g(m1)-ganglioside and 1-2-dielaidoylphosphatidylethanolamine

Acid-sensitive liposomes composed of unsaturated phosphatidylethanolamine (PE) are efficient vehicles for cytoplasmic delivery of the target cells. We have recently shown that liposomes composed of dioleoyl-PE (DOPE) and dipalmitoyl-succinylglycerol (DPSG) retain the acid-sensitivity after exposure to human plasma. In the present work, we have extended these observations to investigate the role of ganglioside GM1 on the blood residence time of these liposomes. Small (d approximately 100 nm) unilamellar liposomes composed of DOPE and DPSG (4:1, molar ratio) became progressively less acid-sensitive when increasing amounts of GM1 were included in the lipid composition. However, partial sensitivity to acid (40-50% release of entrapped contents at pH 4) could be retained up to 5% GM1, even for liposomes which had been exposed to human plasma. Inclusion of GM1 in the lipid composition only slightly increased the release of entrapped contents in the presence of human plasma. The biodistribution of i.v. injected GM1-containing liposomes was studied by following the entrapped 125I-labeled tyraminylinulin marker in Balb/c mice. Inclusion of up to 5% GM1 showed a transient increase in the blood level and a concomitant decrease of liver and spleen uptake of liposomes. Thus, these liposomes are pH-sensitive, plasma-stable and show a relatively prolonged residence time in circulation. They are potentially significant drug carriers in vivo.

Topics: Animals; Drug Stability; Fluoresceins; G(M1) Ganglioside; Humans; Hydrogen-Ion Concentration; Inulin; Kinetics; Liposomes; Liver; Mice; Mice, Inbred BALB C; Phosphatidylethanolamines; Plasma; Spleen; Triglycerides; Tyramine

A novel type of liposome bilayer destabilization catalyzed by the enzyme, beta-galactosidase, is described. Unsaturated phosphatidylethanolamine (PE), an HII-phase-forming lipid, does not form stable liposomes at physiological temperature and pH. However, stable unilamellar liposomes can be prepared by mixing PE with a minimum of 5 mol% ganglioside GM1, a micellar-phase-forming lipid. Treatment of these GM1/PE liposomes with beta-galactosidase induces a rapid leakage (3-6 min) of the entrapped fluorescent dye, calcein. The studies indicate that liposome destabilization is the result of catalytic degradation of GM1, rather than a stoichiometric binding of GM1 by beta-galactosidase. Kinetic data indicate that the destabilization takes place via liposome collision. This simple, rapid method of liposome destabilization by beta-galactosidase will be useful in designing a liposome-based signal amplification mechanism for assays involving enzymes.

Topics: beta-Galactosidase; Drug Stability; Fluoresceins; Fluorescent Dyes; G(M1) Ganglioside; Galactosidases; Hydrogen-Ion Concentration; Kinetics; Lipid Bilayers; Liposomes; Phosphatidylethanolamines; Temperature

Two-dimensional crystals of cholera toxin bound to receptors in a lipid membrane give diffraction extending to 15 A resolution. Three-dimensional structure determination reveals a ring of five B subunits on the membrane surface, with one-third of the A subunit occupying the center of the ring. The remaining mass of the A subunit appears to penetrate the hydrophobic interior of the membrane. Cleavage of a disulfide bond in the A subunit, which activates the toxin, causes a major conformational change, with the A subunit mostly exiting from the B ring.

Topics: Cholera Toxin; G(M1) Ganglioside; Liposomes; Macromolecular Substances; Microscopy, Electron; Models, Molecular; Phosphatidylethanolamines; Protein Conformation