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Colacci A, Bartoli S, Bonora B, Guidotti L, Lattanzi G, Mazzullo M, Niero A, Perocco P, Silingardi P, Grilli S. Chloroform Bioactivation Leading to Nucleic Acids Binding. TUMORI JOURNAL 2018; 77:285-90. [PMID: 1746048 DOI: 10.1177/030089169107700401] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Chloroform was bound covalently to DNA, RNA and proteins of rat and mouse organs in vivo after i.p. injection. Covalent Binding Index values of rat and mouse liver DNA classify chloroform as a weak initiator. Labelings of RNA and proteins from various organs of both species were higher than that of DNA. In an in vitro cell-free system, chloroform was bioactivated by cytochrome P450-dependent microsomal fractions, by cytosolic GSH-transferases from rat and mouse liver, and particularly by the latter enzymes from mouse lung. This observation suggests that GSH plays a role In the binding of chloroform metabolites to DNA. The presence of both microsomal and cytosolic enzymatic systems in the standard incubation mixture generally led to an additive or synergistic bioactivating effect for rat and mouse, respectively.
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Affiliation(s)
- A Colacci
- Istituto Nazionale per la Ricerca sul Cancro, IST-Genova, Italy
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Hrudey SE, Backer LC, Humpage AR, Krasner SW, Michaud DS, Moore LE, Singer PC, Stanford BD. Evaluating Evidence for Association of Human Bladder Cancer with Drinking-Water Chlorination Disinfection By-Products. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART B, CRITICAL REVIEWS 2015; 18:213-41. [PMID: 26309063 PMCID: PMC4642182 DOI: 10.1080/10937404.2015.1067661] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Exposure to chlorination disinfection by-products (CxDBPs) is prevalent in populations using chlorination-based methods to disinfect public water supplies. Multifaceted research has been directed for decades to identify, characterize, and understand the toxicology of these compounds, control and minimize their formation, and conduct epidemiologic studies related to exposure. Urinary bladder cancer has been the health risk most consistently associated with CxDBPs in epidemiologic studies. An international workshop was held to (1) discuss the qualitative strengths and limitations that inform the association between bladder cancer and CxDBPs in the context of possible causation, (2) identify knowledge gaps for this topic in relation to chlorine/chloramine-based disinfection practice(s) in the United States, and (3) assess the evidence for informing risk management. Epidemiological evidence linking exposures to CxDBPs in drinking water to human bladder cancer risk provides insight into causality. However, because of imprecise, inaccurate, or incomplete estimation of CxDBPs levels in epidemiologic studies, translation from hazard identification directly to risk management and regulatory policy for CxDBPs can be challenging. Quantitative risk estimates derived from toxicological risk assessment for CxDBPs currently cannot be reconciled with those from epidemiologic studies, notwithstanding the complexities involved, making regulatory interpretation difficult. Evidence presented here has both strengths and limitations that require additional studies to resolve and improve the understanding of exposure response relationships. Replication of epidemiologic findings in independent populations with further elaboration of exposure assessment is needed to strengthen the knowledge base needed to better inform effective regulatory approaches.
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Affiliation(s)
- Steve E. Hrudey
- Environmental and Analytical Toxicology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | | | | | - Stuart W. Krasner
- Metropolitan Water District of Southern California, Los Angeles, California, USA
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Stagg NJ, LeBaron MJ, Eisenbrandt DL, Gollapudi BB, Klaunig JE. Assessment of Possible Carcinogenicity of Oxyfluorfen to Humans Using Mode of Action Analysis of Rodent Liver Effects. Toxicol Sci 2012; 128:334-45. [DOI: 10.1093/toxsci/kfs157] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Hrudey SE. Chlorination disinfection by-products, public health risk tradeoffs and me. WATER RESEARCH 2009; 43:2057-92. [PMID: 19304309 DOI: 10.1016/j.watres.2009.02.011] [Citation(s) in RCA: 241] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 02/05/2009] [Accepted: 02/09/2009] [Indexed: 05/19/2023]
Abstract
Since 1974 when trihalomethanes (THMs) were first reported as disinfection by-products (DBPs) in drinking water, there has been an enormous research effort directed at understanding how DBPs are formed in the chlorination or chloramination of drinking water, how these chlorination DBPs can be minimized and whether they pose a public health risk, mainly in the form of cancer or adverse reproductive outcomes. Driven by continuing analytical advances, the original DBPs, the THMs, have been expanded to include over 600 DBPs that have now been reported in drinking water. The historical risk assessment context which presumed cancer could be mainly attributed to exposure to environmental carcinogens played a major role in defining regulatory responses to chlorination DBPs which, in turn, strongly influenced the DBP research agenda. There are now more than 30 years of drinking water quality, treatment and health effects research, including more than 60 epidemiology studies on human populations, directed at the chlorination DBP issue. These provide considerable scope to reflect on what we know now, how our understanding has changed, what those changes mean for public health risk management overall and where we should look to better understand and manage this issue in the future.
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Maronpot RR. Biological Basis of Differential Susceptibility to Hepatocarcinogenesis among Mouse Strains. J Toxicol Pathol 2009; 22:11-33. [PMID: 22271974 PMCID: PMC3246016 DOI: 10.1293/tox.22.11] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 11/07/2008] [Indexed: 12/13/2022] Open
Abstract
There is a vast amount of literature related to mouse liver tumorigenesis generated over the past 60 years, not all of which has been captured here. The studies reported in this literature have generally been state of the art at the time they were carried out. A PubMed search on the topic "mouse liver tumors" covering the past 10 years yields over 7000 scientific papers. This review address several important topics related to the unresolved controversy regarding the relevance of mouse liver tumor responses observed in cancer bioassays. The inherent mouse strain differential sensitivities to hepatocarcinogenesis largely parallel the strain susceptibility to chemically induced liver neoplasia. The effects of phenobarbital and halogenated hydrocarbons in mouse hepatocarcinogenesis have been summarized because of recurring interest and numerous publications on these topics. No single simple paradigm fully explains differential mouse strain responses, which can vary more than 50-fold among inbred strains. In addition to inherent genetics, modifying factors including cell cycle balance, enzyme induction, DNA methylation, oncogenes and suppressor genes, diet, and intercellular communication influence susceptibility to spontaneous and induced mouse hepatocarcinogenesis. Comments are offered on the evaluation, interpretation, and relevance of mouse liver tumor responses in the context of cancer bioassays.
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Affiliation(s)
- Robert R Maronpot
- Maronpot Consulting, LLC, 1612 Medfield Road, Raleigh, NC 27607-4726, USA
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Auttachoat W, Germolec DR, Collins BJ, Luebke RW, White KL, Guo TL. Immunotoxicological profile of chloroform in female B6C3F1 mice when administered in drinking water. Drug Chem Toxicol 2009; 32:77-87. [DOI: 10.1080/01480540802433880] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Clewell HJ, Andersen ME. Applying Mode-of-Action and Pharmacokinetic Considerations in Contemporary Cancer Risk Assessments: An Example with Trichloroethylene. Crit Rev Toxicol 2008; 34:385-445. [PMID: 15560567 DOI: 10.1080/10408440490500795] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The guidelines for carcinogen risk assessment recently proposed by the U.S. Environmental Protection Agency (U.S. EPA) provide an increased opportunity for the consideration of pharmacokinetic and mechanistic data in the risk assessment process. However, the greater flexibility of the new guidelines can also make their actual implementation for a particular chemical highly problematic. To illuminate the process of performing a cancer risk assessment under the new guidelines, the rationale for a state-of-the-science risk assessment for trichloroethylene (TCE) is presented. For TCE, there is evidence of increased cell proliferation due to receptor interaction or cytotoxicity in every instance in which tumors are observed, and most tumors represent an increase in the incidence of a commonly observed, species-specific lesion. A physiologically based pharmacokinetic (PBPK) model was applied to estimate target tissue doses for the three principal animal tumors associated with TCE exposure: liver, lung, and kidney. The lowest points of departure (lower bound estimates of the exposure associated with 10% tumor incidence) for lifetime human exposure to TCE were obtained for mouse liver tumors, assuming a mode of action primarily involving the mitogenicity of the metabolite trichloroacetic acid (TCA). The associated linear unit risk estimates for mouse liver tumors are 1.5 x 10(-6) for lifetime exposure to 1 microg TCE per cubic meter in air and 0.4 x 10(-6) for lifetime exposure to 1 microg TCE per liter in drinking water. However, these risk estimates ignore the evidence that the human is likely to be much less responsive than the mouse to the carcinogenic effects of TCA in the liver and that the carcinogenic effects of TCE are unlikely to occur at low environmental exposures. Based on consideration of the most plausible carcinogenic modes of action of TCE, a margin-of-exposure (MOE) approach would appear to be more appropriate. Applying an MOE of 1000, environmental exposures below 66 microg TCE per cubic meter in air and 265 microg TCE per liter in drinking water are considered unlikely to present a carcinogenic hazard to human health.
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Anand SS, Philip BK, Palkar PS, Mumtaz MM, Latendresse JR, Mehendale HM. Adaptive tolerance in mice upon subchronic exposure to chloroform: Increased exhalation and target tissue regeneration. Toxicol Appl Pharmacol 2006; 213:267-81. [PMID: 16630638 DOI: 10.1016/j.taap.2006.02.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2005] [Revised: 02/07/2006] [Accepted: 02/08/2006] [Indexed: 10/24/2022]
Abstract
The aims of the present study were to characterize the subchronic toxicity of chloroform by measuring tissue injury, repair, and distribution of chloroform and to assess the reasons for the development of tolerance to subchronic chloroform toxicity. Male Swiss Webster (SW) mice were given three dose levels of chloroform (150, 225, and 300 mg/kg/day) by gavage in aqueous vehicle for 30 days. Liver and kidney injury were measured by plasma ALT and BUN, respectively, and by histopathology. Tissue regeneration was assessed by (3)H-thymidine incorporation into hepato- and nephro-nuclear DNA and by proliferating cell nuclear antigen staining. In addition, GSH and CYP2E1 in liver and kidney were assessed at selected time points. The levels of chloroform were measured in blood, liver, and kidney during the dosing regimen (1, 7, 14, and 30 days). Kidney injury was evident after 1 day with all three doses and sustained until 7 days followed by complete recovery. Mild to moderate liver injury was observed from 1 to 14 days with all three dose levels followed by gradual decrease. Significantly higher regenerative response was evident in liver and kidney at 7 days, but the response was robust in kidney, preventing progression of injury beyond first week of exposure. While the kidney regeneration reached basal levels by 21 days, moderate liver regeneration with two higher doses sustained through the end of the dosing regimen and 3 days after that. Following repeated exposure for 7, 14, and 30 days, the blood and tissue levels of chloroform were substantially lower with all three dose levels compared to the levels observed with single exposure. Increased exhalation of (14)C-chloroform after repeated exposures explains the decreased chloroform levels in circulation and tissues. These results suggest that toxicokinetics and toxicodynamics (tissue regeneration) contribute to the tolerance observed in SW mice to subchronic chloroform toxicity. Neither bioactivation nor detoxification appears to play a decisive role in the development of this tolerance.
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Affiliation(s)
- Sathanandam S Anand
- Department of Toxicology, College of Pharmacy, The University of Louisiana at Monroe, 700 University Avenue, Sugar Hall #306, Monroe, LA 71209-0495, USA.
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Abstract
Flubendazole was suspended in deionized water or olive oil and administered by gavage once daily to pregnant rats on Days 8-15 of pregnancy to examine if the embryolethal and teratogenic doses were affected by the vehicles used. Flubendazole in olive oil caused a statistically significant increase in embryolethality at doses of 7.83 mg/kg per day and higher, with complete resorption in all dams at 31.33 mg/kg per day. When flubendazole was suspended in deionized water, a significant increase in embryolethality occurred only at a maternal dose of 125.32 mg/kg per day. The proportion of litters with anomalous fetuses was significantly increased at doses of 31.33 mg/kg per day and above when flubendazole was administered in deionized water, but increased at doses at four times lower when flubendazole was administered as in olive oil. Administered as a single dose in olive oil on any one of Days 6-12 of pregnancy, a flubendazole dose of 31.33 mg/kg caused significant increases in embryolethality and decreased fetal body weights on Days 7-9, with an 82.7% incidence of embryolethality on Day 8, with complete resorption in 5 of the 8 dams. The critical periods for teratogenic effects were between Days 8 and 11 of pregnancy, with Day 9 being the most critical. Fetuses with gross, skeletal, or internal anomalies were seen in dams given a single dose of as low as 7.83 mg/kg.
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Affiliation(s)
- Haruo Yoshimura
- National Veterinary Assay Laboratory, Ministry of Agriculture, Forestry and Fisheries, 1-15-1 Tokura, Kokubunji, 185-8511 Tokyo, Japan.
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George MH, Olson GR, Doerfler D, Moore T, Kilburn S, DeAngelo AB. Carcinogenicity of bromodichloromethane administered in drinking water to Male F344/N Rats and B6C3F1 mice. Int J Toxicol 2002; 21:219-30. [PMID: 12055023 DOI: 10.1080/10915810290096351] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A life-time exposure study was conducted to assess the carcinogenicity of bromodichloromethane (BDCM) administered in the drinking water to male F344/N rats and B6C3F(1) mice. In mouse, the calculated mean daily BDCM concentrations (measured concentrations corrected for on-cage loss of chemical) were 0.06, 0.28 and 0.49 g/l. Time-weighted water consumption of 135, 97, and 89 ml/kg/day resulted in mean daily doses of 8.1, 27.2, and 43.4 mg BDCM/kg/day. No changes in feed consumption, final body weight, or survival were observed. Kidney weights were significantly depressed at 27.2 and 43.4 mg BDCM/kg/day. There was no increase in neoplasia in the liver, kidney, spleen, testis, bladder, sections along the alimentary tract, excised lesions, or at any other organ site. In rat, the corrected mean daily BDCM concentrations were 0.06, 0.33, and 0.62 g/l. Time-weighted water consumption of 65, 63, and 59 ml/kg/day yielded 3.9, 20.6 and 36.3 mg BDCM/kg/day. No alterations in feed consumption, body weight gain, and survival were seen. Kidney weight was significantly depressed in the 36.3-mg/kg/day treatment group. There was a significantly enhanced prevalence and multiplicity of hepatocellular adenomas at 3.9 mg BDCM/kg/day (15.5% and 0.16/animal vs. 2.2% and 0.02/animal for the control). Hepatocellular carcinomas increased from 2.2% and 0.02/animal for the control and 3.9 mg BDCM/kg/day to 8.3% and 0.10/animal at 20.6 mg BDCM/kg/day. The combined neoplasms were enhanced at 3.9 and 20.6 mg BDCM/kg/day. Liver neoplasia was depressed to the control value at 36.3 mg BDCM/kg. The prevalence of basophilic and clear cell, but not eosinophilic cells, altered foci of cells declined with increasing dose. BDCM did not increase cancer in the large bowel, renal tubules, or in any of the other tissues examined. Renal tubular hyperplasia was observed at 36.3 mg BDCM/kg (15.8% vs. 8.7% for the control group). Under the conditions of the study, BDCM in the drinking water was not carcinogenic in the male B6C3F(1) mouse, but was carcinogenic in the male F344/N rat based on an increased hepatocellular neoplasia.
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Affiliation(s)
- Michael H George
- National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA
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Greim H, Reuter U. Classification of carcinogenic chemicals in the work area by the German MAK Commission: current examples for the new categories. Toxicology 2001; 166:11-23. [PMID: 11518606 DOI: 10.1016/s0300-483x(01)00438-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) introduced an extended classification scheme in 1998. In addition to the traditional three categories still used to date, now called: Category 1 (human carcinogen); Category 2 (animal carcinogen); and Category 3 (suspected carcinogen), two new Categories (4 and 5) were added. Classification of substances into the new Categories 4 and 5 is based on the knowledge of mode of action and the potency of carcinogens. The essential feature of substances classified in the new Categories 4 and 5 is that exposure to these chemicals does not contribute significantly to the risk of cancer to man, provided that an appropriate exposure limit (MAK value) is observed. Chemicals known to act typically by non-genotoxic mechanisms are classified in Category 4. Genotoxic chemicals for which low carcinogenic potency can be assessed on the basis of dose-response relationships and toxicokinetics are classified in Category 5. Since the use of this scheme for 3 years, various chemicals have been classified in one of the new categories. However, in several cases data to sufficiently substantiate a MAK value are missing. Such substances are now classified in a subcategory of Category 3, called Category 3 A, which indicates that further data are required for final classification. Examples are given for classification of dichloromethane into Category 3 A, chloroform and sulfuric acid into Category 4 and ethanol into Category 5.
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Affiliation(s)
- H Greim
- Institute for Toxicology and Environmental Hygiene, Technische Universität München, Hohenbachernstrasse 15-17, D-85354 Freising-Weihenstephan, Germany.
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Clewell HJ, Gentry PR, Gearhart JM, Allen BC, Andersen ME. Comparison of cancer risk estimates for vinyl chloride using animal and human data with a PBPK model. THE SCIENCE OF THE TOTAL ENVIRONMENT 2001; 274:37-66. [PMID: 11453305 DOI: 10.1016/s0048-9697(01)00730-6] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Vinyl chloride (VC) is a trans-species carcinogen, producing tumors in a variety of tissues, from both inhalation and oral exposures, across a number of species. In particular, exposure to VC has been associated with a rare tumor, liver angiosarcoma, in a large number of studies in mice, rats, and humans. The mode of action for the carcinogenicity of VC appears to be a relatively straightforward example of DNA adduct formation by a reactive metabolite, leading to mutation, mistranscription, and neoplasia. The objective of the present analysis was to investigate the comparative potency of a classic genotoxic carcinogen across species, by performing a quantitative comparison of the carcinogenic potency of VC using data from inhalation and oral rodent bioassays as well as from human epidemiological studies. A physiologically-based pharmacokinetic (PBPK) model for VC was developed to support the target tissue dosimetry for the cancer risk assessment. Unlike previous models, the initial metabolism of VC was described as occurring via two saturable pathways, one representing low capacity-high affinity oxidation by CYP2E1 and the other (in the rodent) representing higher capacity-lower affinity oxidation by other isozymes of P450, producing in both cases chloroethylene oxide (CEO) and chloroacetaldehyde (CAA) as intermediate reactive products. Depletion of glutathione by reaction with CEO and CAA was also described. Animal-based risk estimates for human inhalation exposure to VC using total metabolism estimates from the PBPK model were consistent with risk estimates based on human epidemiological data, and were lower than those currently used in environmental decision-making by a factor of 80.
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Affiliation(s)
- H J Clewell
- KS Crump Group, Inc., ICF Consulting, Ruston, LA 71270, USA.
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Kaneko T, Wang PY, Sato A. Relationship between blood/air partition coefficients of lipophilic organic solvents and blood triglyceride levels. Toxicology 2000; 143:203-8. [PMID: 10755706 DOI: 10.1016/s0300-483x(99)00170-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The blood/air partition coefficient is one of the important parameters for understanding the pharmacokinetics of organic solvents. In conventional pharmacokinetic models, the partition coefficient has been used as a constant value for each solvent. However, blood triglyceride content varies according to a diet, and the variation may affect the partition coefficient of lipophilic organic solvents. In this study, the relationship between the blood/air partition coefficient of lipophilic organic solvents and plasma triglyceride concentrations was clarified. Corn oil (4.0 ml/kg) was administered orally to male Wistar rats, and blood samples were collected 3 h after the administration, when the plasma triglyceride level reached a peak. Control rats received the same amount of distilled water via the same route. The blood/air partition coefficients of five types of lipophilic solvents (m-xylene, trichloroethylene, 1,1,1-trichloroethane, chloroform and carbon tetrachloride) were determined in these two groups of blood samples. The hematological and biochemical parameters were also examined in the same blood samples. Although the mean plasma triglyceride level in the oil group increased about 3.3 times compared with that in the control group, the increase in the blood/air partition coefficients of the five lipophilic solvents was relatively low (approximately 1.2-1.5 times). We concluded that the diet has no significant effect on the blood/air partition coefficients of organic solvents, and the value can be used as a constant parameter for each solvent in a physiological simulation model.
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Affiliation(s)
- T Kaneko
- Department of Environmental Health, Medical University of Yamanashi, Tamaho, Japan.
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Brennan RJ, Schiestl RH. Positive responses to carcinogens in the yeast DEL recombination assay are not due to selection of preexisting spontaneous revertants. Mutat Res 1998; 421:117-20. [PMID: 9748530 DOI: 10.1016/s0027-5107(98)00168-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- R J Brennan
- Department of Cancer Cell Biology, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115-6021, USA.
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Melnick RL, Kohn MC, Dunnick JK, Leininger JR. Regenerative hyperplasia is not required for liver tumor induction in female B6C3F1 mice exposed to trihalomethanes. Toxicol Appl Pharmacol 1998; 148:137-47. [PMID: 9465273 DOI: 10.1006/taap.1997.8302] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Chloroform (TCM), a water disinfection by-product, induced liver tumors in female mice when administered by gavage in corn oil but not when given in drinking water at comparable daily doses. Because short-term studies showed that the gavage doses also induced liver toxicity, it has been suggested that the liver tumor response occurs secondary to cytotoxicity and consequent regenerative hyperplasia induced by oxidative metabolism of TCM to the toxic dihalocarbonyl intermediate. This study compares dose-response relationships of gavage-administered chlorinated/brominated trihalomethanes for hepatotoxicity, replicative DNA synthesis, and hepatocarcinogenicity in female B6C3F1 mice. The liver tumor data were obtained from previously published studies. Because bromine is a better leaving group than chlorine, metabolism of bromodichloromethane (BDCM) should produce the same intermediates as would be formed from TCM. Hence, the toxicity and carcinogenicity of BDCM was expected to be qualitatively similar to that of TCM. Dose responses for liver weight, serum sorbitol dehydrogenase and alanine aminotransferase (ALT) activities, hepatocyte degeneration, and hepatocyte labeling index (LI, a measure of replicative DNA synthesis) in female mice were similar following 3 weeks of gavage administration (once per day, 5 days per week) with TCM, BDCM, or chlorodibromomethane (CDBM). Fits of composite data for these trihalomethanes to a Hill equation model revealed sigmoidal dose responses for ALT activity and hepatocyte LI and a nearly linear low-dose response for liver tumor incidence. For this family of chemicals, the mouse liver tumor response was not associated with an elevated hepatocyte LI at doses of approximately 1 mmol/kg or less. High incidences of liver tumors were observed with BDCM and CDBM at doses that had a marginal effect or no effect on the hepatocyte LI. Thus, the carcinogenic effects of trihalomethanes are not simply a consequence of cytotoxicity and regenerative hyperplasia. The possible contributions from other activation pathways, including GSH conjugation and reductive metabolism, need to be considered in assessments of the carcinogenicity of the trihalomethanes.
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Affiliation(s)
- R L Melnick
- Environmental Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
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Golden RJ, Holm SE, Robinson DE, Julkunen PH, Reese EA. Chloroform mode of action: implications for cancer risk assessment. Regul Toxicol Pharmacol 1997; 26:142-55. [PMID: 9356278 DOI: 10.1006/rtph.1997.1161] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Risk assessment methodology, particularly pertaining to potential human carcinogenic risks from exposures to environmental chemicals, is undergoing intense scrutiny from scientists, regulators, and legislators. The current practice of estimating human cancer risk is based almost exclusively on extrapolating the results of chronic, high-dose studies in rodents to estimate potential risk in humans. However, many scientists are questioning whether the logic used in this current risk assessment methodology is the best way to safeguard public health. A major tool of human cancer risk assessment is the linearized multistage (LMS) model. The LMS model has been identified as an aspect of risk assessment that could be improved. One way to facilitate this improvement is by developing a way to incorporate a carefully derived, more biologically relevant mechanism of action data on carcinogenesis. Recent data on chloroform indicate that the dose-response relationship for chloroform-induced tumors in rats and mice is nonlinear, based upon events secondary to cell necrosis and subsequent regeneration as the likely mode of action for the carcinogenic effects of chloroform. In light of these data, there is a sound scientific basis for removing some of the uncertainty that accompanies current cancer risk assessments of chloroform. The following points summarize the critical data: (1) a substantial body of data demonstrates a lack of direct in vivo or in vitro genotoxicity of chloroform; (2) chloroform induces liver and kidney tumors in long-term rodent cancer bioassays only at doses that induce frank toxicity at these target sites; (3) the chloroform doses required to produce tumors in susceptible species exceed the MTD, often by a considerable margin; (4) cytotoxicity and compensatory cell proliferation are associated with the chloroform doses required to induce liver or kidney tumors in susceptible rodent species; (5) there are no instances of chloroform-induced tumors that are not preceded by this pattern of dose-dependent toxic responses; (6) it is biologically plausible that cytolethality leads to chronically stimulated cell proliferation and related events such as inflammation and growth stimulation which act to initiate and promote the carcinogenic process; and (7) the consistently linked cellular events of cytolethality and subsequent cell proliferation, for which doses of no adverse effect have been clearly shown to exist, are one of the biological prerequisites for chloroform-induced tumors in animals. Based on these data, it is inappropriate to extrapolate cancer risk from high doses that produce necrosis and regenerative cell proliferation to low doses that do not with a model that presumes genotoxicity and a linear dose-response relationship. The weight of the scientific evidence concerning chloroform-induced tumors in rodents is consistent with and supports a cancer risk assessment methodology based on mode of action as the basis for establishing regulatory standards for this compound.
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Affiliation(s)
- R J Golden
- Environmental Risk Sciences, Inc., 1000 Thomas Jefferson Street, N.W., Washington, DC 20007, USA
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Semino G, Lilly P, Andersen ME. A pharmacokinetic model describing pulsatile uptake of orally-administered carbon tetrachloride. Toxicology 1997; 117:25-33. [PMID: 9020196 DOI: 10.1016/s0300-483x(96)03546-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Many rodent bioassays have been conducted using oral gavage for delivery of test chemicals. Highly lipophilic compounds are generally administered to rodents dissolved in corn oil, a dosing vehicle shown to influence xenobiotic toxicity, carcinogenicity and pharmacokinetics by altering chemical absorption processes. In this paper, we present a multi-compartmental description of the gastrointestinal (GI) tract linked to a physiologically based pharmacokinetic (PB-PK) model to describe the complex oral uptake of carbon tetrachloride (CCl4) administered in corn oil and 0.25% Emulphor. The GI submodel was described using a series of subcompartments, each subcompartment described with an absorption constant (Ka, 1/h), a bioavailability term (A, unitless), and a compartment emptying time (T, h). The model was parameterized by fitting multi-peak blood and exhaled breath chamber concentration-time profiles following oral gavage of CCl4 in corn oil and aqueous vehicles to male Fischer 344 rats. Successful fitting of experimental data was accomplished by varying values of Ka, A, and T until adequate fits were obtained. Values of Ka and A required to fit data from aqueous gavage were greater than corn oil. Utilization of the multi-compartmental GI tract submodel provided increased precision in fitting complex oral uptake profiles compared to previously used one- and two-compartment oral uptake models. This model provides estimates of absorption rate constants and bioavailabilities as well as providing a framework for generation of more complete, physiologically-realistic descriptions of oral absorption.
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Affiliation(s)
- G Semino
- Laboratorio di Tossicologia, Istituto di Scienze Farmacologiche, University of Milan, Italy
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18
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Lilly PD, Simmons JE, Pegram RA. Effect of subchronic corn oil gavage on the acute toxicity of orally administered bromodichloromethane. Toxicol Lett 1996; 87:93-102. [PMID: 8914616 DOI: 10.1016/0378-4274(96)03765-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Bromodichloromethane (BDCM) is a by-product of water chlorination and is the second most common trihalomethane (THM) in finished drinking water. It has been reported that delivery of THMs in corn oil can influence the site and magnitude of toxic and carcinogenic responses in rodents, perhaps by inducing metabolizing enzymes or altering tissue composition. To determine if corn oil influences the acute toxicity of BDCM, adult male F-344 rats were pretreated 5 days/week for 6 weeks with oral doses of corn oil or water at a volume of 5 ml/kg. Following pretreatment, animals were gavaged with a single dose of 0, 200 or 400 mg BDCM/kg in 10% Emulphor. Urine was collected at timed intervals over a 48-h period following BDCM administration. Rats were sacrificed at this time and organs and blood removed. Urine and serum were analyzed for indicators of toxicity. Corn oil pretreatment did not enhance the acute hepato- or nephrotoxicity of BDCM, suggesting that vehicle effects noted in previous THM toxicity and carcinogenicity studies are more likely due to pharmacokinetic differences between administration in corn oil and aqueous gavage vehicles than to altered tissue composition or physiological changes.
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Affiliation(s)
- P D Lilly
- Curriculum in Toxicology, University of North Carolina at Chapel Hill 27599, USA
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19
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Potter CL, Chang LW, DeAngelo AB, Daniel FB. Effects of four trihalomethanes on DNA strand breaks, renal hyaline droplet formation and serum testosterone in male F-344 rats. Cancer Lett 1996; 106:235-42. [PMID: 8844978 DOI: 10.1016/0304-3835(96)04331-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
All four possible trihalomethanes (THMs) containing bromine and chlorine, as well as perchloroethylene (PCE), were evaluated for their ability to produce DNA strand breaks, alpha 2u-globulin rich renal deposits, and testosterone changes in male F-344 rats. Rats received daily equimolar doses (0.75 or 1.5 mmol/kg) of THMs or PCE (1000 mg/kg) in 4% Emulphor vehicle by oral gavage for 7 days. No significant DNA strand breaks were produced by any THM or PCE treatment. PCE treatment produced increased hyaline droplet formation in renal tubules. However, all THM treatments reduced or eliminated the appearance of renal hyaline droplets. All four THM treatments also produced a decrease in serum testosterone concentrations on day 7, which might account for decreased hyaline droplet formation. No significant increase in cell proliferation, measured by [3H]thymidine incorporation in vivo, appeared in this 1-week study.
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Affiliation(s)
- C L Potter
- National Risk Management Research Laboratory, US Environmental Protection Agency, Cincinnati, OH 45268, USA.
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20
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Farooqui MY, Ybarra B, Piper J, Tamez A. Effect of dosing vehicle on the toxicity and metabolism of unsaturated aliphatic nitriles. J Appl Toxicol 1995; 15:411-20. [PMID: 8666726 DOI: 10.1002/jat.2550150512] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effect of dosing vehicle on toxicity and metabolism of unsaturated aliphatic nitriles was investigated in male Sprague-Dawley rats. Five unsaturated aliphatic nitriles--acrylonitrile, methacrylonitrile, allylnitrile, crotononitrile and fumaronitrile--were prepared in five different dosing vehicles--saline, corn oil, safflower oil, mineral oil, olive oil and Tween-20. Groups of six male rats were given 0.5 LD50 doses of the nitriles by gavage and they were observed for 12 It for cholinomimetic and central nervous system effects. Cyanide and glutathione levels were determined in blood and various organs at 1, 3 and 6 h after nitrile administration and thiocyanate levels were determined at 6 h after nitrile administration. The results indicate that all the vehicles studied potentiated the toxicity of all the nitriles compared to nitriles administered in saline and significantly increased their metabolism to cyanide and thiocyanate and nitrile-induced depletion of glutathione in rats. This behavior of vehicles illustrates the difficulty of identifying suitable vehicles for administration of lipophilic compounds in toxicology studies.
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Affiliation(s)
- M Y Farooqui
- Department of Biology, College of Arts and Sciences, University of Texas Pan American, Edinburg 78539, USA
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21
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Appendix B: Chlorinated alkanes. Regul Toxicol Pharmacol 1994. [DOI: 10.1016/s0273-2300(05)80027-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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22
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Faroon OM, Williams M, O'Connor R. A review of the carcinogenicity of chemicals most frequently found at National Priorities List sites. Toxicol Ind Health 1994; 10:203-30. [PMID: 7855869 DOI: 10.1177/074823379401000309] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Several studies have shown that numerous National Priorities List (NPL) sites have been contaminated with arsenic (747), cadmium (791), chloroform (596), or nickel (664). The National Toxicology Program (NTP, 1991) has classified these substances as known human carcinogens (arsenic and certain arsenic compounds) or as substances that may reasonably be anticipated to be carcinogens (cadmium and certain cadmium compounds, chloroform, and nickel and certain nickel compounds). The general population is probably exposed to low levels of these hazardous substances through drinking water, eating food, or inhaling contaminated air. People working or living near industries and facilities that manufacture and use chloroform, nickel, arsenic, or cadmium may be exposed to higher than background levels of these hazardous substances. Multiple pathways of exposure may exist for populations near hazardous waste sites. For example, high levels of chloroform (1,890 ppb) were found in well water near a waste site; high levels of cadmium exposure may exist for individuals living near cadmium-contaminated waste sites.
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Affiliation(s)
- O M Faroon
- Division of Toxicology, U.S. Department of Health and Human Services Atlanta, Georgia
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23
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Lipsky MM, Skinner M, O'Connell C. Effects of chloroform and bromodichloromethane on DNA synthesis in male F344 rat kidney. ENVIRONMENTAL HEALTH PERSPECTIVES 1993; 101 Suppl 5:249-252. [PMID: 8013415 PMCID: PMC1519423 DOI: 10.1289/ehp.93101s5249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We have been investigating the actions of chloroform (CHCl3) and bromodichloromethane (BDCM) in rat kidney after different routes of exposure. Male F344 rats were exposed by gavage with corn oil or water as the diluting vehicle. All experiments lasted 30 days with gavage exposures 5 days per week for 4 weeks (20 doses). All animals were injected IP with bromodeoxyuridine (BrdU) 3 times over a 6-day period at 50 mg/kg/injection. Kidney tissue was fixed and slides were stained with hematoxylin and eosin for routine viewing and by the PAP (peroxidase-antiperoxidase) technique using anti-BrdU to label cells in DNA synthesis. There were no significant changes in gross parameters evaluated between the control rats and the rats exposed to CHCl3 or BDCM. Rats exposed via corn oil gavage to CHCl3 displayed a segment-specific epithelial cell necrosis (6/6 high dose, 2/6 low dose). The lesions were primarily localized to the second segment of the proximal tubule, although some spread to cells in the first segment was occasionally observed. No histologic lesions were observed in the kidneys of rats exposed to BDCM. Preliminary results indicate a significant increase in DNA synthesis in the CHCl3-treated rats and a slight increase in DNA synthesis in BDCM-treated rats with corn oil as the diluent. The increase in BrdU labeling was primarily in cells of the S2 segment of the proximal tubule and interstitial cells of CHCl3-exposed animals and in cells of the S3 segment of BDCM-exposed animals.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M M Lipsky
- Department of Pathology, University of Maryland School of Medicine, Baltimore 21201
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24
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Gallo JM, Cheung LL, Kim HJ, Bruckner JV, Gillespie WR. A physiological and system analysis hybrid pharmacokinetic model to characterize carbon tetrachloride blood concentrations following administration in different oral vehicles. JOURNAL OF PHARMACOKINETICS AND BIOPHARMACEUTICS 1993; 21:551-74. [PMID: 8145131 DOI: 10.1007/bf01059114] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Oral absorption of chemicals can be influenced significantly by the administration vehicle or diluent. It has been observed that the oral absorption of carbon tetrachloride (CCl4) and other volatile organic chemicals is markedly affected by the dosing vehicle, with administration in oils producing erratic blood concentration-time profiles with multiple peaks. Analysis of this type of data by a compartmental modeling approach can be difficult, and requires numerous assumptions about the absorption processes. Alternatively, a system analysis method with few assumptions may provide a more accurate description of the observed data. In the current investigations, a nonlinear system analysis approach was applied to blood CCl4 concentration-time data obtained following iv and oral administration. The oral regimens consisted of 25 mg CCl4/kg body wt given as an aqueous emulsion, in water, as pure chemicals, and in corn oil. The system analysis procedure, based upon a disposition decomposition method, provided an absorption input rate function, F, for each regimen. A physiological pharmacokinetic model, based primarily on parameters available in the literature, and the F input functions, formed a hybrid model that adequately described the observed blood CCl4 concentration-time data. The same physiological pharmacokinetic model, employing conventional first-order absorption input schemes, did not predict the data as well. Overall, the system analysis approach allowed the oral absorption of CCl4 to be characterized accurately, regardless of the vehicle. Though system analysis is based on general mathematical properties of a system's behavior rather than on its causal mechanisms, this work demonstrates that it can be a useful adjunct to physiological pharmacokinetic models.
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Affiliation(s)
- J M Gallo
- Department of Pharmaceutics, College of Pharmacy, University of Georgia, Athens
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25
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Glaze WH, Andelman JB, Bull RJ, Conolly RB, Hertz CD, Hood RD, Pegram RA. Determining Health Risks Associated With Disinfectants and Disinfection By-products: Research Needs. ACTA ACUST UNITED AC 1993. [DOI: 10.1002/j.1551-8833.1993.tb05955.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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Oredipe OA, Barth RF, Dwivedi C, Webb TE. Dietary glucarate-mediated inhibition of initiation of diethylnitrosamine-induced hepatocarcinogenesis. Toxicology 1992; 74:209-22. [PMID: 1519243 DOI: 10.1016/0300-483x(92)90140-a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Previously, it has been reported that calcium glucarate is a potent inhibitor of chemical carcinogenesis, including phenobarbital-promoted diethylnitrosamine-initiated hepatic toxicity expressed as altered hepatic foci in rats. The purpose of the present study was to determine whether calcium glucarate could inhibit the immediate and delayed appearance of altered hepatic foci when fed to rats during the initiation phase of diethylnitrosamine-induced hepatocarcinogenesis. The effects of dietary mode of administration of calcium glucarate on the initiation phase of hepatocarcinogenesis were also examined. Since diethylnitrosamine is not known to undergo glucuronidation and calcium glucarate has been shown to enhance clearance of circulating estrogens, an indirect mechanism of action of calcium glucarate was also evaluated by pretreating rats with an anti-estrogen, tamoxifen, prior to partial hepatectomy and administration of diethylnitrosamine. Calcium glucarate significantly inhibited both the early and delayed appearance of altered hepatic foci and exerted maximal inhibition when administered by gavage prior to diethylnitrosamine. Maximal inhibition was obtained when calcium glucarate was provided continuously in the diet of animals up to 5 and 7 months. Pretreatment of animals with tamoxifen before partial hepatectomy and diethylnitrosamine resulted in maximal inhibition of the initiation phase of hepatocarcinogenesis. This suggests but does not prove that the anti-carcinogenic activity of calcium glucarate was due to decreased liver proliferation. In the present study, the proliferation of ductular epithelial and oval cells appeared to be associated with the administration of diethylnitrosamine. Collectively, our data suggest that calcium glucarate inhibited the initiation phase of diethylnitrosamine-induced hepatocarcinogenesis.
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Affiliation(s)
- O A Oredipe
- Department of Pathology, Ohio State University, Columbus 43210
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27
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Mehendale HM. Role of hepatocellular regeneration and hepatolobular healing in the final outcome of liver injury. A two-stage model of toxicity. Biochem Pharmacol 1991; 42:1155-62. [PMID: 1716097 DOI: 10.1016/0006-2952(91)90249-5] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- H M Mehendale
- Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson 39216-4505
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28
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Lenz SD, Carlton WW. Decreased incidence of diphenylamine-induced renal papillary necrosis in Syrian hamsters given dimethylsulphoxide. Food Chem Toxicol 1991; 29:409-18. [PMID: 1874470 DOI: 10.1016/0278-6915(91)90082-i] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The renal papillotoxicity of diphenylamine dissolved in dimethylsulphoxide (DMSO) was investigated in male Syrian hamsters, male Sprague-Dawley rats and female Mongolian gerbils. When diphenylamine in DMSO was administered orally to male Syrian hamsters (400, 600 or 800 mg/kg body weight/day for up to 9 days), the incidence of renal papillary necrosis was almost zero. Hamsters pretreated with DMSO (0.5 ml/100 g body weight/day) and 1 hr later given 400, 600 or 800 mg diphenylamine in peanut oil/kg body weight/day for 3 consecutive days had significantly reduced incidences of renal papillary necrosis (0/10, 0/10 and 1/10 in the low-, mid- and high-dose groups, respectively) when compared with hamsters given similar doses of diphenylamine but not pretreated with DMSO (5/10, 7/10 and 5/10 in the low-, mid- and high-dose groups, respectively). Focal, apex-limited renal papillary necrosis was observed in two Sprague-Dawley rats given 800 mg diphenylamine in DMSO/kg body weight/day orally for 9 days. Focal, intermediate renal papillary necrosis was observed in two additional rats administered 800 mg diphenylamine in DMSO/kg/day orally for 9 days. Renal papillary necrosis was not observed in any of the Mongolian gerbils. The results of these studies suggest that DMSO protects against diphenylamine-induced renal papillary necrosis in male Syrian hamsters.
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Affiliation(s)
- S D Lenz
- Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47906
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29
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Merrick BA, Robinson M, Condie LW. Cardiopathic effect of 1,2,3-trichloropropane after subacute and subchronic exposure in rats. J Appl Toxicol 1991; 11:179-87. [PMID: 1918791 DOI: 10.1002/jat.2550110305] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
1,2,3-Trichloropropane (1,2,3-TCP) is an industrial water contaminant with potential for human exposure by the oral route. The systemic toxicology of 1,2,3-TCP was evaluated after subacute or subchronic exposure in male and female Sprague-Dawley rats. Animals were treated with 0.01, 0.05, 0.20 and 0.80 mmol kg-1 day-1 for 10 days and 0.01, 0.05, 0.10 and 0.40 mmol kg-1 day-1 for 90 days. Chemical exposure was by oral gavage in corn oil. Lethality did not occur in either study. Toxicity was observed primarily in the high dose group of subacute and subchronically treated rats of both sexes. Weight gain suppression occurred at a dose of 0.8 mmol kg-1 (118 mg kg-1) after 10 days. After 90 days of exposure to 0.40 mmol kg-1, the final body weights were 81% and 86% of control values for males and females, respectively. When major organ weights were normalized by body weight, liver and kidney values were generally increased relative to control in the two highest dose groups after 10- and 90-day chemical exposure. Serum chemistries and histopathology indicated a mild hepatotoxic response to 1,2,3-TCP in the high dose group of each study but did not support any renal toxicity. Thymic weight reduction due to atrophy occurred at 10 days of exposure in high dose groups but was normal in all groups after the 90-day treatment. The primary histological finding in this study was an inflammation-associated cardiopathy produced by 1,2,3-TCP. Myocardial necrosis and degeneration occurred in a diffuse pattern with marked eosinophilia of affected cells. Male and female animals showed a cardiopathic response only at a dose of 0.8 mmol kg-1 1,2,3-TCP after the 10-day exposure.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B A Merrick
- Health Effects Research Laboratory, US Environmental Protection Agency, Cincinnati, OH 45268
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30
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Kim HJ, Odend'hal S, Bruckner JV. Effect of oral dosing vehicles on the acute hepatotoxicity of carbon tetrachloride in rats. Toxicol Appl Pharmacol 1990; 102:34-49. [PMID: 2296770 DOI: 10.1016/0041-008x(90)90081-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Although carbon tetrachloride (CCl4) is of concern as a drinking water contaminant, it has been necessary in most oral toxicity studies to give CCl4 in an oil vehicle due to its limited water solubility. The primary objective of our study was to assess the influence of dosing vehicles on the acute hepatotoxicity of CCl4. Fasted 200- to 230-g rats were generally found to be more susceptible to CCl4 hepatotoxicity than fasted 300- to 330-g rats. A time-course study revealed that corn oil did not delay the onset or time of maximal liver injury by an oral 100 mg/kg dose of CCl4, but did reduce the extent of injury relative to that when the chemical was given undiluted or as an aqueous emulsion. Fasted 200- to 230-g male Sprague-Dawley rats were given 0, 10, 25, 50, 100, 250, 500, or 1000 mg CCl4/kg body wt by gavage: in corn oil; as an aqueous emulsion; as the undiluted chemical; and in the 10 and 25 mg/kg doses only, in water. Blood and liver samples were taken 24 hr after dosing for measurement of serum and microsomal enzymes. Pathological examination of liver samples was also conducted. Dose-dependent increases in serum enzyme levels and pathological changes and dose-dependent decreases in microsomal P450 and glucose-6-phosphatase activity were observed in each vehicle group. Both the 10 and 25 mg/kg oral doses of CCl4 in water caused significant elevations in serum enzymes and hepatic centrolobular vacuolation. The study revealed that acute hepatotoxicity was less pronounced at each dosage level in rats given CCl4 in corn oil than in other vehicle groups. These findings demonstrate that dosing vehicles can significantly influence the acute hepatotoxicity of CCl4 in rats and are a cause for additional consideration and review of the practice of routinely using vegetable oils as a diluent in studies of volatile organic compound (VOC) toxicity. The use of aqueous Emulphor emulsions appears more appropriate in acute toxicity studies of VOC drinking water contaminants such as CCl4, in that the emulsion did not substantially alter the toxicity of CCl4 from that of undiluted CCl4 or CCl4 ingested in water.
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Affiliation(s)
- H J Kim
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Georgia, Athens 30602
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31
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Kim HJ, Bruckner JV, Dallas CE, Gallo JM. Effect of dosing vehicles on the pharmacokinetics of orally administered carbon tetrachloride in rats. Toxicol Appl Pharmacol 1990; 102:50-60. [PMID: 2296771 DOI: 10.1016/0041-008x(90)90082-6] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The primary objectives of this investigation were to determine whether oil and aqueous dosage vehicles alter the pharmacokinetics of orally administered carbon tetrachloride (CCl4) in rats, and to relate vehicle effects on CCl4 absorption and bioavailability to alterations of the acute hepatotoxicity of CCl4 seen in a companion study (H.J. Kim, S. Odend'hal, and J. V. Bruckner, 1990, Toxicol. Appl. Pharmacol. 102, 34-49). Fasted 200- to 230-g male Sprague-Dawley rats with indwelling arterial cannulas received 25 mg CCl4/kg body wt by gavage: in corn oil; as an Emulphor aqueous emulsion; in water; and as pure undiluted chemical. The 25 mg/kg dose was also given iv in PEG 400 through an indwelling jugular cannula. Serial blood samples were taken from the iv and gavage animals and analyzed for CCl4 content to obtain blood concentration-versus-time profiles. CCl4 was absorbed very rapidly from the GI tract, as peak concentrations of CCl4 in the blood were reached within 3-6 min of dosing in the aqueous emulsion and water groups. These peak levels were higher than those in the undiluted CCl4 group and substantially higher than those in the corn oil group. Corn oil markedly delayed the absorption of CCl4 from the GI tract and produced secondary peaks in the blood concentration-versus-time profiles. Elimination of CCl4 from the bloodstream of the iv group followed a triexponential pattern. CCl4 was eliminated from the blood at approximately the same rate in the iv and po groups, as reflected by similar elimination rate constant and half-life values. There was a high degree of correlation of both Cmax and AUC0(120) with hepatotoxicity. CCl4 was apparently less acutely hepatotoxic in corn oil due to delay and prolongation of CCl4 absorption, resulting in a marked decrease in the concentration of the chemical in the arterial blood. These findings suggest that corn oil has sufficient effect on the pharmacokinetics of orally administered CCl4 to require an appraisal of its use in studies of the acute oral toxicity of CCl4 and other volatile organic chemicals (VOCs). The use of aqueous Emulphor emulsions appears appropriate in studies of VOC contaminants of drinking water, in that the emulsion did not substantially alter the pharmacokinetics or hepatotoxicity of CCl4 from that ingested in water.
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Affiliation(s)
- H J Kim
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Georgia, Athens 30602
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32
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Abstract
This article presents a summary of the proceedings of the Symposium and Workshop on Reducing Uncertainty in Risk Assessment, held at Michigan State University, on May 18-19, 1987. Participants addressed four topic areas: safety factors in noncarcinogen risk assessment; relevance of biological data in risk assessment; upper and lower bounds in carcinogenic risk assessment; and exposure assessment. One additional issue, risk communication, was discussed as a result of participant interest. Consensus recommendations in these five areas, resulting from the deliberations of the workshop groups, are presented. In addition to the specific recommendations, some general conclusions could be drawn. One was that the increased understanding of underlying mechanisms of toxicity, gained in the last decade, should be incorporated as much as possible into the risk assessment process. A second conclusion was that more effort should be devoted to increasing this understanding and developing the best methods for applying this knowledge to risk assessment. Last, more effort should be made to improve the communication of these assessments to the public and to policy makers so that the best and most complete information is utilized in risk management decisions.
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Affiliation(s)
- M A Kamrin
- Center for Environmental Toxicology, Michigan State University, East Lansing 48824
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Merrick BA, Robinson M, Condie LW. Differing hepatotoxicity and lethality after subacute trichloroethylene exposure in aqueous or corn oil gavage vehicles in B6C3F1 mice. J Appl Toxicol 1989; 9:15-21. [PMID: 2926094 DOI: 10.1002/jat.2550090105] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Subacute toxicity of trichloroethylene (TCE) was evaluated in male and female B6C3F1 mice using corn oil or aqueous gavage vehicles. Mice received oral doses of TCE five times a week for 4 weeks at 600, 1200 and 2400 mg/kg/day for males and 450, 900 and 1800 mg/kg/day for females. Vehicle control mice were dosed with either corn oil or a 20% aqueous solution of Emulphor. A dose-related increase in lethality occurred in male and female mice receiving TCE in Emulphor but not corn oil during the first week of treatment. Lethality was consistent with central nervous system depressant effects of TCE. After 4 weeks of exposure, body weights were not altered by TCE but liver/body weight ratios were uniformly increased by TCE administered in either vehicle in both sexes. Only male mice treated with TCE in corn oil, however, sustained elevations in serum enzyme levels, accompanied by liver histopathology. TCE in corn oil produced inflammation-associated focal necrosis in 30-40% of the male mice, with increasing severity from low to high dose. Lipid accumulation, as indicated by Oil-Red O staining, was most prevalent in male mice treated with TCE in corn oil but also occurred to a lesser degree in animals receiving either gavage vehicle alone. This study indicates that the type of oral gavage vehicle is an important factor in determining the nature of TCE toxicity.
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Affiliation(s)
- B A Merrick
- Toxicology and Microbiology Division, US Environmental Protection Agency, Cincinnati, OH 45268
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