Anti-endotoxin activity of a novel synthetic lipid A analog.

Lipid As from non-toxic bacteria such as Rhodobacter capsulatus and Rhodobacter sphaeroides have been shown to antagonize the immunostimulatory effects of lipid A and LPS from pathogenic bacteria. We have biologically characterized a series of synthetic LPS antagonists including the proposed structures of the lipid A and R. sphaeroides containing fatty acid side chains ester-linked to the disaccharide backbone, as well as an analog of R. capsulatus lipid A containing ether-linked alkyloxy side chains (E5531). In vitro assays utilizing LPS-stimulated human monocytes or whole blood demonstrated that low nanomolar concentrations of E5531 inhibited cellular activation as indicated by decreased release of the cytokines TNF-a, and interleukins-1, 6, and 8. E5531 also inhibited LPS-induced release of cytokines and nitric oxide from murine macrophages. Synthetic antagonists at up to 100 microM were devoid of agonistic activity in murine and human in vitro systems. In vivo, E5531 blocked induction of TNF-a by LPS and reduced LPS-induced lethality in mice. These in vitro and in vivo results indicate that E5531 may have clinical therapeutic utility as an antagonist of endotoxin-mediated morbidity and mortality.