Excitation of Fluorescent Lipid Probes Accelerates Supported Lipid Bilayer Formation via Photosensitized Lipid Oxidation

Abstract

Fluorescent lipid probes are commonly used to label membranes of cells and model membranes like giant vesicles, liposomes, and supported lipid bilayers (SLB). Here, we show that excitation of fluorescent lipid probes with BODIPY-like conjugates results in a significant acceleration of the rupture and SLB formation process for unsaturated phospholipid vesicles on SiO 2 surfaces. The resulting SLBs also have smaller measured masses, which is indicative of a reduction in membrane thickness and/or membrane density. The excitation of fluorescent probes with NBD and Texas Red conjugates does not accelerate the SLB formation process. In the absence of fluorescent probes or light, the inclusion of oxidized phospholipids also accelerates SLB formation. The excitationinduced acceleration caused by BODIPY-like probes is eliminated when the probes are present with saturated phospholipids not susceptible to oxidation, and it is attenuated when a lipophilic antioxidant (α-tocopherol) is present. These results suggest that BODIPY−phospholipid conjugates are photosensitizers, and their excitation causes oxidation of lipid membranes, which significantly alters membrane properties.

Tubulation of Supported Lipid Bilayer Membranes Induced by Photosensitized Lipid Oxidation

“…In our previous work, we observed that illuminated vesicles composed of DOPC and 2% TR-DHPE ruptured on SiO 2 surfaces similarly to the same vesicles that had not been illuminated, suggesting that TR-DHPE is an ineffective photosensitizer for lipid oxidation, at least at the 2% level. 36 Thus, the lack of light-triggered membrane tubulation in SLBs containing TR-DHPE agrees with our earlier conclusions. We also probed lower concentrations of TF-PC by forming SLBs containing 1 and 0.5 mol % TF-PC (Figure S3).…”

“…A previous work from our group showed that the exposure of vesicles containing TF-PC to highintensity broadband light resulted in the acceleration of the vesicle rupture and SLB formation. 36 Prior to analysis of lighttriggered SLB tubulation, we examined the formation of SLBs from DOPC precursor vesicles with and without TF-PC to show that the presence of 2% TF-PC does not significantly alter the formation of SLB membranes. Figure S1 shows vesicles containing 2% TF-PC form SLB membranes much the same as the vesicles that are composed solely of DOPC.…”

“…In this study, we demonstrate that lipid oxidation, initiated by the membrane-linked photosensitizer TopFluor-PC (TF-PC), 36 causes the tubulation of SLBs. Photo-oxidation occurs when a photosensitizer is excited, creating reactive species that attack the surrounding lipids; photodynamic therapy exploits this process and has become an approved cancer treatment method in recent years.…”

Structural and Nanotribological Properties of a BODIPY Self-Assembly

“…In addition to the advantages of high extinction coefficients and high quantum yields, BODIPY is reasonably stable to physiological environment because of the insensitivity to the polarity and pH conditions (Karolin et al, 1994;Loudet and Burgess, 2007). Therefore, BODIPY dyes have been widely applied in a variety of fields including fluorescence labeling agents (Madhu et al, 2013;Kim et al, 2016;Baxter and Wittenberg, 2019), chemosensors (Atilgan et al, 2010;Wang et al, 2015;Yu et al, 2016), fluorescent switches (Golovkova et al, 2005;Moreno et al, 2016), photovoltaics/ optoelectronics (Lee and Hupp, 2010;Bura et al, 2012;El-Khouly et al, 2014) and so on.…”