Effect of Mycotoxins on the Synthesis of Estrogen and Expression of Corticotrophin-Releasing Hormone In Vitro and In Vivo

Background: Pregnancy causes many physiological changes in a woman¡¦s body, and differential hormone production is responsible for most of these changes. Placental estrogens and corticotrophin-releasing hormone (CRH) play pivotal roles in the control of pregnancy and parturition. Mycotoxins are chemicals produced by fungus and many of them are toxic. Studies have shown that some mycotoxins could disrupt the proper functioning of human endocrine system.;Objectives: This study investigated the effect of three mycotoxins, zearalenone, zeranol and aflatoxin B1, on the synthesis of estrogen and the expression of CRH in cell and animal model systems.;Methods: In the cell model, mRNA expression of genes was determined by real-time PCR. Changes in protein level were analysed by western blot. Transcriptional activity was determined by EMSA. In the animal study, pregnant ICR mice were treated with mycotoxins from embryo day 13.5 to embryo day 16.5. On embryo day 17.5, the drug-treated mice were sacrificed. Plasma hormones were measured by ELISA. The placentas were collected to determine the changes of gene expression by real-time PCR and western blot.;Results: Our results demonstrated that zearalenone had the strongest inhibitory effect on aromatase activity with a Ki value of 1.12muM. Zeranol was less potent than zearalenone, while aflatoxin B1 had no obvious effect on the activity. At the transcriptional level, none of these three mycotoxins could affect aromatase III expression in JEG-3 cells and T98G cells. Zearalenone and zeranol showed specific inhibition of CYP19A1 expression or promoter I.3 and II transcription in MCF-7 cells, while aflatoxin B1 had null effect in the same cells.;Regarding CRH expression, only zeranol and aflatoxin B1 significantly increased the mRNA level in JEG-3 cells. Zeranol stimulated the CRH transcription at 0.1nM in JEG-3 cells by increasing CRE binding activity, and PKCdelta and ERK-1/2 were found to be activated. In a mouse model, the rates of preterm birth and fetal resorption were increased by zeranol. The induced preterm labor was related to the increased expression of CRHR1 and Relaxin 1 in placenta. The induced fetal resorption was related to decreased expression of ERK, Cdk2 & 4, Cyclin D1 and Bcl-xL in placenta.;Aflatoxin B1 could also induce CRH expression in JEG-3 cells at 10nM. The results illustrated that PKC and ERK signaling pathways were involved and the activation of C/EBP could be the underlying molecular mechanism. Animal study demonstrated that aflatoxin B1 induced preterm labor in mice with increased plasma concentrations of estrogen and CRH. Aflatoxin B1 also increased the expression of COX-2 and decreased the expression of 15-HPGD in murine placenta. The increased CRH expression was mediated by PKC signal transduction pathways.;Conclusions: These three mycotoxins could differentially regulate CRH, CYP19A1, relaxin expression, which could induce preterm labor in pregnant mice. Results of the present study may provide some scientific data for establishing the exposure limit of mycotoxins during pregnancy.