Sex-specific Effects of Endocrine-disrupting Chemicals on Brain Monoamines and Cognitive Behavior

The period of brain sexual differentiation is characterized by the development of hormone-sensitive neural circuits that govern the subsequent presentation of sexually dimorphic behavior in adulthood. Perturbations of hormones by endocrine-disrupting chemicals (EDCs) during this developmental period interfere with an organism's endocrine function and can disrupt the normative organization of male- or female-typical neural circuitry. This is well characterized for reproductive and social behaviors and their underlying circuitry in the hypothalamus and other limbic regions of the brain; however, cognitive behaviors are also sexually dimorphic, with their underlying neural circuitry potentially vulnerable to EDC exposure during critical periods of brain development. This review provides recent evidence for sex-specific changes to the brain's monoaminergic systems (dopamine, serotonin, norepinephrine) after developmental EDC exposure and relates these outcomes to sex differences in cognition such as affective, attentional, and learning/memory behaviors.

Developmental exposure to indoor flame retardants and hypothalamic molecular signatures: Sex-dependent reprogramming of lipid homeostasis

Polybrominated diphenyl ethers (PBDEs) are a class of flame-retardant organohalogen pollutants that act as endocrine/neuroendocrine disrupting chemicals (EDCs). In humans, exposure to brominated flame retardants (BFR) or other environmentally persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and novel organophosphate flame retardants has been associated with increasing trends of diabetes and metabolic disease. However, the effects of PBDEs on metabolic processes and their associated sex-dependent features are poorly understood. The metabolic-disrupting effects of perinatal exposure to industrial penta-PBDE mixture, DE-71, on male and female progeny of C57BL/6N mouse dams were examined in adulthood. Dams were exposed to environmentally relevant doses of PBDEs daily for 10 weeks (p.o.): 0.1 (L-DE-71) and 0.4 mg/kg/d (H-DE-71) and offspring parameters were compared to corn oil vehicle controls (VEH/CON). The following lipid metabolism indices were measured: plasma cholesterol, triglycerides, adiponectin, leptin, and liver lipids. L-DE-71 female offspring were particularly affected, showing hypercholesterolemia, elevated liver lipids and fasting plasma leptin as compared to same-sex VEH/CON, while L- and H-DE-71 male F1 only showed reduced plasma adiponectin. Using the quantitative Folch method, we found that mean liver lipid content was significantly elevated in L-DE-71 female offspring compared to controls. Oil Red O staining revealed fatty liver in female offspring and dams. General measures of adiposity, body weight, white and brown adipose tissue (BAT), and lean and fat mass were weighed or measured using EchoMRI. DE-71 did not produce abnormal adiposity, but decreased BAT depots in L-DE-71 females and males relative to same-sex VEH/CON. To begin to address potential central mechanisms of deregulated lipid metabolism, we used RT-qPCR to quantitate expression of hypothalamic genes in energy-regulating circuits that control lipid homeostasis. Both doses of DE-71 sex-dependently downregulated hypothalamic expression of Lepr, Stat3, Mc4r, Agrp, Gshr in female offspring while H-DE-71 downregulated Npy in exposed females relative to VEH/CON. In contrast, exposed male offspring displayed upregulated Stat3 and Mc4r. Intestinal barrier integrity was measured using FITC-dextran since it can lead to systemic inflammation that leads to liver damage and metabolic disease, but was not affected by DE-71 exposure. These findings indicate that maternal transfer of PBDEs disproportionately endangers female offspring to lipid metabolic reprogramming that may exaggerate risk for adult metabolic disease.

Uncovering Evidence for Endocrine-Disrupting Chemicals That Elicit Differential Susceptibility through Gene-Environment Interactions

Exposure to endocrine-disrupting chemicals (EDCs) is linked to myriad disorders, characterized by the disruption of the complex endocrine signaling pathways that govern development, physiology, and even behavior across the entire body. The mechanisms of endocrine disruption involve a complex system of pathways that communicate across the body to stimulate specific receptors that bind DNA and regulate the expression of a suite of genes. These mechanisms, including gene regulation, DNA binding, and protein binding, can be tied to differences in individual susceptibility across a genetically diverse population. In this review, we posit that EDCs causing such differential responses may be identified by looking for a signal of population variability after exposure. We begin by summarizing how the biology of EDCs has implications for genetically diverse populations. We then describe how gene-environment interactions (GxE) across the complex pathways of endocrine signaling could lead to differences in susceptibility. We survey examples in the literature of individual susceptibility differences to EDCs, pointing to a need for research in this area, especially regarding the exceedingly complex thyroid pathway. Following a discussion of experimental designs to better identify and study GxE across EDCs, we present a case study of a high-throughput screening signal of putative GxE within known endocrine disruptors. We conclude with a call for further, deeper analysis of the EDCs, particularly the thyroid disruptors, to identify if these chemicals participate in GxE leading to differences in susceptibility.

Effects of Chronic Dietary Exposure to Phytoestrogen Genistein on Uterine Morphology in Mice

Genistein is naturally occurring in plants and binds to estrogen receptors. Humans are mainly exposed through diet, but the use of supplements is increasing as genistein is claimed to promote health and alleviate menopausal symptoms. We analyzed diverse uterine features in adult mice chronically fed genistein for different times. The luminal epithelium height was increased in females treated with 500 and 1000 ppm at PND 95, and the width of the outer myometrium was increased in females treated with 1000 ppm at PND 65 compared to that in controls. An increase in proliferation was noted in the inner myometrium layer of animals exposed to 300 ppm genistein at PND 185 compared to that in controls. Luminal hyperplasia was greater in the 1000 ppm group at PND 65, 95, and 185, although not statistically different from control. These results indicate that genistein may exert estrogenic activity in the uterus, without persistent harm to the organ.

Ambient Exposure to Agricultural Pesticides during Pregnancy and Risk of Cerebral Palsy: A Population-Based Study in California

Cerebral palsy (CP) is the most common neuro-motor disability in young children. Disruptions of maternal hormone function during pregnancy have been linked to CP risk. We investigated whether prenatal exposure to pesticide compounds with endocrine-disrupting action affect CP risk. We conducted a case-control study of 3905 CP cases and 39,377 controls born between 1998 and 2010 in California to mothers who lived in proximity (within 2 km) to any agricultural pesticide application recorded in the California Pesticide Use Reporting (PUR) system. We focused on 23 pesticides considered endocrine disruptors that are frequently used, and we found that exposure to any of the 23 pesticides in the first trimester was associated with elevated CP risks in female offspring (OR = 1.19; 95% CI: 1.05-1.35) but not males (OR = 0.99; 95% CI: 0.89-1.09) compared to the unexposed offspring. Positive associations were estimated for 15 pesticides suspected to affect the estrogen and 7 pesticides suspected to affect the thyroid hormone system. Our study suggests that first trimester exposure to pesticides that are suspected endocrine disruptors are associated with CP risk in female offspring. Pesticide exposures in early pregnancy may have sex-specific influences on the neuro-motor development of the fetus by interfering with endocrine systems.

Effect of the plastic pollutant bisphenol A on the biology of aquatic organisms: A meta-analysis

Plastic pollution is a global environmental concern. In particular, the endocrine-disrupting chemical bisphenol A (BPA) is nearly ubiquitous in aquatic environments globally, and it continues to be produced and released into the environment in large quantities. BPA disrupts hormone signalling and can thereby have far-reaching physiological and ecological consequences. However, it is not clear whether BPA has consistent effects across biological traits and phylogenetic groups. Hence, the aim of this study was to establish the current state of knowledge of the effect of BPA in aquatic organisms. We show that overall BPA exposure affected aquatic organisms negatively. It increased abnormalities, altered behaviour and had negative effects on the cardiovascular system, development, growth and survival. Early life stages were the most sensitive to BPA exposure in invertebrates and vertebrates, and invertebrates and amphibians seem to be particularly affected. These data provide a context for management efforts in the face of increasing plastic pollution. However, data availability is highly biased with respect to taxonomic groups and traits studies, and in the geographical distribution of sample collection. The latter is the case for both measurements of the biological responses and assessing pollution levels in water ways. Future research effort should be directed towards biological systems, such as studying endocrine disruption directly, and geographical areas (particularly in Africa and Asia) which we identify to be currently undersampled.

A Novel Action of Endocrine-Disrupting Chemicals on Wildlife; DDT and Its Derivatives Have Remained in the Environment

Huge numbers of chemicals are released uncontrolled into the environment and some of these chemicals induce unwanted biological effects, both on wildlife and humans. One class of these chemicals are endocrine-disrupting chemicals (EDCs), which are released even though EDCs can affect not only the functions of steroid hormones but also of various signaling molecules, including any ligand-mediated signal transduction pathways. Dichlorodiphenyltrichloroethane (DDT), a pesticide that is already banned, is one of the best-publicized EDCs and its metabolites have been considered to cause adverse effects on wildlife, even though the exact molecular mechanisms of the abnormalities it causes still remain obscure. Recently, an industrial raw material, bisphenol A (BPA), has attracted worldwide attention as an EDC because it induces developmental abnormalities even at low-dose exposures. DDT and BPA derivatives have structural similarities in their chemical features. In this short review, unclear points on the molecular mechanisms of adverse effects of DDT found on alligators are summarized from data in the literature, and recent experimental and molecular research on BPA derivatives is investigated to introduce novel perspectives on BPA derivatives. Especially, a recently developed BPA derivative, bisphenol C (BPC), is structurally similar to a DDT derivative called dichlorodiphenyldichloroethylene (DDE).