Genomic analysis of Fisher F344 rat kidneys from a reproductive study following dietary ochratoxin A exposure

Ochratoxin A (OTA) is a mycotoxin produced by species of Penicillium and Aspergillus, and is found in many commodities including cereal grains, nuts, and coffee. OTA is a renal carcinogen and nephrotoxin at high concentrations, targeting the proximal tubules. This study uses transcriptomics and the previously reported apical data (Bondy et al., 2021) to infer mode-of-action of OTA toxicity in male and female rats exposed to low doses of OTA in utero and throughout development. Our findings support a male-specific activation of the innate and adaptive immune responses in F1 pups to OTA exposure. This was not found in the female F1 pups, and may be due to female-specific increased p38 activity and VDR signaling. Differentially expressed genes related to karyomegaly, MAPK activity, and immune activation appears to develop from in utero exposure to OTA whereas those related to decreased kidney and liver function, and changes to reproductive pathways occur in both rat generations. Together, these transcriptional results confirm that dietary exposure to OTA causes renal toxicity as well as alterations to hepatic and reproductive pathways in rats. In utero exposure of rats to OTA results in sex-specific alterations in immune response pathways, VDR signaling, and p38 activity.

A one-generation reproductive toxicity study of the mycotoxin ochratoxin A in Fischer rats

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus and Penicillium molds. Grain-based foods account for most human dietary exposures to OTA. OTA is a teratogen, but its reproductive and developmental effects are poorly understood. A one-generation reproductive toxicity study was conducted with groups of 16 male and 16 female Fischer rats exposed to 0, 0.026, 0.064, 0.16, 0.4 or 1.0 mg OTA/kg in diet. Dams exposed to 1.0 mg OTA/kg diet had statistically significant F1 pup losses between implantation and postnatal day (PND 4). Delays in preputial separation (PPS) and vaginal opening (VO) were indicative of delayed puberty in F1 rats. Mild renal lesions in nursing pups indicated that exposure prior to weaning impacted the kidneys. The developing kidney was more susceptible to OTA than the adult kidney. Significant increases in multi-oocyte follicles (MOFs) and proportional changes in resting and growing follicles were observed in F1 female ovaries. Plasma testosterone was reduced in F0 males, and there were negative effects on sperm quality in F0 and F1 male rats. The results confirm that continuous dietary exposure to OTA causes post-implantation fetotoxicity in dams, and renal and reproductive toxicity in their male and female offspring.

Comparison of the inhibition of deoxynivalenol and T-2 toxin on bovine and porcine platelet function

A platelet model system has been used to investigate the inhibitory effects of deoxynivalenol (DON, vomitoxin) and T-2 toxin, alone and in combination. In both bovine and porcine systems, the most dramatic effect observed was the instability in the platelet aggregates formed in the presence of the mycotoxins. Bovine platelets were more sensitive to the inhibitory effects of both of the mycotoxins than porcine platelets and in both species T-2 toxin was a more effective platelet inhibitor than DON. The mycotoxins may inhibit platelet function by a similar mechanism since an additive inhibitory response was observed when DON and T-2 toxin were added together to platelet suspensions.

Comparison of the inhibitory effect of T-2 toxin on bovine platelet function with that of other known platelet inhibitors

The inhibitory effects of T-2 toxin on bovine platelet function and thromboxane A(2) production were compared with those of the known inhibitors of human platelet function, acetylsalicylic acid, dipyridamole and verapamil. T-2 toxin (1 × 10(-3)M) effectively inhibited bovine platelet aggregation (33.2-64.3%), whereas neither acetylsalicylic acid nor dipyridamole did so. T-2 toxin appeared to be a less effective inhibitor of platelet aggregation than the calcium channel blocker, verapamil. T-2 toxin (1 × 10(-3)M) added to platelet suspensions together with verapamil, produced an additive inhibitory response. T-2 toxin (2.5 × 10(-4)M) effectively inhibited the release of thromboxane A(2) from ADP-stimulated bovine platelets as did acetylsalicylic acid and verapamil but not dipyridamole. T-2 toxin appears to inhibit bovine platelets by a biochemical mechanism distinct from that of the other inhibitors.

Brominated diphenyl ether (BDE) levels in liver, adipose, and milk from adult and juvenile rats exposed by gavage to the DE-71 technical mixture

Brominated diphenyl ethers (BDEs) are used as flame retardants in consumer products. Rodent studies indicate that the liver, thyroid, and nervous system of developing animals are targets of BDEs. To explore the relationship between exposure and health in developing animals, BDE accumulation in adult and juvenile rats was examined in conjunction with changes in liver weight and serum thyroxine (T4). Adult (F0) rats received the commercial BDE mixture DE-71 by gavage at doses of 0.5, 5, and 25 mg kg(-1) body weight (bw)/day for 21 weeks. F0 rats were mated and exposure continued throughout breeding, pregnancy, lactation, and postweaning until the pups (F1 generation) reached postnatal day (PND) 42. Milk was collected from lactating dams. Adipose and liver samples were collected from F0 and F1 males and females for BDE congener analysis. Congener prevalence in rat tissues mimicked congener prevalence in wildlife and humans. Tissue concentrations of all congeners except BDE-153 were lower than would be expected based on dose proportionality, confirming that BDE-153 has a high capacity for bioaccumulation. BDEs were transferred from maternal tissues to milk during lactation. Milk congener profiles differed from maternal tissue profiles indicating that degree of bromination and maternal sequestration influenced BDE transfer to milk. Female F1 rats accumulated more BDEs than F1 males, indicating that female rats were less able to metabolize and/or excrete BDEs. Significant effects on liver weight and serum T4 levels were observed in adults and juveniles in the middle and high dose groups, corresponding to BDE levels in the μg g(-1) range. Although it remains to be determined how human liver and thyroid are affected by exposure to much lower BDE levels, the present study confirmed that gender and reproductive status influence BDE accumulation in tissues and BDE transfer to the neonate via milk.

Oral (gavage), in utero and postnatal exposure of Sprague-Dawley rats to low doses of tributyltin chloride. Part 1: Toxicology, histopathology and clinical chemistry

Tributyltin (TBT) is a biocide that contaminates foods, especially shellfish. TBT is an endocrine disrupter in several marine species and is neurotoxic and immunotoxic in mammals. We have examined the effects of exposure to low doses of tributyltin chloride (TBTC) from day 8 of gestation until adulthood. Pregnant rats were gavaged daily with 0, 0.025, 0.25 or 2.5 mg TBTC/kg body weight from day 8 of gestation until weaning. Stomach contents of suckling pups contained undetectable levels of TBT and dibutyltin (DBT) levels were detectable only in the highest TBTC dose used, indicating negligible lactational transfer to pups. Post weaning, pups were gavaged daily with the same dose of TBTC administered to their mothers and sacrificed on post-natal days (PND) 30 (males and females), 60 (females) and 90 (males). TBTC had no effects on dams' body weights, food consumption, litter size, sex ratio or survival of pups to weaning. However, all doses of TBTC significantly affected parameters of the growth profile of the pups (mean body weights, average slope, curvature) and the ratio of weekly food consumption to weekly body weight gain indicated enhanced food conversion to body mass in females but a decreased conversion in males. Liver, spleen and thymus weights were also affected by TBTC. In male pups dosed at 2.5 mg/kg/day, reduced serum thyroxine levels were evident, indicating that the thyroid is a target for TBTC toxicity. No histopathological lesions were seen in the liver but elevated serum alanine aminotransferase, gamma-glutamyl transferase and amylase indicated hepatotoxicity. Significant decreases in liver weights in female pups exposed to 0.025 mg/kg/day TBTC were observed at PND 60. Decreases in spleen and thymus weights also pointed towards toxic effects of TBTC on the immune system. The 0.025 mg/kg/day TBTC should have been a no affect dose and yet this dose caused significant effects on growth profiles, decreased liver weights and elevated serum GGT levels in females.

The mammalian testis accumulates lower levels of organochlorine chemicals compared with other tissues

Tissues were obtained from three separate experiments in order to quantify the tissue distribution of organochlorine chemicals that are thought to be potential reproductive toxicants in males: 1) Sprague Dawley rats received 1 microCi of 14C-Aldrin or 14C-Dieldrin (20.6 microCi/micromole) i.p. once a week for three weeks. One week and four weeks after the last injection, tissues were harvested and stored at -80 degrees C. Tissue 14C levels were quantified by scintillation spectrometry. 2) Cis- or trans-nonachlor (0, 0.25, 2.5, 25 mg/kg body weight) were administered daily in corn oil to male rats by gavage for 28 days. Tissues were harvested and frozen at -80 degrees C on the 29th day. Organochlorine residues were extracted and quantified by gas chromatography with electron capture detection. 3) Technical grade toxaphene (0, 0.1, 0.4 or 0.8 mg/kg body weight) was ingested daily by female cynomolgus monkeys of reproductive age for 18 months prior to being mated with control males. Dosing continued during pregnancy and lactation. Their infants received toxaphene via breast milk, and upon weaning, they ingested the same dose as their mothers for 48 to 49 weeks until, at 77 to 80 weeks of age, tissues were harvested and stored at -80 degrees C. Organochlorine residues were extracted and quantified as previously stated. In all three experiments, organochlorine residues in the testis were lower than in most of the other reproductive tract and nonreproductive tract tissues we examined. For example, testicular aldrin and dieldrin levels were <5% the epididymal content; testicular cis- and trans-nonachlor were <25% the epididymal content and, testicular toxaphene levels were <15% of the epididymal content. The reasons for the low degree of accumulation by the testis in comparison with other tissues are unknown. However, the lower testicular content may afford germ cells some protection from the potentially toxic effects of these chemicals.

trans-Nonachlor and cis-nonachlor toxicity in Sprague-Dawley rats: comparison with technical chlordane

cis-Nonachlor and trans-nonachlor are bioaccumulating components of the pesticide chlordane, which can be detected in various environmental biota and in humans. Existing studies have focused on the potential adverse health effects of the parent chlordane mixture. Comparable toxicity data are nonexistent for individual chlordane constituents such as trans-nonachlor, cis-nonachlor, or oxychlordane, which are among the most common chlordane-related environmental contaminants and tissue residues. In this study, rats were administered cis-nonachlor, trans-nonachlor, or technical chlordane by gavage for 28 days at doses of 0.25 to 25 mg/kg body weight. Residue analyses indicated that trans-nonachlor accumulation in adipose was greater than cis-nonachlor when rats were administered each chemical under identical conditions of dose and exposure. For all test chemicals, the major metabolite oxychlordane accumulated in adipose tissue. Adipose tissue residue levels of all test chemicals and the major metabolite were higher in female rats. The liver was a target organ in male and female rats, indicated by increased liver weight and histopathological changes consistent with microsomal enzyme induction. Hepatic changes were most pronounced in rats treated with trans-nonachlor. Elevated kidney weights and depressed organic ion transport were observed in males treated with trans-nonachlor and chlordane. Although in general, changes in target organs and clinical chemistry endpoints were similar for all 3 test chemicals, the approximate toxicity ranking from most to least toxic was trans-nonachlor > technical chlordane > cis-nonachlor.

A comparison of clinical, histopathological and cell-cycle markers in rats receiving the fungal toxins fumonisin B1 or fumonisin B2 by intraperitoneal injection

Fumonisins B1 and B2 (FB1 and FB2) are fungal secondary metabolites produced by members of the genus Fusarium. Although FB1 is usually detected in greater quantities, FB2 frequently co-occurs in contaminated feeds and foods and contributes to the total toxin load. In the present study, the comparative toxicity of FB1 and FB2 was examined in male Sprague-Dawley rats administered toxin (0.75 mg/kg body weight) or vehicle control intraperitoneally (ip) for 2, 4 or 6 consecutive days. Clinical changes, including elevated serum cholesterol, alanine aminotransferase (ALT), creatinine and protein, were slightly more pronounced in FB1-treated rats. The most consistent hematological change was an increase in vacuolated bone marrow cells, which was more pronounced in FB1-treated rats. Histopathological changes were similar in FB1- and FB2-treated rats and included single cell necrosis in kidneys and liver, cytoplasmic vacuolation in adrenal cortex and lymphocytolysis in thymus. In the liver mRNA expression for the cyclin kinase inhibitor p21 gene was significantly increased in FB1- and FB2-treated rats, compared to controls. Expression of mRNA for the cyclin D1 gene was significantly depressed in FB2-treated rats. Hepatic cyclin E mRNA was elevated in response to FB1 and FB2 compared to controls. In FB2-treated animals this corresponded with decreased liver p27 mRNA expression. Hepatic proliferating cell nuclear antigen (PCNA) transcription was elevated in FB1- but not FB2- treated rats. Changes in liver microsomal protein levels of p27, cyclin E and PCNA were similar to changes in gene expression. In contrast, cyclin D1 protein levels were elevated in rats treated with FB1 and, to a lesser extent, FB2. The data indicate that FB1 and FB2 can alter the expression of genes associated with the cell cycle, and indicate a need for a further understanding of the mechanistic basis of FB1 and FB2 toxicity.

Retrospective evaluation of serum ornithine carbamyltransferase activity as an index of hepatotoxicity in toxicological studies with rats

The sensitivity of elevated serum ornithine carbamyltransferase (OCT) as an index of hepatotoxicity in rats was assessed in different studies conducted over a number of years and originally designed to examine the toxicity or carcinogenicity of a variety of test chemicals and diets. Changes in serum OCT activities were compared with the more widely used clinical endpoints, alanine aminotranserase (ALT) and aspartate aminotransferase (AST). In the first study, rats received a single oral dose of the hepatotoxic and hepatocarcinogenic fungal toxin aflatoxin B(1) (AFB(1)). The increase in enzyme levels between control and AFB(1)-treated rats was greater for serum OCT than for ALT or AST. This response was similar to the changes in serum enzyme levels in studies where rats ingested a hepatotoxic and hepatocarcinogenic choline deficient (CD) diet. When rats were exposed to the hepatotoxic and nephrotoxic fungal toxin fumonisin B(1) (FB(1)) by intraperitoneal injection for 6 days, serum AST and ALT were significantly elevated above control levels while OCT was unaffected. The peroxisome proliferator ciprofibrate caused elevated ALT and AST but not OCT at week 52 of dietary exposure, after the development of liver nodules and tumours. Of the two liver-specific enzymes examined in all of the studies, ALT was more consistently predictive of hepatotoxicity than OCT.

Immunomodulation by fungal toxins

The availability of immunotoxicity data for fungal toxins varies considerably for different toxins. The following is a comprehensive review of the most recent literature on the immunotoxicity of aflatoxins, fumonisins, gliotoxin, ochratoxins, patulin, and trichothecenes. Aflatoxin is an immunomodulating agent that acts primarily on cell-mediated immunity and phagocytic cell function. In addition to further characterization of aflatoxin-induced immunotoxicity in various species, some recent studies have focused on ameliorating the effects of aflatoxin by supplementing or amending the diet. The immunomodulatory effects of ochratoxins have also been considered for many years. Notably, recent studies have examined immune function in the offspring of rats and mice exposed to ochratoxin pre- and perinatally. Fumonisin toxicity has been characterized relatively recently in comparison to aflatoxin and ochratoxin, and fumonisin-induced immunotoxicity is an area of active research. As these studies progress, they may also clarify the role of sphingolipid metabolism in immune function. The most recent study of patulin immunotoxicity in mice indicates that exposure to levels found in foods and feeds would not likely result in immunotoxicity. Exposure to gliotoxin would most likely be by infection with gliotoxin-producing fungi. Although the toxin is immunosuppressive in vitro, the link between immunosuppression and the presence of gliotoxin in infected tissues in vivo has yet to be made. The trichothecenes can both suppress and stimulate immune function. By comparison, more information is available on the molecular events associated with trichothecene-induced immunomodulation than for any other fungal toxins. The molecular basis of immune function modulation by fungal toxins remains a frontier for future research.

Cytotoxicity of nephrotoxic fungal toxins to kidney-derived LLC-PK1 and OK cell lines

The nephrotoxic fungal toxins ochratoxin A (OA), ochratoxin B (OB) and citrinin (CIT) are natural contaminants of foods and feeds. While cytotoxicity assays have proven useful for establishing relative toxicity and structure function relationships within groups of fungal toxins, a drawback of in vitro bioassays is their susceptibility to variation depending on endpoint, target cell, and dosing strategy. These variables were explored for OA, OB, CIT using two continuous kidney cell lines (LLC-PK1 and OK) and four cytotoxicity assay endpoints. The nephrotoxic antibiotic gentamicin was used as a positive control for cytotoxicity throughout. In general, fungal toxin-induced cytotoxicity was more pronounced in LLC-PK1 cultures using mitochondrial dehydrogenase inhibition (MTT assay) as the endpoint. Altered dosing strategy, but not seeding density, consistently influenced cytotoxicity: CIT was more toxic to cells when added at the time of seeding, whereas OA was more toxic when added 24 h after cultures were seeded. Toxicity rankings for the fungal toxins were consistent with in vivo studies and were, in order of most to least toxic, OA > OB > CIT. The data indicate that LLC-PK1 and OK cells compare favorably to existing models in terms of sensitivity to nephrotoxic fungal toxins, but also that relatively minor changes in assay protocols can affect the cytotoxicity of individual toxins and comparative toxicity within a group of toxins.

Glutathione S-transferase-placental form expression and proliferation of hepatocytes in fumonisin B1-treated male and female Sprague-Dawley rats

Fumonisin B1 (FB1), a mycotoxin produced by a common corn contaminant Fusarium moniliforme and a hepatocarcinogen in rats, has been previously suggested to act as a poor initiator, but a better promoter of gamma-glutamyltranspeptidase (GGT)-positive rat liver preneoplastic lesions. Using glutathione S-transferase-placental form (GSTP) as a more sensitive marker of initiation, we have further evaluated the initiating capacity of various doses of purified FB1 administered (a) intraperitoneally (i.p.) to male Sprague-Dawley (SD) rats for 4 days and (b) orally (PO) to male and female SD rats for 11 days. Compared to their respective controls, significant increases in GSTP-positive hepatocytes were observed in male rats administered FB1 i.p. at 10 mg/kg body weight/day for 4 days, as well as in male and female rats treated with 35 and 75 mg/kg body weight/day FB1 p.o. for 11 days. The percentage section area of liver occupied by GSTP-positive mini-foci comprising of three to 12 cells was increased significantly in male rats given 10 mg/kg FB1 i.p., or in p.o.-treated males and females with 75 mg/kg FB1. Both i.p. and p.o. FB1 treatments resulted in dose-related enhanced hepatocyte proliferation as measured by proliferating cell nuclear antigen (PCNA) labeling with significant increases in the number of PCNA-positive nuclei at the same i.p. and p.o. dose levels where the number of GSTP-positive cells were elevated. In all studies, enhanced PCNA and GSTP expression occurred at FB1 doses which, based on serum biochemical and histopathological data previously reported from our laboratory, were shown to be hepatotoxic. Therefore, our data suggest that in a manner similar to known genotoxic carcinogens, FB1 has the capacity to initiate GSTP-positive hepatocytes with their subsequent development into GSTP mini-foci at exposure levels that induce enhanced hepatocyte proliferation in response to liver toxicity. In SD rats, this occurs as early as within 4 days of i.p. treatment or 11 days of p.o. treatment.

Gavage administration of the fungal toxin fumonisin B1 to female Sprague-Dawley rats

The fungal toxin fumonisin B1 (FB1) is a contaminant of corn-based foods and feeds produced by members of the genus Fusarium. Fumonisin B1 toxicity was examined using gavage administration of purified toxin to female Sprague-Dawley rats. For 11 consecutive days each rat received a single dose of FB1 at the following concentrations: control (saline), 1, 5, 15, 35, or 75 mg FB1/kg body weight/d. Significantly depressed body weight and food consumption occurred at 35 and 75 mg FB1/kg/d. By the end of the dosing period there were no significant changes in food consumption. Kidneys and bone marrow were most sensitive to FB1 exposure. Changes in renal morphology were observed from 5 to 75 mg FB1/kg/d, accompanied by transient changes in urine osmolality and urine enzyme levels. Increased cellular vacuolation was the primary change associated with bone-marrow toxicity, starting at doses of 5 mg FB1/kg/d. Hepatotoxicity was indicated by reduced liver weight, elevated serum alanine amonitransferase (ALT), and mild histopathological changes occurring at doses of 15 mg FB1/kg/d and higher. Increased cytoplasmic vacuolation of adrenal cortex cells occurred in rats treated with 15 mg FB1/kg/d and higher, indicating that the adrenals are also potential targets of FB1. Elevated serum cholesterol, which is a consistent response to FB1 was observed at 5 mg FB1/kg/d and higher. Based on responses in this study, gavage is an appropriate substitute for longer feeding studies. Compared to previous work with male rats, gender-related difference in FB1 responses lacked consistency but indicated that males may be marginally more sensitive than female Sprague-Dawley rats.

Toxicity of fumonisin B1 to B6C3F1 mice: a 14-day gavage study

Fumonisin B1 (FB1) is a fungal toxin produced by members of the genus Fusarium. Ingestion of FB1 causes species-specific neurotoxic, nephrotoxic, hepatotoxic and pulmonary effects. The clinical, haematological and pathological responses of adult male and female B6C3F1 mice to FB1 were assessed following 14 daily gavage doses ranging from 1 to 75 mg FB1/kg body weight/day. There were no consistent sex-related changes. Although all responses were modest, the most notable effects of FB1 were on the liver, bone marrow, adrenals and kidneys. In the liver, hepatocellular single cell necrosis, mitosis and anisokaryosis were observed, accompanied by elevated serum ALT. In the kidneys, minor histopathological changes were confined to female mice, while mild decreases in ion transport and increases in blood urea nitrogen were seen only in males. Small changes in glutathione levels were observed in the kidneys and livers of male mice. Adrenal cortical cell vacuolation was observed at 15 mg FB1/kg and higher in females and from 35 mg FB1/kg in males. Serum cholesterol was elevated in both male and female mice, possibly due to FB1-induced changes in lipid metabolism in the liver and adrenals. Although bone marrow cell numbers were unchanged, increases in vacuolated myeloid cells and lymphocytes were observed in female mice. In general, the degree of changes observed indicate that mice are not as sensitive a model of FB1 toxicity as rats.

The effects of fumonisin B1 on several markers of nephrotoxicity in rats

Rats were injected intraperitoneally with saline or fumonisin B1 (FB1) at doses of 7.5 and 10.0 mg FB1/kg for 4 days. For each day of dosing, 24-hr urine samples were collected and analyzed for creatinine and protein content and the enzymes gamma-glutamyl-transpeptidase, lactate dehydrogenase, and N-acetyl-beta-D-glucosaminidase. Twenty-four hours after the last dose, animals were killed and kidneys removed for ion transport measurement and histopathology. Significant increases in urine volume and decreases in urine osmolality were observed in both FB1 dose groups. Creatinine excretion was decreased only in the 10 mg FB1/kg group on the final day of the study. Urine protein excretion was elevated in both treated groups and found to be due primarily to high-molecular-weight proteins indicative of increased glomerular permeability. Enzymuria, a marker of tubular cell damage, was also observed with increases in the urinary excretion of all three enzymes measured. In renal cortical slices tubular transport of the anion p-aminohippuric acid was reduced by 75-80% and cationic transport of tetraethylammonium was reduced by 40% in the FB1-treated animals. While these results suggest significant alterations in renal function, only minor histopathologic changes were observed in the kidneys of both dose groups. Results of the present study indicate that urine volume, proteinuria, enzymuria, and ion transport are sensitive indicators of early FB1-induced nephrotoxicity.

Glutathione S-transferases and P-glycoprotein in normal rat hepatocytes and hepatoma cells: analysis using flow cytometry

Using indirect immunofluorescence with fluorescein isothiocyanate-conjugated antibodies, in combination with flow cytometry (FCM), we have developed a technique to detect the alpha, mu and pi isozymes of GST in cell suspensions from normal rat liver, and in H4IIE cells, a rat hepatoma cell line. Cell suspensions fixed in 1% paraformaldehyde were observed to require cell membrane permeation with lysolecithin to allow access and binding of antibodies to immunoreactive proteins within the cytoplasm. FCM analysis indicated normal rat hepatocytes to be positive for GST alpha and mu, but not GST pi, and the H4IIE cells to be positive for all three GST isozymes. Further analysis by FCM for the expression of P-glycoprotein (mdr), a membrane-associated protein product of the multidrug resistance gene, showed an association between the presence of GST pi and mdr in the two cell types. Thus, mdr was detected in significant amounts in H4IIE cells, but not in rat hepatocytes. The method described here has potential applications in screening, sorting and further characterisation for GST pi-positive hepatocytes for mechanistic studies during sequential rat liver carcinogenesis, as well as for characterisation of human tumors for the expression of different GST isozymes and P-glycoprotein during therapeutic management.

Role of gender and strain in vomitoxin-induced dysregulation of IgA production and IgA nephropathy in the mouse

Prolonged dietary exposure of female B6C3F1 mice to the trichothecene vomitoxin results in hyperproduction of immunoglobulin A (IgA) with a concurrent immunopathology that mimics human IgA nephropathy. To assess the role of gender and strain in the mouse model, semipurified AIN-76A diet containing 25 ppm vomitoxin was fed to B6C3F1 male mice and to B6C3F1, BALB/c, C3H/HeN, C3H/HeJ, and C57BL/6 female mice for 8 wk, and immunopathologic indicators of IgA nephropathy were compared to mice fed clean diet. At the cessation of the experiment, all treatment groups weighed less than respective controls. Serum IgA was increased in male and female B6C3F1 mice as well as in C3H/HeJ, C57BL/6, and BALB/c female mice compared to corresponding controls. Serum IgA levels were two- to sixfold higher in B6C3F1 male treatment animals compared to female treatment groups from all strains. In contrast, at wk 8 serum IgG levels were unaffected or decreased, and serum IgM was decreased in all groups at wk 8. There was a trend toward increased IgA production by Peyer's patch (PP) lymphocytes isolated from treatment mice as compared to controls in all groups except the C3H/HeJ mice. Notably, IgA levels were 18-fold higher in B6C3F1 male treatment PP cultures than in B6C3F1 female treatment cultures. Hematuria was significantly greater in treatment mice than respective controls at both wk 4 and 8. Increased mesangial IgA deposition was also detectable in all treatment groups except the C57BL/6 mouse. The results suggested that the male B6C3F1 mouse and the five strains of female mice exhibited many of the immunopathologic effects found in IgA nephropathy and that IgA elevation was more marked in male B6C3F1 than female B6C3F1 mice.

Dietary exposure to the trichothecene vomitoxin (deoxynivalenol) stimulates terminal differentiation of Peyer's patch B cells to IgA secreting plasma cells

The effects of 8 weeks of dietary exposure to the fungal toxin vomitoxin (25 ppm) on the kinetics of in vitro immunoglobulin (Ig) production and appearance of IgA-secreting cells in lymphocyte culture were assessed in the B6C3F1 mouse. The feeding regimen resulted in an IgA:IgG serum ratio of 2.4 compared to 0.4 in controls indicating that there was dysregulation of IgA production in the systemic compartment. Prior toxin feeding had no effect on viability of Peyer's patch (PP) or splenic lymphocyte cultures. IgA production, as determined by enzyme-linked immunosorbent assay, was significantly greater in treatment PP and splenic lymphocytes cultured for 2-11 days than in corresponding controls. Similar trends were found for IgG production in PP cultures although levels were much lower. There were 1.7 and 2.0 times more IgA-producing cells, as measured by the ELISPOT assay, in freshly prepared PP and splenic lymphocytes from treatment mice compared to control mice, respectively. In contrast, after 2 days there were 10.9, 3.2, and 12.4 times more IgA-secreting cells in concanavalin A (Con A), LPS, and unstimulated treatment PP cultures, respectively, and 4.0, 2.0, and 3.5 times times more IgA-secreting cells in 2-day treatment spleen cultures, respectively. Both IgA and IgG secretion in Con A-stimulated cultures were significantly greater when treatment T cells and control B cells were combined than when control T cells and control B cells were combined. Increased Ig secretion attributable to T cell effects was not observed in LPS-stimulated or unstimulated PP reconstitution cultures or in spleen reconstituted cultures with and without mitogen. The results provide evidence that dietary vomitoxin enhances terminal differentiation of IgA secreting cells in PP. This and resultant migration of IgA secreting cells into the systemic compartment favor a shift from IgG to IgA as the primary serum isotype.

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.

Effect of dietary administration of the trichothecene vomitoxin (deoxynivalenol) on IgA and IgG secretion by Peyer's patch and splenic lymphocytes

Prolonged dietary exposure of mice to the trichothecene vomitoxin induces abnormally high levels of serum IgA and kidney mesangial IgA accumulation in a manner that is highly analogous to the human glomerulonephritis IgA nephropathy. In this study, the capacity of Peyer's patch and splenic lymphocytes to produce IgA and IgG were compared in B6C3F1 mice that were fed diets with and without 25 ppm vomitoxin for up to 12 wk. Serum IgA increased 2-, 4- and 8-fold after 4, 8 and 12 wk, respectively, of vomitoxin exposure and it became the primary serum isotype, whereas serum IgG was unaffected. On termination of the experiment there were increased numbers of IgA-secreting cells in Peyer's patches after 8 wk of toxin exposure and in the spleen after 4, 8 and 12 wk of toxin exposure. There were also increased numbers of IgG-secreting cells in Peyer's patches on termination of the experiment at 4, 8 and 12 wk but no effects was observed in the spleen. Supernatant IgA and IgA-secreting cell numbers were also markedly elevated in lymphocyte cultures obtained from Peyer's patches and, to a lesser extent, from spleens of treated mice compared with controls. Based on output of treated mice relative to corresponding controls, IgA secretion was greatest in concanavalin-A-stimulated and unstimulated Peyer's patch cultures. Enhanced IgG secretion and IgG-secreting cells were also observed in mitogen-stimulated and unstimulated Peyer's patch lymphocyte cultures of treated relative to control mice, but differences in splenocyte cultures were negligible. Based on total Ig output, IgA production was 8- to 20-fold greater than IgG production in both control and treatment Peyer's patch cultures. In contrast, vomitoxin treatment caused a shift from primarily IgG production in lipopolysaccharide-stimulated spleen cultures to equivalent IgA production. These data provide in vitro evidence that ingestion of vomitoxin promotes terminal differentiation of IgA-secreting progenitors in the Peyer's patch and, to a lesser extent, in the spleen. These functional changes are consistent with the shift from IgG to IgA as the primary serum isotype.

Alteration of immune function following dietary mycotoxin exposure

Mycotoxins are a group of structurally diverse fungal secondary metabolites that elicit a wide spectrum of toxicologic effects. Of particular interest is the capacity of some mycotoxins to alter normal immune function when present in foods at levels below observable overt toxicity. Aflatoxin, patulin, citrinin, and zearalenone experimentally alter immunity, and recent evidence suggests that the immunologic effects of ochratoxin A and trichothecenes may have particular significance to human and animal health. For example, the capacity of ochratoxin A to inhibit natural killer cell activity and increase growth of transplantable tumour cells has been associated with renal and hepatic carcinomas in mice and might similarly contribute to human cancer. Impaired resistance to pathogenic microorganisms occurs after exposure to the trichothecenes T-2 toxin and vomitoxin. This may predispose food animals to infectious disease and could result in decreased productivity as well as increased animal-to-human transmission of pathogens such as Salmonella and Listeria. Vomitoxin also alters normal mucosal immune function, specifically at the level of regulation of development, differentiation, and homing of IgA-producing plasma cells. Interestingly, vomitoxin-induced enhancement of IgA production in the systemic compartment contributes to manifestations in the mouse that are highly analogous to human IgA nephropathy, the most common form of human glomerulonephritis worldwide. Over the long term, the extrapolation of mycotoxin-induced immunologic effects observed in inbred mice to actual disease in livestock and humans will require investigations that both simulate natural exposure conditions as well as improve understanding of the cellular and molecular bases for these effects among different species.

Elevated membrane IgA+ and CD4+ (T helper) populations in murine Peyer's patch and splenic lymphocytes during dietary administration of the trichothecene vomitoxin (deoxynivalenol)

Recent investigations indicate that dietary exposure to the trichothecene vomitoxin increases total and antigen-specific serum immunoglobulin A (IgA) and glomerular IgA accumulation in mice. In this study, the effects of 25 ppm dietary vomitoxin on the histological and lymphocytic profile of component immune organs in the mucosal lymphocyte migratory pathway were evaluated in the B6C3F1 mouse. Vomitoxin administration resulted in marked stimulation of the size and frequency of germinal centres in Peyer's patches, mesenteric lymph nodes and the spleen. A slight increase in the percentage of B cells in the Peyer's patch was observed, although vomitoxin treatment had no effect on the percentage of B cells in the spleen. The percentage of IgA+ cells in Peyer's patches and spleen were approximately twice that of controls at 4, 8 and 12 wk of vomitoxin exposure whereas the percentage of IgG+ cells decreased in these two organs. Exposure to vomitoxin increased the percentage of T cells in Peyer's patches and the spleen. The percentage of CD4+ cells (T helper subset) increased slightly in Peyer's patches and more markedly (30-50%) in the spleen following vomitoxin treatment. Contrastingly, there was only a slight increase in the percentage of CD8+ cells (T cytotoxic/suppressor subset) in the spleens of vomitoxin-treated mice in comparison with controls, and no effect in Peyer's patches. The relative effects of vomitoxin on these two T cells populations was also reflected in increased CD4+: CD8+ ratios in Peyer's patches and spleen. These results are consistent with the hypothesis that dietary vomitoxin modulates normal regulation of the IgA response at the Peyer's patch level and that this is manifested in an altered lymphocyte distribution pattern in both the mucosal and systemic compartment. Notably increased levels of IgA+ and CD4+ cells are indicative of IgA-producing progenitors and T helper subsets, respectively, that in tandem could favour IgA hyperproduction and elevated IgA in serum.

Characterization of the normal bovine platelet aggregation response

1. Bovine platelets are more sensitive to stimulation by platelet activating factor (PAF) than adenosine-di-phosphate (ADP) or thrombin. 2. While epinephrine, arachidonic acid and serotonin are ineffective by themselves as aggregatory stimulants of bovine platelets they enhance the aggregation response of other platelet agonists. 3. There is no correlation between thromboxane A2 production and release and the extent of platelet aggregation in bovine platelets. 4. The dependence of bovine platelet aggregation on a phospholipid pathway and calcium mobilization is indicated.

Structure-function relationship of the action of T-2 toxin on bovine platelets

The effect of the trichothecene mycotoxin, T-2 toxin, on the ultrastructure of bovine platelets was investigated. In both toxin-treated and untreated platelets, the ultrastructure of the resting bovine platelet was characterized by the absence of an extensive open canalicular system and the appearance of granules and vacuoles which frequently impinged on the outer platelet membrane. No major ultrastructural changes were produced by T-2 toxin under conditions in which the platelet aggregation response was significantly inhibited. In bovine platelets exposed to the toxin, as in untreated platelets, there is evidence of pseudopod formation, indicating that T-2 toxin does not impair the initial response of platelets to stimulation. This observation is consistent with the companion function study which showed that, while T-2 toxin can impair both the rate and extent of aggregate formation, the most dramatic change is the relative instability of the platelet aggregates that form in the presence of the toxin.

Inhibitory effect of trichothecene mycotoxins on bovine platelets stimulated by platelet activating factor

Several species of fungi, which infect cereals and grains, can produce a class of compounds, known as trichothecene mycotoxins, which is characterized by a substituted epoxy-trichothecene ring structure. Cattle are susceptible to intoxication from feeds contaminated with T-2 toxin, one of the more potent trichothecene mycotoxins, while swine refuse to ingest feed contaminated with T-2 toxin. The bovine platelet has been used as a model cell system to evaluate the effects of T-2 toxin and its natural metabolites, HT-2 toxin and T-2 tetraol, on cell function in vitro. Due to the lipophilic nature of these mycotoxins, a biologically active phospholipid was used to stimulate the platelets in the presence and absence of the toxins. The mycotoxin T-2 toxin and its major metabolite HT-2 toxin inhibited platelet activating factor-stimulated bovine platelets, suspended in homologous plasma, in a concentration but not time dependent manner. Significant inhibition of platelet function (p less than 0.01) occurred with 135 ng T-2 toxin per 10(6) platelets and with 77 ng HT-2 toxin per 10(6) platelets. These mycotoxins exerted an additive inhibitory effect on the platelet aggregation response. In contrast, the minor metabolite T-2 tetraol had no inhibitory effect on platelet function and had no influence on the responses of T-2 toxin or HT-2 toxin when the mycotoxins were present together in the platelet suspensions.(ABSTRACT TRUNCATED AT 250 WORDS)