Sylvie Bégu

Synthesis and characterisation of ibuprofen-anchored MCM-41 silica and silica gel

A non-steroidal anti-inflammatory drug (ibuprofen) has been anchored inside the mesoporous channels of MCM-41-type silica and on a silica gel surface. The relevant anchoring procedure through an ester function has been investigated. It uses the epoxide ring opening of 3-glycidoxypropylsilane grafted on the silica surface by the carboxylic-group-containing ibuprofen. The control of the surface modification and of the anchoring efficiency was achieved by comparison of spectroscopic data with those obtained using homogeneous counterparts. The use of nanostructured silica allowed an accurate verification of the different surface modifications and also a higher drug loading.

Investigation of the interface in silica-encapsulated liposomes by combining solid state NMR and first principles calculations.

In the context of nanomedicine, liposils (liposomes and silica) have a strong potential for drug storage and release schemes: such materials combine the intrinsic properties of liposome (encapsulation) and silica (increased rigidity, protective coating, pH degradability). In this work, an original approach combining solid state NMR, molecular dynamics, first principles geometry optimization, and NMR parameters calculation allows the building of a precise representation of the organic/inorganic interface in liposils. {(1)H-(29)Si}(1)H and {(1)H-(31)P}(1)H Double Cross-Polarization (CP) MAS NMR experiments were implemented in order to explore the proton chemical environments around the silica and the phospholipids, respectively. Using VASP (Vienna Ab Initio Simulation Package), DFT calculations including molecular dynamics, and geometry optimization lead to the determination of energetically favorable configurations of a DPPC (dipalmitoylphosphatidylcholine) headgroup adsorbed onto a hydroxylated silica surface that corresponds to a realistic model of an amorphous silica slab. These data combined with first principles NMR parameters calculations by GIPAW (Gauge Included Projected Augmented Wave) show that the phosphate moieties are not directly interacting with silanols. The stabilization of the interface is achieved through the presence of water molecules located in-between the head groups of the phospholipids and the silica surface forming an interfacial H-bonded water layer. A detailed study of the (31)P chemical shift anisotropy (CSA) parameters allows us to interpret the local dynamics of DPPC in liposils. Finally, the VASP/solid state NMR/GIPAW combined approach can be extended to a large variety of organic-inorganic hybrid interfaces.

Preparation and characterization of siliceous material using liposomes as template

Material synthesis using unilamellar liposomes with a high sol-gel temperature transition phase as a template leads to a new silica material.

The control of dendritic cell maturation by pH-sensitive polyion complex micelles.

Double-hydrophilic block copolymer micelles were designed as vectors for ex vivo dendritic cell engineering to improve the delivery of therapeutic molecules in such immune cells. Polymethacrylic acid-b-polyethylene oxide (PMAA(2100)-b-POE(5000))/poly-L-lysine micelles were optimised and showed a hydrodynamic diameter of 30 nm with a peculiar core organised with hydrogen bonds as well as hydrophobic domains. The micelles proved high stability in physiological conditions (pH and ionic strength) and were also able to disassemble under acidic conditions mimicking acidic endolysosomes. The efficient endocytosis of the optimised micelles tested on bone marrow-derived dendritic cells was monitored by fluorescence-activated cell sorting and microscopy analysis. Finally, the micelle biocompatibility permitted a complete control of the dendritic cell-maturation process widening the therapeutical potential of such engineered dendritic cells for cancer vaccines as well as for immunomodulation in autoimmune diseases.

Characterization of a phospholipid bilayer entrapped into non-porous silica nanospheres

Using liposomes as templates is one of the paths leading to the synthesis of silica spherical particles. In these particles, the silica wall is assembled onto the external surface of the liposome. Generally, the walls of the resulting silica spheres are porous and in the specific case of liposome templating, the exact state of the trapped lipids is undocumented. In this work we describe the characterization of a new non-porous silica material obtained by templating liposomes. We show that the liposomes trapped in the nanospheres retain most of the structural and dynamic properties of the free liposomes. Also, as a consequence of the non-porous nature of the silica cladding the inner aqueous pool is permanently retained. To the best of our knowledge, silica nanospheres with such promising properties have so far not been obtained. These properties make these hybrid silica nano-spheres, referred to as liposils, potentialy good candidates for the storage and delivery of drugs.

pH-sensitive double-hydrophilic block copolymer micelles for biological applications

In the recent years, double-hydrophilic block copolymer (DHBC) micelles have appeared as potential vectors for pharmaceutical applications due to their simple preparation method in aqueous solvent. The present study aims at underscoring the strategy for the choice of the partners in the formulation of DHBC micelles presenting a good stability in physiological conditions (pH 7.4, 0.15 mol/L NaCl) and a pH-sensitivity allowing their disassembly at pH 5. Using light scattering and Laser-Doppler electrophoresis, micelles of polymethacrylic acid-b-polyethylene oxide complexing either poly-l-lysine (PLL) or an oligochitosan were characterised. Whatever the polyamine counter-polyion considered, the micelles were perfectly formed for an amine/methacrylic acid molar charge ratio of one. They were characterised by a hydrodynamic diameter of 28 nm for PLL and 60 nm for oligochitosan and by a neutral zeta potential. The stability study as a function of the pH and of the ionic strength revealed different behaviours. Oligochitosan micelles were stable until pH 7 and unstable at 0.15 mol/L NaCl. On the contrary, PLL micelles were stable in physiological conditions and disassembled at pH 5. As a conclusion, the choice of the partners to formulate double-hydrophilic block copolymer based-micelles is strategic in order to obtain well-adapted vectors applied to the pharmaceutical field.

Density Functional Theory-Based Conformational Analysis of a Phospholipid Molecule (Dimyristoyl Phosphatidylcholine)

The conformational space of the dimyristoyl phosphatidylcholine (DMPC) molecule has been studied using density functional theory (DFT), augmented with a damped empirical dispersion energy term (DFT-D). Fourteen ground-state isomers have been found with total energies within less than 1 kcal/mol. Despite differences in combinations of their torsion angles, all these conformers share a common geometric profile, which includes a balance of attractive, repulsive, and constraint forces between and within specific groups of atoms. The definition of this profile fits with most of the structural characteristics deduced from measured NMR properties of DMPC solutions. The calculated vibrational spectrum of the molecule is in good agreement with experimental data obtained for DMPC bilayers. These results support the idea that DMPC molecules preserve their individual molecular structures in the various assemblies.

Development of tripartite polyion micelles for efficient peptide delivery into dendritic cells without altering their plasticity

For many years, a great deal of interest has been focusing on the optimization of peptide presentation by dendritic cells (DCs) using peptide-encapsulated particles, in order to enhance the immune response. Nowadays, DCs are also known to be involved in peripheral tolerance, inducing anergy or regulatory T lymphocytes. To preserve the plasticity of DCs, we formulated non-cytotoxic pH-sensitive polyion complex micelles based on an original tripartite association of polymethacrylic acid-b-polyethylene oxide, poly-L-lysine and fluorescent-peptide: OVAFITC peptide, as a model drug. We demonstrated that the OVAFITC peptide was successfully entrapped into the micelles, released into DC endosomes thanks to the pH-sensitivity property of the micelles, and efficiently loaded onto MHC class II molecules. The phenotype as well as the cytokinic secretion profile of the mature and immature DCs loaded with peptide-encapsulated micelles was unaltered by the tripartite polyion micelles. The efficient loading of the peptide by immature and mature DCs was shown by the in vitro proliferation of OVA-specific transgenic T cells. Therefore, the present results show that the tripartite polyion complex micelles can be used as efficient peptide vectors immunogically inert for ex vivo DCs engineering without modifying their intrinsic immune plasticity.

Laser-induced primary and secondary hemostasis dynamics and mechanisms in relation to selective photothermolysis of port wine stains

BACKGROUND Superficial vascular anomalies such as port wine stains are commonly treated by selective photothermolysis (SP). The endovascular laser-tissue interactions underlying SP are governed by a photothermal response (thermocoagulation of blood) and a hemodynamic response (thrombosis). Currently it is not known whether the hemodynamic response encompasses both primary and secondary hemostasis, which platelet receptors are involved, and what the SP-induced thrombosis kinetics are in low-flow venules. OBJECTIVES To (1) define the role and kinetics of primary and secondary hemostasis in laser-induced thrombus formation and (2) determine which key platelet surface receptors are involved in the hemodynamic response. METHODS 532-nm laser-irradiated hamster dorsal skin fold venules were studied by intravital fluorescence microscopy following fluorescent labeling of platelets with 5(6)-carboxyfluorescein. Heparin and fluorescently labeled anti-glycoprotein Ib-α (GPIbα) and anti-P-selectin antibodies were administered to investigate the role of coagulation and platelet receptors, respectively. Lesional sizes were quantified by software. RESULTS Laser irradiation consistently produced sub-occlusive thermal coagula. Thrombosis was triggered in all irradiated venules in a thermal coagulum-independent manner and peaked at 6.25min post-irradiation. Heparin decreased the maximum thrombus size and caused thrombosis to reach a maximum at 1.25min. Immunoblocking of GPIbα abated the extent of thrombosis, whereas immunoblocking of P-selectin had no effect. CONCLUSIONS The hemodynamic response ensues the photothermal response in a thermal coagulum-independent manner and involves primary and secondary hemostasis. Primary hemostasis is mediated by constitutively expressed GPIbα but not by activation-dependent P-selectin.

Quercetin topical application, from conventional dosage forms to nanodosage forms.

Skin is a multifunctional organ with activities in protection, metabolism and regulation. Skin is in a continuous exposure to oxidizing agents and inflammogens from the sun and from the contact with the environment. These agents may overload the skin auto-defense capacity. To strengthen skin defense mechanisms against oxidation and inflammation, supplementation of exogenous antioxidants is a promising strategy. Quercetin is a flavonoid with very pronounced effective antioxidant and antiinflammatory activities, and thus a candidate of first choice for such skin supplementation. Quercetin showed interesting actions in cellular and animal based models, ranging from protecting cells from UV irradiation to support skin regeneration in wound healing. However, due to its poor solubility, quercetin has limited skin penetration ability, and various formulation approaches were taken to increase its dermal penetration. In this article, the quercetin antioxidant and antiinflammatory activities in wound healing and supporting skin against aging are discussed in detail. In addition, quercetin topical formulations from conventional emulsions to novel nanoformulations in terms of skin penetration enhancement are also presented. This article gives a comprehensive review of quercetin for topical application from biological effects to pharmaceutical formulation design for the last 25 years of research.