Bilayer Interactions among Unsaturated Phospholipids, Sterols, and Ceramide

Abstract

Using differential scanning calorimetry and lifetime analysis of trans-parinaric acid fluorescence, we have examined how cholesterol and cholesteryl phosphocholine (CholPC) affect gel-phase properties of palmitoyl ceramide (PCer) in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dioleyol-sn-glycero-3-phosphocholine (DOPC) bilayers. By H NMR, we also measured fluid-phase interactions among these lipids using deuterated analogs of POPC, PCer, and cholesterol. The PCer-rich gel phase in POPC bilayers (9:1 molar ratio of POPC to PCer) was partially and similarly dissolved (and thermostability decreased) by both cholesterol and CholPC (sterol was present equimolar to PCer, or in fourfold excess). In DOPC bilayers (4:1 DOPC/PCer molar ratio), CholPC was much more efficient in dissolving the PCer-rich gel phase when compared to cholesterol. This can be interpreted as indicating that PCer interaction with POPC was stronger than PCer interaction with DOPC. PCer-CholPC interactions were also more favored in DOPC bilayers compared to POPC bilayers. In the fluid POPC-rich phase, cholesterol increased the order of the acyl chain of d-PCer much more than did CholPC. In DOPC-rich fluid bilayers, both cholesterol and CholPC increased d-PCer acyl chain order, and the ordering induced by CholPC was more efficient in DOPC than in POPC bilayers. In fluid POPC bilayers, the ordering of 3-d1-cholesterol by PCer was weak. In summary, we found that in the gel phase, sterol effects on the PCer-rich gel phase were markedly influenced by the acyl chain composition of the fluid PC. The same was true for fluid-phase interactions involving the sterols. Our results further suggest that PCer did not display high affinity toward either of the sterols used. We conclude that the nature of unsaturated phospholipids (POPC versus DOPC) in bilayers has major effects on the properties of ceramide gel phases and on sterol-ceramide-phospholipid interactions in such complex bilayers.

Natural Ceramides and Lysophospholipids Cosegregate in Fluid Phosphatidylcholine Bilayers

“…Saturated ceramides interact favorably with palmitoyl SM (PSM), and together they form a gel phase whose thermostability is intermediate between pure PSM and pure hydrated PCer crystals (18). The miscibility of ceramides with unsaturated phosphatidylcholines is much less ideal, as revealed by a scanning calorimetry of binary PCer/POPC or PCer/ DOPC bilayers, which show broad and complex gel melting endotherms (15). When PCers are included in bilayer membranes, they tend to segregate laterally at very low concentrations (0-5 mol%) if the acyl chains of the co-lipids are fully saturated (e.g., PSM or dipalmitoyl phosphatidylcholine) or have at least one saturated acyl chain (e.g., POPC) (14,30,36).…”

“…Because ceramides typically have saturated acyl chains, they tend to favor interactions with other lipids that also have saturated acyl chains, such as SMs (14). The major reason that ceramides interact with phospholipids instead of with cholesterol, for example, is that the phospholipid headgroup can shield the hydrophobic part of ceramide from unfavorable interactions with interfacial water (15). Interactions between ceramides or between ceramide and cholesterol are not thermodynamically favored because there is no large headgroup to shield the hydrophobic parts from unfavorable interactions with interfacial water; however, if a phosphocholine headgroup is attached to the 3-OH group of cholesterol (generating cholesteryl phosphorylcholine), N-palmitoyl ceramide (PCer) interacts with this large-headgroup cholesterol analog and even forms fluid bilayers at an equimolar ratio of the two components (16).…”

“…Interactions between ceramides or between ceramide and cholesterol are not thermodynamically favored because there is no large headgroup to shield the hydrophobic parts from unfavorable interactions with interfacial water; however, if a phosphocholine headgroup is attached to the 3-OH group of cholesterol (generating cholesteryl phosphorylcholine), N-palmitoyl ceramide (PCer) interacts with this large-headgroup cholesterol analog and even forms fluid bilayers at an equimolar ratio of the two components (16). The authors have recently shown that the affinity of PCer for cholesteryl phosphorylcholine is lower than the affinity PCer has for 1-palmitoyl-2-oleoyl-sn-glycero-3phosphocholine (POPC), but it is higher than for 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (15).…”

C24:0 and C24:1 sphingolipids in cholesterol-containing, five- and six-component lipid membranes

“…This points to lCer as a very suitable Cer to form stiff gel domains that could also accommodate a significant amount of other lipids such as Chol, as pCer is able to do under specific conditions of high Chol and pCer concentrations 40,47 , or in a lipid environment deprived of a fluid phase 46 . In summary, while pCer and Chol have a strong tendency to displace each other from the same interaction sites [62][63][64] , lCer (and lSM) could offer a solution for cells to fine tune the biophysical properties of their membranes, particularly in the presence of a wide variety of different N-acyl sphingolipids, which is the situation in living cell membranes.…”

Nobiletin-loaded composite penetration enhancer vesicles restore the normal miRNA expression and the chief defence antioxidant levels in skin cancer

“…The higher EE% in ceramide containing vesicles compared to their counterparts not containing ceramide is attributed to the more lipophilicity of ceramide compared to lecithin, as well as the ability of ceramide to create a matrix for drug encapsulation 34 , 68 . Ceramide is a very lipophilic molecule belonging to sphingolipids family; its backbone is composed of long chain sphingoid base with another chain composed of amide linked fatty acid 86 , however, ceramides can not form bilayers alone 34 , 87 – 89 . On the other hand, in case of composite PEVs (F10-F13), the inclusion of ceramide (F27-F30) displayed a significant decrease in the EE% of composite PEVs ( P < 0.05).…”