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) and in patients with ticrynafen hepatitis (antiliver/kidney microsome2). 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 (permilligram 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. Immunfluorescence 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 microsomal1 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.(HEPATOLGOY 1990; 11: 850‐858.) Copyright © 1990 American Association for the Study of Liver Diseases