Sialylneolacto-N-tetraose c (LSTc)-bearing liposomal decoys capture influenza A virus.

Influenza is a severe disease in humans and animals with few effective therapies available. All strains of influenza virus are prone to developing drug resistance due to the high mutation rate in the viral genome. A therapeutic agent that targets a highly conserved region of the virus could bypass resistance and also be effective against multiple strains of influenza. Influenza uses many individually weak ligand binding interactions for a high avidity multivalent attachment to sialic acid-bearing cells. Polymerized sialic acid analogs can form multivalent interactions with influenza but are not ideal therapeutics due to solubility and toxicity issues. We used liposomes as a novel means for delivery of the glycan sialylneolacto-N-tetraose c (LSTc). LSTc-bearing decoy liposomes form multivalent, polymer-like interactions with influenza virus. Decoy liposomes competitively bind influenza virus in hemagglutination inhibition assays and inhibit infection of target cells in a dose-dependent manner. Inhibition is specific for influenza virus, as inhibition of Sendai virus and respiratory syncytial virus is not observed. In contrast, monovalent LSTc does not bind influenza virus or inhibit infectivity. LSTc decoy liposomes prevent the spread of influenza virus during multiple rounds of replication in vitro and extend survival of mice challenged with a lethal dose of virus. LSTc decoy liposomes co-localize with fluorescently tagged influenza virus, whereas control liposomes do not. Considering the conservation of the hemagglutinin binding pocket and the ability of decoy liposomes to form high avidity interactions with influenza hemagglutinin, our decoy liposomes have potential as a new therapeutic agent against emerging influenza strains.

Formation of supported bilayers on silica substrates.

We have investigated the formation of phospholipid bilayers of the neutral (zwitterionic) lipid dimyristoyl-phosphatidylcholine (DMPC) on various glass surfaces from vesicles in various aqueous solutions and temperatures using a number of complementary techniques: the surface forces apparatus (SFA), quartz crystal microbalance (QCM), fluorescence recovery after photobleaching (FRAP), fluorescence microscopy, and streaming potential (SP) measurements. The process involves five stages: vesicle adhesion to the substrate surfaces via electrostatic and van der Waals forces, steric interactions with neighboring vesicles, rupture, spreading via hydrophobic fusion of bilayer edges, and ejection of excess lipid, trapped water, and ions into the solution. The forces between DMPC bilayers and silica were measured in the SFA in phosphate buffered saline (PBS), and the adhesion energy was found to be 0.5-1 mJ/m(2) depending on the method of bilayer preparation. This value is stronger than the expected adhesion predicted by van der Waals interactions. Theoretical analysis of the bilayer-silica interaction shows that the strong attraction is likely due to an attractive electrostatic interaction between the uncharged bilayer and negatively charged silica owing to the surfaces interacting at "constant potential." However, the bilayer-silica interaction in distilled water was found to be repulsive at all distances, which is attributed to the surfaces interacting at "constant charge." These results are consistent with QCM measurements that show vesicles readily forming bilayers on silica in high salt but only weakly adhering in low salt conditions. We conclude that the electrostatic interaction is the most important interaction in determining the adhesion between neutral bilayers and charged hydrophilic surfaces. SP and FRAP experiments gave insights into the bilayer formation process as well as information on the surface coverage, lateral diffusion of the lipid molecules, and surface potential of the bilayers during the spreading process.