Inhibition of alcohol dehydrogenase by chloral hydrate and trichloroethanol: possible role in the chloral hydrate-ethanol interaction

Trichloroethylene: Mechanistic, epidemiologic and other supporting evidence of carcinogenic hazard

The chlorinated solvent trichloroethylene (TCE) is a ubiquitous environmental pollutant. The carcinogenic hazard of TCE was the subject of a 2012 evaluation by a Working Group of the International Agency for Research on Cancer (IARC). Information on exposures, relevant data from epidemiologic studies, bioassays in experimental animals, and toxicity and mechanism of action studies was used to conclude that TCE is carcinogenic to humans (Group 1). This article summarizes the key evidence forming the scientific bases for the IARC classification. Exposure to TCE from environmental sources (including hazardous waste sites and contaminated water) is common throughout the world. While workplace use of TCE has been declining, occupational exposures remain of concern, especially in developing countries. The strongest human evidence is from studies of occupational TCE exposure and kidney cancer. Positive, although less consistent, associations were reported for liver cancer and non-Hodgkin lymphoma. TCE is carcinogenic at multiple sites in multiple species and strains of experimental animals. The mechanistic evidence includes extensive data on the toxicokinetics and genotoxicity of TCE and its metabolites. Together, available evidence provided a cohesive database supporting the human cancer hazard of TCE, particularly in the kidney. For other target sites of carcinogenicity, mechanistic and other data were found to be more limited. Important sources of susceptibility to TCE toxicity and carcinogenicity were also reviewed by the Working Group. In all, consideration of the multiple evidence streams presented herein informed the IARC conclusions regarding the carcinogenicity of TCE.

Chloral hydrate enhances ethanol-induced inhibition of methanol oxidation in mice

Several studies indicated that chloral hydrate can prolong the disappearance time of ethanol from blood in mice. This seems to result from inhibition of the enzyme alcohol dehydrogenase by chloral hydrate and trichloroethanol, its main metabolite. We examined the effect of both these compounds on the disappearance time of methanol in mice. Also the effect of a combination of ethanol and chloral hydrate on the disappearance time of methanol was examined. Several groups of six mice each received methanol (1 g/kg i.p.) followed immediately by one of the following treatments: saline (10 ml/kg); chloral hydrate (0.4 g/kg); trichloroethanol (0.36 g/kg); ethanol (4 g/kg); or a combination of chloral hydrate (0.2 g/kg) and ethanol (4 g/kg). The concentrations of methanol in blood were measured at 1, 2, 4, and 8 h after its administration and were used to calculate some approximate indicators of methanol elimination in each group. The results show that all the above treatments do prolong the disappearance time of methanol in the blood of mice to varying extents. The ethanol-chloral hydrate combination produced the most pronounced effect.