TY - JOUR T1 - Role of Nitric Oxide in Down-Regulation of CYP2B1 Protein, but Not RNA, in Primary Cultures of Rat Hepatocytes JF - Molecular Pharmacology JO - Mol Pharmacol SP - 209 LP - 216 DO - 10.1124/mol.60.1.209 VL - 60 IS - 1 AU - Luc Ferrari AU - Ning Peng AU - James R. Halpert AU - Edward T. Morgan Y1 - 2001/07/01 UR - http://molpharm.aspetjournals.org/content/60/1/209.abstract N2 - There are conflicting reports about the role of nitric oxide in the down-regulation of cytochrome P450 that occurs when animals or cultured hepatocytes are exposed to inflammatory stimuli. Here, we investigated the participation of NO in the down-regulation of CYP2B1 by bacterial endotoxin (LPS) in rat hepatocytes cultured on Matrigel. LPS caused the down-regulation of CYP2B1 mRNA to 20% of control values within 12 h of treatment, and this was not reversed by concentrations of NO synthase inhibitors that completely blocked NO production. LPS was several orders of magnitude more potent in the down-regulation of CYP2B1 mRNA than in induction of NO production. In contrast, concentrations of LPS in the 1 to 100 ng/ml range induced NO production and produced a rapid down-regulation of CYP2B1 protein to 30% and <5% of control at 6 and 24 h, respectively, that could be completely prevented both by inhibitors of NO synthase and by LY83583, which prevents NO synthase-2 induction. The blockade of CYP2B1 down-regulation by NO synthase inhibitors was reversed by arginine, and the NO donors S-nitrosoglutathione andS-nitroso-N-acetylpenicillamine mimicked CYP2B1 protein suppression. Taken together, these experiments demonstrate two independent mechanisms of CYP2B1 down-regulation by LPS: a rapid, NO-dependent suppression of the protein occurring at high concentrations of LPS and a slower, NO-independent pretranslational suppression occurring at low concentrations of LPS. P450cytochrome P450NOSnitric-oxide synthaseLPSbacterial lipopolysaccharideILinterleukinPBphenobarbitalTNFtumor necrosis factorNMANω-monomethyl-l-arginineAGaminoguanidineGSNOS-nitrosoglutathioneSNAPS-nitroso-N-acetylpenicillamineSSCstandard saline citratePRODpentoxyresorufinO-dealkylaseNOxnitrate + nitrite ER -