Nitric oxide signaling as a common target of organohalogens and other neuroendocrine disruptors

Persistent autism-relevant behavioral phenotype and social neuropeptide alterations in female mice offspring induced by maternal transfer of PBDE congeners in the commercial mixture DE-71

Polybrominated diphenyl ethers (PBDEs) are ubiquitous persistent organic pollutants (POPs) that are known neuroendocrine disrupting chemicals with adverse neurodevelopmental effects. PBDEs may act as risk factors for autism spectrum disorders (ASD), characterized by abnormal psychosocial functioning, although direct evidence is currently lacking. Using a translational exposure model, we tested the hypothesis that maternal transfer of a commercial mixture of PBDEs, DE-71, produces ASD-relevant behavioral and neurochemical deficits in female offspring. C57Bl6/N mouse dams (F0) were exposed to DE-71 via oral administration of 0 (VEH/CON), 0.1 (L-DE-71) or 0.4 (H-DE-71) mg/kg bw/d from 3 wk prior to gestation through end of lactation. Mass spectrometry analysis indicated in utero and lactational transfer of PBDEs (in ppb) to F1 female offspring brain tissue at postnatal day (PND) 15 which was reduced by PND 110. Neurobehavioral testing of social novelty preference (SNP) and social recognition memory (SRM) revealed that adult L-DE-71 F1 offspring display deficient short- and long-term SRM, in the absence of reduced sociability, and increased repetitive behavior. These effects were concomitant with reduced olfactory discrimination of social odors. Additionally, L-DE-71 exposure also altered short-term novel object recognition memory but not anxiety or depressive-like behavior. Moreover, F1 L-DE-71 displayed downregulated mRNA transcripts for oxytocin (Oxt) in the bed nucleus of the stria terminalis (BNST) and supraoptic nucleus, and vasopressin (Avp) in the BNST and upregulated Avp1ar in BNST, and Oxtr in the paraventricular nucleus. Our work demonstrates that developmental PBDE exposure produces ASD-relevant neurochemical, olfactory processing and behavioral phenotypes that may result from early neurodevelopmental reprogramming within central social and memory networks.

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.

Nitric oxide and sex differences in dendritic branching and arborization

Nitric oxide (NO) is an important signaling molecule with many functions in the nervous system. Derived from the enzymatic conversion of arginine by several nitric oxide synthases (NOS), NO plays significant roles in neuronal developmental events such as the establishment of dendritic branching or arbors. A brief summary of the discovery, molecular biology, and chemistry of NO, and a description of important NO-mediated signal transduction pathways with emphasis on the role for NO in the development of dendritic branching during neurodevelopment are presented. Important sex differences in neuronal nitric oxide synthase expression during neuronal development are considered. Finally, a survey of endogenous and exogenous substances that disrupt dendritic patterning is presented with particular emphasis on how these molecules may drive NO-mediated sex differences in dendritic branching.

Perinatal exposure to octabromodiphenyl ether mixture, DE-79, alters the vasopressinergic system in adult rats

Polybrominated diphenyl ethers (PBDEs) are persistent environmental pollutants considered as neurotoxicants and endocrine disruptors with important biological effects ranging from alterations in growth, reproduction, and effects on the hypothalamus-pituitary-adrenal axis. The vasopressinergic (AVPergic) system is a known target for pentaBDEs mixture (DE-71) and the structurally similar chemicals, polychlorinated biphenyls. However, the potential adverse effects of mixtures containing octaBDE compounds, like DE-79, on the AVPergic system are still unknown. The present study aims to examine the effects of perinatal DE-79 exposure on the AVPergic system. Dams were dosed from gestational day 6 to postnatal day 21 at doses of 0 (control), 1.7 (low) or 10.2 (high) mg/kg/day, and male offspring from all doses at 3-months-old were subjected to normosmotic and hyperosmotic challenge. Male offspring where later assessed for alterations in osmoregulation (i.e. serum osmolality and systemic vasopressin release), and both vasopressin immunoreactivity (AVP-IR) and gene expression in the hypothalamic paraventricular and supraoptic nuclei. Additionally, to elucidate a possible mechanism for the effects of DE-79 on the AVPergic system, both neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and mRNA expression were investigated in the same hypothalamic nuclei. The results showed that perinatal DE-79 exposure AVP-IR, mRNA expression and systemic release in adulthood under normosmotic conditions and more evidently under hyperosmotic stimulation. nNOS-IR and mRNA expression were also affected in the same nuclei. Since NO is an AVP regulator, we propose that disturbances in NO could be a mechanism underlying the AVPergic system disruption following perinatal DE-79 exposure leading to osmoregulation deficits.

The environmental pollutant BDE-209 regulates NO/cGMP signaling through activation of NMDA receptors in neurons

The common flame retardant decabrominated diphenyl ether (BDE-209) is a persistent organic pollutant. Epidemiological studies have revealed that prenatal or postnatal exposure to BDE-209 can result in delayed cognitive development, and BDE-209 has been shown to be toxic to cultured neurons with maturation interference effects. However, its neurotoxic mechanism remains unclear. Nitric oxide/cyclic guanosine monophosphate (NO/cGMP) signaling plays an important role in regulating neuronal maturation. We examined the influence of BDE-209 (100, 200, and 400 nM) on NO production and cGMP levels signaling in rodent neurons in vitro, with or without pretreatment N-methyl-D-aspartate (NMDA) receptor antagonism. We found that nanomolar concentrations of BDE-209 affected levels of the second messengers NO and cGMP, and that these effects could be blocked by NMDA receptor antagonism. Moreover, BDE-209 activation of NMDA receptors inhibited the expression of phosphodiesterases (PDEs), which modulate intracellular cGMP levels, and increased the Bcl-2/Bax ratio, favoring apoptosis induction. Our studies implicate the NMDA-NO/cGMP pathway in the pathogenic mechanism through which BDE-209 induces neurotoxicity.

Perinatal exposure to organohalogen pollutants decreases vasopressin content and its mRNA expression in magnocellular neuroendocrine cells activated by osmotic stress in adult rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are environmental pollutants that produce neurotoxicity and neuroendocrine disruption. They affect the vasopressinergic system but their disruptive mechanisms are not well understood. Our group reported that rats perinatally exposed to Aroclor-1254 (A1254) and DE-71 (commercial mixtures of PCBs and PBDEs) decrease somatodendritic vasopressin (AVP) release while increasing plasma AVP responses to osmotic activation, potentially emptying AVP reserves required for body-water balance. The aim of this research was to evaluate the effects of perinatal exposure to A1254 or DE-71 (30mgkg/day) on AVP transcription and protein content in the paraventricular and supraoptic hypothalamic nuclei, of male and female rats, by in situ hybridization and immunohistochemistry. cFOS mRNA expression was evaluated in order to determine neuroendocrine cells activation due to osmotic stimulation. Animal groups were: vehicle (control); exposed to either A1254 or DE-71; both, control and exposed, subjected to osmotic challenge. The results confirmed a physiological increase in AVP-immunoreactivity (AVP-IR) and gene expression in response to osmotic challenge as reported elsewhere. In contrast, the exposed groups did not show this response to osmotic activation, they showed significant reduction in AVP-IR neurons, and AVP mRNA expression as compared to the hyperosmotic controls. cFOS mRNA expression increased in A1254 dehydrated groups, suggesting that the AVP-IR decrease was not due to a lack of the response to the osmotic activation. Therefore, A1254 may interfere with the activation of AVP mRNA transcript levels and protein, causing a central dysfunction of vasopressinergic system.

Endocrine Disruption of Vasopressin Systems and Related Behaviors

Endocrine disrupting chemicals (EDCs) are chemicals that interfere with the organizational or activational effects of hormones. Although the vast majority of the EDC literature focuses on steroid hormone signaling related impacts, growing evidence from a myriad of species reveals that the nonapeptide hormones vasopressin (AVP) and oxytocin (OT) may also be EDC targets. EDCs shown to alter pathways and behaviors coordinated by AVP and/or OT include the plastics component bisphenol A (BPA), the soy phytoestrogen genistein (GEN), and various flame retardants. Many effects are sex specific and likely involve action at nuclear estrogen receptors. Effects include the elimination or reversal of well-characterized sexually dimorphic aspects of the AVP system, including innervation of the lateral septum and other brain regions critical for social and other non-reproductive behaviors. Disruption of magnocellular AVP function has also been reported in rats, suggesting possible effects on hemodynamics and cardiovascular function.

Aroclor 1254 inhibits cell viability and induces apoptosis of human A549 lung cancer cells by modulating the intracellular Ca(2+) level and ROS production through the mitochondrial pathway

To study the acute toxic effects of PCBs on airway exposure, the cell viability, apoptosis and mitochondrial functions of human lung cancer cell line A549 were measured and compared after Aroclor 1254 exposure for different time. The results showed that Aroclor 1254 could inhibit cell viability and increase cell apoptosis in a concentration- and time-dependent manner. The mitochondrial apoptosis pathway was confirmed playing an important role. ROS elevation was an early response within 1h treatment of Aroclor 1254. Then after 4 h of Aroclor 1254 exposure, the intracellular calcium level increased and mitochondrial transmembrane potential (ΔΨm) collapsed, accompanying with Cytochrome c (Cyt-c) leakage, boosting expression of Bax, Apaf-1 and miRNA155, which were involved in the mitochondrial apoptosis pathway. After 24 h of Aroclor 1254 exposure, ROS returned to normal level, but cell apoptosis rate was higher than that at 4 h with ΔΨm continued collapsing and intracellular calcium increased. In conclusion, Aroclor 1254 could suppress cell viability and induce apoptosis in A549 cells, which was associated with ROS over-production and elevated cellular Ca(2+) level, which may result in mitochondrial dysfunction, inducing expression of Bax/Cyt-c/Apaf-1 and miRNA155.

The PBDE metabolite 6-OH-BDE 47 affects melanin pigmentation and THRβ MRNA expression in the eye of zebrafish embryos

Polybrominated diphenyl ethers and their hydroxyl-metabolites (OH-BDEs) are commonly detected contaminants in human serum in the US population. They are also considered to be endocrine disruptors, and are specifically known to affect thyroid hormone regulation. In this study, we investigated and compared the effects of a PBDE and its OH-BDE metabolite on developmental pathways regulated by thyroid hormones using zebrafish as a model. Exposure to 6-OHBDE 47 (10–100 nM), but not BDE 47 (1–50 μM), led to decreased melanin pigmentation and increased apoptosis in the retina of zebrafish embryos in a concentration-dependent manner in short-term exposures (4 – 30 hours). Six-OH-BDE 47 exposure also significantly decreased thyroid hormone receptor β (THRβ) mRNA expression, which was confirmed using both RT-PCR and in situ hybridization (whole mount and paraffin- section). Interestingly, exposure to the native thyroid hormone, triiodothyronine (T3) also led to similar responses: decreased THRβ mRNA expression, decreased melanin pigmentation and increased apoptosis, suggesting that 6-OH-BDE 47 may be acting as a T3 mimic. To further investigate short-term effects that may be regulated by THRβ, experiments using a morpholino gene knock down and THRβ mRNA over expression were conducted. Knock down of THRβ led to decreases in melanin pigmentation and increases in apoptotic cells in the eye of zebrafish embryos, similar to exposure to T3 and 6-OH-BDE 47, but THRβ mRNA overexpression rescued these effects. Histological analysis of eyes at 22 hpf from each group revealed that exposure to T3 or to 6-OH-BDE 47 was associated with a decrease of melanin and diminished proliferation of cells in layers of retina near the choroid. This study suggests that 6-OH-BDE 47 disrupts the activity of THRβ in early life stages of zebrafish, and warrants further studies on effects in developing humans.

Effects of acute exposure to the non-steroidal anti-inflammatory drug ibuprofen on the developing North American Bullfrog (Rana catesbeiana) tadpole

A variety of pharmaceutical chemicals can represent constituents of municipal effluent outflows that are dispersed into aquatic receiving environments worldwide. Increasingly, there is concern as to the potential of such bioactive substances to interact with wildlife species at sensitive life stages and affect their biology. Using a combination of DNA microarray, quantitative real-time polymerase chain reaction, and quantitative nuclease protection assays, we assessed the ability of sub-lethal and environmentally relevant concentrations of ibuprofen (IBF), a non-steroidal anti-inflammatory agent and prevalent environmental contaminant, to function as a disruptor of endocrine-mediated post-embryonic development of the frog. While the LC50 of IBF for pre-metamorphic Rana catesbeiana tadpoles is 41.5 mg/L (95% confidence interval: 32.3-53.5 mg/L), exposure to concentrations in the ppb range elicited molecular responses both in vivo and in organ culture. A nominal concentration of 15 μg/L IBF (actual = 13.7 μg/L) altered the abundance of 26 mRNA transcripts within the liver of exposed pre-metamorphic R. catesbeiana tadpoles within 6 d. IBF-treated animals demonstrated subsequent disruption of thyroid hormone-mediated reprogramming in the liver transcriptome affecting constituents of several metabolic, developmental, and signaling pathways. Cultured tadpole tail fin treated with IBF for 48 h also demonstrated altered mRNA levels at drug concentrations as low as 1.5 μg/L. These observations raise the possibility that IBF may alter the post-embryonic development of anuran species in freshwater environs, where IBF is a persistent or seasonal pollutant.

Hexabromocyclododecane and polychlorinated biphenyls increase resistance of hepatocellular carcinoma cells to cisplatin through the phosphatidylinositol 3-kinase/protein kinase B pathway

Hepatocellular carcinoma (HCC) is one of the most common cancers in China with high mortality, high chemotherapy resistance incidence, and poor prognosis. This study aimed to investigate the influence of polychlorinated biphenyls (PCBs) and hexabromocyclododecane (HBCD) on chemoresistance of HCC cells (HepG2, MHCC97H, and MHCC97L) to cisplatin and to explore the potential molecular mechanism. Cell viability, DNA damage, the expression level and activity of nuclear factor-κB (NF-κB), p53/Mdm4, and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway were measured. The results showed that HBCD and PCBs could significantly reduce the chemosensitivity of HCC cells to cisplatin, increasing the cell viability and decreasing DNA damage. Moreover, HBCD and PCBs could induce the transcriptional activity of NF-κb and suppress the p53 expression in HepG2 and MHCC97H cells. In MHCC97L cells, however, opposite changes for NF-κB protein expression, NF-κB transcriptional activity, and p53/Mdm4 expression were observed after HBCD and PCBs exposure. Further investigation revealed that HBCD and PCBs exposure significantly increased the expression level of p-Akt and mammalian target of rapamycin (mTOR) in HepG2 and MHCC97H cells, but reduced that in MHCC97L cells. PI3K inhibitor LY294002 could relieve the influence of HBCD and PCBs on chemoresistance in HepG2 and MHCC97H cells. Taken together, HBCD and PCBs at low concentrations could increase the resistance of HCC cells to cisplatin through modulation on NF-κB pathway activation and p53 function, which is associated with the activity of PI3K/Akt pathway.

Milestones on Steroids and the Nervous System: 10 years of basic and translational research

During the last 10 years, the conference on 'Steroids and Nervous System' held in Torino (Italy) has been an important international point of discussion for scientists involved in this exciting and expanding research field. The present review aims to recapitulate the main topics that have been presented through the various meetings. Two broad areas have been explored: the impact of gonadal hormones on brain circuits and behaviour, as well as the mechanism of action of neuroactive steroids. Relationships among steroids, brain and behaviour, the sexual differentiation of the brain and the impact of gonadal hormones, the interactions of exogenous steroidal molecules (endocrine disrupters) with neural circuits and behaviour, and how gonadal steroids modulate the behaviour of gonadotrophin-releasing hormone neurones, have been the topics of several lectures and symposia during this series of meetings. At the same time, many contributions have been dedicated to the biosynthetic pathways, the physiopathological relevance of neurosteroids, the demonstration of the cellular localisation of different enzymes involved in neurosteroidogenesis, the mechanisms by which steroids may exert some of their effects, both the classical and nonclassical actions of different steroids, the role of neuroactive steroids on neurodegeneration, neuroprotection, and the response of the neural tissue to injury. In these 10 years, this field has significantly advanced and neuroactive steroids have emerged as new potential therapeutic tools to counteract neurodegenerative events.