Aflatoxin B1 augments the synthesis of corticotropin releasing hormone in JEG-3 placental cells

Mycotoxin toxicity and its alleviation strategy on female mammalian reproduction and fertility

BACKGROUND

Mycotoxin, a secondary metabolite of fungus, found worldwide and concerning in crops and food, causes multiple acute and chronic toxicities. Its toxic profile includes hepatotoxicity, carcinogenicity, teratogenicity, estrogenicity, immunotoxicity, and neurotoxicity, leading to deleterious impact on human and animal health. Emerging evidence suggests that it adversely affects perinatal health and progeny by its ability to cross placental barriers.

AIM OF REVIEW

Due to its wide occurrence and potential toxicity on reproductive health, it is essential to understand the mechanisms of mycotoxin-related reproductive toxicity. This review summarizes the toxicities and mechanisms of mycotoxin on maternal and offspring reproduction among mammalian species. Approaches for effective mycotoxin alleviation are also discussed, providing strategies against mycotoxin contamination.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The profound mycotoxin toxicities in female mammalian reproduction affect follicle assembly, embryo development, and fetus growth, thereby decreasing offspring fertility. Factors from endocrine system such as hypothalamic-pituitary-gonadal axis and gut-ovarian axis, placenta ABC transporters, organelle and cytoskeleton dynamics, cell cycle control, genomic stability, and redox homeostasis are found to be closely related to mycotoxin toxicities. Approaches from physical, chemical, biological, and supplementation of natural antioxidants are discussed for the mycotoxin elimination, while their applications are not widespread. Available ways for mycotoxin and its toxicities alleviation need further study. Since a species-, time-, and dose-specific response might exist in mycotoxin toxicities, more consideration should be given to the protocols for mycotoxin toxicity studies, such as experimental animal models, exposure duration, and dosage. Specific mechanism for mycotoxin, especially form a molecular biology perspective, could be investigated with multi-omics technologies and advanced imaging techniques. Mass spectrometry with algorithms may provide more accurate exposure assessments, and it may be further helpful to identify the high-risk individuals in the future.

A Novel Multicellular Placental Barrier Model to Investigate the Effect of Maternal Aflatoxin B1 Exposure on Fetal-Side Neural Stem Cells

Ingestion of food toxins such as aflatoxin B₁ (AFB₁) during pregnancy may impair fetal neurodevelopment. However, animal model results may not be accurate due to the species' differences, and testing on humans is ethically impermissible. Here, we developed an in vitro human maternal-fetal multicellular model composed of a human hepatic compartment, a bilayer placental barrier, and a human fetal central nervous system compartment using neural stem cells (NSCs) to investigate the effect of AFB₁ on fetal-side NSCs. AFB₁ passed through the HepG2 hepatocellular carcinoma cells to mimic the maternal metabolic effects. Importantly, even at the limited concentration (0.0641 ± 0.0046 μM) of AFB_1, close to the national safety level standard of China (GB-2761-2011), the mixture of AFB₁ crossing the placental barrier induced NSC apoptosis. The level of reactive oxygen species in NSCs was significantly elevated and the cell membrane was damaged, causing the release of intracellular lactate dehydrogenase (p < 0.05). The comet experiment and γ-H2AX immunofluorescence assay showed that AFB₁ caused significant DNA damage to NSCs (p < 0.05). This study provided a new model for the toxicological evaluation of the effect of food mycotoxin exposure during pregnancy on fetal neurodevelopment.

Aflatoxin B1 targeted gene expression profiles in human placental primary trophoblast cells

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Gene expression profiles were studied in human primary trophoblast cells.

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170 genes were significantly dysregulated in aflatoxin B1-exposed trophoblasts.

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AhR-mediated estrogen receptor signalling was dysregulated in response to AFB1.

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Transcripts involved in endocrine signalling and energy homeostasis were disrupted.

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Cellular growth and development, cell cycle and DNA repair processes were affected.

Aflatoxin B1 (AFB1) is a mycotoxin produced by Aspergillus flavus and A. parasiticus. A high exposure (40 nM and 1 µM AFB1 for 72 h) was used to study mechanistic effects of AFB1 on gene expression patterns in human primary trophoblast cells, isolated from full term placentae after delivery. Gene expression profiling was conducted, and Ingenuity pathway analysis (IPA) software was used to identify AFB1-regulated gene networks and regulatory pathways.

In response to 40 nM AFB1, only 7 genes were differentially expressed whereas 1 µM AFB1 significantly dysregulated 170 genes (124 down- and 46 upregulated, ±1.5-fold, p < 0.05) in AFB1-exposed trophoblasts when compared to controls. The top downregulated genes were involved in endocrine signalling and biosynthesis of hormones, and lipid and carbohydrate metabolism. The top upregulated genes were involved in protein synthesis and regulation of cell cycle. The main canonical pathways identified by IPA were associated with endocrine signalling including growth hormone signalling, and corticotropin releasing hormone signalling. Furthermore, genes involved in aryl hydrocarbon receptor (AhR)-mediated estrogen receptor signalling were dysregulated in response to AFB1.

Our findings indicate that a high concentration 72 h AFB1 exposure caused relatively moderate number of changes on transcript level to human placental primary trophoblast cells. However, these preliminary results need to be confirmed with human-relevant concentrations of AFB1.

Advances in the Total Synthesis of Aflatoxins

Aflatoxins, which are produced by Aspergillus flavus, Aspergillus nomius, and Aspergillus parasiticus, are a group of pentacyclic natural products with difuran and coumarin skeletons. They mainly include aflatoxin B1, B2, G1, G2, M1, and M2. Biologically, aflatoxins are of concern to human health as they can be present as contaminants in food products. The unique skeletons of aflatoxins and their risk to human health have led to the publication of nine remarkable total syntheses (including three asymmetric syntheses) and ten formal total syntheses (including four asymmetric formal syntheses) of aflatoxins in the past 55 years. To better understand the mechanism of the biological activity of aflatoxins and their presence in samples from the food industry, this review summarizes progress in the total synthesis of aflatoxins.

Aflatoxin B1 disrupts transient receptor potential channel activity and increases COX-2 expression in JEG-3 placental cells

Aflatoxins are fungal metabolites which pose a major threat to food safety. Although these mycotoxins are established hepatocarcinogens, their effect on the reproductive organ is unknown. Transient Receptor Potential Channels (TRPs) are ubiquitously expressed in human tissues, including the placenta. These channels are associated with various functions in the placenta. The fetus and the placenta are especially sensitive to xenobiotic assault; therefore, exposure to the aflatoxins during gestation might lead to the undesirable outcome. Previously we have shown that aflatoxin B1 administered in late gestation may increase cox-2 expression in mouse placentae. In the present study, we examined the effect of aflatoxin B1 on COX-2 by using the placental cell model JEG-3 and the respective signaling pathway. In our result, COX-2 expression was induced by the mycotoxin administration. The intracellular calcium levels were also increased in cells by aflatoxin B1 treatment as little as 1 nM. Immunoblot result showed that some TRP expressions were elevated. As inflated intracellular calcium might activate MAPKs, the underlying signaling pathway was investigated. With the help of TRP-specific inhibitors, the mycotoxin appeared to increase the expression of TRPC-3 and activate PKCβ and ERK. The significance of COX-2 in pregnancy has been well established. Exposure to this mycotoxin may perturb the physiological processes dictated by COX-2 in pregnancy.

Exposure to aflatoxin B1 in late gestation alters protein kinase C and apoptotic protein expression in murine placenta

Mycotoxins are chemicals with diverse toxicities that are produced by fungi. Aflatoxin B1 is commonly found in plant food, and is generally regarded as one of the most toxic mycotoxins. In the present study, pregnant ICR mice were given p.o. daily doses of aflatoxin B1 at 0, 0.05, 0.5, 5mg/kg for 4days (from E13.5 to E16.5). Compared to the control group, time of delivery was shortened and low birth weight was induced in mice treated with 0.5 and 5mg aflatoxin B1/kg, respectively. Placental tissue isolated from pregnant mice at E17.5 showed that the mRNA expression of crh was increased in aflatoxin-treated groups. This upregulation might signify premature delivery. Further analysis indicated that Pkc proteins were activated and Bcl-2 was reduced in the placental tissue of the aflatoxin-treated groups. Reduction of the anti-apoptotic proteins, on the other hand, might affect the morphorgenesis and maintenance of the placenta.