Abloesungs- und Widerstandsphaenomene in periodisch-verengten Rohren bei niederen Reynolds-Zahlen

Flow separation and resistance phenomena in sinusoidally constricted tubes of different geometrical shapes were studied experimentally and numerically at low Reynolds numbers (10"-"4#<=#Re#<=#10"2). Flow separation is demonstrated to occur even for creeping flow (Re<<1), with the geometrical parameters chosen adequately. Surprisingly, when the amplitude-to-wavelength ratio #gamma# is kept constant and only the ratio of the mean radius to the wavelength (titled #delta#) is varied, separation under creeping flow conditions is found to take place solely for small values of #delta#, whereas flows under the influence of inertia (Re>1) tend to separate for small values of #delta# as predicted by the classical concept of flow separation. This behaviour demands explanation. As far as kinematics is concerned, the separation zones have a very symmetrical appearance for creeping flow; become rather unsymmetrical with the beginning influence of inertia and regain a more symmetrical shape only for higher Re before the transition to turbulence takes place. For one specific #gamma# it could be shown numerically that as #delta# was increased the Re-Number for beginning separation first increases, but then decreases after having reached a maximum to yield a creeping flow separation. (orig.)49 refs.Available from TIB Hannover: RA 1396(1995,5) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Membrane interactions of ternary phospholipid/cholesterol bilayers and encapsulation efficiencies of a RIP II protein

Membrane interactions of liposomes of ternary phospholipid/cholesterol bilayers are investigated. These interactions lead to discoidal deformations and regular aggregations and are strongly enhanced by the presence of mistletoe lectin (ML), a RIP 11 type protein. The encapsulation of ML into liposomal nanocapsules is studied with a systematic variation of the lipid composition to monitor its effect on the physical properties: entrapment, mean size, morphology, and stability. Extrusion of multilamellar vesicles through filters 80 nm pore size was used for the generation of liposomes. The mean sizes of liposomes ranged between 120 and 200 nm in diameter with narrow size distributions. The increase in flow rate with pressure for three dioleoylphosphatidylcholine (DOPC/cholesterol (Chol)/dipalmitoylphosphatidylcholine (DPPC) lipid mixtures was linear and allowed to extrapolate to the minimum burst pressure of the liposomal bilayers. From the minimum pressures P(min), the bilayer lysis tensions gamma(1) were determined. The increase in P in and gamma(1) with an increasing content of a saturated phosopholipid (DPPC) indicates that DPPC increases the mechanical strength of lipid bilayers. Apparently, DPPC, like cholesterol, leads to a less compressible surface and a more cohesive membrane. After preparation, vesicle solutions were purified by gel permeation chromatography to separate encapsulated ML from free ML in the extravesicular solution. Purified liposomes were then characterized. The content of entrapped and adsorbed ML was measured using ELISA. Repetitive freezing/thawing cycles prior to extrusion significantly increased ML uptake. On the contrary, adsorption was not affected neither by lipid composition, nor concentration and preparation. Differences in experimental encapsulation efficiency only reflect the differences in the mean vesicle sizes of the different samples as is revealed by a comparison to a theoretical estimate. Cryo-transmission electron microscopy (Cryo-TEM) images show that beside spherical, single-walled liposomes, there is a considerable fraction of discoidally deformed vesicles. Based on our results and those found in the literature, we speculate that the flattening of the vesicles is a consequence of lipid phase separation and the formation of condensed complexes and areas of different bending elasticities. This phenomenon eventually leads to agglomeration of deformed liposomal structures, becoming more pronounced with the increase in the relative amount of saturated fatty acids, presumably caused by hydrophobic interaction. For the same lipid mixture aggregation correlated linearly with the ML content. Finally, tested liposomal samples were kept at 4 degrees C to examine their stability. Only slight fluctuations in diameter and the increase in polydispersity after 3 weeks of storage occurred, with no statistically significant evidence of drug leakage during a time period of 12 days, illustrating physical stability of liposomes

Quantitative analysis of receptor-mediated uptake and pro-apoptotic activity of mistletoe lectin-1 by high content imaging

Abstract Ribosome inactivating proteins (RIPs) are highly potent cytotoxins that have potential as anticancer therapeutics. Mistletoe lectin 1 (ML1) is a heterodimeric cytotoxic protein isolated from European Mistletoe and belongs to RIP class II. The aim of this project was to systematically study ML1 cell binding, endocytosis pathway(s), subcellular processing and apoptosis activation. For this purpose, state of the art cell imaging equipment and automated image analysis algorithms were used. ML1 displayed very fast binding to sugar residues on the membrane and energy-dependent uptake in CT26 cells. The co-staining with specific antibodies and uptake blocking experiments revealed involvement of both clathrin-dependent and -independent pathways in ML1 endocytosis. Co-localization studies demonstrated the toxin transport from early endocytic vesicles to Golgi network; a retrograde road to the endoplasmic reticulum. The pro-apoptotic and antiproliferative activity of ML1 were shown in time lapse movies and subsequently quantified. ML1 cytotoxicity was less affected in multidrug resistant tumor cell line 4T1 in contrast to commonly used chemotherapeutic drug (ML1 resistance index 6.9 vs 13.4 for doxorubicin; IC50: ML1 1.4 ng/ml vs doxorubicin 24000 ng/ml). This opens new opportunities for the use of ML1 as an alternative treatment in multidrug resistant cancers