muramidase and 1-2-bis(10-12-tricosadiynoyl)phosphatidylcholine

Membrane-modification effects, induced by ultraviolet (UV) irradiation in diacetylenic liposomes, were analyzed upon contact with cells, biological membranes, and proteins. Liposomes formulated with mixtures of unsaturated 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine and saturated 1,2-dimyristoyl-sn-glycero-3-phosphocholine, in a 1:1 molar ratio, were compared with those that were UV-irradiated and analyzed in several aspects. Membrane polymerization inherence on size stability was studied as well as its impact on mitochondrial and microsomal membrane peroxidation induction, hemolytic activity, and cell viability. Moreover, in order to gain insight about the possible irradiation effect on interfacial membrane properties, interaction with bovine serum albumin (BSA), lysozyme (Lyso), and apolipoprotein (apoA-I) was studied. Improved size stability was found for polymerized liposomes after a period of 30 days at 4°C. In addition, membrane irradiation had no marked effect on cell viability, hemolysis, or induction of microsomal and mitochondrial membrane peroxidation. Interfacial membrane characteristics were found to be altered after polymerization, since a differential protein binding for polymerized or nonpolymerized membranes was observed for BSA and Lyso, but not for apoA-I. The substantial contribution of this work is the finding that even when maintaining the same lipid composition, changes induced by UV irradiation are sufficient to increase size stability and establish differences in protein binding, in particular, reducing the amount of bound Lyso and BSA, without increasing formulation cytotoxicity. This work aimed at showing that the usage of diacetylenic lipids and UV modification of membrane interfacial properties should be strategies to be taken into consideration when designing new delivery systems.

Topics: Animals; Apolipoprotein A-I; Cattle; Cell Line, Transformed; Cell Survival; Dimyristoylphosphatidylcholine; Diynes; Erythrocytes; Hemolysis; Lipid Bilayers; Lipid Peroxidation; Liposomes; Mice; Microscopy, Electron, Scanning; Muramidase; Particle Size; Phosphatidylcholines; Polymerization; Protein Binding; Serum Albumin; Ultraviolet Rays

A novel electron microscopy specimen protocol shows that the presumed phospholipid bilayer membrane ribbons that wind helically to form the cylinders known as "tubules" are actually flattened tubes. These flattened tubes are alternatively found with a helical twist about the tube's long axis or occasionally flat with no winding or twist. Flat, cylindrically wound and axially twisted segments are routinely found along a single tube's length, and at the helically wound and axially twisted segment junctions, the chiral sense of the structure often, but not always, changes chiral sense.

Topics: Diynes; Freeze Fracturing; Lipid Bilayers; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Muramidase; Phosphatidylcholines

The presence of protein in tubule-forming solutions of the diacetylenic phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine results in the formation of hollow cones rather than the expected hollow cylinders. Differential phase-contrast video microscopy reveals that cones grow from proteinaceous nodules in a fashion similar to cylindrical tubule growth from spherical vesicles. Spatially resolved electron-beam energy-dispersive X-ray fluorescence spectroscopy shows the protein to be associated with the cone wall. Small-angle X-ray scattering shows that, like the protein-free cylinders, the cones are multilamellar with essentially identical interlamellar spacing.

Topics: Diynes; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Muramidase; Phosphatidylcholines; Phospholipids; Phosphorylcholine; Scattering, Radiation; X-Rays