An AFM Study of Lipid Monolayers. 2. Effect of Cholesterol on Fatty Acids

Abstract

In this study the effect of cholesterol in Langmuir-Blodgett monolayers of fatty acids of varying chain lengths was investigated by atomic force microscopy (AFM). Domain formation due to lateral phase separation was studied at different lipid compositions and surface pressures. A small amount of cholesterol is miscible with palmitic acid (C16:0) and forms a flat monolayer while excess cholesterol forms a rougher cholesterolrich phase. No miscibility was observed in monolayers of lignoceric acid (C24:0) and cholesterol. For the ternary mixed monolayer (palmitic acid, lignoceric acid, and cholesterol) the two fatty acids formed separate domains and the miscibility of cholesterol in the two phases showed behavior corresponding to that of the binary fatty acid-cholesterol systems. From the shape, size, and height differences of the domains one can conclude that the driving force to minimize the interfacial length between different phases is reduced in the presence of cholesterol. This can be attributed to line active properties of cholesterol.

Human stratum corneum lipid organization as observed by atomic force microscopy on Langmuir–Blodgett films

“…The deposited lipid Wlm was left for 25 min for the solvent to evaporate, and thereafter compressed to 22 mN/m at a speed of 1 mN/m per minute, with a maximum barrier speed of 10 mm/min (cf. Ekelund et al, 1999;Sparr et al, 1999). Three isotherm cycles were performed to ensure reproducibility.…”

Mixed layers of DPPC and a linear poly(ethylene glycol)-b-hyperbranched poly(glycerol) block copolymer having a cholesteryl end group

“…In order to study the capability of penetration of synthetic molecules into cell membranes, simplified models are often employed. Typical examples in this context are Langmuir monolayers of phospholipids at the air-water interface, which represent a half leaflet analogue of biological membranes [6][7][8][9]. Due to the simple preparation and characterization of Langmuir films, they are used to study the interactions between membrane components [10], protein interactions with the lipid matrix [11], and the penetrability for synthetic molecules [12][13][14].…”

“…Another essential component in biological membranes is cholesterol, which is responsible for stabilization and fluidization of the membranes [7,[24][25][26][27][28]. Numerous publications investigate the interaction of cholesterol and phospholipids in mixed Langmuir and LB films [29][30][31][32][33][34][35][36][37][38][39][40][41].…”

Cryo-TEM of isolated milk fat globule membrane structures in cream

“…Phase separation may also occur in the presence of cholesterol. 17 It has been shown that lateral phase separation of cholesterol leads to deformed non-spherical vesicles. 18 Facetted vesicular structures have been observed by Mel 'nikova et al 19 in mixed systems of dioctadecyldimethylammonium bromide (DODAB) and dioleoyl phosphatidylethanolamine (DOPE) (4:1).…”