Zinc Homeostasis, Reactive Oxygen Species Imbalance and Bisphenol-A Exposure in the Preimplantation Mouse Embryo: a possible adverse outcome pathway

Abstract

Bisphenol-A (BPA) is a ubiquitous xenoestrogen found in plastic products used for food containers, paper products, water pipes, etc. Individuals exposed to BPA are susceptible to detrimental effects; with poor oocyte quality, sperm motility, and impaired embryo implantation observed in mouse models at levels as low as 100 µg/kg/day. To investigate the mechanism through which BPA affects embryo development, oocytes were retrieved from 8-10-week-old mice and fertilized using IVF. The embryos were divided into 4 groups and exposed to increasing BPA concentrations (10 - 200 µM) for 18 hours, then were graded daily based on morphological appearance and development. A subgroup of the treated embryos (n = 10/group) were further evaluated for induction of apoptosis, overproduction of ROS, and zinc depletion. Mouse oocytes were treated with BPA (up to 300 µΜ), then, using RT-PCR, we preformed gene expression studies for AZGP1, an important gene in zinc homeostasis. Cultured day 5 mouse embryos that were exposed to BPA concentrations > 50 µM had fewer progressions to blastocysts, lower blastocyst grades, and more were arrested as compared to controls (p<0.05). Enhancement of ROS production and increased apoptosis associated with zinc depletion were evident in embryos treated with increasing concentrations of BPA (p<0.05). Gene expression studies showed downregulation of the AZGP1 gene in oocytes exposed to high BPA concentrations (p<0.01). This work may help women experiencing infertility that were exposed to high levels of BPA, as well as women suffering from diseases associated with zinc deficiency.