Toxic Effects of Benzo[b]fluoranthene on Developmental Competence of Ovine Oocytes During In Vitro Culture

Benzo[b]fluoranthene (B[b]F) as one of the common Polycyclic aromatic hydrocarbons (PAHs) with ≤ 2.5 µm (PM 2.5) can be found in various environmental sources polluted air, water, and soil. Previous reports have revealed that B[b]F may reproductive toxicity in the female reproductive system through of oxidative stress, excessive autophagy, and apoptosis. In this study, we sought to investigate the impact of B[b]F on meiotic and cytoplasmic maturation, the production of internal reactive oxygen species (ROS), blastocyst formation, and the expression levels of mRNA associated with apoptotic ( BAX and Caspase3 ), anti-apoptotic ( BCL2 ), Growth Differentiation Factor 9 ( GDF9 ), and Bone Morphogenetic Protein 15 ( BMP15 ) genes in ovine oocytes. In this study, in vitro maturation (IVM) of oocytes was conducted using varying concentrations of B[b]F (0, 1, 2, 5, and 10 µM). After a 24-hour period of IVM, assessments were made regarding meiotic and cytoplasmic maturation, as well as the levels of intracellular reactive ROS. The approach mentioned facilitates the assessment of the impact that varying concentrations of B[b]F have on the maturation processes and oxidative stress levels in oocytes. Embryonic cleavage and blastocyst formation following in vitro fertilization were also assessed in each group. Alterations of BAX , Caspase3 , BCL2, GDF9 , and BMP15 were analysed following IVM . In the presence of 5 µM B[b]F, 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 2, 5, and 10 µM of AFB1 ( P < 0.05 ). Rates of cleavage and blastocyst formation observed in the presence of B[b]F were lower than those recorded in the Control group ( P < 0.05 ). Apoptosis-related gene analysis in AFB1 treated groups (5 µM) revealed a higher expression of the BAX and Caspase3 genes, and a lower expression of the BCL2 gene as compared with the Control group ( P < 0.05 ). Additionally, our data showed that expression patterns of GDF9 and BMP15 decreased in the 5 µM group when compared to the Control group ( P < 0.05 ). We showed that exposure of oocytes to B[b]F leads to a reduced nuclear and cytoplasmic maturation that may ultimately impair the embryonic development in the sheep. Furthermore, alterations in GDF9 and BMP15 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 B[b]F in the ovine model.