Morrison D C, Bucklin S E
Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City 66160-7832, USA.
Scand J Infect Dis Suppl. 1996;101:3-8.
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 interacting with humoral and cellular mediator systems to stimulate production 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-negative sepsis, we have developed several experimental models in which mice have been pretreated with various agents to make them sensitive to Gram-negative (E. coli, pseudomonas) infection and/or the lethal effects of endotoxin. For the former, both cyclophosphamide (which renders mice 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 protected approximately five- to 10-fold (as assessed by increases in LD50) if they are sensitive to LPS lethality (D-gal treatment) but 500-fold if they are resistant to LPS lethality. Importantly, different antibiotics that have been documented to cause different amounts of endotoxin release in vitro also differ in their protective efficacy in vivo. Thus, imipenem, which causes relatively low endotoxin release, is significantly more protective (8-fold) than ceftazidime or meropenem (3-fold, P < 0.005) under conditions of equivalent MICs. Lethality data correlate well with circulating levels of interleukin-6 (Il-6) in vivo and with induction of Il-6 in ex vivo studies in which anticoagulated mouse blood is incubated with bacteria and antibiotics. Finally, antiendotoxin agents manifest additional levels of protection in vivo under conditions 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 sepsis.
内毒素脂多糖（LPS）是革兰氏阴性菌外膜的主要成分。从细菌释放后，LPS通过与体液和细胞介质系统相互作用，作为一种强大的促炎刺激物，刺激一系列炎症分子的产生。已知细胞壁活性抗生素会促进内毒素释放。为了评估抗生素诱导的内毒素释放在革兰氏阴性菌败血症发病机制中的作用，我们建立了几种实验模型，其中用各种药物预处理小鼠，使其对革兰氏阴性菌（大肠杆菌、假单胞菌）感染和/或内毒素的致死作用敏感。对于前者，环磷酰胺（使小鼠中性粒细胞减少）和可逆性肝毒素D-半乳糖胺（D-gal）都已被使用。D-gal还使小鼠对内毒素的致死作用敏感。如果对LPS致死性敏感（D-gal处理），用细胞壁活性抗生素治疗的感染小鼠受到的保护约为5至10倍（通过LD50增加评估），但如果对LPS致死性有抗性，则受到的保护为500倍。重要的是，已证明在体外引起不同量内毒素释放的不同抗生素在体内的保护效果也不同。因此，在等效MIC条件下，引起相对较低内毒素释放的亚胺培南的保护作用（8倍）明显高于头孢他啶或美罗培南（3倍，P<0.005）。致死率数据与体内白细胞介素-6（Il-6）的循环水平以及体外研究中Il-6的诱导情况密切相关，在体外研究中，将抗凝小鼠血液与细菌和抗生素一起孵育。最后，在单独使用抗生素无保护作用的条件下，抗内毒素药物在体内表现出额外的保护水平。总的来说，这些结果强烈表明抗生素诱导的内毒素释放是实验性革兰氏阴性菌败血症的一个重要促成因素。
