A novel synthetic lipid A analog with low endotoxicity, DT-5461, prevents lethal endotoxemia

Abstract

Bacterial endotoxin (lipopolysaccharide [LPS]) causes severe damage to the host organism as a result of excessive release of inflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-α), from mononuclear phagocytes during gram-negative bacterial infection. We evaluated the ability of a novel synthetic lipid A analog with low endotoxicity, DT- 5461, to antagonize LPS-induced IL-1 and TNF-α production in cells of monocyte/macrophage lineage and examined the protective effect of DT-5461 against lethal endotoxic shock in mice. The IL-1- or TNF-α-inducing activity of DT-5461 is 100,000 to 10,000 times less active than that of Escherichia coli LPS (EcLPS) or synthetic lipid A. DT-5461 significantly inhibited EcLPS- induced IL-1 and TNF-α release when murine peritoneal macrophages were incubated with DT-5461 2 h prior to EcLPS stimulation at the same concentration (1 μg/ml). The antagonistic effect of DT-5461 on the production of IL-1 and TNF-α induced by EcLPS occurred in a concentration- dependent manner. DT-5461 also inhibited IL-1 and TNF-α induction when murine peritoneal macrophages were stimulated by LPS from Salmonella typhimurium or synthetic lipid A, as well as by EcLPS, but not by muramyl dipeptides. This indicated that DT-5461 specifically antagonized the action of LPS. DT-5461 also antagonized EcLPS-mediated activation of human peripheral blood monocytes. DT-5461 blocked the binding of fluorescein isothiocyanate-labelled LPS to murine peritoneal macrophages as well as it did the binding of EcLPS and synthetic lipid A, i.e., in a concentration- dependent fashion. Injection of DT-5461 2 h before EcLPS challenge prevented the production of serum IL-1 and TNF-α in D-galactosamine-treated mice. Furthermore, this treatment modality protected mice against LPS-induced lethal toxicity. This study suggests that DT-5461 possesses a potent LPS antagonistic effect and may be useful in a protective strategy against lethal endotoxemia caused by gram-negative bacterial infection.