Induction of rat liver drug-metabolizing enzymes by tetrachloroethylene.
The effect of tetrachloroethylene on Phase I and II drug-metabolizing enzymes in rat liver was examined. Rats were treated orally with tetrachloroethylene daily for five days, at doses of 125, 250, 500, 1,000 and 2,000 mg/kg. The higher doses (> 500 mg/kg) of tetrachloroethylene induced the hepatic microsomal 7-pentoxyresorufin O-depentylase and 7-benzyloxyresorufin O-debenzylase activities associated with the CYP2B subfamily. 7-ethoxyresorufin O-deethylase activity was also induced about 2-fold compared with that of control rats at 500, 1,000, and 2,000 mg/kg dose levels of tetrachloroethylene. However, 7-ethoxycoumarin O-deethylase and 7-methoxyresorufin O-demethylase activities were increased significantly at only the 1,000 mg/kg dose level of tetrachloroethylene (1.4- and 1.5-fold). Although other cytochrome P450-mediated monooxygenase activities such as nitrosodimethylamine N-demethylase, aminopyrine N-demethylase and erythromycin N-demethylase were also induced by tetrachloroethylene, the relative induction to control activity was lower than those of 7-pentoxyresorufin O-depentylase and 7-benzyloxyresorufin O-debenzylase. Western immunoblotting showed that the levels of CYP2B1 and CYP2B2 proteins in liver microsomes were increased at doses of 1,000 and 2,000 mg/kg of tetrachloroethylene. In addition to cytochrome P450-mediated monooxygenases, there was significant induction of the Phase II drug-metabolizing enzymes, DT-diaphorase, glutathione S-transferase activities towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene, and UDP-glucuronyltransferase activities towards 4-nitrophenol and 7-hydroxycoumarin. The results indicate that tetrachloroethylene induces both Phase I (CYP2B-mediated monooxygenase) and Phase II drug-metabolizing enzymes (DT-diaphorase, glutathione S-transferase and UDP-glucuronyltransferase) in the rat liver.
Hanioka
N
N
Division of Environmental Chemistry, National Institute of Health Sciences, Tokyo, Japan.
Jinno
H
H
Toyo'oka
T
T
Nishimura
T
T
Ando
M
M
D000284:Administration, Oral; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D015153:Blotting, Western; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013750:Tetrachloroethylene / Q000008:administration & dosage / Q000633:toxicity*
D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C025619:steroid 16-beta-hydroxylase; D013750:Tetrachloroethylene