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M Fischer

Publications and source records attributed to M Fischer.

At least 253 records · Page 14Linked to original sources

[Concentration-dependent changes in the latency and amplitude of somatosensory-evoked potentials by desflurane, isoflurane and sevoflurane].

PURPOSE: Comparison of the influence of desflurane, isoflurane, and sevoflurane on the parameters of cortical somatosensory evoked potentials (SEP). METHODS: A total of 41 patients were randomly allocated to either the isoflurane, desflurane or sevoflurane group. Following induction with propofol and intubation, concentration of the volatile anaesthetic was kept constant at 1.3, 1.0, and 0.7 MAC for 15 minutes each in randomised sequences. No opioids or N2O were used. Cortical somatosensory evoked potentials were recorded following median nerve stimulation at the wrist with 1.5 times motor threshold current. SEP were evaluated for latencies of peak N20 and P25 as well as peak-to-peak amplitude N20P25. Measurements at the end of the 15 minute equilibration intervals were compared by analysis of variance for repeated measurements. Latencies and the logarithm of the amplitudes were assumed to be normally distributed. RESULTS: SEP could be recorded in all patients and at all concentrations. Latency of cortical SEP increased with anaesthetic concentration in a linear manner. No differences in latency increase were found between the three anaesthetics (ANOVA). In contrast, the decrease in amplitude with increasing anaesthetic concentration was non-linear. It was large from control to 0.7 MAC, but small in the range between 0.7 and 1.3 MAC. Amplitude reduction was larger with isoflurane than with sevoflurane or desflurane. CONCLUSION: 1) Sevoflurane and desflurane are better suited for anaesthetic management during intraoperative electrophysiological monitoring than isoflurane, because SEP amplitudes are better preserved. 2) SEP amplitude is less altered by changing anaesthetic concentrations in the concentration range from 0.7 to 1.3 MAC than SEP latency.

Adult↗

[Normal accommodative convergence excess--long-term follow-up of conservative therapy with bifocal eyeglasses].

BACKGROUND: In patients with normaccommodative convergence excess it is possible to reduce or eliminate the excess of accommodative convergence by adding plus lenses. The resulting reduction of near deviation can lead to an improvement in the quality of binocular vision at near, and also to a better compensation of an esophoria at near. The aim of the paper was to study long term results in patients with small angle esotropia and esophoria and accommodative convergence excess treated by bifocals. METHODS: Clinical data of 91 patients were analysed retrospectively. Among them were 13 patients with esophoria, 32 patients with microesotropia and 46 with microesotropia and a phoric component. An orthoptic status was performed every three months and at every examination it was tried to reduce the added plus lenses. The mean follow up was 5.6 +/- 2.4 years (range: 1.1-13.2). RESULTS: The mean onset of strabismus was similar in all groups: i.e. 2.5 (+/- 1.7) years. The patients received their first bifocals on average 3.4 (+/- 1.9) years later. In 40 of the 91 patients the near addition could be stopped because of sufficient decrease of accommodative convergence excess during the follow-up period. The convergence excess decreased continuously in all patients with esophoria and microesotropia and the additional plus lenses could be stopped on average after 6.4 (3.5-8.4) years (esophoria) and 5.0 (2.6-8.1) years (microesotropia) respectively. In patients with microesotropia and an additional phoric deviation bifocals were only partly successful to reduce the convergence excess. The basic angle decompensated in more than half of the patients (27 out of 46) and was operated in 14 cases by unilateral resection/recession procedure. After the operation the convergence excess decreased rapidly and the bifocals could be stopped after 4.4 (3.4-7.4) years. In the remaining 19 cases it was possible to reduced the convergence excess with bifocals in 8 patients after about 8.1 (4.1-9.3) years and in some of the remaining 11 cases a Fadenoperation has been suggested. CONCLUSION: While wearing bifocals the accommodative convergence excess decreased completely in patients with esophoria and microesotropia. In the condition with markedly reduced binocular vision and a large phoric component at far and near, the convergence excess decreased only in some of the patients while wearing bifocals. Conventional strabismus surgery to reduce the basic angle has a positive influence. A Fadenoperation is only necessary in a few cases.

Accommodation, Ocular↗

Somatic hypermutation in normal and transformed human B cells.

In the human, most IgM+IgD+ as well as CD5+ peripheral blood B cells express unmutated V genes and thus can be assigned to a pre-germinal centre (GC) stage of development. The memory B-cell compartment generated in the GC reaction and characterized by cells bearing somatically mutated V-region genes consists not only of class-switched cells, but also of IgM-only B cells and perhaps a subset of IgM+IgD+B cells expressing the CD27 antigen. Comparison of the rearranged V-region genes of human B-cell lymphomas with those of the normal B-cell subsets allows the identification of the progenitor cells of these tumours in terms of their stage of maturation. On this basis, most B-cell non-Hodgkin lymphomas, and in addition Hodgkin and Reed-Sternberg (HRS) cells in Hodgkin's disease (HD), are derived from B cells at a GC or post-GC stage of development. The mutation pattern indicates that the precursors of the tumour clones have been stringently selected for expression of a functional antigen receptor with one notable exception: HRS cells in classical (but not lymphocyte-predominant) HD appear to be derived from "crippled" GC B cells. Sequence analysis of rearranged V genes amplified from single tonsillar GC B cells revealed that the somatic hypermutation process introduces deletions and/or insertions into V-region genes more frequently than indicated by previous investigations. Presumably, this feature of the hypermutation mechanism is often responsible for the generation of heavy chain disease, and also several types of chromosomal translocations of oncogenes into immunoglobulin loci in human B-cell lymphomas.

Animals↗

Oxygen-dependent regulation of the expression of the catalase gene katA of Lactobacillus sakei LTH677.

The catalase gene katA of Lactobacillus sakei LTH677 was cloned and expressed in Escherichia coli UM2, Lactobacillus casei LK1, and Lactobacillus curvatus LTH1432. The last host is a catalase-deficient plasmid-cured derivative of a starter organism used in meat fermentation. The regulation of katA expression was found to be the same in L. sakei LTH677 and the recombinant strains. The addition of H2O2 to anaerobic cultures, as well as a switch to aerobic conditions, resulted in a strong increase in KatA activity. The expression was investigated in more detail with L. sakei LTH677 and L. curvatus LTH4002. The recombinant strain LTH4002 did not accumulate H2O2 under glucose-limited aerobic conditions and remained viable in the stationary phase. Under inductive conditions, the katA-specific mRNA and the apoenzyme were synthesized de novo. Deletion derivatives of the katA promoter were produced, and the regulatory response was investigated by fusion to the beta-glucuronidase reporter gene gusA and expression in L. sakei LTH677. The fact that gene expression was subject to induction was confirmed at the level of transcription and protein synthesis. A small putative regulatory sequence of at least 25 bp was identified located upstream of the -35 site. Competition experiments performed with L. sakei LTH677 harboring the fusion constructs consisting of the katA promoter and gusA revealed that an activator protein is involved in the transcriptional induction of katA.

Aerobiosis↗

Inhibition of human peripheral blood mononuclear cell proliferation by Streptococcus pyogenes cell extract is associated with arginine deiminase activity.

Streptococcus pyogenes (group A Streptococcus) cell extracts (CE) have a remarkably powerful and dose-dependent inhibitory effect on antigen, superantigen, or mitogen-stimulated human peripheral blood mononuclear cell (PBMC) proliferation in vitro. Purification of the inhibitory component present in S. pyogenes type M5 (Manfredo strain) CE by anion-exchange chromatography followed by gel filtration chromatography showed that the inhibitor had an approximate native molecular mass of 100 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified inhibitory fractions followed by silver staining gave a single band with an approximate molecular mass of 47 kDa, indicating that the inhibitor is composed of two identical subunits. NH2-terminal sequencing of the protein revealed that it was identical to the previously characterized streptococcal acid glycoprotein (SAGP); this protein possesses between 31.5 and 39.0% amino acid identity with arginine deiminase (AD) from Mycoplasma hominis, Mycoplasma arginini, Pseudomonas putida, and Pseudomonas aeruginosa. AD enzyme activity was present in unfractionated CE prepared from a range of streptococcal strains, and partially purified inhibitory fractions of Manfredo CE also had high levels of activity. The inhibitory effect of Manfredo CE was overcome by the addition of L-arginine to proliferation assays in which human PBMC were stimulated with phytohemagglutinin. We conclude that SAGP, or its homolog, possesses AD activity and that the potent inhibition of proliferation of human T cells by streptococcal CE is due to activity of this enzyme.

Amino Acid Sequence↗

Differentiation of phylogenetically related slowly growing mycobacteria based on 16S-23S rRNA gene internal transcribed spacer sequences.

Interspecific polymorphisms of the 16S rRNA gene (rDNA) are widely used for species identification of mycobacteria. 16S rDNA sequences, however, do not vary greatly within a species, and they are either indistinguishable in some species, for example, in Mycobacterium kansasii and M. gastri, or highly similar, for example, in M. malmoense and M. szulgai. We determined 16S-23S rDNA internal transcribed spacer (ITS) sequences of 60 strains in the genus Mycobacterium representing 13 species (M. avium, M. conspicuum, M. gastri, M. genavense, M. kansasii, M. malmoense, M. marinum, M. shimoidei, M. simiae, M. szulgai, M. triplex, M. ulcerans, and M. xenopi). An alignment of these sequences together with additional sequences available in the EMBL database (for M. intracellulare, M. phlei, M. smegmatis, and M. tuberculosis) was established according to primary- and secondary-structure similarities. Comparative sequence analysis applying different treeing methods grouped the strains into species-specific clusters with low sequence divergence between strains belonging to the same species (0 to 2%). The ITS-based tree topology only partially correlated to that based on 16S rDNA, but the main branching orders were preserved, notably, the division of fast-growing from slowly growing mycobacteria, separate branching for M. simiae, M. genavense, and M. triplex, and distinct branches for M. xenopi and M. shimoidei. Comparisons of M. gastri with M. kansasii and M. malmoense with M. szulgai revealed ITS sequence similarities of 93 and 88%, respectively. M. marinum and M. ulcerans possessed identical ITS sequences. Our results show that ITS sequencing represents a supplement to 16S rRNA gene sequences for the differentiation of closely related species. Slowly growing mycobacteria show a high sequence variation in the ITS; this variation has the potential to be used for the development of probes as a rapid approach to mycobacterial identification.

Base Sequence↗

2-Chlorodeoxyadenosine (cladribine) in combination with low-dose cyclosporin prevents rejection after allogeneic heart and liver transplantation in the rat.

The purine analogue 2-chlorodeoxyadenosine (2-CDA) has been shown to possess synergistic immunosuppressive properties when given together with cyclosporin (CSA) in a rat small bowel transplant model. The present study investigated the immunosuppressive potency of 2-CDA alone and in combination after liver or heart transplantation in a fully allogeneic rat model with 5 animals in each group. Immunosuppression was provided with CSA 10 mg/kg body weight (BW)/day orally or 2-CDA 0.1 mg/kg/BW day intravenously or both compounds together in the dosages mentioned. Animals were sacrificed on day 10 following transplantation, and graft histology was assessed. In addition, cardiac graft function was evaluated by palpation immediately prior to sacrificing the animal. CSA given alone was able to mitigate but not prevent rejection. 2-CDA alone did not exhibit any detectable immunosuppressive effect. When CSA was combined with 2-CDA, no rejection was seen in 80% of the liver allografts and in 60% of heart allografts, and only mild rejection was observed in the remaining animals. All hearts of the combined treatment group, however, beat strongly. From these findings it is concluded that 2-CDA alone has no, but together with CSA a strong immunosuppressive effect in preventing solid organ allograft rejection.

Animals↗

The use of transgenic mice in the investigation of transmissible spongiform encephalopathies.

The prion, the transmissible agent that causes spongiform encephalopathies such as scrapie, bovine spongiform encephalopathy and Creutzfeldt-Jakob disease, is believed to be devoid of nucleic acid and to be identical to PrPSc (prion protein: scrapie form), a modified form of the normal host protein PrPC (prion protein: cellular form) which is encoded by the single copy gene Prnp. The 'protein only' hypothesis proposes that PrPSc, when introduced into a normal host, causes the conversion of PrPC into PrPSc; it therefore predicts that an animal devoid of PrPC should be resistant to prion diseases. The authors generated homozygous Prnp(o/o) ('PrP knockout') mice and showed that, after inoculation with prions, these mice remained free from scrapie for at least two years while wild-type controls all died within six months. There was no propagation of prions in the Prnp(o/o) animals. Surprisingly, heterozygous Prnp(o/+) mice, which express PrPC at about half the normal level, also showed enhanced resistance to scrapie despite high levels of infectious agent and PrPSc in the brain at an early stage. After introduction of murine PrP transgenes, Prnp(o/o) mice became highly susceptible to mouse--but not to hamster--prions, while the insertion of Syrian hamster PrP transgenes rendered the mice susceptible to hamster prions but much less susceptible to mouse prions. These complementation experiments enabled the application of reverse genetics. The authors prepared animals transgenic for genes encoding PrP with amino terminal deletions of various lengths and found that PrP that lacks 48 amino proximal amino acids (which comprise four of the five octa repeats of PrP) is still biologically active.

Animals↗

Anti-carcinoembryonic antigen antibodies versus somatostatin analogs in the detection of metastatic medullary thyroid carcinoma: are carcinoembryonic antigen and somatostatin receptor expression prognostic factors?

BACKGROUND: Surgery is currently the only potentially curative approach in the treatment of medullary thyroid carcinoma (MTC). In many instances however, postsurgically elevated or rising plasma calcitonin and/or carcinoembryonic antigen (CEA) levels indicate persistent metastatic disease, although conventional diagnostic procedures (computed tomography (CT), magnetic resonance imaging (MRI), and invasive venous catheterization) fail to localize the responsible lesions. Recently, anti-CEA antibodies and somatostatin analogs have shown promising results in the staging of MTC. The aim of this study was to compare the sensitivity of both methodologies, especially for the detection of occult MTC, and to assess whether there may be correlations between the scintigraphic behavior and the patients' prognosis. METHODS: A total of 26 patients with medullary thyroid carcinoma were examined at our institution between 1977 and 1996. Ten of them had known disease, 14 had occult metastatic MTC, and 2 were free of disease at the time of presentation. Fourteen patients were investigated with anti-CEA monoclonal antibodies (MAbs) (receiving a total of 35 injections: clones BW431/26, BW431/31, IMACIS, or F023C5, labeled with 99mTc, (111)In or (131)I), and 8 patients were studied with (111)In-labeled octreotide. Two patients received potentially therapeutic doses of (131)I-labeled anti-CEA antibodies. All patients underwent conventional radiologic evaluation (ultrasonography, CT, and MRI) and/or biopsy within 4 weeks. Additional imaging was performed with 99mTc-(V)-DMSA, (131)I-metaiodobenzylguanidine, 201thallium chloride, 99mTc-methylene diphosphate, and/or 18F-fluorodeoxyglucose-positron emission tomography. Clinical follow-up was obtained. RESULTS: All patients with established disease had elevated plasma CEA (range, 6.8-345 ng/mL; calcitonin levels between 92 and 11,497 pg/mL), whereas in 9 of 14 occult cases, levels were < or = 5 ng/mL (range, 0.6-829 ng/mL; calcitonin, 72-2920 pg/mL). In patients with known disease, the overall lesion-based sensitivity was 86% for the anti-CEA MAbs, whereas octreotide was unable to target any tumor in patients with rapidly progressing disease or distant metastases (overall sensitivity, 47%). In all patients with occult MTC, anti-CEA MAbs and octreotide were able to localize at least one lesion (patient-based sensitivity, virtually 100%). In patients with postsurgically persistent hypercalcitoninemia, cervical lymph nodes were identified as the most frequent site of metastases, whereas in patients with occult and slowly progressing disease several years after primary surgery, anti-CEA MAbs and octreotide showed bilateral involvement of mediastinal lymph nodes; however, tumor to nontumor ratios were usually higher with octreotide in these cases. With anti-CEA Mabs, the highest tumor to nontumor ratios were observed in clinically aggressive, rapidly progressing disease. The sensitivity of all other diagnostic modalities was, at < or = 50%, significantly lower. Indication for antitumor effects was observed in a patient receiving 65 mCi of (111)I-labeled F(ab')2 fragments of the clone F023C5. CONCLUSIONS: For the detection of occult MTC, anti-CEA MAbs and octreotide seem to have a sensitivity that is superior to conventional diagnostic modalities, especially also when used in combination. Better detectability with anti-CEA antibodies (which may result in higher CEA expression) seems to be associated with more aggressively growing forms of MTC, whereas somatostatin receptor expression at normal CEA plasma levels and weaker MAb targeting may be associated with a more benign clinical course. This is in accordance with the study of Busnardo et al. (Cancer 1984; 53:278-85), who showed higher CEA serum levels to be associated with a worse prognosis, as well as with the in vitro findings of Reubi et al. (Lab Invest 1991;64:567-73), who demonstrated lower somatostatin receptor expression in less differentiated MTC. Fu

Adult↗

The Saccharomyces cerevisiae CCH1 gene is involved in calcium influx and mating.

The yeast Saccharomyces cerevisiae gene CCH1 (ORF YGR217w) shows high homology with animal calcium channel alpha1-subunit genes. Knock-out mutants were constructed of Cch1 and of Mid1 which is known to mediate Ca2+ influx in response to the alpha-mating pheromone. Cch1 is involved in calcium influx and the late stage of the mating process. The cch1 mutant sensitivity against the alpha-mating pheromone can be reduced by the addition of extra calcium. The product of this gene is likely to interact with the MID1 gene product in Ca influx or its control.

Base Sequence↗

The 1.25 A crystal structure of sepiapterin reductase reveals its binding mode to pterins and brain neurotransmitters.

Sepiapterin reductase catalyses the last steps in the biosynthesis of tetrahydrobiopterin, the essential co-factor of aromatic amino acid hydroxylases and nitric oxide synthases. We have determined the crystal structure of mouse sepiapterin reductase by multiple isomorphous replacement at a resolution of 1.25 A in its ternary complex with oxaloacetate and NADP. The homodimeric structure reveals a single-domain alpha/beta-fold with a central four-helix bundle connecting two seven-stranded parallel beta-sheets, each sandwiched between two arrays of three helices. Ternary complexes with the substrate sepiapterin or the product tetrahydrobiopterin were studied. Each subunit contains a specific aspartate anchor (Asp258) for pterin-substrates, which positions the substrate side chain C1'-carbonyl group near Tyr171 OH and NADP C4'N. The catalytic mechanism of SR appears to consist of a NADPH-dependent proton transfer from Tyr171 to the substrate C1' and C2' carbonyl functions accompanied by stereospecific side chain isomerization. Complex structures with the inhibitor N-acetyl serotonin show the indoleamine bound such that both reductase and isomerase activity for pterins is inhibited, but reaction with a variety of carbonyl compounds is possible. The complex structure with N-acetyl serotonin suggests the possibility for a highly specific feedback regulatory mechanism between the formation of indoleamines and pteridines in vivo.

Alcohol Oxidoreductases↗

Isoform specificity in the relationship of actin to dendritic spines.

Dendritic spines contain high concentrations of actin, but neither the isoforms involved nor the mechanism of accumulation is known. In situ hybridization with specific probes established that beta- and gamma-cytoplasmic actins are selectively expressed at high levels by spine-bearing neurons. Transfecting cultured hippocampal neurons with epitope-tagged actin isoforms showed that cytoplasmic beta- and gamma-cytoplasmic actins are correctly targeted to spines, whereas alpha-cardiac muscle actin, which is normally absent from neurons, formed aggregates in dendrites. The transfected actin cDNAs contained only coding domains, suggesting that spine targeting involves amino acid sequences in the proteins, an interpretation supported by experiments with chimeric cDNAs in which C-terminal actin sequences were found to be determinative in spine targeting. By contrast to actin, microtubule components, including tubulin and MAP2, were restricted to the dendritic shaft domain. The close association of cytoplasmic actins with spines together with their general involvement in cell surface motility further supports the idea that actin motility-based changes in spine shape may contribute to synaptic plasticity.

Actins↗

The active sites of the eukaryotic 20 S proteasome and their involvement in subunit precursor processing.

The 26 S proteasome is the central protease involved in ubiquitin-mediated protein degradation and fulfills vital regulatory functions in eukaryotes. The proteolytic core of the complex is the 20 S proteasome, a cylindrical particle with two outer rings each made of 7 different alpha-type subunits and two inner rings made of 7 different beta-type subunits. In the archaebacterial 20 S proteasome ancestor proteolytically active sites reside in the 14 uniform beta-subunits. Their N-terminal threonine residues, released by precursor processing, perform the nucleophilic attack for peptide bond hydrolysis. By directed mutational analysis of 20 S proteasomal beta-type proteins of Saccharomyces cerevisiae, we identified three active site-carrying subunits responsible for different peptidolytic activities as follows: Pre3 for post-glutamyl hydrolyzing, Pup1 for trypsin-like, and Pre2 for chymotrypsin-like activity. Double mutants harboring only trypsin-like or chymotrypsin-like activity were viable. Mutation of two potentially active site threonine residues in the Pre4 subunit excluded its catalytic involvement in any of the three peptidase activities. The generation of different, incompletely processed forms of the Pre4 precursor in active site mutants suggested that maturation of non-active proteasomal beta-type subunits is exerted by active subunits and occurs in the fully assembled particle. This trans-acting proteolytic activity might also account for processing intermediates of the active site mutated Pre2 subunit, which was unable to undergo autocatalytic maturation.

Amino Acid Sequence↗

Molecular single-cell analysis reveals that CD5-positive peripheral blood B cells in healthy humans are characterized by rearranged Vkappa genes lacking somatic mutation.

B cells expressing the CD5 cell surface antigen are involved in certain B cell malignancies and autoimmune diseases. From studies in the mouse, it emerged that CD5+ B cells represent a separate lineage of B lymphocytes that, in contrast to conventional (CD5-) B cells, are not driven into T cell-dependent immune responses in which rearranged variable (V) region genes are diversified by somatic hypermutation. Against this background it came as a surprise that human disease-involved CD5-positive autoreactive B cells as well as B cell chronic lymphocytic leukemias can harbor somatically mutated V region genes. Recent V gene analyses on CD5+ B cells in healthy adults did not give rise to a clear picture about the fraction of somatically mutated among all CD5+ B cells. In this work we used a molecular single-cell analysis to determine reliably the frequency of mutated CD5+ B cells in healthy humans: single, kappa light chain-expressing CD5+ peripheral blood B cells were isolated by flow cytometry, and rearranged Vkappa genes were amplified by PCR. From one donor, CD5+CD19+ B cells were analyzed. Since CD5+ B cells were found among IgM+IgD+ and IgM+IgD- cells (but almost not among class-switched cells) from two other donors, individual cells corresponding to these IgM-expressing subsets were investigated separately. The sequence analysis of rearranged Vkappa genes revealed that most if not all CD5+ B cells in healthy humans carry unmutated V region genes. From one of the donors, a novel polymorphic Jkappa2 gene segment was identified. To explain the discrepancy between the frequent occurrence of disease-associated somatically mutated CD5+ B cells and the low incidence or absence of somatic mutation in normal CD5+ B cells, we speculate that CD5+ B cells usually do not participate in germinal center reactions, but if they occasionally do so, they may be at an increased risk to become involved in autoimmune diseases or B cell malignancies.

Adult↗

Studies on the NusB protein of Escherichia coli--expression and determination of secondary-structure elements by multinuclear NMR spectroscopy.

The product of the nusB gene of Escherichia coli modulates the efficiency of transcription termination at nut (N utilization) sites of various bacterial and bacteriophage lambda genes. Similar control mechanisms operate in eukaryotic viruses (e.g. human immunodeficiency virus). A recombinant strain of E. coli producing relatively large amounts of NusB protein (about 10% of cell protein) was constructed. The protein could be purified with high yield by anion-exchange chromatography followed by gel-permeation chromatography. The protein is a monomer of 15.6 kDa as shown by analytical ultracentrifugation. Structural studies were performed using protein samples labelled with 15N, 13C and 2H in various combinations. Heteronuclear three-dimensional triple-resonance NMR experiments combined with a semi-automatic assignment procedure yielded the sequential assignment of the 1H, 13C and 15N backbone resonances. Based on experimentally derived scalar couplings, chemical-shift values, amide-exchange data, and a semiquantitative interpretation of NOE data, the secondary structure of NusB has classified as alpha helical, comprising seven alpha helices.

Amino Acid Sequence↗