Abstract
The identification of the bacterial endotoxin receptors for innate immunity, most notably the Toll-like receptor 4 (TLR4), has sparked great interest in therapeutic manipulation of innate immune system. We have recently developed synthetic molecules that have been shown to inhibit TLR4 activation in vitro and in vivo. Here we present the synthesis and the biological characterization of a new molecule, the cationic amphiphile 3,4-bis(tetradecyloxy)benzylamine, with a structure strictly related to the previously developed TLR4 modulators. This compound is able to inhibit in a dose-dependent manner the LPS-stimulated TLR4 activation in HEK cells. In order to characterize the mechanism of action of this compound, we investigated possible interactions with the extracellular components that bind and shuttle LPS to TLR4, namely LBP, CD14, and MD-2. This compound inhibited LBP/CD14-dependent LPS transfer to MD-2.TLR4, resulting in reduced formation of a (LPS-MD-2-TLR4)(2) complex. This effect was due to inhibition of the transfer of LPS from aggregates in solution to sCD14 with little or no effect on LPS shuttling from LPS/CD14 to MD-2. This compound also inhibited transfer of LPS monomer from full-length CD14 to a truncated, polyhistidine tagged CD14. Taken together, our findings strongly suggest that this compound inhibits LPS-stimulated TLR4 activation by competitively occupying CD14 and thereby reducing the delivery of activating endotoxin to MD-2.TLR4.