Hexachlorobenzene as hormonal disruptor--studies about glucocorticoids: their hepatic receptors, adrenal synthesis and plasma levels in relation to impaired gluconeogenesis

Glucocorticoid hormones in relation to environmental exposure to bisphenols and multiclass pesticides among middle aged-women: Results from hair analysis

Bisphenols and pesticides have been shown to alter circulating glucocorticoids levels in animals, but there is limited human data. Moreover, measurements from biological fluids may not be able to reflect long-term status of non-persistent pollutants and glucocorticoids due to the high variability in their levels. Using hair analysis, we examined the associations between glucocorticoid hormones and environmental exposure to multi-class organic pollutants among a healthy female population aged 25-45 years old. Concentrations of four glucocorticoids, four polychlorinated biphenyl congeners (PCBs), seven polybrominated diphenyl ether congeners (PBDEs), two bisphenols and 140 pesticides and their metabolites were measured in hair samples collected from 196 Chinese women living in urban areas. Due to the low detection frequency of some pollutants, associations were explored only on 54 pollutants, i.e. PCB 180, bisphenol A, bisphenol S and 51 pesticides and their metabolites. Using stability-based Lasso regression, there were associations of cortisol, tetrahydrocortisol, cortisone, and tetrahydrocortisone with 14, 10, 13 and 17 biomarkers of exposure to pollutants, respectively, with bisphenol S, p,p'-dichlorodiphenyldichloroethylene, diethyl phosphate, 3,5,6-trichloro-2-pyridinol, thiamethoxam, imidacloprid, fipronil, tebuconazole, trifluralin, pyraclostrobin and 1-(3,4-dichlorophenyl)-3-methylurea being associated with at least three of the four hormones. There were also associations between cortisone/cortisol molar ratio and pollutants, namely dimethyl phosphate, 3-methyl-4-nitrophenol, carbofuran, λ-cyhalothrin, permethrin, fipronil, flusilazole, prometryn and fenuron. Some of these relationships were confirmed by single-pollutant linear regression analyses. Overall, our results suggest that background level of exposure to bisphenols and currently used pesticides may interfere with the glucocorticoid homeostasis in healthy women.

Endocrine disruptors, aryl hydrocarbon receptor and cortisol secretion

PURPOSE

Endocrine disruptors exert a plethora of effects in endocrine tissues, from altered function to carcinogenesis. Given its lipophilic nature, the adrenal cortex represents an ideal target for endocrine disruptors and thus, possibly, xenobiotic-induced adrenocortical dysfunction. However, there is no clear understanding of the effect of endocrine disruptors on adrenal steroidogenesis, in particular as regards the aryl hydrocarbon receptor (AHR) pathway, one of the key mediators.

METHODS

The present review recapitulates available evidence on the effects of AHR ligands on adrenal steroidogenesis, with focus on cortisol secretion.

RESULTS

Short-term exposure to AHR ligands most often induced a stress-like corticosteroid response followed by decreased responsiveness to stressors with long-term exposure. This was observed in several experimental models across species as well as in animals and humans in real-life settings. Prenatal exposure led to different effects according to sex of the offspring, as observed in murine models and in children from mothers in several countries. In vitro findings proved highly dependent on the experimental setting, with reduced cortisol response and steroidogenic enzyme synthesis mostly observed in fish and increased cortisol synthesis and secretion observed in murine and human adrenal cell lines. Of note, no AHR-binding element was detected in steroidogenic enzyme promoters, suggesting the involvement of additional factors.

CONCLUSION

Our review provides evidence for the impact of AHR ligands on adrenocortical function and indicates further avenues of research to better clarify its effects.

Glucocorticoid and mineralocorticoid receptors and corticosteroid homeostasis are potential targets for endocrine-disrupting chemicals

Endocrine-disrupting chemicals (EDCs) have received significant concern, since they ubiquitously exist in the environment and are able to induce adverse health effects on human and wildlife. Increasing evidence shows that the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), members of the steroid receptor subfamily, are potential targets for EDCs. GR and MR mediate the actions of glucocorticoids and mineralocorticoids, respectively, which are two main classes of corticosteroids involved in many physiological processes. The effects of EDCs on the homeostasis of these two classes of corticosteroids have also gained more attention recently. This review summarized the effects of environmental GR/MR ligands on receptor activity, and disruption of corticosteroid homeostasis. More than 130 chemicals classified into 7 main categories were reviewed, including metals, metalloids, pesticides, bisphenol analogues, flame retardants, other industrial chemicals and pharmaceuticals. The mechanisms by which EDCs interfere with GR/MR activity are primarily involved in ligand-receptor binding, nuclear translocation of the receptor complex, DNA-receptor binding, and changes in the expression of endogenous GR/MR genes. Besides directly interfering with receptors, enzyme-catalyzed synthesis and prereceptor regulation pathways of corticosteroids are also important targets for EDCs. The collected evidence suggests that corticosteroids and their receptors should be considered as potential targets for safety assessment of EDCs. The recognition of relevant xenobiotics and their underlying mechanisms of action is still a challenge in this emerging field of research.

This can't be stressed enough: The contribution of select environmental toxicants to disruption of the stress circuitry and response

Integration of the hypothalamic-pituitary-adrenal (HPA) axis and the limbic system through glucocorticoid signaling is imperative in initiating and regulating a suitable stress response following real or perceived threats. Dysfunction of these circuits that results in a persistent or inhibited glucocorticoid secretion can severely affect processing of stressful experiences and lead to risk for developing further psychiatric pathology. Exposure to toxic chemicals found in our environment, including pesticides, metals, and industrial compounds, have been shown to have significant impact on neurological health and disease. Indeed, studies have begun to identify the HPA axis and limbic system as potential targets of many of these environmental chemicals, suggesting a possible environmental risk for damage to the stress circuit and response to stressful stimuli. This review will focus on our current understanding of the impact exposure to environmental toxicants, including bisphenol A and lead, has on the synaptic physiology of the HPA axis and limbic system and how this contributes to an alteration in behavior output. Further, this discussion will provide a starting point to continue to couple novel toxicological and neurological approaches to elaborate our understanding of the influence of environmental chemicals on the stress response and pathology.

The impact of low-dose carcinogens and environmental disruptors on tissue invasion and metastasis

The purpose of this review is to stimulate new ideas regarding low-dose environmental mixtures and carcinogens and their potential to promote invasion and metastasis. Whereas a number of chapters in this review are devoted to the role of low-dose environmental mixtures and carcinogens in the promotion of invasion and metastasis in specific tumors such as breast and prostate, the overarching theme is the role of low-dose carcinogens in the progression of cancer stem cells. It is becoming clearer that cancer stem cells in a tumor are the ones that assume invasive properties and colonize distant organs. Therefore, low-dose contaminants that trigger epithelial-mesenchymal transition, for example, in these cells are of particular interest in this review. This we hope will lead to the collaboration between scientists who have dedicated their professional life to the study of carcinogens and those whose interests are exclusively in the arena of tissue invasion and metastasis.

A review on endocrine disruptors and their possible impacts on human health

Endocrine disruption is a named field of research which has been very active for over 10 years, although the effects of endocrine disruptors in wildlife have been studied mainly in vast since the 1940s. A large number of chemicals have been identified as endocrine disruptors and humans can be exposed to them either due to their occupations or through dietary and environmental exposure (water, soil and air). Endocrine disrupting chemicals are compounds that alter the normal functioning of the endocrine system of both humans and wildlife. In order to understand the vulnerability and risk factors of people due to endocrine disruptors as well as the remedies for these, methods need to be developed in order to predict effects on populations and communities from the knowledge of effects on individuals. For several years there have been a growing interest on the mechanism and effect of endocrine disruptors and their relation with environment and human health effect. This paper, based on extensive literature survey, briefly studies the progress mainly in human to provide information concerning causative substances, mechanism of action, ubiquity of effects and important issues related to endocrine disruptors. It also reviews the current knowledge of the potential impacts of endocrine disruptors on human health so that the effects can be known and remedies applied for the problem as soon as possible.

Endocrine-disrupting chemicals: associated disorders and mechanisms of action

The incidence and/or prevalence of health problems associated with endocrine-disruption have increased. Many chemicals have endocrine-disrupting properties, including bisphenol A, some organochlorines, polybrominated flame retardants, perfluorinated substances, alkylphenols, phthalates, pesticides, polycyclic aromatic hydrocarbons, alkylphenols, solvents, and some household products including some cleaning products, air fresheners, hair dyes, cosmetics, and sunscreens. Even some metals were shown to have endocrine-disrupting properties. Many observations suggesting that endocrine disruptors do contribute to cancer, diabetes, obesity, the metabolic syndrome, and infertility are listed in this paper. An overview is presented of mechanisms contributing to endocrine disruption. Endocrine disruptors can act through classical nuclear receptors, but also through estrogen-related receptors, membrane-bound estrogen-receptors, and interaction with targets in the cytosol resulting in activation of the Src/Ras/Erk pathway or modulation of nitric oxide. In addition, changes in metabolism of endogenous hormones, cross-talk between genomic and nongenomic pathways, cross talk with estrogen receptors after binding on other receptors, interference with feedback regulation and neuroendocrine cells, changes in DNA methylation or histone modifications, and genomic instability by interference with the spindle figure can play a role. Also it was found that effects of receptor activation can differ in function of the ligand.

How porphyrinogenic drugs modeling acute porphyria impair the hormonal status that regulates glucose metabolism. Their relevance in the onset of this disease

This work deals with the study of how porphyrinogenic drugs modeling acute porphyrias interfere with the status of carbohydrate-regulating hormones in relation to key glucose enzymes and to porphyria, considering that glucose modulates the development of the disease. Female Wistar rats were treated with 2-allyl-2-isopropylacetamide (AIA) and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) using different doses of AIA (100, 250 and 500mg/kg body weight) and a single dose of DDC (50mg DDC/kg body weight). Rats were sacrificed 16h after AIA/DDC administration. In the group treated with the highest dose of AIA (group H), hepatic 5-aminolevulinic acid synthase (ALA-S) increased more than 300%, phosphoenolpyruvate carboxykinase (PEPCK) and glycogen phosphorylase (GP) activities were 43% and 46% lower than the controls, respectively, plasmatic insulin levels exceeded normal values by 617%, and plasmatic glucocorticoids (GC) decreased 20%. GC results are related to a decrease in corticosterone (CORT) adrenal production (33%) and a significant reduction in its metabolization by UDP-glucuronosyltransferase (UGT) (62%). Adrenocorticotropic hormone (ACTH) stimulated adrenal production 3-fold and drugs did not alter this process. Thus, porphyria-inducing drugs AIA and DDC dramatically altered the status of hormones that regulate carbohydrate metabolism increasing insulin levels and reducing GC production, metabolization and plasmatic levels. In this acute porphyria model, gluconeogenic and glycogenolytic blockages caused by PEPCK and GP depressed activities, respectively, would be mainly a consequence of the negative regulatory action of insulin on these enzymes. GC could also contribute to PEPCK blockage both because they were depressed by the treatment and because they are positive effectors on PEPCK. These disturbances in carbohydrates and their regulation, through ALA-S de-repression, would enhance the porphyria state promoted by the drugs on heme synthesis and destruction. This might be the mechanism underlying the "glucose effect" observed in hepatic porphyrias. The statistical correlation study performed showed association between all the variables studied and reinforce these conclusions.

In vitro steroidogenic effects of mixtures of persistent organic pollutants (POPs) extracted from burbot (Lota lota) caught in two Norwegian lakes

This study investigated the effects of two mixtures of persistent organic pollutants (POPs) on steroidogenesis in the H295R cell line. The two mixtures were obtained from the livers of burbot (Lota lota) caught in two Norwegian lakes (Mjøsa and Losna) with different contaminant profiles. Steroid hormone levels in the cell culture medium and mRNA levels of 16 genes involved in steroidogenesis were investigated. The crude Lake Mjøsa extract had to be diluted ten times more than the Lake Losna extract in order to prevent cytotoxicity. The ten times diluted Lake Mjøsa mixture had higher levels of DDT and derivates (∑DDTs, 1.7 times) and brominated flame retardants (∑BDEs and HBCD, 15-25 times) than the Lake Losna mixture, which, on the other hand, had higher concentrations of ∑PCBs (1.5 times higher) and also of HCB, ∑HCH isomers and ∑chlordane isomers (5-20 times higher). In the cell culture media, only cortisol levels were increased at the highest exposure concentration to the Lake Mjøsa mixture, while both cortisol and estradiol levels were increased following exposure to the two highest Lake Losna mixture exposure concentrations. Testosterone levels decreased only at the highest exposure concentration of the Lake Losna mixture. Multivariate models suggested that ∑PCBs, and to a lesser extent ∑DDTs, were responsible for the cortisol responses, while estradiol and testosterone alterations were best explained by HCB and ∑PCBs, respectively. Exposure to the mixtures generally increased mRNA levels, with smaller effects exerted by the Lake Mjøsa mixture than the Lake Losna mixture. It was concluded that both mixtures affected steroidogenesis in the H295R cells. Small differences in mixture composition, rather than the high content of brominated flame retardants in the Lake Mjøsa mixture, were suggested to be the most probable reason for the apparent differences in potencies of the two mixtures.

Environmental endocrine disruptors promote adipogenesis in the 3T3-L1 cell line through glucocorticoid receptor activation

The burgeoning obesity and diabetes epidemics threaten health worldwide, yet the molecular mechanisms underlying these phenomena are incompletely understood. Recently, attention has focused on the potential contributions of environmental pollutants that act as endocrine disrupting chemicals (EDCs) in the pathogenesis of metabolic diseases. Because glucocorticoid signaling is central to adipocyte differentiation, the ability of EDCs to stimulate the glucocorticoid receptor (GR) and drive adipogenesis was assessed in the 3T3-L1 cell line. Various EDCs were screened for glucocorticoid-like activity using a luciferase reporter construct, and four (bisphenol A (BPA), dicyclohexyl phthalate (DCHP), endrin, and tolylfluanid (TF)) were shown to significantly stimulate GR without significant activation of the peroxisome proliferator-activated receptor-gamma. 3T3-L1 preadipocytes were then treated with EDCs and a weak differentiation cocktail containing dehydrocorticosterone (DHC) in place of the synthetic dexamethasone. The capacity of these compounds to promote adipogenesis was assessed by quantitative oil red O staining and immunoblotting for adipocyte-specific proteins. The four EDCs increased lipid accumulation in the differentiating adipocytes and also upregulated the expression of adipocytic proteins. Interestingly, proadipogenic effects were observed at picomolar concentrations for several of the EDCs. Because there was no detectable adipogenesis when the preadipocytes were treated with compounds alone, the EDCs are likely promoting adipocyte differentiation by synergizing with agents present in the differentiation cocktail. Thus, EDCs are able to promote adipogenesis through the activation of the GR, further implicating these compounds in the rising rates of obesity and diabetes.

Intrauterine exposure to environmental pollutants and body mass index during the first 3 years of life

OBJECTIVE

We investigated the association between body mass index (BMI) standard deviation score (SDS) and prenatal exposure to hexachlorobenzene, dichlorodiphenyldichloroethylene (DDE), dioxin-like compounds, and polychlorinated biphenyls (PCBs).

METHODS

In this prospective birth cohort study, we assessed a random sample of mother-infant pairs (n = 138) living in Flanders, Belgium, with follow-up until the children were 3 years of age. We measured body mass index as standard deviation scores (BMI SDS) of children 1-3 years of age as well as pollutants measured in cord blood.

RESULTS

DDE correlated with BMI SDS, with effect modification by maternal smoking and the child's age. At 1 year, children of smoking mothers had higher BMI SDS than did children of nonsmoking mothers. At 3 years, this difference was reduced because of the faster rate of decline in BMI SDS in the former group. This relationship held except for children with high levels of DDE. DDE had a small effect on BMI SDS at 3 years of age in children of nonsmoking mothers (difference in BMI SDS for DDE concentrations between the 90th and 10th percentiles = 0.13). On the other hand, smoking enhanced the relation between DDE and BMI SDS at 3 years (difference in BMI SDS for DDE concentrations between the 90th and 10th percentiles = 0.76). Increasing concentrations of PCBs were associated with higher BMI SDS values at all ages (parameter estimate = 0.003 +/- 0.001; p = 0.03).

CONCLUSION

In this study we demonstrated that intrauterine exposure to DDE and PCBs is associated with BMI during early childhood. Future studies are warranted to confirm our findings and to assess possible mechanisms by which these pollutants could alter energy metabolism.

Molecular targets of TBBPA in zebrafish analysed through integration of genomic and proteomic approaches

Tetrabromobisphenol-A (TBBPA) is nowadays one of the most frequently used brominated flame retardants (BFRs) and can be considered as a high production volume chemical. Over the last decade, numerous reports of increasing concentrations of BFRs in the environment and humans have been published. However, the toxicological knowledge on TBBPA, and more specifically its molecular mode of action, is rather fragmentary. In this study two populations of adult zebrafish (Danio rerio) were exposed for 14 days to 0.75 microM and 1.5 microM TBBPA. Subsequently, we employed a combined transcriptomic and proteomic approach to evaluate the molecular effects of TBBPA in zebrafish liver. Oligonucleotide microarrays were used to study the effects on gene expression levels. These results were validated through real-time PCR. The proteome of the liver was analysed by means of differential in-gel electrophoresis (DiGE), an innovative application of traditional 2D-PAGE. Combination of the extracted datasets allowed reassembling of individual molecular responses into a comprehensive overview of affected molecular pathways. Interpretation of the results depicted an interference of thyroid and Vitamin A homeostasis in the exposed zebrafish, TBBPA also elicited responses indicating onset of oxidative stress and general stress responses. Additionally, numerous differentially expressed transcripts could be associated with defence mechanisms or corresponded to metabolizing enzymes. Furthermore, cellular metabolism was clearly affected, illustrated as disturbance of e.g. lipid, carbohydrate, and organic acid metabolic processes. Summarizing, these results enabled us to hypothesize several working mechanisms of TBBPA and demonstrated the potential of a combined genome and proteome approach to generate detailed mechanistic toxicological information.