Giant Vesicles Under Oxidative Stress

We use optical microscopy to observe giant unilamellar vesicles (GUVs) during the initial steps of membrane oxidative damage. A photo-sensitive molecule consisting of a porphyrine linked to a lipid headgroup (PE-porf) is incorporated in the lipid bilayer, thus generating singlet oxygen at the bilayer surface. This system enables studies on the effects of lipid peroxidation in a more controlled fashion, allowing threshold determinations of membrane oxidative damage. We show that irradiation of GUVs containing PE-porf induces immediate increase in vesicle surface area, with accompanying morphological changes. Because porphyrin is rapidly photo-bleached, the oxidation process is halted during the initial formation of hydroperoxides and membrane disruption is avoided. The increase in surface area is quantified as a function of irradiation time and the amount of PE-porf incorporated. The increase in area was related to the migration of hydroperoxides to the polar interface. The coupling of lipid peroxidation to morphological changes of natural membranes may be involved in the activation of different cellular responses to oxidative stress.