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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
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↗
PubMed1994

Impediments to the implementation of environmental policy.

During the past two decades Congress has enacted numerous pieces of legislation for the prevention of environmentally-provoked disease and for reducing ecological risk. The transmutation of these policies into action has been plagued by problems of delay, interagency disagreement, and inadequate resources. As the executive and legislative branches of the federal government try within the next four years to settle and move beyond a number of large environmental health and ecological issues, they must be constantly alerted to the limitations inherent in the implementation phase of the policy process, and not raise public expectations beyond what is realistically achievable in terms of policy impact (i.e. changes in the environment that are associated with measures of government activities).

Environmental Health↗
PubMed1994

Single lung transplantation: a temporal look at rejection, infection, and survival.

Single lung transplantation (SLT) has emerged as routine therapy for selected patients with end-stage lung disease. This study examines the incidence of rejection, infection, and survival during the first posttransplant year. Twenty-one patients (12 male, 9 female; mean age 46 +/- 13 years) underwent 23 SLT procedures (12 left, 11 right lung). Indications were pulmonary fibrosis in six, emphysema in seven, primary pulmonary hypertension in three, Eisenmenger's syndrome in one, pulmonary veno-occlusive disease in one, a-1 antitrypsin deficiency in two, CREST syndrome in one, and retransplantation (graft failure and bronchiolitis obliterans) in two. All were maintained on triple immunotherapy. Survival at 1 year was 100%. The five patients with preoperative pulmonary hypertension had normal hemodynamics at follow up. Freedom from event at 1 year was rejection 23 per cent, all infections 6 per cent, viral 40 per cent, bacterial 55 per cent, fungal 74 per cent. At 1 year, cumulative incidence (events/patient-year) was rejection 1.61, all infections 2.18, viral 0.78, bacterial 1.12, fungal 0.28. Two of 21 patients have developed bronchiolitis obliterans at 1 and 2 years posttransplant. SLT provided safe, effective treatment for a wide variety of end-stage lung diseases. Rejection and infection, although common, may be safely treated with resolution.

Actuarial Analysis↗
PubMed1993

Peptide glyoxals: a novel class of inhibitor for serine and cysteine proteinases.

A series of novel synthetic dipeptides, containing a C-terminal glyoxal grouping (-COCHO), have been tested as inhibitors against typical members of the serine- and cysteine-proteinase families. For example, the sequences benzyloxycarbonyl (Cbz)-Pro-Phe-CHO (I) and Cbz-Phe-Ala-CHO (II), which fulfil the known primary and secondary specificity requirements of chymotrypsin and cathepsin B respectively, have been found to be potent reversible inhibitors of their respective target proteinase. Thus I was found to inhibit chymotrypsin with a Ki of approximately 0.8 microM, whereas II exhibits a Ki of approximately 80 nm against cathepsin B. These Ki values are some 10-fold and 3-fold lower than those reported for the corresponding peptide-aldehyde inhibitors of chymotrypsin and cathepsin B upon which the peptidyl-glyoxals were fashioned. Unexpectedly, the sequence Cbz-Pro-Ala-CHO, which was designed to inhibit elastase-like proteinases, exhibited no inhibitory activity towards porcine pancreatic elastase, even when used at concentrations as high as 200 microM.

Animals↗
PubMed1993

Characterization of the cysteine proteinases of the common liver fluke Fasciola hepatica using novel, active-site directed affinity labels.

The excreted/secreted proteinases of adult and juvenile Fasciola hepatica maintained in vitro were found to hydrolyse the fluorogenic substrates Cbz-Phe-Arg- and Cbz-Arg-Arg-NHMec. This activity was demonstrated to have a classical cysteine proteinase inhibitor profile, with turn-over of both substrates being blocked by pre-incubation with E64 and peptidyl diazomethanes. The Cbz-Arg-Arg-NHMec hydrolysing activity of the mature fluke exhibited an alkaline stability not characteristic of its mammalian lysosomal counterparts. Further, the biotinylated affinity reagents biotin-Phe-Ala-CHN2 and biotin-Phe-Cys(SBzyl)-CHN2 were used to label and characterize these cysteine proteinases in terms of apparent molecular weight and subsite specificity. Adult fluke media were found to contain four species of molecular weights 66, 58, 50 and 25-26 kDa; juvenile media contained three species of molecular weights 66, 54 and 25-26 kDa. The major 25-26 kDa cysteine proteinase common to both stages was shown to have a subsite specificity similar to that of mammalian cathepsin B.

Affinity Labels↗
PubMed1993

Infection in the transplanted and native lung after single lung transplantation.

OBJECTIVE: To analyze a single-center experience with infectious complications of single lung transplantation (SLT) with special emphasis on risk factors for infection in the transplanted and native lung. DESIGN: Consecutive case series. SETTING: University teaching hospital. PATIENTS: Fifteen consecutive SLT recipients (mean age, 43 years; 9 men and 6 women). Mean follow-up was 337 days. RESULTS: Fifteen patients had 24 infectious episodes (1.6 per patient) of which 83 percent were life-threatening, 79 percent involved the lung, airway, or pleural space, and 79 percent occurred in the first 4 months after transplantation. Despite this high infectious morbidity, there were no infectious deaths. The most important infections were bacterial pneumonia (n = 10), cytomegalovirus (CMV) pneumonia (n = 5), and bronchial anastomotic infections (n = 3). Significant risk factors for bacterial pneumonia were a diagnosis of primary or secondary pulmonary hypertension (p < 0.05) and the presence of airway complications of stenosis or dehiscence (p < 0.05). No risk factors for overall lung infections were identified. The native lung was involved in 6 of 16 lung infections and was the exclusive site of infection in 4 cases. Underlying disease in the native lung may have predisposed to infection at that site by a mechanism of inadequate blood flow or impaired ventilation. Three bronchial anastomotic infections (Pseudomonas, Candida, Aspergillus) occurred, all with dehiscence of the anastomosis. These were highly morbid but resolved with antibiotics, stent placement, and surgical retention in two of the three cases. The five episodes of CMV pneumonia caused mild (four patients) or moderate (one patient) dysfunction and responded to antiviral agents without relapse. CONCLUSION: The frequency, complexity, and morbidity of infections after SLT were great, but most infections were manageable and good outcomes were achieved. A pretransplant diagnosis of pulmonary hypertension or posttransplant occurrence of bronchial stenosis or dehiscence were associated with a higher rate of bacterial pneumonia. The underlying disease in the native lung may predispose to infection at that site.

Adolescent↗
PubMed1993

Twin trouble.

Explore the source record for details and available documents.

Adult↗
PubMed1992

Assembly of the oligomeric membrane pore formed by Staphylococcal alpha-hemolysin examined by truncation mutagenesis.

The alpha-hemolysin (alpha HL) from Staphylococcus aureus causes the lysis of susceptible cells such as rabbit erythrocytes (rRBCs). Lysis is associated with the formation of a hexameric pore in the plasma membrane. Here we show that truncation mutants of alpha HL missing 2 to 22 N-terminal amino acids form oligomers on the surfaces of rRBCs but fail to lyse the cells. By contrast, mutants missing 3 or 5 amino acids at the C terminus are very inefficient at oligomerization but do lyse rRBCs, albeit extremely slowly. The C-terminal truncation mutants, retarded as monomers on the cell surface, undergo a conformational change in which the protease-sensitive loop located near the midpoint of the polypeptide chain becomes occluded. Judged by this criterion, polypeptides truncated at the N terminus, frozen as nonlytic oligomers, are in a similar conformation. A second proteolytic site near the N terminus of the polypeptide becomes inaccessible in the lytic pore formed by the wild-type polypeptide, supporting the idea that a second conformational change occurs upon pore formation. These findings suggest a pathway for assembly of the lytic pore in which alpha HL first binds to target cells as a monomer, which is converted to a nonlytic oligomeric intermediate before formation of the pore. In keeping with this model, an N-terminal truncation mutant blocks the slow lysis induced by a C-terminal truncation mutant, presumably by diverting the weakly lytic subunits into inactive oligomers.

Amino Acid Sequence↗
PubMed1992

Functional expression of the alpha-hemolysin of Staphylococcus aureus in intact Escherichia coli and in cell lysates. Deletion of five C-terminal amino acids selectively impairs hemolytic activity.

The alpha-hemolysin gene from Staphylococcus aureus, excluding the 5' region encoding the hydrophobic leader sequence, was amplified from genomic DNA. The identity of the disputed C terminus has been confirmed and revisions made to the internal sequence. The hemolysin is expressed at high levels in Escherichia coli and has been purified to homogeneity from this source. In addition, active [35S-Met]alpha-hemolysin of high specific radioactivity can be generated in an E. coli transcription-translation system. By criteria based on protein chemistry, and biological and electrophysiological assays, the recombinant polypeptide is closely similar to the staphylococcal polypeptide ruling out the possibility of functionally important posttranslational modifications in S. aureus. Convenient new assays utilizing the 35S-labeled polypeptide to measure erythrocyte binding, oligomer formation in detergent and on target cells, and hemolysis have been developed. They have been used to demonstrate that a deletion mutant of alpha-hemolysin, in which five C-terminal amino acids are absent, is severely compromised in its ability both to oligomerize and to lyse rabbit erythrocytes. The mutant polypeptide nevertheless binds tightly to erythrocytes as a monomer, strengthening the idea that oligomerization is required for cell lysis.

Animals↗
PubMed1992

The synthesis, kinetic characterization and application of a novel biotinylated affinity label for cathepsin B.

In this study we report on the synthesis, kinetic characterization and application of a novel biotinylated and active-site-directed inactivator of cathepsin B. Thus the peptidyldiazomethane biotinyl-Phe-Ala-diazomethane has been synthesized by a combination of solid-phase and solution methodologies and has been shown to be a very efficient inactivator of bovine and human cathepsin B. The respective apparent second-order rate constants (k0bs./[I]) for the inactivation of the human and bovine enzymes by this reagent, namely approximately 5.4 x 10(4) M-1.min-1 and approximately 7.8 x 10(4) M-1.min-1, compare very favourably with those values determined for the urethane-protected analogue benzyloxycarbonyl-Phe-Ala-chloromethane first described by Green & Shaw [(1981) J. Biol. Chem. 256, 1923-1928], thus demonstrating that the presence of the biotin moiety at the P3 position is compatible with inhibitor effectiveness. The utilization of this reagent for the detection of cathepsin B in electrophoretic gels, using Western blotting and in combination with a streptavidin/alkaline phosphatase detection system, is also demonstrated. Given that the peptidyldiazomethanes exhibit a pronounced reactivity towards cysteine proteinases, we feel that the present label may well constitute the archetypal example of a wide range of reagents for the selective labelling of this class of proteinase, even in a complex biological milieu containing additional classes of proteinases.

Affinity Labels↗