Application of cryopreserved human hepatocytes in trichloroethylene risk assessment: relative disposition of chloral hydrate to trichloroacetate and trichloroethanol.
BACKGROUND
Trichloroethylene (TCE) is a suspected human carcinogen and a common groundwater contaminant. Chloral hydrate (CH) is the major metabolite of TCE formed in the liver by cytochrome P450 2E1. CH is metabolized to the hepatocarcinogen trichloroacetate (TCA) by aldehyde dehydrogenase (ALDH) and to the noncarcinogenic metabolite trichloroethanol (TCOH) by alcohol dehydrogenase (ADH). ALDH and ADH are polymorphic in humans, and these polymorphisms are known to affect the elimination of ethanol. It is therefore possible that polymorphisms in CH metabolism will yield subpopulations with greater than expected TCA formation with associated enhanced risk of liver tumors after TCE exposure.


METHODS
The present studies were undertaken to determine the feasibility of using commercially available, cryogenically preserved human hepatocytes to determine simultaneously the kinetics of CH metabolism and ALDH/ADH genotype. Thirteen human hepatocyte samples were examined. Linear reciprocal plots were obtained for 11 ADH and 12 ALDH determinations.


RESULTS
There was large interindividual variation in the Vmax values for both TCOH and TCA formation. Within this limited sample size, no correlation with ADH/ALDH genotype was apparent. Despite the large variation in Vmax values among individuals, disposition of CH into the two competing pathways was relatively constant.


CONCLUSIONS
These data support the use of cryopreserved human hepatocytes as an experimental system to generate metabolic and genomic information for incorporation into TCE cancer risk assessment models. The data are discussed with regard to cellular factors, other than genotype, that may contribute to the observed variability in metabolism of CH in human liver.
Bronley-DeLancey
Apryl
A
Department of Biostatistics, Bioinformatics and Epidemiology, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
McMillan
David C
DC
McMillan
JoEllyn M
JM
Jollow
David J
DJ
Mohr
Lawrence C
LC
Hoel
David G
DG
D000328:Adult; D000368:Aged; D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002697:Chloral Hydrate / Q000378:metabolism*; D015925:Cryopreservation; D005023:Ethylene Chlorohydrin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity; D005260:Female; D005838:Genotype; D022781:Hepatocytes / Q000187:drug effects*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D018570:Risk Assessment; D012997:Solvents / Q000633:toxicity; D014238:Trichloroacetic Acid / Q000378:metabolism* / Q000633:toxicity*; D014241:Trichloroethylene / Q000378:metabolism* / Q000633:toxicity*
D012997:Solvents; D014241:Trichloroethylene; D002697:Chloral Hydrate; D014238:Trichloroacetic Acid; D005023:Ethylene Chlorohydrin; C005849:2,2,2-trichloroethanol; D000426:Alcohol Dehydrogenase; D000444:Aldehyde Dehydrogenase