Exogenous molecules from dietary sources such as polyphenols are very efficient in preventing the alteration of lipid membranes by oxidative stress. Among the polyphenols, we have chosen to study rosmarinic acid (RA). We investigated the efficiency of RA in preventing lipid peroxidation and in interacting with lipids. We used liposomes of 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) to show that RA was an efficient antioxidant. By HPLC, we determined that the maximum amount of RA associated with the lipids was ~1 mol%. Moreover, by using Langmuir monolayers, we evidenced that cholesterol decreases the penetration of RA. The investigation of transferred lipid/RA monolayers by atomic force microscopy revealed that 1 mol% of RA in the membrane was not sufficient to alter the membrane structure at the nanoscale. By fluorescence, we observed no significant modification of membrane permeability and fluidity caused by the interaction with RA. We also deduced that RA molecules were mainly located among the polar headgroups of the lipids. Finally, we prepared DLPC/RA vesicles to evidence for the first time that up to 1 mol% of RA inserts spontaneously in the membrane, which is high enough to fully prevent lipid peroxidation without any noticeable alteration of the membrane structure due to RA insertion.
In cosmetics, there is some interest to solubilized polar antioxidant molecules in oil. This is a matrix that can indeed protect these fragile molecules against oxidation and that makes possible the polar antioxidants transfer through the epidermis in order to be delivered within the dermis. Varying the oil formulation allows the achievement of a high content of antioxidants in a natural vegetable oil using an oleo-eco extraction process. However, it was necessary to characterize this content using quantitative and efficient methods such as High-Performance Thin-Layer Chromatography technique. The aim of this work was to develop a method of antioxidant’s characterization with this technique without a preliminary re-extraction of the antioxidants.
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