Brief hypoxic stress suppresses postbacteremic NF-kappaB activation and TNF-alpha bioactivity in perfused liver

Reductions in hepatic O(2) delivery are common early after gram-negative bacteremic sepsis owing to cardiopulmonary dysfunction and derangements in sinusoidal perfusion. Although gram-negative endotoxin and cellular hypoxia independently enhance activation of nuclear factor-kappaB (NF-kappaB) via ge...

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Bibliographic Details
Published in:American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2000-07, Vol.279 (1), p.R99-R108
Main Authors: Loftis, L L, Johanns, C A, Lechner, A J, Matuschak, G M
Format: Article
Language:English
Subjects:
Allopurinol - pharmacology
Animals
Bacteremia - metabolism
Electrophoresis, Polyacrylamide Gel
Enzyme Inhibitors - pharmacology
Escherichia coli Infections - metabolism
Gene Expression
Hypoxia - metabolism
In Vitro Techniques
Liver - metabolism
Liver Function Tests
Male
NF-kappa B - analysis
NF-kappa B - metabolism
Perfusion
Rats
Rats, Sprague-Dawley
Reactive Oxygen Species - metabolism
Stress, Physiological - metabolism
Tumor Necrosis Factor-alpha - biosynthesis
Tumor Necrosis Factor-alpha - genetics
Xanthine Oxidase - antagonists & inhibitors
Xanthine Oxidase - metabolism
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Summary:Reductions in hepatic O(2) delivery are common early after gram-negative bacteremic sepsis owing to cardiopulmonary dysfunction and derangements in sinusoidal perfusion. Although gram-negative endotoxin and cellular hypoxia independently enhance activation of nuclear factor-kappaB (NF-kappaB) via generation of reactive O(2) species (ROS), the combination of these stimuli downregulates hepatic TNF-alpha gene expression. Here we tested the hypothesis that hypoxic suppression of postbacteremic TNF-alpha gene expression is transcriptionally mediated by reduced activation of NF-kappaB. Buffer-perfused rat livers (n = 52) were studied over 180 min after intraportal infection at t = 0 with 10(9) live Escherichia coli (EC), serotype O55:B5, or 0.9% NaCl controls under normoxic conditions, compared with 0.5 h of constant-flow hypoxia (PO(2) approximately 41 +/- 7 Torr) beginning at t = 30 min, followed by 120 min of reoxygenation. In parallel studies, tissue was obtained at peak hypoxia (t = 60 min). To determine the role of xanthine oxidase (XO)-induced ROS in modulating NF-kappaB activity after hypoxia/reoxygenation (H/R), livers were pretreated with the XO inhibitor allopurinol, with results confirmed in organs of tungstate-fed animals. Electrophoretic mobility shift assays were performed on nuclear extracts of whole liver lysates using (32)P-labeled oligonucleotides specific for NF-kappaB. Compared with normoxic EC controls, hypoxia reduced postbacteremic NF-kappaB nuclear translocation and TNF-alpha bioactivity, independent of reoxygenation, tissue levels of reduced glutathione, or posthypoxic O(2) consumption. XO inhibition reversed the hypoxic suppression of NF-kappaB nuclear translocation and ameliorated decreases in cell-associated TNF-alpha. Thus decreases in hepatic O(2) delivery reduce postbacteremic nuclear translocation of NF-kappaB and hepatic TNF-alpha biosynthesis by signaling mechanisms involving low-level generation of XO-mediated ROS.
ISSN:0363-6119