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M A Schmidt

Publications and source records attributed to M A Schmidt.

At least 19 recordsLinked to original sources
PubMed2006

Short communication: assessment of environmental disturbances to the static magnetic field in magnetic resonance installations.

The static magnetic field of MRI scanners can be affected by environmental factors. Magnetic resonance spectroscopy and functional imaging with single-shot echo-planar imaging (EPI) are particularly vulnerable to the movement of lifts, vehicles, trains and other large metallic masses in the vicinity. This work investigates the sensitivity of two different imaging techniques to assess disturbances of the static magnetic field: (i) phase changes in gradient-echo images of a uniform test object; and (ii) image displacement along the phase encoding direction in single-shot EPI images. For the latter a hexane sample was used, and the separation between CH2 and CH3 signals was taken as a reference. Both techniques were evaluated in a site known to be free of any significant environmental disturbances and validated by inducing a magnetic field disturbance. Both techniques provide valuable information in acceptance tests, allowing MRI users to evaluate and manage the environmental conditions surrounding a scanner. The single-shot EPI technique was found to be highly sensitive, being expected to detect magnetic field fluctuations down to 0.005 parts per million (ppm). The phase images method was found to be less sensitive (0.02 ppm) but is more easily available. The single-shot EPI technique was used in acceptance tests and environmental disturbances to the magnetic field of the order of 0.04 ppm were measured at the isocentre on two separate occasions.

Artifacts↗
PubMed2005

Towards normalization of soybean somatic embryo maturation.

Soybean (Glycine max L. Merrill) somatic embryos have been useful for assaying seed-specific traits prior to plant recovery. Such traits could be assessed more accurately if somatic embryos more closely mimicked seed development. Amino acid supplements, carbon source, and abscisic acid and basal salt formulations were tested in an effort to modify existing soybean embryogenesis histodifferentiation/maturation media to further normalize the development of soybean somatic embryos. The resultant liquid medium, referred to as soybean histodifferentiation and maturation medium (SHaM), consists of FNL basal salts, 3% sucrose, 3% sorbitol, filter-sterilized 30 mM glutamine and 1 mM methionine. SHaM-derived somatic embryos are more similar to seed in terms of protein and fatty acid/lipid composition, and conversion ability, than somatic embryos obtained from traditional soybean histodifferentiation and maturation media.

Abscisic Acid↗
PubMed2004

Characterization of M cell formation and associated mononuclear cells during indomethacin-induced intestinal inflammation.

M cells represent an important gateway for the intestinal immune system by delivering luminal antigens through the follicle-associated epithelium to the underlying immune cells. The goal of this study was to characterize this route of antigen uptake during intestinal inflammation by characterizing M cell formation and M cell-associated lymphocytes after indomethacin challenge in rats. We demonstrated increased M cell formation as early as 12 h after a single injection of indomethacin. The elevated M cell counts were determined until day 3 and returned to basal levels after 7 days. Electron microscopic studies revealed an expansion of mononuclear cells inside the M cell pocket that were characterized predominantly as B cells, T cell receptor (TCR)alphabeta- and CD4-positive T cells, whereas other markers such as CD11b, CD8 and CD25 remained unchanged. In situ hybridization studies showed increased expression of interleukin (IL)-4 by lymphocytes during intestinal inflammation in the Peyer's patch follicle. These studies illuminate the relevance of M cells during intestinal inflammation and suggest that M cells derive from epithelial cells in a certain microenvironment.

Animals↗
PubMed2003

Stabilised 111In-labelled DTPA- and DOTA-conjugated neurotensin analogues for imaging and therapy of exocrine pancreatic cancer.

Neurotensin (NT) receptors are overexpressed in exocrine pancreatic cancer and Ewing's sarcoma. The potential utility of native NT in cancer diagnosis and therapy is, however, limited by its rapid degradation in vivo. Therefore, NT analogues were synthesised with modified lysine and arginine derivatives to enhance stability and coupled either to DTPA, to enable high specific activity labelling with indium-111 for imaging, or to DOTA, to enable high specific activity labelling with beta-emitting radionuclides, such as lutetium-177 and yttrium-90. Based on serum stability (4 h incubation at 37 degrees C in human serum) and receptor binding affinity, the five most promising analogues were selected and further evaluated in in vitro internalisation studies in human colorectal adenocarcinoma HT29 cells, which overexpress NT receptors. All five NT analogues bound with high affinity to NT receptors on human exocrine pancreatic tumour sections. The analogues could be labelled with (111)In to a high specific activity. The (111)In-labelled compounds were found to be very stable in serum. Incubation of HT29 cells with the (111)In-labelled analogues at 37 degrees C showed rapid receptor-mediated uptake and internalisation. The most promising analogue, peptide 2530 [DTPA-(Pip)Gly-Pro-(PipAm)Gly-Arg-Pro-Tyr-tBuGly-Leu-OH] was further tested in vivo in a biodistribution study using HT29 tumour-bearing nude mice. The results of this study showed low percentages of injected dose per gram tissue of this (111)In-labelled 2530 analogue in receptor-negative organs like blood, spleen, pancreas, liver, muscle and femur. Good uptake was found in the receptor-positive HT29 tumour and high uptake was present in the kidneys. Co-injection of excess unlabelled NT significantly reduced tumour uptake, showing that tumour uptake is a receptor-mediated process. With their enhanced stability, maintained high receptor affinity and rapid receptor-mediated internalisation, the (111)In-labelled DTPA- and DOTA-conjugated NT analogues are excellent candidates for imaging and therapy of exocrine pancreatic cancer, peptide 2530 being the most promising analogue.

Animals↗
PubMed2002

Effect of MRI noise on cochlear function.

A disadvantage of magnetic resonance imaging (MRI) is the high level of noise produced (peaking between 122 dB and 131 dB). We used otoacoustic emissions (OAEs) as a method to quantify the effect of MRI-generated noise on the cochlea. OAEs were measured in 16 patients before and after MRI and in 16 controls. OAEs decreased in patients after MRI, but the controls, who were not exposed to MRI noise, showed no decrease over the same period. The change in OAEs shows a clear effect of MRI noise on cochlear function, despite use of earplugs. The importance of correctly fitted earplugs cannot be underestimated.

Cochlea↗
PubMed2001

Photochemical reactions and on-line UV detection in microfabricated reactors.

This work presents an application of microfabricated reactors and detectors for photochemical reactions. Two fabrication schemes were demonstrated for the integration of the reaction and the detection modules: coupling individually packaged chips, and monolithic integration of the two functions. In the latter fabrication scheme, we have succeeded in bonding quartz wafers to patterned silicon wafers at low temperature using a Teflon-like polymer-CYTOP[trade mark sign]. Using quartz substrates allows reaction and detection with UV light of lower wavelengths than Pyrex substrates permit. The pinacol formation reaction of benzophenone in isopropanol was the model reaction to demonstrate the performance of the microreactors. The extent of reaction was controlled by varying the flow rate and therefore the on-chip residence time. Crystallization of the product inside the microreactors was avoided by the continuous-flow design. Instead, crystallization was observed in the effluent storage device. Off-chip analysis using HPLC confirms the results obtained from the on-line UV spectroscopy. The quantum yield estimated suggests that the reactor design is effective in improving the overall efficiency of the reactor unit.

Journal Article↗
PubMed2001

Contrast-enhanced magnetic resonance angiography of the iliac arteries: optimization by injection simulation.

Protocols for contrast-enhanced magnetic resonance angiography (CE-MRA) of the iliac arteries were optimized by computer simulations based on an impulse response function (IRF) of contrast agent (CA) concentration as a function of time obtained for 20 patients. Protocols with sequential, centric, and elliptical k-space coverage, different repetition rates (5 and 10 ms), and CA doses (0.1, 0.2, and 0.3 mmol/kg b.w.) were compared in terms of signal-to-noise ratio (SNR), distortion of vessel profiles, and sensitivity to timing errors. IRF-based simulations successfully characterized CA recirculation. Slow-rate CA infusions were found to achieve relatively high enhancement. In terms of SNR, there is no advantage in increasing the repetition rate. Distortion of vessel profiles is more likely in elliptic and centric k-space coverage. Protocols based on sequential k-space coverage and relatively long CA infusions proved to be particularly suited to large-FOV iliac examinations as they are relatively insensitive to timing errors.

Adult↗
PubMed2001

[177Lu-DOTAOTyr3]octreotate: comparison with [111In-DTPAo]octreotide in patients.

The somatostatin analogue [DOTA0,Tyr3]octreotate has a nine-fold higher affinity for the somatostatin receptor subtype 2 as compared with [DOTA0, Tyr3]octreotide. Also, labelled with the beta- and gamma-emitting radionuclide lutetium-177, this compound has been shown to have a very favourable impact on tumour regression and animal survival in a rat model. Because of these reported advantages over the analogues currently used for somatostatin receptor-mediated radiotherapy, we decided to compare [177Lu-DOTA0,Tyr3]octreotate (177Lu-octreotate) with [111In-DTPA0]octreotide (111In-octreotide) in six patients with somatostatin receptor-positive tumours. Plasma radioactivity after 177Lu-octreotate expressed as a percentage of the injected dose was comparable with that after 111In-octreotide. Urinary excretion of radioactivity was significantly lower than after 111In-octreotide, averaging 64% after 24 h. The uptake after 24 h, expressed as a percentage of the injected dose of 177Lu-octreotate, was comparable to that after 111In-octreotide for kidneys, spleen and liver, but was three- to fourfold higher for four of five tumours. The spleen and kidneys received the highest absorbed doses. The doses to the kidneys were reduced by a mean of 47% after co-infusion of amino acids. It is concluded that in comparison with the radionuclide-coupled somatostatin analogues that are currently available for somatostatin receptor-mediated radiotherapy, 177Lu-octreotate potentially represents an important improvement. Higher absorbed doses can be achieved to most tumours, with about equal doses to potentially dose-limiting organs; furthermore, the lower tissue penetration range of 177Lu as compared with 90Y may be especially important for small tumours.

Adolescent↗
PubMed2001

Holding forces of single-particle dielectrophoretic traps.

We present experimental results and modeling on the efficacy of dielectrophoresis-based single-particle traps. Dielectrophoretic forces, caused by the interaction of nonuniform electric fields with objects, have been used to make planar quadrupole traps that can trap single beads. A simple experimental protocol was then used to measure how well the traps could hold beads against destabilizing fluid flows. These were compared with predictions from modeling and found to be in close agreement, allowing the determination of sub-piconewton forces. This not only validates our ability to model dielectrophoretic forces in these traps but also gives insight into the physical behavior of particles in dielectrophoresis-based traps. Anomalous frequency effects, not explainable by dielectrophoretic forces alone, were also encountered and attributed to electrohydrodynamic flows. Such knowledge can now be used to design traps for cell-based applications.

Biophysical Phenomena↗
PubMed2001

Radiotherapeutic efficacy of (153)Sm-CMDTPA-Tyr(3)-octreotate in tumor-bearing rats.

A number of radiolabeled somatostatin analogs have been evaluated in animal tumor models for radiotherapeutic efficacy. The majority of the agents tested have used either high-energy beta-emitters, such as Y-90 or Re-188, or the Auger electron-emitting radionuclide, In-111. Because a medium-energy beta-emitter might have equivalent efficacy compared to high-energy emitters, and lower toxicity to non-target tissues, we have evaluated the therapeutic potential of the beta-emitting nuclide, Sm-153, chelated to the somatostatin analog, CMDTPA-Tyr(3)-octreotate. Using an in vitro binding assay, this octreotate derivative was shown to have high affinity for the somatostatin subtype-2 receptor (IC(50) = 2.7 nM). Biodistribution studies in CA20948 tumor-bearing Lewis rats demonstrate that the Sm-153 labeled compound has high uptake and retention in tumor tissue (1.7% injected dose/g tissue, 4 hrs post injection) and has rapid overall clearance properties from non-target tissue. Radiotherapy studies were carried out using (153)Sm-CMDTPA-Tyr(3)-octreotate and CA20948 tumor bearing Lewis rats at 7 days post implant. Dose regimens consisting of single and multiple i.v. injections of 5.0 mCi/rat (185 MBq) were employed over a time span of 7 days. Suppression of tumor growth rate was observed in all treated animals compared to untreated controls. Greater inhibition of tumor growth was observed in animals that received multiple doses. These studies indicate that medium-energy beta-emitting isotopes have considerable potential for the treatment of somatostatin receptor-positive tumors.

Animals↗
PubMed2001

Modular organization of the AIDA autotransporter translocator: the N-terminal beta1-domain is surface-exposed and stabilizes the transmembrane beta2-domain.

The adhesin involved in diffuse adherence (AIDA-I) of the diarrhoeagenic Escherichia coli strain 2787 (O126:H27) is synthesized as a precursor molecule. This pre-pro-protein is N- and C-terminally processed to generate three distinct domains, which are characteristic for autotransporter secretion systems in Gram-negative bacteria: the N-terminal pre-peptide, the alpha-domain and the C-terminal beta-domain. The outer membrane-integrated beta-domain (AIDAC) is responsible for the surface-presentation of the alpha-domain (AIDA-I) and is thus termed 'translocator'. Characterization of extracted N-terminally truncated forms and of in vitro refolded proteins revealed a core structure at the C-terminus of the translocator which was found to be very stable even in the presence of SDS. Denaturation occurs only after additional incubation at temperatures above 80 degrees C. Reporter-epitope insertions were used to analyze the location of regions of membrane-integrated AIDAC relative to the membrane. The modified topological model developed for the AIDA translocator suggests the N-terminal domain (beta1) encompasses approximately 10 kDa to represent a completely surface-exposed segment while the C-terminal compact core domain (beta2) remains integrated in the membrane as a beta-barrel-like structure. Though the beta2-core structure alone harbours all the information for the outer membrane integration of AIDAC it is additionally stabilized by the beta1-domain. Access to large amounts of complete as well as truncated AIDAC proteins facilitated the study of protein folding by CD and fluorescence spectroscopy. A potential pore forming activity of the translocator using the completely refolded AIDAC or the beta2-core in black-lipid membranes could not be demonstrated.

Adhesins, Escherichia coli↗
PubMed2001

Glycosylation with heptose residues mediated by the aah gene product is essential for adherence of the AIDA-I adhesin.

The diffuse adherence of Escherichia coli strain 2787 (O126:H27) is mediated by the autotransporter adhesin AIDA-I (adhesin-involved-in-diffuse-adherence) encoded by the plasmid-borne aidA gene. AIDA-I exhibits an aberrant mobility in denaturing gel electrophoresis. Deletion of the open reading frame (ORF) A immediately upstream of aidA restores the predicted mobility of AIDA-I, but the adhesin is no longer functional. This indicates that the mature AIDA-I adhesin is post-translationally modified and the modification is essential for adherence function. Labelling with digoxigenin hydrazide shows AIDA-I to be glycosylated. Using carbohydrate composition analysis, AIDA-I contains exclusively heptose residues (ratio heptose:AIDA-I approximately 19:1). The deduced amino acid sequence of the cytoplasmic open reading frame (ORF) A gene product shows homologies to heptosyltransferases. In addition, the modification was completely abolished in an ADP-glycero-manno-heptopyranose mutant. Our results provide direct evidence for glycosylation of the AIDA-I adhesin by heptoses with the ORF A gene product as a specific (mono)heptosyltransferase generating the functional mature AIDA-I adhesin. Consequently, the ORF A gene has been denoted 'aah' (autotransporter-adhesin-heptosyltransferase). Glycosylation by heptoses represents a novel protein modification in eubacteria.

Adhesins, Escherichia coli↗
PubMed2001

Characterization of translocation pores inserted into plasma membranes by type III-secreted Esp proteins of enteropathogenic Escherichia coli.

Many mucosal pathogens use type III secretion systems for the injection of effector proteins into target cells. The type III-secreted proteins EspB and EspD of enteropathogenic Escherichia coli (EPEC) are inserted into the target cell membrane. Together with EspA, these proteins are supposed to constitute a molecular syringe, channelling other effector proteins into the host cell. In this model, EspB and EspD would represent the tip of the needle forming a pore into target cell membranes. Although contact-dependent and Esp-mediated haemolytic activity by EPEC has already been described, the formation of a putative pore resulting in haemolysis has not been demonstrated so far. Here, we show that (i) diffusely adhering (DA)-EPEC strains exhibit a type III-dependent haemolytic activity too; (ii) this activity resides in the secreted proteins and, for DA-EPEC strains, in contrast to EPEC strains, does not require bacterial contact; and (iii) pores are introduced into the target cell membrane. Osmoprotection revealed a minimal pore size of 3-5 nm. The pores induced by type III-secreted proteins of DA-EPEC were characterized by electron microscopy techniques. Analysis by atomic force microscopy demonstrated the pores to be composed of six to eight subunits with a lateral extension of 55-65 nm and to be raised 15-20 nm above the membrane plane. We could also demonstrate an association of EspB and EspD with erythrocyte membranes and an interaction of both proteins with each other in vitro. These results, together with the homologies of EspB and EspD to proposed functional domains of other pore-forming proteins (Yop/Ipa), strongly support the idea that both proteins are directly involved in pore formation, which might represent the type III secretion system translocon.

Animals↗
PubMed2001

Anatomic validation of a novel method for left ventricular volume and mass measurements with use of real-time 3-dimensional echocardiography.

Assessment of left ventricular (LV) volumes and mass is a critical element in the evaluation of patients with cardiovascular disease. However, most non-invasive methods used for the quantitative measurements of LV volume and mass have important intrinsic limitations. Real-time 3-dimensional echocardiography (RT3D echo) is a new technique capable of acquiring volumetric images without cardiac or respiratory gating. The purpose of this study was to develop and validate a system for rapid LV volume and mass measurements with the use of RT3D echo images. To this end, in 11 explanted sheep hearts, the left ventricle was instrumented with a latex balloon and filled with known volumes of saline solution. Two independent observers made volume calculations from images acquired with RT3D echo. In addition, 21 open-chest sheep were imaged with RT3D echo for LV mass calculation. Anatomic LV mass was determined after removing the heart. A strong correlation was observed between the actual LV volumes and those calculated from the RT3D echo images (r = 0.99; y = 1.31 + 0.98x; standard error of the estimate = 2.2 mL). An analysis of intraobserver and interobserver variabilities revealed high indexes of agreement. A strong correlation was observed between actual LV mass and that calculated from RT3D echo images (r = 0.94; y = 14.4 + 0.89x; standard error of the estimate = 8.5 gm). Thus RT3D echo images allow rapid and accurate measurements of LV volume and mass. This technique may expand the use of cardiac ultrasonography for the quantitative assessment of heart disease.

Animals↗
PubMed2001

Eustachian valve endocarditis caused by Streptococcus viridans.

A 76-year-old man was admitted for ethanol detoxification. He was found to be in atrial fibrillation with a rapid ventricular response that was refractory to electrical and chemical cardioversion attempts. The patient subsequently developed respiratory distress. A transesophageal echocardiogram revealed a vegetation attached to the eustachian valve and blood cultures grew Streptococcus viridans. After treatment with appropriate antibiotics, the patient converted to sinus rhythm with sotalol hydrochloride, and the eustachian valve vegetation resolved. This is the first reported case of eustachian valve endocarditis caused by S viridans.

Aged↗
PubMed2001

The AIDA autotransporter system is associated with F18 and stx2e in Escherichia coli isolates from pigs diagnosed with edema disease and postweaning diarrhea.

Pathogenic Escherichia coli strains are known to cause edema disease (ED) and postweaning diarrhea (PWD) in piglets. Although the exact mechanisms of pathogenicity that lead to ED-PWD remain to be elucidated, E. coli-borne Shiga-like toxin and adhesion-mediating virulence factors such as F18 adhesin or F4 fimbriae are believed to play a central role in ED-PWD. In light of these observations we investigated whether another E. coli adhesin, the plasmid-encoded AIDA (adhesin involved in diffuse adherence) might also be present in ED-PWD-causing E. coli isolates. For rapid screening for the AIDA system in large numbers of isolates, a multiplex PCR method along with a duplex Western blot procedure was developed. When screening 104 strains obtained from pigs with or without ED-PWD, we observed a high prevalence of the AIDA operon in porcine E. coli isolates, with over 25% of all strains being AIDA positive, and we could demonstrate a significant association of the intact AIDA gene (orfB) with ED-PWD, while defects in orfB were associated with the absence of disease. Although our data hint toward a contribution of AIDA to ED-PWD, further studies will be necessary since the presence of the AIDA genes was also associated with the presence of the Shiga-like toxin and F18 adhesin genes, two reported virulence factors for ED-PWD.

Adhesins, Escherichia coli↗
PubMed2000

Evaluation of a radiolabelled cyclic DTPA-RGD analogue for tumour imaging and radionuclide therapy.

Tumours depend on sufficient blood supply for their growth. They are able to promote new blood vessel formation (neoangiogenesis) via angiogenic factors. Inhibition of this process results in tumour involution or necrosis. RGD (Arg-Gly-Asp) peptides are described to antagonise neoangiogenesis, e.g., by binding to alpha(v)beta(3) receptors on blood vessels. In order to visualise neoangiogenesis in tumours in vitro and in vivo, we introduced and tested an RGD analogue [c(Arg-Gly-Asp-D-Tyr-Lys)], coupled to the chelator diethyleletriamepentaacetic acid (DTPA). This analogue can be radiolabelled with both (111)In and (125)I. In autoradiography and immunohistochemistry studies, the (125)I-labelled analogue appeared to bind specifically and with high affinity to alpha(v)beta(3) receptors on neovascular blood vessel sections of different major human cancers, like prostate and breast cancer, which express these receptors. This radioiodinated radiopharmaceutical also bound to and internalised in human carcinoid Bon cells and rat pancreatic CA20948 tumour cells. Internalisation was receptor-specific and appeared to be time and temperature dependent. In vivo in rats, we investigated administration of different peptide amounts (0.1, 0.5, and 100 microg). The best amount of the radiolabelled analogue to be administered to rats appeared to be 0.1 microg/rat, as uptake decreased with increasing peptide amount. We also found receptor-specific accumulation of the (111)In-labelled analogue in the transplantable pancreatic tumour CA20948. The introduction of the DTPA group in this peptide resulted in renal clearance of the radiopharmaceutical, in contrast to the non-DTPA-conjugated compound that is cleared predominantly via the liver. (111)In emits Auger and conversion electrons besides gamma radiation, therefore, this radiopharmaceutical is suitable not only for tumour scintigraphy but also has potential for radionuclide therapy of major human cancers as well. Moreover, after coupling to the chelator DOTA, the analogue could be radiolabelled in a stable way with beta-emitters, e.g., (90)Y and (177)Lu, enlarging its potential. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 186-198 (2000).

Animals↗