Jean Doucet

Organization of Stratum Corneum Lipids in Relation to Permeability: Influence of Sodium Lauryl Sulfate and Preheating

The role of the structural organization of intercorneocyte lipids in the barrier function of human stratum corneum was evaluated by treatment with heat and sodium lauryl sulfate. Measurement of transepidermal water loss in treated samples was used to quantify variations in stratum corneum permeability. Thermodynamic transition of lamellar lipids and their degree of organization were evaluated by differential scanning calorimetry and small-angle X-ray diffraction, respectively. Progressively preheating stratum corneum samples from 75°C to 90°C increased stratum corneum permeability to water vapor, while the fusion temperature of lamellar lipids and the intensity of the X-ray diffraction peaks of the polar lipids decreased. Sodium lauryl sulfate induced similar variations of these three parameters. These results support the hypothesis that, in addition to the chemical nature of intercorneocyte lipids, their structural arrangement and thermodynamic properties play an important role in the barrier function of the stratum corneum to water vapor.

Carbon nanotubes in macrophages: Imaging and chemical analysis by X-ray fluorescence microscopy

X-ray fluorescence microscopy (microXRF) is applied for the first time to study macrophages exposed to unpurified and purified single-walled (SW) and multiwalled (MW) carbon nanotubes (CNT). Investigating chemical elemental distributions allows one to (i) image nanotube localization within a cell and (ii) detect chemical modification of the cell after CNT internalization. An excess of calcium is detected for cells exposed to unpurified SWCNT and MWCNT and related toxicological assays are discussed.

Modifications induced on stratum corneum structure after in vitro iontophoresis: ATR-FTIR and X-ray scattering studies

The aim of the present work was to investigate stratum corneum (s.c.) structure after prolonged in vitro iontophoresis by two physical techniques: ATR-FTIR and X-ray scattering. ATR-FTIR studies showed that iontophoresis induced an important and reversible increase in the hydration of the outer layers of s.c. but no increase in lipid fluidity could be detected. SAXS (small angle X-ray scattering) of s.c. showed that iontophoresis induced a disorganisation of the lipid layers stacking reversible within a few days. No modification of the intralamellar crystalline packing of lipids nor of keratin were observed by WAXS (wide angle X-ray scattering). From our ATR-FTIR and X-ray scattering observations, it can be assumed that the enhancement in transdermal permeation which characterizes iontophoresis is related to the lipid layer stacking disorganisation.

Structure and Function of Human Stratum corneum under Deformation

Background: The stratum corneum (SC) has an important barrier function. The effect of a mechanical stress applied to the SC is controversial on this important physiological parameter. Objective and Methods: To assess both in vitro and in vivo the structure and function of human SC submitted to controlled strains, we measured the transepidermal water loss (TEWL), in vivo, on human skin submitted to controlled strains ranging from 0 to 20% extension imposed by a Densi-score device. We also looked at the structure of the SC by means of X-ray diffraction and transmission electron microscopy. Results: Transmission electron microscopy and X-ray diffraction analysis were performed on harvested and stretched human SC. TEWL was not significantly influenced by the relative deformation applied to the skin. At high strain (60%) imposed in vitro to the SC, lipid bilayers and corneosomes were detached from corneocytes. Only rare corneosomes showed internal disruption. X-ray analysis did not reveal modifications in the supramolecular organization of intercellular lipids while stretching the SC. Conclusion: Submitting human SC to an extension force up to 20% elongation does not significantly alter the barrier function.

Improved DNA/emulsion complex stabilized by poly(ethylene glycol) conjugated phospholipid

Recently, finding correlations between the structure of lipid-DNA complexes and their biological activity is gaining more interest (1–3). One major drawback associated with in vivo lipid mediated gene delivery is relatively low transfection efficiency due to poor stability of the complex upon contact with serum (4,5). Given that the transfection efficiency of lipid-DNA complexes highly depends on its structural and physico-chemical properties, a detailed description of these particles is necessary. Strong electrostatic interactions between positively charged lipid-DNA complexes and negatively charged proteins in the blood are responsible for the rapid aggregation of lipid-DNA complexes upon contact with serum. One way to overcome the problem of serum instability and to prolong their circulation time in the blood is to protect their surface by adding PE-PEG (6). Hong et al. (1) reported reduced aggregation of cationic liposome/DNA complex by incorporating a small amount of PE-PEG into the formulation, but the size of their particles is still very large. Recently, Blessing et al. (7) obtained small and negatively charged plasmid-detergent particles, which because of the absence of targeting ligand, failed to show any biological activity. More recently, Monck et al. (8) reported extended circulation time of small, stabilized plasmid-lipid particles following intravenous administration. In vitro transfection studies performed by Liu et al. (9) showed that the transfection activity of tween 80-containing emulsions was not affected by the presence of serum. More recently, Yi et al. (10) developed a physically stable and serum-resistant, cationic oil-in-water emulsion containing DNA for in vitro delivery. Previously, we reported that intraportal injection of cationic DNA/emulsion resulted in high level of gene expression in the liver but poor transfection efficiency following intravenous administration (11). Based on this study, we report the first physico-chemical study on the development of a new DNA/emulsion formulation stabilized by PE-PEG for in vivo administration.

Hard alpha-keratin degradation inside a tissue under high flux X-ray synchrotron micro-beam: A multi-scale time-resolved study

X-rays interact strongly with biological organisms. Synchrotron radiation sources deliver very intense X-ray photon fluxes within micro- or submicro cross-section beams, resulting in doses larger than the MGy. The relevance of synchrotron radiation analyses of biological materials is therefore questionable since such doses, million times higher than the ones used in radiotherapy, can cause huge damages in tissues, with regard to not only DNA, but also proteic and lipid organizations. Very few data concerning the effect of very high X-ray doses in tissues are available in the literature. We present here an analysis of the structural phenomena which occur when the model tissue of human hair is irradiated by a synchrotron X-ray micro-beam. The choice of hair is supported by its hierarchical and partially ordered keratin structure which can be analysed inside the tissue by X-ray diffraction. To assess the damages caused by hard X-ray micro-beams (1 microm(2) cross-section), short exposure time scattering SAXS/WAXS patterns have been recorded at beamline ID13 (ESRF) after various irradiation times. Various modifications of the scattering patterns are observed, they provide fine insight of the radiation damages at various hierarchical levels and also unexpectedly provide information about the stability of the various hierarchical structural levels. It appears that the molecular level, i.e. the alpha helices which are stabilized by hydrogen bonds and the alpha-helical coiled coils which are stabilized by hydrophobic interactions, is more sensitive to radiation than the supramolecular architecture of the keratin filament and the filament packing within the keratin associated proteins matrix, which is stabilized by disulphide bonds.

MASSIS: A Mass Spectrum Simulation System. 1. Principle and Method:

A mass spectrum simulation system was developed. The simulated spectrum for a given target structure is computed based on the cleavage knowledge and statistical rules established and stored in pivot databases: cleavage rule knowledge, functional groups, small fragments and fragment-intensity relationships. These databases were constructed from correlation charts and statistical analysis of a large population of organic mass spectra using data mining techniques. Since 1980, several systems have been proposed for mass spectrum simulation, but at present there is no commercial software available. This shows the complexity and difficulties in the development of such a system. The reported mass spectral simulation system in this paper could be the first general software for organic chemistry use.

Quantitative Structure Activity Relationships for Carboxamides and Related Compounds Active on Aedes aegypti Adult Females

Aedes aegypti mosquitoes are important vectors in the transmission of severe diseases responsible for million deaths per year. Intensive use of insecticides results in environmental damages and induced resistance in mosquitoes. Search for new molecules devoid of detrimental side effects is therefore an urgent need. In this context, we derived QSAR models for evaluating the acute toxicity of 74 carboxamides and related chemicals to females of Ae. aegypti. These models based on PaDEL, 2D topological descriptors or CODESSA, 2D/3D geometrical and quantum variables, involved multilinear regression (MLR), and various machine learning methods namely support vector machine (SVM), projection pursuit regression (PPR) and artificial neural network (ANN). We considered first the full dataset, and then, a more homogeneous, reduced set of 50 compounds with non-conjugated carbonyl. In all cases, for data fitting and leave-one-out cross-validation, satisfactory results were attained. Good performance was also obtained for extended validation sets. Generally speaking, the modeling methods were broadly equivalent. PaDEL 2D descriptors worked better than 2D/3D CODESSA descriptors. A hybrid model combining the two descriptor sets gave improved results. Setting such QSAR models, linking activity to structural features of examined chemicals, will be of interest for prioritizing experimental tests on new candidates, and evaluate their toxicity and potential synergist effects.