Proteomic analysis of the effects of the immunomodulatory mycotoxin deoxynivalenol

Exploring the dermotoxicity of the mycotoxin deoxynivalenol: combined morphologic and proteomic profiling of human epidermal cells reveals alteration of lipid biosynthesis machinery and membrane structural integrity relevant for skin barrier function

Deoxynivalenol (vomitoxin, DON) is a secondary metabolite produced by Fusarium spp. fungi and it is one of the most prevalent mycotoxins worldwide. Crop infestation results not only in food and feed contamination, but also in direct dermal exposure, especially during harvest and food processing. To investigate the potential dermotoxicity of DON, epidermoid squamous cell carcinoma cells A431 were compared to primary human neonatal keratinocytes (HEKn) cells via proteome/phosphoproteome profiling. In A431 cells, 10 µM DON significantly down-regulated ribosomal proteins, as well as mitochondrial respiratory chain elements (OXPHOS regulation) and transport proteins (TOMM22; TOMM40; TOMM70A). Mitochondrial impairment was reflected in altered metabolic competence, apparently combined with interference of the lipid biosynthesis machinery. Functional effects on the cell membrane were confirmed by live cell imaging and membrane fluidity assays (0.1–10 µM DON). Moreover, a common denominator for both A431 and HEKn cells was a significant downregulation of the squalene synthase (FDFT1). In sum, proteome alterations could be traced back to the transcription factor Klf4, a crucial regulator of skin barrier function. Overall, these results describe decisive molecular events sustaining the capability of DON to impair skin barrier function. Proteome data generated in the study are fully accessible via ProteomeXchange with the accession numbers PXD011474 and PXD013613.

Individual and combined effects of Aflatoxin B1, Deoxynivalenol and Zearalenone on HepG2 and RAW 264.7 cell lines

To understand the combinatorial toxicity of mycotoxins, we measured the effects of individual, binary and tertiary combinations of Aflatoxin B₁ (AFB₁), Deoxynivalenol (DON) and Zearalenone (ZEN) on the cell viability and cellular perturbations of HepG2 and RAW 264.7 cells. The nature of mycotoxins interactions was assessed using mathematical modeling (Chou-Talalay). Mechanisms of cytotoxicity were studied using high content screening (HCS) that probed cytotoxicity responses, such as changes in intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), intracellular calcium ([Ca²⁺]_i) flux, and cell membrane damage. Our results showed that individual cytotoxicity of mycotoxins in a decreasing order was DON>AFB₁>ZEN. Varying combinations of mycotoxins at differing concentrations showed different types of interactions. Most of the mixtures showed increasing toxic effects-synergism and/or addition while antagonistic effects were observed with combination of AFB₁+ZEN. Generally, combination of mycotoxins showed significantly increased intracellular ROS production and [Ca²⁺]_i flux, and decreased MMP in both cell lines, showing that the synergistic and additive effects of mycotoxin combination originate from perturbations of multiple cellular functions. Additionally, this study demonstrated the applicability of HCS for gaining mechanistic understanding on the toxicity of individual as well as combinatorial mycotoxins, and also provided scientific bases for formulating regulatory policies.

The Antagonistic Effect of Mycotoxins Deoxynivalenol and Zearalenone on Metabolic Profiling in Serum and Liver of Mice

Metabolic profiling in liver and serum of mice was studied for the combined toxic effects of deoxynivalenol (DON) and zearalenone (ZEN), through gas chromatography mass spectrum. The spectrum of serum and liver sample of mice, treated with individual 2 mg/kg DON, 20 mg/kg ZEN, and the combined DON + ZEN with final concentration 2 mg/kg DON and 20 mg/kg ZEN for 21 days, were deconvoluted, aligned and identified with MS DIAL. The data matrix was processed with univariate analysis and multivariate analysis for selection of metabolites with variable importance for the projection (VIP) > 1, t-test p value < 0.05. The metabolic pathway analysis was performed with MetaMapp and drawn by CytoScape. Results show that the combined DON and ZEN treatment has an obvious “antagonistic effect” in serum and liver tissue metabolic profiling of mice. The blood biochemical indexes, like alkaline phosphatase, alanine transaminase, and albumin (ALB)/globulin (GLO), reveal a moderated trend in the combined DON + ZEN treatment group, which is consistent with histopathological examination. The metabolic pathway analysis demonstrated that the combined DON and ZEN treatment could down-regulate the valine, leucine and isoleucine biosynthesis, glycine, serine and threonine metabolism, and O-glycosyl compounds related glucose metabolism in liver tissue. The metabolic profiling in serum confirmed the finding that the combined DON and ZEN treatment has an “antagonistic effect” on liver metabolism of mice.

Mycotoxins: cytotoxicity and biotransformation in animal cells

Mycotoxins are secondary metabolites produced by many microfungi. Hitherto, over 300 mycotoxins with diverse structures have been identified. They contaminate most cereals and feedstuffs, which threaten human and animal health by exerting acute, sub-acute and chronic toxicological effects, with some considered as carcinogens. Many mycotoxins at low concentrations are able to induce the expression of cytochrome P450 and other enzymes implicated in the biotransformation and metabolization of mycotoxins in vivo and in vitro. Mycotoxins and their metabolites elicit different cellular disorders and adverse effects such as oxidative stress, inhibition of translation, DNA damage and apoptosis in host cells, thus causing various kinds of cytotoxicities. In this review, we summarize the biotransformation of mycotoxins in animal cells by CYP450 isoforms and other enzymes, their altered expression under mycotoxin exposure, and recent progress in mycotoxin cytotoxicity in different cell lines. Furthermore, we try to generalize the molecular mechanisms of mycotoxin effects in human and animal cells.

Proteomics in food: Quality, safety, microbes, and allergens

Food safety and quality and their associated risks pose a major concern worldwide regarding not only the relative economical losses but also the potential danger to consumer's health. Customer's confidence in the integrity of the food supply could be hampered by inappropriate food safety measures. A lack of measures and reliable assays to evaluate and maintain a good control of food characteristics may affect the food industry economy and shatter consumer confidence. It is imperative to create and to establish fast and reliable analytical methods that allow a good and rapid analysis of food products during the whole food chain. Proteomics can represent a powerful tool to address this issue, due to its proven excellent quantitative and qualitative drawbacks in protein analysis. This review illustrates the applications of proteomics in the past few years in food science focusing on food of animal origin with some brief hints on other types. Aim of this review is to highlight the importance of this science as a valuable tool to assess food quality and safety. Emphasis is also posed in food processing, allergies, and possible contaminants like bacteria, fungi, and other pathogens.

Mycotoxin mechanisms of action and health impact: ‘in vitro’ or ‘in vivo’ tests, that is the question

The aim of this paper is to present examples of in vitro and in vivo tests for mycotoxin mechanisms of action and evaluation of health effects, with a focus on the gut environment and toxicity testing. In vivo investigations may provide information on the net effects of mycotoxins in whole animals, whereas in vitro models represent effective tools to perform simplified experiments under uniform and well-controlled conditions and a suitable alternative to in vivo animal testing providing insights not achievable with animal studies. The main limits of in vitro models are the lack of interactions with other cells and extracellular factors, lack of hormonal or immunological influences, and lack or different levels of in vitro expression of genes involved in the overall response to mycotoxins. The translation of in vitro data into meaningful in vivo effects remains an unsolved problem. The main issues to be considered are the mycotoxin concentration range in accordance with levels encountered in realistic situations, the identification of reliable biomarkers of mycotoxin toxicity, the measurement of the chronic toxicity, the evaluation of single- or multi-toxin challenge. The gastrointestinal wall is the first barrier preventing the entry of undesirable substances. The intestinal epithelium can be exposed to high concentrations of mycotoxins upon ingestion of contaminated food and the amount of mycotoxin consumed via food does not always reflect the amount available to exert toxic actions in a target organ. In vitro digestion models in combination with intestinal epithelial cells are powerful tools to screen and predict the in vivo bioavailability and digestibility of mycotoxins in contaminated food and correctly estimate health effects. In conclusion, in vitro and in vivo tests are complementary approaches for providing a more accurate picture of the health impact of mycotoxins and improved understanding and evaluation of relevant dietary exposure and risk scenarios.

The Food-Associated Ribotoxin Deoxynivalenol Modulates Inducible NO Synthase in Human Intestinal Cell Model

The intestinal epithelium possesses active immune functions including the production of proinflammatory cytokines and antimicrobial molecules such as nitric oxide (NO). As observed with immune cells, the production of NO by the intestinal epithelium is mainly due to the expression of the inducible NO synthase (iNOS or NOS2). Epithelial immune functions could be affected by many factors including pathogenic microorganisms and food-associated toxins (bacterial and fungal). Among the various mycotoxins, deoxynivalenol (DON) is known to alter the systemic and intestinal immunity. However, little is known about the effect of DON on the production of NO by the intestinal epithelium. We studied the impact of DON on the intestinal expression of iNOS using the Caco-2 cell model. In line with its proinflammatory activity, we observed that DON dose-dependently up-regulates the expression of iNOS mRNA. Surprisingly, DON failed to increase the expression of iNOS protein. When testing the effects of DON on cytokine-mediated induction of iNOS, we found that very low concentrations of DON (ie, 1 µM) decrease the amount of iNOS protein but not of iNOS mRNA. We demonstrated that DON's effect on iNOS protein relies on its ability to activate signal pathways and to increase iNOS ubiquitinylation and degradation through the proteasome pathway. Taken together, our results demonstrate that although DON causes intestinal inflammation, it suppresses the ability of the gut epithelium to express iNOS and to produce NO, potentially explaining the increased susceptibility of animals to intestinal infection following exposure to low doses of DON.

Using SILAC proteomics to investigate the effect of the mycotoxin, alternariol, in the human H295R steroidogenesis model

The mycotoxin alternariol (AOH) is an important contaminant of fruits and cereal products. The current study sought to address the effect of a non-toxic AOH concentration on the proteome of the steroidogenic H295R cell model. Quantitative proteomics based on stable isotope labeling by amino acids in cell culture (SILAC) coupled to 1D-SDS-PAGE-LC-MS/MS was applied to subcellular-enriched protein samples. Gene ontology (GO) and ingenuity pathway analysis (IPA) were further carried out for functional annotation and identification of protein interaction networks. Furthermore, the effect of AOH on apoptosis and cell cycle distribution was also determined by the use of flow cytometry analysis. This work identified 22 proteins that were regulated significantly. The regulated proteins are those involved in early stages of steroid biosynthesis (SOAT1, NPC1, and ACBD5) and C21-steroid hormone metabolism (CYP21A2 and HSD3B1). In addition, several proteins known to play a role in cellular assembly, organization, protein synthesis, and cell cycle were regulated. These findings provide a new framework for studying the mechanisms by which AOH modulates steroidogenesis in H295R cell model.

Sub-emetic toxicity of Bacillus cereus toxin cereulide on cultured human enterocyte-like Caco-2 cells

Cereulide (CER) intoxication occurs at relatively high doses of 8 µg/kg body weight. Recent research demonstrated a wide prevalence of low concentrations of CER in rice and pasta dishes. However, the impact of exposure to low doses of CER has not been studied before. In this research, we investigated the effect of low concentrations of CER on the behavior of intestinal cells using the Caco-2 cell line. The MTT (mitochondrial 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and the SRB (sulforhodamine B) reactions were used to measure the mitochondrial activity and cellular protein content, respectively. Both assays showed that differentiated Caco-2 cells were sensitive to low concentrations of CER (in a MTT reaction of 1 ng/mL after three days of treatment; in an SRB reaction of 0.125 ng/mL after three days of treatment). Cell counts revealed that cells were released from the differentiated monolayer at 0.5 ng/mL of CER. Additionally, 0.5 and 2 ng/mL of CER increased the lactate presence in the cell culture medium. Proteomic data showed that CER at a concentration of 1 ng/mL led to a significant decrease in energy managing and H2O2 detoxification proteins and to an increase in cell death markers. This is amongst the first reports to describe the influence of sub-emetic concentrations of CER on a differentiated intestinal monolayer model showing that low doses may induce an altered enterocyte metabolism and membrane integrity.

Cell-based models for mycotoxin screening and toxicity evaluation: an update

This review presents the applications of cell-based models in mycotoxin research, with a focus on models for mycotoxin screening and cytotoxicity evaluation. Various cell-based models, cell and cell culture condition related factors, toxicity endpoints and culture systems as well as predictive value of cell-based bioassays are reviewed. Advantages, drawbacks and technical problems regarding set up and validation of consistent, robust, reproducible and high-throughput cell-based models are discussed. Various cell-based models have been developed and used as screening tests for mycotoxins but the data obtained are difficult to compare. However, the results highlight the potential of cell-based models as promising in vitro platforms for the initial screening and cytotoxicity evaluation of mycotoxins and as a significant analytical approach in mycotoxin research before any animal or human clinical studies. To develop cell-based models as powerful high-throughput laboratory platforms for the analysis of large numbers of samples, there are mainly two fundamental requirements that should be met, i.e. the availability of easy-to-use and, if possible, automated cell platforms and the possibility to obtain reproducible results that are comparable between laboratories. The transition from a research model to a test model still needs optimisation, standardisation, and validation of analytical protocols. The validation of a cell-based bioassay is a complex process, as several critical points, such as the choice of the cellular model, the assay procedures, and the appropriate use and interpretation of the results, must be strictly defined to ensure more consistency in the results. The development of cell-based models exploring the third dimension together with automation and miniaturisation will bring cellular platforms to a level appropriate for cost-effective and large-scale analysis in the field of mycotoxin research.

Applications of flow cytometry to toxicological mycotoxin effects in cultured mammalian cells: a review

This review gives an overview of flow cytometry applications to toxicological studies of several physiological target sites of mycotoxins on different mammalian cell lines. Mycotoxins are secondary metabolites of fungi that may be present in food, feed, air and water. The increasing presence of mycotoxins in crops, their wide distribution in the food chain, and their potential for toxicity demonstrate the need for further knowledge. Flow cytometry has become a valuable tool in mycotoxin studies in recent years for the rapid analysis of single cells in a mixture. In toxicology, the power of these methods lies in the possibility of determining a wide range of cell parameters, providing valuable information to elucidate cell growth and viability, metabolic activity, mitochondrial membrane potential and membrane integrity mechanisms. There are studies using flow cytometry technique on Alternaria, Aspergillus, Fusarium and Penicillium mycotoxins including information about cell type, assay conditions and functional parameters. Most of the studies collected in the literature are on deoxynivalenol and zearalenone mycotoxins. Cell cycle analysis and apoptosis are the processes more widely investigated.

Global protein phosphorylation dynamics during deoxynivalenol-induced ribotoxic stress response in the macrophage

Deoxynivalenol (DON), a trichothecene mycotoxin produced by Fusarium that commonly contaminates food, is capable of activating mononuclear phagocytes of the innate immune system via a process termed the ribotoxic stress response (RSR). To encapture global signaling events mediating RSR, we quantified the early temporal (≤30min) phosphoproteome changes that occurred in RAW 264.7 murine macrophage during exposure to a toxicologically relevant concentration of DON (250ng/mL). Large-scale phosphoproteomic analysis employing stable isotope labeling of amino acids in cell culture (SILAC) in conjunction with titanium dioxide chromatography revealed that DON significantly upregulated or downregulated phosphorylation of 188 proteins at both known and yet-to-be functionally characterized phosphosites. DON-induced RSR is extremely complex and goes far beyond its prior known capacity to inhibit translation and activate MAPKs. Transcriptional regulation was the main target during early DON-induced RSR, covering over 20% of the altered phosphoproteins as indicated by Gene Ontology annotation and including transcription factors/cofactors and epigenetic modulators. Other biological processes impacted included cell cycle, RNA processing, translation, ribosome biogenesis, monocyte differentiation and cytoskeleton organization. Some of these processes could be mediated by signaling networks involving MAPK-, NFκB-, AKT- and AMPK-linked pathways. Fuzzy c-means clustering revealed that DON-regulated phosphosites could be discretely classified with regard to the kinetics of phosphorylation/dephosphorylation. The cellular response networks identified provide a template for further exploration of the mechanisms of trichothecenemycotoxins and other ribotoxins, and ultimately, could contribute to improved mechanism-based human health risk assessment.

Multiclass mycotoxin analysis in food, environmental and biological matrices with chromatography/mass spectrometry

Mold metabolites that can elicit deleterious effects on other organisms are classified as mycotoxins. Human exposure to mycotoxins occurs mostly through the intake of contaminated agricultural products or residues due to carry over or metabolite products in foods of animal origin such as milk and eggs, but can also occur by dermal contact and inhalation. Mycotoxins contained in moldy foods, but also in damp interiors, can cause diseases in humans and animals. Nephropathy, various types of cancer, alimentary toxic aleukia, hepatic diseases, various hemorrhagic syndromes, and immune and neurological disorders are the most common diseases that can be related to mycotoxicosis. The absence or presence of mold infestation and its propagation are seldom correlated with mycotoxin presence. Mycotoxins must be determined directly, and suitable analytical methods are necessary. Hundreds of mycotoxins have been recognized, but only for a few of them, and in a restricted number of utilities, a maximum acceptable level has been regulated by law. However, mycotoxins seldom develop alone; more often various types and/or classes form in the same substrate. The co-occurrence might render the individual mycotoxin tolerance dose irrelevant, and therefore the mere presence of multiple mycotoxins should be considered a risk factor. The advantage of chromatography/mass spectrometry (MS) is that many compounds can be determined and confirmed in one analysis. This review illustrates the state-of-the-art of mycotoxin MS-based analytical methods for multiclass, multianalyte determination in all the matrices in which they appear. A chapter is devoted to the history of the long-standing coexistence and interaction among humans, domestic animals and mycotoxicosis, and the history of the discovery of mycotoxins. Quality assurance, although this topic relates to analytical chemistry in general, has been also examined for mycotoxin analysis as a preliminary to the systematic literature excursus. Sample handling is a crucial step to devise a multiclass analytical method; so when possible, it has been treated separately for a better comparison before tackling the instrumental part of the whole analytical method. This structure has resulted sometimes in unavoidable redundancies, because it was also important to underline the interconnection. Most reviews do not deal with all the possible mycotoxin sources, including the environmental ones. The focus of this review is the analytical methods based on MS for multimycotoxin class determination. Because the final purpose to devise multimycotoxin analysis should be the assessment of the danger to health of exposition to multitoxicants of natural origin (and possibly also the interaction with anthropogenic contaminants), therefore also the analytical methods for environmental relevant mycotoxins have been thoroughly reviewed. Finally, because the best way to shed light on actual risk assessment could be the individuation of exposure biomarkers, the review covers also the scarce literature on biological fluids.