Environmentally relevant exposure to dibutyl phthalate disrupts DNA damage repair gene expression in the mouse ovary†.

Abstract

Phthalates have a history of reproductive toxicity in animal models and associations with adverse reproductive outcomes in women. Human exposure to dibutyl phthalate (DBP) occurs via consumer products (7-10μg/kg/day) and medications (1-233μg/kg/day). Most DBP toxicity studies have focused on high supraphysiological exposure levels; thus, very little is known about exposures occurring at environmentally relevant levels. CD-1 female mice (80days old) were treated with tocopherol-stripped corn oil (vehicle control) or DBP dissolved in oil at environmentally relevant (10 and 100μg/kg/day) or higher (1000μg/kg/day) levels for 30days to evaluate effects on DNA damage response (DDR) pathway genes and folliculogenesis. DBP exposure caused dose-dependent effects on folliculogenesis and gene expression. Specifically, animals exposed to the high dose of DBP had more atretic follicles in their ovaries, while in those treated with environmentally relevant doses, follicle numbers were no different from vehicle-treated controls. DBP exposure significantly reduced the expression of DDR genes including those involved in homologous recombination (Atm, Brca1, Mre11a, Rad50), mismatch repair (Msh3, Msh6), and nucleotide excision repair (Xpc, Pcna) in a dose-specific manner. Interestingly, staining for the DNA damage marker, γH2AX, was similar between treatments. DBP exposure did not result in differential DNA methylation in the Brca1 promoter but significantly reduced transcript levels for the maintenance DNA methyltransferase, Dnmt1, in the ovary. Collectively, these findings show that oral exposure to environmentally relevant levels of DBP for 30days does not significantly impact folliculogenesis in adult mice but leads to aberrant ovarian expression of DDR genes.