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

Fusarium Species and Mycotoxins Contaminating Veterinary Diets for Dogs and Cats

Veterinary diets are intended for diseased animals and may contain cereal grains, mainly maize and/or wheat. These, in turn, are often infected with pathogens of the Fusarium genus, which are able to produce numerous harmful mycotoxins. Forty-two samples of veterinary diets for dogs and cats were analyzed for the presence of Fusarium species and mycotoxins. Species were identified using molecular methods and the ergosterol and mycotoxins (fumonisin B₁, deoxynivalenol, nivalenol and zearalenone) were quantified using HPLC methods. Two Fusarium species were identified: Fusarium proliferatum and Fusarium verticillioides. The highest concentrations of fumonisin B₁, deoxynivalenol, nivalenol and zearalenone were 74.83, 2318.05, 190.90, and 45.84 ng/g, respectively. Only 9.5% of the samples were free from Fusarium mycotoxins. The acceptable limits of mycotoxin content in animal feed, specified by the EU regulations, were not exceeded in any of the samples tested. The mean mycotoxin content in veterinary diets for cats was lower than for dogs. Thus, it is recommended that veterinary diets are examined, since the mycotoxin contamination pose additional risk to animal health. The knowledge on Fusarium occurrence in veterinary diets is scarce and as far as we are aware this is the first report concerning the occurrence of Fusarium spp. and their important secondary metabolites—mycotoxins—in different types of veterinary diets for companion animals in Poland.

Risk to human and animal health related to the presence of 4,15-diacetoxyscirpenol in food and feed

4,15‐Diacetoxyscirpenol (DAS) is a mycotoxin primarily produced by Fusarium fungi and occurring predominantly in cereal grains. As requested by the European Commission, the EFSA Panel on Contaminants in the Food Chain (CONTAM) assessed the risk of DAS to human and animal health related to its presence in food and feed. Very limited information was available on toxicity and on toxicokinetics in experimental and farm animals. Due to the limitations in the available data set, human acute and chronic health‐based guidance values (HBGV) were established based on data obtained in clinical trials of DAS as an anticancer agent (anguidine) after intravenous administration to cancer patients. The CONTAM Panel considered these data as informative for the hazard characterisation of DAS after oral exposure. The main adverse effects after acute and repeated exposure were emesis, with a no‐observed‐adverse‐effect level (NOAEL) of 32 μg DAS/kg body weight (bw), and haematotoxicity, with a NOAEL of 65 μg DAS/kg bw, respectively. An acute reference dose (ARfD) of 3.2 μg DAS/kg bw and a tolerable daily intake (TDI) of 0.65 μg DAS/kg bw were established. Based on over 15,000 occurrence data, the highest acute and chronic dietary exposures were estimated to be 0.8 and 0.49 μg DAS/kg bw per day, respectively, and were not of health concern for humans. The limited information for poultry, pigs and dogs indicated a low risk for these animals at the estimated DAS exposure levels under current feeding practices, with the possible exception of fattening chicken. Assuming similar or lower sensitivity than for poultry, the risk was considered overall low for other farm and companion animal species for which no toxicity data were available. In consideration of the similarities of several trichothecenes and the likelihood of co‐exposure via food and feed, it could be appropriate to perform a cumulative risk assessment for this group of substances.

Heterologous Biosynthesis of the Fungal Sesquiterpene Trichodermol in Saccharomyces cerevisiae

Trichodermol, a fungal sesquiterpene derived from the farnesyl diphosphate pathway, is the biosynthetic precursor for trichodermin, a member of the trichothecene class of fungal toxins produced mainly by the genera of Trichoderma and Fusarium. Trichodermin is a promising candidate for the development of fungicides and antitumor agents due to its significant antifungal and cytotoxic effects. It can also serve as a scaffold to generate new congeners for structure-activity relationship (SAR) study. We reconstructed the biosynthetic pathway of trichodermol in Saccharomyces cerevisiae BY4741, and investigated the effect of produced trichodermol on the host by de novo RNA sequencing (RNA-Seq) and quantitative Real-time PCR analyses. Co-expression of pESC::FgTRI5 using plasmid pLLeu-tHMGR-UPC2.1 led to trichodiene production of 683 μg L^-1, while integration of only the codon-optimized FgTRI5 into the chromosome of yeast improved the production to 6,535 μg L^-1. Subsequent expression of the codon-optimized cytochrome P450 monooxygenase encoding genes, TaTRI4 and TaTRI11, resulted in trichodermol, with an estimated titer of 252 μg L^-1 at shake flask level. RNA-Seq and qPCR analyses revealed that the produced trichodermol downregulated the expression of the genes involved in ergosterol biosynthesis, but significantly upregulated the expression of PDR5 related to membrane transport pathway in S. cerevisiae. Collectively, we achieved the first heterologous biosynthesis of trichodermol by reconstructing its biosynthetic pathway in yeast, and the reconstructed pathway will serve as a platform to generate trichodermin analogs as potential candidates for agrochemicals and anticancer agents through further optimizations.

Toxicological interactions between mycotoxins from ubiquitous fungi: Impact on hepatic and intestinal human epithelial cells

Aflatoxin B1 (AFB1), deoxynivalenol (DON), fumonisin B1 (FB1) and ochratoxin A (OTA) are toxic fungal metabolites co-occurring naturally in the environment. This study aimed to evaluate the toxicological interactions of these mycotoxins concerning additive, antagonistic and synergistic toxicity towards human cells. The theoretical biology-based Combination index-isobologram method was used to evaluate the individual and binary effect of these toxins and determine the type of the interaction using as models Caco-2 (intestinal) and HepG2 (hepatic) cells. Cytotoxicity was assessed using the MTT test at the concentrations of 0.625-20 μM for all the compounds. DON exerted the highest toxicity toward both cells, OTA and AFB1 also showed a dose-effect response, whereas no toxicity was verified for FB1. Synergism or antagonism effects occurred when exposing AFB1-DON and AFB1-OTA on Caco-2 cells at higher or lower concentrations, respectively; while DON-OTA showed synergism throughout all inhibition levels. Concerning HepG2, AFB1-DON exerted a strong synergism, regardless of the level; whereas AFB1-OTA had slight synergism/nearly additive effect; and, OTA-DON had a moderate antagonism/nearly additive effect. Synergistic strengths as high as a dose reduction index of 10 for AFB1-DON were observed in hepatic cells. Taken together our findings indicate that the toxicological effects differ regarding the type of mycotoxins used for combinations and the stronger synergistic effect was observed for mixtures containing DON in both cells. Therefore, even though DON has not been classified as to its carcinogenicity to humans, this mycotoxin may present a serious threat to health, mainly when co-occurring in the environment.

Fusarium graminearum-induced shoot elongation and root reduction in maize seedlings correlate with later seedling blight severity

Fusarium graminearum seedling blight is a common disease of maize (Zea mays). Development of genetic resistance to seedling blight in maize germplasm requires efficient and accurate quantitative assessment of disease severity. Through artificial inoculation experiments under controlled growth conditions, we determined that host genotype, pathogen genotype, and infection dose influence the extent to which F. graminearum induces shoot elongation and inhibits root growth in maize seedlings. A comparison of 15 maize inbred lines showed independent variation of these two fungus-induced effects on seedling growth. In a broader survey with nine commercial maize hybrids and three field-collected fungal isolates, there was significant correlation between these seedling growth responses, as well as with later seedling blight severity. Analysis of variance suggested that this variation and the observed correlative relationships were primarily driven by differing pathogenicity of the three fungal isolates. Together, our results indicate that F. graminearum-induced shoot elongation and root reduction in maize seedlings have distinct underlying physiological mechanisms, and that early observations of seedling growth responses can serve as a proxy for investigating natural variation in host resistance and pathogen aggressiveness at later growth stages.

Role of Glutathione Redox System on the T-2 Toxin Tolerance of Pheasant (Phasianus colchicus)

The purpose of the present study was to evaluate the effects of different dietary concentrations of T-2 toxin on blood plasma protein content, lipid peroxidation and glutathione redox system of pheasant (Phasianus colchicus). A total of 320 one-day-old female pheasants were randomly assigned to four treatment groups fed with a diet contaminated with different concentrations of T-2 toxin (control, 4 mg/kg, 8 mg/kg and 16 mg/kg). Birds were sacrificed at early (12, 24 and 72 hr) and late (1, 2 and 3 weeks) stages of the experiment to demonstrate the effect of T-2 toxin on lipid peroxidation and glutathione redox status in different tissues. Feed refusal and impaired growth were observed with dose dependent manner. Lipid-peroxidation was not induced in the liver, while the glutathione redox system was activated partly in the liver, but primarily in the blood plasma. Glutathione peroxidase activity has changed parallel with reduced glutathione concentration in all tissues. Based on our results, pheasants seem to have higher tolerance to T-2 toxin than other avian species, and glutathione redox system might contribute in some extent to this higher tolerance, in particular against free-radical mediated oxidative damage of tissues, such as liver.

Protective mechanisms involving enhanced mitochondrial functions and mitophagy against T-2 toxin-induced toxicities in GH3 cells

T-2 toxin is the most toxic member of trichothecene mycotoxin. So far, the mechanism of mitochondrial toxicity and protective mechanism in mammalian cells against T-2 toxin are not fully understood. In this study, we aimed to investigate the cellular and mitochondrial toxicity of T-2 toxin, and the cellular protective mechanisms in rat pituitary GH3 cells. We showed that T-2 toxin significantly increased reactive oxygen species (ROS) and DNA damage and caused apoptosis in GH3 cells. T-2 toxin induced abnormal cell morphology, cytoplasm and nuclear shrinkage, nuclear fragmentation and formation of apoptotic bodies and autophagosomes. The mitochondrial degradative morphologies included local or total cristae collapse and small condensed mitochondria. T-2 toxin decreased the mitochondrial membrane potential. However, T-2 toxin significantly increased the superoxide dismutase (SOD) activity and expression of antioxidant genes glutathione peroxidase 1 (GPx-1), catalase (CAT), mitochondria-specific SOD-2 and mitochondrial uncoupling protein-1, -2 and -3 (UCP-1, 2 and 3). Interestingly, T-2 toxin increased adenosine triphosphate (ATP) levels and mitochondrial complex I activity, and increased the expression of most of mitochondrial electron transport chain subunits tested and critical transcription factors controlling mitochondrial biogenesis and mitochondrial DNA transcription and replication. T-2 toxin increased mitophagic activity by increasing the expression of mitophagy-specific proteins NIP-like protein X (NIX), PTEN-induced putative kinase protein 1 (PINK1) and E3 ubiquitin ligase Parkin. T-2 toxin activated the protective protein kinase A (PKA) signaling pathway, which activated the nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/PINK1/Parkin pathway to mediate mitophagy. Taken together, our results suggested that the mammalian cells could increase their resistance against T-2 toxin by increasing the antioxidant activity, mitophagy and mitochondrial function.

Exploring an Artificial Metabolic Route in Fusarium sporotrichioides: Production and Characterization of 7-Hydroxy T-2 Toxin

An artificial metabolic route to an unnatural trichothecene was designed by taking advantage of the broad substrate specificities of the T-2 toxin biosynthetic enzymes of Fusarium sporotrichioides. By feeding 7-hydroxyisotrichodermin, a shunt pathway metabolite of F. graminearum, to a trichodiene synthase-deficient mutant of F. sporotrichioides, 7-hydroxy T-2 toxin (1) was obtained as the final metabolite. Such an approach may have future applications in the metabolic engineering of a variety of fungal secondary metabolites. The toxicity of 7-hydroxy T-2 toxin was 10 times lower than that of T-2 toxin in HL-60 cells.

Genome-wide functional characterization of putative peroxidases in the head blight fungus Fusarium graminearum

Reactive oxygen species (ROS) are associated with various developmental processes and host-pathogen interactions in pathogenic fungi. Peroxidases are a group of ROS-detoxifying enzymes that are involved in the oxidative stress response and in a variety of physiological processes. In this study, we performed a genome-wide functional characterization of putative peroxidase genes in Fusarium graminearum, a head blight pathogen of cereal crops. We identified 31 putative peroxidase genes and generated deletion mutants for these genes. Twenty-six of the deletion mutants showed developmental phenotypes indistinguishable from that of the wild-type, and five deletion mutants exhibited phenotypic changes in at least one phenotypic category. Four deletion mutants, fca6, fca7, fpx1 and fpx15, showed increased sensitivity to extracellular H₂ O₂ . Deletion mutants of FCA7 also exhibited reduced virulence and increased trichothecene production compared with those of the wild-type strain, suggesting that Fca7 may play an important role in the host-pathogen interaction in F. graminearum. To identify the transcription factors (TFs) regulating FCA6, FCA7, FPX1 and FPX15 in response to oxidative stress, we screened an F. graminearum TF mutant library for growth in the presence of H₂ O₂ and found that multiple TFs co-regulated the expression of FCA7 under oxidative stress conditions. These results demonstrate that a complex network of transcriptional regulators of antioxidant genes is involved in oxidative stress responses in this fungus. Moreover, our study provides insights into the roles of peroxidases in developmental processes and host-pathogen interactions in plant-pathogenic fungi.

Microbial Inhibition of Fusarium Pathogens and Biological Modification of Trichothecenes in Cereal Grains

Fungi of the genus Fusarium infect cereal crops during the growing season and cause head blight and other diseases. Their toxic secondary metabolites (mycotoxins) contaminate grains. Several dozen toxic compounds produced by fungal pathogens have been identified to date. Type B trichothecenes—deoxynivalenol, its acetyl derivatives and nivalenol (produced mainly by F. graminearum and F. culmorum)—are most commonly detected in cereal grains. “T-2 toxin” (produced by, among others, F. sporotrichioides) belongs to type-A trichothecenes which are more toxic than other trichothecenes. Antagonistic bacteria and fungi can affect pathogens of the genus Fusarium via different modes of action: direct (mycoparasitism or hyperparasitism), mixed-path (antibiotic secretion, production of lytic enzymes) and indirect (induction of host defense responses). Microbial modification of trichothecenes involves acetylation, deacetylation, oxidation, de-epoxidation, and epimerization, and it lowers the pathogenic potential of fungi of the genus Fusarium. Other modifing mechanisms described in the paper involve the physical adsorption of mycotoxins in bacterial cells and the conjugation of mycotoxins to glucose and other compounds in plant and fungal cells. The development of several patents supports the commercialization and wider application of microorganisms biodegrading mycotoxins in grains and, consequently, in feed additives.

Nitric oxide mediates apoptosis and mitochondrial dysfunction and plays a role in growth hormone deficiency by nivalenol in GH3 cells

Nivalenol (NIV), a type B trichothecenes commonly found in cereal crops, can cause growth impairment in animals. However, limited information about its mechanisms is available. Trichothecenes have been characterized as an inhibitor of protein synthesis and induce apoptosis in cells. Oxidative stress is considered an underlying mechanism. However, whether NIV can induce oxidative stress and apoptosis in rat pituitary cells line GH3 is unclear. The present study showed that NIV significantly reduced the viability of cells and caused oxidative stress in GH3 cells. Further experiments showed that nitric oxide (NO), but not ROS, mediated NIV-induced oxidative stress. Additionally, NIV induced caspase-dependent apoptosis, decrease in mitochondrial membrane potential and mitochondrial ultrastructural changes. However, NIV-induced caspase activation, mitochondrial damage and apoptosis were partially alleviated by Z-VAD-FMK or NO scavenger hemoglobin. Finally, NIV changed the expression of growth-associated genes and pro-inflammatory cytokines. NIV also reduced the GH secretion in GH3 cells, which was reversed by hemoglobin. Taken together, these results suggested that NIV induced apoptosis in caspase-dependent mitochondrial pathway in GH3 cells, which might be an underlying mechanism of NIV-induced GH deficiency. Importantly, NO played a critical role in the induction of oxidative stress, apoptosis and GH deficiency in NIV-treated GH3 cells.

Co-administration of amygdalin and deoxynivalenol disrupted regulatory proteins linked to proliferation of porcine ovarian cells in vitro

Deoxynivalenol (DON) represents one of the most prevalent trichothecene mycotoxin produced by Fusarium species, causing economic and health impacts. On the other hand, amygdalin has been demonstrated to possess both prophylactic and curative properties, thus it has been used as a traditional drug because of its wide range of medicinal benefits, including curing or preventing cancer, relieving fever, suppressing cough, and quenching thirst. The aim of this in vitro study was to evaluate potential effects of natural product amygdalin combined with mycotoxin deoxynivalenol (DON) on the key regulators of cell proliferation and apoptosis in porcine ovarian granulosa cells. Ovarian granulosa cells were incubated for 24h with amygdalin (1, 10, 100, 1000, 10 000 μg.mL-1) combined with deoxynivalenol (1 μg.mL-1), while the control group remained untreated. The presence of proliferative (cyclin B1, PCNA) and apoptotic markers (caspase-3) in porcine ovarian granulosa cells after amygdalin treatment (1, 10, 100, 1000, 10 000 μg.mL-1) combined with deoxynivalneol (1 μg.mL-1) was detected by immunocytochemistry. The presence of proliferative (cyclin B1, PCNA) and apoptotic markers (caspase-3) in porcine ovarian granulosa cells was detected by immunocytochemistry. Co-administration of amygdalin plus DON significantly (p <0.05) increased the number of granulosa cells containing cyclin B1 and PCNA at all tested concetrations, when compared to control. However, percentage of granulosa cells containing major apoptotic marker caspase-3 did not differ after co-administration of amygdalin and DON. In summary, results form this in vitro study indicate that co-exposure of amygdalin and deoxynivalenol  may act to stimulate proliferation-associated peptides in porcine ovarian granulosa cells, and thus alter cell proliferation and normal follicular development.

Fusarium diseases of maize associated with mycotoxin contamination of agricultural products intended to be used for food and feed

Infections of maize with phytopathogenic and toxinogenic Fusarium spp. may occur throughout the cultivation period. This can cause different types of diseases in vegetative and generative organs of the plant. Along with these infections, mycotoxins are often produced and accumulated in affected tissues, which could pose a significant risk on human and animal health when entering the food and feed chain. Most important fungal species infecting European maize belong to the Fusarium sections Discolour and Liseola, the first being more prevalent in cooler and humid climate regions than the second predominating in warmer and dryer areas. Coexistence of several Fusarium spp. pathogens in growing maize under field conditions is the usual case and may lead to multi-contamination with mycotoxins like trichothecenes, zearalenone and fumonisins. The pathways how the fungi gain access to the target organs of the plant are extensively described in relation to specific symptoms of typical rot diseases regarding ears, kernels, rudimentary ears, roots, stem, leaves, seed and seedlings. Both Gibberella and Fusarium ear rots are of major importance in affecting the toxinogenic quality of grain or ear-based products as well as forage maize used for human or animal nutrition. Although rudimentary ears may contain high amounts of Fusarium toxins, the contribution to the contamination of forage maize is minor due to their small proportion on the whole plant dry matter yield. The impact of foliar diseases on forage maize contamination is regarded to be low, as Fusarium infections are restricted to some parts on the leaf sheaths and husks. Mycotoxins produced in rotted basal part of the stem may contribute to forage maize contamination, but usually remain in the stubbles after harvest. As the probability of a more severe disease progression is increasing with a prolonged cultivation period, maize should be harvested at the appropriate maturity stage to keep Fusarium toxin contamination as low as possible. Ongoing surveillance and research is needed to recognise changes in the spectrum of dominating Fusarium pathogens involved in mycotoxin contamination of maize to ensure safety in the food and feed chain.

Structural reorganization of the fungal endoplasmic reticulum upon induction of mycotoxin biosynthesis

Compartmentalization of metabolic pathways to particular organelles is a hallmark of eukaryotic cells. Knowledge of the development of organelles and attendant pathways under different metabolic states has been advanced by live cell imaging and organelle specific analysis. Nevertheless, relatively few studies have addressed the cellular localization of pathways for synthesis of fungal secondary metabolites, despite their importance as bioactive compounds with significance to medicine and agriculture. When triggered to produce sesquiterpene (trichothecene) mycotoxins, the endoplasmic reticulum (ER) of the phytopathogenic fungus Fusarium graminearum is reorganized both in vitro and in planta. Trichothecene biosynthetic enzymes accumulate in organized smooth ER with pronounced expansion at perinuclear- and peripheral positions. Fluorescence tagged trichothecene biosynthetic proteins co-localize with the modified ER as confirmed by co-fluorescence and co-purification with known ER proteins. We hypothesize that changes to the fungal ER represent a conserved process in specialized eukaryotic cells such as in mammalian hepatocytes and B-cells.

Cytotoxic trichothecene-type sesquiterpenes from the sponge-derived fungus Stachybotrys chartarum with tyrosine kinase inhibition

Bioassay-guided fractionation of a sponge associated fungus Stachybotrys chartarum resulted in the isolation of 15 trichothecene-based sesquiterpenes with inhibitory effects against tumor cell lines.

Fusarium Species and Their Associated Mycotoxins

The genus Fusarium includes numerous toxigenic species that are pathogenic to plants or humans, and are able to colonize a wide range of environments on earth. The genus comprises around 70 well-known species, identified by using a polyphasic approach, and as many as 300 putative species, according to phylogenetic species concepts; many putative species do not yet have formal names. Fusarium is one of the most economically important fungal genera because of yield loss due to plant pathogenic activity; mycotoxin contamination of food and feed products which often render them unaccep for marketing; and health impacts to humans and livestock, due to consumption of mycotoxins. Among the most important mycotoxins produced by species of Fusarium are the trichothecenes and the fumonisins. Fumonisins cause fatal livestock diseases and are considered potentially carcinogenic mycotoxins for humans, while trichothecenes are potent inhibitors of protein synthesis. This chapter summarizes the main aspects of morphology, pathology, and toxigenicity of the main Fusarium species that colonize different agricultural crops and environments worldwide, and cause mycotoxin contamination of food and feed.

Protein engineering of Saccharomyces cerevisiae transporter Pdr5p identifies key residues that impact Fusarium mycotoxin export and resistance to inhibition

Cereal infection by the broad host range fungal pathogen Fusarium graminearum is a significant global agricultural and food safety issue due to the deposition of mycotoxins within infected grains. Methods to study the intracellular effects of mycotoxins often use the baker's yeast model system (Saccharomyces cerevisiae); however, this organism has an efficient drug export network known as the pleiotropic drug resistance (PDR) network, which consists of a family of multidrug exporters. This study describes the first study that has evaluated the potential involvement of all known or putative ATP-binding cassette (ABC) transporters from the PDR network in exporting the F. graminearum trichothecene mycotoxins deoxynivalenol (DON) and 15-acetyl-deoxynivalenol (15A-DON) from living yeast cells. We found that Pdr5p appears to be the only transporter from the PDR network capable of exporting these mycotoxins. We engineered mutants of Pdr5p at two sites previously identified as important in determining substrate specificity and inhibitor susceptibility. These results indicate that it is possible to alter inhibitor insensitivity while maintaining the ability of Pdr5p to export the mycotoxins DON and 15A-DON, which may enable the development of resistance strategies to generate more Fusarium-tolerant crop plants.

Hydrolytic Fate of 3/15-Acetyldeoxynivalenol in Humans: Specific Deacetylation by the Small Intestine and Liver Revealed Using in Vitro and ex Vivo Approaches

In addition to deoxynivalenol (DON), acetylated derivatives, i.e., 3-acetyl and 15-acetyldexynivalenol (or 3/15ADON), are present in cereals leading to exposure to these mycotoxins. Animal and human studies suggest that 3/15ADON are converted into DON after their ingestion through hydrolysis of the acetyl moiety, the site(s) of such deacetylation being still uncharacterized. We used in vitro and ex vivo approaches to study the deacetylation of 3/15ADON by enzymes and cells/tissues present on their way from the food matrix to the blood in humans. We found that luminal deacetylation by digestive enzymes and bacteria is limited. Using human cells, tissues and S9 fractions, we were able to demonstrate that small intestine and liver possess strong deacetylation capacity compared to colon and kidneys. Interestingly, in most cases, deacetylation was more efficient for 3ADON than 15ADON. Although we initially thought that carboxylesterases (CES) could be responsible for the deacetylation of 3/15ADON, the use of pure human CES1/2 and of CES inhibitor demonstrated that CES are not involved. Taken together, our original model system allowed us to identify the small intestine and the liver as the main site of deacetylation of ingested 3/15ADON in humans.

Therapeutic effects of three trichothecenes in the silkworm infection assay with Candida albicans

The silkworm infection assay is a useful method for directly evaluating the in vivo therapeutic effects of drug candidates. In the present study, 3 known trichothecenes, trichodermin, epiisororidin E, and verrucarin A, were evaluated as antifungal agents in the silkworm-Candida albicans assay. Trichodermin and epiisororidin E yielded effective therapeutic effects, while verrucarin A exhibited no efficacy in this assay system. These results strongly suggest that trichodermin and epiisororidin E are the lead compounds for developing a new antifungal agent.

Preparation and Characterization of Cysteine Adducts of Deoxynivalenol

Conjugation with the biologically relevant thiol glutathione is one of the metabolic pathways for the mycotoxin deoxynivalenol (DON) in wheat. The occurrence of putative DON-cysteine conjugates has also been shown in wheat, likely in part as a result of degradation of the glutathione conjugates. It was reported that thiols react in vitro with DON at two positions: reversibly at C-10 of the α,β-unsaturated ketone and irreversibly at C-13 of the epoxy group. We synthesized pure DON-cysteine adducts and made analytical standards using quantitative NMR experiments. Compounds were characterized using NMR and LC-HRMS/MS and tested in vitro for toxicity. Cysteine conjugates were much less toxic than DON at the same concentration, and LC-HRMS analysis demonstrated that there was no detectable metabolism of the conjugates in human monocytes or human macrophages.

Natural Phenolic Inhibitors of Trichothecene Biosynthesis by the Wheat Fungal Pathogen Fusarium culmorum: A Computational Insight into the Structure-Activity Relationship

A model of the trichodiene synthase (TRI5) of the wheat fungal pathogen and type-B trichothecene producer Fusarium culmorum was developed based on homology modelling with the crystallized protein of F. sporotrichioides. Eight phenolic molecules, namely ferulic acid 1, apocynin 2, propyl gallate 3, eugenol 4, Me-dehydrozingerone 5, eugenol dimer 6, magnolol 7, and ellagic acid 8, were selected for their ability to inhibit trichothecene production and/or fungal vegetative growth in F. culmorum. The chemical structures of phenols were constructed and partially optimised based on Molecular Mechanics (MM) studies and energy minimisation by Density Functional Theory (DFT). Docking analysis of the phenolic molecules was run on the 3D model of F. culmorum TRI5. Experimental biological activity, molecular descriptors and interacting-structures obtained from computational analysis were compared. Besides the catalytic domain, three privileged sites in the interaction with the inhibitory molecules were identified on the protein surface. The TRI5-ligand interactions highlighted in this study represent a powerful tool to the identification of new Fusarium-targeted molecules with potential as trichothecene inhibitors.

Ribosome quality control is a central protection mechanism for yeast exposed to deoxynivalenol and trichothecin

Background

The trichothecene mycotoxins deoxynivalenol (DON) and trichothecin (TTC) are inhibitors of eukaryotic protein synthesis. Their effect on cellular homeostasis is poorly understood. We report a systematic functional investigation of the effect of DON and TTC on the yeast Saccharomyces cerevisiae using genetic array, network and microarray analysis. To focus the genetic analysis on intracellular consequences of toxin action we eliminated the PDR5 gene coding for a potent pleiotropic drug efflux protein potentially confounding results. We therefore used a knockout library with a pdr5Δ strain background.

Results

DON or TTC treatment creates a fitness bottleneck connected to ribosome efficiency. Genes isolated by systematic genetic array analysis as contributing to toxin resistance function in ribosome quality control, translation fidelity, and in transcription. Mutants in the E3 ligase Hel2, involved in ribosome quality control, and several members of the Rpd3 histone deacetylase complex were highly sensitive to DON. DON and TTC have similar genetic profiles despite their different toxic potency. Network analysis shows a coherent and tight network of genetic interactions among the DON and TTC resistance conferring gene products. The networks exhibited topological properties commonly associated with efficient processing of information. Many sensitive mutants have a "slow growth" gene expression signature. DON-exposed yeast cells increase transcripts of ribosomal protein and histone genes indicating an internal signal for growth enhancement.

Conclusions

The combination of gene expression profiling and analysis of mutants reveals cellular pathways which become bottlenecks under DON and TTC stress. These are generally directly or indirectly connected to ribosome biosynthesis such as the general secretory pathway, cytoskeleton, cell cycle delay, ribosome synthesis and translation quality control. Gene expression profiling points to an increased demand of ribosomal components and does not reveal activation of stress pathways. Our analysis highlights ribosome quality control and a contribution of a histone deacetylase complex as main sources of resistance against DON and TTC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2718-y) contains supplementary material, which is available to authorized users.

Multifaceted impact of trichothecene metabolites on plant-microbe interactions and human health

Fungi present in rhizosphere produce trichothecene metabolites which are small in size and amphipathic in nature and some of them may cross cell membranes passively. Hypocreaceae family of rhizosphere fungi produce trichothecene molecules, however it is not a mandatory characteristic of all genera. Some of these molecules are also reported as growth adjuvant, while others are reported as deleterious for the plant growth. In this review, we are exploring the roles of these compounds during plant-microbe interactions. The three-way interaction among the plants, symbiotic microbial agents (fungi and bacteria), and the pathogenic microbes (bacteria, fungi) or multicellular pathogens like nematodes involving these compounds may only help us to understand better the complex processes happening in the microcosm of rhizosphere. These metabolites may further modulate the activity of different proteins involved in the cell signalling events of defence-related response in plants. That may induce the defence system against pathogens and growth promoting gene expression in plants, while in animal cells, these molecules have reported biochemical and pharmacological effects such as inducing oxidative stress, cell-cycle arrest and apoptosis, and may be involved in maintenance of membrane integrity. The biochemistry, chemical structures and specific functional group-mediated activity of these compounds have not been studied in details yet. Few of these molecules are also recently reported as novel anti-cancer agent against human chondrosarcoma cells.

Functional Agents to Biologically Control Deoxynivalenol Contamination in Cereal Grains

Mycotoxins, as microbial secondary metabolites, frequently contaminate cereal grains and pose a serious threat to human and animal health around the globe. Deoxynivalenol (DON), a commonly detected Fusarium mycotoxin, has drawn utmost attention due to high exposure levels and contamination frequency in the food chain. Biological control is emerging as a promising technology for the management of DON contamination. Functional biological control agents (BCAs), which include antagonistic microbes, natural fungicides derived from plants and detoxification enzymes, can be used to control DON contamination at different stages of grain production. In this review, studies regarding different biological agents for DON control in recent years are summarized for the first time. Furthermore, this article highlights the significance of BCAs for controlling DON contamination, as well as the need for more practical and efficient BCAs concerning food safety.

Nucleophilic Addition of Thiols to Deoxynivalenol

Conjugation of deoxynivalenol (DON) with sulfur compounds is recognized as a significant reaction pathway, and putative DON-glutathione (DON-GSH) conjugates have been reported in planta. To understand and control the reaction of trichothecenes with biologically important thiols, we studied the reaction of DON, T-2 tetraol, and de-epoxy-DON with a range of model thiols. Reaction conditions were optimized for DON with 2-mercaptoethanol. Major reaction products were identified using HRMS and NMR spectroscopy. The results indicate that thiols react reversibly with the double bond (Michael addition) and irreversibly with the epoxide group in trichothecenes. These reactions occurred at different rates, and multiple isomers were produced including diconjugated forms. LC-MS analyses indicated that glutathione and cysteine reacted with DON in a similar manner to the model thiols. In contrast to DON, none of the tested mercaptoethanol adducts displayed toxicity in human monocytes or induced pro-inflammatory cytokines in human macrophages.

Phylogenomics and evolution of secondary metabolism in plant-associated fungi

Fungi produce a myriad of secondary metabolites, compounds that are not required for basic cellular processes, but are thought to be central to ecological functions. Genomic sequencing of fungi has revealed a greater diversity of secondary metabolism than previously realized, including novel taxonomic distributions of known compounds and uncharacterized gene clusters in well-studied organisms. Here we provide an overview of the major groups of metabolites, their ecological functions, the genetic systems that produce them, and the patterns and processes associated with evolutionary diversification of secondary metabolism in plant-associated filamentous ascomycetes.

A Lipid Transfer Protein Increases the Glutathione Content and Enhances Arabidopsis Resistance to a Trichothecene Mycotoxin

Fusarium head blight (FHB) or scab is one of the most important plant diseases worldwide, affecting wheat, barley and other small grains. Trichothecene mycotoxins such as deoxynivalenol (DON) accumulate in the grain, presenting a food safety risk and health hazard to humans and animals. Despite considerable breeding efforts, highly resistant wheat or barley cultivars are not available. We screened an activation tagged Arabidopsis thaliana population for resistance to trichothecin (Tcin), a type B trichothecene in the same class as DON. Here we show that one of the resistant lines identified, trichothecene resistant 1 (trr1) contains a T-DNA insertion upstream of two nonspecific lipid transfer protein (nsLTP) genes, AtLTP4.4 and AtLTP4.5. Expression of both nsLTP genes was induced in trr1 over 10-fold relative to wild type. Overexpression of AtLTP4.4 provided greater resistance to Tcin than AtLTP4.5 in Arabidopsis thaliana and in Saccharomyces cerevisiae relative to wild type or vector transformed lines, suggesting a conserved protection mechanism. Tcin treatment increased reactive oxygen species (ROS) production in Arabidopsis and ROS stain was associated with the chloroplast, the cell wall and the apoplast. ROS levels were attenuated in Arabidopsis and in yeast overexpressing AtLTP4.4 relative to the controls. Exogenous addition of glutathione and other antioxidants enhanced resistance of Arabidopsis to Tcin while the addition of buthionine sulfoximine, an inhibitor of glutathione synthesis, increased sensitivity, suggesting that resistance was mediated by glutathione. Total glutathione content was significantly higher in Arabidopsis and in yeast overexpressing AtLTP4.4 relative to the controls, highlighting the importance of AtLTP4.4 in maintaining the redox state. These results demonstrate that trichothecenes cause ROS accumulation and overexpression of AtLTP4.4 protects against trichothecene-induced oxidative stress by increasing the glutathione-based antioxidant defense.

Methylthiodeoxynivalenol (MTD): insight into the chemistry, structure and toxicity of thia-Michael adducts of trichothecenes

Methylthiodeoxynivalenol (MTD), a novel derivative of the trichothecene mycotoxin deoxynivalenol (DON), was prepared by applying a reliable procedure for the formal Michael addition of methanethiol to the conjugated double bond of DON. Structure elucidation revealed the preferred formation of the hemiketal form of MTD by intramolecular cyclisation between C8 and C15. Computational investigations showed a negative total reaction energy for the hemiketalisation step and its decrease in comparison with theoretical model compounds. Therefore, this structural behaviour seems to be a general characteristic of thia-Michael adducts of type B trichothecenes. MTD was shown to be less inhibitory for a reticulocyte lysate based in vitro translation system than the parent compound DON, which supports the hypothesis that trichothecenes are detoxified through thia-adduct formation during xenobiotic metabolism.

A wheat ABC transporter contributes to both grain formation and mycotoxin tolerance

The mycotoxin deoxynivalenol (DON) acts as a disease virulence factor for Fusarium fungi, and tolerance of DON enhances wheat resistance to Fusarium head blight (FHB) disease. Two variants of an ATP-binding cassette (ABC) family C transporter gene were cloned from DON-treated wheat mRNA, namely TaABCC3.1 and TaABCC3.2. These represent two of three putative genes identified on chromosomes 3A, 3B, and 3D of the wheat genome sequence. Variant TaABCC3.1 represents the DON-responsive transcript previously associated with DON resistance in wheat. PCR-based mapping and in silico sequence analyses located TaABCC3.1 to the short arm of wheat chromosome 3B (not within the FHB resistance quantitative trait locus Fhb1). In silico analyses of microarray data indicated that TaABCC3 genes are expressed in reproductive tissue and roots, and in response to the DON producer Fusarium graminearum. Gene expression studies showed that TaABCC3.1 is activated as part of the early host response to DON and in response to the FHB defence hormone jasmonic acid. Virus-induced gene silencing (VIGS) confirmed that TaABCC3 genes contributed to DON tolerance. VIGS was performed using two independent viral construct applications: one specifically targeted TaABCC3.1 for silencing, while the other targeted this gene and the chromosome 3A homeologue. In both instances, VIGS resulted in more toxin-induced discoloration of spikelets, compared with the DON effects in non-silenced spikelets at 14 d after toxin treatment (≥2.2-fold increase, P<0.05). Silencing by both VIGS constructs enhanced head ripening, and especially so in DON-treated heads. VIGS of TaABCC3 genes also reduced the grain number by more than 28% (P<0.05), both with and without DON treatment, and the effects were greater for the construct that targeted the two homeologues. Hence, DON-responsive TaABCC3 genes warrant further study to determine their potential as disease resistance breeding targets and their function in grain formation and ripening.

Deoxynivalenol inhibits the expression by goblet cells of intestinal mucins through a PKR and MAP kinase dependent repression of the resistin-like molecule β

SCOPE

The food-associated mycotoxin deoxynivalenol (DON) is known to affect intestinal functions. However, its effect on intestinal mucus is poorly characterized.

METHODS AND RESULTS

We analyzed the effects of DON on human goblet cells (HT29-16E cells) and porcine intestinal explants. Results showed that subtoxic doses of DON (as low as 1 μM) decreased mucin (MUC) production. qPCR analysis demonstrated that this inhibition was due to a specific decrease in the level of mRNA encoding for the intestinal membrane-associated (MUC1) and the secreted MUCs (MUC2, MUC3). Mechanistic studies demonstrated that DON effect relied on the activation of the protein kinase R and the mitogen-activated protein kinase p38 ultimately leading to the inhibition of the expression of resistin-like molecule beta, a known positive regulator of MUC expression.

CONCLUSION

Taken together, our results show that at low doses found in food and feed, DON is able to affect the expression and production of MUCs by human and animal goblet cells. Due to the important role of MUCs in the barrier function and in the interaction of commensal bacteria with the host, such effect could explain the observed modifications in the microbial diversity and the increased susceptibility to enteric infection following exposure to DON.

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.

Deoxynivalenol-sulfates: identification and quantification of novel conjugated (masked) mycotoxins in wheat

We report the identification of deoxynivalenol-3-sulfate and deoxynivalenol-15-sulfate as two novel metabolites of the trichothecene mycotoxin deoxynivalenol in wheat. Wheat ears which were either artificially infected with Fusarium graminearum or directly treated with the major Fusarium toxin deoxynivalenol (DON) were sampled 96 h after treatment. Reference standards, which have been chemically synthesized and confirmed by NMR, were used to establish a liquid chromatography-electrospray ionization (LC-ESI)-MS/MS-based "dilute and shoot" method for the detection, unambiguous identification, and quantification of both sulfate conjugates in wheat extracts. Using this approach, detection limits of 0.003 mg/kg for deoxynivalenol-3-sulfate and 0.002 mg/kg for deoxynivalenol-15-sulfate were achieved. Matrix-matched calibration was used for the quantification of DON-sulfates in the investigated samples. In DON-treated samples, DON-3-sulfate was detected in the range of 0.29-1.4 mg/kg fresh weight while DON-15-sulfate concentrations were significantly lower (range 0.015-0.061 mg/kg fresh weight). In Fusarium-infected wheat samples, DON-3-sulfate was the only detected sulfate conjugate (range 0.022-0.059 mg/kg fresh weight). These results clearly demonstrate the potential of wheat to form sulfate conjugates of DON. In order to test whether sulfation is a detoxification reaction in planta, we determined the ability of the sulfated DON derivatives to inhibit in vitro protein synthesis of wheat ribosomes. The results demonstrate that both DON-sulfates can be regarded as detoxification products. DON-15-sulfate was about 44× less inhibitory than the native toxin, and no toxicity was observed for DON-3-sulfate in the tested range.

Rapid analysis of deoxynivalenol in durum wheat by FT-NIR spectroscopy

Fourier-transform-near infrared (FT-NIR) spectroscopy has been used to develop quantitative and classification models for the prediction of deoxynivalenol (DON) levels in durum wheat samples. Partial least-squares (PLS) regression analysis was used to determine DON in wheat samples in the range of <50–16,000 µg/kg DON. The model displayed a large root mean square error of prediction value (1,977 µg/kg) as compared to the EU maximum limit for DON in unprocessed durum wheat (i.e., 1,750 µg/kg), thus making the PLS approach unsuitable for quantitative prediction of DON in durum wheat. Linear discriminant analysis (LDA) was successfully used to differentiate wheat samples based on their DON content. A first approach used LDA to group wheat samples into three classes: A (DON ≤ 1,000 µg/kg), B (1,000 < DON ≤ 2,500 µg/kg), and C (DON > 2,500 µg/kg) (LDA I). A second approach was used to discriminate highly contaminated wheat samples based on three different cut-off limits, namely 1,000 (LDA II), 1,200 (LDA III) and 1,400 µg/kg DON (LDA IV). The overall classification and false compliant rates for the three models were 75%–90% and 3%–7%, respectively, with model LDA IV using a cut-off of 1,400 µg/kg fulfilling the requirement of the European official guidelines for screening methods. These findings confirmed the suitability of FT-NIR to screen a large number of wheat samples for DON contamination and to verify the compliance with EU regulation.

Elimination of damaged mitochondria through mitophagy reduces mitochondrial oxidative stress and increases tolerance to trichothecenes

Trichothecene mycotoxins are natural contaminants of small grain cereals and are encountered in the environment, posing a worldwide threat to human and animal health. Their mechanism of toxicity is poorly understood, and little is known about cellular protection mechanisms against trichothecenes. We previously identified inhibition of mitochondrial protein synthesis as a novel mechanism for trichothecene-induced cell death. To identify cellular functions involved in trichothecene resistance, we screened the Saccharomyces cerevisiae deletion library for increased sensitivity to nonlethal concentrations of trichothecin (Tcin) and identified 121 strains exhibiting higher sensitivity than the parental strain. The largest group of sensitive strains had significantly higher reactive oxygen species (ROS) levels relative to the parental strain. A dose-dependent increase in ROS levels was observed in the parental strain treated with different trichothecenes, but not in a petite version of the parental strain or in the presence of a mitochondrial membrane uncoupler, indicating that mitochondria are the main site of ROS production due to toxin exposure. Cytotoxicity of trichothecenes was alleviated after treatment of the parental strain and highly sensitive mutants with antioxidants, suggesting that oxidative stress contributes to trichothecene sensitivity. Cotreatment with rapamycin and trichothecenes reduced ROS levels and cytotoxicity in the parental strain relative to the trichothecene treatment alone, but not in mitophagy deficient mutants, suggesting that elimination of trichothecene-damaged mitochondria by mitophagy improves cell survival. These results reveal that increased mitophagy is a cellular protection mechanism against trichothecene-induced mitochondrial oxidative stress and a potential target for trichothecene resistance.

Metabolism of the masked mycotoxin deoxynivalenol-3-glucoside in pigs

Plants can metabolize the Fusarium mycotoxin deoxynivalenol (DON) by forming the masked mycotoxin deoxynivalenol-3-β-D-glucoside (D3G). D3G might be cleaved during digestion, thus increasing the total DON burden of an individual. Due to a lack of in vivo data, D3G has not been included in the various regulatory limits established for DON so far. The aim of our study was to contribute to the risk assessment of D3G by determination of its metabolism in pigs. Four piglets received water, D3G (116 μg/kg b.w.) and the equimolar amount of DON (75 μg/kg b.w.) by gavage on day 1, 5 and 9 of the experiment, respectively. Additionally, 15.5 μg D3G/kg b.w. were administered intravenously on day 13. Urine and feces were collected for 24 h and analyzed for DON, D3G, deoxynivalenol-3-glucuronide (DON-3-GlcA), deoxynivalenol-15-GlcA (DON-15-GlcA) and deepoxy-deoxynivalenol (DOM-1) by UHPLC-MS/MS. After oral application of DON and D3G, in total 84.8±9.7% and 40.3±8.5% of the given dose were detected in urine, respectively. The majority of orally administered D3G was excreted in form of DON, DON-15-GlcA, DOM-1 and DON-3-GlcA, while urinary D3G accounted for only 2.6±1.4%. In feces, just trace amounts of metabolites were found. Intravenously administered D3G was almost exclusively excreted in unmetabolized form via urine. Data indicate that D3G is nearly completely hydrolyzed in the intestinal tract of pigs, while the toxin seems to be rather stable after systemic absorption. Compared to DON, the oral bioavailability of D3G and its metabolites seems to be reduced by a factor of up to 2, approximately.

Immunomodulatory effects of selenium and vitamin E on alterations in T lymphocyte subsets induced by T-2 toxin

Abstract Context: T-2 toxin, a potent mycotoxin, has serious effects on immune system.

OBJECTIVE

Here, the effects of a sublethal dose of this toxin on T lymphocyte sub-population levels and the potential protective effects from treatment with selenium or vitamin E were studied.

MATERIALS AND METHODS

After having determined the sublethal dose of the T-2 toxin in Balb/c mice hosts, the post-injection kinetics of changes in T lymphocyte sub-population (CD3(+), CD4(+) and CD8(+) cells) profiles were analyzed via flow cytometry. For these studies, the selenium and vitamin E were either provided to the mice before or concurrent with the toxin.

RESULTS

The results show that after a sublethal dose of T-2 alone, the number of CD8(+) T-lymphocytes was significantly decreased at 12 h and normalized at 48 h. In contrast, level of CD3(+) and CD4(+) T-lymphocytes were significantly increased at 24 h and returned to normal after 48 h. When selenium was injected into the mice 24 h before or concurrent with the T-2, the effects on CD8(+) cells were mitigated. Oddly, only when the selenium was given with the toxin could the effects on the CD3(+) and CD4(+) cells be altered. Vitamin E, when injected 24 h before or concurrent with the T-2 toxin, was only able to impact upon the CD8(+) lymphocyte alterations induced by the toxin.

CONCLUSIONS

Compared with vitamin E, it seems that selenium could assert an important effect against the immunotoxic effects of T-2 toxin against T lymphocytes.

Deoxynivalenol in the gastrointestinal tract of immature gilts under per os toxin application

Deoxynivalenol is also known as vomitoxin due to its impact on livestock through interference with animal growth and acceptance of feed. At the molecular level, deoxynivalenol disrupts normal cell function by inhibiting protein synthesis via binding to the ribosome and by activating critical cellular kinases involved in signal transduction related to proliferation, differentiation and apoptosis. Because of concerns related to deoxynivalenol, the United States FDA has instituted advisory levels of 5 µg/g for grain products for most animal feeds and 10 µg/g for grain products for cattle feed. The aim of the study was to determine the effect of low doses of deoxynivalenol applied per os on the presence of this mycotoxin in selected tissues of the alimentary canal of gilts. The study was performed on 39 animals divided into two groups (control, C; n = 21 and experimental, E; n = 18), of 20 kg body weight at the beginning of the experiment. Gilts received the toxin in doses of 12 µg/kg b.w./day (experimental group) or placebo (control group) over a period of 42 days. Three animals from two experimental groups were sacrificed on days 1, 7, 14, 21, 28, 35 and 42, excluding day 1 when only three control group animals were scarified. Tissues samples were prepared for high performance liquid chromatography (HPLC) analyses with the application of solid phase extraction (SPE). The results show that deoxynivalenol doses used in our study, even when applied for a short period, resulted in its presence in gastrointestinal tissues. The highest concentrations of deoxynivalenol reported in small intestine samples ranged from 7.2 (in the duodenum) to 18.6 ng/g (in the ileum) and in large intestine samples from 1.8 (in transverse the colon) to 23.0 ng/g (in the caecum). In liver tissues, the deoxynivalenol contents ranged from 6.7 to 8.8 ng/g.

Organ damage and hepatic lipid accumulation in carp (Cyprinus carpio L.) after feed-borne exposure to the mycotoxin, deoxynivalenol (DON)

Deoxynivalenol (DON) frequently contaminates animal feed, including fish feed used in aquaculture. This study intends to further investigate the effects of DON on carp (Cyprinus carpio L.) at concentrations representative for commercial fish feeds. Experimental feeding with 352, 619 or 953 μg DON kg⁻¹ feed resulted in unaltered growth performance of fish during six weeks of experimentation, but increased lipid peroxidation was observed in liver, head kidney and spleen after feeding of fish with the highest DON concentration. These effects of DON were mostly reversible by two weeks of feeding the uncontaminated control diet. Histopathological scoring revealed increased liver damage in DON-treated fish, which persisted even after the recovery phase. At the highest DON concentration, significantly more fat, and consequently, increased energy content, was found in whole fish body homogenates. This suggests that DON affects nutrient metabolism in carp. Changes of lactate dehydrogenase (LDH) activity in kidneys and muscle and high lactate levels in serum indicate an effect of DON on anaerobic metabolism. Serum albumin was reduced by feeding the medium and a high dosage of DON, probably due to the ribotoxic action of DON. Thus, the present study provides evidence of the effects of DON on liver function and metabolism.

Deoxynivalenol and oxidative stress indicators in winter wheat inoculated with Fusarium graminearum

This study comprises analyses of contents of mycotoxins, such as deoxynivalenol and zearalenone, as well as the level of oxidative stress in ears of a susceptible wheat cultivar Hanseat and cv. Arina, resistant to a pathogenic fungus Fusarium graminearum. Starting from 48 h after inoculation, a marked increase was observed in the contents of these mycotoxins in ears of wheat; however, the greatest accumulation was recorded in the late period after inoculation, i.e., during development of disease. Up to 120 h after inoculation, in ears of both wheat cultivars, the level of deoxynivalenol was higher than that of zearalenone. The susceptible cultivar was characterized by a much greater accumulation of deoxynivalenol than the resistant cultivar. At the same time, in this cultivar, in the time from 0 to 72 h after inoculation, a marked post-infection increase was observed in the generation of the superoxide radical (O2•-). Additionally, its level, at all the time points after inoculation, was higher than in the control. In wheat cv. Arina, a markedly higher level of O2•- generation in relation to the control was found up to two hours after inoculation and, next, at a later time after inoculation. In turn, the level of semiquinone radicals detected by electron paramagnetic resonance (EPR) increased at later culture times, both in cv. Hanseat and Arina; however, in infested ears of wheat, it was generally lower than in the control. Analysis of disease symptoms revealed the presence of more extensive lesions in ears of a susceptible wheat cv. Hanseat than resistant cv. Arina. Additionally, ergosterol level as a fungal growth indicator was higher in ears of susceptible wheat than in the resistant cultivar.

Stereoselective Luche reduction of deoxynivalenol and three of its acetylated derivatives at C8

The trichothecene mycotoxin deoxynivalenol (DON) is a well known and common contaminant in food and feed. Acetylated derivatives and other biosynthetic precursors can occur together with the main toxin. A key biosynthetic step towards DON involves an oxidation of the 8-OH group of 7,8-dihydroxycalonectrin. Since analytical standards for the intermediates are not available and these intermediates are therefore rarely studied, we aimed for a synthetic method to invert this reaction, making a series of calonectrin-derived precursors accessible. We did this by developing an efficient protocol for stereoselective Luche reduction at C8. This method was used to access 3,7,8,15-tetrahydroxyscirpene, 3-deacetyl-7,8-dihydroxycalonectrin, 15-deacetyl-7,8-dihydroxycalonectrin and 7,8-dihydroxycalonectrin, which were characterized using several NMR techniques. Beside the development of a method which could basically be used for all type B trichothecenes, we opened a synthetic route towards different acetylated calonectrins.

Reaction of (conjugated) deoxynivalenol with sulphur reagents - novel metabolites, toxicity and application

Recently, three novel deoxynivalenol (DON) sulphonates (DONS-1, -2 and -3) formed by transformation of DON with sulphur reagents were discovered. Their structures were elucidated, factors influencing their formation were investigated and their stability was evaluated. The first aim of the present work was to assess the toxicity of the three DONS. The hypothesis was a loss of toxicity of DONS-1 and reduced toxicity of DONS-2 and DONS-3 compared with DON. Three different toxicity tests confirmed this hypothesis, revealing reduction of toxicity by factors of at least 330, 29 and 33 for DONS-1, -2 and -3, respectively. The second objective was to investigate the reaction of DON conjugates with sulphur reagents both in solution and in cereal samples, and to determine the pattern of the formed DONS in DON-contaminated cereals. Reversed phase ultra high performance liquid chromatography-high resolution tandem mass spectrometry demonstrated that also conjugated mycotoxins (DON-3-glucoside, 3-acetyl-DON, 15-acetyl-DON) are converted into DON conjugate sulphonates upon incubation with sodium metabisulphite (SBS) or sodium sulphite in solution. DON conjugate sulphonates of the series 1, 2 and 3 differed in their fragmentation pattern in a similar way as DONS-1, -2 and -3. Treatment of a barley sample contaminated with DON, 3-acetyl-DON and the masked mycotoxin DON-3-glucoside with SBS revealed that the predominantly formed compounds are DONS-3 and DON conjugate sulphonates of the series 3, followed by those of the series 2. Incubation of DON containing maize samples of different moisture contents with 0.5% of SBS or sodium sulphite for 7 days confirmed DONS-3 as main DON transformation product. Both in barley and in maize, SBS and sodium sulphite showed different efficiency for transformation of DON at low moisture contents. These findings provide novel insights into inactivation of DON-contaminated cereals.

Durum wheat (Triticum Durum Desf.) lines show different abilities to form masked mycotoxins under greenhouse conditions

Deoxynivalenol (DON) is the most prevalent trichothecene in Europe and its occurrence is associated with infections of Fusarium graminearum and F. culmorum, causal agents of Fusarium head blight (FHB) on wheat. Resistance to FHB is a complex character and high variability occurs in the relationship between DON content and FHB incidence. DON conjugation to glucose (DON-3-glucoside, D3G) is the primary plant mechanism for resistance towards DON accumulation. Although this mechanism has been already described in bread wheat and barley, no data are reported so far about durum wheat, a key cereal in the pasta production chain. To address this issue, the ability of durum wheat to detoxify and convert deoxynivalenol into D3G was studied under greenhouse controlled conditions. Four durum wheat varieties (Svevo, Claudio, Kofa and Neodur) were assessed for DON-D3G conversion; Sumai 3, a bread wheat variety carrying a major QTL for FHB resistance (QFhs.ndsu-3B), was used as a positive control. Data reported hereby clearly demonstrate the ability of durum wheat to convert deoxynivalenol into its conjugated form, D3G.