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Biomedical subjects

S S Tsang

Publications and source records attributed to S S Tsang.

At least 19 recordsLinked to original sources
PubMed2000

DNA-breaking versus DNA-protecting activity of four phenolic compounds in vitro.

Given the paradoxical effects of phenolics in oxidative stress, we evaluated the relative pro-oxidant and antioxidant properties of four natural phenolic compounds in DNA nicking. The phenolic compounds differed dramatically in their ability to nick purified supercoiled DNA, with the relative DNA nicking activity in the order: 1,2,4-benzenetriol (100% nicking) > gallic acid > caffeic acid > gossypol (20% nicking). Desferrioxamine (0.02 mM) decreased DNA strand breakage by each phenolic, most markedly with gallate (85% protection) and least with caffeic acid (26% protection). Addition of metals accelerated DNA nicking, with copper more effective (approximately 5-fold increase in damage) than iron with all four phenolics. Scavengers revealed the participation of specific oxygen-derived active species in DNA breakage. Hydrogen peroxide participated in all cases (23-90%). Hydroxyl radicals were involved (32-85%), except with 1,2,4-benzenetriol. Superoxide participated (81-86%) with gallic acid and gossypol, but not with caffeic acid or 1,2,4-benzenetriol. With 1,2,4-benzenetriol, scavengers failed to protect significantly except in combination. Thus, in the presence of desferrioxamine, catalase or superoxide dismutase inhibited almost completely. When DNA breakage was induced by Fenton's reagent (ascorbate plus iron) the two catechols (caffeic acid and gossypol) were protective, whereas the two triols (1,2,4-benzenetriol and gallic acid) exacerbated damage.

Antioxidants↗
PubMed1997

Rejoining of DNA double-strand breaks after the introduction of chromosome 11 into a radiosensitive bladder carcinoma cell line.

Insertion of a normal chromosome 11 into tumour cell lines can protect against a sensitivity to irradiation and oxidative stress. A possible mechanism underlying this effect is that there is a correction of a defect in the rejoining of double-strand breaks (dsb) by the chromosome insertion. In order to explore this hypothesis, three cell lines were evaluated for their ability to rejoin dsb: (1) a bladder carcinoma cell line ('parent') previously shown to be sensitive to irradiation and radical generating species; (2) a derivative of this cell line into which a normal chromosome 11 had been inserted by microcell fusion ('hybrid') showing corrected radiosensitivity; and (3) a 'revertant' cell line that had spontaneously lost the insert and reverted to the radiosensitive phenotype. Nuclear extracts from the 3 lines were isolated and evaluated for their capacity to rejoin plasmid (pUC18) DNA broken at defined restriction sites (SalI, EcoRI, KpnI, SmaI) in the lacZ gene. The extent of rejoining was determined by gel electrophoresis and the fidelity of rejoining determined by expression of the lacZ gene in E. coli DH5 alpha bacteria. Results suggest there is no difference between the 'parent', 'hybrid' and 'revertant' nuclear extracts in the fidelity and the total extent of rejoining, regardless of the type of break. However, there is an alteration in the distribution of rejoined products. Nuclear extracts from 'hybrid' cells tend to rejoin linear DNA into circular monomers with a greater efficiency than extracts from both 'parent' and 'revertant' cells. This alteration in distribution is observed when 3'- or 5'-protruding ends are rejoined but not in the rejoining of blunt ends. The results suggest that loci on chromosome 11 are involved in the rejoining of dsb, affecting the relative amount of the different rejoined products. Whether this alteration plays a role in the 'parent' cell's radiosensitivity is yet to be determined.

Cell Fusion↗
PubMed1996

Arsenic and chromium enhance transformation of bovine papillomavirus DNA-transfected C3H/10T1/2 cells.

Tumor promoters such as phorbol esters, teleocidin and okadaic acid increase the numbers of multilayered, transformed foci produced by BPV DNA-transfected C3H/10T1/2 cells. We questioned whether arsenic and chromium, which are known human carcinogens also enhance transformation of BPV DNA-transfected C3H/10T1/2 cells. Cr(III) potassium sulfate at 100 microM enhanced transformation by 1.4-fold, but Cr(VI) as potassium chromate did not enhance transformation, although toxicity of potassium chromate may have prevented enhancement of transformation. Sodium arsenite (As(III) at 5 microM and sodium arsenate (As(V)) at 25 microM both enhanced neoplastic transformation by 6-fold. By comparison, in previous studies, sodium orthovanadate (V(IV)) or vanadyl sulfate (V(IV)) at 4 microM enhanced numbers of transformed foci by 25-50-fold. The comparatively strong enhancement of transformation by vanadium and phorbol esters suggests that neoplastic transformation may occur by mechanisms that are common to these compounds including alteration of tyrosine phosphorylation.

Animals↗
PubMed1995

Reducing the induction to abortion interval in termination of second trimester pregnancies: a comparison of mifepristone with laminaria tent.

OBJECTIVE: To determine whether mifepristone (RU486) is more effective than laminaria tent in shortening the induction-abortion interval in termination of second trimester pregnancies with gemeprost. DESIGN: Prospective randomised comparative trial. SETTING: Department of Obstetrics and Gynaecology in a University teaching hospital. SUBJECTS: Sixty-two women undergoing termination of pregnancy in the second trimester. INTERVENTIONS: The women were allocated at random to one of the two treatment groups. The first group received 600 mg of mifepristone 36 h before administration of gemeprost. In the second group, a medium-sized laminaria tent was inserted 12 h before gemeprost. The pregnancies in both groups were terminated with vaginal gemeprost, 1 mg every 3 h up to a maximum of 5 mg/day. MAIN OUTCOME MEASURES: Induction-abortion intervals, amount of gemeprost required, and incidence of side effects. RESULTS: The median induction-abortion interval in the mifepristone group (7.5 h) was significantly shorter than that in the laminaria tent group (11 h) and significantly fewer gemeprost pessaries were required. There was no significant difference in the amount of narcotic analgesics required or the incidence of side effects between the two groups. CONCLUSIONS: Mifepristone is more effective than laminaria tent in shortening the induction-abortion interval in termination of second trimester pregnancies.

Abortifacient Agents, Nonsteroidal↗
PubMed1994

Evaluation of laboratory tests for lupus anticoagulant in a group of Chinese lupus patients.

The sera of 69 Chinese patients with systemic lupus erythematosus were tested for the presence of lupus anticoagulant (LA) by a panel of laboratory tests: Kaolin clotting time (KCT), dilute Russell viper venom time (DRVVT) and platelet neutralization procedure (PNP). The prevalence of LA varied among the 3 tests (10-19%), and was 10% when LA was considered present if either KCT or DRVVT and the PNP were positive. Concordance was fair between KCT and PNP, but was poor for DRVVT with either of the other 2 tests. Only 2 of our lupus patients had a history of thrombo-embolic disease, and neither were serologically positive for LA. The incidence of thrombo-embolic diseases and that of LA were both too low in this group of Chinese lupus patients for their association to be evaluated.

Adolescent↗
PubMed1994

A morphologic variant of May-Hegglin anomaly in a Chinese girl.

An 8 yr old Chinese girl was investigated for easy bruising and mild thrombocytopenia. Platelet aggregation studies and coagulation tests were found to be normal. The giant platelets and Döhle-like cytoplasmic inclusions in granulocytes confirmed the diagnosis of May-Hegglin anomaly. The father's granulocytes also had Döhle-like inclusions and one paternal aunt had a history of bleeding tendency. Review of literature showed that such Döhle-like inclusions had always been described morphologically as crescentic or spindle-shaped. In this case, however, the shape was roundish, oval or poorly defined. Ultrastructurally, the classic description was electron-dense long rods and needles orientating along the long axis of the "spindle". In this case, the only electron-dense particles were dot-like with a haphazard arrangement.

Asian People↗
PubMed1993

Prevalence of pyruvate kinase deficiency among the Chinese: determination by the quantitative assay.

The prevalence of pyruvate kinase (PK) deficiency among the Chinese population has not been established. Fung et al. (Arch Dis Child 44:373-376, 1969) and Wu et al. (Am J Hematol 20:139-144, 1985) indicate 3.4% and 2.1% PK deficiency prevalence rates, respectively, the higher figure based on Beutler's screening test [3] without confirmatory testing. Neither figure is consistent with the occurrence of hemolytic anemia from this cause in the experiences of hematologists in Hong Kong. Using the standard quantitative assay, we measured PK activity in blood samples from 1,100 local Chinese people. The assay was automated on a centrifugal analyser, and the results were expressed in IU per gram of hemoglobin (IU/g Hb). Blood samples from 497 healthy male adults were measured, and PK activity was found to have a range of 15.2 +/- 5.2 (mean +/- 2 SD). A total of 100 cord blood samples were also measured, and the reference interval for this subgroup was 17.7 +/- 4.8. Additionally, samples from 503 anaemic patients were measured, and all were found to have values above the lower limit of the reference interval. The prevalence of PK deficiency among the Hong Kong Chinese population determined by this study was < 0.1%.

Adolescent↗
PubMed1993

A modified screening procedure to detect pyruvate kinase deficiency.

Beutler's screening procedure was used to detect pyruvate kinase deficiency in the local population. In this test, hemolysate and the reagent mixture are incubated and then placed at a spot on filter paper to be examined for fluorescence. Complete nonfluorescence marks the reaction endpoint, and fluorescence beyond 30 minutes indicates pyruvate kinase deficiency. It was difficult to determine this endpoint due to uneven sedimentation of unhemolyzed red cells on the spot. In this modified technique, the leukocyte-depleted red cell suspension was frozen and thawed for complete red cell lysis before being used for the test. Using both techniques, 493 health individuals and 126 anemic patients were screened for pyruvate kinase deficiency. By the conventional technique, 3.7% remained fluorescent after 30 minutes, whereas by the modified technique, none were fluorescent after 30 minutes. Quantitative assay indicated that all samples had pyruvate kinase activity levels greater than the lower limit of the reference range. We also demonstrated that blood samples from individuals with thalassemia trait were primarily responsible for the aberrant results from the conventional screening procedure.

Fluorescence↗
PubMed1992

Vanadate-induced gene expression in mouse C127 cells: roles of oxygen derived active species.

An underinvestigated aspect of the mitogenic and cell regulatory actions of vanadium is the regulation of gene expression. Among the fifteen cellular genes studied in cultured mouse C127 cells, vanadium (as 10 microM sodium vanadate) increased levels of mRNA of the actin and c-Ha-ras to four times control values. These increases represented de novo synthesis of mRNA, since they were inhibited by actinomycin D. Vanadate did not increase mRNA corresponding to c-src, c-mos, c-myc, p53, HSP70, pODC or RB genes, and expression of c-erb A, c-erb B, c-sis and c-fes genes was undetectable whether vanadium was present or not. Expression of a third gene affected by vanadium, c-jun, was augmented by addition of a reductant or oxidant together with the vanadate. Addition of NADH (marginally effective on its own) or H2O2 (effective alone) dramatically enhanced the effect of vanadate on c-jun gene expression. Catalase inhibited the effect of NADH partly. The vanadate-stimulated expression of actin and c-Ha-ras mRNA were unaffected by oxidants, reductants, metal chelators, or anti-oxidant enzymes. Evidently vanadate acts by two separate mechanisms on these two categories of genes. The alternate hypothesis that the actions of vanadate on actin and c-Ha-ras were mediated by a protein kinase cascade was inconsistent with the following observations. Neither insulin nor epidermal growth factor increased mRNA levels of c-Ha-ras or actin gene. Neither genistein (a tyrosine kinase inhibitor) nor pretreatment with 12-O-tetradecanoylphorbol-13-acetate blocked the actions of vanadate on these genes. Clearly the biological actions of vanadium depend in part on altered expression of genes. Since two of the genes are proto-oncogenes, this mechanism is potentially relevant to the mitogenic responses of cells to vanadium.

Animals↗
PubMed1992

Vanadate enhances transformation of bovine papillomavirus DNA-transfected C3H/10T1/2 cells.

Bovine papillomavirus (BPV) DNA-transfected C3H/10T1/2 cells respond to tumor promoters by enhanced production of transformed foci. Vanadate, a suspected carcinogen, is a mitogen, generates active oxygen species and alters phosphorylation of proteins. We investigated whether vanadate would enhance transformation of BPV DNA-transfected C3H/10T1/2 cells. Transformed foci in BPV DNA transfected C3H/10T1/2 cells exposed continuously to vanadate for 21 days increased in a dose-dependent manner to 50-fold at 4 microM vanadate. This increase was not due to enhanced uptake of BPV DNA post transfection. Neither catalase nor superoxide dismutase inhibited the vanadate-mediated increase in transformed foci but this does not necessarily rule out the involvement of intracellular active oxygen species. At vanadate concentrations greater than 6 microM, cells lost adherence to the Petri plates. We conclude that vanadate is capable of enhancing BPV DNA-mediated cell transformation. Possible mechanisms may involve active oxygen species or altered patterns of protein phosphorylation.

Animals↗
PubMed1991

An unusual case of hairy cell leukemia: death due to leukostasis and intracerebral hemorrhage.

Hairy cell leukemia (HCL) was diagnosed in a 71-year-old Chinese man. His clinical presentation and the characteristics of the hairy cells were typical of classic HCL. However, extreme leukocytosis (195 to 323 x 10(9) cells/L) in peripheral blood was in striking contrast. This leukocytosis, which was much more pronounced than any of the reported cases of HCL with leukocytosis, was associated with leukostasis in the cerebral vasculature and was causally related to a massive intracerebral hemorrhage and death. This mode of death in HCL has not been reported previously.

Aged↗
PubMed1991

Cell transformation induced by bovine papillomavirus DNA as an assay for tumor promoters and chemopreventive agents.

An in vitro assay was designed to examine and quantitate the action of chemical promoters and chemopreventive agents on papillomavirus DNA-carrying cells. Cultured C3H/10T1/2 cells transfected with bovine papillomavirus type 1 DNA (plasmid pdBPV-1) were used as targets, and the frequency of transformed foci was used as an endpoint. The development of foci with a transformed phenotype was greatly enhanced by tumor promoters (e.g., mezerein, 12-O-tetradecanoyl-phorbol-13-acetate, teleocidin, and okadaic acid) and complex mixtures such as extracts of the areca nut, which is an integral part of a betel quid and is linked to oral cancers among chewers. The degree of promotion depended on the length of exposure, the type of promoter, and the time of application after transfection with BPV DNA. The inhibitory effect of chemopreventive agents on transformation can be tested either directly on BPV DNA transfected cells (promoter-independent transformation), or on transfected cells that were exposed to tumor promoters (promoter-dependent transformation). Retinol, and to a lesser degree beta-carotene, exerted an inhibitory effect on promoter-dependent and promoter-independent transformation of BPV DNA transfected cells. The inhibitory effect was conveyed either by the addition of retinol simultaneously with promoters, or after exposure to the promoting agents was completed. The significance of this short-term in vitro assay for the design of chemopreventive trials is discussed.

Animals↗
PubMed1991

Vanadate stimulates ornithine decarboxylase activity in C3H/10T1/2 cells.

Ornithine decarboxylase (ODC) activity of C3H/10T1/2 cells reflects their response to conflicting actions of many tumor promoters and tumor suppressors. In cultured C3H/10T1/2 cells, addition of vanadate (50 nM) increased ODC activity. Over the range 0.05-5 microM, vanadate increased ODC levels in a dose dependent manner to 11 times control levels. The presence of retinoic acid (5 microM) or the absence of fetal calf serum blocked the stimulation by vanadate.

Animals↗
PubMed1990

The effect of retinoids, carotenoids and phenolics on chromosomal instability of bovine papillomavirus DNA-carrying cells.

Antioxidants were found to protect against the genotoxic effects of chemical and physical mutagenic and clastogenic agents. This study focused on the capacity of antioxidants to reduce an intrinsic and persistent chromosome instability. As a model system, strains of C127 cells, which were transformed by bovine papillomavirus (BPV) DNA and which carry BPV DNA varying from 20 to 160 copies, were used. Transformed cells of 10 different strains showed a persistently high incidence of mitotic irregularities detectable at anaphase and telophase (27.3-58.9%), an elevated frequency of cells with micronuclei (6.6-34.7%), and a broad spectrum of nuclear sizes, as measured by image analysis. A 3-day exposure to retinoic acid, retinol, beta-carotene, canthaxanthin, ascorbic acid and ellagic acid greatly reduced the degree of chromosome instability, whereas catechin, eugenol and pyrogallol showed a smaller inhibitory effect, and curcumin had no detectable effect on the frequency of mitotic irregularities. After withdrawal of retinoic acid treatment, the high levels of chromosome instability reappeared. The possibility that the protective effect of the retinoids and carotenoids examined in the model system points to their beneficial administration to human cells with an intrinsic or acquired chromosome instability is discussed.

Antioxidants↗
PubMed1990

Use of peripheral vessels for exchange transfusion.

During a five and a half year period, exchange transfusions were performed through the peripheral vessels in 201 of the 214 infants (94%) who required either double volume or partial plasma exchange transfusions. Peripheral vessel exchange transfusion is simple, practicable, and safe with few complications. Technical difficulties in catheterizing the peripheral artery and vein may be overcome by using a 24 gauge catheter, which causes no more catheter induced haemolysis than standard umbilical catheters.

Bilirubin↗
PubMed1990

Fibrinogen level in health and disease.

The plasma fibrinogen concentration of 47 healthy individuals was measured in order to determine the reference range for our laboratory, which was calculated to be 1.75-3.31 g/l. The plasma fibrinogen concentration of 44 hospital patients was also measured for comparison. These patients were selected because they were free from bleeding tendency and liver disease. The distribution of their fibrinogen levels was Gaussian, but more wide-based than the distribution of our normal controls. The mean fibrinogen value of the patient group was 3.60 g/l, significantly higher than that of the healthy group, which was 2.53 g/l. The reasons why the fibrinogen distribution graph of patients assumed such a pattern and the role of fibrinogen in health and disease are discussed.

Fibrinogen↗
PubMed1989

Promoting activity of betel quid ingredients and their inhibition by retinol.

Ingredients of betel quids, which have been linked to the high incidence of precancerous oral lesions and oral cancers, were examined for their promoting activity. Aqueous extracts were tested using the bovine papillomavirus (BPV) DNA transformation assay, which consists of cultured C3H/10T1/2 cells transfected with the plasmid pdPBV-1 as targets, and the frequency of transformed foci as endpoints. Areca nut extracts enhanced the formation of BPV DNA-induced transformed foci approximately tenfold. No promoting activity was detected in two samples of chewing tobacco examined. The addition of retinol to the areca nut extract inhibited its tumour promoting effect in a dose-dependent manner, completely abolishing the promoting activity at a dose of 10(-6) M. The experimental results are compared with epidemiological data on oral cancer incidences among chewers of different areca nut/tobacco mixtures and with the chemopreventive effect of vitamin A administered to betel quid chewers.

Animals↗