Liposome model

Anthocyanins and anthocyanidins, compounds present with high structural diversity in fruits and wines, showed a pattern as antioxidants different from that of the tea catechins with respect to the effect of substituents. In a liposomal model system induced peroxidation was inhibited increasingly by anthocyanins/ anthocyanidins with an increasing number of hydroxyl groups in the B-ring (Fig. 16.6), while the opposite was seen for the catechins (Seeram and Nair, 2002). For anthocyanidins, the presence of a 3-hydroxy group is important... 

The Case for Charged-Species Transport from Cellular and Liposomal Models... 

Yasuda, T., Dancey, G.F., and Kinsky, S.C. (1977) Immunogenicity of liposomal model membranes in mice Dependence on phospholipid composition. Proc. Natl. Acad. Sci. USA 74, 1234-1236. 

Another way to assess ion channel conductance is to use artificial phospholipid vesicles (liposomes) as cell models. These structures (described in more detail in the next chapter) are commonly used to transport vaccines, drugs, enzymes, or other substances to target cells or organs. The vesicles, which are several hundred nanometres in diameter, do not suffer from interference from residual natural ion channel peptides or ionophores, unlike purified natural cells. A liposome model was used to test the ion transport behaviour of the redox-active hydraphile 12.36. The compound transports Na+ and the process can also be monitored using 23Na NMR spectroscopy.26 The presence of the ferrocene-derived group in the central relay allows the ion transport to be redox-controlled - oxidation to ferrocinium completely prevents Na+ transport for electrostatic reasons. Some representative data from a planar bilayer measurement is shown for hydraphile 12.36 in Figure 12.16. 

Most of the responses which lead to cytochrome c release are triggered by activated proapoptotic members of the Bcl-2 family which are directed to mitochondria, where they insert into the outer membrane. What mediates the specific targeting of these proteins to mitochondria. In a recent work, Lutter et al. (2000) investigated this question using the proapoptotic Bcl-2 member (tBid) as a tool. These authors established a liposome model for cytochrome c release and recreated the lipid constitution of mitochondrial outer... 

For this purpose liposomes are used as lipid phase. Unilamellar liposomes are artificial lipid bilayer vesicles. They can be considered as real model bilayer membranes as they ideally consist of a circular bilayer membrane. The hydrophobic acyl chains are assembled in the hydrophobic core of the liposome whereas the hydrophilic head groups point to the water in the inside and outside of the vesicle. Liposomes can be produced from a variety of lipids and from mixtures of lipids. This possibility allows studying the influence of membrane constituents on the partition of solutes. Kramer et al. (1997) studied the influence of the presence of free fatty acids in membranes on the partition behaviour of propranolol. The influence on a-Tocopherol in membranes on the partition behaviour of desipramine has been reported recently (Marenchino et al. 2004) using a liposome model. 

Corver, J., Ortiz, A., Allison, S. L., Schalich, J., Heinz, F. X., and Wilschut, J. (2000). Membrane fusion activity of tick-borne encephalitis virus and recombinant subviral particles in a liposomal model system. Virology 269, 37-46. 

Rybak ME. Glycoproteins Ilb and Ilia and platelet thrombospondin in a liposome model of platelet aggregation. Thromb Haemost 1986 55 240-245. 

Indole-3-acetic and derivatives with e.g. methyl or methoxy substituents (to vary the ease of oxidation) were oxidized by horseradish peroxidase in the presence of mammalian cells [73]. Substantial cell kill was observed, but treatment with either drug or enzyme alone was ineffective however, similar cytotoxic effects were observed even if the indole was oxidized without cells present and the oxidation products then added to cells. This ruled out peroxyl radicals themselves as the challenging species (the original hypothesis), even though lipid peroxidation and protection by antioxidants (ascorbate, a-tocopherol) was observed in liposome models [23,158,159]. Further biological studies have been summarized [160]. 

An extension of the Tanford s (1980) treatment of the shapes of micelles, based on the molecular-shape analysis and the concept of the shape parameter (ratio between the nonpolar and polar cross-section areas), was introduced by Israelachvili (1991) for a qualitative understanding of the topology of lipid aggregates with different lipid compositions. However, the liposome models are approximate, and a rigorous thermodynamic analysis fails because liposomes are not at the thermodynamic equilibrium. The rigorous analysis would yield a very narrow size distribution, which is never observed in practice, as well as the spontaneous formation, while a high-energy process is typically needed to produce liposomes. 

Whatever the mode of attachment of SIg to cell membranes, the major portion of the Fc part of the molecule is not embedded in the phospholipid bilayer. This is also supported by the fact that CD spectra of all membrane proteins (not lymphocytes specifically) show little conformation, which, as previously mentioned, is the conformation of immunoglobulin domains. Experiments with reconstituted lymphocyte plasma membranes (Chavin and Holliman, 1975) and model membrane systems (Weissman et al., 1974) have not, in general, been very revealing. With reconstituted membranes, very little of the original membrane immunoglobulin becomes reincorporated. Liposome models were tested by... 

Zhang, X., Xiong, Y.L., Chen, J., Zhou, L., 2013. Synergistic inhibition of lipid oxidation by pea protein hydrolysate coupled with licorice extract in a liposomal model system. Journal of Agricultural and Food Chemistry 61, 8452—8461. 

Epigallocatechin gallate suppressed the initiation rate and prolonged the lag phase duration of per-oxyl radical-induced oxidation in a phospholipid liposome model to a greater extent (P <0.01) compared to both Trolox and a-tocopherol (Hu and Kitts 2001). 

Szebeni, J. Winterbomn, C. C., and Cartell, R. W., 1984, Oxidative interactions between hemoglobin and membrane lipid. A liposome model, Biochem. J. 220 685-692. 

Balasinska B, Troszynska A. Total antioxidative activity of evening primrose (Oenothera paradoxa) cake extract measured in vitro by liposome model and murine L1210 cells. J Agric Food Chem 1998 46 3558-3563. 

Dinitrophenyl dipalmitoylphosphatidylethanolamine (DNP-DPPE) is well known for its potential as an antigen in the preparation of immunologically responsive liposomal model [1, 2]. It has been found that this compound was capable of actively sensitizing liposomes toward antibody complement. However, the physicochemical properties of the membrane of DNP-DPPE, especially those of the monolayer at an air/water interface, are not yet clear. As the dinitrophenyl group plays an important role in some immunological reactions, the interaction... 

The in vitro affinity of the modified polymers for cell membranes was examined using a negatively charged liposome model [25]. The experimental principle is illustrated in Fig. 5. An interaction of the polymer with the liposomal membranes usually causes a perturbation of the bilayer. This per-... 

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