Co-exposure to high temperature and mono(2-ethylhexyl) phthalate inhibits mouse antral follicle growth and estradiol synthesis: Phthalate-heat interactions in the ovary

Abstract Humans are ubiquitously exposed to di(2-ethylhexyl) phthalate (DEHP), which is a phthalate plasticizer used in consumer goods that has been identified as a reproductive toxicant. DEHP toxicity is mediated by mono(2-ethylhexyl) phthalate (MEHP), its bioactive metabolite that has been shown to target ovarian processes, including folliculogenesis and steroidogenesis. Simultaneously, humans are ubiquitously exposed to non-chemical stressors like high temperatures, which have also been shown to impair ovarian function. Given the unavoidable exposure to both increasing heat and DEHP, this study tested the hypothesis that exposure to high temperature will exacerbate the negative effects of MEHP exposure on antral follicle function. Antral follicles from CD-1 mice were cultured for 24-96hr with vehicle control (DMSO) or MEHP (0.2-20µg/ml) at a control temperature (CT; 37 °C) or high temperature (HT; 42 °C, 8hr per 24hr) to assess effects on follicle growth and steroidogenesis. Compared to control (CT+DMSO), HT+DMSO and HT+MEHP inhibited the cell cycle and steroidogenic pathway and upregulated follicle-stimulating hormone receptor expression. CT+MEHP, HT+DMSO, and HT+MEHP decreased estradiol levels over time, and HT+DMSO and HT+MEHP also inhibited antral follicle growth compared to CT+DMSO. Therefore, MEHP exposure decreased estradiol levels, while HT exposure and HT+MEHP co-exposure decreased estradiol levels and follicle growth by inhibiting the steroidogenic pathway and cell cycle. Further, several significant interactions were identified, providing the first evidence of a phthalate-heat interaction in a mammalian model. Thus, exposure to ubiquitous chemical and non-chemical stressors, like MEHP and HT, disrupt critical ovarian processes and may potentiate ovarian dysfunction when combined.