Atherosclerotic\nOxidized Lipids Affect Formation and\nBiophysical Properties of Supported Lipid Bilayers and Simulated Membranes

Oxidized lipids arising from oxidative stress are associated\nwith\nmany serious health conditions, including cardiovascular diseases.\nFor example, KDdiA-PC and KOdiA-PC are two oxidized phosphatidylcholines\n(oxPC) directly linked to atherosclerosis, which precipitate heart\nfailure, stroke, aneurysms, and chronic kidney disease. These oxPCs\nare well-characterized in small particles such as low-density lipoprotein,\nbut how their presence affects the biophysical properties of larger\nbilayer membranes is unclear. It is also unclear how membrane mediators,\nsuch as cholesterol, affect lipid bilayers containing these oxPCs.\nHere, we characterize supported lipid bilayers (SLBs) containing POPC,\nKDdiA-PC, or KOdiA-PC, and cholesterol. We used a quartz crystal microbalance\nwith dissipation monitoring (QCM-D), fluorescence microscopy, and\nall-atom molecular dynamics (MD) to examine the formation process,\nbiophysical properties, and specific lipid conformations in simulated\nbilayers. Experimentally, we show that liposomes containing either\noxPC form SLBs by rupturing on contact with SiO<sub>2</sub> substrates,\nwhich differs from the typical adsorption-rupture pathway observed\nwith nonoxidized liposomes. We also show that increasing the oxPC\nconcentration in SLBs results in thinner bilayers that contain defects.\nSimulations reveal that the oxidized <i>sn</i>-2 tails of\nKDdiA-PC and KOdiA-PC bend out of the hydrophobic membrane core into\nthe hydrophilic headgroup region and beyond. The altered conformations\nof these oxPC, which are affected by cholesterol content and protonation\nstate of the oxidized functional groups, contribute to trends of decreasing\nmembrane thickness and increasing membrane area with increasing oxPC\nconcentration. This combined approach provides a comprehensive view\nof the biophysical properties of membranes containing KDdiA-PC and\nKOdiA-PC at the molecular level, which is crucial to understanding\nthe role of lipid oxidation in cardiovascular disease and related\nimmune responses.