Mixed "Antiandrogenic" Chemicals at Low Individual Doses Produce Reproductive Tract Malformations in the Male Rat

Using data on the uncertainty of LOAELs to model the probability of observing adverse effects in low-dose studies of the toxicity of chemical mixtures

Studies of chemical mixtures toxicity are often designed to differentiate mixtures that follow dose-addition from those that follow response-addition. One design used for this purpose doses animals at levels below the levels that separately have been shown to cause a detectable occurence of a common effect. Under response addition, no effects are expected to be observed since no chemical would independently cause an observable response at the administered doses. Effects, however, could be observed if some or all of the chemicals follow dose addition. Thus, any observation of response can be taken as evidence of dose addition. A recent publication estimated interstudy variation in chemicals' LOAELs. These estimates are here used to predict the probability of observing an effect in mixtures that follow response- or dose-addition models. Two case studies are presented. One is on a set of hypothetical mixtures containing from 2 to 20 chemicals. The second is on mixtures of anti-androgenic chemicals. In these studies, LOAEL uncertainty blurred the difference between dose and response models, and for many mixtures, it is not possible to determine whether response or dose additivity occurred. These findings suggest that caution should be taken when using these studies as evidence for dose addition.

Evaluation of the endocrine disrupting potential of Di-isodecyl phthalate

Low molecular weight ortho-phthalates have been implicated in perturbing androgen pathways when administered during the masculinization programming window. Di-isodecyl phthalate (DIDP) is a high molecular weight phthalate and as a high production volume chemical, its ability to disrupt endocrine pathways is important to understand its potential hazard. Both DIDP (and its metabolites) were evaluated to determine the potential to perturb endocrine pathways through a weight of evidence (WoE) assessment in accordance with the European Chemicals Agency (ECHA)/European Food Safety Authority (EFSA) Endocrine Disruptor Guidance (2018). A literature review was performed of toxicological data for DIDP related to estrogen, androgen, thyroid, or steroidogenesis pathways. Literature searches returned 41 relevant articles from which data were extracted and assessed in conjunction with data from 105 high-throughput assays. Because some of the in vitro assays lack metabolic capabilities, an in silico assessment of estrogen (E), androgen (A), thyroid (T) or steroidogenesis (S) activity was conducted. Based on the available evidence for the T pathway, DIDP did not elicit adverse thyroid outcomes in vivo. When considering the T mechanistic data, there was evidence that DIDP induced the liver pregnane X receptor (PXR) and some indication that DIDP increased iodide uptake in the thyroid. As there were no studies evaluating thyroid hormone levels in vivo, a data gap was identified because per the ECHA/EFSA guidance, the lack of this information prevents drawing a conclusion on the T pathway. However, the E, A and S pathways were sufficiently assessed to conclude a limited or lack of E, A or S related apical outcomes in in vivo studies; there was also a lack of endocrine activity in in vitro or in vivo mechanistic studies. These results suggest that DIDP does not meet the ECHA/EFSA criteria for an endocrine disruptor, therefore DIDP is unlikely to disrupt the androgen pathway during development.

Evaluation of the endocrine disrupting potential of Di-isononyl phthalate

Low molecular weight ortho-phthalate compounds have been implicated in disruption of androgen pathways when exposure occurs during the masculinization programming window. Di-isononyl phthalate (DINP) is a high molecular weight phthalate and a high production volume chemical. To understand the potential for DINP and its metabolites to disrupt endocrine pathways, a weight of evidence assessment was conducted according to the European Chemicals Agency (ECHA)/ European Food Safety Authority (EFSA) Endocrine Disruptor Guidance (2018). Toxicological data related to estrogen (E), androgen (A), thyroid (T), or steroidogenesis (S) pathways was assessed. Literature searches returned 110 articles from which data were extracted and assessed in conjunction with 105 high-throughput assays. An in-silico assessment of the EATS activity for DINP metabolites also was conducted. Based on the available evidence, DINP did not elicit thyroid- or estrogen-related apical outcomes in vivo. There were no studies evaluating thyroid hormone levels in vivo which, according to the ECHA/EFSA guidance, constitutes a data gap and prevents a conclusion being drawn on the T-pathway. The E, A, and S-pathways were sufficiently assessed to conclude on the endocrine disrupting potential of DINP. Based on the lack of apical outcomes, DINP did not disrupt the E-pathway. For the A and S-pathways, there was limited evidence to support adverse apical outcomes, so a mode of action assessment using a structured adverse outcome pathway (AOP) framework was performed. No biologically plausible link could be established between the key events in the hypothesized AOP that lead to adverse outcomes. Further, no dose or temporal concordance for A- and S-mediated findings were identified. Therefore, DINP does not meet the ECHA/EFSA criteria to be considered an endocrine disruptor.

In Utero and Lactational Exposure to an Environmentally Relevant Mixture of Phthalates Alters Hypothalamic Gene Expression and Sexual Preference in Rats

Several phthalates, mainly used as plasticizers, are known for their adverse effects on the male genital system. Previously, we demonstrated that an environmentally relevant mixture of six antiandrogenic phthalates (PMix), derived from a biomonitoring study in pregnant Brazilian women, was able to disrupt the reproductive development in male rats. Experimental groups (control, 0.1, 0.5, and 500 mg PMix/kg/day) were established starting from the extrapolated human dose (0.1 mg/kg/day), followed by doses 5 times and 5000 times higher. Pregnant rats received daily oral gavage administration of either vehicle (control) or PMix from gestational day 13 to postnatal day 10. Here, we examined male and female offspring regarding changes in gene expression of key reproductive factors in the hypothalamus and pituitary gland at adulthood and conducted a battery of behavioral tests in males, including partner preference, sexual behavior, and male attractiveness tests. PMix induced some changes in mating-related behavior in males, as demonstrated by the absence of preference for females against males and a higher number of penetrations up to ejaculation in the 0.5 dose group. PMix decreased Esr2 expression in the male hypothalamus across all three doses, and in females at mid and high doses in both the hypothalamus and pituitary. In male hypothalamus, we also observed decreased Kiss1 transcripts in these groups and a reduction in AR at the 0.5 dose group. In summary, our results provide further evidence that phthalates in a mixture, even at low doses, may exert cumulative effects on the structures underlying sexual behavior, which seems to be more sensitive than reproductive endpoints for the same experimental design.

Plasticizer exposure in Germany from 1988 to 2022: Human biomonitoring data of 20 plasticizers from the German Environmental Specimen Bank

The German Environmental Specimen Bank (ESB) annually archives 24-h urine samples since the early 1980s. In this study, we analyzed 420 of these samples from the years 2014 to 2022 for metabolites of 18 phthalates and two substitutes. We merged the new data with the data from previous measurement campaigns to a combined dataset of 1825 samples covering a 35-year period from 1988 to 2022 to investigate time trends, calculate daily intakes and perform an anti-androgenic mixture risk assessment. With the extended set of 41 biomarkers, we are now able to monitor the exposure to all EU-labelled reprotoxic phthalates. Most phthalate exposures continued to decrease since first measurements in the 80s, with biggest drops for DnBP (96.6 %) and DEHP (90.9 %). DiNP and DiDP, seen on the rise in earlier campaigns, now declined. Exposures to the newly included, reprotoxic phthalates were generally negligible. Regarding mixture risk, 5 % of the highly exposed still exceeded the Hazard Index (HI) of 1 in 2009. In the current measurement campaign only three individuals (0.7 %) exceeded the HI of 1 (with exceedances still driven by DEHP and DnBP).In 2022, 20 % of the individuals still had an HI > 0.2, which we propose as a benchmark for interpreting phthalate mixture risk, considering concurrent exposures to other anti-androgens. Exposure to the substitutes DINCH and DEHTP continues to increase, with daily intakes of DEHTP exceeding those of DEHP since 2018. Compared with the United States (US) National Health and Nutrition Examination Survey (NHANES) phthalate exposures seem to align, except for DEHTP with up to ten times higher levels in the US. Human biomonitoring (HBM) is the ideal tool to capture actual mixture exposures per individual, integrating all external exposure sources and pathways, thus we will continue to use HBM in exposure and risk assessment of phthalates and other (anti-androgenic) chemicals.

Pesticide Exposures during Pregnancy and Health Outcomes in Latin America and the Caribbean: A Scoping Review of Human Observational Studies

Background

Latin America and the Caribbean (LAC) are regions with intense pesticide use. Numerous studies have demonstrated the adverse health effects associated with pesticide exposure. The embryonic and fetal periods are particularly susceptible to xenobiotics, with pesticides exhibiting potentially teratogenic effects.

Objectives

The objective was to review the scientific literature on outcomes associated with prenatal pesticide exposure, identifying challenges and gaps in this field.

Methods

We conducted a scoping review using terms related to pesticides, LAC, and pregnancy across six databases. The final search was conducted on 5 March 2024. The inclusion criteria for the studies were as follows: a) being human observational studies involving pregnant women of any age or gestational age duration, newborns from these pregnancies, or both; b) reporting any exposure to pesticide and any adverse outcome; c) having been conducted in any country of LAC; d) having been published between 1 January 2000 and 5 March 2024; e) having the full text available in English, Spanish, or Portuguese; and f) presenting original results. Nonoriginal research papers, such as qualitative studies, reviews, critical analyses, and opinion papers, were excluded. The included studies were categorized and presented based on the outcomes they evaluated.

Results

We included 80 studies conducted in 13 countries; the included studies encompassed obstetric outcomes, anthropometric parameters, congenital anomalies, neurodevelopment, respiratory infections, and childhood leukemia, as well as molecular effects. Organochlorines were the primary type of exposure investigated among the included studies. Many studies relied on indirect measures of pesticide exposure.

Discussion

Adverse outcomes associated with prenatal pesticide exposure have been observed in Latin American and Caribbean populations, consistent with the global literature. Significant knowledge gaps remain, especially regarding groups of pesticides other than organochlorines. Less than half of the countries in LAC have conducted any study on the potential effects of prenatal exposure. Ongoing research into the risks of prenatal exposure is imperative. It is essential to consider the region's unique characteristics, particularly when investigating the risks associated with pesticides authorized exclusively in this region. https://doi.org/10.1289/JHP1043.

Was the massive increase in use of teratogenic agrichemicals in western states (USA) associated with declines in wild ruminant populations between 1994 and 2013?

Population declines were documented in multiple ruminant species in Montana and surrounding states starting in 1995. While weather, food sources, and predation certainly contributed, the declines were often attributed, at least partly, to unexplained factors. Use of teratogenic agrichemicals, notably neonicotinoid insecticides, fungicides, and glyphosate-based herbicides, massively increased regionally in 1994-96. The question explored in this review is whether this vastly increased use of these teratogenic pesticides might have contributed to observed population declines. We provide references and data documenting that specific developmental malformations on vertebrates can be associated with exposure to one or more of these agrichemicals. These pesticides are known to disrupt thyroid and other hormonal functions, mitochondrial functions, and biomineralization, all of which are particularly harmful to developing fetuses. Exposures can manifest as impaired embryonic development of craniofacial features, internal and reproductive organs, and musculoskeletal/integumental systems, often resulting in reproductive failure or weakened neonates. This paper reviews: a) studies of ruminant populations in the region, especially elk and white-tailed deer, prior to and after 1994; b) published and new data on underdeveloped facial bones in regional ruminants; c) published and new data on reproductive abnormalities in live and necropsied animals before and after 1994; and d) studies documenting the effects of exposures to three of the most applied teratogenic chemicals. While answers to the question posed above are complex and insufficient evidence is available for definitive answers, this review provides ideas for further consideration.

A Machine-Learning-Driven Pathophysiology-Based New Approach Method for the Dose-Dependent Assessment of Hazardous Chemical Mixtures and Experimental Validations

Environmental chemicals, such as PFAS, exist as mixtures and are frequently encountered at varying concentrations, which can lead to serious health effects, such as cancer. Therefore, understanding the dose-dependent toxicity of chemical mixtures is essential for health risk assessment. However, comprehensive methods to assess toxicity and identify the mechanisms of these harmful mixtures are currently absent. In this study, the dose-dependent toxicity assessments of chemical mixtures are performed in three methodologically distinct phases. In the first phase, we evaluated our machine-learning method (AI-HNN) and pathophysiology method (CPTM) for predicting toxicity. In the second phase, we integrated AI-HNN and CPTM to establish a comprehensive new approach method (NAM) framework called AI-CPTM that is targeted at refining prediction accuracy and providing a comprehensive understanding of toxicity mechanisms. The third phase involved experimental validations of the AI-CPTM predictions. Initially, we developed binary, multiclass classification, and regression models to predict binary, categorical toxicity, and toxic potencies using nearly a thousand experimental mixtures. This empirical dataset was expanded with assumption-based virtual mixtures, compensating for the lack of experimental data and broadening the scope of the dataset. For comparison, we also developed machine-learning models based on RF, Bagging, AdaBoost, SVR, GB, KR, DT, KN, and Consensus methods. The AI-HNN achieved overall accuracies of over 80%, with the AUC exceeding 90%. In the final phase, we demonstrated the superior performance and predictive capability of AI-CPTM, including for PFAS mixtures and their interaction effects, through rigorous literature and statistical validations, along with experimental dose-response zebrafish-embryo toxicity assays. Overall, the AI-CPTM approach significantly improves upon the limitations of standalone AI models, showing extensive enhancements in identifying toxic chemicals and mixtures and their mechanisms. This study is the first to develop a hybrid NAM that integrates AI with a pathophysiology method to comprehensively predict chemical-mixture toxicity, carcinogenicity, and mechanisms.

Dose addition in mixtures of compounds with dissimilar endocrine modes of action in in vitro receptor activation assays and the zebrafish sexual development test

BACKGROUND

Human exposure to pesticides is being associated with feminisation for which a decrease of the anogenital distance (AGD) is a sensitive endpoint. Dose addition for the cumulative risk assessment of pesticides in food is considered sufficiently conservative for combinations of compounds with both similar and dissimilar modes of action (MoA).

OBJECTIVE

The present study was designed to test the dose addition hypothesis in a binary mixture of endocrine active compounds with a dissimilar mode of action for the endpoint feminisation.

METHODS

Compounds were selected from a list of chemicals of which exposure is related to a decrease of the AGD in rats and completed with reference compounds. These chemicals were characterised using specific in vitro transcriptional activation (TA) assays for estrogenic and androgenic properties, leading to a final selection of dienestrol as an ER-agonist and flutamide, linuron, and deltamethrin as AR-antagonists. These compounds were then tested in an in vivo model, i.e. in zebrafish (Danio rerio), using sex ratio in the population as an endpoint in order to confirm their feminising effect and MoA. Ultimately, the fish model was used to test a binary mixture of flutamide and dienestrol.

RESULTS

Statistical analysis of the binary mixture of flutamide and dienestrol in the fish sexual development tests (FSDT) with zebrafish supported dose addition.

Dose Addition Models Accurately Predict the Subacute Effects of a Mixture of Perfluorooctane Sulfonate and Perfluorooctanoic Acid on Japanese Quail (Coturnix japonica) Chick Mortality

Biomonitoring data have consistently demonstrated that fish, wildlife, and humans are exposed to multiple per- and polyfluoroalkyl substances (PFAS) in drinking water and foods. Despite ubiquitous exposure to mixtures of PFAS, there is a lack of in vivo PFAS mixture research that addresses whether these chemicals act in a cumulative, dose-additive (DA) manner or whether they behave independently. For this reason, there is a critical need for mixtures studies designed to evaluate the cumulative toxicity and potential chemical interactions to support the assessment of human and ecological risks and also to define appropriate regulatory actions. Our primary objective was to evaluate the previously published Japanese quail chick mortality concentration-response data for perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and the mixture of PFOS + PFOA and to use statistical modeling to determine whether the effects of the mixtures were accurately predicted by either DA or response addition modeling. In addition, we wanted to compare different DA models to determine whether one model produced more accurate predictions than the others. Our results support the hypothesis of cumulative effects on shared endpoints from PFOA and PFOS co-exposure and DA approaches for predictive estimates of cumulative effects. Given the limited number of in vivo studies that have been executed with enough individual PFAS and PFAS mixture concentration-response data to test the hypothesis of DA for PFAS mixtures, this re-analysis of the data is an important contribution to our understanding of how PFAS mixtures act. The analysis will provide support for regulatory agencies as they begin to implement PFAS cumulative hazard assessments in higher vertebrates. Environ Toxicol Chem 2024;43:97-104. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Reproductive toxicity following in utero and lactational exposure to a human-relevant phthalate mixture in rats

This rodent (Wistar rats) study examined reproductive effects of in utero/lactational exposure to a mixture of 6 antiandrogenic phthalates (PMix): diisobutyl phthalate, di-n-butyl phthalate, diisopentyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl phthalate, and diisononyl phthalate. The PMix was defined based on exposure data from pregnant women in Brazil. Experimental groups were established by extrapolating the estimated human dose to rats (0.1 mg/kg/day), followed by up to 3 additional doses corresponding to 5, 1000, and 5000 times the starting rat dose: 0 (control), 0.1, 0.5, 100, and 500 mg/kg/day. The fetal experiment assessed gestational exposure effects on fetal gonads, whereas the postnatal experiment evaluated reproductive parameters in males and females after in utero and lactational exposure. Prenatal exposure decreased fetal testicular testosterone production at 0.5 and 500 mg/kg/day. PMix 500 also reduced mRNA expression of steroidogenesis-related genes, upregulated transcript expression of the retinoic acid-degrading enzyme Cyp26b1, and increased multinucleated gonocytes incidence in fetal testes. Postnatal assessment revealed antiandrogenic effects at the highest dose, including reduced anogenital distance, nipple retention, and decreased weight of reproductive organs. Early puberty onset (preputial separation) was observed at the lowest dose in males. In contrast, females did not show significant changes in fetal and adult endpoints. Overall, the PMix recapitulated early and late male rat phthalate syndrome phenotypes at the highest dose, but also induced some subtle changes at lower doses, which warrant confirmation and mechanistic assessments. Our data support the use of epidemiologically defined mixtures for exposure risk assessments over traditional toxicological approaches.

Anti-androgenic activity of novel flame retardants in mixtures: Newly identified contribution from tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO)

In recent decades, male infertility has been on the rise, largely attributed to exposure to chemicals with endocrine-disrupting properties. The adverse effects of disrupting androgen actions on the development and reproductive health of children and adolescents have been extensively studied. Flame retardants (FRs), used in consumer products to delay flammability, have been identified as antagonists of the androgen receptor (AR), potentially leading to adverse outcomes in male reproductive health later in life. This study examined the interaction of eight novel FRs with the AR, employing an in vitro AR-dependent luciferase reporter gene assay utilizing MDA-kb2 cells. The investigation revealed the anti-androgenic activity of tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO), a frequently detected FR in the environment. Furthermore, TDBP-TAZTO contributed to anti-androgenic activity when combined with six other anti-androgenic FRs. The mixture effects were predicted by three commonly employed models: concentration addition (CA), generalized CA, and independent action, with the CA model showcasing the highest accuracy. This suggests that all FRs act through a similar mechanism, as further confirmed by in silico molecular docking, indicating limited synergy or antagonism. Importantly, in the mixtures, each FR contributed to the induction of anti-androgenic effects at concentrations below their individual effective concentrations in single exposures. This raises concern for public health, especially considering the co-detection of these FRs and their potential co-occurrence with other anti-androgenic chemicals like bisphenols. Therefore, our findings, along with previous research, strongly support the incorporation of combined effects of mixtures in risk assessment to efficiently safeguard population health.

Application of AOPs to assist regulatory assessment of chemical risks - Case studies, needs and recommendations

While human regulatory risk assessment (RA) still largely relies on animal studies, new approach methodologies (NAMs) based on in vitro, in silico or non-mammalian alternative models are increasingly used to evaluate chemical hazards. Moreover, human epidemiological studies with biomarkers of effect (BoE) also play an invaluable role in identifying health effects associated with chemical exposures. To move towards the next generation risk assessment (NGRA), it is therefore crucial to establish bridges between NAMs and standard approaches, and to establish processes for increasing mechanistically-based biological plausibility in human studies. The Adverse Outcome Pathway (AOP) framework constitutes an important tool to address these needs but, despite a significant increase in knowledge and awareness, the use of AOPs in chemical RA remains limited. The objective of this paper is to address issues related to using AOPs in a regulatory context from various perspectives as it was discussed in a workshop organized within the European Union partnerships HBM4EU and PARC in spring 2022. The paper presents examples where the AOP framework has been proven useful for the human RA process, particularly in hazard prioritization and characterization, in integrated approaches to testing and assessment (IATA), and in the identification and validation of BoE in epidemiological studies. Nevertheless, several limitations were identified that hinder the optimal usability and acceptance of AOPs by the regulatory community including the lack of quantitative information on response-response relationships and of efficient ways to map chemical data (exposure and toxicity) onto AOPs. The paper summarizes suggestions, ongoing initiatives and third-party tools that may help to overcome these obstacles and thus assure better implementation of AOPs in the NGRA.

Cumulative maternal and neonatal effects of combined exposure to a mixture of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) during pregnancy in the Sprague-Dawley rat

Globally, biomonitoring data demonstrate virtually all humans carry residues of multiple per- and polyfluoroalkyl substances (PFAS). Despite pervasive co-exposure, limited mixtures-based in vivo PFAS toxicity research has been conducted. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are commonly detected PFAS in human and environmental samples and both produce adverse effects in laboratory animal studies, including maternal and offspring effects when orally administered during pregnancy and lactation. To evaluate the effects of combined exposure to PFOA and PFOS, we orally exposed pregnant Sprague-Dawley rats from gestation day 8 (GD8) to postnatal day 2 (PND2) to PFOA (10-250 mg/kg/d) or PFOS (0.1-5 mg/kg/d) individually to characterize effects and dose response curve parameters, followed by a variable-ratio mixture experiment with a constant dose of PFOS (2 mg/kg/d) mixed with increasing doses of PFOA (3-80 mg/kg/d). The mixture study design was intended to: 1) shift the PFOA dose response curves for endpoints shared with PFOS, 2) allow comparison of dose addition (DA) and response addition (RA) model predictions, 3) conduct relative potency factor (RPF) analysis for multiple endpoints, and 4) avoid overt maternal toxicity. Maternal serum and liver concentrations of PFOA and PFOS were consistent between the individual chemical and mixture experiments. Combined exposure with PFOS significantly shifted the PFOA dose response curves towards effects at lower doses compared to PFOA-only exposure for multiple endpoints and these effects were well predicted by dose addition. For endpoints amenable to mixture model analyses, DA produced equivalent or better estimates of observed data than RA. All endpoints evaluated were accurately predicted by RPF and DA approaches except for maternal gestational weight gain, which produced less-than-additive results in the mixture. Data support the hypothesis of cumulative effects on shared endpoints from PFOA and PFOS co-exposure and dose additive approaches for predictive estimates of mixture effects.

Interaction between mono-(2-ethylhexyl) phthalate and retinoic acid alters Sertoli cell development during fetal mouse testis cord morphogenesis

Phthalic acid esters (phthalates) are a class of industrial chemicals that cause developmental and reproductive toxicity, but there are significant gaps in knowledge of phthalate toxicity mechanisms. There is evidence that phthalates disrupt retinoic acid signaling in the fetal testis, potentially disrupting control of spatial and temporal patterns of testis development. Our goal was to determine how a phthalate would interact with retinoic acid signaling during fetal mouse testis development. We hypothesized that mono-(2-ethylhexyl) phthalate (MEHP) would exacerbate the adverse effect of all-trans retinoic acid (ATRA) on seminiferous cord development in the mouse fetal testis. To test this hypothesis, gestational day (GD) 14 C57BL/6 mouse testes were isolated and cultured on media containing MEHP, ATRA, or a combination of both compounds. Cultured testes were collected for global transcriptome analysis after one day in culture and for histology and immunofluorescent analysis of Sertoli cell differentiation after three days in culture. ATRA disrupted seminiferous cord morphogenesis and induced aberrant FOXL2 expression. MEHP alone had no significant effect on cord development, but combined exposure to MEHP and ATRA increased the number of FOXL2-positive cells, reduced seminiferous cord number, and increased testosterone levels, beyond the effect of ATRA alone. In RNA-seq analysis, ATRA treatment and MEHP treatment resulted in differential expression of genes 510 and 134 genes, respectively, including 70 common differentially expressed genes (DEGs) between the two treatments, including genes with known roles in fetal testis development. MEHP DEGs included RAR target genes, genes involved in angiogenesis, and developmental patterning genes, including members of the homeobox superfamily. These results support the hypothesis that MEHP modulates retinoic acid signaling in the mouse fetal testis and provide insight into potential mechanisms by which phthalates disrupt seminiferous cord morphogenesis.

Critical review and analysis of literature on low dose exposure to chemical mixtures in mammalian in vivo systems

Anthropogenic chemicals are ubiquitous throughout the environment. Consequentially, humans are exposed to hundreds of anthropogenic chemicals daily. Current chemical risk assessments are primarily based on testing individual chemicals in rodents at doses that are orders of magnitude higher than that of human exposure. The potential risk from exposure to mixtures of chemicals is calculated using mathematical models of mixture toxicity based on these analyses. These calculations, however, do not account for synergistic or antagonistic interactions between co-exposed chemicals. While proven examples of chemical synergy in mixtures at low doses are rare, there is increasing evidence that, through non-conformance to current mixture toxicity models, suggests synergy. This review examined the published studies that have investigated exposure to mixtures of chemicals at low doses in mammalian in vivo systems. Only seven identified studies were sufficient in design to directly examine the appropriateness of current mixture toxicity models, of which three showed responses significantly greater than additivity model predictions. While the remaining identified studies were unable to provide evidence of synergistic toxicity, it became apparent that many results of such studies were not always explicable by current mixture toxicity models. Additionally, two data gaps were identified. Firstly, there is a lack of studies where individual chemical components of a complex mixture (>10 components) are tested in parallel to the chemical mixture. Secondly, there is a lack of dose-response data for mixtures of chemicals at low doses. Such data is essential to address the appropriateness and validity of future chemical mixture toxicity models.

In utero exposure to a mixture of the perfluoroalkyl-isopropyl pesticide pyrifluquinazon with dibutyl phthalate cumulatively disrupts male rat reproductive development via different mechanisms of action

Administration of individual chemicals and mixtures during sexual differentiation that disrupt the androgen signaling pathway can induce reproductive abnormalities in male rats. In the current study, we co-administered the heptafluoroisopropyl pesticide pyrifluquinazon (PFQ), and dibutyl phthalate (DBP) to pregnant rats during sexual differentiation of the reproductive tract. Both chemicals have been shown to disrupt reproductive tract differentiation in a dose-related manner reducing male anogenital distance (AGD), permanently reducing androgen-dependent tissue weights and sperm counts, and inducing reproductive malformations in male offspring, albeit by different mechanisms of action that converge downstream in the androgen signaling pathway on a common key event. Rats were orally dosed from gestation days 14-18 with dilutions of PFQ and DBP at 0, 12.5, 25, 50, 75 and 100% of the top dose (100 mg/kg PFQ and 750 mg/kg DBP). The mixture ratio was selected such that each chemical would contribute equally to multiple effects on the male offspring reproductive tract and the dose range was designed to determine if the mixture produced additive effects predicted by dose addition or response addition models, or whether significant interactions occurred. Observed data were compared to dose and response addition model predictions. As hypothesized, the mixture reduced F1 male AGD, reproductive organ weights and sperm counts and induced hypospadias with dose addition consistently providing a better prediction of the observed effects than response addition. These results support our hypothesis that chemicals that disrupt the androgen signaling pathway induce dose-additive male reproductive abnormalities regardless of the specific mechanism of action.

Developmental toxicity of Nafion byproduct 2 (NBP2) in the Sprague-Dawley rat with comparisons to hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX) and perfluorooctane sulfonate (PFOS)

Nafion byproduct 2 (NBP2) is a polyfluoroalkyl ether sulfonic acid that was recently detected in surface water, drinking water, and human serum samples from monitoring studies in North Carolina, USA. We orally exposed pregnant Sprague-Dawley rats to NBP2 from gestation day (GD) 14-18 (0.1-30 mg/kg/d), GD17-21, and GD8 to postnatal day (PND) 2 (0.3-30 mg/kg/d) to characterize maternal, fetal, and postnatal effects. GD14-18 exposures were also conducted with perfluorooctane sulfonate (PFOS) for comparison to NBP2, as well as data previously published for hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX). NBP2 produced stillbirth (30 mg/kg), reduced pup survival shortly after birth (10 mg/kg), and reduced pup body weight (10 mg/kg). Histopathological evaluation identified reduced glycogen stores in newborn pup livers and hepatocyte hypertrophy in maternal livers at ≥ 10 mg/kg. Exposure to NBP2 from GD14-18 reduced maternal serum total T₃ and cholesterol concentrations (30 mg/kg). Maternal, fetal, and neonatal liver gene expression was investigated using RT-qPCR pathway arrays, while maternal and fetal livers were also analyzed using TempO-Seq transcriptomic profiling. Overall, there was limited alteration of genes in maternal or F1 livers from NBP2 exposure with significant changes mostly occurring in the top dose group (30 mg/kg) associated with lipid and carbohydrate metabolism. Metabolomic profiling indicated elevated maternal bile acids for NBP2, but not HFPO-DA or PFOS, while all three reduced 3-indolepropionic acid. Maternal and fetal serum and liver NBP2 concentrations were similar to PFOS, but ∼10-30-fold greater than HFPO-DA concentrations at a given maternal oral dose. NBP2 is a developmental toxicant in the rat, producing neonatal mortality, reduced pup body weight, reduced pup liver glycogen, reduced maternal thyroid hormones, and altered maternal and offspring lipid and carbohydrate metabolism similar to other studied PFAS, with oral toxicity for pup loss that is slightly less potent than PFOS but more potent than HFPO-DA.

AOP key event relationship report: Linking androgen receptor antagonism with nipple retention

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A full AOP KER description linking AR antagonism with nipple retention in rodents.

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Described KER 2133 is a non-adjacent KER of an intended AOP delineating anti-androgenicity as a mode for nipple retention.

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A case study for developing and publishing independent units of information under the AOP framework.

In rat developmental and reproductive toxicity studies, nipple/areola retention (NR) in male offspring is a biomarker for reduced androgen signaling during development. This is because nipples normally regress in male rats in response to androgen signaling during critical stages of development. NR is thus included as a mandatory endpoint in several OECD test guidelines for assessment of chemicals, particularly as a readout for anti-androgenic effects relevant for reproductive toxicity. With the growing interest in developing Adverse Outcome Pathways (AOPs) to aid in chemical risk assessment, a more pragmatic approach has been proposed, whereby essential units of knowledge could be developed independently of complete AOPs, not least emergent key event relationships (KERs). Herein, we have developed a KER linking “androgen receptor antagonism” and “increased areola/nipple retention”. The KER is based on a literature review conducted in a transparent semi-systematic manner in peer-reviewed databases with pre-defined inclusion criteria. Twenty-seven papers were included for development of the KER. The results support a qualitative relationship between the two key events (KEs) with a high weight of evidence; i.e., a causal relationship between androgen receptor (AR) antagonism and nipple retention in male rats exists.

Prenatal exposure to phenols and benzophenones in relation to markers of male reproductive function in adulthood

INTRODUCTION

Environmental exposure during fetal life may disrupt testicular development. In humans, a limited number of studies have investigated whether these adverse effects persist into adulthood. Using data from a prospective, population-based birth cohort study, The Copenhagen Mother-Child cohort, the objective was to assess if there is an association between fetal exposure to selected phenols and benzophenones and markers of testicular function in adult men.

METHODS

Pregnant women were recruited in 1997-2001. Their sons were examined clinically at 18-20 years of age, with focus on adult markers of reproductive function (anogenital distance (AGD), semen quality and reproductive hormones). In total, 101 18-20-year-old men were included, whose mothers during pregnancy had a serum sample drawn and analyzed for bisphenol A (BPA) and seven other simple phenols, as well as six benzophenones. To investigate the association between chemical levels (in tertiles, T1-T3) in relation to markers of reproductive function, univariate and multiple linear regression analyses were performed.

RESULTS

In fully adjusted analyses, increased levels of luteinizing hormone (LH) were observed with higher fetal exposure to BPA (percentage difference (95%CI)) (T2: 12% (-8%,36%) and T3: 33% (10%,62%), compared to T1) and benzophenone-3 (BP-3) (T2: 21% (-2%,49%), T3: 18% (-4%,45%)), while no clear association was seen to total testosterone (TT). Higher levels of BPA and BP-3 were associated with a lower TT/LH ratio, although only significant for BPA (p-trend=0.01). No associations were seen to AGD or markers of semen quality.

CONCLUSION

In conclusion, high exposure to BPA and BP-3 was associated with a compensated reduced Leydig cell function but no other changes in markers of reproductive health. As maternal levels of BPA and BP-3 were not correlated, separate effects may be at play. Larger studies on long-term reproductive consequences of prenatal exposures are warranted to validate our findings.

A mixture of 15 phthalates and pesticides below individual chemical no observed adverse effect levels (NOAELs) produces reproductive tract malformations in the male rat

Humans carry residues of multiple synthetic chemicals at any given point in time. Research has demonstrated that compounds with varying molecular initiating events (MIE) that disrupt common key events can act in concert to produce cumulative adverse effects. Congenital defects of the male reproductive tract are some of the most frequently diagnosed malformations in humans and chemical exposures in utero can produce these effects in laboratory animals and humans. Here, we hypothesized that in utero exposure to a mixture of pesticides and phthalates, each of which produce male reproductive tract defects individually, would produce cumulative effects even when each chemical is present at a no observed adverse effect level (NOAEL) specific for male reproductive effects. Pregnant Sprague-Dawley rats were exposed via oral gavage to a fixed-ratio dilution mixture of 5 pesticides (vinclozolin, linuron, procymidone, prochloraz, pyrifluquinazon), 1 pesticide metabolite (dichlorodiphenyldichloroethylene (DDE)), and 9 phthalates (dipentyl, dicyclohexyl, di-2-ethylhexyl, dibutyl, benzyl butyl, diisobutyl, diisoheptyl, dihexyl, and diheptyl) during the critical window of rat fetal masculinization (gestation day 14-18). The top dose (100% dose) contained each compound at a concentration 2-fold greater than the individual chemical NOAEL followed by a dilution series that represented each chemical at NOAEL, NOAEL/2, NOAEL/4, NOAEL/8, NOAEL/15, NOAEL/100, NOAEL/1000. Reduced fetal testis gene expression occurred at NOAEL/15, reduced fetal testis testosterone production occurred at NOAEL/8, reduced anogenital distance, increased nipple retention, and delayed puberty occurred at NOAEL/4, and severe effects including genital malformations and weight reductions in numerous reproductive tissues occurred at NOAEL/2. This study demonstrates that these phthalates and pesticides acted cumulatively to produce adverse effects at doses below which any individual chemical had been shown to produce an effect alone and even though they have different MIEs.

Genomic and Hormonal Biomarkers of Phthalate-Induced Male Rat Reproductive Developmental Toxicity Part II: A Targeted RT-qPCR Array Approach That Defines a Unique Adverse Outcome Pathway

Previously, we demonstrated that exposure to some diortho-phthalate esters during sexual differentiation disrupts male reproductive development by reducing fetal rat testis testosterone production (T Prod) and gene expression in a dose-related manner. The objectives of the current project were to expand the number of test compounds that might reduce fetal T Prod, including phthalates, phthalate alternatives, pesticides, and drugs, and to compare reductions in T Prod with altered testis mRNA expression. We found that PEs that disrupt T Prod also reduced expression of a unique "cluster" of mRNAs for about 35 genes related to sterol transport, testosterone and insulin-like hormone 3 hormone syntheses, and lipoprotein signaling and cholesterol synthesis. However, phthalates had little or no effect on mRNA expression of genes in peroxisome proliferator-activated receptor (PPAR) pathways in the fetal liver, whereas the 3 PPAR agonists induced the expression of mRNA for multiple fetal liver PPAR pathway genes without reducing testis T Prod. In summary, phthalates that disrupt T Prod act via a novel adverse outcome pathway including down regulation of mRNA for genes involved in fetal endocrine function and cholesterol synthesis and metabolism. This profile was not displayed by PEs that did not reduce T Prod, PPAR agonists or the other chemicals. Reductions in fetal testis gene expression and T Prod in utero can be used to establish relative potency factors that can be used quantitatively to predict the doses of individual PEs and mixtures of phthalates that produce adverse reproductive tract effects in male offspring.

Quantification of the Uncertainties in Extrapolating From In Vitro Androgen Receptor Antagonism to In Vivo Hershberger Assay Endpoints and Adverse Reproductive Development in Male Rats

Multiple molecular initiating events exist that disrupt male sexual differentiation in utero including androgen receptor (AR) antagonism and inhibition of synthesis, and metabolism of fetal testosterone. Disruption of androgen signaling by AR antagonists in utero reduces anogenital distance (AGD) and induces malformations in F1 male rat offspring. We are developing a quantitative network of adverse outcome pathways that includes multiple molecular initiating events and key events linking anti-AR activities to permanent reproductive abnormalities. Here, our objective was to determine how accurately the EC50s for AR antagonism in vitro or ED50s for reduced tissue growth in the Hershberger assay (HA) (key events in the adverse outcome pathway) predict the ED50s for reduced AGD in male rats exposed in utero to AR antagonists. This effort included in-house data and published studies from the last 60 years on AR antagonism in vitro and in vivo effects in the HA and on AGD after in utero exposure. In total, more than 250 studies were selected and included in the analysis with data from about 60 potentially antiandrogenic chemicals. The ability to predict ED50s for key events and adverse developmental effects from the in vitro EC50s displays considerable uncertainty with R2 values for HA and AGD of < 6%. In contrast, there is considerably less uncertainty in extrapolating from the ED50s in the HA to the ED50s for AGD (R2 value of about 85%). In summary, the current results suggest that the key events measured in the HA can be extrapolated with reasonable certainty to predict the ED50s for the adverse in utero effects of antiandrogenic chemicals on male rat offspring.

Endocrine disrupting potential of replacement flame retardants - Review of current knowledge for nuclear receptors associated with reproductive outcomes

BACKGROUND AND AIM

Endocrine disrupting chemicals (EDCs) constitute a major public health concern because they can induce a large spectrum of adverse effects by interfering with the hormonal system. Rapid identification of potential EDCs using in vitro screenings is therefore critical, particularly for chemicals of emerging concerns such as replacement flame retardants (FRs). The review aimed at identifying (1) data gaps and research needs regarding endocrine disrupting (ED) properties of replacement FRs and (2) potential EDCs among these emerging chemicals.

METHODS

A systematic search was performed from open literature and ToxCast/Tox21 programs, and results from in vitro tests on the activities of 52 replacement FRs towards five hormone nuclear receptors (NRs) associated with reproductive outcomes (estrogen, androgen, glucocorticoid, progesterone, and aryl hydrocarbon receptors) were compiled and organized into tables. Findings were complemented with information from structure-based in silico model predictions and in vivo information when relevant.

RESULTS

For the majority of the 52 replacement FRs, experimental in vitro data on activities towards these five NRs were either incomplete (15 FRs) or not found (24 FRs). Within the replacement FRs for which effect data were found, some appeared as candidate EDCs, such as triphenyl phosphate (TPhP) and tris(1,3-dichloropropyl)phosphate (TDCIPP). The search also revealed shared ED profiles. For example, anti-androgenic activity was reported for 19 FRs and predicted for another 21 FRs.

DISCUSSION

This comprehensive review points to critical gaps in knowledge on ED potential for many replacement FRs, including chemicals to which the general population is likely exposed. Although this review does not cover all possible characteristics of ED, it allowed the identification of potential EDCs associated with reproductive outcomes, calling for deeper evaluation and possibly future regulation of these chemicals. By identifying shared ED profiles, this work also raises concerns for mixture effects since the population is co-exposed to several FRs and other chemicals.

Vinclozolin-induced mouse penile malformation and "small testis" via miR132, miR195a together with the Hippo signaling pathway

Vinclozolin (VCZ) is a fungicide with antiandrogen activity. Exposure to VCZ in maternal uterus may cause uterine, ovarian and testicular damage, hypospadias and prostate abnormality in the offspring. Hippo pathway, which is highly conservative and may be activated by miR132 and miR195a, can control organ size and tissue regeneration, and participate in injury and deformity. In the present study, VCZ was found to have caused penile malformation in the male offspring and also induced "small testis" when it was administered to the pregnant mice orally at a dose of 400 mg kg^-1 day^-1 on Days 12-18 of gestation. At 1, 3 and 7 weeks of age, VCZ could increase miR132, Mst1, Sav1, phosphorylated Yes-associated protein (pYap) and pLats, and decrease Yap in offspring penises and testes. Besides, it could also raise miR195a both in the testes of 1, 7-week and in the penises of all the three ages. In addition, we found the levels of some cyclin (Ccn) genes elevated in the testes, the expression of the androgen receptor (Ar) gene dereased and Jnks changed in the penises of offspring aged 1, 3 and 7 weeks. The results suggest that that gestational VCZ exposure could not only increase miR132 and miR195a in penises and testes of the offspring, but also activate Hippo pathway and down-regulate Ar. These may directly inhibit cell proliferation, accelerate cell death by up-regulating the expression of some Ccns, and ultimately lead to penile and testicular damage and malformations in the offspring.

Analysis for data-derived extrapolation factors for procymidone

The derivation of Chemical Specific Adjustment Factors (CSAFs) (IPCS, 2005; U.S. EPA, 2014) depends on the choice of appropriate dose metric. EPA and IPCS guidance was applied to derive a CSAF for developmental toxicity for procymidone (PCM). Although kinetic data were not available in humans at any dose, sufficient toxicokinetic data are available in a surrogate species, primates, and from chimeric mice with both rat and human liver cells to offer insights. Alternative approaches were explored in the derivation of the CSAG based on review of the available kinetic data. The most likely dosimetric adjustment is the Cmax based on the character of the critical effect - reduced anogenital distance and increased incidence of hypospadias in male rats, which likely occurs during a small window of time during development of the rat fetus. Cmax is also the default dosimeter from U.S. EPA (1991). However, in this case, the use of Cmax is also likely more conservative than the use of area under the curve (AUC), which otherwise is the default recommendation of the IPCS (2005). Despite human data, estimated tentative CSAF value is 0.48 (range, 0.22 to 0.74). The use of any of these values would be supported by the available data.

Androgens and the masculinization programming window: human-rodent differences

Human male reproductive disorders are common and may have a fetal origin - the testicular dysgenesis syndrome (TDS) hypothesis. In rats, experimentally induced TDS disorders result from disruption of fetal androgen production/action specifically in the masculinization programming window (MPW). MPW androgen action also programs longer anogenital distance (AGD) in male versus female rats; shorter male AGD is correlated with risk and severity of induced TDS disorders. AGD thus provides a lifelong, calibrated readout of MPW androgen exposure and predicts likelihood of reproductive dysfunction. Pregnant rat exposure to environmental chemicals, notably certain phthalates (e.g. diethyl hexl phthalate, DEHP; dibutyl phthalate, DBP), pesticides or paracetamol, can reduce fetal testis testosterone and AGD and induce TDS disorders, provided exposure includes the MPW. In humans, AGD is longer in males than females and the presumptive MPW is 8-14 weeks' gestation. Some, but not all, epidemiological studies of maternal DEHP (or pesticides) exposure reported shorter AGD in sons, but this occurred at DEHP exposure levels several thousand-fold lower than are effective in rats. In fetal human testis culture/xenografts, DEHP/DBP do not reduce testosterone production, whereas therapeutic paracetamol exposure does. In humans, androgen production in the MPW is controlled differently (human chorionic gonadotrophin-driven) than in rats (paracrine controlled), and other organs (placenta, liver, adrenals) contribute to MPW androgens, essential for normal masculinization, via the 'backdoor pathway'. Consequently, early placental dysfunction, which is affected by maternal lifestyle and diet, and maternal painkiller use, may be more important than environmental chemical exposures in the origin of TDS in humans.

Chemical Mixture Calculator - A novel tool for mixture risk assessment

Humans are continuously exposed to complex chemical mixtures from foods and the environment. Experimental models in vivo and in vitro have increased our knowledge on how we can predict mixture effects. To accommodate a need for tools for efficient mixture risk assessment across different chemical classes and exposure sources, we have developed fit-for-purpose criteria for grouping of chemicals and a web-based tool for mixture risk assessment. The Chemical Mixture Calculator (available at www.chemicalmixturecalculator.dk) can be used for mixture risk assessment or identification of main drivers of risk. The underlying database includes hazard and exposure estimates for more than 200 chemicals in foods and environment. We present a range of cumulative assessment groups for effects on haematological system, kidney, liver, nervous system, developmental and reproductive system, and thyroid. These cumulative assessment groups are useful for grouping of chemicals at several levels of refinement depending on the question addressed. We present a mixture risk assessment case for phthalates, evaluated with and without contributions from other chemicals with similar effects. This case study shows the usefulness of the tool as a starting point for mixture risk assessment by the risk assessor, and emphasizes that solid scientific insight regarding underlying assumptions and uncertainties is crucial for result interpretation.

Estrogens and development of the rete testis, efferent ductules, epididymis and vas deferens

Estrogen has always been considered the female hormone and testosterone the male hormone. However, estrogen's presence in the testis and deleterious effects of estrogen treatment during development have been known for nearly 90 years, long before estrogen receptors (ESRs) were discovered. Eventually it was learned that testes actually synthesize high levels of estradiol (E2) and sequester high concentrations in the reproductive tract lumen, which seems contradictory to the overwhelming number of studies showing reproductive pathology following exogenous estrogen exposures. For too long, the developmental pathology of estrogen has dominated our thinking, even resulting in the "estrogen hypothesis" as related to the testicular dysgenesis syndrome. However, these early studies and the development of an Esr1 knockout mouse led to a deluge of research into estrogen's potential role in and disruption of development and function of the male reproductive system. What is new is that estrogen action in the male cannot be divorced from that of androgen. This paper presents what is known about components of the estrogen pathway, including its synthesis and target receptors, and the need to achieve a balance between androgen- and estrogen-action in male reproductive tract differentiation and adult functions. The review focuses on what is known regarding development of the male reproductive tract, from the rete testis to the vas deferens, and examines the expression of estrogen receptors and presence of aromatase in the male reproductive system, traces the evidence provided by estrogen-associated knockout and transgenic animal models and discusses the effects of fetal and postnatal exposures to estrogens. Hopefully, there will be enough here to stimulate discussions and new investigations of the androgen:estrogen balance that seems to be essential for development of the male reproductive tract.

Using the Key Characteristics of Carcinogens to Develop Research on Chemical Mixtures and Cancer

BACKGROUND

People are exposed to numerous chemicals throughout their lifetimes. Many of these chemicals display one or more of the key characteristics of carcinogens or interact with processes described in the hallmarks of cancer. Therefore, evaluating the effects of chemical mixtures on cancer development is an important pursuit. Challenges involved in designing research studies to evaluate the joint action of chemicals on cancer risk include the time taken to perform the experiments because of the long latency and choosing an appropriate experimental design.

OBJECTIVES

The objectives of this work are to present the case for developing a research program on mixtures of environmental chemicals and cancer risk and describe recommended approaches.

METHODS

A working group comprising the coauthors focused attention on the design of mixtures studies to inform cancer risk assessment as part of a larger effort to refine the key characteristics of carcinogens and explore their application. Working group members reviewed the key characteristics of carcinogens, hallmarks of cancer, and mixtures research for other disease end points. The group discussed options for developing tractable projects to evaluate the joint effects of environmental chemicals on cancer development.

RESULTS AND DISCUSSION

Three approaches for developing a research program to evaluate the effects of mixtures on cancer development were proposed: a chemical screening approach, a transgenic model-based approach, and a disease-centered approach. Advantages and disadvantages of each are discussed. https://doi.org/10.1289/EHP8525.

Application of a Framework for Grouping and Mixtures Toxicity Assessment of PFAS: A Closer Examination of Dose-Additivity Approaches

Environmental occurrence and biomonitoring data for per- and polyfluoroalkyl substances (PFAS) demonstrate that humans are exposed to mixtures of PFAS. This article presents a new and systematic analysis of available PFAS toxicity study data using a tiered mixtures risk assessment framework consistent with United States and international mixtures guidance. The lines of evidence presented herein include a critique of whole mixture toxicity studies and analysis of dose-response models based on data from subchronic oral toxicity studies in rats. Based on available data to-date, concentration addition and relative potency factor methods are found to be inappropriate due to differences among sensitive effects and target organ potencies and noncongruent dose-response curves for the same effect endpoints from studies using the same species and protocols. Perfluorooctanoic acid and perfluorooctane sulfonic acid lack a single mode of action or molecular initiating event and our evaluation herein shows they also have noncongruent dose-response curves. Dose-response curves for long-chain perfluoroalkyl sulfonic acids (PFSAs) also significantly differ in shapes of the curves from short-chain PFSAs and perfluoroalkyl carboxylic acids evaluated, and additional differences are apparent when curves are evaluated based on internal or administered dose. Following well-established guidance, the hazard index method applied to perfluoroalkyl carboxylic acids and PFSAs grouped separately is the most appropriate approach for conducting a screening level risk assessment for nonpolymeric PFAS mixtures, given the current state-of-the science. A clear presentation of assumptions, uncertainties, and data gaps is needed before dose-additivity methods, including hazard index , are used to support risk management decisions. Adverse outcome pathway(s) and mode(s) of action information for perfluorooctanoic acid and perfluorooctane sulfonic acid and for other nonpolymer PFAS are key data gaps precluding more robust mixtures methods. These findings can guide the prioritization of future studies on single chemical and whole mixture toxicity studies.

Testing the low dose mixtures hypothesis from the Halifax project

In 2013, 60 scientists, representing a larger group of 174 scientists from 26 nations, met in Halifax, Nova Scotia to consider whether - using published research - it was logical to anticipate that a mixture of chemicals, each thought to be non-carcinogenic, might act together in that mixture as a virtual carcinogen. The group identified 89 such chemicals, each one affecting one or more Hallmark(s) - collectively covering all Hallmarks of Cancer - confirming the possibility that a chemical mixture could induce all the Hallmarks and function as a virtual carcinogen, thereby supporting the concern that chemical safety research that does not evaluate mixtures, is incomplete. Based on these observations, the Halifax Project developed the Low-Dose Carcinogenesis Hypothesis which posits "…that low-dose exposures to [mixtures of] disruptive chemicals that are not individually carcinogenic may be capable of instigating and/or enabling carcinogenesis." Although testing all possible combinations of over 80,000 chemicals of commerce would be impractical, prudence requires designing a methodology to test whether low-dose chemical mixtures might be carcinogenic. As an initial step toward testing this hypothesis, we conducted a mini review of published empirical observations of biological exposures to chemical mixtures to assess what empirical data exists on which to base future research. We reviewed studies on chemical mixtures with the criteria that the studies reported both different concentrations of chemicals and mixtures composed of different chemicals. We found a paucity of research on this important question. The majority of studies reported hormone related processes and used chemical concentrations selected to facilitate studying how mixtures behave in experiments that were often removed from clinical relevance, i.e., chemicals were not studied at human-relevant concentrations. New research programs must be envisioned to enable study of how mixtures of small doses of chemicals affect human health, starting, when at all possible, from non-malignant specimens when studies are done in vitro. This research should use human relevant concentrations of chemicals, expand research beyond the historic focus on endocrine endpoints and endocrine related cancers, and specifically seek effects that arise uniquely from exposure to chemical mixtures at human-relevant concentrations.

Grouping of endocrine disrupting chemicals for mixture risk assessment - Evidence from a rat study

Exposure to mixtures of endocrine disrupting chemicals may contribute to the rising incidence of hormone-related diseases in humans. Real-life mixtures are complex, comprised of chemicals with mixed modes of action, and essential knowledge is often lacking on how to group such chemicals into cumulative assessment groups, which is an essential prerequisite to conduct a chemical mixture risk assessment. We investigated if mixtures of chemicals with diverse endocrine modes of action can cause mixture effects on hormone sensitive endpoints in developing and adult rat offspring after perinatal exposure. Wistar rats were exposed during pregnancy and lactation simultaneously to either bisphenol A and butylparaben (Emix), diethylhexyl phthalate and procymidone (Amix), or a mixture of all four substances (Totalmix). In male offspring, the anogenital distance was significantly reduced and nipple retention increased in animals exposed to Amix and Totalmix, and the mixture effects were well approximated by the dose addition model. The combination of Amix and Emix responded with more marked changes on these and other endocrine-sensitive endpoints than each binary mixture on its own. Sperm counts were reduced by all exposures. These experimental outcomes suggest that the grouping of chemicals for mixture risk assessment should be based on common health outcomes rather than only similar modes or mechanisms of action. Mechanistic-based approaches such as the concept of Adverse Outcome Pathway (AOP) can provide important guidance if both the information on shared target tissues and the information on shared mode/mechanism of action are taken into account.

Maternal exposure to mixtures of dienestrol, linuron and flutamide. Part II: Endocrine-related gene expression assessment on male offspring rat testes

Exposure to endocrine-disrupting compounds (EDCs) during pregnancy and early development can lead to adverse developmental outcomes in offspring. One of the endpoints of concern is feminization. The present study aimed to investigate for any possible correlations with endocrine sensitive parameters in the testes of male rat offspring following dam exposure to three EDCs by assessing the expression of endocrine-related genes. Dienestrol (DIES) [0.37-6.25 μg/kg bw/day], linuron (LIN) [1.5-50 mg/kg bw/day], flutamide (FLU) [3.5-50 mg/kg bw/day] as well as their binary mixtures were administered to sexually mature female rats from gestation day (GD) 6 until postnatal day (PND) 21. Gene expression analysis of Star, Cyp11a1, Cyp17a1, Hsd3b2, Pgr and Insl3 was performed by RT-qPCR. Administration of the anti-androgen FLU alone significantly upregulated Cyp11a1 and Cyp17a1 gene expression while administration of LIN and DIES alone did not alter significantly gene expression. The effects of the binary mixtures on gene expression were not as marked as those seen after single compound administrations. Deregulation of Cyp17a1 in rat pup testis, following administration of FLU alone or in mixtures to dams, was significantly correlated with the observed feminization endpoints in male pups.

Organizing mechanism-related information on chemical interactions using a framework based on the aggregate exposure and adverse outcome pathways

This paper presents a framework for organizing and accessing mechanistic data on chemical interactions. The framework is designed to support the assessment of risks from combined chemical exposures. The framework covers interactions between chemicals that occur over the entire source-to-outcome continuum including interactions that are studied in the fields of chemical transport, environmental fate, exposure assessment, dosimetry, and individual and population-based adverse outcomes. The framework proposes to organize data using a semantic triple of a chemical (subject), has impact (predicate), and a causal event on the source-to-outcome continuum of a second chemical (object). The location of the causal event on the source-to-outcome continuum and the nature of the impact are used as the basis for a taxonomy of interactions. The approach also builds on concepts from the Aggregate Exposure Pathway (AEP) and Adverse Outcome Pathway (AOP). The framework proposes the linking of AEPs of multiple chemicals and the AOP networks relevant to those chemicals to form AEP-AOP networks that describe chemical interactions that cannot be characterized using AOP networks alone. Such AEP-AOP networks will aid the construction of workflows for both experimental design and the systematic review or evaluation performed in risk assessments. Finally, the framework is used to link the constructs of existing component-based approaches for mixture toxicology to specific categories in the interaction taxonomy.

Adverse Outcome Pathway Network-Based Assessment of the Interactive Effects of an Androgen Receptor Agonist and an Aromatase Inhibitor on Fish Endocrine Function

Predictive approaches to assessing the toxicity of contaminant mixtures have been largely limited to chemicals that exert effects through the same biological molecular initiating event. However, by understanding specific pathways through which chemicals exert effects, it may be possible to identify shared "downstream" nodes as the basis for forecasting interactive effects of chemicals with different molecular initiating events. Adverse outcome pathway (AOP) networks conceptually support this type of analysis. We assessed the utility of a simple AOP network for predicting the effects of mixtures of an aromatase inhibitor (fadrozole) and an androgen receptor agonist (17β-trenbolone) on aspects of reproductive endocrine function in female fathead minnows. The fish were exposed to multiple concentrations of fadrozole and 17β-trenbolone individually or in combination for 48 or 96 h. Effects on 2 shared nodes in the AOP network, plasma 17β-estradiol (E2) concentration and vitellogenin (VTG) production (measured as hepatic vtg transcripts) responded as anticipated to fadrozole alone but were minimally impacted by 17β-trenbolone alone. Overall, there were indications that 17β-trenbolone enhanced decreases in E2 and vtg in fadrozole-exposed fish, as anticipated, but the results often were not statistically significant. Failure to consistently observe hypothesized interactions between fadrozole and 17β-trenbolone could be due to several factors, including lack of impact of 17β-trenbolone, inherent biological variability in the endpoints assessed, and/or an incomplete understanding of interactions (including feedback) between different pathways within the hypothalamic-pituitary-gonadal axis. Environ Toxicol Chem 2020;39:913-922. © 2020 SETAC.

Generalized Concentration Addition Model Predicts Glucocorticoid Activity Bioassay Responses to Environmentally Detected Receptor-Ligand Mixtures

Many glucocorticoid receptor (GR) agonists have been detected in waste and surface waters domestically and around the world, but the way a mixture of these environmental compounds may elicit a total glucocorticoid activity response in water samples remains unknown. Therefore, we characterized 19 GR ligands using a CV1 cell line transcriptional activation assay applicable to water quality monitoring. Cells were treated with individual GR ligands, a fixed ratio mixture of full or partial agonists, or a nonequipotent mixture with full and partial agonists. Efficacy varied (48.09%-102.5%) and potency ranged over several orders of magnitude (1.278 × 10-10 to 3.93 × 10-8 M). Concentration addition (CA) and response addition (RA) mixtures models accurately predicted equipotent mixture responses of full agonists (r2 = 0.992 and 0.987, respectively). However, CA and RA models assume mixture compounds produce full agonist-like responses, and therefore they overestimated observed maximal efficacies for mixtures containing partial agonists. The generalized concentration addition (GCA) model mathematically permits < 100% maximal responses, and fell within the 95% confidence interval bands of mixture responses containing partial agonists. The GCA, but not CA and RA, model predictions of nonequipotent mixtures containing both full and partial agonists fell within the same statistical distribution as the observed values, reinforcing the practicality of the GCA model as the best overall model for predicting GR activation. Elucidating the mechanistic basis of GR activation by mixtures of previously detected environmental GR ligands will benefit the interpretation of environmental sample contents in future water quality monitoring studies.

Phthalate metabolites in urine of children and adolescents in Germany. Human biomonitoring results of the German Environmental Survey GerES V, 2014-2017

During the population representative German Environmental Survey of Children and Adolescents (GerES V, 2014-2017) 2256 first-morning void urine samples from 3 to 17 years old children and adolescents were analysed for 21 metabolites of 11 different phthalates (di-methyl phthalate (DMP), di-ethyl phthalate (DEP), butylbenzyl phthalate (BBzP), di-iso-butyl phthalate (DiBP), di-n-butyl phthalate (DnBP), di-cyclohexyl phthalate (DCHP), di-n-pentyl phthalate (DnPeP), di-(2-ethylhexyl) phthalate (DEHP), di-iso-nonyl phthalate (DiNP), di-iso-decyl phthalate (DiDP) and di-n-octyl phthalate (DnOP)). Metabolites of DMP, DEP, BBzP, DiBP, DnBP, DEHP, DiNP and DiDP were found in 97%-100% of the participants, DCHP and DnPeP in 6%, and DnOP in none of the urine samples. Geometric means (GM) were highest for metabolites of DiBP (MiBP: 26.1 μg/L), DEP (MEP: 25.8 μg/L), DnBP (MnBP: 20.9 μg/L), and DEHP (cx-MEPP: 11.9 μg/L). For all phthalates but DEP, GMs were consistently higher in the 3-5 years old children than in the 14-17 years old adolescents. For DEHP, the age differences were most pronounced. All detectable phthalate biomarker concentrations were positively associated with the levels of the respective phthalate in house dust. In GerES V we found considerably lower phthalate biomarker levels than in the preceding GerES IV (2003-2006). GMs of biomarker levels in GerES V were only 18% (BBzP), 23% (MnBP), 23% (DEHP), 29% (MiBP) and 57% (DiNP) of those measured a decade earlier in GerES IV. However, some children and adolescents still exceeded health-based guidance values in the current GerES V. 0.38% of the participants had levels of DnBP, 0.08% levels of DEHP and 0.007% levels of DiNP which were higher than the respective health-based guidance values. Accordingly, for these persons an impact on health cannot be excluded with sufficient certainty. The ongoing and substantial exposure of vulnerable children and adolescents to many phthalates confirms the need of a continued monitoring of established phthalates, whether regulated or not, as well as of potential substitutes. With this biomonitoring approach we provide a picture of current individual and cumulative exposure developments and body burdens to phthalates, thus providing support for timely and effective chemicals policies and legislation.

Mechanisms of Testicular Disruption from Exposure to Bisphenol A and Phtalates

Great attention has been paid in recent years to the harmful effects of various chemicals that interfere with our natural hormone balance, collectively known as endocrine-disrupting chemicals (EDCs) or endocrine disruptors. The effects on the reproductive system of bisphenol A (BPA) and phthalates have received particular attention: while they have a short half-life, they are so widespread that human exposure can be considered as continuous. Evidence is often limited to the animal model, disregarding the likelihood of human exposure to a mixture of contaminants. Data from animal models show that maternal exposure probably has harmful effects on the male fetus, with an increased risk of urogenital developmental abnormalities. After birth, exposure is associated with changes in the hypothalamic-pituitary-testicular axis, hindering the development and function of the male genital pathways through the mediation of inflammatory mechanisms and oxidative stress. The epidemiological and clinical evidence, while generally confirming the association between reproductive abnormalities and some phthalate esters and BPA, is more contradictory, with wildly different findings. The aim of this review is therefore to provide an update of the potential mechanisms of the damage caused by BPA and phthalates to reproductive function and a review of the clinical evidence currently available in the literature.

De Facto Water Reuse: Bioassay suite approach delivers depth and breadth in endocrine active compound detection

Although endocrine disrupting compounds have been detected in wastewater and surface waters worldwide using a variety of in vitro effects-based screening tools, e.g. bioassays, few have examined potential attenuation of environmental contaminants by both natural (sorption, degradation, etc.) and anthropogenic (water treatment practices) processes. This study used several bioassays and quantitative chemical analyses to assess residence-time weighted samples at six sites along a river in the northeastern United States beginning upstream from a wastewater treatment plant outfall and proceeding downstream along the stream reach to a drinking water treatment plant. Known steroidal estrogens were quantified and changes in signaling pathway molecular initiating events (activation of estrogen, androgen, glucocorticoid, peroxisome proliferator-activated, pregnane X receptor, and aryl hydrocarbon receptor signaling networks) were identified in water extracts. In initial multi-endpoint assays geographic and receptor-specific endocrine activity patterns in transcription factor signatures and nuclear receptor activation were discovered. In subsequent single endpoint receptor-specific bioassays, estrogen (16 of 18 samples; 0.01 to 28 ng estradiol equivalents [E2Eqs]/L) glucocorticoid (3 of 18 samples; 1.8 to 21 ng dexamethasone equivalents [DexEqs]/L), and androgen (2 of 18 samples; 0.95 to 2.1 ng dihydrotestosterone equivalents [DHTEqs]/L) receptor transcriptional activation occurred above respective assay method detection limits (0.04 ng E2Eqs/L, 1.2 ng DexEqs/L, and 0.77 ng DHTEqs/L) in multiple sampling events. Estrogen activity, the most often detected, correlated well with measured concentrations of known steroidal estrogens (r² = 0.890). Overall, activity indicative of multiple types of endocrine active compounds was highest in wastewater effluent samples, while activity downstream was progressively lower, and negligible in unfinished treated drinking water. Not only was estrogenic and glucocorticoid activity confirmed in the effluent by utilizing multiple methods concurrently, but other activated signaling networks that historically received less attention (i.e. peroxisome proliferator-activated receptor) were also detected.

Which chemicals should be grouped together for mixture risk assessments of male reproductive disorders?

There is concern about cumulative exposures to compounds that disrupt male sexual differentiation in foetal life, leading to irreversible effects in adulthood, including declines in semen quality, testes non-descent, malformations of the penis and testis cancer. Traditional chemical-by-chemical risk assessment approaches cannot capture the likely cumulative health risks. Past efforts of focusing on combinations of phthalates, a subgroup of chemicals suspected of contributing to these risks, do not go far enough, as they ignore the contribution of other types of chemicals. With the aim of providing criteria for the inclusion of additional chemicals in mixture risks assessments for male reproductive health, this paper examines the mechanisms of action of various chemicals capable of disrupting male sexual differentiation. An Adverse Outcome Pathway (AOP) network for malformations of the male reproductive system is constructed that includes new findings about the role of disruptions of prostaglandin signalling. This network is used to identify pathways that converge at critical nodal points to produce down-stream adverse effects. From this knowledge, combinations of chemicals with different mechanisms of action are predicted that should result in cumulative effects. These predictions are then mapped against evidence from experimental mixture studies with relevant combinations. From the outcome of this analysis it is concluded that cumulative assessment groups for male reproductive health risks should not only include phthalates but also comprise androgen receptor (AR) antagonists, chemicals capable of disrupting steroid synthesis, InsL3 production, prostaglandin signalling and co-planar polychlorinated dibenzo-dioxins together with other dioxin-like compounds. This list goes far beyond what has been suggested previously. A minimum set of chemicals to be assessed together with phthalates includes pesticides such as vinclozolin, prochloraz, procymidone, linuron, the pain killers paracetamol, aspirin and ibuprofen, pharmaceuticals such as finasteride, ketoconazole, and the lipid-lowering drug simvastin, poly-chlorinated dibenzo-dioxins and other dioxin-like pollutants and phenolics such as bisphenol A and butylparaben. AOP network analyses are essential to overcome difficulties in establishing groupings of chemicals for mixture risk assessments that derive from a narrow focus on mechanisms and modes of action.

The current status and future of andrology: A consensus report from the Cairo workshop group

BACKGROUND

In attempting to formulate potential WHO guidelines for the diagnosis of male infertility, the Evidence Synthesis Group noted a paucity of high-quality data on which to base key recommendations. As a result, a number of authors suggested that key areas of research/evidence gaps should be identified, so that appropriate funding and policy actions could be undertaken to help address key questions.

OBJECTIVES

The overall objective of this Consensus workshop was to clarify current knowledge and deficits in clinical laboratory andrology, so that clear paths for future development could be navigated.

MATERIALS AND METHODS

Following a detailed literature review, each author, prior to the face-to-face meeting, prepared a summary of their topic and submitted a PowerPoint presentation. The topics covered were (a) Diagnostic testing in male fertility and infertility, (b) Male fertility/infertility in the modern world, (c) Clinical management of male infertility, and (d) The overuse of ICSI. At the meeting in Cairo on February 18, 2019, the evidence was presented and discussed and a series of consensus points agreed.

RESULTS

The paper presents a background and summary of the evidence relating to these four topics and addresses key points of significance. Following discussion of the evidence, a total of 36 consensus points were agreed.

DISCUSSION

The Discussion section presents areas where there was further debate and key areas that were highlighted during the day.

CONCLUSION

The consensus points provide clear statements of evidence gaps and/or potential future research areas/topics. Appropriate funding streams addressing these can be prioritized and consequently, in the short and medium term, answers provided. By using this strategic approach, andrology can make the rapid progress necessary to address key scientific, clinical, and societal challenges that face our discipline now and in the near future.

Impact of binary waterborne mixtures of nickel and zinc on hypothalamic-pituitary-testicular axis in rats

Several evidences from the literature showed that the coexistence of nickel and zinc in polluted waters is related to the similarity in their geogenic and anthropogenic factors. Although most environmental exposures to metals do not occur singly, there is a paucity of scientific knowledge on the effects of zinc and nickel co-exposure on mammalian reproductive health. The present study investigated the influence of co-exposure to nickel and zinc on male reproductive function in rats. Experimental rats were co-exposed to environmentally relevant concentrations of waterborne nickel (75 and 150 μg NiCl₂ L^-1) and zinc (100 and 200 μg ZnCl₂ L^-1) for 45 successive days. Subsequently, reproductive hormones were assayed whereas the hypothalamus, epididymis and testes of the rats were processed for the assessment of oxidative stress and inflammation indices, caspase-3 activity and histology. Results indicated that co-exposure to nickel and zinc significantly (p < 0.05) abolished nickel-mediated diminution of antioxidant defense mechanisms while diminishing levels of reactive oxygen and nitrogen species and lipid peroxidation in the hypothalamus, epididymis and testes of the exposed rats. Additionally, co-exposure to zinc abated nickel-mediated diminutions in luteinizing hormone, follicle-stimulating hormone, serum and intra-testicular testosterone with concomitant enhancement of sperm production and quality. Further, zinc abrogated nickel-mediated elevation in inflammatory biomarkers including nitric oxide, tumor necrosis factor alpha, interleukin-1 beta as well as caspase-3 activity. The protective influence of zinc on nicked-induced reproductive toxicity was well supported by histological data. Overall, zinc ameliorated nickel-induced reproductive dysfunction via its anti-oxidant, anti-inflammatory, anti-apoptotic and spermato-protective activities in rats.

Endocrine Disruption and Reproductive Pathology

During the past 20 years, investigations involving endocrine active substances (EAS) and reproductive toxicity have dominated the landscape of ecotoxicological research. This has occurred in concert with heightened awareness in the scientific community, general public, and governmental entities of the potential consequences of chemical perturbation in humans and wildlife. The exponential growth of experimentation in this field is fueled by our expanding knowledge into the complex nature of endocrine systems and the intricacy of their interactions with xenobiotic agents. Complicating factors include the ever-increasing number of novel receptors and alternate mechanistic pathways that have come to light, effects of chemical mixtures in the environment versus those of single EAS laboratory exposures, the challenge of differentiating endocrine disruption from direct cytotoxicity, and the potential for transgenerational effects. Although initially concerned with EAS effects chiefly in the thyroid glands and reproductive organs, it is now recognized that anthropomorphic substances may also adversely affect the nervous and immune systems via hormonal mechanisms and play substantial roles in metabolic diseases, such as type 2 diabetes and obesity.