Inhibition of LPS binding on human monocytes by phosphonooxyethyl analogs of lipid A

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Abstract
We investigated the inhibition of LPS binding on human monocytes by synthetic analogs of lipid A. A common characteristic of the analyzed structures is a α-(or β-) phosphonooxyethyl group in position 1 of the GlcN I of the lipid A backbone. Compounds PE-1, PE-2 and PE-3 are analogs of synthetic Escherichia coli lipid A whereas PE-4 represents an analog of tetraacyl precursor Ia (synthetic compound 406). By determining the ability of these preparations to inhibit the binding of FITC-labeled LPS (E. coli 0111:B4) on human monocytes the relationship between their structure and cellular binding affinity was evaluated. The results showed a structure-dependent hierarchy of inhibition capacity. Thus, compound PE-1 inhibited the binding of FITC-LPS only slightly more than PE-2. However, compound PE-3, possessing β-configurated GlcN I, exhibited a drastically decreased inhibition capability. Best inhibition was obtained with compound PE-4. It was furthermore shown by a Lineweaver-Burk plot that the inhibition of LPS binding was due to competition of FITC-LPS and PE-4 for the same binding structure. The synthesis of stable 1-phosphonooxyethyl analogs of precursor Ia with high affinity for LPS receptor structures but lacking cytokine-inducing capacity (like PE-4) may be of relevance for their function as potent antagonists of LPS in therapy of endotoxic shock and sepsis.