Ovarian toxicity of 4-vinylcyclohexene diepoxide: a mechanistic model

Female mammals are born with a finite number of ovarian primordial follicles that cannot be regenerated; thus, chemicals that destroy oocytes contained in these follicles can produce premature ovarian failure (early menopuase in women). Exposure of women to known ovotoxicants, such as contaminants in cigarette smoke, is associated with early menopause. Thus, the potential risks posed by ovotoxic chemicals is of concern. Our studies have focused on the environmental chemical 4-vinylcyclohexene (VCH), which is produced during the manufacture of rubber tires, flame retardants, insecticides, plasticizers, and antioxidants. Dosing of female rats and mice with the ovotoxic diepoxide metabolite of VCH, 4-vinylcyclohexene diepoxide (VCD), for 30 days destroyed the majority of ovarian primordial follicles. Using VCD in rats as a generalized model for ovotoxicity, we determined that 1) repeated daily dosing is required, 2) cell death is via apoptosis, and 3) altered expression of specific genes is involved. An integrated approach at the morphologic, biochemical, and molecular level was used to support these conclusions. Studies in isolated rat small preantral follicles (targeted for VCD-induced ovotoxicity) focused on the role of cell death genes, mitochondrion-associated events, and VCD metabolism. We also evaluated how this information relates to human risk for early menopause. These animal research results provide a better understanding of the potential risk of human exposure to environmental ovarian toxicants and greater insight as to the impact of these toxicants on reproductive health in women.