I. C. Kwon

Preparation of chitosan self-aggregates as a gene delivery system

Hydrophobically modified chitosan containing 5.1 deoxycholic acid groups per 100 anhydroglucose units was synthesized by an EDC-mediated coupling reaction. Formation and characteristics of self-aggregates of hydrophobically modified chitosan were studied by fluorescence spectroscopy and dynamic light scattering method. The critical aggregation concentration (cac) of the self-aggregate was determined by measuring the fluorescence intensity of pyrene as a fluorescent probe. The cac value in PBS solution (pH 7.2) was 1.7x10(-2) mg/ml. Mean diameter of self-aggregates in PBS solution (pH 7.2) was 162 +/- 18 nm with an unimodal size distribution. Charge complex formation between self-aggregates and plasmid DNA was confirmed by electrophoresis on an agarose gel. Migration of DNA on an agarose gel was completely retarded above a charge ratio ( +/-) of 4/1 at pH 7.2. The free DNA dissociated from the complexes was observed by electrophoresis above pH 8.0 at a fixed charge ratio of 4/1. An efficient of COS-1 cells was achieved by self-aggregates/DNA complexes.

Gene delivery to the rat liver using cationic lipid emulsion/DNA complex: comparison between intra-arterial, intraportal and intravenous administration.

Objective To compare the efficiency of intra-arterial, intraportal, and intravenous administration of cationic lipid emulsion/DNA complex, as used for gene transfer to rat liver. Materials and Methods DNA-carrier complex for the in-vivo experiment was prepared by mixing DNA and a cationic lipid emulsion. According to the administration route used (intra-arterial, intraportal, or intravenous), the animals were assigned to one of three groups. The heart, lung, liver, spleen and kidneys were removed and assayed for total protein and luciferase concentration. Results The cationic lipid emulsion/DNA complex used successfully transfected the various organs via the different administration routes employed. Luciferase activity in each organ of untreated animals was negligible. Liver luciferase values were significantly higher in the groups in which intra-arterial or intraportal administration was used. Conclusion The intra-arterial or intraportal administration of cationic lipid emulsion/DNA complex is superior to intravenous administration and allows selective gene transfer to the liver.

Counterion effects on transfection activity of cationic lipid emulsion

Cationic lipid emulsion systems consisting of 1,2-dioleoyl-sn-glycero-3-trimethyl-ammonium-propane (DOTAP) and plasmid DNA with various counterions in the lipid headgroups were prepared. The transfection activity of the cationic lipid emulsion systems was then investigatedin vitro andin vivo. The complex formation of plasmid DNA and lipid emulsion was affected by the counterions through charged headgroup repulsion and also by the salt concentration in the media. As such, the transfection activity of the DOTAP emulsion system can be controlled by changing the counterions.

The Study of Antibiotic Drug-Loaded Polymer Films for the Prevention of the Infection of External Fixation Devices

The purpose of the present study was to develop a polymer film loaded with drug to effectively prevent pin tract infection. It was found that the polymer, poly ethylene-co-vinyl acetate blended with tetrahydrofuran, showed better flexibility and deformability than the other polymers: poly caprolactone18 and poly caprolactone44. Polymer films, poly ethylene-co-vinyl acetate, were divided into five testing groups dependent on the loading concentration of rifampici (5, 10, 15, and 20 wt %). The surface morphology of polymer films was examined by a scanning electron microscopy. It was found that the concentration of drug was a main factor to determine the roughness of the film. Considering the roughness of polymer films, 5 wt % of rifampicin might be the maximum concentration for further applications. Hence, the antibiotic drug-loaded polymer films were manufactured by mixing poly(ethylene-co-vinylacetate) and tetrahydrofuran with rifampicin(antibiotic drug). The film cast was designed as a shape of disk (inner Ø5mm and outer Ø20mm) to be suitable for pins for external fixation in orhtopaedics. The drug-loaded polymer solvent, the amount of 0.6cc, was molded into the disk-shaped film and dried into a airtight box at 15°C for 24 hrs. The drug release characteristics(1, 2, 3, 4 and 5 wt%) were examined as a function of soaking time in phosphate buffered saline (PBS, 10 ml) using an enzyme-linked immunosorbent assay. Rifampicin was linearly released for first 100 hrs(~4 days) for all antibiotic drug-loaded polymer films. Afterward, the drug was released at a slower pace as a function of square root of time until 1000 hrs (~40 days). This slow drug release can be explained by their hydrophobic characteristics of poly ethylene-co-vinyl acetate and rifampicin. The antibiotic drug-loaded polymer film can be intrinsically able to prevent the bacteria adhesion by wrapping the pin track area, and perform active and effective infection-resistant by a sustained antibiotic-release.

Release Profile of a Model Protein Drug Depending on the Stability of Microspheres Based on Polyelectrolyte Complex

Stability and disintegration of natural polyelectrolyte complex microspheres for protein drugs delivery have been extensively investigated because of their great influence on the drug release patterns. In this study, we tested stability of microspheres with alginate (Alg) core layered by either chitosan (Chi) or glycol chitosan (GChi) by examining release profiles of fluorophorelabeled bovine serum albumin (BSA) and lysozyme (Lys) from the microspheres. While GChi shell was disintegrated quickly, Chi-shell microspheres showed good stability in PBS. Disintegration of the coated layer induced the core material instable. The results indicated that while the charges of the shell material provided additional diffusion barrier against the protein release, the key factor to hold the proteins inside the microspheres was the integrity of the outer coating layer.