Biomimesis of linolenic acid transport through model lipidic membranes by differential scanning calorimetry

Multienoic fatty acids, such as linolenic acid, show their ability to interact with and to penetrate into model biomembranes by biomimetic experiments performed to support the absorption route followed by n-3 fatty acid in cells. The thermotropic behavior of model biomembranes, that is, dimyristoylphosphatidylcholine multilamellar or unilamellar vesicles, interacting with linolenic acid was investigated by differential scanning calorimetry. When dispersed in liposomes during their preparation, the examined biomolecule was found to interact with the phospholipid bilayers by modifying the gel to liquid-crystal phase transition of lipid vesicles; this modification is a function of the fatty acid concentration. Calorimetric analysis was also performed on samples obtained by leaving the pure n-3 acid in contact with lipid aqueous dispersions (multilamellar or unilamellar vesicles) and then examining the thermotropic behavior of these systems for increasing incubation times at temperatures higher than the transitional lipid temperature. Linolenic acid (LNA) was able to migrate through the aqueous medium and successively to interact with the vesicle surface and to penetrate into the model membranes, following a flip-flop mechanism, with a faster and higher effect for unilamellar vesicles, caused by the larger lipid surface exposed, compared to the multilamellar ones, although due to the lipophilic nature of LNA, such a transfer is hindered by the aqueous medium. The relevance of the medium in LNA absorption has been well clarified by other biomimetic transfer experiments, which showed the LNA transfer from loaded multilamellar vesicles to empty vesicles. Taken together, the present findings support the hypothesis of a passive n-3 acid transport as the main route of absorption into cell membranes.