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Bing-Hung Chen

Publications and source records attributed to Bing-Hung Chen.

11 recordsLinked to original sources
PubMed2006

Characterization of chondroitin sulfate and its interpenetrating polymer network hydrogels for sustained-drug release.

The goal of this work was to utilize the chondroitin sulfate (CS) based hydrogels for a drug delivery matrix. CS is a good structure/disease-modifying anti-osteroarthritis drug (S/DMOAD). However, the readily water-soluble nature limits its application as a solid-state drug-delivery vehicle. In this study, two methods were used to prepare CS hydrogels: directly crosslinking CS with poly(ethylene glycol) diglycidyl ether (EX-810) abbreviated as CS-EX or forming an interpenetrating polymer network named CS-EX-IPN. The CS-EX-IPN hydrogel was carried out by sequentially crosslinking reaction between CS and EX-810 in one phase and acrylic acid and di(ethylene glycol) diacrylate (DEGDA) as a counter phase. The swelling percent, cross-section morphology, and effective crosslinking density of hydrogels were characterized. The values of compression modulus and effective crosslinking density of CS-EX-IPN were approximately 3.6-fold higher than CS-EX. We also characterized the release of a model drug, diclofenac sodium (DS) and a model protein, bovine serum albumin (BSA), from CS-EX and CS-EX-IPN. The similar release profiles of DS were observed in the both hydrogels but slower release rate of BSA occurred in CS-EX-IPN. The release profiles of the two model drugs fit in a diffusion-controlled mechanism. The D(eff) values are in the order of 10(-5) for DS and 10(-7) for BSA.

Animals↗
PubMed2005

Rheological characteristics of the cationic polyelectrolyte flocculated wastewater sludge.

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The stress-sweep experiments and the small-amplitude-oscillatory-shearing (SAOS) tests were conducted. The stress-sweep measurements demonstrate that addition of polymer coagulants to sludge samples could significantly influence the corresponding complex shear modulus G*. Furthermore, the SAOS tests indicate that the sludge samples treated with polymer coagulants will form more rigid structures. The original sludge samples mostly show typical viscoelastic liquid-like behavior. However, the solid-like behaviors were always observed in the samples treated with polymers.

Elasticity↗
PubMed2005

Properties of human and rabbit cytosolic serine hydroxymethyltransferase are changed by single nucleotide polymorphic mutations.

Serine hydroxymethyltransferase (SHMT) is a key enzyme in the formation and regulation of the folate one-carbon pool. Recent studies on human subjects have shown the existence of two single nucleotide polymorphisms that may be associated with several disease states. One of these mutations results in Ser394 being converted to an Asn (S394N) and the other in the change of Leu474 to a Phe (L474F). These mutations were introduced into the cDNA for both human and rabbit cytosolic SHMT and the mutant enzymes expressed and purified from an Escherichia coli expression system. The mutant enzymes show normal values for kcat and Km for serine. However, the S394N mutant enzyme has increased dissociation constant values for both glycine and tetrahydrofolate (tetrahydropteroylglutamate) and its pentaglutamate form compared to wild-type enzyme. The L474F mutant shows lowered affinity (increased dissociation constant) for only the pentaglutamate form of the folate ligand. Both mutations result in decreased rates of pyridoxal phosphate addition to the mutant apo enzymes to form the active holo enzymes. Neither mutation significantly affects the stability of SHMT or the rate at which it converts 5,10-methenyl tetrahydropteroyl pentaglutamate to 5-formyl tetrahydropteroyl pentaglutamate. Analysis of the structures of rabbit and human SHMT show how mutations at these two sites can result in the observed functional differences.

Animals↗
PubMed2005

Cloning, expression, purification, and characterization of zebrafish cytosolic serine hydroxymethyltransferase.

A cDNA which encodes for zebrafish serine hydroxymethyltransferase (SHMT) has been cloned into a pET43.1a vector as a NdeI-EcoRI insert and transformed into HMS174(DE3) cells. After induction with isopropyl thiogalactoside, the enzyme was purified with a three-step purification protocol and about 15 mg of pure enzyme was obtained per liter of culture. Spectral and structural characteristics of the recombinant zebrafish SHMT are similar to the rabbit and human cytosolic SHMT. Kinetic constants for the natural substrates l-serine and tetrahydrofolate are also comparable to the values obtained previously for the rabbit and human cytosolic enzyme.

Animals↗
PubMed2005

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions.

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) solutions are investigated experimentally. Weak shear thickening at intermediate shear rates takes place for HMHEC at moderate concentrations and becomes more significant at lower temperatures. While this amphiphilic polymer in surfactant-free solution does not turn turbid by heating to 95 degrees C, its mixture with nonionic surfactant shows a lower cloud point temperature than does a pure surfactant solution. For some mixture cases, phase separation takes place at temperatures as low as 2 degrees C. The drop of cloud point temperature is attributed to an additional attractive interaction between mixed micelles via chain bridging. With increasing temperature, the viscosity of an HMHEC-surfactant mixture in aqueous solution first decreases but then rises considerably until around the cloud point. The observed viscosity increase can be explained by the interchain association because of micellar aggregation.

Journal Article↗
PubMed2005

Solubilization of selected free fatty acids in palm oil by biodegradable ethoxylated surfactants.

The solubilization of three major components, viz., palmitic, oleic, and linoleic acids, in palm oil by ethoxylated surfactants was investigated. The results were analyzed in terms of the molecular properties of surfactants and free fatty acids (FFAs). It was found that the solubilities of these FFAs in various micellar solutions depend not only on their octanol-water partition coefficients (Kow), but also on their physicochemical properties. The study on the solubilization kinetics was conducted by choosing palmitic acid as a model solubilizate and Tergitol 15-S-7 as the model surfactant. A first-order film diffusion model, which accounts for the direct uptake of organic molecules at a solid surface into surfactant micelles, was adopted to analyze the effect of surfactant on dissolution of palmitic acid. It was observed that the presence of surfactant reduced the mass-transfer coefficient. Instead, the overall mass-transfer rate was enhanced because of the much higher driving force from the increased solubilization capacity.

Biodegradation, Environmental↗
PubMed2005

Interaction between a nonionic surfactant and a hydrophobically modified 2-hydroxyethyl cellulose.

Interaction between the nonionic surfactant Tergitol 15-S-7 and hydrophobically modified 2-hydroxyethyl cellulose (HMHEC) was studied rheologically in a semidilute regime of HMHEC. The low-shear viscosity of HMHEC was increased with addition of surfactant from 25 to 250 ppm, in which the critical micelle concentration of surfactant was near 39 ppm, and then decreased to a value smaller than that of pure HMHEC with further addition of surfactant to 1000 ppm. An interesting shear-induced phenomenon was observed. The steady-state shear measurements show that there exist crossovers between viscosity-shear rate curves of HMHEC solutions with and without surfactant added, whereas it was not observed in the HEC-surfactant systems. Moreover, added Tergitol 15-S-7 reversed the temperature effect on the viscosity of the HMHEC solution. That is, increasing temperature to or near the cloud point raises the viscosity of the HMHEC-surfactant aggregates, in contrast to the viscosity decrease in the pure HMHEC solutions. A possible mechanism based on the necklace model and the clouding phenomenon is conjecturally introduced to explain such phenomena.

Cellulose↗
PubMed2003

Equilibrium partition of polycyclic aromatic hydrocarbons in a cloud-point extraction process.

A cloud-point extraction (CPE) process using the nonionic surfactant Tergitol 15-S-7, a secondary ethoxylated alcohol, to extract selected polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions is investigated. The CPE process is facilitated at the ambient temperature, ca. 22 degrees C, by the reduction of the cloud-point temperature of the surfactant solution by addition of sodium sulfate. It is observed that the preconcentration factor could be enhanced either by increasing the salt concentration or by decreasing the initial surfactant concentration in the micellar solution. A high preconcentration factor of about 40 was achieved at 1 wt% surfactant concentration with the addition of 0.6 M Na(2)SO(4). It is also noted that the equilibrium partition coefficients of the model PAHs are nearly independent of surfactant concentrations, up to 3 wt%, in this study. Correlations between the equilibrium partition coefficients K(p) of the PAHs and their octanol-water partition coefficients K(ow), as well as K(p) and the molar volume V(x) of these PAHs, indicate that the partition processes of the PAHs in the CPE processes are mainly governed by their hydrophobic affinities to the surfactant aggregates. Furthermore, the effect of added Na(2)SO(4) on the equilibrium partition coefficients is also studied. It is shown that addition of more Na(2)SO(4) to the surfactant solution gives more partition of the PAHs into the surfactant-rich phase.

Journal Article↗
PubMed2003

Temperature effect on IgE binding to CD23 versus Fc epsilon RI.

A chimeric soluble CD23, consisting of the extracellular domain of mouse CD23 and a modified leucine zipper (lz-CD23), has been shown to inhibit IgE binding to the FcepsilonRI. A similar human CD23 construct was also shown to inhibit binding of human IgE to human FcepsilonRI. In both systems, the inhibition was found to be temperature dependent; a 10-fold molar excess of lz-CD23 gave 90-98% inhibition at 4 degrees C, dropping to 20-30% inhibition at 37 degrees C. Surface plasmon resonance analysis of lz-CD23 binding to an IgE-coated sensor chip suggested that the effective concentration of lz-CD23 was lower at the higher temperatures. Analysis of (125)I-IgE binding to CD23(+)-Chinese hamster ovary cells also indicated that increased temperature resulted in a lower percentage of IgE capable of interacting with CD23. In contrast, IgE interacts more effectively with FcepsilonRI(+)-rat basophilic leukemia cells at 37 degrees C compared with 4 degrees C. The results support the concept that the open and closed IgE structures found by crystallography interact differently with the two IgE receptors and suggest that temperature influences the relative percentage of IgE in the respective structural forms. Changes in CD23 oligomerization also plays a role in the decreased binding seen at physiological temperatures.

Animals↗
PubMed2002

Necessity of the stalk region for immunoglobulin E interaction with CD23.

Previously, a soluble mouse CD23 chimera, composed of an N-terminal trimeric isoleucine zipper motif (lz) followed by the entire extracellular region (amino acids 48-331) of CD23 (lz-CD2348-331), was prepared and exhibited strong binding to rodent immunoglobulin E (IgE). In the current study, we report the construction of a similar human chimeric protein (lz-huCD2345-321), as well as a series of murine chimeric lz-CD23 mutants with incremental portions of stalk deleted, to further investigate the role of the stalk region in mediating the CD23-IgE interaction. All chimeric proteins were designed such that the predicted heptad structure of the stalk was retained. IgE binding, as determined by the capacity to inhibit 125I-IgE from binding to FcepsilonRI-bearing RBL-2H3 cells, and by surface plasmon-resonance analysis using an IgE-coated sensor chip, was unchanged from the original lz chimera and the binding parameters were similar to those of cell-surface CD23. The minimal murine chimera that retained IgE-binding activity was lz-CD23139-331, which still contains 35 amino acids of the stalk region. When the lz motif was linked to CD23 amino acid 157 (or higher), significant IgE-binding capacity was lost. With human lz-CD23, as with mouse, deletion of the stalk greatly reduced IgE-binding ability. In summary, the data support the concept that at least a portion of the stalk region of CD23 plays a crucial role in maintaining high-affinity/avidity interaction with IgE. The lz-CD23 constructs represent a possible alternative for both blocking the IgE/FcepsilonRI interaction and inhibiting IgE production by B lymphocytes.

Animals↗