Screening for endogenous substrates reveals that CYP2D6 is a 5-methoxyindolethylamine O-demethylase

Aiming Yu, Jeffrey R. Idle, Tomas Herraiz, Adrian Küpfer, Frank J. Gonzalez

Research output: Contribution to journalArticlepeer-review

106 Scopus citations


The objective of this investigation was to screen for potential endogenous substrates for CYP2D6. Using recombinant CYP2D6, together with hepatic microsomes from CYP2D6-transgenic mice, human liver microsomes, and a specific anti-CYP2D6 monoclonal antibody, it was ascertained that CYP2D6 does not significantly metabolize the endogenous phenylethylamines 2-phenylethylamine, octopamine, synephrine, 3-methoxy-p-tyramine, 4-methoxy-m-tyramine, metanephrine, and normetanephrine, nor the indolethylamines tryptamine, serotonin, 6-methoxytryptamine, and melatonin, nor the β-carbolines harman, norharman and tryptoline. However, the indolethylamines 5-methoxy-N,N-dimethyltryptamine (5-MDMT) and pinoline (6-methoxy-1,2,3,4-tetrahydro-β-carboline) showed relatively high affinity for CYP2D6 in a spectral binding assay (Ks 28 ± 5, and 0.5 ± 0.3 μM (mean ± SEM), respectively) and were O-demethylated only by CYP2D6 in a panel of 15 recombinant common human P450s. Pinoline and 5-MDMT O-demethylase activities were 35- and 11-fold greater in liver microsomes from CYP2D6-humanized mice, respectively, than those in liver microsomes from control mice. Moreover, the increased activities were completely inhibited by an anti-CYP2D6 monoclonal antibody. Kinetic analysis with recombinant CYP2D6 gave Km and kcat values for 5-MDMT and pinoline O-demethylations of 12 ± 1 μM and 65 ± 1 min-1 and 1.8 ± 0.3 μM and 26 ± 1 min-1, respectively. These two substrates can be added to 5-methoxytryptamine, which we have recently reported to be an endogenous CYP2D6 substrate. CYP2D6 is therefore a relatively highly specific, high-affinity, high-capacity 5-methoxyindolethylamine O-demethylase. Polymorphic cytochrome CYP2D6 may therefore exert an influence on mood and behavior by the O-demethylation of these 5-methoxyindolethylamines found in the brain and pineal gland. These processes may also impact on mental and neurological health. The findings may open new vistas for the determination of CYP2D6 phenotype.

Original languageEnglish (US)
Pages (from-to)307-319
Number of pages13
Issue number6
StatePublished - Jun 2003
Externally publishedYes


  • Beta-carbolines
  • Cytochrome P-450 CYP2D6
  • Hydroxylation
  • O-demethylating
  • Oxidoreductases
  • Phenylethylamines
  • Tryptamines

ASJC Scopus subject areas

  • Genetics
  • Pharmacology, Toxicology and Pharmaceutics(all)


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