Adipogenic Effects and Gene Expression Profiling of Firemaster® 550 Components in Human Primary Preadipocytes

House dust-derived mixtures of organophosphate esters alter the phenotype, function, transcriptome, and lipidome of KGN human ovarian granulosa cells

Organophosphate esters (OPEs), used as flame retardants and plasticizers, are present ubiquitously in the environment. Previous studies suggest that exposure to OPEs is detrimental to female fertility in humans. However, no experimental information is available on the effects of OPE mixtures on ovarian granulosa cells, which play essential roles in female reproduction. We used high-content imaging to investigate the effects of environmentally relevant OPE mixtures on KGN human granulosa cell phenotypes. Perturbations to steroidogenesis were assessed using ELISA and qRT-PCR. A high-throughput transcriptomic approach, TempO-Seq, was used to identify transcriptional changes in a targeted panel of genes. Effects on lipid homeostasis were explored using a cholesterol assay and global lipidomic profiling. OPE mixtures altered multiple phenotypic features of KGN cells, with triaryl OPEs in the mixture showing higher potencies than other mixture components. The mixtures increased basal production of steroid hormones; this was mediated by significant changes in the expression of critical transcripts involved in steroidogenesis. Further, the total-OPE mixture disrupted cholesterol homeostasis and the composition of intracellular lipid droplets. Exposure to complex mixtures of OPEs, similar to those found in house dust, may adversely affect female reproductive health by altering a multitude of phenotypic and functional endpoints in granulosa cells. This study provides novel insights into the mechanisms of actions underlying the toxicity induced by OPEs and highlights the need to examine the effects of human relevant chemical mixtures.

Weight of evidence evaluation of the metabolism disrupting effects of triphenyl phosphate using an expert knowledge elicitation approach

Identification of Endocrine-Disrupting Chemicals (EDCs) in a regulatory context requires a high level of evidence. However, lines of evidence (e.g. human, in vivo, in vitro or in silico) are heterogeneous and incomplete for quantifying evidence of the adverse effects and mechanisms involved. To date, for the regulatory appraisal of metabolism-disrupting chemicals (MDCs), no harmonised guidance to assess the weight of evidence has been developed at the EU or international level. To explore how to develop this, we applied a formal Expert Knowledge Elicitation (EKE) approach within the European GOLIATH project. EKE captures expert judgment in a quantitative manner and provides an estimate of uncertainty of the final opinion. As a proof of principle, we selected one suspected MDC -triphenyl phosphate (TPP) - based on its related adverse endpoints (obesity/adipogenicity) relevant to metabolic disruption and a putative Molecular Initiating Event (MIE): activation of peroxisome proliferator activated receptor gamma (PPARγ). We conducted a systematic literature review and assessed the quality of the lines of evidence with two independent groups of experts within GOLIATH, with the objective of categorising the metabolic disruption properties of TPP, by applying an EKE approach. Having followed the entire process separately, both groups arrived at the same conclusion, designating TPP as a "suspected MDC" with an overall quantitative agreement exceeding 85%, indicating robust reproducibility. The EKE method provides to be an important way to bring together scientists with diverse expertise and is recommended for future work in this area.

Organophosphate ester flame retardants and plasticizers affect the phenotype and function of HepG2 liver cells

Exposure to the organophosphate esters (OPEs), used as flame retardants and plasticizers, is associated with a variety of adverse health effects including an increase in the incidence of fatty liver diseases. The goal of this study was to investigate the effects of six OPEs, all detected in Canadian house dust, on the phenotype and function of HepG2 liver cells. We used high-content imaging to investigate the effects of these OPEs on cell survival, mitochondria, oxidative stress, lipid droplets, and lysosomes. Effects on the autophagy/lipophagy pathway were evaluated using confocal microscopy. The triaryl OPEs (isopropylated triphenylphosphate [IPPP], tris(methylphenyl) phosphate [TMPP], and triphenyl phosphate [TPHP]) were more cytotoxic than non-triaryl OPEs (tris(2-butoxyethyl) phosphate [TBOEP], tris(1-chloro-2-propyl) phosphate [TCIPP], and tris(1,3-dichloro-2-propyl) phosphate [TDCIPP]). Exposure to most OPEs increased total mitochondria, reduced reactive oxygen species, and increased total lipid droplet areas and lysosomal intensity. Potency ranking was done using the lowest benchmark concentration/administered equivalent dose method and toxicological prioritization index analyses to integrate all phenotypic endpoints. IPPP, TBOEP, and TPHP ranked as the most potent OPEs, whereas TMPP, TCIPP, and TDCIPP were relatively less bioactive. Confocal microscopic analysis demonstrated that IPPP reduced the colocalization of lipid droplets (PLIN2), lysosomes (LAMP1), and autophagosomes (p62), disrupting autophagy. In contrast, TBOEP rescued cells from bafilomycin A1-induced inhibition of autophagy and/or increased autophagic flux. Together, these data demonstrate that OPEs have adverse effects on HepG2 cells. Further, OPE-induced dysregulation of autophagy may contribute to the association between OPE exposure and adverse effects on liver lipid homeostasis.

Impact of Exposure to a Mixture of Organophosphate Esters on Adrenal Cell Phenotype, Lipidome, and Function

Organophosphate esters (OPEs) are used primarily as flame retardants and plasticizers. Previously, we reported that adrenal cells are important targets of individual OPEs. However, real-life exposures are to complex mixtures of these chemicals. To address this, we exposed H295R human adrenal cells to varying dilutions (1/1000K to 1/3K) of a Canadian household dust-based OPE mixture for 48 hours and evaluated effects on phenotypic, lipidomic, and functional parameters. Using a high-content screening approach, we assessed phenotypic markers at mixture concentrations at which there was greater than 70% cell survival; the most striking effect of the OPE mixture was a 2.5-fold increase in the total area of lipid droplets. We then determined the response of specific lipid species to OPE exposures with novel, nontargeted lipidomic analysis of isolated lipid droplets. These data revealed that house dust OPEs induced concentration-dependent alterations in the composition of lipid droplets, particularly affecting the triglyceride, diglyceride, phosphatidylcholine, and cholesterol ester subclasses. The steroid-producing function of adrenal cells in the presence or absence of a steroidogenic stimulus, forskolin, was determined. While the production of 17β-estradiol remained unaffected, a slight decrease in testosterone production was observed after stimulation. Conversely, a 2-fold increase in both basal and stimulated cortisol and aldosterone production was observed. Thus, exposure to a house dust-based mixture of OPEs exerts endocrine-disrupting effects on adrenal cells, highlighting the importance of assessing the effects of environmentally relevant mixtures.

Toxicological Mechanisms and Potencies of Organophosphate Esters in KGN Human Ovarian Granulosa Cells as Revealed by High-throughput Transcriptomics

Despite the growing number of studies reporting potential risks associated with exposure to organophosphate esters (OPEs), their molecular mechanisms of action remain poorly defined. We used the high-throughput TempO-Seq™ platform to investigate the effects of frequently detected OPEs on the expression of ∼3000 environmentally responsive genes in KGN human ovarian granulosa cells. Cells were exposed for 48 h to one of five OPEs (0.1 to 50 μM): tris(methylphenyl) phosphate (TMPP), isopropylated triphenyl phosphate (IPPP), tert-butylphenyl diphenyl phosphate (BPDP), triphenyl phosphate (TPHP), or tris(2-butoxyethyl) phosphate (TBOEP). The sequencing data indicate that four OPEs induced transcriptional changes, whereas TBOEP had no effect within the concentration range tested. Multiple pathway databases were used to predict alterations in biological processes based on differentially expressed genes. At lower concentrations, inhibition of the cholesterol biosynthetic pathway was the predominant effect of OPEs; this was likely a consequence of intracellular cholesterol accumulation. At higher concentrations, BPDP and TPHP had distinct effects, primarily affecting pathways involved in cell cycle progression and other stress responses. Benchmark concentration (BMC) modelling revealed that BPDP had the lowest transcriptomic point of departure. However, in vitro to in vivo extrapolation modeling indicated that TMPP was bioactive at lower concentrations than the other OPEs. We conclude that these new approach methodologies provide information on the mechanism(s) underlying the effects of data-poor compounds and assist in the derivation of protective points of departure for use in chemical read-across and decision-making.

Skeletal effects following developmental flame-retardant exposure are specific to sex and chemical class in the adult Wistar rat

Introduction: Accumulating evidence reveals that endocrine disrupting chemicals (EDCs) can disrupt aspects of metabolic programming, suggesting that skeletal development may be at risk, a possibility that is rarely examined. The commercial flame retardant (FR) mixture, Firemaster 550 (FM 550), has repeatedly been shown to negatively influence metabolic programming, raising concerns that skeletal integrity may consequently be impaired. We have previously shown that gestational and lactational exposure to 1,000 µg FM 550 negatively affected sex-specific skeletal traits in male, but not female, rats assessed at 6 months of age. Whether this outcome is primarily driven by the brominated (BFR) or organophosphate ester (OPFR) portions of the mixture or the effects persist to older ages is unknown. Materials and methods: To address this, in the present study, dams were orally exposed throughout gestation and lactation to either 1,000 μg BFR, 1,000 µg OPFR, or 2,000 µg FM 550. Offspring (n = 8/sex/exposure) were weaned at PND 21 and assessed for femoral cortical and trabecular bone parameters at 8 months of age by high-resolution X-ray micro-computed tomography (micro-CT). Serum levels of serotonin, osteocalcin, alkaline phosphatase, and calcium were quantified. Results: FM 550 affected both sexes, but the females were more appreciably impacted by the OPFRs, while the males were more vulnerable to the BFRs. Conclusion: Although sex specificity was expected due to the sexual dimorphic nature of skeletal physiology, the mechanisms accounting for the male- and female-specific phenotypes remain to be determined. Future work aims to clarify these unresolved issues.

Early life organophosphate ester exposures and bone health at age 12 years: The Health Outcomes and Measures of the Environment (HOME) Study

BACKGROUND

No human studies have evaluated early life organophosphate ester (OPE) exposures with bone health outcomes, despite evidence of osteotoxicity.

OBJECTIVES

We assessed associations of urinary OPE metabolites measured across early life with areal bone mineral density (aBMD) and bone mineral content (BMC) at age 12 years.

METHODS

Among 223 mother-child dyads enrolled in the Health Outcomes and Measures of the Environment (HOME) Study, we quantified concentrations of bis-2-chloroethyl phosphate (BCEP), bis-(1,3-dichloro-2-propyl) (BDCIPP), di-n-butyl phosphate (DnBP), and diphenyl phosphate (DPHP) in urine collected from mothers during pregnancy and children at ages 1, 2, 3, 5, and 8 years. At age 12 years, we performed dual energy x-ray absorptiometry and calculated aBMD and BMC z-scores at six skeletal sites. We estimated overall and sex-stratified BMD/BMC z-score differences per interquartile range (IQR) increase in OPE concentrations at multiple exposure timepoints: gestation (average) and 1-3 (average), 5, and 8 years.

RESULTS

In adjusted models, overall associations of BCEP and BDCIPP with total hip and 1/3rd distal radius aBMD and BMC varied significantly by exposure timepoint, as did BDCIPP with whole body aBMD. For example, differences (95 % CI) in total hip aBMD z-score per IQR increase in BDCIPP were 0.33 (0.01, 0.64), -0.10 (-0.34, 0.14), -0.18 (-0.40, 0.05), and 0.14 (-0.09, 0.38) for concentrations during gestation and at 1-3, 5, and 8 years, respectively. Overall DnBP and DPHP associations were generally null at all timepoints. We observed sex-specific associations for some timepoints and skeletal sites. For example, an IQR increase in 8-year DPHP was associated with a 0.21 (0.05, 0.38) greater total hip aBMD z-score among females but -0.19 (-0.43, 0.05) lower z-score among males.

DISCUSSION

Early life OPE exposures may be associated with sex- and exposure period-dependent alterations in early adolescent bone mineral accrual and strength.

Liver immune and lipid metabolism disorders in mice induced by triphenyl phosphate with or without high fructose and high fat diet

Organophosphorus flame retardants (OPFRs) are frequently detected in food and human samples, and epidemiological studies have found that human exposure to aryl-OPFRs (triphenyl phosphate, TPP) is associated with lipid metabolism. Although toxicity studies suggest a potential obesity risk from TPP exposure, the molecular mechanism remains unclear. This study investigated the subchronic dietary effects on mouse liver significantly changed proteins (SCPs) and elucidated the underlying molecular mechanisms of TPP with or without a high-fructose and high-fat (HFF) diet. Male C57BL/6J mice were exposed to low-dose TPP (corresponding to the oral reference dose, 10 μg/kg body weight (bw)/day) and high-dose TPP (1000 μg/kg bw/day) for 12 weeks. The results showed that exposure to TPP generated changes of liver function and organelle damage as well as increases in total cholesterol and triglyceride levels. TPP exposure at a low dose damaged the liver immune system via major histocompatibility complex-related proteins involved in antigen processing and presentation. TPP exposure at a high dose caused disorders of the biosynthesis of unsaturated fatty acids and steroid hormones, thereby inducing lipid accumulation in the liver. Although 10 μg/kg TPP did not cause serious lipid metabolism disorders in the liver, significant overexpression of fatty acid-binding protein 5, malic enzyme 1, and other related SCPs was observed, which led to disorders of cholesterol metabolism and lipogenesis to activate the proliferator-activated receptor signaling pathway and thus induced potential obesity risks. In addition, lipid metabolism disorders related to TPP were aggravated under the HFF diet, impairing liver mitochondrial and endoplasmic reticulum function in mice by altering the activity of cytochrome P450 enzyme subfamilies. These findings provide an in-depth understanding of the molecular toxicity mechanisms and health risks associated with subchronic exposure to TPP under different dietary regimes.

Triphenyl phosphate disturbs placental tryptophan metabolism and induces neurobehavior abnormal in male offspring

Epidemiological studies have shown that prenatal triphenyl phosphate (TPhP) exposure is related to abnormal neurobehavior in children. However, the neurodevelopmental toxicity of TPhP in mammals is limited. To study the neurodevelopmental toxicity of TPhP in mammals and investigate the underlying mechanism, we used a mouse intrauterine TPhP exposure model. We measured the inflammatory factors (IL-6, TNFα) and NFκB levels, and tryptophan metabolism in placentae, detected the fetal brain transcriptome, hippocampal neuron development and neurobehavioral in the male offspring. The results showed that the protein level of IL-6, TNFα and NFκB in the placenta of the TPhP treatment group (1, 5 mg/kg) were significantly increased. Change of the protein level of these pro-inflammatory factors in maternal serum or fetal brain was not observed. Expression of genes along tryptophan-serotonin metabolism pathway were significantly decreased. While, the concentration of 5-HT levels in the placenta or fetal brain were significantly increased. Consistent with the increased 5-HT, the Nissl body was reduced in the hippocampus of treatment group. The expression of serotonergic neuron gene markers including Tph2, Htr1A, Htr2A, Pet1 and Lmx1b in the hippocampus of treatment group was significantly decreased. The neurobehavioral test showed that TPhP decreased center time that represent anxiety-like behavior, and reduced learning and memory in male offspring. Meanwhile, expression of genes along tryptophan-kynurenine metabolism pathway were significantly increased. The result of the transcriptome analysis of fetal brain showed that the differentially expressed genes are mainly involved in the transcription regulation of DNA as a template in the nucleus, and the enriched pathways are mainly signal pathways regulated by axon guidance and neurotrophic factors, dopaminergic and cholinergic synapses, suggest that not only serotonergic neuronal was affected. Overall, this study demonstrates that TPhP has the potential to induce placental inflammatory response in the placenta, disturb placental tryptophan metabolism, compromise the neuronal development and synaptic transmission, and cause abnormal neurobehavior in male offspring.

Remodeling on adipocytic physiology of organophosphorus esters in mature adipocytes

The emerging endocrine disruption chemicals organophosphate esters (OPEs) pose high risk of metabolic disruption. However, limited information is available on physiological disturbance of OPEs on adipose, a major endocrine and metabolic organ. In this study, physiological change was investigated after exposing 3T3-L1fully differentiated adipocytes to six OPEs at non-cytotoxic concentrations. We found two chlorinated-OPEs (tris-(2-chloro-1-(chloromethyl) ethyl) phosphate (TDCPP) and tris(2-chloroisopropyl) phosphate (TCPP)) and two alkyl-OPEs (tributyl phosphate (TBP) and tris (2-butoxyethyl) phosphate (TBEP)) induced inflammation-like adipokines (chemoattractant protein 1 and interleukin-6), respectively. Increment of insulin-resistance-related hormones (resistin and leptin) were observed under TDCPP, TCPP, and TBP exposure. Functional and mechanistic investigation revealed that all of the compounds inhibited lipolysis at basal level through dephosphorylated HSL^ser563, the rate limiting enzyme of lipolysis. Triphenyl phosphate (TPhP), tricresyl phosphate (TCP), TDCPP, TBP and TBEP enhanced glucose uptake at both basal and insulin-stimulated status. We evidenced that impact was independent of the classical pIRS^ser639/pAKT^ser473 nor the insulin-independent AMPK pathway. The elevated mRNA of slc2a4 and its transcriptional factor LXRα may, at least partially, explain for the increase of glucose uptake. Given the focus within the endocrine disruption on glands, it would be prudent not to ignore endocrinal impact on adipocytes.

An integrative epi-transcriptomic approach identifies the human cartilage chitinase 3-like protein 2 (CHI3L2) as a potential mediator of B12 deficiency in adipocytes

Vitamin B12 has multiple biochemical functions including in the one-carbon cycle generating a methyl group for DNA methylation, and metabolism of fatty acids and amino acids to generate energy via the citric acid cycle. The aim of our study was to use a combined epigenomic and transcriptomic approach to identify novel genes mediating the effect of B12 on adipogenesis.Human pre-adipocytes (CHUB-S7) were treated with a range of B12 (0-500 nM) concentrations from the day of cell seeding until harvesting in discovery and validation experiments prior to genome-wide methylation analysis using the Illumina HumanMethylation 450Beadchip. For transcriptomic analysis, RNA-seq libraries were run on the Illumina HiSeq 2500. To further investigate the expression of any genes on human adipogenesis, a second human preadipocyte strain was studied (SGBS) by real-time quantitative PCR (qRT-PCR).A combined epigenetic and transcriptomic approach in differentiated human pre-adipocyte cell line, CHUB-S7, identified that the Human cartilage chitinase 3-like protein 2 (CHI3L2) gene was hypo-methylated and had increased expression in low B12 conditions. Furthermore, there was an approximately 1000-fold increase in CHI3L2 expression in the early days of adipocyte differentiation, which paralleled an increase of lipid droplets in differentiated SGBS cells and an increased expression level of markers of mature adipocytes.In summary, we have identified a potential role of the human cartilage chitinase 3-like protein 2 (CHI3L2) in adipocyte function in the presence of low B12 levels.

Triphenyl phosphate disturbs the lipidome and induces endoplasmic reticulum stress and apoptosis in JEG-3 cells

Triphenyl phosphate (TPP) is a frequently used aryl organophosphate flame retardant. Epidemiological studies have shown that TPP and its metabolite diphenyl phosphate (DPP) can accumulate in the placenta, and positively correlated with abnormal birth outcomes. TPP can disturb placental hormone secretion through the peroxisome proliferator-activated receptor γ (PPARγ) pathway. However, the extent and mechanism of placental toxicity mediation by TPP remains unknown. In this study, we used JEG-3 cells to investigate the role of PPARγ-regulated lipid metabolism in TPP-mediated placental toxicity. The results of lipidomic analysis showed that TPP increased the production of triglycerides (TG), fatty acids (FAs), and phosphatidic acid (PA), but decreased the levels of phosphatidylethanol (PE), phosphatidylserine (PS), and sphingomyelin (SM). TG accumulation was accompanied by increased levels of sterol regulatory element binding transcription factor 1 (SREBP1), acetyl-coA carboxylase (ACC), and fatty acid transport protein (CD36). Although PPARγ and its target CCAAT/enhancer binding proteins (C/EBPα) was decreased, the TG content and gene expression of SREBP1, ACC, and CD36 decreased when TPP was co-exposed to the PPARγ antagonist GW9662. TPP also induced inflammatory responses, endoplasmic reticulum stress (ERS), and cell apoptosis. Expression of genes related to ERS and apoptosis were attenuated by GW9662. Together, these results show that TPP can disturb lipid metabolism and cause lipid accumulation through PPARγ, induce ERS, and cell apoptosis. Our findings reveal that the developmental toxicity of TPP through placental toxicity should not be ignored.

Effects of flame retardants on ovarian function

Flame retardants have been added to a variety of consumer products and are now found ubiquitously throughout the environment. Epidemiological, in vivo, and in vitro studies have shown that polybrominated diphenyl ether (PBDE) flame retardants may have a negative impact on human health; this has resulted in their phase-out and replacement by alternative flame retardants, such as hexabromocyclododecane (HBCDD), tetrabromobisphenol A (TBBPA), and organophosphate esters (OPEs). Evidence suggests that some of these chemicals induce ovarian dysfunction and thus may be detrimental to female fertility; however, the effects of many of these flame retardants on the ovary remain unclear. In this review, we present an overview of the effects of brominated and organophosphate ester flame retardants on ovarian function and discuss the possible mechanisms which may mediate these effects.

Effects of an Environmentally Relevant Mixture of Organophosphate Esters Derived From House Dust on Endochondral Ossification in Murine Limb Bud Cultures

Organophosphate esters (OPEs) are used widely as flame retardants and plasticizers but much remains unknown about their potential toxicity. Previously, we reported that 4 individual OPEs suppress endochondral ossification in murine limb bud cultures. However, real-life exposure is to complex OPE mixtures. In the present study, we tested the hypothesis that a Canadian household dust-based OPE mixture will affect endochondral ossification in gestation day 13 CD1 mouse embryo limb buds expressing fluorescent markers for the major cell populations involved in the process: collagen type II alpha 1-enhanced cyan fluorescent protein (proliferative chondrocytes), collagen type X alpha 1-mCherry (hypertrophic chondrocytes), and collagen type I alpha 1-yellow fluorescent protein (osteoblasts). Limbs were cultured for 6 days in the presence of vehicle or dilutions of the OPE mixture (1/1 000 000, 1/600 000, and 1/300 000). All 3 OPE mixture dilutions affected cartilage template development and the progression of endochondral ossification, as indicated by the fluorescent markers. The expression of Sox9, the master regulator of chondrogenesis, was unchanged, but the expression of Runx2 and Sp7, which drive chondrocyte hypertrophy and osteoblastogenesis, was dilution-dependently suppressed. RNA-seq revealed that exposure to the 1/300 000 dilution of the OPE mixture for 24 h downregulated 153 transcripts and upregulated 48 others by at least 1.5-fold. Downregulated transcripts were enriched for those related to the immune system and bone formation. In contrast, upregulated transcripts were enriched for those with stress response functions known to be regulated by ATF4 activation. Thus, exposure to the mixture of OPEs commonly found in house dust may have adverse effects on bone formation.

DNA methylation during human adipogenesis and the impact of fructose

BACKGROUND

Increased adipogenesis and altered adipocyte function contribute to the development of obesity and associated comorbidities. Fructose modified adipocyte metabolism compared to glucose, but the regulatory mechanisms and consequences for obesity are unknown. Genome-wide methylation and global transcriptomics in SGBS pre-adipocytes exposed to 0, 2.5, 5, and 10 mM fructose, added to a 5-mM glucose-containing medium, were analyzed at 0, 24, 48, 96, 192, and 384 h following the induction of adipogenesis.

RESULTS

Time-dependent changes in DNA methylation compared to baseline (0 h) occurred during the final maturation of adipocytes, between 192 and 384 h. Larger percentages (0.1% at 192 h, 3.2% at 384 h) of differentially methylated regions (DMRs) were found in adipocytes differentiated in the glucose-containing control media compared to adipocytes differentiated in fructose-supplemented media (0.0006% for 10 mM, 0.001% for 5 mM, and 0.005% for 2.5 mM at 384 h). A total of 1437 DMRs were identified in 5237 differentially expressed genes at 384 h post-induction in glucose-containing (5 mM) control media. The majority of them inversely correlated with the gene expression, but 666 regions were positively correlated to the gene expression.

CONCLUSIONS

Our studies demonstrate that DNA methylation regulates or marks the transformation of morphologically differentiating adipocytes (seen at 192 h), to the more mature and metabolically robust adipocytes (as seen at 384 h) in a genome-wide manner. Lower (2.5 mM) concentrations of fructose have the most robust effects on methylation compared to higher concentrations (5 and 10 mM), suggesting that fructose may be playing a signaling/regulatory role at lower concentrations of fructose and as a substrate at higher concentrations.

Triphenyl phosphate exposure induces kidney structural damage and gut microbiota disorders in mice under different diets

Exposure of humans to organophosphate flame retardants (OPFRs) and the consequent health risk have increased owing to the latter's widespread application. Although triphenyl phosphate (TPP), an OPFR, is a potential chemical determinant of liver function damage, its effects on kidney function in mice under high fructose/fat (HFF) diet are still unclear. In this study, C57BL/6J mice were fed HFF to generate an obesity model and mice were exposed to low dose (0.01 mg/kg/day; TPP-L) and high dose (1 mg/kg/day; TPP-H) of TPP for 12 weeks. Results showed that TPP-L and TPP-H combined with HFF, as well as TPP-H alone, caused kidney structural damage and gut microbiota disorders in mice. Inflammatory response induced by nuclear factor kappa B (NF-κB p65)/nod-like receptor protein 3 (NLRP3) and caspase-3 promoted kidney structure damage, as well as accumulation of triglyceride and total cholesterol and the protein residues in urine. Although TPP-L did not cause obvious structural damage in the kidneys, 0.01 mg/kg TPP induced significant inflammation and gut microbiota disorders. These findings provide new insights regarding health risk assessment after chronic exposure to TPP and HFF alone, as well as a combination of TPP with HFF in mice.

Receptor-Bound Perfluoroalkyl Carboxylic Acids Dictate Their Activity on Human and Mouse Peroxisome Proliferator-Activated Receptor γ

In in vitro cell assays, nominal concentrations of a test chemical are most frequently used in the description of its dose-response curves. Although the biologically effective concentration (BEC) is considered as the most relevant dose metric, in practice, it is very difficult to measure. In this work, we attempted to determine the BEC of long-chain perfluoroalkyl carboxylic acids (PFCAs) in peroxisome proliferator-activated receptor γ (PPARγ) activity assays. In both adipogenesis and transcriptional activity assays with human and mouse cells, PPARγ activity of 7 PFCAs first increased and then decreased with their carbon chain length. The binding affinity of these PFCAs with the ligand-binding domain of PPARγ was measured by fluorescence competitive binding assay and showed very poor correlation with their receptor activity (r² = 0.002-0.047). Internal concentrations of the PFCAs in the cells were measured by LC-MS/MS. Although their correlation with the receptor activity increased significantly, it is still low (r² = 0.41-0.82). Using the binding affinity constant, internal concentration, and PPARγ concentration measured by immunoassays, concentrations of receptor-bound PFCAs in cells were calculated, which exhibited excellent correlation with PPARγ activity in both adipogenesis and transcriptional activity assays (r² = 0.91-0.93). These results demonstrate that the concentration of receptor-bound PFCA is the BEC that dictates its activity on human and mouse PPARγ in cell assays. In the absence of any direct detection method, our approach can be used to calculate the target-site concentration of other ligands.

Triphenyl phosphate is a selective PPARγ modulator that does not induce brite adipogenesis in vitro and in vivo

Triphenyl phosphate (TPhP) is an environmental PPARγ ligand, and growing evidence suggests that it is a metabolic disruptor. We have shown previously that the structurally similar ligand, tributyltin, does not induce brite adipocyte gene expression. Here, using in vivo and in vitro models, we tested the hypothesis that TPhP is a selective PPARγ ligand, which fails to induce brite adipogenesis. C57BL/6 J male mice were fed either a low or very high-fat diet for 13 weeks. From weeks 7-13, mice were injected intraperitoneally, daily, with vehicle, rosiglitazone (Rosi), or TPhP (10 mg/kg). Compared to Rosi, TPhP did not induce expression of browning-related genes (e.g. Elovl3, Cidea, Acaa2, CoxIV) in mature adipocytes isolated from inguinal adipose. To determine if this resulted from an effect directly on the adipocytes, 3T3-L1 cells and primary human preadipocytes were differentiated into adipocytes in the presence of Rosi or TPhP. Rosi, but not TPhP, induced expression of brite adipocyte genes, mitochondrial biogenesis and cellular respiration. Further, Rosi and TPhP-induced distinct proteomes and phosphoproteomes; Rosi enriched more regulatory pathways related to fatty acid oxidation and mitochondrial proteins. We assessed the role of phosphorylation of PPARγ in these differences in 3T3-L1 cells. Only Rosi protected PPARγ from phosphorylation at Ser273. TPhP gained the ability to stimulate brite adipocyte gene expression in the presence of the CDK5 inhibitor and in 3T3-L1 cells expressing alanine at position 273. We conclude that TPhP is a selective PPARγ modulator that fails to protect PPARγ from phosphorylation at ser273.

Developmental Exposure to the Flame Retardant Mixture Firemaster 550 Compromises Adult Bone Integrity in Male but not Female Rats

Flame retardants (FRs) are used in a variety of common items from furniture to carpet to electronics to reduce flammability and combustion, but the potential toxicity of these compounds is raising health concerns globally. Organophosphate FRs (OPFRs) are becoming more prevalent as older, brominated FRs are phased out, but the toxicity of these compounds, and the FR mixtures that contain them, is poorly understood. Work in a variety of in vitro model systems has suggested that FRs may induce metabolic reprogramming such that bone density is compromised at the expense of increasing adiposity. To address this hypothesis, the present studies maternally exposed Wistar rat dams orally across gestation and lactation to 1000 µg daily of the FR mixture Firemaster 550 (FM 550) which contains a mixture of brominated FRs and OPFRs. At six months of age, the offspring of both sexes were examined for evidence of compromised bone composition. Bone density, composition, and marrow were all significantly affected, but only in males. The fact that the phenotype was observed months after exposure suggests that FM 550 altered some fundamental aspect of mesenchymal stem cell reprogramming. The severity of the phenotype and the human-relevance of the dose employed, affirm this is an adverse outcome meriting further exploration.

Screening of House Dust from Chinese Homes for Chemicals with Liver X Receptors Binding Activities and Characterization of Atherosclerotic Activity Using an in Vitro Macrophage Cell Line and ApoE-/- Mice

BACKGROUND

Atherosclerotic cardiovascular disease has become the leading cause of death worldwide, and environmental pollutants are increasingly recognized as risk factors for atherosclerosis. Liver X receptors (LXRs) play a central role in atherosclerosis; however, LXR activity of organic pollutants and associated potential risk of atherosclerosis have not yet been characterized.

OBJECTIVES

This study aimed to explore whether LXR-antagonistic chemicals are present in indoor house dust and, if so, to characterize this activity in relation to changes in macrophages in vitro and cardiovascular disease indicators in vivo in an atherosclerosis ApoE-/- mouse model.

METHODS

We used a His-LXRα-pull-down assay and a nontarget high-resolution mass spectrometry method to screen house dust collected from Chinese homes for LXRα- and LXRβ-antagonist activity. A chemical identified in this manner was assessed for its ability to induce cholesterol efflux and foam cell formation in RAW264.7 macrophages, to down-regulate the expression of two LXR-dependent genes, ABCA1 and ABCG1, and finally to induce atherosclerotic lesions in vivo using an ApoE-/- mouse model.

RESULTS

We identified the flame retardants triphenyl phosphate (TPHP) and 2-ethylhexyl diphenyl phosphate (EHDPP) in house dust samples and demonstrated their ability to antagonize LXRs. The potency of TPHP was similar to that of the LXR-antagonist SR9238. TPHP could also inhibit cholesterol efflux and promote foam cell formation in RAW264.7 macrophages and mouse peritoneal macrophages and significantly promoted atherosclerotic lesion formation in the ApoE-/- mouse model.

CONCLUSIONS

We found LXR-antagonist chemicals in environmental samples of indoor dust from Chinese homes. One of the chemicals, TPHP, was able to promote the development of atherosclerotic lesions in the ApoE-/- mouse model. These results highlight the need to assess the LXR-antagonist activities of pollutants in future environmental management programs. https://doi.org/10.1289/EHP5039.

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.

Adipogenic Activity of Oligomeric Hexafluoropropylene Oxide (Perfluorooctanoic Acid Alternative) through Peroxisome Proliferator-Activated Receptor γ Pathway

Hexafluoropropylene oxide trimer acid (HFPO-TA) and hexafluoropropylene oxide dimer acid (HFPO-DA) have been used as perfluorooctanoic acid (PFOA) alternatives in the fluoropolymer industry for years. Their widespread environmental distribution, high bioaccumulation capability, and human exposure have caused great concern. Nevertheless, their potential toxicity and health risk remain largely unknown. In the present study, we compared potential disruption effects of HFPO-TA, HFPO-DA, and PFOA on peroxisome proliferator-activated receptor γ (PPARγ) via the investigation of receptor binding, receptor activity, and cell adipogenesis effects. The receptor binding experiment showed HFPO-TA exhibited 4.8-7.5 folds higher binding affinity with PPARγ than PFOA, whereas HFPO-DA exhibited weaker binding affinity than PFOA. They also showed agonistic activity toward PPARγ signaling pathway in HEK 293 cells in the order of HFPO-TA > PFOA > HFPO-DA. Molecular docking simulation indicated HFPO-TA formed more hydrogen bonds than PFOA, whereas HFPO-DA formed fewer hydrogen bonds than PFOA. HFPO-TA promoted adipogenic differentiation and lipid accumulation in both mouse and human preadipocytes with potency higher than PFOA. Adipogenesis in human preadipocytes is a more sensitive end point than mouse preadipocytes. Collectively, HFPO-TA exerts higher binding affinity, agonistic activity, and adipogenesis activity than PFOA. The potential health risk of HFPO-TA should be of concern.

Effects of triphenyl phosphate exposure during fetal development on obesity and metabolic dysfunctions in adult mice: Impaired lipid metabolism and intestinal dysbiosis

Previous in vitro studies have implied that triphenyl phosphate (TPHP) may act as an obesogen. However, its specific contributions to the progression of obesity and related metabolic diseases are still unclear in vivo in mice. In this study, we evaluated the effects of in utero and lactational exposure to three doses of TPHP (10, 100, and 1000 μg/kg BW) on obesity and metabolic dysfunctions in adult male mice fed a low-fat diet (LFD) or high-fat diet (HFD), by examining body weight, liver weight, histopathology, blood biochemistry, gene expression, and gut microbiota compositions and metabolic functions. Results showed that TPHP exposure led to increased body weight, liver weight, fat mass, hepatic steatosis, impaired glucose homeostasis, and insulin resistance, and mRNA levels of genes involved in lipid metabolism, especially lipogenesis and lipid accumulation, were significantly altered by TPHP treatment. Gas chromatography-mass spectrometry (GC-MS) analysis further supported the changes in fatty acid composition. Intestinal flora measurements by 16S rRNA gene sequencing and ¹H NMR based fecal metabolomics indicated that TPHP treatment modulated gut microbiome composition and influenced host-gut co-metabolism, especially for bile acids and short chain fatty acids (SCFAs). These results suggest that fetal exposure to TPHP can promote the development of obesity and metabolic dysfunctions in adult mice.

A case-control study of exposure to organophosphate flame retardants and risk of thyroid cancer in women

Background

Growing evidence demonstrates that exposure to organophosphate flame retardants (PFRs) is widespread and that these chemicals can alter thyroid hormone regulation and function. We investigated the relationship between PFR exposure and thyroid cancer and whether individual or temporal factors predict PFR exposure.

Methods

We analyzed interview data and spot urine samples collected in 2010–2013 from 100 incident female, papillary thyroid cancer cases and 100 female controls of a Connecticut-based thyroid cancer case-control study. We measured urinary concentrations of six PFR metabolites with mass spectrometry. We estimated odds ratios (OR) and 95% confidence intervals (95% CI) for continuous and categories (low, medium, high) of concentrations of individual and summed metabolites, adjusting for potential confounders. We examined relationships between concentrations of PFR metabolites and individual characteristics (age, smoking status, alcohol consumption, body mass index [BMI], income, education) and temporal factors (season, year) using multiple linear regression analysis.

Results

No PFRs were significantly associated with papillary thyroid cancer risk. Results remained null when stratified by microcarcinomas (tumor diameter ≤ 1 cm) and larger tumor sizes (> 1 cm). We observed higher urinary PFR concentrations with increasing BMI and in the summer season.

Conclusions

Urinary PFR concentrations, measured at time of diagnosis, are not linked to increased risk of thyroid cancer. Investigations in a larger population or with repeated pre-diagnosis urinary biomarker measurements would provide additional insights into the relationship between PFR exposure and thyroid cancer risk.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4553-9) contains supplementary material, which is available to authorized users.