title: Role of nitric oxide in downregulation of cytochrome P450 1a1 and NADPH: Quinone oxidoreductase 1 by tumor necrosis factor-alpha and lipopolysaccharide.
abstract: We previously demonstrated that tumor necrosis factor alpha (TNF-alpha) and lipopolysaccharide (LPS) downregulate aryl hydrocarbon receptor (AhR)-regulated genes, such as cytochrome P450 1a1 (Cyp1a1) and NADPH: quinone oxidoreductase 1 (Nqo1) gene expression, yet the mechanisms involved remain unknown. The correlation between the inflammation-mediated suppression of AhR-regulated genes and the TNF-alpha or LPS-induced nitric oxide (NO) production especially in murine hepatoma Hepa 1c1c7 cells has been questioned; therefore we investigated whether NO is involved in the modulation of Cyp1a1 and Nqo1 by TNF-alpha or LPS in Hepa 1c1c7 cells. A significant dose-dependent increase in the inducible nitric oxide synthase (NOS2) expression and NO production were observed by various concentrations of TNF-alpha (1, 5, and 10 ng/mL) and LPS (1 and 5 microg/mL) which was completely inhibited by a NOS2 inhibitor, L-N6-(1-iminoethyl) lysine (L-NIL) (1 mM). Furthermore, TNF-alpha and LPS significantly induced NOS2 expression. Both TNF-alpha and LPS repressed the beta-naphthoflavone (betaNF)-mediated induction of Cyp1a1 and Nqo1 at mRNA and activity levels. The downregulation of Cyp1a1, but not Nqo1, was significantly prevented by L-NIL. However, proxynitrite decomposer, iron tetrakis (N-methyl-4'-pyridyl) porphyrinato (FeTMPyP) (5 microM) did not affect TNF-alpha- and LPS-mediated downregulation of Cyp1a1 and Nqo1 at mRNA and activity levels. These results show that NO, but not peroxynitrite, may be involved in TNF-alpha- and LPS-mediated downregulation of Cyp1a1 without affecting the downregulation of Nqo1.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Negar
authors.initials: N
authors.lastname: Gharavi
authors.forename: Ayman O S
authors.initials: AO
authors.lastname: El-Kadi
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007249:Inflammation / Q000201:enzymology / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008239:Lysine / Q000031:analogs & derivatives / Q000494:pharmacology; D008665:Metalloporphyrins / Q000494:pharmacology; D051379:Mice; D016660:NAD(P)H Dehydrogenase (Quinone); D009252:NADPH Dehydrogenase / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D030421:Peroxynitrous Acid / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D019324:beta-Naphthoflavone / Q000494:pharmacology
chemical_list: C492721:5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato-iron(III); D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D008665:Metalloporphyrins; C090663:N(6)-(1-iminoethyl)lysine; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D019324:beta-Naphthoflavone; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D016660:NAD(P)H Dehydrogenase (Quinone); C491732:Nqo1 protein, mouse; D009252:NADPH Dehydrogenase; D008239:Lysine