Mono-(2-ethylhexyl) phthalate (MEHP), the active metabolite of di-(2-ethylhexyl) phthalate (DEHP), is a plasticizer with endocrine disruptor activity that has been shown to stimulate basal steroid biosynthesis in Leydig cells. The mechanism by which it does so is unknown. Using MA-10 mouse tumor Leydig cells, we assessed the effects of MEHP on reactive oxygen species (ROS) levels, and on the signal transduction pathways that mobilize cholesterol. Exposure to 0–300 μM MEHP stimulated basal progesterone production in a dose-dependent manner. Progesterone stimulation was correlated with increases in the phosphorylation of hormone-sensitive lipase (HSL; aka cholesteryl ester hydrolase), which is involved in the production of free cholesterol, and of steroidogenic acute regulatory (STAR) protein expression. Co-treating MA-10 cells with MEHP and the ROS scavenger N-acetyl cysteine (NAC) blocked the activation of HSL, blunted MEHP-induced STAR, and reduced basal progesterone formation. These observations suggest that ROS generation by MEHP leads to activation of HSL and increase in STAR which, together, result in increased free-cholesterol bioavailability and progesterone formation.
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