Tetrabromobisphenol-A Promotes Early Adipogenesis and Lipogenesis in 3T3-L1 Cells

Perturbation of lipid metabolism in 3T3-L1 at different stages of preadipocyte differentiation and new insights into the association between changed metabolites and adipogenesis promoted by TBBPA or TBBPS

Tetrabromobisphenol A (TBBPA) and tetrabromobisphenol S (TBBPS) are widely distributed brominated flame retardants. While TBBPA has been demonstrated to stimulate adipogenesis, TBBPS is also under suspicion for potentially inducing comparable effects. In this study, we conducted a non-targeted metabolomics to examine the metabolic changes in 3T3-L1 cells exposed to an environmentally relevant dose of TBBPA or TBBPS. Our findings revealed that 0.1 µM of both TBBPA and TBBPS promoted the adipogenesis of 3T3-L1 preadipocytes. Multivariate analysis showed significant increases in glycerophospholipids, sphingolipids, and steroids relative levels in 3T3-L1 cells exposed to TBBPA or TBBPS at the final stage of preadipocyte differentiation. Metabolites set composed of glycerophospholipids was found to be highly effective predictors of adipogenesis in 3T3-L1 cells exposed to TBBPA or TBBPS (revealed from the receiver operating characteristic curve with an area under curve > 0.90). The results from metabolite set enrichment analysis suggested both TBBPA and TBBPS exposures significantly perturbed steroid biosynthesis in adipocytes. Moreover, TBBPS additionally disrupted the sphingolipid metabolism in the adipocytes. Our study presents new insights into the obesogenic effects of TBBPS and provides valuable information about the metabolites associated with adipogenesis induced by TBBPA or TBBPS.

Establishment and validation of a prediction model for gestational diabetes

AIM

To develop a visual prediction model for gestational diabetes (GD) in pregnant women and to establish an effective and practical tool for clinical application.

METHODS

To establish a prediction model, the modelling set included 1756 women enrolled in the Zunyi birth cohort, the internal validation set included 1234 enrolled women, and pregnant women in the Wuhan cohort were included in the external validation set. We established a demographic-lifestyle factor model (DLFM) and a demographic-lifestyle-environmental pollution factor model (DLEFM) based on whether the women were exposed to environmental pollutants. The least absolute shrinkage and selection lasso-logistic regression analyses were used to identify the independent predictors of GD and construct a nomogram for predicting its occurrence.

RESULTS

The DLEFM regression analysis showed that a family history of diabetes (odd ratio [OR] 2.28; 95% confidence interval [CI] 1.05-4.71), a history of GD in pregnant women (OR 4.22; 95% CI 1.89-9.41), being overweight or obese before pregnancy (OR 1.71; 95% CI 1.27-2.29), a history of hypertension (OR 2.61; 95% CI 1.41-4.72), sedentary time (h/day) (OR 1.16; 95% CI 1.08-1.24), monobenzyl phthalate (OR 1.95; 95% CI 1.45-2.67) and Q4 mono-ethyl phthalate concentration (OR 1.85; 95% CI 1.26-2.73) were independent predictors. The area under the receiver operating curves for the internal validation of the DLEFM and the DLFM constructed using these seven factors was 0.827 and 0.783, respectively. The calibration curve of the DLEFM was close to the diagonal line. The DLEFM was thus the more optimal model, and the one which we chose.

CONCLUSIONS

A nomogram based on preconception factors was constructed to predict the occurrence of GD in the second and third trimesters. It provided an effective tool for the early prediction and timely management of GD.

Co-occurrence of tetrabromobisphenol a and debromination products in human hair across China: Implications for exposure sources and health effects on metabolic syndrome

The large usage of Tetrabromobisphenol A (TBBPA) in consumer products leads to ubiquitous distribution globally, however, studies on the occurrence of their debromination compounds were rather scarce. Also, though many studies illustrate the effectiveness of hair analysis to assess human exposure to organic pollutants, evidence on the associations with health implications is still fairly limited. Herein, 598 participants from across China were employed to investigate chronic, low-level exposure to TBBPA and debromination products by hair analysis. The geomean concentrations of TBBPA, 2,2',6-tribromobisphenol A (Tri-BBPA), 2,2'- and 2,6-dibromobisphenol A (Di-BBPA), and 2-monobromobisphenol A (Mo-BBPA) were 1.07, 0.145, 0.135, and 0.894 ng/g, respectively, indicating nonnegligible health risks of debromination products. Hair analyte levels correlated with population age and population density among sampling regions. Sexual- and spatial-variations were observed with higher concentrations in females and in E-waste recycling sites. Logistic regression models showed that TBBPA exposure (adjusted odds ratio (OR): 1.02, 95 % confidential interval (CI): 1.01-1.05) was positively associated with risk of metabolic syndrome by adjusting for various covariates. These findings imply usefulness of hair as an alternative biomonitoring tool to assess human exposure to TBBPA and relative health effects, which highlights public concerns on co-exposure to these chemicals.

Perinatal triphenyl phosphate exposure induces metabolic dysfunctions through the EGFR/ERK/AKT signaling pathway: Mechanistic in vitro and in vivo studies

Triphenyl phosphate (TPhP), a widely used organophosphate-flame retardant, is ubiquitously found in household environments and may adversely affect human health. Evidence indicates that TPhP exposure causes metabolic dysfunctions in vivo; however, the underlying mechanism of such adverse effects has not been comprehensively investigated. Herein, we utilized two in vitro models including mouse and human preadipocytes to delineate adipogenic mechanisms of TPhP. The results revealed that both mouse and human preadipocytes exposed to TPhP concentration-dependently accumulated more fat through a significant upregulation of epidermal growth factor receptor (EGFR). We demonstrated that TPhP significantly promoted adipogenesis through the activation of EGFR/ERK/AKT signaling pathway as evident by a drastic reduction in adipogenesis of preadipocytes cotreated with inhibitors of EGFR and its major effectors. Furthermore, we confirmed the mechanism of TPhP-induced metabolic dysfunctions in vivo. We observed that male mice perinatally exposed to TPhP had a significant increase in adiposity, hepatic triglycerides, insulin resistance, plasma insulin levels, hypotension, and phosphorylated EGFR in gonadal fat. Interestingly, an administration of a potent and selective EGFR inhibitor significantly ameliorated the adverse metabolic effects caused by TPhP. Our findings uncovered a potential mechanism of TPhP-induced metabolic dysfunctions and provided implications on toxic metabolic effects posed by environmental chemicals.

Schisandra chinensis-derived gomisin C suppreses lipid accumulation by JAK2-STAT signaling in adipocyte

Gomisin C is a lignan isolated from the fruit of Schisandra chinensis. The current study aimed to investigate the effect of gomisin C on lipid accumulation in adipocytes and its underlying mechanism. Gomisin C effectively inhibited lipid accumulation by downregulating adipogenic factors such as PPARγ and C/EBPα. Gomisin C-mediated suppression of lipid accumulation occurred in the early adipogenic stage; C/EBPβ was downregulated by 55%, while KLF2 was upregulated by 1.5-fold. Gomisin C significantly reduced the production of reactive oxygen species but upregulated antioxidant enzymes, including catalase, SOD1, and Gpx at the mRNA level. Gomisin C regulated NRF2-KEAP1 pathway by increasing NRF2 and decreasing KEAP1, in protein abundance. Furthermore, gomisin C suppressed the JAK2-STAT signaling pathway by decreasing phosphorylation. Taken together, gomisin C reduced early adipogenesis and ROS production by inhibiting the JAK2-STAT signaling pathway but activating the NRF2-KEAP1 signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01263-8.

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.

Associations between exposure to brominated flame retardants and metabolic syndrome and its components in U.S. adults

BACKGROUND

Humans are simultaneously exposed to numerous of environmental brominated flame retardants (BFRs). We aim to explore the overall associations of BFRs mixture on metabolic syndrome (MetS) and its components and further identify significant chemicals.

METHODS

This study included 4641 adults from the National Health and Nutrition Examination Survey (NHANES) in 2007-2016. The weighted logistic regression was conducted to estimate the association of a single BFR exposure with MetS and its components. Meanwhile, the weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) were adopted to evaluate the overall associations of BFRs mixture on MetS and its components, and to identify significant chemicals. We also evaluated potential associations modified by sex.

RESULTS

In the weighted logistic regression model, PBB153 were positively associated with MetS in a dose-dependent manner (P_trend < 0.05). For its components, increasing quartiles of most BFRs were positively associated with abdominal obesity, hypertriglyceridemia, and low HDL. However, we found no statistically significant associations between BFRs and hypertension and hyperglycemia. WQS analyses found that BFRs mixture was positively associated with MetS (OR: 1.30; 95%CI:1.14, 1.46), abdominal obesity (OR: 1.15; 95%CI:1.03, 1.27), hypertriglyceridemia (OR:1.43; 95%CI:1.19, 1.67), and low HDL (OR: 1.15; 95%CI:1.01, 1.29). BKMR showed associations in a similar direction as WQS for BFRs mixture. For MetS, hypertriglyceridemia and Low HDL, PBB153, PBDE28 and PBDE209 were the most heavily weighting chemicals and had the highest the posterior inclusion probabilities in the WQS and BKMR, respectively. BFRs showed stronger associations of MetS and its components in males than in females.

CONCLUSIONS

The present study suggested exposure to BFRs mixture was positively associated with MetS and its components in adults, and PBB153, PBDE28 and PBDE209 were the significant chemicals. However, prospective cohort studies are still needed to confirm the causal effect between BFRs mixture and MetS.

Potential obesogenic effects of TBBPA and its alternatives TBBPS and TCBPA revealed by metabolic perturbations in human hepatoma cells

To date, increasing numbers of studies have shown the obesogenic effects of tetrabromobisphenol A (TBBPA). Tetrabromobisphenol S (TBBPS) and tetrachlorobisphenol A (TCBPA) are two common alternatives to TBBPA, and their environmental distributions are frequently reported. However, their toxicity and the associated potential health risks are poorly documented. Herein, we performed untargeted metabolomics to study the metabolic perturbations in HepG2 cells exposed to TBBPA and its alternatives. Consequently, no loss of cellular viability was observed in HepG2 cells exposed to 0.1 μmol/L and 1 μmol/L TBBPA, TBBPS and TCBPA. However, multivariate analysis and metabolic profiles revealed significant perturbations in glycerophospholipid and fatty acyl levels in HepG2 cells exposure to TBBPS and TCBPA. The evident increases in the glucose 1-phosphate and fructose 6-phosphate levels in HepG2 cells were proposed to be induced by the promotion of PGM1/PGM2 and GPI gene expression and the suppression of UPG2 and GFPT1/GFPT2 gene expression. Our results suggest that TBBPS and TCBPA are more likely to disrupt liver metabolic homeostasis and potentially drive liver dysfunction than TBBPA. Our study is significant for the re-evaluation of the health risks associated with TBBPA and its alternatives TBBPS and TCBPA.

Antioxidant and anti-obesity effects of in vitro digesta of germinated buckwheat

Buckwheat germinated on days of 3, 5, and 7 was digested in vitro, and the antioxidant and anti-obesity effects of the digesta were evaluated. In vitro digesta of 5 days germinated buckwheat (GBD5) showed significantly higher antioxidant activity in DPPH, ABTS, total phenolic content, total flavonoid content, and ferric reducing antioxidant power by 5.3, 1.3, 2.0, 3.2, and 2.8-fold, respectively than in vitro digesta of non-germinated buckwheat. GBD5 exerted inhibitory effect on total lipid accumulation in 3T3-L1 adipocyte in a dose-dependent manner, with over 25% reduction at 400 µg/mL. Additionally, GBD5 significantly downregulated genes related to adipocyte differentiation and fat accumulation. GBD5 possessed different metabolite profiles compared to others such as higher content of γ-aminobutyric acid and succinic acid. Therefore, GBD5 has potent antioxidant effects and suppresses fat accumulation-related genes and proteins expression, which could act as a new functional substance.

Halogenated bisphenol a analogues induce PPARγ-independent toxicity within human hepatocellular carcinoma cells

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TBBPA and TCBPA alone or as binary mixtures decreases cell viability.

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TBBPA or TCBPA alone or as a mixture enhances effects of reference PPARγ ligands.

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Overexpression of PPARγ does not mitigate nor enhance the effects of TBBPA.

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TBBPA and TCBPA induce toxicity within HepG2 cells in a PPARγ-independent manner.

Tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) – both halogenated bisphenol (BPA) analogues – are suspected ligands of peroxisome proliferator-activated receptor gamma (PPARγ). While previous studies have shown that TBBPA and TCBPA activate PPARγ within cell-free assays, the downstream effects of TBBPA- and TCBPA-induced PPARγ activation on cellular transcription and physiology have not been thoroughly investigated. Therefore, the objective of this study was to determine whether exposure to TBBPA or TCBPA (either alone or in combination) alters levels of neutral lipids and fatty acid synthase (FASN) – an enzyme that catalyzes synthesis of long-chain saturated fatty acids – within intact cells in a PPARγ-dependent manner. For this study, we relied on human hepatocellular carcinoma (HepG2) cells as a model since these liver cells express basal levels of PPARγ and have been used to study lipoprotein metabolism and regulation of drug metabolizing enzymes. Although exposure to TBBPA and TCBPA alone did not affect cell viability nor neutral lipid and FASN levels in a concentration-dependent manner, exposure to binary mixtures of TBBPA and TCBPA resulted in a concentration-dependent decrease in cell viability in the absence of concentration-dependent effects on neutral lipid and FASN levels. Interestingly, exposure to TBBPA or TCBPA alone or as a mixture enhanced the effects of a reference PPARγ agonist (ciglitazone) and antagonist (GW 9662) on cell viability (but not neutral lipid levels), suggesting that these two halogenated BPA analogues may interact synergistically with ciglitazone and GW 9662 to induce cytotoxicity. However, overexpression of PPARγ did not mitigate nor enhance the effects of TBBPA – a potent PPARγ ligand predicted by ToxCast’s cell-free competitive binding assays – on cell viability, neutral lipid levels, nor the cellular transcriptome. Overall, our findings suggest that halogenated BPA analogues such as TCBPA and TBBPA induce toxicity within HepG2 cells in a PPARγ-independent manner.

G protein-coupled estrogen receptor 1 mediates proliferation and adipogenic differentiation of goat adipose-derived stem cells through ERK1/2-NF-κB signaling pathway

Adipose tissue formation and moderate fat deposition are important for the production performance and eating quality of livestock meats. The self-renewal and adipogenic differentiation of adipose-derived stem cells are responsible for the formation and development of adipose tissue. In addition, estrogen targeting G protein-coupled estrogen receptor 1 (GPER1) has been reported to modulate cell proliferation and differentiation during tissue and organ development. However, the potential correlation among estrogen, GPER1, proliferation, and adipogenic differentiation in goat adipose-derived stem cells (gADSCs) is still unclear. Herein, we demonstrated that 17β-estradiol enhances the proliferative ability of gADSCs, indicated by the increased cell number and cell viability, accompanied by up-regulated expressions of cyclin D1 and PCNA. Meanwhile, the adipogenic differentiation is promoted by 17β-estradiol, supported by higher ccumulation of intracellular lipids and increased expressions of PPARγ, ACC, and FABP4. Notably, these activities are all obviously reduced by administration with GPER1 antagonist G15, but GPER1 agonist G1 enhances cell proliferation and adipogenic differentiation. Moreover, GPER1 silencing diminishes cell proliferation and adipogenic differentiation. In parallel, 17β-estradiol elevates the protein level of nuclear p-p65. Furthermore, the phosphorylation of p65 is enhanced by G1 but inhibited by G15 and GPER1 silencing. In addition, the phosphorylation of p65 is mediated by ERK1/2, suggesting that estrogen targeting GPER1 regulates cell proliferation and adipogenic differentiation of gADSCs through the ERK1/2-NF-κB signaling pathway. This study may provide a strong theoretical basis for improving meat quality, flavor, and cold resistance of livestock.

Adipogenic Activity of Chemicals Used in Plastic Consumer Products

Bisphenols and phthalates, chemicals frequently used in plastic products, promote obesity in cell and animal models. However, these well-known metabolism-disrupting chemicals (MDCs) represent only a minute fraction of all compounds found in plastics. To gain a comprehensive understanding of plastics as a source of exposure to MDCs, we characterized the chemicals present in 34 everyday products using nontarget high-resolution mass spectrometry and analyzed their joint adipogenic activities by high-content imaging. We detected 55,300 chemical features and tentatively identified 629 unique compounds, including 11 known MDCs. Importantly, the chemicals extracted from one-third of the products caused murine 3T3-L1 preadipocytes to proliferate, and differentiate into adipocytes, which were larger and contained more triglycerides than those treated with the reference compound rosiglitazone. Because the majority of plastic extracts did not activate the peroxisome proliferator-activated receptor γ and the glucocorticoid receptor, the adipogenic effects are mediated via other mechanisms and, thus, likely to be caused by unknown MDCs. Our study demonstrates that daily-use plastics contain potent mixtures of MDCs and can, therefore, be a relevant yet underestimated environmental factor contributing to obesity.

ENDOCRINE DISRUPTING CHEMICALS AND OBESITY: THE EVOLVING STORY OF OBESOGENS

Increase in obesity pandemic all over the world consequently leads to the investigation of possible causes. In addition to the traditional explanation using the so-called caloric model, the field of endocrine disruptors (EDs), especially subgroup called obesogens, offered more light on the pathogenetic mechanisms involved. After the Second World War a correlation between an increased production of exogenous pollutants and actual obesity epidemic was suggested. "Obesogen hypothesis" implies that molecules called obesogens inadequately stimulate the development of adipose cells and lipid accumulation in existing adipose cells, as well as change metabolic balance or hormonal control of appetite and satiety, leading to an increase in body fat mass. The list of obesogens includes some industrial chemicals, biocides, pharmaceuticals, pollutants, and smoke. EDs from the group of obesogens may exert their effects by the impairment in the programming development of adipocytes, by an increase in energetic depot in the adipose tissue, and by influencing neuroendocrine control of appetite and satiety. Increased scientific evidence on obesogens and their mechanisms of action may help to prevent obesity and mitigate deleterious effects of the environment on human life and development. New translational studies are needed to explain the possible mechanism proposed.

Transcriptomic Analysis of the Differential Nephrotoxicity of Diverse Brominated Flame Retardants in Rat and Human Renal Cells

Brominated flame retardants (BFRs) are environmentally persistent, are detected in humans, and some have been banned due to their potential toxicity. BFRs are developmental neurotoxicants and endocrine disruptors; however, few studies have explored their potential nephrotoxicity. We addressed this gap in the literature by determining the toxicity of three different BFRs (tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and tetrabromodiphenyl ether (BDE-47)) in rat (NRK 52E) and human (HK-2 and RPTEC) tubular epithelial cells. All compounds induced time- and concentration-dependent toxicity based on decreases in MTT staining and changes in cell and nuclear morphology. The toxicity of BFRs was chemical- and cell-dependent, and human cells were more susceptible to all three BFRs based on IC₅₀s after 48 h exposure. BFRs also had chemical- and cell-dependent effects on apoptosis as measured by increases in annexin V and PI staining. The molecular mechanisms mediating this toxicity were investigated using RNA sequencing. Principal components analysis supported the hypothesis that BFRs induce different transcriptional changes in rat and human cells. Furthermore, BFRs only shared nine differentially expressed genes in rat cells and five in human cells. Gene set enrichment analysis demonstrated chemical- and cell-dependent effects; however, some commonalities were also observed. Namely, gene sets associated with extracellular matrix turnover, the coagulation cascade, and the SNS-related adrenal cortex response were enriched across all cell lines and BFR treatments. Taken together, these data support the hypothesis that BFRs induce differential toxicity in rat and human renal cell lines that is mediated by differential changes in gene expression.

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.

A Data-Driven Transcriptional Taxonomy of Adipogenic Chemicals to Identify White and Brite Adipogens

BACKGROUND

Chemicals in disparate structural classes activate specific subsets of the transcriptional programs of peroxisome proliferator-activated receptor-γ (PPARγ) to generate adipocytes with distinct phenotypes.

OBJECTIVES

Our objectives were to a) establish a novel classification method to predict PPARγ ligands and modifying chemicals; and b) create a taxonomy to group chemicals on the basis of their effects on PPARγ's transcriptome and downstream metabolic functions. We tested the hypothesis that environmental adipogens highly ranked by the taxonomy, but segregated from therapeutic PPARγ ligands, would induce white but not brite adipogenesis.

METHODS

3T3-L1 cells were differentiated in the presence of 76 chemicals (negative controls, nuclear receptor ligands known to influence adipocyte biology, potential environmental PPARγ ligands). Differentiation was assessed by measuring lipid accumulation. mRNA expression was determined by RNA-sequencing (RNA-Seq) and validated by reverse transcription-quantitative polymerase chain reaction. A novel classification model was developed using an amended random forest procedure. A subset of environmental contaminants identified as strong PPARγ agonists were analyzed by their effects on lipid handling, mitochondrial biogenesis, and cellular respiration in 3T3-L1 cells and human preadipocytes.

RESULTS

We used lipid accumulation and RNA-Seq data to develop a classification system that a) identified PPARγ agonists; and b) sorted chemicals into likely white or brite adipogens. Expression of Cidec was the most efficacious indicator of strong PPARγ activation. 3T3-L1 cells treated with two known environmental PPARγ ligands, tetrabromobisphenol A and triphenyl phosphate, which sorted distinctly from therapeutic ligands, had higher expression of white adipocyte genes but no difference in Pgc1a and Ucp1 expression, and higher fatty acid uptake but not mitochondrial biogenesis. Moreover, cells treated with two chemicals identified as highly ranked PPARγ agonists, tonalide and quinoxyfen, induced white adipogenesis without the concomitant health-promoting characteristics of brite adipocytes in mouse and human preadipocytes.

DISCUSSION

A novel classification procedure accurately identified environmental chemicals as PPARγ ligands distinct from known PPARγ-activating therapeutics.

CONCLUSION

The computational and experimental framework has general applicability to the classification of as-yet uncharacterized chemicals. https://doi.org/10.1289/EHP6886.

Environmental Estrogens and Their Biological Effects through GPER Mediated Signal Pathways

Many environmental chemicals have been found to exert estrogenic effects in cells and experimental animals by activating nuclear receptors such as estrogen receptors and estrogen-related receptors. These compounds include bisphenols, pesticides, polybrominated diphenyl ethers (PBDEs), organophosphate flame retardants, phthalates and metalloestrogens. G protein-coupled estrogen receptor (GPER) exists widely in numerous cells/tissues of human and other vertebrates. A number of studies have demonstrated that GPER plays a vital role in mediating the estrogenic effects of environmental pollutants. Even at very low concentrations, these chemicals may activate GPER pathways, thus affect many aspects of cellular functions including proliferation, metastasis and apoptosis, resulting in cancer progression, cardiovascular disorders, and reproductive dysfunction. This review summarized the environmental occurrence and human exposure levels of these pollutants, and integrated current experimental evidence toward revealing the underlying mechanisms of pollutant-induced cellular dysfunction via GPER. The GPER mediated rapid non-genomic actions play an important role in the process leading to the adverse effects observed in experimental animals and even in human beings.

Flame Retardants-Mediated Interferon Signaling in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a growing concern worldwide, affecting 25% of the global population. NAFLD is a multifactorial disease with a broad spectrum of pathology includes steatosis, which gradually progresses to a more severe condition such as nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and eventually leads to hepatic cancer. Several risk factors, including exposure to environmental toxicants, are involved in the development and progression of NAFLD. Environmental factors may promote the development and progression of NAFLD by various biological alterations, including mitochondrial dysfunction, reactive oxygen species production, nuclear receptors dysregulation, and interference in inflammatory and immune-mediated signaling. Moreover, environmental contaminants can influence immune responses by impairing the immune system’s components and, ultimately, disease susceptibility. Flame retardants (FRs) are anthropogenic chemicals or mixtures that are being used to inhibit or delay the spread of fire. FRs have been employed in several household and outdoor products; therefore, human exposure is unavoidable. In this review, we summarized the potential mechanisms of FRs-associated immune and inflammatory signaling and their possible contribution to the development and progression of NAFLD, with an emphasis on FRs-mediated interferon signaling. Knowledge gaps are identified, and emerging pharmacotherapeutic molecules targeting the immune and inflammatory signaling for NAFLD are also discussed.

Life-Time Environmental Chemical Exposure and Obesity: Review of Epidemiological Studies Using Human Biomonitoring Methods

The exponential global increase in the incidence of obesity may be partly attributable to environmental chemical (EC) exposure. Humans are constantly exposed to ECs, primarily through environmental components. This review compiled human epidemiological study findings of associations between blood and/or urinary exposure levels of ECs and anthropometric overweight and obesity indices. The findings reveal research gaps that should be addressed. We searched MEDLINE (PubMed) for full text English articles published in 2006-2020 using the keywords "environmental exposure" and "obesity". A total of 821 articles were retrieved; 102 reported relationships between environmental exposure and obesity indices. ECs were the predominantly studied environmental exposure compounds. The ECs were grouped into phenols, phthalates, and persistent organic pollutants (POPs) to evaluate obesogenic roles. In total, 106 articles meeting the inclusion criteria were summarized after an additional search by each group of EC combined with obesity in the PubMed and Scopus databases. Dose-dependent positive associations between bisphenol A (BPA) and various obesity indices were revealed. Both individual and summed di(2-ethylhexyl) phthalate (DEHP) and non-DEHP metabolites showed inconsistent associations with overweight and obesity indices, although mono-butyl phthalate (MBP), mono-ethyl phthalate (MEP), and mono-benzyl phthalate (MBzP) seem to have obesogenic roles in adolescents, adults, and the elderly. Maternal exposure levels of individual POP metabolites or congeners showed inconsistent associations, whereas dichlorodiphenyldichloroethylene (DDE) and perfluorooctanoic acid (PFOA) were positively associated with obesity indices. There was insufficient evidence of associations between early childhood EC exposure and the subsequent development of overweight and obesity in late childhood. Overall, human evidence explicitly reveals the consistent obesogenic roles of BPA, DDE, and PFOA, but inconsistent roles of phthalate metabolites and other POPs. Further prospective studies may yield deeper insights into the overall scenario.

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.

Adipose Tissue and Endocrine-Disrupting Chemicals: Does Sex Matter?

Obesity and metabolic-related diseases, among which diabetes, are prominent public health challenges of the 21st century. It is now well acknowledged that pollutants are a part of the equation, especially endocrine-disrupting chemicals (EDCs) that interfere with the hormonal aspect. The aim of the review is to focus on adipose tissue, a central regulator of energy balance and metabolic homeostasis, and to highlight the significant differences in the endocrine and metabolic aspects of adipose tissue between males and females which likely underlie the differences of the response to exposure to EDCs between the sexes. Moreover, the study also presents an overview of several mechanisms of action by which pollutants could cause adipose tissue dysfunction. Indeed, a better understanding of the mechanism by which environmental chemicals target adipose tissue and cause metabolic disturbances, and how these mechanisms interact and sex specificities are essential for developing mitigating and sex-specific strategies against metabolic diseases of chemical origin. In particular, considering that a scenario without pollutant exposure is not a realistic option in our current societies, attenuating the deleterious effects of exposure to pollutants by acting on the gut-adipose tissue axis may constitute a new direction of research.

Chemical Structure-Related Adipogenic Effects of Tetrabromobisphenol A and Its Analogues on 3T3-L1 Preadipocytes

Tetrabromobisphenol A (TBBPA), the most widely used brominated flame retardant, is reported to potentially possess risks in inducing obesity or obesity-related metabolic diseases. Considering the increasing environmental contamination of TBBPA analogues and their high structural similarities to the parent compound, whether they could influence adipogenesis or not remains to be elucidated. In this study, two of the most prevalent TBBPA derivatives [i.e., TBBPA bis(allyl ether) (TBBPA-BAE) and TBBPA bis(2,3-dibromopropyl ether) (TBBPA-BDBPE)] and their byproducts [i.e., TBBPA mono(allyl ether) (TBBPA-MAE) and TBBPA mono(2,3-dibromopropyl ether) (TBBPA-MDBPE)], together with TBBPA, were screened for their capacities in activating peroxisome proliferator-activated receptor-γ (PPARγ) and glucocorticoid receptor (GR), the key nuclear receptors involved in adipogenesis, and their structure-related effects on differentiation of 3T3-L1 preadipocytes were explored. The results indicated that the binding affinities of TBBPA and its analogues for the PPARγ ligand-binding domain (PPARγ-LBD) and GR, as well as their effects on PPARγ transactivation, followed the order of TBBPA > TBBPA-MAE > TBBPA-MDBPE > TBBPA-BAE, TBBPA-BDBPE. Nevertheless, TBBPA-MAE and TBBPA-MDBPE showed higher potentials in promoting adipogenesis in 3T3-L1 cells than did TBBPA, as evidenced by intracellular triglyceride contents and adipogenic biomarkers at both protein and transcriptional levels. The etherified group at position 4 of TBBPA phenolic rings was crucial in chemical-induced adipogenic effects, which was related with the recruitment of PPARγ and GR-mediated networks and some other unidentified signaling pathways. The findings on the disturbance of TBBPA analogues on adipogenesis revealed their potential risk in causing obesity and other lipid metabolism-related human health concerns.

Bisphenol A and Phthalates in Diet: An Emerging Link with Pregnancy Complications

Endocrine-disrupting chemicals (EDCs) are exogenous substances that are able to interfere with hormone action, likely contributing to the development of several endocrine and metabolic diseases. Among them, Bisphenol A (BPA) and phthalates contaminate food and water and have been largely studied as obesogenic agents. They might contribute to weight gain, insulin resistance and pancreatic β-cell dysfunction in pregnancy, potentially playing a role in the development of pregnancy complications, such as gestational diabetes mellitus (GDM), and adverse outcomes. Pregnancy and childhood are sensitive windows of susceptibility, and, although with not univocal results, preclinical and clinical studies have suggested that exposure to BPA and phthalates at these stages of life might have an impact on the development of metabolic diseases even many years later. The molecular mechanisms underlying this association are largely unknown, but adipocyte and pancreatic β-cell dysfunction are suspected to be involved. Remarkably, transgenerational damage has been observed, which might be explained by epigenetic changes. Further research is needed to address knowledge gaps and to provide preventive measure to limit health risks connected with exposure to EDCs.

Nuclear receptors are the major targets of endocrine disrupting chemicals

Endocrine disrupting chemicals (EDCs) are exogenous substances that are suspected to cause adverse effects in the endocrine system mainly by acting through their interaction with nuclear receptors such as the estrogen receptors α and β (ERα and ERβ), the androgen receptor (AR), the pregnan X receptor (PXR), the peroxisome proliferator activated receptors α and γ (PPARα, PPARγ) and the thyroid receptors α and β (TRα and TRβ). More recently, the retinoid X receptors (RXRα, RXRβ and RXRγ), the constitutive androstane receptor (CAR) and the estrogen related receptor γ (ERRγ) have also been identified as targets of EDCs. Finally, nuclear receptors still poorly studied for their interaction with environmental ligands such as the progesterone receptor (PR), the mineralocorticoid receptor (MR), the glucocorticoid receptor (GR), the retinoic acid receptors (RAR α, RARβ and RARγ), the farnesoid X receptor (FXR) and the liver X receptors α and β (LXRα and LXβ) as well are suspected targets of EDCs. Humans are generally exposed to low doses of pollutants, therefore the aim of current research is to identify the targets of EDCs at environmental concentrations. In this review, we analyze recent works referring that nuclear receptors are targets of EDCs and we highlight which EDCs are able to act at low concentrations.

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

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

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.

Thyroid receptor antagonism as a contributory mechanism for adipogenesis induced by environmental mixtures in 3T3-L1 cells

We previously demonstrated that indoor house dust extracts could induce adipogenesis in pre-adipocytes, suggesting a potential role for indoor contaminant mixtures in metabolic health. Herein, we investigated the potential role of thyroid receptor beta (TRβ) antagonism in adipogenic effects (dust-induced triglyceride accumulation and pre-adipocyte proliferation) following exposure to environmental mixtures (indoor house dust extracts). Concentrations of specific flame retardants were measured in extracts, and metabolic health information was collected from residents (n = 137). 90% of dust extracts exhibited significant adipogenic activity, >60% via triglyceride accumulation, and >70% via pre-adipocyte proliferation. Triglyceride accumulation was positively correlated with concentrations of each of twelve flame retardants, despite most being independently inactive; this suggests a putative role for co-exposures or mixtures. We further reported a positive correlation between dust-induced triglyceride accumulation and serum thyroid stimulating hormone concentrations, negative correlations with serum free triiodothyronine and thyroxine concentrations, and a positive and significant association between dust-induced triglyceride accumulation and residents' body mass index (BMI). We hypothesized that inhibition of TR antagonism might counteract these effects, and both addition of a TR agonist and siRNA knock-down of TR resulted in decreased dust-induced triglyceride accumulation in a subset of samples, bolstering this as a contributory mechanism. These results highlight a contributory role of environmental TR antagonism as a putative factor in metabolic health, suggesting that further research should evaluate this mechanism and determine whether in vitro adipogenic activity could have utility as a biomarker for metabolic health in residents.

Endocrine-Mediated Mechanisms of Metabolic Disruption and New Approaches to Examine the Public Health Threat

Obesity and metabolic disorders are of great societal concern and generate substantial human health care costs globally. Interventions have resulted in only minimal impacts on disrupting this worsening health trend, increasing attention on putative environmental contributors. Exposure to numerous environmental contaminants have, over decades, been demonstrated to result in increased metabolic dysfunction and/or weight gain in cell and animal models, and in some cases, even in humans. There are numerous mechanisms through which environmental contaminants may contribute to metabolic dysfunction, though certain mechanisms, such as activation of the peroxisome proliferator activated receptor gamma or the retinoid x receptor, have received considerably more attention than less-studied mechanisms such as antagonism of the thyroid receptor, androgen receptor, or mitochondrial toxicity. As such, research on putative metabolic disruptors is growing rapidly, as is our understanding of molecular mechanisms underlying these effects. Concurrent with these advances, new research has evaluated current models of adipogenesis, and new models have been proposed. Only in the last several years have studies really begun to address complex mixtures of contaminants and how these mixtures may disrupt metabolic health in environmentally relevant exposure scenarios. Several studies have begun to assess environmental mixtures from various environments and study the mechanisms underlying their putative metabolic dysfunction; these studies hold real promise in highlighting crucial mechanisms driving observed organismal effects. In addition, high-throughput toxicity databases (ToxCast, etc.) may provide future benefits in prioritizing chemicals for in vivo testing, particularly once the causative molecular mechanisms promoting dysfunction are better understood and expert critiques are used to hone the databases. In this review, we will review the available literature linking metabolic disruption to endocrine-mediated molecular mechanisms, discuss the novel application of environmental mixtures and implications for in vivo metabolic health, and discuss the putative utility of applying high-throughput toxicity databases to answering complex organismal health outcome questions.