PubMed Health⌕ Search

Biomedical subjects

K L Ng

Publications and source records attributed to K L Ng.

At least 19 recordsLinked to original sources
PubMed2006

A two-stage refinement approach for the enhancement of excretory production of an exoglucanase from Escherichia coli.

Hyper-expression of a secretory exoglucanase, Exg, encoded by the cex gene of Cellulomonas fimi was previously shown to saturate the SecYEG pathway and result in dramatic cell death of recombinant Escherichia coli (Z.B. Fu, K.L. Ng, T.L. Lam, W.K.R. Wong, Cell death caused by hyper-expression of a secretory exoglucanase in Esherichia coli, Protein Expr. Purif. 42 (2005) 67-77). We propose here that the cell lysate ratio (Pre/Mat RQ) of the unprocessed precursor Exg protein (Pre-Exg) and its processed mature product (Mat-Exg) reflects the capacity of E. coli to secrete Exg. A Pre/Mat RQ of 20/80, designated the "Critical Value," was an important threshold measurement. A rise in the Pre/Mat RQ triggered a mass killing effect. The use of various secretion signal peptides did not improve the viability of cells expressing high levels of Pre-Exg under strong tac promoter control. However, use of the weaker vegG promoter in conjunction with a change in start codon of the spa leader sequence from ATG to TTG in a pM1vegGcexL plasmid construct resulted in a high level (0.9 U ml(-1)) of excreted Exg in shake-flask cultures. This was 50% higher than the best result obtained from plasmid construct lacUV5par8cex, using the lacUV5 promoter and the ompA leader sequence. Variations in the excreted Exg activities were attributable to differences in the Pre/Mat RQ values of the induced cultures harboring pM1vegGcexL and lacUV5par8cex. These values were 18/82 and 10/90, respectively. Employing fed-batch cultivation in two-liter fermentors, an induced JM101(pM1vegGcexL) culture yielded 4.5 U ml(-1) of excreted Exg, which was over six fold greater that previously reported. Our results illustrate the successful application of the Pre/Mat RQ ratio as a guide to the attainment of a maximum level of secreted/excreted Exg.

Cell Death↗
PubMed2006

Prevalence of microplastics in Singapore's coastal marine environment.

Microplastics have been recently identified as marine pollutants of significant concern due to their persistence, ubiquity and potential to act as vectors for the transfer and exposure of persistent organic pollutants to marine organisms. This study documents, for the first time, the presence and abundance of microplastics (>1.6 microm) in Singapore's coastal environment. An optimized sampling protocol for the collection and analysis of microplastics was developed, and beach sediments and seawater (surface microlayer and subsurface layer) samples were collected from nine different locations around the coastline. Low density microplastics were separated from sediments by flotation and polymer types were identified using Fourier transform infrared (FTIR) spectrometry. Synthetic polymer microplastics identified in beach sediments included polyethylene, polypropylene, polystyrene, nylon, polyvinyl alcohol and acrylonitrile butadiene styrene. Microplastics were detected in samples from four out of seven beach environments, with the greatest quantity found in sediments from two popular beaches in the eastern part of Singapore. Polyethylene, polypropylene and polystyrene microplastics were also found in the surface microlayer (50-60 microm) and subsurface layer (1m) of coastal waters. The presence of microplastics in sediments and seawater is likely due to on-going waste disposal practices from industries and recreational activities, and discharge from shipping.

Bathing Beaches↗
PubMed2005

Cell death caused by hyper-expression of a secretory exoglucanase in Escherichia coli.

Induced expression of a gene fusion between the ompA leader sequence and the Cellulomonas fimi cex gene encoding a secretory exoglucanase, Exg, engineered in the Tac-cassette excretion vector was lethal to Escherichia coli. An exponentially growing culture harboring the recombinant construct suffered slow growth and 99.9% of its cells died within 60-100 min after induction. This abnormality was found to have a close correlation with the rapid increase in the relative amount of the OmpA/Exg fusion precursor (Pre-Exg) compared to its processed product (Mat-Exg). Analysis of subcellular fractions revealed the presence of Pre-Exg in the inner membrane of cultures expressing high levels but not low levels of Pre-Exg. As only Pre-Exg but not Mat-Exg was detectable in the cytoplasm, and Exg was shown by cross-linking experiments to be physically associated with the Sec proteins, it was concluded that secretion and processing of Pre-Exg took place in the SecYEG translocation machinery. The results were in line with the previous speculation that accumulation of unprocessed precursor proteins in the cytoplasmic membrane was detrimental, and supported the idea that cell death was caused by some unusual tie-up of Pre-Exg with the SecYEG translocation machinery, thus imposing an inhibitory effect on the secretion of endogenous secretory proteins. A new model, designated "Saturated Translocation," was proposed to explain the interchangeable lethal and non-lethal properties of Pre-Exg, and to address the possible scenarios that might occur in the course of cell death triggered by secretion of Pre-Exg.

Bacterial Outer Membrane Proteins↗
PubMed2005

Novel growth hormone receptor mutation in a Chinese patient with Laron syndrome.

Laron syndrome, growth hormone (GH) insensitivity syndrome, caused by a mutation of the GH receptor (GHR) gene, is extremely rare in the Chinese population. We report a Chinese girl diagnosed with Laron syndrome at age 1.9 years with height -4.9 SDS, basal GH 344 mIU/ml, IGF-I <12 ng/ml, IGFBP-3 <0.2 mg/ml, and undetectable GHBP. A novel mutation of the GHR, not previously described, was identified at the donor splice site of intron 6.

Amino Acid Substitution↗
PubMed2003

Severe acute respiratory syndrome in children: experience in a regional hospital in Hong Kong.

OBJECTIVE: To report the clinical, laboratory, and radiologic features of children with severe acute respiratory syndrome (SARS) and to examine the difference between the younger and older age groups. DESIGN: Retrospective descriptive cohort study. SETTING: A regional hospital in Hong Kong. PATIENTS: Children younger than 18 yrs with SARS. RESULTS: Twenty-one children were included, with a mean age of 10.7 +/- 5.1 yrs. Children with SARS presented with fever, nonproductive cough, malaise, chills, headache, myalgia, and loss of appetite. Examination of the chest showed minimal auscultatory findings. Common laboratory findings included lymphopenia, thrombocytopenia, and mild elevations of activated partial thromboplastin time, alanine transaminase, lactic dehydrogenase, and creatine phosphokinase. Bacteriologic and virologic studies were all negative for common pathogens. Unilateral focal opacity was the commonest finding in chest radiography. High-resolution computerized tomography of the thorax was an early diagnostic tool if the chest radiograph was negative. The clinical course was less severe in comparison with adult patients. However, adolescents (age, > or =12 yrs) resembled adults in their clinical features. When compared with the younger age group, the adolescents had significantly higher temperatures, more constitutional upset, and a greater need for steroid treatment. Children younger than 12 yrs seemed less ill but had more coughing. On the whole, the outcome was favorable. CONCLUSION: Severe acute respiratory syndrome affects children, but the course is less severe. Nevertheless, the disease could have a significant psychosocial impact on children because of the potential seriousness of the disease in their adult family members.

Adolescent↗
PubMed2003

Consensus statement on iodine deficiency disorders in Hong Kong.

This article reviews the available data on the study of iodine deficiency disorders in Hong Kong and to discuss the approach towards preventing such disorders in Hong Kong. The importance of iodine and iodine deficiency disorders is described, and the available data on the dietary iodine intake and urinary iodine concentration in different populations of Hong Kong are summarised and discussed. Dietary iodine insufficiency among pregnant women in Hong Kong is associated with maternal goitrogenesis and hypothyroxinaemia as well as neonatal hypothyroidism. Borderline iodine deficiency exists in the expectant mothers in Hong Kong. Women of reproductive age, and pregnant and lactating women should be made aware and educated to have an adequate iodine intake, such as iodised salt, as an interim measure. A steering group involving all stakeholders should be formed to advise on the strategy of ensuring adequate iodine intake, including universal iodisation of salt in Hong Kong. Continuous surveillance of iodine status in the Hong Kong population is necessary.

Deficiency Diseases↗
PubMed2003

Gastrointestinal Cytomegalovirus infection in non-human immunodeficiency virus infected patients.

This is a retrospective study of fourteen patients who had proven Cytomegalovirus (CMV) infection of the gastrointestinal tract with no Human Immunodeficiency virus infection. The median age was 60.5 (Range 28 to 81) years. Eight patients were below (Group 1) and six above sixty five years old (Group 2). Areas of gastro-intestinal involvement were: oesophagus (2), stomach (1), colon (10) and multiple sites (1). Seven patients from Group 1 had received immunosuppressive therapy at the time of presentation and one had diabetes mellitus. We found a high prevalence of co-morbidities such as chronic renal failure and diabetes mellitus in Group 2. At median follow up of 13.9 months, there was a mortality rate of 50%. Only four patients were treated with ganciclovir. Our study concludes that the gastrointestinal CMV diseases in young patients were associated with immunosuppression whereas the older patients had chronic renal failure or diabetes.

Adult↗
PubMed2003

Audit of investigations in patients with iron deficiency anaemia.

BACKGROUND: Patients with iron deficiency anaemia (IDA) are commonly referred to the gastroenterologists for exclusion of gastrointestinal (GI) pathologies. The British Society of Gastroenterology (BSG) has published a guideline for management of IDA. As recommended by this guideline, all patients should have examinations of both upper and lower GI tract with the exception of pre-menopausal women younger than 45 years old. The primary aim of this audit was to determine how thoroughly patients referred to our unit at the Singapore General Hospital had been investigated. The secondary aim was to determine the yield rate of gastroscopy and lower gastrointestinal investigations (colonoscopy or barium enema) in our patients. METHODS: We reviewed the case notes of patients who underwent gastroscopy for indication of anaemia between the period from April to December 1999. We classified iron deficiency anaemia as having haemoglobin of lower than reference range with either low ferritin level or iron/ TIBC ratio of less than 10%. RESULTS: Of a total of 326 patients reviewed, 172 patients (65 men, 109 women) met the inclusion criteria of IDA. The median age for the group was 59 (Range 16 to 88) years old and there were 107 (62.2%) women. There were 31 female patients younger than 45 years old (group A) and 141 patients in group B which included all the males and females older than 45 years old. Due to the method of data retrieval, all of the patients in group A fulfilled the standard set by the BSG guideline in that they all underwent gastroscopy. In this group, few gastrointestinal pathologies were found (one patient with peptic ulcer and two patients with colonic cancer). In terms of finding potential gastrointestinal causes of IDA, the yield rate of gastroscopy and colonoscopy were 3.2% and 13.6% respectively. In group B, 96 patients (68%) underwent upper and lower gastrointestinal investigations. Evaluation with gastroscopy showed peptic ulcer disease in 31 patients (21.7%) and gastric cancer in 9 patients (6.3%). Only 96 patients (68.1%) in group B had lower gastrointestinal investigations. Twenty-six patients were found to have gastrointestinal disorders (12 patients with colon cancer, 10 colonic polyps, one Crohn's disease, one colonic tuberculosis and two haemorrhoids). The yield rate of gastroscopy and colonoscopy were 31.2% and 25% respectively. CONCLUSION: In this study of patients with confirmed IDA, we found much higher incidence of gastrointestinal disorders in the group of male and postmenopausal women than in the group with premenopausal women. Furthermore, over 30% of patients in this group did not undergo lower gastrointestinal tract investigations as recommended by the BSG guideline. We also found two cases of colonic cancer in the latter group. We would recommend bidirectional endoscopy for postmenopausal women and men with IDA. For premenopausal women, we would recommend similar approach unless there are clinical pointers to dietary iron deficiency or menorrhagia.

Adolescent↗
PubMed2002

Appendicitis following blunt abdominal trauma.

A young boy presented with history of abdominal trauma. History and initial clinical findings suggested a soft tissue injury. Due to increasing abdominal pain and fever, we proceeded with an exploratory laparotomy with a diagnosis of intra-abdominal injury, at which we found a perforated appendix. Appendicitis following blunt abdominal trauma needs high index of suspicion.

Abdominal Injuries↗
PubMed2001

Retention modelling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography. II. Calculations of adsorption coefficients in unbuffered eluents.

Previous models for the retention behaviour of carboxylic acids in ion-exclusion chromatography are applicable only when the degree of ionisation of the analyte is constant over the entire chromatographic peak. When solutions of sulfuric acid are used as eluents, this condition applies only when the eluent concentration is considerably higher than that of the analyte. Since it is common for dilute solutions of sulfuric acid to be used as eluents, a retention model which accounts for unbuffered eluents has been developed. This model also considers the effects on retention of hydrophobic adsorption of the undissociated and dissociated forms of the analyte onto the stationary phase substrate, as well as the effects of organic solvents added to the eluent. The derivation of this model is presented and it has been evaluated using a comprehensive set of retention data obtained using three different sulfonated stationary phases over a range of eluent conditions. The adsorption coefficients calculated from the model are in accordance with expected trends and showed that both the undissociated and dissociated forms of the analyte acids were retained by hydrophobic adsorption effects, although this adsorption was much stronger for the undissociated analytes.

Adsorption↗
PubMed2000

Pituitary-gonadal axis in male undermasculinisation.

AIMS: To study the value of assessing serum concentrations of luteinising hormone (LH), follicle stimulating hormone (FSH), testosterone, and dihydrotestosterone (DHT) in patients with male undermasculinisation not caused by androgen insensitivity. METHODS: A retrospective study of a register of cases of male undermasculinisation (20 with abnormal testes, eight with 5alpha-reductase deficiency, three with testosterone biosynthetic defects, seven with Drash syndrome, and 210 undiagnosed). RESULTS: A human chorionic gonadotropin (hCG) stimulation test was performed in 66 of 185 children with male undermasculinisation. In 41 of 66 patients the dose of hCG was either 1000 U or 1500 U on three consecutive days. The rise in testosterone was related to basal serum testosterone and was not significantly different between the two groups. Testosterone:DHT ratio in patients with 5alpha-reductase deficiency was 12.5-72.8. During early infancy, baseline concentrations of LH and FSH were often within normal reference ranges. In patients with abnormal testes, median pre-LHRH (luteinising hormone releasing hormone) concentrations of LH and FSH were 2 and 6.4 U/l, respectively, and post-LHRH concentrations were 21 and 28 U/l. An exaggerated response to LHRH stimulation was observed during mid-childhood in children where the diagnosis was not clear and in all children with abnormal testes. CONCLUSIONS: The testosterone:DHT ratio following hCG stimulation is more reliable than the basal testosterone:DHT ratio in identifying 5alpha-reductase deficiency. During infancy, the LHRH stimulation test may be more reliable in identifying cases of male undermasculinisation due to abnormal testes than basal gonadotrophin concentrations.

Adolescent↗
PubMed1999

Retention modelling of electrostatic and adsorption effects of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography.

The retention mechanism of aliphatic and aromatic carboxylic acids in ion-exclusion chromatography has been investigated with consideration of simultaneous electrostatic repulsion effects and hydrophobic adsorption effects. A mathematical relationship between the retention factor of the analyte and the mobile-phase composition (sulfuric acid concentration and percentage of methanol), the type of analyte (pKa and hydrophobicity) and some physical characteristics of the stationary phase has been derived. Thirteen carboxylic acids (comprising mono- and divalent, aliphatic and aromatic acids) were chosen and used to acquire retention data on three different cation-exchange stationary phases (in which the sulfonate functional groups are bound to polystyrene-divinylbenzene, polymethacrylate or silica) using 14 mobile-phase compositions of varying pH and percent methanol. These retention data were used to derive the parameters necessary to solve the retention model using non-linear regression. In this way, a quantitative measure of the effects of adsorption phenomena on analyte retention were obtained. The model was then used to optimise the separation of nine carboxylic acids.

Carboxylic Acids↗
PubMed1999

Effect of dietary macronutrients on food intake, body weight, and tail width in the marsupial S. crassicaudata.

The role of dietary fat, as opposed to total energy intake, in the etiology of obesity is controversial. The aim of this study was to determine the effect of macronutrient content, specifically changes in dietary fat on body weight, fat stores, and food intake in S. crassicaudata, a marsupial that stores about 25% of total body fat in its tail. Female animals were divided into three groups (n = 7-9) matched for food intake per gram of body weight. Each group of animals was fed, ad lib an isocaloric diet (1.01 kcal/g), which contained either 10, 20, or 40% of calories from fat. Body weight, food intake, and tail width (an index of body fat stores) were measured daily. Over 21 days, cumulative energy intake was less (p = 0.026) in the 40% fat group compared to the 10% fat group. Despite the differences in food intake, body weight in each group remained stable throughout the study, so that at day 21 there were no differences in the body weights between the three groups. In contrast, tail width increased in the animals who received the 40% fat diet compared to either the 10% (p = 0.016) or 20% (p = 0.001) fat intake groups, whereas there was no significant change in tail width in either of these two groups. These observations indicate that macronutrient composition has a role, independent of total calories in the regulation of food intake and body fat stores, specifically that dietary fat promotes adiposity, independent of total caloric intake.

Animals↗
PubMed1999

Sexual dimorphism in the neonatal gonad.

The neonatal gonad has two distinct forms (i.e., is sexually dimorphic), as judged by morphological and endocrine characteristics. The dimorphic process begins early in embryogenesis. It is well established by the time of birth, by which time the genital ridge has developed into either a testis or an ovary. The mechanisms involved in sex determination involve the Y chromosome, autosomal genes, transcription factors and possibly other unidentified control networks. This review paper describes the morphological changes that occur and the endocrine functions in the developing gonads. It highlights a number of important differences in fetal and neonatal gonadal function. The testis has early histological definition, several determining genes, delayed germ cell maturation, early autonomous steroid secretion, luteinizing hormone (LH) receptor and steroid enzyme expression, high fetal testicular testosterone content, prominent postnatal Leydig and Sertoli cells and high postnatal serum testosterone levels. The ovary has a prolonged monomorphic state, probably one determining gene, germ cells in early meiotic arrest, delayed expression of LH receptor and aromatase, low ovarian oestradiol content, prominent postnatal follicles and low postnatal serum oestradiol levels.

Embryonic and Fetal Development↗
PubMed1997

Fundamentals for establishing a risk communication program.

This paper provides a suggested outline for developing a risk communication organizational plan that could be used by a variety of federal, state, or private agencies. Drawing on various techniques presented in the literature and on the authors' insights, suggestions are provided as to how to formulate and convey risk messages. First, the paper provides a few risk communication fundamentals including definitions, the goal of informing vs. influencing, the importance of public participation in risk management, building trust and credibility, the consideration of outrage, and the importance of oral and visual communications. Second, a stepwise approach synthesized by the authors is presented that can be applied in developing a risk communication program. The approach is a 13-step method based on the premise that the risk communication program should be dynamic, flexible, and involve interaction with the public at every possible step.

Communication↗
PubMed1995

Neurosarcoidosis masquerading as glioma of the optic chiasm in a child.

We present a case of sarcoidosis in a 14-year-old girl who presented with a short history of visual disturbance. Computed tomography and magnetic resonance imaging (MRI) demonstrated enlargement of the optic chiasm and prechiasmic optic nerves. Post-contrast MRI showed marginal enhancement of the affected areas of the optic pathways. A diagnosis of optic nerve glioma and arachnoid gliomatosis was made; surgical confirmation was not sought due to the risk to vision associated with biopsy. A rapid clinical deterioration led to repeat MRI which demonstrated extensive enhancing soft tissue throughout the basal cisterns with extension into the brain. Biopsy confirmed a diagnosis of sarcoidosis.

Adolescent↗
PubMed1995

CT and MR appearance of otolaryngologic packing materials.

PURPOSE: To examine the CT and MR appearances of four packing materials commonly used in otolaryngologic surgery. METHODS: The CT and MR appearances of bismuth and iodoform paraffin paste, aqueous betadine gauze, calcium sodium alginate, and triadocortyl cream were examined. CT attenuation values were measured using phantoms containing packing materials. MR characteristics were examined by packing the external auditory meati of volunteers. Two illustrative case reports also are presented. RESULTS: Bismuth and iodoform paraffin paste has a high CT attenuation (> 3000 Hounsfield units) resulting in severe image degradation attributable to streak artifact. Aqueous betadine gauze was of high attenuation (258 Hounsfield units; SD, 16.5) but did not cause image degradation. The attenuation values of calcium sodium alginate and triadocortyl creme coincided with those of muscle and fat, respectively. On MR, calcium sodium alginate and bismuth and iodoform paraffin paste had imaging characteristics similar to muscle and aqueous betadine gauze had appearances similar to bone marrow. Triadocortyl cream had a high signal equal to that of fat on T1-weighted images but a lower signal similar to bone marrow on T2-weighted images. CONCLUSIONS: The presence of bismuth and iodoform paraffin paste can give rise to clinically important image degradation on CT. More seriously, residual packing material may be misinterpreted as infection or tissue necrosis.

Adolescent↗