Increased catalytic activity of cytochrome P-450IIE1 in pericentral hepatocytes compared to periportal hepatocytes isolated from pyrazole-treated rats.
Cytochrome P-450IIE1 is induced by a variety of agents, including acetone, ethanol and pyrazole. Recent studies employing immunohistochemical methods have shown that P-450IIE1 was expressed primarily in the pericentral zone of the liver. In order to evaluate whether catalytic activity of P-450IIE1 is preferentially localized in the pericentral zone of the liver acinus, the oxidation of aniline and p-nitrophenol, two effective substrates for P-450IIE1, by periportal and pericentral hepatocytes isolated from pyrazole-treated rats was determined. Periportal and pericentral hepatocytes were prepared by a digitonin-collagenase procedure; the marker enzymes glutamine synthetase and gamma-glutamyl transpeptidase indicated reasonable separation of the two cell populations. Viability, yield and total cytochrome P-450 content were similar for the periportal and pericentral hepatocytes. Pericentral hepatocytes oxidized aniline and p-nitrophenol at rates that were 2-4-fold greater than periportal hepatocytes under a variety of conditions. Carbon monoxide inhibited the oxidation of the substrates with both preparations and abolished the increased oxidation found with the pericentral hepatocytes. Pyrazole or 4-methylpyrazole, added in vitro, effectively inhibited the oxidation of aniline and p-nitrophenol and prevented the augmented rate of oxidation by the pericentral hepatocytes. Western blots carried out using isolated microsomes revealed a more than 2-fold increase in immunochemical staining with microsomes isolated from the pericentral hepatocytes, which correlated to the 2-4-fold increase in the rate of oxidation of aniline or p-nitrophenol by the pericentral hepatocytes. These results suggest that functional catalytic activity of cytochrome P-450IIE1 is preferentially localized in the pericentral zone of the liver acinus, and that most of the induction by pyrazole of P-450IIE1 appears to occur within the pericentral zone.
Dicker
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Department of Biochemistry, Mount Sinai School of Medicine, New York, NY 10029.
McHugh
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Cederbaum
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AI
D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology; D002384:Catalysis; D019392:Cytochrome P-450 CYP2E1; D000077604:Fomepizole; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D009596:Nitrophenols / Q000378:metabolism; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014018:Tissue Distribution; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D000814:Aniline Compounds; D009596:Nitrophenols; D011720:Pyrazoles; C031280:pyrazole; D002248:Carbon Monoxide; D000077604:Fomepizole; D019392:Cytochrome P-450 CYP2E1; D010089:Oxidoreductases, N-Demethylating; D005723:gamma-Glutamyltransferase; D005974:Glutamate-Ammonia Ligase; C023650:aniline; C024836:4-nitrophenol