Yamaira I Gonzalez | PubMed Health

PubMed2006

Stabilization of catanionic vesicles via polymerization.

Polymerizable cationic surfactant methacryloyloxyoctyl trimethylammonium bromide (MOTB) and anionic surfactant sodium 4-(omega-methacryloyloxyoctyl)oxy benzene sulfonate (MOBS) were synthesized. Stable catanionic vesicles can spontaneously form upon mixing the two oppositely charged surfactants in aqueous solution, which was further permanently fixed by polymerization. Surface tensiometry, nuclear magnetic resonance (NMR), static and dynamic laser light scattering (LLS), and cryogenic transmission electron microscopy (cryo-TEM) were used in combination to characterize the catanionic vesicles before and after polymerization. The kinetics of formation and breakdown of unpolymerized catanionic vesicles were studied in detail employing stopped-flow light scattering. In contrast to unpolymerized vesicles, the polymerized ones exhibit permanent stability under external perturbations such as dilution or adding excess MOTB. A tentative explanation is proposed about why free radical polymerization can successfully fix the catanionic vesicles, the structure of which is well-known to be in dynamic equilibrium exchange with unimers.

Journal Article↗

PubMed2003

Interaction of apolipoprotein A-I with lecithin-cholesterol vesicles in the presence of phospholipase C.

Here we study the anti-nucleating mechanism of apolipoprotein A-I (apo A-I) on model biliary vesicles in the presence of phospholipase C (PLC) utilizing dynamic light scattering (DLS), steady-state fluorescence spectroscopy, cryogenic transmission electron microscopy (cryo-TEM), and UV/Vis spectroscopy. PLC induces aggregation of cholesterol-free lecithin vesicles from an initial, average size of 100 nm to a maximal size of 600 nm. The presence of apo A-I likely inhibits vesicle aggregation by shielding the PLC-generated hydrophobic moieties, which results in vesicles of an average size of 200 nm. A similar phenomenon is observed in cholesterol-enriched lecithin vesicles. Whereas PLC alone produces aggregates of 300 nm, no aggregation is observed when apo A-I is present along with PLC. However, the ability of apo A-I to inhibit aggregation is temporary, and after 8 h, a broad particle size distribution with sizes as high as 800 nm is observed. Apo A-I possibly induces the formation of small apo A-I/lecithin/cholesterol complexes of about 5-20 nm similar to the discoidal pre-HDL complexes found in blood when it can no longer effectively shield all the DAG molecules. Concomitant with formation of complexes, DAG molecules coalesce into large oil droplets, which account for the large particles observed by light scattering. Thus, apo A-I acts as an anti-nucleating agent by two mechanisms, anti-aggregation and microstructural transition. The mode of protection is dependent on the cholesterol content and the relative amounts of DAG and apo A-I present. This study supports the possibility of apo A-I solubilizing lipids in bile in a similar fashion as it does in blood and also delineates the mechanism of formation of the complexes.

Apolipoprotein A-I↗