Biomedical subjects

S I Hong

Publications and source records attributed to S I Hong.

At least 19 recordsLinked to original sources

PubMed2006

Enhanced wear and fatigue properties of Ti-6Al-4V alloy modified by plasma carburizing/CrN coating.

In this study, a newly developed duplex coating method incorporating plasma carburization and CrN coating was applied to Ti-6Al-4V and its effects on the wear resistance and fatigue life were investigated. The carburized layer with approximately150 microm in depth and CrN coating film with 7.5 microm in thickness were formed after duplex coating. Hard carbide particles such as TiC And V(4)C(3) were formed in the carburized layer. XRD diffraction pattern analysis revealed that CrN film had predominant [111] and [200] textures. The hardness (Hv) was significantly improved up to about 1,960 after duplex coating while the hardness value of original Ti-6Al-4V was 402. The threshold load for the modification and/or failure of CrN coating was measured to be 32 N using the acoustic emission technique. The wear resistance and fatigue life of duplex-coated Ti-6Al-4V improved significantly compared to those of un-treated specimen. The enhanced wear resistance can be attributed to the excellent adhesion and improved hardness of CrN coating film for the duplex-coated Ti-6Al-4V. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the surface, resulting in the enhanced fatigue life.

Alloys↗

PubMed2006

Production of penicillic acid by Aspergillus sclerotiorum CGF.

The production of penicillic acid by Aspergillus sclerotiorum CGF for the biocontrol of Phytophthora disease was investigated in submerged fermentation using media composed of different nutrients. Soluble starch was found to be the most effective substrate among the carbon sources used, and produced the highest penicillic acid concentration of 2.98 mg ml(-1). When organic nitrogen sources were used, pharmamedia, yeast extract, and polypeptone-S were found to be suitable organic nitrogen sources (2.46-2.71 mg ml(-1)). The production of penicillic acid was not detected in when inorganic nitrogen sources were used. Only Na2HPO4, among the metal ions and phosphate salts tested, increased the production of penicillic acid (approximately 20%). When A. sclerotiorum CGF was cultured in optimal medium [8.0% (w/v) soluble starch, 0.6% (w/v) yeast extract, and 0.3% (w/v) Na2HPO4], maximum penicillic acid concentration (approximately 9.40 mg ml(-1)) and cell mass (approximately 17.4 g l(-1)) were obtained after 12 days.

Aspergillus↗

PubMed2004

Production of cellulases and hemicellulases by Aspergillus niger KK2 from lignocellulosic biomass.

To investigate the production of cellulases and hemicellulases from Aspergillus niger KK2, solid state fermentation (SSF) was performed by using different ratios of rice straw and wheat bran. When A. niger KK2 was grown on rice straw alone as a solid support in SSF, the maximum FPase activity was 19.5 IU g(-1) in 4 days. Also, CMCase (129 IU g(-1)), beta-glucosidase (100 IU g(-1)), xylanase (5070 IU g(-1)) and beta-xylosidase (193 IU g(-1)) activities were concurrently obtained after 5-6 days of fermentation. The higher enzyme activities produced by A. niger KK2 is a significant advantage from the viewpoint of practical saccharification reaction. Cellulases and hemicellulases produced by A. niger KK2 might be applied to pulp and paper industry, feed industry and chemical industry.

Aspergillus niger↗

PubMed2003

Independent exponential feeding of glycerol and methanol for fed-batch culture of recombinant Hansenula polymorpha DL-1.

As a novel feeding strategy for optimizing human epidermal growth factor (hEGF) production with a recombinant Hansenula polymorpha DL-1 using the methanol oxidase (MOX) promoter in H. polymorpha DL-1, independent exponential feeding of two substrates was used. A simple kinetic model considering the cell growth on two substrates was established and used to calculate the respective feeding rates of glycerol and methanol. In the fedbatch culture with methanol-only feeding, the optimal set point of specific growth rate on methanol was found to be 0.10 h-1. When the fed-batch cultures were conducted by the independent feeding of glycerol and methanol, the actual specific growth rate on glycerol and methanol was slightly lower than the set point of specific growth rate. By the uncoupled feeding of glycerol and methanol the volumetric productivity of hEGF increased from 6.4 to 8.0 mg/(L.h), compared with methanol-only feeding.

Alcohol Oxidoreductases↗

PubMed2002

Xylanase production in solid state fermentation by Aspergillus niger mutant using statistical experimental designs.

The initial moisture content, cultivation time, inoculum size and concentration of basal medium were optimized in solid state fermentation (SSF) for the production of xylanase by an Aspergillus niger mutant using statistical experimental designs. The cultivation time and concentration of basal medium were the most important factors affecting xylanase activity. An inoculum size of 5 x 10(5) spores/g, initial moisture content of 65%, cultivation time of 5 days and 10 times concentration of basal medium containing 50 times concentration of corn steep liquor were optimum for xylanase production in SSF. Under the optimized conditions, the activity and productivity of xylanase obtained after 5 days of fermentation were 5,071 IU/g of rice straw and 14,790 IU l(-1) h(-1), respectively. The xylanase activity predicted by a polynomial model was 5,484 IU/g of rice straw.

Aspergillus niger↗

PubMed2002

Improvement for the production of clavulanic acid by mutant Streptomyces clavuligerus.

AIMS: To improve the production of clavulanic acid through the development of strains, the selection of a production medium and a pH shift strategy in a bioreactor. METHODS AND RESULTS: Streptomyces clavuligerus mutant 15 was selected by antibacterial activities. As a result of pH control in a 2.5 l bioreactor, the highest productivity (3.37 microg x ml(-1) x h(-1)) was obtained at a controlled pH of 7.0. CONCLUSIONS: The highest level of production obtained was an increase of about 36% compared with a non-controlled pH. When the production of clavulanic acid reached the maximum level, the pH was shifted from 7.0 to 6.0 for reduction in decomposition rate. The maximum concentration of clavulanic acid was maintained for 24 h as a result of the pH shift control, and a significant reduction in the decomposition of clavulanic acid was obtained. SIGNIFICANCE AND IMPACT OF THE STUDY: Clavulanic acid decomposition was considerably reduced as a result of the pH shift control. The results of this study can be applied for the efficient production of beta-lactamase inhibitory antibiotics.

Bioreactors↗

PubMed2001

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-induced apoptosis is dependent on activation of cysteine and serine proteases.

We examined the role of caspases and serine protease(s) in cell death induced by tumour necrosis factor-related apoptosis-inducing ligand (TRAIL). After incubation of adenocarcinoma cells with TRAIL, caspase-3, -8 were activated and the cleavage of Bid induced the release of cytochrome c, from the mitochondria to the cytosol. Tetrapeptide inhibitors of caspase-1, -2, -3, and -8 suppressed DNA fragmentation and attenuated the release of cytochrome c, whereas inhibitors of caspase-5 did not. Interestingly, the general serine protease(s) inhibitor 4-(2-aminoethyl)benzylsulfonyl fluoride (AEBSF) resulted in the arrest of apoptosis. However, the AEBSF did not prevent the release of mitochondrial cytochrome c during TRAIL-induced apoptosis. From these results, we postulate that serine protease(s) may be involved in post-mitochondrial apoptotic events, that lead to the activation of the initiator, caspase-9.

Apoptosis↗

PubMed2001

Growth-inhibitory effect of adenovirus-mediated p53 gene transfer on medulloblastoma cell line, Daoy, harboring mutant p53.

To improve the survival rate, gene therapy, such as the replacement of inactivated tumor suppressor genes, has become a new investigational adjuvant treatment modality for human malignancies. We investigated the effect of adenovirus(Ad)-mediated transfer of wildtype p53 tumor suppressor gene on the medulloblastoma cell line, Daoy, which harbors mutant-type p53 gene. At 50 multiplicity of infection (moi), immunohistochemical staining with p53 monoclonal antibody showed positive staining in all cells 2 days after Ad-CMV-p53 infection. The high expression of wild-type p53 protein was detected in Ad-CMV-p53-infected cells, and expression of wild-type p53 protein peaked on day 2 after the infection. The growth of Ad-CMV-p53-infected cells was greatly suppressed in vitro, and the Ad-CMV-p53 treatment significantly reduced the tumor mass in vivo. The mean weight of Ad-CMV- infected tumors was only 16% of those which were mock infected, and 25% of those which were Ad-CMV-beta-gal infected. On microscopic examination, Ad-CMV-p53-infected tumors showed numerous apoptotic bodies. This Ad-CMV-p53 gene transfer showed high transduction efficacy and expression, resulting in significant growth inhibition of Daoy harboring mutant type p53.

Adenoviruses, Human↗

PubMed2001

Protein kinase C activation by PMA rapidly induces apoptosis through caspase-3/CPP32 and serine protease(s) in a gastric cancer cell line.

Phorbol 12-myristate 13-acetate (PMA) rapidly induced cell death in SNU-16 gastric adenocarcinoma cells. DNA ladder formation and caspase-3/CPP32 activation were observed in PMA treated cells indicating that PMA induces apoptosis. z-DEVD-fmk, specific inhibitor of caspase-3/CPP32, inhibited the induction of apoptosis by PMA, demonstrating that caspase/CPP32 are critically involved in PMA-induced apoptosis. The serine protein inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride effectively blocked apoptosis, and also prevented caspase-3/CPP32 activation. Go6983, a specific inhibitor of PKC, almost completely suppressed apoptosis and caspase-3/CPP32 activation. Furthermore, 1,2-dihexanoyl-sn-glycerol, an endogenous activator of PKC, induced apoptosis detected by DNA fragmentation and Hoechst 33258 nuclear staining. From these results, we conclude that PMA is not only a tumor promoter, but can also induce apoptosis in gastric cancer cells. PMA-induced apoptosis appears to be mediated through activation of protein kinase C, and the activation of serine protease(s) and caspase-3/CPP32 may be the molecular mechanisms by which PMA induces apoptosis.

Adenocarcinoma↗

PubMed2000

Mitomycin C induces apoptosis in a caspases-dependent and Fas/CD95-independent manner in human gastric adenocarcinoma cells.

We investigated the mechanism of mitomycin C (MMC)-induced apoptosis in SNU-16 human gastric adenocarcinoma cells. Caspase-8 and caspase-3 were activated in MMC-treated cells whereas caspase-1 was not activated, and cytochrome c was released from mitochondrial membrane to cytosol suggesting that caspase-9 was activated during the MMC-induced apoptotic process. Protein kinase C (PKC) delta was cleaved to its characteristic 40 kDa fragment in a caspase-3-dependent manner; on the other hand PKC zeta was cleaved to approximately 40 kDa independently of caspase-3 in the drug-induced apoptosis of the cells. Incubation with z-DEVD-fmk and benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk) almost completely abrogated MMC-induced DNA fragmentation, indicating that activation of these caspases was crucially involved in MMC-induced apoptosis. Activation of caspase-8 in response to Fas triggering by recruitment of caspase-8 to the Fas has also been found, however, MMC did not induce FasL and Fas expression, as evidenced by reverse transcriptase-polymerase chain reaction and Western blotting. Taken together, these findings indicate that MMC-induced apoptosis in SNU-16 cells was mediated by caspase-8, caspase-9, and caspase-3 activation independently of FasL/Fas interactions.

Adenocarcinoma↗

PubMed2000

Protein kinase C activation by phorbol ester increases in vitro invasion through regulation of matrix metalloproteinases/tissue inhibitors of metalloproteinases system in D54 human glioblastoma cells.

To elucidate possible mechanisms of phorbol 12-myristate 13-acetate (PMA) induced in vitro invasiveness of glioblastoma cells, we examined expression levels of membrane-type 1 matrix metalloproteinase (MT1-MMP), MMP-2, MMP-9 and tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 using Western blotting and gelatin zymography assay, and found that PMA induced the secretion of MMP-9, activated MMP-2 proenzyme to fully active form of 59 kDa, down-regulated the TIMP-1 and TIMP-2 secretion, and increased MT1-MMP on the cell surface. However, PKC inhibitor Go 6983 reversed all of these effects brought about by PMA. We, therefore, conclude the activation of PKC by PMA in these cells plays a critical role in the regulation of MMPs/TIMPs system, which has a major role in tumor invasion and metastasis.

Brain Neoplasms↗

PubMed2000

Bioconversion of cellulose into ethanol by nonisothermal simultaneous saccharification and fermentation.

The kinetic characteristics of cellulase and beta-glucosidase during hydrolysis were determined. The kinetic parameters were found to reproduce experimental data satisfactorily and could be used in a simultaneous saccharification and fermentation (SSF) system by coupling with a fermentation model. The effects of temperature on yeast growth and ethanol production were investigated in batch cultures. In the range of 35-45 degrees C, using a mathematical model and a computer simulation package, the kinetic parameters at each temperature were estimated. The appropriate forms of the model equation for the SSF considering the effects of temperature were developed, and the temperature profile for maximizing the ethanol production was also obtained. Briefly, the optimum temperature profile began at a low temperature of 35 degrees C, which allows the propagation of cells. Up to 10 h, the operating temperature increased rapidly to 39 degrees C, and then decreased slowly to 36 degrees C. In this nonisothermal SSF system with the above temperature profile, a maximum ethanol production of 14.87 g/L was obtained.

Bioreactors↗

PubMed2000

Influence of glutathione S-transferase M1 and T1 genotypes on larynx cancer risk among Korean smokers.

Glutathione S-transferase (GST) isoenzymes are involved in the detoxification of major carcinogens present in tobacco smoke. It is thus conceivable that deficiency in GST activity due to homozygous deletions of the GSTM1 and GSTT1 genes (the null genotypes) may modulate susceptibility to smoking-induced cancers. The influence of the GSTM1 and GSTT1 null genotypes on larynx cancer risk among the Korean population were evaluated using peripheral blood DNA from 82 larynx cancer patients and 63 healthy controls, all of whom were male current smokers. Increased larynx cancer risk was related to the GSTM1 null genotype (odds ratio (OR)=3.53, 95% confidence interval (CI)=1.27-9.83). The OR associated with the GSTT1 null genotype was also increased, but did not reach statistical significance (OR=1.83, 95% CI=0.70-4.79). Individuals lacking both the GSTM1 and GSTT1 genes were at a significantly higher risk for larynx cancer than individuals with both genes present (OR=4.04, 95% CI=1.33-12.30). These data confirm that the GSTM1 null genotype is an important risk modifier for larynx cancer among Korean smokers and combined GSTM1 and GSTT1 null genotypes could be a useful predictor of genetic susceptibility to larynx cancer.

Adult↗

PubMed2000

Matrix metalloproteinases in human gliomas: activation of matrix metalloproteinase-2 (MMP-2) may be correlated with membrane-type-1 matrix metalloproteinase (MT1-MMP) expression.

To evaluate possible roles of matrix metalloproteinase (MMP)-1, -2, tissue inhibitor of metalloproteinase (TIMP)-1, -2 and membrane-type-1 matrix metalloproteinase (MT1-MMP) in invasion of human gliomas, expressions of these proteins were investigated in ten cases of human glioma and two meningioma tissues and eight human glioma cell lines. In gelatin zymography, MMP-2 activities of glioblastomas were higher than astrocytomas. The activated form of MMP-2 was seen in five of six cases of glioblastomas, but not in astrocytomas. MMP-9 activity was detected in all cases of malignant astrocytomas but the reactivity of MMP-9 was weaker than that of MMP-2. MT1-MMP mRNA expression in glioblastomas was higher than that in astrocytomas. Five cases of glioblastomas with activated form of MMP-2 had MT1-MMP expressions. In vitro, human glioma cell lines with high expression of MT1-MMP also showed high MMP-2 activity. TIMP-1 transcripts were constitutively present in almost all glioma tissues and cell lines, whereas TIMP-2 mRNA were weak especially in malignant gliomas. Imbalance of TIMP-2/MMP-2 was observed using immunoprecipitation analysis in a glioma cell line. High expression of MMP-2 and MT1-MMP is possibly involved in invasiveness of malignant glioma.

Animals↗

PubMed2000

TNF-alpha induces apoptosis mediated by AEBSF-sensitive serine protease(s) that may involve upstream caspase-3/CPP32 protease activation in a human gastric cancer cell line.

In the present study, we investigated the role of caspase-3/CPP32 and serine protease(s) in cell death induced by TNF-alpha in SNU-16 human gastric adenocarcinoma cells. Apoptosis induced in SNU-16 cells by TNF-alpha was accompanied by the activation of caspase-3/CPP32. After treatment with TNF-alpha, PKCdelta cleaved to its characteristic 40 kDa fragment in a caspase-3/CPP32 dependent manner. Incubation with z-DEVD-fmk completely abrogated TNF-alpha-induced DNA fragmentation, indicating that activation of caspase-3/CPP32 was crucially involved in TNF-alpha-induced apoptosis. In addition, serine protease inhibitor, 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF), clearly inhibited all the features of apoptosis including DNA fragmentation and chromatin condensation. Furthermore, in the AEBSF treated SNU-16 cells, only intact PKCdelta was detected by immunoblot analysis, suggesting that activation of caspase-3/CPP32 was blocked. Thus, the AEBSF-sensitive step may involve an upstream caspase-3/CPP32 protease activation. Taken together, these results suggest that both caspase-3/CPP32 and serine protease(s) are activated and play an important role in TNF-alpha induced apoptosis in SNU-16 cells.

Adenocarcinoma↗

PubMed2000

Clinical usefulness of serum and plasma vascular endothelial growth factor in cancer patients: which is the optimal specimen?

Vascular endothelial growth factor (VEGF) is secreted by various human cancer cells and plays a key role in cancer angiogenesis and metastasis. Recently, evidence of VEGF storage in blood cells including platelets has been reported. The serum VEGF levels were reported to increase during clotting as a result of its release from platelets, and plasma sample instead of serum was recommended for measuring the circulating VEGF more accurately. However, platelets have been implicated in tumor metastasis since circulating tumor cells forming aggregates with platelets were observed. The purpose of this study was to clarify which is an optimal specimen to measure VEGF in cancer patients, serum or plasma. We measured serum and plasma VEGF levels and platelet counts in 173 cancer patients and 42 healthy people, and found that serum VEGF levels were significantly higher than matched plasma VEGF and the VEGF difference (serum VEGF - plasma VEGF) correlated with platelet counts (r=0.624, p<0.05) in both cancer patients and healthy controls. We selected cancer patients with normal platelet counts (130-400x103/microl, Plt-normal cancer group). Interestingly, serum VEGF levels were higher in Plt-normal cancer group than in healthy controls. The theoretical platelet-derived VEGF in serum, calculated based on actual blood platelet counts (pg per 106 platelets), was also significantly higher in Plt-normal cancer group than in normal controls. It is, therefore, suggested that, although the serum VEGF levels are affected by blood platelets, platelet-derived VEGF also reflect biology of cancer cells, and that serum would be the more useful specimen for measurement of circulating VEGF in cancer patients for prognosis.

Blood Specimen Collection↗

PubMed2000

Growth inhibitory effect on glioma cells of adenovirus-mediated p16/INK4a gene transfer in vitro and in vivo.

The tumour suppressor gene p16/INK4a encodes a specific inhibitor of the cyclin D-dependent kinases CDK4 and CDK6. p16/INK4a prevents the association of CDK4 with cyclin D1, and subsequently inhibits phosphorylation of retinoblastoma tumour suppressor protein (pRb), thus preventing exit from the G1 phase. In human cancers, the estimated frequency of genetic alteration involving the p16/INK4a locus is believed to be second only to alteration of p53. A high frequency (greater than 50%) of homozygous p16/INK4a gene deletion has been demonstrated in glioblastoma tissues and p16/INK4a is altered in 80% of glioma cell lines. Therefore, restoration of p16/INK4a would suppress cell proliferation and induce cell growth arrest. We showed here that restoration of p16/INK4a expression in p16 negative U87MG, U251MG and partially deleted U373MG by Ad-CMV-p16/INK4a induced growth suppression in vitro and in vivo. Expression of p16 transferred by Ad-CMV-p16/INK4a in glioma cells was highly efficient and maintained for more than seven days. In addition, we found that the endogenous status of p16 and Rb might affect the expression of exogenous p16/INK4a gene and inhibitory effect of cell proliferation. Even though, there were several factors affecting the efficiency of Ad-CMV-p16/INK4 gene transfer, our results suggest that Ad-CMV-p16 gene therapy strategy is potentially useful and warrants further clinical investigation for the treatment of gliomas.

Adenoviridae↗

PubMed1998

Differential expression of protein kinase C isoforms in diethylnitrosamine-initiated rat liver.

Although protein kinase C (PKC), a family of 12 related isoforms, plays an important role in carcinogenesis, little is known about the specific role of each isoform in the initiation stage of hepatocarcinogenesis. The subcellular distribution of PKC isoforms in the early stages of diethylnitrosamine (DEN)-initiated hepatocarcinogenesis was therefore examined. Three-week-old female Sprague-Dawley rats were intraperitoneally injected twice in 1 week with DEN; all animals were sacrificed at 1, 2 and 24 h and 3 and 7 days after the second injection. PKCalpha and -beta expression in both cytosolic and particulate fractions decreased as a result of 1 h of DEN treatment and this effect lasted for 7 days. In both fractions, PKCepsilon expression showed a marked increase by DEN treatment, while the expression of PKCdelta and -zeta was almost unchanged. These results suggest that differential expression of PKC isoforms may play an important role in the early stage of DEN-initiated hepatocarcinogenesis in rats.

Animals↗