EVIDENCE FOR ANTIBIOTIC-MEDIATED ENDOTOXIN RELEASE AS A CONTRIBUTING FACTOR TO LETHALITY IN EXPERIMENTAL GRAM-NEGATIVE SEPSIS

Endotoxic lipopolysaccharide (LPS) is a major constituent of the outer membrane of the Gram-negative microbe. Following its release from the bacterium, LPS serves as a potent proinflammatory stimulus by interac ting with humoral and cellular mediator systems to stimulate productio n of an array of inflammatory molecules. Cell-wall active antibiotics are known to promote endotoxin release. To assess the contribution of antibiotic-induced endotoxin release in the pathogenesis of Gram-negat ive sepsis, we have developed several experimental models in which mic e have been pretreated with various agents to make them sensitive to G ram-negative (E. coli, pseudomonas) infection and/or the lethal effect s of endotoxin. For the former, both cyclophosphamide (which renders m ice neutropenic) and the reversible hepatotoxin D-galactosamine (D-gal ) have been used. D-gal also sensitized mice to the lethal effects of LPS, Infected mice treated with cell-wall active antibiotics are prote cted approximately five- to 10-fold (as assessed by increases in LD(50 )) if they are sensitive to LPS lethality (D-gal treatment) but 500-fo ld if they are resistant to LPS lethality. Importantly, different anti biotics that have been documented to cause different amounts of endoto xin release in vitro also differ in their protective efficacy in vivo. Thus, imipenem, which causes relatively low endotoxin release, is sig nificantly more protective (8-fold) than ceftazidime or meropenem (3-f old, P <0.005) under conditions of equivalent MICs. Lethality data cor relate well with circulating levels of interleukin-6 (Il-6) in vivo an d with induction of Il-6 in ex vivo studies in which anticoagulated mo use blood is incubated with bacteria and antibiotics, Finally, antiend otoxin agents manifest additional levels of protection in vivo under c onditions in which antibiotics alone are not protective, Collectively, these results strongly implicate antibiotic-induced endotoxin release as a significant contributing factor in experimental Gram-negative se psis.