Estrogenic action by tris(2,6-dimethylphenyl) phosphate, an impurity in resorcinol bis[di(2,6-dimethylphenyl) phosphate] flame retardant formulations, impairs the development of female reproductive functions

Abstract Background Developmental exposure to environmental chemicals with estrogen-like activity has been suspected to permanently impair women’s health. Objectives In this study, we used a mouse model to evaluate whether a chemical having putative estrogen-like action detected by in vitro study, namely tris(2,6-dimethylphenyl) phosphate (TDMPP) impairs sexual differentiation of the brain. Methods To induce developmental exposure, TDMPP was administered subcutaneously to dams from gestational day 14 to parturition and to pups from postnatal day 0 to 9 at two different doses (TDMPP-high and TDMPP-low groups, respectively). To compare the results between TDMPP and typical estrogen exposures, 17β-estradiol was administered at two different doses on the same treatment schedule (E2-low and E2-high groups, respectively). A vehicle control group was formed by administering an equivalent volume of sesame oil to dams and to pups. Results Although there was no specific impairment in female ovary morphology, precocious puberty, detected by vaginal opening, and irregular estrous cycles, detected by vaginal cytology after sexual maturation, were found in TDMPP- and E2-treated groups, but not in the vehicle control group. In addition, lower lordosis response during reproductive behavioral tests was found in TDMPP- or E2-treated groups. To further clarify whether TDMPP directly affects sexual differentiation of the brain, we evaluated the transfer of TDMPP into the brain and the formation of sexual dimorphic nuclei. We detected a certain amount of TDMPP and its metabolites in the mouse brain after treatment, and masculinization of sexual dimorphic nuclei in the hypothalamus of female mice, suggesting the direct impact of TDMPP in developing brain. Discussion Taken together, the experimental evidence demonstrates that TDMPP directly enters the fetal and neonatal brain, inducing changes of sex-related brain structures, and impairing female reproductive functions.