Cadmium disrupts signaling of the hypoxia-inducible (HIF) and transforming growth factor (TGF-β) pathways in placental JEG-3 trophoblast cells via reactive oxygen species

Epidemiologic studies indicate an association between exposure to cadmium (Cd) and placental-related pregnancy disorders. While a precise mechanism is unknown, oxidative imbalance and dysregulation of the hypoxia inducible factor (HIF) and transforming growth factor beta (TGF-beta) pathways have been implicated in placental disease pathogenesis. Here we investigated key oxidative and placentation pathways in JEG-3 placental trophoblast cells treated with Cd alone, environmental water samples predominated by Cd with low concentrations of other metals (e.g. inorganic arsenic (iAs)) collected from a waste-site, and a matched mixture of Cd and iAs prepared in the laboratory. The induction of cytosolic reactive oxygen species (ROS), expression of metallothionein (MT) isoforms, HIF1 alpha and downstream targets, and expression of TGF beta pathway-associated genes and proteins were assessed. Additionally, the effect of pre-treatment with the antioxidant N-acetyl cysteine (NAC) on ROS generation and effects on HIF, MT and TGF-beta signaling pathways was examined. Cd and Cd-mixture treated cells displayed higher levels of ROSs with accompanying disruption of HIF and TGF beta pathway signaling versus controls, with the Cd-mixture eliciting a greater effect. Conversely, pretreatment with NAC reduced Cd-induced ROS production and disruption of HIF, MT and TGF beta pathway signaling. The results indicate that treatment of placental trophoblast cells with Cd results in increased production of ROSs that disrupt placentation pathways involved in disease pathogenesis. Also, co-occurrence of Cd with other toxic metals, particularly arsenic, may induce detrimental health effects that are currently underestimated when analyzed as single metals.