Biomedical subjects

C N Ong

Publications and source records attributed to C N Ong.

At least 37 records · Page 2Linked to original sources

PubMed2000

Comparative analysis of tea catechins and theaflavins by high-performance liquid chromatography and capillary electrophoresis.

This paper describes the simultaneous determination of catechins and theaflavins in green and black teas, using reversed-phase high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The tea polyphenols analyzed included (+)-catechin, catechin gallate, (-)-epicatechin, epicatechin-3-gallate, epigallocatechin, epigallocatechin-3-gallate, theaflavin, theaflavin-3-monogallate, theaflavin-3'-monogallate and theaflavin-3,3'-gallate. These polyphenols together with six other tea ingredients such as caffeine, adenine, theophylline, quercetin, gallic acid and caffeic acid were separated within 27 min by HPLC and in less than 10 min by CE. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE were found to be reliable and compatible. The reproducibility of the within-day assay using both methods was generally >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <2%. The analysis time of CE was three-times faster, however it is five-times less sensitive than HPLC, which has detection limits of 0.05 microg/ml and 0.5 microg/ml for catechins and theaflavins, respectively.

Biflavonoids↗

PubMed2000

Salvia miltiorrhiza inhibits cell growth and induces apoptosis in human hepatoma HepG(2) cells.

Salvia miltiorrhiza (SM) is a traditional Chinese herbal medicine, commonly used to treat liver diseases in China for centuries. Several earlier studies have indicated that SM exhibits anti-tumor properties, but its mechanism remains to be elucidated. In this study, we evaluated the molecular mechanism of SM in a human hepatoma cell line, HepG(2). Our results show that SM exerted clear cytotoxic effects, and strongly inhibited the proliferation of HepG(2) cells. It was also observed that SM treatment caused apoptotic cell death as evaluated by: (a), morphological changes by using acridine orange/ethidium bromide staining; (b), DNA fragmentation by TdT-mediated dUTP nick end labeling (TUNEL); and (c), sub-G(1) cell analysis. Furthermore, depletion of intracellular glutathione (GSH) and reduction of mitochondrial membrane potential were found to be involved in the initiation of apoptosis by SM.

Antineoplastic Agents, Phytogenic↗

PubMed2000

Caloric restriction prevents oxidative damage induced by the carcinogen clofibrate in mouse liver.

Long-term caloric restriction in rodents is known to decrease levels of oxidative damage, which may contribute to an 'anti-ageing' effect. We show here that a shorter period (10 months) of caloric restriction had only small effects on levels of oxidative DNA and protein damage in the livers of mice, but completely attenuated increased oxidative damage caused by the carcinogen clofibrate. Since clofibrate is thought to exert its actions by increasing oxidative damage, our data suggest that 10 months of caloric restriction can increase the resistance of tissues to agents inducing oxidative stress. This may be an important factor in explaining how caloric restriction decreases cancer incidence.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2000

Ebselen induces apoptosis in HepG(2) cells through rapid depletion of intracellular thiols.

Ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one, is a synthetic seleno-organic compound with antioxidant capability. In the present study, we systematically examined the ability of ebselen to induce apoptosis in a human hepatoma cell line, HepG(2). Ebselen-induced apoptosis was evaluated by (i) TdT-mediated dUTP nick end labeling assay; (ii) analysis of sub-G1 cells; (iii) cell morphology, including cell size and granularity examination; and (iv) DNA gel electrophoresis. The results showed that ebselen was able to induce typical apoptosis in HepG(2) cells in a dose- and time-dependent manner. In order to explore the possible mechanisms involved in ebselen-induced apoptosis, the effect of ebselen on intracellular thiol concentrations including reduced glutathione (GSH) and protein thiols and the effect of N-acetylcysteine (NAC) and buthionine sulfoximine (BSO) pretreatment on ebselen-induced apoptosis were investigated. It was found that (i) ebselen rapidly depleted intracellular GSH and protein thiols, moreover, the depletion preceded the occurrence of apoptosis; (ii) NAC, a precursor of intracellular GSH synthesis, significantly alleviated ebselen-induced apoptosis; and (iii) BSO, a specific inhibitor of intracellular GSH synthesis, augmented ebselen-induced apoptosis significantly. Taken together, the present study demonstrates that ebselen is able to induce apoptosis in HepG(2) cells, most probably through rapid depletion of intracellular thiols.

Antioxidants↗

PubMed2000

Lead exposure among small-scale battery recyclers, automobile radiator mechanics, and their children in Manila, the Philippines.

Blood lead (PbB) and hemoglobin levels (Hb) were determined in 40 battery repair/recycling shop workers, 16 radiator repair shop workers, and 20 children living in the immediate vicinity of these shops. Unexposed residents with similar socioeconomic status were also investigated. Mean PbB level was significantly higher for battery workers (54.23 microg/dL) when compared to radiator workers (20.04 microg/dL) and unexposed adults (12.56 microg/dL) (P<0.001). Among battery workers, 94% had PbB levels above the WHO permissible exposure limit of 40 microg/dL for males and 30 microg/dL for females. There was no demarcation between workplace and living quarters; therefore, workers' families were similarly exposed to hazards. Children living in the immediate vicinity of battery shops also had significantly higher mean PbB levels (49.88 microg/dL) compared to radiator shop children (11.84 microg/dL) and unexposed children (9.92 microg/dL). For workers with PbB > 40 microg/dL, 90% were anemic (Hb < 13 g/dL for males and <11.5 g/dL for females). Linear regression showed a correlation (r=-0.214; P=0.03) between Hb level and log(10)PbB. There was no significant relationship between anemia and blood lead in children (r=-0.146). We conclude that radiator repair activities appeared to increase the body burden of lead, although not up to a level significantly different from unexposed counterparts. Battery recycling/repair activities, however, significantly increased blood lead levels in workers and their children.

Adult↗

PubMed2000

Involvement of oxidative stress in crystalline silica-induced cytotoxicity and genotoxicity in rat alveolar macrophages.

Alveolar macrophages (AMs) occupy a key position in silica-induced pulmonary fibrosis, although the mechanisms are yet to be elucidated. In the present study we examined the involvement of oxidative stress and reactive oxygen species formation in silica-induced cytotoxicity and genotoxicity in cultured rat AMs. A lucigenin-dependent chemiluminescence test was used to determine superoxide anion (O(-)(2)), and a 2',7'-dichlorofluorescin diacetate fluorescence test was employed to measure the hydrogen peroxide (H(2)O(2)) level. The cytotoxic and genotoxic effects caused by silica in AMs were examined by lactate dehydrogenase (LDH) leakage and single-cell gel electrophoresis (comet assay), respectively. The results showed that silica enhanced O(-)(2) and H(2)O(2) formation in AMs. There were clear dose- and time-dependent relationships in silica-induced cytotoxicity and genotoxicity. Furthermore, superoxide dismutase and catalase were able to reduce silica-induced LDH leakage and DNA damage, with concurrent significant inhibition on silica-induced oxidative stress in AMs. These findings provide convincing evidence that oxidative stress mediates the silica-induced cytotoxicity and genotoxicity. The understanding of such a mechanism may provide a scientific basis for the possible application of antioxidants in preventing the hazardous effects of silica.

Animals↗

PubMed2000

Protective effect of ebselen on aflatoxin B1-induced cytotoxicity in primary rat hepatocytes.

Recent studies have shown that aflatoxin B1 enhances reactive oxygen species formation and causes oxidative damage, which may ultimately contribute to the cytotoxicity and carcinogenic effect of aflatoxin B1. Ebselen, 2-phenyl-1,2-benzoisoseleazol-3(H)-one, a synthetic seleno-organic compound has been shown to possess glutathione peroxidase-like activity and free radical scavenging ability. Thus present study was designed to investigate the protective effect of ebselen on aflatoxin B1-induced cytotoxicity in primary rat hepatocytes. Aflatoxin B1-induced cytotoxicity and lipid peroxidation were determined by lactate dehydrogenase leakage and malondialdehyde generation, respectively. Intracellular reactive oxygen species level was measured using the fluorescent probe 2',7'-dichlorofluorescin diacetate, and the intracellular reduced glutathione concentration was determined with a fluorometric method. Ebselen was found to display a dose-dependent protective effect on lactate dehydrogenase leakage and malondialdehyde generation caused by aflatoxin B1 exposure. The results also demonstrate that ebselen efficiently inhibits the intracellular reactive oxygen species formation in aflatoxin B1-treated hepatocytes in a dose and time-dependent manner. It was also noted that ebselen was able to increase the intracellular reduced glutathione concentration, both in the control and in aflatoxin B1-treated hepatocytes. The protection of ebselen against aflatoxin B1 cytotoxicity, however, was not affected by lowering the concentration of intracellular reduced glutathione. The overall data indicate that ebselen possesses a potent protective effect against aflatoxin B1-induced cytotoxicity, and the main mechanism involved in the protection may be its strong capability in inhibiting intracellular reactive oxygen species formation and preventing oxidative damage.

Aflatoxin B1↗

PubMed2000

Critical role of reactive oxygen species and mitochondrial permeability transition in microcystin-induced rapid apoptosis in rat hepatocytes.

Microcystin-LR (M-LR) is a specific hepatotoxin. At present, the exact toxic mechanism of its action remains unclear though apoptosis is believed to be involved. This study was designed to investigate the role of reactive oxygen species (ROS) and mitochondrial permeability transition (MPT) in the M-LR-induced apoptotic process. Morphologic changes such as cell shrinkage, externalization of cell membrane phosphatidylserine, DNA fragmentation, and nuclear condensation suggest that M-LR causes rapid apoptosis in hepatocytes. Confocal microscopy revealed that M-LR exposure led to the onset of MPT and mitochondrial depolarization, evidenced by (1) redistribution of calcein fluorescence from cytosol to mitochondria, and (2) loss of mitochondrial tetramethyrhodamine methyl ester (TMRM) fluorescence; both occurred before apoptosis. Moreover, there was a significant and rapid increase of ROS level before the onset of MPT and loss of MMP, indicating a critical role of ROS in M-LR-induced apoptosis. Deferoxamine (DFO), an iron chelator, prevented the increase of ROS production, delayed the onset of MPT, and, subsequently, cell death. In addition, a specific MPT inhibitor, cyclosporin A (CsA), blocked the M-LR-induced ROS formation, onset of MPT, and mitochondrial depolarization as well as cell death. Thus, we conclude that the M-LR-induced ROS formation leads to the onset of MPT and apoptosis.

Animals↗

PubMed2000

Inhibition of ebselen on aflatoxin B(1)-induced hepatocarcinogenesis in Fischer 344 rats.

Aflatoxin B(1) (AFB(1)), a potent hepatocarcinogen, enhances ROS formation and causes oxidative DNA damage, which may play a role in its carcinogenicity. We have demonstrated recently that ebselen, an organic selenium compound, protects against the cytotoxicity of AFB(1) through its antioxidant capability. The present study was designed to investigate the effect of ebselen on AFB(1)-induced hepatocarcinogenesis in an animal model. Fischer 344 rats were first treated with either deionized water or ebselen (5 mg/kg, 5 days/week) via gavage for 4 weeks, then given AFB(1) (0.4 mg/kg, gavage, once a week) or AFB(1) plus ebselen (5 mg/kg, 5 days/week) for another 24 weeks. The results showed that the hepatocarcinogenicity of AFB(1) in rats was significantly reduced by ebselen treatment as indicated by a decrease in: (i) serum gamma-glutamyl transpeptidase activity; (ii) expression of mRNAs of liver alpha-fetoprotein and the placental form of glutathione S-transferase (GST-P); and (iii) the area and mean density of staining of liver GST-P foci. Ebselen treatment significantly reduced the formation of hepatic AFB(1)-DNA adducts and 8-hydroxydeoxyguanosine caused by AFB(1) exposure. These findings suggest that ebselen can inhibit the carcinogenicity of AFB(1). In addition to the reduction of AFB(1)-DNA adduct formation, the protective effect of ebselen against AFB(1)-induced oxidative DNA damage may also, at least in part, contribute to its anticarcinogenic property.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2000

Homocysteine, folate, vitamin B12, and cardiovascular risk in Indians, Malays, and Chinese in Singapore.

OBJECTIVE: To examine the hypothesis that the higher rates of coronary heart disease (CHD) in Indians (South Asians) compared with Malays and Chinese is partly attributable to differences in blood concentrations of homocysteine, and related blood concentrations of folate and vitamin B12. DESIGN: Cross sectional study of the general population. SETTING: Singapore. PARTICIPANTS: Random sample of 726 fasting subjects aged 30 to 69 years. MAIN RESULTS: Mean plasma total homocysteine concentrations did not show significant ethnic differences; values were Indians (men 16.2 and women 11.5 mumol/l), Malays (men 15.0 and women 12.5 mumol/l), and Chinese (men 15.3 and women 12.2 mumol/l). Similarly, the proportions with high plasma homocysteine (> 14.0 mumol/l) showed no important ethnic differences being, Indians (men 60.0 and women 21.9%), Malays (men 53.9 and women 37.8%), and Chinese (men 56.6 and women 30.6%). Mean plasma folate concentrations were lower in Indians (men 8.7 and women 10.9 nmol/l) and Malays (men 8.5 and women 10.8 nmol/l), than Chinese (men 9.7 and women 13.8 nmol/l). Similarly, the proportions with low plasma folate (< 6.8 nmol/l) were higher in Indians (men 44.9 and women 36.6%) and Malays (men 45.3 and women 24.5%) than Chinese (men 31.4 and women 12.6%). Mean plasma vitamin B12 concentrations were lowest in Indians (men 352.5 and women 350.7 pmol/l), then Chinese (men 371.1 and women 373.7 pmol/l), and then Malays (men 430.5 and women 486.0 pmol/l). CONCLUSION: While there were ethnic differences for plasma folate and vitamin B12 (in particular lower levels in Indians), there was no evidence that homocysteine plays any part in the differential ethnic risk from CHD in Singapore and in particular the increased susceptibility of Indians to the disease.

Adult↗

PubMed2000

Microcystic cyanobacteria extract induces cytoskeletal disruption and intracellular glutathione alteration in hepatocytes.

Microcystins are a group of highly liver-specific toxins, although their exact mechanisms of action remain unclear. We examined the effects of microcystic cyanobacteria extract (MCE) collected from a contaminated water source on the organization of cellular microtubules (MTs) and microfilaments (MFs) in hepatocytes. We also investigated the effects on lactate dehydrogenase (LDH) leakage and intracellular glutathione (GSH). Primary cultured rat hepatocytes exposed to MCE (equivalent to 125 microg/mL lyophilized algae cells) showed a characteristic disruption of MTs and MFs in a time-dependent manner. Under these conditions, MCE caused aggregation of MTs and MFs and a severe loss of MTs in some cells. Moreover, MCE-induced cytoskeletal alterations preceded the LDH leakage. On the other hand, the treatment of cells with MCE led to a dose-dependent increase of intracellular GSH. However, time-course study showed a biphasic change of intracellular GSH levels with a significant increase in the initial stage followed by a decrease after prolonged treatment. Furthermore, pretreatment with N-acetylcystein (NAC), a GSH precursor, significantly enhanced the intracellular GSH level and decreased the MCE-induced cytotoxicity as well as cytoskeleton changes. In contrast, buthionine-(S, R)-sulfoximine, a specific GSH synthesis inhibitor, increased the cell susceptibility to MCE-induced cytotoxicity by depleting the intracellular GSH level. These findings suggest that intracellular GSH plays an important role in MCE-induced cytotoxicity and cytoskeleton changes in primary cultured rat hepatocytes. Increasing intracellular GSH levels protect cells from MCE-induced cytotoxicity and cytoskeleton changes.

Animals↗

PubMed1999

Lag-time measurement of antioxidant capacity using myoglobin and 2, 2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid): rationale, application, and limitation.

The application of a simple lag-time assay for antioxidant capacity using myoglobin and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) or ABTS has been studied for its general application conditions. In the presence of an antioxidant, the ABTS(*+) radical-cation-forming chromogenic reaction, catalyzed by myoglobin and initiated by hydrogen peroxide (H(2)O(2)), has a lag period, and its duration is linearly correlated to the concentration of that antioxidant. The high linearity between the lag time and the antioxidant concentration remained unchanged regardless of the assay conditions. It was also found that the linearity was better for antioxidants at lower concentrations. The change of assay condition could significantly affect the relative antioxidant value of a chemical to the standard (ascorbic acid), although not to a large extent. Most of antioxidants investigated were found suitable to be assayed using this method. Some antioxidants, e.g., genistein, however, were not, probably due to their low reactivity toward ferrylmyoglobin or ABTS(*+). In conclusion, the lag-time assay is a reliable method for measuring the antioxidant capacity, provided caution is taken for antioxidants that mainly act through lowering the rate of the chromogenic reaction.

Antioxidants↗

PubMed1999

Reference values and action levels of biological monitoring in occupational exposure.

The primary objectives of biological monitoring are (1) to prevent health impairment, (2) to assist in the assessment of risk, and (3) to evaluate the effectiveness of environmental controls. An efficient way to achieve these objectives would be to enforce the compliance of biological exposure standards at the workplace. However, biological monitoring should be viewed in the total context of control and prevention of work-related diseases, and not merely to comply with permissible standards. Biological monitoring depends very much on the conditions that the chemical is absorbed and how it is metabolised. Genetic diversity could therefore contribute to significant differences in this aspect. Furthermore, many of the reference values established have so far not been fully validated and therefore their usefulness is rather limited. This paper reviews and illustrates using some recent findings to show that biological reference values are influenced not just by the above mentioned issues, but also factors such as (1) health and nutritional status of the exposed population, (2) social and cultural factors, and (3) climatic conditions. Caution has to be taken when considering having an action level for some of the biological reference value. Biological reference values set without considering people, technology, and working conditions would be fraught with difficulties in implementation.

Benzene↗

PubMed1999

Genotoxicity of microcystic cyanobacteria extract of a water source in China.

The water pollution of toxic cyanobacteria (blue-green algae) is a worldwide problem and worsens with industrialization. Microcystins are potent cyclic heptapeptidic hepatotoxins produced mainly by Microcystis aeruginosa, and their hepatotoxicity has been well-documented. In contrast, information on the genotoxic effects of microcystins is relatively scarce. In our present study, the genotoxicity of microcystic cyanobacteria extract (MCE) of a water source in China was studied using Salmonella typhimurium assay (Ames test), comet assay (Single cell gel electrophoresis) and mouse micronucleus test. Results from Ames test indicated that MCE had strong mutagenicity regardless of the presence of S9. Moreover, MCE was able to induce DNA damage in primary cultured rat hepatocytes examined by comet assay. In addition, MCE also enhanced bone marrow micronucleated polychromatic erythrocytes in mice. The analysis of HPLC showed that the main component of MCE was microcystin-LR. The understanding of the potent genotoxicity of MCE will help to establish the possible link between water cyanobacteria contamination and high risk of primary liver cancer found in some endemic areas.

Animals↗

PubMed1999

Sodium selenite-induced oxidative stress and apoptosis in human hepatoma HepG2 cells.

The 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 microM) 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.

Apoptosis↗

PubMed1999

Automated high-performance liquid chromatographic method with precolumn reduction for the determination of ubiquinol and ubiquinone in human plasma.

We developed a gradient HPLC method with automated precolumn reduction for direct electrochemical detection of ubiquinol-10 (CoQ10H2) and total coenzyme Q10 (TQ10) in human plasma. The concentration of ubiquinone-10 (CoQ10) was calculated by subtraction of CoQ10H2 from TQ10. Preparation of reducing agent and precolumn reduction was performed by a programmable auto-injector. The two mobile phases used were: A, 100% of methanol containing 50 mM sodium perchlorate and 10 mM perchloric acid; and B, a mixture of ethanol and tert.-butanol (80:20, v/v). Sample preparation was simply a deproteinisation process with 10-fold ethanol. A good linear relationship was obtained for CoQ10H2 concentration from 0.1 to 3 micromol/l. The detection limit was 2.5 nmol/l with an injection volume of 20 microl. The analytical recovery and reproduciblity were generally >90%. To validate the method, 18 freshly collected plasma samples of normal healthy subjects were analysed. The mean ratio of CoQ10H2/CoQ10 was 93:7. The proposed method is sensitive, reliable and can be used for clinical investigation.

Automation↗

PubMed1999

Protective effect of ebselen against hydrogen peroxide-induced cytotoxicity and DNA damage in HepG2 cells.

The protective effect of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one), a selenoorganic compound, against hydrogen peroxide (H2O2)-induced cytotoxicity and DNA damage was investigated in a human hepatoma cell line, HepG2. The inhibitory effect of H2O2 on cell growth was determined using the tetrazolium dye colorimetric test (MTT test), and the cytotoxicity and lipid peroxidation were estimated by lactate dehydrogenase (LDH) leakage and malondialdehyde (MDA) formation, respectively. DNA damage was detected using single cell gel electrophoresis (comet assay), and intracellular reactive oxygen species (ROS) formation was measured using a fluorescent probe 2',7'-dichlorofluorescein diacetate (DCFH-DA). The results showed that H2O2 suppressed the growth of HepG2 cells and the addition of ebselen significantly reduced the suppression. Furthermore, ebselen also displayed a dose-dependent reduction of LDH leakage and MDA formation in H2O2-treated cells. The results also demonstrate that ebselen was able to reduce the ROS formation and DNA damaging effect caused by H2O2 in a dose-dependent manner. These findings suggest that ebselen has a strong protective ability against the cytotoxicity and DNA damaging effect caused by reactive oxygen species.

Azoles↗

PubMed1999

Mitochondrial damage by the "pro-oxidant" peroxisomal proliferator clofibrate.

Clofibrate is a peroxisome proliferator that can cause hepatic cancer in rodents. It has been suggested that oxidative damage is involved in this hepatocarcinogenesis, although the data are conflicting. We confirmed that clofibrate causes oxidative damage in nuclei from the livers of mice treated with this substance, measured both as protein carbonyls and levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in DNA. In addition, clofibrate also affects mitochondria, causing elevated levels of carbonyls and 8-OHdG, increased state 4 respiration and decreased adenosine triphosphatase (ATPase) activity. No evidence for clofibrate-induced lipid peroxidation in mitochondria was obtained. We propose that mitochondria may be a major target of injury and a source of oxidative stress in clofibrate-treated animals.

Animals↗