In vitro toxicological effects of estrogenic mycotoxins on human placental cells: structure activity relationships.

Zearalenone (ZEN) is a non-steroid estrogen mycotoxin produced by numerous strains of Fusarium which commonly contaminate cereals. After oral administration, ZEN is reduced via intestinal and hepatic metabolism to α- and ß-zearalenol (αZEL and ßZEL). These reduced metabolites possess estrogenic properties, αZEL showing the highest affinity for ERs. ZEN and reduced metabolites cause hormonal effects in animals, such as abnormalities in the development of the reproductive tract and mammary gland in female offspring, suggesting a fetal exposure to these contaminants. In our previous work, we have suggested the potential impact of ZEN on placental cells considering this organ as a potential target of xenobiotics. In this work, we first compared the in vitro effects of αZEL and ßΖΕL on cell differentiation to their parental molecule on human trophoblast (BeWo cells). Secondly, we investigated their molecular mechanisms of action by investigating the expression of main differentiation biomarkers and the implication of nuclear receptor by docking prediction. Conversely to ZEN, reduced metabolites did not induce trophoblast differentiation. They also induced significant changes in ABC transporter expression by potential interaction with nuclear receptors (LXR, PXR, PR) that could modify the transport function of placental cells. Finally, the mechanism of ZEN differentiation induction seemed not to involve nuclear receptor commonly involved in the differentiation process (PPARγ). Our results demonstrated that in spite of structure similarities between ZEN, αZEL and ßZEL, toxicological effects and toxicity mechanisms were significantly different for the three molecules.

Metabolism and transfer of the mycotoxin zearalenone in human intestinal Caco-2 cells.

The mycotoxin zearalenone (ZEA) is found worldwide as contaminant in cereals and grains. It is implicated in reproductive disorders and hyperestrogenic syndromes in animals and humans exposed by food. We investigated metabolism and transfer of ZEA using the human Caco-2 cell line as a model of intestinal epithelial barrier. Cells exposed to 10-200 microM ZEA showed efficacious metabolism of the toxin. alpha-zearalenol and beta-zearalenol were the measured preponderant metabolites (respectively 40.7+/-3.1% and 31.9+/-4.9% of total metabolites, after a 3h exposure to 10 microM ZEA), whereas ZEA-glucuronide and alpha-zearalenol glucuronide were less produced (respectively 8.2+/-0.9% and 19.1+/-1.3% of total metabolites, after a 3h exposure to 10 microM ZEA). Cell production of reduced metabolites was strongly inhibited by alpha-and beta-hydroxysteroid dehydrogenase inhibitors, and Caco-2 cells exhibited alpha-hydroxysteroid dehydrogenase type II and beta-hydroxysteroid dehydrogenase type I mRNA. After cell apical exposure to ZEA, alpha-zearalenol was preponderantly found at the basal side, whereas beta-zearalenol and both glucuronides were preferentially excreted at the apical side. As alpha-zearalenol shows the strongest estrogenic activity, the preferential production and basal transfer of this metabolite suggests that intestinal cells may contribute to the manifestation of zearalenone adverse effects.

Zearalenone exposure modulates the expression of ABC transporters and nuclear receptors in pregnant rats and fetal liver.

The mycotoxin zearalenone (ZEN) is produced by a variety of Fusarium fungi and contaminates numerous cereals, fruits and vegetables. Interacting with the estrogen receptors, ZEN and reduced metabolites zearalenols cause hormonal effects in animals. Few data are available on the effects of repeated exposure to ZEN, particularly during pregnancy. The aim of our work was to assess the impact of this toxin on the expression of ABC transporters and nuclear receptors in fetal liver and pregnant rats that were exposed daily (gestation day 7-20) to 1 mg/kg ZEN. Significant variations were observed, depending on the tissue type, the tissue origin (maternal or fetal), and the time of analysis after the last exposure to ZEN (4 h or 24 h). The modulations of expression were independent of the magnitude of tissue impregnation by ZEN and its metabolites. The maternal uterus was the most sensitive tissue: Abcb1a, Abcb1b and Abcg2 mRNA and protein expressions were induced at both times, while Abcc1, Abcc3 and Esr1 mRNA and protein expressions were inhibited then induced 4 h and 24 h after exposure, respectively. In the fetal liver, Abcb1a and Esr1 protein expression was inhibited at both times, while mRNA expression was induced 24 h after the last exposure to ZEN. These results suggested that ZEN exposure could impact maternal and fetal exposure to ABC transporters substrates, and influence fetus development through nuclear receptor modulation.

Induction of cells differentiation and ABC transporters expression by a myco-estrogen, zearalenone, in human choriocarcinoma cell line (BeWo).

The mycotoxin zearalenone, produced by Fusarium species, is a worldwide contaminant of concern in cereals and other plant products. Due to its estrogenic activity, zearalenone (ZEA) is known to have toxicological effect in animals on reproductive system and the placental transfer of ZEA was suggested by in vivo studies. Although passive diffusion is the principal transport mechanism across the placenta, several carrier-mediated transport protein such as ABC transporter (P-gp, MRP1, MRP2, BCRP) have been identified in the placenta. In this work, we have investigated the effect of ZEA on trophoblast differentiation and ABC transporter expression by using an in vitro model of transplacental barrier, the BeWo cell line. In the presence of 10 microM ZEA morphological (syncytium formation) and biochemical (hCG secretion) differentiation of BeWo cells were observed after a 48h exposure. Results were compared to 17beta-estradiol (E2) and an inducer of syncytialisation (forskolin). The influence of cell differentiation and ZEA exposure on expression profiles of major ABC transporters was investigated in BeWo cells: expression of mRNA MRP1, MRP2 and BCRP was induced after 24h of ZEA exposure. Induction of P-gp, MRP1, and MRP2 protein was observed after 48h of ZEA exposure. Similar results were obtained after forskolin exposure. Our study reported for the first time the implication of a food contaminant in biological effect and ABC transporter expression modulation in human choriocarcinoma cells.