A systematic evaluation of the potential effects of trichloroethylene exposure on cardiac development

The trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine inhibits lipopolysaccharide-induced inflammation transcriptomic pathways and cytokine secretion in a macrophage cell model

Studies have shown that the trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) inhibits cytokine secretion in pathogen stimulated fetal membrane tissue but little is known about the mechanism for these effects, including which cell types or transcriptomic pathways are impacted. Macrophages play a critical role in fetal membrane immune responses during infection. We tested the hypothesis that DCVC inhibits lipopolysaccharide (LPS) stimulated inflammation pathways in macrophage-like THP-1 cells. We treated THP-1 cells for 24 h then treated with 1, 5, or 10 μM DCVC for 24 h. After a 4 h incubation with lipopolysaccharide (LPS), we collected RNA and cell media. We performed transcriptomic analysis using RNA sequencing for 5 μM DCVC treatments and quantified cytokine release (IL-1β, IL-6, and TNF-α) for 1, 5 and 10 μM DCVC treatments. RNA sequencing analysis revealed 1399 differentially expressed genes (FDR < 0.05 and log 2 fold change magnitude>2.5) in cells co-treated with DCVC and LPS compared to LPS alone. For example, TNF had a log2(fold-change) = -3.5 with the addition of DCVC. Pathways downregulated (adjusted p-value<0.05) in DCVC+LPS treatments versus LPS-only treatments included: "acute inflammatory response", "production of molecular mediator of immune response" and "phagocytosis". LPS increased IL-1β, IL-6, and TNF-α levels in culture media (p < 0.001), but this was inhibited by co-treatment with DCVC (p < 0.001 for LPS vs. LPS + DCVC treatments). Our results demonstrate that DCVC suppresses inflammatory responses in macrophages.

Charting a Path Forward: Assessing the Science of Chemical Risk Evaluations under the Toxic Substances Control Act in the Context of Recent National Academies Recommendations

BACKGROUND

In 2016, Congress enacted the Frank R. Lautenberg Chemical Safety for the 21st Century Act ("the Lautenberg Act"), which made major revisions to the main U.S. chemical safety law, the 1976 Toxic Substances Control Act (TSCA). Among other reforms, the Lautenberg Act mandates that the U.S. Environmental Protection Agency (U.S. EPA) conduct comprehensive risk evaluations of chemicals in commerce. The U.S. EPA recently finalized the first set of such chemical risk evaluations.

OBJECTIVES

We examine the first 10 TSCA risk evaluations in relation to risk science recommendations from the National Academies to determine consistency with these recommendations and to identify opportunities to improve future TSCA risk evaluations by further implementing these key approaches and methods.

DISCUSSION

Our review of the first set of TSCA risk evaluations identified substantial deviations from best practices in risk assessment, including overly narrow problem formulations and scopes; insufficient characterization of uncertainty in the evidence; inadequate consideration of population variability; lack of consideration of background exposures, combined exposures, and cumulative risk; divergent approaches to dose-response assessment for carcinogens and noncarcinogens; and a flawed approach to systematic review. We believe these deviations result in underestimation of population exposures and health risks. We are hopeful that the agency can use these insights and have provided suggestions to produce chemical risk evaluations aligned with the intent and requirements of the Lautenberg Act and the best available science to better protect health and the environment-including the health of those most vulnerable to chemical exposures. https://doi.org/10.1289/EHP9649.

Cx43 overexpression is involved in the hyper-proliferation effect of trichloroethylene on human embryonic stem cells

Trichloroethylene (TCE) is a major environmental contaminant. Maternal exposure of TCE is linked to developmental defects, but the mechanisms remain to be elucidated. Along with a strategy of 3Rs principle, human embryonic stem cells (hESCs) are regarded as most promising in vitro models for developmental toxicity studies. TCE interfered with hESCs differentiation, but no report was available for TCE effects on hESCs proliferation. Here, we aimed to explore the toxic effects and mechanisms of TCE on hESCs proliferation. Treatment with TCE, did not affect the pluripotency genes expression. However, TCE enhanced hESCs proliferation, manifested by increased cell number, PCNA expression and EdU incorporation. Moreover, TCE exposure upregulated the protein expression levels of Cx43 and cyclin-dependent kinases. Knockdown of Cx43 attenuated the TCE-induced cell hyper-proliferation and CDK2 upregulation. Furthermore, TCE increased Akt phosphorylation, and the inhibition of Akt blocked the TCE-induced Cx43 overexpression and cell proliferation. In conclusion, TCE exposure resulted in upregulation of Cx43 via Akt phosphorylation, consequently stimulated CDK2 expression, contributing to hyper-proliferation in hESCs. Our study brings to light that TCE stimulated the proliferation of hESCs via Cx43, providing a new research avenue for the causes of TCE-induced developmental toxicity.

Maternal trichloroethylene exposure and metabolic gene polymorphisms may interact during fetal cardiovascular malformation

This study aimed to analyze the potential association between trichloroethylene (TCE) exposure and congenital heart disease (CHD) and to explore the effect of metabolic enzyme gene polymorphisms on heart development. A multicenter case-control study was conducted. The trichloroethylene concentrations were measured by UPLC-MSMS in urine. Fourteen SNPs in the GSTA1, GSTP1, MPO, NAT1, NAT2, CYP1A1, CYP1A2, CYP2E1 and EPHX1 genes were genotyped using an improved multiplex ligation detection reaction (iMLDR) technique. A total of 283 cases and 331 controls with maternal urine and/or venous blood were included in the present study. The median NAcDCVC was 7.65 ng/mL in the case group and 7.43 ng/mL in the control group. There was no significant difference in the NAcDCVC concentration between the CHD subtypes and controls (P > 0.05). The GA/AA of GSTA1 rs3957357 could increase the risk of CHDs under the dominant model (aOR = 2.26, 95 % CI: 1.31, 3.90), but other SNPs were not associated with CHDs (P > 0.05). GA or AA genotypes of GSTA1 rs3957357 with lower levels of TCE exposure were 3.53 times at risk relative to mothers carrying the wild type genotype. In conclusion, maternal exposure to trichloroethylene alone is not associated with the occurrence of fetal CHD and CHD subtypes. Maternal GSTA1 rs3957357 may increase the risk of CHD in offspring. TCE exposure and metabolic gene polymorphisms probably interact with each other to induce fetal cardiovascular malformation, but larger sample size studies are needed to confirm this hypothesis.

Curcumin reverses hepatic epithelial mesenchymal transition induced by trichloroethylene by inhibiting IL-6R/STAT3

OBJECTIVE

Epithelial mesenchymal transition (EMT) and inflammation have been identified as carcinogenic agents. This study aims to investigate whether inhibition of trichloroethylene (TCE) associated hepatocellular carcinoma (HCC) by curcumin is associated with inflammation and EMT.

METHODS

In the current study, TCE sub-chronic cell model was induced in vitro, and the effects of TCE on cell proliferation, migration, invasion, and expression of functional proteins were verified by Western blot, MTT, clone formation, wound healing, Transwell. The detoxification effect of curcumin on TCE was explored by a mouse tumor-bearing experiment.

RESULTS

TCE induces hepatocyte migration, colony formation, and EMT in vitro. In vivo studies have shown that curcumin significantly reduces the mortality of mice and control the occurrence and size of liver tumors by inhibiting the IL-6/STAT3 signaling pathway. In vitro, curcumin inhibits the proliferation of HepG2 cells as determined by MTT assay. In addition, curcumin significantly inhibited the protein expression of IL-6R, STAT3, snail, survivin, and cyclin D1 in THLE-2 and HepG2 cells induced by IL-6.

CONCLUSION

Curcumin has anti-inflammatory and anti-proliferative effects, and inhibits the development of HCC induced by TCE by reversing IL-6/STAT3 mediated EMT.

The effects of temperature and relative humidity on trichloroethylene sorption capacities of building materials under conditions relevant to vapor intrusion

In this research, the sorption capacities of trichloroethylene (TCE) vapors were investigated at ppbv concentrations on building materials in the temperature range from 283.15 K to 303.15 K and at relative humidity levels of 50% and 85%. These are conditions that are relevant to vapor intrusion investigations. Such interactions of TCE with different materials at different temperatures/ relative humidity have been studied to a very limited extent, and not yet at all at the extremely low concentration ranges in vapor intrusion scenarios. The sorption capacities of the building materials decrease as temperature increases. The isotherms are for the most part linear, indicating that the adsorption process takes place in the Henry's Law regime, except for cinderblock. The isosteric heats of adsorption have been calculated. The sorption capacities of glass wool and nylon carpet increased slightly when the relative humidity increased from 0% to 85% whereas the sorption capacities of printer paper, drywall, and cinderblock decreased significantly at elevated humidity levels. The influence of humidity is complicated since under certain conditions it may enhance sorption or inhibit sorption. The sorption capacities of the studied materials are in a range indicating the possibility of these processes should not be overlooked during vapor intrusion investigations.

Assessment of potential cardiovascular risk in trichloroethylene exposure by serum methylated arginine levels

Trichloroethylene (TCE) is a widely used solvent in industrial applications and has toxic effects on various systems. Methylated arginine amino acids (eg asymmetric dimethyl arginine (ADMA), symmetric dimethyl arginine (SDMA)) cause the development of cardiovascular disease by inhibiting NO synthesis, which is considered to be heart-protector. The aim of this study is to determine the risk of cardiovascular diseases in TCE exposure by methylated arginine biomarkers. About 98 controls and 100 TCE-exposed male subjects were included in the study. Trichloroacetic acid (urinary metabolite of TCE), arginine, homoarginine, citrulline ADMA, SDMA, and N-monomethyl L-arginine (L-NMMA) levels were found significantly higher than control group (p < 0.001). The strongest correlation was found between ADMA and Trichloroacetic acid (TCA) level (r = 0.453, p < 0.01). Long-term TCE exposure, may be an important risk factor for cardiovascular diseases by increasing methylated arginine levels.

Removal mechanism and quantitative control of trichloroethylene in a post-plasma-catalytic system over Mn–Ce/HZSM-5 catalysts

The optimization of the TCE degradation process was achieved and the TCE degradation pathway in the PPC system was proposed.

Downregulation of miR-133a contributes to the cardiac developmental toxicity of trichloroethylene in zebrafish

Trichloroethylene (TCE), a widely used organic solvent, is a common environmental pollutant. Increasing evidence indicates that maternal TCE exposure is associated with congenital cardiac defects, but the underlining mechanisms remain largely unknown. In this study, we revealed that TCE exposure significantly induced heart defects and dysfunctions in zebrafish embryos. Heart tissues were dissected and subjected to high throughput sequencing and qPCR to identify differentially expressed miRNAs and mRNAs. The effects of miRNA were further verified by microinjection of antagomir or agomir. Reactive Oxygen Species (ROS) and cell proliferation were measured by using dichlorodihydrofluorescein diacetate (DCFH-DA) and EdU staining, respectively. Our results showed that 19 miRNAs were downregulated whereas 48 miRNAs were upregulated in the heart of zebrafish embryos. The downregulation of miR-133a and the upregulation of miR-182 were further validated. Moreover, we found that miR-133a agomir significantly alleviated the TCE-induced heart defects while miR-133a antagomir mimicked the toxic effect of TCE on heart development. Furthermore, miR-133a agomir significantly counteracted TCE-induced ROS production and excessive cell proliferation in the heart of zebrafish embryos. In conclusion, our results indicate that miR-133a mediates TCE-induced ROS generation, leading to excessive cell proliferation and heart defects.

AHR-mediated oxidative stress contributes to the cardiac developmental toxicity of trichloroethylene in zebrafish embryos

Trichloroethylene (TCE), a widely used chlorinated solvent, is a common environmental pollutant. Current evidence shows that TCE could induce heart defects during embryonic development, but the underlining mechanism(s) remain unclear. Since activation of the aryl hydrocarbon receptor (AHR) could induce oxidative stress, we hypothesized that AHR-mediated oxidative stress may play a role in the cardiac developmental toxicity of TCE. In this study, we found that the reactive oxygen species (ROS) scavenger, N-Acetyl-L-cysteine (NAC), and AHR inhibitors, CH223191 (CH) and StemRegenin 1, significantly counteracted the TCE-induced heart malformations in zebrafish embryos. Moreover, both CH and NAC suppressed TCE-induced ROS and 8-OHdG (8-hydroxy-2' -deoxyguanosine). TCE did not affect ahr2 and cyp1a expression, but increased cyp1b1 expression, which was restored by CH supplementation. CH also attenuated the TCE-induced mRNA expression changes of Nrf2 signalling genes (nrf2b, gstp2, sod2, ho1, nqo1) and cardiac differentiation genes (gata4, hand2, c-fos, sox9b). In addition, the TCE enhanced SOD activity was attenuated by CH. Morpholino knockdown confirmed that AHR mediated the TCE-induced ROS and 8-OHdG generation in the heart of zebrafish embryos. In conclusion, our results suggest that AHR mediates TCE-induced oxidative stress, leading to DNA damage and heart malformations in zebrafish embryos.

Systematic evaluation of mechanistic data in assessing in utero exposures to trichloroethylene and development of congenital heart defects

The hypothesis that in utero exposures to low levels of trichloroethylene (TCE) may increase the risk of congenital heart defects (CHDs) in offspring remains a subject of substantial controversy within the scientific community due primarily to the reliance on an inconsistent and unreproducible experimental study in rats. To build on previous assessments that have primarily focused on epidemiological and experimental animal studies in developing conclusions, the objective of the current study is to conduct a systematic evaluation of mechanistic data related to in utero exposures to TCE and the development of CHDs. The evidence base was heterogeneous; 79 mechanistic datasets were identified, characterizing endpoints which ranged from molecular to organismal responses in seven species, involving both in vivo and in vitro study designs in mammalian and non-mammalian models. Of these, 24 datasets were considered reliable following critical appraisal using a study quality tool that employs metrics specific to the study type. Subsequent synthesis and integration demonstrated that the available mechanistic data: 1) did not support the potential for CHD hazard in humans, 2) did not support the biological plausibility of a response in humans based on organization via a putative adverse outcome pathway for valvulo-septal cardiac defects, and 3) were not suitable for serving as candidate studies in risk assessment. Findings supportive of an association were generally limited to in ovo chicken studies, in which TCE was administered in high concentration solutions via direct injection. Results of these in ovo studies were difficult to interpret for human health risk assessment given the lack of generalizability of the study models (including dose relevance, species-specific biological differences, variations in the construct of the study design, etc.). When the mechanistic data are integrated with findings from previous evaluations of human and animal evidence streams, the totality of evidence does not support CHDs as a critical effect in TCE human health risk assessment.

HNF4a transcription is a target of trichloroethylene toxicity in the embryonic mouse heart

In exploration of congenital heart defects produced by TCE, Hepatocyte Nuclear Factor 4 alpha (HNF4a) transcriptional activity was identified as a central component. TCE exposure altered gene transcription in the chick heart in a non-monotonic pattern where only low dose exposure inhibited transcription by HNF4a. As the chick embryo is non-placental, we examine here HNF4a as a target of TCE in developing mouse embryos. Benfluorex and Bi6015, published agonist and antagonist, respectively, of HNF4a were compared to low dose TCE exposure. Pregnant mice were exposed to 10 ppb (76 nM) TCE, 5 μM Benfluorex, 5 μM Bi6015, or a combination of Bi6015 and TCE in drinking water. Litters (E12) were collected during a sensitive window in heart development. Embryonic hearts were collected, pooled for extraction of RNA and marker expression was examined by quantitative PCR. Multiple markers, previously identified as sensitive to TCE exposure in chicks or as published targets of HNF4a transcription were significantly affected by Benfluorex, Bi6015 and TCE. Activity of TCE and both HNF4a-specific reagents on transcription argues that HNF4a is a component of TCE cardiotoxicity and likely a proximal target of low dose exposure during development. The effectiveness of these reagents after delivery in maternal drinking water suggests that neither maternal metabolism, nor placental transport is protective of exposure.

Complex epigenetic patterns in cerebellum generated after developmental exposure to trichloroethylene and/or high fat diet in autoimmune-prone mice

Trichloroethylene (TCE) is an environmental contaminant associated with immune-mediated inflammatory disorders and neurotoxicity. Based on known negative effects of developmental overnutrition on neurodevelopment, we hypothesized that developmental exposure to high fat diet (HFD) consisting of 40% kcal fat would enhance neurotoxicity of low-level (6 μg per kg per day) TCE exposure in offspring over either stressor alone. Male offspring were evaluated at ∼6 weeks of age after exposure beginning 4 weeks preconception in the dams until weaning. TCE, whether used as a single exposure or together with HFD, appeared to be more robust than HFD alone in altering one-carbon metabolites involved in glutathione redox homeostasis and methylation capacity. In contrast, opposing effects of expression of key enzymes related to DNA methylation related to HFD and TCE exposure were observed. The mice generated unique patterns of anti-brain antibodies detected by western blotting attributable to both TCE and HFD. Taken together, developmental exposure to TCE and/or HFD appear to act in complex ways to alter brain biomarkers in offspring.

PPAR-Mediated Toxicology and Applied Pharmacology

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor family, attract wide attention as promising therapeutic targets for the treatment of multiple diseases, and their target selective ligands were also intensively developed for pharmacological agents such as the approved drugs fibrates and thiazolidinediones (TZDs). Despite their potent pharmacological activities, PPARs are reported to be involved in agent- and pollutant-induced multiple organ toxicity or protective effects against toxicity. A better understanding of the protective and the detrimental role of PPARs will help to preserve efficacy of the PPAR modulators but diminish adverse effects. The present review summarizes and critiques current findings related to PPAR-mediated types of toxicity and protective effects against toxicity for a systematic understanding of PPARs in toxicology and applied pharmacology.

Trichloroethylene in drinking water throughout gestation did not produce congenital heart defects in Sprague Dawley rats

BACKGROUND

Trichloroethylene (TCE) was negative for developmental toxicity after inhalation and oral gavage exposure of pregnant rats but fetal cardiac defects were reported following drinking water exposure throughout gestation. Because of the deficiencies in this latter study, we performed another drinking water study to evaluate whether TCE causes heart defects.

METHODS

Groups of 25 mated Sprague Dawley rats consumed water containing 0, 0.25, 1.5, 500, or 1,000 ppm TCE from gestational day 1-21. TCE concentrations were measured at daily formulation, when placed into water bottles each day and when water bottles were removed from cages. Four additional mated rats per group were used for plasma measurements. At termination, fetal hearts were carefully dissected fresh and examined.

RESULTS

All TCE concentrations were >90% of target when initially placed in water bottles and when bottles were placed on cages. All dams survived with no clinical signs. Rats in the two higher dose groups consumed less water/day than other groups but showed no changes in maternal or fetal weights. The only fetal cardiac observation was small (<1 mm) membranous ventricular septal defect occurring in all treated and water control groups; incidences were within the range of published findings for naive animals. TCE was not detected in maternal blood, but systemic exposure was confirmed by detecting its primary oxidative metabolite, trichloroacetic acid, although only at levels above the quantitation limit in the two higher dose groups.

CONCLUSIONS

Ingesting TCE in drinking water ≤1,000 ppm throughout gestation does not cause cardiac defects in rat offspring.

Prenatal toxicity of the environmental pollutants on neuronal and cardiac development derived from embryonic stem cells

Pesticides, antibiotics, and industrial excipients are widely used in agriculture, medicine, and chemical industry, respectively. They often end up in the environment, not only being not easily decomposed but also being accumulated. Moreover, they may cause serious toxic problems such as reproductive and developmental defects, immunological toxicity, and carcinogenesis. Hence, they are called environmental pollutants. It is known that the environmental pollutants easily enter the body through various channels such as respiration, ingestion of food, and skin contact etc. in everyday life. If they enter the mother through the placenta, they can cause the disturbance in embryo development as well as malfunction of organs after birth because early prenatal developmental process is highly sensitive to toxic chemicals and stress. Embryonic stem cells (ESCs) that consist of inner cell mass of blastocyst differentiate into distinct cell lineages via three germ layers such as the ectoderm, mesoderm, and endoderm due to their pluripotency. The differentiation process initiated from ESCs reflects dynamic nature of embryonic development. Therefore, ESCs have been used as a useful tool to investigate early developmental toxicities of a variety of stress. Based on relatively recent scientific results, this review would address toxicity of a few chemical substances that have been widely used as pesticide, antibiotics, and industrial excipient on ESCs based-prenatal developmental process. This review further suggests how they act on the viability of ESCs and/or early stages of cardiac and neuronal development derived from ESCs as well as on expression of pluripotency and/or differentiation markers through diverse mechanisms.

Environmental Exposures in Reproductive Health

Our genetic makeup and environment interact. Evidence has emerged demonstrating preconception and prenatal exposure to toxic agents have a profound effect on reproductive health. We cannot change our genetics, but we can change our environment. Health providers can protect pregnancies from harmful exposures. Pregnancy is the most critical time-window for human development, when any toxic exposure can cause lasting damage to brain development. Reproductive care professionals can provide useful information to patients and refer patients to appropriate specialists when hazardous exposure is identified. Clinical experience and expertise in communicating risks of treatment are transferable to environmental health.

Role of selective blocking of bradykinin B1 receptor in attenuating immune liver injury in trichloroethylene-sensitized mice

Trichloroethylene (TCE) is able to induce trichloroethylene hypersensitivity syndrome (THS) with multi-system immune injuries. In our previous study, we found kallikrein-kinin system (KKS) activation, including the bradykinin B1 receptor (B1R), which contributed to immune organ injury in TCE sensitized mice. However, the mechanism of B1R mediating immune dysfunction is not clarified. The present study initiates to investigate the potential mechanism of B1R on liver injury. We establish a TCE sensitized BALB/c mouse model to explore the mechanism with or without a B1R inhibitor R715. We found B1R expression was increased in TCE sensitization-positive mice. As expect, hepatocyte intracellular organelles and mitochondria disappeared, glycogen particles reduced significantly as well in TCE sensitization-positive mice via the transmission electron microscopic examination, meanwhile, R715 alleviated the deteriorate above. The blockade of B1R resulted in a significant decreased p-ERK1/2 and increased p-AKT expression. The expression of CD68 kupffer cell and its relative cytokine, including IL-6 and TNF-α, increased in TCE sensitization-positive mice and decreased in R715 pretreatment TCE sensitization-positive mice. Together, the results demonstrate B1R plays a key role in ERK/MAPK and PI3K/AKT signal pathway activation and inflammation cytokine expression in immune liver injury induced by TCE. B1R exerts a pivotal role in the development of TCE induced liver injury.

Role of Risk of Bias in Systematic Review for Chemical Risk Assessment: A Case Study in Understanding the Relationship Between Congenital Heart Defects and Exposures to Trichloroethylene

The National Academy of Science has recommended that a risk of bias (RoB; credibility of the link between exposure and outcome) assessment be conducted on studies that are used as primary data sources for hazard identification and dose-response assessment. Few applications of such have been conducted. Using trichloroethylene and congenital heart defects (CHDs) as a case study, we explore the role of RoB in chemical risk assessment using the National Toxicology Program's Office of Health Assessment and Translation RoB tool. Selected questions were tailored to evaluation of CHD and then applied to 12 experimental animal studies and 9 epidemiological studies. Results demonstrated that the inconsistent findings of a single animal study were likely explained by the limitations in study design assessed via RoB (eg, lack of concurrent controls, unvalidated method for assessing outcome, unreliable statistical methods, etc). Such limitations considered in the context of the body of evidence render the study not sufficiently reliable for the development of toxicity reference values. The case study highlights the utility of RoB as part of a robust risk assessment process and specifically demonstrates the role RoB can play in objectively selecting candidate data sets to develop toxicity values.

Trichloroethylene perturbs HNF4a expression and activity in the developing chick heart

Exposure to trichloroethylene (TCE) is linked to formation of congenital heart defects in humans and animals. Prior interactome analysis identified the transcription factor, Hepatocyte Nuclear Factor 4 alpha (HNF4a), as a potential target of TCE exposure. As a role for HNF4a is unknown in the heart, we examined developing avian hearts for HNF4a expression and for sensitivity to TCE and the HNF4a agonist, Benfluorex. In vitro analysis using a HNF4a reporter construct showed both TCE and HFN4a to be antagonists of HNF4a-mediated transcription at the concentrations tested. HNF4a mRNA is expressed transiently in the embryonic heart during valve formation and cardiac development. Embryos were examined for altered gene expression in the presence of TCE or Benfluorex. TCE altered expression of selected mRNAs including HNF4a, TRAF6 and CYP2C45. There was a transition between inhibition and induction of marker gene expression in embryos as TCE concentration increased. Benfluorex was largely inhibitory to selected markers. Echocardiography of exposed embryos showed reduced cardiac function with both TCE and Benfluorex. Cardiac contraction was reduced by 29% and 23%, respectively at 10 ppb. The effects of TCE and Benfluorex on autocrine regulation of HNF4a, selected markers and cardiac function argue for a functional interaction of TCE and HNF4a. Further, the dose-sensitive shift between inhibition and induction of marker expression may explain the nonmonotonic-like dose response observed with TCE exposure in the heart.

Application of Adverse Outcome Pathways to U.S. EPA's Endocrine Disruptor Screening Program

BACKGROUND

The U.S. EPA's Endocrine Disruptor Screening Program (EDSP) screens and tests environmental chemicals for potential effects in estrogen, androgen, and thyroid hormone pathways, and it is one of the only regulatory programs designed around chemical mode of action.

OBJECTIVES

This review describes the EDSP's use of adverse outcome pathway (AOP) and toxicity pathway frameworks to organize and integrate diverse biological data for evaluating the endocrine activity of chemicals. Using these frameworks helps to establish biologically plausible links between endocrine mechanisms and apical responses when those end points are not measured in the same assay.

RESULTS

Pathway frameworks can facilitate a weight of evidence determination of a chemical's potential endocrine activity, identify data gaps, aid study design, direct assay development, and guide testing strategies. Pathway frameworks also can be used to evaluate the performance of computational approaches as alternatives for low-throughput and animal-based assays and predict downstream key events. In cases where computational methods can be validated based on performance, they may be considered as alternatives to specific assays or end points.

CONCLUSIONS

A variety of biological systems affect apical end points used in regulatory risk assessments, and without mechanistic data, an endocrine mode of action cannot be determined. Because the EDSP was designed to consider mode of action, toxicity pathway and AOP concepts are a natural fit. Pathway frameworks have diverse applications to endocrine screening and testing. An estrogen pathway example is presented, and similar approaches are being used to evaluate alternative methods and develop predictive models for androgen and thyroid pathways. https://doi.org/10.1289/EHP1304.