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Biomedical subjects

J Wegener

Publications and source records attributed to J Wegener.

33 records · Page 2Linked to original sources
PubMed1998

The polarity of choroid plexus epithelial cells in vitro is improved in serum-free medium.

The influence of culture conditions on the development of normal characteristics of the choroid plexus epithelium has been investigated in vitro with respect to polarity, barrier properties, transport, and secretory activity. Withdrawal of serum supplement in the culture medium of cells grown on filters caused morphologically visible changes by an increased trimming of microvilli at the apical membrane side, which is accompanied by an increased expression of the Na+,K+-ATPase. Moreover cells under serum-free conditions exhibit structural changes in tight junctional zonula occludens protein-1 (ZO-1) organization, a reduced permeability, and a drastically increased electrical resistance from 150 ohms x cm2 in the presence of serum to 1,500 ohms x cm2 after serum withdrawal. Under these conditions, cell monolayers are able to build up a transcellular proton gradient and to secrete fluid into the upper (apical) filter compartment, which is accompanied by a polarized secretion of proteins like transthyretin. Active transport of the dyes fluorescein and phenol red by the organic anion transporter is found to be driven by the Na+,K+-ATPase. We come to the conclusion that removal of serum favors the differentiation process of the plexus epithelium in vitro, which brings the cell culture model closer to the physiological situation in vivo. We present preliminary evidence that epidermal growth factor may be one component in serum preventing the proper in vitro differentiation.

Animals↗
PubMed1997

Impedance and shear wave resonance analysis of ligand-receptor interactions at functionalized surfaces and of cell monolayers.

The present paper scrutinizes the application of impedance spectroscopy and quartz-crystal microbalance (QCM) measurements in the analysis of composite layers of receptor containing lipid bilayers, and their interaction with external ligands or pore-forming peptides. The formation of supramolecular structures and their analysis will be discussed. Impedance measurement allows one to follow the adsorption of proteins on artificial membranes. This method is even more suitable for quantifying changes in membrane conductivity induced by channel peptides incorporated into the lipid membrane. The QCM is another sophisticated method for analyzing ganglioside-lectin and ganglioside-toxin interactions. A critical comparison between both methods will be given. Moreover, we will demonstrate that the QCM method, especially in combination with impedance analysis, is a completely new approach for determining electrical and viscoelastic properties of epithelial and endothelial cell monolayers that form controlled barriers in vivo.

Animals↗
PubMed1997

Porcine choroid plexus cells in culture: expression of polarized phenotype, maintenance of barrier properties and apical secretion of CSF-components.

We have successfully cultured choroid plexus epithelial cells from porcine brain in pure form by the addition of cytosine arabinoside to the culture medium which prevented growth of other contaminating cells. We characterized the cells in culture by the presence of desmoplakin, fibronectin, thrombospondin, and the zonula occludens protein ZO-1 in comparison to frozen fractions of the isolated choroid plexus tissue. The cells in culture express those marker proteins and moreover exhibit a polarized phenotype which was expected from the presence of tight junction strands that correlate to an electrical resistance of 120 Ohm.cm2 measured across the cell monolayer on a permeable support. Permeability studies with fluorescein-labeled dextrans also indicate a biochemical tightness. The polarity of the cells is demonstrated by the presence of microvilli and cilia on the surface of the cultured cells as well as by the laser scanning microscopic determination of the apical localization of the ZO-1-protein and the Na+K(+)-ATPase. Thrombospondin and fibronectin were found to be localized at the basolateral membrane side. The cells in culture secrete medium containing prealbumin predominantly into the apical compartment which demonstrates that they are able to release medium containing CSF-proteins and therefore verifies the usefulness of this in vitro model.

Animals↗
PubMed1996

Impedance analysis of epithelial and endothelial cell monolayers cultured on gold surfaces.

The present study describes a new method to determine transepithelial and transendothelial electrical resistances (TER) of cultured cell monolayers which is based on impedance analysis. To obtain impedance data of the epithelia or endothelia under investigation, we developed special measuring chambers that allow to culture the cells on gold surfaces that are used as measuring electrodes. Impedance analysis is carried out in the frequency range from 1 to 10(5) s-1 under normal culture conditions using a self-developed continuous wave impedance spectrometer. Evaluation of impedance data is achieved by fitting (NLSQ) the parameters of appropriate equivalent circuits to the experimental data. We investigated cell monolayers of primary cultured endothelial cells isolated from porcine brain microvessels, epithelial cells from porcine choroid plexus as well as those of the epithelial cell line MDCK. Transepithelial resistances were found to be in good agreement with published data. The main advantages of the new technique are the ability (i) to use multi-electrode arrays that allow to determine TERs at different locations of a given cell monolayer; (ii) to carry out impedance analysis under normal culture conditions; and (iii) to obtain TER values of cell monolayers grown on impermeable supports, which means that conditions cells are normally exposed to in ordinary culture dishes are maintained.

Animals↗
PubMed1996

Double-mode impedance analysis of epithelial cell monolayers cultured on shear wave resonators.

The viscoelastic behavior of epithelial cells (MDCK-I and MDCK-II) grown on AT-cut quartz crystals with a fundamental resonance at 5 MHz was investigated by impedance spectroscopy. Using the electromechanical model recently derived by Martin et al. [(1991) Anal Chem 63: 2272-2281] for Newtonian liquids in contact with shear wave resonators we quantified the viscous damping arising from the adherent cells by fitting the impedance data with a modified Butterworth-Van Dyke circuit in the region of the resonance frequency. Impedance spectroscopy was additionally performed in the frequency range from 1 Hz to 1 MHz to scrutinize the passive electrical properties of the epithelial cell layers using an additional platinum electrode. These data allow one to document the cell layers' integrity as well as the electrode coverage. We were able to confirm that the presence of a cell-layer mainly increases damping of the shear wave and does not exhibit a pure mass-load behavior. These findings were supported by the discovery that the inductance L in the electromechanical model was less influenced by the cell-layer than the resistance R. The apparent cell-viscosities determined by our method are 0.097 poise for MDCK-I and 0.142 poise for MDCK-II cell-layers. These low apparent viscosities may be explained in terms of a considerable spacing between the cells immobilized via their focal contacts and the quartz surface.

Animals↗
PubMed1996

Economic evaluation of allogeneic bone marrow transplantation: a rudimentary model to generate estimates for the timely formulation of clinical policy.

PURPOSE: To provide an evidence-based approach to the formulation of clinical policy with respect to allogeneic bone marrow transplantation (BMT) that involves perceived trade offs between two major factors: costs and consequences. The report also highlights key informational deficiencies. PATIENTS AND METHODS: Adults with acute myeloid leukemia (AML) in second complete remission (2CR) and those with acute lymphoblastic leukemia (ALL) in first complete remission (1CR) were assigned to BMT or control groups solely on the availability of a suitable donor. All hospital-borne costs were estimated, based on services used according to manual chart review, in four categories: diagnostic and therapeutic costs, professional fees, drug costs, and ward costs. Incremental costs and incremental life-years were calculated, and the quotient determined a cost per life-year gained by BMT for AML (2CR) and ALL (1CR). RESULTS: The incremental cost (in 1992 Canadian dollars) per life-year gained by BMT (cost-effectiveness) for AML (2CR) was $29,200; and for ALL (1CR) it was minus $29,200. CONCLUSION: For AML (2CR), allogeneic BMT creates better outcomes than standard treatment, but is more costly. For ALL (1CR), both the costs and outcomes are similar for BMT and standard therapy. Quality adjustments made to life-years gained did not change these conclusions.

Adolescent↗
PubMed1996

Applications of impedance spectroscopy in biochemistry and biophysics.

The present study is intended to demonstrate the application of impedance spectroscopy to two very different fields of biophysical research. The core component of our measuring setup is a self-constructed continuous wave impedance spectrometer together with special measuring chambers which are individually designed for the systems under investigation. We directed our attention towards: i) the investigation of solid supported lipid bilayers in general, especially systems which are suitable for protein reconstitution such as dimethyldioctadecylammonium bromide (DODAB) immobilized onto a gold electrode, precovered with a negatively charged monolayer of 3-mercaptopropionic acid. Impedance spectroscopy allows to study the stability, the thickness and the electrode coverage of those artificial membranes as well as the observation of ion transport mediated by ionophores like gramicidin D incorporated into a DODAB-bilayer. ii) The characterization of the passive electrical properties of epithelial and endothelial cell monolayers in general and especially the determination of their transepithelial (transendothelial) electrical resistances as a measure for epithelial barrier function. From impedance spectra, as reported here, we are able to follow the formation and modulation of cell layer permeability to small ions.

Animals↗
PubMed1991

Notes on technical progress in veterinary public health.

Scientific and technical progress in the field of veterinary public health (VPH) over the last one hundred years has contributed to the protection of consumer health and the environment. This report presents examples of the success achieved in the control of epizootics of tuberculosis, brucellosis, rabies and trichinellosis, which are also zoonotic diseases. The discussion also considers hygiene measures in relation to Listeria in food as well as certain challenges resulting from the spread of latent infections among farm animals. The increasing incidence of Salmonella infections among humans is also considered. Other important VPH tasks include the control of chemical residues of varying origin and of toxic biological substances in foods. Examples are also presented of measures taken and problems which arise in connexion with ensuring that meat is produced under hygienic conditions (meat inspection). The principles involved in efficient controls of establishments and products are outlined. Technical progress in consumer protection is exemplified by the processes of pasteurisation, cooling and freezing, and the limitation of additives. Other important tasks arise in the disposal of animal carcasses and wastes, and in the fields of animal welfare and genetic engineering. Future activities in VPH will depend upon proper education, onward and postgraduate training for veterinarians, and suitable infrastructures for research, examination and surveillance.

Animals↗
PubMed1975

The role of the marabou stork (Leptoptilos crumeniferus (Lesson)) in Kenya in the spread of echinococcosis from the abattoir.

In experiments, adult marabou storks were fed with hydatid fluid of viable Echinococcus cysts obtained from sheep and goats. On microscopic examination of the birds' faeces no scolices were found, the only remaining undigested parts of the parasites fed being the chitinous hooks of the rostellum. The feeding trials have shown that the marabou does not play a role in the spread of echinococcosis from the abattoir.

Abattoirs↗
PubMedDate not supplied

Five-year prospective follow-up report of the Astra tech standard dental implant in clinical treatment.

Between 1994 and 1999, 515 Astra standard implants were placed and documented prospectively in 107 patients. Of these implants, 364 were placed in original jawbone, 38 in areas augmented with local osteoplasty, and 113 in bone grafts from the iliac crest. The main indications for implantation were an atrophic edentulous alveolar crest (n = 361) and a shortened dental arch (n = 113). Single-tooth implants were excluded. In a special clinical examination, 56 patients with 258 implants were investigated. The average in situ time of the implants was 34.2 months. Failing osseointegration (n = 10), peri-implantitis (n = 10), and implant fracture (n = 1) in 15 patients resulted in the failure of 21 implants (4.1%). Three patients with 8 implants died from malignant tumor. Currently, 27 implants have been lost to follow-up, and 488 implants remain in situ (95.9%). Under analyses with different implant success criteria, the success rate decreased to 85%. Based on the results in this patient population, this implant was found to be a useful alternative to established implant systems for the indications analyzed.

Alveolar Bone Loss↗