Abstract
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.
Abbreviations
- P450
- cytochrome P450
- NOS
- nitric-oxide synthase
- LPS
- bacterial lipopolysaccharide
- IL
- interleukin
- PB
- phenobarbital
- TNF
- tumor necrosis factor
- NMA
- Nω-monomethyl-l-arginine
- AG
- aminoguanidine
- GSNO
- S-nitrosoglutathione
- SNAP
- S-nitroso-N-acetylpenicillamine
- SSC
- standard saline citrate
- PROD
- pentoxyresorufinO-dealkylase
- NOx
- nitrate + nitrite
- Received October 12, 2000.
- Accepted April 9, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
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