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Biomedical subjects

A Ng

Publications and source records attributed to A Ng.

At least 55 records · Page 3Linked to original sources
PubMed2000

Design and solution structure of a well-folded stack of two beta-hairpins based on the amino-terminal fragment of human granulin A.

Four amino acid substitutions were introduced into a peptide corresponding to the amino-terminal subdomain (30-31 residues) of human granulin A (HGA) in order to assess the contributions of a hydrophobic framework and other interactions to structure stabilization of the stack of two beta-hairpins. The resulting hybrid peptide, HGA 1-31 (D1V, K3H, S9I, Q20P) with four free cysteines, spontaneously formed a uniquely disulfide-bonded isomer with an expected [1-3, 2-4] disulfide pairing pattern. This peptide was characterized in detail by use of NMR and shown to assume a highly stable structure in solution, in contrast to the amino-terminal 1-30 fragment of human granulin A. The prototype peptide, or HGA 1-30 (C17S, C27S), had lower resistance to chemical reduction and proteolysis, broad NH and H(alpha) proton resonances, lower proton resonance dispersion, and no slowly exchanging amide protons. Two other peptides, HGA 1-30 (C17S, Q20P, C27S) and HGA 1-31 (D1V, K3H, S9I, C17S, C27S), with either Pro20 stabilizing a potential reverse turn or with a hydrophobic cluster consisting of Val1, His3, and Ile9, had sharper and slightly better dispersed NH and H(alpha) proton resonances, but still no slowly exchanging amide protons. The solution structure of HGA 1-31 (D1V, K3H, S9I, Q20P) indicates that it adopts a well-folded conformation of a stack of two beta-hairpins, as found for the amino-terminal subdomain of the prototypic carp granulin-1 with representative beta-hairpin stacks. These results highlight the importance of both hydrophobic and turn-stabilizing interactions for the structural integrity of the hairpin stack scaffold. The conformational stability appears to be maintained by a combination of the well-formed second beta-hairpin and two hydrophobic clusters, one located at the interface between the two beta-hairpins and the other on "top" of the first beta-hairpin. The implications of these findings for the design of conformationally stable hairpin stacks are discussed.

Amino Acid Sequence↗
PubMed2000

Esterified phenolics of the cell walls of chufa (Cyperus esculentusL. ) tubers and their role in texture.

Chufas (Cyperus esculentus) are edible tubers that, like Chinese waterchestnut (CWC), are very crisp when raw and do not soften when cooked. The present study compares the mechanical properties of chufas with those of potato and CWC in relation to the carbohydrate and phenolic compositions of the cell walls. The cutting toughness of raw chufa was higher than that of raw CWC and potato; its value decreased on boiling, as also observed with CWC, but remained over twice that of raw potato. Chufa cell walls were rich in xylose, arabinose, glucose, uronic acid, and galactose, with minor quantities of mannose. The cell walls of the parenchyma exhibited a uniform pH-dependent autofluorescence indicating the presence of cinnamic acid derivatives. Analysis of these revealed that peeled tuber cell walls are rich in ferulic acid, whereas p-coumaric acid dominates the monomeric phenol fraction of the skin. Cell wall material from both skin and peeled tubers contains a significant amount of different diferulic acids ( approximately 20% of the wall ferulic acid), consisting mainly of the 8-O-4'-, 8-5'-, and 5-5'-dimers. These are potentially available to form thermally stable cross-links between polysaccharides within the wall and between cells. This may confer thermal stability of texture.

Carbohydrates↗
PubMed2000

Physicochemical characteristics of onion (Allium cepa L.) tissues.

The structure and mechanical properties of onions are important factors affecting their textural quality. The onion bulb consists of several layers of pigmented, papery scales surrounding fleshy storage scales that comprise an upper epidermis, an intermediate parenchyma tissue, and a lower epidermis. The purpose of this study was to examine the chemical composition of cell walls from the papery scales and outer fleshy scales of onion (Allium cepa L. cv. Sturon) in relation to their mechanical properties. Cell-wall material (CWM) was prepared from the component tissues and analyzed for its carbohydrate and phenolic composition. The CWMs were rich in uronic acid and glucose, with smaller quantities of arabinose, galactose, and xylose. In the fleshy scales, the lower epidermis contained relatively more galactose-rich pectic polysaccharides, whereas the upper epidermis and the papery scales contained virtually no galactose. Analysis of mechanical properties showed that the order of strength of the tissues was papery scales > fleshy scales, which were in the order lower epidermis > upper epidermis > intermediate parenchyma. The upper epidermis of fleshy scales was stronger in the vertical than the horizontal direction, and both orientations showed negligible notch sensitivity. Cyclohexane-trans-1,2-diaminetetraacetate-induced vortex-induced cell separation of the intermediate layer of fleshy scales indicated that calcium cross-linking may play an important role in cell-cell adhesion. A small but significant amount of ferulic acid was found in the walls, predominantly in the thick cuticle of the lower epidermis of fleshy scales. Alkali-labile wall-bound flavonoids were also detected.

Carboxylic Acids↗
PubMed2000

Treatment-related leukaemia--a clinical and scientific challenge.

The development of a second tumour, including treatment-related leukaemia (TRL), is the most devastating complication of intensive cancer chemotherapy. This is especially relevant in the paediatric population as over 70% of children diagnosed with a malignancy will now live at least 5 years. Most TRLs are myeloid leukaemias and carry an overall poor prognosis when compared with their de novo counterparts. Despite the well known association with specific cytotoxic agents, improved understanding of the pathogenesis and risk factors of TRL is ultimately essential if we are to develop successful strategies for prevention and treatment. Here we review these aspects, together with the clinical and diverse biological features of this complication and the efficacy of current therapy.

Antineoplastic Agents, Alkylating↗
PubMed2000

Congenital spinal astrocytoma: how favourable is the long-term outcome?

An infant born with a low grade cervical astrocytoma and the adverse neuro-developmental outcome despite successful resection of the tumour are described. This case adds to the literature on this rare condition and the need for improvement in the management of these infants.

Astrocytoma↗
PubMed2000

Successful treatment of aspergillus brain abscess in a child with acute lymphoblastic leukemia.

Cerebral aspergillosis carries a high mortality in immunocompromised patients. However, favorable outcome can be achieved by the prolonged use of antifungal agents and the maintenance of adequate drug levels. The authors report a 2-year-old girl who developed an aspergillus brain abscess during treatment for acute lymphoblastic leukemia. Predisposing factors for the fungal infection and details of the antifungal therapy are described. Prolonged treatment with AmBisome and 5-flucytosine successfully eradicated the lesion, but the girl's antileukemic therapy was compromised due to the infection. She developed a central nervous system and bone marrow relapse 9 and 15 months, respectively, after the initial presentation. The report emphasizes the need for further consideration of effective, long-term antifungal prophylaxis and a careful balance between aggressive treatment for severe infection and antileukemic therapy.

Amphotericin B↗
PubMed2000

Transfusion-associated graft-vs-host disease. A fatal case caused by blood from an unrelated HLA homozygous donor.

Transfusion-associated graft-vs-host disease (TA-GVHD) is a rare complication of transfusion. We report fatal TA-GVHD in a 63-year-old coronary artery bypass patient of European descent after an RBC transfusion from an unrelated donor. The patient had mild lymphocytopenia and received 2 80-mg doses of methylprednisolone and 7 units of RBCs. On day 14 after the transfusion, he had fever, elevated liver enzyme levels, and a macular rash. Pancytopenia and bone marrow aplasia developed. On day 26, he had a massive gastrointestinal hemorrhage and died. At autopsy, histopathologic findings of the skin, liver, bone marrow, and gastrointestinal tract were consistent with TA-GVHD. One donor of the transfused RBCs (3 days old at transfusion) had a 1-way HLA match with the patient. A method using multiplex polymerase chain reaction is presented. This patient with TA-GVHD and mild immune suppression suggests that blood component irradiation guidelines may need to be reevaluated.

Bone Marrow↗
PubMed2000

Recurrence of Helicobacter pylori infection and duodenal ulcer relapse, following successful eradication in an urban east Asian population.

We aimed to determine the rate of Helicobacter pylori (HP) recurrence and duodenal ulcer relapse in patients of a hospital in Singapore over a period of at least one year from the time of eradication. Ninety-six consecutive duodenal ulcer patients with biopsy-proven HP eradication and healed ulcer were seen at 3-month intervals, and follow-up endoscopy was performed when dyspepsia recurred, at the end of one year after eradication, or at the time of recall if the patient had been lost to follow-up. HP status was determined by antral and corpus biopsies and by antral cultures. Sixty-five had been given triple therapy, and 31 received dual therapy with omeprazole + amoxycillin or clarythromycin. Median time to follow-up endoscopy was 12 months. Six patients (6.25%) were positive for HP infection after eradication. Recurrence of HP infection was detected at 9 and 10 months after confirmation of HP eradication in two patients, and at between 13 and 20 months in the remaining four. Two of these had recurrent duodenal ulcer; all but one had erosive duodenitis. Two other patients had recurrent duodenal ulcer despite absence of HP reinfection; they admitted to taking low-dose aspirin. It was concluded that the recurrence of HP infection is low at the end of one year after successful eradication therapy in this urban East Asian population. Ulcer relapse occurred in 4.17% (4/96) of patients, and was associated with recurrent HP infection or NSAID exposure.

Adolescent↗
PubMed1999

Interleukin-8 serum levels in patients with benign prostatic hyperplasia and prostate cancer.

OBJECTIVES: Using arbitrarily primed polymerase chain reaction (AP-PCR) ribonucleic acid (RNA) fingerprinting, we discovered a messenger RNA (mRNA) that encoded the cytokine interleukin-8 (IL-8) that was up-regulated in the peripheral blood leukocytes (PBLs) of patients with metastatic prostate cancer (CaP) compared with similar cells from healthy individuals. We compared the total prostate-specific antigen (PSA) levels, the free/total (f/t) PSA ratios, and the immunoreactive IL-8 serum concentrations in patients with either biopsy-confirmed benign prostatic hyperplasia (BPH) or CaP. METHODS: The sera from 35 apparently healthy normal volunteers and 146 patients with biopsy-confirmed BPH and CaP obtained from two academic centers were retrospectively examined to determine the serum levels of IL-8, total PSA (tPSA), and the f/t PSA ratio. Logistic regression and trend analysis statistical methods were used to assess the results. RESULTS: Normals (n = 35), BPH patients (n = 53), patients with clinical Stages A to C CaP (n = 81), and patients with metastatic CaP (n = 1 2) had mean levels of IL-8 of 6.8, 6.5, 15.6, and 27.8 pg/mL, respectively. The IL-8 serum concentrations correlated with increasing CaP stage and also differentiated BPH from clinical Stages A, B, C, or D CaP better than tPSA and performed similarly to the f/t PSA ratio. The combination of the IL-8 levels and f/t PSA ratios using multivariate logistic regression analysis distinguished BPH from Stages A, B, C, or D CaP or only Stages A and B with a receiver operating characteristic area under the curve of 89.8% and 87.5%, respectively (P <0.0001). CONCLUSIONS: The IL-8 serum concentration in our clinically well-defined patient sample was independent of the f/t PSA ratio as a predictor of CaP. When test samples are controlled for extraneous clinical origin of inflammation or infection, the combination of the IL-8 and f/t PSA assay results may offer an improved approach for distinguishing BPH from CaP.

Adult↗
PubMed1999

13C MAS NMR studies of the effects of hydration on the cell walls of potatoes and Chinese water chestnuts.

13C NMR with magic angle spinning (MAS) has been employed to investigate the cell walls of potatoes and Chinese water chestnuts over a range of hydration levels. Both single-pulse excitation (SPEMAS) and cross-polarization (CPMAS) experiments were carried out. Hydration led to a substantial increase in signal intensities of galactan and galacturonan in the SPEMAS spectra and a decrease in line width, implying mobilization in the backbone and side chains of pectin. In CPMAS spectra of both samples, noncellulose components showed signal loss as hydration increased. However, the signals of some galacturonan in the 3(1) helix configuration remained in the spectra even when the water content was as high as 110%. Cellulose was unaffected. It is concluded that the pectic polysaccharides experience a distribution of molecular conformations and mobility, whereas cellulose remained as typical rigid solid.

Cell Wall↗
PubMed1999

Novel immunoblot assay using four recombinant antigens for diagnosis of Epstein-Barr virus primary infection and reactivation.

A new immunoblot assay, composed of four Epstein-Barr virus (EBV)-encoded recombinant proteins (virus capsid antigen [VCA] p23, early antigen [EA] p138, EA p54, and EBNA-1 p72), was compared with an immunofluorescence assay on a total of 291 sera. The test was accurate in 94.5% of cases of primary EBV infection, while an immunoglobulin G anti-VCA p23 band with strong intensity correlated with reactivation.

Antigens, Viral↗
PubMed1998

Measurements of the equation of state of deuterium at the fluid insulator-metal transition

A high-intensity laser was used to shock-compress liquid deuterium to pressures from 22 to 340 gigapascals. In this regime deuterium is predicted to transform from an insulating molecular fluid to an atomic metallic fluid. Shock densities and pressures, determined by radiography, revealed an increase in compressibility near 100 gigapascals indicative of such a transition. Velocity interferometry measurements, obtained by reflecting a laser probe directly off the shock front in flight, demonstrated that deuterium shocked above 55 gigapascals has an electrical conductivity characteristic of a liquid metal and independently confirmed the radiography.

Journal Article↗
PubMed1998

Induction therapy for rectal carcinoma.

Induction, or preoperative therapy for rectal carcinoma, is a controversial topic which appears to have clinical utility in a number of distinct settings that range from early stage to locally advanced disease. Common to all treatment scenarios is the intent of reducing the likelihood of recurrence in the pelvis following surgery. An additional and evolving role is a reduction in the extent of surgery following a complete or partial clinical response to the induction regimen. While radiation as a single modality can lead to downstaging and, perhaps, a reduction in local recurrence, combined modality with 5-fluorouracil (5-FU) and radiation appears to have a greater therapeutic benefit that may be further enhanced by the administration of leucovorin.

Antidotes↗
PubMed1998

Contribution of meat fat to dietary arachidonic acid.

Arachidonic acid (AA) in the diet can be efficiently absorbed and incorporated into tissue membranes, resulting in an increased production of thromboxane A2 by platelets and increased ex vivo platelet aggregability. Results from previous studies have shown that AA is concentrated in the membrane phospholipids of lean meats. However, the concentration of AA in the visible fat portion of meats also may be significant despite being ignored in most studies. The aim of this study was to accurately quantitate the AA content of visible fat and the lean portion of beef, lamb, pork, chicken, duck, and turkey. The visible fat of meat contained a significant quantity of AA, ranging from 20 to 180 mg/100 g fat, whereas the AA content of the lean portion of meat was lower, ranging from 30 to 99 mg/100 g lean meat. Beef and lamb meats contained lower levels of AA in both the visible fat and lean portion than that from the other species. The highest level of AA in lean meat was in duck (99 mg/100 g), whereas pork fat had the highest concentration for the visible fats (180 mg/100 g). The lean portions of beef and lamb contained the higher levels of n-3 polyunsaturated fatty acids (PUFA) compared with white meats which were high in AA and low in n-3 PUFA. The present data indicate that the visible meat fat can make a contribution to dietary intake of AA, particularly for consumers with high intakes of fat from pork or poultry meat.

Adipose Tissue↗
PubMed1998

Public attitudes towards the autopsy in China.

The autopsy rate in China has fallen within the last few years. The attitudes of the public have become an important factor for its decline. Attitudes towards autopsy were surveyed from 400 subjects residing in the 27 provinces of China. Among the 299 survey forms returned, 284 were completed correctly, the remaining 15 being incomplete. The response rate was 71%. More than half of the responding members considered autopsy beneficial. However their perception of autopsy was quite inaccurate and prejudicial, lacking complete information. The two most frequent reasons for not accepting an autopsy were the lack of awareness towards the practice of autopsy and the wariness of body disfigurement after the autopsy was performed. It was suggested that the most appropriate way to change public perception of autopsy was through education. The primary tool for reaching the public was through the media. In addition, the approach to obtaining consent for autopsy should be improved.

Adult↗
PubMed1998

Arterial oxygen saturation profiles in healthy preterm infants.

AIM: To construct a reference range of SpO2 values in healthy preterm infants using a simple data logging device. METHODS: Thirty three healthy preterm infants were monitored for a continuous period of 4 hours at rest using an Ohmeda Biox 3700 E Pulse Oximeter and an electronic data logger (Rustrack Ranger). Stored data were downloaded and saved as individual files on a personal computer. RESULTS: The study group median and 5th and 95th percentiles were used to construct a cumulative frequency curve of time against SpO2 value, representing the normal reference range of SpO2 profiles in healthy preterm infants. CONCLUSION: Comparison of an infant's SpO2 profile against this curve may be more helpful in guiding supplemental oxygen treatment in that individual than a figure for a mean SPO2 and its standard deviation.

Arteries↗
PubMed1998

A study of early amniocentesis for prenatal cytogenetic diagnosis.

A prospective pilot study for early amniocentesis was conducted over 4 years including 279 early amniocenteses (EAs at 10-14 weeks' gestation) and 181 mid-trimester amniocenteses (MAs at 15 weeks upwards). The study was performed with EA and MA utilizing the same proceduralists, techniques, and cytogenetics laboratory. Patients were offered either procedure and the cytogenetics laboratory was not prospectively informed of the gestational age of each sampled pregnancy. In the early amniocenteses, less fluid was sampled and there were trends for (i) less cells and clones being available for analysis, less successful cultures, and a slightly longer reporting time; (ii) more multiple insertions (12.9 per cent of specimens vs. 9.9 per cent) and more bloody fluids (5.4 per cent specimens vs. 4.4 per cent); and (iii) a higher rate of pregnancy loss (2.2 per cent of EA vs. 0.6 per cent of MA). The multiple insertion rates for both EA and MA were comparatively high and were related to an increased frequency of blood-stained fluids. For EA specimens, the rates of amniotic fluid leakage, preterm delivery, and pregnancy loss were moderate and not significantly increased over the MA group. This study adds more weight to the view that EA is a reasonably safe procedure and a reliable alternative to chorionic villus biopsy to provide early prenatal cytogenetic diagnosis.

Adult↗