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Biomedical subjects

D H Chung

Publications and source records attributed to D H Chung.

66 records · Page 4Linked to original sources
PubMed1992

Detection of Mycobacterium tuberculosis in clinical samples from patients with tuberculosis or other pulmonary diseases by polymerase chain reaction.

Polymerase chain reaction (PCR) using primers targeting the IS6110 repetitive sequence was employed to detect Mycobacterium tuberculosis in 228 samples from patients with tuberculosis or other pulmonary diseases and controls, and the results were compared with culture and clinical findings. None of culture negative samples from 17 healthy controls were PCR positive. Of 109 active tuberculosis patients under chemotherapy, 88 (80.7%) were PCR positive and were significantly higher than 63 (57.8%) positive by culture. Fifty-nine (93.7) of 63 culture positive and 29 (63.0%) of 46 culture negative specimens contained M. tuberculosis detectable by PCR. In 41 specimens from inactive tuberculosis patients who visited to the chest clinic because of chest problems, 16 (39.0%) also gave PCR positive results. In addition, 14 (46.7%) of 30 specimens submitted for M. tuberculosis culture from patients with pulmonary diseases were PCR positive. Presumptive diagnosis of these PCR positive patients was bronchitis, pneumonia, bronchial asthma, etc. Therefore, this study suggests that PCR is sensitive and specific in detecting M. tuberculosis in clinical specimens. However, the interpretation of the PCR results in specimens from patients with pulmonary diseases should be done cautiously in areas with a high prevalence of tuberculosis.

Base Sequence↗
PubMed1992

Bombesin stimulates growth of human gastrinoma.

BACKGROUND: We have previously reported the first establishment and characterization of a functioning human gastrinoma (PT) xenograft. Bombesin, the equivalent of the mammalian gastrin-releasing peptide, has trophic effects on normal and neoplastic tissues of the gastrointestinal tract; the effects of gut hormones on the growth of gastrinoma are not known. The purpose of this study was twofold: (1) to determine the presence of various gut peptides in PT and (2) to determine the effect of bombesin on the growth of PT xenografts. METHODS: PT tumors were examined for expression (mRNA and protein) of various gut peptides by Northern hybridization and immunohistochemistry. In addition, PT xenografts were implanted as 3 mm2 pieces bilaterally subcutaneously in athymic nude mice. Mice were divided into two groups to receive either bombesin (5 micrograms/kg) or saline administered as intraperitoneal injections every 8 hours. Tumor area was measured twice weekly until mice were sacrificed (day 28), when tumor and normal pancreas were removed, weighed, and assayed for DNA and protein content. RESULTS: Both mRNAs and peptides of gastrin and chromogranin A were present in PT tumors. Bombesin significantly stimulated growth of PT tumors from day 18 until mice were sacrificed (day 28). As expected, bombesin stimulated pancreatic growth. CONCLUSIONS: We have demonstrated for the first time that bombesin is a trophic hormone for gastrinoma. The unique cell line PT contains gastrin and chromogranin A and will be a useful model to define the biologic mechanisms controlling the growth of human gastrinomas.

Animals↗
PubMed1992

Detection of extrapulmonary tuberculosis with gallium-67 scan and computed tomography.

We evaluated 23 patients with extrapulmonary tuberculosis (TB) with 67Ga imaging to assess its usefulness in the diagnosis of this condition. We performed computed tomography (CT) in 17 patients to assess CT features of extrapulmonary TB in comparison with findings from 67Ga scans. Nineteen of 23 patients (83%) had positive findings on 67Ga scans. One of five patients with tuberculous mediastinal lymphadenopathy, two patients with cervical lymphadenitis and a patient with renal TB had negative 67Ga scans. It was observed that the detection of previously unrecognized primary foci of TB, without concomitant pulmonary TB, was possible using 67Ga imaging in five patients (22%). The 67Ga scan was relatively sensitive for the localization of extrapulmonary TB. It is suggested that the 67Ga scan could serve as a screening method, when followed by CT and ultrasonography, for the initial detection of occult tuberculous lesions, especially in patients with prolonged fever.

Adult↗
PubMed1992

Cytokine regulation of gut ornithine decarboxylase gene expression and enzyme activity.

BACKGROUND: The enzyme ornithine decarboxylase (ODC) catalyzes the rate-limiting step in polyamine biosynthesis and is important for gut mucosal repair after systemic injury (e.g., burns); however, the mechanisms responsible for the injury-mediated induction of ODC are not known. The purpose of this study was to determine whether interleukin-1 (IL-1) or tumor necrosis factor (TNF), which are released immediately after injury, regulates gut mucosal ODC enzyme activity and gene expression. METHODS: In vivo: In experiment 1, 64 male BALB/c mice received either recombinant IL-1 beta (2 x 10(4) units/kg administered intraperitoneally) or saline solution. In experiment 2, 64 mice received either recombinant TNF-alpha (100 micrograms/kg administered intraperitoneally) or saline solution. We determined ODC enzyme activity and ODC mRNA levels in small intestine and kidneys at 2, 4, 12, and 24 hours after injection. In vitro: We also determined the ODC enzyme activity in intestinal epithelial crypt cells after either IL-1 beta or TNF-alpha treatment. RESULTS: IL-1, but not TNF, increased small intestinal ODC enzyme activity. In addition, IL-1 increased ODC enzyme activity in intestinal epithelial crypt cells at 5 and 6 hours after treatment. Both IL-1 and TNF increased small intestinal ODC mRNA levels. Neither agent affected ODC enzyme activity or ODC mRNA levels in the kidney. CONCLUSIONS: These results suggest that the cytokine-mediated induction of ODC in the small intestine is tissue specific, that the induction occurs at multiple cellular levels, and that ODC may play a vital role in the restoration of gut mucosa that occurs after injury.

Animals↗
PubMed1991

Requirements for in vitro growth of human thymocytes.

Since it is difficult to study human thymocyte maturation in vitro, we have developed an in vitro thymocyte culture system which has allowed us to select the optimal growth conditions for thymocyte subpopulations. Three thymocyte subpopulations (CD3-CD1-, CD1+CD3-, and CD3+CD1-) were isolated by a single step percoll density gradient centrifugation and indirect panning procedure using anti-CD1 and anti-CD3 monoclonal antibodies, and their purity was checked by flow cytometry. The combination of concanavalin A (Con A), tetradecanoylphorbol acetate (TPA), and IL-2 was shown to be the most reliable stimulus for the proliferation of CD3-CD1- thymocytes for up to 15 days in a culture system in vitro. Flow cytometric analysis for the phenotypic change of CD3-CD1- thymocytes revealed a steady increase of CD3 antigen after a 3-day cultivation, whereas there was no change in CD1 antigen intensity. A combination of Con A and IL-2 was both sufficient and necessary to induce growth of CD3+CD1- thymocytes. The major population of immature cortical thymocytes (CD3-CD1+ or CD3+CD1+), which are considered to be the most unresponsive dead-end cells, could not be maintained or stimulated with any combination used in this experiment, even in the presence of thymic accessory cells.

Antigens, CD↗
PubMed1989

Immunochemical assay applied to mycotoxin biosynthesis: ELISA comparison of sterigmatocystin production by Aspergillus versicolor and Aspergillus nidulans.

Conventional thin layer and instrumental methods for analyzing mycotoxins and their precursors are time-consuming and make the investigation of mycotoxin biosynthesis particularly difficult. As an alternative, sensitive enzyme-liked immunosorbent assays (ELISAs) can be utilized to analyze for these compounds. In this report, sterigmatocystin production in test tube cultures of Aspergillus versicolor ATCC 18643 and Aspergillus nidulans ATCC 32610 were compared using competitive ELISA. Polyclonal antiserum that was prepared against a sterigmatocystin hemiacetal-bovine serum albumin conjugate exhibited greatest specificity for sterigmatocystin hemiacetal and sterigmatocystin with less reactivity for O-methylsterigmatocystin. The antiserum could be used to detect as little as 50 ng/ml sterigmatocystin in ELISA. Direct ELISA could be performed on diluted culture broth and on mycelial extracts solubilized with N,N-dimethylformamide. Aspergillus versicolor ATCC 18643 produced more sterigmatocystin in SLS medium than in YES medium, and showed maximal levels at between 9 to 12 days incubation. Approximately 75% of sterigmatocystin was detectable in mycelium (254 micrograms/ml culture) compared to the extracellular fraction (87 micrograms/ml culture). Aspergillus nidulans exhibited qualitatively similar patterns of growth and toxigenesis in SLS medium but accumulated maximal levels of only 15 micrograms mycelial sterigmatocystin/ml culture and 5 micrograms extracellular sterigmatocystin/ml broth, respectively.

Aspergillus↗
PubMed1987

Structure of the yeast HIS5 gene responsive to general control of amino acid biosynthesis.

The nucleotide sequence of a 2.1 kb DNA fragment bearing the HIS5 gene of Saccharomyces cerevisiae, which encodes histidinol-phosphate aminotransferase (EC 2.6.1.9), has been determined. An open reading frame of 1,152 bp was found. S1 nuclease mapping indicated that the major transcription starts at position -37 from the ATG codon and the minor (approximately 20%) at -34 in both repressive and derepressive conditions. Northern analysis indicated that transcription of the HIS5 gene is under the general control of amino acid biosynthesis. The 5' noncoding region of the gene, thus far examined up to position -616, contains three copies of sequences homologous to the short repeats of the consensus sequence, 5'-AATGTGACTC-3', suggested for general amino acid control in the HIS1, HIS3, HIS4, and TRP5 at positions -336, -275 and -205. The consensus sequence closest to the open reading frame was shown to be necessary but not sufficient for general amino acid control, by examination of beta-galactosidase appearance in S. cerevisiae cells carrying various mutant HIS5 promoter regions fused to the lac'Z gene and inserted at the leu2 locus of chromosome III.

Amino Acid Sequence↗
PubMedDate not supplied

Prevention of mucosal atrophy: role of glutamine and caspases in apoptosis in intestinal epithelial cells.

Glutamine starvation induces apoptosis in enterocytes; therefore glutamine is important in the maintenance of gut mucosal homeostasis. However, the molecular mechanisms are unknown. The caspase family of proteases constitutes the molecular machinery that drives apoptosis. Caspases are selectively activated in a stimulus-specific and tissue-specific fashion. The aims of this study were to (1) identify specific caspases activated by glutamine starvation and (2) determine whether a general caspase inhibitor blocks glutamine starvation-induced apoptosis in intestinal epithelial cells. Rat intestinal epithelial (RIE-1) cells were deprived of glutamine. Specific caspase activation was measured using fluorogenic substrate assay. Apoptosis was quantified by DNA fragmentation and Hoechst nuclear staining. Glutamine starvation of RIE-1 cells resulted in the time-dependent activation of caspases 3 (10 hours) and 2 (18 hours), and the induction of DNA fragmentation (12 hours). Caspases 1 and 8 remained inactive ZVAD-fluoromethyl ketone, a general caspase inhibitor, completely blocked glutamine starvation-induced caspase activation, DNA fragmentation, and nuclear condensation. These results indicate that glutamine starvation selectively activates specific caspases, which leads to the induction of apoptosis in RIE-1 cells. Furthermore, inhibition of caspase activity blocked the induction of apoptosis, suggesting that caspases are potential molecular targets to attenuate apoptotic responses in the gut.

Amino Acid Chloromethyl Ketones↗
PubMedDate not supplied

Effect of eccentric load cycling on microleakage of Class V flowable and packable composite resin restorations.

Class V composite restorations are subject to the stresses that induce non-carious cervical lesions. This study evaluated the effect of eccentric oblique load on microleakage of restorations. Class V cavities were randomly prepared on the buccal surfaces of 40 recently extracted premolars and restored with composite resin according to manufacturers' directions. Teeth were randomly assigned to one of four treatment groups with 10 teeth per group: (1) flowable resin (Revolution) without load cycling; (2) packable resin (Prodigy Condensable) without load cycling; (3) flowable resin with load cycling (200,000 cycles) and (4) packable resin with load cycling (200,000 cycles). All teeth were then immersed in 2% methylene blue solution for 24 hours after thermocycling (500 cycles). Dye penetration was measured (scores 0-3). The results indicated that adding load cycling significantly increased microleakage (p < 0.05). No significant differences in microleakage were observed for flowable resin vs packable resin. Gingival margins had significantly more microleakage (p < 0.05) than occlusal margins.

Analysis of Variance↗