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Amyloid beta (Aβ) adsorption onto lipid membranes depending on the condition of a lipid was investigated by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aβ aggregation depending on the different hardness of lipid membrane has not been clarified yet although it is important to understand Alzheimer's disease. Aβ (1-40) on three different lipid membranes having different transition temperatures has been evaluated using ToF-SIMS in the previous study, and in this study, the differences between Aβ on liquid crystalline-phase lipid membranes and that on gel-phase lipid membranes were investigated in order to clarify the mechanisms of aggregation and peptide folding change. ToF-SIMS secondary ion images clearly showed Aβ distribution on lipid membranes. Because ToF-SIMS data is extremely complicated although it contains rich information, it was analysed by principal component analysis (PCA). Score images indicated by PCA are consistent with the images of secondary ions related to Aβ and are clearer than the secondary ion images. Moreover, PCA results suggest the difference between Aβ on different lipid membranes in terms of amino acid fragment ions, and the orientation of Aβ on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was indicated. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The adsorption behaviour of amyloid beta (Aβ), thought to be a key peptide for understanding Alzheimer's disease, was investigated by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aβ aggregates depending on the lipid membrane condition though it has not been fully understood yet. In this study, Aβ samples on different lipid membranes, 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC), were observed with ToF-SIMS and the complex ToF-SIMS data of the Aβ samples was interpreted using data analysis techniques such as principal component analysis (PCA), gentle-SIMS (G-SIMS) and g-ogram. DOPC and DMPC are liquid crystal at room temperature, while DPPC is gel at room temperature. As primary ion beams, Bi and Ar cluster ion beams were used and the effect of an Ar cluster ion for evaluating biomolecules was also studied. The secondary ion images of the peptide fragment ions indicated by G-SIMS and g-ogram were consistent with the PCA results. It is suggested that Aβ is adsorbed homogeneously on the liquid-crystalline-phase lipid membranes, while it aggregates along the lipid on the gel-phase lipid membrane. Moreover, in the results using the Ar cluster, the influence of contamination was reduced. [ABSTRACT FROM AUTHOR]

Abstract: The growth of giant vesicles (GVs) can be considered as a consecutive process of swelling/detachment/deformation, which is a response of lipid membranes on solid surfaces to the solvent and environmental factors such as temperature and ionic strength. The electroformation method allows to visualize the responses to such factors. The additive effect of the protein on the growth of GVs, composed of zwitterionic phospholipids, was herein investigated using the electroformation method. Proteins denatured by a pH-shift (to be in the Molten Globule state) perturbed the lipid membranes, resulting in the acceleration of GV growth. The GVs detached from the electrode showed deformation close to a stomatocyte. It was revealed that common factor for the response of lipid membranes was the variation of the apparent area elastic modulus associated with the interaction between proteins and lipid membranes. The present finding affords better understanding about the response of lipid membranes on solid surfaces under a variety of environment factors. [Copyright &y& Elsevier]

Abstract: The protofibrils of amyloid fibrils have recently drawn an attention due to their cytotoxicity although the physicochemical properties of the protofibrils as an intermediate of fibrillation process have still remained unclear. We investigated the growth behavior of the protofibrils of amyloid β protein with 40 amino acid residues in the presence of various liposomes and the membrane perturbation (calcein leakage). The growth behavior of protofibrils was apparently correlated with the protofibrils-induced calcein leakage. From the binding experiment using a hydrophobic fluorescence probe and the quartz crystal microbalance method combined with the planar lipid membrane, it is suggested that the apparent correlation between the growth behavior of protofibrils and their membrane perturbation resulted from the physicochemical properties of protofibrils such as hydrophobicity and the stability of hydrogen bonds. The protofibrils were found to show the highest hydrophobicity and the highest instability of hydrogen bonds of the proteins used in this study (monomer, protofibrils, matured fibrils, and other three typical proteins). It is anticipated that such properties of protofibrils were advantageous both for the binding of protofibrils with monomer (growth behavior) and for the binding of lipid bilayer membranes (membrane perturbation). [Copyright &y& Elsevier]

Abstract: The transfer of 22-NBD-cholesterol (22-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3-ol) between two liposome membranes was quantitatively analyzed by using the fluorescence resonance energy transfer (FRET) method. Liposomes labeled with both 22-NBD-cholesterol and a rhodamine-labeled phosphatidylethanolamine (Rh-DHPE) were used as donor liposomes, and the 22-NBD-cholesterol transfer from these donor liposomes to acceptor liposomes prepared from same type of phosphatidylcholine was monitored. The transfer kinetics was found to be composed of a fast and a slow phase, and all kinetic measurements could be fitted with a bi-exponential model. The results obtained indicate that the 22-NBD-cholesterol transfer kinetics between liposome membranes depends on the fluidity of the liposome used and that the curvature may affect the kinetics. Furthermore, the behavior of 22-NBD-cholesterol in lipid membrane is similar to that of the oxysterol 25-hydroxycholesterol rather than cholesterol. It is proposed that 22-NBD-cholesterol can be a useful fluorescent probe to mimic the intermembrane transfer of oxidized cholesterols like 25-hydroxycholesterol, rather than that of cholesterol itself. [Copyright &y& Elsevier]

Abstract: The permeation of calcein across the phospholipid bilayer membrane is a key phenomenon in the detection system using liposomes as a sensor unit. The behavior of the calcein release from the liposome was analyzed by a first-order kinetic to obtain the permeability coefficient, P s [cm/s]. The P s value for the neutral liposome, prepared by zwitterionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), was found to depend on both the diameter of liposome and the temperature. The membrane fluidity of the POPC liposome, evaluated by the hydrophobic probe, 1-(4-trimethyl-aminophenyl)-6-diphenyl-1,3,5-hexatriene, was also dependent on the liposome diameter and the temperature. The P s values for various neutral liposomes under gel phase or liquid-crystalline phase were correlated with their membrane fluidity, although some data were a little scattered, possibly due to the lamellarity. It is therefore considered that the membrane fluidity dominates the permeability of calcein across the neutral phospholipid membrane. Based on the above results, the P s value for liposomes immobilized on the solid surface is discussed. [Copyright &y& Elsevier]

Abstract: Based on a number of experiments it is concluded that the fluorescein labeled β-heptapeptide fluoresceinyl-NH-CS-(S)-β 3hAla-(S)-β 3hArg-(R)-β 3hLeu-(S)-β 3hPhe-(S)-β 3hAla-(S)-β 3hAla-(S)-β 3hLys-OH translocates across lipid vesicle bilayers formed from DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine). The conclusion is based on the following observations: (i) addition of the peptide to the vicinity of micrometer-sized giant vesicles leads to an accumulation of the peptide inside the vesicles; (ii) if the peptide is injected inside individual giant vesicles, it is released from the vesicles in a time dependent manner; (iii) if the peptide is encapsulated within sub-micrometer-sized large unilamellar vesicles, it is released from the vesicles as a function of time; (iv) if the peptide is submitted to immobilized liposome chromatography, the peptide is retained by the immobilized DOPC vesicles. Furthermore, the addition of the peptide to calcein-containing DOPC vesicles does not lead to significant calcein leakage and vesicle fusion is not observed. The finding that derivatives of the β-heptapeptide (S)-β 3hAla-(S)-β 3hArg-(R)-β 3hLeu-(S)-β 3hPhe-(S)-β 3hAla-(S)-β 3hAla-(S)-β 3hLys-OH can translocate across phospholipid bilayers is supported by independent measurements using Tb3+-containing large unilamellar vesicles prepared from egg phosphatidylcholine and wheat germ phosphatidylinositol (molar ratio of 9:1) and a corresponding peptide that is labeled with dipicolinic acid instead of fluorescein. The experiments show that this dipicolinic acid labeled β-heptapeptide derivative also permeates across phospholipid bilayers. The possible mechanism of the translocation of the particular β-heptapeptide derivatives across the membrane of phospholipid vesicles is discussed within the frame of the current understanding of the permeation of certain oligopeptides across simple phospholipid bilayers. [Copyright &y& Elsevier]

The dielectric response of lipid bilayer membrane vesicles (liposomes) prepared using either phosphatidylcholine from egg (EPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was analyzed at a frequency range of 0.1 to 100 MHz. A marked dielectric dispersion for EPC and POPC liposome suspensions was observed above 1 MHz. An appropriate analysis of the dielectric dispersion curve was performed using the Cole-Cole equation and the Debye equation and was found to provide a method for the determination of dielectric parameters. Among the dielectric parameters, the characteristic frequency of a second dispersion around 50 MHz varied corresponding with changes in the test conditions. Of particular note is that an anomalous change in the characteristic frequency in the presence of protein corresponded to the degree of hydrophobic interaction between proteins and liposomes. The value of the frequency around 50 MHz, as well as the decrease in permittivity over the frequency range tested, are indicators of the interaction between proteins and liposomes. [Copyright &y& Elsevier]

Abstract: The interaction between the neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes and cell membrane of Streptomyces griseus induced by the heat treatment at specific temperature was investigated, focusing on the internalization of the neutral POPC liposomes with S. griseus cells. In an attempt to clarify the modes of liposome internalization, various kinds of inhibitors of endocytotic pathways were used to treat S. griseus cells. The efficiency of the heat treatment on liposome–cell membrane interactions was finally characterized based on the hydrophobic, electrostatic interactions and hydration effect. In fact, the internalization of the neutral liposomes into these cells was found to show higher rate and greater amount at higher temperatures. The kinetic study showed that the maximum amount of the internalized liposomes was, respectively, 469×105 and 643×105 liposomes/cell at 37 and 41°C. The internalization of the neutral liposomes induced by the heat treatment was characterized, implying that the endocytosis occurred. The interactions involving the internalization, adsorption, and fusion of these liposomes with S. griseus cells were mainly contributed by the hydrophobic interaction and the unstable hydrogen bonds caused by the loss of water of surface hydration of cell membrane rather than the electrostatic interaction under the specific heat condition. [Copyright &y& Elsevier]

A catalytic reaction of H2O2 production by an amyloid β-peptide (Aβ)–Cu complex with cholesterol incorporated in a liposome was kinetically analyzed. The Michaelis–Menten model was applied to the H2O2 production reaction using cholesterol as the substrate catalyzed by the Aβ–Cu complex. The K m value for the Aβ–Cu complex catalytic reaction with cholesterol-containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes (K m=0.436 μM for Aβ(1–40); K m=0.641 μM for Aβ(1–42)) was found to be smaller than that with cholesterol-containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes (K m=0.585 μM for Aβ(1–40), K m=0.890 μM for Aβ(1–42)). The results imply that membrane properties could play an important role in the interactions of the Aβ–Cu complex with cholesterol in these liposomes. Considering the physical states of the cholesterol/POPC (liquid disordered phase) and cholesterol/DPPC (liquid ordered phase) liposomes in the present reaction conditions, the data obtained suggests that the H2O2-generating activity of the Aβ–Cu complex, accompanied by oxidation of membrane-incorporated cholesterol, could be effected by the phase of the liposome membranes. [Copyright &y& Elsevier]

Abstract: An antioxidative liposome catalyst, LIPOzyme, that mimics both superoxide dismutase (SOD) and peroxidase (POD)-like activities has been developed by using liposomes modified with simple ligands (dodecanoyl-histidine, Dodec-His) and metal ions (Mn). The SOD-like activity is dependent on the stability of the ligand–metal complex on the liposome membrane, with the value being higher for the DPPC liposome and at a higher pH. The POD-like activity was found to be maximal in the case of DMPC liposome, in which the ligand–metal complex is inserted more deeply into the membrane. It was thus shown that liposome modified with simple ligands can exhibit different enzyme-like activities depending on the characteristics of the liposome membrane. [Copyright &y& Elsevier]

Abstract: Hydrophobic interactions between nine model proteins and net-neutral lipid bilayer membranes (liposomes) under stress conditions were quantitatively examined by using immobilized liposome chromatography (ILC). Small or large unilamellar liposomes were composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and immobilized in a gel matrix by utilizing covalent coupling between amino-containing lipids and activated gel beads or avidin–biotin biospecific binding. Retardation of bovine carbonic anhydrase (CAB) in ILC was pronounced at particular temperatures (50 and 60°C) where the local hydrophobicity of theses protein molecules becomes sufficiently large. Protein-induced leakage of a hydrophilic dye (calcein) from immobilized liposomes interior was also drastically enhanced at particular temperatures where large retardation was observed. For other proteins examined, similar results were also observed. The specific capacity factor of the proteins characteristic for the ILC and the amount of calcein released from immobilized liposomes were successfully expressed as a function of the product of the local hydrophobicities of proteins and liposomes, regardless of protein species and the type of the stress conditions applied (denaturant and heating). These findings indicate that lipid membranes have an ability to non-specifically recognize local hydrophobicities of proteins to form stress-mediated supramolecular assemblies with proteins, which may have potential applications in bioprocesses such as protein refolding and separation. ILC was thus found to be a very useful method for the quantitative detection of dynamic protein–liposome interactions triggered by stress conditions. [Copyright &y& Elsevier]

A biological membrane is the front line of defense for cells against various environmental stresses such as heat and reactive oxygen species (ROS) and is expected to play an important role in the antioxidant system with antioxidant enzymes, similarly to its chaperone-like function in cooperation with heat shock proteins. The oxidative stress response of superoxide dismutase (SOD), which is known to catalyze the dismutation of O2 − to H2O2, was investigated in the presence of artificial membranes, liposomes, in order to obtain fundamental information on the biological ROS scavenging system. SOD lost its activity in the presence of H2O2 and was found to have two loops including one which contains an α-helix which presents the substrate O2 − to the activity center of SOD (Cu(II)). From circular dichroism analysis of SOD in the presence of H2O2, the contents of the α-helix in SOD were found to decrease in correspondence with the inactivation and conformational change of SOD, suggesting that the conformation of the α-helix loops affects SOD activity. In the presence of liposomes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), SOD was not inactivated in the presence of H2O2 although the contents of its α-helix structure were decreased. The oxidized SOD was found to interact with the liposome surface under oxidative stress using dielectric dispersion analysis. Based on these results, a possible mechanism of SOD protection against ROS on liposomes was presented. [Copyright &y& Elsevier]