Aflatoxin B1 impairs in vitro early developmental competence of ovine oocytes

Aflatoxin is considered as one of the most harmful mycotoxins in the world to be found in human food and animal feed. Previous reports have revealed that Aflatoxin B1 (AFB1) may disrupt gamete development through epigenetic modifications as well as promotion of oxidative stress, excessive autophagy, and apoptosis. Therefore, in this study we aimed to address the effects of AFB1 on the meiotic and cytoplasmic maturation, internal reactive oxygen species (ROS) production, mitochondrial membrane potential (ΔΨm), blastocyst formation as well as mRNA alterations for the apoptotic (BAX and Caspase3), anti-apoptotic (BCL2), and DNA methyltransferase (DNMTs) genes in ovine oocytes. To accomplish this, maturation of oocytes was performed in presence of increasing AFB1 concentrations (0, 10, 50, and 100 μM). Meiotic and cytoplasmic maturation, intracellular ROS level, and ΔΨm were evaluated following 24 h of IVM. Embryonic cleavage and blastocyst formation following fertilization were also assessed. We also investigated alterations of BAX, BCL2,Caspase3, DNMT1, DNMT3a, and DMT3b mRNA levels in mature oocytes. In the presence of 50 and 100 μM AFB1, the number of oocytes reaching the metaphase II stage decreased and the oocytes presented with lower intracellular levels of GSH (P < 0.05). Furthermore, intracellular ROS production in matured oocytes reached the highest-level following exposure to 50 and 100 μM of AFB1 (P < 0.05). Reduction of ΔΨm was clearly evident in the AFB1-treated groups (P < 0.05). Rates of cleavage and blastocyst formation decreased in the presence of AFB1 as compared with those recorded in the Control group (P < 0.05). Apoptosis-related gene analysis in AFB1 treated groups (10 and 50 μM) revealed a higher abundance of the BAX and Caspase3 genes, and a lower abundance of the BCL2 gene as compared with the Control group (P < 0.05). Additionally, our data showed that relative abundances of DNMT3b gene decreased in the 10 μM group when compared to the Control group (P < 0.05). We showed that exposure of oocytes to AFB1 leads to a reduced nuclear and cytoplasmic maturation that may ultimately impair the embryonic development in the sheep oocyte. Furthermore, alterations in DNA methylation and initiation of apoptosis through excessive ROS generation could be a prime molecular mechanism responsible for the disruption of oocyte developmental competence in the presence of AFB1 in the ovine model.