Revealing mercury species-specific transfer and toxicity mechanisms in placental trophoblasts

Environmental mercury (Hg) follows a biogeochemical cycle resulting in a variety of Hg species. Therefore, human exposure to the three Hg species inorganic Hg via crops and air, methyl Hg through fish consumption and ethyl Hg due to the use as antiseptic agent in medical applications is a rising concern. Especially pregnant women and their developing fetus present a vulnerable population. However, little is known about its transfer and toxicity in placental barrier building cells. Here, Hg species-specific transfer and toxicity in placental trophoblasts, which are the main cell type involved in nutrient transfer, were investigated by using the established BeWo b30 in vitro model. The transfer of inorganic Hg was much lower compared to the organic Hg species and all three species were able to perturb barrier integrity. This was accompanied by a less pronounced cytotoxicity of HgCl₂ compared to the two organic species. The energy charge value indicated an increase for inorganic Hg and a decrease for organic Hg compounds. Regarding antioxidative defense, inorganic Hg elevated GSSG levels, while organic Hg decreased GSH. Activity of antioxidative defense related enzymes showed a decrease upon Hg species treatment and all three species induced both apoptotic and necrotic cell death.