Biomedical subjects

A Becker

Publications and source records attributed to A Becker.

At least 235 records · Page 13Linked to original sources

PubMed1998

Sensitivity and density of glutamate receptor subtypes in the hippocampal formation are altered in pentylenetetrazole-kindled rats.

Kindling induced by 13 intraperitoneal injections of 40 mg/kg pentylenetetrazole (PTZ) over a period of 4 weeks resulted in a significant long-lasting increase in both the convulsive susceptibility of animals to the convulsant and the density of the specific [3H]-L-glutamate binding sites in the hippocampus. The quisqualate- and kainate-sensitive [3H]-L-glutamate binding sites were increased 24 h after the final PTZ injection, whereas the N-methyl-D-aspartate (NMDA)-sensitive sites had only a tendency to be enhanced. Furthermore, we investigated [3H]-L-glutamate binding on metabotropic receptors and found a significant increase in the hippocampus following PTZ kindling. In addition, in hippocampal tissue of kindled rats (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD)-stimulated inositol phosphate formation is increased. It can be concluded that the increase in metabotropic glutamate receptor (mGluR) density may be the expression of a specific enhancement in susceptibility of the glutamatergic systems to this excitatory amino acid developing in the course of PTZ-induced kindling.

2-Amino-5-phosphonovalerate↗

PubMed1998

Xanthan gum biosynthesis and application: a biochemical/genetic perspective.

Xanthan gum is a complex exopolysaccharide produced by the plant-pathogenic bacterium Xanthomonas campestris pv. campestris. It consists of D-glucosyl, D-mannosyl, and D-glucuronyl acid residues in a molar ratio of 2:2:1 and variable proportions of O-acetyl and pyruvyl residues. Because of its physical properties, it is widely used as a thickener or viscosifier in both food and non-food industries. Xanthan gum is also used as a stabilizer for a wide variety of suspensions, emulsions, and foams. This article outlines aspects of the biochemical assembly and genetic loci involved in its biosynthesis, including the synthesis of the sugar nucleotide substrates, the building and decoration of the pentasaccharide subunit, and the polymerization and secretion of the polymer. An overview of the applications and industrial production of xanthan is also covered.

Carbohydrate Sequence↗

PubMed1998

The Sinorhizobium meliloti MucR protein, which is essential for the production of high-molecular-weight succinoglycan exopolysaccharide, binds to short DNA regions upstream of exoH and exoY.

Sinorhizobium meliloti (Rhizobium meliloti) is able to produce two different exopolysaccharides, succinoglycan and galactoglucan. Mutations in the mucR gene of S. meliloti result in the stimulation of galactoglucan synthesis, while the type of succinoglycan produced is modified. In culture supernatants of a mucR mutant, low-molecular-weight succinoglycan is present, whereas no high-molecular-weight succinoglycan could be detected. The biosynthesis of succinoglycan is directed by the products of the exo gene cluster. Two DNA fragments from this cluster, one located in front of the exoH gene and one in the intergenic region between the divergently transcribed genes exoX and exoY, were shown to represent effective binding sites for MucR. Whereas the latter binding site contains an inverted repeat motif, the former does not. However, the binding of MucR did not strongly modify the transcription of the exo genes involved. In the mucR mutant the expression levels of exoH-lacZ and exoX-lacZ transcriptional fusions were found to be increased 1.5- and 1.7-fold, respectively. On the other hand, the expression level of an exoY-lacZ transcriptional fusion was found to be 1.5-fold lower in the mucR mutant than in the wild-type background. Comparison of the DNA sequences of MucR-binding sites provides insight into the structural requirements for binding of MucR.

Bacterial Proteins↗

PubMed1998

Effect of bolus epinephrine on systemic hemodynamics in canine anaphylactic shock.

OBJECTIVE: Epinephrine (Epi) is considered to be the drug of choice for anaphylactic shock (AS). However, the benefit of this drug on improving systemic hemodynamics in AS has never been shown. We used a canine ragweed model of AS to determine if an intravenous bolus of Epi hastened the recovery of hemodynamics and modified mediator release (Med) compared with no treatment (NT). METHODS: In one protocol (n = 8), the effects on hemodynamics of two intravenous doses of Epi (0.01 and 0.025 mg/kg) were examined for 3 h postshock in respective studies approximately three weeks apart under pentobarbital anesthesia in the same animal. In five other dogs, left ventricular (LV) mechanics were additionally determined by sonomicrometric techniques to determine changes in contractility as defined by the preload recruitable stroke-work (SW) relationship. RESULTS: Compared with NT values, Epi treatments produced only transient increases in mean arterial pressure (MAP) and cardiac output (CO) post-challenge. By 20 min postshock, CO in the Epi studies were generally lower (p < 0.05) and BP was not different from NT values. With Epi treatment, SW was reduced for a given LV end-diastolic volume compared with the control study. Epi treatments also caused relatively higher plasma thromboxane B2 concentrations postshock. CONCLUSION: Our findings indicate that, when given immediately postshock, bolus-Epi did not hasten recovery and caused impairment in LV mechanics in canine AS.

Adrenergic alpha-Agonists↗

PubMed1998

Iron center, substrate recognition and mechanism of peptide deformylase.

Eubacterial proteins are synthesized with a formyl group at the N-terminus which is hydrolytically removed from the nascent chain by the mononuclear iron enzyme peptide deformylase. Catalytic efficiency strongly depends on the identity of the bound metal. We have determined by X-ray crystallography the Fe2+, Ni2+ and Zn2+ forms of the Escherichia coli enzyme and a structure in complex with the reaction product Met-Ala-Ser. The structure of the complex, with the tripeptide bound at the active site, suggests detailed models for the mechanism of substrate recognition and catalysis. Differences of the protein structures due to the identity of the bound metal are extremely small and account only for the observation that Zn2+ binds more tightly than Fe2+ or Ni2+. The striking loss of catalytic activity of the Zn2+ form could be caused by its reluctance to change between tetrahedral and five-fold metal coordination believed to occur during catalysis. N-terminal formylation and subsequent deformylation

Amidohydrolases↗

PubMed1998

Adenine nucleotides modulate epithelial wound healing in vitro.

BACKGROUND: Adenine nucleotides have been demonstrated to enhance structural and functional regeneration in experimental renal injury in rats. The mechanism of adenine nucleotide action have not been elucidated. The aim of this study was to characterize the effects of adenine nucleotides on intestinal epithelial wound healing in vitro. METHODS: The effects of adenine nucleotides on cell migration, cell proliferation and cell adhesion were studied in the non-transformed small intestinal epithelial cell line IEC-6 using an in vitro wounding model, a colorimetric BrdU assay and a hexosaminidase adhesion assay. RESULTS: The adenine nucleotides ADP and ATP were found to significantly stimulate epithelial cell restitution (migration) in vitro. Stimulation of epithelial restitution averaged 42% for ADP and 57% for ATP. In addition, adenine nucleotides inhibited the proliferation of rat small intestinal epithelial cells, averaging 56% for ADP and 74% for ATP. Enhancement of intestinal epithelial restitution and inhibition of epithelial cell proliferation by adenine nucleotides were mediated through transforming growth factor (TGF)-beta-independent pathways. CONCLUSION: These findings suggest that adenine nucleotides exert functional effects on intestinal epithelial cell populations and may play a role in the morphogenesis of the gastrointestinal tract and its remodeling after injury.

Adenine Nucleotides↗

PubMed1998

Patient education for discharge after coronary bypass surgery in the 1990s: are patients adequately prepared?

Short hospitalizations for patients undergoing coronary artery bypass grafting (CABG) require continuous nursing evaluation of patients' discharge education. Six institutions collaborated in surveying 300 postoperative patients with CABG to identify learning priorities and patients' perceptions of the effectiveness of discharge education. Data analysis from the self-administered questionnaire demonstrated consistent patient priorities across institutions. Differences in teaching methods and content did not affect perceived preparedness or importance scores. Regional experience demonstrates that variable teaching efforts meet patients' priorities and provide high overall patient preparedness for discharge. Patients with the shortest hospitalizations had higher preparedness scores.

Adult↗

PubMed1998

Self-care actions to manage fatigue among myasthenia gravis patients.

Fatigue is the most frequently reported symptom by myasthenia gravis (MG)patients. Despite the prevalence of fatigue, treatment protocols are lacking, thus patients are left to self-manage. The purpose of this study was to describe self-care actions used to manage fatigue among patients with MG. A national sample (N = 250) of MG patients responded to two structured instruments. The Fatigue Survey (FS), modified with permission of authors Hubsky and Sears; and the Myasthenia Gravis Fatigue Scale (MGFS). Both instruments were based on the concept of fatigue. Participants identified three major categories of self-managed actions: mental interventions (76%), physical interventions (78%) and rest/sleep (80%). A subset of the respondents (N = 36) reported using aerobic exercise to attempt to relieve fatigue which is usually contradicted with MG. No significant difference in fatigue scores was found between those reporting aerobic exercise to be helpful and those not finding exercise helpful. However, those utilizing aerobic exercise reported the highest functional status categories. A question arises as to whether aerobic exercise is performed by the least ill MG patients, or aerobic exercise improves functional status. When demographic and functional status variables were associated with fatigue scores and selfcare actions, only gender and functional status were significantly correlated with fatigue score. Effective self-care actions include stress reduction techniques, pacing all activities and increased rest and sleep. Further investigation into the role of aerobic exercise is indicated as a self-care action for MG fatigue.

Activities of Daily Living↗

PubMed1998

Specific amino acid substitutions in the proline-rich motif of the Rhizobium meliloti ExoP protein result in enhanced production of low-molecular-weight succinoglycan at the expense of high-molecular-weight succinoglycan.

The production of the acidic exopolysaccharide succinoglycan (EPS I) by Rhizobium meliloti exoP* mutants expressing an ExoP protein lacking its C-terminal cytoplasmic domain and by mutants characterized by specific amino acid substitutions in the proline-rich motif (RX4PX2PX4SPKX9IXGXMXGXG) located from positions 443 to 476 of the ExoP protein was analyzed. The absence of the C-terminal cytoplasmic ExoP domain (positions 484 to 786) and the substitution of both arginine443 by isoleucine443 and proline457 by serine457 within the proline-rich motif resulted in enhanced production of low-molecular-weight (LMW) EPS I at the expense of high-molecular-weight (HMW) EPS I. The ratios of HMW to LMW EPS I of the wild type and mutant strains increased with osmolarity.

Amino Acid Sequence↗

PubMed1998

Xanthomonas campestris pv. campestris gum mutants: effects on xanthan biosynthesis and plant virulence.

Xanthan is an industrially important exopolysaccharide produced by the phytopathogenic, gram-negative bacterium Xanthomonas campestris pv. campestris. It is composed of polymerized pentasaccharide repeating units which are assembled by the sequential addition of glucose-1-phosphate, glucose, mannose, glucuronic acid, and mannose on a polyprenol phosphate carrier (L. Ielpi, R. O. Couso, and M. A. Dankert, J. Bacteriol. 175:2490-2500, 1993). A cluster of 12 genes in a region designated xpsI or gum has been suggested to encode proteins involved in the synthesis and polymerization of the lipid intermediate. However, no experimental evidence supporting this suggestion has been published. In this work, from the biochemical analysis of a defined set of X. campestris gum mutants, we report experimental data for assigning functions to the products of the gum genes. We also show that the first step in the assembly of the lipid-linked intermediate is severely affected by the combination of certain gum and non-gum mutations. In addition, we provide evidence that the C-terminal domain of the gumD gene product is sufficient for its glucosyl-1-phosphate transferase activity. Finally, we found that alterations in the later stages of xanthan biosynthesis reduce the aggressiveness of X. campestris against the plant.

Base Sequence↗

PubMed1998

Comparison of Roche Cobas Amplicor Mycobacterium tuberculosis assay with in-house PCR and culture for detection of M. tuberculosis.

The new Roche Cobas Amplicor Mycobacterium tuberculosis assay, which is a semiautomated version of the manually performed Roche Amplicor M. tuberculosis test, was compared to culture and an IS6110-based in-house PCR protocol. A total of 1,681 specimens from 833 patients, including specimen types other than sputum, were tested in parallel by both the in-house PCR and the Cobas Amplicor M. tuberculosis assay. After we resolved discrepant PCR results, the sensitivity, specificity, and positive and negative predictive values for the Cobas Amplicor M. tuberculosis assay were 66.33, 99.71, 94.36, and 97.66%, respectively. The corresponding values for the in-house PCR were 91.08, 99.85, 97.87, and 99.37%, respectively. For culture- and smear-positive specimens, the sensitivity of the Cobas Amplicor M. tuberculosis test was 96.42% (in-house PCR, 100%). If only smear-negative sputum specimens were considered, the Cobas Amplicor M. tuberculosis assay exhibited a sensitivity of 45.45% (in-house PCR, 63.63%) relative to that of culture. With a modified protocol for DNA extraction (washing of samples plus ultrasonication), both PCR methods performed better with gastric aspirates than with sputum samples (sensitivity of the Cobas Amplicor M. tuberculosis assay with smear-negative gastric aspirates, 70.00%; sensitivity of in-house PCR, 90.00%). With dithiothreitol being used for liquefaction of specimens in this study, the Cobas Amplicor M. tuberculosis assay exhibited an inhibition rate of 9.16%. In our view, the new Cobas Amplicor M. tuberculosis test (i) is well suited for typing of smear-positive specimens, (ii) may also be applied to gastric aspirates and other types of specimens if DNA extraction methods are modified appropriately, and (iii) exhibits a sensitivity with smear-negative sputum specimens which makes it recommendable that a minimum of three samples from the same patient be tested.

Bronchoalveolar Lavage Fluid↗

PubMed1998

Effects of anaphylaxis mediators on partitioned pulmonary vascular resistance during ragweed shock in dogs.

We examined the effect of anaphylactic shock on the longitudinal distribution of pulmonary vascular resistance (PVR) in ragweed-sensitized dogs in which PVR was partitioned into an upstream arterial component (Rus) and a downstream venous and capillary component (Rds). We also assessed whether Rus and Rds would be reduced by pretreatment with histamine H1- and H2-receptor blocking agents and with cyclooxygenase and lipoxygenase pathway inhibitors. Anesthetized animals were examined on separate occasions 3 wk apart in which one of the treatments was randomly given. The pulmonary arterial occlusion technique was used to determine segmental pressure drops. During ragweed challenge, PVR increased approximately 4 times compared with the preshock value (3.04 vs. 12. 07 mmHg . l-1 . min; P < 0.05). Although both Rus and Rds increased postshock, the greatest relative increase occurred in Rds. None of the treatments reduced partitioned resistances compared with no treatment. Our results show that, under conditions of anaphylactic shock, increases in Rus and Rds could not be ascribed to release of histamine or products of the cyclooxygenase and lipoxygenase pathways.

Allergens↗

PubMed1998

Sensitivity, specificity and predictive value of modified assays for activated protein C resistance in children.

Very little data is available assessing the clinical utility of coagulation-based APC resistance assays compared to DNA-based analysis for the factor V Leiden mutation in children. Therefore, the clinical utility of four aPTT-based assays for APC resistance was evaluated in 169 children, ages 3 months through 16 years. The prevalence of the Arg506 to Gln mutation was 7/169 (4.1%). Using cutoff points derived from the normal PCR-screened population (n = 162), two assays for APC resistance (APC-SR and n-APC-SR) gave poor concordance with the PCR assay (sensitivity 29% and 57%, respectively). Two modified assays (FDAPC-SR and n-FDAPC-SR), in which patient plasma was prediluted 1:5 in factor V deficient plasma, gave excellent concordance (sensitivity 100%). The predictive value of a positive test was 0.25, 0.44, 1.00 and 0.88 for the APC-SR, n-APC-SR, FDAPC-SR and n-FDAPC-SR, respectively. The FDAPC-SR and n-FDAPC-SR tests gave excellent discrimination using cutoff values derived from the total population (n = 169) without regard to previous PCR screening results.

Adolescent↗

PubMed1998

The t(8;21) translocation is not consistently associated with high Bcl-2 expression in de novo acute myeloid leukemias of adults.

Chromosomal translocations are commonly found in de novo acute myeloid leukemia (AML) cells, and the fusion proteins produced from these genetic abnormalities are assumed to contribute directly to leukemogenesis and/or progression. The AML1/ETO fusion protein, created by translocations between chromosomes 8 and 21 [t(8;21); G. Nucifora and J. D. Rowley, Leuk. Lymphoma, 14: 353-362, 1994; K. L. Rhoades et al., Proc. Natl. Acad. Sci. USA, 93: 11895-11900, 1996] can induce anti-apoptotic Bcl-2 expression in vitro and was proposed to thereby promote the survival of t(8;21)-bearing AML cells (L. Klampfer et al., Proc. Natl. Acad. Sci. USA, 93: 14059-14064, 1996). We confirm that cells of the t(8;21)-bearing Kasumi cell line do express high levels of Bcl-2 protein, as reported previously. However, we show that primary AML cells with (8;21) chromosomal translocations generally express low levels of Bcl-2 protein relative to normal bone marrow-derived myeloid cells and to AML samples with other simple karyotypic abnormalities. We note that p53 mutations are present in the myeloid cell lines expressing AML-ETO protein from chromosomal translocations (Kasumi and SKNO) or from transfected fusion genes (U937) but were undetected in our analyses of 28 primary t(8;21)-bearing AML cell samples from de novo AMLs. Because wild-type p53 can transcriptionally down-regulate bcl-2, we speculate that p53 mutations may contribute to the association of t(8;21) chromosomal abnormalities with higher Bcl-2 expression levels in leukemia cell lines. We also note that some t(8;21)-bearing samples from pediatric and older adult patients do express somewhat higher levels of Bcl-2 than t(8;21)-bearing samples from young adult patients. This suggests that Bcl-2 overexpression could occur in these AML cells by an as yet undefined, p53-independent mechanism and could contribute to the reported association of t(8;21) karyotypes with poor clinical outcomes in childhood AML patients and/or to typically poor clinical outcomes in elderly AML patients.

Acute Disease↗

PubMed1998

Relevance of oxygen in radiation oncology. Mechanisms of action, correlation to low hemoglobin levels.

At the beginning of this century Schwarz (1909) and Holthusen (1921) observed the influence of oxygen on the radiosensitivity of cells. In 1951 Hollaender et al. described that E. coli needed 3-fold higher radiation doses when treated under anoxic conditions compared to normoxic conditions. This led to the evaluation of the oxygen enhancement ratio (OER) for photons (X-rays), neutrons and heavy ions. It was found that the OER for conventional radiation therapy (RT) with photons is much higher (about 3) than the OER for neutron-RT (only 1.5) or heavy ions. According to a hypothesis free radicals which are produced by radiation are fixed in the presence of oxygen. Radicals are interacting with DNA, macromolecules and membranes. The DNA lesion can be followed by cell death. There is some evidence that tumor cells respond to hypoxia with the expression of a variety of genes coding for oxygen regulated proteins such as c-jun, VEGF or p53. Hypoxia also enhances the genetic instability of tumor cells. Oxygen tensions in malignant tumors can be determined under clinical routine conditions by using a computerized polarographic needle electrode system (Eppendorf, Hamburg, Germany). Several studies in the past years showed that tumors are in general more hypoxic than the surrounding normal tissue and that a marked variability of intra- as well as intertumoral pO2 values exist (for review see Vaupel and Höckel 1998). Moreover, it has been shown in different tumor entities that the oxygenation status influences the local control rate and overall survival. Furthermore, the oxygenation status obtained at one site (primary) is significantly related at other sites (lymph node metastases) in patients with squamous cell carcinoma of the head and neck (SCCHN). In addition, there is a significant correlation between hemoglobin level and tumor oxygenation in patients with SCCHN. There is some evidence that the oxygenation status can be improved by the correction of a low hemoglobin level and consequently, the curative chance might rise.

Cell Hypoxia↗

PubMed1997

Increased cellular triglyceride levels in human monocytic and rat smooth muscle cells after lovastatin.

Beta-hydroxy-beta-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors reduce plasma LDL cholesterol by upregulating hepatic LDL receptors. However, their effects on lipid metabolism in extrahepatic cells may also contribute to their therapeutic benefit. We examined the effects of lovastatin (LOV) on cellular lipid levels in the human monocytic Mono Mac 6sr and cultured rat smooth muscle cells. In both cell types, LOV produced a dose-dependent increase in cellular triglycerides. This increase was observed in cells grown in the absence of exogenous lipids in the culture medium, but was more pronounced after additions of oleic acid (50 to 200 microM) and VLDL (50 to 200 microg ml-1). In Mono Mac 6sr cells grown in medium containing 10% delipidated FCS for the last 16 h, the LOV-induced rise in triglyceride levels was completely reversed by 2 mM mevalonic acid and was associated with a decrease in cellular cholesterol. However, when cells were maintained in lipoprotein-replete medium, the LOV-induced rise in triglycerides did not correlate with cellular cholesterol. LOV also reduced cellular cholesterol esterification and increased the synthesis of fatty acids and their incorporation into triglycerides and phospholipids. Increased triglyceride levels were also seen in Mono Mac 6sr cells treated with the lanosterol demethylase inhibitor RS-21607 and the acylcoenzyme A:cholesterol acyltransferase inhibitor SaH 58035. Our findings suggest that the LOV-induced triglyceride accumulation involves changes in intracellular cholesterol pools regulating cellular fatty acid concentrations. Although decreased cholesterol levels in cells participating in plaque formation are beneficial, the impact of the herein described shift in intracellular neutral lipid metabolism on other cellular functions warrants further investigation.

Acetates↗

PubMed1997

Dopamine D1-deficient mutant mice do not express the late phase of hippocampal long-term potentiation.

The possible involvement of the dopamine D1 receptor subtype in mechanisms of long-term potentiation (LTP) of the Schaffer collateral-commissural input of CA1 neurones was investigated using D1-deficient mutant mice. In transversal hippocampus slices from mice lacking the D1 receptor a normal post-tetanic and short-term potentiation could be induced after applying a triple 100 Hz tetanization. However, the potentiated fEPSP in the mutant mice declined to control value about 140 min following tetanization, whereas in the wild type mice a normal, non-decremental LTP was observed. These data support the idea that besides the glutamatergic system, the synergistic activation of dopaminergic synapses is necessary for LTP maintenance.

Animals↗

PubMed1997

Chloride and proton transport in bacteriorhodopsin mutant D85T: different modes of ion translocation in a retinal protein.

Replacement of aspartate 85 (D85) in bacteriorhodopsin (BR) by threonine but not be asparagine creates at pH<7 an anion-binding site in the molecular similar to that in chloride pump halorhodopsin. Binding of various anions to BR-D85T causes a blue shift of the absorption maximum by maximally 57 nm. Connected to this color change is a change in the absorption difference spectrum of the initial state and the longest living photo intermediate from a positive difference maximum at 460 nm in the absence of transported anions to one at 630 nm in their presence. Increasing anion concentration cause decreasing decay times of this intermediate. At physiological pH, BR-D85T but not BR-D85N transports chloride ions inward in green light, protons outward in blue or green light and protons inward in white light (directions refer to the intact cell). The proton movements are observable also in BR-D85N. Thus, creation of an anion-binding site in BR is responsible for chloride transport and introduction of anion-dependent spectroscopic properties at physiological pH. The different transport modes are explained with the help of the recently proposed IST model, which states that after light-induced isomerization of the retinal an ion transfer step and an accessibility change of the active site follow. The latter two steps occur independently. In order to complete the cyclic event, the accessibility change, ion transfer and isomerization state have to be reversed. The relative rates of accessibility changes and ion transfer steps define ultimately the vectoriality of ion transfers. All transport modes described here for the same molecule can satisfactorily be described in the framework of this general concept.

Anions↗