Liposome surface potential

Another membrane property physically affected by flavonoids is the surface potential. Working with liposomes composed of PC and PS, we found that (—)-epicatechin and certain procyanidins (dimer to hexamer) decreased liposome surface potential. This effect relied on both, procyanidin concentration and number of monomeric units [Verstraeten et al., 2003]. On the other hand, when liposomes were composed exclusively of PC, it was found that (—)-epi-catechin dimers Al and B2, and the trimers A and C2 increased liposome surface potential in a concentration-dependent manner [Verstraeten et al.,... 

The surface potential can play an important role in the behavior of liposomes in vivo and in vitro (e.g.. Senior, 1987). In general, charged liposomes ai e more stable against aggregation and fusion than uncharged vesicles. However, physically stable neutral liposomes have been described (e.g.. Van Dalen et al., 1988). They are sufficiently stabilized by repulsive hydration forces, which counteract the attractive van der Waals forces. 

In order to obtain an estimate of the surface potential, the C potential of individual liposomes can be measured (>0.2 ym) by microelectrophoresis (e.g., Crommelin, 1984). This technique also offers the opportunity to detect the presence of structures with deviating electrophoretic mobility and, therefore, deviating composition. 

An alternative approach is the use of pH-sensitive fluorophores (Lichtenberg and Barenholz, lOSS). These probes are located at the lipid-water interface and their fluorescence behavior reflects the local surface pH, which is a function of the surface potential at the interface. This indirect approach allows the use of vesicles independent of their particle size. Recently, techniques to measure the C potential of Liposome dispersions on the basis of dynamic light scattering became commercially available (Muller et al., 1986). 

Austin et al. [132] measured the ionic strength dependence of the liposome-water distribution of several acidic and basic drugs and modelled the data with a combination of electrostatic and ion pair models. They concluded that the increased apparent Dmw values at higher ionic strength were due primarily to the reduction in surface potential and not to ion pairing. Ion pairing was also excluded because the apparent Dmw varied at fixed ionic strength with the... 

M. S. Fernandez, Determination of surface potential in liposomes, Biochim. Biophys. Acta 646, 23-26 (1981). 

Woodle M, et al. Sterically stabilized liposomes. Reduction in electrophoretic mobility but not electrostatic surface potential. Biophys J 1992 61 902. 

The charge on the liposomal surface is a property that has major effects on the stability, biodistribution, and cellular uptake of liposomes, and is governed by lipid headgroup composition and by pH. It can be monitored by micro electrophoresis (i.e., capillary zone electrophoresis), or by measurement of the zeta potential (Egorova, 1994). 

The opposite effect, the inhibition of PKC, has also been studied. It was concluded that inhibition by mono- and divalent cations is related to the reduction of surface potential of the studied PS/PC liposomes by ion binding according to the Gouy-Chapman theory. Later, the same authors studied the inhibitory effect of the local anesthetics tetracaine and procaine on PKC in liposomes [10]. The local anesthetics significantly reduced the negatively charged surface potential, T, of phospholipid bilayers. The anesthetics were even capable of changing the surface potential to... 

The surface-modified purpose-specific versions of liposomes (mannosylated liposomes) offer potentials of exquisite levels of specificity and targetability. The affinity and selectivity of the... 

Two pivotal discoveries enabled the full potential of liposomes to be realized. The first was the discovery in the late 1980s and early 1990s that the presence of additional molecules such as poly(oxyethylene) bonded onto the liposome surface deaeased their clearance by partially preventing liver and spleen uptake of i.v. injected liposomes. These are now often referred to as stealth liposomes as this effect enables them to escape recognition by the liver and spleen with the benefit of long circulation times. This observation was made almost in parallel with the discovery that polystyrene nanoparticles coated with a poly(oxyethylene) polymer also showed reduced fiver and spleen uptake. It is likely that a reduction in the coating of these liposomes by plasma proteins (opsonization), and their reduced aggregation in the blood are responsible for the increased circulation time of... 

The measurements of the electrophoretic mobility of liposomes, cells, and organelles/ By this method, one can observe the -potential of the cell surface. It will be seen later (electrokinetic potential) that this potential ( ) can be related to the surface potential. 

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