Profiling the cytotoxic effects of naled and other pesticides in primary human placental cytotrophoblasts

Placental cytotrophoblasts (CTBs) play critical roles in placentation, including implantation, barrier function, uterine invasion, and maternal endovascular remodeling. Impairment of CTB function is linked with common pregnancy complications. In this context, environmental chemicals can contribute to CTB dysfunction. Evidence suggests that prenatal exposures to pesticides affect the placenta and contribute to pregnancy complications and adverse developmental outcomes. Despite being restricted in the European Union, dimethyl 1,2-dibromo-2,2 dichloroethyl phosphate (naled), a common organophosphate pesticide, is widely used in vector control and agriculture in the United States and abroad. In this study, we investigated the placentotoxic activity of naled in second-trimester primary human CTBs. We assessed the cytotoxicity of naled and 67 pesticides using the neutral red lysosomal cellular uptake assay and the lactate dehydrogenase release assay. Naled was one of the most toxic compounds (∼15th percentile), impairing viability and inducing cell death at levels similar to federally restricted pesticides (methoxychlor and triclosan) and at lower concentrations than other commonly used compounds in the organophosphate class (e.g. chlorpyrifos, dichlorvos, and malathion). Naled significantly altered expression of 297 genes (unadjusted P < 0.01, absolute fold change >1.5 with 10 or 30 µM), including molecules important in regulating the environmental stress response and developmental processes. Using a benchmark modeling approach, we identified specific genes and related pathways that may serve as early indicators of naled-response in CTBs at physiologically relevant exposure levels. Thus, our data suggest that naled may alter critical human CTB functions in vivo.