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Biomedical subjects

G Walker

Publications and source records attributed to G Walker.

At least 19 recordsLinked to original sources
PubMed2006

Barriers to implementing a policy not to attempt resuscitation in acute medical admissions: prospective, cross sectional study of a successive cohort.

OBJECTIVE: To establish whether acutely unwell patients admitted to hospital wish to participate in discussions about resuscitation. DESIGN: Prospective, cross sectional study of a successive cohort of patients. SETTING: Admission through the emergency department. PARTICIPANTS: 374 adult patients. MAIN OUTCOME MEASURE: Whether acutely unwell patients wished to participate in discussions about resuscitation. RESULTS: Of the total sample, 74 patients consented to take part in the study and provide full data. Of the remaining patients, 189 could not be approached for practical reasons and 111 did not wish to participate. Of the 74 patients who read the leaflet, 65 (88%) reported having little or no prior knowledge, 70 (96%) understood it, 56 (77.8%) preferred for resuscitation decisions to be discussed with them, and 55 (77.5%) did not mind discussing resuscitation within 24 hours of admission and overall showed a decline in their anxiety score. CONCLUSION: Many patients admitted through the emergency department for medical reasons cannot participate in their decision not to attempt resuscitation within 24 hours of admission. Patients who were willing to participate rated the information leaflet that was provided positively.

Adult↗
PubMed2006

Mutation of the tumour suppressor p33ING1b is rare in melanoma.

BACKGROUND: The p33ING1b gene is involved in the p53-dependent response to DNA damage following exposure to ultraviolet radiation, and has recently been reported to be mutated in 20% of melanoma tumours. OBJECTIVES: We sought to assess the p33ING1b mutation rate in our large panels of fresh melanomas and melanoma cell lines. METHODS: We screened 83 primary melanomas and 55 melanoma cell lines for mutations in p33ING1b by single-strand conformational polymorphism analysis and by direct sequencing. RESULTS: In contrast to previous reports, we found no somatic p33ING1b mutations in our panel of melanomas. We found that some of the discrepancy between our results and previously published studies may be due to inadvertent amplification of the ING1 pseudogene (INGX), and/or contamination of some samples with murine Ing1. CONCLUSIONS: p33ING1b mutations in melanoma are rare. We have highlighted the importance of allele-specific primer design to avoid pseudogene amplification, and also the necessity to confirm the genetic identity and species of origin of individual cell lines. Further studies are needed to clarify the possible role of p33ING1b in melanoma tumorigenesis.

Animals↗
PubMed2005

Quantification of in-stent restenosis parameters in rabbits by Micro-CT.

PURPOSE: The well-defined model of angioplasty and stent implantation in the rabbit aorta is useful in experimental studies of restenosis. This study was performed to evaluate the feasibility of Micro-CT for quantification of in-stent restenosis in a rabbit aortic in-stent-restenosis model. MATERIAL AND METHODS: To induce in-stent restenosis seven female New Zealand rabbits underwent balloon dilation and denudation prior to stenting the abdominal aorta. After six weeks on atherogenic diet, animals were killed and the aorta was perfused with contrast agent. Micro-CT morphometric analysis of balloon and stent injured arteries obtained by 700 transverse sections (voxel size 10 microm) was compared to conventional histological analysis. RESULTS: Intimal hyperplasia was present in stented and balloon injured arteries with a moderate intimal area assessed by Micro-CT and conventional histology (3.91 +/- 0.5 mm(2) vs. 4.18 +/- 0.42; r = 0.9). High significant correlations between Micro-CT image analysis and conventional histomorphometry were obtained for lesion size, size of media, size of lumen and stent area (r = 0.84 to 0.96). CONCLUSION: Micro-CT is feasible for quantitative information about restenosis following balloon angioplasty and stent implantation and has the potential to become a standard technique in many laboratories which will augment serial histology as the reference method for ex-vivo studies of restenosis.

Algorithms↗
PubMed2004

Development and in vivo evaluation of an oral insulin-PEG delivery system.

Insulin-monomethoxypoly(ethylene glycol) derivatives were obtained by preparation of mono- and di-terbutyl carbonate insulin derivatives, reaction of available protein amino groups with activated 750 Da PEG and, finally, amino group de-protection. This procedure allowed for obtaining high yield of insulin-1PEG and insulin-2PEG. In vivo studies carried out by subcutaneous injection into diabetic mice demonstrated that the two bioconjugates maintained the native biological activity. In vitro, PEGylation was found to enhance the hormone stability towards proteases. After 1 h incubation with elastase, native insulin, insulin-1PEG and insulin-2PEG undergo about 70, 30 and 10% degradation, respectively, while in the presence of pepsin protein degradation was 100, 70 and 50%, respectively. The attachment of low molecular weight PEG did not significantly (P >0.05) alter insulin permeation behavior across the intestinal mucosa. Insulin-1PEG was formulated into mucoadhesive tablets constituted by the thiolated polymer poly(acrylic acid)-cysteine. The therapeutic agent was sustained released from these tablets within 5 h. In vivo, by oral administration to diabetic mice, the glucose levels were found to decrease of about 40% since the third hour from administration and the biological activity was maintained up to 30 h. According to these results, the combination of PEGylated insulin with a thiolated polymer used as drug carrier matrix might be a promising strategy for oral insulin administration.

Administration, Oral↗
PubMed2004

Positive N-methyl-D-aspartate receptor modulation by selective glycine transporter-1 inhibition in the rat dorsal spinal cord in vivo.

In this study we have employed the selective glycine transporter-1 (GlyT-1) and GlyT-2 transporter inhibitors R-(-)-N-methyl-N-[3-[(4-trifluoromethyl)phenoxy]-3-phenyl-propyl]glycine (1:1) lithium salt (Org 24598) and 4-benzyloxy-3,5-dimethoxy-N-[1-(dimethylaminocyclopently)methyl]benzamide (Org 25543), respectively, and microdialysis perfusion to determine the effect of GlyT transporter inhibition on extracellular amino acid concentrations in the lumbar dorsal spinal cord of the halothane-anaesthetised rat. Reverse dialysis of Org 24598 (0.1-10 microM) induced a concentration-related increase in extracellular glycine accompanied by a progressive increase in citrulline, but not aspartate, glutamate or GABA, efflux. Org 25543 (10 microM) by the same route induced a similar increase in glycine levels without affecting the efflux of other amino acids quantified. To test the hypothesis that the increase in citrulline efflux resulted from activation of the N-methyl-D-aspartate receptor (NMDA-R)/nitric oxide synthase (NOS) signalling cascade, the sensitivity was determined of GlyT-1 inhibition-induced effects to NMDA-R antagonism or NOS inhibition. Co-administration by reverse dialysis of the selective NMDA-R channel blocker MK-801 (0.5 mM) or the selective antagonist of the strychnine-insensitive glycine site, 7-chlorokynurenic acid (1 mM), with Org 24598 (10 microM) did not affect the uptake inhibition-induced increase in glycine efflux, but did significantly attenuate the increase in extracellular citrulline. Similarly, co-administration with Org 24598 of the isoform non-selective and selective neuronal NOS inhibitors Nomega-nitro-L-arginine methyl ester (1 mM) or 1-(2-trifluoromethylphenyl)imidazole (0.2 mM), respectively, prevented Org 24598-induced citrulline efflux with no effect on increased glycine efflux. These data provide evidence that the observed increased in extracellular citrulline is a consequence of positive modulation of NMDA-R, secondary to increased extracellular glycine and support a protective role for GlyT-1 against fluctuations in extracellular glycine uptake at glutamatergic synapses in the dorsal spinal cord. Such a mechanism could be important to NMDA-R-mediated synaptic plasticity in the spinal cord and be of relevance to the clinical usage of GlyT-1 inhibitors.

Amino Acid Transport Systems, Neutral↗
PubMed2004

Predicting outcome in ex-premature infants supported with extracorporeal membrane oxygenation for acute hypoxic respiratory failure.

OBJECTIVE: To identify predictors of outcome in ex-premature infants supported with extracorporeal membrane oxygenation (ECMO) for acute hypoxic respiratory failure. METHODS: Retrospective review of ex-premature infants with acquired acute hypoxic respiratory failure requiring ECMO support in the United Kingdom from 1992 to 2001. Review of follow up questionnaires completed by general practitioners and local paediatricians. RESULTS: Sixty four ex-premature infants (5-10 each year) received ECMO support, despite increased use of advanced conventional treatments over the decade. The most common infective agent was respiratory syncytial virus (85% of cases). Median birth gestation was 29 weeks and median corrected age at the time of ECMO support was 42 weeks. Median ECMO support duration was relatively long, at 229 hours. Survival to hospital discharge and to 6 months was 80%, remaining similar throughout the period of review. At follow up, 60% had long term neurodisability and 79% had chronic pulmonary problems. Of pre-ECMO factors, baseline oxygen dependence, younger age, and inpatient status were associated with non-survival (p < or = 0.05). Of ECMO related factors, patient complications were independently associated with adverse neurodevelopmental outcome and death (p < 0.01). CONCLUSIONS: Survival rates for ex-premature infants after ECMO support are favourable, but patients suffer a high burden of morbidity during intensive care and over the long term. At the time of ECMO referral, baseline oxygen dependence is the most important predictor of death, but no combination of the factors considered was associated with a mortality that would preclude ECMO support.

Acute Disease↗
PubMed2003

Androgen receptor antigen density and S-phase fraction in prostate cancer: a pilot study.

PURPOSE: To determine whether quantitative flow cytometric androgen receptor density expression (MFC ratio) in prostate cancer was associated with S-phase fraction. METHODS: Flow cytometry was performed to determine DNA aneuploidy, S-phase fraction, percentage of androgen receptor (AR)-positive cells, and MFC ratio in prostate cancer patients. RESULTS: MFC ratio showed distinct clustering. Eight patients had a low MFC ratio of 1.78-2.74, while 10 patients had high MFC ratios between 4.99 and 6.48. The S-phase fraction had average values of 11.05 vs 4.92 in tumors with high vs low MFC ratio (P<0.01). CONCLUSION: S-phase fraction was significantly higher in tumors with high AR density.

Aged↗
PubMed2003

Patterns of biofilm succession on a sheltered rocky shore in Hong Kong.

Successional patterns are dependent on the nature of the substratum, water flow, concentrations of organics as well as the availability of bacteria, algal spores and invertebrate larvae in the coastal environment. Bacteria play an especially important role in biofilm formation as they are generally the earliest colonizers. In the present study, both winter and summer biofilm succession patterns were examined on glass coverslips inverted on experimental racks attached at two tidal levels on a sheltered shore in Hong Kong. In the succession, bacteria were followed by diatoms and cyanobacteria. Encrusting algae appeared in the late stages of the experiment (day 80 in summer and day 60 in winter). Colonization by bacteria was much slower in summer and their density remained low throughout the experimental period. The first appearance of diatoms and cyanobacteria, however, was more rapid in the summer. Bacteria and diatoms on the low-shore surfaces also had a faster succession rate than on the high-shore surfaces, suggesting that desiccation/aerial temperature are the causal factors for such differences.

Analysis of Variance↗
PubMed2002

Fate of Cryptosporidium oocysts in an immobilised titanium dioxide reactor with electric field enhancement.

We have undertaken simple proof of principle experiments to find out if electric field enhanced photo-oxidation using immobilised titanium dioxide will damage Cryptosporidium oocysts. Using a simple Petri dish reactor and two forms of immobilised titanium catalyst (sol-gel and thermal-film) we have tested the ability of this technology to affect Cryptosporidium oocysts permeability assessed by propidium iodide exclusion. Test and control reactor runs were significantly different (P = 0.007). The thermal-film reactor had the greatest effect (approximately 27% of the seed) and was statistically distinguishable from the sol-gel reactor and the controls. The sol-gel reactor showed an increase in oocyst permeability, but was not statistically distinguishable from one of the controls. The enhanced performance of the thermal film reactor is attributed to the superior conversion of photochemical holes to hydroxyl radicals at the surface of this catalyst.

Animals↗
PubMed2001

Proteolytic cleavage of inducible nitric oxide synthase (iNOS) by calpain I.

Proteolytic degradation of inducible nitric oxide synthase (iNOS or NOS2; EC 1.14.13.39) is one of the key steps by which the synthetic glucocorticoid dexamethasone controls the amount of iNOS protein and thus the production of nitric oxide (NO) in interferon-gamma-stimulated RAW 264.7 cells. In the present study we examined the role of the calmodulin (CaM)-binding site present within iNOS protein for the proteolytic degradation by the calcium-dependent neutral cysteine protease calpain I (EC 3.4.22.17). Using pulse chase experiments as well as cell-free degradation assays we show that the iNOS monomer is a direct substrate for cleavage by calpain I. Two structural determinants are involved in proteolytic cleavage, the canonical CaM-binding domain present at amino acids 501-532 and a conformational determinant located within iNOS. The access of the CaM-binding region appears to be critical for substrate cleavage as incubation of in vitro synthesized iNOS with purified CaM inhibits iNOS degradation by calpain I. Moreover, cytosolic CaM levels are decreased upon treatment of RAW 264.7 cells with dexamethasone as assessed by immunoprecipitation. The data shown herein provide novel insights into the underlying mechanisms involved in the anti-inflammatory actions of glucocorticoids.

Animals↗
PubMed2001

Settlement of Pomatoceros lamarkii (Serpulidae) larvae on biofilmed surfaces and the effect of aerial drying.

The settlement responses of Pomatoceros lamarkii (Polychaeta: Serpulidae) larvae to biofilms of varying age on slate surfaces and to dried biofilms on slate surfaces were investigated in the laboratory. Settlement experiments were performed as multi-treatment, still water assays. Larvae did not settle on clean, non-biofilmed slates but settled on biofilms up to 28 days old. Settlement intensity was closely related to the bacterial density of a biofilm. Drying a biofilmed surface for 1-2 h at 20 degrees C to simulate a single tidal emersion completely negated the former inductive effect of the biofilm. Drying also negated the larval settlement-inducing effect that normally results from the presence of conspecific adults. The settlement inhibition lasted for approximately 5 days following a single drying event. Larvae settled readily on biofilms exposed to formalin and antibiotics. Treating biofilms with formalin or antibiotics before or after drying had no effect upon larval avoidance of dried biofilms. Freeze-drying a biofilm had the same effect as aerial drying. The biofilm drying effect could not be mimicked by exposing biofilms to hyper-saline seawater. The finding that P. lamarkii larvae do not settle on dried biofilms could have significance in explaining the natural distribution of this species in the intertidal.

Journal Article↗
PubMed2001

Recruitment, activation and retention of caspases-9 and -3 by Apaf-1 apoptosome and associated XIAP complexes.

During apoptosis, release of cytochrome c initiates dATP-dependent oligomerization of Apaf-1 and formation of the apoptosome. In a cell-free system, we have addressed the order in which apical and effector caspases, caspases-9 and -3, respectively, are recruited to, activated and retained within the apoptosome. We propose a multi-step process, whereby catalytically active processed or unprocessed caspase-9 initially binds the Apaf-1 apoptosome in cytochrome c/dATP-activated lysates and consequently recruits caspase-3 via an interaction between the active site cysteine (C287) in caspase-9 and a critical aspartate (D175) in caspase-3. We demonstrate that XIAP, an inhibitor-of-apoptosis protein, is normally present in high molecular weight complexes in unactivated cell lysates, but directly interacts with the apoptosome in cytochrome c/dATP-activated lysates. XIAP associates with oligomerized Apaf-1 and/or processed caspase-9 and influences the activation of caspase-3, but also binds activated caspase-3 produced within the apoptosome and sequesters it within the complex. Thus, XIAP may regulate cell death by inhibiting the activation of caspase-3 within the apoptosome and by preventing release of active caspase-3 from the complex.

Apoptosis↗
PubMed2001

MS/NMR: a structure-based approach for discovering protein ligands and for drug design by coupling size exclusion chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy.

A protocol is described for rapidly screening small organic molecules for their ability to bind a target protein while obtaining structure-related information as part of a structure-based drug discovery and design program. The methodology takes advantage of and combines the inherent strengths of size exclusion gel chromatography, mass spectrometry, and NMR to identify bound complexes in a relatively universal high-throughput screening approach. Size exclusion gel chromatography in the spin column format provides the high-speed separation of a protein-ligand complex from free ligands. The spin column eluent is then analyzed under denaturing conditions by electrospray ionization mass spectrometry (MS) for the presence of small molecular weight compounds formerly bound to the protein. Hits identified by MS are then individually assayed by chemical shift perturbations in a 2D 1H-15N HSQC NMR spectrum to verify specific interactions of the compound with the protein and identification of the binding site on the protein. The utility of the MS/NMR assay is demonstrated with the use of the catalytic fragment of human fibroblast collagenase (MMP-1) as a target protein and the screening of a library consisting of approximately 32 000 compounds for the identification of molecules that exhibit specific binding to the RGS4 protein.

Chromatography, Gel↗
PubMed2001

Introduction to the Rhizocephala (Crustacea: Cirripedia).

Knowledge about the Rhizocephala (parasitic barnacles) has increased exponentially over the past two decades. This introduction broadly reviews this progress, touching on rhizocephalan morphology, life-cycles, larval biology, and the effects on the crustacean hosts. Members representing both orders, the Kentrogonida and Akentrogonida, are discussed. The recent discovery regarding the vermigon stage further highlights the intricacy of the kentrogonid life-cycle. Because rhizocephalans are found in most world regions, occurring on their respective hosts from the deep ocean to freshwater, their importance is now being recognized.

Animals↗
PubMed2001

Beyond the classical receptive field in the visual cortex.

We have investigated the organization of regions outside the classical receptive field (CRF) for neurons in the visual cortex. First, we have determined the incidence and nature of interactions from outside the CRF. We find interaction from regions outside the CRF for a majority of cortical cells and it is almost always of a suppressive nature. Second, we have determined that most interaction is from specific well-defined regions outside the CRF. These regions are generally as effective as what is found for a complete annulus. Third, it is possible to reverse the inhibition from outside the CRF by the addition of a second grating that is orthogonal to the preferred orientation. This disinhibition may completely offset the suppressive influence of the surround. Additional experiments suggest that this process is not necessarily involved in figure/ground analysis.

Animals↗