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Biomedical subjects

B C Tan

Publications and source records attributed to B C Tan.

At least 19 recordsLinked to original sources
PubMed2006

Lichens as bioindicators of atmospheric heavy metal pollution in Singapore.

Lichens have been used as bioindicators in various atmospheric pollution assessments in several countries. This study presents the first data on levels of heavy metals (As, Cd, Cu, Ni, Pb, and Zn) in lichens at different locations in Singapore, Southeast Asia. Singapore is a fully industrialised island nation, with a prevailing tropical climate and a population of 4 million people within a confined land area of less than 700 km2. The ubiquitous lichen species, Dirinaria picta was collected from six sample sites across Singapore and analysed for heavy metals using inductively coupled plasma mass spectrometry (ICPMS). No significant relationship existed between metal levels in lichen and soil, indicating that accumulated metals in lichen are primarily derived from the atmosphere. Peak concentrations of zinc (83.55 microg g(-1)), copper (45.13 microg g(-1)) and lead (16.59 microg g(-1)) in lichens were found at Sembawang, Jurong and the National University of Singapore campus which are locations associated with heavy petroleum and shipping industries, and road traffic respectively. The mean heavy metal levels of lichen samples in Singapore were found to be at the upper range of values reported in the literature for temperate countries.

Air Pollution↗
PubMed2006

Marjolin's ulcer--a near forgotten entity.

We report a case of a 55-year-old man who presented with a 6-month history of a fungating ulcer on the right hand at the site of a previously healed ulcer that had been present for 40 years. Histopathological examination of four-quadrant biopsy specimens showed a moderately differentiated squamous cell carcinoma (SCC). A transradiocarpal amputation with stump closure using radial flap was performed as it was not possible to achieve a functionally and cosmetically acceptable hand after a wide excision with 2 cm tumour-free margin. It is our intention to highlight this rare condition as reminder to consider this entity as a differential diagnosis of chronic non-healing skin ulcer.

Acro-Osteolysis↗
PubMed2001

Causes of childhood blindness in Malaysia: results from a national study of blind school students.

A national study was conducted in children attending six schools for the blind in Malaysia to identify the anatomical site and underlying causes of blindness (BL) and severe visual impairment (SVI), with a view to determine the potentially preventable and treatable causes so that appropriate control measures can be implemented in the future. The standardized clinical examination of eyes was performed and the findings were recorded on the WHO Prevention of Blindness Programme eye examination record form for children with blindness and low vision. A total of 358 children aged between 7 and 17 years were examined, of whom 332 (92.7%) were blind or severely visually impaired. The results relate to these 332 children. Lens was the major anatomical site (22.3%) of visual loss followed by retina (20.8%), whole globe (17.2%), cornea (15.1%), optic nerve (8.7%) and uvea (5.1%). Glaucoma was responsible for BL/SVI in 7.2% and others in 3.6% of cases. Hereditary diseases were responsible for visual loss in 29.5%, intrauterine factors in 4.5%, perinatal factors in 9% and childhood factors in 7.8% of cases. However, the aetiology was unknown in 49.1% of cases which included congenital anomalies of the globe. Childhood cataract and corneal scarring are major treatable causes of BL/SVI that can benefit from future intervention strategies. Perinatal screening for intrauterine factors and hereditary eye diseases, and appropriate interventional therapy will help in reducing the prevalence of childhood blindness.

Adolescent↗
PubMed2001

Localization and targeting of the VP14 epoxy-carotenoid dioxygenase to chloroplast membranes.

Abscisic acid (ABA) is a key regulator of seed dormancy and plant responses to environmental challenges. ABA is synthesized via an oxidative cleavage of 9-cis epoxy-carotenoids, the first committed and key regulatory step in the ABA biosynthetic pathway. Vp14 of maize encodes an epoxy-carotenoid dioxygenase that is soluble when expressed in E. coli. An important goal has been to determine how the soluble VP14 protein is targeted to epoxy-carotenoid substrates that are located in the thylakoid and envelope membranes of chloroplasts and other plastids. Using an in vitro chloroplast import assay, we have shown that VP14 is imported into chloroplasts with cleavage of a short stroma-targeting domain. The mature VP14 exists in two forms, one which is soluble in stroma and the other bound to thylakoid membranes. Analysis of a series of truncated VP14 mutants mapped the membrane targeting signal to the 160 amino acid N-terminal sequence. A putative amphipathic alpha-helix within this region is essential, but not sufficient, for the membrane targeting. Either deletion of or insertion of helix breaking residues into this region abolished the membrane binding, whereas a chimeric protein carrying just the amphipathic region fused with bacterial glutathione S-transferase failed to associate with the thylakoid membrane. The membrane-bound VP14 was partially resistant to chaotropic washes such as 0.1 M Na2CO3 (pH 11.5) and 6 M urea. Unlabelled recombinant VP14 inhibited the tight binding of imported VP14, suggesting that VP14 is associated with specific components of the thylakoid membrane.

Amino Acid Sequence↗
PubMed1997

Genetic control of abscisic acid biosynthesis in maize.

Abscisic acid (ABA), an apocarotenoid synthesized from cleavage of carotenoids, regulates seed maturation and stress responses in plants. The viviparous seed mutants of maize identify genes involved in synthesis and perception of ABA. Two alleles of a new mutant, viviparous14 (vp14), were identified by transposon mutagenesis. Mutant embryos had normal sensitivity to ABA, and detached leaves of mutant seedlings showed markedly higher rates of water loss than those of wild type. The ABA content of developing mutant embryos was 70% lower than that of wild type, indicating a defect in ABA biosynthesis. vp14 embryos were not deficient in epoxy-carotenoids, and extracts of vp14 embryos efficiently converted the carotenoid cleavage product, xanthoxin, to ABA, suggesting a lesion in the cleavage reaction. vp14 was cloned by transposon tagging. The VP14 protein sequence is similar to bacterial lignostilbene dioxygenases (LSD). LSD catalyzes a double-bond cleavage reaction that is closely analogous to the carotenoid cleavage reaction of ABA biosynthesis. Southern blots indicated a family of four to six related genes in maize. The Vp14 mRNA is expressed in embryos and roots and is strongly induced in leaves by water stress. A family of Vp14-related genes evidently controls the first committed step of ABA biosynthesis. These genes are likely to play a key role in the developmental and environmental control of ABA synthesis in plants.

Abscisic Acid↗
PubMed1997

Specific oxidative cleavage of carotenoids by VP14 of maize.

The plant growth regulator abscisic acid (ABA) is formed by the oxidative cleavage of an epoxy-carotenoid. The synthesis of other apocarotenoids, such as vitamin A in animals, may occur by a similar mechanism. In ABA biosynthesis, oxidative cleavage is the first committed reaction and is believed to be the key regulatory step. A new ABA-deficient mutant of maize has been identified and the corresponding gene, Vp14, has been cloned. The recombinant VP14 protein catalyzes the cleavage of 9-cis-epoxy-carotenoids to form C25 apo-aldehydes and xanthoxin, a precursor of ABA in higher plants.

Abscisic Acid↗
PubMed1996

Patient profile and survival in 270 computer tomography-staged patients with nasopharyngeal cancer treated at the Singapore General Hospital.

This is a report analysing the patient profile and survival results in 270 patients with nasopharyngeal carcinoma treated with radiation therapy between July 1987 and December 1988. The patients had a median age of 52.6 months, and a male-female ratio of 2.5:1. Ninety-four percent of patients were Chinese. The commonest presentation was that of a neck mass (found in approximately 65% of patients). Approximately two-thirds presented with disease more advanced than Ho's stage II. At a median follow-up of 52.6 months, the 5-year actuarial survival rate was 53% and the freedom from relapse rate was 57%. One hundred and seven patients died within the observation period. Of these, 46 patients had disease in the post nasal space, 41 in the neck and 60 in sites outside the head and neck.

Actuarial Analysis↗
PubMed1989

Lung cancer metastases--management.

Distant metastases from lung cancer is a common occurrence in a common malignancy. Almost every organ may be involved but the extra-thoracic sites posing common clinical problems are brain metastases, cord compression, painful bone metastases or pathological fractures, nodal spread and liver involvement. A review of the records of 225 lung cancer patients referred to the Therapeutic Radiology Department, Singapore General Hospital, during the calender year 1985 showed a metastatic rate of 13.8% at referral. On subsequent follow up, an additional 49 patients (21.7%) developed metastases clinically. The organs involved were bone (21 patients), spinal cord (21 patients), brain (18 patients), liver (13 patients), other lung (7 patients) and other sites (17 patients). The management of metastases to the brain, bone and liver, and spinal cord compression will be discussed.

Adenocarcinoma↗
PubMed1989

Conservation breast treatment: a viable option locally.

Conservation treatment in carcinoma of the breast is a viable option in the West but is still an uncommon practice locally. Many reasons have been put forth, including the late stage of the tumour we see and the small breast size. This paper presents 25 cases treated by lumpectomy and irradiation with satisfactory cosmetic results, although the follow-up period is short. The introduction of this technique may encourage women to seek treatment earlier, without the fear of losing their breasts.

Adult↗
PubMed1989

Stellate- and foci-formation of mouse fibroblast cells transfected with various cancer cell DNA.

Two methods of DNA-mediated gene-transfer, namely, CaPO4 co-precipitation and polybrene/DMSO-induction were used to analyse oncogenes from various cancer cell-lines. Third time transfection of mouse fibroblast cells, NIH/3T3 with 10, 100, 1,000 and 3,000 ng of DNA from spontaneous human hepatoma cells produced 41, 4, 45 and 56 foci, respectively. It appears that 100 ng of this hepatoma cell DNA gave the least effective transformation ability. However, with two spontaneous mammary cancer cell lines, 100 ng DNA gave the highest number of foci. In general, during the initial transfection, the cells appeared semi-transformed, showing stellate growth patterns. With repeated transfections they gave way to foci. However, with aflatoxin-induced rat hepatoma cell (JB-1) DNA, only stellate growths persisted to indicate intermediate transformation. Transfection of the epithelial-like normal rat liver cell line, BL8 with JB-1 DNA produced haphazard growth pattern, although a hepatoma-associated enzyme, gamma-glutamyl transferase was introduced into the BL8 cells which previously had no detectable enzyme activity.

Animals↗
PubMed1988

Radiotherapy of early glottic cancer Singapore, 1978-1981.

This study analyses the results of primary radiotherapy for 44 patients with early glottic cancer (Tis, T1 stage) given at the Therapeutic Radiology Department, Singapore General Hospital during the 4-year period from 1978 to 1981. Irradiation was delivered using cobalt teletherapy with free set-ups, and without "air-gap" compensation. Total doses of 55Gy to 64Gy were given in daily fractions of 1.8Gy, treating five times a week. The crude 5-year survival rate for Tis/T1a tumours was 88.9% and for T1b lesions, 81%. On correcting for deaths from intercurrent disease, the survival rates improved to 95.5% and 92.6% respectively. In 33 cases where the quality of voice after radiation was assessed, 15 patients (45.4%) retained good voice quality with an additional 11 patients (33.3%) having acceptable voice quality. In seven cases the voice after radiation was rated as poor. Nine patients had local recurrence, giving a rate of 20.4%. One other patient had cervical node metastasis and subsequently developed lung secondaries. Surgery, solely or with re-irradiation, was an effective treatment for local recurrence. Re-irradiation alone failed to control any case with recurrence.

Carcinoma, Squamous Cell↗
PubMed1988

Hyperthermia with radiotherapy.

The use of hyperthermia together with radiotherapy in the treatment of relatively radioresistant tumours has been widely studied. In this preliminary non control study we used a 8MHz RF capacitive heating machine together with temperature probes inserted into the tumours under local anaesthesia. 27 patients with advanced post-radiation tumour recurrences as well as known radioresistant tumours were selected for treatment with hyperthermia and radiation. 7 patients withdrew from the study because of their intolerance to heat. 3 patients received superficial skin burns. Of the 20 patients studied, we were able to obtain moderate hyperthermia in most cases. 2 patients showed complete responses and 13 partial responses, giving rise to a total response rate of 75%. Some of the technical difficulties in achieving satisfactory hyperthermia are discussed. These include insertion of multiple probes into the body and the problem of achieving uniform heating of the tumour. Advances in hyperthermia can be expected with the development of improved methods of heat delivery and temperature measurements. However, presently methods of heat delivery can be improved by careful adjustment of the heating applicators and manipulation of cooling pads to avoid areas of excessive heating. Further clinical trials should be carried out to establish the optimum technique of hyperthermia.

Adult↗
PubMed1987

Advanced colorectal carcinoma--5 year survival of 76 cases treated at the Department of Therapeutic Radiology, Singapore General Hospital.

The results of 76 cases of advanced colorectal carcinoma treated at the Department of Therapeutic Radiology, Singapore General Hospital, from 1977 to 1978, are presented. All cases had "Curative" Surgery and were given adjuvant radiotherapy or chemotherapy or both. All were adenocarcinoma and had lymph node involvement as well as tumour infiltration through the bowel wall. 44 cases of rectal carcinoma were given radiotherapy to the pelvis followed by I/V 5-fluorouracil for at least one year. 32 cases of colon cancer were given I/V 5-fluorouracil for at least one year. 20 of these cases had cancer of the sigmoid colon and were given pelvic irradiation as well. The five year actuarial survival rates were 27.8% for rectal cancer and 24.3% for colon cancer.

Actuarial Analysis↗
PubMed1985

Radiotherapy of carcinoma of the uterine cervix in Singapore, 1973-1975.

The results of 322 patients with uterine cervix carcinoma treated by radiotherapy at the Singapore General Hospital in the 3-year period from 1973 to 75 are presented. Two hundred seventy-nine patients were treated with a combination of intracavitary radium, using Fletcher-Suit applicators and cobalt teletherapy; the remaining 43 patients received only cobalt teletherapy. One hundred thirty-four patients (41.6%) presented with FIGO Stage III disease. Only 46 patients (14.3%) presented with Stage I disease, showing that patients tended to present late in the disease course. Five-year actuarial (uncorrected) survival rates of 86.7% for Stage I, 65.0% for Stage II, 41.4% for Stage III and 4.9% for Stage IV were obtained with corresponding 10 year rates of 79.6%, 60.2%, 35.2% and 0%. The overall 5 and 10 year survival rates were 54.0% and 48.2%, respectively. The survival rates "flattened off" at about 7-8 years, reflecting late deaths after the fifth anniversary of treatment. Non-severe complications consisted mainly of chronic proctitis (41.3%) and vaginal stenosis (20.8%). Major complications were intestinal stricture (1.2%) and fistula formation (1.6%).

Adult↗