Effect of ceramide N-acyl chain and polar headgroup structure on the properties of ordered lipid domains (lipid rafts)

Ceramides are sphingolipids that greatly stabilize ordered membrane domains (lipid rafts), and displace cholesterol from them. Ceramide-rich rafts have been implicated in diverse biological processes. Because ceramide analogues have been useful for probing the biological function of ceramide, and may have biomedical applications, it is important to characterize how ceramide structure affects membrane properties, including lipid raft stability and composition. In this report, fluorescence quenching assays were used to evaluate the effect of analogues of ceramide with different N-acyl chains or different sphingoid backbones on raft stability and sterol content. The effect of replacing 18 mol% of sphingomyelin (SM) with ceramide in vesicles composed of a 1: 1 (mol:mol) mixture of SM and dioleoylphosphatidylcholine (DOPC), with or without 25 mol% sterol, was examined. In the absence of sterol, the thermal stability of the SM-rich ordered domains increased with ceramide N-acyl chain length in the order C-2:0 similar to C6:0 similar to C8:0