ABSTRACT
We have investigated the influence of ethanolamine plasmalogens on iron-induced oxidation of arachidonic acid in dipalmitoylphosphatidylcholine (DPPC) vesicles. Lipoperoxidation was induced by the addition of 50 microM FeSO4 and studied above (50 degrees C) and below (15 degrees C) the gel-to liquid transition temperature of the vesicles, at two different pH values (7.4 or 6.4). The extent of peroxidation was measured as thiobarbituric reactive product formed and the influence exerted by ethanolamine plasmalogens (PEPL) in this process was compared to that of dipalmitoylphosphatidylethanolamine (DPPE) and diacylphosphatidylethanolamines (DAPE). The extent of peroxidation of arachidonic acid embedded in DPPC vesicles was similar at the two temperatures and greater at 50 degrees C under acidic conditions. However, the peroxidative process was significantly decreased at 50 degrees C in the presence of PEPL, but not of DPPE or DAPE and the inhibitory effect was enhanced at pH 6.4. The possibility that a different phase distribution of the phospholipids, namely a transition from a lamellar to a hexagonal phase, may play a role in the scavenger effect of ethanolamine plasmalogens is discussed.
Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Arachidonic Acid/chemistry , Ferrous Compounds/chemistry , Lipid Peroxidation/drug effects , Plasmalogens/chemistry , 1,2-Dipalmitoylphosphatidylcholine/metabolism , Animals , Arachidonic Acid/metabolism , Brain/metabolism , Calorimetry , Cattle , Ferrous Compounds/metabolism , Ferrous Compounds/pharmacology , Kinetics , Liposomes , Phosphatidylethanolamines/chemistry , Phosphatidylethanolamines/metabolism , Plasmalogens/pharmacology , TemperatureABSTRACT
The spontaneous transfer between membranes of GM3, a ganglioside present in a vesicular form of aggregation instead of micellar form like the majority of gangliosides in aqueous medium, has been studied. Upon incubation of GM3 in the presence of dipalmitoylphosphatidylcholine (DPPC) large unilamellar vesicles at 50 degrees C, mixed GM3/DPPC vesicles are formed. The maximum amount of GM3 that can be inserted into vesicles is about 8%. The temperature dependence of the kinetics has been followed by the excimer formation technique, using the fluorescent analogue pyrenyldodecanoyl-GM3. The transfer of ganglioside from its vesicles to DPPC vesicles depends on the physicochemical characteristics of both the donor and of the acceptor vesicles and increases with the temperature (k = 0.006 0.012, 0.037 at 30, 41 and 50 degrees C, respectively), with a major break point at 41 degrees C and a minor one at 35 degrees C. These temperatures correspond to the gel- to liquid-crystalline transition of DPPC (Tm = 41.3 degrees C), and to a temperature transition displayed by GM3 ganglioside. Similar experiments performed with erythrocyte ghosts yielded a rate constant of 0.04 at 37 degrees C. For the transfer of ganglioside from DPPC (donor) to DMPC (acceptor) the rate constants were 0 at 15 degrees C (both phospholipids in the gel phase), 0.005 at 37 degrees C (donor in the gel phase, acceptor in the fluid phase) and 0.04 at 50 degrees C (both phospholipids in the fluid phase).(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
G(M3) Ganglioside/chemistry , Liposomes/chemistry , 1,2-Dipalmitoylphosphatidylcholine/chemistry , Chromatography, Gel , Dimyristoylphosphatidylcholine/chemistry , Fluorescent Dyes/chemistry , Gangliosides/chemistry , Kinetics , Membrane Fusion , Micelles , TemperatureABSTRACT
The thermotropic behavior of a series of synthetic fatty acyl ethylesters (FAEE) in multilamellar liposomes has been studied by differential scanning calorimetry and monitoring the changes in polarization emitted by the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Their thermotropic behaviour has been compared to that of the homologous fatty acids (FA) from which they are synthesized in vivo in the presence of ethanol. Compared to the correspondent FA, saturated FAEE show, depending on the chain length, a minor rigidifying effect or even a slight fluidizing effect on phospholipid bilayers. Unsaturated FAEE show, compared to the homologous FA, slightly greater fluidizing properties. The difference between FA and FAEE is more evident in single component phospholipid liposomes in the gel phase, and in mixed liposomes of two lipids at temperatures at which microdomains of gel and liquid zones coexist. The calorimetric data suggest that FAEE are completely miscible with phospholipids both in the gel and liquid phases; they appear to destabilize the bilayer wherein the ethoxy head group interferes with the intrinsic phospholipid interactions.
