Biomedical subjects

C K Ho

Publications and source records attributed to C K Ho.

At least 127 records · Page 7Linked to original sources

PubMed1991

Cigarette smoking among school children in Singapore. Part III--Knowledge and attitudes towards smoking.

In the third article in this series which mainly assesses the knowledge of school children on the harmful effects of smoking, findings showed that the majority (90%) of school children surveyed were aware of the harmful effects. Current smokers appeared to be the least knowledgeable (69.4%) whilst non-smokers (89.3%) and experimenters (93.7%) were the most knowledgeable. Lung cancer (49%), smoking is bad for health (25%), smoking is bad for passive smokers (7%) and for heart disease (6%) were the most common responses given by the children on the specific ill effects caused by smoking. Smokers and non-smokers alike agreed that smoking is addictive, the proportions agreeing, once again, being lowest among smokers and highest among non-smokers. This trend was also observed when respondents were asked for their attitudes towards smoking--whether cigarette smoking was harmful and whether smoking made a person popular. The majority of respondents felt that a boy or girl who smoked "looked bad"--39% thought so of boys, while a higher proportion (55%), had the same impression of girls. The main reasons for giving up smoking given by ex-smokers were its harmful effects on health (49%), there being no more "kick" to it (16%), peer pressure (13%) and the disapproval of parents and teachers (13%). Among current smokers, at least half stated that they would like to stop smoking. Most of them had tried to kick the habit before but failed in their attempts. Finally, among the non-smokers, only 0.4% of boys and 0.1% of girls indicated that they might smoke in the future.

Adolescent↗

PubMed1991

Cigarette smoking among school children in Singapore. Part II--Development of the smoking habit.

The second in this series on smoking among school children in Singapore aims to define the characteristics of young smokers. Results show that of respondents who had ever smoked, the median age of experimentation with smoking was 12 years. This was seen among boys as well as girls. The median age at which current smokers went on to smoke regularly was 14 years, approximately two years after trying their first cigarette. Friends and parents were the main sources of the first cigarette for all categories of smokers, whether they be ex smokers, experimenters or current smokers. Among the reasons as to why current smokers smoked, the leading two were "to relax" (46.4%) and "out of sheer curiosity" (22.3%). Boys tend more to smoke with friends of the same sex (40.6%) whilst girls preferred mixed company (45.5%) when they smoked. Fathers played a major role in the development and continuation of smoking among those who had ever smoked before--52.0% of boys and 51.6% of girls currently smoking reported that their fathers smoked as well.

Adolescent↗

PubMed1991

Growth inhibition and differentiation in HL-60 leukemia cells induced by 1,25-dihydroxyvitamin D3 and tumor necrosis factor alpha.

Various concentrations of 1,25-dihydroxyvitamin D3 (vit D3; 10(-9)-10(-7) M) and recombinant human tumor necrosis factor alpha (rTNF-alpha; 60-960 U/ml) were used to induce growth inhibition and differentiation of the human promyelocytic leukemia cell line HL-60 based on growth kinetics, colony formation, morphological analysis, nonspecific esterase (NSE) activity, surface antigen expression, and cytokine release. Both vit D3 (10(-8)-10(-7) M) and rTNF-alpha (60-960 U/ml) were antiproliferative against the HL-60 cells, and a cooperative effect was noted when the two inducers were used in combination. After 5 days of incubation, vit D3 induced the HL-60 cells to differentiate into monocytes/macrophages, resulting in the formation of 3.0% +/- 0.4%, 18% +/- 2.0%, and 43% +/- 3.8% of morphologically mature cells at 10(-9), 10(-8), and 10(-7) M, respectively. The induced cells were NSE positive and expressed monocyte-associated antigens (EBM11, CD11b, and HLA-DR). Conversely, rTNF-alpha (60-960 U/ml) was unable to trigger the HL-60 cells to differentiate. However, rTNF-alpha could apparently increase the proportion of the morphologically mature and NSE-/antigen-positive cells when used in combination with vit D3 (10(-9)-10(-8) M). Following differentiation induction, HL-60 cells from vit D3-treated HL-60 cultures acquired the ability to secrete certain monokines, including interleukin 1 beta (IL-1 beta), prostaglandin E2 (PGE2), and granulocyte-macrophage colony-stimulating factor (GM-CSF), and adding rTNF-alpha in addition to vit D3 invariably increased the production of IL-1 beta and PGE2.

Antigens, Surface↗

PubMed1991

Effect of lipopolysaccharide on the production of colony-stimulating factors by the stromal cells in long-term bone marrow culture.

The production of colony-stimulating factors (CSFs) by murine bone marrow stromal cells was studied with Dexter long-term bone marrow culture (LTBMC). For induction of CSF release, various concentrations (0.5-40.0 microgram/ml) of bacterial lipopolysaccharide (LPS) were added to nonrecharged 3-week-old LTBMCs consisting of an intact or macrophage-depleted adherent cell layer. The depletion of monocytes/macrophages from freshly prepared bone marrow cell suspension was performed by carbonyl-iron incorporation before establishment of LTBMC. The supernatants (Sup) of normal LTBMCs contained a low level of macrophage colony-stimulating factor (M-CSF) that was produced by the adherent cells but not by the nonadherent cell elements. No colony inhibitor was found in the Sup of LTBMCs, whereas a colony-promoting activity (CPA) was detected in medium conditioned by the adherent marrow cells (AC-CM). CPA could enhance the colony formation of myeloid progenitor cells when used in combination with recombinant murine granulocyte-macrophage colony-stimulating factor (GM-CSF). The production of CSFs peaked at about 24 h after refeeding, but it then declined to only half the optimal activity at the end of the week. Addition of LPS to the intact LTBMC invariably increased the production of a GM-CSF-like cytokine. The release of this cytokine was dose dependent and peaked at a dosage of 20 micrograms/ml of LPS at 24 h after treatment. In contrast, macrophage-depleted marrow-adherent cells failed to respond to LPS for CSF secretion. These results suggest that LPS can stimulate marrow macrophages to directly release CSF or to potentiate the production of CSF by other stromal cells.

Animals↗

PubMed1990

Detection of the target progenitor cells of granulomonopoietic enhancing activity.

Macrophage-derived granulomonopoietic enhancing activity (GM-EA) is a novel mediator that amplifies colony formation of myeloid progenitor cells (CFU-GM) in conjunction with colony-stimulating factors (CSFs), and is distinct from other hematopoietic synergizing factors such as interleukin (IL)-1, IL-4, and IL-6. In the present study, we try to ascertain whether or not there is a GM-EA-specific responsive myeloid progenitor cell population. Human bone marrow cells deleted of adherent cells and T lymphocytes were separated by velocity sedimentation into three subpopulations with respective sedimentation rates (millimeters per hour) of 7.4 +/- 0.4, 6.0 +/- 0.6, and 4.7 +/- 0.3. These subpopulations corresponded to the day 7 CFU-GM, day 14 CFU-GM, and the earlier myeloid progenitor cells, pre-CFU-GM, respectively. Pre-CFU-GM failed to respond to the colony-inducing effect of GM-CSF but could be stimulated by GM-EA alone to generate small clusters (5 to 25 cells) in soft agar after 14 days of incubation. Correspondingly, suspension preculture of the fractionated bone marrow cells also showed that only the progenitor cells with low sedimentation rate (4.7 mm/h) could be activated by GM-EA to generate CFU-GM. Taken together, our results suggest that the specific target cell of GM-EA is the pre-CFU-GM, and that GM-EA acts on these cells as a growth/maturation factor, but on the day 7 and day 14 CFU-GM as a synergistic growth factor.

Bone Marrow↗

PubMed1990

Induction of thymidine kinase activity and clonal growth of certain leukemic cell lines by a granulocyte-derived factor.

Normal polymorphonuclear neutrophils (PMNs) constitutively secrete a mediator designated granulocyte-derived factor (GDF) that can enhance the uptake of 3H-thymidine (3- to 20-fold) by the molt-3, CTV-1, and K562 leukemic cell lines in a dose-dependent manner. GDF is heat labile (56 degrees C for 30 minutes) and acid labile (pH 2.0) and is sensitive to treatment with bacterial protease type IV. Our preliminary studies suggest that GDF is non-dialyzable (molecular weight cutoff, 12,000), binds to diethylaminoethyl (DEAE), and has an apparent molecular weight (mol wt) of about 40 Kd. Production of GDF is unaffected by treatment of PMN with activating agents (interferon gamma, OK432, phorbol ester, calcium ionophore, poly I:C) or metabolic inhibitors (actinomycin-D and cyclohexamide), suggesting that GDF is constitutively secreted. Despite the marked enhancement of 3H-thymidine uptake, cell number and the rate of DNA synthesis in GDF responsive cultures remain unchanged. In contrast, the clonogenic efficiency of the responsive cells is greatly increased in the presence of GDF. These phenomena occur in parallel to an amplification of the level of thymidine kinase activity in the sensitive cells. GDF is distinct from a panel of different lymphokines and monokines in antigenicity and biochemical and functional characteristics, and is possibly a novel cytokine that can alter the pattern of DNA synthesis and growth characteristics of certain hematopoietic cells. However, its biologic and physiologic significance remains to be determined.

Biological Transport↗

PubMed1990

Accumulation of pre-tRNA splicing '2/3' intermediates in a Saccharomyces cerevisiae mutant.

In an effort to identify genes involved in the excision of tRNA introns in Saccharomyces cerevisiae, temperature-sensitive mutants were screened for intracellular accumulation of intron-containing tRNA precursors by RNA hybridization analysis. In one mutant, tRNA splicing intermediates consisting of the 5' exon covalently joined to the intron ('2/3' pre-tRNA molecules) were detected in addition to unspliced precursors. The mutant cleaves pre-tRNA(Phe) in vitro at the 3' exon/intron splice site, generating the 3' half molecule and 2/3 intermediate. The 5' half molecule and intron are not produced, indicating that cleavage at the 5' splice site is suppressed. This partial splicing activity co-purifies with tRNA endonuclease throughout several chromatographic steps. Surprisingly, the splicing defect does not appreciably affect cell growth at normal or elevated temperatures, but does confer a pseudo cold-sensitive phenotype of retarded growth at 15 degrees C. The mutant falls into the complementation group SEN2 previously defined by the isolation of mutants defective for tRNA splicing in vitro [Winey, M. and Culbertson, M.R. (1988) Genetics, 118, 609-617], although its phenotypes are distinct from those of the previous sen2 isolates. The distinguishing genetic and biochemical properties of this new allele, designated sen2-3, suggests the direct participation of the SEN2 gene product in tRNA endonuclease function.

Base Sequence↗

PubMed1990

Orientation of the plane of occlusion.

A study was made of 28 dentulous Chinese Singaporean adults, using lateral skull radiographs. Various craniofacial reference lines and their relations to the maxillary occlusal line were analyzed. The orientation of the natural occlusal line in Chinese adults differed significantly from Swedish white adults. The Frankfort horizontal line in particular was considered disadvantageous as a clinical reference plane largely because of the acknowledged variation of its inclination between Chinese Singaporean and Swedish white adults. The shallow anatomic cant of the maxillary occlusal line in the Chinese patient could be misrepresented by a steep mechanical inclination on the articulator.

Adult↗

PubMed1990

Parasitological evaluation of a foodhandler population cohort in Panama: risk factors for intestinal parasitism.

A nonconcurrent, prospective intestinal parasitic disease study in a group of 200 foodhandlers employed in the Panama Canal Area was conducted in mid-1985 as part of an established occupational health medical surveillance program. The study included a review of laboratory testing (i.e., coprological exam), preexisting medical record data, and patient interview information to calculate estimates of incidence and risk factors associated with acquisition of Giardia lamblia and other protozoan/helminthic intestinal parasites. Significant increases in risk of infection were detected for specific native Indian and West Indian employee groups when compared with their Hispanic Panamanian (i.e., Latinos) or North American (i.e., U.S. born) counterparts. A three- to fourfold higher rate of infection was also documented during a one-year period when semiannual rather than annual examinations were conducted. No difference in the therapeutic efficacy of parasitological cure of Metronidazole versus Quinacrine was found when used in the treatment of individuals with asymptomatic G. lamblia infections (85% in both groups). The appropriateness of mass therapy of asymptomatically infected foodhandlers is discussed.

Adult↗

PubMed1990

Mortality trends in the coronary care unit.

To evaluate the clinical features, complication rates, and mortality from infarction in the coronary care unit, we analysed all cases of acute myocardial infarction admitted to the Coronary Care Unit of the Singapore General Hospital over a 4 month period in 1988. There were 184 cases of acute infarction with a male:female ratio of 3.4:1. Fifty-five percent of patients were aged 60 years or above. Complications included congestive cardiac failure in 40%, sustained ventricular tachycardia in 9%, cardiogenic shock in 18% and complete heart block in 8%. The overall in-hospital mortality was 20.6%. Multiple logistic regression analysis of clinical variables showed that of the clinical variables, age (elderly patients) and the diabetes were independently associated with a higher mortality as well as development of cardiogenic shock and sustained ventricular tachycardia. Comparing our results with previous smaller studies of CCU outcome in 1975 and 1967, there was a marked increase in the proportion of elderly patients in 1988 but despite this the overall mortality rate was not significantly different. Age is the most important clinical variable predicting outcome from infarction.

Adult↗

PubMed1990

Biological monitoring of workers exposed to inorganic lead in Singapore.

Medical surveillance of workers exposed to a lead hazard is a common practice in many countries. In Singapore, legislation on periodic medical examinations for lead exposed workers in factories was introduced in 1985. This paper discusses the results of the laboratory tests in workers exposed to inorganic lead in 1987. The WHO recommended that the health-based limit for lead absorption be 40 micrograms/dL for adult male workers. Taking this level, we could divide the factories into a "higher risk" category and a "lower risk" one, the latter not having a single result of blood lead of 40 micrograms/dL or above. The former category included factories manufacturing PVC and lead storage batteries, with the highest level of 79.6 micrograms/dL found in PVC manufacture. Of the 3 main races in Singapore, the Chinese have the lowest blood lead levels after adjusting for the type of industry, age and duration of exposure to lead. Age was correlated with the duration of lead exposure. The higher blood lead levels in Malays and Indians may have been contributed to by eating habits (eating with hands). The higher prevalence of smoking among Malays may also be contributory. The results in this study, while reassuring that no worker was found with blood lead above 80 micrograms/dL, also indicated that workers in some factories were still exposed to a health risk.

Adult↗

PubMed1990

Cigarette smoking among school children in Singapore. Part I--Smoking prevalence.

A cross sectional nationally representative survey of 33,110 school-going children in Singapore aged between 9 and 20 years was carried out to obtain, for the first time, baseline information on smoking among the school-going population in Singapore. The survey was carried out among students attending vocational institutes and public sector schools in Singapore in 1987. The overall smoking prevalence was found to be 2% (3% among boys and 0.2% among girls). Ex-smokers comprised 2% of respondents whilst those who had only experimented with smoking made up 9% of the respondents. Analyses of the data showed that cigarette smoking was more prevalent among Malays, among boys, among older children, and among the less academically inclined. On average, boys smoked a median of 20 cigarettes a week and girls, 12 cigarettes a week. On an international basis, the smoking prevalence among the school-going population in Singapore is significantly lower than that of developed countries like Australia, England and Wales and neighbouring countries such as Malaysia.

Adolescent↗

PubMed1989

Differential modulating effects of retinoic acid on interferon antiviral activity.

The effect of retinoic acid (RA) on the antiviral activity of interferons (IFNs) alpha and beta in the U937 and WISH cells was examined to ascertain whether or not RA could reduce the effectiveness of IFN-induced resistance to viral infection. Our results indicate that in the U937 cells, RA (0.1-1.0 microM) had neither enhancing nor suppressive effect on the antiviral activity of IFN-alpha or beta against the Semliki Forest virus (SFV). However, in the WISH cells, RA had different effects on IFNs alpha and beta. Thus, while RA (0.1-50 microM) invariably suppressed the activity of IFN-alpha, it enhanced the action of IFN-beta at low dose (0.1-1.0 microM) but became suppressive at higher concentrations (greater than or equal to 10 microM). Furthermore, higher antiviral activity was consistently obtained when RA (0.1-10 microM) was added prior to either IFN-alpha or IFN-beta comparing to cultures with IFN alone. In addition, direct correlation between antiviral activity and the amplitude of 2-5 oligoadenylate (A) synthetase activity was not observed. These results suggest that modulation of IFN antiviral activity by RA varies with different systems and is dependent on the sequence of treatment.

2',5'-Oligoadenylate Synthetase↗

PubMed1989

Induction of differentiation in HL-60 cells by retinoic acid and lymphocyte-derived differentiation-inducing factor but not by recombinant G-CSF and GM-CSF.

Various concentrations of retinoic acid (RA, 10(-9) to 10(-7) M), lymphocyte-derived differentiation-inducing factor (DIF, 10-30%), and recombinant human G-CSF (100-4000 U/ml) and GM-CSF (100-4000 U/ml) were used to induce the differentiation of the HL-60 promyelocytic leukemia cells. Retinoic acid at a concentration of 10(-7) M could significantly inhibit the growth of HL-60 cells both in suspension and in soft agar cultures, and induced these cells to differentiate into mature granulocytes capable of reducing nitro-blue tetrazolium and ingesting latex beads. Thirty per cent (v/v) DIF was also an effective inducer of HL-60 cell differentiation, but it triggered the cells to mature into monocytes rather than granulocytes. In contrast, rG-CSF and rGM-CSF had no growth inhibitory effect on HL-60 cells either in suspension or in agar cultures at all concentrations tested, nor could these factors induce HL-60 cells to acquire the more mature granulocytic or monocytic phenotypes. Furthermore, rG-CSF/rGM-CSF had no differentiation-enhancing effect when added to RA-containing HL-60 cultures. These results argue against the efficacy of using CSFs for the treatment of myelocytic leukemia based on the principle of differentiation induction.

Cell Differentiation↗

PubMed1989

The relationship of upper facial proportions and the plane of occlusion to anatomic reference planes.

A study was made of 28 dentulous Chinese (Singaporean) adults by using lateral skull radiographs. The dimensions of the maxillae and various craniofacial reference lines related to prosthodontic use were analyzed. The craniofacial reference angles that reflect the vertical height and horizontal depth of the maxillae in Chinese adults differed significantly from the norms obtained in a white North American adult population. By comparison, Chinese adults have a vertically high and horizontally receded upper face that could cause planes such as the Frankfort horizontal plane or an arbitrary axis-orbitale plane to assume a steeper anterior inclination, thus modifying the mechanical inclination of the maxillary cast and occlusal plane on the articulator.

Adult↗

PubMed1989

Enhancement of interferon-induced 2-5 oligoadenylate synthetase activity by retinoic acid in human histiocytic lymphoma U937 cells and WISH cells.

The effect of retinoic acid (RA) on the level of interferon (IFN)-induced 2-5 oligoadenylate (2-5A) synthetase activity was examined in human histiocytic lymphoma U937 cells and WISH cells** in order to ascertain the role of this polymerase in interaction between IFNs and RA. Cultures containing both IFNs (1-100 U/ml) and RA (0.1-10 microM) consistently had higher levels of enzyme activity than corresponding cells treated with IFN alone and this was true for all three types of IFNs in both cell lines. The potentiating effect of RA was dose- and time-dependent and under optimal conditions, the induction of the synthetase was synergistic between IFN-beta (10-100 U/ml) and RA (0.1-10 microM). Furthermore, pretreatment (but not posttreatment) with RA followed by subsequent treatment with IFNs preferentially induced higher levels of enzyme activity in U937 cells but not in WISH cells. In addition, our results indicated that the modulating effect of RA on IFNs did not involve interaction at the receptor level and the level of enhancement of 2-5A synthetase activity was not in parallel with either cell-growth arrest or promotion of differentiation. Lastly, the present study raises the possibility that interactions between IFNs and RA, in either a synergistic or antagonistic manner, may be mediated through amplification of the 2-5A system.

2',5'-Oligoadenylate Synthetase↗

PubMed1989

Dual function of monocytes on the regulation of granulopoiesis.

The intrinsic balance of monocyte-derived mediators in the regulation of granulopoiesis was studied. Both the granulocyte macrophage colony-stimulating factors (GM-CSFs) and the colony inhibitory factor (prostaglandin E2; PGE2), were found to be elaborated by cultured monocytes, and most of these mediators were secreted during the first 4 days after monocyte cultivation. The concentration of monocytes in culture had a direct effect on the amount of mediator production. A maximum amount of mediators was noted to range from 2 x 10(5)-2 x 10(6) monocytes per 35 mm Petri dish. It was also found that the monocytes responded to the exogenous stimulus (lipopolysaccharide, LPS) in a biphasic manner. The optimal concentration of LPS in stimulating production of the tested mediators was 3.2 micrograms/ml. At higher concentrations (greater than 3.2 micrograms/ml), both the release of GM-CSFs and PGE2 were suppressed. The addition of indomethacin to the culture system resulted in a confirmatory increase in GM-CSFs production at LPS concentration higher than 3.2 micrograms/ml. The response of monocytes to endogenous regulators (GM-CSFs and PGE2) was also determined. The addition of GM-CSFs to the cultures promoted PGE2 production by monocytes in dose-dependent with an optimal concentration of around 450 units/ml. Alternatively, treatment of monocytes with PGE2 (10(-9) to 10(-10) M) also enhanced, to a certain extent, the production of GM-CSFs. The coincidence of the peaks of GM-CSFs and PGE2 release demonstrated in vitro suggested the existence of an intrinsic balance mechanism in the regulation of granulopoiesis by monocytes.

Adult↗

PubMed1988

Testing for intron function in the essential Saccharomyces cerevisiae tRNA(SerUCG) gene.

The gene sup61+, which codes for the essential Saccharomyces cerevisiae tRNA(SerUCG), is the only single-copy tRNA gene in this organism know to contain an intron. To assess the role of this intron in tRNA gene expression, an intron-deleted sup61+ gene was constructed in vitro and introduced into the yeast genome. Isogenic intron- and intron+ strains were found to be indistinguishable by criteria that include growth rates, ability to undergo meiosis, levels of mature tRNA(SerUCG) transcribed in vivo, and the suppressor efficiency of amber- and ochre-specific alleles of this gene.

Genes, Fungal↗