Roles of nitric oxide in inflammatory downregulation of human cytochromes P450

Free Radic Biol Med. 2008 Mar 15;44(6):1161-8. doi: 10.1016/j.freeradbiomed.2007.12.010. Epub 2007 Dec 23.


The purpose of this study was to determine the role of nitric oxide (NO) in the downregulation of human cytochrome P450 (CYP) enzymes and mRNAs by an inflammatory stimulus in cultured human hepatocytes. We focused on CYP2B6 because previous studies showed that rat CYP2B proteins undergo an NO-dependent degradation in response to inflammatory stimuli. To ensure high-level expression of CYP2B6, the inducer phenytoin was present at all times. Stimulation of cells with a mixture of tumor necrosis factor-alpha, interleukin-1, and interferon-gamma (ILmix) downregulated CYP2B6 mRNA and protein to 9 and 19% of control levels. The NO donor NOC-18 downregulated CYP2B6 protein to 30% of control, with only a small effect on CYP2B6 mRNA. Nitric oxide synthase inhibitors attenuated the downregulation of CYP2B6 protein but not mRNA by ILmix. These findings demonstrate that the posttranscriptional NO-dependent downregulation of CYP2B enzymes, observed previously in rat hepatocytes, is conserved in human CYP2B6. This mechanism is specific for CYP2B6 among the enzymes tested. No evidence was found for regulation of CYP2E1 mRNA or protein by NO. NOC-18 treatment downregulated CYP3A4 mRNA to 50% of control. However, NOS inhibitors failed to block the effects of ILmix on CYP3A4 expression.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adolescent
  • Adult
  • Aryl Hydrocarbon Hydroxylases / drug effects
  • Aryl Hydrocarbon Hydroxylases / metabolism*
  • Blotting, Western
  • Cells, Cultured
  • Child
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP2E1 / drug effects
  • Cytochrome P-450 CYP2E1 / metabolism
  • Cytochrome P-450 CYP3A / drug effects
  • Cytochrome P-450 CYP3A / metabolism
  • Down-Regulation
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme Inhibitors / pharmacology
  • Female
  • Gene Expression
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism*
  • Humans
  • Infant
  • Inflammation / metabolism*
  • Male
  • Middle Aged
  • Nitric Oxide / metabolism*
  • Oxidoreductases, N-Demethylating / drug effects
  • Oxidoreductases, N-Demethylating / metabolism*
  • RNA, Messenger / analysis
  • Reverse Transcriptase Polymerase Chain Reaction


  • Enzyme Inhibitors
  • RNA, Messenger
  • Nitric Oxide
  • Cytochrome P-450 CYP2E1
  • Aryl Hydrocarbon Hydroxylases
  • CYP2B6 protein, human
  • Cytochrome P-450 CYP2B6
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • Oxidoreductases, N-Demethylating