Induction of CYP2A5 by pyrazole and its derivatives in mouse primary hepatocytes

Arch Toxicol. 1998 May;72(6):336-41. doi: 10.1007/s002040050511.


Mouse liver CYP2A5 is induced by several structurally unrelated compounds. In intact mouse liver, pyrazole (PYR) and 4-hydroxypyrazole (4-OH) induce selectively the expression of CYP2A5 while expression of other CYPs is decreased. In this study we exposed mouse primary hepatocytes to PYR, 4-OH, 4-methylpyrazole (4Me; 0.1-20 mM) and 4-iodopyrazole (4-I; 0.1-5.0 mM). PYR and its derivatives increased coumarin 7-hydroxylase activity, with 4-1 and 4-OH being the strongest inducers, by 114-fold and 41-fold, respectively. However, only 4-1 treatment increased markedly the CYP2A5 protein content. CYP2B9/10-mediated pentoxyresorufin O-deethylase activity (PROD) was decreased by 80% by 4-Me and 4-1, and by 50% by 4-OH while PYR had no marked effect. PYR and 4-Me increased 2- to 3-fold the CYPA1/2-mediated ethoxyresorufin O-deethylase activity (EROD) while 4-OH and 4-1 had no marked effect on this enzyme. The time of exposure markedly affected the inducibility of 4-OH such that induction was 7-fold stronger when it was added to the incubation medium 24 h after the isolation of hepatocytes compared to exposure 3 h after their isolation. Cimetidine prevented the induction of coumarin 7-hydroxylase activity by PYR and 4-OH by 46 and 74%, respectively indicating that their effects on the expression of CYP2A5 are, at least partly, mediated via their metabolites. The data demonstrate that the regulation of CYP2A5 is different from other monooxygenases and that the effects of pyrazole and its derivatives are different in vivo and in vitro. Also, the timing of exposure markedly affects the inducibility of 4-OH in hepatocytes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aryl Hydrocarbon Hydroxylases*
  • Cells, Cultured
  • Cytochrome P-450 CYP1A1 / drug effects
  • Cytochrome P-450 CYP2A6
  • Cytochrome P-450 CYP2B1 / drug effects
  • Cytochrome P-450 Enzyme System / biosynthesis*
  • Cytochrome P450 Family 2
  • Enzyme Induction
  • Enzyme Inhibitors / pharmacology*
  • Fomepizole
  • L-Lactate Dehydrogenase / metabolism
  • Liver / cytology
  • Liver / drug effects*
  • Liver / enzymology
  • Male
  • Mice
  • Mice, Inbred DBA
  • Mixed Function Oxygenases / biosynthesis*
  • Pyrazoles / pharmacology*


  • Enzyme Inhibitors
  • Pyrazoles
  • 4-iodopyrazole
  • pyrazole
  • 4-hydroxypyrazole
  • Fomepizole
  • Cytochrome P-450 Enzyme System
  • Mixed Function Oxygenases
  • L-Lactate Dehydrogenase
  • Aryl Hydrocarbon Hydroxylases
  • Cyp2a5 protein, mouse
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP2A6
  • Cytochrome P-450 CYP2B1
  • Cytochrome P450 Family 2