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Biomedical subjects

J H Choi

Publications and source records attributed to J H Choi.

At least 19 recordsLinked to original sources
PubMed2001

High critical current density and enhanced irreversibility field in superconducting MgB2 thin films.

The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has already been demonstrated. One possible drawback, however, is that the magnetic field at which superconductivity is destroyed is modest. Furthermore, the field which limits the range of practical applications-the irreversibility field H*(T)-is approximately 7 T at liquid helium temperature (4.2 K), significantly lower than about 10 T for Nb-Ti (ref. 6) and approximately 20 T for Nb3Sn (ref. 7). Here we show that MgB2 thin films that are alloyed with oxygen can exhibit a much steeper temperature dependence of H*(T) than is observed in bulk materials, yielding an H* value at 4.2 K greater than 14 T. In addition, very high critical current densities at 4.2 K are achieved: 1 MA cm-2 at 1 T and 105 A cm-2 at 10 T. These results demonstrate that MgB2 has potential for high-field superconducting applications.

Journal Article↗
PubMed2001

Inhibition of cytokine-induced vascular cell adhesion molecule-1 expression; possible mechanism for anti-atherogenic effect of Agastache rugosa.

Adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1) play an important role during the early stages of atherogenesis. Agastache rugosa has an anti-atherogenic effect in low density lipoprotein receptor -/- mice. Moreover, A. rugosa reduced macrophage infiltration and VCAM-1 expression has been localized in aortic endothelium that overlies early foam cell lesions. This study ascertained that tilianin (100 microM), a major component of A. rugosa, inhibits the tumor necrotic factor-alpha (TNF-alpha)-induced expression of VCAM-1 by 74% in cultured human umbilical vein endothelial cells (HUVECs). Also, tilianin (100 microM) reduced TNF-alpha-induced activation of nuclear factor-kappaB in HUVECs.

Animals↗
PubMed2001

Platelet-activating factor-induced early activation of NF-kappa B plays a crucial role for organ clearance of Candida albicans.

In this study, we have investigated the mechanisms underlying organ susceptibility to candida infection. Infection of BALB/c mice with Candida albicans led to both an early (1-8 h) and late (24-48 h) activation of NF-kappaB in the organs resistant to C. albicans, including the lung and spleen. In susceptible organs such as the kidneys, early activation of NF-kappaB was not observed. The kinetics of TNF-alpha mRNA expression paralleled those of NF-kappaB activation in all organs examined. Blocking the effects of endogenous platelet-activating factor (PAF) by pretreatment with the PAF antagonist BN50739 or antioxidants significantly reduced the early activity of NF-kappaB and TNF-alpha mRNA expression, and increased the recovery of C. albicans in the lung and spleen. Importantly, administration of PAF 5 min prior to the infection resulted in the appearance of early activities of NF-kappaB and TNF-alpha mRNA expression, followed by a nearly complete clearance of the organisms in the kidneys. Pretreatment with anti-TNF-alpha Ab resulted in an enhanced susceptibility to C. albicans, and the PAF-mediated resistance was abrogated by anti-TNF-alpha in all organs examined. These data indicated that endogenously produced PAF in response to C. albicans is a key molecule involved in the early activation of NF-kappaB, which, in turn, renders the organ resistant to the fungus by promoting the production of anti-candidal proinflammatory cytokines such as TNF-alpha. Susceptible organs, including the kidneys, lack the capacity to generate a sufficient PAF-induced early NF-kappaB response.

Adjuvants, Immunologic↗
PubMed2001

Excision repair of adozelesin-N3 adenine adduct by 3-methyladenine-DNA glycosylases and UvrABC nuclease.

Adozelesin is a synthetic analog of the antitumor antibiotic CC-1065, which alkylates the N3 of adenine in the minor groove in a sequence-selective manner. Since the cytotoxic potency of a DNA alkylating agent can be modulated by DNA excision repair system, we investigated whether nucleotide excision repair (NER) and base excision repair (BER) enzymes are able to excise the bulky DNA adduct induced by adozelesin. The UvrABC nuclease and 3-methyladenine-DNA glycosylase, that exhibit a broad spectrum of substrate specificity, were selected as typical NER and BER enzymes, respectively. The adozelesin-DNA adduct was first formed in the radiolabeled restriction DNA fragment and its excision by purified repair enzymes was monitored on a DNA sequencing gel. The treatment of the DNA adduct with a purified UvrABC nuclease and sequencing gel analysis of cleaved DNA showed that UvrABC nuclease was able to incise the adozelesin adduct. The incision site corresponded to the general nuclease incision site. Excision of this adduct by 3-methyladenine-DNA glycosylases was determined following the treatment of the DNA adduct with a homogeneous recombinant bacterial, rat and human 3-methyladenine-DNA glycosylases. Abasic sites generated by DNA glycosyalses were cleaved by the associated lyase activity of the E. coli formamidopyrimidine-DNA glycosylase (Fpg). Resolution of cleaved DNA on a sequencing gel showed that the DNA glycosylase from different sources could not release the N3-adenine adducts. A cytotoxicity assay using E. coli repair mutant strains showed that E. coli mutant strains defective in the uvrA gene were more sensitive to cell killing by adozelesin than E. coli mutant strain defective in the alkA gene or the wild type. These results suggest that the NER pathway seems to be the major excision repair system in protecting cells from the cytotoxicity of adozelesin.

Alkylation↗
PubMed2001

Proteolytic cleavage of epidermal growth factor receptor by caspases.

Apoptotic proteases cleave and inactivate survival signaling molecules such as Akt/PKB, phospholipase C (PLC)-gamma1, and Bcl-2. We have found that treatment of A431 cells with tumor necrosis factor-alpha in the presence of cycloheximide resulted in the cleavage of epidermal growth factor receptor (EGFR) as well as the activation of caspase-3. Among various caspases, caspase-1, caspase-3 and caspase-7 were most potent in the cleavage of EGFR in vitro. Proteolytic cleavage of EGFR was inhibited by both YVAD-cmk and DEVD-fmk in vitro. We also investigated the effect of caspase-dependent cleavage of EGFR upon the mediation of signals to downstream signaling molecules such as PLC-gamma1. Cleavage of EGFR by caspase-3 significantly impaired the tyrosine phosphorylation of PLC-gamma1 in vitro. Given these results, we suggest that apoptotic protease specifically cleaves and inactivates EGFR, which plays crucial roles in anti-apoptotic signaling, to abrogate the activation of EGFR-dependent downstream survival signaling molecules.

Amino Acid Chloromethyl Ketones↗
PubMed2001

Hematein inhibits tumor necrotic factor-alpha-induced vascular cell adhesion molecule-1 and NF-kappaB-dependent gene expression in human vascular endothelial cells.

Monocyte adhesion to the endothelium via adhesion molecules is one of the earliest events in atherogenesis. It has been suggested that vascular cell adhesion molecule-1 (VCAM-1) plays a very important role in the recruitment of monocytes in atherosclerosis. The aim of our study was to evaluate whether hematein can influence the expression of VCAM-1 and the transcription of nuclear factor-kappaB (NF-kappaB)-dependent genes. Immunohistochemistry revealed that mouse aortic artery endothelial cells express VCAM-1 after feeding a high cholesterol diet for 8 weeks. Hematein dose dependently suppressed TNF-alpha-induced VCAM-1 in both surface (30.8%) and soluble protein (65%) production in HUVECs. The transcription level of VCAM-1 was measured by Northern blot analysis, and decreased VCAM-1 protein expression was associated with a reduction of VCAM-1 mRNA expression. Transient transfection study of NF-kappaB promoter construct and electrophoretic mobility shift assay suggested that hematein inhibited both NF-kappaB-dependent gene expression and NF-kappaB activation induced by TNF-alpha. Our results suggest that the down-regulation of VCAM-1 expression by hematein may in part be due to the inhibition of NF-kappaB-dependent gene expression.

Animals↗
PubMed2001

Constituents and the antitumor principle of Allium victorialis var. platyphyllum.

To search for cytotoxic components from Allium victorialis, MTT assays on each extract and an isolated component, gitogenin 3-O-lycotetroside, were performed against cancer cell lines. Cytotoxicities of most extract were shown to be comparatively weak, though IC50 values of CHCl3 fraction was found to be <31.3-368.4 microg/ml. From the incubated methanol extract at 36 degrees C, eleven kinds of organosulfuric flavours were predictable by GC-MS performance. The most abundant peak was revealed to be 2-vinyl-4H-1,3-dithiin (1) by its mass spectrum. Further, this extract showed significant cytotoxicities toward cancer cell lies. Silica gel column chromatography of the n-butanol fraction led to the isolation of gitogenin 3-O-lycotetroside (3) along with astragalin (4) and kaempferol 3, 4'-di-O-beta-D-glucoside (5). This steroidal saponin exhibited significant cytotoxic activities (IC50, 6.51-36.5 microg/ml) over several cancer cell lines. When compound 3 was incubated for 24 h with human intestinal bacteria, a major metabolite was produced and then isolated by silica gel column chromatography. By examining parent- and prominent ion peak in FAB-MS spectrum of the metabolite, the structure was speculated not to be any of prosapogenins of 3, suggesting that spiroketal ring were labile to the bacterial reaction. These suggest that disulfides produced secondarily are the antitumor principles.

Allium↗
PubMed2001

Epidural naloxone reduces intestinal hypomotility but not analgesia of epidural morphine.

PURPOSE: Epidural morphine is associated with decreased bowel motility and increased transit time. Low doses of intravenous naloxone reduce morphine-induced pruritus without reversing analgesia, but the effect of epidural naloxone on bowel motility has not been studied. Therefore we evaluated bowel motility and analgesia when naloxone was co-administered with morphine into the epidural space. METHODS: Forty-three patients having combined thoracic epidural and general anesthesia for subtotal gastrectomy were randomly assigned to one of two study groups. All received a bolus dose of 3 mg epidural morphine at the beginning of surgery, followed by a continuous epidural infusion containing 3 mg morphine in 100 ml bupivacaine 0.125% with either no naloxone (control group, n = 18) or a calculated dose of 0.208 microg x kg(-1) x hr(-1) of naloxone (experimental group, n = 25) for 48 hr. We measured the time to the first postoperative passage of flatus and feces to evaluate the restoration of bowel function, and visual analog scales (VAS) for pain during rest and movement. Scores were assessed at 2, 4, 8, 16, 24, 36 and 48 hr postoperatively. RESULTS: The experimental group had a shorter time to the first postoperative passage of flatus (5 1.9 +/- 1 6.6 hr vs 87.0 +/- 19.5 hr, P < 0.001 ) and feces (95.3 +/- 25.0 hr vs 132.9 +/- 29.4 hr, P < 0.001). No differences were found in either resting or active VAS between the two groups. CONCLUSION: Epidural naloxone reduces epidural morphine-induced intestinal hypomotility without reversing its analgesic effects.

Analgesia, Epidural↗
PubMed2001

Fibrosarcoma in bizarre parosteal osteochondromatous proliferation.

Bizarre parosteal osteochondromatous proliferation (BPOP) is a rare benign lesion predominantly involving the small bones of the hands and feet. Malignant transformation in BPOP has not been documented in the English literature. This report presents the coexistence of fibrosarcoma with BPOP in the right distal fibula of an 18-year-old woman.

Adolescent↗
PubMed2001

Dicaffeoyl- or digalloyl pyrrolidine and furan derivatives as HIV integrase inhibitors.

Human immunodeficiency virus (HIV) integrase (IN) catalyzes the integration of HIV DNA copy into the host cell DNA. Such integration is essential for the production of progeny viruses, and therefore therapeutic agents that can inhibit this process should be effective anti-HIV agents. We have previously reported the inhibitory activity of dicaffeoylglucosides against HIV IN. In the present study, we have synthesized and tested dicaffeoyl or digalloyl compounds joined through a five-membered heterocyclic ring as HIV IN inhibitors to explore the SARs of this family of compounds. The starting heterocyclic diols were prepared from L-tartaric acid, diethyl L-tartarate or D-(+)-ribonic gamma-lactone. We found that the HIV IN inhibitory activities of dicaffeoyl derivatives were comparable to that of L-chicoric acid (IC(50)=24.9 microM). On the other hand, digalloyl derivatives were more potent than L-chicoric acid with IC(50) values of 4.7--15.6 microM.

Caffeic Acids↗
PubMed2001

Polymerase chain reaction (PCR) for human herpesvirus 8 and heteroduplex PCR for clonality assessment in angiolymphoid hyperplasia with eosinophilia and Kimura's disease.

BACKGROUND: Recently, human herpesvirus 8 (HHV-8) has been isolated from almost all cases of Kaposi's sarcoma. It has not been found in most cutaneous hemangioproliferative disorders other than Kaposi's sarcoma. Benign vascular lesions including Kimura's disease were not found to contain the HHV-8 DNA sequence. However, there has been contradictory data concerning the presence of HHV-8 in angiolymphoid hyperplasia with eosinophilia (ALHE). Clonality studies in ALHE and Kimura's disease were rare. METHODS: We performed polymerase chain reaction (PCR)-based analysis to determine whether HHV-8 is present and heteroduplex analysis of rearranged T-cell receptor (TCR) gene for clonality assessment in paraffin-embedded skin biopsy samples of 7 ALHE and 2 Kimura's disease, taken from immunocompetent patients. RESULTS: HHV-8 could not be identified in all the cases of ALHE and Kimura's disease. Although 2 cases (2/7) of ALHE and 2 cases (2/2) of Kimura's disease showed positive result for PCR analysis of TCR, all the cases were negative for heteroduplex-PCR. CONCLUSIONS: We suggest that HHV-8 may not involve in a pathogenetic role in ALHE and Kimura's disease and the failure to demonstrate clonality may be consistent with the reactive nature of these diseases and lack of malignant transformation. In addition, heteroduplex-PCR can be applied to confirm doubtful cases of lymphoma in that heteroduplex-PCR is more specific than PCR as seen in our study.

Adolescent↗
PubMed2001

Graves' disease presenting as elephantiasic pretibial myxedema and nodules of the hands.

A 67-year-old man presented with a 2-year history of asymptomatic, firm, multiple nodules and plaques and cerebriform hypertrophy of both lower legs and feet, and well-defined, skin-colored, firm nodules and tumors on both hands. He had been diagnosed as having Graves' disease 3 years previously, and had been treated with 10 mg of methimazole and 100 microg of thyroxin (T4) daily for 2 years. Physical examination revealed nonpitting edema, flesh-colored to erythematous, firm, confluent, polypoid nodules and fissured plaques extending from the shins to the dorsa of both feet (Fig. 1), and round to oval, firm, skin-colored, walnut-to-egg-sized tumors on all 10 fingers and the ulnar side of the dorsum of the right hand (Fig. 2). The thyroid gland was diffusely enlarged; however, there was no exophthalmos, and extraocular movements were normal. There was no weight loss, loss of appetite, tremor, heat intolerance, diarrhea, or fatigue. On laboratory evaluation, thyroid-stimulating hormone (TSH) had a markedly low titer of < 0.05 microU/mL (normal: 0.4-5.0), and the TSH receptor antibody was extremely high at 73.8% (normal: < 15%). Serum free triiodothyronine (T3), T4, antimicrosome, and antithyroglobulin antibodies were normal or negative. Skin biopsy samples from the shin and hand disclosed extensive mucin deposition throughout the dermis.

Aged↗
PubMed2001

Prevalence of endoscopic reflux esophagitis among Koreans.

BACKGROUND AND AIM: Although reflux esophagitis is believed to be common in the Western population, very few epidemiologic data on reflux esophagitis in Koreans are available. The aims of this study were to evaluate the prevalence of endoscopic reflux esophagitis in patients who came for a physical check-up at Korea University Hospital, and to study the relationship between various factors relevant to reflux disease. METHODS: This study was carried out prospectively on 7,015 patients who received an esophagogastroduodenoscopy from September 1996 to December 1997. Most of the patients were free of symptoms and had come for their self-paid check-up. RESULTS: The overall prevalence of reflux esophagitis was 3.4%, and most of the patients had a mild degree of esophagitis representing grade 1 in 98.3% and grade 2 in 1.7%. The male: female ratio for esophagitis was 7 : 1, and the body mass index (BMI) was significantly higher in patients with reflux esophagitis. A hiatal hernia was found in 166 patients with esophagitis (68.6%), but only in 9.2% patients without esophagitis (P < 0.05). Smoking and alcohol consumption were associated with the development of reflux esophagitis (P < 0.05). CONCLUSIONS: The prevalence of endoscopic reflux esophagitis among Koreans is 3.4%, and most of the patients had a mild grade esophagitis. Smoking, alcohol consumption, the presence of a hiatal hernia and a higher BMI are associated with the development of reflux esophagitis.

Esophagitis, Peptic↗
PubMed2001

Treatment of "Cyrano" angioma with pulsed dye laser.

BACKGROUND: Hemangiomas of the nasal tip, the so-called Cyrano nose, are often deep, disfiguring, and persistent. OBJECTIVE: To evaluate the effect of treatment with pulsed dye laser on Cyrano nose. METHODS: A 3-month-old boy with hemangioma of the nasal tip of 1-months duration underwent six sessions of pulsed dye laser treatment with a 7 mm collimated beam at fluences of 5.75-6.5 J/cm2, 6 weeks apart. RESULTS: Initial improvement was noted after two treatments, and the lesion showed a marked reduction in size and improvement in color over a total treatment period of 9 months. CONCLUSION: Treatment with the 585 nm pulsed dye laser should be considered in the management of infants with mild to moderate degrees of nasal tip hemangiomas since it effectively reduces the lesions with minimal adverse effects.

Hemangioma↗
PubMed2001

Endoscopic removal of sharp foreign bodies impacted in the esophagus.

BACKGROUND AND STUDY AIMS: Impacted sharp foreign bodies in the esophagus can be very difficult to manage. When attempts are made to remove such objects inappropriately, life-threatening complications such as perforation can occur. The aim of this study was to evaluate the safety and efficacy of endoscopic removal of impacted sharp foreign bodies in the esophagus using proximal dilatation with an oral side balloon or transparent cap. PATIENTS AND METHODS: A total of 22 patients (10 men, 12 women) with impacted sharp foreign bodies in the esophagus underwent endoscopic extraction. The following technique was successfully performed at our hospital. An oral side balloon (Top Co., Japan) for esophageal variceal sclerotherapy was attached to the distal part of the endoscope. With the patient under local anesthesia, the endoscope was inserted as far as the proximal part of the esophageal foreign body. The oral side balloon was then gradually inflated. Dilatation of the proximal part of the esophagus made it possible to release the impacted sharp foreign body from the esophageal wall. A transparent cap was used for foreign bodies in the upper esophagus when there were difficulties with the oral side balloon. RESULTS: The types of foreign body removed were fish bones (n = 9), press-through packages (n = 8), chicken bones (n =3), dentures (n = 1), and a wrist watch (n = 1). Endoscopic removal was successful in all but one of the cases, in which a fish bone had to be extracted surgically. CONCLUSIONS: The proximal dilatation method using an oral side balloon or transparent cap is safe and effective in removing sharp foreign bodies from the esophagus, avoiding surgery and possible perforation.

Adult↗
PubMed2001

Idiopathic eruptive macular pigmentation: report of 10 cases.

Idiopathic eruptive macular pigmentation (IEMP) is a rare disease. IEMP is characterized by asymptomatic, pigmented macules involving the neck, trunk, and proximal extremities. This study describes 10 cases of idiopathic eruptive macular pigmentation seen during a 9-year period at the Asan Medical Center, Seoul, Korea. We present these characteristic consecutive cases to provide more insight into the clinical picture and course of IEMP. Skin lesions of 8 patients were multiple brown macules involving the trunk, face, neck, and extremities. In 2 patients, multiple dark brown macules and patches were noted. The age of onset varied from 1 to 20 years. Tentative diagnoses were usually ashy dermatosis (erythema dyschromicum perstans), fixed drug eruption, or mastocytosis. The history of any erythema and drug medication was absent. Darier's sign was absent. Skin biopsy specimens showed increased pigmentation of the basal layer in an otherwise normal epidermis. Pigmentary incontinence, melanophages, and mild perivascular lymphohistiocytic infiltrate in the papillary dermis were also revealed. Mast cells could not be found. The lesions gradually disappeared during a period of several months to years. The alleged rarity of IEMP may be partially caused by medical unfamiliarity with this entity, despite its clinical and histopathologic characteristic picture. Treatment of IEMP is unnecessary because spontaneous resolution of the lesions can be expected within several months to a few years.

Adolescent↗