Placental Toxicology of Pesticides

The placenta used to be regarded as an organ protecting the fetus from exposure to toxic chemicals. However, we now know that xenobiotics can cross through the placenta and enter the fetal blood stream (Barr et al., 2007). In addition, some toxicants may accumulate in the placenta and potentially affect its development or function. Therefore, understanding how the placenta affects xenobiotics, and conversely, what the latter do to the placenta, should provide a basis for the use of this organ as a tool to investigate and predict some aspects of developmental toxicity (Myllynen et al., 2005). In this sense, the placenta is a key tool for biomonitoring xenobiotic exposure. Furthermore, it provides a large sample for analysis and is the most accessible and readily available component of the triad motherinfant-placenta. The cumulative effects of pregnancy-related events are shown by the placenta, which also reflects the intrauterine environment, and may be examined to a degree that is usually impossible in the infant. A critical issue for placenta toxicological analysis is the availability and appropriate use of biomarkers, as these provide measures of the exposure, toxic effects and individual susceptibility to toxicants. However, as epidemiological studies cannot resolve all the confounding factors, further experiments are also necessary. Thus, in vitro, in vivo and ex vivo models have been used in attempts to elucidate the toxicology of the toxicants occurring in the human placenta. Nevertheless, these approaches have their limitations. Despite having common physiological functions, placentas from different species are not homogeneous in their morphology, transport or metabolism of xenobiotics, thereby making it difficult to obtain a good representative model of the human placenta (Prouillac & Lecoeur, 2010). Moreover, changes in the placental function due to chemical exposure may also depend on the gestational period in which this occurs. Consequently, little research has been carried out into the biochemical and molecular toxicity of xenobiotics in human placenta.