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Biomedical subjects

G Fischer

Publications and source records attributed to G Fischer.

At least 199 records · Page 11Linked to original sources
PubMed1998

Experiences with novel techniques for reduction of stent flow in transjugular intrahepatic portosystemic shunts.

The transjugular intrahepatic portosystemic shunt (TIPS) may deteriorate liver function and can cause encephalopathy in patients with cirrhosis of the liver. Then reduction of TIPS flow may be required. We here report several attempts to reduce shunt flow in TIPS-induced encephalopathy or liver function impairment with novel techniques. Three patients with cirrhosis of the liver were investigated: Two with severe recurrent encephalopathy and one with impaired liver function following TIPS insertion. Insertion of a reducing stent was ineffective to decrease shunt flow velocity in one patient with severe coagulopathy. Sufficient reduction of shunt flow was achieved by embolizing the space around the hourglass waist of the reducing stent with an occlusion emulsion. Insertion of a conventional stent within the preexisting TIPS with or without additional embolization reduced TIPS flow in the other patients. After reduction of shunt flow encephalopathy improved and liver function returned to the level before TIPS, respectively. During follow-up no occlusion of TIPS was observed. Thus, reduction of shunt flow velocity can be achieved by insertion of an additional stent into a curve-shaped TIPS. Embolization can be helpful to decrease TIPS flow, particularly in patients with severe coagulopathy. Reduction of TIPS flow can correct TIPS-induced complications.

Blood Flow Velocity↗
PubMed1998

[Psychotherapy research--how it should (not) be done. An expert reanalysis of comparative studies by Grawe et al. (1994)].

22 psychotherapy outcome studies used in the Bernese meta-analysis by Grawe, Donati and Bernauer (1994) for a treatment comparison between behavioural and psychoanalytic-psychodynamic treatment concepts were reanalysed by 12 expert psychotherapy researchers independent of each other. Three clinical criteria served as basic criteria for the assessment of the methodological quality of the 22 comparative studies: treatment dosage, therapists' competence or expertise, and an adequate realisation of the intended treatment concept. The expert ratings were then compared with an evaluation of an assessment of a research team from the University of Ulm and with the one from the Bernese research team. Contrary to the Bernese meta-analysis, both the experts and the Ulm research group conclude that only 5 or 8 of the 22 studies, respectively, could be accepted for a relatively fair comparison between the treatments under study. Out of the 5/8 studies, none could be considered fully suitable for a treatment comparison, at the most only moderately suitable. These remaining 5 or 8 studies, respectively, do not prove superiority of one treatment over the other. Hence, the "Dodo Bird Verdict" stands up under scrutiny.

Behavior Therapy↗
PubMed1998

[Extracranial cephalic schwannomas. Apropos of 13 cases].

The authors report a series of 13 extracranial cephalic schwannomas, treated between 1981 and 1998. Schwannomas are rare and benign tumors derived from Schwann cells. Cephalic sites represent 2.5% of all schwannomas. Their diagnosis is often delayed, because symptoms mainly consist of compression disorders. There is a female predominance. The age distribution is homogeneous. There are no risk factors. There is no predominant side. The orbit and jugular foramen are the most frequent sites. The trigeminal nerve is usually involved. CT scan and magnetic resonance imaging (MRI) specify the topography and characteristics of the tumor and can contribute to the diagnosis. Macroscopically, schwannoma is a well-demarcated, ovoid or spherical, brownish tumor, off-centered from the nerve. It is composed of soft, easily fragmented tissue. The diagnosis is often obvious on microscopic examination and rarely requires immunohistochemical confirmation. The only treatment is surgical. It consists enucleation after opening the epineurium, using on operating microscope, without disruption of the nerve. Total excision ensures recovery. The authors have observed only one recurrence (first patient operated without microscope). Compression disorders regress completely. Nerve injuries have a variable prognosis. Malignant transformation is exceptional. Type II neurofibromatosis must be excluded in young patients.

Adolescent↗
PubMed1998

Experience with allogeneic and syngeneic blood stem cell transplantation in patients with hematological malignancies.

Between 1995 and 1997 twenty two patients with different hematological diseases ( CML n=10, AML n=6, ALL n=l, NHL n=3, SAA n=1,solid tumor n=1 ) and a median age of 37 (range, 20 to 55) years received unmanipulated peripheral blood stem cell (PBSC) transplants from HLA-identical sibling donors at our institution. Myeloablative chemotherapy consisted of cyclophosphamide (CY) and total body irradiation in 11, and chemotherapy alone in 11 patients. For graft-versus host-disease (GVHD) prophylaxis all patients were given cyclosporine A and methotrexate according to the Seattle protocol. PBSC were mobilized by granulocyte colony-stimulating factor (G-CSF) given at 10 microg/kg body weight (b.w.)/day for four days. Harvest of PBSC was started on day 5 and continued on day 6 if necessary. A median of 1 leukapheresis (range, 1 to 2) was performed and a median of 5.7 x 10(6) CD34+cells/kg b.w. (1.34 to 21.5) were obtained. Ten patients received G-CSF (5 microg/kg b.w.) starting on day one after PBSCT until neutrophil recovery. Absolute neutrophil counts >0.5 x 10(9)/L and ANC >1.0 x 10(9)/L were reached after a median of 13 (range 8 to 18) and 15 (range 9 to 19) days after PBSCT. Unsupported platelet counts >20 x 10(9)/L and 50 x 10(9)/L were reached after 17 (range 8 to 32) and 22 (range 13 to 40) days after PBSCT, respectively. Incidence of acute GVHD grade I to IV was 52%, extensive chronic GVHD occurred in 25% of patients. After a median observation time of 11 (range, 3 to 34) months twelve patients (55%) are alive and well. In summary, infusion of allogeneic PBSC after myeloablative therapy allows rapid and sustained hematologic reconstitution. Incidence of acute GVHD is not increased, for assessment of chronic GVHD longer observation times and larger patient numbers are required.

Adult↗
PubMed1998

Matched unrelated donor marrow transplantation in patients with advanced acute leukemia.

Patients with advanced acute leukemia (AL) have a poor prognosis with death due to disease or complications of therapy. High-dose chemoradiotherapy followed by allogeneic marrow transplantation (BMT) has been used to overcome resistance of the leukemic clone resulting in long-term survival of up to 20%. Due to lack of suitable related donors BMT from an HLA-compatible unrelated donor (MUD) has been increasingly applied in these patients during the last years. Between January 1991 and August 1997 twenty five patients with advanced acute myeloid (n=19) or lymphoid (n=6) leukemia, 11 males and 14 females, age 22 to 41 (median 32) years received MUD (n=22) or 1-antigen mismatched unrelated donor (n=3) grafts. In four patients an autologous BMT had been performed previously. For conditioning all patients were given total body irradiation containing regimens. Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine (CSA) and methotrexate (n=24) or CSA and methylprednisone (n=1). In 23 patients (92%) class II region compatibility was assessed by DRB1, DRB3, DRB5, and DQB1 allele typing by hybridization of amplified DNA with ligation based typing. In 2 patients HLA-DR typing was performed by two colour fluorescence cytotoxicity test and mixed lymphocyte cultures. As of November 1997 10/25 patients (40%) are surviving leukemia-free after a median observation time of 17 (range, 3 to 38) months. Transplant-related mortality was an overall of 36% and 28% in patients receiving their first BMT. In 6/25 patients (24%) relapse occurred 2 to 26 months after BMT. Incidence of acute GVHD grade I to IV was 85%. The probability of relapse projected at 3 years was 35%. High-dose chemoradiotherapy followed by MUD marrow infusion has a curative potential for patients with advanced acute leukemia and offers the chance of long-term leukemia-free survival. Currently, up to 80% of patients with acute myelogenous leukemia (AML) and acute lymphoid leukemia (ALL) under the age of 50 years achieve complete hematological remission (CR) with conventional dose chemotherapy. However, in patients who are refractory to induction chemotherapy or relapse prognosis is still poor. There, high-dose chemoradiotherapy followed by allogeneic marrow infusion has been used to overcome resistance of the refractory leukemic clone and has resulted in long-term survival. For selected patients lacking a human leukocyte antigen (HLA) compatible family donor marrow transplantation (BMT) with a suitable unrelated marrow donor (MUD) has become a feasible and effective treatment. Here, we report our experience in patients with advanced acute leukemia given marrow grafts from unrelated donors.

Acute Disease↗
PubMed1998

Long term follow up after allogeneic stem cell transplantation for chronic myelogenous leukemia.

Between January 1983 and July 1997, 83 patients (35 female, 48 male) with a median age of 37 (19-57) years with chronic myelogenous leukemia (CML) were admitted for bone marrow transplantation (BMT) at the University hospital of Vienna. Fifty-six patients were in chronic phase, 17 in accelerated and 10 had blast crisis. Marrow donors were: HLA-identical siblings in 62 patients, 2-antigen mismatched related donor in 2, HLA-identical unrelated donors (MUD) in 17 and 1-antigen mismatched unrelated donor in 2 patients. The median time from diagnosis to BMT was 22 (2-91) months. Conditioning therapy consisted of cyclophosphamide (CY) and total body irradiation or CY and busulfan. For graft-versus-host disease (GVHD) prophylaxis methotrexate (MTX) alone, MTX and cyclosporine A (CSA), CSA alone or CSA and methylprednisone were given. Durable engraftment was documented in 75 of 77 patients (97%). As of July 31, 1997 48 patients are alive (58%), 36 (56%) after sibling transplantation with a median observation time of 77 months and 12 (63%) after MUD transplantation with a median observation time of 13 months. Overall survival for patients in chronic phase (CP) at time of BMT is 64%, 53% for patients in acceleration and 30% for patients in blast crisis (BC). Disease-free survival (DFS) after sibling BMT and unrelated donor transplantation is 53% and 58%, respectively. Ten patients (12%) experienced relapse of CML. Transplant-related mortality was 33% after sibling and 32% after MUD transplantation. Thus, sibling and unrelated donor BMT offer high cure rates with acceptable toxicity to patients with CML.

Adult↗
PubMed1997

Sequence-specific and phosphorylation-dependent proline isomerization: a potential mitotic regulatory mechanism.

Pin1 is an essential and conserved mitotic peptidyl-prolyl isomerase (PPIase) that is distinct from members of two other families of conventional PPIases, cyclophilins and FKBPs (FK-506 binding proteins). In response to their phosphorylation during mitosis, Pin1 binds and regulates members of a highly conserved set of proteins that overlaps with antigens recognized by the mitosis-specific monoclonal antibody MPM-2. Pin1 is here shown to be a phosphorylation-dependent PPIase that specifically recognizes the phosphoserine-proline or phosphothreonine-proline bonds present in mitotic phosphoproteins. Both Pin1 and MPM-2 selected similar phosphorylated serine-proline-containing peptides, providing the basis for the specific interaction between Pin1 and MPM-2 antigens. Pin1 preferentially isomerized proline residues preceded by phosphorylated serine or threonine with up to 1300-fold selectivity compared with unphosphorylated peptides. Pin1 may thus regulate mitotic progression by catalyzing sequence-specific and phosphorylation-dependent proline isomerization.

Amino Acid Isomerases↗
PubMed1997

Intramolecular assistance of cis/trans isomerization of the histidine-proline moiety.

Peptidyl-prolyl cis/trans isomerization is a slow conformational interconversion in the polypeptide backbone that is frequently rate-limiting in refolding of proteins and is thought to play a role in cellular restructuring of proteins. In order to probe the influence of positively charged amino acids located in sequence segments adjacent to proline, the rotational barriers of Arg-Pro- and His-Pro-containing peptides were determined by isomer-specific proteolysis and dynamic NMR spectroscopy for Suc-Ala-His-Pro-Phe-NH-Np, Ac-Ala-Arg-Pro-Ala-Lys-NH2, Ac-Ala-His-Pro-Ala-Lys-NH2, angiotensin III, thyrotropin-releasing hormone (TRH), and [His(3-Me)2]TRH in aqueous solution. In contrast to the guanidinium group of arginine, the protonated side chain of histidine preceding proline led to an acceleration of the prolyl isomerization up to 10-fold relative to the unprotonated state. Both arginine and histidine residues succeeding proline in an amino acid sequence proved to be ineffective. Under basic and acidic conditions the kinetic solvent deuterium isotope effects Kc-->tH20/Kc-->tD20 for angiotensin III were 1.0 +/- 0.1 and 2.0 +/- 0.1, respectively. The results are interpreted in terms of intramolecular general acid catalysis of prolyl bond rotation by the imidazolium group that is without precedent in intermolecular catalysis.

Angiotensin III↗
PubMed1997

Catalysis of protein folding by parvulin.

Recently a new family of prolyl isomerases was discovered, which is unrelated with the cyclophilins or the FK-506 binding proteins. Parvulin, the smallest member of this new family, is a protein with only 92 residues, but parvulin-like domains occur in several large proteins that are apparently involved in protein folding or activation processes. We show here that, in addition to its activity in assays with proline-containing tetrapeptides, parvulin catalyzes the proline-limited folding of a variant of ribonuclease T1 with a kcat/Km value of 30,000 M-1 s-1. This value is much smaller than the kcat/Km value of 1.1x10(7) M-1 s-1 determined for the parvulin-catalyzed prolyl isomerization in the tetrapeptide succinyl-Ala-Leu-Pro-Phe-4-nitroanilide. Parvulin itself unfolds and refolds reversibly in a simple two-state reaction with a Gibbs free energy of stabilization of 28 kJ/mol at 10 degrees C. Most of the unfolded parvulin molecules refold in a slow reaction that involves prolyl isomerization and is catalyzed by cyclophilin, another prolyl isomerase. Moreover, parvulin accelerates its own refolding in an autocatalytic fashion, and the rate of refolding increases tenfold when the concentration of parvulin is increased from 0.5 to 3.0 microM. Apparently, small single-domain prolyl isomerases catalyze prolyl isomerization much better in short peptides than in protein folding reactions, presumably because the prolyl bonds are less accessible in refolding protein chains. It is possible that the additional domains of the large prolyl isomerases improve the affinity for protein substrates.

Catalysis↗
PubMed1997

A protease-free assay for peptidyl prolyl cis/trans isomerases using standard peptide substrates.

Peptidyl prolyl cis/trans isomerases (PPIases) are ubiquitous and abundant enzymes catalyzing peptide bond cis/trans isomerization adjacent to proline in peptides and proteins. An uncoupled protease-free assay of PPIase activity has been developed using the standard tetrapeptide substrates of the proteolytically coupled test system. Differences in the UV/vis absorption spectra of cis and trans conformations of Suc-Ala-Xaa-Pro-Phe-(Y-) anilide (Xaa = Ala, Leu, Phe; Y = 4-nitro, 2,4-difluoro) were exploited to monitor the time course of the cis/trans isomerization subsequent to a solvent jump from 0.47 M LiCl/trifluoroethanol into aqueous solution. The utility of the assay has been demonstrated by the determination of the Michaelis-Menten constants of cytosolic cyclophilin (Cyp18) and of the proteolytically sensitive FK506-binding protein-like PPIase SlyD from Escherichia coli. Furthermore, similar inhibition constants were estimated for the reversible inhibition of human Cyp18 by cyclosporin A (CsA) with both the proteolytically coupled and the novel uncoupled PPIase assay.

Catalysis↗
PubMed1997

A time-resolved FTIR difference study of the plastoquinone QA and redox-active tyrosine YZ interactions in photosystem II.

In this paper, we present the first time-dependent measurements of flash-induced infrared difference spectra of photosystem II (PSII) using Fourier transform infrared (FTIR) spectroscopy. With this experimental approach, we were able to obtain the YZoxQA-/YZQA vibrational difference spectrum of Tris-washed, PSII-enriched samples in the absence of hydroxylamine at room temperature (16 +/- 2 degrees C), with a spectral resolution of 4 cm-1 and a temporal resolution of 50 ms. In order to determine the dominant species in the FTIR spectrum at a particular point in time after an excitation flash, the decay kinetics of YZox and QA- were independently monitored by EPR and chlorophyll a fluorescence, respectively, under the same experimental conditions. These measurements confirmed that the addition of DCMU to Tris-washed PSII samples does not significantly affect the YZox decay, but does substantially slow down the QA- decay. By making use of the difference in the decay kinetics using DCMU, the QA-/QA signals could be separated from the YZox/YZ signals and a pure QA-/QA difference spectrum obtained. By comparison of the YZoxQA-/YZQA difference spectrum with the pure QA-/QA difference spectrum, a large differential band at 1706/1699 cm-1 could be identified and associated with YZ oxidation. In contrast, an intense band at 1478 cm-1, whose DCMU-sensitive decay follows the QA- decay based on the chlorophyll a fluorescence measurements, was present in all of the time-resolved spectra. Since no significant reversible Chl+ radicals could be detected by the EPR measurements under our experimental conditions, we confirm that this band most likely arises only from the semiquinone anion QA- [Berthomieu, C., Nabedryk, E., Mäntele, W., & Breton, J. (1990) FEBS Lett. 269, 363-367].

Benzoquinones↗
PubMed1997

Modular structure of the trigger factor required for high activity in protein folding.

The Escherichia coli trigger factor is a peptidyl-prolyl cis/trans isomerase (PPIase) which catalyzes proline-limited protein folding extremely well. It has been found associated with nascent protein chains as well as with the chaperone GroEL. The trigger factor utilizes protein regions outside the central catalytic domain for catalyzing refolding of unfolded proteins efficiently. Here we produced several fragments which encompass individual domains or combinations of the middle FKBP-like domain (M) with the N-terminal (N) and C-terminal (C) regions, respectively. These fragments appear to be stably folded. They show ordered structure and cooperative urea-induced unfolding transitions, and the far-UV CD spectrum of the intact trigger factor is well represented by the sum of the spectra of the fragments. This suggests that the native trigger factor shows a modular structure, which is composed of three fairly independent folding units. In the intact protein there is a slight mutual stabilization of these units. The high enzymatic activity in protein folding could not be restored by fusing alternatively the N or the C-terminal regions to the catalytic domain (in NM and MC constructs, respectively). Surprisingly, the high folding activity of the intact trigger factor has been regained partially by functional complementation of the overlapping NM and MC constructs.

Amino Acid Isomerases↗
PubMed1997

Conformational state of a 25-mer peptide from the cyclophilin-binding loop of the HIV type 1 capsid protein.

Recently a 25-residue part of Gag polyprotein from HIV type 1 (HIV-1) was reported to bind to the cytosolic 18 kDa cyclophilin (Cyp18) with an IC50 value of 180 microM. This peptide corresponds to the Cyp18-binding domain of HIV-1 Gag. A replacement of Gly with Ala in the cyclophilin-binding loop of HIV-1 Gag polyprotein results in the prevention of the packaging of Cyp18 into virions. We found only two conformers of this peptide among 16 possible expected conformers, owing to cis/trans isomerization of four peptidyl-prolyl bonds. Although this finding implicates the existence of a stabilizing structure, we were not able to detect secondary structure formation by 1H-NMR and CD spectroscopy. We characterized the peptide as a substrate for Cyp18 by two-dimensional exchange 1H-NMR spectroscopy. Surprisingly, we found similar binding characteristics for a peptide corresponding to 25-mer peptide containing the above-mentioned Gly to Ala substitution.

Amino Acid Sequence↗
PubMed1997

Identification of Doppler microembolic signals with a bigate probe in patients with prosthetic heart valves.

BACKGROUND AND PURPOSE: The applicability of a bigate probe, simultaneously harvesting two spatially separated vessel segments, in the identification of Doppler microembolic signals (MES) was evaluated. METHODS: One hundred and ninety-seven patients with artificial heart valves were bilaterally monitored over two segments of each middle cerebral artery, with a minimal distance of 5 mm between them, using 2 MHz probes. Time delay in the appearance of high intensity transients between the two segments was calculated off-line, using dedicated software, integrated in the Doppler device. RESULTS: Bigate monitoring was feasible in 96% of patients. MES prevalence and counts were 37% and 26 (18-44) respectively. All but 8.8% of the 2932 MES signals recorded appeared in both Doppler channels, with a time delay of 4.4 (4.2-4.7) msec (range between 0 and 34 msec). Time delay in 97% of artifact signals was under 1 msec. Application of 1 msec as low and 20 msec as high cut-off point between MES and artifacts resulted in the correct identification of 97% of artifacts and 89.6% of MES. CONCLUSIONS: The multigate approach is a reliable method for identification of Doppler microembolic signals in patients with prosthetic heart valves. The value of this technique in other patient groups remains to be evaluated.

Aortic Valve↗
PubMed1997

The Escherichia coli SlyD is a metal ion-regulated peptidyl-prolyl cis/trans-isomerase.

In Escherichia coli as many as nine different genes coding for proteins with significant homology to peptidyl-prolyl cis/trans-isomerases (PPIases) have been found. However, for three of them, the histidine-rich SlyD, the homologous gene product of ORF149, and parvulin-like SurA, it was not known whether these proteins really possess PPIase activity. To gain access to the full set of PPIases in E. coli, SlyD, the N-terminal fragment of SlyD devoid of the histidine-rich region, as well as the protein product of ORF149 of E. coli named SlpA (SlyD-like protein) were cloned, overexpressed, and purified to apparent homogeneity. On the basis of the amino acid sequences, both proteins proved to be of the FK506-binding protein type of PPIases. Only when using trypsin instead of chymotrypsin as helper enzyme in the PPIase assay, the enzymatic activity of full-length SlyD and its N-terminal fragment can be measured. For Suc-Ala-Phe-Pro-Arg-4-nitroanilide as substrate, kcat/Km of 29,600 M-1 s-1 for SlyD and 18,600 M-1 s-1 for the N-terminal fragment were obtained. Surprisingly, the PPIase activity of SlyD is reversibly regulated by binding of three Ni2+ ions to the histidine-rich, C-terminal region. Because the PPIase activity of SlpA could be established as well, we now know eight distinct PPIases with proven enzyme activity in E. coli.

Amino Acid Isomerases↗
PubMed1997

Comparative mutational analysis of peptidyl prolyl cis/trans isomerases: active sites of Escherichia coli trigger factor and human FKBP12.

A low degree of amino acid sequence similarity to FK506-binding proteins (FKBPs) has been obtained for the peptidyl prolyl cis/trans isomerase (PPIase) domain of E. coli trigger factor (TF) that was thought to be significant with regard to the enzymatic properties of the bacterial enzyme. We examined whether the alteration of a negatively charged side-chain at position 37 (FKBP numbering) and a phenylalanine at position 99, both highly conserved through both types of enzymes, leads to parallel effects on the catalytic activity of both FKBP12 and TF-PPIase domain in a series of tetrapeptide substrates with different P1 subsites. For the latter enzyme, substitution of Glu178 by Val or Lys, which aligns to Asp37 in human FKBP12, enhanced the PPIase activity, whereas a strongly decreased enzymatic activity was determined for the Asp37Leu and Asp37Val variants of FKBP12. Regardless of the P1 subsite of the substrate used for the assay, mutation of Phe233Tyr generated a protein variant of the TF-PPIase domain with about 1% of the wild type PPIase activity. Dependent on the substrate nature, a moderate decrease as well as a 4.8-fold increase in k(cat)/K(M) could be determined for the corresponding Phe99Tyr FKBP12 variant. Neither of the mutations of the TF-PPIase domain was able to implant FK506 inhibition found as a major characteristic of the FKBP family of PPIases.

Amino Acid Isomerases↗