Endocrine-disrupting organotin compounds are potent inducers of adipogenesis in vertebrates

Endocrine Disruptors and Obesity

PURPOSE OF REVIEW

The purpose of this review was to summarise current evidence that some environmental chemicals may be able to interfere in the endocrine regulation of energy metabolism and adipose tissue structure.

RECENT FINDINGS

Recent findings demonstrate that such endocrine-disrupting chemicals, termed "obesogens", can promote adipogenesis and cause weight gain. This includes compounds to which the human population is exposed in daily life through their use in pesticides/herbicides, industrial and household products, plastics, detergents, flame retardants and as ingredients in personal care products. Animal models and epidemiological studies have shown that an especially sensitive time for exposure is in utero or the neonatal period. In summarising the actions of obesogens, it is noteworthy that as their structures are mainly lipophilic, their ability to increase fat deposition has the added consequence of increasing the capacity for their own retention. This has the potential for a vicious spiral not only of increasing obesity but also increasing the retention of other lipophilic pollutant chemicals with an even broader range of adverse actions. This might offer an explanation as to why obesity is an underlying risk factor for so many diseases including cancer.

Characterization of Adipogenic Chemicals in Three Different Cell Culture Systems: Implications for Reproducibility Based on Cell Source and Handling

The potential for chemical exposures to exacerbate the development and/or prevalence of metabolic disorders, such as obesity, is currently of great societal concern. Various in vitro assays are available to assess adipocyte differentiation, though little work has been done to standardize protocols and compare models effectively. This study compares several adipogenic cell culture systems under a variety of conditions to assess variability in responses. Two sources of 3T3-L1 preadipocytes as well as OP9 preadipocytes were assessed for cell proliferation and triglyceride accumulation following different induction periods and using various tissue culture plates. Both cell line and cell source had a significant impact on potencies and efficacies of adipogenic chemicals. Gene expression analyses suggested that differential expression of nuclear receptors involved in adipogenesis underlie the differences between OP9 and 3T3-L1 cells; however, there were also differences based on 3T3-L1 cell source. Induction period modulated potency and efficacy of response depending on cell line and test chemical, and large variations were observed in triglyceride accumulation and cell proliferation between brands of tissue culture plates. Our results suggest that the selection of a cell system and differentiation protocol significantly impacts the detection of adipogenic chemicals, and therefore, influences reproducibility of these studies.

Levels of TBT and other selected organotin compounds in duplicate diet samples

Organotin compounds (OTs) are ubiquitous contaminants with a broad range of applications ranging from biocides and pesticides to catalysts for the production of polyurethane foams and silicones. The deleterious effects of some OTs (particularly tributyltin - TBT) upon wildlife and experimental animals are well documented and include endocrine disruption, immunotoxicity, neurotoxicity, genotoxicity and metabolic dysfunction in which obesity is included. However, virtually no data on the current human exposure levels is available. In order to bridge this gap, we quantified for the first time the levels of OTs in duplicate diet samples from members of the University of Aveiro in Portugal. OTs were detected in 32% of the 28 diet samples analyzed, at relatively low levels. TBT and monobutyltin were detected only in two samples and dibutyltin was detectable in three samples. Dioctyltin was quantified in four samples and monooctyltin in three samples. Phenyltins were below the detection limit in all the diet samples analyzed. Overall, for the vast majority of the samples (89%), the estimated daily intakes (EDI) of organotins through food were much lower than the established tolerable daily intakes (TDI). Hence, for the majority of the participants the risk associated with food ingestion is low.

The unexpected teratogenicity of RXR antagonist UVI3003 via activation of PPARγ in Xenopus tropicalis

The RXR agonist (triphenyltin, TPT) and the RXR antagonist (UVI3003) both show teratogenicity and, unexpectedly, induce similar malformations in Xenopus tropicalis embryos. In the present study, we exposed X. tropicalis embryos to UVI3003 in seven specific developmental windows and identified changes in gene expression. We further measured the ability of UVI3003 to activate Xenopus RXRα (xRXRα) and PPARγ (xPPARγ) in vitro and in vivo. We found that UVI3003 activated xPPARγ either in Cos7 cells (in vitro) or Xenopus embryos (in vivo). UVI3003 did not significantly activate human or mouse PPARγ in vitro; therefore, the activation of Xenopus PPARγ by UVI3003 is novel. The ability of UVI3003 to activate xPPARγ explains why UVI3003 and TPT yield similar phenotypes in Xenopus embryos. Our results indicate that activating PPARγ leads to teratogenic effects in Xenopus embryos. More generally, we infer that chemicals known to specifically modulate mammalian nuclear hormone receptors cannot be assumed to have the same activity in non-mammalian species, such as Xenopus. Rather they must be tested for activity and specificity on receptors of the species in question to avoid making inappropriate conclusions.

Mechanisms of Action of Compounds That Enhance Storage Lipid Accumulation in Daphnia magna

Accumulation of storage lipids in the crustacean Daphnia magna can be altered by a number of exogenous and endogenous compounds, like 20-hydroxyecdysone (natural ligand of the ecdysone receptor, EcR), methyl farnesoate, pyrirproxyfen (agonists of the methyl farnesoate receptor, MfR), and tributyltin (agonist of the retinoid X acid receptor, RXR). This effect, analogous to the obesogenic disruption in mammals, alters Daphnia's growth and reproductive investment. Here we propose that storage lipid accumulation in droplets is regulated in Daphnia by the interaction between the nuclear receptor heterodimer EcR:RXR and MfR. The model was tested by determining changes in storage lipid accumulation and on gene transcription in animals exposed to different effectors of RXR, EcR, and MfR signaling pathways, either individually or in combination. RXR, EcR, and MfR agonists increased storage lipid accumulation, whereas fenarimol and testosterone (reported inhibitors of ecdysteroid synthesis and an EcR antagonist, respectively) decreased it. Joint effects of mixtures with fenarimol, testosterone, and ecdysone were antagonistic, mixtures of juvenoids showed additive effects following a concentration addition model, and combinations of tributyltin with juvenoids resulted in greater than additive effects. Co-exposures of ecdysone with juvenoids resulted in deregulation of ecdysone- and farnesoid-regulated genes, accordingly with the observed changes in lipid accumulation These results indicate the requirement of ecdysone binding to the EcR:RXR:MfR complex to regulate lipid storage and that an excess of ecdysone disrupts the whole process, probably by triggering negative feedback mechanisms.

The commonly used nonionic surfactant Span 80 has RXRα transactivation activity, which likely increases the obesogenic potential of oil dispersants and food emulsifiers

Obesity has reached pandemic proportions, and there is mounting evidence that environmental exposures to endocrine disrupting chemicals known as "obesogens" may contribute to obesity and associated medical conditions. The Deepwater Horizon (DWH) oil spill resulted in a massive environmental release of crude oil and remediation efforts applied large quantities of Corexit dispersants to the oil spill. The Corexit-enhanced Water Accommodated Fraction (CWAF) of DWH crude oil contains PPARγ transactivation activity, which is attributed to dioctyl sodium sulfosuccinate (DOSS), a probable obesogen. In addition to its use in oil dispersants, DOSS is commonly used as a stool softener and food additive. Because PPARγ functions as a heterodimer with RXRα to transcriptionally regulate adipogenesis we investigated the potential of CWAF to transactivate RXRα and herein demonstrated that the Corexit component Span 80 has RXRα transactivation activity. Span 80 bound to RXRα in the low micromolar range and promoted adipocyte differentiation of 3T3-L1 preadipocytes. Further, the combination of DOSS and Span 80 increased 3T3-L1 adipocyte differentiation substantially more than treatment with either chemical individually, likely increasing the obesogenic potential of Corexit dispersants. From a public health standpoint, the use of DOSS and Span 80 as food additives heightens concerns regarding their use and mandates further investigations.

Environmental Chemicals Modulate Polar Bear (Ursus maritimus) Peroxisome Proliferator-Activated Receptor Gamma (PPARG) and Adipogenesis in Vitro

We studied interactions between polar bear peroxisome proliferator-activated receptor gamma (pbPPARG) and selected compounds using a luciferase reporter assay and predictions through molecular docking. Furthermore, we studied adipogenesis by liver and adipose tissue extracts from a polar bear and three synthetic mixtures of contaminants in murine 3T3-L1 preadipocytes and polar bear adipose tissue-derived stem cells (pbASCs). PCB153 and p,p'-DDE antagonized pbPPARG, although their predicted receptor-ligand affinity was weak. PBDEs, tetrabromobisphenol A, and PCB170 had a weak agonistic effect on pbPPARG, while hexabromocyclododecane, bisphenol A, oxychlordane, and endosulfan were weak antagonists. pbPPARG-mediated luciferase activity was suppressed by synthetic contaminant mixtures reflecting levels measured in polar bear adipose tissue, as were transcript levels of PPARG and the PPARG target gene fatty acid binding protein 4 (FABP4) in pbASCs. Contaminant extracts from polar bear tissues enhanced triglyceride accumulation in murine 3T3-L1 cells and pbASCs, whereas triglyceride accumulation was not affected by the synthetic mixtures. Chemical characterization of extracts using nontarget methods revealed presence of exogenous compounds that have previously been reported to induce adipogenesis. These compounds included phthalates, tonalide, and nonylphenol. In conclusion, major legacy contaminants in polar bear adipose tissue exert antagonistic effects on PPARG, but adipogenesis by a mixture containing emerging compounds may be enhanced through PPARG or other pathways.

PCB and OCP accumulation and evidence of hepatic alteration in the Atlantic bluefin tuna, T. thynnus, from the Mediterranean Sea

Persistent organic pollutants (POPs) are known to act as "obesogens", being fat-soluble and affecting lipid metabolism. The Atlantic bluefin tuna, Thunnus thynnus, are top pelagic predators prone to bioaccumulate and biomagnify environmental contaminants. This study aimed at evaluating POPs-induced ectopic lipid accumulation in liver of adult tuna from the Mediterranean Sea. PCBs and organochlorine pesticides were measured in tuna liver, and marked morphological changes observed, namely poorly compacted tissues, intense vacuolization, erythrocyte infiltration and presence of melanomacrophages. The expression of perilipin, a lipid-droplet marker, positively correlated with the gene expression of PPARγ, a master regulator of adipogenesis, and its heterodimeric partner, RXRα. Changes in metabolites involved in fatty acid biosynthesis and ketogenesis were also observed. Although male bluefin tuna appeared to be more sensitive than females to the adverse effects of environmental obesogens, the alterations observed in tuna liver of both sexes suggest a potential onset of hepatic steatosis.

Fish condition factor, peroxisome proliferator activated receptors and biotransformation responses in Sarotherodon melanotheron from a contaminated freshwater dam (Awba Dam) in Ibadan, Nigeria

The relationship between condition factor (CF), peroxisome proliferator-activated receptors (PPARs), phase 1 biotransformation (CYP1A isoforms) and contaminant burden has been studied in Sarotherodon melanotheron from a contaminated tropical freshwater dam (Awba Dam) and compared to a reference site (Modete Dam) in Southwest, Nigeria. A total of 89 fish (57 males and 32 females) was collected from Awba Dam and 95 fish (48 males and 47 females) from the reference site. In general, fish sampled from Awba Dam were bigger than reference site. Sediment samples were also collected from both sites for contaminant analysis. Expression of ppar and cyp1 isoforms was analyzed using validated real-time PCR, while CYP1A and PPAR protein levels were analyzed using immunochemical method with specific antibodies. CYP-mediated catalytic responses (EROD, MROD and BROD) were performed by biochemical methods. We observed significant increases in ppar and cyp1 isoforms mRNA in both male and female fish from Awba Dam, compared to the reference site. Catalytic activities of EROD, MROD and BROD paralleled cyp1 transcript levels. Sex-related differences in PPAR and CYP1A protein levels were also observed, showing higher CYP1A proteins in males, compared with females, and higher PPAR proteins in females compared with males. Principal component analysis (PCA) biplot showed positive relationships between biological responses (ppar isoforms), condition factor (CF) and sediment PCBs, PAHs, OCPs and heavy metal concentrations. The present study shows that S. melanotheron inhabiting Awba Dam are severely affected by different classes of environmental contaminants that target metabolic processes (PPAR) and biotransformation pathways (CYP1A) in male and female fish, compared to a reference site. Interestingly, fish from Awba Dam were exhibiting good growth (evidence by high CF values) that paralleled increases in the transcriptional activation of ppar and cyp1 isoforms, despite the high contaminant burdens, suggesting a possible contaminant-induced obesogenic effects.

Dynamics of nuclear receptor gene expression during Pacific oyster development

BACKGROUND

Nuclear receptors are a highly conserved set of ligand binding transcription factors, with essential roles regulating aspects of vertebrate and invertebrate biology alike. Current understanding of nuclear receptor regulated gene expression in invertebrates remains sparse, limiting our ability to elucidate gene function and the conservation of developmental processes across phyla. Here, we studied nuclear receptor expression in the early life stages of the Pacific oyster, Crassostrea gigas, to identify at which specific key stages nuclear receptors are expressed RESULTS: We used quantitative RT-PCR to determine the expression profiles of 34 nuclear receptors, revealing three developmental key stages, during which nuclear receptor expression is dynamically regulated: embryogenesis, mid development from gastrulation to trochophore larva, and late larval development prior to metamorphosis. Clustering of nuclear receptor expression patterns demonstrated that transcriptional regulation was not directly related to gene phylogeny, suggesting closely related genes may have distinct functions. Expression of gene homologs of vertebrate retinoid receptors suggests participation in organogenesis and shell-formation, as they are highly expressed at the gastrulation and trochophore larval initial shell formation stages. The ecdysone receptor homolog showed high expression just before larval settlement, suggesting a potential role in metamorphosis.

CONCLUSION

Throughout early oyster development nuclear receptors exhibited highly dynamic expression profiles, which were not confined by gene phylogeny. These results provide fundamental information on the presence of nuclear receptors during key developmental stages, which aids elucidation of their function in the developmental process. This understanding is essential as ligand sensing nuclear receptors can be disrupted by xenobiotics, a mode of action through which anthropogenic environmental pollutants have been found to mediate effects.

Editor's Highlight: Screening ToxCast Prioritized Chemicals for PPARG Function in a Human Adipose-Derived Stem Cell Model of Adipogenesis

The developmental origins of obesity hypothesis posits a multifaceted contribution of factors to the fetal origins of obesity and metabolic disease. Adipocyte hyperplasia in gestation and early childhood may result in predisposition for obesity later in life. Rodent in vitro and in vivo studies indicate that some chemicals may directly affect adipose progenitor cell differentiation, but the human relevance of these findings is unclear. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARG) is the master regulator of adipogenesis. Human adipose-derived stem cells (hASC) isolated from adipose tissue express endogenous isoforms of PPARG and represent a biologically relevant cell-type for evaluating activity of PPARG ligands. Here, a multi-endpoint approach based on a phenotypic adipogenesis assay was applied to screen a set of 60 chemical compounds identified in ToxCast Phase I as PPARG active (49) or inactive (11). Chemicals showing activity in the adipogenesis screen were further evaluated in a series of 4 orthogonal assays representing 7 different key events in PPARG-dependent adipogenesis, including gene transcription, protein expression, and adipokine secretion. An siRNA screen was also used to evaluate PPARG-dependence of the adipogenesis phenotype. A universal concentration-response design enabled inter-assay comparability and implementation of a weight-of-evidence approach for bioactivity classification. Collectively, a total of 14/49 (29%) prioritized chemicals were identified with moderate-to-strong activity for human adipogenesis. These results provide the first integrated screening approach of prioritized ToxCast chemicals in a human stem cell model of adipogenesis and provide insight into the capacity of PPARG-activating chemicals to modulate early life programming of adipose tissue.

Effects of long-term endocrine disrupting compound exposure on Macaca mulatta embryonic stem cells

Endocrine disrupting chemicals (EDCs) exert significant effects on health and physiology, many traceable to effects on stem cell programming underlying development. Understanding risk of low-level, chronic EDC exposure will be enhanced by knowledge of effects on stem cells. We exposed rhesus monkey embryonic stem cells to low levels of five EDCs [bisphenol A (BPA), atrazine (ATR), tributyltin (TBT), perfluorooctanoic acid (PFOA), and di-(2-ethylhexyl) phthalate (DEHP)] for 28days, and evaluated effects on gene expression by RNAseq transcriptome profiling. We observed little effect of BPA, and small numbers of affected genes (≤119) with other EDCs. There was substantial overlap in effects across two, three, or four treatments. Ingenuity Pathway analysis indicated suppression of cell survival genes and genes downstream of several stress response mediators, activation of cell death genes, and modulations in several genes regulating pluripotency, differentiation, and germ layer development. Potential adverse effects of these changes on development are discussed.

Peroxisome proliferator-activated receptor gamma (PPARγ) in brown trout: Interference of estrogenic and androgenic inputs in primary hepatocytes

Peroxisome proliferator-activated receptor gamma (PPARγ) is a pivotal regulator of lipid and glucose metabolism in vertebrates. Here, we isolated and characterized for the first time the PPARγ gene from brown trout (Salmo trutta f. fario). Hormones have been reported to interfere with the regulatory function of PPARγ in various organisms, albeit with little focus on fish. Thus, primary hepatocytes isolated from juveniles of brown trout were exposed to 1, 10 and 50μM of ethinylestradiol (EE2) or testosterone (T). A significant (3 fold) decrease was obtained in response to 50μM of EE2 and to 10 and 50μM of T (13 and 14 folds), while a 3 fold increase was observed at 1μM of EE2. Therefore, trout PPARγ seems a target for natural/synthetic compounds with estrogenic or androgenic properties and so, we advocate considering PPARγ as another alert sensor gene when assessing the effects of sex-steroid endocrine disruptors.

A brominated flame retardant 2,2',4,4' tetrabrominated diphenyl ether (BDE-47) leads to lipogenesis in the copepod Tigriopus japonicus

De novo lipogenesis (DNL) is a fatty acid synthesis process that requires several genes, including sterol regulatory element binding protein (SREBP), ATP-citrate lyase (ACLY), and acetyl-CoA carboxylase (ACC). DNL up-regulation is able to induce fat accumulation through an increase in fatty acids. To investigate the relationship between DNL up-regulation and the accumulation of fatty acids and lipid droplets in response to 2,2',4,4' tetrabrominated diphenyl ether (BDE-47), we examined DNL in the copepod Tigriopus japonicus. Transcription levels of DNL-related genes were increased after exposure to 2.5μg/L BDE-47 for 24h. After exposure to 2.5μg/L BDE-47, palmitic acid was significantly increased (P<0.05) at days 1 and 4, along with upregulation of fatty acid synthesis-related genes (e.g., desaturases and elongases). However, docosahexaenoic acid and arachidonic acid were down-regulated at days 1 and 4, showing an antagonistic effect. Lipid droplet area significantly increased in Nile red staining analysis after 24h of exposure to 2.5μg/L BDE-47 in T. japonicus, while DNL was down-regulated in response to 500μM salicylate (a lipogenesis inhibitor), indicating that BDE-47 exposure is closely associated with an increase in fatty acids in this copepod. This study provides a better understanding of the effects of BDE-47 on DNL in copepods.

Tributyltin chloride induces renal dysfunction by inflammation and oxidative stress in female rats

Tributyltin chloride (TBT) is an organometallic pollutant that is used as a biocide in antifouling paints. TBT induces several toxic and endocrine-disrupting effects. However, studies evaluating the effects of TBT on renal function are rare. This study demonstrates that TBT exposure is responsible for improper renal function as well as the development of abnormal morphophysiology in mammalian kidneys. Female rats were treated with TBT, and their renal morphophysiology was assessed. Morphophysiological abnormalities such as decreased glomerular filtration rate and increased proteinuria levels were observed in TBT rats. In addition, increases in inflammation, collagen deposition and α-smooth muscle actin (α-SMA) protein expression were observed in TBT kidneys. A disrupted cellular redox balance and apoptosis in kidney tissue were also observed in TBT rats. TBT rats demonstrated reduced serum estrogen levels and estrogen receptor-α (ERα) protein expression in renal cortex. Together, these data provide in vivo evidence that TBT is toxic to normal renal function and that these effects may be associated with renal histopathology complications, such as inflammation and fibrosis.

On the Utility of ToxCast™ and ToxPi as Methods for Identifying New Obesogens

BACKGROUND

In ToxCast™ Phase I, the U.S. EPA commissioned screening of 320 pesticides, herbicides, fungicides, and other chemicals in a series of high-throughput assays. The agency also developed a toxicological prioritization tool, ToxPi, to facilitate using ToxCast™ assays to predict biological function.

OBJECTIVES

We asked whether top-scoring PPARγ activators identified in ToxCast™ Phase I were genuine PPARγ activators and inducers of adipogenesis. Next, we identified ToxCast™ assays that should predict adipogenesis, developed an adipogenesis ToxPi, and asked how well the ToxPi predicted adipogenic activity.

METHODS

We used transient transfection to test the ability of ToxCast™ chemicals to modulate PPARγ and RXRα, and differentiation assays employing 3T3-L1 preadipocytes and mouse bone marrow-derived mesenchymal stem cells (mBMSCs) to evaluate the adipogenic capacity of ToxCast™ chemicals.

RESULTS

Only 5/21 of the top scoring ToxCast™ PPARγ activators were activators in our assays, 3 were PPARγ antagonists, the remainder were inactive. The bona fide PPARγ activators we identified induced adipogenesis in 3T3-L1 cells and mBMSCs. Only 7 of the 17 chemicals predicted to be active by the ToxPi promoted adipogenesis, 1 inhibited adipogenesis, and 2 of the 7 predicted negatives were also adipogenic. Of these 9 adipogenic chemicals, 3 activated PPARγ, and 1 activated RXRα.

CONCLUSIONS

ToxCast™ PPARγ and RXRα assays do not correlate well with laboratory measurements of PPARγ and RXRα activity. The adipogenesis ToxPi performed poorly, perhaps due to the performance of ToxCast™ assays. We observed a modest predictive value of ToxCast™ for PPARγ and RXRα activation and adipogenesis and it is likely that many obesogenic chemicals remain to be identified.

CITATION

Janesick AS, Dimastrogiovanni G, Vanek L, Boulos C, Chamorro-García R, Tang W, Blumberg B. 2016. On the utility of ToxCast™ and ToxPi as methods for identifying new obesogens. Environ Health Perspect 124:1214-1226; http://dx.doi.org/10.1289/ehp.1510352.

Prioritizing Environmental Chemicals for Obesity and Diabetes Outcomes Research: A Screening Approach Using ToxCast™ High-Throughput Data

BACKGROUND

Diabetes and obesity are major threats to public health in the United States and abroad. Understanding the role that chemicals in our environment play in the development of these conditions is an emerging issue in environmental health, although identifying and prioritizing chemicals for testing beyond those already implicated in the literature is challenging. This review is intended to help researchers generate hypotheses about chemicals that may contribute to diabetes and to obesity-related health outcomes by summarizing relevant findings from the U.S. Environmental Protection Agency (EPA) ToxCast™ high-throughput screening (HTS) program.

OBJECTIVES

Our aim was to develop new hypotheses around environmental chemicals of potential interest for diabetes- or obesity-related outcomes using high-throughput screening data.

METHODS

We identified ToxCast™ assay targets relevant to several biological processes related to diabetes and obesity (insulin sensitivity in peripheral tissue, pancreatic islet and β cell function, adipocyte differentiation, and feeding behavior) and presented chemical screening data against those assay targets to identify chemicals of potential interest.

DISCUSSION

The results of this screening-level analysis suggest that the spectrum of environmental chemicals to consider in research related to diabetes and obesity is much broader than indicated by research papers and reviews published in the peer-reviewed literature. Testing hypotheses based on ToxCast™ data will also help assess the predictive utility of this HTS platform.

CONCLUSIONS

More research is required to put these screening-level analyses into context, but the information presented in this review should facilitate the development of new hypotheses.

CITATION

Auerbach S, Filer D, Reif D, Walker V, Holloway AC, Schlezinger J, Srinivasan S, Svoboda D, Judson R, Bucher JR, Thayer KA. 2016. Prioritizing environmental chemicals for obesity and diabetes outcomes research: a screening approach using ToxCast™ high-throughput data. Environ Health Perspect 124:1141-1154; http://dx.doi.org/10.1289/ehp.1510456.

Developmental Exposure to Environmental Chemicals and Metabolic Changes in Children

The incidence of childhood obesity, type 2 diabetes, and other forms of metabolic disease have been rising over the past several decades. Although diet and physical activity play important roles in these trends, other environmental factors also may contribute to this significant public health issue. In this article, we discuss the possibility that widespread exposure to endocrine-disrupting chemicals (EDCs) may contribute to the development of metabolic diseases in children. We summarize the epidemiological evidence on exposure to environmental chemicals during early development and metabolic outcomes in infants and children. Prenatal exposure to EDCs, particularly the persistent organic pollutant DDT and its metabolite DDE, may influence growth patterns during infancy and childhood. The altered growth patterns associated with EDCs vary according to exposure level, sex, exposure timing, pubertal status, and age at which growth is measured. Early exposure to air pollutants also is linked to impaired metabolism in infants and children. As a result of these and other studies, professional health provider societies have called for a reduction in environmental chemical exposures. We summarize the resources available to health care providers to counsel patients on how to reduce chemical exposures. We conclude with a discussion of environmental policies that address chemical exposures and ultimately aim to improve public health.

The Environmental Pollutant Tributyltin Chloride Disrupts the Hypothalamic-Pituitary-Adrenal Axis at Different Levels in Female Rats

Tributyltin chloride (TBT) is an environmental contaminant that is used as a biocide in antifouling paints. TBT has been shown to induce endocrine-disrupting effects. However, studies evaluating the effects of TBT on the hypothalamus-pituitary-adrenal (HPA) axis are especially rare. The current study demonstrates that exposure to TBT is critically responsible for the improper function of the mammalian HPA axis as well as the development of abnormal morphophysiology in the pituitary and adrenal glands. Female rats were treated with TBT, and their HPA axis morphophysiology was assessed. High CRH and low ACTH expression and high plasma corticosterone levels were detected in TBT rats. In addition, TBT leads to an increased in the inducible nitric oxide synthase protein expression in the hypothalamus of TBT rats. Morphophysiological abnormalities, including increases in inflammation, a disrupted cellular redox balance, apoptosis, and collagen deposition in the pituitary and adrenal glands, were observed in TBT rats. Increases in adiposity and peroxisome proliferator-activated receptor-γ protein expression in the adrenal gland were observed in TBT rats. Together, these data provide in vivo evidence that TBT leads to functional dissociation between CRH, ACTH, and costicosterone, which could be associated an inflammation and increased of inducible nitric oxide synthase expression in hypothalamus. Thus, TBT exerts toxic effects at different levels on the HPA axis function.

Deleterious effects of tributyltin on porcine vascular stem cells physiology

The vascular functional and structural integrity is essential for the maintenance of the whole organism and it has been demonstrated that different types of vascular progenitor cells resident in the vessel wall play an important role in this process. The purpose of the present research was to observe the effect of tributyltin (TBT), a risk factor for vascular disorders, on porcine Aortic Vascular Precursor Cells (pAVPCs) in term of cytotoxicity, gene expression profile, functionality and differentiation potential. We have demonstrated that pAVPCs morphology deeply changed following TBT treatment. After 48h a cytotoxic effect has been detected and Annexin binding assay demonstrated that TBT induced apoptosis. The transcriptional profile of characteristic pericyte markers has been altered: TBT 10nM substantially induced alpha-SMA, while, TBT 500nM determined a significant reduction of all pericyte markers. IL-6 protein detected in the medium of pAVPCs treated with TBT at both doses studied and with a dose response. TBT has interfered with normal pAVPC functionality preventing their ability to support a capillary-like network. In addition TBT has determined an increase of pAVPC adipogenic differentiation. In conclusion in the present paper we have demonstrated that TBT alters the vascular stem cells in terms of structure, functionality and differentiating capability, therefore effects of TBT in blood should be deeply explored to understand the potential vascular risk associated with the alteration of vascular stem cell physiology.

Trialkyltin Rexinoid-X Receptor Agonists Selectively Potentiate Thyroid Hormone Induced Programs of Xenopus laevis Metamorphosis

The trialkyltins tributyltin (TBT) and triphenyltin (TPT) can function as rexinoid-X receptor (RXR) agonists. We recently showed that RXR agonists can alter thyroid hormone (TH) signaling in a mammalian pituitary TH-responsive reporter cell line, GH3.TRE-Luc. The prevalence of TBT and TPT in the environment prompted us to test whether they could also affect TH signaling. Both trialkyltins induced the integrated luciferase reporter alone and potentiated TH activation at low doses. Trimethyltin, which is not an RXR agonist, did not. We turned to a simple, robust, and specific in vivo model system of TH action: metamorphosis of Xenopus laevis, the African clawed frog. Using a precocious metamorphosis assay, we found that 1nM TBT and TPT, but not trimethyltin, greatly potentiated the effect of TH treatment on resorption phenotypes of the tail, which is lost at metamorphosis, and in the head, which undergoes extensive remodeling including gill loss. Consistent with these responses, TH-induced caspase-3 activation in the tail was enhanced by cotreatment with TBT. Induction of a transgenic reporter gene and endogenous collagenase 3 (mmp13) and fibroblast-activating protein-α (fap) genes were not induced by TBT alone, but TH induction was significantly potentiated by TBT. However, induction of other TH receptor target genes such as TRβ and deiodinase 3 by TH were not affected by TBT cotreatment. These data indicate that trialkyltins that can function as RXR agonists can selectively potentiate gene expression and resultant morphological programs directed by TH signaling in vivo.

Adult exposure to tributyltin affects hypothalamic neuropeptide Y, Y1 receptor distribution, and circulating leptin in mice

Tributyltin (TBT), a pesticide used in antifouling paints, is toxic for aquatic invertebrates. In vertebrates, TBT may act in obesogen- inducing adipogenetic gene transcription for adipocyte differentiation. In a previous study, we demonstrated that acute administration of TBT induces c-fos expression in the arcuate nucleus. Therefore, in this study, we tested the hypothesis that adult exposure to TBT may alter a part of the nervous pathways controlling animal food intake. In particular, we investigated the expression of neuropeptide Y (NPY) immunoreactivity. This neuropeptide forms neural circuits dedicated to food assumption and its action is mediated by Y1 receptors that are widely expressed in the hypothalamic nuclei responsible for the regulation of food intake and energy homeostasis. To this purpose, TBT was orally administered at a dose of 0.025 mg/kg/day/body weight to adult animals [male and female C57BL/6 (Y1-LacZ transgenic mice] for 4 weeks. No differences were found in body weight and fat deposition, but we observed a significant increase in feed efficiency in TBT-treated male mice and a significant decrease in circulating leptin in both sexes. Computerized quantitative analysis of NPY immunoreactivity and Y1-related β-galactosidase activity demonstrated a statistically significant reduction in NPY and Y1 transgene expression in the hypothalamic circuit controlling food intake of treated male mice in comparison with controls. In conclusion, the present results indicate that adult exposure to TBT is profoundly interfering with the nervous circuits involved in the stimulation of food intake.

Tributyltin disrupts feeding and energy metabolism in the goldfish (Carassius auratus)

Tributyltin (TBT) can induce obesogen response. However, little is known about the adverse effects of TBT on food intake and energy metabolism. The present study was designed to investigate the effects of TBT, at environmental concentrations of 2.44 and 24.4 ng/L (1 and 10 ng/L as Sn), on feeding and energy metabolism in goldfish (Carassius auratus). After exposure for 54 d, TBT increased the weight gain and food intake in fish. The patterns of brain neuropeptide genes expression were in line with potential orexigenic effects, with increased expression of neuropeptide Y and apelin, and decreased expression of pro-opiomelanocortin, ghrelin, cocaine and amphetamine-regulated transcript, and corticotropin-releasing factor. Interestingly, the energy metabolism indicators (oxygen consumption, ammonia exertion and swimming activity) and the serum thyroid hormones were all significantly increased at the 2.44 ng/L TBT group in fish. However, no changes of energy metabolism indicators or a decrease of thyroid hormones was found at the 24.4 ng/L TBT group, which indicated a complex disrupting effect on metabolism of TBT. In short, TBT can alter feeding and energy metabolism in fish, which might promote the obesogenic responses.

Triphenyltin induces imposex in Nucella lapillus through an aphallic route

Triphenyltin (TPT) was used until recently as a biocide in antifouling systems and nowadays is still applied as an agriculture pesticide in some countries. This compound is known to cause imposex (the imposition of male characters in females of gastropod molluscs) in a very limited number of species, when compared with tributyltin (TBT), the universally recognized imposex-causing agent. In this study, we tested if TPT could induce imposex in females of the dog-whelk Nucella lapillus. Experimental groups of 40 females were injected with a volume of 2μL/g of soft tissue wet weight (ww) of one of the following treatments, using DMSO as a solvent carrier: DMSO (solvent control); 1μg/g ww of TBT (positive control); 0.2, 1 and 5μg/g ww of TPT and a non-injected group (negative control). Concentrations were confirmed in the organism tissues by means of chemical analyses of a pool of 10 specimens at T0 and then after the imposex analysis at T56days. After 8-week trial, results pointed out statistically significant differences between treatments, with both TPT and TBT positively inducing imposex. However, imposex development in TPT-injected females differed from that of TBT, since females that developed imposex presented an aphallic condition (no penis development) while the TBT-treated females developed standard imposex (with penis formation). These results suggest that TPT and TBT act differently in the sequential process of female masculinization, casting new insights about the hypothetical pathways underlying imposex development.

BMI and BMD: The Potential Interplay between Obesity and Bone Fragility

Recent evidence demonstrating an increased fracture risk among obese individuals suggests that adipose tissue may negatively impact bone health, challenging the traditional paradigm of fat mass playing a protective role towards bone health. White adipose tissue, far from being a mere energy depot, is a dynamic tissue actively implicated in metabolic reactions, and in fact secretes several hormones called adipokines and inflammatory factors that may in turn promote bone resorption. More specifically, Visceral Adipose Tissue (VAT) may potentially prove detrimental. It is widely acknowledged that obesity is positively associated to many chronic disorders such as metabolic syndrome, dyslipidemia and type 2 diabetes, conditions that could themselves affect bone health. Although aging is largely known to decrease bone strength, little is yet known on the mechanisms via which obesity and its comorbidities may contribute to such damage. Given the exponentially growing obesity rate in recent years and the increased life expectancy of western countries it appears of utmost importance to timely focus on this topic.

Obesogens: an emerging threat to public health

Endocrine disrupting chemicals (EDCs) are defined as exogenous chemicals, or mixtures of chemicals, that can interfere with any aspect of hormone action. The field of endocrine disruption is historically rooted in wildlife biology and reproductive endocrinology where EDCs are demonstrated contributors to infertility, premature puberty, endometriosis, and other disorders. Recently, EDCs have been implicated in metabolic syndrome and obesity. Adipose tissue is a true endocrine organ and, therefore, an organ that is highly susceptible to disturbance by EDCs. A subset of EDCs, called "obesogens," promote adiposity by altering programming of fat cell development, increasing energy storage in fat tissue, and interfering with neuroendocrine control of appetite and satiety. Obesity adds more than $200 billion to US healthcare costs and the number of obese individuals continues to increase. Hence, there is an urgent, unmet need to understand the mechanisms underlying how exposures to certain EDCs may predispose our population to be obese. In this review, we discuss the history of obesogen discovery from its origins in reproductive biology to its latest role in the transgenerational inheritance of obesity in mice. We discuss the development of adipose tissue in an embryo, maintenance of adipocyte number in adults, how EDC disruption programs stem cells to preferentially make more adipocytes, the mechanisms by which chemicals can permanently alter the germline epigenome, and whether there are barriers to EDCs in the gametes.

Uppsala Consensus Statement on Environmental Contaminants and the Global Obesity Epidemic

Summary: From the lectures presented at the 2nd International Workshop on Obesity and Environmental Contaminants, which was held in Uppsala, Sweden, on 8–9 October 2015, it became evident that the findings from numerous animal and epidemiological studies are consistent with the hypothesis that environmental contaminants could contribute to the global obesity epidemic. To increase awareness of this important issue among scientists, regulatory agencies, politicians, chemical industry management, and the general public, the authors summarize compelling scientific evidence that supports the hypothesis and discuss actions that could restrict the possible harmful effects of environmental contaminants on obesity.

Peroxisome proliferator-activated receptors and biotransformation responses in relation to condition factor and contaminant burden in tilapia species from Ogun River, Nigeria

A major development in fishery science has been the Fulton's condition factor (CF) as a reliable physiological index of fish growth and health status (Fulton 1902). As a general rule, CF-value greater than 1 (>1) should be regarded as an indicator for good growth and health. Therefore, exposure of fish to contaminants in the environment will be expected to produce a reduction in scope for growth, since energy for growth will be allocated to overcome stressful conditions. In the present study, we hypothesized that tilapia species from Ogun River (Nigeria) are experiencing severe contaminant-induced obesogen effects leading to high CF (≥ 2) in fish with pathological alterations. The environmental obesogen hypothesis has related the interaction between environmental pollutants and PPAR isoform activation In this respect, peroxisome proliferator-activated receptors (PPARs) and biotransformation responses in relation to contaminant burden were investigated in a total of 1074 specimens of Tilapias species (Tilapia guineensis, Sarotherodon galileaus and Oreochromis niloticus) collected from three areas with different degrees of anthropogenic contamination and from a putative control site along the Ogun River. Liver mRNA expression of cytochrome cyp1 isoforms (cyp1a, 1b and 1c) and PPAR isoforms (ppar-α, β and γ) were analyzed using validated real-time PCR. Fish were also analyzed for CF and muscle contaminant burden (aliphatic and polycyclic aromatic hydrocarbons, organochlorine pesticides, and polychlorinated biphenyls). A significant increase in mRNA expression of cyp1- and ppar isoforms was observed in fish from polluted areas, and these results paralleled data on PCBs and PAHs tissue concentrations. Further, cyp1 isoforms showed clear sex-related differences, with higher mRNA expression in male fish than in females. Principal component analysis revealed a relationship between cyp1 isoforms, ppar-α, β, PCBs and PAHs and these interactions may suggest a crosstalk between AhR- and PPARs mediated pathways on metabolic and energetic processes. The PCA biplot also highlighted a positive relationship between ppar-γ, body weight, total length and PAHs. The CF for fish from all the sites was ≥ 2 indicating that this parameter may not be a reliable index for evaluating fish growth and health condition, especially in wild fish population exposed to complex cocktails of environmental pollutants.

Novel functions of PXR in cardiometabolic disease

Cardiometabolic disease emerges as a worldwide epidemic and there is urgent need to understand the molecular mechanisms underlying this chronic disease. The chemical environment to which we are exposed has significantly changed in the past few decades and recent research has implicated its contribution to the development of many chronic human diseases. However, the mechanisms of how exposure to chemicals contributes to the development of cardiometabolic disease are poorly understood. Numerous chemicals have been identified as ligands for the pregnane X receptor (PXR), a nuclear receptor functioning as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. In the past decade, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied by many laboratories and the role of PXR as a xenobiotic sensor has been well-established. The identification of PXR as a xenobiotic sensor has provided an important tool for the study of new mechanisms through which xenobiotic exposure impacts human chronic diseases. Recent studies have revealed novel and unexpected roles of PXR in modulating obesity, insulin sensitivity, lipid homeostasis, atherogenesis, and vascular functions. These studies suggest that PXR signaling may contribute significantly to the pathophysiological effects of many known xenobiotics on cardiometabolic disease in humans. The discovery of novel functions of PXR in cardiometabolic disease not only contributes to our understanding of "gene-environment interactions" in predisposing individuals to chronic diseases but also provides strong evidence to inform future risk assessment for relevant chemicals. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Obesogens: an emerging threat to public health

Endocrine disrupting chemicals (EDCs) are defined as exogenous chemicals, or mixtures of chemicals, that can interfere with any aspect of hormone action. The field of endocrine disruption is historically rooted in wildlife biology and reproductive endocrinology where EDCs are demonstrated contributors to infertility, premature puberty, endometriosis, and other disorders. Recently, EDCs have been implicated in metabolic syndrome and obesity. Adipose tissue is a true endocrine organ and, therefore, an organ that is highly susceptible to disturbance by EDCs. A subset of EDCs, called "obesogens," promote adiposity by altering programming of fat cell development, increasing energy storage in fat tissue, and interfering with neuroendocrine control of appetite and satiety. Obesity adds more than $200 billion to US healthcare costs and the number of obese individuals continues to increase. Hence, there is an urgent, unmet need to understand the mechanisms underlying how exposures to certain EDCs may predispose our population to be obese. In this review, we discuss the history of obesogen discovery from its origins in reproductive biology to its latest role in the transgenerational inheritance of obesity in mice. We discuss the development of adipose tissue in an embryo, maintenance of adipocyte number in adults, how EDC disruption programs stem cells to preferentially make more adipocytes, the mechanisms by which chemicals can permanently alter the germline epigenome, and whether there are barriers to EDCs in the gametes.

Obesity: epigenetic regulation – recent observations

Genetic and environmental factors, especially nutrition and lifestyle, have been discussed in the literature for their relevance to epidemic obesity. Gene-environment interactions may need to be understood for an improved understanding of the causes of obesity, and epigenetic mechanisms are of special importance. Consequences of epigenetic mechanisms seem to be particularly important during certain periods of life: prenatal, postnatal and intergenerational, transgenerational inheritance are discussed with relevance to obesity. This review focuses on nutrients, diet and habits influencing intergenerational, transgenerational, prenatal and postnatal epigenetics; on evidence of epigenetic modifiers in adulthood; and on animal models for the study of obesity.

Pharmacological evaluation of the mechanisms involved in increased adiposity in zebrafish triggered by the environmental contaminant tributyltin

One proposed contributing factor to the rise in overweight and obesity is exposure to endocrine disrupting chemicals. Tributyltin chloride (TBT), an organotin, induces adipogenesis in cell culture models and may increases adipose mass in vivo in vertebrate model organisms. It has been hypothesized that TBT acts via the peroxisome proliferator activated receptor (PPAR)γ-dependent pathway. However, the mechanisms involved in the effects of TBT exposure on in vivo adipose tissue metabolism remain unexplored. Semitransparent zebrafish larvae, with their well-developed white adipose tissue, offer a unique opportunity for studying the effects of toxicant chemicals and pharmaceuticals on adipocyte biology and whole-organism adiposity in a vertebrate model. Within hours, zebrafish larvae, treated at environmentally-relevant nanomolar concentrations of TBT, exhibited a remarkable increase in adiposity linked to adipocyte hypertrophy. Under the experimental conditions used, we also demonstrated that zebrafish larvae adipose tissue proved to be highly responsive to selected human nuclear receptor agonists and antagonists. Retinoid X receptor (RXR) homodimers and RXR/liver X receptor heterodimers were suggested to be in vivo effectors of the obesogenic effect of TBT on zebrafish white adipose tissue. RXR/PPARγ heterodimers may be recruited to modulate adiposity in zebrafish but were not a necessary requirement for the short term in vivo TBT obesogenic effect. Together, the present results suggest that TBT may induce the promotion of triacylglycerol storage in adipocytes via RXR-dependent pathways without necessary using PPAR isoforms.

Tributyltin promoted hepatic steatosis in zebrafish (Danio rerio) and the molecular pathogenesis involved

Endocrine disruptor effects of tributyltin (TBT) are well established in fish. However, the adverse effects on lipid metabolism are less well understood. Since the liver is the predominant site of de novo synthesis of lipids, the present study uses zebrafish (Danio rerio) to examine lipid accumulation in the livers and hepatic gene expression associated with lipid metabolism pathways. After exposure for 90 days, we found that the livers in fish exposed to TBT were yellowish in appearance and with accumulation of lipid droplet, which is consistent with the specific pathological features of steatosis. Molecular analysis revealed that TBT induced hepatic steatosis by increasing the gene expression associated with lipid transport, lipid storage, lipiogenic enzymes and lipiogenic factors in the livers. Moreover, TBT enhanced hepatic caspase-3 activity and up-regulated genes related to apoptosis and cell-death, which indicated steatotic livers of fish exposed to TBT and the subsequent liver damage were likely due to accelerated hepatocyte apoptosis or cell stress. In short, TBT can produce multiple and complex alterations in transcriptional activity of lipid metabolism and cell damage, which provides potential molecular evidence of TBT on hepatic steatosis.

The expression of selected genes linked to metabolic homeostasis in obese pansteatitis-suffering Mozambique tilapia, Oreochromis mossambicus (Peters)

The Oreochromis mossambicus (Peters) population inhabiting Lake Loskop, South Africa, is characterized by a high incidence of obesity and pansteatitis. We investigated potential links between the impaired health of Lake Loskop O. mossambicus and the endocrine system by assessing the expression of selected genes associated with the thyroid and adrenal endocrine axes as well as peroxisome proliferator-activated receptor gamma (pparg). Moreover, contaminant-induced thyroid and/or metabolic modulation in Lake Loskop water was evaluated using juvenile O. mossambicus in laboratory exposures. The expression of thyroid hormone receptor alpha (thra) and type 2 deiodinase (dio2) was higher in Lake Loskop O. mossambicus than fish from another population, suggesting a degree of thyroid disruption. The altered gene expression may be a consequence, rather than cause of obesity. Expression of dio2 and pparg was higher in juvenile O. mossambicus exposed to unfiltered compared to filtered lake water, and our data suggest fasting as causative factor. Micro-organism abundance can therefore be a confounding factor in studies applying molecular markers to test for thyroid modulation by environmental waters. Pansteatitis was not a significant source of variance in the expression of any of the genes investigated, suggesting that the disease is not associated with disrupted endocrine signalling.

The Mammalian "Obesogen" Tributyltin Targets Hepatic Triglyceride Accumulation and the Transcriptional Regulation of Lipid Metabolism in the Liver and Brain of Zebrafish

Recent findings indicate that different Endocrine Disrupting Chemicals (EDCs) interfere with lipid metabolic pathways in mammals and promote fat accumulation, a previously unknown site of action for these compounds. The antifoulant and environmental pollutant tributyltin (TBT), which causes imposex in gastropod snails, induces an “obesogenic” phenotype in mammals, through the activation of the nuclear receptors retinoid X receptor (RXR) and peroxisome proliferator-activated receptor gamma (PPARγ). In teleosts, the effects of TBT on the lipid metabolism are poorly understood, particularly following exposure to low, environmental concentrations. In this context, the present work shows that exposure of zebrafish to 10 and 50 ng/L of TBT (as Sn) from pre-hatch to 9 months of age alters the body weight, condition factor, hepatosomatic index and hepatic triglycerides in a gender and dose related manner. Furthermore, TBT modulated the transcription of key lipid regulating factors and enzymes involved in adipogenesis, lipogenesis, glucocorticoid metabolism, growth and development in the brain and liver of exposed fish, revealing sexual dimorphic effects in the latter. Overall, the present study shows that the model mammalian obesogen TBT interferes with triglyceride accumulation and the transcriptional regulation of lipid metabolism in zebrafish and indentifies the brain lipogenic transcription profile of fish as a new target of this compound.

Polycystic ovary syndrome (PCOS) and endocrine disrupting chemicals (EDCs)

Polycystic ovary syndrome (PCOS) is a heterogeneous disorder of unclear etiopathogenesis that is likely to involve genetic and environmental components synergistically contributing to its phenotypic expression. Endocrine disrupting chemicals (EDCs) and in particular Bisphenol A (BPA) represent a group of widespread pollutants intensively investigated as possible environmental contributors to PCOS pathogenesis. Substantial evidence from in vitro and animal studies incriminates endocrine disruptors in the induction of reproductive and metabolic aberrations resembling PCOS characteristics. In humans, elevated BPA concentrations are observed in adolescents and adult PCOS women compared to reproductively healthy ones and are positively correlated with hyperandrogenemia, implying a potential role of the chemical in PCOS pathophysiology, although a causal interference cannot yet be established. It is plausible that developmental exposure to specific EDCs could permanently alter neuroendocrine, reproductive and metabolic regulation favoring PCOS development in genetically predisposed individuals or it could accelerate and/or exacerbate the natural course of the syndrome throughout life cycle exposure.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Endocrine disruptors and obesity

The increasing incidence of obesity is a serious global public health challenge. Although the obesity epidemic is largely fueled by poor nutrition and lack of exercise, certain chemicals have been shown to potentially have a role in its aetiology. A substantial body of evidence suggests that a subclass of endocrine-disrupting chemicals (EDCs), which interfere with endocrine signalling, can disrupt hormonally regulated metabolic processes, especially if exposure occurs during early development. These chemicals, so-called 'obesogens' might predispose some individuals to gain weight despite their efforts to limit caloric intake and increase levels of physical activity. This Review discusses the role of EDCs in the obesity epidemic, the latest research on the obesogen concept, epidemiological and experimental findings on obesogens, and their modes of action. The research reviewed here provides knowledge that health scientists can use to inform their research and decision-making processes.

Peroxisome proliferator-activated receptor gamma signaling in human sperm physiology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the PPARs, which are transcription factors of the steroid receptor superfamily. PPARγ acts as an important molecule for regulating energy homeostasis, modulates the hypothalamic-pituitary-gonadal (HPG) axis, and is reciprocally regulated by HPG. In the human, PPARγ protein is highly expressed in ejaculated spermatozoa, implying a possible role of PPARγ signaling in regulating sperm energy dissipation. PPARγ protein is also expressed in Sertoli cells and germ cells (spermatocytes). Its activation can be induced during capacitation and the acrosome reaction. This mini-review will focus on how PPARγ signaling may affect fertility and sperm quality and the potential reversibility of these adverse effects.

Tributyltin differentially promotes development of a phenotypically distinct adipocyte

OBJECTIVE

Environmental endocrine disrupting chemicals (EDCs) are increasingly implicated in the pathogenesis of obesity. Evidence implicates various EDCs as being proadipogenic, including tributyltin (TBT), which activates the peroxisome proliferator activated receptor-γ (PPARγ). However, the conditions required for TBT-induced adipogenesis and its functional consequences are incompletely known.

METHODS

The costimulatory conditions necessary for preadipocyte-to-adipocyte differentiation were compared between TBT and the pharmacological PPARγ agonist troglitazone (Trog) in the 3T3-L1 cell line; basal and insulin-stimulated glucose uptake were assessed using radiolabeled 2-deoxyglucose.

RESULTS

TBT enhanced expression of the adipocyte marker C/EBPα with coexposure to either isobutylmethylxanthine or insulin in the absence of other adipogenic stimuli. Examination of several adipocyte-specific proteins revealed that TBT and Trog differentially affected protein expression despite comparable PPARγ stimulation. In particular, TBT reduced adiponectin expression upon maximal adipogenic stimulation. Under submaximal stimulation, TBT and Trog differentially promoted adipocyte-specific gene expression despite similar lipid accumulation. Moreover, TBT attenuated Trog-induced adipocyte gene expression under conditions of cotreatment. Finally, TBT-induced adipocytes exhibited altered glucose metabolism, with increased basal glucose uptake.

CONCLUSIONS

TBT-induced adipocytes are functionally distinct from those generated by a pharmacological PPARγ agonist, suggesting that obesogen-induced adipogenesis may generate dysfunctional adipocytes with the capacity to deleteriously affect global energy homeostasis.

Effect-Directed Analysis of Human Peroxisome Proliferator-Activated Nuclear Receptors (PPARγ1) Ligands in Indoor Dust

Agonism of human peroxisome proliferator-activated nuclear receptor gamma (PPARγ1) was recently observed in 15 of 25 samples of indoor dust extracts at environmentally relevant exposure levels. In this study, an effect-directed analysis approach was used to identify the primary contributors of PPARγ1 activity in the dust extracts. Three dust extracts showing significant PPARγ1 activity were fractionated with normal phase high-performance liquid chromatography (NP-HPLC) and each fraction was tested for PPARγ1 activity. Three dust extracts showed a similar PPARγ1 activity distribution in the NP-HPLC fractions. In most active fractions, fatty acids (FAs), including oleic acid, stearic acid, palmitic acid and myristic acid, were the primary chemicals identified using gas-chromatography mass spectrometry (GC-MS). Chemical measurements of the FAs in house dust extracts revealed a positive and significant correlation with the observed PPARγ1 activity. To test the role of FAs in the activity, a mixture of four FAs was prepared in the ratios measured in the dust samples and tested for activity. The activity of this mixture was 30-50% of the activity observed in the dust extracts, suggesting they were contributing to the observed activity, but also suggesting additional unknown compounds are likely still present in the dust extracts. To tentatively identify sources of FAs in the dust samples, FAs were quantified in human/animal hair, dead skin cells, and cooking oil. FAs were abundant in all samples and our data indicate that all of these may be sources to indoor dust.

Activation of Human Peroxisome Proliferator-Activated Nuclear Receptors (PPARγ1) by Semi-Volatile Compounds (SVOCs) and Chemical Mixtures in Indoor Dust

Recently, we reported that several semi-volatile compounds (SVOCs) were competitive ligands for human peroxisome proliferator-activated nuclear receptor gamma (PPARγ1). We also observed significant binding from chemicals extracted from house dust at a concentration of 3 mg dust/mL in the dosing medium. To follow up on this study, a commercially available reporter gene assay (GeneBLAzer PPARγ1 non-DA Assay, Invitrogen) was used to investigate the PPARγ1 activation by 30 common SVOCs (e.g., brominated flame retardants, organophosphates, and phthalates) and in house dust extracts. Twenty-eight SVOCs or their metabolites were either confirmed or for the first time were found to be weak or moderate PPARγ1 agonists. We also observed activation in 15 of 25 dust extracts examined. In some cases, activation was as high as 50% of the activation of the positive control (rosiglitazone). Furthermore, there was a significant and positive correlation (r = 0.7, p < 0.003) between data collected from this reporter assay and our previous ligand binding assay tested on the same dust extracts. Our results suggest that many SVOCs ubiquitous in house dust, or their metabolites, are possible PPARγ1 agonists. Also, chemical mixtures present in house dust at environmentally relevant levels can activate human PPARγ1 in a transfected cell culture system, and further research is needed to identify the primary chemical(s) driving this activity.

Transcriptomes analysis of Aeromonas molluscorum Av27 cells exposed to tributyltin (TBT): Unravelling the effects from the molecular level to the organism

Aeromonas molluscorum Av27 cells were exposed to 0, 5 and 50 μM of TBT and the respective transcriptomes were obtained by pyrosequencing. Gene Ontology revealed that exposure to 5 μM TBT results in a higher number of repressed genes in contrast with 50 μM of TBT, where the number of over-expressed genes is greater. At both TBT concentrations, higher variations in gene expression were found in the functional categories associated with enzymatic activities, transport/binding and oxidation-reduction. A number of proteins are affected by TBT, such as the acriflavin resistance protein, several transcription-related proteins, several Hsps, ABC transporters, CorA and ZntB and other outer membrane efflux proteins, all of these involved in cellular metabolic processes, important to maintain overall cell viability. Using the STRING tool, several proteins with unknown function were related with others involved in degradation processes, such as the pyoverdine chromophore biosynthetic protein, that has been described as playing a role in the Sn-C cleavage of organotins. This approach has allowed a better understanding of the molecular effects of exposure of bacterial cells to TBT. Furthermore it contributes to the knowledge of the functional genomic aspects of bacteria exposed to this pollutant. Furthermore, the transcriptomic data gathered, and now publically available, constitute a valuable resource for comparative genome analysis.

Alteration of cellular lipids and lipid metabolism markers in RTL-W1 cells exposed to model endocrine disrupters

This work investigates the suitability of the rainbow trout liver cell line (RTL-W1) as an in-vitro model to study the ability of model endocrine disrupters, namely TBT, TPT, 4-NP, BPA and DEHP, to act as metabolic disrupters by altering cellular lipids and markers of lipid metabolism. Among the tested compounds, BPA and DEHP significantly increased the intracellular accumulation of triacylglycerols (TAGs), while all the compounds -apart from TPT-, altered membrane lipids - phosphatidylcholines (PCs) and plasmalogen PCs - indicating a strong interaction of the toxicants with cell membranes and cell signaling. RTL-W1 expressed a number of genes involved in lipid metabolism that were modulated by exposure to BPA, TBT and TPT (up-regulation of FATP1 and FAS) and 4-NP and DEHP (down-regulation of FAS and LPL). Multiple and complex modes of action of these chemicals were observed in RTL-W1 cells, both in terms of expression of genes related to lipid metabolism and alteration of cellular lipids. Although further characterization is needed, this might be a useful model for the detection of chemicals leading to steatosis or other diseases associated with lipid metabolism in fish.

Human Bisphenol A Exposure and the "Diabesity Phenotype"

Bisphenol A (BPA), a known endocrine disruptor, is a food contaminant suspected of being a contributing factor to the present-day increase in obesity, diabetes, and cardiovascular disease. This issue is of increasing interest in the field of diabetes research and has become a matter of concern for regulatory agencies and food industries. Recently, the number of studies involving BPA has increased exponentially, but there are still many gaps in the knowledge of the relationship between actual BPA exposure and cardiometabolic risk and of the modalities of food intake exposure, all of which prevents sound judgments concerning the risks to human health. This review focuses on the association between human exposure to BPA and obesity, thyroid function, diabetes, insulin resistance, metabolic syndrome, cardiovascular diseases, and BPA content in food. Many cross-sectional studies support, sometimes contradictorily, an adverse effect of BPA exposure on obesity, diabetes, and cardiovascular diseases. Few prospective studies support an adverse effect of BPA exposure on such pathologies. Moreover, no intervention studies have been conducted to evaluate the causality of such associations. This is mainly due to lack of an appropriate database of BPA content in foods, thus hindering any estimation of the usual dietary BPA intake.

Phenotypic malignant changes and untargeted lipidomic analysis of long-term exposed prostate cancer cells to endocrine disruptors

Endocrine disruptors (EDs) are a class of environmental toxic molecules able to interfere with the normal hormone metabolism. Numerous studies involve EDs exposure to initiation and development of cancers, including prostate cancer. In this work, three different EDs (aldrin, aroclor 1254 and chlorpyrifos (CPF)) were investigated as potential inducers of a malignant phenotype in DU145 prostate cancer cells after a chronic exposure. Epithelial to mesenchymal transition (EMT) induction, proliferation, migration, colony formation and release of metalloproteinase 2 (MMP-2) were analyzed in 50-day exposed cells to the selected EDs. As a result, aldrin and CPF exposure led to an EMT induction (loss of 16% and 14% of E-cadherin levels, respectively, compared to the unexposed cells). Aroclor and CPF presented an increased migration (134% and 126%, respectively), colony formation (204% and 144%, respectively) and MMP-2 release (137% in both cases) compared to the unexposed cells. An untargeted lipidomic analysis was performed to decipher the lipids involved in the observed transformations. As general results, aldrin exposure showed a global decrease in phospholipids and sphingolipids, and aroclor and CPF showed an increase of certain phospholipids, glycosphingolipids as well as a remarkable increase of some cardiolipin species. Furthermore, the three exposures resulted in an increase of some triglyceride species. In conclusion, some significant changes in lipids were identified and thus we postulate that some lipid compounds and lipid metabolic pathways could be involved in the acquisition of the malignant phenotype in exposed prostate cancer cells to the selected EDs.

Association of Exposure to Di-2-Ethylhexylphthalate Replacements With Increased Insulin Resistance in Adolescents From NHANES 2009-2012

CONTEXT

Di-isononyl phthalate (DINP) and di-isodecyl phthalate (DIDP) are environmental chemicals increasingly used to replace di-2-ethylhexylphthalate (DEHP) and commonly found in processed foods. Phthalate exposures, in particular DEHP, have been associated with insulin resistance in adolescents, but there are no data regarding the two substitutes, DINP and DIDP.

OBJECTIVE

This study aimed to examine associations of DINP, DIDP, and DEHP with insulin resistance outcomes.

DESIGN, SETTING, AND PARTICIPANTS

This was a cross-sectional analysis of 2009-2012 National Health and Nutrition Examination Surveys (NHANES) composed of 356 fasting 12-19-year-olds.

MAIN OUTCOME MEASURES

Insulin resistance as a categorical outcome expressed as homeostatic model assessment of insulin resistance (HOMA-IR), using a cut point of 4.39 to define insulin resistance. We also examined continuous HOMA-IR as an outcome in secondary analyses.

RESULTS

Controlling for demographic and behavioral factors, diet, age, body mass index, and urinary creatinine, for each log increase in DINP metabolite, a 0.08 (P = .001) increase in HOMA-IR was identified. Compared with the first tertile of DINP (23.4% adjusted prevalence), the third tertile was associated with a 34.4% prevalence (95% confidence interval [CI], 27.3-41.6%; P = .033) of insulin resistance. Similarly, compared with the first tertile of DEHP (20.5% adjusted prevalence), the third tertile had 37.7% prevalence (95% CI 29.8-45.6%; P = .003).

CONCLUSIONS

Urinary DINP concentrations were associated with increased insulin resistance in this cross-sectional study of adolescents. The previously identified association of DEHP with insulin resistance was also confirmed. Further, longitudinal studies are needed to confirm these associations, with the possibility to assess opportunities for intervention.