Granulomas are organized inflammatory lesions formed in response to persistent stimuli such as infections. Murine infection with Leishmania donovani results in granulomas in the liver, seeded by infected Kupffer cells, and serves as a well-defined model of infection-induced granuloma formation. The resolution of granulomatous inflammation requires dynamic shifts in immune-cell activation states, imposing metabolic demands. As mediators of cell signaling, lipid metabolism plays a key role in regulating inflammation and infection. How lipid changes are spatially linked to altered immune cell transcription remains unresolved. We performed a multimodal imaging analysis combining MALDI mass spectrometry, spatial and single cell transcriptomics, proteomics of flow-sorted macrophages and histopathology of L. donovani induced hepatic granulomas. Using this spatially-integrated approach, we identified LPCAT2-mediated membrane re-modelling of myeloid cells as a novel feature of these granulomas. Our study provides new insights into local immunometabolic changes associated with granuloma formation and macrophage activation.

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) allows spatial molecular profiling. Despite many successful applications, an appropriate control of technical variations is still lacking for result reproducibility assessment and for maximizing the MSI data quality. To address this, we introduce a novel quality control standard (QCS) design and data analysis pipeline accounting for variability due to sample preparation and instrument performance. Firstly, we created a tissue mimicking QCS consisting of propranolol in a gelatin matrix. We showed that this QCS mimics ion suppression of propranolol in the tissue. Next, a three-day batch experiment demonstrated the QCS's performance to longitudinal technical variations, establishing it as an effective indicator of batch effects. Then three computational approaches for batch effect correction were applied for the first time to MALDI-MSI data, leading to a significant reduction of QCS variation and to improved sample clustering by using multivariate principal component analysis. Altogether, we offer the designed QCS in combination with a data correction pipeline for MALDI-MSI users for batch effect evaluation and correction.

OBJECTIVE:In temporal lobe epilepsy (TLE), detection of the epileptogenic zone predicts a good surgical outcome. When submitted to 18F-fluorodeoxyglucose positron emission tomography (PET), some patients display lateralized, focal hypometabolism in the temporal lobe (PET+), whereas others appear normometabolic (PET-). However, the mechanism behind this metabolic difference remains unclear. This study aimed to identify differential molecular mechanisms in these patient subtypes. METHODS:Neocortical and hippocampal biopsies of TLE patients (n = 3 PET+, n = 3 PET-) and nonepileptic postmortem controls (n = 3) were analyzed for lipid distribution using mass spectrometry imaging (MSI). Laser capture microdissection of the neocortical gray matter and hippocampal cornu ammonis and dentate gyrus was guided by MSI-derived lipid profiles and histological annotations. Dissected areas were then subjected to liquid chromatography- tandem mass spectrometry-based label-free quantitative proteomic analysis. RESULTS:MSI showed distinct lipid profiles, namely, phosphatidylserines were more abundant in PET+ samples in both the neocortex and hippocampus. Proteomic analysis showed significant differences between TLE and nonepileptic postmortem controls involving pathways in neuron excitability and neurotransmitter transporters, which were upregulated in TLE. Compared to PET-, all PET+ specimens displayed significantly dysregulated calcium signaling. Additionally, the neocortex of PET+ patients showed a shift from mitochondrial to cytosolic (cytoplasm of the cell) processes, whereas the hippocampus was characterized by a disruption of glycosylation and polyamine metabolism. SIGNIFICANCE:The applied spatial omics approach demonstrated localized molecular differences between metabolic subtypes of TLE patients. These findings may further specify these TLE subtypes and provide leads for targeted treatment.

Understanding tissue complexity requires spatially resolved multi-omics data at single-cell resolution. Here, we present a workflow integrating high-resolution matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) with Xenium spatial transcriptomics (SPT) on a single tissue section. This strategy ensures pixel-scale spatial correspondence between metabolic and transcriptomic features, avoiding misalignment issues of serial sections, where even minor offsets result in sampling different cells. We investigated MALDI-MSI compatibility with downstream SPT revealing that the number of transcripts per cell decreased by ~ 30% after MSI, whilst cell recovery and cell-type assignments are preserved. Validated using mouse brain and demonstrated using human glioblastoma tissues, we achieved pixel-scale modality co-registration, enabling per-cell MALDI spectra extraction aligned with gene expression. Integrated clustering revealed enhanced cell-type resolution and identified metabolic heterogeneity within transcriptionally defined populations. This facilitates precise correlations of a cell's function and its biochemical state, providing a holistic view of cellular function, heterogeneity, and interaction in health and disease. Our workflow provides a scalable path to multi-omic atlases, advancing both data integration and translational research.

AbstractBackgroundCancer cachexia is a multifactorial metabolic syndrome characterized by systemic inflammation and ongoing skeletal muscle loss resulting in weakness, poor quality of life, and decreased survival. Whereas lipid accumulation in skeletal muscle is associated with cancer cachexia as well as the prognosis of cancer patients, surprisingly little is known about the nature of the lipids that accumulate in the muscle during cachexia, and whether this is related to inflammation. We aimed to identify the types and distributions of intramyocellular lipids in patients with and without cancer cachexia.MethodsRectus abdominis muscle biopsies were collected during surgery of patients with pancreatic ductal adenocarcinoma (n = 10 without cachexia, n = 20 cachectic without inflammation (CRP < 10 mg/L), n = 10 cachectic with inflammation (CRP ≥ 10 mg/L). L3‐CT scans were analysed to assess body composition based on validated thresholds in Hounsfield units (HU). Muscle sections were stained with Oil‐Red O and H&E to assess general lipid accumulation and atrophy. Untargeted lipidomic analyses were performed on laser‐microdissected myotubes using LC–MS/MS. The spatial distribution of intramyocellular lipids with differential abundance between groups was visualized by mass‐spectrometry imaging. Genes coding for inflammation markers and enzymes involved in de novo ceramide synthesis were studied by qPCR.ResultsMuscle radiation attenuation was lower in cachectic patients with inflammation (median 24.3 [18.6–30.8] HU) as compared with those without inflammation (34.2 [29.3–38.7] HU, P = 0.033) or no cachexia (37.4 [33.9–42.9] HU, P = 0.012). Accordingly, intramyocellular lipid content was lower in non‐cachectic patients (1.9 [1.6–2.1]%) as compared with those with cachexia with inflammation (5.5 [4.5–7.3]%, P = 0.002) or without inflammation (4.8 [2.6–6.0]%, P = 0.017). Intramyocellular lipid accumulation was associated with both local IL‐6 mRNA levels (rs = 0.57, P = 0.015) and systemic CRP levels (rs = 0.49, P = 0.024). Compared with non‐cachectic subjects, cachectic patients had a higher relative abundance of intramyocellular glycerophospholipids and a lower relative abundance of glycerolipids. Furthermore, increases in several intramyocellular lipids such as SM(d36:1), PC(34:1), and TG(48:1) were found in cachectic patients with inflammation and correlated with specific cachexia features. Altered intramyocellular lipid species such as PC(34:1), LPC(18:2), and TG(48:1) showed an uneven distribution in muscle sections of cachectic and non‐cachectic patients, with areas featuring abundance of these lipids next to areas almost devoid of them.ConclusionsIntramyocellular lipid accumulation in patients with cachexia is associated with both local and systemic inflammation, and characterized by changes in defined lipid species such as glycerolipids and glycerophospholipids.

BACKGROUND: The metabolic alterations occurring within the arterial architecture during atherosclerosis development remain poorly understood, let alone those particular to each arterial tunica. We aimed to identify, in a spatially resolved manner, the specific metabolic changes in plaque, media, adventitia, and cardiac tissue between control and atherosclerotic murine aortas. Second, we assessed their translatability to human tissue and plasma for cardiovascular risk estimation. METHODS: In this observational study, mass spectrometry (MS) imaging was applied to identify region-specific metabolic differences between atherosclerotic (n=11) and control (n=11) aortas from low-density lipoprotein receptor-deficient mice, via histology-guided virtual microdissection. Early and advanced plaques were compared within the same atherosclerotic animals. Progression metabolites were further analyzed by MS imaging in 9 human atherosclerotic carotids and by targeted MS in human plasma from subjects with elective coronary artery bypass grafting (cardiovascular risk group, n=27) and a control group (n=27). RESULTS: MS imaging identified 362 local metabolic alterations in atherosclerotic mice (log2 fold-change, >= 1.5; P <= 0.05). The lipid composition of cardiac tissue is altered during atherosclerosis development and presents a generalized accumulation of glycerophospholipids, except for lysolipids. Lysolipids (among other glycerophospholipids) were found at elevated levels in all 3 arterial layers of atherosclerotic aortas. Lysophosphatidylcholine(18:0; P=0.024) and lysophosphatidic acid(18:1; P=0.025) were found to be significantly elevated in advanced plaques as compared with mouse-matched early plaques. Higher levels of both lipid species were also observed in fibrosis-rich areas of advanced- versus early-stage human samples. They were found to be significantly reduced in human plasma from subjects with elective coronary artery bypass graft (P<0.001 and P=0.031, respectively), with lysophosphatidylcholine(18:0) showing significant association with cardiovascular risk (odds ratio, 0.479 [95% CI, 0.225-0.883]; P=0.032) and diagnostic potential (AUC, 0.778 [95% CI, 0.638-0.917]). CONCLUSIONS: An altered phospholipid metabolism occurs in atherosclerosis, affecting both the aorta and the adjacent heart tissue. Plaque-progression lipids lysophosphatidylcholine(18:0) and lysophosphatidic acid(18:1), as identified by MS imaging on tissue, reflect cardiovascular risk in human plasma.

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) progressing to metabolic dysfunction-associated steatohepatitis (MASH), characterized by hepatic inflammation, has significantly increased in recent years due to unhealthy dietary practices and sedentary lifestyles. Cathepsin D (CTSD), a lysosomal protease involved in lipid homeostasis, is linked to abnormal lipid metabolism and inflammation in MASH. Although primarily intracellular, CTSD can be secreted extracellularly. Our previous proteomics research has shown that inhibition of extracellular CTSD results in more anti-inflammatory effects and fewer potential side effects compared to intracellular CTSD inhibition. However, the correlation between reduced side effects and alterations in the hepatic lipid composition remains unknown. This study aims to investigate the correlation between intra- and extracellular CTSD inhibition and potential alterations in the hepatic lipid composition in MASH. Low-density lipoprotein receptor knockout (Ldlr-/-) mice were fed a high-fat diet for 10 weeks and received subcutaneous injections every 2 days of vehicle, intracellular CTSD inhibitor (GA-12), or extracellular CTSD inhibitor (CTD-002). Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was used to visualize and compare the lipid composition in liver tissues. Hepatic phosphatidylcholine remodeling was observed with both inhibitors, suggesting their therapeutic potential in treating MASH. Treatment with an intracellular CTSD inhibitor resulted in elevated levels of cardiolipin, reactive oxygen species, phosphatidylinositol, phosphatidylethanolamine, and lipids that are linked to mitochondrial dysfunction and inflammation, and induced more oxidative stress. The observed modifications in lipid composition demonstrate the clinical advantages of extracellular CTSD inhibition as a potentially beneficial therapeutic approach for MASH.

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Instituto de Salud Carlos III co-supported by FEDER grants and co-funded by the European Union Background Thoracic aortic aneurysms (TAAs) curse silently and asymptomatic. The vast majority are idiopathic, representing 80-95% of the cases. Nevertheless, there is an association between TAA and the presence of bicuspid aortic valve (BAV) constituting BAV an independent risk factor of TAA. The presence of BAV accelerates the growth of the aneurysm affecting younger patients than those with tricuspid aortic valve (TAV). Evidence points to a profound remodeling of the media and adventitia layers, but the underlying mechanisms are unknown, especially the metabolic changes taking place and their in situ localization. Purpose Our aim was to identify, in a spatially resolved manner, the in situ metabolic alterations occurring in TAA human aortas while differentiating between BAV and TAV patients. In a further step, we sought to identify the changes happening particularly within the media and adventitia layers. Methods Mass spectrometry imaging (MSI) was applied to identify metabolic differences between human aortas with (TAA) and without (C) dilatation classified according to their aortic valve and obtained from cardiac surgeries. Clinical groups consisted on TAV-C (n=11), BAV-C (n=12), TAV-TAA (n=12) and BAV-TAA (n=12). Subsequent virtual microdissection histologically guided was applied to identify the specific metabolic changes located within media and/or adventitia. Changes were considered significant if FDR>2 and p-value <0.05. Results Purine metabolism resulted altered in BAV-TAA patients while no differences were found in TAV-TAA ones. Particularly, we detected a significant increase of aortic ATP (FC= 2.92; p-value= 0.030), ADP (FC= 2.04; p-value= 0.020), AMP (FC= 2.42; p-value= 0.011) and GDP (FC= 2.29; p-value= 0.046) in BAV-TAA vs. BAV-C subjects. In contrast, we found an in situ increment in pyrimidine metabolism resulting UDP and UMP increased in both, TAV and BAV associated TAAs. When comparing the arterial layers, media layer was found to be the major driver of BAV-TAA with no nucleotides changes in adventitia. However, TAV-TAA media and adventitia layer behave similarly with the exception of a massive increase of ATP (FC=50.23, p=0.046) in adventitia with no alteration in media of TAV-TAA vs. TAV-C patients. Conclusions Idiopathic TAAs course differently in subjects with bicuspid and tricuspid valves both in terms of mechanisms of action and arterial remodeling within the aortic layers. These findings suggest that TAA patients with bicuspid or tricuspid aortic valve should be treated as independent groups for optimal disease management.

Supplementary Figure S1 This supplementary figure depicts the ion suppression of erlotinib of different histological compartments of the pancreas and its specific measurement on tissue sections.

Purpose Cholangiocarcinoma (CCA) is a malignancy arising from the bile duct epithelium and has a poor outcome. Sulfatides are lipid components of lipid rafts, and are implicated in several cancer types. In the liver, sulfatides are specifically present in the bile ducts. Here, sulfatide abundance and composition were analyzed using mass spectrometry imaging in intrahepatic CCA (iCCA) tumor tissue, and correlated with tumor biology and clinical outcomes. Methods Sulfatides were analyzed in iCCA (n = 17), hepatocellular carcinoma (HCC, n = 10) and colorectal liver metastasis (CRLM, n = 10) tumor samples, as well as tumor-distal samples (control, n = 16) using mass spectrometry imaging. Levels of sulfatides as well as the relative amount in structural classes were compared between groups, and were correlated with clinical outcomes for iCCA patients. Results Sulfatide localization was limited to the respective tumor areas and the bile ducts. Sulfatide abundance was similar in iCCA and control tissue, while intensities were notably higher in CRLM in comparison with control (18-fold, P < 0.05) and HCC tissue (47-fold, P < 0.001). Considerable variation in sulfatide abundance was observed in iCCA tumors. A high ratio of unsaturated to saturated sulfatides was associated with reduced disease-free survival (10 vs. 20 months) in iCCA. The sulfatide pattern in HCC deviated from the other groups, with a higher relative abundance of odd- versus even-chain sulfatides. Conclusion Sulfatides were found in tumor tissue of patients with iCCA, with sulfatide abundance per pixel being similar to bile ducts. In this explorative study, sulfatide abundance was not related to overall survival of iCCA patients. A high ratio of unsaturated to saturated sulfatides was associated with earlier tumor recurrence in patients with iCCA.

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.

Supplemental material and methods file

Mass spectrometry imaging (MSI) is used in many aspects of clinical research, including pharmacokinetics, toxicology, personalised medicine, and surgical decision-making. Maximising its potential requires the spatial integration of MSI images with imaging data from existing clinical imaging modalities, such as histology and MRI. To ensure that the information is properly integrated, all contributing images must be accurately aligned. This process is called image registration and is the focus of this review. In light of the ever-increasing spatial resolution of MSI instrumentation and a diversification of multi-modal MSI studies (e.g., spatial omics, 3D-MSI), the accuracy, versatility, and precision of image registration must increase accordingly. We review the application of image registration to align MSI data with different clinically relevant ex vivo and in vivo imaging techniques. Based on this, we identify steps in the current image registration processes where there is potential for improvement. Finally, we propose a roadmap for community efforts to address these challenges in order to increase registration quality and help MSI to fully exploit its multi-modal potential.

Glycosylation plays an important role in the progression of esophageal adenocarcinoma (EAC). Being able to image these glycosylation changes directly in endoscopic resection specimens could provide useful insights into the molecular mechanisms of the disease progression and potential markers for EAC staging. For this purpose, both 3D and 2.5D matrix-assisted laser/desorption ionization (MALDI) mass spectrometry imaging (MSI) have been employed in this study to investigate glycosidase-cleaved N-glycans in a total of 24 formalin-fixed paraffin-embedded esophageal local excision specimens spanning all stages of disease progression, namely from non-dysplastic Barrett’s esophagus to metastatic EAC. 3D-MSI was first used to estimate the number of sections needed to sufficiently cover the molecular heterogeneity of each stage of progression. This analysis showed that a total of four sections out of 20 were sufficient. This subset of four sections was measured for all remaining specimens and is called 2.5D-MSI. Subsequent analyses of the 2.5D-MSI datasets revealed significant elevations of five high-mannose N-glycans (Man3, Man4, Man6, Man7, and Man8) in EAC and three complex (Hex6HexNAc5, Hex6HexNAc5NeuAc1, Hex7HexNAc6) N-glycans in metastatic EAC as compared to previous stages of the disease. The augmented levels of these glycans in EAC could be explained by publically available gene expression data of enzymes involved in glycan synthesis and processing. As the role of glycosylation is gaining more interest in MSI and cancer research, our results show the added value of combining localized N-glycan levels, as provided by MSI, with gene expression to gain a deeper understanding of the mechanisms behind N-glycan changes. This gives evidence at multiple levels that specific N-glycosylation plays an important role during progression of dysplasia to EAC and could play a role in patient surveillance.

Cells often adopt different phenotypes, dictated by tissue-specific or local signals such as cell-cell and cell-matrix contacts or molecular micro-environment. This holds in extremis for macrophages with their high phenotypic plasticity. Their broad range of functions, some even opposing, reflects their heterogeneity, and a multitude of subsets has been described in different tissues and diseases. Such micro-environmental imprint cannot be adequately studied by single-cell applications as cells are detached from their context, while histology-based assessment lacks the phenotypic depth due to limitations in marker combination. Here, we present a novel, integrative approach in which 15-color multispectral imaging allows comprehensive cell classification based on multi-marker expression patterns, followed by downstream analysis pipelines to link their phenotypes to contextual, micro-environmental cues such as their cellular (“community”) and metabolic (“local lipidome”) niches in complex tissue. The power of this approach is illustrated for myeloid subsets and associated lipid signatures in murine atherosclerotic plaque.

Intestinal ischemia-reperfusion (IR) injury is a severe clinical condition, and unraveling its pathophysiology is crucial to improve therapeutic strategies and reduce the high morbidity and mortality rates. Here, we studied the dynamic proteome and phosphoproteome in the human intestine during ischemia and reperfusion, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to gain quantitative information of thousands of proteins and phosphorylation sites, as well as mass spectrometry imaging (MSI) to obtain spatial information. We identified a significant decrease in abundance of proteins related to intestinal absorption, microvillus, and cell junction, whereas proteins involved in innate immunity, in particular the complement cascade, and extracellular matrix organization increased in abundance after IR. Differentially phosphorylated proteins were involved in RNA splicing events and cytoskeletal and cell junction organization. In addition, our analysis points to mitogen-activated protein kinase (MAPK) and cyclin-dependent kinase (CDK) families to be active kinases during IR. Finally, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MSI presented peptide alterations in abundance and distribution, which resulted, in combination with Fourier-transform ion cyclotron resonance (FTICR) MSI and LC-MS/MS, in the annotation of proteins related to RNA splicing, the complement cascade, and extracellular matrix organization. This study expanded our understanding of the molecular changes that occur during IR in the human intestine and highlights the value of the complementary use of different MS-based methodologies.

MALDI MS imaging (MSI) is a powerful analytical tool for spatial peptide detection in heterogeneous tissues. Proper sample preparation is crucial to achieve high quality, reproducible measurements. Here we developed an optimized protocol for spatially resolved proteolytic peptide detection with MALDI time-of-flight MSI of fresh frozen prostate tissue sections. The parameters tested included four different tissue washes, four methods of protein denaturation, four methods of trypsin digestion (different trypsin densities, sprayers, and incubation times), and five matrix deposition methods (different sprayers, settings, and matrix concentrations). Evaluation criteria were the number of detected and excluded peaks, percentage of high mass peaks, signal-to-noise ratio, spatial localization, and average intensities of identified peptides, all of which were integrated into a weighted quality evaluation scoring system. Based on these scores, the optimized protocol included an ice-cold EtOH+H2 O wash, a 5 min heating step at 95°C, tryptic digestion incubated for 17h at 37°C and CHCA matrix deposited at a final amount of 1.8 μg/mm2 . Including a heat-induced protein denaturation step after tissue wash is a new methodological approach that could be useful also for other tissue types. This optimized protocol for spatial peptide detection using MALDI MSI facilitates future biomarker discovery in prostate cancer and may be useful in studies of other tissue types.