Low Environmental Contamination by Lead in Pregnant Women: Effect on Calcium Transfer in Human Placental Syncytiotrophoblasts

Abstract

There is an extensive literature on the neurotoxic effects of lead (Pb) on the developing fetus; however, little is known about the mechanisms of action at low levels. Heavy metals are known to affect calcium (Ca^{2 +} ) homeostasis through perturbation of Ca^{2 +} channels and pumps and interference with protein kinase C (PKC) and Ca^{2 +} binding protein (CaBP). During pregnancy, placental Ca^{2 +} exchange is one of the most important mechanisms for fetal survival. This ion is an essential element for healthy fetal growth and development. The aim of the present study was to determine the influence of low maternal blood Pb levels on Ca^{2 +} levels in serum and placenta and placental Ca^{2 +} transfer. Blood samples (maternal and cord) and placental tissue were obtained at birth from 30 women residing in southwest Quebec. Total ²⁺and Pb levels were measured in maternal and umbilical cord samples and placental tissue at term. The placentas were taken for trophoblast cell isolation and Ca^{2 +} incorporation kinetic experiments. Data showed that Ca^{2 +} in maternal blood did not influence Ca^{2 +} uptake by syncytiotrophoblast. However, although maternal and cord blood Pb levels were low, maternal blood Pb concentration was significantly linked to a decrease in Ca^{2 +} uptake by syncytiotrophoblast. This suggests that exposure to very levels of Pb significantly modifies Ca^{2 +} transfer in syncytiotrophoblasts.

This research was funded by the Toxic Substances Research Initiative (TSRI) of Health Canada. We acknowledge the contributions of Caroline Müller (from the Biological Sciences Department of Université du Québec à Montréal), Louise Laplante and Denise Vachon for taking blood samples for the first and the second pregnancy trimesters, and the nurses of the Centre Hospitalier Régional du Suroît (CHRS) for their help. We also thank A. Smargiassi, G. St-Amour, and J. Morrissette, who administered the questionnaires.