Mass Spectrometry Imaging of In Vitro Cryptosporidium parvum-Infected Cells and Host Tissue

Cryptosporidium parvum is a zoonotic-relevant parasite belonging to the phylum Alveolata (subphylum Apicomplexa). One of the most zoonotic-relevant etiologies of cryptosporidiosis is the species C. parvum, infecting humans, cattle and wildlife. C. parvum-infected intestinal mucosa as well as host cells infected in vitro have not yet been the subject of extensive biochemical investigation. Efficient treatment options or vaccines against cryptosporidiosis are currently not available. Human cryptosporidiosis is currently known as a neglected poverty-related disease (PRD), being potentially fatal in young children or immunocompromised patients. In this study, we used a combination of atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) and liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to determine and locate molecular biomarkers in in vitro C. parvum-infected host cells as well as parasitized neonatal calf intestines. Sections of C. parvum-infected and non-infected host cell pellets and infected intestines were examined to determine potential biomarkers. Human ileocecal adenocarcinoma cells (HCT-8) were used as a suitable in vitro host cell system. More than a thousand different molecular signals were found in both positive- and negative-ion mode, which were significantly increased in C. parvum-infected material. A database search in combination with HPLC-MS/MS experiments was employed for the structural verification of markers. Our results demonstrate some overlap between the identified markers and data obtained from earlier studies on other apicomplexan parasites. Statistically relevant biomarkers were imaged in cell layers of C. parvum-infected and non-infected host cells with 5 µm pixel size and in bovine intestinal tissue with 10 µm pixel size. This allowed us to substantiate their relevance once again. Taken together, the present approach delivers novel metabolic insights on neglected cryptosporidiosis affecting mainly children in developing countries.

Metabolic reprogramming of hepatocytes by Schistosoma mansoni eggs

Background & Aims

Schistosomiasis is a parasitic infection which affects more than 200 million people globally. Schistosome eggs, but not the adult worms, are mainly responsible for schistosomiasis-specific morbidity in the liver. It is unclear if S. mansoni eggs consume host metabolites, and how this compromises the host parenchyma.

Methods

Metabolic reprogramming was analyzed by matrix-assisted laser desorption/ionization mass spectrometry imaging, liquid chromatography with high-resolution mass spectrometry, metabolite quantification, confocal laser scanning microscopy, live cell imaging, quantitative real-time PCR, western blotting, assessment of DNA damage, and immunohistology in hamster models and functional experiments in human cell lines. Major results were validated in human biopsies.

Results

The infection with S. mansoni provokes hepatic exhaustion of neutral lipids and glycogen. Furthermore, the distribution of distinct lipid species and the regulation of rate-limiting metabolic enzymes is disrupted in the liver of S. mansoni infected animals. Notably, eggs mobilize, incorporate, and store host lipids, while the associated metabolic reprogramming causes oxidative stress-induced DNA damage in hepatocytes. Administration of reactive oxygen species scavengers ameliorates these deleterious effects.

Conclusions

Our findings indicate that S. mansoni eggs completely reprogram lipid and carbohydrate metabolism via soluble factors, which results in oxidative stress-induced cell damage in the host parenchyma.

Impact and implications

The authors demonstrate that soluble egg products of the parasite S. mansoni induce hepatocellular reprogramming, causing metabolic exhaustion and a strong redox imbalance. Notably, eggs mobilize, incorporate, and store host lipids, while the metabolic reprogramming causes oxidative stress-induced DNA damage in hepatocytes, independent of the host's immune response. S. mansoni eggs take advantage of the host environment through metabolic reprogramming of hepatocytes and enterocytes. By inducing DNA damage, this neglected tropical disease might promote hepatocellular damage and thus influence international health efforts.

High-resolution AP-SMALDI MSI as a tool for drug imaging in Schistosoma mansoni

Schistosoma mansoni is a parasitic flatworm causing schistosomiasis, an infectious disease affecting several hundred million people worldwide. Schistosomes live dioeciously, and upon pairing with the male, the female starts massive egg production, which causes pathology. Praziquantel (PZQ) is the only drug used, but it has an inherent risk of resistance development. Therefore, alternatives are needed. In the context of drug repurposing, the cancer drug imatinib was tested, showing high efficacy against S. mansoni in vitro. Besides the gonads, imatinib mainly affected the integrity of the intestine in males and females. In this study, we investigated the potential uptake and distribution of imatinib in adult schistosomes including its distribution kinetics. To this end, we applied for the first time atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging (AP-SMALDI MSI) for drug imaging in paired S. mansoni. Our results indicate that imatinib was present in the esophagus and intestine of the male as early as 20 min after in vitro exposure, suggesting an oral uptake route. After one hour, the drug was also found inside the paired female. The detection of the main metabolite, N-desmethyl imatinib, indicated metabolization of the drug. Additionally, a marker signal for the female ovary was successfully applied to facilitate further conclusions regarding organ tropism of imatinib. Our results demonstrate that AP-SMALDI MSI is a useful method to study the uptake, tissue distribution, and metabolization of imatinib in S. mansoni. The results suggest using AP-SMALDI MSI also for investigating other antiparasitic compounds and their metabolites in schistosomes and other parasites.

Intracellular Parasites Toxoplasma gondii and Besnoitia besnoiti, Unveiled in Single Host Cells Using AP-SMALDI MS Imaging

The obligate intracellular apicomplexan parasites Toxoplasma gondii and Besnoitia besnoiti are important causes of disease in both humans and cattle. To date, effective specific treatments are lacking for both infections. To counteract severe symptoms leading to, e.g., disabilities and even abortion in the case of human toxoplasmosis and bovine besnoitiosis, novel targets are required for development of drugs and vaccines. A promising emerging technique for molecular characterization of organisms is high-resolution atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) which enables semiquantitative visualization of metabolite distributions. MSI was here used to trace and characterize lipid metabolites in primary bovine umbilical vein endothelial cells (BUVECs) upon infection with tachyzoites, an early and pathogenic fast-replicating life stage of T. gondii and B. besnoiti. A cell bulk, derived from noninfected controls and parasite-infected cell pellets, was analyzed by AP-SMALDI MSI in technical and biological triplicates. Multivariate statistical analysis including hierarchical clustering and principle component analysis revealed infection-specific metabolites in both positive- and negative-ion mode, identified by combining database search and LC-MS² experiments. MSI analyses of host cell monolayers were conducted at 5 μm lateral resolution, allowing single apicomplexan-infected cells to be allocated. This is the first mass spectrometry imaging study on intracellular T. gondii and B. besnoiti infections and the first detailed metabolomic characterization of B. besnoiti tachyzoites. MSI was used here as an efficient tool to discriminate infected from noninfected cells at the single-cell level in vitro.

Tissue- and sex-specific lipidomic analysis of Schistosoma mansoni using high-resolution atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging

Schistosomes are human pathogens causing the neglected tropical disease schistosomiasis, which occurs worldwide in (sub-)tropical regions. This infectious disease is often associated with poverty, and more than 700 million people are at risk of infection. Exploitation of novel habitats and limited therapeutic options brought schistosomes into research focus. Schistosomes are the only trematodes that have evolved separate sexes. They are covered by their metabolically active tegument, a surface area representing the interface between male and female in their permanent mating contact but also between parasite and host. The tegument comprises, besides others, numerous specific lipid compounds. Limited information is available on the exact lipid composition and its spatial distribution. We used atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) to characterize the Schistosoma mansoni tegument surface in comparison to tissue sections of whole worms or couples. We found that phosphatidylcholines (PC) and specific phosphatidylethanolamines (PE) are significantly more abundant inside the worm body compared to the tegument. On the other hand, the latter was found to be enriched in sphingomyelins (SM), phosphatidylserines (PS), lysophosphatidylcholines (LPC), and specific PE species. We further investigated lipid classes concerning number of carbon atoms in fatty acyl chains as well as the degree of unsaturation and found pronounced differences between the tegument and whole-worm body. Furthermore, differences between male and female teguments were found. The lipid composition of S. mansoni tissues has been investigated in an untargeted, spatially resolved manner for the first time.

WHO-defined Neglected Tropical Diseases, including schistosomiasis, are a burden for a significant part of the human world population. The fight against the diecious trematode Schistosoma mansoni can be supported by investigations of the specific molecular communication in male/female and in worm/host interactions. Improving the knowledge about S. mansoni is mandatory, since there is justified fear of the possibility of resistance development against the only available drug Praziquantel. We used mass spectrometry imaging as a powerful tool to provide topographic and tissue-specific information on the parasite. We investigated single male and female worms, as well as mating couples, regarding both, their inner tissue, and their intact surfaces, the tegument. We found highly specific lipid species and visualized their local distributions and abundances in high-resolution molecular images. Our findings may help to improve knowledge of the complex life cycles and of molecular communication mechanisms of schistosomes and may help to develop new drugs and strategies for treatment of the infectious disease.

Autarkic desorption electrospray ionization source for on-site analysis of consumer goods

A battery-powered DESI source with integrated solvent/gas supply and novel sampling geometry is presented for daily-goods analysis.

Robustness of the non-neuronal cholinergic system in rat large intestine against luminal challenges

Acetylcholine and atypical esters of choline such as propionyl- and butyrylcholine are produced by the colonic epithelium and are released when epithelial receptors for short-chain fatty acids (SCFA) are stimulated by propionate. It is assumed that the SCFA used by the choline acetyltransferase (ChAT), the central enzyme for the production of these choline esters, originate from the colonic lumen, where they are synthesized during the bacterial fermentation of carbohydrates. Therefore, it seemed to be of interest to study whether the non-neuronal cholinergic system in the colonic epithelium is affected by maneuvers intended to stimulate or to inhibit colonic fermentation by changing the intestinal microbiota. In two series of experiments, rats were either fed with a high fiber diet (15.5% (w/v) crude fibers in comparison to 4.6% (w/w) in the control diet) or treated orally with the antibiotic vancomycin. High fiber diet induced an unexpected decrease in the luminal concentration of SCFA in the colon, but an increase in the caecum, suggesting an upregulation of colonic SCFA absorption, whereas vancomycin treatment resulted in the expected strong reduction of SCFA concentration in colon and caecum. MALDI MS analysis revealed a decrease in the colonic content of propionylcholine by high fiber diet and by vancomycin. High fiber diet caused a significant downregulation of ChAT expression on protein and mRNA level. Despite a modest increase in tissue conductance during the high fiber diet, main barrier and transport properties of the epithelium such as basal short-circuit current (I_sc), the flux of the paracellularly transported marker, fluorescein, or the I_sc induced by epithelial acetylcholine release evoked by propionate remained unaltered. These results suggest a remarkable stability of the non-neuronal cholinergic system in colonic epithelium against changes in the luminal environment underlying its biological importance for intestinal homeostasis.

Strategy for marker-based differentiation of pro- and anti-inflammatory macrophages using matrix-assisted laser desorption/ionization mass spectrometry imaging

Macrophages are large phagocytes playing a crucial role in the development and progression of atherosclerosis. The phenotypic polarization and activation of macrophages in atherosclerotic plaques depends on their complex micro-environment and at the same time has a major impact on the vulnerability or stability of advanced atherosclerotic lesions. Many in vitro and in vivo studies have been designed to define markers for macrophage subtypes to better understand the mechanism of plaque progression but they have rather added to the confusion. Nonetheless, some of the in vitro defined macrophage subtypes, like the pro-inflammatory M1 or the anti-inflammatory M2a/b/c macrophage, have been shown to be present in atherosclerotic plaques. Herein, we developed a comprehensive workflow to distinguish between human in vitro differentiated pro-inflammatory M1 and anti-inflammatory M2a and M2c macrophages. The cells were analyzed using qPCR and FACS analyses for defining suitable markers on the transcript (mRNA) and protein level as well as MALDI MSI for the assignment of metabolic markers, which can be used for the identification of the corresponding macrophage subtypes in atherosclerotic plaques. Data obtained using both qPCR and FACS analyses were in agreement with the literature. For the analysis of the macrophages with MALDI MSI, a comprehensive workflow was developed and the obtained data were subjected to different statistical analysis methods like principal component analysis (PCA) to define markers for each macrophage type. Our MALDI MSI results revealed that the method produces reliable and reproducible results but that the heterogeneity of the monocytes derived from different donors is too high to define universal markers on the metabolic level. Moreover, the results show that a sample set of three biological replicates is not sufficient to obtain representative data and therefore we recommend performing ring experiments in which the samples are measured by different laboratories.

Real-Time Food Authentication Using a Miniature Mass Spectrometer

Food adulteration is a threat to public health and the economy. In order to determine food adulteration efficiently, rapid and easy-to-use on-site analytical methods are needed. In this study, a miniaturized mass spectrometer in combination with three ambient ionization methods was used for food authentication. The chemical fingerprints of three milk types, five fish species, and two coffee types were measured using electrospray ionization, desorption electrospray ionization, and low temperature plasma ionization. Minimum sample preparation was needed for the analysis of liquid and solid food samples. Mass spectrometric data was processed using the laboratory-built software MS food classifier, which allows for the definition of specific food profiles from reference data sets using multivariate statistical methods and the subsequent classification of unknown data. Applicability of the obtained mass spectrometric fingerprints for food authentication was evaluated using different data processing methods, leave-10%-out cross-validation, and real-time classification of new data. Classification accuracy of 100% was achieved for the differentiation of milk types and fish species, and a classification accuracy of 96.4% was achieved for coffee types in cross-validation experiments. Measurement of two milk mixtures yielded correct classification of >94%. For real-time classification, the accuracies were comparable. Functionality of the software program and its performance is described. Processing time for a reference data set and a newly acquired spectrum was found to be 12 s and 2 s, respectively. These proof-of-principle experiments show that the combination of a miniaturized mass spectrometer, ambient ionization, and statistical analysis is suitable for on-site real-time food authentication.

Epithelial propionyl- and butyrylcholine as novel regulators of colonic ion transport

BACKGROUND AND PURPOSE

The colonic surface epithelium produces acetylcholine, released after the binding of propionate to GPCRs for this short-chain fatty acid (SCFA). This epithelial acetylcholine then induces anion secretion via stimulation of acetylcholine receptors. The key enzyme responsible for acetylcholine synthesis, choline acetyltransferase, is known to be unselective as regards the fatty acid used for esterification of choline. As the colonic epithelium is permanently exposed to high concentrations of different SCFAs produced by bacterial fermentation, we investigated whether choline esters other than acetylcholine, propionylcholine and butyrylcholine, are produced by the colonic epithelium, too, and whether these 'atypical' esters are able to stimulate the acetylcholine receptors involved in the regulation of colonic ion transport.

EXPERIMENTAL APPROACH

Desorption electrospray ionization mass spectroscopy (DESI-MS), Ussing chamber and Ca(2+) -imaging experiments were performed on rat distal colon.

KEY RESULTS

DESI-MS analyses revealed the production of acetylcholine, propionylcholine and butyrylcholine in the surface epithelium. Relative expression rates were 2-3% in comparison with acetylcholine. In Ussing chamber experiments, both atypical choline esters caused a concentration-dependent increase in short-circuit current, that is, stimulated anion secretion. Inhibitor experiments in the absence and presence of the submucosal plexus revealed the involvement of neuronal and epithelial acetylcholine receptors. While butyrylcholine obviously stimulated both nicotinic and muscarinic receptors, propionylcholine predominantly acted on muscarinic receptors.

CONCLUSIONS AND IMPLICATIONS

These results suggest a novel pathway for communication between intestinal microbes producing SCFA and the host via modification of epithelial production of choline esters involved in the paracrine regulation of the colonic epithelium.

DESI MS based screening method for phthalates in consumer goods

Phthalates are used as plasticizes in many everyday items, but some of them are known as hormone disruptors, being especially harmful during childhood. The European Union therefore restricted their application in children's toys and certain food packaging to 0.1%w. Due to the ever increasing number of plastic-containing consumer goods, rapid screening methods are needed to ensure and improve consumer safety in the future. In this study we evaluated the performance of desorption electrospray ionization (DESI) mass spectrometry (MS) for rapid quantitative screening of phthalates in toys. DESI allowed for direct surface sampling of the toys under atmospheric conditions with minimal sample preparation, while the high performance mass spectrometer used provided a high sensitivity and reliable identification via accurate mass measurements, high mass resolving power and MS/MS capabilities. External calibration curves for six banned phthalates (DBP, BBP, DEHP, DNOP, DINP and DIDP) were obtained from matrix-matched reference materials. Coefficients of determination were greater than 0.985, LOQs ranged from 0.02%w (DIDP) to 2.26%w (DINP) and the relative standard deviation of the calibration curve slope was less than 7.8% for intraday and 11.4% for interday comparison. The phthalate contents of eleven authentic samples were determined in a proof-of-concept approach using DESI MS and results were compared to those from confirmatory methods. The phthalate content was correctly assigned with relative deviations ranging from -20% to +10% for the majority of samples. Given further optimization and automation, DESI MS is likely to become a useful tool for rapid and accurate phthalate screening in the future.

Luminal cholinergic signalling in airway lining fluid: a novel mechanism for activating chloride secretion via Ca²⁺-dependent Cl⁻ and K⁺ channels

BACKGROUND AND PURPOSE

Recent studies detected the expression of proteins involved in cholinergic metabolism in airway epithelial cells, although the function of this non-neuronal cholinergic system is not known in detail. Thus, this study focused on the effect of luminal ACh as a regulator of transepithelial ion transport in epithelial cells.

EXPERIMENTAL APPROACH

RT-PCR experiments were performed using mouse tracheal epithelial cells for ChAT and organic cation transporter (OCT) transcripts. Components of tracheal airway lining fluid were analysed with desorption electrospray ionization (DESI) MS. Effects of nicotine on mouse tracheal epithelial ion transport were examined with Ussing-chamber experiments.

KEY RESULTS

Transcripts encoding ChAT and OCT1-3 were detected in mouse tracheal epithelial cells. The DESI experiments identified ACh in the airway lining fluid. Luminal ACh induced an immediate, dose-dependent increase in the transepithelial ion current (EC₅₀: 23.3 µM), characterized by a transient peak and sustained plateau current. This response was not affected by the Na⁺-channel inhibitor amiloride. The Cl⁻-channel inhibitor niflumic acid or the K⁺-channel blocker Ba²⁺ attenuated the ACh effect. The calcium ionophore A23187 mimicked the ACh effect. Luminal nicotine or muscarine increased the ion current. Experiments with receptor gene-deficient animals revealed the participation of muscarinic receptor subtypes M₁ and M₃.

CONCLUSIONS AND IMPLICATIONS

The presence of luminal ACh and activation of transepithelial ion currents by luminal ACh receptors identifies a novel non-neuronal cholinergic pathway in the airway lining fluid. This pathway could represent a novel drug target in the airways.

Analysis of colorectal adenocarcinoma tissue by desorption electrospray ionization mass spectrometric imaging

Negative ion desorption electrospray ionization (DESI) was used for the analysis of an ex vivo tissue sample set comprising primary colorectal adenocarcinoma samples and colorectal adenocarcinoma liver metastasis samples. Frozen sections (12 μm thick) were analyzed by means of DESI imaging mass spectrometry (IMS) with spatial resolution of 100 μm using a computer-controlled DESI imaging stage mounted on a high resolution Orbitrap mass spectrometer. DESI-IMS data were found to predominantly feature complex lipids, including phosphatidyl-inositols, phophatidyl-ethanolamines, phosphatidyl-serines, phosphatidyl-ethanolamine plasmalogens, phosphatidic acids, phosphatidyl-glycerols, ceramides, sphingolipids, and sulfatides among others. Molecular constituents were identified based on their exact mass and MS/MS fragmentation spectra. An identified set of molecules was found to be in good agreement with previously reported DESI imaging data. Different histological tissue types were found to yield characteristic mass spectrometric data in each individual section. Histological features were identified by comparison to hematoxylin-eosin stained neighboring sections. Ions specific to certain histological tissue types (connective tissue, smooth muscle, healthy mucosa, healthy liver parenchyma, and adenocarcinoma) were identified by semi-automated screening of data. While each section featured a number of tissue-specific species, no potential global biomarker was found in the full sample set for any of the tissue types. As an alternative approach, data were analyzed by principal component analysis (PCA) and linear discriminant analysis (LDA) which resulted in efficient separation of data points based on their histological types. A pixel-by-pixel tissue identification method was developed, featuring the PCA/LDA analysis of authentic data set, and localization of unknowns in the resulting 60D, histologically assigned LDA space. Novel approach was found to yield results which are in 95% agreement with the results of classical histology. KRAS mutation status was determined for each sample by standard molecular biology methods and a similar PCA/LDA approach was developed to assess the feasibility of the determination of this important parameter using solely DESI imaging data. Results showed that the mutant and wild-type samples fully separated. DESI-MS and molecular biology results were in agreement in 90% of the cases.

Analysis of triglycerides in food items by desorption electrospray ionization mass spectrometry

The triglyceride composition and oxidation behavior of edible oil and margarine samples were analyzed by desorption electrospray ionization mass spectrometry (DESI-MS). For the characterization of the lipids, the chain length and the degree of unsaturation of the fatty acids were determined. The measurements were carried out in positive ion mode; the triglycerides were detected as alkali metal or ammonium adducts. The DESI solvent was water/methanol 1:1 (v/v); measurements were carried out both with and without the addition, as an ionizing agent, of ammonium acetate that enhances the signal intensity of the ammonium adduct ions. The spectra were interpreted for both cases and intensities were compared. Triglyceride monomers and dimers were observed in the spectra. Tandem mass spectrometric (MS/MS) measurements were carried out to determine the structure of the triglycerides. It was demonstrated that the terminal fatty acids in the sn1- or sn3-position are more likely to be cleaved than the internal fatty acid (sn2-position). Characteristic triglyceride patterns were obtained using a simple and rapid sample preparation protocol comprising the simple deposition of samples onto a glass carrier surface. The triglyceride data was analyzed by principal component analysis (PCA). The different edible oils were clearly separated and the hydrogenated derivatives were identified by their triglyceride spectra. The oxidation of the oil samples was observed and the oxidation products were detected and identified. This method provides a fast and simple technique for the detection and analysis of triglycerides in oil- or fat-containing samples ranging from food items to tissue samples. The potential application areas include nutritional studies, the food industry and cosmetics.