Biomedical subjects

Ho Keun Yi

Publications and source records attributed to Ho Keun Yi.

11 recordsLinked to original sources

PubMed2006

Hydrophilic nanofibrous structure of polylactide; fabrication and cell affinity.

Microstructure and architecture of the scaffolds along with the surface chemistry exert profound effect on biological activity (cell distribution, proliferation, and differentiation). For the biological activity, scaffolds in tissue engineering have been widely designed. The objective of this study was to develop hydrophilic nanofibrous structure of polylactides (PLLA) polymer in the form of nonwoven mat by electrospinning technique, and further evaluate the fibroblast NIH3T3 cell proliferation, morphology, and cell-matrix interaction. Hydrophilicity of the PLLA fibers was improved by adding small fraction of low molecular weight polyethylene glycol (PEG) into the electrospinning solution. Four different ratio types (100/0, 80/20, 70/30, and 50/50) of PLLA/PEG electrospun matrices were fabricated, and the pore characteristics, tensile properties, contact angle, and hydrolytic degradation were observed. Furthermore, scanning electron microscope (SEM) and fluorescence actin staining images were used for micro-observation of cell-matrix interaction and cell morphology. It was found that the electrospun mat of PLLA/PEG (80/20), composed of fibers with diameters in the range 540-850 nm, majority of pore diameter less than 100 microm, tensile strength 8 MPa, elongation 150%, porosity more than 90%, and improved hydrophilicity with slow hydrolytic degradation, is favorable for biological activity of NIH3T3 fibroblast cell. Based on these results, the correct composition of PLLA and PEG in the porous electrospun matrix (i.e., PLLA/PEG (80/20)) will be a better candidate rather than other compositions of PLLA/PEG as well as hydrophobic PLLA for application in tissue engineering.

3T3 Cells↗

PubMed2006

Preproghrelin Leu72Met polymorphism is not associated with type 2 diabetes mellitus.

Ghrelin is a novel gut-brain peptide, which exerts somatotropic, orexigenic, and adipogenic effects. Genetic variants of ghrelin have been associated with both obesity and insulin metabolism. In this study, we determined a role of preproghrelin Leu72Met polymorphism on type 2 diabetes mellitus and its relationship to variables studied. Genotypes were assessed by polymerase chain reaction. Frequencies of the Leu72Met polymorphism were found to be 35.4% in the type 2 diabetic patients and 32.5% in the normal controls. The Leu72Met polymorphism was not associated with hypertension, macroangiopathy, retinopathy, serum cholesterol, triglyceride, blood urea nitrogen, HbA(1c), lipoprotein (a), fasting insulin, or 24-hour urinary protein levels in the type 2 diabetic group. However, the Leu72Met polymorphism was clearly associated with serum creatinine levels in the diabetic group, as the Met72 carriers exhibited lower serum creatinine levels than the Met72 noncarriers. Our data indicate that the preproghrelin Leu72Met polymorphism is not associated with type 2 diabetes mellitus. However, the Leu72Met polymorphism is associated with serum creatinine levels. These data suggest that Met72 carrier status may be a predictable marker for diabetic nephropathy or renal impairment in type 2 diabetes mellitus.

Aged↗

PubMed2005

PTEN/MMAC1 enhances the growth inhibition by anticancer drugs with downregulation of IGF-II expression in gastric cancer cells.

PTEN/MMAC1 is a tumor suppressor gene that is mutated in a variety of advanced and metastatic cancers. Its major function is likely to be the phosphatase activity that regulates the phosphotidylinositol (PI)3-kinase/Akt pathway. On the other hand, IGF system plays an important role in cell proliferation and cell survival via PI3-kinase/Akt and mitogen-activated protein kinase pathways in many cancer cells. To evaluate effect of PTEN on cell growth and IGF system in gastric cancer, human gastric adenocarcinoma cells (SNU-5 & -216) were transfected with human PTEN cDNA. Those PTEN- transfected gastric cancer cells had a lower proliferation rate than the pcDNA3-transfected cells. PTEN overexpression induced a profound decrease in the IGF-II and IGF-IR expression levels, and downregulation of IGF-II expression by PTEN was mediated through the regulation of the IGF-II promoter. In addition, a PI3-kinase inhibitor, LY294002, induced the downregulation of IGF-II expression. The PTEN-overexpressing SUN-5 and -216 cells were more sensitive to death induced by etoposide and adriamycin that induce DNA damage than the pcDNA3-transfected cells. These findings suggest that PTEN suppresses the cell growth through modulation of IGF system and sensitizing cancer cells to cell death by anticancer drugs.

Antineoplastic Agents↗

PubMed2004

Committed memory effector type 2 cytotoxic T (Tc2) cells are ineffective in protective anti-tumor immunity.

Cytotoxic CD8+ T cells (Tc) are a major effector cell population in protection against tumor growth and classified into Tc1 or Tc2 based on their cytokine-secreting profiles. However, their relative tumor protective roles remain undefined. In the present study, CD8+ memory T cells were obtained from mice given with CT26-IL 12 and tumor-specific Tc1 and Tc2 cells were induced by in vitro primary stimulation (1 degrees). In vivo anti-tumor immunity and in vitro cytotoxicity of 1 degrees Tc2 memory effector cells were highly protective comparably to 1 degrees Tc1, but they secreted high level of IFNgamma as well as IL 4 and IL 5. Moreover, memory cells obtained again from tumor-protected mice by either 1 degrees Tc1 or Tc2 transfer showed indistinguishable, Tc1-like, cytokine profiles. These results strongly suggest that 1 degrees Tc2 cells are insufficiently polarized. Tc2 memory effector cells were therefore examined for their transitional anti-tumor activity during consecutive stimulation until Th2 commitment. Secondary stimulation (2 degrees) markedly reduced secretion of IFNgamma (by 94%) and in vivo tumor protection (by 83%). Tertiary (3 degrees) and further stimulation completely abrogated both of tumor protective activity and IFNgamma secretion of Tc2 cells. This progressive loss of activity following repeated stimulation was accompanied by a reduction of in vitro cytotoxicity to CT26 tumor cells. In addition, when 1 degrees Tc2 cells were trans-differentiated to Tc1 during secondary stimulation, 2 of 6 cultures recovered tumor protective activity concomitantly with IFNgamma secretion, indicating that repeated stimulation does not deteriorate tumor protective activity of 2 degrees Tc2 cells. Collectively, these data demonstrate that highly committed Tc2 cells are ineffective in tumor protection.

Animals↗

PubMed2004

Novel biodegradable electrospun membrane: scaffold for tissue engineering.

Nonwoven fibrous matrixes have been widely used as scaffolds in tissue engineering, and modification of microstructure of these matrices is needed to organize cells in three-dimensional space with spatially balanced proliferation and differentiation required for functional tissue development. The objective of this study was fabrication of nanofibrous matrix from novel biodegradable poly(p-dioxanone-co-L-lactide)-block-poly(ethylene glycol) (PPDO/PLLA-b-PEG) copolymer, and to examine cell proliferation, morphology of cell-matrix interaction with the electrospun nanofibrous matrix. The electrospun structure composed of PPDO/PLLA-b-PEG fibers with an average diameters of 380 nm, median pore size 8 microm, porosity more than 80% and mechanical strength 1.4 MPa, is favorable for cell-matrix interaction and supports the active biocompatibility of the structure. NIH 3T3 fibroblast cell seeded on the structure tend to maintain phenotypic shape and guided growth according to nanofiber orientation. Good capability of the nanofibrous structure for supporting the cell attachment and proliferation are observed. This novel biodegradable scaffold will be applicable for tissue engineering based upon its unique architecture, which acts to support and guide cell growth.

3T3 Cells↗

PubMed2004

In vitro immunomodulatory activity of Bo-yang-hwan-o-tang.

Bo-yang-hwan-o-tang (BHT), an herbal decoction has been mainly used for improvement of blood flow in oriental medicine. Its in vivo immunomodulation was recently demonstrated but the effective mechanisms have not been described. This study was carried out to evaluate in vitro immunomodulatory activity of BHT. Water extract of BHT significantly promoted in vitro proliferative responses of mouse spleen cells (SPC) and also further enhanced the proliferation of SPC stimulated with anti-CD3 antibody. Unexpectedly, addition of BHT extract did not affect proliferation of both resting and CD3-activated T cells, whereas it showed a strong mitogenic activity on B cells. Flow cytometric analysis of CFSE-stained SPC showed that BHT-mediated enhancement of CD3-activated SPC proliferation is due to T cell, but not B cell, division. Mixed culture experiment combining T and mitomycin C-treated B cells demonstrated that BHT-mediated enhancement of CD3-activated T cell proliferation was dependent on the presence of B cells. However, B cell-derived factors were not involved in BHT effect on T cell proliferation. In the presence of B cells, BHT treatment resulted in a great enhancement in IL-2 production of CD3-activated T cells, and BHT effect on T cell proliferation was completely abrogated by addition of exogenous IL-2, indicating that IL-2 plays a critical role in BHT-mediated enhancement of CD3-activated T cell proliferation. Taken together, our data revealed that BHT possesses a potent B cell mitogenic activity and also can enhance activated T cell response through B cell regulation.

Animals↗

PubMed2003

Novel polymeric micelles of amphiphilic triblock copolymer poly (p-dioxanone-co-L-lactide)-block-poly (ethylene glycol).

PURPOSE: The objective of this study is to characterize the micelles of novel block copolymer of poly (p-Dioxanone-co-L-Lactide)-block-Poly (ethylene glycol) (PPDO/PLLA-b-PEG-) and evaluate its ability to induce gene transfection. METHODS: The ability of the block copolymer to self-assemble was determined by viscometery, dye solublization, NMR spectra and dynamic light scattering. The Trypan blue assay for in vitro biocompatibility of the block copolymer was carried out with NIH 3T3, CT-26 and MCF-7 cells, and beta-glactosidase assay was applied to measure the transfection efficiency of the block copolymer on MCF-7 breast cancer cell. RESULTS: Depending on the block lengths and molecular weights, solubility of the polymeric samples in water was varied. Diluted aqueous solution properties of the copolymer were studied. 1,6-Diphenyl-1,3,5-hexatriene solubilization and 1H NMR spectra carried out in CDCl3 and D2O, were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity, and lower negative zeta potential of -3 to -14 mV were observed on the aqueous copolymer dispersion. Copolymer was found with almost no cytotoxic effect and was able to promote the transfection efficiency (about 3-fold) in MCF-7 cells. CONCLUSIONS: The PPDO/PLLA-b-PEG copolymer has ability to assemble into nanoscopic structures in aqueous environment, which enable to enhance gene transfection.

Animals↗

PubMed2002

Enhanced expression of insulin-like growth factor binding protein-3 sensitizes the growth inhibitory effect of anticancer drugs in gastric cancer cells.

Insulin-like growth factor (IGF)-I and -II are potent mitogens and their mitogenic effects are modulated by IGF binding proteins (IGFBPs). In this study, we evaluated whether the enhanced expression of IGFBP-3 may increase the sensitivity of human gastric cancer cells to the anticancer drugs. We further investigated the potential mechanism for the growth inhibitory effect of anticancer drug induced-IGFBP-3 expression. These IGFBP-3-expressing gastric cancer cells showed a lower proliferation rate than IGFBP-3-non-expressing cells. Treatment with anticancer drugs resulted in up-regulation of IGFBP-3 expression in IGFBP-3-expressing cells. Interestingly the anticancer drug-induced-growth inhibition was more evident in IGFBP-3-expressing cells causing the IGFBP-3 expressing cells but not the IGFBP-3 non-expressing cells to accumulate in the G1/G0 phase and induce apoptosis. The exogenous addition of IGFBP-3 inhibited the growth of IGFBP-3-non-expressing cells, causing them to undergo apoptosis. Our data suggest that IGFBP-3 may have an important role in the biology of gastric cancer cell growth and provides a potential marker for predicting the responsiveness to anticancer drugs.

Antineoplastic Agents↗

PubMed2002

Regulation of lymphocyte clustering by CD30-mediated ICAM-1 up-regulation.

CD30 is expressed transiently on activated B and T lymphocytes and constitutively on several B- and T cell lymphomas. CD30 functions include participation in negative selection of thymocytes, costimulation of activated T cells, isotype switching of B cells, and regulation of the effector activity of cytotoxic lymphocytes. Although CD30 is not a marker for T helper 2 (TH2) cells, it may participate in the polarization of TH1 and TH2 cells. The pleiotropic functions of CD30 are initiated by interaction of CD30-expressing cells with other immune competent cells expressing CD30-L and providing the signals for modulation of effector cell activity. Here, we report that CD30 signals generated by anti-CD30 on activated, normal murine T cells strongly up-regulate the expression of intercellular adhesion molecule 1 (ICAM-1, CD54), and to a lesser extent, ICAM-2 (CD102). CD30 signals moreover delay the subsequent decline of ICAM expression. CD30 cross-linking did not alter the expression of CD11a/CD18 (LFA-1), the counter receptor for ICAM abundant on T cells. CD30-mediated ICAM-1 up-regulation is independent of cytokine secretion and appears to be transmitted directly through NF-kappaB activation. CD30-mediated up-regulation of ICAM-1 expression led to a significant increase in cluster formation of lymph node cells. Increased lymphocyte self-aggregation mediated by CD30 may set the stage for fraternal signaling to modulate lymphocyte function.

Animals↗

PubMed2002

Induction of apoptosis in K562 cells by dominant negative c-myb.

OBJECTIVE: The aberrant expression of c-myb in leukemic cells suggests that c-myb may play an important role in leukemogenesis. Therefore, disrupting c-myb function might provide a strategy for controlling leukemic cell growth. Use of dominant negative mutants as a strategy for inhibiting oncogene function has attracted considerable attention. The aim of this study was to induce apoptosis in K562 cells by dominant negative c-myb (DN-myb). MATERIALS AND METHODS: We constructed a DN-myb plasmid containing the DNA-binding domain of c-myb and transfected the dominant negative mutant, like its wild-type (WT) counterpart, into K562 cells. Consequently, cell viability and induction of apoptosis were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, nuclear condensation, DNA fragmentation, and Western hybridization analysis for expression of poly(ADP-ribose) polymerase. In addition, the effect of DN-myb on bcl-2 promoter activity and expression of bcl-2 and bcr-abl was studied. RESULTS: We observed that DN-myb, cotransfected with WT c-myb and a chloramphenicol acetyltransferase reporter construct containing the bcl-2 promoter, bound competitively to the bcl-2 promoter and significantly decreased the activation of chloramphenicol acetyltransferase induced by WT c-myb. Moreover, the inactivation of transcription induced by DN-myb reduced not only the expression of bcl-2 but also the expression of bcr-abl. Further functional studies focused on the effect of DN-myb on the induction of apoptosis in K562 cells. Transfection of DN-myb into K562 cells caused a significant reduction in cell proliferation when cells were exposed to low concentrations of DNA-damaging agents (approximately 30% of control) and remarkably increased apoptosis. CONCLUSIONS: Our data demonstrate that disruption of c-myb function by dominant negative c-myb is an effective strategy to induce apoptosis of leukemic cells. The results of these studies support the thesis that dominant negative c-myb gene therapy may be useful for treatment of leukemia patients.

3T3 Cells↗

PubMed2002

Nitric oxide-cyclic GMP signaling pathway in the regulation of rabbit clitoral cavernosum tone.

We investigated the role of nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling in the regulation of rabbit clitoral cavernosum (CC) tone. Tension measurements, reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and NADPH-diaphorase staining were performed in CC. In the precontracted CC strips with phenylephrine (10(-5) M), acetylcholine (ACh) relaxed, dependent on dosage. Pretreatment with atropine, N(omega) nitro-L-arginine-methyl ester (NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), guanylate cyclase inhibitor abolished the ACh-induced relaxations, but tetrodotoxin (TTX) did not. Sodium nitroprusside relaxed the strips in the presence of atropine and NAME, but not in the presence of ODQ. Electrical field stimulation (EFS) relaxed the strips dependent on stimulus strength. Pretreatment with TTX, NAME, or ODQ abolished the EFS-induced relaxation, but atropine did not. L-Arginine partially restored the inhibited response to ACh and EFS. The inducible NO synthase (iNOS) and neuronal NOS (nNOS) mRNAs and iNOS and endothelial NOS (eNOS) proteins were identified in the CC. NADPH-diaphorase staining revealed the positivity on the nerve trunks and fine nerve fibers in the CC. Finally, results demonstrate that the nNOS, ENOS, and the NO-cGMP signaling pathway are involved in the regulation of clitoral tumescence.

Acetylcholine↗