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

Delay of the onset of puberty in female rats by prepubertal exposure to T-2 toxin

Growing evidence has revealed the deleterious influence of environmental and food contaminants on puberty onset and development in both animals and children, provoking an increasing health concern. T-2 toxin, a naturally-produced Type A trichothecene mycotoxin which is frequently found in cereal grains and products intended for human and animal consumption, has been shown to impair the reproduction and development in animals. Nevertheless, whether this trichothecene mycotoxin can disturb the onset of puberty in females remains unclear. To clarify this point, infantile female rats were given a daily intragastric administration of vehicle or 187.5 μg/kg body weight of T-2 toxin for five consecutive days from postnatal day 15 to 19, and the effects on puberty onset were evaluated in the present study. The results revealed that the days of vaginal opening, first dioestrus, and first estrus in regular estrous cycle were delayed following prepubertal exposure to T-2 toxin. The relative weights of reproductive organs uterus, ovaries, and vagina, and the incidence of corpora lutea were all diminished in T-2 toxin-treated rats. Serum levels of gonadotropins luteinizing hormone, follicle-stimulating hormone, and estradiol were also reduced by T-2 toxin treatment. The mRNA expressions of hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary GnRH receptor displayed significant reductions following exposure to T-2 toxin, which were consistent with the changes of serum gonadotropins, delayed reproductive organ development, and delayed vaginal opening. In conclusion, the present study reveals that prepubertal exposure to T-2 toxin delays the onset of puberty in immature female rats, probably by the mechanism of disturbance of hypothalamic-pituitary-gonadal (HPG) axis function. Considering the vulnerability of developmental children to food contaminants and the relative high level of dietary intake of T-2 toxin in children, we think the findings of the present study provide valuable information for the health risk assessment in children.

Regulation of glucocorticoid sensitivity in thymocytes from burn-injured mice

Glucocorticoids (GC) are important steroid hormones that regulate metabolism, development, and the immune system. GC are produced continuously, and maximal levels are reached following stress-related stimuli. Previous studies have demonstrated that increased GC production following thermal injury was responsible for thymic involution. Although GC are mainly synthesized by the adrenal glands, there is increasing evidence that GC may also be produced in nonadrenal tissues. The thymus was reported to express steroidogenic enzymes and to release GC. 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is predominantly a reductase in cells and is essential for the local reactivation of GC. Here, we report that increased GC-induced apoptosis in thymocytes from burn-injured mice is related to increased glucocorticoid receptor (GR) expression and 11beta-HSD1 expression in thymocytes at day 1 postburn injury. In vitro, thymocytes were able to convert 11-dehydrocorticosterone (DHC) to corticosterone (CORT), which induced their apoptosis, and this was pharmacologically inhibited by 18beta-glycyrrhetinic acid, a specific 11beta-HSD inhibitor. Moreover, 11beta-HSD1 expression was confirmed in the 267S3 thymoma-derived cell line, and its activity was responsible for greater sensitivity of these cells to CORT-induced apoptosis. Finally, proinflammatory cytokines [tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-6] increased thymocyte sensitivity to DHC-induced apoptosis through a mechanism involving 11beta-HSD1. Overall, we have shown that burn injury induced 11beta-HSD1 expression in thymocytes, which led to a greater sensitivity of these cells to CORT-induced apoptosis. Increased expression of 11beta-HSD1 and GR may play a role in intrathymic T cell development and can be major determinants of GC sensitivity after a trauma.

Stachybotrys chartarum, trichothecene mycotoxins, and damp building-related illness: new insights into a public health enigma

Damp building-related illnesses (DBRI) include a myriad of respiratory, immunologic, and neurologic symptoms that are sometimes etiologically linked to aberrant indoor growth of the toxic black mold, Stachybotrys chartarum. Although supportive evidence for such linkages is limited, there are exciting new findings about this enigmatic organism relative to its environmental dissemination, novel bioactive components, unique cellular targets, and molecular mechanisms of action which provide insight into the S. chartarum's potential to evoke allergic sensitization, inflammation, and cytotoxicity in the upper and lower respiratory tracts. Macrocyclic trichothecene mycotoxins, produced by one chemotype of this fungus, are potent translational inhibitors and stress kinase activators that appear to be a critical underlying cause for a number of adverse effects. Notably, these toxins form covalent protein adducts in vitro and in vivo and, furthermore, cause neurotoxicity and inflammation in the nose and brain of the mouse. A second S. chartarum chemotype has recently been shown to produce atranones-mycotoxins that can induce pulmonary inflammation. Other biologically active products of this fungus that might contribute to pathophysiologic effects include proteinases, hemolysins, beta-glucan, and spirocyclic drimanes. Solving the enigma of whether Stachybotrys inhalation indeed contributes to DBRI will require studies of the pathophysiologic effects of low dose chronic exposure to well-characterized, standardized preparations of S. chartarum spores and mycelial fragments, and, coexposures with other environmental cofactors. Such studies must be linked to improved assessments of human exposure to this fungus and its bioactive constituents in indoor air using both state-of-the-art sampling/analytical methods and relevant biomarkers.

A 90-day subchronic toxicity study of nivalenol, a trichothecene mycotoxin, in F344 rats

A subchronic toxicity study of nivalenol (NIV), a trichothecene mycotoxin, was conducted in male and female F344 rats fed diet containing 0, 6.25, 25 or 100 ppm concentration for 90 days. Decrease of body weight and loose stools were observed at 100 ppm in both sexes from the start of the experiment, and body weight reduction was also observed at 25 ppm in males from week 6. At necropsy, many organs demonstrated reduced absolute weights at 100 ppm in both sexes, mostly due to the reduction in the body growth, with reduction of relative thymus weight also being evident in females. Hematologically, decrease of the white blood cell count was found at 100 ppm in males and from 6.25 ppm in females. In addition, decreased platelet counts in both sexes, red blood cell counts in males, and the hemoglobin concentration in females were detected at 100 ppm. Histopathologically, treatment-related changes were predominantly observed in the hematopoietic and immune organs and the anterior pituitary in both sexes and female reproductive organs at 100 ppm, such as thymic atrophy, hypocellularity in the bone marrow, diffuse hypertrophy of basophilic cells with increase of castration cells in the anterior pituitary, and increase of ovarian atretic follicles. Based on the hematological data, the no-observed-adverse-effect level of NIV was determined to be less than 6.25 ppm (0.4 mg/kg body weight/day for both males and females).

Neurotoxicity and Inflammation in the Nasal Airways of Mice Exposed to the Macrocyclic Trichothecene Mycotoxin Roridin A: Kinetics and Potentiation by Bacterial Lipopolysaccharide Coexposure

Macrocyclic trichothecene mycotoxins produced by indoor air molds potentially contribute to symptoms associated with damp building illnesses. The purpose of this investigation was to determine (1) the kinetics of nasal inflammation and neurotoxicity after a single intranasal instillation of roridin A (RA), a representative macrocyclic trichothecene; and (2) the capacity of lipopolysaccharide (LPS) to modulate RA's effects. C57Bl/6 female mice were intranasally instilled once with 50 mul of RA (500 mug/kg body weight [bw]) in saline or saline only and then nose and brain tissues were collected over 72 h and processed for histopathologic and messenger RNA (mRNA) analysis. RA-induced apoptosis specifically in olfactory sensory neurons (OSNs) after 24 h postinstillation (PI) causing marked atrophy of olfactory epithelium (OE) that was maximal at 72 h PI. Concurrently, there was marked bilateral atrophy of olfactory nerve layer of the olfactory bulbs (OBs) of the brain. In the ethmoid turbinates, upregulated messenger RNA (mRNA) expression of the proapoptotic gene FAS and the proinflammatory cytokines tumor necrosis factor-alpha, interleukin (IL)-6, IL-1, and macrophage inhibitory protein-2 was observed from 6 to 24 h PI, whereas expression of several other proapoptotic genes (PKR, p53, Bax, and caspase-activated DNAse) was detectable only at 24 h PI. Simultaneous exposure to LPS (500 ng/kg bw) and a lower dose of RA (250 mug/kg bw) magnified RA-induced proinflammatory gene expression, apoptosis, and inflammation in the nasal tract. Taken together, the results suggest that RA markedly induced FAS and proinflammatory cytokine expression prior to evoking OSN apoptosis and OE atrophy and that RA's effects were augmented by LPS.

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.

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

Myelotoxic effects of aflatoxin B1 (AFB1) and T-2 toxin on the proliferation of the granulocyte-macrophage progenitor cells to granulocyte, macrophage and granulocyte-macrophage (GM) colonies were investigated in male CD-1 mice by a semisolid in vitro culture technique. Mice received 0, 0.03, 0.145 and 0.7 mg/kg or 0, 0.1, 0.5, and 2.5 mg/kg body weight of AFB1 and T-2 toxin, respectively, for 2 weeks on alternate days. Granulocyte, macrophage, and GM-colonies were suppressed in the group that received the highest dose of AFB1 (0.7 mg/kg body weight). Treatment with T-2 toxin activated granulocyte colonies at 0.5 mg/kg and macrophage colonies at 0.1 and 2.5 mg/kg but suppressed GM-colonies at 0.5 and 2.5 mg/kg body weight. Bone marrow cells from normal CD-1 mice were cultured with different concentrations of AFB1 (1-50 microM) or T-2 toxin (1-10 nM) in vitro. Significant activation of granulocyte colonies with 1 microM AFB1 and suppression of all three types of colonies with the highest concentration of AFB1 (50 microM) were observed. The suppression of granulocyte and GM-colonies associated with T-2 toxin was concentration-dependent. The greatest suppression occurred in macrophage colonies with three highest concentrations of T-2 toxin (3, 6, and 10 nM). Results suggest that AFB1 is myelotoxic both in vivo and in vitro, whereas T-2 toxin is more toxic in vitro.

Immunotoxicity of mycotoxins

The immune system is primarily responsible for defense against invading organisms. The effects of several mycotoxins on the immune responses have been investigated; however, most data concern laboratory animals. In some instances, farm animals and cells derived from livestock species have been employed to evaluate the immunotoxicity of mycotoxins. Immune responses are highly variable, and cost considerations usually preclude the use of dairy cattle as experimental models. Immunosuppression caused by aflatoxin B1 has been demonstrated in various livestock species (e.g., turkeys, chickens, and pigs) and also in laboratory animals (mice, guinea pigs, and rabbits). The response of bovine lymphocytes to aflatoxin in vitro is similar to that of other laboratory animals. Trichothecenes are potent immunosuppressive agents that directly affect immune cells and also modify immune responses as a consequence of tissue damage elsewhere. Sheep and calves treated with fusarium T-2 toxin develop leukopenia and decreased functioning of peripheral lymphocytes. Immunosuppressive effects of ochratoxin A, rubratoxin B, and patulin have been reported. Citrinin produced lymphopenia but stimulated responses against antigens. Antibodies against mycotoxins conjugated to proteins have been produced and are useful for analytical purposes.

Resistance of C57Bl/6 mice to immunosuppressive effects of aflatoxin B1 and relationship with neuroendocrine mechanisms

Aflatoxin B1 (AFB1) a secondary metabolite of Aspergillus flavus and A. parasiticus, is known for its carcinogenicity and immunosuppressive effects. We previously reported on the immunosuppressive effects of AFB1 in Swiss and CD-1 mice. This study concerned the involvement of the hypothalamus-pituitary-adrenal gland axis in the immunosuppressive effects of AFB1 in C57Bl/6 mice. Animals were treated orally with 30, 150 or 750 micrograms/kg AFB1 daily for four weeks. Splenic lymphocytes were assayed to investigate their phenotyping using flow cytometry, proliferative response against mitogens and allogeneic lymphocytes, cytolytic cell activity, and IL-2 production. Antibody-mediated immunocompetence was checked using sheep red blood cell (SRBC)-challenged animals by plaque-forming cell assay and enzyme-linked immunosorbent assay. The dose of AFB1 for the immunosuppressive effects on blastogenic response, IL-2 production, and primary antibody production of splenic cells was much higher than previous studies involving other mice strains. AFB1 decreased the amount of circulating anti-SRBC antibody, and the helper-T cell and B cell populations in phenotyping splenic lymphocytes. There were no significant changes in natural killer cell activity, mixed lymphocyte response, hypothalamic biogenic amine concentrations, and corticotropin releasing factor, and of adrenocorticotropic hormone and corticosterone in plasma. Results were confirmed using adrenalectomized mice. The hypothalamic-pituitary-adrenal axis does not appear to have a major role in AFB1-induced immunotoxicity.

Increased endotoxin sensitivity following T-2 toxin treatment is associated with increased absorption of endotoxin

Oral exposure to T-2 Toxin (T-2) in experimental animals results in a syndrome similar to that observed in endotoxemia. Endotoxins are lipopolysaccharide, outer-membrane components of gram-negative bacteria which induce acute, inflammatory responses. In the present study, several aspects of endotoxin pathophysiology were investigated in mice following simultaneous exposure to T-2 and endotoxin, including mortality, hypothermia, tumor necrosis factor-alpha (TNF-alpha) and corticosterone production, and thymic weight. The disposition of endotoxin was also assessed, Acute, simultaneous exposure to T-2 (4 mg/kg, po) and endotoxin (3 micrograms/mouse, ip) resulted in increased mortality, hypothermia, TNF-alpha production, and thymic atrophy compared to treatment with either T-2 of endotoxin alone. Pretreatment of mice with endotoxin, a regime that renders the animals resistant to the effects of endotoxin, reduced many endotoxin effects in animals treated simultaneously with T-2 and endotoxin. Upon further investigation, it was observed that T-2 increased the absorption rate of endotoxin: as the peak height of serum endotoxin increased, the time-to-peak decreased, and the area under the curve was unchanged in animals treated simultaneously with T-2 and endotoxin. It was concluded that increased endotoxin absorption accounted for the increases in mortality, hypothermia, and TNF-alpha associated with T-2 exposure.