Characterization of a human liver cytochrome P-450 involved in the oxidation of debrisoquine and other drugs by using antibodies raised to the analogous rat enzyme.

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Abstract
Debrisoquine 4-hydroxylase activity is a prototype for genetic polymorphism in oxidative drug metabolism in humans; .apprx. 10% of Caucasian populations exhibit the poor metabolizer phenotype, and the clearance of at least 14 other drugs has been shown to be deficient in patients exhibiting this phenotype. Antibodies prepared to a cytochrome P-450 responsible for debrisoquine 4-hydroxylation in rats inhibited the oxidation of debrisoquine and sparteine, encainide and propranolol, 3 other drugs suggested to be associated with this phenotype, in human liver microsomes. The antibodies did not inhibit the oxidation of 7 other cytochrome P-450 substrates. The antibodies recognized a single polypeptide of MW 51,000 after combined sodium dodecyl sulfate/polyacrylamide electrophoresis and immunochemical staining of human liver microsomes. The intensity of this band was significantly correlated with debrisoquine 4-hydroxylase activity when liver microsomes from 44 organ donors were examined. Immunoprecipitation of in vitro translation products of total liver RNA revealed major electrophoretic bands corresponding to the cytochrome P-450 in rats and humans. The level of translatable mRNA coding for the debrisoquine-hydroxylating cytochrome P-450 was an order of magnitude less in human liver than in rat liver. The availability of these antibodies provides a biochemical basis for further basic and clinical studies on the role of a particular cytochrome P-450 polymorphism in humans.