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Biomedical subjects

Andreas Schmid

Publications and source records attributed to Andreas Schmid.

At least 19 recordsLinked to original sources
PubMed2007

Surface ATRP of hydrophilic monomers from ultrafine aqueous silica sols using anionic polyelectrolytic macroinitiators.

A convenient two-step route was developed to prepare new anionic ATRP macroinitiators from near-monodisperse poly(2-hydroxyethyl methacrylate) precursors by partial esterification with 2-bromoisobutyryl bromide, followed by esterification of the remaining hydroxyl groups using excess 2-sulfobenzoic acid cyclic anhydride. These new macroinitiators can be electrostatically adsorbed onto ultrafine cationic Ludox CL silica sols; subsequent surface polymerization of various hydrophilic monomers in aqueous solution at room temperature afforded a range of polymer-grafted ultrafine silica sols. The resulting sterically stabilized particles were characterized by dynamic light scattering, transmission electron microscopy, aqueous electrophoresis, FTIR spectroscopy, and elemental microanalyses.

Journal Article↗
PubMed2006

Identification of tyrosines in the putative regulatory site of the Ca2+ channel TRPV6.

In HEK293 cells, transfected with the Ca2+ channel protein TRPV6, Ca2+ influx is increased and TRPV6 is tyrosine phosphorylated following addition of the tyrosine phosphatase inhibitor N,N-dimethyl-hydroxamido hydroxovanadate to cells. This effect of DMHV is enhanced by co-transfection of cells with the tyrosine kinase Src and the tyrosine phosphatase 1B. It is abolished when cells had been treated with PP1, an inhibitor of Src family tyrosine kinases. PTP1B interacts with the N-terminal domain of TRPV6 within a region of amino acids 1-191 as shown by co-immunoprecipitation, bimolecular fluorescence complementation and the yeast 2-hybrid system. Point mutation of both tyrosines 161 and 162 in the TRPV6 protein abolishes the DMHV-effect on Ca2+ influx and tyrosine phosphorylation by Src. Single mutations of Y161 or Y162 shows that each of both tyrosines alone is sufficient for the DMHV-effect. We conclude that phosphorylation/dephosphorylation of tyrosines in position 161 and 162 is essential for regulation of Ca2+ influx through TRPV6 Ca2+ channels in HEK293 cells.

Amino Acid Sequence↗
PubMed2006

Facile synthesis of highly biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine)-coated gold nanoparticles in aqueous solution.

Diblock copolymers comprising a highly biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) block were evaluated for the synthesis of sterically stabilized gold nanoparticles in aqueous solution. The PDMA block becomes partially protonated on addition of HAuCl4, and the remaining nonprotonated tertiary amine groups reduce the AuCl4- counterion to zerovalent gold in situ. This approach results in the adsorption of the PDMA block onto the gold nanoparticle surface while the PMPC chains serve as a stabilizing block, producing highly biocompatible gold sols in aqueous solution at ambient temperature without any external reducing agent. The size and shape of gold nanoparticles could be readily controlled by tuning synthesis parameters such as the block composition and the relative and absolute concentrations of the PMPC-PDMA diblock copolymer and HAuCl4. These highly biocompatible gold sols have potential biomedical applications.

Biocompatible Materials↗
PubMed2006

Non-NMDA-type glutamate receptors are essential for maturation but not for initial assembly of synapses at Drosophila neuromuscular junctions.

The assembly of glutamatergic postsynaptic densities (PSDs) seems to involve the gradual recruitment of molecular components from diffuse cellular pools. Whether the glutamate receptors themselves are needed to instruct the structural and molecular assembly of the PSD has hardly been addressed. Here, we engineered Drosophila neuromuscular junctions (NMJs) to express none or only drastically reduced amounts of their postsynaptic non-NMDA-type glutamate receptors. At such NMJs, principal synapse formation proceeded and presynaptic active zones showed normal composition and ultrastructure as well as proper glutamate release. At the postsynaptic site, initial steps of molecular and structural assembly took place as well. However, growth of the nascent PSDs to mature size was inhibited, and proteins normally excluded from PSD membranes remained at these apparently immature sites. Intriguingly, synaptic transmission as well as glutamate binding to glutamate receptors appeared dispensable for synapse maturation. Thus, our data suggest that incorporation of non-NMDA-type glutamate receptors and likely their protein-protein interactions with additional PSD components triggers a conversion from an initial to a mature stage of PSD assembly.

Animals↗
PubMed2006

The efficiency of recombinant Escherichia coli as biocatalyst for stereospecific epoxidation.

Styrene is efficiently converted into (S)-styrene oxide by growing Escherichia coli expressing the styrene monooxygenase genes styAB of Pseudomonas sp. strain VLB120 in an organic/aqueous emulsion. Now, we investigated factors influencing the epoxidation activity of recombinant E. coli with the aim to improve the process in terms of product concentration and volumetric productivity. The catalytic activity of recombinant E. coli was not stable and decreased with reaction time. Kinetic analyses and the independence of the whole-cell activity on substrate and biocatalyst concentrations indicated that the maximal specific biocatalyst activity was not exploited under process conditions and that substrate mass transfer and enzyme inhibition did not limit bioconversion performance. Elevated styrene oxide concentrations, however, were shown to promote acetic acid formation, membrane permeabilization, and cell lysis, and to reduce growth rate and colony-forming activity. During biotransformations, when cell viability was additionally reduced by styAB overexpression, such effects coincided with decreasing specific epoxidation rates and metabolic activity. This clearly indicated that biocatalyst performance was reduced as a result of product toxicity. The results point to a product toxicity-induced biological energy shortage reducing the biocatalyst activity under process conditions. By reducing exposure time of the biocatalyst to the product and increasing biocatalyst concentrations, volumetric productivities were increased up to 1,800 micromol/min/liter aqueous phase (with an average of 8.4 g/L(aq) x h). This represents the highest productivity reported for oxygenase-based whole-cell biocatalysis involving toxic products.

Biotransformation↗
PubMed2006

Real-time analysis of cAMP-mediated regulation of ciliary motility in single primary human airway epithelial cells.

Airway ciliary beat frequency regulation is complex but in part influenced by cyclic adenosine monophosphate (cAMP)-mediated changes in cAMP-dependent kinase activity, yet the cAMP concentration required for increases in ciliary beat frequency and the temporal relationship between ciliary beat frequency and cAMP changes are unknown. A lentiviral gene transfer system was developed to express a fluorescence resonance energy transfer (FRET)-based cAMP sensor in ciliated cells. Expression of fluorescently tagged cAMP-dependent kinase subunits from the ciliated-cell-specific foxj1 promoter enhanced expression in fully differentiated ciliated human airway epithelial cells, and permitted simultaneous measurements of ciliary beat frequency and cAMP (represented by the FRET ratio). Apical application of forskolin (1 microM, 10 microM, 20 microM) and, in permeabilized cells, basolateral cAMP (20 microM, 50 microM, 100 microM) caused dose-dependent, albeit similar and simultaneous-increases in cAMP and ciliary beat frequency. However, decreases in cAMP preceded decreases in ciliary beat frequency, suggesting that either cellular cAMP decreases before ciliary cAMP or the dephosphorylation of target proteins by phosphatases occur at a rate slower than the rate of cAMP hydrolysis.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2006

Direct interaction between ER membrane-bound PTP1B and its plasma membrane-anchored targets.

The ubiquitously expressed protein tyrosine phosphatase PTP1B is involved in the regulation of numerous cellular signaling pathways. PTP1B is anchored to the ER membrane while many of its substrates are localized to the plasma membrane. This spatial separation raises the question how PTP1B can interact with its targets. In our study we demonstrate direct interaction of PTP1B with the Ser/Thr kinase PKCdelta, the non-receptor tyrosine kinase Src and the insulin receptor which all are key enzymes in cellular signaling cascades. Protein complex formation was visualized in vivo using Bimolecular Fluorescence Complementation (BiFC). We demonstrate that complex formation of PTP1B with plasma membrane-anchored proteins is possible without detachment of PTP1B from the ER. Our data indicate that the dynamic ER membrane network is in constant contact to the plasma membrane. Local attachments of the two membrane systems enable a direct communication of ER- and plasma membrane-anchored proteins. The reported formation of membrane junctions is an important step towards the understanding of signal transmissions between the ER and the plasma membrane.

Cell Line↗
PubMed2006

Epithelial organic cation transporters ensure pH-dependent drug absorption in the airway.

Most inhaled beta(2)-adrenergic agonist and anticholinergic bronchodilators have low lipid solubility because of their transient or permanent positive net charge at physiologic pH. Airway absorption of these cationic drugs is incompletely understood. We examined carrier-mediated mechanisms of cationic drug uptake by human airway epithelia. Airway tissues and epithelial cells, obtained from lung donors without preexisting lung disease, were evaluated for organic cation transporter expression by quantitative RT-PCR and immunofluorescence. For in vitro functional studies on primary airway epithelial cells, uptake of the cationic fluorophore 4-[4-(dimethylamino)-styryl]-N-methylpyridinium (ASP+) was characterized. Quantitative RT-PCR analysis demonstrated high mRNA levels for two polyspecific organic cation/carnitine transporters, OCTN1 and OCTN2, in human airway epithelia. Immunofluorescence of human airway sections confirmed OCTN1/2 protein expression, with a predominant localization to the apical portion of epithelial cells. Primary airway epithelial cells showed a carrier-mediated, temperature-sensitive and saturable uptake of ASP(+). Seventy-five to eighty percent of ASP(+) uptake was inhibited by L-carnitine, an OCTN2-carried zwitterion. The uptake was pH dependent, with approximately 3-fold lower rates at acidic (pH 5.7) than at alkaline (pH 8.2) extracellular pH. Albuterol and formoterol inhibited ASP(+) uptake, suggesting that all these molecules are carried by the same transport mechanism. These findings demonstrate the existence and functional role of a pH-dependent organic cation uptake machinery, namely OCTN1 and OCTN2, in human airway epithelia. We suggest that epithelial OCTN1/2 are involved in the delivery of inhaled cationic bronchodilators to the airway tissue.

Adrenergic beta-Agonists↗
PubMed2006

Enantioselective substrate binding in a monooxygenase protein model by molecular dynamics and docking.

The two-component flavoenzyme styrene monooxygenase (SMO) is an efficient alternative to several chemical epoxidation catalysts on a preparative scale. A first homology model of the catalytic domain (StyA) of SMO was constructed (Protein Data Bank ID 2HD8) based on the structure of para-hydroxybenzoate hydroxylase. The StyA protein structure was optimized by restrained molecular dynamics to reproduce specific pre-S binding orientations of styrene. Effects of all 10 point mutations examined were explained by the distance of the site to the styrene and FAD binding sites. Thirteen of 20 ligands could be accommodated in a catalytically active binding orientation, and predicted affinities correlated well with experimental turnover and inhibition. The binding cavity is almost completely hydrophobic except for a hydrogen-bonded network formed by three water molecules, the backbone of residues 300-302, and the flavin ribityl, similar to P293, and three crystal waters in para-hydroxybenzoate hydroxylase suggest that P302, T47, and the waters in StyA are a vital component of the catalytic mechanism. The current optimized and validated StyA model provides a good starting point for elucidation of the structural basis of StyA ligand binding and catalysis. Novel insights in the binding of ligands to SMO/StyA, provided by the current protein model, will aid the rational design of mutants with specific, altered enantioselective properties.

Binding Sites↗
PubMed2006

Polystyrene-silica nanocomposite particles via alcoholic dispersion polymerization using a cationic azo initiator.

Submicrometer-sized polystyrene-silica nanocomposite particles have been prepared by alcoholic dispersion polymerization of styrene using commercial alcoholic silica sols of 13 or 22 nm diameter as the sole stabilizing agent. The key to the formation of colloidally stable nanocomposite particles is the selection of a cationic azo initiator (use of nonionic or anionic initiators leads either to the formation of silica-stabilized polystyrene latex particles with very low silica contents or to the precipitation of polystyrene, respectively). Neither surface modification of the silica sol nor the addition of surfactant or polymeric stabilizers is required for successful nanocomposite syntheses. The purified polystyrene-silica nanocomposite particles have relatively narrow particle size distributions, with mean diameters ranging from 331 to 464 nm as judged by disk centrifuge photosedimentometry. Thermogravimetric analyses indicated mean silica contents of 13-26 wt. %, depending on the synthesis conditions. Calcination of the polystyrene-silica nanocomposite particles leads to the formation of hollow silica shells, which indicates a well-defined core-shell morphology for the original nanocomposite particles.

Journal Article↗
PubMed2006

Bruchpilot promotes active zone assembly, Ca2+ channel clustering, and vesicle release.

The molecular organization of presynaptic active zones during calcium influx-triggered neurotransmitter release is the focus of intense investigation. The Drosophila coiled-coil domain protein Bruchpilot (BRP) was observed in donut-shaped structures centered at active zones of neuromuscular synapses by using subdiffraction resolution STED (stimulated emission depletion) fluorescence microscopy. At brp mutant active zones, electron-dense projections (T-bars) were entirely lost, Ca2+ channels were reduced in density, evoked vesicle release was depressed, and short-term plasticity was altered. BRP-like proteins seem to establish proximity between Ca2+ channels and vesicles to allow efficient transmitter release and patterned synaptic plasticity.

Action Potentials↗
PubMed2006

Isolated spinal accessory neuropathy in an adolescent: a case study.

We describe a case of dynamic scapular winging due to trapezius muscle paresis following a sport-related injury of the accessory nerve. The typical clinical findings related to the peripheral nerve involved, the importance of neurophysiologic work-up, and possibilities for treatment are discussed.

Accessory Nerve Injuries↗
PubMed2006

[Cardiovascular preparticipation screening of competitive athletes].

Cardiovascular deaths during or following sport activities repeatedly raise the question about a practicable preparticipation screening for athletes to prevent such adverse events. In Germany and most European countries, well-equipped sports medicine centers evaluate the health of the Olympic athletes through regular checkups, which include a detailed medical history and thorough physical examination as well as an ECG at rest, a stress ECG, and an echocardiography. In professional sports, guidelines for this screening differ according to the federations, however, most of them intend to follow the recommendations of the Olympic sports system. For nonprofessional competitive sports, there are no guidelines for preparticipation screening, although these athletes train at the same level of intensity as professional athletes. The main issue in this international debate is the question of cost-effectiveness and how to finance preventive measures.

Adult↗
PubMed2006

High-dose-rate (HDR) or pulsed-dose-rate (PDR) perioperative interstitial intensity-modulated brachytherapy (IMBT) for local recurrences of previously irradiated breast or thoracic wall following breast cancer.

PURPOSE: In patients receiving salvage high-dose-rate (HDR) or pulsed-dose-rate (PDR) brachytherapy for a local recurrence on the chest wall or in the previously treated breast, clinical outcome and benefit were investigated. All patients had previously been treated with full-dose adjuvant external-beam irradiation (EBRT). Disease-free interval after salvage treatment, local tumor control and side effects were analyzed retrospectively. PATIENTS AND METHODS: Between 1996 and 2002, a total of 32 consecutive patients were treated. 13 patients initially treated with mastectomy and postoperative irradiation and 19 patients initially treated with breast-conserving surgery and postoperative irradiation developed a local recurrence. The mean dose of previous radiation therapy was 58 Gy (range, 42-64 Gy), applied by conventional fractionation. After implantation +/- surgery of recurrent disease and CT-based 3-D planning, 15 patients were irradiated with HDR-IMBT (intensity-modulated brachytherapy) with a mean dose of 28 Gy (range, 10-30 Gy, 2 x 2.5 Gy/day at 6-h daily interfraction interval) and 17 patients received PDR-IMBT with a mean dose 30 Gy (range, 10-45 Gy, 5 x 1 Gy/day at 2-h pulse intervals). Four patients underwent additional EBRT using a dose of 24-40 Gy electrons. Treatment was performed only on working days. RESULTS: After a mean post-implant follow-up of 19 months (range, 1-83 months), no signs of local recurrence were observed in 20 of the 32 patients. In twelve patients, local recurrence occurred after a mean follow-up of 13 months (range, 1-78 months). 20 of the 32 patients experienced an additional systemic progress. In one patient, an EORTC/RTOG grade 3 side effect (ulceration of the skin) was described, which was followed by a local recurrence 12 months posttherapeutically. CONCLUSION: Perioperative interstitial HDR/PDR-IMBT of localized breast or thoracic wall recurrences following previous full-dose EBRT appears to be a meaningful salvage treatment with acceptable toxicity.

Adult↗
PubMed2006

Success in elite cycling: A prospective and retrospective analysis of race results.

The development of peak performances is a main research focus in sports science. It is unclear how many former top junior athletes achieve success in the elite class later. The aim of the present study was to examine the careers of athletes who participated in major junior or adult/elite cycling events using prospective and retrospective analysis of competition results. The official results of major junior (age < or = 18 years) and elite (age > 18 years) cycling races from 1980 to 2004 were analysed. Age-related aspects, career lengths, and success were compared between riders who presented results in both junior and elite races (JUNIOR ELITE) and riders who had no junior race results (ELITE ONLY). Altogether, 27,454 results of 8004 athletes from 108 countries were collected. We found that 29.4% of the elite athletes had participated in junior World Championships, and that 34% of the participants in junior World Championships later participated in major elite competitions. JUNIOR ELITE athletes are significantly more successful in several cycling disciplines and have their first and last elite result at a younger age than ELITE ONLY athletes. No difference was found in career lengths. The data presented here emphasize the importance of long-term training programmes in the development of peak performance in cycling.

Adolescent↗
PubMed2006

Effect of manual lymph drainage on the course of serum levels of muscle enzymes after treadmill exercise.

OBJECTIVE: Improving muscular recovery after exercise is an important topic in sports medicine. The aim of the present study was to evaluate the effect of manual lymph drainage on the course of serum levels of muscle enzymes after an extended treadmill exercise. DESIGN: Fourteen recreational athletes (seven women, seven men) were included in the study. The participants underwent a graded exercise test on a treadmill ergometer to determine the individual anaerobic threshold (IAT). Seven days after the graded exercise test, all subjects performed 30 mins of treadmill exercise at an intensity equivalent to IAT. The subjects were randomized into two groups of seven persons. One group was treated with manual lymph drainage (ML), whereas the control group (CG) received no treatment after the endurance exercise at IAT level. RESULTS: After an increase immediately after exercise, a fast decrease in lactate dehydrogenase (LDH) and in aspartate aminotransferase (AST) concentration was observed, with significantly lower values for LDH after 48 hrs in the subjects having received lymph drainage treatment. The course of creatine kinase (CK) levels was comparable, but did not reach significance. CONCLUSION: Manual lymph drainage after treadmill exercise was associated with a faster decrease in serum levels of muscle enzymes. This may indicate improved regenerative processes related to structural damage of muscle cell integrity.

Adult↗
PubMed2006

Power output during stage racing in professional road cycling.

PURPOSE: The aim of the study was to evaluate the power output during a multistage professional road race using direct power measurements and to compare these results with the performance measurements using competition heart rate recordings. METHODS: Six professional road cyclists performed an incremental cycling test during which peak power output, power output, and heart rate at the lactate threshold (LT) and at a lactate increase of 1 mM above the LT (LT + 1) were assessed. During a six-stage road race competition, power output was measured directly (SRM crankset). To analyze the time spent at different intensities during competition, the amount of competition time spent below LT (zone 1), between the LT and LT + 1 (zone 2), and above LT + 1 (zone 3) determined during laboratory testing were calculated for power output and heart rate. RESULTS: During the five mass start stages, a mean power output of 220 +/- 22 W (3.1 +/- 0.2 W x kg(-1)) with a mean heart rate of 142 +/- 5 bpm was measured. Average power output during an uphill time trial was 392 +/- 60 W (5.5 +/- 0.4 W x kg(-1)) with a mean heart rate of 169 +/- 3 bpm. For the mass start stages, the average distribution of exercise time spent in different intensities calculated for power output and heart rate was 58 versus 38% for zone 1, 14 versus 38% for zone 2, and 28 versus 24% for zone 3. CONCLUSION: Most of the competition time during the mass start stages was spent at intensities near the LT. Compared with power output, heart rate measurement underestimated the time spent at intensity zones 1 and 3, and overestimated the time spent in zone 2.

Adult↗