Dibutyltin Compounds Effects on PPARγ/RXRα Activity, Adipogenesis, and Inflammation in Mammalians Cells

Evaluation of Lipids and Lipid-Related Transcripts in Human and Ovine Theca Cells and an in Vitro Mouse Model Exposed to the Obesogen Chemical Tributyltin

BACKGROUND

Exposure to obesogenic chemicals has been reported to result in enhanced adipogenesis, higher adipose tissue accumulation, and reduced ovarian hormonal synthesis and follicular function. We have reported that organotins [tributyltin (TBT) and triphenyltin (TPT)] dysregulate cholesterol trafficking in ovarian theca cells, but, whether organotins also exert lipogenic effects on ovarian cells remains unexplored.

OBJECTIVE

We investigated if environmentally relevant exposures to organotins [TBT, TPT, or dibutyltin (DBT)] induce lipid dysregulation in ovarian theca cells and the role of the liver X receptor (LXR) in this effect. We also tested the effect of TBT on oocyte maturation and neutral lipid accumulation, and lipid-related transcript expression in cumulus cells and preimplantation embryos.

METHODS

Primary theca cell cultures derived from human and ovine ovaries were exposed to TBT, TPT, or DBT (1, 10, or 50   ng / ml ). The effect of these chemical exposures on neutral lipid accumulation, lipid abundance and composition, lipid homeostasis-related gene expression, and cytokine secretion was evaluated using liquid chromatography-mass spectrometry (LC-MS), inhibitor-based methods, cytokine secretion, and lipid ontology analyses. We also exposed murine cumulus-oocyte complexes to TBT and evaluated oocyte maturation, embryo development, and lipid homeostasis-related mRNA expression in cumulus cells and blastocysts.

RESULTS

Exposure to TBT resulted in higher intracellular neutral lipids in human and ovine primary theca cells. In ovine theca cells, this effect was dose-dependent, independent of cell stage, and partially mediated by LXR. DBT and TPT resulted in higher intracellular neutral lipids but to a lesser extent in comparison with TBT. More than 140 lipids and 9 cytokines were dysregulated in TBT-exposed human theca cells. Expression of genes involved in lipogenesis and fatty acid synthesis were higher in theca cells, as well as in cumulus cells and blastocysts exposed to TBT. However, TBT did not impact the rates of oocyte maturation or blastocyst development.

DISCUSSION

TBT induced dyslipidemia in primary human and ovine theca cells, which may be responsible for some of the TBT-induced fertility dysregulations reported in rodent models of TBT exposure. https://doi.org/10.1289/EHP13955.

Producing polyglycerol polyester polyol for thermoplastic polyurethane application: A novel valorization of glycerol, a by-product of biodiesel production

The production of biodiesel generates glycerol as a by-product that needs valorization. Glycerol, when converted to polyglycerol, is a potential polyol for bio-based thermoplastic polyurethane (TPU) production. In this study, a novel polyglycerol polyester polyol (PPP) was developed from refined glycerol and coconut oil-based polyester polyol. Glycerol was first converted to glycerol acetate and then polymerized with coconut oil-based polyester polyol (CPP) as secondary polyol and phthalic anhydride. The resulting PPP polymerized at 220 °C and OH:COOH molar ratio of 2.5 exhibited an OH number of <100 mg KOH·g sample-1, an acid number of <10 mg KOH·g sample-1, and a molecular weight (MW) of 3697 g mol-1 meeting the polyol requirement properties for TPU (Handlin et al., 2001; Parcheta et al., 2020) [1-2]. Fourier-transform infrared (FTIR) spectroscopic characterization determined that higher reaction temperatures increase the polymerization rate and decrease the OH and acid numbers. Further, higher OH:COOH molar ratios decrease the polymerization rate and acid number, and increase the OH number. Gel permeation chromatography determined the molecular weight of PPP and suggested two distinct molecular structures which differ only in the number of moles of CPP in the structure. A differential scanning calorimetric (DSC) experiment on a sample of PPP-based polyurethane revealed that it was able to melt and remelt after 3 heating cycles which demonstrates its thermoplastic ability. The novel PPP derived from the glycerol by-product of biodiesel industries can potentially replace petroleum-derived polyols for TPU production.

The mechanism underlying pentabromoethylbenzene-induced adipogenesis and the obesogenic outcome in both cell and mouse model

Convergent evidence links traditional brominated flame retardants (BFRs) exposure to weight gain, while the obesogenic potency of new BFRs (NBFRs) remain largely unknown. Aiding by luciferase-reporter gene assay, the present study revealed only pentabromoethylbenzene (PBEB), an alternative for penta-BDEs, binds with retinoid X receptor α (RXRα) but not peroxisomeproliferator receptor γ (PPARγ) among the seven testing NBFRs. An apparent induction of adipogenesis in 3T3-L1 cells was observed at nanomolar of PBEB, much lower than penta-BFRs. Mechanistic research uncovered PBEB initiated the adipogenesis by demethylated CpG sites in the PPARγ promoter region. Specifically, activation RXRα by PBEB strengthened the activity of RXRα/PPARγ heterodimer, tightened the interaction between the heterodimer and PPAR response elements, and further enhanced adipogenesis. RNA sequencing combined with k-means clustering analysis exposed adenosine 5'-monophosphate (AMP)-activated protein kinase and phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) signaling as two predominant pathways that enriched in PBEB-induced lipogenesis. The obesogenic outcome was further corroborated in offspring mice when the maternal mice exposed to environmental relevant doses of PBEB. We found the male offspring exhibited adipocyte hypertrophy and increased weight gain in the epididymal white adipose tissue (eWAT). Consistent with in vitro findings, the reduction in protein phosphorylation of both AMPK and PI3K/AKT were observed within eWAT. Thus, we posited PBEB disrupts the pathways controlling adipogenesis and adipose tissue maintenance, supporting its potential as an environmental obesogen.

Organotin mixtures reveal interactions that modulate adipogenic differentiation in 3T3-L1 preadipocytes

Organotin chemicals (butyltins and phenyltins) are the most widely used organometallic chemicals worldwide and are used in industrial applications, such as biocides and anti-fouling paints. Tributyltin (TBT) and more recently, dibutyltin (DBT) and triphenyltin (TPT) have been reported to stimulate adipogenic differentiation. Although these chemicals co-exist in the environment, their effect in combination remains unknown. We first investigated the adipogenic effect of eight organotin chemicals (monobutyltin (MBT), DBT, TBT, tetrabutyltin (TeBT), monophenyltin (MPT), diphenyltin (DPT), TPT, and tin chloride (SnCl4)) in the 3T3-L1 preadipocyte cell line in single exposures at two doses (10 and 50 ng/ml). Only three out of the eight organotins induced adipogenic differentiation with TBT eliciting the strongest adipogenic differentiation (in a dose-dependent manner) followed by TPT and DBT, as demonstrated by lipid accumulation and gene expression. We then hypothesized that, in combination (TBT, DBT, and TPT), adipogenic effects will be exacerbated compared to single exposures. However, at the higher dose (50 ng/ml), TBT-induced differentiation was reduced by TPT and DBT when in dual or triple combination. We tested whether TPT or DBT would interfere with adipogenic differentiation stimulated by a peroxisome proliferator-activated receptor (PPARγ) agonist (rosiglitazone) or a glucocorticoid receptor agonist (dexamethasone). Both DBT50 and TPT50 reduced rosiglitazone-, but not dexamethasone-stimulated adipogenic differentiation. In conclusion, DBT and TPT interfere with TBT's adipogenic differentiation possibly via PPARγ signaling. These findings highlight the antagonistic effects among organotins and the need to understand the effects and mechanism of action of complex organotin mixtures on adipogenic outcomes.

Regulation of adipogenesis through retinoid X receptor and/or peroxisome proliferator-activated receptor by designed lignans based on natural products in 3T3-L1 cells

We previously synthesized two retinoid X receptor (RXR) agonists, 4'-hydroxy-3'-propyl-[1,1'-biphenyl]-3-propanoic acid ethyl ester (4'OHE) and 6-hydroxy-3'-propyl-[1,1'-biphenyl]-3-propanoic acid ethyl ester (6OHE), based on the structure of magnaldehyde B, a natural product obtained from Magnolia obovata. 4'OHE and 6OHE exhibited different selectivities for peroxisome proliferator-activated receptor (PPAR)/RXR heterodimers. To examine the regulatory effects of these compounds in adipogenesis, 3T3-L1 mouse preadipocytes were treated with a differentiation cocktail with or without test compounds to induce differentiation, and subsequently treated with test compounds in insulin-containing medium every alternate day. Lipid droplets were stained with Oil Red O to examine lipid accumulation. In addition, adipogenesis-related gene expression was measured using RT-qPCR and immunoblotting. The results showed that a PPARγ agonist, 4'OHE, which exerts agonistic effects on PPARγ and RXRα, enhanced adipogenesis similar to rosiglitazone. However, unlike GW501516, a PPARδ agonist, 6OHE and its hydrolysis product (6OHA), which exert agonistic effects on PPARδ and RXRα, suppressed adipogenesis. In a manner similar to 6OHE and 6OHA, bexarotene, an RXR agonist, suppressed adipocyte differentiation, and its anti-adipogenic effect was reversed by an RXR antagonist. Furthermore, 6OHA and bexarotene inhibited the increase in Pparγ2 and Cebpa mRNA levels 2 days after the induction of differentiation. We demonstrated the adipogenic effect of 4'OHE and anti-adipogenic effects of 6OHE and 6OHA in 3T3-L1 cells. Previously, RXR agonists have been reported to positively regulate the differentiation of mesenchymal stem cells into adipocytes, but our current data showed that they inhibited the differentiation of preadipocytes, at least 3T3-L1 cells, into adipocytes.

Exploration of hub genes involved in PCOS using biological informatics methods

BACKGROUND

The aim of this study was to find underlying genes and their interaction mechanism crucial to the polycystic ovarian syndrome (PCOS) by analyzing differentially expressed genes (DEGs) between PCOS and non-PCOS subjects.

METHODS

Gene expression data of PCOS and non-PCOS subjects were collected from gene expression omnibus (GEO) database. GEO2R were used to calculating P value and logFC. The screening threshold of DEGs was P < .05 and | FC | ≥ 1.2. GO annotation and Kyoto encyclopedia of genes and genomes (KEGG) signaling pathway enrichment analysis was performed by using DAVID (2021 Update). The protein-protein interaction (PPI) network of DEGs was constructed by using the STRING database, and the hub genes were recognized through Hubba plugin of Cytoscape software.

RESULTS

PCOS and non-PCOS subjects shared a total of 174 DGEs, including 14 upregulated and 160 downregulated genes. The GO biological processes enriched by DEGs mainly involved actin cytoskeleton organization, positive regulation of NF-κB signaling pathway, and positive regulation of canonical Wnt signaling pathway. The DEGs were significantly enriched in cytoplasm, nucleus and cytosol. Their molecular functions mainly focused on protein binding, calmodulin binding and glycerol-3-phosphate dehydrogenase activity. The PI3K/Akt signaling pathway and glycosaminoglycan biosynthesis were highlighted as critical pathways enriched by DEGs. 10 hub genes were screened from the constructed PPI network, of which EGF, FN1 and TLR4 were mainly enriched in the PI3K/Akt signaling pathway.

CONCLUSION

In this study, a total of 174 DEGs and 10 hub genes were identified as new candidate targets for insulin resistance (IR) in PCOS individuals, which may provide a new direction for developing novel treatment strategies for PCOS.

Morphological profiling of environmental chemicals enables efficient and untargeted exploration of combination effects

Environmental chemicals are commonly studied one at a time, and there is a need to advance our understanding of the effect of exposure to their combinations. Here we apply high-content microscopy imaging of cells stained with multiplexed dyes (Cell Painting) to profile the effects of Cetyltrimethylammonium bromide (CTAB), Bisphenol A (BPA), and Dibutyltin dilaurate (DBTDL) exposure on four human cell lines; both individually and in all combinations. We show that morphological features can be used with multivariate data analysis to discern between exposures from individual compounds, concentrations, and combinations. CTAB and DBTDL induced concentration-dependent morphological changes across the four cell lines, and BPA exacerbated morphological effects when combined with CTAB and DBTDL. Combined exposure to CTAB and BPA induced changes in the ER, Golgi apparatus, nucleoli and cytoplasmic RNA in one of the cell lines. Different responses between cell lines indicate that multiple cell types are needed when assessing combination effects. The rapid and relatively low-cost experiments combined with high information content make Cell Painting an attractive methodology for future studies of combination effects. All data in the study is made publicly available on Figshare.

Peroxisome Proliferator-Activated Receptor Activation in Precision-Cut Bovine Liver Slices Reveals Novel Putative PPAR Targets in Periparturient Dairy Cows

Metabolic challenges experienced by dairy cows during the transition between pregnancy and lactation (also known as peripartum), are of considerable interest from a nutrigenomic perspective. The mobilization of large amounts of non-esterified fatty acids (NEFA) leads to an increase in NEFA uptake in the liver, the excess of which can cause hepatic accumulation of lipids and ultimately fatty liver. Interestingly, peripartum NEFA activate the Peroxisome Proliferator-activated Receptor (PPAR), a transcriptional regulator with known nutrigenomic properties. The study of PPAR activation in the liver of periparturient dairy cows is thus crucial; however, current in vitro models of the bovine liver are inadequate, and the isolation of primary hepatocytes is time consuming, resource intensive, and prone to errors, with the resulting cells losing characteristic phenotypical traits within hours. The objective of the current study was to evaluate the use of precision-cut liver slices (PCLS) from liver biopsies as a model for PPAR activation in periparturient dairy cows. Three primiparous Jersey cows were enrolled in the experiment, and PCLS from each were prepared prepartum (−8.0 ± 3.6 DIM) and postpartum (+7.7± 1.2 DIM) and treated independently with a variety of PPAR agonists and antagonists: the PPARα agonist WY-14643 and antagonist GW-6471; the PPARδ agonist GW-50156 and antagonist GSK-3787; and the PPARγ agonist rosiglitazone and antagonist GW-9662. Gene expression was assayed through RT-qPCR and RNAseq, and intracellular triacylglycerol (TAG) concentration was measured. PCLS obtained from postpartum cows and treated with a PPARγ agonist displayed upregulation of ACADVL and LIPC while those treated with PPARδ agonist had increased expression of LIPC, PPARD, and PDK4. In PCLS from prepartum cows, transcription of LIPC was increased by all PPAR agonists and NEFA. TAG concentration tended to be larger in tissue slices treated with PPARδ agonist compared to CTR. Use of PPAR isotype-specific antagonists in PCLS cultivated in autologous blood serum failed to decrease expression of PPAR targets, except for PDK4, which was confirmed to be a PPARδ target. Transcriptome sequencing revealed considerable differences in response to PPAR agonists at a false discovery rate-adjusted p-value of 0.2, with the most notable effects exerted by the PPARδ and PPARγ agonists. Differentially expressed genes were mainly related to pathways involved with lipid metabolism and the immune response. Among differentially expressed genes, a subset of 91 genes were identified as novel putative PPAR targets in the bovine liver, by cross-referencing our results with a publicly available dataset of predicted PPAR target genes, and supplementing our findings with prior literature. Our results provide important insights on the use of PCLS as a model for assaying PPAR activation in the periparturient dairy cow.

Dibutyltin dichloride exposure affects mouse oocyte quality by inducing spindle defects and mitochondria dysfunction

Dibutyltin dichloride (DBTCl) is a widespread environmental pollutant that is frequently employed as a light and heat sustainer for polyvinyl chloride (PVC) plastics and is a teratogen in vivo. Nevertheless, its destructiveness in mammalian oocytes remains unclear. This study highlighted the consequences of DBTCl vulnerability on mouse oocyte. Our results revealed that exposure to 5.0 mg/kg/day of DBTCl for ten days reduced the number of mature follicles and oocytes in the ovaries and inhibited the meiotic maturation of oocytes. Single-cell transcriptomic analysis indicated that DBTCl exposure interfered with the expression of more than 400 genes in oocytes, including those involved in multiple biological pathways. Specifically, DBTCl exposure impaired spindle assembly and chromosome alignment. In addition, DBTCl exposure caused mitochondrial dysfunction, which led to the accumulation of reactive oxygen species (ROS) and induced apoptosis. In summary, our study illustrates that mitochondrial dysfunction and redox perturbation are the major causes of the reduced quality of oocytes exposed to DBTCl.

An evaluation of maternal serum dynamic thiol-disulfide homeostasis and ischemia modified albumin changes in pregnant women with COVID-19

Objective:

It is thought that oxidative stress, free radicals, reactive oxygen species and reactive nitrogen species affect the pathophysiology of coronavirus disease-2019 (COVID-19). This study aimed to evaluate the oxidative status in pregnant patients with COVID-19 infection according to the changes seen in the levels of maternal serum thiol-disulfide and ischemia-modified albumin (IMA).

Materials and Methods:

A study group was formed of 40 pregnant women with confirmed COVID-19 infection (study group) and a control group of 40 healthy pregnant women with no risk factors determined. In this prospective, case-controlled study, analyses were made of the maternal serum native thiol, total thiol, disulfide, IMA, and disulfide/native thiol concentrations.

Results:

The maternal serum native thiol and total thiol concentrations in the study group were determined to be statistically significantly lower (p=0.007 and p=0.006, respectively), and the disulfide/native thiol ratio was higher but not to a level of statistical significance (p=0.473). There was no difference between the two groups regarding IMA levels (p=0.731).

Conclusion:

The thiol-disulfide balance was seen to shift in the oxidant direction in pregnancies with COVID-19, which might support the view that ischemic processes play a role in the etiopathogenesis of this novel disease.

Integrated Genomic and Bioinformatics Approaches to Identify Molecular Links between Endocrine Disruptors and Adverse Outcomes

Exposure to Endocrine Disrupting Chemicals (EDC) has been linked with several adverse outcomes. In this review, we examine EDCs that are pervasive in the environment and are of concern in the context of human, animal, and environmental health. We explore the consequences of EDC exposure on aquatic life, terrestrial animals, and humans. We focus on the exploitation of genomics technologies and in particular whole transcriptome sequencing. Genome-wide analyses using RNAseq provides snap shots of cellular, tissue and whole organism transcriptomes under normal physiological and EDC perturbed conditions. A global view of gene expression provides highly valuable information as it uncovers gene families or more specifically, pathways that are affected by EDC exposures, but also reveals those that are unaffected. Hypotheses about genes with unknown functions can also be formed by comparison of their expression levels with genes of known function. Risk assessment strategies leveraging genomic technologies and the development of toxicology databases are explored. Finally, we review how the Adverse Outcome Pathway (AOP) has exploited this high throughput data to provide a framework for toxicology studies.

Viscoelastic Polyurethane Foams with Reduced Flammability and Cytotoxicity

Consistent and proper use of respiratory protective devices (RPD) is one of the essential actions that can be taken to reduce the risk of exposure to airborne hazards, i.e., biological and nonbiological aerosols, vapours, and gases. Proper fit of the facepiece and comfort properties of RPDs play a crucial role in effective protection and acceptance of RPDs by workers. The objective of the present paper was to develop viscoelastic polyurethane foams for use in RPD seals characterised by proper elasticity, allowing for the enhancement of the device fit to the face and the capability of removing moisture from the skin in order to improve the comfort of RPD use. Moreover, it was pivotal to ensure the non-flammability of the foams, as well as a simultaneous reduction in their cytotoxicity. The obtained foams were characterised using scanning electron microscopy, infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Measurements also involved gel fraction, apparent density, compression set, rebound resilience, wettability, flammability, and cytotoxicity. The results are discussed in the context of the impact of modifications to the foam formulation (i.e., flame-retardant type and content) on the desired foam properties. The test results set directions for future works aimed to develop viscoelastic polyurethane foams that could be applied in the design of respiratory protective devices.

Transgenerational metabolomic fingerprints in mice ancestrally exposed to the obesogen TBT

BACKGROUND

Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorders such as obesity, insulin resistance and hepatic dysfunction. Concern is growing about the consequences of perinatal EDC exposure on disease predisposition later in life. Metabolomics are promising approaches for studying long-term consequences of early life EDC exposure. These approaches allow for the identification and characterization of biomarkers of direct or ancestral exposures that could be diagnostic for individual susceptibility to disease and help to understand mechanisms through which EDCs act.

OBJECTIVES

We sought to identify metabolomic fingerprints in mice ancestrally exposed to the model obesogen tributyltin (TBT), to assess whether metabolomics could discriminate potential trans-generational susceptibility to obesity and recognize metabolic pathways modulated by ancestral TBT exposure.

METHODS

We used non-targeted ¹H NMR metabolomic analyses of plasma and liver samples collected from male and female mice ancestrally exposed to TBT in two independent transgenerational experiments in which F3 and F4 males became obese when challenged with increased dietary fat.

RESULTS

Metabolomics confirmed transgenerational obesogenic effects of environmentally relevant doses of TBT in F3 and F4 males, in two independent studies. Although females never became obese, their specific metabolomic fingerprint evidenced distinct transgenerational effects of TBT in female mice consistent with impaired capacity for liver biotransformation.

DISCUSSION

This study is the first application of metabolomics to unveil the transgenerational effects of EDC exposure. Very early, significant changes in the plasma metabolome were observed in animals ancestrally exposed to TBT. These changes preceded the onset of obesogenic effects elicited by increased dietary fat in the TBT groups, and which ultimately resulted in significant changes in the liver metabolome. Development of metabolomic fingerprints could facilitate the identification of individuals carrying the signature of ancestral obesogen exposure that might increase their susceptibility to other risk factor such as increased dietary fat.

The new kids on the block: Emerging obesogens

The current obesity epidemic is calling for action in the determination of contributing factors. Although social and life-style factors have been traditionally associated with metabolic disruption, a subset of endocrine-disrupting chemicals (EDCs), called obesogens are garnering increasing attention for their ability to promote adipose tissue differentiation and accumulation. For some chemicals, such as tributyltin, there is conclusive evidence regarding their ability to promote adipogenesis and their mechanism of action. In recent years, the list of chemicals that exert obesogenic potential is increasing. In this chapter, we review current knowledge of the most recent developments in the field of emerging obesogens with a specific focus on food additives, surfactants, and sunscreens, for which the mechanism of action remains unclear. We also review new evidence relative to the obesogenic potential of environmentally relevant chemical mixtures and point to potential therapeutic approaches to minimize the detrimental effects of obesogens. We conclude by discussing the available tools to investigate new obesogenic chemicals, strategies to maximize reproducibility in adipogenic studies, and future directions that will help propel the field forward.

Dibutyltin (DBT) inhibits in vitro androgen biosynthesis of rat immature Leydig cells

Dibutyltin (DBT) is an organotine widely applied in stabilizing plastics and de-worm poultry agents. But the effects of DBT on immature Leydig cells remain elusive. Thus, the present study aims to investigate whether in vitro exposure to DBT affects immature Leydig cell function of androgen production and delineate the underlying mechanisms. 35 days old rat immature Leydig cells were isolated and exposed to DBT at different concentrations (0, 0.1, 0.5, and 1 μM). It was found that 0.5 and 1 μM DBT lowered androgen production from immature Leydig cells under basal conditions. DBT at 1 μM lowered androgen production from immature Leydig cells under the stimulations from luteinizing hormone or 8-Br-cAMP. DBT at 1 μM lowered 22R-hydroxycholesterol and pregnenolone-mediated androgen production from immature Leydig cells. DBT at 0.1, 0.5, and 1 μM down-regulated the mRNA expression levels of Lhcgr, Star, Cyp11a1, Hsd3b1, and Nr5a1. Further investigation found that DBT at 1 μM directly inhibited CYP11A1 and 3β-HSD1 enzyme activities. In conclusion, this study told us that in vitro exposure to DBT inhibited androgen biosynthesis in immature Leydig cells by selectively interfering with the expressions and enzyme activities of CYP11A1 and 3β-HSD1.

Tributyltin triggers lipogenesis in macrophages via modifying PPARγ pathway

Tributyltin (TBT), a bioaccumulative and persistent environmental pollutant, has been proposed as a metabolism disruptor and obesogen through targeting peroxisome proliferator-activated receptor gamma (PPARγ) receptor pathway. However, it remains unknown whether this biological effect occurs in macrophage, a cell type which cooperates closely with hepatocytes and adipocytes to regulate lipid metabolism. This study for the first time investigated the effect of TBT on PPARγ pathway in macrophages. Our results indicated that nanomolar levels of TBT was able to strongly activate PPARγ in human macrophages. TBT treatment also markedly increased the intracellular lipid accumulation, and enhanced the expression of lipid metabolism-related genes in macrophages, while these effects were all significantly down-regulated in PPARγ-deficient macrophages, confirming the involvement of PPARγ in TBT-induced lipogenesis. Next, a mouse model that C57BL/6 mice were orally exposed to TBT with the doses (250 and 500 μg/kg body weight) lower than NOAEL (no observed adverse effect level) was used to further investigate the in vivo mechanisms. And the in vivo results were consistent with cellular assays, confirming the induction of PPARγ and the increased expression of lipogenesis-regulating and lipid metabolism-related genes by TBT in vivo. In conclusion, this study not only provided the first evidence that TBT stimulated lipogenesis, activated PPARγ and related genes in human macrophages, but also provided insight into the mechanism of TBT-induced metabolism disturbance and obesity through targeting PPARγ via both in vitro cellular assays and in vivo animal models.

Obesity and endocrine-disrupting chemicals

Obesity is now a worldwide pandemic. The usual explanation given for the prevalence of obesity is that it results from consumption of a calorie dense diet coupled with physical inactivity. However, this model inadequately explains rising obesity in adults and in children over the past few decades, indicating that other factors must be important contributors. An endocrine-disrupting chemical (EDC) is an exogenous chemical, or mixture that interferes with any aspect of hormone action. EDCs have become pervasive in our environment, allowing humans to be exposed daily through ingestion, inhalation, and direct dermal contact. Exposure to EDCs has been causally linked with obesity in model organisms and associated with obesity occurrence in humans. Obesogens promote adipogenesis and obesity, in vivo, by a variety of mechanisms. The environmental obesogen model holds that exposure to obesogens elicits a predisposition to obesity and that such exposures may be an important yet overlooked factor in the obesity pandemic. Effects produced by EDCs and obesogen exposure may be passed to subsequent, unexposed generations. This "generational toxicology" is not currently factored into risk assessment by regulators but may be another important factor in the obesity pandemic as well as in the worldwide increases in the incidence of noncommunicable diseases that plague populations everywhere. This review addresses the current evidence on how obesogens affect body mass, discusses long-known chemicals that have been more recently identified as obesogens, and how the accumulated knowledge can help identify EDCs hazards.

Obesogens: How They Are Identified and Molecular Mechanisms Underlying Their Action

Adult and childhood obesity have reached pandemic level proportions. The idea that caloric excess and insufficient levels of physical activity leads to obesity is a commonly accepted answer for unwanted weight gain. This paradigm offers an inconclusive explanation as the world continually moves towards an unhealthier and heavier existence irrespective of energy balance. Endocrine disrupting chemicals (EDCs) are chemicals that resemble natural hormones and disrupt endocrine function by interfering with the body's endogenous hormones. A subset of EDCs called obesogens have been found to cause metabolic disruptions such as increased fat storage, in vivo. Obesogens act on the metabolic system through multiple avenues and have been found to affect the homeostasis of a variety of systems such as the gut microbiome and adipose tissue functioning. Obesogenic compounds have been shown to cause metabolic disturbances later in life that can even pass into multiple future generations, post exposure. The rising rates of obesity and related metabolic disease are demanding increasing attention on chemical screening efforts and worldwide preventative strategies to keep the public and future generations safe. This review addresses the most current findings on known obesogens and their effects on the metabolic system, the mechanisms of action through which they act upon, and the screening efforts through which they were identified with. The interplay between obesogens, brown adipose tissue, and the gut microbiome are major topics that will be covered.

Environmental Obesogens and Their Impact on Susceptibility to Obesity: New Mechanisms and Chemicals

The incidence of obesity has reached an all-time high, and this increase is observed worldwide. There is a growing need to understand all the factors that contribute to obesity to effectively treat and prevent it and associated comorbidities. The obesogen hypothesis proposes that there are chemicals in our environment termed obesogens that can affect individual susceptibility to obesity and thus help explain the recent large increases in obesity. This review discusses current advances in our understanding of how obesogens act to affect health and obesity susceptibility. Newly discovered obesogens and potential obesogens are discussed, together with future directions for research that may help to reduce the impact of these pervasive chemicals.

Transgenerational effects of obesogens

Obesity and associated disorders are now a global pandemic. The prevailing clinical model for obesity is overconsumption of calorie-dense food and diminished physical activity (the calories in-calories out model). However, this explanation does not account for numerous recent research findings demonstrating that a variety of environmental factors can be superimposed on diet and exercise to influence the development of obesity. The environmental obesogen model proposes that exposure to chemical obesogens during in utero and/or early life can strongly influence later predisposition to obesity. Obesogens are chemicals that inappropriately stimulate adipogenesis and fat storage, in vivo either directly or indirectly. Numerous obesogens have been identified in recent years and some of these elicit transgenerational effects on obesity as well as a variety of health end-points after exposure of pregnant F0 females. Prenatal exposure to environmental obesogens can produce lasting effects on the exposed animals and their offspring to at least the F4 generation. Recent results show that some of these transgenerational effects of obesogen exposure can be carried across the generations via alterations in chromatin structure and accessibility. That some chemicals can have permanent effects on the offspring of exposed animals suggests increased caution in the debate about whether and to what extent exposure to endocrine-disrupting chemicals and obesogens should be regulated.

Human Indoor Exposome of Chemicals in Dust and Risk Prioritization Using EPA's ToxCast Database

Humans spend most of their time indoors and thus have long-term exposure to chemicals. Dust is a sink for most indoor chemicals, and its ingestion is an important pathway for chemical uptake. Therefore, the chemical atlas from dust is an ideal environmental sample to investigate the indoor exposome and associated risk. In this study, we aimed to establish an indoor exposome database through comprehensive data mining on the occurrence of identified compounds in dust, and we prioritize chemicals of health concern. Through an extensive literature review (2849 articles), 355 chemicals and their concentrations were documented and analyzed for human exposure. Together with 81 compounds without concentration and 75 volatile organic compounds, we have established an indoor exposome database with 511 chemicals. Sixteen toxicological end points were selected for toxicity prioritization. Toxic equivalency factor (TEF)-based toxicity, calculated from EPA's ToxCast database, revealed a comprehensive atlas of the chemicals that had a primary contribution. Many of the prioritized compounds are currently neglected or are not actively studied. Overall, this investigation provides one of the most comprehensive analyses on chemical occurrence in indoor dust and prioritizes their chemical toxicity. Our findings can be used as a database for future exposome studies of the indoor environment and provide guidance for indoor risk assessments.

Dibutyltin Dichloride Retards Leydig Cell Developmental Regeneration in Adult Rat Testis

Dibutyltin dichloride (DBTCl), widely used as plastic stabilizer, can cause comprehensive toxicity. The present study aims to investigate the effects of DBTCl on rat Leydig cell developmental regeneration and characterize the related mechanism. Adult male Sprague Dawley rats were randomly divided into four groups and gavaged with saline (control) or 5, 10, or 20 mg/kg/day of DBTCl consecutively for 10 days. At the end of the DBTCl treatment, all rats received a single intraperitoneal injection (i.p.,) of 75 mg/kg ethane dimethane sulfonate (EDS) to eliminate all the adult Leydig cells and to induce Leydig cell developmental regeneration. Leydig cell developmental regeneration was evaluated by measuring the levels of serum testosterone, luteinizing hormone, and follicle-stimulating hormone on days 7, 35, and 56 post-EDS. Leydig cell gene and protein expression levels, as well as cell morphology and cell counts were also carried out on day 56 post-EDS. The present study found that DBTCl significantly reduced serum testosterone levels on days 35 and 56 post-EDS, but increased serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels on day 56 at ≥ 5 mg/kg/day. The mRNA and protein levels of Leydig (Lhcgr, Scarb1, Star, Cyp11a1, Hsd17b3, and Hsd11b1) and Sertoli cells (Fshr, Amh, and Sox9) were significantly downregulated in the DBTCl-treated testes compared to the control. Immunohistochemical staining showed that DBTCl-treatment caused fewer regenerated Leydig cells and impaired Sertoli cell development and function in the testis on day 56 post-EDS. In conclusion, the present study demonstrates that DBTCl retards rat Leydig cell developmental regeneration by downregulating steroidogenesis-related enzymes at the gene and protein levels, inhibiting Leydig cell proliferation and impairing Sertoli cell function and development.

Organotin exposure stimulates steroidogenesis in H295R Cell via cAMP pathway

Organotin compounds (OTs) are used in a range of industrial products, such as antifouling paints, agricultural pesticides and stabilizers. Owing to potential endocrine-disrupting effects, human exposure to such compounds is a concern. Nevertheless, little is known about the adverse effect of OTs on adrenocortical function in organisms. In this study, the human adrenocortical carcinoma cell (H295R) model was used to investigate effects of OTs on steroidogenesis and potential causes for such endocrine disruption was examined. H295R cells were exposed to several commonly used OTs, including triphenyltin (TPT), tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT), and the production level of steroid hormones were quantified. TPT and TBT decreased the production levels of 17β-estradiol, aldosterone, and cortisol, but increased that of testosterone. Furthermore, the expression levels of ten major steroidogenic genes (HMGR, StAR, CYP11A1, 3βHSD2, CYP17, CYP19A1, CYP21, CYP11B1, CYP11B2, and 17βHSD) were examined and both up-regulation of CYP11B2 and down-regulation of StAR, 3βHSD2, CYP19A1, CYP21 and CYP11B1 by TPT and TBT were observed. Intracellular levels of ATP and cyclic adenosine monophosphate (cAMP) and the activity of adenylate cyclase (AC) decreased in the H295R cells treated with TPT and TBT. No obvious changes in H295R were found with the treatment of DBT and MBT. These results suggest that OTs may stimulate steroidogenesis in vitro via inhibition of cAMP signaling pathway.

Effect of Dibutyltin Dilaurate on Triglyceride Metabolism through the Inhibition of the mTOR Pathway in Human HL7702 Liver Cells

Dibutyltin dilaurate (DBTD) has multiple applications in daily life. However, DBTD is easily deposited in the liver and affects liver functions. This study was designed to explore the effects of DBTD on triglyceride metabolism in human normal hepatocyte HL7702 cells. Our results showed that the intracellular fat contents were dose-dependently decreased by DBTD. The expression of lipolysis genes and proteins were elevated while the lipogenesis genes and proteins were diminished by DBTD. The phosphorylation levels of ribosomal S6 kinase 1 were reduced by both rapamycin and DBTD, indicating that the mTOR pathway was suppressed possibly. The decreased sterol regulatory element-binding protein 1C (SREBP1C) transcription levels, as well as the increased peroxisome proliferator-activated receptor alpha (PPARα) transcription levels, caused by rapamycin and DBTD corresponded to the inactive mTOR pathway. In conclusion, it was possible that DBTD reduced the intracellular triglyceride through depressing the mTOR pathway and affecting its downstream transcription factors.

Insight into the endocrine disrupting effect and cell response to butyltin compounds in H295R cell: Evaluated with proteomics and bioinformatics analysis

The widespread use of organotin compounds (OTs) as biocides in antifouling paints and agricultural applications poses a serious threat to the ecosystem and humans. Butyltin compounds (BTs), especially tributyltin (TBT), are considered to be endocrine disrupting chemicals in marine organisms. The underlying mechanism of disrupting effects on mammals, however, has not been sufficiently investigated. To determine the effect and action of these biocides, the present study evaluated the effects of BTs on human adrenocortical carcinoma cells (H295R) with a focus on endocrine disrupting effect. Two-dimensional electrophoresis (2-DE) and subsequent mass finger printing were used to identify proteins expression profiles from the cells after exposure to 0.1μM BTs for 48h. In total, 89 protein spots showed altered expression in at least two treatment groups and 69 of these proteins were subsequently identified. Bioinformatic analysis of the proteins indicated that BTs involved in the regulation of hormone homeostasis, lipid metabolism, cell death, and energy production. IPA analysis revealed LXR/RXR (liver X receptor/retinoid X receptor) activation, FXR/RXR (farnesoid X receptor/retinoid X receptor) activation and fatty acid metabolism were the top three categories on which BTs acted and these systems play vital roles in sterol, glucose and lipid metabolism. The expression of LXR and FXR mRNA in H295R cells was stimulated by TBT, confirming the ability of TBT to activate this nuclear receptor. In summary, the differentially expressed proteins discovered in this study may participate in the toxic actions of BTs, and nuclear receptor activation and lipid metabolism may play important roles in such actions of BTs.

Effects of environmental stressors on lipid metabolism in aquatic invertebrates

Lipid metabolism is crucial for the survival and propagation of the species, since lipids are an essential cellular component across animal taxa for maintaining homeostasis in the presence of environmental stressors. This review aims to summarize information on the lipid metabolism under environmental stressors in aquatic invertebrates. Fatty acid synthesis from glucose via de novo lipogenesis (DNL) pathway is mostly well-conserved across animal taxa. The structure of free fatty acid (FFA) from both dietary and DNL pathway could be transformed by elongase and desaturase. In addition, FFA can be stored in lipid droplet as triacylglycerol, upon attachment to glycerol. However, due to the limited information on both gene and lipid composition, in-depth studies on the structural modification of FFA and their storage conformation are required. Despite previously validated evidences on the disturbance of the normal life cycle and lipid homeostasis by the environmental stressors (e.g., obesogens, salinity, temperature, pCO₂, and nutrients) in the aquatic invertebrates, the mechanism behind these effects are still poorly understood. To overcome this limitation, omics approaches such as transcriptomic and proteomic analyses have been used, but there are still gaps in our knowledge on aquatic invertebrates as well as the lipidome. This paper provides a deeper understanding of lipid metabolism in aquatic invertebrates.

Effects of Perinatal Exposure to Dibutyltin Chloride on Fat and Glucose Metabolism in Mice, and Molecular Mechanisms, in Vitro

BACKGROUND

The organotin dibutyltin (DBT) is used in the manufacture of polyvinyl chloride (PVC) plastics, in construction materials, and in medical devices. Previous animal studies showed detrimental effects of DBT during in utero development at relatively high doses, but little was known about the effects of DBT exposure at environmentally relevant doses on endpoints such as obesity and metabolic disease.

OBJECTIVES

We tested the potential obesogenic effects of DBT using in vitro and in vivo models.

METHODS

We evaluated the effects of DBT on nuclear receptor activation and adipogenic potential using human and mouse multipotent mesenchymal stromal stem cells (MSCs). We also evaluated the effects of perinatal exposure to environmentally relevant doses of DBT in C57BL/6J mice.

RESULTS

DBT activated human and mouse PPARγ and RXRα in transient transfection assays, increased expression of adipogenic genes, promoted adipogenic differentiation and increased lipid accumulation in mouse and human MSCs, in vitro. DBT-induced adipogenic differentiation was abolished by the PPARγ antagonist T0070907, indicating that DBT was acting primarily through PPARγ. Perinatal exposure to low doses of DBT led to increased fat storage, decreased glucose tolerance, and increased circulating leptin levels in male, but not female, mice.

CONCLUSIONS

DBT acted as an obesogen by inducing lipid accumulation in human and mouse MSCs through a PPARγ-dependent pathway. In vivo exposure to biologically relevant doses of DBT during perinatal development led to increased fat storage, elevated leptin levels in plasma, and glucose intolerance in mice. Based on these findings, we posit that monitoring of DBT levels in human samples may aid in understanding and potentially preventing the rising rates of metabolic disorders in human populations. https://doi.org/10.1289/EHP3030.