism or status. It is therefore crucial to understand to which extent animals can stabilize their lipid composition in the presence of external stressors, such as chemicals that are released into the environment. We developed a MALDI MS imaging workflow for two important aquatic model organisms, the zebrafish (Danio rerio) and water flea (Daphnia magna). Owing to the heterogeneous structure of these organisms, developing a suitable sample preparation workflow is a highly non-trivial but crucial part of this work and needs to be established first. Relevant parameters and practical considerations in order to preserve tissue structure and composition in tissue sections are discussed for each application. All measurements were based on high mass accuracy enabling reliable identification of imaged compounds. In zebrafish we demonstrate that a detailed mapping between histology and simultaneously determined lipid composition is possible at various scales, from extended structures such as the brain or gills down to subcellular structures such as a single axon in the central nervous system. For D. magna we present for the first time a MALDI MSI workflow, that demonstrably maintains tissue integrity during cryosectioning of non-preserved samples, and allows the mapping of lipids in the entire body and the brood chamber inside the carapace. In conclusion, the lipid signatures that we were able to detect with our method provide an ideal basis to analyze changes caused by pollutants in two key aquatic model organisms.

Three-dimensional quantitative mass spectrometry imaging in complex system: From subcellular to whole organism

Mass spectrometry imaging (MSI) has been applied for label-free three-dimensional (3D) imaging from position array across the whole organism, which provides high-dimensional quantitative data of inorganic or organic compounds that may play an important role in the regulation of cellular signaling, including metals, metabolites, lipids, drugs, peptides, and proteins. While MSI is suitable for investigation of the spatial distribution of molecules, it has a limitation with visualization and quantification of multiple molecules. 3D-MSI, however, can be applied toward exploring metabolic pathway as well as the interactions of lipid-protein, protein-protein, and metal-protein in complex systems from subcellular to the whole organism through an untargeted methodology. In this review, we highlight the methods and applications of MS-based 3D imaging to address the complexity of molecular interaction from nano- to micrometer lateral resolution, with particular focus on: (a) common and hybrid 3D-MSI techniques; (b) quantitative MSI methodology, including the methods using a stable isotope labeling internal standard (SILIS) and SILIS-free approaches with tissue extinction coefficient or virtual calibration; (c) reconstruction of the 3D organ; (d) application of 3D-MSI for biomarker screening and environmental toxicological research. 3D-MSI quantitative analysis provides accurate spatial information and quantitative variation of biomolecules, which may be valuable for the exploration of the molecular mechanism of the disease progresses and toxicological assessment of environmental pollutants in the whole organism. Additionally, we also discuss the challenges and perspectives on the future of 3D quantitative MSI.

Covalent organic framework modified carbon cloth for ratiometric electrochemical sensing of bisphenol A and S

A novel ratiometric electrochemical sensor was developed based on a carbon cloth electrodeposited with silver nanoparticles and drop-coated by covalent organic framework (COF-LZU1) for simultaneous determination of bisphenol A (BPA) and bisphenol S (BPS). Carbon cloth exhibited a significantly larger electrochemical active area than common glassy carbon electrodes (27.5 times). Silver nanoparticles not only provided a stable reference signal but also enhanced electroactivity for the oxidation of BPA and BPS. COF-LZU1 with good adsorption performance and large periodic π-arrays promoted the enrichment of BPA and BPS to further increase the current response. Compared with the traditional single-signal electrochemical sensor, the developed ratiometric sensor exhibited better reproducibility and a wider linear range for BPA and BPS from 0.5 to 100 μM with a limit of detection of 0.15 μM. Furthermore, the developed sensor showed excellent stability and superior anti-interference ability. The real sample analysis for BPA and BPS has been successfully carried out in mineral water, electrolyte drink, tea, juice, and beer with recoveries of 88.3-111.7%. The developed ratiometric sensor is expected to be a candidate for the preparation of other electrochemical sensors and the analysis of additional practical samples.

The Exposome and Toxicology: A Win-Win Collaboration

The development of the exposome concept has been one of the hallmarks of environmental and health research for the last decade. The exposome encompasses the life course environmental exposures including lifestyle factors from the prenatal period onwards. It has inspired many research programs and is expected to influence environmental and health research, practices, and policies. Yet, the links bridging toxicology and the exposome concept have not been well developed. In this review, we describe how the exposome framework can interface with and influence the field of toxicology, as well as how the field of toxicology can help advance the exposome field by providing the needed mechanistic understanding of the exposome impacts on health. Indeed, exposome-informed toxicology is expected to emphasize several orientations including (1) developing approaches integrating multiple stressors, in particular chemical mixtures, as well as the interaction of chemicals with other stressors, (2) using mechanistic frameworks such as the adverse outcome pathways to link the different stressors with toxicity outcomes, (3) characterizing the mechanistic basis of long-term effects by distinguishing different patterns of exposures and further exploring the environment-DNA interface through genetic and epigenetic studies, and (4) improving the links between environmental and human health, in particular through a stronger connection between alterations in our ecosystems and human toxicology. The exposome concept provides the linkage between the complex environment and contemporary mechanistic toxicology. What toxicology can bring to exposome characterization is a needed framework for mechanistic understanding and regulatory outcomes in risk assessment.

Classification of target tissues of Eisenia fetida using sequential multimodal chemical analysis and machine learning

Acquiring comprehensive knowledge about the uptake of pollutants, impact on tissue integrity and the effects at the molecular level in organisms is of increasing interest due to the environmental exposure to numerous contaminants. The analysis of tissues can be performed by histological examination, which is still time-consuming and restricted to target-specific staining methods. The histological approaches can be complemented with chemical imaging analysis. Chemical imaging of tissue sections is typically performed using a single imaging approach. However, for toxicological testing of environmental pollutants, a multimodal approach combined with improved data acquisition and evaluation is desirable, since it may allow for more rapid tissue characterization and give further information on ecotoxicological effects at the tissue level. Therefore, using the soil model organism Eisenia fetida as a model, we developed a sequential workflow combining Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) for chemical analysis of the same tissue sections. Data analysis of the FTIR spectra via random decision forest (RDF) classification enabled the rapid identification of target tissues (e.g., digestive tissue), which are relevant from an ecotoxicological point of view. MALDI imaging analysis provided specific lipid species which are sensitive to metabolic changes and environmental stressors. Taken together, our approach provides a fast and reproducible workflow for label-free histochemical tissue analyses in E. fetida, which can be applied to other model organisms as well.

A Matrix Sublimation Device with an Integrated Solvent Nebulizer for MALDI-MSI

The current matrix deposition methods in MALDI-mass spectrometry imaging (MALDI-MSI) face technical problems related to the inhomogeneous distribution of crystals and the low analyte extraction and cocrystallization efficiency. In this work, an integrated matrix sublimation device with synchronous solvent nebulization was developed for MALDI-MSI. Droplets of solvents were directly introduced into the chamber of the sublimator by using a miniaturized ultrasonic nebulizer unit. The synchronous and asynchronous working modes of solvent nebulization and matrix sublimation were systematically investigated. Imaging of both protein and small metabolite distributions in mouse brain tissue sections was successfully performed using the developed matrix deposition device. The sensitivity and quality of the images were clearly improved in synchronous mode compared with those of the conventional spray and sublimation methods. These results demonstrate that the integrated device with both solvent nebulization and matrix sublimation is a useful tool in MALDI-MSI applications.

In situ metabolic profile and spatial distribution of ocular tissues: New insights into dry eye disease

PURPOSE

Dry eye disease (DED) is a chronic multifactorial disorder affecting millions of people, yet the pathogenesis mechanisms still remain unclear. Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is a novel in situ visualization approach combined high-throughput mass spectrometry and molecular imaging. We aimed to explore the in situ ocular metabolic changes via MALDI-MSI to accelerate the recognition of DED pathogenesis.

METHODS

Experimental dry eye was established in Wistar rats by subcutaneous injection of scopolamine. The induction of DED was assessed by tear film breakup time, sodium fluorescein, histopathological staining and cell apoptosis. MALDI-MSI was applied to explore in situ ocular metabolomic in DED rats, and histopathological staining from same sections were used for side-by-side comparison with MALDI to annotate different tissue structures in the eye.

RESULTS

Considering the complexity of ocular tissue, we visualized the metabolites in specific ocular regions (central cornea, peripheral cornea, fornix conjunctiva, eyelid conjunctiva and aqueous humor), and identified metabolites related to DED, with information of relative abundance and spatial signatures. In addition, integrative pathway analysis illustrated that, several metabolic pathways such as glycerophospholipid, sphingolipid phenylalanine, and metabolism of glycine, serine and threonine were significantly altered in certain regions in the dry eye tissue. Moreover, we discussed how the metabolic pathways with spatiotemporal signatures might be involved in the DED process.

CONCLUSIONS

Our data exploit the advantages of in situ analysis of MALDI-MSI to accurately analyze the region-specific metabolic behaviors in DED, and provide new clues to uncover DED pathogenesis.

Mass spectrometry imaging revealed alterations of lipid metabolites in multicellular tumor spheroids in response to hydroxychloroquine

Three-dimensional (3D) multicellular tumor spheroids (MCTS) that mimic the complex tumor microenvironment provide a good platform for in vitro study of drug and endogenous metabolites. Hydroxychloroquine (HCQ) has shown anti-tumor activity in a variety of tumor models. However, the effect of the drug on the alteration of lipid metabolism spatial composition and distribution in the MCTS model is not clear. Herein, we utilized matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) in the analysis of A549 lung cancer multicellular spheroids to investigate the in situ spatial distribution of HCQ and its effect on lipid metabolism. We have successfully observed the spatial variations of HCQ in the inner region of the spheroid at different drug-treated time points. The MSI results also demonstrated that HCQ treatment altered the spatial composition of lipids in the inner and outer regions of treated spheroids. Furthermore, the lipidomic results showed that the identified phosphatidylcholines (PC), lysophosphatidylcholines (LPC), phosphatidylethanolamines (PE), lysophosphatidylethanolamines (LPE), phosphatidylinositols (PI), ceramides (Cer), glucosylceramides (CerG), and diglycerides (DG) were significantly up-regulated, and phosphatidylglycerol (PG) and triglycerides (TG) were remarkable down-regulated. MSI method combined with LC-MS/MS profiling of endogenous metabolites can obtain more detailed information about how spheroids respond to drug and spatial distribution information, thus fostering a better understanding of the relationship between drug-altered lipid metabolism and cancer microenvironment.

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.

Environmental level bisphenol A accelerates alterations of the reno-cardiac axis by the MAPK cascades in male diabetic rats: An analysis based on transcriptomic profiling and bioinformatics

In humans and animal models, the kidneys and cardiovascular systems are negatively affected by BPA from the environment. It is considered that BPA have some potential estrogen-like and non-hormone-like properties. In this study, RNA-sequencing and its-related bioinformatics was used as the basic strategy to clarify the characteristic mechanisms of kidney-heart axis remodeling and dysfunction in diabetic male rats under BPA exposure. We found that continuous BPA exposure in diabetic rats aggravated renal impairment, and caused hemodynamic disorders and dysfunctions. There were 655 and 125 differentially expressed genes in the kidney and heart, respectively. For the kidneys, functional annotation and enrichment, and gene set enrichment analyses identified bile acid secretion related to lipid synthesis and transport, and MAPK cascade pathways. For the heart, these bioinformatics analyses clearly pointed to MAPKs pathways. A total of 12 genes and another total of 6 genes were identified from the kidney tissue and heart tissue, respectively. Western blotting showed that exposure to BPA activated MAPK cascades in both organs. In this study, the exacerbated remodeling of diabetic kidney-heart axis under BPA exposure and diabetes might occur through hemodynamics, metabolism disorders, and the immune-inflammatory response, as well as continuous estrogen-like stimulation, with focus on the MAPK cascades.

New Advances in Tissue Metabolomics: A Review

Metabolomics offers a hypothesis-generating approach for biomarker discovery in clinical medicine while also providing better understanding of the underlying mechanisms of chronic diseases. Clinical metabolomic studies largely rely on human biofluids (e.g., plasma, urine) as a more convenient specimen type for investigation. However, biofluids are non-organ specific reflecting complex biochemical processes throughout the body, which may complicate biochemical interpretations. For these reasons, tissue metabolomic studies enable deeper insights into aberrant metabolism occurring at the direct site of disease pathogenesis. This review highlights new advances in metabolomics for ex vivo analysis, as well as in situ imaging of tissue specimens, including diverse tissue types from animal models and human participants. Moreover, we discuss key pre-analytical and post-analytical challenges in tissue metabolomics for robust biomarker discovery with a focus on new methodological advances introduced over the past six years, including innovative clinical applications for improved screening, diagnostic testing, and therapeutic interventions for cancer.

Breast cancer proliferation and deterioration-associated metabolic heterogeneity changes induced by exposure of bisphenol S, a widespread replacement of bisphenol A

Exposure to bisphenol A (BPA) is considered to be associated with the increased incidence of breast cancer. As a widespread replacement of BPA, the effect of bisphenol S (BPS) on breast tumor programming has not been studied. We reported that BPS exposure significantly promoted proliferation and deterioration of breast tumor by nonmonotonic dose response. The mechanisms were investigated by molecular biology and mass spectrometry-based lipidomics, proteomics and imaging. BPS exposure induced the spatially intratumor heterogeneity of morphology-driven lipids and proteins. The more significant proliferation resulted from BPS-10 (10 μg/kg body weight /day) exposure was evidenced by the variations of spatial distribution of lipids related to ceramide-sphingomyelin signaling pathway, proteins related to chromosomal stability and cell proliferation in central necrotic regions of breast tumor. In contrast, the BPS-100 exposure obviously accelerated deterioration of breast tumor by the variations of spatial distribution of proteins that were associated with the stability of nucleic acid structure in peripheral neoplastic regions. Accordingly, dysregulation of metabolism and protein function as well as DNA methylation and hypoxic tumor microenvironment could be applied to predict the possibility of tumorigenesis, proliferation and metastasis that might be caused by other bisphenol analogs.

Three-Dimensional Imaging of Whole-Body Zebrafish Revealed Lipid Disorders Associated with Niemann-Pick Disease Type C1

Imaging of lipids of whole-body specimens in two-dimensional (2D) analysis provides a global picture of the lipid changes in lipid-disturbed diseases, enabling a better understanding of lipid functions and lipid-modulation processes in different organs. However, 2D imaging of a single cross section can hardly characterize the whole-body lipid alterations. In this work, a three-dimensional matrix-assisted laser desorption/ionization mass spectrometry imaging (3D MALDI-MSI) approach was developed for analysis of whole-body zebrafish, for the first time, and applied to identify altered lipids and map their spatial distributions by using a zebrafish model of Niemann-Pick disease type C1 (NPC1), a neurovisceral lipid storage disorder causing both neurodegenerative disorder and visceral organ damage. The constructed 3D fish model provided comprehensive information on the 3D distribution of lipids of interest and allowed direct correlations between these lipids and organs of the fish. Obtained results revealed that several sphingolipids and phospholipids showed significant alterations and exhibited different localization patterns in various organs such as the brain, spinal cord, intestines, and liver-spleen region in the npc1 gene mutant fish compared to those of the wild type. The whole-body 3D MALDI-MSI approach revealed unique lipid signatures for different NPC1-affected organs, which might offer insights into the link between the impaired lipid storage and subsequent clinical symptoms, such as neurodegeneration and hepatosplenomegaly.

Distribution of perfluorooctane sulfonate in mice and its effect on liver lipidomic

Perfluorooctane sulfonate (PFOS) is an emerging persistent organic pollutant (POP), and the harm caused by the enrichment of PFOS in living organism has attracted more and more attention. In this work, animal exposure model to PFOS was established. Mass spectrometry (MS), mass spectrometry imaging (MSI), hematoxylin and eosin (H&E) staining and lipidomics were combined for the study of the organ targeting of PFOS, the toxicity and possible mechanism caused by PFOS. PFOS most accumulated in the liver, followed by the lungs, kidneys, spleen, heart and brain. Combined with H&E staining and matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) results, it was found that the accumulation of PFOS indeed caused damage in particular areas of specific organ, like in the liver and in the marginal area of the heart. This work found that PFOS could cross the blood-brain barrier, entered the brain and caused the neurotoxicity, which was surprising and might be the reason that high dose of PFOS could cause convulsions. From the liver lipidomic analysis, we found that PFOS exposure mainly affected glycerophospholipid metabolism and sphingolipid metabolism. The up-regulated ceramide and lysophosphatidylcholine (LPC) might lead to liver cell apoptosis, and the decrease in liver triglyceride (TG) content might result in insufficient energy in mice and cause liver morphological damage. Phosphatidylcholine (PC) synthesis via phosphatidylethanolamine N-methyltransferase (PEMT) pathway might be a mechanism of self-protection in animals against PFOS induced inflammation. This study might provide new insight into underlying toxicity mechanism after exposure to PFOS.

Metabolomics reveals the reproductive abnormality in female zebrafish exposed to environmentally relevant levels of climbazole

Climbazole (CBZ) ubiquitously detected in the aquatic environment may disrupt fish reproductive function. Thus far, the previous study has focused on its transcriptional impact of steroidogenesis-related genes on zebrafish, but the underlying toxic mechanism still needs further investigation at the metabolic level. In this study, adult zebrafish were chronically exposed to CBZ at concentrations of 0.1 (corresponding to the real concentration in surface water), 10, and 1000 μg/L and evaluated for reproductive function by egg production, with subsequent ovarian tissue samples taken for histology, metabolomics, and other biochemical analysis. After 28 days' exposure, fecundity was significantly decreased in all exposure groups, with the inhibition of oocytes in varying developmental stages to a certain degree. The decrease in retinoic acid and sex hormones, down-regulated genes important in steroidogenesis, and increase in oxidized/reduced glutathione ratio and occurrence of apoptotic cells were observed in zebrafish ovaries following exposure to CBZ even at environmentally realistic concentrations, suggesting that alternations in steroidogenesis and oxidative stress can play significant roles in CBZ-triggered reproductive toxicity. Besides, mass spectrometry imaging analysis validated the results from metabolomics analysis. Our findings provide novel perspectives for unveiling the mechanism of reproductive dysfunction by CBZ and highlight its risk to fish reproduction.

Spatially Resolved Mass Spectrometry at the Single Cell: Recent Innovations in Proteomics and Metabolomics

Biological systems are composed of heterogeneous populations of cells that intercommunicate to form a functional living tissue. Biological function varies greatly across populations of cells, as each single cell has a unique transcriptome, proteome, and metabolome that translates to functional differences within single species and across kingdoms. Over the past decade, substantial advancements in our ability to characterize omic profiles on a single cell level have occurred, including in multiple spectroscopic and mass spectrometry (MS)-based techniques. Of these technologies, spatially resolved mass spectrometry approaches, including mass spectrometry imaging (MSI), have shown the most progress for single cell proteomics and metabolomics. For example, reporter-based methods using heavy metal tags have allowed for targeted MS investigation of the proteome at the subcellular level, and development of technologies such as laser ablation electrospray ionization mass spectrometry (LAESI-MS) now mean that dynamic metabolomics can be performed in situ. In this Perspective, we showcase advancements in single cell spatial metabolomics and proteomics over the past decade and highlight important aspects related to high-throughput screening, data analysis, and more which are vital to the success of achieving proteomic and metabolomic profiling at the single cell scale. Finally, using this broad literature summary, we provide a perspective on how the next decade may unfold in the area of single cell MS-based proteomics and metabolomics.

Airborne fine particulate matter induces cognitive and emotional disorders in offspring mice exposed during pregnancy

Gestational exposure to PM_2.5 is associated with adverse postnatal outcomes. PM_2.5 can enter alveoli by using intratracheal instillation, even penetrate through lung cells into the blood circulation. Subsequently, they are transferred across the placenta and fetal blood brain barrier, causing the adverse birth outcomes of offspring. This study demonstrated that the gestational exposure resulted in cognitive and emotional disorders in female offspring although the offspring were not exposed to PM_2.5. Placental metabolic pathways modulated fetal brain development and played a pivotal role for maternal-placental-fetal interactions in the fetal programming of adult behavioral and mental disorders. Samples of fetus, offspring hippocampus and placenta from the mice exposed to PM_2.5 were investigated using a comprehensive approach including mass spectrometry-based lipidomics and three-dimensional imaging. The exposure induced the neuro-degeneration in hippocampus, impairment of placental cytoarchitecture, and reprogramming of lipidome, which might affect the modulation of maternal-fetal cross-talk and result in the behavior disorders of offspring. The variation of spatial distribution of lipids was profoundly affected in dorsal pallium and hippocampal formation regions of fetal brain, offspring hippocampus, as well as labyrinth and junctional zones of placenta. The abundance alteration of lipid markers associated with neurodegenerative diseases was validated in transgenic mouse model with Alzheimer's disease and human cerebrospinal fluid from patients with Parkinson's disease. The finding could help with the selection of more suitable heterogeneous-related substructures targeting PM_2.5 exposure and the exploration of PM_2.5-induced toxicological effects on neurodegenerative diseases.

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.

Co-administration of lipopolysaccharide and D-galactosamine induces genotoxicity in mouse liver

The acute liver injury (ALI) and hepatic fibrosis caused by the co-treatment of lipopolysaccharide (LPS)/D-galactosamine (D-GalN) have been extensively studied. However, whether LPS/D-GalN are genotoxic has been left unknown. In this study, male mice were divided into eight groups with eight animals in each group. For acute challenge of LPS/D-GalN, the mice in each group received a combination of LPS/D-GalN via intraperitoneal injection at the dose of 25 μg/kg/250 mg/kg, 25 μg/kg/500 mg/kg, or 50 μg/kg/500 mg/kg body weight. An additional group for chronic administration of test compounds was conducted by i.p. injection of LPS/D-GalN (10 μg/kg/100 mg/kg) every other day for 8 weeks. Saline solution (0.9%) and cyclophosphamide (CTX) (50 mg/kg body weight) given by i.p. injection was used as the negative and positive control, respectively. The results of single cell gel electrophoresis (SCGE) assay indicated that acute exposure of the mice to LPS/D-GalN caused severe DNA damage in hepatic cells, but not in the brain, sperm or bone marrow cells, which evidenced the genotoxicity of LPS/D-GalN administrated in combination. Interestingly, the chronic administration of LPS/D-GalN triggered significant genotoxic effects not only in hepatic but also in brain cells, with negative results in sperm and bone marrow cells. Histopathological examination in the liver and brain tissues revealed changes consistent with the SCGE results. The present study indicates genotoxic potential of LPS/D-GalN co-administered in mice, which may serve as an in vivo experimental model for relevant genotoxic study.

MALDI-MS Imaging Analysis of Noninflammatory Type III Rotaxane Dendrimers

Rotaxane dendrimers with hyperbranched macromolecular interlocked structures and size modulation capacity demonstrate drug binding and release ability upon external stimuli. Mass spectrometry imaging (MSI) can offer the high-throughput screening of endogenous/exogenous compounds. Herein, we reported a novel method to display the in situ spatial distribution of label-free monodispersed type III rotaxane dendrimers (RDs) G1 (first generation, size ∼1.5 nm) and G2 (second generation, size ∼5 nm) that were explored as potential drug vehicles in spleen tissue by using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-MSI). Experimental results indicated that the trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) matrix exhibited the best performance for monodispersed type III RDs G1 and G2. The optimized method was successfully applied to map the in vivo spatial distribution of type III RDs G1 and G2 in the spleen from intraperitoneally injected mice. The MALDI-MSI images revealed that RDs G1 and G2 were relatively stable in the spleen within 24 h after administration. It was found that the identified type III RDs G1 and G2 penetrated through the tunica serosa and were predominantly localized in red pulp regions of spleens. They were also mapped in a marginal zone of spleens simultaneously. There was almost no toxicity of type III RDs G1 and G2 to mice spleens from the H&E results. Furthermore, the type III RDs did not induce the expression of inflammatory cytokines from peripheral blood mononuclear cells (PBMCs) or THP-1 monocytes. The MSI analysis not only demonstrated its ability to image select rotaxane dendrimers in a rapid and efficient manner but also provided tremendous assistance on the applications of the further treatment of cancerous tissue as safe drug carriers. Furthermore, the new strategy demonstrated in this study could be applied on other label-free mechanically interlocked molecules, molecular machines, and macromolecules, which opened a new path to evaluate the toxicological and pharmacokinetic characteristics of these novel materials at the suborgan level.

Preparation of Frozen Sections of Multicellular Tumor Spheroids Coated with Ice for Mass Spectrometry Imaging

Increasing studies have utilized mass spectrometry imaging (MSI) that is a label-free tool to investigate drug penetration and drug biotransformation in multicellular tumor spheroids (MCTS). Currently, the gelatin-assisted sectioning method is widely used to prepare frozen sections of MCTS for MSI. However, owing to the limited transparency of frozen gelatin, MCTS with diameters less than 500 μm that closely mimic solid tumors are difficult to be detected when cryosectioning. In order to identify the presence of MCTS, hematoxylin and eosin staining for frozen sections and dye pretreatment for MCTS were employed in previous works, which either increased the analytical time and cost in sample preparation or caused signal suppression in sample analysis. Herein, a new sectioning method was developed to prepare MCTS frozen sections. MCTS was coated with ice to ensure good visibility for small-size MCTS. The optimal cutting temperature compound was added around the ice block to assist the formation of frozen sections. A precast frozen mold was prepared to allow the acquisition of complete MCTS frozen sections. The developed method was applied to investigate lipid distribution in MCTS by using matrix-assisted laser desorption/ionization MSI. Compared to the gelatin-assisted sectioning method, our method did not cause signal suppression and analyte delocalization. Thus, this method provides an easy, universal, and innovative strategy to prepare MCTS frozen sections for further MSI analysis. Besides, we applied our method to investigate the penetration of bisphenol A in MCTS.

Lipid metabolism disorders contribute to hepatotoxicity of triclosan in mice

Previous in vivo exposure studies focused mainly on nuclear receptors involved in hepatotoxicity of triclosan (TCS). As liver plays a vital role in metabolic processes, dysregulations in lipid metabolism have been identified as potential drivers of pathogenesis. Investigation of changes in lipid metabolism might widen our understanding of toxicological effects as well as the underlying mechanism occurring in the liver. In this study, we comprehensively assessed the effect of TCS exposure on hepatic lipid metabolism in mice. Our results showed that TCS induced significant changes in hepatic free fatty acid pool by upregulation of fatty acid uptake and de novo fatty acid synthesis. Besides, hepatic levels of lipids, including acyl carnitine (AcCa), ceramide (Cer), triacylglycerols (TG), phosphatidylcholine (PC), lysophosphatidylcholine (LPC), phosphatidylethanolamine (PE) were also increased, together with upreguation of genes associated to TG synthesis, fatty acid oxidation and inflammation in TCS exposure group. These changes in lipid homeostasis could contribute to membrane instability, lipid accumulation, oxidative stress and inflammation. Our results suggested that TCS exposure could induce hepatic lipid metabolism disorders in mice, which would further contribute to the liver damage effects of TCS.

Hepatotoxic effects of inhalation exposure to polycyclic aromatic hydrocarbons on lipid metabolism of C57BL/6 mice

Inhalation from ambient air and cigarette smoke is a common route of human exposure to polycyclic aromatic hydrocarbons (PAHs). Little information is available regarding hepatotoxicities of inhaled PAHs so for. In this study, we evaluated the toxic effects of intratracheally instilled benzo[a]pyrene (B[a]P) on hepatic lipid metabolism of C57BL/6 mice at relevant environmental exposure levels by using two different mass-based lipidomics approaches. The results of mass spectrometry imaging analysis showed that both the abundance and spatial distribution of several lysophosphatidylcholine (LysoPC), phosphatidylcholine (PC) and sphingomyelin (SM) in the liver section were different and changed after inhalation exposure to B[a]P. Liquid chromatography coupled with mass spectrometry-based lipidomics analysis and multivariate statistical analysis found that B[a]P exposure markedly altered glycerophospholipids, glycerolipids, and fatty acid metabolism in the mouse liver, with increasing of triacylglycerol (TG), phosphatidylinositol (PI) and PC, and decreasing of LysoPCs phosphatidylethanolamines (PEs), lysophosphatidylethanolamine (LysoPEs), free fatty acids (FFAs) and eicosanoids. B[a]P-induced lipid metabolic disorders showed a time-dependent effect, which generated three response trajectories with different change trends. Consequently, B[a]P exposure induced alteration of hepatic lipids by promoting the uptake from blood or the biosynthesis and transformation in the liver, might contribute to non-alcoholic fatty liver disease, hepatocyte membrane injury, inflammation, and signal system disturbance.