Inhibition on Human Liver Cytochrome P450 3A4 by Constituents of Fennel (Foeniculum Vulgare): Identification and Characterization of a Mechanism-Based Inactivator

J Agric Food Chem. 2007 Dec 12;55(25):10162-7. doi: 10.1021/jf0713253. Epub 2007 Nov 8.


Fennel, a seed of Foeniculum vulgare, is used as a culinary spice and traditional medicine. The methanolic extract of fennel showed a characteristic of mechanism-based inactivation on erythromycin N-demethylation mediated by human liver microsomal cytochrome P450 3A4 (CYP3A4). The present study was conducted to identify the fennel constituent having the inhibition. Thirteen compounds have been isolated from a methanol extract of fennel and tested for their inhibition on CYP3A4. Among them, 5-methoxypsoralen (5-MOP) showed the strongest inhibition with an IC50 value of 18.3 microM and a mixed type of inhibition. In addition, with the preincubation time of 20 min only 5-MOP showed preincubation time dependency; the IC50 value decreased from 18.3 microM with a preincubation time of 0 min to 4.6 microM with a preincubation time of 20 min. Further investigation on 5-MOP showed the characteristics of time-dependent inhibition, requirement of NADPH, lack of protecting effect of nucleophiles, and recovery of CYP3A4 activity by the competitive inhibitor. This result suggests that the inhibitory activity of CYP3A4 by 5-MOP was a mechanism-based inactivation. The kinetic parameter for mechanism-based inactivation was characterized by a KI value of 15.0 microM and a kinact value of 0.098 min(-1).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Methoxypsoralen
  • Cytochrome P-450 CYP3A
  • Cytochrome P-450 Enzyme Inhibitors*
  • Enzyme Inhibitors / pharmacology*
  • Foeniculum / enzymology*
  • Humans
  • Kinetics
  • Liver / enzymology*
  • Methoxsalen / analogs & derivatives*
  • Methoxsalen / isolation & purification
  • Methoxsalen / pharmacology
  • NADP / pharmacology
  • Seeds / enzymology*


  • Cytochrome P-450 Enzyme Inhibitors
  • Enzyme Inhibitors
  • 5-Methoxypsoralen
  • NADP
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Methoxsalen