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Wambaugh JF, Wetmore BA, Ring CL, Nicolas CI, Pearce R, Honda G, Dinallo R, Angus D, Gilbert J, Sierra T, Badrinarayanan A, Snodgrass B, Brockman A, Strock C, Setzer W, Thomas RS. Assessing Toxicokinetic Uncertainty and Variability in Risk Prioritization. Toxicol Sci 2019; 172:235-251. [PMID: 31532498 PMCID: PMC8136471 DOI: 10.1093/toxsci/kfz205] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
High(er) throughput toxicokinetics (HTTK) encompasses in vitro measures of key determinants of chemical toxicokinetics and reverse dosimetry approaches for in vitro-in vivo extrapolation (IVIVE). With HTTK, the bioactivity identified by any in vitro assay can be converted to human equivalent doses and compared with chemical intake estimates. Biological variability in HTTK has been previously considered, but the relative impact of measurement uncertainty has not. Bayesian methods were developed to provide chemical-specific uncertainty estimates for 2 in vitro toxicokinetic parameters: unbound fraction in plasma (fup) and intrinsic hepatic clearance (Clint). New experimental measurements of fup and Clint are reported for 418 and 467 chemicals, respectively. These data raise the HTTK chemical coverage of the ToxCast Phase I and II libraries to 57%. Although the standard protocol for Clint was followed, a revised protocol for fup measured unbound chemical at 10%, 30%, and 100% of physiologic plasma protein concentrations, allowing estimation of protein binding affinity. This protocol reduced the occurrence of chemicals with fup too low to measure from 44% to 9.1%. Uncertainty in fup was also reduced, with the median coefficient of variation dropping from 0.4 to 0.1. Monte Carlo simulation was used to propagate both measurement uncertainty and biological variability into IVIVE. The uncertainty propagation techniques used here also allow incorporation of other sources of uncertainty such as in silico predictors of HTTK parameters. These methods have the potential to inform risk-based prioritization based on the relationship between in vitro bioactivities and exposures.
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Affiliation(s)
- John F. Wambaugh
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
| | - Barbara A. Wetmore
- National Exposure Research Laboratory, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
| | - Caroline L. Ring
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831
| | - Chantel I. Nicolas
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831
- Office of Pollution Prevention and Toxics, U.S. EPA, Washington, D.C. 20460
| | - Robert Pearce
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831
| | - Gregory Honda
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
- Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37831
| | | | | | | | | | | | | | | | | | - Woodrow Setzer
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
| | - Russell S. Thomas
- National Center for Computational Toxicology, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711
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Truong L, Ouedraogo G, Pham L, Clouzeau J, Loisel-Joubert S, Blanchet D, Noçairi H, Setzer W, Judson R, Grulke C, Mansouri K, Martin M. Predicting in vivo effect levels for repeat-dose systemic toxicity using chemical, biological, kinetic and study covariates. Arch Toxicol 2018; 92:587-600. [PMID: 29075892 PMCID: PMC5818596 DOI: 10.1007/s00204-017-2067-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Accepted: 09/18/2017] [Indexed: 11/29/2022]
Abstract
In an effort to address a major challenge in chemical safety assessment, alternative approaches for characterizing systemic effect levels, a predictive model was developed. Systemic effect levels were curated from ToxRefDB, HESS-DB and COSMOS-DB from numerous study types totaling 4379 in vivo studies for 1247 chemicals. Observed systemic effects in mammalian models are a complex function of chemical dynamics, kinetics, and inter- and intra-individual variability. To address this complex problem, systemic effect levels were modeled at the study-level by leveraging study covariates (e.g., study type, strain, administration route) in addition to multiple descriptor sets, including chemical (ToxPrint, PaDEL, and Physchem), biological (ToxCast), and kinetic descriptors. Using random forest modeling with cross-validation and external validation procedures, study-level covariates alone accounted for approximately 15% of the variance reducing the root mean squared error (RMSE) from 0.96 log10 to 0.85 log10 mg/kg/day, providing a baseline performance metric (lower expectation of model performance). A consensus model developed using a combination of study-level covariates, chemical, biological, and kinetic descriptors explained a total of 43% of the variance with an RMSE of 0.69 log10 mg/kg/day. A benchmark model (upper expectation of model performance) was also developed with an RMSE of 0.5 log10 mg/kg/day by incorporating study-level covariates and the mean effect level per chemical. To achieve a representative chemical-level prediction, the minimum study-level predicted and observed effect level per chemical were compared reducing the RMSE from 1.0 to 0.73 log10 mg/kg/day, equivalent to 87% of predictions falling within an order-of-magnitude of the observed value. Although biological descriptors did not improve model performance, the final model was enriched for biological descriptors that indicated xenobiotic metabolism gene expression, oxidative stress, and cytotoxicity, demonstrating the importance of accounting for kinetics and non-specific bioactivity in predicting systemic effect levels. Herein, we generated an externally predictive model of systemic effect levels for use as a safety assessment tool and have generated forward predictions for over 30,000 chemicals.
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Affiliation(s)
- Lisa Truong
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
- Currently at Oregon State University, Corvallis, USA
| | - Gladys Ouedraogo
- L'Oréal Safety Research Department, 1 Avenue E. Schueller, 93600, Aulnay-Sous-Bois, France
| | - LyLy Pham
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Jacques Clouzeau
- L'Oréal Safety Research Department, 1 Avenue E. Schueller, 93600, Aulnay-Sous-Bois, France
| | - Sophie Loisel-Joubert
- L'Oréal Safety Research Department, 1 Avenue E. Schueller, 93600, Aulnay-Sous-Bois, France
| | - Delphine Blanchet
- L'Oréal Safety Research Department, 1 Avenue E. Schueller, 93600, Aulnay-Sous-Bois, France
| | - Hicham Noçairi
- L'Oréal Safety Research Department, 1 Avenue E. Schueller, 93600, Aulnay-Sous-Bois, France
| | - Woodrow Setzer
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Richard Judson
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Chris Grulke
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
| | - Kamel Mansouri
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA
- Currently at Scitovation LLC, Research Triangle Park, NC, USA
| | - Matthew Martin
- National Center for Computational Toxicology, Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, NC, 27711, USA.
- Currently at Pfizer, Inc, Drug Safety Research and Development, 445 Eastern Point Road, MS 8274-1224, Groton, CT, 06340, USA.
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Benford D, Bolger PM, Carthew P, Coulet M, DiNovi M, Leblanc JC, Renwick AG, Setzer W, Schlatter J, Smith B, Slob W, Williams G, Wildemann T. Application of the Margin of Exposure (MOE) approach to substances in food that are genotoxic and carcinogenic. Food Chem Toxicol 2010; 48 Suppl 1:S2-24. [PMID: 20113851 DOI: 10.1016/j.fct.2009.11.003] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Revised: 10/30/2009] [Accepted: 11/02/2009] [Indexed: 11/19/2022]
Abstract
This paper presents the work of an expert group established by the International Life Sciences Institute - European branch (ILSI Europe) to follow up the recommendations of an international conference on "Risk Assessment of Compounds that are both Genotoxic and Carcinogenic: New Approaches". Twelve genotoxic and carcinogenic chemicals that can be present in food were selected for calculation of a Margin of Exposure (MOE) between a point of departure on the dose-response for oral carcinogenicity in animal studies and estimates of human dietary exposure. The MOE can be used to support prioritisation of risk management action and, if the MOE is very large, on communication of a low level of human health concern. Depending on the approaches taken in determining the point of departure and the estimation of exposure, it is possible to derive very different values for the MOE. It is therefore essential that the selection of the cancer endpoint and mathematical treatment of the data are clearly described and justified if the results of the MOE approach are to be trusted and of value to risk managers. An outline framework for calculating an MOE is proposed in order to help to ensure transparency in the results.
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Williams LAD, Conrad J, Vogler B, Rösner H, Porter RBR, Setzer W, Barton EN, Levy HG, Mika S, Klaiber I, Nkurunziza JP, Kraus W. In vitro anti-proliferation/cytotoxic activity of epingaione and its derivatives on the human SH-SY5Y neuroblastoma and TE-671 sarcoma cells. W INDIAN MED J 2007; 56:5-10. [PMID: 17621837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Epingaione (4-Methyl-1-(5-methyl-2, 3,4,5-tetrahydro-[2,3']bifuranyl-5-yl)-pentan-2-one) was isolated as one of the major lipophilic secondary metabolites from the leaves and stems of Bontia daphnoides L. The compound gave 79.24% and 50.83% anti-proliferation/cytotoxic activity on the human SH-SY5Y neuroblastoma and TE-671 sarcoma cells in vitro at 50 pg/mL, respectively. Epingaione was transformed into eleven derivatives under laboratory conditions using ethanol, some gave greater anti-proliferation/cytotoxic activity on the cancer cell lines tested. One of the derivatives (compound 2) with enhanced cytotoxic activity was elucidated as 5'-Ethoxy-5-methyl-5-(4-methyl-2-oxo-pentyl)-2,3,4,5-tetrahydro-5'H-[2,3']bifuranyl-2'-one. Both epingaione and compound 2 caused an accumulation of arrested or dead SH-SY5Y neuroblastoma in the m-phase of the cell cycle as revealed by the m-phase specific marker KE 67.
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Affiliation(s)
- L A D Williams
- The University of Hohenheim, Institutes for Bio-organic Chemistry , Garbenstr 30, D-70593 Stuttgart, Germany.
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Abbott BD, Lau C, Buckalew AR, Logsdon TR, Setzer W, Zucker RM, Elstein KH, Kavlock RJ. Effects of 5-fluorouracil on embryonic rat palate in vitro: fusion in the absence of proliferation. Teratology 1993; 47:541-54. [PMID: 8367827 DOI: 10.1002/tera.1420470606] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
5-Fluorouracil (5-FU) inhibits the enzyme thymidylate synthetase (TS) which results in inhibition of DNA synthesis. 5-FU is teratogenic in many species, inducing cleft palate, limb, and tail defects. In the present study, gestation day (GD) 14 embryonic rat craniofacial explants were exposed to 5-FU in organ culture with increasing concentrations and durations of exposure. Palates exposed to 5-FU were morphologically abnormal and craniofacial shape, size, and palatal fusion pattern were affected with the severity of effects dependent on concentration and duration of exposure. Cleft palate was induced in vitro as opposing palates overlapped in a narrowed oral cavity. Palates exposed to higher levels of 5-FU were growth inhibited, but fused even though proliferation ceased and few cells were available to participate in elevation and fusion. This was demonstrated as a biphasic concentration-response profile for palatal fusion in which 0.05 to 0.15 micrograms 5-FU/ml produced decreasing rates of palatal fusion, while exposure to 0.15 to 3.0 micrograms/ml resulted in progressively increasing rates of fusion. The effects of 5-FU were detected biochemically as a reduction in TS activity which was concentration and time dependent during the first 12 hours, with a return to control levels by 24 hours. During the first day, 5-FU did not alter protein levels, but DNA levels significantly decreased at the high concentration, 2.0 micrograms/ml. After 5 days in culture, both DNA and protein decreased with increasing 5-FU concentration and duration of exposure. Also by the end of the culture period, 3H-TdR incorporation had decreased in a concentration dependent manner. It is concluded that progressive inhibition of proliferation and growth in organ culture results in two different morphological outcomes: cleft palate resulting from a narrowed oral cavity and increased incidence of anterior palatal fusion under conditions of strong growth reduction. This study demonstrates that elevation and fusion can occur in the absence of growth and proliferation. Based on these observations, severe inhibition of growth or proliferation would not necessarily be sufficient to induce cleft palate.
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Affiliation(s)
- B D Abbott
- Developmental Toxicology Division, Environmental Protection Agency, Research Triangle Park, North Carolina 27711
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