Addition of Cleaved Tail Fragments during Lipid Oxidation Stabilizes Membrane Permeability Behavior

Lipid oxidation has been linked to plasma membrane damage leading to cell death. In previous work, we examined the effect of oxidation on bilayer permeability by replacing defined amounts of an unsaturated lipid species with the corresponding phospholipid product that would result from oxidative tail scission of that species. This study adds the cleaved tail fragment, better mimicking the chemical results of oxidation. Permeability of PEG12-NBD, a small, uncharged molecule, was measured for vesicles with oxidation concentration corresponding to between 0 and 18 mol % of total lipid content. Permeability was measured using a microfluidic trap to capture the vesicles and spinning disk confocal microscopy (SDCM) to measure the transport of fluorescent PEG12-NBD at the equatorial plane. The thicknesses of lipid bilayers containing oxidized species were estimated by measuring capacitance of a black lipid membrane while simultaneously measuring bilayer area. We found that relative to chemically modeled oxidized bilayers without tail fragments, bilayers containing cleaved tail groups were less permeable for the same degree of oxidation. Curiously, membrane capacitance measurements indicated that the addition of tail fragments to chemically modeled oxidized bilayers also thinned these bilayers relative to samples with no tail fragments; in other words, the more permeable membranes were thicker. Above 12.5% chemically modeled oxidation, compositions both with and without the cleaved tail groups showed pore formation. This work highlights the complexity of the relationship between chemically modeled lipid bilayer oxidation and cell membrane properties.