Presence of functional cytochrome P-450 on isolated rat hepatocyte plasma membrane.
Antibodies against cytochrome P-450 are found in some children with autoimmune hepatitis (antiliver/kidney microsome 1) and in patients with ticrynafen hepatitis (antiliver/kidney microsome 2). For an immune reaction against cytochrome P-450 to possibly destroy the hepatocytes, one must assume that cytochrome P-450 is present on the plasma membrane surface of hepatocytes. In a first series of experiments, plasma membranes were prepared with a technique based on the electrostatic attachment of isolated hepatocytes to polyethyleneimine-coated beads. After vortexing, beads were coated with a very pure plasma membrane fraction. Microsomal contamination, judged from the specific activities of glucose-6-phosphatase or NADH-cytochrome c reductase, was less than 1%. Nevertheless, the specific content (per milligram of protein) of CO-binding cytochrome P-450 was 20% of that in microsomes; the specific benzo(a)pyrene hydroxylase activity was 25%, and ethoxycoumarin deethylase 11%. Immunoblots showed the presence of cytochromes P-450 UT-A, UT-H, PB-B, ISF-G and PCN-E, the last three isoenzymes being inducible by, respectively, phenobarbital, 3-methylcholanthrene and dexamethasone. In a second series of experiments, nonpermeabilized isolated hepatocytes from untreated rats were incubated with anticytochrome P-450 antibodies. Immunofluorescence and immunoperoxidase staining confirmed the presence of cytochromes P-450 UT-A, PB-B and ISF-G on the membrane. In a last series of experiments, human antiliver-kidney microsomal 1 antibodies were found to react specifically with rat liver plasma membrane cytochrome P-450 UT-H (IID subfamily). We conclude that several cytochrome P-450 isoenzymes are present, active and inducible on the plasma membrane surface of hepatocytes. It is therefore conceivable that immunization against plasma membrane cytochrome P-450 might lead to the immunological destruction of hepatocytes in some patients.
Loeper
J
J
Unité de Recherche de Physiopathologie Hépatique, INSERM U-24, Hôpital Beaujon, Clichy, France.
Descatoire
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Maurice
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Beaune
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Feldmann
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Larrey
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Pessayre
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D000818:Animals; D015415:Biomarkers; D002462:Cell Membrane / Q000201:enzymology; D002469:Cell Separation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D051381:Rats
D015415:Biomarkers; D007527:Isoenzymes; D003577:Cytochrome P-450 Enzyme System; D009251:NADPH-Ferrihemoprotein Reductase