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Biomedical subjects

Joseph Demeester

Publications and source records attributed to Joseph Demeester.

6 recordsLinked to original sources
PubMed2003

Mobility and stability of gene complexes in biogels.

The tenacious secretions lining the conductive airways of cystic fibrosis (CF) patients may pose a significant barrier to successful gene therapy to the lung. In this work, we evaluated the diffusion of nanospheres and cationic DOTAP lipoplexes through CF sputum and the influence of CF mucus components on the physicochemical properties and gene expression of cationic DOTAP lipoplexes and neutral, pegylated GL67 lipoplexes. The number of particles transported through the sputum was extremely low (<0.5%) and strongly depending on the size of the particles, with almost no transport for the largest nanospheres (560 nm). For small particles (<150 nm), the low transport was primarily due to the long distance they have to travel through the sputum, while for larger particles also sterical obstruction was responsible for the low transport. Upon exposure of the cationic DOTAP lipoplexes to albumin, linear DNA or mucin (at concentration ratios expected to occur in vivo) a significant decrease in gene transfection activity was observed. This was primarily due to aggregation of the lipoplexes. However, exposure of pegylated GL67 lipoplexes to the same components did not affect their gene transfection activity. Indeed, it was determined that CF mucus components did not interact significantly with these neutral, pegylated GL67 lipoplexes.

Biological Transport↗
PubMed2003

Encoding microcarriers by spatial selective photobleaching.

Bead-based assays on very large numbers of molecules in gene expression studies, drug screening and clinical diagnostics, require the encoding of each of the microspheres according to the particular ligand bound to its surface. This allows mixing the uniquely encoded microspheres and subjecting them to an assay simultaneously. When a particular microsphere gives a positive reaction, the substance on its surface can be identified by reading the code. Previously reported techniques for colour encoding polymer microspheres only allow for a limited number of unique codes. Graphical encoding methods use metallic particles, which are rather uncommon in screening applications. Here, we demonstrate a new approach to encode polymer microspheres that are commonly used in screening applications, such as polystyrene microspheres, with a method that provides a virtually unlimited number of unique codes. Patterns can be written in fluorescently dyed microspheres by 'spatial selective photobleaching' and can be identified by confocal microscopy. Such encoded microparticles can find broad application in the collection and analysis of genetic information, high-throughput screening, medical diagnostics and combinatorial chemistry, and can also be used for labelling of consumer goods or as security labels to prevent counterfeiting.

Microspheres↗
PubMed2002

A comparison between the use of dynamic mechanical analysis and oscillatory shear rheometry for the characterisation of hydrogels.

In this study the use of dynamic mechanical analysis (DMA) for the mechanical characterisation of pharmaceutical hydrogels was evaluated. DMA was used in two different modes, the "controlled force" and the "multi-strain" (MS). The results obtained on dextran methacrylate hydrogels of various compositions were compared to those obtained using an oscillatory shear rheometer. The best agreement was found between the MS-DMA and the rheometer results. The moduli measured in MS-DMA were extrapolated towards zero compression to obtain the modulus of the hydrogels. This procedure resulted in good agreement with the data obtained with the rheometer. Hydrogels were analysed after swelling to equilibrium with both methods, DMA and rheology. A scaling between the elastic modulus (G') and the equilibrium swollen polymer volume fraction (v(2,s)) could be found, although the best correlation between G' and v(2,s) was obtained with the rheometer.

Hydrogels↗
PubMed2002

On the transport of lipoplexes through cystic fibrosis sputum.

PURPOSE: The aim of this study was to examine the extent to which plasmid DNA (pDNA) complexed to cationic liposomes diffuse through cystic fibrosis (CF) sputum. The influence of the physical and chemical properties of the sputa was evaluated. We further investigated whether degradation of the sputa by recombinant human DNase I (rhDNase I) enhances the transport. METHODS: The transport of lipoplexes was studied through layers of CF sputa placed between the donor and acceptor compartment of vertical diffusion chambers. The content of the acceptor compartment was analyzed by confocal fluorescence microscopy, gel electrophoresis and Southern blotting. The influence of linear DNA present in the CF sputa on the size, surface charge and gene expression of the lipoplexes was evaluated by dynamic light scattering, particle electrophoresis and transfection experiments. RESULTS: Lipoplexes were observed in the acceptor compartments. However, the percent of diffused lipoplexes was low: 0.05/% +/- 0.01%. It was found that both steric obstruction by the sputa as well as the long" distance the lipoplexes have to travel were responsible for this low transport. Surprisingly, the transport occurred better through more viscoelastic sputa. The DNA in the CF sputa also retarded the transport, which was attributed to aggregation of the lipoplexes by the DNA. Finally, rhDNase I moderately enhanced the diffusion of lipoplexes. CONCLUSIONS: CF sputum drastically retards the diffusion of lipoplexes. DNA in the sputa aggregates the lipoplexes. This may lower the transport of lipoplexes through the sputa and gene expression. Pretreatment of CF patients with rhDNase I may enhance the efficiency of CF gene therapy, as it allows a better transport of the lipoplexes through the sputum and as it partly removes the sputum which will result in a thinner sputum layer on top of the epithelial cells.

Analysis of Variance↗
PubMed2002

Encoding microcarriers: present and future technologies.

In answer to the ever-increasing need to carry out many assays simultaneously in drug screening and drug discovery, several microcarrier-based multiplex technologies have arisen in the past few years. The compounds to be screened are attached to the surface of microcarriers, which can be mixed together in a vessel that contains the target analyte. Each microcarrier has to be encoded to know which compound is attached to its surface. In this article, the methods that have been developed for the encoding of microcarriers are reviewed and discussed.

Biological Assay↗