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Biomedical subjects

T W Chung

Publications and source records attributed to T W Chung.

At least 19 recordsLinked to original sources
PubMed2004

Effects of alginate coated on PLGA microspheres for delivery tetracycline hydrochloride to periodontal pockets.

The effects of alginate coated on tetracycline (Tc) loaded poly (D, L-lactic-co-glycolic acid) (PLGA) microspheres fabricated by double emulsion solvent evaporation technique for local delivery to periodontal pocket were investigated. Alginate coated PLGA microspheres showed smoother surface but enlarged their particle sizes compared with those of uncoated ones. In addition, alginate coated microspheres enhanced Tc encapsulation efficiency (E.E.) from 11.5 +/- 0.5% of uncoated ones to 17.9 +/- 0.5%. Moreover, all of the coated PLGA microspheres even fabricated at different conditions could prolong Tc release from 9-12 days with 50% or higher in cumulative release of Tc compared with those of uncoated ones. The swelling ratios of PLGA microspheres for alginate coated or uncoated ones, one of the possible mechanisms for enhancing Tc release for the coated ones, were measured. The results showed that 20% or higher in swelling ratio for the coated microspheres at the earlier stage of hydration (e.g. < or = 24 h) could be an important factor to result in high Tc release compared to the uncoated ones. In conclusion, alginate coated Tc loaded PLGA microspheres could enhance Tc delivery to periodontal pocket by enhancing drug encapsulated efficiency, released quantities and sustained release period compared with uncoated ones.

Alginates↗
PubMed2003

Release of ciprofloxacin from poloxamer-graft-hyaluronic acid hydrogels in vitro.

Recently, in situ gel formation has extensively been studied to enhance ocular bioavailability and duration of the drug activity. In this study, we report grafting of poloxamer onto the hyaluronic acid for application of tissue engineering oriented ophthalmic drug delivery system. Graft copolymers were prepared by coupling mono amine-terminated poloxamer (MATP) with hyaluronic acid (HA) backbone using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxylsuccinimide (NHS) as coupling agents. The coupling of MATP with HA was clarified by 1H NMR and FT-IR spectroscopy. The gelation temperature of graft copolymers was dependent on the content of HA and the concentration of poloxamer. From drug release studies in vitro, ciprofloxacin was sustainedly released from the poloxamer-g-hyaluronic acid hydrogel due to the in situ gel formation of the copolymer and viscous properties of HA.

Ciprofloxacin↗
PubMed2001

Molecular cloning and characterization of Mycobacterium bovis BCG pcp gene encoding pyrrolidone carboxyl peptidase.

The Mycobacterium bovis bacilli Calmette-Guerin (BCG) pcp gene that encodes the pyrrolidone carboxyl peptidase (Pcp) was cloned from a lambdagtll genomic library and sequenced. The nucleotide sequence contains a 669 bp open reading frame coding for a protein of 222 amino acid residues with a calculated molecular mass of 23,209 Da. The deduced amino acid sequence is highly homologous to the Pcps from Bacillus amyloliquefaciens, Pseudomonas fluorescens, Bacillus subtilis, Streptococcus pyogenes, and Staphylococcus aureus. A multiple sequence alignment revealed highly conserved domains. The BCG pcp gene was overexpressed in Escherichia coli. The Pcp was purified to homogeneity. The recombinant protein was further confirmed by an enzymatic assay.

Amino Acid Sequence↗
PubMed2001

Effects of the rate of solvent evaporation on the characteristics of drug loaded PLLA and PDLLA microspheres.

We investigated the effects of the rate of solvent removal by varying ambient pressure at a fixed temperature on the morphology, particle sizes, drug encapsulation efficiency and releases pattern of lidocaine loaded poly-L-lactatide (PLLA) and poly-D,L-lactatide (PDLLA) microspheres, prepared with O/W emulsion-solvent evaporation process. Prepared in the fast rate of solvent evaporation (FRSE) process by reducing ambient pressure, smoothly morphological surface of drug loaded PLLA and PDLLA microspheres was observed. While in the normal rate of solvent evaporation (NRSE) process, roughness or pinhole surface was only found at drug loaded PLLA microspheres. Fabricated in the FRSE process, both PLLA and PDLLA microspheres showed smaller particle sizes and lower drug encapsulation efficiencies than those prepared in NRSE process. In regard to two materials, PLLA microspheres had higher drug encapsulation efficiencies than PDLLA ones for both processes. Although initial burst releases of drug were observed for both PLLA and PDLLA microspheres prepared in whatever solvent removal process, drug release for PLLA microspheres was slightly less than that for PDLLA ones in the earlier stage of drug release. However, in the subsequent stage of drug release, there was no difference between two materials. In corporation with different crystalline characteristics of PLA polymer and its derivatives, FRSE process by reducing ambient pressure could be further applied to produce different characteristics of microspheres for drug delivery.

Lidocaine↗
PubMed2001

Molecular cloning and functional expression of the rfaE gene required for lipopolysaccharide biosynthesis in Salmonella typhimurium.

The rfaE (WaaE) gene of Salmonella typhimurium is known to be located at 76min on the genetic map outside of the rfa gene cluster encoding core oligosaccharide biosynthesis of lipopolysaccharide(LPS). The rfaE mutant synthesizes heptose-deficient LPS; its LPS consists of only lipid A and 3-deoxy-D-manno-octulosonic acid (KDO), and the rfaE gene is believed to be involved in the formation of ADP-L-glycero-D-manno-heptose. Mutants, which make incomplete LPS, are known as rough mutants. Salmonella typhimurium deep-rough mutants affected in the heptose region of the inner core often show reduced growth rate, sensitivity to high temperature and hypersensitivity to hydrophobic antibiotics. We have cloned the rfaE gene of S. typhimurium. The chromosomal region carrying this gene was isolated by screening a genomic library of S. typhimurium using the complementation of S. typhimurium rfaE mutant. The 2.6-Kb insert in the plasmid pHEPs appears to carry a functional rfaE gene. SL1102 (rfaE543) makes heptose-deficient LPS and has a deep rough phenotype, but pHEPs complement the rfaE543 mutation to give the smooth phenotype. The sensitivity of SL1102 to bacteriophages (P22.c2, Felix-O, Br60) which use LPS as their receptor for adsorption is changed to that of wild-type strain. The permeability barrier of SL1102 to hydrophobic antibiotics (novobiocin) is restored to that of wild-type. LPS produced by SL1102 (rfaE543) carrying pHEPs makes LPS indistinguishable from that of smooth strains. The rfaE gene encoded a polypeptide of 477 amino acid residues highly homologous to the S. enterica rfaE protein (98% identity), E. coli (93% identity), Yersenia pestis (85% identity), Haemophilus influenzae (70% identity) and Helicobacter pyroli (41% identity) with a molecular weight 53 kDa.

Amino Acid Sequence↗
PubMed2001

Growth of endothelial cells on different concentrations of Gly-Arg-Gly-Asp photochemically grafted in polyethylene glycol modified polyurethane.

To improve endothelial cell adhesion and growth on the surface of polyethylene glycol modified polyurethane (PU-PEG), cell adhesive peptide Gly-Arg-Gly-Asp (GRGD) was photochemically grafted to the surface. The surface grafted GRGD-N-Succinimidyl-6-[4'-azido-2'-nitrophenylamino]hexanoate (SANPAH) on a PU-PEG surface was performed by adsorption and subsequent ultraviolet irradiation. Fourier transform infrared spectra (FTIR) and electron spectroscopy for chemical analysis (ESCA) confirmed the GRGD grafted to form a PU-PEG-GRGD surface. The composition fraction of nitrogen calculated from ESCA analysis for the PU-PEG-GRGD surface was well correlated with the concentration of GRGD to be immobilized. Human umbilical vein endothelial cells (ECs) were well adhered and growing on the PU-PEG-GRGD surface. Moreover, the viability of ECs growing on PU-PEG-GRGD surfaces, analyzed by MTT test, was also well correlated with the GRGD concentrations immobilized on the surface. With photochemical techniques, we could manipulate different contents of GRGD to form multiple regions of PU-PEG-GRGD surface that could enhance the growth of ECs on the surface, and the enhancement efficiency was well correlated with GRGD contents.

Cell Adhesion↗
PubMed1999

A method using biodegradable polylactides/polyethylene glycol for drug release with reduced initial burst.

Post-coating of biodegradable polylactides (PLA)/polyethylene glycol (PEG) microspheres with a gelatin film produced by dipping the microspheres into a gelatin solution to reduce the initial drug release burst was investigated. Biodegradable block PLA/PEG microspheres, prepared by w/o emulsion/solvent evaporation, showed that the hydrophilic segment PEG protruded to the sphere surface. However, these microspheres also showed a large burst release in the initial period. Post-coating of the PLA/PEG microspheres with a gelatin film by dipping the microspheres into a dilute gelatin solution effectively inhibited the initial burst release rate in the drug release tests. Post-coating of gelatin reduced 98% of the burst release. With thicker coatings, there were slower releasing rates, and the release rate can be simply related to the coating thickness.

Anti-Arrhythmia Agents↗
PubMed1999

PE-PEG/LEH can reduce its interactions with plasma expanders indexed through viscosity measurements.

To investigate whether PE-PEG coated LEH (PE-PEG/LEH) can reduce its interaction with different plasma expanders and possibly suspended in those expanders, we measured the viscosity of PE-PEG/LEH suspended in different plasma expanders as an index for the interactions. The results showed that lower viscosity values for PE-PEG/LEH were observed compared with LEH especially in low shear rate regions (e.g., 7.72 +/- 1.46 cp vs. 14.91 +/- 1.03 cp for gamma = 2.25 sec-1, respectively). Moreover, the viscosity values for PE-PEG/LEH suspended in fibrinogen suspensions were much less than those of LEH in the same media at low shear rate regions (e.g., 7.72 +/- 1.59 cp vs. 25.78 +/- 1.59 cp, gamma = 2.25 sec-1, respectively). Similar results were observed for PE-PEG/LEH suspended in 1.83% of oxypolygelatin (Gel) suspensions and 1.5% hydrooxyethyl starch (HES) compared to LEH in the same suspension media. On contrast, PE-PEG/LEH suspended in dextran (Dex) showed that dramatically increasing the viscosity values in low shear rates compared with LEH suspended in the same media (e.g., 78.87 +/- 0.56 cp vs. 51.08 +/- 3.52 cp, gamma = 2.25 sec-1, respectively) were observed. Since only minor interactions with Gel, HES or fibrinogen suspensions were observed, we suggest that PE-PEG/LEH suspended in those media but not in Dex can possibly serve for resuscitation oxygen-carrying fluids.

Animals↗
PubMed1999

Changes in viscosity of low shear rates and viscoelastic properties of oxidative erythrocyte suspensions.

We exposed erythrocytes in soluble hemoglobin and Fe+2, in which hydroxyl radical (OH*) might be generated, and measured low shear rate viscosity and viscoelasticity of erythrocyte suspensions at Hct of 40%. The quantities of the lipid peroxidation product, malonyldialdehyde (MDA), for oxidized samples were higher than that for control (e.g., 2.20 +/- 0.46 nmol and 1.70 +/- 0.42 nmol, n = 6, p = 0.01, respectively). The viscosity values of oxidized erythrocyte suspensions for all tested shear rates were higher than those for the control samples (p < 0.05 or better, n = 6). Dynamic viscosity (eta') of oxidized erythrocyte samples was higher than that of control samples at the tested shear stress of 30 mPa whereas it was not observed in elasticity values (eta"). We tentatively concluded from the study, that oxidized erythrocytes would be more prone to form aggregates and increase viscosity of blood at low shear rates. Therefore, they might impair blood flow in the microcirculation.

Adult↗
PubMed1998

Reducing lipid peroxidation stress of erythrocyte membrane by alpha-tocopherol nicotinate plays an important role in improving blood rheological properties in type 2 diabetic patients with retinopathy.

The effects of alpha-tocopherol nicotinate on blood viscoelasticity and viscosity and on lipid peroxidation stress in erythrocyte membranes in patients with Type 2 DM were investigated. Thirteen Type 2 diabetic subjects with retinopathy were given alpha-tocopherol nicotinate 300 mg tds, after meals, for 3 months. The treatment resulted in significant reductions of blood viscosity at different shear rates (e.g. -2.23 +/- 2.82 p<0.015, gamma = 1.5 s(-1)) and viscoelasticity (p<0.004); resistance of erythrocyte deformation (p<0.001) and lipid peroxidation stress in red cell membrane (malondialdehyde or MDA reduced by 0.17 +/- 0.13 nmol l(-1) p<0.005). Plasma viscosity, red cell rigidity, and HbA1c were unchanged. There were negative linear correlations between the indices of red cell deformability and the levels of MDA of red cell membrane both pre- and post-treatment (e.g. R = -0.79, p<0.001; R = -0.78, p<0.002, n = 13; pre- and post-, respectively). We suggest that the improvements of rheological properties of blood and red cell deformability by alpha-tocopherol nicotinate are mainly attributed to reducing lipid peroxidation stress on membrane of red blood cells. The treatment may be useful in slowing deterioration of microangiopathy in Type 2 DM.

Aged↗
PubMed1998

A biotin-avidin labeled enzyme immunoassay for the quantitation of serum TSH using protein-layered solid phase.

A sensitive enzyme immunoassay for serum TSH has been developed utilizing the tight binding between biotin and avidin, and three layered protein polystyrene beads as solid phase. To increase binding capacity of TSH and sensitivity of the assay, the polystyrene beads were coated sequentially with mouse immunoglobulin as first layer, rabbit antimouse immunoglobulin as second layer and monoclonal anti-TSH as third layer. A serum sample was incubated simultaneously with a monoclonal anti-TSH immobilized polystyrene beads and a second monoclonal anti-TSH covalently attached to biotin. After washing, the antibody bound serum TSH-anti-TSH-biotin complex is reacted with horseradish peroxidase (HRP)-labeled avidin. Following a second wash, the bound HRP activity was measured colorimetrically. Reproducible results were obtained within 4 hours for serum TSH in the range between 0 microIU/ml and 50 microIU/ml with detection limit of 0.1 microIU per test.

Animals↗
PubMed1998

Increment of efficiency in the identification of noble genes by colony hybridization assay. (Screening of low redundant clones from human fetal cDNA library).

For the rapid identification of noble genes in a specific tissue by computer analysis from the cDNA sequences determined by single-pass cDNA sequencing, clone redundancy was one of the major obstacles. To facilitate the efficiency in identification of noble genes, it was necessary to reduce the number of clones to be sequenced by eliminating the redundant clones for a rapid analysis. In order to increase the probability of isolating noble sequences from the cDNA clones of human fetal liver tissue origin, colony hybridization assay was adopted and redundant clones were efficiently removed. Four cDNA clones highly redundant in the human fetal liver cDNA libraries including alpha-globin, gamma-globin, serum albumin and H19 RNA sequences were selected as the probes. Two hundreds and sixty two cDNA clones were randomly selected and tested with the probes for hybridization properties. The identity of each cDNA clone giving positive or negative signals in the hybridization assay was determined by DNA homology search with the nucleic acid databases. Among the 76 clones giving positive signals, 57 clones (75%) were found to be identical to the probe sequences and could be eliminated by colony hybridization assay before neucleotide sequencing.

Cloning, Molecular↗
PubMed1998

An engineering model to characterize oxygen transfer rates for liposome encapsulated hemoglobin (LEH).

An engineering model was designed to evaluate oxygen transfer rates for LEH and other oxygen carriers under wall shear rates from 150 sec-1 to 450 sec-1. The results showed that increasing the shear rates (or flow rates) of oxygen carriers flowed inside of hollow fiber tubes would increase oxygen transfer rates to outside media. The values of overall oxygen transfer rate coefficients for LEH, based on 1 g/dl of hemoglobin contents, were about 2 to 2.5 times higher than those values for human blood at all of tested shear rates (e.g., 5.1 x 10(-5) cm/sec and 2.1 x 10(-5) cm/sec for LEH and blood at wall shear rates of 450 sec-1, respectively). Moreover, the results of oxygen transfer efficiency for LEH calculated by this model were consistent with the similar results reported by Usuba et al.[3] obtained by animal study. With an engineering model, we possibly estimate the effects of other factors such as viscosity on the oxygen transfer rates for LEH in microcirculation.

Biomechanical Phenomena↗
PubMed1997

Peptide-specific CTL induction in HBV-seropositive PBMC by stimulation with peptides in vitro: novel epitopes identified from chronic carriers.

Cytotoxic T lymphocytes (CTL) recognize and destroy virus-infected cells, and it has been established that epitope-based peptides could induce such CTL in vivo as well as in vitro. In this study attempts were made to define the epitopes that are recognized by the CTL, and thus a series of 9- to 10-mer peptides derived from the amino acid sequences of hepatitis B virus (HBV) proteins were synthesized on the basis of the previously described HLA-A2 peptide binding motif. The binding assay of the synthetic peptides using transporter-associated with antigen processing (TAP)-deficient human cell line, T2, showed that eight out of 11 peptides tested enhanced the expression of HLA-A2 molecules on the T2 cell surface. Some of these peptides triggered activation of CTL in peripheral blood mononuclear cells of HBV-seropositive chronic carriers. The activated CTL in turn recognized and killed the T2 cells pulsed with the same peptides. This study shows that novel HLA-A2-restricted epitopes exist in the natural repertoire of immunity against HBV. These findings can be useful in developing peptide-based therapeutics against viral infections.

Carrier State↗
PubMed1997

Molecular cloning of the leuB genes from Mycobacterium bovis BCG and Mycobacterium tuberculosis.

A gene responsible for the biosynthesis of leucine has been cloned by the complementation of the Escherichia coli leuB6 auxotroph mutant after transformation with the Mycobacterium bovis BCG genomic DNA library, which was constructed by ligating the partially digested BCG DNA with Sau3A1 into the pUC19 digested with BamHI. Sequencing of the leuB gene of BCG revealed an ORF (open reading frame) of 1.011 bp encoding isopropylmalate dehydrogenase with a calculated molecular weight of 42 kDa. The leuB gene of Mycobacterium tuberculosis isolated from Korean tuberculosis patient is shown to be identical to that of BCG except one bp.

3-Isopropylmalate Dehydrogenase↗
PubMed1997

Complete sequence of the UPP gene encoding uracil phosphoribosyltransferase from Mycobacterium bovis BCG.

The nucleotide sequence of a 799 bp fragment of Mycobacterium bovis BCG containing the putative upp gene that encodes a uracil phosphoribosyltransferase (UPRTase [EC 2.4.2.9]) has been determined. The upp gene of BCG has an open reading frame (ORF) of 621 bp (207 amino acids) starting with GTG (position 112) and ending with TGA (position 733), and its molecular mass was calculated to be 21,864 Da. Comparative analyses of the deduced amino acid sequence of BCG UPRTase with the UPRTase of six bacterial genera revealed that 24% (50/211) of the residues are perfectly conserved and 32% (67/211) of the residues are well conserved.

Amino Acid Sequence↗
PubMed1997

Cloning and sequencing of the secY gene homolog from Mycobacterium bovis BCG.

The complete nucleotide sequence of a 1,513 bp fragment of Mycobacterium bovis BCG containing the secY gene homolog and partial adk gene that encodes an adenylate kinase has been determined. The secY gene of BCG has an open reading frame of 441 amino acids with homology to the SecY protein family. Comparative analyses of the deduced amino acid sequence of additional partial ORF revealed strong similarity to the known adenylate kinases.

Amino Acid Sequence↗