Comparison of the mechanisms of estrogen disrupting effects between triphenyl phosphate (TPhP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP)

Molecular insights into the effects of tetrachlorobisphenol A on puberty initiation in Wistar rats

Tetrachlorobisphenol A (TCBPA) is the chlorinated derivative of bisphenol A (BPA). Several studies have found that BPA adversely affects the reproductive activity largely through binding to estrogen receptors and the critical period of BPA exposure advances the vaginal opening time in the female offspring via the kisspeptin/G protein-coupled receptor 54 (KGG) system. However, whether TCBPA can affect puberty initiation via KGG and the roles of estrogen receptors in this process remain unknown. Therefore, this study investigated the influence of TCBPA on the onset time of puberty in Wistar rats and the related molecular mechanisms by combing in vitro GT1-7 cells and molecular docking. In female Wistar rats, TCBPA at ≥100 mg/kg bw/day (49.2 μmol/L in rat body) markedly advanced vaginal opening time and increased serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and gonadotropin-releasing hormone (GnRH). It also increased the relative gene expression of LH receptor (LHR), GnRH1, and FSH receptor (FSHR) in hypothalamic-pituitary-gonadal (HPG) axis tissues. In GT1-7 cells, TCBPA increased genes and proteins associated with KGG pathway and activated the extracellular-regulated protein kinase 1/2 (Erk1/2) and phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) pathways via G protein-coupled estrogen membrane receptor 1 (GPER1) and estrogen receptor alpha (ERα). Docking analyses supported its interactions with GPER1 and ERα, and treatment with specific inhibitors of ERα- and GPER1-modulated PI3K/Akt and Erk1/2 signaling suppressed its effects. Taken together, TCBPA-induced advancement of puberty initiation in Wistar rats thus results primarily from increased LH, GnRH, and FSH secretion together with GnRH1, FSHR, and LHR upregulation driven by ERα- and GPER1-modulated Erk1/2 and PI3K/Akt signaling. Our results provide new molecular insights into the reproductive toxicity of EDCs.

Reproductive hormones, organophosphate esters and semen quality: Exploring associations and mediation effects among men from an infertility clinic

Accumulating evidence indicates that organophosphate esters (OPEs) exposure may affect semen quality. As a crucial factor in male reproduction, reproductive hormones might be linked organophosphate esters (OPEs) exposure and semen quality. This study aimed to explore the mediating role of reproductive hormones on the association between OPEs exposure and semen quality. Five serum reproductive hormones, semen quality, and 16 urinary OPE metabolites were measured among 491 reproductive-aged men from a reproductive center. The associations of urinary OPE metabolites with reproductive hormones and semen quality were assessed using multivariable linear regression models, and the mediating role of reproductive hormones was evaluated by mediation analyses. We found that follicle stimulating hormone (FSH) was positively associated with diphenyl phosphate (DPHP) that in turn was negatively associated with sperm total count. In addition, inverse associations were exhibited between serum FSH and sperm concentration, sperm total count, total motility, and progressive motility (all Ptrend <0.05). Mediation analysis further showed that FSH mediated 13.7% of the inverse association of DPHP and sperm total count. Although further investigations are required, our results suggest that FSH was an intermediate mechanism in the associations between OPEs exposure and impaired semen quality.

Effects of trichlorobisphenol A on the expression of proteins and genes associated with puberty initiation in GT1-7 cells and the relevant molecular mechanism

This study evaluated the effects of Cl3BPA on kisspeptin-G-protein coupled receptor 54 (GPR54)/gonadotropin-releasing hormone (GnRH) (KGG) signals and analyzed the roles of estrogen receptor alpha (ERɑ) and G-protein coupled estrogen receptor 1 (GPER1) in regulating KGG signals. The results showed that Cl3BPA at 50 μM increased the levels of intracellular reactive oxygen species (ROS) and GnRH, upregulated the protein levels of kisspeptin and the expression of fshr, lhr and gnrh1 genes related to KGG in GT1-7 cells. In addition, 50 μM Cl3BPA significantly upregulated the phosphorylation of extracellular regulated protein kinases 1/2 (Erk1/2), the protein levels of GPER1 and the expression of the gper1 as well as the most target genes associated with mitogen-activated protein kinase (MAPK)/Erk1/2 pathways. Specific signal inhibitor experiments found that Cl3BPA activated KGG signals by activating the GPER1-mediated MAPK/Erk1/2 signaling pathway at the mRNA level. A docking test further confirmed the interactions between Cl3BPA and GPER1. The findings suggest that Cl3BPA might induce precocious puberty by increasing GnRH secretion together with KGG signaling upregulation, which is driven by GPER1-mediated signaling pathway. By comparison, ClxBPAs with fewer chlorine atoms had more obvious effects on the expression of proteins and partial genes related to KGG signals in GT1-7 cells.

Prenatal exposure to replacement flame retardants and organophosphate esters and childhood adverse respiratory outcomes

BACKGROUND

The association of prenatal exposure to organophosphate esters (OPEs) and replacement brominated flame retardants (RBFRs) with respiratory outcomes has not been previously investigated in humans, despite reports that these chemicals can cross the placenta and alter lung development as well as immune functions.

METHODS

In a cohort of 342 pregnant women recruited between 2003 and 2006 in the greater Cincinnati, Ohio Metropolitan area, we measured indoor dust OPEs and RBFRs at 20 weeks of gestation and urinary OPEs at 16 and 26 weeks of gestation and at delivery. We performed generalized estimating equations and linear mixed models adjusting for covariates to determine the associations of prenatal OPEs and RBFRs exposures with adverse respiratory outcomes in childhood, reported every six months until age 5 years and with lung function at age 5 years. We used multiple informant modeling to examine time-specific associations between maternal urinary OPEs and the outcomes.

RESULTS

Dust concentrations of triphenyl phosphate (TPHP) (RR: 1.40, 95% CI: 1.18-1.66), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (RR: 1.51, 95% CI: 1.23-1.85), and bis(2-ethylhexyl) tetrabromophthalate (RR: 1.57, 95% CI: 1.28-1.94) were associated with higher risk of wheezing during childhood. Dust TPHP concentrations were associated with higher risk of respiratory infections (RR: 1.43, 95% CI: 1.08-1.94), and dust tris-(2-chloroethyl) phosphate concentrations were associated with hay fever/allergies (RR: 1.11, 95% CI: 1.01-1.21). We also found that dust tris-(2-chloroethyl) phosphate loadings were associated with lower lung function. Urinary OPEs mainly at week 16 of gestation tended to be associated with adverse respiratory outcome, while bis(1-chloro-2-propyl) phosphate and diphenyl phosphate at delivery were associated with lower risk of hay fever/allergies.

CONCLUSIONS

In-utero exposure to OPEs and RBFRs may be a risk factor for adverse respiratory outcomes in childhood, depending on the timing of exposure.

Accumulation of organophosphorus pollutants in adipose tissue of obese women - metabolic alterations

Organophosphorus pesticides (OPPs) and organophosphate esters (OPEs) are organophosphorus compounds created as substitutes for persistent environmental pollutants, namely organochlorines pesticides and brominated flame retardants, respectively. However, there is evidence that organophosphorus compounds are also widespread across the environment and have adverse effects on biota. In humans, OPPs and OPEs were reported to be carcinogenic, neurotoxic, hepatotoxic, nephrotoxic, amongst others. As lipophilic compounds, these accumulate in fat tissues as adipose tissue. Yet biomonitoring studies and analytical methodologies to assess these compounds in the human body are scarce, particularly in adipose tissue. In this study, the presence of six OPPs and seven OPEs was determined in samples of subcutaneous adipose tissue (scAT) and visceral adipose tissue (vAT) from 188 adult obese women. OPPs and OPEs were quantified by gas chromatography (GC) flame photometric detection and confirmed in GC tandem mass spectrometry. The detection frequencies ranged between 0.5-1.6% and 48-53%, respectively for OPPs and OPEs. Organophosphorus pollutants were present in both adipose tissues and median concentrations were 0.008 ± 0.020 μg/g scAT and 0.009 ± 0.020 μg/g vAT. A total of 32 Spearman's correlations were found between organophosphorus pollutants concentrations in adipose tissue and several biochemical parameters (18 positive and 14 negative). Our results show that anthropometric and hormonal parameters, cholesterol, glycaemia, macrominerals, urea and sedimentation velocity might be influenced by the presence of these compounds. The presence of organophosphorus pollutants in the environmental and their possible effect on female metabolic processes is concerning. Particularly because presently OPEs usage is not controlled or limited by any regulation. More studies are needed to fully understand these pollutants behaviour and hazard effects on human health, biota, and the environment so control regulations can be drawn to prevent and lessen their effects.

Endoplasmic reticulum stress participates in apoptosis of HeLa cells exposed to TPHP and OH-TPHP via the eIF2α-ATF4/ATF3-CHOP-DR5/P53 signaling pathway

Purpose

Triphenyl phosphate (TPHP) is a widely used organophosphate flame retardant, which can be transformed in vivo into diphenyl phosphate (DPHP) and 4-hydroxyphenyl phosphate (diphenyl) ester (OH-TPHP) through biotransformation process. Accumulation of TPHP and its derivatives in biological tissues makes it necessary to investigate their toxicity and molecular mechanism.

Methods

The present study evaluated the cellular effects of TPHP, DPHP, and OH-TPHP on cell survival, cell membrane damage, oxidative damage, and cell apoptosis using HeLa cells as in vitro model. RNA sequencing and bioinformatics analysis were conducted to monitor the differently expressed genes, and then RT-qPCR and Western bolt were used to identify potential molecular mechanisms and key hub genes.

Results

Results showed that OH-TPHP had the most significant cytotoxic effect in HeLa cells, followed by TPHP; and no significant cytotoxic effects were observed for DPHP exposure within the experimental concentrations. Biological function enrichment analysis suggested that TPHP and OH-TPHP exposure may induce endoplasmic reticulum stress (ERS) and cell apoptosis. The nodes filtering revealed that ERS and apoptosis related genes were involved in biological effects induced by TPHP and OH-TPHP, which may be mediated through the eukaryotic translation initiation factor 2α/activating transcription factor 4 (ATF4)/ATF3- CCAAT/ enhancer-binding protein homologous protein (CHOP) cascade pathway and death receptor 5 (DR5) /P53 signaling axis.

Conclusion

Above all, these findings indicated that ERS-mediated apoptosis might be one of potential mechanisms for cytotoxicity of TPHP and OH-TPHP.

Machine learning reveals common transcriptomic signatures across rat brain and placenta following developmental organophosphate ester exposure

Toxicogenomics is a critical area of inquiry for hazard identification and to identify both mechanisms of action and potential markers of exposure to toxic compounds. However, data generated by these experiments are highly dimensional and present challenges to standard statistical approaches, requiring strict correction for multiple comparisons. This stringency often fails to detect meaningful changes to low expression genes and/or eliminate genes with small but consistent changes particularly in tissues where slight changes in expression can have important functional differences, such as brain. Machine learning offers an alternative analytical approach for "omics" data that effectively sidesteps the challenges of analyzing highly dimensional data. Using 3 rat RNA transcriptome sets, we utilized an ensemble machine learning approach to predict developmental exposure to a mixture of organophosphate esters (OPEs) in brain (newborn cortex and day 10 hippocampus) and late gestation placenta of male and female rats, and identified genes that informed predictor performance. OPE exposure had sex specific effects on hippocampal transcriptome, and significantly impacted genes associated with mitochondrial transcriptional regulation and cation transport in females, including voltage-gated potassium and calcium channels and subunits. To establish if this holds for other tissues, RNAseq data from cortex and placenta, both previously published and analyzed via a more traditional pipeline, were reanalyzed with the ensemble machine learning methodology. Significant enrichment for pathways of oxidative phosphorylation and electron transport chain was found, suggesting a transcriptomic signature of OPE exposure impacting mitochondrial metabolism across tissue types and developmental epoch. Here we show how machine learning can complement more traditional analytical approaches to identify vulnerable "signature" pathways disrupted by chemical exposures and biomarkers of exposure.

Lipid metabolic disturbance induced by triphenyl phosphate and hydroxy metabolite in HepG2 cells

Triphenyl phosphate (TPHP) has been widely used as flame retardants and been detected with increasing frequency in environment. TPHP can transform into mono-hydroxylated phosphate (OH-TPHP) and diester diphenyl phosphate (DPHP) through biotransformation. So far, information on the cytotoxicity and molecular regulatory mechanisms of TPHP metabolites are still limit. This study investigated the adverse effects of TPHP, OH-TPHP, and DPHP in HepG2 cells in terms of cell proliferation, lactate dehydrogenase release, reactive oxygen species generation, and mitochondrial membrane potential. The transcriptomic changes were measured using RNA sequencing, and bioinformatics characteristics including biological functions, signal pathways and protein-protein interaction were analyzed to explore the potential molecular mechanisms. Results displayed that the order of cytotoxicity was OH-TPHP> TPHP> DPHP. The prioritized biological functions changes induced by TPHP and OH-TPHP were correlated with lipid metabolism. Significant lipid accumulation was observed as confirmed by increased total cholesterol and triglycerides contents, and enhanced oil red O staining. Enrichment of PPARα/γ and down-stream genes suggested the participation of PPARs signal pathway in lipid metabolism disorder. In addition, TPHP and OH-TPHP induced endoplasmic reticulum stress (ERS), which was further confirmed by the ERS inhibitor experiment. In general, TPHP and OH-TPHP had obvious cytotoxic effects in HepG2 cells. PPARs signal pathway and endoplasmic reticulum stress may be involved in the lipid metabolism disorder induced by TPHP and OH-TPHP.

Exposure to tris(2,6-dimethylphenyl) phosphate interferes with sexual differentiation via estrogen receptors 2a and 2b in zebrafish

Tris(2,6-dimethylphenyl) phosphate (TDMPP), an emerging organophosphate flame retardant, is frequently detected in multiple environmental media. Although TDMPP has been proven as a compound with estrogenic activity, its feminizing effects on reproductive system remain unclear. This study investigated the adverse effects of TDMPP on gonadal development by exposing zebrafish for 105 days from 15 days post-fertilization. Exposure to TDMPP (0.5 and 5 μM, corresponding to about 200 and 2000 μg/L) induced ovarian formation in aromatase mutant (cyp19a1a-/-) line which normally presents all-male phenotype for deficiency of endogenous estrogen (E2), suggesting its feminizing effect on sexual differentiation. In addition, TDMPP also interfered with other aspects of reproduction by delaying puberty onset, retarding sexual maturation, impairing gametogenesis and subfertility. Molecular docking and reporter gene assay indicated that all three nuclear estrogen receptors (nERs) can be binded to and activated by TDMPP. Using a series of nERs mutant lines, we confirmed the indispensable role of esr2a and esr2b in mediating the feminizing effects of TDMPP. Further analysis revealed that the prominent effects of TDMPP on sexual differentiation correlated to upregulation of female-promoting genes and downregulation of male-promoting genes. Taken together, the present study provided unequivocal genetic evidence for estrogenic effects of TDMPP on reproductive system and its molecular mechanisms of action.

Triphenyl phosphate proved more potent than its metabolite diphenyl phosphate in inducing hepatic insulin resistance through endoplasmic reticulum stress

Triphenyl phosphate (TPHP) is a widely used flame retardant and plasticizer and has been detected extensively in environmental media, wildlife and human bodies. Several epidemiological and animal studies have revealed that TPHP exposure is positively associated with glucose homeostasis disruption and diabetes. However, the effects of TPHP on hepatic glucose homeostasis and the underlying mechanisms remain unclear. The present work aimed to investigate the cytotoxicity and glucose metabolism disruption of TPHP and its metabolite diphenyl phosphate (DPHP) within hepatocytes. The cell viability assay undertaken on human normal liver (L02) cells showed that TPHP exhibited more potent hepatotoxicity than DPHP. RNA sequencing (RNA-seq) data showed that TPHP and DPHP presented different modes of toxic action. Insulin resistance is one of the predominant toxicities for TPHP, but not for DPHP. The insulin-stimulated glucose uptake and glycogen synthesis were impaired by TPHP, while DPHP exhibited no significant impairment on these factors. TPHP exposure induced endoplasmic reticulum (ER) stress, and the ER stress antagonist 4-PBA restored the impairment of insulin-stimulated glucose uptake and glycogen synthesis induced by TPHP. TPHP could also induce liver ER stress and insulin resistance in mice. Taken together, the results suggested that TPHP induces more potent insulin resistance through ER stress than its metabolite DPHP.

Bisphenol AF Promoted the Growth of Uterus and Activated Estrogen Signaling Related Targets in Various Tissues of Nude Mice with SK-BR-3 Xenograft Tumor

Environmental estrogens can promote the growth, migration, and invasion of breast cancer. However, few studies evaluate adverse health impacts of environmental estrogens on other organs of breast cancer patients. Therefore, the present study investigated the effects of environmental estrogen bisphenol AF (BPAF) on the main organs of female Balb/cA nude mice with SK-BR-3 xenograft tumor by detecting the organ development and gene expression of targets associated with G protein-coupled estrogen receptor 1 (GPER1)-mediated phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinase (MAPK) signaling pathways in hypothalamus, ovary, uterus, liver, and kidney. The results showed that BPAF at 20 mg/kg bw/day markedly increased the uterine weight and the uterine coefficient of nude mice compared to SK-BR-3 bearing tumor control, indicating that BPAF promoted the growth of uterus due to its estrogenic activity. Additionally, BPAF significantly up-regulated the mRNA relative expression of most targets related to nuclear estrogen receptor alpha (ERα) and GPER1-mediated signaling pathways in the hypothalamus, followed by the ovary and uterus, and the least in the liver and kidney, indicating that BPAF activated different estrogen activity related targets in different tissues. In addition, BPAF markedly up-regulated the mRNA expression of GPER1 in all tested tissues, and the molecular docking showed that BPAF could dock into GPER1. Because gene change is an early event of toxicity response, these findings suggested that BPAF might aggravate the condition of breast cancer patients through exerting its estrogenic activity via the GPER1 pathway in various organs.

Occurrence, distribution and risk assessment of organophosphate esters (OPEs) in water sources from Northeast to Southeast China

With the wide utilization of organophosphate esters (OPEs) in recent years, OPEs have been detected more frequently in the aquatic environment. However, the distribution of OPEs in drinking source water has rarely been investigated across a large region. In this study, the occurrence and distribution of 13 OPEs were investigated in 23 source water sites from Northeast to Southeast (spacing greater than 3320 km) with a direct injection ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method. Total OPEs ranged from 218.8 to 636.6 ng/L, with a mean of 380.8 ng/L. The average detected concentration of OPEs in southern cities was higher than that in northern cities. Chlorinated OPEs accounted for 64.74% of the total concentration. Triethyl phosphate (TEP), tri (2-chloroethyl) phosphate (TCEP), and tri (chloropropyl) phosphate (TCPP) were detected in all water samples. Rainfall is a significant factor that affects the OPE concentration (less rainfall, higher concentration). China's OPE concentrations have rapidly reached a median level when compared to those of other countries. Ecological risk assessment showed that most OPEs have no or low risk to organisms (fish, crustacea, algae), except tricresyl phosphate (TCP), which is medium risk. The risk of OPEs in less-rain regions needs to be of greater concern, especially TCP.