Role of nitric oxide in down-regulation of CYP2B1 protein, but not RNA, in primary cultures of rat hepatocytes.
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 and S-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.
Ferrari
L
L
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Peng
N
N
Halpert
J R
JR
Morgan
E T
ET
D000818:Animals; D002478:Cells, Cultured; D019362:Cytochrome P-450 CYP2B1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D020030:Nitric Oxide Donors; D012333:RNA, Messenger; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D019362:Cytochrome P-450 CYP2B1