Toxic effects and possible mechanisms of hydrogen sulfide and/or ammonia on porcine oocyte maturation in vitro

Previous studies suggest that hydrogen sulfide (H2S) and ammonia (NH3) are two major air pollutants which can cause damage to porcine health. However, the mechanisms underlying toxic effects of these compounds on porcine oocyte maturation are not clear. To clarify the mechanism, we evaluated the oocyte quality by detecting some events during oocytes maturation. In our study, porcine oocytes were cultured with different concentrations of Na2S and/or NH4Cl in vitro and the rate of the first polar body extrusion decreased significantly. Also, actin filament was seriously disrupted to damage the cytoskeleton which resulted in reduced rate of oocyte maturation. We explored the reactive oxygen species (ROS) generation and found that the ROS level was increased significantly after Na2S treatment but not after NH4Cl treatment. Moreover, early stage apoptosis rate was significantly increased and autophagy protein LC3 B expression level was higher in oocytes treated with Na2S and/or NH4Cl, which might be caused by ROS elevation. Additionally, exposure to Na2S and/or NH4Cl also caused ROS generation and early apoptosis in cumulus cells, which might further affect oocyte maturation in vitro. In summary, our data suggested that exposure to H2S and/or NH3 decreased porcine oocyte maturation in vitro, which might be caused by actin disruption, ROS generation, early apoptosis and autophagy.