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Title: Mechanism Involved in Trichloroethylene-Induced Liver Cancer: Importance to Environmental Cleanup

Abstract

The objective of this project is to develop critical data for improving risk-based cleanup standards for trichloroethylene (TCE). Importance to DOE. Cleanup costs for chlorinated solvents found on DOE sites are most frequently driven by TCE because it is the most widespread contaminant and is generally present at the highest concentrations. Data that would permit increases in risk-based standards for TCE would reduce complex wide cleanup costs by hundreds of millions of dollars. Current Regulatory Actions that Research will Impact. EPA is currently reviewing its risk assessment for TCE. Richard J. Bull has worked with EPA on this review by writing the mode of action section of their determination. A presentation by James Cogliano of EPA at the 1999 Annual Society of Toxicology Meeting indicates that they have accepted the concept of nonlinear extrapolation for liver tumor induction by TCE. This project will end in FY 1999 with its major technical and policy objectives satisfied.

Authors:
;
Publication Date:
Research Org.:
Pacific Northwest National Lab., Richland, WA (US)
Sponsoring Org.:
USDOE Office of Environmental Management (EM) (US)
OSTI Identifier:
827051
Report Number(s):
EMSP-54684-1999
R&D Project: EMSP 54684; TRN: US200425%%220
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 1 Jun 1999
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 63 RADIATION, THERMAL, AND OTHER ENVIRONMENTAL POLLUTANT EFFECTS ON LIVING ORGANISMS AND BIOLOGICAL MATERIALS; DOLLARS; EXTRAPOLATION; INDUCTION; LIVER; NEOPLASMS; RISK ASSESSMENT; SOLVENTS; US EPA

Citation Formats

Bull, Richard J., and Thrall, Brian D. Mechanism Involved in Trichloroethylene-Induced Liver Cancer: Importance to Environmental Cleanup. United States: N. p., 1999. Web. doi:10.2172/827051.
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Bull, Richard J., & Thrall, Brian D. Mechanism Involved in Trichloroethylene-Induced Liver Cancer: Importance to Environmental Cleanup. United States. doi:10.2172/827051.
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Bull, Richard J., and Thrall, Brian D. Tue . "Mechanism Involved in Trichloroethylene-Induced Liver Cancer: Importance to Environmental Cleanup". United States. doi:10.2172/827051. https://www.osti.gov/servlets/purl/827051.
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@article{osti_827051,
title = {Mechanism Involved in Trichloroethylene-Induced Liver Cancer: Importance to Environmental Cleanup},
author = {Bull, Richard J. and Thrall, Brian D.},
abstractNote = {The objective of this project is to develop critical data for improving risk-based cleanup standards for trichloroethylene (TCE). Importance to DOE. Cleanup costs for chlorinated solvents found on DOE sites are most frequently driven by TCE because it is the most widespread contaminant and is generally present at the highest concentrations. Data that would permit increases in risk-based standards for TCE would reduce complex wide cleanup costs by hundreds of millions of dollars. Current Regulatory Actions that Research will Impact. EPA is currently reviewing its risk assessment for TCE. Richard J. Bull has worked with EPA on this review by writing the mode of action section of their determination. A presentation by James Cogliano of EPA at the 1999 Annual Society of Toxicology Meeting indicates that they have accepted the concept of nonlinear extrapolation for liver tumor induction by TCE. This project will end in FY 1999 with its major technical and policy objectives satisfied.},
doi = {10.2172/827051},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jun 01 00:00:00 EDT 1999},
month = {Tue Jun 01 00:00:00 EDT 1999}
}
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Technical Report:
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DOI:  10.2172/827051
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  • 'The Pacific Northwest National Lab. was awarded ten (10) Environmental Management Science Program (EMSP) research grants in Fiscal Year 1996. This section gives a summary of how each grant is addressing significant DOE cleanup issues, including those at the Hanford Site. The technical progress made to date in each of these research projects is addressed in more detail in the individual progress reports contained in this document. This research is primarily focused in three areas-Tank Waste Remediation, Soil and Groundwater Cleanup, and Health Effects.'

  • ; ; ; ...
    'The objective of this project is to develop critical data for changing risk-based clean-up standards for trichloroethylene (TCE). The project is organized around two interrelated tasks: Task 1 addresses the tumorigenic and dosimetry issues for the metabolites of TCE that produce liver cancer in mice, dichloroacetate (DCA) and trichloroacetate (TCA). Early work had suggested that TCA was primarily responsible for TCE-induced liver tumors, but several, more mechanistic observations suggest that DCA may play a prominent role. This task is aimed at determining the basis for the selection hypothesis and seeks to prove that this mode of action is responsible formore » TCE-induced tumors. This project will supply the basic dose-response data from which low-dose extrapolations would be made. Task 2 seeks specific evidence that TCA and DCA are capable of promoting the growth of spontaneously initiated cells from mouse liver, in vitro. The data provide the clearest evidence that both metabolites act by a mechanism of selection rather than mutation. These data are necessary to select between a linear (i.e. no threshold) and non-linear low-dose extrapolation model. As of May of 1998, this research has identified two plausible modes of action by which TCE produces liver tumors in mice. These modes of action do not require the compounds to be mutagenic. The bulk of the experimental evidence suggests that neither TCE nor the two hepatocarcinogenic metabolites of TCE are mutagenic. The results from the colony formation assay clearly establish that both of these metabolites cause colony growth from initiated cells that occur spontaneously in the liver of B 6 C 3 F 1 mice, although the phenotypes of the colonies differ in the same manner as tumors differ, in vivo. In the case of DCA, a second mechanism may occur at a lower dose involving the release of insulin. This observation is timely as it was recently reported that occupational exposures to trichloroethylene results in 2 to 4-fold elevations in serum insulin concentrations, as well. The increases in insulin have not been shown responsible for the induction of liver tumors. Therefore, this problem is a subject of a proposal to the Office of Biological and Environmental Research Low-Dose Initiative. However, even if this is demonstrated to be the most sensitive mechanism for liver tumor induction, it is unlikely to contribute to induction of cancer at lower doses, since this involves modification of normal endocrine function. As doses are decreased to levels that do not induce increase in serum insulin level, there should be no risk from this metabolite either. Therefore, there is clearly a rational basis for considering a margin of exposure for low dose extrapolation of liver cancer risks for TCE.'« less

  • ;
    The project is organized around two interrelated tasks: Task 1 develops the basic dosimetry parameters and provides in vivo data describing the mode of action tumorigenic and for the metabolites of TCE that produce liver cancer in mice, dichloroacetate (DCA) and trichloroacetate (TCA). Early work suggested that TCA was primarily responsible for TCE-induced liver tumor. More recent, mechanistic observations indicated that DCA played a prominent role. Therefore, studies were designed to determine whether the effects of DCA were mediated through a mode of action that affects primarily tumor growth rates. Task 2 seeks specific evidence that TCA and DCA aremore » capable of promoting the growth of spontaneously initiated cells from mouse liver, in vitro. The data provide the clearest evidence that both metabolites act by a mechanism of selection rather than mutation. These data are necessary to select between a linear (i.e. no threshold) and non-linear low-dose extrapolation models.« less

  • ;
    Trichloroethylene (TCE) is a common contaminant of groundwater as a result of poor disposal practices of the past. As a consequence, this solvent is the focus of many clean-up operations of uncontrolled hazardous waste sites. TCE is carcinogenic in both mice and rats, but at different sites, the liver and kidney, respectively (NCI 1976; NTP 1988; NTP 1990). Liver tumor induction in mice has been the tumor most critical from the standpoint of environmental regulation (Bull 2000). Under the proposed cancer risk guidelines of the Environmental Protection Agency (EPA 1996), identifying the dose-response behavior of key events involved in carcinogenicmore » responses can be used for developing alternative risk assessments. A major difficulty in developing alternative approaches for TCE is the fact that three of its metabolites are capable of inducing liver cancer in mice (Bull et al. 1990; Daniel et al. 1992; DeAngelo et al. 1999; Pereria 1996). Two of these metabolites have distinct modes of action, dichloroacetate (DCA) and trichloroacetate (TCA). The third metabolite, chloral hydrate, is probably active as a result of its conversion to one or both of these two metabolites. Ordinarily, the first approach to assigning causality to a metabolite in tumorigenesis would be an attempt to measure its concentration in the body and associate that with tumorigenic concentrations observed when the compound is itself administered. This can be done with relative ease with TCA. However, it has been more difficult with DCA since blood levels of this metabolite after exposure to carcinogenic doses of DCA fall rapidly below detection limits (Kato-Weinstein et al. 1998; Merdink et al. 1998). Mutations in the ras protooncogene have been used to determine if distinct patterns of DNAsequence alterations can provide indications of the type of DNA damage that might be produced by carcinogens. The presence of ras mutations in chemically-induced tumors was suggested as a means o f determining whether a chemical was genotoxic (Wiseman et al. 1986). However, the 7 discovery that spontaneous tumors also contain this oncogene indicated that this assumption may not be correct (Fox and Watanabe 1985). Several non-genotoxic carcinogens have been shown to produce tumors with a H-ras mutation frequency considerably below those that result spontaneously (Maronpot et al. 1995). Among these chemicals are a class called peroxisome proliferators, of which TCA and TCE are members. DCA and TCE were found to induce tumors with similar H-ras mutation spectra (Anna et al. 1994), whereas only limited data have been available on TCA (Fereira-Gonzalez et al. 1995). Thus, a major focus of this research was to evaluate whether the pattern and frequency of H-ras mutations in TCE-induced tumors could be explained by the same parameters in tumors induced by the metabolites TCA or DCA. The present project was organized around three interrelated objectives: The first objective addressed the pharmacokinetic questions regarding the formation and elimination of DCA and TCA in mice administered TCE and whether levels of these metabolites may account for the tumors induced by TCE. The second objective was to investigate potential molecular mechanisms by which TCA and DCA may, in the absence of directly causing mutations, promote the clonal growth and expansion of precancerous cell populations within mouse liver. The third objective was to investigate whether the genotype of tumors induced by TCA and DCA can be used to establish the relative roles of these metabolites in TCE-induced cancer. In particular, the focus of the latter studies was to compare the incidence and spectra of mutations in the H-ras gene (codon 61) to determine if the reported similarities in the genotype of DCA- and TCE-induced tumors have a causal relationship.« less

  • ; ; ; ... - Toxicology Letters
    No abstract prepared.