Title

Investigation of the role of endotoxin in the pathogenesis of experimental gram-negative sepsis

Date of Completion

January 1999

Keywords

Health Sciences, Pharmacology|Health Sciences, Pathology|Health Sciences, Immunology

Degree

Ph.D.

Abstract

The kinetics profile of endotoxin liberation by bacterial multiplication and by antibiotic bactericidal action was investigated in vitro in a bacterial kill-kinetic model and in vivo in a rat E. coli peritonitis/sepsis model. The impact of a derivative of human immunoglobulin G, 5S-IgG on endotoxin liberation was also assessed. Results demonstrated the antibiotic-induced endotoxin liberation by comparing the endotoxin concentrations after antibiotic administration with the base endotoxin levels. The absolute amount of antibiotic-mediated endotoxin release, however, was no greater than the amount of endotoxin released during bacterial multiplication. This indicates the importance of effective antibiotic therapy in elimination of bacteria, the source of endotoxin. In addition, 5S-IgG demonstrated its anti-endotoxin activity as evidenced by the observation of decreased endotoxin concentrations with the presence of 5S-IgG. ^ The kinetic profile of endotoxin-mediated TNF-α induction was investigated in vitro in human monocyte-enriched peripheral blood mononuclear cells (PBMC) and in vivo in a rat endotoxin septic shock model. In response to endotoxin, PBMC cells produced significant amounts of TNF-α. 5S-IgG showed its moderate anti-endotoxin activity by partially inhibiting the endotoxin mediated TNF-α release when given before triggering of TNF-α induction. However, this inhibitory effect rapidly diminished when 5S-IgG was administered after the occurrence of TNF-α induction. Similar results were obtained from animal study in which endotoxin challenge initiated substantial amounts of TNF-α release into the rat circulatory system leading to death. The inhibitory effect of 5S-IgG on endotoxin mediated TNF-α release and the resultant protective effect against endotoxin lethality were related to the timing of its administration relative to the endotoxin dosing. 5S-IgG showed its moderate anti-endotoxin activity by partially suppressing the endotoxin mediated TNF-α release and decreasing the overall mortality only when given before triggering of TNF-α induction. Collectively, these results support the hypothesis that the development of grain-negative sepsis may be a self-perpetuating process, which is initiated by the release of endotoxin, and the development of sepsis or its sequelae may no longer be affected by the persistence release of endotoxin into the circulation. ^