Deoxynivalenol induces p38 interaction with the ribosome in monocytes and macrophages

Deoxynivalenol modulated mucin expression and proinflammatory cytokine production, affecting susceptibility to enteroinvasive Escherichia coli infection in intestinal epithelial cells

Deoxynivalenol (DON) is a common mycotoxin in crops that could induce intestinal inflammation, affecting the susceptibility of intestinal epithelial cells (IECs) to pathogen infection. This study aimed to investigate DON's effects on mucin and cytokine production as part of the local immune system and how it affected intestinal susceptibility to pathogen infection. Caco-2 cells were exposed to DON followed by acute enteroinvasive Escherichia coli (EIEC) infection. An increase in EIEC attachment to DON-exposed cells was observed, probably in part, mediated by secretory MUC5AC mucins and membrane-bound MUC4 and MUC17 mucins. Additionally, DON with EIEC posttreatment led to significant changes in the gene expression of several proinflammatory cytokines (IL1α, IL1β, IL6, IL8, TNFα, and MCP-1), which may be in part, mediated by NK-κB and/or MAPK signaling pathways. These data suggested DON may exert immunomodulatory effects on IECs, altering the IEC susceptibility to bacterial infection. PRACTICAL APPLICATION: The results suggested that DON might modulate immune responses by affecting mucus and cytokine production, which may affect the susceptibility of intestinal epithelial cells to pathogen infection.

HLA gene variations and mycotoxin toxicity: Four case reports

Mycotoxins are produced by certain molds that can cause many health effects. We present four human cases of prolonged consistent mycotoxins exposure linked to genetic variations in human leukocyte antigen (HLA) alleles. The HLA-DR/DQ isotype alleles are linked to mycotoxins susceptibility due to the lack of proper immune response; individuals with these alleles are poor eliminators of mycotoxins from their system. Four subjects with variations in their HLA-DR alleles were exposed to mycotoxins from living in mold-infested houses and experienced persistent mold-related symptoms long after moving out from the mold-infested houses and only exposed to the levels of molds found in the ambient air. From one of the subjects, two urine samples were collected ~ 18 months apart after the cessation of exposure. Urinary elimination rate was extremely slow for two of the mycotoxins (ochratoxin A [OTA] and mycophenolic acid [MPA]) detected in both samples. In 18 months, decline in OTA level was only ~ 3-fold (estimated t½ of ~ 311 days) and decline in MPA level was ~ 11-fold (estimated t½ of ~ 160 days), which was ~ 10- and ~ 213-fold slower than expected in individuals without HLA-DR alleles, respectively. We estimated that ~ 4.3 and ~ 2.2 years will be required for OTA and MPA to reach < LLQ in urine, respectively. Three other subjects with variations in HLA-DR alleles were members of a family who lived in a mold-infested house for 4 years. They kept experiencing mold-related issues >2 years after moving to a non-mold-infested house. Consistent exposure was confirmed by the presence of several mycotoxins in urine >2 years after the secession of higher than background (from outdoor ambient air) exposure. This was consistent with the extremely slow elimination of mycotoxins from their system. Variations in HLA-DR alleles can, consequently, make even short periods of exposure to chronic exposure scenarios with related adverse health effects. It is, therefore, important to determine genetic predisposition as a reason for prolonged/lingering mold-related symptoms long after the cessation of higher than background exposure. Increased human exposure to mycotoxins is expected from increased mold infestation that is anticipated due to rising CO2, temperature, and humidity from the climate change with possibly increased adverse health effects, especially in individuals with genetic susceptibility to mold toxicity.

Recalling the reported toxicity assessment of deoxynivalenol, mitigating strategies and its toxicity mechanisms: Comprehensive review

Mycotoxins frequently contaminate a variety of food items, posing significant concerns for both food safety and public health. The adverse consequences linked to poisoning from these substances encompass symptoms such as vomiting, loss of appetite, diarrhea, the potential for cancer development, impairments to the immune system, disruptions in neuroendocrine function, genetic damage, and, in severe cases, fatality. The deoxynivalenol (DON) raises significant concerns for both food safety and human health, particularly due to its potential harm to vital organs in the body. It is one of the most prevalent fungal contaminants found in edible items used by humans and animals globally. The presence of harmful mycotoxins, including DON, in food has caused widespread worry. Altered versions of DON have arisen as possible risks to the environment and well-being, as they exhibit a greater propensity to revert back to the original mycotoxins. This can result in the buildup of mycotoxins in both animals and humans, underscoring the pressing requirement for additional investigation into the adverse consequences of these modified mycotoxins. Furthermore, due to the lack of sufficient safety data, accurately evaluating the risk posed by modified mycotoxins remains challenging. Our review study delves into conjugated forms of DON, exploring its structure, toxicity, control strategies, and a novel animal model for assessing its toxicity. Various toxicities, such as acute, sub-acute, chronic, and cellular, are proposed as potential mechanisms contributing to the toxicity of conjugated forms of DON. Additionally, the study offers an overview of DON's toxicity mechanisms and discusses its widespread presence worldwide. A thorough exploration of the health risk evaluation associated with conjugated form of DON is also provided in this discussion.

From ribosome to ribotoxins: understanding the toxicity of deoxynivalenol and Shiga toxin, two food borne toxins

Ribosomes that synthesize proteins are among the most central and evolutionarily conserved organelles. Given the key role of proteins in cellular functions, prokaryotic and eukaryotic pathogens have evolved potent toxins to inhibit ribosomal functions and weaken their host. Many of these ribotoxin-producing pathogens are associated with food. For example, food can be contaminated with bacterial pathogens that produce the ribotoxin Shiga toxin, but also with the fungal ribotoxin deoxynivalenol. Shiga toxin cleaves ribosomal RNA, while deoxynivalenol binds to and inhibits the peptidyl transferase center. Despite their distinct modes of action, both groups of ribotoxins hinder protein translation, but also trigger other comparable toxic effects, which depend or not on the activation of the ribotoxic stress response. Ribotoxic stress response-dependent effects include inflammation and apoptosis, whereas ribotoxic stress response-independent effects include endoplasmic reticulum stress, oxidative stress, and autophagy. For other effects, such as cell cycle arrest and cytoskeleton modulation, the involvement of the ribotoxic stress response is still controversial. Ribotoxins affect one organelle yet induce multiple toxic effects with multiple consequences for the cell. The ribosome can therefore be considered as the cellular "Achilles heel" targeted by food borne ribotoxins. Considering the high toxicity of ribotoxins, they pose a substantial health risk, as humans are highly susceptible to widespread exposure to these toxins through contaminated food sources.

Analysis of RIOK2 Functions in Mediating the Toxic Effects of Deoxynivalenol in Porcine Intestinal Epithelial Cells

Deoxynivalenol (DON) is a type of mycotoxin that threatens human and livestock health. Right open reading frame kinase 2 (RIOK2) is a kinase that has a pivotal function in ribosome maturation and cell cycle progression. This study aims to clarify the role of the RIOK2 gene in DON-induced cytotoxicity regulation in porcine intestinal epithelial cells (IPEC-J2). Cell viability assay and flow cytometry showed that the knockdown of RIOK2 inhibited proliferation and induced apoptosis, cell cycle arrest, and oxidative stress in DON-induced IPEC-J2. Then, transcriptome profiling identified candidate genes and pathways that closely interacted with both DON cytotoxicity regulation and RIOK2 expression. Furthermore, RIOK2 interference promoted the activation of the MAPK signaling pathway by increasing the phosphorylation of ERK and JNK. Additionally, we performed the dual-luciferase reporter and ChIP assays to elucidate that the expression of RIOK2 was influenced by the binding of transcription factor Sp1 with the promoter region. Briefly, the reduced expression of the RIOK2 gene exacerbates the cytotoxic effects induced by DON in IPEC-J2. Our findings provide insights into the control strategies for DON contamination by identifying functional genes and effective molecular markers.

Deoxynivalenol: Mechanisms of action and its effects on various terrestrial and aquatic species

Deoxynivalenol, a type B trichothecene mycotoxin produced by Fusarium species of fungi, is a ubiquitious contaminant of cereal grains worldwide. Chronic, low dose consumption of feeds contaminated with DON is associated with a wide range of symptoms in terrestrial and aquatic species including decreased feed intake and feed refusal, reduced weight gain, and altered nutritional efficiency. Acute, high dose exposure to DON may be associated with more severe symptoms such as vomiting, diarrhea, intestinal inflammation and gastrointestinal hemorrhage. The toxicity of DON is partly related to its ability to disrupt eukaryotic protein synthesis via binding to the peptidyl transferase site of the ribosome. Moreover, DON exerts its effects at the cellular level by activating mitogen activated protein kinases (MAPK) through a process known as the ribotoxic stress response (RSR). The outcome of DON-associated MAPK activation is dose and duration dependent; acute low dose exposure results in immunostimulation characterized by the upregulation of cytokines, chemokines and other proinflammatory-related proteins, whereas longer term exposure to higher doses generally results in apoptosis, cell cycle arrest, and immunosuppression. The order of decreasing sensitivity to DON is considered to be: swine > rats > mice > poultry ≈ ruminants. However, studies conducted within the past 10 years have demonstrated that some species of fish, such as rainbow trout, are highly sensitive to DON. The aims of this review are to explore the effects of DON on terrestrial and aquatic species as well as its mechanisms of action, metabolism, and interaction with other Fusarium mycotoxins. Notably, a considerable emphasis is placed on reviewing the effects of DON on different species of fish.

The toxicity mechanisms of DON to humans and animals and potential biological treatment strategies

Deoxynivalenol, also known as vomitotoxin, is produced by Fusarium, belonging to the group B of the trichothecene family. DON is widely polluted, mainly polluting cereal crops such as wheat, barley, oats, corn and related cereal products, which are closely related to lives of people and animals. At present, there have been articles summarizing DON induced toxicity, biological detoxification and the protective effect of natural products, but there is no systematic summary of this information. In addition to ribosome and endoplasmic reticulum, recent investigations support that mitochondrion is also organelles that DON can damage. DON can't directly act on mitochondria, but can indirectly cause mitochondrial damage and changes through other means. DON can indirectly inhibit mitochondrial biogenesis and mitochondrial electron transport chain activity, ATP production, and mitochondrial transcription and translation. This review will provide the latest progress on mitochondria as the research object, and systematically summarizes all the toxic mechanisms of DON. Here, we discuss DON induced mitochondrial-mediated apoptosis and various mitochondrial toxicity. For the toxicity of DON, many methods have been derived to prevent or reduce the toxicity. Biological detoxification and the antioxidant effect of natural products are potentially effective treatments for DON toxicity.

Combined Effect of Deoxynivalenol (DON) and Porcine Circovirus Type 2 (Pcv2) on Inflammatory Cytokine mRNA Expression

A host’s immune system can be invaded by mycotoxin deoxynivalenol (DON) poisoning and porcine circovirus type 2 (PCV2) infections, which affect the host’s natural immune function. Pro-inflammatory cytokines, IL-1β and IL-6, are important regulators in the process of natural immune response, which participate in inflammatory response and enhance immune-mediated tissue damage. Preliminary studies have shown that DON promotes PCV2 infection by activating the MAPK signaling pathway. Here, we explored whether the mRNA expression of IL-1β and IL-6, induced by the combination of DON and PCV2, would depend on the MAPK signaling pathway. Specific pharmacological antagonists U0126, SP600125 and SB203580, were used to inhibit the activities of ERK, JNK and p38 in the MAPK signaling pathway, respectively. Then, the mRNA expression of IL-1β and IL-6 in PK-15 cells was detected to explore the effect of the MAPK signaling pathway on IL-1β and IL-6 mRNA induced by DON and PCV2. The results showed that PK-15 cells treated with DON or PCV2 induced the mRNA expression of IL-1β and IL-6 in a time- and dose-dependent manner. The combination of DON and PCV2 has an additive effect on inducing the mRNA expression of IL-1β and IL-6. Additionally, both DON and PCV2 could induce the mRNA expression of IL-1β and IL-6 via the ERK and the p38 MAPK signal pathways, while PCV2 could induce it via the JNK signal pathway. Taken together, our results suggest that MAPKs play a contributory role in IL-1β and IL-6 mRNA expression when induced by both DON and PCV2.

Nrf2: a main responsive element in cells to mycotoxin-induced toxicity

Nuclear factor erythroid 2-like 2 (Nrf2) is a transcription factor participating in response to cellular oxidative stress to maintain the redox balance. Generation of reactive oxygen species (ROS) and, in consequence, oxidative stress, are physiological as well as pathological processes which take place in almost all types of cells. Nrf2, in response to oxidative stress, activates expression and production of antioxidant enzymes to remove free radicals. However, the role of Nrf2 seems to be more sophisticated and its increased expression observed in cancer cells allows to draw a conclusion that its role is tissue—and condition—dependent. Interestingly, Nrf2 might also play a crucial role in response to environmental factors like mycotoxins. Thus, the aim of the study is to review the role of Nrf2 in cells exposed to most common mycotoxins to check if the Nrf2 signaling pathway serves as the main response element to mycotoxin-induced oxidative stress in human and animal cells and if it can be a target of detoxifying agents.

Deoxynivalenol Has the Capacity to Increase Transcription Factor Expression and Cytokine Production in Porcine T Cells

Deoxynivalenol (DON) is a Fusarium mycotoxin that frequently contaminates the feed of farm animals. Pigs with their monogastric digestive system are in particular sensitive to DON-contaminated feed. At high concentrations, DON causes acute toxic effects, whereas lower concentrations lead to more subtle changes in the metabolism. This applies in particular to the immune system, for which immunosuppressive but also immunostimulatory phenomena have been described. Research in human and rodent cell lines indicates that this may be partially explained by a binding of DON to the ribosome and subsequent influences on cell signaling molecules like mitogen-activated protein kinases. However, a detailed understanding of the influence of DON on functional traits of porcine immune cells is still lacking. In this study, we investigated the influence of DON on transcription factor expression and cytokine production within CD4⁺, CD8⁺, and γδ T cells in vitro. At a DON concentration, that already negatively affects proliferation after Concanavalin A stimulation (0.8 μM) an increase of T-bet expression in CD4⁺ and CD8⁺ T cells was observed. This increase in T-bet expression coincided with elevated levels of IFN-γ and TNF-α producing T-cell populations. Increases in T-bet expression and cytokine production were found in proliferating and non-proliferating T cells, although increases were more prominent in proliferating cell subsets. Differently, IL-17A production by CD4⁺ T cells was not influenced by DON. In addition, frequencies of regulatory T cells and their expression of Foxp3 were not affected. In γδ T cells, GATA-3 expression was slightly reduced by DON, whereas T-bet levels were only slightly modulated and hence IFN-γ, TNF-α, or IL-17A production were not affected. Our results show for the single-cell level that DON has the capacity to modulate the expression of transcription factors and related cytokines. In particular, they suggest that for CD4⁺ and CD8⁺ T cells, DON can drive T-cell differentiation into a pro-inflammatory type-1 direction, probably depending on the already prevailing cytokine milieu. This could have beneficial or detrimental effects in ongoing immune responses to infection or vaccination.

Deoxynivalenol: toxicological profiles and perspective views for future research

Deoxynivalenol (DON) is a secondary metabolite mainly produced by the fungi Fusarium in agricultural crops, widely existing in feeds and cereal-based foodstuffs. Because of the high occurrence and potentials to induce a variety of toxic effects on animals and humans, DON has been a very harmful exogenous dietary toxicant threating public health. The focus of this review is to summarise the DON-induced broad spectrum of adverse health effects, to probe the current state of knowledge of combined toxicity of DON with other mycotoxins and its derivatives, and to put forward prospective ideas that multi-generational toxicity of DON and its overall impacts on intestinal-immuno-neuroendocrine system could receive more attention in future investigations. The general aim is to provide a scientific basis for the necessity to re-consider risk-assessment and regulations.

Deoxynivalenol Affects Proliferation and Expression of Activation-Related Molecules in Major Porcine T-Cell Subsets

The Fusarium mycotoxin deoxynivalenol (DON) contaminates animal feed worldwide. In vivo, DON modifies the cellular protein synthesis, thereby also affecting the immune system. However, the functional consequences of this are still ill-defined. In this study, peripheral blood mononuclear cells from healthy pigs were incubated with different DON concentrations in the presence of Concanavalin A (ConA), a plant-derived polyclonal T-cell stimulant. T-cell subsets were investigated for proliferation and expression of CD8α, CD27, and CD28, which are involved in activation and costimulation of porcine T cells. A clear decrease in proliferation of all ConA-stimulated major T-cell subsets (CD4⁺, CD8⁺, and γδ T cells) was observed in DON concentrations higher than 0.4 µM. This applied in particular to naïve CD4⁺ and CD8⁺ T cells. From 0.8 μM onwards, DON induced a reduction of CD8α (CD4⁺) and CD27 expression (CD4⁺ and CD8⁺ T cells). CD28 expression was diminished in CD4⁺ and CD8⁺ T cells at a concentration of 1.6 µM DON. None of these effects were observed with the DON-derivative deepoxy-deoxynivalenol (DOM-1) at 16 µM. These results indicate that DON reduces T-cell proliferation and the expression of molecules involved in T-cell activation, providing a molecular basis for some of the described immunosuppressive effects of DON.

JNK activation induced by ribotoxic stress is initiated from 80S monosomes but not polysomes

Translation is a costly, but inevitable, cell maintenance process. To reduce unnecessary ATP consumption in cells, a fine-tuning mechanism is needed for both ribosome biogenesis and translation. Previous studies have suggested that the ribosome functions as a hub for many cellular signals such as ribotoxic stress response, mammalian target of rapamycin (mTOR), and ribosomal S6 kinase (RSK) signaling. Therefore, we investigated the relationship between ribosomes and mitogen-activated protein kinase (MAPK) activation under ribotoxic stress conditions and found that the activation of c-Jun N-terminal kinases (JNKs) was suppressed by ribosomal protein knockdown but that of p38 was not. In addition, we found that JNK activation is driven by the association of inactive JNK in the 80S monosomes rather than the polysomes. Overall, these data suggest that the activation of JNKs by ribotoxic stress is attributable to 80S monosomes. These 80S monosomes are active ribosomes that are ready to initiate protein translation, rather than polysomes that are already acting ribosomes involved in translation elongation.

Transcriptome analysis of immune response in fat greenling (Hexagrammos otakii) against Vibrio harveyi infection

Fat greenling (Hexagrammos otakii) is an important aquaculture fish species in northern China. Unfortunately, Vibrio infections have caused considerable losses to the fat greenling aquaculture industry. However, the study on immune response of fat greenling against Vibrio species has not been reported yet. In this paper, the immune response of fat greenling against V. harveyi at gene expression level was studied by transcriptome analysis. A total of 189753 high-quality unigenes with a N50 length of 672bp were obtained by transcriptome profiling, which provided abundant data for the future study of fat greenling. Comparative analysis showed that 5425 differentially expressed genes (DEGs) were identified on day 3 post-infection (3dpi), containing 1837 up-regulated and 3588 down-regulated genes. Further annotation and analysis revealed that the DEGs were enriched in complement and coagulation cascades, ribosome, oxidative phosphorylation, glycine, serine and threonine metabolism and peroxisome proliferator-activated receptor (PPAR) signaling pathway. These pathways were mainly associated with phagocytosis and pathogen clearance, rarely involved in bacteria adhesion and pathogen identification, which suggested that the host might begin to clear and kill the invading bacteria on 3dpi. The research might provide a valuable resource to further study immune response and suggest strategies against V. harveyi infection in fat greenling.

Trichothecenes: immunomodulatory effects, mechanisms, and anti-cancer potential

Paradoxically, trichothecenes have both immunosuppressive and immunostimulatory effects. The underlying mechanisms have not been fully explored. Early studies show that dose, exposure timing, and the time at which immune function is assessed influence whether trichothecenes act in an immunosuppressive or immunostimulatory fashion. Recent studies suggest that the immunomodulatory function of trichothecenes is also actively shaped by competing cell-survival and death-signaling pathways. Autophagy may also promote trichothecene immunosuppression, although the mechanism may be complicated. Moreover, trichothecenes may generate an "immune evasion" milieu that allows pathogens to escape host and vaccine immune defenses. Some trichothecenes, especially macrocyclic trichothecenes, also potently kill cancer cells. T-2 toxin conjugated with anti-cancer monoclonal antibodies significantly suppresses the growth of thymoma EL-4 cells and colon cancer cells. The type B trichothecene diacetoxyscirpenol specifically inhibits the tumor-promoting factor HIF-1 in cancer cells under hypoxic conditions. Trichothecin markedly inhibits the growth of multiple cancer cells with constitutively activated NF-κB. The type D macrocyclic toxin Verrucarin A is also a promising therapeutic candidate for leukemia, breast cancer, prostate cancer, and pancreatic cancer. The anti-cancer activities of trichothecenes have not been comprehensively summarized. Here, we first summarize the data on the immunomodulatory effects of trichothecenes and discuss recent studies that shed light on the underlying cellular and molecular mechanisms. These mechanisms include autophagy and major signaling pathways and their crosstalk. Second, the anti-cancer potential of trichothecenes and the underlying mechanisms will be discussed. We hope that this review will show how trichothecene bioactivities can be exploited to generate therapies against pathogens and cancer.

Embryotoxicity Caused by DON-Induced Oxidative Stress Mediated by Nrf2/HO-1 Pathway

Deoxynivalenol (DON) belongs to the type B group of trichothecenes family, which is composed of sesquiterpenoid metabolites produced by Fusarium and other fungi in grain. DON may cause various toxicities, such as cytotoxicity, immunotoxicity, genotoxicity as well as teratogenicity and carcinogenicity. In the present study, we focus on a hypothesis that DON alters the expressions of Nrf2/HO-1 pathway by inducing embryotoxicity in C57BL/6 mouse (5.0, 2.5, 1.0, and 0 mg/kg/day) and BeWo cell lines (0 and 50 nM; 3 h, 12 h and 24 h). Our results indicate that DON treatment in mice during pregnancy leads to ROS accumulation in the placenta, which results in embryotoxicity. At the same time Nrf2/HO-1 pathway is up-regulated by ROS to protect placenta cells from oxidative damage. In DON-treated BeWo cells, the level of ROS has time-effect and dose-effect relationships with HO-1 expression. Moderate increase in HO-1 protects the cell from oxidative damage, while excessive increase in HO-1 aggravates the oxidative damage, which is called in some studies the "threshold effect". Therefore, oxidative stress may be the critical molecular mechanism for DON-induced embryotoxicity. Besides, Nrf2/HO-1 pathway accompanied by the "threshold effect" also plays an important role against DON-induced oxidative damage in this process.

Quantitative profiling of the in vivo enzymatic activity of ricin reveals disparate depurination of different pulmonary cell types

The plant-derived toxins ricin and abrin, operate by site-specific depurination of ribosomes, which in turn leads to protein synthesis arrest. The clinical manifestation following pulmonary exposure to these toxins is that of a severe lung inflammation and respiratory insufficiency. Deciphering the pathways mediating between the catalytic activity and the developing lung inflammation, requires a quantitative appreciation of the catalytic activity of the toxins, in-vivo. In the present study, we monitored truncated cDNA molecules which are formed by reverse transcription when a depurinated 28S rRNA serves as template. We found that maximal depurination after intranasal exposure of mice to 2LD50 ricin was reached 48h, where nearly 40% of the ribosomes have been depurinated and that depurination can be halted by post-exposure administration of anti-ricin antibodies. We next demonstrated that the effect of ricin intoxication on different cell types populating the lungs differs greatly, and that outstandingly high levels of damage (80% depurination), were observed in particular for pulmonary epithelial cells. Finally, we found that the magnitude of depurination induced by the related plant-derived toxin abrin, was significantly lower in comparison to ricin, and can be attributed mostly to reduced depurination of pulmonary epithelial cells by abrin. This study provides for the first time vital information regarding the scope and timing of the catalytic performance of ricin and abrin in the lungs of intact animals.

Effects of oral exposure to naturally-occurring and synthetic deoxynivalenol congeners on proinflammatory cytokine and chemokine mRNA expression in the mouse

The foodborne mycotoxin deoxynivalenol (DON) induces a ribotoxic stress response in mononuclear phagocytes that mediate aberrant multi-organ upregulation of TNF-α, interleukins and chemokines in experimental animals. While other DON congeners also exist as food contaminants or pharmacologically-active derivatives, it is not known how these compounds affect expression of these cytokine genes in vivo. To address this gap, we compared in mice the acute effects of oral DON exposure to that of seven relevant congeners on splenic expression of representative cytokine mRNAs after 2 and 6h. Congeners included the 8-ketotrichothecenes 3-acetyldeoxynivalenol (3-ADON), 15-acetyldeoxynivalenol (15-ADON), fusarenon X (FX), nivalenol (NIV), the plant metabolite DON-3-glucoside (D3G) and two synthetic DON derivatives with novel satiety-inducing properties (EN139528 and EN139544). DON markedly induced transient upregulation of TNF-α IL-1β, IL-6, CXCL-2, CCL-2 and CCL-7 mRNA expressions. The two ADONs also evoked mRNA expression of these genes but to a relatively lesser extent. FX induced more persistent responses than the other DON congeners and, compared to DON, was: 1) more potent in inducing IL-1β mRNA, 2) approximately equipotent in the induction of TNF-α and CCL-2 mRNAs, and 3) less potent at upregulating IL-6, CXCL-2, and CCL-2 mRNAs. EN139528's effects were similar to NIV, the least potent 8-ketotrichothecene, while D3G and EN139544 were largely incapable of eliciting cytokine or chemokine mRNA responses. Taken together, the results presented herein provide important new insights into the potential of naturally-occurring and synthetic DON congeners to elicit aberrant mRNA upregulation of cytokines associated with acute and chronic trichothecene toxicity.

Regulation of IL-8 promoter activity by verrucarin A in human monocytic THP-1 cells

Macrocyclic trichothecenes have been frequently detected in fungi in water-damaged buildings and exhibited higher toxicity than the well-studied trichothecenes; however, the mechanism underlying their toxicity has been poorly understood. In this study, transcriptional regulation of the cytokine interleukin (IL)-8 by a macrocyclic trichothecene, verrucarin A (VA), in human monocytic THP-1 cells is reported. Consistent with previous findings, VA was 100-fold more cytotoxic than deoxynivalenol (DON), while ochratoxin A (OA) was not cytotoxic. In cells transduced with the wild-type IL-8 promoter luciferase construct, VA induced a biphasic dose response composed of an upregulation of luciferase expression at low concentrations of 0.01-1 ng/ml and a downregulation at high levels of 10 ng/ml and higher. In contrast, DON induced a sigmoid-shaped dose response with the EC50 of 11.6 ng/ml, while OA did not markedly affect the IL-8 expression. When cells were transduced with IL-8 promoter with a mutation of transcription factor nuclear factor-κB (NF-κB)-binding site, VA (1 ng/ml), DON (1000 ng/ml), and tumor necrosis factor (TNF) α (20 ng/ml)-induced luciferase expression were impaired. In addition, the NF-κB inhibitor caffeic acid phenethyl ester inhibited VA-, DON-, and TNFα-induced luciferase expression. Mutation of the CCAAT/enhancer-binding protein (CEBP) β binding site of the IL-8 promoter affected only DON-, but not VA- and TNFα-induced luciferase expression. Taken together, these results suggested that VA activated IL-8 promoter via an NF-κB-dependent, but not CEBPβ-dependent, pathway in human monocytes.

Deoxynivanelol and fumonisin, alone or in combination, induce changes on intestinal junction complexes and in E-cadherin expression

Fusariotoxins such as fumonisin B1 (FB1) and deoxynivalenol (DON) cause deleterious effects on the intestine of pigs. The aim of this study was to evaluate the effect of these mycotoxins, alone and in combination, on jejunal explants from piglets, using histological, immunohistochemical and ultrastructural assays. Five 24-day old pigs were used for sampling the explants. Forty-eight explants were sampled from each animal. Explants were incubated for 4 hours in culture medium and medium containing FB1 (100 µM), DON (10 µM) and both mycotoxins (100 µM FB1 plus 10 µM DON). Exposure to all treatments induced a significant decrease in the normal intestinal morphology and in the number of goblet cells, which were more severe in explants exposed to DON and both mycotoxins. A significant reduction in villus height occurred in groups treated with DON and with co-contamination. Expression of E-cadherin was significantly reduced in explants exposed to FB1 (40%), DON (93%) and FB1 plus DON (100%). The ultrastructural assay showed increased intercellular spaces and no junction complexes on enterocytes exposed to mycotoxins. The present data indicate that FB1 and DON induce changes in cell junction complexes that could contribute to increase paracellular permeability. The ex vivo model was adequate for assessing intestinal toxicity induced by exposure of isolated or associated concentrations of 100 µM of FB1 and 10 µM of DON.

Dynamic changes in ribosome-associated proteome and phosphoproteome during deoxynivalenol-induced translation inhibition and ribotoxic stress

Deoxynivalenol (DON), a trichothecene mycotoxin produced by Fusarium that commonly contaminates cereal-based food, interacts with the ribosome to cause translation inhibition and activate stress kinases in mononuclear phagocytes via the ribotoxic stress response (RSR). The goal of this study was to test the hypothesis that the ribosome functions as a platform for spatiotemporal regulation of translation inhibition and RSR. Specifically, we employed stable isotope labeling of amino acids in cell culture (SILAC)-based proteomics to quantify the early (≤ 30 min) DON-induced changes in ribosome-associated proteins in RAW 264.7 murine macrophage. Changes in the proteome and phosphoproteome were determined using off-gel isoelectric focusing and titanium dioxide chromatography, respectively, in conjunction with LC-MS/MS. Following exposure of RAW 264.7 to a toxicologically relevant concentration of DON (250 ng/ml), we observed an overall decrease in translation-related proteins interacting with the ribosome, concurrently with a compensatory increase in proteins that mediate protein folding, biosynthesis, and cellular organization. Alterations in the ribosome-associated phosphoproteome reflected proteins that modulate translational and transcriptional regulation, and others that converged with signaling pathways known to overlap with phosphorylation changes characterized previously in intact RAW 264.7 cells. These results suggest that the ribosome plays a central role as a hub for association and phosphorylation of proteins involved in the coordination of early translation inhibition as well as recruitment and maintenance of stress-related proteins-both of which enable cells to adapt and respond to ribotoxin exposure. This study provides a template for elucidating the molecular mechanisms of DON and other ribosome-targeting agents.

Early phosphoproteomic changes in the mouse spleen during deoxynivalenol-induced ribotoxic stress

The trichothecene mycotoxin deoxynivalenol (DON) targets the innate immune system and is of public health significance because of its frequent presence in human and animal food. DON-induced proinflammatory gene expression and apoptosis in the lymphoid tissue have been associated with a ribotoxic stress response (RSR) that involves rapid phosphorylation of mitogen-activated protein kinases (MAPKs). To better understand the relationship between protein phosphorylation and DON's immunotoxic effects, stable isotope dimethyl labeling-based proteomics in conjunction with titanium dioxide chromatography was employed to quantitatively profile the immediate (≤ 30min) phosphoproteome changes in the spleens of mice orally exposed to 5mg/kg body weight DON. A total of 90 phosphoproteins indicative of novel phosphorylation events were significantly modulated by DON. In addition to critical branches and scaffolds of MAPK signaling being affected, DON exposure also altered phosphorylation of proteins that mediate phosphatidylinositol 3-kinase/AKT pathways. Gene ontology analysis revealed that DON exposure affected biological processes such as cytoskeleton organization, regulation of apoptosis, and lymphocyte activation and development, which likely contribute to immune dysregulation associated with DON-induced RSR. Consistent with these findings, DON impacted phosphorylation of proteins within diverse immune cell populations, including monocytes, macrophages, T cells, B cells, dendritic cells, and mast cells. Fuzzy c-means clustering analysis further indicated that DON evoked several distinctive temporal profiles of regulated phosphopeptides. Overall, the findings from this investigation can serve as a template for future focused exploration and modeling of cellular responses associated with the immunotoxicity evoked by DON and other ribotoxins.

Deoxynivalenol impairs the immune functions of neutrophils

SCOPE

Deoxynivalenol (DON), a mycotoxin produced by Fusarium spp., is toxic to many animal species, with pigs being the most sensitive species to the toxin. The aim of the present study was to determine the effects of DON on pig polymorphonuclear cells (PMNs), the first line of defense against infection.

METHODS AND RESULTS

PMNs isolated from pig blood samples were stimulated with LPS to mimic infection. DON (0.5-10 μM) altered three main functions of pig PMNs: LPS-induced secretion of IL-8, chemotaxis, and phagocytosis capability. This alteration of PMN properties was due to apoptotis induced by DON exposure. Using Western blot and flow cytometry, we demonstrated that this process included the permeabilization of the mitochondrial outer membrane and the activation of caspase-3. The effect of DON was mediated by the phosphorylation of the p38 mitogen-activated protein kinase within the first 30 min of exposure.

CONCLUSION

This study provides evidence that low concentrations of DON can alter the immune functions of porcine PMNs and suggests the involvement of p38 mitogen-activated protein kinase in the signal transduction pathway. These immunosuppressive effects of DON may have implications for humans and/or animals when eating contaminated food/feed.

The food contaminant deoxynivalenol activates the mitogen activated protein kinases in the intestine: interest of ex vivo models as an alternative to in vivo experiments

Trichothecenes induce changes in the intestinal barrier function through decreased expression of cell junction proteins and apoptosis of enterocytes. The mitogen activated protein kinases (MAPK) play an important role in the signaling pathways of cell turnover and differentiation. Using ex vivo and in vivo approaches, the purpose of this study was to investigate the ability of low doses of DON to induce histological changes in the intestine and to activate the MAPK ERK 1/2, p38 and JNK. Twelve weaning piglets received during four weeks a control diet or a DON-contaminated diet (2.3 mg DON/kg feed). Six weaning piglets were used to prepare jejunal explants (ex vivo model). Explants were exposed during 4 h to vehicle, 5 or 10 μM DON. Intestinal changes were graded using a histological score. Pigs fed a DON-diet and explants exposed to DON showed a significant decrease in the jejunal score. In both models, the toxin significantly enhanced phosphorylation of ERK 1/2 and p38, whereas the increased phosphorylation of JNK was non significant. Taken together these results indicate that in vivo or ex vivo exposure of intestinal tissue to DON lead to similar intestinal lesions and activation of MAPK. These effects could impair the homeostasis of intestinal tissue in the aspects of barrier function and immune protection. The similarity of the in vivo and ex vivo results provides also strong evidence that the jejunal explant model is a good alternative for toxicological studies in intestinal tissue.

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.

Inflammatory cytokine gene expression in THP-1 cells exposed to Stachybotrys chartarum and Aspergillus versicolor

Very little is known about the mechanisms that occur in human cells upon exposure to fungi as well as their mycotoxins. A better understanding of toxin-regulated gene expression would be helpful to identify safe levels of exposure and could eventually be the basis for establishing guidelines for remediation scenarios following a water intrusion event. In this research, cytokine mRNA expression patterns were investigated in the human monocytic THP-1 cell line exposed to fungal extracts of various fragment sizes obtained from Stachybotrys chartarum RTI 5802 and/or Aspergillus versicolor RTI 3843, two common and well-studied mycotoxin producing fungi. Cytokine mRNA expression was generally upregulated 2-10 times following a 24 h exposure to fungal extracts. Expression of the proinflammatory interleukin-1β, interleukin-8, and tumor necrosis factor-α genes increased while the anti-inflammatory gene interleukin-10 also increased albeit at very low level, suggesting that negative feedback regulation mechanism of production of proinflammatory cytokines initiated upon 24 h of incubation. In addition, submicron size extracts of A. versicolor caused significant death of THP-1 cells, whereas extracts of S. chartarum caused no cell death while the mixture of the two fungi had an intermediate effect. There was no general correlation between gene expression and fragment sizes, which suggests that all submicron fragments may contribute to inflammatory response.

Trichothecene toxicity in eukaryotes: cellular and molecular mechanisms in plants and animals

Trichothecenes are sesquiterpenoid mycotoxins commonly found as contaminants in cereal grains and are a major health and food safety concern due to their toxicity to humans and farm animals. Trichothecenes are predominantly produced by the phytopathogenic Fusarium fungus, and in plants they act as a virulence factor aiding the spread of the fungus during disease development. Known for their inhibitory effect on eukaryotic protein synthesis, trichothecenes also induce oxidative stress, DNA damage and cell cycle arrest and affect cell membrane integrity and function in eukaryotic cells. In animals, trichothecenes can be either immunostimulatory or immunosuppressive and induce apoptosis via mitochondria-mediated or -independent pathway. In plants, trichothecenes induce programmed cell death via production of reactive oxygen species. Recent advances in molecular techniques have led to the elucidation of signal transduction pathways that manifest trichothecene toxicity in eukaryotes. In animals, trichothecenes induce mitogen-activated protein kinase (MAPK) signalling cascades via ribotoxic stress response and/or endoplasmic reticulum stress response. The upstream signalling events that lead to the activation trichothecene-induced ribotoxic stress response are discussed. In plants, trichothecenes exhibit elicitor-like activity leading to the inductions MAPKs and genes involved in oxidative stress, cell death and plant defence response. Trichothecenes might also modulate hormone-mediated defence signalling and abiotic stress signalling in plants.

Ricin and Shiga toxins: effects on host cell signal transduction

Shiga toxins and ricin are potent inhibitors of protein synthesis. In addition to causing inhibition of protein synthesis, these toxins activate proinflammatory signaling cascades that may contribute to the severe diseases associated with toxin exposure. Treatment of cells with Shiga toxins and ricin have been shown to activate a number of signaling pathways including those associated with the ribotoxic stress response, Nuclear factor kappa B activation, inflammasome activation, the unfolded protein response, mTOR signaling, hemostasis, and retrograde trafficking. In this chapter, we review our current understanding of these signaling pathways as they pertain to intoxication by Shiga toxins and ricin.

Central inflammation and sickness-like behavior induced by the food contaminant deoxynivalenol: a PGE2-independent mechanism

Deoxynivalenol (DON), one of the most abundant trichothecenes found on cereals, has been implicated in mycotoxicoses in both humans and farm animals. Low-dose toxicity is characterized by reduced weight gain, diminished nutritional efficiency, and immunologic effects. The levels and patterns of human food commodity contamination justify that DON consumption constitutes a public health issue. DON stability during processing and cooking explains its large presence in human food. We characterized here DON intoxication by showing that the toxin concomitantly affects feeding behavior, body temperature, and locomotor activity after both per os and central administration. Using c-Fos expression mapping, we identified the neuronal structures activated in response to DON and observed that the pattern of neuronal populations activated by the toxin resembled those induced by inflammatory signals. By real-time PCR, we report the first evidences for a DON-induced central inflammation, attested by the strong upregulation of interleukin-1β, interleukin-6, tumor necrosis factor-α, cyclooxygenase-2, and microsomal prostaglandin synthase-1 (mPGES-1) messenger RNA. However, silencing prostaglandins E2 signaling pathways using mPGES-1 knockout mice, which are resistant to cytokine-induced sickness behavior, did not modify the responses to the toxin. These results reveal that, despite strong similarities, behavioral changes observed after DON intoxication differ from classical sickness behavior evoked by inflammatory cytokines.

Aerobic and anaerobic de-epoxydation of mycotoxin deoxynivalenol by bacteria originating from agricultural soil

One hundred and fifty soil samples collected from different crop fields in southern Ontario, Canada were screened to obtain microorganisms capable of transforming deoxynivalenol (DON) to de-epoxy DON (dE-DON). Microbial DON to dE-DON transformation (i.e. de-epoxydation) was monitored by using liquid chromatography-ultraviolet-mass spectrometry (LC-UV-MS). The effects of growth substrates, temperature, pH, incubation time and aerobic versus anaerobic conditions on the ability of the microbes to de-epoxydize DON were evaluated. A mixed microbial culture from one composite soil sample showed 100% DON to dE-DON biotransformation in mineral salts broth (MSB) after 144 h of incubation. Treatments of the culture with selective antibiotics followed an elevated temperature (50°C) for 1.5 h considerably reduced the microbial diversity. Partial 16S-rRNA gene sequence analysis of the bacteria in the enriched culture indicated the presence of at least six bacterial genera, namely Serratia, Clostridium, Citrobacter, Enterococcus, Stenotrophomonas and Streptomyces. The enriched culture completely de-epoxydized DON after 60 h of incubation. Bacterial de-epoxydation of DON occurred at pH 6.0-7.5, and a wide array of temperatures (12-40°C). The culture showed rapid de-epoxydation activity under aerobic conditions compared to anaerobic conditions. This is the first report on microbial DON to dE-DON transformation under aerobic conditions and moderate temperatures. The culture could be used to detoxify DON contaminated feed and might be a potential source for gene(s) for DON de-epoxydation.

Toxicological mechanisms and potential health effects of deoxynivalenol and nivalenol

Produced by the mould genus Fusarium, the type B trichothecenes include deoxynivalenol (DON), nivalenol (NIV) and their acetylated precursors. These mycotoxins often contaminate cereal staples, posing a potential threat to public health that is still incompletely understood. Understanding the mechanistic basis by which these toxins cause toxicity in experimental animal models will improve our ability to predict the specific thresholds for adverse human effects as well as the persistence and reversibility of these effects. Acute exposure to DON and NIV causes emesis in susceptible species such as pigs in a manner similar to that observed for certain bacterial enterotoxins. Chronic exposure to these mycotoxins at low doses causes growth retardation and immunotoxicity whereas much higher doses can interfere with reproduction and development. Pathophysiological events that precede these toxicities include altered neuroendocrine responses, upregulation of proinflammatory gene expression, interference with growth hormone signalling and disruption of gastrointestinal tract permeability. The underlying molecular mechanisms involve deregulation of protein synthesis, aberrant intracellular cell signalling, gene transactivation, mRNA stabilisation and programmed cell death. A fusion of basic and translational research is now needed to validate or refine existing risk assessments and regulatory standards for DON and NIV. From the perspective of human health translation, biomarkers have been identified that potentially make it possible to conduct epidemiological studies relating DON consumption to potential adverse human health effects. Of particular interest will be linkages to growth retardation, gastrointestinal illness and chronic autoimmune diseases. Ultimately, such knowledge can facilitate more precise science-based risk assessment and management strategies that protect consumers without reducing availability of critical food sources.

Deoxynivalenol: mechanisms of action, human exposure, and toxicological relevance

The trichothecene mycotoxin deoxynivalenol (DON) is produced in wheat, barley and corn following infestation by the fungus Fusarium in the field and during storage. Colloquially known as "vomitoxin" because of its emetic effects in pigs, DON has been associated with human gastroenteritis. Since DON is commonly detected in cereal foods, there are significant questions regarding the risks of acute poisoning and chronic effects posed to persons ingesting this trichothecene. A further challenge is how to best manage perceived risks without rendering critical food staples unavailable to an ever-expanding world population. In experimental animal models, acute DON poisoning causes emesis, whereas chronic low-dose exposure elicits anorexia, growth retardation, immunotoxicity as well as impaired reproduction and development resulting from maternal toxicity. Pathophysiologic effects associated with DON include altered neuroendocrine signaling, proinflammatory gene induction, disruption of the growth hormone axis, and altered gut integrity. At the cellular level, DON induces ribotoxic stress thereby disrupting macromolecule synthesis, cell signaling, differentiation, proliferation, and death. There is a need to better understand the mechanistic linkages between these early dose-dependent molecular effects and relevant pathological sequelae. Epidemiological studies are needed to determine if relationships exist between consumption of high DON levels and incidence of both gastroenteritis and potential chronic diseases. From the perspective of human health translation, a particularly exciting development is the availability of biomarkers of exposure (e.g. DON glucuronide) and effect (e.g. IGF1) now make it possible to study the relationship between DON consumption and growth retardation in susceptible human populations such as children and vegetarians. Ultimately, a fusion of basic and translational research is needed to validate or refine existing risk assessments and regulatory standards for this common mycotoxin.

Deoxynivalenol-induced proinflammatory gene expression: mechanisms and pathological sequelae

The trichothecene mycotoxin deoxynivalenol (DON) is commonly encountered in human cereal foods throughout the world as a result of infestation of grains in the field and in storage by the fungus Fusarium. Significant questions remain regarding the risks posed to humans from acute and chronic DON ingestion, and how to manage these risks without imperiling access to nutritionally important food commodities. Modulation of the innate immune system appears particularly critical to DON's toxic effects. Specifically, DON induces activation of mitogen-activated protein kinases (MAPKs) in macrophages and monocytes, which mediate robust induction of proinflammatory gene expression-effects that can be recapitulated in intact animals. The initiating mechanisms for DON-induced ribotoxic stress response appear to involve the (1) activation of constitutive protein kinases on the damaged ribosome and (2) autophagy of the chaperone GRP78 with consequent activation of the ER stress response. Pathological sequelae resulting from chronic low dose exposure include anorexia, impaired weight gain, growth hormone dysregulation and aberrant IgA production whereas acute high dose exposure evokes gastroenteritis, emesis and a shock-like syndrome. Taken together, the capacity of DON to evoke ribotoxic stress in mononuclear phagocytes contributes significantly to its acute and chronic toxic effects in vivo. It is anticipated that these investigations will enable the identification of robust biomarkers of effect that will be applicable to epidemiological studies of the human health effects of this common mycotoxin.

Hematopoietic cell kinase associates with the 40S ribosomal subunit and mediates the ribotoxic stress response to deoxynivalenol in mononuclear phagocytes

The trichothecene deoxynivalenol (DON) binds to eukaryotic ribosomes and triggers p38-driven proinflammatory gene expression in the macrophage-a response that is dependent on both double-stranded RNA-activated protein kinase (PKR) and hematopoietic cell kinase (Hck). Here we elucidated critical linkages that exist among the ribosome and these kinases during the course of DON-induced ribotoxic stress in mononuclear phagocytes. Similar to PKR inhibitors, Hck inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyramidine (PP2) suppressed p38 activation and p38-driven interleukin 8 (IL-8) expression in the U937 human monocyte cell line. U937 cells stably transfected with a PKR antisense vector (U9K-A1) displayed marked reduction of DON-induced p38 activation and IL-8 expression as compared to cells transfected with empty vector (U9K-C2), with both responses being completely ablated by PP2. Western analysis of sucrose density gradient fractions revealed that PKR and Hck interacted with the 40S ribosomal subunit in U9K-C2 but not U9K-A1 cells. Subsequent transfection and immunoprecipitation studies with HeLa cells indicated that Hck interacted with ribosomal protein S3. Consistent with U937 cells, DON induced p38 association with the ribosome and phosphorylation in peritoneal macrophages from wild-type but not PKR-deficient mice. DON-induced phosphorylation of ribosome-associated Hck in RAW 264.7 murine macrophages was also suppressed by 2-aminopurine (2-AP). Both 2-AP and PP2 inhibited DON-induced phosphorylation of p38 as well as two kinases, apoptosis signal-regulating kinase 1 and mitogen-activated protein kinase 3/6, known to be upstream of p38. Taken together, PKR and Hck were critical for DON-induced ribosomal recruitment of p38, its subsequent phosphorylation, and, ultimately, p38-driven proinflammatory cytokine expression.

A genome-wide screen in Saccharomyces cerevisiae reveals a critical role for the mitochondria in the toxicity of a trichothecene mycotoxin

Trichothecene mycotoxins synthesized by Fusarium species are potent inhibitors of eukaryotic translation. They are encountered in both the environment and in food, posing a threat to human and animal health. They have diverse roles in the cell that are not limited to the inhibition of protein synthesis. To understand the trichothecene mechanism of action, we screened the yeast knockout library to identify genes whose deletion confers resistance to trichothecin (Tcin). The largest group of resistant strains affected mitochondrial function, suggesting a role for fully active mitochondria in trichothecene toxicity. Tcin inhibited mitochondrial translation in the wild-type strain to a greater extent than in the most resistant strains, implicating mitochondrial translation as a previously unrecognized site of action. The Tcin-resistant strains were cross-resistant to anisomycin and chloramphenicol, suggesting that Tcin targets the peptidyltransferase center of mitochondrial ribosomes. Tcin-induced cell death was partially rescued by mutants that regulate mitochondrial fusion and maintenance of the tubular morphology of mitochondria. Treatment of yeast cells with Tcin led to the fragmentation of the tubular mitochondrial network, supporting a role for Tcin in disruption of mitochondrial membrane morphology. These results provide genome-wide insight into the mode of action of trichothecene mycotoxins and uncover a critical role for mitochondrial translation and membrane maintenance in their toxicity.

Suppression of insulin-like growth factor acid-labile subunit expression--a novel mechanism for deoxynivalenol-induced growth retardation

Consumption of deoxynivalenol (DON), a trichothecene mycotoxin commonly detected in cereal-based foods, causes impaired growth in many animal species. While growth retardation is used as a basis for regulating DON levels in human food, the underlying mechanisms remain poorly understood. Oral exposure of mice to DON rapidly induces multiorgan expression of proinflammatory cytokines, and this is followed by upregulation of several suppressors of cytokine signaling (SOCS), some of which are capable of impairing growth hormone (GH) signaling. The purpose of this study was to test the hypothesis that impairment of the GH axis precedes DON-induced growth retardation in the mouse. Subchronic dietary exposure of young (4-week old) mice to DON (20 ppm) over a period of 2-8 weeks was found to (1) impair weight gain, (2) result in a steady-state plasma DON concentration (40-60 ng/ml), (3) downregulate hepatic insulin-like growth factor acid-labile subunit (IGFALS) mRNA expression, and (4) reduce circulating insulin-like growth factor 1 (IGF1) and IGFALS levels. Acute oral exposure to DON at 0.5-12.5 mg/kg body weight (bw) markedly suppressed hepatic IGFALS mRNA levels within 2 h in a dose-dependent fashion, whereas 0.1 mg/kg bw was without effect. DON-induced IGFALS mRNA upregulation occurred both with and without exogenous GH treatment. These latter effects co-occurred with robust hepatic suppressors of cytokine signaling 3 upregulation. Taken together, these data suggest that oral DON exposure perturbs GH axis by suppressing two clinically relevant growth-related proteins, IGFALS and IGF1. Both have potential to serve as biomarkers of effect in populations exposed to this common foodborne mycotoxin.

Induction of suppressors of cytokine signaling by the trichothecene deoxynivalenol in the mouse

Deoxynivalenol (DON), a trichothecene mycotoxin found in grains and cereal-based foods worldwide, impairs weight gain in experimental animals but the underlying mechanisms remain undetermined. Oral exposure to DON induces rapid and transient upregulation of proinflammatory cytokine expression in the mouse. The latter are known to induce several suppressors of cytokine signaling (SOCS), some of which impair growth hormone (GH) signaling. We hypothesized that oral exposure to DON will induce SOCS expression in the mouse. Real-time PCR and cytokine bead array revealed that oral gavage with DON rapidly (1 h) induced tumor necrosis factor-alpha and interleukin-6 mRNA and protein expression in several organs and plasma, respectively. Upregulation of mRNAs for four well-characterized SOCS (CIS [cytokine-inducible SH2 domain protein], SOCS1, SOCS2, and SOCS3) was either concurrent with (1 h) or subsequent to cytokine upregulation (2 h). Notably, DON-induced SOCS3 mRNAs in muscle, spleen and liver, with CIS1, SOCS1, and SOCS2 occurring to a lesser extent. Hepatic SOCS3 mRNA was a very sensitive indicator of DON exposure with SOCS3 protein being detectable in the liver well after the onset of cytokine decline (5 h). Furthermore, hepatic SOCS upregulation was associated with about 75% suppression of GH-inducible insulin-like growth factor acid labile subunit. Taken together, DON-induced cytokine upregulation corresponded to increased expression of several SOCS, and was associated with suppression of GH-inducible gene expression in the liver.

Satratoxin G interaction with 40S and 60S ribosomal subunits precedes apoptosis in the macrophage

Satratoxin G (SG) and other macrocyclic trichothecene mycotoxins are potent inhibitors of eukaryotic translation that are potentially immunosuppressive. The purpose of this research was to test the hypothesis that SG-induced apoptosis in the macrophage correlates with binding of this toxin to the ribosome. Exposure of RAW 264.7 murine macrophages to SG at concentrations of 10 to 80 ng/ml induced DNA fragmentation within 4 h that was indicative of apoptosis. To relate these findings to ribosome binding of SG, RAW cells were exposed to different toxin concentrations for various time intervals, ribosomal fractions isolated by sucrose density gradient ultracentrifugation and resultant fractions analyzed for SG by competitive ELISA. SG was found to specifically interact with 40S and 60S ribosomal subunits as early as 5 min and that, at high concentrations or extended incubation times, the toxin induced polysome disaggregation. While co-incubation with the simple Type B trichothecene DON had no effect on SG uptake into cell cytoplasm, it inhibited SG binding to the ribosome, suggesting that the two toxins bound to identical sites and that SG binding was reversible. Although both SG and DON induced mobilization of p38 and JNK 1/2 to the ribosome, phosphorylation of ribosomal bound MAPKs occurred only after DON treatment. SG association with the 40S and 60S subunits was also observed in the PC-12 neuronal cell model which is similarly susceptible to apoptosis. To summarize, SG rapidly binds small and large ribosomal subunits in a concentration- and time-dependent manner that was consistent with induction of apoptosis.