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Biomedical subjects

B Walker

Publications and source records attributed to B Walker.

At least 37 records · Page 2Linked to original sources
PubMed1995

Cytokine profile of circulating T cells of leprosy patients reflects both indiscriminate and polarized T-helper subsets: T-helper phenotype is stable and uninfluenced by related antigens of Mycobacterium leprae.

Cytokine profiles of circulating mononuclear cells were studied with the aim of delineating T-cell subsets in leprosy patients with active disease. Using reverse transcriptase-polymerase chain reaction (RT-PCR) for cytokine mRNA and enzyme-linked immunoassay (ELISA) for the secreted products, interferon-gamma (IFN-gamma), interleukin-4 (IL-4), IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) were studied. Three antigens, native Mycobacterium leprae, a recombinant antigen LSR/A15 of M. leprae and peptide 624 spanning 58-77 amino acids of the latter, were used to induce cytokine expression and release. Half of the subjects, irrespective of the clinical type or antigen used, showed a mixed T-helper type 0 (Th0)-like cytokine pattern, with evidence of the concomitant presence of IFN-gamma and IL-4. The remainder showed a polarized pattern based on the type of leprosy. Lepromatous patients with disseminated disease had Th2-type cytokines, with IL-4 but not IFN-gamma. In contrast, tuberculoid leprosy patients with localized disease showed a Th1-like profile, with the presence of IFN-gamma but not IL-4. Of interest was the stability of the Th phenotype for M. leprae-related antigens. Both the recombinant and the peptide antigens induced the same phenotype as the natural M. leprae bacillus in all except four of 45 leprosy patients.

Antigens, Bacterial↗
PubMed1995

Environmental health and African Americans: challenges and opportunities.

Demographic shifts and other social and economic forces as well as the increasing concerns about environmental determinants of disease and dysfunction have focused more attention on the disproportionate burden of environmental risk on blacks and other minorities. This article reviews these developments and identifies related challenges and opportunities confronting the medical community in the prevention of environmentally provoked disease among black Americans.

Black or African American↗
PubMed1994

Surface labeling of key residues during assembly of the transmembrane pore formed by staphylococcal alpha-hemolysin.

Structural changes in staphylococcal alpha-hemolysin (alpha HL) that occur during oligomerization and pore formation on membranes have been examined by using a simple gel-shift assay to determine the rate of modification of key single-cysteine mutants with the hydrophilic sulfhydryl reagent, 4-acetamido-4'-((iodoacetyl)amino)stilbene-2,2'-disulfonate (IASD). The central glycine-rich loop of alpha HL lines the lumen of the transmembrane channel. A residue in the loop remains accessible to IASD after assembly, in keeping with the ability of the pore to pass molecules of approximately 1000 Da. By contrast, residues near the N-terminus, which are critical for pore function, become deeply buried during oligomerization, while a residue at the extreme C-terminus increases in reactivity after assembly, consistent with a location in the part of the pore that projects from the surface of the lipid bilayer.

Animals↗
PubMed1994

Identification and characterization of the cysteine and serine proteinases of the trematode, Haplometra cylindracea and determination of their haemoglobinase activity.

The excreted/secreted proteinases of Haplometra cylindracea maintained in vitro, were found to hydrolyse the fluorogenic substrates, Z-ArgArg-NHMec and Z-PheArg-NHMec. This activity was shown to be typically that of cysteine proteinases, as turn-over of both substrates could be blocked by pre-incubation with peptidyl diazomethyl ketones. The biotinylated affinity reagent, biotin-Phe Ala-DMK, used in combination with Z-PheTyr(OBut)-DMK, was employed for the labelling and characterization of these cysteine proteinase activities. Three cathepsin B-like species were detected, with molecular weights of 48, 22-23 and 14 kDa, together with a cathepsin L-like enzyme, with a molecular weight of 55 kDa. The proteinases were also found to have hydrolytic activity towards the substrate, Z-GlyGlyArg-NHMec, which could be blocked by pre-incubation with either of the serine proteinase-selective reagents, Z-Argp(OPh)2 or biotin-Lysp(OPh)2, showing the activity to be trypsin-like. Using the biotinylated affinity label to characterize the trypsin-like enzymes revealed two molecular species with molecular weights of 20 and 24 kDa.

Affinity Labels↗
PubMed1994

Modeling the growth of Yersinia enterocolitica in donated blood.

BACKGROUND: Sepsis and death subsequent to the transfusion of blood containing Yersinia enterocolitica is an increasing problem. The organisms probably originate from bacteremia in the donor and can subsequently multiply at low temperature. STUDY DESIGN AND METHODS: Reported here are experiments with a strain of Y. enterocolitica associated with a case of transfusion-associated bacteremia. RESULTS: It was found that the rapid early killing of Y. enterocolitica injected into donated blood does not require viable phagocytes and can be explained by complement-mediated killing. Complement resistance in Y. enterocolitica is known to be plasmid-coded. It is expressed at 37 degrees C, but not at 20 degrees C, and is favored by calcium-deficient culture media. Y. enterocolitica organisms induced to express complement resistance were still killed in donated blood, though the initial rate was slower. Such organisms multiplied in plasma at 37 degrees C, but were killed after 6 hours of incubation at 20 degrees C, presumably because complement resistance genes are switched off at this temperature. CONCLUSION: This experiment is thought to reflect the natural history of Y. enterocolitica contamination of blood, in which complement-resistant organisms in the donor blood encounter lower temperatures after donation. These observations suggest that the practice of plasma depletion may have contributed to the increased incidence of mortality due to Y. enterocolitica contamination of donated blood.

Blood↗
PubMed1994

A pore-forming protein with a protease-activated trigger.

alpha-Hemolysin (alpha HL) is a 293 amino acid pore-forming toxin, which is secreted as a water-soluble monomer by Staphylococcus aureus. By forming a hexameric pore, alpha HL damages the plasma membranes of target cells. Previous studies established that alpha HL proteins with nicks near the midpoint of a central glycine-rich loop are held together by a domain-domain interaction and are hemolytically active. In contrast, alpha HL proteins comprising two alpha HL truncation mutants that overlap in the central loop have no or greatly reduced pore-forming activity, even though the two chains again form a tight complex. Based on these findings, overlap mutants have now been designed that are activated when redundant amino acids in the loop are removed by proteases. Further, the identity of the activating enzyme can be specified by additional mutagenesis of the protease recognition site in the overlap sequence. Mutants of alpha HL that are activated by tumor-associated proteases might be useful components of immunotoxins.

Animals↗
PubMed1994

A pore-forming protein with a metal-actuated switch.

Staphylococcal alpha-hemolysin, a pore-forming exotoxin, is a polypeptide of 293 amino acids that is secreted by Staphylococcus aureus as a water-soluble monomer. It assembles to form hexameric pores in lipid bilayers. Previous studies of pore formation have established the involvement of a central glycine-rich loop. Here, we show that when five consecutive histidine residues replace amino acids 130-134 at the midpoint of the loop, they provide a switch with which pore activity can be (i) turned off by micromolar concentrations of divalent zinc ions and (ii) turned back on with the chelating agent EDTA. Planar bilayer recordings show that Zn2+ and EDTA can act on open channels from either side of the bilayer and thus demonstrate that the central loop lines part of the conductive pathway. Our results suggest that genetically-engineered pore-forming proteins might make useful components of metal ion sensors.

Bacterial Toxins↗
PubMed1994

Synthesis of a cyclic analogue of the C-loop region of epidermal growth factor, containing 1-aminocyclopropane-1-carboxylic acid.

We report the synthesis of a cyclic analogue of epidermal growth factor sequence 33-42 with substitution of 1-aminocyclopropane-1-carboxylic acid for glycine at position 39 (N-acetyl-Cys-Val-Ile-Gly-Tyr-Ser-ACPCA-Asp-Arg-Cys-NH2). The analogue was synthesised by solid-phase methods, using t-Boc chemistry and acid-labile side-chain protecting groups. The use of the 4-methoxybenzyl protecting group for C- and N-terminal cysteine residues resulted in the spontaneous formation of the desired intramolecular disulfide bond after HF deprotection.

Amino Acid Sequence↗
PubMed1994

Interdisciplinary evaluation of cerebral hemodynamics in the treatment of arteriovenous fistulae associated with giant varices.

The techniques for the treatment of intracranial arteriovenous fistulae include angiographic balloon occlusion of the fistula as well as direct surgical attack. Regardless of the method, the occurrence of severe hyperemia caused by a lack of autoregulation after obliteration of the fistula remains a significant concern. We report the use of single photon emission computed tomography and transcranial Doppler studies to assess the occurrence of hyperemia during trial balloon occlusion of such fistulae in two patients. Single photon emission computed tomography and transcranial Doppler studies confirmed the lack of hyperemia during the test occlusion, allowing consideration of treatment plans involving acute fistula occlusion without the difficulty imposed by gradual occlusion and permitting a more accurate evaluation of risk. The purpose of this report is to illustrate how clinical evaluation of intracranial hemodynamics can contribute significantly to treatment decisions.

Adult↗
PubMed1994

The detection, quantification and partial characterisation of cathepsin B-like activity in human pathological synovial fluids.

In this study, the levels of the cysteine proteinase--cathepsin B were measured in diseased synovial fluids using a steady state fluorometric assay. Cathepsin B-like activity was shown to be present in all the samples analysed, with the rheumatoid arthritic synovial fluids possessing significantly higher concentrations (mean value ca. 416 mg/l) than the osteoarthritic fluids (mean value ca. 142.4 mg/l). In addition, upon treatment with pepsin, all of the rheumatoid arthritis samples were shown to possess additional cathepsin B-like activity, suggesting the presence of a reservoir of latent precursor molecules. By utilising a recently developed biotinylated affinity label for cathepsin B-like proteinases and sheep anti-(human cathepsin B) antibodies, used in combination with SDS-PAGE and Western blotting, the rheumatoid arthritic synovial cathepsin B was shown to exist in two forms with apparent molecular masses of M(r) 29,000 and 42,000. We propose that the former is a functionally active proteinase, whereas the latter is a pepsin activatable proform which, when cleaved by this aspartyl proteinase, is converted into a catalytically competent species of M(r) 20,000.

Affinity Labels↗
PubMed1994

Psychosocial needs of family caregivers of terminally ill patients.

The primary caregivers (mean age = 63 yr.) of 28 terminally ill veterans (mean age = 67 yr.) who were living at home were surveyed for their concrete and psychosocial needs. The caregivers also completed the Beck Depression Inventory, the Life Satisfaction Index, the Provision of Social Relations scale, and the Burden Inventory. The rank order of concrete and psychosocial needs is reported for these caregivers. Increased scores on depression were associated with decreased life satisfaction as was low social support. Not surprisingly, higher numbers of concrete and psychosocial needs were associated with increases in depression.

Adult↗
PubMed1994

Prediction of tolerance to carotid artery occlusion using transcranial Doppler ultrasound.

Surgical sacrifice of the carotid artery is a frequently anticipated event during the treatment of certain aneurysms and tumors. The ability to predict tolerance to carotid artery occlusion is therefore of benefit when planning procedures in which the carotid artery is at risk. A trial of carotid artery occlusion using an angiographic balloon during concurrent neurological examination or blood flow studies is an accepted method for testing tolerance, but it carries the risks of an angiogram and cannot be performed at the bedside. Transcranial Doppler ultrasound (TCD) is a noninvasive modality that permits measurement of blood velocity in cerebral vessels. The immediate effects of carotid artery occlusion on middle cerebral artery (MCA) perfusion can be obtained by insonating this artery during manual carotid artery compression. To compare the TCD response to carotid artery compression with the data obtained with more formal testing, the MCA of 22 patients was insonated during manual carotid artery compression and the results compared with the clinical tolerance to balloon occlusion in all patients and to blood flow studied by single photon emission computerized tomography before or during balloon occlusion in 14 of the 22 patients. Surgery was planned to treat giant unruptured aneurysms in 17 cases, intracranial tumors in three, a carotid-cavernous fistula in one, and a carotid artery injury in one. Fifteen patients showed a reduction in TCD flow velocities by no more than 65%; of these, 14 (93%) clinically tolerated the balloon occlusion test. Of the seven patients showing a TCD flow velocity decrease of more than 65%, six (86%) developed a transient focal deficit during the occlusion. It is concluded that the change in MCA velocity measured with TCD studies during manual carotid artery occlusion is a useful predictor of the clinical and blood flow responses to a trial of carotid artery occlusion with an angiographic balloon.

Adult↗