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The role of endogenous versus exogenous sources in the exposome of putative genotoxins and consequences for risk assessment. Arch Toxicol 2022; 96:1297-1352. [PMID: 35249149 PMCID: PMC9013691 DOI: 10.1007/s00204-022-03242-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 02/01/2022] [Indexed: 12/21/2022]
Abstract
AbstractThe “totality” of the human exposure is conceived to encompass life-associated endogenous and exogenous aggregate exposures. Process-related contaminants (PRCs) are not only formed in foods by heat processing, but also occur endogenously in the organism as physiological components of energy metabolism, potentially also generated by the human microbiome. To arrive at a comprehensive risk assessment, it is necessary to understand the contribution of in vivo background occurrence as compared to the ingestion from exogenous sources. Hence, this review provides an overview of the knowledge on the contribution of endogenous exposure to the overall exposure to putative genotoxic food contaminants, namely ethanol, acetaldehyde, formaldehyde, acrylamide, acrolein, α,β-unsaturated alkenals, glycation compounds, N-nitroso compounds, ethylene oxide, furans, 2- and 3-MCPD, and glycidyl esters. The evidence discussed herein allows to conclude that endogenous formation of some contaminants appears to contribute substantially to the exposome. This is of critical importance for risk assessment in the cases where endogenous exposure is suspected to outweigh the exogenous one (e.g. formaldehyde and acrolein).
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Vincent MJ, Kozal JS, Thompson WJ, Maier A, Dotson GS, Best EA, Mundt KA. Ethylene Oxide: Cancer Evidence Integration and Dose-Response Implications. Dose Response 2019; 17:1559325819888317. [PMID: 31853235 PMCID: PMC6906442 DOI: 10.1177/1559325819888317] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/11/2019] [Accepted: 10/15/2019] [Indexed: 11/16/2022] Open
Abstract
The International Agency for Research on Cancer (IARC) and the United States
Environmental Protection Agency (USEPA) classified ethylene oxide (EtO) as a
known human carcinogen. Critically, both noted that the epidemiological evidence
based on lymphoid and breast cancers was “limited,” but that the evidence in
animal studies was “sufficient” and “extensive” (respectively) and that EtO is
genotoxic. The USEPA derived one of the highest published inhalation unit risk
(IUR) values (3 × 10−3 per [µg/m3 EtO]), based on results
from 2 epidemiological studies. We performed focused reviews of the
epidemiological and toxicological evidence on the carcinogenicity of EtO and
considered the USEPA’s reliance on a genotoxic mode of action to establish EtO’s
carcinogenicity and to determine likely dose–response patterns. Higher quality
epidemiological studies demonstrated no increased risk of breast cancers or
lymphohematopoietic malignancies (LHM). Similarly, toxicological studies and
studies of early effect biomarkers in animals and humans provided no strong
indication that EtO causes LHM or mammary cancers. Ultimately, animal data are
inadequate to define the actual dose–response shape or predict tumor response at
very low doses with any confidence. We conclude that the IARC and USEPA
classification of EtO as a known human carcinogen overstates the underlying
evidence and that the IUR derived by USEPA grossly overestimates risk.
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3
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Filser JG, Klein D. A physiologically based toxicokinetic model for inhaled ethylene and ethylene oxide in mouse, rat, and human. Toxicol Lett 2018; 286:54-79. [DOI: 10.1016/j.toxlet.2017.07.896] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 07/20/2017] [Accepted: 07/25/2017] [Indexed: 01/18/2023]
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4
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Kirman C, Hays S. Derivation of endogenous equivalent values to support risk assessment and risk management decisions for an endogenous carcinogen: Ethylene oxide. Regul Toxicol Pharmacol 2017; 91:165-172. [DOI: 10.1016/j.yrtph.2017.10.032] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 09/08/2017] [Accepted: 10/26/2017] [Indexed: 01/26/2023]
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Filser JG, Artati A, Li Q, Pütz C, Semder B, Klein D, Kessler W. Novel and existing data for a future physiological toxicokinetic model of ethylene and its metabolite ethylene oxide in mouse, rat, and human. Chem Biol Interact 2015; 241:76-86. [DOI: 10.1016/j.cbi.2015.04.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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6
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Filser JG, Kessler W, Artati A, Erbach E, Faller T, Kreuzer PE, Li Q, Lichtmannegger J, Numtip W, Klein D, Pütz C, Semder B, Csanády GA. Ethylene oxide in blood of ethylene-exposed B6C3F1 mice, Fischer 344 rats, and humans. Toxicol Sci 2013; 136:344-58. [PMID: 24068676 PMCID: PMC3858200 DOI: 10.1093/toxsci/kft218] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 09/09/2013] [Indexed: 02/04/2023] Open
Abstract
The gaseous olefin ethylene (ET) is metabolized in mammals to the carcinogenic epoxide ethylene oxide (EO). Although ET is the largest volume organic chemical worldwide, the EO burden in ET-exposed humans is still uncertain, and only limited data are available on the EO burden in ET-exposed rodents. Therefore, EO was quantified in blood of mice, rats, or 4 volunteers that were exposed once to constant atmospheric ET concentrations of between 1 and 10 000 ppm (rodents) or 5 and 50 ppm (humans). Both the compounds were determined by gas chromatography. At ET concentrations of between 1 and 10 000 ppm, areas under the concentration-time curves of EO in blood (µmol × h/l) ranged from 0.039 to 3.62 in mice and from 0.086 to 11.6 in rats. At ET concentrations ≤ 30 ppm, EO concentrations in blood were 8.7-fold higher in rats and 3.9-fold higher in mice than that in the volunteer with the highest EO burdens. Based on measured EO concentrations, levels of EO adducts to hemoglobin and lymphocyte DNA were calculated for diverse ET concentrations and compared with published adduct levels. For given ET exposure concentrations, there were good agreements between calculated and measured levels of adducts to hemoglobin in rats and humans and to DNA in rats and mice. Reported hemoglobin adduct levels in mice were higher than calculated ones. Furthermore, information is given on species-specific background adduct levels. In summary, the study provides most relevant data for an improved assessment of the human health risk from exposure to ET.
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Affiliation(s)
- Johannes Georg Filser
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
- †Institut für Toxikologie und Umwelthygiene, Technische Universität München, München, Germany
| | - Winfried Kessler
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Anna Artati
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Eva Erbach
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Thomas Faller
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Paul Erich Kreuzer
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Qiang Li
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Josef Lichtmannegger
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Wanwiwa Numtip
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Dominik Klein
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
- †Institut für Toxikologie und Umwelthygiene, Technische Universität München, München, Germany
| | - Christian Pütz
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - Brigitte Semder
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
| | - György András Csanády
- *Institute of Molecular Toxicology and Pharmacology, Helmholtz Zentrum München, 85764 Neuherberg, Germany; and
- †Institut für Toxikologie und Umwelthygiene, Technische Universität München, München, Germany
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7
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Wu KY, Chiang SY, Shih WC, Huang CCJ, Chen MF, Swenberg JA. The application of mass spectrometry in molecular dosimetry: ethylene oxide as an example. MASS SPECTROMETRY REVIEWS 2011; 30:733-756. [PMID: 21328599 DOI: 10.1002/mas.20299] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mass spectrometry plays an increasingly important role in the search for and quantification of novel chemically specific biomarkers. The revolutionary advances in mass spectrometry instrumentation and technology empower scientists to specifically analyze DNA and protein adducts, considered as molecular dosimeters, derived from reactions of a carcinogen or its active metabolites with DNA or protein. Analysis of the adducted DNA bases and proteins can elucidate the chemically reactive species of carcinogens in humans and can serve as risk-associated biomarkers for early prediction of cancer risk. In this article, we review and compare the specificity, sensitivity, resolution, and ease-of-use of mass spectrometry methods developed to analyze ethylene oxide (EO)-induced DNA and protein adducts, particularly N7-(2-hydroxyethyl)guanine (N7-HEG) and N-(2-hydroxyethyl)valine (HEV), in human samples and in animal tissues. GC/ECNCI-MS analysis after HPLC cleanup is the most sensitive method for quantification of N7-HEG, but limited by the tedious sample preparation procedures. Excellent sensitivity and specificity in analysis of N7-HEG can be achieved by LC/MS/MS analysis if the mobile phase, the inlet (split or splitless), and the collision energy are properly optimized. GC/ECNCI-HRMS and GC/ECNCI-MS/MS analysis of HEV achieves the best performance as compared with GC/ECNCI-MS and GC/EI-MS. In conclusion, future improvements in high-throughput capabilities, detection sensitivity, and resolution of mass spectrometry will attract more scientists to identify and/or quantify novel molecular dosimeters or profiles of these biomarkers in toxicological and/or epidemiological studies.
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Affiliation(s)
- Kuen-Yuh Wu
- Institute of Occupational Medicine and Industrial Hygiene, College of Public Health, National Taiwan University, Taipei, Taiwan.
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8
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Thier R, Bolt HM. Carcinogenicity and genotoxicity of ethylene oxide: new aspects and recent advances. Crit Rev Toxicol 2000; 30:595-608. [PMID: 11055837 DOI: 10.1080/10408440008951121] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Long-term inhalation studies in rodents have presented unequivocal evidence of experimental carcinogenicity of ethylene oxide, based on the formation of malignant tumors at multiple sites. However, despite a considerable body of epidemiological data only limited evidence has been obtained of its carcinogenicity in humans. Ethylene oxide is not only an important exogenous toxicant, but it is also formed from ethylene as a biological precursor. Ethylene is a normal body constituent; its endogenous formation is evidenced by exhalation in rats and in humans. Consequently, ethylene oxide must also be regarded as a physiological compound. The most abundant DNA adduct of ethylene oxide is 7-(2-hydroxyethyl)guanine (HOEtG). Open questions are the nature and role of tissue-specific factors in ethylene oxide carcinogenesis and the physiological and quantitative role of DNA repair mechanisms. The detection of remarkable individual differences in the susceptibility of humans has promoted research into genetic factors that influence the metabolism of ethylene oxide. With this background it appears that current PBPK models for trans-species extrapolation of ethylene oxide toxicity need to be refined further. For a cancer risk assessment at low levels of DNA damage, exposure-related adducts must be discussed in relation to background DNA damage as well as to inter- and intraindividual variability. In rats, subacute ethylene oxide exposures on the order of 1 ppm (1.83 mg/m3) cause DNA adduct levels (HOEtG) of the same magnitude as produced by endogenous ethylene oxide. Based on very recent studies the endogenous background levels of HOEtG in DNA of humans are comparable to those that are produced in rodents by repetitive exogenous ethylene oxide exposures of about 10 ppm (18.3 mg/m3). Experimentally, ethylene oxide has revealed only weak mutagenic effects in vivo, which are confined to higher doses. It has been concluded that long-term human occupational exposure to low airborne concentrations to ethylene oxide, at or below current occupational exposure limits of 1 ppm (1.83 mg/m3), would not produce unacceptable increased genotoxic risks. However, critical questions remain that need further discussions relating to the coherence of animal and human data of experimental data in vitro vs. in vivo and to species-specific dynamics of DNA lesions.
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Affiliation(s)
- R Thier
- Institut für Arbeitsphysiologie an der Universität Dortmund, Germany
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9
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Csanády GA, Denk B, Pütz C, Kreuzer PE, Kessler W, Baur C, Gargas ML, Filser JG. A physiological toxicokinetic model for exogenous and endogenous ethylene and ethylene oxide in rat, mouse, and human: formation of 2-hydroxyethyl adducts with hemoglobin and DNA. Toxicol Appl Pharmacol 2000; 165:1-26. [PMID: 10814549 DOI: 10.1006/taap.2000.8918] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ethylene (ET) is a gaseous olefin of considerable industrial importance. It is also ubiquitous in the environment and is produced in plants, mammals, and humans. Uptake of exogenous ET occurs via inhalation. ET is biotransformed to ethylene oxide (EO), which is also an important volatile industrial chemical. This epoxide forms hydroxyethyl adducts with macromolecules such as hemoglobin and DNA and is mutagenic in vivo and in vitro and carcinogenic in experimental animals. It is metabolically eliminated by epoxide hydrolase and glutathione S-transferase and a small fraction is exhaled unchanged. To estimate the body burden of EO in rodents and human resulting from exposures to EO and ET, we developed a physiological toxicokinetic model. It describes uptake of ET and EO following inhalation and intraperitoneal administration, endogenous production of ET, enzyme-mediated oxidation of ET to EO, bioavailability of EO, EO metabolism, and formation of 2-hydroxyethyl adducts of hemoglobin and DNA. The model includes compartments representing arterial, venous, and pulmonary blood, liver, muscle, fat, and richly perfused tissues. Partition coefficients and metabolic parameters were derived from experimental data or published values. Model simulations were compared with a series of data collected in rodents or humans. The model describes well the uptake, elimination, and endogenous production of ET in all three species. Simulations of EO concentrations in blood and exhaled air of rodents and humans exposed to EO or ET were in good agreement with measured data. Using published rate constants for the formation of 2-hydroxyethyl adducts with hemoglobin and DNA, adduct levels were predicted and compared with values reported. In humans, predicted hemoglobin adducts resulting from exposure to EO or ET are in agreement with measured values. In rodents, simulated and measured DNA adduct levels agreed generally well, but hemoglobin adducts were underpredicted by a factor of 2 to 3. Obviously, there are inconsistencies between measured DNA and hemoglobin adduct levels.
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Affiliation(s)
- G A Csanády
- GSF, Neuherberg, Germany/Technische Universität München, Germany
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10
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Zhao C, Tyndyk M, Eide I, Hemminki K. Endogenous and background DNA adducts by methylating and 2-hydroxyethylating agents. Mutat Res 1999; 424:117-25. [PMID: 10064855 DOI: 10.1016/s0027-5107(99)00013-5] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Detection of 7-alkylguanine DNA adducts is useful to assess human exposure to and the resulting DNA damage caused by simple alkylating agents. The background 7-methylguanine (7-MG) and 7-hydroxyethylguanine (7-HEG) adduct levels were determined in human and rat tissues, using thin-layer chromatography (TLC) combined with high pressure liquid chromatography (HPLC). In addition, these two adduct levels were also compared in various tissues between smokers and non-smokers. The results demonstrated that the background level of 7-alkylguanine adducts in WBC and lung tissues of non-smokers was 2.9 and 4.0 adducts/107 nucleotides, respectively. In smokers with lung cancers 7-MG adduct level in lung samples (6.3+/-1.9 adducts/107 nucleotides) and in bronchus samples (6.1+/-1.5 adducts/107 nucleotides) was significantly higher than that in WBC samples (3.3+/-0.9 adducts/107 nucleotides). 7-HEG adduct levels obtained from the same individuals were 0.8+/-0.3 in lung, 1.0+/-0.8 in bronchus and 0.6+/-0.2 adducts/107 nucleotides in WBC, respectively. Animal studies showed that background levels of 7-MG (2.1-2.5 adducts/107 nucleotides) in control rats were approximately 2-4-fold higher than 7-HEG levels (0.6-0.9 adducts/107 nucleotides). After a 3-day exposure to 300 ppm ethene, 7-HEG adducts accumulated to a similar extent in different tissues of rats, with the mean adduct level of 5.6-7.0 in liver, 7.4 in lymphocytes and 5.5 adducts/107 nucleotides in kidney.
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Affiliation(s)
- C Zhao
- Center for Nutrition and Toxicology, Department of Biosciences, Karolinska Institute, NOVUM, S-141 57 Huddinge, Sweden
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11
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Abstract
On occasion of the 25th year of publication of Toxicologic Pathology, the Editor has asked for a report about recent progress in the area addressed by an article entitled “Olefinic Hydrocarbons: A First Risk Estimate,” one of the top 10 most frequently cited papers of the journal (3). Because general issues of risk assessment have very recently been addressed in this journal (6), I will focus on new specific aspects of ethene carcinogenicity.
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Affiliation(s)
- H M Bolt
- Institut für Arbeitsphysiologie an der Universität Dortmund, Germany
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12
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Abstract
Although ethylene oxide is a proven genotoxic carcinogen in experimental animals, its human carcinogenicity is still being debated. Alkylations (hydroxyethylation) of DNA and proteins by ethylene oxide are well established. Ethylene oxide is metabolically formed from ethylene, which is a natural body constituent. Thus, endogenous sources of ethylene/ethylene oxide contribute to background alkylations of physiological macromolecules. There are now experimentally well established data sets on the background hydroxyethylations of the N-terminal valine of hemoglobin and of the 7-N position of guanine in DNA, in laboratory animals as well as in humans: A review of these data leads to the conclusion that these background levels display remarkable consistency between the different species studied and, as far as DNA adducts are concerned, also between different tissues. From the existing database it can be deduced that in rats a hemoglobin alkylation, equivalent to the level of normal background, would be caused by repetitive external atmospheric exposures to ethylene oxide (6 hr/day, 5 days/week for several weeks) of about 30 ppb. On the contrary, in the same species, a DNA alkylation, equivalent to the level of normal background, would be caused by similar repetitive exposures to ethylene oxide at about 1-2 ppm. This paradox is unresolved. It points, however, to the biological importance of endogenous DNA alkylations and questions current regulatory procedures of assessing the risk of minute doses of exogenous carcinogens.
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Affiliation(s)
- H M Bolt
- Institut für Arbeitsphysiologie, Universität Dortmund, Germany.
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13
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Filser JG, Kreuzer PE, Greim H, Bolt HM. New scientific arguments for regulation of ethylene oxide residues in skin-care products. Arch Toxicol 1994; 68:401-5. [PMID: 7979955 DOI: 10.1007/s002040050089] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Ethylene oxide (EO) occurs as a contaminant of skin-care products because current commercial preparations of polyglycol ethers may contain ethylene oxide monomer residues, up to the order of 1 ppm. Using current regulatory worst-case assumptions, the presence of EO in skin-care products might lead to a maximal human daily external ethylene oxide dose of about 2.8 micrograms, and a consecutive maximal daily absorbed dose of 0.39 microgram. Two methods of toxicokinetic analysis have been used to compare this possible EO load by use of skin-care products with the inevitable load of EO which is produced endogenously in the organism. On the basis of a previous assessment of the endogenous production of ethylene and ethylene oxide (Filser et al. 1992) it is inferred that the absorbed EO dose of 0.39 microgram is about 1/30 of the unavoidable human endogenous load by endogenous EO. Alternatively, for a second calculation molecular dosimetry data have been used which were based on experimental quantification of the hydroxyethyl adduct of EO to the N-terminal valine of hemoglobin (HOEtVal) in rats. If the worst-case assumptions for human EO absorption from skin-care products are transferred to the rat species, the associated internal EO doses are about 1/110 of the internal EO doses which were calculated from the background HOEtVal concentrations observed in untreated animals. The divergence between both lines of calculation is mainly due to differences in HOEtVal background concentrations between man and rat.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J G Filser
- GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Toxikologie, Oberschleissheim, Germany
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Filser JG, Schwegler U, Csanády GA, Greim H, Kreuzer PE, Kessler W. Species-specific pharmacokinetics of styrene in rat and mouse. Arch Toxicol 1993; 67:517-30. [PMID: 8285850 DOI: 10.1007/bf01969264] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The pharmacokinetics of styrene were investigated in male Sprague-Dawley rats and male B6C3F1 mice using the closed chamber technique. Animals were exposed to styrene vapors of initial concentrations ranging from 550 to 5000 ppm, or received intraperitoneal (i.p.) doses of styrene from 20 to 340 mg/kg or oral (p.o.) doses of styrene in olive oil from 100 to 350 mg/kg. Concentration-time courses of styrene in the chamber atmosphere were monitored and analyzed by a pharmacokinetic two-compartment model. In both species, the rate of metabolism of inhaled styrene was concentration dependent. At steady state it increased linearly with exposure concentration up to about 300 ppm; more than 95% of inhaled styrene was metabolized and only small amounts were exhaled unchanged. At these low concentrations transport to the metabolizing enzymes and not their metabolic capacity was the rate limiting step for metabolism. Pharmacokinetic behaviour of styrene was strongly influenced by physiological parameters such as blood flow and especially the alveolar ventilation rate. At exposure concentrations of styrene above 300 ppm the rate of metabolism at steady state was progressively limited by biochemical parameters of the metabolizing enzymes. Saturation of metabolism (Vmax) was reached at atmospheric concentrations of about 700 ppm in rats and 800 ppm in mice, Vmax being 224 mumol/(h.kg) and 625 mumol/(h.kg), respectively. The atmospheric concentrations at Vmax/2 were 190 ppm in rats and 270 ppm in mice. Styrene accumulates preferentially in the fatty tissue as can be deduced from its partition coefficients in olive oil:air and water:air which have been determined in vitro at 37 degrees C to be 5600 and 15. In rats and mice exposed to styrene vapors below 300 ppm, there was little accumulation since the uptake was rate limiting. The bioaccumulation factor body:air at steady state (K'st*) was rather low in comparison to the thermodynamic partition coefficient body:air (Keq) which was determined to be 420. K'st* increased from 2.7 at 10 ppm to 13 at 310 ppm in the rat and from 5.9 at 20 ppm to 13 at 310 ppm in the mouse. Above 300 ppm, K'st* increased considerably with increasing concentration since metabolism became saturated in both species. At levels above 2000 ppm K'st* reached its maximum of 420 being equivalent to Keq. Pretreatment with diethyldithiocarbamate, administered intraperitoneally (200 mg/kg in rats, 400 mg/kg in mice) 15 min prior to exposure of styrene vapours, resulted in effective inhibition of styrene metabolism, indicating that most of the styrene is metabolized by cytochrome P450-dependent monooxygenases.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- J G Filser
- GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Toxicologie, Neuherberg, Germany
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15
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Krishnan K, Gargas ML, Fennell TR, Andersen ME. A physiologically based description of ethylene oxide dosimetry in the rat. Toxicol Ind Health 1992; 8:121-40. [PMID: 1502695 DOI: 10.1177/074823379200800301] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A physiologically based pharmacokinetic (PB-PK) model providing a quantitative description of ethylene oxide (ETO) dosimetry in the rat was developed by integrating information on physiology, tissue solubility of ETO, and rate constants for ETO metabolism and binding. The PB-PK model consisted of nine compartments; liver, lung, testis, brain, fat, venous blood, arterial blood, richly perfused and poorly perfused tissues. The tissue: air partition coefficients of ETO, determined by vial equilibration, were similar among the various tissues (range 44-83). The rate constants for glutathione (GSH) conjugation, hydrolysis, and hemoglobin (Hb)- and DNA-binding were estimated from published data and by conducting in vivo inhalation exposure studies. The model adequately predicted the concentrations of Hb and DNA adducts, hepatic and extrahepatic GSH, and urinary N-acetyl-S-(2-hydroxyethyl)-cysteine following inhalation exposures of 1.2 to 1,200 ppm and intravenous administration of 1 to 100 mg/kg of ETO in male Fischer-344 and Sprague-Dawley rats. There was no evidence of nonlinearity in the overall elimination of ETO in the dose range examined. However, nonlinearities in the components of this first order elimination process (namely GSH conjugation, hydrolysis, exhalation) were found to occur at high exposure concentrations. Characterization of the individual metabolic pathways that affect the tissue dosimetry of ETO is important for interspecies extrapolation and risk assessment for this chemical.
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Affiliation(s)
- K Krishnan
- Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709
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16
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Filser JG, Denk B, Törnqvist M, Kessler W, Ehrenberg L. Pharmacokinetics of ethylene in man; body burden with ethylene oxide and hydroxyethylation of hemoglobin due to endogenous and environmental ethylene. Arch Toxicol 1992; 66:157-63. [PMID: 1303633 DOI: 10.1007/bf01974008] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The inhalation pharmacokinetics and the endogenous production of ethylene has been determined in healthy volunteers with respect to the formation of the carcinogen ethylene oxide. Ethylene showed a low degree of accumulation in the body determined in six subjects, the thermodynamic partition coefficient "body/air" being 0.53 +/- 0.23 (mean +/- SD) and the accumulation factor "body/air" at steady-state being 0.33 +/- 0.13 (mean +/- SD). The rate of metabolism was directly proportional to the exposure concentration. Only 2% of ethylene inhaled was metabolized to ethylene oxide, whereas 98% of ethylene was exhaled unchanged. The rate of the endogenous production of ethylene was 32 +/- 12 nmol/h (mean +/- SD), as calculated from exhalation data from 14 subjects. The resulting body burden was 0.44 +/- 0.19 nmol/kg (mean +/- SD). By analyzing published data on ethylene oxide in man its half-life was estimated to be 42 min. Using the pharmacokinetic parameters of ethylene and ethylene oxide, the body burden of ethylene oxide due to the sum of the exposure to environmental ethylene of about 15 ppb and to endogenous ethylene exposure of 0.44 nmol/kg was predicted to be 0.25 nmol/kg. In the blood of five non-smokers and one smoker the hemoglobin adduct resulting from the reaction of ethylene oxide with the N-terminal valine, N-(2-hydroxyethyl)valine, was quantified by gas chromatography/mass spectrometry. The value of 20 +/- 5 pmol/g Hb (mean +/- SD) found in the non-smokers corroborated the steady-state level of 18 +/- 3 pmol/g Hb (mean +/- SD) calculated from the pharmacokinetic approach.
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Affiliation(s)
- J G Filser
- GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Toxikologie, Neuherberg, FRG
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Filser JG. The closed chamber technique--uptake, endogenous production, excretion, steady-state kinetics and rates of metabolism of gases and vapors. Arch Toxicol 1992; 66:1-10. [PMID: 1580790 DOI: 10.1007/bf02307263] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The "closed chamber technique" (CCT) is presented. It allows investigation of pharmacokinetics of volatile substances in vivo in animals and in man and in vitro using tissue fractions. During the exposure period only the atmospheric concentrations of the substance are measured. The concentration-time data obtained are pharmacokinetically analyzed by a two compartment model describing uptake, endogenous production and excretion of the unchanged substance and its metabolic elimination. Using this model, pharmacokinetics of ethylene have been determined in rats and man. For both species, the results compared well with an estimation based on an allometric species scaling. Furthermore, the applicability of CCT is demonstrated in vivo on several other gases and vapors of solvents, e.g. trichloroethylene and 1,1,1-trichloroethane, and in vitro on 1,2-epoxybutene-3.
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Affiliation(s)
- J G Filser
- GSF-Forschungszentrum für Umwelt und Gesundheit, Institut für Toxikologie, Neuherberg, München, FRG
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van Welie RT, van Dijck RG, Vermeulen NP, van Sittert NJ. Mercapturic acids, protein adducts, and DNA adducts as biomarkers of electrophilic chemicals. Crit Rev Toxicol 1992; 22:271-306. [PMID: 1489508 DOI: 10.3109/10408449209146310] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The possibilities and limitations of using mercapturic acids and protein and DNA adducts for the assessment of internal and effective doses of electrophilic chemicals are reviewed. Electrophilic chemicals may be considered as potential mutagens and/or carcinogens. Mercapturic acids and protein and DNA adducts are considered as selective biomarkers because they reflect the chemical structure of the parent compounds or the reactive electrophilic metabolites formed during biotransformation. In general, mercapturic acids are used for the assessment of recent exposure, whereas protein and DNA adducts are used for the assessment of semichronic or chronic exposure. 2-Hydroxyethyl mercapturic acid has been shown to be the urinary excretion product of five different reactive electrophilic intermediates. Classification of these electrophiles according to their acid-base properties might provide a tool to predict their preference to conjugate with either glutathione and proteins or with DNA. Constant relationships appear to exist in the cases of 1,2-dibromoethane and ethylene oxide between urinary mercapturic acid excretion and DNA and protein adduct concentrations. This suggests that mercapturic acids in some cases may also play a role as a biomarker of effective dose. It is concluded that simultaneous determination of mercapturic acids, protein and DNA adducts, and other metabolites can greatly increase our knowledge of the specific roles these biomarkers play in internal and effective dose assessment. If the relationship between exposure and effect is known, similar to protein and DNA adducts, mercapturic acids might also be helpful in (individual) health risk assessment.
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Affiliation(s)
- R T van Welie
- Department of Pharmacochemistry, Vrije Universiteit, Amsterdam, The Netherlands
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