Hypoxic suppression of E. coli-induced NF-kappa B and AP-1 transactivation by oxyradical signaling

Transactivation of the DNA-binding proteins nuclear factor-kappa B (NF-kappa 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 intraportal gram-negative bacteremia, which collectively have been implicated in posttraumatic liver dysfunction and multiple organ damage. We hypothesized that hypoxic stress of the liver before stimulation by Escherichia coli serotype O55:B5 (EC) amplifies oxyradical-mediated transactivation of NF-kappa B and AP-1 as well as cytokine production compared with noninfectious H/R or gram-negative sepsis without prior hypoxia. Livers from Sprague-Dawley rats underwent perfusion for 180 min with or without 0.5 h of hypoxia (perfusate PO(2), 40 +/- 5 mmHg) followed by reoxygenation and infection with 10(9) EC or 0.9% NaCl infusion. In H/R + EC livers, nuclear translocation of NF-kappa B and AP-1 was unexpectedly reduced in gel shift assays vs. normoxic EC controls, as were perfusate TNF-alpha and IL-1 beta levels. Preceding hypoxic stress paradoxically increased postbacteremic reduced-to-oxidized glutathione ratios plus nuclear localization of I kappa B alpha and phospho-I kappa B alpha, but not JunB/FosB profiles. Notably, xanthine oxidase inhibition increased transactivation as well as cytokine production in H/R + EC livers. Thus brief hypoxic stress of the liver before intraportal gram-negative bacteremia 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 hepatic transcriptional activity and cytokine biosynthesis early in the posttraumatic milieu.