Induction of cytochrome P450 and peroxisomal enzymes by clofibric acid in vivo and in vitro.
We have analysed the induction of microsomal and peroxisomal proteins and their RNAs after treatment of hepatocytes with the peroxisome proliferator, clofibric acid, in vitro and in vivo. After treatment of hepatocytes with 1 mM clofibric acid for 4 days, P450 4A1 RNA is induced 500-fold, and acyl-CoA oxidase and P450 2B1 280-fold, relative to control cultures. These RNAs are detectably induced after administration of 25 microM clofibric acid, and show a similar induction response with increasing doses of clofibric acid. Western blot analysis of the P450 4A and bifunctional enzyme (BFE) proteins showed that both were induced in parallel with increasing doses of clofibric acid, over a range of 25 microM-1 mM. The distribution of the induced proteins was examined by immunocytochemistry. Increasing doses of clofibric acid led to an increase in the average intensity of staining for both proteins throughout the hepatocyte population. There was, however, a graded variation between hepatocytes in the intensity of staining, both for P450 4A and BFE proteins. The heterogeneity in response of the hepatocyte population in vitro may be related to differential sensitivity of hepatocytes to induction in vivo. Therefore, rats were dosed with 0, 50 or 300 mg/kg of clofibric acid for 4 days by gavage, and the livers were examined by immunocytochemistry. After 50 mg/kg of clofibric acid, both P450 4A and BFE were induced mainly in zones 3 and 2 of the liver acinus. However, after 300 mg/kg of clofibric acid, staining for both proteins was strong and homogenous throughout the liver acinus. Thus, hepatocytes from zones 3 and 2 of the acinus are differentially responsive to induction by clofibric acid.
Bars
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RG
Zeneca Central Toxicology Laboratory, Macclesfield, Cheshire, U.K.
Bell
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DR
Elcombe
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CR
D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000096:biosynthesis / Q000235:genetics; D042962:Acyl-CoA Oxidase; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002995:Clofibric Acid / Q000494:pharmacology*; D019362:Cytochrome P-450 CYP2B1; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D004746:Enoyl-CoA Hydratase / Q000096:biosynthesis / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D007150:Immunohistochemistry; D007535:Isomerases / Q000096:biosynthesis / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008830:Microbodies / Q000187:drug effects / Q000201:enzymology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000096:biosynthesis / Q000235:genetics; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000096:biosynthesis / Q000235:genetics; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics; D063994:Peroxisomal Bifunctional Enzyme; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar
D009097:Multienzyme Complexes; D002995:Clofibric Acid; D012313:RNA; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D015094:3-Hydroxyacyl CoA Dehydrogenases; D019362:Cytochrome P-450 CYP2B1; D042926:Cytochrome P-450 CYP4A; D042962:Acyl-CoA Oxidase; D004746:Enoyl-CoA Hydratase; D063994:Peroxisomal Bifunctional Enzyme; D007535:Isomerases