Biomarkers of effect in endocrine disruption: how to link a functional assay to an adverse outcome pathway (original) (raw)
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Computational Toxicology, 2019
Endocrine disrupting chemicals raise a lot of interest and concern regarding their risk for human health and the environment. They represent a broad variety of natural and synthetic chemicals with different levels of endocrine activity evaluation. In particular, for high production volume chemicals, new methods are required to enable the evaluation of the vast number of chemicals for their potential to alter the endocrine system and prioritize them for deeper characterization. The ToxCast program from the US EPA provides data from high throughput screening assays to develop computational tools aimed at rapid in vitro bioactivity screening and prioritization. Using publicly available data (ToxCast and ToxRef databases), we evaluate whether in vitro assay evaluations could predict in vivo outcomes observed in rat long-term studies for more than 400 chemicals. We focus on effects observed in three endocrine and two sex accessory organs and 42 in vitro assays related to pathways associated with endocrine related toxicity. First, using simple statistical correlation we demonstrate that there is no mutual linear correlation between the selected in vitro assays and any in vivo outcome, with balanced accuracies around 50% for each assayoutcome pair. Then, by applying machine learning to investigate potential non-linear correlations, we show that the combination of different in vitro assays is not correlated with the long-term in vivo effects and cannot help to predict them since balanced accuracies are also around 50%. Moreover, the prediction based on in vitro assays is not better than the one based on classical QSAR methods. This study highlights that the selected in vitro assays do not provide information about in vivo outcomes observed in endocrine and associated organs in long-term rat in vivo studies and stresses the need for the development of in vitro assays that reflect the compounds' pharmacokinetic properties. health effects in an intact organism, or its progeny, or (sub)populations" [2]. If sufficiently potent, these functional disruptions can lead to different adverse outcomes at the whole organism level such as developmental and reproductive effects, neurobehavioral troubles, immune disorders or cancers [3]. There are numerous and diverse mechanistic pathways that result in these effects, including activation of nuclear receptors (e.g. estrogen receptor (ER), androgen receptor (AR)),
Environmental Science & Technology, 2014
Thousands of environmental chemicals are subject to regulatory review for their potential to be endocrine disruptors (ED). In vitro high-throughput screening (HTS) assays have emerged as a potential tool for prioritizing chemicals for ED-related whole-animal tests. In this study, 1814 chemicals including pesticide active and inert ingredients, industrial chemicals, food additives, and pharmaceuticals were evaluated in a panel of 13 in vitro HTS assays. The panel of in vitro assays interrogated multiple end points related to estrogen receptor (ER) signaling, namely binding, agonist, antagonist, and cell growth responses. The results from the in vitro assays were used to create an ER Interaction Score. For 36 reference chemicals, an ER Interaction Score >0 showed 100% sensitivity and 87.5% specificity for classifying potential ER activity. The magnitude of the ER Interaction Score was significantly related to the potency classification of the reference chemicals (p < 0.0001). ERα/ERβ selectivity was also evaluated, but relatively few chemicals showed significant selectivity for a specific isoform. When applied to a broader set of chemicals with in vivo uterotrophic data, the ER Interaction Scores showed 91% sensitivity and 65% specificity. Overall, this study provides a novel method for combining in vitro concentration response data from multiple assays and, when applied to a large set of ER data, accurately predicted estrogenic responses and demonstrated its utility for chemical prioritization.
Distinguishing between endocrine disruption and non-specific effects on endocrine systems
Regulatory toxicology and pharmacology : RTP, 2018
The endocrine system is responsible for growth, development, maintaining homeostasis and for the control of many physiological processes. Due to the integral nature of its signaling pathways, it can be difficult to distinguish endocrine-mediated adverse effects from transient fluctuations, adaptive/compensatory responses, or adverse effects on the endocrine system that are caused by mechanisms outside the endocrine system. This is particularly true in toxicological studies that require generation of effects through the use of Maximum Tolerated Doses (or Concentrations). Endocrine-mediated adverse effects are those that occur as a consequence of the interaction of a chemical with a specific molecular component of the endocrine system, for example, a hormone receptor. Non-endocrine-mediated adverse effects on the endocrine system are those that occur by other mechanisms. For example, systemic toxicity, which perturbs homeostasis and affects the general well-being of an organism, can a...
In Vitro Models in Endocrine Disruptor Screening
The public and scientific concern that chemicals present in the human diet and the environment and their ability to disrupt the normal hormonal milieu in humans and wildlife have become a high-profile international issue. In 1998, the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC) convened by the Environmental Protection Agency (EPA) recommended a tiered testing approach for the evaluation of estrogen, androgen, and thyroid-related effects of some 87,000 commercial chemicals and environmental contaminants. The function of this committee concluded with its final report, and the further implementation of the recommended testing strategy has now been carried forward with the assistance of the Endocrine Disruptor Methods Validation Subcommittee. The function of this body is to provide advice to the EPA on scientific and technical issues related specifically to the conduct of studies required for the validation of assays proposed by the EDSTAC as part of the tiered screening program. The EDSTAC recommended and alternative screening batteries encompass four in vitro mammalian assays. The current methodologies and validation status of the proposed in vitro EDSTAC assays are discussed and consist of estrogen/ androgen receptor binding, estrogen/androgen gene transactivation, and minced testis, and one alternate (placental aromatase) in vitro screening assay.
Birth Defects Research Part B: Developmental and Reproductive Toxicology, 2014
Tier 1 of the U.S. EPA Endocrine Disruptor Screening Program comprises 11 studies: five in vitro assays, four in vivo mammalian assays, and two in vivo nonmammalian assays. The battery is designed to detect compounds with the potential to interact with the estrogen, androgen, or thyroid signaling pathways. This article examines the procedures, results, and data interpretation for the five Tier 1 in vitro assays: estrogen receptor (ER) and androgen receptor binding assays, an ER transactivation assay, an aromatase assay, and a steroidogenesis assay. Data are presented from two laboratories that have evaluated approximately 11 compounds in the Tier 1 in vitro assays. Generally, the ER and androgen receptor binding assays and the aromatase assay showed good specificity and reproducibility. As described in the guideline for the ER transactivation assay, a result is considered positive when the test compound induces a reporter gene signal that reaches 10% of the response seen with 1 nM 17-estradiol (positive control). In the experience of these laboratories, this cutoff criterion may result in false-positive responses. For the steroidogenesis assay, there is variability in the basal and stimulated production of testosterone and estradiol by the H295R cells. This variability in responsiveness, coupled with potential cell stress at high concentrations of test compound, may make it difficult to discern whether hormone alterations are specific steroidogenesis alterations (i.e., endocrine active). Lastly, both laboratories had difficulty meeting some recommended performance criteria for each Tier 1 in vitro assay. Data with only minor deviations were deemed valid. Birth
Endocrine disruption: where are we with hazard and risk assessment?
Approaches to assessing endocrine disruptors (EDs) differ across the globe, with some regulatory environments using a hazard-based approach, while others employ risk-based analyses. In session four of the Society of Environmental Toxicology and Chemistry (SETAC) North America Focused Topic Meeting: Endocrine Disruption Chemical Testing: Risk Assessment Approaches and Implications (February 4 – 6, 2014), various aspects related to the hazard and/or risk assessment of EDs were explored. The presentations in the session included an overview of the regulatory environments for assessing and managing endocrine disruptors, and scenarios whereby a hazard-based approach might be most appropriate were discussed. Three case studies for ED assessment, one for an industrial chemical, one for a pharmaceutical, and one for a pesticide, were presented. The topics of non-monotonic dose response relationships as well as potency and threshold effects were also presented in this session, since these co...
This special series of six papers (this introductory paper and 5 other papers) is about the Focused Topic Meeting on Endocrine Disruption Chemical Testing; Risk Assessment Approaches and Implications (4 – 6 February, 2014, Raleigh, North Carolina). The workshop was composed of five sessions that each dealt with a specific topic. Broadly speaking the following themes were addressed: a) the status of the USEPA Endocrine Disruptor Screening Program, b) how data from both EDSP-directed testing and other sources may be interpreted and applied in regulatory settings and c) approaches for moving beyond estrogen, androgen and thyroid pathways to address current challenges and expanding future approaches to EDC testing. The series of publications summarizes the knowledge presented and discussed at the Focused Topic Meeting and organizes the information by session. Where relevant, the summaries are enhanced beyond the original ideas of the presentations during the meeting. It is the intention...
New methods for detection of potential endocrine disruptors
Andrologia, 2000
It has been hypothesized that recent adverse trends in humans are linked to an increased exposure to potential endocrine disrupting agents. These include widely used compounds that mimic the action of sex hormones, including bisphenol A, phthalates and parabens. Since the chemical structure is not sufficient to determine whether a chemical will act as an oestrogen, there is a need for assays that can determine whether a compound interferes with the endocrine systems. The Environmental Protection Agency has recently suggested a testing scheme, composed of an initial screening followed by a more comprehensive investigation of chemicals that are positive in the screening. The screening will use several short-term assays to screen many thousands of compounds for potential endocrine disrupting properties. However, none of these tests determines compound-induced effects on the expression of endogenous genes, which is the cause of the adverse effects. We propose to use a precise quantifica...
Incorporation of a metabolizing system in biodetection assays for endocrine active substances
ALTEX, 2017
Among the in vitro assays for the detection of endocrine active substances (EAS), the CALUX assay (Chemically Activated LUciferase gene eXpression) allows the detection of substances (i.e., ligands) with the potential to interact with various nuclear receptors and affect the subsequent transcriptional response (Sonneveld et al., 2005). Such assessments generally fail to take into account the role of metabolism. Indeed, the majority of cell-based assays use cells that are not metabolically competent and do not include a metabolizing step. Some attempts to assess the role of metabolism in endocrine bioassays have been made previously. Most of these included 1 Introduction Biodetection is gaining importance, especially for samples for which little toxicological data is available (Krewski et al., 2010). In this context, cell culture-based assays are recognized to play an increasingly important role in the detection of endocrine active substances (EAS). These test systems provide insight into the intrinsic biological properties of both pure chemicals and previously uncharacterized mixtures. These test systems may reduce or even eliminate in vivo testing required for safety assessments.