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Biomedical subjects

Y H Koh

Publications and source records attributed to Y H Koh.

30 records · Page 2Linked to original sources
PubMed1999

Calcification in chronic maxillary sinusitis: comparison of CT findings with histopathologic results.

BACKGROUND AND PURPOSE: It is important to differentiate fungal from nonfungal sinusitis in order to determine the optimal treatment for chronic sinusitis. The purpose of this study was to describe the CT findings of calcifications in chronic fungal and nonfungal maxillary sinusitis. METHODS: Five hundred ten patients with pathologically proved chronic maxillary sinusitis were studied with unenhanced CT before undergoing sinonasal surgery. In 36 patients, the CT scans were reviewed retrospectively to ascertain the shape and location of intrasinus calcifications. RESULTS: Calcifications were found in 20 (51%) of 39 patients with fungal sinusitis and in 16 (3%) of 471 patients with nonfungal sinusitis. Direct histopathologic correlation was performed in two of 16 patients with nonfungal sinusitis who had intrasinus calcification. The location of intrasinus calcification was central in 95% of the patients with fungal sinusitis and peripheral in 81% of those with nonfungal sinusitis. Although calcifications with a nodular or linear shape were seen in both fungal and nonfungal sinusitis, fine punctate type calcifications were seen only in those with fungal sinusitis (50%) and round or eggshell type calcifications only in those with nonfungal sinusitis (19%). CONCLUSION: Intrasinus calcifications are different in location and shape between fungal and nonfungal maxillary sinusitis. Although intrasinus calcification is uncommon in nonfungal sinusitis, the CT finding of intrasinus calcification may be helpful for differentiating fungal from nonfungal maxillary sinusitis.

Adolescent↗
PubMed1998

Synaptic vesicle size and number are regulated by a clathrin adaptor protein required for endocytosis.

Clathrin-mediated endocytosis is thought to involve the activity of the clathrin adaptor protein AP180. However, the role of this protein in endocytosis in vivo remains unknown. Here, we show that a mutation that eliminates an AP180 homolog (LAP) in Drosophila severely impairs the efficiency of synaptic vesicle endocytosis and alters the normal localization of clathrin in nerve terminals. Most importantly, the size of both synaptic vesicles and quanta is significantly increased in lap mutants. These results provide novel insights into the molecular mechanism of endocytosis and reveal a role for AP180 in regulating vesicle size through a clathrin-dependent reassembly process.

Adaptor Proteins, Vesicular Transport↗
PubMed1998

Effects of niacin deficiency on the levels of soluble proteins and enzyme activities in various tissues of Japanese quail.

The effects of niacin deficiency on the levels of soluble proteins and enzyme activities of Japanese quail have been investigated. SDS-polyacrylamide gel electrophoresis revealed that in the pectoral muscle the soluble proteins with molecular masses corresponding to 181, 128, 93, 76, 72, 62, 56, 43, 41, 28 and 20 kDa were present in lower amounts but those of 60, 50 and 37 kDa were present in higher amounts. In the heart the soluble proteins with a molecular mass of 181 kDa were present in lower amounts and in the brain those of 43 kDa were present in lower amounts but those of 221 kDa were present in higher amounts. In the intestine the soluble proteins with molecular masses corresponding to 181, 102, 83, 74, 72, 44 and 40 kDa were present in lower amounts but those of 41 kDa and 18 kDa were present in higher amounts. There was a marked reduction in the level of NAD and NADPH in the pectoral muscle of niacin deficient quail but not in other tissues. The specific activity of glyceraldehyde-3-phosphate dehydrogenase decreased markedly both in the liver and pectoral muscle of niacin deficient quail whereas that of 6-phosphogluconate dehydrogenase and malic enzyme decreased markedly in the liver or pectoral muscle, respectively. In contrast, the specific activity of acetylcholinesterase and carboxypeptidase increased markedly in the liver or the pectoral muscle, respectively. The results suggest that a severe niacin deficiency exerted specific effects on levels of some soluble proteins particularly in the pectoral muscle and intestine and on activities of certain enzymes in the liver and the pectoral muscle.

Animals↗
PubMed1998

Overexpression of aldehyde reductase protects PC12 cells from the cytotoxicity of methylglyoxal or 3-deoxyglucosone.

The glycation reaction (Maillard reaction) plays a major role in diabetic complications, since some reaction intermediates are responsible for the modification and cross-linking of long-lived proteins, resulting, in turn, in a deterioration of normal cell function. The reaction intermediates include methylglyoxal (MG) and 3-deoxyglucosone (3-DG), both of which are cytotoxic dicarbonyl compounds and are elevated during hyperglycemia. Aldehyde reductase (ALR) catalyzes the reduction of both compounds. To examine the intracellular role of ALR in the diabetic complications of neural cells, its gene was overexpressed in rat pheochromocytoma PC12 cells, which normally express a low level of ALR. Western blot analysis showed that ALR protein in the ALR gene-transfected cells was more than twice as much as in the control cells. In the parental cells, cytotoxicity, including apoptotic cell death, which was determined by fluorescent microscopy using the fluorescent DNA binding dye Hoechst 33258, was observed at 100 microM MG. In the ALR gene-transfected cells, the cytotoxicity of both MG and 3-DG and apoptotic cell death were decreased. This suggests that intracellular ALR protects neural cells from the cytotoxicity of 3-DG or MG, and that neural cells, which normally express a low level of ALR, might be susceptible to diabetic complications caused by intermediate products of the Maillard reaction, such as 3-DG and MG.

Aldehyde Reductase↗
PubMed1997

Synaptic clustering of the cell adhesion molecule fasciclin II by discs-large and its role in the regulation of presynaptic structure.

The cell adhesion molecule Fasciclin II (FASII) is involved in synapse development and plasticity. Here we provide genetic and biochemical evidence that proper localization of FASII at type I glutamatergic synapses of the Drosophila neuromuscular junction is mediated by binding between the intracellular tSXV bearing C-terminal tail of FASII and the PDZ1-2 domains of Discs-Large (DLG). Moreover, mutations in fasII and/or dlg have similar effects on presynaptic ultrastructure, suggesting their functional involvement in a common developmental pathway. DLG can directly mediate a biochemical complex and a macroscopic cluster of FASII and Shaker K+ channels in heterologous cells. These results indicate a central role for DLG in the structural organization and downstream signaling mechanisms of cell adhesion molecules and ion channels at synapses.

Animals↗
PubMed1997

Primary T-cell lymphoma of the colon.

A 40-year-old woman had been diagnosed with Crohns disease in September 1994, but later examinations revealed a primary T-cell lymphoma of the colon. Colonoscopic and histological examination showed ulcerative lesions simulating Crohns disease involving the entire colon and the terminal ileum, and she was first diagnosed as having Crohns disease. Differential therapeutic strategies, including corticosteroid, had improved the symptoms which were dominated by abdominal pain. When she visited our institute in April 1995, she presented with bloody stool twice a day, 7 kg weight loss in a period of six months and a slightly painful abdomen. Colonoscopic finding showed geographic ulceration on the entire colon, especially rectum and terminal ileum. The histologic examination of specimens from colonoscopic biopsy showed primary peripheral T-cell lymphoma of the colon. Any dense lymphocyte infiltrates seen in the biopsy specimens obtained from lesions simulating ulcerative colitis or Crohns disease should be assessed to exclude intestinal lymphoma.

Adult↗
PubMed1996

Regulation of synapse structure and function by the Drosophila tumor suppressor gene dlg.

Mutations of the tumor suppressor gene discs-large (dlg) lead to postsynaptic structural defects. Here, we report that mutations in dlg also result in larger synaptic currents at fly neuromuscular junctions. By selectively targeting DLG protein to either muscles or motorneurons using Gal-4 enhancer trap lines, we were able to rescue substantially the reduced postsynaptic structure in mutants. Rescue of the physiological defect was accomplished by presynaptic, but not postsynaptic targeting, consistent with our finding that miniature excitatory junctional currents were not changed in dlg mutants. These results suggest that DLG functions in the regulation of neurotransmitter release and postsynaptic structure. We propose that DLG is an integral part of a mechanism by which changes in both neurotransmitter release and synapse structure are accomplished during development and plasticity.

Animals↗
PubMed1994

Changes in Cellular Fatty Acid Composition of Cephalosporium acremonium during Cephalosporin C Production.

Cephalosporium acremonium was cultivated in fermentation medium containing sucrose or methyl oleate as a carbon source for cephalosporin C production. The level of antibiotic production was 48 g of cephalosporin C per liter under optimum conditions when methyl oleate was used. The C(18:1) (oleic acid) methyl ester appeared to be utilized faster than the C(18:2) (linoleic acid) methyl ester in fermentation broth. Physiological characteristics of C. acremonium were investigated by determining the fatty acid composition of the total cellular free lipid. Significant changes in cellular fatty acid composition occurred during inoculum cultivation and fermentation. The percentage of C(18:1) increased from 19.1 to 38.5%, but the percentage of C(18:2) decreased from 56.7 to 36.1%, and there was an increase in pH during inoculum cultivation. The cellular fatty acid composition of C. acremonium grown in fermentation medium containing methyl oleate (methyl oleate medium) was significantly different from that in fermentation medium containing sucrose (sucrose medium). The major fatty acids detected were C(16:0) (palmitic acid), C(18:1), and C(18:2). In methyl oleate medium, the ratio of C(18:1) to C(18:2) increased from 0.34 to 1.37, while the cell morphology changed from hyphae to arthrospores and conidia. In contrast, in sucrose medium, the ratio of C(18:1) to C(18:2) decreased from 0.70 to 0.43, and most of the cells remained hyphal at the end of fermentation. We observed that hyphae contained a higher proportion of C(18:2) but arthrospores and conidia contained a higher proportion of C(18:1).

Journal Article↗
PubMed1994

Smoking restrictions in private workplaces in Singapore.

This survey aims to determine the number and profile of private workplaces in Singapore which have a smoking restriction policy. The response rate was 43%. Of the companies which responded, 59% had some form of smoking restriction. Private companies are more likely to have a smoking restriction policy: (a) where smoking poses inherent fire risks, such as those dealing with inflammable chemicals or gases; (b) where smoking poses inherent detrimental effects to the quality of the products, such as those dealing with precision electronic microcomponents, where a smoke-free and dust-free environment is essential; (c) are larger companies; and (d) have strong management support in initiating and enforcing smoking restriction. Future programmes should give more emphasis to the service industries such as construction, insurance, banking and finance, and smaller companies (with fewer than 100 employees). They should involve the management who play an important role in implementing smoking restriction at their workplace.

Air Conditioning↗