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Biomedical subjects

M Reichert

Publications and source records attributed to M Reichert.

At least 19 recordsLinked to original sources
PubMed2005

Synchronization of rotating helices by hydrodynamic interactions.

Some types of bacteria use rotating helical flagella to swim. The motion of such organisms takes place in the regime of low Reynolds numbers where viscous effects dominate and where the dynamics is governed by hydrodynamic interactions. Typically, rotating flagella form bundles, which means that their rotation is synchronized. The aim of this study is to investigate whether hydrodynamic interactions can be at the origin of such a bundling and synchronization. We consider two stiff helices that are modelled by rigidly connected beads, neglecting any elastic deformations. They are driven by constant and equal torques, and they are fixed in space by anchoring their terminal beads in harmonic traps. We observe that, for finite trap strength, hydrodynamic interactions do indeed synchronize the helix rotations. The speed of phase synchronization decreases with increasing trap stiffness. In the limit of infinite trap stiffness, the speed is zero and the helices do not synchronize.

Bacteria↗
PubMed2005

Early complete donor hematopoietic chimerism in peripheral blood indicates the risk of extensive graft-versus-host disease.

Achievement of complete donor hematopoietic chimerism (CC) is the goal of allogeneic stem cell transplantation (allo-SCT). Persistence of recipient hematopoiesis augments the risk of relapse, which is one of the main reasons for mortality after allo-SCT. Another main reason for morbidity and mortality is severe extensive chronic graft-versus-host disease (cGvHD). We examined chimerism in peripheral blood of 54 allogeneic stem cell recipients using multiplex STR-PCR method and compared it with the timing and severity of cGvHD. In total, 25 patients achieved early CC (by day 100 post transplant) at a median time of 60 days. In total, 21 of them developed extensive cGvHD. In those patients CC uniformly preceded emergence of cGvHD by a mean of 85 days. A total of 26 patients obtained late CC at a median time of 270 days post transplant. Of this group, only eight patients developed extensive disease. Development of cGvHD in those patients preceded achievement of CC in 10 of 13 cases by a mean of 100 days. The difference between early and late CC groups as to the frequency of the extensive cGvHD was statistically significant (P<0.001). Also, there was a significant correlation of the time of CC and time between CC and cGvHD. Additionally, patients with early CC developed significantly more severe cGvHD measured by the need of three-drug treatment to control the disease (P<0.005). It can be concluded that achievement of early complete donor hematopoietic chimerism in peripheral blood is strongly predictive of severe extensive GvHD.

Adolescent↗
PubMed2004

New natural products from the sponge-derived fungus Aspergillus niger.

Fractionation of the EtOAc extract of a static culture of Aspergillus niger isolated from the Mediterranean sponge Axinella damicornis yielded eight secondary metabolites, out of which seven compounds (2-8) proved to be new natural products, whereas one was identified as the known fungal pigment cycloleucomelone (1). The new compounds included the 3,3'-bicoumarin bicoumanigrin (2), the structurally unusual 4-benzyl-1H-pyridin-6-one derivatives aspernigrins A and B (3 and 4), and pyranonigrins A-D (5-8), the latter featuring a novel pyrano[3,2-b]pyrrole skeleton hitherto unprecedented in nature. All structures were elucidated on the basis of extensive one- and two-dimensional NMR spectroscopic studies ((1)H, (13)C, COSY, HMQC, HMBC, NOE difference spectra) and mass spectral analysis. For the two chiral molecules 4 and 5, the absolute configurations were established by quantum chemical calculations of their circular dichroism (CD) spectra. In each case, two independent methods, i.e., a molecular dynamics approach taking into consideration the molecular flexibility, and a conformational analysis followed by Boltzmann weighting of the single CD spectra calculated for the conformers thus obtained, led to identical results without the need of any empirical comparison of chiroptical data reported for reference compounds. Bicoumanigrin (2) showed moderate cytotoxicity against human cancer cell lines in vitro. In addition, aspernigrin B (4) was found to display a strong neuroprotective effect against glutamic acid.

Animals↗
PubMed2003

HUMEX, a study on the survivability and adaptation of humans to long-duration exploratory missions, part I: lunar missions.

The European Space Agency has recently initiated a study of the human responses, limits and needs with regard to the stress environments of interplanetary and planetary missions. Emphasis has been laid on human health and performance care as well as advanced life support developments including bioregenerative life support systems and environmental monitoring. The overall study goals were as follows: (i) to define reference scenarios for a European participation in human exploration and to estimate their influence on the life sciences and life support requirements; (ii) for selected mission scenarios, to critically assess the limiting factors for human health, wellbeing, and performance and to recommend relevant countermeasures; (iii) for selected mission scenarios, to critically assess the potential of advanced life support developments and to propose a European strategy including terrestrial applications; (iv) to critically assess the feasibility of existing facilities and technologies on ground and in space as testbeds in preparation for human exploratory missions and to develop a test plan for ground and space campaigns; (v) to develop a roadmap for a future European strategy towards human exploratory missions, including preparatory activities and terrestrial applications and benefits. This paper covers the part of the HUMEX study dealing with lunar missions. A lunar base at the south pole where long-time sunlight and potential water ice deposits could be assumed was selected as the Moon reference scenario. The impact on human health, performance and well being has been investigated from the view point of the effects of microgravity (during space travel), reduced gravity (on the Moon) and abrupt gravity changes (during launch and landing), of the effects of cosmic radiation including solar particle events, of psychological issues as well as general health care. Countermeasures as well as necessary research using ground-based test beds and/or the International Space Station have been defined. Likewise advanced life support systems with a high degree of autonomy and regenerative capacity and synergy effects were considered where bioregenerative life support systems and biodiagnostic systems become essential. Finally, a European strategy leading to a potential European participation in future human exploratory missions has been recommended.

Adaptation, Physiological↗
PubMed2002

Inhibition of histone deacetylases induces bovine leukemia virus expression in vitro and in vivo.

Packaging into nucleosomes results in a global transcriptional repression as a consequence of exclusion of sequence-specific factors. This inhibition can be relieved by using inhibitors of histone deacetylases, acetylation being a major characteristic of transcriptionally active chromatin. Paradoxically, the expression of only approximately 2% of the total cellular genes is modulated by histone hyperacetylation. To unravel the potential role of this transcriptional control on BLV expression, we tested the effect of two highly specific inhibitors of deacetylases, trichostatin A (TSA) and trapoxin (TPX). Our results demonstrate that treatment with TSA efficiently enhanced long terminal repeat-directed gene expression of integrated reporter constructs in heterologous D17 stable cell lines. To further examine the biological relevance of these observations made in vitro, we analyzed ex vivo-isolated peripheral blood mononuclear cells (PBMCs) from bovine leukemia virus (BLV)-infected sheep. TSA deacetylase inhibitor induced a drastic increase in viral expression at levels comparable to those induced by treatment with phorbol-12-myristate 13-acetate and ionomycin, the most efficient activators of BLV expression known to date. TSA acted directly on BLV-infected B lymphocytes to increase viral expression and does not seem to require T-cell cooperation. Inhibition of deacetylation after treatment with TSA or TPX also significantly increased viral expression in PBMCs from cattle, the natural host for BLV. Together, our results show that BLV gene expression is, like that of a very small fraction of cellular genes, also regulated by deacetylation.

Animals↗
PubMed2001

Adapting pharmacokinetic properties of a humanized anti-interleukin-8 antibody for therapeutic applications using site-specific pegylation.

A neutralizing anti-interleukin-(IL-)8 monoclonal antibody was humanized by grafting the complementary determining regions onto the human IgG framework. Subsequent alanine scanning mutagenesis and phage display enabled the production of an affinity matured antibody with a >100-fold improvement in IL-8 binding. Antibody fragments can be efficiently produced in Escherichia coli but have the limitation of rapid clearance rates in vivo. The Fab' fragment of the antibody was therefore modified with polyethylene glycol (PEG) in order to obtain a more desirable pharmacokinetic profile. PEG (5-40 kDa) was site-specifically conjugated to the Fab' via the single free cysteine residue in the hinge region. In vitro binding and bioassays showed little or no loss of activity. The pharmacokinetic profiles of the 20 kDa, 30 kDa, 40 kDa, and 40 kDa branched PEG-Fab' molecules were evaluated in rabbits. Relative to the native Fab', the clearance rates of the PEGylated molecules were decreased by 44-175-fold. In a rabbit ear model of ischemia/reperfusion injury, all PEGylated Fab' molecules were as efficacious in reducing oedema as the original monoclonal antibody. These studies demonstrate that it is possible to customize the pharmacokinetic properties of a Fab' while retaining its antigen binding activity.

Alanine↗
PubMed2001

Connexin45 directly binds to ZO-1 and localizes to the tight junction region in epithelial MDCK cells.

Zonula occludens protein 1 (ZO-1) is a cytosolic tight junction protein that tethers transmembrane proteins such as occludin, claudin and junctional adhesion molecule to the actin cytoskeleton. The interaction between ZO-1 and claudin or junctional adhesion molecule occurs via the amino-terminal PSD95/Dlg/ZO-1 (PDZ) domains in ZO-1. A yeast two-hybrid screen to search for proteins that interact with the PDZ domains of ZO-1 identified connexin (Cx) 45. Cx45 interacts with the PDZ domains of ZO-1 and ZO-3, but not ZO-2, via a short C-terminal PDZ binding motif (SVWI). In transfected epithelial Madin-Darby canine kidney cells, Cx45 co-localizes with endogenous ZO-1 at or near tight junctions and co-precipitation experiments show that Cx45 and ZO-1 directly interact. Inactivating the C-terminal PDZ-binding motif in Cx45 affects its co-precipitation and co-localization with ZO-1. The growing number of connexins (i.e. Cx43 and Cx45) that can associate with ZO proteins indicate that ZO proteins may play a more general role in organizing gap junctions and/or in recruiting signaling molecules that regulate intercellular communication.

Animals↗
PubMed2001

Role of the proline-rich motif of bovine leukemia virus transmembrane protein gp30 in viral load and pathogenicity in sheep.

The cytoplasmic tail of bovine leukemia virus (BLV) transmembrane protein gp30 has multiple amino acid motifs that mimic those present in signaling proteins associated with B-cell and T-cell receptors. The proline-rich motif of gp30, PX(2)PX(4-5)P, is analogous to the recognition site of Src homology 3 (SH3) domains of signaling molecules. Using site-directed mutagenesis of an infectious molecular clone of BLV, point mutations were introduced which changed three of the prolines of the motif to alanines. The influence of these mutations on the pathogenicity of BLV was studied in sheep which received either (i) plasmid DNA with provirus containing proline-to-alanine mutations (pppBLV), (ii) plasmid DNA with wild-type provirus (wtBLV), or (iii) transfection reagent alone. Although all of the BLV-injected animals seroconverted at approximately the same time, viral loads at later time points were high in five of five of the wtBLV group and two of five of the pppBLV group but low in three of five of the pppBLV group, as determined by semiquantitative PCR. Viral expression was lower in the pppBLV-transfected sheep, as measured by p24 antigen enzyme-linked immunosorbent assay in cultured cells, and serologic titers were lower. Thirty-one months after transfection, four of four wtBLV-transfected sheep had died of leukemia and lymphoma, and all five of the pppBLV-transfected sheep were clinically healthy and had normal peripheral blood lymphocyte counts. These data indicate that the proline-rich motif of gp30 is not required for viral infectivity but is important for high viral load in vivo, suggesting that SH3-mediated gp30 interactions are critical for viral pathogenesis following infection. Absence of interactions with the proline-rich motif may prevent or delay tumorigenesis in sheep.

Amino Acid Motifs↗
PubMed2000

Methods for reducing biosensor membrane biofouling.

The deleterious effect that biofouling has on sensor stability is a serious impediment to the development of long term implanted biosensors. This paper reviews the surface modification strategies currently employed to minimize membrane biofouling of in vivo sensors. Nine sensor modifications are discussed herein: hydrogels, phospholipid-based biomimicry, flow-based systems, Nafion, surfactants, naturally derived materials, covalent attachments, diamond-like carbons, and topology.

Journal Article↗
PubMed2000

Incidence and prevalence of recurrent respiratory papillomatosis among children in Atlanta and Seattle.

The incidence and prevalence of recurrent respiratory papillomatosis (RRP) for children aged <18 years were estimated in 2 US cities, Atlanta and Seattle, in 1996. All otolaryngologists in a 24-county area in metropolitan Atlanta (101 physicians) and an 8-county area in metropolitan Seattle (139 physicians) agreed to participate in the study. Medical record chart abstraction was performed only for children with documented current residence in the study area (21 patients in Atlanta and 14 patients in Seattle). The incidence rate for juvenile RRP was 1.11/100,000 population in Atlanta and 0.36/100, 000 in Seattle. The prevalence rate was 2.59/100,000 population in Atlanta and 1.69/100,000 in Seattle. In neither city did prevalences differ significantly when stratified by sex or race. Extrapolation of these estimates to the US population suggests that 80-1500 incident cases and 700-3000 prevalent cases of juvenile RRP will occur in the United States during 1999.

Adolescent↗
PubMed2000

The PDZ domains of zonula occludens-1 induce an epithelial to mesenchymal transition of Madin-Darby canine kidney I cells. Evidence for a role of beta-catenin/Tcf/Lef signaling.

The integrity of cell-cell contacts such as adherens junctions (AJ) and tight junctions (TJ) is essential for the function of epithelia. During carcinogenesis, the increased motility and invasiveness of tumor cells reflect the loss of characteristic epithelial features, including cell adhesion. While beta-catenin, a component of AJ, plays a well characterized dual role in cell adhesion and signal transduction leading to epithelial cell transformation, little is known about possible roles of tight junction components in signaling processes. Here we show that mutants of the TJ protein zonula occludens protein-1 (ZO-1), which encode the PDZ domains (ZO-1 PDZ) but no longer localize at the plasma membrane, induce a dramatic epithelial to mesenchymal transition (EMT) of Madin-Darby canine kidney I (MDCKI) cells. The observed EMT of these MDCK-PDZ cells is characterized by a repression of epithelial marker genes, a restricted differentiation potential and a significantly induced tumorigenicity. Intriguingly, the beta-catenin signaling pathway is activated in the cells expressing the ZO-1 PDZ protein. Ectopic expression of the adenomatous polyposis coli tumor suppressor gene, known to down-regulate activated beta-catenin signaling, reverts the transformed fibroblastoid phenotype of MDCK-PDZ cells. Thus, cytoplasmic localization of the ZO-1 PDZ domains induces an EMT in MDCKI cells, most likely by modulating beta-catenin signaling.

Animals↗
PubMed2000

New nonsteroidal steroid 5 alpha-reductase inhibitors. Syntheses and structure-activity studies on carboxamide phenylalkyl-substituted pyridones and piperidones.

In the search for nonsteroidal inhibitors of 5 alpha-reductase for the treatment of benign prostatic hyperplasia (BPH), we synthesized diisopropyl (1a-8a) and tert-butyl (1b-8b) benzamides, as well as ethyl benzoates (1c, 3c), which were substituted in 4 position via variable alkyl spacer (n = 0: 1-4, n = 1: 5, 7 and n = 3: 6, 8) with a 1-methyl-2-pyridone (1, 2, 5, 6) or a 1-methyl-2-piperidone (3, 4, 7, 8) moiety mimicking steroidal ring A. The directly connected benzamides (1a-4a, 1b-4b) and benzoates (1c, 3c) were obtained by palladium-catalysed coupling reaction of diethyl(3-pyridyl)-borane with 4-bromobenzoic acid derivatives, followed by alpha-oxidation of the 1-methyl-pyridinium salt and subsequent separation of the regioisomers. Catalytic hydrogenation of the pyridones (1, 2) led to the piperidones (3, 4). The preparation of the benzamides with a methylene (5, 7) and a propylene spacer (6, 8), respectively, started with the reduction of the keto group of 5-benzoyl-1,2-dihydro-1-methyl-2(1H)-pyridone and catalytic hydrogenation of the alkene obtained by Wittig reaction of 5-formyl-1,2-dihydro-1-methyl-2(1H)-pyridone with (2-phenylethyl)triphenylphosphonium bromide, respectively. The phenyl ring was functionalized by Friedel-Crafts reaction, haloform cleavage to give the acid, formation of the acid chloride, and subsequent treatment with the appropriate amines. Again, catalytic hydrogenation of the pyridones (5, 6) led to the piperidones (7, 8). The 5 alpha-reductase inhibitory properties were determined using rat ventral prostate, as well as human BPH tissue as enzyme source, 1 beta-2 beta-[3H]testosterone as substrate and a HPLC procedure for the separation of dihydrotestosterone (DHT). Tested at a concentration of 100 microM, the inhibition values of 1-8 ranged from 0-79%. Significant differences were observed between rat and human enzyme. The most active compound was ethyl 4-(1-methyl-2-oxopiperid-5-yl)benzoate 3c (68%) for the human enzyme and N,N-bis(1-methylethyl)-4-[3-(1,2-dihydro-1-methyl-2-oxopyrid-5-yl) propyl] benzamide 6a (79%) for the rat enzyme.

5-alpha Reductase Inhibitors↗
PubMed2000

The Raf-1 kinase associates with vimentin kinases and regulates the structure of vimentin filaments.

Using immobilized GST-Raf-1 as bait, we have isolated the intermediate filament protein vimentin as a Raf-1-associated protein. Vimentin coimmunoprecipitated and colocalized with Raf-1 in fibroblasts. Vimentin was not a Raf-1 substrate, but was phosphorylated by Raf-1-associated vimentin kinases. We provide evidence for at least two Raf-1-associated vimentin kinases and identified one as casein kinase 2. They are regulated by Raf-1, since the activation status of Raf-1 correlated with the phosphorylation of vimentin. Vimentin phosphorylation by Raf-1 preparations interfered with its polymerization in vitro. A subset of tryptic vimentin phosphopeptides induced by Raf-1 in vitro matched the vimentin phosphopeptides isolated from v-raf-transfected cells labeled with orthophosphoric acid, indicating that Raf-1 also induces vimentin phosphorylation in intact cells. In NIH 3T3 fibroblasts, the selective activation of an estrogen-regulated Raf-1 mutant induced a rearrangement and depolymerization of the reticular vimentin scaffold similar to the changes elicited by serum treatment. The rearrangement of the vimentin network occurred independently of the MEK/ERK pathway. These data identify a new branch point in Raf-1 signaling, which links Raf-1 to changes in the cytoskeletal architecture.

Amino Acid Sequence↗