Complex rhamnolipid mixture characterization and its influence on DPPC bilayer organization.

Rhamnolipids (RL) are one of the most important classes of biosurfactants produced by microorganisms using a wide range of carbon sources, from a simple carbon source like glucose to complex wastes such as the used cooking oils used in this work. The objective of this work was to learn about the rhamnolipid-phospholipid dipalmitoyl phosphatidyl choline (DPPC) molecular interactions through the behaviour observed in the neat products and four RL/DPPC mixtures. Size and z-potential were used to characterize the size and the charge of the vesicles, and small angle X-ray scattering (SAXS) was used to measure the vesicle bilayer characteristics, and the release of carboxyfluorescein to study the bilayer disrupting effect promoted by rhamnolipids. The results show that rhamnolipids are disposed in ordered bilayers with long repeating distances, which are stabilized by the charging of the bilayer and also by a strong fluidity of the bilayers. The ability of rhamnolipids to increase the fluidity of DPPC bilayers may be related with the strong haemolytic power of these molecules.

Niosomes based on synthetic cationic lipids for gene delivery: the influence of polar head-groups on the transfection efficiency in HEK-293, ARPE-19 and MSC-D1 cells.

We designed niosomes based on three lipids that differed only in the polar-head group to analyze their influence on the transfection efficiency. These lipids were characterized by small-angle X-ray scattering before being incorporated into the niosomes which were characterized in terms of pKa, size, zeta potential, morphology and physical stability. Nioplexes were obtained upon the addition of a plasmid. Different ratios (w/w) were selected to analyze the influence of this parameter on size, charge and the ability to condense, release and protect the DNA. In vitro transfection experiments were performed in HEK-293, ARPE-19 and MSC-D1 cells. Our results show that the chemical composition of the cationic head-group clearly affects the physicochemical parameters of the niosomes and especially the transfection efficiency. Only niosomes based on cationic lipids with a dimethyl amino head group (lipid 3) showed a transfection capacity when compared with their counterparts amino (lipid 1) and tripeptide head-groups (lipid 2). Regarding cell viability, we clearly observed that nioplexes based on the cationic lipid 3 had a more deleterious effect than their counterparts, especially in ARPE-19 cells at 20/1 and 30/1 ratios. Similar studies could be extended to other series of cationic lipids in order to progress in the research on safe and efficient non-viral vectors for gene delivery purposes.

Study and formation of vesicle systems with low polydispersity index by ultrasound method.

The formation of liposomes with low polydispersity index by application of ultrasounds was investigated considering methodology specifications such as sonication time and sonication power. Phosphatidylcholine (PC) liposomes were formed by the evaporation-hydration method. The vesicles were sonicated using several sonication conditions. The liposomes were then characterized by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). Correlation functions from DLS were treated by cumulants method and GENDIST to obtain the mean radius and polydispersity index. These calculations allowed to fix an optimal sonication time (3000 s) and a useful interval of ultrasound power between 39 and 91 W. DLS and FFEM results confirmed that vesicle size, lamellarity and the polydispersity index decreased with the increase of sonication power. Thus, we propose a systematic method to form liposomes in which the physical characteristics of the vesicles may be controlled as a function of sonication time and power.

[Unusual imaging findings of Ewing sarcoma in the childhood]. / Manifestaciones radiológicas infrecuentes del sarcoma de Ewing en la infancia.

OBJECTIVES: To review the cases of Ewing's sarcoma (ES) diagnosed in children at our hospital from 1995 to 2005 and to analyze uncommon imaging signs at diagnosis or during the course of the disease. MATERIAL AND METHODS: We reviewed the cases of 21 patients with ES (12 boys and 9 girls) diagnosed between the ages of 2 and 14 years. We analyzed the types of presentation, the imaging findings (plain-films, CT, and MRI), and the patients' evolution. All cases were confirmed at histological study. RESULTS: The following uncommon manifestations were found in 11 patients: 2 vertebral, one cervical, and one dorsal ES that initially manifested as spinal cord compression and as a mediastinal mass, respectively; 2 sacral ES with ascending epidural masses; 1 mandibular ES; 1 costal ES with hemorrhagic cerebral metastases; 3 extraskeletal (thigh, buttocks, and pelvis minor) ES with bone metastases at diagnosis: the first two had spinal cord and nerve compression due to vertebral metastases; 2 ES had benign-appearing radiological findings (cortical lesion of the radius with osseous remodeling of the ulna and an expanding multilocular lesion of the fibula). CONCLUSIONS: Although ES is the second most common malignant bone tumor in children, its unusual imaging findings are less well known. More than half (52.4 %) of our last 21 patients presented some of these manifestations at diagnosis or during follow-up, so radiologists should be aware of them and include ES in the prebiopsy diagnostic possibilities.

Effect of the electrostatic charge on the mechanism inducing liposome solubilization: a kinetic study by synchrotron radiation SAXS.

The anionic surfactant sodium dodecyl sulfate (SDS) was used to induce the initial steps of the solubilization of liposomes. The structural transformations as well as the kinetics associated with this initial period were studied by means of time-resolved small-angle X-ray scattering (SAXS) using a synchrotron radiation source. Neutral and electrically charged (anionic and cationic) liposomes were used to investigate the effect of the electrostatic charges on the kinetics of these initial steps. The mechanism that induces the solubilization process consisted of adsorption of surfactant on the bilayers and desorption of mixed micelles from the liposomes surface to the aqueous medium. In all cases the time needed for desorption of the first mixed micelles was shorter than that for complete adsorption of the surfactant on the liposomes surface. The present work demonstrates that adsorption of the SDS molecules on negatively charged liposomes was slower and release of mixed micelles from the surface of these liposomes was faster than for neutral liposomes. In contrast, in the case of positively charged liposomes, the adsorption and release processes were, respectively, faster and slower than those for neutral vesicles.