Developmental effects: oestrogen-induced vaginal changes and organotin-induced adipogenesis

Maternal exposure to tributyltin alters the breast milk, hormonal profile, and thyroid morphology of dams and induces sex-specific changes in neonate rat offspring

Tributyltin (TBT) is the chemical substance commonly used worldwide to prevent biofouling of vessels. Due to its ability to bioaccumulate and biomagnify, even after being banned, significant concentrations of TBT can be detected in sediment, affecting marine and human life. Although studies have shown that direct exposure to TBT alters physiological parameters in mammals, the relationship between exposure to TBT during pregnancy and lactation, considered critical windows for metabolic programming, has not been fully elucidated. Our hypothesis is that offspring whose mothers were exposed to TBT during critical stages of development may exhibit dysfunctions in endocrine-metabolic parameters. We used pregnant Wistar rats that were divided into groups and received the following treatments from gestational day 7 until the end of lactation by intragastric gavage: vehicle (ethanol 0.01%; Control), low TBT dose (100 ng/kg of body weight (bw)/day; TBT100ng) and high TBT dose (1000 ng/kg bw/day; TBT1000ng). Dams and offspring at birth and weaning (21 days old) were studied. Maternal exposure to TBT promoted dose-dependent changes in dams. The findings for adiposity, milk composition and lipid profile were more pronounced in TBT100 ng dam; however, thyroid morphology was altered in TBT1000 ng dam. Female offspring were differentially affected by the dose of exposure. At birth, females in the TBT100ng group had low body weight, lower naso-anal length (NAL), and higher plasma T4, and at weaning, females in the TBT100ng group had lower insulin and leptin levels. Females in the TBT1000ng group had lower NAL at birth and lower leptinemia and weight of white adipose tissue at weaning. Male offspring from TBT groups showed high T3 at birth, without biometric alterations at birth or weaning. Despite these findings, both sexes exhibited dose-dependent morphological changes in the thyroid gland. Thus, maternal exposure to TBT constitutes an important route of contamination for both dams and offspring.

Effect of a Diet-Induced Obesity on the Progeny Response in a Murine Model

Diet-induced obesity could have detrimental effects on adults and their progeny. The aim of this study was to determine the effect of a high-energy diet on both F1 mice body weight and tissue/organ weight and F2 offspring growth. A simple murine model for obesity was developed using a high-energy diet and mice reared in litters of five or ten, from 30 dams receiving a cafeteria diet of either commercial chow (low energy), or a mixture of commercial chow, chocolate (50% cacao), and salty peanuts (high energy). This diet continued from mating until weaning, when the pups were allocated according to sex into eight groups based on maternal diet, litter size, and post-weaning diet. On day 74, the males were slaughtered, and the females were bred then slaughtered after lactation. As a result, the high-energy maternal diet increased the F1 offspring growth during lactation, while the high-energy post-weaning diet increased the F1 adult body weight and tissue/organ weight. The high-energy maternal diet could negatively affect the onset of the F1 but not the maintenance of breastfeeding of F1 and F2 offspring. For F2 offspring growth, the high energy overlapped the low-energy post-weaning diet, due to problems of gaining weight during lactation.

Global qualitative and quantitative distribution of micropollutants in the deep sea

Micropollutants (MPs) include a wide range of biological disruptors that can be toxic to wildlife and humans at very low concentrations (<1 μg/L). These mainly anthropogenic pollutants have been widely detected in different areas of the planet, including the deep sea, and have impacts on marine life. Because of this potential toxicity, the global distribution, quantity, incidence, and potential impacts of deep-sea MPs were investigated in a systematic review of the literature. The results showed that MPs have reached different zones of the ocean and are more frequently reported in the Northern Hemisphere, where higher concentrations are found. MPs are also concentrated in depths up to 3000 m, where they are also more frequently studied, but also extend deeper than 10,000 m. Potentially toxic metals (PTMs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), organotins, and polycyclic aromatic hydrocarbons (PAHs) were identified as the most prevalent and widely distributed MPs at ≥200 m depth. PTMs are widely distributed in the deep sea in high concentrations; aluminum is the most prevalent up to 3000 m depth, followed by zinc and copper. PCBs, organotins, hexachlorocyclohexanes (HCHs), PAHs, and phenols were detected accumulated in both organisms and environmental samples above legislated thresholds or known toxicity levels. Our assessment indicated that the deep sea can be considered a sink for MPs.

Estrogens counteract tributyltin-induced toxicity in the rat islets of Langerhans

Background

Tributyltin (TBT) is known as an endocrine disruptor able to interfere with estrogen receptors (ERs) leading to toxic effects on the related endocrine pathways. TBT is an obesogen, reported to disrupt glucose homeostasis leading to diabetes. The aim of this study was to assess the influence of TBT and β-estradiol on the pancreatic islets of Langerhans in simultaneous exposures.

Experimental

Pancreatic islets of 15 male rat were isolated and exposed to TBT (10 μM), β-estradiol, and TBT plus β-estradiol for 24 h. Therewith, cellular viability, oxidative stress, apoptosis, and insulin secretion markers were investigated.

Results

TBT decreased the viability and increased the apoptosis, reactive oxygen species, and insulin secretion TBT led to increased amounts of apaptosis, reactive oxygen species (ROS), and insulin secretion in pancreatic islets; however, cellular viability was reduced. Co-exposure with β-estradiol ameliorated the entire mentioned variables near to the control level.

Conclusion

These results showed that β-estradiol protect pancreatic islets of Langerhans against TBT-induced toxicity by counteracting oxidative stress and apoptosis as well as insulin secretion. In this way, it is postulated that pancreatic ER pathways particularly in β-cells might be the determinant target of toxic effects of xenoestrogens like TBT. Hence, evaluation of xenoestrogens-induced ER dysfunction in the endocrine pancreas can be helpful in diabetic risk assessment of these contaminants. Pharmacological modifications of ER pathway in the β-cells seems promising for better management of diabetes.

Disrupting effects of azocyclotin to the hypothalamo-pituitary-gonadal axis and reproduction of Xenopus laevis

Over the past few decades, the hazards associated with the extensive use of organictin compounds have become an issue of extreme concern, while at present the effects of these substances on amphibians remain poorly understood. In the present study, we chose azocyclotin, one of common use acaricides in China. We focused on sexual development and steroidogenesis disrupting effects of azocyclotin in the Xenopus laevis. Tadpoles were exposed to azocyclotin (0.05 and 0.5μg/L) for long-term (4 months) study. Results showed that exposure to azocyclotin caused developmental toxicity, including decreased survival, body weight, body length, gonadosomatic index, hepatosomatic index and female phenotype. At the same time, statistical increase in mean age at completion of metamorphosis was observed in azocyclotin treatments in comparison with control group. Furthermore, hormone concentrations, and steroidogenesis genes expression of adult frog were further evaluated in 28 days exposure. Results demonstrated that the key regulating hormones, e.g. testosterone and pregnenolone, were significantly upregulated. The expression levels of selected steroidogenic genes were also significantly altered. Our study demonstrated that azocyclotin could delay the metamorphosis and disrupt the gonadal differentiation of X. laevis. Steroidogenesis and the expression of genes involved in the hypothalamus-pituitary-gonadal-liver axis in frogs were disrupted after azocyclotin exposure. Azocyclotin showed both androgenic and antiestrogenic activity for X. laevis. Those findings emphasized the influence of azocyclotin on non-target species in the context of ecotoxicological risk assessment.

Non-genomic regulation and disruption of spermatozoal in vitro hyperactivation by oviductal hormones

During capacitation, motility of mammalian spermatozoon is changed from a state of "activation" to "hyperactivation." Recently, it has been suggested that some hormones present in the oviduct are involved in the regulation of this hyperactivation in vitro. Progesterone, melatonin, and serotonin enhance hyperactivation through specific membrane receptors, and 17β-estradiol suppresses this enhancement by progesterone and melatonin via a membrane estrogen receptor. Moreover, γ-aminobutyric acid suppresses progesterone-enhanced hyperactivation through the γ-aminobutyric acid receptor. These hormones dose-dependently affect hyperactivation. Although the complete signaling pathway is not clear, progesterone activates phospholipase C and protein kinases and enhances tyrosine phosphorylation. Moreover, tyrosine phosphorylation is suppressed by 17β-estradiol. This regulation of spermatozoal hyperactivation by steroids is also disrupted by diethylstilbestrol. The in vitro experiments reviewed here suggest that mammalian spermatozoa are able to respond to effects of oviductal hormones. We therefore assume that the enhancement of spermatozoal hyperactivation is also regulated by oviductal hormones in vivo.

In vitro assessment of human nuclear hormone receptor activity and cytotoxicity of the flame retardant mixture FM 550 and its triarylphosphate and brominated components

Firemaster(®) 550 (FM 550) is a mixture of brominated and triarylphosphate flame retardants used in polyurethane foam-based products. The primary components are also used in numerous other applications and are thus common household and industrial contaminants. Our previous animal studies suggested that FM 550 exposure may alter metabolism and cause weight gain. Employing human nuclear receptor (NR) luciferase reporter assays, the goal of this study was to evaluate the agonist actions of FM 550 and its constituent compounds at NRs with known roles in establishing or regulating energy balance. FM 550 was found to have significant agonist activity only at the master regulator of adipocyte differentiation PPARγ. As a result, the concentration response relationships and relative activities of FM 550 at PPARγ were investigated in more detail with the contribution of each chemical component defined and compared to the activities of the prototypical PPARγ environmental ligands triphenyltin and tributyltin. The resulting data indicated that the primary metabolic disruptive effects of FM 550 were likely mediated by the activity of the triarylphosphates at PPARγ, and have identified TPP as a candidate metabolic disruptor that also acts as a cytotoxicant.

Regulation and disruption of hamster sperm hyperactivation by progesterone, 17β-estradiol and diethylstilbestrol

Purpose

Hyperactivation of hamster sperm is dose-dependently enhanced by progesterone (P) and 17β-estradiol (E). In the first part of the present study, enhancement of hyperactivation in response to the concentrations of P and E was examined in detail and in the second part, it was examined whether enhancement of hyperactivation by P and E was disrupted by diethylstilbestrol (DES).

Methods

Hamster spermatozoa were hyperactivated by incubation in modified Tyrode's albumin lactate pyruvate medium with P, E and/or DES. After spermatozoa were recorded using a video-microscope, observations were quantified by manually counting the numbers of total, motile and hyperactivated spermatozoa.

Results

Hyperactivation was enhanced in response to the concentrations of P and E. When spermatozoa were exposed to DES with E, moreover, DES significantly and strongly suppressed P-enhanced hyperactivation by accelerating the effect of E, but DES itself only weakly suppressed P-enhanced hyperactivation.

Conclusions

Enhancement of hyperactivation was regulated by the concentrations of P and E, suggesting that in vivo hamster spermatozoa are hyperactivated through "monitoring" these concentrations in the oviduct. DES in combination with E suppressed P-enhanced hyperactivation, suggesting that DES significantly disrupts hyperactivation by acting as an accelerator of the effect of E.

G protein-coupled estrogen receptor in energy homeostasis and obesity pathogenesis

Obesity and its related metabolic diseases have reached a pandemic level worldwide. There are sex differences in the prevalence of obesity and its related metabolic diseases, with men being more vulnerable than women; however, the prevalence of these disorders increases dramatically in women after menopause, suggesting that sex steroid hormone estrogens play key protective roles against development of obesity and metabolic diseases. Estrogens are important regulators of several aspects of metabolism, including body weight and body fat, caloric intake and energy expenditure, and glucose and lipid metabolism in both males and females. Estrogens act in complex ways on their nuclear estrogen receptors (ERs) ERα and ERβ and transmembrane ERs such as G protein-coupled estrogen receptor. Genetic tools, such as different lines of knockout mouse models, and pharmacological agents, such as selective agonists and antagonists, are available to study function and signaling mechanisms of ERs. We provide an overview of the evidence for the physiological and cellular actions of ERs in estrogen-dependent processes in the context of energy homeostasis and body fat regulation and discuss its pathology that leads to obesity and related metabolic states.

Perinatal exposure to low doses of tributyltin chloride advances puberty and affects patterns of estrous cyclicity in female mice

Tributyltin (TBT), a proven endocrine-disrupting chemical, is well known to induce imposex in female gastropods. Herein we demonstrate the effects of low doses of tributyltin chloride (TBTCl) on the female offspring of KM mice. Pregnant mice were administered by gavage with 0, 1, 10, or 100 μg TBTCl/kg body weight/day from day 6 of pregnancy through the period of lactation. TBTCl dramatically advanced the age of onset of vaginal opening (VO) and first vaginal estrus, and reduced body weights at VO and first estrus. Furthermore, perinatal treatment with TBTCl significantly reduced the number of days between VO and first estrus. In addition, female offspring from dams exposed to 10 and 100 μg kg(-1) TBTCl exhibited altered patterns of estrous cyclicity in adulthood. In conclusion, perinatal exposure to low doses TBTCl result in early puberty and impaired estrous cyclicity in female mice, which suggest that TBTCl might act as an estrogen agonist or/and a disruptor on hypothalamic-pituitary function in the present study.

Effects of perinatal exposure to low doses of tributyltin chloride on pregnancy outcome and postnatal development in mouse offspring

Tributyltin (TBT), an endocrine-disrupting chemical, is well known to induce imposex in female gastropods. In this study, we assessed the effects of low doses of tributyltin chloride (TBTCl) on dams and their offspring. Pregnant mice were administered by gavage with 0, 1, 10, or 100 μg TBTCl/kg body weight/day from day 6 of pregnancy through the period of lactation. There were no TBT treatment-related deaths or clinical signs of toxicity for dams, and no treatment-related effects on body weight, litter sizes, gestational length of dams, and sex ratio, lactational body weight, postnatal survival, age at eruption of incisors, and eye opening of pups. However, at 100 μg/kg, TBTCl retarded the testes descent of male offspring. Behavioral tests showed a significant delay in cliff-drop aversion response in offspring of 10 and 100 μg/kg groups, but no significant difference in the righting reflex between control and TBT-exposed offspring was detectable. These results indicate that neurobehavioral toxicity seems to be one sensitive indicator to assess the risk of low doses of TBT.

Aromatase up-regulation, insulin and raised intracellular oestrogens in men, induce adiposity, metabolic syndrome and prostate disease, via aberrant ER-α and GPER signalling

For some years now, reduced testosterone levels have been related to obesity, insulin resistance, type 2 diabetes, heart disease, benign prostatic hypertrophy and even prostate cancer--often considered guilty more by association, than actual cause--with little attention paid to the important role of increased intracellular oestrogen, in the pathogenesis of these chronic diseases. In the final stage of the steroidogenic cascade, testosterone is metabolised to oestradiol by P450 aromatase, in the cytoplasm of adipocytes, breast cells, endothelial cells and prostate cells, to increase intracellular oestradiol concentration at the expense of testosterone. It follows therefore, that any compound that up-regulates aromatase, or any molecule that mimics oestrogen, will not only increase the activation of the mainly proliferative, classic ER-α, oestrogen receptors to induce adipogenesis and growth disorders in oestrogen-sensitive tissues, but also activate the recently identified transmembrane G protein-coupled oestrogen receptors (GPER), and deleteriously alter important intracellular signalling sequences, that promote mitogenic growth and endothelial damage. This paper simplifies how stress, xeno-oestrogens, poor dietary choices and reactive toxins up-regulate aromatase to increase intracellular oestradiol production; how oestradiol in combination with leptin and insulin cause insulin resistance and leptin resistance through aberrant serine phosphorylation; how the increased oestradiol, insulin and leptin stimulate rapid, non-genomic G protein-coupled phosphorylation cascades, to increase fat deposition and create the vasoconstrictive, dyslipidemic features of metabolic syndrome; how aberrant GPER signalling induces benign prostatic hypertrophy; and how increased intracellular oestradiol stimulates mitogenic change and tumour-cell activators, to cause prostate cancer. In essence, the up-regulation of aromatase produces increased intracellular oestradiol, increases ER-α activation and increases GPER activation, in combination with insulin, to cause aberrant downstream transduction signaling, and thus induce metabolic syndrome and mitogenic prostate growth. To understand this fact, that raised intracellular oestradiol levels in men, induce and promote obesity, gynecomastia, metabolic syndrome, type two diabetes, benign prostatic hypertrophy and prostate cancer, rather than low testosterone, represents a shift in medical thinking, a new awareness, that will reduce the rising incidence of obesity, metabolic syndrome and prostate disease, and significantly improve the health of men worldwide.

The role of oestrogen in the pathogenesis of obesity, type 2 diabetes, breast cancer and prostate disease

A detailed review of the literature was performed in a bid to identify the presence of a common link between specific hormone interactions and the increasing prevalence of global disease. The synergistic action of unopposed oestrogen and leptin, compounded by increasing insulin, cortisol and xeno-oestrogen exposure directly initiate, promote and exacerbate obesity, type 2 diabetes, uterine overgrowth, prostatic enlargement, prostate cancer and breast cancer. Furthermore these hormones significantly contribute to the incidence and intensity of anxiety and depression, Alzheimer's disease, heart disease and stroke. This review, in collaboration with hundreds of evidence-based clinical researchers, correlates the significant interactions these hormones exert upon the upregulation of p450 aromatase, oestrogen, leptin and insulin receptor function; the normal status quo of their binding globulins; and how adduct formation alters DNA sequencing to ultimately produce an array of metabolic conditions ranging from menopausal symptoms and obesity to Alzheimer's disease and breast and prostate cancer. It reveals the way that poor diet, increased stress, unopposed endogenous oestrogens, exogenous oestrogens, pesticides, xeno-oestrogens and leptin are associated with increased aromatase activity, and how its products, increased endogenous oestrogen and lowered testosterone, are associated with obesity, type 2 diabetes, Alzheimer's disease and oestrogenic disease. This controversial break-through represents a paradigm shift in medical thinking, which can prevent the raging pandemic of diabetes, obesity and cancer currently sweeping the world, and as such, it will reshape health initiatives, reduce suffering, prevent waste of government expenditure and effectively transform preventative medicine and global health care for decades.

Determination of TBT in water and sediment samples along the Argentine Atlantic coast

Cases of imposex have been reported for some organisms living in areas of the Argentine Atlantic coast. Since this is one of the known effects of the anti-fouling agent tributyltin (TBT), quantitative determinations of organotins in samples of water and sediments collected from sites along the Argentine coast were carried out. Severe cases of imposex were first reported for two gastropod species living in the Mar del Plata area, and determinations of TBT in samples collected from this site gave extremely high values and showed a close correlation between the degree of imposex and TBT concentration. Recent investigations in the area have shown a significant decrease. Surveys were also conducted in sites that exhibit highly irregular coastal profiles to examine the relevance of physical environments. Alarming concentrations of TBT were determined in most of the sites where heavy boat traffic and/or marine activities occur, demonstrating the urgent need for regulations to avoid further input of TBT. Reports from other sites in South America reveal that this should be a subject of regional concern in order to avoid severe damage to the biodiversity of regional marine organisms.

Are endocrine disruptors among the causes of the deterioration of aquatic biodiversity?

Exposure to environmental pollutants such as endocrine-disrupting compounds (EDCs) is now taken into account to explain partially the biodiversity decline of aquatic ecosystems. Much research has demonstrated that EDCs can adversely affect the endocrine system, reproductive health, and immune function in aquatic species. These toxicological effects include 1) interference with normal hormonal synthesis, release, and transport, 2) impairment of growth, development, and gonadal maturation, and 3) increased sensitivity to environmental stressors. Recent studies also have confirmed that EDCs have carcinogenic and mutagenic potential. In essence, these changes in physiological and biochemical parameters reflect, to some extent, some phenotypic characteristics of the deterioration of aquatic biodiversity. At present, evidence at the molecular level shows that exposure to EDCs can trigger genotoxicity, such as DNA damage, and can reduce genetic diversity. Field studies have also provided more direct evidence that EDCs contribute to the population decrease and biodiversity decline. Evolutionary toxicology and multigenerational toxicity tests have further demonstrated that EDCs can damage an organism's offspring and eventually likely lead to loss of evolutionary potential. Taken together, these results provide some basis for understanding the relationship between variety deterioration and EDC exposure. It is conceivable that there is a causal association between EDC exposure and variety deterioration of aquatic organisms.

Effects of tributyltin (TBT) on in vitro hormonal and biotransformation responses in Atlantic salmon (Salmo salar)

The mechanisms by which the biocide tributyltin (TBT) and its metabolites affect the hormonal and xenobiotic biotransformation pathways in aquatic species are not well understood. In this study hepatocytes isolated from salmon were used to evaluate the mechanistical effects of TBT on fish hormonal and xenobiotic biotransformation pathways. Cells were exposed to 0.01, 0.1, 1, or 5 microM TBT and samples were collected at 0, 12, 24, or 48 h following exposure. Gene expression patterns were evaluated using quantitative polymerase chain reaction (PCR), and cytochrome P-450 (CYP)-mediated enzyme activities were evaluated by ethoxyresorufin, benzyloxyresorufin, and pentoxyresorufin O-deethylase (EROD, BROD, and PROD, respectively) activity assays. Generally, exposure of hepatocytes to 1 microM (at 48 h) and 5 microM TBT (at 12, 24, and 48 h) consistently produced reductions in all mRNA species investigated. TBT produced significant decreases of vitellogen (Vtg) expression at 48 h and modified the expression patterns of estrogen receptors (ERalpha and ERbeta) and androgen receptor-beta (ARbeta) that were dependent on time and TBT concentration. In the xenobiotic biotransformation pathway, TBT produced differential expression patterns that were dependent on exposure time and concentration for all salmonid AhR2 isoforms (AhR2alpha, AhR2beta, AhR2delta, and AhR2gamma). For CYP1A1, CYP3A, AhRR, and Arnt mRNA, TBT produced exposure- and time-specific modulations. Catalytic CYP activities showed that BROD activity increased in an apparent concentration-specific manner in cells exposed to TBT for 12 h. Interestingly, EROD activity showed a TBT concentration-dependent increase at 24 h and PROD at 12 and 48 h of exposure. In general our data show that TBT differentially modulated hormonal and biotransformation responses in the salmon in vitro system. The apparent and consistent decrease of the studied responses with time in 1 and 5 microM exposed hepatocytes suggest a possible transcription inhibitory effect of TBT.