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Fragki S, Piersma AH, Rorije E, Zeilmaker MJ. In vitro to in vivo extrapolation of effective dosimetry in developmental toxicity testing: Application of a generic PBK modelling approach. Toxicol Appl Pharmacol 2017; 332:109-120. [PMID: 28760446 DOI: 10.1016/j.taap.2017.07.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 07/10/2017] [Accepted: 07/28/2017] [Indexed: 11/25/2022]
Abstract
Incorporation of kinetics to quantitative in vitro to in vivo extrapolations (QIVIVE) is a key step for the realization of a non-animal testing paradigm, in the sphere of regulatory toxicology. The use of Physiologically-Based Kinetic (PBK) modelling for determining systemic doses of chemicals at the target site is accepted to be an indispensable element for such purposes. Nonetheless, PBK models are usually designed for a single or a group of compounds and are considered demanding, with respect to experimental data needed for model parameterization. Alternatively, we evaluate here the use of a more generic approach, i.e. the so-called IndusChemFate model, which is based on incorporated QSAR model parametrization. The model was used to simulate the in vivo kinetics of three diverse classes of developmental toxicants: triazoles, glycol ethers' alkoxyacetic acid metabolites and phthalate primary metabolites. The model required specific input per each class of compounds. These compounds were previously tested in three alternative assays: the whole-embryo culture (WEC), the zebrafish embryo test (ZET), and the mouse embryonic stem cell test (EST). Thereafter, the PBK-simulated blood levels at toxic in vivo doses were compared to the respective in vitro effective concentrations. Comparisons pertaining to relative potency and potency ranking with integration of kinetics were similar to previously obtained comparisons. Additionally, all three in vitro systems produced quite comparable results, and hence, a combination of alternative tests is still preferable for predicting the endpoint of developmental toxicity in vivo. This approach is put forward as biologically more plausible since plasma concentrations, rather than external administered doses, constitute the most direct in vivo dose metric.
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Affiliation(s)
- Styliani Fragki
- Center for Health Protection, RIVM, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
| | - Aldert H Piersma
- Center for Health Protection, RIVM, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands; Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80178, 3508 TD Utrecht, The Netherlands.
| | - Emiel Rorije
- Center for Health Protection, RIVM, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
| | - Marco J Zeilmaker
- Center for Health Protection, RIVM, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
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2
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New HBM values for emerging substances, inventory of reference and HBM values in force, and working principles of the German Human Biomonitoring Commission. Int J Hyg Environ Health 2017; 220:152-166. [DOI: 10.1016/j.ijheh.2016.09.007] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Accepted: 09/13/2016] [Indexed: 01/09/2023]
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3
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Gadekar-Shinde S, Reddy B, Khan M, Chavan S, Saini D, Mahajani S. Reactive Distillation for the Production of Methoxy Propyl Acetate: Experiments and Simulation. Ind Eng Chem Res 2017. [DOI: 10.1021/acs.iecr.6b03489] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shambala Gadekar-Shinde
- Sinhgad College of Engineering, Pune, 411041, India
- Chemical
Engineering Department, Bharati Vidyapeeth University College of Engineering (BVUCOE), Pune, 411043, India
- Savitribai Phule Pune University (SPPU), Pune, 411007, India
| | - Bhoja Reddy
- Department
of Chemical Engineering, Indian Institute of Technology, Bombay, Powai,
Mumbai, 400076, India
| | - Mohammad Khan
- Department
of Chemical Engineering, Indian Institute of Technology, Bombay, Powai,
Mumbai, 400076, India
| | - Sanjay Chavan
- Sinhgad College of Engineering, Pune, 411041, India
- Savitribai Phule Pune University (SPPU), Pune, 411007, India
| | - Daulat Saini
- National Chemical Laboratory, Pune, 411008, India
| | - Sanjay Mahajani
- Department
of Chemical Engineering, Indian Institute of Technology, Bombay, Powai,
Mumbai, 400076, India
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4
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Kuempel ED, Sweeney LM, Morris JB, Jarabek AM. Advances in Inhalation Dosimetry Models and Methods for Occupational Risk Assessment and Exposure Limit Derivation. JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 2015; 12 Suppl 1:S18-40. [PMID: 26551218 PMCID: PMC4685615 DOI: 10.1080/15459624.2015.1060328] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The purpose of this article is to provide an overview and practical guide to occupational health professionals concerning the derivation and use of dose estimates in risk assessment for development of occupational exposure limits (OELs) for inhaled substances. Dosimetry is the study and practice of measuring or estimating the internal dose of a substance in individuals or a population. Dosimetry thus provides an essential link to understanding the relationship between an external exposure and a biological response. Use of dosimetry principles and tools can improve the accuracy of risk assessment, and reduce the uncertainty, by providing reliable estimates of the internal dose at the target tissue. This is accomplished through specific measurement data or predictive models, when available, or the use of basic dosimetry principles for broad classes of materials. Accurate dose estimation is essential not only for dose-response assessment, but also for interspecies extrapolation and for risk characterization at given exposures. Inhalation dosimetry is the focus of this paper since it is a major route of exposure in the workplace. Practical examples of dose estimation and OEL derivation are provided for inhaled gases and particulates.
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Affiliation(s)
- Eileen D. Kuempel
- National Institute for Occupational Safety and Health, Education and Information Division, Cincinnati, Ohio
| | - Lisa M. Sweeney
- Henry M. Jackson Foundation for the Advancement of Military Medicine, Naval Medical Research Unit Dayton, Wright-Patterson Air Force Base, Ohio
| | - John B. Morris
- School of Pharmacy, University of Connecticut, Storrs, Connecticut
| | - Annie M. Jarabek
- U.S. Environmental Protection Agency, National Center for Environmental Assessment, Research Triangle Park, North Carolina
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5
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Ball N, Bartels M, Budinsky R, Klapacz J, Hays S, Kirman C, Patlewicz G. The challenge of using read-across within the EU REACH regulatory framework; how much uncertainty is too much? Dipropylene glycol methyl ether acetate, an exemplary case study. Regul Toxicol Pharmacol 2014; 68:212-21. [DOI: 10.1016/j.yrtph.2013.12.007] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Revised: 12/12/2013] [Accepted: 12/18/2013] [Indexed: 10/25/2022]
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6
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Lin Z, Fisher JW, Wang R, Ross MK, Filipov NM. Estimation of placental and lactational transfer and tissue distribution of atrazine and its main metabolites in rodent dams, fetuses, and neonates with physiologically based pharmacokinetic modeling. Toxicol Appl Pharmacol 2013; 273:140-58. [DOI: 10.1016/j.taap.2013.08.010] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 08/07/2013] [Accepted: 08/10/2013] [Indexed: 11/27/2022]
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7
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Yamada T, Tanaka Y, Zhang H, Hasegawa R, Sakuratani Y, Mekenyan O, Yamazoe Y, Yamada J, Hayashi M. A category approach to predicting the hemolytic effects of ethylene glycol alkyl ethers in repeated-dose toxicity. J Toxicol Sci 2012; 37:503-15. [DOI: 10.2131/jts.37.503] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Takashi Yamada
- Chemical Management Center, National Institute of Technology and Evaluation
| | - Yushiro Tanaka
- Chemical Management Center, National Institute of Technology and Evaluation
| | - HuiQi Zhang
- Chemical Management Center, National Institute of Technology and Evaluation
| | - Ryuichi Hasegawa
- Chemical Management Center, National Institute of Technology and Evaluation
| | - Yuki Sakuratani
- Chemical Management Center, National Institute of Technology and Evaluation
| | - Ovanes Mekenyan
- Laboratory of Mathematical Chemistry, University “Prof. Assen Zlatarov” Bourgas
| | - Yasushi Yamazoe
- Graduate School of Pharmaceutical Sciences, Tohoku University
| | - Jun Yamada
- Chemical Management Center, National Institute of Technology and Evaluation
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Pang KS, Durk MR. Physiologically-based pharmacokinetic modeling for absorption, transport, metabolism and excretion. J Pharmacokinet Pharmacodyn 2010; 37:591-615. [PMID: 21153869 DOI: 10.1007/s10928-010-9185-x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Accepted: 11/12/2010] [Indexed: 01/19/2023]
Abstract
The seminal paper on the liver physiologically-based pharmacokinetic (PBPK) model by Rowland et al. (J Pharmacokinet Biopharm 1:123-136, 1973) that described the influence of blood flow, intrinsic clearance, and binding on hepatic clearance had inspired further development of PBPK modeling of the liver, kidney and intestine as well as whole body. Shortly thereafter, a series of papers from Pang and Rowland compared the well-stirred and parallel-tube liver models and sparked further development on clearance concepts in the liver, including those described by the dispersion model. From 2005 onwards, several seminal papers by Rodgers and Rowland, in their recognition of the binding of molecules to tissue acidic and neutral phospholipids, improved the methodology in providing estimates of the tissue-to-plasma coefficient and rendering easy calculation of these hard-to-get constants. The improvement has strongly consolidated the basic premise on PBPK modeling and simulations and these basics have allowed scientists to focus on other important variables: membrane barriers, and transporter and enzyme and their heterogeneities that further impact drug disposition. In particular, the PBPK models have delved into sequential metabolism and futile cycling to illustrate how transporters and enzymes could affect the metabolism of drugs and metabolites. PBPK models that are especially pertinent to metabolite kinetics are being utilized in drug studies and risk assessment. These types of PBPK modeling reveal differences in kinetics between the formed vs. preformed metabolite, showing special considerations for membrane barriers, and the influence of competing pathways and competing organs.
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Affiliation(s)
- K Sandy Pang
- Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, ON, M5S 3M2, Canada.
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Louisse J, de Jong E, van de Sandt JJM, Blaauboer BJ, Woutersen RA, Piersma AH, Rietjens IMCM, Verwei M. The Use of In Vitro Toxicity Data and Physiologically Based Kinetic Modeling to Predict Dose-Response Curves for In Vivo Developmental Toxicity of Glycol Ethers in Rat and Man. Toxicol Sci 2010; 118:470-84. [DOI: 10.1093/toxsci/kfq270] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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10
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Louisse J, Bai Y, Verwei M, de Sandt JJV, Blaauboer BJ, Rietjens IM. Decrease of intracellular pH as possible mechanism of embryotoxicity of glycol ether alkoxyacetic acid metabolites. Toxicol Appl Pharmacol 2010; 245:236-43. [DOI: 10.1016/j.taap.2010.03.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Revised: 02/25/2010] [Accepted: 03/02/2010] [Indexed: 10/19/2022]
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Berthet A, de Batz A, Tardif R, Charest-Tardif G, Truchon G, Vernez D, Droz PO. Impact of biological and environmental variabilities on biological monitoring--an approach using toxicokinetic models. JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE 2010; 7:177-184. [PMID: 20063230 DOI: 10.1080/15459620903530052] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Biological monitoring of occupational exposure is characterized by important variability, due both to variability in the environment and to biological differences between workers. A quantitative description and understanding of this variability is important for a dependable application of biological monitoring. This work describes this variability, using a toxicokinetic model, for a large range of chemicals for which reference biological reference values exist. A toxicokinetic compartmental model describing both the parent compound and its metabolites was used. For each chemical, compartments were given physiological meaning. Models were elaborated based on physiological, physicochemical, and biochemical data when available, and on half-lives and central compartment concentrations when not available. Fourteen chemicals were studied (arsenic, cadmium, carbon monoxide, chromium, cobalt, ethylbenzene, ethyleneglycol monomethylether, fluorides, lead, mercury, methyl isobutyl ketone, penthachlorophenol, phenol, and toluene), representing 20 biological indicators. Occupational exposures were simulated using Monte Carlo techniques with realistic distributions of both individual physiological parameters and exposure conditions. Resulting biological indicator levels were then analyzed to identify the contribution of environmental and biological variability to total variability. Comparison of predicted biological indicator levels with biological exposure limits showed a high correlation with the model for 19 out of 20 indicators. Variability associated with changes in exposure levels (GSD of 1.5 and 2.0) is shown to be mainly influenced by the kinetics of the biological indicator. Thus, with regard to variability, we can conclude that, for the 14 chemicals modeled, biological monitoring would be preferable to air monitoring. For short half-lives (less than 7 hr), this is very similar to the environmental variability. However, for longer half-lives, estimated variability decreased.
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Affiliation(s)
- A Berthet
- Institute for Work and Health, Lausanne University, Lausanne, Switzerland.
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Hissink AM, Kulig BM, Kruse J, Freidig AP, Verwei M, Muijser H, Lammers JHCM, McKee RH, Owen DE, Sweeney LM, Salmon F. Physiologically based pharmacokinetic modeling of cyclohexane as a tool for integrating animal and human test data. Int J Toxicol 2010; 28:498-509. [PMID: 19966142 DOI: 10.1177/1091581809348718] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This report describes a physiologically based pharmacokinetic model for cyclohexane and its use in comparing internal doses in rats and volunteers following inhalation exposures. Parameters describing saturable metabolism of cyclohexane are measured in rats and used along with experimentally determined partition coefficients. The model is evaluated by comparing predicted blood and brain concentrations to data from studies in rats and then allometrically scaling the results to humans. Levels of cyclohexane in blood and exhaled air are measured in human volunteers and compared with model values. The model predicts that exposure of volunteers to cyclohexane at levels of 4100 mg/m(3) ( approximately 1200 ppm) will result in brain levels similar to those in rats exposed to 8000 mg/m(3) (the no-effect level for acute central nervous system effects). There are no acute central nervous system effects in humans exposed to 860 mg/m(3), consistent with model predictions that current occupational exposure levels for cyclohexane protect against acute central nervous system effects.
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13
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Pang KS. Safety testing of metabolites: Expectations and outcomes. Chem Biol Interact 2008; 179:45-59. [PMID: 18926805 DOI: 10.1016/j.cbi.2008.09.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Revised: 09/12/2008] [Accepted: 09/15/2008] [Indexed: 12/18/2022]
Abstract
Metabolites arising from chemical entities, old or new, are often mediators of toxicity. Frequently, metabolites are investigated in test animals, with the expectation that the resultant toxicity or activity will mimic the exposure of their formed counterparts. This communication described observations that showed discrepant kinetics between formed and preformed metabolites in the liver, intestine, and kidney, major drug removal organs. Differences in the observed areas under the curve (AUCs) or the extraction ratios (Es) of formed and preformed metabolites in the liver had been attributed to zonal, enzyme heterogeneity, membrane barriers, or transporters. Preformed and formed metabolite also differed in their handling by the kidney; only the preformed and not the formed metabolite would be filtered. In the intestine, differences in the absorption of the precursor and the metabolite and the flow pattern in the intestine would bring about discrepancy in the time-courses of the formed vs. preformed metabolites. Analytical solutions of the AUCs of the metabolites and extraction ratios, based on physiological modeling of the liver, kidney, and intestine, showed that the AUC of the preformed, administered metabolite was dependent only on metabolite parameters, whereas the AUC of the formed metabolite was modulated additionally by the metabolic, secretory and intestinal absorptive intrinsic clearances of the precursor drug. Hence, administration of the synthetic metabolite would not reflect the toxicity associated with the metabolite formed via bioactivation. However, data on preformed metabolite may be used for simultaneous fitting by a combined model of drug and metabolite. Such a strategy is shown to be successful in risk assessment of environmental chemicals. Upon refinement of the resultant model with data on metabolite transport and handling by modeling and simulations, the resultant model would be more robust to provide improved predictions on metabolite toxicity pursuant to drug administration.
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14
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Hissink AM, Krüse J, Kulig BM, Verwei M, Muijser H, Salmon F, Leenheers LH, Owen DE, Lammers JHCM, Freidig AP, McKee RH. Model studies for evaluating the neurobehavioral effects of complex hydrocarbon solvents. Neurotoxicology 2007; 28:751-60. [PMID: 17493682 DOI: 10.1016/j.neuro.2007.03.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Revised: 03/14/2007] [Accepted: 03/14/2007] [Indexed: 11/16/2022]
Abstract
As part of a project designed to develop a framework for extrapolating acute central nervous system (CNS) effects of hydrocarbon solvents in animals to humans, experimental studies were conducted in rats and human volunteers in which acute CNS effects were measured and toxicokinetic data were collected. A complex hydrocarbon solvent, white spirit (WS) was used as a model solvent and two marker compounds for WS, 1,2,4-trimethyl benzene (TMB) and n-decane (NDEC), were analyzed to characterize internal exposure after WS inhalation. Toxicokinetic data on blood and brain concentrations of the two marker compounds in the rat, together with in vitro partition coefficients were used to develop physiologically based pharmacokinetic (PBPK) models for TMB and NDEC. The rat models were then allometrically scaled to obtain models for inhalatory exposure for man. The human models were validated with blood and alveolar air kinetics of TMB and NDEC, measured in human volunteers. Using these models, it was predicted that external exposures to WS in the range of 344-771mg/m(3) would produce brain concentrations similar to those in rats exposed to 600mg/m(3) WS, the no effect level (NOEL) for acute CNS effects. Assuming similar brain concentration-effect relations for humans and rats, the NOEL for acute CNS effects in humans should be in this range. The prediction was consistent with data from a human volunteer study in which the only statistically significant finding was a small change in the simple reaction time test following 4h exposure to approximately 570mg/m(3) WS. Thus, the data indicated that the results of animal studies could be used to predict a no effect level for acute CNS depression in humans, consistent with the framework described above.
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Timour Q, Biggi-Bernard U, Descotes J. [Hormone replacement therapy: toxicity of glycol ethers]. ACTA ACUST UNITED AC 2006; 36:62-7. [PMID: 17293254 DOI: 10.1016/j.jgyn.2006.09.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2006] [Revised: 05/12/2006] [Accepted: 09/14/2006] [Indexed: 12/01/2022]
Abstract
Glycol ethers (GE) belong to two main series: series E, which include ethylene glycol ethers (EGE) and series P which include propylene glycol ethers (PGE). GE are widely used as solvents in a large number of industrial, household and cosmetic applications. EGE can be found in water paints, varnishes, inks, household products. Severe adverse effects have been noted with pharmaceutical formulations containing diethylene glycol monoethyl-ethers and this led to withdrawal from the French market. The toxicity of GE depends on the molecular weight and the metabolites generated. It can manifest following acute or chronic exposure by disorders of the nervous system, bone marrow, immune system, kidneys as well as fertility, reproduction and embryofetal development. Several EGE are mutagenic. The carcinogenic risk is not known. The most toxic derivatives EGME, EGMEA, EGEE and EGEEA alter male and female fertility, and induce malformations. Taking these toxic effects into consideration, what is the place of GE as absorption promoting agents? An example is DEGEE, which facilitates estradiol penetration when used as a gel in the treatment of estrogen deficiency. This review is intended to address this issue.
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Affiliation(s)
- Q Timour
- Laboratoire de Pharmacologie Médicale (EA 1896), UFR Lyon-Grange-Blanche, 8, avenue Rockefeller, 69373 Lyon cedex 08, France.
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Verwei M, van Burgsteden JA, Krul CAM, van de Sandt JJM, Freidig AP. Prediction of in vivo embryotoxic effect levels with a combination of in vitro studies and PBPK modelling. Toxicol Lett 2006; 165:79-87. [PMID: 16517103 DOI: 10.1016/j.toxlet.2006.01.017] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 01/26/2006] [Accepted: 01/30/2006] [Indexed: 11/21/2022]
Abstract
The new EU legislations for chemicals (Registration, Evaluation and Authorization of Chemicals, REACH) and cosmetics (Seventh Amendment) stimulate the acceptance of in vitro and in silico approaches to test chemicals for their potential to cause reproductive effects. In the current study seven compounds with known in vivo developmental effects were tested in the embryonic stem cell test (EST). The EST correctly classified 5-fluorouracil, methotrexate, retinoic acid, 2-ethoxyacetic acid and 2-methoxyacetic acid for their in vivo embryotoxic potential. The toxicity of 2-methoxyethanol and 2-ethoxyethanol was underestimated due to a lack of metabolic capacity in the EST. This study further investigated the possibility to use in silico techniques to extrapolate in vitro effect concentrations determined in the EST to in vivo exposure levels. This approach was evaluated by comparing in silico predicted in vivo effect levels with effect levels measured in rodents. The in vivo effect levels of 2-methoxyethanol, 2-ethoxyethanol, methotrexate and retinoic acid were correctly predicted with in silico modelling. Contrary, in vivo embryotoxicity of 5-fluorouracil was overestimated following this approach. It is concluded that a combination of in vitro and in silico techniques appears to be a promising alternative test method for risk assessment of embryotoxic compounds.
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Affiliation(s)
- Miriam Verwei
- TNO Quality of Life, PO Box 360, 3700 AJ Zeist, The Netherlands.
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Welsch F. The mechanism of ethylene glycol ether reproductive and developmental toxicity and evidence for adverse effects in humans. Toxicol Lett 2005; 156:13-28. [PMID: 15705484 DOI: 10.1016/j.toxlet.2003.08.010] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Numerous experimental studies have established that only a few among the large family of ethylene glycol ethers (EGEs) elicit toxicity on reproduction in either gender. Notable are the monomethyl (EGME) and monoethyl (EGEE) ethers and their respective acetate esters whose production volumes have dramatically declined. Oxidation to the respective monoalkoxy acids is a prerequisite for toxicity. The most potent EGE reproductive toxicant is EGME (via 2-methoxyacetic acid; MAA), which elicits developmental phase-specific insults on either conceptus or on testes. Toxicity at either target site is markedly attenuated by simple physiological compounds such as acetate, formate, glycine, D-glucose and serine. Lack of solid EGME occupational exposure data and the need to improve the scientific foundations for animal data extrapolations, prompted the development of physiologically based pharmacokinetic (PBPK) models for pregnancy application. Interspecies (mouse-rat) and different exposure routes (including inhalation) were experimentally validated. Such PBPK models were then extrapolated to potential occupational exposures, using rather limited human MAA pharmacokinetic data. PBPK model predictions of human blood levels upon simulated inhalation exposure to the 5 ppm threshold limit value (TLV) for 8 h were approximately 60 microM were well below those causing adverse effects in pregnant mice or rats. This conclusion concurs with the lack of objective analytical chemistry data for EGME/MAA in occupational settings, regardless of the potential route of exposure. There are no exposure data that can be linked in a cause-and-effect association to adverse human reproductive outcomes.
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Affiliation(s)
- Frank Welsch
- Orbitox, International Toxicology Consultants, 1 Caliente Place, Santa Fe, NM 87508, USA.
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Corley RA, Gies RA, Wu H, Weitz KK. Development of a physiologically based pharmacokinetic model for propylene glycol monomethyl ether and its acetate in rats and humans. Toxicol Lett 2005; 156:193-213. [PMID: 15705496 DOI: 10.1016/j.toxlet.2003.12.078] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Propylene glycol monomethyl ether (PM), along with its acetate, is the most widely used of the propylene glycol ether family of solvents. The most common toxic effects of PM observed in animal studies include sedation, very slight alpha(2u)-globulin mediated nephropathy (male rats only) and hepatomegally at high exposures (typically > 1000 ppm). Sedation in animal studies usually resolves within a few exposures to 3000 ppm (the highest concentration used in subchronic and chronic inhalation studies) due to the induction of metabolizing enzymes. Data from a variety of pharmacokinetic and mechanistic studies have been incorporated into a PBPK model for PM and its acetate in rats and mice. Published controlled exposure and workplace biomonitoring studies have also been included for comparisons of the internal dosimetry of PM and its acetate between laboratory animals and humans. PM acetate is rapidly hydrolyzed to PM, which is further metabolized to either glucuronide or sulfate conjugates (minor pathways) or propylene glycol (major pathway). In vitro half-lives for PM acetate range from 14 to 36 min depending upon the tissue and species. In vivo half-lives are considerably faster, reflecting the total contributions of esterases in the blood and tissues of the body, and are on the order of just a few minutes. Thus, very little PM acetate is found in vivo and, other than potential portal of entry irritation, the toxicity of PM acetate is related to PM. Regardless of the source for PM (either PM or its acetate), rats were predicted to have a higher Cmax and AUC for PM in blood than humans, especially at concentrations greater than the current ACGIH TLV of 100 ppm. This would indicate that the major systemic effects of PM would be expected to be less severe in humans than rats at comparable inhalation exposures.
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Affiliation(s)
- R A Corley
- Biological Monitoring and Modeling Group, 902 Battelle Blvd., P.O. Box 999, MSIN P7-59, Richland, WA 99352, USA.
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Frederick CB, Lomax LG, Black KA, Finch L, Scribner HE, Kimbell JS, Morgan KT, Subramaniam RP, Morris JB. Use of a hybrid computational fluid dynamics and physiologically based inhalation model for interspecies dosimetry comparisons of ester vapors. Toxicol Appl Pharmacol 2002; 183:23-40. [PMID: 12217639 DOI: 10.1006/taap.2002.9451] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Numerous inhalation studies have demonstrated that exposure to high concentrations of a wide range of volatile acids and esters results in cytotoxicity to the nasal olfactory epithelium. Previously, a hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of organic acids in the rodent and human nasal cavity. This study extends this methodology to a representative volatile organic ester, ethyl acrylate (EA). An in vitro exposure of explants of rat olfactory epithelium to EA with and without an esterase inhibitor demonstrated that the organic acid, acrylic acid, released by nasal esterases is primarily responsible for the olfactory cytotoxicity. Estimates of the steady-state concentration of acrylic acid in olfactory tissue were made for the rat nasal cavity by using data from a series of short-term in vivo studies and from the results of CFD-PBPK computer modeling. Appropriate parameterization of the CFD-PBPK model for the human nasal cavity and to accommodate human systemic anatomy, metabolism, and physiology allowed interspecies dose comparisons. The CFD-PBPK model simulations indicate that the olfactory epithelium of the human nasal cavity is exposed to at least 18-fold lower tissue concentrations of acid released from EA than the olfactory epithelium of the rat nasal cavity under the same exposure conditions. The magnitude of this difference varies with the specific exposure scenario that is simulated and with the specific dataset of human esterase activity used for the simulations. The increased olfactory tissue dose in rats relative to humans may be attributed to both the vulnerable location of the rodent olfactory tissue (comprising greater than 50% of the nasal cavity) and the high concentration of rat olfactory esterase activity (comparable to liver esterase activity) relative to human olfactory tissue. These studies suggest that the human olfactory epithelium is protected from vapors of organic esters significantly better than rat olfactory epithelium due to substantive differences in nasal anatomy, nasal and systemic metabolism, systemic physiology, and air flow. Although the accumulation of acrylic acid in the nasal tissues may be a primary concern for nasal irritation and human risk assessment, acute animal inhalation studies to evaluate lethality (LD50-type studies) conducted at very high vapor concentrations of ethyl acrylate indicated that a different mechanism is primarily responsible for mortality. The rodent studies demonstrated that systemic tissue nonprotein sulfhydryl depletion is a primary cause of death at exposure concentrations more than two orders of magnitude above the concentrations that induce nasal irritation. The CFD-PBPK model adequately simulated the severe depletion of glutathione in systemic tissues (e.g., liver and lung) associated with acute inhalation exposures in the 500-1000 ppm range. These results indicate that the CFD-PBPK model can simulate both the low-dose nasal tissue dosimetry associated with irritation and the high-dose systemic tissue dosimetry associated with mortality. In addition, the comparison of simulation results for ethyl acetate and acetone to nasal deposition data suggests that the CFD-PBPK model has general utility as a tool for dosimetry estimates for a wide range of other esters and slowly metabolized vapors.
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Affiliation(s)
- Clay B Frederick
- Toxicology Department, Rohm and Haas Company, Spring House, Pennsylvania 19477, USA.
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El-Zein RA, Abdel-Rahman SZ, Morris DL, Legator MS. Exposure to ethylene glycol monomethyl ether: clinical and cytogenetic findings. ARCHIVES OF ENVIRONMENTAL HEALTH 2002; 57:371-6. [PMID: 12530607 DOI: 10.1080/00039890209601424] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Glycol ethers are known reproductive and developmental toxins in laboratory animals, but little is known about their genotoxic effects in humans. In the current article, the authors tested the hypothesis that human in utero exposure to ethylene glycol monomethyl ether (EGME) is associated with the development of specific congenital anomalies and elevated levels of chromosome aberrations. The authors conducted a clinical and cytogenetic evaluation of 41 offspring of 28 females occupationally exposed to EGME for an average duration of 4.6 yr. Six offspring of 5 women who were occupationally exposed to EGME during pregnancy exhibited characteristic dysmorphic features that were not observed in 35 offspring of 23 women who worked in the same facility, but who were not pregnant at the time of exposure. Persistent cytogenetic damage was observed exclusively in all 6 in-utero-exposed offspring, but not in their 12 match non-in-utero-exposed controls. The study characterizes EGME as a human teratogen, as indicated by the prevalence of characteristic dysmorphic features and persistent cytogenetic damage in individuals exposed in utero to this chemical.
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Affiliation(s)
- Randa A El-Zein
- Department of Epidemiology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA
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Sweeney LM, Tyler TR, Kirman CR, Corley RA, Reitz RH, Paustenbach DJ, Holson JF, Whorton MD, Thompson KM, Gargas ML. Proposed occupational exposure limits for select ethylene glycol ethers using PBPK models and Monte Carlo simulations. Toxicol Sci 2001; 62:124-39. [PMID: 11399800 DOI: 10.1093/toxsci/62.1.124] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Methoxyethanol (ethylene glycol monomethyl ether, EGME), ethoxyethanol (ethylene glycol monoethyl ether, EGEE), and ethoxyethyl acetate (ethylene glycol monoethyl ether acetate, EGEEA) are all developmental toxicants in laboratory animals. Due to the imprecise nature of the exposure data in epidemiology studies of these chemicals, we relied on human and animal pharmacokinetic data, as well as animal toxicity data, to derive 3 occupational exposure limits (OELs). Physiologically based pharmacokinetic (PBPK) models for EGME, EGEE, and EGEEA in pregnant rats and humans have been developed (M. L. Gargas et al., 2000, Toxicol. Appl. Pharmacol. 165, 53-62; M. L. Gargas et al., 2000, Toxicol. Appl. Pharmacol. 165, 63-73). These models were used to calculate estimated human-equivalent no adverse effect levels (NAELs), based upon internal concentrations in rats exposed to no observed effect levels (NOELs) for developmental toxicity. Estimated NAEL values of 25 ppm for EGEEA and EGEE and 12 ppm for EGME were derived using average values for physiological, thermodynamic, and metabolic parameters in the PBPK model. The uncertainties in the point estimates for the NOELs and NAELs were estimated from the distribution of internal dose estimates obtained by varying key parameter values over expected ranges and probability distributions. Key parameters were identified through sensitivity analysis. Distributions of the values of these parameters were sampled using Monte Carlo techniques and appropriate dose metrics calculated for 1600 parameter sets. The 95th percentile values were used to calculate interindividual pharmacokinetic uncertainty factors (UFs) to account for variability among humans (UF(h,pk)). These values of 1.8 for EGEEA/EGEE and 1.7 for EGME are less than the default value of 3 for this area of uncertainty. The estimated human equivalent NAELs were divided by UF(h,pk) and the default UFs for pharmacodynamic variability among animals and among humans to calculate the proposed OELs. This methodology indicates that OELs (8-h time-weighted average) that should protect workers from the most sensitive adverse effects of these chemicals are 2 ppm EGEEA and EGEE (11 mg/m(3) EGEEA, 7 mg/m(3) EGEE) and 0.9 ppm (3 mg/m(3)) EGME. These recommendations assume that dermal exposure will be minimal or nonexistent.
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Affiliation(s)
- L M Sweeney
- The Sapphire Group, Inc., 2928 Idaho Falls Drive, Suite 100, Beavercreek, Ohio 45431, USA.
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