Metabolism of melatonin by human cytochromes p450

Drug Metab Dispos. 2005 Apr;33(4):489-94. doi: 10.1124/dmd.104.002410. Epub 2004 Dec 22.

Abstract

In humans, the pineal hormone melatonin (MEL) is principally metabolized to 6-hydroxymelatonin (6-HMEL), which is further conjugated with sulfate and excreted in urine. MEL O-demethylation represents a minor reaction. The exact role of individual human cytochromes P450 (P450s) in these pathways has not been established. We used a panel of 11 recombinant human P450 isozymes to investigate for the first time the 6-hydroxylation and O-demethylation of MEL. CYP1A1, CYP1A2, and CYP1B1 all 6-hydroxylated MEL, with CYP2C19 playing a minor role. These reactions were NADPH-dependent. CYP2C19 and, to some extent CYP1A2, O-demethylated MEL. The K(m) (microM) and V(max) (k(cat), pmol min(-1) pmol(-1) P450) for 6-hydroxylation were estimated as 19.2 +/- 2.01 and 6.46 +/- 0.22 (CYP1A1), 25.9 +/- 2.47 and 10.6 +/- 0.32 (CYP1A2), and 30.9 +/- 3.76 and 5.31 +/- 0.21 (CYP1B1). These findings confirm the suggestion of others that CYP1A2 is probably the foremost hepatic P450 in the 6-hydroxylation of MEL and a single report that CYP1A1 is also able to mediate this reaction. However, this is the first time that CYP1B1 has been shown to 6-hydroxylate MEL. The IC50 for the CYP1B1-selective inhibitor (E)-2,4,3',5'-tetramethoxystilbene was estimated to be 30 nM for MEL 6-hydroxylation by recombinant human CYP1B1. Comparison of brain homogenates from wild-type and cyp1b1-null mice revealed that MEL 6-hydroxylation was clearly mediated to a significant degree by CYP1B1. CYP1B1 is not expressed in the liver but has a ubiquitous extrahepatic distribution, and is found at high levels in tissues that also accumulate either MEL or 6-HMEL, such as intestine and cerebral cortex, where it may assist in regulating levels of MEL and 6-HMEL.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aryl Hydrocarbon Hydroxylases / genetics
  • Aryl Hydrocarbon Hydroxylases / metabolism
  • Brain / enzymology
  • Brain / metabolism
  • Chromatography, Liquid
  • Cytochrome P-450 CYP1B1
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism*
  • DNA, Complementary / genetics
  • Humans
  • Hydroxylation
  • In Vitro Techniques
  • Isoenzymes / metabolism
  • Male
  • Mass Spectrometry
  • Melatonin / metabolism*
  • Mice
  • Mice, Knockout

Substances

  • DNA, Complementary
  • Isoenzymes
  • Cytochrome P-450 Enzyme System
  • Aryl Hydrocarbon Hydroxylases
  • CYP1B1 protein, human
  • Cyp1b1 protein, mouse
  • Cytochrome P-450 CYP1B1
  • Melatonin