Damage mechanisms of bisphenols on the quality of mammalian oocytes

The extensive use of bisphenols in the plastics industry globally is a major growing concern for human health. Bisphenol compounds are easily leached out from plastic containers to food, beverages, and drinking water and contaminate the natural environment. Daily exposure of bisphenol compounds increases their load and impairs various organs, including the reproductive system. Bisphenol compounds directly or indirectly affect ovarian functions, such as folliculogenesis, steroidogenesis, oogenesis, and thereby oocyte quality. Bisphenol A (BPA) and its structural analogues act as endocrine disruptors and induce generation of reactive oxygen species (ROS) within the ovary. Excess levels of ROS induce death pathways in follicular steroidogenic cells and affect ovarian steroidogenesis. The reduced level of estradiol-17β impairs follicular growth and development that reduces the number and quality of oocytes. In addition, excess levels of ROS in follicular fluid trigger meiotic instability, which further deteriorates oocyte quality. The high level of ROS generates oxidative stress that triggers various death pathways in germ cells as well as in oocytes, induces follicular atresia, and depletes ovarian reserve. Although growing evidence indicates the destructive effects of bisphenol compounds at the level of ovary, potential effects and underlying mechanisms that deteriorate oocyte quality remain poorly understood. Therefore, this review summarizes the mechanisms by which bisphenols cause damage to the ovary, impair oocyte quality, and affect women's fertility.