Reduction of Kiss1 expression in the anteroventral periventricular nucleus is associated with atrazine-induced attenuation of the luteinizing hormone surge in female rats

Endocrine toxicity of atrazine and its underlying mechanisms

Atrazine (ATR) is one of the most widely utilized herbicides globally and is prevalent in the environment due to its extensive use and long half-life. It can infiltrate the human body through drinking water, ingestion, and dermal contact, and has been recognized as an environmental endocrine disruptor. This study aims to comprehensively outline the detrimental impacts of ATR on the endocrine system. Previous research indicates that ATR is harmful to various bodily systems, including the reproductive system, nervous system, adrenal glands, and thyroi d gland. The toxic effects of ATR on the endocrine system and its underlying molecular mechanisms are summarized as follows: influencing the expression of kisspeptin in the HPG axis, consequently affecting steroid synthesis; disrupting DNA synthesis and meiosis, as well as modifying DNA methylation levels, leading to reproductive and developmental toxicity; impacting dopamine by altering Nurr1, VMAT2, and DAT expression, consequently affecting dopamine synthesis and transporter expression, and influencing other neurotransmitters, resulting in neurotoxicity; and changing adipose tissue synthesis and metabolism by reducing basal metabolism, impairing cellular oxidative phosphorylation, and inducing insulin resistance. Additionally, a compilation of natural products used to mitigate the toxic effects of ATR has been provided, encompassing melatonin, curcumin, quercetin, lycopene, flavonoids, vitamin C, vitamin E, and other natural remedies. It is important to note that existing research predominantly relies on in vitro and ex vivo experiments, with limited population-based empirical evidence available.

Molecular insights into the effects of tetrachlorobisphenol A on puberty initiation in Wistar rats

Tetrachlorobisphenol A (TCBPA) is the chlorinated derivative of bisphenol A (BPA). Several studies have found that BPA adversely affects the reproductive activity largely through binding to estrogen receptors and the critical period of BPA exposure advances the vaginal opening time in the female offspring via the kisspeptin/G protein-coupled receptor 54 (KGG) system. However, whether TCBPA can affect puberty initiation via KGG and the roles of estrogen receptors in this process remain unknown. Therefore, this study investigated the influence of TCBPA on the onset time of puberty in Wistar rats and the related molecular mechanisms by combing in vitro GT1-7 cells and molecular docking. In female Wistar rats, TCBPA at ≥100 mg/kg bw/day (49.2 μmol/L in rat body) markedly advanced vaginal opening time and increased serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and gonadotropin-releasing hormone (GnRH). It also increased the relative gene expression of LH receptor (LHR), GnRH1, and FSH receptor (FSHR) in hypothalamic-pituitary-gonadal (HPG) axis tissues. In GT1-7 cells, TCBPA increased genes and proteins associated with KGG pathway and activated the extracellular-regulated protein kinase 1/2 (Erk1/2) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) pathways via G protein-coupled estrogen membrane receptor 1 (GPER1) and estrogen receptor alpha (ERα). Docking analyses supported its interactions with GPER1 and ERα, and treatment with specific inhibitors of ERα- and GPER1-modulated PI3K/Akt and Erk1/2 signaling suppressed its effects. Taken together, TCBPA-induced advancement of puberty initiation in Wistar rats thus results primarily from increased LH, GnRH, and FSH secretion together with GnRH1, FSHR, and LHR upregulation driven by ERα- and GPER1-modulated Erk1/2 and PI3K/Akt signaling. Our results provide new molecular insights into the reproductive toxicity of EDCs.

Mechanisms of Neurotoxicity Associated with Exposure to the Herbicide Atrazine

Atrazine is an herbicide commonly used on crops to prevent broadleaf weeds. Atrazine is an endocrine-disrupting chemical mainly targeting the neuroendocrine system and associated axes, especially as a reproductive toxicant through attenuation of the luteinizing hormone (LH). Current regulatory levels for chronic exposure are based on no observed adverse effect levels (NOAELs) of these LH alterations in rodent studies. Atrazine has also been studied for its effects on the central nervous system and neurotransmission. The European Union (EU) recognized the health risks of atrazine exposure as a public health concern with no way to contain contamination of drinking water. As such, the EU banned atrazine use in 2003. The United States recently reapproved atrazine's use in the fall of 2020. Research has shown that there is a wide array of adverse health effects that are seen across multiple models, exposure times, and exposure periods leading to dysfunction in many different systems in the body with most pointing to a neuroendocrine target of toxicity. There is evidence of crosstalk between systems that can be affected by atrazine exposure, causing widespread dysfunction and leading to changes in behavior even with no direct link to the hypothalamus. The hypothetical mechanism of toxicity of atrazine endocrine disruption and neurotoxicity can therefore be described as a web of pathways that are influenced through changes occurring in each and their multiple feedback loops with further research needed to refine NOAELs for neurotoxic outcomes.

Endocrine disrupting chemicals (EDCs) and the neuroendocrine system: Beyond estrogen, androgen, and thyroid

Hundreds of anthropogenic chemicals occupy our bodies, a situation that threatens the health of present and future generations. This chapter focuses on endocrine disrupting compounds (EDCs), both naturally occurring and man-made, that affect the neuroendocrine system to adversely impact health, with an emphasis on reproductive and metabolic pathways. The neuroendocrine system is highly sexually dimorphic and essential for maintaining homeostasis and appropriately responding to the environment. Comprising both neural and endocrine components, the neuroendocrine system is hormone sensitive throughout life and touches every organ system in the body. The integrative nature of the neuroendocrine system means that EDCs can have multi-system effects. Additionally, because gonadal hormones are essential for the sex-specific organization of numerous neuroendocrine pathways, endocrine disruption of this programming can lead to permanent deficits. Included in this review is a brief history of the neuroendocrine disruption field and a thorough discussion of the most common and less well understood neuroendocrine disruption modes of action. Also provided are extensive examples of how EDCs are likely contributing to neuroendocrine disorders such as obesity, and evidence that they have the potential for multi-generational effects.

Developmental atrazine exposure in zebrafish produces the same major metabolites as mammals along with altered behavioral outcomes

Atrazine (ATZ) is the second most commonly applied agricultural herbicide in the United States. Due to contamination concerns, the U.S. EPA has set the maximum contaminant level in potable water sources at 3 parts per billion (ppb; μg/l). Depending on the time of year and sampling location, water sources often exceed this limit. ATZ is an endocrine disrupting chemical in multiple species observed to target the neuroendocrine system. In this study the zebrafish vertebrate model was used to test the hypothesis that a developmental ATZ exposure generates metabolites similar to those found in mammals and alters morphology and behavior in developing larvae. Adult AB zebrafish were bred, embryos were collected, and exposed to 0, 0.3, 3, or 30 ppb ATZ from 1 to 120 h post fertilization (hpf). Targeted metabolomic analysis found that zebrafish produce the same major ATZ metabolites as mammals: desethyl atrazine (DEA), deisopropyl atrazine (DIA), and diaminochloroatrazine (DACT). The visual motor response test at 120 hpf detected hyperactivity in larvae in the 0.3 ppb treatment group and hypoactivity in the 30 ppb treatment group (p < 0.05). Further analysis into behavior during the dark and light phases showed zebrafish larvae exposed to 0.3 ppb ATZ had an increase in total distance moved in the first light phase and time spent moving in the first dark and light phases (p < 0.05). Alternatively, a decrease in total distance moved was observed in the second and third dark phases in zebrafish exposed to 30 ppb ATZ (p < 0.05). No significant differences were observed for any of the morphological measurements following ATZ exposure from 1 to 120 hpf (p > 0.05). These findings suggest that a ATZ exposure during early development generates metabolite profiles similar to mammals and leads to behavioral alterations supporting ATZ as a neurodevelopmental toxicant.

Role of kisspeptin neurons as a GnRH surge generator: Comparative aspects in rodents and non-rodent mammals

Ovulation is an essential phenomenon for reproduction in mammalian females along with follicular growth. It is well established that gonadal function is controlled by the neuroendocrine system called the hypothalamus-pituitary-gonadal (HPG) axis. Gonadotropin-releasing hormone (GnRH) neurons, localized in the hypothalamus, had been considered to be the head in governing the HPG axis for a long time until the discovery of kisspeptin. In females, induction of ovulation and folliculogenesis has been linked to a surge mode and pulse mode of GnRH releases, respectively. The mechanisms of how the two modes of GnRH are differently regulated had long remained elusive. The discovery of kisspeptin neurons, distributed in two hypothalamic nuclei, such as the arcuate nucleus in the caudal hypothalamus and preoptic area or the anteroventral periventricular nucleus in the rostral hypothalamic regions, and analyses of the detailed functions of kisspeptin neurons have led marked progress on the understanding of different mechanisms regulating GnRH surges (ovulation) and GnRH pulses (folliculogenesis). The present review will focus on the role of kisspeptin neurons as the GnRH surge generator, including the sexual differentiation of the surge generation system and factors that regulate the surge generator. Comparative aspects between mammalian species are especially focused on.