Towards the understanding of the behavior of single-chained ether phospholipids in model biomembranes: interactions with phosphatidylethanolamines in Langmuir monolayers.

Three single-chained ether lipids of comparable chemical structure but different biological activities (namely natural platelet activating factor - PAF, its deacetylated precursor - lyso-PAF and synthetic compound - edelfosine - ED) have been investigated in mixed Langmuir monolayers with phosphatidylethanolamines, PEs (DSPE, SOPE and DOPE), serving as model of inner shell of cellular membrane. The aim of undertaken studies was to verify the correlation between minor differences in chemical structures of the investigated ether lipids and their behavior in membrane-mimicking environment. To reach this goal the interactions between particular ether lipids and PEs have been analyzed with ΔG(Exc) values derived from the surface pressure-area isotherms. To get insight into miscibility between film components, Brewster angle microscopy, enabling direct visualization of monolayers structure, has been applied. The obtained results prove significant differences in both mixing properties and the interactions in the investigated systems. On one hand, they are related to the structure of polar head-groups of the studied ether lipids, which determine their capability of hydrogen bond(s) formation with head-groups of PEs. Edelfosine, lacking this property, interacts with PEs the most unfavorably among all the investigated compounds. Another important parameter in this context is the structure of PEs monolayers - the most closely packed DSPE film was found to be most unfavorable for incorporation of ether lipid molecules. Our results prove that the analysis of the interaction between ether lipids and components of biomembrane in Langmuir monolayers is a potent method to explain differences in biological activity of the investigated ether lipids.