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S Lesieur

Publications and source records attributed to S Lesieur.

11 recordsLinked to original sources
PubMed2000

Phase behavior of fully hydrated DMPC-amphiphilic cyclodextrin systems.

With the aim of exploring relationships between the chemical structure and the physico-chemical properties of amphiphilic beta-cyclodextrin, a reappraisal of the obtaining of pure heptakis (2,3-di-O-hexanoyl)-beta-cyclodextrin (beta-CDC(6)) was undertaken. In this paper the chemical characterization of the newly synthesized beta-CDC(6) and its ability to form mixed structures with dimyristoylphosphatidylcholine (DMPC) are reported. Miscibility of the two amphiphiles is examined: (i) in monolayers formed at the air-water interface by analyzing the surface pressure-area isotherms; and (ii) in fully hydrated mixtures by differential scanning calorimetry (DSC) and X-ray diffraction at small and wide angles. Results demonstrate that the beta-cyclodextrin derivative is partially miscible to the phospholipid: intimate mixing occurs at beta-CDC(6) molar ratios smaller than 7-15 mol%, depending on the dimensional scale considered, while beyond these compositions phase separation is observed. At the air-water interface, the miscibility region of the two compounds shows non-ideal behavior characterized by the non-additivity of the molecular areas in the mixed monolayers. At the three-dimension level, the formation of a beta-CDC(6)/DMPC mixed lamellar phase occurs except at beta-CDC(6) molar ratios close to 5 mol% at which a highly ordered structure is depicted below the solid-to-liquid state transition of the DMPC hydrocarbon chains. At beta-CDC(6) contents higher than 7 mol%, the mixed assemblies coexist with excess amphiphilic cyclodextrin which then forms a separated hexagonal structure.

Calorimetry, Differential Scanning↗
PubMed1998

Methodology for vesicle permeability study by high-performance gel exclusion chromatography.

A methodology based on high-performance gel exclusion chromatography (HPLC-GEC) has been developed to perform permeability studies of vesicles. Encapsulation of two marker isothiocyanate fluorescein (FITC) dextrans of 4400 and 40,500 molecular mass was used as a model system. Combination of two TSK-PW columns, one efficient in vesicle sizing (G6000 PW), the other in that of dextrans (G4000 PW), was required to achieve complete particle separation and to remove entirely the unentrapped dextran after encapsulation into vesicles. Coupling fluorescence and light scattering detection allowed to control the efficiency of the separation, to quantify the vesicle leakage and to follow both the integrity of the vesicles and changes in their size. This methodology can be applied to other fields such as encapsulation of water soluble compounds and drug delivery systems.

Chromatography, Gel↗
PubMed1998

New sterically stabilized vesicles based on nonionic surfactant, cholesterol, and poly(ethylene glycol)-cholesterol conjugates.

Monomethoxypoly(ethylene glycol) cholesteryl carbonates (M-PEG-Chol) with polymer chain molecular weights of 1000 (M-PEG1000-Chol) and 2000 (M-PEG2000-Chol) have been newly synthesized and characterized. Their aggregation behavior in mixture with diglycerol hexadecyl ether (C16G2) and cholesterol has been examined by cryotransmission electron microscopy, high-performance gel exclusion chromatography, and quasielastic light scattering. Nonaggregated, stable, unilamellar vesicles were obtained at low polymer levels with optimal shape and size homogeneity at cholesteryl conjugate/ lipids ratios of 10 mol% M-PEG1000-Chol or 5 mol% M-PEG2000-Chol, corresponding to the theoretically predicted brush conformational state of the PEG chains. At 20 mol% M-PEG1000-Chol or 10 mol% M-PEG2000-Chol, the saturation threshold of the C16G2/cholesterol membrane in polymer is exceeded, and open disk-shaped aggregates are seen in coexistence with closed vesicles. Higher levels up to 30 mol% lead to the complete solubilization of the vesicles into disk-like structures of decreasing size with increasing PEG content. This study underlines the bivalent role of M-PEG-Chol derivatives: while behaving as solubilizing surfactants, they provide an efficient steric barrier, preventing the vesicles from aggregation and fusion over a period of at least 2 weeks.

Cholesterol↗
PubMed1998

Evaluation of the hydrophobic drug loading characteristics in nanoprecipitated amphiphilic cyclodextrin nanospheres.

The aim of this work was to evaluate the loading capacity and the association characteristics of the hydrophobic drug progesterone on amphiphilic cyclodextrin nanospheres prepared by the nanoprecipitation method. The colloidal suspensions were prepared in the presence or absence of two different surfactants, Pluronic F68 and Tween 80. The physicochemical characteristics of the nanospheres were assessed using a nanosizer, zetameter, and transmission electron microscope. The physical state of the drug was verified using differential scanning calorimetry (DSC) and x-ray diffraction (XRD) methods. The in vitro progesterone release was investigated at 37 degrees C after dilution of the suspensions in sink conditions. Nanospheres with a mean diameter from 100 to 300 nm and a low degree of polydispersity were prepared from amphiphilic hexanoyl-gamma-cyclodextrin. The progesterone loading capacity was not affected by the formulation parameters tested. The DSC and XRD studies demonstrated the absence of the crystalline domains of progesterone in loaded nanospheres. The DSC studies also demonstrated the presence of interactions between the drug and carrier. The release of the drug from the carrier was extremely rapid and was governed by a partition phenomenon that depends only on the solubility of the drug in the release medium. From these results, we concluded that with this method, the progesterone is molecularly associated at the surface of the cyclodextrin nanospheres, probably through hydrophobic interactions in specific sites. The release profiles obtained can be of value when an improvement in the bioavailability of the drug is desired.

Calorimetry, Differential Scanning↗
PubMed1997

Structure of in-serum transfecting DNA-cationic lipid complexes.

Noticeable modifications of in-serum transfection efficiency of dioctadecylamidoglycyl-spermine (DOGS)-DNA complexes are observed, depending on DNA condensation conditions. The structures of the complexes are studied, keeping in mind the variability of lipid polymorphism, by cryo-transmission electron microscopy and X-ray diffraction. By increasing both pH and ionic strength, well-organised lamellar structures with a period of 65 A replace supramicellar aggregates. A relationship between the structures and their in-vitro transfection activity is established. Efficiency in the presence of serum is maintained when a lamellar arrangement is involved.

3T3 Cells↗
PubMed1997

Thermotropic phase behavior of in vivo extracted human stratum corneum lipids.

The thermotropic phase behavior of lipids extracted either in vivo from inner forearm (SCLE) or plantar callus (PC) was investigated by differential scanning calorimetry and small angle X-ray diffraction. PC composition was chromatographically modified (MPC) by eliminating the more polar lipids in order to evaluate their role. Analysis of composition confirms the potential use of PC as a source of stratum corneum lipids. MPC and SCLE exhibit similar differential scanning calorimetry (DSC) profiles with a main transition around 50 degrees C attributed to the solid-to-liquid phase transition of the ceramides. The absence of a transition around 50 degrees C for PC suggests the possible perturbation of ceramide packing by the significantly high proportion of phospholipids. X-ray data suggest a high miscibility of sebum components in stratum corneum lipids with possible modification of chain packing. The MPC patterns show a lipid phase separation which underscores the role of polar lipids in cholesterol/free fatty acids/sterol esters/ceramides structural cohesion.

Adult↗
PubMed1995

Partition coefficient of a surfactant between aggregates and solution: application to the micelle-vesicle transition of egg phosphatidylcholine and octyl beta-D-glucopyranoside.

The mechanism of the solubilization of egg phosphatidylcholine containing 10% (M/M) of egg phosphatidic acid unilamellar vesicles by the nonionic detergent, octyl beta-D-glucopyranoside, has been investigated at both molecular and supramolecular levels by using fluorescence and turbidity measurements. In the lamellar region of the transition, the solubilization process has been shown to be first a function of the initial size before reaching an equilibrium aggregation state at the end of this region (the onset of the micellization process). The analysis during the solubilization process of the evolution of both the fluorescence energy transfer between N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-phosphatidylethanolamine (NBD-PE) and N-(lissamine rhodamine B sulfonyl)-phosphatidylethanolamine (Rho-PE) and the fluorescence of 6-dodecanoyl-2-dimethylaminoaphtalene (Laurdan) has allowed us to determine the evolution of the detergent partitioning between the aqueous and the lipidic phases, i.e., the evolution of the molar fraction of OG in the aggregates (XOG/Lip) with its monomeric detergent concentration in equilibrium ([OG]H2O), throughout the vesicle-to-micelle transition without isolating the aqueous medium from the aggregates. The curve described by XOG/Lip versus [OG]H2O shows that the partition coefficient of OG is changing throughout the solubilization process. From this curve, which tends to a value of 1/(critical micellar concentration), five different domains have been delimited: two in the lamellar part of the transition (for 0 < [OG]H2O < 15.6 mM), one in the micellization part, and finally two in the pure micellar region (for 16.5 < [OG]H2O < 21 mM). The first domain in the lamellar part of the transition is characterized by a continuous variation of the partition coefficient. In the second domain, a linear relation relates XOG/Lip and [OG]H2O, indicating the existence of a biphasic domain for which the detergent presents a constant partition coefficient of 18.2 M-1. From the onset to the end of the solubilization process (domain 3), the evolution of (XOG/Lip) with [OG]H2O can be fitted by a model corresponding to the coexistence of detergent-saturated lamellar phase with lipid-saturated mixed micelles, both in equilibrium with an aqueous phase, i.e., a three-phase domain. The micellar region is characterized first by a small two-phase domain (domain 4) with a constant partition coefficient of 21 M-1, followed by a one-phase mixed-micellar domain for which XOG/Lip no longer linearly depends on [OG]H2O. The results are discussed in terms of a phase diagram.

Animals↗
PubMed1993

Reconstitution of non-ionic monoalkyl amphiphile-cholesterol vesicles by dilution of lipids-octylglucoside mixed micelles.

Kinetic aspects of the formation of non-ionic surfactant vesicles (NSV) using the mixed micelle dilution procedure are examined. Mixed micelles composed of a mixture of lipids, i.e. diglycerol hexadecylether (C16G2), cholesterol (CHOL), dicetylphosphate (DCP) and detergent, octylglucoside (OG), were diluted with detergent-free buffer added either instantaneously or progressively at different rates ranging from 3.47 x 10(-2) to 6.94 x 10(-4) ml/min. The resulting particles were analysed by quasielastic light scattering (QELS), high performance liquid chromatography (HPLC) on gel exclusion column and cryogenic transmission electron microscopy (cryo-TEM). NSV exhibit mean diameters (MD) varying from 100 to 600 nm depending on the kinetics of OG removal. When the dilution of mixed micelles is instantaneous the vesicles are characterized by a spherical shape and MD values close to 100 nm. They show narrow size distribution and stability for 2 months. NSV recovered with progressive micelle dilution, at fast buffer addition rates (3.47 x 10(-2) and 1.39 x 10(-2) ml/min) exhibit MD values of 170-240 nm, elongated shapes, low polydispersities and 2-month stabilities. When the rate of buffer addition is lowered to 6.94 x 10(-4) ml/min, unstable particles with larger MD values and broad size distributions are obtained. Turbidity monitoring at 350 nm and 25 degrees C was used to characterize the lipids-OG mixed aggregate rearrangements either as a function of time when detergent-free buffer was continously added to the mixed micelles or after equilibrium setting when the micelles were instantaneously diluted. In the latter case the intermediate aggregates were also analysed by QELS. For continuous dilutions, the molecular composition of aggregates, [OG/lip]agg, as well as the OG concentration in the aqueous medium, [OG]bulk, were determined at the break points observed on the plots of optical density (OD) versus total OG concentration ([OG]tot). [OG/lip]agg and [OG]bulk values are independent of the rate of buffer addition, suggesting that the micelle to NSV transition is not mainly limited by the kinetics of the molecular processes involved during detergent removal from the mixed aggregates. The examination of the apparent partition coefficient of OG between the aqueous phase and the lipidic aggregates shows, however, that OG depletion from the bilayered structures is more difficult than its elimination from the mixed micelles. QELS analysis of the intermediate lipids-detergent aggregates, performed with time, demonstrates very slow supramolecular rearrangements during the vesicle closure. These rearrangements explain the significant increase in both size and polydisperity of the final vesicles observed with slow rates of buffer addition.

Cholesterol↗
PubMed1991

Size analysis and stability study of lipid vesicles by high-performance gel exclusion chromatography, turbidity, and dynamic light scattering.

Vesicles of egg phosphatidylcholine (EPC) and phosphatidic acid (EPA) were prepared by reverse-phase evaporation (REV) followed either by sequential extrusion through polycarbonate membranes with pore diameters of 0.8, 0.4, 0.2, 0.1, and 0.05 micron or by filtration through 0.8-micron cellulosic or 0.22-micron polyvinylidene fluoride (PVF) membranes. The resulting vesicles ranging from 130 to 640 nm in mean diameter (REVs) were characterized by high-performance liquid chromatography (HPLC) using a TSK G6000 PW gel exclusion column. The efficiency of this technique to determine vesicle size parameters was studied by the analysis of the chromatograms in combination with dynamic light scattering (DLS) determination of the mean diameters (MD) of the fractionated vesicles in the region of the elution profile maxima. The HPLC TSK G6000 PW gel exclusion provides a reproducible and fast method of size characterization for lipid vesicles having MD up to 1 micron, the best selectivity being obtained in the 20- to 500-nm MD range. HPLC analysis of REV's demonstrates that: (i) both the average size and polydispersity of the vesicles decrease with decreasing pore size of the membranes, cellulosic or PVF "tortuous" ones being less efficient than "straight bores" polycarbonate ones; (ii) mixed EPC/EPA REVs sequentially extruded down through 0.2-micron polycarbonate membranes are highly deformable without rupture of the bilayer; and (iii) the mean size of extruded REV's is stable for at least 1 week. The role of EPA on the size stability of mixed EPC/EPA vesicles was studied by coupling HPLC gel exclusion and turbidity analysis of pure EPC and EPC/EPA (mole ratio: 91/9) sonicated small unilamellar vesicles as a function of time. The apparent size variation of EPC vesicles observed over a week, is mainly due to their aggregation which is significantly reduced by the introduction of a small amount of EPA in the vesicle membrane.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Self-evolving microstructured systems upon enzymatic catalysis.

The consequences of cell microstructuration on enzyme functions is discussed in the framework of self-evolving microstructured systems. Molecular assemblies of amphiphiles or lipids are spontaneously formed by self-organisation. Among these different structures, reversed micelles, liquid crystalline mesophases and vesicles are hosts for enzymatic reaction studies. Inside a living cell, phospholipid metabolism is responsible for membrane structural modifications; the catalytic behaviour of lipolytic enzymes, mainly phospholipase (PL) A2, is described in relation with structural aspects of biological membranes. The implication in cellular regulation events of PLC and PLD is discussed in relation with the role of their reaction products as second messengers in membrane fusion processes. The in vitro synthesis of dialkyl phosphatidylcholines, via the enzymatic 'salvage pathway' which leads to the formation of vesicles upon phospholipid formation, is considered in relation with autopoiesis. More recent studies on self-evolving systems based on enzyme-surfactants reactions are detailed. The interactions between amphiphilic aggregates and enzymes allow to explore the OG/octanol/water phase diagram. Enzymatic formation of dipalmitoylphosphatidylcholine (DPPC) liposomes and non-ionic surfactant vesicles (NSV), starting from mixed micelles or open structures, finally sets an example of a biomimetic self-evolving system.

Cholesterol↗