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Biomedical subjects

W Choi

Publications and source records attributed to W Choi.

At least 19 recordsLinked to original sources
PubMed2006

Protective effects of Glycyrrhiza uralensis Fisch. on the cognitive deficits caused by beta-amyloid peptide 25-35 in young mice.

Amyloid beta protein (Abeta) may be involved in the progression of Alzheimer's disease (AD), by acting as a neurotoxin and eliciting oxidative stress. This study was designed to determine the effects of Glycyrrhiza uralensis Fisch. water extract (GWE) on the cognitive deficits and oxidative stress induced by the administration of Abeta(25-35) in mice. Mice in two of the four animal groups were fed an experimental diet containing either 0.5 or 1% GWE for the entire 6-week experimental period. Control mice and a further experimental group were fed a non-GWE diet. Abeta(25-35) was administered to the three experimental groups by intracerebroventricular (i.c.v.) injection (10 microg/10 microl/mouse) once per week in weeks 5 and 6 of the experimental period. Behavioral changes were assessed using both a passive avoidance (after the injection of Abeta(25-35) in week 5) and the Morris water-maze tests (after the injection of Abeta(25-35) in week 6). Control animals were administered vehicle alone. The prolonged consumption of a diet containing GWE ameliorated the cognitive deficits caused by the i.c.v. injections of Abeta(25-35). Treatment with Abeta(25-35) led to higher concentrations of thiobarbituric acid reactive substances in the brain, and GWE attenuated this response. There was a decrease in catalase activity in the group provided with 1% GWE. Acetylcholinesterase activity was significantly reduced in the brains of all GWE-treated animals compared to that in the non-GWE-fed experimental group. These results suggest that GWE exerts a protective effect against the cognitive impairments often observed in AD, and that in mice this effect is mediated by antioxidant actions against oxidative stress.

Aging↗
PubMed2005

Distribution and functional characterization of human Nav1.3 splice variants.

The focus of the present study is the molecular and functional characterization of four splice variants of the human Nav1.3 alpha subunit. These subtypes arise due to the use of alternative splice donor sites of exon 12, which encodes a region of the alpha subunit that resides in the intracellular loop between domains I and II. This region contains several important phosphorylation sites that modulate Na+ channel kinetics in related sodium channels, i.e. Nav1.2. While three of the four Nav1.3 isoforms, 12v1, 12v3 and 12v4 have been previously identified in human, 12v2 has only been reported in rat. Herein, we evaluate the distribution of these splice variants in human tissues and the functional characterization of each of these subtypes. We demonstrate by reverse transcriptase-polymerase chain reaction (RT-PCR) that each subtype is expressed in the spinal cord, thalamus, amygdala, cerebellum, adult and fetal whole brain and heart. To investigate the functional properties of these different splice variants, each alpha subunit isoform was cloned by RT-PCR from human fetal brain and expressed in Xenopus oocytes. Each isoform exhibited functional voltage-dependent Na+ channels with similar sensitivities to tetrodotoxin (TTX) and comparable current amplitudes. Subtle shifts in the V 1/2 of activation and inactivation (2-3 mV) were observed among the four isoforms, although the functional significance of these differences remains unclear. This study has demonstrated that all four human splice variants of the Nav1.3 channel alpha subunit are widely expressed and generate functional TTX-sensitive Na+ channels that likely modulate cellular excitability.

Alternative Splicing↗
PubMed2005

A pilot-scale photocatalyst-membrane hybrid reactor: performance and characterization.

We developed and tested a pilot-scale photocatalyst-membrane hybrid reactor for water treatment. The performance of the pilot-scale reactor was evaluated by monitoring the degradation efficiency of several organic pollutants and the membrane suction pressure at different operating conditions. The concentration of humic acids rather increased in the initial period of UV illumination and then decreased gradually, which could be ascribed to the photoinduced desorption of humic acids from the TiO2 surface. The decoloring rate of methylene blue was faster than that of rhodamine B, whereas the order of mineralization rates of the dyes was reversed. 4-chlorophenol of 100 ppb was fully degraded under UV irradiation in 2 hours, which suggests that this hybrid reactor would be more suitable in removing micropollutants in water. The reactor was operated with either continuous or intermittent suction mode. In a continuous suction mode, the formation of TiO2 cake layers on the membrane surface occurred and caused a substantial increase in suction pressure. However, no further fouling (or suction pressure build-up) took place with an intermittent suction mode with the 9-min suction and 3-min pause period. The photocatalyst-membrane hybrid reactor system developed in this study could be an attractive option for controlling micropollutants in water.

Biodegradation, Environmental↗
PubMed2004

Parental exposure to polycyclic aromatic hydrocarbons and the risk of childhood brain tumors: The SEARCH International Childhood Brain Tumor Study.

Experimental evidence suggests that parental exposure to polycyclic aromatic hydrocarbons (PAH), which occurs primarily through tobacco smoke, occupational exposure, and air pollution, could increase the risk of cancer during childhood. Population-based case-control studies carried out in seven countries as part of the SEARCH Program compared data for 1,218 cases of childhood brain tumors and 2,223 controls (1976-1994). Parental occupational exposure to PAH during the 5-year period before birth was estimated with a job exposure matrix. Risk estimates were adjusted for child's age, sex, and study center. Paternal preconceptional occupational exposure to PAH was associated with increased risks of all childhood brain tumors (odds ratio (OR) = 1.3, 95% confidence interval: 1.1, 1.6) and astroglial tumors (OR = 1.4, 95% confidence interval: 1.1, 1.7). However, there was no trend of increasing risk with predicted level of exposure. Paternal smoking alone (OR = 1.4) was also associated with the risk of astroglial tumors in comparison with nonsmoking, non-occupationally-exposed fathers. Risks for paternal occupational exposure were higher, with (OR = 1.6) or without (OR = 1.7) smoking. Maternal occupational exposure to PAH before conception or during pregnancy was rare, and this exposure was not associated with any type of childhood brain tumor. This large study supports the hypothesis that paternal preconceptional exposure to PAH increases the risk of brain tumors in humans.

Adolescent↗
PubMed2003

Computer-assisted treatment planning and analysis.

The Invisalign orthodontic system (Align Technology, Inc, Santa Clara, CA) is a series of clear removable appliances that is worn by a patient to correct malocclusions. Introduced in 1999, it has been applied to successfully correct an increasingly wide variety of malocclusions. Part of the success of the system is because of the innovative technologies inherent in the design of the appliances. During the development of the system, many challenges and issues needed to be overcome to realize the product. Many of these issues were not specific to Invisalign, and represented general problems in the area of computer-aided orthodontics. The general problems of developing a virtual model of a patient's dentition appropriate for use in orthodontics, performing a treatment plan on a virtual dentition model, and analyzing how accurately the virtual treatment plan executed in the patient's mouth are presented.

Computer Simulation↗
PubMed2003

Validation of Align Technology's Treat III digital model superimposition tool and its case application.

OBJECTIVE: An assessment of the efficacy and accuracy of three-dimensional computer-based predictive orthodontic systems requires that new methods of treatment analysis be developed and validated. DESIGN: Invisalign is a digitally fabricated, removable orthodontic appliance that has been commercially available since 1999. It is made up of two main components: 1) computerized graphical images of a patient's teeth moving through a series of stages from initial to final position; 2) pressure formed clear plastic appliances made from stereolithography models of the images in the first component. SETTING AND SAMPLE POPULATION: The manufacturer of Invisalign (Align Technology, Inc.) has created a software tool that can be used to superimpose digital models to evaluate treatment outcomes in three dimensions. Using this software, research was conducted to determine if a single operator could repeatedly superimpose two identical digital models using 12 selected points from the palatal rugae over 10 trials. The tool was then applied to one subject's orthodontic treatment. EXPERIMENT VARIABLES: The output from this tool includes rotations, translations and morphological changes. For this study, translations and rotations were chosen. RESULTS: The results showed that the digital superimposition was reproducible, and that after multiple trials, the superimposition error decreased. The average error in x, y, z, Rx, Ry and Rz after 10 trials was determined to approach approximately 0.2 mm in translation and less than 1 degree in rotation, with a standard deviation of 0.15 mm and 0.7 mm, respectively. The treatment outcome from a single Invisalign-treated bicuspid extraction case was also evaluated tooth-by-tooth in x, y, z, Rx, Ry and Rz dimensions. CONCLUSION: Using the palate, as a stable reference seemed to work well and the evaluation of the single case showed that many, but not all, of the planned movements occurred.

Adult↗
PubMed2001

Human kinesin superfamily member 4 is dominantly localized in the nuclear matrix and is associated with chromosomes during mitosis.

In a previous study, we identified the human counterpart of murine kinesin superfamily member 4 (KIF4), a microtubule-based motor protein [Oh, Hahn, Torrey, Shin, Choi, Lee, Morse and Kim (2000) Biochim. Biophys. Acta 1493, 219-224]. As an initial step to understand the function(s) of human KIF4, its subcellular localization in HeLa cells was examined by using immunocytochemical and subcellular fractionation methods, and it was found that most KIF4 is localized in the nucleus. Since murine KIF4 is known to transport cytoplasmic vesicles, dominant nuclear localization of the human counterpart was somewhat surprising. Subsequent subnuclear fractionation revealed predominant association of KIF4 with the nuclear matrix. These results clearly indicate that human KIF4 is, at least, a nuclear protein. In further confirmation of this conclusion, the hexapeptide PKLRRR (amino acids 773-778) in the molecule was found to function as a nuclear localization signal. During the mitotic phase of the cell cycle, human KIF4 was associated with the chromosomes, suggesting that human KIF4 might be a microtubule-based mitotic motor, with DNA as its cargo.

Adenocarcinoma↗
PubMed2001

A simple rule for classification of polychlorinated dibenzo-p-dioxin congeners on the basis of IR frequency patterns.

The IR spectra of 76 dioxin congeners with zero to eight chlorines have been calculated by the DFT (B3LYP) method. Close inspection of the calculated spectra provides a simple rule for IR spectral analysis in polychlorinated dibenzo-p-dioxins (PCDDs). All congeners with a common structural motif of chlorine substitution in either of two benzene rings share the same main IR frequency, and the chlorination of one ring has little influence on the vibrational frequencies of the other ring. As a result, the main ring vibrational frequencies of all dioxin congeners could be classified into 10 groups according to the chlorine substitution pattern. This simplifies the complex IR spectral analysis of PCDDs to identifying two main peaks in essence, each of which corresponds to either of two chlorinated benzene rings. The systematic trend originates from the mass effect of the substituted chlorines. The C-H bending (in plane) character in the ring skeleton vibration mode is affected in quite different ways, depending on whether the chlorine is substituted on longitudinal or lateral positions. In particular, when all the lateral positions (2, 3, 7, 8) are chlorinated in PCDDs, the vibrational frequency of a b(1u) mode (or its analogues in other symmetry) gives a characteristic IR peak around 1392 cm(-1). This peak is unique to all toxic congeners and could be used as an indicator for them.

Chlorine↗
PubMed2001

Lysophosphatidylcholine derived from deer antler extract suppresses hyphal transition in Candida albicans through MAP kinase pathway.

A family of 2-lysophosphatidylcholines (lyso-PCs) was isolated from deer antler extract, guided exclusively by hyphal transition inhibitory activity in Candida albicans. Structural determination of the isolated lyso-PCs by spectroscopic methods, including infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR, 2D correlation spectroscopy NMR, fast atom bombardment mass spectrometry and tandem mass spectrometry, confirmed that the natural products were composed of at least four different lyso-PCs varying in fatty acid moiety at the sn-1 position of the glycerol backbone. The major lyso-PCs were confirmed as 1-stearoyl-, 1-oleoyl-, 1-linoleoyl- and 1-palmitoyl-2-lyso-sn-glycero-3-phosphatidylcholines. Lyso-PC specifically suppressed the morphogenic transition from yeast to hyphae in C. albicans, without affecting the growth of either yeast or hyphae. Lyso-PC exerted hyphal transition that suppressed activity in the broad spectrum of the Candida species, such as C. albicans, Candida krusei, Candida guilliermondii and Candida parapsilosis. Northern analysis indicated that the suppression was mediated through the mitogen-activated protein kinase pathway.

Animals↗
PubMed2001

Visible light-induced degradation of carbon tetrachloride on dye-sensitized TiO2.

This study investigated an application of TiO2 photocatalyst sensitized with tris(4,4'-dicarboxy-2,2'-bipyridyl)ruthenium-(II) complex to CCl4 degradation under visible light irradiation. By injecting electrons from the photoexcited sensitizer to the conduction band, the sensitized TiO2 degraded CCl4 under the irradiation of lambda > 420 nm. The quantum yield of CCl4 dechlorination was about 10(-3). The dechlorination rate of CCl4 was reduced in the presence of dissolved O2 due to its competition for conduction band electrons. The photolysis rate was dependent on pH due to the strong pH dependence of the sensitizer adsorption on TiO2 surface with a maximum degradation rate achieved at pH approximately 3. A two-site Langmurian model successfully described the adsorption of the sensitizer on TiO2 particles. The monolayer coverage was achieved at the added sensitizer concentration of 10 microM at [TiO2] = 0.5 g/L. However, the photolysis rate of CCl4 showed a maximum at a sensitizer surface coverage of 0.3 monolayer. Since the photoinduced electron injection gradually depleted active sensitizer molecules on TiO2, sacrificial electron donors to regenerate the sensitizer were sought. 2-Propanol as an electron donor was efficient in the present RuIIL3/TiO2/CCl4 system, which showed no sign of deceleration in the dechlorination rate up to 6 h of irradiation.

Carbon Tetrachloride↗
PubMed2001

Chronic hepatitis: in vivo proton MR spectroscopic evaluation of the liver and correlation with histopathologic findings.

PURPOSE: To correlate the in vivo hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopic features of the chronic hepatitis-involved liver with the histopathologic stages of fibrosis. MATERIALS AND METHODS: Seventy-five patients with chronic hepatitis were examined with (1)H MR spectroscopy, which was performed in the right hepatic lobe. The peak areas of glutamine and glutamate complex (Glx), phosphomonoesters (PME), glycogen and glucose complex (Glyu), and lipid were measured on the liver spectra. The histopathologic features were correlated with the in vivo (1)H MR spectroscopic findings at each stage of chronic hepatitis. Fifteen healthy volunteers also were included as a control group. RESULTS: (1)H MR spectroscopy depicted Glx, PME, Glyu, and lipid in all livers. In the normal livers, the calculated mean (+/- SD) relative metabolite-to-lipid ratios of Glx, PME, and Glyu were 0.14 +/- 0.04, 0.03 +/- 0.01, and 0.21 +/- 0.04, respectively. The mean value of each metabolite-to-lipid ratio was significantly different between all stages of chronic hepatitis, and with the exception of the mean ratio at the interval between stages 0 and 1 (P > .05), the mean value increased significantly with increasing stage (P < .05). A pronounced peak was demonstrated at 3.9-4.1 ppm at (1)H MR spectroscopy of all stages of chronic hepatitis except stage 0. CONCLUSION: The increased Glx, PME, and Glyu levels relative to the lipid content with chronic hepatitis indicated the severity of fibrosis and thus were concordant with the histopathologic stages. In vivo (1)H MR spectroscopy might be a substitute for liver biopsy in the diagnosis and staging of chronic hepatitis.

Adolescent↗
PubMed2001

The predictive parameters of erythropoietin hyporesponsiveness in patients on continuous ambulatory peritoneal dialysis.

BACKGROUND: The present study was aimed at investigating the predictive parameters of erythropoietin (epoetin) hyporesponsiveness in patients on continuous ambulatory peritoneal dialysis (CAPD). METHODS: We studied 40 patients with end-stage renal disease who had been receiving CAPD for at least 6 months and epoetin therapy for at least more than 2 months. Pearson's simple correlation and multiple stepwise linear regression analysis was used to discover what parameter can predict epoetin resistance. We expressed epoetin resistance index (ERI) as weekly epoetin dose/hematocrit/body weight'. The dose of epoetin is titrated by about 25% every 2 to 4 weeks to maintain a target hematocrit level between 33% and 36%. RESULTS: We analyzed the relationship between ERI and other predictive parameters by Pearson's correlation. These results showed ERI has a statistically significant correlation with transferrin saturation (TS) (r = -0.327, p = 0.042), total weekly Kt/Vurea (r = -0.423, p = 0.018), serum albumin level (r = -0.458, p = 0.003), normalized protein catabolic rate (nPCR) (r = -0.479, p = 0.006), normalized protein equivalent of total nitrogen appearance (nPNA) (r = -0.488, p = 0.005) and serum C-reactive protein (CRP) (r = 0.332, p = 0.036). Regression analysis was performed using stepwise linear regression for multiple variables to discover the most independent variable which is correlated with ERI. ERI was entered as a dependent variable, whereas the other parameters (age, duration of peritoneal dialysis, serum albumin level, CRP, serum ferritin, total weekly Kt/Vurea, nPCR, nPNA, serum iPTH, serum aluminium, TS) were entered as independent variables. This analysis showed CRP is the most significant variable and, if CRP is excluded, nPNA is the significant variable. CRP has a statistically significant correlation with serum albumin level (r = -0.418, p = 0.007) and total weekly Kt/Vurea (r = -0.366, p = 0.043). High CRP group has more increased level of ERI (p < 0.05), age (p < 0.05) and serum creatinine level (p < 0.05) than normal control, but more decreased level of serum albumin (p < 0.01) and serum iron levels (p < 0.05). CONCLUSION: These results indicate that CRP is the most important predictor of epoetin hyporesponsiveness.

Adult↗
PubMed2000

Cross-resistance of a chlorpyrifos-methyl resistant strain of Oryzaephilus surinamensis (Coleoptera: Cucujidae) to fumigant toxicity of essential oil extracted from Eucalyptus globulus and its major monoterpene, 1,8-cineole.

The fumigant toxicities of eucalyptus essential oil and 1,8-cineole, the major component of eucalyptus oil, were tested against a chlorpyrifos-methyl resistant strain and a reference strain of the sawtoothed grain beetle, Oryzaephilus surinamensis (L.). The resistant strain showed 1.9- and 2.2-fold higher tolerance against essential oil and 1,8-cineole fumigation toxicity, respectively, relative to the susceptible strain. The increased tolerance for the essential oil may be the result of cross-resistance. The resistance mechanisms in the resistant strain are discussed in relation to elevated detoxifying enzymes such as cytochrome P450 and esterases.

Journal Article↗
PubMed2000

Molecular characterization of human SUR2-containing K(ATP) channels.

The distribution of human sulfonylurea receptor-2 (SUR2)-containing K(ATP) channels was investigated using reverse transcriptase-polymerase chain reaction (RT-PCR). mRNA for SUR2B was detected in a variety of tissues including brain, skeletal, cardiac and smooth muscle, whereas SUR2A message was restricted to cardiac and skeletal muscle. An additional splice variant of SUR2 that lacked exon 17 was also identified by RT-PCR in tissues expressing both SUR2A and SUR2B or SUR2B alone. Quantification of RNA for SUR2 exon 17+ and SUR2 exon 17- splice variants using real-time Taqman PCR indicated differential levels of expression in brain, kidney, skeletal muscle, heart and small intestine. Interestingly, the SUR2 exon 17+ variant is the major species expressed in all tissues examined in this study. Each of the SUR2 splice variants transiently expressed with the inward rectifier Kir 6.2 formed functional K(ATP) channels in HEK 293 cells as assessed either by changes in DiBAC(4)(3) fluorescence responses or glyburide-sensitive whole cell currents. Collectively, our findings demonstrate that various SUR2 splice variants have distinct expression patterns and can form functional K(ATP) channels.

ATP-Binding Cassette Transporters↗
PubMed2000

Identification of the human homologue of mouse KIF4, a kinesin superfamily motor protein.

A combination of RT-PCR with cDNA library screening led to the identification of the human homologue of murine KIF4 (mKIF4), a microtubule-based motor protein. The nucleotide sequence of human KIF4 (hKIF4) comprised part of the 5' untranslated region (UTR), a long open reading frame (ORF) encoding 1232 amino acids, and the entire 3' UTR. Homologies with mKIF4 were 82% and 85% for nucleotides and amino acids, respectively. A single transcript of 5. 0 kb was highly expressed in hematopoietic tissues including fetal liver, spleen, and thymus, and adult thymus and bone marrow. Comparison of the ORF with that of mKIF4 revealed some dissimilarities in the putative cargo binding domain which might affect binding specificities.

Amino Acid Sequence↗
PubMed2000

Expression of translationally controlled tumor protein mRNA in human colon cancer.

The translationally controlled tumor protein (TCTP) was first identified as a tumor-associated protein. Here we described the expression profile of TCTP mRNA using a panel of normal human tissues. We also investigated the cell-cycle-dependent expression of the TCTP mRNA using synchronized cultures of Saccahromyces cerevisiae. The TCTP gene was constantly expressed through the yeast cell cycle. The expression of TCTP mRNA from three human colon carcinoma cell lines and their tumors xenografted in a nude mouse was studied. Our data imply that the TCTP is a housekeeping gene and that its deregulation may be involved in the tumor development of colon carcinoma.

Adenocarcinoma↗
PubMed2000

Cyberostracism: effects of being ignored over the Internet.

Ostracism is such a widely used and powerful tactic that the authors tested whether people would be affected by it even under remote and artificial circumstances. In Study 1, 1,486 participants from 62 countries accessed the authors' on-line experiment on the Internet. They were asked to use mental visualization while playing a virtual tossing game with two others (who were actually computer generated and controlled). Despite the minimal nature of their experience, the more participants were ostracized, the more they reported feeling bad, having less control, and losing a sense of belonging. In Study 2, ostracized participants were more likely to conform on a subsequent task. The results are discussed in terms of supporting K. D. Williams's (1997) need threat theory of ostracism.

Adolescent↗