Exploding vesicles

Abstract

While studying fatty acid vesicles as model primitive cell membranes, we encountered a dramatic phenomenon in which light triggers the sudden rupture of micron-scale dye-containing vesicles, resulting in rapid release of vesicle contents. We show that such vesicle explosions are caused by an increase in internal osmotic pressure mediated by the oxidation of the internal buffer by reactive oxygen species (ROS). The ability to release vesicle contents in a rapid, spatio-temporally controlled manner suggests many potential applications, such as the targeted delivery of cancer chemotherapy drugs, and the controlled deposition of functionalized nanoparticles in microfluidic devices. Recent observations of light-triggered lysosome rupture in vivo suggest the possibility that a common mechanism may underlie light-triggered vesicle explosions and lysosome rupture. FindingsVesicles are bilayer membrane structures that encapsulate an internal aqueous compartment. Fatty acid vesicles have been studied as models of primitive cell membranes at the origin of life [1][2][3][4][5][6][7], and phospholipid vesicles (liposomes) have been widely studied as models of modern cell and organelle membranes [8,9] and as drug delivery vehicles [10][11][12]. We first observed the phenomenon of "exploding vesicles" during microscopic observations of large (approximately 4 μm in diameter) oleate vesicles containing 10 mM HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt, a water-soluble, membrane-impermeable fluorescent dye), in 0.2 M Nabicine buffer, pH 8.5. The vesicles were prepared by extrusion and dialysis, so that the fluorescent dye was present only inside the vesicles while the buffer was present in both inner and outer solutions [13]. To our surprise, we observed that these vesicles suddenly exploded shortly (approximately 0.5 sec) after being exposed to intense illumination from a metal halide lamp (estimated irradiance 2.5 W/mm 2 ), and released their encapsulated dye along with smaller internal vesicles ( Figure 1A; Additional File 1 Figure S1; Additional File 2). The actual vesicle rupture appeared to take place in < 2 ms (3 frames in a recording from a high-speed camera: Additional File 3); this estimate is an upper limit because of the time required for diffusion of the released dye away from the vesicle. We observed similar vesicle explosions using vesicles containing different internal fluorescent dyes, such as calcein and Rose Bengal (a photodynamic therapy drug).To distinguish between physical rupture and rapid permeabilization of the vesicle membrane, we labeled the vesicles with a membrane-localized dye (Rh-DHPE, Lissamine rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine). Upon illumination, we observed that the vesicle membrane burst open on one side and then quickly recoiled ( Figure 1B; Additional File 4). When using slightly lower illumination intensity, we observed the gradual rupture of the multiple layers of multilamellar vesicles, starting from the outer layers and progressing to...

Phosphorylation, oligomerization and self-assembly in water under potential prebiotic conditions

“…Preparing the liposomes with both dyes afforded a merged-image suggesting an “uneven-enclosed” structure ( Fig. 2h ), probably from the changes in internal osmotic pressure 22 and interlayer-distances 23 when both dyes are present. Preliminary reactions of octanoic acid with DAP under the paste-reaction conditions gave rise to smaller vesicle-like structures ( Supplementary Fig.…”

A Cell-Targeted Photodynamic Nanomedicine Strategy for Head and Neck Cancers

“…The intensity of Pc 4 (red) fluorescence in this ‘targeted’ test group increased with incubation time, suggesting increased lysosomal uptake of the nanoformulation followed by possible release of Pc 4 into the cytoplasmic compartment. This release is possibly a combined effect of low pH-catalyzed lysosomal degradation of the acid-labile micellar polymer of the nanovehicle and photo-triggered rupture of the lysosomal vesicles due to the action of the confocal laser light with the lysosome-trapped Pc 4 30,37,38 . These results indicate that the EGFR-targeted nanoformulation can undergo receptor-mediated rapid internalization in EGFR-overexpressing SCC-15 cells and subsequently result in rapid cytoplasmic release of Pc 4 from the internalized vehicles.…”

Photochemically driven redox chemistry induces protocell membrane pearling and division

“…The vesicles contained 2 mM HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt, a water-soluble, membrane-impermeable fluorescent dye) (7) and were illuminated by an EXFO 120 W metal halide lamp. We reasoned that since most fluorescent dyes, such as HPTS, generate reactive oxygen species (ROS) under illumination, this phenomenon might be caused by the radicalmediated oxidation and fragmentation of the internal buffer solute, bicine, leading to increased internal osmolarity, as previously seen in the case of spherical vesicles that explode under similar conditions (8). The fact that the sphere-to-filament transition is reversible shows directly that growth into a filamentous form does not involve topological changes in vesicle structure.…”