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Biomedical subjects

S K Choi

Publications and source records attributed to S K Choi.

At least 91 records · Page 5Linked to original sources
PubMed1996

Optically controlled collisions of biological objects to evaluate potent polyvalent inhibitors of virus-cell adhesion.

BACKGROUND: The biochemical and biomechanical determinants of adhesion between two biological objects following a collision are complex, and may vary from one system to another. We wished to develop an assay in which all the relevant factors, including the components of the solution, the relative orientation and the relative collision velocity, are under the user's control. RESULTS: A new assay is described in which two mesoscale particles are caused to collide using two independently controlled optical tweezers (optically controlled collision, OPTCOL). This assay enables precise examination of the probability of adhesion under biologically relevant conditions. The OPTCOL assay was used to evaluate the probability of adhesion of a single erythrocyte to a single virus-coated microsphere, in the absence and presence of a sialic acidbearing inhibitor. Inhibition constants for the most effective inhibitors could not be measured using other types of assays. The best inhibitor prevented attachment 50 % of the time at a sialic acid concentration of 35 pmol l-1; it is the most potent known inhibitor of attachment of influenza virus to erythrocytes. CONCLUSIONS: OPTCOL is a versatile new bioassay for studying dynamic interactions in biochemistry. It offers an approach to investigating interactions between moving biological objects that is both quantitative and interpretable. The simplicity of the OPTCOL technique suggests broad applicability to the study of adhesion of mesoscale (1-100 microm) objects in the areas of cell biology, microbiology, medicinal chemistry, and biophysics.

Cell Adhesion↗
PubMed1996

Monomeric inhibitors of influenza neuraminidase enhance the hemagglutination inhibition activities of polyacrylamides presenting multiple C-sialoside groups.

BACKGROUND: Influenza viruses use hemagglutinin (HA) arrays to bind to sialic acid moieties on the surface of cells; crosslinking of erythrocytes by this mechanism leads to hemagglutination. A number of synthetic polymers containing multiple sialic acid (Neu5Ac) groups as side chains are potent inhibitors of this process. Inhibition may be due to two mechanisms: polyvalent binding of the inhibitor's multiple Neu5Ac side chains to multiple HA sites on the viral surface, or steric stabilization of the viral particle by a layer of the adsorbed, water-swollen polymer, which prevents adhesion to the erythrocyte. The balance between these two effects is not yet known. RESULTS: Polyacrylamides with multiple C-sialosides (PA(Neu5Ac)) were 2-20 fold more effective as inhibitors of virally mediated hemagglutination when assayed in the presence of Neu2en-NH2, a potent monomeric inhibitor of influenza neuraminidase (NA). The ability of monomeric inhibitors of NA to enhance the inhibition of hemagglutination in this assay correlated with the affinity of the monomer for NA. CONCLUSIONS: We propose that inhibitors of NA act by competing with the C-sialosides of PA(Neu5Ac) for binding to the active sites of the NA. Competitive displacement of Neu5Ac causes an expansion of the layer of polymeric gel absorbed to the virus, enhancing its inhibitory effect. This study provides an example of synergy between two ligands directed toward the active sites of two different proteins, and reinforces the conclusion that steric stabilization is important for the activity of polyvalent inhibitors.

Acrylic Resins↗
PubMed1996

Effects of nitric oxide on detrusor relaxation.

PURPOSE: Recently we (1994) reported the photo-induced adequate nitric oxide (PIANO) system, in which an NO- or NO2-carrying molecule which has been photoactivated to release NO, could be exploited to investigate the role of NO in various smooth muscle functions. This study was designed to characterize the effect of nitric oxide (NO) exploiting PIANO on rat detrusor relaxation by isometric tension recording and measuring changes in cGMP content. MATERIALS AND METHODS: Exposure to ultraviolet light was used (1 to 60 seconds) to evoke PIANO in the presence of streptozotocin, an NO-carrier, and N omega-nitro-L-arginine (L-NOARG), an NO2-carrier. During relaxation the cyclic guanosine monophosphate (cGMP) content was measured by radioimmunoassay. RESULTS: Rat detrusor strips were reversibly relaxed upon NO generation via PIANO. Pyrogallol, an O2 generator, significantly (p < 0.01) diminished PIANO-mediated relaxation. During PIANO-mediated relaxation, the tissue level of cyclic GMP significantly (p < 0.05) increased over that of the control. Furthermore, methylene blue, a guanylate cyclase inhibitor, significantly (p < 0.01) inhibited both the relaxation and the increase of cGMP. CONCLUSION: We concluded that rat detrusor muscle was capable of responding to NO, and these findings might lead to a treatment for bladder instability and detrusor hyperreflexia, by the use of intravesical instillation of NO donors.

Animals↗
PubMed1995

Cloning of a novel crystal protein gene cry1K from Bacillus thuringiensis subsp. morrisoni.

A novel crystal protein gene cry1K has been cloned and sequenced from a Bacillus thuringiensis subsp. morrisoni BF190 isolated from phylloplane. The upstream promoter region of cry1K was almost identical with that of cry1B. The deduced amino acid sequence of Cry1K contains 1215 amino acid residues with an estimated molecular mass of 137 kDa. Comparison of the amino acid sequence of the Cry1K with that of Cry proteins revealed that Cry1K is most closely related to Cry1B and Cry1I. Cry1K has a high degree of identity with Cry1B in the region between initiator codon and conserved sequence block 1, and with Cry1F in the region between conserved block 3 and 5. Protein inclusion purified from a recombinant strain of B. thuringiensis expressing the cry1K gene was found to have a different insect-host specificity from Cry1B, Cry1I and Cry1F, Cry1K was found to be selectively toxic to Artogeia rapae and not active to Plutella xylostella.

Amino Acid Sequence↗
PubMed1995

cDNA cloning and gene expression of lebocin, a novel member of antibacterial peptides from the silkworm, Bombyx mori.

A cDNA encoding lebocin, a novel member of insect antibacterial peptides, was isolated from the fat body cDNA library of Bombyx mori larvae immunized with Escherichia coli. The cDNA was 844 bp long and had an open reading frame (ORF) containing a probable signal peptide (16 amino acids), a putative prosegment (104 amino acids) and a mature peptide (32 amino acids) followed by 27 additional amino acids at its carboxyl-terminus. Northern blot analysis showed that lebocin gene expression was inducible by bacterial injection, occurred tissue-specifically in the fat bodies and continued at least for 48 h post-infection. These results suggest that lebocin has a unique precursor structure and shows typical gene expression pattern as insect antibacterial peptide.

Amino Acid Sequence↗
PubMed1995

Baculovirus-mediated production of the human growth hormone in larvae of the silkworm, Bombyx mori.

To express the cDNA encoding human growth hormone (hGH) in larvae of Bombyx mori, B. mori nuclear polyhedrosis virus (BmNPV) was employed as an expression vector. For the construction of the recombinant virus, the hGH cDNA was inserted into the downstream of the strong polyhedrin promoter to achieve a high level expression. Immunoblot analysis revealed that the virus-mediated hGH was synthesized in the larvae and secreted into the hemolymph. The yield of the recombinant hGH synthesized in the larvae reached to a level of 160 micrograms/ml of hemolymph after purification. The purified recombinant hGH was confirmed to have both the same molecular weight and amino acid sequence at its N-terminal region as those of the natural counterpart. In addition, the biological activity of the recombinant hGH was comparable to that of the natural hGH in the growth-stimulating effect on rat Nb 2 Node lymphoma cells.

Animals↗
PubMed1995

Occurrence of novel types of nitric oxide synthase in the silkworm, Bombyx mori.

Nitric oxide (NO) synthase activity was detected in fat body and the Malpighian tubles of the silkworm, Bombyx mori. Main NO synthase activity in the fat body was Ca(2+)/calmodulin-dependent, inducible by bacterial lipopolysaccharide (LPS) and required NADPH, FAD, FMN, dithiothreitol (DTT) and tetrahydrobiopterin (BH4) as cofactors for the full expression of the activity. The Malpighian tubles contained two types of NO synthase. One was Ca(2+)-independent, calmodulin-dependent and constitutive and the other was Ca(2+)-dependent and constitutive. The former NO synthase required the same cofactors as fat body NO synthase. The activity of Malpighian tuble NO synthases increased dramatically at the end of the last instar period, just prior to spinning. These results indicate that B. mori contains new types of NO synthase, suggesting the wide distribution and different characteristics of this enzyme among vertebrates and invertebrates.

Amino Acid Oxidoreductases↗
PubMed1995

Pudendal neuropathy is not related to physiologic pelvic outlet obstruction.

UNLABELLED: Chronic straining because of pelvic outlet obstruction is hypothesized to cause pudendal neuropathy (PN) by stretch injury. PURPOSE: The aim of this study was to determine any association between PN and pelvic outlet obstruction. METHODS: One hundred forty-seven constipated patients were evaluated by cinedefecography and pudendal nerve terminal motor latency assessment. PN was defined as a latency longer than 2.2 ms. Pelvic outlet obstructive patterns of evacuation included paradoxic contraction, nonrelaxation of the puborectalis muscle, or failure of opening of the anal canal. RESULTS: Median length of constipation including straining during evacuation was eight (range, 1-47) years. Ninety-one (62 percent) subjects had a normal pattern of evacuation, and 56 (38 percent) had an obstructed pattern. Both groups had a similar median age (68 vs. 69 years, respectively; P > 0.05) and same median length of symptoms. Overall incidence of PN was 23.8 percent (10.9 percent unilateral and 12.9 percent bilateral). There was no difference in the incidence of PN between patients with normal evacuation and patients with obstructed evacuation (24.2 percent vs. 23.2 percent, respectively; P > 0.05). Patients with PN had a similar incidence of physiologic pelvic outlet obstruction as did patients without PN. However, median age of patients with PN was higher than those without PN (73 vs. 66 years, respectively; P > 0.05). CONCLUSION: There was a difference in the incidence of PN between normal and obstructed patterns of evacuation. Therefore, the espoused theory that obstructed defecation causes PN appears flawed.

Adolescent↗
PubMed1995

Gastric juice ammonia vs CLO test for diagnosis of Helicobacter pylori infection.

The aim of the present study was to compare the gastric juice ammonia test to the CLO test for the diagnosis of H. pylori infection in culture-proven cases by receiver operating characteristic (ROC) curve analysis. We studied 75 subjects (44 with chronic gastritis, 10 with gastric ulcer, 6 with duodenal ulcer, 8 with gastric cancer, and 7 normal) by endoscopy with biopsy for tissue diagnosis, culture of H. pylori. CLO test, and by gastric juice ammonia determinations. The culture-positive group had significantly higher intragastric ammonia levels (13.7 +/- 5.8 mg/dl) than the negative group (4.9 +/- 2.4 mg/dl, P < 0.01). In ROC curve analysis, the gastric juice ammonia test showed higher true positive and lower false positive ratios than the CLO test (P < 0.05). In conclusion, the measurement of intragastric juice ammonia levels was considered to be simpler, quicker, and overall a more valuable method for diagnosing H. pylori infection.

Ammonia↗
PubMed1995

The action of philanthotoxin-343 and photolabile analogues on locust (Schistocerca gregaria) muscle.

The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR). Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at the distal end of the toxin molecule were generally 2-3 fold less potent than PhTX-343. When these compounds were tested in subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V. during application of photolabile toxin combined with either neural stimulation of the muscle or L-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible.

Animals↗
PubMed1995

Labeling studies of photolabile philanthotoxins with nicotinic acetylcholine receptors: mode of interaction between toxin and receptor.

BACKGROUND: The nicotinic acetylcholine receptors (nAChRs) and glutamate receptors are ligand-gated cation channels composed of five separate polypeptide chains. A 43 kDa protein of unknown function is noncovalently associated with the cytoplasmic side of nAChR in vivo. The venoms of many wasps and spiders contain toxins that block the activity of these channels. Philanthotoxin-433 (PhTX-433) is a non-competitive channel blocker found in the venom of the wasp Philanthus. We have used a photolabile derivative to investigate how PhTX-433 interacts with nAChRs. RESULTS: A radiolabeled PhTX analog, containing a photolabile group substituted on one of its aromatic rings, photocrosslinked to all five subunits (alpha, alpha 1, beta, gamma, delta) of purified nAChR in the absence of the 43 kDa protein. In the presence of the 43 kDa protein, the alpha subunit was preferentially labeled. Proteolysis of the receptor after crosslinking indicated that the hydrophobic end (head) of the PhTx-433 analog bound to the cytoplasmic loop(s) of the alpha-subunit. Binding is inhibited by other non-competitive channel blockers such as the related polyamine-amide toxins from spiders and chlorpromazine. CONCLUSIONS: These results, coupled with previous structure/activity studies, lead to a putative model of the binding of PhTx and related polyamine toxins to nAChRs in vitro. The 43 kDa protein appears to influence the orientation of toxin binding. Further binding studies are necessary to confirm the model and to define how toxins enter the receptor and how they are oriented within it. A precise understanding of ligand/receptor interaction is crucial for the design of drugs specific for a particular subtype of receptor.

Animals↗
PubMed1995

Distribution of cryV-type insecticidal protein genes in Bacillus thuringiensis and cloning of cryV-type genes from Bacillus thuringiensis subsp. kurstaki and Bacillus thuringiensis subsp. entomocidus.

DNA dot blot hybridizations with a cryV-specific probe and a cryI-specific probe were performed to screen 24 Bacillus thuringiensis strains for their cryV-type (lepidopteran- and coleopteran-specific) and cryI-type (lepidopteran-specific) insecticidal crystal protein gene contents, respectively. The cryV-specific probe hybridized to 12 of the B. thuringiensis strains examined. Most of the cryV-positive strains also hybridized to the cryI-specific probe, indicating that the cryV genes are closely related to cryI genes. Two cryV-type genes, cryV1 and cryV465, were cloned from B. thuringiensis subsp. kurstaki HD-1 and B. thuringiensis subsp. entomocidus BP465, respectively, and their nucleotide sequences were determined. The CryV1 protein was toxic to Plutella xylostella and Bombyx mori, whereas the CryV465 protein was toxic only to Plutella xylostella.

Amino Acid Sequence↗
PubMed1995

Epithelial healing time and rate of the cornea after myopic epikeratoplasty.

This study was performed to investigate the corneal epithelial healing time and rate according to the method for promoting the reepithelization after myopic epikeratoplasty. A prospective study was conducted on 30 myopic epikeratoplasties which were divided into 3 groups according to the method for promoting the epithelial healing. The groups consisted of 10 eyes with pressure patches, 10 eyes with Acuvue disposable contact lens (CL) and 10 eyes with SeeQuence disposable CL. The cornea epithelial healing time were 3.4, 3.5 and 3.4 postoperative days for the pressure patch, Acuvue CL and SeeQuence CL groups, respectively. The corneal epithelial healing rates during postoperative 1, 2, and 3 days were 0.33, 0.78, and 0.44 mm2/hour for the pressure patch group; 0.24, 0.92 and 0.37 mm2/hour for the Acuvue CL group; and 0.30, 0.79 and 0.38 mm2/hour for the SeeQuence CL group. These results suggest that a disposable contact lens may not hinder epithelial healing compared with a pressure patch.

Adult↗
PubMed1995

Differentiation of malignant from benign pancreatic mass by Tl-201 abdominal SPECT.

The aim of the present study was to evaluate the ability of Tl-201 abdominal SPECT to differentiate between chronic focal pancreatitis and pancreatic malignancy. Seventeen patients (12 men, 5 women; mean age, 56 years; 9 pancreatic cancer, 8 chronic pancreatitis) with pancreatic mass were prospectively investigated with Tl-201 abdominal SPECT. In all patients, CT and/or US could not clarify the nature of the pancreatic mass. Focal hot uptake was present in 8 of 9 patients with pancreatic cancer, while it was present in 2 of 8 patients with chronic pancreatitis. Therefore, the sensitivity and specificity of the present study were 89% and 75%, respectively. A significant difference of Tl-201 uptakes was noted between benign and malignant masses (p < 0.05). Therefore, we concluded that Tl-201 abdominal SPECT was a useful test in differentiation of malignant from benign pancreatic mass, especially when the differentiation could not be made by other imaging modalities.

Abdomen↗
PubMed1994

Five-year results of radial keratotomy in the myopia over 6 diopters.

A number of studies have documented the reasonable efficacy and safety of radial keratotomy, but most based upon results obtained in low or moderate myopia or short term follow up after surgery. We complied 5 year and longer follow up data on 91 consecutive radial keratotomy surgeries on high myopia (over -6.00 diopters) performed by one surgeon 5 year-follow up was obtained on 21 (23%) of these eyes. The mean spherical equivalent before surgery was -11.02 diopters (D), the average keratometry value was 44.40 D, and all of the eyes had an uncorrected visual acuity of 0.04 or less. The average change in spherical equivalent was 3.44 D for eyes examined at 1 year, compared with 3.05 D for eyes at 3 years and 2.87 D at 5 years after surgery. Average keratometry value were 42.30 D at 1 year, 41.60 D at 3 years, and 41.30 D at 5 years after surgery. In our study, the decrease in spherical equivalent of 0.57 D was statistically significant (P < 0.05), as was the reduction in average keratometry value of 1.00 D. The effect of the surgery on spherical equivalent continued to regress through all the 5 years of follow up. However, the keratometric measurement decreased up to 5 years which indicated progressive flattening of the cornea. Also we divided these eyes into 2 groups, lower-myopic group (-6.00 D-(-)9.75 D) and higher-myopic group (over -10.00 D). In each category, the changes in spherical equivalent were 3.60 D, 2.21 D at 5 years, compared with 3.65 D, 3.25 D at 1 year respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Production of monoclonal antibodies against human chorionic gonadotropin by hybridoma cultures in calcium alginate capsules.

A new method of making microcapsules with calcium alginate gel was developed and the cultivation of the encapsulated hybridoma cells producing monoclonal antibodies against human chorionic gonadotropin was investigated. A high cell density of 2.0 x 10(8) cells/cm3 in the capsules led to a high dilution rate of 0.67 per hour and resulted in the high volumetric monoclonal antibody productivity of 652.8 mg/l/day, which was 20-30 times higher than those of traditional continuous suspension cultures. However, long-term continuous culture was not achieved with this capsule system probably because of the limitation in nutrient supply and the accumulation of waste products. Also the analysis of oxygen transfer in this system showed that oxygen supply was not enough to support such a high cell density.

Alginates↗
PubMed1993

Bench-scale production of acrylamide using the resting cells of Brevibacterium sp. CH2 in a fed-batch reactor.

Effects of various organic acids and salts on the stabilization of nitrile hydratase were investigated. The stability of the nitrile hydratase of Brevibacterium CH2 during storage was greatly enhanced by the addition of n-butyric acid. Effects of temperature, pH, and concentrations of acrylonitrile and n-butyric acid on acrylamide production by the resting cells were also investigated. Acrylamide production per unit dry weight of the cells increased 1.33 times by the addition of 0.05% n-butyric acid. A 20% acrylamide solution was successfully produced in a bench-scale reactor (12 l) with only a trace amount of salts after 10 h of hydration reaction under optimum reaction conditions without using an isotonic substrate. The conversion yield was nearly 100%, and acrylic acid as a by-product was not produced. Final acrylamide production of 400 g g-1 cells and productivity of 20 g/(g cells l-1 x h-1) were obtained.

Acrylamide↗