Lipopolysaccharide (LPS) endotoxin is the bacterial product responsible for the clinical syndrome of Gram-negative septicemia and endotoxic shock. During sepsis, microbial antigens, such as LPS, activate monocytes and macrophages to produce several proinflammatory cytokines, among which tumor necrosis factor-a (TNF-alpha) appears to be very important for the development of endotoxic shock. The endotoxic properties of LPS principally reside in the lipid A (LIP A) component, which is the primary immunostimulatory center of Gram-negative bacteria. In recent years there has been a continuous effort to identify molecules able to antagonize the deleterious effects of endotoxic shock. In this study we show that a novel LIP A fraction from the LPS of Halomonas magadiensis (Hm), a Gram-negative xtremophilic and alkaliphilic bacterium, significantly inhibits the synthesis of TNF-alpha by human monocytes activated by Escherichia coli LPS. LIP A from Hm exerts these effects by interfering with E. coli LPS for activation of Toll-like receptor 4 expressed in human cells. This result defines Hm LIP A as a novel class of LPS antagonist whose structural features could be utilized for the design of compounds for the treatment of Gram-negative sepsis.
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