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Biomedical subjects

H Choi

Publications and source records attributed to H Choi.

At least 73 records · Page 4Linked to original sources
PubMed2001

Oxidation of polycyclic aromatic hydrocarbons by ozone in the presence of sand.

A series of soil slurry experiments was performed to investigate the characteristics of PAHs removal by ozone in various conditions. Gaseous ozone was bottled into the aqueous phase in the presence of soil contaminated by PAHs. The effects of soil media, OH radical scavengers, ozone dosage, and humic acid were examined at the given experimental conditions. There exists a substantial difference in the removal of PAH according to the types of soil media tested. Baked sand showed the highest removal efficiency compared to the others. The descending order of removal rate was: BS > S > GB. This is considered to be due to the OH radical effect produced by catalytic reactions of ozone with the reactive site on the and. This is qualitatively proved by the experiment of scavenging OH radicals using tert-butanol. The comparison of half-lives of ozone in sand and glass bead columns further supports this hypothesis. It was found that about 22% of enhancement of phenanthrene destruction was accomplished by OH radicals produced by the catalytic ozone decomposition. The rate of ozone consumption for the phenanthrene oxidation was obtained as 1.88 mg/mgO3/min.

Catalysis↗
PubMed2001

Primary tubercolous osteomyelitis of the sternum.

We present an 82-year-old woman with anterior sternal pain diagnosed as primary mycobacterial osteomyelitis of the sternum. She was treated with simultaneous wide resection and reconstruction of the chest wall. On admission, computed tomographic scan showed a sclerotic sternal mass with soft tissue reaction. Mycobacterium tuberculosis was grown in initial culture. First-line antituberculous medication and local debridement failed. The successful result was achieved by extensive sternal and chondral resection followed by simultaneous bilateral pectoralis major muscle flap positioning.

Aged↗
PubMed2000

Enhancement of paclitaxel production by temperature shift in suspension culture of Taxus chinensis.

Effect of temperature shift during culture period on cell growth and paclitaxel was investigated to optimize paclitaxel production in suspension culture of Taxus chinensis. Cell growth showed the optimum at 24 degrees C while paclitaxel synthesis showed the maximum at 29 degrees C. To minimize the inhibitory effect of higher temperature on cell growth, temperature was shifted after a certain period of culture time at 24 degrees C. Paclitaxel synthesis in plant cell culture increased dramatically during day 14 to day 21 regardless of treatment, reaching the maximum production of 137.5 mg paclitaxel/L. When the temperature was maintained at 29 degrees C after day 21, the specific productivity of paclitaxel was sustained for prolonged period of 42 days. The possible relationship between temperature and paclitaxel synthetic pathway was also suggested.

Journal Article↗
PubMed2000

Formulation and in vivo evaluation of omeprazole buccal adhesive tablet.

For the development of omeprazole buccal adhesive tablets, we studied the release and bioavailability of omeprazole delivered by buccal adhesive tablets composed of sodium alginate, hydroxypropylmethylcellulose (HPMC), magnesium oxide and croscarmellose sodium. Croscarmellose sodium enhanced the release of omeprazole from the tablets. The analysis of the release mechanism showed that croscarmellose sodium changed the release profile of omeprazole from first- to zero-order release kinetics by forming porous channels in the tablet matrix. However, it decreased the bioadhesive forces and stability of omeprazole tablets in human saliva. The tablet is composed of omeprazole-sodium alginate-HPMC-magnesium oxide-croscarmellose sodium (20:24:6:50:10 mg). It may be attached to the human cheek without collapse and it enhanced the stability of omeprazole in human saliva for at least 4 h, giving a fast release of omeprazole. The plasma concentration of omeprazole in hamsters increased to reach a maximum of 370 ng/ml at 45 min after buccal administration and remained at the high level of 146-366 ng/ml for 6 h. The buccal bioavailability of omeprazole in hamsters was 13.7+/-3.2%. These results demonstrate that the omeprazole buccal adhesive tablet would be useful to deliver omeprazole which degrades very rapidly in acidic aqueous medium and undergoes hepatic first-pass metabolism after oral administration.

Adhesiveness↗
PubMed2000

High frequency of cytogenetic aberration in transgenic oat (Avena sativa L.) plants.

Cytological abnormalities were observed in transgenic oat (Avena sativa L. cv. GAF/Park-1) produced by microprojectile bombardment of mature seed-derived highly regenerative tissues. Of the plants from 48 independent transgenic lines examined, plants from only 20 lines (42%) were karyotypically normal (2n=6x=42) without detectable chromosomal aberrations; plants from 28 lines (58%) had chromosomal variation, i.e. aneuploids and structural changes. No significant difference in cytological aberration was observed between the two different culturing systems used for transformation: 57% chromosomal abnormalities in plants derived from D'BC2 medium (2.0 mg/l 2,4-D, 0. 1 mg/l BAP and 5.0 µM cupric sulfate) used for tissue initiation and maintenance and 60% in plants from tissue initiated on D'BC2 and maintained on DBC3 (1.0 mg/l 2,4-D, 0.5 mg/l BAP and 5.0 µM cupric sulfate). Comparative differences in chromosomal status frequently occurred among plants regenerated from the same T(0) line. The most common cytological aberration in transgenic plants was aneuploidy, followed by deletion of chromosomal segments; no change in ploidy level was observed. In contrast, nontransgenic plants, regenerated from tissues comparable in age and culture media to that used for transgenic tissues, had a much lower percentage of karyotypic abnormality (0-14%). Our data indicate that some stress(es) imposed by the transformation process, e.g. osmotic treatment, bombardment and selection, leads to cytological variation in transgenic oat plants, an observation similar to that observed in our recent studies with transgenic barley plants.

Journal Article↗
PubMed2000

Genetic dissection of c-myc apoptotic pathways.

All biological functions mediated by the c-myc oncoprotein require an intact transactivation domain (TAD). We compared TAD mutants for their ability to promote apoptosis of 32D myeloid cells in response to interleukin-3 (IL-3) deprivation and exposure to chemotherapeutic drugs, and to activate ornithine decarboxylase, an endogenous c-myc target. Different sub-regions of the TAD were required to mediate each function. cDNA microarrays were then used to identify multiple c-myc-regulated transcripts, some of which were also modulated by IL-3 or cytotoxic drugs, as well as by specific sub-regions of the TAD. Several of the c-myc-regulated transcripts had also been previously identified as targets for IFN-gamma. The functional consequences of their deregulation were manifested by a marked sensitivity of c-myc-overexpressing cells to IFN-gamma-mediated apoptosis. Our results establish that several well-characterized functions of c-myc are separable and correlate with the expression of a novel group of target genes, some of which also mediate the apoptotic action of IFN-gamma.

Animals↗
PubMed2000

Different hippocampal molecular requirements for short- and long-term retrieval of one-trial avoidance learning.

Rats were trained in one-trial step-down inhibitory avoidance and tested either 3 h or 31 days later. Ten minutes prior to the retention test, through indwelling cannulae placed in the CA1 region of the dorsal hippocampus, they received 0.5 microl infusions of: saline, a vehicle (2% dimethylsulfoxide in saline), the glutamate NMDA receptor blocker, aminophosphonopentanoic acid (AP5) (5.0 microg), the AMPA/kainate receptor blocker, cyanonitroquinoxaline dione (CNQX) (0.25 or 1.25 microg), the metabotropic receptor antagonist, methylcarboxyphenylglycine (MCPG) (0.5 or 2.5 microg), the inhibitor of calcium/calmodulin-dependent protein kinase II (KN62) (3.5 microg), the inhibitor of cAMP-dependent protein kinase (PKA), Rp-cAMPs (0.1 or 0.5 microg), the stimulant of the same enzyme, Sp-cAMPs (0.1 or 0.5 microg), or the inhibitor of the mitogen-activated protein kinase (MAPK) kinase, PD098059 (10 or 50 microM). CNQX, KN62 and PD098059 were dissolved in the vehicle; the other drugs were dissolved in saline. All these drugs, at the same doses, had been previously found to affect short- and long-term memory formation of this task. Retrieval measured 3 h after training (short-term memory) was blocked by CNQX and MCPG, and was unaffected by all the other drugs. In contrast, retrieval measured at 31 days was blocked by MCPG, Rp-cAMPs and PD098059, enhanced by Sp-cAMPs, and unaffected by CNQX, AP5 or KN62. The results indicate that, in CA1, glutamate metabotropic receptors are necessary for the retrieval of both short- and long-term memory; AMPA/kainate receptors are necessary for short-term but not long-term memory retrieval, and NMDA receptors are uninvolved in retrieval. Both the PKA and MAPK signalling pathways are required for the retrieval of long-term but not short-term memory.

Animals↗
PubMed2000

Design and synthesis of anticonvulsive agents as gamma-vinyl GABA-based potential dual acting prodrugs and their biological activities.

For the development of new anticonvulsive agents, gamma-vinyl GABA (vigabatrin) and GABA mimetics derivatives were covalently coupled as potential dual acting prodrugs and evaluated for their anticonvulsive activities. Among the prepared compounds, 11 showed the most potent anticonvulsive activity, a shorter onset time and a broader spectrum compared to vigabatrin.

Animals↗
PubMed2000

Effect of formulation and processing variables on the characteristics of microspheres for water-soluble drugs prepared by w/o/o double emulsion solvent diffusion method.

80% except for acetaminophen, due to its lower solubility in water and higher solubility in corn oil. The release profile of the drug was pH dependent. In acidic medium, the release rate was much slower, however, the drug was released quickly at pH 7.4. Tacrine showed unexpected release profiles, probably due to ionic interaction with polymer matrix and the shell structure and the highest release rate was obtained at pH 2.0. The prepared microspheres had a sponge-like inner structure with or without central hollow core and the surface was dense with no apparent pores.

Acetaminophen↗
PubMed2000

Effect of vehicles and pressure sensitive adhesives on the permeation of tacrine across hairless mouse skin.

The purpose of this study was to investigate the feasibility of developing transdermal drug delivery (TDD) system for tacrine used for treating the symptoms of Alzheimer's disease. The effects of various vehicles on the percutaneous absorption of tacrine in solution formulation and in pressure sensitive adhesive (PSA) matrix across the hairless mouse skin were evaluated using flow-through diffusion cell system at 37 degrees C. The permeation profiles of tacrine from solutions were different depending on vehicles used. The flux of tacrine increased significantly as its concentration in the solutions increased. The permeation rate of tacrine was higher in acrylic adhesives with hydroxyl functional group and without functional group than in polyisobutylene adhesive matrix. Incorporation of vehicles into the acrylic adhesive matrix significantly enhanced the permeation rate and shortened the lag time of tacrine. The maximum flux obtained from pressure sensitive adhesive matrix seemed to be high enough to obtain therapeutic effect.

Adhesives↗
PubMed2000

ABFs, a family of ABA-responsive element binding factors.

Abscisic acid (ABA) plays an important role in environmental stress responses of higher plants during vegetative growth. One of the ABA-mediated responses is the induced expression of a large number of genes, which is mediated by cis-regulatory elements known as abscisic acid-responsive elements (ABREs). Although a number of ABRE binding transcription factors have been known, they are not specifically from vegetative tissues under induced conditions. Considering the tissue specificity of ABA signaling pathways, factors mediating ABA-dependent stress responses during vegetative growth phase may thus have been unidentified so far. Here, we report a family of ABRE binding factors isolated from young Arabidopsis plants under stress conditions. The factors, isolated by a yeast one-hybrid system using a prototypical ABRE and named as ABFs (ABRE binding factors) belong to a distinct subfamily of bZIP proteins. Binding site selection assay performed with one ABF showed that its preferred binding site is the strong ABRE, CACGTGGC. ABFs can transactivate an ABRE-containing reporter gene in yeast. Expression of ABFs is induced by ABA and various stress treatments, whereas their induction patterns are different from one another. Thus, a new family of ABRE binding factors indeed exists that have the potential to activate a large number of ABA/stress-responsive genes in Arabidopsis.

Abscisic Acid↗
PubMed2000

Pharmacological demonstration of the differential involvement of protein kinase C isoforms in short- and long-term memory formation and retrieval of one-trial avoidance in rats.

RATIONALE: The hippocampal protein kinase C (PKC) family is involved in the early events of consolidation of long-term potentiation (LTP) and long-term memory (LTM). Results so far are indecisive about which PKC isoform is involved and as to whether any of them plays a role in short-term memory (STM) processes, which have recently been shown to be separate from those of LTM in the hippocampus-dependent one-trial step-down inhibitory avoidance task. OBJECTIVES: To measure the effect of two PKC inhibitors, one (Gö 6976) selective to the calcium-dependent isoforms alpha and beta I, and the other (Gö 7874) unspecific as to PKC isoforms on the formation and retrieval of STM and LTM of one-trial inhibitory avoidance. METHODS: Rats bilaterally implanted with cannulae in the CA1 region of the dorsal hippocampus were trained in one-trial step-down inhibitory avoidance. The effect of these two drugs on STM and LTM formation was investigated as follows. Animals were infused 10 min before or 50, 110, or 170 min after inhibitory avoidance training with a vehicle (2% dimethylsulfoxide in saline), or with Gö 6976 (0.92 nM or 4.6 nM) or Gö 7874 (1.96 nM or 8 nM) dissolved in the vehicle. Infusion volume was 0.5 microliter in all cases. Animals were tested 1.5 h and 3 h after training for STM and at 24 h for LTM. In order to study the effects of these compounds on retrieval, they were infused into the hippocampus 10 min prior to STM testing at 3 h (see above) or 10 min before LTM testing at 24 h. In addition, the effect of Gö 6976 and Gö 7874 was studied on general activity measured in an open field, and on performance in an elevated plus maze. RESULTS: STM was suppressed by 4.6 nM Gö 6976 given 10 min before or 50 min after training. LTM was cancelled by the higher dose of the two compounds given 10 min before, or 50 min or 110 min after training. None of the two compounds infused 170 min post-training affected the retrieval of STM measured 10 min later. However, both compounds given 10 min before testing inhibited the retrieval of LTM measured at 24 h. This effect cannot be attributed to influences on locomotor activity or anxiety levels, since the drugs had no effect on performance in the open field but were mildly "anxiogenic" (pro-conflict) and reduced the number of entries into open and closed arms and rearings. CONCLUSIONS: LTM consolidation requires in part alpha- and/or beta 1-PKC and in part other PKC isoforms. STM formation requires instead only alpha and/or beta I-PKC and during a more limited period of time. In addition, PKC appears not to be necessary for the retrieval of STM, but is crucial for the retrieval of LTM. These findings further point to a biochemical separation of STM and LTM, as ascertained in numerous previous studies.

Animals↗
PubMed2000

Cadmium blocks hypoxia-inducible factor (HIF)-1-mediated response to hypoxia by stimulating the proteasome-dependent degradation of HIF-1alpha.

Cadmium is a substantial industrial and environmental pollutant which seriously impairs erythropoiesis. Cd has been demonstrated to aggravate anemia by suppressing erythropoietin gene expression in anemic patients. As hypoxic induction of erythropoietin mRNA depends on a transcription factor, hypoxia-inducible factor 1 (HIF-1), we hypothesized that Cd suppresses the hypoxic activation of HIF-1. In hypoxic Hep3B cells, all mRNAs of various genes, which are known to be upregulated by HIF-1 activation under hypoxia, were suppressed by Cd in a dose-dependent manner. Cd inhibited the hypoxia-induced activity of luciferase in 293 cells which was transfected with a reporter plasmid carrying a hypoxia response element. By electrophoretic mobility gel shift assay, Cd inhibited the DNA-binding activity of HIF-1 in hypoxic Hep3B cells. Cd reduced the amount of HIF-1alpha protein in hypoxia, whereas it didn't affect HIF-1 alpha mRNA levels. Moreover, Cd inhibited HIF-1alpha accumulation induced by cobalt and desferrioxamine. Antioxidants and a proteasome inhibitor prevented the HIF-1alpha degradation caused by Cd. The possibility that oxidative stress mediates this action of Cd was examined. Cd didn't affect protein oxidation and reduced glutathione levels in hypoxic cells. These results indicate that Cd triggers a redox/proteasome-dependent degradation of HIF-1alpha protein, reducing HIF-1 activity and in turn suppressing the hypoxic induction of hypoxia-inducible genes.

Cadmium↗
PubMed2000

Active properties of the urinary bladder: in vitro comparative studies between adult and neonatal rats.

OBJECTIVE: To determine, using in vitro comparative studies, developmental aspects associated with the active properties of the urinary bladder in neonatal and adult rats. MATERIALS AND METHODS: Urinary bladders were removed from neonatal (1-3 days old) and adult (15 weeks old) male Sprague-Dawley rats. Anterior longitudinal muscle strips were obtained from each group and isometric tensions recorded. Nerve-mediated contractions elicited by electrical field stimulation (0.8 ms pulse) or carbachol-induced contractile responses in neonatal and adult bladder strips were compared. Contractile tensions were normalized using the wet weight of the bladder strip or by using the percentage contraction induced by 60 mmol/L KCl. RESULTS: Nerve-mediated contractile responses showed that the muscarinic component predominated in the neonatal rat bladder, which contrasted with the predominant purinergic components in adult bladder. The pattern of spontaneous activity and carbachol-induced contraction differed in the two groups. Small spontaneous contractions in the basal state occurred in adult bladder strips, while short-lived large spontaneous contractions were present in neonatal strips. The amplitude of carbachol-induced contractions generated in the neonatal bladder was larger than that in the adult bladder. In addition, the time to achieve peak contraction elicited by carbachol (5 micromol/L) was shorter in the neonatal bladder. Repetitive carbachol applications induced an attenuation of the contractile response (desensitization), but the neonatal bladder was more resistant to desensitization than the adult bladder. CONCLUSIONS: These results show that nerve-mediated or agonist-induced contractile patterns, and spontaneous activity, in the neonatal bladder differ from those of the adult bladder in rats. The results suggest that in addition to neural immaturity, there are functional differences between the bladders of adult and neonatal rats.

Adenosine Triphosphate↗
PubMed2000

The management of children with complete ureteric duplication: selective use of uretero-ureterostomy as a primary and salvage procedure.

OBJECTIVE: To determine the optimum management of duplex urinary tracts with refluxing or obstructed units. PATIENTS AND METHODS: Sixty-three children (19 boys and 44 girls) with complete duplex-system anomalies (84 duplex system units) who underwent corrective surgery by one surgeon (H.C.) between March 1983 and June 1997 were reviewed, analysing their diagnosis and treatment. RESULTS: Most children had presented with urinary tract infection; a ureterocele was found in 26 renal units, reflux in 12 and a combined anomaly in 18. Ectopic insertion of the ureter causing incontinence was found in six and ureteric obstruction in nine ureteric units. Patients were managed so that whenever possible, functional renal tissue was preserved; thus surgical strategies were basically staged, conservative, and planned preoperatively on the basis of renal function. Initial surgery was undertaken in 71 units (all patients; ureterocele incision in 12, upper pole nephrectomy in 30, ureteric reimplantation in 14, uretero-ureterostomy in 13 and others in two). The median (range) follow-up was 7.6 (2.1-16) years. Secondary procedures were undertaken in 24 units (34%); ureterocele incision (11 of 12 units) was the most common procedure of additional surgery, followed by ureteric reimplantation (six of 27 units), upper pole nephrectomy (eight of 37 units) and uretero-ureterostomy (two of 18 units). CONCLUSIONS: Uretero-ureterostomy was the most successful nephron-sparing additional operation. When the upper pole is salvageable, uretero-ureterostomy may be the preferred alternative for managing complete duplex system anomalies.

Adolescent↗