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Biomedical subjects

M Kehoe

Publications and source records attributed to M Kehoe.

At least 19 recordsLinked to original sources
PubMed2001

Phase I study of the BLP25 (MUC1 peptide) liposomal vaccine for active specific immunotherapy in stage IIIB/IV non-small-cell lung cancer.

Active specific immunotherapy with liposomal vaccines targeted to the mucinous carcinoma-associated glycoprotein MUC1 have shown promising results in animal models. The aim of this phase I study was to evaluate the safety and immunogenicity of 2 dose levels of the MUC1 liposomal vaccine preparation BLP25. Patients with stage IIIB or IV non-small-cell lung cancer received either 20 microg or 200 microg of the liposomal BLP25 vaccine preparation. Injections were administered subcutaneously at weeks 0, 2, 5, and 9. Immunological responses to vaccination were measured by antibody production, cytotoxic T lymphocytes (CTL), and proliferative T-helper cells. Seventeen patients were entered on study; 12 patients completed the vaccination protocol. Two patients, 1 in each dose group, developed clinically insignificant grade 3 lymphopenia during the study. Nonhematologic toxicities were mild and self-limiting, and there were no significant long-term injection site reactions. Immunological assays revealed the generation of CTLs against MUC1-positive tumor cell lines in 5 of 12 evaluable patients. These patients did not have CTLs prior to receiving the vaccine. No significant humoral response to the vaccination was observed. No objective antitumor responses were observed. Of the 12 patients completing all the vaccinations, 4 had stable disease. Median survival time was 5.4 months in the 20 microg group and 14.6 months in the 200 microg group. In summary, the BLP25 liposomal vaccine was well tolerated and elicited a primarily cellular immune response in these lung cancer patients. This study forms the basis for further clinical exploration of the MUC1 liposomal vaccine, BLP25.

Journal Article↗
PubMed2001

Guillain-Barré syndrome--a patient guide and nursing resource.

Guillain-Barré Syndrome (GBS) is an illness characterized by acute neuromuscular paralysis. A review of the history, course of the disease, current treatments, and nursing interventions, as well as excerpts from a patient teaching guide developed by the author for patients with GBS is included in this paper. The objectives are to present information about GBS, first at a level of understanding appropriate for patients and their families, and then to provide a more indepth discussion for health care providers. Despite the potential severity of GBS, the expected outcomes are encouraging. GBS affects 1-2.73 individuals per 100,000/year (Hahn, 1998). The symptoms can range from numbness and tingling with mild weakness to total paralysis requiring mechanical ventilation. Once diagnosed, patients are usually treated with intravenous immune globulin (i.v. IG), which significantly reduces the duration of the illness (Hughes, 1997; Guillain-Barré Syndrome Study Group, 1985). Neuroscience nurses can make a difference in the recovery of their patients by anticipating potential complications and attending to their special needs during the acute and recovery phases of their illness. Aside from physical care, being able to support and teach the patient and family about GBS is crucial. Use of a patient and family teaching guide is one strategy for providing education and support.

Adolescent↗
PubMed1999

Streptolysin O: inhibition of the conformational change during membrane binding of the monomer prevents oligomerization and pore formation.

Streptolysin O is a four-domain protein toxin that permeabilizes animal cell membranes. The toxin first binds as a monomer to membrane cholesterol and subsequently assembles into oligomeric transmembrane pores. Binding is mediated by a C-terminally located tryptophan-rich motif. In a previous study, conformational effects of membrane binding were characterized by introducing single mutant cysteine residues that were then thiol-specifically derivatized with the environmentally sensitive fluorophoracrylodan. Membrane binding of the labeled proteins was accompanied by spectral shifts of the probe fluorescence, suggesting that the toxin molecule had undergone a conformational change. Here we provide evidence that this change corresponds to an allosteric transition of the toxin monomer that is required for the subsequent oligomerization and pore formation. The conformational change is reversible with reversal of binding, and it is related to temperature in a fashion that closely parallels the temperature-dependency of oligomerization. Furthermore, we describe a point mutation (N402E) that, while compatible with membrane binding, abrogates the accompanying conformational change. At the same time, the N402E mutation also abolishes oligomerization. These findings corroborate the contention that the target membrane acts as an allosteric effector to activate the oligomerizing and pore-forming capability of streptolysin O.

Alanine↗
PubMed1998

Assembly mechanism of the oligomeric streptolysin O pore: the early membrane lesion is lined by a free edge of the lipid membrane and is extended gradually during oligomerization.

Streptolysin O (SLO) is a bacterial exotoxin that binds to cell membranes containing cholesterol and then oligomerizes to form large pores. Along with rings, arc-shaped oligomers form on membranes. It has been suggested that each arc represents an incompletely assembled oligomer and constitutes a functional pore, faced on the opposite side by a free edge of the lipid membrane. We sought functional evidence in support of this idea by using an oligomerization-deficient, non-lytic mutant of SLO. This protein, which was created by chemical modification of a single mutant cysteine (T250C) with N-(iodoacetaminoethyl)-1-naphthylamine-5-sulfonic acid, formed hybrid oligomers with active SLO on membranes. However, incorporation of the modified T250C mutant inhibited subsequent oligomerization, so that the hybrid oligomers were reduced in size. These appeared as typical arc lesions in the electron microscope. They formed pores that permitted passage of NaCl and calcein but restricted permeation of large dextran molecules. The data indicate that the SLO pore is formed gradually during oligomerization, implying that pores lined by protein on one side and an edge of free lipid on the other may be created in the plasma membrane. Intentional manipulation of the pore size may extend the utility of SLO as a tool in cell biological experiments.

Animals↗
PubMed1998

Streptolysin O: a proposed model of allosteric interaction between a pore-forming protein and its target lipid bilayer.

Streptolysin O, a polypeptide of 571 amino acids, belongs to the family of thiol-activated toxins that permeabilize animal cell membranes. The protein binds as a monomer to membrane cholesterol. Binding involves a conserved region close to the C-terminus and triggers subsequent polymerization into large arc- and ring-shaped structures surrounding pores of up to 30 nm. Besides the C-terminus, a distantly located region spanning residues 213-305 is involved in oligomerization and in membrane insertion. Here, we searched for conformational effects of monomer binding to the latter functionally important region. To this end, single cysteine substitution mutants were produced and derivatized with the polarity-sensitive fluorophore acrylodan. Fluorimetric measurements revealed that binding of the monomer to membranes is accompanied by distinct environmental changes at amino acid residues 218, 248, 266, and 277. Conspicuously, the environment of residues 218 and 266 became more hydrophilic, suggesting movement of these residues out of hydrophobic protein pockets. Upon oligomerization, further alterations in all side-chain environments were observed. The membrane-bound monomer thus differs in conformation from both the monomer in solution and the subunit of the oligomer. The putative binding site of the molecule is linked to remote domains involved in oligomerization and membrane insertion in an apparently allosteric fashion. It is proposed that allostery is responsible for restricting oligomerization to the membrane-bound state of the toxin.

2-Naphthylamine↗
PubMed1997

Truncation patterns in English-speaking children's word productions.

This study examines English-speaking children's truncation patterns (i.e., syllable deletion patterns) in multisyllabic words to determine if they are consistent with metrical constraints or perceptual biases. It also examines segmental influences on children's truncations. Children, age 22-34 months, produced three-syllable novel and real words and four-syllable real words, which varied across stress and segmental pattern. Results revealed a significant stress pattern effect on truncation rate, but findings were not consistent with metrical or perceptual salience predictions. The clearest account of the findings came from an analysis of truncation rate across individual words: Children truncated WSW (weak-strong-weak) words and words that contained intervocalic sonorants more frequently than other words. Analysis of truncation patterns in SWW and SWSW words revealed that final unstressed syllables were more frequently preserved than nonfinal unstressed syllables. Findings support the interaction between metrical, syllabic, and acoustic salience factors in children's multisyllabic word productions.

Child Language↗
PubMed1996

Membrane-penetrating domain of streptolysin O identified by cysteine scanning mutagenesis.

Streptolysin O (SLO), a polypeptide of 571 amino acids, belongs to a family of highly homologous toxins that bind to cell membranes containing cholesterol and then polymerize to form large transmembrane pores. A conserved region close to the C terminus contains the single cysteine residue of SLO and has been implicated in membrane binding, which has been the only clear assignment of function to a part of the sequence. We have used a cysteine-less active mutant of SLO to introduce single cysteine residues at 19 positions distributed throughout the sequence. The cysteines were derivatized with the polarity-sensitive fluorophore acrylodan, and the fluorescence emission of the label was examined at the different stages of SLO pore assembly. With several mutants, oligomerization on membranes was accompanied by emission blue-shifts, indicating movement of the label into a more hydrophobic environment. These effects were essentially confined to the range of amino acids 213-305. With oligomeric mutants L274C, S286C, and S305C, additional environmental alterations were induced when different nondenaturing detergents were used to dislodge the membrane lipids from the oligomers. The corresponding amino acid residues thus insert into the lipid bilayer during pore formation. Conversely, the spectra of oligomeric mutants A213C and T245C were not affected by detergents. Devoid of contact with the lipid bilayer, these amino acid residues probably participate in the interaction of SLO molecules within the oligomer.

2-Naphthylamine↗
PubMed1996

Molecular architecture of a toxin pore: a 15-residue sequence lines the transmembrane channel of staphylococcal alpha-toxin.

Staphylococcus aureus alpha-toxin is a hydrophilic polypeptide of 293 amino acids that produces heptameric transmembrane pores. During assembly, the formation of a pre-pore precedes membrane permeabilization; the latter is linked to a conformational change in the oligomer. Here, 41 single-cysteine replacement toxin mutants were thiol-specifically labelled with the polarity-sensitive fluorescent probe acrylodan. After oligomerization on membranes, only the mutants with acrylodan attached to residues in the sequence 118-140 exhibited a marked blue shift in the fluorescence emission maximum, indicative of movement of the fluorophore to a hydrophobic environment. Within this region, two functionally distinct parts could be identified. For mutants at positions 126-140, the shifts were partially reversed after membrane solubilization by detergents, indicating a direct interaction of the label with the membrane lipids. Membrane insertion of this sequence occurred together with the final pre-pore to pore transition of the heptamer. Thus residues 126-140 constitute a transmembrane sequence in the pore. With labelled residues 118-124, pre-pore assembly was the critical event to induce the spectral shifts, which persisted after the removal of membrane lipids and hence probably reflects protomer-protomer contacts within the heptamer. Finally, a derivative of the mutant N121C yielded occluded pores which could be opened by reductive reversal of the modification. Therefore this residue probably lines the lumen of the pore.

2-Naphthylamine↗
PubMed1996

Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin: prototypes of pore-forming bacterial cytolysins.

Staphylococcal alpha-toxin, streptolysin-O, and Escherichia coli hemolysin are well-studied prototypes of pore-forming bacterial cytotoxins. Each is produced as a water-soluble single-chain polypeptide that inserts into target membranes to form aqueous transmembrane pores. This review will compare properties of the three toxin prototypes, highlighting the similarities and also the differences in their structure, mode of binding, mechanism of pore formation, and the responses they elicit in target cells. Pore-forming toxins represent the most potent and versatile weapons with which invading microbes damage the host macroorganism.

Amino Acid Sequence↗
PubMed1996

Streptococcal cysteine protease augments lung injury induced by products of group A streptococci.

Streptococcus pyogenes infections in humans may be associated with severe clinical manifestations, including adult respiratory distress syndrome and a toxic shock-like syndrome. These observations have led to the investigation of products of group A streptococci that may contribute to increased virulence. Streptococcal pyrogenic exotoxin B is a highly conserved precursor of an extracellular cysteine protease that is secreted by S. pyogenes. We investigated the ability of this streptococcal cysteine protease (SCP) to act synergistically with either streptococcal cell wall antigen (SCW) or streptolysin-O (SLO) to augment lung injury in rats. Intratracheal administration of either SCW or SLO alone caused lung injury, as measured by pulmonary vascular leak. Bronchoalveolar lavage (BAL) fluid analysis showed that SCW induced neutrophil accumulation and appearance of interleukin-1beta and tumor necrosis factor alpha. In contrast, SLO induced neither neutrophil influx nor significant cytokine elevations in BAL fluids. Intratracheal administration of SCP with either SCW or SLO resulted in synergistic augmentation of lung vascular permeability and accumulation of BAL neutrophils. The synergy was reduced when SCP was either heat inactivated or coinstilled with a peptide inhibitor of the protease. SCP in the presence of SCW resulted in a significant increase in BAL fluid tumor necrosis factor alpha content but not in immunoreactive interleukin-1beta. Moreover, the copresence of SAP with SAW resulted in increased BAL fluid nitrite-nitrate levels, indicative of nitric oxide production. These data demonstrate that SCP acts synergistically with other S. pyogenes products (SCW or SLO) to increase tissue injury and provide additional evidence that SCP may function as an important virulence factor in group A streptococcal infections.

Animals↗
PubMed1995

Kinetics of streptolysin O self-assembly.

Streptolysin O is a member of a family of membrane-damaging toxins that bind to cell membranes containing cholesterol and then polymerize to form large pores. We have examined the kinetics of toxin action using 125I-labelled streptolysin O. Binding of toxin monomers to membranes displays first-order kinetics and is reversible; the rate of desorption from red cells shows a marked dependence on temperature. To study oligomerization, toxin was bound to erythrocytes at 0 degrees C. Oligomer formation was then triggered by a sudden temperature shift and stopped by solubilization of membranes with deoxycholate. While at moderately high streptolysin O concentrations oligomerization behaves as a reaction of second order, the kinetic pattern changes with increasing toxin concentration. We show that this can be accounted for by the assumption of a two-step reaction mechanism: two membrane-bound monomers first associate into a start complex, which then is rapidly extended by the sequential addition of further monomers up to the final oligomer size.

Animals↗
PubMed1995

Correct oligomerization is a prerequisite for insertion of the central molecular domain of staphylococcal alpha-toxin into the lipid bilayer.

Staphylococcal alpha-toxin is a primarily hydrophilic molecule that binds as a monomer to target membranes and then aggregates to form amphiphilic oligomers that represent water-filled transmembrane channels. Current evidence indicates that a region located in the center of the molecule inserts deeply into the bilayer. In the present study, we sought to determine whether membrane insertion was triggered by the oligomerization process, and whether insertion correlated with pore formation. Double mutants of alpha-toxin were prepared in which His-35 was replaced by Arg, and cysteine residues were introduced at positions 69, 130 and 186. Substitution of His-35 with Arg rendered the toxin molecules incapable of proper oligomerization, so that they remained in nonlytic form after binding to membranes. The sulfhydryl groups were labelled with the polarity-sensitive fluorescent dye acrylodan. Functionally intact, single mutant toxins containing only the cysteine residues were utilized as controls. Measurements of the fluorescence emission spectrum of acrylodan were performed for the active and inactive alpha-toxin mutants in free solution and in membrane-bound form. The collective results demonstrate that proper oligomerization is required for membrane insertion of the central region in the alpha-toxin molecule, and that lack of insertion correlates with absence of pore formation.

2-Naphthylamine↗
PubMed1995

Acoustic correlates of stress in young children's speech.

This study examined the acoustic correlates of stress in children's productions of familiar words. Previous research has employed experimental words rather than familiar words to examine children's phonetic marking of stress, or has not adequately controlled for phonetic environment. Subjects in this study included 22 children, aged 18-30 months, and 6 adults. Fundamental frequency, duration, and amplitude measures were extracted from stressed and unstressed syllables in two types of comparisons: one that controlled phonetic environment and syllable position (interword) and one that measured the relative effects of stress within the same word (intraword). When the tokens were analyzed on the basis of target stress pattern, results revealed no differences between adults and children in their acoustic marking of stress. Listener judgments showed that approximately 30% of children's two-syllable productions were coded unreliably or were perceived as inaccurately stressed. Overall findings indicate that children control fundamental frequency, amplitude, and duration to derive perceptually identifiable stress contrasts in the majority of their productions but they are not completely adult-like in their marking of stress.

Adult↗
PubMed1994

Histidine residues near the N terminus of staphylococcal alpha-toxin as reporters of regions that are critical for oligomerization and pore formation.

Chemical modification of histidine residues in staphylococcal alpha-toxin leads to loss of functional activity. Site-directed mutants of the toxin in which each of the four histidine residues was replaced by several amino acids were therefore produced. The mutant proteins were purified and characterized. Exchange of H-259 or H-144 was sometimes tolerated without reduction in hemolytic activity. These histidine residues are thus not essential for toxin function. Exchange of H-35 and H-48, however, had marked effects. H-35 mutant toxins bound with high affinity to rabbit erythrocytes but displayed faulty oligomerization and were unable to form pores. H-48 mutant toxins also had severely impaired hemolytic activity due probably to faulty hexamerization. We interpret these results to indicate that the N-terminal domain of alpha-toxin in the region of H-35 and H-48 is involved in protomer-protomer interactions that underlie the hexamerization and pore-forming process.

Animals↗
PubMed1994

Cardiac allotransplantation across the ABO-blood group barrier by the neutralization of preformed antibodies: the baboon as a model for the human.

The baboon, like the human, expresses A and/or B blood group antigens on its tissues. Anti-A and anti-B antibodies are directed against these antigens, the epitopes of which are carbohydrate structures. Portions of these carbohydrates have been synthesized (trisaccharides A and B, respectively). When infused intravenously, the synthetic trisaccharides form a complex with the specific antibodies and neutralize their activity preventing them from binding to the antigen targets on a transplanted organ. In nonimmunosuppressed, hyperimmunized baboons, the continuous intravenous infusion of the specific trisaccharide alone (for 6 days) inhibited rejection of ABO-incompatible cardiac allografts, extending survival from a mean of 19 min (n = 3) to 8 days (n = 2), at which time the grafts failed from cellular (not vascular) rejection. The combination of long-term pharmacologic immunosuppression plus trisaccharide infusion (for periods of 8 to 19 days) extended survival to a mean of > 28 days (n = 4) with one heart functioning > 52 days. Accommodation clearly occurred in three of the four cases. This form of therapy may permit cadaveric organ allotransplantation across the ABO blood-group barrier in the human.

ABO Blood-Group System↗
PubMed1993

Staphylococcus aureus alpha-toxin. Production of functionally intact, site-specifically modifiable protein by introduction of cysteine at positions 69, 130, and 186.

Staphylococcal alpha-toxin, the prototype of an oligomerizing, pore-forming cytotoxin, is sensitive to biochemical modifications and cannot be labeled with biotin or fluorescein under preservation of its biological activity. In this study, we have used site-directed mutagenesis to introduce cysteine residues at positions 69, 130, and 186. Each mutant was fully and rapidly reactive with several sulfhydryl-specific reagents, indicating superficial location. Coupling of SH-groups with fluorescein-maleimide or biotin-maleimide was tolerated without loss of hemolytic activity at position 130, and the formed hexamers were visible on target cells by fluorescence microscopy and could be detected on electroblots by reaction with streptavidin-peroxidase. At the two other positions, modification caused significant loss of activity. However, the labeled proteins still bound to red cells, as shown by fluorescence microscopy and electroblotting. Intrinsically labeled alpha-toxin represents a novel tool to study the interaction of this pore-former with target membranes.

Amino Acid Sequence↗
PubMed1993

Specific intravenous carbohydrate therapy. A new concept in inhibiting antibody-mediated rejection--experience with ABO-incompatible cardiac allografting in the baboon.

Heterotopic allografting of ABO-incompatible donor hearts in recipient baboons "hyperimmunized" against the incompatible A or B antigen (n = 3) was followed by hyperacute antibody-mediated vascular rejection within a mean of 19 min. The A and B epitopes against which these antibodies are directed are carbohydrates that can be synthesized. The continuous i.v. infusion of the specific synthetic A or B trisaccharide, beginning immediately pre-transplant and continued posttransplant for several days, prolonged allograft survival to a mean of 8 days (n = 2) and prevented antibody-mediated rejection, graft failure resulting from acute cellular rejection. The addition of triple pharmacologic immunosuppressive therapy (n = 4) resulted in prolongation of graft survival to a mean of > 28 days, with one heart still beating at 52 days; all grafts showed features of cellular rejection. "Accommodation" would appear to have developed in several baboons as graft function continued for periods of up to 39 days after discontinuation of carbohydrate therapy. Specific i.v. carbohydrate therapy should allow organ allografting to be performed across the ABO blood group barrier in humans. Furthermore, if the carbohydrate epitopes on the organs of discordant animals (e.g., the pig) against which human xenoreactive antibodies are directed can be confirmed, then this form of therapy might allow successful discordant organ xenotransplantation in man.

ABO Blood-Group System↗