Effects of Mono-2-ethylhexyl Phthalate (MEHP) on Cell Death in the Human Trophoblast Cell Line, HTR-8/SV neo

Abstract

Di-(2-ethylhexyl) phthalate (DEHP), a plasticizer found in polyvinyl chloride products is currently the most commonly used plasticizer, with two million tons of it being manufactured every year (Koch, Drexler, and Angerer, 2002). DEHP is found in everyday items such as clothing, pharmaceutical items, chemicals, building materials, food packaging materials, and toys. Phthalates have become such a worldwide concern that in 2005, the European Union approved the ban of toxic phthalates in toys and other childcare items (Schettler et al., 2005). DEHP is not covalently linked to plastic, meaning that it can leach out and contaminate the external environment (Martino-Andrade and Chahoud, 2009). Therefore, it is not surprising that DEHP can be found in household dust and air. The main route of human exposure to DEHP is through ingestion; however, it is possible to be exposed to DEHP through inhalation and dermal contact as well. The active metabolite of DEHP is mono-(2-ethylhexyl) phthalate (MEHP), which is formed when DEHP is rapidly hydrolyzed by lipases in the gut (Tomita et al., 1986). In a recent National Health and Nutrition Examination Survey (NHANES) cohort study, MEHP was found in nearly all of the urine samples analyzed. MEHP is rapidly metabolized in the body and has a half life of less than one day; therefore, the fact that MEHP was found in almost all of the urine samples in the study suggests daily, widespread population exposure. (Jepsen et al., 2004). To date, most research on the adverse effects of MEHP has focused on the male reproductive system. Many studies confirm that exposure to MEHP in males can lead to testicular atrophy, decreased testicular weight, and decreased testosterone levels ("Phthalates", 2010). Despite the large amounts of research done on MEHP's effect on the male reproductive system, research on MEHP's effect on the female reproductive system is extremely sparse (Meeker et al., 2009). Thus far, researchers have found a correlation between increased phthalate exposure and a higher risk for preterm birth (Meeker et al., 2009) ; however, the mechanisms in which this may occur has not yet been explored in depth. One mechanism of MEHP toxicity is through apoptosis. Park et al. (2001) showed that administration of MEHP in male rats leads to a significant increase in apoptosis in spermatogenic cells. In addition, Andriana et al.(2004) found in spermatogenic and Sertoli cells that at lower concentrations, MEHP treatment leads to apoptosis and at higher concentrations MEHP activates necrotic pathways. Many studies have been done focusing on the effect of phthalate stimulated cell death in males. Therefore, the focus of this study was to determine whether or not cell death could also be a mode of MEHP toxicity in females. The model used in this study is a chorionic extravillous trophoblast cell line, HTR8-Svneo (Graham et al., 1993). Extravillous trophoblast cells are needed for deep invasion of the placental bed and are essential for proper placental function and for establishing the fetal-maternal interface (Pijenenborg et al., 2010). If cell death were shown to be a mode of MEHP toxicity in females, it could prove to be detrimental. Apoptosis has been shown to impair trophoblast invasion in to the placenta, causing adverse effects such as preeclampsia and intrauterine growth restriction (Kadyrov et al., 2006). Therefore, it is imperative to study the effects that MEHP may have on trophoblast cell death. The purpose of this study is to investigate MEHP stimulated cell death in human extravillous chorionic trophoblast cells by investigating the two cell death mechanisms, apoptosis and necrosis. I hypothesize that MEHP will induce apoptosis in extravillous chorionic trophoblast cells.