Septic shock, systemic inflammatory response syndrome

and multiple organ failure caused by infections correlate with high mortality. In infections with gram-negative bacteria, these systemic inflammatory responses are caused by lipopolysaccharide (LPS), the major component of the outer membrane. LPS triggers the production of various cytokines (TNF-a , IL-1b and IL-6 etc.), chemokines (IL-8 and monocyte chemoattractant protein 1 etc.), and biologically active components implicated in inflammation (tissue factor, platelet activating factor, prostaglandins, thromboxanes, leukotrienes and nitric oxide etc.) via toll-like receptor 4 (TLR4)-dependent or -independent pathways. These substances play a pivotal role for triggering septic shock. Although several animal models for LPS-induced lethal shock have been developed, they are not always satisfactory in terms of rapid clearance of LPS from the circulation and necessity of large quantity of LPS for causing lethal shock. Since these aspects are different from clinical cases, infection-induced shock models are necessary for analyzing the protective effect of antibiotics in vivo. When D-galactosamine (GalN)-sensitized mice were infected intraperitoneally (i.p.) with Escherichia coli or Pseudomonas aeruginosa and then treated with antibiotics, mice showed septic shock with differences in outcome, depending on different amounts of LPS released from bacilli by treatment with imipenem (IPM) and ceftazidime (CAZ). b-Lactam antibiotics such as IPM block the final step of peptidoglycan biosynthesis in the outer membrane and preferentially bind to penicillin-binding protein-2 (PBP-2). As result, they cause rapid killing and spheroplast formation of gram-negative bacteria with relatively little release of LPS. In contrast, fosfomycin (FOF) binds to UDP-N-acetyl-glucosamine enolpyruvate transferase and irreversibly inactivates this enzyme which catalyzes the first step of peptidoglycan biosynthesis in the bacterial cytoplasm. Recently, interesting studies showed that FOF suppressed TNF-a production by human monocytes and murine macrophages stimulated with LPS. We recently established a new endotoxin shock model based on infection with high numbers (10 colony forming units (CFU)) of attenuated Salmonella typhimurium. In this model severe thrombosis and liver dysfunction following lethal shock is observed in LPS-responder but not in LPSnonresponder mice, suggesting that this shock is potentially mediated by host responses to LPS released during infection. The result about suppression of TNF-a production by FOF and its enantiomer FOF encouraged us to investigate beneficial effects of FOF in infection-induced lethal models. We demonstrated in this study that the therapeutic effects of FOF and IPM were timeand dose-dependent using a novel endotoxin shock model.