Early maturation of gonadotropin-releasing hormone secretion and sexual precocity after exposure of infant female rats to estradiol or dichlorodiphenyltrichloroethane

A systematic review of association between use of hair products and benign and malignant gynecological conditions

Hair products often contain chemicals like para-phenylenediamine (PPD) and endocrine-disrupting chemicals (EDCs); giving rise to concerns about the possible adverse effects such as hormonal disturbances and carcinogenicity. The objective of this systematic review was to evaluate the association between the use of different hair products and benign and malignant gynecological conditions. Studies were identified from three databases including PubMed, Embase, and Scopus, and evaluated in accordance with PRISMA guidelines. The risk of bias was assessed using the Newcastle-Ottawa Scale. A total of 17 English-language studies met the inclusion criteria. Associations of hair relaxer or hair dye use with breast and ovarian cancer were observed in at least one well-designed study, but these findings were not consistent across studies. Further sub-analysis showed 1.08 times (95 % CI: 1.01-1.15) increased risk of breast cancer in females with permanent hair dye use. Chang et al. reported strong association between uterine cancer risk and hair relaxer use (HR 1.8, 95 % CI: 1.12-2.88), with no observed association with hair dye use. Studies conducted by Wise et al. and James-Todd et al. for benign gynecological conditions; including uterine leiomyoma (IRR 1.17, 95 % CI: 1.06-1.30), early onset of menarche (RR 1.4, 95 % CI: 1.1-1.9), and decreased fecundability (FR 0.89, 95 % CI: 0.81-0.98) revealed positive associations with hair relaxer use, but these findings were based on small sample sizes. In summary, the available evidence regarding personal use of hair products and gynecological conditions is insufficient to determine whether a positive association exists.

Association between exposure to persistent organic pollutants and pubertal timing in boys and girls: A systematic review and meta-analysis

In recent years, the phenomenon of abnormal pubertal timing in children has become increasingly common worldwide. Persistent organic pollutants (POPs) may be one of the risk factors contributing to this phenomenon, but the relationship between them is unclear based on current evidence. The purpose of this study was to determine the association of POPs exposure with pubertal timing in girls and boys by conducting a systematic review and meta-analysis. We searched PubMed and Embase databases for studies before June 1, 2023. Meta-analysis was performed by pooling relative risk (RR) or odds ratio (OR) or prevalence ratio (PR) or hazard ratio (HR) estimates with 95 % confidence intervals (CIs). Subgroup analysis, publication bias assessment and sensitivity analysis were also carried out. A total of 21 studies were included, involving 2479 boys and 8718 girls. The results of meta-analysis showed that exposure to POPs was significantly associated with delayed pubertal timing in girls (RR: 0.85; 95 % CI: 0.79-0.91; p < 0.001). There was no statistically significant association between exposure to POPs and pubertal timing in boys (RR: 1.18; 95 % CI: 0.99-1.40; p = 0.070). Subgroup analysis showed that there may be gender differences in the effects of exposure to POPs on pubertal timing. Our results suggested that exposure to POPs could delay pubertal timing in girls. However, based on current evidence, no significant association was found between POPs exposure and pubertal timing in boys.

Oestrogens and progesterone in human milk and their effects on infant health outcomes: A narrative review

Human milk (HM) is a complex biological system that contains a wide range of bioactive components including oestrogens and progesterone. Whilst maternal oestrogens and progesterone concentrations drop rapidly after birth, they remain detectable in HM across lactation. Phytoestrogens and mycoestrogens, which are produced by plants and fungi, are also present in HM and can interact with oestrogen receptors to interfere with normal hormone functions. Despite the potential impact of HM oestrogens and progesterone on the infant, limited research has addressed their impact on the growth and health of breastfed infants. Furthermore, it is important to comprehensively understand the factors that contribute to these hormone levels in HM, in order to establish effective intervention strategies. In this review, we have summarized the concentrations of naturally occurring oestrogens and progesterone in HM from both endogenous and exogenous sources and discussed both maternal factors impacting HM levels and relationships with infant growth.

Bisphenol S induces oxidative stress-mediated impairment of testosterone synthesis by inhibiting the Nrf2/HO-1 signaling pathway

Bisphenol S (BPS) is an environmental endocrine disruptor widely used in industrial production. BPS induces oxidative stress and exhibits male reproductive toxicity in mice, but the mechanisms by which BPS impairs steroid hormone synthesis are not fully understood. Nuclear factor erythroid 2-related factor 2(Nrf2)/HO-1 signaling is a key pathway in improving cellular antioxidant defense capacities. Therefore, this study explored the effects of exposure to BPS on testosterone synthesis in adult male mice and its mechanisms with regard to the Nrf2/HO-1 signaling pathway. Adult male C57BL/6 mice were orally exposed to BPS (2, 20, and 200 mg/kg BW) with sesame oil as a vehicle (0.1 ml/10 g BW) per day for 28 consecutive days. The results showed that compared with the control group, serum testosterone levels were substantially reduced in the 20 and 200 mg/kg BPS treatment groups, and testicular testosterone levels were reduced in all BPS treatment groups. These changes were accompanied by a prominent decrease in the expression levels of testosterone synthesis-related enzymes (STAR, CYP11A1, CYP17A1, HSD3B1, and HSD17B3) in the mouse testis. In addition, BPS induced oxidative stress in the testis by upregulating the messenger RNA and protein levels of Keap1 and downregulating the levels of Nrf2, HO-1, and downstream antioxidant enzymes (CAT, SOD1, and Gpx4). In summary, our results indicate that exposure of adult male mice to BPS can inhibit Nrf2/HO-1 signaling and antioxidant enzyme activity, which induces oxidative stress and thereby may impair testosterone synthesis in testicular tissues, leading to reproductive damage.

Age at menarche and chemical exposure: per- and polyfluoroalkyl substances (PFAS), dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), and polychlorinated biphenyls (PCBs)

CONTEXT

Humans are now exposed to a multitude of chemicals throughout the life course, some of which may affect growth and development owing to their endocrine-like activity.

OBJECTIVE

To assess the relationship of suspect toxicants to maturation, specifically to age at menarche.

METHODS

We conducted two systematic reviews of age at menarche and PFOA, PFOS, PCBs and DDE/DDT based on publications indexed by pubmed.

RESULTS

16 unique reports were identified. Most studies of PFOA and PFOS reported either no association or delays in the age at menarche; only one reported an earlier age. Studies of DDT and DDE were more mixed. Reports on PCBs varied by PCB congener group with an equal number of them reporting delays and no association but one an acceleration. Sources of variation in results include the timing of exposure assessment (prenatal vs. postnatal), level of the toxicant, and sample size. No obvious pattern to the variation in results could be tied to those sources of variation.

CONCLUSION

The absence of consistent evidence from multiple reports of earlier age at menarche suggests that these toxicants may not be responsible for accelerated sexual maturation in girls. However, human populations naturally vary in the variety and levels of exposure, making the comparison of studies difficult. Further, studies vary in methodology, complicating aggregation of results and generalisations.

Perinatal exposure to the fungicide ketoconazole alters hypothalamic control of puberty in female rats

INTRODUCTION

Estrogenic endocrine disrupting chemicals (EDCs) such as diethylstilbestrol (DES) are known to alter the timing of puberty onset and reproductive function in females. Accumulating evidence suggests that steroid synthesis inhibitors such as ketoconazole (KTZ) or phthalates may also affect female reproductive health, however their mode of action is poorly understood. Because hypothalamic activity is very sensitive to sex steroids, we aimed at determining whether and how EDCs with different mode of action can alter the hypothalamic transcriptome and GnRH release in female rats.

DESIGN

Female rats were exposed to KTZ or DES during perinatal (DES 3-6-12μg/kg.d; KTZ 3-6-12mg/kg.d), pubertal or adult periods (DES 3-12-48μg/kg.d; KTZ 3-12-48mg/kg.d).

RESULTS

Ex vivo study of GnRH pulsatility revealed that perinatal exposure to the highest doses of KTZ and DES delayed maturation of GnRH secretion before puberty, whereas pubertal or adult exposure had no effect on GnRH pulsatility. Hypothalamic transcriptome, studied by RNAsequencing in the preoptic area and in the mediobasal hypothalamus, was found to be very sensitive to perinatal exposure to all doses of KTZ before puberty with effects persisting until adulthood. Bioinformatic analysis with Ingenuity Pathway Analysis predicted "Creb signaling in Neurons" and "IGF-1 signaling" among the most downregulated pathways by all doses of KTZ and DES before puberty, and "PPARg" as a common upstream regulator driving gene expression changes. Deeper screening ofRNAseq datasets indicated that a high number of genes regulating the activity of the extrinsic GnRH pulse generator were consistently affected by all the doses of DES and KTZ before puberty. Several, including MKRN3, DNMT3 or Cbx7, showed similar alterations in expression at adulthood.

CONCLUSION

nRH secretion and the hypothalamic transcriptome are highly sensitive to perinatal exposure to both DES and KTZ. The identified pathways should be exploredfurther to identify biomarkers for future testing strategies for EDC identification and when enhancing the current standard information requirements in regulation.

Perinatal exposure to low doses of cypermethrin induce the puberty-related hormones and decrease the time to puberty in the female offspring

Pyrethroid insecticides are ubiquitously detected in environmental media, food, and urine samples. Our previous epidemiological study reported a correlation between increased pyrethroid exposure and delayed pubertal development in Chinese girls. In this study, we further investigated the effects of perinatal exposure to low doses of cypermethrin (CP) on pubertal onset and hypothalamic-pituitary-ovarian axis in the female mice offspring. The treatment of CP with 60 μg/kg/day from gestation day 6 (GD6) to postnatal day 21 (PND21) significantly decreased the time to puberty in the female offspring. Exposure of CP increased the serum levels of gonadotropin-releasing hormone (GnRH) and the expression of GnRH genes in a dose-dependent manner in the female offspring. CP also induced the serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), as well as the expression of gonadotropin subunit genes [LHβ, FSHβ, and chorionic gonadotropin α (Cgα)]. Furthermore, CP induced serum estradiol (E₂) levels and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in the ovary. In accordance with the in vivo tests, administration of CP (6.7, 20, and 60 μg/L) stimulated a dose-dependent increase in the synthesis and secretion of the puberty-related hormones in the explants of hypothalamus, pituitary, and ovary. The interference with calcium channels in the ovary may be responsible for CP-induced pubertal onset. Our study provided evidence that perinatal exposure to low doses of CP induced puberty-related hormones and decreased the time to puberty in the female offspring.

Early programming of reproductive health and fertility: novel neuroendocrine mechanisms and implications in reproductive medicine

BACKGROUND

According to the Developmental Origins of Health and Disease (DOHaD) hypothesis, environmental changes taking place during early maturational periods may alter normal development and predispose to the occurrence of diverse pathologies later in life. Indeed, adverse conditions during these critical developmental windows of high plasticity have been reported to alter the offspring developmental trajectory, causing permanent functional and structural perturbations that in the long term may enhance disease susceptibility. However, while solid evidence has documented that fluctuations in environmental factors, ranging from nutrient availability to chemicals, in early developmental stages (including the peri-conceptional period) have discernible programming effects that increase vulnerability to develop metabolic perturbations, the impact and eventual mechanisms involved, of such developmental alterations on the reproductive phenotype of offspring have received less attention.

OBJECTIVE AND RATIONALE

This review will summarize recent advances in basic and clinical research that support the concept of DOHaD in the context of the impact of nutritional and hormonal perturbations, occurring during the periconceptional, fetal and early postnatal stages, on different aspects of reproductive function in both sexes. Special emphasis will be given to the effects of early nutritional stress on the timing of puberty and adult gonadotropic function, and to address the underlying neuroendocrine pathways, with particular attention to involvement of the Kiss1 system in these reproductive perturbations. The implications of such phenomena in terms of reproductive medicine will also be considered.

SEARCH METHODS

A comprehensive MEDLINE search, using PubMed as main interface, of research articles and reviews, published mainly between 2006 and 2021, has been carried out. Search was implemented using multiple terms, focusing on clinical and preclinical data from DOHaD studies, addressing periconceptional, gestational and perinatal programming of reproduction. Selected studies addressing early programming of metabolic function have also been considered, when relevant.

OUTCOMES

A solid body of evidence, from clinical and preclinical studies, has documented the impact of nutritional and hormonal fluctuations during the periconceptional, prenatal and early postnatal periods on pubertal maturation, as well as adult gonadotropic function and fertility. Furthermore, exposure to environmental chemicals, such as bisphenol A, and maternal stress has been shown to negatively influence pubertal development and gonadotropic function in adulthood. The underlying neuroendocrine pathways and mechanisms involved have been also addressed, mainly by preclinical studies, which have identified an, as yet incomplete, array of molecular and neurohormonal effectors. These include, prominently, epigenetic regulatory mechanisms and the hypothalamic Kiss1 system, which likely contribute to the generation of reproductive alterations in conditions of early nutritional and/or metabolic stress. In addition to the Kiss1 system, other major hypothalamic regulators of GnRH neurosecretion, such as γ-aminobutyric acid and glutamate, may be targets of developmental programming.

WIDER IMPLICATIONS

This review addresses an underdeveloped area of reproductive biology and medicine that may help to improve our understanding of human reproductive disorders and stresses the importance, and eventual pathogenic impact, of early determinants of puberty, adult reproductive function and fertility.

A Putative Adverse Outcome Pathway Network for Disrupted Female Pubertal Onset to Improve Testing and Regulation of Endocrine Disrupting Chemicals

The average age for pubertal onset in girls has declined over recent decades. Epidemiological studies in humans and experimental studies in animals suggest a causal role for endocrine disrupting chemicals (EDCs) that are present in our environment. Of concern, current testing and screening regimens are inadequate in identifying EDCs that may affect pubertal maturation, not least because they do not consider early-life exposure. Also, the causal relationship between EDC exposure and pubertal timing is still a matter of debate. To address this issue, we have used current knowledge to elaborate a network of putative adverse outcome pathways (pAOPs) to identify how chemicals can affect pubertal onset. By using the AOP framework, we highlight current gaps in mechanistic understanding that need to be addressed and simultaneously point towards events causative of pubertal disturbance that could be exploited for alternative test methods. We propose 6 pAOPs that could explain the disruption of pubertal timing by interfering with the central hypothalamic trigger of puberty, GnRH neurons, and by so doing highlight specific modes of action that could be targeted for alternative test method development.

Effects on Puberty of Nutrition-Mediated Endocrine Disruptors Employed in Agriculture

Pesticide residues are largely found in daily consumed food because of their extensive use in farming and their long half-life, which prolongs their presence in the environment. Many of these pesticides act as endocrine-disrupting chemicals after pre- or postnatal exposure, significantly affecting, among other things, the time of puberty onset, progression, and completion. In humans, precocious or delayed puberty, and early or delayed sexual maturation, may entail several negative long-term health implications. In this review, we summarize the current evidence on the impact of endocrine-disrupting pesticides upon the timing of the landmarks of female and male puberty in both animals (vaginal opening, first estrus, and balanopreputial separation) and humans (thelarche, menarche, gonadarche). Moreover, we explore the possible mechanisms of action of the reviewed endocrine-disrupting pesticides on the human reproductive system. Access to safe, healthy, and nutritious food is fundamental for the maintenance of health and wellbeing. Eliminating the presence of hazardous chemicals in largely consumed food products may increase their nutritional value and be proven beneficial for overall health. Consequently, understanding the effects of human exposure to hazardous endocrine-disrupting pesticides, and legislating against their circulation, are of major importance for the protection of health in vulnerable populations, such as children and adolescents.

Menstrual Cycle Patterns and Irregularities in Hired Latinx Child Farmworkers

PURPOSE

This study identifies the menstrual cycle irregularities of Latinx child and adolescent farmworkers.

METHODS

Child and adolescent farmworkers aged 13 to 20 years completed questionnaires about menstrual cycle patterns in 2019, and wore silicone passive collection wristbands for pesticide detection in 2018. Menstrual cycle irregularities were determined from the American College of Obstetricians and Gynecologists committee opinion.

RESULTS

Half of participants experienced any menstrual cycle irregularity; the most frequent irregularities were cycle length (38.6%) and having gone 90 days or more without a menstrual period (20.4%). Pesticides were detected in 92.9% of the wristbands; most participants were exposed to an endocrine disrupting chemical (EDC) pesticide.

CONCLUSION

Half of Latinx children and adolescents hired farmworkers experience irregular menstrual cycles, and most are exposed to EDCs. Inclusion of occupational and menstrual histories in child and adolescent medical visits is critical.

Multi- and Transgenerational Outcomes of an Exposure to a Mixture of Endocrine-Disrupting Chemicals (EDCs) on Puberty and Maternal Behavior in the Female Rat

BACKGROUND

The effects of endocrine-disrupting chemicals (EDCs) on fertility and reproductive development represent a rising concern in modern societies. Although the neuroendocrine control of sexual maturation is a major target of EDCs, little is known about the potential role of the hypothalamus in puberty and ovulation disruption transmitted across generations.

OBJECTIVES

We hypothesized that developmental exposure to an environmentally relevant dose of EDC mixture could induce multi- and/or transgenerational alterations of sexual maturation and maternal care in female rats through epigenetic reprograming of the hypothalamus. We investigated the transmission of a disrupted reproductive phenotype via the maternal germline or via nongenomic mechanisms involving maternal care.

METHODS

Adult female Wistar rats were exposed prior to and during gestation and until the end of lactation to a mixture of the following 13 EDCs: di-n-butyl phthalate (DnBP), di(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA), vinclozolin, prochloraz, procymidone, linuron, epoxynaxole, dichlorodiphenyldichloroethylene, octyl methoxynimmate, 4-methylbenzylidene camphor (4-MBC), butylparaben, and acetaminophen. Perinatally exposed offspring (F1) were mated with unexposed males to generate germ cell (F2) and transgenerationally exposed (F3 and F4) females. Sexual maturation, maternal behavior, and hypothalamic targets of exposure were studied across generations.

RESULTS

Germ cell (F2) and transgenerationally (F3) EDC-exposed females, but not F1, displayed delayed pubertal onset and altered folliculogenesis. We reported a transgenerational alteration of key hypothalamic genes controlling puberty and ovulation (Kiss1, Esr1, and Oxt), and we identified the hypothalamic polycomb group of epigenetic repressors as actors of this mechanism. Furthermore, we found a multigenerational reduction of maternal behavior (F1-F3) induced by a loss in hypothalamic dopaminergic signaling. Using a cross-fostering paradigm, we identified that the reduction in maternal phenotype was normalized in EDC-exposed pups raised by unexposed dams, but no reversal of the pubertal phenotype was achieved.

DISCUSSION

Rats developmentally exposed to an EDC mixture exhibited multi- and transgenerational disruption of sexual maturation and maternal care via hypothalamic epigenetic reprogramming. These results raise concerns about the impact of EDC mixtures on future generations. https://doi.org/10.1289/EHP8795.

Endocrine disrupting chemicals (EDCs) and sex steroid receptors

Sex-steroid receptors (SSRs) are essential mediators of estrogen, progestin, and androgen signaling that are critical in vast aspects of human development and multi-organ homeostasis. Dysregulation of SSR function has been implicated in numerous pathologies including cancers, obesity, Type II diabetes mellitus, neuroendocrine disorders, cardiovascular disease, hyperlipidemia, male and female infertility, and other reproductive disorders. Endocrine disrupting chemicals (EDCs) modulate SSR function in a wide variety of cell and tissues. There exists strong experimental, clinical, and epidemiological evidence that engagement of EDCs with SSRs may disrupt endogenous hormone signaling leading to physiological abnormalities that may manifest in disease. In this chapter, we discuss the molecular mechanisms by which EDCs interact with estrogen, progestin, and androgen receptors and alter SSR functions in target cells. In addition, the pathological consequences of disruption of SSR action in reproductive and other organs by EDCs is described with an emphasis on underlying mechanisms of receptors dysfunction.

Cellular and molecular features of EDC exposure: consequences for the GnRH network

The onset of puberty and the female ovulatory cycle are important developmental milestones of the reproductive system. These processes are controlled by a tightly organized network of neurotransmitters and neuropeptides, as well as genetic, epigenetic and hormonal factors, which ultimately drive the pulsatile secretion of gonadotropin-releasing hormone. They also strongly depend on organizational processes that take place during fetal and early postnatal life. Therefore, exposure to environmental pollutants such as endocrine-disrupting chemicals (EDCs) during critical periods of development can result in altered brain development, delayed or advanced puberty and long-term reproductive consequences, such as impaired fertility. The gonads and peripheral organs are targets of EDCs, and research from the past few years suggests that the organization of the neuroendocrine control of reproduction is also sensitive to environmental cues and disruption. Among other mechanisms, EDCs interfere with the action of steroidal and non-steroidal receptors, and alter enzymatic, metabolic and epigenetic pathways during development. In this Review, we discuss the cellular and molecular consequences of perinatal exposure (mostly in rodents) to representative EDCs with a focus on the neuroendocrine control of reproduction, pubertal timing and the female ovulatory cycle.

The impact of endocrine-disrupting chemical exposure in the mammalian hypothalamic-pituitary axis

The hypothalamic-pituitary axis (HP axis) plays a critical and integrative role in the endocrine system control to maintain homeostasis. The HP axis is responsible for the hormonal events necessary to regulate the thyroid, adrenal glands, gonads, somatic growth, among other functions. Endocrine-disrupting chemicals (EDCs) are a worldwide public health concern. There is growing evidence that exposure to EDCs such as bisphenol A (BPA), some phthalates, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and biphenyls (PBBs), dichlorodiphenyltrichloroethane (DDT), tributyltin (TBT), and atrazine (ATR), is associated with HP axis abnormalities. EDCs act on hormone receptors and their downstream signaling pathways and can interfere with hormone synthesis, metabolism, and actions. Because the HP axis function is particularly sensitive to endogenous hormonal changes, disruptions by EDCs can alter HP axis proper function, leading to important endocrine irregularities. Here, we review the evidence that EDCs could directly affect the mammalian HP axis function.

Safeguarding Female Reproductive Health against Endocrine Disrupting Chemicals-The FREIA Project

Currently available test methods are not well-suited for the identification of chemicals that disturb hormonal processes involved in female reproductive development and function. This renders women's reproductive health at increasing risk globally, which, coupled with increasing incidence rates of reproductive disorders, is of great concern. A woman's reproductive health is largely established during embryonic and fetal development and subsequently matures during puberty. The endocrine system influences development, maturation, and function of the female reproductive system, thereby making appropriate hormone levels imperative for correct functioning of reproductive processes. It is concerning that the effects of human-made chemicals on the endocrine system and female reproductive health are poorly addressed in regulatory chemical safety assessment, partly because adequate test methods are lacking. Our EU-funded project FREIA aims to address this need by increasing understanding of how endocrine disrupting chemicals (EDCs) can impact female reproductive health. We will use this information to provide better test methods that enable fit-for-purpose chemical regulation and then share our knowledge, promote a sustainable society, and improve the reproductive health of women globally.

Single-Cell Gene Profiling Reveals Social Status-Dependent Modulation of Nuclear Hormone Receptors in GnRH Neurons in a Male Cichlid Fish

Gonadotropin-releasing hormone (GnRH) is essential for the initiation and maintenance of reproductive functions in vertebrates. To date, three distinct paralogue lineages, GnRH1, GnRH2, and GnRH3, have been identified with different functions and regulatory mechanisms. Among them, hypothalamic GnRH1 neurons are classically known as the hypophysiotropic form that is regulated by estrogen feedback. However, the mechanism of action underlying the estrogen-dependent regulation of GnRH1 has been debated, mainly due to the coexpression of low levels of estrogen receptor (ER) genes. In addition, the role of sex steroids in the modulation of GnRH2 and GnRH3 neurons has not been fully elucidated. Using single-cell real-time PCR, we revealed the expression of genes for estrogen, androgen, glucocorticoid, thyroid, and xenobiotic receptors in GnRH1, GnRH2, and GnRH3 neurons in the male Nile tilapia Oreochromis niloticus. We further quantified expression levels of estrogen receptor genes (ERα, ERβ, and ERγ) in three GnRH neuron types in male tilapia of two different social statuses (dominant and subordinate) at the single cell level. In dominant males, GnRH1 mRNA levels were positively proportional to ERγ mRNA levels, while in subordinate males, GnRH2 mRNA levels were positively proportional to ERβ mRNA levels. These results indicate that variations in the expression of nuclear receptors (and possibly steroid sensitivities) among individual GnRH cells may facilitate different physiological processes, such as the promotion of reproductive activities through GnRH1 neurons, and the inhibition of feeding and sexual behaviors through GnRH2 neurons.

Experimental Approaches for Characterizing the Endocrine-Disrupting Effects of Environmental Chemicals in Fish

Increasing industrial and agricultural activities have led to a disturbing increase of pollutant discharges into the environment. Most of these pollutants can induce short-term, sustained or delayed impacts on developmental, physiological, and behavioral processes that are often regulated by the endocrine system in vertebrates, including fish, thus they are termed endocrine-disrupting chemicals (EDCs). Physiological impacts resulting from the exposure of these vertebrates to EDCs include abnormalities in growth and reproductive development, as many of the prevalent chemicals are capable of binding the receptors to sex steroid hormones. The approaches employed to investigate the action and impact of EDCs is largely dependent on the specific life history and habitat of each species, and the type of chemical that organisms are exposed to. Aquatic vertebrates, such as fish, are among the first organisms to be affected by waterborne EDCs, an attribute that has justified their wide-spread use as sentinel species. Many fish species are exposed to these chemicals in the wild, for either short or prolonged periods as larvae, adults, or both, thus, studies are typically designed to focus on either acute or chronic exposure at distinct developmental stages. The aim of this review is to provide an overview of the approaches and experimental methods commonly used to characterize the effects of some of the environmentally prevalent and emerging EDCs, including 17 α-ethinylestradiol, nonylphenol, BPA, phthalates, and arsenic; and the pervasive and potential carriers of EDCs, microplastics, on reproduction and growth. In vivo and in vitro studies are designed and employed to elucidate the direct effects of EDCs at the organismal and cellular levels, respectively. In silico approaches, on the other hand, comprise computational methods that have been more recently applied with the potential to replace extensive in vitro screening of EDCs. These approaches are discussed in light of model species, age and duration of EDC exposure.

Perturbation of Nuclear Hormone Receptors by Endocrine Disrupting Chemicals: Mechanisms and Pathological Consequences of Exposure

Much of the early work on Nuclear Hormone Receptors (NHRs) focused on their essential roles as mediators of sex steroid hormone signaling in reproductive development and function, and thyroid hormone-dependent formation of the central nervous system. However, as NHRs display tissue-specific distributions and activities, it is not surprising that they are involved and vital in numerous aspects of human development and essential for homeostasis of all organ systems. Much attention has recently been focused on the role of NHRs in energy balance, metabolism, and lipid homeostasis. Dysregulation of NHR function has been implicated in numerous pathologies including cancers, metabolic obesity and syndrome, Type II diabetes mellitus, cardiovascular disease, hyperlipidemia, male and female infertility and other reproductive disorders. This review will discuss the dysregulation of NHR function by environmental endocrine disrupting chemicals (EDCs), and the associated pathological consequences of exposure in numerous tissues and organ systems, as revealed by experimental, clinical, and epidemiological studies.

Lavender Products Associated With Premature Thelarche and Prepubertal Gynecomastia: Case Reports and Endocrine-Disrupting Chemical Activities

CONTEXT

Previous case reports associated prepubertal gynecomastia with lavender-containing fragrances, but there appear to be no reports of premature thelarche.

OBJECTIVE

To add to a case series about lavender-fragranced product use and breast growth in children and to measure endocrine-disrupting chemical activity of essential oil components.

DESIGN, SETTING, AND PATIENTS

Patients experiencing premature thelarche or prepubertal gynecomastia with continuous exposure to lavender-fragranced products were evaluated in the pediatric endocrinology departments of two institutions. Mechanistic in vitro experiments using eight components of lavender and other essential oils were performed at National Institute of Environmental Health Sciences.

MAIN OUTCOME MEASURES

Case reports and in vitro estrogen and androgen receptor gene expression activities in human cell lines with essential oils.

RESULTS

Three prepubertal girls and one boy with clinical evidence of estrogenic action and a history of continuous exposure to lavender-containing fragrances were studied. Breast growth dissipated in all patients with discontinuation of the fragranced products. Some of the components tested elicited estrogenic and antiandrogenic properties of varying degrees.

CONCLUSION

We report cases of premature thelarche that resolved upon cessation of lavender-containing fragrance exposure commonly used in Hispanic communities. The precise developmental basis for such conditions could be multifactorial. In vitro demonstration of estrogenic and antiandrogenic properties of essential oil components suggests essential oils in these cases could be considered a possible source and supports a possible link with idiopathic prepubertal breast development. Whether the level of lavender oil estrogenic potency is sufficient to cause these effects is unknown.

Endocrine disrupters and possible contribution to pubertal changes

The onset of puberty strongly depends on organizational processes taking place during the fetal and early postnatal life. Therefore, exposure to environmental pollutants such as Endocrine disrupting chemicals (EDCs) during critical periods of development can result in delayed/advanced puberty and long-term reproductive consequences. Human evidence of altered pubertal timing after exposure to endocrine disrupting chemicals is equivocal. However, the age distribution of pubertal signs points to a skewed distribution towards earliness for initial pubertal stages and towards lateness for final pubertal stages. Such distortion of distribution is a recent phenomenon and suggests environmental influences including the possible role of nutrition, stress and endocrine disruptors. Rodent and ovine studies indicate a role of fetal and neonatal exposure to EDCs, along the concept of early origin of health and disease. Such effects involve neuroendocrine mechanisms at the level of the hypothalamus where homeostasis of reproduction is programmed and regulated but also peripheral effects at the level of the gonads or the mammary gland.

Contribution of the Endocrine Perspective in the Evaluation of Endocrine Disrupting Chemical Effects: The Case Study of Pubertal Timing

Debate makes science progress. In the field of endocrine disruption, endocrinology has brought up findings that substantiate a specific perspective on the definition of endocrine disrupting chemicals (EDCs), the role of the endocrine system and the endpoints of hormone and EDC actions among other issues. This paper aims at discussing the relevance of the endocrine perspective with regard to EDC effects on pubertal timing. Puberty involves particular sensitivity to environmental conditions. Reports about the advancing onset of puberty in several countries have led to the hypothesis that the increasing burden of EDCs could be an explanation. In fact, pubertal timing currently shows complex changes since advancement of some manifestations of puberty (e.g. breast development) and no change or delay of others (e.g. menarche, pubic hair development) can be observed. In a human setting with exposure to low doses of tenths or hundreds of chemicals since prenatal life, causation is most difficult to demonstrate and justifies a translational approach using animal models. Studies in rodents indicate an exquisite sensitivity of neuroendocrine endpoints to EDCs. Altogether, the data from both human and animal studies support the importance of concepts derived from endocrinology in the evaluation of EDC effects on puberty.

Inhibitor of Differentiation-3 and Estrogenic Endocrine Disruptors: Implications for Susceptibility to Obesity and Metabolic Disorders

The rising global incidence of obesity cannot be fully explained within the context of traditional risk factors such as an unhealthy diet, physical inactivity, aging, or genetics. Adipose tissue is an endocrine as well as a metabolic organ that may be susceptible to disruption by environmental estrogenic chemicals. Since some of the endocrine disruptors are lipophilic chemicals with long half-lives, they tend to bioaccumulate in the adipose tissue of exposed populations. Elevated exposure to these chemicals may predispose susceptible individuals to weight gain by increasing the number and size of fat cells. Genetic studies have demonstrated that the transcriptional regulator inhibitor of differentiation-3 (ID3) promotes high fat diet-induced obesity in vivo. We have shown previously that PCB153 and natural estrogen 17β-estradiol increase ID3 expression. Based on our findings, we postulate that ID3 is a molecular target of estrogenic endocrine disruptors (EEDs) in the adipose tissue and a better understanding of this relationship may help to explain how EEDs can lead to the transcriptional programming of deviant fat cells. This review will discuss the current understanding of ID3 in excess fat accumulation and the potential for EEDs to influence susceptibility to obesity or metabolic disorders via ID3 signaling.

Comparative approaches to understanding thyroid hormone regulation of neurogenesis

Thyroid hormone (TH) signalling, an evolutionary conserved pathway, is crucial for brain function and cognition throughout life, from early development to ageing. In humans, TH deficiency during pregnancy alters offspring brain development, increasing the risk of cognitive disorders. How TH regulates neurogenesis and subsequent behaviour and cognitive functions remains a major research challenge. Cellular and molecular mechanisms underlying TH signalling on proliferation, survival, determination, migration, differentiation and maturation have been studied in mammalian animal models for over a century. However, recent data show that THs also influence embryonic and adult neurogenesis throughout vertebrates (from mammals to teleosts). These latest observations raise the question of how TH availability is controlled during neurogenesis and particularly in specific neural stem cell populations. This review deals with the role of TH in regulating neurogenesis in the developing and the adult brain across different vertebrate species. Such evo-devo approaches can shed new light on (i) the evolution of the nervous system and (ii) the evolutionary control of neurogenesis by TH across animal phyla. We also discuss the role of thyroid disruptors on brain development in an evolutionary context.

Pyrethroid Insecticide Cypermethrin Accelerates Pubertal Onset in Male Mice via Disrupting Hypothalamic-Pituitary-Gonadal Axis

Pyrethroids, a class of insecticides that are widely used worldwide, have been identified as endocrine-disrupting chemicals (EDCs). Our recent epidemiological study reported on an association of increased pyrethroids exposure with elevated gonadotropins levels and earlier pubertal development in Chinese boys. In this study, we further investigated the effects of cypermethrin (CP), one of the most ubiquitous pyrethroid insecticides, on hypothalamic-pituitary-gonadal (HPG) axis and pubertal onset in male animal models. Early postnatal exposure to CP at environmentally relevant doses (0.5, 5, and 50 μg/kg CP) significantly accelerated the age of puberty onset in male mice. Administration of CP induced a dose-dependent increase in serum levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone in male mice. CP did not affect gonadotropin-releasing hormone (GnRH) gene expression in the hypothalamus, but CP at higher concentrations stimulated GnRH pulse frequency. CP could induce the secretion of LH and FSH, as well as the expression of gonadotropin subunit genes [chorionic gonadotropin α (CGα), LHβ, and FSHβ] in pituitary gonadotropes. CP stimulated testosterone production and the expression of steroidogenesis-related genes [steroidogenic acute regulatory (StAR) and Cytochrome p 450, family 11, subfamily A, polypeptide 1 (CYP11A1)] in testicular Leydig cells. The interference with hypothalamic sodium channels as well as calcium channels in pituitary gonadotropes and testicular Leydig cells was responsible for CP-induced HPG axis maturation. Our findings established in animal models provide further evidence for the biological plausibility of pyrethroid exposure as a potentially environmental contributor to earlier puberty in males.

Luteinizing Hormone Secretion during Gonadotropin-Releasing Hormone Stimulation Tests in Obese Girls with Central Precocious Puberty

OBJECTIVE

Girls with precocious puberty have high luteinizing hormone (LH) levels and advanced bone age. Obese children enter puberty at earlier ages than do non-obese children. We analyzed the effects of obesity on LH secretion during gonadotropin-releasing hormone (GnRH) tests in girls with precocious puberty.

METHODS

A total of 981 subjects with idiopathic precocious puberty who had undergone a GnRH stimulation testing between 2008 and 2014 were included in the study. Subjects were divided into three groups based on body mass index (BMI). Auxological data and gonadotropin levels after the GnRH stimulation test were compared.

RESULTS

In Tanner stage 2 girls, peak stimulated LH levels on GnRH test were 11.9±7.5, 10.4±6.4, and 9.1±6.1 IU/L among normal-weight, overweight, and obese subjects, respectively (p=0.035 for all comparisons). In Tanner stage 3 girls, peak stimulated LH levels were 14.9±10.9, 12.8±7.9, and 9.6±6.0 IU/L, respectively (p=0.022 for all comparisons). However, in Tanner stage 4 girls, peak stimulated LH levels were not significantly different among normal, overweight, and obese children. On multivariate analysis, BMI standard deviation score was significantly and negatively associated with peak LH (β=-1.178, p=0.001).

CONCLUSION

In girls with central precocious puberty, increased BMI was associated with slightly lower peak stimulated LH levels at early pubertal stages (Tanner stages 2 and 3). This association was not valid in Tanner stage 4 girls.

An Emerging Role of micro-RNA in the Effect of the Endocrine Disruptors

Endocrine-disrupting chemicals (EDCs) are diverse natural and synthetic chemicals that may alter various mechanisms of the endocrine system and produce adverse developmental, reproductive, metabolic, and neurological effects in both humans and wildlife. Research on EDCs has revealed that they use a variety of both nuclear receptor-mediated and non-receptor-mediated mechanisms to modulate different components of the endocrine system. The molecular mechanisms underlying the effects of EDCs are still under investigation. Interestingly, some of the effects of EDCs have been observed to pass on to subsequent unexposed generations, which can be explained by the gametic transmission of deregulated epigenetic marks. Epigenetics is the study of heritable changes in gene expression that occur without a change in the DNA sequence. Epigenetic mechanisms, including histone modifications, DNA methylation, and specific micro-RNAs (miRNAs) expression, have been proposed to mediate transgenerational transmission and can be triggered by environmental factors. MiRNAs are short non-coding RNA molecules that post-transcriptionally repress the expression of genes by binding to 3′-untranslated regions of the target mRNAs. Given that there is mounting evidence that miRNAs are regulated by hormones, then clearly it is important to investigate the potential for environmental EDCs to deregulate miRNA expression and action.

Delayed Neuroendocrine Sexual Maturation in Female Rats After a Very Low Dose of Bisphenol A Through Altered GABAergic Neurotransmission and Opposing Effects of a High Dose

Rat sexual maturation is preceded by a reduction of the interpulse interval (IPI) of GnRH neurosecretion. This work aims at studying disruption of that neuroendocrine event in females after early exposure to a very low dose of bisphenol A (BPA), a ubiquitous endocrine disrupting chemical. Female rats were exposed to vehicle or BPA 25 ng/kg·d, 25 μg/kg·d, or 5 mg/kg·d from postnatal day (PND)1 to PND5 or PND15. Exposure to 25 ng/kg·d of BPA for 5 or 15 days was followed by a delay in developmental reduction of GnRH IPI studied ex vivo on PND20. After 15 days of exposure to that low dose of BPA, vaginal opening tended to be delayed. In contrast, exposure to BPA 5 mg/kg·d for 15 days resulted in a premature reduction in GnRH IPI and a trend toward early vaginal opening. RNA sequencing analysis on PND20 indicated that exposure to BPA resulted in opposing dose effects on the mRNA expression of hypothalamic genes involved in gamma aminobutyric acid A (GABAA) neurotransmission. The study of GnRH secretion in vitro in the presence of GABAA receptor agonist/antagonist confirmed an increased or a reduced GABAergic tone after in vivo exposure to the very low or the high dose of BPA, respectively. Overall, we show for the first time that neonatal exposure to BPA leads to opposing dose-dependent effects on the neuroendocrine control of puberty in the female rat. A very low and environmentally relevant dose of BPA delays neuroendocrine maturation related to puberty through increased inhibitory GABAergic neurotransmission.

Developmental Exposure to Ethinylestradiol Affects Reproductive Physiology, the GnRH Neuroendocrine Network and Behaviors in Female Mouse

During development, environmental estrogens are able to induce an estrogen mimetic action that may interfere with endocrine and neuroendocrine systems. The present study investigated the effects on the reproductive function in female mice following developmental exposure to pharmaceutical ethinylestradiol (EE2), the most widespread and potent synthetic steroid present in aquatic environments. EE2 was administrated in drinking water at environmentally relevant (ENVIR) or pharmacological (PHARMACO) doses [0.1 and 1 μg/kg (body weight)/day respectively], from embryonic day 10 until postnatal day 40. Our results show that both groups of EE2-exposed females had advanced vaginal opening and shorter estrus cycles, but a normal fertility rate compared to CONTROL females. The hypothalamic population of GnRH neurons was affected by EE2 exposure with a significant increase in the number of perikarya in the preoptic area of the PHARMACO group and a modification in their distribution in the ENVIR group, both associated with a marked decrease in GnRH fibers immunoreactivity in the median eminence. In EE2-exposed females, behavioral tests highlighted a disturbed maternal behavior, a higher lordosis response, a lack of discrimination between gonad-intact and castrated males in sexually experienced females, and an increased anxiety-related behavior. Altogether, these results put emphasis on the high sensitivity of sexually dimorphic behaviors and neuroendocrine circuits to disruptive effects of EDCs.

Association of PAEs with Precocious Puberty in Children: A Systematic Review and Meta-Analysis

Background: Precocious puberty (PP) currently affects 1 in 5000 children and is 10 times more common in girls. Existing studies have tried to detect an association between phathalic acid esters (PAEs) and PP, but the results did not reach a consensus. Objective: To estimate the association between PAEs and children with PP based on current evidence. Methods: Databases including PubMed (1978 to March 2015), OVID (1946 to March 2015), Web of Science (1970 to March 2015), EBSCO (1976 to March 2015), CNKI (1979 to March 2015), WANFANG DATA (1987 to March 2015), CBM (1978 to March 2015) and CQVIP (1989 to March 2015) were searched to identify all case-control studies that determined the exposure and concentration of PAEs and their metabolites in children with PP. Meta-analysis of the pooled standard mean difference (SMD) and odds ratio (OR) with 95% confidence intervals (CI) were calculated. Results: A total of 14 studies involving 2223 subjects were finally included. The pooled estimates showed that PP was associated with di-(2-ethylhexyl)-phthalate (DEHP) exposure (OR: 3.90, 95% CI: 2.77 to 5.49). Besides, the concentration of DEHP (SMD: 1.73, 95% CI: 0.54 to 2.91) and di-n-butyl phthalate (DBP) (SMD: 4.31, 95% CI: 2.67 to 5.95) in the PP group were significantly higher than those in the control group, respectively, while no difference was detected between case and control groups in either serum or urinary concentration of mono-(2-ethylhexyl)-phthalate (MEHP), monobutyl phthalate (MBP), mono(2-ethyl-5-oxohexyl) phthalate(MEOHP), mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP), monomethyl phthalate (MMP), monobenzyl phthalate (MBzP) or monoethyl phthalate (MEP). Conclusions: Exposure of DEHP and DBP might be associated with PP risk for girls, however, there is no evidence to show an association between the exposure to most PAE metabolites and PP. Given the moderate strength of the results, well-designed cohort studies with large sample size should be performed in future.

Developmental variations in environmental influences including endocrine disruptors on pubertal timing and neuroendocrine control: Revision of human observations and mechanistic insight from rodents

Puberty presents remarkable individual differences in timing reaching over 5 years in humans. We put emphasis on the two edges of the age distribution of pubertal signs in humans and point to an extended distribution towards earliness for initial pubertal stages and towards lateness for final pubertal stages. Such distortion of distribution is a recent phenomenon. This suggests changing environmental influences including the possible role of nutrition, stress and endocrine disruptors. Our ability to assess neuroendocrine effects and mechanisms is very limited in humans. Using the rodent as a model, we examine the impact of environmental factors on the individual variations in pubertal timing and the possible underlying mechanisms. The capacity of environmental factors to shape functioning of the neuroendocrine system is thought to be maximal during fetal and early postnatal life and possibly less important when approaching the time of onset of puberty.

Effects of the endocrine-disrupting chemical DDT on self-renewal and differentiation of human mesenchymal stem cells

BACKGROUND

Although the global use of the endocrine-disrupting chemical DDT has decreased, its persistence in the environment has resulted in continued human exposure. Accumulating evidence suggests that DDT exposure has long-term adverse effects on development, yet the impact on growth and differentiation of adult stem cells remains unclear.

OBJECTIVES

Human mesenchymal stem cells (MSCs) exposed to DDT were used to evaluate the impact on stem cell biology.

METHODS

We assessed DDT-treated MSCs for self-renewal, proliferation, and differentiation potential. Whole genome RNA sequencing was performed to assess gene expression in DDT-treated MSCs.

RESULTS

MSCs exposed to DDT formed fewer colonies, suggesting a reduction in self-renewal potential. DDT enhanced both adipogenic and osteogenic differentiation, which was confirmed by increased mRNA expression of glucose transporter type 4 (GLUT4), lipoprotein lipase (LpL), peroxisome proliferator-activated receptor gamma (PPARγ), leptin, osteonectin, core binding factor 1 (CBFA1), and FBJ murine osteosarcoma viral oncogene homolog (c-Fos). Expression of factors in DDT-treated cells was similar to that in estrogen-treated MSCs, suggesting that DDT may function via the estrogen receptor (ER)-mediated pathway. The coadministration of ICI 182,780 blocked the effects of DDT. RNA sequencing revealed 121 genes and noncoding RNAs to be differentially expressed in DDT-treated MSCs compared with controls cells.

CONCLUSION

Human MSCs provide a powerful biological system to investigate and identify the molecular mechanisms underlying the effects of environmental agents on stem cells and human health. MSCs exposed to DDT demonstrated profound alterations in self-renewal, proliferation, differentiation, and gene expression, which may partially explain the homeostatic imbalance and increased cancer incidence among those exposed to long-term EDCs.

Associations between serum vitamin D levels and precocious puberty in girls

PURPOSE

Vitamin D deficiency has been linked to chronic diseases, such as diabetes mellitus, obesity and autoimmune disease. However, data on the vitamin D status and its association with precocious puberty in girls are limited. We aimed to investigate the association between serum 25-hydroxyvitamin D (25OHD) and precocious puberty in girls.

METHODS

A total of 60 girls with central precocious puberty (CPP) and 30 control girls were enrolled. Anthropometric measurement and serum level of 25OHD were estimated for all subjects.

RESULTS

There was a significant difference in the mean serum 25OHD concentration between the precocious puberty group and the control group (17.1±4.5 ng/mL vs. 21.2±5.0 ng/mL, P<0.05). Forty-two of the 60 girls with CPP (70%) had vitamin D deficiency (defined as serum 25OHD<20 ng/mL) and 18 (30%) had vitamin D insufficiency. Of the 30 girls in the control group, vitamin D deficiency was seen in 13 subjects (43.3%), 15 subjects (50%) had vitamin D insufficiency, and 2 subjects (6.7%) had sufficient serum vitamin D (defined as serum 25OHD>30 ng/mL). Vitamin D deficient girls had a significantly higher odds ratio (OR, 3.05; 95% CI, 1.22-7.57, P=0.021).

CONCLUSION

These results showed that vitamin D levels may be associated with precocious puberty. Further studies are required to establish the potential effect of vitamin D status on puberty.

Estrogen Deficiency and the Origin of Obesity during Menopause

Sex hormones strongly influence body fat distribution and adipocyte differentiation. Estrogens and testosterone differentially affect adipocyte physiology, but the importance of estrogens in the development of metabolic diseases during menopause is disputed. Estrogens and estrogen receptors regulate various aspects of glucose and lipid metabolism. Disturbances of this metabolic signal lead to the development of metabolic syndrome and a higher cardiovascular risk in women. The absence of estrogens is a clue factor in the onset of cardiovascular disease during the menopausal period, which is characterized by lipid profile variations and predominant abdominal fat accumulation. However, influence of the absence of these hormones and its relationship to higher obesity in women during menopause are not clear. This systematic review discusses of the role of estrogens and estrogen receptors in adipocyte differentiation, and its control by the central nervous systemn and the possible role of estrogen-like compounds and endocrine disruptors chemicals are discussed. Finally, the interaction between the decrease in estrogen secretion and the prevalence of obesity in menopausal women is examined. We will consider if the absence of estrogens have a significant effect of obesity in menopausal women.

Pubertal timing after neonatal diethylstilbestrol exposure in female rats: neuroendocrine vs peripheral effects and additive role of prenatal food restriction

We studied the effects of neonatal exposure to diethylstilbestrol (DES) on pubertal timing in female rats. We examined associated neuroendocrine changes and effects of prenatal food restriction. Age at vaginal opening was advanced after exposure to 10 μg/kg/d of DES and delayed after 1 μg/kg/d (subcutaneous injections). Using this lower dose, pulsatile GnRH secretion was slower at 25 days of age. Both doses reduced KiSS1 mRNA levels at 15 days of age. Using functional Kisspeptin promoter assay, 1 or 10 μM DES reduced or increased KISS1 transcription, respectively. Leptin stimulatory effect on GnRH secretion in vitro (15 days of age) was reduced after prenatal food restriction and neonatal DES exposure (higher dose), both effects being cumulative. Thus, alterations in pubertal timing by DES neonatally are not unequivocally toward precocity, the level of exposure being critical. We provide evidence of neuroendocrine disruption and interaction with prenatal food availability.

Early neuroendocrine disruption in hypothalamus and hippocampus: developmental effects including female sexual maturation and implications for endocrine disrupting chemical screening

The timing of puberty has been mainly studied in females for several reasons, including the possible evaluation of a precise timer (i.e. menarcheal age) and concerns with respect to the high prevalence of precocity in females as opposed to males. Human evidence of altered female pubertal timing after exposure to endocrine disrupting chemicals (EDCs) is equivocal. Among the limiting factors, most studies evaluate exposure to single EDCs at the time of puberty and hardly assess the impact of lifelong exposure to mixtures of EDCs. Some rodent and ovine studies indicate a possible role of foetal and neonatal exposure to EDCs, in accordance with the concept of an early origin of health and disease. Such effects possibly involve neuroendocrine mechanisms because the hypothalamus is a site where homeostasis of reproduction, as well as control of energy balance, is programmed and regulated. In our previous studies, pulsatile gonadotrophin-releasing hormone (GnRH) secretion control via oestrogen, glutamate and aryl hydrocarbon receptors was shown to be involved in the mechanism of sexual precocity after early postnatal exposure to the insecticide dichlorodiphenyltrichloroethane. Very recently, we have shown that neonatal exposure to the potent synthetic oestrogen diethylstilbestrol (DES) is followed by early or delayed puberty depending on the dose, with consistent changes in developmental increase of GnRH pulse frequency. Moreover, DES results in reduced leptin stimulation of GnRH secretion in vitro, an effect that is additive with prenatal food restriction. Thus, using puberty as an endpoint of the effects of EDC, it appears necessary to consider pre- and perinatal exposure to low doses and to pay attention to the other conditions of prenatal life, such as energy availability, keeping in mind the possibility that puberty could not only be advanced, but also delayed through neuroendocrine mechanisms.

Brief maternal exposure of rats to the xenobiotics dibutyl phthalate or diethylstilbestrol alters adult-type Leydig cell development in male offspring

Maternal exposure to estrogenic xenobiotics or phthalates has been implicated in the distortion of early male reproductive development, referred to in humans as the testicular dysgenesis syndrome. It is not known, however, whether such early gestational and/or lactational exposure can influence the later adult-type Leydig cell phenotype. In this study, Sprague-Dawley rats were exposed to dibutyl phthalate (DBP; from gestational day (GD) 14.5 to postnatal day (PND) 6) or diethylstilbestrol (DES; from GD14.5 to GD16.5) during a short gestational/lactational window, and male offspring subsequently analysed for various postnatal testicular parameters. All offspring remained in good health throughout the study. Maternal xenobiotic treatment appeared to modify specific Leydig cell gene expression in male offspring, particularly during the dynamic phase of mid-puberty, with serum INSL3 concentrations showing that these compounds led to a faster attainment of peak values, and a modest acceleration of the pubertal trajectory. Part of this effect appeared to be due to a treatment-specific impact on Leydig cell proliferation during puberty for both xenobiotics. Taken together, these results support the notion that maternal exposure to certain xenobiotics can also influence the development of the adult-type Leydig cell population, possibly through an effect on the Leydig stem cell population.

Male specific association between xenoestrogen levels in placenta and birthweight

BACKGROUND

Fetal exposure to endocrine disrupting chemicals may increase the risk for adverse health effects at birth or later in life.

OBJECTIVES

The objective of this study is to analyze the combined effect of xenoestrogens on reproductive and perinatal growth outcomes (child birthweight, early rapid growth and body mass index (BMI) at 14 months) using the biomarker total effective xenoestrogen burden (TEXB).

METHODS

490 placentas were randomly collected in the Spanish prospective birth cohort Environment and Childhood (INMA) project. TEXB was used to assess the estrogenicity of placental samples in two fractions: that largely attributable to environmental organohalogenated xenoestrogens (TEXB-alpha), and that mostly due to endogenous estrogens (TEXB-beta), both expressed in estrogen equivalent units (Eeq) per gram of tissue. Linear or logistic regression models were performed adjusting for cohort and confounders. Sex interactions were investigated.

RESULTS

The median TEXB-alpha level was 0.76 pM Eeq/g (interquartile range (iqr): 1.14). In multivariate models, higher TEXB-alpha levels (third tertile, >1.22 pM Eeq/g; iqr: 1.73) were associated with increased birthweight in boys but not in girls (β=148.2 g, 95% CI: 14.01, 282.53, p(int)=0.057). Additionally, higher TEXB-alpha values in boys were related with a lower risk of early rapid growth (OR=0.37; 95% CI: 0.15, 0.88) and with a non significant association with larger BMI z-scores at 14 months of age (β=0.29; 95% CI: -0.11, 0.69).

CONCLUSIONS

These findings suggest that prenatal exposure to xenoestrogens may increase birthweight in boys, which might have an impact on child obesity and other later health outcomes.

Temporal window in which exposure to estradiol permanently modifies ovarian function causing polycystic ovary morphology in rats

OBJECTIVE

To investigate the developmental window in which E(2) exposure produces irreversible changes in ovarian function resulting in polycystic ovary.

DESIGN

Basic experimental study.

SETTING

University animal laboratory.

ANIMAL(S)

Thirty Sprague-Dawley rats were administered a single E(2) valerate dose (10 mg/kg of weight) at 1, 7, 14, 21, or 30 days of age. Control rats were injected with the vehicle at 1 day of age. All rats were sacrificed at 6 months of age.

INTERVENTION(S)

Observation of vaginal opening, estrous cyclicity by vaginal smears, and ovarian morphometry in the 6-month-old rat.

MAIN OUTCOME MEASURE(S)

Measurement of ovarian noradrenaline by high-performance liquid chromatography coupled with electrochemical detection, serum levels of LH by enzyme-linked immunoassay, P, androstenedione, and E(2) by enzyme immunoassay.

RESULT(S)

Rats exposed to E(2) at 1, 7, or 14 days of life did not show estrual cycling activity and maintained a polycystic ovary (PCO) condition throughout the entirety of the study. However, if the exposure to E(2) occurred after postnatal day 21, the PCO-induced condition was reversible. In rats that developed a permanent PCO condition, we observed significant effects of E(2) on ovarian morphology if exposure occurred on postnatal day 1 and a presumable effect on the hypothalamus if the exposure occurred between postnatal days 1 and 14.

CONCLUSION(S)

Our findings suggest that in rats, the most sensitive period for the promotion of an irreversible PCO morphology by estrogenic compounds is during neonatal early follicular development.

[Endocrine disruptors and obesity: obesogens]

Incidence and prevalence of owerweight and obesity have greatly increased over the past three decades in almost all countries around the world. This phenomenon is not easily explained by lifestyle changes in populations with very different initial habits. This has led to consider the influence of other factors, the so-called endocrine disruptors, and more specifically obesogens. This study reviewed the available evidence about polluting chemical substances which may potentially be obesogens in humans: DES, genistein, bisphenol A, organotins (TBT, TPT), and phthalates. The first three groups of substances mainly act upon estrogen receptors, while organotins and phthalates activate PPARγ. It was concluded that evidence exists of the obesogenic effect of these chemical substances in tissues and experimental animals, but few data are available in humans.

Early developmental actions of endocrine disruptors on the hypothalamus, hippocampus, and cerebral cortex

Sex steroids and thyroid hormones play a key role in the development of the central nervous system. The critical role of these hormonal systems may explain the sensitivity of the hypothalamus, the cerebral cortex, and the hippocampus to endocrine-disrupting chemicals (EDC). This review examines the evidence for endocrine disruption of glial-neuronal functions in the hypothalamus, hippocampus, and cerebral cortex. Focus was placed on two well-studied EDC, the insecticide dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyls (PCB). DDT is involved in neuroendocrine disruption of the reproductive axis, whereas polychlorinated biphenyls (PCB) interact with both the thyroid hormone- and sex steroid-dependent systems and disturb the neuroendocrine control of reproduction and development of hippocampus and cortex. These results highlight the impact of EDC on the developing nervous system and the need for more research in this area.

Neuroendocrine disruption of pubertal timing and interactions between homeostasis of reproduction and energy balance

The involvement of environmental factors such as endocrine disrupting chemicals (EDCs) in the timing of onset of puberty is suggested by recent changes in age at onset of puberty and pattern of distribution that are variable among countries, as well as new forms of sexual precocity after migration. However, the evidence of association between early or late pubertal timing and exposure to EDCs is weak in humans, possibly due to heterogeneity of effects likely involving mixtures and incapacity to assess fetal or neonatal exposure retrospectively. The neuroendocrine system which is crucial for physiological onset of puberty is targeted by EDCs. These compounds also act directly in the gonads and peripheral sex-steroid sensitive tissues. Feedbacks add to the complexity of regulation so that changes in pubertal timing caused by EDCs can involve both central and peripheral mechanisms. In experimental conditions, several neuroendocrine endpoints are affected by EDCs though only few studies including from our laboratory aimed at EDC involvement in the pathophysiology of early sexual maturation. Recent observations support the concept that EDC cause disturbed energy balance and account for the obesity epidemic. Several aspects are linking this system and the reproductive axis: coexisting neuroendocrine and peripheral effects, dependency on fetal/neonatal programming and the many factors cross-linking the two systems, for instance leptin, adiponectin, Agouti Related Peptide (AgRP). This opens perspectives for future research and, hopefully, measures preventing the disturbances of homeostasis caused by EDCs.

Early homeostatic disturbances of human growth and maturation by endocrine disrupters

PURPOSE OF REVIEW

We attempt to delineate and integrate aspects of growth and development that could be affected by endocrine disrupters [endocrine-disrupting compounds (EDC)], an increasing public health concern.

RECENT FINDINGS

Epidemiological and experimental data substantiate that fetal and early postnatal life are critical periods of exposure to endocrine disrupters, with possible transgenerational effects. The EDC effects include several disorders of the reproductive system throughout life (abnormalities of sexual differentiation, infertility or subfertility and some neoplasia) and disorders of energy balance (obesity and metabolic syndrome). The mechanisms are consistent with the concept of 'developmental origin of adult disease'. They could involve cross-talk between the factors controlling reproduction and those controlling energy balance, both in the hypothalamus and peripherally.

SUMMARY

Due to ubiquity of endocrine disrupters and lifelong stakes of early exposure, individual families should be provided by pediatricians with recommendations following the precautionary principle, that is prevention or attenuation of conditions possibly detrimental to health before the evidence of such adverse effects is complete and undisputable.

Hypothesis: exposure to endocrine-disrupting chemicals may interfere with timing of puberty

A recent decline in onset of puberty - especially among girls - has been observed, first in the US in the mid-1990s and now also in Europe. The development of breast tissue in girls occurs at a much younger age and the incidence of precocious puberty (PP) is increasing. Genetic factors and increasing prevalence of adiposity may contribute, but environmental factors are also likely to be involved. In particular, the widespread presence of endocrine-disrupting chemicals (EDCs) is suspected to contribute to the trend of earlier pubertal onset. The factors regulating the physiological onset of normal puberty are poorly understood. This hampers investigation of the possible role of environmental influences. There are many types of EDCs. One chemical may have more than one mode of action and the effects may depend on dose and duration of the exposure, as well as the developmental stage of the exposed individual. There may also be a wide range of genetic susceptibility to EDCs. Human exposure scenarios are complex and our knowledge about effects of mixtures of EDCs is limited. Importantly, the consequences of an exposure may not be apparent at the actual time of exposure, but may manifest later in life. Most known EDCs have oestrogenic and/or anti-androgenic actions and only few have androgenic or anti-oestrogenic effects. Thus, it appears plausible that they interfere with normal onset of puberty. The age at menarche has only declined by a few months whereas the age at breast development has declined by 1 year; thus, the time span from initiation of breast development to menarche has increased. This may indicate an oestrogen-like effect without concomitant central activation of the hypothalamic-pituitary axis. The effects may differ between boys and girls, as there are sex differences in age at onset of puberty, hormonal profiles and prevalence of precocius puberty.