Mechanism of hepatic heme oxygenase-1 induction by isoflurane.
BACKGROUND
The heme oxygenase pathway represents a major cell and organ protective system in the liver. The authors recently showed that isoflurane and sevoflurane up-regulate the inducible isoform heme oxygenase 1 (HO-1). Because the activating cascade remained unclear, it was the aim of this study to identify the underlying mechanism of this effect.


METHODS
Rats were anesthetized with pentobarbital intravenously or with isoflurane per inhalation (2.3 vol%). Kupffer cell function was inhibited by dexamethasone or gadolinium chloride. Nitric oxide synthases were inhibited by either N(omega)-nitro-L-arginine methyl ester or S-methyl thiourea. N-acetyl-cysteine served as an antioxidant, and diethyldithiocarbamate served as an inhibitor of cytochrome P450 2E1. Protein kinase C and phospholipase A2 were inhibited by chelerythrine or quinacrine, respectively. HO-1 was analyzed in liver tissue by Northern blot, Western blot, immunostaining, and enzymatic activity assay.


RESULTS
In contrast to pentobarbital, isoflurane induced HO-1 after 4-6 h in hepatocytes in the pericentral region of the liver. The induction was prevented in the presence of dexamethasone (P < 0.05) and gadolinium chloride (P < 0.05). Inhibition of nitric oxide synthases or reactive oxygen intermediates did not affect isoflurane-mediated HO-1 up-regulation. In contrast, chelerythrine (P < 0.05) and quinacrine (P < 0.05) resulted in a blockade of HO-1 induction.


CONCLUSIONS
The up-regulation of HO-1 by isoflurane in the liver is restricted to parenchymal cells and depends on Kupffer cell function. The induction is independent of nitric oxide or reactive oxygen species but does involve protein kinase C and phospholipase A2.
Hoetzel
Alexander
A
Department of Anesthesiology and Critical Care Medicine, University of Freiburg, Germany.
Leitz
Daniel
D
Schmidt
Rene
R
Tritschler
Eva
E
Bauer
Inge
I
Loop
Torsten
T
Humar
Matjaz
M
Geiger
Klaus K
KK
Pannen
Benedikt H J
BH
D000111:Acetylcysteine / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D015152:Blotting, Northern; D015153:Blotting, Western; D003907:Dexamethasone / Q000494:pharmacology; D004050:Ditiocarb / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D051547:Heme Oxygenase-1 / Q000096:biosynthesis*; D007150:Immunohistochemistry; D007530:Isoflurane / Q000494:pharmacology*; D007550:Isothiuronium / Q000031:analogs & derivatives / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D012313:RNA / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects
D018685:Anesthetics, Inhalation; D000893:Anti-Inflammatory Agents; D004791:Enzyme Inhibitors; D007550:Isothiuronium; D012313:RNA; D003907:Dexamethasone; D004050:Ditiocarb; D005682:Gadolinium; D007530:Isoflurane; D019001:Nitric Oxide Synthase; D051547:Heme Oxygenase-1; C027744:S-methylisothiopseudouronium; D019331:NG-Nitroarginine Methyl Ester; D000111:Acetylcysteine