The Effects of Photosensitized Lipid Oxidation on Supported Lipid Bilayer Formation and Membrane Deformation

Abstract

Lipid oxidation by reactive oxygen species (ROS) has a number of negative consequences in biology. Additionally, photosensitized lipid oxidation has been explored as a way to trigger drug release from liposomal containers. In this work we explore the effects of photosensitized lipid oxidation on the interactions of phospholipid vesicles with SiO2 surfaces. Using quartz crystal microbalance with dissipation monitoring (QCM-D), we determined that light exposure radically alters the pathway of supported lipid bilayer (SLB) formation for vesicles that contain lipid-conjugated fluorophores. Instead of the well-established two-step adsorption-rupture pathway, vesicles that have undergone photosensitized peroxidation rupture immediately upon encountering the SiO2 surface. The alteration of the vesicle rupture pathway seems to be dependent on the molecular position of the fluorescent moiety. Vesicles containing phospholipids with a BODIPY fluorophore conjugated to their fatty acid tails show the most pronounced effects. On the other hand, vesicles containing lipids with NBD conjugated to their head or tail groups show negligible differences compared to controls. We also show that antioxidants such as alpha-tocopherol (vitamin E) can attenuate the effects of photo peroxidation on the rupture pathway. Fluorescence microscopy was also used to observe lipid oxidation of a SLB, the effects of which cause membrane defects, namely membrane tubulation followed by vesiculation. Image analysis has been used to probe the characteristics of these defects, including the length of the tubes, the diameter of the subsequent vesicles, and the rate of growth of each. A direct correlation has been observed between tube length and vesicle diameter, and that the rate of growth for tubulation and vesiculation slows over time.