Search PubMed⌕ Search

Biomedical subjects

J Walker

Publications and source records attributed to J Walker.

At least 55 records · Page 3Linked to original sources
PubMed2002

Deliberate self-poisoning with rodenticide: a diagnostic dilemma.

A 71-year-old man presented with a recurrent bleeding diathesis requiring frequent blood transfusions, vitamin K and fresh frozen plasma. Extensive investigations revealed vitamin K deficiency. After repeated interviews the patient admitted to deliberately ingesting rat poison. Superwarfarins are an uncommon cause of deranged clotting and specialised tests are available to identify them. They can cause prolonged coagulation abnormalities and may require treatment with oral vitamin K for several months after just a single dose.

4-Hydroxycoumarins↗
PubMed2001

Bacteriophytochromes are photochromic histidine kinases using a biliverdin chromophore.

Phytochromes comprise a principal family of red/far-red light sensors in plants. Although phytochromes were thought originally to be confined to photosynthetic organisms, we have recently detected phytochrome-like proteins in two heterotrophic eubacteria, Deinococcus radiodurans and Pseudomonas aeruginosa. Here we show that these form part of a widespread family of bacteriophytochromes (BphPs) with homology to two-component sensor histidine kinases. Whereas plant phytochromes use phytochromobilin as the chromophore, BphPs assemble with biliverdin, an immediate breakdown product of haem, to generate photochromic kinases that are modulated by red and far-red light. In some cases, a unique haem oxygenase responsible for the synthesis of biliverdin is part of the BphP operon. Co-expression of this oxygenase with a BphP apoprotein and a haem source is sufficient to assemble holo-BphP in vivo. Both their presence in many diverse bacteria and their simplified assembly with biliverdin suggest that BphPs are the progenitors of phytochrome-type photoreceptors.

Amino Acid Sequence↗
PubMed2001

Diagnosis of malaria in a remote area of the Philippines: comparison of techniques and their acceptance by health workers and the community.

OBJECTIVE: To compare the efficacies of remote symptom-based diagnosis of malaria, rapid diagnostic tests and microscopy in an area of low endemicity in the Philippines. METHODS: In Trial I, 350 symptomatic patients were tested within their villages using malaria Plasmodium falciparum (Pf)/Plasmodium vivax (Pv) immunochromatographic tests (ICT tests) and blood films stored and read under local conditions. The slides were later restained and read. In Trial II, unsupervised volunteer barangay health workers prepared ICT tests and slides after brief training. These slides were read at rural health units. Twenty-seven barangay health workers and 72 community members were later questioned about the three diagnostic strategies. FINDINGS: A history of fever alone was sensitive (95.4%) but poorly specific (16.5%) for predicting parasitaemia. The inclusion of other symptoms reduced the sensitivity to below 85%, while specificity remained low. The axillary temperature was poorly predictive. ICT tests achieved high sensitivity (97.9%) but many cases indicated as positive by ICT tests were negative by microscopy. Further analysis of these cases in Trial I indicated that ICT tests were detecting low-level parasitaemias missed by microscopy, and that local microscopy had poor accuracy. ICT tests were well accepted and accurately performed by barangay health workers. CONCLUSION: These tests meet a strong desire in the community for blood-based diagnosis and may increase the compliance and treatment-seeking behaviour of patients.

Adult↗
PubMed2001

Serum of cytomegalovirus-infected mice induces monocyte chemoattractant protein-1 expression by endothelial cells.

Inflammation plays a central role in atherogenesis. It was hypothesized that infection of apolipoprotein E-deficient mice with murine cytomegalovirus (MCMV) increases serum levels of proinflammatory cytokines, which may induce "proatherosclerotic" changes in endothelial cells (ECs). Serum samples were collected from uninfected and infected mice. ELISA was used to determine cytokine serum levels and monocyte chemoattractant protein-1 (MCP-1) levels in the supernatant of mouse ECs incubated with serum-containing medium. Serum samples from infected mice induced MCP-1 expression by ECs. These serum samples contain interferon (IFN)-gamma, whereas IFN-gamma was undetectable in serum samples from uninfected mice. Preincubating infected mouse serum with anti-IFN-gamma monoclonal antibody significantly decreased serum-induced EC expression of MCP-1. Thus, MCMV infection increases IFN-gamma serum levels, such serum can induce MCP-1 in ECs, and the serum-induced MCP-1 expression is due, at least in part, to IFN-gamma. If these changes in EC function also occur in vivo in response to infection, they could exacerbate atherogenesis.

Animals↗
PubMed2001

Increasing the rate of chromatin remodeling and gene activation--a novel role for the histone acetyltransferase Gcn5.

Histone acetyltransferases (HATs) such as Gcn5 play a role in transcriptional activation. However, the majority of constitutive genes show no requirement for GCN5, and even regulated genes, such as the yeast PHO5 gene, do not seem to be affected significantly by its absence under normal activation conditions. Here we show that even though the steady-state level of activated PHO5 transcription is not affected by deletion of GCN5, the rate of activation following phosphate starvation is significantly decreased. This delay in transcriptional activation is specifically due to slow chromatin remodeling of the PHO5 promoter, whereas the transmission of the phosphate starvation signal to the PHO5 promoter progresses at a normal rate. Chromatin remodeling is equally delayed in a galactose-inducible PHO5 promoter variant in which the Pho4 binding sites have been replaced by Gal4 binding sites. By contrast, activation of the GAL1 gene by galactose addition occurs with normal kinetics. Lack of the histone H4 N-termini leads to a similar delay in activation of the PHO5 promoter. These results indicate that one important contribution of HATs is to increase the rate of gene induction by accelerating chromatin remodeling, rather than to affect the final steady-state expression levels.

Acetyltransferases↗
PubMed2001

Identification of a novel spliceoform of inositol polyphosphate 4-phosphatase type Ialpha expressed in human platelets: structure of human inositol polyphosphate 4-phosphatase type I gene.

Inositol polyphosphate 4-phosphatases (IP4Ps) are enzymes involved in the regulation of phosphoinositide 3-kinase (PI3K) signaling. IP4Ps catalyze the hydrolysis of the D-4 position phosphoester of the PI3K generated lipid second messenger, phosphatidylinositol 3,4-bisphosphate. Western blot analysis detected the expression of a novel 110 kDa form of IP4P type Ialpha in mouse spleen, heart, lung, and uterus. In addition, the 110 kDa form of IP4P type Ialpha was found to be the major form of this enzyme expressed in human platelets, MEG-01 megakaryocytes and Jurkat T-cells. RT-PCR analysis of MEG-01 megakaryocytes and Jurkat T-cells indicates that the 110-kDa form of IP4P Ialpha is derived from an alternatively spliced mRNA that encodes an additional internal domain of 40 amino acids not present in the two previously described brain IP4P Ialpha spliceoforms. The predicted molecular mass of this spliceoform is 109,968 Da, consistent with its apparent molecular mass estimated by Western blot analysis. The novel domain is proline rich and contains a PEST sequence characteristic of proteins that are rapidly degraded by the calpain family of proteases. Analysis of genomic DNA sequence indicates that the IP4P type I gene consists of 25 exons and that this novel spliceoform is obtained as a result of an unusual type of differential splicing involving the use of an alternative 5'-GU donor splice site during the excision of intron 15. In addition, we show that all three known spliceoforms of IP4P Ialpha result from alternative splicing involving exon 15 and 16 indicating that structural variability in this region of the enzyme may be important for its function.

Alternative Splicing↗
PubMed2001

Cloning and structural analysis of partial acetylcholine receptor subunit genes from the parasitic nematode Teladorsagia circumcincta.

Nematode nicotinic acetylcholine receptors (nAChRs) are the sites of action for the anthelmintic drug levamisole. Recent findings indicate that the molecular mechanism of levamisole resistance may involve changes in the number and/or functions of target nAChRs. Accordingly, we have used an RT-PCR approach to isolate and characterise partial cDNA clones (tca-1 and tca-2) encoding putative nAChR subunits from the economically important trichostrongyloid, Teladorsagia circumcincta. The predicted tca-1 gene product is a 248 aa fragment (TCA-1) which contains structural motifs typical of ligand-binding (alpha-) subunits, and which shows very high sequence similarities (98.8 and 97.2% amino acid identities) to the alpha-subunits encoded by tar-1 and hca-1 from Trichostrongylus colubriformis and Haemonchus contortus, respectively. Sequence analyses of partial tca-1 cDNAs from one levamisole-resistant and two susceptible populations of T. circumcincta revealed polymorphism at the predicted amino acid level, but there was no apparent association of any particular tca-1 allele with resistance. tca-2 encodes a 67 aa fragment (TCA-2) containing the TM4 transmembrane domain and carboxyl terminus of a putative nAChR structural (non-alpha) subunit. The deduced amino acid sequence of TCA-2 shows highest similarity (75% amino acid identity) to ACR-2, a structural subunit involved in forming levamisole-gated ion channels in Caenorhabditis elegans, but low similarity (43% identity) to the corresponding regions of TAR-1 and HCA-1. tca-2 is the first nAChR subunit gene of this type to be isolated from parasitic nematodes, and it provides a basis for further characterisation of structural subunits in trichostrongyloids.

Amino Acid Sequence↗
PubMed2001

Tamoxifen mutagenesis and carcinogenesis in livers of lambda/lacI transgenic rats: selective influence of phenobarbital promotion.

Administration of tamoxifen (TAM) (20 mg/kg per day p.o.) for 6 weeks to female lambda/lacI transgenic rats caused a 4-fold increase in mutation frequency (MF) at the lacI gene locus in the livers of dosed animals compared with controls. After cessation of dosing, the MF showed a further increase with time at 2, 12 and 24 weeks, respectively. Phenobarbital promotion of similarly treated animals resulted in no increase in mutation frequency compared with TAM alone. Treatment with phenobarbital or TAM+phenobarbital resulted in time-dependent increases in liver weight compared with the corresponding controls. There was an increase in cell proliferation in the phenobarbital and TAM+phenobarbital groups, and at 24 weeks in the TAM dosed animals compared with controls. There was also a progressive increase in the number of GST-P expressing foci in the livers of TAM and TAM + phenobarbital rats compared with controls. The induction of cell proliferation and GSTP foci in the rat liver by phenobarbital is consistent with its ability to promote tamoxifen-initiated liver tumours in the rat. If the lacI gene is regarded as being representative of the rat genome in general (albeit that the gene is bacterial) the above observations suggest that promotion by tamoxifen confers selective advantage on mutated genes at loci that contribute to the tumour phenotype and that promotion of rat liver tumours by tamoxifen is not dependent simply upon the enhancement of cellular proliferation.

Animals↗
PubMed2001

Anxiety sensitivity: predictor of sleep-related impairment and medication use in chronic insomnia.

The relationship between anxiety sensitivity and sleep was investigated in a sample of 53 adults with chronic insomnia. Using hierarchical regression analyses, and after controlling for the propensity to worry and the presence of psychiatric comorbidity, results showed that anxiety sensitivity reliably improved the prediction of sleep-related impairment and frequency of hypnotic medication use, but not actual sleep disturbance. Specifically, fear of cognitive dyscontrol was associated with greater sleep-related impairment. There was a trend towards fear of physical distress predicting more frequent medication use. Implications of these findings for the treatment of insomnia are discussed and suggestions for future research are made.

Adult↗
PubMed2001

Predictors of complications after inguinal lymphadenectomy.

OBJECTIVE: The aim of this study was to identify predictors of complications in patients undergoing inguinal lymphadenectomy (LND) in the treatment of vulvar carcinoma. METHODS: Clinical information was abstracted from records of patients with invasive vulvar cancer. All patients underwent LND. Closed suction drains were placed in groin incisions and removed when output was less than 30 ml/24 h. Associations between variables were studied by chi(2) and t tests. RESULTS: Sixty-seven patients undergoing 112 LND were evaluated. Eighty-eight percent of patients underwent radical vulvar surgery and LND while 12% underwent LND alone. Patients were treated with either unilateral (22) or bilateral (45) LND. Seventy-three percent received extended postoperative prophylactic antibiotics. The median duration of suction drainage was 15 days for one drain and 14 days for two drains. Early postoperative cellulitis (<30 days after surgery) developed in 35.4%, early wound breakdown in 19.4%, early lymphedema in 4.8%, and early lymphocyst formation in 13.1%. Late cellulitis (>30 days after surgery) developed in 22.2%, late wound breakdown in 3.2%, late lymphedema in 29.5%, and late lymphocysts in 5%. Patients developing early cellulitis were more likely to have early wound breakdown (P = <0.001, RR 14.2) or early lymphocyst formation (P = 0.016, RR 7.6). Type of procedure, antibiotic use, need for adjuvant therapy, and duration of suction drainage did not influence early complications. Early complications and management strategies did not predict late complications. CONCLUSIONS: Chronic lymphedema occurs in nearly 30% of patients after LND. Late complications after LND were not predicted by early complications. New strategies for prevention of chronic lymphedema are needed.

Adult↗
PubMed2001

Facilitation of enkephalins catabolism inhibitor-induced antinociception by drugs classically used in pain management.

The aim of this study was to investigate the facilitatory effects of subanalgesic or low doses of different drugs (acetylsalicylic acid, ibuprofen and morphine) on the antinociceptive responses induced by the endogenous opioid peptides, enkephalins, protected from their catabolism by the dual enkephalin-degrading enzymes inhibitor RB101. According to the analgesic profile of the three studied compounds different antinociceptive assays were used: the hot plate and formalin tests in mice, and the tail flick and paw pressure tests on inflamed paws in rats and polyarthritic rats. Facilitatory effects of subanalgesic doses of acetylsalicylic acid and ibuprofen on RB101-induced antinociceptive responses were observed in the early and late phases of the formalin test, respectively. In the hot plate, tail flick and paw pressure tests, the dose-dependent analgesic effects of RB101 were strongly potentiated by subanalgesic doses of morphine (0.5 mg/kg), while in these tests, acetylsalicylic acid and ibuprofen were unable to modify the RB101-induced antinociceptive responses. The synergism in antinociceptive effects observed with the combination of RB101 and morphine supported by isobolographic analysis, may have interesting clinical implications, considering both the lack of opiate drawbacks observed with RB101 and the high potentiation of its antinociceptive effects with very low doses of morphine.

Analgesics↗
PubMed2001

Liquid chromatography electrospray-mass spectrometry of urinary aflatoxin biomarkers: characterization and application to dosimetry and chemoprevention in rats.

A liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) method for the measurement of aflatoxin biomarkers in urine has been developed and validated. The two major aflatoxin-DNA adducts formed in rat tissues, aflatoxin N(7)-guanine and its imidazole ring opened derivative, 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl formamido)-9-hydroxy-aflatoxin B(1), were detected and quantified in urine by the LC-ESI-MS/MS technique. Other metabolites derived from the conjugation and/or oxidation of aflatoxin B(1) measured in the urine of dosed rats included aflatoxin P(1), aflatoxin P(1)-glucuronide, aflatoxin Q(1), aflatoxin M(1), 8,9-dihydro-8,9-dihydroxy aflatoxin B(1), aflatoxin B(1)-mercapturic acid, the aflatoxin-cysteine glycine adduct derived from the aflatoxin-glutathione conjugate, aflatoxin M(1)P(1) and the aflatoxin B(1)-dialcohol. For in vivo studies to determine the dosimetry of certain aflatoxin metabolites, aflatoxin B(2) was used as an internal standard for recovery since this compound is not naturally produced in rats. In the final method using the internal standard, the coefficient of variation of six replicate analyses of in vivo rat urine samples for aflatoxin N(7)-guanine, aflatoxin B(1)-mercapturic acid, and aflatoxin M(1) was 12.5, 12.8, and 5.8%, respectively. Further, the LC-ESI-MS/MS method to detect aflatoxin N(7)-guanine in in vivo rat urine samples was at least 20-fold more sensitive than prior techniques. Using the LC-ESI-MS/MS technique, the dosimetry, on a weekly basis, of major urinary aflatoxin metabolites was assessed in animals chronically dosed over a 5-week period. Of particular importance was the application of this method to determine the modulation of levels of urinary aflatoxin metabolites by treatment with oltipraz, a chemopreventive agent that can completely ablate aflatoxin hepatocarcinogenesis in the rat. After 1 week, oltipraz administration diminished urinary aflatoxin N(7)-guanine, aflatoxin B(1)-mercapturic acid and aflatoxin M(1) levels by 83, 92, and 82%, respectively. The magnitude of this reduction was persistent at the day 14, 21, 28, and 35-day time points with the average decrease of aflatoxin N(7)-guanine, aflatoxin B(1)-mercapturic acid and aflatoxin M(1) being 73, 92, and 90%, respectively. Importantly, even under circumstances where the oltipraz intervention was most efficient in reducing aflatoxin metabolite levels, the LC-ESI-MS/MS method was still sensitive enough to detect the reduced biomarker content. This outcome has important translational implications for the application and analysis of the efficacy of primary and secondary prevention interventions in human populations where ambient exposure levels are low, but the toxicologic hazards of these exposures remain high.

Aflatoxins↗
PubMed2001

Identification of canine helper T-cell epitopes from the fusion protein of canine distemper virus.

The fusion protein of canine distemper virus (CDV-F), a 662 amino-acid envelope protein, was used as the target molecule for identification of canine T helper (Th) epitopes. A library of 94 peptides, each 17 residues in length overlapping by 10 residues and covering the entire sequence of CDV-F, was screened using a lymphocyte proliferation assay with peripheral blood mononuclear cells (PBMC) obtained from dogs inoculated with canine distemper virus (CDV) vaccine. Initially we observed low and inconsistent proliferation of PBMC in response to these peptides, even when using cells obtained from dogs that had received multiple doses of CDV. Subsequently, the use of expanded cell populations derived by in vitro stimulation of canine PBMC with pools of peptides allowed the identification of a number of putative canine Th-epitopes within the protein sequence of CDV-F. There were two major clusters of Th-epitopes identified close to the cleavage site of the F0 fusion protein, while some others were scattered in both the F1 and F2 fragments of the protein. Some of these peptides, in particular peptide 35 (p35), were stimulatory in dogs of different breeds and ages. The identification of such promiscuous canine Th-epitopes encouraged us to assemble p35 in tandem with luteinising hormone releasing hormone (LHRH) a 10 amino-acid residue synthetic peptide representing a B-cell epitope which alone induces no antibody in dogs. The totally synthetic immunogen was able to induce the production of very high titres of antibodies against LHRH in all dogs tested. These results indicate that p35 could be an ideal candidate for use as a Th-epitope for use in outbred dogs.

Amino Acid Sequence↗
PubMed2001

Change management in primary care: design and evaluation of an internet-delivered course.

OBJECTIVES: To deliver and evaluate an internet course in change management for primary care professionals. DESIGN: A 12-week course delivered over the internet. Respondents were allocated into two groups: one had access to the course tutor individually, while the other could also communicate with the rest of the learner group. Learning outcomes were assessed by means of pre- and post-intervention questionnaires and by interviews with some participants. SUBJECTS: 111 primary care professionals. RESULTS: Subjects showed significant improvements on all learning outcomes. The group with access to the course tutor alone completed more units and had greater improvements in their learning outcomes. More of this group completed the course and completed a portfolio. Respondents who could communicate with other members of the group did not find this a positive experience. CONCLUSION: The internet can be used to deliver learning in change management to primary care professionals. Access to a discussion forum did not improve, and possibly impaired learning. More work is needed on the mentoring of internet learning.

Computer-Assisted Instruction↗
PubMed2001

The ubiquitin-specific protease UBP14 is essential for early embryo development in Arabidopsis thaliana.

The ubiquitin/26S proteasome pathway is a major route for selectively degrading cytoplasmic and nuclear proteins in eukaryotes. In this pathway, chains of ubiquitins become attached to short-lived proteins, signalling recognition and breakdown of the modified protein by the 26S proteasome. During or following target degradation, the attached multi-ubiquitin chains are released and subsequently disassembled by ubiquitin-specific proteases (UBPs) to regenerate free ubiquitin monomers for re-use. Here, we describe Arabidopsis thaliana UBP14 that may participate in this recycling process. Its amino acid sequence is most similar to yeast UBP14 and its orthologues, human IsoT1-3 and Dictyostelium UbpA, and it can functionally replace yeast UBP14 in a ubp14Delta mutant. Like its orthologues, AtUBP14 can disassemble multi-ubiquitin chains linked internally via epsilon-amino isopeptide bonds using Lys48 and can process some, but not all, translational fusions of ubiquitin linked via alpha-amino peptide bonds. However, unlike its yeast and Dictyostelium orthologues, AtUBP14 is essential in Arabidopsis. T-DNA insertion mutations in the single gene that encodes AtUBP14 cause an embryonic lethal phenotype, with the homozygous embryos arresting at the globular stage. The arrested seeds have substantially increased levels of multi-ubiquitin chains, indicative of a defect in ubiquitin recycling. Taken together, the data demonstrate an essential role for the ubiquitin/26S proteasome pathway in general and for AtUBP14 in particular during early plant development.

Amino Acid Sequence↗