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  • Chemistry  (3)
  • intestinal delivery  (2)
  • multidrug resistance  (2)
  • 75.25+z  (1)
  • 1995-1999  (8)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Direct experimental investigation of spin-reorientation phase transitions in an antiferromagnetic CoNiCu/Cu superlattice (1996)
    Springer
    JETP letters 64 (1996), S. 826-831 
    Details
    ISSN: 1090-6487
    Keywords: 75.50.Ee ; 75.70.Cn ; 75.30.Kz ; 75.25+z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The characteristic features of phase transitions induced by an external magnetic field and of the corresponding changes in the relative orientations of the spins in the ferromagnetic CoNiCu layers of a multilayer film, which are coupled by an antiferromagnetic exchange interaction via nonmagnetic Cu interlayers, are studied using a magnetooptic method for visualizing the fringing fields. It is established that the magnetization reversal process in this nanocomposite material proceeds by a spin-flop orientational phase transition on account of the formation and motion of specific domain walls as well as by incoherent rotation of the spins toward the applied field. It is shown that, depending on the direction of the external magnetic field with respect to the easy axis, asymmetric canted phases also arise as a result of such transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567247
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of Pluronic P85 Unimers and Micelles on Drug Permeability in Polarized BBMEC and Caco-2 Cells (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1525-1532 
    Details
    ISSN: 1573-904X
    Keywords: pluronic block copolymer ; intestinal delivery ; drug ; micelles ; blood brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Using polarized bovine brain microvessel endothelial cells (BBMEC) monolayers as in vitro model of the blood brain barrier and Caco-2 monolayers as a model of the intestinal epithelium, the present work investigates the effects of Pluronic P85 block copolymer (P85) on the transport of the P-gycoprotein (P-gp)- dependent probe, rhodamine 123 (R123). Methods. The permeability and cell efflux studies are performed with the confluent cell monolayers using Side-Bi-Side diffusion cells. Results. At concentrations below the critical micelle concentration, P85 inhibits P-gp efflux systems of the BBMEC and Caco-2 cell monolayers resulting in an increase in the apical to basolateral permeability of R123. In contrast, at high concentrations of P85 the drug incorporates into the micelles, enters the cells and is then recycled back out to the apical side resulting in decrease in Rl 23 transport across the cell monolayers. Apical to basolateral permeability of micelle-incorporated R123 in BBMEC monolayers was increased by prior conjugation of P85 with insulin, suggesting that modified micelles undergo receptor-mediated transcytosis. Conclusions. Pluronic block copolymers can increase membrane transport and transcellular permeability in brain microvessel endothelial cells and intestinal epithelium cells. This suggests that these block copolymers may be useful in designing formulations to increase brain and oral absorption of select drugs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011942814300
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  • 3
    Electronic Resource
    Electronic Resource
    Inhibition of Multidrug Resistance-Associated Protein (MRP) Functional Activity with Pluronic Block Copolymers (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 396-401 
    Details
    ISSN: 1573-904X
    Keywords: block copolymer ; cancer ; multidrug resistance ; Pluronic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Using monolayers of human pancreatic adenocarcinoma cells (Panc-1) that express multidrug resistance-associated protein (MRP), the present work investigates the effects of Pluronic block copolymers on the functional activity of MRP. Methods. The studies examined the accumulation and efflux of the MRP selective probe fluorescein (FLU) in Panc-1 cell monolayers with and without Pluronic P85 (P85), Pluronic L81 (L81) and Pluronic F108 (F108). Results. Treatment of Panc-1 cells with P85 resulted in concentration-dependent increases in FLU accumulation and elimination of FLU sequestration in vesicular compartments in these cells. The effects of P85 were selective for FLU in the Panc-1 cell monolayers. Inhibition of MRP-mediated transport was dependent on the composition of Pluronic block copolymer: the more hydrophobic copolymer had the greater effect on FLU uptake in Panc-1 monolayers (L81 〉 P85 〉 F108). Conclusions. This paper demonstrates for the first time that Pluronic block copolymers inhibit multidrug resistance-associated protein (MRP). The similarities in the effects of Pluronic block copolymers on MRP and P-glycoprotein drug efflux systems suggest that a single unifying mechanism may explain the inhibition observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018873702411
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  • 4
    Electronic Resource
    Electronic Resource
    Fundamental Relationships Between the Composition of Pluronic Block Copolymers and Their Hypersensitization Effect in MDR Cancer Cells (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 1373-1379 
    Details
    ISSN: 1573-904X
    Keywords: doxorubicin ; rhodamine ; multidrug resistance ; Pluronic ; block copolymers ; hypersensitization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Previous studies have demonstrated that Pluronic block copolymers hypersensitize multiple drug resistant (MDR) cancer cells, drastically increasing the cytotoxic effects of anthracyclines and other anticancer cytotoxics in these cells. This work evaluates the dose dependent effects of these polymers on (i) doxorubicin (Dox) cytotoxicity and (ii) cellular accumulation of P-glycoprotein probe, rhodamine 123 (R123) in MDR cancer cells. Methods. Dox cytotoxicity and R123 accumulation studies are performed on monolayers of drug-sensitive (KB, MCF-7, Aux-Bl) and MDR (KBv, MCF-7/ADR, CHrC5) cells. Results. Both tests reveal strong effects of Pluronic copolymers observed at concentrations below the critical micelle concentration (CMC) and suggest that these effects are due to the copolymer single chains ('unimers'). Using block copolymers with various lengths of hydrophobic propylene oxide (PO) and hydrophilic ethylene oxide (EO) segments these studies suggest that the potency of Pluronic unimers in MDR cells increases with elevation of the hydrophobicity of their molecule. Optimization of Pluronic composition in R123 accumulation and Dox cytotoxicity studies reveals that Pluronic copolymers with intermediate lengths of PO chains and relatively short EO segments have the highest net efficacy in MDR cells. Conclusions. The relationship between the structure of Pluronic block copolymers and their biological response modifying effects in MDR cells is useful for determining formulations with maximal efficacy with respect to MDR tumors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018942823676
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  • 5
    Electronic Resource
    Electronic Resource
    Competitive reactions in solutions of DNA and water-soluble interpolyelectrolyte complexes (1995)
    New York : Wiley-Blackwell
    Biopolymers 35 (1995), S. 523-531 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of competitive binding of two polyanions - DNA and synthetic fluorescence-tagged poly(methacrylate) (PMA*) - with the polycation-quencher poly(N-ethyl-4-vinyl-pyridinium) (PEVP) was studied by fluorescence quenching technique. It was found that ability of DNA to displace PMA *from the water-soluble nonstoichiometric interpolyelectrolyte complex (NPEC) formed by PMA* and PEVP - NPEC(PMA*-PEVP) - and to form water-soluble NPEC(DNA-PEVP) \documentclass{article}\pagestyle{empty}\begin{document}$$ NPEC(PMA^{*}\hbox{-}PEVP) + DNA \Leftrightarrow NPEC(DNA\hbox{-}PEVP) + PMA^{*}$$\end{document} can be determined by the parameter Ψ = PPMA*/PPEVP where PPMA* and PPEVP are the degrees of polymerization of PMA* and PEVP, respectively. In the case of Ψ 〈 1 the decrease of Ψ leads to the shift of the reaction equilibrium to the right, which can be explained by the gain of entropy due to the increase of the total number of polymeric particles in the solution. Introduction of alkali metal cations into the reaction mixture results in the shift of the reaction equilibrium, and according to their ability to shift the equilibrium to the right the cations can be arranged in the series Na+ 〉 K+ 〉 Li+. The substitution of native DNA by denatured DNA practically does not affect the reaction equilibrium in solutions of NaCl and KCl but considerably shifts it to the right in solutions of LiCl. The data obtained are in accordance with the differences in the selectivity of alkali cations binding with competitive polyanions. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360350511
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of Pluronic Block Copolymers on Drug Absorption in Caco-2 Cell Monolayers (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 850-855 
    Details
    ISSN: 1573-904X
    Keywords: block copolymer ; intestinal delivery ; drug ; micelles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The present work characterizes the effects of Pluronic copolymers on the transport of a P-gp-dependent probe, rhodamine 123 (R123) in Caco-2 cell monolayers. Methods. The accumulation and efflux studies were performed on the confluent Caco-2 monolayers using fluorescent probes with and without Pluronic copolymers. Results. At concentrations below the critical micelle concentration single chains ("unimers”) of Pluronic P85 enhanced the accumulation and inhibited the efflux of R123 in Caco-2 monolayers. The transport of the P-gp-independent probe, rhodamine 110 was not altered under these conditions. In contrast the micelles increased R123 accumulation to a much lower extent when compared to the unimers and enhanced R123 efflux in Caco-2 monolayers. Conclusions. Pluronic P85 unimers increase accumulation of a P-gp-dependent drug in Caco-2 monolayers through inhibition of the P-gp efflux system. The mechanism of the micelle effect is not known, however, it is very similar to the micelle effects in BBMEC. This has been previously shown to involve vesicular transport of the micelle-incorporated drug. The study suggests that Pluronic copolymers can be useful in increasing oral absorption of select drugs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011964213024
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature controllable interpolyelectrolyte substitution reactions (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1057-1062 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The competitive binding of fluorescence-tagged poly(methacrylate) polyanions and poly(phosphate) polyanions with different poly(N-alkyl-4-vinylpyridinium) polycation quenchers (alkyl = methyl, ethyl and propyl) was studied in the region 278÷333 K by fluorescence quenching technique. The equilibrium of this interpolyelectrolyte substitution reaction proved to be temperature sensitive except in the case when the poly(N-methyl-4-vinylpyridinium) polycation was used. Thermodynamic parameters of the reaction were determined. The possibility of effective temperature control of the interpolyelectrolyte reaction might be important for understanding, prediction and utilization of transformation processes of complex particles formed by electrostatically complementary (biological) macromolecules.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Manipulation of Electric Charge on Vesicles by Means of Ionic Surfactants: Effects of Charge on Vesicle Mobility, Integrity, and Lipid Dynamics (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 690-695 
    Details
    ISSN: 0947-6539
    Keywords: liposomes ; phospholipids ; surfactants ; vesicles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A combination of electrophoresis, dynamic light scattering, conductometry, and fluorescence spectroscopy was applied to investigate vesicles (both in the “solid” and “liquid” states) that had been imparted with electric charge through the incorporation of ionic amphiphiles. These amphiphilic compounds comprised cardiolipin (with two negative charges), sodium dodecyl sulfate (with one negative charge), and cetylpyridinium bromide (with one positive charge). By this means it was discovered that negative vesicles could be converted into neutral vesicles, and then into positive vesicles, by the addition of a cationic surfactant. The amount of cationic surfactant required for the conversion depended upon the mobility of the surfactant within the bilayer. Vesicles were found to be capable of absorbing large amounts of surfactant, both cationic and anionic, before ultimately disintegrating and releasing their contents. Mixtures of cationic and anionic vesicles were able to exchange surfactant, and thereby neutralize each other's charges, without any concurrent vesicle fusion. This phenomenon is reliable only if the vesicles are in the liquid state. Finally, a biphasic exchange process was observed in which a surfactant rapidly departs from one bilayer and then enters another, while a fluorescently labeled lipid travels the reverse path only slowly.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970030507
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