title: Bidirectional effects of hepatic ischemia/reperfusion on E. coli-induced TNF-alpha gene expression.
abstract: We tested the hypothesis that gram-negative bacteremia (GNB) and brief (30 min) reductions in the hepatic O2 supply by low-flow ischemia differentially modulate tumor necrosis factor-alpha (TNF-alpha) gene expression owing to sequence-specific activation of cyclooxygenase vs. complement (C) pathways. Buffer-perfused Sprague-Dawley rat livers (n = 82) were studied over 180 min after intraportal 10(9) live E. coli serotype 055:B5 (EC) or 0.9% NaCl (NS) at t = 0. Compared with EC and NS controls receiving constant-flow perfusion, sequential GNB and ischemia/reperfusion (I/R) were studied in EC + 30 I/R and NS + 30 I/R livers, in which 30 min of ischemia (I) beginning 0.5 h after EC or NS was followed by 120 min of reperfusion (R). This sequence was reversed in 30 I/R + EC and 30 I/R + NS groups. Bacterial clearance, bioactive and antigenic TNF-alpha, prostaglandin E2 (PGE2), and hepatic O2 uptake and performance were serially assessed. Venous TNF-alpha increased in EC controls to peak at 155 +/- 29 U/ml after 180 min (P < 0.001 vs. NS controls) as did hepatic TNF-alpha mRNA. Both TNF-alpha transcripts and protein levels were markedly attenuated in EC + 30 I/R (P < 0.001 vs. EC) despite equivalent EC clearance by Kupffer cells. Indomethacin (10(-5) M) decreased I/R-induced PGE2 secretion and restored TNF-alpha to control levels. In contrast, TNF-alpha levels in 30 I/R + EC perfusates exceeded those of EC + 30 I/R livers (P < 0.05) and were indistinguishable from EC controls. Allopurinol pretreatment but not heat inactivation of C or infusion of soluble human complement receptor type 1 inhibited TNF-alpha production in 30 I/R + EC organs. These results identify a novel sequence-dependent interaction whereby hepatic O2 deprivation after GNB downregulates TNF-alpha via generation of cyclooxygenase metabolites, whereas ischemia preceding GNB increases cytokine expression via reactive O2 species but not C activation.
authors.affiliation: Department of Internal Medicine, Saint Louis University School of Medicine, Missouri 63110-0250, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Epperly
authors.forename: A J
authors.initials: AJ
authors.lastname: Lechner
authors.forename: C A
authors.initials: CA
authors.lastname: Johanns
authors.forename: R O
authors.initials: RO
authors.lastname: Webster
authors.forename: G M
authors.initials: GM
authors.lastname: Matuschak
mesh_terms: D000818:Animals; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D016207:Cytokines / Q000235:genetics; D004926:Escherichia coli / Q000502:physiology*; D015870:Gene Expression; D066298:In Vitro Techniques; D007511:Ischemia / Q000235:genetics* / Q000473:pathology; D008099:Liver / Q000473:pathology; D008102:Liver Circulation; D008297:Male; D010100:Oxygen / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000235:genetics* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics*
chemical_list: D016861:Cyclooxygenase Inhibitors; D016207:Cytokines; D014409:Tumor Necrosis Factor-alpha; D010100:Oxygen