Lipid oxidation has been implicated as a potential molecular mechanism of oxidative damage in a variety of disease states, including atherosclerosis, neurodegenerative diseases, and hyperbaric oxygen toxicity. We have studied the kinetics of photo-induced phospholipid bilayer oxidation using giant unilamellar vesicles (GUVs) as model membranes. Incorporating rhodamine-labeled 1,2-dipalmitoyl-sn-glycero-3-phosphoethanoamine (Rh-DPPE) as photosensitizer to generate highly reactive singlet oxygen at the surface of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) GUVs, we observed a two-phase morphological transformation. Within minutes of irradiation, the membrane area increased, resulting in vesicle flattening and high-amplitude membrane fluctuations. After reaching a maximum area, the membrane began contracting, causing the GUVs to became tumid with a surface tension sufficient to exceed the critical limit for pore formation. The periodic micron-scale opening of pores was observed as step-decreases in vesicle size below pre-oxidation dimensions. The growth and shrinkage behaviors were analyzed as consecutive rate-limiting reaction steps, allowing estimates of molecular size changes and the rate constants of the underlying chemical events. Dependence of these kintetics on irradiation intensity and on concentrations of Rh-DPPE and DOPC were considered. Furthermore, experiments varying membrane DOPC content were repeated at ten-fold increased aqueous viscosity to slow down fluid leakage and allow for more accurate measurement of pore closure rates. The calculated decreased line tension with higher DOPC concentration suggests that oxidation products stabilize pores and compromize membrane barrier properties.

Photooxidation-induced morphological deformation of lipid bilayers: Kinetics of surface area changes

247th National Meeting (2014)

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