Size Control of Mixed Egg Yolk Phosphatidylcholine (EggPC)/Oleate Vesicles

Abstract

Incorporation of surfactants into vesicles lead to structural change of the vesicles followed by vesicle-to-micelle transition. The studies on this process have contributed to size regulation of vesicles prepared by removing detergent from detergent-phospholipid mixed micelles. [1][2][3][4] Fatty acids are one kind of surfactants whose properties are different from the others, that is, the fatty acids exist as micellar form above pH 9 but they can spontaneously form vesicles in the appropriate conditions. [5][6][7][8][9] Luisi et al. have made interesting reports using dynamic light scattering, freeze fracture electron microscopy and cryotransmission electron microscopy as follows: when sodium oleate micellar solution was added into suspension of preformed oleate vesicles or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles, the size of newly formed vesicles was similar to that of the preformed vesicles and preformed vesicles remarkably expedited the rate of new vesicles organization.10-13) They called this phenomenon "matrix effect". However, normally average vesicular size in matrix effect was close to the size of preformed vesicles as far as the sizes were evaluated by quasielastic light scattering, which leading us to some misunderstanding of size distribution of newly formed vesicles.To obtain more precise information relating size distribution with easier techniques, we started to study on this effect by the combination of gel filtration chromatography/quasielastic light scattering and found that the technique could provide more detailed insight into size distribution of newly formed vesicles without misapprehension as detection with mere dynamic light scattering technique. The study of this report deals with the effect of size variation of preformed vesicles as well as the influence of molar ratios EggPC/oleate on the size distribution of newly formed vesicles. Oleate solution was added to preformed egg yolk phosphatidylcholine vesicles with two original sizes followed by gel filtration on Sephacryl S-1000. The size of the vesicles and phospholipid and oleate concentrations of each fraction after gel filtration were analyzed. The results showed the final size distribution was somewhat dependent on the former vesicular size. ExperimentalMaterials Egg yolk phosphatidylcholine (EggPC; purity of PCϭ98.8%) was purchased from Nihon Yushi (Tokyo, Japan). Oleic acid sodium salt (98%), boric acid (99.5%), sodium chloride and calcein were purchased from Nacalai Tesque (Kyoto, Japan). All these materials were used without further purification. Methods. Preparation of Liposomal SuspensionLiposomes were prepared by the extrusion method as described below. A desired amount of phospholipids was dissolved in chloroform/methanol (2 : 1, v/v) mixture, dried into a thin film on the wall of a glass tube under a stream of nitrogen. The remaining solvent was then removed under reduced pressure for more than 6 h. The lipids were then resuspended in a borate buffer solution (0.15 M NaCl, 0.1 M borate, pH 8.5) cont...

New Vesicle Formation upon Oleate Addition to Preformed Vesicles

“…We started to study to clear the mechanism. The results of our study using gel exclusion chromatography showed the presence of new small vesicles after addition of oleate in micellar form to preformed vesicles 7,8) in contrast to the results reported by Luisi et al Therefore, in this report, we study profoundly size distribution of new vesicles upon oleate addition in different forms to preformed egg yolk phosphatidylcholine (EggPC) vesicles.…”

“…3). The elution profile after oleate micellar addition to preformed EggPC vesicles with a size of 50 nm has been reported, 7,8) and the reported profile is similar to the profile after addition of oleate in vesicular form (Fig. 2C).…”

“…7,8) One-day incubation was confirmed to be sufficient because the elution patterns on gel chromatography of the samples of 1-d incubation were not different from those of 1-h incubation. Gel exclusion profiles of preformed oleate vesicles (50 nm, 260 nm) and preformed EggPC vesicles (50 nm, 175 nm) before mixing are shown in Fig.…”

Fatty acid vesicles

“…Although the physicochemical properties of fatty acid vesicles have been studied to some extent in the last three decades, there are still many aspects that require more detailed studies, e.g. regarding a model explaining the matrix effect [47][48][49] and fatty acid vesicle reproduction [26 • ]. The permeability of fatty acid vesicles to various classes of molecules remains largely unexplored.…”

Spectroscopic studies of D-α-tocopherol concentration-induced transformation in egg phosphatidylcholne vesicles

“…The results of this study, using dynamic light scattering, turbidometry and optical microscopy methods, show that in aqueous solutions, the amphiphilic properties of PC lead to the formation of supramolecular aggregates, ranging in size from small single-bilayer vesicles and small unilamellar vesicles to giant multilamellar vesicles. This occurs as a result of dynamic intermolecular interactions that exist within a single phase [37]. It is known that the size of the formed vesicles depends on Laplace pressure, interfacial tension, concentration, temperature and the presence of other components.…”