Search

25-hydroxycholesterol (25-OH), a molecule with unusual behavior at the air/water interface, being anchored to the water surface alternatively with a hydroxyl group at C(3) or C(25), has been investigated in mixtures with main membrane phospholipids (phosphatidylcholines - PCs, and phosphatidylethanolamines - PEs), characteristic of the outer and inner membrane leaflet, respectively. To achieve this goal, the classical Langmuir monolayer approach based on thermodynamic analysis of interactions was conducted in addition to microscopic imaging of films (in situ with BAM and after transfer onto mica with AFM), surface-sensitive spectroscopy (PM-IRRAS), as well as theoretical calculations. Our results show that the strength of interactions is primarily determined by the kind of polar group (strong, attractive interactions leading to surface complexes formation were found to occur with PCs while weak or repulsive ones with PEs). Subsequently, the saturation of phosphatidylcholines apolar chain(s) was found to be crucial for the structure of the formed complexes. Namely, saturated PC (DPPC) does not have preferences regarding the orientation of 25-OH molecule in surface complexes (which results in the two possible 25-OH arrangements), while unsaturated PC (DOPC) enforces one specific orientation of oxysterol (with C(3)-OH group). Our findings suggest that the transport of 25-OH between inner and outer membrane leaflet can proceed without orientation changes, which is thermodynamically advantageous. This explains results found in real systems showing significant differences in the rate of transmembrane transport of 25-OH and the other chain-oxidized oxysterols compared to their ring-oxidized analogues or cholesterol.

In this paper we tested how oxysterols influence on fusion process between viral lipid envelope and host cells membranes. For this purpose, the Zika virus was selected, while dendritic cell (DC) and neural cell (NC) membranes were chosen as target membranes. The investigated systems were modeled as multicomponent Langmuir monolayers and characterized using surface manometry and imaging in micro- (Brewster angle microscopy, BAM) and nanoscale (Atomic Force Microscopy, AFM) to monitor local heterogeneity. The fusion process was conducted by mixing viral and host cell membranes devoid and in the presence of oxysterols: 25-hydroxycholesterol (25-OH) and 7β-hydroxycholesterol (7β-OH) as representatives of chain- and ring-oxidized oxysterols, respectively. Our results show that oxysterols hinder the fusion with host cell membranes by modifying their biophysical properties. Moreover, oxysterols applied to an already infected membrane reverse the changes caused by the infection. It could therefore be concluded that oxysterols may display antiviral activity in two ways: they prevent the healthy membrane from viral infection by blocking the fusion process; and protect already infected membrane from pathological changes induced by the virus.