The influence of the internal content of negatively charged liposomes on their interaction with high‐density lipoprotein

Abstract

The release of the internal content of negatively charged phosphatidylcholine/phosphatidylserine vesicles under the influence of high density lipoprotein was studied. Under standard conditions (the same composition outside and inside the compartment) the leakage of negative liposomes increased significantly. However, a high internal concentration of calcein provoked a sealing effect, exhibited both in sucrose and in calcein release. This sealing effect is not related to the size of vesicles, the fluidity of the membrane, the distribution of phosphatidylserine molecules, or the membrane potential. Our data indicate that surface potential influences this effect, probably in addition to a lateral pressure effect such as with cholesterol. The surface potential, as measured by the water-lipid partition coefficient of fatty acids, is strongly affected by internal ionic strength when liposomes contain calcein as well as other polyanions (6-carboxyfluorescein, sodium citrate).The liposome-mediated transfer of drugs to cells is currently the object of many investigations (see [l] for a review). Numerous factors are crucial to the transfer: the encapsulation ratio, the stability of vesicles in serum, the overall clearance rate, the specificity of the interaction and the internalization yield of vesicles. The influence of many of these different factors has been analyzed, viz. size, charges, or composition of vesicles. Several generally accepted rules appear to be applied by most authors. For instance, negatively charged vesicles in a liquid crystal state are often used. Cholesterol is generally added in order to restrain the HDL-provoked leakage of the internal content of the liposomes. With this procedure, a weak internalization yield is obtained, even in uitro where poly(ethy1ene glycol) can be added to increase the fusion process [2].The role of HDL particles in the disruption of PtdCho vesicles is now well documented [3], but almost nothing is known about HDL-negatively charged vesicles interactions. In order to assess the use of this kind of liposome in uivo, we investigated its interaction with serum lipoproteins. This paper is devoted to the influence of the internal content of negative vesicles on their interaction with HDL particles. We show that high internal ionic strength decreases the vesicles surface potential. This leads to a very strong attenuation of HDLvesicle interaction, corresponding to a sealing effect analogous to the one observed with cholesterol.

Membrane Anchorage Brings About Fusogenic Properties in a Short Synthetic Peptide

“…First, intentionally, we synthesized a short peptide, to avoid its ability to traverse the membrane. Second, the system contains a relative high mole ratio of cholesterol, which will favor membrane sealing (Anholt et al, 1982;Vidal et al, 1984). The relative contribution of each of these parameters to the nonleakiness cannot be assessed from the present data.…”

LDL-mediated targeting of liposomes to leukemic lymphocytes in vitro.

“…The unencapsulated markers ([3H]sucrose or calcein) or drug (Hygromycin B) were removed by gel-filtration on an AcA 202 column (1.5 x 10 cm). The internal volume was measured as previously described (Vidal et al, 1984) by the assay of [3H]sucrose encapsula-2466 tion. Phospholipid concentration was determined according to the method of Bartlett (1959).…”

“…Small unilamellar vesicles were prepared from mixtures of phosphatidylcholine (12 jimol on an AcA 202 column (1.5 x 10 cm). The internal volume was measured as previously described (Vidal et al, 1984) PDP-DPPE distribution in the two leaflets of the lipid bilayer was measured by adding DTT (10 mM) to the liposome suspension, which freed 2-thiopyridone exposed on both leaflets of the membrane, or by adding coenzyme A (5 mM) which freed it only on the outer leaflet. The 2-thiopyridone (2-TP) released was measured spectrophotometrically at 343 nm using a molar extinction coefficient of 8.08 x103 M/cm .…”

Pharmacokinetic characterization of phosphatidylserine liposomes in the rat

“…A significant incorporation of liposomal phospholipids occurs also in plasma by high density lipoproteins (HDL) (see, e.g. Scherphof et al, 1978;Vidal et al, 1984;William & Tall, 1988 liposomes (Damen et al, 1981), or the concentration of HDL phospholipid is in excess over that of liposomes (Bienvenue et al, 1985) phospholipid transfer from liposomes to HDL is an irreversible process, the rate of which depends solely on the liposomal phospholipid concentration. Phospholipids incorporated into HDL are then removed from plasma by reactions involving the uptake of the whole lipoprotein or the independent movement of the lipid moiety (Eisenberg, 1984).…”