Choon Nam Ong
Email Address
eriocn@nus.edu.sg
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Publication Use of capillary electrophoresis for thalassaemia screening(1994) Law, H.-Y.; Ng, I.; Ong, J.; Ong, C.-N.; INSTITUTE OF MOLECULAR & CELL BIOLOGY; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEThis paper describes the use of high-performance capillary electrophoresis (HPCE) for screening of thalassaemias. Preparation of globin was performed by adding 1 mL of haemolysate to 20 volumes of cold acidified acetone. Separation of globins was accomplished in a 25 mM disodium phosphate buffer at pH 11.8 using an uncoated capillary column of 50 cm x 75 μm (i.d.). Distinct peaks of alpha, beta and gamma were resolved within 6 min. The coefficient of variations for within-day and between-day runs were 4.7% and 6.37%, respectively. Using this simple and rapid procedure up to 30 specimens could be analysed in a single day. This method appears to be reliable and can be used for mass screening of various haemoglobinopathies.Publication Translocation and effects of gold nanoparticles after inhalation exposure in rats(2007) Yu, L.E.; Balasubramaniam, K.S.; Yung, L.-Y.L.; Hartono, D.; Ong, C.-N.; Shui, G.; Wenk, M.R.; Tan, Y.-L.; Ong, W.-Y.; PHYSIOLOGY; DIVISION OF ENVIRONMENTAL SCIENCE & ENGG; ANATOMY; BIOCHEMISTRY; CHEMICAL & BIOMOLECULAR ENGINEERING; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEPublication Anticancer effects of aloe-emodin on HepG2 cells: Cellular and proteomic studies(2007) Lu, G.D.; Chung, M.C.M.; Shen, H.-M.; Ong, C.N.; BIOCHEMISTRY; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEPublication Luteolin sensitizes tumor necrosis factor-α-induced apoptosis in human tumor cells(2004-10-07) Shi, R.-X.; Ong, C.-N.; Shen, H.-M.; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINETumor necrosis factor-α (TNFα) activates both cell death and cell survival pathways, which render most cancer cells resistant to its cytotoxicity. In this study, we found that pretreatment with luteolin, a plant flavonoid, greatly sensitized TNFα-induced apoptotic cell death in a number of human cancer cell lines; including colorectal cancer COLO205, HCT116 cells and cervical cancer HeLa cells. In the search of the molecular mechanisms responsible for the sensitization effect of luteolin, we discovered that luteolin inhibited TNFα-induced activation of nuclear transcription factor-kappa B (NF-κB), the main survival factor in TNFα signaling. As a result, luteolin suppressed the expression of NF-κB-targeted antiapoptotic genes, including A20 and cellular inhibitor of apoptosis protein-1 (c-IAP1). The role of A20 and c-IAP1 was further confirmed by ectopic expression of these two genes, which significantly protected cell death induced by luteolin followed by TNFα. In addition, inhibition of NF-κB by luteolin led to augmentation and prolongation of c-Jun N-terminal kinase (JNK) activation induced by TNFα. Suppression of JNK activation, either by a synthetic JNK inhibitor (SP600125) or by overexpression of the dominant negative forms of JNK kinase 1 (JNKK1) and JNK kinase 2 (JNKK2), conferred significant protection against apoptotic cell death induced by luteolin and TNFα, suggesting that NF-κB and JNK are closely associated with the sensitization effect of luteolin. Data from this study reveal a novel function of luteolin and enhance the value of luteolin as an anticancer agent.Publication Zinc supplementation decreases the development of atherosclerosis in rabbits(2006) Ren, M.; Rajendran, R.; Watt, F.; Ning, P.; Jenner, A.; Halliwell, B.; Tan, Kwong Huat B.; Choon, Nam O.; PHARMACOLOGY; PHYSICS; BIOCHEMISTRY; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEDeveloping atherosclerotic plaques in cholesterol-fed rabbits are enriched in iron but depleted in zinc. In order to examine further the role of zinc, New Zealand White rabbits were fed a high-cholesterol 1% (w/w) diet with zinc (1 g/kg) supplementation for 8 weeks. After the 8-week period, the average atherosclerotic lesion cross-sectional areas in the aortas of the animals fed with the zinc supplement were significantly decreased (1.0 mm2) compared with lesion areas of the animals fed only on the high-cholesterol diet (3.1 mm2). Using nuclear microscopy, a technique for mapping and measuring trace elements in tissue sections, lesion zinc levels (24 ppm) were observed to be unchanged in the zinc-fed rabbits compared to controls. However, average lesion Fe levels in the zinc-fed group were measured at 32 ppm, whereas in the control group the average Fe levels were significantly higher at 43 ppm (P = 0.03). Our data support the concept that zinc may have an antiatherogenic effect by decreasing iron levels in the lesion, possibly leading to inhibition of iron-catalyzed free radical reactions. © 2006 Elsevier Inc. All rights reserved.Publication Autophagy and oxidative stress associated with gold nanoparticles(2010) Li, J.J.; Bay, B.-H.; Hartono, D.; Yung, L.Y.L.; Ong, C.-N.; ANATOMY; EPIDEMIOLOGY & PUBLIC HEALTH; CHEMICAL & BIOMOLECULAR ENGINEERINGElemental metal nanoparticles like cadmium and silver are known to cause oxidative stress and are also highly toxic. Yet for gold nanoparticles (AuNPs), it is not well established whether these particles are biologically toxic. Here we show that AuNPs, which were taken up by MRC-5 human lung fibroblasts in vitro, induce autophagy concomitant with oxidative stress. We also observed formation of autophagosomes together with the uptake of AuNPs in the lung fibroblasts as well as upregulation of autophagy proteins, microtubule-associated protein 1 light chain 3 (MAP-LC3) and autophagy gene 7 (ATG 7) in treated samples. AuNP treated cells also generated significantly more lipid hydroperoxides (p-value < 0.05), a positive indication of lipid peroxidation. Verification with western blot analysis for malondialdehyde (MDA) protein adducts confirmed the presence of oxidative damage. In addition, AuNP treatment also induced upregulation of antioxidants, stress response genes and protein expression. Exposure to AuNPs is a potential source of oxidative stress in human lung fibroblasts and autophagy may be a cellular defence mechanism against oxidative stress toxicity. © 2010 Elsevier Ltd.Publication ω-3 fatty acids and selenium as coronary heart disease risk modifying factors in Asian Indian and Chinese males(2004) Manav, M.; Su, J.; Hughes, K.; Lee, H.P.; Ong, C.N.; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEAsian Indian men are reported to have a higher incidence of coronary heart disease than men of other ethnic groups worldwide. Among the many hypotheses, one possible risk factor may be related to their dietary habits. This study estimated the plasma concentrations of fatty acids, antioxidant vitamins, and selenium in Indians and Chinese of Singapore. The study population consisted of 145 Indian men and 147 Chinese men ages 26 to 79 y from a cross-sectional survey, the National University of Singapore Heart Study. Our findings indicated that Indians had lower plasma concentrations of docosahexanoic acid (3.07% versus 3.54%, P < 0.001), α-linolenic acid (0.48% versus 0.57%, P < 0.001), and total ω-3 fatty acids (4.71% versus 5.27%, P < 0.001) than did the Chinese. Arachidonic acid was higher in Indians (4.83%) than in the Chinese (4.51%, P = 0.007). The ratio of ω-3 acid to ω-6 fatty acid was also lower in Indians (0.15) than in the Chinese (0.16, P = 0.007). There were no significant differences in the concentrations of monounsaturated fatty acids, but saturated fatty acids were higher in Indians (39.17%) than in the Chinese (38.28%, P < 0.001). Analysis of vitamins A, C, and E showed no significant differences between Indians (0.67, 5.72, and 13.04 mg/L, respectively) and Chinese (0.68, 6.48, and 12.71 mg/L, respectively); however, serum concentration of selenium in Indians (117.49 μg/L) was significantly lower than in the Chinese (126.72 μg/L, P < 0.001). The results suggest that lower plasma concentrations of ω-3 fatty acids and selenium and higher concentrations of arachidonic acid and saturated fatty acids in Indians may reflect lower intakes of marine foods and, as a consequence, higher susceptibility to coronary heart disease. © 2004 Elsevier Inc. All rights reserved.Publication Growth and glucosinolate profiles of a common Asian green leafy vegetable, Brassica rapa subsp. chinensis var. parachinensis (choy sum), under LED lighting(Elsevier B.V., 2020-02-10) TAN WEE KEE; GOENADIE VIANDRA; LEE HUI WEN; LIANG XU; Loh Chiang Shiong; ONG CHOON NAM; TAN TIANG WAH,HUGH; NUS ENVIRONMENTAL RESEARCH INSTITUTE; SAW SWEE HOCK SCHOOL OF PUBLIC HEALTH; BIOLOGICAL SCIENCESTechnological advancements in light-emitting diode (LED) technology have led to the production, under controlled indoor conditions, of value-added crops that are high in nutritional or nutraceutical contents. In this study, the growth and glucosinolate (GSL) profiles of a common Asian vegetable, Brassica rapa subsp. chinensis var. parachinensis (choy sum or cai xin) were determined under LED lighting. The growth of choy sum was influenced by both the LED light intensity and spectrum, with plants grown under 160 µmol m-2 s-1 red-blue light (160RB) producing the highest shoot biomass (~100–300% increment in adult plants). GSL content was found to vary across growth stages regardless of LED treatment. Total GSLs per gram fresh weight were four times higher in one-leafed seedlings than in adult plants. A shift from a high proportion of aliphatic GSLs in one-leafed seedlings to indolic and aromatic GSLs in three-leafed seedlings and adult plants was attributed to an increase in the proportion of glucobrassicin and/or 4-hydroxy-glucobrassicin, and gluconasturtiin which are known to have anti-cancer properties. Our results will be useful for the production of GSL-enhanced vegetables through urban farming.Publication Sodium selenite-induced oxidative stress and apoptosis in human hepatoma HepG2 cells(1999) Shen, H.-M.; Yang, C.-F.; Ong, C.-N.; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEThe mechanisms involved in the anti-carcinogenic activity of selenium remain to be elucidated. In the present study, we examined sodium selenite- induced oxidative stress and apoptosis in a human hepatoma cell line (HepG2). Sodium selenite (10 μM) exerted clear cytotoxic effect, as shown by the significant increase of lactate dehydrogenase leakage. Selenite- induced DNA alterations in apoptosis were studied by: 1. comet assay; 2. TdT- mediated dUTP nick end-labeling assay. In addition, characteristic apoptotic morphological alterations were also observed in selenite-treated cells. Our results clearly show that Se-induced cell death occurs predominantly in the form of apoptosis. Selenite-induced oxidative stress was evaluated by the measurement of reactive oxygen species production using lucigenin-dependent chemiluminescence. The involvement of glutathione in selenite-induced oxidative stress was further demonstrated by the concurrent decline of intracellular reduced glutathione and increase of oxidized glutathione contents in Se-treated cells. Moreover, the finding that selenite-induced oxidative stress and apoptosis was significantly attenuated by superoxide dismutase, catalase and deferoxamine provides additional evidence to suggest that Se-induced oxidative stress mediates the induction of apoptosis, a mechanism related to the anti-carcinogenic and chemopreventive effect of Se.Publication Combination of orthogonal array design and overlapping resolution mapping for optimizing the separation of heterocyclic amines by capillary zone electrophoresis(1995) Wu, J.; Wong, M.K.; Li, S.F.Y.; Lee, H.K.; Ong, C.N.; CHEMISTRY; COMMUNITY,OCCUPATIONAL & FAMILY MEDICINEThis paper describes the application of combined orthogonal array design and overlapping resolution mapping to the optimization of capillary zone electrophoresis for the separation of heterocyclic amines. The factors affecting resolution, such as buffer pH, organic modifier, concentration of buffer solution, capillary tubing temperature, and electric field strength, were studied in two steps. In the first step, orthogonal array design was used to determine the most important factors and interactions. The experiments were carried out according to an OA16 (215) matrix through sixteen pre-designed trials. Based on the results of the first step, the second set of experiments was performed according to a three-dimensional overlapping resolution mapping scheme, in which eleven pre-planned trials were executed and global optimum conditions for the separation within a reasonable analysis time were obtained. The proposed conditions were successfully applied in the separation of thirteen heterocyclic amines.