Virtually all US inhabitants carry detectable levels of bisphenol-A (BPA) in their tissues. Its estrogenic properties have been recognized for decades. Although BPA had been viewed as weakly estrogenic in the past, it is now likely that exposure to low doses of BPA can produce disruptive effects in androgen and estrogen responsive tissues. Among the potential health consequences of BPA exposure of concern, interference with the normal processes of brain development is viewed as one of the most worrisome. These concerns arise because the developing nervous system is a key target of BPA;gonadal hormone levels mold brain organization, particularly sexual differentiation, during perinatal development. Aberrant brain development is the basis of aberrant behavioral function, whose effects extend across the entire lifespan, even into the realm of neurodegenerative disease. Despite the growing volume of reports on the neurobehavioral consequences of early developmental exposure to BPA, the literature remains fragmentary and somewhat inconsistent. Among the reasons are: data too limited to allow for characterization of dose-response relationships, the tendency to focus on isolated outcome(s), and, glaringly, the absence of definitive information on humans. This proposal confronts these limitations in several ways. (1) It coordinates, to the degree possible, human and animal behavioral indices. (2) It measures exposure biomarkers in both species (in urine, blood, or both). (3) It encompasses several behavioral endpoints, including cognitive function. (4) It provides mechanistic measures. (5) It includes a range of exposure levels from low to high. The project contains three components. In the human component a cohort of children whose mothers were enrolled in a large prospective study in 2000-2005 and provided samples of blood and urine during mid-pregnancy will be contacted again. Previously urinary phthalate metabolites were measured in a subset of these samples and significant associations were discovered with male genital development. A subset of these children were then recontacted at 4-7 years and examined for prenatal phthalate exposure in relation to mother's reports of play behavior, and significant associations (described in this application) were found. The children are now 5-9 years old and mothers will be asked to provide information on their children's cognitive skills, sex-linked play behaviors, social behaviors, and physical activity. These will be examined using stored urine and blood samples, in relation to conjugated and unconjugated BPA, as well as phthalate metabolites when available. In the animal behavior component we will expose rats will be exposed perinatally to BPA and a positive control (DES) and to measure aspects of cognitive function, play behavior, and activity patterns. Conjugated and unconjugated BPA will be determined in rodent serum. In the mechanistic component brain structures and functions especially relevant to sexually dimorphic indices will be assessed. To this end, perinatal exposure to BPA will be related to the volume of two sexually dimorphic brain regions, the anterior ventral periventricular nucleus (AVPV) and the sexually dimorphic nucleus of the preoptic area (SDN-POA) and associated neural markers. The proposed research addresses a question seen by both the public and by scientific review panels as crucial to weighing the risks posed by environmental exposure to BPA. Namely, what are its effects on brain development, and are these gender-specific? By focusing on endpoints recognized as sexually dimorphic, and which arise from sexual differentiation of the brain during early development, a coordinated base of information will ensue that should yield answers to that and related questions in a more definitive manner than has not been possible until now. Data produced will be novel and may not only indicate a new and important endpoint for BPA toxicity based on environmentally relevant levels, but should promote a field that is rather new to environmental health science: use of gender-specific neurodevelopmental endpoints to identify endocrine disruption. Demonstration of differing effects for a currently used (and novel) environmental chemical on male and female developmental endpoints may become a flag for the ability of that chemical to produce endocrine disruption. Moreover, follow-up studies beyond early development may show persistent effects later in life, including potentially aberrant social behaviors, impaired learning and school performance, impaired maternal and child-rearing behaviors and, later, enhanced risks of neurodegenerative disease. These issues are not confined to discussions within the scientific community. The public is an active participant. Pregnant women are especially anxious about exposing their babies to chemicals that may alter brain development. The comprehensive, coordinated body of information this project is designed to procure will provide the basis for decisions by regulatory authorities charged with protecting public health and by women concerned about the future health of their children.
This project will provide unique information on how exposure to bisphenol A (BPA) before birth can alter masculinization and feminization of the brain during prenatal development. Subsequent studies, beyond infancy and childhood, may show persistent effects later in life as well, including potentially aberrant social behaviors, impaired learning and school performance, impaired maternal and child-rearing behaviors and, later, enhanced risks of neurodegenerative disease.
