Biomedical subjects

Hanry Yu

Publications and source records attributed to Hanry Yu.

29 records · Page 2Linked to original sources

PubMed2004

Photo-crosslinkable microcapsules formed by polyelectrolyte copolymer and modified collagen for rat hepatocyte encapsulation.

New anionic polyelectrolyte tetra-copolymers with photo-crosslinkable 4-(4-methoxycinnamoyl)phenyl methacrylate monomer in addition to a HEMA-MMA-MAA ter-copolymer system were synthesized. The tetra-copolymers were used to form photo-crosslinkable microcapsules with modified collagen by complex coacervation for rat hepatocytes encapsulation. The hepatocytes were encapsulated within a two-layered membrane comprising of modified collagen as the inner core and an outer photo-crosslinkable copolymer shell. Upon photo-crosslinking of the microcapsules with UV-Vis light irradiation, the mechanical strength and chemical stability of the microcapsules, and the cellular functions of the encapsulated hepatocytes were enhanced. Particularly, the mechanical stability of the microcapsules was dramatically strengthened. The new photo-crosslinkable tetra-copolymer formulation described in this article has opened a way to the development of hepatocyte microencapsulation technology for bioartifical liver assist device.

Animals↗

PubMed2003

Cloning of rat telomerase catalytic subunit functional domains, reconstitution of telomerase activity and enzymatic profile of pig and chicken tissues.

Telomerase is a ribonucleoprotein polymerase which adds TTAGGG repeats to telomeric ends. Recent studies reported the reverse transcription enzyme activity mostly from the catalytic subunit (TERT) of the enzyme complex. Both human telomerase catalytic subunit (hTERT) and mouse telomerase catalytic subunit (mTERT) had been previously cloned but not rat telomerase catalytic subunit rTERT. In this study, the rTERT functional domains were cloned and was found that its function resemble to mouse and human telomerase. In addition, chicken and pig telomerase activity profile were studied and its enzyme activity is related to its proliferation capability of individual tissues. However, its catalytic subunit does not like mouse, rat and human cases that the telomerase activity could not reconstituted by the in-vitro transfection of mTERT and hTERT cloned vectors. Here we demonstrated that rTERT is similar to mTERT and hTERT but not pig and chicken telomerase. Further studies are needed to verify the malignancy characteristics because nowadays artificial organs/tissues from these animals are used for the transplantation to human body.

Animals↗

PubMed2003

Kinectin anchors the translation elongation factor-1 delta to the endoplasmic reticulum.

Kinectin has been proposed to be a membrane anchor for kinesin on intracellular organelles. A kinectin isoform that lacks a major portion of the kinesin-binding domain does not bind kinesin but interacts with another resident of the endoplasmic reticulum, the translation elongation factor-1 delta (EF-1 delta). This was shown by yeast two-hybrid analysis and a number of in vitro and in vivo assays. EF-1 delta provides the guanine nucleotide exchange activities on EF-1 alpha during elongation step of protein synthesis. The minimal EF-1 delta-binding domain on kinectin resides within a conserved region present in all the kinectin isoforms. Overexpression of the kinectin fragments in vivo disrupted the intracellular localization of EF-1 delta proteins. This report provides evidence of an alternative kinectin function as the membrane anchor for EF-1 delta on the endoplasmic reticulum and provides clues to the EF-1 complex assembly and anchorage on the endoplasmic reticulum.

Endoplasmic Reticulum↗

PubMed2003

Microcapsules with improved mechanical stability for hepatocyte culture.

Packed-bed or fluidized-bed bioreactor filled with microencapsulated hepatocytes has been proposed as one of the promising designs for bioartificial liver assist device (BLAD) because of potential advantages of high mass transport rate and optimal microenvironment for hepatocyte culture. Recently, we have developed a microcapsule system for the encapsulation of hepatocytes. The microcapsules consist of an inner core of modified collagen and an outer shell of terpolymer of methyl methacrylate, methacrylate and hydroxyethyl methacrylate. Cells encapsulated in these microcapsules exhibit enhanced cellular functions. Improving the mechanical stability of the microcapsules to withstand the shear stress induced by high perfusion rate would be crucial to the success of BLAD applications. In this study, we investigated the effects of terpolymer molecular weight (M(w)) on the mechanical property of these microcapsules and the differentiated functions of encapsulated hepatocytes. Six terpolymers with different M(w) were synthesized using radical polymerization in solution by adjusting the reaction temperature and the initiator concentration. All the terpolymers formed microcapsules with the methylated collagen. While the terpolymer M(w) had little effect on the capsule membrane thickness and permeability of serum albumin, the mechanical property of the microcapsules was significantly improved by the higher M(w) of the terpolymer. Differentiated functions of the hepatocytes cultured in the microcapsules, including urea synthesis, albumin synthesis and cytochrome P450 metabolic activity, were not significantly affected by the terpolymer M(w).

Animals↗

PubMed2003

Peripheral nerve regeneration with sustained release of poly(phosphoester) microencapsulated nerve growth factor within nerve guide conduits.

Prolonged delivery of neurotrophic proteins to the target tissue is valuable in the treatment of various disorders of the nervous system. We have tested in this study whether sustained release of nerve growth factor (NGF) within nerve guide conduits (NGCs), a device used to repair injured nerves, would augment peripheral nerve regeneration. NGF-containing polymeric microspheres fabricated from a biodegradable poly(phosphoester) (PPE) polymer were loaded into silicone or PPE conduits to provide for prolonged, site-specific delivery of NGF. The conduits were used to bridge a 10 mm gap in a rat sciatic nerve model. Three months after implantation, morphological analysis revealed higher values of fiber diameter, fiber population and fiber density and lower G-ratio at the distal end of regenerated nerve cables collected from NGF microsphere-loaded silicone conduits, as compared with those from control conduits loaded with either saline alone, BSA microspheres, or NGF protein without microencapsulation. Beneficial effects on fiber diameter, G-ratio and fiber density were also observed in the permeable PPE NGCs. Thus, the results confirm a long-term promoting effect of exogenous NGF on morphological regeneration of peripheral nerves. The tissue-engineering approach reported in this study of incorporation of a microsphere protein release system into NGCs holds potential for improved functional recovery in patients whose injured nerves are reconstructed by entubulation.

Absorbable Implants↗

PubMed2003

Galactosylated PVDF membrane promotes hepatocyte attachment and functional maintenance.

One of the major challenges in BLAD design is to develop functional substrates suitable for hepatocyte attachment and functional maintenance. In the present study, we designed a poly(vinylidene difluoride) (PVDF) surface coated with galactose-tethered Pluronic polymer. The galactose-derived Pluronic F68 (F68-Gal) was adsorbed on PVDF membrane through hydrophobic-hydrophobic interaction between PVDF and the polypropylene oxide segment in Pluronic. The galactose density on the modified PVDF surface increased with the concentration of the F68-Gal solution, reaching 15.4 nmol galactosyl groups per cm2 when a 1 mg/ml of F68-Gal solution was used. The adsorbed F68-Gal remained relatively stable in culture medium. Rat hepatocytes attachment efficiency on F68-Gal modified PVDF membrane was similar to that on collagen-coated surface. The attached hepatocytes on PVDF/F68-Gal membrane self-assembled into multi-cellular spheroids after 1 day of culture. These attached hepatocytes in spheroids exhibited higher cell functions such as albumin synthesis and P450 1A1 detoxification function compared to unmodified PVDF membrane and collagen-coated surface. These results suggest the potential of this galactose-immobilized PVDF membrane as a suitable substrate for hepatocyte culture.

Albumins↗

PubMed2003

Use of ultrathin shell microcapsules of hepatocytes in bioartificial liver-assist device.

We previously encapsulated hepatocytes in ultrathin shell microcapsules and showed them to have enhanced differentiated functions over cells cultured in monolayer. Here we have used these microencapsulated hepatocytes in a bioartificial liver-assisted device (BLAD) with a rat hepatectomy model. Primary rat hepatocytes were encapsulated in 150- to 200-microm microcapsules, using an electrostatic droplet generator. The microencapsulated hepatocytes exhibited good in vitro urea synthesis activity in plasma from rats with fulminant hepatic failure (FHF). The ex vivo hemoperfusion was conducted in FHF rats by perfusing plasma at a rate of 1-2 mL/min through 1.5-2 x 10(8) encapsulated hepatocytes packed into a packed-bed bioreactor. Hemoperfusion with the bioreactor was initiated 5 h after operative induction of liver failure and continued for 7 h. The BLAD-treated rats showed improvements over the control groups in survival time and metabolic indicators, including ammonia and total bilirubin levels. Furthermore, expanded bed adsorption (EBA) detoxification technology using Streamline-SP resin was explored to complement the bioreactor with microencapsulated hepatocytes. In vitro experiments indicated that serum ammonia could be specifically removed in dose-dependent manner, whereas the total serum proteins were unaffected by the resin. In ex vivo experiments, hemoperfusion with the resin was initiated 3 h after operative induction of liver failure and continued for 7 h. The resin-treated rats showed obvious serum ammonia removal with no observable total blood protein and blood cell adsorption. Therefore, Streamline-SP resin can potentially be integrated into a BLAD for improved efficacy.

Ammonia↗

PubMed2002

Polyphosphoester microspheres for sustained release of biologically active nerve growth factor.

Controlled delivery of neurotrophic proteins to a target tissue by biodegradable polymer microspheres has been explored widely for its potential applications in the treatment of various disorders in the nervous system. We investigated in this study the potential of polyphosphoester microspheres as carriers for the sustained release of nerve growth factor (NGF), a water-soluble neurotrophic protein. Two polyphosphoesters (PPEs), P(BHET-EOP/TC) and P(DAPG-EOP), as well as poly(lactide/glycolic acid) (PLGA), were used to fabricate microspheres by a W/O/W emulsion and solvent evaporation/extraction method. With bovine serum albumin as a model protein to optimize processing parameters. P(DAPG-EOP) microspheres exhibited a lower burst effect but similar protein entrapment levels and efficiencies when compared with those made of PLGA. Bioactive NGF could be released for at least 10 weeks from the P(DAPG-EOP) microspheres, as confirmed by a neurite outgrowth assay of the PC12 cells. These NGF containing microspheres were incorporated into the nerve guide conduits that were implanted to bridge a 10 mm gap in a rat sciatic nerve model. Two weeks after implantation, immunostaining with an antibody against the neurofilament protein confirmed the presence of axons at the distal end of regenerated cables within the NGF microsphere-loaded conduits. These results demonstrated the feasibility of using biodegradable PPEs for microencapsulation of NGF and provided a basis for future therapeutic application of the microspheres.

Animals↗

PubMedDate not supplied

An engineered microenvironment for multidimensional microscopy of live cells.

Multidimensional imaging (MD) of live cells is gaining importance in biomedical research as the commercial availability of confocal, nonlinear optical microscopes, environmental chambers, and specific fluorescence probes grows. One crucial aspect of the MD live cell imaging involves the proper immobilization of cells, which refers to the rapid and sufficient immobilization of cells on the microscope stage, neither disrupting the cellular structure and functions nor affecting the optical properties of the cells and the environments. Conventional cell immobilization methods glue the anchoring cells to coated surfaces, but such methods require centrifugation or extended incubation and are not suitable for cells in suspension. Most of the current three-dimensional (3-D) gels either exhibit unsatisfactory optical properties or have adverse effects on cell functions in culture. Recently, an engineered 3-D microcapsule has been developed that involves the complex coacervation of a positively charged collagen and a negatively charged polymer of 2-hydroxyethyl methacrylate--methacrylic acid--methyl methacrylate (HEMA-MMA-MAA). Hence, confocal imaging of live cells in this engineered 3-D microenvironment was investigated for its optical properties and cellular function compatibility. We report here that this microenvironment facilitates efficient cell immobilization, exhibits good optical properties, and can preserve cellular structures and functions, which will be useful in MD imaging of live cells for various applications.

Animals↗

PubMedDate not supplied

Galactosylated poly(vinylidene difluoride) hollow fiber bioreactor for hepatocyte culture.

To overcome the limitations of long-term expression of highly differentiated hepatocyte functions, we have developed a novel bioreactor in which hepatocytes are seeded in a ligand-immobilized hollow fiber cartridge. Galactosylated Pluronic polymer is immobilized on poly(vinylidene difluoride) (PVDF) hollow fiber surface through an adsorption scheme yielding a substrate with hepatocyte-specific ligand and a hydrophilic surface layer, which can resist nonspecific protein adsorption and facilitate cell binding to the galactose ligand. Interestingly, the galactosylated PVDF hollow fiber shows enhanced serum albumin diffusion across the membrane. Freshly isolated rat hepatocytes were seeded and cultured in the extralumenal space of the hollow fiber cartridge for 18 days in a continuously circulated system. Albumin secretion function of the seeded hepatocytes was monitored by analyzing circulating medium by enzyme-linked immunosorbent assay. Urea synthesis and P-450 function (7-ethoxycoumarin dealkylase activity) were measured periodically by doping the circulating medium with NH4Cl and 7-ethoxycoumarin, respectively. Hepatocytes cultured on galactosylated PVDF hollow fibers maintained better albumin secretion and P-450 functions than on unmodified and serum-coated PVDF hollow fibers when cultured in serum-containing medium. Morphological examination by scanning electron microscopy showed that hepatocytes cultured on galactosylated PVDF hollow fibers developed significant aggregation, in contrast to those cultured on unmodified PVDF fibers or on serum-coated PVDF fibers. Transmission electron microscopy images revealed that tight junctions and canaliculus-like structures formed in these aggregates. These results suggest the potential application of this galactosylated PVDF hollow fiber cartridge for the design of a bioartificial liver assist device.

Animals↗

PubMedDate not supplied

Antisense telomerase induced cell growth inhibition, cell cycle arrest and telomerase activity down-regulation in gastric and colon cancer cells.

BACKGROUND: Antisense telomerase RNA (anti-hTR) coupled with 2',5'-linked tetraadenylate (2-5A) shows an inhibitory effect on cell growth and induces apoptosis in certain kinds of cancer. This experiment examined the anti-hTR effect on gastric and colorectal cancer cells. MATERIALS AND METHODS: Gastric cancer cells CRL-5822, CRL-5971 and colorectal cancer cells HTB-38, CCL-247 were treated with repeated doses of anti-hTR. Cell growth and cell cycle parameters were analysed. Telomerase activity was measured by TRAP assay. Control oligonucleotides and normal fibroblast were used as control. RESULTS: After two doses of anti-hTR, the cell viability for CRL-5822, CRL-5971, HTB-38 and CCL-247 cells was reduced to 15%, 12%, 37% and 37%, respectively. The DNA histogram showed cells arrested at the G2/M-phase and the sub-G1 peak found indicated that apoptosis had occurred. CONCLUSION: Anti-hTR demonstrated inhibition of cell growth and cell cycle arrest on gastric and colorectal cancer cells through a telomerase regulation pathway. Its specificity towards cancerous tissues but not normal tissues suggested a potential for anti-cancer therapy.

Adenine Nucleotides↗