Effects of aflatoxin B1 and T-2 toxin on the granulocyte-macrophage progenitor cells in mouse bone marrow cultures

T-2 toxin upregulates the expression of human cytochrome P450 1A1 (CYP1A1) by enhancing NRF1 and Sp1 interaction

T-2 toxin is a major pollutant in crops and feedstuffs. Due to its high toxicity in a variety of organisms, T-2 toxin is of great concern as a threat to humans and to animal breeding. Overexpression of CYP1A1 may contribute to carcinogenesis, and CYP1A1 may be a promising target for the prevention and treatment of human malignancies. Therefore, it is essential to understand the regulatory mechanism by which T-2 toxin induces CYP1A1 expression in human cells. In this study, we confirmed that T-2 toxin (100 ng/mL) induced the expression of CYP1A1 in HepG2 cells through NRF1 and Sp1 bound to the promoter instead of through the well-recognized Aromatic hydrocarbon receptors (AhR). In cells treated with T-2 toxin, Sp1, but not NRF1, was significantly upregulated. However, T-2 toxin apparently promoted the interaction between NRF1 and Sp1 proteins, as revealed by IP analysis. Furthermore, in T-2 toxin-treated HepG2 cells, nuclear translocation of NRF1 was enhanced, while knockdown of Sp1 ablated NRF1 nuclear enrichment. Our results revealed that the upregulation of CYP1A1 by T-2 toxin in HepG2 cells depended on enhanced interaction between Sp1 and NRF1. This finding suggests the tumorigenic features of T-2 toxin might be related to the CYP1A1, which provides new insights to understand the toxicological effect of T-2 toxin.

miR449a/SIRT1/PGC-1α Is Necessary for Mitochondrial Biogenesis Induced by T-2 Toxin

T-2 toxin is one of the type A trichothecenes produced mainly by the Fusarium genus. Due to its broad distribution and highly toxic nature, it is of great concern as a threat to human health and animal breeding. In addition to its ribotoxic effects, T-2 toxin exposure leads to mitochondrial dysfunction, reactive oxygen species (ROS) accumulation and eventually cell apoptosis. We observed that mitochondrial biogenesis is highly activated in animal cells exposed to T-2 toxin, probably in response to the short-term toxic effects of T-2 toxin. However, the molecular mechanisms of T-2 toxin-induced mitochondrial biogenesis remain unclear. In this study, we investigated the regulatory mechanism of key factors in the ROS production and mitochondrial biogenesis that were elicited by T-2 toxin in HepG2 and HEK293T cells. Low dosages of T-2 toxin significantly increased the levels of both mitochondrial biogenesis and ROS. This increase was linked to the upregulation of SIRT1, which is controlled by miR-449a, whose expression was strongly inhibited by T-2 toxin treatment. In addition, we found that T-2 toxin-induced mitochondrial biogenesis resulted from SIRT1-dependent PGC-1α deacetylation. The accumulation of PGC-1α deacetylation, mediated by high SIRT1 levels in T-2 toxin-treated cells, activated the expression of many genes involved in mitochondrial biogenesis. Together, these data indicated that the miR449a/SIRT1/deacetylated PGC-1α axis plays an essential role in the ability of moderate concentrations of T-2 toxin to stimulate mitochondrial biogenesis and ROS production.

Exposure to HT-2 toxin causes oxidative stress induced apoptosis/autophagy in porcine oocytes

T-2 toxin is a main type A trichothecene mycotoxin which is the most toxic trichothecence. T-2 toxin has posed various toxic effects on human and animals in vigorous cell proliferation tissues like lymphoid, hematopoietic and gastrointestinal tissues, while HT-2 toxin is the major metabolite which is deacetylated by T-2 toxin. In this study, we focused on the toxic effects of HT-2 on porcine oocyte maturation. We treated the porcine oocyte with HT-2 toxin in vitro, and we first found that HT-2 treatment inhibited porcine oocyte polar body extrusion and cumulus cell expansion. We observed the disrupted meiotic spindle morphology after treatment, which might be due to the reduced p-MAPK protein level. Actin distribution was also disturbed, indicating that HT-2 affects cytoskeleton of porcine oocytes. We next explored the causes for the failure of oocyte maturation after HT-2 treatment. We found that HT-2 treated oocytes showed the increased ROS level, which indicated that oxidative stress had occurred. We also detected autophagy as well as early apoptosis in the treatment oocytes. Due to the fact that oxidative stress could induced apoptosis, our results indicated that HT-2 toxin caused oxidative stress induced apoptosis and autophagy, which further affected porcine oocyte maturation.

Proteomic changes in chicken primary hepatocytes exposed to T-2 toxin are associated with oxidative stress and mitochondrial enhancement

T-2 toxin is a mycotoxin that is toxic to plants, animals, and humans. However, its molecular mechanism remains unclear, especially in chickens. In this study, using 2D electrophoresis with MALDI-TOF/TOF-MS, 53 proteins were identified as up- or downregulated by T-2 toxin in chicken primary hepatocytes. Functional network analysis by ingenuity pathway analysis showed that the top network altered by T-2 toxin is associated with neurological disease, cancer, organismal injury, and abnormalities. Most of the identified proteins were associated with one of eight functional classes, including cell redox homeostasis, transcriptional or translational regulation, cell cycle or cell proliferation, stress response, lipid metabolism, transport, carbohydrate metabolism, and protein degradation. Subcellular location categorization showed that the identified proteins were predominantly located in the mitochondrion (34%) and interestingly, the expression of all the identified mitochondrial proteins was increased. Further cellular analysis showed that T-2 toxin was able to induce the ROS accumulation and could lead to an increase in mitochondrial mass and adenosine 5'-triphosphate content, which indicated that oxidative stress and mitochondrial enhancement occurred in T-2 toxin-treated cells. Overall, these results characterize the global proteomic response of chicken primary hepatocytes to T-2 toxin, which may lead to a better understanding of the molecular mechanisms underlying its toxicity.

Evaluation of Acute Immunotoxicity of Aerosolized Aflatoxin B(1) in Female C57BL/6N Mice

There is evidence for immunotoxicity of aflatoxin B1 (AFB(1)) in chronic animal feeding studies; however, little information is available as to the effects of inhalation exposure. This study evaluated the acute affects of aerosolized AFB(1) on systemic immune function of female C57BL/6N mice following a single aerosol exposure. Mice were exposed in nose-only inhalation tubes to 0, 2.86, 6.59 and 10 mug AFB(1) aerosol/L air for 90 minutes. A negative control group of untreated mice and a positive control group of cyclophosphamide-treated mice were included to account for day to day variation. Three days following exposure, mice were sacrificed and body, liver, lung, thymus and spleen weights, and complete blood counts and white blood cell differentials were measured. Splenocytes were isolated for flow cytometric analysis of CD4(+) and CD8(+) lymphocytes, CD19(+) B-cells and natural killer cells (NK 1.1(+)). The effect of AFB(1) on humoral immunity was assessed by measuring serum anti-keyhole limpet hemocyanin (KLH) IgM levels. Of the tissues examined, only the thymus weight of AFB(1) exposed mice decreased significantly compared to naive mice; however, the decrease was not dose related and was also observed in the 0 AFB(1) aerosol control group. A decrease in the mean white blood cell count of treated vs. naive mice was observed at all dose levels but was clearly not dose related and was statistically significant only in the 0 and 2.86 mug/L groups. Red blood cell and platelet counts and white blood cell differentials were not significantly affected by AFB(1). The number of CD4(+) (helper T-cells), CD8(+) (cytotoxic T-cells) and CD19(+) (B-cells) decreased in spleens of AFB(1) aerosol exposed mice compared to naive mice; however, the decrease was not dose-related and was also observed in the 0 AFB(1) exposure group. Dose-related changes in the CD4(+)/CD8(+) T-lymphocyte ratios were not observed. The IgM response to KLH was not significantly different in AFB(1) compared to naive mice, suggesting that AFB(1) did not effect antigen-specific antibody production. Based on the results of this study, a single AFB(1) inhalation exposure up to 10 mug/L for 90 minutes (CxT = 900 mug .min/L) did not significantly alter the immune parameters measured in this study. The aerosol vehicle (ethanol) and/or stress could have masked subtle AFB(1)-dependent changes in thymus and spleen weights, and in splenic lymphocyte subpopulations. However, for other immunological parameters, such as the IgM response to KLH, there was clearly no significant effect of AFB(1) aerosol exposure.

Modulation of macrophage activity by aflatoxins B1 and B2 and their metabolites aflatoxins M1 and M2

Aflatoxins are natural contaminants frequently found both in food and feed. Many of them exert immunomodulatory properties in mammals; therefore, the aim of the current study was to investigate immune-effects of AFB1, AFB2, AFM1 and AFM2, alone and differently combined, in J774A.1 murine macrophages. MTT assay showed that AFB1, alone and combined with AFB2, possess antiproliferative activity only at the highest concentration; such effect was not shown by their hydroxylated metabolites, AFM1 and AFM2, respectively. However, the immunotoxic effects of the aflatoxins evaluated in the current study may be due to the inhibition of production of active oxygen metabolites such as NO. Cytofluorimetric assay in macrophages exposed to aflatoxins (10-100 μM) revealed that their cytoxicity is not related to apoptotic pathways. Nevertheless, a significant increase of the S phase cell population accompanied by a decrease in G0/G1 phase cell population was observed after AFB1 treatment. In conclusion, the results of the current study suggest that aflatoxins could compromise the macrophages functions; in particular, co-exposure to AFB1, AFB2, AFM1 and AFM2 may exert interactions which can significantly affect immunoreactivity.

Comparative in vitro and ex-vivo myelotoxicity of aflatoxins B1 and M1 on haematopoietic progenitors (BFU-E, CFU-E, and CFU-GM): species-related susceptibility

Haemato- and myelotoxicity are adverse effects caused by mycotoxins. Due to the relevance of aflatoxins to human health, the present study, employing CFU-GM-, BFU-E- and CFU-E-clonogenic assays, aimed at (i) comparing, in vitro, the sensitivity of human vs. murine haematopoietic progenitors to AFB1 and AFM1 (0.001-50microg/ml), (ii) assessing whether a single AFB1 in vivo treatment (0.3-3mg/kgb.w.) alters the ability of murine bone marrow cells to form myeloid and erythroid colonies, and (iii) comparing the in vitro with the in vitro ex-vivo data. We demonstrated (i) species-related sensitivity to AFB1, showing higher susceptibility of human myeloid and erythroid progenitors (IC(50) values: about 4 times lower in human than in murine cells), (ii) higher sensitivity of CFU-GM and BFU-E colonies, both more markedly affected, particularly by AFB1 (IC(50): 2.45+/-1.08 and 1.82+/-0.8microM for humans, and 11.08+/-2.92 and 1.81+/-0.20microM for mice, respectively), than the mature CFU-E (AFB1 IC(50): 12.58+/-5.4 and 40.27+/-6.05microM), irrespectively of animal species, (iii) regarding AFM1, a species- and lineage-related susceptibility similar to that observed for AFB1 and (iv) lack of effects after AFB1 in vivo treatment on the proliferation of haematopoietic colonies.

Haematotoxicity of trichothecenes

Human toxicosis induced by consumption of foodstuffs contaminated with trichothecenes presents one common major symptom: a haematological perturbation manifesting principally as thrombocytopenia and leukopenia. The patients have rapidly progressing coagulation problems, and compromised resistance to infections. Consequently, they are subject to septicaemia and massive haemorrhages. In horses, cattle, poultry, cats, mice and guinea pigs, subacute and subchronic ingestion of trichothecenes causes a decrease of circulating blood cells frequently associated with bone marrow failure. The origins of haematological effects observed in Fusarium toxin intoxications have been elucidated using in vitro tests. Haematopoietic progenitors are the main target of trichothecenes. Deoxynivalenol (DON) is the least myelotoxic and T-2 the most. As circulating blood cells present a less important sensitivity to these toxins, haematological troubles observed in toxicosis are due to myelotoxicity of these toxins.

Alteration of kinase-mediated signalings in murine peritoneal macrophages by aflatoxin B(1)

Aflatoxin B(1) (AFB(1)) is a potent hepatocarcinogen which is thought to exhibit an impairment of specific and non-specific immunity. Macrophages are responsible for non-specific immunity in host defense against tumors and microorganisms, and release a number of cytotoxic compounds, including nitric oxide (NO). We investigate whether the effect of AFB(1) on signal transduction is related to the decrease of NO production in murine peritoneal macrophages. When macrophages were stimulated with lipopolysaccharide (LPS) after AFB(1)-pretreatment, AFB1 decreased the NO production. The percentage of NO production in AFB(1)-pretreated macrophages was inversely increased by the addition of cholera toxin, phorbol 12-myrisate 13-acetate (PMA) and ionomycin. This suggests that AFB(1) affects the function of signaling constituents, including guanine nucleotide-binding protein (G protein), protein kinase C (PKC) and the calcium ion. AFB(1)-pretreatment significantly decreased PKC activity and tyrosine phosphorylation after LPS-stimulation. Taken together, these data propose that the inhibition of LPS-stimulated NO production by AFB(1) is related to the suppression of kinase-mediated intracellular signal transduction in murine peritoneal macrophages.

Aflatoxin B(1) inhibits CD14-mediated nitric oxide production in murine peritoneal macrophages

Aflatoxin B(1) (AFB(1)), a potent hepatocarcinogen, has been known to impair non-specific and specific immunity. Macrophages play an important role in host defense against tumors and microorganisms and a number of compounds are implicated in macrophage cytotoxicity. Since activated by the reaction of LPS with CD14, macrophages produce nitric oxide (NO) that is a cytotoxic effector molecule in cell killing. In the present study, we investigated whether the alteration of CD14 level on macrophages by AFB(1) affects NO production in murine peritoneal macrophages. When macrophages were stimulated with LPS after AFB(1)-pretreatment, or they were co-treated with LPS and AFB(1), the NO production decreased in a dose-dependent manner. In contrast, when macrophages were post-treated with AFB(1) after LPS-stimulation, NO production was unchanged. DNA, RNA, and protein synthesis were reduced by AFB(1)-pretreatment of macrophages. The addition of anti-CD14 antibodies to the cultures decreased NO production further. FACS analysis showed that the binding of anti-CD14 antibodies to the macrophages was suppressed by AFB(1)-pretreatment followed by LPS-stimulation. However, AFB(1) does not alter the binding anti-CD14 antibodies to the macrophages without LPS-stimulation. In contrast, AFB(1) pretreatment increased an amount of CD14 released in culture medium. Taken together, these data indicate that the reduced NO production in murine peritoneal macrophages by AFB(1)-pretreatment is related to the suppressed expression of CD14 on macrophage membrane and to the increased secretion of it to culture medium after LPS-stimulation.

Intoxicação de bovinos por aflatoxina B1 presente em polpa cítrica: relato de um surto

O presente trabalho relata um surto de intoxicação pela aflatoxina B1 em 150 bovinos machos mestiços, provenientes de um rebanho de 1774 animais, em sistema de confinamento, ingerindo polpa cítrica peletizada comercial, 5kg por animal. Todos os animais foram avaliados clinicamente, e os 18 animais que morreram foram necropsiados e submetidos a exames histopatológicos. A intoxicação foi confirmada pela presença da aflatoxina B1 (5ppm) em amostras da polpa cítrica peletizada utilizada na propriedade e em fragmentos de fígado dos animais que morreram.

Involvement of NO, H2O2 and TNF-alpha in the reduced antitumor activity of murine peritoneal macrophages by aflatoxin B1

Aflatoxin B, (AFB1), a potent hepatocarcinogen, has been known to impair non-specific and specific immune responses. Nitric oxide (NO), hydrogen peroxide (H2O2), superoxide anion (O2-) and tumor necrosis factor-alpha (TNF-alpha) produced by macrophages play an important role in host defense against tumors and microorganisms. In the present studies, we investigated the involvement of those products in the reduced antitumor activities by AFB1. When macrophages are stimulated with LPS after AFB1-pretreatment, the cytolytic activities decrease in a dose-dependent manner. The addition of N(G)-monomethyl arginine (NMMA), anti-TNF-alpha antibodies, catalase and peroxidase decreases antitumor activities further. In contrast, superoxide dismutase (SOD) does not change the antitumor activities. NO and TNF-alpha production was reduced by the addition of NMMA and anti-TNF-alpha antibodies, respectively. Taken together, these data indicate that the reduced antitumor activities in murine peritoneal macrophages are mediated by the suppressed production of NO, TNF-alpha and H2O2 by AFB1 pretreatment, suggesting that the inhibitory effect of AFB1 on those materials may provide the tumors with readily growing condition in vivo.

Inhibition of various functions in murine peritoneal macrophages by aflatoxin B1 exposure in vivo

Aflatoxin B1 (AFB1) has been known to impair specific and nonspecific immunity. In the present study, we tested various functions of murine peritoneal macrophages that were isolated and stimulated with LPS after AFB1 (400 microg/5 ml/kg) was administered every other day for 2 weeks. AFB1 decreased phagocytosis and the production of superoxide anion (O2-) and hydrogen peroxide (H2O2), compared to those of corn oil-treated control group. In addition, the production of NO and TNF-alpha was decreased in macrophages of AFB1-treated mice. In vitro antitumor activity of in vivo AFB1-treated macrophages was reduced against target cell, L929. Taken together, these results suggested that AFBI might have the immunosuppressive effect on macrophages after in vivo exposure, which was related to the antitumor activity reduction.

Modulation of nitric oxide, hydrogen peroxide and cytokine production in a clonal macrophage model by the trichothecene vomitoxin (deoxynivalenol)

Characterization of how vomitoxin (VT) and other trichothecenes affect macrophage regulatory and effector function may contribute to improved understanding of mechanisms by which these mycotoxins impact the immune system. The RAW 264.7 murine cell line was used as a macrophage model to assess effects of the VT on proliferation and the production of nitric oxide (NO), hydrogen peroxide (H2O2) and cytokines. Using the MTT cleavage assay, VT at concentrations of 50 ng/ml or higher was found to significantly decrease proliferation and viability of RAW 264.7 cells without stimulation or with stimulation by lipopolysaccharide (LPS) or interferon (IFN)-gamma. In the absence of an activation agent, VT (25-250 ng/ml) had negligible effects on the production of NO, H2O2, and cytokines. Upon activation with LPS at concentrations of 10 to 100 ng/ml, VT at 25-100 ng/ml markedly enhanced production of H2O2 but was inhibitory at 250 ng/ml. VT enhancement of H2O2 production was observed as early as 12 h after LPS stimulation. When IFN-gamma was used as the stimulant, VT (25-250 ng/ml) delayed peak H2O2 production. VT (25-250 ng/ml) also markedly decreased NO production in cells activated with LPS or IFN-gamma. Interestingly, VT superinduced TNF-alpha and IL-6 production in LPS-stimulated cells and also elevated TNF-alpha in IFN-gamma stimulated cells. These results suggest that VT can selectively and concurrently upregulate or downregulate critical functions associated with activated macrophages.

Alteration of major cytokines produced by mitogen-activated peritoneal macrophages and splenocytes in T-2 toxin-treated male CD-1 mice

Fusarium T-2 toxin has immunotoxic properties that may be related to the modulation of cytokine expression by cells of the immune system. Male CD-1 mice were used to study the effect of in vivo exposure to T-2 toxin on the alteration of interleukin (IL)-1α, tumor necrosis factor α (TNF), and IL-6 in lipopolysaccharide-stimulated peritoneal macrophages, and IL-2, IL-3, and interferon γ (IFNγ) in concanavalin A (Con A)-stimulated splenocytes. Mice were orally dosed with 0, 0.1, 0.5, and 2.5 mg T-2 toxin/kg body weight for 2 weeks on alternate days. Northern blot analysis of IL-1α, TNF, and IL-6 mRNA from activated peritoneal macrophages showed no significant differences between control and treated groups. Measurements of secreted protein by immunoassay demonstrated suppression of these cytokines in all treated groups, suggesting that T-2 toxin affects the translational or post-translational regulation of these cytokines from peritoneal macrophages. Levels of IL-2, IL-3, and IFNγ mRNA from Con A-activated splenocytes were higher in all treated groups. The increases were significant for IL-2 and IFNγ in the groups receiving low (0.1 mg/kg) and high (2.5 mg/kg) doses of T-2 toxin, and for IL-3 in the group receiving a medium (0.5 mg/kg) dose of this toxin (P ≤ 0.05). Results indicated that T-2 toxin given orally at low or medium doses induces transcription or increases mRNA stability of IL-2, IFNγ, and IL-3. Protein levels of all three cytokines were also increased, indicating that T-2 toxin also increases translational/post-translational efficiency of IFNγ, IL-2, and IL-3. Possible mechanisms in the immunosuppressive effects of T-2 toxin may involve endotoxemia resulting after the toxin administration, alteration of the stability of mRNA, or previously described effects of T-2 toxin on protein synthesis.

The effect of aflatoxin B1 on cytokine mRNA and corresponding protein levels in peritoneal macrophages and splenic lymphocytes

Male CD-1 mice were used to test the in vivo effects of aflatoxin B1 (AFB1) on the genetic expression of major cytokines produced by macrophages (interleukin (IL)- 1 alpha, IL-6 and tumour necrosis factor alpha (TNF)) and splenic lymphocytes (IL-2, interferon gamma (IFN gamma), and IL-3), activated in vitro with lipopolysaccharide (LPS) and concanavalin A (Con A), respectively. Animals were treated with 0, 0.03, 0.145 or 0.7 mg AFB1/kg body weight orally every other day for 2 weeks. No significant effects of the toxin on the weights of liver, kidney, spleen, or thymus, or in red blood cell counts were noted, but white blood cell counts were significantly elevated at the low (0.03 mg/kg) dose. Cytokine mRNA levels were measured by Northern blots or cDNA amplification and the secreted protein levels were measured by immunoassay. AFB1 had a marked effect on macrophage-produced cytokines. The mRNA levels increased significantly at the low (IL-1 alpha) or medium dose (IL-6 and TNF), their corresponding protein levels were generally suppressed. The levels of IL-1 alpha secreted protein were significantly suppressed at all dosages, and those of IL-6 and TNF at the high dose. The low dose of AFB1 slightly decreased both mRNA and protein levels of lymphocytic IL-2, IFN gamma, and IL-3, only IL-2 mRNA decreasing significantly (P < or = 0.05). It appears that AFB1 treatment preferentially affects macrophage functions, and in particular, it decouples the close correlation usually observed between transcriptional and translational controls of IL-1 alpha, IL-6 and TNF production by these cells.

Comparison of toxicity induced by T-2 toxin on human and rat granulo-monocytic progenitors with an in vitro model

T-2 toxin is a trichothecene mycotoxin produced by various species of fungi. Trichothecenes are known as major contaminants of cereals and their derivatives. In man as well as in animals, T-2 toxin has been shown to induce alimentary intoxication and, among others, haematological symptoms. Granulo-monocytic progenitors from human umbilical cord blood on the one hand and granulo-monocytic progenitors from rat bone marrow on the other, were cultured in the presence of T-2 toxin (from 10(-7) to 10(-10) M) for 14 days. A study of concentration and effect relationships showed a strong and rapid effect of T-2 toxin on rat colony forming unit-granulocyte and macrophage (CFU-GM) between 5 x 10(-9) M and 10(-9) M. On the other hand, human CFU-GM were able to grow in the presence of the same T-2 toxin concentrations. IC50 were determined on day 7, 10 and 14. They were, respectively, 1.6 x 10(-9) M; 3.6 x 10(-9) M; 1.4 x 10(-9) M for human cells, and 2.2 x 10(-9) M; 3.3 x 10(-9) M; 2.6 x 10(-9) M for rat cells. The present study was prompted by the need to define precisely the cytotoxic and inhibitory T-2 toxin concentrations for rat and human CFU-GM. It is particularly relevant for the investigation of cellular T-2 toxin targets and in order to elucidate the mechanism of trichothecene haematotoxicity.