Sterol Affinity for Bilayer Membranes is Affected by their Ceramide Content and the Ceramide Chain Length

Abo Akademi University, Department of biochemistry and pharmacy, Tykistökatu 6A, 20520 Turku, Finland.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 05/2010; 1798(5):1008-13. DOI: 10.1016/j.bbamem.2009.12.025
Source: PubMed

ABSTRACT It is known that ceramides can influence the lateral organization in biological membranes. In particular ceramides have been shown to alter the composition of cholesterol and sphingolipid enriched nanoscopic domains, by displacing cholesterol, and forming gel phase domains with sphingomyelin. Here we have investigated how the bilayer content of ceramides and their chain length influence sterol partitioning into the membranes. The effect of ceramides with saturated chains ranging from 4 to 24 carbons in length was investigated. In addition, unsaturated 18:1- and 24:1-ceramides were also examined. The sterol partitioning into bilayer membranes was studied by measuring the distribution of cholestatrienol, a fluorescent cholesterol analogue, between methyl-beta-cyclodextrin and large unilamellar vesicle with defined lipid composition. Up to 15 mol% ceramide was added to bilayers composed of DOPC:PSM:cholesterol (3:1:1), and the effect on sterol partitioning was measured. Both at 23 and 37 degrees C addition of ceramide affected the sterol partitioning in a chain length dependent manner, so that the ceramides with intermediate chain lengths were the most effective in reducing sterol partitioning into the membranes. At 23 degrees C the 18:1-ceramide was not as effective at inhibiting sterol partitioning into the vesicles as its saturated equivalent, but at 37 degrees C the additional double bond had no effect. The longer 24:1-ceramide behaved as 24:0-ceramide at both temperatures. In conclusion, this work shows how the distribution of sterols within sphingomyelin-containing membranes is affected by the acyl chain composition in ceramides. The overall membrane partitioning measured in this study reflects the differential partitioning of sterol into ordered domains where ceramides compete with the sterol for association with sphingomyelin.

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    • "For fluorescence measurements, multilamellar vesicles were prepared by probe sonication (sonicated for 2 min with 20% duty cycle and 15 W power output) using a Branson probe sonifier (W-450, Branson Ultrasonics, Danbury, CT, USA). Unilamellar vesicles used for the CTL partitioning assay were prepared by extrusion (200 nm pore diameter) as described previously [36] "
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    ABSTRACT: Sphingomyelin (SM) is a major phospholipid in most cell membranes. SMs are composed of a long-chain base (often sphingosine, 18:1(Δ4t)), and N-linked acyl chains (often 16:0, 18:0 or 24:1(Δ15c)). Cholesterol interacts with SM in cell membranes, but the acyl chain preference of this interaction is not fully elucidated. In this study we have examined the effects of hydrophobic mismatch and interdigitation on cholesterol/sphingomyelin interaction in complex bilayer membranes. We measured the capacity of cholestatrienol (CTL) and cholesterol to form sterol-enriched ordered domains with saturated SM species having different chain lengths (14 to 24 carbons) in ternary bilayer membranes. We also determined the equilibrium bilayer partitioning coefficient of CTL with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes containing 20mol% of saturated SM analogs. Ours results show that while CTL and cholesterol formed sterol-enriched domains with both short and long-chain SM species, the sterols preferred interaction with 16:0-SM over any other saturated chain length SM analog. When CTL membrane partitioning was determined with fluid POPC bilayers containing 20mol% of a saturated chain length SM analog, the highest affinity was seen with 16:0-SM (both at 23 and 37°C). These results indicate that hydrophobic mismatch and/or interdigitation attenuate sterol/SM association and thus affect lateral distribution of sterols in the bilayer membrane.
    Biochimica et Biophysica Acta 07/2011; 1808(7):1940-5. DOI:10.1016/j.bbamem.2011.04.004 · 4.66 Impact Factor
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    • "Recently, we modified the cholesterol/cyclodextrin partitioning method of Niu and Litman [42], to use CTL instead of radioactive cholesterol (at 2 mol%). Furthermore, in our partitioning assay, there is no need to separate acceptor vesicles from cyclodextrin [28] [43], which makes measurements easier to perform. With this method we have shown that CTL partitions more favorably to PSM/POPC (20:80) containing bilayers as compared to POPC alone. "
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    ABSTRACT: We have prepared palmitoyl sphingomyelin (PSM) analogs in which either the 2-NH was methylated to NMe, the 3-OH was methylated to OMe, or both were methylated simultaneously. The aim of the study was to determine how such modifications in the membrane interfacial region of the molecules affected interlipid interactions in bilayer membranes. Measuring DPH anisotropy in vesicle membranes prepared from the SM analogs, we observed that methylation decreased gel-phase stability and increased fluid phase disorder, when compared to PSM. Methylation of the 2-NH had the largest effect on gel-phase instability (T(m) was lowered by ~7°C). Atomistic molecular dynamics simulations showed that fluid phase bilayers with methylated SM analogs were more expanded but thinner compared to PSM bilayers. It was further revealed that 3-OH methylation dramatically attenuated hydrogen bonding also via the amide nitrogen, whereas 2-NH methylation did not similarly affect hydrogen bonding via the 3-OH. The interactions of sterols with the methylated SM analogs were markedly affected. 3-OH methylation almost completely eliminated the capacity of the SM analog to form sterol-enriched ordered domains, whereas the 2-NH methylated SM analog formed sterol-enriched domains but these were less thermostable (and thus less ordered) than the domains formed by PSM. Cholestatrienol affinity to bilayers containing methylated SM analogs was also markedly reduced as compared to its affinity for bilayers containing PSM. Molecular dynamics simulations revealed further that cholesterol's bilayer location was deeper in PSM bilayers as compared to the location in bilayers made from methylated SM analogs. This study shows that the interfacial properties of SMs are very important for interlipid interactions and the formation of laterally ordered domains in complex bilayers.
    Biochimica et Biophysica Acta 04/2011; 1808(4):1179-86. DOI:10.1016/j.bbamem.2011.01.009 · 4.66 Impact Factor
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    • "Studies show that cholesterol prefers to interact with SMs in cell membranes [16] [17]. Model membrane studies show that cholesterol has an increased affinity for bilayer membranes containing SMs as compared to bilayers comprising acyl chain matched glycerophospholipids [18] [19] [20]. This increased affinity of sterols for SM containing membranes relates in part to the more ordered nature of SM species. "
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    ABSTRACT: A sphingomyelin chimera in which the amide-linked acyl chain was replaced with cholesterol carbamate was prepared and its properties examined. The sphingomyelin/cholesterol chimera (N-cholesterol-D-erythro-sphingomyelin) was able to form unilamellar vesicles of defined size when extruded through 200nm pore size membranes. These N-cholesteryl sphingomyelin bilayers were resistant to solubilization by Triton X-100. When N-cholesteryl sphingomyelin was added to N-palmitoyl sphingomyelin (N-palmitoyl-d-erythro-sphingomyelin) bilayers, it increased acyl chain order as determined by 1,6-diphenyl-1,3,5-hexatriene fluorescence anisotropy. N-cholesteryl sphingomyelin was, however, not as good an inducer of membrane order compared to cholesterol on a molar basis. Differential scanning calorimetry studies further showed that the miscibility of N-cholesteryl sphingomyelin with N-palmitoyl-d-erythro-sphingomyelin bilayers was non-ideal, and the effect of N-cholesteryl sphingomyelin on the N-palmitoyl-d-erythro-sphingomyelin gel-fluid transition enthalpy differed from that seen with cholesterol. Together with N-palmitoyl-d-erythro-sphingomyelin, the N-cholesteryl sphingomyelin chimera was able to form sterol-enriched ordered domains in a fluid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer. N-cholesteryl sphingomyelin in the absence of N-palmitoyl-d-erythro-sphingomyelin was unable to form such sterol-enriched ordered domains in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer. However, N-cholesteryl sphingomyelin markedly increased the affinity of cholestatrienol for N-cholesteryl sphingomyelin containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers, suggesting that N-cholesteryl sphingomyelin was able to somehow stabilize sterol interaction in fluid bilayers. Based on our results, we conclude that N-cholesteryl sphingomyelin behaved more like a cholesterol than a sphingolipid in fluid bilayer membranes. Because N-cholesteryl sphingomyelin increased bilayer order, conferred resistance against detergent solubilization, and is not degradable by phospholipases A(2), it could constitute a good lipocomplex matrix for drug delivery vehicles.
    Biochimica et Biophysica Acta 12/2010; 1808(4):1054-62. DOI:10.1016/j.bbamem.2010.12.021 · 4.66 Impact Factor
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