Protein synthesis by mammalian cells treated with C-3-modified analogs of the 12,13-epoxytrichothecenes T-2 and T-2 tetraol

Enterocyte-Based Bioassay via Quantitative Combination of Proinflammatory Sentinels Specific to 8-keto-trichothecenes

Type B 8-keto-trichothecenes are muco-active mycotoxins that exist as inevitable contaminants in cereal-based foodstuffs. Gut-associated inflammation is an early frontline response during human and animal exposure to these mycotoxins. Despite various tools for chemical identification, optimized biomonitoring of sentinel response-associated biomarkers is required to assess the specific proinflammatory actions of 8-keto-trichothecenes in the gut epithelial barrier. In the present study, intoxication with 8-keto-trichothecenes in human intestinal epithelial cells was found to trigger early response gene 1 product (EGR-1) that plays crucial roles in proinflammatory chemokine induction. In contrast, epithelial exposure to 8-keto-trichothecenes resulted in downregulated expression of nuclear factor NF-kappa-B p65 protein, a key transcription factor, during general inflammatory responses in the gut. Based on the early molecular patterns of expression, the inflammation-inducing activity of 8-keto-trichothecenes was quantified using intestinal epithelial cells with dual reporters for EGR-1 and p65 proteins. EGR-1-responsive elements were linked to luciferase reporter while p65 promoter was bound to secretory alkaline phosphatase (SEAP) reporter. In response to conventional inflammagens such as endotoxins and cytokines such as TNF-α, both luciferase and SEAP activity were elevated in a dose-dependent manner. However, as expected from the mechanistic evaluation, 8-keto-trichothecene-exposed dual reporters of luciferase and SEAP displayed contrasting expression patterns. Furthermore, 8-keto-trichothecene-elevated EGR-1-responsive luciferase activity was improved by deficiency of PSMA3, an α-type subunit of the 20S proteasome core complex for ubiquitin-dependent EGR-1 degradation. This molecular event-based dual biomonitoring in epithelial cells is a promising supplementary tool for detecting typical molecular inflammatory pathways in response to 8-keto-trichothecenes in the food matrix.

Appropriateness to set a group health based guidance value for T2 and HT2 toxin and its modified forms

The EFSA Panel on Contaminants in the Food Chain (CONTAM) established a tolerable daily intake (TDI) for T2 and HT2 of 0.02 μg/kg body weight (bw) per day based on a new in vivo subchronic toxicity study in rats that confirmed that immune‐ and haematotoxicity are the critical effects of T2 and using a reduction in total leucocyte count as the critical endpoint. An acute reference dose (ARfD) of 0.3 μg for T2 and HT2/kg bw was established based on acute emetic events in mink. Modified forms of T2 and HT2 identified are phase I metabolites mainly formed through hydrolytic cleavage of one or more of the three ester groups of T2. Less prominent hydroxylation reactions occur predominantly at the side chain. Phase II metabolism involves conjugation with glucose, modified glucose, sulfate, feruloyl and acetyl groups. The few data on occurrence of modified forms indicate that grain products are their main source. The CONTAM Panel found it appropriate to establish a group TDI and a group ARfD for T2 and HT2 and its modified forms. Potency factors relative to T2 for the modified forms were used to account for differences in acute and chronic toxic potencies. It was assumed that conjugates (phase II metabolites of T2, HT2 and their phase I metabolites), which are not toxic per se, would be cleaved releasing their aglycones. These metabolites were assigned the relative potency factors (RPFs) of their respective aglycones. The RPFs assigned to the modified forms were all either 1 or less than 1. The uncertainties associated with the present assessment are considered as high. Using the established group, ARfD and TDI would overestimate any risk of modified T2 and HT2.

Dose-related genotoxic effect of T-2 toxin measured by comet assay using peripheral blood mononuclear cells of healthy pigs

T-2 toxin is the most acutely toxic trichothecene mycotoxin: it inhibits protein, DNA and RNA synthesis. The main goal of this study was to evaluate the rate of DNA damage caused by T-2 toxin in porcine mononuclear cells in increasing concentrations (0.1, 0.5 and 1.0 μmol) and after two different incubation periods (24 and 42 h). The lowest concentration caused DNA damage and about 50% of the treated cells could be categorised as having 1 to 4 scores in comet assay. In parallel with the increase of T-2 toxin concentration, the frequency of intact lymphocytes decreased from 50.2% (0.1 μM) to 36.3% (1.0 μM) in the first 24 h. In case of score 3, the highest concentration of T-2 toxin resulted in a 5-fold change, as compared to the lowest dose. Cells with score 4 were found only after exposure to 1.0 μM T-2 toxin. The exposure time did not have a significant effect on the results, while concentration did (P < 0.0001). However, a significant interaction between concentration and time as fixed factors (P < 0.0001) was found. When these were combined as a single factor, the results showed a significant toxin treatment effect on the results. It was concluded that a time- and dose-dependent DNA damaging effect of T-2 toxin could be demonstrated using peripheral blood mononuclear cells from healthy pigs by comet assay.

Comparative induction of 28S ribosomal RNA cleavage by ricin and the trichothecenes deoxynivalenol and T-2 toxin in the macrophage

Ribosome-inactivating proteins (RIPs) and sesquiterpenoid trichothecene mycotoxins are known to bind to eukaryotic ribosomes, inhibit translation and activate mitogen-activated protein kinases. Here we compared the capacities of the RIP ricin to promote 28S ribosomal RNA (rRNA) cleavage with that of the trichothecenes, deoxynivalenol (DON), and T-2 toxin (T-2). In a cell-free model, exposure to ricin at 300 ng/ml for 30 min depurinated yeast 28S rRNA, however, neither DON (< or = 4 microg/ml) nor T-2 (< or = 2 microg/ml) exhibited this N-glycosidase activity. Incubation of RAW 264.7 macrophages with ricin (20-320 ng/ml), DON (250-5000 ng/ml), or T-2 (2-80 ng/ml) for 6 h, however, generated 28S rRNA-specific products consistent with cleavage sites near the 3' terminal end of murine 28S rRNA. Oligonucleotide extension analysis of treated RAW 264.7 cells revealed that ricin evoked 28S rRNA damage at one site in the alpha-sarcin/ricin (S/R)-loop (A4256) and two other sites (A3560 and A4045) in the peptidyl transferase center. Although DON or T-2 did not damage the S/R loop, these trichothecenes did promote cleavage at A3560 and A4045. In addition, incubation of the cells with ricin (> or = 20 ng/ml), DON (> or = 250 ng/ml), or T-2 (> or = 10 ng/ml) induced RNase activity as well as RNase L mRNA and protein expression. These data suggest that only ricin directly damaged 28S rRNA under cell-free conditions but that ricin, DON, and T-2 promoted intracellular 28S rRNA cleavage, potentially by facilitating the action of endogenous RNases and/or by upregulating RNase expression.

Chicken nucleated blood cells as a cellular model for genotoxicity testing using the comet assay

Mycotoxins can frequently occur in animal feed and human food. T-2 toxin, as the most toxic trichothecene, has been implicated as the causative agent in a variety of animal diseases and is associated with some human diseases. The comet assay was performed as a test for detection of DNA damage caused by T-2 toxin in peripheral blood cells of chicken. The suitability of the comet assay as a biomarker for genotoxic analysis has been applied in studies using human white blood cells. It can be applied to any tissue from which a single cell suspension can be obtained. The method has already been applied to chicken as a foodstuff for detection of irradiation of food containing DNA. However, application of the method on chicken blood cells has not been set up yet. The aim of this research was to develop a protocol for detection of DNA damage induced by T-2 toxin in chicken blood cells. Chickens were administered orally with T-2 toxin and the samples of whole blood were collected at 24 h post treatment. The DNA damage was determined by an increase in the comet parameters in tested animals. Our results show that T-2 toxin had induced significant DNA damage in treated chicken as compared with control animals, indicating that the assay can be used for the assessment of primary DNA damage caused by mycotoxins.

Cancer preventive potential of trichothecenes from Trichothecium roseum

Bioassay-guided separation of extracts from the culture broth and mycelium of the fungus Trichothecium roseum, aiming at the discovery for cancer preventive agents, resulted in the isolation of three new trichothecene sesquiterpenes, trichothecinols A-C (1-3) together with three known analogues, trichothecin (4), trichodermol (5) and trichothecolone (6). Compounds 1-6 exhibited remarkably potent inhibition against Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). Further compound 1 strongly inhibited TPA-induced tumor promotion on mouse skin initiated with 7,12-dimethylbenz[a]anthracene (DMBA) in two-stage carcinogenesis tests. These results suggest that compound 1 might be a valuable lead for further evaluation as a cancer preventive agent. In addition to their cancer preventive activity, compound 2 was found to show modest antifungal activity against Crypotcoccus albidus and Saccharomyces cerevisiae.

Survey of natural occurrence of trichothecene mycotoxins and zearalenone in Korean cereals harvested in 1992 using gas chromatography/mass spectrometry

For the survey of the natural occurrence of trichothecene mycotoxins, produced by species of fungi imperfecti such as Fusarium and Trichothecium, a sensitive analytical method was developed for the simultaneous detection and quantitation of the major trichothecene mycotoxins, viz. T-2 toxin (T-2), HT-2 toxin (HT-2), nivalenol (NIV), fusarenon-X (F-X), deoxynivalenol (DON), 3-acetyl deoxynivalenol (3-Ac DON), and zearalenone (ZEN), using gas chromatography/mass spectrometry-selected ion monitoring (GC/MS-SIM) mode after trimethyl silyl derivatization. The incidence of NIV and DON in 30 barley samples were 93% and 67%, respectively; the average contents of NIV and DON in positive samples were 390 ng/g (range 40-2038) and 106 ng/g (range 5-361) respectively. In 15 maize samples, the incidences of NIV and DON were 53% and 93% respectively and the average contents were 168 ng/g and 145 ng/g, respectively. These results suggest that NIV and DON were the major contaminating trichothecene mycotoxins in Korean barley and maize samples harvested in 1992.

Structure-activity relationships among mycotoxins

Relationships between structural features and biological effects of mycotoxins are reviewed. Structure-activity relationships are characterized at the molecular, subcellular, cellular, or supracellular level. Major chemical and physicochemical factors responsible for bioactivity of mycotoxins are stressed. A variety of chemical families of mycotoxins are then discussed from the point of view of structure-activity relationships. The structurally related families comprise small lactones, macrocyclic lactones, isocoumarin derivatives, aflatoxins and related compounds trichothecenes, anthraquinones, indole-derived tremorgens and selected amino acid-derived mycotoxins such as sporidesmins and cyclosporines. Biological effects of mycotoxins include acute and chronic toxicity, antimicrobial activity, mutagenicity and genotoxicity, carcinogenicity and biochemical modes of action.

Protein synthesis inhibition by 8-oxo-12,13-epoxytrichothecenes

The Fusarium mycotoxin, 4-deoxynivalenol, is an abundant, natural contaminant of corn and wheat. 8-Oxo-12,13-epoxytrichothecenes related to 4-deoxynivalenol were synthesized; they either lacked the 7-hydroxyl but contained a hydroxyl at C-4 (7-deoxynivalenol) or lacked substituents at C-3 and C-7 (3,7-dideoxynivalenol). The ability of these synthetic analogs and their acetylated derivatives to inhibit protein synthesis by cultured mammalian cells was compared to that of 4-deoxynivalenol. Whereas the 50% inhibitory dose (ID50) for murine erythroleukemia cells was about 1 microgram/ml for 4-deoxynivalenol and 3,7-dideoxynivalenol, all of the other analogs were at least 10-fold less potent. When tested at their ID50 dose, all of the 8-oxotrichothecenes, except 4-deoxynivalenol and 3,7-dideoxynivalenol, caused polysome 'run-off', indicating that, at this dose, they are inhibitors of polypeptide chain initiation. With 4-deoxynivalenol and 3,7-dideoxynivalenol, polysomes remained at control levels indicating that these toxins prevent polypeptide chain elongation. From these results and comparisons to previous studies of 8-oxo-12,13-epoxytrichothecenes (trichothecolone, trichothecin, nivalenol and fusarenone X), trichothecenes with substituents at both C-3 and C-4 predominantly inhibit polypeptide chain initiation, whereas those lacking one substituent at either site are inhibitors of chain elongation.

Ovine platelet function and its inhibition by T-2 toxin

Ovine platelets suspended in homologous plasma aggregated effectively in response to adenosine-diphosphate, acid-soluble collagen and aggregated moderately to serotonin and arachidonic acid. Ovine platelet aggregation, in response to each agent, was inhibited in a concentration dependent fashion by T-2 toxin. The platelet aggregates which formed in the presence of T-2 toxin appeared to be less stable than aggregates in comparable control platelet suspensions.