E5531, a synthetic non-toxic lipid A derivative blocks the immunobiological activities of lipopolysaccharide

1 The major pathological responses to Gram-negative bacterial sepsis are tr iggered by endotoxin or lipopolysaccharide. As endotoxin is shed from the b acterial outer membrane, it induces immunological responses that lead to re lease of a variety of cytokines and other cellular mediators. As part of a program aimed at developing a therapeutic agent for septic shock, we have d eveloped E5531, a novel synthetic lipopolysaccharide antagonist. 2 As measured by release by tumour necrosis factor-alpha, human monocytes o r whole blood can be activated by lipopolysaccharide, lipid A, and lipoteic hoic acid (from Gram-positive bacteria). E5531 potently antagonizes activat ion by all these agents while itself being devoid of agonistic activity. 3 The inhibitory activity of E5531 was dependent on time of addition. When 10 nM E5531 was added simultaneously with lipopolysaccharide or 1-3h before addition of lipopolysaccharide, production of tumour necrosis factor-alpha was inhibited by more than 98%. The addition of E5531 1 h after lipopolysa ccharide reduced the efficacy of E5531 by 47%. 4 Antagonistic activity of E5531 was specific for lipopolysaccharide as it was ineffective at inhibiting interferon-gamma mediated NO release of RAW 2 64.7 cells, phorbor 12-myristate 13-acetate stimulated superoxide anion pro duction in human neutrophils, concanavalin A stimulated mitogenic activity in murine thymocytes and tumor necrosis factor-alpha induced E-selectin exp ression in human umbilical vein endothelial cells. 5 E5531 as well as MY4, an anti-CD14 antibody, inhibited radiolabelled lipo polysaccharide binding in human monocytes. 6 These results support our contention that E5531 is a potent antagonist of lipopolysaccharide-induced release of tumour necrosis factor-alpha and oth er cellular mediators and may be an effective therapeutic agent for human s eptic shock due to Gram-negative bacteria.