Biomedical subjects

W Albrecht

Publications and source records attributed to W Albrecht.

At least 19 recordsLinked to original sources

PubMed2005

Licofelone, a novel 5-LOX/COX-inhibitor, attenuates leukocyte rolling and adhesion on endothelium under flow.

The main mechanism of action of non-steroidal anti-inflammatory drugs (NSAIDs) is the inhibition of cycloxygenases COX-1 and COX-2. During recent years, combined 5-LOX/COX-inhibition, interfering with the biosynthesis of both prostaglandins and leukotrienes (LTs), has emerged as a possibility to avoid side effects related to COX-inhibition. The aim of the present study was to investigate if there is a contribution of mechanisms other than the reduction of inflammatory prostaglandins and leukotrienes to the anti-inflammatory effect of the LOX/COX inhibitor licofelone. In a flow chamber assay, licofelone (10-30 microM) dose-dependently decreased both the rolling and adhesion of leukocytes on endothelial cells (EC). In contrast, no effects were found after treatment of EC with the unselective COX-1/COX-2 inhibitor indomethacin (30 microM), the potent and selective 5-LOX inhibitor, ZD-2138 (30 microM), the mainly COX-2 inhibitor aceclofenac (30 microM), the selective COX-2 inhibitor celecoxib (30 microM) and the combination of ZD-2138 with the selective COX-2 inhibitor celecoxib (30 microM). In the presence of licofelone (30 microM) the expression of E-selectin mRNA in cytokine-stimulated EC was attenuated, whereas no NSAID (30 microM) tested showed any effect on E-selectin expression. Moreover, licofelone treatment (30 microM) attenuated expression of VCAM-1 and ICAM-1 on inflammatory EC. The effect of licofelone on leukocyte recruitment was also evaluated in vivo. Using a mouse peritonitis model it was found that leukocyte accumulation was markedly reduced in licofelone treated animals (100mg/kg) compared to untreated mice. Thus, the novel 5-LOX/COX inhibitor licofelone possesses anti-inflammatory activity that, in addition to COX/LOX inhibition, involves effects on leukocyte-endothelial interactions.

Acetates↗

PubMed2005

On the tissue compatibility of poly(ether imide) membranes: an in vitro study on their interaction with human dermal fibroblasts and keratinocytes.

Recently we have developed a novel type of membrane based on poly(ether imide) (PEI) which is considered for biomedical application. To improve its physical and biological performance it was modified by blending with poly(benzimidazole) (PBI). In the present study both membranes were characterized in terms of their physicochemical properties and in vitro tissue compatibility using human dermal fibroblasts and keratinocytes. The modified membrane (PEI*) was more hydrophilic, less porous and had an increased surface (zeta) potential. We further found that blending with PBI tends to promote cell contact, at least initially, as indicated by the improved overall cell morphology, adhesion and spreading of fibroblasts, and the development of focal adhesion complexes. The effects of fibronectin (FN) and serum coating were also beneficial when compared to pure PEI and tissue culture polystyrene (TCP), which correlates to a higher adsorption of both FN and vitronectin detected by ELISA. However, a clear tendency for homotypic cellular interaction particularly of keratinocytes was obtained in contact with membranes, which was much stronger pronounced on PEI*. Although the initial adhesion was greater on PEI*, a surprising decrease in cell growth was observed at later stages of incubation, which may be explained with the membrane-promoted cellular aggregation leading to an easier detachment from the substratum. Thus, membranes based on blends of PEI with PBI could provide a tissue compatible scaffold with lowered adhesive properties, which might be a useful tool for the transfer of cells, for example, to in vitro engineered tissue constructs.

Actins↗

PubMed2005

Membranes for biohybrid liver support: the behaviour of C3A hepatoblastoma cells is dependent on the composition of acrylonitrile copolymers.

Co-polymers based on acrylonitrile, N-vinylpyrrolidone, aminoethylmethacrylate and sodium methallylsulfonate were used to prepare flat membranes by phase inversion. The surface properties of membranes were characterised by water contact angle measurements, atomic force microscopy and X-ray photoelectron spectroscopy (XPS). Membrane permeability was estimated by porosity measurements with water as test liquid. Human C3A hepatoblastoma cells were plated on these materials. Cell-material interaction was characterised by overall cell morphology, formation of focal adhesion contacts and intercellular junctions. Furthermore, cell proliferation was measured and compared with the functional activity of cells as indicated by 7-ethoxycoumarin-O-deethylation. More hydrophilic materials reduced spreading of cells, formation of focal adhesion and subsequent proliferation while homotypic cell adhesion was facilitated in correlation with stronger expressions of intercellular junctions and improved functional activity. In contrast, membranes with stronger adhesivity enhanced cell proliferation but reduced the functional activity of cells. It was concluded that the co-polymerisation of acrylonitrile with hydrophilic co-monomers, such as N-vinylpyrrolidone, could be used to tailor membrane materials for the application in biohybrid liver support systems.

Acrylonitrile↗

PubMed2005

Development of polymer membranes with improved haemocompatibility for biohybrid organ technology.

Biomedical technology has opened up possibilities of treating the failure of internal organs like kidney and liver by artificial organ therapy. Most of these techniques are based on polymer membranes, which allow the removal of excess of water, salts and toxins from the circulation. However, haemodialysis for the replacement of kidney function results in an increased morbidity and mortality of patients after long-term application. Conventional therapy, such as haemofiltration for the treatment of acute liver failure does not improve significantly the survival rate of patients. Biohybrid organ support as a combination of the artificial organ therapy with the functional activity of immobilised cells seems to be a solution of the problem. Membranes applied in these devices have to face both tissue cells and blood. Organ cells in biohybrid organs have to make intimate contact with the surface of membrane but must also develop close cell-cell-connections as a prerequisite for their survival and high functional activity. Blood to be detoxified will contact the other side of membrane and may not become activated by the synthetic material. New polymer membranes based on acrylonitrile were developed to address these requirements by tailoring the composition of copolymers and to be applied in a specific hollow fibre bioreactor with an outer fibre for blood contact, and an inner fibre for tissue contact or vice versa.

Animals↗

PubMed2004

The influence of the chemical composition of cell culture material on the growth and antibody production of hybridoma cells.

The multiplication and antibody production of murine hybridoma cells cultured on five different polymer membranes were tested and compared with conventional tissue culture polystyrene (TCPS). Membranes were prepared from polyacrylonitrile (PAN) and acrylonitrile copolymerized with N-vinylpyrrolidone (NVP20, NVP30), Na-methallylsulfonate (NaMAS) and N-(3-amino-propyl-methacrylamide-hydrochloride) (APMA). Cell number and antibody concentration were quantified as criteria for viability and productivity. Adhesion of hybridoma cells was characterized by vital and scanning electron microscopy. The results suggest that a strong adhesion of cells, observed on APMA and TCPS, increased cell growth but reduced monoclonal antibody production. In contrast membranes with lowered adhesivity such as NVP20 provided favourable conditions for monoclonal antibody production. In addition it was shown that this membrane also possessed a minor fouling as indicated by the low decrease of water flux across the membrane after protein adsorption. It was concluded that NVP20 could be a suitable material for the development of hollow fibre membranes for bioreactors.

Animals↗

PubMed2004

Randomized Phase II trial assessing estramustine and vinblastine combination chemotherapy vs estramustine alone in patients with progressive hormone-escaped metastatic prostate cancer.

Based on the results of combined data from three North American Phase II studies, a randomised Phase II study in the same patient population was performed, using combination chemotherapy with estramustine phosphate (EMP) and vinblastine (VBL) in hormone refractory prostate cancer patients. In all, 92 patients were randomised into a Phase II study of oral EMP (10 mg kg day continuously) or oral EMP in combination with intravenous VBL (4 mg m(2) week for 6 weeks, followed by 2 weeks rest). The end points were toxicity and PSA response in both groups, with the option to continue the trial as a Phase III study with time to progression and survival as end points, if sufficient responses were observed. Toxicity was unexpectedly high in both treatment arms and led to treatment withdrawal or refusal in 49% of all patients, predominantly already during the first treatment cycle. The mean treatment duration was 10 and 14 weeks, median time to PSA progression was 27.2 and 30.8 weeks, median survival time was 44 and 50.9 weeks, and PSA response rate was only 24.6 and 28.9% in the EMP/VBL and EMP arms, respectively. There was no correlation between PSA response and survival. While the PSA response in the patients tested was less than half that recorded in the North American studies, the toxicity of EMP monotherapy or in combination with VBL was much higher than expected. Further research on more effective and less toxic treatment strategies for hormone refractory prostate cancer is mandatory.

Administration, Oral↗

PubMed2003

Novel substituted pyridinyl imidazoles as potent anticytokine agents with low activity against hepatic cytochrome P450 enzymes.

A series of polysubstituted pyridin-4-yl imidazole inhibitors of p38 MAP (mitogen-activated protein) kinase was prepared as small molecular anticytokine agents and drug candidates for the treatment of chronic inflammatory diseases. The contribution of substituents at the pyridinyl and imidazole moiety to selective inhibition of p38 without concomitant cytochrome P450 interaction was evaluated. Placement of a 1-phenylethyl (7e, p38: IC(50) 0.38 microM) or acetyl substituent at the exocyclic nitrogen of several 2-aminopyridine imidazoles led to the identification of potent p38 inhibitors which exceeded the starting lead ML 3375 (p38: IC(50) 0.63 microM) in potency. A preliminary modeling study related the enhanced bioactivity of 7e to a novel interaction between its 1-phenylethylamino side chain and a hydrophobic pocket close to the linker region of p38. The most active p38 inhibitors in this series maintained their efficacy in functional PBMC (peripheral blood mononuclear cells) and whole blood assays. Moreover, cytochrome P450 interaction, which has been linked to the liver toxicity observed for model p38 inhibitors, was very efficiently reduced through introduction of a tetramethylpiperidine substituent at the 1 position of the imidazole nucleus. Combination of both structural features provided 14c (p38: 0.34 microM, inhibition of CYP1A2 0%, 2C9 2.6%, 2C19 7.6% at 10 microM), which was selected for further development.

Aminopyridines↗

PubMed2003

Morphological studies on the culture of kidney epithelial cells in a fiber-in-fiber bioreactor design with hollow fiber membranes.

A hollow fiber-in-fiber-based bioreactor system was tested for the applicability to host kidney epithelial cells as a model system for a bioartificial kidney. Hollow fibers were prepared from polyacrylonitrile (PAN), polysulfone-polyvinylpyrollidinone (PVP) blend (PSU) and poly(acrylonitrile-N-vinylpyrollidinone) copolymer P(AN-NVP). Hollow fibers with smaller and larger diameters were prepared so that the smaller fitted into the larger, with a distance of 50-100 microm in between. The following material combinations as outer and inner fiber were applied: PAN-PAN; PSU-PSU, PSU-P(AN-NVP). Madin-Darby kidney epithelial cells (MDCK) were seeded in the interfiber space and cultured for a period up to 14 days. Light, scanning, and transmission electron microscopy were used to follow the adhesion and growth of cells, and to characterize their morphology. As a result, we found that MDCK cells were able to grow in the interfiber space in mono- and multilayers without signs of systemic degeneration. Comparison of the different materials showed that PAN and P(AN-NVP) provided the best growth conditions, indicated by a tight attachment of cells on hollow fiber membrane, and subsequent proliferation and development of structural elements of normal epithelia, such as tight junctions and microvilli. In conclusion, the fiber-in-fiber design seems to be an interesting system for the construction of a bioartificial kidney.

Acrylic Resins↗

PubMed2003

Combined scintigraphic and pharmacokinetic investigation of enteric-coated mesalazine micropellets in healthy subjects.

BACKGROUND: There is a growing clinical trend to increase the daily dose of mesalazine, which leads to significant compliance issues associated with multiple dosings of current preparations. AIM: To examine the gastrointestinal performance and systemic exposure of a 1.5 g sachet (micropellets) mesalazine formulation, compared with three enteric-coated tablets (500 mg each, Claversal). METHODS: A randomized, two-way, cross-over pharmacoscintigraphic (scintigraphy plus pharmacokinetics) study and a two-way, cross-over, pharmacokinetic-only study were performed in 24 healthy volunteers (12 subjects per investigation). RESULTS: The relative bioavailability of mesalazine was 92% comparing micropellets with Claversal tablets, and the cumulative urine excretion was c. 26% for both preparations, suggesting comparable systemic exposure for the two types of preparation. In the majority of subjects, drug release from the micropellet formulation occurred predominantly in the terminal ileum and ascending colon. The Claversal tablets disintegrated in comparable intestinal sites, albeit at slightly later time points than the micropellets, principally due to slower gastric emptying for the single-unit formulation. CONCLUSION: The 1.5 g micropellet formulation offers comparable delivery properties to the marketed tablets, but with greater convenience of dosing.

Administration, Oral↗

PubMed2002

Polyetherimide: a new membrane-forming polymer for biomedical applications.

Membranes for biohybrid organs such as the biohybrid liver support system have to face 2 different environments, namely blood and tissue cells. Accordingly, the respective membrane surfaces must have optimal properties in terms of biocompatibility for blood or tissue. Flat membranes prepared by a phase inversion process from polyetherimide were modified by binding of tris-(hydroxymethyl)-aminomethane to obtain a surface with hydroxyl groups by binding of polyethylene imine to attach a hydrophilic macromolecule with amine groups useful as a spacer for later bonding of further ligands and by attachment of heparin. The binding of the different ligands was successful as monitored by different physicochemical methods. The blood response of plain polyetherimide was comparable to that of polyacrylonitrile, and it could be further improved by the binding of heparin. The tissue compatibility of polyetherimide and its different modifications was compared with commercial cell culture substrate membranes (Millicell) and found to be comparable for polyetherimide and even better after the modification with tris-(hydroxymethyl)-aminomethane. In conclusion, polyetherimide seems to be an interesting material for the production of membranes for application in biohybrid organ systems.

Complement Activation↗

PubMed2001

Radiotherapy of testicular intraepithelial neoplasia (TIN): a novel treatment regimen for a rare disease.

PURPOSE: Testicular intraepithelial neoplasia (TIN) is a consistent precursor of most invasive germ cell tumors, currently treated by radiotherapy with 20 Gy, which destroys TIN but preserves Leydig cells. Nevertheless, analysis has shown dose-dependent dysfunction even with low therapeutic doses of 20 Gy in some cases. Therefore, we tested a dose reduction regimen by delivering smaller fractional doses to enhance the tolerance of Leydig cells. METHODS AND MATERIALS: Between 1993 and 1999, 9 patients were treated for TIN in a prospective multicenter trial. A total dose of 13 Gy was administered in 10 fractions of 1.3 Gy. Hormonal levels of follicle-stimulating hormone, luteinizing hormone, and testosterone were assayed serially. RESULTS: During a median follow-up time of 36 months, no patient showed evidence of local disease. A first postradiation biopsy was obtained 3-12 months after radiotherapy; 5 patients underwent a second biopsy 2-3 years after treatment. All biopsies showed a Sertoli cell-only pattern. Follicle-stimulating hormone levels continued to increase 1 year after radiotherapy, signaling eradicated spermiogenesis. Luteinizing hormone and testosterone remained within the normal range 2 years after radiotherapy. CONCLUSIONS: In the treatment of TIN, there seems to be a dose reduction potential to 13 Gy by lowering single fractional doses, which enhances the therapeutic ratio in favor of the Leydig cells.

Adult↗

PubMed2001

A new module arrangement for plasmapheresis.

On-line plasmapheresis using microporous membranes for filtration normally requires two external circulations (double treatment) before the detoxified plasma can be returned to the patient. The duomodule, a new filter arrangement developed by our group, integrates both steps in one equipment module using only one external circuit. Separations of aqueous polyethylene glycol (PEG) solutions as well as human plasma were carried out using the duomodule arrangement. The results revealed a considerable decrease of higher molecular substances in the feed solutions and a significant increase of these components in the permeate solution accumulated in the external compartment of the module. In conclusion, the duomodule arrangement seems to be an useful tool for the therapeutic apheresis.

Chemical Fractionation↗

PubMed2001

The suitability of hepatocyte culture models to study various aspects of drug metabolism.

Since the liver is the main organ involved in the metabolism and the toxicity of xenobiotics, isolated rat hepatocytes have been increasingly used in recent years as a model to identify pharmacological and toxicological responses of drugs. However, it is generally recognised that isolated hepatocytes retain most of their functions only for a short period. For this reason, numerous models and techniques have been developed to study and improve the metabolic capacity of hepatocytes in vitro over an extended time period and in application for drug metabolism studies. In the present study, we compared four different cell culture models to fulfill these requirements and have therefore harvested hepatocytes and cultured them in different culture systems over two weeks. In order to prove certain advantages or disadvantages of each model, we compared the metabolic capacity, albumin secretion, the release of cytosolic and mitochondrial enzymes, as well as the capacity to metabolise diclofenac (DF). We found that rat hepatocytes in all studied culture models (except the Unisyn Bioreactor) were able to metabolise DF to the same extent as found in vivo. However, the concentration of metabolites was found to decrease with culture time using the monolayer although the DF metabolite level in the collagen Sandwich culture was higher than that of the monolayer culture. The 3D-membrane bioreactor preserved the metabolic capacity for a prolonged period of time. The concentrations of DF metabolites in the Unisyn hollow fiber bioreactor were below the detection limit, which corresponded to other parameters such as albumin secretion and cytochrome P450 activity, disqualifying this culture system clearly for the use of in vitro primary hepatocyte cultures. The other three systems all have their place in drug metabolism with different advantages. However, our studies clearly showed that hepatocytes cultured within a collagen sandwich or in the 3D-membrane bioreactor qualify to study various aspects of drug metabolisms over a long time period. Further studies are needed to prove if the later two culture models may really help to reduce animal testing.

Alanine Transaminase↗

PubMed2000

Development of membranes for the cultivation of kidney epithelial cells.

The development of biohybrid organs (BHO) will benefit from improved membranes regarding transport and cell contacting properties. Here we describe in a first study the development and testing of membranes made of polyacrylonitrile (PAN) and polysulfone (PSU) for the immobilisation of kidney epithelial cells. Comparative investigations on overall polymer toxicity tested with 3T3 fibroblasts, and morphology and proliferation of Madin-Darby canine kidney (MDCK) cells cultured on the membranes could show that these materials have comparable cell contacting properties like Millicell membranes. Since PAN and PSU have superior membrane forming properties with regard to membrane geometry, i.e. for the preparation of hollow fibres, and porosity, i.e. for immuno isolation, both materials or modifications thereof seem to be suitable for the application in BHO such as biohybrid kidney.

3T3 Cells↗

PubMed2000

Development and application of a high-performance liquid chromatography-based assay for determination of the activity of inosine 5'-monophosphate dehydrogenase in whole blood and isolated mononuclear cells.

With the objective of pharmacodynamic monitoring of the immunosuppressive efficacy of mycophenolate mofetil (MMF) (CellCept, Hoffman-LaRoche, Grenzach-Wyhlen, Germany), a method for determination of the inosine monophosphate dehydrogenase (IMPDH) activity in whole blood cell (WBC) lysates and mononuclear cells (MNCs) was developed. The assay is based on the incubation of WBC lysates or lysed MNCs in the presence of supplemented inosine 5'-monophosphate (IMP) and nicotimamide adenine dinucleotide (NAD). The formation of xanthosine 5'-monophosphate (XMP) was determined by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The analytical method was validated, and the obtained data demonstrated that the amount of XMP in WBC and MNC lysates can be reliably determined by this method. Under assay conditions the rate of XMP formation remained constant within the incubation period of 60 minutes and a quantification of product formation at 30 and 60 minutes proved to be sufficient to reliably characterize the IMPDH activity. Applications of this assay with whole blood indicated extremely high IMPDH-activities in samples from patients with renal transplant receiving MMF. IMPDH monitoring within 10 hours after administration of the morning dose demonstrated a marked enzyme inhibition between 2 hours and 3 hours postdosing, but the activities returned to predose levels within one dose interval. The analysis of isolated cell fractions indicated that the IMPDH-activity is predominantly located in erythrocytes. The contribution of MNCs to the whole blood activity remained below 10%. In order to simulate the in vivo exposure of MNCs to mycophenolic acid, an "erythrocyte- and platelet-free" whole blood was reconstituted by resuspension of isolated MNCs with plasma. This strategy allowed for the reliable measurement of IMPDH activity in the target cells of immunosuppression.

Chromatography, High Pressure Liquid↗

PubMed1999

Impact of cytotoxic treatment on long-term fertility in patients with germ-cell cancer.

More than half of the patients with testicular germ-cell cancer show impaired spermatogenesis before undergoing cytotoxic treatment. The known pre-treatment infertility and the reversibility of the fertility problems observed in some after successful anti-cancer treatment have so far prevented an assessment of the true role of cytotoxic therapy in long-term fertility. The introduction of wait-and-see strategies (surveillance) for testicular cancer patients and recent prospective trials comparing patients with and without cytotoxic treatment have provided the means for estimating the extent to which treatment itself affects long-term fertility. Whether or not spermatogenesis is irreversibly impaired by chemotherapy is determined by the cumulative dose of cisplatin: at doses below 400 mg/m2, long-term effects on sperm production as well as on endocrine function are unlikely to occur. Higher doses should be expected to cause long-term losses of exocrine and endocrine gonadal function. In contrast, for adjuvant retroperitoneal radiotherapy in stage I seminoma patients, no data are available comparing long-term gonadal function with patients on surveillance. However, using modern radiation techniques, radiation doses to the para-aortic field (< 30 Gy) and testis shielding providing testis scatter radiation (< 30 cG), radiation-induced impairment of fertility is very unlikely.

Antineoplastic Agents↗

PubMed1999

Altered vitronectin receptor (alphav integrin) function in fibroblasts adhering on hydrophobic glass.

Function of integrins is crucial for adhesion, movement, proliferation, and survival of cells. In a recent study we found impaired fibronectin receptor function on hydrophobic substrata (G. Altankov et al. J Biomater Sci Polym Edn 1997;8:712-740). Here, we have studied the distribution and function of the vitronectin receptor (alphav integrin) in fibroblasts adhering on hydrophilic glass and hydrophobic octadecyl glass (ODS). The morphology of fibroblasts and the organization of actin cytoskeleton were studied and found to be altered on ODS, where the cells did not spread and possessed condensed actin. Pretreatment of the surfaces with serum or pure vitronectin improved cell morphology on both substrata, resulting in the development of longitudinal actin stress fibers. It was found with biotinylated vitronectin that comparable quantities of vitronectin were adsorbed from single vitronectin solutions or serum on glass and on hydrophobic ODS. The organization of the vitronectin receptors on the ventral cell surface was investigated in permeabilized cells showing normal focal adhesions in fibroblasts plated on glass but none of these structures on ODS. The distribution of alphav integrin on the dorsal cell surface was studied on nonpermeabilized living cells after antibody tagging. While fibroblasts adhering on plain or serum-treated glass developed a linear organization of alphav integrin, cells on plain and serum-treated ODS were not able to reorganize the vitronectin receptor. Studies on signal transduction with antiphosphotyrosine antibodies revealed co-localization of alphav integrin and phosphotyrosine in focal adhesions on glass and serum-treated glass. However, signaling was almost absent on plain ODS and weak on serum-treated ODS. It was concluded that alterations in vitronectin receptor function on the ventral cell surface caused by the hydrophobic material surface inhibit signal transfer and subsequent intracellular events that are important for the organization and function of integrins.

Actins↗

PubMed1999

Functionalized nanoparticles for endotoxin binding in aqueous solutions.

Nanoparticles consisting of a polystyrene core and a polyglycidyl methacrylate shell were prepared by a two-step emulsion polymerization. The size and surface properties of the particles were characterized by scanning electron microscopy, dynamic light scattering and polyelectrolyte titration techniques. Particles were found to be monodisperse with a mean diameter of about 85 nm. Parent particles were modified with a number of different ligands including diamines of increasing chain length, amino acids and corresponding amines and higher molecular weight ligands like polymyxin B. The modified particles were tested for their endotoxin (ET) binding capacity in water and physiological sodium chloride solution with the Limulus amebocyte lysate (LAL) assay. It was found that the ET binding properties of the different ligands depend both on the ability of the ligand to form Coulomb- and van der Waals-interactions with the ET molecule influenced by the nature of the suspension medium. Therefore, the choice of ligands for particle modification has to consider minutely the conditions under which ET has to be removed, e.g. removal from pure water, dialysis fluids, plasma or blood.

Biocompatible Materials↗