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C H Tan

Publications and source records attributed to C H Tan.

At least 55 records · Page 3Linked to original sources
PubMed1999

In situ hybridization and immunohistochemical analysis of the expression of cardiotoxin and neurotoxin genes in Naja naja sputatrix.

Secretory processes and their regulation have been extensively studied in mammalian salivary parotid glands. However, little is known regarding the secretory mechanism in the venom glands of snakes, which invariably produce one of the most complex of all animal secretions. The pharmacologically important and toxic components of the Malayan spitting cobra (Naja naja sputatrix) venom include postsynaptic neurotoxins (NTX), presynaptic neurotoxins (phospholipase A2, PLA2), and cardiotoxins (CTX) which, for convenience, have been collectively referred to as "toxins." We report here for the first time the mechanism of toxin gene expression by studying the accumulated mRNA level and protein synthesis rates for the three toxins over a period of 8 days after stimulation of venom synthesis by manual "milking" of the venom gland. Immunofluorescence and in situ hybridization were used to localize the toxins and their mRNAs in venom gland sections. The rate of protein synthesis, as determined by immunofluorescence and liquid chromatography-mass spectrometry (LC-MS) techniques, increased in parallel with the increase in the toxin mRNA content in the secretory epithelial cells, suggesting that transcriptional regulation of the toxin genes is involved. (J Histochem Cytochem 47:551-560, 1999)

Animals↗
PubMed1999

Postsynaptic alpha-neurotoxin gene of the spitting cobra, Naja naja sputatrix: structure, organization, and phylogenetic analysis.

The venom of the spitting cobra, Naja naja sputatrix contains highly potent alpha-neurotoxins (NTXs) in addition to phospholipase A2 (PLA2) and cardiotoxin (CTX). In this study, we report the complete characterization of three genes that are responsible for the synthesis of three isoforms of alpha-NTX in the venom of a single spitting cobra. DNA amplification by long-distance polymerase chain reaction (LD-PCR) and genome walking have provided information on the gene structure including their promoter and 5' and 3' UTRs. Each NTX isoform is approximately 4 kb in size and contains three exons and two introns. The sequence homology among these isoforms was found to be 99%. Two possible transcription sites were identified by primer extension analysis and they corresponded to the adenine (A) nucleotide at positions +1 and -45. The promoter also contains two TATA boxes and a CCAAT box. Putative binding sites for transcriptional factors AP-2 and GATA are also present. The high percentage of similarity observed among the NTX gene isoforms of N. n. sputatrix as well as with the alpha-NTX and kappa-NTX genes from other land snakes suggests that the NTX gene has probably evolved from a common ancestral gene.

3' Untranslated Regions↗
PubMed1999

Trends in mortality, incidence, hospitalisation, cardiac procedures and outcomes of care for coronary heart disease in Singapore, 1991-1996.

In this study, we used Singapore population-based data from 1991 to 1996 to examine recent trends in mortality, incidence and hospitalisation for acute myocardial infarction (AMI), and explored the roles of primary prevention and medical care interventions in explaining these trends. We examined trends in medical interventions, namely coronary angiography (catheterisation), coronary artery bypass graft (CABG), and percutaneous transluminal coronary angioplasty (PTCA), length of stay, and payment methods, and explored the roles of technological, healthcare financing and delivery, and regulatory factors in influencing the diffusion and outcomes of these medical interventions. During the period 1991 to 1996, there were parallel declines in resident population rates of mortality, incidence and hospitalisation for AMI. The rates of angiograms, CABG and PTCA among residents also increased greatly, with the greatest increase among elderly aged 60 years and above. The rates of invasive cardiac procedures for AMI were all lower in females than in males. The population case-fatality rate of AMI declined slightly only for persons below 40 years of age. The case-fatality rate was higher in females than in males. The number of hospitalisations and cardiac procedures all rose sharply, and was phenomenal for PTCA (247%). The increase in volume of resource use was starkly greater in private hospitals than in restructured hospitals. The ratios of PTCA to CABG from 1991 to 1996 for private and restructured hospitals showed a greater rate of technology substitution in restructured hospitals than in private hospitals. The average length of stay (LOS, 6.7 days) was fairly constant in restructured hospitals. For private hospitals, LOS declined from 7.6 days in 1991 to 5.6 in 1996. LOS varied little among individual restructured hospitals, but widely among private hospitals. The most common method of payment for AMI hospitalisation was Medisave alone (50%), but for CABG surgery, the proportion of payment made through this method was only 12%. Out-of-pocket payments, Medisave, Medishield and private insurance have increased steadily. These data indirectly suggest that primary prevention and medical care interventions might have begun to succeed in reducing the rates of coronary heart disease in Singapore. The sharp increases in cardiac procedures may be explained by changing supply and demand factors for care of AMI and chronic ischaemic heart disease, including consumer preference for cardiac procedures, overuse of medical intervention, and technological change. More studies are needed to test these hypotheses.

Adult↗
PubMed1998

Structure and organization of the cardiotoxin genes in Naja naja sputatrix.

We report the genomic structure, organization and the presence of multiple isoforms of the gene encoding cardiotoxins (CTX) of Naja naja sputatrix. The cardiotoxin gene consists of six CTX isoforms, each (2.2 kb) having three exons and two introns. Two possible transcription initiation sites as well as consensus TATA boxes and transcription factor binding motifs, AP-2, NFIL-6/C/EBP, NF-kappaB and PuF have been identified in the 5'-region of the gene. The CTX gene isoforms show nucleotide variations at specific segments in exon 2 and exon 3, which correspond to the functional domains in the three-finger loop structure of the cardiotoxin molecule. The diverse functions of cardiotoxins together with our findings suggest that the cardiotoxin gene isoforms may have evolved under adaptive pressure through a positive Darwinian selection process.

Amino Acid Sequence↗
PubMed1998

Results of intermediate measures from a population-based, randomized trial of mammographic screening prevalence and detection of breast carcinoma among Asian women: the Singapore Breast Screening Project.

BACKGROUND: Although increasing rates of breast carcinoma incidence have been observed in Asian countries, appropriate strategies for detecting early stage breast carcinoma in such communities have been difficult to formulate, particularly because no large population screening trial specifically involving Asian women has been reported. The objective of this study was to evaluate the effectiveness and quality of mammography as a screening technique for Singaporean women, who are predominantly Chinese. METHODS: In this prospective study, 166,600 women in Singapore ages 50-64 years were randomized to either 2-view mammography without physical examination (67,656) or observation (97,294, controls) over 2 years. RESULTS: Of these women, 28,231 (41.7%) responded and were screened; they were more likely to be married, have more formal education, be working, be Chinese, and be in a higher socioeconomic group (P < 0.001 for all variables). To assess for response bias that could affect outcome, results were also evaluated for nonrespondents (n = 39,425). The incidence rate of cancers among nonrespondents (1 per 1000 woman-years) was less than the 1.3 in women not invited to have screening (P = 0.03, relative risk [RR], 1.3; 95% confidence interval [CI], 1.0-1.7). However, cancers arising from nonrespondents did not differ significantly in stage distribution when compared with cancers within the control group. For every 1000 women screened, 4.8 cancers were detected. The prevalence ratio (the number of cancers detected per 1000 women at first screening divided by the corresponding incidence rate in controls per year) was 3.6 for screened women and 2.4 for women invited to have screening. The majority of cancers detected through screening were early stage, with 64% as either ductal carcinoma in situ (26%) or Stage I disease (38%) and was significantly more than the corresponding 26% in women not invited to have screening (P < 0.001). When only invasive cancers were considered, screened women still had more early cancers, with 65% having no lymph node involvement, compared with 47% in the group not invited to have screening (P = 0.001; RR, 1.4; 95% CI, 1.2-1.7). Women who were screened had half the risk of having Stage II or later cancers (P < 0.0001; RR, 0.5; 95% CI, 0.4-0.7) when compared with women not invited to have screening. This higher detection rate of early cancers through screening was accomplished with acceptable recall rates of 8% for further mammographic films or physical examination and a biopsy rate of 1.0% (10 per 1000 women screened). The interval cancer rate was 2.1 per 10,000 women screened in the first year of follow-up. CONCLUSIONS: These positive results of intermediate measures suggest that, in Asian communities, screening mammography could be an important modality for detecting early stage breast carcinoma. However, the low compliance rates suggest that health education efforts must focus on issues related to acceptability if such programs are to succeed.

Aged↗
PubMed1998

Six isoforms of cardiotoxin in malayan spitting cobra (Naja naja sputatrix) venom: cloning and characterization of cDNAs.

Cardiotoxins are the most abundant toxin components of cobra venom. Although many cardiotoxins have been purified and characterized by amino acid sequencing and other pharmacological and biochemical studies, to date only five cardiotoxin cDNAs from Taiwan cobra (Naja naja atra), three cDNAs from Chinese cobra (Naja atra) and two more of uncertain origin (either Chinese or Taiwan cobra) have been reported. In this paper we show the existence of four isoforms of cardiotoxin by protein analysis and nine cDNA sequences encoding six isoforms of cardiotoxins (CTX 1-3, 4a, 4b and 5) from N. n. sputatrix by cDNA cloning. This forms the first report on the cloning and characterization of several cardiotoxin genes from a single species of a spitting cobra. The cDNAs encoding these isoforms, obtained by reverse transcription-polymerase chain reaction (RT-PCR), were subsequently expressed in Escherichia coli. The native and recombinant cardiotoxins were first characterized by Western blotting and N-terminal protein sequencing. These proteins were also found to have different levels of cytolytic activity on cultured baby hamster kidney cells. Four of the isoforms (CTX 1, 2, 4 and 5) are unique to N. n. sputatrix, with CTX 2 being the most abundant species constituting about 50% of the total cardiotoxins. The isoform CTX 3 (20% constitution) is highly homologous to the cardiotoxins of N. n. atra and N. n. naja, indicating that it may be universally present in all Naja naja subspecies. Our studies suggest that the most hydrophilic isoform (CTX 5) could have evolved first followed by the hydrophobic isoforms (CTX 1, 2, 3 and 4). We also speculate that Asiatic cobras could be the modern descendants of the African and Egyptian counterparts.

Amino Acid Sequence↗
PubMed1998

Synthesis of 17,20alpha/beta-dihydroxy-4-pregnen-3-one and 5beta-pregnanes in spermatozoa of primary and 17alpha-methyltestosterone-induced secondary male grouper (Epinephelus coioides).

The in vitro metabolism of [3H]17-hydroxyprogesterone by spermatozoa of primary and 17alpha-methyltestosterone (MT)-induced secondary male grouper (Epinephelus coioides) has been examined. With only the labeled precursor, the four predominant 5beta-pregnanes (17, 20alpha-dihydroxy-5beta-pregnan-3-one; 5beta-pregnan-3alpha,17, 20alpha-triol; 3alpha,17-dihydroxy-5beta-pregnan-20-one; and 17hydroxy-5beta-pregnan-3,20-dione) accounted for 75% of the total product yield, with the remainder comprising 17, 20alpha-dihydroxy-4-pregnen-3-one (17,20alphaP) and traces (3%) of 17,20beta-dihydroxy-4-pregnen-3-one. This is the first report of the synthesis of these 5beta-pregnanes by teleost spermatozoa. The addition of excess unlabeled precursor caused a marked shift to the synthesis of only 17,20alphaP. The steroidogenic profile in spermatozoa of the primary and secondary males appears similar in both cases. The shift to 17,20alphaP synthesis at high substrate concentration may suggest a gonadotropin (GtH) control of 17, 20alphaP synthesis, involving the competition for 17P between the high-activity, low-capacity 5beta-reductases and the low-activity, high-capacity 20alpha-HSD. Poor spermiation in MT-induced males may thus be due to the lack of 17P arising from low GtH secretion in vivo in the secondary males.

17-alpha-Hydroxyprogesterone↗
PubMed1998

Four new postsynaptic neurotoxins from Naja naja sputatrix venom: cDNA cloning, protein expression, and phylogenetic analysis.

cDNAs encoding 4 short chain alpha-neurotoxins from Malayan spitting cobra (Naja naja sputatrix) venom were cloned and expressed in Escherichia coli. The recombinant toxins possessed identical amino acid sequences to alpha-neurotoxins. This is the first report on cloning and expression of isoforms of neurotoxins from a species of spitting cobra. Two of these isoforms were also identified in the crude venom by reverse phase-high performance liquid chromatography (RP-HPLC), capillary electrophoresis followed by mass spectrometry and characterized by protein sequencing. Based on the variable amino acid residues, the neurotoxins in N. n. sputatrix could be assigned to 2 major groups, 10E11T and 10Q11A, which could be further subdivided into 10E11T28S: 10E11T28G and 10Q11A28S; 10Q11A28G respectively. These substitutions were also found to be unique to N. n. sputatrix neurotoxins. Phylogenetic analysis based on molecular properties of the toxins provided further support for the classification of N. n. sputatrix neurotoxin into 2 fundamental groups.

Amino Acid Sequence↗
PubMed1998

The effect of ketamine pretreatment on propofol injection pain in 100 women.

A controlled, randomised double-blind study was performed to compare the prior intravenous administration of ketamine 10 mg (1 ml) or 0.9% saline (1 ml) on propofol injection pain. One hundred patients of ASA status 1 or 2 presenting for gynaecological surgery were studied. Following an initial 5-ml bolus of propofol into a dorsal hand vein, 30 s after the treatment, 84% of the saline control patients experienced mild or severe pain compared to 26% of those who were given ketamine pretreatment (p < 0.05).

Adolescent↗
PubMed1998

Pain on injection of propofol.

Pain on injection of propofol is a common problem, the cause of which remains unknown. The chemical properties and preparation of propofol, proposed mechanisms for the cause of the pain and clinical strategies to prevent pain on injection of propofol are reviewed in the hope of shedding some light on the subject.

Anesthetics, Intravenous↗
PubMed1998

Population-based mammographic screening in Singapore: what are participants' views?

Mammographic screening for breast cancer has been shown to be an effective tool for reducing mortality from the disease in many studies in the West, if high technical quality and acceptance by the target population are achieved. The objective of the Singapore Breast Screening Project was to determine if the same results could be obtained among local women by inviting a random sample of 69,500 women aged 50 to 64 years for a screening mammogram over two years. To date, the compliance rate among the women invited has been 41.7%. The objective of the present substudy was to determine participants' views on the accessibility and acceptability of organised mammographic screening. Of the three hundred women interviewed, 85% were satisfied with the information given prior to the visit, while 67% needed to change the original appointment given. The majority were satisfied with aspects of the visit such as waiting time, privacy and explanation given during the test. However, 35.1% reported at least moderate discomfort during mammography. A substantial proportion (39.7%) of attenders felt that there was very little hope of cure even if cancer was detected early. When asked the most important reason for attending, most indicated they had taken the opportunity for a free check-up to be assured they were well. Almost all (95.7%) reported a willingness to be screened again, but most would not be willing to pay for a mammogram at the current rates.

Appointments and Schedules↗
PubMed1997

Biosynthesis in vivo and excretion of cortisol by fish larvae.

There is a posthatching rise in levels of endogenous cortisol during the ontogeny of those teleosts studied to date. This is thought to be the result of de novo synthesis of cortisol by the larvae, although there is no direct evidence for this. The present study aimed to demonstrate this process in Asian seabass (Lates calcarifer). Larvae (4 days posthatching) were maintained for up to 12 hours in seawater containing [3H]17 alpha-hydroxyprogesterone. High performance liquid chromatography analysis of extracts of the medium, before and after treatment with glucuronidase, indicates conversion of the precursor to several metabolites. One of these was identified as cortisol on the basis of its isopolarity with authentic standard in thin-layer chromatography, and confirmed by recrystallisation to constant specific activity. Immunohistochemistry on siblings shows that the interrenals are immunoreactive for adrenodoxin (adrenal ferredoxin) and cytochrome P-450(21) (steroid 21-monooxygenase [steroid, hydrogen-donor:oxygen oxidoreductase, 21-hydroxylating]; EC 1.14.99.10), and the pituitary for adrenocorticotrophic hormone. These findings suggest that the pituitary-interrenal axis is functional even at this early stage, and are consistent with the hypothesis that the posthatching rise in endogenous cortisol levels is the result of de novo steroidogenesis.

Animals↗
PubMed1997

Cloning and characterization of cDNAs encoding three isoforms of phospholipase A2 in Malayan spitting cobra (Naja naja sputatrix) venom.

cDNAs encoding three phospholipase A2 (PLA2) isoforms in Naja naja sputatrix were cloned and characterized. One of them encoded an acidic PLA2 (APLA) while the others encoded neutral PLA2 (NPLA-1 and NPLA-2). The specific characteristics of APLA and NPLA were attributed to mutations at nt139 and nt328 from G to C and G to A, respectively, resulting in amino acid substitutions from Asp20 and 83 in APLA to His20 and Asn83 in NPLA. Amino acid sequencing of purified protein also showed the presence of this Asp20 and His20 in APLA and NPLA, respectively. The cDNA encoding one of the PLA2 (NAJPLA-2A), when expressed in Escherichia coli, yielded a protein that exhibited PLA2 activity.

Amino Acid Sequence↗
PubMed1997

Factors determining acceptability of mammography in an Asian population: a study among women in Singapore.

Population-based mammographic screening has been shown to be effective in reducing breast cancer mortality in the West. In Singapore, a project carried out to determine the effectiveness of implementing such a program locally invited 28,000 women between the ages of 50 and 64 years for mammography. The current study, which was part of this larger project, was intended to determine factors contributing to the acceptance of mammographic screening among women in Singapore. A questionnaire was administered in-person to 300 attenders and 260 non-attenders. The respondents were compared with respect to basic demographic characteristics, previous preventive behavior, informal social support, and attitudes towards early detection. We found that screening attenders were more likely to be Chinese than Malays (14 percent of the population) or Indians (seven percent), and to be working outside the home (adjusted odds ratio [OR]) = 4.5, 95 percent confidence interval [CI] = 2.6-7.9). A greater proportion of attenders had a history of other screening tests such as the Pap smear (OR = 4.7, CI = 2.6-8.7 for recent smear compared with never having had a smear). They were also more likely to indicate a sense of personal susceptibility to cancer, but did not differ from non-attenders in terms of believing in cancer prevention, or of preferring to be told if they did have cancer. The strongest independent predictor of attendance, however, was encouragement by her spouse or family member. For women in this population to be persuaded effectively to participate in mammographic screening, it would be important to convince family members of the benefits of the test. At the same time, education targeted specifically at women of the appropriate age group should address the issue of the personal relevance of screening for breast cancer.

Breast Neoplasms↗