A Guide to Your Desired Lipid-Asymmetric Vesicles

Abstract

Liposomes are prevalent model systems for studies on biological membranes. Recently, increasing attention has been paid to models also representing the lipid asymmetry of biological membranes. Here, we review in-vitro methods that have been established to prepare free-floating vesicles containing different compositions of the classic two-chain glycero- or sphingolipids in their outer and inner leaflet. In total, 72 reports are listed and assigned to four general strategies that are (A) enzymatic conversion of outer leaflet lipids, (B) re-sorting of lipids between leaflets, (C) assembly from different monolayers and (D) exchange of outer leaflet lipids. To guide the reader through this broad field of available techniques, we attempt to draw a road map that leads to the lipid-asymmetric vesicles that suit a given purpose. Of each method, we discuss advantages and limitations. In addition, various verification strategies of asymmetry as well as the role of cholesterol are briefly discussed. The ability to specifically induce lipid asymmetry in model membranes offers insights into the biological functions of asymmetry and may also benefit the technical applications of liposomes.

Asymmetric Lipid Vesicles: Techniques, Applications, and Future Perspectives as an Innovative Drug Delivery System

“…Since cellular membranes have different lipid domains in different parts of the membrane that are required to control different cellular activities that are essential for differentiation, proliferation, protein interactions, and cell-to-cell communication [ 48 , 49 , 54 ], symmetric bilayers lack the capacity to emulate these behaviors, thus limiting the information obtained from working with this kind of model. Therefore, asymmetric systems could improve our understanding of cellular processes due to their resemblance with the asymmetric behavior of eukaryotic or bacterial cellular membranes [ 49 , 55 , 56 ].…”

Disruption of liquid/liquid phase separation in asymmetric GUVs prepared by hemifusion

“…To this end, several techniques for preparing asymmetric vesicles in a range of sizes have been described in the literature (recently reviewed in Krompers and Heerklotz 18 and St. Clair et al 19 ).…”

“…To this end, several techniques for preparing asymmetric vesicles in a range of sizes have been described in the literature (recently reviewed in Krompers and Heerklotz 18 and St. Clair et al 19 ). Methods for preparing asymmetric giant unilamellar vesicles (aGUVs) are particularly valuable for optical microscopy studies of phase behavior and include variations of cyclodextrin-mediated lipid exchange, 20,21 water-oil phase transfer, 22 and hemifusion.…”