The steroid receptor coactivator 1 (SRC1) and 3 (SRC3) recruitment as a novel molecular initiating event of 4-n-nonylphenol in estrogen receptor α-mediated pathways

In vitro to in vivo extrapolation for predicting human equivalent dose of phenolic endocrine disrupting chemicals: PBTK model development, biological pathways, outcomes and performance

In vitro to in vivo (IVIVE) leverages in vitro high-throughput biological responses to predict the corresponding in vivo exposures and further estimate the human safe dose. However, for phenolic endocrine disrupting chemicals (EDCs) linked with complicated biological pathways and adverse outcomes (AO), such as bisphenol A (BPA) and 4-nonylphenol (4-NP), plausible estimation of human equivalent doses (HED) by IVIVE approaches considering various biological pathways and endpoints is still challenging. To explore the capabilities and limitations of IVIVE, this study conducted physiologically based toxicokinetic (PBTK)-IVIVE approaches to derive pathway-specific HEDs using BPA and 4-NP as examples. In vitro HEDs of BPA and 4-NP varied in different adverse outcomes, pathways, and testing endpoints and ranged from 0.0013 to 1.0986 mg/kg bw/day and 0.0551 to 1.7483 mg/kg bw/day, respectively. In vitro HEDs associated with reproductive AOs initiated by PPARα activation and ER agonism were the most sensitive. Model verification suggested the potential of using effective in vitro data to determine reasonable approximation of in vivo HEDs for the same AO (fold differences of most AOs ranged in 0.14-2.74 and better predictions for apical endpoints). Furthermore, system-specific parameters of cardiac output and its fraction, body weight, as well as chemical-specific parameters of partition coefficient and liver metabolic were most sensitive for the PBTK simulations. The results indicated that the application of fit for-purpose PBTK-IVIVE approach could provide credible pathway-specific HEDs and contribute to high throughput prioritization of chemicals in a more realistic scenario.

High-Fat Diet Promotes Adipogenesis in Offspring Female Rats Induced by Perinatal Exposure to 4-Nonylphenol

Background

Both high-fat diet (HFD) and 4-nonylphenol (4-NP) could affect fat formation in adipose tissue individually. We investigated whether HFD promote abnormal adipose tissue formation caused by early exposure to 4-NP in life and preliminarily explore the possible mechanisms involved.

Methods

The first-generation rats were treated with HFD on postnatal day after pregnant rats exposure to 5 ug/kg/day 4-NP. Then, the second generation rats started to only receive normal diet without 4-NP or HFD. We analyzed organ coefficient and histopathology of fat tissues, biochemical index, and gene level involved in lipid metabolism in female offspring rats.

Results

HFD and 4-NP interaction synergistically increased birth weight, body weight, and organ coefficients of adipose tissue in offspring female rats. HFD accelerately aggravated abnormal lipid metabolism and increased the adipocyte mean areas around the uterus of the offspring female rats induced by prenatal exposure to 4-NP. HFD also facilitate the regulation of gene expression involved lipid metabolism in offspring female rats induced by perinatal exposure to 4-NP, even passed on to the second generation of female rats. Moreover, HFD and 4-NP interaction synergistically declined the gene and protein expression of estrogen receptor (ER) in the adipose tissue of second-generation female rats.

Conclusion

HFD and 4-NP synergistically regulate the expression of lipid metabolism genes in adipose tissue of F2 female rats and promote adipose tissue generation, leading to obesity in offspring rats, which is closely related to low expression of ER. Therefore, ER genes and proteins may be involved in the synergistic effect of HFD and 4-NP.

Effects of chronic exposure to nonylphenol at environmental concentration on thyroid function and thyroid hyperplasia disease in male rats

The aim of this work was to determine whether chronic exposure to nonylphenol (NP), a representative substance of environmental endocrine disruptors (EEDs), at environmental concentration would have toxic effects on thyroid function and thyroid hyperplasia disease. Two hundred SPF Sprague-Dawley rats were divided into five groups (n = 40 per group): blank control group (corn oil), low-dose NP exposure group (0.4 mg/kg/d), medium-dose NP exposure group (4 mg/kg/d), high-dose NP exposure group (40 mg/kg/d), and estradiol control group (E₂: 30 μg/kg/d). The rats were treated by gavage for 34 weeks, which were sampled twice (17 weeks and 34 weeks respectively). NP accumulation in the thyroid tissue (F = 52.93, P < 0.001) and serum (F = 5.54, P = 0.00) continuously increased in a significant dose-effect relationship. After NP exposure, the serum FT3 levels exhibited a dose-dependent increasing trend (F = 4.68, P = 0.01), while the serum FT4 level showed an opposite trend (F = 3.93, P= 0.01). Compared with the control group, hyperechoic areas (i.e., calcification points) were observed in the high-dose group. Follicular epithelial stratification was extremely severe, the monolayer cubic epithelial cells became flat, and the area of single follicles was even smaller in the high-dose group. In the high-dose NP group, there were numerous mitochondria that were severely swollen. The rough endoplasmic reticulum was abundant, with obvious expansion and vesiculation. The relative expression of ERα (F = 5.29, P = 0.00), ERβ (F = 10.17, P = 0.00), TRα (F = 7.71, P = 0.00), TRβ (F = 3.52.17, P = 0.02) and HMGB1 (F = 10.16, P = 0.01) proteins in the thyroid tissue in each NP exposure group was increased compared with the control group, and the relative expression of proteins increased if the exposure time was prolonged under the same exposure dose. Chronic exposure to NP at environmental concentration could have toxic effects on thyroid function, and induce thyroid hyperplasia disease in male rats.

Exposure to endocrine disruptor alkylphenols and the occurrence of endometrial cancer

Exposure to environmental chemicals with oestrogenic effects has been associated with the development of endometrial cancer (EMCa). EMCa has become the most commonly diagnosed cancer of the female genital tract. To further understand the potential association between exposure to environmental endocrine disruptors and the occurrence of EMCa, we performed a case-control study between 2011 and 2014. We aimed to detect and compare concentrations of a known hormone disruptor, alkylphenol, between women diagnosed with either EMCa or uterine leiomyoma, and those who did not have either of these. Subjects were women diagnosed with either EMCa or uterine leiomyoma (LM) and healthy controls. A structured questionnaire was administered to collect information on lifestyle and health status. Gas chromatography/mass spectrometry was used to measure urinary NP and OP concentrations in participants. Multiple regression analysis was used to examine the association between exposure and outcomes. Overall, 397 women were recruited, including 49 with EMCa, 247 with LM, and 101 controls. Among them, 73.6% showed detectable levels of NP and 61.0% showed detectable levels of OP. The EMCa group had a significantly higher NP concentration than the control group. Higher OP concentrations were also found in participants with EMCa than those with LM and controls. In addition, women in the upper tertile of the NP group had a significantly increased risk of EMCa occurrence (odds ratio [95% confidence interval] = 4.47 [1.69-11.84] for EMCa vs. control). The same was found in the group of women with more than the median level of OP (odds ratio [95% confidence interval] = 4.32 [2.01-9.30] for EMCa vs. LM). Stratification of pre- and post-menopausal groups resulted in a similar association. The results show that NP/OP exposure is associated with EMCa. Further investigations and exposure minimisation are suggested.

Structure-Oriented Research on the Antiestrogenic Effect of Organophosphate Esters and the Potential Mechanism

Organophosphate esters (OPEs) can exhibit various toxicities including endocrine disruption activity. Unfortunately, the low-dose endocrine-disrupting effects mediated by estrogen receptors (ERs) are commonly underestimated for OPEs and their metabolites. Here, structure-oriented research was performed to investigate the estrogenic/antiestrogenic effect of 13 OPEs (including three metabolites) and the potential mechanism. All of the OPEs exerted antiestrogenic activities in both E-screen and MVLN assays. OPEs with bulky substituents, such as phenyl rings (triphenyl phosphate (TPP), tricresyl phosphate (TCP), diphenylphosphoryl chloride, and diphenylphosphite) or relatively long alkyl chains (dibutylbutylphosphonate (DBBP)), exerted relatively strong ER antagonism potency at micromolar concentrations. The established quantitative structure-activity relationship indicated that the antiestrogenic activities of the OPEs mainly depended on the volume, leading eigenvalue, and hydrophobicity of the molecule. Molecular docking revealed that the three OPEs with the bulkiest substituents on the phosphate ester group (TPP, TCP, and DBBP) have a similar interaction mode to the classical ER antagonist 4-hydroxytamoxifen. The correlation between the antiestrogenic activity and the corresponding ER binding affinity was statistically significant, strongly suggesting that the OPEs possess the classical antagonism mechanism of interfering with the positioning of helix 12 in the ER.

In vitro estrogen-disrupting effects of organophosphate flame retardants

Organophosphate flame retardants (OPFRs), as substitutes for polybrominated diphenyl ethers (PBDEs), are frequently detected in the environment and biota due to their widespread use. Thus, there is a need to investigate their potential estrogen-disrupting effects and possible mechanisms of action in an effort to obtain a better risk assessment. In this study, we characterized the activities on estrogen receptor α (ERα) and the estrogen-disrupting potential of fourteen OPFRs, TMP, TEP, TPP, TnBP, TiBP, THP, TPhP, TCP, DPK, MDPP, IDPP, CDP, IPPDP and MPhP, using three in vitro assays representing different specific modes of action (MoAs). In the yeast two-hybrid assay, no OPFRs induced agonistic activity, but TiBP, DPK, TPhP, MDPP, CDP and IPPDP were shown to be hydrophobicity-dependent antagonists and to compete with E₂ for binding to ERα. In the MVLN cell assay, TPhP was the only OPFR among the 14 tested that was able to activate ERα-estrogen responsive element (ERE) pathways. The results from the E-SCREEN assay showed that all tested OPFRs except TMP had estrogenic properties, and G protein-coupled receptor 30 (GPR30) was involved in the estrogenicity of eight OPFRs, TiBP, THP, TPhP, TCP, MDPP, IPPDP, CDP and MPhP. It was also found that in the E-SCREEN assay, the estrogenicity of alkyl-OPFRs but not aryl-OPFRs was closely correlated to hydrophobicity. Our research suggested that most OPFRs were estrogen disruptors, but their related mechanisms were complex and might involve ERα-mediated and/or ERα-independent pathways. Further in vitro studies concerning the estrogenic effects and involved mechanisms of OPFRs, as well as comprehensive evaluations of OPFRs including health and ecological assessments are needed to determine whether they are safe substitutes for PBDEs.