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Biomedical subjects

S Ng

Publications and source records attributed to S Ng.

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

Spontaneous activation of hamster oocytes in vitro.

OBJECTIVES: To observe the time of spontaneous activation of hamster oocytes and to find out the early signs of hamster oocytes activation. METHODS: First, 63 hamster oocytes including activated and non-activated oocytes (group A) and 51 non-activated oocytes (group B) were injected with human sperm and checked for fertilization after 16-18 hours. Then, 20 hamster oocytes were cultured in vitro in medium with or without calcium and examined under light microscope every half an hour up to 9 hours. RESULTS: Under light microscope, hamster oocytes activation were observed to undergo 4 stages: metaphase II stage without meiotic spindle, appearance of meiotic spindle near the first polar body, protrusion of oolemma, and complete extrusion of second polar body with pronucleus formation. After culture for 1.5 hours in vitro, 30%-40% of the oocytes demonstrated meiotic spindle; but after 9 hours, 50% showed complete activation. Culture in medium without calcium showed a little delay in the process of activation. The earliest sign of spontaneous activation in hamster oocytes was the appearance of meiotic spindle near the first polar body. Although group A and B showed no difference, the damage rate was lower in group B (19.7% +/- 16.6%) than in group A (35.9% +/- 5.7%) (P = 0.08), whereas the fertilization rate (18.3% +/- 10.9%) was higher in group B than in group A (14.2% +/- 8.7%) (P = 0.135). CONCLUSIONS: Hamster oocytes may be activated spontaneously early after their removal. It is important to recognize the earliest sign of spontaneous activation and perform intracytoplasmic sperm injection (ICSI) before it happens.

Animals↗
PubMed1998

Human semaphorin K1 is glycosylphosphatidylinositol-linked and defines a new subfamily of viral-related semaphorins.

The semaphorin family contains a large number of secreted and transmembrane proteins, some of which are known to act as repulsive axon guidance cues during development or to be involved in immune function. We report here on the identification of semaphorin K1 (sema K1), the first semaphorin known to be associated with cell surfaces via a glycosylphosphatidylinositol linkage. Sema K1 is highly homologous to a viral semaphorin and can interact with specific immune cells, suggesting that like its viral counterpart, sema K1 could play an important role in regulating immune function. Sema K1 does not bind to neuropilin-1 or neuropilin-2, the two receptors implicated in mediating the repulsive action of several secreted semaphorins, and thus it likely acts through a novel receptor. In contrast to most previously described semaphorins, sema K1 is only weakly expressed during development but is present at high levels in postnatal and adult tissues, particularly brain and spinal cord.

Amino Acid Sequence↗
PubMed1998

Community outbreak of psittacosis in a rural Australian town.

BACKGROUND: Health authorities in Victoria, Australia were notified of three men from a rural town with atypical pneumonia, admitted to hospital over 8 days. Initial serological testing suggested Chlamydia psittaci as the cause. We did a case-control study to find risk factors for psittacosis. METHODS: We searched for cases of pneumonia or severe flu-like illness through family physicians and the regional hospital. We selected three controls per case from the region's electoral roll. We collected blood for serological tests and administered questionnaires to all cases and controls. FINDINGS: We found 16 cases of psittacosis and one died. Most cases were clustered within a small geographical area, with a median age of 58 years (range 23-76), 15 (94%) of whom were male. Keeping, handling, or feeding domestic or wild birds was not associated with illness. Cases spent a median of 17.5 h per week in their garden, compared with a median of 5.2 h for controls (p=0.04) and were more likely to have mowed lawns during the 3 weeks before onset of illness than controls (odds ratio 4.81 [95% CI 1.08-33.37]). INTERPRETATION: We showed that psittacosis outbreaks are not limited to direct contact with birds and pose new challenges for disease control. Modifications may be needed to work outdoors to decrease the risk of psittacosis.

Adult↗
PubMed1998

Dalteparin for deep venous thrombosis: a hospital-in-the-home program.

OBJECTIVE: To assess the efficacy, safety and cost savings of home treatment of lower-limb deep venous thrombosis (DVT). SETTING: A hospital-in-the-home treatment program. PATIENTS: One hundred patients with acute lower limb DVT (53 proximal, 47 distal), and no contraindication to home treatment, were entered into the program from March 1995 to February 1997. INTERVENTION: All patients received dalteparin, 200 units/kg subcutaneously, once daily for a minimum of five days, with commencement of oral anticoagulation (warfarin) on Day 2. Patients with proximal DVT had lung ventilation-perfusion scans performed and were admitted to hospital for at least 24 hours. Patients with distal DVT were discharged directly to home treatment. MAIN OUTCOME MEASURES: Clinical responses and the results of sequential duplex ultrasonography at one week, one month, three months and six months. RESULTS: There were no major, but six minor, bleeding complications, two of which led to dalteparin being withdrawn. Sixteen patients had lung ventilation-perfusion scans showing a high probability of pulmonary embolism. All were asymptomatic, and follow-up for at least three months showed no symptomatic thromboembolic events. Duplex ultrasonography showed progression of thrombosis in the first week of therapy in 13.2% of distal and 2.7% of proximal thromboses. Thereafter, distal DVT improved at a much greater rate than proximal DVT; after six months complete resolution was seen in 60.7% of distal and 18.5% of proximal thromboses, respectively. Cost saving was $197 per bed-day equivalent compared with inpatient care. At 15 months' follow-up, swelling and/or pain was reported by 49% of patients with distal DVT and 66% of those with proximal DVT. CONCLUSIONS: Once-daily dalteparin therapy for DVT in a hospital-in-the-home setting was safe, efficacious and cost effective. However, DVT resolution is a slow process, with significant long term morbidity.

Adolescent↗
PubMed1998

Somatostatin inhibits (d-Arg6, Pro9-NEt) salmon gonadotropin-releasing hormone- and dopamine D1-stimulated growth hormone release from perifused pituitary cells of chinese grass carp, ctenopharyngodon idellus.

In this study, a heterologous radioimmunoassay (RIA) for grass carp GH has been validated and used to monitor the kinetics of GH release from perifused grass carp pituitary cells. To establish the anatomical specificity of GH antiserum used in this RIA, immunohistochemical staining was performed in grass carp pituitary sections. Somatotrophs recognized by this GH antiserum were located mainly in the proximal pars distalis without overlapping with gonadotrophs located in the same area or with lactotrophs located in the rostral pars distalis. The immunoreactivity of somatotrophs was abolished by preabsorbing GH antiserum with purified grass carp GH, suggesting that the possibility of a cross-reactivity of antiserum with other grass carp pituitary hormones is unlikely. Using 125I-labeled carp GH as the RIA tracer, parallelism was observed among the displacement curves of grass carp GH standard, grass carp serum, and culture medium conditioned by grass carp pituitary cells, suggesting that this RIA can be used to quantitate grass carp GH levels in biological samples. Using an in vitro column perifusion system, a superactive gonadotropin-releasing hormone (GnRH) analog (d-Arg6, Pro9-NEt)-sGnRH(sGnRHa, 0.3-30 nM), dopamine (DA, 0.1-10 muM), and the nonselective DA agonist apomorphine (0.1-10 muM) stimulated GH release from grass carp pituitary cells in a dose-dependent manner. The GH-releasing effect of DA was mimicked by the D1 agonists SKF38393 (0.1-10 muM) and SKF77434 (0.1-10 muM), but not by the D2 agonist LY171555 (3 muM). In addition, the GH response to DA (1 muM) was blocked by the D1 antagonist SCH23390 (5 muM) but not by the D2 antagonist (+/-) sulpiride (5 muM), suggesting that the GH-releasing action of DA is mediated through receptors resembling mammalian D1 receptors. Somatostatin-14 (SRIF14, 0.01-100 nM), unlike sGnRHa and DA, induced a dose-dependent suppression on basal GH release. At a high dose (100 nM), SRIF14 also abolished the GH responses to sGnRHa (100 nM), DA (10 muM), and the D1 agonist SKF38393 (3 muM). These results, as a whole, provide evidence that GH release in the grass carp is under the direct regulation of GnRH, DA, and SRIF at the pituitary cell level. The present study also suggests that DA D1 receptors are present in grass carp pituitary cells mediating the GH-releasing action of DA.

Animals↗
PubMed1998

CSF antibiotic prophylaxis for neurosurgical patients with ventriculostomy: a randomised study.

The value of prophylactic antibiotics for patients with ventricular catheter for monitoring and CSF drainage is uncertain. 228 patients were randomised to receive perioperative antibiotics only (Unasyn, Group I) or prolonged antibiotics for the presence of the ventricular catheter (Unasyn and Aztreonam, Group II). The incidence of intracranial and extracranial infection was documented prospectively. Group II patients had a significantly reduced incidence of CSF infection [3/115 (3%) vs 12/113 (11%), p = 0.01] and extracranial infections [23/115 (20%) vs 48/113 (42%), p = 0.002]. CSF pathogens in Group II patients were MRSA and Candida, whereas in Group I, Staphylococci, E coli and Klebsiella. Although prolonged antibiotic prophylaxis significantly reduced the incidence of serious CSF infection as well as extracranial infections, this policy did select resistant or opportunistic pathogens such as Candida and MRSA.

Adolescent↗
PubMed1997

Anticardiolipin IgG subclasses: association of IgG2 with arterial and/or venous thrombosis.

OBJECTIVE: To determine whether the presence of anticardiolipin antibodies (aCL) of a specific IgG subclass is associated with clinical complications of the antiphospholipid antibody syndrome (APS) and whether polymorphisms of Fc receptors for IgG (FcgammaR) with differential binding preferences contribute to an increased risk of thrombotic complications. METHODS: In 60 patients with IgG aCL, we assessed clinical complications of the APS, measured the level of antibody activity, and determined the IgG subclass distribution of aCL by a modified enzyme-linked immunosorbent assay (ELISA) with murine anti-human IgG subclass monoclonal antibodies. Selective IgG subclass adsorption studies were performed to determine the relative contribution of specific IgG subclasses to overall aCL activity. Fcgamma receptor IIA (FcgammaRIIA) genotypes of aCL patients with thrombosis and of non-systemic lupus erythematosus controls were determined by polymerase chain reaction amplification of genomic DNA and allele-specific probes. RESULTS: IgG2 aCL, detected in 75% of the patients, was the major subclass of aCL. Selective adsorption studies demonstrated that IgG2, in contrast to IgG1, was the predominant subclass responsible for aCL reactivity. IgG2 aCL was the only subclass associated with clinical complications, specifically, arterial and/or venous thrombosis (P < 0.04). The presence of FcgammaRIIA-H131, a receptor expressed on platelets, monocytes, and endothelial cells and the only human FcgammaR which efficiently recognizes IgG2, was associated with thrombosis in aCL patients. Among 45 high-titer (>40 GPL [IgG phospholipid] units) aCL patients with thrombosis, 40% were homozygous for FcgammaRIIA-H131, compared with 25% of disease-free controls (P = 0.042). CONCLUSION: While all 4 IgG subclasses are found in autoimmune aCL, only the presence of IgG2 is significantly associated with thrombotic complications. Reactivity in aCL ELISA is largely due to the presence of IgG2 in high-titer patients. The presence of IgG2 aCL, particularly in association with FcgammaRIIA-H131, may be a useful clinical predictor of increased thrombotic risk in patients with autoimmune IgG aCL. Allelic variants of FcgammaRIIA with distinct capacities to interact with IgG subclasses provide a mechanism for genetic susceptibility to an autoantibody-induced prothrombotic state.

Alleles↗
PubMed1997

Modifications in high-density lipoprotein lipid composition and structure alter the plasma distribution of free and liposomal annamycin.

Recent studies have shown that changes in lipoprotein cholesterol and triglyceride concentration alters the plasma distribution of free (Ann.) and liposomal annamycin (LAnn) and that the majority of Ann. is associated with high-density lipoproteins (HDL) following the incubation in plasma of LAnn. To demonstrate that alterations in HDL lipid composition and HDL structure may influence the plasma distribution of Ann. and LAnn, Ann. and LAnn (20 micrograms/mL) were incubated in plasma pretreated with dithionitrobenzoate (DTNB, a compound which inhibits the conversion of free cholesterol to esterified cholesterol) 18 h prior to the experiment or in untreated plasma for 60 min at 37 degrees C. In addition, Ann. and LAnn were co-incubated with DTNB in plasma for 60 min at 37 degrees C. Following incubation the plasma was separated into its HDL, low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), and lipoprotein-deficient plasma (LPDP) fractions by ultracentrifugation and assayed for Ann. by fluorimetry. The HDL plasma cholesterol:triglyceride concentration ratio was significantly decreased following 18 h of DTNB pretreatment compared to untreated plasma controls. No significant differences in LDL/VLDL plasma cholesterol:triglyceride concentration ratio following 18 h of DTNB pretreatment was observed. An increased number of discoidal HDL particles were observed following 18 h of DTNB pretreatment. When Ann. was incubated in plasma pretreated with DTNB for 18 h the percentage of Ann. recovered in the HDL, LDL, and VLDL fractions significantly increased. However, the percentage of Ann. recovered within the LPDP fraction was significantly decreased. When LAnn was incubated in plasma pretreated with DTNB for 18 h the percentage of Ann. recovered in the HDL fraction significantly decreased. The percentage of Ann. recovered in the LPDP fraction significantly increased when LAnn was incubated in plasma pretreated with DTNB for 18 h. No significant differences in Ann. lipoprotein distribution were observed when Ann. and LAnn were co-incubated with DTNB in plasma for 1 h. These findings suggest that the cholesterol:triglyceride concentration ratio and physical structure of HDL maybe important in defining the capacity of HDL to sequester Ann.

Antibiotics, Antineoplastic↗
PubMed1993

Structural investigation of the capsular polysaccharide produced by a novel Klebsiella serotype (SK1). Location of O-acetyl substituents using NMR and MS techniques.

The capsular polysaccharide of Klebsiella SK1 was investigated by methylation analysis, Smith degradation, and 1H NMR spectroscopy. The oligosaccharides (P1 and P2) obtained by bacteriophage phi SK1 degradation of the polymer were studied by methylation analysis, and 1D- and 2D-NMR spectroscopy. The resulting data showed that the parent repeating unit is a branched pentasaccharide having a structure identical to the revised structure recently proposed for Klebsiella serotype K8 capsular polysaccharide. [Formula: see text] The 2D-NMR data showed that one third of the glucuronic acid residues in the SK1 polymer are acetylated at O-2, O-3, or O-4. FABMS studies confirmed the presence of monoacetylated glucuronic acid residues. Thus, the relationship between the Klebsiella K8 and SK1 polymers is akin to that found for Klebsiella polysaccharides K30 and K33, which have been typed as serologically distinct yet their structures differ only in the degree of acetylation.

Acetylation↗
PubMed1992

Peptoids: a modular approach to drug discovery.

Peptoids, oligomers of N-substituted glycines, are described as a motif for the generation of chemically diverse libraries of novel molecules. Ramachandran-type plots were calculated and indicate a greater diversity of conformational states available for peptoids than for peptides. The monomers incorporate t-butyl-based side-chain and 9-fluorenylmethoxy-carbonyl alpha-amine protection. The controlled oligomerization of the peptoid monomers was performed manually and robotically with in situ activation by either benzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluorophosphate or bromotris(pyrrolidino)phosphonium hexaflurophosphate. Other steps were identical to peptide synthesis using alpha-(9-fluorenylmethoxycarbonyl)amino acids. A total of 15 monomers and 10 oligomers (peptoids) are described. Preliminary data are presented on the stability of a representative oligopeptoid to enzymatic hydrolysis. Peptoid versions of peptide ligands of three biological systems (bovine pancreatic alpha-amylase, hepatitis A virus 3C proteinase, and human immunodeficiency virus transactivator-responsive element RNA) were found with affinities comparable to those of the corresponding peptides. The potential use of libraries of these compounds in receptor- or enzyme-based assays is discussed.

Alkylation↗
PubMed1992

Nonabsorbable suture material in cataract surgery: a comparison of Novafil and nylon.

We compared the performance of 10-0 Novafil (polybutester, Davis & Geck, American Cyanamid Company, New South Wales, Australia.) with that of 10-0 nylon (Alcon) in 60 patients undergoing extracapsular cataract extraction and implantation of a posterior chamber intraocular lens. A standard technique was used, and the incision was closed with interrupted sutures of either 10-0 Novafil or 10-0 nylon. Length of follow up ranged from 6 to 26 months (average, 15 months). We assessed the intraoperative handling qualities of the suture materials, as well as their effect on wound healing and inflammation. We also compared the surgically-induced astigmatism in the two suture groups over the first 3 postoperative months and then in long-term follow up (average, 15 months). Sutures removed at long-term follow up were examined by scanning electron microscopy (SEM). Both suture materials handled easily at operation and were well tolerated by all patients. There was no significantly different surgically-induced astigmatism in the two suture groups after 12 weeks (P = .962) or during longer follow up (P = .401). SEM confirmed more advanced biodegradation of nylon as compared with Novafil sutures after they had been in place an average of 18 months.

Adult↗
PubMed1991

Production and characterization of monoclonal antibodies to Ha-ras and N-ras p21.

The mammalian ras family consists of the Ha, Ki and N-ras genes that encode a series of 21,000 dalton proteins (p21). The three ras proteins participate in normal cell physiology and have been implicated in cellular transformation by either overexpression of the normal p21 or by mutation at positions 12, 13, or 61. To help understand the biological roles of the different ras proteins, we have generated monoclonal antibodies (Mabs) to the Ha-ras and N-ras p21. Mab Ha-770, raised to a Ha-specific synthetic peptide, reacts with Ha-ras recombinant p21 (r-p21) as well as cellular Ha-ras p21 by immunoprecipitation. Western blot and sandwich ELISA assays. Mab N-838, raised to an N-ras specific synthetic peptide, reacts with the N-ras recombinant p21 by immunoprecipitation, Western blot and sandwich ELISA assays. Mabs to the Ha-ras and N-ras p21 should be valuable reagents in assessing the individual roles of ras proteins in normal and neoplastic cells.

Amino Acid Sequence↗
PubMed1991

Fetal umbilical artery velocity waveforms and subsequent neonatal outcome.

Flow velocity waveforms (FVWs) from the fetal umbilical artery were recorded from 2178 pregnant women over a 6-year period. All of them had an obstetric factor indicating increased risk of fetal compromise. A total of 6749 studies was recorded. The systolic diastolic (AB) ratio was measured and classified as normal (less than 95th centile), elevated (95-99th centile), high (greater than 99th centile) or extreme (absent diastolic flow). The results of these studies have been related to subsequent fetal and neonatal outcome. An abnormal umbilical artery FVW was associated with shorter gestation and infants with lower birthweight, shorter length and lower ponderal index. There was a highly significant association between an abnormal FVW and the birth of an infant small for gestational age. The significance of the association increased with the increased abnormality of the umbilical artery FVW and this was independent of gestational age. Preterm infants associated with high or extreme AB ratios spent twice as long in the neonatal nursery than those with normal AB ratios. Analysis of 794 pregnancies studies serially indicated that an abnormal FVW in which the AB ratio was increasing, in contrast to a decreasing AB ratio, predicted a poor outcome for both size at birth and duration of neonatal intensive care. We conclude that in high risk pregnancy Doppler umbilical artery FVW studies predict the most compromised fetuses in terms of growth retardation and requirements for neonatal intensive care.

Adult↗
PubMed1991

Activated Val-12 ras p21 in cell culture fluids and mouse plasma.

Activation of ras oncogenes has been associated with a variety of cancers as well as their precursor lesions. Ras proteins activated by substitutions at amino acid positions 12, 13 or 61 have not been identified in normal tissues and therefore their detection may have clinical value. In this study our objective was to determine whether activated ras proteins could be released into the extracellular environment. To test this hypothesis, we used ras-transformed NIH3T3 cells that express an activated p21 containing valine (Val-12 p21) at position 12 instead of the normal glycine (Gly-12 p21) and a monoclonal antibody (mAb) designated DWP that is specific for the activated Val-12 ras proteins. Culture fluids collected from NIH3T3 cells transformed by the activated Val-12 p21 were shown, using mAb DWP in a sandwich ELISA format, to contain the activated Val-12 p21. In contrast, culture fluids from non-Val-12-containing cells were unreactive with mAb DWP. PSV-LM-EJ cells which overexpress the activated Val-12 p21 were injected subcutaneously (SQ) into nude mice to produce tumors. At the time of gross tumor appearance (14-21 days after tumor cell inoculation), plasma was collected from the PSV-LM-EJ tumor-bearing mice as well as from a series of control mice. Employing mAb DWP as a detection reagent in the sandwich ELISA format, we were able to detect the Val-12 p21 in the plasma of the PSV-LM-EJ tumor-bearing mice. Activated Val-12 p21 was not present in the plasma of non-tumor-bearing mice, or in the plasma of mice bearing SQ tumors composed of non-Val-12 p21 ras-transformed cells. This report is the first description of an activated ras protein (Val-12 p21) in the plasma of tumor-bearing mice and demonstrates that the results of the Val-12 p21-specific ELISA could be validated with Western blot format.

3T3 Cells↗
PubMed1990

Differential recall as a source of bias in epidemiologic research.

Differential recall between compared groups is discussed most often in the context of case-control studies. Cases, compared to controls, are suspected of providing a more complete report of their true exposure to an hypothesized risk factor, thereby biasing upwards the estimate of its effect. The present paper describes how differential recall can arise with any observational design in epidemiology; with any class of study variable, not only exposures; and may inflate or deflate the true value of the estimate of effect size. We list a variety of study designs and questionnaire tactics that aim to remedy these problems. The scope and magnitude of the bias created by differential recall and the efficacy of proposed remedies require further study.

Bias↗
PubMed1990

Production and characterization of anti-RAS p21 monoclonal antibodies.

Monoclonal antibodies (MAb) Ras 10 and Ras 11 were raised to an activated human Harvey-ras p21 and shown to react with recombinant p21 as well as p21 derived from human and rodent cells. Characterization studies by ELISA, immunoprecipitation and Western blot procedures demonstrated that MAb Ras 10 (IgG2a) and Ras 11 (IgG2b) react with normal p21, activated p21, and p21 from each of the Harvey, Kirsten and N-ras families. Studies illustrated that MAb Ras 10 and Ras 11 can also be used in flow cytometry and immunohistochemistry to specifically detect cellular p21. ELISA, immunoprecipitation and Western blot studies comparing rat anti-p21 MAb Y13-259 with Ras 10 and Ras 11 demonstrated that Ras 10 and Ras 11 had a greater sensitivity for ras protein detection than Y13-259. Collectively, these studies illustrate that MAb Ras 10 and Ras 11 can be applied to a variety of assay formats to detect ras proteins and, therefore, may be valuable tools in detecting and measuring of ras protein expression in normal, neoplastic and pre-neoplastic cells.

Animals↗