RT Journal Article SR Electronic 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 FD American Society for Pharmacology and Experimental Therapeutics SP 209 OP 216 DO 10.1124/mol.60.1.209 VO 60 IS 1 A1 Luc Ferrari A1 Ning Peng A1 James R. Halpert A1 Edward T. Morgan YR 2001 UL http://molpharm.aspetjournals.org/content/60/1/209.abstract AB 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