Biomedical subjects

S C Choi

Publications and source records attributed to S C Choi.

At least 19 recordsLinked to original sources

PubMed2006

Characteristics of biofilm community formed in the chlorinated biodegradable organic matter-limited tap water.

The aim of this study was to characterize the influence of free chlorine residual on biofilm formation in a chlorinated system in which the biodegradable organic matter (BOM) was limited. The biofilm community was characterized through a community-level physiological profile (CLPP) that was generated using the Biolog GN microplate-based community-level assay. The chlorinated system was run at chlorine residual concentrations of 0.3, 0.5, and 1.0 mg l(-1) with the provision of BOM-limited tap water (0.01 mg l(-1) as assimilable organic carbon and 0.06 mg l(-1) as biodegradable dissolved organic carbon). For comparison, an unchlorinated system was operated in parallel under the same condition. The number of viable heterotrophic bacteria in the biofilm that formed in the chlorinated system over the 3 months of operation averaged 7.2 x 10(3), 4.8 x 10, and 1.6 x 10 CFU cm(-2) for the chlorine residual concentrations of 0.3, 0.5, and 1.0 mg l(-1), respectively. In the unchlorinated system, the average bacterial content was 1.1 x 10(6) CFU cm(-2). Using measures of substrate utilization rate, substrate utilization diversity, and metabolic potential index (MPI), the CLPP patterns demonstrated that the metabolic potentials of the biofilm communities decreased markedly as the chlorine residual levels increased. In particular, the community level of the biofilm that formed in the system with chlorine residual concentration of 1.0 mg l(-1) was the lowest of any biofilm under the tested conditions. The results implied that chlorine residual had a positive biocidal effect on the metabolic potential and/or functional potential of the biofilm community, especially when the BOM level was low. In addition, BOM limitation by itself was not sufficient to control biofilm formation.

Biodegradation, Environmental↗

PubMed2001

Cloning and characterization of a type II integral transmembrane protein gene, Itm2c, that is highly expressed in the mouse brain.

An Itm2C cDNA encoding a member of the mouse type II integral transmembrane protein (Itm2) was cloned from a mouse 13.5 days' post-coitum (dpc) embryonic head cDNA library. The nucleotide sequence and protein prediction analyses indicate that the membrane topology of the mouse Itm2c is a type II integral transmembrane protein with the N-terminus being intracellular and C-terminus, which is considered as either an extracellular or a luminal organelle domain. The predicted protein consists of 269 amino acids with a calculated Mr of 30,482 and a theoretical pI of 8.83. A putative N-glycosylation site was identified at amino acid 171, Asn. The single N-glycosylation site is conserved in the three members of the family in both mice and humans. The amino acid sequence of Itm2C is 41 and 49% identical to those of mouse Itm2A and Itm2B, respectively. A single approximately 2.1 kb transcript was detected with different levels in all of the tissues examined by Northern blot analysis. The Itm2c was highly expressed in both adult and postimplantation embryonic brains, although weak or moderate signals were also detected in other adult tissues. Among the tissues examined, RT-PCR analyses in various adult tissue shows that the Itm2c expression is highest in the adult brain. The results from this study suggest that the cloned Itm2c is a member of the Itm2 family that is specifically expressed in adult brains, unlike other members.

Amino Acid Sequence↗

PubMed2001

A novel Xenopus acetyltransferase with a dynamic expression in early development.

We have isolated a novel acetyltransferase from Xenopus laevis, named Xat-1. Xat-1 cDNA encodes a predicted protein of 846 amino acids that contains tetratricopeptide repeat (TPR) domains mediating protein-protein interactions and a bipartite nuclear localization signal (NLS). Its apparent molecular mass of 98.8 kDa was determined by SDS-PAGE analysis of Xat-1 recombinant protein in vitro translated in rabbit reticulocyte lysate. Xat-1 is homologous to N-terminal acetyltransferase 1 (NAT1), a gene that was originally discovered in yeast. Furthermore, it has many orthologs from human, mouse, Drosophila, C. elegans, and even Arabidopsis, thereby suggesting that these constitute a novel acetyltransferase family whose functions have been not examined. Xat-1 transcripts are expressed at relatively constant levels throughout early embryonic stages. They also exhibit dynamic expression pattern in brain, somites, branchial arches, pronephros, and otic vesicles.

Acetyltransferases↗

PubMed2001

Lack of effect of induction of hypothermia after acute brain injury.

BACKGROUND: Induction of hypothermia in patients with brain injury was shown to improve outcomes in small clinical studies, but the results were not definitive. To study this issue, we conducted a multicenter trial comparing the effects of hypothermia with those of normothermia in patients with acute brain injury. METHODS: The study subjects were 392 patients 16 to 65 years of age with coma after sustaining closed head injuries who were randomly assigned to be treated with hypothermia (body temperature, 33 degrees C), which was initiated within 6 hours after injury and maintained for 48 hours by means of surface cooling, or normothermia. All patients otherwise received standard treatment. The primary outcome measure was functional status six months after the injury. RESULTS: The mean age of the patients and the type and severity of injury in the two treatment groups were similar. The mean (+/-SD) time from injury to randomization was 4.3+/-1.1 hours in the hypothermia group and 4.1+/-1.2 hours in the normothermia group, and the mean time from injury to the achievement of the target temperature of 33 degrees C in the hypothermia group was 8.4+/-3.0 hours. The outcome was poor (defined as severe disability, a vegetative state, or death) in 57 percent of the patients in both groups. Mortality was 28 percent in the hypothermia group and 27 percent in the normothermia group (P=0.79). The patients in the hypothermia group had more hospital days with complications than the patients in the normothermia group. Fewer patients in the hypothermia group had high intracranial pressure than in the normothermia group. CONCLUSIONS: Treatment with hypothermia, with the body temperature reaching 33 degrees C within eight hours after injury, is not effective in improving outcomes in patients with severe brain injury.

Acute Disease↗

PubMed2001

Isolation of neuronal precursors from differentiating P19 embryonal carcinoma cells by neuronal T alpha 1-promoter-driven GFP.

The induction of pluripotent P19 embryonal carcinoma (EC) cells with retinoic acid results in their differentiation into cells that resemble neurons, glia, and fibroblasts. To isolate and enrich the developing neurons from heterogeneously differentiating P19 EC cells, we used a recently introduced protocol combining the expression of green fluorescent protein (GFP) driven by a tissue-specific promoter and fluorescence-activated cell sorting. Cells were transfected with the gene for GFP, which is under the control of the neuronal T alpha 1 tubulin promoter. After four days of retinoic acid treatment, GFP was specifically detected in cells undergoing neuronal differentiation. Sorting of fluorescent differentiating P19 EC transfectants yielded populations highly enriched in neuronal precursors and neurons. Immunoreactivity for nestin and neurofilament was observed in 80 and 25% of the sorted cell population, respectively. These results demonstrate that differentiated neuronal precursor cells can be efficiently isolated from differentiating pluripotent embryonic cells in vitro, suggesting that this method can reproducibly provide homogeneous materials for further studies on neurogenesis.

Antineoplastic Agents↗

PubMed2001

Poly(A) binding protein II in Xenopus laevis is expressed in developing brain and pancreas.

We have isolated Xenopus homolog of poly(A) binding protein II (XPABPII) and examined its expression during early embryogenesis and embryonic gut development. XpabpII encodes a nuclear protein of 296 amino acids that contains an alpha-helical coiled-coil domain and a ribonucleoprotein-type RNA binding domain. XpabpII is expressed both maternally and zygotically. In gastrula and neurula embryos, XpabpII is expressed mainly in ectoderm, neural and epidermal. From tailbud through to tadpole stages, the neural tissue specific expression of XpabpII gradually becomes confined to the specific vesicle regions of developing brain, being detected in the eye, olfactory pit, telencephalon and mesencephalon, but being excluded from the diencephalon region. Intriguingly, XpabpII transcripts are observed in differentiating gut endoderm. XpabpII first becomes visible in the anterior part of a stage 35 embryonic gut in which prospective liver, stomach and pancreas are located. During further development, uniform expression in anterior gut gradually becomes restricted to the pancreas rudiment. At the seventh day of development, when the gut has formed a complex coiled structure in which each organ contains clearly differentiated cell type, XpabpII is detectable exclusively in the pancreas. Taken together, we suggest that XpabpII plays a specific role in the polyadenylation process of genes involved in brain and pancreas development.

Amino Acid Sequence↗

PubMed2001

Dendritic cell-tumor coculturing vaccine can induce antitumor immunity through both NK and CTL interaction.

Immunization of dendritic cells (DC) pulsed with tumor antigen can activate tumor-specific cytotoxic T lymphocytes (CTL) that are responsible for protection and regression. We show here that immunization with bone marrow-derived DC cocultured with tumor cells can induce a protective immunity against challenges to viable tumor cells. In this study, we further investigated the mechanism by which the antitumor activity was induced. Immunization of mice with DC cocultured with murine colon carcinoma. CT-26 cells, augmented CTL activity against the tumor cells. Concomitantly, an increase in natural killer (NK) cell activity was also detected in the same mice. When DC were fixed with paraformaldehyde prior to coculturing with tumor cells, most of the CTL and NK cell activity diminished, indicating that DC are involved in the process of presenting the tumor antigen(s) to CTL. NK cell depletion in vivo produced markedly low tumor-specific CTL activity responsible for tumor prevention. In addition, RT-PCR analysis confirmed the high expression of INF-gamma mRNA in splenocytes after vaccination with DC cocultured with tumors, but low expression in splenocytes from NK-depleted mice. Most importantly, the tumor protective effect rendered to DC by the coculturing with CT-26 cells was not observed in NK-depleted mice, which suggests that DC can induce an antitumor immune response by enhancing NK cell-dependent CTL activation. Collectively, our results indicate that NK cells are required during the priming of cytotoxic T-cell response by DC-based tumor vaccine and seem to delineate a mechanism by which DC vaccine can provide the desired immunity.

Adenocarcinoma↗

PubMed2001

Quantitative analysis of apical root resorption by means of digital subtraction radiography.

OBJECTIVE: This study was performed to assess the diagnostic and quantifying ability of digital subtraction images for simulated apical root resorption, as well as to compare the diagnostic accuracy of conventional intraoral radiographs with digital subtraction images for this condition. STUDY DESIGN: Digital and intraoral radiographs of 10 sound maxillary central incisors and those with simulated apical root resorption were taken with varying horizontal and vertical angulations of the x-ray beam. Paired t tests were used to compare the lengths of the sound teeth on the images with their actual lengths, and the estimated amount of simulated apical root resorption was compared with the actual amount of tooth loss by means of Emago software. The diagnostic accuracy for detecting lesions was also evaluated on conventional intraoral radiographs and digital subtraction images through receiver operating characteristic (ROC) analysis. RESULTS: There were no statistically significant differences between the actual lengths and those measured on the reconstructed images of the sound teeth. The calculated amounts of apical root resorption showed no statistically significant differences in comparison with the actual amounts (P >.05). The diagnostic accuracy of the conventional intraoral radiographs in detecting the lesions was low (ROC area = 0.6446). CONCLUSION: A quantitative analysis of small amounts of apical root resorption can be performed by means of digital subtraction radiography.

Humans↗

PubMed2001

Quantitative analysis of normal major salivary glands using computed tomography.

OBJECTIVES: We sought to calculate the size and the computed tomography (CT) number of normal parotid and submandibular glands and to evaluate their relationship with respect to sex, age, and obesity in the Korean population. STUDY DESIGN: The authors investigated the axial CT images of 42 healthy volunteers. The maximum cross-sectional area (MCSA) was used as an indicator of the size of the gland. Three regions of interest on axial scans were selected to calculate the mean CT number. RESULTS: There was a significant decrease in the mean MCSA of the submandibular gland and the CT number of both glands with age. The MCSA of the submandibular gland in males was larger than that in females. There was a close correlation between the parotid and the submandibular glands with respect to the CT number, as well as between the left and right glands with respect to the MCSA and the CT number. The body mass index was positively correlated with the MCSA of the parotid gland, whereas the body mass indexes and the CT numbers of both glands were negatively correlated. CONCLUSIONS: Both age and obesity are closely correlated with the size and the CT number of the major salivary glands. Moreover, the correlation between the CT numbers of the parotid and the submandibular glands may be used for diagnostic purposes.

Adult↗

PubMed2001

Comparative radiologic study of bone density and cortical thickness of donor bone used in mandibular reconstruction.

OBJECTIVE: The aim of this study was to compare the total cancellous bone density, bone-implant interface density, and cortical thickness of 6 donor bone types commonly used in oral and maxillofacial reconstruction. METHODS: A total of 120 bones from 20 Korean adults-including iliac bones, fibulas, cranial bones, scapulas, ribs, and clavicles-were selected. The implant recipient site was determined by the shape, contour, and anatomical limitations of the bones. The serial cross-sectional images of each bone were then acquired through computed tomography. Total cancellous bone density, bone-implant interface density around the imaginary implant fixture, and the cortical thickness along both sides of the imaginary fixture on each cross-sectional image were evaluated and compared. RESULTS: The cancellous bone density of each donor bone type had a statistically significant difference. The cranial bone showed the highest cancellous bone density, followed by the iliac bone, clavicle, scapula, rib, and fibula (P <.05). The bone-implant interface density of the cranial bone, clavicle, fibula, and scapula each belonged to the same Duncan's group, whereas the rib and iliac bone showed lower bone-implant interface density. In average cortical thickness, the scapula and fibula had a thicker cortex surrounding the imaginary implant than the other bones, and the rib had the thinnest cortex. CONCLUSION: Although more extensive testing is needed to explain the clinical implications of these results, the findings of this study may help clinicians choose the most appropriate donor bone.

Adult↗

PubMed2001

Granulocytic sarcoma occurring in the maxillary gingiva demonstrated by magnetic resonance imaging.

We report the case of a 43-year-old woman presenting with a painless swelling that had developed over 8 months in the maxillary labial vestibule. An oral examination revealed an exophytic, firm, black-pigmented lesion measuring 3.5 x 1.5 cm that bled on palpation. Periapical radiographs showed a slightly enlarged periodontal ligament space of the left central incisor and bone resorption in the region of the missing lateral incisor. Panoramic and other conventional radiographs showed no obvious lytic area, and a magnetic resonance imaging examination demonstrated a low signal intensity lesion on both the T1-weighted and the T2-weighted images. Therefore, granulocytic sarcoma was suspected. Granulocytic sarcoma of the oral cavity is a rare condition, and its diagnosis is usually difficult. Increased awareness of this entity may minimize misinterpretation of radiographic and clinical findings and can assist suitable treatment planning that is essential to this pathosis.

Adult↗

PubMed2001

The role of gastrointestinal endoscopy in long-distance runners with gastrointestinal symptoms.

BACKGROUND: Exercise-related gastrointestinal symptoms are not uncommon among athletes. The occurrence of gastrointestinal bleeding has been reported, especially in long-distance runners. We studied gastrointestinal mucosal damage, using gastrointestinal endoscopy, in competitive long-distance runners. Gastrointestinal blood loss and anaemia before and after running were also assessed. METHODS: Sixteen competitive long-distance runners (all men; age range 16-19 years) participated in the study. All runners completed a symptom questionnaire prior to a 20 km race. Stool occult blood and haematological studies (haemoglobin, haematocrit, serum iron, total iron-binding capacity [TIBC] and ferritin) were performed before and immediately after the race. Gastrointestinal endoscopy was performed to assess macroscopic changes. Colonoscopy was also performed on the patients who had positive stool occult blood before or after the race. RESULTS: Gastrointestinal symptoms were frequently experienced by the runners. Gastritis (n = 16), oesophagitis (n = 6) and gastric ulcer (n = 1) were found at gastroscopy. Colonoscopy was performed on four patients who had positive stool occult blood. One had multiple erosions at the splenic flexure and one had a rectal polyp. Five runners had anaemia, and all of these had at least one endoscopic lesion (three gastritis, two oesophagitis and one multiple erosion at the splenic flexure). There were significant changes in the following haematological parameters after the race: iron (decreased, P = 0.02), ferritin (decreased, P = 0.001) and TIBC (increased, P = 0.00005). CONCLUSIONS: Gastrointestinal symptoms and gastrointestinal mucosal damage are prevalent among long-distance runners. Prior to treatment, gastrointestinal endoscopy should be considered in long-distance runners with gastrointestinal symptoms and/or anaemia.

Adolescent↗

PubMed2001

Intercenter variance in clinical trials of head trauma--experience of the National Acute Brain Injury Study: Hypothermia.

OBJECT: In a recently conducted trial of hypothermia in patients with severe brain injury, differences were found in the effects of hypothermia treatment among various centers. This analysis explores the reasons for such differences. METHODS: The authors reviewed data obtained in 392 patients treated for severe brain injury. Prerandomization variables, critical physiological variables, treatment variables, and accrual methodologies were investigated among various centers. Hypothermia was found to be detrimental in patients older than the age of 45 years, beneficial in patients younger than 45 years of age in whom hypothermia was present on admission, and without effect in those in whom normothermia was documented on admission. Marginally significant differences (p < 0.054) in the intercenter outcomes of hypothermia-treated patients were likely the result of wide differences in the percentage of patients older than 45 years of age and in the percentage of patients in whom hypothermia was present on admission among centers. The trial sensitivity was likely diminished by significant differences in the incidence of mean arterial blood pressure (MABP) less than 70 mm Hg (p < 0.001) and cerebral perfusion pressure (CPP) less than 50 mm Hg (p < 0.05) but not intracranial pressure (ICP) greater than 25 mm Hg (not significant) among patients in the various centers. Hours of vasopressor usage (p < 0.03) and morphine dose (p < 0.001) and the percentage of dehydrated patients varied significantly among centers (p < 0.001). The participation of small centers increased intercenter variance and diminished the quality of data. CONCLUSIONS: For Phase III clinical trials we recommend: 1) a detailed protocol specifying fluid and MABP, ICP, and CPP management: 2) continuous monitoring of protocol compliance; 3) a run-in period for new centers to test accrual and protocol adherence; and 4) inclusion of only centers in which patients are regularly randomized.

Adult↗

PubMed2001

Effect of graded running on esophageal motility and gastroesophageal reflux in fed volunteers.

The effects of different grades of running on esophageal motility and gastroesophageal reflux in the fed state were evaluated. We studied healthy volunteers (male: 12, age: 27 +/- 5 yr) using ambulatory esophageal manometry, pH catheter and portable digital data recorder. Each exercise was performed 30 min after meal, with 20 min of rest between exercises. Subjects exercised on a treadmill at 40% and 70% maximal heart rate. The number of gastroesophageal reflux episodes, the duration of esophageal acid exposure and percent time pH below 4 were significantly (p < 0.01) increased during exercise at 70% maximal heart rate. The frequency of contraction (contraction/min) (p < 0.05), frequency of repetition (p < 0.01), percent of simultaneous contraction (p < 0.01), percent of above 100 mmHg amplitude (p < 0.05), and frequency of 2-peak contraction (p < 0.01) were significantly increased during exercise at 70% maximal heart rate. However, median amplitude and median duration showed no significant changes between each exercise session. Postprandial running exercises induce gastroesophageal reflux, which correlates with exercise intensity. These effects are mediated by disorganized esophageal motility.

Adult↗

PubMed2000

Identification and developmental expression of par-6 gene in Xenopus laevis.

The par genes (partitioning defective) are required to establish polarity in the Caenorhabditis elegans embryo. We have identified the Xenopus homologue of C. elegans PAR-6 (XPAR-6). XPAR-6 is a protein of 377 amino acids with one PDZ domain which is involved in mediating protein-protein interactions. It shares 59% and 58% amino acid identity with the mouse and Drosophila PAR-6, respectively, and 54% overall identity with C. elegans PAR-6. Xpar-6 is expressed both maternally and zygotically. Xpar-6 is first detected in the animal half of the egg, and this pattern of expression persists into the cleavage and blastula stages. At the gastrula stage, the message is detected in animal pole area and in a broad domain of ventral region, but is excluded from dorsal region. With the onset of neurulation, the localized expression of Xpar-6 becomes more obvious, leading to it being enriched in the dorsolateral region along the lateral edges of neural plate and anterior presumptive head region surrounding the anterior border of neural plate. At late tailbud stage, Xpar-6 transcripts show localized expression throughout the head, labeling the branchial arches, eyes, otic vesicles and brain, while more posteriorly Xpar-6 labels the somites, pronephros, tail tip and proctodeum. Therefore, this analysis suggests that Xpar-6 has a regionalized pattern of expression during Xenopus early embryogenesis.

Amino Acid Sequence↗

PubMed2000

A comparative study of the radiological diagnosis of postoperative maxillary cyst.

OBJECTIVES: To compare the diagnostic accuracy for the postoperative maxillary cyst (POMC) of panoramic in combination with Waters' radiography with computed tomography (CT) and of oral and maxillofacial radiologists with non-specialists. STUDY DESIGN: Nineteen cases of POMC and 19 of postoperative changes were assessed using panoramic in combination with Waters' radiographs and CT by five oral and maxillofacial radiologists and five non-specialists on a five-point scale. The areas under the ROC curves were analysed using the Wilcoxon rank sum test to determine any differences in diagnostic accuracy between the two methods and between the two groups. RESULTS: The diagnostic accuracy of CT was higher than that of combined panoramic and Waters' radiographs for the oral and maxillofacial radiologists (P < 0.05), but not for the non-specialists (P > 0.05). The diagnostic accuracy of the oral and maxillofacial radiologists for each method was higher than that of the non-specialists group (P < 0.05). CONCLUSIONS: CT improves the evaluation of POMC. Radiological training and experience leads to more accurate diagnoses.

Adult↗

PubMed1999

Interim analyses with delayed observations in clinical trials.

The interim analyses based on group sequential procedures are not convenient if the response time relative to the patient accrual rate is long. Since in most trials patients are accrued and randomized continuously, the response data from those already randomized will continue to accumulate when a trial terminates at an interim test. One should analyse all observations received after the trial terminates along with the data that led to the decision to terminate the trial. Although the most likely case is that the combined results are significant, it could happen that the combined results are not significant. We examined the likelihood of such an event. Our study indicated that the O'Brien-Fleming type of group sequential tests with conservative boundaries in the early stages protects from such an unsettling event.

Clinical Trials as Topic↗

PubMed1999

Effects of galvanic stimulation of the mastoid process on the gastric motility induced by caloric stimulation.

The effects of galvanic stimulation to the mastoid portion on the vestibuloautonomic symptoms induced by caloric stimulation, such as nausea, vomiting, and vertigo, were evaluated in this study. Gastric motility was measured by electrogastrography (EGG) in 20 healthy volunteers (11 male and nine female) aged 20-30 (average: 25.4) years. Electrical stimulation of the mastoid process with 1.0-3.0 mA, 1.0 ms, 100 Hz was applied using a bipolar-biaural method during caloric stimulation of the external auditory canal. The dominant frequency and power of EGG were determined using running spectral frequency analysis and the time-course of EGG was evaluated in a pseudo three dimensional graphic. Frequency of EGG was classified into normogastria with 3 cpm, bradygastria with lower than 3 cpm, and tachygastria with higher than 3 cpm. At quiescent period, normogastria was 78.7 +/- 3.7%, bradygastria 5.0 +/- 1.1%, and tachygastria 16.4 +/- 3.7%. Caloric stimulation with warm water in the unilateral ear and cold water in the contralateral ear elicited vestibuloautonomic symptoms, with accompanied decreases in normogastria (57.7 +/-4.6%, P < 0.01) and increases in tachygastria (34.8 +/- 4.8%, P < 0.01). Cathodal stimulation to the mastoid process ipsilateral to cold water irrigation during caloric stimulation restored normal pattern of gastric motility: normogastria in 77.1 + 5.3% and tachygastria in 19.3 +/- 4.7%, and relieved vestibuloautonomic symptoms. Cathodal stimulation to the inhibited vestibular system ameliorates the vestibular symptoms induced by caloric stimulation.

Adult↗