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S H Kang

Publications and source records attributed to S H Kang.

At least 37 records · Page 2Linked to original sources
PubMed2000

An approximate unconditional test of non-inferiority between two proportions.

This paper investigates an approximate unconditional test for non-inferiority between two independent binomial proportions. The P-value of the approximate unconditional test is evaluated using the maximum likelihood estimate of the nuisance parameter. In this paper, we clarify some differences in defining the rejection regions between the approximate unconditional and conventional conditional or unconditional exact test. We compare the approximate unconditional test with the asymptotic test and unconditional exact test by Chan (Statistics in Medicine, 17, 1403-1413, 1998) with respect to the type I error and power. In general, the type I errors and powers are in the decreasing order of the asymptotic, approximate unconditional and unconditional exact tests. In many cases, the type I errors are above the nominal level from the asymptotic test, and are below the nominal level from the unconditional exact test. In summary, when the non-inferiority test is formulated in terms of the difference between two proportions, the approximate unconditional test is the most desirable, because it is easier to implement and generally more powerful than the unconditional exact test and its size rarely exceeds the nominal size. However, when a test between two proportions is formulated in terms of the ratio of two proportions, such as a test of efficacy, more caution should be made in selecting a test procedure. The performance of the tests depends on the sample size and the range of plausible values of the nuisance parameter. Published in 2000 by John Wiley & Sons, Ltd.

Child↗
PubMed2000

High-throughput comprehensive peptide mapping of proteins by multiplexed capillary electrophoresis.

A novel multimodal method for peptide mapping of proteins by multiplexed capillary electrophoresis (CE) is presented. By combining charge to size separations in four different channels and micellar electrokinetic chromatography for hydrophobicity-based separations in two different channels in a 96-capillary array, peptide fragments of digested proteins were readily resolved and showed unique fingerprints. Each capillary spanned several diodes in a photodiode array (PDA) for absorption measurement. The 96 capillaries were monitored simultaneously at 214 nm by a single PDA element with 1,024 diodes, and analysis was completed within 45 min. This demonstrates that it is possible to rapidly screen biotechnological products as well as to efficiently optimize separation conditions in CE by a combinatorial approach.

Amino Acid Sequence↗
PubMed2000

Methylation of specific CpG sites in the promoter region could significantly down-regulate p16(INK4a) expression in gastric adenocarcinoma.

Silencing of p16(INK4a) by methylation of the CpG islands in the promoter region has been found to be an alternative mechanism of inactivation in several tumors. However, in gastric carcinoma, the relationship between methylation status and the transcriptional silencing of the p16 gene remains to be clarified. In this study, we investigated whether methylation of a few specific CpG sites in the promoter region could significantly down-regulate p16 activity in the tumorigenesis of gastric carcinoma. By Southern analysis and bisulfite-modified genomic sequencing of 9 gastric-carcinoma cell lines, we found that the 5 cell lines (55.5%) not expressing p16 mRNA had methylated CpG sites at the promoter region of p16. In addition, we analyzed the p16-protein expression of 28 primary gastric carcinomas and their normal counterparts by immunohistochemical staining (IHC) on paraffin sections. Loss of p16 expression was detected in 6 cases (22%). In 5 out of these 6 (83%), the actual p16 gene was inactivated by de novo methylation of the promoter sites. Taken together, these results suggest a strong correlation between de novo methylation of a few specific CpG sites and transcriptional silencing of the p16 gene in gastric carcinoma.

Adenocarcinoma↗
PubMed2000

On-column derivatization for the analysis of homocysteine and other thiols by capillary electrophoresis with laser-induced fluorescence detection.

On-column derivatization and capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection has been developed for the fully automated assay of homocysteine and other thiols. The unique feature of this CE technique comes from the direct injection of a sample including homocysteine, enabling the derivatization with 4-aminosulfonyl-7-fluoro-2,1,3-benzoxadizole (ABD-F) to be accomplished in the capillary. After the derivatization for 10 min at 50 degrees C, the homocysteine was analyzed within 7 min under an applied electric field of 333 V cm(-1). The detection limit obtained for homocysteine with on-column LIF detection was 5.0 nM, as compared to 2.5 nM with pre-column LIF detection. The method is a very simple, fast, and practical approach for the fully automated assay of homocysteine and other thiols contained in low-volume and low-concentration samples.

Electrophoresis, Capillary↗
PubMed2000

Transcriptional inactivation of the tissue inhibitor of metalloproteinase-3 gene by dna hypermethylation of the 5'-CpG island in human gastric cancer cell lines.

The tissue inhibitor of metalloproteinase-3 (TIMP-3), a recently cloned member of TIMP gene family, has been implicated in the negative regulation of tumor cell invasion and tumor growth. Down-regulation of this gene has been shown to occur in a mouse carcinogenesis model, suggesting that it might play a role in the tumor progression of some cancers. In this study, we used human gastric cancer cell lines to investigate whether TIMP-3 gene expression is suppressed in human gastric cancer. We examined whether aberrant DNA methylation of the 5'-CpG island of the TIMP-3 gene is involved in this cancer. Nine of 10 human gastric cancer cell lines completely lost TIMP-3 gene expression compared with normal samples. Southern blot analysis and bisulfite genomic sequencing revealed aberrant hypermethylation near the transcription-start site of the TIMP-3 gene in all cell lines lacking TIMP-3 expression. Treatment of these cell lines with the demethylating agent 5-aza-2'-deoxycytidine restored TIMP-3 gene expression. Our results suggest that the TIMP-3 gene is another early target of tumor-associated aberrant DNA methylation in human gastric carcinogenesis. Consequently, genetic silencing of TIMP-3 may lead to a more malignant and invasive phenotype in these cancer cells.

Animals↗
PubMed2000

Micellar electrokinetic chromatography for the analysis of D-amygdalin and its epimer in apricot kernel.

We have developed a simple, rapid and reproducible method for the determination of D-amygdalin and its epimer by using micellar electrokinetic chromatography (MEKC). Separation of D-amygdalin was performed in a 20 mM sodium borate buffer (pH 8.5) containing 300 mM sodium dodecyl sulfate using a bare fused-silica capillary. The eluates were monitored by the absorbance at 210 nm. The applied electric field was 278 V/cm, and the time needed for the separation of D-amygdalin did not exceed 6 min. The calibration curve for D-amygdalin showed excellent linearity in the concentration range of 5-500 microg/ml. The migration time and the corrected peak area show relative standard deviations (n=6) of 0.86% and 1.48%, respectively. The limit of detection (S/N=3) for D-amygdalin was 2 microg/ml. Under acidic and neutral conditions, amygdalin exists only as the D-form; however, under basic conditions, it shows both the D- and L-forms with a concentration ratio of 1:1.3 (D-amygdalin/L-amygdalin). Results of HPLC, UV-Vis spectrophotometry, and mass spectrometry reconfirmed the identification of D-amygdalin and its epimer. The number of theoretical plates of D-amygdalin is about 100,000 in MEKC, which is significantly higher than approximately 8,000 of HPLC. This method has been successfully applied to the determination of amygdalin epimers in various apricot kernel extracts and pharmaceutical products.

Amygdalin↗
PubMed2000

Incorporating model uncertainties along with data uncertainties in microbial risk assessment.

Much research on food safety has been conducted since the National Food Safety Initiative of 1997. Risk assessment plays an important role in food safety practices and programs, and various dose-response models for estimating microbial risks have been investigated. Several dose-response models can provide reasonably good fits to the data in the experimental dose range, but yield risk estimates that differ by orders of magnitude in the low-dose range. Hence, model uncertainty can be just important as data uncertainty (experimental variation) in risk assessment. Although it is common in risk assessment to account for data uncertainty, it is uncommon to account for model uncertainties. In this paper we incorporate data uncertainties with confidence limits and model uncertainties with a weighted average of an estimate from each of various models. A numerical tool to compute the maximum likelihood estimates and confidence limits is addressed. The proposed method for incorporating model uncertainties is illustrated with real data sets.

Colony Count, Microbial↗
PubMed2000

Impaired adaptation to renal mass reduction in the polycystic rat.

Autosomal dominant polycystic kidney disease (ADPKD) is a serious cause of renal failure. In many renal-disease models, surgical renal mass reduction accelerates disease progression. We explored whether surgical renal mass reduction and the method of renal mass reduction accelerate the course of ADPKD. Studies were conducted in male heterozygous cystic Han:SPRD rats and unaffected littermate controls. Control and cystic rats were subjected to 50% renal mass reduction by uninephrectomy, 50% renal mass reduction by infarction of half of each kidney, or sham operation. Most groups were followed up to the age of 20 weeks, with serial measurements of blood pressure and proteinuria. At 20 weeks, glomerular filtration rate (GFR) and renal plasma flow (RPF) rate were measured. Similar studies to 12 weeks of age were performed in additional groups of control and cystic rats with either sham operation or 50% renal infarction. In noncystic rats, uninephrectomy led to minimal effects on blood pressure and proteinuria and to substantial compensatory renal hypertrophy, hyperfiltration, and hyperperfusion. Similar renal mass reduction by segmental infarction led to greater values for blood pressure and proteinuria and significant compensatory hyperfiltration. In contrast, the cystic rats showed a significant reduction in baseline renal blood flow, more profound increases in blood pressure and proteinuria, and no compensatory increases in GFR and RPF after reduction of renal mass. These studies suggest that the ability of cystic kidneys to respond to acquired loss of nephrons is impaired and that these kidneys are at greater risk when additional renal injury is superimposed.

Animals↗
PubMed2000

Stabilization effect of zeolite on DHFR mRNA in a wheat germ cell-free protein synthesis system.

The effects of zeolites and monocations on the protein synthesis in a cell-free system derived from wheat germ were investigated. M type of synthetic zeolite markedly enhanced the translation efficiency. Whereas this kind of stimulatory effect of zeolite in an Escherichia coli cell-free system resulted from a change in the salt compositions of the reaction solution with the addition of zeolite, the enhancement of protein synthesis in a wheat germ cell-free system was not due to the ion exchange reaction of zeolites. From the results of mRNA stability analysis, it was found that zeolite could stabilize the mRNA in a wheat germ cell-free protein synthesis system. The stabilization of mRNA by the simple addition of zeolites is useful for the enhancement of protein synthesis in a wheat germ cell-free system, since conventional methods to improve mRNA stability, such as the addition of nuclease inhibitor, have not been effective for a wheat germ cell-free system.

Journal Article↗
PubMed2000

Characterization of a novel DNA polymorphism in the human CYP21 gene and application for DNA diagnosis of congenital adrenal hyperplasia.

OBJECTIVES: Congenital adrenal hyperplasia (CAH) is a common endocrine disorder and CYP21 (21-OH, EC 1.14.99.10) deficiency is the most common cause of the disease. The presence of a pseudogene and a wide range of mutation types often makes DNA diagnosis difficult. Analysis of mutant alleles from patients with CAH identified a new DNA polymorphism in exon 10. To test the usefulness of this polymorphism, linkage analysis was performed using three RFLP's at both end of the CYP21 gene in patients and controls. DESIGN AND PATIENTS: Genomic DNA was extracted from 21 unrelated patients and 39 unaffected individuals. Haplotyping analysis was performed for three RFLPs, MspI and Fnu4HI in intron 2 and a new SmaI RFLP in exon 10. All three polymorphic sites were characterized by DNA sequencing and usefulness of these RFLPs for DNA diagnosis was tested in patients' families. MEASUREMENT: CAH patients were diagnosed by clinical symptoms and biochemical tests. Allele frequencies and heterozygosities were studied for three RFLP's in patients and controls using polymerase chain reaction (PCR). RESULTS: A new SmaI RFLP showed a sequence difference as G or A at the nucleotide position 2694 in exon 10. Sequences at the MspI and Fnu4HI polymorphic sites were T or C at the nucleotide position 395 and 453, respectively. All of these RFLPs showed biallelic DNA polymorphisms and codominant segregation in family analysis. Heterozygosities were 0.31 for MspI, 0.48 for Fnu4HI and 0.44 for SmaI in normal individuals. There was no linkage disequilibrium for three RFLPs between patients and controls. CONCLUSIONS: The SmaI RFLP can be useful for linkage analysis and DNA diagnosis in conjunction with RFLPs in intron 2 in CAH families because the polymorphic site is within the active gene at the 3' end. DNA sequencing results revealed that these RFLPs were created by gene conversions as with other mutations in the CYP21 gene.

Adrenal Hyperplasia, Congenital↗
PubMed2000

Development of a centrifugal pump with thick blades.

We have developed a centrifugal blood pump with thick impeller blades (60% of pitch) to obtain a small tip clearance. An unshrouded impeller with 6 backward curved thick blades was used to reduce the dead zone between the shroud and upper casing. A streamline angle in volute was uniform in circumferential direction by continuity and angular momentum conservation. To prove the effectiveness of small tip clearance, performance and hemolysis tests were conducted on pumps with a tip clearance of 0.5, 1.5, and 2.0 mm at exit with the blade thickness of 60% of pitch, and with that of 1.0, 2.0, and 2.5 mm at exit with the thickness of 40% of pitch. The results showed that the smaller the tip clearance, the better the hydrodynamic and hemolytic performance. The best result was seen in the pump with tip clearance of 0.5 mm with a blade thickness of 60% of pitch. These results suggest that a centrifugal pump with thick blades and a small tip clearance can be a promising alternative as a cardiopulmonary bypass pump.

Animals↗
PubMed2000

Aromatase and sulfatase inhibitors from Lepiota americana.

From an edible mushroom Lepiota americana Pk., (Agaricaceae), 2-aminophenoxazin-3-one that inhibited aromatase at IC50 = 5.7 microM and 3 beta-hydroxy-5,8-epidioxyergosta-6,22-diene that inhibited sulfatase at IC50 = 0.9 microM were isolated. Neither 2-aminophenoxazin-3-one was active against sulfatase nor was 3 beta-hydroxy-5,8-epidioxyergosta-6,22-diene active against aromatase.

Agaricales↗
PubMed2000

Nidogen is nonessential and not required for normal type IV collagen localization in Caenorhabditis elegans.

Nidogen (entactin) can form a ternary complex with type IV collagen and laminin and is thought to play a critical role in basement membrane assembly. We show that the Caenorhabditis elegans nidogen homologue nid-1 generates three isoforms that differ in numbers of rod domain endothelial growth factor repeats and are differentially expressed during development. NID-1 appears at the start of embryonic morphogenesis associated with muscle cells and subsequently accumulates on pharyngeal, intestinal, and gonad primordia. In larvae and adults NID-1 is detected in most basement membranes but accumulates most strongly around the nerve ring and developing gonad. NID-1 is concentrated under dense bodies, at the edges of muscle quadrants, and on the sublateral nerves that run under muscles. Two deletions in nid-1 were isolated: cg119 is a molecular null, whereas cg118 produces truncated NID-1 missing the G2 collagen IV binding domain. Neither deletion causes overt abnormal phenotypes, except for mildly reduced fecundity. Truncated cg118 NID-1 shows wild-type localization, demonstrating that the G2 domain is not necessary for nidogen assembly. Both nid-1 mutants assemble type IV collagen in a completely wild-type pattern, demonstrating that nidogen is not essential for type IV collagen assembly into basement membranes.

Alternative Splicing↗
PubMed2000

Spatial distribution and sampling plans for Thrips palmi (Thysanoptera: Thripidae) infesting fall potato in Korea.

The spatial distribution of adult and immature Thrips palmi Karny on fall potato, Solanum tuberosum L., on Cheju Island, Korea, was studied over a 2-yr period by visually inspecting potato leaves. The majority of thrips collected from the leaves were observed in the top one-third of the plant. The within-field spatial patterns of adults and immature thrips were aggregated. The slopes and intercepts of Taylor's power law did not differ among adults and immature thrips. A fixed-precision-level sampling plan was developed using the parameters from Taylor's power law and was tested with resampling simulations using eight independent data sets. Over a wide range of densities, the simulation demonstrated that actual sampling precision (d = SEM/mean) values at d = 0.25 averaged < 0.24 in all cases. A binomial sampling plan for estimating mean density was developed using an empirical model evaluated at tally thresholds (the minimum number of insects present before a leaf is considered infested) of one, three, five, and eight thrips per leaf. Increasing sampling size had little effect on the precision of the estimated mean regardless of tally threshold (T). However, increasing T had a dramatic effect on precision. The best tally threshold for estimating thrips density based on the applicable density ranges and the precision of the model was T = 5. A binomial sampling plan with a tally threshold of five and a fixed sample size of 30 leaves should be an effective replacement for enumerative counts when thrips average < 10 per leaf.

Animals↗
PubMed1999

Selective degradation of unfolded proteins by the self-compartmentalizing HtrA protease, a periplasmic heat shock protein in Escherichia coli.

HtrA, which has a high molecular mass of about 500 kDa, is a periplasmic heat shock protein whose proteolytic activity is essential for the survival of Escherichia coli at high temperatures. To determine the structural organization of HtrA, we have used electron microscopy and chemical cross-linking analysis. The averaged image of HtrA with end-on orientation revealed a six-membered, ring-shaped structure with a central cavity, and its side-on view showed a two-layered structure. Thus, HtrA behaves as a dodecamer consisting of two stacks of hexameric ring. HtrA can degrade thermally unfolded citrate synthase and malate dehydrogenase but cannot when in their native form. HtrA degraded partially unfolded casein more rapidly upon increasing the incubation temperature. However, it hydrolyzed oxidized insulin B-chain, which is fully unfolded, at nearly the same rate at all of the temperatures tested. HtrA also rapidly degraded reduced insulin B-chain generated by treatment of insulin with dithiothreitol but not A-chain or intact insulin. Moreover, HtrA degraded fully unfolded alpha-lactalbumin, of which all four disulfide bonds were reduced, but not the native alpha-lactalbumin and its unfolded intermediates containing two or three disulfide bonds. These results indicate that unfolding of the protein substrates, such as by exposure to high temperatures or reduction of disulfide bonds, is essential for their access into the inner chamber of the double ring-shaped HtrA, where cleavage of peptide bonds may occur. Thus, HtrA with a self-compartmentalizing structure may play an important role in elimination of unfolded proteins in the periplasm of Escherichia coli.

Amino Acid Sequence↗
PubMed1999

Transcriptional repression of the transforming growth factor-beta type I receptor gene by DNA methylation results in the development of TGF-beta resistance in human gastric cancer.

The transforming growth factor-beta (TGF-beta) signaling pathway subserves an essential tumor suppressor function in various cell types. A heteromeric complex composed of TGF-beta type I (RI) and type II (RII) receptors is required for TGF-beta signaling. We have identified a subset of human gastric cancer cell lines which are insensitive to TGF-beta and which express a low level of TGF-beta type I receptor mRNA relative to a gastric cancer cell line which is highly responsive to TGF-beta. Using these cells, we show that hypermethylation of a CpG island in the 5' region of the TGF-beta RI gene provides another potentially important mechanism of escape from negative growth control by TGF-beta. This hypermethylation was found in four of five human gastric cancer cell lines and five out of 40 (12.5%) primary tumors examined. In human gastric cancer cell lines, treatment with the demethylating agent, 5-aza-2'-deoxycytidine, resulted in increased expression of the TGF-beta RI gene, but not the RII gene. Transient transfection of an RI expression vector into the TGF-beta resistant SNU-601 cell line restores TGF-beta responsiveness. These findings suggest that one of the mechanisms of escape from autocrine or paracrine growth control by TGF-beta during carcinogenesis could involve aberrant methylation of CpG islands in the 5' region of the TGF-beta RI gene.

DNA Methylation↗
PubMed1999

Novel cationic amphiphiles as delivery agents for antisense oligonucleotides.

There has been great interest recently in therapeutic use of nucleic acids including genes, ribozymes and antisense oligonucleotides. Despite recent improvements in delivering antisense oligonucleotides to cells in culture, nucleic acid-based therapy is still often limited by the poor penetration of the nucleic acid into the cytoplasm and nucleus of cells. In this report we describe nucleic acid delivery to cells using a series of novel cationic amphiphiles containing cholic acid moieties linked via alkylamino side chains. We term these agents 'molecular umbrellas' since the cationic alkylamino chains provide a 'handle' for binding of nucleic acids, while the cholic acid moieties are likely to interact with the lipid bilayer allowing the highly charged nucleic acid backbone to traverse across the cell membrane. Optimal gene and oligonucleotide delivery to cells was afforded by a derivative (amphiphile 5) containing four cholic acid moieties. With this amphiphile used as a constituent in cationic liposomes, a 4-5 log increase in reporter gene delivery was measured. This amphiphile used alone provided a 250-fold enhancement of oligo-nucleotide association with cells as observed by flow cytometry. A substantial fraction of cells exposed to complexes of amphiphile 5 and fluorescent oligo-nucleotide showed nuclear accumulation of the fluorophore. Enhanced pharmacological effectiveness of antisense oligonucleotides complexed with amphiphile 5 was observed using an antisense splicing correction assay that activates a Luciferase reporter. Intracellular delivery, nuclear localization and pharmacological effectiveness of oligonucleotides using amphiphile 5 were similar to those afforded by commercial cytofectins. However, in contrast to most commercial cytofectins, the umbrella amphiphile showed substantial delivery activity even in the presence of high concentrations of serum.

3T3 Cells↗