Roles of Nitric Oxide in Inflammatory Down-Regulation of Human Cytochromes P450

• Type of Material: Article
• Authors: Alison E. Aitken, Emory University; Choon-Myung Lee, Emory University; Edward T Morgan, Emory University
• Language: English
• Date: 2008-03-15
• Publisher: Elsevier
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2008 Elsevier
• License: Creative Commons Attribution-NonCommerical-NoDerivs 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1016/j.freeradbiomed.2007.12.010
• Title of Journal or Parent Work: Free Radical Biology and Medicine
• ISSN: 0891-5849
• Volume: 44
• Issue: 6
• Start Page: 1161
• End Page: 1168
• Grant/Funding Information: This work was supported by grant GM069971 from the National Institutes of Health.; Hepatocytes were provided by Dr. Steven Strom via the Liver Tissue Procurement and Distribution System, NIH Contract N01-DK-9-2310.; C-M Lee was supported by a Training Grant from the National Institutes of Health (T32ES01287).
• Keywords: cytokines; cytochrome P450; protein degradation; nitric oxide; CYP2B6; inflammation
• Research Categories: Health Sciences, Pharmacology; Biology, General

Abstract

The purpose of this study was to determine the role of nitric oxide (NO) in the down-regulation of human 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 TNFα, IL-1β and IFNγ (ILmix) down-regulated CYP2B6 mRNA and protein to 9% and 19% of control levels. The NO donor NOC-18 down-regulated CYP2B6 protein to 30% of control, with only a small effect on CYP2B6 mRNA. NOS inhibitors attenuated the down-regulation of CYP2B6 protein, but not mRNA, by ILmix. These findings demonstrate that the post-transcriptional NO dependent down-regulation 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 down-regulated CYP3A4 mRNA to 50% of control. However, NOS inhibitors failed to block the effects of ILmix on CYP3A4 expression.