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Biomedical subjects

E Walter

Publications and source records attributed to E Walter.

At least 37 records · Page 2Linked to original sources
PubMed1998

Synthesis of bioadhesive poly(acrylic acid) nano- and microparticles using an inverse emulsion polymerization method for the entrapment of hydrophilic drug candidates.

Bioadhesive latices of water-swollen poly(acrylic acid) nano-and microparticles were synthesized using an inverse (W/O) emulsion polymerization method. They are stabilized by a co-emulsifier system consisting of SpanTM 80 and TweenTM 80 dispersed in aliphatic hydrocarbons. The initial polymerization medium contains emulsion droplets and inverse micelles which solubilize a part of the monomer solution. The polymerization is initiated by free radicals, and particle dispersions with a narrow size distribution are obtained. The particle size is dependent on the type of radical initiator used. With water-soluble initiators, for example ammonium persulfate, microparticles were obtained in the size range of 1 to 10 micrometer indicating that these microparticles originate from the emulsion droplets since the droplet sizes of the W/O emulsion show similar distribution. When lipophilic radical initiators, such as azobis-isobutyronitrile, are used, almost exclusively nanoparticles are generated with diameters in the range of 80 to 150 nm, due to the limited solubility of oligomeric poly(acrylic acid) chains in the lipophilic continuous phase. These poly(acrylic acid) micro- and nanoparticles yielded excellent bioadhesive properties in an in-vitro assay and may, therefore, be suitable for the encapsulation of peptides and other hydrophilic drugs.

Acrylic Resins↗
PubMed1998

[Cholestasis: diagnosis].

Cholestasis may present as extrahepatic (obstructive jaundice), as purely intrahepatic (hepatocellular), as part of a cholestatic hepatitis or as a result of intrahepatic obstruction. Anamnestic clues and clinico-chemical analyses (bilirubin, gamma-GT and alkaline phosphatase) together with sonography and finally ERCP usually will furnish the diagnosis. However, with technical advances computed tomography and MRI cholangiography will soon emerge as often useful techniques in hepatobiliary imaging.

Cholestasis, Extrahepatic↗
PubMed1998

Role of integrin expression in adenovirus-mediated gene delivery to the intestinal epithelium.

Adenoviral vectors are being developed for oral delivery of therapeutic genes to the intestine. Initial studies in the rat using mucolytics and direct application of adenovirus encoded with the interleukin-1 receptor antagonist gene to the jejunum produced limited gene expression. The goal of this study was to determine the role of integrins in adenovirus-mediated gene delivery to the intestinal epithelium. Integrins are involved in cellular differentiation and tight junction formation and mediate adenoviral internalization. Results from Caco-2 and IEC-18 cells suggest that, as enterocytes differentiate, cell-surface integrin expression decreases. Pretreatment of Caco-2 cells with RGD peptides reduced adenoviral transduction efficiency by 80% in undifferentiated cells and 20% in differentiated cells. Both differentiated and undifferentiated IEC-18 cells showed a 70% drop in transduction when pretreated with the peptide. Infection inhibition studies with monoclonal antibodies further suggest that alpha(v)beta3 and alpha6beta1 integrins play significant roles in adenoviral internalization in the intestine. Expression of integrins in cell culture models of the intestine correlated with in vivo expression in intestinal segments. These results indicate that the ileum is a prime target for efficient adenovirus-mediated gene transfer in the rat. To enhance transduction in differentiated enterocytes (probable targets for oral gene delivery), Caco-2 cells were treated with interleukin-1beta (a cytokine known to increase integrin expression) prior to administration of the virus. Transduction efficiency increased four-fold.

Adenoviruses, Human↗
PubMed1998

Overexpression of human intestinal oligopeptide transporter in mammalian cells via adenoviral transduction.

PURPOSE: Our goals are to establish an in vitro screening system and to evaluate a new approach in improving oral absorption of peptides and peptide-like drugs by overexpression of the human intestinal oligopeptide transporter (hPepT1). This study characterizes the expression of hPepT1 in human intestinal Caco-2 cells, rat intestinal epithelial cells (IEC-18), and human cervix epithelial cells (Hela) after adenoviral transduction. METHODS: A recombinant replication-deficient adenovirus carrying the hPepT1 gene was made and used as a vector for the expression of hPepT1. The increase in the uptake permeability of cephalexin and Gly-Sar was determined. The effects of time, dose, apical pH, and substrate specificity were evaluated. RESULTS: A significant increase in the uptake permeability of Gly-Sar and cephalexin was found in all three cell lines after viral transduction. The increase of Gly-Sar permeability in Hela. IEC-18, and Caco-2 cells was 85-, 46-, and 15-fold respectively. Immunoblotting using an antibody against hPepT1 detected high levels of a 85-98-kDa protein in all three infected cell lines. Substrate permeability was dependent on time of infection, inward pH gradients, and multiplicity of infection (MOI). Decreased infectivity and lower hPepT1 expression were observed in differentiated Caco-2 cells. The uptake was inhibited by dipeptides and beta-lactam antibiotics but not amino acids. CONCLUSIONS: Adenoviral infected Hela cells displayed a pronounced level of hPepT1 expression with a low background and high specificity to dipeptides. These features make this system a useful tool for screening of potential substrates. The success of overexpression of hPepT1 in Caco-2 and IEC-18 cells may lead to a novel approach in improving oral absorption of peptides and peptidornimetic drugs.

Adenoviridae↗
PubMed1998

Liver-directed gene transfer: a linear polyethlenimine derivative mediates highly efficient DNA delivery to primary hepatocytes in vitro and in vivo.

Efficient DNA delivery is a prerequisite for the successful implementation of molecular antiviral strategies against chronic viral hepatitis and gene therapy in general. The cationic polymer polyethylenimine (PEI) has recently been explored as a gene transfer vector in various cell types in vitro and in vivo. In this study, we evaluated a linear PEI derivative (lPEI) as a vector for gene and oligodeoxynucleotide transfer into hepatocytes in vitro and in vivo. A simple protocol was developed that allowed transfection of up to 50% of primary hepatocytes in vitro. In addition, fluorescent oligodeoxynucleotides were efficiently delivered to the liver in vivo after intravenous injection into Pekin ducks. Thus, lPEI mediates highly efficient gene and oligodeoxynucleotide transfer into primary hepatocytes and is potentially useful for DNA delivery in vivo.

Animals↗
PubMed1998

Occurrence and management of hepatitis B virus reactivation following kidney transplantation.

A 28-year-old woman was kidney transplanted. She had an inapparent hepatitis B virus (HBV) infection 2 years previously. At the time of transplantation she was hepatitis B surface antigen (HBsAg) negative, anti-HBs, anti-HBc, anti-HBe and anti-HCV antibody positive and her transaminase activities were within the normal range. The donor of the kidney allograft was HBV negative. Twelve weeks after transplantation a life-threatening liver failure occurred with a rapid rise of alanine aminotransferase (ALT) to 1427 U/l and a decrease of the prothrombin time to 25% of normal value. Anti-HBs had become negative, anti-HBc and anti-HBe titers had decreased. HBsAg became positive, associated with a HBV DNA of 3 x 10(8) genome equivalents/ml. Azathioprine and prednisone were withdrawn and foscarnet therapy was started. This therapy led to a decrease of ALT activity associated with an elimination of HBsAg and HBV DNA. Eight months after transplantation liver function tests were within the normal range. Graft rejection did not occur despite low or intermittent cessation of immunosuppressive therapy.

Adult↗
PubMed1997

Preparation of Magnetic Inks: Adsorption of Macromolecular Dispersion Agents on Magnetic Metallic Iron Pigments and Electrical Charge Formation

The interaction between metallic iron pigments (MPs) and the actual constituents of magnetic ink is examined by first determining the adsorption isotherms and analyzing by FTIR the type of bonding that is established between the constituents and MP. Then, following the approach described in a previous paper using model compounds, the formation of electrical charges on MPs is examined through acoustophorometric (Electrokinetic amplitude or ESA) measurements. It is shown that the variation in ESA is related to charge transfer processes and reflects the MP-constituent interactions. Finally, adsorption competitions are shown and the importance of the method of preparation (order of mixing of the ingredients of the ink) is illustrated. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1997

Optimal discriminant analysis for ordinal responses.

Optimal classification formulation is adapted to the context of discrimination when the response is ordinal. The resulting method, optimal discriminant analysis for ordinal responses (ODAO), is presented and compared with two reference discrimination techniques used in this context (proportional-odds ordinal logistic regression and normal discrimination) using a study of prognosis following burn injuries and simulated data. The ODAO method clearly outperforms both reference methods in terms of classification accuracy (in training and validation samples), robustness to outliers, simplicity of use and applicability in clinical settings. ODAO is a promising method for improving classification performance in discrimination with ordinal responses and merits further investigation.

Adult↗
PubMed1997

Adsorption of Stearic Acid and Diethylhexyl Phosphate on Magnetic Metallic Iron Pigments: Electrical Surface Charging and Adsorption Competition

The adsorption of stearic acid and bis(2-ethylhexyl) phosphate, from toluene and THF solutions, on magnetic iron pigments (MP) was examined. Adsorption isotherms as well as the concomitant variations of surface electrical (zeta) potential were determined. The formation of electrical surface charges is explained by charge transfer processes between the solvents, the adsorbates, and MP. An adsorption competition is evidenced when contacting MP with the adsorbates using 14C-labeled stearic acid.

Journal Article↗
PubMed1997

[Therapy of hepatorenal syndrome].

A specific medical therapy for 'the hepatorenal syndrome' (HRS) is not available. However, the increasing knowledge of the mechanisms involved in the development of HRS leads to new therapeutic approaches to this syndrome of functional renal failure. Recognition and prevention of precipitating factors, the correction and treatment of prerenal failure and acute tubular necrosis are particularly important in the treatment of patients with liver cirrhosis, ascites and hepato-renal failure. Vasoconstrictor agents (ornipressin, dopamine) are administered to achieve an improvement of the systemic circulation. Definitive therapy of HRS is liver transplantation.

Hepatorenal Syndrome↗
PubMed1997

The mechanism of uptake of biodegradable microparticles in Caco-2 cells is size dependent.

PURPOSE: To study the uptake of biodegradable microparticles in Caco-2 cells. METHODS: Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 micron, 1 micron, and 10 microns containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 micrograms/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied. RESULTS: The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 micron diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 micron and 6 fold greater than the 10 microns diameter microparticles. Similarly in terms of number the uptake of 0.1 micron diameter microparticles was 2.7 x 10(3) fold greater than the 1 micron and 6.7 x 10(6) greater than the 10 microns diameter microparticles. The efficiency of uptake of 0.1 micron diameter microparticles at 100 micrograms/ml concentration was 41% compared to 15% and 6% for the 1 micron and the 10 microns diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 micron) uptake increased with concentration in the range of 100 micrograms/ml to 500 micrograms/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37 degrees C compared to at 4 degrees C. CONCLUSIONS: The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 micron) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.

Animals↗
PubMed1997

The absence of accessible vitronectin receptors in differentiated tissue hinders adenoviral-mediated gene transfer to the intestinal epithelium in vitro.

PURPOSE: Adenoviral (Ad) vectors have been used as efficient tools for gene therapy in various tissues, whereas in some differentiated epithelium transduction efficiency is almost abolished. METHODS: Caco-2 cell monolayers were chosen as an in vitro model for the differentiated intestinal epithelium. Fluorescence-labeled adenoviral particles were used for binding studies to cell surfaces. Internalization receptors for adenoviral uptake were detected by a fluorescence-labeled vitronectin antibody. Gene expression was studied by using the beta-galactosidase reporter gene. All experiments were done on undifferentiated and differentiated Caco-2 cells. Furthermore, adenoviral particles were allowed to bind to differentiated Caco-2 monolayers followed by a trypsinization step that disintegrates the monolayers and result in a cell suspension. Gene expression was tested after reseeding the cells into dishes. RESULTS: The results from adenoviral binding studies, vitronectin immunofluorescence detection and gene expression are in good agreement and indicate that virion binding as well as the expression of internalization receptors almost disappear in fully differentiated cells. Nonetheless, adenoviral binding to differentiated monolayers seems to be sufficient to cause up to 53% gene expression, but only if internalization of the vector can be induced by disintegrating the monolayers and releasing free vitronectin receptors. CONCLUSIONS: These findings indicate that gene transfer to the intestinal epithelium utilizing adenoviral vectors is poor and ineffective, because of the lack of sufficient internalization receptors. If these receptors can be exposed in differentiated epithelium, transduction can be made more efficient. Alternatively, a viral vector must be developed whose uptake mechanism is independent of integrin receptor expression like the enteral virus Ad40, or Ad5 could be conjugated to ligands that trigger viral internalization by receptor-mediated endocytosis.

Adenoviridae↗
PubMed1996

Hepatitis B virus infection of tupaia hepatocytes in vitro and in vivo.

For the systematic analysis of various clinical and molecular aspects of hepatitis B virus (HBV) infection, an experimental small animal system of HBV infection would be a great advance. The susceptibility to HBV infection, therefore, of hepatocytes from the tree shrew species tupaia belangeri was studied in vitro and in vivo. Primary hepatocytes isolated from livers of tupaias can be reproducibly infected with HBV. In vitro infection results in viral DNA and RNA synthesis in hepatocytes and secretion hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) into culture medium. Tupaias can also be infected with HBV in vivo, resulting in viral DNA replication and gene expression in tupaia livers. Similar to acute, self-limited hepatitis B in humans HBsAg is rapidly cleared from serum, followed by seroconversion to anti-HBe and anti-HBs. These data clearly tht HBV is infectious to tupaia hepatocytes in vitro and transiently in vivo. Tupaias, therefore, may become a useful model for the experimental analysis of various molecular and clinical aspects of HBV infection, including the significance of HBV quasispecies, the steps involved in hepatocarcinogenesis as well as the evaluation of various antiviral strategies.

Animals↗