Submitted on July 18, 2003
Accepted on April 1, 2004
HYPOXIC SUPPRESSION OF E. coli-INDUCED NF-
B and AP-1 TRANSACTIVATION BY OXYRADICAL SIGNALING
George M Matuschak1*, Andrew J Lechner2, Zhoumou Chen3, Subhash Todi4, Timothy M Doyle3, and Laura L Loftis5
1 Division of Pulmonary, Critical Care, and Occupational Medicine, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri, USA; Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri, USA; Department of Critical Care Medicine, Saint John's Mercy Medical Center, St. Louis, Missouri, USA
2 Division of Pulmonary, Critical Care, and Occupational Medicine, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri, USA; Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri, USA
3 Division of Pulmonary, Critical Care, and Occupational Medicine, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri, USA
4 Division of Pulmonary, Critical Care, and Occupational Medicine, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, Missouri, USA; Department of Critical Care Medicine, Saint John's Mercy Medical Center, St. Louis, Missouri, USA
5 Division of Critical Care Medicine, Department of Pediatrics, Saint Louis University School of Medicine, St. Louis, Missouri, USA
* To whom correspondence should be addressed. E-mail: Matuscgm{at}slu.edu.
Transactivation of the DNA binding proteins nuclear factor-
B (NF-B) and activator protein (AP)-1 by de novo oxyradical generation is a stereotypic redox-sensitive process during hypoxic stress of the liver. Systemic trauma is associated with splanchnic hypoxia/reoxygenation (H/R), followed by secondary intraportal gram-negative bacteremia, which collectively have been implicated in post-traumatic liver dysfunction and multiple organ damage. We hypothesized that brief hypoxic stress of the liver preceding stimulation by E. coli serotype O55:B5 (EC) amplifies oxyradical-mediated transactivation of NF-B and AP-1 as well as downstream inflammatory cytokine production, compared to either noninfectious hepatic H/R or gram-negative sepsis without preceding hypoxia. Livers from Sprague-Dawley rats underwent constant-flow perfusion for 180 min with or without 0.5 h of initial hypoxia (perfusate pO2, 40± 5 mm Hg), followed by reoxygenation and intraportal infection with 109 live EC or 0.9% NaCl infusion. In H/R + EC livers, postbacteremic nuclear translocation of NF-B and AP-1 was unexpectedly reduced in both gel shift and transcription protein/DNA array assays compared with normoxic EC controls, as were perfusate TNF-
and IL-1
levels. Preceding hypoxic stress paradoxically increased postbacteremic GSH:GSSG ratios as well as nuclear localization of IB and phospho-IB, but did not change JunB/FosB subunit activation profiles. Notably, prior xanthine oxidase inhibition increased NF-B and AP-1 transactivation as well as cytokine production in H/R + EC livers. Thus, brief hypoxic stress of the liver before stimulation by gram-negative bacteria potently suppresses activation of canonical redox-sensitive transcription factors and production of inflammatory cytokines by mechanisms including xanthine oxidase-induced oxyradicals functioning in an anti-inflammatory signaling role. These results suggest a novel multifunctionality of oxyradicals in decoupling integrated hepatic transcriptional activity and O2-sensitive cytokine biosynthesis early in the post-traumatic milieu.
