Lipoplexes formed from sugar-based gemini surfactants undergo a lamellar-to-micellar phase transition at acidic pH. Evidence for a non-inverted membrane-destabilizing hexagonal phase of lipoplexes

Abstract

The present study aims at a better understanding of the mechanism of transfection mediated by two sugar-based gemini surfactants GS1 and GS2. Previously, these gemini surfactants have been shown to be efficient gene vectors for transfection both in vitro and in vivo. Here, using Nile Red, a solvatochromic fluorescent probe, we investigated the phase behavior of these gemini surfactants in complexes with plasmid DNA, so-called lipoplexes. We found that these lipoplexes undergo a lamellar-to-non-inverted micellar phase transition upon decreasing the pH from neutral to mildly acidic. This normal (non-inverted) phase at acidic pH is confirmed by the colloidal stability of the lipoplexes as shown by turbidity measurements. We therefore propose a normal hexagonal phase, H(I), for the gemini surfactant lipoplexes at acidic endosomal pH. Thus, we suggest that besides an inverted hexagonal (H(II)) phase as reported for several transfection-potent cationic lipid systems, another type of non-inverted non-bilayer structure, different from H(II), may destabilize the endosomal membrane, necessary for cytosolic DNA delivery and ultimately, cellular transfection.

Urothelial endocytic vesicle recycling and lysosomal degradative pathway regulated by lipid membrane composition

“…We must consider previous results related to membrane organization. The association of oleic acid and PE (phosphatidylethanolamine) induces the formation of inverted tubular micelles, which are the basic supramolecular units of H II (inverted hexagonal) arrays (Wasungu et al 2006). Coincident with that result, we observed an increased oleic acid concentration (Calderón and Eynard 2000;Grasso et al 2011a) as well as an increased amount of PE in oleic acidderived urothelial membranes (Bongiovanni et al 2005) compared to control and linoleic acid-derived membranes.…”

Encapsulation Processes by Bilayer Vesicles

“…73 In the resulting H I c phase the polar headgroups of the geminis are exposed on the outside in contact with water. 159 This in contrast to the earlier proposed H II c phase for the lipoplexes. 158 As a consequence, these particles exhibit an unusually high colloidal stability (as shown by turbidity measurements) facilitating their application in in vivo gene delivery experiments.…”

Cationic lipid-mediated nucleic acid delivery: beyond being cationic

“…Saturated PE as colipid reduces transfection efficiency and also inhibits model membrane fusion. Model membrane studies with biological membrane vesicles and various cationic lipid vesicles clearly point indicating the role of inverted hexagonal phase in fusion of lipoplex with the endosomal membrane, (Bentz et al, 1987;Wasungu et al, 2006b).…”