Acute effect of aflatoxin B1 on different inbred mouse strains II

Maternal dietary exposure to mycotoxin aflatoxin B1 promotes intestinal immune alterations and microbiota modifications increasing infection susceptibility in mouse offspring

Mycotoxins are secondary metabolites produced by fungi occurring in food that are toxic to animals and humans. Early-life mycotoxins exposure has been linked to diverse pathologies. However, how maternal exposure to mycotoxins impacts on the intestinal barrier function of progeny has not been explored. Here, exposure of pregnant and lactating C57Bl/6J female mice to aflatoxin B₁ (AFB₁; 400 μg/kg body weight/day; 3 times a week) in gelatine pellets, from embryonic day (E)11.5 until weaning (postnatal day 21), led to gut immunological changes in progeny. The results showed an overall increase of lymphocyte number in intestine, a reduction of expression of epithelial genes related to microbial defence, as well as a decrease in cytokine production by intestinal type 2 innate lymphoid cells (ILC2). While susceptibility to chemically induced colitis was not worsened, immune alterations were associated with changes in gut microbiota and with a higher vulnerability to infection by the protozoan Eimeria vermiformis at early-life. Together these results show that maternal dietary exposure to AFB₁ can dampen intestinal barrier homeostasis in offspring decreasing their capability to tackle intestinal pathogens. These data provide insights to understand AFB₁ potential harmfulness in early-life health in the context of intestinal infections.

Subcellular spatio-temporal intravital kinetics of aflatoxin B1 and ochratoxin A in liver and kidney

Local accumulation of xenobiotics in human and animal tissues may cause adverse effects. Large differences in their concentrations may exist between individual cell types, often due to the expression of specific uptake and export carriers. Here we established a two-photon microscopy-based technique for spatio-temporal detection of the distribution of mycotoxins in intact kidneys and livers of anesthetized mice with subcellular resolution. The mycotoxins ochratoxin A (OTA, 10 mg/kg b.w.) and aflatoxin B1 (AFB1, 1.5 mg/kg b.w.), which both show blue auto-fluorescence, were analyzed after intravenous bolus injections. Within seconds after administration, OTA was filtered by glomeruli, and enriched in distal tubular epithelial cells (dTEC). A striking feature of AFB1 toxicokinetics was its very rapid uptake from sinusoidal blood into hepatocytes (t1/2 ~ 4 min) and excretion into bile canaliculi. Interestingly, AFB1 was enriched in the nuclei of hepatocytes with zonal differences in clearance. In the cytoplasm of pericentral hepatocytes, the half-life (t1/2~ 63 min) was much longer compared to periportal hepatocytes of the same lobules (t1/2 ~ 9 min). In addition, nuclear AFB1 from periportal hepatocytes cleared faster compared to the pericentral region. These local differences in AFB1 clearance may be due to the pericentral expression of cytochrome P450 enzymes that activate AFB1 to protein- and DNA-binding metabolites. In conclusion, the present study shows that large spatio-temporal concentration differences exist within the same tissues and its analysis may provide valuable additional information to conventional toxicokinetic studies.

Climate Change Impact on Aflatoxin Contamination Risk in Malawi's Maize Crops

Malawi is one of the poorest countries in the world, with high levels of malnutrition and little domestic mycotoxin regulation. Domestically grown maize is the largest single source of calories in the country and a large contributor to the economy. This research uses Regional Climate Models (RCMs) to determine the climatic conditions in the three regions of Malawi (Northern, Central and Southern) in 2035 (2020–2049) and 2055 (2040–2069) as compared to the baseline climate of 1971–2000. This climatic data is then used as inputs to the Food and Agriculture Organization's (FAO) AquaCrop model to assess the impact on the growth cycle of two maize varieties grown in each region and sown at three different times during the planting season. Finally, AFLA-maize, a mechanistic model, is applied to determine the impact of these projected changes on the aflatoxin B1 (AFB1) contamination risk. We find that Malawi's climate is projected to get warmer (by 1–2.5°C) and drier (reduction of 0–4% in annual rainfall levels) in all regions, although some uncertainty remains around the changes in precipitation levels. These climatic changes are expected to shorten the growing season for maize, bringing the harvest date forward by between 10 and 25 days for the short-development variety and between 25 and 65 days for the long-development variety. These changes are also projected to make the pre-harvest conditions for Malawian maize more favorable for AFB1 contamination and risk maps for the studied conditions were drawn. Exceedances of EU safety thresholds are expected to be possible in all regions, with the risk of contamination moving northwards in a warming climate.

Involvement of hepatic lipid droplets and their associated proteins in the detoxification of aflatoxin B1 in aflatoxin-resistance BALB/C mouse

The highly potent carcinogen, Aflatoxin B₁, induces liver cancer in many animals including humans but some mice strains are highly resistant. This murine resistance is due to a rapid detoxification of AFB₁. Hepatic lipid droplets (LDs) ultimately impact the liver functions but their potential role in AFB₁ detoxification has not been addressed. This study describes the structural and functional impacts on hepatic LDs in BALB/C mice after exposure to 44 (low dose) or 663 (high dose) μg AFB₁/kg of body weight. After 7 days, the liver of AFB₁-dosed mice did not accumulate any detectable AFB₁ or its metabolites and this was associated with a net increase in gene transcripts of the AhR-mediating pathway. Of particular interest, the livers of high-dose mice accumulated many more LDs than those of low-dose mice. This was accompanied with a net increase in transcript levels of LD-associated protein-encoding genes including Plin2, Plin3 and Cideb and an alteration in the LDs lipid profiles that could be likely due to the induction of lipoxygenase and cyclooxygenase genes. Interestingly, our data suggest that hepatic LDs catalyze the in vitro activation of AFB₁ into AFB₁-exo-8,9-epoxide and subsequent hydrolysis of this epoxide into its corresponding dihydrodiol. Finally, transcript levels of CYP1A2, CYP1B1, GSTA3 and EH1 genes were elevated in livers of high-dose mice. These data suggest new roles for hepatic LDs in the trapping and detoxifying of aflatoxins.

Impact of a Single Oral Acute Dose of Aflatoxin B₁ on Liver Function/Cytokines and the Lymphoproliferative Response in C57Bl/6 Mice

Aflatoxin B₁ (AFB₁), a mycotoxin found in food and feed, exerts harmful effects on humans and animals. The liver is the earliest target of AFB₁, and its effects have been evaluated in animal models exposed to acute or chronic doses. Considering the possibility of sporadic ingestion of AFB₁-contaminated food, this study investigated the impact of a single oral dose of AFB₁ on liver function/cytokines and the lymphoproliferative response in mice. C57BL/6 mice were treated with a single oral AFB₁ dose (44, 442 or 663 μg AFB₁/kg of body weight) on the first day. Liver function (ALT, γ-GT, and total protein), cytokines (IL-4, IFN-γ, and IL-17), histopathology, and the spleen lymphoproliferative response to mitogens were evaluated on the 5th day. Although AFB₁ did not produce any significant changes in the biochemical parameters, 663 μg AFB₁/kg-induced hepatic upregulation of IL-4 and IFN-γ, along with liver tissue injury and suppression of the lymphoproliferative response to ConA (p < 0.05). In conclusion, a single oral dose of AFB₁ exposure can induce liver tissue lesions, liver cytokine modulation, and immune suppression in C57BL/6 mice.

Early toxicology signal generation in the mouse

The rat has been the preferred rodent toxicology species since before regulatory requirements have been in place, and there exists in the pharmaceutical industry and the regulatory agencies a significant amount of historical data for the rat. The resulting experience base with the rat makes the possibility of replacing it with the mouse for regulated toxicology studies untenable for all but the most extreme circumstances. However, toxicologists are very familiar with the mouse as a model for chronic carcinogenicity studies, and there exist multiple preclinical mouse models of disease. The authors evaluated the use of the mouse for early in vivo toxicology signal generation and prioritization of small molecule lead compounds prior to nomination of a development candidate. In five-day oral gavage studies with three test agents in the mouse, the authors were able to identify the same dose-limiting toxicities as those identified in the rat, including examples of compound-mediated hemolysis as well as microscopic lesions in the alimentary canal, kidney, and pancreas. Performing early signal generation studies in the mouse allows for earlier assessment of the safety liabilities of small molecules, requires significantly less compound, and allows evaluation of more compounds earlier in the project's life cycle.

Effects of prolonged administration of aflatoxin B1 and fumonisin B1 in laying Japanese quail

In the present study, 288 8-wk-old Japanese quail were randomly distributed into 6 experimental groups (48 birds per group) and fed the following diets for 140 d: 1) 0 (control); 2) 10 mg of fumonisin B1 (FB1); 3) 50 microg of aflatoxin B1 (AFB1); 4) 50 microg of AFB1 + 10 mg of FB1; 5) 200 microg of AFB1; and 6) 200 microg of AFB1 + 10 mg of FB1/kg of feed. Each treatment consisted of 4 replicates of 12 quail. Egg production and individual egg weight were checked daily. Feed intake and feed conversion were determined weekly. Results showed that by the end of the fifth cycle, average egg weight was lower (P < 0.05) in groups fed 10 mg of FB1/kg, 50 microg of AFB1/kg, 200 microg of AFB1/kg, and 10 mg of FB1 + 50 microg of AFB1/kg of feed. Egg production decreased (P < 0.05) in birds fed 10 mg of FB1/kg by the third, fourth, and fifth cycles. Feed intake was lower (P < 0.05) in birds fed 10 mg of FB1/kg by the fourth and fifth cycles, and in birds fed 50 and 200 microg of AFB1/kg in the fifth cycle. Birds fed 10 mg of FB1 + 50 microg of AFB1/kg consumed less feed (P < 0.05) in the first, second, and fifth cycles. Results indicated that prolonged administration of FB1 and AFB1, singly or in combination at the levels evaluated, may cause economic losses to quail egg producers.

Aflatoxin B1 aldehyde reductase (AFAR) genes cluster at 1p35-1p36.1 in a region frequently altered in human tumour cells

Alterations of the distal portion of the short arm of chromosome 1 (1p) are among the earliest abnormalities of human colorectal tumours. Recently, we have cloned the Aflatoxin B1 aldehyde reductase (AFAR) gene from a smallest region of overlapping deletion that is frequently (48%) hemizygously deleted in sporadic colorectal cancer. AFAR is expressed in a broad range of tissues. Its closely related rat protein is the major factor conferring resistance of rats towards aflatoxin B1-induced liver carcinogenesis. Here, we have identified cDNAs covering two additional human AFAR-related genes localized in close proximity to the previously described AFAR at 1p35-36. We have analysed their structure and tissue-related expression. One of them, AFAR3, carries a Selenocysteine-Insertion Element (SECIS)-like structure that during translation may recode an in-frame TGA-stop codon to a selenocysteine. Two additional AFAR-pseudogenes are localized at Xq25 and 1p12, respectively. AFAR exon sequences share an identity of DNA and amino acids of more than 78%. Also large blocks of intronic sequences can be up to 98.6% identical. Knowledge of the AFAR genes and their structure will be essential in genetic and functional studies, where discrimination of the genes and proteins is a prerequisite for evaluating their individual functions.

Aflatoxin residues in eggs of laying Japanese quail after long-term administration of rations containing low levels of aflatoxin B1

The aim was to evaluate the excretion of residues of aflatoxin B(1) (AFB(1)), aflatoxin M(1) (AFM(1)), aflatoxin B(2a) (AFB(2a)) and aflatoxicol (AFL) in eggs of laying Japanese quail fed rations with low levels of aflatoxin B(1) for 90 days. The quail were randomly assigned into four experimental groups and given prepared rations containing either 0 (controls), 25, 50 or 100 microg AFB(1) kg(-1) feed. Thirty-two eggs per treatment were collected on days 1-7, 10, 20, 30, 60 and 90 of the aflatoxin treatment period, and submitted to aflatoxin analysis by high-performance liquid chromatography. Average egg production and feed consumption were not affected ( p > 0.05) by AFB(1). Egg weight was significantly lower ( p<0.05) only for groups exposed to 100 microg AFB(1) kg(-1). Residues of aflatoxins were detected in eggs at levels that ranged from 0.01 to 0.08 microg kg(-1) (AFB(1)), 0.03-0.37 microg kg(-1) (AFM(1)), 0.01-1.03 microg kg(-1)(AFB(2a)) and 0.01-0.03 microg kg(-1) (AFL). Results indicate that the excretion of aflatoxin residues in quail eggs might occur at relatively low concentrations under conditions of long-term exposure of quail to low levels of AFB(1).

Effect of aflatoxin B1 on CD3 T cells and alkaline phosphatase in the intestine of mice

The aim of the study was to determine the effect of repeated applications of aflatoxin B1 (AFB1) on immunocompetent cells (CD3 T cells) and alkaline phosphatase in the intestinal mucosa. Mice were orally treated with AFB1 for 24 days. The mucosa of the intestine showed a significant decrease in the number of CD3 T cells and a significantly lower level activity of alkaline phosphatase on day 24 in AFB1 treated mice. Similarly, with changes in the small intestine, qualitative haematological parameters were modified in systemic immunity as lymphopenia, and neutropenia, monocytopenia. AFB1 treated animals showed reduction in body weight gain and increased liver weight. We supposed that changes found in the small intestine are secondary to primary systemic haematological lesions. The decrease in CD3 T cells suggests a connection with the decrease in the host's resistance to infectious diseases.

Effect of low levels of dietary aflatoxin B1 on laying japanese quail

In the present study, 256 7-wk-old Japanese quail were randomly distributed into four experimental groups (64 birds per group) and given rations containing 0 (controls), 25, 50, or 100 (g aflatoxin B, (AFB1)/kg feed for 168 d. Each treatment consisted of four replicates of 16 quail. Egg production and individual egg weight were checked daily. Feed consumption and feed use were determined weekly. Eggs laid in the last day of each 28-d laying period were collected and subjected to individual analysis for specific gravity, Haugh units, shell thickness and percentage eggshell. Results showed that average egg production, feed use, and body weights were not affected (P > 0.05) by AFB1. However, feed consumption was lower (P < 0.05) for groups fed 50 or 100 microg AFB1/kg. Egg weight was significantly lower (P < 0.05) only for groups exposed to 50 and 100 microg AFB1/kg. Average egg specific gravity, Haugh units, and shell thickness were not affected (P > 0.05) by AFB1. Percentage eggshell was higher (P < 0.05) in the group fed the ration containing 100 microg AFB1/kg. Treatment associated lesions were observed only in the liver. Hepatic cell vacuolation with fatty infiltration was observed in all liver samples of quail fed AFB1-contaminated rations. Bile duct proliferation and trabecular disorder were found only in livers of quail on the 100-microg AFB1/kg treatment. Results indicated that chronic exposure to AFB1 at levels above 50 microg/kg could adversely affect quail performance, emphasizing the importance of controlling aflatoxin contamination in quail rations.

Aflatoxin B1 residues in eggs of laying hens fed a diet containing different levels of the mycotoxin

The present study was carried out to evaluate the excretion of aflatoxin B1 residues in eggs of young laying hens fed aflatoxin B1-contaminated rations for 8 weeks. To this end, 96 twenty-week-old hens were randomly distributed into four experimental groups (24 birds per group) and given rations containing either 0 (controls), 100 micrograms, 300 micrograms or 500 micrograms aflatoxin B1/kg feed. Egg aflatoxin B1 residues were determined by thin layer chromatography; two samples per treatment per week were used for analysis. Egg production and average egg weights were not affected (p < 0.05) in the groups receiving aflatoxin B1-contaminated rations. Residues of aflatoxin B1 were detected only in the eggs of hens given 500 micrograms/kg feed, at levels that ranged from 0.05 to 0.16 microgram/kg (average: 0.10 microgram/kg). The results indicate that the feed to eggs aflatoxin B1 transmission ratio was approximately 5000:1, emphasizing the importance of controlling aflatoxin levels in rations for laying hens.