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M Schmidt

Publications and source records attributed to M Schmidt.

At least 217 records · Page 12Linked to original sources
PubMed2000

Extraction of accurate structure-factor amplitudes from Laue data: wavelength normalization with wiggler and undulator X-ray sources.

Wavelength normalization is an essential part of processing of Laue X-ray diffraction data and is critically important for deriving accurate structure-factor amplitudes. The results of wavelength normalization for Laue data obtained in nanosecond time-resolved experiments at the ID09 beamline at the European Synchrotron Radiation Facility, Grenoble, France, are presented. Several wiggler and undulator insertion devices with complex spectra were used. The results show that even in the most challenging cases, such as wiggler/undulator tandems or single-line undulators, accurate wavelength normalization does not require unusually redundant Laue data and can be accomplished using typical Laue data sets. Single-line undulator spectra derived from Laue data compare well with the measured incident X-ray spectra. Successful wavelength normalization of the undulator data was also confirmed by the observed signal in nanosecond time-resolved experiments. Single-line undulators, which are attractive for time-resolved experiments due to their high peak intensity and low polychromatic background, are compared with wigglers, based on data obtained on the same crystal.

Journal Article↗
PubMed2000

Nucleotide binding activity of SecA homodimer is conformationally regulated by temperature and altered by prlD and azi mutations.

SecA ATPase is critical for protein translocation across the Escherichia coli inner membrane. To understand this activity further, the high affinity nucleotide binding activity of SecA was characterized. We found that at 4 degrees C SecA homodimer binds one ADP molecule with high affinity. This nucleotide binding activity was conformationally regulated by temperature: at low temperature SecA affinity for ADP was high with a slow exchange rate, whereas at high temperature the converse was true. Azi- and PrlD-SecA proteins that confer azide-resistant and signal sequence suppressor phenotypes were found to have reduced affinity for ADP and accelerated exchange rates compared with wild type SecA. Consistent with this observation, fluorescence and proteolysis studies indicated that these proteins had a conformationally relaxed state at a reduced temperature compared with SecA. The level of Azi- and PrlD-SecA protein was also elevated in inverted membrane vesicles where it displayed higher membrane ATPase activity. These results provide the first direct evidence for conformational regulation of the SecA-dependent nucleotide cycle, its alteration in azi and prlD mutants, and its relevance to in vivo protein export.

Adenosine Diphosphate↗
PubMed2000

Differential modulation of paclitaxel-mediated apoptosis by p21Waf1 and p27Kip1.

The impact of the cyclin dependent kinase (CDK) inhibitors p21Waf1 and p27Kip1 on paclitaxel-mediated cytotoxicity was investigated in RKO human colon adenocarcinoma cells with the ecdysone-inducible expression of p21Waf1 or p27Kip1. Ectopic expression of p27Kip1 arrested cells at G1 phase, whereas p21Waf1 expression arrested cells at G1 and G2. Expression of p21Waf1 after paclitaxel treatment produced much greater resistance to paclitaxel than did expression of p27Kip1. We attributed this difference to the additional block at G2 induced by p21Waf1, which prevented cells from entering M phase and becoming paclitaxel susceptible. Expression of p21Waf1 inhibited p34cdc2 activity and markedly reduced paclitaxel-mediated mitotic arrest, from 87.5 to 23%. In contrast, p27Kip1 expression also inhibited p34cdc2 but reduced mitotic arrest only slightly, from 87. 4 to 74.5%. We concluded that the G2 block produced by p21Waf1, but not by p27Kip1, contributed to their unequal modulation of sensitivity to paclitaxel-mediated apoptosis in RKO cells, and there is no causal relationship between paclitaxel-mediated cytotoxicity and elevation of p34cdc2 activity.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Recombinant antibody toxins specific for ErbB2 and EGF receptor inhibit the in vitro growth of human head and neck cancer cells and cause rapid tumor regression in vivo.

Overexpression of the ErbB2 and epidermal growth factor receptor (EGFR) tyrosine kinases is frequently observed in squamous cell carcinomas of the head and neck, and has been correlated with shorter overall survival. By immunoblot analysis, we have found EGFR and ErbB2 expression in 6 out of 6 established head and neck cancer cell lines. Elevated EGFR protein levels were noted in 3 and elevated ErbB2 levels in 5 of them. Significant expression of EGFR and ErbB2 was also detected in 17 of 47 and 26 of 45 primary tumor samples. Due to their enhanced expression on the tumor cell surface, these receptors can be regarded as suitable targets for directed cancer therapy. We have analyzed the antitumoral activity of recombinant single-chain antibody toxins specific for ErbB2 and EGFR against head and neck cancer cells in vitro and in vivo. The recombinant toxins consist of the variable domains of the heavy and light chains of monoclonal antibodies (MAbs) genetically fused to a truncated Pseudomonas exotoxin A (ETA). At low concentrations, the ErbB2-specific single-chain antibody (scFv) toxin scFv(FRP5)-ETA and the EGFR-specific toxins scFv(225)-ETA and scFv(14E1)-ETA inhibited the in vitro growth of established head and neck cancer cell lines and primary tumor cells. In a nude mouse tumor model, intratumoral injection of the antibody toxins resulted in the rapid regression of subcutaneously growing CAL 27 tumor xenografts, with scFv(FRP5)-ETA and scFv(14E1)-ETA treatment being most effective and leading to the cure of up to 50% of the animals. Our results suggest that EGFR and ErbB2-specific antibody toxins may become valuable therapeutic reagents for the treatment of squamous cell carcinomas of the head and neck.

ADP Ribose Transferases↗
PubMed2000

Stimulation of phosphatidylinositol-4-phosphate 5-kinase by Rho-kinase.

The serine/threonine kinase Rho-kinase was recently identified as a downstream effector of the small GTPase Rho, mediating effects of Rho on the actin cytoskeleton. Also phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) has been implicated in the regulation of actin polymerization. As the synthesis of PI(4,5)P(2) has been suggested to be affected by Rho proteins, we investigated whether Rho-kinase is involved in the control of PI(4,5)P(2) levels. Overexpression of RhoA in HEK-293 cells increased phosphatidylinositol 4-phosphate (PI4P) 5-kinase activity and concomitantly enhanced cellular PI(4,5)P(2) levels, whereas overexpression of the Rho-inactivating C3 transferase decreased both PI4P 5-kinase activity and PI(4,5)P(2) levels. These effects of RhoA could be mimicked by overexpression of wild-type Rho-kinase and of the constitutively active catalytic domain of Rho-kinase, Rho-kinase-CAT. In contrast, a kinase-deficient mutant of Rho-kinase had no effect on PI4P 5-kinase activity. Importantly, the increase in PI4P 5-kinase activity and PI(4,5)P(2) levels by wild-type Rho-kinase, but not by Rho-kinase-CAT, was completely prevented by coexpression of C3 transferase, indicating that the effect of Rho-kinase was under the control of endogenous Rho. In cell lysates, addition of recombinant RhoA and Rho-kinase-CAT stimulated PI4P 5-kinase activity. Finally, the increase in PI(4,5)P(2) levels induced by both Rho-kinase-CAT and RhoA was reversed by the Rho-kinase inhibitor HA-1077. Our data suggest that Rho-kinase is involved in the Rho-controlled synthesis of PI(4,5)P(2) by PI4P 5-kinase.

Cell Line↗
PubMed2000

[A little cough--it is but a minor problem... That can be a dangerous error!].

Although coughing is a useful defensive mechanism, it is, unfortunately, completely non-specific. Almost every pulmonary disease (and a number of extrapulmonary conditions as well) is associated with a cough. In many cases the problem is inflammation to the respiratory mucosae, but also, lamentably, to an increasing extent, a malignant tumour. The commonly heard diagnosis "psychogenic cough" is in reality a real rarity. A 14-point diagnostic program enables a reliable etiological diagnosis to be made in about 90% of the cases, and thus points to the appropriate causal treatment. In all the other cases, there remains antitussive medication--which, however, is still unsatisfactory in severe cases. Of major importance, however, is to ensure that symptomatic treatment with cough inhibitors does not lead to a delay in establishing the diagnosis and thus in initiating essential causal treatment.

Cough↗
PubMed2000

Efficient generation of a hepatitis B virus cytotoxic T lymphocyte epitope requires the structural features of immunoproteasomes.

Interferon (IFN)-gamma-induced cells express the proteasome subunits low molecular weight protein (LMP)2, LMP7, and MECL-1 (multicatalytic endopeptidase complex-like 1), leading to the formation of immunoproteasomes. Although these subunits are thought to optimize MHC class I antigen processing, the extent of their role and the mechanistic aspects involved remain unclear. Herein, we study the proteolytic generation of an human histocompatibility leukocyte antigen (HLA)-Aw68-restricted hepatitis B virus core antigen (HBcAg) cytotoxic T lymphocyte (CTL) epitope that is recognized by peripheral blood lymphocytes from patients with acute self-limited but not chronic hepatitis B virus (HBV). Immunological data suggest that IFN-gamma-induced rather than uninduced HeLa cells process and present the HBV CTL epitope upon infection with HBcAg-expressing vaccinia viruses. Analyses of 20S proteasome digests of synthetic polypeptides covering the antigenic HBcAg peptide demonstrate that only immunoproteasomes efficiently perform the cleavages needed for the liberation of this HBV CTL epitope. Although the concerted presence of the three immunosubunits appears essential, we find that both catalytically active LMP7 and inactive LMP7 T1A support CTL epitope generation. We conclude that LMP7 influences the structural features of 20S proteasomes, thereby enhancing the activity of the LMP2 and MECL-1 catalytic sites, which provide cleavage specificity. Thus, LMP7 incorporation is of greater functional importance for the generation of an HBV CTL epitope than cleavage specificity.

Amino Acid Sequence↗
PubMed2000

Cineradiographic study of forelimb movements during quadrupedal walking in the brown lemur (Eulemur fulvus, Primates: Lemuridae).

Movements of forelimb joints and segments during walking in the brown lemur (Eulemur fulvus) were analyzed using cineradiography (150 frames/sec). Metric gait parameters, forelimb kinematics, and intralimb coordination are described. Calculation of contribution of segment displacements to stance propulsion shows that scapular retroversion in a fulcrum near the vertebral border causes more than 60% of propulsion. The contribution by the shoulder joint is 30%, elbow joint 5%, and wrist joint 1%. Correlation analysis was applied to reveal the interdependency between metric and kinematic parameters. Only the effective angular movement of the elbow joint during stance is speed-dependent. Movements of all other forelimb joints and segments are independent of speed and influence, mainly, linear gait parameters (stride length, stance length). Perhaps the most important result is the hitherto unknown and unexpected degree of scapular mobility. Scapular movements consist of ante-/retroversion, adduction/abduction, and scapular rotation about the longitudinal axis. Inside rotation of the scapula (60 degrees -70 degrees ), together with flexion in the shoulder joint, mediates abduction of the humerus, which is not achieved in the shoulder joint, and is therefore strikingly different from humeral abduction in man. Movements of the shoulder joint are restricted to flexion and extension. At touch down, the shoulder joint of the brown lemur is more extended compared to that of other small mammals. The relatively long humerus and forearm, characteristic for primates, are thus effectively converted into stride length. Observed asymmetries in metric and kinematic behavior of the left and right forelimb are caused by an unequal lateral bending of the spinal column.

Animals↗
PubMed2000

Complex segregation analysis of families ascertained through Gilles de la Tourette syndrome.

Although family and twin studies suggest that genetic factors are involved in the etiology of Tourette syndrome and other related tic disorders, further evidence is needed to demonstrate that the familial transmission is consistent with known genetic factors. We performed a complex segregation analysis that allowed for a variable age of onset of Gilles de la Tourette, other tic disorders and obsessive compulsive phenotype information on 108 extended families, each ascertained through one Tourette proband by using regressive models that are able to incorporate additional explanatory variables and major gene effects. A special version of the S.A.G.E. program, REGTLhunt, was used to explore the likelihood surface of all examined models. Results indicated that the pattern of Tourette and other related tic disorders in our data sample is not consistent with Mendelian inheritance even after modelling explanatory variables such as obsessive compulsive symptomatology.

Adolescent↗
PubMed2000

Coherent membrane supports for parallel microsynthesis and screening of bioactive peptides.

Since its invention the SPOT-synthesis methodology has become one of the most efficient strategies for the miniaturized assembly of large numbers of peptides. The combination of a facile synthetic method with high throughput solid- and solution-phase screening assays qualifies the SPOT-technique as a valuable tool in biomedical research. Recent developments such as the introduction of novel polymeric surfaces, new linker and cleavage strategies as well as automated robot systems extended the scope of practical chemical reactions that can be accommodated as well as the numbers of compounds obtainable by this technique. Thus, highly complex spatially addressed compound arrays have become accessible. Together with the introduction of novel screening assays, the method is excellently suited to elucidate recognition events on the molecular level.

Adsorption↗
PubMed2000

Urokinase receptor up-regulation in head and neck squamous cell carcinoma.

BACKGROUND: Urokinase-type plasminogen activator is important for matrix degradation and motility of cancer cells. For effective invasion, urokinase has to be associated with its cell surface receptor.(1) METHODS: We analyzed 33 head and neck squamous cell carcinomas (hnSCC) and 14 mucosal tissue samples for the expression of urokinase receptor using Northern hybridization and correlated expression levels to clinical and histopathologic data. Urokinase expression was determined by fibrin zymography. RESULTS: The expression of urokinase receptor is significantly increased in hnSCC compared with adjacent mucosa. Expression levels in primary tumors show no statistically significant correlations to T staging, metastasis, recurrence, or differentiation stage of the resected tumors. Furthermore, there was no correlation between urokinase and urokinase receptor expression levels in SCC samples. CONCLUSIONS: Urokinase receptor expression is increased in hnSCC, but it is not useful as a prognostic marker for the metastatic behavior of primary tumors. Comparison of our data with previously published reports is discussed.

Adult↗
PubMed2000

IL-10 induces apoptosis in human monocytes involving the CD95 receptor/ligand pathway.

The cytokine IL-10 exerts potent immunosuppressive and anti-inflammatory effects, although the mechanisms of this action remain largely unknown. In the present study, we investigated the effects of IL-10 in human peripheral blood monocytes. We were able to demonstrate that IL-10 dose- and time-dependently triggers apoptosis in these cells as detected by annexin-V staining, the nick end labeling (TUNEL) procedure, electron microscopy and analysis of DNA laddering. IL-10-induced apoptosis required the activation of proteases of the caspase family, since a peptide caspase inhibitor attenuated cell death and, in addition, the proteolytic activation of caspase-8 was observed. Since caspase-8 has been implicated as a regulator of apoptosis mediated by death receptors, we investigated a potential involvement of the CD95 receptor/ligand system. Indeed, treatment of monocytes with IL-10 induced a dose-dependent up-regulation of CD95 receptor and ligand expression on the monocyte surface. Furthermore, a CD95 ligand-neutralizing antibody significantly inhibited IL-10-induced apoptosis. In summary, our data show that IL-10 triggers monocyte apoptosis involving the CD95 system via an autocrine or paracrine process. Therefore, at least part of the anti-inflammatory properties of IL-10 may involve induction of apoptosis in monocytes.

Animals↗
PubMed2000

Magnetic resonance pharmacological stress for detecting coronary disease. Comparison with echocardiography.

Stress testing is the cornerstone in the diagnosis of patients with suspected coronary artery disease (CAD). Although exercise ECG remains the primary approach for the detection of ischemia in patients with chest pain syndromes, its sensitivity and specificity is limited and exercise ECG does not provide detailed information about the localisation and extent of CAD. Stress echocardiography has been used for the detection of ischemia for more than a decade and has become an increasingly popular noninvasive method for the detection of CAD. In experienced hands wall motion analysis based on stress echocardiography has proved to be as sensitive and specific for the detection of myocardial ischemia as scintigraphic techniques. Recent technical improvements, namely the availability of ultrafast imaging sequences with a significant reduction of imaging time have initiated several studies which examined the combination of pharmacological stress and magnetic resonance imaging (MRI) for the detection of suspected CAD. The most well developed stress-MRI technique is wall motion imaging during dobutamine stress. This technique is analogous to stress echocardiography, but MRI has the inherent advantages of better resolution, higher reproducibility and true long and short axis imaging with contiguous parallel slices. However, the clinical impact of MRI for the diagnosis of CAD is still low. Further technical developments including real time imaging and a reliable automated quantitative analysis of left ventricular function are required before stress-MRI becomes a serious challenge to stress-echocardiography in the clinical arena. Currently, only a few MRI facilities and physicians are dedicated to pharmacological stress testing with MRI and the future clinical impact of this promising technique will depend on its potential to provide information beyond myocardial function including perfusion, metabolism and coronary anatomy in form of a "one-stop"-shop for the cardiac patient.

Cardiotonic Agents↗
PubMed2000

Response characteristics of neurons in the pulvinar of awake cats to saccades and to visual stimulation.

We studied responses of pulvinar neurons in awake cats that were allowed to execute spontaneous eye movements. Extracellular cell activity during saccades, saccade-like image shifts, and various stationary visual stimuli was recorded together with the animals' eye positions. All neurons analyzed had receptive fields that covered most of the central 80x80 degrees of the animals' visual field and did only respond to large (>20 degrees) visual stimuli. According to their response properties, recorded neurons were divided into three populations. The first group, termed "S neurons" (16%), responded when the animals performed saccades but were unresponsive to any of the visual stimuli tested. These neurons do not seem to receive a visual input that is strong enough to drive them. The second group, termed "V neurons" (51%), responded to various visual stimuli including saccade-like image motion when the eyes were stationary, but not when the animals executed saccades. V neurons therefore distinguish retinal image movements that are generated externally from internally generated image motion. Finally, "SV neurons" (31%) responded when the animals made saccades as well as to saccade-like image motion or to stationary stimuli. Although these neurons do not distinguish self-induced retinal image motion from motion generated by external stimulus movements, they must receive non-retinal motion-related input, because responses elicited by saccades had shorter latencies than responses to saccade-like stimulus movements. Only SV neurons resemble response properties of pretectal neurons that project to the pulvinar and that comprise the major subcortical visual input. The functional significance of pulvinar neuronal populations for visual and visuomotor information processing is discussed.

Animals↗
PubMed2000

Three-dimensional contrast-enhanced MRI using an intravascular contrast agent for detection of traumatic intra-abdominal hemorrhage and abdominal parenchymal injuries: an experimental study.

The aim of this study was to compare the performance of 3D MRI in conjunction with an intravascular contrast agent to spiral contrast-enhanced CT, regarding the detection of abdominal parenchymal injuries as well as peritoneal hemorrhage in an animal model. Liver and kidney injuries were created surgically in six female pigs under general anesthesia. All pigs underwent contrast-enhanced spiral CT and 3D MR imaging following administration of an intravascular contrast agent (NC100150 Injection). Two readers rated their confidence independently on MR and CT data sets using a five-point scale for the presence of organ injury and hemoperitoneum. Autopsy findings served as standard of reference. Sensitivity and specificity for MR in detecting hepatic and renal injuries as well as hemoperitoneum was 100%. Computed tomography was less accurate with sensitivity and specificity values of 90 and 94%, respectively. Receiver operating characteristics (ROC) analysis revealed a higher confidence when interpretation was based on MR images. In an animal model 3D MR imaging in conjunction with an intravascular contrast agent proved highly accurate in detecting and localizing parenchymal injuries to the upper abdomen as well as in detecting intraperitoneal blood collections.

Abdominal Injuries↗
PubMed2000

[Endoscopically controlled surgery with the micro-drill and intubation of the lacrimal ducts].

PURPOSE: Operative procedures to manage lacrimal outflow obstruction were made traditionally without endoscopic assistance. For dacryoendoscopy we previously used a 0.5-mm endoscope with a special wash cannula. We now use the microendoscope Vitroptic T for dacryoendoscopy and for endoscopically controlled surgery with a microdrill. METHODS: In an attempt to perform microinvasive lacrimal surgery we use a 1.1-mm endoscope (Vitroptik T) with a wash cannula, a channel for the microoptic and a channel for a microdrill. We report on our initial experiences and on the results of eight patients with stenosis of the lacrimal outflow system who were treated with an endoscopic microdrill and silicone tubing. One patient had lacrimal stenosis after external dacryocystorhinostomy (DCR), and seven patients showed punctual stenosis in the nasolacrimal duct. RESULTS: Using the dacryoendoscope (Vitroptic T) we were able to visualize pathologic changes of the lacrimal outflow system. Intraoperative situations during dacryoendoscopy are demonstrated. The Vitroptic T allows dacryoendoscopy and endoscopically controlled surgery of the lacrimal drainage system. Three months after surgery in six patients (75%) the lacrimal outflow system was patent with the silicone tube in place, and these patients had no epiphora. The patient with re-stenosis after external DCR showed patency. CONCLUSIONS: Dacryoendoscopy and endoscopic controlled surgery of the lacrimal drainage system enables atraumatic and minimally invasive surgery. The Vitroptik T with the microdrill allows endoscopically controlled microsurgery. Possible indications for the microdrill are punctual stenosis and re-stenosis after external DCR.

Dacryocystorhinostomy↗
PubMed2000

Induction of matrix metalloproteinases in keratinocytes by cholesteatoma debris and granulation tissue extracts.

Although it is generally accepted that destruction and remodeling of temporal bone associated with middle ear cholesteatoma is mainly caused by the action of osteoclasts, it has been shown that neutral collagenases also play a role in predigesting the osteoid layer and exposing the mineralized bone to osteoclastic activity. Here we show that gelatinase B (matrix metalloproteinase-9) is over-expressed in cholesteatoma compared to external ear canal skin (EACS). Expression of MMP-9 in cholesteatoma mainly occurs in suprabasal layers, and more rarely in basal layers of cholesteatoma epithelium, as well as in inflammatory cells of the perimatrix. We further analyzed the influence of cholesteatoma debris, cholesteatoma granulation tissue, and cholesteatoma components such as keratin, cholesterol and bacterial endotoxin on the expression of MMPs in EACS keratinocytes. We show that cholesteatoma debris and granulation tissue extract both induced the secretion of MMP-9 by EACS keratinocytes, while keratin. bacterial lipopolysaccharide (LPS) or cholesterol did not show any effect. We further performed co-incubation and immunoprecipitation experiments using neutralizing interleukin-1alpha, EGF, TGF-beta, TGF-alpha, interleukin-6 and TNF-alpha antibodies. Inhibition of MMP-9 up-regulation by debris or granulation tissue extract could be revealed with diverse cytokine antibodies. The results are discussed with regard to previously published studies.

Antibodies↗