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Biomedical subjects

M Schmidt

Publications and source records attributed to M Schmidt.

At least 307 records · Page 17Linked to original sources
PubMed1999

Three-dimensional MR angiography of a nitinol-based abdominal aortic stent graft: assessment of heating and imaging characteristics.

OBJECTIVE: To assess heating- and 3D MRA imaging characteristics of a commonly used aortic stent graft in a 1.5T MR-environment. MATERIALS AND METHODS: A bifurcated stent graft (Vanguard; Boston Scientific, Oakland, N. J.) was evaluated in vitro regarding localized heating effects as well as imaging appearance using fast 3D GRE sequences. To quantitate stent related artifacts, stent wall thickness and luminal diameters were measured. Subsequently eight patients were imaged three months following placement of an aortic stentgraft with 3D MRA. Images were assessed for the presence of stent leaks, luminal patency, and stent configuration. RESULTS: There were no temperature changes associated with the stent during scanning. Wall thickness measurements overestimated true stent thickness, resulting in minimal underestimation of luminal diameters on 3D MRA images. In vivo imaging confirmed these results. Stent patency was confirmed in all 8 patients. CONCLUSION: Contrast-enhanced 3D MRA appears well suited for the evaluation of the abdominal and pelvic vasculature following aortic implantation of a Vanguard stent.

Aged↗
PubMed1999

Proteolytic patterns of head and neck squamous cell carcinoma.

The significance of plasminogen activators and matrix metalloproteases for clinical outcome, growth and metastatic behavior of head and neck squamous cell carcinoma (SCC) is still controversial. The majority of studies has been based on either immunohistological stainings, which provide only limited quantitative information, or in vitro experiments. We analyzed 44 head and neck SCC and 11 mucosa tissue samples for the expression of gelatinolytic or fibrinolytic proteases by quantitative zymographic analysis and compared lytic activities to clinical and histopathological data. We calculated activation ratios for matrix metalloproteinases-2 and -9 (MMP-2 and MMP-9) by separate evaluations of inactive and activated MMP forms. Increased gelatinolytic and fibrinolytic activity was found in head and neck SCC when compared to mucosa. Increased values were caused by MMP-9 and urokinase type plasminogen activator, respectively. No statistically significant correlations of either protease lytic activity or activation ratio could be related to T-stage, metastasis, tissue necrosis or the differentiation stage of tumors. The data recorded are compared with previously published reports.

Carcinoma, Squamous Cell↗
PubMed1999

Immunologic characterization of natural and recombinant Mal f 1 yeast allergen.

BACKGROUND: Individuals with atopic dermatitis (AD) often have IgE antibodies against protein components of Malassezia furfur. The cDNA encoding one of these proteins (Mal f 1) has recently been cloned and sequenced. OBJECTIVE: We sought to express recombinant Mal f 1 (rMal f 1) allergen in large quantities by using different expression systems. The primary aim was to characterize the IgE-binding properties of rMal f 1 in comparison with its natural counterpart in M furfur extract. METHODS: We have expressed and purified Mal f 1 from prokaryotic (Escherichia coli) and eukaryotic cells (baculovirus-infected insect cells). The rMal f 1 produced in both systems has been tested for the ability to be recognized by IgE from patients with specific serum IgE to M furfur by using immunoblotting and the Pharmacia CAP System RAST FEIA. RESULTS: Sixty-one percent of sera from 95 patients showed positive RAST responses to the rMal f 1 produced in the baculovirus expression system and 43% to the E coli -produced rMal f 1. Both the E coli - and baculovirus-produced proteins can specifically inhibit IgE binding to a 36-kd protein band (Mal f 1) in immunoblotting, indicating that the recombinant proteins contain the majority, if not all, the IgE-binding epitopes of Mal f 1. Recombinant Mal f 1 is able to release histamine from basophils of an atopic individual. CONCLUSION: We have expressed and purified rMal f 1, which can bind IgE in a way resembling natural Mal f 1. The ability to produce recombinant allergens with similar properties to their native counterparts has many potential uses, such as accurately diagnosing causes of IgE-mediated allergy.

Allergens↗
PubMed1999

Judgment analysis in clinical nephrology.

To ameliorate the clinical performance of nephrologists, improving their clinical judgment is crucial. No methodology for judgment analysis in nephrology is currently available. Therefore, we designed a trial to assess the intraphysician consistency of the judgment of typical non-end-stage renal disease (ESRD) patients by 24 board-certified nephrologists. The participants were asked to analyze cases to determine the interobserver variability with respect to diagnosis, therapy, prognosis, and strategy of follow-up. They were unaware that every patient was presented on 2 occasions separated by a period of 6 months. Of the 1,288 questionnaires that were completed, 28 cases belonged to 1 of the following 3 groups: (A) patients once with, once without renal histology, (B) patients twice without histology, and (C) patients twice with histology. Only cases of group (A) differed at the 2 occasions of assessment with respect to knowledge of histology. The results from the first and second assessment were compared and analyzed. The median (95% confidence interval) percentages of changed diagnoses were 64% (59% to 68%), 50% (44% to 62%), and 33% (26% to 47%) in groups A, B, and C, respectively, indicating large intraobserver variability. The frequency of changes in diagnoses declined with the degree of confidence in the first diagnosis in all 3 groups. The subjective desire to know the histology was without impact on the frequency of changes in diagnoses. However, a knowledge of the histology enhanced the degree of confidence in the diagnoses. Interestingly, the enormous variability in changing diagnoses from one analysis to the other was not reflected by corresponding changes in the judgment of prognosis, therapy to be prescribed, or strategy of follow-up. The individual judgment with respect to diagnosis of clinical cases is inconsistent and highly dependent on the subjective degree of confidence in the diagnosis. The practical relevant consequences traditionally derived from a diagnosis (therapy, prognosis, and strategy of follow-up) are only marginally, if at all, affected by changing the diagnosis. Thus, the utility of "diagnosis" for judgment analysis in clinical nephrology should be reconsidered.

Adult↗
PubMed1999

Structure and mechanism of ATP-dependent proteases.

A general paradigm for energy-dependent proteases is emerging: ATP may be used to unfold the substrate and translocate it through a narrow channel within the enzyme into a central proteolytic chamber. Different members of the family present intriguing elaborations on this model.

Adenosine Triphosphate↗
PubMed1999

GlaA promoter controlled production of a mutant green fluorescent protein (S65T) by recombinant aspergillus niger during growth on defined medium in batch and fed-batch cultures

The first successful expression of the Aequorea victoria green fluorescent protein (GFP) gene in Aspergillus niger is described. When the wild-type GFP gene was expressed in A. niger, neither the fluorescence nor the full translation product of the wtGFP gene was detectable. However, the expression of a mutant form of the green fluorescent protein (S65TGFP) gene resulted in the formation of a functional fluorescent polypeptide. The synthesis of S65TGFP was used to study glaA promoter controlled heterologous gene expression by recombinant A. niger in batch and fed-batch cultures using a defined growth medium. Cells were grown on xylose as noninducing carbon source, and the production of S65TGFP was accomplished by the addition of maltose. The recombinant protein accumulated up to 10 or 25 mg of S65TGFP g-1 cell dry weight using either a maltose pulse for induction or continuous addition of the inducing carbon source, respectively. Irrespective of the induction protocol, the recombinant protein started to accumulate 2 h after addition of the inducing carbon source and reached its maximum specific concentration 10 h after induction. Bright green fluorescing fungal pellets were first detectable by fluorescence microscopy 4-5 h after the onset of maltose addition.

Journal Article↗
PubMed1999

The base of the proteasome regulatory particle exhibits chaperone-like activity.

Protein substrates of the proteasome must apparently be unfolded and translocated through a narrow channel to gain access to the proteolytic active sites of the enzyme. Protein folding in vivo is mediated by molecular chaperones. Here, to test for chaperone activity of the proteasome, we assay the reactivation of denatured citrate synthase. Both human and yeast proteasomes stimulate the recovery of the native structure of citrate synthase. We map this chaperone-like activity to the base of the regulatory particle of the proteasome, that is, to the ATPase-containing assembly located at the substrate-entry ports of the channel. Denatured but not native citrate synthase is bound by the base complex. Ubiquitination of citrate synthase is not required for its binding or refolding by the base complex of the proteasome. These data suggest a model in which ubiquitin-protein conjugates are initially tethered to the proteasome by specific recognition of their ubiquitin chains; this step is followed by a nonspecific interaction between the base and the target protein, which promotes substrate unfolding and translocation.

Adenosine Triphosphate↗
PubMed1999

Axl expression is associated with adverse prognosis and with expression of Bcl-2 and CD34 in de novo acute myeloid leukemia (AML): results from a multicenter trial of the Swiss Group for Clinical Cancer Research (SAKK).

Receptor tyrosine kinases (RTK) play a significant role in the signal transduction of normal, and malignant hematopoietic cells. We have previously shown that Axl, a novel RTK, is mainly expressed in leukemias of myeloid origin, and that its expression may be associated with cells of monocytic origin. Since expression of certain RTKs in cancer may be associated with different biology and survival, we investigated whether the expression of Axl is associated with clinical characteristics and survival in acute myeloid leukemia (AML). RNA from 54 patients with AML treated in a cooperative group trial was analyzed in a retrospective and blinded manner using a semi-quantitative reverse transcriptase polymerase chain reaction-based assay with primers specific for the Axl gene. Axl expression was found in 19 out of the 54 cases (35%). Axl expression was not detected more frequently in patients of older age, specific FAB categories, or cases with extramedullary disease. However, there existed a correlation between Axl and bcl-2 expression levels. AML cells with high bcl-2 expression showed higher Axl expression (r = 0.32; P = 0.02), and furthermore, Axl transcript numbers were also higher in AML with high CD34 expression (n = 38, r = 0.42; P = 0.008). No significant difference between leukemias expressing and not expressing Axl was found with regard to complete remission rate. However, quantitative Axl expression was associated with worse progression-free and overall survival. Higher Axl levels had worse prognosis for progression-free (beta: 0.68, s.e.: 0.28, P = 0.015) and overall survival (beta: 0.61, s.e.: 0.31, P = 0.05) using multivariate Cox models adjusted for age, Auer rods and leukocyte counts. In conclusion, in this retrospective analysis, no difference with regard to clinical characteristics at diagnosis was found between AML patients whose leukemia cells show Axl expression vs patients whose cells are Axl negative. The association between Axl and bcl-2 and Axl and CD34 expression in de novo AML needs further investigation. Similarly, the negative impact of Axl levels on outcome should be confirmed in a larger cohort.

Acute Disease↗
PubMed1999

Detection of cytogenetic aberrations both in CD90 (Thy-1)-positive and (Thy-1)-negative stem cell (CD34) subfractions of patients with acute and chronic myeloid leukemias.

Acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) are thought to arise from malignant hematopoietic progenitor cells representing early and undifferentiated stem cell clones. In CML there is evidence for a progenitor cell subset free of leukemic clones, depending on the course of the disease. Additionally, it has been suggested that in AML, the early stem cell compartment (CD34+/90+) does not harbor the malignant clone. We analyzed white blood cells from leukemia patients for the presence of aberrant cells in stem cell subfractions. Sixteen patients with CML, six patients with AML, two patients with acute lymphatic leukemia (ALL) and one with chronic myelomonocytic leukemia (CMMOL), all with known cytogenetic abnormalities, were evaluated according to their CD90 (Thy-1)-positive or -negative phenotype. Subsets were sorted on to slides and further characterized by FISH and/or standard cytogenetic testing. The bcr-abl translocation or gross chromosomal abnormalities could be detected in equally high amounts of 92.2% and 89.2% in both stem cell subsets. We conclude, that in progressed AML and CML cells characterized by specific genetic aberrations implicated in the malignant state can be found in the CD34+/CD90+ and CD90- population, thus making CD90 an inappropriate marker to distinguish benign from malignant cells in these leukemias.

Acute Disease↗
PubMed1999

Manipulating the coordination mumber of the ferric iron within the cambialistic superoxide dismutase of Propionibacterium shermanii by changing the pH-value A crystallographic analysis.

The structure of the Propionibacterium freudenreichii subspecies shermanii superoxide dismutase (SOD) was determined at various pH values. As a comparison, the structure of the fluoride coordinated SOD was solved. The SOD crystallizes at pH 6.1 in the space group C2221 with two subunits, A and B, in the asymmetric unit. An increase of the pH value changes the cell parameters slightly but not the symmetry of the crystals. The overall structure of the SOD remains a compact tetrameter and is comparable to that at pH 6.1 no matter whether the pH increases or fluoride is added. At values above pH 7.4, an additional hydroxide ion can bind to the active center. Its position is similar to the binding site of the fluoride. The coordination number changes from five to six if the pH increases or fluoride is added. The binding behavior of the hydroxide ion is different for subunit A and B. Structures at different pH-values are comparable with models derived by spectroscopic methods. The influence of temperature on the binding properties of the hydroxide ion was investigated using analysis of an X-ray structure solved at pH 8.1 and 140 K. Compared to the structure at room temperature, the structural changes are observable but remain small. The consequences of hydroxide binding to the iron are discussed.

Crystallography, X-Ray↗
PubMed1999

Selective cloning of allergens from the skin colonizing yeast Malassezia furfur by phage surface display technology.

The yeast Malassezia furfur, also known as Pityrosporum orbiculare (ovale), is part of the normal microflora of the human skin but has also been associated with different skin diseases including atopic dermatitis. More than 50% of atopic dermatitis patients have positive skin test and specific IgE to M. furfur extracts; however, the pathophysiologic role of these IgE-mediated reactions in the development of the disease remains unknown. The yeast is able to produce a wide panel of IgE-binding proteins, variably recognized by sera of individual patients. In order to assess the contribution of individual components to the disease, highly pure allergen preparations are required. We have cloned M. furfur allergens from a cDNA library displayed on the phage surface, sequenced the inserts and produced recombinant proteins in Escherichia coli. Phage displaying IgE-binding proteins were selectively enriched from the library using IgE from a M. furfur-sensitized atopic dermatitis patient as a ligand. We were able to identify five different inserts coding for IgE-binding polypeptides. Three of the sequenced cDNA encode incomplete gene products with molecular masses of 21.3 kDa (MF 7), 14.4 kDa (MF 8), and 9.7 kDa (MF 9), respectively, having no sequence similarity to known proteins. The other two cDNA encode allergens of 18.2 kDa (Mal f 5) and 17.2 kDa (Mal f 6). Mal f 5 shows significant homology to M. furfur allergens Mal f 2, Mal f 3 and an Aspergillus fumigatus allergen Asp f 3. Mal f 6 has significant homology with cyclophilin. All of the recombinant polypeptides were capable of binding serum IgE from atopic dermatitis patients in immunoblotting experiments. The availability of pure recombinant M. furfur allergens will allow the careful investigation of the role of IgE-binding proteins in atopic dermatitis.

Allergens↗
PubMed1999

Characterization of renal artery stenoses based on magnetic resonance renal flow and volume measurements.

BACKGROUND: The benefits of percutaneous angioplasty of renal artery stenosis is not known. In an attempt to better define the patient subgroup most likely to benefit from a revascularization procedure, the relationship between renal arterial morphology, blood flow volume, and renal volume was investigated using magnetic resonance (MR) techniques. METHODS: Analysis was based on arterial flow volume and renal volume measurements of 130 kidneys in 65 patients with clinically suspected renal vascular disease. Significant renal arterial stenosis (RAS), documented by contrast-enhanced three-dimensional MR angiography, compromised blood supply to 31 kidneys. Renal volume measurements were related to the body mass index to derive the renal volume index (RVI). The RVI of 72 kidneys in 36 patients without evidence of RAS or severe renal insufficiency was used as a standard of reference to differentiate normal-volume from reduced-volume kidneys. RESULTS: Eighteen out of 31 RAS kidneys were significantly reduced in volume (3.08 +/- 0.75); the volume of the remaining 13 kidneys was within one standard deviation of the normal reference value. Flow volumes in kidneys with RAS were significantly reduced compared with kidneys without RAS (91.56 vs. 279.15 ml/min). Based on the RFI values (RFI = flow volume/renal volume), there was only minimal overlap between normal volume kidneys with RAS (0.73 +/- 0.34) and kidneys without RAS (2.02 +/- 0.59). RFI values of small volume kidneys with RAS (1.55 +/- 0.47), on the other hand, overlapped with both groups. CONCLUSIONS: Normal volume kidneys with impaired arterial flow caused by RAS can be differentiated from those without based on a flow index (RFI). These data suggest the existence of a critical cut-off value (flow index <1.2 ml/min per cm3 of renal tissue) beyond which the renal parenchyma starts shrinking.

Adult↗
PubMed1999

Effects of systemic steroid treatment in chronic polypoid rhinosinusitis evaluated with magnetic resonance imaging.

BACKGROUND: The aim of this prospective study was to evaluate the efficacy of a combined (local and systemic) steroid therapy on the extent of chronic polypoid rhinosinusitis and patient symptoms. METHODS AND PATIENTS: Subjects of this study were 20 patients with severe chronic polypoid rhinosinusitis with total or subtotal narrowing of the all sinuses. A nasal budesonide spray (2 x 0.1 mg/day) and an oral fluocortolone medication with a daily reduction during a 12-day period (total dose: 560 mg = group 1) and a 20-day period (total dose: 715 mg = group 2), respectively, were administered. Before and after the steroid treatment we evaluated the extent of the sinusitis with MRI and patient symptoms with symptom-related questionnaires. RESULTS: A significant reduction (> 30%) of the chronic polypoid rhinosinusitis was observed in 50% of MRI findings. The steroid effect on polypoid masses was heterogeneous in different anatomic areas (maxillary sinus 40%, anterior ethmoid 19%, posterior ethmoid 33%, sphenoidal sinus 61%, frontal sinus 46%). Most sinusitis-related symptoms were distinctly diminished in most patients (80%). No major side effects were observed. CONCLUSIONS: A combined short-term steroid therapy is highly effective in chronic polypoid rhinosinusitis, reducing the mucosal inflammation mainly in the large sinuses and reducing the incidence of symptoms significantly. However, this therapy was insufficient in the anterior ethmoid and cannot replace the current surgical treatment concept of the osteomeatal complex in CPR. The indication for such a short-term steroid therapy is the preoperative treatment. It facilitates functional endoscopic sinus surgery by reducing the extent of surgical procedures, the time, and thereby the risks of sinus surgery.

Administration, Inhalation↗
PubMed1999

[1H-MR spectroscopy in anorexia nervosa: reversible cerebral metabolic changes].

PURPOSE: By using localized 1H-MR spectroscopy in the brain of patients with anorexia nervosa we wanted to verify our preliminary results and to look for a reversibility of the metabolic changes under therapy. METHODS: In 22 patients and 17 healthy volunteers (11 follow-up examinations) single voxel 1H-MR spectroscopy (TE = 50 ms, TM = 30 ms, TR = 1500 ms, voxel (2 cm)3, acq.: 256) was used in two different localizations (thalamus and parieto-occipital region). The first examination of the patients was performed before therapy, the follow-up examination at the end of therapy. RESULTS: In both regions of the brain we found a statistically significant elevation of the Cho/Cr-ratio in comparison to normal controls. The follow-up examinations revealed reversibility of the metabolic changes under successful therapy. CONCLUSIONS: 1H-MR spectroscopy reveals metabolic changes in the brain of patients with anorexia nervosa, which are reversible under successful therapy. These metabolic changes can be conclusively explained using a biochemical model.

Adolescent↗
PubMed1999

Increased levels of urokinase receptor in plasma of head and neck squamous cell carcinoma patients.

Urokinase-type plasminogen activator (uPA) is important for matrix degradation and motility of cancer cells. The binding of uPA to its cell surface receptor on cancer cells is essential for effective invasion. A soluble form of urokinase receptor (suPAR) has been described in serum and ascites of ovarian cancer patients and in plasma samples of non-small cell lung cancer patients. Plasma samples from 36 head and neck squamous cell carcinoma patients and 24 healthy control persons were analysed for the presence of suPAR using enzyme-linked immunosorbent assay (ELISA) and the expression levels were correlated with clinical and histopathological data. Significantly elevated levels of suPAR in blood plasma from head and neck cancer patients were observed (p = 0.000), and the suPAR plasma levels decreased after resection of the carcinoma in 8 of 11 patients. suPAR plasma levels of cancer patients showed no significant correlations with T staging, metastasis, recurrence or differentiation stage of the tumours. The significance of suPAR plasma levels in head and neck squamous cell carcinoma patients for prognosis of the disease is discussed.

Adult↗
PubMed1999

A novel animal model for the evaluation of the efficacy of drugs directed against the ErbB2 receptor on metastasis formation.

The ErbB2 receptor tyrosine kinase is often overexpressed in human malignancies and causally involved in transformation. High levels of ErbB2 in tumor cells correlate with an unfavorable prognosis. This makes the ErbB2 receptor an interesting target for tumor therapy, and several strategies have been designed to direct drugs to ErbB2-expressing cells. We established a novel cellular model that allows preclinical evaluation of ErbB2-directed drugs in immunocompetent animals. Renal carcinoma (Renca) cells are an established tumor cell line that originated in Balb/c mice. Upon intravenous transplantation, these cells form pulmonary metastases in Balb/c mice. The transforming genetic lesions in these cells are not fully characterized, but do not seem to involve alterations in ErbB2 gene expression. We transfected Renca cells with the gene encoding the human ErbB2 receptor to provide a target structure for specific drugs and with the bacterial lacZ gene to provide a sensitive means of detection of the tumor cells in the transplanted animals. These genetically modified cells form lung metastasis and can be easily visualized on the surface of lung tissue by staining with an X-gal solution. This allows a quantitative analysis of the number of ErbB2-expressing pulmonary metastasis. We previously used these Renca cells to evaluate the efficacy of an ErbB2-specific tumor toxin on pulmonary metastases in an adjuvant and a palliative treatment setting. In both cases, we achieved a dramatic reduction of disseminated lung lesions. Here we show that even at an advanced stage of metastasis formation, the ErbB2-specific toxin is able to efficiently reduce the number of pulmonary tumors.

Animals↗