Publications by authors named "Edward W Carney"

43 Publications

Systems Modeling of Developmental Vascular Toxicity.

Curr Opin Toxicol 2019 Jun;15(1):55-63

National Center for Computational Toxicology (NCCT), Office of Research and Development (ORD), U.S. Environmental Protection Agency (USEPA) Research Triangle Park NC 27711.

The more than 80,000 chemicals in commerce present a challenge for hazard assessments that toxicity testing in the 21 century strives to address through high-throughput screening (HTS) assays. Assessing chemical effects on human development adds an additional layer of complexity to the screening, with a need to capture complex and dynamic events essential for proper embryo-fetal development. HTS data from ToxCast/Tox21 informs systems toxicology models, which incorporate molecular targets and biological pathways into mechanistic models describing the effects of chemicals on human cells, 3D organotypic culture models, and small model organisms. Adverse Outcome Pathways (AOPs) provide a useful framework for integrating the evidence derived from these and systems to inform chemical hazard characterization. To illustrate this formulation, we have built an AOP for developmental toxicity through a mode of action linked to embryonic vascular disruption (Aop43). Here, we review the model for quantitative prediction of developmental vascular toxicity from ToxCast HTS data and compare the HTS results to functional vascular development assays in complex cell systems, virtual tissues, and small model organisms. ToxCast HTS predictions from several published and unpublished assays covering different aspects of the angiogenic cycle were generated for a test set of 38 chemicals representing a range of putative vascular disrupting compounds (pVDCs). Results boost confidence in the capacity to predict adverse developmental outcomes from HTS data and model computational dynamics for reconstruction of developmental systems biology. Finally, we demonstrate the integration of the AOP and developmental systems toxicology to investigate the unique modes of action of two angiogenesis inhibitors.
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http://dx.doi.org/10.1016/j.cotox.2019.04.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7004230PMC
June 2019

Embryonic vascular disruption adverse outcomes: Linking high throughput signaling signatures with functional consequences.

Reprod Toxicol 2017 06 17;70:82-96. Epub 2017 May 17.

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, 1803 Building, Midland, MI 48674, United States.

Embryonic vascular disruption is an important adverse outcome pathway (AOP) as chemical disruption of cardiovascular development induces broad prenatal defects. High throughput screening (HTS) assays aid AOP development although linking in vitro data to in vivo apical endpoints remains challenging. This study evaluated two anti-angiogenic agents, 5HPP-33 and TNP-470, across the ToxCastDB HTS assay platform and anchored the results to complex in vitro functional assays: the rat aortic explant assay (AEA), rat whole embryo culture (WEC), and the zebrafish embryotoxicity (ZET) assay. Both were identified as putative vascular disruptive compounds (pVDCs) in ToxCastDB and disrupted angiogenesis and embryogenesis in the functional assays. Differences were observed in potency and adverse effects: 5HPP-33 was embryolethal (WEC and ZET); TNP-470 produced caudal defects at lower concentrations. This study demonstrates how a tiered approach using HTS signatures and complex functional in vitro assays might be used to prioritize further in vivo developmental toxicity testing.
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http://dx.doi.org/10.1016/j.reprotox.2017.05.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706853PMC
June 2017

Embryonic vascular disruption adverse outcomes: Linking high-throughput signaling signatures with functional consequences.

Reprod Toxicol 2017 08 13;71:16-31. Epub 2017 Apr 13.

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, 1803 Building, Midland, MI 48674, United States.

Embryonic vascular disruption is an important adverse outcome pathway (AOP) as chemical disruption of cardiovascular development induces broad prenatal defects. High-throughput screening (HTS) assays aid AOP development although linking in vitro data to in vivo apical endpoints remains challenging. This study evaluated two anti-angiogenic agents, 5HPP-33 and TNP-470, across the ToxCastDB HTS assay platform and anchored the results to complex in vitro functional assays: the rat aortic explant assay (AEA), rat whole embryo culture (WEC), and the zebrafish embryotoxicity (ZET) assay. Both were identified as putative vascular disruptive compounds (pVDCs) in ToxCastDB and disrupted angiogenesis and embryogenesis in the functional assays. Differences were observed in potency and adverse effects: 5HPP-33 was embryolethal (WEC and ZET); TNP-470 produced caudal defects at lower concentrations. This study demonstrates how a tiered approach using HTS signatures and complex functional in vitro assays might be used to prioritize further in vivo developmental toxicity testing.
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http://dx.doi.org/10.1016/j.reprotox.2017.04.003DOI Listing
August 2017

Tiered application of the neutral red release and EpiOcular™ assays for evaluating the eye irritation potential of agrochemical formulations.

Regul Toxicol Pharmacol 2016 Nov 28;81:407-420. Epub 2016 Sep 28.

Dow AgroSciences LLC, Indianapolis, IN, USA.

Agrochemical formulations have been underrepresented in validation efforts for implementing alternative eye irritation approaches but represent a significant opportunity to reduce animal testing. This study assesses the utility of the neutral red release assay (NRR) and EpiOcular™ assay (EO) for predicting the eye irritation potential of 64 agrochemical formulations relative to Draize data. In the NRR, formulations with an NRR50 value ≤ 50 mg/mL were categorized as UN GHS Cat 1 and those >250 mg/mL were classified as UN GHS Non Classified (NC). The accuracy, sensitivity, and specificity were 78, 85 and 76% and 73, 85 and 61% for identifying UN GHS 1 and NC formulations, respectively. Specificity was poor for formulations with NRR50 > 50 to ≤250 mg/mL. The EO (ET-40 method) was explored to differentiate formulations that were UN GHS 1/2 and UN GHS NC. The EO resulted in accuracy, sensitivity, and specificity of 65%, 58% and 75% for identifying UN GHS NC formulations. To improve the overall performance, the assays were implemented using a tiered-approach where the NRR was run as a first-tier followed by the EO. The tiered-approach resulted in improved accuracy (75%) and balanced sensitivity (73%) and specificity (77%) for distinguishing between irritating and non-irritating agrochemical formulations.
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http://dx.doi.org/10.1016/j.yrtph.2016.09.028DOI Listing
November 2016

Dietary Route of Exposure for Rabbit Developmental Toxicity Studies.

Toxicol Sci 2016 11 4;154(1):90-100. Epub 2016 Aug 4.

Dow AgroSciences, LLC, Indianapolis, Indiana, USA.

Dietary administration is a relevant route of oral exposure for regulatory toxicity studies of agrochemicals as it mimics potential human intake of the chemical via treated crops and commodities. Moreover, dietary administration of test compounds during a developmental toxicity study can deliver a prolonged and stable systemic exposure to the embryo or fetus at all stages of development. In this study, strategies were employed to optimize rabbit test material consumption via diet. Comparative toxicokinetic profiles of gavage versus dietary administration were evaluated in pregnant or non-pregnant New Zealand White rabbits for 2 novel agrochemicals with different plasma half-lives of elimination (sulfoxaflor, t = 13.5 h and halauxifen, t = 1 h). Dietary administration of sulfoxaflor resulted in stable 24-h plasma concentrations, whereas gavage administration resulted in a 3-fold fluctuation in plasma levels between C and C Dietary administration of sulfoxaflor resulted in a 2-fold higher nominal and diurnal systemic dose when compared with gavage dosing due to C-related maternal toxicity following gavage. Results with the shorter half-life molecule, halauxifen, were more striking with a 6-fold diurnal fluctuation by the dietary route compared with a 368-fold fluctuation between C and C by gavage. Furthermore, plasma halauxifen was detectable only up to 12 h following gavage but up to 24 h following dietary administration. Finally, the presence of these compounds in fetal blood samples was demonstrated, confirming that dietary exposure is appropriate for achieving fetal exposure. Collectively, the results of these studies support the use of dietary exposure in rabbit developmental toxicity studies.
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http://dx.doi.org/10.1093/toxsci/kfw141DOI Listing
November 2016

Grouping 34 Chemicals Based on Mode of Action Using Connectivity Mapping.

Toxicol Sci 2016 06 29;151(2):447-61. Epub 2016 Mar 29.

*Mason Business Center, The Procter & Gamble Company, Cincinnati, Ohio 45040 and.

Connectivity mapping is a method used in the pharmaceutical industry to find connections between small molecules, disease states, and genes. The concept can be applied to a predictive toxicology paradigm to find connections between chemicals, adverse events, and genes. In order to assess the applicability of the technique for predictive toxicology purposes, we performed gene array experiments on 34 different chemicals: bisphenol A, genistein, ethinyl-estradiol, tamoxifen, clofibrate, dehydorepiandrosterone, troglitazone, diethylhexyl phthalate, flutamide, trenbolone, phenobarbital, retinoic acid, thyroxine, 1α,25-dihydroxyvitamin D3, clobetasol, farnesol, chenodeoxycholic acid, progesterone, RU486, ketoconazole, valproic acid, desferrioxamine, amoxicillin, 6-aminonicotinamide, metformin, phenformin, methotrexate, vinblastine, ANIT (1-naphthyl isothiocyanate), griseofulvin, nicotine, imidacloprid, vorinostat, 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) at the 6-, 24-, and 48-hour time points for 3 different concentrations in the 4 cell lines: MCF7, Ishikawa, HepaRG, and HepG2 GEO (super series accession no.: GSE69851). The 34 chemicals were grouped in to predefined mode of action (MOA)-based chemical classes based on current literature. Connectivity mapping was used to find linkages between each chemical and between chemical classes. Cell line-specific linkages were compared with each other and to test whether the method was platform and user independent, a similar analysis was performed against publicly available data. The study showed that the method can group chemicals based on MOAs and the inter-chemical class comparison alluded to connections between MOAs that were not predefined. Comparison to the publicly available data showed that the method is user and platform independent. The results provide an example of an alternate data analysis process for high-content data, beneficial for predictive toxicology, especially when grouping chemicals for read across purposes.
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http://dx.doi.org/10.1093/toxsci/kfw058DOI Listing
June 2016

Evaluation of TOPKAT, Toxtree, and Derek Nexus in Silico Models for Ocular Irritation and Development of a Knowledge-Based Framework To Improve the Prediction of Severe Irritation.

Chem Res Toxicol 2016 05 6;29(5):810-22. Epub 2016 Apr 6.

Toxicology & Environmental Research and Consulting, Dow Chemical Company , 2020 Dow Center, Midland, Michigan 48674, United States.

Assessment of ocular irritation is an essential component of any risk assessment. A number of (Q)SARs and expert systems have been developed and are described in the literature. Here, we focus on three in silico models (TOPKAT, BfR rulebase implemented in Toxtree, and Derek Nexus) and evaluate their performance using 1644 in-house and 123 European Centre for Toxicology and Ecotoxicology of Chemicals (ECETOC) compounds with existing in vivo ocular irritation classification data. Overall, the in silico models performed poorly. The best consensus predictions of severe ocular irritants were 52 and 65% for the in-house and ECETOC compounds, respectively. The prediction performance was improved by designing a knowledge-based chemical profiling framework that incorporated physicochemical properties and electrophilic reactivity mechanisms. The utility of the framework was assessed by applying it to the same test sets and three additional publicly available in vitro irritation data sets. The prediction of severe ocular irritants was improved to 73-77% if compounds were filtered on the basis of AlogP_MR (hydrophobicity with molar refractivity). The predictivity increased to 74-80% for compounds capable of preferentially undergoing hard electrophilic reactions, such as Schiff base formation and acylation. This research highlights the need for reliable ocular irritation models to be developed that take into account mechanisms of action and individual structural classes. It also demonstrates the value of profiling compounds with respect to their chemical reactivity and physicochemical properties that, in combination with existing models, results in better predictions for severe irritants.
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http://dx.doi.org/10.1021/acs.chemrestox.5b00531DOI Listing
May 2016

Acute Toxicity Prediction in Multiple Species by Leveraging Mechanistic ToxCast Mitochondrial Inhibition Data and Simulation of Oral Bioavailability.

Toxicol Sci 2015 Oct 2;147(2):386-96. Epub 2015 Jul 2.

Toxicology Environmental Research and Consulting, The Dow Chemical Company, Midland, 48674 Michigan.

There is great interest in assessing the in vivo toxicity of chemicals using nonanimal alternatives. However, acute mammalian toxicity is not adequately predicted by current in silico or in vitro approaches. Mechanisms of acute toxicity are likely conserved across invertebrate, aquatic, and mammalian species, suggesting that dose-response concordance would be high and in vitro mechanistic data could predict responses in multiple species under conditions of similar bioavailability. We tested this hypothesis by comparing acute toxicity between rat, daphnia, and fish and by comparing their respective acute data to inhibition of mitochondria membrane potential (MMP) using U.S. Environmental Protection Agency ToxCast in vitro high-throughput screening data. Logarithmic scatter plots of acute toxicity data showed a clear relationship between fish, daphnia, and intravenous rat but not oral rat data. Similar plots versus MMP showed a well-delineated upper boundary for fish, daphnia, and intravenous data but were scattered without an upper boundary for rat oral data. Adjustments of acute oral rat toxicity values by simulating fractional absorption and CYP-based metabolism as well as removing compounds with hydrolyzable linkages or flagged as substrates for glucuronidation delineated an upper boundary for rat oral toxicity versus MMP. Mitochondrial inhibition at low concentrations predicted highly acutely toxic chemicals for fish and daphnia but not the rat where toxicity was often attenuated. This use of a single high-throughput screening assay to predict acute toxicity in multiple species represents a milestone and highlights the promise of such approaches but also the need for refined tools to address systemic bioavailability and the impact of limited absorption and first pass metabolism.
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http://dx.doi.org/10.1093/toxsci/kfv135DOI Listing
October 2015

Application of the KeratinoSens™ assay for assessing the skin sensitization potential of agrochemical active ingredients and formulations.

Regul Toxicol Pharmacol 2015 Jul 14;72(2):350-60. Epub 2015 May 14.

The Dow Chemical Company, Midland, MI, United States.

Assessment of skin sensitization potential is an important component of the safety evaluation process for agrochemical products. Recently, non-animal approaches including the KeratinoSens™ assay have been developed for predicting skin sensitization potential. Assessing the utility of the KeratinoSens™ assay for use with multi-component mixtures such as agrochemical formulations has not been previously evaluated and is a significant need. This study was undertaken to evaluate the KeratinoSens™ assay prediction potential for agrochemical formulations. The assay was conducted for 8 agrochemical active ingredients (AIs) including 3 sensitizers (acetochlor, meptyldinocap, triclopyr), 5 non-sensitizers (aminopyralid, clopyralid, florasulam, methoxyfenozide, oxyfluorfen) and 10 formulations for which in vivo sensitization data were available. The KeratinoSens™ correctly predicted the sensitization potential of all the AIs. For agrochemical formulations it was necessary to modify the standard assay procedure whereby the formulation was assumed to have a common molecular weight. The resultant approach correctly predicted the sensitization potential for 3 of 4 sensitizing formulations and all 6 non-sensitizing formulations when compared to in vivo data. Only the meptyldinocap-containing formulation was misclassified, as a result of high cytotoxicity. These results demonstrate the promising utility of the KeratinoSens™ assay for evaluating the skin sensitization potential of agrochemical AIs and formulations.
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http://dx.doi.org/10.1016/j.yrtph.2015.05.006DOI Listing
July 2015

Predicting the future: opportunities and challenges for the chemical industry to apply 21st-century toxicity testing.

J Am Assoc Lab Anim Sci 2015 Mar;54(2):214-23

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan, USA.

Interest in applying 21st-century toxicity testing tools for safety assessment of industrial chemicals is growing. Whereas conventional toxicology uses mainly animal-based, descriptive methods, a paradigm shift is emerging in which computational approaches, systems biology, high-throughput in vitro toxicity assays, and high-throughput exposure assessments are beginning to be applied to mechanism-based risk assessments in a time- and resource-efficient fashion. Here we describe recent advances in predictive safety assessment, with a focus on their strategic application to meet the changing demands of the chemical industry and its stakeholders. The opportunities to apply these new approaches is extensive and include screening of new chemicals, informing the design of safer and more sustainable chemical alternatives, filling information gaps on data-poor chemicals already in commerce, strengthening read-across methodology for categories of chemicals sharing similar modes of action, and optimizing the design of reduced-risk product formulations. Finally, we discuss how these predictive approaches dovetail with in vivo integrated testing strategies within repeated-dose regulatory toxicity studies, which are in line with 3Rs principles to refine, reduce, and replace animal testing. Strategic application of these tools is the foundation for informed and efficient safety assessment testing strategies that can be applied at all stages of the product-development process.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4382627PMC
March 2015

Comparative response of rat and rabbit conceptuses in vitro to inhibitors of histiotrophic nutrition.

Birth Defects Res B Dev Reprod Toxicol 2015 Feb 4;104(1):1-10. Epub 2015 Feb 4.

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan.

Histiotrophic nutrition via the visceral yolk sac is an essential nutritional pathway of the rodent conceptus, and inhibition of this pathway may cause growth retardation, malformations, and death in rodent embryos. Morphologic differences among species during early development indicate that the visceral yolk sac histiotrophic nutrition pathway may be of lesser importance in nonrodent species, including humans. Here, comparative studies were conducted with inhibitors of different steps in the visceral yolk sac histiotrophic nutrition pathway to determine whether the rabbit is similarly responsive to the rat. Early somite stage New Zealand White rabbit and Crl:CD(SD) rat conceptuses (gestation day 9, rabbits; gestation day 10, rats) were exposed for 48 hr to three different histiotrophic nutrition pathway inhibitors using whole embryo culture techniques, after which they were evaluated for growth and malformations. Cubilin antibody, an inhibitor of endocytosis, reduced growth and development and increased malformations in both rat and rabbit embryos, although the rabbit appeared more sensitive. Leupeptin, a lysosomal cysteine protease inhibitor, also impaired growth and development and increased malformations in rat embryos, while in the rabbit it induced malformations and a slight decrease in morphology score but had no effect upon growth. Trypan blue, an inhibitor of endocytosis and endosome maturation, affected all measures in both species to a similar degree at the highest concentration (2500 μg/ml), but rat embryos responded to a greater extent at lower concentrations. Although the specific adverse outcomes appear to be different, these results demonstrate that rabbits, like rats, are sensitive to inhibitors of the histiotrophic nutrition pathway.
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http://dx.doi.org/10.1002/bdrb.21134DOI Listing
February 2015

FutureTox II: in vitro data and in silico models for predictive toxicology.

Toxicol Sci 2015 Feb;143(2):256-67

United States Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Sanofi, Bridgewater, New Jersey 08807, Page One Editorial Services, Boulder, Colorado 80304, Dow Chemical Company, Midland, Michigan 48674, Health and Environmental Sciences Institute, Washington, District of Columbia 20005, University of Washington, Seattle, Washington 98105, United States Food and Drug Administration, Silver Spring, Maryland 20993, Sanofi, Bethesda, Maryland 20814, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, University of North Carolina, Chapel Hill, North Carolina 27599, The Hamner Institutes, Research Triangle Park, North Carolina 27709, and European Commission Joint Research Centre, I-21027 Ispra, Italy.

FutureTox II, a Society of Toxicology Contemporary Concepts in Toxicology workshop, was held in January, 2014. The meeting goals were to review and discuss the state of the science in toxicology in the context of implementing the NRC 21st century vision of predicting in vivo responses from in vitro and in silico data, and to define the goals for the future. Presentations and discussions were held on priority concerns such as predicting and modeling of metabolism, cell growth and differentiation, effects on sensitive subpopulations, and integrating data into risk assessment. Emerging trends in technologies such as stem cell-derived human cells, 3D organotypic culture models, mathematical modeling of cellular processes and morphogenesis, adverse outcome pathway development, and high-content imaging of in vivo systems were discussed. Although advances in moving towards an in vitro/in silico based risk assessment paradigm were apparent, knowledge gaps in these areas and limitations of technologies were identified. Specific recommendations were made for future directions and research needs in the areas of hepatotoxicity, cancer prediction, developmental toxicity, and regulatory toxicology.
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http://dx.doi.org/10.1093/toxsci/kfu234DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4318934PMC
February 2015

A critical assessment of the methodologies to investigate the role of inhibition of apoptosis in rodent hepatocarcinogenesis.

Toxicol Mech Methods 2015 Mar 11;25(3):192-200. Epub 2015 Feb 11.

Toxicology and Environmental Research & Consulting, The Dow Chemical Company , Midland, MI , USA.

Non-genotoxic carcinogens act by promoting the clonal expansion of preneoplastic cells by directly or indirectly stimulating cell division or inhibiting cell loss in the target organ. The specific mode-of-action (MoA) by which some non-genotoxic carcinogens ultimately cause cancer is not completely understood. To date, there are several proposed MoAs for non-genotoxic carcinogens, and some of these propose inhibition of apoptosis as one of the key events. In general, inhibition of apoptosis is considered a necessary step for cell survival and in theory can occur in combination or in association with other key promotional events, such as cell proliferation, oxidative stress and inhibition of intercellular communication to promote carcinogenesis. However, the evidence supporting the role of inhibition of apoptosis as a necessary step in promoting specific chemically induced tumors is often debated. To address this evidence, we reviewed studies that utilized prototypical nuclear receptor-mediated hepatocarcinogens. Based on this review, it is proposed that the ability to determine the importance of inhibition of apoptosis as a key event in the MoA for tumor promotion is hampered by the limitations of the methods utilized for its detection. This review provides an assessment of the strengths and limitations of the current methodology used for detection of apoptosis and provides suggestions for improving its detection, thereby strengthening the weight of evidence supporting inhibition of apoptosis as a key event in a MoA for tumor promotion.
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http://dx.doi.org/10.3109/15376516.2015.1007541DOI Listing
March 2015

Exposure-based validation list for developmental toxicity screening assays.

Birth Defects Res B Dev Reprod Toxicol 2014 Dec 4;101(6):423-8. Epub 2014 Dec 4.

Procter & Gamble, Cincinnati, Ohio.

Validation of alternative assays requires comparison of the responses to toxicants in the alternative assay with in vivo responses. Chemicals have been classified as "positive" or "negative" in vivo, despite the fact that developmental toxicity is conditional on magnitude of exposure. We developed a list of positive and negative developmental exposures, with exposure defined by toxicokinetic data, specifically maternal plasma Cmax . We selected a series of 20 chemicals that caused developmental toxicity and for which there were appropriate toxicokinetic data. Where possible, we used the same chemical for both positive and negative exposures, the positive being the Cmax at a dose level that produced significant teratogenicity or embryolethality, the negative being the Cmax at a dose level not causing developmental toxicity. It was not possible to find toxicokinetic data at the no-effect level for all positive compounds, and the negative exposure list contains Cmax values for some compounds that do not have developmental toxicity up to the highest dose level tested. This exposure-based reference list represents a fundamentally different approach to the evaluation of alternative tests and is proposed as a step toward application of alternative tests in quantitative risk assessment.
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http://dx.doi.org/10.1002/bdrb.21132DOI Listing
December 2014

Distinguishing between maternally-mediated and directly embryotoxic modes-of-action for postimplantation loss induced in rats by 2-amino-2-methylpropanol.

Reprod Toxicol 2014 Nov 1;49:55-64. Epub 2014 Aug 1.

Toxicology and Environmental Research & Consulting, The Dow Chemical Company, Midland, MI 48674, USA.

In rats, 2-amino-2-methylpropanol (AMP) caused an increase in postimplantation loss in an oral reproductive/developmental toxicity screening assay but not in a dermal developmental toxicity assay. Studies were performed to characterize the mode of action and determine whether the postimplantation loss was a result of direct embryotoxicity or a maternally mediated effect. The studies identified that the postimplantation loss occurs shortly after implantation, has a steep dose response with a clear threshold, requires exposure to AMP for a period of approximately 2-3 weeks prior to gestation and does not involve direct embryo toxicity. The uterine histopathology and gene array analysis of decidual swellings suggested AMP acts via a maternally mediated mechanism affecting the ability of the uterus to support an implanted embryo. Since the postimplantation loss occurs only at maternally toxic doses, the implications for human risk assessment are discussed.
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http://dx.doi.org/10.1016/j.reprotox.2014.07.075DOI Listing
November 2014

Human relevance framework evaluation of a novel rat developmental toxicity mode of action induced by sulfoxaflor.

Crit Rev Toxicol 2014 May;44 Suppl 2:45-62

Toxicology & Environmental Research and Consulting, The Dow Chemical Company , Midland, MI , USA.

Sulfoxaflor (CAS# 946578-00-3) is a novel active substance with insecticidal properties mediated via its agonism on the highly abundant insect nicotinic acetylcholine receptor (nAChR). In developmental and reproductive toxicity studies, gestational exposure caused fetal abnormalities (primarily limb contractures) and reduced neonatal survival in rats, but not rabbits, following high-dose dietary exposure. Sulfoxaflor induced these effects via a novel mode of action (MoA) mediated by the fetal-type muscle nAChR with the following key events: (1) binding to the receptor, (2) agonism on the receptor, causing (3) sustained muscle contracture in the near-term fetus and neonatal offspring. This sustained muscle contracture results in misshapen limbs, bent clavicles, and reduced diaphragm function, which compromises respiration in neonatal rats at birth, reducing their survival. This review evaluates the weight of evidence for this MoA based upon the Bradford Hill criteria, includes a cross-comparison of applied and internal doses in a variety of in vitro, ex vivo, and in vivo study designs, examines alternative MoAs, and applies a Human relevance framework (HRF) to ascertain human risk for this rat MoA. The review indicated, with a high level of confidence, that the sulfoxaflor-induced fetal abnormalities and neonatal death in rats occur via a single MoA comprising sustained activation of the rat fetal-type muscle nAChR resulting in a sustained muscle contracture. This MoA is considered not relevant to humans, given fundamental qualitative differences in sulfoxaflor agonism on the rat versus the human muscle nAChR. Specifically, sulfoxaflor does not cause agonism on either the human fetal- or adult-type muscle nAChR.
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http://dx.doi.org/10.3109/10408444.2014.910752DOI Listing
May 2014

Disposition of glycolic acid into rat and rabbit embryos in vitro.

Reprod Toxicol 2014 Jul 2;46:46-55. Epub 2014 Mar 2.

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland 48674, USA.

High dose gavage administration of ethylene glycol (EG) induces teratogenicity in rodents, but not in rabbits, resulting from saturation of intermediate EG metabolism and glycolic acid (GA) accumulation. In vivo, rat embryos sequester GA 2-4-fold higher than maternal blood, a phenomenon absent in rabbits and proposed not to occur in humans. This research explored the mechanisms of GA disposition into rat and rabbit conceptuses using whole embryo culture (WEC). Rat and rabbit embryos concentrated GA from the culture medium. In vitro to in vivo discordance in the rabbit plausibly stemmed from anatomical differences between these models. GA sequestration was attenuated at 4°C in both species. Rat embryos further demonstrated pH-dependence of GA sequestration and inhibition by D-lactic acid. These data suggest GA disposition into rat and rabbit embryos is energy- and pH-dependent, and carrier-mediated. Anatomical and maternal-to-conceptal pH gradient differences likely underlie the lack of enhanced GA disposition in non-rodent species.
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http://dx.doi.org/10.1016/j.reprotox.2014.02.005DOI Listing
July 2014

Incorporating new technologies into toxicity testing and risk assessment: moving from 21st century vision to a data-driven framework.

Toxicol Sci 2013 Nov 19;136(1):4-18. Epub 2013 Aug 19.

* The Hamner Institutes for Health Sciences, Research Triangle Park, North Carolina 27709;

Based on existing data and previous work, a series of studies is proposed as a basis toward a pragmatic early step in transforming toxicity testing. These studies were assembled into a data-driven framework that invokes successive tiers of testing with margin of exposure (MOE) as the primary metric. The first tier of the framework integrates data from high-throughput in vitro assays, in vitro-to-in vivo extrapolation (IVIVE) pharmacokinetic modeling, and exposure modeling. The in vitro assays are used to separate chemicals based on their relative selectivity in interacting with biological targets and identify the concentration at which these interactions occur. The IVIVE modeling converts in vitro concentrations into external dose for calculation of the point of departure (POD) and comparisons to human exposure estimates to yield a MOE. The second tier involves short-term in vivo studies, expanded pharmacokinetic evaluations, and refined human exposure estimates. The results from the second tier studies provide more accurate estimates of the POD and the MOE. The third tier contains the traditional animal studies currently used to assess chemical safety. In each tier, the POD for selective chemicals is based primarily on endpoints associated with a proposed mode of action, whereas the POD for nonselective chemicals is based on potential biological perturbation. Based on the MOE, a significant percentage of chemicals evaluated in the first 2 tiers could be eliminated from further testing. The framework provides a risk-based and animal-sparing approach to evaluate chemical safety, drawing broadly from previous experience but incorporating technological advances to increase efficiency.
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http://dx.doi.org/10.1093/toxsci/kft178DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3829570PMC
November 2013

The teratology society 2012-2017 strategic plan: pushing the boundaries.

Birth Defects Res A Clin Mol Teratol 2013 Jan;97(1):2-7

Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY, USA.

The Teratology Society held its fourth strategic planning session in Albuquerque, NM, April 10-12, 2012, and launched the 2012-2017 Strategic Plan in conjunction with the 2012 annual meeting in Baltimore, MD. Building on the energy of the successful implementation of prior strategic plans (San Diego, 2007; Nashville,TN 2002; Cincinnati, OH 1998), session participants worked to identify barriers to success as a scientific society, as well as impending challenges and opportunities to which the Society needs to respond. The following report provides an overview of the Strategic Planning process, objectives, activities, and conclusions. A total of 23 members were present at the session, and the group included representation from Council, various committees, and different member constituencies. This plan, Pushing the Boundaries, and its three strategic intents: Broaden Our Identity, Expand Our Membership, and Increase Our Influence, will drive the direction of the Teratology Society for the next five years.
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http://dx.doi.org/10.1002/bdra.23109DOI Listing
January 2013

Rabbit whole embryo culture.

Methods Mol Biol 2012 ;889:239-52

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, MI, USA.

Although the rabbit is used extensively in developmental toxicity testing, relatively little is known about the fundamental developmental biology of this species let alone mechanisms underlying developmental toxicity. This paucity of information about the rabbit is partly due to the historic lack of whole embryo culture (WEC) methods for the rabbit, which have only been made available fairly recently. In rabbit WEC, early somite stage embryos (gestation day 9) enclosed within an intact amnion and attached to the visceral yolk sac are dissected from maternal tissues and placed in culture for up to 48 h at approximately 37°C and are continuously exposed to an humidified gas atmosphere mixture in a rotating culture system. During this 48 h culture period, major phases of organogenesis can be studied including cardiac looping and segmentation, neural tube closure, and development of anlagen of the otic system, eyes and craniofacial structures, somites and early phases of limb development (up to bud stage), as well as expansion and closure of the visceral yolk sac around the embryo. Following completion of the culture period, embryos are evaluated based on several growth and development parameters and also are assessed for morphological abnormalities. The ability to sustain embryo development independent of the maternal system allows for exposure at precise development stages providing the opportunity study the direct action of a teratogen or one of its metabolites on the developing embryo. Rabbit WEC is perhaps most useful when used in conjunction with rodent WEC methods to investigate species-specific mechanisms of developmental toxicity.
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http://dx.doi.org/10.1007/978-1-61779-867-2_14DOI Listing
September 2012

A novel mode-of-action mediated by the fetal muscle nicotinic acetylcholine receptor resulting in developmental toxicity in rats.

Toxicol Sci 2012 Jun 29;127(2):522-34. Epub 2012 Mar 29.

Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, MI 48674, USA.

Sulfoxaflor (X11422208), a novel agricultural molecule, induced fetal effects (forelimb flexure, hindlimb rotation, and bent clavicle) and neonatal death in rats at high doses (≥ 400 ppm in diet); however, no such effects occurred in rabbit dietary studies despite achieving similar maternal and fetal plasma exposure levels. Mode-of-action (MoA) studies were conducted to test the hypothesis that the effects in rats had a single MoA induced by sulfoxaflor agonism on the fetal rat muscle nicotinic acetylcholine receptor (nAChR). The studies included cross-fostering and critical windows of exposure studies in rats, fetal ((α1)(2)β1γδ) and adult ((α1)(2)β1δε) rat and human muscle nAChR in vitro agonism experiments, and neonatal rat phrenic nerve-hemidiaphragm contracture studies. The weight of evidence from these studies supported a novel MoA where sulfoxaflor is an agonist to the fetal, but not adult, rat muscle nAChR and that prolonged agonism on this receptor in fetal/neonatal rats causes sustained striated muscle contracture resulting in concomitant reduction in muscle responsiveness to physiological nerve stimulation. Fetal effects were inducible with as little as 1 day of exposure at the end of gestation, but were rapidly reversible after birth, consistent with a pharmacological MoA. With respect to human relevance, sulfoxaflor was shown to have no agonism on human fetal or adult muscle nAChRs. Taken together, the data support the hypothesis that the developmental effects of sulfoxaflor in rats are mediated via sustained agonism on the fetal muscle nAChR during late fetal development and are considered not relevant to humans.
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http://dx.doi.org/10.1093/toxsci/kfs118DOI Listing
June 2012

Toxicokinetic profile of N-(2-aminoethyl)ethanolamine in the female Wistar rat and distribution into the late gestation fetus and milk.

Birth Defects Res B Dev Reprod Toxicol 2012 Apr 27;95(2):107-15. Epub 2012 Mar 27.

Toxicology and Environmental Research and Consulting, Dow Europe GmbH, Horgen, Switzerland.

N-(2-aminoethyl)ethanolamine (AEEA) caused aneurysms of the great vessels in rats exposed in utero and during the first days post partum, exacerbated by postnatal treatment of the lactating dams (Moore et al., 2012). The purpose of this work was to examine the systemic availability of AEEA during gestation and early lactation. The absorption of AEEA was determined following oral administration to nonpregnant and pregnant female Wistar rats. A single dose administered by gavage (0.5 or 50 mg/kg) on gestation day 18 was rapidly and extensively (>90%) absorbed from the gastrointestinal tract (absorption t(1/2) = 0.1-0.2 hr). Elimination from the plasma followed a biphasic pattern, with a rapid elimination phase (t(1/2 α) = 1.6-1.8 hr) followed by a slower phase (t(1/2 β) = 16.7-17.3 hr). Following repeated gavage administration during gestation day 17 to 19, (14) C-AEEA-derived radioactivity readily partitioned into the fetus and was evenly distributed therein, but cleared approximately twofold slower from the fetal blood and tissues than the maternal blood and chorioallantoic placenta. When administered to lactating dams during lactation days 1 to 12, (14) C-AEEA-derived radioactivity preferentially partitioned into the milk reaching levels that were between 1.6- and 2.5-fold higher than the maternal blood. Although the concentration of AEEA equivalents in the maternal blood remained quite consistent, the concentration in the milk fell by almost 40% between lactation days 4 and 12, probably reflecting an increase in milk production over this same period. We confirm exposure of the offspring to AEEA both in utero and during lactation, but that AEEA does not appear to specifically concentrate in the great vessels.
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http://dx.doi.org/10.1002/bdrb.21009DOI Listing
April 2012

Developmental sensitivity to the induction of great vessel malformations by N-(2-aminoethyl)ethanolamine.

Birth Defects Res B Dev Reprod Toxicol 2012 Apr 22;95(2):116-22. Epub 2012 Mar 22.

Toxicology and Environmental Research and Consulting, Dow Europe GmbH, Horgen, Switzerland.

N-(2-Aminoethyl)ethanolamine (AEEA) induced malformations of the great vessels in the offspring of rats treated during gestation and early lactation (Schneider et al., 2012. Birth Defects Res B Dev Reprod Toxicol [in press]). The aim of this study was to determine if in utero exposure alone was sufficient to induce these malformations or whether a peri-postnatal exposure or physiological component was required. Three groups of five time-mated female Wistar Han rats were administered AEEA (250 mg/kg/day) by gavage from gestation day (GD) 6 to GD 19 (groups 1 and 2) or from GD 6 to postnatal day 3 (group 3). Animals were euthanized on GD 21 (group 1) or postnatal day 4 (groups 2 and 3), and the hearts of the offspring were examined for changes to the great vessels. The incidence of malformations in group 1 was 91.1%, and primarily consisted of high aortic arch and abnormal carotid course. One fetus had an aortic aneurysm. All fetuses in groups 2 and 3 were malformed, primarily exhibiting abnormal carotid course and aneurysms, which mainly affected the aorta, ductus arteriosus, and pulmonary trunk. The incidence of high aortic arch was lower relative to group 1. Aneurysms were more prevalent in group 3 compared to group 2. These findings indicate that exposure to AEEA during gestation alone was sufficient to induce malformations of the great vessels and aneurysms, which may be triggered by physiological changes that occur during or after birth, but that the critical period of susceptibility to AEEA-induced aneurysms in the rat extends beyond gestation into the early postnatal period.
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http://dx.doi.org/10.1002/bdrb.21010DOI Listing
April 2012

Assessment of the developmental and reproductive toxicity of diiodomethyl-p-tolylsulfone in rats and rabbits.

Regul Toxicol Pharmacol 2012 Apr 8;62(3):474-81. Epub 2011 Dec 8.

Toxicology & Environmental Research and Consulting, The Dow Chemical Company, 1803 Building, Midland, MI 48674, USA.

Diiodomethyl-p-tolylsulfone (DIMPTS) was tested in developmental toxicity (DT) and reproductive toxicity studies. In the rat DT study, DIMPTS was administered at 0, 100, 300 or 1000 mg/kg/day. Maternal toxicity as evidenced by reductions in body weight gain or feed consumption at 1000 and, to a lesser extent, 300 mg/kg/day. The only developmental effect was umbilical hernia at 1000 mg/kg/day; therefore, NOELs for maternal and developmental toxicity were 100 and 300 mg/kg/day, respectively. In the rabbit DT study, NZW rabbits were gavaged with 0, 0.05, 0.5 and 2mg/kg/day DIMPTS. The NOEL for maternal toxicity was 0.5mg/kg/day, based on thyroid weight increase with histopathology. There were no observed developmental effects. In the two-generation study, CD rats were fed 0, 2.5, 10 or 40 mg/kg/day DIMPTS. Increased thyroid weight and histopathology were observed at all doses with associated pituitary findings in males. Reproductive toxicity at 40 mg/kg/day consisted of increased postimplantation loss, decreased gestation survival and two cases of dystocia, while litter size, pup survival/weight were affected at 10 and 40 mg/kg/day. The NOEL for parental toxicity could not be determined, while the NOEL for reproductive toxicity was 2.5mg/kg/day. The maternal thyroid and reproductive effects in this study were consistent with iodine toxicity.
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http://dx.doi.org/10.1016/j.yrtph.2011.11.017DOI Listing
April 2012

Role of iodine in diiodomethyl-p-tolylsulfone induced reproductive toxicity in rats: proposed mode of action.

Regul Toxicol Pharmacol 2012 Apr 23;62(3):496-503. Epub 2011 Oct 23.

Toxicology & Environmental Research and Consulting, The Dow Chemical Company, 1803 Building, Midland, MI 48674, USA.

The biocide diiodomethyl-p-tolylsulfone (DIMPTS) caused dystocia, decreased neonatal survival and hypothyroidism in rat reproduction studies resembling the effects caused by iodine. One molecule of DIMPTS contains two iodine moieties that are hydrolyzed upon ingestion and systemically absorbed, suggesting iodine toxicity as a probable mode of action for the effects observed in rats. This study compared the effects induced by DIMPTS and an equimolar concentration of its de-iodinated analogue, methyl-p-tolylsulfone (MPTS). Groups of 20 female Sprague Dawley rats were fed diets supplying 80 mg DIMPTS/kg/day, 32 mg MPTS/kg/day or control feed from prior to breeding through lactation and gonadal function, mating performance, conception, gestation, parturition, lactation, survival, growth and development of pups evaluated through postnatal day 7. Serum thyroid hormones and iodine levels in milk and sera were also determined. Females given DIMPTS had increased incidence of vulvar discharge and dystocia, decreased litter size, decreased body weights and feed consumption, increased thyroid weights, thyroid follicular cell hypertrophy with decreased colloid, decreased triidothyronine, and increased thyroid stimulating hormone levels. DIMPTS pups had decreased neonatal survival and body weights. These effects were associated with elevated levels of iodine in milk and sera. In contrast, MPTS did not produce similar effects in adult females or their offspring. These data support the hypothesis that the dystocia, altered neonatal survival and hypothyroidism following repeated dietary administration of DIMPTS were due to excessive iodine released from DIMPTS during absorption and metabolism.
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http://dx.doi.org/10.1016/j.yrtph.2011.10.010DOI Listing
April 2012

Critical evaluation of current developmental toxicity testing strategies: a case of babies and their bathwater.

Birth Defects Res B Dev Reprod Toxicol 2011 Oct 18;92(5):395-403. Epub 2011 Jul 18.

Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan 48674, USA.

This review is the second in a series of four papers emanating from a workshop entitled "Developmental Toxicology-New Directions," which was sponsored by the ILSI Health and Environmental Sciences Institute's (HESI) Developmental and Reproductive Toxicology Technical Committee. The present review analyzes the strengths and weaknesses of current developmental safety testing approaches in an effort to identify those strengths that should be retained in the future versus the weaknesses that should be eliminated. Workshop participants considered the following to be key strengths of current testing approaches: the integrated biology of pregnant animal models including pharmacokinetic and pharmacodynamic processes, the ability to detect low incidence malformations as well as maternally mediated toxicity, and the long history of use coupled with extensive historical data. A number of weaknesses were related to the resource-intensive nature of developmental toxicity testing (e.g., large number of animals, high costs, low throughput, the inability to keep pace with the demand for more toxicity data). Other weaknesses included the use of very high dose levels that often far exceed human exposure levels, the confounding influence of maternal toxicity, sparse understanding of basic developmental mechanisms and genetics of standard animal models relative to mouse or lower organisms, difficulties interpreting low incidence findings, and issues surrounding the interpretation of minor skeletal variations. An appreciation of these strengths and weaknesses is critical for the design of new approaches to developmental toxicity testing in the 21st century.
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http://dx.doi.org/10.1002/bdrb.20318DOI Listing
October 2011

A different approach to validating screening assays for developmental toxicity.

Birth Defects Res B Dev Reprod Toxicol 2010 Dec;89(6):526-30

Procter & Gamble, Cincinnati, Ohio, USA.

Background: There continue to be many efforts around the world to develop assays that are shorter than the traditional embryofetal developmental toxicity assay, or use fewer or no mammals, or use less compound, or have all three attributes. Each assay developer needs to test the putative assay against a set of performance standards, which traditionally has involved testing the assays against a list of compounds that are generally recognized as "positive" or "negative" in vivo. However, developmental toxicity is highly conditional, being particularly dependent on magnitude (i.e. dose) and timing of exposure, which makes it difficult to develop lists of compounds neatly assigned as developmental toxicants or not.

Approach: Here we offer an alternative approach for the evaluation of developmental toxicity assays based on exposures. Exposures are classified as "positive" or "negative" in a system, depending on the compound and the internal concentration. Although this linkage to "internal dose" departs from the recent approaches to validation, it fits well with widely accepted principles of developmental toxicology.

Conclusions: This paper introduces this concept, discusses some of the benefits and drawbacks of such an approach, and lays out the steps we propose to implement it for the evaluation of developmental toxicity assays.
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http://dx.doi.org/10.1002/bdrb.20276DOI Listing
December 2010

Endocrine disruption: historical perspectives and its impact on the future of toxicology testing.

Toxicol Sci 2011 Mar 25;120 Suppl 1:S93-108. Epub 2010 Oct 25.

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan 48674, USA.

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http://dx.doi.org/10.1093/toxsci/kfq329DOI Listing
March 2011

The impact of dose rate on ethylene glycol developmental toxicity and pharmacokinetics in pregnant CD rats.

Toxicol Sci 2011 Jan 15;119(1):178-88. Epub 2010 Oct 15.

Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan 48674, USA.

High-dose bolus exposure of rats to ethylene glycol (EG) causes developmental toxicity mediated by a metabolite, glycolic acid (GA), whose levels increase disproportionately when its metabolism is saturated. However, low-level exposures that do not saturate GA metabolism have a low potential for developmental effects. Toward the goal of developing EG risk assessments based on internal dose metrics, this study examined the differences between fast (bolus) and slow (continuous infusion) dose-rate exposures to EG on developmental outcome and pharmacokinetics. Time-mated female CD rats received sc bolus injections of 0, 1000, or 2000 mg/kg/day of EG on gestation day (GD) 6-15 once daily, whereas three corresponding groups were given the same daily doses as an infusion administered continuously from GD 6-15 via an sc implantable pump. In the sc bolus groups, increases in 11 fetal malformations (major defects) and 12 variations (minor alterations) were seen at the 2000 mg/kg/day dose level, whereas increases in 2 malformations and 2 variations occurred at 1000 mg/kg/day. In contrast, equivalent daily doses of EG given slowly via infusion did not cause any developmental effects. A pharmacokinetics time course was then conducted to compare GD 11-12 kinetics from oral bolus (gavage) exposure versus sc infusion of EG. Although dose rate had a modest impact (8- to 11-fold difference) on peak EG levels, peak levels of GA in maternal blood, kidney, embryo, and exocoelomic fluid were 59, 100, 49, and 56 times higher, respectively, following gavage versus the same dose given by infusion. These data illustrate how high-dose bolus exposure to EG causes a dramatic shift to nonlinear GA kinetics, an event which is highly unlikely to occur following exposures to humans associated with consumer and worker uses.
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http://dx.doi.org/10.1093/toxsci/kfq310DOI Listing
January 2011

Whole embryo culture: a "New" technique that enabled decades of mechanistic discoveries.

Birth Defects Res B Dev Reprod Toxicol 2010 Aug;89(4):304-12

Toxicology and Environmental Research and Consulting, The Dow Chemical Company, Midland, Michigan 48674, USA.

Denis New's development of the rodent whole embryo culture (WEC) method in the early 1960s was a groundbreaking achievement that gave embryologists and teratologists an unprecedented degree of access to the developing postimplantation rodent embryo. In the five decades since its development, WEC has enabled detailed investigations into the regulation of normal embryo development as well as a plethora of research on mechanisms of teratogenesis as induced by a wide range of agents. In addition, WEC is one of the few techniques that has been validated for use in teratogenicity screening of drugs and chemicals. In this review, we retrace the steps leading to New's development of WEC, and highlight many examples in which WEC played a crucial role leading to important discoveries in teratological research. The impact of WEC on the field of teratology has been enormous, and it is anticipated that WEC will remain a preferred tool for teratologists and embryologists seeking to interrogate embryo development for many years to come.
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http://dx.doi.org/10.1002/bdrb.20263DOI Listing
August 2010