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Biomedical subjects

C Miller

Publications and source records attributed to C Miller.

At least 235 records · Page 13Linked to original sources
PubMed1996

Modulation of the mutagenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by phenolic compounds.

NNK is a potent environmental carcinogen generated during tobacco processing and smoking. The carcinogenic response to tobacco smoking is modulated by nutritional factors. In this study, liver microsomes from phenobarbital and beta-naphthoflavone-treated or control hamsters were used to assay the mutagenicity (Salmonella typhimurium TA1535) of NNK. Western analysis of these microsomal preparations revealed an increased expression of protein recognized by polyclonal antibodies specific for P-450 1A2 in beta-naphthoflavone-induced microsomes and P-450 2B1/2B2 in phenobarbital-induced microsomes. Both inducers significantly increased the mutagenicity of NNK. Metabolism of NNK by the three microsomal preparations was compared. Metabolites formed by methyl-hydroxylation of NNK by microsomes from control animals were significantly greater than those formed by alpha-methylene hydroxylation. Phenobarbital treatment had the greatest effect on alpha-methylene hydroxylation while beta-naphthoflavone had the greatest effect on methyl hydroxylation. The antimutagenic action of the polyphenolic compounds ellagic acid, esculetin and propyl gallate correlated with an inhibition of the metabolism of NNK. There were, however, differences in the effects of these compounds on specific pathways of NNK metabolism depending upon the microsomal enzyme induction treatment. This suggests that phenolic compounds have selective affinity for specific P-450 isozymes activating NNK.

Animals↗
PubMed1996

CSF of neuroleptic-naive first-episode schizophrenic patients: levels of biogenic amines, substance P, and peptides derived from chromogranin A (GE-25) and secretogranin II (secretoneurin).

Lumbar cerebrospinal fluid (CSF) was collected from controls and neuroleptic-naive patients with their first acute schizophrenic episode. The CSF was analyzed for several biogenic amines and their metabolites [dopamine,dihydroxyphenylacetic acid (DOPAC), noradrenaline, 5-hydroxytryptamine (5-HT), 5-hydroxyindolacetic acid (5-HIAA)]. For these transmitters, which are stored and secreted from synaptic vesicles, there was no significant difference between controls and schizophrenic patients. As constituents of large dense-core vesicles substance P (SP) and GE-25 (derived from chromogranin A)-and secretoneurin (derived from secretogranin 11)-immunoreactivities were determined. SP-like immunoreactivity levels did not differ between controls and patients; however, GE-25 was elevated and especially the GE-25/secretoneurin ratio was significantly (p < .001) higher in patients. Characterization of the immunoreactivities by high-performance liquid chromatography did not reveal any difference between patients (n = 3) and controls in the processing of the two proproteins chromogranin A and secretogranin II. These data indicate that proteolytic processing of the two widespread constituents of large dense-core vesicles, i.e., chromogranin A and secretogranin II, is not altered in schizophrenic patients. The increase in the chromogranin A /secretoneurin ratio in schizophrenic patients deserves further investigation in order to elucidate its possible pathogenetic significance.

Adult↗
PubMed1996

A symmetry-driven search for electrostatic interaction partners in charybdotoxin and a voltage-gated K+ channel.

A structural model of charybdotoxin bound to a Shaker K+ channel has emerged from mechanistic and mutagenic analysis of toxin-channel interactions. We test this model by predicting through-space electrostatic interactions between specific pairs of channel-toxin residues. Dissociation constants of channel-toxin variants, determined by radiolabeled toxin binding to Shaker-transfected COS membrane fragments, were used to identify pairs of residues located closely enough to interact electrostatically. The results further refine the structural model of the bound complex and produce a more detailed view of the vestibule of the Shaker channel.

Animals↗
PubMed1996

Stoichiometry, organisation and catalytic function of protein X of the pyruvate dehydrogenase complex from bovine heart.

Mammalian pyruvate dehydrogenase complex (PDC) contains a subunit, protein X, which mediates high-affinity binding of dihydrolipoamide dehydrogenase (E3)to the dihydrolipoamide acetyltransferase (E2) core. Precise stoichiometric determinations on bovine heart PDC, by means of two approaches, indicate the presence of 12 mol protein X/mol PDC and 60 mol E2/mol PDC. Studies of the organisation of collagenase-modified PDC by means of covalent cross-linking of N,N'-1,2-phenylenedimaleimide to lipoamide thiols on protein X, reveal that the main cross-linked products have Mr values corresponding to homodimers of protein X. However, significant formation of higher-Mr aggregates indicates that lipoyl domains of protein X can form an interacting network independent of E2 lipoyl domains. These data suggest that either 12 interacting X monomers or 6 interacting X dimers are involved in the binding of six E3 homodimers to the E2/X core. The presence of 60 E2 subunits/complex also supports proposals for a non-integrated external position of protein X. Collagenase-treated PDC possesses residual activity (15 %), indicating that protein-X-linked lipoamide groups can substitute for the lipoyl domains of E2 in overall complex catalysis. Protein-X-mediated diacetylation of dihydrolipoamide moieties is also performed by the modified complex which raises the possibility of a unique catalytic function for protein X.

Acetyl Coenzyme A↗
PubMed1996

Inhibitory gating of an evoked response to repeated auditory stimuli in schizophrenic and normal subjects. Human recordings, computer simulation, and an animal model.

BACKGROUND: Altered sensory response is a prominent feature of schizophrenia. Inhibitory gatting mechanisms, shown by diminished P50 evoked responses to repeated auditory stimuli, seem to be deficient in schizophrenic persons. These inhibitory mechanisms usually are studied by averaging the electroencephalographic responses to many presentations of pairs of stimuli. Although averaging increases signal-to-noise ratio, it may obscure trial-to-trial differences. We compared differences between schizophrenic and normal persons in single trials and averages of P50 response. METHODS: Recordings from 10 schizophrenic patients and 10 normal subjects were analyzed using conventional averaging and single-trial measurements. A computer simulation of both methods examined their ability to extract evoked responses from background activity. Related single-neuron activity in the hippocampus in an animal model also was studied, because neuronal action potentials can be reliably identified in single trials. RESULTS: Averaged evoked potentials showed significant suppression of the P50 response to the second stimulus of the pair in normal patients, but not in schizophrenic patients. Single-trial analysis did not detect a response above background activity. Computer simulations gave similar results, suggesting that failure to detect suppression in single trials comes from inadequate differentiation of signal from noise. Recordings in animals confirmed almost complete suppression of the response of hippocampal pyramidal neurons to the second stimulus. CONCLUSIONS: The normal inhibition of response to repeated auditory stimuli seems to be compromised in schizophrenia. This loss of inhibitory gating could reflect a physiological deficit of hippocampal interneurons that is consonant with other evidence for interneuron pathologic defects in schizophrenia.

Acoustic Stimulation↗
PubMed1996

Peptide chemistry: development of high performance liquid chromatography and capillary zone electrophoresis.

The development of relatively non-compressible supporting media of small particle size as well as pumps that deliver constant flow rates at high pressures has enabled investigators to perform rapid, high resolution liquid chromatography for more than two decades. Studies initiated in this laboratory in 1975, evaluating the compatibility of unprotected peptides with commercially available chromatographic supports and development of solvent systems ultimately led to separations not previously observed with both synthetic peptides and native peptides from tissue extracts. It was rapidly realized however, that recovery of certain molecules could be problematic. To meet the challenges presented by the isolation of natural hormones (such as corticotropin releasing factor and growth hormone releasing hormone) and proteins (such as inhibin and activin) and the need for large quantities of highly purified peptides for clinical investigations, our group invested heavily in identifying new supports (high carbon loading and 300 A pore sizes) and solvent systems (triethylammonium phosphate and trifluoroacetic acid) compatible with reverse phase, size exclusion and ion exchange chromatographies from a practical and economical perspective. More recently, we have contributed to the identification of unusual buffer systems (inclusive of organic modifiers) compatible with capillary zone electrophoresis that will both modulate the capillaries' selectivity, increase resolution and serve as an orthogonal approach to determining peptide purity. From a pragmatic point of view, in this paper we highlight the original and timely contributions (technical and strategical) of this laboratory in the field of analytical and preparative high performance liquid chromatography and capillary zone electrophoresis of synthetic and native biologically active peptides and proteins over the past twenty years.

Amino Acid Sequence↗
PubMed1996

A comparative study of psychological aspects of recurring and non-recurring functional aphonias.

The present study is based on the hypothesis that patients with recurrent attacks of aphonia differ from those with non-recurring attacks of aphonia in their anxiety levels, social assertiveness and stress-coping strategies. A comparison was made between 21 women with recurring aphonia and 19 women with non-recurring aphonia with respect to these three factors. Seventeen healthy women served as volunteers. Compared to patients with non-recurring aphonias, patients with recurring aphonias exhibited a significantly higher level of anxiety and significantly more respect for social norms and codes of propriety. Their coping was also characterized by a higher escape tendency. Patients with recurring aphonias also reported a significantly higher number of problems in their private lives within the preceding 5-year period. In therapy patients should be encouraged to reflect upon a possible rigidity toward social norms and better understand fears regarding conflicts in personal relationships.

Adaptation, Psychological↗
PubMed1996

Evolution of promoter sequences: elements of a canonical promoter for prespore genes of Dictyostelium.

An attempt is made to define a minimal prespore promoter which contains all elements essential for correct regulation of expression of a prespore gene. The prespore genes of Dictyostelium are coregulated during development. Most begin transcription at the same early stage, and activity of all is restricted to prespore tissue during the later slug stage. Sequences 5' to the coding sequences of eight prespore genes were searched for all elements proposed to control transcription and for new elements. The meaningfulness of occurrences of elements and pairs of elements in prespore promoters was evaluated by comparison with frequencies of occurrences in promoters of other, nonprespore genes. These comparisons resulted in definition of a canonical prespore promoter, a stretch of about 200 nucleotides containing at least one of each of three elements. Certain limitations were found on the spacing of elements. Orientation of elements with respect to each other appeared unrestricted. All elements often occurred in multiple copies. This structure suggests that individual copies of each element are not conserved during evolution, but instead continually appear and disappear.

Animals↗
PubMed1996

Similar, and similar concepts.

This paper analyzes English symmetrical predicates such as collide and match. Its point of departure is an analysis of the concept 'similar' from Tversky (1977) that appears to show that similarity is psychologically asymmetrical. One basis for this claim from Tversky is that the sentences North Korea is similar to Red China and Red China is similar to North Korea are assessed as differing in meaning by experimental subjects; this seems to imply that the symmetrical entailment (R x, y <--> R y, x) fails for this concept. Five experiments are presented that show: (1) the apparent asymmetry of similar is reproduced for 20 predicates that are intuitively thought to be symmetrical, including equal and identical; (2) unique linguistic-interpretative properties hold for these symmetrical words, such as reciprocal interpretation when they appear intransitively, for example, North Korea and Red China are similar; (3) the asymmetrical interpretation of subject-complement constructions containing the symmetrical words is a consequence of general linguistic-interpretive principles. On the basis of the experimental findings, we offer an analysis of symmetrical predication. One major claim of the analysis is that symmetry is a property of lexical items and has no special syntax, that is, that John meets is semantically but not syntactically anomalous. A second claim is that the structural positioning of noun phrases in sentences containing symmetricals--rather than inherent semantic properties of the noun phrases themselves--sets their status as Figure and Ground (as described by Talmy, 1985) or Variant and Referent (as described by Tversky, 1977) in the comparison, even if the nouns are nonsense items. Finally, the behavior of symmetrical predicates is shown to vary as a function of their differing lexical class assignments and collateral semantic designations, such as activity versus state. Most generally, it is claimed that a deeper understanding of symmetrical terms comes from analyzing the semantics of syntactic structures in which they appear.

Humans↗
PubMed1996

Interaction of Ca2(+)-activated K+ channels with refolded charybdotoxins mutated at a central interaction residue.

Charybdotoxin is a small peptide blocker of K+ channels, rigidly held in active conformation by three disulfide bonds. The toxin blocks K+ channels by binding to a receptor site located at the external "vestibule", and thus physically occluding the outer opening of the K+ conduction pore. In the blocked complex, K27, a residue on the toxin's molecular surface, projects its epsilon-amino group into the K(+)-selective pore. The results here show that CTX, produced by heterologous expression in E. coli, may be manipulated to place unnatural positively charged residues at position 27. The toxin folds faithfully to its native conformation when the crucial lysine at position 27 is replaced by a cysteine residue, a maneuver that allows specific chemical modification of this side-chain. Replacements of K27 by side-chains slightly shorter or slightly longer than lysine yield active toxins. The toxin variant with ornithine at this position interacts much less strongly with K+ ions in the pore of slowpoke-type Ca2(+)-activated K+ channels than does wild-type toxin. This result argues that the epsilon-amino group of K27 in bound toxin lies only a few ångstroms away from a K+ ion occupying the blocked pore. The peptide folds with high efficiency to form the correct disulfides even in the presence of strong denaturants.

Charybdotoxin↗
PubMed1996

T lymphocyte mediated protection against facultative intracellular bacteria.

Acquired immunity against intracellular bacteria is T cell dependent. T cells play a major role in protection against intracellular bacteria, but bacterial antigens recognized by T cells have been studied less extensively than bacterial antigens recognized by B cells. Using T lymphocytes from animals immunized against Brucella abortus, we have screened a bacterial genomic library for genes encoding antigens recognized by T cells. Lymphocytes that proliferated to B. abortus proteins were characterized for phenotype and cytokine activity. Bovine and murine lymphocytes recognized common bacterial antigens and possessed similar cytokine profiles, suggesting an analogous immune response in these two animal species. In vivo protection afforded by a particular cell type is dependent on the bacterial antigens presented and mechanisms of antigen presentation. MHC class I and class II gene knockout animals infected with B. abortus have demonstrated that protection to B. abortus is especially dependent on CD8+ T cells. Knowing the cells required for protection, vaccines can be designed to elicit the protective subset of lymphocytes. Currently, we are testing several recombinant B. abortus proteins using different immunization strategies. Finally, bacterial genes activated following intracellular phagocytosis are being examined using a novel, reporter system adapted to B. abortus.

Animals↗
PubMed1996

A strongly interacting pair of residues on the contact surface of charybdotoxin and a Shaker K+ channel.

Charybdotoxin, a peptide neurotoxin of known molecular structure, blocks Shaker K+ channels by binding to a receptor at the outer opening of the ion conduction pathway. Analysis of variants of CTX at position 29 and of Shaker at position 449 shows that these two residues interact closely in the channel-toxin complex. The CTX mutation M29I leads to a slight strengthening of block when tested on Shaker-449T; the same CTX mutation weakens block 1700-fold when tested on Shaker-449F. The known position of CTX-29 on the toxin's interaction surface thus locates Shaker-449 within 5 A of the pore axis of the closed channel. All four subunits must carry the 449F mutation to produce a highly toxin-insensitive channel.

Amino Acid Sequence↗
PubMed1996

Cholinergic inhibition of muscle fibres isolated from Schistosoma mansoni (Trematoda:Digenea).

Cholinergic compounds inhibit FMRFamide-induced contractions in dispersed muscle fibres isolated from adult Schistosoma mansoni. Acetylcholine (ACh) was the most effective cholinergic agonist tested with an EC50 < 100 nM. Less effective were propionylcholine and arecoline with EC50 < 1 microM and butyrylcholine and carbachol with EC50 < 10 microM. Choline, muscarine, pilocarpine, nicotine, DMPP (1,1-dimethylphenylpiperazine) and levamisole were all ineffective. Amongst tested antagonists, d-tubocurarine (100 microM), mecamylamine (1 mM), scopolamine (1 mM) and quinuclidinyl benzilate (10 microM) were all ineffective. Bicuculline, picrotoxin and strychnine were also ineffective. However alpha-bungarotoxin, at 100 nM, was able to block the inhibitory ACh effect. From these data it appears that the cholinergic receptor on the schistosome muscle fibres may be of the nicotinic type, but that its pharmacology is different from that of nicotinic receptors of vertebrates as well as of nematodes or a variety of other invertebrates.

Acetylcholine↗
PubMed1996

Nonequilibrium gating and voltage dependence of the ClC-0 Cl- channel.

The gating of ClC-0, the voltage-dependent Cl- channel from Torpedo electric organ, is strongly influenced by Cl- ions in the external solution. Raising external Cl- over the range 1-600 mM favors the fast-gating open state and disfavors the slow-gating inactivated state. Analysis of purified single ClC-0 channels reconstituted into planar lipid bilayers was used to identify the role of Cl- ions in the channel's fast voltage-dependent gating process. External, but not internal, Cl- had a major effect on the channel's opening rate constant. The closing rate was more sensitive to internal Cl- than to external Cl-. Both opening and closing rates varied with voltage. A model was derived that postulates (a) that in the channel's closed state, Cl- is accessible to a site located at the outer end of the conduction pore, where it binds in a voltage-independent fashion, (b) that this closed conformation can open, whether liganded by Cl- or not, in a weakly voltage-dependent fashion, (c) that the Cl(-)-liganded closed channel undergoes a conformational change to a different closed state, such that concomitant with this change, Cl- ion moves inward, conferring voltage-dependence to this step, and (d) that this new Cl(-)-liganded closed state opens with a very high rate. According to this picture, Cl- movement within the pre-open channel is the major source of voltage dependence, and charge movement intrinsic to the channel protein contributes very little to voltage-dependent gating of ClC-0. Moreover, since the Cl- activation site is probably located in the ion conduction pathway, the fast gating of ClC-0 is necessarily coupled to ion conduction, a nonequilibrium process.

Animals↗
PubMed1996

Planar imaging quantification using 3D attenuation correction data and Monte Carlo simulated buildup factors.

A new method to correct for attenuation and the buildup of scatter in planar imaging quantification is presented. The method is based on the combined use of 3D density information provided by computed tomography to correct for attenuation and the application of Monte Carlo simulated buildup factors to correct for buildup in the projection pixels. CT and nuclear medicine images were obtained for a purpose-built nonhomogeneous phantom that models the human anatomy in the thoracic and abdominal regions. The CT transverse slices of the phantom were converted to a set of consecutive density maps. An algorithm was developed that projects the 3D information contained in the set of density maps to create opposing pairs of accurate 2D correction maps that were subsequently applied to planar images acquired from a dual-head gamma camera. A comparison of results obtained by the new method and the geometric mean approach based on published techniques is presented for some of the source arrangements used. Excellent results were obtained for various source-phantom configurations used to evaluate the method. Activity quantification of a line source at most locations in the nonhomogeneous phantom produced errors of less than 2%. Additionally, knowledge of the actual source depth is not required for accurate activity quantification. Quantification of volume sources placed in foam, Perspex and aluminium produced errors of less than 7% for the abdominal and thoracic configurations of the phantom.

Biophysical Phenomena↗
PubMed1996

Nosocomial infections with vancomycin-resistant Enterococcus faecium in liver transplant recipients: risk factors for acquisition and mortality.

The risk factors for acquisition of and mortality due to nosocomial infection with vancomycin-resistant Enterococcus faecium (VREF) in orthotopic liver transplant (OLT) recipients were studied at a tertiary care hospital; 32 VREF-infected OLT patients (cases) were compared with 33 randomly selected OLT recipients (controls). More antibiotics were administered preoperatively to cases (mean, 4 antibiotics per patient for 474 antibiotic-days) than to controls (mean, 1.8 antibiotics per patient for 131 antibiotic-days). Cases were more likely than controls to have received vancomycin therapy preoperatively and to have been hospitalized in the intensive care unit (ICU) preoperatively. Logistic regression revealed that the risk factors for acquisition of VREF infection were surgical reexploration and a prolonged stay in the surgical ICU postoperatively. In the cases, the risk factors for mortality were admission to the ICU preoperatively and hemodialysis. The mortality rate associated with polymicrobial bloodstream infections was 100% despite appropriate therapy. Sixteen and 18 cases received parenteral chloramphenicol and doxycycline, respectively, for treatment of VREF infection. There were no hematologic adverse effects attributed to chloramphenicol treatment. DNA analysis of selected E. faecium isolates suggested that infections were due to multiple clones. In summary, the source of VREF infection in OLT patients is the gastrointestinal tract. Antibiotic selective pressure may contribute to colonization. Infection with VREF is a predictor of morbidity and mortality in OLT patients.

Anti-Bacterial Agents↗