Mode of Action of Liver Tumor Induction by Trichloroethylene and Its Metabolites, Trichloroacetate and Dichloroacetate

• Published in: Environmental health perspectives Vol. 108; no. suppl 2; pp. 241 - 259
• Main Author: Bull, Richard J.
• Format: Journal Article
• Language: English
• Published: United States National Institute of Environmental Health Sciences. National Institutes of Health. Department of Health, Education and Welfare 01.05.2000
• Subjects: Animals; Carcinogens, Environmental - adverse effects; dichloroacetic acid; Dichloroacetic Acid - adverse effects; Dosage; Dose response relationship; Dose-Response Relationship, Drug; Hazard Identification; Hepatocytes; Humans; Lesions; Liver; Liver cancer; Liver Neoplasms - chemically induced; Liver Neoplasms, Experimental - chemically induced; Metabolites; Mice; Mutagens - adverse effects; peroxisome proliferators; Potable water; Risk Assessment; Trichloroacetic Acid - adverse effects; Trichloroethylene - adverse effects; Tumors
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.00108s2241

Trichloroethylene (TCE) induces liver cancer in mice but not in rats. Three metabolites of TCE may contribute-chloral hydrate (CH), dichloroacetate (DCA), and trichloroacetate (TCA). CH and TCA appear capable of only inducing liver tumors in mice, but DCA is active in rats as well. The concentrations of TCA in blood required to induce liver cancer approach the mM range. Concentrations of DCA in blood associated with carcinogenesis are in the sub-µM range. The carcinogenic activity of CH is largely dependent on its conversion to TCA and/or DCA. TCA is a peroxisome proliferator in the same dose range that induces liver cancer. Mice with targeted disruptions of the peroxisome proliferator-activated receptor alpha (PPARα) are insensitive to the liver cancer-inducing properties of other peroxisome proliferators. Human cells do not display the responses associated with PPARα that are observed in rodents. This may be attributed to lower levels of expressed PPARα in human liver. DCA treatment produces liver tumors with a different phenotype than TCA. Its tumorigenic effects are closely associated with differential effects on cell replication rates in tumors, normal hepatocytes, and suppression of apoptosis. Growth of DCA-induced tumors has been shown to arrest after cessation of treatment. The DCA and TCA adequately account for the hepatocarcinogenic responses to TCE. Low-level exposure to TCE is not likely to induce liver cancer in humans. Higher exposures to TCE could affect sensitive populations. Sensitivity could be based on different metabolic capacities for TCE or its metabolites or result from certain chronic diseases that have a genetic basis.