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Armitage JM, Sangion A, Parmar R, Looky AB, Arnot JA. Update and Evaluation of a High-Throughput In Vitro Mass Balance Distribution Model: IV-MBM EQP v2.0. TOXICS 2021; 9:toxics9110315. [PMID: 34822706 PMCID: PMC8625852 DOI: 10.3390/toxics9110315] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 11/15/2021] [Accepted: 11/17/2021] [Indexed: 11/16/2022]
Abstract
This study demonstrates the utility of an updated mass balance model for predicting the distribution of organic chemicals in in vitro test systems (IV-MBM EQP v2.0) and evaluates its performance with empirical data. The IV-MBM EQP v2.0 tool was parameterized and applied to four independent data sets with measured ratios of bulk medium or freely-dissolved to initial nominal concentrations (e.g., C24/C0 where C24 is the measured concentration after 24 h of exposure and C0 is the initial nominal concentration). Model performance varied depending on the data set, chemical properties (e.g., "volatiles" vs. "non-volatiles", neutral vs. ionizable organics), and model assumptions but overall is deemed acceptable. For example, the r2 was greater than 0.8 and the mean absolute error (MAE) in the predictions was less than a factor of two for most neutral organics included. Model performance was not as good for the ionizable organic chemicals included but the r2 was still greater than 0.7 and the MAE less than a factor of three. The IV-MBM EQP v2.0 model was subsequently applied to several hundred chemicals on Canada's Domestic Substances List (DSL) with nominal effects data (AC50s) reported for two in vitro assays. We report the frequency of chemicals with AC50s corresponding to predicted cell membrane concentrations in the baseline toxicity range (i.e., >20-60 mM) and tabulate the number of chemicals with "volatility issues" (majority of chemical in headspace) and "solubility issues" (freely-dissolved concentration greater than water solubility after distribution). In addition, the predicted "equivalent EQP blood concentrations" (i.e., blood concentration at equilibrium with predicted cellular concentration) were compared to the AC50s as a function of hydrophobicity (log octanol-water partition or distribution ratio). The predicted equivalent EQP blood concentrations exceed the AC50 by up to a factor of 100 depending on hydrophobicity and assay conditions. The implications of using AC50s as direct surrogates for human blood concentrations when estimating the oral equivalent doses using a toxicokinetic model (i.e., reverse dosimetry) are then briefly discussed.
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Affiliation(s)
- James M. Armitage
- AES Armitage Environmental Sciences, Inc., Ottawa, ON K1L 8C3, Canada
- Correspondence:
| | - Alessandro Sangion
- ARC Arnot Research and Consulting, Inc., Toronto, ON M4M 1W4, Canada; (A.S.); (R.P.); (A.B.L.); (J.A.A.)
- Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
| | - Rohan Parmar
- ARC Arnot Research and Consulting, Inc., Toronto, ON M4M 1W4, Canada; (A.S.); (R.P.); (A.B.L.); (J.A.A.)
| | - Alexandra B. Looky
- ARC Arnot Research and Consulting, Inc., Toronto, ON M4M 1W4, Canada; (A.S.); (R.P.); (A.B.L.); (J.A.A.)
| | - Jon A. Arnot
- ARC Arnot Research and Consulting, Inc., Toronto, ON M4M 1W4, Canada; (A.S.); (R.P.); (A.B.L.); (J.A.A.)
- Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON M5S 1A8, Canada
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Fischer FC, Henneberger L, Schlichting R, Escher BI. How To Improve the Dosing of Chemicals in High-Throughput in Vitro Mammalian Cell Assays. Chem Res Toxicol 2019; 32:1462-1468. [DOI: 10.1021/acs.chemrestox.9b00167] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Fabian C. Fischer
- Department Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Luise Henneberger
- Department Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Rita Schlichting
- Department Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Beate I. Escher
- Department Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
- Centre for Applied Geoscience, Eberhard Karls University Tübingen, 72074 Tübingen, Germany
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Groothuis FA, Timmer N, Opsahl E, Nicol B, Droge STJ, Blaauboer BJ, Kramer NI. Influence of in Vitro Assay Setup on the Apparent Cytotoxic Potency of Benzalkonium Chlorides. Chem Res Toxicol 2019; 32:1103-1114. [PMID: 31012305 PMCID: PMC6584903 DOI: 10.1021/acs.chemrestox.8b00412] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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The nominal concentration
is generally used to express concentration–effect
relationships in in vitro toxicity assays. However, the nominal concentration
does not necessarily represent the exposure concentration responsible
for the observed effect. Surfactants accumulate at interphases and
likely sorb to in vitro system components such as serum protein and
well plate plastic. The extent of sorption and the consequences of
this sorption on in vitro readouts is largely unknown for these chemicals.
The aim of this study was to demonstrate the effect of sorption to
in vitro components on the observed cytotoxic potency of benzalkonium
chlorides (BAC) varying in alkyl chain length (6–18 carbon
atoms, C6–18) in a basal cytotoxicity assay with
the rainbow trout gill cell line (RTgill-W1). Cells were exposed for
48 h in 96-well plates to increasing concentration of BACs in exposure
medium containing 0, 60 μM bovine serum albumin (BSA) or 10%
fetal bovine serum (FBS). Before and after exposure, BAC concentrations
in exposure medium were analytically determined. Based on freely dissolved
concentrations at the end of the exposure, median effect concentrations
(EC50) decreased with increasing alkyl chain length up
to 14 carbons. For BAC with alkyl chains of 12 or more carbons, EC50’s based on measured concentrations after exposure
in supplement-free medium were up to 25-times lower than EC50’s calculated using nominal concentrations. When BSA or FBS
was added to the medium, a decrease in cytotoxic potency of up to
22 times was observed for BAC with alkyl chains of eight or more carbons.
The results of this study emphasize the importance of expressing the
in vitro readouts as a function of a dose metric that is least influenced
by assay setup to compare assay sensitivities and chemical potencies.
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Affiliation(s)
- Floris A Groothuis
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
| | - Niels Timmer
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
| | - Eystein Opsahl
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
| | - Beate Nicol
- Safety & Environmental Assurance Centre , Unilever U.K. , Colworth Science Park, Sharnbrook, Bedford MK44 1LQ , United Kingdom
| | - Steven T J Droge
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
| | - Bas J Blaauboer
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
| | - Nynke I Kramer
- Institute for Risk Assessment Sciences , Utrecht University , PO Box 80177, 3508 TD Utrecht , The Netherlands
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Combes R, Balls M, Illing P, Bhogal N, Dale J, Duvé G, Feron V, Grindon C, Gülden M, Loizou G, Priston R, Westmoreland C. Possibilities for a New Approach to Chemicals Risk Assessment — The Report of a FRAME Workshop. Altern Lab Anim 2019; 34:621-49. [PMID: 17266394 DOI: 10.1177/026119290603400606] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Robert Combes
- FRAME, Russell & Burch House, 96-98 North Sherwood Street, Nottingham, NG1 4EE, UK.
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Coecke S, Ahr H, Blaauboer BJ, Bremer S, Casati S, Castell J, Combes R, Corvi R, Crespi CL, Cunningham ML, Elaut G, Eletti B, Freidig A, Gennari A, Ghersi-Egea JF, Guillouzo A, Hartung T, Hoet P, Ingelman-Sundberg M, Munn S, Janssens W, Ladstetter B, Leahy D, Long A, Meneguz A, Monshouwer M, Morath S, Nagelkerke F, Pelkonen O, Ponti J, Prieto P, Richert L, Sabbioni E, Schaack B, Steiling W, Testai E, Vericat JA, Worth A. Metabolism: A Bottleneck in In Vitro Toxicological Test Development. Altern Lab Anim 2019; 34:49-84. [PMID: 16522150 DOI: 10.1177/026119290603400113] [Citation(s) in RCA: 106] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Sandra Coecke
- ECVAM, Institute for Health and Consumer Protection, European Commission Joint Research Centre, Ispra, Italy
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Lammel T, Tsoukatou G, Jellinek J, Sturve J. Development of three-dimensional (3D) spheroid cultures of the continuous rainbow trout liver cell line RTL-W1. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2019; 167:250-258. [PMID: 30342358 DOI: 10.1016/j.ecoenv.2018.10.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Revised: 09/29/2018] [Accepted: 10/02/2018] [Indexed: 06/08/2023]
Abstract
In vitro experimental systems based on continuous piscine cell lines can be used as an alternative to animal tests for obtaining qualitative and quantitative information on the possible fate and effect of chemicals in fish. However, their capability to reproduce complex metabolic processes and toxic responses as they occur in vivo is limited due to the lack of organ-specific tissue architecture and functions. Here we introduce a three-dimensional (3D) in vitro experimental system based on spheroidal aggregate cultures (spheroids) of the continuous rainbow trout liver cell line RTL-W1 and provide a first description of their structural and functional properties including growth, viability/longevity, metabolic activity, ultrastructure and cytochrome P450 1A (CYP1A) expression determined by bright-field, multi-photon fluorescence and transmission electron microscopy as well as RT-qPCR analysis. Our results show that RTL-W1 cells in 3D spheroids (ø ~ 150 µm) (including those in the interior) were viable, metabolically active and had higher basal and β-naphthoflavone-induced CYP1A expression levels than conventional 2D cell cultures. Furthermore, they displayed ultrastructural characteristics similar to differentiated hepatocytes. The available evidence suggests that 3D RTL-W1 spheroids may have enhanced hepatotypic functions and be a superior in vitro model to assess hepatic biotransformation, bioaccumulation and chronic toxicity compared to conventional cell monolayer cultures.
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Affiliation(s)
- Tobias Lammel
- Department of Biological and Environmental Sciences, University of Gothenburg, Medicinaregatan 18 A, Box 463, 413 90 Göteborg, Sweden.
| | - Georgia Tsoukatou
- Department of Biological and Environmental Sciences, University of Gothenburg, Medicinaregatan 18 A, Box 463, 413 90 Göteborg, Sweden
| | - Johanna Jellinek
- Department of Biological and Environmental Sciences, University of Gothenburg, Medicinaregatan 18 A, Box 463, 413 90 Göteborg, Sweden
| | - Joachim Sturve
- Department of Biological and Environmental Sciences, University of Gothenburg, Medicinaregatan 18 A, Box 463, 413 90 Göteborg, Sweden
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Casey WM, Chang X, Allen DG, Ceger PC, Choksi NY, Hsieh JH, Wetmore BA, Ferguson SS, DeVito MJ, Sprankle CS, Kleinstreuer NC. Evaluation and Optimization of Pharmacokinetic Models for in Vitro to in Vivo Extrapolation of Estrogenic Activity for Environmental Chemicals. ENVIRONMENTAL HEALTH PERSPECTIVES 2018; 126:97001. [PMID: 30192161 PMCID: PMC6375436 DOI: 10.1289/ehp1655] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
BACKGROUND To effectively incorporate in vitro data into regulatory use, confidence must be established in the quantitative extrapolation of in vitro activity to relevant end points in animals or humans. OBJECTIVE Our goal was to evaluate and optimize in vitro to in vivo extrapolation (IVIVE) approaches using in vitro estrogen receptor (ER) activity to predict estrogenic effects measured in rodent uterotrophic studies. METHODS We evaluated three pharmacokinetic (PK) models with varying complexities to extrapolate in vitro to in vivo dosimetry for a group of 29 ER agonists, using data from validated in vitro [U.S. Environmental Protection Agency (U.S. EPA) ToxCast™ ER model] and in vivo (uterotrophic) methods. In vitro activity values were adjusted using mass-balance equations to estimate intracellular exposure via an enrichment factor (EF), and steady-state model calculations were adjusted using fraction of unbound chemical in the plasma ([Formula: see text]) to approximate bioavailability. Accuracy of each model-adjustment combination was assessed by comparing model predictions with lowest effect levels (LELs) from guideline uterotrophic studies. RESULTS We found little difference in model predictive performance based on complexity or route-specific modifications. Simple adjustments, applied to account for in vitro intracellular exposure (EF) or chemical bioavailability ([Formula: see text]), resulted in significant improvements in the predictive performance of all models. CONCLUSION Computational IVIVE approaches accurately estimate chemical exposure levels that elicit positive responses in the rodent uterotrophic bioassay. The simplest model had the best overall performance for predicting both oral (PPK_EF) and injection (PPK_[Formula: see text]) LELs from guideline uterotrophic studies, is freely available, and can be parameterized entirely using freely available in silico tools. https://doi.org/10.1289/EHP1655.
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Affiliation(s)
- Warren M Casey
- National Toxicology Program Division, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, USA
| | - Xiaoqing Chang
- Integrated Laboratory Systems, Inc., Morrisville, North Carolina, USA
| | - David G Allen
- Integrated Laboratory Systems, Inc., Morrisville, North Carolina, USA
| | - Patricia C Ceger
- Integrated Laboratory Systems, Inc., Morrisville, North Carolina, USA
| | - Neepa Y Choksi
- Integrated Laboratory Systems, Inc., Morrisville, North Carolina, USA
| | - Jui-Hua Hsieh
- Kelly Government Solutions, Research Triangle Park, North Carolina, USA
| | | | - Stephen S Ferguson
- National Toxicology Program Division, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, USA
| | - Michael J DeVito
- National Toxicology Program Division, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, USA
| | | | - Nicole C Kleinstreuer
- National Toxicology Program Division, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, USA
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8
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Timmer N, Scherpenisse P, Hermens JLM, Droge STJ. Evaluating solid phase (micro-) extraction tools to analyze freely ionizable and permanently charged cationic surfactants. Anal Chim Acta 2017; 1002:26-38. [PMID: 29306411 DOI: 10.1016/j.aca.2017.11.051] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 11/15/2017] [Accepted: 11/19/2017] [Indexed: 10/18/2022]
Abstract
Working with and analysis of cationic surfactants can be problematic since aqueous concentrations are difficult to control, both when taking environmental aqueous samples as well as performing laboratory work with spiked concentrations. For a selection of 32 amine based cationic surfactants (including C8- to C18-alkylamines, C14-dialkyldimethylammonium, C8-tetraalkylammonium, benzalkonium and pyridinium compounds), the extraction from aqueous samples was studied in detail. Aqueous concentrations were determined using solid phase extraction (SPE; 3 mL/60 mg Oasis WCX-SPE cartridges) with recoveries of ≥80% for 30 compounds, and ≥90% for 16 compounds. Sorption to glassware was evaluated in 120 mL flasks, 40 mL vials and 1.5 mL autosampler vials, using 15 mM NaCl, where the glass binding of simple primary amines and quaternary ammonium compounds increased with alkyl chain length. Sorption to the outside of pipette tips (≤20% of total amount in solution) when sampling aqueous solutions may interfere with accurate measurements. Polyacrylate solid phase microextraction (PA-SPME) fibers with two coating thicknesses (7 and 35 μm) were tested as potential extraction devices. The uptake kinetics, pH-dependence and influence of ionic strength on sorption to PA fibers were studied. Changing medium from 100 mM Na+ to 10 mM Ca2+ decreases Kfw with one order of magnitude. Results indicate that for PA-SPME neutral amines are absorbed rather than adsorbed, although the exact sorption mechanism remains to be elucidated. Further research remains necessary to establish a definitive applicability domain for PA-SPME. However, results indicate that alkyl chain lengths ≥14 carbon atoms and multiple alkyl chains become problematic. A calibration curve should always be measured together with the samples. In conclusion, it seems that for amine based surfactants PA-SPME does not provide the reliability and reproducibility necessary for precise sorption experiments, specifically for alkyl chain lengths beyond 12 carbon atoms.
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Affiliation(s)
- Niels Timmer
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands
| | - Peter Scherpenisse
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands
| | - Joop L M Hermens
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands
| | - Steven T J Droge
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80177, 3508 TD Utrecht, The Netherlands; Institute for Biodiversity and Ecosystem Dynamics, Department Freshwater and Marine Ecology, P.O. Box 94248, 1090 GE Amsterdam, The Netherlands.
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9
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Fischer FC, Henneberger L, König M, Bittermann K, Linden L, Goss KU, Escher BI. Modeling Exposure in the Tox21 in Vitro Bioassays. Chem Res Toxicol 2017; 30:1197-1208. [DOI: 10.1021/acs.chemrestox.7b00023] [Citation(s) in RCA: 84] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Fabian C. Fischer
- Department
Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Luise Henneberger
- Department
Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Maria König
- Department
Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Kai Bittermann
- Department
Analytical Environmental Chemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Lukas Linden
- Department
Analytical Environmental Chemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Kai-Uwe Goss
- Department
Analytical Environmental Chemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Beate I. Escher
- Department
Cell Toxicology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
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Gilbert D, Mayer P, Pedersen M, Vinggaard AM. Endocrine activity of persistent organic pollutants accumulated in human silicone implants--Dosing in vitro assays by partitioning from silicone. ENVIRONMENT INTERNATIONAL 2015; 84:107-114. [PMID: 26264162 DOI: 10.1016/j.envint.2015.07.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Revised: 05/28/2015] [Accepted: 07/04/2015] [Indexed: 06/04/2023]
Abstract
Persistent organic pollutants (POPs) accumulated in human tissues may pose a risk for human health by interfering with the endocrine system. This study establishes a new link between actual human internal POP levels and the endocrine active dose in vitro, applying partitioning-controlled dosing from silicone to the H295R steroidogenesis assay: (1) Measured concentrations of POPs in silicone breast implants were taken from a recent study and silicone disks were loaded according to these measurements. (2) Silicone disks were transferred into H295R cell culture plates in order to control exposure of the adrenal cells by equilibrium partitioning. (3) Hormone production of the adrenal cells was measured as toxicity endpoint. 4-Nonylphenol was used for method development, and the new dosing method was compared to conventional solvent-dosing. The two dosing modes yielded similar dose-dependent hormonal responses of H295R cells. However, with the partitioning-controlled freely dissolved concentrations (Cfree) as dose metrics, dose-response curves were left-shifted by two orders of magnitude relative to spiked concentrations. Partitioning-controlled dosing of POPs resulted in up to 2-fold increases in progestagen and corticosteroid levels at Cfree of individual POPs in or below the femtomolar range. Silicone acted not only as source of the POPs but also as a sorption sink for lipophilic hormones, stimulating the cellular hormone production. Methodologically, the study showed that silicone can be used as reference partitioning phase to transfer in vivo exposure in humans (silicone implants) to in vitro assays (partition-controlled dosing). The main finding was that POPs at the levels at which they are found in humans can interfere with steroidogenesis in a human adrenocortical cell line.
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Affiliation(s)
- Dorothea Gilbert
- Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark; Department of Environmental Science, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
| | - Philipp Mayer
- Department of Environmental Engineering, DTU Environment, Technical University of Denmark, Miljøvej 113, DK-2800 Kgs. Lyngby, Denmark
| | - Mikael Pedersen
- Division of Food Chemistry, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark
| | - Anne Marie Vinggaard
- Division of Diet, Disease Prevention and Toxicology, National Food Institute, Technical University of Denmark, Mørkhøj Bygade 19, DK-2860 Søborg, Denmark.
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Gülden M, Schreiner J, Seibert H. In vitro toxicity testing with microplate cell cultures: Impact of cell binding. Toxicology 2015; 332:41-51. [DOI: 10.1016/j.tox.2013.11.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Revised: 09/06/2013] [Accepted: 11/17/2013] [Indexed: 11/27/2022]
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Harrill JA, Robinette BL, Freudenrich TM, Mundy WR. Media formulation influences chemical effects on neuronal growth and morphology. In Vitro Cell Dev Biol Anim 2015; 51:612-29. [PMID: 25678462 DOI: 10.1007/s11626-015-9873-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Accepted: 01/21/2015] [Indexed: 12/23/2022]
Abstract
Screening for developmental neurotoxicity using in vitro, cell-based systems has been proposed as an efficient alternative to performing in vivo studies. One tool currently used for developmental neurotoxicity screening is automated high-content imaging of neuronal morphology. While high-content imaging (HCI) has been demonstrated to be useful in detection of potential developmental neurotoxicants, comparison of results between laboratories or assays can be complicated due to methodological differences. In order to determine whether high-content imaging-based developmental neurotoxicity assays can be affected by differences in media formulation, a systematic comparison of serum-supplemented (Dulbecco's modified Eagle's media (DMEM) + 10% serum) and serum-free (Neurobasal A + B27) culture media on neuronal morphology was performed using primary rat cortical neurons. Concentration-response assays for neuritogenesis, axon and dendrite outgrowth, and synaptogenesis were performed in each media type using chemicals with previously demonstrated effects. Marked qualitative and quantitative differences in the characteristics of neurons cultured in the two media types were observed, with increased neuronal growth and less basal cell death in Neurobasal A + B27. Media formulation also affected assay sensitivity and selectivity. Increases in assay sensitivity were observed in Neurobasal A + B27 media as compared to serum-supplemented DMEM. In some instances, a greater difference between effective concentrations for cell death and neurodevelopmental-specific endpoints was also observed in Neurobasal A + B27 media as compared to serum-supplemented DMEM. These data show that media formulation must be considered when comparing data for similar endpoints between studies. Neuronal culture maintained in Neurobasal A + B27 media had several features advantageous for HCI applications including less basal cell death, less cell clustering and neurite fasciculation, and a tendency towards increased sensitivity and selectivity in chemical concentration-response studies.
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Affiliation(s)
- Joshua A Harrill
- Integrated Systems Toxicology Division, National Health and Environmental Effects Research Laboratory (NHEERL), United States Environmental Protection Agency, 109 TW Alexander Drive, Research Triangle Park, NC, 27711, USA
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13
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Armitage JM, Wania F, Arnot JA. Application of mass balance models and the chemical activity concept to facilitate the use of in vitro toxicity data for risk assessment. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:9770-9. [PMID: 25014875 DOI: 10.1021/es501955g] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Practical, financial, and ethical considerations related to conducting extensive animal testing have resulted in various initiatives to promote and expand the use of in vitro testing data for chemical evaluations. Nominal concentrations in the aqueous phase corresponding to an effect (or biological activity) are commonly reported and used to characterize toxicity (or biological response). However, the true concentration in the aqueous phase can be substantially different from the nominal. To support in vitro test design and aid the interpretation of in vitro toxicity data, we developed a mass balance model that can be parametrized and applied to represent typical in vitro test systems. The model calculates the mass distribution, freely dissolved concentrations, and cell/tissue concentrations corresponding to the initial nominal concentration and experimental conditions specified by the user. Chemical activity, a metric which can be used to assess the potential for baseline toxicity to occur, is also calculated. The model is first applied to a set of hypothetical chemicals to illustrate the degree to which test conditions (e.g., presence or absence of serum) influence the distribution of the chemical in the test system. The model is then applied to set of 1194 real substances (predominantly from the ToxCast chemical database) to calculate the potential range of concentrations and chemical activities under assumed test conditions. The model demonstrates how both concentrations and chemical activities can vary by orders of magnitude for the same nominal concentration.
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Affiliation(s)
- James M Armitage
- Department of Physical and Environmental Sciences, University of Toronto Scarborough , 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada
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14
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Kittler K, Fessard V, Maul R, Hurtaud-Pessel D. CYP3A4 activity reduces the cytotoxic effects of okadaic acid in HepaRG cells. Arch Toxicol 2014; 88:1519-26. [DOI: 10.1007/s00204-014-1206-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Accepted: 01/20/2014] [Indexed: 11/29/2022]
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15
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Comparative effects of sodium channel blockers in short term rat whole embryo culture. Toxicol Appl Pharmacol 2013; 272:306-12. [DOI: 10.1016/j.taap.2013.06.023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Revised: 06/16/2013] [Accepted: 06/21/2013] [Indexed: 02/01/2023]
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16
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Groothuis FA, Heringa MB, Nicol B, Hermens JLM, Blaauboer BJ, Kramer NI. Dose metric considerations in in vitro assays to improve quantitative in vitro-in vivo dose extrapolations. Toxicology 2013; 332:30-40. [PMID: 23978460 DOI: 10.1016/j.tox.2013.08.012] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Revised: 07/17/2013] [Accepted: 08/14/2013] [Indexed: 12/17/2022]
Abstract
Challenges to improve toxicological risk assessment to meet the demands of the EU chemical's legislation, REACH, and the EU 7th Amendment of the Cosmetics Directive have accelerated the development of non-animal based methods. Unfortunately, uncertainties remain surrounding the power of alternative methods such as in vitro assays to predict in vivo dose-response relationships, which impedes their use in regulatory toxicology. One issue reviewed here, is the lack of a well-defined dose metric for use in concentration-effect relationships obtained from in vitro cell assays. Traditionally, the nominal concentration has been used to define in vitro concentration-effect relationships. However, chemicals may differentially and non-specifically bind to medium constituents, well plate plastic and cells. They may also evaporate, degrade or be metabolized over the exposure period at different rates. Studies have shown that these processes may reduce the bioavailable and biologically effective dose of test chemicals in in vitro assays to levels far below their nominal concentration. This subsequently hampers the interpretation of in vitro data to predict and compare the true toxic potency of test chemicals. Therefore, this review discusses a number of dose metrics and their dependency on in vitro assay setup. Recommendations are given on when to consider alternative dose metrics instead of nominal concentrations, in order to reduce effect concentration variability between in vitro assays and between in vitro and in vivo assays in toxicology.
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Affiliation(s)
- Floris A Groothuis
- Institute for Risk Assessment Sciences, Utrecht University, PO Box 80177, 3508 TD Utrecht, The Netherlands.
| | - Minne B Heringa
- National Institute of Public Health and the Environment (RIVM), PO Box 1, 3720 BA Bilthoven, The Netherlands.
| | - Beate Nicol
- Unilever U.K., Safety & Environmental Assurance Centre, Colworth Science Park, Sharnbrook, Bedford MK44 1LQ, United Kingdom.
| | - Joop L M Hermens
- Institute for Risk Assessment Sciences, Utrecht University, PO Box 80177, 3508 TD Utrecht, The Netherlands.
| | - Bas J Blaauboer
- Institute for Risk Assessment Sciences, Utrecht University, PO Box 80177, 3508 TD Utrecht, The Netherlands.
| | - Nynke I Kramer
- Institute for Risk Assessment Sciences, Utrecht University, PO Box 80177, 3508 TD Utrecht, The Netherlands.
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17
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Yoon M, Campbell JL, Andersen ME, Clewell HJ. Quantitativein vitrotoin vivoextrapolation of cell-based toxicity assay results. Crit Rev Toxicol 2012; 42:633-52. [DOI: 10.3109/10408444.2012.692115] [Citation(s) in RCA: 162] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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18
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Escher BI, Ashauer R, Dyer S, Hermens JLM, Lee JH, Leslie HA, Mayer P, Meador JP, Warne MSJ. Crucial role of mechanisms and modes of toxic action for understanding tissue residue toxicity and internal effect concentrations of organic chemicals. INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT 2011; 7:28-49. [PMID: 21184568 DOI: 10.1002/ieam.100] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
This article reviews the mechanistic basis of the tissue residue approach for toxicity assessment (TRA). The tissue residue approach implies that whole-body or organ concentrations (residues) are a better dose metric for describing toxicity to aquatic organisms than is the aqueous concentration typically used in the external medium. Although the benefit of internal concentrations as dose metrics in ecotoxicology has long been recognized, the application of the tissue residue approach remains limited. The main factor responsible for this is the difficulty of measuring internal concentrations. We propose that environmental toxicology can advance if mechanistic considerations are implemented and toxicokinetics and toxicodynamics are explicitly addressed. The variability in ecotoxicological outcomes and species sensitivity is due in part to differences in toxicokinetics, which consist of several processes, including absorption, distribution, metabolism, and excretion (ADME), that influence internal concentrations. Using internal concentrations or tissue residues as the dose metric substantially reduces the variability in toxicity metrics among species and individuals exposed under varying conditions. Total internal concentrations are useful as dose metrics only if they represent a surrogate of the biologically effective dose, the concentration or dose at the target site. If there is no direct proportionality, we advise the implementation of comprehensive toxicokinetic models that include deriving the target dose. Depending on the mechanism of toxicity, the concentration at the target site may or may not be a sufficient descriptor of toxicity. The steady-state concentration of a baseline toxicant associated with the biological membrane is a good descriptor of the toxicodynamics of baseline toxicity. When assessing specific-acting and reactive mechanisms, additional parameters (e.g., reaction rate with the target site and regeneration of the target site) are needed for characterization. For specifically acting compounds, intrinsic potency depends on 1) affinity for, and 2) type of interaction with, a receptor or a target enzyme. These 2 parameters determine the selectivity for the toxic mechanism and the sensitivity, respectively. Implementation of mechanistic information in toxicokinetic-toxicodynamic (TK-TD) models may help explain time-delayed effects, toxicity after pulsed or fluctuating exposure, carryover toxicity after sequential pulses, and mixture toxicity. We believe that this mechanistic understanding of tissue residue toxicity will lead to improved environmental risk assessment.
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Affiliation(s)
- Beate I Escher
- Department of Environmental Toxicology (Utox), Swiss Federal Institute of Aquatic Science and Technology (Eawag), Überlandstrasse 133, PO Box 611, 8600 Dübendorf, Switzerland.
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19
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Hermens JLM, Heringa MB, ter Laak TL. Bioavailability in dose and exposure assessment of organic contaminants in (eco)toxicology. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2007; 70:727-30. [PMID: 17613742 DOI: 10.1080/15287390701236157] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The dose is an essential element in toxicology and risk assessment. In most cases, the dose is expressed as a concentration in the external environment. The internal dose is a more direct measure for the exposure in toxicological assays, because it takes differences in bioavailability into account. Because the internal dose is often not measurable, the effective free concentration in a medium or the environment is a useful alternative. This short review discusses the advantages of free concentration measurements of organic compounds for interpretation of effects in sediment and soil tests as well as for in vitro assays.
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Affiliation(s)
- Joop L M Hermens
- Institute for Risk Assessment Sciences, Utrecht University, The Netherlands.
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20
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Gülden M, Seibert H. The improvement of in vitro cytotoxicity testing for the assessment of acute toxicity in fish. Altern Lab Anim 2007; 35:39-46. [PMID: 17411350 DOI: 10.1177/026119290703500108] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The use of fish cell line cytotoxicity tests as alternatives to acute lethality tests with fish is hampered by the clearly lower sensitivity of the fish cell line tests. Recently, it has been shown that this is not a unique feature of fish cells. In fact, the sensitivity of mammalian and human cell lines toward the cytotoxic actions of chemicals, in general, is comparable to that of fish cell lines. Reviewing some of our recent investigations, the objective of this paper is to show that the sensitivity of in vitro cytotoxicity testing and the correspondence between in vitro cytotoxic and acute fish toxic concentrations (LC50) can be increased, if: a) inhibition of cell growth instead of cell death is used as the endpoint; and b) the bioavailable free cytotoxic concentration (ECu50) of chemicals in vitro, instead of the nominal cytotoxic concentration (EC50), is used as the measure of cytotoxic potency. Based on these results, a pragmatic in vitro testing strategy for estimating the minimal aquatic toxic potency of chemicals is proposed.
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Affiliation(s)
- Michael Gülden
- Institute of Toxicology and Pharmacology for Natural Scientists, Kiel Campus, University Medical School of Schleswig-Holstein, Kiel, Germany.
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21
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Schirmer K. Proposal to improve vertebrate cell cultures to establish them as substitutes for the regulatory testing of chemicals and effluents using fish. Toxicology 2006; 224:163-83. [PMID: 16765501 DOI: 10.1016/j.tox.2006.04.042] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2006] [Revised: 04/05/2006] [Accepted: 04/05/2006] [Indexed: 11/18/2022]
Abstract
Cultures of vertebrate cells are widely applied in mechanistic studies in human toxicology as well as in toxicity identification in ecotoxicology. As in vitro models, they display many advantages over whole animal experimentation, pertaining to such characteristics as availability, reproducibility and costs. As well, they satisfy the societal desire to reduce the number of animals in toxicology. For these reasons vertebrate cell models also appear to be a desirable replacement for animals in regulatory tests. Several vertebrate cell models are now accepted for regulatory purposes in human health sciences, with the test for photocytotoxicity using the 3T3 mouse cell line being one example. However, an in vitro alternative to whole animal tests has not yet been established for regulatory risk assessment in ecotoxicology. This review sets out to outline why such a replacement has not yet been possible and explores avenues to improve vertebrate cell cultures so that a replacement of whole animal tests could more likely be achieved. Inasmuch as fish is the most widely used non-mammalian vertebrate in risk assessment and regulation, focus will be on the replacement, by in vitro vertebrate models, of fish.
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Affiliation(s)
- Kristin Schirmer
- Department of Cell Toxicology (CellTox), UFZ-Centre for Environmental Research Leipzig-Halle in the Helmholtz Association, Permoserstr. 15, 04318 Leipzig, Germany.
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Abstract
The use of data from non-animal toxicity methods in risk assessment has mainly been limited to hazard identification and for elucidating mechanisms of toxicity. However, there is a need to extend the use of in vitro tests to hazard characterisation and risk assessment. This might be feasible by: (a) increased use of human cells of different types; (b) better maintenance of differentiated cells in culture for long periods; (c) use of genetically-engineered cells with useful characteristics; (d) development of complex organotypic cell systems; (e) development of co-cultures of different cell types; and (f) development of techniques for long term culturing, repeat dosing and assessment of recovery. Also, it will be necessary to obtain more information on the differences between cells in culture and in situ in tissues, and on the effects of dosing in vitro and in vivo, to develop realistic and meaningful uncertainty factors to allow in vitro information to be used for risk assessment in its own right, and in conjunction with animal data. These issues and a suggested proposal for using in vitro data in risk assessment are discussed.
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Heringa MB, Schreurs RHMM, Busser F, van der Saag PT, van der Burg B, Hermens JLM. Toward more useful in vitro toxicity data with measured free concentrations. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2004; 38:6263-70. [PMID: 15597880 DOI: 10.1021/es049285w] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
In vitro assays and computer models are promising alternatives for in vivo animal testing, but the power of these alternative methods to predict in vivo risk is still very limited. One step forward is to make the outcome of in vitro assays (such as median effect concentrations (EC50 values)) independent of assay conditions such as protein content. Here we show that measured free concentrations of chemicals in the in vitro assay medium result in system-independent EC50 values. We introduce a very simple method to measure free concentrations in miniature test systems using negligible depletion solid-phase microextraction. The generated data are much more suitable for extrapolation to in vivo, provide unbiased input for computational methods (for example, quantitative structure-activity relationships), and can shed an entirely different light on the activity of environmental contaminants.
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Affiliation(s)
- Minne B Heringa
- Institute for Risk Assessment Sciences, Utrecht University, Yalelaan 2, 3584 CL Utrecht, The Netherlands.
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24
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Heringa M, Hermens J. Measurement of free concentrations using negligible depletion-solid phase microextraction (nd-SPME). Trends Analyt Chem 2003. [DOI: 10.1016/s0165-9936(03)01006-9] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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25
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Escher BI, Hermens JLM. Modes of action in ecotoxicology: their role in body burdens, species sensitivity, QSARs, and mixture effects. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2002; 36:4201-17. [PMID: 12387389 DOI: 10.1021/es015848h] [Citation(s) in RCA: 311] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
In contrast to the general research attitude in the basic sciences, environmental sciences are often goal-driven and should provide the scientific basis for risk assessment procedures, cleanup, and precautionary measures and finally provide a decision support for policy and management. Hence, the prominent role of mechanistic studies in ecotoxicology is not only to understand the impact of pollutants on living organisms but also to deduce general principles for the categorization and assessment of effects. The goal of this review is, therefore, not to provide an exhaustive coverage of modes of toxic action and their underlying biochemical mechanisms but rather to discuss critically the application of this knowledge in ecotoxicological risk assessment. Knowing the mechanism or, at least the mode of toxic action is indispensable for developing descriptive and predictive models in ecotoxicology. This review seeks to show the crucial role of target sites, interactions with the target site(s), and mechanisms for an adequate and efficient ecotoxicological risk assessment. Emphasis in the discussion is on target effect concentrations (or target occupancy), species selectivity and species sensitivity, time perspective of effect studies, Quantitative Structure-Activity Relationships (QSAR), and mixture toxicity. A particular focus of this review is on multiple mechanisms. Although the illustrative examples were mainly taken from studies in aquatic ecotoxicology, the proposed conceptual approach is also in principle applicable and even particularly useful for soil and sediment systems. Recommendations for further research and developments include the use of internal effect concentrations and target site concentrations in site-specific risk assessment and as a mixture toxicity parameter as well as general considerations for the derivation of mechanistically meaningful QSAR and other predictive models.
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Affiliation(s)
- Beate I Escher
- Swiss Federal Institute for Environmental Science and Technology (EAWAG), Dübendorf.
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26
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Gülden M, Mörchel S, Tahan S, Seibert H. Impact of protein binding on the availability and cytotoxic potency of organochlorine pesticides and chlorophenols in vitro. Toxicology 2002; 175:201-13. [PMID: 12049848 DOI: 10.1016/s0300-483x(02)00085-9] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In vitro toxicity data are generally based on nominal concentrations and thus depend on both activity and availability of a compound. The aims of the present study were to examine the influence of protein binding on the cytotoxicity of selected organochlorine pesticides and chlorophenols in Balb/c 3T3 cell cultures and to determine parameters of protein binding which can be used to estimate protein bound fractions and to model distribution in vitro. EC(50)-values derived from concentration-effect relationships determined in the presence of various concentrations of bovine serum albumin (BSA) were linearly correlated to BSA concentration. Increasing the BSA concentration from about 1.2 to 40 mg/ml increased the EC(50)-values by factors between 3.4 and 34.4. Molar ratios of substance bound to albumin ranged from 0.11 to 2.42. Calculated fractions bound to albumin in the normal growth medium were 0.075-0.17 (p,p'-DDT, p,p'-DDE, dieldrin, lindane), 0.09-0.1 (4-mono- and 2,4-dichlorophenol), 0.68 (2,4,5-trichlorphenol) and almost 1.0 (pentachlorophenol). At 40 mg/ml BSA any compound was largely bound to albumin (fractions bound > or = 0.74). Distribution modelling revealed that the availability of the highly hydrophobic organochlorines additionally was significantly reduced by partitioning into lipids. The results clearly demonstrate that nominal and relative toxic potencies of organochlorine pesticides and chlorophenols determined in vitro are substantially influenced by effects of protein binding on availability.
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Affiliation(s)
- Michael Gülden
- Institut für Experimentelle Toxikologie, Universitätsklinikum Kiel, Weimarer Str. 8, Haus 3, D-24106 Kiel, Germany.
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27
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Chapter 8 Characterization of analyte binding and freely dissolved concentrations in environmental and biological materials. ACTA ACUST UNITED AC 2002. [DOI: 10.1016/s0166-526x(02)80045-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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28
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Gülden M, Mörchel S, Seibert H. Factors influencing nominal effective concentrations of chemical compounds in vitro: cell concentration. Toxicol In Vitro 2001; 15:233-43. [PMID: 11377096 DOI: 10.1016/s0887-2333(01)00008-x] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In vitro potency data (e.g. EC(50) values), used to characterise the biological activity of chemicals, are generally based on nominal effective concentrations and thus depend on any factor influencing the availability of a compound. In this study the significance of cell binding for the availability of chemicals in vitro is (i) theoretically investigated by means of a simple equilibrium distribution model and (ii) experimentally examined using a bull sperm assay to measure the cytotoxic potency of selected compounds at different cell concentrations. Compounds were selected either to cover a wide range of hydrophobicity (log K(ow)=2.52-5.69) or to represent modes of cell binding other than partitioning into cellular lipids. With the exception of xylene, the EC(50) values increased with increasing cell concentration. The ratios of EC(50) values determined at about 120 x 10(6) and 15 x 10(6) cells/ml were: pentachlorophenol. 1.2, 1-nitronaphthalene: 1.9, thioridazine: 2.7, dieldrin: 4.1, hexachlorophene: 4.1, digitonin: 5.1, methylmercury chloride: 7.9, antimycin A: 10.1 and p,p'-dichlorodiphenyl dichloroethylene (p,p'-DDE): >19.1. The influence of partitioning into cell lipids was rather well predicted by the equilibrium distribution model, except for p,p'-DDE. The results show that cell binding can significantly affect the availability of compounds in vitro and thus toxic potencies and toxic equivalency factors.
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Affiliation(s)
- M Gülden
- Institut für Toxikologie, Universitätsklinikum Kiel, Weimarer Str. 8, Haus 3, D-24106, Kiel, Germany.
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