Date of Award

2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Bioinformatics, Biostatistics, and Epidemiology

College

College of Graduate Studies

Abstract

Trichloroethylene (TCE) is listed with the EPA as a suspected human carcinogen and is ubiquitous in the environment (US EPA 1992). Chloral hydrate (CH) is a sedative drug and a cytochrome P450 (CYP 450)-derived metabolite of TCE (Klaassen 2001). Chloral hydrate is metabolized in the liver to the rodent hepatocarcinogen trichloroacetate (TCA) by aldehyde dehydrogenase (ALDH), and to the non-carcinogenic metabolite trichloroethanol (TCEOH) by alcohol dehydrogenase (ADH) (Klaassen 2001). Both ALDH and ADH are polymorphic in humans which can presumably predict the disposition of chloral hydrate into the carcinogenic vs. non-carcinogenic pathways. The likelihood is then raised that subpopulations of humans will produce greater amounts of TCA relative to TCEOH and hence has greater risk of developing liver tumors after TCE exposure. To determine the variability of chloral hydrate metabolism in humans, the compound (0.05-2.0 mM) is added to human hepatocyte suspensions obtained from commercial sources. Incubations are carried out for 10 min at 37°C, with reactions stopped by the addition of an esterizer solution. The formation of TCA and TCEOH is then measured using headspace gas chromatography with electron-capture detection. The evolution of these metabolites was found to be highly variable with the Vmax means of µTCEOH = 26.32 ± 65.66 and µTCA = 16.79 ± 44.94. Prior to determining human hepatocyte chloral hydrate metabolism, the inter- and intra-individual variability in metabolism of chloral hydrate was determined using rat and mouse liver homogenates from in-bred, genetically equivalent animals. Finally, the calculations are involved in predicting risk using the results of the pharmacokinetics and genetic typing. We believe that chloral hydrate metabolism will show variability among humans, exhibiting sensitive genotypes that have specific kinetics which can be extrapolated to trichloroethylene sensitivity. A prudent approach to this problem merges pharmacology, genetics, and quantitative techniques. The best risk predictors for a high Vmax of both TCEOH and TCA metabolism is the ALDH2 genotype, followed by the ADH3 genotypes. We also suspect the ADH2 genotype would be an important covariate in the model; however none of our samples were of the atypical form. A more diverse and larger sample group would provide support of this study's findings. Here we report a framework to determine risk which incorporates genetic typing.

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