PubMed Health⌕ Search

Biomedical subjects

H T Tan

Publications and source records attributed to H T Tan.

At least 19 recordsLinked to original sources
PubMed2001

Cancer chemopreventive activity of naphthoquinones and their analogs from Avicennia plants.

As a part of screening studies for cancer chemopreventive agents (anti-tumor promoters), six natural and four synthetic naphthoquinones and five of their analogs were tested for their inhibitory activities against Epstein-Barr virus early antigen activation induced by 12-O-tetradecanoylphorbol-13-acetate in Raji cells. Some of the 1,4-naphthoquinones and their analogs were found to show remarkably potent activities, without showing any cytotoxicity. 1,4-Furanonaphthoquinone (5) and its analog (9) isolated from Avicennia plants (Avicenniaceae), having an alcoholic OH group on the dihydrofuran-ring, displayed the most potent activity. Furthermore, avicenol-A (9) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. The result of the present investigation indicated that some of these 1,4-naphthoquinones and their analogs might be valuable as potent cancer chemopreventive agents.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

Cancer chemopreventive agents, 4-phenylcoumarins from Calophyllum inophyllum.

In a search for anti-tumor-promoting agents, we carried out a primary screening of ten 4-phenylcoumarins isolated from Calophyllum inophyllum L. (Guttiferae), by examining their possible inhibitory effects on Epstein--Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate in Raji cells. All of the compounds tested in this study showed inhibitory activity against EBV, without showing any cytotoxicity. Calocoumarin-A (5) showed more potent activity than any of the other compounds tested. Furthermore, calocoumarin-A (5) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. The results of the present investigation indicate that some of these 4-phenylcoumarins might be valuable as potential cancer chemopreventive agents (anti-tumor-promoters).

Animals↗
PubMed2000

Anti-tumor-promoting effects of isoflavonoids on Epstein-Barr virus activation and two-stage mouse skin carcinogenesis.

As a part of screening studies for anti-tumor promoters, fifteen isoflavonoids isolated from plants of the genus Millettia (Leguminosae) were evaluated by examining their possible inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate in Raji cells. All of the compounds tested in this study showed inhibitory activity against EBV, without showing any cytotoxicity. Auriculasin (11) and millepurone (13), which is an oxidized isoflavone analogue, both having one or more prenyl side-chains and a 3',4'-dihydroxyphenyl group in the molecule, showed more potent activity than any of the other compounds tested. Furthermore, millepurone (13) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. The results of the present investigation indicate that some of these isoflavonoids might be valuable anti-tumor promoters.

Animals↗
PubMed2000

Evaluation of the allergenicity of tropical pollen and airborne spores in Singapore.

BACKGROUND: Sensitization to pollen and spores of the Southeast Asian tropical region is not well documented. This study evaluated the allergenicity of the tropical airspora in Singapore. METHODS: On the basis of the results of an aerobiologic survey of the airspora profile of Singapore, crude extracts of 23 main spore (fungal and fern) and pollen types were prepared. A total of 231 patients with asthma and/or allergic rhinitis and 76 healthy controls were evaluated by skin prick test (SPT). Total and specific IgE levels were also quantified by the fluorescence allergosorbent test (FAST). RESULTS: All 23 allergenic extracts tested elicited positive SPT responses. Among the patients with atopic diseases, extracts of oil-palm pollen (Elaeis guineensis) were observed to have the highest frequency of positive reactions (40%), followed by extracts of resam-fern spores (Dicranopteris linearis) (34%) and sea-teak pollen (Podocarpus polystachyus) (33.8%). Fungal spores with the highest SPT responses were Curvularia spp. (26-32%) and Drechslera-like spores (31%). Positive responses to these extracts correlated with total serum IgE levels of the subjects and were significantly associated with the presence of atopic disease. CONCLUSIONS: We have documented sensitization to tropical pollen and spores in our population. Its association with atopy suggests that it has a role in allergic diseases in the tropics.

Adolescent↗
PubMed2000

Chemical constituents of Avicennia alba. Isolation and structural elucidation of new naphthoquinones and their analogues.

Three new naphthoquinones and their analogues, named avicequinone-A (1), -B (2), -C (3), and avicenol-A (4), -B (5), -C (6), respectively, were isolated from the stem bark of Avicennia alba (Avicenniaceae) collected in Singapore, and their structures were elucidated by means of spectral methods. Gillan and co-workers have proposed that the structures of the new phytoalexins isolated from Avicennia marina are 1,2-naphthoquinones 8 and 9. Our synthetic and spectrometric studies showed that these structures should be revised respectively to 1,4-naphthoquinones 2 and 3, named avicequinone-B and -C by us.

Magnetic Resonance Spectroscopy↗
PubMed2000

Severe eosinophilia in disseminated gastric carcinoma.

Peripheral blood eosinophilia is a well-recognised but unusual manifestation of malignancy, and may represent a paraneoplastic phenomenon. We present a case of poorly differentiated adenocarcinoma of the stomach associated with severe peripheral blood eosinophilia A 55-year old man was admitted for abdominal pain of one week duration. An incidental finding of leucocytosis with eosinophilia was noted. After excluding haematological and infectious causes, an oesophagogastroduodenoscopy (OGD) followed by biopsy confirmed the diagnosis. Eosinophilia appears to be a response to cytokine production,and treatment is aimed at the underlying malignancy, and reducing the eosinophil count when necessary, to prevent end-organ damage. Studies have shown that peripheral eosinophilia is associated with disseminated, metastatic disease and hence signifies a poor prognosis,whereas tissue eosinophilia in advanced cancer has a better survival rate.

Abdominal Pain↗
PubMed1999

Ursodeoxycholic acid has no influence on function after restorative proctocolectomy in ulcerative colitis.

BACKGROUND: Poor pouch function is associated with impaired bile acid absorption and increased faecal loss of bile acids. Bile acid replacement therapy might therefore be of clinical benefit, provided that diarrhoea is not aggravated by therapy. AIM: To investigate the role of exogenous bile acid therapy in patients with poor pouch function after restorative proctocolectomy for ulcerative colitis. PATIENTS AND METHODS: Twenty ulcerative colitis patients with poor pouch function (score > 4 on a 12-point score) were recruited for inclusion to a prospective, randomized, double-blind crossover, placebo-controlled trial of ursodeoxycholic acid (10 mg/kg per day in two divided doses for 1 month). RESULTS: A total of 16 patients completed the study. There was no significant difference in the functional score or bowel frequency following treatment irrespective of whether the active treatment was given before or after placebo. CONCLUSIONS: We conclude that ursodeoxycholic acid given over 4 weeks had no influence on functional score or bowel frequency after restorative proctocolectomy for U.C.

Adult↗
PubMed1998

Quality of life after pouch excision.

BACKGROUND: Pouch excision is a devastating experience for patients having restorative proctocolectomy for ulcerative colitis. METHODS: The quality of life among patients having pouch excision for ulcerative colitis was compared with that in those having proctocolectomy and ileostomy for ulcerative colitis using a validated standardized self-administered questionnaire. RESULTS: After pouch excision patients (n = 9) had more troublesome bowel symptoms (mainly from liquid stoma output) than those in the proctocolectomy group (n = 14) (mean(s.d.) score 5.64(0.92) versus 6.13(0.37), P = 0.03). However, the mean scores for the other parameters (systemic symptoms, functional, social and emotional impairment) did not differ significantly. CONCLUSION: Patients having pouch excision for ulcerative colitis have more liquid ileostomy loss but a comparable quality of life to those treated by standard proctocolectomy and ileostomy.

Activities of Daily Living↗
PubMed1997

Results of restorative proctocolectomy in the elderly.

Twenty eight of 227 patients undergoing restorative proctocolectomy for inflammatory bowel disease, familial adenomatous polyposis or functional disease were over the age of 50 years: ages 50 to 60 (n = 13), 60 to 70 (n = 10), and over 70 (n = 5). Major complications occurred in 5 patients over the age of 50 (18%) compared with 43 patients under the age of 50 (23%). Three patients above the age of 50 had their pouch excised (11%) compared with 23 under the age of 50 (12%). Functional outcome was assessed with a 12 point symptom score. This was similar in all age bands: under 50 years (mean = 2.2; sd +/- 2.2; n = 109), 50 to 60 years (mean = 2.5; sd +/- 2.5; n = 12), 60 to 70 years (mean = 2.8; sd +/- 2.3; n = 7) and over 70 years (mean = 4.0; sd +/- 3.7; n = 5): P > 0.05). When analysed for ulcerative colitis alone, no significant differences were seen between the two age groups. Restorative proctocolectomy in the elderly gives results which are comparable to the younger population.

Adenomatous Polyposis Coli↗
PubMed1997

Allergic contact dermatitis from grasses.

This study attempts to demonstrate the existence of allergic contact dermatitis from grass, and to develop a patch test series to screen patients with grass intolerance. 6 common grass species from lawns and military training areas were collected. Solvent extracts of polar, non-polar and volatile fractions were prepared and used for patch testing in 20 control subjects and 46 patients with a history of grass intolerance. The 20 controls had negative responses to patch testing. 5 out of 46 patients had positive patch tests to Axonopus compressus (carpet grass), Ischaemum muticum (seashore centipede grass), Imperata cylindrica (lalang), Panicum maximum (Guinea grass) and Pennisetum purpureum (elephant grass). Reactions to the non-polar fraction for all 5 species were noted. This study demonstrates the existence of allergic contact dermatitis from various common species of grass. In our series, this is seen in 11% of those with a history of grass intolerance.

Adolescent↗
PubMed1995

A ferulic acid ester of sucrose and other constituents of Bhesa paniculata.

A novel derivative of sucrose, beta-(3,6-di-O-feruloyl)-fructofuranosyl-alpha-(2,3,4,6-tetra-O-ac etyl)- glucopyranoside, was isolated from the wood of Bhesa paniculata. Its structure was determined by a combination of 2D 1H-1H and 1H-13C correlation NMR spectroscopy. The known compounds, glycerol 1-9',12'-octadecadienoate, beta-sitosterol, (+/-)-pinoresinol, methyl 3,4-dihydroxybenzoate, 4-hydroxy-3-methoxybenzoic acid, anofinic acid and 2-(1'-methylethenyl)-benzofuran-5-carboxylic acid were also isolated.

Carbohydrate Conformation↗
PubMed1995

Allergens of Bipolaris species.

Skin prick tests done previously revealed a significantly higher percentage of sensitization to an extract of Bipolaris sp. among atopic individuals (34/147, 23.1%) compared to non-atopic individuals. Bipolaris-specific IgE levels were quantified in sera from a representative group of 38 individuals using the Fluorescence Allergosorbent Test (FAST). Result obtained by FAST were found to be comparable to the skin prick test results (r2 = 0.60, p < 0.001 for IgE levels vs wheal sizes; r2 = 0.44, p < 0.001 for IgE levels vs erythema sizes). Characterisation of the extract's allergenic component by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) showed 28 protein bands with molecular weights (MW) ranging from 11 kDa to above 100 kDa. Immunoblotting with sera of 10 Bipolaris-sensitive (skin prick test, 3 +) individuals showed that Bipolaris spore extract contained at least 4 IgE binding proteins (MW 11-13 kDa, 16-17 kDa, 20-22 kDa and 36 kDa). All 10 sera reacted to the protein at MW 20-22 kDa, 2 sera with MW 11-13 kDa, 3 sera with 16-17 kDa and 6 sera with 36 kDa. This study has thus demonstrated that spores of Bipolaris sp. contain allergenic components which may elicit IgE-mediated reactions.

Allergens↗
PubMed1994

House dust mite allergen levels in a Singapore hospital.

House dust mite allergens constitute one of the most important allergens in house dust. In this study, the levels of two common dust mite allergens, Der p I and Der f I, in a general hospital in Singapore were evaluated. Our results showed that these allergens were detected in 42/74 (or 57%) of the dust samples. Der p I was found to be the predominant allergen detected (p < 0.001). The allergen levels were, however, low with only 1/74 having a Der p I concentration above 2 micrograms g-1 dust. None of the samples had Der f I concentrations above this level. Of the various niches studied (mattresses, pillows, sofas, carpets, blinds and floors), the blinds and floors had the lowest concentration of allergen (p < 0.05). These low levels in the hospital compared to homes were attributed to the vigorous cleaning schedule in the hospital, the use of plastic to encased mattresses and pillows, vinyl covered sofas and vinyl lined floors. These practices may be adopted in the home as a means to reduce mite allergen exposure.

Air Conditioning↗
PubMed1991

Small-scale field trials of Bacillus sphaericus (strain 2362) formulations against Mansonia mosquitoes in Malaysia.

Five formulations of Bacillus sphaericus (strain 2362) including aqueous suspension BSP 1, BSP 2, technical powder ABG 6184, corncob granules ABG 6185 (potencies 2 x 10(10), 2 x 10(7), 9.5 x 10(10), 5 x 10(10), 5 x 10(10) spore/g, respectively) and wettable powder ABG 6232 (1,000 BS ITU/mg) were tested against laboratory-cultured late third/early fourth instar larvae of Mansonia uniformis in floating screened cages in small plots at swampy ditches on Penang Island, Malaysia. Mean dosage/response values at 90% mortality levels were 6.93, 95.32, 1.45, 11.92 and 2.86 liters or kg per ha, respectively, for the formulations tested. There were practically no residual effects for the formulations tested with larvae introduced at 48, 96, and 168 h post-treatment. In trials of BSP 1, ABG 6184 and ABG 6185 (1 liter or 1 kg per ha) against immature Mansonia spp. in impounded paddy field ditches, improved efficacy and residual effects were obtained with mean reductions of 93.1, 91.9 and 80.4% at days 3, 7 and 14 posttreatment, respectively.

Animals↗
PubMed1990

Field efficacy of mosquito coil formulations containing d-allethrin and d-transallethrin against indoor mosquitos especially Culex quinquefasciatus Say.

Comparative field efficacy studies of four mosquito coil formulations containing active ingredient of d-allethrin (0.19 or 0.28 w/w) and d-transallethrin (0.12 or 0.16% w/w) and blank coils without active ingredient were carried out in living rooms (mean size 54.1 m3) of residential houses in a squatter area in Butterworth, Malaysia. The major indoor biting mosquitos collected in the test site were that of Culex quinquefasciatus Say (84.7%). Mean percentage reduction of blank coils, coils with 0.19 and 0.28% d-allethrin and coils with 0.12 and 0.16% d-transallethrin were 29.0, 71.7, 70.9, 75.0 and 72.6%, respectively. The use of coils as a mean of personal protection against mosquitos is discussed.

Allethrins↗
PubMed1987

Dissociation of hepatitis B surface antigen (HBsAg) from immobilised anti-HBsAg antibody in a two site immunoradiometric assay: its relevance to hook effect and recycled assay.

The mechanism of the hook effect in a two site immunometric assay of hepatitis B surface antigen (HBsAg) was studied using a novel method. The results showed that HBsAg dissociated from immobilized anti-HBsAg at low as well as high doses of antigen (Ag). This probably was not due to lack of immobilized antibody (Ab) or dissociation of HBsAg non-specifically bound to the immobilized Ab. The dissociated Ag sequestered the labelled Ab in the second reaction and contributed to the decrease in percent binding (B%) of the assay and thus the hook effect. The dissociated Ag could contaminate the recovered pooled labelled Ab in recycled assay and give rise to high non-specific binding. Prolonged washing decreased the side reaction but also the B% of the assay.

Antigen-Antibody Reactions↗