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Biomedical subjects

M Sieber

Publications and source records attributed to M Sieber.

At least 55 records · Page 3Linked to original sources
PubMed1998

BEACOPP, a new dose-escalated and accelerated regimen, is at least as effective as COPP/ABVD in patients with advanced-stage Hodgkin's lymphoma: interim report from a trial of the German Hodgkin's Lymphoma Study Group.

PURPOSE: The HD9 trial aims to evaluate whether moderate dose escalation and/or acceleration of standard polychemotherapy is beneficial for advanced-stage Hodgkin's disease (HD). Two variants of a novel bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, and prednisone (BEACOPP) scheme (standard and escalated dose) are compared with cyclophosphamide, vincristine, procarbazine, and prednisone (COPP)/doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD). PATIENTS AND METHODS: The randomized, three-arm trial recruited patients in stages IIB and IIIA with risk factors and stages IIIB and IV. BEACOPP in baseline dose contains all drug dosages of COPP/ABVD (except vincristine and procarbazine) rearranged in a shorter, 3-week cycle. Escalated BEACOPP uses higher doses of cyclophosphamide, doxorubicin, and etoposide with granulocyte colony-stimulating factor (G-CSF) support. After eight chemotherapy cycles, initial bulky and residual disease is irradiated. The trial is monitored and analyzed by means of a sequential strategy. RESULTS: An interim analysis with 505 assessable patients and a median follow-up of 23 months showed a significant inferiority (according to sequential monitoring strategy) of the COPP/ABVD regimen in progression rate and freedom from treatment failure (FFTF) compared with the pooled results of both BEACOPP variants. The 24-month FFTF rate was 75% for COPP/ABVD and 84% for BEACOPP pooled (P = .034). There was 12% progressive disease with COPP/ABVD and 6% with BEACOPP pooled. Differences in survival were not significant in sequential analysis. The acute toxicity of baseline BEACOPP resembled that of COPP/ABVD; escalated BEACOPP showed increased but manageable hematologic toxicity. CONCLUSION: Combined with local irradiation, BEACOPP in one or both variants shows superior disease control compared with COPP/ABVD, with acceptable acute toxicity. Further follow-up is required to assess the effect of dosage and the effect on survival and late toxicities.

Adolescent↗
PubMed1998

Arginine (348) is a major determinant of the DNA binding specificity of transcription factor E12.

The basic helix-loop-helix proteins (BHLH) E12 and E47 bind to DNA in a cell-type specific fashion as heterodimers with transcription factors such as MyoD, Myf-5, MRF-4, myogenin, and MASH-1 and -2 which are critical regulators of cellular differentiation. We have measured the apparent dissociation constants (KD) of the complexes of E12 and several E12 mutants with various oligonucleotides. Glutamate (345) of E12, which is hydrogen bonded to a CpA dinucleotide, and arginine (348), a residue that does not directly interact with the nucleobases, are major determinants of the DNA binding specificity of E12. R(348) is in direct contact with both the phosphate backbone and the carboxylate of E(345), thereby locking the side chain conformation of E(345). In its locked conformation the glutamate residue interacts favourably only with E-box containing DNA, the natural target of BHLH-proteins, while repulsive interactions destabilise the complexes with all other DNA sequences.

Amino Acid Sequence↗
PubMed1997

High affinity binding of MEF-2C correlates with DNA bending.

To regulate lineage-specific gene expression in many cell types, members of the myocyte enhancer factor-2 (MEF-2) family of transcription factors cooperate with basic helix-loop-helix (bHLH) proteins, which show only limited intrinsic DNA binding specificity. We investigated the DNA binding properties of MEF-2C in vitro and show that the inherent bendability of the MEF site is one of the principal structural characteristics recognized by MEF-2C. Measurements of the apparent dissociation constants of MEF-2C complexes with several DNA sequences revealed that MEF-2C bound with high affinity to DNA sequences containing a MEF site. Mutations in the MEF site which did not affect the bendability of the DNA changed the free energy of binding only marginally. However, reducing the intrinsic bendability of the DNA binding site through an AA-->GC substitution increased the half-maximal binding concentration of MEF-2C by almost one order of magnitude. Electrophoretic mobility shift assays revealed markedly reduced MEF-2C binding to DNA containing 2,6-diaminopurine. On binding to MEF-2C the maximum ellipticity at 275 nm in the CD spectrum of DNA containing a MEF site was red shifted by 4 nm and its intensity reduced significantly, while a slight blue shift of <1 nm was observed for a mutant DNA sequence with reduced bendability (AA-->GC). Bending analysis by circular permutation assay revealed that the DNA in the cognate complex was bent by 49 degrees , while the DNA in the complex with the mutant oligonucleotide was largely unbent.

2-Aminopurine↗
PubMed1997

Quartz crystal microbalance investigation of the interaction of bacterial toxins with ganglioside containing solid supported membranes.

The binding of cholera toxin, tetanus toxin and pertussis toxin to ganglioside containing solid supported membranes has been investigated by quartz crystal microbalance measurements. The bilayers were prepared by fusion of phospholipid-vesicles on a hydrophobic monolayer of octanethiol chemisorbed on one gold electrode placed on the 5 MHz AT-cut quartz crystal. The ability of the gangliosides GM1, GM3, GD1a, GD1b, GT1b and asialo-GM1 to act as suitable receptors for the different toxins was tested by measuring the changes of quartz resonance frequencies. To obtain the binding constants of each ligand-receptor-couple Langmuir-isotherms were successfully fitted to the experimental adsorption isotherms. Cholera toxin shows a high affinity for GM1 (Ka = 1.8.10(8)M-1), a lower one for asialo-GM1 (Ka = 1.0.10(7)M-1) and no affinity for GM3. The C-fragment of tetanus toxin binds to ganglioside GD1a, GD1b and GT1b containing membranes with similar affinity (Ka approximately 10(6)M-1), while no binding was observed with GM3. Pertussis toxin binds to membranes containing the ganglioside GD1a with a binding constant of Ka = 1.6.10(6)M-1, but only if large amounts (40 mol%) of GD1a are present. The maximum frequency shift caused by the protein adsorption depends strongly on the molecular structure of the receptor. This is clearly demonstrated by an observed maximum frequency decrease of 99 Hz for the adsorption of the C-fragment of tetanus toxin to GD1b. In contrast to this large frequency decrease, which was unexpectedly high with respect to Sauerbrey's equation, implying pure mass loading, a maximum shift of only 28 Hz was detected after adsorption of the C-fragment of tetanus toxin to GD1a.

Cholera Toxin↗
PubMed1997

A scanning force- and fluorescence light microscopy study of the structure and function of a model pulmonary surfactant.

The structure of an artificial pulmonary surfactant was studied by scanning force- and fluorescence light microscopy (SFM, and FLM, respectively). The surfactant--a mixture of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG) and recombinant surfactant-associated protein C (SP-C)--was prepared at the air-water interface of a Langmuir film balance and imaged by FLM under various states of compression. In order to visualize their topography by SFM, the films were transferred onto a solid mica support by the Langmuir-Blodgett (LB) technique. We found that a region of high film compressibility of the spread monolayer close to its equilibrium surface pressure (pi = 50 mN/m) was due to the exclusion of layered protrusions with each layer 5.5 to 6.5 nm thick. They remained associated with the monolayer and readily reinserted upon expansion of the film. Comparison with the FLM showed that the protrusions contained the protein in high concentration. The more the film was compressed, the larger was the number of layers on top of each other. The protrusions arose from regions of the monolayer with a distinct microstructure that may have been responsible for their formation. The molecular architecture of the microstructure remains to be elucidated, although some of it can be inferred from spectroscopic data in combination with the SFM topographical images. We illustrate our current understanding of the film structure with a molecular model.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1997

The phase behavior of lipid monolayers containing pulmonary surfactant protein C studied by fluorescence light microscopy.

Three compounds of the pulmonary surfactant--dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and the surfactant associated protein C (SP-C)--were spread at the air-water interface of a Langmuir trough as a model system to mimic the properties of natural surfactant. Fluorescence microscopical images of the film formed at the interface were obtained during compression using a fluorescence dye bound covalently either to phosphatidylcholine or to SP-C. The images were quantified using statistical methods in respect to relative areas and relative fluorescence intensities of the domains found. In the early stage of compression, film pressure rose slightly and was accompanied by a phase separation which could be recognized in the images by the formation of bright and dark domains. On further compression, after a steep increase of film pressure, a plateau region of constant film pressure started abruptly. During compression in the plateau region, fluorescence intensity of the bright domain formed in the early stage of compression increased. The increasing fluorescence intensity, the non-Gaussian intensity distribution of the bright domain, and the small mean molecular area of the film in the plateau region gave rise to the assumption that multilayer structures were formed in the late stage of compression. The formation of the multilayer structures was fully reversible in repeated compression-expansion cycles including the plateau region of the phase diagram. The ability of lipid/SP-C mixtures to form reversible multilayer structures during compression may be relevant to stability in lungs during expiration and inhalation.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1997

The structure of a model pulmonary surfactant as revealed by scanning force microscopy.

The structures formed by a pulmonary surfactant model system of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and recombinant surfactant-associated protein C (SP-C) were studied using scanning force microscopy (SFM) on Langmuir-Blodgett films. The films appeared to be phase separated, in agreement with earlier investigations by fluorescence light microscopy. There were smooth polygonal patches of mostly lipid, surrounded by a corrugated rim rich in SP-C. When the films were compressed beyond the equilibrium surface pressure, the protein-rich phase mediated the formation of layered protrusions. The height of these multilamellar structures embodied equidistant steps slightly higher than a DPPC double layer in the gel phase. At the air-water interface too, a high compressibility at low surface tension was indicative of the exclusion of matter. The exclusion process proved to be fully reversible. The present study demonstrates that some of the matter of the model pulmonary surfactant can move in and out of the active monolayer. The SFM images revealed a lipid-protein complex that was responsible for the reversible exclusion of double-layer structures. This mechanism may be important in the natural system too, to keep the surface tension of the alveolar air/water interface constantly low over the range of area encountered upon breathing.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1997

Impedance and shear wave resonance analysis of ligand-receptor interactions at functionalized surfaces and of cell monolayers.

The present paper scrutinizes the application of impedance spectroscopy and quartz-crystal microbalance (QCM) measurements in the analysis of composite layers of receptor containing lipid bilayers, and their interaction with external ligands or pore-forming peptides. The formation of supramolecular structures and their analysis will be discussed. Impedance measurement allows one to follow the adsorption of proteins on artificial membranes. This method is even more suitable for quantifying changes in membrane conductivity induced by channel peptides incorporated into the lipid membrane. The QCM is another sophisticated method for analyzing ganglioside-lectin and ganglioside-toxin interactions. A critical comparison between both methods will be given. Moreover, we will demonstrate that the QCM method, especially in combination with impedance analysis, is a completely new approach for determining electrical and viscoelastic properties of epithelial and endothelial cell monolayers that form controlled barriers in vivo.

Animals↗
PubMed1997

BEACOPP: an intensified chemotherapy regimen in advanced Hodgkin's disease. The German Hodgkin's Lymphoma Study Group.

PURPOSE: At present, treatment results for patients with advanced-stage Hodgkin's disease remain unsatisfactory. Standard chemotherapy M(C)OPP (nitrogen mustard (cyclophosphamide). vincristine, procabazine, and prednisone). ABVD (adriamycine, bleomycine, vinblastine, and dacarbacine) or M(C)OPP/ABVD +/- radiotherapy fail to achieve long-term complete remission in 35% to 50% of these patients. The BEACOPP (bleomycin, etoposide, adriamycine, cyclophosphamide, vincristine, procarbazine, and prednisone) regimen was developed to improve treatment results by dose intensification achieved by reduced duration of treatment (time intensification) and addition of etoposide. PATIENTS AND METHODS: Thirty untreated patients with advanced Hodgkin's disease stage IIB IV according to the Ann Arbor classification were treated with the time intensified BEACOPP regimen. Each patient was scheduled to receive eight cycles of chemotherapy with consolidating radiotherapy to sites of initial bulk disease and to residual tumor remaining after chemotherapy. RESULTS: All patients were evaluable for assessment of toxicity, treatment response, freedom from treatment failure (FFTF) and survival (SV). Of 30 treated patients, 29 patients received the intended eight cycles of BEACOPP. One patient in clinical CR, terminated the chemotherapy at his own request after six cycles and is at this time, 48 months after the end of treatment, in complete remission. Toxicity was tolerable with WHO grade 3/4 leucopenia in 28% of chemotherapy cycles and one severe (WHO grade 3) infection. No treatment-related death occurred. Cycles could generally be given on schedule. Complete remission (CR) was achieved in all but two patients (93%). At present, only one patient has relapsed. At a median follow-up of 40 months, FFTF-rate is 89% (lower confidence limit: 80%). One patient died due to progressive disease. CONCLUSION: The BEACOPP regimen is feasible at moderate hematopoeitic toxicity. With a FFTF-rate of 89% at a median follow-up of 40 months, the treatment results are very encouraging. A prospective randomised trial has been initiated to compare the BEACOPP regimen with the standard COPP/ABVD regimen in advanced-stage Hodgkin's disease.

Adult↗
PubMed1997

The functional status of the masticatory system of 11-16-year-old adolescents: classification and validity.

Epidemiological studies to assess the prevalence and course of functional disturbances of the masticatory system should be based on a valid and reliable measure of the functional status of the masticatory system. NIELSEN et al. (2, 3) proposed a classification method that included three different classes of dysfunction. This classification was used to compare the results of a sample of 447 11-16-year-old Swiss adolescents with those of the Danish study and to test the validity of this classification method. The two studies showed similar prevalences in two of the three dysfunction classes and a similar pattern of dysfunction categories. Concurrent and construct validity analyses showed significant correlations between the assessment from clinical examination and the subjective judgments of the adolescents. The results demonstrated cross- and concurrent validation of the "Nielsen index" but also stressed the necessity of a careful re-evaluation of the "severe" class criterion. The limitations of the Nielsen index led to the construction of a "Zurich-MAP index". The potential applications of both indices are discussed.

Adolescent↗
PubMed1997

Dose-response relationship of complementary radiotherapy following four cycles of combination chemotherapy in intermediate-stage Hodgkin's disease.

PURPOSE: To determine the appropriate irradiation dose after four cycles of modern combination chemotherapy in nonbulky involved field (IF/BF) and noninvolved extended-field (EF/IF) sites in patients with intermediate-stage Hodgkin's disease (HD). MATERIALS AND METHODS: HD patients in stage I to IIIA with a large mediastinal mass, E stage, or massive spleen involvement were treated with two double cycles of alternating cyclophosphamide, vincristine, procarbazine, and prednisone (COPP) plus doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) followed by EF irradiation in two successive trials (HD1 and HD5). In the HD1 trial (1983 to 1988), 146 patients who responded to chemotherapy were randomized to receive 20 Gy (70 patients) or 40 Gy (76 patients) of EF irradiation in all fields outside bulky disease sites. A cohort of 111 patients who fulfilled the same inclusion criteria in the subsequent trial HD5 (1988 to 1993) were treated with 30 Gy. Bulky disease always received 40 Gy. RESULTS: Freedom-from-treatment-failure (FFTF) and survival (SV) curves showed no differences between the 20-, 30-, and 40-Gy groups. However, acute toxicities were more frequent in the 40-Gy arm. Analysis of relapse patterns showed that 18 of 26 relapsing patients either failed to respond in initial bulky sites (n = 5) or had an extranodal relapse (n = 9) or both (n = 4). After 5 years, the cumulative risk for relapse in bulky sites is 10%, despite 40 Gy of radiation. CONCLUSION: Our results strongly suggest that there is no relevant radiotherapy dose effect in the range between 20 Gy and 40 Gy in IF/BF and EF/IF after 4 months of modern polychemotherapy in patients with intermediate-stage HD. Relapse patterns indicate that patients destined to relapse need more systemic, rather than local, treatment. Based on our data, we conclude that 20 Gy is sufficient in EF/IF of intermediate-stage HD following four cycles of modern polychemotherapy.

Adolescent↗
PubMed1997

Consistency of international genetic evaluations of Holstein bulls.

International genetic evaluations from August 1995 and February 1996 for Holstein bulls from Canada, France, Germany, Italy, The Netherlands, and the US were evaluated for consistency across time. Mean evaluations, expressed on a US basis, were unchanged for US bulls; evaluations for bulls from France, Germany, Italy, and The Netherlands increased about 14 kg for milk and 0.4 kg for fat and protein. Mean genetic merit of US parents of bulls sampled in Canada, France, Germany, The Netherlands, and the US overestimated bull merit. Solutions for country of bull generally were not different for other countries relative to the US; however, evaluations for German and Netherlands bulls were higher than evaluations for US bulls with the same parent merit. French bulls that were full brothers to US bulls had higher evaluations for milk and protein, regardless of country of evaluation. Intercepts for conversion equations to a US basis increased by birth year and decreased for conversions from a US basis. Future international evaluations generally were predicted more accurately by prior international evaluations than by more recently converted national evaluations; however, converted evaluations with substantial increases in data could be better predictors, depending on country. The continued use of the latest international evaluations is recommended. Improvements in methodology that increase the consistency of evaluations across time and location may be possible. Alternatively, users may need to accept some uncertainty and error in international evaluations because of limitations in available data and methodology.

Animals↗
PubMed1996

Impedance analysis of epithelial and endothelial cell monolayers cultured on gold surfaces.

The present study describes a new method to determine transepithelial and transendothelial electrical resistances (TER) of cultured cell monolayers which is based on impedance analysis. To obtain impedance data of the epithelia or endothelia under investigation, we developed special measuring chambers that allow to culture the cells on gold surfaces that are used as measuring electrodes. Impedance analysis is carried out in the frequency range from 1 to 10(5) s-1 under normal culture conditions using a self-developed continuous wave impedance spectrometer. Evaluation of impedance data is achieved by fitting (NLSQ) the parameters of appropriate equivalent circuits to the experimental data. We investigated cell monolayers of primary cultured endothelial cells isolated from porcine brain microvessels, epithelial cells from porcine choroid plexus as well as those of the epithelial cell line MDCK. Transepithelial resistances were found to be in good agreement with published data. The main advantages of the new technique are the ability (i) to use multi-electrode arrays that allow to determine TERs at different locations of a given cell monolayer; (ii) to carry out impedance analysis under normal culture conditions; and (iii) to obtain TER values of cell monolayers grown on impermeable supports, which means that conditions cells are normally exposed to in ordinary culture dishes are maintained.

Animals↗
PubMed1996

[Clinical aspects and primary therapy of Hodgkin's lymphomas].

In spite of intensive research, the etiology and the pathogenesis of Hodgkin's lymphoma are still unclear. Hodgkin's lymphoma is clinically characterized by the appearance of enlarged lymph nodes and systemic symptoms. The diagnosis is exclusively based on the identification of the typical Reed-Sternberg cells surrounded by a mixture of reactive cells. Careful staging aims at determining disease extent and other risk factors which have therapeutic relevance. The appropriate use of modern radio- and chemotherapy results in the cure of approximately 75% of all patients with Hodgkin's lymphoma. The prognosis of patients in limited or intermediate stages is particularly favourable. New treatment strategies aim at reducing therapy related long-term toxicity while preserving the high chance of cure. In contrast, the prognosis of patients in advanced stages is still unsatisfactory. The main goal of the clinical research is to improve treatment results for these patients.

Adolescent↗
PubMed1996

Impedance analysis of supported lipid bilayer membranes: a scrutiny of different preparation techniques.

One topic of this study is the comparison of different preparation techniques to build up solid supported lipid bilayers onto gold substrates. The deposited lipid bilayers were investigated by a.c. impedance spectroscopy. Three different strategies were applied: (1) The gold surface was initially covered with a chemisorbed monolayer of octadecanethiol or 1,2-dimyristoyl-sn-glycero-3-phosphothioethanol (DMPTE). The second monolayer consisting of phospholipids was then deposited onto this hydrophobic surface by (i) the Langmuir-Schaefer-technique, (ii) from lipid solution in n-decane/isobutanol, (iii) by the lipid/detergent dilution technique or (iv) by fusion of vesicles. (2) Charged molecules carrying thiol-anchors for attachment to the gold surface by chemisorption were used. Negatively charged surfaces of 3-mercaptopropionic acid were found to be excellent substrates that allow the attachment of planar lipid bilayers by applying positively charged dimethyldioctadecylammoniumbromide (DODAB) vesicles or negatively charged 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol vesicles in the presence of chelating Ca2+-ions. If positively charged first monolayers of mercaptoethylammoniumhydrochloride were used we were able to attach mixed 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol/1,2-dimyristoyl-sn-glycero- 3-phosphoethanolamine vesicles to form planar lipid bilayers via electrostatic interaction. (3) Direct deposition of lipid bilayers is possible from vesicles containing 1,2-dimyristoyl-sn-glycero-3-phosphothioethanol (DMPTE). A critical amount of more than 50 mol% of DMPTE was found to be necessary to form a solid supported lipid bilayer. Bilayers obtained with these different preparation techniques were scrutinized with respect to their capacitances, kinetics of formation and their long-term stabilities by impedance spectroscopy. The second feature of this paper is the application of the supported bilayers to study ion transport through channel-forming peptides. We used a DODAB-bilayer for the reconstitution of gramicidin D channels. By circular dichroism measurements we verified that the peptide is in its channel conformation. The ion transport of Cs+-ions through the channels was recorded by impedance analysis.

Cesium↗
PubMed1996

Double-mode impedance analysis of epithelial cell monolayers cultured on shear wave resonators.

The viscoelastic behavior of epithelial cells (MDCK-I and MDCK-II) grown on AT-cut quartz crystals with a fundamental resonance at 5 MHz was investigated by impedance spectroscopy. Using the electromechanical model recently derived by Martin et al. [(1991) Anal Chem 63: 2272-2281] for Newtonian liquids in contact with shear wave resonators we quantified the viscous damping arising from the adherent cells by fitting the impedance data with a modified Butterworth-Van Dyke circuit in the region of the resonance frequency. Impedance spectroscopy was additionally performed in the frequency range from 1 Hz to 1 MHz to scrutinize the passive electrical properties of the epithelial cell layers using an additional platinum electrode. These data allow one to document the cell layers' integrity as well as the electrode coverage. We were able to confirm that the presence of a cell-layer mainly increases damping of the shear wave and does not exhibit a pure mass-load behavior. These findings were supported by the discovery that the inductance L in the electromechanical model was less influenced by the cell-layer than the resistance R. The apparent cell-viscosities determined by our method are 0.097 poise for MDCK-I and 0.142 poise for MDCK-II cell-layers. These low apparent viscosities may be explained in terms of a considerable spacing between the cells immobilized via their focal contacts and the quartz surface.

Animals↗
PubMed1996

Are coping strategies related to disease outcome in early breast cancer?

A consecutive series of 107 women with early breast cancer were investigated for coping strategies and disease outcome 5 to 6 years after primary surgical treatment (mastectomy or lumpectomy). Coping was assessed several times during a 3-year investigation period by the Zurich and Freiburg Questionnaires of Coping with Illness (ZQCI, FQCI). Data analysis revealed no significant correlations between coping strategies and the target variable "death from breast cancer". However, significant relations were found between postsurgical tumour size (p < or = 0.01), positive histological node status (p < or = 0.01) and death from breast cancer. The results of a discriminant analysis also indicated that somatic parameters are more important for the course of breast cancer disease than psychological aspects of coping. The role of psychosocial variables for the outcome of cancer disease remains unclear and further studies in this field are necessary.

Adaptation, Psychological↗