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Biomedical subjects

H M Oh

Publications and source records attributed to H M Oh.

At least 19 recordsLinked to original sources
PubMed2001

Microcystin-induced down-regulation of lymphocyte functions through reduced IL-2 mRNA stability.

Here we report that lymphocyte functions were down-regulated by cyanobacterial hepatotoxin microcystin. Treatment of three microcystin (MC) isotypes, MC-LR, MC-YR and nodularin, on B6C3F1 mouse splenocytes produced dose-dependent inhibition of in vitro polyclonal antibody response and lymphoproliferation to LPS. ConA-induced lymphoproliferative response was decreased by MC-YR and nodularin, but no significant effect was observed in the MC-LR treatment. Intraperitoneal administration of nodularin into B6C3F1 mice decreased humoral immune responses to sheep red blood cell (sRBC), and the inhibitory effect became severe when hepatic uptake of nodularin was blocked by rifampicin. Each MC 1 microM suppressed phorbol 12-myristate 13-acetate (PMA) plus ionomycin-induced IL-2 mRNA expression in splenocytes and thymocytes, but not in EL-4 mouse thymoma cells. To further characterize the mechanism for the reduced IL-2 mRNA level, IL-2 mRNA stability was measured using RT-PCR. Deprivation of PMA/ionomycin stimuli from activated splenocytes and blockade of new transcription resulted in destabilization of IL-2 mRNA, which was accelerated by MC treatment. These results demonstrated that MC down-regulated lymphocyte functions and the immunosuppression was mediated, at least in part, through decreased IL-2 mRNA stability.

Animals↗
PubMed2001

Seasonal variation and indirect monitoring of microcystin concentrations in Daechung reservoir, Korea.

Physicochemical and biological water quality, including the microcystin concentration, was investigated from spring to autumn 1999 in the Daechung Reservoir, Korea. The dominant genus in the cyanobacterial blooming season was Microcystis. The microcystin concentration in particulate form increased dramatically from August up to a level of 200 ng liter(-1) in early October and thereafter tended to decrease. The microcystin concentration in dissolved form was about 28% of that of the particulate form. The microcystins detected using a protein phosphatase (PP) inhibition assay were highly correlated with those microcystins detected by a high-performance liquid chromatograph (r = 0.973; P < 0.01). Therefore, the effectiveness of a PP inhibition assay for microcystin detection in a high number of water samples was confirmed as easy, quick, and convenient. The microcystin concentration was highly correlated with the phytoplankton number (r = 0.650; P < 0.01) and chlorophyll-a concentration (r = 0.591; P < 0.01). When the microcystin concentration exceeded about 100 ng liter(-1), the ratio of particulate to dissolved total nitrogen (TN) or total phosphorus (TP) converged at a value of 0.6. Furthermore, the microcystin concentration was lower than 50 ng liter(-1) at a particulate N/P ratio below 8, whereas the microcystin concentration varied quite substantially from 50 to 240 ng liter(-1) at a particulate N/P ratio of >8. Therefore, it seems that the microcystin concentration in water can be estimated and indirectly monitored by analyzing the following: the phytoplankton number and chlorophyll-a concentration, the ratio of the particulate and the dissolved forms of N and P, and the particulate N/P ratio when the dominant genus is toxigenic Microcystis.

Chlorophyll↗
PubMed2001

Shigella septicaemia in adults: report of two cases and mini-review.

INTRODUCTION: We report 2 cases of Shigella septicaemia in adult patients. CLINICAL PICTURE: Two 57-year-old women presented with non-bloody diarrhoea and fever. The first patient was an inmate of a long-term care facility who was schizophrenic and the second patient was a diabetic who recently travelled to Medan, Indonesia. Both patients were febrile, hypotensive and dehydrated. The first patient was neutropenic, thrombocytopenic and had acute renal failure. Blood cultures yielded Shigella flexneri and stool cultures gave negative results for both patients. TREATMENT: Rehydration and intravenous ceftriaxone were instituted. OUTCOME: The patients' symptoms and hypotension resolved. CONCLUSION: Appropriate antibiotics can decrease the severity and duration of Shigella septicaemia.

Ceftriaxone↗
PubMed2000

Suppression of IL-2 and IL-4 gene expression by nodularin through the reduced NF-AT binding activity.

Nodularin is a cyclic peptide produced by cyanobacteria. In the present study, the inhibitory effect of nodularin on T lymphocyte functions was demonstrated. Direct addition of nodularin to B6C3F1 mouse splenocyte cultures produced a concentration-dependent inhibition of the lymphoproliferative response to concanavalin A stimulation. Nodularin inhibited PMA plus ionomycin (Io)-induced IL-2 mRNA expression in murine splenocytes and thymocytes as determined by quantitative/competitive RT-PCR. To further characterize the mechanism for the transcriptional regulation of IL-2, the binding activity of transcription factors, NF-AT, AP-1, NF-kappaB, and Oct, was evaluated by electrophoretic mobility shift assays in mouse splenocytes. Nodularin reduced the NF-AT binding activity in PMA/Io-induced splenocytes, but no significant effect was observed on AP-1, NF-kappaB, or Oct binding activity. Nodularin also inhibited IL-4 mRNA expression in PMA/Io-stimulated murine splenocytes. These results suggest that T lymphocyte is a possible cellular target of nodularin, and the inhibitory effect of nodularin on T-cell specific transcription factor NF-AT induces T-cell dysfunction, which leads to a diminution in IL-2 and IL-4 gene transcription.

Animals↗
PubMed2000

Variation of microcystin content of microcystis aeruginosa relative to medium N:P ratio and growth stage.

Changes in the microcystin content of Microcystis aeruginosa UTEX 2388 were investigated at several N:P ratios of the medium and various growth stages. Under the P-fixed condition, the microcystin content of the cells changed with different medium N:P ratios, with the highest at 2748 microg g-1 at a N:P ratio of 16 after incubation for 7 d. The microcystin content of M. aeruginosa exhibited a high correlation with the total N content regardless of an N-fixed or P-fixed culture. When the N:P ratio of the medium was fixed to 16 : 1, the microcystin content of M. aeruginosa at various growth stages was highest at 2191 microg g-1 after an incubation of 4 d and the chlorophyll-a content showed a similar tendency. There was a highly significant relationship between the microcystin content of M. aeruginosa and the chlorophyll-a concentration in the culture during the incubation. Accordingly, the microcystin content of M. aeruginosa during incubation can be easily estimated and monitored by measuring the in vivo fluorescence changes in the culture.

Biomass↗
PubMed2000

Microcystin production by Microcystis aeruginosa in a phosphorus-limited chemostat.

The production of microcystins (MC) from Microcystis aeruginosa UTEX 2388 was investigated in a P-limited continuous culture. MC (MC-LR, MC-RR, and MC-YR) from lyophilized M. aeruginosa were extracted with 5% acetic acid, purified by a Sep-Pak C(18) cartridge, and then analyzed by high-performance liquid chromatography with a UV detector and Nucleosil C(18) reverse-phase column. The specific growth rate (mu) of M. aeruginosa was within the range of 0.1 to 0.8/day and was a function of the cellular P content under a P limitation. The N/P atomic ratio of steady-state cells in a P-limited medium varied from 24 to 15 with an increasing mu. The MC-LR and MC-RR contents on a dry weight basis were highest at mu of 0.1/day at 339 and 774 microg g(-1), respectively, while MC-YR was not detected. The MC content of M. aeruginosa was higher at a lower mu, whereas the MC-producing rate was linearly proportional to mu. The C fixation rate at an ambient irradiance (160 microeinsteins m(-2) s(-1)) increased with mu. The ratios of the MC-producing rate to the C fixation rate were higher at a lower mu. Accordingly, the growth of M. aeruginosa was reduced under a P limitation due to a low C fixation rate, whereas the MC content was higher. Consequently, increases in the MC content per dry weight along with the production of the more toxic form, MC-LR, were observed under more P-limited conditions.

Culture Media↗
PubMed2000

Nipah viral encephalitis or Japanese encephalitis? MR findings in a new zoonotic disease.

BACKGROUND AND PURPOSE: An epidemic of suspected Japanese encephalitis occurred in Malaysia in 1998-1999 among pig farmers. In neighboring Singapore, an outbreak occurred among pig slaughterhouse workers. It was subsequently established that the causative agent in the outbreak was not the Japanese encephalitis virus but a previously unknown Hendra-like paramyxovirus named Nipah virus. METHODS: The brain MR images of eight patients with Nipah virus infection were reviewed. All patients tested negative for acute Japanese encephalitis virus. Seven patients had contrast-enhanced studies and six had diffusion-weighted examinations. RESULTS: All patients had multiple small bilateral foci of T2 prolongation within the subcortical and deep white matter. The periventricular region and corpus callosum were also involved. In addition to white matter disease, five patients had cortical lesions, three had brain stem involvement, and a single thalamic lesion was detected in one patient. All lesions were less than 1 cm in maximum diameter. In five patients, diffusion-weighted images showed increased signal. Four patients had leptomeningeal enhancement and four had enhancement of parenchymal lesions. CONCLUSION: The brain MR findings in patients infected with the newly discovered Nipah paramyxovirus are different from those of patients with Japanese encephalitis. In a zoonotic epidemic, this striking difference in the appearance and distribution of lesions is useful in differentiating these diseases. Diffusion-weighted imaging was advantageous in increasing lesion conspicuity.

Abattoirs↗
PubMed2000

Attitudes and beliefs of Singapore health care professionals concerning HIV/AIDS.

AIM OF STUDY: This study examines the beliefs and attitudes of Singapore doctors, dentists, and nurses concerning HIV/AIDS and persons living with HIV/AIDS (PWAs). METHOD: A mail survey was done of all doctors and dentists in Singapore as well as a random sample of 1,500 nurses from the Singapore Nursing Board Register. RESULTS: The results showed that respondents held accurate beliefs concerning transmission of HIV via sex and needle sharing but a significant proportion also expressed belief in transmission via everyday social contact. Respondents were aware of universal precautions when treating persons with HIV/AIDS but tended to be overly cautious in low/no risk situations. A substantial proportion of respondents indicated little or no knowledge or experience with AIDS-related conditions and the majority believed that most health care professionals are unprepared to care for PWAs. Further, there was evidence of substantial stigmatisation and fear of treating PWAs, both of which were significantly and negatively correlated with accuracy of beliefs about HIV transmission and universal precautions. CONCLUSION: These results point to important misconceptions about HIV/AIDS held by Singapore health care professionals as well as stigma towards and fear of treating PWAs. These are areas that need to be addressed through better professional education concerning HIV/ AIDS. This education needs to address both the factual misconceptions about HIV/AIDS as well as the stigma associated with this disease and the fears that health care professionals have of treating PWAs.

Acquired Immunodeficiency Syndrome↗
PubMed1999

The methanol extract of Spiraea prunifolia var. simpliciflora root inhibits the generation of nitric oxide and superoxide in RAW 264.7 cells.

It is well established that nitric oxide (NO) and superoxide radicals play pivotal roles in the pathogenesis of inflammatory diseases and fever. This study is undertaken to address whether the methanol extract of Spiraea prunifolia var. simpliciflora root, a traditional medicine as an antipyretic, modulates the generation of NO and superoxide in IFN-gamma primed or polymyristic acetate (PMA) stimulated RAW 264.7 cells, respectively. The generation of NO as well as the expression of inducible nitric oxide synthase (iNOS) protein from IFN-gamma primed RAW 264.7 cells is markedly decreased by the methanol extract in a dose dependent manner. However, the methanol extract does not affect the viability of RAW 264.7 cells, as assessed by methylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) assay. In addition, the methanol extract suppresses the generation of superoxide in PMA-stimulated RAW 264.7 cells in a dose and a time dependent manner. Taken together, anti-pyretic effects of Spiraea prunifolia var. simpliciflora root extract could result from direct suppression of NO and decreased superoxide generation.

Analgesics, Non-Narcotic↗
PubMed1999

Characterization of a biosurfactant, mannosylerythritol lipid produced from Candida sp. SY16.

One yeast strain, SY16, was selected as a potential producer of a biosurfactant, and identified as a Candida species. A biosurfactant produced from Candida sp. SY16 was purified and confirmed to be a glycolipid. This glycolipid-type biosurfactant lowered the surface tension of water to 29 dyne/cm at critical micelle concentration of 10 mg/l (1.5 x 10(-5) M), and the minimum interfacial tension was 0.1 dyne/cm against kerosene. Thin-layer and high-pressure liquid chromatography studies demonstrated that the glycolipid contained mannosylerythritol as a hydrophilic moiety. The hydrophilic sugar moiety of the biosurfactant was determined to be beta-D-mannopyranosyl-(1-->4)-O-meso-erythritol by nuclear magnetic resonance (NMR) and fast atom bombardment mass-spectroscopy analyses. The hydrophobic moiety, fatty acids, of the biosurfactant was determined to be hexanoic, dodecanoic, tetradecanoic, and tetradecenoic acid by gas chromatography-mass spectroscopy. The structure of the native biosurfactant was determined to be 6-O-acetyl-2,3-di-O-alkanoyl-beta-D-mannopyranosyl-(1-->4)-O-meso- erythritol by NMR analyses. We newly determined that an acetyl group was linked to the C-6 position of the D-mannose unit in the hydrophilic sugar moiety.

Candida↗
PubMed1999

Imported malaria in a Singapore hospital: clinical presentation and outcome.

OBJECTIVE: To evaluate the clinical presentation and outcome of imported malaria. METHODS: A retrospective chart review was conducted of patients with imported malaria admitted to the Communicable Disease Centre (CDC), Singapore (a 130-bed tertiary referral center) from January 1992 to December 1993. An imported case was defined as a smear-positive infection that was acquired in another country. RESULTS: Among 200 malaria patients hospitalized at CDC, 168 imported cases (137 males and 31 females, 131 nonresidents and 37 residents) were studied. The mean age was 31.6 6 10.5 years. The countries visited were India (49.4%), Indonesia (16.7%), and Bangladesh (13%). Five patients had chemoprophylaxis and 36 patients had experienced previous malaria infection. The predominant symptoms were fever (97.6%), chills (79.2%), and rigors (67.9%). Hepatomegaly was detected in 56 (33.3%) and splenomegaly in 49 patients (29.2%). Plasmodium vivax was present in 132 patients, Plasmodium falciparum in 29, and mixed P. vivax and P. falciparum in 7 patients. Parasitemia ranged from 0.1% to 8.0%. Of the vivax cases, 130 were treated with chloroquine, followed by primaquine in 123 patients. Quinine was given to 36 patients (29 falciparum malaria and 7 mixed infections). Median time to fever defervescence was 2 days. Complications occurred in three patients (2 with shock and 1 with pulmonary edema). According to World Health Organization gravity criteria, body temperature over 40 degrees C was detected in six patients, bilirubinemia higher than 50 mmol/L in nine, parasitemia over 5% in five, glycemia less than 2.2 mmol/L in two patients. There were five relapses. No death was recorded. CONCLUSION: Plasmodium vivax is the most common cause of imported malaria, with the majority acquired from the Indian subcontinent. Only a few patients presented with severe malaria.

Adolescent↗
PubMed1999

Enhancement of nitric oxide synthesis by the aqueous extract of Spiraea prunifolia var. simpliciflora's root in RAW 264.7 cells.

The effects of aqueous extract of Spiraea prunifolia var. simpliciflora's root, a traditional medicine for the treatment of malaria in Chinese medicine, on the generation of nitric oxide (NO) are investigated in RAW 264.7 cells. NO generation from IFN-gamma primed RAW 264.7 cells is markedly increased by the addition of aqueous extract in a dose-dependent manner. The enhancement of NO generation by the aqueous extract is accompanied by a significantly increased expression of inducible nitric oxide synthase (iNOS). However, the aqueous extract of Spiraea prunifolia var. simpliciflora's root does not affect the viability of RAW 264.7 cells, as assessed by MTT assay. Polymyxin B does not inhibit NO generation by the aqueous extract in IFN-gamma primed RAW 264.7 cells. However, polymyxin B significantly decreases NO generation by lipopolysaccharide (LPS) in IFN-gamma primed RAW 264.7 cells. These data indicate that the signaling pathway of the aqueous extract-induced NO generation is not dependent on PKC. These results strongly support the mechanism by which the aqueous extract may exert anti-malarial effect via direct cytotoxicity of NO as well as NO-mediated modulation of immune functions.

Animals↗
PubMed1999

The neurological manifestations of Nipah virus encephalitis, a novel paramyxovirus.

A novel Hendra-like paramyxovirus named Nipah virus (NiV) was the cause of an outbreak among workers from one abattoir who had contact with pigs. Two patients had only respiratory symptoms, while 9 patients had encephalitis, 7 of whom are described in this report. Neurological involvement was diverse and multifocal, including aseptic meningitis, diffuse encephalitis, and focal brainstem involvement. Cerebellar signs were relatively common. Magnetic resonance imaging scans of the brain showed scattered lesions. IgM antibodies against Hendra virus (HeV) were present in the serum of all patients. Two patients recovered completely. Five had residual deficits 8 weeks later.

Adult↗
PubMed1998

Isolation of a novel pentachlorophenol-degrading bacterium, Pseudomonas sp. Bu34.

A pentachlorophenol (PCP)-degrading bacterium was isolated from possible PCP-contaminated soil from Pusan, Korea and identified as a member of the genus Pseudomonas. It used PCP as its sole source of carbon and energy. This micro-organism was capable of degrading PCP more effectively, certified by the increase in cell density and the decrease in PCP substrate. Pseudomonas sp. Bu34 was able to degrade a much higher concentration of PCP (4000 mg l-1) than any previously reported PCP-degrading bacteria and fungi and to grow in mineral salts solution containing one of a variety of chlorophenols. In non-acclimated strain Bu34, the cell number decreased from 87 to 99.9% in 75-4000 mg l-1 PCP at 24 h. In the acclimated strain the PCP toxic effect did not appear with 75 mg l-1 PCP treatment, but 1000-4000 mg l-1 PCP decreased the cell number of strain Bu34 by 25% to 24 h and then the cell number slightly increased at 48 h. Therefore, it suggested that the maximum resistance of acclimated strain Bu34 to PCP was 4000 mg l-1 PCP. We suggest that strain Bu34 could be used as a micro-organism for the bioremediation of highly PCP-contaminated soils, water or wood products.

Bacterial Typing Techniques↗
PubMed1998

Emerging therapies for sepsis and septic shock.

Despite advances in antimicrobial therapy and medical support, septic shock remains a leading cause of death. Emerging adjunctive therapy for septic shock can be divided into those directed against bacterial components, those directed against host-derived inflammatory-mediators and those designed to limit tissue damage. All trials of new adjunctive therapies for sepsis and septic shock conducted to data have failed to show efficacy. Therapies against endotoxin, tumour necrosis factor, interleukin-1 and platelet activating factor did not reduce mortality. Future effective therapies will probably use combination of agents depending upon the nature of the infection and the type of patient.

Anti-Inflammatory Agents↗
PubMed1997

Typhoid fever in hospitalized children in Singapore.

A study was conducted to determine the clinical features and severity of typhoid fever in children admitted to the Communicable Disease Centre, Singapore. Over a 5 year period (1990-94), 40 children had documented culture-proven typhoid fever. Nine of the 40 children (22.5%) were below the age of 5 years. The predominant presenting symptoms were fever and diarrhoea. Pneumonia and ileus were the only complications observed. No patient in the series died. Ten Salmonella typhi isolates were multi-drug resistant. The majority of the children were treated with chloramphenicol and ceftriaxone. Typhoid fever appears to be a mild disease in Singapore children.

Child↗