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  • 1. Awad, Doaa
    et al.
    Damian, Luminita
    Winterhalter, Mathias
    Karlsson, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Edwards, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry.
    Gabel, Detlef
    Interaction of Na2B12H11SH with dimyristoyl phosphatidylcholine liposomes.2009In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 157, no 2, p. 78-85Article in journal (Refereed)
    Abstract [en]

    Previous investigations have revealed that the boron cluster compound Na2B12H11SH (BSH) is very potent in causing major structural rearrangements of and leakage from phosphatidylcholine liposomes. This somewhat unexpected finding is interesting from a fundamental point of view and may also constitute the basis of future important pharmaceutical/medical applications of BSH. In order to further explore the BSH-lipid interaction, we have studied the effects caused by BSH on dimyristoyl phosphatidylcholine (DMPC) liposomes.

    Cryo-transmission electron microscopy showed that BSH induces aggregation, membrane rupture and increasing wall thickness of the liposomes. Differential scanning calorimetry revealed a BSH dependent shift of the gel to liquid crystalline phase transition temperature of DMPC. The zeta potential of the liposomes decreases with increasing BSH concentrations, and an apparent dissociation constant of 0.23 mM was found.

    BSH caused leakage of liposome-encapsulated carboxyfluorescein; leakage was higher at 23 °C (near the phase transition temperature) than at 15 °C and 37 °C. It induced lipid mixing only at very high concentrations.

  • 2.
    Eriksson, Emma K
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Agmo Hernández, Víctor
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
    Choice of cuvette material can influence spectroscopic leakage and permeability experiments with liposomes.2018In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 215, p. 63-70, article id S0009-3084(18)30129-4Article in journal (Refereed)
    Abstract [en]

    Liposome solute permeability experiments are widely performed to gain information about lipid membrane characteristics. Spectroscopic methods are often used for this purpose, usually monitoring the leakage of a self-quenching fluorescent dye (e.g., carboxyfluorescein, CF) from the liposomes. Hereby, we investigate the effect of liposome-cuvette interactions, a seldom considered detail, on the results obtained from liposomal permeability experiments. The spontaneous leakage of CF from liposomes with different surface properties and phase states is followed using quartz and polystyrene cuvettes, and the results are compared. It is shown that for most lipid compositions the leakage profiles vary notably between different cuvette materials. Reproducibility of the measurements also varies depending on the cuvettes used, with polystyrene providing with more robust results. To explain these observations, the interaction of liposomes with polystyrene and quartz-like surfaces was characterized with the help of the quartz crystal microbalance with dissipation monitoring (QCM-D). Our results show that, while liposomes seldom interact with polystyrene, quartz-liposome interactions are almost unavoidable and have a large impact on the leakage experiments mainly via two mechanisms: i) the rupturing of liposomes on the cuvette surface causing a fast release of encapsulated CF, and ii) the disruption of adsorbed liposomes caused by magnetic stirring. Depending on their composition, the liposomes interact in different ways with quartz, affecting thus the extent of each proposed mechanism. The experiments demonstrate the importance of considering the cuvette material when planning and conducting spectroscopic experiments with liposomes.

  • 3.
    Moulin, Martine
    et al.
    Inst Laue Langevin, Grenoble, France; Keele Univ, Fac Nat Sci, Staffs, England.
    Strohmeier, Gernot A.
    Acib, Austrian Ctr Ind Biotechnol GmbH, Graz, Austria; Graz Univ Technol, Inst Organ Chem, NAWI Graz, Graz, Austria.
    Hirz, Melanie
    Graz Univ Technol, Inst Mol Biotechnol, BioTechMed Graz, NAWI Graz, Graz, Austria.
    Thompson, Katherine C.
    Univ London, Birkbeck Coll, Dept Biol Sci, London, England; Univ London, Birkbeck Coll, Inst Struct & Mol Biol, London, England.
    Rennie, Adrian R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Campbell, Richard A.
    Inst Laue Langevin, Grenoble, France.
    Pichler, Harald
    Acib, Austrian Ctr Ind Biotechnol GmbH, Graz, Austria; Graz Univ Technol, Inst Mol Biotechnol, BioTechMed Graz, NAWI Graz, Graz, Austria.
    Maric, Selma
    Malmö Univ, Fac Hlth & Soc, Biofilms Res Ctr Biointerfaces, Malmö, Sweden; Malmö Univ, Fac Hlth & Soc, Biomed Sci Dept, Malmö, Sweden.
    Forsyth, V. Trevor
    Inst Laue Langevin, Grenoble, France; Keele Univ, Fac Nat Sci, Staffs, England.
    Haertlein, Michael
    Inst Laue Langevin, Grenoble, France.
    Perdeuteration of cholesterol for neutron scattering applications using recombinant Pichia pastoris2018In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 212, p. 80-87Article in journal (Refereed)
    Abstract [en]

    Deuteration of biomolecules has a major impact on both quality and scope of neutron scattering experiments. Cholesterol is a major component of mammalian cells, where it plays a critical role in membrane permeability, rigidity and dynamics, and contributes to specific membrane structures such as lipid rafts. Cholesterol is the main cargo in low and high-density lipoprotein complexes (i.e. LDL, HDL) and is directly implicated in several pathogenic conditions such as coronary artery disease which leads to 17 million deaths annually. Neutron scattering studies on membranes or lipid-protein complexes exploiting contrast variation have been limited by the lack of availability of fully deuterated biomolecules and especially perdeuterated cholesterol. The availability of perdeuterated cholesterol provides a unique way of probing the structural and dynamical properties of the lipoprotein complexes that underly many of these disease conditions. Here we describe a procedure for in vivo production of perdeuterated recombinant cholesterol in lipid-engineered Pichia pastoris using flask and fed-batch fermenter cultures in deuterated minimal medium. Perdeuteration of the purified cholesterol was verified by mass spectrometry and its use in a neutron scattering study was demonstrated by neutron reflectometry measurements using the FIGARO instrument at the ILL.

  • 4. Schaffran, Tanja
    et al.
    Li, Jingyu
    Karlsson, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Edwards, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Physical Chemistry.
    Winterhalter, Mathias
    Gabel, Detlef
    Interaction of N,N,N-trialkylammonioundecahydro-closo-dodecaborates with dipalmitoyl phosphatidylcholine liposomes2010In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 163, no 1, p. 64-73Article in journal (Refereed)
    Abstract [en]

    N,N,N-Trialkylammonioundecahydrododecaborates (1-), a novel class of compounds of interest for use as anions in ionic liquids, interact with DPPC liposomes. Increasing compound concentration causes an increasing negative zeta potential. Dissociation constants demonstrate that the binding capacity increases strongly with longer chain length. N,N,N-Trialkylammonioundecahydrododecaborates with longer alkyl chains show a detergent-like behavior: the compounds incorporate into the liposome membrane and differential scanning calorimetric experiment show already low concentrations cause a complete disappearance of the peak representing the gel-to-liquid crystalline phase transition. In contrast, compounds with shorter alkyl chains only interact with the headgroups of the lipids. Investigations by means of cryo-TEM reveal that all derivatives induce significant morphological changes of the liposomes. N,N,N-Trialkylammonioundecahydrododecaborates with short alkyl chains produce large bilayer sheets, whereas those with longer alkyl chains tend to induce the formation of open or multi-layered liposomes. We propose that the binding of N,N,N-trialkylammonioundecahydrododecaborates is mainly due to electrostatic interactions between the doubly negatively charged cluster unit and the positively charged choline headgroup; the positively charged ammonium group might be in contact with the deeper-lying negatively charged phosphate. For N,N,N-trialkylammonioundecahydrododecaborates with longer alkyl chains hydrophobic interactions with the non-polar hydrocarbon part of the membrane constitute an additional important driving force for the association of the compounds to the lipid bilayer.

  • 5.
    Silvander, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Johnsson, Markus
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Edwards, Katarina
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical Chemistry.
    Effects of PEG-lipids on permeability of phosphatidylcholine/cholesterol liposomes in buffer and in human serum1998In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 97, no 1, p. 15-26Article in journal (Refereed)
    Abstract [en]

    The permeability of liposomal membranes was studied as a function of the amount of incorporated PEG-lipid. The fluorescent dyes ethidium, propidium and 5(6)-carboxy fluorescein were used as markers for measurements of spontaneous leakage. The results show that addition of up to 8 mol% of PEG(2000)-DSPE into liposomal membranes of DSPC/Cho and EPC/Cho reduces the permeability of carboxyfluorescein in buffer solution. In contrast, the leakage of the more amphiphilic dye ethidium was not to any measurable extent affected by PEG-lipid inclusion. Another important difference was that ethidum leakage showed a clear dependence on temperature whereas leakage of carboxyfluorescein from pegylated liposomes did not. We conclude that the mechanisms by which the two dyes permeate the liposomal bilayer are qualitatively different. Both ethidium and carboxyfluorescein did interact with human serum components in a way that made measurements in serum unreliable. The more hydrophilic ethidium analogue propidium was shown not to interact with human serum components to any detectable extent. This made propidium suitable for permeability determinations in human serum. It was found that liposomes composed of pure EPC or EPC with 5 mol% DSPE-PEG, displayed a dramatic increase in permeability when subjected to a medium composed of 20% human serum in buffer. Addition of 40 mol% cholesterol to the EPC bilayers reduced the observed release rate in human serum substantially, whereas no stabilizing effect was observed upon PEG-lipid inclusion.

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