Eulalie Lafarge

Lipid hydroperoxidation significantly changes membrane biophysical properties, yet its effect on the main phase transition of unsaturated phospholipids remains unclear. Here, we investigate how hydroperoxidation of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) influences its phase behavior. Bilayers composed of SOPC and increasing fractions of hydroperoxidized SOPC (SOPC-OOH) were analyzed using differential scanning calorimetry, the band shift of the new solvatochromic probe A10, and Laurdan generalized polarization fluorescence. The incorporation of hydroperoxidized acyl chains perturbed membrane thermodynamics, revealing a complex phase-transition landscape governed by the interplay between acyl-chain ordering and the spatial distribution of –OOH groups. These results highlight the sensitivity of lipid phase behavior to oxidative modifications at the molecular level and provide new insights into how lipid peroxidation modulates membrane organization in cellular and biomimetic systems.

Formation de pores dans les membranes de lipides oxydés: Les membranes biologiques sont principalement composées de lipides s’assemblant en bicouches imperméables empêchant le transport de différentes molécules à l’intérieur de la cellule. L’électroporation est une technique récemment développée, utilisée en thérapie pour insérer des principes actifs ou des gènes à l’intérieur des cellules afin d’augmenter l’efficacité du traitement et réduire les effets secondaires. En appliquant un stress électrique aux membranes, des pores se forment, augmentant considérablement la perméabilité des membranes. L’électroporation est utilisée pour soigner de nombreuses maladies, souvent liées à la présence de lipides oxydés, compromettant les propriétés structurelles et mécaniques des membranes, entrainant le mauvais fonctionnement de mécanismes biologiques essentiels.Il est pertinent d’étudier les membranes hydroperoxydées, afin d’avoir une meilleure caractérisation de leur propriétés mécaniques et structurelles et de l’influence de l’hydroperoxydation sur la perméabilité des membranes et leur capacité à former des pores. Nous avons mis en évidence un amincissement de la membrane accompagné d’une fluidité et élasticité modifiées. Ces changements induisent une augmentation de la perméabilité et de la formation de pores obtenus durant l’électroporation de membranes suspendues.

The standard model of pore formation was introduced more than fifty years ago, and it has been since, despite some refinements, the cornerstone for interpreting experiments related to pores in membranes. A central prediction of the model concerning pore opening under an electric field is that the activation barrier for pore formation is lowered proportionally to the square of the electric potential. However, this has only been scarcely and inconclusively confronted to experiments. In this paper, we study the electropermeability of model lipid membranes composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) containing different fractions of POPC-OOH, the hydroperoxidized form of POPC, in the range 0 to 100 mol %. By measuring ion currents across a 50-μm-diameter black lipid membrane (BLM) with picoampere and millisecond resolution, we detect hydroperoxidation-induced changes to the intrinsic bilayer electropermeability and to the probability of opening angstrom-size or larger pores. Our results over the full range of lipid compositions show that the energy barrier to pore formation is lowered linearly by the absolute value of the electric field, in contradiction with the predictions of the standard model.

Lipid peroxidation is a process which is key in cell signaling and disease, it is exploited in cancer therapy in the form of photodynamic therapy. The appearance of hydrophilic moieties within the bilayer’s hydrocarbon core will dramatically alter the structure and mechanical behavior of membranes. Here, we combine viscosity sensitive fluorophores, advanced microscopy, and X-ray diffraction and molecular simulations to directly and quantitatively measure the bilayer’s structural and viscoelastic properties, and correlate these with atomistic molecular modelling. Our results indicate an increase in microviscosity and a decrease in the bending rigidity upon peroxidation of the membranes, contrary to the trend observed with non-oxidized lipids. Fluorescence lifetime imaging microscopy and MD simulations give evidence for the presence of membrane regions of different local order in the oxidized membranes. We hypothesize that oxidation promotes stronger lipid-lipid interactions, which lead to an increase in the lateral heterogeneity within the bilayer and the creation of lipid clusters of higher order.

Trans-Resveratrol (RV) was encapsulated in multi-lamellar liposomes (MLLs) composed of a mixture of phosphatidylcholine (P100), Tween 80 and water. The P100-to-T80 ratio as well as their water content were chosen based on a previous study to promote transdermal transport of RV. The effect of RV on the size, elasticity, and charge of MLLs was evaluated as well as the effect of encapsulation on the apparent solubility of RV. The diffusion of RV and MLLs in artificial skin, namely Strat-M™, was monitored by confocal Raman imaging, and compared with that of a RV solution and empty MLLs, while the transdermal passage rate was measured by UV-vis spectrophotometry on both artificial and excised human skin. RV was found to remain localized in the outer layer of the skin with less than 3% passing through it over a 24hour period in both skin types. Encapsulation in MLLs drastically increased its transdermal passage: 73 ±10% after 3 h of incubation on excised human skin, and 10% on Strat-M™ after 9 h. Whereas RV in its free form underwent cis isomerization, MLLs protected it up to 9h before undergoing chemical degradation after 24h.