Inhibition of mitogen-induced blastogenesis in human lymphocytes by T-2 toxin and its metabolites

Effect of DON and ZEN and their metabolites DOM-1 and HZEN on B cell proliferation and antibody production

Introduction

The mycotoxins deoxynivalenol (DON) and zearalenone (ZEN), produced by Fusarium fungi, are frequently found in the cereal-rich diet of pigs and can modulate the immune system. Some enzymes or bacteria present in the digestive tract can de-epoxydize DON to deepoxy-deoxynivalenol (DOM-1) and biotransform ZEN into hydrolyzed ZEN (HZEN). The effects of these metabolites on immune cells, particularly with respect to the vaccine responses, are poorly documented. The aim of this study was to address the impact of DON and ZEN and their respective derivatives, on proliferation, and antibody production of porcine B cells in vitro.

Methods

Peripheral blood mononuclear cells (PBMCs), isolated from healthy pigs, were stimulated with the Toll-like receptor (TLR) 7/8-agonist Resiquimod (R848) or the TLR/1/2-agonist Pam3Cys-SKKKK in combination with DON [0.1-1.6 µM] or DOM-1 [1.6 µM and 16 µM] and ZEN [2.5-40 µM] or HZEN [40 µM].

Results

A strong decrease in B-cell proliferation was observed at DON concentrations equal to or exceeding 0.8 µM and at ZEN concentrations equal to or exceeding 20 µM. Treatment with 1.6 µM DON or 40 µM ZEN led to almost a complete loss of live CD79α+ B cells. Moreover, CD21 expression of proliferating IgG+ and IgM+ B-cell subsets was decreased at DON concentrations equal to and exceeding 0.4 µM and at ZEN concentrations equal to or exceeding 10 µM. ELISpot assays revealed a decrease of IgG-secreting B cells at concentrations of and exceeding 0.4 µM and at ZEN concentrations equal to and exceeding 10 µM. ELISA assays showed a decrease of IgM, IgG, and IgA secretion at concentrations equal to or exceeding 0.4 µM DON. ZEN reduced IgM secretion at 20-40 µM (both R848 and Pam3Cys-SKKKK), IgG secretion at 40 µM (both R848 and Pam3Cys-SKKKK) and IgA secretion at 20-40 µM.

Discussion

Our in vitro experiments show that while DON and ZEN impair immunoglobulin production and B-cell proliferation, this effect is abrogated by HZEN and DOM-1.

Zearalenone and the Immune Response

Zearalenone (ZEA) is an estrogenic fusariotoxin, being classified as a phytoestrogen, or as a mycoestrogen. ZEA and its metabolites are able to bind to estrogen receptors, 17β-estradiol specific receptors, leading to reproductive disorders which include low fertility, abnormal fetal development, reduced litter size and modification at the level of reproductive hormones especially in female pigs. ZEA has also significant effects on immune response with immunostimulatory or immunosuppressive results. This review presents the effects of ZEA and its derivatives on all levels of the immune response such as innate immunity with its principal component inflammatory response as well as the acquired immunity with two components, humoral and cellular immune response. The mechanisms involved by ZEA in triggering its effects are addressed. The review cited more than 150 publications and discuss the results obtained from in vitro and in vivo experiments exploring the immunotoxicity produced by ZEA on different type of immune cells (phagocytes related to innate immunity and lymphocytes related to acquired immunity) as well as on immune organs. The review indicates that despite the increasing number of studies analyzing the mechanisms used by ZEA to modulate the immune response the available data are unsubstantial and needs further works.

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.

A comparison of hepatic in vitro metabolism of T-2 toxin in rats, pigs, chickens, and carp

T-2 toxin, a highly toxic member of the type-A trichothecenes, is produced by various Fusarium moulds that can potentially affect human health. It is strongly cytotoxic for human hematopoietic progenitors. Alimentary toxic aleukia (ATA), a disease typically associated with human, is primarily induced by T-2 toxin. A comparison of the metabolism of T-2 toxin incubated with hepatocytes of rats, piglets, chickens, and the hepatic subcellular fractions (microsomes and cytosol) of piglets, chickens, rats, and carp (common carp and grass carp) was carried out. The activities of the recombinant pig CYP3A29 on the transformation of T-2 and HT-2 toxins were preliminary studied. Metabolites were identified by novel LC/MS-IT-TOF. Qualitative similarities and differences across the species were observed. In liver microsomes, HT-2 toxin, neosolaniol (NEO), 3'-OH-T-2, and 3'-OH-HT-2 were detected in rats, chickens, and pigs. 3'-OH-HT-2 and HT-2 toxin was not detectable in common carp and grass crap, respectively. Moreover, in liver microsomes, the hydroxyl metabolites accounted for the largest percentage in carp, whereas the hydrolysis product, HT-2 toxin, was the major one for the land animals. Only hydrolysis products such as NEO and HT-2 toxin were detected in hepatocytes. Recombinant pig CYP3A29 was able to convert T-2 and HT-2 toxins to high rates of 3'-OH-T-2 and 3'-OH-HT-2, respectively. Both CYP450 and carboxylesterase enzymes have been found to play a role in the metabolism of T-2 toxin. Metabolism of T-2 toxin across species produces a similar spectrum of metabolites. Preliminary metabolic studies of carp reveal that ester hydrolysis of T-2 toxin in carp may not play as important a role as is the case with land animals.

T-2 toxin and HT-2 toxin in grain and grain-based commodities in Europe: occurrence, factors affecting occurrence, co-occurrence and toxicological effects

This paper presents an overview of the occurrence of T-2 toxin and HT-2 toxin in cereals in Europe and derived food products, factors influencing the occurrence, co-occurrence with other trichothecenes, and toxicological effects of T-2 and HT-2 in human. Of all cereals, oats showed to be most susceptible to T-2/HT-2 contamination. Particularly, oats grown in Scandinavia and UK in the period 2003-2007 were highly contaminated. This contamination has reduced in 2008 and 2009. In raw cereals, T-2 and HT-2 levels were highly correlated with each other in most instances, with the HT-2 level being two to seven times higher than the T-2 level. The toxin levels showed not to be correlated with levels of deoxynivalenol and nivalenol. The occurrence of T-2 and HT-2 in the field varied between years, regions, cereal grain varieties, sowing time, and precrop. Organically produced cereals contained lower T-2 and HT-2 levels as compared to conventionally grown cereals. Little or no effects from using fungicides was seen. Processing cereals resulted in low T-2 and HT-2 levels in food products, although oat products contained some T-2 and HT-2. The by-products from food processing, often used for animal feeding, frequently were highly contaminated. T-2 and HT-2 showed to have high acute and subacute toxicity, as they caused haematotoxic, immunotoxic, cytotoxic, and dermal effects. Carcinogenicity of T-2 and HT-2 in human has not been proven. Outbreaks of human toxicosis caused by trichothecenes, including T-2 and HT-2, have been reported. The present overview is deemed to be valuable for risk assessments at the European level, planned to be held by EFSA. It also provides directions for further research, including the ecology of the fungi responsible for T-2 and HT-2, and agronomical practices to reduce the contamination in the field.

Mechanisms of deoxynivalenol-induced gene expression and apoptosis

Fusarium infection of agricultural staples such as wheat, barley and corn with concurrent production of deoxynivalenol (DON) and other trichothecene mycotoxins is an increasingly common problem worldwide. In addition to its emetic effects, chronic dietary exposure to DON causes impaired weight gain, anorexia, decreased nutritional efficiency and immune dysregulation in experimental animals. Trichothecenes are both immunostimulatory or immunosuppressive depending on dose, frequency and duration of exposure as well as type of immune function assay. Monocytes, macrophages, as well as T- and B-lymphocytes of the immune system can be cellular targets of DON and other trichothecenes. In vitro exposure to low trichothecene concentrations upregulates expression both transcriptionally and post-transcriptionally of cytokines, chemokines and inflammatory genes with concurrent immune stimulation, whereas exposure to high concentrations promotes leukocyte apoptosis with concomitant immune suppression. DON and other trichothecenes, via a mechanism known as the 'ribotoxic stress response', bind to ribosomes and rapidly activate mitogen-activated protein kinases (MAPKs). The latter are important transducers of downstream signalling events related to immune response and apoptosis. Using cloned macrophages, two critical upstream transducers of DON-induced MAPK activation have been identified. One transducer is double-stranded RNA (dsRNA)-activated protein kinase (PKR), a widely expressed serine/threonine protein kinase that can be activated by dsRNA, interferon and other agents. The other transducer is haematopoetic cell kinase (Hck), a non-receptor associated Src oncogene family kinase. Pharmacological inhibitors and gene suppression studies have revealed that Hck and PKR contribute to DON-induced gene expression and apoptosis. PKR, Hck and other kinases bind to the ribosome and are activated following DON interaction. Future studies will focus on the sequence of molecular events at the ribosome level that drive selective activation of these upstream kinases.

Adverse effects of T-2 toxin on chicken lymphocytes blastogenesis and its protection with Vitamin E

T-2 toxin, a trichothecene mycotoxin that is produced by fusarium species, is prevalent mainly in cereal crops and poultry feed. One of the major effects of this toxin is immunomodulation. The effect of T-2 toxin on chicken lymphocyte proliferation in the presence of mitogens and the subsequent protection with Vitamin E in both fat and water soluble forms was studied using an MTT colorimetric assay. T-2 toxin was administered in concentrations ranging from 0 to 10ng/mL of lymphocytes in the presence of either concanavalin A (ConA) or phytohemagglutinine (PHA-M) at optimum concentration of 333ng/mL and a dilution of 1:160 for ConA and PHA-M, respectively. Lymphocyte proliferation in response to ConA and PHA-M mitogens was depressed at T-2 doses of 1ng/mL or higher (p<0.05). The proliferation was completely abolished at 10ng/mL when the toxin was added at 0 time, while it was decreased by 80% when the toxin was added to the lymphocytes after 24h. The addition of Vitamin E in the fat soluble form (alpha-tocopheryl acetate) did not exert any protection effect against the toxin when it was added at either 25 or 100microg. However, when the water soluble form (Trolox) was added at a concentration of (200microg) (equivalent to 100microM of alpha-tocopherol), it provided considerable protection (p<0.05) against T-2 toxin inhibition of lymphocyte proliferation. The difference in the effect between the two forms of Vitamin E might be related to their relative solubility in the culture media which in turn may affect their availability for protection.

p38 Mitogen-activated protein kinase mediates IL-8 induction by the ribotoxin deoxynivalenol in human monocytes

The effects of the ribotoxic trichothecene deoxynivalenol (DON) on mitogen-activated protein kinase (MAPK)-mediated IL-8 expression were investigated in cloned human monocytes and peripheral blood mononuclear cells (PBMC). DON (250 to 1000 ng/ml) induced both IL-8 mRNA and IL-8 heteronuclear RNA (hnRNA), an indicator of IL-8 transcription, in the human U937 monocytic cell line in a concentration-dependent manner. Expression of IL-8 hnRNA, mRNA and protein correlated with p38 phosphorylation and was completely abrogated by the p38 MAPK inhibitor SB203580. DON at 500 ng/ml similarly induced p38-dependent IL-8 protein and mRNA expression in PBMC cultures from healthy volunteers. Significantly increased IL-6 and IL-1beta intracellular protein and mRNA expression was also observed in PBMC treated with DON (500 ng/ml) which were also partially p38-dependent. Flow cytometry of PBMC revealed that DON-induced p38 phosphorylation varied among individuals relative to both threshold toxin concentrations (25-100 ng/ml) and relative increases in percentages of phospho-p38(+) cells. DON-induced p38 activation occurred exclusively in the CD14(+) monocyte population. DON was devoid of agonist activity for human Toll-like receptors 2, 3, 4, 5, 7, 8 and 9. However, two other ribotoxins, emetine and anisomycin, induced p38 phosphorylation in PBMC similarly to DON. Taken together, these data suggest that (1) p38 activation was required for induction of IL-8 and proinflammatory gene expression in the monocyte and (2) DON induced p38 activation in human monocytes via the ribotoxic stress response.

In vitro cytopathic effects of mycotoxin T-2 on human peripheral blood T lymphocytes

The trichothecene mycotoxin T-2 is reported to exhibit immunotoxic activity. The potential presence of T-2 in foods renders it as public health hazard and its toxicity needs to be better understood. We investigated the in vitro effects of T-2 at sub-toxic (0.1 ng/ml) and toxic (10 ng/ml) levels on freshly isolated human peripheral blood lymphocytes (PBLs). We observed no direct influence on untreated PBLs. The toxic dose of T-2, however, totally inhibited phytohemagglutinin-induced T lymphocyte proliferation and caused early apoptosis that peaked after 8h of exposure. Both major T lymphocyte subsets (CD4+ and CD8+) were affected as they appeared to show a positive response to T-2 at 8h followed by their sharp reduction after 96 h. Further investigation on the naïve (CD45RA+) and memory (CD45RO+) subpopulations confirmed these observations and indicated that T-2 affected equally all the subpopulations studied, although PHA preferentially stimulated CD45RO+ T lymphocytes. Sub-toxic T-2 appeared to exhibit co stimulatory properties to PHA-stimulated cells. These results support the hypothesis that T-2 affects the activation-induced cell death mechanism of T lymphocytes.

T-2 toxin immunotoxicity on human B and T lymphoid cell lines

T-2 toxin belongs to a group of mycotoxins synthesized by Fusarium fungi that are widely encountered as natural contaminants in cereals. Human lymphoid cell lines of T (MOLT-4) or B (IM-9) lineage were used to characterize the cytotoxic effects mediated by T-2 at different concentrations (0.1 pg/ml to 1 microg/ml). After 24 h, membrane damage was observed by Trypan blue dye exclusion in IM-9 cells with a 50% cytotoxic concentration (CC50) of 0.2 ng/ml, whereas CC50 for MOLT-4 cells was 0.6 microg/ml (gmicro). At a T-2 concentration of 0.01 microg/ml, apoptosis was seen in MOLT-4 cells by Annexin V binding as early as after 4 h. T-2 toxin determined sustained (48 h) immunosuppression on both cell lines, as evaluated by BrdU and MTT assays. Cytotoxicity appeared to be due to early apoptosis in MOLT-4 cells, as indicated by increased Annexin V binding and activation of caspase-3, and to direct cell membrane damage in IM-9 cells.

Cellular and molecular mechanisms for immune modulation by deoxynivalenol and other trichothecenes: unraveling a paradox

Macrophages, T cells, and B cells of the immune system are central targets of deoxynivalenol (DON) and other trichothecenes-mycotoxins that can be immunostimulatory or immunosuppressive depending on dose, exposure frequency and timing of functional immune assay. Notably, low dose trichothecene exposure transcriptionally and post-transcriptionally upregulates expression of cytokines, chemokines and inflammatory genes with concurrent immune stimulation, whereas high dose exposure promotes leukocyte apoptosis with concomitant immune suppression. DON and other trichothecenes, via a mechanism known as the ribotoxic stress response, bind to ribosomes and rapidly activate mitogen-activated protein kinases (MAPKs). The latter are important transducers of downstream signaling events related to immune response and apoptosis. Using cloned macrophages, our laboratory has identified two critical upstream transducers of DON-induced MAPK activation. One transducer is double-stranded RNA-(dsRNA)-activated protein kinase (PKR), a widely-expressed serine/theonine protein kinase that can be activated by dsRNA, interferon, and other agents. The second transducer is hematopoetic cell kinase (Hck), a non-receptor associated Src family kinase. Inhibitors and gene silencing studies have revealed that Hck and PKR play roles in DON induced gene expression and apoptosis. Future studies should focus on the molecular linkages between these kinases and trichothecene toxicity.

Deoxynivalenol-induced immunomodulation of human lymphocyte proliferation and cytokine production

Mycotoxins are a structurally diverse group of secondary metabolites produced by different genera of fungi, and include deoxynivalenol (DON), T-2 toxin, aflatoxin B1 (AFB1) and fumonisin B1 (FB1). Despite widespread human exposure and potent immunomodulation in animals, their effects on the human immune system remain to be defined. In this study, the effect of these toxins on human lymphocyte proliferation was evaluated using the MTT assay. Additionally, the effect of DON on cytokine profiles was measured. A 50% inhibition in cell proliferation was observed with a DON concentration of 216 ng/ml. T-2 toxin was more potent with 50% inhibition between 1 and 5 ng/ml. Negligible effects were observed with AFB1 and FB1, and a mixture of DON with either FB1 or AFB1 did not show any synergistic effects in this assay. Short-term treatment of PHA-stimulated lymphocytes with DON (100, 200 and 400 ng/ml) modulated the kinetics of IL-2, IL-4 and IL-6 production. IL-2 levels were up to 12-fold higher (P<0.05) in comparison to control levels at toxin concentrations of 200 and 400 ng/ml 72 h after treatment. IL-4 levels were only slightly elevated and IL-6 levels were slightly inhibited by these DON concentrations. The kinetics of cytokine production was followed for an extended period of 8-9 days at DON concentrations of 200 and 400 ng/ml. At the lower DON concentration (200 ng/ml), IL-2 levels were elevated 17-25-fold with a concomitant mild elevation in IFN-gamma. Consistent with earlier experiments, IL-6 levels were slightly suppressed by DON at this concentration. At 400 ng/ml, IL-2 levels were again significantly (P<0.05) elevated until 6 days post-treatment, while the effects on IL-4 and IL-6 were less marked. These data suggest DON has potent effects on human lymphocyte cytokine production which merit investigation in exposed human populations.

In vitro exposure of human lymphocytes to trichothecenes: individual variation in sensitivity and effects of combined exposure on lymphocyte function

The trichothecenes are mycotoxins produced by fungi of the genus Fusarium, which are commonly present in foods and feed of cereal origin. Owing to the lack of sufficient toxicological data for most of the trichothecenes, in vitro studies may contribute to risk assessments of these toxins. In the present report, human lymphocyte cultures were used to study the individual variation in sensitivity among humans and the effects on in vitro Ig production. Furthermore, proliferative responses of cells exposed to combinations of two of the toxins were studied. Four toxins, T-2 toxin, diacetoxyscirpenol (DAS), nivalenol (NIV) and deoxynivalenol (DON) were included in the study. All four of the tested trichothecenes effectively inhibited mitogen-induced lymphocyte proliferation. There were no statistically significant differences in sensitivity to the toxins between lymphocytes from female and male blood donors. The individual variation in sensitivity, evaluated as the range of IC50 values, was rather limited (within a factor of 3 to 4). Immunoglobulin production by pokeweed-stimulated human lymphocytes was also effectively inhibited with IC50 values similar to the IC50 values in the proliferation tests for DON and NIV. However, IC50 values for Ig synthesis in cultures exposed to T2 were approximately two to three times higher than the corresponding IC50 values found in the proliferation tests. At low levels of exposure, elevated Ig production was observed in lymphocyte cultures from four out of the five blood donors tested. This effect was most pronounced on IgA synthesis. Combinations of NIV with T2, DAS or DON resulted in additive toxicity in the lymphocyte proliferation test, while combinations of DON with T2 or DAS resulted in an inhibition that was slightly lower than what could have been expected from the inhibition produced by the individual toxins. In conclusion, the tested trichothecenes inhibited both proliferation and Ig production in human lymphocytes in a dose-dependent manner with limited variation in sensitivity between individuals. Enhanced Ig production was observed in cell cultures exposed to the lower doses of the toxins. Combined exposure to two of the toxins resulted mainly in additive or antagonistic effects, although synergistic effects cannot be excluded and should be further investigated. These findings indicate that the total intake of type A and B trichothecenes should be taken into account in risk assessments.

In vitro effects of vomitoxin (deoxynivalenol) on T-cell interleukin production and IgA secretion

The exposure of lymphocyte cultures to vomitoxin was used to determine possible mechanisms by which this naturally occurring toxin induces serum immunoglobulin A (IgA) elevation and IgA nephropathy in the mouse. Vomitoxin exposure within the range of 10 to 1000 ng/ml inhibited DNA synthesis, protein synthesis as well as IgA, IgG and IgM production in lymphocyte cultures prepared from the Peyer's patch (PP) and spleen. When purified B cells were cultured in the presence of vomitoxin, inhibition of IgA, IgG and IgM production was similarly observed. However, on 24-hr pulsed co-exposure to vomitoxin and the mitogen concanavalin A (ConA), CD4+/CD8+ cells were capable of inducing a three- to five-fold increase in production of IgA, but not IgG and IgM by cocultured B cells when compared with B cells cocultured with control T cells exposed to the mitogen only. When pulsed for 48 hr with ConA and toxin, CD4+ cells were similarly capable of causing a significant increase in IgA production by B cells. 48-hr pulsed exposure of CD4+ cells to ConA and vomitoxin resulted in significantly increased production of the T helper cytokines IL-4, IL-5 and IL-6 after 5 additional days of culture, compared with ConA-stimulated CD4+ cells alone. These results suggest that vomitoxin was capable of enhancing CD4(+)-mediated help for IgA production by B cells and that this could possibly be mediated by way of increased cytokine production.

Mycotoxicosis: mechanisms of immunosuppression

Mycotoxins are structurally diverse secondary metabolites of fungi that grow on feedstuffs consumed by animals and man. The clinical toxicologic syndromes caused by ingestion of fungal toxins have been characterized in domestic animals, poultry and laboratory animals and range from acute mortality to decreased production. Consumption of some mycotoxins, at levels that do not cause overt clinical mycotoxicosis, suppress immune functions and may decrease resistance to infectious disease. The sensitivity of the immune system to mycotoxin-induced immunosuppression arises from the vulnerability of the continually proliferating and differentiating cells that participate in immunemediated activities and regulate the complex communication network between cellular and humoral components. Mycotoxin-induced immunosuppression may be manifested as depressed T or B lymphocyte activity, suppressed immunoglobulin and antibody production, reduced complement or interferon activity, and impaired macrophage-effector cell function. Although the cellular-molecular basis for many of the specific immunosuppressive effects of mycotoxins are presently unclear, inhibition of DNA, RNA and protein synthesis via a variety of different mechanisms appears to be directly or indirectly responsible for the immunosuppressive action of many mycotoxins.

Cytotoxic and immunotoxic effects of Fusarium mycotoxins using a rapid colorimetric bioassay

A colorimetric MTT (tetrazolium salt) cleavage test was used to evaluate cytotoxicity of twenty-three Fusarium mycotoxins on two cultured human cell lines (K-562 and MIN-GL1) as well as their inhibitory effect on proliferation of phytohemagglutinin-stimulated human peripheral blood lymphocytes. The values of 50% inhibition of lymphocyte blastogenesis were very close to the 50% cytotoxic doses observed with the more sensitive cell line (MIN-GL1). T-2 toxin was the most cytotoxic with CD50 and ID50 values less than 1 ng/ml. Type A trichothecenes were the most cytotoxic followed by the type B trichothecenes; the non-trichothecenes were the least cytotoxic. The MTT cleavage test, in conjunction with cell culture, is a simple and rapid bioassay to evaluate cytotoxicity and immunotoxicity of Fusarium mycotoxins.

Murine lymphocyte proliferation impaired by substituted neosolaniols and calonectrins--Fusarium metabolites associated with trichothecene biosynthesis

The capacity of Fusarium secondary metabolites associated with trichothecene biosynthesis to inhibit murine spleen lymphocyte proliferation was evaluated and compared to that for well known trichothecenes. Activity of these compounds was not specific for B and T lymphocytes since they inhibited [3H]thymidine (TdR) incorporation in unstimulated, Con A- and LPS-stimulated lymphocytes to the same extent. Concentrations of 8-propionyl neosolaniol and 8-butyrylneosolaniol which inhibited [3H]Tdr uptake by 50% (ID50s) were 0.95 and 0.34 ng/ml, respectively. The ID50 for T-2 toxin was 0.26 ng/ml, indicating that there are minor alterations in 12,13-epoxytrichothecene toxicity resulting from the replacement of the isovaleryl moiety on C8 of the trichothecene skeleton with other bulky acyl groups. ID50 values for 4,15-diacetylnivalenol, fusarenon X, deoxynivalenol and 3-acetyldeoxynivalenol were 25, 38, 120 and 1800 ng/ml, respectively. Comparatively, ID50 values for 3,15-dideacetylcalonectrin, 15-deacetylcalonectrin, and 7,8-dihydroxycalonectrin were 390, 2700 and 2400 ng/ml, respectively, indicating that the modified calonectrins had equivalent or less toxicity. Lymphotoxicity of trichothecenes thus decreased upon substitution of acyl groups at the C8 with keto or hydroxy moieties and was also dependent on the nature of substitutions at the C3, C4 and C15 positions. Sambucinol and the trichothecene precursor trichodiene, metabolites which do not contain a 12,13-epoxide, did not inhibit lymphocyte proliferation. The results suggest the need for further assessment of occurrence and in vivo toxicity of Fusarium metabolites, particularly the substituted neosolaniols and calonectrins.

The use of tissue culture for the detection of mycotoxins

After incubation with 20 different mycotoxin standards and extracts from fungi and feed stuffs, fluorescent flow cytometry was used to measure viability of NS-1 cells and compared to microscopic assessment of cytotoxicity on stained HEp-11 monolayers. Both methods gave essentially the same results but the cytometric analysis offered a more quantitative approach and was particularly appropriate in the screening of extracts containing fats. The potential uses of a cytotoxic test in the analysis of feed stuffs and fungal extracts for the presence of mycotoxins are discussed.

Uptake of the naturally occurring 3-alpha-hydroxy isomer of T-2 toxin by a murine B cell hybridoma

The uptake of the naturally occurring 3-alpha-hydroxy isomer of T-2 toxin (alpha-T-2 toxin) was investigated in a murine B cell hybridoma as a model for trichothecene-lymphocyte interactions. alpha-[3H]T-2 toxin was prepared by oxidation of T-2 toxin and reduction with [3H]NaBH4 followed by normal phase and reverse phase high-performance liquid chromatography. Uptake of alpha-[3H]T-2 toxin by hybridoma cells was both time- and concentration-dependent. The antibiotic anisomycin inhibited uptake of alpha-[3H]T-2 toxin by hybridoma cells, which suggests ribosomal involvement in the uptake mechanism. Uptake of alpha-[3H]T-2 toxin was also inhibited by verrucarin A, roridin A and deoxynivalenol, and the inhibition followed a trichothecene structure-activity rank similar to that established for protein synthesis inhibition and in vivo toxicity. The characteristics of uptake of alpha-[3H]T-2 toxin by isolated splenocytes were qualitatively similar to those of the hybridoma but accumulation at equilibrium was less. Accumulation of alpha-[3H]T-2 toxin by erythrocytes, cells lacking ribosomes, did not increase with time and was not affected by the presence of unlabelled toxin. The results suggested that specific accumulation and uptake of alpha-[3H]T-2 toxin by the murine B cell hybridoma and spleen cells were highly consistent with a model based on intracellular binding of T-2 toxin to ribosomes.

Relationship of the hypothalamic-pituitary-adrenal axis with chemically induced immunomodulation. I. Stress-like response after exposure to T-2 toxin

T-2 toxin (T-2), a trichothecene mycotoxin, produced by several members of the genus Fusarium is a cytotoxic feed contaminant and has been shown to by immunomodulatory. It is suspected that T-2 associated immunomodulation is mediated partly through the hypothalamic-pituitary-adrenal (HPA) axis. T-2, prepared in 4% ethanol/corn oil, was administered orally to male CD-1 mice. Endotoxemia was evident 24 h after a single, oral exposure to T-2. Blood levels of corticosterone, indicative of the stress-response, increased 24 h after T-2 exposure. Hypothalamic norepinephrine and serum corticosterone levels increased in a dose-related manner after 2 weeks of T-2 exposure. Endotoxin, detected in the serum of animals exposed to 2.5 mg/kg T-2 for 1 week, was not associated with bacteremia. Neither endotoxin nor bacteremia were detectable after 2 or 4 weeks of T-2 exposure. Exposure to 2.5 mg/kg T-2 also affected several organs. The forestomach was ulcerated, with lymphocytic infiltration, epithelial proliferation, and hyperkeratinization. Increased spleen weight was associated with a proliferative red pulp. No histological changes were observed in the enlarged liver. Gastritis has been associated with increased corticosteroid production; cortical depletion and reduced mass of the thymus are phenomena attributable to increased corticosteroid levels. An increased corticosteroid level has been associated with thymic involution leading potentially to decreased T-dependent antibody response, a known effect of T-2.

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.

Impaired murine resistance to Salmonella typhimurium following oral exposure to the trichothecene T-2 toxin

On orally exposing Salmonella-resistant C3H/HeN mice to the trichothecene T-2 toxin (1 mg/kg body weight), challenging with Salmonella typhimurium, and continuing to dose with T-2 toxin on alternate days for 3 wk, the LD50 for the organism decreased by five orders of magnitude, in comparison with control mice not treated with T-2 toxin. In the absence of S. typhimurium, T-2 toxin did not cause lethal effects when administered at this level. Increased mortality in response to S. typhimurium challenge was dependent on T-2 toxin dose in the range 0 to 1 mg/kg for this regimen. The toxin did not significantly affect intestinal infection but did increase splenic counts in mice challenged with a range of S. typhimurium doses and also accelerated body-weight loss in infected animals. Mice challenged with the organism exhibited similar mortality when T-2 toxin treatment was begun 1 day prior to infection or at 5 or 9 days after infection. A time-related decrease in mortality, relative to that found for the standardized co-challenge described above, was observed when T-2 toxin administration was begun at 9, 13 or 23 days after infection. The results indicated that, depending on the challenge dose of the organism, both early and late phase acquired immune response to S. typhimurium could be impaired by T-2 toxin. Markedly enhanced susceptibility to gram-negative bacterial infection is another manifestation of trichothecene toxicity and may be an important aetiological factor in animal health problems that are associated with these mycotoxins.

Metabolism of T-2 toxin in vascularly autoperfused jejunal loops of rats

The intestinal metabolism of T-2 toxin, a major trichothecene mycotoxin, was investigated in rats using the method of the vascularly autoperfused jejunal loop in situ. Tritium-labeled T-2 toxin was injected into the tied-off intestinal segments at a dose of 5 or 500 nmol, respectively. T-2 toxin and its metabolites in the blood draining from the jejunal loops, in the intestinal lumen, and in the intestinal tissue were determined by HPLC and GLC-MS. There was an extensive metabolic degradation of T-2 toxin, the metabolite pattern being similar for the two dosage levels. During the experimental period of 50 min only some 2% of the total dose appeared in the effluent plasma as unchanged T-2 toxin. Likewise at the end of the experiments unchanged T-2 toxin in the intestinal lumen and tissue was present in minute amounts only (less than 1% of the dose). HT-2 toxin was the main metabolite. About 25% of the total radioactivity administered appeared in the effluent plasma as HT-2 toxin, 18% in the lumen and 10% in the tissue. 3'-OH-HT-2 toxin accounted for 4-7% (effluent plasma), 5% (lumen), and 2% (tissue) of the total dose. Furthermore small amounts (less than 2% of the dose) of 3'-OH-T-2 toxin, T-2 tetraol, and 4-deacetylneosolaniol were found. No glucuronide or sulfate conjugates could be detected. In the jejunal segments which had been exposed to the 5-nmol dose only minimal morphological alterations were observed. On the other hand, in jejunal segments exposed to the high dose marked tissue damage was present. Nevertheless the gut tissue retained its ability to metabolize T-2 toxin. From the present results it is concluded that T-2 toxin is subject to a marked presystemic first pass effect after oral ingestion in vivo.

Inhibition of human lymphocyte transformation by the macrocyclic trichothecenes roridin A and verrucarin A

The effect of in vitro exposure to the macrocyclic trichothecenes roridin A and verrucarin A on human lymphocyte transformation was evaluated in the mitogen-induced blastogenesis assay. Both compounds were capable of inhibiting stimulation of B- and T-cell subsets by a mitogen panel that included leukoagglutinin, concanavalin A, and pokeweed mitogen. Doses of roridin A and verrucarin A which inhibited [3H]thymidine uptake by 50%, as averaged from this mitogen panel, were 20 and 9 pg/ml, respectively. Verrucarol, a compound which results from base hydrolysis of macrocyclic trichothecenes, had no effect on blastogenesis at levels up to 5 X 10(5) pg/ml, indicating that an intact macrocyclic ring was essential for the potent inhibitory activity of roridin A and verrucarin A. The toxicity of these two compounds was extraordinary relative to that reported for non-macrocyclic trichothecenes and could not be predicted quantitatively from previous structure-activity studies on the toxic and biochemical properties of the trichothecenes.

In vitro effects of T-2 toxin on the mitogen responsiveness and antibody-producing ability of human lymphocytes

The effects of T-2 toxin on the in vitro mitogen responses and the antibody-producing ability of human peripheral blood lymphocytes were evaluated. T-2 toxin inhibited the mitogen response to concanavalin A (ConA) at a lower concentration (1.6 ng/ml) as compared to phytohemagglutinin (2.4 ng/ml) and pokeweed mitogen (2.4 ng/ml). Maximum inhibition was observed when the toxin was present during the first 8 h; however, the cultures were not refractory to inhibition until 48 h after culture initiation. The antibody-producing ability was inhibited by T-2 toxin concentrations of greater than or equal to 3.2 ng/ml. T-2 toxin did not induce or interfere with the generation of suppressor cells by ConA. The results of this study indicate that various lymphocyte subpopulations have different susceptibilities to T-2 toxin. The activation process associated with lymphocyte proliferation appears to be one of the most sensitive time periods.

Cytotoxic effect of T-2 mycotoxin on cells in culture as determined by a rapid colorimetric bioassay

We developed a colorimetric assay for determining metabolic activity (viability) of cells exposed to toxic agents. This system is based on the ability of mitochondrial enzymes in viable cells to modify a tetrazolium salt into a blue formazan product that can be detected spectrophotometrically at 570 nm. The assay works equally well for mammalian and insect cell lines and at 48 hr color formation is linear over a cell input range of 1.56-50 X 10(4) cells/ml. The inhibitory effects of T-2 mycotoxin on tetrazolium cleavage in L929 cells is comparable to that observed for protein and DNA synthesis (50% inhibition = 6-8 ng/ml). Using this system to analyze the lethal effect of T-2 toxin on cells from various animal species, it was found that bovine cells were the most sensitive (50% inhibition at 2.2 ng/ml) while hamster cells were the most resistant (50% inhibition at 26.2 ng/ml). Murine cells exhibited intermediate sensitivity (50% inhibition at 10.9 ng/ml). Variable toxin susceptibility was also observed among different cell types. Lymphocytes were 3-fold more sensitive to the T-2 inhibitory effects than comparable tissue culture cell lines. These data indicate that the colorimetric assay system could have broad applications in toxicological studies. Further, the observed differences in species sensitivity may provide insight into the primary mechanism of the T-2 toxin-cell interaction that ultimately leads to cell death.

Comparison of penetration and metabolism of [3H]diacetoxyscirpenol, [3H]verrucarin A and [3H]T-2 toxin in skin

The purpose of this research was to determine the rate of cutaneous penetration and metabolism of [3H]diacetoxyscirpenol (DAS) and [3H]verrucarin A (VCA) and compare these values to previously determined values for [3H]T-2 toxin (T-2), to compare the cutaneous penetration and metabolism of DAS in human and guinea-pig skin, and to compare the effects of dose and of two vehicles, methanol and dimethylsulphoxide (DMSO), on penetration rates. DAS or VCA was applied to the epidermal surface of excised skin, and the receptor fluid bathing the dermal surface was sampled periodically for 48 hr. Whether the applied dose (581 ng/cm2) was dissolved in methanol or DMSO, the rate of penetration through human skin was lower for VCA than for DAS or T-2, the rates for the two latter compounds being similar at this dose. Metabolism of DAS occurred during penetration through excised human skin and did not occur in the receptor fluid as a result of enzymes leaching out of the skin. VCA appeared to be metabolized by human skin, but this conclusion is tentative because of the relative instability of this compound. DAS penetrated significantly (P less than 0.05) faster through excised guinea-pig skin than through human skin. Metabolism of DAS was greater in human skin than in guinea-pig skin. When compared with methanol, DMSO increased the penetration of DAS and VCA by factors of between 7 and 52. At the low dose (79 ng/cm2) DAS penetrated human and guinea-pig skin significantly (P less than 0.05) faster than T-2 using either vehicle.

Experimental T-2 toxicosis in swine following inhalation exposure: effects on pulmonary and systemic immunity, and morphologic changes

Thirty-four, 9- to 11-week-old, male castrated, crossbred, specific pathogen-free derived pigs were exposed to a T-2 toxin aerosol at a nebulized dose of 0 or 9 mg/kg in pairs, each pair consisting of 1 control and 1 T-2 treated pig which were exposed on the same day. Twenty to 30% of the toxin (1.8 to 2.7 mg/kg) was retained by the pigs. Five pairs were killed on each of 1, 3 and 7 days after dosing. Two pairs of pigs were designated as a 0.33-day group when one T-2 treated pig died and the other was killed in a moribund state at 8 to 10 hours after dosing. The pulmonary and systemic immunity and morphologic changes of the lungs and other organs were examined. Bronchoalveolar lavage was performed to obtain alveolar macrophages (AM) and pulmonary lymphocytes (PL). The phagocytic ability of AM and mitogen-induced blastogenic responses of enriched PL and peripheral blood lymphocytes were evaluated. Clinically, all of the T-2 treated pigs vomited and were cyanotic, anorexic, lethargic and laterally recumbent. In the 0.33-, 1-, and 3-day T-2 treated pigs, there was a marked reduction in AM phagocytosis and mitogen-induced blastogenic responses of PL but not of peripheral blood lymphocytes. Mild to moderate, multifocal interstitial pneumonia was seen in the majority of the T-2 treated pigs. In pigs dying following inhalation of T-2 toxin, there was a more severe pneumonia, as well as marked necrosis of lymphoid tissues, severe necrohemorrhagic gastroenteritis and edema of the gall bladder wall, and multifocal necrosis of the heart and pancreas. Thus, inhalation exposure to T-2 toxin can result in clinical signs and morphologic changes resembling those reported previously in pigs given T-2 toxin intravascularly (iv) at a dose of 1.2 mg/kg (approximate LD50) or greater, as well as death. Mild pulmonary injury as well as transient impairment of pulmonary immunity was present in pigs surviving inhalation exposure.

Suppression of immune response in the B6C3F1 mouse after dietary exposure to the Fusarium mycotoxins deoxynivalenol (vomitoxin) and zearalenone

The effect that dietary exposure to the naturally-occurring Fusarium graminearum toxins deoxynivalenol (DON) and zearalenone (ZEA) may have on immune function was assessed in the B6C3F1 mouse. Dietary DON depressed the plaque-forming response to sheep red blood cells, the delayed hypersensitivity response to keyhole limpet haemocyanin and the ability to resist Listeria monocytogenes. Listerial resistance was similarly decreased in control mice fed restricted diets comparable to the dietary restriction caused by DON-induced feed refusal, whereas equivalent food restriction did not decrease the plaque or delayed hypersensitivity responses. ZEA ingestion decreased resistance to L. monocytogenes but did not affect splenic plaque-forming or delayed hypersensitivity responses. Resistance to Listeria was reduced to a greater extent by co-administration of DON and ZEA than by DON alone, whereas the ability of DON to inhibit the delayed hypersensitivity response was significantly lessened in the presence of ZEA. While effects on resistance to Listeria and delayed hypersensitivity were detectable in mice ingesting the mycotoxins for 2-3 wk, these effects disappeared upon extension of the feeding period to 8 wk. In contrast, some effect on the plaque-forming response was detectable with both the 2- and the 8-wk period of mycotoxin ingestion. Immunosuppression can thus result from ingestion of F. graminearum-infected agricultural staples, the suppression being attributable to interactions between direct immunotoxic effects of DON and ZEA and nutritional effects associated with DON-induced food refusal.

Decreased feed consumption and body-weight gain in the B6C3F1 mouse after dietary exposure to 15-acetyldeoxynivalenol

15-Acetyldeoxynivalenol (15-ADON), a biosynthetic precursor of deoxynivalenol (DON), was extracted from rice cultures of Fusarium graminearum R6576 and purified. Growing female B6C3F1 mice were fed semi-purified diets containing 0, 0.5, 2.0 and 5.0 ppm 15-ADON over 56 days and assessed for effects on feed intake, body-weight gain, terminal organ weights and blood clotting function. A significant reduction in feed intake was observed at the 5.0-ppm level after 44 days, whereas reduced rates of weight gain were found to occur at the 5.0-ppm level after only 16 days. Terminal liver, kidney and spleen weights were significantly lower in mice consuming the 5.0-ppm diet when compared with controls. Dietary 15-ADON at the 0.5- and 2.0-ppm levels did not show significant effects on weight gain, feed intake or organ weights. Although mice treated with 15-ADON had significantly decreased bleeding times, other measurements of clotting function indicated no differences between the control and treated groups. Results indicated that 15-ADON was only slightly less toxic than DON and that chronic manifestations of dietary 15-ADON were similar to those found previously for DON. Future risk assessments for DON should therefore include consideration of 15-ADON occurrence and toxicity.

Effects of 8-week exposure of the B6C3F1 mouse to dietary deoxynivalenol (vomitoxin) and zearalenone

Weanling female B6C3F1 mice were fed semi-purified diets containing 0, 0.5, 2.0, 5.0, 10.0 or 25.0 ppm (mg/kg) deoxynivalenol (DON) over 8 wk and were assessed for effects on feed intake, body-weight gain, terminal organ weights, histopathology, haematology and serum immunoglobulin levels. To determine whether DON effects were potentiated by the oestrogen zearalenone (ZEA), a mycotoxin frequently found to occur with DON in cereals, two additional groups of mice were fed diets containing either 10 ppm ZEA or 10 ppm ZEA plus 5 ppm DON. The rate of body-weight gain was significantly reduced (P less than 0.01) for all mice consuming feed containing 2.0 ppm or more of DON, whereas only the mice ingesting the diet containing 25 ppm DON showed a significantly decreased (P less than 0.01) rate of feed consumption. Gross and histopathological evaluation of thymus, spleen, liver, kidney, uterus, small intestine, colon, heart, brain, lungs and bone marrow from control and all mycotoxin-exposed mice revealed that these tissues were normal in appearance and in histological architecture. DON-amended diets did however, cause dose-dependent decreases in the terminal organ weights recorded (thymus, spleen, liver, kidney and brain). In the DON-treated groups, statistically significant dose-dependent decreases in the counts of total circulating white blood cells were associated with an increase in polymorphonuclear neutrophils and a decrease in lymphocytes and monocytes. Dietary DON caused a dose-dependent decrease in serum IgM but, in contrast, a dose-dependent increase in serum IgA. In none of the above instances was 10 ppm ZEA shown to act synergistically or antagonistically with 5 ppm DON. Since dietary DON at levels as low as 2.0 ppm exerted significant effects on the growing B6C3F1 female mouse, future approaches should include studies of the mechanisms by which this mycotoxin affects nutrient utilization and modifies the normal immune response.

Relation of 8-ketotrichothecene and zearalenone analog structure to inhibition of mitogen-induced human lymphocyte blastogenesis

The 50% effective doses of fusarenon X, nivalenol, deoxynivalenol, and 15-acetyldeoxynivalenol required to reduce [3H]thymidine uptake in mitogen-stimulated human lymphocytes by 50% were 18, 72, 140, and 240 ng/ml, respectively. These results indicated that lymphotoxicity of 8-ketotrichothecenes decreased according to the C-4 substituent order acetyl greater than hydroxyl greater than hydrogen, whereas acetylation of position C-15 of deoxynivalenol caused a slight decrease in in vitro toxicity. The 50% effective doses for zearalenone, alpha-zearalenol, beta-zearalenol, alpha-zearalanol, and beta-zearalanol were 3,500, 6,300, 36,000, 3,750, and 33,000 ng/ml, respectively, suggesting that a keto group or alpha-hydroxyl at the position C-6' contributed to the lymphotoxicity of the parent molecule. The inhibitory effects of zearalenone analogs observed in the blastogenesis assay did not correlate with the estrogenic potencies of these compounds. All 8-ketotrichothecenes and zearalenone analogs tested were capable of inhibiting B- and T-cell subsets stimulated by a mitogen panel of leukoagglutinin, concanavalin A, and pokeweed mitogen.