How the replacement of cholesterol by 25-hydroxycholesterol affects the interactions with sphingolipids: The Langmuir Monolayer Study complemented with theoretical calculations

Abstract

In this paper, a representative of chain-oxidized sterols, 25-hydroxycholesterol (25-OH), has been studied in Langmuir monolayers mixed with the sphingolipids sphingomyelin (SM) and ganglioside (GM 1 ) to build lipid rafts. A classical Langmuir monolayer approach based on thermodynamic analysis of interactions was complemented with microscopic visualization of films (Brewster angle microscopy), surface-sensitive spectroscopy (polarization modulation–infrared reflection–absorption spectroscopy) and theoretical calculations (density functional theory modelling and molecular dynamics simulations). Strong interactions between 25-OH and both investigated sphingolipids enabled the formation of surface complexes. As known from previous studies, 25-OH in pure monolayers can be anchored to the water surface with a hydroxyl group at either C(3) or C(25). In this study, we investigated how the presence of additional strong interactions with sphingolipids modifies the surface arrangement of 25-OH. Results have shown that, in the 25-OH/GM 1 system, there are no preferences regarding the orientation of the 25-OH molecule in surface complexes and two types of complexes are formed. On the other hand, SM enforces one specific orientation of 25-OH: being anchored with the C(3)–OH group to the water. The strength of interactions between the studied sphingolipids and 25-OH versus cholesterol is similar, which indicates that cholesterol may well be replaced by oxysterol in the lipid raft system. In this way, the composition of lipid rafts can be modified, changing their rheological properties and, as a consequence, influencing their proper functioning.

Advantages of the classical thermodynamic analysis of single—and multi-component Langmuir monolayers from molecules of biomedical importance—theory and applications

“…This suggested that these two lipids had a strong affinity for each other. Indeed, further studies on interactions in two-component systems confirmed strong affinity of cholesterol to sphingolipids (mainly sphingomyelin and gangliosides [ 78 , 79 ]), which may be explained on the basis of the molecular geometry [ 80 , 81 ]. Specifically, the inverted cone shape of cholesterol (promoting negative curvature structures) fits perfectly with the truncated cone-like shape of sphingomyelin or cone-shape of ganglioside GM 1 (both forming positive curvature structures) [ 81 ].…”

“…Therefore, these mixtures can be considered as artificial lipid rafts, among which the SM/Chol system is used as the simplest model [ 78 , 82 – 85 ].

Figure 2 Δ G exc plots for: ( a ) cholesterol/sphingomyelin and ( b ) cholesterol/ganglioside mixtures (modified from [ 78 , 79 ] with permission from Elsevier and the Royal Society Publishing.

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“… Δ G exc plots for: ( a ) cholesterol/sphingomyelin and ( b ) cholesterol/ganglioside mixtures (modified from [ 78 , 79 ] with permission from Elsevier and the Royal Society Publishing. …”

“…Additional information from the π – A isotherms complemented with BAM, PM-IRRAS and MD simulations revealed that in the 25-OH/GM 1 system, two types of surface complexes are formed since 25-OH is anchored in water with C(3)-OH or C(25)-OH. On the other hand, SM imposes one specific orientation of 25-OH: by anchoring with C(3)-OH in water [ 79 ]. The interactions between sphingolipids and cholesterol or 25-OH may have important biological implications.…”

25-Hydroxycholesterol as a Signaling Molecule of the Nervous System

“…The studies of the properties of raft-forming lipids in Langmuir monolayers show that 25-HC interacts more strongly than cholesterol with sphingomyelin and slightly less strongly with ganglioside GM1. Therefore, 25-HC can participate in the formation of lipid rafts and even displace cholesterol from them [113]. Indeed, the addition of 25-HC to the artifi cial bilayer membrane composed of a mixture of cholesterol and 1-palmitoyl-2-oleoylphosphatidylcholine leads to a shift of cholesterol towards the water surface and increase in its accessibility to external acceptors; which reduces the ability of cholesterol to condense the lipid bilayer [114].…”