Abstract
NADPH-cytochrome P-450 oxidoreductase (CPR) is essential for the catalytic activity of cytochrome P-450 (P-450). On a molar basis, the amount of P-450 exceeds that of CPR in human liver. In this study, we investigated whether drug-drug interactions can occur as a result of competition between P-450 isozymes for this ancillary protein. For this purpose, combinations of P-450 isozymes were coexpressed together with P-450 reductase in Escherichia coli. We show that testosterone inhibited the CYP2D6-mediated bufuralol 1'-hydroxylase activity in bacterial membranes containing both CYP2D6 and CYP3A4 but not in membranes containing CYP2D6 alone. Conversely, bufuralol inhibited the CYP3A4-mediated testosterone 6beta-hydroxylase activity in bacterial membranes containing both CYP3A4 and CYP2D6 but not in membranes containing only CYP3A4. In each case, inhibition was seen even at a P-450 to P-450 reductase ratio of 1.9:1, which is more favorable than the ratio of 4 reported for human liver. The physiological significance of this mechanism was demonstrated by the observation that testosterone inhibited several prototypical P-450 enzyme activities, such as bufuralol 1'-hydroxylase, coumarin 7-hydroxylase, and 7-ethoxyresorufin O-dealkylase, in human liver microsomes, but not if tested against a panel of bacterial membranes containing the human P-450 isozymes that mainly catalyze these reactions.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Aryl Hydrocarbon Hydroxylases*
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Cytochrome P-450 CYP1A1 / antagonists & inhibitors
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Cytochrome P-450 CYP1A1 / metabolism
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Cytochrome P-450 CYP2A6
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Cytochrome P-450 CYP2D6 / biosynthesis
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Cytochrome P-450 CYP2D6 / genetics
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Cytochrome P-450 CYP2D6 / metabolism
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Cytochrome P-450 CYP2D6 Inhibitors
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Cytochrome P-450 CYP3A
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Cytochrome P-450 Enzyme Inhibitors
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Cytochrome P-450 Enzyme System / biosynthesis
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Cytochrome P-450 Enzyme System / genetics
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Cytochrome P-450 Enzyme System / metabolism*
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Drug Interactions
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Enzyme Inhibitors / metabolism
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Enzyme Inhibitors / pharmacology
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Escherichia coli / enzymology
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Escherichia coli / genetics
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Ethanolamines / metabolism*
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Humans
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In Vitro Techniques
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Isoenzymes / antagonists & inhibitors
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Isoenzymes / biosynthesis
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Isoenzymes / genetics
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Isoenzymes / metabolism
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Membranes
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Microsomes, Liver / drug effects
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Microsomes, Liver / enzymology
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Mixed Function Oxygenases / antagonists & inhibitors
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Mixed Function Oxygenases / biosynthesis
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Mixed Function Oxygenases / genetics
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Mixed Function Oxygenases / metabolism
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NADPH-Ferrihemoprotein Reductase / antagonists & inhibitors
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NADPH-Ferrihemoprotein Reductase / biosynthesis
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NADPH-Ferrihemoprotein Reductase / genetics
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NADPH-Ferrihemoprotein Reductase / metabolism*
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Plasmids
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Recombinant Proteins / antagonists & inhibitors
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Recombinant Proteins / biosynthesis
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Steroid Hydroxylases / antagonists & inhibitors
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Steroid Hydroxylases / metabolism
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Testosterone / metabolism*
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Testosterone / pharmacology
Substances
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Cytochrome P-450 CYP2D6 Inhibitors
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Cytochrome P-450 Enzyme Inhibitors
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Enzyme Inhibitors
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Ethanolamines
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Isoenzymes
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Recombinant Proteins
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Testosterone
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bufuralol
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Cytochrome P-450 Enzyme System
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Mixed Function Oxygenases
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Steroid Hydroxylases
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Aryl Hydrocarbon Hydroxylases
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CYP3A protein, human
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Cytochrome P-450 CYP1A1
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Cytochrome P-450 CYP2A6
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Cytochrome P-450 CYP2D6
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Cytochrome P-450 CYP3A
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steroid hormone 6-beta-hydroxylase
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CYP3A4 protein, human
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bufuralol 1'-hydroxylase
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NADPH-Ferrihemoprotein Reductase