Comparative contribution to dextromethorphan metabolism by cytochrome P450 isoforms in vitro: Can dextromethorphan be used as a dual probe for both CYP2D6 and CYP3A activities?

Aiming Yu, Robert L. Haining

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123 Citations (Scopus)

Abstract

Dextromethorphan (DXM) is a widely used probe drug for human CYP2D6 activity both in vitro and in vivo. In humans, DXM is metabolized to dextrorphan (DXO), as well as 3-methoxymorphinan (MEM) and 3-hydroxymorphinan (HYM). The formation of MEM has been attributed primarily to CYP3A4, and the use of DXM has been debated as a simultaneous probe for CYP3A4 and CYP2D6 activities. Recently, we found that highly purified CYP2D6 has significant DXM N-demethylase activity in addition to its well known DXM O-demethylase activity. Therefore, we desired to further compare the contribution to DXM metabolism by individual human cDNA-expressed cytochromes P450, including 2C8, 2C9, 2C18, 2C19, 2D6, 2B6, and 3A4. Metabolites were quantified following separation by high-pressure liquid chromatography and apparent Michaelis-Menten constants determined for the appearance of DXO and MEM. Intrinsic clearance values were estimated for each P450 and normalized using the average percentage content and relative activity factor approaches for comparison. Simplified kinetic models (when [S] ≪ Km, Vmax/Km = Vo/[S]) were used at fixed DXM concentrations of 20 (for DXM N-demethylation) and 0.2 μM (for DXM O-demethylation), as well as 2 μM to mimic plasma DXM concentrations in human extensive metabolizers. The results confirm that CYP2D6 contributes at least 80% to the formation of DXO, and CYP3A4 contributes more than 90% to the formation of MEM. All of our in vitro results are consistent and indicate that DXM as a marker for monitoring both CYP2D6 and CYP3A activities is practical in an average human or human liver microsomal preparation.

Original languageEnglish (US)
Pages (from-to)1514-1520
Number of pages7
JournalDrug Metabolism and Disposition
Volume29
Issue number11
StatePublished - 2001
Externally publishedYes

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Dextromethorphan
Cytochrome P-450 CYP3A
Cytochrome P-450 CYP2D6
Metabolism
Cytochrome P-450 Enzyme System
Protein Isoforms
Dextrorphan
N Demethylating Oxidoreductases
In Vitro Techniques
High pressure liquid chromatography
Metabolites
Human Activities
Liver
Complementary DNA
High Pressure Liquid Chromatography

ASJC Scopus subject areas

  • Pharmacology
  • Toxicology

Cite this

@article{ec35d27c89a84fea89090e8151aada71,
title = "Comparative contribution to dextromethorphan metabolism by cytochrome P450 isoforms in vitro: Can dextromethorphan be used as a dual probe for both CYP2D6 and CYP3A activities?",
abstract = "Dextromethorphan (DXM) is a widely used probe drug for human CYP2D6 activity both in vitro and in vivo. In humans, DXM is metabolized to dextrorphan (DXO), as well as 3-methoxymorphinan (MEM) and 3-hydroxymorphinan (HYM). The formation of MEM has been attributed primarily to CYP3A4, and the use of DXM has been debated as a simultaneous probe for CYP3A4 and CYP2D6 activities. Recently, we found that highly purified CYP2D6 has significant DXM N-demethylase activity in addition to its well known DXM O-demethylase activity. Therefore, we desired to further compare the contribution to DXM metabolism by individual human cDNA-expressed cytochromes P450, including 2C8, 2C9, 2C18, 2C19, 2D6, 2B6, and 3A4. Metabolites were quantified following separation by high-pressure liquid chromatography and apparent Michaelis-Menten constants determined for the appearance of DXO and MEM. Intrinsic clearance values were estimated for each P450 and normalized using the average percentage content and relative activity factor approaches for comparison. Simplified kinetic models (when [S] ≪ Km, Vmax/Km = Vo/[S]) were used at fixed DXM concentrations of 20 (for DXM N-demethylation) and 0.2 μM (for DXM O-demethylation), as well as 2 μM to mimic plasma DXM concentrations in human extensive metabolizers. The results confirm that CYP2D6 contributes at least 80{\%} to the formation of DXO, and CYP3A4 contributes more than 90{\%} to the formation of MEM. All of our in vitro results are consistent and indicate that DXM as a marker for monitoring both CYP2D6 and CYP3A activities is practical in an average human or human liver microsomal preparation.",
author = "Aiming Yu and Haining, {Robert L.}",
year = "2001",
language = "English (US)",
volume = "29",
pages = "1514--1520",
journal = "Drug Metabolism and Disposition",
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number = "11",

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TY - JOUR

T1 - Comparative contribution to dextromethorphan metabolism by cytochrome P450 isoforms in vitro

T2 - Can dextromethorphan be used as a dual probe for both CYP2D6 and CYP3A activities?

AU - Yu, Aiming

AU - Haining, Robert L.

PY - 2001

Y1 - 2001

N2 - Dextromethorphan (DXM) is a widely used probe drug for human CYP2D6 activity both in vitro and in vivo. In humans, DXM is metabolized to dextrorphan (DXO), as well as 3-methoxymorphinan (MEM) and 3-hydroxymorphinan (HYM). The formation of MEM has been attributed primarily to CYP3A4, and the use of DXM has been debated as a simultaneous probe for CYP3A4 and CYP2D6 activities. Recently, we found that highly purified CYP2D6 has significant DXM N-demethylase activity in addition to its well known DXM O-demethylase activity. Therefore, we desired to further compare the contribution to DXM metabolism by individual human cDNA-expressed cytochromes P450, including 2C8, 2C9, 2C18, 2C19, 2D6, 2B6, and 3A4. Metabolites were quantified following separation by high-pressure liquid chromatography and apparent Michaelis-Menten constants determined for the appearance of DXO and MEM. Intrinsic clearance values were estimated for each P450 and normalized using the average percentage content and relative activity factor approaches for comparison. Simplified kinetic models (when [S] ≪ Km, Vmax/Km = Vo/[S]) were used at fixed DXM concentrations of 20 (for DXM N-demethylation) and 0.2 μM (for DXM O-demethylation), as well as 2 μM to mimic plasma DXM concentrations in human extensive metabolizers. The results confirm that CYP2D6 contributes at least 80% to the formation of DXO, and CYP3A4 contributes more than 90% to the formation of MEM. All of our in vitro results are consistent and indicate that DXM as a marker for monitoring both CYP2D6 and CYP3A activities is practical in an average human or human liver microsomal preparation.

AB - Dextromethorphan (DXM) is a widely used probe drug for human CYP2D6 activity both in vitro and in vivo. In humans, DXM is metabolized to dextrorphan (DXO), as well as 3-methoxymorphinan (MEM) and 3-hydroxymorphinan (HYM). The formation of MEM has been attributed primarily to CYP3A4, and the use of DXM has been debated as a simultaneous probe for CYP3A4 and CYP2D6 activities. Recently, we found that highly purified CYP2D6 has significant DXM N-demethylase activity in addition to its well known DXM O-demethylase activity. Therefore, we desired to further compare the contribution to DXM metabolism by individual human cDNA-expressed cytochromes P450, including 2C8, 2C9, 2C18, 2C19, 2D6, 2B6, and 3A4. Metabolites were quantified following separation by high-pressure liquid chromatography and apparent Michaelis-Menten constants determined for the appearance of DXO and MEM. Intrinsic clearance values were estimated for each P450 and normalized using the average percentage content and relative activity factor approaches for comparison. Simplified kinetic models (when [S] ≪ Km, Vmax/Km = Vo/[S]) were used at fixed DXM concentrations of 20 (for DXM N-demethylation) and 0.2 μM (for DXM O-demethylation), as well as 2 μM to mimic plasma DXM concentrations in human extensive metabolizers. The results confirm that CYP2D6 contributes at least 80% to the formation of DXO, and CYP3A4 contributes more than 90% to the formation of MEM. All of our in vitro results are consistent and indicate that DXM as a marker for monitoring both CYP2D6 and CYP3A activities is practical in an average human or human liver microsomal preparation.

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